Transmittance and cathodoluminescence of AlN ceramics sintered with Ca3Al2O6 as sintering additive

Aluminum nitride ceramics were prepared by sintering with 0–4.8 mass% of Ca₃Al₂O₆ (C₃A) as a sintering additive. The transmittance in the range of 260–550 nm increased with increasing amount of C₃A. The cathodoluminescence intensity attributed to oxygen-induced defects decreased with increasing amount of C₃A. From the results, the increase of the transmittance in the range of 260–550 nm was considered to be related to the decrease of the oxygen-induced defect density.     

Analysis of shielded microstrip lines with arbitrary metallizationcross section using a vector finite element method

The finite element method (FEM) with the high-order mixed-interpolation-type triangular element is used to solve the problem of practical microstrip lines with arbitrary metallization cross section. Analyses are carried out to produce the frequency characteristics of propagation constant, characteristic impedance, and attenuation constant of shielded microstrip lines with rectangular, trapezoidal, and semi-trapezoidal strip cross sections. A comparison of the numerical results with those of the existing results shows good agreement and thus verifies the versatility of the FEM. Also, the numerical results show the effects of the metallization cross sections on the transmission properties and thus emphasize the importance of considering the practical microstrip configurations in the design of miniaturized MMICs     

Quantitative trait loci affecting 4-nitroquinoline 1-oxide-induced tongue carcinogenesis in the rat

The incidence of tongue carcinomas (TCs) induced by oral administration of 4-nitroquinoline 1-oxide in rats is strain dependent. The inbred Dark-Agouti (DA) strain showed a much higher susceptibility to large mass-forming infiltrative TCs than did the Wistar-Furth (WF) strain. Our previous study (M. Kitano et al, Jpn. J. Cancer Res., 87: 1097-1101, 1996) on crosses between these two strains postulated a dominant susceptibility gene in DA and a dominant resistance gene in WF rats. The present study mapped these loci by analyzing the backcrosses to each parent with simple sequence repeat polymorphisms. Five quantitative parameters were analyzed: (a) the number of TCs > 5 mm in diameter; (b) the total number of TCs per rat; (c) the diameter of the largest TCs (DTCmax values); (d) the number of non-TC cancers per rat; and (e) and the number of cancers of any site per rat. All of these parameters were closely correlated (P < 0.0001). DA rats had a semidominant gene (Stc1) favoring the development of 4-nitroquinoline 1-oxide-induced cancers on chromosome 19, closely linked to D19Mit9. Peak linkage was observed 4 cM distal from D19Mit9, with a logarithm of the odds (lod) score of 5.72 for the number of large TCs and 6.08 for the DTCmax. On the other hand, WF rats had a semidominant gene (Rtc1) mapped between D1Mit1 and D1Mit3, approximately 20 cM from D1Mit1, with a peak lod score of 3.30 for both the number of large TCs and the DTCmax. The main effect of Rtc1 seemed to be to reduce the size of the TCs. The action of these genes was dose dependent and cooperative. The final incidence of TC in DA, WF, F1, and backcross rats seemed to be explained by combinations of genotype at these two loci. Possible candidate genes for Stc1 and Rtc1 are discussed.     

The effect of gas atmospheres on resistivity of indium tin oxide films at high temperature

The effects of heat treatment in Q₂, O₂ and N₂, and Ar gases on the high temperature (500 C) electrical resistivity of indium tin oxide (ITO) film 52 nm thick prepared by chemical spray pyrolysis method were studied. The partial oxygen pressure effect on the resistivity was found to be to . The resistivity changes for cyclic exchange of O₂ by Ar gas at 500 C. These lead to the conclusion that chemisorption of oxygen atoms in the film surface is dominant for this thin film, for thicker films such as 640 nm oxygen diffusion is found to occur. The Langmuir model of the monolayer isothermal adsorption of oxygen atoms in the surface is applicable to the rapid change of resistivity.     

Alteration of substrate specificity of cholesterol oxidase from Streptomyces sp. by site-directed mutagenesis

Despite the structural similarities between cholesterol oxidasefrom Streptomyces and that from Brevibacterium, both enzymesexhibit different characteristics, such as catalytic activity,optimum pH and temperature. In attempts to define the molecularbasis of differences in catalytic activity or stability, substitutionsat six amino acid residues were introduced into cholesteroloxidase using site-directed mutagenesis of its gene. The aminoacid substitutions chosen were based on structural comparisonsof cholesterol oxidases from Streptomyces and Brevibacterium.Seven mutant enzymes were constructed with the following aminoacid substitutions: L117P, L119A, L119F, V145Q, Q286R, P357Nand S379T. All the mutant enzymes exhibited activity with theexception of that with the L117P mutation. The resulting V145Qmutant enzyme has low activities for all substrates examinedand the S379T mutant enzyme showed markedly altered substratespecificity compared with the wild-type enzyme. To evaluatethe role of V145 and S379 residues in the reaction, mutantswith two additional substitutions in V145 and four in S379 wereconstructed. The mutant enzymes created by the replacement ofV145 by Asp and Glu had much lower catalytic efficiency forcholesterol and pregnenolone as substrates than the wild-typeenzyme. From previous studies and this study, the V145 residueseems to be important for the stability and substrate bindingof the cholesterol oxidase. In contrast, the catalytic efficiencies(k_cat/K_m) of the S379T mutant enzyme for cholesterol and pregnenolonewere 1.8- and 6.0-fold higher, respectively, than those of thewild-type enzyme. The enhanced catalytic efficiency of the S379Tmutant enzyme for pregnenolone was due to a slightly high k_catvalue and a low K_m value. These findings will provide severalideas for the design of more powerful enzymes that can be appliedto clinical determination of serum cholesterol levels and assterol probes.     

