Physical Sciences and Mathematics Commons^™

Dielectric Response Spectrum Of A Damped One-Dimensional Double-Well Oscillator, J. W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer

John R. Hardy Papers

The characteristic features of the dielectric response spectrum associated with the condensation of a "soft" phonon mode during a ferroelectric phase transition can be reproduced by an oscillator moving in a damped linear double-well potential. The behavior of the response function below the transition temperature T_c can be simulated by introducing a linear mean-field coupling which destroys the symmetry of the well. Potentials derived from physically realistic parameters are shown to result in dielectric responses which are in order-of-magnitude agreement with experimental values.

Dielectric Response Spectrum Of A Damped One- Dimensional Double-Well Oscillator, John W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer

Physics Faculty Publications

The characteristic features of the dielectric response spectrum associated with the condensation of a "soft" phonon mode during a ferroelectric phase transition can be reproduced by an oscillator moving in a damped linear double-well potential. The behavior of the response function below the transition temperature T, can be simulated by introducing a linear mean-field coupling which destroys the symmetry of the well. Potentials derived from physically realistic parameters are shown to result in dielectric responses which are in order-of-magnitude agreement with experimental values.

The Role Of Small-Impact-Parameter Electron-Loss Processes On Ion Temperatures Measured By Active-Beam Plasma Diagnostics, A. J.H. Donné, F. J. De Heer, Ronald E. Olson

Physics Faculty Research & Creative Works

The shape of the energy distribution of scattered particles in an active beam scattering experiment can be influenced considerably by the presence of highly charged impurity ions in the plasma. In this work it is shown theoretically that multiply charged impurities have only a small effect on the scattering distribution at low energies (/amu) and at high energies (>75 keV/amu). The effect of the impurities is the most pronounced for energies close to 50 keV/amu. The results of the calculations are in good agreement with experimental results at various energies. Extrapolation to higher beam energies leads to the conclusion …

Calculation Of Electron Scattering For 4He In A Continuum Shell Model, Ming Yu

Masters Theses

Calculations for the electroexcitation of the ⁴He, O+ state have been performed within the context of recoil corrected continuum shell model. Approximations previously employed for inelastic scattering with the recoil corrected continuum shell model are eliminated in the work. The O+ state exhausts only 10% of the energy weighted sum rule and previous shell model calculations for the excitation of this state produce about ten times too much strength. This difficulty is alleviated by the use translationally invariant wave functions and the application of continuum boundary conditions for this particle unbound state. The structure of the O+ state is …

Relativistic And Non-Relativistic Nuclear Charge Form Factors, Tao Wang

Masters Theses

This thesis presents an examination that the two nuclear charge form factors, relativistic and non-relativistic, are equivalent approximately in an appreciable range. The relativistic one is contributed by both vector charge density and tensor charge density. And the non-relativistic charge form factor is contributed by the nuclear densities from experimental electron scattering cross section, these densities are fundamental to much of nuclear structure physics.

The Dirac equation is used to calculate the vector charge density and tensor density, because the charge density from the analysis of the experimental data may be compared with proton charge densities obtained from various models …

Adiabatic Population Transfer In A Three-Level System Driven By Delayed Laser Pulses, J. R. Kuklinski, U. Gaubatz, Foek T. Hioe, K Bergmann

Physics Faculty/Staff Publications

We give a simple analytic solution that describes a novel method for population transfer in a three-level system driven by delayed pulses and which accounts for recent experimental results. This solution describes a procedure that is counter intuitive, and yet it is shown to be, in fact, one of the simplest solutions for multilevel systems arising from the adiabatic theorem. Its possible application to many-level systems is suggested.

Hr Aurigae: An Active Binary ?, Charles G. Loomis, Edward G. Schmidt

Edward Schmidt Publications

Photometric and spectral observations of the variable star HR Aurigae are presented. Based on these data we conclude that this star, previously regarded as a type II Cepheid, is, in fact, an active binary.

