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Articles 34591 - 34620 of 36535

Full-Text Articles in Physical Sciences and Mathematics

Dislocations And The Nematic To Smectic-A Transition For Arbitrary Values Of K1, Anthony Day, T. Lubensky, A. Mckane Feb 1983

Dislocations And The Nematic To Smectic-A Transition For Arbitrary Values Of K1, Anthony Day, T. Lubensky, A. Mckane

Anthony Roy Day

The de Gennes model is used to derive the energy of interacting dislocations in smectic-A liquid crystals. This energy reduces to the energy of interacting vortices in type-II superconductors when the splay elastic constant K1 is zero and to that derived from the Landau-Peierls elastic energy when spatial variations are slow on a scale of the bend and twist penetration depths. Furthermore, it has a well-defined K1→∞ limit. The dislocation energy is used to study the nematic—to—smectic-A transition as a function of K1 in two dimensions and in 4-ε dimensions. No evidence for the Nelson-Toner, anisotropic critical point is found …

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Reflections In A Polished Tube, Laurence A. Marschall, Emma Beth Marschall Feb 1983

Reflections In A Polished Tube, Laurence A. Marschall, Emma Beth Marschall

Physics and Astronomy Faculty Publications

When one of us (E.B.M.) dislodged a metal tube from an electric door chime recently, she inadvertently introduced her father to an attractive and instructive optical phenomenon. Looking down the highly polished inner surface of the cylinder we could see a spot surrounded by a series of bright concentric rings. The pattern looked much like the display of fringes produced by a Fabry-Perot or Michelson interferometer, except that the rings were more evenly spaced instead of crowding together strongly near the edge of the field of view. [excerpt]

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Single-Reflection Film—Substrate Half-Wave Retarders With Nearly Stationary Reflection Properties Over A Wide Range Of Incidence Angles, R. M.A. Azzam, M. Emdadur Rahman Khan Feb 1983

Single-Reflection Film—Substrate Half-Wave Retarders With Nearly Stationary Reflection Properties Over A Wide Range Of Incidence Angles, R. M.A. Azzam, M. Emdadur Rahman Khan

Electrical Engineering Faculty Publications

The complex reflection coefficient for the p polarization of a transparent film on an absorbing or transparent substrate can be made equal to the negative of that for the s polarization, and hence the film—substrate system acts as a half-wave retarder (HWR), by proper selection of film refractive index N1, film thickness d, and angle of incidence Φ. This condition, which generally holds only at normal incidence, becomes possible at oblique incidence also if N1 is within a certain range, 1 < N1 < N̂1 . For a given substrate and given N1, …

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Interpretation Of Anomalies In The Raman Spectrum Of K2Seo4 In Terms Of Oxygen Sublattice Disorder, Nestor Massa, Frank Ullman, John R. Hardy Feb 1983

Interpretation Of Anomalies In The Raman Spectrum Of K2Seo4 In Terms Of Oxygen Sublattice Disorder, Nestor Massa, Frank Ullman, John R. Hardy

John R. Hardy Papers

Raman scattering from K2SeO4 crystals has been studied in the (20-800)-K temperature range. Three portions of the spectrum are discussed: defect-induced scattering, primarily below 100 cm-1, the external mode spectrum below 200 cm-1, and the internal mode spectra in two regions, 300-500 and 800-950 cm-1. The temperature dependence of the low-frequency, defect-induced scattering has been correlated (in previous studies) with the temperature dependence of certain nonzero-wave-vector phonons that have been observed by others using inelastic neutron scattering. Close to the incommensurate transition temperature, Ti= 129 K, a large enhancement …

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Quality Factor For Low Doses Of High-Let Radiations, Werner Hofmann, Robert Katz Feb 1983

Quality Factor For Low Doses Of High-Let Radiations, Werner Hofmann, Robert Katz

Robert Katz Publications

The International Commission on Radiological Protection (ICRP77) and the International Commision on Radiation Units and Measurements (ICRU70) have recommended that the evaluation of radiation hazards be based on the “dose equivalent” defined as the product of the absorbed dose and some modifying factors, the most important of which is the quality factor (Q). The quality factor is intended to allow for the effect on the resulting detriment of the microscopic distribution of the absorbed energy. It is therefore defined as a function of the collision stopping power (L∞) in water at the point of interest. Thus Q rises …

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Track Formation In Plastics, Robert Katz Jan 1983

