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1999

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Articles 811 - 840 of 2555

Full-Text Articles in Physical Sciences and Mathematics

Electrochemical Behavior Of Riboflavin On Glassy Carbon Electrode, Hong Li, Lincai Jiang May 1999

Electrochemical Behavior Of Riboflavin On Glassy Carbon Electrode, Hong Li, Lincai Jiang

Journal of Electrochemistry

The electrochemical behavior of riboflavin(RF) on glassy carbon has been investigated by using potential sweep,rotating ring_disc electrode and the measurement of differential capacitance. It is shown that a single well_behaved oxidation_reduction wave corresponding to a reversible two_electrons reaction apears in medium of pH<6,and the adsorption of RFH2 formed by electro_reduction is weak and hence its solubility is good.In medium of pH>6,there are two separating but overlapping partly oxidation_reduction waves corresponding to two_step one_electron reaction.The adsorptions of RFH and RFH2 produced by reduction reactions in medium of 610,the solubilities of the adsorbed species produced by electro_reduction are good.

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The Behaviors Of Capacity Loss Of Limn2o4 Cathodeat Elevated Temperatures, Xiaohong Hu, Hanxi Yang, Xinping Ai, Shengxian Li, Xinlin Hong May 1999

The Behaviors Of Capacity Loss Of Limn2o4 Cathodeat Elevated Temperatures, Xiaohong Hu, Hanxi Yang, Xinping Ai, Shengxian Li, Xinlin Hong

Journal of Electrochemistry

The capacity loss of spinel LiMn2O4 cathode at elevated temperatures was evaluated by constant current charge_discharge methods and it was found that serious capacity loss and cycleability decrease occured at above 50 , especially for the charged cells. The mechanisms for this phenomena were examined by atomic emission and infrared spectrometry of the electrolyte, XRD measurment of the cycled elecrode and microelectrode voltammetry of LiMn2O4 at room and elevated temperatures. The results showed that with increasing temperature, Mn and Li ions tended to redistribute partly in the spinel framework due to the disproportion of Mn3+ ions and this results in …

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Some Electrochemical Studies On The Bionic Nereistoxin Pesticide_(Ch3)2nhch(Ch2s2o3)2nah2o, Changgeng Zhang May 1999

Some Electrochemical Studies On The Bionic Nereistoxin Pesticide_(Ch3)2nhch(Ch2s2o3)2nah2o, Changgeng Zhang

Journal of Electrochemistry

A study of cyclic voltammetric behavior of the nereistoxin pesticide known as Shachongdan is reported. The effects of scan rate, electrolyte pH, and concentration are discussed.The study shows that this electrode process is an irreversible electrode reaction. The saturate adsorption of dihydronereistoxin on the electrode is also discussed with the saturate adsorption amount of 8.2310-10 mol/cm2.

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In Situ Ftir Spectroelectrochemical Study Of Palladium Hexacyanoferrate Thin Film Deposited On Glassy Carbon Electrode, Aili Bo May 1999

In Situ Ftir Spectroelectrochemical Study Of Palladium Hexacyanoferrate Thin Film Deposited On Glassy Carbon Electrode, Aili Bo

Journal of Electrochemistry

The electrochemically deposited Palladium hexacyanoferrate thin film on Glassy Carbon electrode (PdHCF|GC) has been studied in HCl, KCl and NaCl solutions by in_situ external reflection FTIR spectroelectrochemical technique. It is found that the behavior of the electroactive PdHCF film can be understood in terms of two states: Pd2Fe(II)(CN)6 formed in the inner layer and (M+)2Fe(II)(CN)6 (M+: electrolyte cation) formed in the outer layer. The inner layer is oxidized at Em=0.87 V in 1 mol/L KCl, while for the outer layer Em=0.77 V(vs. Ag/AgCl). In 1 mol/L NaCl or HCl solutions, half_wave potentials of these two layers are not well resolved, …

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Preface (1999), Association Of Christians In The Mathematical Sciences May 1999

