离散事件系统结构化状态反馈控制逻辑

离散事件系统(Discrete Event System,DES)是从制造系统、通讯系统、资源管理系统和城市/空中交通系统等人工系统中抽象出来的.这种系统可认为是离散的(在时间上和状态空间内)、异步的(即是由事件驱动而不是由时钟驱动),并且一般是非确定性的,所以处理这类系统的方法与连续时间系统迥然不同.在已有的处理 DES 的方法中,Wonham 和他的学生所提出的一种概念模型方法已引起了广泛的注意.在这方法中,他们成功地将计算机科学的一些概念和方法引入到控制中,新领域的出现和新方法论的发展使控制科学产生了新的活力.     

快速退火对大直径CZSi单晶中原生微缺陷的影响

本文利用快速退火对 8″直拉硅单晶片中的流动图形缺陷(FPDs)进行了研究.首先用Secco腐蚀液腐蚀了大直径直拉硅片,利用光学显微镜观察了FPDs的宏观分布,并用原子力显微镜(AFM)对原生FPDs的微观形貌进行观察,证明了 FPDs是一种空位型原生缺陷,然后采用了高温快速热处理,分别在N2、N2/O2(3;)、Ar三种气氛中对原生直拉单晶硅片进行了处理.对比退火前后FPDs密度的变化,分析了高温快速热处理对直拉硅单晶片中FPDs的影响,实验表明1200℃快速热处理180s可以显著降低硅片表面的FPDs.     

Acute toxicity and hepatotoxicokinetic studies of Tamarindus indica extract

Tamarindus indica is widely used as a food and beverage and in traditional medicine. The apparent lack of dose standardization in herbal medicine necessitates the evaluation of the lethality T. indica on Artemia salina nauplii and chicken embryos via in vitro and in vivo techniques. Furthermore, hepatotoxicokinetics of the crude extract and fractions on Wister rats was also assessed. At concentrations of 200, 20 and 2 μg/mL, crude extract and fractions showed brine shrimp death percentages ranging from 86.70% to 3.30% and the sub-fractions showed death percentage ranges of 46.70% to 3.30%. Calculated LD?? values ranged from 832 μg/mL to 5,019 μg/mL. Dosing Wister rats with 25% and 50% concentration of LD?? determined for crude extract and fractions on chicken embryos showed an elevation in the ALT and AST levels in the serum. Brine shrimps and chicken embryos showed a positive correlation, with R2 values of 0.541 and 0.588 (P ≤ 0.05) for fractions and subfractions, respectively, as media for the lethality assay. Dose standardization in folk herbal medicine is imperative as T. indica used as food and medicine has been shown to be toxic at high doses. Brine shrimp and chicken embryos may be comparably used as medium for toxicity assay.     

幂群与它的生成群

设г是G上的幂群,即以G的非空子集为元素,在G的子集的运算之下所成的群.P_1,P_2是这样的两个性质 P_1:对任意g∈G,存g∈G,存在A∈г,使得g∈A. P_2:对任意A,B∈г,如果A≠B,则A∩B=φ. 本文得出了群G上的幂群г分别具有性质P_1或P_2的充要条件.     

Effects of fractionation and combinatorial evaluation of Tamarindus indica fractions for antibacterial activity

Six fractions, named TiA - TiF, were obtained by fractionating the crude ethanol extract of the stem bark of Tamarindus indica using column chromatographic techniques. On TLC, fraction TiB showed five bands, TiC three bands, while TiD and TiE showed two bands each. TiC, TiD and TiE were re-eluted with different solvent systems to yield two fractions each, while TiB yielded four. These subfractions were designated B1-B4; C1-C2; D1-D2 and E1-E2, respectively. Tannins, flavonoids and alkaloids, among other components, were detected, albeit in different proportions with respect to fractions and subfractions and were compartmentalized with respect to the solvent systems used. The in vitro antibacterial activity of fractions and subfractions was tested separately and in combinations using the agar well diffusion technique. The susceptibly of test strains (expressed as %) were: 83.3% (TiA and TiB), 75.0% (crude extract and TiC), 66.7% (TiD), 50.0% (TiE) and 16.7% (TiF) when used singly, whereas in combination, the corresponding susceptibilities were 100% (CE), 83.3% (DE), 66.7% (AB, AF, BC, BD, DE and EF), 50% (AC and CD), 33.3% (BE and BF) and 16.7% (AD) against Gram negative bacteria strains and 100% (EF), 80% (DE), 60% (AB, BC and CE), 40% (AC, BD, BF, CF and DF) and 20% (AE, AF, BE and CD) against Gram positive strains. Percentage susceptibility with combinatorial use of re-fractions ranged from 85.7-57.1% and 60-40% against Gram negative and positive strains (TiB subfractions), respectively, 100-85.7% and 40-0% against Gram negative and positive strains (TiC, TiD and TiE sub-fractions).     

Effects of post-thermal treatments on morphological and optical properties of NiO/Ni(OH)2 thin films synthesized by solution growth

Room temperature deposition of PVP capped nanostructured NiO/Ni(OH)₂ thin film, the morphological and optical characterizations by solution growth technique are reported. The nanostructured thin films which were deposited on optical glass substrates were annealed at different temperatures and then subjected to structural, morphological and optical characterizations. X-ray diffraction measurements of the films revealed that higher temperatures during the thermal treatment enhanced the crystallinity of the thin films. The SEM surface micrographs show non-interconnected uniformly deposited fibre-like structures with approximate lengths between 400 and 1200 nm. The optical band gap energy roughly decreased from about 2.7 eV to about 2.2 eV with thermal treatment. The absorbance of the thin films annealed at 300 and 400 °C was as high as 90% in the visible region of the electromagnetic spectrum. These materials could be useful in solar thermal conversion processes.     

New neolignan glycoside and an unusual benzoyl malic acid derivative from Maytenus senegalensis leaves

Further investigation of the methanol leaf extract of Maytenus senegalensis led to the isolation of six compounds, including mayselignoside (1) and an unusual benzoyl malic acid derivative, benzoyl R-(+)-malic acid (2). Two known lignan derivatives (+)-lyoniresinol (3) and ( ? )-isolariciresinol (4), a known neolignan derivative dihydrodehydrodiconiferyl alcohol (5) and the triterpenoid, β-amyrin (6) were also isolated. The structures of these compounds were elucidated by a combination of 1D and 2D NMR and mass spectroscopy. All compounds were tested for cytotoxicity against mouse lymphoma cell line (L5178Y) and for antimicrobial activity against strains of bacteria and fungi. None of the compounds showed promising cytotoxic and/or antimicrobial activities.