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Physics Faculty Research & Creative Works

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Articles 1681 - 1710 of 1959

Full-Text Articles in Physical Sciences and Mathematics

Summary Abstract: Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale Jan 1985

Summary Abstract: Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale

Physics Faculty Research & Creative Works

No abstract provided.

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Evidence For Uncorrelated Electron Capture And K-Shell Excitation In S13++He Collisions, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron Jan 1985

Evidence For Uncorrelated Electron Capture And K-Shell Excitation In S13++He Collisions, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron

Physics Faculty Research & Creative Works

Evidence is presented for a two-step process in ion-atom collisions in which two independent interactions occur in a single encounter. Measurements for 15200-MeVS13++He collisions indicate that uncorrelated projectile K-shell excitation and capture of a target electron occur in a single collision with one target atom. The results are in reasonable qualitative agreement with theoretical predictions of this two-step process. © 1985 The American Physical Society.

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Spin-1 Exchange-Interaction Model Of Ferromagnetism, Harry A. Brown Jan 1985

Spin-1 Exchange-Interaction Model Of Ferromagnetism, Harry A. Brown

Physics Faculty Research & Creative Works

The spin-exchange operator for spin S=1 and a constant-coupling-like approximation are used to evaluate the thermodynamic properties of a system described by a two-spin Hamiltonian that includes dipole and quadrupole interactions. The dipole and quadrupole moments and the exchange energy are found as functions of temperature. There is a critical temperature, Tc, which depends on the coordination number of the lattice at which the system undergoes a second-order phase transition. Below Tc, both magnetic moments, simultaneously, take on nonzero values and have infinite derivatives there while the derivative of the exchange energy is discontinuous. Comparison is made with other results …

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Erratum: Normalized Line Shapes For Far-Wing Continuum Spectra: The Rb-Xe Satellite Band (Physical Review A(1985) 32, 5 (3150-3152)), Ronald James Bieniek Jan 1985

Erratum: Normalized Line Shapes For Far-Wing Continuum Spectra: The Rb-Xe Satellite Band (Physical Review A(1985) 32, 5 (3150-3152)), Ronald James Bieniek

Physics Faculty Research & Creative Works

Recent advances in experimental spectroscopy offer the promise of yielding much detailed information about molecular potentials and collisional interactions from a study of the light emitted or absorbed in the far wings of atomic lines. However, readily manipulable, accurate theoretical expressions and methods are needed to extract such knowledge. Straightforward formulas, based on the distorted-wave approximation, for the normalized emission intensity in the far wing of a pumped atomic line are given here. By normalizing theoretical spectra with respect to the strength of the atomic line, one obtains a convenient form for the analysis of experimental differential spectra that are …

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Electron Capture In Pseudo-Two-Electron Systems: Ar8++He, M. Kimura, Ronald E. Olson Jan 1985

Electron Capture In Pseudo-Two-Electron Systems: Ar8++He, M. Kimura, Ronald E. Olson

Physics Faculty Research & Creative Works

Molecular-structure calculations using the pseudopotential method have been performed on the (ArHe)8+ system. The cross section for single-electron capture in Ar8++He collisions was calculated for energies from 20 eV to 10 keV/amu. The perturbed-stationary-state method [M. Kimura, H. Sato, and R. E. Olson, Phys. Rev. A 28, 2085 (1983)], modified to include electron translation factors appropriate to two-electron systems, was used. The total cross section is relatively energy independent with a value of approximately 2.5x10-15 cm2. The n=4 level of Ar7+ is found to be preferentially populated, with the 4f level being dominant. © 1985 The …

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Interaction Of Electric And Magnetic Charges: Addendum, I. Adawi Jan 1985

Interaction Of Electric And Magnetic Charges: Addendum, I. Adawi

Physics Faculty Research & Creative Works

The problem of a head-on collision between a spherically symmetric electric and magnetic charge is reconsidered. The assumption of the equality of the electric and magnetic forces made earlier is abandoned as it does not follow from the model. It is shown that the rotational angular momentum a charge acquires is determined by the amount of the angular momentum which the charge removes from the field by virtue of its extension. The interaction energy of each charge with the dipole it induces in the other charge is equal to the rotational energy of the charge itself. This results in simple …

