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排序方式: 共有243条查询结果,搜索用时 359 毫秒
71.
J Christensen-Dalsgaard W Dappen SV Ajukov ER Anderson HM Antia S Basu VA Baturin G Berthomieu B Chaboyer SM Chitre AN Cox P Demarque J Donatowicz WA Dziembowski M Gabriel DO Gough DB Guenther JA Guzik JW Harvey F Hill G Houdek CA Iglesias AG Kosovichev JW Leibacher P Morel CR Proffitt J Provost J Reiter EJ Rhodes FJ Rogers IW Roxburgh MJ Thompson RK Ulrich 《Science (New York, N.Y.)》1996,272(5266):1286-1292
Data from the Global Oscillation Network Group (GONG) project and other helioseismic experiments provide a test for models of stellar interiors and for the thermodynamic and radiative properties, on which the models depend, of matter under the extreme conditions found in the sun. Current models are in agreement with the helioseismic inferences, which suggests, for example, that the disagreement between the predicted and observed fluxes of neutrinos from the sun is not caused by errors in the models. However, the GONG data reveal subtle errors in the models, such as an excess in sound speed just beneath the convection zone. These discrepancies indicate effects that have so far not been correctly accounted for; for example, it is plausible that the sound-speed differences reflect weak mixing in stellar interiors, of potential importance to the overall evolution of stars and ultimately to estimates of the age of the galaxy based on stellar evolution calculations. 相似文献
72.
AE Pashitski A Gurevich AA Polyanskii DC Larbalestier A Goyal ED Specht DM Kroeger JA DeLuca JE Tkaczyk 《Science (New York, N.Y.)》1997,275(5298):367-369
Magneto-optical imaging was used to visualize the inhomogeneous penetration of magnetic flux into polycrystalline TlBa2Ca2Cu3Ox films with high critical current densities, to reconstruct the local two-dimensional supercurrent flow patterns and to correlate inhomogeneities in this flow with the local crystallographic misorientation. The films have almost perfect c-axis alignment and considerable local a- and b-axis texture because the grains tend to form colonies with only slightly misaligned a and b axes. Current flows freely over these low-angle grain boundaries but is strongly reduced at intermittent colony boundaries of high misorientation. The local (<10-micrometer scale) critical current density Jc varies widely, being up to 10 times as great as the transport Jc (scale of approximately 1 millimeter), which itself varies by a factor of about 5 in different sections of the film. The combined experiments show that the magnitude of the transport Jc is largely determined by a few high-angle boundaries. 相似文献
73.
D P Hsieh L M Beltran M Y Fukayama D W Rice J J Wong 《Journal of the Association of Official Analytical Chemists》1986,69(3):510-512
One hundred mg aflatoxin M1 was produced and purified for toxicological studies. Aspergillus flavus NRRL 3251 was cultured on rice to produce aflatoxins B1, B2, M1, and M2, B1 and B2 were separated from M1 and M2 by a normal phase low pressure liquid chromatography (LC) column. M1 was then separated from M2 by a reverse phase low pressure LC column. Recoveries of aflatoxins from the LC columns were about 90%. The purified M1 was confirmed by ultraviolet-visible spectrometry, mass spectrometry, nuclear magnetic resonance spectrometry, optical rotation, and its mutagenicity to Salmonella typhimurium TA98. 相似文献
74.
Influence of the timing of nitrogen additions during synthetic grape must fermentations on fermentation kinetics and nitrogen consumption 总被引:2,自引:0,他引:2
Beltran G Esteve-Zarzoso B Rozès N Mas A Guillamón JM 《Journal of agricultural and food chemistry》2005,53(4):996-1002
Nitrogen deficiencies in grape musts are one of the main causes of stuck or sluggish wine fermentations. In the present study, we have supplemented nitrogen-deficient fermentations with a mixture of ammonium and amino acids at various stages throughout the alcoholic fermentation. The timing of the nitrogen additions influenced the biomass yield, the fermentation performance, the patterns of ammonium and amino acid consumption, and the production of secondary metabolites. These nitrogen additions induced a nitrogen-repressed situation in the cells, and this situation determined which nitrogen sources were selected. Glutamine and tryptophan were the main amino acids consumed in all the fermentations. Ammonium is the preferred nitrogen source for biomass production but was hardly consumed when it was added in the final stages of the fermentation. The higher ammonium consumption in some fermentations correlated with a greater synthesis of glycerol, acetate, and acetaldehyde but with a lower synthesis of higher alcohols. 相似文献
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GJ EAMENS PD KIRKLAND MJ TURNER JA GARDNER† MP WHITE‡ CL HORNITZKY 《Australian veterinary journal》1988,65(4):120-123
Toxigenic strains of Pasteurella multocida were readily differentiated from non-toxigenic strains by an agarose overlay method using bovine turbinate cells or bovine lung cells. Cells which were young and densely confluent were best suited to this assay. The incubation period required to distinguish toxigenic strains was dependent on the confluence of the monolayers, which was affected by the seeding rate, cell passage level and growth time prior to overlay. The agarose overlay method correctly identified 11 of 11 reference strains of Pasteurella multocida, and visible cytotoxic changes were present in the monolayers after 48 to 65 h. Outbreaks of the enzootic form of atrophic rhinitis in 2 New South Wales piggeries were associated with the isolation of toxigenic type D strains of P. multocida. 相似文献
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