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1.
Abstract Accretion discs in astrophysics are fundamental for converting gravitational binding energy into observed electromagnetic radiation. We study the behavior of waves in a two dimensional supersonic Keplerian flow inside a given gravitational potential. We present the effects of shearing and rotation on short waves, and the numerical study of the dynamical stability of such flows with respect to various perturbations. We show that a large class of dynamical effects, due to pressure and associated to short time scales, may be excited. 相似文献
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Petrology of gedrite-bearing rocks in mid-crustal ductile shear zones from the Eastern Ghats Belt, India 总被引：1，自引：0，他引：1
A suite of metapelitic, basic and quartzofeldspathic rocks intruded by enderbitic gneiss from the southernmost tip of the Eastern Ghats Belt, India, and metamorphosed at c. 750–800 °C, 6 kbar, were subjected to repeated ductile shear deformation, hydration, cooling and accompanying alkali metasomatism along narrow shear zones. Gedrite-bearing assemblages developed in the shear zones traversing metapelitic rocks. Interpretation of the reaction textures in an appropriate P–T grid in the system FMASH, an isothermal–isobaric μ H2O – μ Na2O grid in the system NFMASH, and geothermobarometric data suggest a complex evolutionary history for the gedrite-bearing parageneses. Initially, gedrite-bearing assemblages were produced due to increase in μ Na2O at nearly constant but high μ H2O accompanying cooling. Gedrite was partially destabilized to orthopyroxene+albite due to progressively increasing μ Na2O . During further cooling and at increased μ H2O a second generation of gedrite appeared in the rocks. 相似文献
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Sea floor and shallow seismic data sets of terminal submarine fan lobes can provide excellent planform timeslices of distributive deep‐water systems but commonly only limited information on cross‐sectional architecture. Extensive outcrops in the Tanqua depocentre, south‐west Karoo Basin, provide these three‐dimensional constraints on lithofacies distributions, stacking patterns, depositional geometries and the stratigraphic evolution of submarine lobe deposits at a scale comparable with modern lobe systems. Detailed study (bed‐scale) of a single‐lobe complex (Fan 3) over a 15 km by 8 km area has helped to define a four‐fold hierarchy of depositional elements from bed through to lobe element, lobe and lobe complex. The Fan 3 lobe complex comprises six distinct fine‐grained sandstone packages, interpreted as lobes, which display compensational stacking patterns on a 5 km scale. Between successive lobes are thin‐bedded, very fine‐grained sandstones and siltstones that do not change lithofacies over several kilometres and therefore are identified as a different architectural element. Each lobe is built by many lobe elements, which also display compensational stacking patterns over a kilometre scale. Thickness variations of lobe elements can be extremely abrupt without erosion, particularly in distal areas where isopach maps reveal a finger‐like distal fringe to lobes. Lobe deposits, therefore, are not simple radial sheet‐dominated systems as commonly envisaged. 相似文献
5.
The penaeid prawns Fenneropenaeus indicus and Metapenaeus monoceros support shallow-water prawn fisheries in the south-west Indian Ocean. They are sympatric and have similar life histories, including developmental stages that depend on estuarine and marine habitats and a short dispersal duration. Nevertheless, M. monoceros juveniles display a more generalist habitat preference in estuaries and recruit to offshore habitats during a different season than F. indicus. We hypothesised that these differences would affect dispersal patterns, leading to dissimilar geographic genetic structure between the two taxa. Given their short dispersal phase, we also hypothesised that the Mozambique Channel would form a barrier to dispersal between the southeastern African mainland and Madagascar sites. Population differentiation was assessed based on analysis of mitochondrial DNA control-region sequences. Both species displayed high haplotype and low nucleotide diversity. Pairwise ?ST statistics supported the existence of admixed populations along the African mainland sites for both species, with geographic distance isolating populations at the extremes of the sampled range (Kenya and east coast of South Africa). The Madagascar population differed significantly from African mainland populations. The concordant patterns in population differentiation suggest that F. indicus and M. monoceros can be considered as single African stocks, or fisheries management units. 相似文献
6.