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Relative Fluorescence Efficiencies For The Dissociative Excitation Of Some Hg-Halides By N2(A ³Σu+), Laird D. Schearer Jan 1985

Relative Fluorescence Efficiencies For The Dissociative Excitation Of Some Hg-Halides By N2(A ³Σu+), Laird D. Schearer

Physics Faculty Research & Creative Works

No abstract provided.

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Electron Capture By Slow Alq+ Ions Colliding With Hydrogen, R. A. Phaneuf, M. Kimura, H. Sato, Ronald E. Olson Jan 1985

Electron Capture By Slow Alq+ Ions Colliding With Hydrogen, R. A. Phaneuf, M. Kimura, H. Sato, Ronald E. Olson

Physics Faculty Research & Creative Works

Total electron-capture cross sections have been measured for collisions of Alq+ (q=210) with H and H2 in the 20120-eV/amu energy range. The general trend of the cross sections for both H and H2 is an approximately linear increase with ionic charge state. The Al2++H and Al3++H systems were investigated theoretically using the molecular-orbital method with a pseudopotential to represent the Al3+ ion core. Coupled-channel calculations realize good agreement with experiment. An anomalously small cross section for Al2++H is attributed to the fact that of the 1 and 3 entrance channels, only the 1 …

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Raman Studies Of Heavily Implanted, Dye-Laser-Annealed Gaas, H. D. Yao, A. Compaan, Edward Boyd Hale Jan 1985

Raman Studies Of Heavily Implanted, Dye-Laser-Annealed Gaas, H. D. Yao, A. Compaan, Edward Boyd Hale

Physics Faculty Research & Creative Works

Raman scattering is used to study the annealing behavior produced by 10 nsec, 565 nm dye laser pulses in high dose ion-implanted GaAs. Samples were prepared with Sn and Cd implantations of 2, 5, and 10 x 1015 cm2. The Raman spectra indicate that the threshold for epitaxial growth lies between 0.2 - 0.3 J cm2. Best carrier activation (∼ 2%), however, is achieved at ∼1.6 J cm2 for the Sn-implanted sample (n-type). For Cd implantation the electrical activation appears to be very high ({greater-than or approximate} 50%) for low pulse energies({less-than or approximate} 0.3 J cm2) but decreases for …

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The Spin‐Exchange Ferromagnet With Dipole And Quadrupole Interactions, Harry A. Brown Jan 1985

The Spin‐Exchange Ferromagnet With Dipole And Quadrupole Interactions, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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A Continental Well-Aged Aerosol In The Guinean Savannah At The Level Of A Trough Along The Itcz, F. Desalmand, Josef Podzimek, R. Serpolay Jan 1985

A Continental Well-Aged Aerosol In The Guinean Savannah At The Level Of A Trough Along The Itcz, F. Desalmand, Josef Podzimek, R. Serpolay

Physics Faculty Research & Creative Works

Simultaneous measurements of Aitken nuclei, cloud condensation nuclei and aerosol particles sizes larger than 0.3 μm in the Guinean savannah during the dry season show an aerosol of very exceptional physical properties: numerous cloud condensation nuclei (2000-3000 per cm3) active at low supersaturation (or slight 'undersaturation'), absence of very small Aitken nuclei active at 180% of supersaturation and concentrations of large aerosol particles (D > 0.3 μm) between 30 and 60 per cm3. The analysis of the aerosol behavior during a 'typical' 24-hr period of the dry season and during a fog situation indicates that (1) the aerosol is a very …

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Effects Of Iron Implantation On The Aqueous Corrosion Of Magnesium, S. Akavipat, Edward Boyd Hale, C. E. Habermann, P. L. Hagans Jan 1985

