Quantum phase transitions in the S=1/2 distorted diamond chain

By means of the second derivative of the ground-state and first-excited energy, the quantum phase transitions (QPTs) for the distorted diamond chain (DDC) with ferromagnetic and antiferromagnetic frustrated interactions and the trimerized case are investigated, respectively. Our results show the plentiful quantum phases owing to the spin interaction competitions in the model. Meanwhile, by using the transfer-matrix renormalization-group technique, we study the two-site thermal entanglement of the DDC model in the thermodynamic limit for a further understanding of the QPTs.

High-power AlGaInP laser diodes with current-injection-free region near the laser facet

A high-power AlGaInP laser diode with current-injection-free region near the facet is successfully fabricated by metaorganic chemical vapor deposition (MOCVD) using the (100) direction n-GaAs substrates with a misorientation of 15 deg toward the (011) direction. The maximum continuous wave output power is about 90 mW for the traditional structure. In comparison, the maximum output power is enhanced by about 67%, and achieves 150 mW for LDs with current-infection-free regions. The fundamental transverse-mode operation is obtained up to 70 mW. Output characteristics at high temperatures are also improved greatly for an LD with a current-injection-free region, and the highest operation temperature is 70 C at 50 mW without kink. The threshold current is about 33 mA, the operation current and the slope efficiency at 100 mW are 120 mA and 0.9 mW/mA, respectively. The lasing wavelength is 658.4 nm at room-temperature 50 mW. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

X-ray diffraction analysis on gallium-indium interdiffusion in quantum dot superlattices

Thermal-induced interdiffusion in InAs/GaAs quantum dot superlattices is studied by high-resolution x-ray diffraction rocking curve and photoluminescence techniques. With increasing annealing temperatures, up to 300 meV a blueshift of the emission peak position and down to 16.6 meV a narrowing of the line width are found in the photoluminescence spectra, and respective intensity of the higher-order satellite peaks to lower-order ones in the x-ray rocking curves decreases. Dynamical theory is employed to simulate the measured x-ray diffraction data. Excellent agreement between the experimental curves and the simulations is achieved when the composition, thickness and stress variations caused by interdiffusion are taken into account. It is found that the significant In-Ga intermixing occurs even in the as-grown InAs/GaAs quantum dots. The estimated diffusion coefficient is 1.8 x 10(-17) cm(2) (.) s(-1) at 650 degreesC, 3.2 x 10(-17) cm(2 .) s(-1) at 750 degreesC, and 1.2 x 10(-14) cm(2 .) s(-1) at 850 degreesC.

Fracture properties of PECVD silicon nitride thin films by long rectangular memrane bulge test

Bulge test combined with a refined load-deflection model for long rectangular membrane was applied to determine the mechanical and fracture properties of PECVD silicon nitride (SiNx) thin films. Plane-strain modulus E-ps prestress s(0), and fracture strength s(max) of SiNx thin films deposited both on bare Si substrate and on SiO2-topped Si substrate were extracted. The SiNx thin films on different substrates possess similar values of E-ps and s(0) but quite different values of s(max). The statistical analysis of fracture strengths were performed by Weibull distribution function and the fracture origins were further predicted.

基于上下文图模型文本表示的文本分类研究

传统的基于“词袋”的文本表示方法假定词的权重只和它本身的出现频率有关，而忽略上下文信息。 本文提出了一种基于上下文的图模型文本表示方法，使用一种类似PageRank的图模型来建立词和词之间的相 互推荐关系，该方法克服了传统文本表示认为词和词之间相互独立，忽略词的上下文环境的缺陷。在复邑中文 文本分类和20newsgroup英文文本分类的语料库上的实验表明，我们的方法可以有效地提升文本分类的性能。

模糊动态抢占调度算法

针对不确定任务特征,提出应用模糊理论进行动态抢占调度.用语言模糊集来描述任务的不确定特征和不同的优先级等级,利用最大隶属度原理确定任务的优先级等级,采用优先调度高优先级等级任务的调度策略提高重要任务的调度成功率,实现具有不确定任务特征的抢占调度.与传统的EDF和LSF算法相比较,仿真表明,所提算法能够提高重要任务的调度成功率,并降低重要任务的截止期错失率;同时,任务间的平均切换次数大大小于LSF的平均切换次数,而与EDF保持相当.该方法可应用于计算机控制系统的控制任务调度,并借鉴于其它具有不确定任务特征或具有有限优先级等级的实时调度问题研究中.

