Optimal diffusion in ecological dynamics with Allee effect in a metapopulation

How diffusion impacts on ecological dynamics under the Allee effect and spatial constraints? That is the question we address. Employing a microscopic minimal model in a metapopulation (without imposing nonlinear birth and death rates) we evince --- both numerically and analitically --- the emergence of an optimal diffusion that maximises the survival probability. Even though, at first such result seems counter-intuitive, it has empirical support from recent experiments with engineered bacteria. Moreover, we show that this optimal diffusion disappears for loose spatial constraints.Comment: 16 pages; 6 figure

Thermoelectrical regulation of microinjection moulds

Microinjection is one of the major replication techniques for producing low cost micro parts. The small scale of the microinjection processes presents different challenges from those usually encountered in conventional injection moulding. One particular aspect, very important for part quality, is mould temperature control. In conventional injection moulding, the temperature control system is set to a fixed value during the injection cycle. In microinjection moulding such behaviour is not acceptable, which as lead to the development of “active” control temperature of the mould named “variotherm” systems. In the present paper a study will be presented for the implementation of thermo electric elements in dynamic temperature control of microinjection moulds and its impact on the process cycle time and part quality

Statistical mixing and aggregation in Feller diffusion

We consider Feller mean-reverting square-root diffusion, which has been applied to model a wide variety of processes with linearly state-dependent diffusion, such as stochastic volatility and interest rates in finance, and neuronal and populations dynamics in natural sciences. We focus on the statistical mixing (or superstatistical) process in which the parameter related to the mean value can fluctuate - a plausible mechanism for the emergence of heavy-tailed distributions. We obtain analytical results for the associated probability density function (both stationary and time dependent), its correlation structure and aggregation properties. Our results are applied to explain the statistics of stock traded volume at different aggregation scales.Comment: 16 pages, 3 figures. To be published in Journal of Statistical Mechanics: Theory and Experimen

LINFOMAS CUTÂNEOS DE CÉLULAS T: PAPEL DAS CÉLULAS NK E T CIRCULANTES NA DEFESA ANTI-TUMORAL

O cancro é uma doença complexa caracterizada por um crescimento descontrolado de células próprias do organismo. O sistema imune tem a capacidade de identificar estas células e desenvolver mecanismos de forma a elimina-las. Na tentativa de melhorar o conhecimento sobre como o sistema imune reage perante a presença de células neoplásicas, têm sido realizados numerosos estudos, envolvendo diferentes tipos de tumores. Os linfomas cutâneos de células T (LCCT), grupo de patologias malignas caracterizado pela proliferação de linfócitos T (LT) na pele, têm sido alvos destes estudos. Contudo, embora alguns demonstrem que as células imunológicas intervêm ao longo da evolução da doença, este assunto é ainda controverso