Synchronized abandonments in a single server unreliable queue

We consider a single server unreliable queue represented by a 2-dimensional continuous-time Markov chain. At failure times, the present customers leave the system. Moreover, customers become impatient and perform synchronized abandonments, as long as the server is down. We analyze this model and derive the main performance measures using results from the basic q-hypergeometric series.     

A convergent approach to batzelladine alkaloids. Total syntheses of (+)-batzelladine E, (−)-dehydrobatzelladine C,and (+)-batzelladine K

We recently reported a convergent strategy to access the polycyclic guanidinium alkaloid (+)-batzelladine B via an aldol addition–retro-aldol–aza-Michael addition cascade. Here we describe the application of this approach toward the total syntheses of (+)-batzelladine E, (?)-dehydrobatzelladine C, and (+)-batzelladine K. The identification of suitable methods to functionalize a common tropane core by electrophilic alkynylation and nucleophilic 1,2-addition were essential to generalizing this approach. We provide evidence for the intermediacy of an acylallene species in the cascade reaction.     

Disposable mercury-free cell-on-a-chip devices with integrated microfabricated electrodes for the determination of trace nickel(II) by adsorptive stripping voltammetry

This work reports the fabrication of disposable three-electrode cells with integrated sputtered metal-film electrodes. The working electrode was a bismuth-film electrode (BiFE) while the reference and counter electrodes were made of Ag and Pt, respectively. The deposition of the metal layers was carried out by sputtering of the respective metals on a silicon substrate while the exact geometry of the electrodes was defined via a metal mask placed on the substrate during the deposition process. Initially, the electrodes were characterised by cyclic voltammetry. The utility of these devices was tested for the trace determination of Ni(II) by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (the presence of oxygen, the DMG concentration, the preconcentration potential, the accumulation time and the SW parameters), as well as potential interferences, were investigated. Using the selected conditions, the 3sigma limit of detection was 100 ng L(-1) for Ni(II) (for 90 s of preconcentration) and the relative standard deviation for Ni(II) was 2.3% at the 10 microg L(-1) level (n=8). Finally, the method was applied to the determination of Ni(II) in a certified river water sample.     

Molecular dynamics simulations of pure methane and carbon dioxide hydrates: lattice constants and derivative properties

ABSTRACT

We report extensive molecular dynamics simulation results of pure methane and carbon dioxide hydrates at pressure and temperature conditions that are of interest to various practical applications. We focus on the calculation of the lattice constants of the two pure hydrates and their dependence on pressure and temperature. The calculated lattice constants are correlated using second order polynomials which are functions of either temperature or pressure. Finally, the obtained correlations are used in order to calculate two derivative properties, namely the isothermal compressibility and the isobaric thermal expansion coefficient. The current simulation results are also compared against reported experimental measurements and other simulation studies and good agreement is found for the case of isothermal compressibility. On the other hand, for the case of isobaric thermal expansion coefficient good agreement is found only with other simulation studies, while the simulation studies are in disagreement with experiments, particularly at low temperatures.     

怀菊花中微量铁的测定

为探讨邻二氮菲分光光度法测定怀菊花中微量元素铁含量的可行性,怀菊花的药理功效、食用营养价值与微量元素含量可能存在的关系,根据铁离子与特定显色剂显色产生可见吸收,采用混合酸y（HNO3）：V（HClO4）=4＋1对怀菊花样品湿法消化处理,在pH2～9的溶液中试剂与铁生成稳定的橙色络合物,并用分光光度法测定了怀菊花中微量元素铁含量。结果表明,所选的怀菊花中铁含量303．9～337．9μg／g,加标回收率为90．2％～100．6％。分光光度法操作简便、干扰离子少,测量快速、结果准确度和灵敏度高,易推广和 普及使用。     

关于强Armendariz环和强拟Armendariz环

提出了强拟Armendariz环的概念,给出了强Armendariz环和强拟Armendariz环上的一些结果.     

