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Hydrocarbons and nitriles are produced in Triton's stratosphere by energetic electrons from Neptune's magnetosphere and other charged particle sources. Laboratory plasma experiments reported here show a substantial yield of molecules from low pressure flows of 10(-3) CH4 in N2 appropriate to Triton if both CH4 and N2 are saturated at the surface. An active magnetosphere similar to that of Uranus would result in a flux approximately 0.3 erg cm-2 s-1 of 0.1-1 MeV electrons in Triton's stratosphere; molecular production rates are then 10(6)-10(8) cm-2 s-1 for NH3, C2H2, HCN, and NCCN; tens of hundreds of gm cm-2 of these compounds per 10(9) yr (and lesser quantities of at least eight other molecules experimentally detected) would freeze to fine-grained white condensates in the lower stratosphere and sediment to the surface. Along with dark/colored organic haze produced in the stratosphere and other heteropolymers produced at the surface, these condensates are subjects to redistribution by aeolian processes and may appear as lag deposits and/or sediment layers. A simple eddy diffusion model indicates abundances approximately 10(19) molec cm-2 for HCN and C2H2, and > 10(17) molec cm-2 for NCCN, CH3CCH, CH2CCH2, and CH3CN in the stratosphere; these and other organic molecules will be detectable by IRIS if the stratosphere is (as expected) heated through ultraviolet and visible light absorption by the haze. 相似文献
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根据美国和欧洲的科学期刊发表的文章,回顾近几年来核测井方面的重要进(?)利用光电效应进行的密度测量,已成为目前识别主要岩石类型的普通方法。天然放射性和子激发的次生伽马射线能谱测量,使得测井资料可以用来进行元素分析。人们熟知的测井法,如补偿中子和密度测井,在薄层识别的数据分析方面得到了改进。除天然伽马测量外,着中子孔隙度和伽马密度测量的引入,近年来随钻核测井也有了很大的进展。现在可以把种放射性同位素注入地层,并通过它们的特征伽马谱探测出来。测井探头响应的计算机模已在下井仪设计和确定其环境校正方面得到广泛的应用。蒙特卡罗程序已在小型计算机并行处理器上运行,而以前需要大型计算机。 相似文献
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The concentration of selected trace metals (Cu, Pb and Zn) in salt-marsh sediments from within the Erme Estuary have been measured in order to assess possible historical sources of pollution. The Erme Estuary, south Devon, UK is an Area of Outstanding Natural Beauty and has remained largely unaffected by industrialisation, although a number of small silver–lead mines were in operation in the 1800s. Five cores reveal comparable geochemical profiles. An increase of lead at 40 cm depth is observed, reaching maximum values of 427 ppm. Less distinct trends are revealed by zinc and copper, probably reflecting the lack of widespread mining for ores of these elements within the catchment and possible post-depositional mobility rendering the metal concentrations non-contemporaneous with the chemostratigraphy of lead. The geochemical analysis of the salt-marsh sediments provides a fairly robust chemostratigraphic scheme and the likely sources of mine waste can be pinpointed within the catchment. Based upon reference to the historical mining record of these mines chemostratigraphic dating of the sediments can be achieved in order to provide an estimate of salt-marsh accretion rates and sea-level rise. 相似文献
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Trace element distribution during the reproductive cycle of female and male spiny and Pacific scallops, with implications for biomonitoring 总被引：1，自引：0，他引：1
Trace element concentrations and contents in gills, gonad, kidneys, mantle, muscle and remainder during the reproductive cycle of female and male spiny and Pacific scallops, from the Strait of Georgia, BC, Canada, were quantified by using ICPMS. The elements investigated were chromium, manganese, iron, cobalt, nickel, selenium, molybdenum, cadmium, tin and mercury. For all ten elements, the tissue distribution was to some extent influenced by species, sex and reproductive status. The implications of the present study in relation to the design of biomonitoring programmes are: (1) care should be taken to ensure an equal/constant sex composition when making interannual comparisons of pooled samples. Preferably the sexes should be monitored separately. (2) the practice of obtaining pooled samples in the interspawn phase is applicable only to monitoring long-term trends in contaminant levels, while the reproductive status should be heeded when studying short-term changes. (3) the present study confirms that direct temporal or spatial comparisons of absolute accumulated element concentrations are only valid intraspecifically. 相似文献
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Predicting copper toxicity in estuarine and marine waters using the Biotic Ligand Model 总被引：6，自引：0，他引：6
The Biotic Ligand Model (BLM) has proven efficient in predicting the toxicity of a variety of metals to freshwater organisms. Consequently, the US EPA has proposed its use for calculating freshwater copper criteria. This study evaluates the BLM for use in estuarine and marine waters. Studies were conducted using the bivalve, Mytilus sp. and 48-h embryo-larval development chronic estimator test methods. These are the most sensitive taxa and test in the US EPA saltwater copper criteria database. Samples from five locations around the USA were tested. There is a strong relationship between measured and BLM predicted copper EC50s (log transformed data, r2 = 0.76, p < 0.001, n = 44). The BLM predicted within a factor ±2 of measured EC50s in 41 of 44 cases. However, the BLM tends to predict lower EC50s when measured EC50s are approximately 10 μg Cu/L. This may be due to limitations of the metal-dissolved organic matter interaction model. 相似文献
