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The Effect Of Continuous Stirring On Off-Critical And Critical Samples Of A Phase Separating Binary Liquid Mixture, Nalini Easwar Jan 1992

The Effect Of Continuous Stirring On Off-Critical And Critical Samples Of A Phase Separating Binary Liquid Mixture, Nalini Easwar

Physics: Faculty Publications

The effect of shear on phase separation in a continuously stirred mixture of isobutyric acid and water has been studied. The data for the onset of phase separation in the stirred samples that are as far away as 500 mK from the critical point compare favorably with the theory of Onuki and Takasue and with similar measurements on very off-critical mixtures of 2-6 lutidine plus water reported by Min et al. However, as the composition gets closer to the critical composition significant differences arise. The main feature is that the measured suppression in temperature peaks at an off-critical composition …

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The Effect Of Diamagnetic Dilution On The Spin-Phonon Interaction And Scattering Cross Section In Fe1-Xznxf2, Christian Binek Jan 1992

The Effect Of Diamagnetic Dilution On The Spin-Phonon Interaction And Scattering Cross Section In Fe1-Xznxf2, Christian Binek

Christian Binek Publications

The temperature dependences of the first moments of phonon Raman scattering lines are studied for Fe1-xZnxF2. The diamagnetic dilution diminishes the spin-phonon coupling strength of phonons with both A1g and Eg symmetry in proportion to the decrease in the ordering temperature TN. Moreover, the Eg mode shows an asymmetrical lineshape for Zn concentrations x>0.3. It is explained by an unresolved superposition of two modes, one of which is ascribed to perturbed ZnF2 with broken translational symmetry.

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Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel Jan 1992

Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel

Physics Articles and Papers

High-resolution Auger electron spectra of La1.85Sr0.15CuO4 and La1.85Ba0.15CuO4 have been measured. The experimental Auger line shapes of the oxygen KLL and copper L2,3VV transitions are compared with those generated from local-density-approximation linear-muffin-tin-orbital band-structure calculations. An analysis based on this comparison is used to determine the Coulomb parameters Up and Ud of the oxygen and copper atoms, respectively. For this purpose, an extended version of Cini and Sawatzky’s expression for the theoretical Auger line shape is used, taking into account the multiplet structure of the Auger final …

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Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi Jan 1992

Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi

Physics Articles and Papers

We report generalized-gradient-approximation (GGA) density-functional studies of Cr, V, and Pd, using an all-electron, general-potential linearized-augmented-plane-wave technique. These calculations were undertaken in order to assess the utility of the GGA as an improvement over the local-density approximation in describing transition-metal magnetism. It is found that although the tendency towards magnetism is enhanced, both V and Pd are correctly predicted to be nonmagnetic with the recent GGA functional of Perdew (PW GGA-II) as with the Langreth-Mehl-Hu (LM) functional. Calculations for commensurate antiferromagnetic Cr show that the PW GGA-II predicts an overly large moment of 1.4μB while the LM functional yields …

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Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes Jan 1992

Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes

Physics Articles and Papers

We have analytically evaluated, up to fourth order, all logarithmic terms in the perturbation expansion of the magnetization scrM for the Kondo model. All nonlogarithmic terms have been evaluated up to third order. When these results are compared with the claimed universal function scrM(H/TH) calculated with the Bethe ansatz, we find that the two cannot be made to agree whatever the form of TH. We conclude that such universal functions do not exist.

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Track Structure Model Of Cell Damage In Space Flight, Robert Katz, Francis A. Cucinotta, John W. Wilson, Judy L. Shinn, Duc M. Ngo Jan 1992

Track Structure Model Of Cell Damage In Space Flight, Robert Katz, Francis A. Cucinotta, John W. Wilson, Judy L. Shinn, Duc M. Ngo

Robert Katz Publications

Cell damage by high linear energy transfer (LET) radiations has been described by a phenomenological model (track theory) for more than 20 years. With track theory, molecules of biological significance (dry enzymes and viruses) act as one-hit detectors. Recent additions to tire class of one-hit detectors arc Escherichia coil B, and single- and double-strand breaks in SV-40 virus in EO buffer, where indirect effects predominate. The response of cells (survival, transformation, and chromosome aberration) to these radiations is typically described by a four-parameter model whose numerical values are determined from the equations of the theory being fit to experimental …

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Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon Jan 1992

Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon

Faculty Publications

We study the phenomenon of slip length using molecular dynamics and direct simulation Monte Carlo simulations of a dilute gas. Our work extends the range of Knudsen numbers that have been previously studied. In a recent paper, Bhattacharya and Lie [Phys. Rev. 43, 761 (1991)] suggest a logarithmic dependence of slip length on Knudsen number. By a simple redefinition of the mean free path, we obtain good agreement between simulation results and Maxwell theory for slip length. The anomalies seen by Bhattacharya and Lie appear to be due to their definition of the mean free path.

