Comparative study of elastic scattering of low-energy electrons, positrons and protons in solids

The differential cross section (DCS) and total cross section (TCS) for elastic scattering of 0.1 eV–1 keV electrons, positrons and protons by atoms bound in solids (Z = 3–82) are calculated using the partial wave expansion technique. The DCS for low-energy positrons decreases in the forward direction due to the cancellation of the electrostatic interaction by the polarization of the atom. This cancellation effect for positrons results in a much smaller TCS than that for electrons at low energy, whereas, at high energy, they are close to each other due to dominant electrostatic interaction. The DCS for protons shows a strong forward scattering. This results in a TCS much greater than that for positrons, whereas, for large angles, the DCS is equal to that of positrons (except for very low energy).     

Identification of three core regions essential for protein splicing of the yeast Vma1 protozyme. A random mutagenesis study of the entire Vma1-derived endonuclease sequence

The translation product of the VMA1 gene of Saccharomyces cerevisiae undergoes protein splicing, in which the intervening region is autocatalytically excised and the franking regions are ligated. The splicing reaction is catalyzed essentially by the in-frame insert, VMA1-derived endonuclease (VDE), which is a site-specific endonuclease to mediate gene homing. Previous mutational analysis of the splicing reaction has been concentrated extensively upon the splice junctions. However, it still remains unknown which amino acid residues are crucial for the splicing reaction within the entire region of VDE and its neighboring elements. In this work, a polymerase chain reaction-based random mutagenesis strategy was used to identify such residues throughout the overall intervening sequence of the VMA1 gene. Splicing-defective mutant proteins were initially screened using a bacterial expression system and then analyzed further in yeast cells. Mutations were mapped at the N- and C-terminal splice junctions and around the N-terminal one-third of VDE. We identified four potent mutants that yielded aberrant products with molecular masses of 200, 90, and 80 kDa. We suggest that the conserved His362, newly identified as the essential residue for the splicing reaction, contributes to the first cleavage at the N-terminal junction, whereas His736 assists the second cleavage by Asn cyclization at the C-terminal junction. Mutations in these regions did not appear to destroy the endonuclease activity of VDE.     

A 43-Gb/s full-rate-clock 4:1 multiplexer in InP-based HEMT technology

This paper describes a full-rate-clock 4:1 multiplexer (MUX) in a 0.13-/spl mu/m InP-based HEMT technology for 40-Gb/s and above optical fiber link systems. To reduce output jitter, the serialized data are retimed at the final stage by a retimer, a D-type flip-flop, which has a symmetric layout with an optimized spacing to the ground that minimizes coupling capacitances. A phase adjuster, composed of an exclusive OR and a delay switch, uses external control signals to change each phase of the serialized data and clock entering the retimer and gives a correct timing for the clock to drive the retimer. A clock distributor with a simple wired splitter divides the clock into two clocks with high gain and low current. The MUX integrates 1355 HEMTs formed using electron beam lithography. A chip mounted in a test module operated at up to 47 Gb/s with a power consumption of 7.9 W for a single supply voltage of -5.2 V.     

High power with low electric power consumption activemulti-mode-interferometer laser diode for fibre-amplifier

Active multi-mode interferometer laser diodes (LDs), implemented in InGaAsP/InP, achieved a significant reduction of 40% (at 0.4 W output) in electric power consumption compared to regular single lobe LDs. With them, a high output power of 0.7 W was also obtained at 14XX nm     

Development of a shrouded wind turbine with a flanged diffuser

We have developed a wind turbine system that consists of a diffuser shroud with a broad-ring flange at the exit periphery and a wind turbine inside it. The flanged-diffuser shroud plays a role of a device for collecting and accelerating the approaching wind. Emphasis is placed on positioning the flange at the exit of a diffuser shroud. Namely, the flange generates a low-pressure region in the exit neighborhood of the diffuser by vortex formation and draws more mass flow to the wind turbine inside the diffuser shroud. To obtain a higher power output of the shrouded wind turbine, we have examined the optimal form of the flanged diffuser, such as the diffuser open angle, flange height, hub ratio, centerbody length, inlet shroud shape and so on. As a result, a shrouded wind turbine equipped with a flanged diffuser has been developed, and demonstrated power augmentation for a given turbine diameter and wind speed by a factor of about 4-5 compared to a standard (bare) wind turbine. In a field experiment using a prototype wind turbine with a flanged diffuser shroud, the output performance was as expected and equalled that of the wind tunnel experiment.     

