Academic Commons Search Results
http://academiccommons.columbia.edu/catalog.rss?f%5Bsubject_facet%5D%5B%5D=Physics&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usHolographic Jet Quenching
http://academiccommons.columbia.edu/catalog/ac:178237
Ficnar, Andrejhttp://dx.doi.org/10.7916/D8M04417Wed, 08 Oct 2014 18:16:26 +0000In this dissertation we study the phenomenon of jet quenching in quark-gluon plasma using the AdS/CFT correspondence.
We start with a weakly coupled, perturbative QCD approach to energy loss, and present a Monte Carlo code for computation of the DGLV radiative energy loss of quarks and gluons at an arbitrary order in opacity. We use the code to compute the radiated gluon distribution up to n=9 order in opacity, and compare it to the thin plasma (n=1) and the multiple soft scattering (n=\infty) approximations. We furthermore show that the gluon distribution at finite opacity depends in detail on the screening mass and the mean free path.
In the next part, we turn to the studies of how heavy quarks, represented as "trailing strings" in AdS/CFT, lose energy in a strongly coupled plasma. We study how the heavy quark energy loss gets modified in a "bottom-up" non-conformal holographic model, constructed to reproduce some properties of QCD at finite temperature and constrained by fitting the lattice gauge theory results. The energy loss of heavy quarks is found to be strongly sensitive to the medium properties. We use this model to compute the nuclear modification factor R_AA of charm and bottom quarks in an expanding plasma with Glauber initial conditions, and comment on the range of validity of the model.
The central part of this thesis is the energy loss of light quarks in a strongly coupled plasma. Using the standard model of "falling strings", we present an analytic derivation of the stopping distance of light quarks, previously available only through numerical simulations, and also apply it to the case of Gauss-Bonnet higher derivative gravity. We then present a general formula for computing the instantaneous energy loss in non-stationary string configurations. Application of this formula to the case of falling strings reveals interesting phenomenology, including a modified Bragg-like peak at late times and an approximately linear path dependence. Based on these results, we develop a phenomenological model of light quark energy loss and use it compute the nuclear modification factor R_AA of light quarks in an expanding plasma. Comparison with the LHC pion suppression data shows that, although R_AA has the right qualitative structure, the overall magnitude is too low, indicating that the predicted jet quenching is too strong.
In the last part of the thesis we consider a novel idea of introducing finite momentum at endpoints of classical (bosonic and supersymmetric) strings, and the phenomenological consequences of this proposal on the energy loss of light quarks. We show that in a general curved background, finite momentum endpoints must propagate along null geodesics and that the distance they travel in an AdS5-Schwarzschild background is greater than in the previous treatments of falling strings. We also argue that this leads to a more realistic description of energetic quarks, allowing for an unambiguous way of distinguishing between the energy in the dual hard probe and the energy in the color fields surrounding it. This proposal also naturally allows for a clear and simple definition of the instantaneous energy loss. Using this definition and the "shooting string" initial conditions, we develope a new formula for light quark energy loss. Finally, we apply this formula to compute the nuclear modification factor R_AA of light hadrons at RHIC and LHC, which, after the inclusion of the Gauss-Bonnet quadratic curvature corrections to the AdS5 geometry, shows a reasonably good agreement with the recent data.Physics, Theoretical physics, Nuclear physicsaf2440PhysicsDissertationsTowards inducing superconductivity into graphene
http://academiccommons.columbia.edu/catalog/ac:178213
Efetov, Dmitri K.http://dx.doi.org/10.7916/D8VX0F3TTue, 07 Oct 2014 18:11:08 +0000Graphenes transport properties have been extensively studied in the 10 years since its discovery in 2004, with ground-breaking experimental observations such as Klein tunneling, fractional quantum Hall effect and Hofstadters butterfly. Though, so far, it turned out to be rather poor on complex correlated electronic ground states and phase transitions, despite various theoretical predictions. The purpose of this thesis is to help understanding the underlying theoretical and experimental reasons for the lack of strong electronic interactions in graphene, and, employing graphenes high tunability and versatility, to identify and alter experimental parameters that could help to induce stronger correlations.
In particular graphene holds one last, not yet experimentally discovered prediction, namely exhibiting intrinsic superconductivity. With its vanishingly small Fermi surface at the Dirac point, graphene is a semi-metal with very weak electronic interactions. Though, if it is doped into the metallic regime, where the size of the Fermi surface becomes comparable to the size of the Brillouin zone, the density of states becomes sizeable and electronic interactions are predicted to be dramatically enhanced, resulting in competing correlated ground states such as superconductivity, magnetism and charge density wave formation. Following these predictions, this thesis first describes the creation of metallic graphene at high carrier doping via electrostatic doping techniques based on electrolytic gates. Due to graphenes surface only properties, we are able to induce carrier densities above n>10¹⁴cm⁻²(εF>1eV) into the chemically inert graphene. While at these record high carrier densities we yet do not observe superconductivity, we do observe fundamentally altered transport properties as compared to semi-metallic graphene. Here, detailed measurements of the low temperature resistivity reveal that the electron-phonon interactions are governed by a reduced, density dependent effective Debey temperature - the so-called Bloch-Grüneisen temperature ΘBG. We also probe the transport properties of the high energy sub-bands in bilayer graphene by electrolyte gating. Furthermore we demonstrate that electrolyte gates can be used to drive intercalation reactions in graphite and present an all optical study of the reaction kinetics during the creation of the graphene derived graphite intercalation compound LiC₆, and show the general applicability of the electrolyte gates to other 2-dimensional materials such as thin films of complex oxides, where we demonstrate gating dependent conductance changes in the spin-orbit Mott insulator Sr₂IrO₄.
Another, entirely different approach to induce superconducting correlations into graphene is by bringing it into proximity to a superconductor. Although not intrinsic to graphene, Cooper pairs can leak in from the superconductor and exist in graphene in the form of phase-coherent electron-hole states, the so-called Andreev states. Here we demonstrate a new way of fabricating highly transparent graphene/superconductor junctions by vertical stacking of graphene and the type-II van der Waals superconductor NbSe₂. Due to NbSe₂'s high upper critical field of Hc₂= 4 T we are able to test a long proposed and yet not well understood regime, where proximity effect and quantum Hall effect coexist.Physics, Nanosciencede2175PhysicsDissertationsElectronic and optical properties of titanate-based oxide heterostructures
http://academiccommons.columbia.edu/catalog/ac:178191
Park, Se Younghttp://dx.doi.org/10.7916/D8959G33Tue, 30 Sep 2014 18:16:27 +0000In this thesis we study properties of transition metal oxide heterostructures and superlattices, including electronic structures, optical responses, and metal-insulator transitions.
We start with a general discussion of the properties of transition metal oxides, primarily ABO₃ (A: rare earth ion, B: transition metal, O:oxygen) perovskites. We introduce the effect of A-site substitution on the electronic and magnetic properties in bulk perovskites, followed by the basic properties of oxide heterostructures and superlattices composed of two different ABO₃ perovskites focusing on the metal insulator transitions and properties of the interface electron gas.
Next, we present calculations of the charge density profile, subband occupancy and ellipsometry spectra of the electron gas at the LaAlO₃/SrTiO₃ interface. The calculations employ self-consistent Hartree and random phase approximations. We discuss the dependence of spatial structure and subband occupancy on the magnitude of the polarization charge at the interface and spatial structure of the dielectric constant. The response to applied AC electric fields is calculated and the results are presented in terms of the ellipsometry angles. Our results show a dip in the ellipsometry spectrum near the longitudinal optic phonon frequency of the SrTiO₃ and a peak at higher energy, which are related to the in-plane Drude response and the out-of-plane plasmon excitation, respectively. The relation of the features to the subband occupancies and the in-plane conductivities is given.
We conclude with the study of thickness dependent metal-insulator transitions in superlattices composed of Mott insulating GdTiO₃ and band insulating SrTiO₃ using a first-principles GGA+U method. The structural and metal-insulator phase diagrams with respect to the number of unit cells, n, of SrTiO₃ and on-site correlation U are presented, showing that there are two different insulating phases for n>1 and n=1. For superlattices with n>1 the insulating phase involves both charge and orbital ordering with associated structures in Ti-O bond lengths but for n=1 superlattices, we find an insulating phase driven by orbital ordering within the quasi one-dimensional bonding bands across the SrO layer. The inconsistencies with experiment suggests the importance of the many-body correlations.Physicssp2829PhysicsDissertationsMagma migration and magmatic solitary waves in 3-D
http://academiccommons.columbia.edu/catalog/ac:177438
Wiggins, Chris H.; Spiegelman, Marc W.http://dx.doi.org/10.7916/D8Z31X5JFri, 19 Sep 2014 12:35:06 +0000Numerical studies of fluid flow in the mantle suggest that magma migration is an inherently time-dependent process that produces magmatic solitary waves from obstructions in melt flux. Previous work has considered one and two dimensional problems. Here we present the results of three dimensional calculations that utilize a new, efficient multigrid scheme. We demonstrate that one and two dimensional solitary waves are unstable and break up into sets of 3-D solitary waves which are perfectly spherical when propagating through a uniform porosity medium. While these waves are not solitons, their non-linear interactions are qualitatively similar. The solitary waves are highly opportunistic and establish efficient pathways for migration by linking up with nearby waves. When the initial condition is a random distribution of porosity, the porosity structure can organize into elongate, time-dependent channels formed from chains of solitary waves. These results are natural consequences of the assumptions that the matrix is permeable and viscously deformable. We suggest that solitary waves are likely to exist in the mantle and may contribute to the episodicity of mantle magmatism.Physics, Geophysicschw2, msw6Applied Physics and Applied Mathematics, Earth and Environmental SciencesArticlesThe Chiral and U(1)_A Symmetries of the QCD Phase Transition using Chiral Lattice Fermions
http://academiccommons.columbia.edu/catalog/ac:175885
Lin, Zhongjiehttp://dx.doi.org/10.7916/D86D5R4TMon, 07 Jul 2014 11:40:06 +0000With regard to the nature of the finite-temperature QCD phase transition and the fate of the chiral and anomalous axial symmetries associated with it, we present in this thesis two parallel sets of investigations into the QCD phase transition region between 139 and 195 MeV. Both studies adopt the Iwasaki gauge action augmented with the dislocation suppression determinant ratio with 2+1 flavors of chiral fermions. This choice of lattice action accurately reproduces the SU(2)_L × SU(2)_R and U(1)_A symmtries of the continuum.
The first study simulates QCD thermodynamics on a line of constant physics that represents 200 MeV pions and physical kaons using domain wall fermions (DWF) at three space-time volumes: 16³ × 8, 24³ × 8, and 32³ × 8, where the largest volume varies in linear size between 5.6 fm (at T = 139 MeV) and 4.0 fm (at T = 195 MeV). The chiral condensates, connected and disconnected susceptibilities and the Dirac eigenvalue spectrum are reported and compared between different volumes as well as with the staggered results. We find a pseudo-critical temperature, T_c , of approximately 165 MeV and strong finite volume dependence below T_c. Clear evidence is seen for U(1)_A symmetry breaking above T_c which is quantitatively explained by the measured density of near-zero modes in accordance with the dilute instanton gas approximation.
The second study targets on a line of constant physics with pions of physical mass, which is the very first study using a chiral lattice fermion formulaation. We continue to use the basic setup from the m_π ≈ 200 MeV simulations, except that we use a generalized form of domain wall fermions, known as the M ̈bius fermions, to further reduce the residual chiral symmetry breaking present in the domain wall formulation with finite extent in the fifth dimension. Preliminary results including the chiral condensates and the susceptibilities are reported for two space-time volumes of 32³ × 8 and 64³ × 8. We observe a dramatic increase in the disconnected susceptibilities and a shift in the pseudo-critical temperature from 165 MeV to about 154 MeV, when the pion mass is decreased from 200 MeV to 135 MeV.PhysicsPhysicsDissertationsChip scale low dimensional materials: optoelectronics and nonlinear optics
http://academiccommons.columbia.edu/catalog/ac:175882
Gu, Tingyihttp://dx.doi.org/10.7916/D8FX77KJMon, 07 Jul 2014 11:39:57 +0000The CMOS foundry infrastructure enables integration of high density, high performance optical transceivers. We developed integrated devices that assemble resonators, waveguide, tapered couplers, pn junction and electrodes. Not only the volume standard manufacture in silicon foundry is promising to low-lost optical components operating at IR and mid-IR range, it also provides a robust platform for revealing new physical phenomenon.
The thesis starts from comparison between photonic crystal and micro-ring resonators based on chip routers, showing photonic crystal switches have small footprint, consume low operation power, but its higher linear loss may require extra energy for signal amplification. Different designs are employed in their implementation in optical signal routing on chip. The second part of chapter 2 reviews the graphene based optoelectronic devices, such as modulators, lasers, switches and detectors, potential for group IV optoelectronic integrated circuits (OEIC).
In chapter 3, the highly efficient thermal optic control could act as on-chip switches and (transmittance) tunable filters. Local temperature tuning compensates the wavelength differences between two resonances, and separate electrode is used for fine tuning of optical pathways between two resonators. In frequency domain, the two cavity system also serves as an optical analogue of Autler-Towns splitting, where the cavity-cavity resonance detuning is controlled by the length of pathway (phase) between them. The high thermal sensitivity of cavity resonance also effectively reflects the heat distribution around the nanoheaters, and thus derives the thermal conductivity in the planar porous suspended silicon membrane.
Chapter 4 and 5 analyze graphene-silicon photonic crystal cavities with high Q and small mode volume. With negligible nonlinear response to the milliwatt laser excitation, the monolithic silicon PhC turns into highly nonlinear after transferring the single layer graphene with microwatt excitation, reflected by giant two photon absorption induced optical bistability, low power dynamic switching and regenerative oscillation, and coherent four-wave-mixing from high Kerr coefficient. The single layer graphene lowers the operational power 20 times without enhancing the linear propagation loss.
Chapter 6 moves onto high Q ring resonator made of plasma enhanced chemical vapor deposition grown silicon nitride (PECVD SiN). PECVD SiN grown at low temperature is compatible with CMOS processing. The resonator enhanced light-matter interaction leads to molecular absorption induced quality factor enhancement and thermal bistability, near the critical coupling region.
In chapter 7, carrier transport and recombination in InAs quantum dots based GaAs solar cells are characterized by current-voltage curve. The parameters include voltage dependent ideality factor, series and shunt resistance. The device variance across the wafer is analyzed and compared. Quantum dots offers extra photocurrent by extending the absorption edge further into IR range, but the higher recombination rate increases the dark current as well. Different dots sized enabled by growth techniques are employed for comparison.Optics, Electrical engineering, Physicstg2342Electrical Engineering, Mechanical EngineeringDissertationsHow Rotation affects Instabilities and the Plasma Response to Magnetic Perturbations in a Tokamak Plasma
http://academiccommons.columbia.edu/catalog/ac:175361
DeBono, Bryanhttp://dx.doi.org/10.7916/D8J964HRMon, 07 Jul 2014 11:29:36 +0000This thesis presents the systematic study of the multimode external kink mode structure and dynamics in the High-Beta Tokamak Extended-Pulse experiment (HBT-EP) when the plasma rotation is externally controlled using a source of toroidal momentum input. The capabilities of the HBT-EP tokamak to study rotation physics was greatly extended during a 2009-2010 major upgrade, when a new adjustable conducting wall, a high-power modular control coil array system, and an extensive set of 216 poloidal and radial magnetic sensors were installed on the machine. HBT-EP was additionally equipped with a biased edge electrode which made it possible to adjust the plasma ion and plasma magnetohydrodynamics (MHD) mode rotation frequencies by imparting an electromagnetic torque on the plasma. The design of this biased edge electrode, and its capability to torque the plasma is described. The rotation frequency of the helical kink modes was directly inferred from analysis of the magnetics dataset. To directly measure the plasma ion acceleration as the plasma was torqued by the biased electrode, a novel high-throughput and fast-response spectroscopic rotation diagnostic was installed on HBT-EP. This spectroscopic rotation diagnostic was designed to measure the velocity of He ions, therefore when conducting experiments using the spectroscopic rotation diagnostic a gas mixture of 90%D and 10%He was used. With its current power supplies the bias probe is capable of accelerating the primary m/n=3/1 helical kink mode (which has a natural rotation frequency between +7-+9kHz) to somewhere between -50kHz-+25kHz depending on the probe bias. At a probe voltage of +175V the He impurity ions were seen to accelerate by 3km/sec. Biorthogonal decomposition (BD) analysis was applied to the large magnetics dataset and used to determine the multimode m/n spectrum of the helical kink modes present in HBT-EP. The dominant helicities present as revealed by the BD are the m/n=3/1 and m/n=6/2 modes, which represent about 85% and 8% of the total MHD activity respectively. This percentages remain consistent across the entire range of 3/1 mode rotation frequencies obtainable from the bias probe, (-50kHz-25kHz). The Hilbert transform technique was also applied to magnetic sensor data to determine the instantaneous amplitude and frequency of the total MHD activity. The total MHD amplitude was seen to decrease with increasing plasma rotation, a 35% reduction as the 3/1 mode was accelerated from +6-+24kHz. Active MHD spectroscopy experiments using a resonant magnetic perturbation (RMP) are able to excite a clear three-dimensional plasma response. Plasma rotation is theoretically expected to increase plasma stability to external resonant error elds, and in HBT-EP the plasma amplitude response to a m/n=3/1 RMP increases by a factor of 2.7 when the plasma rotation is decreased from +25kHz to +-2kHz. As the RMP amplitude increases, slower plasmas are seen to disrupt at a lower perturbation amplitude than unperturbed or rapidly rotating modes. The 6/2 helical kink mode also shows an amplitude and phase response to the 3/1 RMP, and like the 3/1 mode the amplitude response is largest when the plasma is slowly rotating. The ratio between the plasma 6/2 amplication and the 3/1 amplication to a 3/1 RMP is nearly constant, regardless of the plasma rotation or the RMP amplitude.Plasma physics, Animal sciences, Physicsbad2115Applied Physics and Applied Mathematics, Applied PhysicsDissertationsNeural network models of decision making with learning on multiple timescales
http://academiccommons.columbia.edu/catalog/ac:173494
Iigaya, Kiyohitohttp://dx.doi.org/10.7916/D8BR8Q81Fri, 25 Apr 2014 15:29:37 +0000Animals can quickly learn to make appropriate decisions according to their environment that can change over a wide range of timescales. Yet the neural computation underling the adaptive decision making is not well understood. To investigate basic computational principles and neural mechanisms, here we study simple neural network models for decision making with learning on multiple timescales, and we test our model's predictions in experimental data. We provide basic network models for value-based decision making under uncertainty.Physics, NeurosciencesNeuroscienceDissertationsThe Physics of Ultracold S₂ Molecules: Optical Production and Precision Measurement
http://academiccommons.columbia.edu/catalog/ac:173497
Osborn, Christopherhttp://dx.doi.org/10.7916/D8GH9G16Fri, 25 Apr 2014 15:26:10 +0000Ultracold molecules provide an exciting testing ground for studies of fundamental interactions, new states of matter, and metrology. Diatomic molecules based on two-electron atoms are especially suitable for precise tests of interatomic interactions, molecular quantum electrodynamics, electron-proton mass ratio variations, and other measurements in molecular and fundamental physics. This thesis describes the construction of a new strontium apparatus, from initial vacuum system setup through characterization of ultracold atom samples, followed by a new method of efficient, all-optical production of ultracold ^88Sr₂ molecules in an optical lattice, with detection via optical fragmentation. High-Q spectra of the weakly bound molecules in magnetic fields are studied, yielding precise binding energies, anomalously large molecular g factors resulting from large nonadiabatic effects, and strongly enhanced magnetic susceptibility. The thesis then concludes with an outlook on future experiments in our lab, including studies of forbidden molecular transitions, and longer term studies of fundamental physics from deeply bound Sr₂.PhysicsPhysicsDissertationsGravitation and Multimessenger Astrophysics
http://academiccommons.columbia.edu/catalog/ac:175203
Bartos, Imrehttp://dx.doi.org/10.7916/D8FT8J3BWed, 16 Apr 2014 09:55:24 +0000Gravitational waves originate from the most violent cosmic events, which are often hidden from traditional means of observation. Starting with the first direct observation of gravitational waves in the coming years, astronomy will become richer with a new messenger that can help unravel many of the yet unanswered questions on various cosmic phenomena.
