Physical Sciences and Mathematics Commons^™

More On Twinkling, Terry L. Smith, Jay S. Huebner

Terry L. Smith

Addendum to Why Magnification Works , The Physics Teacher, 1994, 32, 102.

Absence Of Size Dependence Of The Kondo Resistivity, V. Chandrasekhar, P. Santhanam, N. A. Penebre, Richard A. Webb, H. Vloeberghs, C. Van Haesendonck, Y. Bruynseraede

Faculty Publications

We have measured the low temperature resistivity of AuFe wires in the dilute magnetic impurity limit as a function of wire width, temperature, and magnetic field. When the width dependence of the electron-electron interaction contribution to the resistivity is taken into account, the temperature dependence of the remaining Kondo contribution to the resistivity of all samples with the same impurity concentration is identical. Similar behavior is observed for the magnetic field dependent resistivity. Thus, the Kondo contribution to the resistivity is independent of width down to 38 nm, much smaller than the Kondo length ξ_K=ħv_F/k_{B …}

Discrete Singularity Method And Its Application To Incompressible Flows., S K. Venkatesan Dr.

Doctoral Theses

The smooth flow of a fluid has sprung many surprises. A flow which at an instant of time is quite regular and orderly could produce on the slightest of disturbance a complex bewildering varieties of flows, broadly termed as turbulence. Direct numerical simulation of the Navier-Stokes equations have shown that it is quite possible that these turbulent flows are solutions of the Navier-Stokes equations. In fact it is by now well recognized that many non-linear systems produce chaos quite similar to turbulence. However the large number of scales and their complex interactions involved make turbulence difficult to understand. Direct numerical …

Why Magnification Works, Terry L. Smith, Jay S. Huebner

Terry L. Smith

The simplest way to magnify the view of a small object is to bring the object closer to the eye, and of course science teachers know about magnifying glasses, telescopes, and microscopes.But why magnification works seems intuitive and is not usually explained to our students. We present here a few ideas on magnification that we use in our classroom and some general information on vision that we hope will be helpful to other teachers.

Neutron Reflection Interferometry: Physical Principles Of Surface Analysis With Phase Information, Vladimir Gudkov, G. I. Opat, A. G. Klein

Faculty Publications

It is shown that the analysis of surface layers by neutron reflection interferometry is considerably enhanced by performing the reflectometry with phase information. We discuss two methods of providing such information. One method involves physically adding an extra reference layer, whose amplitude and phase are known theoretically. The other uses the Lloyd's mirror configuration, in which a directly propagating ray that interferes with the reflected ray supplies the phase information. The methods have much in common with holography.

Comparison Of Suppression Across Frequencies, Linda M. Thibodeau, Marc A. Fagelson

Marc A. Fagelson

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, …

Cp-Odd Nucleon Potential, Vladimir Gudkov, Xiao-Gang He, Bruce H.J. Mckellar

Faculty Publications

The P-odd and CP-odd nucleon potential for different models of CP violation in the one-meson exchange approximation is studied. It is shown that the main contribution is due to the π-meson exhcange which leads to a simple one-parameter CP-odd nucleon potential.

Supersymmetry And The Tunneling Problem In An Asymmetric Double Well, Asim Gangopadhyaya, Prasanta K. Panigrahi, Uday P. Sukhatne

Physics: Faculty Publications and Other Works

The techniques of supersymmetric quantum mechanics are applied to the calculation of the energy difference between the ground state and the first excited state of an asymmetric double well. This splitting, originating from the tunneling effect, is computed via a systematic, rapidly converging perturbation expansion. Perturbative calculations to any order can be easily carried out using a logarithmic perturbation theory. Our approach yield substantially better results than alternative widely used semiclassical analyses.

In-Medium Behavior Of The Qcd ϴ Term And The Value Of Cp Violation In Nuclei, Vladimir Gudkov

Faculty Publications

The expectation value of the θ term in QCD for nuclear matter is estimated in the nucleon gas approximation. There is no significant renormalization (to an accuracy ∼10%) of the CP violation in nuclei due to the similar behaviors for the in-medium values of the θ term and quark condensates.

