发电机氢气纯度下降原因分析及处理

红河发电厂#1机300MW汽轮发电机组在2008下半年出现氢气纯度下降速度变快,靠频繁补氢置换维持的异常情况,通过阶段性SIS趋势分析以及现场试验,最终判断为氢侧密封油箱自动补排油浮球阀存在关闭不严问题,并制定现场措施解决了发电机氢纯度下降速度快的问题,保证了发电机氢系统的稳定运行。     

直流电源系统在国内外的应用状况

随着电网技术的不断发展,对站用直流电源系统的供电可靠性和安全性提出了更高的要求,这也使得国内外电力行业对该系统的关注度逐渐提高。结合对四川省10年间直流电源系统统计数据的分析和CIGRE工作的经验,对直流电源系统在国内外的应用情况进行了论述。     

改进禁忌算法在无功优化中的应用

提出一种基于改进禁忌算法的无功优化方法,该算法不仅对初值没有特殊要求,而且减少了在候选解集中为了达到一定数量满足约束的个体而进行的大量搜索与计算;同时解决了禁忌算法在高精度情形下,无法爬坡的缺点。最后在IEEE30节点系统上验证了该算法的优越性。     

Listeria monocytogenes contamination patterns for the smoked fish processing environment and for raw fish

Reliable data on the sources of Listeria monocytogenes contamination in cold-smoked fish processing are crucial in designing effective intervention strategies. Environmental samples (n = 512) and raw fish samples (n = 315) from two smoked fish processing facilities were screened for L. monocytogenes, and all isolates were subtyped by automated ribotyping to examine the relationship between L. monocytogenes contamination from raw materials and that from environmental sites. Samples were collected over two 8-week periods in early spring and summer. The five types of raw fish tested included lake whitefish, sablefish, farm-raised Norwegian salmon, farm-raised Chilean salmon, and feral (wild-caught) salmon from the U.S. West Coast. One hundred fifteen environmental samples and 46 raw fish samples tested positive for L. monocytogenes. Prevalence values for environmental samples varied significantly (P < 0.0001) between the two plants; plant A had a prevalence value of 43.8% (112 of 256 samples), and plant B had a value of 1.2% (3 of 256 samples). For plant A, 62.5% of drain samples tested positive for L. monocytogenes, compared with 32.3% of samples collected from other environmental sites and 3.1% of samples collected from food contact surfaces. Ribotyping identified 11 subtypes present in the plant environments. Multiple subtypes, including four subtypes not found on any raw fish, were found to persist in plant A throughout the study. Contamination prevalence values for raw fish varied from 3.6% (sablefish) to 29.5% (U.S. West Coast salmon), with an average overall prevalence of 14.6%. Sixteen separate L. monocytogenes subtypes were present on raw fish, including nine that were not found in the plant environment. Our results indicate a disparity between the subtypes found on raw fish and those found in the processing environment. We thus conclude that environmental contamination is largely separate from that of incoming raw materials and includes strains persisting, possibly for years, within the plant. Operational and sanitation procedures appear to have a significant impact on environmental contamination, with both plants having similar prevalence values for raw materials but disparate contamination prevalence values for the environmental sites. We also conclude that regular L. monocyrogenes testing of drains, combined with molecular subtyping of the isolates obtained, allows for efficient monitoring of persistent L. monocytogenes contamination in a processing plant.     

The evaluation and adoption of annual legumes by smallholder maize farmers for soil fertility maintenance and food diversity in central Malawi

We studied the process of assessment and adoption of 10 grain- and green-manure legumes by smallholder maize farmers differing in resource endowment in Chisepo, central Malawi. The legumes had been promoted with the farmers from 1998 to 2004, primarily as a way to diversify food production and maintain the fertility of their soils. Farmers (n?=?136) were surveyed in 2004 at the end of the period of promotion to assess the degree of awareness and uptake of the legumes and the reasons for adoption. A follow-up survey was conducted in 2007 among a broader sample of Chisepo farmers (n?=?84) to measure the persistence of adoption. An Analytic Hierarchy Process (AHP) was used in 2004 to create scales of priority and as a tool to compare predicted with actual legume uptake. Actual adoption of food grain legumes reflected predictions by the AHP but it over-predicted uptake of the non-food legumes. The AHP helped us understand how farmer perceptions and needs influence adoption, as well as limitations with the legumes. Suitability for food was the most important criterion that farmers identified for adoption, followed by contribution to soil fertility and suppression of weeds. Over 75 % of the farmers surveyed in 2004 were aware of most of the legumes. Frequent use of the grain legumes was reported in 2004 (79 % for CG7 groundnut, 77 % for soyabean and 47 % for pigeonpea) by both the better-resourced (wealthier) and less-well-resourced (poorer) farm households. Awareness rose to over 90 % of farmers surveyed in 2007 but adoption fell somewhat to 67 % for soyabean, 57 % for CG7 groundnut and 43 % with pigeonpea among the wealthier farmers, while Bambara groundnut rose to 38 %. Fifty-two percent of poorer farmers reported adoption of CG7, 46 % soyabean, 35 % Bambara groundnut and 27 % pigeonpea in 2007. There was greater uptake by the wealthier farmers than those with fewer resources. Overall, although the legumes were promoted for maintenance of soil fertility, farmers were largely interested in and mainly adopted those legumes they considered most useful for food diversity and security, and with potential for market sale. Only a few wealthier farmers used mucuna and tephrosia among the green manure legumes. Improving the food value of vigorous and productive multi-purpose legumes, particularly mucuna, may help raise the farmers’ interest, with secondary benefits for soil fertility.     

