气相色谱-氮磷检测器检测食品中稻瘟净研究

为克服食品中复杂成分的干扰,提高稻瘟净的提取、净化效率及检测灵敏度,对已有稻瘟净的方法进行改进:用乙腈提取目标物稻瘟净,采用正己烷:丙酮(1∶1,V/V)替代传统工艺中毒性较强的二氯甲烷提取液;植物源性食品采用石墨化碳黑小柱对提取液进行净化,动物源性食品采用氧化铝柱对提取液进行净化;采用氮磷检测器(NPD)检测,方法检出限为0.001mg/kg。测定食品中稻瘟净加标回收率在91.3%～97.5%之间,适应于成分复杂的食品中稻瘟净的测定。     

毛细管气相色谱柱的使用及常见故障的分析与研究

目的:介绍毛细管气相色谱柱的正确安装与使用.方法:对在使用毛细管气相色谱柱时遇到的问题进行综合分析.并提出切实可行的解决办法.结果:从理论和实际这两方面总结了解决问题的方法.结论:毛细管气相色谱法以其分析速度快、分离效果好、适用性强、已被广泛应用,通过本文的介绍,为广大从事毛细管气相色谱分析的工作者提供了方便.     

用于气体分析的气相色谱技术

本文从色谱柱、检测器、如何减小峰形拖尾、如何选择定值方法等四个方面,论述了气相色谱在气体分析中的应用技术。     

气相色谱仪TCD检定结果的测量不确定度评定

通过分析测量气相色谱仪TCD灵敏度检定过程中各分量引入的测量不确定度来源,对TCD灵敏度的各测量不确定度分量进行了量化,得出标准样品进样量的不确定度是最大的。评定结果为TCD灵敏度的相对合成标准不确定度为1.0%,扩展不确定度为2.0%(k=2)。     

双检测器串联色谱柱分析六味地黄丸

对高效液相色谱系统进行了改造并用于中药六味地黄丸的分析。紫外检测器与蒸发光散射检测器串联以提高峰容量;升高分析温度串联色谱柱以增加柱效。结果显示,紫外检测器共检测到156个峰,蒸发光散射检测器检测到195个峰,其中41个色谱峰为可以认证的共有峰,所构建的系统非常适宜于中草药指纹图谱的研究。     

调节阀安装注意事项及常见故障检修

气动调节阀是自动调节系统中重要的、必不可少的环节,在工厂的运用非常普遍,尤其在石油化工行业,每年都要对调节阀进行检修。结合实践过程中的经验,文章简介对投运时应注意事项、常见故障分析及检修要点,以便有针对性地开展工作,最大限度地提高工效和经济效益。     

气相色谱-质谱联用仪的日常维护

本文作者以型号Agilent 6890 597x四极杆气相色谱-质谱联用仪为例,从载气系统、质谱真空系统、进样系统、色谱柱使用、质谱系统的日常维护等方面进行了较为详尽的阐述与故障分析,以求本文对大家在仪器实际操作过程中能有所帮助.其它型号的气相色谱-质谱联用仪亦可以作参考。     

用氦离子化检测器的高分辨率气相色谱测定永久气体

评价了氦离子化检测器(HID)与毛细管色谱柱结合分析痕量气体的能力，研究了两种不同毛细管柱，带有分子筛PLOT（多孔层开品管柱）熔硅柱和带有PS-256（聚苯乙烯-255）厚膜的WCOT（涂壁开口管柱）破璃柱。尽管使用了分流进样系统，但该柱在测定气全中痕量杂质时可以比经典的填充色谱柱具有明显的优点，也研究了柱上直接进样，并取得了有希望的结果。     

气相色谱的定性方法与定量方法

本文主要对气相色谱分析中的定性方法和定量方法进行了阐述。     

直接进样的热导检测器(TCD)色谱法测定高纯氦中Ne、O2、N2

主要是通过直接进样的热导检测器色谱系统来检测高纯氦中的微量杂质(Ne、O2、N2),解决了目前高纯氦分析中始终存在的难题--氖的测定.这项工作具有技术上的突破,并且有实用、可推广的现实意义.     

Novel view of the origin of thermal and intrinsic breakdowns

A novel view is presented on the origin of thermal and intrinsic breakdowns from the analysis of published data for pynax glass and several polymers. For the former, the Origin is not due to failure of thermal balance between joule heating and its dissipation, but to charge injection from the anode, by which the current surge to the cathode is afforded and, when the cathode cannot accommodate the neutralized charge carriers, those neutralized species would pile up and advance the cathode-front back to the anode and, finally, a filamentary conductive path is constructed between the electrodes. It is suggested that the occurrence of intrinsic breakdown is determined by the number of electrons which are injected from the cathode by tunnelling because an individual electron gives rise to a certain amount of damage on its passage through the insulator by momentum transfer. From the analysis of time delay before the onset of breakdown, we can estimate the electron affinity of an insulator.     

