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Physics Faculty Research & Creative Works

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Articles 1591 - 1620 of 1959

Full-Text Articles in Physical Sciences and Mathematics

One-Dimensional Quantum Transport In The Presence Of Traps, Paul Ernest Parris Sep 1989

One-Dimensional Quantum Transport In The Presence Of Traps, Paul Ernest Parris

Physics Faculty Research & Creative Works

A study is made of the survival probability P(t) for a quantum particle moving coherently on an ordered one-dimensional chain containing randomly placed irreversible traps in concentration q. We consider two separate models of the trapping process, focusing on the long-time limit of each. In the first model, intended to describe substitutional traps, the trapping impurities act as disruptive absorbing barriers which prevent further motion along the chain. For this model it is shown that -ln[P(t)]1/4t1/4. The second model is intended to describe interstitial trapping impurities which do not disrupt the transport. It is argued for this case …

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Resonant Dielectronic And Direct Excitation In Crystal Channels, Sheldon Datz, Charles Randy Vane, Peter F. Dittner, J. P. Giese, J. C. Gomez Del Campo, N. L. Jones, Herbert F. Krause, Philip D. Miller, Michael Schulz, Harald Schone, Thomas M. Rosseel Aug 1989

Resonant Dielectronic And Direct Excitation In Crystal Channels, Sheldon Datz, Charles Randy Vane, Peter F. Dittner, J. P. Giese, J. C. Gomez Del Campo, N. L. Jones, Herbert F. Krause, Philip D. Miller, Michael Schulz, Harald Schone, Thomas M. Rosseel

Physics Faculty Research & Creative Works

We have observed dielectronic and direct excitation of H-like S15+ and Ca19+ and He-like Ti20+ ions in silicon channels caused by collision with weakly bound target electrons which behave as a free-electron gas. As in vacuo, relaxation of the doubly excited states can occur radiatively leading to ions of decreased charge, but in a crystal channel collisional effects can cause double ionization. The effects are seen in both the x-ray yields and charge-state fractions, and, in the case of Ti20+, in charge-state x-ray coincidences.

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Single And Double-Electron Removal From H− In Energetic Collisions With Multiply-Charged Argon Ions, F. Melchert, W. Debus, M. Liehr, Ronald E. Olson, E. Salzborn Jul 1989

Single And Double-Electron Removal From H− In Energetic Collisions With Multiply-Charged Argon Ions, F. Melchert, W. Debus, M. Liehr, Ronald E. Olson, E. Salzborn

Physics Faculty Research & Creative Works

Absolute cross-sections have been measured and compared to CTMC-calculations for single and double-electron removal from H− in collisions with Arq+ ions (q ≤ 8) at Ec.m. = 50 keV. The single-electron removal cross-sections are found to scale with q1.3, and for the H− + Ar4+ system, this cross-section is found to have a weak energy dependence from 3 keV to 100 keV. A major implication of our measurements is that plasma neutralizers based on multiply charged ions for high-efficiency conversion of intense H− beams into H0 gain little in expected reduced …

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Long-Range Hopping In Substitutionally Disordered Solids, Paul Ernest Parris May 1989

Long-Range Hopping In Substitutionally Disordered Solids, Paul Ernest Parris

Physics Faculty Research & Creative Works

A theoretical approach for studying charge-carrier and energy diffusion due to long-range hopping in substitutionally disordered solids is presented. Unlike some earlier theories, which invoke a pair approximation to treat back-transfer processes, the current theory makes use of the exact solution to an appropriate single-defect problemone in which long-range jumps into, out of, and between both the defect site and all other active sites in the lattice are explicitly included. From this exact solution a new long-range effective-medium theory is constructed to describe the configurationally averaged transport properties of the disordered system.

