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71.
Dissolved organic matter was isolated from coastal and open-ocean surface waters having a wide range of biological productivities, and from seawater of intermediate depths. Approximately 50% of the organic matter was recovered by the use of activated-charcoal chromatography. The organic matter isolated from different types of water masses exhibited varying spectroscopic characteristics, and stable carbon-isotope compositions. The ability of the isolated organic matter to interact with copper ions also varied, but over a relatively narrow range which was not exceeded by more than a factor of two by similarly isolated terrigenous organic matter. 相似文献
72.
The solubilities and aqueous activity coefficients of polychlorinated biphenyls were measured in distilled and saline water (30? salinity). Solubilities in distilled water ranged from 3 · 10?4 g/l for dichlorobiphenyls to 6 · 10?6 g/l for heptachlorobiphenyls; values in artificial seawater were about five times lower than the corresponding values in distilled water. In both cases, the solubilities decreased regularly with increasing degree of chlorination. The corresponding activity coefficients are inversely proportional to the chlorine content and range from 4 · 107 to 4 · 109 in distilled water and from 3 · 108 to 1.5 · 1010 in saline water. Both the solubilities and activity coefficients agree well with those predicted from additivity considerations. The physical chemical aspects discussed in this paper can be applied in determining the solubility behavior of other stable organic molecules in the marine environment. 相似文献
73.
Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro to examine the relation between spall strength and maximum spall ejecta thickness. The impact experiments carried out with 0.04- to 0.2-g, 5- to 6-km/sec projectiles produced decimeter- to centimeter-sized craters and demonstrated crater efficiencies of 6 × 10?9 g/erg, an order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80%) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 g yield values of b = d(log Nf)/d log(m) ?0.5 ?0.6, where N is the cumulative number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejecta resides in a few large fragments. The large fragments are plate-like with mean values of B/A and C/A 0.8 0.2, respectively (A = long, B = termediate, and C = short fragment axes). The small equant-dimensioned fragments (with mass < 0.1 g and B ~ 0.1 mm) represent material which has been subjected to shear failure. The dynamic tensile strenght of San Marcos gabbro was determined at strain rates of 104 to 105 sec?1 to be 147 ± 9 MPa. This is 3 to 10 times greater than inferred from quasi-static (strain rate 100 sec?1) loading experiments. Utilizing these parameters in a continuum fracture model predicts a tensile strenght of , where ε is strain rate. It is suggested that the high spall strenght of basic igneous rocks gives rise to enhanced cratering efficiencies due to spall in the <102-m crater diamter strength-dominated regime. Although the impact spall mechanism can enhance cratering efficiencies it is unclear that resulting spall fragments achieve sufficient velocities such that fragments of basic rocks can escape from the surfaces of planets such as the Moon or Mars. 相似文献
74.
S. Hubrig M. Briquet P. De Cat M. Schller T. Morel I. Ilyin 《Astronomische Nachrichten》2009,330(4):317-329
We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B‐type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B‐type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three β Cephei stars and two stars suspected to be β Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3σ has been diagnosed in two normal B‐type stars, the nitrogen‐rich early B‐type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of β Cephei stars have detected magnetic fields: Out of 13 β Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected β Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non‐magnetic pulsating stars in the H‐R diagram. We find that their domains in the H‐R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i ‐values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
75.
ABSTRACTSeveral hundred million people in sub-Saharan Africa are at risk of being without access to electricity by 2030 despite the ongoing work aimed at achieving the United Nations’ Sustainable Development Goal 7—sustainable energy for all. Based on qualitative interviews, quantitative surveys, observation, and participation in Kenya and Senegal between 2010 and 2018, the author aims to explain why the rate of progress is slower than intended. The findings highlight three strong hindrances: lack of affordability due to extreme poverty, mismatch between the village-level outreach of grid-based electricity systems and the geography of settlements, and lack of consideration given to gender inequality. The findings also provide new insights into the ways that decentralized small-scale solar power increasingly meets some of the shortcomings of centralized grids in addressing these three issues, even in rural areas where grids are already present. The author concludes that the ways in which village communities have combined the use of solar-powered energy with grid-supplied energy indicates the importance of the former and the need to intensify efforts to improve solar power delivery models and integrate them fully in energy sector strategies. 相似文献
76.
