Global Phase Time and Wave Function for the Kantowski-Sachs Anisotropic Universe

A consistent quantization with a clear notion of time and evolution is given for the anisotropic Kantowski–Sachs cosmological model. It is shown that a suitable coordinate choice allows to obtain a solution of the Wheeler–DeWitt equation in the form of definite energy states, and that the results can be associated to two disjoint equivalent theories, one for each sheet of the constraint surface.     

Preliminary study of the thermally stimulated blue luminescence of ulexite

In this paper, novel results on the blue thermally stimulated luminescence (TSL) emission of ulexite (NaCaB₅O₆(OH)₆·5H₂O) have been studied. The four maxima appearing at 60, 110, 200 and 240°C on the TSL glow curves of this borate could be respectively associated to: (i) the first dehydration (NaCaB₅O₆(OH)₆·5H₂O→NaCaB₅O₆(OH)₆·3H₂O), (ii) the creation-annihilation of the three-hydrated phase, (iii) the Na-coordinated chains dehydroxylation and the starting point of the alkali self-diffusion through the lattice and (iv) the amorphisation of the lattice. These results are fairly well correlated with the differential thermal analyses (DTA), in situ thermal observations under environmental scanning electron microscope (TESEM) and thermal X-ray diffraction (TXRD) techniques.     

General theoretical results on rectilinear embedability of graphs

In the design of certain kinds of electronic circuits the following question arises: given a non-negative integerk, what graphs admit of a plane embedding such that every edge is a broken line formed by horizontal and vertical segments and having at mostk bends? Any such graph is said to bek-rectilinear. No matter whatk is, an obvious necessary condition fork-rectilinearity is that the degree of each vertex does not exceed four. Our main result is that every planar graphH satisfying this condition is 3-rectilinear: in fact, it is 2-rectilinear with the only exception of the octahedron. We also outline a polynomial-time algorithm which actually constructs a plane embedding ofH with at most 2 bends (3 bends ifH is the octahedron) on each edge. The resulting embedding has the property that the total number of bends does not exceed 2n, wheren is the number of vertices ofH.     

Diffusion effects on the interfacial tension of immiscible polymer blends

Most methods of measuring the interfacial tension between two immiscible polymers are based on the analysis of the shape that a drop of one polymer immersed in the other one exhibits under the action of flow or gravity. In such a situation, the small, yet nonzero mutual solubility between the two polymers acts toward mass transfer between the drop and the surrounding fluid. In this work, diffusion effects on the interfacial tension of the pair polyisobutylene/polydimethylsiloxane have been investigated by drop deformation under shear flow. When the drop was made of polyisobutylene, drop size decreased with time due to diffusion. Drop shrinkage was associated with a significant increase in interfacial tension, until an apparent plateau value was reached. The effect was attributed to a selective migration of molecular weights, which would act to enrich the drop with higher molar mass material. To support such an interpretation, drop viscosity was evaluated by drop shape analysis and it was actually found to increase with time. In some cases, the ratio between drop and continuous phase viscosity became higher than the critical value for drop breakup in shear flow. Upon inverting the phases (i.e., when the drop was made of polydimethylsiloxane), no significant transient effects were observed. In the light of these results, the problem of what are the correct values of interfacial tension and viscosity ratio for a polymer blend of a certain composition will also be discussed. Received: 25 January 1999 Accepted: 24 May 1999     

Crystal growth of MnxCd1-xGa2Se4 (0.00 x 0.20)

Crystals of Mn_xC_1-xGa₂Se₄ (0.00 x 0.20) have been grown the vapour phase by chemical transport modified by the t ime variation of the temperature profile procedure. Crystals with dimensions up to 15 × 2 × 2 mm were obtained and characterized by EPR spectroscopy.