On a software availability model with imperfect maintenance

In this paper we consider a general software availability model and derive compound availability measures, such as the joint probability of software availability and the remaining number of errors. The results given here generalize the results given in Kim et al. (1982).     

高分子缓释化肥的缓释性能研究

对一种含氮、磷、钾三种营养元素的高分子型缓释化肥—MSF,分别在去离子水及土壤溶液中进行了养分释放规律的研究.实验结果显示:在120天内,MSF在去离子水中失重不到40%,氮、磷、钾三种营养元素也只分别溶出了30%,28%和38%;而在土壤溶液中,在120天内,MSF失重接近100%,氮,磷,钾三种营养元素基本完全转化为小分子物质溶入土壤溶液中.实验结果表明:(1)MSF初期溶出率较低,能显著的减少淋溶损失.(2)MSF能在土壤溶液中完全降解,养分的可利用率高.(3)MSF水解反应缓慢,性能较为稳定,便于存放和使用.     

Ribosome kinetics and aa-tRNA competition determine rate and fidelity of peptide synthesis

It is generally accepted that the translation rate depends on the availability of cognate aa-tRNAs. In this study it is shown that the key factor that determines translation rate is the competition between near-cognate and cognate aa-tRNAs. The transport mechanism in the cytoplasm is diffusion, thus the competition between cognate, near-cognate and non-cognate aa-tRNAs to bind to the ribosome is a stochastic process. Two competition measures are introduced; C(i) and R(i) (i = 1, 64) are quotients of the arrival frequencies of near-cognates vs. cognates and non-cognates vs. cognates, respectively. Furthermore, the reaction rates of bound cognates differ from those of bound near-cognates. If a near-cognate aa-tRNA binds to the A site of the ribosome, it may be rejected at the anti-codon recognition step or proofreading step or it may be accepted. Regardless of its fate, the near-cognates and non-cognates have caused delays of varying duration to the observed rate of translation. Rate constants have been measured at a temperature of 20 °C by (Gromadski, K.B., Rodnina, M.V., 2004. Kinetic determinants of high-fidelity tRNA discrimination on the ribosome. Mol. Cell 13, 191–200). These rate constants have been re-evaluated at 37 °C, using experimental data at 24.5 °C and 37 °C (Varenne, S., et al., 1984. Translation in a non-uniform process: effect of tRNA availability on the rate of elongation of nascent polypeptide chains. J. Mol. Biol. 180, 549–576). The key results of the study are: (i) the average time (at 37 °C) to add an amino acid, as defined by the ith codon, to the nascent peptide chain is: τ(i) = 9.06 + 1.445 × [10.48C(i) + 0.5R(i)] (in ms); (ii) the misreading frequency is directly proportional to the near-cognate competition, E(i) = 0.0009C(i); (iii) the competition from near-cognates, and not the availability of cognate aa-tRNAs, is the most important factor that determines the translation rate – the four codons with highest near-cognate competition (in the case of E. coli) are [GCC] > [CGG] > [AGG] > [GGA], which overlap only partially with the rarest codons: [AGG] < [CCA] < [GCC] < [CAC]; (iv) based on the kinetic rates at 37 °C, the average time to insert a cognate amino acid is 9.06 ms and the average delay to process a near-cognate aa-tRNA is 10.45 ms and (vii) the model also provides estimates of the vacancy times of the A site of the ribosome – an important factor in frameshifting.     

重庆都市圈土壤重金属元素形态分析

选取重庆市表层土壤样品,采用Tessier A连续提取法研究了土壤中Hg、Cd、Cr、Cu、Zn、Ni等6种重金属元素进行形态分析。结果表明,在该区域表层土壤中Cd以离子交换态为主,其余的重金属元素均以残渣态为主,说明Cd较活泼,对环境有潜在的影响力,Hg、Cu、Zn、Ni、Cr相对比较稳定。     

考虑中间库存缓冲区的多目标设备不完美预防维修策略研究

针对考虑库存缓冲区的多目标设备维修问题,以设备维修能力为约束条件,获得随机故障设备的不完美预防维修策略。首先,利用准更新过程,表示出设备的随机故障次数。其次,结合设备故障次数表达式,以最大设备可用度和最小生产总成本为多目标构建不完美预防维修模型,使用粒子群算法求解,优化设备可用度与生产总成本,获得更新周期内的库存量和预防维修周期两个决策变量的最优值。最后,通过算例分析,验证了多目标不完美预防维修模型的可用性。     

Product availability in competitive and cooperative dual-channel distribution with stock-out based substitution

This paper investigates the impact of customers’ stock-out based substitution on the product availability and the channel efficiency of a dual-channel supply chain, which consists of a supplier distributing a single product to customers through both its wholly owned direct channel and an independent retailer. The supplier and its retailer, with the objective of optimizing their own profit, simultaneously choose their own base-stock level to satisfy the stochastic demand from the customers whose channel preferences are heterogeneous and may be affected by each channel’s product availability. The customers dynamically substitute between the two channels in the event of a stock-out. The result shows that the effect of the stock-out based substitution may increase or decrease the efficiency of a decentralized supply chain. It is found that while the integrated supplier–retailer may consolidate the base-stock levels to benefit from stock-out based substitution, the independent supplier and retailer are more inattentive to customers’ stock-out based substitution. Thus, the competitive base-stock levels of the decentralized dual-channel supply chain rarely agree with the system optimal levels. Various contracts are examined to shed light on channel coordination mechanisms. In addition, it is shown that the channel efficiency of the dual-channel distribution can be improved by the emergence of Stackelberg leadership from either the supplier or the retailer.     

离散时间单部件可修系统瞬时可用度的渐近稳定性

针对离散时间下修理有延迟的单部件可修系统,研究了有限时间约束下的系统瞬时可用度模型.证明了该系统瞬时可用度的渐近稳定性,并得到了系统稳态可用度的表达式.结果表明系统瞬时可用度的稳定性对离散时间系统和连续时间系统具有一致性,进一步说明了离散时间下瞬时可用度模型的有效性,同时也加强了研究有限时间段内系统瞬时可用度波动的理论基础.     

jsNMR: an embedded platform‐independent NMR spectrum viewer

jsNMR is a lightweight NMR spectrum viewer written in JavaScript/HyperText Markup Language (HTML), which provides a cross‐platform spectrum visualizer that runs on all computer architectures including mobile devices. Experimental (and simulated) datasets are easily opened in jsNMR by (i) drag and drop on a jsNMR browser window, (ii) by preparing a jsNMR file from the jsNMR web site, or (iii) by mailing the raw data to the jsNMR web portal. jsNMR embeds the original data in the HTML file, so a jsNMR file is a self‐transforming dataset that may be exported to various formats, e.g. comma‐separated values. The main applications of jsNMR are to provide easy access to NMR data without the need for dedicated software installed and to provide the possibility to visualize NMR spectra on web sites. Copyright © 2015 John Wiley & Sons, Ltd.     

QZSS导航系统在亚太地区的初步性能评估

QZSS系统是由日本宇宙航空研究开发机构研发和实施的区域性卫星导航及增强系统。利用实测数据分别从系统可见性、定位服务和增强服务三个方面就QZSS系统在亚太地区的服务性能展开评估分析。结果显示:QZSS系统对日本测区的可用性提升最为显著;有QZSS系统协同配合的GPS系统的定位精度、可用性和可靠性较单一GPS系统均有提升,尤其在高截止高度角情况下这种改善更为显著;QZSS系统提供的L1-SAIF增强信号能显著提升GPS系统实时导航的精度。