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Academic Commons Search Resultsen-usCollagen Fiber Orientation and Dispersion in the Upper Cervix of Non-Pregnant and Pregnant Women
https://academiccommons.columbia.edu/catalog/ac:205884
Yao, Frank; Gan, Yu; Myers, Kristin M.; Vink, Joy-Sarah Yumiko; Wapner, Ronald J.; Hendon, Christine P.10.7916/D8H41RXNWed, 05 Jul 2017 13:44:05 +0000The structural integrity of the cervix in pregnancy is necessary for carrying a pregnancy until term, and the organization of human cervical tissue collagen likely plays an important role in the tissue’s structural function. Collagen fibers in the cervical extracellular matrix exhibit preferential directionality, and this collagen network ultrastructure is hypothesized to reorient and remodel during cervical softening and dilation at time of parturition. Within the cervix, the upper half is substantially loaded during pregnancy and is where the premature funneling starts to happen. To characterize the cervical collagen ultrastructure for the upper half of the human cervix, we imaged whole axial tissue slices from non-pregnant and pregnant women undergoing hysterectomy or cesarean hysterectomy respectively using optical coherence tomography (OCT) and implemented a pixel-wise fiber orientation tracking method to measure the distribution of fiber orientation. The collagen fiber orientation maps show that there are two radial zones and the preferential fiber direction is circumferential in a dominant outer radial zone. The OCT data also reveal that there are two anatomic regions with distinct fiber orientation and dispersion properties. These regions are labeled: Region 1—the posterior and anterior quadrants in the outer radial zone and Region 2—the left and right quadrants in the outer radial zone and all quadrants in the inner radial zone. When comparing samples from nulliparous vs multiparous women, no differences in these fiber properties were noted. Pregnant tissue samples exhibit an overall higher fiber dispersion and more heterogeneous fiber properties within the sample than non-pregnant tissue. Collectively, these OCT data suggest that collagen fiber dispersion and directionality may play a role in cervical remodeling during pregnancy, where distinct remodeling properties exist according to anatomical quadrant.Cervix uteri, Pregnancy--Physiological aspects, Collagen, Mechanical engineering, Obstetrics, Gynecologywy2169, yg2327, kmm2233, jyv2101, rw2191, cpf2115Electrical Engineering, Obstetrics and Gynecology, Mechanical EngineeringArticlesApplications of Graphene-based Nano Electro Mechanical Systems
https://academiccommons.columbia.edu/catalog/ac:209058
Lee, Sunwoo10.7916/D8J38STBThu, 15 Jun 2017 16:08:14 +0000This thesis describes studies of a two-dimensional (2D), hexagonal arrangement of carbon atoms, graphene. Because of graphene’s reduced dimensionality, the 2D material possesses many desirable mechanical and electrical properties compared to its three-dimensional (3D) counterpart, graphite. In fact, its mechanical strength and electrical mobility are one of the strongest and fastest in the world, prompting much excitements from science and engineering communities alike ever since its first experimental demonstration in 2004. The first part of this thesis deals with graphene in material level. Chapter 1 provides an introduction to graphene. Chapter 2 describes chemical vapor deposition (CVD) synthesis of graphene and various transfer techniques. Chapter 3 describes characterization of graphene using optical inspection, oxidation test, Raman spectroscopy, and electrical transport.
The second part of this thesis concerns graphene in device level, electro-mechanical implementation in particular. Chapter 4 gives an introduction to graphene nano-electro- mechanical systems (GNEMS), where the material’s mechanical and electrical prowess can best be combined, and describes fabrication process as well as transduction mechanism. Chapter 5 shows how GNEMS can be used to build a pressure sensor or an accelerometer. Chapter 6 is a study of the graphene resonators for signal processing such as in RF filters or oscillators. Chapter 7 describes the graphene - silicon nitride heterostructure resonators.
