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1992

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Articles 1 - 30 of 190

Full-Text Articles in Physics

Giant Suppression Of Flux-Flow Resistivity In Heavy-Ion Irradiated Tl2Ba2Ca2Cu3O10 Films: Influence Of Linear Defects On Vortex Transport, R.C. Budhani, M. Suenaga, Sy_Hwang Liou Dec 1992

Giant Suppression Of Flux-Flow Resistivity In Heavy-Ion Irradiated Tl2Ba2Ca2Cu3O10 Films: Influence Of Linear Defects On Vortex Transport, R.C. Budhani, M. Suenaga, Sy_Hwang Liou

Si-Hwang Liou Publications

A large shift of the onset of flux-flow resistivity and the irreversibility line Hirr (T) to higher temperatures is observed in Tl2Ba2Ca2Cu3O10 films containing linear defects created by Ag+21 ion irradiation. The Hirr(T), which has a characteristic ssL shape in highly anisotropic Tl and Bi based cuprates, becomes more like that of YBa2Cu3O7 in the presence of these defects. The Jc at 77 K also shows a large increase as a result of flux localization at the defects. The transport data ...


Measurement Of Ionization And Phonon Production By Nuclear Recoils In A 60 G Crystal Of Germanium At 25 Mk, Tom Shutt, B. Ellman, P. D. Barnes Jr., Alan Cummings, Angela Da Silva, John Emes, Y. Giraud-Héraud, Eugene E. Haller, Andrew E. Lange, Ron R. Ross, J. Rich, Bernard Sadoulet, G. Smith, W. Stockwell, C. Stubbs, N. Wang, S. White, Betty A. Young, D. Yvon Dec 1992

Measurement Of Ionization And Phonon Production By Nuclear Recoils In A 60 G Crystal Of Germanium At 25 Mk, Tom Shutt, B. Ellman, P. D. Barnes Jr., Alan Cummings, Angela Da Silva, John Emes, Y. Giraud-Héraud, Eugene E. Haller, Andrew E. Lange, Ron R. Ross, J. Rich, Bernard Sadoulet, G. Smith, W. Stockwell, C. Stubbs, N. Wang, S. White, Betty A. Young, D. Yvon

Physics

We report on the first measurement of the absolute phonon energy and the amount of ionization produced by the recoil of nuclei and electrons in a 60 g germanium cyrstal at a temperature of ≊25 mK. We find good agreement between our results and previous measurements of ionization yield from nuclear recoils in germanium. Our device achieves 10:1 discrimination between neutrons and photons in the few keV energy range, demonstrating the feasibility of this technique for large reductions of background in searches for direct interactions of weakly interacting massive particle dark matter.


Simultaneous High Resolution Meausurement Of Phonons And Ionization Created By Particle Interactions In A 60 G Germanium Crystal At 25 Mk, Tom Shutt, N. Wang, B. Ellman, Y. Giraud-Héraud, C. Stubbs, Peter D. Barnes Jr., A. Cummings, Angela Da Silva, John Emes, Eugene E. Haller, Andrew E. Lange, J. Rich, R. R. Ross, B. Sadoulet, G. Smith, W. Stockwell, S. White, Betty A. Young, D. Yvon Dec 1992

Simultaneous High Resolution Meausurement Of Phonons And Ionization Created By Particle Interactions In A 60 G Germanium Crystal At 25 Mk, Tom Shutt, N. Wang, B. Ellman, Y. Giraud-Héraud, C. Stubbs, Peter D. Barnes Jr., A. Cummings, Angela Da Silva, John Emes, Eugene E. Haller, Andrew E. Lange, J. Rich, R. R. Ross, B. Sadoulet, G. Smith, W. Stockwell, S. White, Betty A. Young, D. Yvon

Physics

We demonstrate simultaneous high energy resolution (rms≊800 eV) measurements of ionization and phonons created by particle interactions in a semiconductor crystal of macroscopic size (60 g germanium) at 25 mK. We present first studies of charge collection at biases below 1 V/cm, and find that, contrary to commonly held opinion, the full recoil energy of particle interactions is recovered as phonons when charge trapping is negligible. We also report an unanticipated correlation between charge collection and phonon energy at very low bias, and discuss this effect in terms of charge trapping.


