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811.
WEP的安全技术分析及对策 总被引:6,自引:2,他引:4
在对无线局域网WLAN标准IEEE80 2 .11的WEP描述的基础上 ,笔者深入研究了WEP协议的设计上和实际应用中存在的密钥序列重复使用、消息认证和完整性等严重安全漏洞 ;详细分析了标准无线局域网中WEP协议解决方案 ;提出了WEP的改进算法WEP2 ,WEP2将IV大小增加到 12 8bit,以增强抗攻击能力 ;分析了AES解决方案的可行性 ;在密钥再生与分配方面 ,提出在MAC层实现经认证的密钥交换 ,用来改善WEP的安全脆弱性等解决措施。最后 ,还对今后的研究方向作出进一步的展望 相似文献
812.
Studies on toxicities and tolerances of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) in the brown alga Isochrysis galbana and in the green-lipped mussel Perna viridis were conducted by short-term bioassays using endpoints growth production and mortality, respectively. The 5-day EC(50) and 24-h LC(50) of these heavy metals were determined in the brown alga and mussel, respectively. The EC(50) values calculated for the alga were 0.74 mg/l for Cd, 0.91 mg/l for Cu, 1.40 mg/l for Pb and 0.60 mg/l for Zn. The LC(50) values for the mussels were 1.53 mg/l for Cd, 0.25 mg/l for Cu, 4.12 mg/l for Pb and 3.20 mg/l for Zn. These LC(50) values were within the concentration ranges as reported by other authors who used P. viridis as the test organism. Based on these EC(50) and LC(50) values, the alga was most sensitive to Zn, followed by Cd, Cu and Pb while the mussel was most sensitive to Cu, followed by Cd, Zn and Pb. Differences in the trophic levels, metal handling strategies, biology and ecology of the primary producer (brown alga) and the primary consumer (mussel) are believed to be the plausible causes for the different toxicities and tolerances of the metals studied. 相似文献
813.
To study respiratory health effects of long-term exposure to ambient air pollutant mixture, we observed 7058 school children 5-16 years of age living in the four Chinese cities of Lanzhou, Chongqing, Wuhan, and Guangzhou. These children were enrolled from elementary schools located in eight districts, one urban district and one suburban district in each of the above cities. Ambient levels of PM(2.5), PM(10-2.5), total suspended particles (TSP), SO(2), and NO(x) were measured in these districts from 1993 to 1996. Based on a cluster analysis of arithmetic mean concentrations of PM(2.5), PM(10-2.5), (TSP-PM(10)), SO(2), and NO(x), we classified these children into four ordinal categories of exposure to ambient air pollutant mixtures. We tested for exposure-response relationships using logistic regression models, controlling for relevant covariates. We observed monotonic, positive relationships of exposure to the pollutant mixture with prevalence rates of cough with phlegm and wheeze. Other outcomes were not associated with the exposure in a monotonic exposure-response pattern. Even so, odds ratios for cough, phlegm, bronchitis, and asthma in the higher exposure district clusters were all higher than in the lowest exposure district cluster. We found evidence that exposure to the pollutant mixtures had adverse effects on children living in the four Chinese cities. 相似文献
814.
The treatment of chromium-containing leather waste (CCLW), the major solid waste generated at the post-tanning operations of leather processing, has the potential to generate value-added leather chemicals. Various alkali and enzymatic hydrolysis were compared, and calcium oxide was found to be important for effective (but still incomplete) hydrolysis. Three possible reasons are given for the incomplete hydrolysis under alkaline conditions. Data for 19 amino acids are presented for four different treatment products. On the basis of the results, a novel three-step CCLW treatment process is proposed. The gelatin extracted in the first step is chemically modified to produce leather finishing agents. The collagen hydrolysates isolated in the second step are used as proteinic retanning agents by chemical modification. The remaining chrome cake is further hydrolyzed with acids in the third step, and the obtained chromium-containing protein hydrolysates could be used for the preparation of chromium-containing retanning agents for leather industry. The proposed three-step process provides a feasible zero discharge process for the treatment of CCLW. 相似文献
815.
816.
Tillage, intercrop, and controlled drainage-subirrigation influence atrazine, metribuzin, and metolachlor loss 总被引:2,自引:0,他引:2
Gaynor JD Tan CS Drury CF Ng HY Welacky TW van Wesenbeeck IJ 《Journal of environmental quality》2001,30(2):561-572
Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] have been found with increasing occurrence in rivers and streams. Their continued use will require changes in agricultural practices. We compared water quality from four crop-tillage treatments: (i) conventional moldboard plow (MB), (ii) MB with ryegrass (Lolium multiflorum Lam.) intercrop (IC), (iii) soil saver (SS), and (iv) SS + IC; and two drainage control treatments, drained (D) and controlled drainage-subirrigation (CDS). Atrazine (1.1 kg a.i. ha-1), metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazine-5(4H)-one] (0.5 kg a.i. ha-1), and metolachlor (1.68 kg a.i. ha-1) were applied preemergence in a band over seeded corn (Zea mays L.) rows. Herbicide concentration and losses were monitored from 1992 to spring 1995. Annual herbicide losses ranged from < 0.3 to 2.7% of application. Crop-tillage treatment influenced herbicide loss in 1992 but not in 1993 or 1994, whereas CDS affected partitioning of losses in most years. In 1992, SS + IC reduced herbicide loss in tile drains and surface runoff by 46 to 49% compared with MB. The intercrop reduced surface runoff, which reduced herbicide transport. Controlled drainage-subirrigation increased herbicide loss in surface runoff but decreased loss through tile drainage so that total herbicide loss did not differ between drainage treatments. Desethyl atrazine [6-chloro-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine] comprised 7 to 39% of the total triazine loss. 相似文献
817.
