A novel PWM strategy to minimize the surge voltage forcurrent-source converters

This paper presents a novel technique of pulsewidth modulation (PWM) wave control to minimize the surge voltage at the turn-off of switching devices. Two kinds of sawtooth carriers with different hypotenuses are employed to obtain a PWM waveform with minimum surge voltage, where each sawtooth carrier appears alternately at every 60° interval relative to the sinusoidal wave cycle. It is difficult to analyze the output waveforms because they are complicated. In order to obtain the analytical result, a frequency analysis approach using a switching function is proposed the results of which are verified experimentally     

Simultaneous analysis of amino acids and carboxylic acids by capillary electrophoresis-mass spectrometry using an acidic electrolyte and uncoated fused-silica capillary

A simple, low-cost capillary electrophoresis-mass spectrometry (CE-MS) method is demonstrated for the simultaneous analysis of amino acids and small carboxylic acids (glycerate, lactate, fumarate, succinate, malate, tartrate, citrate, iso-citrate, cis-aconitate, and shikimate). All CE-MS experiments were performed using a single uncoated fused-silica capillary and with a single separation electrolyte, formic acid. For CE polarity, the CE inlet was set as the anode, and the MS side was set as the cathode. By using high-speed sheath gas flow, the apparent mobilities of all compounds were sped up; thus, the migration times of the carboxylic acids were reduced. In positive ion mode ESI-MS detection, small carboxylic acids were detected faintly as m/z = [M + 18](+) or [M + 23](+), after protonated molecule detection (m/z = [M + 1](+)) of the amino acids. In negative ion mode, all of these small carboxylic acids were detected clearly as deprotonated molecules (m/z = [M - 1](-)), after detection of the amino acids. By changing the polarity of the MS during CE separation, both amino acids and small carboxylic acids were detectable in a single electrophoresis analysis run. With this method, the diurnal metabolic changes of pineapple leaves were observed as reflecting Crassulacean acid metabolism.     

Effects of α-radiation on a direct disposal system for spent nuclear fuel – (2) review of research into safety assessments of direct disposal of spent nuclear fuel in Europe and North America

The Japanese geological disposal programme has started researching disposal of spent nuclear fuel (SF) in deep geological strata (hereafter “direct disposal of SF”) as an alternative management option other than reprocessing followed by vitrification and deep geological disposal of high-level radioactive waste (HLW). In the case of direct disposal of SF, the radioactivity of the waste is higher and the potential effects of the radiation are greater. Specific examples of the possible effects of radiation include: increased amounts of canister corrosion; generation of oxidizing chemical species in conjunction with radiation degradation of groundwater and accompanying oxidation of reducing groundwater; and increase in the dissolution rate and the solubility of SF. Therefore, the influences of radiation, which are not expected to be significant in the case of geological disposal of vitrified waste, must be considered in safety assessments for direct disposal of SF. Focusing especially on the effects of α-radiation in safety assessment, this study has reviewed safety assessments in countries other than Japan that are planning direct disposal of SF. The review has identified issues relevant to safety assessment for the direct disposal of SF in Japan.     

Inhibition of the growth of cariogenic bacteria in vitro by plant flavanones

Phytoalexins, defensive compounds produced by plants against microbial infections, were purified from Sophora exigua (Leguminosae) and their growth inhibitory effects on oral cariogenic bacteria were determined in vitro. Among three isolated compounds, 5,7,2',4'-tetrahydroxy-8-lavandulylflavanone completely inhibited the growth of oral bacteria including primary cariogenic mutans streptococci, other oral streptococci, actinomycetes, and lactobacilli, at concentrations of 1.56 to 6.25 micrograms/ml.     