Track Formation In Plastics, Robert Katz

Robert Katz Publications

It is proposed that the “threshold for etchable track formation” in plastics is associated with the linear density of activated polymeric clusters along the path of an ion, in the “grain-count regime.” Existing data for CR-39 reveal a change in etching rate in the neighborhood of z/β having the value of about 15-20. We infer that this defines the transition from the grain count regime to the track width regime, as the activation cross-section exceeds the cross-sectional area of the cluster. This interpretation is consistent with available data for the G value for polymer scission and the dose of gamma-rays …

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Complex Reflection Coefficients For The Parallel And Perpendicular Polarizations Of A Film-Substrate System, R. M.A. Azzam, M. Emdadur Rahman Khan Jan 1983

Complex Reflection Coefficients For The Parallel And Perpendicular Polarizations Of A Film-Substrate System, R. M.A. Azzam, M. Emdadur Rahman Khan

Electrical Engineering Faculty Publications

The complex reflection coefficients Rv(ø,ζ) of a film-substrate system for the parallel (v = p) and perpendicular (v = s) polarizations are examined in detail as functions of the angle of incidence ø(0 ≤ ø ≤ 90°) and the reduced normalized film thickness ζ(0 ≤ ζ < 1). For definiteness, the reflection of light of wavelength λ = 0.6328 µm by the air–SiO2–Si system is assumed. Families of circles that represent the constant-angle-of-incidence contours, their envelopes, and the associated constant-thickness contours ofRp and Rs are all presented in the complex plane. Furthermore, the amplitude-reflectance and phase-shift functions, |Rv|(ø,ζ) and argRv(ø,ζ) …

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1/Z Expansion Calculation Of The Bethe Logarithm For The Ground State Lamb Shift Of Two-Electron Ions, S. P. Goldman, Gordon W. F. Drake Jan 1983

1/Z Expansion Calculation Of The Bethe Logarithm For The Ground State Lamb Shift Of Two-Electron Ions, S. P. Goldman, Gordon W. F. Drake

Physics Publications

The leading two terms in the 1/Z expansion of the two-electron Bethe logarithm are calculated by the application of a new finite basis set method. The results can be expressed in the form ln epsilon (1s 2 1S)=ln(19.77(Z-0.0063) 2). The high-Z behaviour appears to differ from that of a previous variational calculation by Aashamar and Austvik (1976).

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Lifetime Of The 2p State In He Ii, Gordon W. F. Drake, J. Patel, A. Van Wijngaarden Jan 1983

Lifetime Of The 2p State In He Ii, Gordon W. F. Drake, J. Patel, A. Van Wijngaarden

Physics Publications

When a beam of spin-polarized metastable He+(2s12) ions is quenched by an electric field E', the emitted radiation intensity contains an asymmetry term proportional to (kE)(P'k×E), where P' is the spin-polarization vector and k is the direction of observation. The resulting asymmetry is nearly proportional to the level width of the 2p12 state in He+. The measured asymmetry 0.007 602 70.000 020 3 corresponds to a lifetime 2p=(0.99920.0026)×10-10 sec, in fair agreement with the theoretical value 2p=0.9972×10-10 sec. © 1983 The American Physical Society.

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Theory Of Josephson-Type Oscillations In A Moving Charge-Density Wave - Errata, S. E. Barnes, A. Zawadowski Jan 1983

Theory Of Josephson-Type Oscillations In A Moving Charge-Density Wave - Errata, S. E. Barnes, A. Zawadowski

Physics Articles and Papers

Errata to Original Article: S. E. Barnes and A. Zawadowski, Theory of Josephson-Type Oscillations in a Moving Charge-Density Wave, Physical Review Letters, 51, 1499 (1983).

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Theory Of Josephson-Type Oscillations In A Moving Charge-Density Wave, S. E. Barnes, A. Zawadowski Jan 1983

Theory Of Josephson-Type Oscillations In A Moving Charge-Density Wave, S. E. Barnes, A. Zawadowski

Physics Articles and Papers

A theory of Josephson-type phenomena is presented, in which the two macroscopic quantum states are the two components of an incommensurate charge-density wave with opposite wave vectors. The Fermi levels of these two states are split for a moving charge-density wave and impurity scattering induces quantum oscillations. Such oscillations may be responsible for the observed narrow-band noise in materials such as NbSe3 and TaS3.

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Non-Mean-Field Interpretation Of The Irreversibility Line In Spin-Glasses, A. P. Malozemoff, S. E. Barnes, B. Barbara Jan 1983

Non-Mean-Field Interpretation Of The Irreversibility Line In Spin-Glasses, A. P. Malozemoff, S. E. Barnes, B. Barbara

Physics Articles and Papers

Susceptibility data on an amorphous GdAl spin-glass show an irreversibility onset line t=-A-H2/φ- and a susceptibility crossover line t=+A+H2/φ+ (t is reduced temperature; H is field). The exponents φ are both close to 3, and the amplitudes A differ only by a factor of 2. In contrast to earlier explanations of the irreversibility in terms of a de Almeida-Thouless mean-field instability, here both crossovers are explained in terms of a non-mean-field scaling theory.