Determination Of The Neutron Spin Structure Function, P. L. Anthony, R. G. Arnold, H. R. Band, H. Borel, P.E. Bosted, V. Breton, G. D. Cates, T. E. Chupp, F. S. Dietrich, J. Dunne, R. Erbacher, J. Fellbaum, H. Fonvielle, R. Gearhart, R. Holmes, E. W. Hughes, J. R. Johnson, D. Kawall, C. Keppel, S. E. Kuhn, R. M. Lombard-Nelsen, J. Marroncle, T. Maruyama, W. Meyer, Z. E. Meziani, H. Middleton, J. Morgenstern, N. R. Newbury, G. G. Petratos, R. Pitthan, R. Prepost, Y. Roblin, S. E. Rock, S. H. Rokni, G. Shapiro, T. Smith, P. A. Souder, M. Spengos, F. Staley, L. M. Stuart, Z. M. Szalata, Y. Terrien, A. K. Thompson, J. L. White, M. Woods, J. Xu, C. C. Young, G. Zapalac, E142 Collaboration

Physics Faculty Publications

The spin structure function of the neutron g₁ⁿ has been determined over the range 0.03 < x < 0.6 at an average Q² of 2 (GeV/c)² by measuring the asymmetry in deep inelastic scattering of polarized electrons from a polarized ³He target at energies between 19 and 26 GeV. The integral of the neutron spin structure function is found to be f-¹₀ gⁿ₁(x)dx = -0.022 ± 0.011. Earlier reported proton results together with the Bjorken sum rule predict f-¹₀ gⁿ₁(x)dx = -0.059 ± 0.019.

Sign Correlations And The Mechanism For Parity Violation, Vladimir Gudkov

Faculty Publications

The problem of possible sign correlations of P-odd effects due to parity mixing on the compound nuclear stage is discussed. For an unambiguous test of the conventional model of parity violation on the compound nuclear stage, it is not enough only to measure the sign correlation of P-odd effects on some resonances, but it is necessary also to know the neutron decay amplitudes for each resonance.

Geometrical Phases And Symmetries In Dissipative Systems, Adam S. Landsberg

WM Keck Science Faculty Papers

A geometrical phase is constructed for dissipative dynamical systems possessing continuous symmetries. It emerges as the natural analog of the holonomy associated with the adiabatic variation of parameters in quantum-mechanical and classical Hamiltonian systems. In continuous media, the physical manifestation of this phase is a spatial shift of a wave pattern, typically a translation or rotation. An illustration associated with pattern formation in fluids is provided.

Recoil Effects And Cp Violation In Neutron Scattering, Vladimir Gudkov

Faculty Publications

The problem of the imitation of CP violation in neutron scattering is discussed. The thermal motion of nuclei cannot contribute to symmetry-violating effects. The influence of the nuclear depolarization due to neutron scattering is estimated.

Effects Of Wind, Density, And Bathymetry On A One-Layer Southern Ocean Model, John M. Klinck

CCPO Publications

Steady solutions from a one-layer, wind-driven, primitive equation model are analyzed to determine the importance of wind forcing, pressure gradient force due to the climatological density distribution and bottom form drag on circulation in the Southern Ocean. Five simulations are discussed: three wind-forced simulations, with differing bathymetry (flat bottom, 15% bathymetry, and full bathymetry), one case with full bathymetry forced with the density-induced pressure force, and one case with full bathymetry forced by both wind and density-induced pressure gradients. The simulations presented here confirm the previous speculation (Munk and Palmen, 1951) that form drag is effective in balancing the driving …

Multi-Ball Collisions, Terry L. Smith, Jay S. Huebner

Terry L. Smith

Explanation to use the "double-ball" demonstration as a model for the supernova core bounce.

