Using gap-crossing capacity to evaluate functional connectivity of two Atlantic rainforest birds and their response to fragmentation

One of the main consequences of habitat loss and fragmentation is the increase in patch isolation and the consequent decrease in landscape connectivity. In this context, species persistence depends on their responses to this new landscape configuration, particularly on their capacity to move through the interhabitat matrix. Here, we aimed first to determine gap-crossing probabilities related to different gap widths for two forest birds (Thamnophilus caerulescens, Thamnophilidae, and Basileuterus culicivorus, Parulidae) from the Brazilian Atlantic rainforest. These values were defined with a playback technique and then used in analyses based on graph theory to determine functional connections among forest patches. Both species were capable of crossing forest gaps between patches, and these movements were related to gap width. The probability of crossing 40 m gaps was 50% for both species. This probability falls to 10% when the gaps are 60 m (for B. culicivorus) or 80 m (for T caerulescens). Actually, birds responded to stimulation about two times more distant inside forest trials (control) than in gap-crossing trials. Models that included gap-crossing capacity improved the explanatory power of species abundance variation in comparison to strictly structural models based merely on patch area and distance measurements. These results highlighted that even very simple functional connectivity measurements related to gap-crossing capacity can improve the understanding of the effect of habitat fragmentation on bird occurrence and abundance.

Dependence of Response Functions and Orbital Functionals on Occupation Numbers

Explicitly orbital-dependent approximations to the exchange-correlation energy functional of density functional theory typically not only depend on the single-particle Kohn-Sham orbitals but also on their occupation numbers in the ground-state Slater determinant. The variational calculation of the corresponding exchange-correlation potentials with the optimized effective potential (OEP) method therefore also requires a variation of the occupation numbers with respect to a variation in the effective single-particle potential, which is usually not taken into account. Here it is shown under which circumstances this procedure is justified.

Bayesian inference for a skew-normal IRT model under the centred parameterization

Item response theory (IRT) comprises a set of statistical models which are useful in many fields, especially when there is interest in studying latent variables. These latent variables are directly considered in the Item Response Models (IRM) and they are usually called latent traits. A usual assumption for parameter estimation of the IRM, considering one group of examinees, is to assume that the latent traits are random variables which follow a standard normal distribution. However, many works suggest that this assumption does not apply in many cases. Furthermore, when this assumption does not hold, the parameter estimates tend to be biased and misleading inference can be obtained. Therefore, it is important to model the distribution of the latent traits properly. In this paper we present an alternative latent traits modeling based on the so-called skew-normal distribution; see Genton (2004). We used the centred parameterization, which was proposed by Azzalini (1985). This approach ensures the model identifiability as pointed out by Azevedo et al. (2009b). Also, a Metropolis Hastings within Gibbs sampling (MHWGS) algorithm was built for parameter estimation by using an augmented data approach. A simulation study was performed in order to assess the parameter recovery in the proposed model and the estimation method, and the effect of the asymmetry level of the latent traits distribution on the parameter estimation. Also, a comparison of our approach with other estimation methods (which consider the assumption of symmetric normality for the latent traits distribution) was considered. The results indicated that our proposed algorithm recovers properly all parameters. Specifically, the greater the asymmetry level, the better the performance of our approach compared with other approaches, mainly in the presence of small sample sizes (number of examinees). Furthermore, we analyzed a real data set which presents indication of asymmetry concerning the latent traits distribution. The results obtained by using our approach confirmed the presence of strong negative asymmetry of the latent traits distribution. (C) 2010 Elsevier B.V. All rights reserved.

Bayesian Estimation of the Logistic Positive Exponent IRT Model

A Bayesian inference approach using Markov Chain Monte Carlo (MCMC) is developed for the logistic positive exponent (LPE) model proposed by Samejima and for a new skewed Logistic Item Response Theory (IRT) model, named Reflection LPE model. Both models lead to asymmetric item characteristic curves (ICC) and can be appropriate because a symmetric ICC treats both correct and incorrect answers symmetrically, which results in a logical contradiction in ordering examinees on the ability scale. A data set corresponding to a mathematical test applied in Peruvian public schools is analyzed, where comparisons with other parametric IRT models also are conducted. Several model comparison criteria are discussed and implemented. The main conclusion is that the LPE and RLPE IRT models are easy to implement and seem to provide the best fit to the data set considered.

Quantified Interference: Information Theory and Information Flow

The paper investigates which of Shannon’s measures (entropy, conditional entropy, mutual information) is the right one for the task of quantifying information flow in a programming language. We examine earlier relevant contributions from Denning, McLean and Gray and we propose and motivate a specific quantitative definition of information flow. We prove results relating equivalence relations, interference of program variables, independence of random variables and the flow of confidential information. Finally, we show how, in our setting, Shannon’s Perfect Secrecy theorem provides a sufficient condition to determine whether a program leaks confidential information.