Preface (1999), Association Of Christians In The Mathematical Sciences

ACMS Conference Proceedings 1999

Twelfth ACMS Conference on Mathematics from a Christian Perspective

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Introduction (1999), Association Of Christians In The Mathematical Sciences May 1999

Introduction (1999), Association Of Christians In The Mathematical Sciences

ACMS Conference Proceedings 1999

Twelfth ACMS Conference on Mathematics from a Christian Perspective

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Self-Association Of Rifamycin B: Possible Effects On Molecular Recognition, Daniel W. Armstrong, Jeffrey Schneiderheinze, Usha Nair, Linda J. Magid, Paul D. Butler May 1999

Self-Association Of Rifamycin B: Possible Effects On Molecular Recognition, Daniel W. Armstrong, Jeffrey Schneiderheinze, Usha Nair, Linda J. Magid, Paul D. Butler

Chemistry Faculty Research & Creative Works

The macrocyclic antibiotic rifamycin B was found to be highly surface-active and to aggregate in aqueous solution. The aggregational behavior was studied using small-angle neutron scattering (SANS). Aqueous solutions of rifamycin B showed pronounced scattering at both small-length scales (Q ≥ 0.1 Å-1) and at large-length scales (Q ≤ 0.1 Å-1). The larger association colloids appear to be rather open low-density aggregates. The addition of 10% 2-propanol greatly reduces the number and size of the aggregates. Somewhat higher amounts of alcohol appear to completely suppress or eliminate aggregation. The suppression of aggregation coincides with the appearance and enhancement of enantioselective …

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Table Of Contents (1999), Association Of Christians In The Mathematical Sciences May 1999

Table Of Contents (1999), Association Of Christians In The Mathematical Sciences

ACMS Conference Proceedings 1999

Twelfth ACMS Conference on Mathematics from a Christian Perspective

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Schedule (1999), Association Of Christians In The Mathematical Sciences May 1999

Schedule (1999), Association Of Christians In The Mathematical Sciences

ACMS Conference Proceedings 1999

Twelfth ACMS Conference on Mathematics from a Christian Perspective

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Metallicity Calibration Of A Ddo Cn Index And Other Low-Resolution Indices For G And K Stars, B. J. Taylor May 1999

Metallicity Calibration Of A Ddo Cn Index And Other Low-Resolution Indices For G And K Stars, B. J. Taylor

Faculty Publications

Metallicity calibrations of low-resolution parameters are potentially useful for (at least) two problems: the properties of moving groups, and the supermetallicity problem in K giants. In this paper, metallicity calibrations are derived for six sets of parameters. One of these parameters is the DDO CN index deltaCN. This parameter and three others are calibrated for use with evolved G and K stars. Two additional sets of low-resolution parameters are calibrated for use with G and K dwarfs. The calibrations are derived by comparing the input data with two catalogs of homogenized high-dispersion results from diverse authors (see Taylor 1995, 1999a). …

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On F-Squares And Their Critical Sets, L. F. Fitina, Jennifer Seberry, D. Sarvate May 1999

On F-Squares And Their Critical Sets, L. F. Fitina, Jennifer Seberry, D. Sarvate

Faculty of Informatics - Papers (Archive)

We define the notion of critical set of an F-square, following the definition of critical set in latin squares, and then give critical sets for certain classes of F-squares. We also generalise certain results obtained for critical sets of latin squares, and look at minimal such sets. We show that critical sets of F-squares need to be studied as well as critical sets for latin squares as the techniques used differ considerably. We obtain theorems for the sizes of critical sets of types F(n; 1,n — 1), F(n;1, 1, n — 2), and F(n; 2, 2, ... , 2).

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Optically Pumped Electron Spin Filter, Herman Batelaan, A. S. Green, B. A. Hitt, Timothy J. Gay May 1999

Optically Pumped Electron Spin Filter, Herman Batelaan, A. S. Green, B. A. Hitt, Timothy J. Gay

Timothy J. Gay Publications

This paper reports the first experimental demonstration of an optically pumped electron spin filter. Unpolarized electrons produced in a cold-cathode discharge drift through a mixture of spin-polarized Rb and a nitrogen or helium buffer gas. Through spin-exchange collisions with the Rb, the drifting electrons become polarized along the optical pumping axis. We study the role of the buffer gas in both the optical pumping and the spin transfer to the free electrons. This spin filter produces electron beams with currents and polarizations comparable to first-generation GaAs polarized electron sources.