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Ultrahigh Vacuum Chamber For Synchrotron X-Ray Diffraction From Films Adsorbed On Single-Crystal Surfaces, Jr Dennison, S. K. Wang, S. N. Ehrlich Jan 1992

Ultrahigh Vacuum Chamber For Synchrotron X-Ray Diffraction From Films Adsorbed On Single-Crystal Surfaces, Jr Dennison, S. K. Wang, S. N. Ehrlich

Journal Articles

An ultrahigh vacuum chamber has been developed for structural analysis of adsorbed films and single-crystal surfaces using synchrotron x-ray diffraction. It is particularly well suited for investigations of physisorbed and other weakly bound films. The chamber is small enough to transport and mount directly on a standard four-axis diffractometer and can also be used independently of the x-ray diffractometer. A low-current, pulse-counting, low-energy electron diffraction/Auger spectroscopy system with a position-sensitive detector enables in situ characterization of the film and substrate while the sample is located at the x-ray scattering position. A closed-cycle He refrigerator and electron bombardment heater provide controlled …

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Translation Of 'Kamalakanta: A Collection Of Satirical Essays And Reflections', Monish Ranjan Chatterjee Jan 1992

Translation Of 'Kamalakanta: A Collection Of Satirical Essays And Reflections', Monish Ranjan Chatterjee

Electrical and Computer Engineering Faculty Publications

This venture was born initially out of the desire to make those works of Bengali literature which have moved me profoundly, and which I consider first-rate by any yardstick, available to friends and fellow enthusiasts who cannot read the original. In attempting to channel literary and philosophical masterpieces into a different medium, I Have experienced firsthand the formidable challenge that a translator must face because not only of the barrier imposed by the languages involved, but perhaps more so because .of his or her own severely inadequate faculty being called upon to match both the genius and the inspiration of …

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Simulations Of Phase Transitions In Rb2Zncl4, H. M. Lu, John R. Hardy Jan 1992

Simulations Of Phase Transitions In Rb2Zncl4, H. M. Lu, John R. Hardy

John R. Hardy Papers

Structural relaxations, molecular-dynamics simulations, and lattice-dynamics calculations were performed to study the phase transitions in Rb2ZnCl4, using intermolecular and intramolecular potentials generated from ab initio quantum-chemistry calculations for the whole molecular ion ZnCl4 2-. Compared with an earlier treatment of the system by a polarizable-ion model, the present approach emphasizes the static effect of the electron covalency within the molecular ions that affects strongly both the intermolecular and intramolecular interactions. The calculations gave a close agreement with experiment on the static structures of the Pnam and the Pna21 phases and the transition …

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Raman Scattering And Lattice-Dynamical Calculations Of Crystalline Kno3, H. M. Lu Jan 1992

Raman Scattering And Lattice-Dynamical Calculations Of Crystalline Kno3, H. M. Lu

John R. Hardy Papers

The Raman spectrum of a KNO3 single crystal was measured at both room and liquid-nitrogen temperatures. Lattice-dynamical calculations, based on the rigid-ion approximation and empirical potentials, were performed. The possibility of a phase transition at 217 K was investigated by measuring the temperature dependence of the Raman spectrum.

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Extrapolation Procedures In Mott Electron Polarimetry, Timothy J. Gay, M. A. Khakoo, J. A. Brand, J. E. Furst, W. V. Meyer, W. M. K. P. Wijayaratna, F. B. Dunning Jan 1992

Extrapolation Procedures In Mott Electron Polarimetry, Timothy J. Gay, M. A. Khakoo, J. A. Brand, J. E. Furst, W. V. Meyer, W. M. K. P. Wijayaratna, F. B. Dunning

Timothy J. Gay Publications

In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A to the values they would have for scattering from single atoms. These extrapolations involve the dependence of A on either the gold film thickness t or the maximum detected electron energy loss in the target ΔE. Using a concentric cylindrical-electrode Mott polarimeter, we have studied and compared these two types of extrapolations over the electron energy range 20-100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the …

