Growth mechanisms for atypical forms of silicon nanowires

An investigation was carried out into the growth mechanisms for atypical forms of silicon nanowires (Si-NWs) synthesized using a vapor-liquid-solid growth process assisted by hydrogen radicals. Sn or Au nanoparticles, which act as catalysts during Si-NW growth, were produced by hydrogen radical treatment of Sn or Au thin films covering a silicon substrate. The Si-NWs were synthesized from silane gas excited by hydrogen radicals in the presence of these nanoparticle catalysts. In addition to normal Si-NW structures, atypical forms such as tapered, branched, bent, corrugated and block types, were synthesized. The growth of tapered, branched and bent-type Si-NWs was caused by contraction of the catalytic nanoparticles, adhesion of nanoparticles to the side wall of growing Si-NWs, and non-uniform supersaturation of the nanoparticles with Si, respectively. Growth of corrugated- and block-type Si-NWs was induced by an excess supply of Si atoms to the growing Si-NWs.     

MICROSOLIDIFICATION PROCESS IN MULTICOMPONENT SYSTEM

In conventional solidification of multicomponent mixtures, a mushy zone appears between the pure solid and liquid regions and promotes stable solidification by accepting the rejected solute regionally. From the standpoint that the fineness of inhomogeneity influences the mechanical properties in material processing, the linking of macro heat transfer and microsolidification in the mushy zone was studied. First, the crystal growth and its accompanying concentration field near the advancing front of the mushy zone were observed precisely by using the light absorption method. It was clarified that the mushy zone consisted of the leading front in which the frame structure formed with an accompanying concentration boundary layer and a growing region where the solidification proceeds by fattening of the crystals. Second, the mechanism of side-branch evolution was studied in conjunction with interfacial instability due to constitutional supercooling and curvature supercooling around the primary arm surface. Summarizing these results, the microsolidification process is discussed quantitatively in relation to macro heat transfer.     

Effect of TiO2 nanoparticles aggregation in silicate thin coating films on photocatalytic behavior for antifouling materials

Two types of disperser namely, a high speed agitation bead mill and a colloidal mill, were used for the dispersion behavior control of TiO₂ nanoparticles (20 nm in average primary diameter) in an aqueous suspension. A composite thin film raging in thickness from 90 to 400 nm was prepared from the coating suspension following the addition of a commercial ethyl silicate oligomer binder into the prepared suspension by means of a spray coating method. The mean aggregate size of TiO₂ nanoparticles in the aqueous suspension was found to be 80 nm and 290 nm in diameter, respectively, when using the agitated bead and colloidal milling methods. Large aggregates on the order of several hundred nanometers were found to remain in the suspension after colloidal milling. Further, a fine dispersion of TiO₂ nanoparticles in the thin film produced using the agitation bead milling process promoted the photocatalytic activity and enhanced transparency of the film for visible light. The aggregate structure of TiO₂ nanoparticles in an aqueous suspension was well maintained in the film prepared by a spray coating process.     

Linearity performance comparison of cascode current source and single-device current source IDPs; analyses,simulations and measurements

The input differential pair (IDP) is usually a major source of nonlinear distortion in any op-amp. This is especially true if the input signal has a large common-mode component, as is the case when an op-amp functions as a unity-gain buffer or as part of a single-ended sample-hold (S/H) circuit. In this paper, we analyse the distortion of the commonly used cascode current source IDP structure and explain the sources of its nonlinear behaviour. Next, a special design technique is proposed which enhances the linearity of IDPs. The circuit uses a single device current source that has the same channel length while its width is double those of IDP devices. Theoretical analysis, as well as simulation and experimental results, is given to confirm the improved linearity of a unity gain buffer. Simulations predict improvements up to 20 dB. 15 dB total harmonic distortion (THD) reduction was also achieved for a 15 MHz input signal based on measurement of a test chip. The method is valuable as power supply voltages shrink, and the design offers extra voltage headroom at input.     

Peak identification of L X-ray spectra of elemental Np and U

The L X-ray photons emitted by transuranic (TRU) elements are expected to be useful for developing nondestructive TRU monitors. Energy spectra of L X-rays emitted by ²⁴¹Am, ²³⁸Pu and ²³⁹Pu sources were measured by a transition edge sensor (TES) microcalorimeter, which allowed precise peak identification with high energy resolution. In the measurements using the TES microcalorimeter, the full width at half-maximum energy resolution was 62.6 eV at 17.222 keV for ²³⁹Pu source, 62.5 eV at 17.222 keV for ²³⁸Pu source and 60.9 eV at 17.751 keV for ²⁴¹Am source. This study demonstrates the separation of ²⁴¹Am and plutonium isotopes by L X-ray spectroscopy using a TES microcalorimeter.     