The Weakest Bond: Experimental Observation Of Helium Dimer, Fei Luo, George C. Mcbane, Geunsik Kim, Clayton F. Giese, W. Ronald Gentry Dec 1992

The Weakest Bond: Experimental Observation Of Helium Dimer, Fei Luo, George C. Mcbane, Geunsik Kim, Clayton F. Giese, W. Ronald Gentry

Peer Reviewed Articles

Helium dimer ion was observed after electron impact ionization of a supersonic expansion of helium with translational temperature near 1 mK. The dependence of the ion signal on source pressure, distance from the source, and electron kinetic energy was measured. The signal was determined to arise from ionization of neutral helium dimer.


Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson Dec 1992

Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson

Physics

We discuss the statistical mechanics of magnetic flux lines in a finite-thickness slab of type-II superconductor. The long wavelength properties of a flux-line liquid in a slab geometry are described by a hydrodynamic free energy that incorporates the boundary conditions on the flux lines at the sample's surface as a surface contribution to the free energy. Bulk and surface weak disorder are modeled via Gaussian impurity potentials. This free energy is used to evaluate the two-dimensional structure factor of the flux-line tips at the sample surface. We find that surface interaction always dominates in determining the decay of translational ...


Calculation Of The Residual Resistivity And The Thermoelectric Power Of Sp Impurities In Silver, Thomas Vojta, Ingrid Mertig, Rudolf Zeller Dec 1992

Calculation Of The Residual Resistivity And The Thermoelectric Power Of Sp Impurities In Silver, Thomas Vojta, Ingrid Mertig, Rudolf Zeller

Physics Faculty Research & Creative Works

We present ab initio calculations for the residual resistivity and the thermopower of sp impurities in silver. The calculations are based on density-functional theory and the Korringa-Kohn-Rostoker Greens-function method. The linearized Boltzmann equation is solved by means of a Fermi-surface harmonic expansion to calculate the residual resistivity, taking into account the anisotropic electronic properties of the dilute alloy. The thermoelectric power was obtained from the energy dependence of the residual resistivity by means of Mott's formula. The results are in satisfying agreement with highly precise experimental results and confirm experimentally obtained deviations from a quadratic dependence on the valence ...


Rigid Chiral Membranes, Philip C. Nelson, Thomas Powers Dec 1992

Rigid Chiral Membranes, Philip C. Nelson, Thomas Powers

Department of Physics Papers

Statistical ensembles of flexible two-dimensional fluid membranes arise naturally in the description of many physical systems. Typically one encounters such systems in a regime of low tension but high stiffness against bending, which is just the opposite of the regime described by the Polyakov string. We study a class of couplings between membrane shape and in-plane order which break 3-space parity invariance. Remarkably there is only one
such allowed coupling (up to boundary terms); this term will be present for any lipid bilayer composed of tilted chiral molecules. We calculate the renormalization-group behavior of this relevant coupling in a simplified ...


Explosion Of A Liquid Film In Contact With A Pulse-Heated Solid Surface Detected By The Probe-Beam Deflection Method, P.T. Leung, Andrew C. Tam, Nhan Do, Leander Klees, Wing P. Leung Dec 1992

Explosion Of A Liquid Film In Contact With A Pulse-Heated Solid Surface Detected By The Probe-Beam Deflection Method, P.T. Leung, Andrew C. Tam, Nhan Do, Leander Klees, Wing P. Leung

Physics Faculty Publications and Presentations

The threshold for explosive vaporization of a liquid layer on an opaque solid surface heated by an ultraviolet excimer pulsed laser is studied by a photoacoustic probe-beam deflection method. The probe beam traverses the liquid in the vicinity of the laser-heated liquid-solid interface. Below the explosion threshold, photoacoustic generation in the solid occurs only through a thermoelastic mechanism, which results mainly in shear waves that do not couple well into the liquid. Above the explosion threshold, photoacoustic pulses in the solid are also produced by explosive recoil, hence producing longitudinal pulses in the solid that couple well into the liquid ...


