20,570 research outputs found
On Binomial Ideals associated to Linear Codes
Recently, it was shown that a binary linear code can be associated to a
binomial ideal given as the sum of a toric ideal and a non-prime ideal. Since
then two different generalizations have been provided which coincide for the
binary case. In this paper, we establish some connections between the two
approaches. In particular, we show that the corresponding code ideals are
related by elimination. Finally, a new heuristic decoding method for linear
codes over prime fields is discussed using Gr\"obner bases
Finite elements for contact problems in two-dimensional elastodynamics
A finite element approach for contact problems in two dimensional elastodynamics was proposed. Sticking, sliding, and frictional contact were taken into account. The method consisted of a modification of the shape functions, in the contact region, in order to involve the nodes of the contacting body. The formulation was symmetric (both bodies were contactors and targets), in order to avoid interpenetration. Compatibility over the interfaces was satisfied. The method was applied to the impact of a block on a rigid target. It is shown that the formulation can be applied to fluid structure interaction, and to problems involving material nonlinearity
Report No. 3: Assessment of Possible Migration Pressure and its Labour Market Impact Following EU Enlargement to Central and Eastern Europe
Study for the Department for Education and Employment of the United Kingdom, Bonn 1999 (117 pages).
Prospects for a Nuclear Optical Frequency Standard based on Thorium-229
The 7.6-eV-isomer of Thorium-229 offers the opportunity to perform high
resolution laser spectroscopy of a nuclear transition. We give a brief review
of the investigations of this isomer. The nuclear resonance connecting ground
state and isomer may be used as the reference of an optical clock of very high
accuracy using trapped and laser-cooled thorium ions, or in a compact
solid-state optical frequency standard of high stability.Comment: 5 pages, 1 figure; Proceedings of the 7th Symposium on Frequency
Standards and Metrology, 5-11 October 2008; reference added for section
On the recombination in high-order harmonic generation in molecules
We show that the dependence of high-order harmonic generation (HHG) on the
molecular orientation can be understood within a theoretical treatment that
does not involve the strong field of the laser. The results for H_2 show
excellent agreement with time-dependent strong field calculations for model
molecules, and this motivates a prediction for the orientation dependence of
HHG from the N_2 3s_g valence orbital. For both molecules, we find that the
polarization of recombination photons is influenced by the molecular
orientation. The variations are particularly pronounced for the N_2 valence
orbital, which can be explained by the presence of atomic p-orbitals.Comment: 6 pages 7 figure
Transition from connected to fragmented vegetation across an environmental gradient: scaling laws in ecotone geometry
A change in the environmental conditions across spaceâfor example, altitude or latitudeâcan cause significant changes in the density of a vegetation type and, consequently, in spatial connectivity. We use spatially explicit simulations to study the transition from connected to fragmented vegetation. A static (gradient percolation) model is compared to dynamic (gradient contact process) models. Connectivity is characterized from the perspective of various species that use this vegetation type for habitat and differ in dispersal or migration range, that is, âstep lengthâ across the landscape. The boundary of connected vegetation delineated by a particular step length is termed the â hull edge.â We found that for every step length and for every gradient, the hull edge is a fractal with dimension 7/4. The result is the same for different spatial models, suggesting that there are universal laws in ecotone geometry. To demonstrate that the model is applicable to real data, a hull edge of fractal dimension 7/4 is shown on a satellite image of a piñonâjuniper woodland on a hillside. We propose to use the hull edge to define the boundary of a vegetation type unambiguously. This offers a new tool for detecting a shift of the boundary due to a climate change
- âŠ