Shift‐invert Lanczos method for the symmetric positive semidefinite Toeplitz matrix exponential

The Lanczos method with shift‐invert technique is exploited to approximate the symmetric positive semidefinite Toeplitz matrix exponential. The complexity is lowered by the Gohberg–Semencul formula and the fast Fourier transform. Application to the numerical solution of an integral equation is studied. Numerical experiments are carried out to demonstrate the effectiveness of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

Two-body threshold spectral analysis, the critical case

We study in dimension d?2 low-energy spectral and scattering asymptotics for two-body d-dimensional Schrödinger operators with a radially symmetric potential falling off like −γr−2, γ>0. We consider angular momentum sectors, labelled by l=0,1,…, for which γ>²(l+d/2−1). In each such sector the reduced Schrödinger operator has infinitely many negative eigenvalues accumulating at zero. We show that the resolvent has a non-trivial oscillatory behaviour as the spectral parameter approaches zero in cones bounded away from the negative half-axis, and we derive an asymptotic formula for the phase shift.     

有限重数的Dirichlet移位

In this paper, we show that a multiplication operator on the Dirichlet space D is unitarily equivalent to Dirichlet shift of multiplicity n ＋ 1 （n ≥ 0） if and only if its symbol is c zn＋1 for some constant c. The result is very different from the cases of both the Bergman space and the Hardy space.     

Red top-emitting organic light-emitting device with improved efficiency and saturated color

In this work, characteristics of microcavity top-emitting red organic light-emitting device (TEROLED) having metallic electrodes had been examined. The TEOLED shows the higher efficiency in comparison with that of the bottom OLED. However, color variation with the increasing view angles is also observed. For the purpose of diminishing the blue-shift of resonant wavelength (RW) in the device with increasing view angle, the effect of out-coupling layer on the emission properties of the TEOLED is discussed in detail. Finally, the out-coupling layer was introduced in theory without sacrificing the efficiency through precise optical simulation.     

一种基于分子内质子转移发色团的硫化氢荧光探针的合成及其生物成像研究

硫化氢在许多生理过程中扮演十分重要的角色,因此检测和成像生物体内的硫化氢具有十分重要的意义。该研究成功制备了一种基于分子内质子转移发色团的硫化氢荧光探针(DHCD)。在PBS-DMSO(磷酸盐-二甲基亚砜,99∶1,体积比,pH 7.45)缓冲溶液中,DHCD的荧光强度与NaHS的浓度在0～10μmol/L范围内呈现良好的线性关系,检出限为0.84μmol/L。该探针对硫化氢的响应具有较大的Stokes位移(～165 nm)、高灵敏度和选择性。此外,合成的探针拥有良好的细胞渗透性和低的毒性,可用于HeLa细胞中硫化氢的荧光成像,在生物分析中具有潜在应用价值。     

Dual Metal Active Sites in an Ir1/FeOx Single‐Atom Catalyst: A Redox Mechanism for the Water‐Gas Shift Reaction

Herein, we report a theoretical and experimental study of the water‐gas shift (WGS) reaction on Ir₁/FeO_x single‐atom catalysts. Water dissociates to OH* on the Ir₁ single atom and H* on the first‐neighbour O atom bonded with a Fe site. The adsorbed CO on Ir₁ reacts with another adjacent O atom to produce CO₂, yielding an oxygen vacancy (O_vac). Then, the formation of H₂ becomes feasible due to migration of H from adsorbed OH* toward Ir₁ and its subsequent reaction with another H*. The interaction of Ir₁ and the second‐neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe³⁺?O???Ir²⁺?O_vac to Fe²⁺?O_vac???Ir³⁺?O with the involvement of O_vac. The redox mechanism for WGS reaction through a dual metal active site (DMAS) is different from the conventional associative mechanism with the formation of formate or carboxyl intermediates. The proposed new reaction mechanism is corroborated by the experimental results with Ir₁/FeO_x for sequential production of CO₂ and H₂.     

In Situ Dispersion of Palladium on TiO2 During Reverse Water–Gas Shift Reaction: Formation of Atomically Dispersed Palladium

The application of single‐atom catalysts (SACs) to high‐temperature hydrogenation requires materials that thermodynamically favor metal atom isolation over cluster formation. We demonstrate that Pd can be predominantly dispersed as isolated atoms onto TiO₂ during the reverse water–gas shift (rWGS) reaction at 400 °C. Achieving atomic dispersion requires an artificial increase of the absolute TiO₂ surface area by an order of magnitude and can be accomplished by physically mixing a precatalyst (Pd/TiO₂) with neat TiO₂ prior to the rWGS reaction. The in situ dispersion of Pd was reflected through a continuous increase of rWGS activity over 92 h and supported by kinetic analysis, infrared and X‐ray absorption spectroscopies and scanning transmission electron microscopy. The thermodynamic stability of Pd under high‐temperature rWGS conditions is associated with Pd‐Ti coordination, which manifests upon O‐vacancy formation, and the artificial increase in TiO₂ surface area.     

BIMP‐Catalyzed 1,3‐Prototropic Shift for the Highly Enantioselective Synthesis of Conjugated Cyclohexenones

A bifunctional iminophosphorane (BIMP)‐catalysed enantioselective synthesis of α,β‐unsaturated cyclohexenones through a facially selective 1,3‐prototropic shift of β,γ‐unsaturated prochiral isomers, under mild reaction conditions and in short reaction times, on a range of structurally diverse substrates, is reported. α,β‐Unsaturated cyclohexenone products primed for downstream derivatisation were obtained in high yields (up to 99 %) and consistently high enantioselectivity (up to 99 % ee). Computational studies into the reaction mechanism and origins of enantioselectivity, including multivariate linear regression of TS energy, were carried out and the obtained data were found to be in good agreement with experimental findings.     

中法激光时间比对和探测基本物理的相关空间计划

激光时间比对T2L2(Time Transfer by Laser Link)是法国蔚蓝海岸天文台(OCA)和法国空间中心(CNES)进行的新一代的时间传递计划,将于2008年年中随Jason-2卫星发射上天,并开始观测。它利用激光脉冲在空间的传播来实现地面—卫星,地面—地面远距离时钟的同步,精度比现有的微波比对方式提高1~2个数量级。中国拥有5个固定激光测距站和2个流动激光测距站,基于良好的地理位置和中法双方比较成熟的激光测距技术,中法激光站之间的时间比对和中国内部激光站之间的时间比对是该计划的重要内容。本文系统描述了T2L2的主要内容和关键技术,初步估算了该计划的精度和稳定度,对中法之间的时间比对做出了初步的观测规划。同时,简单介绍了目前世界上精密时钟的发展现况、T2L2的应用前景及正在研究中的TIPO、ASTRODⅠ、ACES、EGE等探测基本物理的相关空间计划。     

Rashba自旋-轨道相互作用对一维谐振子势场中电子性质的影响

分析了Rashba自旋-轨道相互作用对一维谐振子势场中电子性质的影响,发现该自旋-轨道相互作用能够导致能级之间的自旋翻转,并且自旋翻转的性质明显依赖于自旋-轨道耦合系数和参考系坐标之间的关系.