A New Equation for Predicting the Dielectric Constant of a Mixture

The dielectric constant of a compound consisting of two different materials was simulated using the Monte Carlo and finite element methods. In the high concentration range of the higher dielectric constant material, the simulated value of the dielectric constant showed a "parallel-model"-like tendency. On the other hand, in the low concentration range of the higher dielectric constant material, the compound showed a "serial-model"-like behavior. Around 65% content of the higher dielectric constant material, it exhibited results similar to the logarithmic mixing rule. After careful consideration of these results, a new equation to predict the dielectric constant of the compound was derived. The agreement between the dielectric constant calculated by the new equation and the measured values was better than in any other case reported before.     

Optical Properties, Electronic Structure and Magnetism of α′-Na x V2O5

The optical properties of sodium-deficient α′-Na _x V₂O₅ (0.85 ≤ x ≤ 1.00) single crystals are analyzed using ellipsometry, and infrared reflectivity techniques. In sodium deficient samples, the optical absorption peak associated to the fundamental electronic gap develops in the middle of the pure α′-NaV₂O₅ gap at ～0.44 eV, and the material remains insulating up to the maximal achieved hole concentration of about 15%. Nonmetallic behavior under hole doping provoked reinterpretation of the α′-NaV₂O₅ optical spectra. We argue that the absorption peak at about 0.9 eV corresponds to the photoionization energy of a large polaron.     

Fundamental design and electrical characteristics of superconducting commutatorless motor

Since there are no iron cores in the rotor and stator windings of superconducting synchronous motors, some reactances are intrinsically smaller than those of conventional motors. Thus the low synchronous reactance would be expected to improve the torque-ampere ratio stability and the overload capacity in case of the variable-speed drive system of a load-commutated inverter due to the small armature reaction. Moreover, the low subtransient reactance may contribute to lessen the voltage stress during the shortened commutating period, especially in current source-type inverter (CSI) systems. In this paper, after presenting analytical formulas needed for a machine design, one design algorithm is described, citing one example of an experimental CSI-fed superconducting motor of 30 kVA which will be fabricated. Further, the distinguished features in its operation, as expected in the foregoing, are verified by the computer simulation study in comparison with a conventional machine in terms of a high specific power density, an extension of stable power limit, and so on.     

Oxidation of silicon carbide in a wet atmosphere

The effects of water vapour on oxidation of pressureless-sintered silicon carbide containing alumina as a densifying aid were studied in a wet air flow with 10, 20, 30 and 40vol% H₂O at 1300° C for 100h. The oxidation kinetics were determined in a wet air flow with 20 vol % H₂O and in a dry air flow at 1300° C for times up to 360 h. The weight gain on oxidation showed an increasing tendency with increasing water vapour content. Water vapour in the atmosphere strongly influenced oxidation and accelerated the reaction. Oxidation in a wet atmosphere proceeded in a diffusion-controlled manner, in the same process as that for the dry atmosphere. No remarkable differences were noticed in the microstructure of the oxide layer and the surface roughness between the samples oxidized under the four wet conditions, but the surface roughness increased with increasing oxidation time. Water vapour evidently accelerated the devitrification of amorphous silica and promoted oxidation. Oxidation in a wet atmosphere (10 to 40 vol % H₂O for 100 h and 20 vol % H₂O up to 360 h) had a slight degrading effect on the flexural strength. The microstructure or surface roughness of the oxide layer formed during oxidation presumably had very little effect on the room-temperature strength.     

New approaches to the management of acute and chronic cardiac allograft rejection

There are still many problems to be faced in the field of heart transplantation. Acute and chronic rejection are still the major medical obstacles. In this review, we describe recent research in this field undertaken in our laboratory. The induced intercellular adhesion molecule-1 (ICAM-1) and MHC class II antigen resulting from rejection can be visualized in vivo by radioimmunoscintigraphy. This non-invasive method is sensitive for detecting early rejection and allows quantitative assessment of rejection. Short-term administration of monoclonal antibodies to ICAM-1 and leukocyte function-associated antigen-1 (LFA-1) results in an indefinite acceptance of cardiac allografts by induction of antigen-specific tolerance, as evidenced by acceptance of the secondary skin allografts. The characteristics and possible mechanisms of this tolerance induction are discussed. Immunohistopathologic features of graft coronary arteriopathy are shown. Adhesion molecules, cytokines, and growth factors are associated with intimal hyperplasia and phenotypic transformation of smooth muscle cells in the allograft coronary arteries. Dramatic reduction in this intimal hyperplasia was demonstrated by antisense gene therapy targeting cyclin-dependent kinase 2 kinase. We hope that these investigations will contribute to the improvement of the management of patients who undergo heart transplantation.