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Full-Text Articles in Physics
Real Space Information From Fluctuation Electron Microscopy: Applications To Amorphous Silicon, Parthapratim Biswas, Raymond Atta-Fynn, S. Chakraborty, D. A. Drabold
Real Space Information From Fluctuation Electron Microscopy: Applications To Amorphous Silicon, Parthapratim Biswas, Raymond Atta-Fynn, S. Chakraborty, D. A. Drabold
Faculty Publications
Ideal models of complex materials must satisfy all available information about the system. Generally, this information consists of experimental data, information implicit to sophisticated interatomic interactions and potentially other a priori information. By jointly imposing first-principles or tight-binding information in conjunction with experimental data, we have developed a method: experimentally constrained molecular relaxation (ECMR) that uses all of the information available. We apply the method to model medium range order in amorphous silicon using fluctuation electron microscopy (FEM) data as experimental information. The paracrystalline model of medium range order is examined, and a new model based on voids in amorphous …
Relativistic Multiple Scattering Theory And The Relativistic Impulse Approximation, Khin Maung Maung, John W. Norbury, Trina Coleman
Relativistic Multiple Scattering Theory And The Relativistic Impulse Approximation, Khin Maung Maung, John W. Norbury, Trina Coleman
Faculty Publications
It is shown that a relativistic multiple scattering theory for hadron - nucleus scattering can be consistently formulated in four dimensions in the context of meson exchange. We give a multiple scattering series for the optical potential and discuss the differences between the relativistic and non- relativistic versions. We develop the relativistic multiple scattering series by separating out the one-boson exchange term from the rest of the Feynman series. However, this particular separation is not absolutely necessary and we discuss how to include other terms. We then show how to make a three- dimensional reduction for hadron - nucleus scattering …
Experimentally Constrained Molecular Relaxation: The Case Of Hydrogenated Amorphous Silicon, Parthapratim Biswas, Raymond Atta-Fynn, D. A. Drabold
Experimentally Constrained Molecular Relaxation: The Case Of Hydrogenated Amorphous Silicon, Parthapratim Biswas, Raymond Atta-Fynn, D. A. Drabold
Faculty Publications
We have extended our experimentally constrained molecular relaxation technique [P. Biswas et al., Phys. Rev. B 71, 54204 (2005)] to hydrogenated amorphous silicon: a 540-atom model with 7.4% hydrogen and a 611-atom model with 22% hydrogen were constructed. Starting from a random configuration, using physically relevant constraints, ab initio interactions, and the experimental static structure factor, we construct realistic models of hydrogenated amorphous silicon. Our models confirm the presence of a high-frequency localized band in the vibrational density of states due to Si-H vibration that has been observed in recent vibrational transient grating measurements on plasma enhanced chemical …
Measurement Of Population Dynamics In Stimulated Raman Adiabatic Passage, Alina Gearba, H. A. Camp, M. L. Trachy, G. Veshapidze, M.H. Shah, H.U. Jang, B.D. Depaola
Measurement Of Population Dynamics In Stimulated Raman Adiabatic Passage, Alina Gearba, H. A. Camp, M. L. Trachy, G. Veshapidze, M.H. Shah, H.U. Jang, B.D. Depaola
Faculty Publications
The temporal evolution of populations has been directly measured for a three-level ladder system undergoing coherent excitation by stimulated Raman adiabatic passage (STIRAP). The measurement technique makes use of charge transfer as diagnostic. The method is model independent and has a temporal resolution of a few nanoseconds. The temporal evolution is measured for several values of the delay between the pump and Stokes laser pulses that are part of the STIRAP excitation scheme. The corresponding quantum Liouville equations are solved and the results of the calculations are compared with experiment.
Multiscale Mode Dynamics Of A Tethered Membrane, Ras B. Pandey, Kelly L. Anderson, B. L. Farmer
Multiscale Mode Dynamics Of A Tethered Membrane, Ras B. Pandey, Kelly L. Anderson, B. L. Farmer
Faculty Publications
Stochastic dynamics of a tethered membrane with a bond-fluctuating coarse-grained Monte Carlo simulation shows, in addition to diffusion, nondiffusive behavior sensitive to the type of membrane, its size, and quality of the solvent. Motion of the membrane’s center node is described by the variation of the mean-square displacement (R2n) with time step (t), i.e., R2n∝t2ν with the exponent ν≃1/8−1∕6 in the short time followed by subdiffusive power laws (i.e., ν∼1∕5, 1∕10) in the intermediate time regimes before reaching diffusion ν=1. The crossover between in-plane wrinkle modes is identified from the segmental (node) motion of the membrane.