Density Effect In Cu K-Shell Ionization By 5.1-Gev Electrons, W. E. Meyerhof, D. G. Jensen, D. M. Kawall, S. E. Kuhn, D. W. Spooner, Z. E. Meziani, D.. N. Faust

Physics Faculty Publications

We have made an absolute measurement of the Cu K-shell impact ionization cross section by 5.1-GeV electrons, which demonstrates directly a density effect predicted by Fermi in 1940. By determining the ratio of the K x-ray yield from a thin front and back layer of the target by a novel grazing emission method, we have verified the effect of transition radiation on the x-ray production, suggested by Sorensen and reported by Bak et al.

Energetic Protons And Deuterons Emitted Following Μ⁻ Capture By ³He Nuclei, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, S. E. Kuhn, Y. M. Shin, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig

Physics Faculty Publications

Spectra of energetic protons and deuterons emitted following negative muon capture from rest in ³He have been measured for the first time. Significant capture strength is observed at high energy transfers (mμ- E_v >60 MeV) for the two-body and three-body breakup channels, indicative of the importance of nucleon-nucleon correlations and meson exchange currents in the capture process. A simple plane wave impulse approximation calculation reproduces the proton spectrum reasonably well, but underpredicts the deuteron rate at the highest energies by a large factor.

Magnetic Response Of A Single, Isolated Gold Loop, V. Chandrasekhar, Richard A. Webb, M. J. Brady, M. B. Ketchen, W. J. Gallagher, A. Kleinsasser

Faculty Publications

Measurements have been made of the low-temperature magnetic response of single, isolated, micron-size Au loops. The magnetic response is found to contain a component which oscillates with the applied magnetic flux with a fundamental period of Φ₀=h/e. The amplitude of the oscillatory component corresponds to a persistent current of ≃(0.3–2.0)ev_F/L, 1 to 2 orders of magnitude larger than predicted by current theories.

Single-Electron Charging Effects In Insulating Wires, Venkat Chandrasekhar, Zvi Ovadyahu, Richard A. Webb

Faculty Publications

We present measurements of the transport properties of 0.75-μm-long, narrow, insulating indium oxide wires and rings. These devices have no apparent tunnel barriers, yet they exhibit effects similar to those found in series arrays of very small-capacitance tunnel junctions: highly nonlinear I-V characteristics and a zero-bias conductance which is periodic in a voltage applied by means of a lateral gate. These effects are due to the influence of single-electron charging on transport through localized states in the insulating regime.

Universal Scaling Of Nonlocal And Local Resistance Fluctuations In Small Wires, H. Haucke, S. Washburn, A. D. Benoit, C. P. Umbach, Richard A. Webb

Faculty Publications

Resistance fluctuations in small metal samples result from coherent transport of the carriers. The wave functions of the carriers extend into regions which are not accessible classically. We have directly measured the length dependence of the nonlocal magnetoresistance fluctuations in Sb and Au wires by studying regions of our samples separated from the classical current path by a distance L which varied from 3L_cphi down to 0.2L_cphi (where L_cphi is the phase coherence length for the carriers in the metal). These fluctuations decay exponentially with L/L_cphi. Measurements along the classical current paths scale more slowly …

Time And The Physical Universe, Norman E. Ramsey

DSLS 1989-1990

(This information was taken from the Distinguished Scientist Lecture Series Program 1989-1990).

Norman F. Ramsey is the Higgins Professor ofPhysics at Harvard University. He has been a Harvard faculty member since 1947. Norman Ramsey received his A.B. and M.A. from Columbia University and degrees from Cambridge University. In1940 he received aPh.D. from Columbia University for molecular beam studies of rotational magnetic moments of molecules. He was awarded an Sc.D. by Cambridge University in1954 and by Oxford University in1973, as well as honorary D.Sc.'s from Case-Western Reserve University, Middlebury College, and Rockefeller University. After periods at the Carnegie Institution of Washington, …

Frontiers Of Material Research, Mildred S. Dresselhaus

DSLS 1989-1990

(This information was taken from the Distinguished Scientist Lecture Series Program 1989-1990).

