Physical Sciences and Mathematics Commons^™

Driven Diffusion Of Particles, First-Passage Front, And Interface Growth, R. Bidaux, Ras B. Pandey

Faculty Publications

We study a computer-simulation model for driven particles on a discrete lattice where a fraction p of the lattice sites is randomly occupied by frozen impurities (barriers), and an imposed bias governs the particles’ hopping through the lattice. These particles (the carriers) are initially released from a source of wetting fluid from one end of the lattice in order to wet and the dry lattice on their trails. We study the transport of particles, frontier of their trail, and the growth of the interface between the wet and dry regions as a function of the biased field and the number …

Proposal For A Dod Combined Battlefield Electromagnetic Environmental Effects (E3) Initiative, George H. Baker Iii

Department of Integrated Science and Technology - Faculty Scholarship

The presentation emphasizes the growing importance of electromagnetic survivability and compatibility. Operation Desert Storm demonstrated the clear military advantage provided by sophisticated electronic weapon and communication systems. In addition, the offensive tactic of taking out the enemy's eyes and ears during the air war paid off, giving our military decisive air superiority. The lessons for the future are clear. High-tech electronics now so dominates the battlefield that the outcome of future conflicts could well be decided by electronics attrition rather than human casualties. Our Desert Storm experience thus accentuates the importance of guaranteeing that our electronic systems will not be …

Order And Chaos In Semiconductor Microstructures, W. A. Lin, John B. Delos, Robert E. Jensen

Arts & Sciences Articles

The semiclassical theory of ballistic electron transport in semiconductor microstructures provides a description of the quantum conductance fluctuations in terms of the classical distributions for the lengths and directed areas of the scattering trajectories. Because the classical dynamics differs for integrable (circular) and chaotic (stadium) scattering domains, experimental measurements of the conductance of these microstructures provide a unique probe of the quantum properties of classically regular and chaotic systems. To advance these theoretical and experimental studies we compare geometrical formulas for the classical distributions of lengths and areas with numerical simulations for microstructures examined in recent experiments, we assess the …

Quantal And Classical Correspondence Of Double Scattering, Jianyi Wang, Ronald E. Olson, Karoly Tokési

Physics Faculty Research & Creative Works

Electron emission from atom-atom collisions is analyzed within the framework, of both quantal and classical dynamics. We examine the effect of explicit electron-electron (e-e) interactions on the ejected electron spectra in hard collisions involving simultaneous excitation and ionization in the collision of two structured atoms. A double scattering sequence represented by a second order Bom approximation has been shown to give a dominant contribution over the single scattering to projectile ionization. A classical simulation confirms the double scattering process is analogous to the Thomas two-step capture mechanism. We find good agreement between quantal and classical calculations, showing the convergence of …

Resonant And Non-Resonant Pieces Of The D\Rightarrow \Bar{K}Π Semileptonic Transition Amplitude, Joseph Schechter, A. Subbaraman, S. Surya

Physics - All Scholarship

We compare the resonant and non-resonant contributions in various regions of phase space for the D\rightarrow \bar{K}\p semileptonic transition amplitude, computed in a chiral model which incorporates the heavy quark symmetry. Remarks on the significance for experiment and for chiral perturbation theory are made. hep-ph/yymmnnn

Transition From Quantum To Quasi-Classical Behaviour Of The Binary Encounter Peak In Collisions Of 0.6 To 3.6 Mev Amu“¹ I23+ And Xe21+ With He And Ar, J. L. Shinpaughfg, W. Wolff, H. E. Wolff, U. Ramm, O. Jagutzki, H. Schmidt-Böcking, J. Wangt, Ronald E. Olson

Physics Faculty Research & Creative Works

Double differentia] cross sections are reported for the production of binary encounter electrons in collisions of 0.6 MeV amu^-1 I²³⁺ and 1.4, 2.4, and 3.6 MeV amu^-1 Xe²¹⁺ projectiles incident on He and Ar targets. Electron energy spectra were measured between 0: and 45: in the case of the two lower projectile energies, and between 17.5° and 60- for the two higher projectile energies. The data are compared with quantum mechanical impulse approximation and classical trajectory Monte Carlo calculations. While the quantum model calculation predicts a rapid disappearance of diffraction effects in the binary encounter peak …

