Academic Commons Search Results
http://academiccommons.columbia.edu/catalog.rss?f%5Bsubject_facet%5D%5B%5D=Mechanical+engineering&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Results
enus

Analyses of Energy Infrastructure Serving a Dense Urban Area: Opportunities and Challenges for Wind Power, Building Systems and Distributed Generation
http://academiccommons.columbia.edu/catalog/ac:201677
Waite, Michael B.
http://dx.doi.org/10.7916/D8FT8M6H
Mon, 01 Aug 2016 12:24:37 +0000
This dissertation describes methodologies for evaluating a set of anticipated and recommended energy infrastructure changes essential to achieving deep greenhouse gas emissions reductions in a dense urban area: Deep penetration of gridconnected wind power, widespread adoption of electric heat pumps, multiple potential services from extensive deployment of distributed generation, and increasing focus on auxiliary energy in heating and cooling systems as cities continue to grow in population and height. The focus of the research presented here was New York City and the surrounding New York State electricity supply infrastructure. After developing a wind power model based on an NREL model wind data set, a linear program model showed that after passing a lowcurtailment threshold of 10 GW, energyrelated wind power curtailment is driven largely by continuous operation of baseload generation and misalignment of winter wind power peaks and existing summer electricity demand peaks. Separate analyses showed the potential for increase windgenerated electricity utilization through increased use of heat pumps in New York City.
A suite of models was developed to assess the zonal effects in New York City of deep statewide penetration of wind power and widespread adoption of electric heat pumps in New York City. New York City was found to have highly fluctuating net loads in deep wind penetration scenarios. Further, with large amounts of existing space heating demand replaced by heat pumps, the increased winter electricity demand peaks occurred infrequently enough that the additional generation capacity required to meet those loads would have a capacity factor well less than 1%. Smallscale, natural gasfueled internal combustion engines deployed as distributed generation were shown to improve the ability of the system to respond to load fluctuations, to be a more economical option than new large centralized generators at the low capacity factor, and to reduce overall system gas usage due to mitigating partload effects and startup fuel requirements. This distributed generation, which could in reality also include combined heat and power systems as well as battery storage standing alone, connected to rooftop solar or in electric vehicles, also has potential system resilience benefits.
The last research effort described here included longterm monitoring of a highrise mixed use building’s hydronic system before and after a retrofit of hydraulic equipment. Significant annual reductions of 40% energy usage for pumping were computed, primarily due to partload flow control effects. Analysis of the monitoring data, as well as computations related to theoretical performance of hydraulic networks, showed that this approach also has potential to reduce peak loads, particularly in highrise buildings.
Mechanical engineering
mbw2113
Mechanical Engineering
Dissertations

The Stability at the SolidSolid and LiquidSolid Interfaces
http://academiccommons.columbia.edu/catalog/ac:198539
Xiao, Junfeng
http://dx.doi.org/10.7916/D8KK9BS1
Wed, 04 May 2016 15:33:41 +0000
In this thesis, we studied three small subjects in the realm of continuum mechanics: imbibition in fluid mechanics, beam and rod buckling in solid mechanics and shell buckling at the solidliquid interface.
In chapter 2, we examined the radial imbibition into a homogenous semiinfinite porous media from a point source with infinite liquid supply. We proved that in the absence of gravity (or in the regime while gravity is negligible compared to surface tension), the shape of the wet area is a hemisphere, and the radius of the wet area evolves as a function with respect to time. This new law with respect to time has been verified by Finite Element Method simulation in software COMSOL and a series of experiments using packed glass microsphere as the porous media. We also found that even though the imbibition slows down, the flow rate through the point source remains constant. This new result for three dimensional radial imbibition complements the classic LucasWashburn law in one dimension and two dimensional radial imbibition in one plane.
In chapter 3, we studied the elastic beam/rod buckling under lateral constraints in two dimension as well as in three dimension. For the two dimensional case with unique boundary conditions at both ends, the buckled beam can be divided into segments with alternate curved section and straight section. The curved section can be solved by the Euler beam equation. The straight sections, however, are key to the transition between different buckling modes, and the redistributed length of straight sections sets the upper limit and lower limit for the transition. We compared our theoretical model of varying straight sections with Finite Element Method simulation in software ABAQUS, and good agreements are found. We then attempted to employ this model as an explanation with qualitative feasibility for the crawling snake in horizontal plane between parallel walls, which shows unique shape like square wave. For the three dimensional buckling beam/rod confined in cylindrical constraints, three stages are found for the buckling and post buckling processes: initial two dimensional shape, three dimensional spiral/helix shape and final foldup/alpha shape. We characterized the shape at each stage, and then we calculated the transition points between the three stages using geometrical arguments for energy arguments. The theoretical analysis for three dimensional beam/rod are also complemented with Finite Element Method simulations from ABAQUS.
In chapter 4, we investigated the buckling shape of solid shell filled with liquid core in two dimension and three dimension. A material model for liquid is first described that can be readily incorporated in the framework of solid mechanics. We then applied this material model in two dimensional and three dimensional Finite Element Method simulation using software ABAQUS. For the two dimensional liquid core solid shell model, a linear analysis is first performed to identify that ellipse corresponds to lowest order of buckling with smallest elastic energy. Finite Element Method simulation is then performed to determine the nonlinear postbuckling process. We discovered that two dimensional liquid core solid shell structures converge to peanut shape eventually while the evolution process is determined by two dimensionless parameters Kτ/μ and ρR^2/μτ. Amorphous shape exists before final peanut shape for certain models with specific Kτ/μ and ρR^2/μτ. The two dimensional peanut shape is also verified with Lattice Boltzmann simulations. For the three dimensional liquid core solid shell model, the post buckling shape is studied from Finite Element Method simulations in ABAQUS. Depending on the strain loading rate, the deformations show distinctive patterns. Large loading rate induces herringbone pattern on the surface of solid shell which resembles solid core solid shell structure, while small loading rate induces major concave pattern which resemble empty solid shell structure. For both two dimensional and three dimensional liquid core system, small scale ordered deformation pattern can be generated by increasing the shear stress in liquid core.
In the final chapter, we summarized the discoveries in the dissertation with highlights on the role that geometry plays in all of the three subjects. Recommendations for future studies are also discussed.
Mechanical engineering, Mechanics
jx2151
Mechanical Engineering, Earth and Environmental Engineering
Dissertations

Methods for Analysis of Urban Energy Systems: A New York City Case Study
http://academiccommons.columbia.edu/catalog/ac:197659
Howard, Bianca Nichole
http://dx.doi.org/10.7916/D8W66KQW
Fri, 15 Apr 2016 18:25:44 +0000
This dissertation describes methods developed for analysis of the New York City energy system. The analysis specifically aims to consider the built environment and its' impacts on greenhouse gas (GHG) emissions. Several contributions to the urban energy systems literature were made. First, estimates of annual energy intensities of the New York building stock were derived using a statistical analysis that leveraged energy consumption and tax assessor data collected by the Office of the Mayor. These estimates provided the basis for an assessment of the spatial distribution of building energy consumption. The energy consumption estimates were then leveraged to estimate the potential for combined heat and power (CHP) systems in New York City at both the building and microgrid scales. In aggregate, given the 2009 nonbaseload GHG emissions factors for electricity production, these systems could reduce citywide GHG emissions by 10%. The operational characteristics of CHP systems were explored further considering different prime movers, climates, and GHG emissions factors. A combination of mixed integer linear programing and controlled random search algorithms were the methods used to determine the optimal capacity and operating strategies for the CHP systems under the various scenarios. Lastly a multiregional unit commitment model of electricity and GHG emissions production for New York State was developed using data collected from several publicly available sources. The model was used to estimate average and marginal GHG emissions factors for New York State and New York City. The analysis found that marginal GHG emissions factors could reduce by 30% to 370 g CO₂e/kWh in the next 10 years.
Energy, Mechanical engineering, Civil engineering
bnh2111
Mechanical Engineering
Dissertations

Micropolar effect on the cataclastic flow and brittleductile transition in highporosity rocks
http://academiccommons.columbia.edu/catalog/ac:195512
Zheng, Zheyuan; Sun, WaiChing; Fish, Jacob
http://dx.doi.org/10.7916/D8DJ5FH8
Thu, 10 Mar 2016 00:00:00 +0000
A micromechanical distinct element method (DEM) model is adopted to analyze the grainscale mechanism that leads to the brittleductile transition in cohesivefrictional materials. The cohesivefrictional materials are idealized as particulate assemblies of circular disks. While the frictional sliding of disks is sensitive to the normal compressive stress exerted on contacts, normal force can be both caused by interpenetration and longrange cohesive bonding between two particles. Our numerical simulations indicate that the proposed DEM model is able to replicate the gradual shift of porosity change from dilation to compaction and failure pattern from localized failures to cataclastic flow upon rising confining pressure in 2D biaxial tests. More importantly, the micropolar effect is examined by tracking couple stress and microcrack initiation to interpret the transition mechanism. Numerical results indicate that the first invariant of the couple stress remains small for specimen sheared under low confining pressure but increases rapidly when subjected to higher confining pressure. The micropolar responses inferred from DEM simulations reveal that microcracking may occur in a more diffuse and stable manner when the first invariant of the macroscopic couple stress are of higher magnitudes.
Materials science, Mechanical engineering, MaterialsMathematical models, MaterialsComputer simulation, PlasticityMathematical models, Mechanics, Applied, Discrete element method, Rock mechanics
ws2414, jf2695
Civil Engineering and Engineering Mechanics
Articles

Part II: Oxidative Thermal Aging of Pd/Al2O3 and Pd/CexOyZrO2 in Automotive Three Way Catalysts: The Effects of Fuel Shutoff and Attempted Fuel Rich Regeneration
http://academiccommons.columbia.edu/catalog/ac:194298
Zheng, Qinghe; Farrauto, Robert; Deeba, Michel
http://dx.doi.org/10.7916/D8VM4C3D
Mon, 15 Feb 2016 00:00:00 +0000
The Pd component in the automotive three way catalyst (TWC) experiences deactivation during fuel shutoff, a process employed by automobile companies for enhancing fuel economy when the vehicle is coasting downhill. The process exposes the TWC to a severe oxidative aging environment with the flow of hot (800 °C–1050 °C) air. Simulated fuel shutoff aging at 1050 °C leads to Pd metal sintering, the main cause of irreversible deactivation of 3% Pd/Al2O3 and 3% Pd/CexOyZrO2 (CZO) as model catalysts. The effect on the Rh component was presented in our companion paper Part I. Moderate support sintering and PdCexOy interactions were also experienced upon aging, but had a minimal effect on the catalyst activity losses. Cooling in air, following aging, was not able to reverse the metallic Pd sintering by redispersing to PdO. Unlike the aged RhTWCs (Part I), reduction via in situ steam reforming (SR) of exhaust HCs was not effective in reversing the deactivation of aged Pd/Al2O3, but did show a slight recovery of the Pd activity when CZO was the carrier. The Pd+/Pd0 and Ce3+/Ce4+ couples in Pd/CZO are reported to promote the catalytic SR by improving the redox efficiency during the regeneration, while no such promoting effect was observed for Pd/Al2O3. A suggestion is made for improving the catalyst performance.
Chemistry, Mechanical engineering, Catalyst poisoning, AutomobilesCatalytic converters, Palladium compounds
qz2178, rf2182
Earth and Environmental Engineering
Articles

Part I: A Comparative Thermal Aging Study on the Regenerability of Rh/Al2O3 and Rh/CexOyZrO2 as Model Catalysts for Automotive Three Way Catalysts
http://academiccommons.columbia.edu/catalog/ac:194295
Zheng, Qinghe; Farrauto, Robert; Deeba, Michel; Valsamakis, Ioannis
http://dx.doi.org/10.7916/D8416WW9
Mon, 15 Feb 2016 00:00:00 +0000
The rhodium (Rh) component in automotive three way catalysts (TWC) experiences severe thermal deactivation during fuel shutoff, an engine mode (e.g., at downhill coasting) used for enhancing fuel economy. In a subsequent switch to a slightly fuel rich condition, in situ catalyst regeneration is accomplished by reduction with H2 generated through steam reforming catalyzed by Rh0 sites. The present work reports the effects of the two processes on the activity and properties of 0.5% Rh/Al2O3 and 0.5% Rh/CexOyZrO2 (CZO) as model catalysts for RhTWC. A very brief introduction of three way catalysts and system considerations is also given. During simulated fuel shutoff, catalyst deactivation is accelerated with increasing aging temperature from 800 °C to 1050 °C. Rh on a CZO support experiences less deactivation and faster regeneration than Rh on Al2O3. Catalyst characterization techniques including BET surface area, CO chemisorption, TPR, and XPS measurements were applied to examine the roles of metalsupport interactions in each catalyst system. For Rh/Al2O3, strong metalsupport interactions with the formation of stable rhodium aluminate (Rh(AlO2)y) complex dominates in fuel shutoff, leading to more difficult catalyst regeneration. For Rh/CZO, Rh sites were partially oxidized to Rh2O3 and were relatively easy to be reduced to active Rh0 during regeneration.
Chemistry, Mechanical engineering, Catalyst poisoning, AutomobilesCatalytic converters, Rhodium compounds
qz2178, rf2182
Earth and Environmental Engineering
Articles

Citizen Sensors for SHM: Towards a Crowdsourcing Platform
http://academiccommons.columbia.edu/catalog/ac:194289
Ozer, Ekin; Feng, Maria Q.; Feng, Dongming
http://dx.doi.org/10.7916/D8WH2PT2
Mon, 15 Feb 2016 00:00:00 +0000
This paper presents an innovative structural health monitoring (SHM) platform in terms of how it integrates smartphone sensors, the web, and crowdsourcing. The ubiquity of smartphones has provided an opportunity to create lowcost sensor networks for SHM. Crowdsourcing has given rise to citizen initiatives becoming a vast source of inexpensive, valuable but heterogeneous data. Previously, the authors have investigated the reliability of smartphone accelerometers for vibrationbased SHM. This paper takes a step further to integrate mobile sensing and webbased computing for a prospective crowdsourcingbased SHM platform. An iOS application was developed to enable citizens to measure structural vibration and upload the data to a server with smartphones. A webbased platform was developed to collect and process the data automatically and store the processed data, such as modal properties of the structure, for longterm SHM purposes. Finally, the integrated mobile and webbased platforms were tested to collect the lowamplitude ambient vibration data of a bridge structure. Possible sources of uncertainties related to citizens were investigated, including the phone location, coupling conditions, and sampling duration. The field test results showed that the vibration data acquired by smartphones operated by citizens without expertise are useful for identifying structural modal properties with high accuracy. This platform can be further developed into an automated, smart, sustainable, costfree system for longterm monitoring of structural integrity of spatially distributed urban infrastructure. Citizen Sensors for SHM will be a novel participatory sensing platform in the way that it offers hybrid solutions to transitional crowdsourcing parameters.
Mechanical engineering, Information technology, Civil engineering, Structural health monitoring, Human computation, Smartphones
eo2327, mqf2101, df2465
Civil Engineering and Engineering Mechanics
Articles

A VisionBased Sensor for Noncontact Structural Displacement Measurement
http://academiccommons.columbia.edu/catalog/ac:194292
Feng, Dongming; Feng, Maria Q.; Ozer, Ekin; Fukuda, Yoshio
http://dx.doi.org/10.7916/D8CJ8DBF
Mon, 15 Feb 2016 00:00:00 +0000
Conventional displacement sensors have limitations in practical applications. This paper develops a vision sensor system for remote measurement of structural displacements. An advanced template matching algorithm, referred to as the upsampled cross correlation, is adopted and further developed into a software package for realtime displacement extraction from video images. By simply adjusting the upsampling factor, better subpixel resolution can be easily achieved to improve the measurement accuracy. The performance of the vision sensor is first evaluated through a laboratory shaking table test of a frame structure, in which the displacements at all the floors are measured by using one camera to track either highcontrast artificial targets or lowcontrast natural targets on the structural surface such as bolts and nuts. Satisfactory agreements are observed between the displacements measured by the single camera and those measured by highperformance laser displacement sensors. Then field tests are carried out on a railway bridge and a pedestrian bridge, through which the accuracy of the vision sensor in both time and frequency domains is further confirmed in realistic field environments. Significant advantages of the noncontact vision sensor include its low cost, ease of operation, and flexibility to extract structural displacement at any point from a single measurement.
Mechanical engineering, Information technology, Civil engineering, Template matching (Digital image processing), Earth movements and building, Structural health monitoring, Detectors
df2465, mqf2101, eo2327, yf2290
Civil Engineering and Engineering Mechanics
Articles

High resolution quantification of cellular forces for rigidity sensing
http://academiccommons.columbia.edu/catalog/ac:194220
Liu, Shuaimin
http://dx.doi.org/10.7916/D8KP8202
Fri, 05 Feb 2016 00:00:00 +0000
This thesis describes a comprehensive study of understanding the mechanism of rigidity sensing by quantitative analysis using submicron pillar array substrates. From mechanobiology perspective, we explore and study molecular pathways involved in rigidity and force sensing at cellmatrix adhesions with regard to cancer, regeneration, and development by quantification methods. In Chapter 2 and 3, we developed fabrication and imaging techniques to enhance the performance of a submicron pillar device in terms of spatial and temporal measurement ability, and we discovered a correlation of rigidity sensing forces and corresponding proteins involved in the early rigidity sensing events. In Chapter 2, we introduced optical effect arising from submicron structure imaging, and we described a technique to identify the correct focal plane of pillar tip by fabricating a substrate with designedoffset pillars. From calibration result, we identified the correct focal plane that was previously overlooked, and verified our findings by other imaging techniques. In Chapter 3, we described several techniques to selectively functionalize elastomeric pillars top and compared these techniques in terms of purposes and fabrication complexity. Techniques introduced in this chapter included direct labeling, such as stamping of fluorescent substances (organic dye, nanodiamond, qdot) to pillars top, as well as indirect labeling that selectively modify the surface of molds with either metal or fluorescent substances. In Chapter 4, we examined the characteristics of local contractility forces and identified the components formed a sarcomere like contractile unit (CU) that cells use to sense rigidity. CUs were found to be assembled at cell edge, contain myosin II, αactinin, tropomodulin and tropomyosin (Tm), and resemble sarcomeres in size (~2 μm) and function. Then we performed quantitative analysis of CUs to evaluate rigidity sensing activity over ~8 hours time course and found that density of CUs decrease with time after spreading on stiff substrate. However addition of EGF dramatically increased local contraction activity such that about 30% of the total contractility was in the contraction units. This stimulatory effect was only observed on stiff substrate not on soft. Moreover, we find that in the early interactions of cells with rigid substrates that EGFR activity is needed for normal spreading and the assembly of local contraction units in media lacking serum and any soluble EGF. In Chapter 5, we performed high temporal and spatialresolution tracking of contractile forces exerted by cells on submicron elastomeric pillars. We found that actomyosinbased sarcomerelike CUs simultaneously moved opposing pillars in net steps of ~2.5 nm, independent of rigidity. What correlated with rigidity was the number of steps taken to reach a force level that activated recruitment of αactinin to the CUs. When we removed actomyosin restriction by depleting tropomyosin 2.1, we observed larger steps and higher forces that resulted in aberrant rigidity sensing and growth of nontransformed cells on soft matrices. Thus, we conclude that tropomyosin 2.1 acts as a suppressor of growth on soft matrices by supporting proper rigidity sensing.
Nanotechnology, Mechanical engineering, Cellular biology, Dynamics, Rigid, Molecular structureData processing, Nanoelectromechanical systems, Cell adhesion molecules, Biomechanics, Tropomyosins, Cellmatrix adhesions
Mechanical Engineering
Dissertations

Simultaneous Parameter and Input Estimation of a Respiratory Mechanics Model
http://academiccommons.columbia.edu/catalog/ac:192808
Vicario, Francesco; Albanese, Antonio; Wang, Dong; Karamolegkos, Nikolaos; Chbat, Nicolas W.
http://dx.doi.org/10.7916/D88K78T3
Fri, 08 Jan 2016 00:00:00 +0000
Realtime noninvasive estimation of respiratory mechanics in spontaneously breathing patients is still an open problem in the field of critical care. Even assuming that the system is a simplistic firstorder singlecompartment model, the presence of unmeasured patient effort still makes the problem complex since both the parameters and part of the input are unknown. This paper presents an approach to overcome the underdetermined nature of the mathematical problem by infusing physiological knowledge into the estimation process and using it to construct an optimization problem subject to physiological constraints. As it relies only on measurements available on standard ventilators, namely the flow and pressure at the patient’s airway opening, the approach is noninvasive. Additionally, breath by breath, it continually provides estimates of the patient respiratory resistance and elastance as well as of the muscle effort waveform without requiring maneuvers that would interfere with the desired ventilation pattern.
Mechanical engineering, Applied mathematics, Computer science, RespirationMeasurement, RespirationPhysiological aspects, RespirationMathematical models
fv2157, nk2440, nc22
Mechanical Engineering, Biomedical Engineering
Conferences

