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11.
The dry valleys of Antarctica are some of the oldest terrestrial surfaces on the Earth. Despite much study of soil weathering and development, ecosystem dynamics and the occurrence of life in these extreme environments, the reasons behind the exceptionally high salt content of the dry-valley soils have remained uncertain. In particular, the origins of sulphate are still controversial; proposed sources include wind-blown sea salt, chemical weatherings, marine incursion, hydrothermal processes and oxidation of biogenic sulphur in the atmosphere. Here we report measurements of delta18O and delta17O values of sulphates from a range of dry-valley soils. These sulphates all have a large positive anomaly of 17O, of up to 3.4/1000. This suggests that Antarctic sulphate comes not just from sea salt (which has no anomaly of 17O) but also from the atmospheric oxidation of reduced gaseous sulphur compounds, the only known process that can generate the observed 17O anomaly. This source is more prominent in high inland soils, suggesting that the distributions of sulphate are largely explained by differences in particle size and transport mode which exist between sea-salt aerosols and aerosols formed from biogenic sulphur emission. 相似文献
12.
Systematic determination of genetic network architecture. 总被引:39,自引:0,他引:39
13.
Thirty-nine previously unpublished reports of the endangered black-footed ferret from Wyoming are listed with dates, locations, number of animals, sources, and comments. 相似文献
14.
Neuronal function depends crucially on the spatial segregation of specific membrane proteins, particularly the segregation associated with sites of synaptic contact. Understanding the factors governing this localization of proteins is a major goal of cellular neurobiology. A conspicuous example of synaptic specialization is the almost exclusive localization of vertebrate skeletal muscle acetylcholine (ACh) receptors to the subsynaptic membrane of the neuromuscular junction (for example, refs 1,2). The localization of other membrane proteins in skeletal muscle has been much less studied, but a knowledge of their distribution is crucial for understanding the factors governing regional specialization. We have explored the distribution in muscle of the voltage-gated Na channel responsible for the action potential using the loose patch-clamp technique, and have measured Na currents in 5-10 micron-diameter membrane patches as a function of distance from the end plate region of snake and rat muscle fibres. Here we report that the Na current density immediately adjacent to the endplate is 5-10-fold higher than at regions away from the endplate. The increased Na current density falls off rapidly with distance, reaching the background level 100-200 micron from the endplate. Although one might expect ACh receptors to be concentrated near the region of ACh release, such a concentration for Na channels, which propagate the impulse throughout the length of the cell, is surprising and suggests that factors similar to those responsible for concentrating ACh receptors at the endplate also operate to concentrate Na channels. 相似文献
15.
M L Kashyap S G de Mendoza M Campbell C Y Chen R F Lutmer C J Glueck 《Experientia》1978,34(8):1044-1045
Marked urinary loss of lipoprotein lipase activator in experimental rat nephrotic syndrome may be partly responsible for its deficiency in plasma very low density lipoproteins. 相似文献
16.
Margaret Campbell 《Annals of science》2013,70(6):639-655
It is argued that de Vries did not see Mendel's paper until 1900, and that, while his own theory of inheritance may have incorporated the notion of independent units, this pre-Mendelian formulation was not the same as Mendel's since it did not apply to paired hereditary units. Moreover, the way in which the term ‘segregation’ has been applied in the secondary literature has blurred the distinction between what is explained and the law which facilitates explanation. 相似文献
17.
To assess the potential hazard from radioactive wastes, a plant with known radiosensitivity, Tradescantia clone 02, was grown in radioactive soil obtained from uranium mill tailings. The levels of radiation on these tailings varied from 0.03mR/hr (background) to a maximum of 3.00 mR/hr. Tradescantia grown in soil with a radiation level greater than 0.10 mR/hr evidenced significantly reduced reproductive integrity and fecundity, as measured by the number of stunted hairs per stamen, pollen viability, and numbers of somatic mutations. Based on these data, the radioactivity from uranium mill tailings has the potential to alter normal plant succession due to its detrimental effect on any species that is relatively radiosensitive. 相似文献
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Zusammenfassung Der Serotoningehalt der Schleimhaut von 14 gastrointestinalen Geweben von Sprague-Dawley Rattenmännchen und -weibchen wurde nach i.p. Injektion von Reserpin spektrophotofluorimetrisch gemessen. Die Verteilung von Serotonin im Magendarmkanal 4 und 16 h nach der Reserpininjektion zeigte, dass Magengewebe und Kolongewebe nach 16 h mehr entleert waren als nach 4 h, während Dünndarm und Appendix nach 4 h mehr entleert waren als nach 16 h.
This research was supported by U.S.P.H.S. grant No. AM 07909, toJ. H. Thompson. 相似文献
This research was supported by U.S.P.H.S. grant No. AM 07909, toJ. H. Thompson. 相似文献
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