Extended rotational diffusion and orientational relaxation of symmetric top molecules in a strong dc electric field: second-rank orientational correlation functions

Second-rank orientational correlation functions (pertaining to Kerr effect relaxation and Raman scattering) are obtained using the extended rotational diffusion (J-diffusion) model of symmetric top polar molecules in a strong constant external field. It is shown that the shape of the molecule noticeably affects all second-rank correlation functions and relaxation times in the rare collision limit. In the opposite limit of frequent collisions, the quantities of interest are shown to be shape independent as a consequence of vanishingly small inertial effects. An interpolation formula for the orientation relaxation times in the intermediate regime between the rare and frequent collision limits is also given.     

Colloid transport of radionuclides in soils

Radionuclides undergo redistribution and change existence forms (and, therefore, migration dynamics) not only immediately after they enter into the environment, but also during migration. The latter can be associated with changes in the delivery medium (for example, as strongly contaminated wastewaters is diluted by natural), decrease in the concentration of radionuclides (during their sorption and coprecipitation on soil or host rock microparticles), or change in carrier forms (dissolution of fuel matrices). In view of the multifactor nature and complexity of these processes, we set ourselves the task to summarize results obtained at the GEOKHI RAS on the forms of existence and migration dynamics of radionuclides in radioactively contaminated soils. As objects for study we used soils typical of the forest-steppe zone of the Eastern Ural Radioactive Trace (EURT) and taken at a distance of 2 through 8 km from the Trace axis and 2–4 km from the accident place, as well as samples of the high-water bed soils and sediments of the Enisey River, taken 60 km downstream from the Mining Chemical Combine (MCC).     

SOME FEATURES OF FRAGMENTATION OF AN ALUMINUM PROJECTILE AT VARIOUS VELOCITIES OF PENETRATION INTO A MESH BUMPER

Journal of Applied Mechanics and Technical Physics - The fragmentation of projectiles penetrating into thin discrete bumpers is accompanied by material ejections from the front part of the...     

Mellin–Barnes representations of Feynman diagrams,linear systems of differential equations,and polynomial solutions

We argue that the Mellin–Barnes representations of Feynman diagrams can be used for obtaining linear systems of homogeneous differential equations for the original Feynman diagrams with arbitrary powers of propagators without recourse to the integration-by-parts technique. These systems of differential equations can be used (i) for the differential reductions to sets of basic functions and (ii) for counting the numbers of master integrals.     

Computational optimization analysis of a gas-jet target in a laser-plasma short-wave radiation source

A computational method is developed for optimizing the xenon gas jet used as the target in a laserplasma short-wave radiation source. The method is based on numerical hydrodynamic simulation of the jet flowing from the nozzle into vacuum, followed by computation of the optimization criterion describing the observed intensity of plasma glow. The application of this method permits an unambiguous and objective choice of optical experimental geometries and flow conditions; as a result, the radiation yield can be increased by several times. The calculated results are compared with available experimental data.     

Specific features of the crystal and phase structure of binary systems 5,6-(3′,4′-furazano)-1,2,3,4-tetrazine-1,3-dioxide-2,4-dinitro-2,4-diazapentane

Methodological foundations of a physical analysis of the structure of a crystallized binary system constituted by 5,6-(3′,4′-furazano)-1,2,3,4-tetrazine-1,3-dioxide and 2,4-dinitro-2,4-diazapentane by optical microscopy, NMR tomography, and X-ray diffraction analysis were developed. First results were obtained, which characterize specific features of the crystallization process and parameters of crystals being formed in a eutectic mixture and molecular compound.     

Inertial and bias effects in the rotational brownian motion of rodlike molecules in a uniaxial potential

Inertial effects in the rotational brownian motion in space of a rigid dipolar rotator (needle) in a uniaxial potential biased by an external field giving rise to asymmetry are treated via the infinite hierarchy of differential-recurrence relations for the statistical moments (orientational correlation functions) obtained by averaging the Euler-Langevin equation over its realizations in phase space. The solutions of this infinite hierarchy for the dipole correlation function and its characteristic times are obtained using matrix continued fractions showing that the model simultaneously predicts both slow overbarrier (or interwell) relaxation at low frequencies accompanied by intermediate frequency Debye relaxation due to fast near-degenerate motion in the wells of the potential (intrawell relaxation) as well as the high frequency resonance (Poley) absorption due to librations of the dipole moments. It is further shown that the escape rate of a brownian particle from a potential well as extended to the Kramers turnover problem via the depopulation factor yields a close approximation to the longest (overbarrier) relaxation time of the system. For zero and small values of the bias field parameter h, both the dipole moment correlation time and the longest relaxation time have Arrhenius behavior (exponential increase with increasing barrier height). While at values of h in excess of a critical value however far less than that required to achieve nucleation, the Arrhenius behavior of the correlation time disappears.