Mirrorless All‐Optical Bistability In Bacteriorhodopsin, D.V.G.L.N. Rao, F. J. Aranda, B. J. Wiley, J. A. Akkar, D. L. Kaplan, J. F. Roach

Physics Faculty Publications

We report direct observations of all‐optical mirrorless bistability associated with saturable absorption in three kinds of bacteriorhodopsin (BR) samples: wild‐type BR in water solution and dispersed in thin films of a polymer matrix as well as water solution of the genetically engineered mutant BR_D96N. The experiments are carried out with picosecond pulses at 532 nm. The values measured for the saturation intensity are explained in terms of the relaxation of the excited M state population to the B state of the BR photocycle for the three kinds of samples studied.

Review Of Genius In The Shadows: A Biography Of Leo Szilard, The Man Behind The Bomb By William Lanouette And Bela Silard, David W. Hafemeister

Physics

No abstract provided.

Numerical Study Of A High-Order Quasiconserved Quantity In The Henon-Heiles Problem, Paul Finkler, C. Edward Jones, Glenn A. Sowell

Physics Faculty Publications

Recent efforts to derive and study a quasiconserved quantity K in the Henon-Heiles problem in terms of a single set of variables are discussed. Numerical results are given, showing how the value of such a quantity varies with time and order in a power-series expansion for K in terms of monomials of the coordinates and velocities. The lowest order in the power series for K corresponds to n =4 and the highest order to n =27, so that 24 orders are included in the series. The results are compared with an earlier study by the authors [Phys. Rev. A 42, …

Numerical Study Of A High-Order Quasiconserved Quantity In The Henon-Heiles Problem, Paul Finkler, C. Edward Jones, Glenn A. Sowell

Paul Finkler Papers

Recent efforts to derive and study a quasiconserved quantity K in the Henon-Heiles problem in terms of a single set of variables are discussed. Numerical results are given, showing how the value of such a quantity varies with time and order in a power-series expansion for K in terms of monomials of the coordinates and velocities. The lowest order in the power series for K corresponds to n =4 and the highest order to n =27, so that 24 orders are included in the series. The results are compared with an earlier study by the authors [Phys. Rev. A 42, …

A Masing [Fe Xi] Line, Gary J. Ferland

Physics and Astronomy Faculty Publications

I draw attention to a maser which occurs within the ground term of Fe¹⁰⁺. In many photoionized environments, infrared fine-structure lines and the [O I] λ6300 line become optically thick but maser amplification of ionic fine-structure lines is unusual. During the course of development of a code designed to simulate gas under radiative-collisional equilibrium, the radiative transfer of roughly 500 ionic/atomic emission lines was treated using escape probabilities. Nearly all forbidden lines can become optically thick under extreme conditions, but the ³Pj = 1, 0 [Fe XI] 6.08 μm transition is the only line …

On The Escape Of Oxygen And Hydrogen From Mars, Jane L. Fox

Physics Faculty Publications

Escape rates of oxygen atoms from dissociative recombination of O₂⁺ above the Martian exobase are computed in light of new information from ab initio calculations of the dissociative recombination process, and our recently revised understanding of the Martian dayside ionosphere. Only about 60% of the dissociative recombinations occur in channels in which the O atoms are released with energies in excess of the escape velocity. Futhermore, we find that the computed escape fluxes for O depend greatly on the nature of the ion loss process that has been found necessary to reproduce the topside ion density profiles measured …

Photoabsorption Spectra Of Atoms In Parallel Electric And Magnetic Fields, J. M. Mao, K. A. Rapelje, S. J. Blodgett-Ford, John B. Delos, A. König, H. Rinneberg

Arts & Sciences Articles

Measurements have been made of the absorption spectrum of Ba from the 6s6p 1P1 level to states near the ionization threshold in parallel electric and magnetic fields. The absorption spectrum shows oscillations superposed on a smooth background. Each oscillation is correlated with a closed orbit of the electron. At strong electric fields, trajectories are regular, and closed orbits form orderly patterns. For weak electric fields, trajectories are chaotic, and many more closed orbits are present. Many of these are produced by bifurcations as the electric field is reduced.