The ongoing construction of advanced gravitational wave observatories requires disruptive innovations in many aspects of detector technology in order to achieve the sensitivity that lets us reach cosmic events. We present the development of a component of this technology, the Advanced LIGO Optical Timing Distribution System. This technology aids the detection of relativistic phenomena through ensuring that time, at least for the observatories, is absolute.
Gravitational waves will be used to look into the depth of cosmic events and understand the engines behind the observed phenomena. As an example, we examine some of the plausible engines behind the creation of gamma ray bursts. We anticipate that, by reaching through shrouding blastwaves, efficiently discovering off-axis events, and observing the central engine at work, gravitational wave detectors will soon transform the study of gamma ray bursts. We discuss how the detection of gravitational waves could revolutionize our understanding of the progenitors of gamma ray bursts, as well as related phenomena such as the properties of neutron stars.
One of the most intriguing directions in utilizing gravitational waves is their combination with other cosmic messengers such as photons or neutrinos. We discuss the strategies and ongoing efforts in this direction. Further, we present the first observational constraints on joint sources of gravitational waves and high energy neutrinos, the latter of which is created in relativistic plasma outflows, e.g., in gamma ray burst progenitors.
High energy neutrinos may be created inside a relativistic outflow burrowing its way out of a massive star from the star's collapsed core. We demonstrate how the detection of high energy neutrinos can be used to extract important information about the supernova/gamma-ray burst progenitor structure. We show that, under favorable conditions, even a few neutrinos are sufficient to probe the progenitor structure, opening up new possibilities for the first detections, as well for progenitor population studies.
We present the science reach and method of an ongoing search for common sources of gravitational waves and high energy neutrinos using the initial LIGO/Virgo detectors and the partially completed IceCube detector. We also present results on the sensitivity of the search. We argue that such searches will open the window onto source populations whose electromagnetic emission is hardly detectable.Physics, Astrophysicsib2179PhysicsDissertationsA Search For Electron Antineutrino Disappearance with the Double Chooz Far Detector
http://academiccommons.columbia.edu/catalog/ac:172267
Toups, Matthew Henryhttp://dx.doi.org/10.7916/D8MP51B9Tue, 01 Apr 2014 15:09:26 +0000We present a search for electron antineutrino disappearance at the Chooz nuclear power plant in Chooz, France. Using the Double Chooz far detector and 101.5 days of detector run time, we measure sin^2(2θ(subscript 13)) = 0.086 ± 0.041 (stat.) ± 0.030 (syst.) from a rate and shape fit. A combined analysis of T2K and Double Chooz data finds that sin^2(2θ(subscript 13)) = 0 is excluded at the 3σ level.Particle physics, Physicsmht2114PhysicsDissertationsMicro-Raman spectroscopic visualization of lattice vibrations and strain in He+- implanted single-crystal LiNbO3
http://academiccommons.columbia.edu/catalog/ac:172060
Huang, Hsu-Cheng; Dadap, Jerry I.; Herman, Irving P.; Bakhru, Hassaram; Osgood, Jr., Richard M.http://dx.doi.org/10.7916/D8BC3WKFThu, 27 Mar 2014 13:04:05 +0000Scanning micro-Raman spectroscopy has been utilized to image and investigate strain in He+-implanted congruent LiNbO3 samples. By using abruptly patterned implanted samples, we show that the spatial two-dimensional mapping of the Raman spectral peaks can be used to image the strain distribution and determine its absolute magnitude. We demonstrate that both short- and long-range length-scale in-plane and out-of-plane strain and stress states can be determined using the secular equations of phonon-deformation-potential theory. We also show that two-dimensional Raman imaging can be used to visualize the relaxation of strain in the crystal during low-temperature annealing.Electrical engineering, Physicshh2362, jid5, iph1, rmo1Electrical Engineering, Applied Physics and Applied MathematicsArticlesThe E and B EXperiment: A balloon-borne cosmic microwave background anisotropy probe
http://academiccommons.columbia.edu/catalog/ac:171485
Hillbrand, Seth Nathanielhttp://dx.doi.org/10.7916/D8KD1VZQFri, 07 Mar 2014 16:33:25 +0000The E and B Experiment (EBEX), is a balloon-borne sub-orbital cosmic microwave background polarimeter, designed to measure polarization levels in the microwave spectrum. EBEX recently completed an 11-day Antarctic long duration balloon (LDB) science flight in January, 2013. ~1000 transition edge sensor bolometric detectors in three frequency bands centered at 150, 250 and 410 GHz sampled a large segment of the southern sky. Over 1.5TB of data were collected during the LDB flight. In this thesis, we describe the design and performance of the EBEX software components monitoring and controlling the system during the flight, including automation, telemetry, data storage and readout array management. We also describe the design and development of a novel attitude reconstruction system for a balloon-borne pointed observation platform based on a daytime star camera and 3-axis gyroscopes. The data gathered during the LDB flight are analyzed and the results presented showing attitude reconstruction error at less than 20" RMS for an 80 second interval.Physicssnh2103PhysicsDissertationsThe Physics of Ultracold Sr_2 Molecules: Optical Production and Precision Measurement
http://academiccommons.columbia.edu/catalog/ac:173488
Osborn, Christopherhttp://dx.doi.org/10.7916/D8FT8J2WTue, 04 Mar 2014 17:31:17 +0000Ultracold molecules provide an exciting testing ground for studies of fundamental interactions, new states of matter, and metrology. Diatomic molecules based on two-electron atoms are especially suitable for precise tests of interatomic interactions, molecular quantum electrodynamics, electron-proton mass ratio variations, and other measurements in molecular and fundamental physics. This thesis describes the construction of a new strontium apparatus, from initial vacuum system setup through characterization of ultracold atom samples, followed by a new method of efficient, all-optical production of ultracold ^{88}Sr_2 molecules in an optical lattice, with detection via optical fragmentation. High-Q spectra of the weakly bound molecules in magnetic fields are studied, yielding precise binding energies, anomalously large molecular g factors resulting from large nonadiabatic effects, and strongly enhanced magnetic susceptibility. The thesis then concludes with an outlook on future experiments in our lab, including studies of forbidden molecular transitions, and longer term studies of fundamental physics from deeply bound Sr_2.PhysicsPhysicsDissertationsProduction of Heavy Particles by Protons on Protons
http://academiccommons.columbia.edu/catalog/ac:167194
Afek, Y.; Margolis, B.; Polvani, Lorenzo M.http://dx.doi.org/10.7916/D8JW8BSFTue, 19 Nov 2013 15:41:23 +0000We calculate the production of heavy particles in the multi-GeV energy range using parton-model and statistical considerations. We discuss both central production and fragmentation. Our picture has implications for the question of the existence of a limiting temperature in hadron interactions.Physics, Applied mathematicslmp3Applied Physics and Applied MathematicsArticlesGeneralized Kirchhoff Vortices
http://academiccommons.columbia.edu/catalog/ac:167191
Polvani, Lorenzo M.; Flierl, G. R.http://dx.doi.org/10.7916/D8PN93H5Tue, 19 Nov 2013 15:36:28 +0000A family of exact solutions of the Euler equations is presented: they are generalizations of the Kirchhoff vortex to N confocal ellipses. Special attention is given to the case N=2, for which the stability is analyzed with a method similar to the one used by Love [Proc. London Math. Soc. 1, XXV 18 (1893)] for the Kirchhoff vortex. The results are compared with those for the corresponding circular problem.Applied mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesWave–Wave Interaction of Unstable Baroclinic Waves
http://academiccommons.columbia.edu/catalog/ac:167188
Pedlosky, Joseph; Polvani, Lorenzo M.http://dx.doi.org/10.7916/D8TD9V7HTue, 19 Nov 2013 15:20:56 +0000Two slightly unstable baroclinic waves in the two-layer Phillips model are allowed to interact with each other as well as the mean flow. A theory for small dissipation rates is developed to examine the role of wave–wave interaction in the dynamics of vacillation and aperiodicity in unstable systems.
It is shown that the form of the dissipation mechanism as well as the overall dissipation timescale determines the nature of the dynamics. In particular, dissipation proportional to potential vorticity is shown to expunge amplitude vacillation due to wave–mean flow interactions.
Wave–wave interaction, however, can yield amplitude vacillation. As the dissipation is decreased, the solutions evolve from steady waves (although propagating) to periodic vacillation until finally at small dissipation rates, chaotic behavior is obtained.
This occurs in a range of relative growth rates of the two waves which depends on the strength of the wave–wave and wave–mean flow interactions.Atmospheric sciences, Applied mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesThe Effect of Dissipation on Spatially Growing Nonlinear Baroclinic Waves
http://academiccommons.columbia.edu/catalog/ac:167185
Polvani, Lorenzo M.; Pedlosky, J.http://dx.doi.org/10.7916/D8Z60KZCTue, 19 Nov 2013 15:16:34 +0000The question of convective (i.e., spatial) instability of baroclinic waves on an f-plane is studied in the context of the two-layer model. The viscous and inviscid marginal curves for linear convective instability are obtained. The finite-amplitude problem shows that when dissipation is O(1) it acts to stabilize the waves that are of Eady type. For very small dissipation the weakly nonlinear analysis reveals that at low frequencies, contrary to what is known to occur in the temporal problem, in addition to the baroclinic component a barotropic correction to the “mean” flow is generated by the nonlinearities, and spatial equilibration occurs provided the ratio of shear to mean flow does not exceed some critical value. In the same limit, the slightly dissipative nonlinear dynamics reveals the presence of large spatial vacillations immediately downstream of the source, even if asymptotically (i.e., very far away from the source) the amplitudes are found to reach steady values. No case of period doubling or aperiodic behavior was found. The results obtained seem to be qualitatively independent of the form chosen to model the dissipation.Atmospheric sciences, Physics, Applied mathematicslmp3Applied Physics and Applied MathematicsArticlesFilamentation of Unstable Vortex Structures via Separatrix Crossing: A Quantitative Estimate of Onset Time
http://academiccommons.columbia.edu/catalog/ac:167182
Polvani, Lorenzo M.; Flierl, G. R.; Zabusky, N. J.http://dx.doi.org/10.7916/D82Z13FRTue, 19 Nov 2013 15:09:06 +0000The onset of filamentation for compact vortex structures in two-dimensional incompressible flows is elucidated. An estimate is presented for the filamentation time of an unstably perturbed Kirchhoff ellipse, obtained from a linear analysis of the geometry of the instantaneous corotating streamfunction.Applied mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesTwo-Layer Geostrophic Vortex Dynamics. Part 1. Upper-Layer V-States and Merger
http://academiccommons.columbia.edu/catalog/ac:167179
Polvani, Lorenzo M.; Flierl, G. R.; Zabusky, N. J.http://dx.doi.org/10.7916/D86Q1V53Tue, 19 Nov 2013 15:02:02 +0000We generalize the methods of two-dimensional contour dynamics to study a two-layer rotating fluid that obeys the quasi-geostrophic equations. We consider here only the case of a constant-potential-vorticity lower layer. We derive equilibrium solutions for monopolar (rotating) and dipolar (translating) geostrophic vortices in the upper layer, and compare them with the Euler case. We show that the equivalent barotropic (infinite lower layer) case is a singular limit of the two-layer system. We also investigate the effect of a finite lower layer on the merger of two regions of equal-sign potential vorticity in the upper layer. We discuss our results in the light of the recent laboratory experiments of Griffiths and Hopfinger (1986). The process of filamentation is found to be greatly suppressed for equivalent barotropic dynamics on scales larger than the radius of deformation. We show that the variation of the critical initial distance for merger as a function of the radius of deformation and the ratio of the layers at rest is closely related to the existence of vortex-pair equilibria and their geometrical properties.Applied mathematics, Physics, Atmospheric scienceslmp3Applied Physics and Applied MathematicsArticlesChaotic Lagrangian Trajectories around an Elliptical Vortex Patch Embedded in a Constant and Uniform Background Shear Flow
http://academiccommons.columbia.edu/catalog/ac:167176
Polvani, Lorenzo M.; Wisdom, J.http://dx.doi.org/10.7916/D8BG2KWDTue, 19 Nov 2013 14:50:47 +0000The Lagrangian flow around a Kida vortex [J. Phys. Soc. Jpn. 5 0, 3517 (1981)], an elliptical two‐dimensional vortex patch embedded in a uniform and constant background shear, is described by a nonintegrable two‐degree‐of‐freedom Hamiltonian. For small values of shear, there exist large chaotic zones surrounding the vortex, often much larger than the vortex itself and extremely close to its boundary. Motion within the vortex is integrable. Implications for two‐dimensional turbulence are discussed.Physics, Applied mathematicslmp3Applied Physics and Applied MathematicsArticlesTwo-Layer Geostrophic Vortex Dynamics. Part 2. Alignment and Two-Layer V-States
http://academiccommons.columbia.edu/catalog/ac:167173
Lorenzo M., Polvanihttp://dx.doi.org/10.7916/D8G44N6TTue, 19 Nov 2013 13:38:39 +0000The process of alignment, a new fundamental interaction between vortices in a stratified and rapidly rotating fluid, is defined and studied in detail in the context of the two-layer quasi-geostrophic model. Alignment occurs when two vortices in different density layers coalesce by reducing their horizontal separation. It is found that only vortices whose radii are comparable with or larger than the Rossby deformation radius can align. In the same way as the merger process (in a single two dimensional layer) is related to the reverse energy cascade of two-dimensional turbulence, geostrophic potential vorticity alignment is related the barotropic-to baroclinic energy cascade of geostrophic turbulence in two layers. It is also shown how alignment is intimately connected with the existence of two-layer doubly connected geostrophic potential vorticity equilibria (V-states), for which the analysis of the geometry of the stream function in the corotating frame is found to be a crucial diagnostic. The finite-area analogues of the hetons of Hogg and Stommel (1985) are also determined : they consist of a propagating pair of opposite-signed potential vorticity patches located in different layers.Atmospheric sciences, Physics, Applied mathematicslmp3Applied Physics and Applied MathematicsArticlesRossby Wave Breaking, Microbreaking, Filamentation, and Secondary Vortex Formation: The Dynamics of a Perturbed Vortex
http://academiccommons.columbia.edu/catalog/ac:167170
Polvani, Lorenzo M.; Plumb, R. Alanhttp://dx.doi.org/10.7916/D8KW5CXTTue, 19 Nov 2013 12:41:03 +0000The behavior of an isolated vortex perturbed by topographically forced Rossby waves is studied using the method of Contour Dynamics. For a single-contour vortex a distinct forcing threshold exists above which the wave breaks in a dynamically significant way, leading to a disruption of the vortex. This breaking is distinguished from the process of weak filamentary breaking described by Dritschel and classified here as microbreaking; the latter occurs in nondivergent flow even at very small forcing amplitudes but does not affect the vortex in a substantial manner. In cases with finite Rossby deformation radius (comparable with the vortex radius) neither breaking nor microbreaking occurs below the forcing threshold. In common with previous studies using high-resolution spectral models, the vortex is not diluted by intrusion of outside air, except during remerger with a secondary vortex shed previously from the main vortex during a breaking event. The kinematics of the breaking process and of the vortex interior and the morphology of material ejected from the vortex are described. When the Rossby radius is finite there is substantial mixing in the deep interior of the vortex, even when the vortex is only mildly disturbed. Implications for the stratospheric polar vortex are discussed.Atmospheric sciences, Aeronomy, Physicslmp3Applied Physics and Applied MathematicsArticlesTime-Dependent Fully Nonlinear Geostrophic Adjustment
http://academiccommons.columbia.edu/catalog/ac:167071
Kuo, Allen C.; Polvani, Lorenzo M.http://hdl.handle.net/10022/AC:P:22170Fri, 08 Nov 2013 17:33:37 +0000Shock-capturing numerical methods are employed to integrate the fully nonlinear, rotating 1D shallow-water equations starting from steplike nongeostrophic initial conditions (a Rossby adjustment problem). Such numerical methods allow one to observe the formation of multiple bores during the transient adjustment process as well as their decay due to rotation. It is demonstrated that increasing the rotation and/or the nonlinearity increases the rate of decay. Additionally, the time required for adjustment to be completed and its dependence on nonlinearity is examined; this time is found to be highly measure dependent. Lastly, the final adjusted state of the system is observed through long time integrations. Although the bores that form provide a mechanism for dissipation, their decay results in a final state in very good agreement with the one computed by well-known (dissipationless) conservation methods.Physics, Geophysics, Applied mathematicslmp3Applied Physics and Applied MathematicsArticlesWave-Vortex Interaction in Rotating Shallow Water. Part 1. One Space Dimension
http://academiccommons.columbia.edu/catalog/ac:167056
Kuo, Allen C.; Polvani, Lorenzo M.http://hdl.handle.net/10022/AC:P:22165Fri, 08 Nov 2013 16:01:40 +0000Using a physical space (i.e. non-modal) approach, we investigate interactions between fast inertio-gravity (IG) waves and slow balanced flows in a shallow rotating fluid. Specifically, we consider a train of IG waves impinging on a steady, exactly balanced vortex. For simplicity, the one-dimensional problem is studied first; the limitations of one-dimensionality are offset by the ability to define balance in an exact way. An asymptotic analysis of the problem in the small-amplitude limit is performed to demonstrate the existence of interactions. It is shown that these interactions are not confined to the modification of the wave field by the vortex but, more importantly, that the waves are able to alter in a non-trivial way the potential vorticity associated with that vortex. Interestingly, in this one-dimensional problem, once the waves have traversed the vortex region and have propagated away, the vortex exactly recovers its initial shape and thus bears no signature of the interaction. Furthermore, we prove this last result in the case of arbitrary vortex and wave amplitudes. Numerical integrations of the full one-dimensional shallow-water equations in strongly nonlinear regimes are also performed: they confirm that time-dependent interactions exist and increase with wave amplitude, while at the final state the vortex bears no sign of the interaction. In addition, they reveal that cyclonic vortices interact more strongly with the wave field than anticyclonic ones.Geophysics, Applied mathematics, Physicslmp3Applied Physics and Applied MathematicsArticlesThe Effect of a Hadley Circulation on the Propagation and Reflection of
Planetary Waves in a Simple One-Layer Model
http://academiccommons.columbia.edu/catalog/ac:167050
Esler, J. Gavin; Polvani, Lorenzo M.; Plumb, R. Alanhttp://hdl.handle.net/10022/AC:P:22163Fri, 08 Nov 2013 15:34:53 +0000The effect of a simple representation of the Hadley circulation on the propagation and nonlinear reflection of planetary-scale Rossby waves in the winter hemisphere is investigated numerically in a single-layer shallow-water model.
