A hierarchical porous carbon membrane from polyacrylonitrile/polyvinylpyrrolidone blending membranes:Preparation,characterization and electrochemical capacitive performance

Novel hierarchical porous carbon membranes were fabricated through a simple carbonization procedure of well-defined blending polymer membrane precursors containing the source of carbon polyacrylonitrile （PAN） and an additive of polyvinylpyrrolidone （PVP）, which was prepared using phase inversion method. The as-fabricated materials were further used as the active electrode materials for supercapacitors. The effects of PVP concentration in the casting solution on structure feature and electrochemical capacitive performance of the as-prepared carbon membranes were also studied in detail. As the electrode material for supercapacitor, a high specific capacitance of 278.0 F/g could be attained at a current of 5 mA/cm2 and about 92.90% capacity retention could be maintained after 2000 charge/discharge cycles in 2 mol/L KOH solution with a PVP concentration of 0.3 wt% in the casting solution. The facile hierarchical pore structure preparation method and the good electrochemical capacitive performance make the prepared carbon membrane particularly promising for use in supercapacitor.     

A highly efficient capillary electrophoresis-based method for size determination of water-soluble CdSe/ZnS core-shell quantum dots

This paper describes a highly efficient method for size determination of water-soluble CdSe/ZnS core-shell quantum dots (QDs) by capillary electrophoresis (CE) using polymer additive as sieving medium. The influence of some factors, such as kinds and concentrations of the sieving medium, pH, concentrations of the background electrolyte (BGE) and applied voltage, on the separation of QDs was investigated. Under the optimal separation conditions, four different sized QDs were successfully separated, and the relative standard deviation (RSD) of the migration times for these QDs was below 1.013%. In addition, an equation was fit by taking into account the correlation existing between the electrophoretic mobilities and the sizes of a set of QDs. The feasibility of this equation to measure the sizes of other QDs was confirmed by comparison with the sizes obtained by transmission electron microscopy (TEM) experiment. This work offers a novel method for size determination of QDs, and provides an important reference on the study of QDs based on CE.     

Effect of mobile phase anionic additives on selectivity,efficiency, and sample loading capacity of cationic drugs in reversed-phase liquid chromatography

In the present work, we study the effect of mobile phase anionic additive type and concentration on the selectivity, efficiency, and sample loading capacity of cationic drugs in reversed-phase liquid chromatography (RPLC). The type and concentration of an anionic additive are known to have a strong effect on the absolute retention of cations in RPLC; in contrast they have only a small effect on the selectivity of one cation relative to a second as seen here. This is mainly due to the similarity of the ion pair formation constants between the selected cations. The limiting retention factors of cations (i.e. the retention factor of the fully ion-paired analyte at very high additive concentration) are roughly proportional to their inherent hydrophobicities (i.e. the retention factor of the analyte in the absence of the anionic additive). With a given anion, differences in ion pairing strength between the solutes are required for effective selectivity adjustment. Based on the Wade–Lucy–Carr (W–L–C) kinetic model of overload peaks, the approach we developed in our previous work was used to study the effect of mobile phase anionic additives type and concentration on the limiting plate count (N₀) and sample loading capacity (ω_0.5) of various cationic drugs. Under linear chromatographic conditions, where the analyte exhibits its smallest peak width and thus maximum apparent plate count, the type and concentration of anionic additives have almost no effect on peak width. In comparison to neutral analytes the sorption isotherms of cationic species are very easily overloaded even when many fewer moles of cations as compared to neutrals are injected. We showed that different anionic additives profoundly affect the cations’ “overload profiles” (i.e. plots of plate count versus amount injected) by changing the sample loading capacities. The increase in sample loading capacities with different anions show the same order as the extent of ion pairing between the anions and the basic analytes. The detrimental effect of sample overloading on peak width can be greatly diminished by using either a stronger ion pairing agent or a higher concentration of a given ion pairing agent. Both effects operate by increasing the sample loading capacity, thereby allowing more solute to be injected. We believe that the increase in sample loading capacity described above is due in part to the increase in the number of ion-exchange sites as more anions sorb to the stationary phase. At the same time, the formation of a neutral ion-paired analyte also increases the amount of cation which can be loaded onto the stationary phase by allowing a greater fraction of the analyte to be present in the stationary phase as an electrically neutral (i.e. ion-paired) species.     