The Effect of Endogenous Pectinases on the Consistency of Tomato–Carrot Purée Mixes

Tomato and carrot were subjected to a split-stream process designed to produce a tomato–carrot suspension with reduced consistency. Raw tomatoes, containing pectinmethylesterase and endo-polygalacturonase, were mixed with thermally pretreated (blanched versus cooked) carrots containing different levels of solubilized pectin. After mixing the vegetables, tomato pectinases were shown to act on both tomato and carrot pectin in case an incubation step at medium temperature level (30 min, 40 °C), to allow enzyme action, was performed. Carrot pectin, when present in a mix of tomato and blanched (5 min, 95 °C) carrot, was solubilized as well as depolymerized, whereas depolymerization of the thermo-solubilized carrot pectin by the tomato pectinases was observed in the tomato–carrot purée containing cooked (30 min, 95 °C) carrots. The final serum pectin properties were however similar for both purée types. Carrot contributed more to the consistency of the purée mix compared with tomato but by stimulating the action of the tomato pectinases at mild temperature (30 min, 40 °C), this contribution was lost which resulted in a consistency reduction of the purée mix. This purée liquefaction was larger for the tomato–carrot purée containing blanched instead of cooked carrots. Based on the results, it is suggested that the liquefying effect is related to solubilization and degradation of pectin that is counteracted by a reduction in particle size. The purée mix containing cooked carrot showed in this respect smaller particle sizes than the mix containing blanched carrot.     

Grapefruit juice enhance the uptake of coenzyme Q10 in the human intestinal cell-line Caco-2

Coenzyme Q10 (CoQ10) is very widely consumed by humans as a food supplement. However, CoQ10 is taken up from the intestine into the circulation at a low rate. The absorption of compounds from the gastrointestinal tract is one of the important determinants for oral bioavailability. Secretory transport limits the oral bioavailability of compounds. It has been reported that efflux transport of CoQ10 is mediated by P-glycoprotein (P-gp) in Caco-2 cells. We tried to improve intestinal absorption of CoQ10 by modulating P-gp. Since grapefruit juice (GFJ) is reported to inhibit P-gp function, we investigated the effect of GFJ on the transport of CoQ10 by Caco-2 cells. In the presence of GFJ, the basal-to-apical transport of CoQ10 was decreased and the uptake of CoQ10 was increased. These findings suggest that the combined administration of CoQ10 and GFJ could enhance CoQ10 absorption.     

Impact of Changes in Sugar Exudate Created by Biological Damage to Tomato Plants on the Persistence of Escherichia coli O157:H7

ABSTRACT: The survival of enteric pathogens on vegetable leaves improves due to presence of phytopathogens. Phytopathogen damage alters the microenvironment on the leaf surface. The objective of this study was to identify differences in sugar concentrations in tomato leaves damaged by biotropic plant pathogens and determine if these differences affect Escherichia coli O157:H7 survival. E. coli O157:H7 survived better on tomato plants damaged by Xanthomonas campestris than on healthy plants (P = 0.012). The most common sugars and sugar alcohols in the damaged leaf exudate were glucose, fructose, inositol, and sucrose. The abundance of sucrose and inositol differed between the healthy and infected plants (P < 0.05). In this study, it was found that phytopathogen damaged plants increased sugar availability on the leaf surface for E. coli O157:H7 to proliferate. Keeping plants free from biological damage can limit the amount of leaching of sugars that could allow human pathogens to proliferate. There is the possibility of increasing food safety of vegetable products by limiting phytopathogenic damage to plants.