The effect of breakdowns on U-shaped production lines

Consider a synchronized line performing assembly or fabrication tasks. Tasks are grouped into stations and stations are positioned on a line that is U-shaped. Stations may break down and be repaired. Small buffer inventories may be placed between stations to lessen the effect of breakdowns at one station on production at other stations. This paper investigates the effect of the U-shape of the line on the line effectiveness. We find that effectiveness increases when the line is U-shaped, compared with the traditional straight line shape.     

Do not forget the breakdowns and the maintenance operations in FMS design problems!

The increase in the number of flexible manufacturing systems is nowadays one of the main trends in the mechanical industry. Because of the complexity of such systems, careful studies are required to make the appropriate design choices in order to avoid an economical disaster. The queueing network theory provides adequate tools to deal with these problems.

Most of the analytical models neglect the breakdowns and the maintenance operations which disturb the smooth working of the factory.

This paper presents an easy way of modelling these perturbations so that they can be taken into account when evaluating the performances of an FMS (production rate, machine utilization,...). A comparison between the analytical results and the ones obtained by simulation demonstrates the accuracy of the proposed modelling technique.     

The effect of machine breakdowns and interstage storage on the performance of production line systems

Both machine breakdowns and interstage storage can significantly affect the efficiency of a production line. In this paper we use an exact analytic model to conduct a detailed study of how these two factors affect the throughput of a line. Based on the empirical results, a simple heuristic method is given to estimate the amount of storage space required to offset the negative effect of machine breakdowns. The results provide useful guidelines for designing or analysing production line systems.     

Predictable scheduling of a single machine with breakdowns and sensitive jobs

Production schedules released to the shop floor have two important functions: allocating shop resources to different jobs to optimize some measure of shop performance and serving as a basis for planning external activities such as material procurement, preventive maintenance and delivery of orders to customers. Schedule modification may delay or render infeasible the execution of external activities planned on the basis of the predictive schedule. Thus it is of interest to develop predictive schedules that can absorb disruptions without affecting planned external activities while maintaining high shop performance. We present a predictable scheduling approach, that inserts additional idle time into the schedule to absorb the impacts of breakdowns. The effects of disruptions on planned support activities are measured by the deviations of job completion times in the realized schedule from those in the predictive schedule. We apply our approach to minimizing total tardiness on a single machine with stochastic machine failures. We then extend the procedure to consider the case where job processing times are affected by machine breakdowns, and provide specialized rescheduling heuristics. Extensive computational experiments show that this approach provides high predictability with minor sacrifices in shop performance.     

Genetic algorithm for job-shop scheduling with machine unavailability and breakdowns

The job-shop scheduling problem (JSSP) is considered to be one of the most complex combinatorial optimisation problems. In our previous attempt, we hybridised a Genetic Algorithm (GA) with a local search technique to solve JSSPs. In this research, we propose an improved local search technique, Shifted Gap-Reduction (SGR), which improves the performance of GAs when solving relatively difficult test problems. We also modify the new algorithm for JSSPs with machine unavailability and breakdowns. We consider two scenarios of machine unavailability. First, where the unavailability information is available in advance (predictive) and, secondly, where the information is known after a real breakdown (reactive). We show that the revised schedule is mostly able to recover if the interruptions occur during the early stages of the schedules.     

Modelling and optimisation of a two-server queue with multiple vacations and working breakdowns

This paper presents a steady-state analysis of an M/M/2 queue with heterogeneous servers (Server 1 and Server 2). Server 1 is reliable and may leave for a vacation when the system becomes empty. Sever 2 is unreliable and may break down while serving customers. When a breakdown occurs, Server 2 reduces the service rate rather than halting service. We formulate this queueing model as a quasi birth-and-death (QBD) process, using the matrix geometric method to compute the stationary distribution of system size. We also develop several measures to evaluate the performance of the system. A cost model based on system performance measures is formulated as a heuristic cost optimisation problem subject to stability conditions. A canonical particle swarm optimisation algorithm is used to obtain numerical solutions for the approximate optimal service rates of Server 1 and Server 2. Moreover, we present numerical results showing the effects of various parameters on the approximate optimal service rates as well as a practical example illustrating the application of the proposed model.     

PMN-xPT陶瓷的介电温谱拟合与分析

用双机制模型分析、拟合了不同PT组份弛豫型铁电陶瓷PMN-xPT的介电行为.研究表明随着PT组份的增加,极化机制发生明显的变化.通过分析极化机制随频率变化的情况,解释了Tm与ω的V-F关系的拟合参数随频率区间改变的现象.     

High cycle fatigue of welded joints: The TCD experience

This paper reports on the use of two methods for the prediction of high cycle fatigue failure in welded joints. The development of these methods – known as the crack modelling method and the theory of critical distances – is described, summarising previously published work on test specimens using steels and aluminium alloys. It is concluded that the methods work well, predicting fatigue strength with errors of less than 20% in the great majority of cases. Certain types of joint were found to give rise to large, conservative errors, but similar errors also occurred when using other, well established, methods of prediction. Some restrictions also arise with the use of the TCD for bodies having very small section thicknesses. Finally, two case studies, described here for the first time, illustrate the issues that arise when making predictions during investigations into the failure of welded joints in real engineering components in service.