Effects Of Iron Implantation On The Aqueous Corrosion Of Magnesium, S. Akavipat, Edward Boyd Hale, C. E. Habermann, P. L. Hagans

Physics Faculty Research & Creative Works

The influence of the implantation of iron ions on the corrosion of magnesium and an AlZn-rich magnesium alloy (AZ91C) has been studied. Anodic polarization measurements in a dilute chloride-containing alkaline solution were used to evaluate corrosion resistance. A range of ion energies (50-180 keV) and doses (1016-2 x 1017 Fe+ ions cm-2) have been evaluated. Both the iron-implanted pure magnesium and the alloy AZ91C gave improved polarization measurements. A systematic positive shift of the open-circuit potential with increasing iron dose was found. In AZ91C at a dose of 1017 Fe+ ions cm-2, there was a + 0.6 V more noble …

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Charge Transfer Of Hydrogen Ions And Atoms In Metal Vapors, T. J. Morgan, Ronald E. Olson, A. S. Schlachter, J. W. Gallagher Jan 1985

Charge Transfer Of Hydrogen Ions And Atoms In Metal Vapors, T. J. Morgan, Ronald E. Olson, A. S. Schlachter, J. W. Gallagher

Physics Faculty Research & Creative Works

Cross sections and equilibrium fractions for energetic H+, H−, and H0 in collisions with metal vapor targets have been compiled and evaluated. Both experimental and theoretical results are reported. Sources of errors are discussed, and recommended values for the data are presented. © 1985, American Institute of Physics for the National Institute of Standards and Technology. All rights reserved.

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Satellite Structure In Laser-Assisted Charge-Transfer Cross Sections, Y. P. Hsu, Ronald E. Olson Jan 1985

Satellite Structure In Laser-Assisted Charge-Transfer Cross Sections, Y. P. Hsu, Ronald E. Olson

Physics Faculty Research & Creative Works

A six-state coupled-channel calculation has been performed on the laser-assisted charge-transfer collision H++Na+Latin small letter h with stroke. A greatly enhanced charge-transfer cross section is observed for low-energy collisions if the photon energy is matched to the classical satellite frequency. This frequency is determined by the location of an extremum in the difference of potential energies between the laser-pumped initial and final molecular states. The stationary-phase method has been used to reproduce the general features and the magnitude of the cross-section structure. © 1985 The American Physical Society.

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Spin-Exchange Cross Sections For Hydrogen-Atomalkali-Metal-Atom Collisions, H. R. Cole, Ronald E. Olson Jan 1985

Spin-Exchange Cross Sections For Hydrogen-Atomalkali-Metal-Atom Collisions, H. R. Cole, Ronald E. Olson

Physics Faculty Research & Creative Works

The pseudopotential molecular-structure method has been used to calculate the X1 and a3 interaction potentials for the alkali-metal-atom hydrogen-atom systems. These potentials were then used in a quantum-mechanical calculation to determine the spin-exchange cross sections in the energy range from 2.5x10-4 eV to 2.5 eV. The cross sections follow the general form Q1/2=a-b lnv. However, abundant structure on the cross sections is present due to orbiting resonances induced by the deeply bound well of the X1 molecular state. The spin-exchange cross sections range from 17x10-16 to 25x10-16 cm2 at room temperature for H(F=1) transferring to H(F=0) in collision with unpolarized …

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Threshold Effect In Mg-Doped Lithium Niobate, K. L. Sweeney, L. E. Halliburton, D. A. Bryan, R. R. Rice, Robert Gerson, H. E. Tomaschke Dec 1984

Threshold Effect In Mg-Doped Lithium Niobate, K. L. Sweeney, L. E. Halliburton, D. A. Bryan, R. R. Rice, Robert Gerson, H. E. Tomaschke