Vibrational Excitations In Percolation: Localization And Multifractality, Armin Bunde, H. Eduardo Roman, Stefanie Russ, Amnon Aharony, A. Brooks Harris Nov 1992

Vibrational Excitations In Percolation: Localization And Multifractality, Armin Bunde, H. Eduardo Roman, Stefanie Russ, Amnon Aharony, A. Brooks Harris

Department of Physics Papers

We discuss localized excitations on the incipient infinite percolation cluster. Assuming a simple exponential decay of the amplitudes ψi in terms of the chemical (minimal) path, we show theoretically that the ψ’s are characterized by a logarithmically broad distribution, and display multifractal features as a function of the Euclidean distance. The moments of ψi exhibit novel crossover phenomena. Our numerical simulations of fractons exhibit a nontrivial distribution of localization lengths, even when the chemical distance is fixed. These results are explained via a generalization of the theory.


Modeling Sio Maser Emission From Late-Type Stars, Philip B. Lockett, Moshe Elitzur Nov 1992

Modeling Sio Maser Emission From Late-Type Stars, Philip B. Lockett, Moshe Elitzur

Physics and Astronomy Faculty Publications

We have performed a thorough study of both radiative and collisional pumping of the SiO masers around late-type stars, carefully considering the combined and separate actions of each type of pump in order to gauge its effectiveness. We find that collisional pumping is severely underestimated when the model calculations use a small number (less than about 18) of rotational levels in each vibrational state. We have developed a procedure that corrects this problem and gives results that are nearly independent of the number of levels utilized in the calculations. We recognize, but do not solve, an important problem that afflicts ...


Non-Relativistic Qcd For Heavy Quark Systems, Simon Catterall, F. R. Devlin, I. T. Drummond, R. R. Horgan, A. D. Simpson Nov 1992

Non-Relativistic Qcd For Heavy Quark Systems, Simon Catterall, F. R. Devlin, I. T. Drummond, R. R. Horgan, A. D. Simpson

Physics

We employ a nonrelativistic version of QCD (NRQCD) to study heavy quark-antiquark bound states in the lowest approximation without fine structure. We use gluon configurations on a 16^3 by 48 lattice at beta=6.2 from the UKQCD collaboration. For quark masses in the vicinity of the b we obtain bound state masses for S, P and both types of D wave. We also detect signals for two types of hybrids (quark,antiquark,gluon states). The results are sufficiently accurate to confirm that the values of the D wave mass from both lattice D waves coincide indicating that the ...


Characterization Of Boron Carbide Thin Films Fabricated By Plasma Enhanced Chemical Vapor Deposition From Boranes, Sunwoo Lee, John Mazurowski, G. Ramseyer, Peter A. Dowben Nov 1992

Characterization Of Boron Carbide Thin Films Fabricated By Plasma Enhanced Chemical Vapor Deposition From Boranes, Sunwoo Lee, John Mazurowski, G. Ramseyer, Peter A. Dowben

Peter Dowben Publications

We have fabricated boron carbide thin films on Si(111) and other substrates by plasma-enhanced chemical-vapor deposition (PECVD). The PECVD of boron carbides from nido-cage boranes, specially nido-pentaborane(9) (B5H9), and methane ( CH4) is demonstrated. The band gap is closely correlated with the boron to carbon ratio and can range from 0.77 to 1.80 eV and is consistent with the thermal activation barrier of 1.25 eV for conductivity. We have made boron carbide by PECVD from pentaborane and methane that is sufficiently isotropic to obtain resistivities as large as 1010 ...


