Physical Sciences and Mathematics Commons^™

Realizable Renormalization Group And Finite-Size Scaling, Miron Kaufman, K. K. Mon

Miron Kaufman

We propose a sequence of renormalization-group transformations which are exact on hierarchical lattices and we argue, by employing finite-size scaling, that the corresponding sequence of critical exponents converges towards the exact values associated with a Bravais lattice. A test of this method is also presented.

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.

Electron Detachment In Negative-Ion Collisions. Ii. The Dynamical Complex Potential, T. S. Wang, John B. Delos

Arts & Sciences Articles

No abstract provided.

Coexistence And Spinodal Curves In Directionally Bonded Liquids Using The Four-Cluster Approximation, Erik Bodegom, Paul H. Meijer

Physics Faculty Publications and Presentations

We derive the phase diagrams and spinodals of binary liquid systems with anisotropic interactions, such as hydrogen-bonded molecules. The work is based on the four-particle cluster variation method, using a different potential for different contact points. It is shown that the introduction of a cluster larger than previously used by Barker and Fock, leads to a considerable improvement in the shape of the phase diagram and avoids some of the difficulties encountered in their calculation. Phase diagrams are displayed for various choices of the parameters: the number of contact points, the interaction potential, and the order of the approximation.

H- And He In A Uniform Magnetic Field: Ground-State Wave Functions, Energies, And Binding Energies For Fields Below 109 G, Chang-Hwan Park, Anthony F. Starace

Anthony F. Starace Publications

Wave functions, energies, and binding energies for the lowest singlet states of H- and He in uniform magnetic fields B<10⁹ G are calculated using an adiabatic approximation in hyperspherical coordinates. In computing the angular part of the wave functions, a coupled expansion in one-electron oblate spheroidal angle functions is used. In addition to contracting the two-electron wave function radially, the magnetic field is found to distort the angular part of the wave function mainly by reducing the ss¹S character of the state and replacing it with an sd ¹D character. Results for energies and binding energies …

Electron Detachment In Negative-Ion Collisions. I. Time-Dependent Theory And Models For A Propagator, T. S. Wang, John B. Delos

Arts & Sciences Articles

A theory of electron detachment in slow collisions of negative ions with atoms is developed. The theory is based on assumptions that are similar to, but more general than, the assumptions made in earlier papers: The motion of the nuclei is described semiclassically, the electronic wave function is expanded in a partially diabatic basis that includes a discrete state and a continuum, and certain couplings are assumed to be small. With such assumptions the Schrödinger equation is reduced to a nondenumerably infinite set of coupled differential equations, and then to a single integro-differential equation (an equation with "memory"). It is …

Two-Electron Lamb Shifts And 1s2s 3s1-1s2p 3pj Transition Frequencies In Helium-Like Ions [1], S. P. Goldman, Gordon W. F. Drake

Physics Publications

The leading terms in the 1/Z expansion of the two-electron Bethe logarithm are calculated for the states 1s2 1S0, 1s2s 1S1, 1s2s 3S1, 1s2p 1P1 and 1s2p 3PJ by the use of a novel finite basis set method. The resulting QED terms are combined with other relativistic and mass polarisation corrections to obtain total transition frequencies. The results are compared with recent measurements in helium-like ions from Li+ to Fe24+.

Esr And Magnetization Of The Spin-Glass Cumn At Low Concentrations, F. R. Hoekstra, G. J. Nieuwenhuys, K. Baberschke, S. E. Barnes

Physics Articles and Papers

We have determined the resonance frequency ω versus resonant field H diagram for CuMn with Mn concentrations 2, 3.5, and 5 at.%, both when H⃗ is parallel and antiparallel to the cooling field H⃗_c. From the parallel measurements we find anisotropy energy density constants K that are in agreement with K values determined from transverse susceptibility and torque measurements. However, the K values determined from the remanence reversal of dc magnetization are smaller by a factor of approximately 2. We suggest that this is caused by a breakdown of rigid-body spin rotations. By combining the parallel data with …

Esr In Situ With A Josephson Tunnel Junction, K. Baberschke, K. D. Bures, S. E. Barnes

Physics Articles and Papers

The in situ electron-spin resonance of a voltage-biased NbAuNb Josephson junction is reported. The Au barrier is doped with Gd or ¹⁶⁷Er ions. Sharp resonances appear in the I-V curves at frequencies equivalent to the crystal-field splitting of AuGd (1.0 and 1.7 GHz) and to the hyperfine splitting of Au¹⁶⁷Er (2.87 GHz). The principle of this new type of ESR-Josephson-junction spectrometer, as well as its application, is discussed.

Esr Relaxation In Spin Glasses, S. E. Barnes

Physics Articles and Papers

The Bloch-Hasegawa theory for the ESR of magnetic alloys is adapted and extended to spin glasses in the paramagnetic regime, that is, for temperatures T>T_G, the cusp temperature. Negative residual widths, reduced thermal broadening, and a possible critical divergence of the residual width are all explained in terms of minor extensions of the standard theory.