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Mobile-Agent Planning In A Market-Oriented Environment, Jonathan Bredin, David Kotz, Daniela Rus May 1999

Mobile-Agent Planning In A Market-Oriented Environment, Jonathan Bredin, David Kotz, Daniela Rus

Computer Science Technical Reports

We propose a method for increasing incentives for sites to host arbitrary mobile agents in which mobile agents purchase their computing needs from host sites. We present a scalable market-based CPU allocation policy and an on-line algorithm that plans a mobile agent's expenditure over a multihop ordered itinerary. The algorithm chooses a set of sites at which to execute and computational priorities at each site to minimize execution time while preserving a prespecified budget constraint. We present simulation results of our algorithm to show that our allocation policy and planning algorithm scale well as more agents are added to the …

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Instant Preheating, Gary Felder, Lev Kofman, Andrei Linde May 1999

Instant Preheating, Gary Felder, Lev Kofman, Andrei Linde

Physics: Faculty Publications

We describe a new efficient mechanism of reheating. Immediately after rolling down the rapidly moving inflaton field φ produces particles χ, which may be either bosons or fermions. This is a nonperturbative process which occurs almost instantly; no oscillations or parametric resonance is required. The effective masses of the χ particles may be very small at the moment when they are produced, but they “fatten” when the field φ increases. When the particles χ become sufficiently heavy, they rapidly decay to other, lighter particles. This leads to an almost instantaneous reheating accompanied by the production of particles with masses which …

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Particle Sizing In Strongly Turbid Suspensions With The One-Beam Cross-Correlation Dynamic Light-Scattering Technique, Anthony J. Adorjan, James A. Lock, Thomas W. Taylor, Padetha Tin, William V. Meyer, Anthony E. Smart May 1999

Particle Sizing In Strongly Turbid Suspensions With The One-Beam Cross-Correlation Dynamic Light-Scattering Technique, Anthony J. Adorjan, James A. Lock, Thomas W. Taylor, Padetha Tin, William V. Meyer, Anthony E. Smart

Physics Faculty Publications

The utility of the one-beam cross-correlation dynamic light-scattering system for sizing small particles in suspension was previously limited by its small-intensity signal-to-baseline ratio for strongly turbid suspensions. We describe three improvements in the optical system and sample cell that raise the ratio to a value comparable with that of other cross-correlation dynamic light-scattering systems. These improvements are (i) using a square cross-sectional sample cell to minimize the attenuation of the incident beam and singly scattered light, (ii) placing a 200-mu m-wide slit between the sample cell and the detector fibers to mask off the region of weak single scattering and …

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Modeling The High-Speed Switching Of Far-Infrared Radiation By Photoionization In A Semiconductor, Thomas E. Wilson May 1999

Modeling The High-Speed Switching Of Far-Infrared Radiation By Photoionization In A Semiconductor, Thomas E. Wilson

Physics Faculty Research

Data from an earlier study [T. Vogel et al., Appl. Opt. 31, 329 (1992)] on the subnanosecond switching of 119-μm radiation in high-resistivity silicon by pulsed UV laser radiation, is compared with a refined one-dimensional numerical multilayer model accounting for the generation, recombination, and diffusion of the free carriers on the resulting far-infrared optical properties of the silicon. The inclusion of recent measurements for carrier-density and temperature-dependent transport parameters leads to improved agreement between experiment and theory.

