Structure and Reactions of an Isolable Ge=Si Doubly Bonded Compound,Tetra(<Emphasis Type="Italic">t</Emphasis>-butyldimethylsilyl)germasilene

Tetra(t-butyldimethylsilyl)germasilene (8b) was synthesized using di(t-butyldimethylsilyl)hydridogermyllithium prepared by the germa-metallation of the corresponding dihydridogermane. Tetrasilylgermasilene 8b was obtained as single crystals by recrystallization from hexane at rt. The molecular structure of 8b is similar to those of the corresponding disilene 8a and digermene 8c but with an intermediate unsaturated bond length and twist angle between those of 8a and 8c. The reactions of 8b with methanol and 2,3-dimethylbutadiene gave the corresponding adducts. Equilibrium between 8b and the corresponding (trisilylsilyl)(silyl)germylene is suggested by the reaction of 8b with triethylsilane giving the germylene insertion product into the Si–H bond.     

Fracture Model of Fine Bulk Powder Structures

ABSTRACT

Using several line powders (particle size 15-65 μ m). the rheological parameters of tensile strength ( σ_f,mb) and plastic deformation coefficient (Y) were experimentally measured at ambient and elevated temperatures. In order to be aeratable. the rheological parameters of a specific powder should satisfy the equation of σ_f,mb = 0.11Y^{0 89.}The formation of agglomerates or dead zones can be predicted. By introducing the “Quasi porous solid body model,” the theoretical derivation of the criterion characteristic curve was accomplished using solid fracture theory.     

Electrons on the Surface of Superfluid 3He

A review of recent investigations of transport properties of surface state electrons on superfluid ³He is given. The surface state electrons in this temperature region form the Wigner solid (WS), a triangular lattice of electrons with a typical lattice constant of 1 μm. The WS is accompanied with a shallow corrugation of He surface commensurate with the WS. A model is introduced to interpret the observed WS resistivity. The model takes into account specular quasiparticle (QP) reflection from the moderately corrugated free surface, and treats the QP as if it is a quasiclassical particle. After adopting anisotropic properties of superfluid ³He order parameter and QP energy, the model provides satisfactory account of the observed properties. Preliminary results of mobility measurements of ions trapped below superfluid ³He-B are also given.     

Evaluation of the change in chemical structure of acrylonitrile butadiene rubber after high-pressure hydrogen exposure

The influence of high-pressure hydrogen on the chemical structure of organic materials is essential for designing suitable materials for the safe and efficient use of hydrogen. In this paper, we clarify the cause and mechanism of “explosive failure by decompression” (XDF) in rubber used under high-pressure hydrogen circumstances, and the chemical structure of acrylonitrile butadiene rubber (NBR), which is commonly used for O-rings, was analyzed after exposure to hydrogen at 100 MPa. Solid-state nuclear magnetic resonance (NMR) and liquid-phase NMR for ¹H and ¹³C, as well as infrared and Raman spectroscopy, were employed for the evaluation. The results show no evidence of structural changes in NBR such as hydrogenation of the olefinic bonds in butadiene or of the cyano groups in acrylonitrile.     

Velocity measurements of reactive and non‐reactive flows by NO‐LIF method using NO2 photodissociation

Velocities of reactive and non‐reactive flows, where NO₂ molecules were seeded, were measured by a NO‐based Laser Induced Fluorescence (LIF) method. NO₂ dilute gases were injected from a round tube with an inner diameter of 2 cm and its flow rate was 10 liters/minute or 20 liters/minute. Experiments were performed for 4 conditions—non‐reactive flows of NO₂ dilute gases at two flow rates, an unburnt gas flow of the premixed flame with NO₂ addition, and an unburnt gas flow of the diffusion flame with NO₂ addition. NO molecules were produced in flows by planar emissions of 355 nm laser rays from an Nd:YAG laser system, and NO‐LIF images were taken in a pre‐determined delay. An ICCD camera, a dye laser excited by an excimer laser, and Nd:YAG laser were strictly synchronized by a pulse generator. NO‐LIF signals, which were emitted by photochemically produced NO from NO₂, were strong enough to measure the NO displacements in the case of non‐reactive flows, while with only a few ppm concentrations of NO₂ added it was possible to measure the velocity in detail. Although fluctuations of NO trajectories were observed at the flow rate of 20 liters/minute, instantaneous velocities were measured accurately. In the case of the unburnt gas of the diffusion flame, NO‐LIF signals were also strong, and profiles of NO produced by NO₂ photodissociation were clearly measured. Profiles of NO produced by NO₂ photodissociation in the unburnt gas of the premixed flame were also clearly measured, even in the vicinity of the reaction zone. It can be seen that velocities were measured correctly in the unburnt regions of the premixed and the diffusion flames. With this method, it was possible to measure velocities of both steady and unsteady flows. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(1): 40–52, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20038     