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Magnetic Resonance In The Spin-Glass (Lagd)Al2, M. Zomack, K. Baberschke, S. E. Barnes Jan 1983

Magnetic Resonance In The Spin-Glass (Lagd)Al2, M. Zomack, K. Baberschke, S. E. Barnes

Physics Articles and Papers

ESR has been measured in the spin-glass (La1-xGdx)Al2, 1≤x≤15 at.% for 1, 3, 9, and 35 GHz, corresponding to different applied magnetic fields and in the temperature range of 100 mK to 30 K. The comparison of data for different frequencies shows that the linewidth depends very much on the frequency and/or field and therefore the temperature Tmin of the linewidth minimum is not an intrinsic parameter and the shift of the resonance position is almost independent of frequency. The former effect is analyzed and theoretically explained in terms of the temperature dependence …

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Γ8(3) Resonance In Esr Of (Ery)Al2 Single Crystals, U. Döbler, K. Baberschke, S. E. Barnes Jan 1983

Γ8(3) Resonance In Esr Of (Ery)Al2 Single Crystals, U. Döbler, K. Baberschke, S. E. Barnes

Physics Articles and Papers

Angle-dependent ESR results are given for 500-, 2500-, and 5000-ppm Er-doped YAl2 single crystals. An almost perfect analysis of the X- and Q-band data is achieved if the admixture of the first excited state Γ8(2) into the ground state Γ8(3) via the Zeeman interaction is taken into consideration. This enables us to determine the crystal electric field (CEF) parameter x=-0.322(20) and W=-0.29(2) K. The g-value shift yields N(EF)JΔg=+0.09(5) and the thermal broadening of the linewidth |N(EF)JΔH|=0.059(5). The precision of the experimental data allows, in principle, the determination …

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Basic Physics Of Emp, Beam Weapons, And Abm, David W. Hafemeister Jan 1983

Basic Physics Of Emp, Beam Weapons, And Abm, David W. Hafemeister

Physics

No abstract provided.

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Preliminary Rovibrational Analysis Of The Nν6+Ν1−Nν6 Vibration In Hcn⋅⋅⋅Hf, E. Kyrö, K. Mcmillan, M. Eliades, D. Danzeiser, P. Shoja-Chaghervand, Shannon Lieb, J. W. Bevan Jan 1983

Preliminary Rovibrational Analysis Of The Nν6+Ν1−Nν6 Vibration In Hcn⋅⋅⋅Hf, E. Kyrö, K. Mcmillan, M. Eliades, D. Danzeiser, P. Shoja-Chaghervand, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

A preliminary rotation‐vibration analysis of the n=0 and n=1 subbands associated with the nν6+ν1−nν6 hydrogen‐bonded vibration in HCN⋅⋅⋅HF has been completed. The following excited staterotational constantsB′ and band origin frequencies ν0 have been determined for the complex. The results are consistent with a rotation‐vibration interaction constant α1=−68.3±1 MHz which correlates with an excited stater(N⋅⋅⋅F) internuclear distance of 2.762 Å, a decrease of 0.034 Å relative to the ground state.Excited state lifetimes associated with assigned transitions are demonstrated to be …

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Gravity‐Induced Density And Concentration Profiles In Binary Mixtures Near Gas–Liquid Critical Lines, R. F. Chang, J. M. H. Levelt Sengers, T. Doiron, J. Jones Jan 1983

Gravity‐Induced Density And Concentration Profiles In Binary Mixtures Near Gas–Liquid Critical Lines, R. F. Chang, J. M. H. Levelt Sengers, T. Doiron, J. Jones

Physics Publications

We have calculated gravity‐induced density and concentration gradients using scaled equations of state fashioned after that of Leung and Griffiths for binary mixtures near gas–liquid critical lines. The mixtures considered here are those of helium‐3 and helium‐4 and of carbon dioxide and ethane. Our calculations show that the density profiles for both mixtures in any proportion of the components are similar to those of pure fluids. The concentration gradients in the helium mixture have the same appearance as the density gradients. In the carbon dioxide–ethane system, however, the form of the concentration profile varies greatly, depending on the overall composition. …