Dr. Dresselhaus is currently Institute Professor at the Massachusetts Institute of Technology. She was formerly the holder of the Abby Rockefeller Mauze Chair in Electrical Engineering and in Physics at MIT. She is also affiliated with the Center for materials and Engineering, and with the Francis Bitter National Magnet Laboratory at MIT where some of the experimental work of her group is carried out. Dr. Dresselhaus holds professorships in MIT's Department of Electrical Engineering and Computer Science and the Department of Physics.

Dr. Dresselhaus was born in Brooklyn …

Experimental Study Of Nonlinear Conductance In Small Metallic Samples, Richard A. Webb, S. Washburn, C. P. Umbach

Faculty Publications

We have directly observed current-dependent, nonlinear contributions to the conductance fluctuations of phase-coherent metallic wires and loops. The fluctuations in the current-voltage curves are reproducible, asymmetric about I=0, and in qualitative agreement with theoretical predictions. In ac measurements, the nonlinear terms also generate large harmonic signals of the conductance fluctuations whose dependence on the drive current can be understood qualitatively. The spectra of harmonics from loops and wires have different dependences on the voltage across the sample.

Normal-Metal Aharonov-Bohm Effect In The Presence Of A Transverse Electric Field, S. Washburn, H. Schmid, D. Kern, Richard A. Webb

Faculty Publications

The effects of transverse electric fields on the conductance fluctuations in an Sb loop have been studied. We show that the electric field can be used to tune the position (or phase) of Aharonov-Bohm oscillations as well as to alter the aperiodic conductance fluctuation patterns. We disucss two mechanisms which might cause the observed dependence of the fluctuation pattern on transverse electric field. The first is the electrostatic Aharonov-Bohm effect, and the second is the spatial shifting of the electron trajectories by the electric field.

Length-Independent Voltage Fluctuations In Small Devices, A. Benoit, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

Conductance fluctuations in one-dimensional lines of length L shorter than the phase-coherence length L_φ are not universal but diverge as L^-2. Using the Onsager relations and voltage additivity, we show that the voltage fluctuations are independent of the distance between voltage probes. The antisymmetric (Hall-type) contribution to the voltage fluctuations is constant for all values of L. Measurements of the voltage fluctuations and correlation function between different regions in Au and Sb lines confirm these results.

Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

Universal conductance fluctuations in wires and Aharonov-Bohm oscillations in loops are not symmetric about H=0. The observation of asymmetry in the periodic oscillations is possible when the phase-coherence length of the wave function is comparable to the separation of the voltage probes. In both cases, four-probe measurements yield resistances which depend on lead configuration. The asymmetries appear like Hall voltages, and are consistent with Onsager's relations.

Observation Of Resonant Tunneling In Silicon Inversion Layers, A. B. Fowler, G. L. Timp, J. J. Wainer, Richard A. Webb

Faculty Publications

Measurements of the temperature and carrier-density dependence of the strongly localized conductance of short silicon inversion layers are reported. At the lowest temperatures we observe well-isolated, large conductance peaks whose width and temperature dependence are only consistent with resonant tunneling and are inconsistent with Mott hopping. Several new features are observed which we believe may be the result of Coulomb interactions.

Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki

Faculty Publications

We report large logarithmic corrections to the conductivity of two-dimensional electrons and holes in GaSb-InAs-GaSb double heterostructures. From ∼ 40 mK to 1 K, the conductivity increased with the logarithm of the temperature but with a slope as much as 30 times larger than estimated from the theories of weak localization and carrier interaction. The discrepancy apparently results from electron-hole interactions not included in the theory.

Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki

Faculty Publications

We report large logarithmic corrections to the conductivity of two-dimensional electrons and holes in GaSb-InAs-GaSb double heterostructures. From ∼ 40 mK to 1 K, the conductivity increased with the logarithm of the temperature but with a slope as much as 30 times larger than estimated from the theories of weak localization and carrier interaction. The discrepancy apparently results from electron-hole interactions not included in the theory.