Silicon Photonic Devices and Their Applications
http://academiccommons.columbia.edu/catalog/ac:193245
Li, Ying
http://dx.doi.org/10.7916/D8CJ8D8J
Thu, 07 Jan 2016 00:00:00 +0000
Silicon photonics is the study and application of photonic systems, which use silicon as an optical medium. Data is transferred in the systems by optical rays. This technology is seen as the substitutions of electric computer chips in the future and the means to keep tack on the Moore’s law. Cavity optomechanics is a rising field of silicon photonics. It focuses on the interaction between light and mechanical objects. Although it is currently at its early stage of growth, this field has attracted rising attention. Here, we present highly sensitive optical detection of acceleration using an optomechanical accelerometer. The core part of this accelerometer is a slottype photonic crystal cavity with strong optomechanical interactions. We first discuss theoretically the optomechanical coupling in the airslot modegap photonic crystal cavity. The dispersive coupling gom is numerically calculated. Dynamical parametric oscillations for both cooling and amplification, in the resolved and unresolved sideband limit, are examined numerically, along with the displacement spectral density and cooling rates for the various operating parameters. Experimental results also demonstrated that the cavity has a large optomechanical coupling rate. The optically induced spring effect, damping and amplification of the mechanical modes are observed with measurements both in air and in vacuum. Then, we propose and demonstrate our optomechanical accelerometer. It can operate with a resolution of 730 ng/Hz¹/² (or equivalently 40.1 aN/Hz¹/²) and with a transduction bandwidth of ≈ 85 kHz. We also demonstrate an integrated photonics device, an onchip spectroscopy, in the last part of this thesis. This new type of onchip microspectrometer is based on the Vernier effect of two cascaded microring cavities. It can measure optical spectrum with a bandwidth of 74nm and a resolution of 0.22 nm in a small footprint of 1.5 mm².
Optics, Mechanical engineering, SiliconOptical properties, Photonics, Optomechanics, PhotonicsIndustrial applications
yl2584
Electrical Engineering, Mechanical Engineering
Dissertations

Bilinear System Identification by MinimalOrder State Observers
http://academiccommons.columbia.edu/catalog/ac:192617
Vicario, Francesco; Phan, Minh Q.; Longman, Richard W.; Betti, Raimondo
http://dx.doi.org/10.7916/D87944DV
Tue, 05 Jan 2016 15:44:01 +0000
Bilinear systems offer a promising approach for nonlinear control because a broad class of nonlinear problems can be reformulated and approximated in bilinear form. System identification is a technique to obtain such a bilinear approximation for a nonlinear system from inputoutput data. Recent discretetime bilinear model identification methods rely on InputOutputtoState Representations (IOSRs) derived via the interaction matrix technique. A new formulation of these methods is given by establishing a correspondence between interaction matrices and the gains of fullorder bilinear state observers. The new interpretation of the identification methods highlights the possibility of utilizing minimalorder bilinear state observers to derive new IOSRs. The existence of such observers is discussed and shown to be guaranteed for special classes of bilinear systems. New bilinear system identification algorithms are developed and the corresponding computational advantages are illustrated via numerical examples.
Mechanical engineering, Mathematics, Aerospace engineering
fv2157, rwl4, rb68
Mechanical Engineering, Civil Engineering and Engineering Mechanics
Conferences

A LinearTimeVarying Approach for Exact Identification of Bilinear DiscreteTime Systems by Interaction Matrices
http://academiccommons.columbia.edu/catalog/ac:192623
Vicario, Francesco; Phan, Minh Q.; Longman, Richard W.; Betti, Raimondo
http://dx.doi.org/10.7916/D8Q81CT0
Tue, 05 Jan 2016 00:00:00 +0000
Bilinear systems offer a promising approach for nonlinear control because a broad class of nonlinear problems can be reformulated in bilinear form. In this paper system identification is shown to be a technique to obtain such a bilinear approximation of a nonlinear system. Recent discretetime bilinear model identification methods rely on InputOutputtoState Representations. These IOSRs are exact only for a certain class of bilinear systems, and they are also limited by high dimensionality and explicit bounds on the input magnitude. This paper offers new IOSRs where the bilinear system is treated as a linear timevarying system through the use of specialized input signals. All the mentioned limitations are overcome by the new approach, leading to more accurate and less computationally demanding identification methods for bilinear discretetime models, which are also shown via examples to be applicable to the identification of bilinear models approximating more general nonlinear systems.
Mechanical engineering, Mathematics, Astrophysics, Astrodynamics, Bilinear forms, Discretetime systemsMathematical models, Matrices
fv2157, rwl4, rb68
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Conferences

Bilinear Observer/Kalman Filter Identification
http://academiccommons.columbia.edu/catalog/ac:192626
Vicario, Francesco; Phan, Minh Q.; Betti, Raimondo; Longman, Richard W.
http://dx.doi.org/10.7916/D8FQ9WCD
Tue, 05 Jan 2016 00:00:00 +0000
Bilinear systems are important per se since several phenomena in engineering and other fields are inherently bilinear. Even more interestingly, bilinear systems can approximate more general nonlinear systems, providing a promising approach to handle various nonlinear identification and control problems, such as satellite attitude control. This paper develops and demonstrates via numerical examples a method for discretetime statespace model identification for bilinear systems in the presence of noise in the process and in the measurements. The formulation relies on a bilinear observer which is proven to have properties similar to the linear Kalman filter under the sole additional assumption of stationary white excitation input, and on a novel approach to system identification based on the estimation of the observer residuals. The latter are used to construct a new, noisefree identification problem, in which the observer is identified and the matrices of the system statespace model are recovered. The resulting method represents the bilinear counterpart of the Observer/Kalman filter Identification (OKID) approach for linear systems, originally developed for the identification of lightlydamped structures and distributed by NASA.
Mechanical engineering, Mathematics, Aerospace engineering, Bilinear forms, Discretetime systemsMathematical models, Kalman filtering, Space flightMathematical models
fv2157, rb68, rwl4
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Conferences

OKID as a Unified Approach to System Identification
http://academiccommons.columbia.edu/catalog/ac:192629
Vicario, Francesco; Phan, Minh Q.; Betti, Raimondo; Longman, Richard W.
http://dx.doi.org/10.7916/D869739X
Tue, 05 Jan 2016 00:00:00 +0000
This paper presents a unified approach for the identification of linear statespace models from inputoutput measurements in the presence of noise. It is based on the established Observer/Kalman filter IDentification (OKID) method of which it proposes a new formulation capable of transforming a stochastic identification problem into a (simpler) deterministic problem, where the Kalman filter corresponding to the unknown system and the unknown noise covariances is identified. The system matrices are then recovered from the identified Kalman filter. The Kalman filter can be identified with any deterministic identification method for linear statespace models, giving rise to numerous new algorithms and establishing the Kalman filter as the unifying bridge from stochastic to deterministic problems in system identification.
Mechanical engineering, Mathematics, Aerospace engineering, System identification, Space flightMathematical models, Kalman filtering, Statespace methods
fv2157, rb68, rwl4
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Conferences

Extension of OKID to OutputOnly System Identification
http://academiccommons.columbia.edu/catalog/ac:192587
Vicario, Francesco; Phan, Minh Q.; Betti, Raimondo; Longman, Richard W.
http://dx.doi.org/10.7916/D8GQ6XGB
Tue, 05 Jan 2016 00:00:00 +0000
Observer/Kalman filter IDentification (OKID) is a successful approach for the estimation, from measured inputoutput data, of the linear statespace model describing the dynamic behavior of a structure. From such a mathematical model, it is possible to recover the modal parameters, which can be exploited to update a detailed numerical model of the structure, e.g. a Finite Element Model (FEM), to be used to predict the structural response to future excitation and to evaluate damage scenarios. This paper extends OKID to outputonly system identification, i.e. to the case where only the response of the structure is measured and the input is unknown. The approach is suitable for structural health monitoring based on modal parameters, in particular for those civil infrastructures whose excitation is random in nature and in the way it is applied to the structure (e.g. wind, traffic) and therefore is difficult to measure. The paper rigorously proves the applicability of the OKID approach to the outputonly case, presents the resulting new algorithms and demonstrates them via a numerical example.
Mechanical engineering, Engineering, Civil engineering, Structural analysis (Engineering)Mathematical models, Finite element methodMathematical models, Structural engineering
fv2157, rb68, rwl4
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Conferences

An AllInteraction Matrix Approach to Linear and Bilinear System Identification
http://academiccommons.columbia.edu/catalog/ac:192641
Phan, Minh Q.; Vicario, Francesco; Longman, Richard W.; Betti, Raimondo
http://dx.doi.org/10.7916/D8DV1JMF
Tue, 05 Jan 2016 00:00:00 +0000
This paper is a brief introduction to the interaction matrices. Originally formulated as a parameter compression mechanism, the interaction matrices offer a unifying framework to treat a wide range of problems in system identification and control. We retrace the origin of the interaction matrices, and describe their applications in selected problems in system identification.
Mechanical engineering, Applied mathematics, Computer science, System identification, Matrices, Markov processesMathematical models
fv2157, rwl4, rb68
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Conferences

Generalized Framework of OKID for Linear StateSpace Model Identification
http://academiccommons.columbia.edu/catalog/ac:192638
Vicario, Francesco; Phan, Minh Q.; Longman, Richard W.; Betti, Raimondo
http://dx.doi.org/10.7916/D8P84BMQ
Tue, 05 Jan 2016 00:00:00 +0000
This paper presents a generalization of observer/Kalman filter identification (OKID). OKID is a method for the simultaneous identification of a linear dynamical system and the associated Kalman filter from inputoutput measurements corrupted by noise. OKID was originally developed at NASA as the OKID/ERA algorithm. Recent work showed that ERA is not the only way to complete the OKID process and paved the way to the generalization of OKID as an approach to linear system identification. As opposed to other approaches, OKID is explicitly formulated via state observers providing an intuitive interpretation from a control theory perspective. The extension of the OKID framework to more complex identification problems, including nonlinear systems, is also discussed.
Mechanical engineering, Applied mathematics, Computer science, Statespace methods, Kalman filtering, Linear systems, Control theoryMathematical models
fv2157, rwl4, rb68
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Conferences

Superspace and Subspace Identification of Bilinear Models by DiscreteLevel Inputs
http://academiccommons.columbia.edu/catalog/ac:192778
Phan, Minh Q.; Vicario, Francesco; Longman, Richard W.; Betti, Raimondo
http://dx.doi.org/10.7916/D8XS5V4C
Tue, 05 Jan 2016 00:00:00 +0000
When excited by an input consisting of a number of discrete levels, a bilinear system becomes a linear timevarying system whose dynamics switches from one linear subsystem to another depending on the input level. This paper describes an identification method that uses the concept of a superstate of a linear switching system as a superstate of the bilinear system. In a superspace method, these superstates are used directly to identify a bilinear system model. In a subspace method, two or more superstate representations are intersected to find a reduced dimension subspace prior to identification of a bilinear model.
Mechanical engineering, Mathematics, Aerospace engineering, Space flightMathematical models, Statespace methods, Bilinear forms
fv2157, rwl4, rb68
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Conferences

Material Wear in Multilayered Separable Electrical Contacts: Modeling and Experimentation
http://academiccommons.columbia.edu/catalog/ac:191555
Wang, Yuanyuan
http://dx.doi.org/10.7916/D8X63MM4
Sat, 28 Nov 2015 00:00:00 +0000
In electrical contacts, thin films of nickel and gold or silver are traditionally plated on top of a copper base plate to provide corrosion resistance and wear protection. Most recently, the rising cost of noble metals and intensified competition in manufacturing technology has driven the industry towards thinner plating layers, which gives rise to questions regarding how interfacial contact and wear is affected by plating thickness and material characteristics. This study uses a combination of finite element analysis and exsitu wear measurement to determine the effect of gold plating thickness on wear performance under linear reciprocating sliding contact. Correlations between predicted and measured results lead to insight into the stress state within the multilayer system under contact conditions as well as a wear map for gold platings that can be used to inform future connector designs. The middle layer material, Ni, is relatedly inexpensive, but takes a relatively long time to deposit. Because this deposition time has a direct influence on the cost of manufacturing, it is important to reduce the Ni thickness as well. This project thus determines how different combinations of Ni and Au properties influence wear and subsurface layer exposure, which is critical for determining the makeup of future, lowcost, connector designs.
Mechanical engineering, Mechanical wear, Goldplating, Nickelplating, Corrosion resistant materials, Manufacturing industriesTechnological innovations
yw2387
Mechanical Engineering
Dissertations

Determining Material Parameters for Critical State Plasticity Models Based on Multilevel Extended Digital Database
http://academiccommons.columbia.edu/catalog/ac:191089
Liu, Yang; Sun, WaiChing; Fish, Jacob
http://dx.doi.org/10.7916/D8WM1D13
Tue, 17 Nov 2015 00:00:00 +0000
This work presents a new staggered multilevel material identification procedure for phenomenological critical state plasticity models. The emphasis is placed on cases in which available experimental data and constraints are insufficient for calibration. The key idea is to create a secondary virtual experimental database from highfidelity models, such as discrete element simulations, then merge both the actual experimental data and secondary database as an extended digital database (EDD) to determine material parameters for the phenomenological macroscopic critical state plasticity model. The calibration procedure therefore consists of two steps. First, the material parameters of the discrete (distinct) element method (DEM) simulations are identified via the standard optimization procedure. Then, the calibrated DEM simulations are used to expand the experimental database with new simulated loading histories. This expansion of database provides additional constraints necessary for calibration of the phenomenological critical state plasticity models. The robustness of the proposed material identification framework is demonstrated in the context of the Dafalias–Manzari plasticity model.
Materials science, Mechanical engineering, MaterialsMathematical models, MaterialsComputer simulation, PlasticityMathematical models, Mechanics, Applied
yl2683, ws2414, jf2695
Civil Engineering and Engineering Mechanics
Articles

The Characterization of Mechanical Behaviors of Two Dimensional Nanomaterials with Grains and Grain Boundaries
http://academiccommons.columbia.edu/catalog/ac:189352
An, Sung Joo
http://dx.doi.org/10.7916/D8RV0N5K
Fri, 09 Oct 2015 00:00:00 +0000
Graphene, two dimensional lattice of covalent bonds of carbon atoms, has been studied as a prospective new material for the next generation. Pristine graphene, mechanically exfoliated graphene from graphite, has gained much attention due to its outstanding properties: conductivity, permeability, transparency, and mechanical stability. While pristine graphene has shown great promise as an innovative new material, the limitations from the randomness of sizes and domains are challenging for uniform mass production. In this dissertation, we present graphene produced by chemical vapor deposition (CVD) synthesis for producing designated sizes and domains. In order to prospect the utilization, the mechanical stability of CVD graphene should be determined. We first present mechanical properties of CVD graphene. Introducing transfer method, we present how to minimize damages on graphene during the fabrication. For the measurement of mechanical properties of CVD graphene, we introduce nanoindentation test with AFM and nanoindenter. Experimental results are demonstrated by the results of FEA analysis on the basis of nonlinear elastic behaviors. Through the experiment and simulation, we verify the ultrahigh mechanical strength of CVD graphene. We also present defectengineered graphene for the utilization. To determine the change of the status of defects on pristine graphene, we employed plasma etching to induce defects gradually. Through the observation of change of defects from sp3 type to sp2 type on pristine graphene, we understand how the phase changes depending on defects. Using nanoindentation, the mechanical strength of defective graphene is determined and we discuss its utilization based on the mechanical stability. We next exploit grains and grain boundaries of polycrystalline graphene. Transmission electron microscope (TEM) is used for precise observation of suspended membrane with grains and grain boundaries. Applying the same nanoindentation test, we compare the values of grain boundaries to pristine lattice in order to determine how grains and grain boundaries affect the ultrahigh mechanical properties of graphene as defects. We finally present angular dependence of the mechanical properties of grains and grain boundaries. Although previous research reported the angular dependence of graphene regarding its mechanical strength, it was questionable that tilt angles among grains could not affect mechanical strength based on our previous experimental data. Therefore, here we reveal that how tilt angles among grains affect the mechanical properties. Furthermore, we investigate the crack propagation at rupture of graphene in both nanoindentation and ebeam exposure. Hence, we conclude the dissertation by a discussion of directions for future work, proposing wellstitched condition of graphene, and HR TEM for the verification of real structure of grain boundaries to apply into simulation. Therefore, this thesis is an arrangement of the outstanding mechanical properties of graphene from pristine graphene to CVD graphene in both small grain and large grain type, and from macroscopic region of interests over suspended membrane to microscopic observation such as the mechanical behaviors of grains and grain boundaries.
Mechanical engineering, Materials science, Nanotechnology
sa2295
Mechanical Engineering
Dissertations

Citizen Sensors for SHM: Use of Accelerometer Data from Smartphones
http://academiccommons.columbia.edu/catalog/ac:189133
Feng, Maria Q.; Fukuda, Yoshio; Mizuta, Masato; Ozer, Ekin
http://dx.doi.org/10.7916/D80C4V6C
Tue, 06 Oct 2015 00:00:00 +0000
Ubiquitous smartphones have created a significant opportunity to form a lowcost wireless Citizen Sensor network and produce big data for monitoring structural integrity and safety under operational and extreme loads. Such data are particularly useful for rapid assessment of structural damage in a large urban setting after a major event such as an earthquake. This study explores the utilization of smartphone accelerometers for measuring structural vibration, from which structural health and postevent damage can be diagnosed. Widely available smartphones are tested under sinusoidal wave excitations with frequencies in the range relevant to civil engineering structures. Largescale seismic shaking table tests, observing input ground motion and response of a structural model, are carried out to evaluate the accuracy of smartphone accelerometers under operational, whitenoise and earthquake excitations of different intensity. Finally, the smartphone accelerometers are tested on a dynamically loaded bridge. The extensive experiments show satisfactory agreements between the reference and smartphone sensor measurements in both time and frequency domains, demonstrating the capability of the smartphone sensors to measure structural responses ranging from lowamplitude ambient vibration to highamplitude seismic response. Encouraged by the results of this study, the authors are developing a citizenengaging and dataanalytics crowdsourcing platform towards a smartphonebased Citizen Sensor network for structural health monitoring and postevent damage assessment applications.
Physics, Mechanical engineering, Civil engineering
mqf2101, yf2290, mm4230, eo2327
Civil Engineering and Engineering Mechanics
Articles

A CableDriven Pelvic Robot: Human Gait Adaptation and Rehabilitation Studies
http://academiccommons.columbia.edu/catalog/ac:189634
Vashista, Vineet
http://dx.doi.org/10.7916/D80K27XN
Tue, 22 Sep 2015 21:23:39 +0000
Walking is a state of continuous imbalance that requires a complex control strategy and cyclic activation of leg muscles to achieve successful inter‐limb coordination. Neuro‐musculoskeletal impairments, such as stroke, cerebral palsy, and spinal cord injury, affect one's ability to voluntarily contract muscles to normal amplitudes. This change in muscle activation pattern reduces the joint level torque generation and as a result impairs the ability to walk normally. Technological advances over the last two decades have resulted in the development of rigid link robotic exoskeletons that aim to improve gait deficits. These devices reduce repetitive and manual labor of therapists while providing objective measurement of the therapy during the gait rehabilitation. Despite the development of these robotic devices, no consensus has emerged about the superiority of robotaided gait rehabilitation over the traditional methods. This may be because of the inherent complexity of the human musculoskeletal system and the constraints that rigid linked systems impose on the human movement.
In this work, we present a cabledriven Active Tethered Pelvic Assist Device (ATPAD) for gait rehabilitation that can apply a controlled external wrench to the human pelvis in any direction and at any point of the gait cycle for a specified duration. The ATPAD does not add undesirable inertia on the user and does not constrain the user's motion during training. The ATPAD provides a technological platform to scientifically study human adaptation in gait due to externally applied forces and moments on the pelvis. Human studies with the ATPAD can motivate new gait rehabilitation paradigms which can potentially be used to correct gait deficits in human walking.
The human nervous system is capable of modifying the motor commands in response to alterations in the movement conditions. Several studies have demonstrated the flexibility of human locomotion despite motor impairments and have shown the potential of using such paradigms for gait rehabilitation. In this work, we present a number of human experiments using the cabledriven ATPAD to propose novel force interventions that induce adaptation in human gait kinematics and kinetics. In particular, stance phase gait interventions have been developed for gait rehabilitation of hemiparetic patients. In these interventions, the external force vector was applied to the pelvis to target weight bearing during walking and to promote longer stance durations. A singlesession force training experiment with hemiparetic stroke patients was also conducted as a part of this work. It is shown that hemiparetic stroke patients improved the ground reaction force symmetry, forward propulsion effort, and stance phase symmetry during walking.
In this work, the ATPAD is also used to develop an intervention to apply external gait synchronized forces on the pelvis to reduce the user's effort during walking. The external forces were directed in the sagittal plane to assist the trailing leg during the forward propulsion and vertical deceleration of the pelvis during the gait cycle. A pilot experiment with five healthy subjects was conducted. This study provides a novel approach to study the role of external forces in altering the walking effort, such understanding is important while designing assistive devices for individuals who spend higher than normal effort during walking.
Robotics, Mechanical engineering, Biomechanics
vv2233
Mechanical Engineering
Dissertations