Observability Of Atmospheric Glories And Supernumerary Rainbows, James A. Lock

Physics Faculty Publications

The finite spatial coherence width of sunlight at the Earth imposes restrictions on the production of scattering phenomena based on the interference of light waves. With the spatial coherence properties of sunlight taken into account, the visibility of the supernumerary rainbow sequence adjacent to the primary rainbow and the radii of the water droplets that produce the optimum glory intensity were calculated. A substantial reduction was found in the contrast of all the supernumeraries beyond the first few, and the peak observability of the glory occurred for water droplets with radii between 10 and 20 µm.

Study Of The Dependence Of The Electron Emission Spectra On The Projectile Charge In H⁺, He2++He Collisions, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo method (CTMC) has been used to calculate doubly differential ionized-electron cross sections for the impact of He2+ and H+ on He at collision energies of 50 and 100 keV amu-1. The results exhibit the capture to the continuum peak and agree in both shape and magnitude with experimental data. The dependence of the cross sections on the projectile charge ZP is analyzed and it is found to be very asymmetric with regard to the capture to the continuum peak. This behavior is in agreement with very recent experimental data. Large deviations from the Z2P scaling …

Kaon Transitions And Predictions Of Chiral Symmetry, Jf Donoghue, Br Holstein

Barry R Holstein

We describe a set of kaonic electromagnetic and semileptonic weak decay processes which are completely predicted within the framework of chiral symmetry (and, therefore, of low-energy QCD), emphasizing where present problems exist and suggesting future experiments.

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, …

Deviations From Bulk Transport Measurements In Semi-Insulating Gaas, N. C. Halder, David C. Look

Physics Faculty Publications

Because of the high bulk resistivity of semi‐insulating GaAs, surface or near‐surface effects can change the apparent magnitudes of resistivity, mobility, and carrier concentration. We consider the following causes: (1) above‐surface conduction, such as that due to impurities in a porous oxide; (2) subsurface conduction, due to sawing and polishing damage; (3) tunneling conduction in surface states; and (4) changes in near‐surface conduction due to the modification of surface potential by surface states or absorbates. The most important of these effects appear to be subsurface damage and surface potential changes.

The Electrical Noise Of Carbon Fibers, R.O. Dillon

Roger Kirby Publications

The low-frequency excess electrical noise has been measured on carbon fibers with a wide range of crystalline perfection and corresponding electrical and mechanical properties. Fibers include those prepared from ex-PAN and ex-pitch polymers, and a catalytic-chemical vapor deposited filament. The extensional (Young's) moduli of these fibers varied from about 220 to 890 GPa (35–130 Msi), while the electrical resistivities varied from about 19 to 1 µΩ m. The low-frequency electrical noise of each fiber was found to be proportional to l² and to vary as 1/f^α, where f is the frequency and α is about 1.15. …

Doubly Differential Detachment Cross Sections For 0.5-Mev H- On He Including Projectile Excitation To H(N=2), Chih-Ray Liu, Anthony F. Starace

Anthony F. Starace Publications

Detailed theoretical results are presented for the electron-detachment cross section, doubly differential in both the electron momentum and angle, for the process 0.5-MeV H^-+He→H(n=2)+ e^-+He*. As discussed briefly elsewhere [C. R. Liu and A. F. Starace, Phys. Rev. Lett. 62, 407 (1989)], the laboratory-frame doubly differential cross sections (DDCS’s) for electron detachment in the forward direction are shown to depend sensitively on the low-energy states of the H(n=2)- e^- three-body system. In particular, the angular dependence of characteristic cusp and shape resonance features is presented. We find that the projectile frame …

The Period-Decline-Rate Relation For Pulsating Stars, Edward G. Schmidt, Kathryn H. Wiese

Edward Schmidt Publications

The relationships between the periods and the rate of decline in V and R for pulsating stars are investigated. It is shown that these relationships are useful for making preliminary estimates of periods for stars with little data. These estimates can then be used to optimize times of further observations.

Bethe Stopping-Power Theory For Heavy-Target Atoms, P.T. Leung

Physics Faculty Publications and Presentations

The Bethe stopping-power theory is considered in the context of heavy target atoms in which the relativistic effects of the target electrons are partially accounted for within the semirelativistic and independent-particle description. Numerical results show that, for target elements with large atomic numbers, these relativistic effects can become comparable with other corrections such as the shell correction, the Barkas effect, and the Bloch term.