Two Measurements Of B0 B-0 Mixing, J. Bartelt, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

We have measured the B0B¯0 mixing probability, χd, using a sample of 965 000 BB¯ pairs from Υ(4S) decays. Counting dilepton events, we find χd=0.157±0.016±0.018+0.028−0.021. Using tagged B0 events, we find χd=0.149±0.023±0.019±0.010. The first (second) error is statistical (systematic). The third error reflects a ±15% uncertainty in the assumption, made in both cases, that charged and neutral B pairs contribute equally to dilepton events. We also obtain a limit on the CP impurity in the B0d system, ‖Re(ε0B)‖

Convective Turing Patterns, D. A. Vasquez, J. W. Wilder, Boyd F. Edwards

All Physics Faculty Publications

Turing patterns involve regions of different chemical compositions which lead to density gradients that, in liquids, are potentially unstable hydrodynamically. Nonlinear hydrodynamics coupled with a model of Turing pattern formation show that convection modifies and coexists with some Turing patterns and excludes others, and thereby plays a significant role in pattern selection.

Solar Cycle And Seasonal Variationsin F Region Electrodynamics At Millstone Hill, M. J. Buonsanto, M. E. Hagan, J. E. Salah, Bela G. Fejer

Bela G. Fejer

Incoherent scatter radar observations of ion drifts taken at Millstone Hill (42.6°N, 288.5°E) during 73 experiments in the period February 1984 to February 1992 are used to construct, for the first time at this station, average quiet-time E×B drift patterns for both solar cycle maximum and minimum, for the summer, winter, and equinox seasons. The daily variation of V⊥N shows a reversal from northward to southward drifts near noon, and a return to northward drifts in the premidnight hours. The weaker southward drift in the afternoon in summer noted by Wand and Evans (1981) is shown to occur only at …

Semiclassical Approach To Quantum-Mechanical Problems With Broken Supersymmetry, Ranabir Dutt, Asim Gangopadhyaya, Avinash Khare, A. Pagnamenta, Uday P. Sukhatne

Physics: Faculty Publications and Other Works

The semiclassical WKB approximation method is reexamined in the context of nonrelativistic quantum-mechanical bound-state problems with broken supersymmetry (SUSY). This gives rise to an alternative quantization condition (denoted by BSWKB) which is different from the standard WKB formula and also different from the previously studied supersymmetric (SWKB) formula for unbroken SUSY. It is shown that to leading order in ħ, the BSWKB condition yields exact energy eigenvalues for shape-invariant potentials with broken SUSY (harmonic oscillator, Pöschl-Teller I and II) which are known to be analytically solvable. Further, we show explicitly that the higher-order corrections to these energy eigenvalues, up to …

Photoluminescence Spectroscopy Of Zinc Germanium Diphosphide (Zngep2), Jack E. Mccrae

Theses and Dissertations

Zinc germanium diphosphide (ZnGeP₂) is a chalcopyrite semiconductor with strong nonlinear optical properties and potential application to Air Force interests. The characteristics of this material have been studied using photoluminescence (PL) spectroscopy. The PL spectrum is dominated by transitions from the conduction band to a deep acceptor level, and features in the spectrum suggest that more than one transition is being observed. The PL is partially polarized, and the degree of polarization appears to differ for each feature in the spectrum. The relative PL intensity of these features are seen to depend upon the wavelength of the excitation …

Resonant Two-Color Detachment Of H- With Excitation Of H(N=2), Ning-Yi Du, Anthony F. Starace, N.A. Cherepkov

Anthony F. Starace Publications

The cross sections for resonant two-color, two-photon detachment of H^- with excitation of the degenerate H(2s) and H(2p) levels are calculated within a semiempirical adiabatic hyperspherical representation. The first photon, with energy ω₁=0.4017 a.u., is resonant with the well-known Feshback ¹P⁰ resonance below the H(n=2) threshold. The second photon, with energy ω₂≥0.126 05 a.u., scans the energy region above the H(n=2) threshold over which long-range dipole-field-induced cross-section oscillations are predicted to occur. Such Gailitis-Damburg oscillations have not yet been observed experimentally. Results for various pairs …