Interaction among agents that plan

The development of practical agent languages has progressed significantly over recent years, but this has largely been independent of distinct developments in aspects of multiagent cooperation and planning. For example, while the popular AgentSpeak(L) has had various extensions and improvements proposed, it still essentially a single-agent language. In response, in this paper, we describe a simple, yet effective, technique for multiagent planning that enables an agent to take advantage of cooperating agents in a society. In particular, we build on a technique that enables new plans to be added to a plan library through the invocation of an external planning component, and extend it to include the construction of plans involving the chaining of subplans of others. Our mechanism makes use of plan patterns that insulate the planning process from the resulting distributed aspects of plan execution through local proxy plans that encode information about the preconditions and effects of the external plans provided by agents willing to cooperate. In this way, we allow an agent to discover new ways of achieving its goals through local planning and the delegation of tasks for execution by others, allowing it to overcome individual limitations.

O Congresso Nacional: alternativas de representação politica e paradigmas eleitorais

Este trabalho visa analisar a estrutura de funcionamento do Sistema Eleitoral Brasileiro. Sistema este que - procuro demonstrar - não valoriza os partidos políticos como canais apropriados de interação entre Sociedade e Estado. Desta realidade, é decorrente o fato de existirem, no Brasil, muitos partidos políticos inorgânicos - quanto às ações -, e frágeis - quanto à representatividade. É hipótese básica desta obra o fato de existirem grupos políticos que se beneficiam de práticas nocivas à democracia participativa, via sistema eleitoral. Assim sendo, a realidade auferida nas urnas é distinta da realidade da representação política. O Congresso Nacional, locus que é objeto das maiores distorções, é o meu ponto de referência para este estudo. É a partir deste centro de poder político que se pode vislumbrar o modo de reprodução, em outras esferas de poder, da engenharia institucional existente. A metodologia deste estudo é seccionada em duas partes: . Na parte teórica (capítulos II e III), procuro fazer uma análise comparativa entre as propostas passíveis - a cada item - de adoção, posicionando-me em relação às mesmas. . Na parte prática (capítulo IV), elaboro uma proposta de agenda para reformas no sistema eleitoral, condizentes com o que foi estudado anteriormente.

Portfolio choice with a correlated background risk : theory and evidence

We extend the static portfolio choice problem with a small background risk to the case of small partially correlated background risks. We show that respecting the theories under which risk substitution appears, except for the independence of background risk, it is perfectly rational for the individual to increase his optimal exposure to portfolio risk when risks are partially negatively correlated. Then, we test empirically the hypothesis of risk substitutability using INSEE data on French households. We find that households respond by increasing their stockholdings in response to the increase in future earnings uncertainty. This conclusion is in contradiction with results obtained in other countries. So, in light of these results, our model provides an explanation to account for the lack of empirical consensus on cross-country tests of risk substitution theory that encompasses and criticises all of them.

Essays on consumer brand engagement

Apesar do crescente interesse no conceito de engajamento da marca ainda existe discordância quanto aos seus conceitos fundamentais. Esta tese de doutorado explora a natureza da construção engajamento da marca do consumidor (EMC). No primeiro artigo, EMC é avaliada no âmbito da Teoria da Expectância para explicar e esclarecer como a antecipação de possíveis resultados de se envolver com uma marca, sendo tais resultados classificados como “primeiro nível” (resultante do esforço pessoal alocado para interagir com uma marca) e “segundo nível” (ou nível final, representando a consequência dos resultados de primeiro nível) e uma nova definição de EMC é formulada. Um arcabouço teórico abrangente é proposto para engajamento da marca, usando o Teoria Organizacional de Marketing para Expansão de Fronteiras (TOMEF) como referência para os pontos de contato entre o consumidor e a marca. A partir dos fundamentos teóricos das dimensões cognitivas, emocionais e comportamentais do EMC, quinze proposições teóricas são desenvolvidas para incorporar uma perspectiva multilateral às doutrinas teóricas do construto. No segundo artigo, quatro estudos são usados para desenvolver uma escala de engajamento da marca do consumidor. O Estudo 1 (n = 11) utiliza revisão da literatura e entrevistas em profundidade com os consumidores para gerar os itens da escala. No Estudo 2, oito especialistas avaliam 144 itens quanto a validade de face e validade de conteúdo. No Estudo 3 dados coletados com alunos de graduação (n = 172) é submetida à análise fatorial exploratória (AFE) e confirmatória (AFC) para redução adicional de itens. Trezentos e oitenta e nove respostas de um painel de consumidores são usados no Estudo 4 para avaliar o ajuste do modelo, usando a análise fatorial confirmatória (AFC) e Modelagem por Equações Estruturais (MEE). A escala proposta possui excelentes níveis de validade e confiabilidade. Finalmente, no terceiro papel, uma escala de engajamento do consumidor de Vivek et al. (2014) é replicada (n = 598) junto à consumidores em uma feira automotiva, para estender o debate sobre formas de medição do constructo usando a perspectiva da Teoria de Resposta ao Item (TRI). Embora o modelo desenvolvido com base na teoria clássica de teste (TCT) usando AFC, um modelo de resposta gradual (MRG) identifica cinco itens que têm baixos níveis de poder discriminante e com baixos níveis de informação. A abordagem usando TRI indica um possível caminho para melhorias metodológicas futuras para as escalas desenvolvidas na área de marketing em geral, e para a escala engajamento do consumidor, em particular.