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1990

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Articles 1 - 30 of 169

Full-Text Articles in Physics

Relaxation Time Of The Order Parameter In A High-Temperature Superconductor, G.L. Eesley, J. Heremans, M.S. Meyer, G.L. Doll, Sy_Hwang Liou Dec 1990

Relaxation Time Of The Order Parameter In A High-Temperature Superconductor, G.L. Eesley, J. Heremans, M.S. Meyer, G.L. Doll, Sy_Hwang Liou

Si-Hwang Liou Publications

We present femtosecond time-resolved measurements on the high-Tc superconductor Tl2Ba2Ca2Cu3O10. At temperatures below Tc, we observe a relaxation process which is distinct from the equilibration of hot carriers in the normal state. Our results demonstrate an increasing relaxation rate as the superconducting gap opens. This is consistent with the behavior of conventional metallic superconductors.


Power Law Exponents For A Spreading Front And Growing Interface In An Irreversible Wetting, Evan Willett, Ras B. Pandey Dec 1990

Power Law Exponents For A Spreading Front And Growing Interface In An Irreversible Wetting, Evan Willett, Ras B. Pandey

Faculty Publications

Using computer simulations, the power-law behavior of the interface growth of a spreading fluid is studied in a two-dimensional lattice model. The interface width exponent v and the dynamical exponent k for the evolution of the front are consistent with their dynamical scaling relation. The magnitude of these exponents seems to depend upon the nature of the substrate and the concentration of the carriers of the wetting fluid.


Laser Cvd And Plasma Cvd Of Cro2 Films And Cobalt Doped Cro2 Films Using Organometallic Precursors, Peter A. Dowben, Marshall Onellion Dec 1990

Laser Cvd And Plasma Cvd Of Cro2 Films And Cobalt Doped Cro2 Films Using Organometallic Precursors, Peter A. Dowben, Marshall Onellion

Peter Dowben Publications

Chromium dioxide is deposited as a ferromagnetic layer onto selected portions of a substrate or over the entire substrate. Chromium hexacarbonyl vapor is introduced into a vacuum deposition chamber at e.g. 10 milliTorr and oxygen is introduced at e.g. 15 to 100 milliTorr. A UV laser beam is focused onto the substrate to form the CrO2 layer photolytically. The CrO2 layer can also be deposited by RF plasma deposition. This technique can also be employed for depositing MoC2, WC2, Mo2φ3, MoO2 or WO2. Magnetic recording or memory devices are produced without ...


The Relationship Of The Virtual Orbitals Of Self-Consistent-Field Theory To Temporary Negative Ions In Electron Scattering From Molecules, Donghai Chen, Gordon A. Gallup Dec 1990

The Relationship Of The Virtual Orbitals Of Self-Consistent-Field Theory To Temporary Negative Ions In Electron Scattering From Molecules, Donghai Chen, Gordon A. Gallup

Gordon Gallup Publications

The theory given here shows how certain of the virtual orbitals of self-consistent field (SCF) theory provide a natural ingredient for constructing basis functions to study the shape resonances associated with temporary molecular ions. We give specific calculations of resonant behavior in H2, N2, ethylene, cyclopropene, and cyclobutene. In addition, we show how the theory can rationalize the relationship between Koopmans' theorem values of the energy of a resonance and the experimental values. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.


Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans Dec 1990

Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans

Physics Faculty Publications

Previous attempts to passivate the n‐type (100)GaAs surface have significantly reduced only the surface recombination centers, but not the surface acceptors which pin the Fermi level. Here we show that a 100 Å molecular beam epitaxial layer grown at 200 °C reduces the effective surface potential energy − eϕs from 0.70 to 0.17 eV, nearly eliminates light sensitivity, and permits nonalloyed ohmic contacts. After a 10 min, 450 °C anneal, − eϕs increases only to 0.22 eV.


