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Articles 1 - 30 of 30
Full-Text Articles in Physics
Performance Of A C4f8o Gas Radiator Ring Imaging Cherenkov Detector Using Multi-Anode Photomultiplier Tubes, Raymond Mountain, Marina Artuso, Chaouki Boulahouache, S. Blusk
Performance Of A C4f8o Gas Radiator Ring Imaging Cherenkov Detector Using Multi-Anode Photomultiplier Tubes, Raymond Mountain, Marina Artuso, Chaouki Boulahouache, S. Blusk
Physics - All Scholarship
We report on test results of a novel ring imaging Cherenkov (RICH) detection system consisting of a 3 meter long gaseous C4F8O radiator, a focusing mirror, and a photon detector array based on Hamamatsu multi-anode photomultiplier tubes. This system was developed to identify charged particles in the momentum range from 3-70 GeV/c for the BTeV experiment.
Effects Of Disorder On Electron Transport In Arrays Of Quantum Dots, Alan Middleton, Shantenu Jha
Effects Of Disorder On Electron Transport In Arrays Of Quantum Dots, Alan Middleton, Shantenu Jha
Physics - All Scholarship
We investigate the zero-temperature transport of electrons in a model of quantum dot arrays with a disordered background potential. One effect of the disorder is that conduction through the array is possible only for voltages across the array that exceed a critical voltage $V_T$. We investigate the behavior of arrays in three voltage regimes: below, at and above the critical voltage. For voltages less than $V_T$, we find that the features of the invasion of charge onto the array depend on whether the dots have uniform or varying capacitances. We compute the first conduction path at voltages just above $V_T$ …
Notes On (Twisted) Lattice Supersymmetry, Simon Catterall
Notes On (Twisted) Lattice Supersymmetry, Simon Catterall
Physics - All Scholarship
We describe a new approach to the problem of putting supersymmetric theories on the lattice. The basic idea is to discretize a {\it twisted} formulation of the supersymmetric theory. For certain theories with extended supersymmetry these twisted formulations contain only integer spin fields. The twisting exposes a scalar nilpotent supercharge which generates an exact lattice symmetry. We gives examples from quantum mechanics, sigma models and Yang-Mills theories.
Dirac-Kähler Fermions And Exact Lattice Supersymmetry, Simon Catterall
Dirac-Kähler Fermions And Exact Lattice Supersymmetry, Simon Catterall
Physics - All Scholarship
We discuss a new approach to putting supersymmetric theories on the lattice. The basic idea is to start from a {\it twisted} formulation of the underlying supersymmetric theory in which the fermions are represented as grassmann valued antisymmetric tensor fields. The original supersymmetry algebra is replaced by a twisted algebra which contains a scalar nilpotent supercharge Q. Furthermore the action of the theory can then be written as the Q-variation of some function. The case of {\cal N}=2 super Yang-Mills theory in two dimensions is discussed in some detail. We then present our proposal for discretizing this theory and derive …
Lattice Formulation Of {\Cal N}=4 Super Yang-Mills Theory, Simon Catterall
Lattice Formulation Of {\Cal N}=4 Super Yang-Mills Theory, Simon Catterall
Physics - All Scholarship
We construct a lattice action for {\cal N}=4 super Yang-Mills theory in four dimensions which is local, gauge invariant, free of spectrum doubling and possesses a single exact supersymmetry. Our construction starts from the observation that the fermions of the continuum theory can be mapped into the component fields of a single real anticommuting Kahler-Dirac field. The original supersymmetry algebra then implies the existence of a nilpotent scalar supercharge Q and a corresponding set of bosonic superpartners. Using this field content we write down a Q-exact action and show that, with an appropriate change of variables, it reduces to a …
Grain Boundary Scars On Spherical Crystals, Mark Bowick, Thomas Einert, Peter Lipowsky, Jorg Schilling, Andreas R. Bausch
Grain Boundary Scars On Spherical Crystals, Mark Bowick, Thomas Einert, Peter Lipowsky, Jorg Schilling, Andreas R. Bausch
Physics - All Scholarship
We present an experimental system suitable for producing spherical crystals and for observing the distribution of lattice defects (disclinations and dislocations) on a significant fraction (50%) of the sphere. The introduction of fluorescently labeled particles enables us to determine the location and orientation of grain boundary scars. We find that the total number of scars and the number of excess dislocations per scar agree with theoretical predictions and that the geometrical centers of the scars are roughly positioned at the vertices of an icosahedron.