77.
利用谐波振幅和峰谷值2种方法,计算江苏地电台站渗流方位角,并尝试利用渗流方位角进行映震分析,结果表明:①使用2种方法计算的渗流方位角相差不大,由此所得地震对应关系应基本可靠;②高邮地电台渗流方位角与高邮-宝应MS 4.9地震对应关系较好。因此,对江苏地区开展渗流方位角变化特征分析具有一定意义。 相似文献
78.
黄海中南部近岸海域春季鱼类浮游生物群落空间格局研究 总被引:6,自引:1,他引:5
根据2015年春季在黄海中南部近岸海域进行的鱼类浮游生物大型浮游生物网水平拖网数据,采用生态多样性指数和多元统计分析等方法,研究了该海域鱼类浮游生物的种类组成和群落空间格局及其与环境因子的关系。结果表明,本次调查共采集到鱼类浮游生物35种,其中鱼卵21种,仔稚鱼23种。鱼类浮游生物隶属于8目18科34属,优势种为鳀(Engraulis japonicus)、鲬(Platycephalus indicus)、鱼衔属(Callionymus spp.)和小黄鱼(Pseudosciaena polyactis)。其中,鳀和鱼衔属主要分布于海州湾渔场海域,鲬主要分布于吕泗渔场海域,小黄鱼多分布于吕泗渔场北部海域。生态类型包括半咸水型、沿岸型和近海型种类。聚类分析表明,鱼类浮游生物群落可划分为以鱼衔属、鳀为优势种的站位组A(主要分布于海州湾海域)、以小黄鱼、黄鲫(Setipinna taty)等为优势种的站位组B(主要位于江苏沿岸海域)和以鲬为优势种的站位组C(主要位于江苏沿岸-近海海域),以站位组B的群落物种多样性指数和均匀度指数最高。各站位组的鱼类浮游生物的生态类型和适温类型组成不同,这与其所处的海域生境有关。典范对应分析(CCA)表明,影响春季黄海中南部鱼类浮游生物群落空间结构的主要环境因子为水深和表层温度。同时也受洋流、底质类型等多种因素的综合影响。研究结果初步揭示了黄海中南部近岸海域鱼类浮游生物群落的空间格局,可为今后科学制定该海域水产种质资源保护区、资源量化管理等资源养护管理措施提供科学依据与技术支撑。 相似文献
79.
Horizontal distributions of phytoplankton abundance,species composition as well as environmental factors were investigated in the surface waters of southern South China Sea(SCS) in early summer(May 16 to June 7) of 2009.In most areas of southern SCS,the concentrations of nitrogen and phosphorus were very low and DIN/DIP ratios usually were lower than the Redfield N/P Ratio of 16:1.Nitrogen nutrients were significant lower in the upwelling region off Vietnam.A total of 144 taxa of phytoplankton were identified in the study area.The dominant genera were Prorocentrum,Gonyaulax,Gyrodinium,Scrippsiella and Chaetoceros,respectively.Spatial patterns of early-summer phytoplankton abundance and species composition should be mainly controlled by the upwelling off Vietnam and the discharge of Mekong River in the southern SCS.Diatoms dominated in the nutritious Mekong River Estuary or upwelling region off Vietnam;while dinoflagellates dominated in the oligotrophic pelagic region.The canonical correspondence analysis(CCA) indicates that most of diatoms favor higher levels of silicate and phosphorus,as well as lower temperature;while most of dinoflagellates favor the lower silicate and phosphorous and higher temperature.Correlation and CCA results indicate that silicate,nitrate and temperature were the most relevant environmental factors to regulate the horizontal pattern of early-summer phytoplankton in the surface waters of southern SCS. 相似文献