Model-Independent Measurement Of The Excited Fraction In A Magneto-Optical Trap, M. H. Shah, H. A. Camp, M. L. Trachy, G. Veshapidze, M.A. Gearba, B.D. Depaola
Model-Independent Measurement Of The Excited Fraction In A Magneto-Optical Trap, M. H. Shah, H. A. Camp, M. L. Trachy, G. Veshapidze, M.A. Gearba, B.D. Depaola
Faculty Publications
In many experiments involving a magneto-optical trap (MOT) it is of great importance to know the fraction of atoms placed in an excited state due to the trapping process. Generally speaking, researchers have had to use overly simplistic and untested models to estimate this fraction. In this work, the excited fractions of 87Rb atoms in a MOT are directly measured using a charge transfer technique, for a range of MOT parameters. Simple models are then fit to the measured fractions. Using the results of this work, the excited fraction of 87Rb atoms trapped in a MOT can be …
Split Quaterionic Representation Of Sdym (Su(1,1) Instantons In S2- × S2+, Sungwook Lee, Khin Maung Maung
Split Quaterionic Representation Of Sdym (Su(1,1) Instantons In S2- × S2+, Sungwook Lee, Khin Maung Maung
Faculty Publications
Using split‐quaternions, we find explicit SDYM SU(1,1) instanton solutions in S2- × S2+ which is the conformal compactification of the semi‐Euclidean 4‐spacetime R2+2 of split signature (-,-,+,+). It is also shows that SDYM and ASDYM fields in S2- × S2+ can be described as simple split-quaternionic 2-forms.
Parametrizations Of Inclusive Cross Sections For Pion Production In Proton-Proton Collisions. Ii. Comparison To New Data, John W. Norbury, Lawrence W. Townsend
Parametrizations Of Inclusive Cross Sections For Pion Production In Proton-Proton Collisions. Ii. Comparison To New Data, John W. Norbury, Lawrence W. Townsend
Faculty Publications
A set of new, precise data have recently been made available by the NA49 Collaboration for charged pion production in proton-proton and proton-Carbon reactions at 158 GeV. The current paper compares this new data to five currently available arithmetic parameterizations. Although a precise fit is not expected, two of the parameterizations do not work very well but the other three are able to provide a moderately good, but not precise fit to the proton-proton data. The best two of these three parameterizations are scaled to the proton-Carbon data and again provide a moderately good, but not precise fit.
Threshold Meson Production And Cosmic Ray Transport, John W. Norbury, Lawrence W. Townsend, Ryan B. Norman
Threshold Meson Production And Cosmic Ray Transport, John W. Norbury, Lawrence W. Townsend, Ryan B. Norman
Faculty Publications
An interesting accident of nature is that the peak of the cosmic ray spectrum, for both protons and heavier nuclei, occurs near the pion production threshold. The Boltzmann transport equation contains a term which is the cosmic ray flux multiplied by the cross section. Therefore when considering pion and kaon production from proton - proton reactions, small cross sections at low energy can be as important as larger cross sections at higher energy. This is also true for subthreshold kaon production in nuclear collisions, but not for subthreshold pion production.
Differential Cross Sections For Electromagnetic Dissociation, John W. Norbury, Anne Adamczyk
Differential Cross Sections For Electromagnetic Dissociation, John W. Norbury, Anne Adamczyk
Faculty Publications
Differential cross; sections for electromagnetic dissociation in nucleus-nucleus collisions are calculated. The kinetic energy distributions is parameterized with a Boltzmann distribution and the angular distribution is assumed isotropic in the projectile frame. In order to be useful for three-dimensional transport codes, these cross sections are available in both the projectile and lab frames. Comparison between theory and experiment is good. The formalism applies to single and multiple nucleon removal, a particle removal, and fission in electromagnetic reactions of nuclei. (c) 2006 Elsevier B.V. All rights reserved.
Parameterized Total Cross Sections For Pion Production In Nuclear Collisions, John W. Norbury, Lawrence W. Townsend
Parameterized Total Cross Sections For Pion Production In Nuclear Collisions, John W. Norbury, Lawrence W. Townsend
Faculty Publications
Total inclusive cross sections for neutral and charged pion production in proton–nucleus and nucleus–nucleus reactions have been calculated and compared to experiment. Nucleon–nucleon theoretical cross sections have been scaled up to nuclear collisions using a scaling factor similar to (APAT)2/3, where AP and AT are the nucleon numbers of the projectile and target nuclei. Variations in the power of this scaling factor have been studied and a good fit to experiment is obtained with a small modification of the power. Theoretical cross sections are written in a form that is very …