Observers for Bilinear StateSpace Models by Interaction Matrices
http://academiccommons.columbia.edu/catalog/ac:187857
Phan, Minh Q.; Vicario, Francesco; Longman, Richard W.; Betti, Raimondo
http://dx.doi.org/10.7916/D8W37VKR
Fri, 21 Aug 2015 00:00:00 +0000
This paper formulates a bilinear observer for a bilinear statespace model. Relationship between the bilinear observer gains and the interaction matrices are established and used in the design of such observer gains from inputoutput data. In the absence of noise, the question of whether a deadbeat bilinear observer exists that would cause the state estimation error to converge to zero identically in a finite number of time steps is addressed. In the presence of noise, an optimal bilinear observer that minimizes the state estimation error in the same manner that a Kalman filter does for a linear system is presented. Numerical results illustrate both the theoretical and computational aspects of the proposed algorithms.
Mechanical engineering
fv2157, rwl4, rb68
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Articles

Linear State Representations for Identification of Bilinear DiscreteTime Models by Interaction Matrices
http://academiccommons.columbia.edu/catalog/ac:187836
Vicario, Francesco; Phan, Minh Q.; Betti, Raimondo; Longman, Richard W.
http://dx.doi.org/10.7916/D84X571T
Thu, 13 Aug 2015 00:00:00 +0000
Bilinear systems can be viewed as a bridge between linear and nonlinear systems, providing a promising approach to handle various nonlinear identification and control problems. This paper provides a formal justification for the extension of interaction matrices to bilinear systems and uses them to express the bilinear state as a linear function of inputoutput data. Multiple representations of this kind are derived, making it possible to develop an intersection subspace algorithm for the identification of discretetime bilinear models. The technique first recovers the bilinear state by intersecting two vector spaces that are defined solely in terms of inputoutput data. The new inputoutputtostate relationships are also used to extend the Equivalent Linear Model method for bilinear system identification. Among the benefits of the proposed approach, it does not require data from multiple experiments, and it does not impose specific restrictions on the form of input excitation.
Mechanical engineering, Aerospace engineering
fv2157, rb68, rwl4
Civil Engineering and Engineering Mechanics, Mechanical Engineering
Articles

Friction and wear measurements of bovine articular cartilage against nonnative materials
http://academiccommons.columbia.edu/catalog/ac:187094
Oungoulian, Sevan Richard
http://dx.doi.org/10.7916/D86972N0
Mon, 11 May 2015 15:33:01 +0000
The three studies reported in this thesis investigate the friction and wear properties of articular cartilage.
The aim of the first study presented was to examine the functional properties and biocompatibility of glutaraldehydefixed bovine articular cartilage for potential use as a resurfacing material in joint arthroplasty. Treated cartilage disks were fixed over a range of glutaraldehyde concentrations and incubated, along with an untreated control group, at 37 °C for up to 28 days. The equilibrium compressive modulus increased nearly twofold in the treated samples when compared to day 0 control, and maintained that property value from day 1 to day 28; the minimum friction coefficient did not change significantly with fixation and incubation time, whereas the time constant for the frictional response decreased twofold at most. Live explants cocultured with fixed explants showed no qualitative difference in cell viability over 28 days of incubation. Cartilageoncartilage frictional measurements were performed under the configuration of migrating contact for a subset of treated explants over a period of 28 days exhibited either no significant difference or slightly lower friction coefficient values than the untreated control group. These results suggest that a properly titrated glutaraldehyde treatment can reproduce the desired functional properties of native articular cartilage and maintain these properties for at least 28 days invitro.
The aim of the second study was to determine whether the latestgeneration particle analyzers are capable of detecting cartilage wear debris generated during in vitro loading experiments that last 24 h or less, by producing measurable content significantly above background noise levels otherwise undetectable through standard biochemical assays. Immature bovine cartilage disks were tested against glass using reciprocal sliding under unconfined compression creep for 24 h. Control groups were used to assess various sources of contamination. Results demonstrated that cartilage samples subjected to frictional loading produced particulate volume significantly higher than background noise and contamination levels at all tested time points. The particle counter used was able to detect very small levels of wear), whereas no significant differences were observed in biochemical assays for collagen or glycosaminoglycans among any of the groups or time points.
The aim of the final study was to measure the wear response of immature bovine articular cartilage tested against glass or alloys used in hemiarthroplasties. Two cobalt chromium alloys and a stainless steel alloy were selected for these investigations. The surface roughness of one of the cobalt chromium alloys was also varied within the range considered acceptable by regulatory agencies. Cartilage disks were tested in a configuration that promoted loss of interstitial fluid pressurization to replicate conditions believed to occur in hemiarthroplasties. Results showed that considerably more damage occurred in cartilage samples tested against smooth stainless steel and rough cobalt chromium alloys compared to smooth glass, and smooth cobalt chromium alloys. The two materials producing the greatest damage also exhibited higher equilibrium friction coefficients. Cartilage damage occurred primarily in the form of delamination at the interface between the superficial tangential zone and the transitional middle zone, with much less evidence of abrasive wear at the articular surface. These results suggest that cartilage damage from frictional loading occurs as a result of subsurface fatigue failure leading to the delamination. Surface chemistry and surface roughness of implant materials can have a significant influence on tissue damage, even when using materials and roughness values that satisfy regulatory requirements.
Mechanical engineering
so2271
Mechanical Engineering
Dissertations

A stabilized finite element formulation for monolithic thermohydromechanical simulations at finite strain
http://academiccommons.columbia.edu/catalog/ac:186086
Sun, WaiChing
http://dx.doi.org/10.7916/D8765DFZ
Mon, 06 Apr 2015 12:46:33 +0000
An adaptively stabilized monolithic finite element model is proposed to simulate the fully coupled thermohydromechanical behavior of porous media undergoing large deformation. We first formulate a finitedeformation thermohydromechanics field theory for nonisothermal porous media. Projectionbased stabilization procedure is derived to eliminate spurious pore pressure and temperature modes due to the lack of the twofold infsup condition of the equalorder finite element. To avoid volumetric locking due to the incompressibility of solid skeleton, we introduce a modified assumed deformation gradient in the formulation for nonisothermal porous solids. Finally, numerical examples are given to demonstrate the versatility and efficiency of this thermohydromechanical model.
Materials science, Mechanical engineering
ws2414
Civil Engineering and Engineering Mechanics
Articles

Characterization and Modeling of Ferromagnetic Particulate Nanocomposites for Strain and Fracture Sensing
http://academiccommons.columbia.edu/catalog/ac:185280
Jang, SungHwan
http://dx.doi.org/10.7916/D8Q23Z4R
Fri, 27 Mar 2015 00:00:00 +0000
This dissertation investigates the multiphysical behavior of multiwalled carbon nanotubes (MWCNTs)/polydimenthylsiloxane (PDMS) composites containing chainstructured nickel particles for strain sensing. Compared with traditional strain gauges, this novel strain sensor exhibits high flexibility, large elongation, and high strain sensitivity and therefore has a wide application in structural health monitoring and fracture detection with minimal surface preparation. The scope of this study covers the material fabrication, numerical simulation of microstructure evolution, micromechanicsbased characterization and modeling for the multiphysical properties, and experimental investigation of the strain sensitivity in sensing applications. MWCNT/PDMS composites with chainstructured ferromagnetic particles were fabricated using a solution casting method under an external magnetic field. Different concentrations of MWCNTs, as well as ferromagnetic particles, were well mixed in the prepolymer matrix. An external magnetic field was applied during the curing process to align the particles into a chain structure. The morphology of MWCNTs and chainstructured nickel particles in the PDMS were investigated using an optical microscope and a scanning electron microscope. The electrical properties such as a percolation threshold and electrical conductivity of MWCNT/PDMS composites with different concentrations of chainstructured ferromagnetic particles were investigated for strain sensing application. For MWCNT/PDMS composites, a simplified model has been developed to predict their effective electrical conductivity. MWCNTs are well dispersed in a PDMS matrix, and the mixture is then cured and cast into thin films for electrical characterization. The MWCNTs are assumed to be statistically uniformly distributed in the PDMS matrix with the threedimensional (3D) waviness. As the proportion of MWCNTs increases to a certain level, namely the percolation threshold, the discrete MWCNTs start to connect with each other, forming a 3D network which exhibits a significant increase in the effective electrical conductivity. The eightchain model has been used to predict the effective electrical conductivity of the composite, in which the contact resistance between MWCNTs has been considered through the Simmons' equation. The eightchain network features can be significantly changed to adjust to modifications to the mixing process, MWCNT length and diameter, and clustering and curling of MWCNTs. A Gaussian statisticsbased formulation is used to calculated the effective length of a single MWCNT which is well dispersed in the matrix. The modeling results for the effective electrical conductivity agree with the experiments very well, they are highly dependent on the contact resistance between MWCNTs and the waviness of the MWCNTs. The effect of internanotube distance and diameter of MWCNTs on the effective electrical conductivity of the MWCNT/PDMS composite is also discussed.Micromechanicsbased modeling method of the microstructure evolution of ferromagnetic particles moving in the PDMS prepolymer has been developed to understand the alignment mechanism and to optimize the fabrication procedure. Under a uniformly applied magnetic field, in the neighborhood of ferromagnetic particles, the magnetic field will be significantly distorted and the magnetic force induced will align particles into short chains, which will further merge into long chains. The experiments have been simulated with the equivalent inclusion method. This study has led to the development of a novel strain sensor. Both MWCNTs and ferromagnetic particles enhanced the electrical conductivity of the nanocomposites, but they exhibited different effects on the strain sensitivity of the sensor. When the proportion of MWCNTs that are well dispersed in PDMS is higher than the percolation threshold, the strain sensitivity reduces with the increase of MWCNTs in general; whereas a higher volume fraction of FPs produces a higher strain sensitivity when the chainstructure of FPs is sustained. The mechanisms causing this interesting phenomenon have been demonstrated through the microstructural evolution and micromechanicsbased modeling method. These findings indicate that an optimal design of the volume fraction of FPs and MWCNTs exists to achieve the best strain sensitivity of this type of sensors. It is demonstrated that the nanocomposites containing 20 vol.% of nickel particles and 0.35 wt.% MWCNTs exhibits a high strain sensitivity of ~80.
Civil engineering, Mechanical engineering, Engineering
sj2527
Civil Engineering and Engineering Mechanics
Dissertations

Domestic Septic Tanks for Treating Sewage and Biogas Generation
http://academiccommons.columbia.edu/catalog/ac:183894
Modjinou, Mawufemo
http://dx.doi.org/10.7916/D81G0K40
Tue, 03 Mar 2015 00:00:00 +0000
This study is to design a novel septic tank, named Anaerobic Upflow Domestic Septic Tank (AUDST) to recover biogas as energy and treat domestic sewage. The green technology proposes alternate options to existing Domestic Septic Tanks (DST), encourages anaerobically pretreatment to reduce bacteria, pollutants, Total Suspended Solids (TSS), Chemical oxygen demand (COD) and Biological oxygen demand (BOD) before the effluent is discharged or is removed by cesspit trucks. Studies have shown that DST in homes partially treat or just store sewage. Again, these DST have to be emptied from time to time because it lack features that will sustain anaerobic activity and usually the sludge is disposed of directly into the sea, water bodies and even into open places such as “Lavender Hills’’ without any treatment or disinfection. These practices cause severe public health and environmental problems. To tackle the challenge at household level, DST are redesigned to treat domestic sewage with less management, low operating cost, low secondary discharge of pollutants. The proposed new design concept is operated through three (3) units: such as desilting, anaerobic digestion and facultative filtration units. The anaerobic digestion stage is made up of baffle and anaerobic filter for accommodating sludge and providing a more intimate contact between anaerobic biomass and sewage which improves treatment performance. The anaerobic unit is fitted with locally woven baskets prefilled with packing materials. The aim is to strengthen the biological treatment process at this stage. The Facultative Filtration unit of the model is also packed with filtering media such as gravels (36mm in diameter) that is low in cost, and has a high durability to produce effluent with lower pollutants and suspended solids content to meet Ghana’s Environmental Protection Agency (EPA) standards for the discharge of domestic effluents.
Mechanical engineering, Environmental engineering
mm4488
Industrial Engineering and Operations Research
Master's theses

The Tribological Effects of Lubricating Oil Containing NanometerScale Diamond Particles
http://academiccommons.columbia.edu/catalog/ac:184199
Marko, Matthew David
http://dx.doi.org/10.7916/D8FF3R6G
Fri, 13 Feb 2015 00:00:00 +0000
This dissertation investigates the tribological effects of diamond nanoparticles as a lubricant mineral oil additive. A numerical code was developed that models the sliding contact observed in a standard fourball test of sliding contact. Fourball experimental tests were conducted both of neat mineral oil and mineral oil with the diamond nanoparticle additives, varying the trial times, temperatures, nanoparticle concentrations, and loads. The numerical results matched the experimental data remarkably by adjusting the lubricant thermal conductivity to account for the enhanced conductivity of diamond; demonstrating that thermal enhancements are the primary cause of the wear reduction properties of diamond nanoparticle additives.
Mechanical engineering
Mechanical Engineering
Dissertations

Simultaneous Iterative Learning and Feedback Control Design
http://academiccommons.columbia.edu/catalog/ac:182998
Chinnan, Anil Philip
http://dx.doi.org/10.7916/D8NC6000
Tue, 10 Feb 2015 00:00:00 +0000
Iterative learning controllers aim to produce high precision tracking in operations where the same tracking maneuver is repeated over and over again. Modelbased iterative learning control laws are designed from the system Markov parameters which could be inaccurate. Chapter 2 examines several important learning control laws and develops an understanding of how and when inaccuracy in knowledge of the Markov parameters results in instability of the learning process. While an iterative learning controller can compensate for unknown repeating errors and disturbances, it is not suited to handle nonrepeating, stochastic errors and disturbances, which can be more effectively handled by a feedback controller. Chapter 3 explores feedback and iterative learning combination controllers, showing how a onetime step behind disturbance estimator and onerepetition behind disturbance estimator can be incorporated together in such a combination. Since learning control applications are finitetime by their very nature, frequency response based design techniques are not best suited for designing the feedback controller in this context. A finitetime feedback controller design approach is more appropriate given the overall aim of zero tracking error for the entire trajectory, even for shorter trajectories where the system response is still in its transient phase and has not yet reached steady state. Chapter 4 presents a combination of finitetime feedback and learning control as a natural solution for such a control objective, showing how a finitetime feedback controller and an iterative learning controller can be simultaneously synthesized during the learning process. Finally, Chapter 5 examines different configurations where a combination of a feedback controller and an iterative learning controller can be implemented. Numerical results are used to illustrate the feedback and iterative controller designs developed in this thesis.
Electrical engineering, Mechanical engineering, Robotics
apc2113
Electrical Engineering
Dissertations

Structural Identification, Health Monitoring and Uncertainty Quantification under Incomplete Information with Minimal Requirements for Identifiability
http://academiccommons.columbia.edu/catalog/ac:194310
Mukhopadhyay, Suparno
http://dx.doi.org/10.7916/D8ZG6R1C
Wed, 21 Jan 2015 00:00:00 +0000
Structural identification is the inverse problem of estimating the physical parameters, e.g. element masses and stiffnesses, of a model representing a structural system, using response measurements obtained from the actual structure subjected to operational or welldefined experimental excitations. It is one of the principal focal areas of modal testing and structural health monitoring, with the identified model finding a wide variety of applications, from obtaining reliable response predictions to timely detection of structural damage (location and severity) and consequent planning and validating of maintenance/retrofitting operations. However, incomplete instrumentation of the monitored system and ambient vibration testing generally result in spatially incomplete and arbitrarily normalized measured modal information, often making the inverse problem illconditioned and resulting in nonunique identification results. The problem of parameter identifiability addresses the question of whether or not a parameter set of interest can be identified from the available information. The identifiability of any parameter set of interest depends on the number and location of sensors on the monitored system. In this dissertation we study the identifiability of the mass and stiffness parameters of sheartype systems, including 3dimensional laterallytorsionally coupled rigid floor systems, with incomplete instrumentation, simultaneous to the development of algorithms to identify the complete mass and stiffness matrices of such systems. Both inputoutput and outputonly situations are considered, and mode shape expansion and mass normalization approaches are developed to obtain the complete mass normalized mode shape matrix, starting from the incomplete modal parameters identified using any suitable experimental or operational modal analysis technique. Methods are discussed to decide actuator/sensor locations on the structure which will ensure identifiability of the mass and stiffness parameters. Several possible minimal and nearminimal instrumentation setups are also identified. The minimal a priori information necessary in outputonly situations is determined, and different scenario of available a priori information are considered. Additionally, tests for identifiability are discussed for both pre and postexperiment applications. The different theoretical discussions are illustrated using numerical simulations and experimental data. It is shown that the proposed identification algorithms are able to obtain reliably accurate physical parameter estimates even under the constraints of minimal instrumentation, minimal a priori information, and unmeasured input. The different actuator/sensor placement rules and identifiability tests are useful for both experiment design purposes, to determine the necessary number and location of sensors, as well as in identifying possibilities of multiple solutions postexperiment. The parameter identification methods are applied for structural health monitoring using experimental data, and an approach is discussed for probabilistic characterization of structural damage location and severity. A perturbation based uncertainty propagation approach is also discussed for the identification of the distributions of mass and stiffness parameters, reflecting the variability in the test structure, using very limited measured and a priori information.
Civil engineering, Mechanics, Mechanical engineering, Structural analysis (Engineering), Structural health monitoring, Mechanical engineeringMathematical models
sm3315
Civil Engineering and Engineering Mechanics
Dissertations

Micro and Nanoscale Aptasensors for Detection of Low Molecular Weight Biomarkers Towards Clinical Diagnostic Applications
http://academiccommons.columbia.edu/catalog/ac:192850
Yang, Jaeyoung
http://dx.doi.org/10.7916/D88S4NPS
Tue, 23 Dec 2014 00:00:00 +0000
Biosensors have been developed for their potential applications to clinical diagnostics, particularly for detection of diseaserelevant biomarkers. As affinity biosensors have emerged for the application, aptamers, i.e., oligonucleotide receptors, have gained much attention due to their ability to offer high affinity, specificity, stability, and rapid, low cost production. While aptame based biosensors, called aptasensors, have shown great promise as a clinical assay tool, their sensitive detection of low molecular weight biomarkers is challenging. In this thesis, we present microfluidic aptasensors for label free and sensitive detection of low molecular weight analytes by focusing on arginine vasopressin (AVP), an oligopeptide hormone and a clinically important biomarker. We first present an integrated microfluidic aptasensor for label free detection of AVP by mass spectrometry. The integrated device selectively extracts AVP from human plasma ultrafiltrate samples and then repeatedly deposits the AVP on a MALDI plate for further analyte enrichment, thereby enabling highly sensitive AVP measurements. To further explore aptamer based detection of AVP, we have developed an optomagnetic aptasensor capable of detecting a low molecular weight analyte using magnetic nanoparticles (MNPs). In this aptasensor, second to be presented in the thesis, an inhibition assay principle is used, in which degrees of MNP clustering depend on the ATP concentration. The clustering state is then measured by an optomagnetic readout system that provides information about the distribution of cluster sizes, thus enabling us to relate the signal to the analyte concentration in a simple mix and read manner. A proof of concept demonstration of the sensor operation is provided using adenosine triphosphate (ATP) as a model small molecule analyte. We next exploit surface enhanced Raman spectroscopy (SERS) for detection of AVP. A SERS active substrate with aptamer functionalized leaning nanopillars is used for sensitive and specific detection of AVP labeled with a Raman tag. Large area Raman mapping on the substrate enables reliable SERS based AVP quantification, and microfluidic integration allows rapid and efficient analyte detection. Lastly, a competitive binding assay format is employed for label free detection of AVP. We finally present a microfluidic aptasensor that integrates aptamer based selective analyte preconcentration with conductance based graphene nanosensing for detection of AVP. In the integrated device, low abundance AVP is enriched via solidphase aptamer based selective preconcentration, and then measured by a graphene field effect transistor (FET) based nanosensor through aptamer based competitive binding, allowing sensitive and label free detection of AVP. We conclude the thesis by a discussion of directions for future work, proposing strategies for pursuing technological advancements to ultimately enable highly sensitive and rapid detection of AVP in human bodily fluids in clinical diagnostic settings.
Mechanical engineering
jy2344
Mechanical Engineering
Dissertations