Physics Faculty Research & Creative Works

Optical absorption spectra were obtained after reducing (i.e., vacuum annealing) a series of LiNbO3 crystals grown from melts having various Mg concentrations and Li/Nb ratios. A band peaking at 500 nm, and assigned to oxygen vacancies containing two electrons, was the only absorption present in one set of crystals following reduction. In contrast, two overlapping bands peaking near 1200 and 760 nm were present in the other set of crystals immediately after the reduction. The 1200-nm band is assigned to a previously unreported electron trap and the 760-nm band to oxygen vacancies containing only one electron. These data are interpreted …

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Increased Optical Damage Resistance In Lithium Niobate, D. A. Bryan, Robert Gerson, H. E. Tomaschke Dec 1984

Increased Optical Damage Resistance In Lithium Niobate, D. A. Bryan, Robert Gerson, H. E. Tomaschke

Physics Faculty Research & Creative Works

We have confirmed greatly improved resistance to photorefractive damage in compositions of lithium niobate containing 4.5 at. % MgO or more. Holographic diffraction measurements of photorefraction demonstrated that the improved performance is due to a hundredfold increase in the photoconductivity, rather than a decrease in the Glass current. The diffraction efficiency shows an Arrhenius dependence on temperature, with an activation energy of 0.1 eV for the damage-resistant compositions, compared with 0.5 eV for undoped or low-magnesium compositions. The damage-resistant compositions are distinguished by a 2.83-μm absorption line instead of the usual 2.87-μm line due to the OH-stretch vibration.

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Microprocessor-Based Pressure Controller, E. Redd, John T. Park Dec 1984

Microprocessor-Based Pressure Controller, E. Redd, John T. Park

Physics Faculty Research & Creative Works

A device for automatic control of pressure in an ion-atom scattering experiment has been constructed. The system was modeled to achieve the minimum time for transition from one pressure to another. The pressure controller "learns" the system response and iterates the parameters used in "profiling" the valve voltage to reduce the transition time. The device has been used with two different scattering chambers and has worked well with both.

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Angular Differential And Total Cross Sections For The Excitation Of Atomic Hydrogen To Its N=2 Level By 25-150-Kev Hydrogen Molecular Ions, Jerry Peacher, Paul J. Martin, Denver G. Seely, John E. Aldag, Thomas J. Kvale, E. Redd, D. M. Blankenship, V. C. Sutcliffe, John T. Park Aug 1984

Angular Differential And Total Cross Sections For The Excitation Of Atomic Hydrogen To Its N=2 Level By 25-150-Kev Hydrogen Molecular Ions, Jerry Peacher, Paul J. Martin, Denver G. Seely, John E. Aldag, Thomas J. Kvale, E. Redd, D. M. Blankenship, V. C. Sutcliffe, John T. Park

Physics Faculty Research & Creative Works

Experimentally and theoretically determined differential and total cross sections are reported for excitation of atomic hydrogen to its n=2 level by 25-150-keV hydrogen molecular ions. The differential cross sections decrease 3-4 orders of magnitude over the measured center-of-mass scattering-angular range from 0 to 4.5 mrad. The results of a first Born approximation and two other theoretical calculations based upon the Glauber approximation are presented and compared with the experimental results. Both calculations based on the Glauber approximation agree fairly well with the experimental results. The Born approximation agrees moderately well with the experimental results at the very small scattering angles …

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Full Second-Order Distorted-Wave Calculation Without Approximations For Atomic Excitation By Electron Impact, Don H. Madison Jul 1984

Full Second-Order Distorted-Wave Calculation Without Approximations For Atomic Excitation By Electron Impact, Don H. Madison

Physics Faculty Research & Creative Works

A new technique has been developed for evaluating second-order distorted-wave amplitudes for atomic excitation without making any approximations. By this technique, second-order amplitudes with arbitrary distorted waves and arbitrary Green's functions in the interaction can be evaluated with comparable difficulty. The utility of the method is demonstrated through a practical calculation of the second-order distorted-wave approximation for electron excitation of the 2p state of hydrogen.

