7,322 research outputs found
spectra in elementary cellular automata and fractal signals
We systematically compute the power spectra of the one-dimensional elementary
cellular automata introduced by Wolfram. On the one hand our analysis reveals
that one automaton displays spectra though considered as trivial, and on
the other hand that various automata classified as chaotic/complex display no
spectra. We model the results generalizing the recently investigated
Sierpinski signal to a class of fractal signals that are tailored to produce
spectra. From the widespread occurrence of (elementary) cellular
automata patterns in chemistry, physics and computer sciences, there are
various candidates to show spectra similar to our results.Comment: 4 pages (3 figs included
Accelerating exhaustive pairwise metagenomic comparisons
In this manuscript, we present an optimized and parallel version of our previous work IMSAME, an exhaustive gapped aligner for the pairwise and accurate comparison of metagenomes. Parallelization strategies are applied to take advantage of modern multiprocessor architectures. In addition, sequential optimizations in CPU time and memory consumption are provided. These algorithmic and computational enhancements enable IMSAME to calculate near optimal alignments which are used to directly assess similarity between metagenomes without requiring reference databases. We show that the overall efficiency of the parallel implementation is superior to 80% while retaining scalability as the number of parallel cores used increases. Moreover, we also show thats equential optimizations yield up to 8x speedup for scenarios with larger data.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec
Localization, Coulomb interactions and electrical heating in single-wall carbon nanotubes/polymer composites
Low field and high field transport properties of carbon nanotubes/polymer
composites are investigated for different tube fractions. Above the percolation
threshold f_c=0.33%, transport is due to hopping of localized charge carriers
with a localization length xi=10-30 nm. Coulomb interactions associated with a
soft gap Delta_CG=2.5 meV are present at low temperature close to f_c. We argue
that it originates from the Coulomb charging energy effect which is partly
screened by adjacent bundles. The high field conductivity is described within
an electrical heating scheme. All the results suggest that using composites
close to the percolation threshold may be a way to access intrinsic properties
of the nanotubes by experiments at a macroscopic scale.Comment: 4 pages, 5 figures, Submitted to Phys. Rev.
Efficiency Guarantees in Auctions with Budgets
In settings where players have a limited access to liquidity, represented in
the form of budget constraints, efficiency maximization has proven to be a
challenging goal. In particular, the social welfare cannot be approximated by a
better factor then the number of players. Therefore, the literature has mainly
resorted to Pareto-efficiency as a way to achieve efficiency in such settings.
While successful in some important scenarios, in many settings it is known that
either exactly one incentive-compatible auction that always outputs a
Pareto-efficient solution, or that no truthful mechanism can always guarantee a
Pareto-efficient outcome. Traditionally, impossibility results can be avoided
by considering approximations. However, Pareto-efficiency is a binary property
(is either satisfied or not), which does not allow for approximations.
In this paper we propose a new notion of efficiency, called \emph{liquid
welfare}. This is the maximum amount of revenue an omniscient seller would be
able to extract from a certain instance. We explain the intuition behind this
objective function and show that it can be 2-approximated by two different
auctions. Moreover, we show that no truthful algorithm can guarantee an
approximation factor better than 4/3 with respect to the liquid welfare, and
provide a truthful auction that attains this bound in a special case.
Importantly, the liquid welfare benchmark also overcomes impossibilities for
some settings. While it is impossible to design Pareto-efficient auctions for
multi-unit auctions where players have decreasing marginal values, we give a
deterministic -approximation for the liquid welfare in this setting
In situ behaviour of a stiff layered clay subject to thermal loading: Observations and interpretation
George Stephenson Medal 2008, atorgada per la Institution of Civil Engineers del Regne UnitThe paper presents an interpretation of an in situ heating test carried out on Opalinus clay in the Mont Terri underground laboratory. Opalinus clay is a stiff, strongly bedded, Mesozoic clay of marine origin. When subjected to thermal loading, saturated stiff clays exhibit a strong pore pressure response that significantly affects the hydraulic and mechanical behaviour of the material. The observations gathered in the in situ test have provided an opportunity to examine the integrated thermo-hydro-mechanical (THM) response of this sedimentary clay. Coupled THM numerical analyses have been carried out to provide a structured framework for interpretation, and to enhance understanding of THM clay behaviour. Numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law especially developed for this type of material. The law includes degradation of bonding by damage. By performing three-dimensional computations, it has been possible to incorporate anisotropy of material parameters and of in situ stresses. The 3D simulation has proved able to furnish a satisfactory representation of the development of the in situ test and of the main observed patterns of behaviour. A sensitivity analysis has also been carried out to examine the potential effect of various key or uncertain parameters. The critical examination of test observations and the results of the numerical analyses have allowed the classification, by differing degrees of significance, of the various coupled phenomena present in the problem.Peer ReviewedAward-winningPostprint (published version
Quality of life in children surviving cancer: A personality and multi-informant perspective [IF: 1.5]
Objective: To describe quality of life (QoL) of children surviving cancer in relation to their personality, using self- and maternal reports and examining differences with healthy referents. Method: Sixty-seven children who survived childhood cancer were compared with eighty-one healthy children on QoL and personality characteristics. Results: Children who survived cancer reported higher QoL than healthy children, whereas there were no differences for personality. Two main effects emerged for informant with children rating themselves as less neurotic and more conscientious than their mothers. The correspondence between mothers and children was substantially higher for survivors for QoL and personality ratings. QoL and trait measures share substantial variance, and personality traits significantly predict QoL. Parental personality ratings explained child QoL beyond children's personality ratings. Conclusions: Personality traits contribute to quality of life, indicating that personality significantly influences child's quality of life beyond the experience of a negative life event such as surviving cancer and its treatment. From a diagnostic perspective, parental trait ratings are informative in addition to children's ratings of personality to understand children's QoL
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