Experimental studies on the thermal and hydraulic performance of the fuel stack of the VHTR: Part II. HENDEL multi-channel test rig with twelve fuel rods

Tests on heat transfer and fluid-dynamics of the mock-up fuel stack of the Very High Temperature Gas Cooled Reactor (VHTR) were performed by the multi-channel test rig (T_{1 - M}) of the Helium Engineering Demonstration Loop (HENDEL). The T_{1 - M} simulated one column of the fuel stack in the VHTR core and contained twelve simulated fuel rods. The heat generation rate of each fuel rod was varied to simulate the power distribution of the VHTR core in the horizontal plane. In parallel with this experiment, a three-dimensional thermal analysis code was developed in order to check the experimental temperature distribution of the fuel stack.Experimental results showed that the distribution of the helium gas flow rate was influenced by the temperature distortion in the mock-up fuel stack. The maximum deviation of the helium gas flow rate from the mean value was 10% in the case of an asymmetric power distribution test at a low Reynolds number. The variation of the calculated temperature distribution in the fuel stack was about 17-35°C in each case, indicating that the temperature distortion in the fuel stack was flattened by thermal conduction in the graphite block.     

Three-dimensional finite element analysis for prevailing torque of bolt-nut connection having slight pitch difference

Journal of Mechanical Science and Technology - In a vast industrial field, the bolt-nut connection is widely used and unitized as an important machine component. In order to improve safety and for...     

Spherical tokamak generation and merging on UTST using ex‐vessel poloidal field coils only

We successfully generated two spherical tokamaks (ST) at two null points by using ex‐vessel poloidal field (PF) coils only and succeeded in merging them. This scheme is called a double null merging (DNM) scheme. First, two pairs of ex‐vessel PF coils generate two null points where the poloidal field is zero at the upper and lower regions inside the vacuum vessel. Then a poloidal flux swing generates two STs at two null points, because the distance to the wall along the magnetic field is long at the null points. Finally, the coil currents push two STs toward the mid‐plane and merge them into a single ST. Since a magnetic reconnection during merging transforms magnetic energy into thermal energy, this merged ST plasma is expected to have a high beta. It must be noted that the DNM scheme generates an ST without a center solenoid coil. The DNM scheme was demonstrated on the TS‐3/4 (Japan) and MAST (UKAEA). However, these devices have all PF coils inside the vacuum vessels, and the initial plasmas were generated around the PF coils, not the null points. Since internal coils are not feasible in a fusion reactor due to high neutron flux, it is important to demonstrate the DNM scheme by using ex‐vessel PF coils. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(4): 18–24, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21254     

Enzymatic synthesis of myristoyl disaccharides and their surface activity

The condensation of trehalose, maltose, cellobiose, sucrose, turanose, palatinose, lactose and melibiose with myristic acid by a lipase (triacylglycerol acylhydrolase; EC 3.1.1.3) from Candida antarctica was examined at 60 °C in a mixture of pyridine and 2‐methyl‐2‐propanol (20/80 by vol.). The reactivity of trehalose was the highest among the tested disaccharides, and maltose and palatinose followed. Cellobiose and lactose were poor substrates for condensation. Condensation of all the disaccharides except for cellobiose and lactose with myristic acid was carried out at various initial disaccharide concentrations to estimate the initial reaction rate. Plots of the initial rates for monomyristoyl disaccharide formation versus the initial disaccharide concentration normalized by the solubility of the disaccharide in the mixture indicated that palatinose was the best substrate, and that trehalose, turanose and maltose were the next best ones. The surface activity of the monoacyl disaccharides scarcely depended on the type of disaccharide. Copyright © 2007 Society of Chemical Industry     

Video‐based analysis for facial skin appearance with automatic face tracking

In this article, a video‐based analysis for facial skin appearance with an automatic face tracking technique is proposed. The change of skin appearance under various illuminations is observed by illuminating the face from various light source positions, and the changes in facial appearance are recorded as a video stream during this measurement. The recorded video stream is then analyzed to obtain the bidirectional reflectance distribution function (BRDF) at each position of the facial skin. Automatic face tracking is necessary to compensate the facial movement in order to obtain an accurate BRDF measurement at each position. Since conventional face tracking techniques cannot be used for a face illuminated from various light source positions, a new face tracking technique that is robust to the various face shadings has been developed. Experimental studies show the effectiveness of both the proposed video‐based analysis technique and the automatic face tracking technique. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 477–484, 2008