Design and analysis of a GaAs-based 850-nm vertical-cavity surface-emitting laser with different doping in the reflection regions

The present paper deals with the analysis of a non-oxide type of vertical-cavity surface-emitting laser (VCSEL) for operation at 850 nm. The modeling and characterization of the VCSEL is presented in the context of design considerations. Efforts are made to emphasize the behavioral features of the proposed VCSEL, in view of the analytical investigation, which has been performed through a series of simulations for various relevant parameters that are vital for the determination of the VCSEL characteristics. Some of these parameters are the intensity and refractive-index distributions, gain response, spontaneous emission, material gain variations, etc. The results obtained are compared with the oxide-confined VCSEL. It is observed that the proposed model of the VCSEL is suitable at the operating wavelength of 850 nm.     

Enantioselective Acetalization by Dynamic Kinetic Resolution for the Synthesis of γ-Alkoxybutenolides by Thiourea/Quaternary Ammonium Salt Catalysts: Application to Strigolactones

Although acetalization is a fundamental transformation in organic synthesis, intermolecular asymmetric acetalization remains an unsolved problem. In this study, a thiourea-ammonium hybrid catalyst was shown to promote the O-alkylation of enols with a racemic γ-chlorobutenolide through dynamic kinetic resolution to give chiral acetals with good enantioselectivity. The catalyst simultaneously activates both the nucleophile and electrophile in a multifunctional manner. This method was applied to the asymmetric synthesis of several strigolactones. DFT calculations suggest that hydrogen-bonding interactions between the chlorine atom of the γ-chlorobutenolide and the tosylamide hydrogen atom of the catalyst, as well as other types of noncovalent catalyst–substrate interactions, are crucial for achieving high stereoselectivity.     

Characterization of intermediate values of the triangle inequality II

In [Mineno K., Nakamura Y., Ohwada T., Characterization of the intermediate values of the triangle inequality, Math. Inequal. Appl., 2012, 15(4), 1019–1035] there was established a norm inequality which characterizes all intermediate values of the triangle inequality, i.e. C _n that satisfy 0 ≤ C _n ≤ Σ _j=1 ⁿ ‖x _j ‖ ? ‖Σ _j=1 ⁿ x _j ‖, x ₁,...,x _n ∈ X. Here we study when this norm inequality attains equality in strictly convex Banach spaces.     

Photoreactivity of crystals of a rhodium dithionite complex with ethyltetramethylcyclopentadienyl ligands: crystal surface morphology changes and degradation

A photoreactive rhodium dithionite complex [(RhCp(Et))(2)(μ-CH(2))(2)(μ-O(2)SSO(2))] (1(Et)) with Cp(Et) (η(5)-C(5)Me(4)Et) ligands was newly synthesized. Upon short-time irradiation with low intensity light, two kinds of stepwise surface morphology changes of the crystal 1(Et) were observed. Prolonged irradiation with high intensity light caused cracking and breaking down of the crystal.     

Minerals and aligned collagen fibrils in tilapia fish scales: structural analysis using dark-field and energy-filtered transmission electron microscopy and electron tomography

The mineralized structure of aligned collagen fibrils in a tilapia fish scale was investigated using transmission electron microscopy (TEM) techniques after a thin sample was prepared using aqueous techniques. Electron diffraction and electron energy loss spectroscopy data indicated that a mineralized internal layer consisting of aligned collagen fibrils contains hydroxyapatite crystals. Bright-field imaging, dark-field imaging, and energy-filtered TEM showed that the hydroxyapatite was mainly distributed in the hole zones of the aligned collagen fibrils structure, while needle-like materials composed of calcium compounds including hydroxyapatite existed in the mineralized internal layer. Dark-field imaging and three-dimensional observation using electron tomography revealed that hydroxyapatite and needle-like materials were mainly found in the matrix between the collagen fibrils. It was observed that hydroxyapatite and needle-like materials were preferentially distributed on the surface of the hole zones in the aligned collagen fibrils structure and in the matrix between the collagen fibrils in the mineralized internal layer of the scale.     