Crystalline Particle Packings On A Sphere With Long Range Power Law Potentials, Mark Bowick, Angelo Cacciuto, David R. Nelson, Alex Travesset
Crystalline Particle Packings On A Sphere With Long Range Power Law Potentials, Mark Bowick, Angelo Cacciuto, David R. Nelson, Alex Travesset
Physics - All Scholarship
The original Thomson problem of "spherical crystallography" seeks the ground state of electron shells interacting via the Coulomb potential; however one can also study crystalline ground states of particles interacting with other potentials. We focus here on long range power law interactions of the form 1/r^gamma (0 < \gamma < 2), with the classic Thomson problem given by gamma=1. At large R/a, where R is the sphere radius and a is the particle spacing, the problem can be reformulated as a continuum elastic model that depends on the Young's modulus of particles packed in the plane and the universal (independent of the pair potential) geometrical interactions between disclination defects. The energy of the continuum model can be expressed as an expansion in powers of the total number of particles, M sim (R/a)^2, with coefficients explicitly related to both geometric and potential-dependent terms. For icosahedral configurations of twelve 5-fold disclinations, the first non-trivial coefficient of the expansion agrees with explicit numerical evaluation for discrete particle arrangements to 4 significant digits; the discrepancy in the 5th digit arises from a contribution to the energy that is sensitive to the particular icosadeltahedral configuration and that is neglected in the continuum calculation. In the limit of a very large number of particles, an instability toward grain boundaries can be understood in terms of a "Debye{--}Huckel" solution, where dislocations have continuous Burgers' vector "charges". Discrete dislocations in grain boundaries for intermediate particle numbers are discussed as well.
Footprints Of Statistical Anisotropies, Christian Armendariz-Picon
Footprints Of Statistical Anisotropies, Christian Armendariz-Picon
Physics - All Scholarship
We propose and develop a formalism to describe and constrain statistically anisotropic primordial perturbations. Starting from a decomposition of the primordial power spectrum in spherical harmonics, we find how the temperature fluctuations observed in the CMB sky are directly related to the coefficients in this harmonic expansion. Although the angular power spectrum does not discriminate between statistically isotropic and anisotropic perturbations, it is possible to define analogous quadratic estimators that are direct measures of statistical anisotropy. As a simple illustration of our formalism we test for the existence of a preferred direction in the primordial perturbations using full-sky CMB maps. …
The Clash Of Symmetries In A Randall-Sundrum-Like Spacetime, Gareth Dando, Aharon Davidson, Damien P. George, Raymond R. Volkas, Kameshwar C. Wali
The Clash Of Symmetries In A Randall-Sundrum-Like Spacetime, Gareth Dando, Aharon Davidson, Damien P. George, Raymond R. Volkas, Kameshwar C. Wali
Physics - All Scholarship
We present a toy model that exhibits clash-of-symmetries style Higgs field kink configurations in a Randall-Sundrum-like spacetime. The model has two complex scalar fields Phi_{1,2}, with a sextic potential obeying global U(1)xU(1) and discrete Phi_1Phi_2 interchange symmetries. The scalar fields are coupled to 4+1 dimensional gravity endowed with a bulk cosmological constant. We show that the coupled Einstein-Higgs field equations have an interesting analytic solution provided the sextic potential adopts a particular form. The 4+1 metric is shown to be that of a smoothed-out Randall-Sundrum type of spacetime. The thin-brane Randall-Sundrum limit, whereby the Higgs field kinks become step functions, …
Isobar Rescattering Model And Light Scalar Mesons, Joseph Schechter
Isobar Rescattering Model And Light Scalar Mesons, Joseph Schechter
Physics - All Scholarship
We use a toy model to discuss the problem of parameterizing the possible contribution of a light scalar meson, sigma, to the final state interactions in the non leptonic decays of heavy mesons.
