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Articles 21751 - 21780 of 21971

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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A Rapid Affinity Chromatography Procedure For The Isolation Of Glucose-6-Phosphate Dehydrogenase From Human Erythrocytes, Chris Craney, M. Goffredo Jan 1983

A Rapid Affinity Chromatography Procedure For The Isolation Of Glucose-6-Phosphate Dehydrogenase From Human Erythrocytes, Chris Craney, M. Goffredo

Chris L. Craney

The isolation of glucose-6-phosphate dehydrogenase from outdated human erythrocytes (type AB+) utilizing NADP+ affinity chromatography and gel-permeation chromatography (Bio-Gel P-150) yields a fully active, homogeneous preparation. The procedure is faster and gives a higher yield than previous reports.

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Recognition Of Student Input In Computer-Assisted Language Learning, Carol Chapelle, Joan Jamieson Jan 1983

Recognition Of Student Input In Computer-Assisted Language Learning, Carol Chapelle, Joan Jamieson

Carol Chapelle

Computerized instruction has captured the interest of many educators as a means of individualizing language study for their students. The quality of this individualization is maximally dependent on the degree to which a computer can understand what the student communicates to it usually by typing a message on the keyboard. This article provides an overview of this student communication, or input: its types, its recognition, and some uses of its recognition. A general understanding of the potential of student-computer interaction will enlighten those who are examining Computer Assisted Language Learning (CALL) lessons for use in their curriculum. Some of this …

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Xanes In (Tmtsef)2re04: Polarization Dependence Of The Se K-Edge, Juana Vivó Acrivos, S.S. P. Parkin Jan 1983

Xanes In (Tmtsef)2re04: Polarization Dependence Of The Se K-Edge, Juana Vivó Acrivos, S.S. P. Parkin

Juana Vivó Acrivos

We have measured XANES (X-ray Absorption Near Edge Spectra) near the Re Li (i=l,II,III) edges in (TMTTF)2Re04 and (TMTSeF) 2Re04 and the Se K edge in the latter compound. An important dependence of the XANES at the Se K edge on the polarisation of the incident beam with respect to the crystal axes was observed, whose interpretation can give information on the symmetry of the unoccupied conduction band states. The positions of the Re L edges were compared with those in several inorganic compounds containing Re in various oxidation states, and were found to be, within experimental error, the same …

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Sources Of Nosocomial Infections In Immunocompromised Patients (Letter), B. Burt Gerstman Jan 1983

Sources Of Nosocomial Infections In Immunocompromised Patients (Letter), B. Burt Gerstman

B. Burt Gerstman

No abstract provided.

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First Vhf Auroral Radarinterferometer Observations, J. Providakes, W. E. Swartz, D. T. Farley, Bela G. Fejer Jan 1983

First Vhf Auroral Radarinterferometer Observations, J. Providakes, W. E. Swartz, D. T. Farley, Bela G. Fejer

Bela G. Fejer

The radar interferometer technique first used at the magnetic equator in Peru is also a very powerful means for studying auroral plasma instabilities. We present here the first results, obtained with a 49.92 MHz, 20-25 KW peak power pulsed radar located in Ithaca, NY (42.5° N, 76.4° W). Strong auroral echoes were obtained during several highly active periods. Phase differences between the signals received on the two antennas accurately determine the E-W position, within the scattering volume, of localized scattering centers, and changes in this phase determine the corresponding velocity. The signal Doppler shift describes radial (essentially N-S) motion. The …

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A Statistical Interpretation Of The Rotational Temperature Of No Desorbed For Ru(001), Stephen E. Bialkowski Jan 1983

A Statistical Interpretation Of The Rotational Temperature Of No Desorbed For Ru(001), Stephen E. Bialkowski

Stephen E. Bialkowski

A simple model of the rotational state of NO prior to thermal desorption from Ru(001) surface is developed in terms of the rotational heat capacity. The predicted rotational temperature of the desorbed species is consistent with known data on this system. The model is extended to predict translational energy anisotropy in the desorbed NO.

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Assessment Of Chlorination By Human Neutrophils, Thomas Goyne, Christopher Foote, Robert Lehrer Dec 1982

Assessment Of Chlorination By Human Neutrophils, Thomas Goyne, Christopher Foote, Robert Lehrer

Thomas Goyne

No abstract provided.

