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51.
Nikolaos Askitas 《manuscripta mathematica》1996,89(1):35-47
We prove that the action of the orthogonal group of an integral, unimodular lattice whose rank and signature satisfy a certain
indefiniteness condition acts transitively on pairs of mutually orthogonal elements with the same isometric invariants. 相似文献
52.
When a glassy polymer containing a uniformly dispersed solute is brought in contact with a penetrant, solute diffusion will be associated with the transport mechanism and penetration velocity of the penetrant in the polymer. Analysis and prediction of mechanisms of diffusional solute release may be obtained through a new dimensionless number, the swelling interface number, Sw, which compares the relative mobilities of the penetrant and the solute in the presence of macromolecular relaxations in the polymer. It is shown that a sufficient and necessary criterion for time-independent diffusional solute release rates from these swellable systems is that the Sw be smaller than 10?2. The swelling interface number Sw may be related to easily determined structural and thermodynamic parameters of the solute/polymer/penetrant system. Preliminary experimental results of dynamic water swelling of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) and diffusional release of theophylline from initially glassy copolymers show that decreasing values of Sw are related to increased pseudo-case-II transport kinetics of the solute. 相似文献
53.
Nikolaos A. Peppas Robert Gurny Eric Doelker Pierre Buri 《Journal of membrane science》1980,7(3):241-253
A drug diffusion model for the case of diffusion of an initially uniformly distributed drug through a polymeric matrix is presented and solved. Drug diffusion from a single surface is analyzed for the case of countercurrent diffusion of a solvent which is thermodynamically compatible with the polymer. Due to swelling, considerable volume expansion is observed leading to a moving-boundary diffusion problem. Drug concentration profiles within the polymer and drug release rates can be determined. The results are in agreement with experimental data obtained for the system of KCl distributed in hydrophilic hydroxypropyl methyl cellulose matrices, in the form of tablets. 相似文献
54.
On , we prove the existence of sharp logarithmic Sobolev inequalities with higher fractional derivatives. Let s be a positive real number. Any function f ∈ satisfies with be any number and where the operators in Fourier spaces are defined by . To cite this article: A. Cotsiolis, N.K. Tavoularis, C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
55.
John?Ellis Nikolaos?E.?MavromatosEmail author Dimitri?V.?Nanopoulos 《General Relativity and Gravitation》2005,37(10):1665-1670
Generic cosmological models in non-critical string theory have a time-dependent dilaton background at a late epoch. The cosmological
deceleration parameter q
0 is given by the square of the string coupling, g
s
2, up to a negative sign. Hence the expansion of the Universe must accelerate eventually, and the observed value of q
0 corresponds to g
s
2 ∼ 0.6. In this scenario, the string coupling is asymptotically free at large times, but its present rate of change is imperceptibly
small.
First Award in the 2005 Essay Competition of the Gravity Research Foundation. - Ed. 相似文献
56.
Existence of Solutions and of Multiple Solutions for Nonlinear Nonsmooth Periodic Systems 总被引:1,自引:0,他引:1
Evgenia H. Papageorgiou Nikolaos S. Papageorgiou 《Czechoslovak Mathematical Journal》2004,54(2):347-371
In this paper we examine nonlinear periodic systems driven by the vectorial p-Laplacian and with a nondifferentiable, locally Lipschitz nonlinearity. Our approach is based on the nonsmooth critical point theory and uses the subdifferential theory for locally Lipschitz functions. We prove existence and multiplicity results for the sublinear problem. For the semilinear problem (i.e. p = 2) using a nonsmooth multidimensional version of the Ambrosetti-Rabinowitz condition, we prove an existence theorem for the superlinear problem. Our work generalizes some recent results of Tang (PAMS 126(1998)). 相似文献
57.
Evgenia H. Papageorgiou Nikolaos S. Papageorgiou 《Proceedings of the American Mathematical Society》2004,132(2):429-434
In this paper we study a nonlinear periodic problem driven by the ordinary scalar p-Laplacian and with a Carathéodory nonlinearity. We establish the existence of at least two nontrivial solutions. Our approach is variational based on the smooth critical point theory and using the ``Second Deformation Theorem".
58.
We demonstrate that both the linear (diffraction) and the nonlinear dynamics of two-dimensional waveguide arrays are considerably more complex and versatile than their one-dimensional counterparts. The discrete diffraction properties of these arrays can be effectively altered, depending on the propagation Bloch k-vector within the first Brillouin zone of the lattice. In general, this diffraction behavior is anisotropic and therefore permits the existence of a new class of discrete elliptic solitons in the nonlinear regime. 相似文献
59.
Skaropoulos NC Yagridou HD Chrissoulidis DP 《The Journal of the Acoustical Society of America》2003,113(6):3001-3011
An exact, analytical solution is developed for the problem of acoustic-wave scattering from a cluster of ideal, gaseous, spherical bubbles in an unbounded, homogeneous, host fluid. This solution takes into account all modes of oscillation of the bubbles as well as all interactions between them; it is applicable to a wide range of bubble sizes and excitation frequencies. In the low frequency regime, the theory of this paper is shown to reduce to the "monopole" approximation, the effect of higher-order modes being non-negligible only for very small bubble-to-bubble separations. A numerical study of interactive backscattering from small clusters, comprising up to three ideal bubbles, is presented. Interactions between the bubbles are shown to produce downward shifts in the resonance frequency of the cluster, when the scattering configuration is symmetric. Furthermore, asymmetries of the scattering configuration are shown to generate sharp resonances at frequencies above the resonance of the symmetric mode. The results of this paper agree with previous theoretical and experimental work. 相似文献
60.
A new feature extraction process is proposed for gait representation and recognition. The new system is based on the Radon transform of binary silhouettes. For each gait sequence, the transformed silhouettes are used for the computation of a template. The set of all templates is subsequently subjected to linear discriminant analysis and subspace projection. In this manner, each gait sequence is described using a low-dimensional feature vector consisting of selected Radon template coefficients. Given a test feature vector, gait recognition and verification is achieved by appropriately comparing it to feature vectors in a reference gait database. By using the new system on the Gait Challenge database, very considerable improvements in recognition performance are seen in comparison to state-of-the-art methods for gait recognition. 相似文献