Device For Dispersal Of Micrometer- And Submicrometer-Sized Particles In Vaccum, D. P. Sheehan, M. Carillo, W. Heidbrink Dec 1990

Device For Dispersal Of Micrometer- And Submicrometer-Sized Particles In Vaccum, D. P. Sheehan, M. Carillo, W. Heidbrink

Physics and Biophysics: Faculty Scholarship

A simple, versatile device for dispersing micrometer‐ and submicrometer-sized particles in vacuum is described. The source allows control of particle size (0.5 μm≤l≤200 μm) and particle flux density up to roughly 107 cm−2 s−1. Several types of microparticles were successfully dispersed.


Single Transfer-Excitation Resonance Observed Via The Two-Photon Decay In He-Like Ge30+, Paul H. Mokler, S. Reusch, A. Warczak, Zbigniew Stachura, T. Kambara, Alfred K. Muller, Reinhold S. Schuch, Michael Schulz Dec 1990

Single Transfer-Excitation Resonance Observed Via The Two-Photon Decay In He-Like Ge30+, Paul H. Mokler, S. Reusch, A. Warczak, Zbigniew Stachura, T. Kambara, Alfred K. Muller, Reinhold S. Schuch, Michael Schulz

Physics Faculty Research & Creative Works

We measured the 2E1 decay of the 1s2s 1S0 →1s2 1S0 transition in He-like germanium for 12- to 19-MeV/u Ge31+ +H2 collisions. The resonant population of the 2s2p 1P1 state by transfer excitation was isolated due to its cascading to the 1s2s 1S0 state. The experimental cross sections compare well with calculations using dielectronic recombination rates. The method gives the unique possibility to populate selectively the 1S0 state in heavy He-like ions.


Virasoro Model Space, Hoseong La, Philip C. Nelson, A S. Schwarz Dec 1990

Virasoro Model Space, Hoseong La, Philip C. Nelson, A S. Schwarz

Department of Physics Papers

The representations of a compact Lie group G can be studied via the construction of an associated “model space”. This space has the property that when geometrically quantized its Hilbert space contains every irreducible representation of G just once. We construct an analogous space for the group Diff S1. It is naturally a complex manifold with a holomorphic, free action of Diff S1 preserving a family of pseudo-Kahler structures.All of the “good” coadjoint orbits are obtained from our space by Hamiltonian constraint reduction. We briefly discuss the connection to the work of Alekseev and Shatashvili.


Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. I. Experiments On Dy/Co, Dy/Fe, And Tb/Fe, Z.S. Shan, David J. Sellmyer Dec 1990

Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. I. Experiments On Dy/Co, Dy/Fe, And Tb/Fe, Z.S. Shan, David J. Sellmyer

David Sellmyer Publications

Experimental investigations of magnetic and structural properties for rare-earth–transition-metal (RE-TM) compositionally modulated films (CMF) are presented in this paper. In particular, ARE/BTM including ARE=Dy and Tb and BTM=Fe, Co, and Ni, are studied. The layer thickness and temperature dependence of magnetic properties, which can be interpreted in terms of the antiferromagnetic coupling of RE and TM moments and their atomic distributions, are reported. These ARE/BTM CMF with nanoscale layer thicknesses exhibit perpendicular magnetic anisotropy (PMA) and the range of the layer thickness required for PMA is determined. The origin ...


Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. Ii. Theoretical Analysis Of Magnetization And Perpendicular Magnetic Anisotropy, Z.S. Shan, David J. Sellmyer, Sitaram Jaswal, Y.J. Wang, J.X. Shen Dec 1990

Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. Ii. Theoretical Analysis Of Magnetization And Perpendicular Magnetic Anisotropy, Z.S. Shan, David J. Sellmyer, Sitaram Jaswal, Y.J. Wang, J.X. Shen

David Sellmyer Publications

Systematic studies of rare-earth–transition-metal amorphous compositionally modulated films (CMF) permit the development of a detailed model for understanding the magnetization and perpendicular magnetic anisotropy and their distributions along the film normal. It is shown that the single-ion anisotropy of rare-earth ions with orbital angular momentum is the major contributor to the perpendicular anisotropy for this class of CMF. The calculated results agree well with the experimental data for Dy/Co and Tb/Fe CMF when the individual layer thicknesses are small enough (<10 Å); these films have structures which can be characterized as compositionally modulated amorphous alloys.


Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams Dec 1990

Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams

Senior Theses and Projects

The purpose of this lab is to help the student become more familiar with, or get a better feel for what is actually occurring, when observing the effects of double slit diffraction patterns. In most sophomore labs dealing with double slit diffraction, the student simply determines the diffraction angle, and slit spacing, from marking the positions of the maxima on the screen. No attempt is made to measure the relative intensity of the interference pattern, and see how the experimental data compare with the theory of interference and diffraction. In an attempt to further clarify this phenomena, we will attempt ...


United States Patent: Metaginsulator Composites Having Improved Properties And Method For Their Preparation, Chia-Ling Chien, Gang Xiao, Sy-Hwang Liou Nov 1990

United States Patent: Metaginsulator Composites Having Improved Properties And Method For Their Preparation, Chia-Ling Chien, Gang Xiao, Sy-Hwang Liou

Si-Hwang Liou Publications

Improved cermets having superior properties comprising a ferromagnetic metal and an insulator. By controlling process conditions, cermets having high magnetization and high coercivity as well as chemical stability, wear resistance and corrosion resistance are prepared. The cermets of this invention find particular utility as high density recording media.


Anomalous Dimensions Of Anisotropic Gauge Theory Operators, David G. Robertson, Frank Wilczek Nov 1990

Anomalous Dimensions Of Anisotropic Gauge Theory Operators, David G. Robertson, Frank Wilczek

Physics Faculty Scholarship

The anomalous dimensions of the anisotropic dimension four operators in SU(N) gauge theory coupled to fermions are calculated to lowest order. The possibility of comparison with numerical simulations is pointed out.


Effects Of Magnetic Field And Temperature On The Critical Current Hysteresis In Tl-Ca-Ba-Cu-O Thin Films, Hung-Lun Chang, Jenh-Yih Juang, Sy_Hwang Liou, Tzeng-Ming Uen, Yih-Shun Gou Nov 1990

Effects Of Magnetic Field And Temperature On The Critical Current Hysteresis In Tl-Ca-Ba-Cu-O Thin Films, Hung-Lun Chang, Jenh-Yih Juang, Sy_Hwang Liou, Tzeng-Ming Uen, Yih-Shun Gou

Si-Hwang Liou Publications

The behavior of the critical current density of Tl-Ca-Ba-Cu-O superconducting thin films in a cycling magnetic field was investigated. The hysteresis of the transport Jc manifested similar features to those found in polycrystalline Y-Ba-Cu-O and granular Nb, Al thin films in zero-field cooling. However, a novel result of the transport Jc in field-cooled samples has been observed. The results were attributed to the presence of a saturated trapped magnetic flux in the weaklink network. The effects of temperature on both the trapped flux and the transport Jc suggest the existence of various states of the trapped flux ...


Radiative Transfer In Astronomical Masers. I. The Linear Maser, Moshe Elitzur Nov 1990

Radiative Transfer In Astronomical Masers. I. The Linear Maser, Moshe Elitzur

Physics and Astronomy Faculty Publications

This is the first in a series of three papers presenting a comprehensive, unified approach for radiative transfer in astronomical maser sources. This paper provides the general formalism and presents the detailed analytic solution of the linear maser, including the case of a source illuminated by background radiation.


Using Refraction Caustics To Monitor Evaporation Of Liquid Drop Lenses, James A. Lock, Jearl D. Walker, James H. Andrews Nov 1990

Using Refraction Caustics To Monitor Evaporation Of Liquid Drop Lenses, James A. Lock, Jearl D. Walker, James H. Andrews

Physics Faculty Publications

Irregularities in the perimeter of a water droplet adhering to a vertical pane of glass cause perturbations in the curvature of the droplet surface. When laser light passes through such a droplet, the perturbations produce a far field refraction caustic, which is a section of the caustic known as the parabolic umbilic in the catastrophe theory classification. As the water evaporates and the droplet surface curvature changes, the section of the parabolic umbilic caustic on the viewing screen also changes. We determine the evolution of curvature of the droplet surface by observing the evolution of the far field caustic and ...


