6,075 research outputs found
The Bak-Sneppen Model on Scale-Free Networks
We investigate by numerical simulations and analytical calculations the
Bak-Sneppen model for biological evolution in scale-free networks. By using
large scale numerical simulations, we study the avalanche size distribution and
the activity time behavior at nodes with different connectivities. We argue the
absence of a critical barrier and its associated critical behavior for infinite
size systems. These findings are supported by a single site mean-field analytic
treatment of the model.Comment: 5 pages and 3 eps figures. Final version appeared in Europhys. Let
Desempeño de los sistemas de vigilancia de salud pública durante la pandemia de influenza A (H1N1) en las Américas: prueba de un nuevo método basado en la Ley de Benford
The A(H1N1) influenza pandemic has been a challenge for public health surveillance systems in all countries. An objective evaluation has not been conducted, as yet, of the performance of those systems during the pandemic. This paper presents an algorithm based on Benford’s Law and the mortality ratio in order to evaluate the quality of the data and the sensitivity of surveillance systems. It analyses records of confirmed cases reported to the Pan American Health Organization by its 35 member countries between epidemiological weeks 13 and 47 in 2009. Seventeen countries did not fulfil Benford’s Law, and mortality exceeded the regional average in 40% of the countries. The results suggest uneven performance by surveillance systems in the different countries, with the most frequent problem being low diagnostic coverage. Benford’s Law proved to be a useful tool for the evaluation of a public health surveillance system’s performance
Epigenetic control of the EWS-FLI1 promoter in Ewing's sarcoma
Q2Q1Ewing sarcoma (ES) is a primary bone marrow tumor that very rarely develops in extra-osseous tissues, such as lung. The hallmark of ES tumors is a translocation between chromosomes 11 and 22, resulting in a fusion protein, commonly referred to as EWS-FLI1. The epigenetic profile (histone acetylation and methylation enrichment of the promoter region) that may regulate the expression of the aberrant transcription factor EWS-FLI1, remains poorly studied and understood. Knowledge of epigenetic patterns associated with covalent histone modification and expression of enzymes associated with this process, can contribute to the understanding of the molecular basis of the disease, as well as to the identification of possible molecular targets involved in expression of the EWS-FLI1 gene, so that therapeutic strategies may be improved in the future. In the present study, the transcriptional activation and repression of the EWS-FLI1 fusion gene in ES was accompanied by selective deposition of histone markers on its promoter. The EWS-FLI1 fusion gene was evaluated in two patients with ES using conventional cytogenetic, fluorescence in situ hybridization and nested PCR assays, which revealed that the aberrant expression of the EWS-FLI1 gene is accompanied by enrichment of H3K4Me3, H3K9ac and H3K27ac at the promoter region.N/
Integration of PV Distributed Generators into Electrical Networks for Investment and Energy Purchase Costs Reduction by Using a Discrete–Continuous Parallel PSO
The problem of optimally integrating PV DGs into electrical networks to reduce annual costs (which include energy purchase and investment costs) was addressed in this research by presenting a new solution methodology. For such purpose, we used a Discrete–Continuous Parallel Particle Swarm Optimization method (DCPPSO), which considers both the discrete and continuous variables associated with the location and sizing of DGs in an electrical network and employs a parallel processing tool to reduce processing times. The optimization parameters of the proposed solution methodology were tuned using an external optimization algorithm. To validate the performance of DCPPSO, we employed the 33- and 69-bus test systems and compared it with five other solution methods: the BONMIN solver of the General Algebraic Modeling System (GAMS) and other four discrete–continuous methodologies that have been recently proposed. According to the findings, the DCPPSO produced the best results in terms of quality of the solution, processing time, and repeatability in electrical networks of any size, since it showed a better performance as the size of the electrical system increased. © 2022 by the authors
Simulating the Laurentide Ice Sheet of the Last Glacial Maximum
In the last decades, great effort has been made to reconstruct the Laurentide Ice Sheet (LIS) during the Last Glacial Maximum (LGM; ca. 21 000 years before present, 21 kyr ago). Uncertainties underlying its modelling have led to notable differences in fundamental features such as its maximum elevation, extent and total volume. As a result, the uncertainty in ice dynamics and thus in ice extent, volume and ice stream stability remains large. We herein use a higher-order three-dimensional ice sheet model to simulate the LIS under LGM boundary conditions for a number of basal friction formulations of varying complexity. Their consequences for the Laurentide ice streams, configuration, extent and volume are explicitly quantified. Total volume and ice extent generally reach a constant equilibrium value that falls close to prior LIS reconstructions. Simulations exhibit high sensitivity to the dependency of the basal shear stress on the sliding velocity. In particular, a regularised Coulomb friction formulation appears to be the best choice in terms of ice volume and ice stream realism. Pronounced differences are found when the basal friction stress is thermomechanically coupled: the base remains colder, and the LIS volume is lower than in the purely mechanical friction scenario counterpart. Thermomechanical coupling is fundamental for producing rapid ice streaming, yet it leads to a similar ice distribution overall.</p