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Bound-States, Virtual States, And Non-Exponential Decay Via Path-Integrals, Br Holstein Dec 1982

Bound-States, Virtual States, And Non-Exponential Decay Via Path-Integrals, Br Holstein

Barry R Holstein

Using path integral techniques we demonstrate how three quantum-mechanical phenomena-alpha decay, nonexponential decay, and resonant scattering-can be treated. This procedure is an algebraic one yet reproduces the usual results obtained via solution of the Schrödinger equation via WKB methods.

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Market Gardening In Thailand: The Origins Of An Ethnic Chinese Monopoly, James A. Hafner Dec 1982

Market Gardening In Thailand: The Origins Of An Ethnic Chinese Monopoly, James A. Hafner

James A Hafner

No abstract provided.

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Asymptotic Integration Of $Y^(N) +P(T)Y^Gamma =F(T)$ Under Mild Integral Smallness Conditions, William F. Trench Dec 1982

Asymptotic Integration Of $Y^(N) +P(T)Y^Gamma =F(T)$ Under Mild Integral Smallness Conditions, William F. Trench

William F. Trench

No abstract provided.

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Crystal Structures Of Trans-Acetyldicarbonyl- (Eta5-Cyclopentadienyl)(Dimethylphenylphosphane)- Molybdenum(Ii) And Trans-Acetyldicarbonyl- (Eta5-Cyclopentadienyl)(Ethyldiphenylphosphane)- Molybdenum(Ii), Matthew T. Whited, Gretchen E. Hofmeister, Connor J. Hodges, Laramie T. Jensen, Samuel H. Keyes, Aurapat Ngamnithiporn, Daron E. Janzen Dec 1982

Crystal Structures Of Trans-Acetyldicarbonyl- (Eta5-Cyclopentadienyl)(Dimethylphenylphosphane)- Molybdenum(Ii) And Trans-Acetyldicarbonyl- (Eta5-Cyclopentadienyl)(Ethyldiphenylphosphane)- Molybdenum(Ii), Matthew T. Whited, Gretchen E. Hofmeister, Connor J. Hodges, Laramie T. Jensen, Samuel H. Keyes, Aurapat Ngamnithiporn, Daron E. Janzen

Daron E Janzen, Ph.D.

No abstract provided.

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Centers Of Polymer Research; Polymer Science In The South And West Of Japan, Otto Vogl, T. Kunitake, J. Kiji Dec 1982

Centers Of Polymer Research; Polymer Science In The South And West Of Japan, Otto Vogl, T. Kunitake, J. Kiji

Otto Vogl

No abstract provided.

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Symposium On Functional Polymers, Kunming, Yunnan, People’S Republic Of China, Otto Vogl, K. Takemoto Dec 1982

Symposium On Functional Polymers, Kunming, Yunnan, People’S Republic Of China, Otto Vogl, K. Takemoto

Otto Vogl

No abstract provided.

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Centers Of Polymer Research; Polymer Science In The Nagoya Area, Otto Vogl, M. Nagasawa, Y. Yamashita Nov 1982

Centers Of Polymer Research; Polymer Science In The Nagoya Area, Otto Vogl, M. Nagasawa, Y. Yamashita

Otto Vogl

No abstract provided.

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U.S.-Swedish Workshop On Photodegradation And Photostabilization Of Polymers, Otto Vogl, Bengt Ranby Nov 1982

U.S.-Swedish Workshop On Photodegradation And Photostabilization Of Polymers, Otto Vogl, Bengt Ranby

Otto Vogl

No abstract provided.

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Spin Systems On Hierarchical Lattices. Introduction And Thermodynamic Limit, Robert B. Griffiths, Miron Kaufman Nov 1982

Spin Systems On Hierarchical Lattices. Introduction And Thermodynamic Limit, Robert B. Griffiths, Miron Kaufman

Miron Kaufman

A number of exactly soluble models in statistical mechanics can be produced with the use of spins interacting with nearest neighbors on a hierarchical lattice. A general definition and several examples of such lattices are given, and the topological properties of one of these, the "diamond" lattice, are discussed in detail. It is shown that the free energy has a well-defined thermodynamic limit for a large class of discrete spin models on hierarchical lattices.

