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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
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Relative Contributions of Uranium, Thorium, and Potassium to Heat Production in the Earth 总被引:1,自引:0,他引:1
Data from a wide variety of igneous rock types show that the ratio of potassium to uranium is approximately 1 X 10(4). This suggests that the value of K/U approximately 1 X 10(4) is characteristic of terrestrial materials and is distinct from the value of 8 X 10(4) found in chondrites. In a model earth with K/U approximately 10(4), uranium and thorium are the dominant sources of radioactive heat at the present time. This will permit the average terrestrial concentrations of uranium and thorium to be 2 to 4.7 times higher than that observed in chondrites. The resulting models of the terrestrial heat production will be considerably different from those for chondritic heat production because of the longer half-life of U(238) and Th(238) compared with K(40). 相似文献
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SUMMARY A three-year-old neutered female Border Collie was presented with in-appetence, vomiting and diarrhoea. Abdominal radiographs revealed an obstructive pattern but no physical obstruction was evident at laparotomy. A diagnosis of chronic intestinal pseudo-obstruction was made based on histopathological changes in intestinal biopsies. Treatment was unsuccessful and the dog deteriorated progressively until euthanased five weeks after presentation. 相似文献
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Dorr PM Baker RB Almond GW Wayne SR Gebreyes WA 《Journal of the American Veterinary Medical Association》2007,230(2):244-250
OBJECTIVE: To identify important pathogens and characterize their serologic and pathologic effects in porcine circovirus type 2 (PCV2)-infected pigs in relation to pig age and type of swine production system. DESIGN: Cross-sectional study. ANIMALS: 583 conventionally reared pigs. PROCEDURES: 3- (n = 157), 9- (149), 16- (152), and 24-week-old (125) pigs from 41 different 1-, 2-, and 3-site production systems (5 pigs/age group/farm) were euthanized and necropsied. Pigs with and without PCV2 infection were identified (via PCR assay); infection with and serologic responses to other pathogens and pathologic changes in various tissues (including lungs) were assessed. Logistic regression models were constructed for effects overall and within each age group and type of production system. RESULTS: Compared with PCV2-negative pigs, PCV2-positive pigs were more likely to have swine influenza virus (SIV) type A and Mycoplasma hyopneumoniae infections and sample-to-positive (S:P) ratios for SIV H1N1 from 0.50 to 0.99; also, PCV2-positive pigs had higher serum anti-porcine reproductive and respiratory syndrome virus (PRRSV) antibody titers and more severe lung tissue damage. Infection with SIV (but lower SIV H1N1 S:P ratio) was more likely in 3-week-old PCV2-positive pigs and evidence of systemic disease was greater in 16-week-old PCV2-positive pigs than in their PCV2-negative counterparts. By site type, associations of coinfections and disease effects between PCV2-positive and -negative pigs were greatest in 3-site production systems. CONCLUSIONS AND CLINICAL RELEVANCE: In PCV2-positive pigs, coinfections with SIV, M. hyopneumoniae, and PRRSV are important, having the greatest effect in the early to late nursery phase and in 3-site production systems. 相似文献
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选择经产、胎次相同和产奶量相近的荷斯坦奶牛40头,配对分组设计分为对照组和试验组,每组20头。对照组全程饲喂基础日粮,试验组饲喂基础日粮 瘤胃稳定性脂肪。结果:瘤胃稳定性脂肪对奶牛采食量无显著影响(P>0.05);试验组牛产奶量显著升高(P<0.05),乳脂率呈上升趋势(P>0.05),但乳蛋白率未见显著变化(P>0.05);试验组奶牛外周血白细胞总数和淋巴细胞数轻度上升(P>0.05),牛奶SCC呈下降趋势(P>0.05)。结果表明,补充瘤胃稳定性脂肪可提高产奶量,对于改善机体免疫机能有一定的作用。 相似文献
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DO Gough AG Kosovichev J Toomre E Anderson HM Antia S Basu B Chaboyer SM Chitre J Christensen-Dalsgaard WA Dziembowski A Eff-Darwich JR Elliott PM Giles PR Goode JA Guzik JW Harvey F Hill JW Leibacher MJPFG Monteiro O Richard T Sekii H Shibahashi M Takata MJ Thompson S Vauclair SV Vorontsov 《Science (New York, N.Y.)》1996,272(5266):1296-1300
Global Oscillation Network Group data reveal that the internal structure of the sun can be well represented by a calibrated standard model. However, immediately beneath the convection zone and at the edge of the energy-generating core, the sound-speed variation is somewhat smoother in the sun than it is in the model. This could be a consequence of chemical inhomogeneity that is too severe in the model, perhaps owing to inaccurate modeling of gravitational settling or to neglected macroscopic motion that may be present in the sun. Accurate knowledge of the sun's structure enables inferences to be made about the physics that controls the sun; for example, through the opacity, the equation of state, or wave motion. Those inferences can then be used elsewhere in astrophysics. 相似文献