Novel Results For Quasiclassical Linear Transport In Metallic Multilayers, Horacio E. Camblong Nov 1992

Novel Results For Quasiclassical Linear Transport In Metallic Multilayers, Horacio E. Camblong

Physics and Astronomy

We analyze the linear transport behavior of metallic multilayers via the Kubo formula for a Hamiltonian with zero-range spin-dependent potentials. We find a direct connection between the Boltzmann and the Kubo approaches. Our two-point transport theory validates the quasiclassical approach for multilayered structures and introduces a new treatment of interfaces via angle-dependent coherent transmission coefficients.


Katz Model Prediction Of Caenorhabditis Elegans Mutagenesis On Sts-42, Francis A. Cucinotta, John W. Wilson, Robert Katz, Gautam Badhwar Nov 1992

Katz Model Prediction Of Caenorhabditis Elegans Mutagenesis On Sts-42, Francis A. Cucinotta, John W. Wilson, Robert Katz, Gautam Badhwar

Robert Katz Publications

The Katz track structure model has been applied to describe recessive lethal mutagenesis in the nematode Caenorhabditis elegans after exposure to heavy ions. Based on models of the cosmic-ray environment and heavy-ion transport, mutation rates for the International Microgravity Laboratory 1 (IML-1) experiment on the Space Transportation System 42 (STS-42) are predicted and the results are discussed.


Variationally Stable Treatment Of Two- And Three-Photon Detachment Of H- Including Electron-Correlation Effects, Chih-Ray Liu, Bo Gao, Anthony F. Starace Nov 1992

Variationally Stable Treatment Of Two- And Three-Photon Detachment Of H- Including Electron-Correlation Effects, Chih-Ray Liu, Bo Gao, Anthony F. Starace

Anthony F. Starace Publications

A variationally stable, adiabatic hyperspherical treatment of two- and three-photon detachment of H- is presented. Results are compared with analytic predictions of a zero-range potential model of H-. Detailed comparisions are made also with other theoretical results which include the effects of electron correlations. We predict analytically (and demonstrate numerically) an extreme sensitivity of the theoretical predictions to any errors in the value of the electron affinity employed. In an Appendix we show that the low-intensity limit of the Keldysh treatment [Sov. Phys. JETP 20, 1307 (1965)] of detachment of an electron bound in a zero-range potential agrees with the ...


Exact Enumeration And Scaling For Fragmentation Of Percolation Clusters, Boyd F. Edwards, M. F. Gyure, M. V. Ferer Nov 1992

Exact Enumeration And Scaling For Fragmentation Of Percolation Clusters, Boyd F. Edwards, M. F. Gyure, M. V. Ferer

All Physics Faculty Publications

The fragmentation properties of percolation clusters yield information about their structure. Monte Carlo simulations and exact cluster enumeration for a square bond lattice and exact calculations for the Bethe lattice are used to study the fragmentation probability as(p) of clusters of mass s at an occupation probability p and the likelihood bs′s(p) that fragmentation of an s cluster will result in a daughter cluster of mass s′. Evidence is presented to support the scaling laws as(pc)∼s and bs′s(pc)=sg(s′/s), with φ=2-σ given ...


Renormalization-Group Study Of The Standard Model And Its Extensions: The Standard Model, H. Arason, Diego Castano, B. Kesthelyi, S. Mikaelian, E. J. Piard, P. Ramond, B. D. Wright Nov 1992

Renormalization-Group Study Of The Standard Model And Its Extensions: The Standard Model, H. Arason, Diego Castano, B. Kesthelyi, S. Mikaelian, E. J. Piard, P. Ramond, B. D. Wright

Chemistry and Physics Faculty Articles

In this paper we present a comprehensive analysis of the running of all the couplings of the standard model to two loops, including threshold effects. Our purpose is twofold—to determine what the running of these parameters may indicate for the physics of the standard model and to provide a template for the study of its extensions up to the Planck mass.