长江三角洲及其附近地区两千年来水灾的研究 总被引:6,自引:1,他引:5
通过对长江三角洲及其附近地区两千年来水灾生成频率和强度的分析。认为两晋、南北朝时期和南宋、元、明、清时期是两千年来本区的主要水灾期。对照两千年来中国东部气候变化、海面升降与长江口河道变迁关系,认为在本区水灾生成事件中,气候因素起着主导控制作用。当然,人类活动对本区水灾生成的影响也不容忽视。本地区近百年来的旱涝灾害规律可用非线性科学的方法进行研究,旱涝灾害的准60年、准35年和准11年的长周期变化与地球自转速度、地极移动和太阳黑子活动的3个周期变化基本一致。本地区气候系统的行为具有混沌特征。这是线性逼近和周期叠加预报方法难以得出灾害预报正确结果的原因,但气候系统半个月的确定性预测可以实现。 相似文献
818.
Tan X Bi Y Su Y Li Y He J Yi P Yan J Wang C Wang F Vanhoorne M 《Journal of environmental monitoring : JEM》2000,2(6):666-669
This article presents the results of carbon disulfide exposure measurements in a Chinese viscose rayon factory. The objectives of the study were to identify the external exposure levels at a large factory and to investigate the 2-thiothiazolidine-4-carboxylic acid (TTCA) concentrations in the urine of the subjects who were exposed to carbon disulfide in the working place atmosphere. The metabolism of carbon disulfide in the exposed subjects was also studied in order to demonstrate the best points in time for the internal exposure sampling. The measurement of the amount of personal exposure to carbon disulfide in the air of the workplace was performed by GC-FPD; the presence of TTCA in the workers urine was analyzed by use of a modified HPLC method. The kinetics of TTCA excretion was studied by analyses at different time-points both during and after exposure to carbon disulfide in the subjects. A total of 155 personal samples were obtained. The carbon disulfide concentration in the staple viscose hall was 13.72 +/- 1.12 mg m-3 in terms of the geometric mean +/- geometric standard deviation, and was 20.05 +/- 1.33 mg m-3 in the filament spinning hall. The TTCA values in the subjects who worked in the staple spinning hall were 1.18 +/- 0.43 mg g-1 creatinine and 1.07 +/- 0.38 mg g-1 creatinine for subjects working in the filament spinning hall. The best time for TTCA sampling is at the end of the working shift, the TTCA excretion was stable for a period of 4-12 h after exposure of the subjects to the carbon disulfide. It might be that the Chinese have different anthropometric characteristics; a sampling bias may therefore appear among different races. 相似文献
819.
基于AVHRR的成都平原城市热岛效应演变趋势分析 总被引:7,自引:0,他引:7
作为城市气候主要特征之一的热岛效应有日渐明显的趋势,给城市发展和市民生活带来一系列负面影响。对2000~2006年春季下午NOAA气象卫星遥感数据的处理和分析发现,随着城市的扩张,成都平原城市热岛效应的规模呈扩大趋势。成都市区热岛强度一般为5℃-7℃,局部地方极值可达8℃以上;市中心区热岛强度相对减弱,东部工业区热岛高温区面积逐渐缩小,市区西南部热岛明显发展,致使2003年起热岛次高温区在二、三环路附近大致呈环状分布。热岛演变与近几年城市建设和改造活动密切相关。研究成果为政府相关部门缓解热岛效应、改善人居环境提供了参考依据。 相似文献
820.
上海潜在滨海旅游资源调查及开发研究 总被引:1,自引:0,他引:1
上海市的海岸线蜿蜒460km,涉及5区1县,潜在滨海旅游资源亟待开发。为了更好地了解和掌握潜在上海滨海旅游资源的现状,结合上海独特的自然禀赋和社会经济条件,参照《旅游资源分类、调查与评价(国家标准)》(GB/T18972-2003),在对上海潜在滨海旅游资源普查的基础上,研究了上海潜在滨海旅游资源分类,分析了潜在滨海旅游资源特征和资源富集区状况,选划出上海应重点开发的6大潜在滨海旅游资源区,并分别就各资源区的开发对策与建议提出初步构想。 相似文献