Anomalous mechanical characteristics of Au/Cu nanocomposite processed by Cu electroplating

An Au/Cu nanocomposite is produced by electroplating Cu on a nanoporous Au, and its mechanical characteristics are investigated by hardness tests. The Au/Cu nanocomposite showed a lower hardness and a lower elastic modulus than the nanoporous Au. Furthermore, annealing caused the nanocomposite to harden twice. Large lattice strains in the Au lattice for the nanocomposite were observed by high-resolution transmission electron microscopy. Also, first-principle calculations showed that lattice strains induce the decreased elastic modulus. Therefore, both the inverse mixing behaviour and the hardening via annealing are suggested to be related to the large lattice strains.     

High-Resolution Proton Magnetic Resonance Analysis of Polypropylenes

The dyad and triad tacticities of polypropylenes were determined quantitatively with the aid of a computer form the 100-MHz proton magnetic resonance spectra in o-dichlorobenzene solution at 165[ddot]C. The contents of tactic dyad and traid evaluated from the 100-MHz PMR spectra are in fair agreement with the values determined from the 220-MHz PMR and ¹³C-(¹H) spectra, respectively. The fraction soluble in boiling ethyl ether of polymer prepared with the Ti(O-n-Bu)Cl₃-AlEt₂ Cl catalyst shows a character of stereorandomness, and the ethyl ether-soluble portion of polymer polymerized with the TiCl₃-AlEt₂ Cl catalyst has a character of stereoblock sequence. Furthermore, by IR analysis, it has become apparent that the former has a (CH₂)₂ group formed by two propylene units in a tail-to-tail arrangement.     

Effects of Heat Treatment on Photocatalytic Property of Sol-Gel Derived Polycrystalline TiO2

Polycrystalline TiO₂ in the bulk form was prepared by hydrothermal treatment of amorphous TiO₂ gel, and its photocatalytic activity for degradation of ethanol and physical properties were investigated after drying and calcination (300–650°C). The maximum photocatalytic activity reached when the polycrystalline TiO₂ was calcinated at temperatures from 300 to 500°C, which was almost the same as for a commercial TiO₂ powder. It was markedly reduced above 600°C. Photocatalytic activity of TiO₂ was affected by crystal growth of anatase, progress of sintering, anatase-rutile transformation and morphology of the polycrystalline TiO₂. It was a characteristic of the polycrystalline TiO₂ prepared in this study that the photocatalytic activity did not vary so much with the calcination temperature in the range of 300–500°C.     

Enantioselective Acetalization by Dynamic Kinetic Resolution for the Synthesis of γ‐Alkoxybutenolides by Thiourea/Quaternary Ammonium Salt Catalysts: Application to Strigolactones

Although acetalization is a fundamental transformation in organic synthesis, intermolecular asymmetric acetalization remains an unsolved problem. In this study, a thiourea‐ammonium hybrid catalyst was shown to promote the O‐alkylation of enols with a racemic γ‐chlorobutenolide through dynamic kinetic resolution to give chiral acetals with good enantioselectivity. The catalyst simultaneously activates both the nucleophile and electrophile in a multifunctional manner. This method was applied to the asymmetric synthesis of several strigolactones. DFT calculations suggest that hydrogen‐bonding interactions between the chlorine atom of the γ‐chlorobutenolide and the tosylamide hydrogen atom of the catalyst, as well as other types of noncovalent catalyst–substrate interactions, are crucial for achieving high stereoselectivity.     

热弹流润滑椭圆接触区内表面凹陷现象的研究

通过理论分析和光干涉实验 ,考察了纯滑动热弹流润滑椭圆接触区内当卷吸速度与接触椭圆短轴成 0°和 45°角时出现的油膜局部增厚现象 ,即固体表面在接触区出现凹陷的现象 .解释了玻璃盘 -钢滚子接触副表面凹陷的形成原因 ,揭示了凹陷的深度、位置和形状随卷吸速度及接触椭圆短轴夹角的变化规律 .