The third part of this thesis considers the integration of GNEMS at a system level. Chapter 8 depicts integration of graphene resonators onto a taped-out CMOS die using post-processing.
This work, in conjunction with numerous other work done by fellow researchers in the field, tries to provide an overview - from the material synthesis to device fabrication and characterization, and further to system level integration - in utilizing graphene, and graphene NEMS in particular, for sensing and signal processing applications.Nanoelectromechanical systems, Chemical vapor deposition, Electromechanical devices, Graphene, Electrical engineering, Materials science, Mechanical engineeringsl3229Electrical EngineeringThesesSimultaneous Iterative Learning and Feedback Control Design
https://academiccommons.columbia.edu/catalog/ac:182998
Chinnan, Anil Philip10.7916/D8NC6000Mon, 12 Jun 2017 17:39:32 +0000Iterative learning controllers aim to produce high precision tracking in operations where the same tracking maneuver is repeated over and over again. Model-based 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 non-repeating, 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 one-time step behind disturbance estimator and one-repetition behind disturbance estimator can be incorporated together in such a combination.
Since learning control applications are finite-time by their very nature, frequency response based design techniques are not best suited for designing the feedback controller in this context. A finite-time 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 finite-time feedback and learning control as a natural solution for such a control objective, showing how a finite-time 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, Roboticsapc2113Electrical EngineeringThesesExperimental investigations of the role of proximity approximation in near-field radiative transfer
https://academiccommons.columbia.edu/catalog/ac:189127
Gu, Ning10.7916/D89P311QThu, 08 Jun 2017 16:10:59 +0000The 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 near-field 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 near-field radiative cooling.
In recent years, several experiments measuring the enhanced near-field radiation between a micro-sphere 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 bi-material micro-cantilever. My thesis has focused on two aspects of near-field radiative transfer between a micro-sphere and a substrate: (1) to enable quantitative comparison between experimental measurement and theoretical/numerical prediction of near-field 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 near-field radiation between a micro-sphere and a substrate has been developed. In previous experimental apparatuses, radiative transfer was measured between a micro-sphere 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 micro-sphere and an infinite plane. Measurements for micro-spheres 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, Physicsng2220Electrical EngineeringThesesMulti-Input Multi-Output Repetitive Control Theory And Taylor Series Based Repetitive Control Design
https://academiccommons.columbia.edu/catalog/ac:144391
Xu, Kevin10.7916/D8SB4CPNWed, 07 Jun 2017 02:40:49 +0000Repetitive control (RC) systems aim to achieve zero tracking error when tracking a periodic command, or when tracking a constant command in the presence of a periodic disturbance, or both a periodic command and periodic disturbance. This dissertation presents a new approach using Taylor Series Expansion of the inverse system z-transfer function model to design Finite Impulse Response (FIR) repetitive controllers for single-input single-output (SISO) systems, and compares the designs obtained to those generated by optimization in the frequency domain. This approach is very simple, straightforward, and easy to use. It also supplies considerable insight, and gives understanding of the cause of the patterns for zero locations in the optimization based design. The approach forms a different and effective time domain design method, and it can also be used to guide the choice of parameters in performing in the frequency domain optimization design. Next, this dissertation presents the theoretical foundation for frequency based optimization design of repetitive control design for multi-input multi-output (MIMO) systems. A comprehensive stability theory for MIMO repetitive control is developed. A necessary and sufficient condition for asymptotic stability in MIMO RC is derived, and four sufficient conditions are created. One of these is the MIMO version of the approximate monotonic decay condition in SISO RC, and one is a necessary and sufficient condition for stability for all possible disturbance periods. An appropriate optimization criterion for direct MIMO is presented based on minimizing a Frobenius norm summed over frequencies from zero to Nyquist. This design process is very tractable, requiring only solution of a linear algebraic equation. An alternative approach reduces the problem to a set of SISO