马尔可夫过程H-值可加泛函的向前向后鞅分解

本文研究了马尔可夫H-值可加泛函的向前向后鞅分解.利用Lyons-Meyer-Zheng鞅分解得到了泛函数极限定理所必需的极大不等式和紧性结果,在最小条件限度内得到了马尔可夫过程经验测度的泛函中心极限定理,将该定理从实值情形推广到了希尔伯特值情形.     

Availability of inspected systems subject to shocks – A matrix algorithmic approach

We examine the limiting average availability of a maintained system that deteriorates due to random shock process and as a response to its usage (wear out). System’s failures are not self-announcing, hence, failures must be detected via inspection. We consider randomly occurring shocks that arrive according to a Poisson process and cumulatively damage the system. Two models are considered: in Model 1 the shock and wear out processes are independent of the external environment and in Model 2, the shocks arrival rate, the shock magnitudes and the wear out rate are governed by a random environment which evolves as a Markov process. We obtain the system’s availability for both models.     

RANDOM PENALTIES AND RENEWABLE RESOURCES: A MECHANISM TO REACH OPTIMAL LANDINGS IN FISHERIES

Abstract Recent literature considers illegal landings a moral hazard problem that arises because individual landings are unobservable. The literature proposes incentive schemes to solve the information problem. However, most of the proposed schemes raise huge information requirements and social budget balance is not secured. In this paper, we suggest a random penalty mechanism that reduces the information requirements and secures budget balance in the case of a given number of licensed vessels. In the random penalty mechanism, aggregate landings are measured through stock sizes and the natural growth function. If aggregate landings are below optimal landings, each fisherman receives a subsidy. If aggregate catches are above optimal landings, the mechanism works such that either the fisherman is randomly selected and pays a fine or the fisherman is not selected and receives a subsidy. The fine and subsidy can be designed such that budget balance is secured. Provided risk aversion is sufficiently large and the fine is high enough, the random penalty mechanism will generate optimal individual landings. The budget balance combined with risk aversion drives the result for this advanced tax/subsidy system that does not exhaust the resource rents. The budget balance creates interdependence between fishermen that secure optimality.     

条件Erlang分布双参数加法定理的推广

X(m)和Y(k)服从参数(m,λ)和(k,μ)的Erlang分布且相互独立.证明了在X(m)相似文献   

存在不精确数据情况下的环境效率分析

针对环境效率评价问题中存在不精确数据的一类典型问题进行了深入的分析,在回顾现有的不精确数据处理方法以及环境效率评价方法的基础上,基于加性DEA模型,提出一种新的环境效率评价方法.该方法不仅能够求解各个投入/产出数据的最佳精确值,而且能够进一步分析各个决策单元的无效性.通过算例分析对模型及方法的优越性进行了说明,提出的方法克服了现有不精确数据处理方法的局限性,能够有效地处理环境效率分析问题中的不精确数据,得到更为准确的环境管理信息,为环境管理提供更为有效的决策依据.     

Feynman-Kac Formula for Left Continuous Additive Functionals and Extended Kato Class Measures

The perturbation of the generator of a Borel right process by a signed measure is investigated, using probabilistic and analytic potential theoretical methods. We establish a Feynman-Kac formula associated with measures charging no polar set and belonging to an extended Kato class. A main tool of this approach is the validity of a Khas’minskii Lemma for Stieltjes exponentials of positive left continuous additive functionals.      

液相色谱-电喷雾电离三级四极杆质谱法测定茶叶中6种烟碱类农药残留

应用液相色谱-电喷雾电离三级四极杆质谱(LC-ESI-MS/MS)方法测定茶叶中呋虫胺、噻虫嗪、噻虫胺、吡虫啉、啶虫咪和噻虫啉烟碱类农药残留.前处理方法包括添加同位素内标吡虫啉-D4,乙腈提取,再用活性碳和Oasis(HLB)固相小柱净化.该方法采用正离子方式,多反应监测每种烟碱类杀虫剂各两对离子进行定性、定量分析.方法在0.01～0.4 mg/kg范围内具有良好的线性关系.实验了3个添加水平0.02、0.04和0.2 mg/kg,回收率范围为80.1%～106.1%;相对标准偏差小于9.7%;方法检出限(LOQ)均为0.02 mg/kg.本方法简便、快速、准确,各项技术指标满足国内外法规的要求,可用于茶叶样品中烟碱类农药残留的确证检测.