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Su(3) X Su(2) X U(1)Su(3): The Residual Symmetry Of Conformal Gravity, James Thomas Wheeler Jan 1992

Su(3) X Su(2) X U(1)Su(3): The Residual Symmetry Of Conformal Gravity, James Thomas Wheeler

All Physics Faculty Publications

SUe 4) x SU(2) is shown to characterize the possible choices of spacetime metric constructible from the gauge fields of the conformal group. When this symmetry is broken by the choice of metric, exactly the SU(3) x SU(2) x U(l) symmetry of the standard model remains. The conformal group consists of Lorentz transformations, translations, inverse translations and dilations. Treated in the standard way, conformal symmetry fails as a unifying gauge group: dilations make the mass spectrum continuous, and the inverse translational gauge field is auxiliary. The theory reduces back to the Poincare group.

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Analysis Of Experiments In Helium Microbeam Mixing, J B. Davis, R E. Benenson, David Peak Jan 1992

Analysis Of Experiments In Helium Microbeam Mixing, J B. Davis, R E. Benenson, David Peak

All Physics Faculty Publications

We have continued to investigate ion-beam mixing in bilay-er targets irradiated by 2-MeV He+ microbeams at room temperature. Although we have previously reported a linear dependence of interface width on dose for Cu/Al targets 1, more extensive results have not supported this conclusion, within statistical uncertainty, it appears that the interface width in Cu/Al (1) is proportional to the square root of dose, at constant dose rate, (2) is larger in Al than in Cu, for the same dose, (3) is proportional to the 1/4 power of dose rate, and (4) is absent at liquid nitrogen temperature. Calculations …

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Optical Rectification At Semiconductor Surfaces, Shun Lien Chuang, Stefan Schmitt-Rink, Benjamin I. Greene, Peter N. Saeta, Anthony F. J. Levi Jan 1992

Optical Rectification At Semiconductor Surfaces, Shun Lien Chuang, Stefan Schmitt-Rink, Benjamin I. Greene, Peter N. Saeta, Anthony F. J. Levi

All HMC Faculty Publications and Research

We show that far-infrared radiation can be generated in the depletion field near semiconductor surfaces via the inverse Franz-Keldysh effect or electric-field-induced optical rectification. This mechanism is conceptually different from those previously proposed and accounts for many recent experimental observations.

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Fractal Character Of Two-Dimensional Fluid Mixing At Both Continuum And Atomic Levels, H. Z. Cao, John R. Hardy, R. W. Douglass, P. T. Dawkins, Steven Dunbar Jan 1992

Fractal Character Of Two-Dimensional Fluid Mixing At Both Continuum And Atomic Levels, H. Z. Cao, John R. Hardy, R. W. Douglass, P. T. Dawkins, Steven Dunbar

John R. Hardy Papers

Studies in two dimensions have been made of the evolution of an initially linear interface between two liquid areas by both continuum hydrodynamics and molecular dynamics. It was found that at both levels the interface evolves into a fractal curve. While the limiting fractal dimensionalities (D) of the continuum and molecular interfaces differ, this difference is no greater than that that can be induced in the hydrodynamic results by marked changes in the initial conditions and/or fluid parameters. There is, however, a marked qualitative difference in the initial values of D. This is discussed and shown to …

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Raman Scattering And Lattice-Dynamical Calculations Of Crystalline Kno3, D. Liu, F. G. Ullman, John R. Hardy Jan 1992

Raman Scattering And Lattice-Dynamical Calculations Of Crystalline Kno3, D. Liu, F. G. Ullman, John R. Hardy

John R. Hardy Papers

The Raman spectrum of a KNO3 single crystal was measured at both room and liquid-nitrogen temperatures. Lattice-dynamical calculations, based on the rigid-ion approximation and empirical potentials, were performed. The possibility of a phase transition at 217 K was investigated by measuring the temperature dependence of the Raman spectrum.

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Production Of A High-Density State-Selected Metastable Neon Beam, J. A. Brand, J. E. Furst, Timothy J. Gay, L. D. Shearer Jan 1992

Production Of A High-Density State-Selected Metastable Neon Beam, J. A. Brand, J. E. Furst, Timothy J. Gay, L. D. Shearer

Timothy J. Gay Publications

We have developed a high-density source of metastable neon and have selectively quenched both metastable species using a standing-wave dye laser. The source is compact, stable, and produces an average intensity of 3.6 x 1014 sr -1 s -1 and a density on target of 7.7 x 106 cm-3.

