Chemical reactions in cracks of aluminum crystals: Generation of hydrogen from water

Pure hydrogen is generated from water molecules which are dissociated by specific aluminum particles called activated Al powder. Reaction mechanism of Al atoms with H₂O molecules is investigated in micro-cracks of Al crystals. It becomes obvious that hydrogen atoms exist in Al crystal mainly in states of AlH₃ hydrides. It is concluded that virgin walls of micro-cracks right after the creation provide virtually Al radical atoms of (Al−) or (Al=) with one or two free bonds, which react with H₂O molecules via surface diffusion resulting in producing AlH₃ and eventually in producing H₂. The production of H₂ seems to be a result of micro-tribochemical reactions in cracks, which are produced by mechanical crushing of Al crystals in water; tips of cracks as stress-focused points play a major role to create AlH_3. Peculiar environments of nano-spaces in micro-cracks surrounded by reactive atoms enable us to realize unusual chemical reactions at low temperatures as exemplified in the present paper.     

On the high-resistivity contacts to YBa2Cu3O7 thin films, electrical behavior in the regime of high temperatures and high-bias voltages

We prepared in-situ Au contacts on high-quality epitaxial YBa₂Cu₃O₇ (YBCO) films. Very high specific contact resistivity values up to ∼10⁻² Ω cm² at 4.2 K were obtained on 12×5 μm² contact areas. This resistivity value decreased by two orders of magnitude as the temperature was raised to room temperature. In the temperature range T<200 K, the contacts showed non-ohmic behavior suggesting the presence of a well-defined insulating native Y-Ba-Cu-O barrier between the two electrodes. The electrical transport in this barrier layer was analyzed in the limit of high temperatures and high voltages to follow Mott's variable-range hopping conduction mechanism with physically reasonable parameters describing the localized states in the barrier. The high-resistivity contacts were tested successfully in quasiparticles injection experiments where the critical current I_c of the YBCO microbridge could be strongly suppressed on injection of an additional current through the contact into the superconducting channel.     

Equivariant quantization of orbifolds

Equivariant quantization is a new theory that highlights the role of symmetries in the relationship between classical and quantum dynamical systems. These symmetries are also one of the reasons for the recent interest in quantization of singular spaces, orbifolds, stratified spaces, etc. In this work, we prove the existence of an equivariant quantization for orbifolds. Our construction combines an appropriate desingularization of any Riemannian orbifold by a foliated smooth manifold, with the foliated equivariant quantization that we built in Poncin et al. (2009) [19]. Further, we suggest definitions of the common geometric objects on orbifolds, which capture the nature of these spaces and guarantee, together with the properties of the mentioned foliated resolution, the needed correspondences between singular objects of the orbifold and the respective foliated objects of its desingularization.     

Cooperative effect of La-doping and template on surface photoelectron characteristics of mesoporous nano-TiO2

A mesoporous La-doped nano-TiO₂ was prepared by the sol-gel method using polyethylene glycol as the template. A combination of surface photovoltaic (SPV) and photoacoustic technologies, aided by laser Raman technology, was used to probe the photoexcited charge transfer transition behaviors in the surface space charge region of the sample. The results confirm that the lanthanum doping was responsible for inhibiting the transformation from the anatase to rutile form and grain growth, thus strengthening the microstructure that was formed after removal of the template clearly. The experiment reveals that appropriate La-doping resulted in an obvious increase in the SPV response. By contrast, the remainder of the template had a somewhat negative effect on the SPV response of the samples. The effect of both the La-doping and the removal of the template on the nonradiative de-excitation process of the main band-gap can be negligible, in spite of the nonradiative de-excitation processes of the sub-band-gap of the La-undoped sample, in which the surface states possessed the donor characteristic, being more obvious than that of the La-doped samples. The results showed that the electron-phonon interactions on the surfaces resulting from the nonradiative de-excitation process were closely dependent on the effect of quantum confinement of the mesoporous nano-TiO₂.     

Study of solid-state reactions in Sm(Co,Fe, Cu,Zr)z 2:17-type alloys by means of in situ electrical resistivity measurements

In the present work, solid-state reactions in Sm₂(Co, Fe, Cu, Zr)₁₇-type alloys have been investigated by means of in situ electrical resistivity measurements. Changes in the electrical resistivity of a Sm(Co_0.74Fe_0.1Cu_0.12Zr_0.04)_8.5 alloy after solid solution treatment at 1190 °C, quenching to room temperature, and during isothermal ageing at temperatures between 400 and 900 °C, have indicated microstructural/phase changes occurring at temperatures below those commonly used for the development of high coercivity in Sm(Co, Fe, Cu, Zr)_z-type materials. Subsequent crystallographic and magnetic transition measurements have shown a high degree of correlation with respect to the changes observed in the electrical resistivity during isothermal ageing.     