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First-Order Transitions In Defect Structures At A Second-Order Critical Point, Miron Kaufman, Robert B. Griffiths Nov 1982

First-Order Transitions In Defect Structures At A Second-Order Critical Point, Miron Kaufman, Robert B. Griffiths

Miron Kaufman

On certain hierarchical lattices the order parameter on a defect line increases discontinuously at the bulk critical temperature for q-state Potts models when q is sufficiently large, even though the bulk order parameter increases continuously. It is suggested that the same behavior may occur for two-dimensional lattices with 2 < q <= 4.

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Excited States And Photochemistry Of Saturated Molecules. 11. Potential Energy Surfaces In Low-Lying States Of Ethane, James W. Caldwell, Mark S. Gordon Oct 1982

Excited States And Photochemistry Of Saturated Molecules. 11. Potential Energy Surfaces In Low-Lying States Of Ethane, James W. Caldwell, Mark S. Gordon

Mark S. Gordon

Ab initio calculations at both the restricted Hartree-Fock (RHF) and singly excited configuration interaction (SEC I) levels have been carried out on sections of the potential energy surfaces for a number of low-lying excited singlet electronic states of ethane. All vertical states below the first ionization potential are predominantly Rydberg in character, as are all minima detected on the potential energy surfaces. The lowest 1Eg state is predicted to have only a very small (""" 1 kcal/mol) barrier separating its minimum-energy structure from the 1A" ethylidene + 1 ~/ H2 products. Since the vertical Eg molecule has more than enough …

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Centers Of Polymer Research; Polymer Science In Osaka, Japan: Part Ii, Otto Vogl, T. Otsu, K. Hatada Oct 1982

Centers Of Polymer Research; Polymer Science In Osaka, Japan: Part Ii, Otto Vogl, T. Otsu, K. Hatada

Otto Vogl

No abstract provided.

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Regression Analysis In Health Services Research: The Use Of Dummy Variables, Paula Diehr, Lincoln Nayak Polissar Sep 1982

Regression Analysis In Health Services Research: The Use Of Dummy Variables, Paula Diehr, Lincoln Nayak Polissar

Paula Diehr

Dummy variables frequently are used in regression analysis but often in an incorrect fashion. A brief review of examples in the medical care literature showed that the interpretation of dummy variable regression coefficients and their significance was often incorrect or unclear. This article shows how dummy variables can be used and assessed properly. The importance of testing for the joint effect of a group of dummy variables is stressed. It also gives a standard and useful extension of the dummy variable technique to testing for the effect of collections of variables.

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Gas-Phase Photolysis Of 2,2-Dimethylbutane, 2,2,3-Trimethylbutane, 2,2,3-Trimethyl-2-Silabutane, And 2,2,3,3-Tetramethyl-2-Silabutane At 147 Nm, Daryl J. Doyle, S. K. Tokach, Mark S. Gordon, Robert D. Koob Sep 1982

Gas-Phase Photolysis Of 2,2-Dimethylbutane, 2,2,3-Trimethylbutane, 2,2,3-Trimethyl-2-Silabutane, And 2,2,3,3-Tetramethyl-2-Silabutane At 147 Nm, Daryl J. Doyle, S. K. Tokach, Mark S. Gordon, Robert D. Koob

Mark S. Gordon

The 147-nm photolyses of 2,2-dimethylbutane, 2,2,3-trimethylbutane, 2,2,3-trimethyl-2-silabutane (isopropyltrimethylsilane), and 2,2,3,3-tetramethyl-2-silabutane (tert-butyltrimethylsilane) are reported. In addition, the mercury-sensitized photolyses of i-C4H10, trimethylsilane, and mixtures of i-C4H10 and trimethylsilane are reported which give disproportionation to combination (D/C) ratios of 2.1 ::1::0.2 and 0.28::1::0.05 for (CH3) 3C + (CH3) 3C and (CH3)gSi + (CH3)gSi, respectively, and D/C ratios of 1.86::1:: 0.15 and 0.55 ::1:: 0.08 for (CH3)gC + (CH3)aSi to form 2-methyl-2-silapropene and i-C4H8, respectively. With the completion of this work, several trends and generalizations can be drawn concerning the importance of various processes in linear vs. branched alkanes and alkylsilanes. These conclusions …

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Centers Of Polymer Research; Polymer Science In Osaka, Japan: Part I, Otto Vogl, T. Otsu, K. Hatada Sep 1982

Centers Of Polymer Research; Polymer Science In Osaka, Japan: Part I, Otto Vogl, T. Otsu, K. Hatada

Otto Vogl

No abstract provided.

