方差分量谱分解估计的几个性质

对于线性混合模型中方差分量的估计，虽有多种方法，但一般情况下只有方差分析估计和谱分解估计有显式解，本文就线性混合模型中含两个方差分量的情形，对方差分析估计和谱分解估计进行了比较，证明了在一些条件下两个估计的方差相等，由此推出谱分解估计也具有方差分析估计的某些优良性．文末用实例进一步说明了文中的结果．     

构造高分辨率格式的反扩散混合法

In this paper we study a kind of mixed anti-diffusion method for partial differntial equations. Firstly, we use the method to construct some difference schemes for the conservation laws. The schemes are of second order accuracy and are total variation decreasing (TVD). In particular, there are only three knots involved in the schemes. Secondly, we extend the method to construct a few high accuracy difference schemes for elliptic and parabolic equations. Numerical experiments are carried out to illustrate the efficiency of the method.     

A novel editing technique for F MRI: Molecule-specific imaging

A novel technique is proposed to facilitate the selective imaging of specific molecules from a mixture. The application of the technique presented here demonstrates the ability to selectively produce ¹⁹F MR images of either trifluoroacetic acid or the perfluorocarbon emulsion Oxypherol-ET (perfluorotributylamine), when both molecules are present simultaneously. Selective detection is based on the presence of homonuclear J-modulation in one molecule and differential spin-spin relaxation time (T₂). Perfluorotributylamine, an A₃B₂ system, is subject to homonuclear J-modulation, which produces a null signal from the antiphase components of the triplet (A₃) when an echo time is used in a spin-echo image. At this echo time the second molecule, in this example trifluoroacetic acid, a non-coupled spin system, is selectively imaged. At longer echo times, e.g., TE = 1/J there is substantial recovery of the J-modulated signal, which may be solely observed due to T₂ decay of the trifluoroacetic acid signal. The method is demonstrated both using phantoms and in vivo.     

Synthesis of isomerically pure carboxylate- and sulfonate-substituted xanthene fluorophores

Xanthene-based fluorophores such as fluorescein and rhodamine are typically prepared by acid-catalyzed condensation of the appropriate resorcinol or 3-aminophenol with phthalic anhydride. Condensation of substituted phthalic anhydride species results in functionalized fluorophores that are formed as mixed isomers. Crystallization approaches to isomer separation have been reported elsewhere for symmetric fluorescein carboxylates. We describe crystallization-based separation of protected fluorescein sulfonates and coupling conditions to form sulfonamides, precursors for carboxylate-substituted rhodamines, and precursors for asymmetrically substituted fluoresceins and rhodafluors.     

纳米金属颗粒膜的二次谐波增强效应

纳米尺寸金属颗粒膜可以产生较大的表面二次谐波增强。本文测量了用溅射法制备的钠米尺寸Ａｕ颗粒的反射二次谐波，其增强因子可达１０２数量级，理论计算了局域场因子与波长的关系曲线。对于用Ｎｄ：ＹＡＧ激光器输出的１．０６μｍ波长的基频光，可以获得较强的倍频光的局域场增强，对金属颗粒尺寸对局域场因子的影响进行了计算和分析。     

Convexity of trace functionals and Schrödinger operators

Let H be a semi-bounded self-adjoint operator on a separable Hilbert space. For a certain class of positive, continuous, decreasing, and convex functions F we show the convexity of trace functionals of the form tr(F(H+U−ε(U)))−ε(U), where U is a bounded, self-adjoint operator and ε(U) is a normalizing real function—the Fermi level—which may be identical zero. If additionally F is continuously differentiable, then the corresponding trace functional is Fréchet differentiable and there is an expression of its gradient in terms of the derivative of F. The proof of the differentiability of the trace functional is based upon Birman and Solomyak's theory of double Stieltjes operator integrals. If, in particular, H is a Schrödinger-type operator and U a real-valued function, then the gradient of the trace functional is the quantum mechanical expression of the particle density with respect to an equilibrium distribution function f=−F^′. Thus, the monotonicity of the particle density in its dependence on the potential U of Schrödinger's operator—which has been understood since the late 1980s—follows as a special case.     

Adatom Hypothesis as a Predominant Mechanism of Surface Enhanced Raman Scattering: A Review of Experimental Argumentation

A contemporary review of research concerning the mechanism of surface enhanced Raman scattering (SERS) is presented and it is stated that this problem is yet to be solved. The necessity to yet once again analyze some of the familiar experimental observations and the deep-rooted beliefs and revise quantitative evaluations of SERS enhancement via major mechanisms (electromagnetic and chemical) with allowance made for most important experimental characteristics of SERS is substantiated. The characteristics are enumerated and the role they play in the above evaluations is sketched. Attention is focused mainly on electrochemical aspects of SERS problem, which to a large extent define the content and salient features of SERS and provide basic experimental justification for the so-called adatom hypothesis.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 899–935.Original Russian Text Copyright © 2005 by Lazorenko-Manevich.In memory of Vladislav Vladimirovich Marinyuk     

用于X射线时空分辨测量的弯晶谱仪

为了测量激光聚变产生的0.2～0.37 nm范围内的等离子体X射线, 设计了一种基于空间和时间分辨的聚焦型弯晶谱仪. 将在700℃时弯曲后的LiF(2d＝0.403 nm)晶体作为色散元件, 布喇格衍射角的变化范围为30～67.5°, 弯晶粘贴在离心率和焦距分别为0.9586和1350 mm的椭圆形不锈钢基底上. 利用弯晶谱仪配X光CCD相机在星光Ⅱ激光(0.35 μm, 60～80J, 700 ps)装置上摄取了钛平面靶发射的X射线光谱, 实验结果表明它的光谱分辨率能达到0.001 nm.     

高能量激光诱导铝等离子体的发射光谱研究

用钕玻璃激光器 (～ 2 5J)烧蚀铝靶获得等离子体 ,以氩气作为保护气体 ,分析了环境气压、等离子体的观测高度、工作电压、激光功率密度对谱线强度的影响 ,并进行了简短的讨论。实验结果表明 ,环境气压为 88kPa时谱线强度最大 ;相同气压下随着观测高度的增大 ,谱线强度明显减弱 ,在气压为 88kPa观测位置距样品表面 1 5～ 2mm时谱线强度较强 ;并且随着激光工作电压、功率密度的增大 ,谱线强度逐渐提高。     

The interplay between molecular orientation, film morphology and luminescence properties of tetracene thin films on epitaxial AlOx/Ni3Al(1 1 1)

We report a systematic study of the interplay between molecular orientation, film morphology and luminescence properties of tetracene thin films on epitaxial alumina films on Ni₃Al(1 1 1), employing high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and photoluminescence spectroscopy (PL). If deposited at low temperatures, tetracene forms laterally disordered and compact films in which at least the first monolayer is oriented parallel to the substrate. For thicknesses in the range of 10 Å or below, these as-deposited films show no luminescence, while thicker films exhibit weak luminescence from higher layers. On annealing to 210 K, tetracene films dewet the AlO_x/Ni₃Al(1 1 1) surface and transform into an island morphology. At the same time, molecules tend to re-orient into a more upright configuration. In this island configuration, even thin films show luminescence. We can thus conclude that in spite of the insulating nature of the surface, the interaction of flat-lying tetracene molecules with AlO_x/Ni₃Al(1 1 1) is strong enough to provide at least one efficient non-radiative decay channel.