3,039 research outputs found
Preferential attachment growth model and nonextensive statistical mechanics
We introduce a two-dimensional growth model where every new site is located,
at a distance from the barycenter of the pre-existing graph, according to
the probability law , and is attached to
(only) one pre-existing site with a probability ; is the number of links of the site of the
pre-existing graph, and its distance to the new site). Then we
numerically determine that the probability distribution for a site to have
links is asymptotically given, for all values of , by , where is the function
naturally emerging within nonextensive statistical mechanics. The entropic
index is numerically given (at least for not too large) by , and the characteristic number of links by . The particular case belongs to the same
universality class to which the Barabasi-Albert model belongs. In addition to
this, we have numerically studied the rate at which the average number of links
increases with the scaled time ; asymptotically, , the exponent being close to for , and zero otherwise.
The present results reinforce the conjecture that the microscopic dynamics of
nonextensive systems typically build (for instance, in Gibbs -space for
Hamiltonian systems) a scale-free network.Comment: 5 pages including 5 figures (the original colored figures 1 and 5a
can be asked directly to the authors
Hierarchical characterization of complex networks
While the majority of approaches to the characterization of complex networks
has relied on measurements considering only the immediate neighborhood of each
network node, valuable information about the network topological properties can
be obtained by considering further neighborhoods. The current work discusses on
how the concepts of hierarchical node degree and hierarchical clustering
coefficient (introduced in cond-mat/0408076), complemented by new hierarchical
measurements, can be used in order to obtain a powerful set of topological
features of complex networks. The interpretation of such measurements is
discussed, including an analytical study of the hierarchical node degree for
random networks, and the potential of the suggested measurements for the
characterization of complex networks is illustrated with respect to simulations
of random, scale-free and regular network models as well as real data
(airports, proteins and word associations). The enhanced characterization of
the connectivity provided by the set of hierarchical measurements also allows
the use of agglomerative clustering methods in order to obtain taxonomies of
relationships between nodes in a network, a possibility which is also
illustrated in the current article.Comment: 19 pages, 23 figure
Central charges and boundary fields for two dimensional dilatonic black holes
In this paper we first show that within the Hamiltonian description of
general relativity, the central charge of a near horizon asymptotic symmetry
group is zero, and therefore that the entropy of the system cannot be estimated
using Cardy's formula. This is done by mapping a static black hole to a two
dimensional space. We explain how such a charge can only appear to a static
observer who chooses to stay permanently outside the black hole. Then an
alternative argument is given for the presence of a universal central charge.
Finally we suggest an effective quantum theory on the horizon that is
compatible with the thermodynamics behaviour of the black hole.Comment: 16 pages, no figures, LaTex 2e, references adde
ANÁLISE DA EVOLUÇÃO DAS RELAÇÕES DE COAUTORIA NOS PROGRAMAS DE PÓS-GRADUAÇÃO EM COMPUTAÇÃO NO BRASIL
This paper describes the basis for a study of the dynamic relationships of (co- )authorship among full time professors from Brazilian Computer Science graduate programs. 889 researchers were identified, working in 45 graduate programs. A robust entity resolution heuristic was developed, allowing the identification of (co-)authorship relationships among researchers with accuracy above 96%. The social network analysis allowed for the discovery of some interesting phenomena about the dynamics of the Brazilian scientific production, related to the increasing in the production within and among graduate programs.Este trabalho descreve as bases para um estudo da dinâmica de relações de coautoria entre pesquisadores associados aos programas de pós-graduação em Ciência da Computação, avaliados pela CAPES no triênio 2007-2009. Ao todo, foram identificados 889 pesquisadores permanentes nos 45 programas de pós-graduação avaliados. Uma heurística robusta de resolução de entidades foi desenvolvida, possibilitando a identificação das relações de coautoria entre pesquisadores, com uma taxa de acerto superior a 96%. Com base na análise das redes de coautoria foi possível observar fenômenos interessantes da dinâmica da pesquisa brasileira, relacionados especialmente ao aumento da produção conjunta inter e intra programas de pós-graduação
Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up
Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated
Linkage disequilibrium and population structure in wild and cultivated populations of rubber tree (Hevea brasiliensis).