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Seawifs Satellite Ocean Color Data From The Southern Ocean, Jk Moore, Mr Abbott, Rg Richman, Walker O. Smith Jr., Et Al May 1999

Seawifs Satellite Ocean Color Data From The Southern Ocean, Jk Moore, Mr Abbott, Rg Richman, Walker O. Smith Jr., Et Al

VIMS Articles

SeaWiFS estimates of surface chlorophyll concentrations are reported for the region of the U.S. JGOFS study in the Southern Ocean (similar to 170 degrees W, 60 degrees S). Elevated chlorophyll was observed at the Southern Ocean fronts, near the edge of the seasonal ice sheet, and above the Pacific-Antarctic Ridge. The elevated chlorophyll levels associated with the Pacific-Antarctic Ridge are surprising since even the crest of the ridge is at depths > 2000 m. This elevated phytoplankton biomass is likely the result of mesoscale physical-biological interactions where the Antarctic Circumpolar Current (ACC) encounters the ridge. Four cruises surveyed this region between …

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Surfaces Of The Perovskite Manganites La1-XCaXMno3, Jaewu Choi, Jiandi Zhang, Sy-Hwang Liou, Peter A. Dowben, E. Ward Plummer May 1999

Surfaces Of The Perovskite Manganites La1-XCaXMno3, Jaewu Choi, Jiandi Zhang, Sy-Hwang Liou, Peter A. Dowben, E. Ward Plummer

Department of Physics and Astronomy: Faculty Publications

Angle-resolved core-level photoemission has been utilized to study the surfaces of crystalline thin films of manganite La1-xCaxMnO3 (x=0.1 and 0.35). It is found that both the surface termination and Ca surface concentration depend on the bulk Ca concentration. For La0.65Ca0.35MnO3, the terminal layer is predominately Mn-O, while for La0.9Ca0.1MnO3, the majority of the surface is La/Ca-O terminated. Both surfaces exhibit a large enhancement in the Ca concentration compared to the bulk with the La0.9Ca0.1MnO3 sample, having a larger …

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Elizabeth River Tbt Monitoring Report On Tbt Methodology Detection Limit, Precision And Linearity, Michael A. Unger May 1999

Elizabeth River Tbt Monitoring Report On Tbt Methodology Detection Limit, Precision And Linearity, Michael A. Unger

Reports

The purpose of this project was to determine the accuracy, precision, linearity and Method Detection Limit (MDL) for tributyltin (TBT) analytical techniques available at the Virginia Institute of Marine Science prior to implementing an environmental monitoring program in the Elizabeth River, Virginia. This precursory work is to document the ability of analytical techniques to accurately detect TBT in ambient water samples at concentrations of 1 ng/L and greater.

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Novel One-Phase Synthesis Of Thiol-Functionalized Gold, Palladium, And Iridium Nanoparticles Using Superhydride, Chanel K. Yee, Rainer Jordan, Abraham Ulman, Henry White, Alexander H. King, Miriam Rafailovich, Jonathan Sokolov May 1999

Novel One-Phase Synthesis Of Thiol-Functionalized Gold, Palladium, And Iridium Nanoparticles Using Superhydride, Chanel K. Yee, Rainer Jordan, Abraham Ulman, Henry White, Alexander H. King, Miriam Rafailovich, Jonathan Sokolov

Alexander H. King

A new, facile, general one-phase synthesis for thiol-functionalized gold, palladium, and iridium nanoparticles, using tetrahydrofuran (THF) as the solvent and lithium triethylborohydride (Superhydride) as the reducing agent, is presented. For octadecanethiol-functionalized gold (Au/ODT) nanoparticles, HRTEM of drop-cast particle-films revealed the formation of spherical particles of d = 4 ± 0.3 nm average size. Electron diffraction shows fcc packing arrangement, similar to that of bulk gold. The crystalline gold cores are surrounded with closely packed n-alkyl chains mainly in an all-trans conformation, adopting orthorhombic packing as confirmed by FTIR spectroscopy. Particles are arranged in a discrete solidlike assembly with a correlation …

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The Peculiar Motions Of Early-Type Galaxies In Two Distant Rregions — Ii. The Spectroscopic Data, Gary Wegner, Matthew Colless, R. P. Saglia, Robert K. Mcmahan May 1999

