Biomedical subjects

Miguel A Muñoz

Publications and source records attributed to Miguel A Muñoz.

11 recordsLinked to original sources

PubMed2006

Kardar-Parisi-Zhang interfaces bounded by long-ranged potentials.

We study unbinding transitions of a nonequilibrium Kardar-Parisi-Zhang interface in the presence of long-ranged substrates. Both attractive and repulsive substrates, as well as positive and negative Kardar-Parisi-Zhang nonlinearities, are considered, leading to four different physical situations. A detailed comparison with equilibrium wetting transitions as well as with nonequilibrium unbinding transitions in systems with short-ranged forces is presented, yielding a comprehensive picture of unbinding transitions and of their classification into universality classes. These nonequilibrium transitions may play a crucial role in the dynamics of the wetting or growth of systems with intrinsic anisotropies.

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PubMed2005

Mean-field limit of systems with multiplicative noise.

A detailed study of the mean-field solution of Langevin equations with multiplicative noise is presented. Three different regimes depending on noise intensity (weak, intermediate, and strong noise) are identified by performing a self-consistent calculation on a fully connected lattice. The most interesting, strong-noise, regime is shown to be intrinsically unstable with respect to the inclusion of fluctuations, as a Ginzburg criterion shows. On the other hand, the self-consistent approach is shown to be valid only in the thermodynamic limit, while for finite systems the critical behavior is found to be different. In this last case, the self-consistent field itself is broadly distributed rather than taking a well defined mean value; its fluctuations, described by an effective zero-dimensional multiplicative noise equation, govern the critical properties. These findings are obtained analytically for a fully connected graph, and verified numerically both on fully connected graphs and on random regular networks. The results presented here shed some doubt on what is the validity and meaning of a standard mean-field approach in systems with multiplicative noise in finite dimensions, where each site does not see an infinite number of neighbors, but a finite one. The implications of all this on the existence of a finite upper critical dimension for multiplicative noise and Kardar-Parisi-Zhang problems are briefly discussed.

Journal Article↗

PubMed2005

Entangled networks, synchronization, and optimal network topology.

A new family of graphs, entangled networks, with optimal properties in many respects, is introduced. By definition, their topology is such that it optimizes synchronizability for many dynamical processes. These networks are shown to have an extremely homogeneous structure: degree, node distance, betweenness, and loop distributions are all very narrow. Also, they are characterized by a very interwoven (entangled) structure with short average distances, large loops, and no well-defined community structure. This family of nets exhibits an excellent performance with respect to other flow properties such as robustness against errors and attacks, minimal first-passage time of random walks, efficient communication, etc. These remarkable features convert entangled networks in a useful concept, optimal or almost optimal in many senses, and with plenty of potential applications in computer science or neuroscience.

Animals↗

PubMed2005

Nonperturbative fixed point in a nonequilibrium phase transition.

We apply the nonperturbative renormalization group method to a class of out-of-equilibrium phase transitions (usually called "parity-conserving" or, more properly, "generalized voter" class) which is out of the reach of perturbative approaches. We show the existence of a genuinely nonperturbative fixed point, i.e., a critical point that does not seem to be Gaussian in any dimension.

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PubMed2005

Langevin description of critical phenomena with two symmetric absorbing states.

On the basis of general considerations, we propose a Langevin equation accounting for critical phenomena occurring in the presence of two symmetric absorbing states. We study its phase diagram by mean-field arguments and direct numerical integration in physical dimensions. Our findings fully account for and clarify the intricate picture known so far from the aggregation of partial results obtained with microscopic models. We argue that the direct transition from disorder to one of two absorbing states is best described as a (generalized) voter critical point and show that it can be split into an Ising and a directed percolation transition in dimensions larger than one.

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PubMed2005

Integration of Langevin equations with multiplicative noise and the viability of field theories for absorbing phase transitions.

Efficient and accurate integration of stochastic (partial) differential equations with multiplicative noise can be obtained through a split-step scheme, which separates the integration of the deterministic part from that of the stochastic part, the latter being performed by sampling exactly the solution of the associated Fokker-Planck equation. We demonstrate the computational power of this method by applying it to the most absorbing phase transitions for which Langevin equations have been proposed. This provides precise estimates of the associated scaling exponents, clarifying the classification of these nonequilibrium problems, and confirms or refutes some existing theories.

Journal Article↗

PubMed2004

Numerical study of the Langevin theory for fixed-energy sandpiles.

