Dynamic structure factor and collective excitations of neutral and Coulomb fluids

The dynamic sructure factor as the basic quantity describing the collective excitations in a fluid is considered. We consider the cases of neutral and Coulombic fluids. The classical method of moments is applied to construct the dynamic structure factor satisfying all known sum rules. An interpolational formula is found which expresses the dynamic characteristics of a classical or quantum fluid system in terms of its static correlation parameters. The analytical results based on the theory of moments are compared with Molecular dynamics data for various model systems.Comment: 20 pages, 4 figures, to be published in Physica Script

Ground-state energy of a high-density electron gas in a strong magnetic field

The high-density electron gas in a strong magnetic field B and at zero temperature is investigated. The quantum strong-field limit is considered in which only the lowest Landau level is occupied. It is shown that the perturbation series of the ground-state energy can be represented in analogy to the Gell-Mann Brueckner expression of the ground-state energy of the field-free electron gas. The role of the expansion parameter is taken by $r_B= (2/3 \pi^2) (B/m^2) (\hbar r_S/e)^3$ instead of the field-free Gell-Mann Brueckner parameter r_s.Comment: 4 pages, 2 figures, to appear in the proceedings of the 1999 International Conference on Strongly Coupled Coulomb Systems (St.Malo

The use of relativistic action in strong-field nonlinear photoionization

Nonlinear relativistic ionization phenomena induced by a strong linearly polarized laser field are considered. The starting point is the classical relativistic action for a free electron moving in the electromagnetic field created by a strong laser beam. This action has been used to calculate semiclassical transition rates. Simple analytical expressions for the ionization rate, the photoelectron emission velocity and for the drift momentum distribution of the photoelectron have been found. The analytical formulas apply to nonrelativistic bound systems as well as to initial states with an energy corresponding to the upper boundary of the lower continuum and to the tunnel as well as the multiphoton regime. In the case of a nonrelativistic bound system we recover the Keldysh formula for the ionization rate. Relativistic effects in the initial state lead to a weak enhancement of the rate of sub-barrier ionization and to the appearance of a nonzero photoelectron leaving velocity.Comment: 6 pages, 2 figure

Development of protective coatings for tantalum T-22 alloy Final summary report

Oxidation resistance tests of protective coatings for tantalum allo