Thin strain-relaxed SiGe grown by ultrahigh vacuum chemical vapor deposition

Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si_0.7Ge_0.3 layers with the diameter of 125 mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50 keV Ar⁺ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe.     

Preparing polymer brushes on polytetrafluoroethylene films by free radical polymerization

Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4′-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA.     

Parameter determination of a thermal desorption model

A new method for the analysis of thermal desorption spectra is presented, based on the experimental peak maximum functions for temperatureT _m(β) and pressureP _m(β) and a rigorous mathematical treatment. The resonant heating rate β_r is determined, satisfyingT _m(β_r)=T _r, whereT _r is the resonant temperature defined byA exp(−E _d/(RT _r))=1. Desorption energyE _d and frequency factorA can be determined simultaneously with relatively high robustness towards statistical experimental errors as demonstrated by computer-simulated thermal desorption spectra.     

Large Sample Properties of Mixture Models with Covariates for Competing Risks

We study the large-sample properties of a class of parametric mixture models with covariates for competing risks. The models allow general distributions for the survival times and incorporate the idea of long-term survivors. Asymptotic results are obtained under a commonly assumed independent censoring mechanism and some modest regularity conditions on the survival distributions. The existence, consistency, and asymptotic normality of maximum likelihood estimators for the parameters of the model are rigorously derived under general sufficient conditions. Specific conditions for particular models can be derived from the general conditions for ready check. In addition, a likelihood-ratio statistic is proposed to test various hypotheses of practical interest, and its asymptotic distribution is provided.     

K2O-ZnO-Al2O3-B2O3-SiO2系掺Cr3+透明莫来石微晶玻璃的研究

采用了X射线衍射、透射电镜和吸收光谱及荧光光谱技术研究了K2O－ZnO-Al2O3-B2O3－SiO2系掺Cr^3 玻璃的析晶性能和光谱。研究结果表明：在K2O－Al2O3-B2O3-SiO2系掺Cr^3 玻璃的基础上引入ZnO后，析晶性能明显改善；析晶温度降低，析出的纳米莫来石微晶均匀、规则；微晶玻璃的发光强度明显增强。     

Use of a long-spacer-side-chain liquid crystalline polysiloxane containing a crown ether as a stationary phase for capillary gas chromatography

A new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC-11) has been prepared and coated on a fused silica capillary column. The main chroma-tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC-3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side chain.     

外来的捕食物种对濒危物种的影响

In this paper, an important problem arising from conservation biology is considered. Namely, how does the introduced species affect the survival of a native endangered species through predation? By using Kamke comparison theorem and some results in Cui and Chen‘s paper (1998), some sufficient conditions that guarantee the permanence of the species and global stability of a unique positive periodic solution are obtained. Biological implication of these results are discussed.     

几类数列通项的矩阵求法

本利用矩阵给出了几类数列的通项公式的求法，把数列通项公式的求法转化为矩阵幂的计算，思路简单、计算简便，并能判别其敛散性。