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Articles 21511 - 21540 of 21971

Full-Text Articles in Physical Sciences and Mathematics

Asymptotic Properties Of Positive Summation-Integral Operators, Tian-Xiao He Dec 1987

Asymptotic Properties Of Positive Summation-Integral Operators, Tian-Xiao He

Tian-Xiao He

No abstract provided.

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On Minimal And Quasi-Minimal Supported Bivariate Splines, Tian-Xiao He Dec 1987

On Minimal And Quasi-Minimal Supported Bivariate Splines, Tian-Xiao He

Tian-Xiao He

No abstract provided.

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Semiclassical Treatment Of The Double Well, Br Holstein Dec 1987

Semiclassical Treatment Of The Double Well, Br Holstein

Barry R Holstein

The double well potential V(x)= 1/4 λ(x2-α2)2 is addressed using both semiclassical path integral and instanton techniques. The basic physics of the two-state system is shown to arise, and energy levels calculated via the two methods are compared.

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Comment On "Percolation In Isotropic Elastic Media.", Anthony Day, M. Thorpe Dec 1987

Comment On "Percolation In Isotropic Elastic Media.", Anthony Day, M. Thorpe

Anthony Roy Day

No abstract provided.

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Efficient Application Of The Schauder-Tychonoff Theorem To Functional Perturbations Of $X^(N)=0$, William F. Trench Dec 1987

Efficient Application Of The Schauder-Tychonoff Theorem To Functional Perturbations Of $X^(N)=0$, William F. Trench

William F. Trench

No abstract provided.

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Spectral Dimensionality Of Random Superconducting Networks, Anthony Roy Day, W. Xia, M. F. Thorpe Dec 1987

Spectral Dimensionality Of Random Superconducting Networks, Anthony Roy Day, W. Xia, M. F. Thorpe

Anthony Roy Day

We compute the spectral dimensionality d-tilde of random superconducting-normal networks by directly examining the low-frequency density of states at the percolation threshold. We find that d-tilde=4.1±0.2 and 5.8±0.3 in two and three dimensions, respectively, which confirms the scaling relation d-tilde=2d/(2-s/ nu ), where s is the superconducting exponent and nu the correlation-length exponent for percolation. We also consider the one-dimensional problem where scaling arguments predict, and our numerical simulations confirm, that d-tilde=0. A simple argument provides an expression for the density of states of the localized high-frequency modes in this special case. We comment on the connection between our calculations …

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Stability Of Networks Under Tension And Pressure, Anthony Roy Day, H. Yan, M. F. Thorpe Dec 1987

Stability Of Networks Under Tension And Pressure, Anthony Roy Day, H. Yan, M. F. Thorpe

Anthony Roy Day

The number of zero-frequency modes of an elastic network is an important quantity in determining the stability of the network. We present a constraint-counting method for finding this number in general central-force networks that are under an external tension. The technique involves isolating the backbone and then counting constraints in the same way as for free standing networks. A detailed example of this counting is given for a random two-dimensional network subject to an external tension. The results are shown to agree with the number of zero-frequency modes as determined by a direct matrix diagonalization.

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“Macromolecules 86": An International Conference On Functional Polymers And Biopolymers, Otto Vogl, Geoffrey C. Eastmond Dec 1987

“Macromolecules 86": An International Conference On Functional Polymers And Biopolymers, Otto Vogl, Geoffrey C. Eastmond

Otto Vogl

No abstract provided.