Hydrogen production by catalytic near-critical water gasification and steam reforming of glucose

Near-critical water gasification (NCWG) and steam reforming (SR) were investigated for the production of hydrogen from a biomass model compound (glucose) using fixed bed tubular reactor. Ruthenium/carbon and nickel/yttria stabilized zirconia (YSZ) were utilized to enhance the reaction rates of the two processes for NCWG and SR, respectively. NCWG experiments were performed at 200 bar and 360–450 °C, while SR experiments were conducted at 500–800 °C and atmospheric pressure. Although in both cases complete carbon gasification is achieved, gas composition, hydrogen selectivity and overall energy efficiency show strong dependencies on the type of process itself and the associated operating conditions. It is shown that operating the reforming reaction of glucose at high pressures and low temperatures (NCWG) results in a significant amount of methane and trace amounts of carbon monoxide. In contrast, gasification of glucose at atmospheric pressures and high temperatures (SR) leads to a methane-free gas stream that contains few percents of carbon monoxide. Considering energy recovery and neglecting the heat losses, the maximum cold gas efficiency of the NCWG and SR reached 78% and 91%, respectively. The features of the two catalytic reaction processes are discussed in terms of the experiments and process simulations.     

Effect of metal ion location in reaction medium on formation process and structure of PtCu–CuO nanoparticles supported on carbon and γ-Fe2O3

The process of nanoparticle formation by radiochemical synthesis in a heterogeneous system has been investigated considering the effects of the metal ion location in the reaction medium. PtCu nanoparticles supported on carbon and γ-Fe₂O₃ were synthesized using a high-energy electron beam. The metal ions in the precursor were categorized as those dissolved in solution, adsorbed on support, and precipitated. The ratio of metal ions in the solution was varied prior to the electron beam irradiation and its effects on the synthesized particle structures were examined. The nanoparticles were characterized by inductively coupled plasma-atomic emission spectrometry, transmission electron microscopy, X-ray diffraction, and X-ray absorption spectroscopy. A PtCu alloy and CuO were immobilized on the support in all the samples. The PtCu alloy nanoparticle composition depended on the Cu ion content in the solution. The nanoparticle formation mechanism could be explained using the obtained results. Metal ions present in the solution resulted in formation of the alloy. The adsorbed ions also contributed to the alloy formation by desorbing from the support when irradiated. On the other hand, alloy formation with Pt from the precipitated Cu ions was found to be difficult.     

Aluminium content in foods with aluminium-containing food additives

The aluminium (Al) content of 105 samples, including bakery products made with baking powder, agricultural products and seafoods treated with alum, was investigated. The amounts of Al detected were as follows (limit of quantification: 0.01 mg/g): 0.01-0.37 mg/g in 26 of 57 bakery products, 0.22-0.57 mg/g in 3 of 6 powder mixes, 0.01-0.05 mg/g in all three agricultural products examined, 0.03-0.90 mg/g in 4 of 6 seafood samples, 0.01-0.03 mg/g in 3 of 11 samples of instant noodles, 0.04-0.14 mg/g in 3 of 4 samples of vermicelli, 0.01 mg/g in 1 of 16 soybean products, but none in soybeans. Amounts equivalent to the PTWI of a 16 kg infant were detected in two samples of bakery products, two samples of powder mixes and one sample of salted jellyfish, if each sample was taken once a week. These results suggest that certain foods, depending on the product and the intake, might exceed the PTWI of children, especially infants.     

Ultrafast optical and magneto-optical studies of III–V ferromagnetic semiconductors

Abstract

We use ultrafast optical techniques to investigate the dynamics of charge and spin carriers and coherent phonons as well as magnetic order in III-V ferromagnetic semiconductors. We observe a rich array of dynamical phenomena that are absent in traditional nonmagnetic semiconductors or metallic ferromagnets. Very short charge and spin lifetimes of the photoinjected carriers (～2ps) and multi-level charge decay dynamics are observed, which are attributed to a large density of mid-bandgap states introduced during low temperature molecular beam epitaxy (LT-MBE) growth and highly p-type Mn doping. During the very short free carrier lifetime, the coercivity of the system is seen to be reduced. We attribute this photo-induced ‘softening’ to the transient modification of carrier-mediated ferromagnetic exchange coupling between Mn spins. After the photogenerated free electrons are trapped by defects, periodic oscillations appear in differential reflectivity due to the coherent generation of acoustic phonon wavepackets.