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111.
112.
Reuven Peleg 《Israel Journal of Mathematics》1971,9(3):330-336
Using a technique of R. Ellis we prove the existence of many weakly mixing (w.m.) flows which are distal extensions of a given
w.m. flow. Then we indicate two w.m. minimal flows whose product has a minimal non-w.m. subflow.
This work was done under the helpful supervision of Professor H. Furstenberg as a part of the author’s Ph.D. thesis to be
submitted to the Hebrew University of Jerusalem. 相似文献
113.
Yiping Chen Gerald Paul Reuven Cohen Shlomo Havlin Stephen P. Borgatti Fredrik Liljeros H. Eugene Stanley 《Physica A》2007
We study the statistical properties of a recently proposed social networks measure of fragmentation F after removal of a fraction q of nodes or links from the network. The measure F is defined as the ratio of the number of pairs of nodes that are not connected in the fragmented network to the total number of pairs in the original fully connected network. We compare this measure with the one traditionally used in percolation theory, P∞, the fraction of nodes in the largest cluster relative to the total number of nodes. Using both analytical and numerical methods, we study Erd?s–Rényi (ER) and scale-free (SF) networks under various node removal strategies. We find that for a network obtained after removal of a fraction q of nodes above criticality, P∞≈(1-F)1/2. For fixed P∞ and close to criticality, we show that 1-F better reflects the actual fragmentation. For a given P∞, 1-F has a broad distribution and thus one can improve significantly the fragmentation of the network. We also study and compare the fragmentation measure F and the percolation measure P∞ for a real national social network of workplaces linked by the households of the employees and find similar results. 相似文献
114.
Reuven Segev 《International Journal of Non》2007,42(2):250-257
For the stress analysis in a plastic body Ω, we prove that there exists a maximal positive number C, the load capacity ratio, such that the body will not collapse under any external traction field t bounded by CY0, where Y0 is the yield stress. The load capacity ratio depends only on the geometry of the body and is given by
115.
The origin of magnetic fields in astrophysical objects is a challenging problem in astrophysics. Throughout the years, many scientists have suggested that non-minimal gravitational-electromagnetic coupling (NMGEC) could be the origin of the ubiquitous astrophysical magnetic fields. We investigate the possible origin of intense magnetic fields by NMGEC near rotating black holes, connected with quasars and gamma-ray bursts. Whereas these intense magnetic fields are difficult to explain astrophysically, we find that they are easily explained by NMGEC. 相似文献
116.
Gordon R 《Optics letters》2012,37(5):912-914
Perfect lensing using negative refractive index materials and radiationless electromagnetic interference both provides extreme subwavelength focusing by "amplifying" evanescent wave components that are usually lost. This Letter provides a relation between the achievable focus spot size, the amplification available, and the focal length. This may be considered as a revised version of Abbe's diffraction limit for focusing systems that have evanescent wave amplification. It is useful in comparing the amplification achieved in various subwavelength focusing implementations as well as determining when it is better to use existing near-field techniques, such as simple diffraction from an aperture or slit, than to attempt complicated superfocusing. 相似文献