Detection of characteristic signals from as-doped (<1 at.%) regions of silicon by transmission electron microscopy and convergent-beam electron diffraction

Characteristic signals were detected from As-doped (< 1 at.%) regions of silicon by dark-field transmission electron microscopy and convergent-beam electron diffraction. A slight intensity increase was observed in 220 dark-field images, which may be explained by an increase of scattering amplitude due to the As doping. The doped region showed a much higher intensity in 004 dark-field images. The characteristic high intensity was observed for specimens with As concentrations of about 0.09-0.8 at.%. Convergent-beam electron diffraction patterns obtained from the As-doped region showed a characteristic rocking curve for 004 reflection. These characteristics should originate from incoherent elastically scattered electrons due to a static lattice distortion around the doped As atoms. The observed characteristics in dark-field images and rocking curves of the 004 reflection should be a good probe not only for investigating the concentration of doped atoms in Si lattice, but also for the amount of impurity and/or point defects in other crystalline materials.     

A novel assay method for glycosphingolipid deacylase by enzyme-linked immunochemical detection of lysoglycosphingolipid

Lysoglycosphingolipids consist of a sphingoid long-chain base and monosaccharide or complex sugar, and they lack the fatty acyl group present in native glycosphingolipids. Less than 1 pmol of lyso-Forssman glycolipid and lysoganglioside GM1 were detected on a thin-layer chromatogram by an enzyme-linked immunochemical coloration method with anti-Forssman glycolipid antibody (FOM-1) and cholera toxin B subunit, respectively. Each spot between 1 and 100 pmol lyso-Forssman glycolipid was immunostained as densely as that of the same amount of native Forssman glycolipid. The density of the lyso-Forssman glycolipid spots increased proportionally with increment in the amount of lysoglycolipid. The density of spots of 0.2–100 pmol lysoganglioside GM1 was also proportional to the amount of each lyso-GM1 spot. These results indicated that less than 1 to 100 pmol of deacylated glycosphingolipid was quantifiable by the immunochemical coloration method with sugar chain-specific antibodies. Glycosphingolipid deacylase, which cleaved an amide bond between the sphingoid long-chain base and fatty acyl chain in ceramide of glycosphingolipid, was assayed by detecting the lyso-Forssman glycolipid produced. Lipophilic compounds, recovered from an aliquot of the reaction mixture of Forssman glycolipid and crude enzyme at appropriate times, were analyzed by thin-layer chromatography. It was found that lyso-Forssman glycolipid was produced in the first 1–2 h by the enzyme and production increased with incubation time. This coloration method is more sensitive and specific than the visualization method with a non-specific reagent such as orcinol-sulfuric acid reagent.     

Synthesis of the Bi-2222 Compounds of Bi–Sr–Ln(Zr)–Cu–O (Ln = Sm,Eu, Gd,and Dy)

Bi-based superconducting compounds with the 2222 structure has been already synthesized in the Bi₂Sr₂- (Ln_1−x Ce _x )₂Cu₂O_10+y (Ln = Sm, Eu, and Gd) systems. One of the characteristics of these compounds is the existence of the fluorite-like (Ln_1−x Ce _x )₂O₂ block between two CuO₅ pyramids in the crystal structure. The tetravalent ions of Ce⁴⁺ are reported to be necessary to stabilize the 2222 structure. Recently, we have discovered that the Bi-2222 phase could be composed in the Bi₂Sr₂(Ln_2−x Zr _x )Cu₂O _z (Ln = Sm, Eu, Gd, and Dy) systems, where Zr⁴⁺ is used as a new tetravalent ion stabilizing the 2222 structure in stead of Ce⁴⁺. In the new system, nearly single 2222 phase samples have been obtained at the nominal composition of x=0.5 (Ln = Sm, Eu, and Gd) and in the range of 0.1≤x≤0.3 (Ln = Dy). Among them, the sample with Ln = Gd has the smallest resistivity at 273 K. But it is a semiconductor, and the conduction process at low temperatures is assumed to be followed by a two-dimensional VRH. The experimental results for the Gd samples with a partial substitution of Pb for Bi in the Bi₂Sr₂(Gd_2−x Zr _x )Cu₂O _z system are also reported.     

A Bidirectional Isolated DC–DC Converter as a Core Circuit of the Next-Generation Medium-Voltage Power Conversion System

This paper describes a bidirectional isolated dc-dc converter considered as a core circuit of 3.3-kV/6.6-kV high-power-density power conversion systems in the next generation. The dc-dc converter is intended to use power switching devices based on silicon carbide (SiC) and/or gallium nitride, which will be available on the market in the near future. A 350-V, 10-kW and 20 kHz dc-dc converter is designed, constructed and tested. It consists of two single-phase full-bridge converters with the latest trench-gate insulated gate bipolar transistors and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive and control circuit losses from the whole loss. Moreover, loss analysis is carried out to estimate effectiveness in using SiC-based power switching devices. Loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc-dc converter. As a result, the overall efficiency may reach 99% or higher     

A New Neutral-Point-Clamped PWM Inverter

A new neutral-point-clamped pulsewidth modulation (PWM) inverter composed of main switching devices which operate as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential has been developed. This inverter output contains less harmonic content as compared with that of a conventional type. Two inverters are compared analytically and experimentally. In addition, a new PWM technique suitable for an ac drive system is applied to this inverter. The neutral-point-clamped PWM inverter adopting the new PWM technique shows an excellent drive system efficiency, including motor efficiency, and is appropriate for a wide-range variable-speed drive system.     

