Preparation and characterization of quenched KNbO3-Nb2O5 glass

KNbO₃-Nb₂O₅ glasses were prepared with molar ratio of K/(K + Nb) from 0.16 to 0.5 by using a twin-roller quenching apparatus. Most KNbO₃-Nb₂O₅ glasses crystallized to stable phases such as KNbO₃, K₂Nb₄O₁₁, K₃Nb₇O₁₉, KNb₃O₈ and K₂Nb₈O₂₁ via metastable phases after heat treatment and K₄Nb₆O₁₇ glass directly crystallized to K₄Nb₆O₁₇ crystal. KNbO₃ glass consisted of the corner-shared NbO₆ octahedra, while the amounts of the edge-shared NbO₆ octahedra in the KNbO₃-Nb₂O₅ glass structure increased with decreasing K⁺ ion content. The band gap energies and the ionic conductivity of the KNbO₃-Nb₂O₅ glasses increased with increasing K⁺ ion content, but the density and the activation energy of the ionic conduction decreased. The glasses possessed high dielectric constants appfoaching those of ferroelectric crystals at high temperature around the crystallization temperature. The dielectric constants of the glasses, however decreased greatly with decreasing temperature and with increasing frequency.     

Hindered oscillation and e.s.r. spectra of alkyl free radicals trapped in irradiated polyethylene crystals

Structures of alkyl radicals trapped in solution grown crystals of polyethylene and urea-polyethylene complex were studied in detail. A twisted configuration of methylene group with angle of 4.6° from the regular trans-trans configuration was found for the rigid state configuration of the alkyl radical at 77K. Temperature dependences of hyperfine splitting widths due to the β-protons were observed, and analysed in terms of the hindered oscillation of the β-methylene group. The value of the potential barrier height of hindered oscillation was found to be 900 kcal/mol for polyethylene crystal and 600 kcal/mol for urea-polyethylene complex; indicating that the radical site in urea-polyethylene complex is more mobile than that in polyethylene crystal.     

Mössbauer effect of SrLnFeO4 (Ln=La,Pr, Nd,Sm, Eu,Gd)

The Mössbauer effect has been studied in SrLnFeO₄ compounds (Ln=La, Pr, Nd, Sm, Eu, Gd) with K₂NiF₄ structure in the temperature range between 80K and 459K. The N?el temperture was determined to be 330±5K for SrLaFeO₄, 250±5K for SrPrFeO₄, 270±5K for SrNdFeO₄ and 400±10K for SrSmFeO₄. The results of the combined magnetic and quadrupole interactions indicated that the direction of internal magnetic field is perpendicular to the Z-axis of the EFG tensor and parallel to the c-axis of the crystal structure.     

Structural genomics of membrane proteins

A program on the structural genomics of membrane proteins has started at the BIRC, AIST, involving other academic institutions and industrial companies. Emphasis is being put on the development of techniques for the structural determination of membrane proteins of biological importance and ligand-receptor interactions by means of electron microscopy, X-ray diffraction, NMR, and computer simulation. Most efforts at the present stage, however, are being directed to finding suitable expression and purification systems and crystallization conditions for such proteins. The program is expected to be linked with the human full-length cDNA project and should lead to medical and industrial uses.     

Corrosion Kinetics and Strength Degradation of Sintered δ-Silicon Carbide in Potassium Sulfate Melts

Pressureless sintered α-SiC ceramics containing carbon and boron as sintering aids and hot-pressed SiC containing aluminum nitride as a sintering aid were corroded in K₂SO₄ melts at 1080° to 1150°C. SiC ceramics were oxidized and dissolved into K₂SO₄ melts. Since the corrosion of SiC ceramics in K₂SO₄ melts proceeded autocatalytically, a reaction product such as K₂S_1.44 was suspected to promote the corrosion reaction. The corrosion resistance of SiC containing AlN in K₂SO₄ melt was superior to that of SiC containing boron and carbon. Apparent activation energies for the corrosion of SiC ceramics were 309 to 331 kJ mol^-1. The fracture strength of the specimens corroded by K₂SO₄ melt degraded to 40% to 70% of the original values up to a 20% weight loss and then was almost constant up to 45% weight loss.     

Initiation of a fibrinolytic system in hepatic resection: the roles of tissue-type plasminogen activator and plasminogen activator inhibitor-1

The factors related to the initiation of fibrinolysis, especially with regard to the tissue-type plasminogen activator (tPA) and the plasminogen activator inhibitor-1 (PAI-1), were investigated in 15 patients who underwent hepatic resection, and the findings were compared between those with normal livers and those with diseased livers. It was found that tPA increased before hepatic division, whereas PAI-1 increased after hepatic division and reached a peak immediately following the operation. Plasminogen decreased during hepatectomy, reaching its lowest point on postoperative day 1, and increasing later. Decreased levels of both plasminogen and the alpha 2-plasmin inhibitor were considered to be partly due to plasmin formation in the blood. Patients with a diseased liver tended to have higher intraoperative values of euglobulin lysis activity and higher postoperative values of plasminogen activator, but significantly lower postoperative values of alpha 2-plasmin inhibitor than those with a normal liver. The results of this study suggest that activation of the fibrinolytic system occurs both during hepatectomy and in the early postoperative period, and that patients with a diseased liver are prone to develop hyperfibrinolysis during hepatectomy. Moreover, the increased levels of both tPA and PAI-1 can serve as one of the most sensitive markers for the vital reaction against surgical stress.     

Evaluation of SCC crack behavior in zirconium and zircaloy-2 using nonlinear fracture mechanics parameters

Applicability of nonlinear fracture mechanics parameters, i.e. J-integral, crack tip opening displacement (CTOD), and crack tip opening angle (CTOA), to evaluation of stress corrosion crack (SCC) propagation rate was investigated using fully annealed zirconium plates and Zircaloy-2 tubing, both of which produce SCC with comparatively large plastic strain in an iodine environment at high temperatures.Tensile SCC tests were carried out at 300°C for center-notched zirconium plates and internal gas pressurization SCC tests at 350°C, for Zircaloy-2 tubing, to measure the SCC crack propagation rate. The J-integral around semi-elliptical SCC cracks produced in Zircaloy-2 tubing was calculated by a three-dimensional finite element method (FEM) code.The test results revealed that the SCC crack propagation rate dc/dt could be expressed as a function of the J-integral, which is the most frequently used parameter in nonlinear fracture mechanics, by the equation dc/dt = C · Jⁿ, where C and n were experimental constants.Among the other parameters, CTOD and CTOA, the latter appeared to be useful for assessing the crack propagation rate, because it had a tendency to hold a constant value at various crack depths.     

A Method for Improving String Pattern Matching Machines

This correspondence describes an efficient string pattern matching machine to locate all occurrences of any of a finite number of keywords and phrases in an arbitrary text string. Some conditions are defined on the states of the machine in order to improve the speed and size of the machine by Aho and Corasick [1]. The pattern matching algorithm is partitioned into various cases by combining these conditions. Finally, the correspondence illustrates the proposed approach by applying it to the analysis of the machines for a simple search.