Opportunities for and Hurdles to Combined Heat and Power in New York City
http://academiccommons.columbia.edu/catalog/ac:178486
Saba, Alexis; Howard, Bianca Nichole; Gerrard, Michael; Modi, Vijay
http://dx.doi.org/10.7916/D84748H7
Mon, 13 Oct 2014 00:00:00 +0000
Combined heat and power (CHP or cogeneration) is the simultaneous production of electricity and thermal energy from a single fuel source. In many ways, New York City is a hospitable environment for CHP development. Nonetheless, there are also many characteristics of New York that make it a difficult place to advance CHP. The utility infrastructure is dense and complexand largely underneath a dense and complex built environment. This paper first seeks to quantify the potential for CHP development in New York City and describe the primary hurdles to optimal deployment in Parts I and II. Part III provides policy solutions for overcoming these hurdles and recommendations for how stakeholders can use information and analysis to maximize the opportunities for CHP.
Environmental law, Mechanical engineering, Climate change
bnh2111, mbg2, vm2
Sabin Center for Climate Change Law, Mechanical Engineering, Law
Reports

OKID as a general approach to linear and bilinear system identification
http://academiccommons.columbia.edu/catalog/ac:178859
Vicario, Francesco
http://dx.doi.org/10.7916/D8WS8RVC
Mon, 13 Oct 2014 00:00:00 +0000
This work advances the understanding of the complex world of system identification, i.e. the set of techniques to find mathematical models of dynamical systems from measured inputoutput data, and exploits wellestablished approaches for linear systems to address nonlinear system identification problems. We focus on observer/Kalman filter identification (OKID), a method for simultaneous identification of a linear statespace model and the associated Kalman filter from noisy inputoutput measurements. OKID, developed at NASA, resulted in a very successful algorithm known as OKID/ERA (OKID followed by eigensystem realization algorithm). We show how ERA is not the only method to complete the OKID process, developing novel algorithms based on the preliminary estimation of the Kalman filter output residuals. The new algorithms do not only show potential for better performance, they also cast light on OKID, explicitly establishing the Kalman filter as central to linear system identification in the presence of noise, paralleling its role in signal estimation and filtering. The Kalman filter embedded in the OKID core equation is capable of converting the original problem, affected by random noise, into a purely deterministic problem. The new interpretation leads to the extension of OKID to outputonly system identification, providing a new tool for applications in structural health monitoring, and raises OKID to the level of a unified approach for inputoutput and outputonly linear system identification. Any algorithm for linear system identification formulated in the absence of noise can now optimally handle noisy data via a preliminary step consisting in solving the OKID core equation. The OKID framework developed for linear system identification is then extended to bilinear systems, which are of interest because several natural phenomena are inherently bilinear and also because highorder bilinear models are universal approximators for a wide class of nonlinear systems. The formulation of an optimal bilinear observer for bilinear statespace models, similar to the Kalman filter in the linear case, leads to the development of an extension of OKID to bilinear system identification. This is the first application of OKID to nonlinear problems, not only because bilinear systems are themselves nonlinear, but also because one can think of bilinear OKID as a technique to find bilinear approximations of nonlinear systems. Furthermore, the same strategy adopted in this work could be used to extend OKID directly to other classes of nonlinear models.
Engineering, Mechanical engineering, Civil engineering
fv2157
Mechanical Engineering
Dissertations

Patch contribution to nearfield radiative energy transfer and van derWaals pressure between two halfspaces
http://academiccommons.columbia.edu/catalog/ac:177846
Zheng, Yi; Narayanaswamy, Arvind
http://dx.doi.org/10.7916/D8ZG6QT8
Fri, 03 Oct 2014 00:00:00 +0000
Nearfield effects in fluctuational electrodynamics leads to enhancement of radiative energy transfer as well as the emergence of van der Waals and/or Casimir pressure. While much has been learned from the analysis of nearfield interactions between two halfspaces separated by a vacuum gap, we shed new light on the problem by finding how much of a surface patch on one of the halfspaces contributes to the energy transfer or van der Waals pressure at any location within the vacuum gap. We show that energy transfer and fluctuationinduced van der Waals pressure at any point on the surface of one halfspace are qualitatively and quantitatively different due to the dissimilar zones of influence of interactions. We also show that the contributions from different surface patches are qualitatively similar for halfspaces with dielectric materials (silica, silicon carbide) and halfspaces with metals (gold).
Physical chemistry, Mechanical engineering
yz2308, an2288
Mechanical Engineering
Articles

Investigation of Plastic Strain Recovery and Creep in Thin Film Nanocrystalline Metals
http://academiccommons.columbia.edu/catalog/ac:189310
Ghazi Esfahani, Nastaran
http://dx.doi.org/10.7916/D8JQ0ZKF
Tue, 30 Sep 2014 00:00:00 +0000
In this study an automatically controlled planestrain bulge test system is used to characterized the mechanical behavior of nanocrystalline thin film samples. The freestanding thin film of copper with average grain size of 35nm is fabricated with thermal evaporation or sputtering. The tests are performed to measure Young's modulus, determine the strain rate for creep and monitor plastic strain recovery at room temperature and at 100°C Based on the experimental strain rate during the creep, The value for diffusion coefficient of copper is obtained. This value is in agreement with the diffusion coefficient resulted from numerical simulation for nanocrystalline copper film in another work and is about 4 orders of magnitude more than the value for conventional coarse grain one. By monitoring the plastic strain recovery, it is observed that it occurs in two rates, a fast temporary one follow by a slower rate. This phenomena can be explained due to grain boundary based deformation mechanisms for this grain size. We also develop a continuum model to prescribe grain boundary diffusion as the dominant deformation mechanism for nanocrystalline thin film with a preexisting void. The model is implemented using FEA software Abaqus. The numerical result indicates that plastic strain recovery occurs and it has two rates. A parametric study on different factors which can affect the recovery is performed and the strain recovery rates obtained from each parameter are compared with the experimental one.
Mechanical engineering
nng2107
Mechanical Engineering
Dissertations

The Rheology of Nanoparticle Additives: An Investigation Utilizing Mesh Free Methods
http://academiccommons.columbia.edu/catalog/ac:178164
Kyle, Jonathan Paul
http://dx.doi.org/10.7916/D8610XW2
Tue, 23 Sep 2014 00:00:00 +0000
This dissertation applies mesh free computational methods to investigate the rheological impact of arbitrarily shaped nanoparticle additives in shearing interfaces. Specifically, Smoothed Particle Hydrodynamics is used for its flexibility in modeling moving fluidstructure interfaces, the ability to model nonNewtonian fluids, as well as having the capability to add any additional physics deemed appropriate. With this modeling technique, a sufficient theory for the nonEinstein like rheological modification seen with certain nanoparticle additives is achieved based on surface tension effects between the additives and solvent. Computational results are compared with experiment resulting in good agreement.
Mechanical engineering
jpk2128
Mechanical Engineering
Dissertations

A multiscale overlapped coupling formulation for largedeformation strain localization
http://academiccommons.columbia.edu/catalog/ac:177549
Sun, WaiChing; Mota, Alejandr
http://dx.doi.org/10.7916/D8GQ6W87
Mon, 22 Sep 2014 00:00:00 +0000
We generalize the multiscale overlapped domain framework to couple multiple rateindependent standard dissipative material models in the finite deformation regime across different length scales. We show that a fully coupled multiscale incremental boundaryvalue problem can be recast as the stationary point that optimizes the partitioned incremental work of a threefield energy functional. We also establish infsup tests to examine the numerical stability issues that arise from enforcing weak compatibility in the threefield formulation. We also devise a new block solver for the domain coupling problem and demonstrate the performance of the formulation with onedimensional numerical examples. These simulations indicate that it is sufficient to introduce a localization limiter in a confined region of interest to regularize the partial differential equation if loss of ellipticity occurs.
Civil engineering, Mechanical engineering
ws2414
Civil Engineering and Engineering Mechanics
Articles

LargeArea Graphene Synthesized by Chemical Vapor Deposition for HighPerformance, Flexible Electronics
http://academiccommons.columbia.edu/catalog/ac:188933
Petrone, Nicholas Walker
http://dx.doi.org/10.7916/D8V1233G
Mon, 08 Sep 2014 00:00:00 +0000
Graphene is an ideal candidate for use in flexible fieldeffect transistors (FETs) which require both high flexibility and high operating frequencies, because it offers exceptional electronic properties (room temperature mobility in excess of 10,000 cm² Vⁱ s⁻¹ and high saturation velocity of 37x10⁷ cm s⁻¹) as well as outstanding mechanical performance (strain limits up to 25%). Indeed, graphene FETs (GFETs) fabricated on rigid substrates from single crystals of mechanically exfoliated graphene have demonstrated unity power gain cutoff frequencies, fmax, up to 34 GHz, even at modestly scaled channel lengths of 600 nm. However, in order to realize commercial production of graphenebased technologies, it is essential to integrate largearea graphene produced by scalable synthesis methods into device fabrication. Chemical vapor deposition (CVD) offers a promising method to produce lowcost, largearea films of graphene, crucial for the commercial realization of graphenebased technologies. However, the electronic performance of CVDgrown graphene has remained problematic. Compared to exfoliated graphene, CVD graphene exhibits lower mobility, greater impurity doping, and higher asymmetry between electron and hole conduction, indicative of disorder and scattering processes that are not present in exfoliated samples. In order to achieve commercial scalability of highperformance graphenebased technologies, it is prerequisite to minimize disorder present in CVD graphene and achieve equivalent electronic properties to exfoliated graphene. In this work, I present a detailed study of the electronic transport behavior of CVD graphene in which the predominant sources of intrinsic disorder, grainboundary scattering, is eliminated and extrinsic disorder, transfer induced contamination and substrateinduced scattering, are minimized. Grain boundaries within fabricated devices are eliminated by varying the CVD synthesis conditions to yield CVD graphene with large grain sizes, up to 250 μm in dimension. Processrelated contamination is minimized by employing a novel drytransfer technique that greatly reduces the extrinsic doping in CVD graphene devices, and samples are transferred onto hexagonal boron nitride (hBN), a dielectric which minimizes substrateinduced scattering and permits for the most precise assessment of the intrinsic performance of graphene. By minimizing the presence of these three predominant sources of disorder in CVD graphene, measurements presented in this work are the first demonstration that largearea graphene can not only be synthesized but also transferred onto arbitrary substrates while reproducibly achieving electrical performance comparable to that of highquality exfoliated graphene. Related research demonstrates that the CVD graphene synthesized in this work additionally demonstrates equivalent mechanical properties to exfoliated graphene. After demonstrating that CVD graphene films can achieve both exceptional electronic and mechanical properties, the synthesis and transfer methods developed are subsequently applied to the fabrication of highperformance, flexible, radiofrequency FETs (RFFETs), an application demanding both highfrequency operation and high mechanical flexibility. Methods to fabricate RFFETs on flexible substrates using CVD graphene as the active channel material are presented. Devices fabricated with channel lengths of 500 nm show extrinsic values of unity current gain cutoff frequency, fT, and unity power gain cutoff frequency, fmax, up to 10.7 GHz and 3.7 GHz, respectively, and strain limits of 1.75%. By reducing the channel length to 260 nm, extrinsic values of fT and fmax increase to 23.6 GHz and 6.5 GHz, respectively, with intrinsic fmax = 28.2 GHz and strain limits of 2% attainable. Flexible graphene RFFETs fabricated with channel lengths of 260 nm not only represent the highest values of fmax achieved in any flexible technology to date, but they also show an order of magnitude improvement in strain limit over flexible technologies demonstrating the next highest reported value of fmax. The structure of flexible GFETs is further improved by encapsulating the graphene channel in hBN dielectric layers and by implementing a self aligned fabrication scheme. RFFETs fabricated with channel lengths of 375 nm demonstrate extrinsic cutoff frequencies fT and fmax of 12.0 GHz and 10.6 GHz, respectively, and intrinsic fT and fmax of 29.7 GHz and 15.7 GHz, respectively. The improved extrinsic cutoff frequencies indicate that using both a selfaligned fabrication scheme and hBN encapsulation are paramount to improving RF performance in flexible GFETs. Collectively, this work demonstrates that CVD graphene can achieve both outstanding electronic and mechanical performance and establishes CVD graphene as a competitive semiconductor technology for use in flexible RFFETs. As such, it reveals the potential of CVD graphene as a material to enable a widerange of flexible technologies requiring both high frequency operation and high mechanical flexibility.
Nanotechnology, Mechanical engineering, Electrical engineering
nwp2105
Mechanical Engineering
Dissertations

Nearfield Radiative Momentum, Energy and Entropy Transfer in Fluctuational Electrodynamics
http://academiccommons.columbia.edu/catalog/ac:177593
Zheng, Yi
http://dx.doi.org/10.7916/D8NG4NTW
Tue, 19 Aug 2014 00:00:00 +0000
Quantum and thermal fluctuations of electromagnetic fields, which give rise to Planck's law of blackbody radiation, are also responsible for van der Waals and Casimir forces, as well as nearfield radiative energy transfer between objects. Electromagnetic waves transport energy, momentum, and entropy. For classical thermal radiation, the dependence of the above mentioned quantities on the temperature is wellknown mainly due to Planck's work. When nearfield effects, namely the collective influence of diffraction, interference, and tunneling of waves, become important, Planck's theory is no longer valid. Of momentum, energy, and entropy transfer, the role of nearfield effects on momentum transfer between two halfspaces separated by a vacuum gap (van der Waals pressure in the vacuum gap) was first determined by Lifshitz, using Rytov's theory of fluctuational electrodynamics in 1956. Subsequently, Dzyaloshinskii, Lifshitz, and Pitaevskii, employing sophisticated methods from quantum field theory, generalized Lifshitz' result for van der Waals pressure in a vacuum layer to the case of van der Waals pressure in a dissipative layer between two halfspaces. The influence of nearfield effects on radiative transfer was appreciated only in the late 1960s and, subsequently, in the last two decades because of the enhancement in radiative transfer due to electromagnetic surface waves. The role played by nearfield effects on entropy transfer has not been investigated so far, at least when the temperature distribution is nonuniform. In this thesis, I investigate the transport of momentum, energy, and entropy due to electromagnetic fluctuations with nearfield effects taken into consideration. For momentum transfer, I give a new perspective to the theory of van der Waals pressure by obtaining the results of Dzyaloshinskii, Lifshitz, and Pistaevskii without having to use any quantum field theory. I show that the computation of van der Waals pressure between objects on the imaginary frequency axis is only a numerical/mathematical convenience, not a physical necessity. For energy transfer, I identify some of the similarities and differences between energy and momentum transfer. I solve a problem in nearfield radiative transfer between two halfspaces to identify the differences, mainly with an aim of identifying features that make it likely that the proximity approximation for computing nearfield radiative transfer between two curved objects is as valid as the proximity approximation for van der Waals forces between curved surfaces. The analysis shows qualitative differences between energy and momentum transfer. Finally, I solve for the first time the entropy transfer between halfspaces at different temperatures taking nearfield effects into account. I wanted to calculate the momentum and entropy transfer between two halfspaces in order to solve the more complicated problem of van der Waals pressure in a layer of dissipative material between two halfspaces at different temperatures, namely the problem of Dzyaloshinskii, Lifshitz, and Pitaevskii but under conditions of thermal nonequilibrium. My hypothesis was that the knowledge of nonequilibrium entropy transfer in a vacuum gap would furnish us the solution. I have not been successful in that endeavor, though. This work is focused on three aspects of momentum, energy and entropy transfer in fluctuational electrodynamics: (1) a transparent formalism of determining the van der Waals and Casimir force in a dissipative planar multilayered system, (2) a formalism of surface integrals of dyadic Green's functions for radiative energy and momentum transfer between objects of arbitrary shapes and sizes at different temperatures, and (3) a theory of evaluating entropy density and entropy flux at both thermal equilibrium and nonequilibrium while taking into account the influence of nearfield effects. My doctoral research is devoted to establishing a general theory of momentum and energy transfer between arbitrarily shaped objects at thermal nonequilibrium and at a microscopic length scale, which urges a more careful, deeper, and complete thermodynamic study of nearfield radiative heat transfer.
Mechanical engineering
yz2308
Mechanical Engineering
Dissertations

Dynamic energy dissipation using nanostructures: mechanisms and applications
http://academiccommons.columbia.edu/catalog/ac:176143
Xu, Jun
http://dx.doi.org/10.7916/D8BR8QBX
Mon, 07 Jul 2014 00:00:00 +0000
The emerging subject of mechanical impact protection at nanoscale where solids, fluids interact closely, has raised many multidisciplinary and challenging questions which cannot be answered by the analogy from their macroscopic counterparts. A series of counterintuitive phenomena have been observed without further profound theoretical explanations. It is pretty straightforward to take advantage of these novel properties for fascinating applications which cannot be achieved by traditional materials and structures. Among various exciting areas, one of the most promising and ever expanding topics is the impact protection at nanoscale. Primarily inspired by the excellent mechanical properties of carbon nanotube (CNT), a waterfilled CNT system for impact protection is designed. The nanoconfined water molecules enhance the stiffness of the tube and also help to stabilize the tube such that the buckling force and the postbuckling plateau is higher than empty CNTs, indicating a much higher energy dissipation performance. Also, the energy dissipation performance is dependent on the aspect ratio which is similar in its bulk counterpart. Additional support may come from adjacent tubes in CNT bundle and forests and the actual energy dissipation per unit volume/mass is improved. Unlike the tube or beam shape, once the single layer graphene is rolled into a spherical shell, it becomes buckyball whose mechanical properties are seldom studied. Thus, firstly, the quasistatic and dynamic behavior of buckyball is investigated based on MD simulation. Buckyball may be categorized according to the mechanical behavior. The forcedisplacement curve obey the continuum shell model prediction perfectly except for the slight difference in coefficient change due to the size effect. Interestingly, it is discovered that larger buckyball cannot recover to its original shape after unloading while the smaller buckyball can. Stronger van der Waals interaction between the buckled layer and the bottom layer may be the responsible reason for the nonrecovery phenomenon. The buckled shape should have higher strain energy such that more mechanical energy is dissipated. Motivated by the novel behavior of buckyball, the various stacking forms of buckyball are investigated. By analogy for the 1D granular energy dissipation system, a 1D long chain buckyball system is designed and studied. With relatively small elastic deformations of C60 buckyballs during impact, a modified Hertz contact model is proposed, with critical parameters calibrated via MD simulations for given impact loading conditions. The major energy dissipation mechanism for the buckyball chain is the wave reflection among the deformation layers, covalent potential energy, van der Waals interactions as well as the atomistic kinetic energy. For nonrecovery buckyballs such as C720, energy mitigation effect is more obvious. Over 99% and 90% of impact energy for C720 and C60 chain systems could be mitigated under particular impact conditions. Moreover, protective system based on short 1D vertical and horizontal alignments and various pseudo 3D stacking forms with different packing densities are also studied. It is found that stacking form with higher occupation density yields higher energy absorption and proves the available buckyball in bulk is ready for impact protection. In addition, to quantify the material behavior, prove the recently suggested new theories and discover new phenomenon, desktop experiments serves as an important part of this thesis research. The governing factors, i.e. pretreatment temperatures, solidtoliquid mass ratio, particle size and electrolyte concentration are parametrically studied. Experiments show that the optimum processing pretreatment temperature is about 1000 degree; with higher zeolite mass ratio. Also, the dynamic behavior of zeolite beta/water system is investigated and the system has a better dynamic performance than quasistatic since the infiltration pressure increases due to the water molecule inertia effect. To conclude, impact dynamics and energy dissipation/mitigation at nanoscale is a lasting topic in mechanics related research area whose knowledge is highly desire in engineering application with the advancement of material science, physics and chemistry.
Mechanical engineering, Environmental engineering
Earth and Environmental Engineering
Dissertations