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Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 1. The Unstablelayer And Gradient Drift Waves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker Dec 1987

Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 1. The Unstablelayer And Gradient Drift Waves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker

Bela G. Fejer

Electric field and plasma density instrumentation on board a sounding rocket launched from Punta Lobos, Peru, detected intense electrostatic waves indicative of plasma instabilities in the daytime equatorial electrojet. Simultaneous measurements taken by the Jicamarca radar showed strong 3-m type 1 electrojet echoes as well as evidence of kilometer scale horizontally propagating waves. The in situ electric field wave spectra displayed three markedly different height regions within the unstable layer: (1) a two-stream region on the topside between 103 and 111 km where the electron current was considered to be strongest, (2) a gradient drift region between 90 and 106.5 …

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The Condor Equatorial Electrojetcampaign: Radar Results, E. Kudeki, Bela G. Fejer, D. T. Farley, C. Hanuise Dec 1987

The Condor Equatorial Electrojetcampaign: Radar Results, E. Kudeki, Bela G. Fejer, D. T. Farley, C. Hanuise

Bela G. Fejer

A review of the experimental and theoretical background to the Condor equatorial electrojet campaign is followed by the presentation and discussion of VHF radar interferometer and HF radar backscatter data taken concurrently with two rocket in situ experiments reported in companion papers (Pfaff et al., this issue (a, b). Both experiments were conducted in strongly driven periods with the on-line radar interferometer displaying signatures of what has been interpreted in earlier radar work (Kudeki et al., 1982) as kilometer scale gradient drift waves. Low-frequency density fluctuations detected by in situ rocket sensors confirm the earlier interpretation. VHF radar/rocket data comparisons …

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Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 2. Two-Streamwaves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker Dec 1987

Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 2. Two-Streamwaves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker

Bela G. Fejer

Both primary and secondary two-stream (Farley-Buneman) waves have been detected by in situ electric field and plasma density probes in the strongly driven daytime equatorial electrojet over Peru. Simultaneous Jicamarca radar observations showed strong vertical and oblique 3-m type 1 echoes, also indicative of the two-stream mechanism. The rocket data show the two-stream region on the topside of the unstable layer to be situated between 103 and 111 km where the electron current was the strongest. This region was characterized by broadband plasma oscillations extending past 1 kHz in the rocket frame. Furthermore, above 106.5 km, where the electron density …

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Theoretical Study Of The Environmental Effects On The Hyperfine Fields Of Ni And Fe In Ni0.75fe0.25, H. Ebert, H. Winter, B. Gyorffy, Duane D. Johnson, F. J. Pinski Nov 1987

Theoretical Study Of The Environmental Effects On The Hyperfine Fields Of Ni And Fe In Ni0.75fe0.25, H. Ebert, H. Winter, B. Gyorffy, Duane D. Johnson, F. J. Pinski

Duane D. Johnson

The dependence of the hyperfine fields Bhf of Ni and Fe in Ni0.75Fe0.25 on the surrounding atomic configuration has been studied by performing charge selfconsistent 6 shell-cluster Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) bandstructure calculations. By replacing the CPA- scatterers in the various shells around the central atom by Ni - or Fe-atoms, respectively, it could be shown that the hyperfine fields vary linearly with the number of Fe-atoms within a given shell and that the changes of Bhf due to simultaneous changes of the atomic configurations of different shells are additive. The changes of the hyperfine fields upon ordering of …

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First Polymer Discussions Of Dresden In Gaussig: Polymer Blends, Otto Vogl, Elizabeth Klemm Nov 1987

First Polymer Discussions Of Dresden In Gaussig: Polymer Blends, Otto Vogl, Elizabeth Klemm

Otto Vogl

No abstract provided.

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Prey Depletion By Odonate Larvae: Combining Evidence From Multiple Field Experiments, Clay L. Pierce, Dan M. Johnson, Thomas H. Martin, Charles N. Watson, Robert E. Bohanan, Philip H. Crowley Oct 1987

Prey Depletion By Odonate Larvae: Combining Evidence From Multiple Field Experiments, Clay L. Pierce, Dan M. Johnson, Thomas H. Martin, Charles N. Watson, Robert E. Bohanan, Philip H. Crowley