Operating results and simulations on a fuel cell for residential energy systems

This paper describes the performance evaluation of a polymer electrolyte fuel cell (PEFC) prototype and demonstration experiments of the electric power and domestic hot water system using it from a pragmatic view-point. Three types of demonstration experiments were carried out applying standard electric power and hot water demands. It was shown that the primary energy reduction rate of this system as compared to the conventional system reached up to 24% under double daily start and stop (DSS) operation. The amount of primary energy reduction in experiments using the energy demand of a household in Sapporo in winter exceeded the experimental results of the standard energy demand, demonstrating that the effects of the introduction of a fuel cell in cold regions could be considerable, in particular, during the winter season.     

Promotion of allergic immune responses by intranasally-administrated nanosilica particles in mice

With the increase in use of nanomaterials, there is growing concern regarding their potential health risks. However, few studies have assessed the role of the different physical characteristics of nanomaterials in allergic responses. Here, we examined whether intranasally administered silica particles of various sizes have the capacity to promote allergic immune responses in mice. We used nanosilica particles with diameters of 30 or 70 nm (nSP30 or nSP70, respectively), and conventional micro-sized silica particles with diameters of 300 or 1000 nm (nSP300 or mSP1000, respectively). Mice were intranasally exposed to ovalbumin (OVA) plus each silica particle, and the levels of OVA-specific antibodies (Abs) in the plasma were determined. Intranasal exposure to OVA plus smaller nanosilica particles tended to induce a higher level of OVA-specific immunoglobulin (Ig) E, IgG and IgG1 Abs than did exposure to OVA plus larger silica particles. Splenocytes from mice exposed to OVA plus nSP30 secreted higher levels of Th2-type cytokines than mice exposed to OVA alone. Taken together, these results indicate that nanosilica particles can induce allergen-specific Th2-type allergic immune responses in vivo. This study provides the foundations for the establishment of safe and effective forms of nanosilica particles.     

亚硝酸钙阻锈剂的应用研究综述

阐述了亚硝酸钙对新鲜和硬化混凝土性质的影响,分析了亚硝酸离子对混凝土主钢筋腐蚀的阻锈机理,并总结了亚硝酸离子在不同混凝土环境下的阻锈效果,为亚硝酸钙阻锈剂的工程应用提供了理论基础和技术支持.     

Minichromosome formation in Chlorella cells irradiated with electron beams

Three minichromosomes, miniP7, miniB7, and miniK4 of 800 kbp, 450 kbp, and 550 kbp, respectively, were obtained from Chlorella vulgaris chromosome I by electron-beam irradiation. Two of them were structurally characterized: MiniP7 was formed by the deletion of an internal 180 kbp close to the right end of chromosome I. The 180-kbp region with a small interspersed nuclear element (SINE)-like element on its left terminus was translocated to another chromosome, leaving a footprint-like structure on miniP7. MiniB7 was a hybrid of chromosome I and another chromosome, retaining the left telomere and the centromere of chromosome I. The centromeric repetitive elements served as a rearrangement point in the miniB7 formation. These examples showed the complicated mechanisms involved in the minichromosome formation. The minichromosomes thus obtained can be useful for isolating the fundamental structural elements of a chromosome. Moreover, they may serve as starting materials or a vector to generate artificial chromosomes carrying useful genes.     

Enhanced enzyme activity and enantioselectivity of lipases in organic solvents by crown ethers and cyclodextrins

Lipases from Candida rugosa (CRL) and Pseudomonas cepacia (PCL) were co-lyophilized with cyclic oligoethers including four crown ethers and nine cyclodextrins (CyDs), and their transesterification activity and enantioselectivity in organic solvents were evaluated. The PCL co-lyophilized with each additive showed simultaneously enhanced enzyme activity and enantioselectivity when compared to the native lipase lyophilized from buffer alone; in contrast, such enhancement was not observed for the co-lyophilized CRL. Among the cyclic oligoethers examined, permethylated betaCyD (Me1.78betaCyD), as the most suitable additive, was used for the optimization of both the co-lyophilized PCL preparation and reaction conditions by determining the effects of varying the additive/lipase ratio, aqueous pH, the nature of organic solvents, and temperature. The initial rate determined for the transesterification between racemic 2,2-dimethyl-1,3-dioxolane-4-methanol and vinyl butyrate in diisopropyl ether at 30 degrees C increased by up to 17-fold and the enantioselectivity represented by E could be doubled. While there was an inverse correlation between temperature and enantioselectivity, with the Me1.78betaCyD-PCL co-lyophilizate, the reaction rate even at 0 degrees C was much higher than that at higher temperatures in the native PCL-catalyzed reaction. Hence, this method seems to be of practical use for the large-scale production of optically active compounds.