Observations of high-field domains in GaxIn1 ? xSb Gunn diodes

The properties of high-field domains in GaxIn1-xSb Gunn diodes (0.4 < x < 0.82) have been studied by measuring the surface potential on the diodes. The domain velocities vary with the Ga composition x, 5.3?6.1×106 cm/s for0.8 > x > 0.55 and 10×106 cm/s for x = 0.4, but they are almost independent of the applied voltage, even if the electron concentration is increased by the impact ionisation in the domain at high applied voltages for the small-x samples.     

Solar-hydrogen energy system-model applied to isolated island

Comparison between a petroleum energy system and a solar-hydrogen energy system is studied in the case where an industry is newly introduced to an isolated island. Assuming a hybrid energy system composed of petroleum, solar energy, hydrogen energy and electric energy, we investigate an optimum economy with the use of computer-aided LP (Linear Programming) and QP (Quadratic Programming) models taking account of the cost functions originated from the acquisition prices of the primary energy and the transport prices. Furthermore, the modified LP model makes it possible to take account of the uncertainties arising from the acquisition instability and environmental protection. Some conditions are clarified under which the introduction of a solar-hydrogen energy system is highly feasible.     

Reaction of poly(epichlorohydrin) with sodium diethyldithiocarbamate and RI-UV dual-detector GPC of the product

Summary The chlorine in poly(epichlorohydrin) was found to be substituted by diethyldithiocarbamate (ETC) group by the reaction with NaETC in tetrahydrofuran at 60°C. The reaction product was analyzed by RI-UV dual-detector GPC. The composition i.e. the percentage of the chlorine replaced by the ETC group was found to be invariant with the elution count. This result might indicate the absence of polymer effect in the carbamation of poly(epichlorohydrin).     

Determination of assigned configurational parameters for cross propagation in radical copolymerization of methyl methacrylate and trityl methacrylate

Summary Copolymer of methyl methacrylate-d₈(M₁) with a small amount of trityl methacrylate(M₂) was radically prepared in tetrahydrofuran and converted into the copolymer of methyl methacrylate-d₈ with a small amount of undeuterated methyl methacrylate by the selective hydrolysis of the trityl group and subsequent methylation with diazomethane. From the ¹H NMR spectrum of the derived copolymer the assigned coisotactic parameters ₁₂ and ₂₁ were determined to be 0.14 and 0.61, respectively. This may be the first example of the unequivocal determination of assigned configurational parameters in cross propagation for copolymerization.     

Acidophilic xylanase from Aureobasidium pullulans: efficient expression and secretion in Pichia pastoris and mutational analysis

A yeast-like fungus Aureobasidium pullulans var. melanigenum strain ATCC 20524 produces an extracellular acidophilic endo-1,4-beta-xylanase with an optimum pH of 2.0 [Ohta et al., J. Biosci. Bioeng., 92, 262-270 (2001)]. The xynI cDNA encoding the precursor protein (XynI) was expressed in the methylotrophic yeast Pichia pastoris under the control of the alcohol oxidase I gene promoter. The 34 amino acid prepro-signal peptide of the A. pullulans XynI directed the efficient secretion of 178 mg of active xylanase per liter of the culture medium. The secretion level of the xylanase with its own signal peptide was comparable to that of the mature protein fused to the prepro leader from Saccharomyces cerevisiae alpha-mating factor and twofold higher than that of the mature protein fused to the pre-type signal peptide from P. pastoris acid phosphatase. The N-terminal amino acid sequence and the apparent M(r) of 24 kDa of the secreted recombinant protein indicated the native-like processing of the A. pullulans XynI signal sequence in P. pastoris. The three-dimensional model and mutational analysis of the xynI gene product showed that Asp-73 and Glu-157 residues located at the upper and lower edges of the active site cleft, respectively, play a significant role in its low pH optimum.     

