Triple differential cross-sections for near threshold (e, 2e) process for hydrogen

The resonance Raman (RR) spectra of nickel octaethyl porphyrin, Ni(OEP), in CH₂Cl₂ (solvent) at different excitations such as 514.5, 488.0, 441.6 and 406.7 nm are recorded and analysed. The results of the theory of distortion-induced RR intensity is applied to the observed spectra to determine the excited electronic state symmetry of porphyrin in Ni(OEP). It is concluded that the porphyrin molecule (D_4h structure) attains a non-polar distorted structure of D₂ symmetry rather than S₄ symmetry in CH₂Cl₂ solution.     

电子碰撞激发氢原子和氦离子散射微分截面的计算

本文详细介绍计算电子碰撞激发散射截面的扭曲波玻恩近似（DWBA）理论模型,并对低能DWBA模型进行修正。利用修正的DWBA模型计算了电子碰撞激发氢原子和氦离子1s-2s 和1s-2p的散射微分截面。将关于氢原子由基态到n=2态的电子碰撞激发散射微分截面与绝对实验测量数据比较,发现二者符合得很好,这验证了我们对DWBA修正的正确性。本文工作为拟合强场诱导的氦原子非序列双电离关联电子动量谱提供了有效的理论方法。     

Local Structure of Nanoscopic Magnesium Hydroxide ­Fluorides Studied by Natural Abundance 25Mg Solid State NMR Spectroscopy

Along with X‐ray diffraction measurements, ²⁵Mg solid state NMR experiments were performed in natural abundance at 9.4 T on crystalline and mechanically milled samples of MgO, Mg(OH)₂, MgF₂, and magnesium hydroxide fluorides Mg(OH)_xF_2–x prepared on mechanochemical and sol‐gel syntheses routes. In addition to single pulse and spin‐echo sequences, both static ¹H‐²⁵Mg CP and ¹⁹F‐²⁵Mg CP measurements allowed the registration of ²⁵Mg spectra in attractive short measurement times. Although an assignment of different magnesium species in magnesium hydroxide fluorides is only hardly possible, position and line shapes of ²⁵Mg spectra of magnesium hydroxide fluorides reflect chemically reliable trends. All samples studied here show a sixfold fluorine, oxygen, or mixed fluorine / oxygen coordination of magnesium, also in highly disordered samples.     

氩离子原子过程参数的系统计算与评估：Ⅰ电子碰撞激发

利用准相对论扭曲波玻恩近似加交换方法，在组态平均近似下，系统地计算了类氢、类氦、类锂氩离子n≤6的各组态之间的碰撞激发过程截面。并和已有的理论结果进行了详细的对比分析。计算结果和相对论扭曲波近似的计算结果符合得很好，相对偏差一般都小于10％。由于没有考虑共振效应。计算的结果与强耦合方法的计算结果在入射电子能量较低的情况下有较大偏差，其他情况则符合较好，相对偏差一般在15％以内。该方法可以方便地计算大量应用所需的原子过程参数。     

Coordination of a mesogenic Schiff-base with Mn, Co, Ni, Cu and Zn: Synthesis, spectral studies and crystal structures

A novel mesogenic (nematic) Schiff-base, N,N′-di-4-(4′-pentyloxybenzoate)salicylidene diaminoethane, H₂dpbsde (abbreviated as H₂L⁵) was synthesized and its structure studied. The Schiff-base crystallizes in the non-centrosymmetric space group Pna2₁ with Z = 4, and the mesogenic isomorphous nickel and copper complexes, [NiL⁵]₂ and [CuL⁵], in the centrosymmetric space group P2₁/c with Z = 4. The (L⁵)²⁻ species coordinates to the metal ions through two phenolate oxygens and two azomethine nitrogens. Both the [NiL⁵]₂ and [CuL⁵] complexes involve cis-MN₂O₂ planes; the former complex has a low-spin distorted square-pyramidal geometry with a Ni–Ni bonding of 3.337 Å and the latter, a square-planar geometry.     

