A Simple and Effective Component Procurement Policy for Stochastic Assembly Systems

We examine the component procurement problem in a single-item, make-to-stock assembly system. The suppliers are uncapacitated and have independent but non-identically distributed stochastic delivery lead times. Assembly is instantaneous, product demand follows a Poisson process and unsatisfied demand is backordered. The objective is to minimize the sum of steady-state holding and backorder costs over a pre-specified class of replenishment policies. To keep the analysis tractable, we impose a synchronization assumption that no mixing occurs between sets of component orders. Combining existing results from queueing theory with original results concerning distributions that are closed under maximization and translation, we derive a simple approximate solution to the problem when lead time variances are identical. In simulations, our derived policy is within 2% of optimal and significantly outperforms policies that ignore either component dependence or lead time stochasticity. It is also quite robust with respect to various model assumptions, except the synchronization one.     

表面单层组装多环芳烃荧光行为的Monte Carlo模拟

用MonteCarlo方法模拟了惰性基片表面单层组装多环芳烃 (传感元素 )的荧光行为 ,考察了基片表面传感元素固定化百分率、传感元素激发百分率 (光吸收效率 )以及传感元素分子在介质中相互缔合形成激基缔合物趋势大小 (用P表示 ,P值介于 0到 1)等因素对传感元素激基缔合物荧光发射强度与单体荧光发射强度之比所产生的影响 .结果表明 ,具有中等光吸收效率的多环芳烃适宜于作为传感元素 ,中等固定化密度的基片可能具有比较理想的传感性能     

Determination and identification of synthetic cannabinoids and their metabolites in different matrices by modern analytical techniques – a review

Synthetic cannabinoids have gained popularity due to their easy accessibility and psychoactive effects. Furthermore, they cannot be detected in urine by routine drug monitoring. The wide range of active ingredients in analyzed matrices hinders the development of a standard analytical method for their determination. Moreover, their possible side effects are not well known which increases the danger.     

Improving the detection limit in capillary isotachophoresis using asymmetric neutralisation reaction boundary

An online method involving transient electrokinetic dosing and ITP with neutralization reaction boundary (NRB) and/or carrier ampholyte-free isoelectric focusing (CAF IEF) was developed for the preconcentration, preseparation, and analytical determination of glyphosate in aqueous samples containing low concentrations of the analyte of interest. Various parameters were investigated in the framework of an optimization study with the aim of achieving the maximum concentration limit of detection (cLOD) decrease in minimum time. The proposed method used CAF IEF and/or ITP with NRB. The sample was dosed to the column on the stationary reaction boundary (CAF IEF) and/or moving reaction boundary (ITP with NRB), whereat a sharp pH step exists. Here, charge reversal was due to the ampholytes, and/or acid accumulation occurred because of charge loss. Similarly, the accumulated sample was mobilized with TE and analyzed using classical ITP in the second analytical column. Glyphosate (GLY), the analyte of interest, was chosen as a model substance for ITP with NRB and preconcentration as well as focusing preconcentration and CAF IEF using the asymmetric purpose-built NRB. On one side of the asymmetric boundary was the zone of acidic pH; while the opposite side comprised a neutral/basic non-conductive zone of the ampholyte—in this case, GLY. Such an arrangement enables the use of a lower pH on the acidic side, which allows the focusing of strongly acidic ampholytes and the accumulation of weak acids. The electrolyte composition and the dosing time were optimized, and a 14-fold accumulation was achieved in 25 min compared to that by classical ITP and a 180-fold accumulation was achieved through CAF IEF and preconcentration with a glyphosate sample. Both methods are simple and can be conducted using all commercial ITP systems.     

Über die Schmelzpunkte,insbesondere der Bromide

Ohne Zusammenfassung     

The Levich problem with an eccentric segmented electrode on rotating disk

Using the common diffusion-layer (high Peclet number) approximation, the limiting diffusion currents are calculated for three-segment circular electrode embedded eccentrically in a rotating disk. Both the total currents and directional characteristics are checked experimentally over broad range of the eccentricity λ. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 4, pp. 459–469. The text was submitted by the authors in English.     

Estimate of mass-transfer rate via Nernst model with Ohmic losses

The limiting-current technique, employed e.g. in electrodiffusion flow diagnostics, is based on an oversimplified electrochemical concept, which accounts only for the convective transport of depolarizers across a diffusion layer with constant bulk and wall concentrations. However, there are additional transport resistances that cannot be neglected: Faradaic resistance at surface of working electrode, and Ohmic losses in the bulk of electrolyte solution. Effect of these additional resistances is analyzed using the Nernst model of a two-electrode cell (no reference electrode). The Faradaic resistances due to electrode kinetics are considered for a single redox couple O + ne = R according to the Butler-Volmer electrode kinetics. The effect of Ohmic losses is accounted for, considering primary current distribution for a uniformly accessible circular electrode.     

Periodic flows of pseudoplastic fluids in pipes

Experimental results on the flow enhancement during flow of clay slurries (n = 0.15) through oscillating pipes are compared with theoretical predictions. The agreement is fairly good, especially in the oscillating boundary layer flow regime. Flow enhancement of order 10⁸ was found with the slurries used.