Biomedical subjects
Publications and source records attributed to V Beato.
We show that characteristic features of noise-induced spatiotemporal patterns in excitable media can be effectively controlled by applying delayed feedback. Actually, by variation of the time delay and of the strength of the feedback one can deliberately change both spatial and temporal coherence, as well as adjust the characteristic time scales.
We investigate Turing pattern formation in the presence of additive dichotomous fluctuations in the context of an extended system with diffusive coupling and FitzHugh-Nagumo kinetics. The fluctuations vary in space and/or time. Depending on the realization of the dichotomous switching the system is, at a given time (for spatial disorder at a given position) in one of two possible excitable dynamical regimes. Each of the two excitable dynamics for itself does not support pattern formation. With proper dichotomous fluctuations, however, the homogeneous steady state is destabilized via a Turing instability. We investigate the influence of different switching rates (different correlation length of the spatial disorder) on pattern formation. We find three distinct mechanisms: For slow switching existing boundaries become unstable, for high rates the system exhibits "effective bistability" which allows for a Turing instability. For medium rates the fluctuations create spatial structures via a new mechanism where the influence of the fluctuations is twofold. First they produce local inhomogeneities, which then grow (again caused by fluctuations) until the whole space is covered. Utilizing a nonlinear map approach we show bistability of a period-one and a period-two orbit being associated with the steady homogeneous and the Turing pattern state, respectively. Finally, for purely static dichotomous disorder we find destabilization of homogeneous steady states for finite nonzero correlation length of the disorder resulting again in Turing patterns.
We study both experimentally and numerically the temporal coherence of noise-induced wave nucleations in excitable media subjected to external fluctuations with finite correlation time. The experiments are performed with the light-sensitive variant of the Belousov-Zhabotinsky (BZ) reaction forced by an exponentially correlated dichotomous fluctuating illumination. We find that there exists an optimal correlation time for which nucleations coherence reaches a maximum. The same behavior is obtained in numerical simulations with a stochastic Oregonator model, modified to describe the light-sensitive BZ reaction.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
This article presents the results of a prospective multivariable study of elderly patients aged over 70 years, hospitalized in an Internal Medicine Department of a Central Lisbon Hospital. The study aimed to identify, at the beginning of hospital admission (HA), predictive factors of hospital mortality (HM) and mortality at 6 months, of duration of HA, of admission to a nursing home at the time of discharge and during a period of 6 months thereafter and of hospital readmission during the 6 months following discharge. The study included 158 patients with a mean hospital stay of 15 days and a hospital mortality of 12%. The main pathologies responsible for hospital admission were cerebrovascular accident (22%), heart failure (20%) and pneumonia (16%). Mortality at 6 months was 29% and hospital readmission in the 6 months thereafter was 24%. When the patient was cared for by the spouse there was a statistically significant correlation with a shorter duration of admission (p = 0.006). Mean hospital stay was not significantly associated with any other variable. A subjective medical evaluation (SME) at the start of HA (p = 0.001), a low Barthel score prior to and at the time of HA, low serum albumin (p = 0.001) and a high leucocyte count (p = 0.005) were correlated with a higher HM. Nursing home admission was only positively correlated with cerebrovascular pathology. Mortality at 6 months was significantly correlated with the SME (p = 0.001), a low Barthel score prior to admission (p < 0.008) and at the time of HA (p < 0.001), nursing home residency (p < 0.005) and a low mental test score (p < 0.01). Hospital readmission at 6 months was influenced by the SME (p < 0.04) and by the reduction in the Barthel score caused by the illness and HA (p = 0.004). These correlations enabled the development of mathematical models that predict HM and mortality at 6 months and admission to a nursing home at the time of discharge and during a period of 6 months thereafter. They could be important in identifying elderly patients' needs early in the hospital admission and in the improvement of the strategy necessary for a successful and dignified hospital discharge.