A Mössbauer Effect Study Of The Microscopic Magnetic Properties Of Nd₂Fe₁₇ And Nd₂Fe₁₇N₂.₆, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. J. Buschow Nov 1992

A Mössbauer Effect Study Of The Microscopic Magnetic Properties Of Nd₂Fe₁₇ And Nd₂Fe₁₇N₂.₆, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. J. Buschow

Chemistry Faculty Research & Creative Works

The Mössbauer spectra of Nd2Fe17 and Nd 2Fe17N2.6 have been measured at various temperatures between 78 and 295 K and analyzed with a model that is based on the Wigner-Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron-diffraction measurements or band-structure calculations. Upon nitrogenation of Nd2Fe17, the weighted average isomer shift increases from 0.060 to 0.164 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase ...


Direct Picosecond Measurement Of Photoinduced Cooper Pair Breaking In Lead, John F. Federici, Benjamin I. Greene, Peter N. Saeta, Douglas R. Dykaar, F. Sharifi, R. C. Dynes Nov 1992

Direct Picosecond Measurement Of Photoinduced Cooper Pair Breaking In Lead, John F. Federici, Benjamin I. Greene, Peter N. Saeta, Douglas R. Dykaar, F. Sharifi, R. C. Dynes

All HMC Faculty Publications and Research

We report on a direct kinetic measurement of Cooper-pair breaking in superconducting lead. A 100-fs pulse of visible light was used to excite a thin-film lead sample, while the Cooper-pair density was optically probed using an ultrashort pulse of broadband far-infrared radiation. Subsequent to the absorption of the visible light, a rapid (ps) change in the far-infrared optical transmission was observed, corresponding to the breaking of Cooper pairs and the collapse of the superconducting gap.


A Technique For The Evaluation Of Double Excitation Of Atoms By Fast Protons And Antiprotons, Jack C. Straton, James H. Mcguire, Zheng Chen Nov 1992

A Technique For The Evaluation Of Double Excitation Of Atoms By Fast Protons And Antiprotons, Jack C. Straton, James H. Mcguire, Zheng Chen

Physics Faculty Publications and Presentations

A technique for evaluating cross sections for two-electron excitation in collisions of atoms with fast particles of charge ZP is presented. The atomic wave function is approximated by a sum of pair products of one-electron wave functions, with the coefficients chosen by diagonalizing the fully correlated twoelectron Hamiltonian. Thus spatial correlation is included in both the asymptotic and scattering regions by using these configuration-interaction (Cl) wave functions for initial, intermediate, and final states. Use of CI wave function also allows the first-order contributions to be expressed in closed, analytical form. Both the energy-conserving and energy-nonconserving parts of the second-order amplitude ...


Linear Theory Of Non-Neutral Plasma Equilibrium In A Tilted Magnetic Field, Ross L. Spencer, Grant W. Hart Nov 1992

Linear Theory Of Non-Neutral Plasma Equilibrium In A Tilted Magnetic Field, Ross L. Spencer, Grant W. Hart

Faculty Publications

A linear perturbation expansion has been found that allows the rapid and accurate calculation of the response of a non-neutral plasma to a tilted magnetic field. The results of the calculation have been found to agree with previous three-dimensional equilibrium calculations, and also to agree with Keinigs' [Phys. Fluids 24, 860 (1981)] calculation of zero-frequency resonances caused by magnetic field errors. This expansion also allows the perturbed velocity to be calculated. It is speculated that this perturbed flow may be related to the enhanced radial transport in a non-neutral plasma with a tilted magnetic field.


