Physical Sciences and Mathematics Commons^™

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.

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, …

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.

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 …

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 …

Spectral Equivalence Of Bosons And Fermions In One-Dimensional Harmonic Potentials, Michael Crescimanno, Adam S. Landsberg

WM Keck Science Faculty Papers

Recently, Schmidt and Schnack [Physica A 260, 479 (1998)], following earlier references, reiterate that the specific heat of N noninteracting bosons in a one-dimensional harmonic well equals that of N noninteracting fermions in the same potential. We show that this peculiar relationship between heat capacities results from a more dramatic equivalence between Bose and Fermi systems. Namely, we prove that the excitations of such Bose and Fermi systems are spectrally equivalent. Two complementary proofs of this equivalence are provided; one based on a combinatoric argument, the other from analysis of the underlying dynamical symmetry group.

Dirac Theory Of Ring-Shaped Electron Distributions In Atoms, P Krekora, R E. Wagner, Q Su, Rainer Grobe

Faculty publications – Physics

The time-dependent Dirac equation is solved numerically on a space-time grid for an atom in a strong static magnetic field and a laser field. The resonantly induced relativistic motion of the atomic electron leads to a ringlike spatial probability density similar to the features that have been recently predicted [Wagner, Su, and Grobe, Phys. Rev. Lett. 84, 3282 (2000)] based on a phase-space method. We further demonstrate that spin-orbit coupling for a fast-moving electron in such an atom becomes significant and the time dependence of the spin can dephase even if initially aligned parallel to the direction of the static …

Significance Of The Sagnac Effect, Pal R. Molnar

Pal R. Molnar

During the historical development, the notions of electrodynamics and the theory light have become complicated complexes of concepts [1]. And what is more, nowadays they are wholly confused. The laws of electrodynamics in present form are not valid in rotating and deforming systems [2]. These turbulent notion-complexes -of which inadequacy to the inner connections are verified by experiments, measurements results, as well as certain electrodynamical states and processes- have to be broken open, disintegrated, then disjoined. Henceforth, we must search those genuine, pure and simple electrodynamical ideas, which can already join in the immanent natural well and adequate manner. Consequently, …

Higher Twist Corrections And Maxima For Dis On A Proton In The High Density Qcd Region, E. Gotsman, Eugene Levin, U. Maor, L. Mclerran, Kirill Tuchin

Kirill Tuchin

We show that the ratio of different structure functions have a maximum which depends on energy. We argue, using the Golec-Biernat and Wusthoff model as well as the eikonal approach, that these maxima are functions of the saturation scale. We analyze leading and higher twist contributions for different observables to check whether a kinematic region exists where high parton density effects can be detected experimentally.

The Ep → E'P Η Reaction At And Above The S₁₁ (1535) Baryon Resonance, R. Thompson, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, L. M. Qin, L. B. Weinstein, Et Al., The Clas Collaboration

Physics Faculty Publications

New cross sections for the reaction ep → ep η are reported for total center of mass energy W = 1.5-1.86 GeV and invariant momentum transfer Q² = 0.25-1.5 (GeV/c)². This large kinematic range allows extraction of important new information about response functions, photocouplings, and etaN coupling strengths of baryon resonances. Newly observed structure at W ~ 1.65 GeV is shown to come from interference between S and P waves and can be interpreted with known resonances. Improved values are derived for the photon coupling amplitude for the S₁₁(1535) resonance.

Electroproduction Of The Λ(1520) Hyperon, M. Bektasoglu, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, S. E. Kuhn, R. A. Niyazov, L. B. Weinstein, Et Al., The Clas Collaboration

Physics Faculty Publications

The reaction e^→pe′K⁺Λ(1520) with Λ(1520)→p′K⁻ was studied at electron beam energies of 4.05, 4.25, and 4.46 GeV, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cos θ_K+, φ_K+, Q², and W dependencies of Λ(1520) electroproduction are presented for the kinematic region 0.9 < Q² < 2.4 GeV² and 1.95 < W < 2.65 GeV. Also, the Q² dependence of the Λ(1520) decay angular distribution is presented for the first time. The cosθ_K+ angular distributions suggest t-channel diagrams dominate the production process. Fits to the Λ(1520) t-channel helicity frame decay angular distributions indicate the m …