Microstructures formed by secondary growth of fired ZSM-5 seed crystals

Oriented ZSM-5 seed crystals on an α-Al₂O₃ porous substrate were hydrothermally treated in a raw sol. The ZSM-5 membranes were fabricated via secondary growth of the seed crystals. For some samples, the seed-applied substrate was fired at 300 or 600 °C before the secondary growth in order to enhance adhesion between the substrate and the seed crystals. The influence of the firing on the subsequent secondary growth of the seed crystals was examined by XRD, SEM, and TEM. The TEM images of the sample fired at 300 °C showed that the resulting membrane was continuous, and in the membrane, large ZSM-5 particles were distributed in a porous matrix. The ZSM-5 particles were slightly smaller than the used seed crystals. HR-TEM observations showed that the porous matrix is comprised of ZSM-5 micro-crystals, and the part adjacent to the large ZSM-5 crystals has the same crystallographic orientation as the large crystals. The TEM images of the sample fired at 600 °C showed that the resulting layer is comprised of particles with a core-shell structure. The core consisted of ZSM-5 micro-crystals, whereas the shell was composed of large ZSM-5 rod-like crystals. It is inferred that the formation of these interesting microstructures is related to the degradation of the template agent, NPr₄OH, in the seed crystals by firing at 300 and 600 °C. The part including no template is dissolved by a hydrothermal treatment, and the dissolved species is re-crystallized via reaction with a template agent in the used raw sol, resulting in the formation of interesting microstructures.     

Silicalite-l Synthesis from Silicate Aqueous Solutions Including Amines as a Base

Aqueous silicate solutions could be prepared from a silicon alkoxide using amines as a base. The synthesis of silicalite-1 conducted by hydrothermally treating the solutions after the addition of NPrⁿ₄Br (TPABr), was examined focusing on triethylamine (NEt₃) as the amine. The aqueous solutions with chemical compositions of Si(OEt)₄ (TEOS) : NEt₃ : TPABr : H₂O = 1 : ≥0.5 : ≥0.8 : 200 led to silicalite-1 crystallization upon hydrothermal treatment at 130C for 4 days. The resulting crystals had a small thin coffin shape. With increasing the added amounts of NEt₃ and TPABr, the crystal size decreased. Among the investigated conditions, the smallest silicalite-1 crystal measuring about 1.0 × 0.7 × 0.4 um was obtained at starting compositions of NEt₃/TEOS ≥2.0 and TPABr/TEOS ≥3.2. The increase in the TPA content of the starting solutions accelerated the crystal nucleation of silicalite-1, so that the obtained crystals became smaller. During the hydrothermal synthesis, an amorphous silica gel was formed before the crystallization commenced. The increase in the NEt₃ content may suppress the formation of the silica gel, and/or facilitate its dissolution, thereby the supersaturation degree of silicate species in the solution was increased, giving small silicalite-1 crystals. When an aqueous suspension of the smallest silicalite-1 crystals was spread onto a glass substrate by a dip-coating method, an ordered mono-grain layer of the silicalite-1 crystals oriented with the straight channels normal to the substrate surface was obtained.     

Involvement of actin and polarisome in morphological change during spore germination of Saccharomyces cerevisiae

We studied the morphological changes of Saccharomyces cerevisiae ascospores during germination. Initiation of germination is followed by polarization of actin patches, maintaining their localization to the site of cell surface growth. Loss of polarisome components, Spa2p, Pea2p, Bud6p or Bni1p, results in depolarization of actin patches. Green fluorescent protein-fused polarisome components exhibit the polarized localization, implying that polarisome is involved in the polarized outgrowth during germination. At the late stage of germination, we found that actin patches temporally depolarize before bud emergence. The observation that loss of Cla4p extends the polarized growth period suggests that Cla4p is involved in the actin-depolization step. Actin polarization in the initial stage is accelerated by overexpression of Ras2p, whereas hyperpolarization is continuously observed by overexpression of Rho1p. Thus, yeast spore germination is a morphological event that is regulated by a number of factors implicated in mitotic bud morphogenesis.     

Spectral linewidth and resonant frequency characteristics ofInGaAsP/InP multiquantum well lasers

The spectral linewidth and resonant frequency characteristics of 1.3-μm InGaAsP/InP multi-quantum-well lasers grown by liquid-phase epitaxy were investigated and compared to those of the conventional double heterostructure (DH) lasers. A decrease in spectral linewidth and an increase in resonant frequency f_r with decreasing well thickness were observed. Moreover, the linewidth enhancement factor α was reduced to ~2 for well thicknesses of less than ~200 Å, while that of the DH laser was ~6. An f_r of 9 GHz, which is twice as large as that of conventional DH lasers, was achieved at an optical power of 5.3 mW/facet