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Spectroscopy Of The 6p3/2Np States Of Barium, J. Greg Story, E. G. Yap, William E. Cooke May 1989

Spectroscopy Of The 6p3/2Np States Of Barium, J. Greg Story, E. G. Yap, William E. Cooke

Physics Faculty Research & Creative Works

The 6p3/2np states of barium have been observed for n values between 14 and 21. The energies, linewidths, and transition strengths have been measured and characterized in terms of one- and two-electron interactions, using a single-configuration approximation.

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Shake-Off Measurements Of Electron-Ion-Scattering Phase Shifts, J. Greg Story, William E. Cooke May 1989

Shake-Off Measurements Of Electron-Ion-Scattering Phase Shifts, J. Greg Story, William E. Cooke

Physics Faculty Research & Creative Works

Continuum electrons are produced in a specific l state with high-energy resolution using shake-off photoionization. This process is well characterized, so that the photoionization signal is an accurate measurement of the difference between the continuum electrons wave-function phase and that produced by a hydrogenic interaction. Measurements are reported showing the phase of a Ba++e- in a d wave, in cases where it is well behaved, and in cases where doubly excited resonances produce rapid phase variations.

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Electron-Electron Interactions In Transfer And Excitation In F⁸⁺ →₂ Collisions, Michael Schulz, J. P. Giese, J. K. Swenson, Sheldon Datz, Peter F. Dittner, Herbert F. Krause, Harald Schone, Charles Randy Vane, Malika Benhenni, Stephen M. Shafroth Apr 1989

Electron-Electron Interactions In Transfer And Excitation In F⁸⁺ →₂ Collisions, Michael Schulz, J. P. Giese, J. K. Swenson, Sheldon Datz, Peter F. Dittner, Herbert F. Krause, Harald Schone, Charles Randy Vane, Malika Benhenni, Stephen M. Shafroth

Physics Faculty Research & Creative Works

We have measured projectile Auger electrons emitted after collisions of H-like F with H2. The cross sections for emission of KLL, KLM, KLN, and KLO Auger electrons show maxima as a function of the projectile energy. One maximum in the KLL emission cross section is due to resonant transfer and excitation. A second maximum in the cross section for KLL emission as well as the maxima in the emission cross section for the higher-n Auger electrons are attributed to a new transfer and excitation process. This involves excitation of a projectile electron by one target electron accompanied by …

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One-Dimensional Trapping Kinetics At Zero Temperature, Paul Ernest Parris Mar 1989

One-Dimensional Trapping Kinetics At Zero Temperature, Paul Ernest Parris

Physics Faculty Research & Creative Works

The asymptotic decay of the survival probability is calculated for a quantum particle moving at zero temperature on a one-dimensional tight-binding chain possessing randomly placed irreversible traps of strength γ. The survival probability exhibits a decay, P(t) ~ exp(-At1/4), which is slower than that associated with a diffusing particle.

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Condensation Coefficient Measurement For Water In The Umr Cloud Simulation Chamber, Donald E. Hagen, John L. Schmitt, Max B. Trueblood, John C. Carstens, Daniel R. White, Darryl J. Alofs Mar 1989

Condensation Coefficient Measurement For Water In The Umr Cloud Simulation Chamber, Donald E. Hagen, John L. Schmitt, Max B. Trueblood, John C. Carstens, Daniel R. White, Darryl J. Alofs

Physics Faculty Research & Creative Works

A systematic series of condensation coefficient measurements of water have been made using the University of Missouri-Rolla cooled-wall expansion chamber which simulates the thermodynamics of cloud. This coefficient is seen to decrease from a value near unity, at the outset of simulation, to a value in the neighborhood of 0.01 toward the end of a simulation. Final values of this coefficient are sufficiently low as to contribute significantly to the broadening of the drop-size distribution in cloud.