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Thermal Propagation And Stability In Superconducting Films, Kenneth E. Gray, Robert T. Kampwirth, John F. Zasadzinski, Stephen P. Ducharme Jan 1983

Thermal Propagation And Stability In Superconducting Films, Kenneth E. Gray, Robert T. Kampwirth, John F. Zasadzinski, Stephen P. Ducharme

Stephen Ducharme Publications

Thermal propagation and stable hot spots (normal domains) are studied in various high Tc superconducting films (Nb3Sn, Nb, NbN and Nb3Ge). The prediction of the thermal propagation velocity of the long-standing model of Broom and Rhoderick (1960) is verified quantitatively in the regime of its validity. A new energy balance model is shown to give reasonable quantitative agreement of the dependence of the propagation velocity on the length of short normal domains. The steady state (zero velocity) measurements indicate the existence of two distinct situations for films on high thermal conductivity (sapphire) substrates. For low power per unit area the …

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Alternatives In Quantum Theory, Richard C. Heyser Jan 1983

Alternatives In Quantum Theory, Richard C. Heyser

Unpublished Writings

Quantum mechanical descriptions in terms of momentum and position are identified as alternatives under the condition of equal complex-vaulted Lebesgue square integrability. While this does not change any of the formal results obtained in quantum mechanics, it does shed a different interpretive light on the steps that lead up to these results. Instead of being independent, even in concept, momentum and position are identified as being the same thing, merely seen from different views. Neither is required to complement the descriptive capability of the other, since each forms a complete alternative in its own right. Apparent complementarity, as well as …

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Seam Wave Characteristics In An Eastern U.S. Coal, Paul J. Wolfe, Timothy G. Holdeman, Benjamin H. Richard Jan 1983

Seam Wave Characteristics In An Eastern U.S. Coal, Paul J. Wolfe, Timothy G. Holdeman, Benjamin H. Richard

Physics Faculty Publications

No abstract provided.

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Ion-Atom Differential Cross Sections At Intermediate Energies, Ronald E. Olson Jan 1983

Ion-Atom Differential Cross Sections At Intermediate Energies, Ronald E. Olson

Physics Faculty Research & Creative Works

The classical-trajectory Monte Carlo method has been used to calculate H++H(1s) electron-capture and ionization differential cross sections in the range 25-200 keV. The results indicate the importance of including excited product states to describe the small-angle electron-capture scattering. Angular scattering of the electron removed by the ionization process has been studied as a function of ejected-electron velocity ve. The classical calculations are in reasonable agreement with coupled-channel results of Shakeshaft [Phys. Rev. A 18, 1930 (1978)] as to the "electron capture to the continuum" (ECC) component of the ionization process where this term is defined as the ejected electron being …

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Ion Scattering From State-Selected Rydberg Atoms, G. A. Kohring, A. E. Wetmore, Ronald E. Olson Jan 1983

Ion Scattering From State-Selected Rydberg Atoms, G. A. Kohring, A. E. Wetmore, Ronald E. Olson

Physics Faculty Research & Creative Works

Classical-trajectory Monte Carlo calculations have been performed for collisions of protons with state-selected hydrogenic Rydberg atoms. The examples investigated were Rydberg atoms in the n=10, l=9 level with ml=0 and 9. The collision velocity range was 0.1 to 1.0 a.u. (2.2x107 to 2.2x108 cm/s). The ionization cross sections were found to be relatively insensitive to changes in the ml levels. However, the charge-transfer cross sections showed considerable enhancement if the Rydberg electron is orientated in a plane which is parallel to the direction of the incident projectile. © 1983 The American Physical Society.

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Molecular Treatment Of Charge Transfer In Li+ +Ca Collisions, M. Kimura, H. Sato, Ronald E. Olson Jan 1983

Molecular Treatment Of Charge Transfer In Li+ +Ca Collisions, M. Kimura, H. Sato, Ronald E. Olson

Physics Faculty Research & Creative Works

The perturbed-stationary-state method, appended with electron translation factors, has been applied to charge transfer in Li+ +Ca collisions for energies from 0.1 to 20 keV/amu. The Born-Oppenheimer wave functions and eigenvalues were generated using the pseudopotential technique, which reduced the many-electron system to a simpler two-electron problem. The molecular ground-state X +1 is calculated to be bound and has the potential-well parameters Re=6.20a0, De=1.11 eV, e=235 cm-1, and Be=0.263 cm-1. From the scattering computations, a representative value for the charge-transfer cross section is 4x10-15 cm2 at 5 keV/amu. The cross section decreases rapidly as the energy is reduced below 1 …