Controlled Biosynthesis Of Greigite (Fe3S4) In Magnetotactic Bacteria, Brigid R. Heywood, Dennis A. Bazylinski, Anthony J. Garratt-Reed, Stephen Mann, Richard B. Frankel Nov 1990

Controlled Biosynthesis Of Greigite (Fe3S4) In Magnetotactic Bacteria, Brigid R. Heywood, Dennis A. Bazylinski, Anthony J. Garratt-Reed, Stephen Mann, Richard B. Frankel

Physics

No abstract provided.


Simple Overdense Rf Plasma Source, R. Mcwilliams, D. Edrich, R. C. Platt, D. P. Sheehan Nov 1990

Simple Overdense Rf Plasma Source, R. Mcwilliams, D. Edrich, R. C. Platt, D. P. Sheehan

Physics and Biophysics: Faculty Scholarship

A simple, gas‐fed, radio‐frequency‐driven plasma source is described. By use of lower hybrid waves, noble gas plasmas were produced with electron densities up to 10^12 cm -3 over a range of magnetic fields from 400 G to 1.5 kG and rf frequencies from 2–220 MHz.


Ab Initio Studies Of The Phase Transitions In K2Seo4, H. M. Lu, John R. Hardy Nov 1990

Ab Initio Studies Of The Phase Transitions In K2Seo4, H. M. Lu, John R. Hardy

John R. Hardy Papers

An ab initio model is developed for the potentials in ionic molecular solids in which the electron covalency within the molecular ions substantially affects the interionic interactions. By treating the intermolecular and intramolecular interactions on the basis of the true electron charge densities of the molecular ions, this new model leads to an accurate parameter-free description of the potentialenergy surfaces for such crystals. We performed first-principles static structural relaxation, supercell molecular-dynamics simulation, and lattice-dynamics studies for the room-temperature paraelectric phase and the lower-temperature ferroelectric superstructure of K2SeO4 and predicted with good accuracy the transition from the former ...


Optical Properties And Electronic Structures Of The Intermetallic Compounds Auga2 And Ptga2, Kwang-Joo Kim, Bruce N. Harmon, Liang-Yao Chen, David W. Lynch Nov 1990

Optical Properties And Electronic Structures Of The Intermetallic Compounds Auga2 And Ptga2, Kwang-Joo Kim, Bruce N. Harmon, Liang-Yao Chen, David W. Lynch

Physics and Astronomy Publications

The electronic structures of AuGa2 and PtGa2 have been studied with use of spectroscopic ellipsometry and the dielectric functions have been determined in the 1.2–5.5-eV region. Both compounds show interband absorption at low photon energies (<1.3 eV). The interband absorption for AuGa2 is strong at about 2 eV while that for PtGa2 shows a broad structure in the range 2.5–4.5 eV, with a shoulder at 3.3 eV. The observed interband features in ε2 can be interpreted in terms of self-consistent relativistic band-structure calculations using the linear augmented-plane-wave method. The interband contribution to the imaginary part of the dielectric function εb2 has been calculated including the effect of the electric dipole matrix elements. The overall agreement is good between the band calculations and the ellipsometry results in the 1.2–5.5-eV region for both the magnitude and the positions of the structures. Below 1.2 eV the calculational results for both compounds show interband absorption, which is also qualitatively suggested by the ellipsometry results.


Photoemission Study Of Au On A-Si:H, Tun-Wen Pi, A.-B. Yang, C. G. Olson, David W. Lynch Nov 1990

Photoemission Study Of Au On A-Si:H, Tun-Wen Pi, A.-B. Yang, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

We report a high-resolution photoemission study of Au evaporated on rf-sputtered a-Si:H at room temperature. Three regions of coverage can be classified according to the behavior of the valence-band and core-level spectra: an unreacted region with an equivalent thickness of 2 Å, followed by an intermixed Au/a-Si overlayer (∼9 Å), and a dual-phase region at higher coverage. Au adatoms are dispersed in the unreacted region. They subsequently cluster in the intermixed region, where they attach to Si atoms that are not hydrogen bonded, suggesting that the intermixed Si is mainly from those that have dangling bonds ...


