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A number of different splash-form Australasian tektites and one Muong Nong tektite from Laos have been investigated by room temperature 57Fe Mössbauer effect spectroscopy. Multiple spectra of thailandite samples have been obtained in order to establish uncertainties in fitted parameters. Results indicate that most of the samples investigated have Fe3+/Fe2+ ratios that are close to zero. The Muong Nong tektite shows the largest Fe3+/Fe2+ ratio and this is interpreted in terms of proposed mechanisms for the formation of this class of tektite that have been presented in the literature. 相似文献
173.
A technique for measuring local stresses in metallic specimens is proposed and tested. The technique depends on the experimental measurement of temperature changes in stressed members due to adiabatic elastic deformation. At a free boundary in a body under plane stress, these temperature changes are directly related to the value of the tangential principal stress. The technique is suited for measurement of stress-concentration effects, since the temperature changes can be measured with thermocouples featuring extremely small junctions. A simple stress-concentration geometry, the finitewidth strip with a central circular hole, is chosen as a model system for this study. Heat transfer in this geometry due to the temperature gradients produced by elastic deformation is analyzed. It is shown that the ratio of the temperature change at a reference section to the change at the locale of the stress concentration can be used to determine the stress-concentration factor, allowing for heat-transfer effects. An experimental measurement system capable of obtaining reproducible results with the thermal-measurement technique is described, and experimental results are given for the model geometry which agree favorably with theoretical predictions. Application of the technique to other problems is discussed. 相似文献
174.
B.D. Dunlap G.K. Shenoy F.Y. Fradin C.D. Barnet C.W. Kimball 《Journal of magnetism and magnetic materials》1979,13(3):319-321
Mössbauer effect measurements of the 151 Eu resonance in the Chevrel phase superconductor Sn0.75Eu0.25Mo6S8 have been used to obtain the temperature dependence of the Eu paramagnetic relaxation rate. This consists of a temperature independent part arising from spin-spin interactions and a part linear in T due to the Korringa process. From the slope we obtain = 0.0033/Eu atom-spin, where is the exchange coupling between the rare-earth spin and the conduction electron spin, and N(EF) is the local density of states. This value is roughly one order of magnetude lower than that measured in binary superconductors, and accounts for the very weak dependence of the transition temperature on magnetic impurity concentration. 相似文献
175.
当网络上(诸如交通网络、通讯网络)有多种不同物资或信息同时分别从相应的发点输送到相应的收点,要求每条线路上各类物资或信息的输送量总和不超过线路的容量时,寻求所有物资的最大输送量的问题,就是所谓网络多种物资的最大流问题,这个问题在生产实际和理论上都有着重要的意义,1963年T.C.Hu提出了求两类物资联合最大流的标号方法,但是为了保证有限步达到最大流,要求边的容量是偶数。 本文是文献[3]的继续,用图论的语言描述了两类物资最大流问题极流的特征,并对标号方法作了一点修改,使得有限步得到最大流,或者在某一步得到极流后,保证以后的迭代是从极流到极流.这样因极流的个数是有限的,并且最大流总可以在极流上达到,从而保证了有限步内得到所要求的最大流,无须对边的容量作任何限制, 本文所提的算法是使图形特征很强的标号算法和线性规划的极点迭代结合起来,这就使得有可能把这种方法,推广到更大的一类问题中,例如,研究容量的改变对最大流量的影响。 相似文献
176.
R. A. Dunlap S. Jha H. H. Seyoum G. M. Julian R. A. Pappas J. W. Blue 《Hyperfine Interactions》1983,16(1-4):689-692
Hyperfine fields have been measured at Cd, Sn and Sb sites in several Ni, Rh, Ir and Pt-based Heusler alloys. The Cd fields at 77 K were found to be ?95 k0e, ?108(4) k04, ±166(5) k0e and +196(9) k0e in RhMnSb, IrMnSn, IrMnSb and PtMnGa, respectively. Sn-site fields were found to be ±53(5) k0e and ±62(5) k0e in NiMnSb and PtMnSb, respectively, and the Sb-site fields, +276(5) k0e, +65(5) k0e and +210(5) k0e in NiMnSb, IrMnSb and PtMnSb, respectively. Results are discussed in terms of 5sp site hyperfine field systematics in Clb Heusler alloys. 相似文献
177.
A P Zens P T Fogle T A Bryson R B Dunlap R R Fisher P D Ellis 《Journal of the American Chemical Society》1976,98(13):3760-3764
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