Stabilized finite element formulation for incompressible flow on distorted meshes

Flow computations frequently require unfavourably meshes, as for example highly stretched elements in regions of boundary layers or distorted elements in deforming arbitrary Lagrangian Eulerian meshes. Thus, the performance of a flow solver on such meshes is of great interest. The behaviour of finite elements with residual‐based stabilization for incompressible Newtonian flow on distorted meshes is considered here. We investigate the influence of the stabilization terms on the results obtained on distorted meshes by a number of numerical studies. The effect of different element length definitions within the elemental stabilization parameter is considered. Further, different variants of residual‐based stabilization are compared indicating that dropping the second derivatives from the stabilization operator, i.e. using a streamline upwind Petrov–Galerkin type of formulation yields better results in a variety of cases. A comparison of the performance of linear and quadratic elements reveals further that the inconsistency of linear elements equipped with residual‐based stabilization introduces significant errors on distorted meshes, while quadratic elements are almost unaffected by moderate mesh distortion. Copyright © 2008 John Wiley & Sons, Ltd.     

A coupled finite volume method for the solution of flow processes on complex geometries

CFD modelling of ‘real‐life’ thermo‐fluid processes often requires solutions in complex three‐dimensional geometries, which can result in meshes containing aspects that are badly distorted. Cell‐centred finite volume methods (CC‐FV), typical of most commercial CFD tools, are computationally efficient, but can lead to convergence problems on meshes that feature cells with highly non‐orthogonal shapes. The control volume‐finite element method (CVFE) uses a vertex‐based approach and handles distorted meshes with relative ease, but is computationally expensive. A combined vertex‐based—cell‐centre technique (CFVM), detailed in this paper, allows solutions on distorted meshes where purely cell‐centred solutions procedures fail. The method utilizes the ability of the vertex‐based approach to resolve the flow field on a distorted mesh, enabling well established cell‐centred physical models to be employed in the solution of other transported quantities. The vertex‐based flow code is verified against a manufactured 3D solution and error norms are compared on meshes with various degrees of distortion. The CFVM method is validated with benchmark solutions for thermally driven flow and turbulent flow. Finally, the method is illustrated on three‐dimensional turbulent flow over an aircraft wing on a distorted mesh where purely cell‐centred techniques fail. The CFVM is relatively straightforward to embed within generic CC based CFD tools allowing it to be employed in a wide variety of processing applications. Copyright © 2006 John Wiley & Sons, Ltd.     

Elastic and inelastic scattering of 270 MeV3He particles from58Ni,90Zr,116Sn and208Pb

Differential cross-section angular distributions for the elastic scattering of 270 MeV³He particles from⁵⁸Ni,⁹⁰Zr,¹¹⁶Sn and²⁰⁸Pb have been measured. Optical model analysis of the cross-sections has yielded the optical model parameters for³He particles at 270 MeV. Angular distributions have also been measured for the inelastic excitation of the low-lying levels in the above mentioned nuclei. A collective model analysis using the distorted wave Born approximation (DWBA) of these cross-sections with the distorted waves generated by the optical model parameters determined from the elastic scattering analysis, has yielded the reduced transition probability (B(EL)) values consistent with those reported in the literature.     

CYCLIC OXYPHOSPHORANES

Abstract

A review on pertinent information on cyclic oxyphosphoranes is presented. Recent X-ray structures and variable temperature ¹H NMR investigations of cyclic pentaoxyphosphoranes reveals a preference for a boat conformation for saturated six-membered rings in apical-equatorial orientations of trigonal bipyramids. These studies include five-, six-, and seven-membered rings and show that the solid state structures are retained in solution. Apical-equatorial ring pseudorotations are more facile for five-membered rings, whereas ligand exchange via diequatorial ring placement is more facile for the larger rings. The importance of the apical-equatorial ring orientation for phosphorinanes appearing as trigonal bipyramidal intermediates in enzymatic reactions of cyclic AMP analogs is emphasized.     

目标跟踪与定位中的视觉标定算法研究

目标跟踪与定位中的一个重要步骤就是摄像机标定,其目的是估计摄像机的外部和内部参数。在严格的几何约束关系之上建立准确的数学模型,提出一种快速得到摄像机中心的方法,然后通过合理的求解次序获得其他摄像机参数,保证了标定参数的精度。利用计算出来的标定参数校正失真图像中的各个像素位置以重新得到像素间原来的空间关系,从而产生精确的不失真图像,并且利用摄像机标定参数对标定模板上的点进行位置计算后,再和实际位置比较进行检验。图像的校正效果实验以及精度验算的结果表明：提出的算法得到了准确可靠的标定参数,和其他算法相比有效提高了精度,能够满足运动跟踪时目标特征位置估计的精度要求。