In the first instance, waves are forced by a zonal wavenumber three topography centered in the extratropics. In the linear limit the location of the low-latitude critical line at which the waves are absorbed is displaced poleward by the Hadley circulation. At finite forcing amplitude the critical layer regions where the waves break are found to be displaced poleward by a similar distance. The Hadley circulation is also found to inhibit the onset of nonlinear reflection by increasing the dissipation of wave activity in the critical layer.
Second, for waves generated by an isolated mountain, the presence of the Hadley circulation further inhibits nonlinear reflection by generating a strong westerly flux of wave activity within the critical layer. This westerly flux is shown to be largely advective and is explained by the poleward displacement of the critical line into the region of westerly flow. A simple expression is derived for the minimum zonal wind strength allowing propagation in the case of a quasigeostrophic β-plane flow when the mean meridional wind ̅υ greater than 0.Geophysics, Atmospheric sciences, Physicslmp3Applied Physics and Applied MathematicsArticlesNonlinear Geostrophic Adjustment, Cyclone/Anticyclone Asymmetry, and Potential Vorticity Rearrangement
http://academiccommons.columbia.edu/catalog/ac:167047
Kuo, Allen C.; Polvani, Lorenzo M.http://hdl.handle.net/10022/AC:P:22162Fri, 08 Nov 2013 14:20:08 +0000Within the context of the rotating shallow water equations, it is shown how initially unbalanced states possessing certain symmetries dynamically evolve to lose those symmetries during nonlinear geostrophic adjustment. Using conservation law methods, it is demonstrated that the adjustment of equal and opposite (circular) mass imbalances results in a balanced end state where cyclones are stronger than anticyclones; the reverse holds true for momentum imbalances. In both cases, the degree of this asymmetry is shown to be directly proportional to the amount of initial imbalance (a measure of the nonlinearity occurring during time-dependent adjustment). On the other hand, the degree of asymmetry is maximal for imbalances of Rossby deformation scale. As for the potential vorticity, it is shown that its final profile can be noticeably different from its initial one; from an Eulerian perspective, this rearrangement is not confined to uniform shifts of potential vorticity fronts. Direct 2D numerical initial value problems confirm the asymmetry in the predicted final states and establish a relatively fast time scale for adjustment to complete. The robustness of these results is confirmed by studying, in addition, the adjustment of elliptical mass imbalances. The numerical integrations reveal that, during geostrophic adjustment, potential vorticity rearrangement occurs irreversibly on a fast wave time scale.Physics, Geophysics, Applied mathematicslmp3Applied Physics and Applied MathematicsArticlesObservational Properties of Gigaelectronvolt-Teraelectronvolt Blazars and the Study of the Teraelectronvolt Blazar RBS 0413 with VERITAS
http://academiccommons.columbia.edu/catalog/ac:166933
Senturk, Gunes Demethttp://hdl.handle.net/10022/AC:P:22118Mon, 04 Nov 2013 12:17:45 +0000Blazars are active galactic nuclei with a relativistic jet directed towards the observer's line of sight. Characterization of the non-thermal continuum emission originating from the blazar jet is currently an essential question in high-energy astrophysics. A blazar spectral energy distribution (SED) has a typical double-peaked shape in the flux vs. energy representation. The low-energy component of the SED is well-studied and thought to be due to synchrotron emission from relativistic electrons. The high-energy component, on the other hand, is still not completely understood and the emission in this part of the blazar spectrum can extend to energies as high as tera electron volts in some objects. This portion of the electromagnetic spectrum is referred to as the very-high-energy (VHE or TeV, E > 0.1 TeV) regime. At the time of this writing, more than half a hundred blazars have been detected to emit TeV gamma rays, representing the high energy extreme of these objects and constituting a population of its own. Most of these TeV blazars have also been detected in the high-energy (HE or GeV, 0.1 GeV < E < 0.1 TeV) gamma-ray range.
In this work, we report on our discovery of the TeV emission from the blazar RBS 0413 and perform a detailed data analysis on this source, including contemporaneous multi-wavelength observations to characterize the broad-band SED and test various emission models for the high-energy component. Further, we extend our focus on the high-energy component to all archival TeV-detected blazars and study their spectral properties in the framework of GeV and TeV gamma-ray observations. To do this, we assemble for the first time the GeV and TeV spectra of a complete sample of TeV-detected blazars available in the archive to date. In the Appendix we present an analysis method for improved observations of large zenith angle targets with VERITAS.Physics, Astrophysicsgds2110PhysicsDissertationsThe Study of Transition Metal Oxides using Dynamical Mean Field Theory
http://academiccommons.columbia.edu/catalog/ac:166930
Dang, Hung Thehttp://hdl.handle.net/10022/AC:P:22116Mon, 04 Nov 2013 11:55:30 +0000In this thesis, we study strong electron correlation in transition metal oxides. In the systems with large Coulomb interaction, especially the on-site interaction, electrons are much more correlated and cannot be described using traditional one-electron picture, thus the name "strongly correlated systems". With strong correlation, there exists a variety of interesting phenomena in these systems that attract long-standing interests from both theorists and experimentalists. Transition metal oxides (TMOs) play a central role in strongly correlated systems, exhibiting many exotic phenomena. The fabrication of heterostructures of transition metal oxides opens many possible directions to control bulk properties of TMOs as well as revealing physical phases not observed in bulk systems.
Dynamical mean-field theory (DMFT) emerges as a successful numerical method to treat the strong correlation. The combination of density functional and dynamical mean-field theory (DFT+DMFT) is a prospective ab initio approach for studying realistic strongly correlated materials. We use DMFT as well as DFT+DMFT methods as main approaches to study the strong correlation in these materials.
We focus on some aspects and properties of TMOs in this work. We study the magnetic properties in bulk TMOs and the possibility of enhancing the magnetic order in TMO heterostructures. We work on the metallic/insulating behaviors of these systems to understand how the metal-insulator transition depends on the intrinsic parameters of materials. We also investigate the effect of a charged impurity to the neighborhood of a correlated material, which can be applied, for example, to the study of muon spin relaxation measurements in high-Tc superconductors.PhysicsPhysicsDissertationsTheory of thermal nonequilibrium entropy in near-field thermal radiation
http://academiccommons.columbia.edu/catalog/ac:166229
Narayanaswamy, Arvind; Zheng, Yihttp://hdl.handle.net/10022/AC:P:21929Thu, 03 Oct 2013 16:10:56 +0000We propose a theoretical formalism to evaluate the entropy density and entropy flux that takes into account near-field effects, i.e., interference, diffraction, and tunneling of waves. Using the fluctuation-dissipation 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 near-field thermal radiation.Mechanical engineering, Nanoscience, Physicsan2288, yz2308Mechanical EngineeringArticlesChemical Vapor Deposition Grown Pristine and Chemically Doped Monolayer Graphene
http://academiccommons.columbia.edu/catalog/ac:177571
Zhao, Liuyanhttp://hdl.handle.net/10022/AC:P:21666Wed, 18 Sep 2013 16:22:55 +0000Chemical vapor deposition growth has been a popular technique to produce large-area, high-quality monolayer graphene on Cu substrates ever since its first demonstration in 2009. Pristine graphene grown in such a way owns the natures of zero charge carriers and zero band gap. As an analogy to semi-conductor studies, substitutional doping with foreign atoms is a powerful way to tailor the electronic properties of this host materials. Within such a context, this thesis focuses on growing and characterizing both pristine and chemically-doped CVD grown monolayer graphene films at microscopic scales. We first synthesized pristine graphene on Cu single crystals in ultra-high-vacuum and subsequently characterized their properties by scanning tunneling microscopy/spectroscopy (STM/S), to learn the effects of Cu substrate crystallinity on the quality of graphene growth and understand the interactions between graphene films and Cu substrates. In the subsequent chapters, we chemically doped graphene with nitrogen (N) and boron (B) atoms, and characterized their topographic and electronic structures via STM/S. We found that both N and B dopants substitionally dope graphene films, and contribute electron and hole carriers, respectively, into graphene at a rate of approximately 0.5 carrier/dopant. Apart from this, we have made comparisons between N- and B-doped graphene films in aspects of topographic features, dopant distribution and electronic perturbations. In the last part of this thesis, we used Raman spectroscopy mapping to investigate the N dopant distribution within and across structural grains. Future experiments are also brief discussed at the end of the thesis.Condensed matter physics, Physicslz2227PhysicsDissertationsTopics in vacuum decay
http://academiccommons.columbia.edu/catalog/ac:165209
Abad, Ali Masoumi Khalilhttp://hdl.handle.net/10022/AC:P:21643Mon, 16 Sep 2013 11:50:04 +0000If a theory has more than one classically stable vacuum, quantum tunneling and thermal jumps make the transition between the vacua possible. The transition happens through a first order phase transition started by nucleation of a bubble of the new vacuum. The outward pressure of the truer vacuum makes the bubble expand and consequently eat away more of the old phase. In the presence of gravity this phenomenon gets more complicated and meanwhile more interesting. It can potentially have important cosmological consequences. Some aspects of this decay are studied in this thesis. Solutions with different symmetry than the generically used O(4) symmetry are studied and their actions calculated. Vacuum decay in a spatial vector field is studied and novel features like kinky domain walls are presented. The question of stability of vacua in a landscape of potentials is studied and the possible instability in large dimension of fields is shown. Finally a compactification of the Einstein-Maxwell theory is studied which can be a good lab to understand the decay rates in compactification models of arbitrary dimensions.Physicsam2809PhysicsDissertationsProbing Electronic and Thermoelectric Properties of Single Molecule Junctions
http://academiccommons.columbia.edu/catalog/ac:165142
Widawsky, Jonathan R.http://hdl.handle.net/10022/AC:P:21604Fri, 13 Sep 2013 13:30:57 +0000In an effort to further understand electronic and thermoelectric phenomenon at the nanometer scale, we have studied the transport properties of single molecule junctions. To carry out these transport measurements, we use the scanning tunneling microscope-break junction (STM-BJ) technique, which involves the repeated formation and breakage of a metal point contact in an environment of the target molecule. Using this technique, we are able to create gaps that can trap the molecules, allowing us to sequentially and reproducibly create a large number of junctions. By applying a small bias across the junction, we can measure its conductance and learn about the transport mechanisms at the nanoscale. The experimental work presented here directly probes the transmission properties of single molecules through the systematic measurement of junction conductance (at low and high bias) and thermopower. We present measurements on a variety of molecular families and study how conductance depends on the character of the linkage (metal-molecule bond) and the nature of the molecular backbone. We start by describing a novel way to construct single molecule junctions by covalently connecting the molecular backbone to the electrodes. This eliminates the use of linking substituents, and as a result, the junction conductance increases substantially. Then, we compare transport across silicon chains (silanes) and saturated carbon chains (alkanes) while keeping the linkers the same and find a stark difference in their electronic transport properties. We extend our studies of molecular junctions by looking at two additional aspects of quantum transport - molecular thermopower and molecular current-voltage characteristics. Each of these additional parameters gives us further insight into transport properties at the nanoscale. Evaluating the junction thermopower allows us to determine the nature of charge carriers in the system and we demonstrate this by contrasting the measurement of amine-terminated and pyridine-terminated molecules (which exhibit hole transport and electron transport, respectively). We also report the thermopower of the highly conducting, covalently bound molecular junctions that we have recently been able to form, and learn that, because of their unique transport properties, the junction power factors, GS2, are extremely high. Finally, we discuss the measurement of molecular current-voltage curves and consider the electronic and physical effects of applying a large bias to the system. We conclude with a summary of the work discussed and an outlook on related scientific studies.Physics, Nanotechnology, Quantum physicsjrw2139Applied Physics and Applied MathematicsDissertationsThe Effective Field Theory Approach to Fluid Dynamics, Modified Gravity Theories, and Cosmology
http://academiccommons.columbia.edu/catalog/ac:165139
Wang, Junpuhttp://hdl.handle.net/10022/AC:P:21602Fri, 13 Sep 2013 13:08:10 +0000The effective field theory approach is powerful in understanding the low energy phenomena without invoking the UV degrees of freedom. We construct a low energy Lagrangian for ordinary fluid systems (in constrast to superfluid), pure from symmetry considerations and EFT principles. The dynamical fields are the Goldstone excitations, associated with spontaneously broken spacetime translations. It is organized as derivatively coupled theory involving multiple scalar fields. This formalism enables us to study fluid's quantum mechanical properties and dissipative effects. Cosmological models can be built by naturally coupling the fluid EFT to gravity. From the EFT point of view, GR is the unique low energy theory for the spin-2 graviton field and any infrared modification corresponds to adding new degrees of freedom. We focus on two popular classes of modified gravity models, --- the chameleon like theories and the Galileon theory, --- and perform a few reliability checks for their qualifications as modified gravity theories. Furthermore, guiled by the EFT spirit, we develop a cosmological model where primordial inflation is driven by a `solid', defined, in a similar manner as the EFT of fluid. The symmetry breaking pattern differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard EFT description of adiabatic perturbations, with crucial consequences for the dynamics of cosmological perturbations, and exhibits various unusual features.Physicsjw2551PhysicsDissertationsThe Effective Field Theory Approach to Fluid Dynamics, Modified Gravity Theories, and Cosmology
http://academiccommons.columbia.edu/catalog/ac:164394
Wang, Junpuhttp://hdl.handle.net/10022/AC:P:21391Wed, 21 Aug 2013 10:42:06 +0000The effective field theory approach is powerful in understanding the low energy phenomena without invoking the UV degrees of freedom. We construct a low energy Lagrangian for ordinary fluid systems (in constrast to superfluid), pure from symmetry considerations and EFT principles. The dynamical fields are the Goldstone excitations, associated with spontaneously broken spacetime translations. It is organized as derivatively coupled theory involving multiple scalar fields. This formalism enables us to study fluid's quantum mechanical properties and dissipative effects. Cosmological models can be built by naturally coupling the fluid EFT to gravity. From the EFT point of view, GR is the unique low energy theory for the spin-2 graviton field and any infrared modification corresponds to adding new degrees of freedom. We focus on two popular classes of modified gravity models, --- the chameleon like theories and the Galileon theory, --- and perform a few reliability checks for their qualifications as modified gravity theories. Furthermore, guiled by the EFT spirit, we develop a cosmological model where primordial inflation is driven by a `solid', defined, in a similar manner as the EFT of fluid. The symmetry breaking pattern differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard EFT description of adiabatic perturbations, with crucial consequences for the dynamics of cosmological perturbations, and exhibits various unusual features.Physicsjw2551PhysicsDissertationsProbing Electronic and Thermoelectric Properties of Single Molecule Junctions
http://academiccommons.columbia.edu/catalog/ac:164391
Widawsky, Jonathan R.http://hdl.handle.net/10022/AC:P:21389Tue, 20 Aug 2013 17:01:35 +0000In an effort to further understand electronic and thermoelectric phenomenon at the nanometer scale, we have studied the transport properties of single molecule junctions. To carry out these transport measurements, we use the scanning tunneling microscope-break junction (STM-BJ) technique, which involves the repeated formation and breakage of a metal point contact in an environment of the target molecule. Using this technique, we are able to create gaps that can trap the molecules, allowing us to sequentially and reproducibly create a large number of junctions. By applying a small bias across the junction, we can measure its conductance and learn about the transport mechanisms at the nanoscale. The experimental work presented here directly probes the transmission properties of single molecules through the systematic measurement of junction conductance (at low and high bias) and thermopower. We present measurements on a variety of molecular families and study how conductance depends on the character of the linkage (metal-molecule bond) and the nature of the molecular backbone. We start by describing a novel way to construct single molecule junctions by covalently connecting the molecular backbone to the electrodes. This eliminates the use of linking substituents, and as a result, the junction conductance increases substantially. Then, we compare transport across silicon chains (silanes) and saturated carbon chains (alkanes) while keeping the linkers the same and find a stark difference in their electronic transport properties. We extend our studies of molecular junctions by looking at two additional aspects of quantum transport - molecular thermopower and molecular current-voltage characteristics. Each of these additional parameters gives us further insight into transport properties at the nanoscale. Evaluating the junction thermopower allows us to determine the nature of charge carriers in the system and we demonstrate this by contrasting the measurement of amine-terminated and pyridine-terminated molecules (which exhibit hole transport and electron transport, respectively). We also report the thermopower of the highly conducting, covalently bound molecular junctions that we have recently been able to form, and learn that, because of their unique transport properties, the junction power factors, GS², are extremely high. Finally, we discuss the measurement of molecular current-voltage curves and consider the electronic and physical effects of applying a large bias to the system. We conclude with a summary of the work discussed and an outlook on related scientific studies.Physics, Nanotechnology, Quantum physicsjrw2139Applied Physics and Applied MathematicsDissertationsImpact of Friction and Scale-Dependent Initial Stress on Radiated Energy-Moment Scaling
http://academiccommons.columbia.edu/catalog/ac:162546
Shaw, Bruce E.http://hdl.handle.net/10022/AC:P:20808Wed, 19 Jun 2013 14:53:22 +0000The radiated energy coming from an event depends on a number of factors,
including the friction and, crucially, the initial stress. Thus we cannot deduce
any scaling laws without considering initial stress. However, by simulating long