Study on the Dissociation Behavior of Gas Hydrate in Porous Sediment Based on Fractal Theory

The dissociation process of gas hydrate was regarded as a gas-solid reaction without solid production layer when the temperature was above the zero centigrade. Based on the shrinking core model and the fractal theory, a fractional dimension dynamical model for gas hydrate dissociation in porous sediment was established. The new approach of evaluating the fractal dimension of the porous media was also presented. The fractional dimension dynamical model for gas hydrate dissociation was examined with the previous experimental data of methane hydrate and carbon dioxide hydrate dissociations, respectively. The calculated results indicate that the fractal dimensions of porous media acquired with this method agree well with the previous study. With the absolute average deviation (AAD) below 10%, the present model provided satisfactory predictions for the dissociation process of methane hydrate and carbon dioxide hydrate.

Hydrogen production characteristics of the organic fraction of municipal solid wastes by anaerobic mixed culture fermentation

The hydrogen production from the organic fraction of municipal solid waste (OFMSW) by anaerobic mixed culture fermentation was investigated using batch experiments at 37 degrees C. Seven varieties of typical individual components of OFMSW including rice, potato, lettuce, lean meat, oil, fat and banyan leaves were selected to estimate the hydrogen production potential. Experimental results showed that the boiling treated anaerobic sludge was effective mixed inoculum for fermentative hydrogen production from OFMSW. Mechanism of fermentative hydrogen production indicates that, among the OFMSW, carbohydrates is the most optimal substrate for fermentative hydrogen production compared with proteins, lipids and lignocelluloses. This conclusion was also substantiated by experimental results of this study. The hydrogen production potentials of rice, potato and lettuce were 134 mL/g-VS, 106 mL/g-VS, and 50 mL/g-VS respectively. The hydrogen percentages of the total gas produced from rice, potato and lettuce were 57-70%, 41-55% and 37-67%. 2008 International Association for Hydrogen Energy.

掺Er3+玻璃上转换发光特性研究

采用高温熔制工艺制备了掺Er3+硅酸盐玻璃，应用Judd-Ofelt 理论计算了Er3+光谱参数， 发现玻璃中含有0.15 mol%Er2O3 时各参数取得最大值；分析了玻璃的吸收光谱随Er3+离子浓度的变 化关系；上转换光谱分析表明在522 nm、544 nm、658 nm 处有较强的绿光和红光，分别对应于 2H11/2→4I15/2、4 S3/2→4I15/2、4 F9/2→4I15/2 的跃迁，且522 nm 绿光强度和658nm 红光强度要远大于544 nm 绿光强度. 分析了上转换发光强度随泵浦功率和Er3+离子浓度的变化关系，揭示了上转换发光机制 主要是激发态吸收和能量转换，且均为双光子吸收过程.

径流曲线法在黄土区小流域地表径流预测中的初步应用

径流曲线法是目前国际上预测无径流观测资料地区降水地表产流的主要模型,由于气候、水文及下垫面的差异,在黄土高原地区的应用受到限制。利用黄土高原地区3个小流域的303场降雨径流资料,针对黄土高原降雨地表径流特点优化模型中的初损率λ,并提出降雨强度修正函数,将降雨强度因子引入径流曲线法。优化后的模型效率E达到0.812,实测径流深与预测径流深的线性回归决定系数R2达到0.822。改进后的SCS-CN模型可用于黄土区小流域降雨地表产流预报,对黄土高原无资料地区侵蚀产流预报、指导水土保持工程配置和设计具有重要的理论和工程实践意义。

半干旱区施氮和灌溉条件下覆膜对春玉米产量及氮素平衡的影响

以典型半干旱区干湿砂质新成土(Ust-Sandic Entisols)为供试土壤进行田间试验,研究地膜覆盖、施氮及补充灌水量对春玉米(Zea maysL.)产量、土壤矿质氮(NO3--N和NH4+-N)及氮素平衡的影响。结果表明,0—100 cm土体范围内,随着土层加深,播前和收获后土壤NO3--N含量呈降低趋势,NH4+-N有所增加,但变幅不大;总矿质氮量(NO3--N和NH4+-N)表现为下降。说明地膜覆盖和施氮并没有使NO3--N深层累积量增加,这可能与土壤本身供氮能力严重不足有关。与不施氮相比,施氮各处理氮肥表观损失量增加;与不覆膜相比,作物氮素累积量比不覆膜显著增加(P<0.05)。在低灌(80 mm)覆膜和高灌(160 mm)覆膜条件下,玉米的氮肥利用率均比不覆膜提高了18.8%,说明覆膜低灌在相同施氮条件下,可节约80 mm灌水。但低灌(80 mm)与高灌(160 mm)不覆膜间氮肥利用率差异不显著,表明在相同施氮条件下,覆膜可有效提高氮肥利用率,减少氮素损失。综合考虑子粒产量和氮肥利用率,"覆膜+补灌80 mm+施氮90 kg/hm2"可能为本试验条件下较优的栽培模式。