Enhanced Azidolysis by the Formation of Stable Ser–His Catalytic Dyad in a Glycoside Hydrolase Family 10 Xylanase Mutant

Glycoside hydrolases require carboxyl groups as catalysts for their activity. A retaining xylanase from Streptomyces olivaceoviridis E-86 belonging to glycoside hydrolase family 10 possesses Glu128 and Glu236 that respectively function as acid/base and nucleophile. We previously developed a unique mutant of the retaining xylanase, N127S/E128H, whose deglycosylation is triggered by azide. A crystallographic study reported that the transient formation of a Ser–His catalytic dyad in the reaction cycle possibly reduced the azidolysis reaction. In the present study, we engineered a catalytic dyad with enhanced stability by site-directed mutagenesis and crystallographic study of N127S/E128H. Comparison of the Michaelis complexes of N127S/E128H with pNP-X₂ and with xylopentaose showed that Ser127 could form an alternative hydrogen bond with Thr82, which disrupts the formation of the Ser–His catalytic dyad. The introduction of T82A mutation in N127S/E128H produces an enhanced first-order rate constant (6 times that of N127S/E128H). We confirmed the presence of a stable Ser–His hydrogen bond in the Michaelis complex of the triple mutant, which forms the productive tautomer of His128 that acts as an acid catalyst. Because the glycosyl azide is applicable in the bioconjugation of glycans by using click chemistry, the enzyme-assisted production of the glycosyl azide may contribute to the field of glycobiology.     

A method for estimating visceral fat from the elasticity of lumbar subcutaneous fat

Since metabolic syndrome is a cause of lifestyle-related diseases, and its early diagnosis and an evaluation of visceral fat are important, this study proposes a new method of estimating the amount of fat. The goal of this study is to estimate visceral fat from estimation of subcutaneous fat and total fat. The subcutaneous fat is estimated from the elasticity of the lumbar area, and the total fat is estimated from body information such as the abdominal vertical and lateral width, and body weight. Finally, the estimated subcutaneous fat is subtracted from the estimated total fat to calculate the visceral fat. Measurement tests conducted to verify the constructed visceral fat estimation model showed good results, with a correlation of 0.96 between the visceral fat area estimated by the proposed method and the actual measured area. The reproducibility of the estimation model was also verified by the cross validation method.     

Measuring System for Dynamic Characteristics of Semiconductor Switching Elements and Switching Loss of Thyristors

Thyristors today are used in various electrical apparatus where high operational reliability is of prime importance. For better operational reliability, it is essential that thyristors be used most effectively. It especially is important to predict quantitatively the thyristor's internal impedance (dynamic impedance) which varies by time and by switching loss as transiential stress is applied to the thyristor when it is turned-on and -off, and to design a thyristor circuit basing on the predicted dynamic impedance. This article introduces an outline of a measuring system which can be used for quantitative determination of dynamic characteristics of thyristors and discusses switching loss determined with the measuring system. The measuring system consists primarily of two A/D converters. Dynamic characteristics of a thyristor, either of a normal type or high-speed type, can be quantitatively measured in one turn-on or turn-off operation. This article also discusses the effect of variation of the element area of the thyristor on the switching loss.     

Analysis of abnormal grain growth of oriented LiCoO2 prepared by slip casting in a strong magnetic field

The relationship between the development of the crystallographic orientation and the grain growth behavior were studied. The degree of orientations of the green compacts and sintered samples were evaluated by the Lotgering factor. The f(0 0 l) of all the samples were drastically increased with the increasing applied magnetic field strength. The f(0 0 l) of the samples sintered at 1223 K were improved in comparison to those of the green compacts. However, the f(0 0 l) value of the samples sintered at 1273 K were not increased at 4 T or lower. To characterize the grain growth process, these samples were analyzed using electron backscatter diffraction (EBSD). The sintered samples prepared in the magnetic field at 4 T or lower showed abnormal grain growth. The samples with an applied magnetic field of 8 T or higher had no abnormal grain growth. It was revealed that the orientation angle of the particles has an effect on the grain growth.     