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Elastic Angular Differential Cross Sections For Quasi-One-Electron Collision Systems At Intermediate Energies: (Na⁺, Li⁺)+H And (Mg⁺, Be⁺)+He, Jerry Peacher, E. Redd, Denver G. Seely, Timothy Gay, D. M. Blankenship, John T. Park Feb 1989

Elastic Angular Differential Cross Sections For Quasi-One-Electron Collision Systems At Intermediate Energies: (Na⁺, Li⁺)+H And (Mg⁺, Be⁺)+He, Jerry Peacher, E. Redd, Denver G. Seely, Timothy Gay, D. M. Blankenship, John T. Park

Physics Faculty Research & Creative Works

Measurements of elastic angular differential cross sections have been carried out for four quasi-one-electron collision systems at intermediate energies. Data are presented for Na++H collisions at laboratory energies of 35.94, 51.75, 63.89, and 143.75 keV, for Li++H collisions at energies of 19.44 and 43.75 keV, for Mg++He collisions at energies of 30, 66.7, and 150 keV, and for Be++He collisions at an energy of 56.25 keV. The highest energy in each case corresponds to a projectile velocity of (1/2 a.u. Born and Eikonal calculations, in which we model the projectile ion as …

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Exciton Diffusion At Finite Frequency: Luminescence Observables For Anisotropic Percolating Solids, Paul Ernest Parris Jan 1989

Exciton Diffusion At Finite Frequency: Luminescence Observables For Anisotropic Percolating Solids, Paul Ernest Parris

Physics Faculty Research & Creative Works

A study is made of the luminescence intensities associated with exciton diffusion and trapping on a three-dimensional anisotropic percolating lattice. The calculation is based upon a relationship that exists between the frequency dependent diffusion tensor at frequencies comparable to the inverse excitation lifetime, and luminescence observables such as the host and trap luminescence intensities for conditions of constant illumination. The present approach allows the study of crossover behavior in percolative systems that are of intermediate transport dimensionality 2 < dt < 3. Our results suggest that curvature seen in luminescence observables near the transition need not always be a direct reflection of the critical indices associated with classical isotropic percolation. We have identified three possible sources of deviation from the classical behavior: (1) the radiative time scale of the luminescence measurements, (2) the functional dependence of the luminescence yields on the diffusion tensor, and (3) the demands of dimensional crossover in the critical region arising from the anisotropy of the medium.

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Mössbauer Effect Studies Of Nd₂Fe₁₄₋ₓsiₓb And Y₃Fe₁₄₋ₓsiₓb, Oran Allan Pringle, Gary J. Long, G. K. Marasinghe, William Joseph James, Antoni T. Pedziwiatr, W. E. Wallace, Fernande Grandjean Jan 1989

Mössbauer Effect Studies Of Nd₂Fe₁₄₋ₓsiₓb And Y₃Fe₁₄₋ₓsiₓb, Oran Allan Pringle, Gary J. Long, G. K. Marasinghe, William Joseph James, Antoni T. Pedziwiatr, W. E. Wallace, Fernande Grandjean

Physics Faculty Research & Creative Works

No abstract provided.

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N, L Distributions For Electron-Capture From H(1s) By C⁶⁺And O8+, Ronald E. Olson, D. R. Schultz Jan 1989

N, L Distributions For Electron-Capture From H(1s) By C⁶⁺And O8+, Ronald E. Olson, D. R. Schultz

Physics Faculty Research & Creative Works

Total cross sections for electron-capture from the ground state of hydrogen by C6+(40, 50, 60, 80, 100 and 120 keV/u) and O8+(40, 50, 60, 80, 100, 120 and 140keV/u) have been calculated using the classical-trajectory Monte Carlo (CTMC) technique. We tabulate these cross sections as a function of projectile energy for (i) capture to all product states, (ii) capture to product n-levels, and (iii) capture to product n, l-levels. The results of these calculations agree with and extend previous CTMC n, ldistribution results. © 1989 IOP Publishing Ltd.