Use Of Raman Spectroscopy In Characterizing Soft X-Ray Multilayers: Tools In Understanding Structure And Interfaces, Ming Cai, Qi Wang, David D. Allred, Larry V. Knight, Dorian M. Hatch, A. Reyes-Mena, Guizhong Zhang Oct 1992

Use Of Raman Spectroscopy In Characterizing Soft X-Ray Multilayers: Tools In Understanding Structure And Interfaces, Ming Cai, Qi Wang, David D. Allred, Larry V. Knight, Dorian M. Hatch, A. Reyes-Mena, Guizhong Zhang

Faculty Publications

Our group is studying the structure and interfaces of soft x-ray multilayers by various techniques including x-ray diffraction and Raman spectroscopy. Raman spectroscopy is particularly useful since it is sensitive to the identity of individual bonds and thus can potentially characterize the abruptness of interfaces in multilayers. Blocking interfacial mixing is very important in achieving and maintaining high reflectivity. We report our studies of the as-deposited and postannealed structure of Mo/Si and W/C multilayers. The Mo/Si system is probably the most widely studied multilayer currently because of its potential applications for soft x-ray projection lithography for the ...


Symmetry Breaking In A Generalized Skyrme Model, Joseph Schechter Oct 1992

Symmetry Breaking In A Generalized Skyrme Model, Joseph Schechter

Physics

We first outline the calculations of the neutron-proton mass difference and of the axial singlet matrix element (relevant to the "proton spin" puzzle) in a generalized Skyrme model of pseudoscalars and vectors. These two calculations are, perhaps surprisingly, linked to each other and furthermore are sensitive to some fine details of symmetry breaking in the effective meson Lagrangian. This provides a motivation for us to examine these symmetry breaking terms more closely. We find a qualitatively new feature in the symmetry breaking pattern of the vector meson system and discuss its significance. (Talk at Workshop on "Baryons as Skyrme Solitons ...


Effective Hadron Dynamics: From Meson Masses To The Proton Spin Puzzle, Joseph Schechter, A Subbaraman, H. Weigel Oct 1992

Effective Hadron Dynamics: From Meson Masses To The Proton Spin Puzzle, Joseph Schechter, A Subbaraman, H. Weigel

Physics

We construct a three flavor chiral Lagrangian of pseudoscalars and vectors with special emphasis on the symmetry breaking terms. Comparing tree level two and three point functions with experiment allows us to first, fix the parameters of the model (including the light quark mass ratios) and second, to predict m(K^{*+})-m(K^{*\circ}),\, \Gamma(K^*\rightarrow K\pi) and \Gamma(\phi\rightarrow K {\overline K}). The last mentioned quantities come out reasonably well, in contrast to an ``ordinary" SU(3) treatment. For this purpose we need ``second order" symmetry breakers involving the vector fields analogous to those needed for ...


Interaction Of Profiled Light With Contrapropagating Acoustic Waves: Fourier Transform Approach, Partha P. Banerjee, Chen-Wen Tarn, Jaw-Jueh Liu Oct 1992

Interaction Of Profiled Light With Contrapropagating Acoustic Waves: Fourier Transform Approach, Partha P. Banerjee, Chen-Wen Tarn, Jaw-Jueh Liu

Electrical and Computer Engineering Faculty Publications

A straightforward Fourier-transform approach is employed to investigate acousto-optic interaction between an input optical beam with arbitrary profile and contrapropagating cw sound in the Bragg regime. The process can be analyzed in terms of the simultaneous scattering of light by the two sound waves in the interaction region. Analytic expressions for the equivalent transfer functions are obtained and the scattered light profiles are plotted.


