Digital Commons Network^™

Calculations Of Surface Effects On Phonon Modes And Raman Intensities Of Ge Quantum Dots, Shang-Fen Ren, Wei Cheng

Faculty publications – Physics

Phonon modes and Raman intensities of Ge quantum dots (QDs) with two different types of surfaces, a free standing surface or a fixed surface, in a size range from five atoms to 7 nm in diameter, are calculated by using a microscopic valence force field model. The results are compared, and the effects of surfaces on phonon properties of QDs are investigated. It is found that phonon modes and Raman intensities of QDs with these two different types of surfaces have obvious differences which clearly reveal the effects of the surfaces of QDs. The calculated results agree with existing experimental …

Dephasing Model For Spatially Extended Atomic States In Cyclotronlike Resonances, R E. Wagner, S Radovich, J Gillespie, Q Su, Rainer Grobe

Faculty publications – Physics

In recent work, the formation of ring-shaped electron distributions for hydrogen atoms in resonant static magnetic-laser fields has exclusively been associated with the impact of relativity. In this note we will generalize this statement and show that the nonlinearity associated with the nuclear binding force can trigger similarly shaped steady-state charge clouds in atoms under suitable conditions. The dephasing model, based on modeling the quantum-mechanical state by a classical ensemble of quasiparticles evolving with slightly different cyclotron periods, can recover features, in the two lowest-order resonances as well as the Coulomb-field-induced charge distributions.

Electronic Transport Through A Nuclear-Spin-Polarization-Induced Quantum Wire, Yuriy V. Pershin Dr, S. N. Shevchenko, I. D. Vagner, P. Wyder

Faculty Publications

Electron transport in a low-dimensional structure—the nuclear-spin-polarization-induced quantum wire is theoretically studied. In the proposed system the local nuclear-spin polarization creates the effective hyperfine field that confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear-spin polarization. The influence of the nuclear-spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed.

Electric-Field-Induced Relativistic Larmor-Frequency Reduction, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

Using the numerical solution to the time-dependent Dirac equation we show that the effect of relativity on the usual Larmor period for an electron in a magnetic field can be enhanced drastically if a suitably scaled and aligned static electric field is added to the interaction. This electric field does not change the electron's speed but leads to an elliptical spin precession due to relativity. This spin precession is accompanied by a position-dependent spin distribution.

Abstracts Of Papers, 80th Annual Meeting Of The Virginia Academy Of Science, May 22-24, 2002, Hampton University, Hampton, Virginia

Virginia Journal of Science

Abstracts of papers that were presented at the 80th annual meeting of the Virginia Academy of Science.

Calculations On The Size Effects Of Raman Intensities Of Silicon Quantum Dots, Wei Cheng, Shang-Fen Ren

Faculty publications – Physics

Raman intensities of Si quantum dots (QD's) with up to 11489 atoms (about 7.6 nm in diameter) for different scattering configurations are calculated. First, phonon modes in these QD's, including all vibration frequencies and vibration amplitudes, are calculated directly from the lattice-dynamic matrix by using a microscopic valence force field model combined with the group theory. Then the Raman intensities of these quantum dots are calculated by using a bond-polarizability approximation. The size effects of the Raman intensity in these QD's are discussed in detail based on these calculations. The calculations are compared with the available experimental observations. We are …

Study Of The Effectiveness Of A Web-Based Interactive Homework, Jie Liang

Theses and Dissertations

With increased use of the web in teaching there is growing interest in the effectiveness of web-based tools in facilitating student learning. I have conducted a case study on the effectiveness of web-based tutorial alternative. I designed a web-based homework tutorial about two-dimensional kinematics and conducted two experiments to evaluate its effectiveness. The evaluation focused on student?s performance and attitude. In Experiment 1, the experimental group and control group worked with the interactive web-based and regular homework respectively. Both groups worked at home. In Experiment 2, the experimental group worked with the interactive web-based homework used in Experiment 1 in …

2002 : Final Year Degree Projects In Physics, Pamphlet, Dublin Institute Of Technology

DIT Publications

No abstract provided.

