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921.
Waterborne pathogens represent a significant health risk in both developed and developing countries with sensitive sub-populations including children, the elderly, neonates, and immune-compromised people, who are particularly susceptible to enteric infections. Annually, approximately 1.8 billion people utilize a faecally contaminated water source, and waterborne diseases are resulting in up to 2.1 million human mortalities globally. Although groundwater has traditionally been considered less susceptible to contamination by enteric pathogens than surface water due to natural attenuation by overlying strata, the degree of microbial removal attributable to soils and aquifers can vary significantly depending on several factors. Thus, accurate assessment of the variable presence and concentration of microbial contaminants, and the relative importance of potentially causative factors affecting contaminant ingress, is critical in order to develop effective source (well) and resource (aquifer) protection strategies. “Traditional” and molecular microbiological study designs, when coupled with hydrogeological, hydrochemical, isotopic, and geophysical methods, have proven useful for analysis of numerous aspects of subsurface microbial dynamics. Accordingly, this overview paper presents the principal microbial techniques currently being employed (1) to predict and identify sources of faecal contamination in groundwater, (2) to elucidate the dynamics of contaminant migration, and (3) to refine knowledge about the hydrogeological characteristics and behaviours of aquifer systems affected by microbial contamination with an emphasis on carbonate aquifers, which represent an important global water supply. Previous investigations carried out in carbonate aquifers in southern Italy are discussed.  相似文献   
922.
Active and break spells of the Indian summer monsoon   总被引:6,自引:0,他引:6  
In this paper, we suggest criteria for the identification of active and break events of the Indian summer monsoon on the basis of recently derived high resolution daily gridded rainfall dataset over India (1951–2007). Active and break events are defined as periods during the peak monsoon months of July and August, in which the normalized anomaly of the rainfall over a critical area, called the monsoon core zone exceeds 1 or is less than −1.0 respectively, provided the criterion is satisfied for at least three consecutive days. We elucidate the major features of these events. We consider very briefly the relationship of the intraseasonal fluctuations between these events and the interannual variation of the summer monsoon rainfall.  相似文献   
923.
924.
The effects of natural fish oil,DHA oil and soybean lecithin in microparticulate diets on stress tolerance of larval gilthead seabream(Sparus aurata)were investigated after 15 days feeding trials.The tolerance of larval gilthead seabream to various stress factors such as exposure to air(lack of dissolved oxygen),changes in water temperature(low)and salinity(high) were determined.This study showed that microparticulate diet with natural fish oil and soybean lecithin was the most effective for in-creasing the tolerance of larval gilthead seabream to various stresses,and that microparticulate diet with natural fish oil and palmitic acid(16:0)was more effective than microparticulate diet with DHA oil and soybean lecithin.  相似文献   
925.
中国地壳运动观测网络GPS区域站采用了严格同步环、连续4天、高站点重复率的观测方案,为了优化观测方案,以青藏块体东北缘GPS区域网1999年和2001年观测资料为例,对区域GPS观测方案进行了对比试验和分析。结果表明:①同步环连续3天和连续4天观测的基线重复率和站点速度结果基本一致,可以采用站点连续3天观测的方案;②异步环有站点重复观测与无站点重复观测对比,站点速度差别很小(亚毫米级),优化观测时可以大大降低或取消异步环站点重复率;③同步环整体解算(带IGS站)与环内站点单独触算(带IGS站),其站点速率差异可达1mm以上,因此优化观测时还应尽量采用同步环观测方案。  相似文献   
926.
