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利用一个时变电离层理论模式，研究武昌地区（３０．５°Ｎ，１１４．４°Ｅ）电离层Ｆ１－ｌｅｄｓｅ现象．表明利用当前关于中性气体和太阳辐射的经验模式，观测到的Ｆ１－ｌｅｄｇｅ出现与演化的基本规律将可基于现有电离层理论加以再现．指出较明显的Ｆ１－ｌｅｄｇｅ结构同较低的中性原子－分子含量比有直接关系，并同原子－分子成份的过渡高度、背景温度及其垂直分布形态有一定联系．同Ｆ１－ｌｅｄｇｅ形态相关联的Ｆ１－Ｆ２谷，其出现主要是由于亚稳态氧离子参与光化过程，以及电离气体参与具有一定垂直变化的输运过程． 相似文献
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To assess the vulnerability of ground water to contamination in the karstic Upper Floridan aquifer (UFA), age-dating tracers and selected anthropogenic and naturally occurring compounds were analyzed in multiple water samples from a public supply well (PSW) near Tampa, Florida. Samples also were collected from 28 monitoring wells in the UFA and the overlying surficial aquifer system (SAS) and intermediate confining unit located within the contributing recharge area to the PSW. Age tracer and geochemical data from the earlier stage of the study (2003 through 2005) were combined with new data (2006) on concentrations of sulfur hexafluoride (SF6 ), tritium (3 H), and helium-3, which were consistent with binary mixtures of water for the PSW dominated by young water (less than 7 years). Water samples from the SAS also indicated mostly young water (less than 7 years); however, most water samples from monitoring wells in the UFA had lower SF6 and 3 H concentrations than the PSW and SAS, indicating mixtures containing high proportions of older water (more than 60 years). Vulnerability of the PSW to contamination was indicated by predominantly young water and elevated nitrate-N and volatile organic compound concentrations that were similar to those in the SAS. Elevated arsenic (As) concentrations (3 to 19 μg/L) and higher As(V)/As(III) ratios in the PSW than in water from UFA monitoring wells indicate that oxic water from the SAS likely mobilizes As from pyrite in the UFA matrix. Young water found in the PSW also was present in UFA monitoring wells that tap a highly transmissive zone (43- to 53-m depth) in the UFA. 相似文献
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The objective of this project was to empower people of Blyth Valley in Northumberland (northeast England) to contribute to the management of their coastal heritage. A group of volunteers, the Links Conservation Group, working in collaboration with the environmental managers (Blyth Valley Borough Council), scientists, local specialists and other volunteers, surveyed the biodiversity, social, cultural and industrial history and profiles of the dunes, as well as their perceived value to local residents. The Group used this information to develop management plans for the dunes. The recommendations have contributed to planning processes at three levels: (i) national coastal management plans; (ii) regional plans; and (iii) plans for further action at the local community level. 相似文献
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本文详细介绍了在美国阿拉斯加州用非开挖技术,穿越河流铺设４条油管的工程,穿越长度１３０３ｍ,管径５００ｍｍ。文章介绍了在－５０℃的气温下钻进的情况,包括钻孔液成分泥浆马达和导向等问题。 相似文献
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Surface seawater samples were collected in the Irish Sea and Liverpool Bay area from the R.V. Prince Madog during the period of 25-31 of March 2006. VOCs were purged with nitrogen, pre-concentrated on a SPME fibre and analysed immediately on a GC-MS. Target compounds quantified were halogenated (0.2-1400 ng L(-1)), BTEXs and mono-aromatics (1.5-2900 ng L(-1)), aliphatic hydrocarbons and others (0.6-15,800 ng L(-1)). Day and night sampling was performed at a single station and suggested that factors such as sunlight and tide affect the presence of many of these compounds. Sample variability was high due to the variable weather conditions at the station. Poor correlations were found between marine phytopigments and selected VOCs. Principal component analysis (PCA) analysis showed that chlorinated compounds such as 1,2-dichloroethane, 1,1,1-trichloroethane, trichloroethene, tetrachloroethene and carbon tetrachloride, predominantly from anthropogenic sources, originated from the River Mersey. Other brominated and iodinated compounds quantified were more likely to be from biogenic sources including novel marine compounds such as 2-chloropropane, 1-bromoethane and 1-chlorobutane. 相似文献
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新近的大陆地壳化学组分模型建立在各种地球物理、地质和岩石学条件上，并显示较宽的组分变化范围。其中ＳｉＯ２变化在（５７￣６４）ωＢ％，Ｋ２Ｏ为（１．１￣２．４）０６ωＢ％。大多数不相容元素有较高含量估值的模型暗示着这些元素在贫化地幔中极端亏损（〉７０％）。地壳热流制约着大陆地壳内产热元素（ＨＰＥ：Ｋ，Ｔｈ，Ｕ）的丰度，因而，为检验各种模型提供了一条明确而重要的途径。大陆热流中地壳放射性成因组分应在１ 相似文献
69.