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Homogeneous Nucleation Rate For Water, Donald E. Hagen, James L. Kassner Apr 1984

Homogeneous Nucleation Rate For Water, Donald E. Hagen, James L. Kassner

Physics Faculty Research & Creative Works

Homogeneous nucleation rate data for water extending over an exceptionally large domain of rate (J), supersaturation ratio (S), and temperature (T) was recently published. Because it spans a large J-S-T surface, this data constitutes a good test of nucleation theory. Here classical nucleation theory is used to analyze this data. By adjusting only the sticking coefficient, we are able to obtain a good fit between theory and experiment. It was necessary to include an increase in the water molecular density associated with the finite water compressibility.

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Elastic Differential Cross Sections For Small-Angle Scattering Of 25-, 40-, And 60-Kev Protons By Atomic Hydrogen, Eduard P. Rille, Jerry Peacher, E. Redd, Thomas J. Kvale, Denver G. Seely, D. M. Blankenship, Ronald E. Olson, John T. Park Feb 1984

Elastic Differential Cross Sections For Small-Angle Scattering Of 25-, 40-, And 60-Kev Protons By Atomic Hydrogen, Eduard P. Rille, Jerry Peacher, E. Redd, Thomas J. Kvale, Denver G. Seely, D. M. Blankenship, Ronald E. Olson, John T. Park

Physics Faculty Research & Creative Works

Elastic angular differential cross sections for small-angle scattering of protons by atomic hydrogen have been measured. The technique utilized unambigously distinguishes the elastically and inelastically scattered ions. The cross sections fall monotonically by 3 orders of magnitude in the angular range from 0.5 to 3.0 mrad, in the center-of-mass system. The experimental data obtained are in very good agreement with a multistate calculation and in fair agreement with both our Glauber-approximation and classical-trajectory Monte Carlo results.

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Additional Remarks To The Schrödinger Spin‐Exchange Ferromagnet, Harry A. Brown Jan 1984

Additional Remarks To The Schrödinger Spin‐Exchange Ferromagnet, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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Non-Linear Oscillation, Automodulation And Anelasticity, Tetsuro Suzuki, Manfred Wuttig Jan 1984

Non-Linear Oscillation, Automodulation And Anelasticity, Tetsuro Suzuki, Manfred Wuttig

Physics Faculty Research & Creative Works

The auto modulation observed in the course of internal friction is discussed as a special example of the universal nature of non-linear oscillations. Universal features of non-linear oscillations are the requirement of energy supply or negative damping and the period doubling route to chaos. The negative damping responsible for the auto modulation is described in terms of the soliton model for twinning deformation. © 1984 The Japan Society of Applied Physics.

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Resonant Electron Transfer And Excitation In Two-, Three-, And Four- Electron Caq +20 And Vq +23 Ions Colliding With Helium, J. A. Tanis, E. M. Bernstein, W. G. Graham, M. P. Stockli, M. Clark, Robert H. Mcfarland, T. J. Morgan, K. H. Berkner, A. S. Schlachter, J. W. Stearns Jan 1984

Resonant Electron Transfer And Excitation In Two-, Three-, And Four- Electron Caq +20 And Vq +23 Ions Colliding With Helium, J. A. Tanis, E. M. Bernstein, W. G. Graham, M. P. Stockli, M. Clark, Robert H. Mcfarland, T. J. Morgan, K. H. Berkner, A. S. Schlachter, J. W. Stearns

Physics Faculty Research & Creative Works

Significant new evidence is reported for resonant transfer and excitation in ion-atom collisions. This process, which is analogous to dielectronic recombination, occurs when a target electron is captured simultaneously with the excitation of the projectile followed by photon emission. Strong resonant behavior with structure, in agreement with theoretical calculations, is observed in the cross section for projectile K x rays coincident with single electron capture for 100-360-MeV Ca16+,17+,18+20 and 180-460-MeV V19+,20+,21+23 ions colliding with helium. © 1984 The American Physical Society.

