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981.
Ashfaque H. Bokhari Abdul R. Kashif Asghar Qadir 《General Relativity and Gravitation》2003,35(6):1059-1076
Curvature collineations are symmetry directions for the Riemann tensor, as isometries are for the metric tensor and Ricci collineations are for the Ricci tensor. Complete listings of many metrics possessing some minimal symmetry have been given for a number of symmetry groups for the latter two symmetries. It is shown that a claimed complete listing of cylindrically symmetric static metrics by their curvature collineations [1] was actually incomplete and is completed here. It turns out that in this complete list, unlike the previous claim, there are curvature collineations that are distinct from the set of isometries and of Ricci collineations. The physical interpretation of some of the metrics obtained is given. 相似文献
982.
We introduce a dynamic force spectroscopy technique enabling the quantitative measurement of conservative and dissipative tip-sample forces in ambient conditions. In difference to the commonly detected force-vs-distance curves dynamic force microscopy allows to measure the full range of tip-sample forces without hysteresis effects caused by a jump-to-contact. The approach is based on the specific behavior of a self-driven cantilever (frequency-modulation technique). Experimental applications on different samples (Fischer-sample, silicon wafer) are presented. 相似文献
983.
984.
985.
986.
987.
E. Gantner U. Kuhnes H. J. Ache 《Journal of Radioanalytical and Nuclear Chemistry》1992,161(2):561-574
The application, the advantage and limits of neutron monitoring techniques, such as Hf-monitors, fissile material accumulation and concentration monitors are being discussed. The active neutron counting technique applied to emptied pulsed extraction columns containing Hf-sieve plates allows conclusive answers as to the position of the plates in the columns. Pu-accumulations on Hf-sieve plates in pulsed extraction columns can be estimated within a factor of two, whereby the detection limit is about equal to or less than 1 g Pu/plate. Fissile material concentration changes of 1.1 g/l can be detected in the case of235U in solution and of 0.4 Pu/l if a239Pu/240Pu ratio of 4 to 1 is assumed. 相似文献
988.
989.
Polarized absorption and emission spectra, and temperature dependences of the fluorescence lifetimes and intensities for the chromium-doped LiNbGeO5 laser crystal are presented. Crystal symmetry and comparison with the infrared fluorescence properties of the Cr-doped Mg2SiO4 and Y3Al5O12 laser crystals seem to identify the active center as a Cr4+ ion in a tetrahedral site. 相似文献
990.