Integration of PV Distributed Generators into Electrical Networks for Investment and Energy Purchase Costs Reduction by Using a Discrete–Continuous Parallel PSO
The problem of optimally integrating PV DGs into electrical networks to reduce annual costs (which include energy purchase and investment costs) was addressed in this research by presenting a new solution methodology. For such purpose, we used a Discrete–Continuous Parallel Particle Swarm Optimization method (DCPPSO), which considers both the discrete and continuous variables associated with the location and sizing of DGs in an electrical network and employs a parallel processing tool to reduce processing times. The optimization parameters of the proposed solution methodology were tuned using an external optimization algorithm. To validate the performance of DCPPSO, we employed the 33- and 69-bus test systems and compared it with five other solution methods: the BONMIN solver of the General Algebraic Modeling System (GAMS) and other four discrete–continuous methodologies that have been recently proposed. According to the findings, the DCPPSO produced the best results in terms of quality of the solution, processing time, and repeatability in electrical networks of any size, since it showed a better performance as the size of the electrical system increased
Bioprospecting and characterization of poly-bhydroxyalkanoate (PHAs) producing bacteria isolated from Colombian sugarcane producing areas
Bioprospecting for poly-b-hydroxyalkanoate (PHA)-accumulating micro-organisms was carried out in sugarcane growing areas of Colombia. They were isolated in unbalanced culture medium (highcarbon/nitrogen ratio) with sucrose, fructose and glucose used as carbon source. PHAs producing bacteria were identified by staining with Sudan black and solubilising cellular components in sodiumhypochlorite. A arbitrary scale was established (ranging from 1 to 4) for selecting the best strains, acording to growth, staining with Sudan black and solubilising cellular material. 108 isolates rated higher than 2 were obtained by using this scale; 44 of these were selected for evaluating them in a balloon flask for their ability to grow in sucrose. Scheffe’s test grouped the isolates evaluated in the balloon flask for polymer production and productivity. The 6 best isolates were evaluated in a fermenter to determine their kinetic growth profiles, substrate consumption and polymer accumulation. Differential scanning calorimeter (DSC) was used on the recovered polymer for determining fusion temperature and the conclusion was reached that 2 strains accumulated poly--hydroxybutyrate (PHB) and another 4 accumulated hydroxy-butyrate copolymers and other monomer units. These 6 strains were molecularly characterised by partially sequencing the 16s rRNA ribosomal gene, localizing them in 4 clusters on the taxonomic tree
EpidemiologĂa de las enfermedades reumáticas en MĂ©xico. Un estudio de 5 regiones basado en la metodologĂa COPCORD
To estimate the prevalence of musculoskeletal (MSK) disorders and to describe predicting variables associated with rheumatic diseases in 5 regions of MĂ©xico
Class of correlated random networks with hidden variables
We study a class models of correlated random networks in which vertices are
characterized by \textit{hidden variables} controlling the establishment of
edges between pairs of vertices. We find analytical expressions for the main
topological properties of these models as a function of the distribution of
hidden variables and the probability of connecting vertices. The expressions
obtained are checked by means of numerical simulations in a particular example.
The general model is extended to describe a practical algorithm to generate
random networks with an \textit{a priori} specified correlation structure. We
also present an extension of the class, to map non-equilibrium growing networks
to networks with hidden variables that represent the time at which each vertex
was introduced in the system
Análisis de las formaciones dunares activas de la flecha del Fangar (Delta del Ebro)
Este artĂculo muestra los trabajos realizados sobre los campos de dunas activas de la
Flecha del Fangar al amparo del Proyecto de Investigación “Cuantificación y
Contribución del Transporte Eólico en los Procesos Dinámicos y Ambientales en el
Delta del Ebro. AplicaciĂłn a su GestiĂłn Integrada y a la ConservaciĂłn de los
Ambientes Marginales” (AGITE), concedido por el Ministerio de Educación y Ciencia
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dentro del Plan Nacional de I+D+i (2005-2008). En dicho proyecto se ha podido
analizar cuál es la morfodinámica de dicho campo, cómo es su estructura interna, y
cuáles son los mecanismos que gobiernan su dinámica, aspectos desarrollados en
una Tesis Doctoral (Sánchez, 2008) defendida recientemente. En el marco del
proyecto, también se han realizado otros trabajos globales de todo el delta, tendentes
aumentar el conocimiento de la zona, y evaluar el interés y la percepción social que
tiene la problemática actual del delta
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