Laser Induced Modification and Integration of Glasses
http://academiccommons.columbia.edu/catalog/ac:176624
Kongsuwan, Panjawat
http://dx.doi.org/10.7916/D8RV0KVQ
Mon, 07 Jul 2014 00:00:00 +0000
Glasses have been widely used as substrates in new technologies especially flat panel displays (FPD), organic lightemitting diode (OLED) lighting, and labonachip (LOC) applications. They are inexpensive, chemically inert with excellent optical, mechanical and thermal properties. In addition, they are biocompatible, and some compositions possess bioactive properties which are highly desirable in biomedical applications. This dissertation seeks to develop fundamental understanding of feature formation mechanisms and changes in morphology, structural, and mechanical properties of glasses induced by lasers in both high (a femtosecond laser) and low (a continuous wave laser) intensity regimes, and to investigate novel processes for modification and integration of glasses. Due to its nonlinear absorption capability in glasses, a femtosecond laser is used to generate internal features inside glass. Their morphology, structure, and mechanical properties such as modulus, hardness, ductility, and fracture toughness are experimentally characterized. Fundamental understanding of the feature formation and these property changes is developed through differential interference contrast (DIC) microscopy, spatially resolved Raman spectroscopy, spatially resolved nanoindentation, and predictive numerical simulations. The improved understanding lays ground work to investigate novel processes of transmission welding (TW) and single step channeling (SSC) in glasses. Joining or sealing of glasses in FPD, OLED, and LOC applications are currently based on adhesives. They are susceptible to moisture permeability and require high curing temperatures of entire parts for a long period of time. TW is investigated and the mechanism of joint formation is analyzed. A numerical model, developed to predict the welding widths, demonstrates the inverse teardropshaped absorption volume like the experimental weld seam geometry. Using indentation fracture analysis, the joint is determined to have better mechanical properties than the base material. Fabrication of microfluidic networks in LOC using traditional lithographic processes, or other hybrid processes is cumbersome because they involve multiple steps. SSC is investigated, and numerical models are also developed and experimentally validated to predict the channel lengths resulting from different laser and focusing parameters. The understanding of the channel formation mechanism, and the channel length variation corresponding to the working parameters is developed. TW has the potential to achieve a reliable, highly localized sealing process while SSC has the potential to simplify LOC designs requiring no adhesive for FPD and biomedical industry, respectively. Reduction of the risk of early failure for loadbearing biomedical implants could be achieved by coating bioactive glass onto bioinert metallic substrates. High bioactivity of bioactive glass accelerates the bonebonding time. Coatings of 45S5 Bioglass, which has the highest rate of bioactivity by plasma spraying and enameling usually fail due to its significant crystallization and weak adhesion to the substrates. Double layer coating by a continuous wave (CW) laser is investigated to produce a dense bond coat having a strong adhesion and a porous top coat having high bioactivity. The morphology and microstructure of the resultant laser coatings are experimentally characterized. A mixed interfacial layer is found at the glasstitanium interface indicating a relatively strong chemical bonding. The top coat is examined revealing a porous structure with low crystallinity. A numerical model is developed to aid in understanding laser sintering mechanisms and is validated experimentally to predict the overall porosity and crystallinity of laser coating.
Mechanical engineering
Mechanical Engineering
Dissertations

Bimaterial microcantileverbased thermal sensing techniques
http://academiccommons.columbia.edu/catalog/ac:188481
Canetta, Carlo Benedetto
http://dx.doi.org/10.7916/D8K35RT3
Mon, 07 Jul 2014 00:00:00 +0000
Understanding thermal transport at the nanoscale has important implications for stateoftheart engineering systems. Thermal management in electronic devices and nanostructuring of devices for thermoelectric energy conversion are two examples of important engineering problems which will benefit directly from improved understanding of nanoscale thermal transport. To this end, development of new techniques in thermal metrology is key to the advancement of this research topic. The ability to sense smaller magnitudes of heat transfer than currently possible will enable us to measure thusfar elusive phenomena such as the effects of molecular chain alignment on thermal conductivity in polymer nanowires, or even heat transport through single molecules. Bimaterial cantilevers act as thermometers. A beam, made up of two material layers, will bend due to thermal stimuli because of the mismatch in thermal expansion coefficients for the two material layers. If the dimensions of the cantilever are scaled down to yield a bimaterial microcantilever, this can be an extremely sensitive thermal sensor. This thesis focuses on the development of bimaterial microcantilever based thermal sensing for the study of nanoscale heat transfer. A microcantilever design optimized for thermal sensitivity is presented, along with a reliable process for fabrication of such sensors. With these optimized cantilevers, we can push past the picowattlimit and measure subpicowatt heat fluxes. In order to harness the high thermal sensitivity of these cantilevers for the purposes of thermal conduction measurements, a new measurement technique which we call the dualcantilever technique is introduced, whereby a nanostructure is suspended between two cantilevers and thermal conduction measurements can be performed on this single nanostructure. Thermal measurements on single polymeric nanowires are performed to show the effectiveness of this method. The theory for the thermal and mechanical models of the dualcantilever scheme is developed to corroborate the effectiveness of the technique. Making use of versatile and highly sensitive bimaterial microcantilever sensors, this thesis seeks to enhance the measurement methods available for the study of nanoscale thermal transport effects.
Mechanical engineering
cbc2009
Mechanical Engineering
Dissertations

Genetic Analysis and Cell Manipulation on Microfluidic Surfaces
http://academiccommons.columbia.edu/catalog/ac:196650
Zhu, Jing
http://dx.doi.org/10.7916/D8SN0712
Mon, 07 Apr 2014 14:56:31 +0000
Personalized cancer medicine is a cancer care paradigm in which diagnostic and therapeutic strategies are customized for individual patients. Microsystems that are created by MicroElectroMechanical Systems (MEMS) technology and integrate various diagnostic and therapeutic methods on a single chip hold great potential to enable personalized cancer medicine. Toward ultimate realization of such microsystems, this thesis focuses on developing critical functional building blocks that perform genetic variation identification (singlenucleotide polymorphism (SNP) genotyping) and specific, efficient and flexible cell manipulation on microfluidic surfaces. For the identification of genetic variations, we first present a beadbased approach to detect singlebase mutations by performing singlebase extension (SBE) of SNP specific primers on solid surfaces. Successful genotyping of the SNP on exon 1 of HBB gene demonstrates the potential of the device for simple, rapid, and accurate detection of SNPs. In addition, a multistep solutionbased approach, which integrates SBE with masstagged dideoxynucleotides and solidphase purification of extension products, is also presented. Rapid, accurate and simultaneous detection of 4 loci on a synthetic template demonstrates the capability of multiplex genotyping with reduced consumption of samples and reagents. For cell manipulation, we first present a microfluidic device for cell purification with surfaceimmobilized aptamers, exploiting the strong temperature dependence of the affinity binding between aptamers and cells. Further, we demonstrate the feasibility of using aptamers to specifically separate target cells from a heterogeneous solution and employing environmental changes to retrieve purified cells. Moreover, spatially specific capture and selective temperaturemediated release of cells on designspecified areas is presented, which demonstrates the ability to establish cell arrays on predefined regions and to collect only specifically selected cell groups for downstream analysis. We also investigate tunable microfluidic trapping of cells by exploiting the large compliance of elastomers to create an array of celltrapping microstructures, whose dimensions can be mechanically modulated by inducing uniform strain via the application of external force. Cell trapping under different strain modulations has been studied, and capture of a predetermined number of cells, from single cells to multiple cells, has been achieved. In addition, to address the lack of aptamers for targets of interest, which is a major hindrance to aptamerbased cell manipulation, we present a microfluidic device for synthetically isolating celltargeting aptamers from a randomized singlestrand DNA (ssDNA) library, integrating cell culturing with affinity selection and amplification of cellbinding ssDNA. Multiround aptamer isolation on a single chip has also been realized by using pressuredriven flow. Finally, some perspectives on future work are presented, and strategies and notable issues are discussed for further development of MEMS/microfluidicsbased devices for personalized cancer medicine.
Engineering, Biomedical engineering, Mechanical engineering
jz2340
Mechanical Engineering
Dissertations

RealTime Noninvasive Estimation of Intrapleural Pressure in Mechanically Ventilated Patients: a Feasibility Study
http://academiccommons.columbia.edu/catalog/ac:171242
Albanese, Antonio; Karamolegkos, Nikolaos ; Haider, Syed W.; Seiver, Adam; Chbat, Nicolas W.
http://dx.doi.org/10.7916/D8GT5K7Q
Mon, 03 Mar 2014 00:00:00 +0000
A method for realtime noninvasive estimation of intrapleural pressure in mechanically ventilated patients is proposed. The method employs a simple firstorder lung mechanics model that is fitted in realtime to flow and pressure signals acquired noninvasively at the opening of the patient airways, in order to estimate lung resistance (RL), lung compliance (CL) and intrapleural pressure (Ppl) continuously in time. Estimation is achieved by minimizing the sum of squared residuals between measured and model predicted airway pressure using a modified Recursive Least Squares (RLS) approach. Particularly, two different RLS algorithms, namely the conventional RLS with Exponential Forgetting (EFRLS) and the RLS with Vectortype Forgetting Factor (VFFRLS), are considered in this study and their performances are first evaluated using simulated data. Simulations suggest that the conventional EFRLS algorithm is not suitable for our purposes, whereas the VFFRLS method provides satisfactory results. The potential of the VFFRLS based method is then proved on experimental data collected from a mechanically ventilated pig. Results show that the method provides continuous estimated lung resistance and compliance in normal physiological ranges and pleural pressure in good agreement with invasive esophageal pressure measurements.
Biomedical engineering, Mechanical engineering
aa2932, nk2440, nc22
Mechanical Engineering, Biomedical Engineering
Conferences

Transient Respiratory Response to Hypercapnia: Analysis via a Cardiopulmonary Simulation Model
http://academiccommons.columbia.edu/catalog/ac:171073
Albanese, Antonio; Chbat, Nicolas W.; Ursino, Mauro
http://dx.doi.org/10.7916/D86M34V3
Wed, 26 Feb 2014 00:00:00 +0000
In recent years, our group has developed a comprehensive cardiopulmonary (CP) model that comprises the heart, systemic and pulmonary circulations, lung mechanics and gas exchange, tissue metabolism, and cardiovascular and respiratory control mechanisms. In this paper, we analyze the response of the model to hypercapnic conditions and hence focus on the chemoreflex control mechanism. Particularly, we have enhanced the peripheral chemoreceptor model in order to better reflect respiratory control physiology. Using the CO2 fraction in the inspired air as input to the CP model, we were able to analyze the transient response of the system to CO2 step input at different levels, in terms of alveolar gas partial pressures, tidal volume, minute ventilation and respiratory frequency. Model predictions were tested against experimental data from human subjects. Results show good agreement for all the variables under study during the transient phases and low root mean square errors at steady state. This indicates the potential for the model to be used as a valid tool for clinical practice and medical research, providing a complementary way to experiencebased clinical decisions.
Biomedical engineering, Mechanical engineering
aa2932, nc22
Mechanical Engineering, Biomedical Engineering
Conferences

Thin Film Mechanics
http://academiccommons.columbia.edu/catalog/ac:173485
Cooper, Ryan Christopher
http://dx.doi.org/10.7916/D8PR7T1V
Wed, 26 Feb 2014 00:00:00 +0000
This doctoral thesis details the methods of determining mechanical properties of two classes of novel thin films suspended twodimensional crystals and electron beam irradiated microfilms of polydimethylsiloxane (PDMS). Thin films are used in a variety of surface coatings to alter the optoelectronic properties or increase the wear or corrosion resistance and are ideal for micro and nanoelectromechanical system fabrication. One of the challenges in fabricating thin films is the introduction of strains which can arise due to application techniques, geometrical conformation, or other spurious conditions. Currently, inadequate models exist to model strain within thin films, making it difficult to produce structurally robust thin films and to prevent premature failure of a coating ordevice. It is thus imperative to understand and quantify thin film behavior under strain, both to aid in the development of new materials and processing techniques, as well as to enable the implementation of thin films into new designs. Chapters 24 focus on two dimensional materials. This is the intrinsic limit of thin filmsbeing constrained to one atomic or molecular unit of thickness. These materials have mechanical, electrical, and optical properties ideal for micro and nanoelectromechanical systems with truly novel device functionality. As such, the breadth of applications that can benefit from a treatise on two dimensional film mechanics is reason enough for exploration. This study explores the anomylously high strength of two dimensional materials. Furthermore, this work also aims to bridge four main gaps in the understanding of material science: bridging the gap between ab initio calculations and finite element analysis, bridging the gap between ab initio calculations and experimental results, nano scale to microscale, and microscale to mesoscale. A nonlinear elasticity model is used to determine the necessary elastic constants to define the strainenergy density function for finite strain. Then, ab initio calculationsdensity functional theoryis used to calculate the nonlinear elastic response. Chapter 2 focuses on validating this methodology with atomic force microscope nanoindentation on molybdenum disulfide. Chapter 3 explores the convergence criteria of three density functional theory solvers to further verify the numerical calculations. Chapter 4 then uses this model to investigate the role of grain boundaries on the strength of chemical vapor deposited graphene. The results from these studies suggest that two dimensional films have remarkably high strengthreaching the intrinsic limit of molecular bonds. Chapter 5 explores the viscoelastic properties of heterogeneous polydimethylsiloxane (PDMS) microfilms through dynamic nanoindentation. PDMS microfilms are irradiated with an electron beam creating a 3 mthick film with an increased crosslink density. The change in mechanical properties of PDMS due to thermal history and accelerator have been explored by a variety of tests, but the effect of electron beam irradiation is still unknown. The resulting structure is a stiff microfilm embedded in a soft rubber with some transformational strain induced by the crosslinking volume changes. Chapter 5 employs a combination of dynamic nanoindentation and finite element analysis to determine the change in stiffness as a function of electron beam irradiation. The experimental results are compared to the literature. The results of these experimental and numerical techniques provide exciting opportunities in future research. Two dimensional materials and flexible thin films are exciting materials for novel applications with new form factors, such as flexible electronics and microfluidic devices. The results herein indicate that you can accurately model the strength of two dimsensional materials and that these materials are robust against nanoscale defects. The results also reveal local variation of mechanical properties in PDMS microfilms. This allows one to design substrates that flex with varying amounts of strain on the surface. Combining the mechanics of two dimensional materials with that of a locally irradiated PDMS film could achieve a new class of flexible microelectromechanical systems. Largescale growth of two dimensional materials will be structurally robusteven in the presence of nanostructural defectsand PDMS microfilms can be irradiated to vary strain of the electromechanical systems. These systems could be designed to investigate electromechanical coupling in two dimensional films or for a substitute to traditional silicon microdevices.
Mechanical engineering, Materials science
rc2555
Mechanical Engineering
Dissertations

A Theoretical Study on the Effect of Curvature on Nearfield Radiative Transfer
http://academiccommons.columbia.edu/catalog/ac:181088
Sasihithlu, Karthik
http://dx.doi.org/10.7916/D8TQ5ZGG
Mon, 06 Jan 2014 00:00:00 +0000
The dissertation focuses on the theoretical analysis of nearfield electromagnetic wave effects in thermal radiative transfer i.e. wave effects like interference, diffraction, and tunneling effects, that become important when analyzing energy transfer via electromagnetic waves over subwavelength distances. In particular, the focus will be on the enhanced thermal radiative transfer between bodies made of polar dielectric materials which support surface phonon polaritons (SPPs). When two such bodies are brought in close proximity to each other, the enhanced nearfield radiation due to tunneling of SPPs can exceed the classical black body limit by several orders of magnitude. This enhanced radiation at nanoscale gaps finds applications in nearfield thermophotovoltaics, heat assisted magnetic recording and nearfield radiative cooling. While the dependence of nearfield radiative transfer on the gap between two planar objects is well understood, the effect of curvature on nearfield radiative transfer is unclear. In particular, the relevance of an approximate method to predict the nearfield interaction between curved bodies (called the proximity approximate method) is disputed. Hence, the computation of nearfield radiative transfer between curved bodies, such as between two spherical bodies, become important. The existing method for computing nearfield radiative transfer between two spheres is highly inefficient in probing small gaps where the nearfield enhancement is most observed. The objective of this work is not only to simplify this computational framework which would enable us to probe smaller gaps and understand the effect of curvature on nearfield radiative transfer better, but also to provide a method to extend this to unequal sized spheres with large size disparities, so that comparison can be made with existing experimental measurements for nearfield radiative transfer between a sphere and a plane. In this regard a simplified form of vector translation addition theorem has been proposed which is valid for general nearfield electromagnetic scattering problems. The range of validity of this approximation for the translation addition theorem has been discussed and recursion relations have been derived for computing the translation coefficients under this approximation. A method for normalizing the translation coefficients has also been proposed, and the computation of these normalized translation coefficients has been shown to depend only on ratios of successive orders of Bessel and Hankel functions which are computationally inexpensive. An analysis of the dependence of normalized translation coefficients on the size ratio of the two spheres has allowed us to extend the computation of nearfield radiative transfer calculations to spheres with large size disparities. Based on the computations, I have shown that the surface phonon polariton mediated radiative transfer between two spheres of effective radius R = (R_1 R_2)/(R_1 + R_2), where R_1 and R_2 are the radii of the individual spheres, and minimum gap, d, scales as R/d as the nondimensional gap d/R goes to 0. I have proposed a modified form of proximity approximation to satisfy the continuity requirement between farfield and nearfield radiative transfer between the spheres. The validity of this modified form of proximity approximation at different frequencies has also been discussed. This method can be applied to approximate the nearfield radiative transfer between, not just spherical surfaces, but other general curved surfaces such as between cylindrical or conical surfaces.
Mechanical engineering
ks2683
Mechanical Engineering
Dissertations

Lifshitz theory of van der Waals pressure in dissipative media
http://academiccommons.columbia.edu/catalog/ac:166217
Zheng, Yi; Narayanaswamy, Arvind
http://hdl.handle.net/10022/AC:P:21926
Thu, 03 Oct 2013 00:00:00 +0000
We derive a firstprinciples method of determining the van der Waals or Casimir pressure in a dissipative and dispersive planar multilayered system by calculating the Maxwell stress tensor in a fictitious layer of vacuum, that is eventually made to vanish, introduced in the structure. This is illustrated by calculating the van der Waals pressure in a thin film with dissipative properties embedded between two semiinfinite media.
Mechanical engineering, Atomic physics, Molecular physics
yz2308, an2288
Mechanical Engineering
Articles

Theory of thermal nonequilibrium entropy in nearfield thermal radiation
http://academiccommons.columbia.edu/catalog/ac:166229
Narayanaswamy, Arvind; Zheng, Yi
http://hdl.handle.net/10022/AC:P:21929
Thu, 03 Oct 2013 00:00:00 +0000
We propose a theoretical formalism to evaluate the entropy density and entropy flux that takes into account nearfield effects, i.e., interference, diffraction, and tunneling of waves. Using the fluctuationdissipation theorem, expressions for entropy density and entropy flux in a vacuum cavity between planar multilayered media are derived in terms of local density of photons, local density of accessible microscopic states, and velocity of energy transmission. The proposed method is used to determine the maximum work that can be extracted and a thermodynamic limit of the energy conversion efficiency that can be obtained in nearfield thermal radiation.
Mechanical engineering, Nanoscience, Physics
an2288, yz2308
Mechanical Engineering
Articles

A Microfluidic Approach to Selection and Enrichment of Aptamers for Biomolecules and Cells
http://academiccommons.columbia.edu/catalog/ac:177562
Kim, Jinho
http://hdl.handle.net/10022/AC:P:21697
Fri, 20 Sep 2013 00:00:00 +0000
This thesis presents microfluidic devices for selection and amplification of nucleic acids (aptamers) that bind to specific targets. Aptamers are very attractive molecules in many biological applications due to their interesting properties including high target binding affinities and stability. Using conventional platforms for aptamer generation (SELEX, systematic evolution of ligands by exponential enrichment) is laborintensive and time consuming. Microfluidic devices have been developed to improve the aptamer enrichment efficiency. However, aptamer generation using these devices is still inefficient because they require complicated flow control components for sample and reagent handling and additional offchip processes. We developed microfluidic SELEX platforms for rapid isolation of aptamers that possess greatly simplified designs which enable easy chip fabrication and operation. The simplicity of the devices is achieved by utilizing a combination of beadbased selection and amplification of target binding nucleic acids, and gelbased electrokinetic transfer of nucleic acids. In the devices, nucleic acids that bind to targets are isolated on targetfunctionalized microbeads or target cells in a microchamber and electrokinetically transported to another chamber through a gelfilled microchannel by an electric field. The strands are then hybridized onto reverse primers immobilized on microbeads and amplified via polymerase chain reaction (PCR) using onchip temperature control. The amplified strands are separated from the beads and electrophoretically transferred back into the selection chamber for subsequent SELEX rounds. Using the devices, we demonstrated enrichment of targetbinding nucleic acids against human immunoglobulin E (IgE), the glucoseboronic acid complex, and MCF7 cancer cells. With the physical and functional integration allowed by the monolithic design realized in our devices, the total process time for selection of aptamers was drastically reduced compared with that required by conventional aptamer selection platforms. Moreover, the binding affinities of the selected strands using our devices are comparable to those of aptamers obtained using the conventional platforms.
Mechanical engineering
jk3185
Mechanical Engineering
Dissertations