The recently proposed Langevin equation, aimed to capture the relevant critical features of stochastic sandpiles and other self-organizing systems, is studied numerically. The equation is similar to the Reggeon field theory, describing generic systems with absorbing states, but it is coupled linearly to a second conserved and static (nondiffusive) field. It has been claimed to represent a different universality class, including different discrete models: the Manna as well as other sandpiles, reaction-diffusion systems, etc. In order to integrate the equation, and surpass the difficulties associated with its singular noise, we follow a numerical technique introduced by Dickman. Our results coincide remarkably well with those of discrete models claimed to belong to this universality class, in one, two, and three dimensions. This provides a strong backing for the Langevin theory of stochastic sandpiles, and to the very existence of this meagerly understood universality class.

Journal Article↗

PubMed2004

Location-aware access to hospital information and services.

Hospital workers are highly mobile; they are constantly changing location to perform their daily work, which includes visiting patients, locating resources, such as medical records, or consulting with other specialists. The information required by these specialists is highly dependent on their location. Access to a patient's laboratory results might be more relevant when the physician is near the patient's bed and not elsewhere. We describe a location-aware medical information system that was developed to provide access to resources such as patient's records or the location of a medical specialist, based on the user's location. The system is based on a handheld computer which includes a trained backpropagation neural-network used to estimate the user's location and a client to access information from the hospital information system that is relevant to the user's current location.

Algorithms↗

PubMed2003

Stochastic theory of synchronization transitions in extended systems.

We propose a general Langevin equation describing the universal properties of synchronization transitions in extended systems. By means of theoretical arguments and numerical simulations we show that the proposed equation exhibits, depending on parameter values: (i) a continuous transition in the bounded Kardar-Parisi-Zhang universality class, with a zero largest Lyapunov exponent at the critical point; (ii) a continuous transition in the directed percolation class, with a negative Lyapunov exponent, or (iii) a discontinuous transition (that is argued to be possibly just a transient effect). Cases (ii) and (iii) exhibit coexistence of synchronized and unsynchronized phases in a broad (fuzzy) region. This reproduces almost all of the reported features of synchronization transitions, providing a unified theoretical framework for the analysis of synchronization transitions in extended systems.

Fuzzy Logic↗

PubMed2003

[Secondary prevention of coronary heart disease is less agressive in patients over 64 years].

INTRODUCTION AND OBJECTIVES: Although elderly people has a higher incidence of coronary heart disease, this group is seldom included in clinical trials. Studies performed in Spain on elderly coronary heart disease patients have been conducted in hospital settings. The aim of our study was to analyse wether the management of coronary heart disease patients over 64 years of age cared by family physicians differed from that of the rest. PATIENTS AND METHOD: Cross-sectional multicentre study embedded in a clinical trial on 1,022 patients with stable coronary heart disease in which socio-demographic variables, comorbidity, treatment and cardiovascular risk- factor control were collected. RESULTS: Mean age was 64 10, 74.0% were men and 53.8% of subjects were over 64 years. Patients over 64 years had a greater cardiovascular comorbidity (87.7 vs 82.6%; p = 0.002) and received lower number of drugs than the rest in the prevention of recurrences (60.4 vs 70.9%; p < 0.001). Probability to receive less than two drugs on secondary prevention by subjects over 64 years was 0.45 (95% CI, 0.30-0.68) despite comorbidity, sex and cardiovascular risk profile.Conclusions. Coronary heart disease patients over 64 years receive less drugs for coronary event recurrence prevention than their younger counterparts despite their worse cardiovascular risk profile.

Aged↗

PubMed2002

Interface depinning versus absorbing-state phase transitions.

According to recent numerical results from lattice models, the critical exponents of systems with many absorbing states and order parameter coupled to a nondiffusive conserved field coincide with those of the linear interface depinning model within computational accuracy. In this paper the connection between absorbing-state phase transitions and interface pinning in quenched disordered media is investigated. For that, we present an heuristic mapping of the interface dynamics in a disordered medium into a Langevin equation for the active-site density and show that a Reggeon-field-theory-like description, in which the order parameter appears coupled to an additional nondiffusive conserved field, emerges rather naturally. Reciprocally, we construct a mapping from a discrete model belonging in the absorbing state with a conserved-field class to a discrete interface equation, and show how a quenched disorder, typical of the interface representation is originated. We discuss the character of the possible noise terms in both representations, and overview the critical exponent relations. Evidence is provided that, at least for dimensions larger that one, both universality classes are just two different representations of the same underlying physics.

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