The Peculiar Motions Of Early-Type Galaxies In Two Distant Rregions — Ii. The Spectroscopic Data, Gary Wegner, Matthew Colless, R. P. Saglia, Robert K. Mcmahan

Dartmouth Scholarship

We present the spectroscopic data for the galaxies studied in the EFAR project, which is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. We have obtained 1319 spectra of 714 early-type galaxies over 33 observing runs on 10 different telescopes. We describe the observations and data reductions used to measure redshifts, velocity dispersions and the Mgb and Mg2 Lick linestrength indices. Detailed simulations and intercomparison of the large number of repeat observations lead to reliable error estimates for all quantities. The measurements from different observing runs are calibrated to a common …

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The Effects Of Charge Transfer On The Thermal Equilibrium Of Photoionized Nebulae, J. B. Kingdon, Gary J. Ferland May 1999

The Effects Of Charge Transfer On The Thermal Equilibrium Of Photoionized Nebulae, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Charge transfer can affect both the ionization and thermal balance of astrophysical plasmas. Using the most recent rate coefficients and energy defects, we calculate the heating/cooling rates for charge transfer reactions between hydrogen and elements up to Z=30. We incorporate these values into the photoionization code CLOUDY. Results from models approximating a wide range of astrophysical objects and conditions suggest that charge transfer can make a significant contribution to the heating near the H ionization front, particularly in objects with a hard ionizing continuum or enhanced abundances. Charge transfer heating can also be important in regimes in which the usual …

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Unlv Residence Hall Recycling & Reuse Program For Move-In And Move-Out, Angela Michelson May 1999

Unlv Residence Hall Recycling & Reuse Program For Move-In And Move-Out, Angela Michelson

UNLV Theses, Dissertations, Professional Papers, and Capstones

The goal of this thesis was to develop a program for the UNLV Residence Hall Recycling & Reuse Program for Move-In and Move-Out that would collect unwanted and unneeded materials from the residents and put them to use. Move-In collected cardboard boxes for recycling while Move-Out collected usable items such as shoes, clothes, food, bedding, and school supplies for resale. In order to have a good collection turnout, a combination of advertising and resident and staff education was conducted. Letters were sent to Resident Assistants (RA’s) and Complex Coordinators and posters and other advertisements were placed in high traffic areas …

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Ultrasonically Initiated Free Radical-Catalyzed Emulsion Polymerization Of Methyl Methacrylate (Ii): Radical Generation Process Studies And Kinetic Data Interpretation, H. C.Joe Chou, James O. Stoffer May 1999

Ultrasonically Initiated Free Radical-Catalyzed Emulsion Polymerization Of Methyl Methacrylate (Ii): Radical Generation Process Studies And Kinetic Data Interpretation, H. C.Joe Chou, James O. Stoffer

Chemistry Faculty Research & Creative Works

In the previous work, we have studied the effects of acoustic intensity, argon gas flow rate, surfactant concentration, and initial monomer concentration on polymerization rate, polymer particle number, and polymer molecular weight in the ultrasonically initiated emulsion polymerization of methyl methacrylate. In this study, radical trapping experiments were used to investigate the effect of acoustic intensity, argon gas flow rate, and sodium lauryl sulfate concentration on the extent of free radical generation in aqueous sodium dodecyl sulfate solutions. In these radical trapping experiments, aqueous solutions of sodium lauryl sulfate were ultrasonically irradiated in the presence of a radical scavenger. The …

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Plant And Soil Enantioselective Biodegradation Of Racemic Phenoxyalkanoic Herbicides, J. M. Schneiderheinze, Daniel W. Armstrong, Alain Berthod May 1999

Plant And Soil Enantioselective Biodegradation Of Racemic Phenoxyalkanoic Herbicides, J. M. Schneiderheinze, Daniel W. Armstrong, Alain Berthod

