A gravitational field in the Plebanski spacetime

The gravitational wave equation in the Plebanski spacetime has been reduced to a one-dimensional wave equation with a real short-range potential. We then find that the superradiance phenomenon occurs.     

Thermal transformations in soils studied by Mössbauer spectroscopy and x-ray diffraction

Mossbauer spectroscopy and X-ray diffraction techniques were used to investigate the iron oxides and other mineral phase developments in calcareous and noncalcareous soil samples after firing at ≈ 1000°C. Well crystalline haematite with larger particle size was produced in the fired non-calcareous soil. On the other hand, while goethite in the strongly calcareous natural material was transformed into haematite at the oven drying temperature, non of the latter was detected after firing at 1050°C. This could be related to the reaction between CaO, quartz and aluminosilicates at 800°C to produce calcium aluminosilicates which may have hindered the growth of haematite above this temperature.     

Two-dimensional percolation and classical string theory

Both two-dimensional percolation and classical string theory are shown to correspond toc=0 in the 2d conformal algebra. Therefore, despite being different theories, they have the same underlying conformal structure.     

Energy levels for the Coulomb potential with cut-off

Zusammenfassung Die Absorptionsbanden der Alkalihalogenidkristalle werden auf Elektronen zurückgeführt, die an leeren Gitterstellen eingefangen sind. Als Feld wird ein bei kleinen Distanzen horizontal abgeschnittenes Coulomb-Feld angesetzt. Die Eigenwerte werden im ganzen Energiebereich aus einer genauen Reihenentwicklung der Lösungen der Schrödinger-Gleichung bestimmt.     

Effects of temperature and thermo-mechanical couplings on material instabilities and strain localization of inelastic materials

A general framework for rate-independent, small-strain, thermoinelastic material behaviour is presented, which includes thermo-plasticity and -damage as particular cases. In this context, strain localization and the development of material instabilities are investigated to highlight the roles of thermal effects and thermomechanical couplings. During a loading process, it is shown that two conditions play the essential roles and correspond to the singularity of the isothermal and the adiabatic acoustic tensors. Under quasi-static conditions, strain localization (in a classical sense) may occur when either of these two conditions is met. It involves a jump in temperature rate in the latter case, whereas temperature rate remains continuous in the former, but a discontinuity in the spatial derivatives of the heat flux must occur. This is consistent with the condition of stationarity of acceleration waves, which are shown to be homothermal and propagate with a velocity related to the eigenvalues of the isothermal acoustic tensor. A linear perturbation analysis further clarifies the above findings. In particular, for a quasi-static path of an infinite medium, failure of positive definiteness of either of the acoustic tensors corresponds to bifurcations in wave-like modes of arbitrary wave-length and infinite rate of growth. Under dynamic conditions, unbounded growth of perturbations is associated only to the short wavelength regime and corresponds to divergence growth or flutter phenomena relative to the isothermal acoustic tensor.     

Multiphase percolation and Josephson model for high-temperature superconductivity

A four-phase percolation problem is used to simulate the Josephson model for high-temperature superconductivity both as a four-phase and a three-phase system. We implement the method on an IBM PC microcomputer using PASCAL language.     

Crystal and molecular structure ofpp-diphenyl-p-tetrakis (perfluoromethyl)ethylene glycol phosphinate

The title compound crystallizes in space groupP¯1 (No. 2) witha=8.796(6),b=10.754(3),c=12.271(2) Å,=68.56(2),=67.68(3),=78.87(4)°, andZ=2. The structure was solved by direct methods and refined by full-matrix least squares toR=0.048. In the tetrahedral geometry around phosphorus, the P-O(22) bond of 1.464(2) Å is shorter than expected. The OO hydrogen bond results in dimer formation, and the substituted glycol shows staggered conformation along the C(12)-C(3) vector.