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Effects Of Polar Substituents On Carbon-Silicon Multiple Bonds, Mark S. Gordon Aug 1982

Effects Of Polar Substituents On Carbon-Silicon Multiple Bonds, Mark S. Gordon

Mark S. Gordon

The results of ab initio calculations on the effects of fluorine and lithium substitution on silaethyne and silaethylene and their isomers are presented. It is found that fluorine has a strong stabilizing effect when attached to silicon. This results in the predictions (a) that a distorted 1-fluoro-1-silaethyne is the most stable structure of HCSiF and (b) that 1,1-difluoro- 1-silaethylene is much lower in energy than 1,2-difluoromethylsilylene. Approximate correlation corrections are added to study the HC~iF - FHC=Si and HC==SiLi - LiHC=Si potential energy surfaces.

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Centers Of Polymer Research; Polymer Science In Tokyo, Japan, Part Iii: Suburban Area, Otto Vogl, I. Uematsu, A. Abe Aug 1982

Centers Of Polymer Research; Polymer Science In Tokyo, Japan, Part Iii: Suburban Area, Otto Vogl, I. Uematsu, A. Abe

Otto Vogl

No abstract provided.

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Centers Of Polymer Research; Polymer Science In Tokyo, Japan, Part Ii: Suburban Area, Otto Vogl, I. Uematsu, A. Abe Jul 1982

Centers Of Polymer Research; Polymer Science In Tokyo, Japan, Part Ii: Suburban Area, Otto Vogl, I. Uematsu, A. Abe

Otto Vogl

No abstract provided.

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Polymer Science In The Peoples Republic Of China, Otto Vogl, K. Takemoto Jun 1982

Polymer Science In The Peoples Republic Of China, Otto Vogl, K. Takemoto

Otto Vogl

No abstract provided.

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In-Situ Measurements Ofwave Electric Fields In The Equatorial Electrojet, R. C. Pfaff, M. C. Kelley, Bela G. Fejer, N. C. Maynard, K. D. Baker Jun 1982

In-Situ Measurements Ofwave Electric Fields In The Equatorial Electrojet, R. C. Pfaff, M. C. Kelley, Bela G. Fejer, N. C. Maynard, K. D. Baker

Bela G. Fejer

Electric field wave measurements have been performed on two sounding rockets in the equatorial ionosphere. During a daytime flight from Chilca, Peru, intense electrostatic waves were detected on the upward directed electron density gradient. During a nighttime flight from Kwajalein Atoll, similar waves were detected on a downward directed gradient. These results are in agreement with a gradient drift instability explanation of the generation of the waves. The wave amplitudes were as high as 5 mV/m implying perturbation drifts comparable to the driving drift velocities. Power spectra from the turbulent region show a peak at long wavelengths, followed by a …

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Long Wavelength Irregularities In The Equatorial Electrojet, E. Kudeki, D. T. Farley, Bela G. Fejer Jun 1982

Long Wavelength Irregularities In The Equatorial Electrojet, E. Kudeki, D. T. Farley, Bela G. Fejer

Bela G. Fejer

We have used the radar interferometer technique at Jicamarca to study in detail irregularities with wavelengths of a few kilometers generated in the unstable equatorial electrojet plasma during strong type 1 conditions. In-situ rocket observations of the same instability process are discussed in a companion paper. These large scale primary waves travel essentially horizontally and have large amplitudes. The vertical electron drift velocities driven by the horizontal wave electric fields reach or exceed the ion-acoustic velocity even though the horizontal phase velocity of the wave is considerably smaller. A straightforward extension to the long wavelength regime of the usual linear …

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Subduction Of The Caribbean Plate And Basement Uplifts In The Overriding South American Plate, James N. Kellogg, William E. Bonini May 1982

Subduction Of The Caribbean Plate And Basement Uplifts In The Overriding South American Plate, James N. Kellogg, William E. Bonini

James N Kellogg

Abstract. The new tectonic interpretations presented in this paper are based on geologic field mapping and gravity data supplemented by well logs, seismic profiles, and radiometric and earthquake data. The present Caribbean-South American plate boundary is the South Caribbean marginal fault, where subduction is indicated by folding and thrusting in the deformed belt and a seismic zone that dips 30o to the southeast and terminates 200 km below the Maracaibo Basin. The Caribbean-South American convergence rate is estimated as 1.9 +_. 0.3 cm/yr on the basis of the 390-km length of the seismic zone and a thermal equilibration time of …

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