Showing papers by "Polytechnic University of Catalonia published in 2002"
TL;DR: The authors reviewed the connection between ocean basins via the "atmospheric bridge" through an examination of previous work augmented by analyses of 50 years of data from the National Centers for Environmental Prediction- National Center for Atmospheric Research (NCEP-NCAR) reanalysis project and coupled atmospheric general circulation (AGCM)-mixed layer ocean model experiments.
Abstract: During El Nino-Southern Oscillation (ENSO) events, the atmospheric response to sea surface temperature (SST) anomalies in the equatorial Pacific influences ocean conditions over the remainder of the globe. This connection between ocean basins via the ''atmospheric bridge'' is reviewed through an examination of previous work augmented by analyses of 50 years of data from the National Centers for Environmental Prediction- National Center for Atmospheric Research (NCEP-NCAR) reanalysis project and coupled atmospheric general circulation (AGCM)-mixed layer ocean model experiments. Observational and modeling studies have now established a clear link between SST anomalies in the equatorial Pacific with those in the North Pacific, north tropical Atlantic, and Indian Oceans in boreal winter and spring. ENSO-related SST anomalies also appear to be robust in the western North Pacific during summer and in the Indian Ocean during fall. While surface heat fluxes are the key component of the atmospheric bridge driving SST anomalies, Ekman transport also creates SST anomalies in the central North Pacific although the full extent of its impact requires further study. The atmospheric bridge not only influences SSTs on interannual timescales but also affects mixed layer depth (MLD), salinity, the seasonal evolution of upper-ocean temperatures, and North Pacific SST variability at lower fre- quencies. The model results indicate that a significant fraction of the dominant pattern of low-frequency (.10 yr) SST variability in the North Pacific is associated with tropical forcing. AGCM experiments suggest that the oceanic feedback on the extratropical response to ENSO is complex, but of modest amplitude. Atmosphere- ocean coupling outside of the tropical Pacific slightly modifies the atmospheric circulation anomalies in the Pacific-North America (PNA) region but these modifications appear to depend on the seasonal cycle and air- sea interactions both within and beyond the North Pacific Ocean.
1,668 citations
TL;DR: A set of tools to construct positional weight matrices from known transcription factor binding sites in a species or taxon-specific manner and to search for matches in DNA sequences are developed.
Abstract: We have developed a set of tools to construct positional weight matrices from known transcription factor binding sites in a species or taxon-specific manner, and to search for matches in DNA sequences.
1,136 citations
TL;DR: In this paper, the authors show that random uniform immunization of individuals does not lead to the eradication of infections in all complex networks, and that the absence of any critical immunization threshold is due to the unbounded connectivity fluctuations of scale-free networks.
Abstract: Complex networks such as the sexual partnership web or the Internet often show a high degree of redundancy and heterogeneity in their connectivity properties. This peculiar connectivity provides an ideal environment for the spreading of infective agents. Here we show that the random uniform immunization of individuals does not lead to the eradication of infections in all complex networks. Namely, networks with scale-free properties do not acquire global immunity from major epidemic outbreaks even in the presence of unrealistically high densities of randomly immunized individuals. The absence of any critical immunization threshold is due to the unbounded connectivity fluctuations of scale-free networks. Successful immunization strategies can be developed only by taking into account the inhomogeneous connectivity properties of scale-free networks. In particular, targeted immunization schemes, based on the nodes' connectivity hierarchy, sharply lower the network's vulnerability to epidemic attacks.
1,082 citations
TL;DR: The large connectivity fluctuations usually found in these networks strengthen considerably the incidence of epidemic outbreaks and defines a new epidemiological framework characterized by a highly heterogeneous response of the system to the introduction of infected individuals with different connectivity.
Abstract: We present a detailed analytical and numerical study for the spreading of infections with acquired immunity in complex population networks. We show that the large connectivity fluctuations usually found in these networks strengthen considerably the incidence of epidemic outbreaks. Scale-free networks, which are characterized by diverging connectivity fluctuations in the limit of a very large number of nodes, exhibit the lack of an epidemic threshold and always show a finite fraction of infected individuals. This particular weakness, observed also in models without immunity, defines a new epidemiological framework characterized by a highly heterogeneous response of the system to the introduction of infected individuals with different connectivity. The understanding of epidemics in complex networks might deliver new insights in the spread of information and diseases in biological and technological networks that often appear to be characterized by complex heterogeneous architectures.
