RESEARCH OF AERO-DAMPING FOR BLUNT WITH SPIKE

基于模态数据和准定常理论,建立了减阻盘-杆-后体这一弹性结构的气动阻尼分析方法;通过刚性模型的动导数风洞试验获得气动阻尼以验证方法可靠性后,计算分析了减阻杆结构在指定工况的气动阻尼特性. 结果表明： 所建方法可用于减阻杆系统的气动阻尼计算;计算工况的气动阻尼值均为正值,对减阻杆系统的振动起抑制作用;存在产生负气动阻尼的影响因素,各项因素对气动阻尼影响的量值有所不同,有待进一步研究.     

关于椭圆性质的几点注记

以椭圆为研究对象,利用积分几何理论求出了椭圆的周长公式,利用微分几何理论求出椭圆的切线方程并证明了椭圆的凸性,最后利用射影几何理论,研究了椭圆的一些度量性质.     

Chiral silver phosphate-catalyzed cycloisomeric kinetic resolution of α-allenic alcohols

A kinetic resolution of α-allenic alcohols is realized through chiral silver phosphate-catalyzed cycloisomerization with high stereoselectivity (selectivity factor up to 189) and tolerance of a variety of functional groups. A mechanistic model is proposed to interpret the origin of the high stereoselectivity and broad substrate scope.     

Ultrasmall near-infrared Ag2Se quantum dots with tunable fluorescence for in vivo imaging

A strategy is presented that involes coupling Na(2)SeO(3) reduction with the binding of silver ions and alanine in a quasi-biosystem to obtain ultrasmall, near-infrared Ag(2)Se quantum dots (QDs) with tunable fluorescence at 90 °C in aqueous solution. This strategy avoids high temperatures, high pressures, and organic solvents so that water-dispersible sub-3 nm Ag(2)Se QDs can be directly obtained. The photoluminescence of the Ag(2)Se QDs was size-dependent over a wavelength range from 700 to 820 nm, corresponding to sizes from 1.5 ± 0.4 to 2.4 ± 0.5 nm, with good monodispersity. The Ag(2)Se QDs are less cytotoxic than other nanomaterials used for similar applications. Furthermore, the NIR fluorescence of the Ag(2)Se QDs could penetrate through the abdominal cavity of a living nude mouse and could be detected on its back side, demonstrating the potential applications of these less toxic NIR Ag(2)Se QDs in bioimaging.     

Cell-selective metabolic glycan labeling based on ligand-targeted liposomes

A cell-specific metabolic glycan labeling strategy has been developed using azidosugars encapsulated in ligand-targeted liposomes. The ligands are designed to bind specific cell-surface receptors that are only expressed or up-regulated in target cells, which mediates the intracellular delivery of azidosugars. The delivered azidosugars are metabolically incorporated into cell-surface glycans, which are then imaged via a bioorthogonal reaction.     

热屏优化对大直径单晶硅生长影响的数值模拟

通过对28英寸热场生长300 mm硅单晶过程中结晶速率、固液界面形状、晶体中热应力及晶体中氧含量的数值计算提出了在该热场条件下热屏的优化方案。数值计算结果表明:对热屏底端与晶体表面和熔体自由液面的距离以及热屏材料(优化前热屏使用单一石墨材料,优化后采用辐射率较高的内壁材料结合反射率较高的外壁材料组成复合式热屏)的优化可以减少主加热器对晶体的热辐射使得固液界面更加平坦,藉此增加结晶速率,减小晶体内热应力和熔体中氧含量。     

Reaction mechanism and chemoselectivity of gold(Ⅰ)-catalyzed cycloaddition of 1-(1-alkynyl) cyclopropyl ketones with nucleophiles to yield substituted furans

The mechanisms of gold(Ⅰ)-catalyzed cycloaddition of 1-(1-alkynyl) cyclopropyl ketones with nucleophiles have been investigated using density functional theory calculations at the B3LYP/6-31G(d,p) level of theory.A polarizable continuum model(PCM) has been established in order to evaluate the effects of solvents on the reactions.The results of the calculations indicate that the first step of the catalytic cycle is the cyclization of the carbonyl oxygen onto the triple bond which forms a new and stable resonance structure of an oxonium ion and a carbocation intermediate.The subsequent ring expansion step results in the formation of the final product and regeneration of the catalyst.Furthermore,the regioselectivity and effect of substituents has been discussed,including an analysis of energy,bond length,and natural bond orbital(NBO) charge distributions in the rate-determining step.Our computational results are consistent with earlier experimental observations.     

Energy band gap engineering in borate ultraviolet nonlinear optical crystals: ab?initio studies

The development of ultraviolet (UV) nonlinear optical (NLO) crystals demands optical materials with wide energy band gaps. Here we report first-principles studies on the electronic structures in several UV NLO borates with representative structures. Combined with model analysis, we find that the oxygen non-bonding 2p orbitals play an important role on the top of valence bands. The energy band gap can be adjusted by modifying the coordination environment around the oxygen atoms. Under ideal conditions the energy band gaps achieve 9?eV if the non-bonding orbitals are totally eliminated, despite the original values varying from 6.6 to 8.3?eV.     

Zinc‐Diluted Magnetic Metal Formate Perovskites: Synthesis,Structures, and Magnetism of [CH3NH3][MnxZn1−x(HCOO)3] (x=0–1)

The preparation, structures, and magnetic properties of a series of metal formate perovskites [CH₃NH₃][Mn_xZn_1?x(HCOO)₃] were investigated. The isostructural solid solution can be prepared in the complete range of x=0–1. The metal–organic perovskite structures consist of an anionic NaCl type [Mn_xZn_1?x(HCOO)₃^?] framework with CH₃NH₃⁺ templates located in the nearly cubic cavities and forming hydrogen bonds to the framework. When the proportion of Mn increased (i.e., x changed from 0 to 1), the lattice dimensions and metal–oxygen and metal–metal distances show a slight, nonlinear increase because of the increased averaged metal ionic radius and the local structure distortion. Through the series, the magnetism changes from the long‐range ordering of spin‐canted antiferromagnetism for x≥0.40 to paramagnetism when x≤0.30, and the percolation limit was estimated to be x_P=0.31(2) for this simple cubic lattice. In the low‐temperature region, enhancement of magnetization and the gradual decrease and final disappearance of coercive field, remnant magnetization, and spin‐flop field upon dilution were observed through this isotropic Heisenberg magnetic series. IR spectroscopic and thermal properties were also investigated.     

Perturbation theory of selfadjoint matrices and sign characteristics under generic structured rank one perturbations

For selfadjoint matrices in an indefinite inner product, possible canonical forms are identified that arise when the matrix is subjected to a selfadjoint generic rank one perturbation. Genericity is understood in the sense of algebraic geometry. Special attention is paid to the perturbation behavior of the sign characteristic. Typically, under such a perturbation, for every given eigenvalue, the largest Jordan block of the eigenvalue is destroyed and (in case the eigenvalue is real) all other Jordan blocks keep their sign characteristic. The new eigenvalues, i.e. those eigenvalues of the perturbed matrix that are not eigenvalues of the original matrix, are typically simple, and in some cases information is provided about their sign characteristic (if the new eigenvalue is real). The main results are proved by using the well known canonical forms of selfadjoint matrices in an indefinite inner product, a version of the Brunovsky canonical form and on general results concerning rank one perturbations obtained.