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Multiple-Ionization Collision Dynamics, R. (Ronald) E. Olson, J. Ullrich, H. Schmidt-Böcking Jan 1989

Multiple-Ionization Collision Dynamics, R. (Ronald) E. Olson, J. Ullrich, H. Schmidt-Böcking

Physics Faculty Research & Creative Works

The 1.4-MeV/u U32++Ne collision system is studied in detail in order to elucidate the dynamics of multiple ionization in energetic, heavy-ion atom collisions. Differential cross sections versus recoil-ion charge state, calculated by the n-body classical-trajectory Monte Carlo method, are presented for the and cphi angle dependences of the projectile, recoil ion, and ejected electrons. The calculations show a high degree of ejected-electron asymmetry towards the projectile side of the target nucleus which strongly effects the transverse-momentum balance between the heavy particles. Experimental and calculated cross sections differential in the recoil-ion charge state and transverse momentum are found to …

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Three-Body Interactions In Proton-Helium Angular Scattering, R. Dörner, J. Ullrich, H. Schmidt-Böcking, Ronald E. Olson Jan 1989

Three-Body Interactions In Proton-Helium Angular Scattering, R. Dörner, J. Ullrich, H. Schmidt-Böcking, Ronald E. Olson

Physics Faculty Research & Creative Works

H++He scattering at 0.5 MeV has been investigated using a coincidence technique that completely determines the three-body transverse momentum exchange in single ionization collisions. Three scattering regions could be distinctly recognized that are dominated by proton"helium-nucleus, proton-electron, or electron"helium-nucleus interactions. Calculations and the experimental data show that the coupling between the electronic and nuclear degrees of freedom is required to understand the dynamics for more than 97% of the ionizing collisions. © 1989 The American Physical Society.

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Large-Angle Scattering In Positron-Helium And Positron-Krypton Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson Jan 1989

Large-Angle Scattering In Positron-Helium And Positron-Krypton Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

We have calculated differential cross sections as a function of the projectile scattering angle for positron-helium and positron-krypton collisions using the classical-trajectory Monte Carlo technique. These intermediate- velocity collisions have been simulated by various independent-electron and n-electron models, using both screened Coulomb and quantum model potentials to approximate the effects of electron-electron interactions. These several models all indicate that scattering of positrons to large angles in ionizing collisions persists to high impact velocities. In a previous work [Phys. Rev. A 38, 1866 (1988)] we proposed that the recent experiments that have measured the total cross section for positronium formation could …

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Strong Continuum-Continuum Couplings In The Direct Ionization Of Ar And He Atoms By 6-Mev/U U38+ And Th38+ Projectiles, D. Schneider, D. Dewitt, A. S. Schlachter, Ronald E. Olson, W. G. Graham, J. R. Mowat, R. (Robert) D. Dubois, D. H. Loyd, V. Montemayor, G. Schiwietz Jan 1989

Strong Continuum-Continuum Couplings In The Direct Ionization Of Ar And He Atoms By 6-Mev/U U38+ And Th38+ Projectiles, D. Schneider, D. Dewitt, A. S. Schlachter, Ronald E. Olson, W. G. Graham, J. R. Mowat, R. (Robert) D. Dubois, D. H. Loyd, V. Montemayor, G. Schiwietz

Physics Faculty Research & Creative Works

Doubly differential cross sections have been measured as a function of the electron energy and observation angle for electron emission following collisions of 6-MeV/u U38+ and Th38+ on He and Ar. The electron-emission data show an enhancement at forward angles and a decrease at backward angles with respect to scaled-cross-section results based on the Born approximation. Comparison with classical-trajectory Monte Carlo calculations suggests that the deviation from the Born approximation can be explained by continuum-continuum couplings. By comparing with previously published data, we found that the forward enhancement as well as the backward decrease follow a q/vp (q,vp …

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Electron Removal From Molecular Hydrogen By Fully Stripped Ions At Intermediate Energies, L. Meng, C. O. Reinhold, Ronald E. Olson Jan 1989

Electron Removal From Molecular Hydrogen By Fully Stripped Ions At Intermediate Energies, L. Meng, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

