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931.
Bjørn Ian Dundas 《K-Theory》1999,18(1):77-92
We give a measure of the difference between Waldhausen's definition of the Ktheory of a simplicial ring and the definition we obtain by extending Quillen's definition degreewise. This has computational advantages as the degreewise Ktheory sometimes is simpler to work with. 相似文献
932.
Vlad Ionescu 《Integral Equations and Operator Theory》1999,34(1):45-55
Based on the Ben Artzi-Gohberg result concerning the equivalence between the invertibility of theL
2-operator
and the exponential dichotomic evolution defined byA(t), the time-varying counterpart of the Redheffer theorem is considered under relaxed conditions. 相似文献
933.
We consider the problem of the identification of continuous functionsf∶[0, 1]→R, by means of the sums
. This is not possible, in general, but we prove that it may be the case under auxiliary conditions. We also study the behaviour
of a well known exceptional function.
Sunto Consideriamo il problema dell’identificazione delle funzioni continuef:[0,1]→ →R, mediante le somme . Ciò non è, in generale, possibile: dimostriamo però tale possibilità sotto condizioni ausiliarie. Studiamo inoltre il comportamento di una ben nota funzione eccezionale.相似文献
934.
Christian Mazza 《Probability Theory and Related Fields》1999,113(2):171-190
We consider the ±J spin glass on a finite graph G=(V,E), with i.i.d. couplings. Our approach considers the Z
2 local gauge invariance of the system. We see the gauge group as a graph theoretic linear code ? over GF(2). The gauge is fixed by choosing a convenient linear supplement of ?. Assuming some relation between the disorder parameter
p and the inverse temperature of the thermal bath β
pb
, we study percolation in the random interaction random cluster model, and extend the results to dilute spin glasses.
Received: 5 May 1997 / Revised version: 9 April 1998 相似文献
935.
We consider the harmonic extension AN of an H-type group N with Lie algebra n = v + z, and [v, v] = z. We characterize the
positive definite spherical functions on AN. 相似文献
936.
Nahum Zobin 《Journal of Geometric Analysis》1999,9(3):491-511
Consider the Sobolev space W
∞
k
(Ω) of functions with bounded kth derivatives defined in a planar domain. We study the problem of extendability of functions
from W
∞
k
(Ω) to the whole ℝ2 with preservation of class, i.e., surjectivity of the restriction operator W
∞
k
(ℝ2) → W
∞
k
(Ω). 相似文献
937.
A continuum limit of the Toda lattice field theory, called the SDiff(2) Toda equation, is shown to have a Lax formalism and an infinite hierarchy of higher flows. The Lax formalism is very similar to the case of the self-dual vacuum Einstein equation and its hyper-Kähler version, however now based upon a symplectic structure on a cylinderS
1×R. An analogue of the Toda lattice tau function is introduced. The existence of hidden SDiff(2) symmetries are derived from a Riemann-Hilbert problem in the SDiff(2) group. Symmetries of the tau function turn out to have commutator anomalies, hence give a representation of a central extension of the SDiff(2) algebra. 相似文献
938.
Thomas M. Liggett 《Probability Theory and Related Fields》1996,106(4):495-519
Summary. Branching random walks and contact processes on the homogeneous tree in which each site has d+1 neighbors have three possible types of behavior (for d≧ 2): local survival, local extinction with global survival, and global extinction. For branching random walks, we show that
if there is local extinction, then the probability that an individual ever has a descendent at a site n units away from that individual’s location is at most d
− n/2
, while if there is global extinction, this probability is at most d
−n
. Next, we consider the structure of the set of invariant measures with finite intensity for the system, and see how this
structure depends on whether or not there is local and/or global survival. These results suggest some problems and conjectures for contact processes on trees. We prove some and
leave others open. In particular, we prove that for some values of the infection parameter λ, there are nontrivial invariant measures which have a density tending to zero in all directions, and hence are different
from those constructed by Durrett and Schinazi in a recent paper.
Received: 26 April 1996/In revised form: 20 June 1996 相似文献
939.
Summary We derive and analyze the hierarchical basis-multigrid method for solving discretizations of self-adjoint, elliptic boundary value problems using piecewise linear triangular finite elements. The method is analyzed as a block symmetric Gauß-Seidel iteration with inner iterations, but it is strongly related to 2-level methods, to the standard multigridV-cycle, and to earlier Jacobi-like hierarchical basis methods. The method is very robust, and has a nearly optimal convergence rate and work estimate. It is especially well suited to difficult problems with rough solutions, discretized using highly nonuniform, adaptively refined meshes. 相似文献
940.