1,016 citations
TL;DR: It is found that the connectivity structure of the Internet presents statistical distributions settled in a well-defined stationary state and the large-scale properties are characterized by a scale-free topology consistent with previous observations.
Abstract: We study the large-scale topological and dynamical properties of real Internet maps at the autonomous system level, collected in a 3-yr time interval. We find that the connectivity structure of the Internet presents statistical distributions settled in a well-defined stationary state. The large-scale properties are characterized by a scale-free topology consistent with previous observations. Correlation functions and clustering coefficients exhibit a remarkable structure due to the underlying hierarchical organization of the Internet. The study of the Internet time evolution shows a growth dynamics with aging features typical of recently proposed growing network models. We compare the properties of growing network models with the present real Internet data analysis.
694 citations
TL;DR: A complete view of the current state of the art with respect to layout problems from an algorithmic point of view is presented.
Abstract: Graph layout problems are a particular class of combinatorial optimization problems whose goal is to find a linear layout of an input graph in such way that a certain objective cost is optimized. This survey considers their motivation, complexity, approximation properties, upper and lower bounds, heuristics and probabilistic analysis on random graphs. The result is a complete view of the current state of the art with respect to layout problems from an algorithmic point of view.
665 citations
TL;DR: The analysis of some species-rich, well-defined food webs shows that they display the so-called small world behavior shared by a number of disparate complex systems, suggesting that communities might be self-organized in a non-random fashion that might have important consequences in their resistance to perturbations.
606 citations
TL;DR: In this article, the authors study epidemic dynamics in bounded scale-free networks with soft and hard connectivity cutoffs and show that the induced epidemic threshold is very small even at a relatively small cutoff, showing that the neglection of connectivity fluctuations in such networks leads to a strong overestimation of the epidemic threshold.
Abstract: Many real networks present a bounded scale-free behavior with a connectivity cutoff due to physical constraints or a finite network size. We study epidemic dynamics in bounded scale-free networks with soft and hard connectivity cutoffs. The finite size effects introduced by the cutoff induce an epidemic threshold that approaches zero at increasing sizes. The induced epidemic threshold is very small even at a relatively small cutoff, showing that the neglection of connectivity fluctuations in bounded scale-free networks leads to a strong overestimation of the epidemic threshold. We provide the expression for the infection prevalence and discuss its finite size corrections. The present paper shows that the highly heterogeneous nature of scale-free networks does not allow the use of homogeneous approximations even for systems of a relatively small number of nodes.
592 citations
TL;DR: A dynamical model of epidemic spreading on complex networks in which there are explicit correlations among the node's connectivities finds an epidemic threshold inversely proportional to the largest eigenvalue of the connectivity matrix that gives the average number of links.
Abstract: We study a dynamical model of epidemic spreading on complex networks in which there are explicit correlations among the node's connectivities. For the case of Markovian complex networks, showing only correlations between pairs of nodes, we find an epidemic threshold inversely proportional to the largest eigenvalue of the connectivity matrix that gives the average number of links, which from a node with connectivity k go to nodes with connectivity k('). Numerical simulations on a correlated growing network model provide support for our conclusions.
521 citations
TL;DR: The combination of Fenton, Fenton-like and photon-Fenton reactions has been proved to be highly effective for the treatment of such a type of wastewaters, and several advantages for the technique application arise from the study.
421 citations
TL;DR: In this paper, a stabilized finite element method is proposed to solve the transient Navier-Stokes equations based on the decomposition of the unknowns into resolvable and subgrid scales.
TL;DR: Large morphological effects frequently can be achieved by small changes, according to this model, and similar morphologies can be produced by different changes, consistent with why predicting the morphological outcomes of molecular experiments is challenging.
