Narrow Results

We present a stochastic approach to modeling the dynamics of coexistence of prey and predator populations. It is assumed that the space of coexistence is explicitly subdivided in a grid of cells. Each cell can be occupied by only one individual of each species or can be empty. The system evolves in time according to a probabilistic cellular automaton composed by a set of local rules which describe interactions between species individuals and mimic the process of birth, death and predation. By performing computational simulations, we found that, depending on the values of the parameters of the model, the following states can be reached: a prey absorbing state and active states of two types. In one of them both species coexist in a stationary regime with population densities constant in time. The other kind of active state is characterized by local coupled time oscillations of prey and predator populations. We focus on the self-organized structures arising from spatio-temporal dynamics of the coexistence. We identify distinct spatial patterns of prey and predators and verify that they are intimally connected to the time coexistence behavior of the species.

I analyze a model of electoral competition in which candidates’ need of credibility restricts their policy choice to a subset of the policy space, their ideology set. I focus on three party competition where candidates care about winning and their share of votes. I show that centrist parties are highly disadvantaged compared to leftist and rightist ones losing the election under a wide range of parameters. I also show that centrist parties’ winning opportunities increase under a run-off system.

Fuzzy spatial models map a substantial degree of preference indifference. It has been shown that different definitions of covering result in different elements in the uncovered set when preference indifference is present. We consider several of the most frequently used definitions of covering relations found in the literature. The first definition that we examine yields an uncovered set, some of the elements of which are not Pareto efficient. Given that there is no reason to expect a set of players comprising a majority to settle for a Pareto deficient outcome, the remainder of the paper considers the ability of alternative definitions to avoid such a result.

Software to generate animations of American Sign Language (ASL) has important accessibility benefits for the significant number of deaf adults with low levels of written language literacy. We have implemented a prototype software system to generate an important subset of ASL phenomena called "classifier predicates," complex and spatially descriptive types of sentences. The output of this prototype system has been evaluated by native ASL signers. Our generator includes several novel models of 3D space, spatial semantics, and temporal coordination motivated by linguistic properties of ASL. These classifier predicates have several similarities to iconic gestures that often co-occur with spoken language; these two phenomena will be compared. This article explores implications of the design of our system for research in multimodal gesture generation systems. A conceptual model of multimodal communication signals is introduced to show how computational linguistic research on ASL relates to the field of multimodal natural language processing.

We offer insights on how distance-related trade costs may best be inferred from price-dispersion measures. Using a simple spatial model of price dispersion, we argue that measures of price dispersion that are not spatially informed can mislead researchers into concluding that distance-related costs are small even when such costs are the major determinant of price dispersion. With intra-United States data on eleven goods, we find that distance-related costs are large and are indeed underestimated when inferred from standard, non-spatial, price dispersion measures. Our empirical findings have implications for studies of market integration policies (such as trade liberalization and currency unions) and the significance of economic geography.