9,151 research outputs found
Micro-bias and macro-performance
We use agent-based modeling to investigate the effect of conservatism and
partisanship on the efficiency with which large populations solve the density
classification task--a paradigmatic problem for information aggregation and
consensus building. We find that conservative agents enhance the populations'
ability to efficiently solve the density classification task despite large
levels of noise in the system. In contrast, we find that the presence of even a
small fraction of partisans holding the minority position will result in
deadlock or a consensus on an incorrect answer. Our results provide a possible
explanation for the emergence of conservatism and suggest that even low levels
of partisanship can lead to significant social costs.Comment: 11 pages, 5 figure
Análise do comércio do caranguejo-uçá, Ucides cordatus (Linnaeus, 1763), no município de Macapá-AP.
O caranguejo-uçá é um importante recurso pesqueiro que se encontra sobre explorado em todo litoral brasileiro. Desempenha papel tanto econômico, quando fonte de renda para os atores da cadeia produtiva, quanto ecológico, na manutenção dos ecossistemas de mangues. No Amapá têm ocorrência em três municípios (Amapá, Calçoene e Oiapoque), e é comercializado principalmente no município de Macapá, tornando de fundamental importância a caracterização desta atividade, uma vez que este é o primeiro estudo sobre o comércio da espécie no Estado. Durante nove meses (outubro/2008 a junho/2009) foram realizadas visitas mensais (n=32) às feiras do Mercado Central do Igarapé das Mulheres para aplicação de entrevistas com os vendedores de caranguejo, e para o levantamento de dados biométricos de largura e comprimento do tefalotórax (CC e LC) dos animais comercializados. Aleatoriamente, foram adquiridos 854 exemplares machos que apresentaram LC média de 85,4 mm e CC médio de 65 mm. Verificou-se que os caranguejos comercializados são capturados principalmente nos municípios amapaenses. Os resultados obtidos indicam que há alterações de preço durante o ano, e que essa oscilação está relacionada à oferta com que este recurso é disponibilizado. Os dados obtidos mostram ainda, que houve comercialização durante o período de defeso na Feira do Mercado Central e que os animais comercializados procedem em maior parte de municípios paraenses. De modo geral, concluímos que a Portaria Estadual está sendo respeitada em relação ao tamanho mínimo de captura e a não comercialização de fêmeas, no entanto, os caranguejos continuam a serem comercializados no período legalmente proibido
Random Networks with Tunable Degree Distribution and Clustering
We present an algorithm for generating random networks with arbitrary degree
distribution and Clustering (frequency of triadic closure). We use this
algorithm to generate networks with exponential, power law, and poisson degree
distributions with variable levels of clustering. Such networks may be used as
models of social networks and as a testable null hypothesis about network
structure. Finally, we explore the effects of clustering on the point of the
phase transition where a giant component forms in a random network, and on the
size of the giant component. Some analysis of these effects is presented.Comment: 9 pages, 13 figures corrected typos, added two references,
reorganized reference
Analytical solution of a model for complex food webs
We investigate numerically and analytically a recently proposed model for
food webs [Nature {\bf 404}, 180 (2000)] in the limit of large web sizes and
sparse interaction matrices. We obtain analytical expressions for several
quantities with ecological interest, in particular the probability
distributions for the number of prey and the number of predators. We find that
these distributions have fast-decaying exponential and Gaussian tails,
respectively. We also find that our analytical expressions are robust to
changes in the details of the model.Comment: 4 pages (RevTeX). Final versio
Vortex core size in interacting cylindrical nanodot arrays
The effect of dipolar interactions among cylindrical nanodots, with a
vortex-core magnetic configuration, is analyzed by means of analytical
calculations. The cylinders are placed in a N x N square array in two
configurations - core oriented parallel to each other and with antiparallel
alignment between nearest neighbors. Results comprise the variation in the core
radius with the number of interacting dots, the distance between them and dot
height. The dipolar interdot coupling leads to a decrease (increase) of the
core radius for parallel (antiparallel) arrays
Descoberta e genotipagem de SNPs em cajueiro via sequencimento de representações genômicas reduzidas.
Bioecology of the crab Ucides cordatus (Crustacea, Decapoda) in mangroves influenced by the Amazon River, Brazil.
The mangrove crab (Ucides cordatus) is a valuable fishery resource, overfished along the Brazilian coast. This study aimed to obtain bioecological data on this crab along the coast of the State of Amapá. Six bimonthly samplings were conducted between December 2008 and January 2010. Transects were used to estimate the density (burrows m-2) and population abundance (individuals m-2). All the animals were subjected to biometrics, with females being classified according to their stage of gonadal maturation. The mean density (1.09 burrows m-2) and abundance (0.31 individuals m-2) were influenced by the climate with the highest values ​​in summer (1.17 burrows m-2 and 0.34 individuals m-2). The male to female ratio was 1.38:1 showing significant difference in the proportion of sexes. The individuals showed sexual dimorphism, with linear measurements significantly higher in males. The sampled animals also had larger carapace length and width (CL and CW) compared to crabs studied in other Brazilian states. There was a positive relationship between CW and CL and individual weight (IW) and CW for males (R2 = 0.83 and 0.90) and females (R2 = 0.79 and 0.84). The growth was negative allometric (CL increases to a lesser extent than CW) for both sexes. The highest frequency of ovigerous females (78%) and in maturation stage IV (38%) occurred in the CW size class between 59.8 and 67.5 mm. The peak of mature females occurred in May and August, showing a reproductive period different from those in other Brazilian states
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