Clay L. Pierce

In this paper we re-analyze previously published data regarding the response of several prey populations to manipulation of predaceous larval dragonfly (Insecta: Odonata) densities in four separate field enclosure experiments. Using a computer-intensive "rerandomization" approach to testing hypotheses, we show that the individual experiments were not sufficiently powerful to consistently reject false null hypotheses. Combining the data from three comparable experiments, we can enhance the power associated with such tests. Three prey categories (Trichoptera, Oligochaeta, and large Cladocera), constituting less than one-third of the typical odonate diet, were found to be consistently depleted in enclosures with odonate larvae; but the …

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Synthesis Of Polymers And Polymer Liquid Crystals: A Euchem Conference In Lahti, Finland, Otto Vogl, Franciska Sundholm Oct 1987

Synthesis Of Polymers And Polymer Liquid Crystals: A Euchem Conference In Lahti, Finland, Otto Vogl, Franciska Sundholm

Otto Vogl

No abstract provided.

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Molecular And Electronic Structure Of Si3h6, Mark S. Gordon, David Bartol Sep 1987

Molecular And Electronic Structure Of Si3h6, Mark S. Gordon, David Bartol

Mark S. Gordon

The ground state of disilylsilylene ((SiH3)2Si) is predicted to be the closed-shell (lAin C2 symmetry) state, about 6 kcal/mol below the lowest triplet es, in C2v symmetry) at the MP4/6-31 0( d) //3-21 0* level of theory. A second triplet with a very small Si-Si-Si angle e A in C2 symmetry) is found to be more than 30 kcal/mol above the ground state. The global minimum on the Si3H6 ground-state surface is predicted to be trisilacyclopropane, 18.3 and 9.7 kcalfmol, respectively, below (SiH3)2Si and SiH3SiH=SiH2•

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Ab Initio Calculations On Some C3sih4 Isomers, George W. Schriver, Mark J. Fink, Mark S. Gordon Sep 1987

Ab Initio Calculations On Some C3sih4 Isomers, George W. Schriver, Mark J. Fink, Mark S. Gordon

Mark S. Gordon

Restricted Hartree-Fock ab initio calculations have been performed on various isomers of silacyclobutadiene (C3SiH 4). Geometry optimizations were performed by using various basis sets. Geometric results were similar, but proper description of relative energies required the larger 6-31G* basis. Calculations treating election correlation at the MP2 level were performed on the seven lowest energy structures. These calculations gave similar results. The most stable species found is 2-methylsilacycloprop-2-en-1-ylidene. Silacyclobutadiene is almost 60 kcal mol- 1 less stable, while silatetrahedrane lies a further 32 kcal mol-1 higher in energy. The most stable isomer with normal valence is 2-silabut-1-en-3-yne, 28.2 kcal mol-1 above …

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Electron Beam Effects In The Analysis Of Compound Semiconductors And Devices, Nancy Burnham, Ll Kazmerski, Ab Swartzlander, Aj Nelson, Se Asher Aug 1987

Electron Beam Effects In The Analysis Of Compound Semiconductors And Devices, Nancy Burnham, Ll Kazmerski, Ab Swartzlander, Aj Nelson, Se Asher

Nancy A. Burnham

The effects of electron beams on the analysis of CuInSe2surfaces are examined in this paper. Potential changes in the surface chemistry—including oxidation and desorption—under a range of incident probe conditions, are investigated for possible artifactual information generation. Emphasis is placed on the relationships between beam conditions and oxygen chemisorption and physisorption, since oxygen treatments of devices utilizing this semiconductor are critical to performance. Single crystals and polycrystalline thin films are analyzed and compared to establish the beam‐induced phenomena.

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Surface-Enhanced Raman Study Of The Effect Of Ph And Electrode Potential On The Surface Concentrations Of The Electroactive Forms Of Pyridinecarboxaldehydes, Dennis Evans, Mark Anderson Aug 1987

Surface-Enhanced Raman Study Of The Effect Of Ph And Electrode Potential On The Surface Concentrations Of The Electroactive Forms Of Pyridinecarboxaldehydes, Dennis Evans, Mark Anderson

Mark R. Anderson

No abstract is currently available.

