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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
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 …
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
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 …
Molecular And Electronic Structure Of Si3h6, Mark S. Gordon, David Bartol
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•
Ab Initio Calculations On Some C3sih4 Isomers, George W. Schriver, Mark J. Fink, Mark S. Gordon
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 …
Π Bond Strengths In The Second And Third Periods, Michael W. Schmidt, Phi N. Truong, Mark S. Gordon
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.
Thermal Decomposition Of Methanethiol And Ethanethiol, Kim K. Baldridge, Mark S. Gordon, Douglas E. Johnson
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 …
Heats Of Formation For Third-Period Hydrides: Test Of An Extended Basis Set, Mark S. Gordon, John Heitzinger
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.
Ground-State Potential Energy Surface Of Phosphine Oxide, Jerry A. Boatz, Michael W. Schmidt, Mark S. Gordon
Ground-State Potential Energy Surface Of Phosphine Oxide, Jerry A. Boatz, Michael W. Schmidt, Mark S. Gordon
Mark S. Gordon
A network of elimination reactions of H3PO in its ground state is examined by using ab initio (3-21G* and 6-31G** with MP3 perturbation corrections) wave functions. In addition to the eliminations, several isomerizations and internal rotations of the parent compound and its fragments are investigated. The insertion and reactive scattering reactions of H2 + HPO, which are characterized more fully with MP4(SDTQ) perturbation corrections, are followed by using the intrinsic reaction coordinate and energy-localized orbitals.
Insertion Of Methylene Into Ethane And Cyclopropane, Mark S. Gordon, J. A. Boatz, David R. Gano, Marie G. Friederichs
Insertion Of Methylene Into Ethane And Cyclopropane, Mark S. Gordon, J. A. Boatz, David R. Gano, Marie G. Friederichs
Mark S. Gordon
The insertions of methylene into the CH and CC bonds of ethane and into a CC bond of cyclopropane are calculated by using third-order perturbation theory with the 6-31G(d) basis set. At this level of theory, the barriers for these reactions are predicted to be 0.2, 46.0, and 2.2 kcaljmol, respectively. Thus, the introduction of strain has a dramatic effect on the barrier to insertion into a heavy atom-heavy atom bond.
Potential Energy Surfaces For Polyatomic Reaction Dynamics, Donald G. Truhlar, Rozeanne Steckler, Mark S. Gordon
Potential Energy Surfaces For Polyatomic Reaction Dynamics, Donald G. Truhlar, Rozeanne Steckler, Mark S. Gordon
Mark S. Gordon
The last few years have seen an explosive growth of interest in detailed studies of polyatomic reaction dynamics. Improved experimental techniques, more powerful semiclassical dynamical methods, and accurate electronic structure capabilities have all combined to focus attention on detailed dynamical questions for larger and larger systems. Many of these questions have previously been tackled primarily for atom-diatom or diatom-diatom collisions or isolated triatomics. 1- 5 Although of course the final word on such simpler systems has not been said (and never will be), we will focus in the present review on more complicated cases. Thus the "polyatomic" in the title …
Fish Acute Toxicity Syndromes And Their Use In The Qsar Approach To Hazard Assessment, Steven P. Bradbury, James M. Mckim, Gerald J. Niemi
Fish Acute Toxicity Syndromes And Their Use In The Qsar Approach To Hazard Assessment, Steven P. Bradbury, James M. Mckim, Gerald J. Niemi
Steven P. Bradbury
Implementation of the Toxic Substances Control Act of 1977 creates the need to reliably establish testing priorities because laboratory resources are limited and the number of industrial chemicals requiring evaluation is overwhelming. The use of quantitative structure activity relationship (QSAR) models as rapid and predictive screening tools to select more potentially hazardous chemicals for in-depth laboratory evaluation has been proposed. Further implementation and refinement of quantitative structure-toxicity relationships in aquatic toxicology and hazard assessment requires the development of a "mode-of-action" database. With such a database, a qualitative structure-activity relationship can be formulated to assign the proper mode of action, and …
Physiological Response Of Rainbow Trout (Salmo Gairdneri) To Acute Fenvalerate Lntoxication, Steven P. Bradbury, James M. Mckim, Joel R. Coats
Physiological Response Of Rainbow Trout (Salmo Gairdneri) To Acute Fenvalerate Lntoxication, Steven P. Bradbury, James M. Mckim, Joel R. Coats
Steven P. Bradbury
The physiological responses of rainbow trout (Salmo gairdneri) to fenvalerate intoxication during aqueous exposure were examined to provide information about the pyrethroid mode of action in fish. Trout (n = 4) were exposed to 412 ± 50 μg/liter fenvalerate and died in 10.9 ± 1.5 hr. Brain, liver, and carcass fenvalerate concentrations associated with mortality were 0.16 ± 0.05, 3.62 ± 0.57, and 0.25 ± 0.05 mg/kg, respectively. Visible signs of intoxication included elevated cough rate, tremors, and seizures. Histopathological examination of gill tissue showed damage consistent with irritation. An evaluation of respiratory-cardiovascular and blood chemistry responses indicated an elevated …
The Further Geometry Of Grain Boundaries In Hexagonal Close-Packed Metals, Fu-Rong Chen, Alexander H. King
The Further Geometry Of Grain Boundaries In Hexagonal Close-Packed Metals, Fu-Rong Chen, Alexander H. King
Alexander H. King
A technique is given for finding partial DSC vectors appropriate to crystals with more than one atom per lattice site. The DSC lattice is made up of vectors that represent displacements of one crystal with respect to the other that leave the boundary structure shifted, but not complete. A new, rapid method for finding the step vectors associated with perfect DSC dislocations is described. Partial DSC vectors and step vectors for perfect DSC dislocations in hexagonal close-packed crystals are determined. The availability of reactions between lattice partial dislocations and grain boundaries in hexagonal close-packed crystals is also assessed.
Interaction Between Magnetic And Compositional Order In Ni‐Rich Ni C Fe1−C Alloys (Invited), J. B. Staunton, Duane D. Johnson, B. L. Gyorffy
Interaction Between Magnetic And Compositional Order In Ni‐Rich Ni C Fe1−C Alloys (Invited), J. B. Staunton, Duane D. Johnson, B. L. Gyorffy
Duane D. Johnson
We have developed a first‐principles electronic theory of concentration fluctuations in spin polarized binary alloys. It is a mean field theory of the state of compositional order and it is based on the local spin density (LSD) approximation for describing the electrons. The usual averages over the statistical mechanical ensemble are carried out with the aid of the self‐consistent Korringe–Kohn–Rostoker coherent‐potential approximation (SCF‐KKR‐CPA). To illustrate the main consequences of the theory we study the compositional short‐range order in the Ni c Fe1−c alloy system. We find that the ordering energy is almost entirely of magnetic origin.
Estimating The Value Of Water Quality Improvements In A Recreational Demand Framework, Nancy E. Bockstael, Catherine Kling, W. Michael Hanemann
Estimating The Value Of Water Quality Improvements In A Recreational Demand Framework, Nancy E. Bockstael, Catherine Kling, W. Michael Hanemann
Catherine Kling
With the advent of Executive Order 12291, policymakers involved in water quality regulation are increasingly interested in assessing the benefits of their programs. Several methods for valuing water quality improvements using recreational demand models have been developed by economists, most of which depend on observing recreationists visiting an array of sites with varying water quality and costs of access. In this paper, three general types of models are described: systems of demands, discrete choice models, and the hedonic travel cost approach; the latter two models are demonstrated using a common data set on water quality and swimming behavior in the …