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171.
[formula: see text] The synthesis of 1,3-difluoro-2,4-diphenylbenzene has been accomplished in one step from 1,2-diphenylcyclobutene using the environmentally benign difluorocarbene precursor sodium chlorodifluoroacetate. In addition, the preparation of the previously unknown compound 1,3-difluoro-2,4-di-n-propylbenzene has been accomplished in one step from 1,2-di-n-propylcyclobutene using Seyferth's reagent (Ph-Hg-CF3) and sodium chlorodifluoroacetate. 相似文献
172.
Priplata A Niemi J Salen M Harry J Lipsitz LA Collins JJ 《Physical review letters》2002,89(23):238101
Noise can enhance the detection and transmission of weak signals in certain nonlinear systems, via a mechanism known as stochastic resonance. Here we show that input noise can be used to improve motor control in humans. Specifically, we show that the postural sway of both young and elderly individuals during quiet standing can be significantly reduced by applying subsensory mechanical noise to the feet. We further demonstrate with input noise a trend towards the reduction of postural sway in elderly subjects to the level of young subjects. These results suggest that noise-based devices, such as randomly vibrating shoe inserts, may enable people to overcome functional difficulties due to age-related sensory loss. 相似文献
173.
174.
Andreas Losch Radan Salomonovic Ullrich Steiner Lewis J. Fetters Jacob Klein 《Journal of Polymer Science.Polymer Physics》1995,33(12):1821-1831
We have used nuclear reaction analysis to measure diffusion coefficients D in couples consisting of hydrogenated polybutadienes of structure (C2H3(C2H5))x(C4H8)1?x and their partly deuterated counterparts. The 1,2- and 1,4-olefinic isomers are randomly distributed along the chains and the mean vinyl fraction x varies between 0.38 and 0.94. We find that the effective monomeric mobility D0 [defined by D = D0(Ne/N2) for each copolymer, where N is the backbone length and Ne the entanglement spacing] decreases monotonically with increasing vinyl content x. Over the range of microstructures and temperatures T (?14?40°C) investigated we find log(D0/T) varies smoothly with (T ? Tg), where Tg is the glass transition temperature of the respective melts. An analysis of our data in terms of a simple activated rate process model suggests that D0 is controlled by thermally activated hopping of segments whose effective volume is close to that of the respective statistical segment lengths of the copolymeric chains. ©1995 John Wiley & Sons, Inc. 相似文献
175.
James D. Lewis 《Mathematische Nachrichten》1996,178(1):249-269
Let Y be a smooth projective algebraic surface over ?, and T(Y) the kernel of the Albanese map CH0(Y)deg0 → Alb(Y). It was first proven by D. Mumford that if the genus Pg(Y) > 0, then T(Y) is 'infinite dimensional'. One would like to have a better idea about the structure of T(Y). For example, if Y is dominated by a product of curves E1 × E2, such as an abelian or a Kummer surface, then one can easily construct an abelian variety B and a surjective 'regular' homomorphism B?z2 → T(Y). A similar story holds for the case where Y is the Fano surface of lines on a smooth cubic hypersurface in P4. This implies a sort of boundedness result for T(Y). It is natural to ask if this is the case for any smooth projective algebraic surface Y ? Partial results have been attained in this direction by the author [Illinois. J. Math. 35 (2), 1991]. In this paper, we show that the answer to this question is in general no. Furthermore, we generalize this question to the case of the Chow group of k—cycles on any projective algebraic manifold X, and arrive at, from a conjectural standpoint, necessary and sufficient cohomological conditions on X for which the question can be answered affirmatively. 相似文献
176.
A fully coupled consolidation model has been developed for the simulation of the surface subsidence above gas reservoirs. The model is based on the Biot Theory and the material balance equation for hydrocarbon reservoirs. The model is extremely versatile and can handle such complex situations as vertical cross-sections where several gas reservoirs and aquifers are exploited at different levels. Computer runs were used to generate several reservoir formation profiles and the surface subsidence bowl for a variety of conditions. These results indicate the importance of various parameters which are disregarded in proelasticity models. 相似文献
177.
Combination of pinhole imaging of laser produced plasma soft X-ray emission and X-ray streak photography allows simultaneous space and time resolved study of the axial development of the high density region of the plasma created from a plane Cu target by a 6 nsec 1.06 μ laser pulse. 相似文献
178.
Relaxed controls induce convexity of the velocity sets in optimal control problems, permitting a general existence theory. Here we obtain complete convexity, of the set of control-trajectory pairs, by relaxing the problem constraints to admit certain measures on the product of the control and trajectory spaces. It is proved that these measures are just unit mixtures of control-trajectory pairs and that admitting them does not alter the minimum value of the control problems. This can be used to derive necessary and sufficient conditions for optimality of dynamic programming type. 相似文献
179.
Lewis Wheeler 《Journal of Elasticity》1971,1(2):121-124
In recent separate investigations, Kirchhoff's classical uniqueness theorem of elastodynamics has been extended in two ways. Gurtin and Toupin generalized the theorem to encompass bodies possessing an elasticity tensor that obeys the semi-strong ellipticity condition, whereas the author has extended the theorem to unbounded regions. These two results are brought together in the present paper.
Resume Dans deux études récentes, le champ d'application du théoréme classique de Kirchhoff sur l'unicité de l'élastodynamique a été élargi de deux manières différentes. Gurtin et Toupin l'ont généralisé pour inclure les corps possédant un tenseur d'élasticité obéissant à la condition d'ellipticité demi-forte, alors que le présent auteur l'a étendu aux régions non finies. Ces deux résultats ont été combinés dans la présente communication.相似文献
180.