Characterization of Natural Chromite Samples from Ophiolite Complexes in the Philippines by 57Fe Mössbauer Spectroscopy

Mössbauer spectroscopy was applied to natural chromite samples from ophiolite complexes in the Philippines. Chemical and structural characterization of the chromite samples was also carried out using X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and X-ray fluorescence spectrometry (XRF). The Mössbauer spectra of the samples consisted of quadrupole doublets ascribable to Fe³⁺ in octahedral site, Fe³⁺ in tetrahedral site, and Fe²⁺ in tetrahedral site. The relative percentage of Fe³⁺ and Fe²⁺ ions suggested that these Philippine samples were formed under relatively high oxygen fugacity.     

在6H-SiC衬底上用低压MOVPE法生长AlN和GaN的过程中用(AlN/GaN)多层缓冲层来控制残余应力

人们已提出用BAlGaN四元系材料制备紫外光谱区的光发射器件.GaN和AlN二元系是这种四元材料在器件应用中的基础材料.6H-SiC衬底在氮化物生长中因其晶格失配小是一大优势,而且SiC衬底的热膨胀系数也和AlN的很接近.然而,对于AlN外延层来说,需要控制其中的残余应力,因为在SiC衬底上直接生长的AlN外延层中存在着因晶格失配所产生的压缩应力.另一方面,在SiC衬底上直接生长的GaN外延层中存在着拉伸应力.这种拉伸应力起源于GaN比衬底有着更大的热膨胀系数.本文讨论了在6H-SiC衬底上生长的氮化物外延层中残余应力的类型、数量及控制.为此目的,提出了在6H-SiC衬底上,无论是生长AlN,还是生长GaN,都可以采用(GaN/AlN)多层缓冲层的办法,作为控制残余应力的有效方法.我们还讨论了AlN和GaN外延层的结晶质量和残余应力间的关系.     

Enhancement in age hardenability of sintered Ti–5Fe alloy by Zr addition processed by pulsed electric current sintering

The age-hardenable Ti–5Fe–5Zr (wt. %, 5Zr) alloy has been consolidated by pulsed electric current sintering, following a β solution treatment, and the results are compared with a Ti–5Fe (0Zr) alloy. The precipitation sequence measured at 640°C ageing is β?+?athermal ω?→?β?+?isothermal ω?→?β?+?α. At the peak hardness isothermal ω phase forms at 20?s of ageing. The Zr addition retards the precipitation kinetics of the α phase; as a result, the α phase nucleates at latest at 300?s ageing in the overaged state. Fe is partitioned into β, while it is depleted from the α phases. There is Zr enrichment near the α/β interface when the α phase precipitates due to a solute drag effect; the growth rate of the α phase in the 5Zr alloy is significantly reduced compared with that in the 0Zr alloy.     

Spin-projected QM/MM Free Energy Simulations for Oxidation Reaction of Guanine in B−DNA by Singlet Oxygen

Guanine is the most susceptible base to oxidation damage induced by reactive oxygen species including singlet oxygen (¹O₂, ¹Δ_g). We clarify whether the first step of guanine oxidation in B−DNA proceeds via either a zwitterionic or a diradical intermediate. The free energy profiles are calculated by means of a combined quantum mechanical and molecular mechanical (QM/MM) method coupled with the adaptive biasing force (ABF) method. To describe the open-shell electronic structure of ¹O₂ correctly, the broken-symmetry spin-unrestricted density functional theory (BS−UDFT) with an approximate spin projection (AP) correction is applied to the QM region. We find that the effect of spin contamination on the activation and reaction free energies is up to ∼8 kcal mol⁻¹, which is too large to be neglected. The QM(AP−ULC−BLYP)/MM-based free energy calculations also reveal that the reaction proceeds through a diradical transition state, followed by a conversion to a zwitterionic intermediate. Our computed activation energy of 5.2 kcal mol⁻¹ matches experimentally observed range (0∼6 kcal mol⁻¹).     

Enantioselective synthesis of (−)-elenolic acid and (−)-ajmalicine

A secoiridoid monoterpene (?)-elenolic acid and a representative heteroyohimbine alkaloid (?)-ajmalicine have been synthesized enantio- and stereoselectively using L-ethyl lactate as a chiral starting material.     

Isolation, identification and pharmacological studies on three toxic metabolites from a mushroom, Hebeloma spoliatum.

Three metabolites, tentatively named HS-A, -B and -C, were isolated from a mushroom, Hebeloma spoliatum, as the fatal toxic principles to mice. HS-A was identified as 3-acetyl-2-(3'-hydroxy-3'-methyl)glutarylcrustulinol, which has been isolated from Hebeloma crustuliniforme and H. sinapizans as a cytotoxic principle. HS-B and -C were deduced to be 3,21-diacetyl-2-(3'-hydroxy-3'-methyl)glutarylcrustulinol and 3-acetyl-2-(3'-hydroxy-3'-methyl)glutarylanhydrocrustulinol, respectively, from their chemical and spectral data. Intraperitoneal administration of HS-A, -B and -C at a dose of 100 mg/kg caused death after paralysis of the limbs in mice. The compounds caused relaxation of mouse small intestine contracted by acetylcholine chloride or barium chloride treatment in vitro. They appear to exhibit a papaverine-like relaxation effect.     

Statistical manifolds with almost contact structures and its statistical submersions

In this paper, we discuss statistical manifolds with almost contact sturctures. We define a Sasaki-like statistical manifold. Moreover, we consider Sasaki-like statistical submersions, and we study Sasaki-like statistical submersion with the property that the curvature tensor with respect to the affine connection of the total space satisfies the condition (2.12).     

Fast polarimetry system for the application to spin quantum non-demolition measurement

We report the development of a fast pulse polarimeter for the application to quantum non-demolition measurement of atomic spin (spin QND). The developed system was tunable to the atomic resonance of a ytterbium atom and has narrow laser line width suitable for spin QND. Using the developed polarimeter, we successfully demonstrated the measurement of the vacuum noise, with 10⁶ to 10⁷ photon number per pulse. PACS 42.25.Ja; 42.50.Lc; 42.55.Px     

Positron annihilation in synthetic zeolites

Both lifetime and angular correlation of positron annihilation have been measured for a series of synthetic zeolites for which the void structures are known fairly well. All of the zeolites had long lifetime components and a narrow momentum component which are ascribable to o-Ps and p-Ps annihilations in the voids, respectively. The correlation between the width of the p-Ps narrow component and the size of the largest voids showed a remarkable agreement with a theoretical estimate based on the spherical potential well model. The measurement of p-Ps momentum thus appears to be prospective as a tool to determine the size of voids of materials. The lifetime of the long lifetime component, on the other hand, showed a poor correlation with the void size even from a qualitative viewpoint, suggesting that factors other than the simple void size effect are dominant in determining the o-Ps lifetimes. Discussion is made on the cause of the different dependences of o-Ps and p-Ps annihilation parameters on the void size. It has also been found that p-Ps fraction is always larger than one third of the o-Ps fraction in all the zeolites studied. A discussion is presented on this point, too.Formerly, RIISOM