625 research outputs found

    Los mercados de trabajo en Europa central Desempleo, cambio estructural e instituciones / Labour markets in Central Europe

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    En el primer epígrafe, analizaremos el desempleo en las economías en transición y observaremos los flujos entre las situaciones alternativas del mercado laboral. Posteriormente, utilizaremos este enfoque para resumir los factores principales que podrían afectar a los niveles de desempleo de los nuevos Estados miembros que se incorporarán en 2004. Finalmente, ofreceremos una breve perspectiva general de los resultados econométricos empíricos sobre las diferencias entre las características del mercado laboral de la actual Europa de los Quince y de los nuevos Estados miembros

    Perturbation resilience for the facility location problem

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    We analyze a simple local search heuristic for the facility location problem using the notion of perturbation resilience: an instance is γ-perturbation resilient if all costs can be perturbed by a factor of γ without changing the optimal solution. We prove that local search for FLP succeeds in finding the optimal solution for γ-perturbation resilient instances for γ≥3, and we show that this is tight

    Nachruf auf Eberhard Lehmann

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    Multiple sequence alignment based on set covers

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    We introduce a new heuristic for the multiple alignment of a set of sequences. The heuristic is based on a set cover of the residue alphabet of the sequences, and also on the determination of a significant set of blocks comprising subsequences of the sequences to be aligned. These blocks are obtained with the aid of a new data structure, called a suffix-set tree, which is constructed from the input sequences with the guidance of the residue-alphabet set cover and generalizes the well-known suffix tree of the sequence set. We provide performance results on selected BAliBASE amino-acid sequences and compare them with those yielded by some prominent approaches

    Nanoscale Electronic Order in Iron Pnictides

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    The charge distribution in RFeAs (R=La, Sm) iron pnictides is probed using As NQR. Whereas undoped and optimally-doped/overdoped compounds feature a single charge environment, two charge environments are detected in the underdoped region. Spin- lattice relaxation measurements show their coexistence at the nanoscale. Together with the quantitative variations of the spectra with doping, they point at a local electronic order in the iron layers, where low- and high-doping-like regions would coexist. Implications for the interplay of static magnetism and superconductivity are discussed

    Random Shortest Paths: {Non-Euclidean} Instances for Metric Optimization Problems

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    Probabilistic analysis for metric optimization problems has mostly been conducted on random Euclidean instances, but little is known about metric instances drawn from distributions other than the Euclidean. This motivates our study of random metric instances for optimization problems obtained as follows: Every edge of a complete graph gets a weight drawn independently at random. The distance between two nodes is then the length of a shortest path (with respect to the weights drawn) that connects these nodes. We prove structural properties of the random shortest path metrics generated in this way. Our main structural contribution is the construction of a good clustering. Then we apply these findings to analyze the approximation ratios of heuristics for matching, the traveling salesman problem (TSP), and the k-median problem, as well as the running-time of the 2-opt heuristic for the TSP. The bounds that we obtain are considerably better than the respective worst-case bounds. This suggests that random shortest path metrics are easy instances, similar to random Euclidean instances, albeit for completely different structural reasons

    A genome-wide assessment of stages of elevational parapatry in Bornean passerine birds reveals no introgression: implications for processes and patterns of speciation

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    Topographically complex regions often contain the close juxtaposition of closely related species along elevational gradients. The evolutionary causes of these elevational replacements, and thus the origin and maintenance of a large portion of species diversity along elevational gradients, are usually unclear because ecological differentiation along a gradient or secondary contact following allopatric diversification can produce the same pattern. We used reduced representation genomic sequencing to assess genetic relationships and gene flow between three parapatric pairs of closely related songbird taxa (Arachnothera spiderhunters, Chloropsis leafbirds, and Enicurus forktails) along an elevational gradient in Borneo. Each taxon pair presents a different elevational range distribution across the island, yet results were uniform: little or no gene flow was detected in any pairwise comparisons. These results are congruent with an allopatric “species-pump” model for generation of species diversity and elevational parapatry of congeners on Borneo, rather than in situ generation of species by “ecological speciation” along an elevational gradient
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