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Measuring Airborne Alpha Radioactivity, Greg Taft Jan 1992

Measuring Airborne Alpha Radioactivity, Greg Taft

Honors Theses, 1963-2015

This project develops alpha spectroscopy to measure the airborne concentrations of attached and unattached radon progeny. The system is designed and constructed to be used in homes, thus is portable, fast, and easy to use.

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Multicriticality, Scaling Operators And Mkdv Flows For The Symmetric Unitary One Matrix Models, Konstantinos N. Anagnostopoulos, Mark Bowick Jan 1992

Multicriticality, Scaling Operators And Mkdv Flows For The Symmetric Unitary One Matrix Models, Konstantinos N. Anagnostopoulos, Mark Bowick

Physics - All Scholarship

We present a review of the Symmetric Unitary One Matrix Models. In particular we compute the scaling operators in the double scaling limit and the corresponding mKdV flows. We briefly discuss the computation of the space of solutions to the string equation as a subspace of Gr (0) \Theta Gr (0) which is invariant under the mKdV flows.

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Covariant Phase Space Formulation Of Parametrized Field Theories, Charles G. Torre Jan 1992

Covariant Phase Space Formulation Of Parametrized Field Theories, Charles G. Torre

All Physics Faculty Publications

Parametrized field theories, which are generally covariant versions of ordinary field theories, are studied from the point of view of the covariant phase space: the space of solutions of the field equations equipped with a canonical (pre)symplectic structure. Motivated by issues arising in general relativity, we focus on phase space representations of the space‐time diffeomorphism group, construction of observables, and the relationship between the canonical and covariant phase spaces.

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Is General Relativity An "Already Parametrized" Theory?, Charles G. Torre Jan 1992

Is General Relativity An "Already Parametrized" Theory?, Charles G. Torre

All Physics Faculty Publications

Beginning with the work of Dirac and of Arnowitt, Deser, and Misner in the late 1950s and early 1960s, and then after subsequent development by Kuchař, the canonical dynamical structure of general relativity has often been viewed as that of a parametrized field theory in which the many-fingered spacetime variables are hidden among the geometrodynamical field variables. This paradigm of general relativity as an "already parametrized" theory forms the basis for one of the most satisfactory resolutions of the problems of time and observables in classical and quantum gravity. However, despite decades of effort, no identification of many-fingered spacetime variables …

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Fragmentation Of Percolation Clusters At The Percolation Threshold, M. F. Gyure, Boyd F. Edwards Jan 1992

Fragmentation Of Percolation Clusters At The Percolation Threshold, M. F. Gyure, Boyd F. Edwards

All Physics Faculty Publications

A scaling theory and simulation results are presented for fragmentation of percolation clusters by random bond dilution. At the percolation threshold, scaling forms describe the average number of fragmenting bonds and the distribution of cluster masses produced by fragmentation. A relationship between the scaling exponents and standard percolation exponents is verified in one dimension, on the Bethe lattice, and for Monte Carlo simulations on a square lattice. These results further describe the structure of percolation clusters and provide kernels relevant to rate equations for fragmentation.

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Ionospheric Simulation Compared With Dynamics Explorer Observations For November 22, 1981, Jan Josef Sojka, M. D. Bowline, Robert W. Schunk, J. D. Craven, L. A. Frank, J. R. Sharber, J. D. Winningham, L. H. Brace Jan 1992

Ionospheric Simulation Compared With Dynamics Explorer Observations For November 22, 1981, Jan Josef Sojka, M. D. Bowline, Robert W. Schunk, J. D. Craven, L. A. Frank, J. R. Sharber, J. D. Winningham, L. H. Brace

All Physics Faculty Publications

Dynamics Explorer (DE) 2 electric field and particle data have been used to constrain the inputs of a time-dependent ionospheric model (TDIM) for a simulation of the ionosphere on November 22, 1981. The simulated densities have then been critically compared with the DE 2 electron density observations. This comparison uncovers a model-data disagreement in the morning sector trough, generally good agreement of the background density in the polar cap and evening sector trough, and a difficulty in modelling the observed polar F layer patches. From this comparison, the consequences of structure in the electric field and precipitation inputs can be …

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Solar Cycle Dependence Of Spacecraft Charging In Low Earth Orbit, T. B. Frooninckx, Jan Josef Sojka Jan 1992

