Biochemical Studies of Mitochondrial Malate: Quinone Oxidoreductase from Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis and infects almost one-third of the global human population. A lack of effective drugs and vaccines and the emergence of drug resistant parasites highlight the need for the development of new drugs. The mitochondrial electron transport chain (ETC) is an essential pathway for energy metabolism and the survival of T. gondii. In apicomplexan parasites, malate:quinone oxidoreductase (MQO) is a monotopic membrane protein belonging to the ETC and a key member of the tricarboxylic acid cycle, and has recently been suggested to play a role in the fumarate cycle, which is required for the cytosolic purine salvage pathway. In T. gondii, a putative MQO (TgMQO) is expressed in tachyzoite and bradyzoite stages and is considered to be a potential drug target since its orthologue is not conserved in mammalian hosts. As a first step towards the evaluation of TgMQO as a drug target candidate, in this study, we developed a new expression system for TgMQO in FN102(DE3)TAO, a strain deficient in respiratory cytochromes and dependent on an alternative oxidase. This system allowed, for the first time, the expression and purification of a mitochondrial MQO family enzyme, which was used for steady-state kinetics and substrate specificity analyses. Ferulenol, the only known MQO inhibitor, also inhibited TgMQO at IC₅₀ of 0.822 μM, and displayed different inhibition kinetics compared to Plasmodium falciparum MQO. Furthermore, our analysis indicated the presence of a third binding site for ferulenol that is distinct from the ubiquinone and malate sites.     

Void formation in silica glass induced by thermal oxidation after Zn ion implantation

Thermal annealing effects on Zn⁺ ion-implanted silica glass (a-SiO₂) have been studied in order to control void formation. Void formation in a-SiO₂ with Zn⁺ ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn⁺ ions of 60 keV were implanted into a-SiO₂ to a fluence of 1.0 × 10¹⁷ ions/cm². After the implantation, thermal annealing at 600 or 700 °C for 1 h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10-15 nm in diameter are formed in the depth region around the projected range. The size of the Zn nanoparticles increases after the annealing at 600 °C in oxygen gas. Annealing in oxygen gas at 700 °C for 1 h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO₂ substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10-25 nm in diameter inside the a-SiO₂. These results indicate that the oxidation at 700 °C for 1 h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids.     

Non–steady state solidification of superconducting oxides

The non–steady state solidification of RE123 (RE = Y, Nd) superconductive oxides was investigated by using an undercooling growth method. In both the Y– and Nd–systems, RE123 crystals grew steadily in the initial growth stage, but the growth rates decreased gradually in the later stage under the constant growth temperature. In the case of Nd–system, the substitution ratio of Hd/Ba in the grown Nd123 crystal was found to be gradually changed. The liquid compositions revealed that the liquid composition was close to the ternary equilibrium point after the growth rates decreased. This non-steady growth of Nd123 crystal is intrinsically caused since the composition of grown Nd123 solid solution is not on the 422–123 line and the residual liquid composition gradually shifts to the ternary equilibrium point to compensate for the mass balance during 123 growth. On the other hand, in the case of the Y–system, the evaluation of the volume fraction of Y211 particles showed that the volume fractions in the grown crystal were lower than those expected from the initial composition. On the contrary, those in liquid were higher and had similar valuesirrespective of the initial compositions and growth conditions. This accumulation of 211 phase particles near the 123/liquid interface would reduce the diffusion of the solute elements, which have the partition ratio of less than unity, away from the 123 interface. Therefore, such a large volumefraction would enhance the compositional shift close to the growth interface and cause locally a final transient to decrease the growth rate of the 123 crystal, if there is a compositional shift from the line connecting 123 and 211 compositions.     

基于小波变换的分形随机信号的卡尔曼滤波

本文基于多尺度卡尔曼滤波方法来估计淹没在加性高斯白噪声中的分形布朗运动.针对每一尺度,给出了相应的动态系统参数和运动模型方程以及更精确的估计算法.并与多尺度维纳滤波进行了对比,计算机仿真结果证明了其优越性.     

Time-dependent dielectric breakdown of SiO2 films in a wide electric field range

We have performed time dependent dielectric breakdown measurement of SiO₂ films in the electric field (E_OX) range 7–13.5 MV/cm and evaluated the electric field dependence of intrinsic lifetime, using both area and temperature dependences of oxide lifetime. We have evaluated the electric field dependence of time to breakdown (t_BD) below 125°C, because the activation energy of intrinsic lifetime changes at 125°C t_BD of 7.1 and 9.6 nm oxides is not proportional to exp(E_OX) but proportional to exp(1/E_OX). This suggests that the breakdown mechanism of 9.6 and 7.1 nm oxides is the same and adheres to the anode hole injection model. However, the breakdown mechanism of 4.0 nm oxides is not the same as that of 7.1 and 9.6 nm oxides. The slope of log(t_BD) versus 1/E_OX plot in 4.0 nm oxide increases with decreasing oxide fields. The intrinsic lifetime in the positive gate bias decreases with increasing oxide thicknesses in the range of electric fields employed in the present experiment.     

Dependence on the sample width of signals from a near-field optical microscope

We numerically investigated signals from a scanning near-field optical microscope (NOM) for samples of various sizes by using the finite-difference time-domain method. Under the usual conditions that apply to detection, the signal intensity depends on the width of the sample, even though the sample will be wider than the wavelength, which is much larger than the aperture, i.e., the lateral resolution of the NOM. This is an obstacle to measuring the local optical constant of samples by means of obtaining the signal intensity. When waves propagating in all directions are collected, this dependence on the sample width is reduced. The whole angle detection is important for observing the distribution of the optical constants.     

Development of thickness measurement program for transparent conducting oxide thin films

The gallium doped zinc oxide has been one of the candidates for the transparent conducting oxide thin film electrode. It is not suitable to use a conventional light interference method to measure the thickness of the gallium doped zinc oxide thin film because the refractive index and extinction coefficient of the thin film is unknown during the optimization of the deposition conditions. In this paper, we report on the details of the film thickness program which uses the measured optical and electric properties and relationship between the plasma frequency and the optical constant of the film. The obtained film thickness of the prepared gallium doped zinc oxide thin film using the program was comparable with thicknesses measured by a cross-sectional analysis of the atomic force microscopy and the surface profiler. Moreover, the optical constant of refractive index and extinction coefficient of the film could also be estimated.     

40-Gb/s ICs for future lightwave communications systems

This paper describes the device, circuit design, and packaging technologies applicable to 40-Gb/s-class future lightwave communications systems. A 0.1-μm gate InAlAs-InGaAs high electron mobility transistors (HEMTs) with InP recess etch stopper was adopted mainly for IC fabrication. Fabricated ICs demonstrate excellent data-multiplexing, demultiplexing, and amplifying operation at 10 Gb/s     

Capacity design and performance of call admission control incellular CDMA systems

Since code-division multiple-access (CDMA) capacity is interference limited, call admission control (CAC) must guarantee both a grade of service (GoS), i.e., the blocking rate, and a quality of service (QoS), i.e., the loss probability of communication quality. This paper describes the development of a new capacity design method based on these two concepts. Theoretical expressions for GoS and QoS as functions of traffic intensity and CAC thresholds are first derived from the traffic theory viewpoint, and then a design method using these expressions is presented. At that time, two strategies for CAC are assumed. One is based on the number of users, and the other is based on the interference level. Computer simulation results are presented that strongly support the proposed design method. Furthermore, numerical examples and a performance comparison of the two strategies considering various propagation parameters, nonuniform traffic distributions, and various transmission rates are shown