Scaling Approach To Spin-Glass Phenomena, S. E. Barnes, A. P. Malozemoff, B. Barbara

Physics Articles and Papers

The scaling model of spin-glass phenomena is extended to consider both longitudinal and transverse order parameters q₁ and q_t. The lowest-order coupling in the free energy goes as q_l²q_t². The field (h) dependence of the reduced temperature t for transverse freezing is found to be t∼h^4/δ where δ is the conventional nonlinear susceptibility field exponent (χ∼h^2/δ). While the transverse correlation length diverges at t=0, the longitudinal correlation length remains finite.

The Feasibility Of The X-Ray Laser Pumped With A Nuclear Explosion, David W. Hafemeister

Physics

Recent reports have indicated that an x-ray laser pumped with a nuclear explosion at a wavelength of 1.4nm (0.9 keV) has made some initial progress. It has been proposed to extend the development of this device to establish it as part of a layered ballistic missile defensive system to protect the United States against a nuclear attack. This paper will discuss the following aspects on the feasibility of this system: (1) Conditions affecting the efficiency of the X-ray laser; (2) Angular resolution and size of.the laser rods; (3) Energy on targets; (4) Basing Modes; (5) Countermeasures; and (6) Legal constraints.

Velocity Measurements Of Humans By Computers, J. B. Rafert, R. C. Nicklin

Faculty Publications

Distance and time, two fundamental quantities, are discussed early in most introductory physics courses. By dividing a change in distance by time to get velocity, and by dividing a change in velocity by time to get acceleration, two more important quantities result. With these the real world of automobiles and jet planes and applications of Newton's second law is available for interpretation from an analytical point of view. In order to get students thinking reliably about these important ideas it seems important to have direct measurements of distance and time over short enough intervals to talk sensibly about "instantaneous" velocities.

Dissociative Attachment To Rovibrationally Excited H2, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Using a local-width resonant model, the cross sections for dissociative attachment of low-energy electrons to a rovibrationally excited H_2 molecule in its ground electronic state are obtained. There are 294 such rovibrational levels. Only the contribution of the ^2Σ_u^+ resonant state of H^−_2 to the attachment process is investigated. Assuming a Maxwellian distribution for electron energies, the dissociative attachment cross sections are converted into attachment rates for various rovibrational levels of H_2. A significant enhancement of attachment rates occurs for endoergic reactions only, and the maximum possible rate for attachment to the ground electronic state of H_2 is about 10^(−8) …

Turbulent Suppression Of Spinodal Decomposition, D. J. Pine, Nalini Easwar, James V. Maher, W. I. Goldburg

Physics: Faculty Publications

Light scattering experiments reveal a strong suppression of phase separation near the critical point of a vigorously stirred binary liquid mixture. For stirring Reynolds numbers R ranging from 6.0 × 10³ to 4.5 × 10³, the apparent critical temperature is depressed by ∼1 mK to ∼50 mK. This temperature depression ΔT_c can be fitted to a power law ΔT_c∼Rλ where λ∼2. The magnitude of ΔT_c is consistent with simple models which attribute the effect to the suppression of composition fluctuations by shear; however, these models predict λ≃0.80 in contrast to the observed value …

Delineation Of A Coal Burn Edge With Seismic Refraction, Karen D. Sontag, Paul J. Wolfe

Physics Faculty Publications

No abstract provided.

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

Physics Faculty Research & Creative Works

No abstract provided.

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.

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.

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 …

Multiple Ionization Of Rare Gases By H+ And He+ Impact, R. D. Dubois, L. H. Toburen, M. Eugene Rudd

M. Eugene Rudd Publications

Absolute cross sections for multiple ionization (σ_q)of He, Ne, Ar, and Kr are presented for proton-impact energies between 10 and 4000 keV. Charge states up to 6 + are observed for Kr. The results are obtained by measuring relative yields of multiply charged ions with a time-of-flight spectrometer and normalizing to total ion-production cross sections σ_T= ∑qσ_q. The results are compared with existing proton- and electron-impact data. Relative multiple- to single-ionization cross-section ratios are also presented for He⁺ impact.

Probability Densities And The Random Variable Transformation Theorem, John D. Ramshaw

Physics Faculty Publications and Presentations

D. T. Gillespie has recently derived and discussed a random variable transformation (RVT) theorem relating the joint probability densities of functionally dependent sets of random variables.....

It is hoped that the present discussion will help to disseminate this basic relation among a wider circle of nonspecialists.

Biomineralizationof Fe3O4 In Bacteria, R. B. Frankel, G. C. Papaefthymiou

Physics

No abstract provided.

