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云南禄丰煤岩与围岩中富勒烯（C60）物质的初步探索 总被引：3，自引：0，他引：3
中国云南煤中是否存在富勒烯还没有科学定论。本工作运用高效液相色谱方法，对中国云南禄丰晚三叠世煤岩及其围岩中是否存在天然富勒烯物质的问题进行了探索性研究；同时发展了适于从复杂地质样品中分离纯化富勒烯和定性与定量检测富勒烯的一套技术方法。结果显示，从定性角度有两个样品确实存在富勒烯。本文据此提出，富勒烯的赋存与煤岩／围岩交互相上的含煤碳质泥岩有着密切的关系。下一步研究应着重调查比煤岩与顶板和底板界面层并大力研究其中天然富勒烯的地学成因。本工作的意义还在于为今后我国加入和独立开展以富勒烯类物质（如C60／C70）及其衍生物质（如He C60 C70)作为地球化学示踪物的古地球突变大事件的研究，奠定了实验方法学基础。 相似文献
2.
Uranium transport in Archaean sediments was investigated by means of two carefully selected suites of variably weathered sediment samples from different localities of the Pongola Supergroup, Kaapvaal Craton, South Africa. U remobilization on a micron- to meter-scale was analyzed using U fission-track micromapping and α-spectrometry bulk measurements. These studies were supported by ore microscopy, neutron activation analysis and γ-spectrometry. By combining particle track technique and α-spectrometry detailed information is obtained on the U transport history of weathered surface samples. A simple model of U redistribution processes in geologic systems based on238U-series disequilibria is developed and applied to the samples investigated. Some implications for γ-radiometric field methods are discussed. 相似文献
3.
This study compares the composition, species richness and biomass of macrofaunal and algal assemblages on intertidal boulder shores as compared with those on adjacent rock-platforms, at six sites along the southwest coast of South Africa. Of 214 species identified, 175 were recorded on boulder shores and 124 on rock-platform shores; of these, 99 species were common to both habitat types, 92 were exclusive to boulders, and 23 were exclusive to rock-platforms. Significant differences in community structure (F(1,95) = 13.02, p < 0.01) (PERMANOVA test), species richness (F(1,95) = 14.28, p < 0.01), biomass (F(1,95) = 9.45, p < 0.01) and diversity (F(1,95) = 578.83, p < 0.01) (two-way ANOVA) were detected between the two habitat types. Average dissimilarity of community structure between rock-platform and boulder shores was 87.96% (SIMPER analysis). The increased species richness and biomass on boulder shores extended across all tidal levels, but was most marked in the highshore. These results confirm that boulder shores along the southwestern Cape support a distinct biota, richer and very different from that on adjacent rock-platforms, and rich in boulder-dependent species. We propose that boulder shores merit separate management and conservation targets as compared to rock-platforms, though the ecology of boulder shores in the region remains very poorly known and requires further study. 相似文献
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Summary In the present study inhomogeneous, partly uraniferous leucoxene/rutile aggregates and brannerite grains from the Elliot Lake area, Canada, and the Pongola basin, South Africa, were identified by ore microscopy. This observation accords with the fact that U–Ti phases are second only to uraninite as the most important uranium minerals in Precambrian conglomerates. The observed U–Ti phases, however, are somewhat indefinitive. They often merge into each other and represent authigenic constituents pseudomorphous after detrital titanium minerals. Microprobe work has confirmed the existence of a continuous mineral series recognized optically which ranges from uranium-free leucoxene/rutile to uranium-enriched brannerite. However, the presence of metamict brannerite can only be verified by X-ray diffraction after prolonged heating, a process which may synthesize the latter mineral. The actual occurrence of brannerite in Precambrian conglomerates must, therefore, be regarded with reservation and it is suggested that redistribution and subsequent adsorption of uranium on Ti phases during diagenesis and/or metamorphism of the conglomerates did not lead to the formation of authigenic brannerite, but rather resulted in microcrystalline leucoxene/rutile admixtures containing uranium in varying amounts.