A decentralized control system for cooperative transportation by multiple non-holonomic mobile robots

In this paper, we propose a decentralized control system for transporting a single object by multiple non-holonomic mobile robots. Each agent used in the proposed system has two arms, which can steer around a joint offset from the centre point between two driving wheels. One of these mobile robots acts as a leader, who is assumed to be able to plan and to manipulate the omnidirectional motion of the object by using a resolved velocity control. Other robots, referred to as followers, cooperatively transport the object by keeping a constant relative position with the object using a simple PI control. Different from conventional leader–follower type systems that transport an object by multiple robots in coordination, the present followers can plan an action based on their local coordinate and need no absolute positional information. In addition, as a special case, a system consisting of only two robots is introduced, in which the follower robot not only has an arm length controller to follow the leader but also has a fuzzy controller as an avoidance controller to avoid obstacles or a posture controller to keep a desired posture of the object. Simulation results are given to demonstrate the good performance of the proposed systems.     

Vacuum seal for a rectangular flange

A new vacuum seal for a rectangular flange used in r.f. equipments, was developed. The vacuum seal consists of a recess with a flat surface, machined into a rectangular flange, a rectangular metal gasket with a raised projection on one face, and a mating flange with a recess and raised projection. No leak greater than 1 × 10⁻¹⁰ Pa m³/s was found in leak tests, before and after baking cycles (100 °C, 12 h).     

Polar-Polar Interaction and Boundary Phase Structure Between Reinforcement and Matrix in a Polymer Composite

This paper describes an attempt to correlate the nature of polar-polar interaction between the reinforcement and matrix in a polymer composite with the boundary phase structure formed in contact with the reinforcement. It is shown by analyzing the mechanical dispersion data that the reinforcement-matrix interaction of Kevlar fiber reinforced poly(hydroxypropyl ether of bisphenol A) (P) is increased by blending poly(ethylene oxide) (E) or poly(ethylene adipate) (A) as a part of matrix, and that E is more efficient than A for the increase of the interaction. These results can be supported at the molecular level from the inspection of the Fourier transform infrared spectra on the Kevlar fiber coated with matrix polymers and the mixture of matrix polymers with benzanilide, which is used as a model compound of Kevlar fiber. It can be shown from the electron spectroscopy for chemical analysis on the films of PIE and P/A blend polymers formed on nylon 6 substrate (N), which is also used as a model material for the reinforcement, that A concentrates on the N-facing side for P/A film and that E concentrates on the air-facing side for PIE film. This result indicates the different susceptibility between P/A and PIE blends to the surface force from N, and hence, it likewise indicates the different interaction with the reinforcement in each blend, as shown by the mechanical dispersion data.     

Amphiphilic Poly(Amino Acid) Nanoparticles Induce Size‐Dependent Dendritic Cell Maturation

Size‐regulated amphiphilic poly(amino acid) nanoparticles (NPs) composed of poly(γ‐glutamic acid) (γ‐PGA) and the hydrophobic amino acid derivative, L ‐phenylalanine ethyl ester (Phe) are prepared to evaluate the effects of particle size on dendritic cell (DC) uptake of NPs and their immune stimulatory activities as delivery carriers and adjuvants. The size of the Phe‐conjugated γ‐PGA NPs (γ‐PGA–Phe NPs) is easily controlled by regulating the aggregated γ‐PGA–Phe numbers. Each of the differently sized γ‐PGA–Phe NPs could efficiently encapsulate ovalbumin (OVA), and the amount of encapsulated OVA per milligram of NPs is almost the same despite the differences in size. The DC uptake of small NPs is lower than for the larger NPs, but the effect of DC activation by NPs is high in the small sizes. The DC activation is significantly affected by the size of the NPs, which suggests that not only the uptake process of the NPs, but also the surface interactions between the NPs and DCs, is important for the induction of DC maturation. The precisely size‐controllable γ‐PGA–Phe NPs have significant potential as an antigen carrier and vaccine adjuvant. These results should provide guidelines for adjuvant design in the development of an effective vaccine.     

Preparation of helical carbon and graphite films using morphology-retaining carbonization

Helical carbon and graphite films were prepared from iodine-doped helical polyacetylene (H-PA) film using currently developing morphology-retaining carbonization. It was found from scanning electron microscopy (SEM) observations that the hierarchical helical morphology of the H-PA film remains unchanged even after the carbonization at 800 °C. Besides, the weight loss of the film due to the carbonization was very small, which was only a few percent to the weight of the film before doping. Furthermore, the graphite film prepared by the subsequent heating at 2600 °C still retained the same morphology as those in the original H-PA film and in the helical carbon film prepared at 800 °C. X-ray diffraction (XRD) and Raman scattering measurements were then pursued. The results showed that graphitic crystallization proceeds in the carbon film through the heat treatment at 2600 °C. Transmission electron microscopy (TEM) image of a single helical graphitic fibril was also observed by ultrasonicating the graphite film in ethanol. Carbonization of the H-PA films by way of iodine doping was found to afford helical carbon and graphite films, where spiral morphologies and even helical fibril structures were completely preserved.