Temporal and spatial distributions of contaminants in sediments of Santa Monica Bay,California 总被引：6，自引：0，他引：6
Contaminant inputs from wastewater discharge, a major source of contamination to Santa Monica Bay (SMB), have declined drastically during the last three decades as a result of improved treatment processes and better source control. To assess the concomitant temporal changes in the SMB sediments, a study was initiated in June 1997, in which 25 box cores were collected using a stratified random sampling design. Five sediment strata corresponding to the time intervals of 1890-1920, 1932-1963, 1965-1979, 1979-1989, and 1989-1997 were identified using (210)Pb dating techniques. Samples from each stratum were analyzed for metals, 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolites (DDTs), polychlorinated biphenyls (PCBs), and total organic carbon (TOC). Samples from the 1965-1979, 1979-1989, and 1989-1997 strata were also analyzed for polycyclic aromatic hydrocarbons (PAHs) and linear alkylbenzenes (LABs). Sediment metal concentrations increased from 1890-1979 and were similar during the time intervals of 1965-1979, 1979-1989, and 1989-1997, although the mass emissions of trace metals from sewage inputs declined substantially during the same time period. Trace organic contamination in SMB was generally highest in sediments corresponding to deposition during the years of 1965-1979 or 1979-1989 and showed a decline in concentration in the 1989-1997 stratum. Temporal trends of contamination were greatest in sediments collected from areas near the Hyperion Treatment Plant (HTP) outfall system and on the slope of Redondo Canyon. The highest contaminant concentrations were present in sediments near the HTP 7-mile outfall in the 1965-1979 stratum. Elevated trace metal and organic concentrations were still present in the 1989-1997 stratum of most stations, suggesting that sediment contaminants have moved vertically in the sediment column since sludge discharges from the 7-mile outfall (a dominant source of contamination to the bay) ceased in 1987. The widespread distributions of DDTs and PCBs in SMB and highly confined distribution of LABs around the HTP outfall system were indicative of a dispersal mechanism remobilizing historically deposited contaminants to areas relatively remote from the point of discharge. 相似文献
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The effects of a simulated spill of sunflower oil in salt marsh sediments were compared with an experiment with linseed oil. Sunflower and linseed oil penetrated the sediments at the same rates but different adsorption of the oils onto sediment particles resulted in the establishment of anaerobic conditions at shallower depths in sediments contaminated with linseed oil than with sunflower oil. The total lipid content of sunflower oil contaminated sediments remained almost stable for 6 months, whilst only 40% of linseed oil remained in the sediment after 2 months. Numbers of culturable heterotrophic bacteria and aerobic oil degrading bacteria in muddy sediment increased rapidly in response to the presence of the oils but bacterial numbers in sandy sediments increased more slowly for sunflower oil. Changes in fatty acid composition indicate similar degradation pathways for both oils but sunflower oil degraded more slowly than linseed oil and thus has the potential for longer lasting effects in marine environments. 相似文献