sequences of events, where the system evolves to a statistically steady-state, we can obtain the appropriate distribution of initial stresses consistent with the dynamics and a given friction. We examine a variety of frictions, including power-law slip dependence, and explore a variety of scaling relations, with the aim of elucidating their radiated energy-moment scaling. We find, contrary to expectations, that apparent stress is not seen to increase with earthquake size for power-law weakening. For small and for large events, little change in apparent stress is seen with increasing rupture size, while intermediate sized events interpolate in between. We find the origin of this unexpected lack of size dependence in systematic changes of initial stress, with bigger events tending to sample regions of lower initial stress. To understand radiated energy-moment scaling, scale-dependent initial stress needs to be considered.Plate tectonics, Physicsbes11Lamont-Doherty Earth ObservatoryBook chaptersInitiation propagation and termination of elastodynamic ruptures
associated with segmentation of faults and shaking hazard
http://academiccommons.columbia.edu/catalog/ac:162517
Shaw, Bruce E.http://hdl.handle.net/10022/AC:P:20801Wed, 19 Jun 2013 12:15:28 +0000Using a model of a complex fault system, we examine the initiation, propagation, and termination of ruptures and their relationship to fault geometry and shaking hazard. We find concentrations of epicenters near fault step overs and ends; concentrations of terminations near fault ends; and persistent propagation directivity effects. Taking advantage of long sequences of dynamic events, we directly measure shaking hazards, such as peak ground acceleration exceedance probabilities, without need for additional assumptions. This provides a new tool for exploring shaking hazard from a physics-based perspective, its dependence on various physical parameters, and its correlation with other geological and seismological observables. Using this capability, we find some significant aspects of the shaking hazard can be anticipated by measures of the epicenters. In particular, asymmetries in the relative peak ground motion hazard along the faults appear well correlated with asymmetries in epicentral locations.Plate tectonics, Physicsbes11Lamont-Doherty Earth ObservatoryArticlesDynamic heterogeneities versus fixed heterogeneities in earthquake models
http://academiccommons.columbia.edu/catalog/ac:162505
Shaw, Bruce E.http://hdl.handle.net/10022/AC:P:20795Wed, 19 Jun 2013 10:26:12 +0000A debate has raged over whether fixed material and geometrical heterogeneities, or alternatively dynamic stress heterogeneities, arising through frictional instabilities dominate earthquake complexity. It may also be that both types of heterogeneities interact and are important. This paper makes a first step in examining this interaction, combining two previously separate lines of research. One line examined friction, which has attractors (the subset of the phase space that the system evolves towards in the long run) on homogeneous faults, which are simple, and then added fixed heterogeneities to the faults to obtain complex attractors. Another line examined frictions, which produced complex attractors on homogeneous faults. Here, we examine frictions, which produce complex attractors on homogeneous faults, and study them on heterogeneous faults, in order to study the interaction of dynamic stress heterogeneities and fixed fault heterogeneities. We consider two types of fixed heterogeneities: an additive noise and a multiplicative noise to the frictional strength of the fault. Because of the linearity of the bulk elastodynamics, the attractor is unaffected by additive fixed noise in the strength of the fault: adding an arbitrary function of space, fixed in time, to the friction leaves the resulting attractor unchanged. In contrast, multiplicative fixed noise multiplying the friction can have a profound effect on the resulting attractor. In the small multiplicative noise amplitude limit, the frictional weakening attractor is little perturbed; at finite amplitudes, fixed heterogeneities substantially alter the attractor. We see, as one consequence, a shift toward longer length events at larger amplitudes. Fixed heterogeneities are seen to reduce the irregularities created by the frictional instability we study, but by no means destroy them. We quantify this by examining a measure of variability of the importance in hazard estimates, the coefficient of variation of large event recurrence times. The coefficient of variation is seen to remain substantial even for large fixed heterogeneities. For friction that weakens with time, so the underlying uniform fault attractor is simple, fixed heterogeneities increase irregularity. For all frictions examined, at low fixed heterogeneity the stress concentrations left over by the ends of the large events dominate where most of the small events occur, while at higher heterogeneity the stress irregularities left over by fixed fault heterogeneities begin to dominate where the small events occur. This may be the strongest signature of fixed heterogeneities, and should be examined further in the Earth. Finally, in what may have important implications for more sophisticated estimates of earthquake hazard, we see a correlation of locations with lower strength drop having higher variation in large event repeat times.Plate tectonics, Physicsbes11Lamont-Doherty Earth ObservatoryArticlesExistence of continuum complexity in the elastodynamics of repeated fault ruptures
http://academiccommons.columbia.edu/catalog/ac:162484
Shaw, Bruce E.; Rice, James R.http://hdl.handle.net/10022/AC:P:20789Tue, 18 Jun 2013 14:38:25 +0000What are the origins of earthquake complexity? The possibility that some aspects of the complexity displayed by earthquakes might be explained by stress heterogeneities developed through the self-organization of repeated ruptures has been suggested by some simple self-organizing models. The question of whether or not even these simple self-organizing models require at least some degree of material heterogeneity to maintain complex sequences of events has been the subject of some controversy. In one class of elastodynamic models, previous work has described complexity as arising on a model fault with completely uniform material properties. Questions were raised, however, regarding the role of discreteness, the relevance of the nucleation mechanism, and special parameter choices, in generating the complexity that has been reported. In this paper, we examine the question of whether or not continuum complexity is achieved under the stringent conditions of continuous loading, and whether the results are similar to previously claimed findings of continuum complexity or its absence. The elastodynamic model that we use consists of a 1-D fault boundary with friction, a steady slowly moving 1-D boundary parallel to the fault, and a 2-D scalar elastic media connecting the two boundaries. The constitutive law used involves a pair of sequential weakening processes, one occurring over a small slip (or velocity) and accomplishing a small fraction of the total strength drop, and the other at larger slip (or velocity) and providing the remaining strength drop. The large-scale process is motivated by a heat weakening instability. Our main results are as follows. (1) We generally find complexity of type I, a broad distribution of large event sizes with nonperiodic recurrence, when the modeled region is very long, along strike, compared to the layer thickness. (2) We find that complexity of type II, with numerous small events showing a power law distribution, is not a generic result but does definitely exist in a restricted range of parameter space. For that, in the slip weakening version of our model, the strength drop and nucleation size in the small slip process must be much smaller than in the large slip process, and the nucleation length associated with the latter must be comparable to layer thickness. This suggests a basis for reconciling different previously reported results. (3) Bulk dispersion appears to be relatively unimportant to the results. In particular, motions on the fault plane are seen to be relatively insensitive to a wide range of changes in the dispersion in the bulk away from the fault, both at long wavelengths and at short wavelengths. In contrast, the fault properties are seen to be very important to the results. (4) Nucleation from slip weakening and time-dependent weakening showed similar large-scale behavior. However, not all constitutive laws are insensitive to all nucleation approximations; those making a model “inherently discrete” and hence grid-dependent, in particular, can affect large scales. (5) While inherent discreteness has been seen to be a source of power law small-event complexity in some fault models, it does not appear to be the cause of the complexity in the attractors examined here, and reported in earlier work, fortuitously in the pecial parameter range, with the same class of continuum fault models and same or very similar constitutive relations. Continuum homogeneous dynamic complexity does indeed exist, although that includes type II small-event complexity only under restricted circumstances.Plate tectonics, Mechanics, Physicsbes11Lamont-Doherty Earth ObservatoryArticlesPrecision Search for Muon Antineutrino Disappearance Oscillations Using a Dual Baseline Technique
http://academiccommons.columbia.edu/catalog/ac:162005
Cheng, Gary Chia Lihttp://hdl.handle.net/10022/AC:P:20634Fri, 07 Jun 2013 16:14:10 +0000A search for short baseline muon antineutrino disappearance with the SciBooNE and MiniBooNE experiments at Fermi National Accelerator Laboratory in Batavia, Illinois is presented. Short baseline muon antineutrino disappearance measurements help constrain sterile neutrino models. The two detectors observe muon antineutrinos from the same beam, therefore the combined analysis of their data sets serves to partially constrain some of the flux and cross section uncertainties. A likelihood ratio method was used to set a 90% confidence level upper limit on muon antineutrino disappearance that dramatically improves upon prior sterile neutrino oscillation limits in the Δm^2=0.1-100 eV^2 region.Physics, Particle physicsgcc2113PhysicsDissertationsControl study of two-particle correlations in heavy ion collisions at RHIC-PHENIX
http://academiccommons.columbia.edu/catalog/ac:161549
Vazquez, Erichttp://hdl.handle.net/10022/AC:P:20454Fri, 24 May 2013 09:34:46 +0000Measurements at the Relativistic Heavy Ion Collider (RHIC) have provided indirect measurements of jets in a heavy ion environment using the two- particle correlation method in the presence of a high-pT particle. These measurements have offered insight into the formation of a new state of dense nuclear matter called the Quark-Gluon Plasma (QGP) through the observation of jet quenching. However, the two-particle methodology has also shown to be biased towards di-jet production near the surface of the medium being created. Here, a detailed study using the PHENIX detector is provided, in an attempt to measure a more accurate jet-induced two-particle correlation measurement than previously published and to reduce the bias observed in two-particle correlation measurements. The reduction in surface bias emission is performed via the requirement of two antipodal high-pT particles (a.k.a. "2+1" correlation) in an attempt to control the production point of the di-jet. The measurements made in Au+Au collisions when compared to p+p collisions show that the method provides additional sensitivity to the jet quenching previously observed in two-particle correlation method.Nuclear physics, Physics, Particle physicsev2122PhysicsDissertationsThe Effective Field Theory Approach to Fluid Dynamics
http://academiccommons.columbia.edu/catalog/ac:161458
Endlich, Solomonhttp://hdl.handle.net/10022/AC:P:20419Thu, 23 May 2013 11:24:11 +0000In this thesis we initiate a systematic study of fluid dynamics using the effective field theory (EFT) program. We consider the canonical quantization of an ordinary fluid in an attempt to discover if there is some kind of quantum mechanical inconsistency with ordinary fluids at zero temperature. The system exhibits a number of peculiarities associated with the vortex degrees of freedom. We also study the dynamics of a nearly incompressible fluid via (classical) effective field theory. In the kinematical regime corresponding to near incompressibility (small fluid velocities and accelerations), compressional modes are, by definition, difficult to excite, and can be dealt with perturbatively. We systematically outline the corresponding perturbative expansion, which can be thought of as an expansion in the ratio of fluid velocity and speed of sound. This perturbation theory allows us to compute many interesting quantities associated with sound-flow interactions. Additionally, we also improve on the so-called vortex filament model, by providing a local field theory describing the dynamics of vortex-line systems and their interaction with sound, to all orders in perturbation theory. Next, we develop a cosmological model where primordial inflation is driven by a 'solid'. The low energy EFT describing such a system is just a less symmetric version of the action of a fluid---it lacks the volume preserving diffeomorphism. The symmetry breaking pattern of this system differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard effective field theory description of adiabatic perturbations, with crucial consequences for the dynamics of cosmological perturbations. And finally, we introduce dissipative effects in the effective field theory of hydrodynamics. We do this in a model-independent fashion by coupling the long-distance degrees of freedom explicitly kept in the effective field theory to a generic sector that "lives in the fluid'', which corresponds physically to the microscopic constituents of the fluid. At linear order in perturbations, the symmetries, the derivative expansion, and the assumption that this microscopic sector is thermalized, allow us to characterize the leading dissipative effects at low frequencies via three parameters only, which correspond to bulk viscosity, shear viscosity, and---in the presence of a conserved charge---heat conduction. Using our methods we re-derive the Kubo relations for these transport coefficients.Theoretical physics, Physics, Condensed matter physicssge2104PhysicsDissertationsPrecision Lattice Calculation of Kaon Decays with Möbius Domain Wall Fermions
http://academiccommons.columbia.edu/catalog/ac:161136
Yin, Hantaohttp://hdl.handle.net/10022/AC:P:20325Tue, 14 May 2013 17:27:36 +0000We report our recent development in algorithms and progress in measurements in lattice QCD. The algorithmic development includes the forecasted force gradient integrator, and further theoretical development and implementation of the Möbius domain wall fermions. These new technologies make it practical to simulate large 48^3*96 and 64^3*128 lattice ensembles with (5.5fm)^3 boxes and 140MeV pion. The calculation was performed using the Möbius domain wall fermions and the Iwasaki gauge action. Simulated directly at physical quark masses, these ensembles are of great value for our ongoing and future lattice measurement projects. With the help of measurement techniques such as the eigCG algorithm and the all mode averaging method, we perform a direct, precise lattice calculation of the semileptonic kaon decay K→πlν using these newly generated high quality lattice ensembles. Our main result is the form factor f^+_{Kπ}(q^2) evaluated directly at zero momentum transfer q^2=0. Free of various systematic errors, this new result can be used to determine the CKM matrix element Vus to a very high precision when combined with experimental input. The calculation also provides results for various low energy strong interaction constants such as the pseudoscalar decay constants f_K and f_π, and the neutral kaon mixing matrix element B_K. These calculations are naturally performed by reusing the propagators calculated for the kaon semileptonic decay mentioned above. So they come with no or very low additional cost. The results allow us to also determine these important low energy constants on the lattice to unprecedented accuracy.Physics, Particle physics, Theoretical physicshy2242PhysicsDissertationsPrecision Lattice Calculation of Kaon Decays with Möbius Domain Wall Fermions
http://academiccommons.columbia.edu/catalog/ac:160818
Yin, Hantaohttp://hdl.handle.net/10022/AC:P:20151Wed, 01 May 2013 18:02:44 +0000We report our recent development in algorithms and progress in measurements in lattice QCD. The algorithmic development includes the forecasted force gradient integrator, and further theoretical development and implementation of the Möbius domain wall fermions. These new technologies make it practical to simulate large 48^3*96 and 64^3*128 lattice ensembles with (5.5fm)^3 boxes and 140MeV pion. The calculation was performed using the Möbius domain wall fermions and the Iwasaki gauge action. Simulated directly at physical quark masses, these ensembles are of great value for our ongoing and future lattice measurement projects.With the help of measurement techniques such as the eigCG algorithm and the all mode averaging method, we perform a direct, precise lattice calculation of the semileptonic kaon decay K→πlν using these newly generated high quality lattice ensembles. Our main result is the form factor f^+_{Kπ}(q^2) evaluated directly at zero momentum transfer q^2=0. Free of various systematic errors, this new result can be used to determine the CKM matrix element Vus to a very high precision when combined with experimental input. The calculation also provides results for various low energy strong interaction constants such as the pseudoscalar decay constants f_K and f_π, and the neutral kaon mixing matrix element B_K. These calculations are naturally performed by reusing the propagators calculated for the kaon semileptonic decay mentioned above. So they come with no or very low additional cost. The results allow us to also determine these important low energy constants on the lattice to unprecedented accuracy.Particle physics, Physics, Theoretical physicshy2242PhysicsDissertationsLearning the Rules of the Game: The Nature of Game and Classroom Supports When Using a Concept-Integrated Digital Physics Game in the Middle School Science Classroom
http://academiccommons.columbia.edu/catalog/ac:160791
Stewart Jr., Philliphttp://hdl.handle.net/10022/AC:P:20088Wed, 01 May 2013 11:57:32 +0000Games in science education is emerging as a popular topic of scholarly inquiry. The National Research Council recently published a report detailing a research agenda for games and science education entitled Learning Science Through Computer Games and Simulations (2011). The report recommends moving beyond typical proof-of-concept studies into more exploratory and theoretically-based work to determine how best to integrate games into K-12 classrooms for learning , as well as how scaffolds from within the game and from outside the game (from peers and teachers) support the learning of applicable science. This study uses a mixed-methods, quasi-experimental design with an 8th grade class at an independent school in southern Connecticut to answer the following questions: 1. What is the nature of the supports for science content learning provided by the game, the peer, and the teacher, when the game is used in a classroom setting? 2. How do the learning gains in the peer support condition compare to the solo play condition, both qualitatively and quantitatively? The concept-integrated physics game SURGE (Scaffolding Understanding through Redesigning Games for Education) was selected for this study, as it was developed with an ear towards specific learning theories and prior work on student understandings of impulse, force, and vectors. Stimulated recall interviews and video observations served as the primary sources and major patterns emerged through the triangulation of data sources and qualitative analysis in the software QSR NVivo 9. The first pattern which emerged indicated that scaffolding from within the game and outside the game requires a pause in game action to be effective, unless that scaffolding is directly useful to the player in the moment of action. The second major pattern indicated that both amount and type of prior gaming experience has somewhat complex effects on both the uses of supports and learning outcomes. In general, a high correlation was found between students who were more successful navigating supports from the game, the teacher, and the peer and higher gain scores from pre- to posttest. However, students with a lot of prior game experience that found the game to be easy without much assistance did not do as well from pre- to posttest as they did not need as much assistance from the game to do well and therefore missed out on important physics connections to impulse, force, and vectors. However, those students with little prior game experience did not find game scaffolds as useful and did not do as well from pre- to posttest without significant teacher and peer support to bolster or supplant the game's intended scaffolding. Implications for educators, educational game designers, and games in science education researchers are presented. It is argued that teachers must find ways to extract those scaffolds from the game which are easy to miss or require failure to activate so that all students, even those who find the game easy, are exposed to the intended learning in the game. Ideally, game designers are encouraged to find new ways to present scaffolds such that players of any ability can benefit from the connections from the game to physics.Science education, Physicspms2127Science Education, Mathematics, Science, and TechnologyDissertationsCharged Particle Multiplicity and Open Heavy Flavor Physics in Relativistic Heavy Ion Collisions at the LHC