The Cleo Rich Detector, Raymond Mountain, Marina Artuso, R. Ayad, Konstantin Vladimirovich Bukin
The Cleo Rich Detector, Raymond Mountain, Marina Artuso, R. Ayad, Konstantin Vladimirovich Bukin
Physics - All Scholarship
We describe the design, construction and performance of a Ring Imaging Cherenkov Detector (RICH) constructed to identify charged particles in the CLEO experiment. Cherenkov radiation occurs in LiF crystals, both planar and ones with a novel ``sawtooth''-shaped exit surface. Photons in the wavelength interval 135--165 nm are detected using multi-wire chambers filled with a mixture of methane gas and triethylamine vapor. Excellent pion/kaon separation is demonstrated.
Haloes Of K-Essence, Christian Armendariz-Picon, Eugene A. Lim
Haloes Of K-Essence, Christian Armendariz-Picon, Eugene A. Lim
Physics - All Scholarship
We study gravitationally bound static and spherically symmetric configurations of k-essence fields. In particular, we investigate whether these configurations can reproduce the properties of dark matter haloes. The classes of Lagrangians we consider lead to non-isotropic fluids with barotropic and polytropic equations of state. The latter include microscopic realizations of the often-considered Chaplygin gases, which we find can cluster into dark matter halo-like objects with flat rotation curves, while exhibiting a dark energy-like negative pressure on cosmological scales. We complement our studies with a series of formal general results about the stability and initial value formulation of non-canonical scalar field …
Toy Model For Two Chiral Nonets, Joseph Schechter, Amir H. Fariborz, Renata Jora
Toy Model For Two Chiral Nonets, Joseph Schechter, Amir H. Fariborz, Renata Jora
Physics - All Scholarship
Motivated by the possibility that nonets of scalar mesons might be described as mixtures of "two quark" and "four quark" components, we further study a toy model in which corresponding chiral nonets (containing also the pseudoscalar partners) interact with each other. Although the "two quark" and "four quark" chiral fields transform identically under SU(3)_L \times SU(3)_R transformations they transform differently under the U(1)_A transformation which essentially counts total (quark + antiquark) content of the mesons. To implement this we formulate an effective Lagrangian which mocks up the U(1)_A behavior of the underlying QCD. We derive generating equations which yield Ward …
Fine Structure Of Beta Decay Endpoint Spectrum, Joseph Schechter, Samina S. Masood, Salah Nasri
Fine Structure Of Beta Decay Endpoint Spectrum, Joseph Schechter, Samina S. Masood, Salah Nasri
Physics - All Scholarship
We note that the fine structure at the endpoint region of the beta decay spectrum is now essentially known using neutrino oscillation data, if the mass of one neutrino is specified. This may help to identify the effects of nonzero neutrino masses in future experiments. An exact treatment of phase space kinematics is used. This work is independent of theoretical models. Additional restrictions due to the assumption of a so-called "complementary ansatz" for the neutrino mass matrix are also discussed.