Photoemission Study Of Cr On A-Si:H, Tun-Wen Pi, C. G. Olson, David W. Lynch Nov 1990

Photoemission Study Of Cr On A-Si:H, Tun-Wen Pi, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

We report a synchrotron-radiation photoemission study of Cr evaporated on rf-sputtered a-Si:H at room temperature. The evolution of the interface qualitatively follows that on c-Si, despite differences in the valence-band emission. The interface begins with an inactive layer (≤1 Å) of Cr, followed by an intermixed Cr/a-Si:H layer (≤12 Å). With further Cr deposition, bulklike Cr metal begins to develop on top of these. Some features exhibited by the Cr/a-Si:H interface are specific to a-Si:H surfaces. For instance, Cr adatoms are found around the dangling-bond neighborhood at coverages below ...


Predictions Of Cell Damage Rates For Lifesat Missions, Francis A. Cucinotta, William Atwell, Alva C. Hardy, Michael J. Golightly, John W. Wilson, Lawrence W. Townsend, Judy Shinn, John E. Nealy, Robert Katz Nov 1990

Predictions Of Cell Damage Rates For Lifesat Missions, Francis A. Cucinotta, William Atwell, Alva C. Hardy, Michael J. Golightly, John W. Wilson, Lawrence W. Townsend, Judy Shinn, John E. Nealy, Robert Katz

Robert Katz Publications

Radiological experiments with cell cultures are expected to be performed on Lifesat to study possible gravitational dependence on cellular response. Predictions of cell damage rates for well-studied systems are expected to help guide in the selection of orbits and the design of experiments. In this report we estimate the fractions of cell death and neoplastic transformation of C3H10T1/2 cells (cultured mouse cells) for the proposed Lifesat orbits. The parametric cellular track model of Katz et al. (refs. 1 and 2) is employed using cellular response parameters derived from the experiments of Yang et al. (refs. 3 and 4). The ...


Some "Do's" And "Don't'S" For Using Computers In Science Instruction, Glenn A. Sowell, Robert Fuller Nov 1990

Some "Do's" And "Don't'S" For Using Computers In Science Instruction, Glenn A. Sowell, Robert Fuller

Robert G. Fuller Publications and Presentations

As science researchers and professors, we have had a fairly broad collection of experiences in using computers, from batch-processing and number crunching in large computer systems using FORTRAN and symbolic languages to teaching problem-solving courses for nonscience students using personal computers. While we claim no special computer expertise, we both own computers and are frequently called upon to offer advice to our colleagues who are greater novices than we are. Hence, on the basis of reflections on our experiences and observations of what we have seen other people and institutions do, we have compiled a list of “Do’s” and ...


Laser-Induced Detachment Processes In An Electric Field, Bo Gao, Anthony F. Starace Nov 1990

Laser-Induced Detachment Processes In An Electric Field, Bo Gao, Anthony F. Starace

Anthony F. Starace Publications

An analytic momentum-space wave function for an electron in both laser and static uniform electric fields is presented. It is used to obtain analytic multiphoton detachment cross sections in a static, uniform electric field which include effects of static-field-induced electron-photon interactions. These general results are not restricted to weak laser intensities or to weak static-field strengths and depend only on (a) the electric dipole approximation and (b) the approximation that final-state electron-atom interactions are ignored. Four specific predictions of our general formulas for the most interesting case of linearly polarized light polarized along the static-field direction are presented for weakly ...


