669 research outputs found
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
On the distribution of high-frequency stock market traded volume: a dynamical scenario
This manuscript reports a stochastic dynamical scenario whose associated
stationary probability density function is exactly a previously proposed one to
adjust high-frequency traded volume distributions. This dynamical conjecture,
physically connected to superstatiscs, which is intimately related with the
current nonextensive statistical mechanics framework, is based on the idea of
local fluctuations in the mean traded volume associated to financial markets
agents herding behaviour. The corroboration of this mesoscopic model is done by
modelising NASDAQ 1 and 2 minute stock market traded volume
On a comparative study between dependence scales determined by linear and non-linear measures
In this manuscript we present a comparative study about the determination of
the relaxation (\textit{i.e.}, independence) time scales obtained from the
correlation function, the mutual information, and a criterion based on the
evaluation of a nonextensive generalisation of mutual entropy. Our results show
that, for systems with a small degree of complexity, standard mutual
information and the criterion based on its nonextensive generalisation provide
the same scale, whereas for systems with a higher complex dynamics the standard
mutual information presents a time scale consistently smaller.Comment: 14 pages. To appear in Physica
Psychophysiological assessment of stress under ecological settings: A systematic review
Stress can negatively impact one’s health and well-being, however despite the recent evolution in stress assessment research methodologies, little agreement still exist about stress conceptualization and assessment. In an attempt to summarize and reflect on this evolution this paper aimed to systematically review research evidence of ecological approaches on psycho-physiological stress assessment. Thus, a literature search of electronic databases was conducted spanning 22 years (1990 – 2012) and 55 studies were reviewed. Studies were considered for inclusion if they contemplated both psychological and physiological measures of stress under ecological settings. This review focused on five themes: methodologies terminology; research population; study design; measurement and technology. Findings support the need to use a common methodology terminology in order to increase scientific rigor. Additionally, there seems to be an increasing tendency for the use of these methods by multidisciplinary teams among both clinical and non-clinical populations aiming to understand the relationship between stress and disease. Most of the studies reviewed contemplated a time-based protocol and different conceptualizations of stress were found resulting in the use of different subjective measures. Findings reinforce the importance of combining subjective and objective measures while also controlling for possible time or situation dependent confounders. Advances in technology were evident and different assessment techniques were found. The benefits and challenges of ecological protocols to assess stress are discussed and recommendations for future research are provided, aiming to overcome previous limitations and advance scientific knowledge in the area
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
- …