Direct Visualization Of Dislocation Dynamics In Grain Boundary Scars, Mark Bowick, Peter Lipowsky, Jan H. Meinke, David R. Nelson, Andreas R. Bausch
Direct Visualization Of Dislocation Dynamics In Grain Boundary Scars, Mark Bowick, Peter Lipowsky, Jan H. Meinke, David R. Nelson, Andreas R. Bausch
Physics - All Scholarship
Mesoscale objects with unusual structural features may serve as the analogues of atoms in the design of larger-scale materials with novel optical, electronic or mechanical behaviour. In this paper we investigate the structural features and the equilibrium dynamics of micron-scale spherical crystals formed by polystyrene particles adsorbed on the surface of a spherical water droplet. The ground state of sufficiently large crystals possesses finite-length grain boundaries (scars). We determine the elastic response of the crystal by measuring single-particle diffusion and quantify the fluctuations of individual dislocations about their equilibrium positions within a scar determining the dislocation spring constants. We observe …
Photo-Induced Current Measurements In Chlamydomonas Cell Suspensions, Collin D. Capano
Photo-Induced Current Measurements In Chlamydomonas Cell Suspensions, Collin D. Capano
Honors Capstone Projects - All
In order to fully understand the principles behind phototaxis in flagellate algae, it is necessary to measure the electric currents these cells create when processing light stimuli. Many different techniques have been developed to do this. One of these techniques, measuring from cell suspensions, has a number of advantages over the others that makes it highly desirable. However, the lab that first developed this method of recording did not describe the setup very well. The result is that in the thirteen years since it was first reported, only one other independent lab has been able to reproduce the results despite …
Studies On Novel Semiconductor Detectors And Front-End Electronics For Heavy Flavor Decay Studies, Gustavo Kertzscher
Studies On Novel Semiconductor Detectors And Front-End Electronics For Heavy Flavor Decay Studies, Gustavo Kertzscher
Honors Capstone Projects - All
I have studied novel semiconductor detectors designed to provide precise space point information of the trajectory of charged subatomic particles produced in high energy physics (HEP) collisions. The technological thrust aims toward maintaining good performance of these detectors in a hard radiation environment for an extended period of time. My studies approached two different types of silicon devices: a whole wafer comprised of test structures and pixel devices designed for the inner vertex detector of the BTeV experiment, and small test structures of a novel type of quasi-3D detectors developed in the context of the CERN RD50 collaboration. This collaboration …
Formation Of Molecular Hydrogen On Analogues Of Interstellar Dust Grains: Experiments And Modelling, Gianfranco Vidali, Joe Roser
Formation Of Molecular Hydrogen On Analogues Of Interstellar Dust Grains: Experiments And Modelling, Gianfranco Vidali, Joe Roser
Physics - All Scholarship
Molecular hydrogen has an important role in the early stages of star formation as well as in the production of many other molecules that have been detected in the interstellar medium. In this review we show that it is now possible to study the formation of molecular hydrogen in simulated astrophysical environments. Since the formation of molecular hydrogen is believed to take place on dust grains, we show that surface science techniques such as thermal desorption and time-of-flight can be used to measure the recombination efficiency, the kinetics of reaction and the dynamics of desorption. The analysis of the experimental …
Weak Point Disorder In Strongly Fluctuating Flux-Line Liquids, Panayotis Benetatos, M. Cristina Marchetti
Weak Point Disorder In Strongly Fluctuating Flux-Line Liquids, Panayotis Benetatos, M. Cristina Marchetti
Physics - All Scholarship
We consider the effect of weak uncorrelated quenched disorder (point defects) on a strongly fluctuating flux-line liquid. We use a hydrodynamic model which is based on mapping the flux-line system onto a quantum liquid of relativistic charged bosons in 2+1 dimensions [P. Benetatos and M. C. Marchetti, Phys. Rev. B 64, 054518, (2001)]. In this model, flux lines are allowed to be arbitrarily curved and can even form closed loops. Point defects can be scalar or polar. In the latter case, the direction of their dipole moments can be random or correlated. Within the Gaussian approximation of our hydrodynamic model, …
Molecular Hydrogen Formation On Ice Under Interstellar Conditions, Hagai B. Perets, Gianfranco Vidali, Joe Roser, Sol Swords
Molecular Hydrogen Formation On Ice Under Interstellar Conditions, Hagai B. Perets, Gianfranco Vidali, Joe Roser, Sol Swords
Physics - All Scholarship
The results of experiments on the formation of molecular hydrogen on low density and high density amorphous ice surfaces are analyzed using a rate equation model. The activation energy barriers for the relevant diffusion and desorption processes are obtained. The more porous morphology of the low density ice gives rise to a broader spectrum of energy barriers compared to the high density ice. Inserting these parameters into the rate equation model under steady state conditions we evaluate the production rate of molecular hydrogen on ice-coated interstellar dust grains.
