Ordered states and structural transitions in a system of Abrikosov vortices with periodic pinning

A system of Abrikosov vortices in a quasi-two-dimensional HTSC plate is considered for various periodic lattices of pinning centers. The magnetization and equilibrium configurations of the vortex density for various values of external magnetic field and temperature are calculated using the Monte Carlo method. It is found that the interaction of the vortex system with the periodic lattice of pinning centers leads to the formation of various ordered vortex states through which the vortex system passes upon an increase or a decrease in the magnetic field. It is shown that ordered vortex states, as well as magnetic field screening processes, are responsible for the emergence of clearly manifested peaks on the magnetization curves. Extended pinning centers and the effect of multiple trapping of vortices on the behavior of magnetization are considered. Melting and crystallization of the vortex system under the periodic pinning conditions are investigated. It is found that the vortex system can crystallize upon heating in the case of periodic pinning.     

Global Analysis of the Flows of Fluids with Pressure-Dependent Viscosities

 To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments. While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small, special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place. Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are global in time, for a large class of physically meaningful viscosity-pressure relationships. (Accepted May 1, 2002) Published online November 15, 2002 Communicated by S. S. ANTMAN     

Activation energy of hydrogen migration by relay in the O2/Pt19/SnO2/H2 + n H2O system

In the framework of investigation of active and stable electrocatalysts for fuel cells, the hydrogen migration by relay with the consecutive formation of H₂O molecules in the O₂/Pt₁₉/SnO₂/H₂·nH₂O → O/Pt₁₉/SnO₂·nH₂O + H₂O system was simulated. The simulations were performed by the density functional theory (DFT) method with the generalized gradient adjustment (GGA=PBE) under periodic boundary conditions in the projector augmented plane wave (PAW) basis set with a pseudo-potential using the VASP program package. At the cathode on the platinum cluster surface, the oxygen molecules without a barrier form peroxide complexes that dissociate with an energy decrease. The protons transferred via the proton-conducting channels from the anode to cathode form first OH groups bound to the platinum cluster and then H₂O molecules that are easily separated from the cluster (～0.2 eV). The proton transfer process proceeds by relay and involves several water molecules.     

Platinum nanoparticles on the antimony-doped tin dioxide surface: Quantum-chemical modeling

The interaction of Pt₂₉ nanoparticles with pristine and reduced (110) and (100) SnO₂ surfaces doped with Sb has been modeled using the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that the introduction of antimony contributes to dispersion of substrate particles and, in some cases, leads to an increase in the energy of interaction with platinum and to the fixation of platinum nanoparticles on the surface.     

Oxygen behavior on the platinum surface: A quantum-chemical modeling

The dissociation of molecular oxygen and the migration of O atoms over the (100) and (111) platinum crystal surfaces have been modeled by the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that the barrier to dissociation of the dioxygen molecule on the (100) surface is lower than that on the (111) surface. Oxygen atoms migrate over the (100) surface more readily than over the (111) surface. On the basis of these data, it is suggested that the Pt(100) surface is most efficient for dioxygen activation.     

Quantum-chemical investigation of influence of solvation on structure and energy characteristics of lithium borohydride and aluminohydride

Institute of New Chemical Problems, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 6, pp. 9–19, November–December, 1990.     

Simulation of the geometric and electronic structures and properties of extrinsic defects involving germanium in lead telluride

Cluster simulation of the bulk and surface of crystalline lead telluride has been performed in the framework of the hybrid density functional theory B3LYP method with the use of the LANL2 pseudopotential with the corresponding double-zeta basis set. Different variants of doping germanium atoms in a PbTe single crystal and at its surface have been examined. Clusters of different sizes have been considered. For the optimal cluster, containing 112 atoms, the state where a germanium atom occupies a cationic position is the most stable. Impurity atoms, as well as impurity atoms and vacancies, show a weak tendency for association. Formation of a singular surface is accompanied by differential relaxation. The charge state of germanium atoms in the bulk and at the surface is virtually the same and somewhat decreases upon association with vacancies.