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Π Bond Strengths In The Second And Third Periods, Michael W. Schmidt, Phi N. Truong, Mark S. Gordon Aug 1987

Π Bond Strengths In The Second And Third Periods, Michael W. Schmidt, Phi N. Truong, Mark S. Gordon

Mark S. Gordon

All possible pi bonds formed between the elements C, N, 0, Si, P, and S are considered. The pi bond strengths are estimated by the cis-trans rotation barriers (where possible) and by hydrogenation energies. The ability of these elements to form strong pibonds is in the order 0 > N "" C » S > P > Si. In addition, computed bond lengths and vibrational stretching frequencies are reported for both the singly and doubly bound compounds. The structure of the lowest triplet state of each double-bonded compound is given, along with the singlet-triplet splitting.

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Cp Violation In K-]3-Pi, Jf Donoghue, Br Holstein, G Valencia Jul 1987

Cp Violation In K-]3-Pi, Jf Donoghue, Br Holstein, G Valencia

Barry R Holstein

No abstract provided.

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The Systematic Design Of A Composite Electrolyte, Michael Setter, J. Wagner Jul 1987

The Systematic Design Of A Composite Electrolyte, Michael Setter, J. Wagner

Michael P. Setter

No abstract provided.

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Thermal Decomposition Of Methanethiol And Ethanethiol, Kim K. Baldridge, Mark S. Gordon, Douglas E. Johnson Jul 1987

Thermal Decomposition Of Methanethiol And Ethanethiol, Kim K. Baldridge, Mark S. Gordon, Douglas E. Johnson

Mark S. Gordon

Selected ground-state decomposition pathways for methanethiol and ethanethiol are considered, using ab initio electronic structure calculations including electron correlation. The decomposition of methanethiol to form methylene and hydrogen sulfide requires a large activation energy (108.3 kcaljmol). In contrast, the energy required for the homolytic cleavage of the C-S bond is calculated to be just 67.2 kcaljmol. For ethanethiol, carbene formation is more competitive with radical processes. Here, the activation energy for the 1,1 elimination of H2S to form ethylidene (76.9 kcaljmol) is smaller than that for the direct formation of ethylene via a 1,2 elimination (106.6 kcaljmol) and only 12 …

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Problems, Lawrence Stout May 1987

Problems, Lawrence Stout

Lawrence N. Stout

No abstract provided.

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Electrochemical Reduction Of 1,1,4,4-Tetraphenylbutatriene, Tsu-Yu Chen, Mark Anderson, Dennis Peters May 1987

Electrochemical Reduction Of 1,1,4,4-Tetraphenylbutatriene, Tsu-Yu Chen, Mark Anderson, Dennis Peters

Mark R. Anderson

Polarograms and cyclic voltammograms for reduction of 1,1,4,4-tetraphenylbutatriene at mercury electrodes in dimethylformamide containing tetra-n-butylammonium perchlorate exhibit four waves; the first and second waves are due to stepwise formation of the radical anion and dianion of the starting material, whereas the third and fourth waves are attributable to reduction of 1,1,4,4-tetraphenyl-1,2-butadiene and 1,1,4,4-tetraphenyl-1-butene, respectively. Electrolysis of 1,1,4,4-tetraphenylbutatriene at potentials corresponding to the second wave yields 1,1,4,4-tetraphenyl-1,3-butadiene exclusively; at a slightly more negative potential, the latter undergoes reduction to 1,1,4,4-tetraphenyl-1-butene. When 1,1,4,4-tetraphenylbutatriene is electrolyzed in the presence of glacial acetic acid and at any potential on the first or second wave, …

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On The Height Variation Of The Equatorial F-Region Vertical Plasmadrifts, J. E. Pingree, Bela G. Fejer May 1987

On The Height Variation Of The Equatorial F-Region Vertical Plasmadrifts, J. E. Pingree, Bela G. Fejer