The Higgs Sector On A Two-Sheeted Space Time, Cosmin Macesanu, Kameshwar C. Wali
The Higgs Sector On A Two-Sheeted Space Time, Cosmin Macesanu, Kameshwar C. Wali
Physics - All Scholarship
We present a general formalism based on the framework of non-commutative geometry, suitable to the study the standard model of electroweak interactions, as well as that of more general gauge theories. Left- and right-handed chiral fields are assigned to two different sheets of space-time (a discretized version of Kaluza-Klein theory). Scalar Higgs fields find themselves treated on the same footing as the gauge fields, resulting in spontaneous symmetry breaking in a natural and predictable way. We first apply the formalism to the Standard Model, where one can predict the Higgs mass and the top Yukawa coupling. We then study the …
Linking Physics And Algorithms In The Random-Field Ising Model, Alan Middleton, Jan H. Meinke
Linking Physics And Algorithms In The Random-Field Ising Model, Alan Middleton, Jan H. Meinke
Physics - All Scholarship
The energy landscape for the random-field Ising model (RFIM) is complex, yet algorithms such as the push-relabel algorithm exist for computing the exact ground state of an RFIM sample in time polynomial in the sample volume. Simulations were carried out to investigate the scaling properties of the push-relabel algorithm. The time evolution of the algorithm was studied along with the statistics of an auxiliary potential field. At very small random fields, the algorithm dynamics are closely related to the dynamics of two-species annihilation, consistent with fractal statistics for the distribution of minima in the potential (``height''). For $d=1,2$, a correlation …
Flux Qubits And Readout Device With Two Independent Flux Lines, Britton Plourde, T. L. Robertson
Flux Qubits And Readout Device With Two Independent Flux Lines, Britton Plourde, T. L. Robertson
Physics - All Scholarship
We report measurements on two superconducting flux qubits coupled to a readout Superconducting QUantum Interference Device (SQUID). Two on-chip flux bias lines allow independent flux control of any two of the three elements, as illustrated by a two-dimensional qubit flux map. The application of microwaves yields a frequency-flux dispersion curve for 1- and 2-photon driving of the single-qubit excited state, and coherent manipulation of the single-qubit state results in Rabi oscillations and Ramsey fringes. This architecture should be scalable to many qubits and SQUIDs on a single chip.
Exploring Optimization For The Random-Field Ising Model, Alan Middleton, D. Clay Hambrick, Jan H. Meinke
Exploring Optimization For The Random-Field Ising Model, Alan Middleton, D. Clay Hambrick, Jan H. Meinke
Physics - All Scholarship
The push-relabel algorithm can be used to calculate rapidly the exact ground states for a given sample with a random-field Ising model (RFIM) Hamiltonian. Although the algorithm is guaranteed to terminate after a time polynomial in the number of spins, implementation details are important for practical performance. Empirical results for the timing in dimensions d=1,2, and 3 are used to determine the fastest among several implementations. Direct visualization of the auxiliary fields used by the algorithm provides insight into its operation and suggests how to optimize the algorithm. Recommendations are given for further study of the RFIM.
The Btev Rich Front End Electronics, Marina Artuso
The Btev Rich Front End Electronics, Marina Artuso
Physics - All Scholarship
We report on the design and testing of novel mixed analog and digital front end ASICs custom made for the single photon detectors considered for the BTeV RICH system. The key features are reviewed, as well as results achieved using electronics bench tests and beam studies.
