基于自适应发送波束成形的STB〖JP9〗C-〖JP〗OFDM系统

提出了一种基于信道特性的自适应发送波束成形空时分组码正交频分复用(STB〖JP9〗C-〖J P〗OFDM)系统方案. 给出了最大接收信噪比条件下最优发射权值的闭式解和性能仿真结果. 该系统能最大限度地利用所有的分集资源并对发射功率进行最优分配. 与传统的STB〖JP9〗C-〖JP〗OFDM系统相比，系统性能有明显的提高，而与系统较复杂的空时格码OFDM系统和TC〖JP9〗M-〖JP〗STB〖JP9〗C-〖JP〗OFDM系统相比，在高信噪比条件下能获得较大信噪比增益. 讨论了存在信道估计偏差时，自适应发送波束成形STB〖JP9〗C-〖JP〗OFDM系统的性能.     

有固定波长转换器的全光环网波长分配算法

采用波分复用技术的全光网是目前宽带网络研究的方向之一,波长分配是其中主要的算法问题,具有重要的理论和应用价值.研究了具有任意固定波长转换器的环形光网上的波长分配问题.首先,提出了两个对环网上的请求集合预处理的算法,这两个算法可以将请求集合分解成一些连续的循环序列;然后,采用置换群来描述具有固定波长转换器的光环网,基于这种数学表示,提出了对环网上的波长信道进行分解的算法;基于这些算法,进一步提出了一个波长分配算法,该算法对于环形光网上的任意固定转换模式都能给出一个较好的波长分配方案.     

集群制移动通信系统在铁路公务通信网中的应用

介绍了铁路集群移动通信网的网络构成、网络功能、工作方式及信令方式等等，指出了集群移动通信系统是一种新型的调度信息系统，已在铁路公务通信网中大量使用。     

Faecal contamination of greywater and associated microbial risks

The faecal contamination of greywater in a local treatment system at Viby?sen, north of Stockholm, Sweden was quantified using faecal indicator bacteria and chemical biomarkers. Bacterial indicator densities overestimated the faecal load by 100-1000-fold when compared to chemical biomarkers. Based on measured levels of coprostanol, the faecal load was estimated to be 0.04 g person(-1) day(-1). Prevalence of pathogens in the population and the faecal load were used to form the basis of a screening-level quantitative microbial risk assessment (QMRA) that was undertaken for rotavirus, Salmonella typhimurium, Campylobacter jejuni, Giardia lamblia and Cryptosporidium parvum. The different exposure scenarios simulated--direct contact, irrigation of sport fields and groundwater recharge--gave unacceptably high rotavirus risks (0.04 < Pinf < 0.60) despite a low faecal load. The poor reduction of somatic coliphages, which were used as a virus model, in the treatment was one main reason and additional treatment of the greywater is suggested. Somatic coliphages can under extreme circumstances replicate in the wastewater treatment system and thereby underestimate the virus reduction. An alternative QMRA method based on faecal enterococci densities estimated similar risks as for rotavirus. Growth conditions for Salmonella in greywater sediments were also investigated and risk modelling based on replication in the system increased the probability of infection from Salmonella 1000-fold, but it was still lower than the risk of a rotavirus infection.     

U_stor中一种数据传输系统的设计与实现

在分析广域网文件传输协议FTP和TCP协议原理的基础上,提出了一种将FTP数据连接复用的文件传输系统,介绍了系统结构和实现系统的关键技术,最后给出实验评价,结果表明:该文件传输系统对批量小文件的传输较其它广域网传输方法具有更好的性能。     

Effects of acid adaptation on the survival of Listeria monocytogenes on modified atmosphere packaged vegetables

The survival and growth of Listeria monocytogenes and L. innocua on ready-to-use (RTU) packaged vegetables (lettuce, swedes, dry coleslaw mix, bean-sprouts) were studied. The effects of acid adaptation of Listeria spp. on their survival during subsequent storage were also investigated. Listeria innocua behaviour was similar to that of L. monocytogenes on all vegetables examined. The survival and growth patterns of Listeria varied with the packaged product. Populations on packaged lettuce and swedes significantly increased ( P  < 0.05, by 1–1.5 log cycles) during a 14-day storage period. During the same period, Listeria counts gradually decreased (by 1–1.5 log cycles) on coleslaw mix. Acid adaptation enhanced survival of Listeria spp. during storage in packages of vegetables which had relatively high in-pack CO₂ levels (i.e. 25% in packaged coleslaw, bean-sprouts). It is concluded that adapting listerial cells to mildly acidic conditions rendered cultures more resistant to relatively high (25–30%) CO₂ atmospheres.     

2019年冻鱼糜制品中食源性致病菌污染状况分析

目的 了解冻鱼糜制品中食源性致病菌污染状况。方法 从全国范围内采集冻鱼糜制品4 516份，按照食品安全国家标准《食品微生物学检验》相应标准的规定，对样品中单核细胞增生李斯特菌、副溶血性弧菌、小肠结肠炎耶尔森氏菌、致泻大肠埃希菌进行检验。结果 单核细胞增生李斯特菌检出率6.02%（272/4 516），副溶血性弧菌检出率0.84%（38/4 516），小肠结肠炎耶尔森氏菌检出率0.84%（38/4 516），致泻大肠埃希菌检出率0.91%（41/4 516）。单核细胞增生李斯特菌的污染在4种食源性致病菌中较为突出，且不同产地的样品中单核细胞增生李斯特菌的污染差异较大。除副溶血性弧菌以外，其余3种食源性致病菌在散装样品中的检出率均高于预包装样品。结论 市售冻鱼糜制品存在致病菌污染，需要关注其健康风险。     

Assessment of fermentation as a household technology for improving food safety: a joint FAO/WHO workshop

Food safety and nutritional aspects of lactic acid fermentation processes for the purpose of complementary food preparation at household scale in tropical countries were assessed during an FAO/WHO workshop held in Pretoria, South Africa in December 1995.

Lactic acid fermentation was evaluated in particular, taking into consideration that microbial fermentation is only a part of the food preparation processes involving other operations such as soaking, cooking and the use of germinated cereals. The latter are of special interest as they enable the preparation of semiliquid porridges of high-nutrient density.

The present state of knowledge concerning the antimicrobial effects imparted by the acidity in lactic-fermented foods was reviewed, as well as the nutritional benefits of fermentation and use of germinated cereals. Areas requiring further research were identified and prioritized.

It was concluded that high priority should be given to research on: the effect of lactic acid fermentation on viruses, parasites, some bacteria and mycotoxins; risk assessment using the HACCP approach, health education of food handlers and consumer perception of fermented foods; characterization and optimization of fermentation processes and development of appropriate starters; and some physiological and nutritional effects of consumption of fermented foods.     

Pre-Compensation for Rayleigh Fading Channels in Time Division Duplex OFDM Systems

Coherent demodulation results in good detection performance but requires channel estimation. Fading pre-compensation (precoding) at the transmitter can lead to low-complex receiver structures with good performance capabilities, without the need for channel estimation. Time division duplex systems based on orthogonal frequency division multiplex (OFDM) are particularly suited to this because intersymbol interference effects can be neglected, simplifying transmitter adjustments. Methods that involve amplitude and/or phase pre-compensation are compared in terms of resulting bit error rate and increase in peak-to-average power ratio. Dynamic channels degrade the performance as the block lengths get longer. For a certain block length the performance degrades below that of traditional differential decoding. A block length of up to 40 times that used in the Digital European Cordless Telephone system, DECT, is possible using channel estimation and ideal Wiener prediction.