With 10 Figures 相似文献
U–Ti-Phasen aus präkambrischen Quarz-Geröll-Konglomeraten des Elliot Lake-Gebietes, Canada, und des Pongola-Beckens, Südafrika
Zusammenfassung Im Untersuchungsmaterial, das aus dem Elliot Lake-Gebiet, Canada, und dem Pongola-Becken, Südafrika, stammt, konnten Leukoxen/Rutil-Aggregate, die teilweise Uran-führend sind, und Brannerit mikroskopisch bestimmt werden. Dies stimmt mit vielfach mitgeteilten Beobachtungen überein, daß in präkambrischen Konglomeraten U–Ti-Phasen, nach Uraninit, die wichtigsten Uranminerale darstellen. Die festgesteilten U–Ti-Phasen sind recht wenig definiert und gehen oft graduell ineinander über. Es sind authigene Konglomeratkomponenten, die im allgemeinen pseudomorph nach detritischen Titanmineralen sind. Ein kontinuierlicher Übergang von Uran-freiem Leukoxen/Rutil zu Uran-reichem Brannerit konnte mittels der Mikrosonde ebenfalls mineralgeochemisch bestätigt werden. Wegen des metamikten Charakters des Probenmaterials kann jedoch die Anwesenheit von Brannerit, mittels Röntgendiffraktometrie, erst nach längerem Glühen der Proben verifiziert werden, was möglicherweise zu einer Synthetisierung von Brannerit führt. Sein Auftreten in präkambrischen Konglomeraten ist deshalb nicht gesichert, und es wird vorgeschlagen, daß diagenetische oder/und metamorphe Umlagerungen von Uran eher zur Bildung uranhaltiger mikrokristalliner Leukoxen/Rutil-Aggregate als von authigenem Brannerit führen.
With 10 Figures 相似文献
5.
A. Stupp 《Monthly notices of the Royal Astronomical Society》2000,311(2):251-268
We investigate wave amplification through the electron–cyclotron maser mechanism. We calculate absorption and emission coefficients without any approximations, also taking into account absorption by the ambient thermal plasma. A power-law energy distribution for the fast electrons is used, as indicated by X-ray and microwave observations.
We develop a model for the saturation length and amplification ratio of the maser, scan a large parameter space and calculate the absorption and emission coefficients for every frequency and angle.
Previous studies concluded that the unobservable Z mode dominates in the νp ≈ ν B region, and that millisecond spikes are produced in the region ν p ν B <0.25. We find that the observable O and X modes can produce emission in the 0.8< ν p ν B <2 region, which is expected at the footpoints of a flaring magnetic loop. The important criterion for observability is the saturation length and not the growth rate, as was assumed previously, and, even when the Z mode is the most strongly amplified, less strongly amplified O or X modes are still intense enough to be observed.
The brightness temperature computed with our model for the saturation length is found to be of order 1016 K and higher. The emission is usually at a frequency of 2.06 ν B , and at angles of 30°–60° to the magnetic field. The rise time of the amplified emission to maximum is a few tenths of a millisecond to a few milliseconds, and the emission persists for as long as new fast electrons arrive in the maser region. 相似文献
We develop a model for the saturation length and amplification ratio of the maser, scan a large parameter space and calculate the absorption and emission coefficients for every frequency and angle.
Previous studies concluded that the unobservable Z mode dominates in the ν
The brightness temperature computed with our model for the saturation length is found to be of order 10
6.
Despite its legal prohibition since 1998, the nylon monofilament net is still widely used in Senegalese artisanal fisheries. To achieve a complete ban on monofilament use, it is necessary to understand the main arguments for its continued use and what alternatives exist. Using a field experiment among local fishers as well as empirical knowledge and a literature review, this article highlights the challenges to the eradication of nylon monofilament. Our study shows that in a context where decision-makers pay too much attention to social, economic and political stakes, the efficiency of nylon monofilament nets confers a major advantage upon which fishers rely, and this counters any regulatory action against this type of gear. Moreover, numerous studies globally have indicated that communication campaigns that focus on the ghost-fishing power of this type of net seem to be inappropriate. We concluded that the issue of continued use of monofilament should be addressed through an integrated fisheries management programme that reduces overcapacity and fosters sustainable fishing practices. 相似文献
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