Compact mid-infrared trace gas sensor based on difference-frequency generation of two diode lasers in periodically poled LiNbO3

3 (PPLN) crystal pumped by two single-frequency diode lasers. A maximum DFG power of 1.6 μW at 3.6 μm was generated with a pump power of 61.4 mW at 832 nm and a signal power of 41.5 mW at 1083 nm incident on a 19-mm-long PPLN crystal, which corresponds to a conversion efficiency of 335 μW W^-2 cm^-1. Received: 16 June 1998     

HBx介导的促肝癌作用

乙型肝炎病毒（Hepatitis B virus,HBV）感染是诱发原发性肝癌的主要原因之一.HBV存在4个相互重叠的开放读码框：S,C,P和X区.其中X基因表达的蛋白HBx被认为是诱导肝癌发生的一种多功能致癌蛋白,它可以作用于众多信号通路及细胞因子从而诱发肝癌.本文根据最新的研究,选择其中p53和NF-κB两条信号通路及HBx与表观遗传修饰的相关性进行了探讨,目的在于部分揭示HBV感染诱发肝癌的发病机理.     

Physical characterization of a new composition of oxidized zirconium-2.5 wt% niobium produced using a two step process for biomedical applications

Zirconium and particularly Zr-2.5 wt%Nb (Zr2.5Nb) alloy are useful for engineering bearing applications because they can be oxidized in air to form a hard surface ceramic. Oxidized zirconium (OxZr) due to its abrasion resistant ceramic surface and biocompatible substrate alloy has been used as a bearing surface in total joint arthroplasty for several years. OxZr is characterized by hard zirconium oxide (oxide) formed on Zr2.5Nb using one step thermal oxidation carried out in air. Because the oxide is only at the surface, the bulk material behaves like a metal, with high toughness. The oxide, furthermore, exhibits high adhesion to the substrate because of an oxygen-rich diffusion hardened zone (DHZ) interposing between the oxide and the substrate.In this study, we demonstrate a two step process that forms a thicker DHZ and thus increased depth of hardening than that can be obtained using a one step oxidation process. The first step is thermal oxidation in air and the second step is a heat treatment in vacuum. The second step drives oxygen from the oxide formed in the first step deeper into the substrate to form a thicker DHZ. During the process only a portion of the oxide is dissolved. This new composition (DHOxZr) has approximately 4-6 μm oxide similar to that of OxZr. The nano-hardness of the oxide is similar but the DHZ is approximately 10 times thicker. The stoichiometry of the oxide is similar and a secondary phase rich in oxygen is present through the entire thickness. Due to the increased depth of hardening, the critical load required for the onset of oxide cracking is approximately 1.6 times more than that of the oxide of OxZr. This new composition has a potential to be used as a bearing surface in applications where greater depth of hardening is required.     

Photoluminescence of patterned arrays of vertically stacked InAs/GaAs quantum dots

We report on photoluminescence measurements of vertically stacked InAs/GaAs quantum dots grown by molecular beam epitaxy on focused ion beam patterned hole arrays with varying array spacing. Quantum dot emission at 1.24 eV was observed only on patterned regions, demonstrating preferential nucleation of optically active dots at desired locations and below the critical thickness for dot formation at these growth conditions. Photoluminescence measurements as a function of varying focused ion beam irradiated hole spacing showed that the quantum dot emission intensity increased with decreasing array periodicity, consistent with increasing dot density.     

Solvothermal synthesis and characterization of CdSe nanocrystals with controllable phase and morphology

Zinc blende (ZB) CdSe hollow nanospheres were solvothermally synthesized from the reaction of Cd(NO₃)₂·4H₂O with a homogeneously secondary Se source, which was first prepared by dissolving Se powder in the mixture of ethanol and oleic acid at 205 °C. As Se power directly reacted with Cd(NO₃)₂·4H₂O in the above mixed solvents, wurtzite (W) CdSe solid nanoparticles were produced. Time-dependent experiments suggested that the formation of CdSe hollow nanospheres was attributed to an inside-out Ostwald ripening process. The influences of reaction time, temperature and ethanol/oleic acid volume ratio on the morphology, phase and size of the hollow nanospheres were also studied. Infrared (IR) spectroscopy investigations revealed that oleic acid with long alkene chains behaved as a reducing agent to reduce Se powder to Se²⁻ in the synthesis. Photoluminescence (PL) measurements showed that the ZB CdSe hollow nanospheres presented an obvious blue-shifted emission by 42 nm, and the W CdSe solid nanoparticles exhibited a band gap emission of bulk counterpart.