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Linear Inversion Method To Obtain Aerosol Size Distributions From Measurements With A Differential Mobility Analyzer, Donald E. Hagen, Darryl J. Alofs Jan 1983

Linear Inversion Method To Obtain Aerosol Size Distributions From Measurements With A Differential Mobility Analyzer, Donald E. Hagen, Darryl J. Alofs

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The Use of a Differential Mobility Analyzer to Perform Aerosol Size Spectrum Measurements Requires an Inversion Method to Go from the Measured Sensor Responses to the Desired Size Spectrum Information. Here We Present a Linear Inversion Method that Can Be Run on a Microcomputer or a Small Minicomputer. It Does Not Use Some of the Approximations Made in the Techniques Currently Available and Hence Gives Better Inversion Accuracy. the Method Shows Good Immunity to Both Random and Systematic Experimental Error. It is Applied to Numerous Test Case Aerosols. © 1983 Elsevier Science Publishing Co., Inc.

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On The Schrödinger Spin‐Exchange Ferromagnet, Harry A. Brown Jan 1983

On The Schrödinger Spin‐Exchange Ferromagnet, Harry A. Brown

Physics Faculty Research & Creative Works

The thermodynamic behavior of a ferromagnet whose interactions are described by the Schrödinger spin‐exchange operator is investigated. The transition temperatures, magnetization, susceptibility, exchange energy, heat capacity, and entropy are calculated for general spin and lattice coordination number using the constant‐coupling approximation. Both first‐ and second‐order phase transitions are found. Comparison with some results of the high‐temperature expansion method shows some qualitative agreement. Copyright © 1983 WILEY‐VCH Verlag GmbH & Co. KGaA

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Physics, Robert B. Witmer, Wilbur O. Weisser Jan 1983

Physics, Robert B. Witmer, Wilbur O. Weisser

UND Departmental Histories

This departmental history was written on the occasion of the UND Centennial in 1983.

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Are There Any Shock-Heated Galaxies?, Gary J. Ferland, Hagai Netzer Jan 1983

Are There Any Shock-Heated Galaxies?, Gary J. Ferland, Hagai Netzer

Physics and Astronomy Faculty Publications

We study the spectroscopic characteristics of low ionization nuclear emission-line regions (Liners) in galaxies, and compare them with other active galactic nuclei. We show the results of new, extensive photoionization model calculations and use them to investigate line ratio diagrams, such as [O III] λ5007/Hβ versus [O II] λ3727/[O III] λ5007, and [O I] λ6300/[O III] λ5007 versus [O III] λ3727/[O III] λ5007. On the diagrams broad line objects, Seyfert 2 galaxies, and Liners form a continuous smooth sequence of decreasing ionization parameter. This suggests a common origin for line excitation in …

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Intermediate-Band Photometry Of Stars In Three Clusters Containing Classical Cepheids, Edward G. Schmidt Jan 1983

Intermediate-Band Photometry Of Stars In Three Clusters Containing Classical Cepheids, Edward G. Schmidt

Edward Schmidt Publications

Four-color and Hβ photometry has been carried out of stars in three sparse and distant clusters which are thought to contain Cepheids. From these data the distance moduli and color excesses of the clusters have been derived. In general the new values agree with those in the literature but are somewhat more precise.

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Nitrogen Escape From Mars, Jane L. Fox, Alexander Dalgarno Jan 1983

Nitrogen Escape From Mars, Jane L. Fox, Alexander Dalgarno

Physics Faculty Publications

The escape rate of nitrogen from Mars is calculated to be 2.3×105 s−1 for low solar flux conditions and 8.9×105 s−1 for high solar flux conditions. The major source of energetic atoms is dissociative recombination of ground state and vibrationally excited N2+ ions. The measured 15N/14N isotope ratio can be reproduced by postulating an early dense atmosphere during which little differentiation occurred.

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Observation Of Biexcitonic Optical Bistability And Optical Limiting In Cucl, N. Peyghambarian, H. M. Gibbs, M. C. Rushford, D. A. Weinberger Jan 1983

Observation Of Biexcitonic Optical Bistability And Optical Limiting In Cucl, N. Peyghambarian, H. M. Gibbs, M. C. Rushford, D. A. Weinberger

Physics: Faculty Publications

Experimental evidence for the occurrence of optical bistability using the biexciton two-photon resonance in CuCl is presented. These observations agree with recent theoretical predictions that require an intensity of 10 MW/cm2 and 10-μm-thick etalons with 90% reflective coatings. Earlier much less demanding predictions neglected two important physical effects: unsaturable background absorption at the biexciton from the tail of the exciton resonance and broadening of the biexciton resonance with intensity.

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