http://academiccommons.columbia.edu/catalog/ac:159130
Chen, Yujiaohttp://hdl.handle.net/10022/AC:P:19740Fri, 12 Apr 2013 12:10:04 +0000In this thesis, two independent measurements are presented: the measure- ments of centrality dependence and pseudo-rapidity dependence of charged particle multiplicities, and the measurements of centrality dependence of open heavy flavor suppression. These measurements are carried out with the Pb+Pb collisions data at the LHC energy and = 2.76 TeV with the ATLAS detector. For the charged particle measurements, charged particles are reconstructed with two algorithms (2-point "tracklet" and full tracking) from the pixel detector only. Measurements are presented of the per-event charged particle density distribution, dNch/d η and the average charged par- ticle multiplicity in the pseudo-rapidity interval |η| <0.5 in several intervals of collision centrality. The results are compared to previous mid-rapidity measurements at the LHC and RHIC. The variation of the mid-rapidity charged particle yield per colliding nucleon pair with the number of partic- ipants is consistent with the lower √sNN results measured at RHIC. The shape of the dNch/η distribution is found to be independent of centrality within the systematic uncertainties of the measurement. For the open heavy flavor suppression measurements, muons identified by the muon spectrom- eter are classified as heavy flavor decays and background contributions by using a fitting procedure with templates from Monte Carlo samples. Results are presented for the per-event muon yield as a function of muon transverse momentum, pT, over the range of 4 pT 14 GeV. Over that momentum range single muon production results largely from heavy quark decays. The centrality dependence of the muon yields is characterized by the "central to peripheral" ratio, RCP. Using this measure, muon production from heavy quark decays is found to be suppressed by a centrality-dependent factor that increases smoothly from peripheral to central collisions. Muon production is suppressed by approximately a factor of two in central collisions relative to peripheral collisions. Within the experimental errors, the observed sup- pression is independent of muon pT for all centralities. Furthermore, the pT dependence of the relative muon yields in Pb+Pb collisions to p+p colli- sions with the same center of mass collision energy per nucleon is presented by the nuclear modification factor RAA, which is defined as the ratio of a spectrum from heavy ion collisions to the same but scaled spectrum from nucleon-nucleon collisions . The observed RAA has little dependence on pT within the uncertainties quoted here. The results for RAA indicate a factor of about 3 suppression in the yield of muons in the most central (0-10%) collisions compared to the p+p collisions.Physicsyc2420PhysicsDissertationsXENON100 Dark Matter Search: Scintillation Response of Liquid Xenon to Electronic Recoils
http://academiccommons.columbia.edu/catalog/ac:156964
Lim, Kyungeunhttp://hdl.handle.net/10022/AC:P:19131Wed, 20 Feb 2013 11:40:51 +0000Dark matter is one of the missing pieces necessary to complete the puzzle of the universe. Numerous astrophysical observations at all scales suggest that 23 % of the universe is made of nonluminous, cold, collisionless, nonbaryonic, yet undiscovered dark matter. Weakly Interacting Massive Particles (WIMPs) are the most well-motivated dark matter candidates and significant efforts have been made to search for WIMPs. The XENON100 dark matter experiment is currently the most sensitive experiment in the global race for the first direct detection of WIMP dark matter. XENON100 is a dual-phase (liquid-gas) time projection chamber containing a total of 161 kg of liquid xenon (LXe) with a 62kg WIMP target mass. It has been built with radiopure materials to achieve an ultra-low electromagnetic background and operated at the Laboratori Nazionali del Gran Sasso in Italy. WIMPs are expected to scatter off xenon nuclei in the target volume. Simultaneous measurement of ionization and scintillation produced by nuclear recoils allows for the detection of WIMPs in XENON100. Data from the XENON100 experiment have resulted in the most stringent limits on the spin-independent elastic WIMP- nucleon scattering cross sections for most of the significant WIMP masses. As the experimental precision increases, a better understanding of the scintillation and ionization response of LXe to low energy (< 10 keV) particles is crucial for the interpretation of data from LXe based WIMP searches. A setup has been built and operated at Columbia University to measure the scintillation response of LXe to both electronic and nuclear recoils down to energies of a few keV, in particular for the XENON100 experiment. In this thesis, I present the research carried out in the context of the XENON100 dark matter search experiment. For the theoretical foundation of the XENON100 experiment, the first two chapters are dedicated to the motivation for and detection medium choice of the XENON100 experiment, respectively. A general review about dark matter focusing on WIMPs and their direct detection with liquid noble gas detectors is presented in Chap. 1. LXe as an attractive WIMP detection medium is explained in Chap. 2. The XENON100 detector design, the detector, and its subsystems are detailed in Chap. 3. The calibration of the detector and the characterized detector response used for the discrimination of a WIMP-like signal against background are explained in Chap. 4. In an effort to understand the background, anomalous electronic recoils were studied extensively and are described in Chap. 5. In order to obtain a better understanding of the electronic recoil background of XENON100, including an estimation of the electronic recoil background contribution, as well as to interpret dark matter results such as annual modulation, measurement of the scintillation yield of low-energy electrons in LXe was performed in 2011, with the dedicated setup mentioned above. The results from this measurement are discussed in Chap. 6. Finally, the results for the latest science data from XENON100 to search for WIMPs, comprising 225 live-days taken over 13 months during 2011 and 2012 are explained in Chap. 7.Physics, AstrophysicsPhysicsDissertationsThe Light Response of the XENON100 Time Projection Chamber and the Measurements of the Optical Parameters with the Xenon Scintillation Light
http://academiccommons.columbia.edu/catalog/ac:156958
Choi, BinWed, 20 Feb 2013 11:20:24 +0000The XENON program is a phased project using liquid xenon as a sensitive detector medium in search for weakly interacting massive particles (WIMPs). These particles are the leading candidates to explain the non-baryonic, cold dark matter in our Universe. XENON100, the successor experiment of XENON10, has increased the target liquid xenon mass to 61 kg with a 100 times reduction in background rate enabling a large increase in sensitivity to WIMP- nucleon interaction cross-section. To-date, the most stringent limit on this cross-section over a wide range of WIMP masses have been obtained with XENON100. XENON100 is a detector responding to the scintillation of xenon and the work of this thesis will mainly focus on the light response of the detector. Chapter 1 describes the evidences for dark matter and some of the detection methods, roughly divided by the indirect and the direct detection. In the section 1.2.2 for direct detection, a treatment of interaction rate of WIMPs is introduced. Chapter 2 is a description of the XENON100 detector, some of the main characteristics of liquid xenon, followed by the detector design. In Chapter 3, the light response of the XENON100 time projection chamber (TPC) is explained, including the Monte Carlo simulation work that was carried out prior to the main data taking. The Monte Carlo provided the basic idea of understanding the detector in the early stage of design and calibration, but the actual corrections of the light signals were determined later with the real data. Several optical parameters are critical in explaining the light response, such as the quantum efficiency (QE) of the photomultipliers (PMTs) used in the detector and the reflectivity of the teflon (Polytetrafluoroethylene, PTFE) material that surrounds the liquid xenon target volume and defines the TPC. Since the few existing measurements of reflectivity of PTFE in liquid xenon were performed in different conditions and thus could not be applied, the XENON collaboration put some effort in setting up a reliable and an independent measurement for these parameters. The QE of the Hamamatsu R8520 PMTs at liquid xenon temperature was measured at the Columbia Nevis Laboratory, as described in Chapter 4. A similar but a revised setup was built later at the University of Muenster in Germany for measuring the reflectivity of the PTFE (Chapter 5). These measurements are important for a deeper understanding of XENON100 and the next phase of the program with a XENON1T as well as for other liquid xenon experiments. Chapter 6 explains the details of the energy scale derived from the measurement of the light signals in XENON100 and the cuts used for the analysis, which has led to the most recent scientific results from this experiments. In 2012, the XENON100 dark matter results from 225 live days set the most stringent limit on the spin-independent elastic WIMP- nucleon interaction cross section for WIMP masses above 8 GeV/c 2, with a minimum of 2 × 10and minus;45 cm 2 at 55 GeV/c 2 and 90% confidence level. With this result XENON100 continues to be the leading experiment in the direct search for dark matterPhysicsbc2196PhysicsDissertationsIncorporation of Nonconventional Crystalline Materials onto the Integrated Photonics Platform
http://academiccommons.columbia.edu/catalog/ac:156940
Gaathon, Ophirhttp://hdl.handle.net/10022/AC:P:19125Wed, 20 Feb 2013 10:24:55 +0000Applications that span from sensing, to large bandwidth communication, to acoustic filtering, to high-resolution imaging and display, to quantum information processing (QIP) and to advance electronics have a growing need for new device types and materials. These advanced devices require electrical and optical properties that, in some cases, can only be provided by truly single-crystal thin-films of nonconventional materials, such as lithium niobate (LN, LiNbO3), yttrium aluminum garnet (YAG, Y3Al5O12) and diamond. In order to incorporate those crystals into existing multi-scale integrated system platforms, new technologies must be developed that can supply high-quality, single-crystal, thin-films in the desired thin-film architecture. Unfortunately, production of thin-films of single-crystals is not always possible via growth. Here, the use of Crystal Ion Slicing (CIS) technique to realize single-crystal thin-films of three of the nonconventional crystals is described. The fabrication techniques vary greatly between different crystals. Thus, new exfoliation chemistries must be developed for each material system. Detailed description of the investigation into exfoliation of LN, YAG and diamond is presented. The most mature CIS application is for LN crystals. Here, the development of several important complementary fabrication methods is presented. This includes description of polishing and bonding techniques that are necessary for successful incorporation of thin-films. Further, a lateral patterning technology of thin-films using femtosecond laser ablation is demonstrated. In addition, an ion-implantation patterning method and its application in nonlinear optics is presented. Finally, a novel polarization dependent plasmonic filter is described. In addition, a detailed description of the fabrication methods of single-crystal thin-films of YAG for acoustical and optical applications is presented. It is shown that the thermal exfoliation is the preferred method for YAG. After the thermal exfoliation, the films are subject to additional thermal cycle to anneal the films. This process high-temperature annealing is introduced to promote relaxation of film by eliminating residual strain and increasing the films' radius of curvature, both attributed to the ion-implantation process. Thus, detailed description of the post-exfoliation process is presented. The mechanical quality of the films is investigated with specific attention to the annealing behavior. Finally, the fabrication process and optical characterization of single-crystal thin-films of diamond is described. The work on diamond is focused on developing a parallel fabrication process for high-optical-quality single-crystal diamond membranes for quantum information processing (QIP) applications. The diamond membranes, with thickness as small as 200 nm and over 100 μm on their side, exhibit nitrogen-vacancy emission spectra including the zero phonon line (ZPL) peak of negatively charged centers. The films are patterned and sliced in parallel from a single-crystal diamond sample. The compatibility of the membrane with planar optical devices is demonstrated by the formation of two-dimensional photonic crystal patterns in 200 nm films. The films are produced by a combination of thermal annealing, chemical etching and oxygen plasma. Analysis of the films quality and optimization of the exfoliation process is evaluated by a verity of experimental techniques including: Atomic force microscope (AFM), optical microscopy, scanning electron microscopy (SEM), Raman and fluorescence spectroscopy, optical profilometry and nanoindentation.Physics, Engineeringog2126Applied Physics and Applied Mathematics, Electrical EngineeringDissertationsGraphene NanoElectroMechanical Resonators and Oscillators
http://academiccommons.columbia.edu/catalog/ac:156928
Chen, Changyaohttp://hdl.handle.net/10022/AC:P:19098Mon, 18 Feb 2013 11:07:37 +0000Made of only one sheet of carbon atoms, graphene is the thinnest yet strongest material ever exist. Since its discovery in 2004, graphene has attracted tremendous research effort worldwide. Guaranteed by the superior electrical and excellent mechanical properties, graphene is the ideal building block for NanoElectroMechanical Systems (NEMS). In the first parts of the thesis, I will discuss the fabrications and measurements of typical graphene NEMS resonators, including doubly clamped and fully clamped graphene mechanical resonators. I have developed a electrical readout technique by using graphene as frequency mixer, demonstrated resonant frequencies in range from 30 to 200 MHz. Furthermore, I developed the advanced fabrications to achieve local gate structure, which led to the real-time resonant frequency detection under resonant channel transistor (RCT) scheme. Such real-time detection improve the measurement speed by 2 orders of magnitude compared to frequency mixing technique, and is critical for practical applications. Finally, I employed active balanced bridge technique in order to reduce overall electrical parasitics, and demonstrated pure capacitive transduction of graphene NEMS resonators. Characterizations of graphene NEMS resonators properties are followed, including resonant frequency and quality factor ($Q$) tuning with tension, mass and temperatures. A simple continuum mechanics model was constructed to understand the frequency tuning behavior, and it agrees with experimental data extremely well. In the following parts of the thesis, I will discuss the behavior of graphene mechanical resonators in applied magnetic field, {i.e.} in Quantum Hall (QH) regime. The couplings between mechanical motion and electronic band structure turned out to be a direct probe for thermodynamic quantities, {i.e.}, chemical potential and compressibility. For a clean graphene resonators, with quality factors of $1 \times 10^4 $, it underwent resonant frequency oscillations as applied magnetic field increases. The chemical potential of graphene shifts smoothly within each LL, causing the resonant frequency to change in an explicit pattern. Between LLs, the finite compressibility caused the resonant frequency changing dramatically. The overall oscillations of resonant frequency with the applied magnetic field could be fitted with only disorder potential as free parameter. Compared with conventional electronic transport technique, such mechanical measurements proven to be a more direct and powerful tool, which we used o study the properties of graphene's ground states in broken symmetry states. In the last part this thesis, I will present the study of graphene NEMS oscillators with positive feedback loop. The demonstrated oscillators are self-sustained (without external radio frequency, RF, stimulus), and the oscillation frequencies can be controlled by tension{i.e.}, (applied gate voltage). I also carefully studied the influence of feedback gain and phase, as well as linewidth compression as function of temperature.Nanotechnology, Mechanical engineering, Physicscc2759Mechanical EngineeringDissertationsQuantum Hall transport in graphene and its bilayer
http://academiccommons.columbia.edu/catalog/ac:156080
Zhao, Yuehttp://hdl.handle.net/10022/AC:P:18862Wed, 30 Jan 2013 12:17:46 +0000Graphene has generated great interest in the scientific community since its discovery because of the unique chiral nature of its carrier dynamics. In monolayer graphene, the relativistic Dirac spectrum for the carriers results in an unconventional integer quantum Hall effect, with a peculiar Landau Level at zero energy. In bilayer graphene, the Dirac-like quadratic energy spectrum leads to an equally interesting, novel integer quantum Hall effect, with a eight-fold degenerate zero energy Landau level. In this thesis, we present transport studies at high magnetic field on both monolayer and bilayer graphene, with a particular emphasis on the quantum Hall (QH) effect at the charge neutrality point, where both systems exhibit broken symmetry of the degenerate Landau level at zero energy. We also present data on quantum Hall edge transport across the interface of a graphene monolayer and bilayer junction, where peculiar edge state transport is observed. We investigate the quantum Hall effect near the charge neutrality point in bilayer graphene, under high magnetic fields of up to 35~T using electronic transport measurements. In the high field regime, we observe a complete lifting of the eight-fold degeneracy of the zero-energy Landau level, with new quantum Hall states corresponding to filling factors $\nu=0$, 1, 2 and 3. Measurements of the activation energy gap in tilted magnetic fields suggest that the Landau level splitting at the newly formed $\nu=$1, 2 and 3 filling factors does not exhibit low-energy spin flip excitation. These measurements are consistent with the formation of a quantum Hall ferromagnet. In addition, we observed insulating behavior in the two terminal resistance of the $\nu=$0 state at high fields. For monolayer graphene, we report on magneto-resistance measurements at the broken-symmetry of the zero-energy Landau level, using both a conventional two-terminal measurement of suspended graphene devices, which is sensitive to bulk and edge conductance, and a Corbino measurement on high mobility on-substrate devices, which is sensitive to the bulk conductance only. At $\nu=0$, we observe a vanishing conductance with increasing magnetic fields in both cases. By examining the resistance changes of this insulating state with varying perpendicular and in-plane fields, we probe the spin-active components of the excitations in total fields of up to 45 Tesla. Our results strongly suggest that the $\nu=0$ quantum Hall state in single layer graphene is not spin polarized, while a spin-polarized state with spin-flip excitations forms at $\nu=1$. For monolayer and bilayer graphene junction system, we first present a surface potential study across the monolayer/bilayer interface. Then we present experimental investigations of the edge state transition across the interface in the quantum Hall regime. Both monolayer graphene (MG) and bilayer graphene (BG) develop their own Landau levels under high magnetic field. While transport measurements show their distinct quantum Hall effects in the separate parts of the monolayer and bilayer respectively, the transport measurement across the interface exhibits unusual transverse transport behavior. The transverse resistance across the MG/BG interface is asymmetric for opposite sides of the Hall bar, and its polarity can be changed by reversing the magnetic field direction. When the quantum Hall plateaus of MG and BG overlap, quantized resistance appears only on one side of the Hall bar electrode pairs that sit across the junction. These experimental observations can be ascribed to QH edge state transport across the MG/BG interface. We also present sample fabrication details, particularly the efforts to eliminate mobility-limiting factors, including cleaning polymer residue from the electron beam lithography process via thermal annealing and removing/changing the substrate by suspending multi-probe graphene devices.Physicsyz2444PhysicsDissertationsExploring the String Landscape: The Dynamics, Statistics, and Cosmology of Parallel Worlds