De Haas-Van Alphen Oscillations In The Quasi-Two-Dimensional Organic Conductor Κ-(Et)2cu(Ncs)2: The Magnetic Breakdown Approach, V. M. Gvozdikov, Yuriy V. Pershin Dr, E. Steep, A. G. M. Jansen, P. Wyder

Faculty Publications

We present both experimental data and an analytic theory for the de Haas–van Alphen ~dHvA! effect in the two-dimensional organic single-crystal conductor k -(ET)2Cu(NCS)2. We show that the magnetization oscillation pattern and the fast Fourier transform (FFT) spectrum of our measurements are well described theoretically within the coherent magnetic breakdown (MB) model for a two-dimensional Fermi surface consisting of two open sheets and closed pockets connected by magnetic breakdown centers. The spectrum of Landau quantized energy levels changes substantially due to the MB. Landau bands develop whose bandwidth and relative distance between them oscillate in inverse magnetic field. These oscillations …

Anomalous Conductance Distribution In Quasi-One-Dimensional Gold Wires: Possible Violation Of The One-Parameter Scaling Hypothesis, Pritiraj Mohanty, Richard A. Webb

Faculty Publications

We report measurements of conductance distribution in a set of quasi-one-dimensional gold wires. The distribution includes the second cumulant or the variance which describes the universal conductance fluctuations, and the third cumulant which denotes the leading deviation. We have observed an asymmetric contribution—or, a nonvanishing third cumulant—contrary to the expectation for quasi-one-dimensional systems in the noninteracting theories in the one-parameter scaling framework, which include the perturbative diagrammatic calculations and the random matrix theory.

Women In Physics In The United States, Megan Urry, Sheila Tobias, Kim Budil, Howard Georgi, Kristine Lang, Dongqi Li, Laurie Mcneil, Peter N. Saeta, Jennifer Sokoloski, Sharon Stephenson, Aparna Venkatesan, Yevgeniya Zastavker

All HMC Faculty Publications and Research

Presents an overview of the status of women in physics in the U.S. Under-representation of women; Highlights of the report 'Women in Physics, 2000'; Efforts to increase the number of women in the profession; Issues for women activists.

Physical And Chemical Characterization Of Single Atmospheric Aerosols: Laboratory Studies Of Interactions Of Acidic Trace Gases With Sea -Salt Aerosols, And, Development Efforts For An Aerosol Charging System Using A Corona Discharge, Matthew Brigham Loomis

Doctoral Dissertations

There has long been an interest for in situ analysis of single atmospheric aerosols. To this end, the Flytrap instrument was developed under a NASA Phase I and Phase II Small Business Innovative Research Grant. The centerpiece of the instrument was a spherical void electrodynamic levitator that was used to suspend and optically characterize the physical and chemical properties of individual aerosols. Physical measurements of the aerosols were conducted with the aid of a Mie scattering system while chemical characterization was conducted with a Raman spectroscopy microprobe. A large effort focused on development of a system for charging and trapping …

Mode Conversion And Wave -Particle Interaction Processes In The Solar Wind, Edisher Kh Kaghashvili

Doctoral Dissertations

This thesis presents the theoretical study of wave coupling and wave-particle interaction processes in the solar corona and wind. We first investigate the effect of an inhomogeneous velocity field on the propagation of waves in the solar atmosphere. We find that coupling between Alfven waves and fast magnetosonic waves can occur for parameters characterizing the coronal holes. For streamer conditions, the Alfven wave couples to the slow magnetosonic mode. In the inner corona, it seems that these two possible ways of coupling do not occur simultaneously in the same structures, while beyond 5--10 R⊙ , where the plasma beta is …

Publisher's Note: Η Photoproduction On The Proton For Photon Energies From 0.75 To 1.95 Gev [Phys. Rev. Lett. 89, 222002 (2002)], M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, S. Stepanyan, L. B. Weinstein, Et Al., Clas Collaboration

Physics Faculty Publications

No abstract provided.

Bouncing Branes, Emil Prodanov

Articles

Two classical scalar fields are minimally coupled to gravity in the Kachru-Shulz-Silverstein scenario with a rolling fifth radius. A Tolman wormhole solution is found for a R x S^3 brane with Lorentz metric and for a R x AdS_3 brane with positive definite metric.