Abstract: Generation of morphological diversity remains a challenge for evolutionary biologists because it is unclear how an ultimately finite number of genes involved in initial pattern formation integrates with morphogenesis. Ideally, models used to search for the simplest developmental principles on how genes produce form should account for both developmental process and evolutionary change. Here we present a model reproducing the morphology of mammalian teeth by integrating experimental data on gene interactions and growth into a morphodynamic mechanism in which developing morphology has a causal role in patterning. The model predicts the course of tooth-shape development in different mammalian species and also reproduces key transitions in evolution. Furthermore, we reproduce the known expression patterns of several genes involved in tooth development and their dynamics over developmental time. Large morphological effects frequently can be achieved by small changes, according to this model, and similar morphologies can be produced by different changes. This finding may be consistent with why predicting the morphological outcomes of molecular experiments is challenging. Nevertheless, models incorporating morphology and gene activity show promise for linking genotypes to phenotypes.
TL;DR: This work presents a simple model of proteome evolution that is able to reproduce many of the observed statistical regularities reported from the analysis of the yeast proteome, and suggests that the observed patterns can be explained by a process of gene duplication and diversification that would evolve proteome networks under a selection pressure.
Abstract: The next step in the understanding of the genome organization, after the determination of complete sequences, involves proteomics. The proteome includes the whole set of protein-protein interactions, and two recent independent studies have shown that its topology displays a number of surprising features shared by other complex networks, both natural and artificial. In order to understand the origins of this topology and its evolutionary implications, we present a simple model of proteome evolution that is able to reproduce many of the observed statistical regularities reported from the analysis of the yeast proteome. Our results suggest that the observed patterns can be explained by a process of gene duplication and diversification that would evolve proteome networks under a selection pressure, favoring robustness against failure of its individual components.
TL;DR: In this paper, the recently developed multiplicative regularized contrast source inversion method is applied to microwave biomedical applications, which is fully iterative and avoids solving any forward problem in each iterative step.
Abstract: In this paper, the recently developed multiplicative regularized contrast source inversion method is applied to microwave biomedical applications. The inversion method is fully iterative and avoids solving any forward problem in each iterative step. In this way, the inverse scattering problem can efficiently be solved. Moreover, the recently developed multiplicative regularizer allows us to apply the method blindly to experimental data. We demonstrate inversion from experimental data collected by a 2.33-GHz circular microwave scanner using a two-dimensional (2-D) TM polarization measurement setup. Further some results of a feasibility study of the present inversion method to the 2-D TE polarization and the full-vectorial three-dimensional measurement will be presented as well.
TL;DR: In this article, the degradation of the organic content of a bleaching Kraft mill effluent (BKME) has been carried out by using Fenton reagent and irradiation providing the conditions needed for the simultaneous occurrence of Fenton and photo-Fenton reactions.
Abstract: The degradation of the organic content of a bleaching Kraft mill effluent (BKME) has been carried out by using Fenton reagent and irradiation providing the conditions needed for the simultaneous occurrence of Fenton and photo-Fenton reactions. The main parameters that govern the complex reactive system, i.e. light intensity, temperature, pH, Fe(II) and H 2 O 2 initial concentrations, and O 2 presence in solution have been studied. Concentrations of Fe(II) between 0 and 800 ppm, and H 2 O 2 between 0 and 10,000 ppm were chosen. Temperatures above 25 and up to 70 °C have a beneficial effect on total organic carbon (TOC) decay rate. The presence of small amounts of O 2 seems to be enough to ensure the reaction progress. The combination of Fenton and photo-Fenton reactions has been proved to be highly effective for the treatment of such a type of wastewaters, and important advantages concerning the application of this combination of reactions arise from the study.
TL;DR: In this article, the authors deal with the strong discontinuity approach and show the links with the decohesive fracture mechanics provided by that approach, on the basis of 1D continuum damage models.
TL;DR: In this paper, the authors studied the crystallinity, accessibility and unit cell structure changes occurring in three types of regenerated cellulose fibres (lyocell, modal and viscose) that were mercerised with caustic soda solutions of different concentrations.
16 Nov 2002
TL;DR: A framework for performance modeling and prediction that is faster than cycle-accurate simulation, more informative than simple benchmarking, and is shown useful for performance investigations in several dimensions is presented.
Abstract: Cycle-accurate simulation is far too slow for modeling the expected performance of full parallel applications on large HPC systems. And just running an application on a system and observing wallclock time tells you nothing about why the application performs as it does (and is anyway impossible on yet-to-be-built systems). Here we present a framework for performance modeling and prediction that is faster than cycle-accurate simulation, more informative than simple benchmarking, and is shown useful for performance investigations in several dimensions.