http://academiccommons.columbia.edu/catalog/ac:155499
Ahlqvist, Stein Pontushttp://hdl.handle.net/10022/AC:P:15784Tue, 15 Jan 2013 10:32:23 +0000This dissertation explores various facets of the low-energy solutions in string theory known as the string landscape. Three separate questions are addressed - the tunneling dynamics between these vacua, the statistics of their location in moduli space, and the potential realization of slow-roll inflation in the flux potentials generated in string theory. We find that the tunneling transitions that occur between a certain class of supersymmetric vacua related to each other via monodromies around the conifold point are sensitive to the details of warping in the near-conifold regime. We also study the impact of warping on the distribution of vacua near the conifold and determine that while previous work has concluded that the conifold point acts as an accumulation point for vacua, warping highly dilutes the distribution in precisely this regime. Finally we investigate a novel form of inflation dubbed spiral inflation to see if it can be realized near the conifold point. We conclude that for our particular models, spiral inflation seems to rely on a de Sitter-like vacuum energy. As a result, whenever spiral inflation is realized, the inflation is actually driven by a vacuum energy.Physicsspa2111Physics, MathematicsDissertationsSimultaneous Immersion Mirau Interferometry
http://academiccommons.columbia.edu/catalog/ac:153355
Lyulko, Oleksandra V.http://hdl.handle.net/10022/AC:P:14948Mon, 15 Oct 2012 11:37:35 +0000The present work describes a novel imaging technique for label-free no-UV vibration-insensitive imaging of live cells in an epi-illumination geometry. This technique can be implemented in a variety of imaging applications. For example, it can be used for cell targeting as a part of a platform for targeted cell irradiations - single-cell microbeam. The goal of microbeam facilities is to provide biological researchers with tools to study the effects of ionizing radiation on live cells. A common way of cell labeling - fluorescent staining - may alter cellular metabolism and UV illumination presents potential damage for the genetic material. The new imaging technique will allow the researchers to separate radiation-induced effects from the effects caused by confounding factors like fluorescent staining or UV light. Geometry of irradiation endstations at some microbeam facilities precludes the use of transmitted light, e.g. in the Columbia University's Radiological Research Accelerator Facility microbeam endstation, where the ion beam exit window is located just below the sample. Imaging techniques used at such endstations must use epi-illumination. Mirau Interferometry is an epi-illumination, non-stain imaging modality suitable for implementation at a microbeam endstation. To facilitate interferometry and to maintain cell viability, it is desirable that cells stay in cell growth medium during the course of an experiment. To accommodate the use of medium, Immersion Mirau Interferometry has been developed. A custom attachment for a microscope objective has been designed and built for interferometric imaging with the possibility of immersion of the apparatus into cell medium. The implemented data collection algorithm is based on the principles of Phase-Shifting Interferometry. The largest limitation of Phase-Shifting Interferometry is its sensitivity to the vertical position of the sample. In environments where vibration isolation is difficult, this makes image acquisition challenging. This problem was resolved by integration of polarization optics into the optics of the attachment to enable simultaneous creation and spatial separation of two interferograms, which, combined with the background image, are used to reconstruct the intensity map of the specimen. Giving the name Simultaneous Immersion Mirau Interferometry to this approach, simultaneous acquisition of all interferograms per image has eliminated the issue of vibrations. The designed compound microscope attachment has been manufactured and tested; the system produces images of quality, sufficient to perform targeted cellular irradiation experiments.Physics, OpticsPhysics, Center for Radiological Research, Radiation OncologyDissertationsFabrication and Characterization of Optoelectronics Devices Based on III-V Materials for Infrared Applications by Molecular Beam Epitaxy
http://academiccommons.columbia.edu/catalog/ac:153295
Al Torfi, Aminhttp://hdl.handle.net/10022/AC:P:14908Thu, 11 Oct 2012 16:32:50 +0000Optoelectronic devices based on III-V materials operating in infrared wavelength range have been attracting intensive research effort due to their applications in optical communication, remote sensing, spectroscopy, and environmental monitoring. The novel semiconductor lasers and photodetectors structures and materials investigated in this thesis cover the spectral range from 1.3µm to 12µm. This spectral region includes near-infrared (NIR), mid-infrared (MIR) and long wavelength infrared. This thesis demonstrated infrared optoelectronic devices, based on III-V compound semiconductors grown by Molecular Beam Epitaxy (MBE,) utilizing various combinations of novel III-V materials, device structures and substrate orientations. This thesis will be presented in two parts; the first part focuses on two types of photodetectors; type-II InAs/GaSb superlattice IR detector and AlGaAsSb/InGaAsSb mid-infrared heterojunction p-i-n photodetector. The second part of this thesis focuses on the three types of quantum well (QW) lasers; phosphor-free1.3µm InAlGaAs strain-compensated multiple-quantum-well (SCMQW) lasers on InP (100), InGaAsNSb/GaAs quantum wells (QWs) grown on GaAs (411)A substrates and mid-infrared InGaAsSb lasers with digitally grown tensile-strained AlGaAsSb barriers. Type-II InAs/GaSb superlattice IR detectors with various spectral ranges were grown by MBE. Two superlattice structures with 15 monolayers (ML) of InAs/12ML GaSb and 17ML InAs/7ML GaSb are discussed. Based on X-ray diffraction (XRD) measurements both InAs/GaSb superlattices exhibit excellent material qualities with the full width at half maximum (FWHM) of the 0th-order peak about 20arcsec, which is among the narrowest ever reported. The 50% cutoff wavelengths at 80K of the two photodiodes with 15ML InAs/12ML GaSb and 17ML InAs/7ML GaSb superlattices are measured to be 10.2 µm and 6.6 µm, respectively. Mid-infrared heterojunction p-i-n photodetector, AlGaAsSb/InGaAsSb lattice-matched to GaSb grown by solid source molecular beam epitaxy using As and Sb valved crackers greatly facilitated the lattice-matching of the quaternary InGaAsSb absorbing layer to the GaSb substrates, as characterized by X-ray diffraction. The resulting device exhibited low dark current and a breakdown voltage of 32V at room temperature. A record Johnson-noise-limited detectivity of 9.0 × [10]^10 cm Hz^(1/2)/W was achieved at 290K. The 50% cutoff wavelength of the device was 2.57 µm. Thus, our result has clearly demonstrated the potential of very high-performance lattice-matched InGaAsSb p-i-n photodetectors for mid-infrared wavelengths. For phosphor-free1.3 µm InAlGaAs multiple-quantum-well (MQW) lasers, the substrate temperature has been found to be a critical growth parameter for lattice-matched InAl(Ga)As layers in the laser structures. As shown by X-ray diffraction measurements, in the temperature range of 485-520° C, spontaneously ordered superlattices (SLs) with periods around 7-10 nm were formed in the bulk InAl(Ga)As layers. Based on photoluminescence (PL) measurements, a large band gap reduction of 300 meV and a broadened PL peak were observed for the In_0.52 Al_0.48 As layers with SL, as compared to those without SL. The undesirable, spontaneously-ordered SL can be avoided by using MBE growth temperatures higher than 530 °C. This results in a high laser performance. Threshold-current density as low as 690 A/cm² and T_0 as high as 80 K were achieved for InAlGaAs laser bars emitting at 1310 nm. InGaAsNSb/GaAs QWs on GaAs (411)A exhibited remarkably enhanced photoluminescence efficiency compared with the same structures on conventional GaAs (100) substrates. It was further observed that the optimum growth temperature for (411)A was 30 °C higher than that for (100). To explain this phenomenon, a model based on the self-assembling of local rough surface domains into a unique global smooth surface at the lowest energy state of the system is proposed. Lastly, the digital-growth approach for tensile-strained AlGaAsSb barriers improved the reliability and controllability of MBE growth for the MQW active region in the mid-infrared InGaAsSb quantum well lasers. The optical and structural qualities of InGaAsSb MQW were improved significantly, as compared to those with random-alloy barriers due to the removal of growth interruption at the barrier/well interfaces in digital growth. As a result, high-performance devices were achieved in the InGaAsSb lasers with digital AlGaAsSb barriers. A low threshold current density of 163 A/cm² at room temperature was achieved for 1000-µm-long lasers emitting at 2.38 µm. An external differential quantum efficiency as high as 61% was achieved for the 880-µm-long lasers, the highest ever reported for any lasers in this wavelength range.Electrical engineering, Optics, Physicsaa2227Electrical Engineering, Applied Physics and Applied MathematicsDissertationsLattice models of glasses and Potts models for community detection
http://academiccommons.columbia.edu/catalog/ac:153235
Darst, Richard Kennethhttp://hdl.handle.net/10022/AC:P:14886Thu, 11 Oct 2012 13:59:58 +0000In Part I, we construct a configurationally constrained lattice glass model following the example of Biroli and Mezard (Phys. Rev. Lett., 82, 025501 (2001)), which we denote t154. By examining the relaxation, atomic motion, Stokes-Einstein relationship violation, time-dependent displacement (van Hove function), wavevector-dependent relaxation, and multi-point correlations S4 and chi4, we can show that this new model satisfies all minimal requirements set by the observed phenomena of dynamical heterogeneity of supercooled liquids, though with a drastically different theoretical basis from existing lattice models of glasses based on kinetic facilitation. We then proceed to perform a more detailed comparison between lattice glass models, including t154 and a model by Ciamarra et. al. (Phys. Rev. E 68 066111 (2003)), with traditional facilitated models. We study two forms of dynamical sensitivity: sensitivity to boundary conditions, and a sensitivity to initial conditions. By comparison to atomistic computer simulation, we find evidence that the lattice glass models better describe glassy behavior. We conclude by discussing the implications of our findings for contrasting theories of the glass transition. In Part II, we change our focus and examine community detection in graphs from a theoretical standpoint. Many disparate community definitions have been proposed, however except for one, few have been analyzed in any great detail. In this work, we, for the first time, formally study a definition based on internal edge density. Using the concept that internal edge density is the fraction of intra-community edges relative to the maximal number of intra-community edges, we produce a rich framework to use as the basis of community detection. We discuss its use in local and global community detection algorithms, and how our methods can extend to overlapping and hierarchical communities, and weighted, directed, and multi-graphs. In order to validate our definition, we use the recently proposed affiliation graph model and both theoretically and computationally demonstrate the suitability of edge density to solve this problem. We see that internal edge density can perform successful detection on this benchmark under a variety of conditions. We then discuss the limitations of edge density, the types of community structure it will and will not be able to successfully detect, and emphasize the importance of detailed study of real-world community structure in order to produce evidence-based community detection algorithms.Chemistry, Physicsrkd2107ChemistryDissertationsAn Accelerator Measurement of Atomic X-ray Yields in Exotic Atoms and Implications for an Antideuteron-Based Dark Matter Search
http://academiccommons.columbia.edu/catalog/ac:166530
Aramaki, Tsuguohttp://hdl.handle.net/10022/AC:P:14873Wed, 10 Oct 2012 11:05:57 +0000The General AntiParticle Spectrometer (GAPS) is a novel approach for indirect dark mat- ter searches that exploits cosmic antideuterons. The low energy antideuteron provides a clean dark matter signature, since the antideuteron production by cosmic ray interactions is suppressed at low energy, while the WIMP-WIMP annihilation can produce low energy an- tideuterons. GAPS utilizes a distinctive detection method using atomic X-rays and charged particles from the exotic atom as well as the timing, stopping range and dE/dX energy deposit of the incoming particle, which provides excellent antideuteron identification. Prior to the future balloon experiment, an accelerator test was conducted in 2004 and 2005 at KEK, Japan to measure the atomic X-rays of antiprotonic exotic atoms produced by different targets. In 2005, solid targets were tested to avoid the bulky fixture of the gas target and also to have flexibility of the detector geometry in the flight experiment. Recently, we have developed a simple cascade model and the parameters were fitted with the experimental results. The cascade model was extended to the antideuteronic exotic atom for the GAPS flight experiment. GEANT4 simulation was conducted to obtain optimized cuts on the timing, stopping range, dE/dX energy deposit, atomic X-rays, and annihilation products, in order to eliminate the background. Based on the simulation results, we have estimated the GAPS sensitivity with the antideuteron flux. GAPS has a strong potential to detect a dark matter signature.Physics, Astrophysicsta2159PhysicsDissertationsJet Quenching in Relativistic Heavy Ion Collisions at the LHC
http://academiccommons.columbia.edu/catalog/ac:147698
Angerami, Aaronhttp://hdl.handle.net/10022/AC:P:13442Thu, 07 Jun 2012 14:58:42 +0000Jet production in relativistic heavy ion collisions is studied using Pb+Pb collisions at a center of mass energy of 2.76 TeV per nucleon. The measurements reported here utilize data collected with the ATLAS detector at the LHC from the 2010 Pb ion run corresponding to a total integrated luminosity of 7 µ b^(-1). The results are obtained using fully reconstructed jets using the anti-k t algorithm with a per-event background subtraction procedure. A centrality-dependent modification of the dijet asymmetry distribution is observed, which indicates a higher rate of asymmetric dijet pairs in central collisions relative to periphal and pp collisions. Simultaneously the dijet angular correlations show almost no centrality dependence. These results provide the first direct observation of jet quenching. Measurements of the single inclusive jet spectrum, measured with jet radius parameters R=0.2, 0.3, 0.4 and 0.5, are also presented. The spectra are unfolded to correct for the finite energy resolution introduced by both detector effects and underlying event fluctuations. Single jet production, through the central-to-peripheral ratio R CP, is found to be suppressed in central collisions by approximately a factor of two, nearly independent of the jet p T. The R CP is found to have a small but significant increase with increasing R, which may relate directly to aspects of radiative energy loss.Physics, Nuclear physics, Particle physicsara2014PhysicsDissertationsTransit Dosimetry for Patient Treatment Verification with an Electronic Portal Imaging Device
http://academiccommons.columbia.edu/catalog/ac:146689
Berry, Sean Lawrencehttp://hdl.handle.net/10022/AC:P:13155Mon, 07 May 2012 10:46:35 +0000\The complex and individualized photon fluence patterns constructed during intensity modulated radiation therapy (IMRT) treatment planning must be verified before they are delivered to the patient. There is a compelling argument for additional verification throughout the course of treatment due to the possibility of data corruption, unintentional modification of the plan parameters, changes in patient anatomy, errors in patient alignment, and even mistakes in identifying the correct patient for treatment. Amorphous silicon (aSi) Electronic Portal Imaging Devices (EPIDs) can be utilized for IMRT verification. The goal of this thesis is to implement EPID transit dosimetry, measurement of the dose at a plane behind the patient during their treatment, within the clinical process. In order to achieve this goal, a number of the EPID's dosimetric shortcomings were studied and subsequently resolved. Portal dose images (PDIs) acquired with an aSi EPID suffer from artifacts related to radiation backscattered asymmetrically from the EPID support structure. This backscatter signal varies as a function of field size (FS) and location on the EPID. Its presence can affect pixel values in the measured PDI by up to 3.6%. Two methods to correct for this artifact are offered: discrete FS specific correction matrices and a single generalized equation. The dosimetric comparison between the measured and predicted through-air dose images for 49 IMRT treatment fields was significantly improved (p << .001) after the application of these FS specific backscatter corrections. The formulation of a transit dosimetry algorithm followed the establishment of the backscatter correction and a confirmation of the EPID's positional stability with linac gantry rotation. A detailed characterization of the attenuation, scatter, and EPID response behind an object in the beam's path is necessary to predict transit PDIs. In order to validate the algorithm's performance, 49 IMRT fields were delivered to a number of homogeneous and heterogeneous slab phantoms. A total of 33 IMRT fields were delivered to an anthropomorphic phantom. On average, 98.1% of the pixels in the dosimetric comparison between the measured and predicted transit dose images passed a 3%/3mm gamma analysis. Further validation of the transit dosimetry algorithm was performed on nine human subjects under an institutional review board (IRB) approved protocol. The algorithm was shown to be feasible for patient treatment verification. Comparison between measured and predicted transit dose images resulted in an average of 89.1% of pixels passing a 5%/3mm gamma analysis. A case study illustrated the important role that EPID transit dosimetry can play in indicating when a treatment delivery is inconsistent with the original plan. The impact of transit dosimetry on the clinical workflow for these nine patients was analyzed to identify improvements that could be made to the procedure in order to ease widespread clinical implementation. EPID transit dosimetry is a worthwhile treatment verification technique that strikes a balance between effectiveness and efficiency. This work, which focused on the removal of backscattered radiation artifacts, verification of the EPID's stability with gantry rotation, and the formulation and validation of a transit dosimetry algorithm, has improved the EPID's dosimetric performance. Future research aimed at online transit verification would maximize the benefit of transit dosimetry and greatly improve patient safety.Physicsslb2006Applied Physics and Applied Mathematics, Radiation OncologyDissertationsSearch for gravitons using merged jets from Z boson decays with the ATLAS experiment