The tribological behavior of graphene and its role as a protective coating
http://academiccommons.columbia.edu/catalog/ac:165924
SandozRosado, Emil Jose
http://hdl.handle.net/10022/AC:P:21664
Wed, 18 Sep 2013 00:00:00 +0000
The scope of this thesis is to explore the fundamental tribological behavior of graphene as a twodimensional (2D) nanomaterial and evaluate its performance as a protective coating. Graphene is the strongest material ever measured, gasimpermeable, chemically and thermally stable, and atomicallythin, making it an excellent candidate as a protective coating. The fundamental tribological behavior of graphene and other 2D materials under sliding conditions has only just begun to be explored. In particular, the wear of graphene has hardly been explored. The objective of this work is to investigate the tribological behavior of graphene through atomistic simulation as well as experimental testing under various sliding regimes and length scales. Wear in a graphene monolayer, after scratch tests with a nanoindenter, was characterized for the first time using Raman spectroscopy, revealing new insights into the failure of graphene after sliding. These sliding tests revealed a new frictional phenomenon where friction increased linearly with sliding length over large distances. This was caused by delamination likely due to the coalescence of small bubbles of gas trapped between the graphene monolayer and substrate during sliding, confirmed with atomic force microscopy. Furthermore, atomistic simulations of an asperity sliding over a graphene bubble mimicked experimental results, further supporting this bubble coalescence hypothesis. Graphene's potential as an anticorrosive coating was demonstrated for macroscale, commerciallyavailable electrical connectors. It was demonstrated that even a monolayer of graphene can prevent oxide and reduce electrical contact resistance by orders of magnitude.
Mechanical engineering
ejs2166
Mechanical Engineering
Dissertations

Experimental investigations of the role of proximity approximation in nearfield radiative transfer
http://academiccommons.columbia.edu/catalog/ac:189127
Gu, Ning
http://dx.doi.org/10.7916/D89P311Q
Mon, 16 Sep 2013 00:00:00 +0000
The nature of thermal radiative transfer changes significantly as the nominal gap between two objects becomes comparable to or smaller than the characteristic wavelength given by Wien's displacement law. At larger gaps, conventional theory of blackbody radiation is sufficient to describe the radiative transfer; at smaller gaps, however, wave effects such as evanescent wave tunneling, interference and diffraction render the classical theory invalid. The change in radiative transfer between two objects is most dramatic when they can support electromagnetic surface polaritons because of the high local density of states at the interface between the object and vacuum. When two objects of polar dielectric materials are close enough, the enhanced nearfield radiation due to surface phonon polariton tunneling can exceed the blackbody limit by several orders of magnitude. This enhanced radiation at nanoscale has potential applications in energy transfer, heat assisted magnetic recording and nearfield radiative cooling. In recent years, several experiments measuring the enhanced nearfield radiation between a microsphere and a plane substrate have been reported. To measure the radiative transfer, the magnitude of which can be less than 10 nW, the sensor of choice is the bimaterial microcantilever. My thesis has focused on two aspects of nearfield radiative transfer between a microsphere and a substrate: (1) to enable quantitative comparison between experimental measurement and theoretical/numerical prediction of nearfield radiative transfer. (2) to develop a comprehensive thermal model for the experimental measurement procedure. To enable the first task, an improved experimental apparatus to measure the nearfield radiation between a microsphere and a substrate has been developed. In previous experimental apparatuses, radiative transfer was measured between a microsphere and a truncated plane surface. This was necessary because of the optical configuration. Our new apparatus overcomes this drawback with a newly designed optical path. With this new apparatus, the experiments are truly between a microsphere and an infinite plane. Measurements for microspheres with wide range of radii from 2.5 µ; to 25 µ; have been conducted. The experimental measurements are compared to the numerical prediction using the modified proximity proximation. In contrast to van der Waals force and Casimir force measurements in which the proximity approximation agree better when applied to larger spheres, in radiative heat transfer measurements, the modified proximity approximation agree better for smaller spheres. This surprising finding is explained by the difference in nature of radiative transfer and forces. To go along with the improved apparatus, we have also modified the method of data acquisition, calibration procedures and the thermal model for the experiment. In terms of data collection, we can now eliminate the effects of spurious forces; the second change we have implemented in the experiment is that the substrate is translated at a constant velocity, as opposed to discrete steps. We have developed a thermal model for the new experimental procedure.
Mechanical engineering, Electrical engineering, Physics
ng2220
Electrical Engineering, Mechanical Engineering
Dissertations

Addressing Stability Robustness, Period Uncertainties, and Startup of MultiplePeriod Repetitive Control for Spacecraft Jitter Mitigation
http://academiccommons.columbia.edu/catalog/ac:165159
Ahn, Edwin S.
http://hdl.handle.net/10022/AC:P:21614
Fri, 13 Sep 2013 00:00:00 +0000
Repetitive Control (RC) is a relatively new form of control that seeks to converge to zero tracking error when executing a periodic command, or when executing a constant command in the presence of a periodic disturbance. The design makes use of knowledge of the period of the disturbance or command, and makes use of the error observed in the previous period to update the command in the present period. The usual RC approaches address one period, and this means that potentially they can simultaneously address DC or constant error, the fundamental frequency for that period, and all harmonics up to Nyquist frequency. Spacecraft often have multiple sources of periodic excitation. Slight imbalance in reaction wheels used for attitude control creates three disturbance periods. A special RC structure was developed to allow one to address multiple unrelated periods which is referred to as MultiplePeriod Repetitive Control (MPRC). MPRC in practice faces three main challenges for hardware implementation. One is instability due to model errors or parasitic high frequency modes, the second is degradation of the final error level due to period uncertainties or fluctuations, and the third is bad transients due to issues in startup. Regarding these three challenges, the thesis develops a series of methods to enhance the performance of MPRC or to assist in analyzing its performance for mitigating optical jitter induced by mechanical vibration within the structure of a spacecraft testbed. Experimental analysis of MPRC shows contrasting advantages over existing adaptive control algorithms, such as FilteredX LMS, Adaptive Model Predictive Control, and Adaptive Basis Method, for mitigating jitter within the transmitting beam of Laser Communication (LaserCom) satellites.
Mechanical engineering, Electrical engineering, Aerospace engineering
esa2121
Mechanical Engineering
Dissertations

Laser Surface Texturing, Crystallization and Scribing of Thin Films in Solar Cell Applications
http://academiccommons.columbia.edu/catalog/ac:164387
Wang, Hongliang
http://hdl.handle.net/10022/AC:P:21385
Tue, 20 Aug 2013 00:00:00 +0000
Thin films have been considered for use in terrestrial solar cell applications because of their significantly reduced cost compared with bulk crystalline silicon. However, their overall efficiency and stability are less than that of their bulk crystalline counterpart. The work presented in this thesis seeks to investigate these issues via a series of experimental and numerical analysis of the influences of laser processing on microstructure, optical and electrical properties of two absorber materials, aSi:H (hydrogenated amorphous silicon) and CdTe (cadmium telluride). aSi:H thin film solar cells suffer from disadvantages of low efficiencies and light induced degradation. A onestep laser processing is investigated for introducing lighttrapping structure and crystallization on aSi:H thin films, which can potentially simultaneously alleviate the two weaknesses of aSi:H. The nanoscale conical and pillarshaped spikes formed on the surface of aSi:H films by irradiation of both femtosecond (fs) infrared and nanosecond (ns) excimer lasers enhanced light absorption, while the formation of a mixture of hydrogenated nanocrystalline silicon (ncSi:H) and aSi:H after crystallization suggests that the overall material stability can potentially improve. It is shown that growth is a more dominant spike formation mechanism in excimer laser processing, rather than ablation which is dominant during fs laser texturing. Experimental and analytical approaches are also developed revealing the effect of hydrogen on texturing behavior and crystallization during excimer laser irradiation, and a stepbystep crystallization process is proposed to prevent the hydrogen from diffusing out in order to reduce the defect density. In addition, a comparison of absorptance spectra for various surface morphologies and crystallinity is developed and the absorptance across the solar spectrum shows that the combination of surface texturing and crystallization induced by laser processing is very promising for aSi:H thin film solar cell applications. CdTe thinfilm solar cells are the basis of a significant technology with major commercial impact on terrestrial photovoltaic production, since CdTe leads to substantial cost reduction. Laser scribing is a key process used to increase thinfilm solar panel efficiency through the formation of serial interconnections to reduce photocurrent and resistance losses. Currently, scribing is performed using glassside laser processes which have led to increased scribe quality. Defects formed during scribing such as micro cracks, film delamination, thermal effect and tapered sidewall geometries, however, still keep solar panels from reaching their theoretical efficiencies. In this study, a ns Nd:YAG laser operating at the fundamental (1064nm) or frequencydoubled (532nm) wavelengths is employed for pattern 1 (P1) and 2 (P2) scribing on CdTe thinfilm solar cells. The experimental investigation shows that film removal mechanisms for different materials are due to laserinduced ablation, thermal stress and microexplosion processes. The formation mechanisms and mitigation techniques of the defects during microexplosion process are studied. A fullycoupled thermal and mechanical finite element model is developed to analyze the laserinduced spatiotemporal temperature and thermal stress distribution responsible for SnO2:F film removal, and a plasma expansion model is also investigated to simulate the film removal of CdTe/Cds multilayer due to the microexplosion process. The characterization of removal qualities will enable the process optimization and design required to enhance solar module efficiency.
Mechanical engineering
hw2288
Mechanical Engineering
Dissertations

van der Waals energy and pressure in dissipative media: Fluctuational electrodynamics and mode summation
http://academiccommons.columbia.edu/catalog/ac:163097
Narayanaswamy, Arvind; Zheng, Yi
http://hdl.handle.net/10022/AC:P:21019
Thu, 11 Jul 2013 00:00:00 +0000
We derive the van der Waals energy and pressure in a planar multilayer system with arbitrary number of dissipative films between two halfspaces. A unique feature of this work is that the entire analysis is performed on the real frequency axis instead of summation over Matsubara frequencies on the imaginary frequency axis. The expression we obtain for van der Waals energy is a generalization of van Kampen and Schram's result for dissipationless media. By considering a specific case of a vacuum gap between multilayer objects with dissipative films, we show that the van der Waals energy due to the vacuum gap can not be interpreted simply as a sum of free energy of normal modes.
Mechanical engineering, Molecular physics
an2288, yz2308
Mechanical Engineering
Articles

A Green's function formalism of energy and momentum transfer in fluctuational electrodynamics
http://academiccommons.columbia.edu/catalog/ac:163107
Narayanaswamy, Arvind; Zheng, Yi
http://hdl.handle.net/10022/AC:P:21022
Thu, 11 Jul 2013 00:00:00 +0000
Radiative energy and momentum transfer due to fluctuations of electromagnetic fields arising due to temperature difference between objects is described in terms of the crossspectral densities of the electromagnetic fields. We derive relations between thermal nonequilibrium contributions to energy and momentum transfer and surface integrals of tangential components of the dyadic Green's functions of the vector Helmholtz equation. The expressions derived here are applicable to objects of arbitrary shapes, dielectric functions, as well as magnetic permeabilities. For the case of radiative transfer, we derive expressions for the generalized transmissivity and generalized conductance that are shown to obey reciprocity and agree with theory of black body radiative transfer in the appropriate limit.
Mechanical engineering, Molecular physics
an2288, yz2308
Mechanical Engineering
Articles

Subpicowatt resolution calorimetry with a bimaterial microcantilever sensor
http://academiccommons.columbia.edu/catalog/ac:163088
Canetta, Carlo Benedetto; Narayanaswamy, Arvind
http://hdl.handle.net/10022/AC:P:21016
Thu, 11 Jul 2013 00:00:00 +0000
We have designed and fabricated bimaterial microcantilevers with low conductance by minimizing the width and thickness of the cantilevers while keeping them suitable for detection with an optical deflection technique. The conductance of a cantilever is determined experimentally to be 330 ± 20 nWK−1. Using this cantilever, we have measured less than 1 pW of heat flow through the cantilever. The thermal noiselimited resolution of the cantilever is expected to be ≈ 50 fW. Such cantilevers give us additional tools to probe thermal transport through nanostructures, especially through single molecules where picowattlevel sensitivity is necessary.
Mechanical engineering, Nanoscience
cbc2009, an2288
Mechanical Engineering
Articles

Soliton dynamics in the multiphoton plasma regime
http://academiccommons.columbia.edu/catalog/ac:163155
Husko, Chad A.; Combrie, Sylvain; Colman, Pierre; Zheng, Jiangjun; De Rossi, Alfredo; Wong, Chee Wei
http://hdl.handle.net/10022/AC:P:21037
Thu, 11 Jul 2013 00:00:00 +0000
Solitary waves have consistently captured the imagination of scientists, ranging from fundamental breakthroughs in spectroscopy and metrology enabled by supercontinuum light, to gap solitons for dispersionless slowlight, and discrete spatial solitons in lattices, amongst others. Recent progress in strongfield atomic physics include impressive demonstrations of attosecond pulses and highharmonic generation via photoionization of freeelectrons in gases at extreme intensities of 1014 W/cm2. Here we report the first phaseresolved observations of femtosecond optical solitons in a semiconductor microchip, with multiphoton ionization at picojoule energies and 1010 W/cm2 intensities. The dramatic nonlinearity leads to picojoule observations of freeelectroninduced blueshift at 1016 cm−3 carrier densities and selfchirped femtosecond soliton acceleration. Furthermore, we evidence the timegated dynamics of soliton splitting onchip, and the suppression of soliton recurrence due to fast freeelectron dynamics. These observations in the highly dispersive slowlight media reveal a rich set of physics governing ultralowpower nonlinear photonplasma dynamics.
Mechanical engineering, Atomic physics
cah2116, jz2356, cww2104
Mechanical Engineering
Articles

Next generation Advanced Laser Fluorometry (ALF) for characterization of natural aquatic environments: new instruments
http://academiccommons.columbia.edu/catalog/ac:162952
Chekalyuk, Alexander M.; Hafez, Mark A.
http://hdl.handle.net/10022/AC:P:20968
Tue, 09 Jul 2013 00:00:00 +0000
The new optical design allows single or multiwavelength excitation of laserstimulated emission (LSE), provides optimized LSE optical collection for spectral and temporal analyses, and incorporates swappable modules for flowthrough and smallvolume sample measurements. The basic instrument configuration uses 510 nm laser excitation for assessments of chlorophylla, phycobiliprotein pigments, variable fluorescence (F_v/F_m) and chromophoric dissolved organic matter (CDOM) in CDOMrich waters. The threelaser instrument configuration (375, 405, and 510 nm excitation) provides additional Fv/Fm measurements with 405 nm excitation, CDOM assessments in a broad concentration range, and potential for spectral discrimination between oil and CDOM fluorescence. The new measurement protocols, analytical algorithms and examples of laboratory and field measurements are discussed.
Mechanical engineering, Chemical oceanography
ac2709, mh3170
LamontDoherty Earth Observatory
Articles

Multiscale Experimental Analysis in Plasticity: Linking Dislocation Structures to Continuum Fields
http://academiccommons.columbia.edu/catalog/ac:166490
Oztop, Muin S.
http://hdl.handle.net/10022/AC:P:20881
Fri, 28 Jun 2013 00:00:00 +0000
Plastic deformation in metals is a complex phenomenon and is result of competition between different complicated mechanisms, and among all, dislocation nucleation and motion are the most dominant ones. Dislocation evolution is known to be a multiscale phenomenon, and has been incorporated to crystal plasticity theories to analyze the size effect in metals for almost a decade ago. Although the theories suffice to predict the size effect in metals, they are largely phenomenological. Here a novel experimental method is developed to resolve the complexity in plastic deformation due to dislocations and to extract new material length scales that can be incorporated to numerical models. A continuumbased quantity: the geometrically necessary dislocation density (GND) that describes the signed part of the overall dislocations is measured on a nickel single crystal sample using recently developed high resolution electron backscatter diffraction (HREBSD) over different field of view, 90 μm^2 − 1mm^2 with various step sizes, 50 nm to 2, 500 nm . The net Burgers vector density, which includes the information of the direction of the overall dislocation motion and also quantifies the flux of atoms changing positions due to dislocations, is measured for the first time using continuum methods. A new parameter, β, that is extracted from the net Burger vector density to monitor dislocation activity on crystallographic slip planes is measured. Measurements reveals patterning in GND densities and a distribution of length scales rather than a single length scale as assumed. The length scales, such as dislocation spacing, and dislocation cell sizes are quantified. The linear relationship between dislocation spacing and dislocation cell size is obtained, where the slope of the linear fit varies with different crystallographic slip systems and the number of the active slip systems. The slope ranges between 2329 for dominantly single slip regions, whereas it ranges between 1316 for multislip regions, which agrees with the findings from TEM analysis in the literature showing how a continuum based method can be used to obtain same material parameters. The experimental measurements and the assumptions are elaborated in a detailed analysis. The effect of step size in EBSD results is presented, and the information loss with increasing the step size is shown. The uncertainty in GND density from the HREBSD measurements is found to be 10^13, which is two order of magnitude less than results from traditional diffraction methods. The effect of dislocation mobility on microstructure evolution has been also investigated, specifically tantalum single crystal specimens tested at 77 K and 293 K. The results unraveled occurrences of different deformation mechanisms: kink shear, and twinning at low temperatures. Interactions between dislocations and twin formations are observed and striking microstructure differences are examined. The dislocations density measurement results on tantalum are unique in the experimental sense and data can be used to extract length scale information. The experimental observations have been exploited to build the foundations of a numerical model. The effect of microstructure evolution on mechanical response has been investigated numerically based upon experimental observations. One of the main outcome of the experimental analysis the variation of GND densities in cell walls has been incorporated into a strain gradient plasticity framework. The proposed model is demonstrated with constrained shear and pure bending problems. The results presented show patterning in the GND density profile depending on the prescribed initial variation of the saturation value of GND densities and also change in overall mechanical response depending on the complexity of the prescribed profile.
Mechanical engineering, Materials science
mso2109
Mechanical Engineering
Dissertations

Modification and Integration of Shape Memory Alloys Through Thermal Treatments and Dissimilar Metal Joining
http://academiccommons.columbia.edu/catalog/ac:161525
Satoh, Gen
http://hdl.handle.net/10022/AC:P:20399
Wed, 22 May 2013 00:00:00 +0000
While Shape Memory Alloys (SMAs) have been the topic of numerous studies throughout their history, over fifty years after the first observation of the shape memory effect, their widespread use is still limited by the complexity of tuning the shape memory response and furthermore the difficulty in incorporating the materials selectively into practical systems. Recent advancements, however, show the promise of SMAs for use in microelectromechanical systems (MEMS) and medical devices where their unique properties can provide advanced functionalities. This dissertation investigates the use of laserbased treatments for the modification of shape memory properties as well as the joining of a shape memory alloy to a dissimilar metal through a novel process. The shape memory properties of SMAs are a strong function of composition, thermal treatments, microstructure, ambient temperature, and stress state. These effects are often intertwined, further disguising their true relationships. The use of thermal annealing for the formation of nonequilibrium precipitates in Tirich NiTi thin films is investigated for control over martensitic microstructure, transformation temperatures, and shape memory recovery. Modifications to shape memory properties are investigated through the use of temperaturedependent optical microscopy, temperaturedependent Xray diffraction, and nanoindentation. As shape memory alloys are increasingly applied at smaller length scales due to advantages in achievable actuation frequency and the growth of microscale applications in medical devices, the anisotropy of the shape memory response at the grain level becomes an important consideration for optimizing device performance. The formation of crystallographic texture in NiTi thin films through controlled melting and abnormal grain growth during solidification is investigated through the use of xray diffraction and electron backscatter diffraction measurements. An experimentally validated MonteCarlo grain growth model is developed to predict the texture formation based on the anisotropy in the surface energy between the growing grains and the adjacent liquid. Despite their unique properties, SMAs are not expected to entirely replace more commonly used alloys in most conceivable applications. Rather, these materials are envisioned to be used selectively, where their properties are most advantageous. Joining dissimilar metals, however, is oftentimes made difficult by the formation of brittle intermetallics when the two base materials are mixed. A novel joining process, Autogenous Laser Brazing, is described for the joining of a shape memory alloy to a dissimilar metal. The morphology and strength of the resultant joints is experimentally characterized. Fundamental understanding of the joint formation mechanism is developed through spatiallyresolved composition and phase measurements and predictive numerical simulations. The ability to form joints between materials with different geometries is crucial for the wide applicability of a joining process. To this end, the Autogenous Laser Brazing process is further developed for application to tubular structures. The laser scanning scheme is revised to provide uniform heating both in the circumferential and radial directions. The resultant joints are characterized using spatially resolved phase and material property maps and are found to be formed under a different mechanism than the wire samples.
Mechanical engineering
gs2358
Mechanical Engineering
Dissertations