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Quantifying the spatial and temporal distribution of recharge is usually a prerequisite for effective ground water flow modeling. In this study, an analytic element (AE) code (GFLOW) was used with a nonlinear parameter estimation code (UCODE) to quantify the spatial and temporal distribution of recharge using measured base flows as calibration targets. The ease and flexibility of AE model construction and evaluation make this approach well suited for recharge estimation. An AE flow model of an undeveloped watershed in northern Wisconsin was optimized to match median annual base flows at four stream gages for 1996 to 2000 to demonstrate the approach. Initial optimizations that assumed a constant distributed recharge rate provided good matches (within 5%) to most of the annual base flow estimates, but discrepancies of >12% at certain gages suggested that a single value of recharge for the entire watershed is inappropriate. Subsequent optimizations that allowed for spatially distributed recharge zones based on the distribution of vegetation types improved the fit and confirmed that vegetation can influence spatial recharge variability in this watershed. Temporally, the annual recharge values varied >2.5-fold between 1996 and 2000 during which there was an observed 1.7-fold difference in annual precipitation, underscoring the influence of nonclimatic factors on interannual recharge variability for regional flow modeling. The final recharge values compared favorably with more labor-intensive field measurements of recharge and results from studies, supporting the utility of using linked AE-parameter estimation codes for recharge estimation. 相似文献
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Because of the ubiquitous nature of anthropogenic nitrate (NO3(-)) in many parts of the world, determining background concentrations of NO3(-) in shallow ground water from natural sources is probably impossible in most environments. Present-day background must now include diffuse sources of NO3(-) such as disruption of soils and oxidation of organic matter, and atmospheric inputs from products of combustion and evaporation of ammonia from fertilizer and livestock waste. Anomalies can be defined as NO3(-) derived from nitrogen (N) inputs to the environment from anthropogenic activities, including synthetic fertilizers, livestock waste, and septic effluent. Cumulative probability graphs were used to identify threshold concentrations separating background and anomalous NO(3)-N concentrations and to assist in the determination of sources of N contamination for 232 spring water samples and 200 well water samples from karst aquifers. Thresholds were 0.4, 2.5, and 6.7 mg/L for spring water samples, and 0.1, 2.1, and 17 mg/L for well water samples. The 0.4 and 0.1 mg/L values are assumed to represent thresholds for present-day precipitation. Thresholds at 2.5 and 2.1 mg/L are interpreted to represent present-day background concentrations of NO(3)-N. The population of spring water samples with concentrations between 2.5 and 6.7 mg/L represents an amalgam of all sources of NO3(-) in the ground water basins that feed each spring; concentrations > 6.7 mg/L were typically samples collected soon after springtime application of synthetic fertilizer. The 17 mg/L threshold (adjusted to 15 mg/L) for well water samples is interpreted as the level above which livestock wastes dominate the N sources. 相似文献
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航空重力测量的历史回顾 总被引：1，自引：0，他引：1
在本世纪５０年代末到６０年代,首次报导的航空重力测量尝试,是利用固定翼飞行器所进行的可行性试验。仪器系统是由海上重力仪、摄影测量照像机和定位多卜勒雷达,以及一些仅用于测定高度变化的沸点测高器组成的。试验的几条测线经过相对较高的地形区域。一般情况下重力仪运行正常,但该系统在对航空能力的控制和测量,以及计算艾维改正、飞行稳定性对于精确测量飞行器的垂向运动中受到限制。这些试验表明,航空重力测量可获得±１０×１０－５ｍ／ｓ２的精度。１９６５年１月,空军的剑桥研究实验室开始了一项深入细致的计划,对现有的和… 相似文献
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Ground water budget analysis in arid basins is substantially aided by integrated use of numerical models and environmental isotopes. Spatial variability of recharge, storage of water of both modern and pluvial age, and complex three-dimensional flow processes in these basins provide challenges to the development of a good conceptual model. Ground water age dating and mixing analysis with isotopic tracers complement standard hydrogeologic data that are collected and processed as an initial step in the development and calibration of a numerical model. Environmental isotopes can confirm or refute a priori assumptions of ground water flow, such as the general assumption that natural recharge occurs primarily along mountains and mountain fronts. Isotopes also serve as powerful tools during postaudits of numerical models. Ground water models provide a means of developing ground water budgets for entire model domains or for smaller regions within the model domain. These ground water budgets can be used to evaluate the impacts of pumping and estimate the magnitude of capture in the form of induced recharge from streams, as well as quantify storage changes within the system. The coupled analyses of ground water budget analysis and isotope sampling and analysis provide a means to confirm, refute, or modify conceptual models of ground water flow. 相似文献