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Dipole Moment And Potential Energy Functions Of The X ¹Σ + And A 1Σ+ States Of Nah, W. T. Zemke, Ronald E. Olson, K. K. Verma, W. C. Stwalley, B. Liu Jan 1984

Dipole Moment And Potential Energy Functions Of The X ¹Σ + And A 1Σ+ States Of Nah, W. T. Zemke, Ronald E. Olson, K. K. Verma, W. C. Stwalley, B. Liu

Physics Faculty Research & Creative Works

Calculated radiative transition probabilities between all vibrational levels in the X 1Σ+ state (υ=0-21) and in the A 1Σ+ state (υ=0-32) of NaH are given. In addition, the calculated spontaneous emission lifetimes for vibrational- rotational levels (J=0,1) and the calculated dipole moments for these same levels are given. The calculations use new hybrid potential energy curves based on Rydberg-Klein-Rees (RKR) and ab initio potential curves. The RKR curve for the X state is new. The calculations use new ab initio dipole moment functions of internuclear distance. © 1984 American Institute of Physics.

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Molecular-State Cross-Section Calculations For H+Csh-+Cs+, Ronald E. Olson, M. Kimura, H. Sato Jan 1984

Molecular-State Cross-Section Calculations For H+Csh-+Cs+, Ronald E. Olson, M. Kimura, H. Sato

Physics Faculty Research & Creative Works

Pseudopotential molecular-structure calculations have been used to obtain the seven lowest 1 and 1 states of CsH. These states and their associated radial and rotational coupling terms have been used to calculate the cross sections for H-+Cs+ ion-pair production in H+Cs(6s) and H+Cs*(6p) collisions at energies from 0.1 to 10 keV. The ion-ion mutual neutralization cross section, H-+Cs+ H+Cs, is also presented. The cross-section calculations were done with the perturbed-stationary-state method, modified to include two-electron translation factors. The ion-pair production cross section for ground-state reactants is in good agreement with experiment; collisions of H with excited Cs*(6p) show an order-of-magnitude …

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A Three-Spin Interaction Model, Harry A. Brown Jan 1984

A Three-Spin Interaction Model, Harry A. Brown

Physics Faculty Research & Creative Works

A three-spin interaction in the form of a box product, σ1 x σ2 · σ3, is considered. The thermodynamic behavior is investigated using an effective field theory. A second-order phase transition is found and the magnetization and energy per spin appear to be very similar to those of an ordinary Heisenberg ferromagnet. © 1984.

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Electron-Ion Recombination In Gas Mixtures Of Helium, Nitrogen, And Carbon Dioxide, Ian M. Littlewood, M. C. Cornell, Kaare J. Nygaard Jan 1984

Electron-Ion Recombination In Gas Mixtures Of Helium, Nitrogen, And Carbon Dioxide, Ian M. Littlewood, M. C. Cornell, Kaare J. Nygaard

Physics Faculty Research & Creative Works

A study has been conducted to determine the electron-ion recombination rates in gas mixtures of helium, nitrogen, and carbon dioxide. Measurements were made as functions of electric field strength, gas pressure, and gas composition. In gas mixtures containing only nitrogen and carbon dioxide, the rates were dependent on pressure. This dependence is interpreted as being due to the separate effects of two- and three-body recombination processes. No pressure dependence was observed for mixtures containing helium. In such mixtures, two-body recombination appears to be dominant. Moreover, the addition of relatively low concentrations of helium to the discharge leads to a dramatic …

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The Homogeneous Nucleation Of Nonane, G. W. Adams, John L. Schmitt, R. A. Zalabsky Jan 1984

The Homogeneous Nucleation Of Nonane, G. W. Adams, John L. Schmitt, R. A. Zalabsky

Physics Faculty Research & Creative Works

The homogeneous nucleation rate of n-nonane has been measured as a function of temperature and supersaturation ratio in a precision fast-expansion chamber. The measured nucleation rate ranges from 102 to 105 drops/cm3 over the temperature range 215-270 K. The results have been compared to the classical theory and to the classical theory with the RKC replacement factor. The RKC theory functional form is the basis for an empirical rate equation to fit the data. A full listing of the thermodynamic constants used for the reduction of the data is given. © 1984 American Institute of Physics.

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