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Biomedical subjects

J Buceta

Publications and source records attributed to J Buceta.

14 recordsLinked to original sources
PubMed2004

Outbreaks of Hantavirus induced by seasonality.

Using a model for rodent population dynamics, we study outbreaks of Hantavirus infection induced by the alternation of seasons. Neither season by itself satisfies the environmental requirements for propagation of the disease. This result can be explained in terms of the seasonal interruption of the relaxation process of the mouse population toward equilibrium, and may shed light on the reported connection between climate variations and outbreaks of the disease.

Animals↗
PubMed2004

Extinction in population dynamics.

We study a generic reaction-diffusion model for single-species population dynamics that includes reproduction, death, and competition. The population is assumed to be confined in a refuge beyond which conditions are so harsh that they lead to certain extinction. Standard continuum mean field models in one dimension yield a critical refuge length L(c) such that a population in a refuge larger than this is assured survival. Herein we extend the model to take into account the discreteness and finiteness of the population, which leads us to a stochastic description. We present a particular critical criterion for likely extinction, namely, that the standard deviation of the population be equal to the mean. According to this criterion, we find that while survival can no longer be guaranteed for any refuge size, for sufficiently weak competition one can make the refuge large enough (certainly larger than L(c)) to cause extinction to be unlikely. However, beyond a certain value of the competition rate parameter it is no longer possible to escape a likelihood of extinction even in an infinite refuge. These unavoidable fluctuations therefore have a severe impact on refuge design issues.

Animals↗
PubMed2004

Comprehensive study of phase transitions in relaxational systems with field-dependent coefficients.

We present a comprehensive study of phase transitions in single-field systems that relax to a nonequilibrium global steady state. The mechanism we focus on is not the so-called Stratonovich drift combined with collective effects, but is instead similar to the one associated with noise-induced transitions in the manner of Horsthemke-Lefever in zero-dimensional systems. As a consequence, the noise interpretation (e.g., Itô vs Stratonovich) merely shifts the phase boundaries. With the help of a mean-field approximation, we present a broad qualitative picture of the various phase diagrams that can be found in these systems. To complement the theoretical analysis we present numerical simulations that confirm the findings of the mean-field theory.

Journal Article↗
PubMed2003

Dynamics of two granules.

We study the dynamics of two particles that interact only when in contact. In this sense, although not in every particular, the interactions mimic those in granular materials. The detailed solution of the dynamics allows an analysis of the backscattering behavior of the first particle and of the energy dissipation in the system as a function of various parameters.

Journal Article↗
PubMed2003

Spatial patterns induced purely by dichotomous disorder.

We study conditions under which spatially extended systems with coupling in the manner of Swift and Hohenberg exhibit spatial patterns induced purely by the presence of quenched dichotomous disorder. Complementing the theoretical results based on a generalized mean-field approximation, we also present numerical simulations of particular dynamical systems that exhibit the proposed phenomenology.

Journal Article↗
PubMed2003

Noise-driven mechanism for pattern formation.

We extend the mechanism for noise-induced phase transitions proposed by Ibañes et al. [Phys. Rev. Lett. 87, 020601 (2001)] to pattern formation phenomena. In contrast with known mechanisms for pure noise-induced pattern formation, this mechanism is not driven by a short-time instability amplified by collective effects. The phenomenon is analyzed by means of a modulated mean field approximation and numerical simulations.

Journal Article↗
PubMed2002

Switching-induced Turing instability.

We propose a mechanism for inducing a Turing instability in systems whose only stable state is pattern-free and homogeneous. Global alternation between two dynamics, each of which has the same homogeneous stable state, may induce a Turing instability that leads to pattern formation. We determine what kind of alternation can drive the system to a Turing instability, and show that the appearance of the induced spatiotemporal structure depends on the ratio of two characteristic times, one determined by the external forcing and the other by the instability that drives the system at short times. The mechanism is illustrated by means of theoretical calculations and numerical simulations on two well-known biological models that are relevant in morphogenesis.

Journal Article↗
PubMed2002

Pattern formation induced by nonequilibrium global alternation of dynamics.

We recently proposed a mechanism for pattern formation based on the alternation of two dynamics, neither of which exhibits patterns. Here we analyze the mechanism in detail, showing by means of numerical simulations and theoretical calculations how the nonequilibrium process of switching between dynamics, either randomly or periodically, may induce both stationary and oscillatory spatial structures. Our theoretical analysis by means of mode amplitude equations shows that all features of the model can be understood in terms of the nonlinear interactions of a small number of Fourier modes.

Journal Article↗
PubMed2001

Stationary and oscillatory spatial patterns induced by global periodic switching.

We propose a new mechanism for pattern formation based on the global alternation of two dynamics, neither of which exhibits patterns. When driven by either one of the separate dynamics, the system goes to a spatially homogeneous state associated with that dynamics. However, when the two dynamics are globally alternated sufficiently rapidly, the system exhibits stationary spatial patterns. Somewhat slower switching leads to oscillatory patterns. We support our findings by numerical simulations and discuss the results in terms of the symmetries of the system and the ratio of two relevant characteristic times, the switching period and the relaxation time to a homogeneous state in each separate dynamics.

Journal Article↗
PubMed2001

Random Ginzburg-Landau model revisited: reentrant phase transitions.

We analyze the phase diagram of the random Ginzburg-Landau model, where a quenched dichotomous noise affects the control parameter. We show that the system exhibits two types of counterintuitive reentrant second-order phase transitions. In the first case, increasing the coupling drives the system from a disordered to an ordered state and then back to a disordered state. In the second case, increasing the intensity of the quenched noise, the system goes from an ordered phase to a disordered phase and back to an ordered state. We discuss the general mechanism that produces these reentrant phase transitions, showing that it may appear in other physical systems, such as a modification of the spin-1 Blume-Capel model proposed to describe the critical behavior of helium mixtures in a random medium.

Journal Article↗
PubMed2000

Finite resolution effects in the analysis of the scaling behavior of rough surfaces

We investigate the influence of finite spatial resolution in the analysis of the scaling behavior of rough surfaces. We analyze such an effect for two usual measurement methods: the local width and the height-height correlation function. We show that while the correlation function is insensitive to finite resolution effects for practical purposes, the local width presents correction terms to the scaling law, leading to an effective value of the local roughness exponent smaller than the theoretically expected. We also show that a functional scaling relation can only be properly formulated in terms of the height-height correlation function.

Journal Article↗
PubMed2000

Negative resistance and anomalous hysteresis in a collective molecular motor

A spatially extended model for a collective molecular motor is presented. The system is driven far from equilibrium by a quenched additive noise. As a result, it exhibits anomalous transport properties, namely, negative resistance and a clockwise hysteresis cycle. The phase diagram and the region of negative resistance are calculated using a Weiss mean field theory. Intuitive explanations of the anomalous transport properties as well as details of its energetics are given.

Journal Article↗
PubMed1993

Relaxation therapy in the treatment of bronchial asthma: effects on basal spirometric values.

Eighteen asthmatic children were divided into two 9-patient groups matched with respect to severity of the disease. The first group received a 6-week asthma self-management programme which included progressive relaxation training. The second group received the same programme without the relaxation training component. State anxiety and spirometric data (FEV1, FVC and FEV1/FVC%) for both groups, obtained before and after each session with the therapist, showed that relaxation is effective in reducing state anxiety but does not modify basal spirometric values.

Adolescent↗