TL;DR: Treatment with oral citicoline within the first 24 hours after onset in patients with moderate to severe stroke increases the probability of complete recovery at 3 months, and the overall safety ofciticoline was similar to placebo.
Abstract: Background and Purpose— No single neuroprotective agent has been shown to influence outcome after acute stroke. Citicoline has been studied worldwide in many clinical trials with positive findings,...
TL;DR: Asim provides a modular and reusable framework for creating many models that helps break down the performance-modeling problem into individual pieces that can be modeled separately, while its reusability allows using a software component repeatedly in different contexts.
Abstract: The longevity and usefulness of a microprocessor performance model has historically depended on the model writer's skills and discipline. However, at Compaq the models became extremely complex and unmanageable because designers lacked a structured way to develop them. To cope with these complexities, Compaq researchers began developing Asim in late 1998 to allow model writers to faithfully represent the detailed timing of complex modern machines and effectively manage the large software projects needed to model such machines. Asim addresses these needs by providing a modular and reusable framework for creating many models. The framework's modularity helps break down the performance-modeling problem into individual pieces that can be modeled separately, while its reusability allows using a software component repeatedly in different contexts.
31 Aug 2002
TL;DR: This paper presents a Named Entity Extraction (NEE) system for the CoNLL 2002 competition, which makes use of binary AdaBoost classifiers.
Abstract: This paper presents a Named Entity Extraction (NEE) system for the CoNLL 2002 competition. The two main sub-tasks of the problem, recognition (NER) and classification (NEC), are performed sequentially and independently with separate modules. Both modules are machine learning based systems, which make use of binary AdaBoost classifiers.
TL;DR: The first ever found completely stable spatiotemporal vortex solitons are demonstrated and it is concluded that stable spinning sol itons are possible as a result of competition between focusing and defocusing nonlinearities.
Abstract: We introduce spatiotemporal spinning solitons (vortex tori) of the three-dimensional nonlinear Schrodinger equation with focusing cubic and defocusing quintic nonlinearities The first ever found completely stable spatiotemporal vortex solitons are demonstrated A general conclusion is that stable spinning solitons are possible as a result of competition between focusing and defocusing nonlinearities
TL;DR: It is shown that cryptolepine interacts with the CC sites of the DNA fragment d(CCTAGG)2 in a base-stacking intercalation mode, which is the first DNA intercalator complex, from ∼90 solved by X-ray crystallography, to bind a nonalternating DNA sequence.
Abstract: Cryptolepine, a naturally occurring indoloquinoline alkaloid used as an antimalarial drug in Central and Western Africa, has been found to bind to DNA in a formerly unknown intercalation mode. Evidence from competition dialysis assays demonstrates that cryptolepine is able to bind CG-rich sequences containing nonalternating CC sites. Here we show that cryptolepine interacts with the CC sites of the DNA fragment d(CCTAGG)(2) in a base-stacking intercalation mode. This is the first DNA intercalator complex, from approximately 90 solved by X-ray crystallography, to bind a nonalternating (pyrimidine-pyrimidine) DNA sequence. The asymmetry of the drug induces a perfect stacking with the asymmetric site, allowing for the stability of the complex in the absence of hydrogen bonding interactions. The crystal structure of this antimalarial drug-DNA complex provides evidence for the first nonalternating intercalation and, as such, provides a basis for the design of new anticancer or antimalarial drugs.
Proceedings Article•
01 Jan 2002TL;DR: A procedure for rule extraction from support vector machines is proposed: the SVM+Prototypes method, which allows to give explanation ability to SVM.
Abstract: Support vector machines (SVMs) are learning systems based on the statistical learning theory, which are exhibiting good generalization ability on real data sets Nevertheless, a possible limitation of SVM is that they generate black box models In this work, a procedure for rule extraction from support vector machines is proposed: the SVM+Prototypes method This method allows to give explanation ability to SVM Once determined the decision function by means of a SVM, a clustering algorithm is used to determine prototype vectors for each class These points are combined with the support vectors using geometric methods to define ellipsoids in the input space, which are later transfers to if-then rules By using the support vectors we can establish the limits of these regions
TL;DR: This paper develops a solution procedure that considers each objective separately and search for a set of efficient solutions instead of a single optimum within the framework of the evolutionary approach known as scatter search.