Abalone Haliotis diversicolor supertexta is an important economic mollusk. The settlement and metamorphosis are two critical stages during its development period, which has direct influence on abalone survival and production. The influence of reactive oxygen species (hydrogen peroxide) on abalone embryo and juvenile development were examined in this study. Larvae of Haliotis diversicolor supertexta were induced to settlement and metamorphose by exposure to seawater supplemented with hydrogen peroxide. They had the best performance at 800 μmol/L. The concentration of 1 000 μmol/L or higher was toxic to the larvae, as the larvae could settle down only at benthic diatom plates without complete metamorphosis. In addition, H2O2 adding time was critical to the larval performance. 24h after two-day post-fertilization was proved to be the optimal adding time. In this paper, two action mechanisms of hydrogen peroxide are discussed: (1) hydrogen peroxide has direct toxicity to ciliated cells, thus cause apoptosis; (2) hydrogen peroxide, as a product from catecholamines' autoxidation process in vivo, can reverse this process to produce neuro-transmitters to induce abalone metamorphosis.  相似文献   
927.
Based on the sequence data of the nuclear ribosomal DNA internal transcribed spacer (ITS) 1, 5.8 S, and ITS 2, the molecular phylogeny was analyzed on Ulvaceae species collected from Qingdao coasts in summer of 2007, including 15 attached Ulva and Enteromorpha samples from 10 locations and 10 free-floating Enteromorpha samples from seven locations. The result supported the monophyly of all free-floating Enteromorpha samples, implying the unialgal composition of the free-floating Enteromorpha, and the attached Ulvaceae species from Qingdao coasts were grouped into other five clades, suggesting that they were not the biogeographic origin of the free-floating Enteromorpha in that season. Supported by NSFC (40506030); the Innovative Key Project of the Chinese Academy of Sciences (KZCX2-YW-209); Science & Technology Project of Qingdao City (06-2-2-12-JCH)  相似文献   
928.
929.
We determined Ar/Ar eruption ages of eight extrusions from the Pleistocene Coso volcanic field, a long-lived series of small volume rhyolitic domes in eastern California. Combined with ion-microprobe dating of crystal ages of zircon and allanite from these lavas and from granophyre geothermal well cuttings, we were able to track the range of magma-production rates over the past 650 ka at Coso. In ≤230 ka rhyolites we find no evidence of protracted magma residence or recycled zircon (or allanite) from Pleistocene predecessors. A significant subset of zircon in the ~85 ka rhyolites yielded ages between ~100 and 200 Ma, requiring that generation of at least some rhyolites involves material from Mesozoic basement. Similar zircon xenocrysts are found in an ~200 ka granophyre. The new age constraints imply that magma evolution at Coso can occur rapidly as demonstrated by significant changes in rhyolite composition over short time intervals (≤10’s to 100’s ka). In conjunction with radioisotopic age constraints from other young silicic volcanic fields, dating of Coso rhyolites highlights the fact that at least some (and often the more voluminous) rhyolites are produced relatively rapidly, but that many small-volume rhyolites likely represent separation from long-lived mushy magma bodies.  相似文献   
930.
Examining the direct and indirect effects of climatic factors on vegetation growth is critical to understand the complex linkage between climate change and vegetation dynamics. Based on the Moderate Resolution Imaging Spectroradiometer(MODIS) Normalized Difference Vegetation Index(NDVI) data and meteorological data(temperature and precipitation) from 2001 to 2012, the trend of vegetation dynamics were examined in the Ziya-Daqing basins, China. The path analysis was used to obtain the information on the relationships among climatic factors and their effects on vegetation growth. It was found that the trends of growing season NDVI were insignificant in most plain dry land, while the upward trends were significant in forest, grass and dry land in Taihang Mountains. According to the path analysis, in 23% of the basins the inter-annual NDVI variation was dominated by the direct effect of precipitation, in 5% by the direct effects of precipitation and temperature, and in less than 1% by the direct effect of temperature or indirect effects of these two climatic factors. It indicated that precipitation significantly affected the vegetation growth in the whole basins, and this effect was not regulated by temperature. Precipitation increase(especially in July, August and September) was favorable to greenness enhancement. Summer temperature rising showed negative effect on plant productivity enhancement, but temperature rise in April was beneficial for the vegetation growth. When April temperature increases by 1℃, the onset date of greenness for natural vegetation will be 2 days in advance. There was a lag-time effect of precipitation or temperature on monthly NDVI for all land use types except grass.  相似文献   
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