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The transition from body-centered cubic to hexagonal close-packed phase in iron has been studied in a diamond anvil cell with synchrotron radiation. The hexagonal close-packed phase, when it first appears, has a ratio of lattice parameters that is significantly larger than normal. This is attributed to a displacive mechanism that causes a distortion of the hexagonal close-packed structure in a body-centered cubic matrix. The hexagonal close-packed phase adjacent to a boundary with the body-centered cubic phase is stretched in the c direction and compressed in the a direction when it first forms. 相似文献
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Diamond anvil presses of a new design were used to compress samples of beryllium-7 oxide to 120, 210, and 270 kilobars. The decay constant for the conversion of beryllium-7 to lithium-7 by electron capture was measured for compressed and uncompressed samples. A least-squares fit of the equation (lambda(c)-lambda)/lambda = KpP to the experimental data, where lambda(C) and lambda are the decay constants of the compressed sample and an uncompressed sample, respectively, and P is pressure, yields a value of (2.2 +/- 0.1) x 10(-5) kbar(-1) for the constant K(p). 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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Bassett WA 《Science (New York, N.Y.)》1994,266(5191):1662-1663
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Samples of olivine (Fo(0)Fa(100), Fo(60)Fa(40), Fo(80)Fa(20), and Fo(100)Fa(0)) and of spinel (Fo(50)Fa(50), Fo(2)Fa(100), where Fo is forsterite and Fa is fayalite) were subjected to pressures up to 250 kilobars in a diamond anvil press and were heated in situ up to ~ 1700 degrees C by an infrared beam from a continuous-wave YAG (yttrium-aluminum-garnet) laser. The brightness temperature was determined from the intensity of incandescence of the sample by means of an optical pyrometer. X-ray diffraction patterns of the samples, obtained after quenching and unloading, show conclusively that these compositions disproportionate to (Mg, Fe)O and SiO(s) (stishovite) under these conditions. 相似文献
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The objectives were to determine the association of maturing patterns with growth rates and body weights and to estimate heritabilities and genetic and phenotypic correlations among these characters of sheep. Records of 1,109 range ewes from the Montana Agricultural Experiment Station Red Bluff Research Ranch at Norris were analyzed. Body weight and degree of maturity of body weight at birth, weaning, 12 mo of age, 18 mo of age and maturity (body weight only), and absolute growth rate (AGR), absolute maturing rate (AMR) and relative growth rate (RGR) over various age intervals were examined. Mature weight, required to calculate degree of maturity and AMR, was estimated by the average of the fall weights taken at 42, 54, 66 and 78 mo of age. Heritability estimates were .53 +/- .12 for mature weight and from .26 to .46 for immature weights. Genetic correlations among body weights at all ages were positive and generally large between immature weights and mature weights. Heritability estimates for degree of maturity ranged from .63 +/- .12 at 12 mo of age to .19 +/- .11 at 30 mo of age, at which time maturity was being approached. Genetic correlations between degree of maturity and body weight at the same age were positive; however, degree of maturity at all ages was negatively correlated with mature weight. Animals more mature at any age or stage during growth tended to be more mature at later stages, to be lighter at maturity, and to grow faster and weigh more up to 12 mo of age. Heritability estimates for AGR, RGR and AMR were moderate to high and were similar for the same age intervals. Selection for any one of the measures of growth rate would tend to expand the shape of the growth curve toward heavier weights and lower degree of maturity for any interval. 相似文献