A classical phase-space model of the hydrogen molecule is presented and applied to the study of the electron-capture and -ionization processes in collisions of fully stripped ions with H2 at intermediate impact energies and charge states from 1 to 10. The model is based on the independent-electron and the impact-parameter approximations. The electron impinging-ion and electron target-nuclei interactions are exactly taken into account. The interaction between the electrons is approximated by model potentials. The calculated total cross sections for production of free electrons and capture of one electron are in good agreement with different experimental data. The ratio between the …

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Single- And Double-Ionization Cross Sections For Angular Scattering Of Fast Protons By Helium, R. (Ronald) E. Olson, J. Ullrich, R. Dörner, H. Schmidt-Böcking Jan 1989

Single- And Double-Ionization Cross Sections For Angular Scattering Of Fast Protons By Helium, R. (Ronald) E. Olson, J. Ullrich, R. Dörner, H. Schmidt-Böcking

Physics Faculty Research & Creative Works

The angular scattering of H+ by He has been investigated for single ionization at energies of 0.5, 1.0, and 3.0 MeV; and for double ionization at 1.0 MeV. The classical-trajectory Monte Carlo method has been used within one- and two-electron models to illustrate the collision dynamics. The angular differential single-ionization cross sections are in good agreement with experiment and display the combined effects of proton scattering from the He nucleus and its electrons. The relative fraction of double ionization, as a function of scattering angle, shows a maximum at 0.9 mrad that is in agreement with the experiments of …

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Classical Two-Center Effects In Ejected-Electron Spectra From P+, P-, And He2++He Collisions At Intermediate Energies, C. O. Reinhold, Ronald E. Olson Jan 1989

Classical Two-Center Effects In Ejected-Electron Spectra From P+, P-, And He2++He Collisions At Intermediate Energies, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

Doubly and singly differential cross sections for electron emission have been calculated by means of the classical trajectory Monte Carlo method for the p+, p-, and He2++He systems at impact energies of 50 and 100 keV/amu. The calculations for the p+ and He2++He systems exhibit the capture to the continuum peak and agree in both shape and magnitude with experimental data. Analysis of the classical trajectories has helped to understand the dynamical formation of this peak. The dependence of the cross sections on the projectile charge (-1, +1, and +2) is analyzed and …

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Spin-Polarized ³He Nuclear Targets And Metastable 4he Atoms By Optical Pumping With A Tunable, Nd:Yap Laser, C. L. Bohler, Laird D. Schearer, M. Leduc, P. J. Nacher, L. Zachorowski, R. G. Milner, R. D. Mckeown, C. E. Woodward Dec 1988

Spin-Polarized ³He Nuclear Targets And Metastable 4he Atoms By Optical Pumping With A Tunable, Nd:Yap Laser, C. L. Bohler, Laird D. Schearer, M. Leduc, P. J. Nacher, L. Zachorowski, R. G. Milner, R. D. Mckeown, C. E. Woodward

Physics Faculty Research & Creative Works

Several Nd:YAP lasers were constructed which could be broadly tuned in the 1083-nm region which includes the helium 23S-23P transition, using a Lyot filter and thin, uncoated etalons within the laser cavity. 1 W of power could be extracted at 1083 nm through a 1% transmitting output coupler. This laser beam was used to optically pump metastable 4He and 3He 23S helium atoms in a weak discharge cell, spin polarizing the metastable ensemble. In a 3He cell the polarization is transferred to the nuclear spin system. A 3He target cell at 0.3 …

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Nd:Lna Laser Optical Pumping Of ⁴He: Application To Space Magnetometers, R. E. Slocum, Laird D. Schearer, P. Tin, R. Marquedant Dec 1988

Nd:Lna Laser Optical Pumping Of ⁴He: Application To Space Magnetometers, R. E. Slocum, Laird D. Schearer, P. Tin, R. Marquedant

