Gravitational Stability of a Moving Water-Steam Interface in Hydrothermal Systems

The stability of a hydrothermal system is considered. In this system a water layer overlies a superheated-steam layer in a reservoir with relatively low permeability located between two parallel high-permeability strata. The solution of the steady-state bounded problem with a phase transition interface separating the water and steam zones is obtained on the assumption that the convective energy transfer is small as compared with the conductive transfer. An investigation of the normal stability of the phase transition interface shows that stable configurations almost always exist in the geothermal system considered on the permeability range bounded from above by the value k 10^-15 m². Thus, the criterion of predominance of conductive transfer, which is simultaneously the criterion of existence of the fundamental solution, turns out to be the criterion of stability of the phase interface in the geothermal system considered. The fairly high value of the permeability satisfying this criterion makes it possible to explain the existence of stable natural geothermal reservoirs in which a water layer overlies a steam layer.     

Degenerate ground state in a mesoscopic YBa2Cu3O(7-x) grain boundary Josephson junction

We have measured the current-phase relationship I(varphi) of symmetric 45 degrees YBa2Cu3O7-x grain boundary Josephson junctions. Substantial deviations of the Josephson current from conventional tunnel-junction behavior have been observed: (i) The critical current exhibits, as a function of temperature T, a local minimum at a temperature T*. (ii) At T approximately T*, the first harmonic of I(phi) changes sign. (iii) For T相似文献   

Universal Margin Factors and Selection Criteria in Variable Environment

For nonautonomous dynamical systems, the principle of inheriting local properties by global Poincaré maps is developed. Using this method, a selection criterion for systems of close competitors is found: to gain competitive advantage, it suffices to outproduce other populations with a margin. The margin factor in question remains uniformly bounded as the number of competitors in the community grows.     

Mapping the triplet potential energy surface of 1-methyl-8-nitronaphthalene

Spin-unrestricted calculations and time-dependent DFT were used to characterize structure and reactivity of 1-methyl-8-nitronaphthalene (1) in the triplet state. Four hybrid models (B3LYP, PBE0, MPW1K, BHLYP) with significantly different amount of the exact exchange were employed. The triplet potential energy surface of 1 was mapped by using the UB3LYP and UMPW1K techniques. Both hybrid models provided qualitatively consistent pictures for the potential energy landscape. Thirty-one stationary points, of which 15 were minima, were found at the UB3LYP level of theory. Three minima corresponding to the nitro form of 1 were located on the triplet surface; just one was found for the singlet ground state. Two reaction paths leading from 1 either to a nitrite-type intermediate (2) or to the aci-form (3) were characterized. For both paths, reaction products were of diradical nature. The lower activation energy was obtained for the triplet-state tautomerization affording 3. The ground state of triplet multiplicity was predicted for two isomers of the aci-form. The triplet diradical 3 is expected to react through the thermal population of a close-lying singlet excited state. The results are discussed in relation to mechanisms of photoinduced rearrangements of peri-substituted nitronaphthalenes that can be used to develop novel photolabile protecting groups.     

Existence of a family of soliton-like solutions for the Kawahara equation

Existence is proved for a family of soliton-like solutions for the nonlinear evolution equation u_t–+uu_x+u_xxx-u_xxxxx=O. The problem is reduced to investigating the fixed points of the operator