Synthesis,crystal structure,and antimicrobial studies of <Emphasis Type="Italic">trans</Emphasis>-[Pd(PPh<Subscript>3</Subscript>)<Subscript>2</Subscript>(imidazolidine-2-thione)<Subscript>2</Subscript>]Cl<Subscript>2</Subscript> · 3.5H<Subscript>2</Subscript>O

The palladium(II) complex, [Pd(PPh₃)₂(Imt)₂]Cl₂ · 3.5H₂O (I) (Imt = imidazolidine-2-thione), has been synthesized and characterized by IR, NMR, and X-ray crystallography. An upfield shift in the >C=S resonance of Imt in the ¹³C NMR spectrum and a downfield shift in the N-H resonance in ¹H NMR are consistent with the sulfur coordination of Imt to palladium(II). In the crystal structure of I, the central palladium atom is coordinated to two thione sulfur atoms of Imt and to two phosphorus atoms possessing a square-planar environment with the average cis and trans bond angles of 89.60° and 167.31°, respectively. The title complex was screened for antimicrobial effects, and the results showed that it exhibits moderate activities against gram-negative bacteria (E. coli, P. aeruginosa). The complexes also exhibited significant activities against yeast (C. albicans, S. serevisaiae).     

Nanoscience and nanotechnology in Venezuela

Nanoscale research in Venezuela is briefly reviewed, with emphasis on research groups, research lines, and institutions involved. A summary exploration is made of international collaboration through scientific co-authorship, as well of the efforts to build nano capacities, available infrastructure, relationships to the productive sector and a weak presence in Venezuelan public policies, although there is some expectation that the situation may soon begin to change.     

Surface morphologic and structural analysis of IR irradiated silver

The microstructural morphological changes in laser irradiated targets are investigated. Nd:YAG laser (1064 nm, ∼12 ns nominal, 1.1 MW) is used to irradiate 4 N pure (99.99%) fine polished and annealed silver samples in ambient air and under vacuum ∼10⁻⁶ Torr. The laser spot size and power density at tight focus are 12 μm and 3×10¹¹ W/cm², respectively. SEM micrographs and X-ray diffractograms of the exposed and unexposed targets reveal the surface texture and structural changes, respectively. Amongst the ablation mechanisms involved, exfoliation and hydrodynamic sputtering are found to be dominant. Surface modifications appear in the form of craters and ripples formation. Heat is conducted non-uniformly through narrow channels at the surface. Thermal stresses induced by the laser do not disturb inter planar distance of the target. On the other hand irradiation causes significant variations in grain size and diffracted X-rays intensities.     

An analytical simulator for deploying IP telephony

Deploying IP telephony or voice over IP (VoIP) is a major and challenging task. This paper describes an analytical design and planning simulator to assess the readiness of existing IP networks for the deployment of VoIP. The analytical simulator utilizes techniques used for network flows and queuing network analysis to compute two key performance bounds for VoIP: delay and bandwidth. The simulator is GUI‐based and has an interface with drag‐and‐drop features to easily construct any generic network topology. The simulator has an engine that automates and implements the analytical techniques. The engine determines the number of VoIP calls that can be sustained by the constructed network while satisfying VoIP QoS requirements and leaving adequate capacity for future growth. As a case study, the paper illustrates how the simulator can be utilized to assess the readiness to deploy VoIP for a typical network of a small enterprise. We have made the analytical simulator publicly available in order to improve and ease the process of VoIP deployment. Copyright © 2008 John Wiley & Sons, Ltd.     

Rapid TLC Method for Estimation of Mevalonic Acid in the Leaves of Medicinal Plants

A simple, rapid, specific and sensitive thin layer chromatographic (TLC) method has been developed for the quantitative estimation of mevalonic acid (MVA) in leaves of medicinal plants; Artemisia annua, Psorelia corylifolia, Vinca rosea, Withania somnifera and Barleria proinites. The assay procedure involved conversion of MVA to its lactone, mevalonolactone (MVAL). Mevalonic acid was extracted from the leaf tissues of plants. Separation of MVAL was carried out on silica gel 60 F₂₅₄ TLC plates using benzene:acetone (3:2) as the mobile phase. The densitometric determination of MVAL was performed at 600 nm after derivatization with anisaldehyde reagent in absorption–reflectance mode. The method was validated over the linearity range of 100–500 ng spot^?1 and correlation coefficient for the calibration curve was >0.99. The average recovery of MVAL, used as internal standard, was higher than 98%. The lower limit of detection was found to be 50 ng spot^?1.     

Markovnikov addition of vinyl acetate with azoles catalyzed by potassium tert-butoxide

A simple and efficient methodology for Markovnikov addition of azoles with vinyl acetate catalyzed by potassium tert-butoxide is described.N-heterocyclic compounds are synthesized from simple and commercially available starting materials under mild conditions in high yields.     

呼图壁种牛场草原生态站鼠类群落初步研究

本文根据１９９５年７￣８月的调查资料并采用聚类分析方法对呼图壁种牛场草原生态站鼠类群落及其演替进行了分析研究。结果表明：该地区的鼠类可划分为２种群落，灰仓鼠＋小家鼠为主的农田居民点鼠类群落，五趾跳鼠＋根田鼠为主的荒漠草原鼠类群落，种的多样性和生态环境的差异有关，随着人类经济活动的增加，经营时间的不同，鼠类群落受到的影响程度也不一样，在荒漠向人工环境转化过程中存在于其中的鼠类也呈现有规律的演替现象。     

Ion acoustic soliton propagation in a magnetized relativistic plasma

Summary The Korteweg-de Vries equation for ion acoustic waves in the presence of weakly relativistic ion streaming velocity is derived in a magnetic plasma. It is found that relativistic effects are important in the solitary wave propagation for both fast and slow modes. Earlier results are reconfirmed. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Observation of B Meson decays to b1pi and b1K

We present the results of searches for decays of B mesons to final states with a b1 meson and a charged pion or kaon. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 382x10(6) BB[over ] pairs produced in e+e- annihilation. The results for the branching fractions are, in units of 10(-6), B(B+-->b1(0)pi+)=6.7+/-1.7+/-1.0, B(B+-->b1(0)K+)=9.1+/-1.7+/-1.0, B(B0-->b1(-/+)pi(+/-))=10.9+/-1.2+/-0.9, and B(B0-->b1(-)K+)=7.4+/-1.0+/-1.0, with the assumption that B(b1-->omega pi)=1. We also measure charge and flavor asymmetries A(ch)(B+-->b1(0)pi+)=0.05+/-0.16+/-0.02, Ach(B+-->b1(0)K+)=-0.46+/-0.20+/-0.02, A(ch)(B0-->b1(-/+)pi(+/-))=-0.05+/-0.10+/-0.02, C(B0-->b1(-/+)pi(+/-))=-0.22+/-0.23+/-0.05, DeltaC(B0-->b1(-/+)pi(+/-))=-1.04+/-0.23+/-0.08, and A(ch)(B0-->b1(-)K+)=-0.07+/-0.12+/-0.02. The first error quoted is statistical, and the second systematic.