Abstract: Among rubber tree species, which belong to the Hevea genus of the Euphorbiaceae family, Hevea brasiliensis (Willd. ex Adr.de Juss.) Muell. Arg. is the main commercial source of natural rubber production worldwide. Knowledge of the population structure and linkage disequilibrium (LD) of this species is essential for the efficient organization and exploitation of genetic resources. Here, we obtained single-nucleotide polymorphisms (SNPs) using a genotyping-by-sequencing (GBS) approach and then employed the SNPs for the following objectives: (i) to identify the positions of SNPs on a genetic map of a segregating mapping population, (ii) to evaluate the population structure of a germplasm collection, and (iii) to detect patterns of LD decay among chromosomes for future genetic association studies in rubber tree. A total of 626 genotypes, including both germplasm accessions (368) and individuals from a genetic mapping population (254), were genotyped. A total of 77,660 and 21,283 SNPs were detected by GBS in the germplasm and mapping populations, respectively. The mapping population, which was previously mapped, was constructed with 1,062 markers, among which only 576 SNPs came from GBS, reducing the average interval between two adjacent markers to 4.4 cM. SNPs from GBS genotyping were used for the analysis of genetic structure and LD estimation in the germplasm accessions. Two groups, which largely corresponded to the cultivated and wild populations, were detected using STRUCTURE and via principal coordinate analysis. LD analysis, also using the mapped SNPs, revealed that non-random associations varied along chromosomes, with regions of high LD interspersed with regions of low LD. Considering the length of the genetic map (4,693 cM) and the mean LD (0.49 for cultivated and 0.02 for wild populations), a large number of evenly spaced SNPs would be needed to perform genome-wide association studies in rubber tree, and the wilder the genotypes used, the more difficult the mapping saturation
Genome of the Avirulent Human-Infective Trypanosome—Trypanosoma rangeli
Background: Trypanosoma rangeli is a hemoflagellate protozoan parasite infecting humans and other wild and domestic mammals across Central and South America. It does not cause human disease, but it can be mistaken for the etiologic agent of Chagas disease, Trypanosoma cruzi. We have sequenced the T. rangeli genome to provide new tools for elucidating the distinct and intriguing biology of this species and the key pathways related to interaction with its arthropod and mammalian hosts. Methodology/Principal Findings: The T. rangeli haploid genome is ,24 Mb in length, and is the smallest and least repetitive trypanosomatid genome sequenced thus far. This parasite genome has shorter subtelomeric sequences compared to those of T. cruzi and T. brucei; displays intraspecific karyotype variability and lacks minichromosomes. Of the predicted 7,613 protein coding sequences, functional annotations could be determined for 2,415, while 5,043 are hypothetical proteins, some with evidence of protein expression. 7,101 genes (93%) are shared with other trypanosomatids that infect humans. An ortholog of the dcl2 gene involved in the T. brucei RNAi pathway was found in T. rangeli, but the RNAi machinery is non-functional since the other genes in this pathway are pseudogenized. T. rangeli is highly susceptible to oxidative stress, a phenotype that may be explained by a smaller number of anti-oxidant defense enzymes and heatshock proteins. Conclusions/Significance: Phylogenetic comparison of nuclear and mitochondrial genes indicates that T. rangeli and T. cruzi are equidistant from T. brucei. In addition to revealing new aspects of trypanosome co-evolution within the vertebrate and invertebrate hosts, comparative genomic analysis with pathogenic trypanosomatids provides valuable new information that can be further explored with the aim of developing better diagnostic tools and/or therapeutic targets
Avian influenza virus (H11N9) in migratory shorebirds wintering in the Amazon region, Brazil
Aquatic birds are the natural reservoir for avian influenza viruses (AIV). Habitats in Brazil provide stopover and wintering sites for water birds that migrate between North and South America. The current study was conducted to elucidate the possibility of the transport of influenza A viruses by birds that migrate annually between the Northern and Southern Hemispheres. In total, 556 orotracheal/cloacal swab samples were collected for influenza A virus screening using real-time RT-PCR (rRT-PCR). The influenza A virus-positive samples were subjected to viral isolation. Four samples were positive for the influenza A matrix gene by rRT-PCR. From these samples, three viruses were isolated, sequenced and characterized. All positive samples originated from a single bird species, the ruddy turnstone (Arenaria interpres), that was caught in the Amazon region at Caeté Bay, Northeast Pará, at Ilha de Canelas. To our knowledge, this is the first isolation of H11N9 in the ruddy turnstone in South America. (Résumé d'auteur
DOSAGEM DE MISTURA BETUMINOSA A FRIO E SEU ESTUDO SOB EFEITOS DE CARGAS ESTÁTICAS E REPETIDAS1
RESUMO Este trabalho apresenta os resultados de uma pesquisa experimental que objetivou estudar o comportamento mecânico de uma mistura betuminosa a frio sob efeitos de cargas estáticas e repetidas. Após a caracterização dos agregados e do ligante empregados na pesquisa, efetuou-se a mistura, a partir da dosagem Marshall, obtendo o teor de projeto equivalente a 8,5% de emulsão. Nesse teor de emulsão, moldaram-se várias amostras, que foram submetidas aos ensaios de módulo de resiliência, resistência à tração por compressão diametral e fadiga. A caracterização dos agregados e do ligante mostrou-se concordante com vários estudos, exceto o resíduo da peneiração, que não atendeu à exigência do IBP (1999). Para os ensaios com as misturas asfálticas, empregaram-se três corpos de prova, pesando cada um deles cerca de 1.200 g, compactados com 75 golpes em cada uma de suas faces. Observou-se que a estabilidade e a fluência Marshall de 620 kgf e de 4,20 mm, respectivamente, superaram o limite mínimo recomendado na especificação de serviço do DNIT (2010a). Com relação aos ensaios de módulo de resiliência e de resistência à tração por compressão diametral, obtiveram-se os valores de 1.616 MPa e 0,44 MPa, respectivamente, quando se verificou que os resultados foram bem inferiores aos encontrados em misturas a quente. Esse mesmo comportamento foi observado no ensaio de fadiga que, na maioria dos níveis de tensão aplicados, foi inferior a 1.000 aplicações do carregamento
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