Dayside Red Auroras At Very High Latitudes: The Importance Of Thermal Excitation, Vincent B. Wickwar, W Kofman

All Physics Faculty Publications

Extensive radar observations have been made from Sondrestrom of the F region in the daytime sector between 70 and 79° Λ. Regions of enhanced electron temperature and electron density are found in close association with the velocity reversal in the morning and afternoon convection cells. From the radar measurements, calculations are made of the contributions to the atomic oxygen emission at 6300A from dissociative recombination and thermal excitation. The latter mechanism, in particular, in the enhancement regions gives rise to intensities that are comparable to those observed at very high latitudes during the past decade.

Ionospheric Currents And F-Region Plasma Boundaries Near The Dayside Cusp, S Vennerstrom, E Friis-Christensen, T S. Jorgensen, C. E. Rasmussen, C R. Clauer, Vincent B. Wickwar

All Physics Faculty Publications

Observational evidence of the location of a dayside high‐latitude ionospheric current (DPY current) with respect to the different regimes of the high‐latitude magnetosphere is obtained by analyzing data from the magnetometer chain along the west coast of Greenland in conjunction with simultaneous measurements from the newly established incoherent‐scatter radar facility at Sondre Stromfjord. The latitudinal location of the DPY current is compared with the location of the maximum F‐region electron temperature and with the location of the plasma convection reversal from sunward to antisunward. The maximum in the F‐region electron temperature roughly coincides with the velocity reversal boundary, while the …

On The Reversal From “Sunward” To “Antisunward” Plasma Convection In The Dayside High Latitude Ionosphere, T S. Jorgensen, E Friis-Christensen, Vincent B. Wickwar, J D. Kelly, C R. Clauer, P M. Banks

All Physics Faculty Publications

Preliminary observations of dayside high latitude ionospheric plasma convection with the Sondrestrom incoherent‐scatter radar indicate that plasma can be observed to enter the polar cap region through rotational reversals at most local times between dawn and dusk and not just in a narrow region around noon. Assuming that rotational reversals are signatures of a solar wind‐magnetosphere interaction which drives magnetospheric convection, the observations indicate that this interaction occurs over a longitudinally wide area of the dayside magnetosphere. The observations also show that the distribution of F‐region plasma in the polar cap is dependent on ionization sources anywhere between dawn and …

Very High Electron Temperatures In The Daytime F-Region At Sondrestrom, W Kofman, Vincent B. Wickwar

All Physics Faculty Publications

Sondrestrom observations show that a characteristic F‐region signature of the interaction between the magnetosphere and ionosphere is a narrow band of elevated electron temperatures. Its location is associated with the ion convection reversal in the morning and evening convection cells. Typically, near 500 km altitude, the temperature is 3500 to 4000 K. However, on 24 April 1983, a geomagnetically very active day with Kp values of 6‐ during the period of interest, the electron temperature reached 6000 K in the afternoon convection reversal. The ion velocities were between 1 and 2 km/s on both sides of the reversal. There was …

Mithras: A Brief Description, O De La Beaujardiere, Vincent B. Wickwar, M J. Baron, J Holt, R M. Wand, W L. Oliver, P Bauer, M Blanc, C Senior, D Alcayde, G Caudal, J Foster, E Nielsen, R Heelis

All Physics Faculty Publications

Between May 1981 and June 1982 an intensive campaign of 33 coordinated observations was carried out using the three incoherent-scatter radars capable of probing the auroral zone. During this period the groups operating the Dynamic Explorer satellites and the STARE radar made special efforts to acquire data coincident with the radar observations. The objective of these MITHRAS experiments and subsequent analysis is to further our understanding of the interactions of the magnetosphere, the ionosphere, and the thermosphere, with special emphasis on local time/universal time variations. Three experimental modes with different time resolution and spatial coverage were used to examine different …

Thermospheric Neutral Wind At –39° Azimuth During The Daytime Sector At Sondrestrom, Vincent B. Wickwar

All Physics Faculty Publications

Measurements with the Sondrestrom radar have been used to examine the daytime thermospheric neutral wind and to relate that wind to other geophysical parameters. Ion drag is found to be particularly important for determining the wind pattern. However, evidence is presented that the wind pattern is significantly influenced by soft particle precipitation and, possibly, by Joule heating.

Observations Of Interplanetary Magnetic Field And Of Ionospheric Plasma Convection In The Vicinity Of The Dayside Polar Cleft, C R. Clauer, P M. Banks, A Q. Smith, T S. Jorgensen, E Friis-Christensen, S Vennerstrom, Vincent B. Wickwar

All Physics Faculty Publications

Dayside ionospheric convection at high latitudes has been examined during a series of experiments using the Sondrestrom radar together with ancillary observations of the interplanetary magnetic field (IMF) by the IMP‐8 spacecraft. The radar experiments obtained a latitude coverage of 67.6° Λ to 81.30° Λ and a temporal resolution of between 14 to 25 minutes. A total of 17 rotations through the dayside cleft region during April, June and July, 1983 have been examined. The observations show two convection cells with sunward flow at lower latitudes and antisunward flow at higher latitudes. The flow commonly rotates through a 180° angle …