design problems, one for each input-output pair. The performances of the resulting designs are studied by extensive examples. Both approaches are seen to be able to create RC designs with fast monotonic decay of the tracking error. Finally, this dissertation presents an analysis of using an experiment design sequence for parameter identification based on the theory of iterative learning control (ILC), a sister field to repetitive control. This is suggested as an alternative to the results in optimal experiment design. Modified ILC laws that are intentionally non-robust to model errors are developed, as a way to fine tune the use of ILC for identification purposes. The non-robustness with respect to its ability to improve identification of system parameters when the model error is correct is studied. It is demonstrated that in many cases the approach makes the learning particularly sensitive to relatively small parameter errors in the model, but sensitivity is sometimes limited to parameter errors of a specific sign.Electrical engineering, Mechanical engineeringkx2101Electrical EngineeringThesesRobustification and Optimization in Repetitive Control For Minimum Phase and Non-Minimum Phase Systems
https://academiccommons.columbia.edu/catalog/ac:vq83bk3jct
Prasitmeeboon, Pitcha Prasitmeeboon10.7916/D8FT8SD8Tue, 02 May 2017 22:25:26 +0000Repetitive control (RC) is a control method that specifically aims to converge to zero tracking error of a control systems that execute a periodic command or have periodic disturbances of known period. It uses the error of one period back to adjust the command in the present period. In theory, RC can completely eliminate periodic disturbance effects. RC has applications in many fields such as high-precision manufacturing in robotics, computer disk drives, and active vibration isolation in spacecraft.
The first topic treated in this dissertation develops several simple RC design methods that are somewhat analogous to PID controller design in classical control. From the early days of digital control, emulation methods were developed based on a Forward Rule, a Backward Rule, Tustin’s Formula, a modification using prewarping, and a pole-zero mapping method. These allowed one to convert a candidate controller design to discrete time in a simple way. We investigate to what extent they can be used to simplify RC design. A particular design is developed from modification of the pole-zero mapping rules, which is simple and sheds light on the robustness of repetitive control designs.
RC convergence requires less than 90 degree model phase error at all frequencies up to Nyquist. A zero-phase cutoff filter is normally used to robustify to high frequency model error when this limit is exceeded. The result is stabilization at the expense of failure to cancel errors above the cutoff. The second topic investigates a series of methods to use data to make real time updates of the frequency response model, allowing one to increase or eliminate the frequency cutoff. These include the use of a moving window employing a recursive discrete Fourier transform (DFT), and use of a real time projection algorithm from adaptive control for each frequency. The results can be used directly to make repetitive control corrections that cancel each error frequency, or they can be used to update a repetitive control FIR compensator. The aim is to reduce the final error level by using real time frequency response model updates to successively increase the cutoff frequency, each time creating the improved model needed to produce convergence zero error up to the higher cutoff.
Non-minimum phase systems present a difficult design challenge to the sister field of Iterative Learning Control. The third topic investigates to what extent the same challenges appear in RC. One challenge is that the intrinsic non-minimum phase zero mapped from continuous time is close to the pole of repetitive controller at +1 creating behavior similar to pole-zero cancellation. The near pole-zero cancellation causes slow learning at DC and low frequencies. The Min-Max cost function over the learning rate is presented. The Min-Max can be reformulated as a Quadratically Constrained Linear Programming problem. This approach is shown to be an RC design approach that addresses the main challenge of non-minimum phase systems to have a reasonable learning rate at DC.
Although it was illustrated that using the Min-Max objective improves learning at DC and low frequencies compared to other designs, the method requires model accuracy at high frequencies. In the real world, models usually have error at high frequencies. The fourth topic addresses how one can merge the quadratic penalty to the Min-Max cost function to increase robustness at high frequencies. The topic also considers limiting the Min-Max optimization to some frequencies interval and applying an FIR zero-phase low-pass filter to cutoff the learning for frequencies above that interval.Electrical engineering, Mechanical engineeringpp2246Electrical EngineeringTheses