Quantitative determination of the population biological activity of biological sludges used in the activated sludge waste water treatment process

The population biological activity of biological sludges used in the activated sludge waste water treatment process is defined as that minimum amount of biological sludge, still able to reduce in a 21 h contact period, the soluble COD of a waste water by one half the value equivalent to the BOD_5d. This A_mg^BOD50% 21 h value was determined by incubating hundred fold serial dilutions of a biological sludge with a previously sterilized waste water and by plotting the residual soluble COD remaining after a 21 h incubation period vs the sludge dilution. The method allows any given biological sludge to be readily assayed on any given waste water. Biological sludges were found stable for periods up to three months in the frozen state or when stored at 4°C. Lyophilization of biological sludges resulted in a severe loss of population biological activity. Biological sludges of trade waste water treatment plants were followed for periods up to 70 days. A correlation was found between the population biological activity and changes in environmental factors such as reduced N and P nutrient feeding, reduced aeration or changes in pH. Minor changes resulted in a decrease in population biological activity. Drastic changes resulted in a modified shape of the soluble COD vs biological sludge dilution curves, presumably reflecting deep modifications of the waste water-treating biological community.     

The effect of global cross flows on the flow field and local heat transfer performance of miniature centrifugal fans

Centrifugal fans are often integrated into thermal management solutions for a range of applications. Consequently, centrifugal fan designs can be subjected to varying environmental conditions, many of which can alter fan performance characteristics and ultimately influence the heat transfer performance of the cooling solution. Global cross flows are a commonly encountered practical operating condition, particularly in the cooling of electronics. Air-cooled electronic enclosures often incorporate miniature centrifugal fans to maintain reliable component operating temperatures at a local level, while larger system level fans are used to simultaneously control the ambient temperature within the enclosure. This type of operating condition has been investigated by introducing a uniform crossing air flow above a centrifugal fan inlet. Two scaled miniature centrifugal fan designs were selected to fundamentally assess the influence on local velocity field and heat transfer performance. This was achieved experimentally using Particle Image Velocimetry, and a combined infrared and heated-thin-foil technique developed for the accurate measurement of local heat transfer coefficients. the introduction of a crossing air flow above the fan inlet indirectly reduced both the local and global thermal performance of the centrifugal fan, and the resultant distorted inflow shifted the surface heat transfer distribution at the fan outlet from an axisymmetric to asymmetric profile. However, strategic positioning of components relative to a centrifugal fan can maintain the average component heat transfer coefficient at a similar level to a case without any cross flow. Results also indicate issues associated with the implementation of miniature centrifugal fan designs into crossing air flow environments, with reductions in thermal performance of over 30% observed.     

Kairomones and their use for management of entomophagous insects

In laboratory experiments conducted to compare the kairomonal activity forMicroplitis croceipes (Cresson) of frass fromHeliothis zea (Boddie) larvae fed on different host plants,M. croceipes females responded to extracts of frass from larvae reared on cotton or soybeans but not on corn. The lack of response to frass from larvae reared on corn was shown to be a result of a lack of some appropriate chemical(s) in the corn.Lepidoptera: Noctuidae.Hymenoptera: Braconidae.In cooperation with the University of Georgia College of Agriculture Experiment Stations, Coastal Plain Station, Tifton, Georgia 31793. Accepted for publication February 9, 1981.Mention of a proprietary product in this paper does not constitute an endorsement by this product by the USDA.     

运用2.4GHz无线技术串连所有装置

随着科技的发达,人们的生活真是越来越舒适了。我们轻松地利用遥控器开启车库大门、电视机、录像机、DVD放映机,我们也能以无线电话、呼叫器、以PDA随时随地进行通讯联络。我们甚至能运用无线技术来监看婴儿房的动静。无线技术已成为生活中不可或缺的一部份,并且被视为理所当然的必须品。还记得必须从沙发上起身去按电视机按钮的日子吗? 现在即使是更换遥控器电池,就会被认为是不方便的事。近年来,我们对无线技术的接纳度已日趋成熟。我们不仅希望使用各种无线装置,更希望这些装置传输速度更快、价格更低廉、并能提供更高的频宽。我们也希望无线装置、家庭剧院系统以及数据网络能具备安全、稳定、以及可靠等特性;并且在彼此紧邻相近时,不会产生相互干扰的现象。而这个趋势将促使现今领先市场的红外线(IR)、27MHz、以及900MHz在内的装置难以继续发展;因此2.4GHz无线技术将取而代之成为市场的主流。     

无线芯片商的生存之道

过去两年来,消费品市场的供应链出现一系列深刻的结构调整.无线芯片供应商面临一个关键问题:哪些公司将成为蠢笨的巨人,哪些公司能够灵巧地适应新环境并生存下来?     

Human immunodeficiency virus type 2 envelope glycoprotein binds to CD8 as well as to CD4 molecules on human T cells

We report here that human immunodeficiency virus type 2 (HIV-2) envelope glycoprotein (gp105), but not HIV-1 gp120, can bind to CD8 molecules as well as to CD4 molecules on human T cells. This phenomenon may lead to differences in the life cycles of HIV-1 and HIV-2, and it may be related to the differences in disease manifestations of HIV-1 and HIV-2 infection, including longer survival of HIV-2-infected patients.