Exciton recombination dynamics in CdSe nanowires: bimolecular to three-carrier Auger kinetics

Ultrafast relaxation dynamics of charge carriers in CdSe quantum wires with diameters between 6 and 8 nm are studied as a function of carrier density. At high electron-hole pair densities above 10(19) cm(-3) the dominant process for carrier cooling is the "bimolecular" Auger recombination of one-dimensional (1D) excitons. However, below this excitation level an unexpected transition from a bimolecular (exciton-exciton) to a three-carrier Auger relaxation mechanism occurs. Thus, depending on excitation intensity, electron-hole pair relaxation dynamics in the nanowires exhibit either 1D or 0D (quantum dot) character. This dual nature of the recovery kinetics defines an optimal intensity for achieving optical gain in solution-grown nanowires given the different carrier-density-dependent scaling of relaxation rates in either regime.     

Crystallization and electrical characteristics of Ge1Cu2Te3 films for phase change random access memory

Phase change random access memory (PCRAM) requires an advanced phase change material to lower its power consumption and to enhance its data retention and endurance abilities. The present work investigated the crystallization behaviors and electrical properties of Ge₁Cu₂Te₃ compound films with a low melting point of about 500 °C for PCRAM application. Sputter-deposited Ge₁Cu₂Te₃ amorphous films showed a high crystallization temperature of about 250 °C. The Ge₁Cu₂Te₃ amorphous film showed an electrical resistance decrease of over 10²-fold and exhibited a small increase in thickness of 2.0% upon crystallization. The Ge₁Cu₂Te₃ memory devices showed reversible switching behaviors and exhibited a 10% lower power consumption for the reset operation than the conventional Ge₂Sb₂Te₅ memory devices. Therefore, the Ge₁Cu₂Te₃ compound is a promising phase change material for PCRAM application.     

Synchronous averaging for asynchronous sampling data

The progress of digital audio technology has enabled the familiar use of products such as CD and DAT in acoustic measurement. For example, a signal reproduced with a CD player is inputted into a subject for measurement and a DAT recorder records its response. However, the sampling cannot be synchronized completely with the input signal, although both nominal sample rates are set up equally, because the player and recorder work independently. The most popular solution is to use software to perform the synchronous addition after converting the recorded signal into the original sampling rate. However, the rate conversion also has an error due to the windowing in the high‐frequency region of the processed signal. This paper proposes a new method for averaging asynchronous sampling data to solve these problems. To evaluate performance, the transfer function of only measuring equipment estimated from asynchronous sampling data was compared with the measurement results in synchronous sampling conditions. Both results agreed within 0.1 dB, so the effectiveness of the new method was confirmed. In measuring the frequency response of a BPF when white noise is introduced, the proposed method was compared with the method using rate conversion. As a result, the noise reduction was almost the same, and the processing time was reduced to about one‐fourth. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(2): 33– 41, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20455     

A study on modeling methodology of oligopolistic virtual market and its application into resource allocation problem

Recently, manufacturing systems have become large scale and complex. The social scientific approach is one of the promising methods to facilitate effective operation for the resource allocation problems in manufacturing systems, since the approach takes an analogy of social systems which are optimal and robust in nature. In this paper, the authors first propose a modeling methodology for an oligopolistic virtual market, and develop an oligopolistic virtual market as an experimental model. Then they clarify several important characteristics of the oligopolistic virtual market by computer simulation experiments, and try to apply the proposed method into a utility computing operational problem to validate its effectiveness into resource allocation problems. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 77–85, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20628     

Development of the Measurement System of Image Rejection Ratio for the Sideband-Separating Receiver

We developed a measurement system of image rejection ratio for the sideband-separating receiver. This system comprises a horn moved by a motor slider, a harmonic mixer and a signal generator. We have installed the system on the Nobeyama 45-m millimeter telescope and compared the image rejection ratio measured by this system with that obtained from molecular line observations of celestial objects. We confirmed that we can measure image rejection ratio with an accuracy of ±10% with our system. By using the system, we can tune the applied bias voltage of mixer chips to the best performance of image rejection ratio and accurate calibration of the intensity of molecular line observations becomes possible. This is the first IRR measurement system developed for practical use with the 2SB receiver system.