Liouville Invariance in Quantum and Classical Mechanics

The density-matrix and Heisenberg formulations of quantum mechanics follow—for unitary evolution—directly from the Schrödinger equation. Nevertheless, the symmetries of the corresponding evolution operator, the Liouvillian L = i[, H], need not be limited to those of the Hamiltonian H. This is due to L only involving eigenenergy differences, which can be degenerate even if the energies themselves are not. Remarkably, this possibility has rarely been mentioned in the literature, and never pursued more generally. We consider an example involving mesoscopic Josephson devices, but the analysis only assumes familiarity with basic quantum mechanics. Subsequently, such L-symmetries are shown to occur more widely, in particular also in classical mechanics. The symmetry's relevance to dissipative systems and quantum-information processing is briefly discussed. PACS: 03.65.-w, 03.67.-a, 45.20.Jj, 74.50.+r     

Nonlinear Response and Observable Signatures of Equilibrium Entanglement

We investigate how equilibrium entanglement is manifested in the nonlinear response of an N-qubit system. We show that in the thermodynamic limit the irreducible part of the nth-order nonlinear susceptibility indicates that the eigenstates of the system contain entangled (n + 1)-qubit clusters. This opens the way to a directly observable multiqubit entanglement signature. We show that the irreducible part of the static cubic susceptibility of a system of four flux qubits, as a function of external parameters, behaves as a global 4-qubit entanglement measure introduced in Ref. (20). We discuss the possibility of extracting purely-entanglement-generated contribution from the general multipoint correlators in a multiqubit system.      

A method for preparation of a high-quality high temperature superconducting ceramics

An improved method for hot pressing of high temperature superconducting (HTSC) powders prepared by conventional solid phase synthesis of the initial BaCO₃, CuO and Ln₂O₃ allows one to obtain HTSC targets and magnetic shields possessing a high degree of homogeneity. By sputtering such targets HTSC films with critical current density of 3.3·10⁶ A/cm² have been deposited. Shields, prepared according to this method, show a shielding coefficient of 10⁵ andH _c of 79 Öe in the constant magnetic field and in the alternating magnetic field the amplitude is 90 Öe in the frequency range of 70–3000 Hz.     

Mathematical Models of the State of a Real Gas

Journal of Engineering Physics and Thermophysics - An overview of the development of mathematical models used to describe the relationship between the parameters of the state of real gases is...     

Mechanism and kinetics of sintering of nonstoichiometric Y-Ba-Cu-O powders

Using high-resolution optical and scanning electron microscopy with x-ray microanalysis at temperatures of 880 to 920°C, we studied the kinetics and mechanism of the formation of intergranular contacts during sintering of powder-substrate models and also studied the mechanism of shrinkage during sintering of Y-Ba-Cu-O compacts with a stoichiometric composition and two nonstoichiometric compositions, Y_0.95Ba₂Cu₃O_y and Y_1.05Ba₂Cu₃O_y. The formation and the shrinkage of powders of different compositions were found to be described by equations of different degrees, which points to different diffusion sintering mechanisms. Powders with stoichiometric and hyperstoichiometric compositions are sintered by a volume diffusion mechanism, which is controlled by the slowest ion, Y³⁺. Powders with a substoichiometric composition (Y-0.95) are sintered like a liquid phase, i.e., is controlled by diffusion through liquid or solid layers where new phases with higher diffusion coefficients are formed as a result of segregation effects.     

Mathematical modeling of cyclic processes

The identification of cyclic chemical-engineering processes via high-degree linear differential equations is presented. Based on the elaborated approach, the identification of the cyclic process of the gaslift extraction of hydrocarbons from drowned wells of oil-and-gas condensate fields was performed. Analytical solutions of the mathematical model possessing stability and a good correlation with the experimental data are obtained.     

Thermal-shock resistance of composite materials based on periclase and chromium oxide

Conclusions The possibility of controlling the structure, thus making it possible to obtain thermal-shock resistant materials in the MgO-Cr₂O₃ system, by combined synthesis and sintering in the same firing, has been studied. The fracture diagrams in load-bend coordinates and the criteria of thermal-shock resistance used to evaluate the tendency of the material to resist the movement of a crack have been studied. An effective composition for a thermal-shock resistant material based on pure magnesium chromite has been obtained.Translated from Ogneupory, No. 8, pp. 44–47, August, 1981.     

The thermal conductivity of periclase and periclase — Spinel refractories

Conclusions It was established that it is possible to vary the thermal conductivity of periclase and periclase- spinel refractories within fairly wide limits by varying their phase composition and structure.Translated from Ogneupory, No. 3, pp. 48–50, March, 1975.