Molecular simulation and macroscopic modeling of the diffusion of hydrogen, carbon monoxide and water in heavy n-alkane mixtures

The self-diffusion coefficient of hydrogen (H(2)), carbon monoxide (CO) and water (H(2)O) in n-alkanes was studied by molecular dynamics simulation. Diffusion in a few pure n-alkanes (namely n-C(8), n-C(20), n-C(64) and n-C(96)) was examined. In addition, binary n-C(12)-n-C(96) mixtures with various compositions as well as more realistic five- and six-n-alkane component mixtures were simulated. In all cases, the TraPPE united atom force field was used for the n-alkane molecules. The force field for the mixture of n-alkanes was initially validated against experimental density values and was shown to be accurate. Moreover, macroscopic correlations for predicting diffusion coefficient of H(2), CO and H(2)O in n-alkanes and mixtures of n-alkanes were developed. The functional form of the correlation was based on the rough hard sphere theory (RHS). The correlation was applied to simulation data and an absolute average deviation (AAD) of 5.8% for pure n-alkanes and 3.4% for n-alkane mixtures was obtained. Correlation parameters vary in a systematic way with carbon number and so they can be used to provide predictions in the absence of any experimental or molecular simulation data. Finally, in order to reduce the number of adjustable parameters, for the n-alkane mixtures the "pseudo-carbon number" approach was used. This approach resulted in relatively higher deviation from MD simulation data (AAD of 18.2%); however, it provides a convenient and fast method to predict diffusion coefficients. The correlations developed here are expected to be useful for engineering calculations related to the design of the Gas-to-Liquid process.     

旋流燃烧器复合小火焰模型的大涡模拟

对低旋燃烧器内的流动和燃烧进行了大涡模拟,其中化学反应分别采用传统的扩散小火焰模型和所提出的复合小火焰模型描述。复合小火焰模型借助于燃烧区索引的概念区分当地的燃烧模式,若当地的燃烧为扩散燃烧,则调用扩散小火焰库,否则调用预混小火焰库。数值结果与实验数据的对比表明,采用大涡模拟方法结合小火焰模型能够很好地模拟实验室尺度的低旋燃烧器,且采用复合小火焰模型能够得到更加符合实际的结果。     

Optimal and equilibrium balking strategies in the single server Markovian queue with catastrophes

We consider a Markovian queue subject to Poisson generated catastrophes. Whenever a catastrophe occurs, all customers are forced to abandon the system, the server is rendered inoperative and an exponential repair time is set on. We assume that the arriving customers decide whether to join the system or balk, based on a natural reward-cost structure. We study the balking behavior of the customers and derive the corresponding Nash equilibrium and social optimal strategies.     

Chemical analyses of martian soil and rocks obtained by the Pathfinder Alpha Proton X-ray spectrometer

The US Mars Pathfinder spacecraft, which landed on the red planet on the 4th of July 1997, carried an Alpha Proton X-ray Spectrometer (APXS) that obtained the chemical composition of martian soil and rocks. The principles of the APXS operation are based on three interactions of alpha particles with matter: Rutherford alpha backscattering; (, p) nuclear reactions; and X-ray generation by charged particles and X-ray excitation. The APXS, as was implemented on the Pathfinder mission, uses for all three modes of operation a monoenergetic beam of alpha particles from about 40 mCi of ²⁴⁴Cm radioisotope. It employs Si charged particle detectors for alpha and proton modes and a specially designed silicon PIN detector for its X-ray mode that does not require cooling for its operation. The APXS can detect all of the elements (except H and He) present above a few tenths of a percent for all major elements and several hundred ppm for many minor and trace elements.

The APXS on Pathfinder was transported to various locations on the martian surface by the Sojourner rover which enabled it to analyze multiple soil and rock samples selected by the science team from the lander camera images. The APXS performed excellently under the adverse martian environment conditions and provided important information about the chemical composition of the martian soil and rocks. All of the analyzed rocks at the Pathfinder site were found to have high concentrations of silica, sulfur and iron, and low in magnesium, similar to those of the terrestrial basaltic andesites and definitely different from the SNC meteorites that are believed to have originated from Mars. All of the soil samples analyzed by the APXS have similar composition and are very close to the soil analyses obtained by the two Viking missions. The information derived from the Pathfinder APXS has significant implications about the origin and evolution of planet Mars.