Thermal Conductivity of FiberReinforced Lightweight Cement Composites
http://academiccommons.columbia.edu/catalog/ac:161111
Hochstein, Daniel Peter
http://hdl.handle.net/10022/AC:P:20303
Tue, 14 May 2013 00:00:00 +0000
This dissertation describes the development of a multiscale mathematical model to predict the effective thermal conductivity (ETC) of fiberreinforced lightweight cement composites. At various stages in the development of the model, the results are compared to experimental values and the model is calibrated when appropriate. Additionally at each stage the proposed model and its results are compared to physical upper and lower bounds placed on the ETC for the different types of structural models. Fiberreinforced lightweight cement mortar is a composite material that contains various components at different scales. The model development begins with a study of neat cement paste and is then extended to include normal weight fine aggregate, lightweight aggregate, and reinforcing fibers. This is accomplished by first considering cement mortar, then models for lightweight cement mortar and fiberreinforced cement mortar are considered separately, and finally these two are joined together to study fiberreinforced lightweight cement mortar. Two different experimental techniques are used to determine the ETC of the different materials. The flash method is used to determine the ETC of the neat cement paste and cement mortar samples, and a recently developed transient technique is used for the remainder of the samples. The model for the ETC of cement paste is derived from a lumped parameter model considering the watercement ratio and saturation of the paste. The results are calibrated using experimental data generated during this project and are in good agreement with values found in the literature. The models for the ETC of cement mortar, fiberreinforced cement mortar, lightweight cement mortar, and fiberreinforced lightweight cement mortar are all based on a differential multiphase model (DM model). This is capable of predicting the ETC of a composite material with various ellipsoidal inclusion phases. It is shown how the DM model can be modified to include information about the maximum volume fraction of the inclusions. A linear packing model is introduced which allows the gradation of the different inclusion phases to be considered. Additionally other factors that affect the ETC are discussed, including the presence of an interfacial transition zone around the inclusions and the relative size of the different constituent phases. The model developed in this report is not only able to predict the effective thermal conductivity for a material, but it can also be used to minimize the effective thermal conductivity by optimizing the structure of the composite. This is done through proper selection of the types and amounts of the various constituents, along with their size, shape, and gradation.
Civil engineering, Mechanical engineering
dph2115
Civil Engineering and Engineering Mechanics
Dissertations

Convergence of Vector Spherical Wave Expansion Method Applied to NearField Radiative Transfer
http://academiccommons.columbia.edu/catalog/ac:158617
Sasihithlu, Karthik; Narayanaswamy, Arvind
http://hdl.handle.net/10022/AC:P:19618
Wed, 03 Apr 2013 00:00:00 +0000
Nearfield radiative transfer between two objects can be computed using Rytov’s theory of fluctuational electrodynamics in which the strength of electromagnetic sources is related to temperature through the fluctuationdissipation theorem, and the resultant energy transfer is described using the dyadic Green’s function of the vector Helmholtz equation. When the two objects are spheres, the dyadic Green’s function can be expanded in a series of vector spherical waves. Based on comparison with the convergence criterion for the case of radiative transfer between two parallel surfaces, we derive a relation for the number of vector spherical waves required for convergence in the case of radiative transfer between two spheres. We show that when electromagnetic surface waves are active at a frequency the number of vector spherical waves required for convergence is proportional to Rmax /d when d/Rmax → 0, where Rmax is the radius of the larger sphere, and d is the smallest gap between the two spheres. This criterion for convergence applies equally well to other nearfield electromagnetic scattering problems.
Mechanical engineering
ks2683, an2288
Mechanical Engineering
Articles

Proximity Effects in Radiative Heat Transfer
http://academiccommons.columbia.edu/catalog/ac:158620
Narayanaswamy, Arvind; Sasihithlu, Karthik
http://hdl.handle.net/10022/AC:P:19619
Wed, 03 Apr 2013 00:00:00 +0000
Though the dependence of nearfield radiative transfer on the gap between two planar objects is well understood, that between curved objects is still unclear. We show unequivocally that the surface polariton mediated radiative transfer between two spheres of equal radii R and minimum gap d scales as R/d as the nondimensional gap d/R→0. We discuss the proximity approximation form that is being used at present to compare with experimental observations and suggest a modified form in order to satisfy the continuity requirement between farfield and nearfield radiative transfer between the spheres.
Mechanical engineering
an2288, ks2683
Mechanical Engineering
Articles

NearField Radiative Heat Transfer Between a Sphere and a Substrate
http://academiccommons.columbia.edu/catalog/ac:158626
Narayanaswamy, Arvind; Shen, Sheng ; Chen, Gang
http://hdl.handle.net/10022/AC:P:19621
Wed, 03 Apr 2013 00:00:00 +0000
Nearfield force and energy exchange between two objects due to quantum electrodynamic fluctuations give rise to interesting phenomena such as Casimir and van der Waals forces and thermal radiative transfer exceeding Planck’s theory of blackbody radiation. Although significant progress has been made in the past on the precise measurement of Casimir force related to zeropoint energy, experimental demonstration of nearfield enhancement of radiative heat transfer is difficult. In this work, we present a sensitive technique of measuring nearfield radiative transfer between a microsphere and a substrate using a bimaterial atomic force microscope cantilever, resulting in “heat transferdistance” curves. Measurements of radiative transfer between a sphere and a flat substrate show the presence of strong nearfield effects resulting in enhancement of heat transfer over the predictions of the Planck blackbody radiation theory.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Phonon Transport Across a Vacuum Gap
http://academiccommons.columbia.edu/catalog/ac:158613
Narayanaswamy, Arvind; Sellan, D. P.; Landry, E. S.; Sasihithlu, Karthik; McGaughey, A. J. H. ; Amon, C. H.
http://hdl.handle.net/10022/AC:P:19617
Wed, 03 Apr 2013 00:00:00 +0000
Phonon transport across a silicon/vacuumgap/silicon structure is modeled using lattice dynamics calculations and Landauer theory. The phonons transmit thermal energy across the vacuum gap via atomic interactions between the leads. Because the incident phonons do not encounter a classically impenetrable potential barrier, this mechanism is not a tunneling phenomenon. While some incident phonons transmit across the vacuum gap and remain in their original mode, many are annihilated and excite different modes. We show that the heat flux due to phonon transport can be 4 orders of magnitude larger than that due to photon transport predicted from nearfield radiation theory.
Mechanical engineering
an2288, ks2683
Mechanical Engineering
Articles

Surface Phononpolariton Mediated Thermal Conductivity Enhancement of Amorphous Thin Films
http://academiccommons.columbia.edu/catalog/ac:158638
Narayanaswamy, Arvind; Chen, Gang ; Chen, DyeZone
http://hdl.handle.net/10022/AC:P:19625
Wed, 03 Apr 2013 00:00:00 +0000
We predict theoretically that the effective inplane thermal conductivity of polar, amorphous thin films can be increased by surface phononpolaritons significantly beyond their intrinsic bulk values. We show that the thermal conductivity due to surface phononpolaritons increases with decreasing film thickness. In particular, for a 40nmthick film of amorphous silicon dioxide, we calculate a total thermal conductivity of 4 W m−1 K−1 at 500 K, which is an increase of ∼100% over the intrinsic phonon thermal conductivity.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Thermal Nearfield Radiative Transfer Between Two Spheres
http://academiccommons.columbia.edu/catalog/ac:158632
Narayanaswamy, Arvind; Chen, Gang
http://hdl.handle.net/10022/AC:P:19623
Wed, 03 Apr 2013 00:00:00 +0000
Radiative energy transfer between closely spaced bodies is known to be significantly larger than that predicted by classical radiative transfer because of tunneling due to evanescent waves. Theoretical analysis of nearfield radiative transfer is mainly restricted to radiative transfer between two halfspaces or spheres treated in the dipole approximation (very small sphere) or proximity force approximation (radius of sphere much greater than the gap). Spheresphere or sphereplane configurations beyond the dipole approximation or proximity force approximation have not been attempted. In this work, the radiative energy transfer between two adjacent nonoverlapping spheres of arbitrary diameters and gaps is analyzed numerically. For spheres of small diameter (compared to the wavelength), the results coincide with the dipole approximation. We see that the proximity force approximation is not valid for spheres with diameters much larger than the gap, even though this approximation is well established for calculating forces. From the numerical results, a regime map is constructed based on two nondimensional length scales for the validity of different approximations.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Thermal Radiation from Photonic Crystals: A Direct Calculation
http://academiccommons.columbia.edu/catalog/ac:158641
Narayanaswamy, Arvind; Chen, Gang ; Chen, DyeZone ; Luo, Chiyan ; Joannopoulos, J. D.
http://hdl.handle.net/10022/AC:P:19626
Wed, 03 Apr 2013 00:00:00 +0000
A classical simulation of equilibrium thermal emissivity from dispersive, lossy photonic crystals is presented. Normal emission results consistent with those assuming Kirchoff's law are obtained; i.e., a photonic crystal does not emit more than what a blackbody does. Significant enhancement, however, can be achieved over the radiation intensity from a uniform slab, indicating the potential usefulness of photonic crystals in incandescent lighting and thermal photovoltaic applications.A classical simulation of equilibrium thermal emissivity from dispersive, lossy photonic crystals is presented. Normal emission results consistent with those assuming Kirchoff's law are obtained; i.e., a photonic crystal does not emit more than what a blackbody does. Significant enhancement, however, can be achieved over the radiation intensity from a uniform slab, indicating the potential usefulness of photonic crystals in incandescent lighting and thermal photovoltaic applications.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Thermal Emission Control with OneDimensional Metallodielectric Photonic Crystals
http://academiccommons.columbia.edu/catalog/ac:158644
Narayanaswamy, Arvind; Chen, Gang
http://hdl.handle.net/10022/AC:P:19627
Wed, 03 Apr 2013 00:00:00 +0000
We have analyzed thermal emission from onedimensional metallodielectric periodic structures using a Green’s function technique together with the fluctuationdissipation theorem. We show that such simple structures exhibit excellent selective emission characteristics with a controllable transition frequency in the infrared and even visible range. Such simple structures should be easy to fabricate and have applications in thermophotovoltaics and potentially in incandescent bulbs.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Nearfield Thermal Radiation Between Two Closely Spaced Glass Plates Exceeding Planck’s Blackbody Radiation Law
http://academiccommons.columbia.edu/catalog/ac:158629
Narayanaswamy, Arvind; Chen, Gang ; Hu, Lu ; Chen, Xiaoyuan
http://hdl.handle.net/10022/AC:P:19622
Wed, 03 Apr 2013 00:00:00 +0000
This work reports experimental studies on radiative heat flux between two parallel glass surfaces. Small polystyrene particles are used as spacers to maintain a micronsized gap between two optical flats. By carefully choosing the number of particles and performing the measurement in a highvacuum environment, the experiment is designed to ensure that the radiative heat flux is the dominant mode of heat transfer. The experimental results clearly demonstrate that the radiative heat flux across micronsized gaps can exceed the farfield upper limit given by Planck’s law of blackbody radiation. The measured radiative heat flux shows reasonable agreement with theoretical predictions.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Surface Modes for Near Field Thermophotovoltaics
http://academiccommons.columbia.edu/catalog/ac:158647
Narayanaswamy, Arvind; Chen, Gang
http://hdl.handle.net/10022/AC:P:19628
Wed, 03 Apr 2013 00:00:00 +0000
Thermal radiative energy transfer between closely spaced surfaces has been analyzed in the past and shown not to obey the laws of classical radiation heat transfer owing to evanescent waves and, more recently, electromagnetic surface modes. We have analyzed the energy transfer between layered media, one of the layers being the thermal source, using a Green’s functions method and the fluctuationdissipation theorem. Based on the analysis, we propose a structure that can utilize the surface modes to increase the power density and efficiency of low temperature thermophotovoltaic generators. © 2003 American Institute of Physics.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Thermal conductance of bimaterial microcantilevers
http://academiccommons.columbia.edu/catalog/ac:158635
Narayanaswamy, Arvind; Chen, Gang ; Goh, Shireen ; Shen, Sheng
http://hdl.handle.net/10022/AC:P:19624
Wed, 03 Apr 2013 00:00:00 +0000
In this letter, based on the beam theory and the thermal analysis of a bimaterial cantilever, we demonstrate that the effective thermal conductance of the cantilever and the temperature at the tip of the cantilever can be determined by measuring the bending of the cantilever in response to two different thermal inputs: power absorbed at the tip and ambient temperature.
Mechanical engineering
an2288
Mechanical Engineering
Articles

Neurofuzzy application for concrete strength prediction using combined nondestructive tests
http://academiccommons.columbia.edu/catalog/ac:158498
Na, U. J.; Park, T. W.; Feng, Maria Q.; Chung, L.
http://hdl.handle.net/10022/AC:P:19611
Tue, 02 Apr 2013 00:00:00 +0000
The application of the neurofuzzy inference system to predict the compressive strength of concrete is presented in this study. The adaptive neurofuzzy inference system (ANFIS) is introduced for training and testing the data sets consisting of various parameters. To investigate the influence of various parameters which affect the compressive strength, 1551 data pairs are collected from the technical literature. These data sets cover early and late compressive strengths from 3 to 365 days and low and high strength in the range 6·3–107·7 MPa. To reflect the effects of other uncertain parameters and in situ conditions, the results of nondestructive tests (NDTs) such as ultrasonic pulse velocity (UPV) and rebound hammer test are also included as input parameters, in addition to mix proportion and curing histories. For the testing of trained ANFIS models, 20 cube specimens and 210 cylinders are prepared, and compressive test and NDTs are conducted. For the comparative study of the applicability of ANFIS models combined with NDT results, four ANFIS models are developed. Depending on whether the input parameters of ANFIS models include NDT results or not, these are distinguished from each other. Among the four models, the ‘ANFISUR' model having the parameters for both UPV and rebound hammer test results shows the best accuracy in the prediction of compressive strength.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Nonlinear Static Procedure for Fragility Curve Development
http://academiccommons.columbia.edu/catalog/ac:158492
Shinozuka, Masanobu; Feng, Maria Q.; Kim, HoKyung; Kim, SangHoon
http://hdl.handle.net/10022/AC:P:19609
Mon, 01 Apr 2013 00:00:00 +0000
This study examines the fragility curves of a bridge by two different analytical approaches; one utilizes the timehistory analysis and the other uses the capacity spectrum method. The latter approach is one of the simplified nonlinear static procedures recently developed for buildings. In this respect, a sample of 10 nominally identical but statistically different bridges and 80 groundmotion time histories are considered to account for the uncertainties related to the structural capacity and ground motion, respectively. The comparison of fragility curves by the nonlinear static procedure with those by timehistory analysis indicates that the agreement is excellent for the state of at least minor damage, but not as good for the state of major damage where nonlinear effects clearly play a crucial role. Overall, however, the agreement is adequate even in the state of major damage considering the large number of typical assumptions under which the analyses of fragility characteristics are performed.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Use of Microwaves for Damage Detection of Fiber Reinforced PolymerWrapped Concrete Structures
http://academiccommons.columbia.edu/catalog/ac:158495
Feng, Maria Q.; De Flaviis, Franco; Kim, Yoo Jin
http://hdl.handle.net/10022/AC:P:19610
Mon, 01 Apr 2013 00:00:00 +0000
Jacketing technology using fiber reinforced polymer (FRP) composites is being applied for seismic retrofit and rehabilitation of reinforced concrete (RC) columns designed and constructed under older specifications. In this study, the authors develop an electromagnetic (EM) imaging technology for detecting such damage as voids and debonding between the jacket and the column, which may significantly weaken the structural performance of the column otherwise attainable by jacketing. This technology is based on the reflection analysis of a continuous EM wave sent toward and reflected from layered FRP–adhesiveconcrete medium: Voids and debonding areas will generate air gaps which produce additional reflections of the EM wave. In this study, dielectric properties of various materials involved in the FRPjacketed RC column were first measured using a planewave reflectometer. The measured properties were then used for a computer simulation of the proposed EM imaging technology. The simulation demonstrated the difficulty in detecting damage by using plane waves, as the reflection contribution from the voids and debonding is very small compared to that from the jacketed column. In order to alleviate this difficulty, dielectric lenses were designed and fabricated, focusing the EM wave on the bonding interface. Finally, three concrete columns were constructed and wrapped with glass–FRP jackets with various voids and debonding conditions artificially introduced in the bonding interface. Using the proposed EM imaging technology involving the especially designed and properly installed lenses, these voids and debonding areas were successfully detected. This technology can be used to assess the jacket bonding quality during the initial jacket installation stage and to detect debonding between the column and the jacket caused by earthquake and other destructive loads.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

A technique to Improve the Empirical Mode Decomposition in the HilbertHuang Transform
http://academiccommons.columbia.edu/catalog/ac:158503
Feng, Maria Q.; Chen, Yangbo
http://hdl.handle.net/10022/AC:P:19533
Fri, 29 Mar 2013 00:00:00 +0000
The Hilbertbased timefrequency analysis has promising capacity to reveal the timevariant behaviors of a system. To admit wellbehaved Hilbert transforms, component decomposition of signals must be performed beforehand. This was first systematically implemented by the empirical mode decomposition (EMD) in the HilbertHuang transform, which can provide a timefrequency representation of the signals. The EMD, however, has limitations in distinguishing different components in narrowband signals commonly found in freedecay vibration signals. In this study, a technique for decomposing components in narrowband signals based on waves’ beating phenomena is proposed to improve the EMD, in which the time scale structure of the signal is unveiled by the Hilbert transform as a result of wave beating, the order of component extraction is reversed from that in the EMD and the end effect is confined. The proposed technique is verified by performing the component decomposition of a simulated signal and a free decay signal actually measured in an instrumented bridge structure. In addition, the adaptability of the technique to timevariant dynamic systems is demonstrated with a simulated timevariant MDOF system.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Variation of Modal Parameters of a Highway Bridge Extracted from Six Earthquake Records
http://academiccommons.columbia.edu/catalog/ac:158512
Feng, Maria Q.; Ulusoy, Hasan; Gomez, Hugo
http://hdl.handle.net/10022/AC:P:19532
Fri, 29 Mar 2013 00:00:00 +0000
Between 2005 and 2010 six earthquakes triggered a monitoring system consisting of 11 acceleration channels installed on the West Street OnRamp, a threespan curved highway bridge located in the city of Anaheim, California. In this paper, three different system identification techniques are applied to the acceleration records to investigate and corroborate the dynamic properties of the bridge, that is, vibration frequencies, associated damping ratios and mode shapes. The identification techniques are applied to each one of the six seismic events. The identified frequencies and damping ratios are shown to be dependent variables of the earthquake intensity. In general, larger earthquake intensities result in reduced vibration frequencies and higher damping ratios of the bridge. Sensitivity analysis using a simple finite element model reveals that soil softening at the abutments considerably contributes to the variation in frequencies because of changes in the support conditions and ultimately in the global stiffness of the structure. In addition, mathematical models in the state space description are identified from the recorded response and excitation measurements. The state space models successfully replicate the bridge measured response to the earthquake from which it is constituted. The models also provide a reasonable prediction of the bridge response to a different earthquake.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Statistical Analysis of Fragility Curves
http://academiccommons.columbia.edu/catalog/ac:158182
Feng, Maria Q.; Shinozuka, Masanobu ; Kim, HoKyung ; Kim, SangHoon
http://hdl.handle.net/10022/AC:P:19479
Wed, 27 Mar 2013 00:00:00 +0000
This paper presents a statistical analysis of structural fragility curves. Both empirical and analytical fragility curves are considered. The empirical fragility curves are developed utilizing bridge damage data obtained from the 1995 Hyogoken Nanbu (Kobe) earthquake. The analytical fragility curves are constructed on the basis of the nonlinear dynamic analysis. Twoparameter lognormal distribution functions are used to represent the fragility curves with the parameters estimated by the maximum likelihood method. This paper also presents methods of testing the goodness of fit of the fragility curves and estimating the confidence intervals of the two parameters (median and logstandard deviation) of the distribution. An analytical interpretation of randomness and uncertainty associated with the median is provided.
Civil engineering, Mechanical engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Application of Neural Networks for Estimation of Concrete Strength
http://academiccommons.columbia.edu/catalog/ac:158191
Feng, Maria Q.; Kim, JongIn ; Kim, Doo Kie ; Yazdani, Frank
http://hdl.handle.net/10022/AC:P:19482
Wed, 27 Mar 2013 00:00:00 +0000
The uniaxial compressive strength of concrete is the most widely used criterion in producing concrete. Although testing of the uniaxial compressive strength of concrete specimens is done routinely, it is performed on the 28th day after concrete placement. At this point, it is too late to make improvements if the test result does not satisfy the required strength. Therefore, the strength estimation before the placement of concrete is highly desirable. This study presents the first effort in applying neural networkbased system identification techniques to predict the compressive strength of concrete based on concrete mix proportions. Backpropagation neural networks were developed, trained, and tested using actual data sets of concrete mix proportions provided by two readymixed concrete companies. The compressive strengths estimated by the neural networks were verified by laboratory testing results. This study demonstrated that the neural network techniques are effective in estimating the compressive strength of concrete based on the mix proportions. Application of these techniques will contribute significantly to the concrete quality assurance.
Civil engineering, Mechanical engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Fragility analysis of bridges under ground motion with spatial variation
http://academiccommons.columbia.edu/catalog/ac:158185
Feng, Maria Q.; Kim, SangHoon
http://hdl.handle.net/10022/AC:P:19480
Wed, 27 Mar 2013 00:00:00 +0000
Seismic ground motion can vary significantly over distances comparable to the length of a majority of highway bridges on multiple supports. This paper presents results of fragility analysis of highway bridges under ground motion with spatial variation. Ground motion time histories are artificially generated with different amplitudes, phases, as well as frequency contents at different support locations. Monte Carlo simulation is performed to study dynamic responses of an example multispan bridge under these ground motions. The effect of spatial variation on the seismic response is systematically examined and the resulting fragility curves are compared with those under identical support ground motion. This study shows that ductility demands for the bridge columns can be underestimated if the bridge is analyzed using identical support ground motions rather than differential support ground motions. Fragility curves are developed as functions of different measures of ground motion intensity including peak ground acceleration, peak ground velocity, spectral acceleration, spectral velocity and spectral intensity. This study represents a first attempt to develop fragility curves under spatially varying ground motion and provides information useful for improvement of the current seismic design codes so as to account for the effects of spatial variation in the seismic design of longspan bridges.
Civil engineering, Mechanical engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Microwave Reflection Tomographic Array fo rDamage Detection of Civil Structures
http://academiccommons.columbia.edu/catalog/ac:158188
Feng, Maria Q.; Kim, Yoo Jin ; Jofre, Luis ; De Flaviis, Franco
http://hdl.handle.net/10022/AC:P:19481
Wed, 27 Mar 2013 00:00:00 +0000
Microwave tomographic imaging technology using a bifocusing operator has been developed in order to detect the internal voids/objects inside concrete structures. The imaging system consists of several cylindrical or planar array antennas for transmitting and receiving signals, and a numerical focusing operator is applied to the external signals both in transmitting and in receiving fields. An imaging algorithm using a numerical focusing operator was developed, which allows the recovery of a twodimensional object from its scattered field. Numerical simulation demonstrated that a subsurface image can be successfully reconstructed by using the proposed tomographic imaging technology. For experimental verification, a prototype planar antenna array was fabricated and tested on a concrete specimen.
Electrical engineering, Civil engineering, Mechanical engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