Solar Cycle Dependence Of Spacecraft Charging In Low Earth Orbit, T. B. Frooninckx, Jan Josef Sojka

All Physics Faculty Publications

Recent experimental evidence has shown that Defense Meteorological Satellite Program (DMSP) polar orbiting spacecraft at 840 km can develop electric potentials as severe as −1430 V while at high magnetic latitudes. To explore this charging region, an analysis of DMSP F6, F7, F8, and F9 satellite precipitating particle and ambient plasma measurements taken during periods of high, medium, and low solar flux is performed. One hundred eighty-four charging events ranging from −46 to −1430 V are identified, and an extreme solar cycle dependence is found as charging is most frequent and severe during solar minimum. Satellite measurements and time-dependent ionospheric …

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On The Standing Wave Mode Of Giant Pulsations, K. Takahashi, N. Sato, J. Warnecke, H. Luhr, Harlan E. Spence, Y. Tonegawa Jan 1992

On The Standing Wave Mode Of Giant Pulsations, K. Takahashi, N. Sato, J. Warnecke, H. Luhr, Harlan E. Spence, Y. Tonegawa

Physics & Astronomy

Both odd-mode and even-mode standing wave structures have been proposed for giant pulsations. Unless a conclusion is drawn on the field-aligned mode structure, little progress can be made in understanding the excitation mechanism of giant pulsations. In order to determine the standing wave mode, we have made a systematic survey of magnetic field data from the AMPTE CCE spacecraft and from ground stations located near the geomagnetic foot point of CCE. We selected time intervals when CCE was close to the magnetic equator and also magnetically close to Syowa and stations in Iceland, and when either transverse or compressional Pc …

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Alloy Scattering In P-Type Alxga1-Xas, David C. Look, D. K. Lorance, J. R. Sizelove, C. E. Stutz, K. R. Evans, D. W. Whitson Jan 1992

Alloy Scattering In P-Type Alxga1-Xas, David C. Look, D. K. Lorance, J. R. Sizelove, C. E. Stutz, K. R. Evans, D. W. Whitson

Physics Faculty Publications

The hole mobility of Be‐doped ( ~ 2 × 1017 cm-3) AlxGa1-xAs, for x=0–1, is analyzed both theoretically and experimentally. Alloy scattering is very important, and in fact reduces the hole mobility from 150 to less than 90 cm2/V s at x=0.5. The main parameter in the alloy scattering formulation, the alloy potential Eal, is found to be about 0.5 eV for p‐type AlxGa1-xAs.

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Densities And Vibrational Distribution Of H3+ In The Jovian Auroral Ionosphere, Y. H. Kim, Jane L. Fox, H. S. Porter Jan 1992

Densities And Vibrational Distribution Of H3+ In The Jovian Auroral Ionosphere, Y. H. Kim, Jane L. Fox, H. S. Porter

Physics Faculty Publications

Observations of the H3+ infrared emission at 2 and 4 μm have suggested that H3+ is in local thermodynamic equilibrium (LTE) in the region of the Jovian ionosphere from which the emissions originate. We have tested this assumption by calculating the vibrational distribution of H3+ over the altitude range of 350 to 1500 km above the methane cloud tops (1 to 4 × 10−3 μbar). We have constructed a model of the Jovian auroral ionosphere in which the neutral temperatures are enhanced over those of the mid-latitude ionosphere, as suggested by observations and …

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Real And Virtual Images Using A Classroom Hologram, Dale W. Olson Jan 1992

Real And Virtual Images Using A Classroom Hologram, Dale W. Olson

Faculty Work

No abstract provided.

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The Application Of Liquid Junctions For Characterization Of Semiconductor Materials, Wu-Mian Shen Jan 1992

The Application Of Liquid Junctions For Characterization Of Semiconductor Materials, Wu-Mian Shen

Dissertations, Theses, and Capstone Projects

In this study, liquid junctions were used to characterize silicon and silicon subjected to various reactive ion etching (RIE); surface optimization of CuInSe{dollar}\sb2{dollar}; and photo-modification of InSe. Impedance spectroscopy and modulation spectroscopies such as electrolyte electroreflectance (EER), photoreflectance (PR), and photoreflectance in the presence of electrolyte (EPR) were the major methodologies that were used for investigating the dielectric properties of the semiconductors and their interface with the ambients. It was shown that the above experimental techniques provide information about the flat-band potential, doping density, Fermi level pinning, the density and distribution of surface states, energy gap and broadening parameter related …

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