1,4-双(4′-溴苯酰基)苯的合成工艺改进

以对苯二甲酰氯和溴苯为原料,无水氯化铝粉末为催化剂,合成了1,4-双(4′-溴苯酰基)苯,其结构经1HNMR,IR和DSC表征。     

Structural and optical characterization of type II In0.14Ga0.86As0.13Sb0.87/GaSb heterostructure doped with zinc grown by liquid phase epitaxy

In_0.14Ga_0.86As_0.13Sb_0.87 quaternary solid solutions lattice-matched to GaSb (0 0 1) substrates were grown by liquid phase epitaxy, which were intentionally doped with Zn in a wide range. Two main vibrational bands are observed in their Raman spectra over the doping range investigated. The assignment of the observed modes to GaAs-like and (GaSb + InAs)-like mixture modes is discussed. The comparison of the experimental results with obtained ones by the modified random-element isodisplacement (MREI) model allows to confirm that the bands correspond to the vibrational modes associated with longitudinal- and transverse-optical (LO and TO) modes of the binary compounds GaAs and (GaSb + InAs). The low-temperature photoluminescence (LT-PL) of p-type In_xGa_1−xAs_ySb_1−y was studied as a function of zinc concentration added to the melt solution. Low temperature photoluminescence spectra show the presence of an emission band that has been related to radiative emission involving Zn-acceptors. For low carrier concentration, the photoluminescence line shape could be explained in terms of a direct transition following a simple k-selection rule. For degenerate concentrations, however, it is properly interpreted in terms of non-k-conserving transitions which arise from indirect recombination of holes in a highly filled valence band.     

A policy improvement method for constrained average Markov decision processes

This brief paper presents a policy improvement method for constrained Markov decision processes (MDPs) with average cost criterion under an ergodicity assumption, extending Howard's policy improvement for MDPs. The improvement method induces a policy iteration-type algorithm that converges to a local optimal policy.     

Load‐regulated CSMA

In this paper, we derive throughput of a threshold‐based transmission policy, namely load‐regulated carrier sense multiple access (CSMA), taking into account the propagation delay of the medium and the offered load at different probabilities of the fading channel. In case of the saturated load‐regulated CSMA, a trivial relationship between deterministic offered load to the channel at a particular fading channel condition and the maximum possible offered load has been shown. We further extend the load regulation concept into multi‐channel domain. Both single and multi‐channel load‐regulated CSMA improves the throughput of the system compared with the existing CSMA system, which does not consider channel fading to control the packet transmissions. Copyright © 2008 John Wiley & Sons, Ltd.     

An efficient approach for solving the lot-sizing problem with time-varying storage capacities

We address the dynamic lot size problem assuming time-varying storage capacities. The planning horizon is divided into T periods and stockouts are not allowed. Moreover, for each period, we consider a setup cost, a holding unit cost and a production/ordering unit cost, which can vary through the planning horizon. Although this model can be solved using O(T³) algorithms already introduced in the specialized literature, we show that under this cost structure an optimal solution can be obtained in O(T log T) time. In addition, we show that when production/ordering unit costs are assumed to be constant (i.e., the Wagner–Whitin case), there exists an optimal plan satisfying the Zero Inventory Ordering (ZIO) property.     

大学生课外科技活动中专利文献的利用

专利文献作为重要的科技信息资源,在大学生课外科技活动中起着重要的作用.本文针对当前大学生专利文献利用的状况,提出了有效利用专利信息应采取的措施,包括提高知识产权意识、重视专利文献检索及充分利用网上专利信息资源等.旨在提高大学生对专利文献利用的重视程度,增强其科技创新能力.     

基于改进基线算法的线性规划灵敏度问题研究

针对基线算法由于计算方面的无记忆性而在线性规划灵敏度方面的难实现问题,提出了改进的基线算法,并分别讨论了在价值系数C、技术系数矩阵A及资源向量b等各种情况发生变化的条件下,如何采用改进的基线算法进行灵敏度分析,从而能够简便、快捷的获得新的最优解.最后通过实例进行了说明.     

C-去甲-D-高甾烷的合成工艺改进

以海可吉宁为原料,经乙酰化反应制得海可吉宁乙酸酯(2);2用硼氢化钠还原得到C12-羟基化合物(3);3与对甲苯磺酰氯反应成酯得化合物(4);4经重排反应合成了具有异甾环骨架的烯烃化合物(5),总收率62.6%. 5的结构经1H NMR, MS和IR表征.用正交实验优化了3的合成工艺,使3的收率达95.2%;考察了重排反应溶剂对环内双键[5a(Δ17a(18)-olefin)]和环外双键[5b(Δ13(17a)-olefin)]异构体比例的影响,结果表明,以无水吡啶为溶剂时,5的收率达到86.1%,且5a含量达到100%.     

有机合成反应中副反应的影响因素讨论

有机合成反应中副反应的产生和控制是反应成败的一个关键因素。对有机合成反应中常见副反应产生的过程进行了分析和总结,并讨论了传质、传热、加料方式、原料配比等合成工艺条件与这些副反应产生的相关性。可帮助学生更好地理解和分析有机合成反应工艺条件的选择和控制。     

初中化学实验的改进与创新

对初中化学的4个实验——空气中氧气含量的测定、氢气在空气中的燃烧、金属与盐酸或稀硫酸的反应、水排气与气排水进行了改进与创新。