Effect of changing groundwater levels caused by land-use changes on greenhouse gas fluxes from tropical peat lands

Monthly measurements of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes in peat soils were carried out and compared with groundwater level over a year at four sites (drained forest, upland cassava,upland and lowland paddy fields) located in Jambi province, Indonesia. Fluxes from swamp forest soils were also measured once per year as the native state of this investigated area. Land-use change from drained forest to lowland paddy field significantly decreased the CO₂ (from 266 to 30 mg C m^–2 h^–1) and N₂O fluxes (from 25.4 to 3.8 g N m^–2 h^–1), but increased the CH₄ flux (from 0.1 to 4.2 mg C m^–2 h^–1) in the soils. Change from drained forest to cassava field significantly increased N₂O flux (from 25.4 to 62.2 g N m^–2 h^–1), but had no significant influence on CO₂ (from 266 to 200 mg C m^–2 h^–1) and CH₄ fluxes (from 0.1 to 0.3 mg C m^–2 h^–1) in the soils. Averaged CO₂ fluxes in the swamp forests (94 mg C m^–2 h^–1) were estimated to be one-third of that in the drained forest. Groundwater levels of drained forest and upland crop fields had been lowered by drainage ditches while swamp forest and lowland paddy field were flooded, although groundwater levels were also affected by precipitation. Groundwater levels were negatively related to CO₂ flux but positively related to CH₄ flux at all investigation sites. The peak of the N₂O flux was observed at –20 cm of groundwater level. Lowering the groundwater level by 10 cm from the soil surface resulted in a 50 increase in CO₂ emission (from 109.1 to 162.4 mg C m^–2 h^–1) and a 25% decrease in CH₄ emission (from 0.440 to 0.325 mg C m^–2 h^–1) in this study. These results suggest that lowering of groundwater level by the drainage ditches in the peat lands contributes to global warming and devastation of fields. Swamp forest was probably the best land-use management in peat lands to suppress the carbon loss and greenhouse gas emission. Lowland paddy field was a better agricultural system in the peat lands in terms of C sequestration and greenhouse gas emission. Carbon loss from lowland paddy field was one-eighth of that of the other upland crop systems, although the Global Warming Potential was almost the same level as that of the other upland crop systems because of CH₄ emission through rice plants.     

Measurement of self-diffusion coefficients in Li ionic conductors by using the short-lived radiotracer of 8Li

For the effective use of short-lived radioactive beams, soon to be available at the Tokai Radioactive Ion Accelerator Complex, the authors have developed a radiotracer method for diffusion studies in solids. The experimental test was performed by the measurement of the diffusion coefficients of Li in a sample of the compound βLiAl using an α-emitting radiotracer of ⁸Li (T_1/2=0.84 s). It was found that the time-dependent yields of the α particles from the diffusing ⁸Li that was initially implanted in the sample could be used as a measure of the diffusivity of the tracer in a nondestructive way. The method was applied to measure the self-diffusion coefficients of Li in βLiGa, and for investigating how the Li diffusion in the Li ionic conductors is affected by the concentration of atomic defects (i.e., the existence of the atomic vacancies of Li and the defects in Ga sites that are replaced by Li).     

Cooperative manipulation of a floating object by some space robots with joint velocity controllers: application of a tracking control method using the transpose of the generalized Jacobian matrix

We have studied the cooperative manipulation of floating object by several space robots. For these cooperative motions, we have reported that a tracking control method using the transpose of the generalized Jacobian matrix (GJM) can be utilized for robots with joint torque controllers. For cooperative motions by some robots with joint velocity controllers, we proposed a tracking control method using the transpose of the GJM. Simulation results show the effectiveness of the proposed control method.     

Evaluation of vector magnetic property in a three-phase induction motor model core with visualization of streamline

In this paper, a streamline display method for magnetic flux density and magnetic field strength vectors in a three-phase induction motor model core is presented, and the relationship between streamlines and magnetic properties is investigated. It is possible to visualize the vector magnetic properties distribution by representing the magnetic flux density and the magnetic field strength vector with the streamlines. In addition, the time variation of the streamlines of the magnetic flux density and magnetic field strength vectors, and magnetic energy was compared. It was clear that the magnetic energy did not necessarily increase in the areas where the magnetic flux density and magnetic field strength increased because these vectors have the spatial phase difference.