Different Core-Hole Lifetime And Screening In The Surface Of W(110), D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

High-resolution 4f photoemission spectra from clean W(110) show that the natural lifetime width and the (electron-hole)-pair singularity index are both larger in the first atomic layer than in the bulk. Phonon broadening for the surface and bulk components are smaller than theoretical estimates, and little excess broadening is detected in the surface layer. These findings are very different from the conventional picture of surface-atom core-level line shapes and have implications extending to other systems.

Low-Lying Negative-Ion States Of Calcium, A.R. Johnston, Gordon A. Gallup, Paul Burrow

Paul Burrow Publications

Studies of electron transmission through Ca vapor reveal two prominent resonances in the range 0–4 eV. The energies and widths of these temporary anion states suggest that they may be assigned to the strongly mixed (4s²3d) ²D and (4s4p²)²D states of Ca^-. This interpretation is supported by ab initio configuration-interaction calculations and is consistent with previously unassigned structure observed in the photodetachment cross section.

Hamiltonian Formulation Of Induced Gravity In Two Dimensions, Charles G. Torre

Aerospace, Physics, and Space Science Faculty Publications

A Hamiltonian formulation of the theory of induced gravity in two dimensions is constructed. This formulation differs from previous efforts in that the formalism is covariant under all relevant transformation groups. In particular, spatial diffeomorphism covariance and/or invariance is manifest throughout; the phase space carries a representation of the Lie algebra of the spacetime diffeomorphism group; the group of conformal isometries is projectively represented on the phase space as a symmetry group. The key ingredient that allows covariance with respect to the above groups is the enlargement of the gravitational phase space by the inclusion of the cotangent bundle over …

Accurate Calibration Of The Four-Detector Photopolarimeter With Imperfect Polarizing Optical Elements, R. M.A. Azzam, Ali G. Lopez

Electrical Engineering Faculty Publications

The first three columns of the instrument matrix A of the four-detector photopolarimeter (FDP) are determined by Fourier analysis of the output current vector I(P) as a function of the azimuth angle P of the incident linearly polarized light. Therefore 12 of the 16 elements of A are measured free of the imperfections of the (absent) quarter-wave retarder (QWR). The effect of angular beam deviation by the polarizer is compensated for by taking the average, (1/2) [I(P) + I(P + 180°)], of the FDP output at 180°-apart, optically equivalent, angular positions of the polarizer. The remaining fourth column of A …

Angular And Energy Distributions Of Electrons From 7.5- 150-Kev Proton Collisions With Oxygen And Carbon Dioxide, Wen-Qin Cheng, M. Eugene Rudd, Ying-Yuan Hsu

M. Eugene Rudd Publications

Cross sections for the ejection of electrons, differential in the angle and energy of emission, were measured for proton collisions with two molecular gases, oxygen and carbon dioxide, over the primary energy range of 7.5-150 keV and an angular range of 10° to 160°. The energy distributions, obtained by integration over the angle, were fitted by an analytical model. A discrepancy in the angular distributions compared to those of Gibson and Reid [J. Phys. E 17, 1227 (1984); J. Phys. B 19, 3265 (1986); Radiat. Res. 112, 418 (1987); Australian Atomic Energy Commission Report No. AAEC/E659, 1987 (unpublished)] is discussed. …

Analysis Of Experimental Nucleation Data For Silver And Sio Using Scaled Nucleation Theory, Barbara N. Hale, Paul R. Kemper, Joseph A. Nuth

Physics Faculty Research & Creative Works

The experimental vapor phase nucleation data of Nuth et al., for silver [J. A. Nuth, K. A. Donnelly, B. Donn, and L. U. Lilleleht, J. Chem. Phys. 77, 2639 (1982)] and SiO [J. A. Nuth and B. Donn, J. Chem. Phys. 85, 1116 (1986)] are reanalyzed using a scaled model for homogeneous nucleation [B. N. Hale, Phys. Rev. A 33, 4156 (1986)]. The approximation is made that the vapor pressure at the nucleation site is not diminished significantly from that at the source (crucible). It is found that the data for ln S have a temperature dependence consistent with the …

Quantum Transport In The Presence Of Random Traps, John Wm Edwards, Paul Ernest Parris

Physics Faculty Research & Creative Works

We calculate the asymptotic decay of a quantum particle moving in a d-dimensional medium doped with randomly placed trapping impurities, focusing on contributions from slowly decaying long-wavelength modes centered in large compact regions devoid of traps. By averaging the decay over the statistical distribution associated with these regions we find that the survival probability, P(t) ~exp(-At^d/(d+3)), decays more slowly in any dimension than for diffusive transport.