Synchrotron Radiation Induced Chemical Vapor Deposition Of Thin Films From Metal Hexacarbonyls*, Derrick C. Mancini, Shikha Varma, John K. Simons, Richard A. Rosenberg, Peter A. Dowben Nov 1990

Synchrotron Radiation Induced Chemical Vapor Deposition Of Thin Films From Metal Hexacarbonyls*, Derrick C. Mancini, Shikha Varma, John K. Simons, Richard A. Rosenberg, Peter A. Dowben

Peter Dowben Publications

We have studied the initial stages of synchrotron radiation [SR] induced chemical vapor deposition [CVD] of metal-containing thin films from metal hexacarbonyl gases. We have measured the dependence of the initial deposition rate upon gas pressure at room temperature. Substrates were exposed to SR for single fills of the electron storage ring at constant pressure of Mo(CO)6, Cr(CO)6, or W(CO) 6 gas. Deposition was monitored in situ by Auger electron spectroscopy using the SW as the excitation source. The presence of metal, carbon, and oxygen in the deposited films was observed, and the results are ...


Collisional Excitation Of Co By 2.3 Ev H Atoms, George C. Mcbane, Scott H. Kable, Paul L. Houston, George C. Schatz Oct 1990

Collisional Excitation Of Co By 2.3 Ev H Atoms, George C. Mcbane, Scott H. Kable, Paul L. Houston, George C. Schatz

Peer Reviewed Articles

Vibrational and rotational distributions of CO excited by collisions with 2.3 eV H atoms have been obtained by monitoring the products with vacuum ultraviolet (VUV) laser induced fluorescence. Translational-to-vibrational (T→V) transfer is dominated by the dynamics of collisions occurring in the two wells on the H+CO potential energy surface, one characterizing the HCO radical and the other characterizing COH. The measured vibrational distributions agree well with the results of trajectory calculations performed on the ab initio potential energy surface of Bowman, Bittman, and Harding (BBH). The measured rotational distributions show two significant differences from the calculated ones ...


Heterotic Conformal Field Theory And Gepner’S Construction, Darwin Chang, Asim Gangopadhyaya, Alok Kumar, Jin Wang Oct 1990

Heterotic Conformal Field Theory And Gepner’S Construction, Darwin Chang, Asim Gangopadhyaya, Alok Kumar, Jin Wang

Physics: Faculty Publications and Other Works

We discuss some general properties of heterotic conformal field theory in which conformal anomalies c are different for the left-moving and right-moving sectors. It is precisely this type of theory that can be applied immediately to the construction of heterotic string theory. We discuss a general way of constructing such a theory using free fermions. The construction is then applied to generalize Gepner's construction of superstring solutions using the tensor products of N=2 superconformal field theories.


Wetting Transitions In A Cylindrical Pore, Andrea J. Liu, Douglas J. Durian, Eric Herbolzheimer, S. A. Safran Oct 1990

Wetting Transitions In A Cylindrical Pore, Andrea J. Liu, Douglas J. Durian, Eric Herbolzheimer, S. A. Safran

Department of Physics Papers

The wetting behavior of two-phase systems confined inside cylindrical pores is studied theoretically. The confined geometry gives rise to wetting configurations, or microstructures, which have no analog in the well-studied planar case. Many features observed in experiments on binary liquid mixtures in porous media, previously interpreted in terms of random fields, are shown to be consistent with wetting in a confined geometry with no randomness.


Hyper-Resistivity To Global-Superconductivity Transition By Annealing In Quench-Condensed Pb Films, Richard P. Barber Jr., Rolfe Eldridge Glover Iii Oct 1990

Hyper-Resistivity To Global-Superconductivity Transition By Annealing In Quench-Condensed Pb Films, Richard P. Barber Jr., Rolfe Eldridge Glover Iii

Physics

The rapid rise in resistance occurring in barely conducting quench-condensed Pb films cooled through temperatures characteristic of the bulk superconducting transition is found to be strongly current dependent, the resistance increasing rapidly with decreasing current and temperature. Annealing the same film at temperatures below 40 K changes the behavior to that of a conventional superconductor with resistance that drops as the film current and temperature decrease. Experimental evidence suggests this results from a transition from quasiparticle-dominated to Josephson-dominated tunneling.