Bela G. Fejer

We have used improved incoherent scatter radar measurements at the Jicamarca Radio Observatory to study the height variation of the F region vertical plasma drift velocity (driven by the zonal electric field) during moderately quiet conditions. Preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km, but with considerable day-to-day variations in the value of the slope. On the average, the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours. Simultaneous vertical and zonal drift measurements confirm that the measured height …

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Heats Of Formation For Third-Period Hydrides: Test Of An Extended Basis Set, Mark S. Gordon, John Heitzinger Apr 1987

Heats Of Formation For Third-Period Hydrides: Test Of An Extended Basis Set, Mark S. Gordon, John Heitzinger

Mark S. Gordon

The extended basis set developed by McLean and Chandler for third-period atoms is combined with the -311G hydrogen basis and augmented by polarization functions to predict the heats of formation of third-period hydrides at the full MP4 computational level. The calculated heats of formation are at least as accurate as those predicted for second-row hydrides by using MP4/6-311G(d,p) wave functions, with a root mean square error of approximately 4 kcaljmol.

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Molecular Clouds And Cloud Cores In The Inner Galaxy, N Z. Scoville, Min S. Yun, D B. Sanders, D P. Clemens, W H. Waller Apr 1987

Molecular Clouds And Cloud Cores In The Inner Galaxy, N Z. Scoville, Min S. Yun, D B. Sanders, D P. Clemens, W H. Waller

Min S. Yun

A compilation of CO emission regions and their measured parameters is presented which represents a nearly complete accounting of the molecular clouds in the first quadrant of the Galaxy. Emission regions associated with radio H II regions have systematically brighter CO peaks that are a factor of two to three times larger and have twice the mean velocity dispersion as the general cloud population. Both the H II region clouds and the hot core regions have a Galactic distribution characteristic of a spiral arm population, whereas the colder clouds are much less confined in Galactic azimuthal angle. Virial masses are …

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Electrochemical Reduction Of Phenylpropadiene At Mercury Cathodes In Dimethylformamide: Isomerization Of The Allene To 1-Phenyl-1-Propyne, Tsu-Yu Chen, Mark Anderson, Steven Grossman, Dennis Peters Mar 1987

Electrochemical Reduction Of Phenylpropadiene At Mercury Cathodes In Dimethylformamide: Isomerization Of The Allene To 1-Phenyl-1-Propyne, Tsu-Yu Chen, Mark Anderson, Steven Grossman, Dennis Peters

Mark R. Anderson

Polarograms and cyclic voltammograms exhibit two waves for reduction of phenylpropadiene at a mercury electrode in dimethylformamide containing tetra-n-butylammonium perchlorate, the f i t wave signals reduction of phenylpropadiene to 1-phenyl-1-propene and the second wave is attributable to reduction of 1-phenyl-1-propene to 1-phenylpropane. However, the fmt wave is abnormally small because phenylpropadiene undergoes substantial rearrangement to 1-phenyl-1-propyne, which is reducible to 1-phenylpropane at nearly the same potential as 1-phenyl-1-propene. Controlled-potential electrolyses of phenylpropadiene, 1-phenyl-1-propene, and 1-phenyl-1-propyne at mercury pool cathodes have verified the processes elucidated by means of polarography and cyclic voltammetry. In the presence of diethyl malonate (a proton …

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The Effect Of Age On The Care Of Women With Breast Cancer In Community Hospitals, Paula Diehr, Joe Chu Mar 1987

The Effect Of Age On The Care Of Women With Breast Cancer In Community Hospitals, Paula Diehr, Joe Chu

Paula Diehr

We studied the process of care received by 1,680 female breast cancer patients treated in 17 community hospitals. The probability of receiving various diagnostic, consultation, therapy, or rehabilitation services was almost always significantly associated with patient age for one or more disease stages. Most often there was a linear trend for older patients to receive fewer services (e.g., biopsies prior to definitive treatment, number of lymph nodes examined, chemotherapy, radiation therapy) but other age patterns also were found. Age was not significantly associated with clinical staging or estrogen receptors.

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