Metabolic disturbance of tryptophan-nicotinamide conversion pathway by putative endocrine disruptors, bisphenol A and styrene monomer

Bisphenol A, a monomer of polycarbonate plastics, disturbed the conversion pathway of the amino acid tryptophan to the vitamin nicotinamide. The conversion ratio of tryptophan to nicotinamide was reduced to 1/15 by feeding a diet containing 1% bisphenol A. A putative disturbing reaction is kynurenine-->3-hydroxykynurenine, which is catalyzed by kynurenine monohydroxylase. This is an FAD-enzyme and requires NADPH as a coenzyme. Styrene monomer (1% addition to a normal diet) did not affect the food intake or the body weight, but slightly reduced the conversion ratio of tryptophan-nicotinamide.     

Energy absorption in blends of polycarbonate with ABS and SAN

Polycarbonate and its blends with ABS and SAN were tested to study the energy absorbing properties and the deformation mechanism. In tension and impact tests, these blends were found to possess a high energy absorbing capability, high yield strength and large rupture elongation. ABS and SAN particles in the blends deform in a ductile manner to an elongation of more than 100% under a tensile stress. In an elongation test of ABS under a hydraulic pressure of 90×10⁵ N m^–2, the transformation from crazing to a cold-drawing mechanism was found to occur. The large elongation of ABS and SAN in the blends is attributed to the cold drawing which occurs under the influence of the pressure acting on the dispersed ABS and SAN, caused by the difference between the elastic moduli of the dispersoid and the matrix.     

Defect levels in chromium-doped silicon

The transient capacitance technique has been used to study the chromium-related levels in the silicon band gap. Chromium was diffused at temperature of 1100 and 1150°C for 0.5 and 3 hr. Five different levels at E_c?0.11 eV, E_c?0.21 eV, E_c?0.28 eV, E_c?0.36 eV and E_c?0.45 eV were obtained from the Arrheniu plots of the electron thermal-emission rates. The number of levels in the upper half of the band gap decreased from five to two with an increase of Cr-diffusion period. Two levels were located at E_c?0.20 eV (donor) and E_c?0.43 eV (acceptor). A donor level was also observed at E_v + 0.25 eV. The donor level was not affected by the diffusion condition. The majority carrier capture cross sections of the three dominant levels have been measured by the transient capacitance technique modified by the pulse transformer. The values were σ_n = 4.1 × 10^?15 cm² for the upper donor at E_c?0.20 eV, σ_n = 2.0 × 10^?16 cm² for the acceptor at E_c ?0.43 eV and σ_p = 9.1 × 10^?18 cm² for the lower donor at E_v + 0.25 eV, and were independent of temperature. The three dominant levels are due to distinct chromium centers.     

Submicron bubble garnets and their characterizations

New Submicron (0.5-1.0 mum diam) bubble garnets have been developed. In order to reduce saturation induction4piMsas low as possible, suitable choice of amounts of nonmagnetic ions substituting for ferric ions in both tetrahedral and octahedral sites were studied in (YSm)3(FeAl)5O12, (YSmLu)3- (FeGaSc)5O12, (YSmLu)3(FeAlSc)5O12and (LaLuSm)3- (FeGa)5O12garnet systems. For example, in (YSmLu)3- (FeAlSc)5O12a film with the following properties was grown; strip widthw = 0.7mum, film thicknessh= 0.7mum, quality factorq=2.8, Curie temperatureTc= 140degC and4piMs=770G. The temperature properties of those films could be improved drastically by doping with a small amount of Gd ion. Wall mobilities μw of those films are in the region from 200 to 500cm/s/Oe. Preceding these material studies, several film characterization methods have been investigated. Film thickness was measured by Fluorescent X-ray method, strip width by using a highly sensitivity TV camera, and bubble collapse field by FMR resonance technique respectively.     

Discovery of insect anti-juvenile hormones in plants.?2U

Two simple chromenes with anti-JH activity have been isolated and identified from the bedding plant Ageratum houstoianum. By contact and fumigation these compounds induce precocious metamorphosis and sterilization in several hemipteran species of insects. Certain holometabolous species are sterilized, forced into diapause, or both. Each of these biological actions is equivalent to removal of the corpora allata, which produce the JH's, and is reversible by treatment with exogenous JH. Thus, the action of these compounds is to stop the production or depress the titer of the JH's. To our knowledge, this is the first discovery of anti-JH, and we hope it will guide the way to the emergence of a fourth generation of safe and insect-specific pesticides.