Chemistry Faculty Research & Creative Works

The biodegradation of the chiral phenoxyalkanoic herbicides 2-(2,4- dichlorophenoxy)propionic aid (2,4-DP) and 2-(4-chloro-2- methylphenoxy)propionic acid (MCPP) was investigated using enantioselective HPLC and chiroptical detection. Racemic mixtures of 2,4-DP and MCPP were applied to three species of turf grass, four species of broadleaf weeds, and soil. Preferential degradation of the S- (-) enantiomer of each herbicide was observed in most species of broadleaf weeds and soil, while the degradation in all species of grass occurred without enantioselectivity. The biodegradation in all systems appeared to follow pseudo first-order kinetics with the fastest degradation occurring in broadleaf weeds, followed by the grasses. The …

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Using Haptic Vector Fields For Animation Motion Control, Bruce Randall Donald, Frederick Henle May 1999

Using Haptic Vector Fields For Animation Motion Control, Bruce Randall Donald, Frederick Henle

Computer Science Technical Reports

We are exploring techniques for animation authoring and editing using a haptic force-feedback device. In our system, a family of animations is encoded by a bundle of trajectories. This bundle in turn defines a time-varying, higher-order vector field on a configuration space for the animation. A haptic input device provides a low-dimensional parameterization of the resulting dynamical system, and the haptic force feedback permits browsing and editing of the space of animations, by allowing the user to experience the vector field as physical forces.

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Voltammetry Of Metallofullerenes And Higher Fullerenes, Mark Anderson, Harry Dorn, Steven Stevenson, Susanne Dana May 1999

Voltammetry Of Metallofullerenes And Higher Fullerenes, Mark Anderson, Harry Dorn, Steven Stevenson, Susanne Dana

Mark R. Anderson

No abstract is currently available.

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Search For BS0-B̅S0, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration May 1999

Search For BS0-B̅S0, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

A search for Bs0-B̅s0 oscillations is performed in a sample of Bs0 semileptonic decays collected using dilepton triggers at the Tevatron Collider during 1992–1995. The Bs0 is reconstructed using φ mesonlepton correlations; its initial production flavor is determined with the second lepton in the event. From a signal of 1068 with a Bs0 purity of 61%, we obtain a limit on the Bs0-B̅s0 oscillation frequency of Δms>5.8 ps-1 at 95% confidence level.

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The Mean Spherical Approximation For A Dipolar Yukawa Fluid, Douglas Henderson, Dezso Boda, Istvan Szalai, Kwong-Yu Chan May 1999

The Mean Spherical Approximation For A Dipolar Yukawa Fluid, Douglas Henderson, Dezso Boda, Istvan Szalai, Kwong-Yu Chan

Faculty Publications

The dipolar hard sphere fluid (DHSF) is a useful model of a polar fluid. However, the DHSF lacks a vapor–liquid transition due to the formation of chain-like structures. Such chains are not characteristic of real polar fluids. A more realistic model of a polar fluid is obtained by adding a Lennard–Jones potential to the intermolecular potential. Very similar results are obtained by adding a Yukawa potential, instead of the Lennard–Jones potential. We call this fluid the dipolar Yukawa fluid (DYF). We show that an analytical solution of the mean spherical approximation (MSA) can be obtained for the DYF. Thus, the …

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Surface Composition Of CoXNi1-XO Solid Solutions By X-Ray Photoelectron And Auger Spectroscopies, M. W. Nydegger, G. Couderc, Marjorie Langell May 1999

Surface Composition Of CoXNi1-XO Solid Solutions By X-Ray Photoelectron And Auger Spectroscopies, M. W. Nydegger, G. Couderc, Marjorie Langell

Marjorie A. Langell Publications

The surface and bulk compositions of the mixed metal oxide CoxNi1-xO have been compared over the entire range of stoichiometry 0 ≤ x ≤ 1. The materials, which were formed as polycrystalline solid solutions, were shown to be well-ordered and homogeneous in the bulk, but tend to deviate in their surface composition for x > 0.6. Auger and X-ray photoelectron spectroscopy gave comparable results and indicated that the surface composition for samples showing deviation from bulk stoichiometry was compatible with the formation of a spinel-like NiCo2O4 surface phase. XPS binding energies and spectral …

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