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 …

Hall-Effect Depletion Corrections In Ion-Implanted Samples: Si29 In Gaas, David C. Look

Physics Faculty Publications

The sheet free‐carrier concentration in a thin, conducting layer on an insulating substrate is lower than the net, sheet‐dopant concentration because of free‐carrier depletion in the surface and interface regions. Here we develop an algorithm to give the true, net sheet‐donor concentration from the measured sheet‐Hall concentration under the assumption of a Gaussian donor profile, which is usually sufficiently accurate for ion‐implanted samples. Correction curves are generated for Si²⁹ ions implanted into GaAs at energies of 60, 100, 130, 150, and 200 keV, and at doses of 1×10¹¹–2×10¹⁴ ions/cm². Also, the …

Equatorial F-Regionvertical Plasma Drifts During Solar Maxima, Bela G. Fejer, E. R. De Paula, I. S. Batista, E. Bonelli, R. F. Woodman

Bela G. Fejer

Incoherent scatter radar measurements at Jicamarca are used to study the effects of large solar fluxes and magnetic activity on the F region vertical plasma drifts. The average drifts from the two last solar maxima are almost identical except in the late afternoon-early evening sector where their variations with solar flux and magnetic activity are strongly season dependent. The average evening winter (May-August) drifts appear to remain almost constant after a certain solar flux level is reached but increase with magnetic activity. The equinoctial evening drifts increase systematically with solar-flux but decrease with magnetic activity. Very large prereversal enhancement velocities, …

Silicon Crystallite Formation In Ion-Implanted Quartz, U. B. Ramabadran, H. E. Jackson, Gary C. Farlow

Physics Faculty Publications

Rapid thermally annealed silicon‐implanted x‐cut α‐quartz samples have been examined by Rutherford backscattering and Raman microprobe spectroscopy. The data indicate that the silicon has diffused at 1200 °C to form a buried layer of crystallites of size 1–10 μm. The crystallites are preferentially oriented and under substantial stress.

Particle Tracks In Diverse Media, Robert Katz

Robert Katz Publications

When energetic heavy ions pass into a medium, they create a trail of excitations, ionizations, and secondary electrons whose effect is represented through their average radial “dose” distribution. The structure of the track depends on this and on the observed “end point.” Tracks may be observed microscopically or through the gross effect of a particle beam. We take the medium to be an assemblage of “targets” whose response to gamma rays is approximated by the cumulative Poisson distribution. While most detectors are 1-hit systems, we have discovered 2-hit and up to 8-hit response. Folding the gamma-ray response into the radial …

Layer-By-Layer Growth Of Solid Argon Films On Graphite As Studied By Neutron Diffraction, J. Z. Larese, Q. M. Zhang, L. Passell, J. M. Hastings, John R. Dennison, H. Taub

All Physics Faculty Publications

The layer-by-layer growth of solid argon films on graphite at T=10 K is studied using elastic neutron diffraction. The growth is characterized by individual layers with commensurate in-plane lattice constants. As the coverage is increased beyond two layers, evidence of the coexistence of ABC and ABA stacking is apparent, with the ABC sequence dominating as the film thickens. A continuous decrease in the Debye-Waller factor also occurs as the film thickness grows, indicating a crossover from two-dimensional to three-dimensional behavior. As the coverage is increased beyond about four nominal layers, there is evidence of bulk crystallite formation. The diffraction results …

Recoil Distributions In Particle Transfer, James H. Mcguire, Jack C. Straton, W. J. Axmann, T. Ishihara, E. Horsdal

Physics Faculty Publications and Presentations

Classical Thomas peaks in various fast second-order particle transfer processes are quantum mechanically broadened by energy nonconservation in the intermediate states of collision. This quantum broadening is considered in observable velocity distributions of recoil particles.