Η Photoproduction On The Proton For Photon Energies From 0.75 To 1.95 Gev, M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, S. Stepanyan, J. Yun, Et Al., Clas Collaboration

Physics Faculty Publications

Differential cross sections for γp→ηp have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W = 1.75  GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S₁₁ resonance with mass ∼1.8  GeV couples to the ηN channel.

Effect Of Applied Academics On The Final English Course Grade Of Associate Of Science Degree Students In Automotive Service Management Technology, Kathleen Habel

Abraham S. Fischler College of Education ETD Archive

Traditionally, students enrolled in two-year Automotive Service Management Technology degree programs, had a difficult time succeeding in required general education courses, especially math, English composition, and physics. They enrolled in classes open to the general student population but found that the material had little meaning or relevance to their chosen field of study. According to college records, the pass rate was less than the norm for liberal arts students. Because of this, faculty and staff decided that class material needed to be presented through applied academics. The new curriculum demonstrated the relevance of subject matter in general education classes to …

Critique Of The Wigner Tunneling Speed And A Proposed Alternative, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

In the context of superluminal propagation of wave packets through potential barriers, the tunneling speed is usually characterized by the Wigner velocity. We propose an alternative speed that takes into account the interference between the incoming and the reflected waves and leads to a better estimation of arrival time for a wave packet entering the tunneling region. This arrival time is derived by an extrapolation from inside the barrier. The analytical theory is based on the stationary phase approximation whose validity is justified by a comparison with the numerical solution of the time-dependent Dirac equation.

Abstracts Of Papers, 79th Annual Meeting Of The Virginia Academy Of Science, May 22-25, 2001, James Madison University, Harrisonburg, Virginia

Virginia Journal of Science

Abstracts of papers that were presented at the 79th Annual Meeting of the Virginia Academy of Science, May 22-25, 2001, James Madison University, Harrisonburg, Virginia.

Scaling In One-Dimensional Localized Absorbing Systems, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

Numerical study of the scaling of transmission fluctuations in the one-dimensional localization problem in the presence of absorption is carried out. Violations of single-parameter scaling for lossy systems are found and explained on the basis of a new criterion for different types of scaling behavior derived by Deych et al.

Electronic Structure Of Superconducting Mgb₂ And Related Binary And Ternary Borides, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman

Physics Faculty Research & Creative Works

First-principles full potential linear muffin-tin orbital-generalized gradient approximation electronic structure calculations of the new medium-T_c superconductor (MTSC) MgB₂ and related diborides indicate that superconductivity in these compounds is related to the existence of P_x,y-band holes at the γ point. Based on these calculations, we explain the absence of medium-T_c superconductivity for BeB₂, AlB₂, ScB₂, and YB₂. The simulation of a number of MgB₂-based ternary systems using a supercell approach demonstrates that (i) the electron doping of MgB₂ (i.e., MgB_2-yX_y with X=Be, …

Phonon Modes In Inas Quantum Dots, Shang-Fen Ren, G Qin, Deyu Lu

Faculty publications – Physics

Phonon modes in spherical InAs quantum dots (QDs) with up to 11 855 atoms (about 8.5 nm in diameter) are calculated by using a valence force field model, and all the vibration frequencies and vibration amplitudes of the QDs are calculated directly from the lattice-dynamic matrix. The projection operators of the irreducible representations of the group theory are employed to reduce the computational intensity, which further allows us to investigate the quantum confinement effect of phonon modes with different symmetries. It is found that the size effects of phonon modes depend on the symmetry of the modes. For zinc-blende structure, …

In-Situ Spectroscopic Studies Of Electronic Processes In Buckminsterfullerene Thin Films, Gordon Chambers

Doctoral

This study attempts to develop an understanding of the electronic processes active within the solid state of C60. The emphasis throughout the work has been upon the generation and spectroscopic identification of any species, which could potentially contribute to electronic conduction in thin films of C60. The relative importance of these inter-and intramolecular processes in terms of their contribution to the electronic transport is discussed through the comparison of the properties of the molecule with the properties of the bulk solid

Initially the low intensity optical properties of the C60 molecule in solution and in solid were assessed. Vibrational spectroscopy …

Velocity Field Distributions Due To Ideal Line Vortices, Thomas D. Levi, David C. Montgomery