Short-Pulse Detachment Of H- In The Presence Of A Static Electric Field, Qiaoling Wang, Anthony F. Starace

Anthony F. Starace Publications

Quantum interference effects occurring in photodetachment of H^- in the presence of a uniform, static electric field are shown theoretically to be controllable through use of short laser pulses having characteristic times comparable to photodetached electron reflection times. In particular, calculated cross sections for single-photon detachment by two laser pulses that are delayed and phase shifted relative to one another are shown to oscillate as a function of the relative phases of the laser pulses at fixed photodetached electron energy.

Characteristics Of Ion Flow In The Quiet Inner Plasma Sheet, V. Angelopoulos, C. F. Kennel, F. V. Coroniti, R. Pellat, Harlan E. Spence, Margaret G. Kivelson, Raymond J. Walker, W. Baumjohann, W. C. Feldman, J. T. Gosling, C. T. Russell

Physics & Astronomy

Abstract

We use AMPTE/IRM and ISEE 2 data to study the properties of the high beta (β_i > 0.5) plasma sheet, the inner plasma sheet (IPS). Bursty bulk flows (BBFs) are excised from the two databases, and the average flow pattern in the non-BBF (quiet) IPS is constructed. At local midnight this ensemble-average flow is predominantly duskward; closer to the flanks it is mostly earthward. The flow pattern agrees qualitatively with calculations based on the Tsyganenko [1987] model (T87), where the earthward flow is due to the ensemble-average cross tail electric field and the duskward flow is the diamagnetic drift …

Pseudostable Bubbles, Marcelo Gleiser

Dartmouth Scholarship

The evolution of spherically symmetric unstable scalar field configura- tions (“bubbles”) is examined for both symmetric (SDWP) and asymmet- ric (ADWP) double-well potentials. Bubbles with initial static energiesE0 ∼< Ecrit, where Ecrit is some critical value, shrink in a time scale deter- mined by their linear dimension, or “radius”. Bubbles with E0 ∼> Ecrit evolve into time-dependent, localized configurations which are very long-lived com- pared to characteristic time-scales in the models examined. The stability of these configurations is investigated and possible applications are briefly discussed.

Altering The Gd(0001) Surface Electronic Structure With Hydrogen Adsorption, Dongqi Li, Jiandi Zhang, Peter A. Dowben, M. Onellion

Peter Dowben Publications

Hydrogen adsorption on Gd(0001) has been studied with angle-resolved photoemission. Hydrogen adsorption attenuates the surface state near E_F on the clean Gd(0001) surfaces and induces two two-dimensional bands which are at 3.8 eV and about 6 eV near Γ¯. The state with the smaller binding energy has dz2 character at Γ¯ and disperses away from E_F about 1 eV. The state at the greater binding energy disperses toward E_F about 0.5–1 eV. At low substrate temperatures (120–130 K), the hydrogen chemisorption on the Gd(0001) surface results in a work-function decrease of 0.2 eV. The correlation between the …

Resistivity Of The High-Temperature Metallic Phase Of Vo2, Werner W. Schulz, Philip B. Allen, Renate M. Wentzcovitch, Paul C. Canfield

Paul C. Canfield

Measurements are reported on the electrical resistivity ρ(T) along the c axis of a single crystal of VO2, from the metal-insulator transition at T=333 K up to 840 K. The temperature dependence is very linear, and a fit to Bloch-Grüneisen theory gives a residual resistivity ρ0=65 μΩ cm and a ratio ρ(840 K)/ρ0=8. With the help of a local-density-approximation band-structure calculation, we further pursue the conventional (Bloch-Boltzmann) interpretation by extracting the electron-phonon coupling constant λ=1.1 and the mean free path l(800 K)=3.3 Å. The short mean free path implies that the conventional interpretation is internally inconsistent. The most likely explanation …