http://academiccommons.columbia.edu/catalog/ac:146686
Penson, Alexander Vincenthttp://hdl.handle.net/10022/AC:P:13154Mon, 07 May 2012 10:40:57 +0000A search is presented for anomalous production of a pair of gauge bosons (ZZ or WZ) from the decay of a narrow massive resonance. Data corresponding to 2.0 fb-1 of integrated luminosity collected by the ATLAS experiment from proton-proton collisions at 7 TeV. Events with two charged leptons and either two resolved jets or one merged jet are analyzed and found to be consistent with the Standard Model background expectation. In the absence of an excess, lower limits on the mass of a resonance are set using the original Randall-Sundrum (RS1) model as a benchmark. The observed (expected) lower limit on the mass of an excited graviton decaying to ZZ is 870 (950) GeV at 95% confidence level. Limits are also set on a more recent version of the Randall-Sundrum model where Standard Model particles are allowed to propagate in the five dimensional bulk. An excited graviton in this model is excluded for masses between 500 and 630 GeV.Physicsavp2106PhysicsDissertationsUsing machine learning to predict gene expression and discover sequence motifs
http://academiccommons.columbia.edu/catalog/ac:146375
Li, Xuejinghttp://hdl.handle.net/10022/AC:P:13057Mon, 30 Apr 2012 11:25:11 +0000Recently, large amounts of experimental data for complex biological systems have become available. We use tools and algorithms from machine learning to build data-driven predictive models. We first present a novel algorithm to discover gene sequence motifs associated with temporal expression patterns of genes. Our algorithm, which is based on partial least squares (PLS) regression, is able to directly model the flow of information, from gene sequence to gene expression, to learn cis regulatory motifs and characterize associated gene expression patterns. Our algorithm outperforms traditional computational methods e.g. clustering in motif discovery. We then present a study of extending a machine learning model for transcriptional regulation predictive of genetic regulatory response to Caenorhabditis elegans. We show meaningful results both in terms of prediction accuracy on the test experiments and biological information extracted from the regulatory program. The model discovers DNA binding sites ab intio. We also present a case study where we detect a signal of lineage-specific regulation. Finally we present a comparative study on learning predictive models for motif discovery, based on different boosting algorithms: Adaptive Boosting (AdaBoost), Linear Programming Boosting (LPBoost) and Totally Corrective Boosting (TotalBoost). We evaluate and compare the performance of the three boosting algorithms via both statistical and biological validation, for hypoxia response in Saccharomyces cerevisiae.Physicsxl2118PhysicsDissertationsNanomaterials from Nanocomponents: Synthesis and Properties of Hybrid Nanomaterials
http://academiccommons.columbia.edu/catalog/ac:144730
Akey, Austin Josephhttp://hdl.handle.net/10022/AC:P:12610Fri, 17 Feb 2012 14:55:08 +0000This thesis consists of two series of investigations into two different classes of hybrid nanomaterials, their formation and properties. In the first part of this thesis, hybrid nanomaterials composed of cadmium selenide nanoparticles and single-walled carbon nanotubes (SWNTs) are discussed; a novel synthetic method for these hybrids is presented, and an anomalous photoluminescence behavior is examined. Our experiments show that SWNTs can be decorated with CdSe nanoparticles at high loading densities, following the removal of the nanoparticle surface ligands and replacement with pyridine. The resulting hybrids are thermally stable up to 350ºC and mechanically stable against sonication. The photoluminescence Stokes shift in the bound nanoparticles is shown to be reduced relative to that of unbound nanoparticles. This difference is attributed to Forster resonance energy transfer from the nanoparticles to the nanotube, leading to hot luminescence in the nanoparticles. The second part of this thesis focuses on formation strategies and mechanisms for nanoparticle superlattices. Supercrystals, as they are called, are formed using lithographically-patterned reservoirs and capillary channels, giving control over both supercrystal dimensions and placement; these supercrystals form within a few hours, much faster than those previously reported. These results are extended to the formation of large-area (> 10 µm lateral dimension) thick (> 1 µm) supercrystals on substrates, and the formation mechanism probed by in situ small-angle x-ray scattering. Both monocomponent and binary supercrystals are examined.Materials science, PhysicsApplied Physics and Applied Mathematics, Materials Science and EngineeringDissertationsForce and Conductance Spectroscopy of Single Molecule Junctions
http://academiccommons.columbia.edu/catalog/ac:143847
Frei, Michaelhttp://hdl.handle.net/10022/AC:P:12363Fri, 27 Jan 2012 12:41:35 +0000Investigation of mechanical properties of single molecule junctions is crucial to develop an understanding and enable control of single molecular junctions. This work presents an experimental and analytical approach that enables the statistical evaluation of force and simultaneous conductance data of metallic atomic point contacts and molecular junctions. A conductive atomic force microscope based break junction technique is developed to form single molecular junctions and collect conductance and force data simultaneously. Improvements of the optical components have been achieved through the use of a super luminescent diode, enabling tremendous increases in force resolution. An experimental procedure to collect data for various molecular junctions has been developed and includes deposition, calibration, and analysis methods. For the statistical analysis of force, novel approaches based on two dimensional histograms and a direct force identification method are presented. The two dimensional method allows for an unbiased evaluation of force events that are identified using corresponding conductance signatures. This is not always possible however, and in these situations, the force based identification of junction rearrangement events is an attractive alternative method. This combined experimental and analytical approach is then applied to three studies: First, the impact of molecular backbones to the mechanical behavior of single molecule junctions is investigated and it is found that junctions formed with identical linkers but different backbone structure result in junctions with varying breaking forces. All molecules used show a clear molecular signature and force data can be evaluated using the 2D method. Second, the effects of the linker group used to attach molecules to gold electrodes are investigated. A study of four alkane molecules with different linkers finds a drastic difference in the evolution of donor acceptor and covalently bonded molecules respectively. In fact, the covalent bond is found to significantly distort the metal electrode rearrangement such that junction rearrangement events can no longer be identified with a clean and well defined conductance signature. For this case, the force based identification process is used. Third, results for break junction measurements with different metals are presented. It is found that silver and palladium junctions rupture with forces different from those of gold contacts. In the case of silver experiments in ambient conditions, we can also identify oxygen impurities in the silver contact formation process, leading to force and conductance measurements of silver-oxygen structures. For the future, this work provides an experimental and analytical foundation that will enable insights into single molecule systems not previously accessible.Physics, Chemistrymf2433Applied Physics and Applied MathematicsDissertationsThe XENON100 Dark Matter Experiment: Design, Construction, Calibration and 2010 Search Results with Improved Measurement of the Scintillation Response of Liquid Xenon to Low-Energy Nuclear Recoils
http://academiccommons.columbia.edu/catalog/ac:143844
Plante, GuillaumeFri, 27 Jan 2012 12:17:29 +0000An impressive array of astrophysical observations suggest that 83% of the matter in the universe is in a form of non-luminous, cold, collisionless, non-baryonic dark matter. Several extensions of the Standard Model of particle physics aimed at solving the hierarchy problem predict stable weakly interacting massive particles (WIMPs) that could naturally have the right cosmological relic abundance today to compose most of the dark matter if their interactions with normal matter are on the order of a weak scale cross section. These candidates also have the added benefit that their properties and interaction rates can be computed in a well defined particle physics model. A considerable experimental effort is currently under way to uncover the nature of dark matter. One method of detecting WIMP dark matter is to look for its interactions in terrestrial detectors where it is expected to scatter off nuclei. In 2007, the XENON10 experiment took the lead over the most sensitive direct detection dark matter search in operation, the CDMS II experiment, by probing spin-independent WIMP-nucleon interaction cross sections down to σχN ~ 5 × 10-44 cm2 at 30GeV/c2. Liquefied noble gas detectors are now among the technologies at the forefront of direct detection experiments. Liquid xenon (LXe), in particular, is a well suited target for WIMP direct detection. It is easily scalable to larger target masses, allows discrimination between nuclear recoils and electronic recoils, and has an excellent stopping power to shield against external backgrounds. A particle losing energy in LXe creates both ionization electrons and scintillation light. In a dual-phase LXe time projection chamber (TPC) the ionization electrons are drifted and extracted into the gas phase where they are accelerated to amplify the charge signal into a proportional scintillation signal. These two signals allow the three-dimensional localization of events with millimeter precision and the ability to fiducialize the target volume, yielding an inner core with a very low background. Additionally, the ratio of ionization and scintillation can be used to discriminate between nuclear recoils, from neutrons or WIMPs, and electronic recoils, from γ or β backgrounds. In these detectors, the energy scale is based on the scintillation signal of nuclear recoils and consequently the precise knowledge of the scintillation efficiency of nuclear recoils in LXe is of prime importance. Inspired by the success of the XENON10 experiment, the XENON collaboration designed and built a new, ten times larger, with a one hundred times lower background, LXe TPC to search for dark matter. It is currently the most sensitive direct detection experiment in operation. In order to shed light on the response of LXe to low energy nuclear recoils a new single phase detector designed specifically for the measurement of the scintillation efficiency of nuclear recoils was also built. In 2011, the XENON100 dark matter results from 100 live days set the most stringent limit on the spin-independent WIMP-nucleon interaction cross section over a wide range of masses, down to σχN ~ 7 x 10-45 cm2 at 50GeV/c2, almost an order of magnitude improvement over XENON10 in less than four years. This thesis describes the research conducted in the context of the XENON100 dark matter search experiment. I describe the initial simulation results and ideas that influenced the design of the XENON100 detector, the construction and assembly steps that lead into its concrete realization, the detector and its subsystems, a subset of the calibration results of the detector, and finally dark matter exclusion limits. I also describe in detail the new improved measurement of the important quantity for the interpretation of results from LXe dark matter searches, the scintillation efficiency of low-energy nuclear recoils in LXe.Physics, Astrophysicsgp2135Astronomy and Astrophysics, PhysicsDissertationsSingle Molecule Junction Conductance and Binding Geometry
http://academiccommons.columbia.edu/catalog/ac:143055
Kamenetska, Mariahttp://hdl.handle.net/10022/AC:P:12159Tue, 10 Jan 2012 13:11:33 +0000This Thesis addresses the fundamental problem of controlling transport through a metal-organic interface by studying electronic and mechanical properties of single organic molecule-metal junctions. Using a Scanning Tunneling Microscope (STM) we image, probe energy-level alignment and perform STM-based break junction (BJ) measurements on molecules bound to a gold surface. Using Scanning Tunneling Microscope-based break-junction (STM-BJ) techniques, we explore the effect of binding geometry on single-molecule conductance by varying the structure of the molecules, metal-molecule binding chemistry and by applying sub-nanometer manipulation control to the junction. These experiments are performed both in ambient conditions and in ultra high vacuum (UHV) at cryogenic temperatures. First, using STM imaging and scanning tunneling spectroscopy (STS) measurements we explore binding configurations and electronic properties of an amine-terminated benzene derivative on gold. We find that details of metal-molecule binding affect energy-level alignment at the interface. Next, using the STM-BJ technique, we form and rupture metal-molecule-metal junctions ~104 times to obtain conductance-vs-extension curves and extract most likely conductance values for each molecule. With these measurements, we demonstrated that the control of junction conductance is possible through a choice of metal-molecule binding chemistry and sub-nanometer positioning. First, we show that molecules terminated with amines, sulfides and phosphines bind selectively on gold and therefore demonstrate constant conductance levels even as the junction is elongated and the metal-molecule attachment point is modified. Such well-defined conductance is also obtained with paracyclophane molecules which bind to gold directly through the Ã° system. Next, we are able to create metal-molecule-metal junctions with more than one reproducible conductance signatures that can be accessed by changing junction geometry. In the case of pyridine-linked molecules, conductance can be reliably switched between two distinct conductance states using sub-nanometer mechanical manipulation. Using a methyl sulfide linker attached to an oligoene backbone, we are able to create a 3-nm-long molecular potentiometer, whose resistance can be tuned exponentially with Angstom-scale modulations in metal-molecule configuration. These experiments points to a new paradigm for attaining reproducible electrical characteristics of metal-organic devices which involves controlling linker-metal chemistry rather than fabricating identically structured metal-molecule interfaces. By choosing a linker group which is either insensitive to or responds reproducibly to changes in metal-molecule configuration, one can design single molecule devices with functionality more complex than a simple resistor. These ambient temperature experiments were combined with UHV conductance measurements performed in a commercial STM on amine-terminated benzene derivatives which conduct through a non-resonant tunneling mechanism, at temperatures varying from 5 to 300 Kelvin. Our results indicate that while amine-gold binding remains selective irrespective of environment, conductance is not temperature independent, in contrast to what is expected for a tunneling mechanism. Furthermore, using temperature-dependent measurements in ambient conditions we find that HOMO-conducting amines and LUMO-conducting pyridines show opposite dependence of conductance on temperature. These results indicate that energy-level alignment between the molecule and the electrodes changes as a result of varying electrode structure at different temperatures. We find that temperature can serve as a knob with which to tune transport properties of single molecule-metal junctions.Physics, Nanosciencemk2743Applied Physics and Applied MathematicsDissertationsProperties of Fragmentation Photons in p+p Collisions at 200 GeV Center-of-Mass Energy
http://academiccommons.columbia.edu/catalog/ac:142601
Hanks, Janette Alicehttp://hdl.handle.net/10022/AC:P:11852Wed, 30 Nov 2011 10:02:26 +0000The strong modification to the production of final state hadrons in heavy ion collisions is a key signature of the hot dense medium produced at energies achieved at the Relativistic Heavy Ion Collider (RHIC). Understanding the mechanisms for the parton energy loss responsible for these modifications is challenging and difficult to constrain with straightforward hadronic measurements, making it necessary to turn to more discriminating probes. One example of such a probe is photons produced by partons as they fragment, fragmentation photons, because the production mechanisms for such photons are similar to those for hadrons, but once produced, fragmentation photons will not interact directly with the medium. The challenge of distinguishing the signal for such jet-associate photons out of the large decay background motivates first making such measurements in the simple p + p environment. Combining data collected by the PHENIX detector during 2005 and 2006, the yield for fragmentation photons was measured to be on the order of several percent of all photons measured in association with a hadron with transverse momentum between 2 and 5 GeV/c. The use of two-particle correlations coupled with a sophisticated method for identifying and removing decay photons has made it possible to further study the jet properties of these fragmentation photons, in the form of pout and root mean square jT. These results will help to constrain both the underlying theoretical description of direct photon production in p + p, and modifications expected in heavy ion collisions.Physics, Nuclear physics, Particle physicsPhysicsDissertationsSpinning Black Hole Pairs: Dynamics and Gravitational Waves
http://academiccommons.columbia.edu/catalog/ac:141916
Grossman, Rebecca I.http://hdl.handle.net/10022/AC:P:11791Fri, 11 Nov 2011 12:06:21 +0000Black hole binaries will be an important source of gravitational radiation for both ground-based and future space-based gravitational wave detectors. The study of such systems will offer a unique opportunity to test the dynamical predictions of general relativity when gravity is very strong. To date, most investigations of black hole binary dynamics have focused attention on restricted scenarios in which the black holes do not spin (and thus are confined to move in a plane) and/or in which they stay on quasi-circular orbits. However, spinning black hole pairs in eccentric orbits are now understood to be astrophysically equally important. These spinning binaries exhibit a range of complicated dynamical behaviors, even in the absence of radiation reaction. Their conservative dynamics is complicated by extreme perihelion precession compounded by spin-induced precession. Although the motion seems to defy simple decoding, we are able to quantitatively define and describe the fully three-dimensional motion of arbitrary mass-ratio binaries with at least one black hole spinning and expose an underlying simplicity. To do so, we untangle the dynamics by constructing an instantaneous orbital plane and showing that the motion captured in that plane obeys elegant topological rules. In this thesis, we apply the above prescription to two formal systems used to model black hole binaries. The first is defined by the conservative 3PN Hamiltonian plus spin-orbit coupling and is particularly suitable to comparable-mass binaries. The second is defined by geodesics of the Kerr metric and is used exclusively for extreme mass-ratio binaries. In both systems, we define a complete taxonomy for fully three-dimensional orbits. More than just a naming system, the taxonomy provides unambiguous and quantitative descriptions of the orbits, including a determination of the zoom-whirliness of any given orbit. Through a correspondence with the rational numbers, we are able to show that all of the qualitative features of the well-studied equatorial geodesic motion around Schwarzschild and Kerr black holes are also present in more general black hole binary systems. This includes so-called zoom-whirl behavior, which turns out to be unexpectedly prevalent in comparable-mass binaries in the strong-field regime just as it is for extreme mass-ratio binaries. In each case we begin by thoroughly cataloging the constant radius orbits which generally lie on the surface of a sphere and have acquired the name "spherical orbits". The spherical orbits are significant as they energetically frame the distribution of all orbits. In addition, each unstable spherical orbit is asymptotically approached by an orbit that whirls an infinite number of times, known as a homoclinic orbit. We further catalog the homoclinic trajectories, each of which is the infinite whirl limit of some part of the zoom-whirl spectrum and has a further significance as the separatrix between inspiral and plunge for eccentric orbits. We then show that there exists a discrete set of orbits that are geometrically closed n-leaf clovers in a precessing orbital plane. When viewed in the full three dimensions, these orbits do not close, but they are nonetheless periodic when projected into the orbital plane. Each n-leaf clover is associated with a rational number, q, that measures the degree of perihelion precession in the precessing orbital plane. The rational number q varies monotonically with the orbital energy and with the orbital eccentricity. Since any bound orbit can be approximated as near one of these periodic n-leaf clovers, this special set offers a skeleton that illuminates the structure of all bound orbits in both systems, in or out of the equatorial plane. A first significant conclusion that can be drawn from this analysis is that all generic orbits in the final stages of inspiral under gravitational radiation losses are characterized by precessing clovers with few leaves, and that no orbit will behave like the tightly precessing ellipse of Mercury. We close with a practical application of our taxonomy beyond the illumination of conservative dynamics. The numerical calculation of the first-order (adiabatic) approximation to radiatively evolving inspiral motion in extreme mass-ratio binaries is currently hindered by prohibitive computational cost. Motivated by this limitation, we explain how a judicious use of periodic orbits can dramatically expedite both that calculation and the generation of snapshot gravitational waves from geodesic sources.Physics, Astrophysicsrg420Physics and Astronomy (Barnard College), PhysicsDissertationsResults from the QUIET Q-Band Observing Season