沉积学数据库存储可由Ｆｏｘｓｅｄｂａ或Ｐａｒａｄｏｘｅｄｂａ来实现。曾为ＩＧＣＰ２６９的ＳＥＤＢＡ项目制作了一个软件，该软件于１９９３年就圆满完成了。全球沉积学数据库将在区域地质研究中得到广泛的应用。该数据库及其所收集的可供检索的数据可用来解释与地质历史和构造相关的地质模型和模拟。为了寻找地下含水层，我们加强了中爪哇省南山（ＳｏｕｔｈｅｒｎＭｏｕｎｔａｉｎ）碳酸盐相的研究。地层解释显示，在灰岩层中夹有一层砂岩层，该砂岩层可望成为储水层。 相似文献
7.
Trace element concentrations in shallow marine sediments of the Buyat-Ratototok district of North Sulawesi, Indonesia, are
affected by submarine disposal of industrial gold mine tailings and unregulated dumping of tailings and wastewater from small-scale
gold mining using mercury amalgamation. Industrial mine tailings contained 590–690 ppm arsenic, 490–580 ppm antimony, and
0.8–5.8 ppm mercury. Tailings-affected sediment As and Sb concentrations were 20–30 times higher than in muddy sediments not
contaminated with tailings, and 50–60 times higher than pre-mining average. Highest mercury concentrations were observed in
sediments affected by small-scale mining using mercury amalgamation (5–29 ppm). Concentrations of most other trace elements
were comparable in sediments affected by both types of mining and were slightly higher than regional averages for sediments
collected before the onset of industrial mining. Elevated concentrations of both As and Sb in approximately equal proportions
suggest tailings dispersal of at least 3.5 km. Mercury released from artisanal gold mining dispersed up to 4 km from river
mouths. Slight increases in concentrations of non-mercury trace elements in areas affected by artisanal mining over pre-industrial
mining concentrations were probably caused by increased rates of erosion.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
8.
Shallow marine sediments and fringing coral reefs of the Buyat-Ratototok district of North Sulawesi, Indonesia, are affected by submarine disposal of tailings from industrial gold mining and by small-scale gold mining using mercury amalgamation. Between-site variation in heavy metal concentrations in shallow marine sediments was partially reflected by trace element concentrations in reef coral skeletons from adjacent reefs. Corals skeletons recorded silicon, manganese, iron, copper, chromium, cobalt, antimony, thallium, and lead in different concentrations according to proximity to sources, but arsenic concentrations in corals were not significantly different among sites. Temporal analysis found that peak concentrations of arsenic and chromium generally coincided with peak concentrations of silica and/or copper, suggesting that most trace elements in the coral skeleton were incorporated into detrital siliciclastic sediments, rather than impurities within skeletal aragonite. 相似文献
9.
An SO2 flux of 1170±400 (1) tonnes per day was measured with a correlation spectrometer (COSPEC) in October and November 1986 from the continuous, nonfountaining, basaltic East Rift Zone eruption (episode 48A) of Kilauea volcano. This flux is 5–27 times less than those of highfountaining episodes, 3–5 times greater than those of contemporaneous summit emissions or interphase Pu'u O'o emissions, and 1.3–2 times the emissions from Pu'u O'o alone during 48A. Calculations based on the SO2 emission rate resulted in a magma supply rate of 0.44 million m3 per day and a 0.042 wt% sulfur loss from the magma upon eruption. Both of these calculated parameters agree with determinations made previously by other methods. 相似文献
10.
The new politics of family planning in the 1990s has involved the articulation of a comprehensive concept of sexual and reproductive health (SRH). Following the ratification of the SRH concept and goals at recent international conferences, one major issue is how governments translate the broad statements into operational policies and programs. The authors consider the ways in which the process is occurring in Indonesia, defining SRH, and reviewing the levels of its attainment in 8 of its components in Indonesia. The policy process in Indonesia is explored with regard to pre-existing reassessments, setting important priorities and moralistic and pragmatic policy orientations. The following SRH components are discussed: family planning, infertility, maternal and child health, HIV/AIDS, sexually transmitted diseases, adolescents' needs, sexual health, and gender issues. In terms of SRH, Indonesia has achieved considerable success in addressing family planning and infant and child mortality, limited success in addressing maternal mortality and HIV/AIDS, and very little progress in addressing STDs, adolescent needs, and positive sexuality. There are few data on gender issues. 相似文献