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排序方式: 共有76条查询结果,搜索用时 46 毫秒
31.
32.
Ruy Luiz Milidiú Eduardo Sany Laber Artur Alves Pessoa 《Journal of Algorithms in Cognition, Informatics and Logic》1999,32(2):195
An important issue related to coding schemes is their compression loss. A simple measure ε of the compression loss due to a coding scheme different than Huffman coding is defined by ε = AC − AH where AH is the average code length of a static Huffman encoding and AC is the average code length of an encoding based on the compression scheme C. When the scheme C is the FGK algorithm, Vitter conjectured that ε ≤ K for some real constant K. Here, we use an amortized analysis to prove this conjecture. We show that ε < 2. Furthermore, we show through an example that our bound is asymptotically tight. This result explains the good performance of FGK that many authors have observed through practical experiments. 相似文献
33.
34.
Ruy Exel 《Bulletin of the Brazilian Mathematical Society》1994,25(2):173-179
We describe both the Bunce-DeddensC
*-algebras and their Toeplitz versions, as crossed products of commutativeC
*-algebras by partial automorphisms. In the latter case, the commutative algebra has, as its spectrum, the union of the Cantor set and a copy of the set of natural numbers , fitted together in such a way that is an open dense subset. The partial automorphism is induced by a map that acts like the odometer map on the Cantor set while being the translation by one on . From this we deduce, by taking quotients, that the Bunce-DeddensC
*-algebras are isomorphic to the (classical) crossed product of the algebra of continuous functions on the Cantor set by the odometer map. 相似文献
35.
Ruy Fabila-Monroy David Flores-Peñaloza Clemens Huemer Ferran Hurtado Jorge Urrutia David R. Wood 《Graphs and Combinatorics》2012,28(3):365-380
For a graph G and integer k ≥ 1, we define the token graph F k (G) to be the graph with vertex set all k-subsets of V(G), where two vertices are adjacent in F k (G) whenever their symmetric difference is a pair of adjacent vertices in G. Thus vertices of F k (G) correspond to configurations of k indistinguishable tokens placed at distinct vertices of G, where two configurations are adjacent whenever one configuration can be reached from the other by moving one token along an edge from its current position to an unoccupied vertex. This paper introduces token graphs and studies some of their properties including: connectivity, diameter, cliques, chromatic number, Hamiltonian paths, and Cartesian products of token graphs. 相似文献
36.
Ruy Alberto Pisani Altafim Ruy Alberto Corrêa Altafim Xunlin Qiu Sebastian Raabe Werner Wirges Heitor Cury Basso Reimund Gerhard 《Applied Physics A: Materials Science & Processing》2012,107(4):965-970
Ferro- or piezoelectrets are dielectric materials with two elastically very different macroscopic phases and electrically charged interfaces between them. One of the newer piezoelectret variants is a system of two fluoroethylenepropylene (FEP) films that are first laminated around a polytetrafluoroethylene (PTFE) template. Then, by removing the PTFE template, a two-layer FEP structure with open tubular channels is obtained. After electrical charging, the channels form easily deformable macroscopic electric dipoles whose changes under mechanical or electrical stress lead to significant direct or inverse piezoelectricity, respectively. Here, different PTFE templates are employed to generate channel geometries that vary in height or width. It is shown that the control of the channel geometry allows a direct adjustment of the resonance frequencies in the tubular-channel piezoelectrets. By combining several different channel widths in a single ferroelectret, it is possible to obtain multiple resonance peaks that may lead to a rather flat frequency-response region of the transducer material. A phenomenological relation between the resonance frequency and the geometrical parameters of a tubular channel is also presented. This relation may help to design piezoelectrets with a specific frequency response. 相似文献
37.
We compute the K-theory groups of the Cuntz–Krieger C
*-algebra O
A
associated to an infinite matrix A of zeros and ones. 相似文献
38.
Ruy Exel 《Bulletin of the Brazilian Mathematical Society》1999,30(1):99-124
The dual action of a locally compact abelian group, in the context of C*-algebraic bundles, is shown to satisfy an integrability property, similar to Rieffel's proper actions. The tools developed include a generalization of Bochner's integral as well as a Fourier inversion formula for operator valued maps.Partially supported by CNPq, Brazil. 相似文献
39.
We first extend the classical Sbrana-Cartan theory of isometrically deformable euclidean hypersurfaces to the sphere and hyperbolic space. Then we construct and characterize a large family of hypersurfaces which admit a unique deformation. This is used to show, by means of explicit examples, that different types of hypersurfaces in the Sbrana-Cartan classification can be smoothly attached. Finally, among other applications, we discuss the existence of complete deformable hypersurfaces in hyperbolic space. 相似文献
40.
The soft tori constitute a continuous deformation, in a very precise sense, from the commutative -algebra to the highly non-commutative -algebra . Since both of these -algebras are known to have a separating family of finite dimensional representations, it is natural to ask whether that is also the case for the soft tori. We show that this is in fact the case.