http://academiccommons.columbia.edu/catalog/ac:141910
Dumoulin, Robert Nicolashttp://hdl.handle.net/10022/AC:P:11789Fri, 11 Nov 2011 11:43:46 +0000The Q/U Imaging ExperimenT (QUIET) is a ground-based telescope located in the high Atacama Desert in Chile, and is designed to measure the polarization of the Cosmic Microwave Background (CMB) in the Q and W frequency bands (43 and 95 GHz respectively) using coherent polarimeters. From 2008 October to 2010 December, data from more than 10,000 observing hours were collected, first with the Q-band receiver (2008 October to 2009 June) and then with the W-band receiver (until the end of the 2010 observing season). The QUIET data analysis effort uses two independent pipelines, one consisting of a maximum likelihood framework and the other consisting of a pseudo-C` framework. Both pipelines employ blind analysis methods, and each provides analysis of the data using large suites of null tests specific to the pipeline. Analysis of the Q-band receiver data was completed in November of 2010, confirming the only previous detection of the first acoustic peak of the EE power spectrum and setting competitive limits on the scalar-totensor ratio, r. In this dissertation, the results from the Q-band observing season using the maximum likelihood pipeline will be presented.Physics, AstrophysicsPhysicsDissertationsHEFT measurement of the hard X-ray size of the Crab Nebula and the hard X-ray optics of the Nuclear Spectroscopic Telescope Array (NuSTAR)
http://academiccommons.columbia.edu/catalog/ac:141649
An, Hongjunhttp://hdl.handle.net/10022/AC:P:11786Wed, 09 Nov 2011 16:55:00 +0000In this thesis, I discuss two topics: The High Energy Focusing Telescope (HEFT) and the Nuclear Spectroscopic Telescope Array (NuSTAR). HEFT is the first experiment done with imaging telescopes in the hard X-ray energy band (~20-70 keV). I briefly describe the instrument and the balloon campaign. The inflight calibration of the Point Spread Function (PSF) is done with a point source observation (~50 minutes of Cyg X-1 observation). With the PSF calibrated, I attempt to measuring the size of the Crab Nebula in this energy band. Analysis for aspect reconstruction, optical axis determination and the size measurement are described in detail. The size of the Crab Nebula is energy dependent due to synchrotron burn-off. The measurement of the size at different energies can provide us with important parameters for the pulsar wind nebula (PWN) model such as the magnetization parameter. With ~60 minutes of observation of the Crab Nebula with HEFT, I measure the size of the Crab Nebula at energies of 25-58 keV. The analysis technique I used for the size measurement here can be used for measuring the size of astrophysical objects whose sizes are comparable to the width of the PSF. NuSTAR is a satellite version of the HEFT experiment although the spatial and spectral resolution of the optics are improved significantly. And thus, the fabrication technique for the HEFT optics needed to be modified. I describe the fabrication technique for the NuSTAR optics, focusing on the epoxy selection and process development and the metrology systems for characterizing the figure of the glass surfaces.Physics, Astrophysicsha2153PhysicsDissertationsQuantum Chromodynamics with Eight and Twelve Degenerate Quark Flavors on the Lattice
http://academiccommons.columbia.edu/catalog/ac:137844
Jin, Xiao-Yonghttp://hdl.handle.net/10022/AC:P:11014Mon, 29 Aug 2011 14:15:28 +0000This thesis is concerned with the behavior of non-abelian gauge theories with many flavors of fermions. In perturbation theory, an infrared fixed point is predicted to exist, and theories become conformal in the low energy limit, in non-abelian gauge theories with the number of fermions just below the threshold of losing asymptotic freedom. With the number of fermion flavors even smaller than the number required for conformal behavior, the coupling constant is expected to run slowly or "walk". However, the exact number of fermion flavors that is required for the conformal behavior is unknown. This thesis probes for non-perturbative evidence for such behavior by simulating SU(3) gauge theories on the lattice with eight and twelve degenerate fermions in the fundamental representation. The naive staggered fermion action with the DBW2 gauge action is used in the simulations. The exact RHMC algorithm with the Omelyan integrator is used for simulating all eight-flavor gauge configurations and twelve-flavor gauge configurations with large masses, mq ≥ 0.01. For the other twelve-flavor simulations with smaller masses, mq < 0.01, the exact HMC algorithm with multiple mass preconditioning and the force gradient integrator is used. Comparisons are also done with previous simulations, which used the Wilson plaquette gauge action and the inexact R algorithm. Both zero temperature (Nt = 32) and finite temperature physics are studied in this thesis. For system with eight flavors, the focus of the zero temperature simulations is on three values of input couplings β = 0.54, 0.56 and 0.58, with two or three quark masses for each coupling value. The zero-temperature, lattice artifact bulk transition found with the Wilson plaquette action in becomes a rapid cross-over with the DBW2 gauge action. At finite temperatures, a first order phase transition is observed at the strongest coupling, β = 0.54. For systems with twelve flavors, a large amount of simulation is done at values of input couplings from β = 0.45 to 0.50. A zero-temperature bulk transition is found with quark masses mq = 0.006 and 0.008, and it ends in a second order critical point at masses slightly larger than 0.008. The system shows a mass-dependent rapid cross-over with quark masses mq ≥ 0.01 around the lattice couplings from β = 0.46 to β = 0.48. A finite temperature study at β = 0.49 shows a drastic change of behavior in the screening masses and other observables, which suggests the existence of a finite temperature >transition. All the evidences gathered in this thesis support the argument that theories of both eight and twelve flavors of fermion in the fundamental representation of SU(3) gauge group are consistent with the behavior one would expected from a theory with spontaneously broken chiral symmetry. The strongest supporting evidence is the linearity of mπ2 ∝ mq at zero temperatures and the existence of a chiral symmetry restoring transition at finite temperatures. We note that other lattice simulations, also exploring the hadronic observables, arrive at a similar conclusion, while simulations of the running of the coupling have claimed that the 12 flavor theory is conformal.Physicsxj2106PhysicsDissertationsFrom Measure Zero to Measure Hero: Periodic Kerr Orbits and Gravitational Wave Physics
http://academiccommons.columbia.edu/catalog/ac:137822
Perez-Giz, Gabehttp://hdl.handle.net/10022/AC:P:11008Mon, 29 Aug 2011 12:13:35 +0000A direct observational detection of gravitational waves - perhaps the most fundamental prediction of a theory of curved spacetime - looms close at hand. Stellar mass compact objects spiraling into supermassive black holes have received particular attention as sources of gravitational waves detectable by space-based gravitational wave observatories. A well-established approach models such an extreme mass ratio inspirals (EMRI) as an adiabatic progression through a series of Kerr geodesics. Thus, the direct detection of gravitational radiation from EMRIs and the extraction of astrophysical information from those waveforms require a thorough knowledge of the underlying geodesic dynamics. This dissertation adopts a dynamical systems approach to the study of Kerr orbits, beginning with equatorial orbits. We deduce a topological taxonomy of orbits that hinges on a correspondence between periodic orbits and rational numbers. The taxonomy defines the entire dynamics, including aperiodic motion, since every orbit is in or near the periodic set. A remarkable implication of this periodic orbit taxonomy is that the simple precessing ellipse familiar from planetary orbits is not allowed in the strong-field regime. Instead, eccentric orbits trace out precessions of multi-leaf clovers in the final stages of inspiral. Furthermore, for any black hole, there is some orbital angular momentum value in the strong-field regime below which zoom-whirl behavior becomes unavoidable. We then generalize the taxonomy to help identify nonequatorial orbits whose radial and polar frequencies are rationally related, or in resonance. The thesis culminates by describing how those resonant orbits can be leveraged for an order of magnitude or more reduction in the computational cost of adiabatic order EMRI trajectories, which are so prohibitively expensive that no such relativistically correct inspirals have been generated to date.Physics, Astrophysics, Applied mathematicsgep1PhysicsDissertationsVisual Noise Due to Quantum Indeterminacies
http://academiccommons.columbia.edu/catalog/ac:135042
Morrison, John Ross; Anderson, Davidhttp://hdl.handle.net/10022/AC:P:10600Tue, 28 Jun 2011 12:24:11 +0000We establish that, due to certain quantum indeterminacies, there must be foundational colours that do not reliably cause any particular experience. This report functions as an appendix to Morrison's "Colour in a Physical World."Philosophy, Physicsjrm2182Philosophy (Barnard College)ArticlesSynthesis and electronic transport in single-walled carbon nanotubes of known chirality
http://academiccommons.columbia.edu/catalog/ac:132056
Caldwell, Robert Victorhttp://hdl.handle.net/10022/AC:P:10342Wed, 11 May 2011 14:31:49 +0000Since their discovery in 1991, carbon nanotubes have proven to be a very interesting material for its physical strength, originating from the pure carbon lattice and strong covalent sp2 orbital bonds, and electronic properties which are derived from the lattice structure lending itself to either a metallic or semiconducting nature among its other properties. Carbon nanotubes have been researched with an eye towards industry applications ranging from use as an alloy in metals and plastics to improve physical strength of the resulting materials to uses in the semiconductor industry as either an interconnect or device layer for computer chips to chemical or biological sensors. This thesis focuses on both the synthesis of individual single-walled carbon nanotubes as well as the electrical properties of those tubes. What makes the work herein different from that of other thesis is that the research has been performed on carbon nanotubes of known chirality. Having first grown carbon nanotubes with a chemical vapor deposition growth in a quartz tube using ethanol vapor as a feedstock to grow long individual single-walled carbon nanotubes on a silicon chip that is also compatible with Rayleigh scattering spectroscopy to identify the chiral indices of the carbon nanotubes in question, those tubes were then transferred with a mechanical transfer process specially designed in our research lab onto a substrate of our choosing before an electrical device was made out of those tubes using standard electron beam lithography. The focus in this thesis is on the work that went into designing and testing this process as well as the initial results of the electronic properties of those carbon nanotubes of known chirality, such as the first known electrical measurements on single individual armchair carbon nanotubes as well as the first known electrical measurements of a single semiconducting carbon nanotube on thin hexagonal boron nitride to study the effects of the surface optical phonons from the boron nitride on the electrical properties of the carbon nanotube. Finally a few research projects are discussed in which carbon nanotubes of known chirality were used in conjunction with first electrical tests on molecules, secondly on a prefabricated complementary metal-oxide-semiconductor integrated circuit as an inverter and lastly to study the photoconductivity generated by a synchrotron laser source to identify the values for the low energy excitonic peak.Physics, Nanotechnologyrvc2101Applied Physics and Applied Mathematics, Mechanical EngineeringDissertationsSpectral Optimization Problems Controlling Wave Phenomena
http://academiccommons.columbia.edu/catalog/ac:131510
Osting, BraxtonFri, 29 Apr 2011 14:32:19 +0000Design problems seek a material arrangement or shape which fully harnesses the physical properties of the material(s) to create an environment in which a particular phenomena is most (or least) pronounced. Mathematically, design problems are formulated as PDE-constrained optimization problems to find the material arrangement that maximizes an objective function which expresses the desired behavior. The PDE constraint describes the relationship between the material and the phenomena of interest. The focus of this thesis is four design problems where the PDE constraint is a time-independent wave equation and the objective function governs some aspect of wave motion. We consider the shape optimization of functions of Dirichlet-Laplacian eigenvalues associated with the set of star-shaped, symmetric, bounded planar regions with smooth boundary. The boundary of such a region is represented using a Fourier-cosine series and the optimization problem is solved numerically using a quasi-Newton method. The method is applied to maximizing two particular nonsmooth functions of the eigenvalues: (a) the ratio of the n-th to first eigenvalues and (b) the ratio of the n-th eigenvalue gap to first eigenvalue. Both are generalizations of the Payne-Pólya-Weinberger ratio. The optimal values of these ratios and regions for which they are attained, for n ≤ 13, are presented and interpreted as a study of the range of the Dirichlet-Laplacian eigenvalues. For both spectral functions and each n, the optimal region has multiplicity two n-th eigenvalue. We consider a system governed by the wave equation with index of refraction n(x), taken to be variable within a bounded region of d-dimensional space and constant outside. The solution of the time-dependent wave equation with spatially-localized initial data spreads and decays with advancing time. The rate of spatially localized energy decay can be measured in terms of the eigenvalues of the scattering resonance problem, a non-selfadjoint eigenvalue problem consisting of the time-harmonic wave (Helmholtz) equation with outgoing radiation condition at infinity. Specifically, the rate of energy escape is governed by the complex scattering eigenfrequency which is closest to the real axis. We study the structural design problem: Find a refractive index profile n* within an admissible class which has a scattering frequency with minimal imaginary part. The admissible class is defined in terms of the compact support of n(x)-1 and pointwise upper and lower (material) bounds on n(x): 0 < n- ≤ n(x) ≤ n+ < ∞. We formulate this problem as a constrained optimization problem and prove that an optimal structure, n* exists. Furthermore, n*(x) is piecewise constant and achieves the material bounds, i.e., n*(x) is n- or n+ almost everywhere. In one dimension, we establish a connection between n*(x) and the well-known class of Bragg structures, where n(x) is constant on intervals whose length is one-quarter of the effective wavelength. Consider a system governed by the time-dependent Schroedinger equation in its ground state. When subjected to weak parametric forcing by an "ionizing field" (time-varying), the state decays with advancing time due to coupling of the bound state to radiation modes. The decay-rate of this metastable state is governed by Fermi's Golden Rule (FGR), which depends on the potential V and the details of the forcing. We pose the potential design problem: find V* which minimizes FGR (maximizes the lifetime of the state) over an admissible class of potentials with fixed spatial support. We formulate this problem as a constrained optimization problem and prove that an admissible optimal solution exists. Then, using quasi-Newton methods, we compute locally optimal potentials. These have the structure of a truncated periodic potential with a localized defect. In contrast to optimal structures for other spectral optimization problems, the optimizing potentials appear to be interior points of the constraint set and to be smooth. The multi-scale structures that emerge incorporate the physical mechanisms of energy confinement via material contrast and interference effects. An analysis of locally optimal potentials reveals local optimality is attained via two mechanisms: (i) decreasing the density of states near a resonant frequency in the continuum and (ii) tuning the oscillations of extended states to make FGR, an oscillatory integral, small. Finally, we explore the performance of optimal potentials via simulations of the time-evolution. We consider a general class of two-dimensional passive propagation media, represented as a planar graph where nodes are capacitors connected to a common ground and edges are inductors. Capacitances and inductances are fixed in time but vary in space. Kirchhoff's laws give the time dynamics of voltage and current in the system. By harmonically forcing input nodes and collecting the resulting steady-state signal at output nodes, we obtain a linear, analog device that transforms the inputs to outputs. We pose the lattice synthesis problem: given a linear transformation, find the inductances and capacitances for an inductor-capacitor circuit that can perform this transformation. Formulating this as an optimization problem, we numerically demonstrate its solvability using gradient-based methods. By solving the lattice synthesis problem for various desired transformations, we design several devices that can be used for signal processing and filtering. In addition to these spectral optimization problems, we study several problems on wave propagation, diffraction, and scattering. The focus is on the behavior of time-harmonic solutions to continuous and discrete wave equations.Applied mathematics, Physics, Materials sciencebro2103Applied Physics and Applied MathematicsDissertationsOn the characterization of the fineâ€scale intermittency of turbulence
http://academiccommons.columbia.edu/catalog/ac:126785
Zubair, Lareef M.http://hdl.handle.net/10022/AC:P:9026Wed, 16 Jun 2010 11:59:11 +0000Some characterization of the fine-scale intermittency of turbulence is attempted utilizing the method of Kuo and Corrsin [J. Fluid Mech. 50, 285 (1971)] and the "envelope method" of Sreenivasan [J. Fluid Mech. 151, 81 (1985)]. It is found that the outcomes of these techniques are sensitively dependent on the details of the methods, and hence cannot be interpreted with complete confidence.Physicslz144International Research Institute for Climate and SocietyArticles