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61.
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63.
The de Sitter spacetime is transitive under a combination of translations and proper conformal transformations. Its usual
family of geodesics, however, does not take into account this property. As a consequence, there are points in de Sitter spacetime
which cannot be joined to each other by any one of these geodesics. By taking into account the appropriate transitivity properties
in the variational principle, a new family of maximizing trajectories is obtained, whose members are able to connect any two
points of the de Sitter spacetime. These geodesics introduce a new notion of motion, given by a combination of translations
and proper conformal transformations, which may possibly become important at very-high energies, where conformal symmetry
plays a significant role. 相似文献
64.
Truc T. Nguyen Allan R. Sampson 《Annals of the Institute of Statistical Mathematics》1991,43(4):793-801
Several characterizations of multivariate stable distributions together with a characterization of multivariate normal distributions and multivariate stable distributions with Cauchy marginals are given. These are related to some standard characterizations of marcinkiewicz.Research supported, in part, by the Air Force Office of Scientific Research under Contract AFOSR 84-0113. Reproduction in whole or part is permitted for any purpose of the United States Government. 相似文献
65.
66.
David D. Sampson Graeme J. Pendock Robert A. Griffin 《Fiber and Integrated Optics》1997,16(2):129-157
Photonic code-division multiple access schemes have been proposed since the 1970s. Although there are many published proposals for new coding schemes, there are many less experimental verifications of these schemes, even fewer reports of successful data transmission, and no commercial systems. We attempt to explain the key factors that have led to the current state-of-the-art. In so doing, we describe the fundamental principles of matched filtering and noise in photonic CDMA schemes. We survey important developments and show how various schemes are related. We review recent experimental advances and compare the published experimental and theoretical performance for different schemes. We discuss the current major issues and likeb future directions. 相似文献
67.
A simple scheme for data transmission by direct modulation of a gain-switched semiconductor laser is demonstrated. Experimental results are presented that show low error rate and low pattern dependence. The sensitivity of the error rate to changes in drive conditions is also measured. Comparison of our direct modulation scheme with external modulation of the same gain-switched laser shows nearly penalty-free operation. 相似文献
68.
LUDVÍK BENEŠ KLÁRA MELÁNOVÁ JAN SVOBODA VÍTĚZSLAV ZIMA 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):289-293
Intercalates of o-, m-, and p-toluidine into α-Zr(HPO4)2 · H2O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom. 相似文献
69.
[structure: see text]. Fertilin beta is an integral membrane sperm protein that is involved in sperm binding to the egg plasma membrane. We synthesized a dimyristoylated fertilin beta peptide and incorporated it into POPC liposomes at 1 mol %. The concentration of fertilin beta peptide required for 50% inhibition is reduced 100-fold to 5.2 +/- 1.6 microM relative to a monomeric control. Moreover, in contrast to the inhibition observed with monomeric peptides, we obtain complete inhibition with the peptidic liposomes. 相似文献
70.
Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality. 相似文献