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Articles 451 - 458 of 458

Full-Text Articles in Physics

The Treatment Of Exchange In Path Integral Simulations Via An Approximate Pseudopotential, Randall W. Hall Jan 1988

The Treatment Of Exchange In Path Integral Simulations Via An Approximate Pseudopotential, Randall W. Hall

Collected Faculty and Staff Scholarship

An approximate form that includes the effects of exchange is suggested for the short time propagator used in path integral simulations. The form is inspired physically by the approximation made in Hartree–Fock treatments of atoms and molecules. The approximate propagator is used with q u a n t i t a t i v e accuracy in two systems: an ideal gas of fermions localized in a three‐dimensional harmonic well and the triplet state of the sodium dimer.

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The Aperiodic Crystal Picture And Free Energy Barriers In Glasses, Randall W. Hall, Peter G. Wolynes Jan 1987

The Aperiodic Crystal Picture And Free Energy Barriers In Glasses, Randall W. Hall, Peter G. Wolynes

Collected Faculty and Staff Scholarship

The aperiodic crystal picture associates the glass transition with freezing into a nonperiodic structure. Dynamics in the glassy state involves activated jumps between different aperiodic free energy minima. Activation barriers may be estimated through the use of freezing theory and the theory of dense solids. The results resemble, but are distinct from, free volume theory. Reasonable fits to experimental data are obtained.

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The Further Geometry Of Grain Boundaries In Hexagonal Close-Packed Metals, Fu-Rong Chen, Alexander H. King Jan 1987

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.

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Nonadiabatic Theory Of Fine-Structure Branching Cross Sections For Na-He, Na-Ne, And Na-Ar Optical Collisions, Linda L. Vahala, P. S. Julienne, Mark D. Havey Jan 1986

Nonadiabatic Theory Of Fine-Structure Branching Cross Sections For Na-He, Na-Ne, And Na-Ar Optical Collisions, Linda L. Vahala, P. S. Julienne, Mark D. Havey

Electrical & Computer Engineering Faculty Publications

The nonadiabatic close-coupled theory of atomic collisions in a radiation field is generalized to include electron spin and is used to consider the weak-field Na–rare-gas (RG) optical collision Na(2S1/2)+RG+nhν μNa(2Pj)+RG+(n-1)hν. The effects of detuning and incident energy on the branching into the atomic Na 3p2P3/2 and 3p2P1/2 states are examined. The cross sections σ(j) are found to have a strong asymmetry between red and blue detuning as well as a complex threshold and resonance structure dependence on energy. A partial cross-section analysis …

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A Laser Interferometric Study Of Electric Field Effects On Methane-Oxygen Flame Plasmas, Mark D. Prairie Jan 1982

A Laser Interferometric Study Of Electric Field Effects On Methane-Oxygen Flame Plasmas, Mark D. Prairie

Masters Theses

A laser interferometer is developed to study the refractive index field, aerodynamic structure, and three dimensional temperature profile of a methane-oxygen flame system under the influence of D.C. electric fields. A combined graphical-numerical method is used to transform the observed interference patterns into radial temperature distributions. The results indicate that the electric field exerts a marked influence on the flame stability, geometry, and charged particle flow. Experimental evidence shows that these effects are most apparent under fuel rich conditions. It is suggested an electric field may change the concentration gradients of reacting species, leading to an altered course of fuel …

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The Effects On Grain-Boundary Processes Of The Steps In The Boundary Plane Associated With The Cores Of Grain-Boundary Dislocations, Alexander H. King, D. A. Smith Jan 1980

The Effects On Grain-Boundary Processes Of The Steps In The Boundary Plane Associated With The Cores Of Grain-Boundary Dislocations, Alexander H. King, D. A. Smith

Alexander H. King

The contribution of the associated steps to the properties of grain-boundary dislocations are investigated. Two methods of step-height determination are given and it is shown that the step height, like the Burgers vector, must be conserved during the reactions of grain-boundary dislocations: this is not always automatic and additional coherent steps must take part in some reactions. The energies associated with steps have been estimated and compared with the elastic energies of grain-boundary dislocations; these comparisons suggest that (a) the reduction of elastic energy alone may not be a sufficient criterion for the progress of a reaction and (b) that …

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Properties And Structure Of Some Chalcogenide Glasses, Amin Ismail Amin Abdel-Latif Jan 1968

Properties And Structure Of Some Chalcogenide Glasses, Amin Ismail Amin Abdel-Latif

Archived Theses and Dissertations

No abstract provided.

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Catalytic Decomposition Of Hydrogen Peroxide By Manganese-Doped Magnesium Hydroxide, Nabih Philobbos Kelada Jan 1968

Catalytic Decomposition Of Hydrogen Peroxide By Manganese-Doped Magnesium Hydroxide, Nabih Philobbos Kelada

Archived Theses and Dissertations

No abstract provided.

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