State-Selective Capture In Collisions Of Protons With Noble Gases, Michael Schulz, D. M. Blankenship, S. W. Bross, A. D. Gaus, Timothy Gay, W. T. Htwe, John T. Park, Jerry Peacher Oct 1992

State-Selective Capture In Collisions Of Protons With Noble Gases, Michael Schulz, D. M. Blankenship, S. W. Bross, A. D. Gaus, Timothy Gay, W. T. Htwe, John T. Park, Jerry Peacher

Physics Faculty Research & Creative Works

We have measured coincidences between neutral H atoms and Lyman-α photons for collisions between 50-keV protons and noble gases as a function of the projectile scattering angle. The coincidences are dominated by capture to the 2p state of the projectile. While the total cross sections depend strongly on the target, the shape of the angular distribution of the differential cross sections was found to depend only weakly on that parameter. The data indicate that electrons are captured predominantly from the outermost shell of the target atom for the collision systems studied here.


Hydrodynamic Instability Of Chemical Waves, D. A. Vasquez, J. W. Wilder, Boyd F. Edwards Oct 1992

Hydrodynamic Instability Of Chemical Waves, D. A. Vasquez, J. W. Wilder, Boyd F. Edwards

All Physics Faculty Publications

We present a theory for the transition to convection for flat chemical wave fronts propagating upward. The theory is based on the hydrodynamic equations and the one‐variable reaction‐diffusion equation that describes the chemical front for the iodate–arsenous acid reaction. The reaction term involves the reaction rate constants and the chemical composition of the mixture. This allows the discussion of the effects of the different chemical variables on the transition to convection. We have studied perturbations of different wavelengths on an unbounded flat chemical front and found that for wavelengths larger than a critical wavelength (λ≳λc ...


State-Selective Capture In Collisions Of Protons With Noble Gases, M. Schulz, D. M. Blakenship, S. W. Bross, A. D. Gaus, Timothy J. Gay, W. Htwe, J. T. Park, J. L. Peacher Oct 1992

State-Selective Capture In Collisions Of Protons With Noble Gases, M. Schulz, D. M. Blakenship, S. W. Bross, A. D. Gaus, Timothy J. Gay, W. Htwe, J. T. Park, J. L. Peacher

Timothy J. Gay Publications

We have measured coincidences between neutral H atoms and Lyman-α photons for collisions between 50-keV protons and noble gases as a function of the projectile scattering angle. The coincidences are dominated by capture to the 2p state of the projectile. While the total cross sections depend strongly on the target, the shape of the angular distribution of the differential cross sections was found to depend only weakly on that parameter. The data indicate that electrons are captured predominantly from the outermost shell of the target atom for the collision systems studied here.


Stars Classified As Constant In The General Catalog Of Variable Stars, Edward G. Schmidt, John R. Chab, Darwin E. Reiswig Oct 1992

Stars Classified As Constant In The General Catalog Of Variable Stars, Edward G. Schmidt, John R. Chab, Darwin E. Reiswig

Edward Schmidt Publications

Photometric observations have been made of 16 stars classified as constant, CST or CST:, in the General Catalog of Variable Stars. One star, U Tauri, was found to be a rapid irregular variable and three others may vary at a low level. In two cases, FV Delphini and FP Geminorum, the star identified as the variable on published finding charts is not variable but a nearby star did vary. It is suggested that the wrong stars were marked on the charts but the possibility remains that the variables may have exhibited constancy during earlier observations.


Competition Between Ponderomotive And Thermal Forces In Short-Scale-Length Laser Plasmas, X. Liu, Donald P. Umstadter Sep 1992

Competition Between Ponderomotive And Thermal Forces In Short-Scale-Length Laser Plasmas, X. Liu, Donald P. Umstadter

Donald Umstadter Publications

Interactions of intense 400-fs laser pulses with a solid target are studied with time-integrated and time-resolved measurements. The latter are accomplished by means of a pump and probe experiment, in which the motion of the critical surface is measured with 250-fs resolution. It is found that when the average electron quiver energy (mvos2/2) becomes comparable to the electron thermal energy (kTe), the ponderomotive force of the high-intensity laser significantly reduces the thermal expansion of a laser plasma. This study is performed in an interesting regime not easily accessible with longer pulse lasers, in which the electron ...