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134.
R. Zinke J. Schulenburg J. Richter 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):147-152
We investigate the ground-state magnetic long-range order of
quasi-one-dimensional quantum Heisenberg antiferromagnets for spin
quantum numbers s = 1/2 and s = 1. We use the coupled
cluster method to calculate the sublattice magnetization and
its dependence on the inter-chain coupling J⊥.
We find that for the unfrustrated spin-1/2 system,
an infinitesimal inter-chain coupling is sufficient to stabilize
magnetic long-range order, in agreement with results obtained
by other methods.
For s = 1, we find that a finite inter-chain coupling
is necessary to stabilize magnetic long-range order.
Furthermore, we consider a quasi one-dimensional spin-1/2 system,
where a frustrating next-nearest neighbor in-chain coupling is included.
We find that for stronger frustration as well, a finite inter-chain coupling
is necessary to have magnetic long-range order in the ground state, and that the strength of the inter-chain coupling necessary
to establish magnetic long-range order is related to the size of the spin gap of the isolated chain. 相似文献
135.
Richter 《Discrete and Computational Geometry》2002,28(3):427-442
Let G be a group of affine transformations of the plane R 2 and let the family F consist of all topological discs in R 2 whose boundary is subject to some smoothness condition (general, rectifiable, piecewise C 1 , piecewise C 2 ). Are any two members D,E ∈ F congruent by dissection with respect to G such that all the pieces in the corresponding dissections of D and E belong to F as well? We give an affirmative answer if G contains all affine transformations and F consists of the discs whose boundary is piecewise C 1 . An example shows that C 1 cannot be replaced by C 2 . Moreover, if G is either the group of equiaffine transformations or the group of similarities, then congruence by dissection of two convex discs D and E turns out to be essentially equivalent to congruence by dissection of the boundaries bd(D ) and bd(E ). 相似文献
136.
Gerard R. Richter. 《Mathematics of Computation》2002,71(238):527-535
We consider a family of tensor product finite element methods for hyperbolic equations in , , which are explicit and generate a continuous approximate solution. The base case (an extension of the box scheme to higher order) is due to Winther, who proved stability and optimal order convergence. By means of a simple counterexample, we show that, for linear approximation with , the corresponding methods are unstable.
137.
R. Bruce Richter Carsten Thomassen 《Transactions of the American Mathematical Society》2002,354(11):4585-4595
We characterize those locally connected subsets of the sphere that have a unique embedding in the sphere -- i.e., those for which every homeomorphism of the subset to itself extends to a homeomorphism of the sphere. This implies that if is the closure of an embedding of a 3-connected graph in the sphere such that every 1-way infinite path in has a unique accumulation point in , then has a unique embedding in the sphere. In particular, the standard (or Freudenthal) compactification of a 3-connected planar graph embeds uniquely in the sphere.
138.
Arbe A Colmenero J Alvarez F Monkenbusch M Richter D Farago B Frick B 《Physical review letters》2002,89(24):245701
We report quasielastic neutron scattering experiments exploring the alpha relaxation in polyisoprene over an unprecedented range in momentum transfer. Corroborating and validating earlier molecular dynamics simulations, the measurements reveal a crossover from a Gaussian regime of sublinear diffusion to a strongly non-Gaussian regime at short distances. We show that a consistent interpretation in terms of a distribution of finite jumps underlying the alpha process is possible. This model leads to a time-dependent non-Gaussian parameter exhibiting all features revealed so far from various simulations. 相似文献
139.
140.
Ryezayeva N Hartmann T Kalmykov Y Lenske H von Neumann-Cosel P Ponomarev VY Richter A Shevchenko A Volz S Wambach J 《Physical review letters》2002,89(27):272502
A high-resolution (gamma,gamma') study of the electric dipole response in 208Pb at the S-DALINAC reveals a resonance structure centered around the neutron emission threshold. Microscopic quasiparticle phonon model calculations in realistic model spaces including the coupling to complex configurations are able to describe the data in great detail. The resonance is shown to result from surface density oscillations of the neutron skin relative to an approximately isospin-saturated core. It also forms an integral part of a toroidal E1 mode representing an example of vortex collective motion in nuclei. 相似文献