Physics Faculty Research & Creative Works

We have observed Hanle signals and n=0, p=1 parametric resonances of 23S1 metastable helium atoms in a discharge cell by optically pumping the helium atoms with a tunable Nd:LNA laser. These resonances were used to construct a sensitive magnetometer for the measurement of very small magnetic fields. Since magnetometer sensitivity is proportional to the slope of the parametric resonance signal (signal amplitude divided by linewidth), the slopes for single-line laser pumping were compared with similar quantities obtained from conventional helium lamp pumping. Laser pumping yielded 45 times greater slopes with comparable power requirements, thus establishing the potential for …

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Resonant Transfer And Excitation In Li-Like F Colliding With H₂, Michael Schulz, Reinhold S. Schuch, Sheldon Datz, Edson L B Justiniano, Philip D. Miller, Harald Schone Nov 1988

Resonant Transfer And Excitation In Li-Like F Colliding With H₂, Michael Schulz, Reinhold S. Schuch, Sheldon Datz, Edson L B Justiniano, Philip D. Miller, Harald Schone

Physics Faculty Research & Creative Works

We have measured coincidences between x rays and projectiles that have captured one electron in F6+ + H2 collisions at projectile energies between 15 and 33 MeV. The cross sections for capture and simultaneous x-ray emission as a function of projectile energy show clear structures. Indications of an unexpectedly high population of high-n states predominantly formed by resonant transfer and excitation (RTE) were found. Above the Kln (n>1) RTE resonance energies another maximum was observed.

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Magnetism And Superconductivity In (Er₀.₁₆Ho₀.₈₄)Rh₄B₄, Oran Allan Pringle, Herbert A. Mook, Steven E. Lambert, M. Brian Maple Nov 1988

Magnetism And Superconductivity In (Er₀.₁₆Ho₀.₈₄)Rh₄B₄, Oran Allan Pringle, Herbert A. Mook, Steven E. Lambert, M. Brian Maple

Physics Faculty Research & Creative Works

The superconducting and ferromagnetic phase boundaries in the (Er1-xHox)Rh4B4 mixed ternary alloy system meet in a multicritical point at xcr ≈ 0.9. For xcr, the compounds first become superconducting as the temperature is lowered, and then lose superconductivity in a transition to ferromagnetism. The coexistence of superconductivity and ferromagnetism for alloys near the erbium-rich end of the phase diagram is well established. It has also been suggested that ferromagnetism and superconductivity coexist in alloys with x just below xcr. We have carried out neutron-diffraction, ac magnetic susceptibility, and heat-capacity …

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Excitation Of The Lowest Autoionizing Levels In Lithiumlike Ions By Electron Impact, Rajesh C. Srivastava, Don H. Madison Nov 1988

Excitation Of The Lowest Autoionizing Levels In Lithiumlike Ions By Electron Impact, Rajesh C. Srivastava, Don H. Madison

Physics Faculty Research & Creative Works

We present theoretical, differential, and total cross sections for electron impact excitation of the lowest autoionizing levels of various lithiumlike ions (viz., Be+, B2+, C3+, O5+, and Ne7+). For these ions, the autoionizing level of interest results from excitation of an inner-shell electron. A distorted-wave Born approximation (with exchange) is used for the calculation. The present results are compared with previous theoretical calculations and it is concluded that the Coulomb-Born approach is unreliable, particularly near threshold.

