Development of a dynamic model for estimating the food web transfer of chemicals in small aquatic ecosystems

A dynamic combined fate and food web model was developed to estimate the food web transfer of chemicals in small aquatic ecosystems (i.e. ponds). A novel feature of the modeling approach is that aquatic macrophytes (submerged aquatic vegetation) were included in the fate model and were also a food item in the food web model. The paper aims to investigate whether macrophytes are effective at mitigating chemical exposure and to compare the modeling approach developed here with previous modeling approaches recommended in the European Union (EU) guideline for risk assessment of pesticides. The model was used to estimate bioaccumulation of three hypothetical chemicals of varying hydrophobicity in a pond food web comprising 11 species. Three different macrophyte biomass densities were simulated in the model experiments to determine the influence of macrophytes on fate and bioaccumulation. Macrophytes were shown to have a significant effect on the fate and food web transfer of highly hydrophobic compounds with log K_OW > = 5. Modeled peak concentrations in biota were highest for the scenarios with the lowest macrophyte biomass density. The distribution and food web transfer of the hypothetical compound with the lowest hydrophobicity (log K_OW = 3) was not affected by the inclusion of aquatic macrophytes in the pond environment. For the three different hypothetical chemicals and at all macrophyte biomass densities, the maximum predicted concentrations in the top predator in the food web model were at least one order of magnitude lower than the values estimated using methods suggested in EU guidelines. The EU guideline thus provides a highly conservative estimate of risk. In our opinion, and subject to further model evaluation, a realistic assessment of dynamic food web transfer and risk can be obtained using the model presented here.     

移动商务 移动互联时代的核动力

最近一段时间来,业界内外的许多人们都在谈论移动互联可能给企业和生活带来的种种好处,人们对它的期望也非常高。几乎所有的硬件生产商、通信运营商和商业站点,无不宣布在这方面的战略性考虑。移动商务可能带来21世纪初最大的商机,其原因就是移动商务的发速度比有线要快得多。移动     

流动电贸智能卡将面世

全球电子商务活动日趋蓬勃,但利用手机进行的电子商务仍处于初步阶段,除因为硬件如WAP手机仍未普及外,显重要的是以手机进行交易的安全问题仍广受质疑。现时流动电贸最主要的保安漏洞是仍未有一种可辨别客户真正身份的技术,令卖方经常遭受损失。     

上网收音机全球电台任你听

互联网虽然无远弗届,并提供无数有用资讯,可是全球仍有不少人对电脑操作感到陌生,想到要用电脑上网才可浏览资讯便觉麻烦,因此目前市场大趋势是把互联网结合其他媒体和媒介应用。而美国最近亦有一间网上电台——企鹅电台(PenguinRadio.com),正在筹备把数千个网上电台,透过人造卫星作全球广播。     

电子商务涉足校园

美国大学校园最近刮起一片利用学生作“营业代表”,为网上公司推广品牌的风气,现时以学生推广教科书及校园用品的情况较为普遍,但发展下去,校园可能成为推广产品的必争之地。     

采用四乙基正硅酸盐的二氧化硅PECVD技术

本文介绍用四乙基正硅酸盐(TEOS)等离子体加速化学气相淀积SiO_2膜的试验研究情况。发现,当采用氧作氧化剂的时候,所产生的膜大约含有1个原子百分比浓度(a/o)的氮或碳。在反应中采用N_2O时,膜中氮浓度略有增加,达到2(a/o)。然而,在没有氧化剂的条件下,氮和碳浓度大致分别为18(a/o)和6(a/o)。膜的台阶覆盖(不考虑氧化剂)接近34％,与主要用硅烷的化学方法淀积的SiO_2膜所达到的10％相比较,有显著的改进。折射率、红外光谱和膜密度,似乎可表征淀积SiO_2膜的特征。TEOS-O_2膜的电特性产生大于6MV/cm的击穿电场,在1MV/cm下,漏电流密度为8×10~(-9)A/cm~2。具有同等厚度的热生长SiO_2的击穿电场和漏电流密度,分别为8MV/cm~2和2×10~(-9)A/cm~2。     

电脑病毒危害上网产品

电脑病毒面世已10多年,贻害了不少电脑用户及企业,每年全球因电脑病毒而导致的损失以逾亿美元计。但电脑科技愈发达,电脑病毒肆虐的地方也愈多,最近便有电脑病毒入侵手提电话及电子手帐(PDA),而病毒又可感染手帐内的其他程式,令用者一旦把资料用红外线传送(俗称beam)给其他人,便同时会把病毒传送出去。     

从存储开始：教你如何构建绿色存储空间

我们生活和工作所遇到的种种电子化应用都和现代数据中心有关,复杂多变的应用和庞大的数据量使得现代数据中心在电力和能源方面的消耗增长显著,严重的电力不足,使得数据中心机房凸显能耗危机,如同一场风暴的酝酿,绿色数据中心的概念已经从＂起点＂升至＂沸点＂。实际上,数据中心的组成包括多个方面,本文将从数据存储与保护的角度来阐述一些有助于绿色节能的新技术,并介绍一些绿色节能的实用窍门。