Dependence Of Binary Encounter Electron Production On The Charge State Of The Recoil Ion, Jee-Ching Wang, Ronald E. Olson, H. Wolf, J. Shinpaugh, W. Wolff, H. Schmidt Böcking

Chemical and Biochemical Engineering Faculty Research & Creative Works

We study the dependence of the production of binary encounter electrons on the charge state of recoil ions for 2.4 MeV u^-l Xe²¹⁺ on He and Ar. Doubly differential cross sections of electron emission are calculated with the ncrMC method. We find that the contributions to the binary electron cross section from various recoil ion charge states reach a maximum near Ar⁵⁺ for the Ar target. In the case of the He target; double ionization dominates over single ionization for alt ejected electron energies above 100 eV. However, an unexpected local drop of double ionization in the …

K-Shell Ionization Of Atoms By Electron And Positron Impact, S. P. Khare, Vandana Saksena, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

In the plane-wave Born approximation (PWBA), scaling relations for K-shell generalized oscillator strengths and energy-loss cross sections of atoms are given. The total K-shell ionization cross sections, obtained at high impact energy, are used to obtain the Bethe collisional parameter c_K for atoms ranging from carbon to gold. These values of c_K are, in general, significantly different from those obtained previously with the help of Fano plots at relatively low impact energies. Furthermore, using Hippler’s modification of the PWBA [Phys. Lett. A 144, 81 (1990)], total K-shell ionization cross sections of various atoms by …

Cellular Track Model For Study Of Heavy Ion Beams, Judy L. Shinn, Robert Katz, Francis A. Cucinotta, John W. Wilson, Duc M. Ngo

Robert Katz Publications

Track theory is combined with a realistic model of a heavy ion beam to study the effects of nuclear fragmentation on cell survival and biological effectiveness . The effects of secondary reaction products are studied as a function of depth in a water column. Good agreement is found with experimental results for the survival of human T-1 cells exposed to monoenergetic carbon, neon, and argon beams under aerobic and hypoxic conditions. The present calculation, which includes the effect of target fragmentation, is a significant improvement over an earlier calculation because of the use of a vastly improved beam model with …

Three-Point Correlation Functions In Uniformly And Randomly Driven Diffusive Systems, K. Hwang, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

Driven far away from equilibrium by both uniform and random external fields, a system of diffusing particles with short-range attractive forces displays many singular thermodynamic properties. Surprisingly, measuring pair correlations in lattice-gas models with saturation drives, we find little difference between the uniform and random cases, even though the underlying symmetries are quite distinct. Motivated by this puzzle, we study three-point correlations using both field-theoretic and simulation techniques. The continuum theory predicts the following: (a) The three-point function is nonzero only for the uniformly driven system; (b) it is odd under a parity transformation; and (c) there exists an infinite …

Transverse Form Factors Of 117sn, H Baghaei, J Dubach, M B. Frodyma, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson

Gerald Alvin Peterson

Transverse elastic and inelastic form factors for low-lying levels in 117Sn have been measured by 180° electron scattering in the momentum transfer range qeff=1.1–2.4 fm-1. The simple independent-particle model fails to account for these data, predicting form factors that are much too large. In better quantitative agreement with the data are the results of more detailed calculations that allow for configuration mixing of valence nucleons, as well as first-order core polarization. As in the similar case of 205Tl, these calculations successfully predict the presence of a deep diffraction minimum observed in the intermediate q region of the elastic M1 form …

Electronic Simulation Of The Temporal Characteristics Of Photon Memory Echoes And Some Related Applications, Yuwen Kuo, Monish Ranjan Chatterjee

Electrical and Computer Engineering Faculty Publications

The characteristics of nonlinear photon memory echoes are investigated by means of SPICE simulations using equivalent resonator ensembles. By developing implicit nonlinear circuit models in the memory echo domain, the triple product formalism of electronic holography, involving correlation and convolution, is tested for the storage and recall of arbitrary signals and/or data bit streams in both time-inverted and nontime-inverted modes. Furthermore, a few specific optical data processing applications are also simulated in which the mixed binary multiplication of two or more binary bit streams is achieved.

Higher order products, optical pattern recognition, and other possible applications are also discussed. It …