Dartmouth Scholarship

We evaluate numerically the velocity field distributions produced by a bounded, two-dimensional fluid model consisting of a collection of parallel ideal line vortices. We sample at many spatial points inside a rigid circular boundary. We focus on “nearest-neighbor” contributions that result from vortices that fall (randomly) very close to the spatial points where the velocity is being sampled. We confirm that these events lead to a non-Gaussian high-velocity “tail” on an otherwise Gaussian distribution function for the Eulerian velocity field. We also investigate the behavior of distributions that do not have equilibrium mean-field probability distributions that are uniform inside the …

Experimental And Theoretical Investigation Of Stratospheric Ozone Depletion In The Northern Hemisphere Caused By Heterogeneous Chemistry, Rune Storvold

Theses (Unassigned)

Stratospheric ozone is of crucial importance for life on Earth. This thin layer protects us from the ultraviolet solar radiation and also works as a greenhouse gas that helps maintaining our climate. Large changes in thickness and vertical distribution of the ozone abundance may have detrimental effects on life on Earth. But even small changes could have considerable impact on UV irradiance, bio-production and cancer rates. During the last decade record low spring time vertical column amounts of stratospheric ozone have been observed over Northern Europe. However, this decrease is not as severe as the depletion observed over Antarctica and …

Large-Scale Synchrony In Weakly Interacting Automata, Eric J. Friedman, Adam S. Landsberg

WM Keck Science Faculty Papers

We study the behavior of two spatially distributed (sandpile) models which are weakly linked with one another. Using a Monte Carlo implementation of the renormalization-group and algebraic methods, we describe how large-scale correlations emerge between the two systems, leading to synchronized behavior.

Effects Of Relativity On The Time-Resolved Tunneling Of Electron Wave Packets, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

We solve numerically the time-dependent Dirac equation for a quantum wave packet tunneling through a potential barrier. We analyze the spatial probability distribution of the transmitted wave packet in the context of the possibility of effectively superluminal peak and front velocities of the electron during tunneling. Both the Dirac and Schrodinger theories predict superluminal tunneling speeds. However, in contrast to the Dirac theory the Schrodinger equation allows a possible violation of causality. Based on an analysis of the tunneling process in full temporal and spatial resolution, we introduce an instantaneous tunneling speed that can be computed inside the potential barrier.

Boolean Functions With Important Cryptographic Properties., Subhamoy Maitra Dr.

Doctoral Theses

In this thesis we concentrate on properties of cryptographically significant Boolean functions.The techniques are mainly combinstorial and provide new resulta on enumeration and construction of such functions. Initially we concentrate on a partieular subset of Boolean functions called the symmetric Boolean functions. A closed form expression for the Walsh transform of an arbitrary symmetric Boolean function is presented. We completely characterize the symmetric functions with maximum nonlinearity and show that the maximum nonlinearity of n-variable symmetrie function can be 2n-1-2[n-1l2], Moreover, new classes of symmetric balanced and symmetric correlation immune functions are considered.We provide a randomised heuristic to construct balanced …

Neutrino Reactions On The Deuteron, S. Nakamura, T. Sato, Vladimir Gudkov, K. Kubodera

Faculty Publications

The cross sections for the ν-d and ν̅ -d reactions are calculated for incident energy up to E_ν=170 MeV with the use of a phenomenological Lagrangian approach. We assess and improve the reliability of the employed calculational method by examining the dependence of the results on various input and approximations that go into the calculation. The main points of improvement over the existing work are (1) use of the “modern” NN potentials, (2) use of the more accurate nucleon weak-interaction form factors, and (3) monitoring the strength of a vertex that governs the exchange-current contribution, with the use …

Diamagnetic Persistent Current In Diffusive Normal-Metal Rings, E. M.Q. Jariwala, P. Mohanty, M. B. Ketchen, Richard A. Webb

Faculty Publications

We have measured a diamagnetic persistent current with flux periodicities of both h/e and h/2e in an array of thirty diffusive mesoscopic gold rings. At the lowest temperatures, the magnitudes of the currents per ring corresponding to the h/e- and h/2e-periodic responses are both comparable to the Thouless energy E_c≡ħ/τ_D, where τ_D is the diffusion time. Taken in conjunction with earlier experiments, our results strongly challenge the conventional theories of persistent current. We consider a new approach associated with the saturation of …