LongTerm Monitoring and Analysis of a Curved Concrete BoxGirder Bridge
http://academiccommons.columbia.edu/catalog/ac:158218
Feng, Maria Q.; Lee, Sungchil; Hong, SeokHee
http://hdl.handle.net/10022/AC:P:19491
Wed, 27 Mar 2013 00:00:00 +0000
Capital investment in national infrastructure is significant. The need to maintain and protect critical infrastructure links has led in recent years to significant developments in the area of structural health monitoring. The objective is to track a structure’s longterm performance, typically using sensors, and to successively compare the most recently measured responses with prior response history. During construction of the West Street OnRamp, a curved concrete box girder bridge, located in the city of Anaheim (California), eleven accelerometers were permanently installed on its bridge deck. The associated data acquisition system was configured to record once a specified threshold acceleration response was exceeded; during the period 2002–2010 a total of 1350 datasets including six earthquakes, for each of the eleven sensors, were acquired. This automatically acquired data was supplemented, during the summer of 2009, with responses measured during controlled vehicle tests. Six accelerometers were additionally installed on the frame of the weighed test vehicle. This paper presents the findings of the analyses of these measured data sets and serves to inform owners and managers as to the potential feedback from their instrumentation investment. All response histories were analyzed using frequency domain techniques for system identification. Extraction of the modal characteristics revealed a continuous reduction, of approximately 5%, in the first three natural frequencies over the period of the study. The measured responses from the vehicle sensors are discussed in the context of identifying the potential for bridge frequency measurement using instrumented vehicles.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

LongTerm Monitoring and Identification of Bridge Structural Parameters
http://academiccommons.columbia.edu/catalog/ac:158221
Feng, Maria Q.; Soyoz, Serdar
http://hdl.handle.net/10022/AC:P:19492
Wed, 27 Mar 2013 00:00:00 +0000
Vibration of a new concrete bridge was monitored and change in the bridge structural stiffness was identified accordingly over a 5year period. This threespan 111m long bridge is instrumented with 13 acceleration sensors at both the superstructure and the columns. The sensor data are transmitted to a server computer wirelessly. Modal parameters of the bridge, that is, the frequencies and the modal shapes were identified by processing 1,707 vibration data sets collected under traffic excitations, based on which the bridge structural parameters, stiffness and mass, and the soil spring values were identified by employing the neural network technique. The identified superstructure stiffness at the beginning of the monitoring was 97% of the stiffness value based on the design drawings. In the identified modal frequencies, a variation from −10% to +10% was observed over the monitoring period. In the identified stiffness values of the bridge superstructure, a variation from −3% to +3% was observed over the monitoring period. Based on the statistical analysis of the collected data for each year, 5% decrease in the first modal frequency and 2% decrease in the superstructure stiffness were observed over the 5year monitoring period. Probability density functions were obtained for stiffness values each year. Stiffness threshold values for the collapse of the bridge under the operational loading can be determined. Then the number of years can be assessed for which the area under the proposed probability density functions is greater than the threshold value. So the information obtained in this study is valuable for studying aging and longterm performance assessment of similar bridges.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Use of Supervisory Control and Data Acquisition for Damage Location of Water Delivery Systems
http://academiccommons.columbia.edu/catalog/ac:158203
Feng, Maria Q.; Shinozuka, Masanobu; Liang, Jianwen
http://hdl.handle.net/10022/AC:P:19486
Wed, 27 Mar 2013 00:00:00 +0000
Urban water delivery systems can be damaged by earthquakes or severely cold weather. In either case, the damage cannot easily be detected and located, especially immediately after the event. In recent years, realtime damage estimation and diagnosis of buried pipelines attracted much attention of researchers focusing on establishing the relationship between damage ratio (breaks per unit length of pipe) and ground motion, taking the soil condition into consideration. Due to the uncertainty and complexity of the parameters that affect the pipe damage mechanism, it is not easy to estimate the degree of physical damage only with a few numbers of parameters. As an alternative, this paper develops a methodology to detect and locate the damage in a water delivery system by monitoring water pressure online at some selected positions in the water delivery systems. For the purpose of online monitoring, emerging supervisory control and data acquisition technology can be well used. A neural networkbased inverse analysis method is constructed for detecting the extent and location of damage based on the variation of water pressure. The neural network is trained by using analytically simulated data from the water delivery system with one location of damage, and validated by using a set of data that have never been used in the training. It is found that the method provides a quick, effective, and practical way in which the damage sustained by a water delivery system can be detected and located.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Baseline Models for Bridge Performance Monitoring
http://academiccommons.columbia.edu/catalog/ac:158197
Feng, Maria Q.; Kim, Doo Kie; Yi, JinHak; Chen, Yangbo
http://hdl.handle.net/10022/AC:P:19484
Wed, 27 Mar 2013 00:00:00 +0000
A baseline model is essential for longterm structural performance monitoring and evaluation. This study represents the first effort in applying a neural networkbased system identification technique to establish and update a baseline finite element model of an instrumented highway bridge based on the measurement of its trafficinduced vibrations. The neural network approach is particularly effective in dealing with measurement of a largescale structure by a limited number of sensors. In this study, sensor systems were installed on two highway bridges and extensive vibration data were collected, based on which modal parameters including natural frequencies and mode shapes of the bridges were extracted using the frequency domain decomposition method as well as the conventional peak picking method. Then an innovative neural network is designed with the input being the modal parameters and the output being the structural parameters of a threedimensional finite element model of the bridge such as the mass and stiffness elements. After extensively training and testing through finite element analysis, the neural network became capable to identify, with a high level of accuracy, the structural parameter values based on the measured modal parameters, and thus the finite element model of the bridge was successfully updated to a baseline. The neural network developed in this study can be used for future baseline updates as the bridge being monitored periodically over its lifetime.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Microwave Subsurface Imaging Technology for Damage Detection
http://academiccommons.columbia.edu/catalog/ac:158194
Kim, Yoo Jin; Feng, Maria Q.; De Flaviis, Franco; Jofre, Luis
http://hdl.handle.net/10022/AC:P:19483
Wed, 27 Mar 2013 00:00:00 +0000
This paper presents a technology for detecting invisible damage inside concrete, which is based on reconstruction of dielectric profile (image) of the concrete illuminated with microwaves sent from and received by antenna arrays controlled by specialized software. The imaging system developed in this study consists of an 8X8 transmitting and an 8X8 receiving arrays, an innovative numerical bifocusing operator for improving image resolution, and imaging software for reconstructing a twodimensional image from the scattered field. The effectiveness of the of the developed technology in detecting steel and voids inside concrete has been demonstrated through numerical simulation and experiments.
Civil engineering, Mechanical engineering, Electrical engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Nonlinear Damping Identification in Precast Prestressed Reinforced Concrete Beams
http://academiccommons.columbia.edu/catalog/ac:158227
Feng, Maria Q.; Franchetti, Paolo; Modena, Claudio
http://hdl.handle.net/10022/AC:P:19494
Wed, 27 Mar 2013 00:00:00 +0000
This article presents a damage detection method for prestressed reinforced concrete (PRC) elements based on free vibration tests and nonlinear damping identification. Integrated static and dynamic experiments were carried out on three precast PRC beam specimens. The static loading induced different levels of damage to the beams. At each damage level, impulsive loading was applied to the beams and the free vibration response was measured. The dynamic response data were processed using different methods including the multiinput multioutput (MIMO) curve fitting and the Hilbert transform techniques. A strong correlation is observed between the level of concrete damage (cracks) and the amount of nonlinear energy dissipation that can be modeled by means of quadratic damping. The nonlinear damping can be extracted from the free vibration response for each vibration mode. The proposed method is suited for quality control when manufacturing precast PRC members, and can be further extended for in situ detection of damage in concrete structures under ambient vibration.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

LargeScale Shake Table Test Verification of Bridge Condition Assessment Methods
http://academiccommons.columbia.edu/catalog/ac:158212
Feng, Maria Q.; Chen, Yangbo; Soyoz, Serdar
http://hdl.handle.net/10022/AC:P:19489
Wed, 27 Mar 2013 00:00:00 +0000
Methods that identify structural component stiffness degradation by pre and postevent low amplitude vibration measurements, based on a linear timeinvariant (LTI) system model, are conceptually justified by examining the hysteresis loops the structural components experience in such vibrations. Two largescale shake table experiments, one on a twocolumn reinforced concrete (RC) bridge bent specimen, and the other on a twospan threebent RC bridge specimen were performed, in which specimens were subjected to earthquake ground motions with increasing amplitude and progressively damaged. In each of the damaged stages between two strong motions, low amplitude vibrations of the specimens were aroused, and the postevent component stiffness coefficients were identified by optimizing the parameters in a LTI model. The stiffness degradation identified is consistent with the experimental hysteresis, and could be quantitatively related to the capacity residual of the components.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Stress–strain model for concrete confined by FRP composites
http://academiccommons.columbia.edu/catalog/ac:158209
Feng, Maria Q.; Youssef, Marwan N.; Mosallam, Ayman S.
http://hdl.handle.net/10022/AC:P:19488
Wed, 27 Mar 2013 00:00:00 +0000
In this paper, a stress–strain model for concrete confined by fiber reinforced polymer (FRP) composites is developed. The model is based on the results of a comprehensive experimental program including largescale circular, square and rectangular short columns confined by carbon/epoxy and Eglass/epoxy jackets providing a wide range of confinement ratios. Ultimate stress, rupture strain, jacket parameters, and crosssectional geometry were found to be significant factors affecting the stress–strain behavior of FRPconfined concrete. Such parameters were analyzed statistically based on the experimental data, and equations to theoretically predict these parameters are presented. Experimental results from this study were compared to the proposed semiempirical model as well as others from the literature.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Damage Detection Based On Damping Analysis Of Ambient Vibration Data
http://academiccommons.columbia.edu/catalog/ac:158224
Feng, Maria Q.; Soyoz, Serdar; Frizzarin, Michele; Franchetti, Paolo; Modena, Claudio
http://hdl.handle.net/10022/AC:P:19493
Wed, 27 Mar 2013 00:00:00 +0000
Enabling an automated, remote and rapid detection of structural damage, sensorbased structural health monitoring is becoming a powerful tool for maintenance of civil engineering structures. In this study, a baselinefree, timedomain damage detection method was developed for concrete structures, which is based on analysis of nonlinear damping from measured structural vibration responses. The efficacy of the proposed method was demonstrated through a largescale concrete bridge model subjected to different levels of seismic damage caused by shaking table tests. By applying the random decrement signature technique, the proposed method successfully identified, from its ambient vibration responses, nonlinear damping of the bridge associated with the seismic damage. The amount of the nonlinear damping increases as the seismic damage becomes more severe. This paper also compares the damage detection results with those obtained by stiffnessbased methods, demonstrating a strong correlation between the increase in nonlinear damping and the decrease in structural stiffness associated with the increase in damage severity.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Instantaneous damage detection of bridge structures and experimental verification
http://academiccommons.columbia.edu/catalog/ac:158215
Feng, Maria Q.; Soyoz, Serdar
http://hdl.handle.net/10022/AC:P:19490
Wed, 27 Mar 2013 00:00:00 +0000
An extended Kalman filtering (EKF) method was developed and applied to instantaneously identify elemental stiffness values of a structure during damaging seismic events based on vibration measurement. This method is capable of dealing with nonlinear as well as linear structural responses. Identification of the structural elemental stiffness enables location as well as quantification of structural damage. The instantaneous stiffness values during an event can provide highly useful information for postevent capacity estimation. In this study, a largescale shaking table test of a threebent concrete bridge model was performed in order to verify the proposed damage detection method. The bridge model was shaken to different damage levels by a sequence of earthquake motions with increasing intensities. The elemental stiffness values of the structure were instantaneously identified in real time during the damaging earthquake excitations using the EKF method. The identified stiffness degradations and their locations agreed well with the structural damage observed by visual inspection and strain measurements. More importantly, the seismic response accelerations analytically simulated using the instantaneous stiffness values thus identified agreed well with the measured accelerations, demonstrating the accuracy of the identified stiffness. This study presents an experimental verification of a structural damage detection method using a realistic bridge model subjected to realistic seismic damage.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Novel Fiber Optic Accelerometer System Using Geometric Moiré Fringe
http://academiccommons.columbia.edu/catalog/ac:158206
Feng, Maria Q.; Kim, DaeHyun
http://hdl.handle.net/10022/AC:P:19487
Wed, 27 Mar 2013 00:00:00 +0000
This paper presents an innovative fiber optic accelerometer system for monitoring vibration of largesize structures. The system is composed of one (or multiple) sensor head and a control unit for driving the sensor and processing sensor data. The sensing mechanism is based on a novel integration of the moiré fringe phenomenon with fiber optics, resulting in accurate and reliable measurement. A prototype fiber optic accelerometer system has been successfully developed, including a sensor head, a lowcost control unit and a software package with a unique algorithm for processing the moiré fringe signals into accelerations with a high resolution. Finally, free vibration and shaking table tests were performed to identify the dynamic characteristics and demonstrate the high performance of the sensor system developed in this study.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Structural Health Monitoring by Recursive Bayesian Filtering
http://academiccommons.columbia.edu/catalog/ac:158230
Feng, Maria Q.; Chen, Yangbo
http://hdl.handle.net/10022/AC:P:19495
Wed, 27 Mar 2013 00:00:00 +0000
A new vision of structural health monitoring (SHM) is presented, in which the ultimate goal of SHM is not limited to damage identification, but to describe the structure by a probabilistic model, whose parameters and uncertainty are periodically updated using measured data in a recursive Bayesian filtering (RBF) approach. Such a model of a structure is essential in evaluating its current condition and predicting its future performance in a probabilistic context. RBF is conventionally implemented by the extended Kalman filter, which suffers from its intrinsic drawbacks. Recent progress on highfidelity propagation of a probability distribution through nonlinear functions has revived RBF as a promising tool for SHM. The central difference filter, as an example of the new versions of RBF, is implemented in this study, with the adaptation of a convergence and consistency improvement technique. Two numerical examples are presented to demonstrate the superior capacity of RBF for a SHM purpose. The proposed method is also validated by largescale shake table tests on a reinforced concrete twospan threebent bridge specimen.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Detection of Ceramic Cracks Using a Distributed HighResolution Brillouin Fiber Optic Sensor
http://academiccommons.columbia.edu/catalog/ac:158239
Feng, Maria Q.; Zou, Lufan; Imai, Michio
http://hdl.handle.net/10022/AC:P:19498
Wed, 27 Mar 2013 00:00:00 +0000
A distributed sensor system is highly desirable for detecting, locating, and monitoring fine cracks at unknown locations in advanced ceramics. This paper presents a distributed highresolution fiber optic sensor based on the Brillouin scattering principle, and its application in ceramic crack detection for the first time. The existence of cracks, together with their locations, is identified by measuring the strain distribution on a sensing fiber bonded to the ceramic surface. By employing the innovative coherent probepump interaction technique, the Brillouin sensor developed in this study achieves a high spatial resolution (100 mm) and measurement accuracy. Capable of detecting and locating fine cracks less than 40 μm, the efficacy of the distributed Brillouin fiber optic sensor is demonstrated through experiments.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Structural Reliability Estimation with VibrationBased Identified Parameters
http://academiccommons.columbia.edu/catalog/ac:158236
Feng, Maria Q.; Soyoz, Serdar; Shinozuka, Masanobu
http://hdl.handle.net/10022/AC:P:19497
Wed, 27 Mar 2013 00:00:00 +0000
This paper presents a unique structural reliability estimation method incorporating structural parameter identification results based on the seismic response measurement. In the shaking table test, a threebent concrete bridge model was shaken to different damage levels by a sequence of earthquake motions with increasing intensities. Structural parameters, stiffness and damping values of the bridge were identified under damaging seismic events based on the seismic response measurement. A methodology was developed to understand the importance of structural parameter identification in the reliability estimation. Along this line, a set of structural parameters were generated based on the Monte Carlo simulation. Each of them was assigned to the base bridge model. Then, every bridge model was analyzed using nonlinear time history analyses to obtain damage level at the specific locations. Last, reliability estimation was performed for bridges modeled with two sets of structural parameters. The first one was obtained by the nonlinear time history analysis with the Monte Carlo simulated parameters which is called nonupdated structural parameters. The second one was obtained by updating the first set in Bayesian sense based on the vibrationbased identification results which is called updated structural parameters. In the scope of this paper, it was shown that residual reliability of the system estimated using the updated structural parameters is lower than the one estimated using the nonupdated structural parameters.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles

Characterization of Electromagnetic Properties for Durability Performance and Saturation in Hardened Cement Mortar
http://academiccommons.columbia.edu/catalog/ac:158233
Feng, Maria Q.; Kwon, SeungJun; Park, Sang Soon
http://hdl.handle.net/10022/AC:P:19496
Wed, 27 Mar 2013 00:00:00 +0000
Electromagnetic (EM) properties—dielectric constant and conductivity are changed with porosity and saturation in cementbased materials. In this paper, dielectric constant and conductivity are measured in cement mortar with 5 different mixture conditions considering saturation. For the same mixture proportions, durability tests including porosity, chloride diffusion, air permeability, sorptivity, and water diffusion are performed. Among the continuously measured EM properties within 5–20 GHz of frequency range for different saturation, results under 60% of saturation which shows stable results are selected and averaged as one value. The averaged measurements utilizing results under 60% of saturation are compared with those from durability tests. Through the normalization using the results of W/C 40% which shows best durability performances, changing ratios of durability characteristics are evaluated with normalized dielectric constant and conductivity. The behaviors of EM properties with different saturation and their relationships with durability performances are studied.
Mechanical engineering, Civil engineering
mqf2101
Civil Engineering and Engineering Mechanics
Articles