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A Neutron Diffraction And Mössbauer Spectral Study Of The Structure And Magnetic Properties Of The Y₂Fe₁₄₋ₓsiₓb Solid Solutions, Gaya Kanishka Marasinghe, Oran Allan Pringle, Gary J. Long, William B. Yelon, Fernande Grandjean Nov 1988

A Neutron Diffraction And Mössbauer Spectral Study Of The Structure And Magnetic Properties Of The Y₂Fe₁₄₋ₓsiₓb Solid Solutions, Gaya Kanishka Marasinghe, Oran Allan Pringle, Gary J. Long, William B. Yelon, Fernande Grandjean

Physics Faculty Research & Creative Works

A neutron diffraction and Mössbauer spectral study of Y2Fe14-xSixB shows that silicon preferentially occupies the 4c, and to a lesser extent, the 8j1 sites in Y2Fe14-xSixB. The trend in the site occupancy is the same as in Nd2Fe14-xSixB. The Curie temperature of Y2Fe14-xSixB increases with increasing silicon content. Neutron diffraction data show that the increase in Curie temperature is accompanied by a contraction of the unit cell. Wigner-Seitz cell calculations, using the Y2Fe …

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Temperature And Supersaturation Dependent Nucleation Rates Of Water By Molecular Cluster Model Calculations, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen Oct 1988

Temperature And Supersaturation Dependent Nucleation Rates Of Water By Molecular Cluster Model Calculations, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen

Physics Faculty Research & Creative Works

Using a microphysical approach to nucleation, we present an extensive study of water nucleation rates for wide ranges of both temperature and supersaturation ratio. Based on the fundamental molecular properties of clusters instead of bulk properties, the microphysical approach is demonstrated to predict good agreement with measured nucleation rates over this broad range of conditions. Predicted critical sizes for nucleation are found to be relatively small, and are in the molecular cluster size regime rather than in a size regime that should be characterized by bulk values. Estimated sticking coefficient values cover the range of ~0.9 to ~0.2 for the …

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High-Pressure Neutron-Scattering Studies Of Graphite And Stage-Two Graphite-Sbcl₅, B. Alzyam, Clive H. Perry, C. Zahopoulos, Oran Allan Pringle, Robert M. Nicklow Jul 1988

High-Pressure Neutron-Scattering Studies Of Graphite And Stage-Two Graphite-Sbcl₅, B. Alzyam, Clive H. Perry, C. Zahopoulos, Oran Allan Pringle, Robert M. Nicklow

Physics Faculty Research & Creative Works

The longitudinal-acoustic (LA) phonons propagating along the c axis in highly oriented pyrolytic graphite (HOPG) were investigated as a function of pressure up to 20 kbar using inelastic-neutron-scattering techniques. The phonon frequencies varied as (P,q)=A(P)sin[c(P)q/2], where A(P) and c(P) indicate the pressure dependences of the zone-center LO frequency of B1g1 symmetry and of the c-axis lattice spacing, respectively. From the measurements, the mode Grüneisen parameter for the LA branch was estimated to be 1.5 x 10-2 kbar-1 (independent of q); the elastic constant C33 for HOPG was found to be 3.40 x 1011 dyn/cm …

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Some Issues Of Thermodynamic Consistency In Binary Nucleation Theory, Gerald Wilemski Apr 1988

Some Issues Of Thermodynamic Consistency In Binary Nucleation Theory, Gerald Wilemski

Physics Faculty Research & Creative Works

The "generalized" Kelvin equations used to determine the critical nucleus composition in some binary nucleation theories are shown to be thermodynamically inconsistent. Also, the surface tension calculated by the method of Flageollet-Daniel, Gamier, and Mirabel [J. Chem. Phys. 78, 2600 (1983)] is shown to be thermodynamically consistent with respect to the dynamic surface tension, contrary to the recent assertion of Spiegel, Zahoransky, and Wittig.

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The Role Of Dephasing In Some Recent Theories Of Quantum Localization, Paul Ernest Parris, Philip W. Phillips Mar 1988

The Role Of Dephasing In Some Recent Theories Of Quantum Localization, Paul Ernest Parris, Philip W. Phillips

Physics Faculty Research & Creative Works

We consider the transport of electrons or excitons through a random environment in the presence of constant site off-diagonal dephasing processes. It is shown that dephasing of this form will always defeat Anderson localization at long times. Some recent theories of quantum localization which depend upon such dephasing processes are, therefore, seen to be inconsistent.

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