Conducting Polymer And Hydrogenated Amorphous Silicon Hybrid Solar Cells, Evan L. Williams, Ghassan E. Jabbour, Qi Wang, Sean E. Shaheen, Eric A. Schiff
Conducting Polymer And Hydrogenated Amorphous Silicon Hybrid Solar Cells, Evan L. Williams, Ghassan E. Jabbour, Qi Wang, Sean E. Shaheen, Eric A. Schiff
Physics - All Scholarship
An organic-inorganic hybrid solar cell with a p-i-n stack structure has been investigated. The p-layer was a spin coated film of PEDOT:PSS poly 3,4-ethylenedioxythiophene polystyrenesulfonate. The i-layer was hydrogenated amorphous silicon a-Si:H, and the n-layer was microcrystalline silicon c-Si. The inorganic layers were deposited on top of the organic layer by the hot-wire chemical vapor deposition technique at 200 °C. These hybrid devices exhibited open circuit voltages VOC as large as 0.88 V and solar conversion efficiencies as large as 2.1%. Comparison of these devices with those incorporating a-SiC:H:B p-layers indicates that the organic layer is acting as an electrically …
Hole Drift-Mobility Measurements In Microcrystalline Silicon, T. Dylla, F. Finger, Eric A. Schiff
Hole Drift-Mobility Measurements In Microcrystalline Silicon, T. Dylla, F. Finger, Eric A. Schiff
Physics - All Scholarship
We have measured transient photocurrents on several p-i-n solar cells based on microcrystalline silicon. For two of these samples, we were able to obtain conclusive hole drift-mobility measurements. Despite the predominant crystallinity of these samples, temperature-dependent measurements were consistent with an exponential-bandtail trapping model for transport, which is usually associated with noncrystalline materials. We estimated valence bandtail widths of about 31 meV and hole band mobilities of 1–2 cm2 /V s. The measurements support mobility-edge transport for holes in these microcrystalline materials, and broaden the range of materials for which mobility-edge transport corresponds to an apparently universal band mobility of …
Temperature-Dependent Open-Circuit Voltage Measurements And Light-Soaking In Hydrogenated Amorphous Silcon Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang
Temperature-Dependent Open-Circuit Voltage Measurements And Light-Soaking In Hydrogenated Amorphous Silcon Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang
Physics - All Scholarship
We present temperature-dependent measurements of the open-circuit voltage VOC(T) in hydrogenated amorphous silicon nip solar cells prepared at United Solar. At room-temperature and above, VOC measured using near-solar illumination intensity differs by as much as 0.04 V for the as-deposited and light-soaked states; the values of VOC for the two states converge below 250 K. Models for VOC based entirely on recombination through deep levels (dangling bonds) do not account for the convergence effect. The convergence is present in a model that assumes the recombination traffic in the as-deposited state involves only bandtails, but which splits the recombination traffic fairly …
Light-Soaking Effects On The Open-Circuit Voltage Of A-Si:H Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, J. Yang
Light-Soaking Effects On The Open-Circuit Voltage Of A-Si:H Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, J. Yang
Physics - All Scholarship
We present measurements on the decline of the open-circuit voltage VOC in a-Si:H solar cells during extended illumination (light-soaking) at 295 K. We used a near-infrared laser that was nearly uniformly absorbed in the intrinsic layer of the cell. At the highest photogeneration rate (about 2x1021 cm-3), a noticeable decline (0.01 V) occurred within about 10 minutes; VOC stabilized at 0.04 V below its initial value after about 200 hours. We found that both the kinetics and the magnitudes of VOC are reasonably consistent with the predictions of a calculation combining a bandtail+defect picture for recombination and a hydrogen-collision model …
Prototype Of Fault Adaptive Embedded Software For Large-Scale Real-Time Systems, Derek Messie, Mina Jung, Jae C. Oh, Shweta Shetty, Steven Nordstrom, Michael Haney
Prototype Of Fault Adaptive Embedded Software For Large-Scale Real-Time Systems, Derek Messie, Mina Jung, Jae C. Oh, Shweta Shetty, Steven Nordstrom, Michael Haney
Electrical Engineering and Computer Science - All Scholarship
This paper describes a comprehensive prototype of large-scale fault adaptive embedded software developed for the proposed Fermilab BTeV high energy physics experiment. Lightweight self-optimizing agents embedded within Level 1 of the prototype are responsible for proactive and reactive monitoring and mitigation based on specified layers of competence. The agents are self-protecting, detecting cascading failures using a distributed approach. Adaptive, reconfigurable, and mobile objects for reliability are designed to be self-configuring to adapt automatically to dynamically changing environments. These objects provide a self-healing layer with the ability to discover, diagnose, and react to discontinuities in real-time processing. A generic modeling environment …