Abstract: In this paper we address the problem of routing school buses in a rural area. We approach this problem with a node routing model with multiple objectives that arise from conflicting viewpoints. From the point of view of cost, it is desirable to minimise the number of buses used to transport students from their homes to school and back. From the point of view of service, it is desirable to minimise the time that a given student spends en route. The current literature deals primarily with single-objective problems and the models with multiple objectives typically employ a weighted function to combine the objectives into a single one. We develop a solution procedure that considers each objective separately and search for a set of efficient solutions instead of a single optimum. Our solution procedure is based on constructing, improving and then combining solutions within the framework of the evolutionary approach known as scatter search. Experimental testing with real data is used to assess the merit of our proposed procedure.
TL;DR: In this article, random copolyesters based on 1,4-butanediol and different ratios between adipic and terephthalic units were synthesized from thermal polycondensation of the appropriate mixture of monomers or by melt transesterification of the mixture of homopolymers.
Abstract: Random copolyesters based on 1,4-butanediol and different ratios between adipic and terephthalic units were synthesized from thermal polycondensation of the appropriate mixture of monomers or by melt transesterification of the mixture of homopolymers. 1H NMR spectroscopy makes feasible the study of the average block lengths of polymers once synthesized and after degradation in different media. Calorimetric data are reported, including those referred to the study of isothermal and nonisothermal crystallizations. Degradability of samples was evaluated by different methods including NMR and thermal analysis, evaluation of molecular weight by gel permeation chromatography or from intrinsic viscosity measures, scanning electron micrographs, and changes in mechanical properties. Distilled water at 70 °C acidic conditions provided by a pH 2.3 aqueous medium and enzymatic media containing lipases from Pseudomonas cepacia or Candida cylindracea were considered in this study. The degradability of the studied copolyesters strongly depends on the terephthalate content and the degradation media. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4141–4157, 2002
TL;DR: This note studies the efficiency of the emergence of social conventions in complex networks, that is, how fast conventions are reached and finds out that scale-free graphs make the system as efficient as fully connected graphs.
15 Dec 2002-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a thermally grown oxide layer (TGO) was formed on top of the NiCrAlY bond coat using a homogeneous α-Al2O3 layer after heat treatment at 1000 °C for 24 and 95 hours.
Abstract: This paper describes recent progress on the research into improving the oxidation behavior of the bond coat using a HVOF nanostructured NiCrAlY coating. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed onto Ni-based alloy to form a nanocrystalline bond coat. The powder and coating structure were characterized by XRD, SEM, and TEM. Oxidation experiments were performed on the coating to form the thermally grown oxide layer (TGO). After heat treatment at 1000 °C for 24 and 95 h, a homogeneous α-Al2O3 layer was formed on top of the bond coat. The oxide layer was analyzed and compared to the coating sprayed using the as-received powder. As shown in the results, the nanostructured characteristic of the coating and the presence of Al2O3 within the cryomilled powders (oxidation occurred during cryomilling process) seem to affect the nucleation of the alumina layer on the top of the coating. The formation of a continuous TGO layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions, such as those presented in the coating sprayed using the as-received powder.
TL;DR: A new phase noise model in the complex domain is introduced and validated by using both simulated and real interferograms, where a novel noise reduction algorithm, which is not based on a windowing process and without the necessity of phase unwrapping, is addressed.
Abstract: This paper addresses the problem of interferometric phase noise reduction in synthetic aperture radar interferometry. A new phase noise model in the complex domain is introduced and validated by using both simulated and real interferograms. This noise model is also derived in the complex wavelet domain, where a novel noise reduction algorithm, which is not based on a windowing process and without the necessity of phase unwrapping, is addressed. The use of the wavelet transform allows to maintain the spatial resolution in the filtered phase image and prevents to filter low coherence areas. By using both, simulated as well as real interferometric phase images, the performance of this algorithm, in terms of noise reduction, spatial resolution maintenance, and computational efficiency, is reported and compared with other conventional filtering approaches.
TL;DR: In this article, a mean field approximation is used to determine the time evolution of the kinetic variables governing the primary crystallization of a highly undercooled/supersaturated liquid, and the application to nanocrystallisation by heat treatment of metallic glasses is studied from the thermodynamic, kinetic and microstructural point of view.