Average Deactivation Time of theHeterogeneous Reaction2 A+B2→2AB

In the present paper we exactly solve the distributed parameter stochastic modelof the heterogeneous catalytic reaction2A+B2→2ABand calculate the averagenumber of reactive steps necessary to deactivate the lattice first,. Resultsare compared with Monte Carlo simulations.shows a nonmonotonic behaviorwith the sticking coefficient probabilitysand the desorption probabilitypd, reachinga maximum value that depends ons,pdand the lattice sizeNFil: Pastor, Veronica Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Dammig Quiña, Pablo Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Salvatierra, Lucas Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Pont. Universidad Catolica Arg."sta.maria de Los Bs.as.". Facultad de Química E Ingeniería-rosario; ArgentinaFil: Irurzun, Isabel Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Mola, Eduardo Elías. Pont. Universidad Catolica Arg."sta.maria de Los Bs.as.". Facultad de Química E Ingeniería-rosario; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Spatiotemporal patterns in the Bär model induced by concentration-dependent diffusivities

We investigate the effects of diffusivity on pattern formation in the excitable 2D Bär model with periodic boundary conditions. Our work generalizes previous findings of Roussel and coworkers in 1D and focusses on the turbulent states, including the spiral breakdown process. Diffusion coefficients (D(u)) quadratically dependent on the activator concentration were studied. Inhibition of the spiral instability was found with a negative linear coefficient in the concentration dependence of D(u). At a given value of e the inhibition can be complete for nonflux boundary conditions while a delay of the instability occurs in systems with periodic boundary conditions. Positive quadratic coefficients in the concentration dependence of D(u) strongly modify the defect statistic in the chaotic zone.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Configurational entropy of a set of dipoles placed on a two-dimensional lattice

In the present work we calculate the configurational entropy of an arbitrary number of dipoles placed on a square lattice. We use a quasi-two-dimensional (Q2D) space to capture the main features determining the occupation statistics of this system. We show that our result is in agreement with both, lattice-gas predictions at low coverages and the exact value derived in the close-packed limit as well. Therefore our equation provides a substantial improvement to the most recent calculations based on semiempirical models and Monte Carlo simulations.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The heterogeneous catalytic reaction 2A + B2 → 2AB exactly solved on a small lattice

We studied a kinetic model of a generic heterogeneous catalytic reaction 2A* þ B* 2 → 2ABg. This reaction includes the steps of adsorption and desorption of reactants A and B2, where B2 requires two neighboring adsorption sites to be adsorbed. We solved the model exactly and without any restriction on a 2 x 2 lattice. Despite the reduced number of sites employed, the solution shows the main general features observed by simulating the mechanism on a large N x N lattice. This result should encourage the search for an analytical solution as a reliable form to unravel details of a chemical reaction prior to performing numerical simulations.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Scaling behavior in the heart rate variability characteristics with age

In this work we study the characteristics of the heart rate variability (HRV) as a function of age and gender. The analyzed data include previous results reported in the literature. The data obtained in this work expand the range of age studied until now revealing new behaviors not reported before. We analyze some measurements in the time domain, in the frequency domain and nonlinear measurements. We report scaling behaviors and abrupt changes in some measurements. There is also a progressive decrease in the dimensionality of the dynamic system governing the HRV, with the increase in age that is interpreted in terms of autonomic regulation of cardiac activity.Fil: Irurzun, Isabel Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Defeo, Magdalena Maria. Gobierno de la Provincia de Buenos Aires. Ministerio de Salud. Hospital Interzonal General de Agudos "prof. Dr. Rodolfo Rossi".; ArgentinaFil: Garavaglia, Leopoldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Thomas Mailland, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Mola, Eduardo Elías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Dielectric breakdown model for conductor-loaded and insulator-loaded composite materials

In the present work we generalize the dielectric breakdown model to describe dielectric breakdown patterns in both conductor-loaded and insulator-loaded composites. The present model is an extension of a previous one [F. Peruani et al., Phys. Rev. E 67, 066121 (2003)] presented by the authors to describe dielectric breakdown patterns in conductor-loaded composites. Particles are distributed at random in a matrix with a variable concentration p. The generalized model assigns different probabilities P(i,k!i8,k8) to breakdown channel formation according to particle characteristics. Dielectric breakdown patterns are characterized by their fractal dimension D and the parameters of the Weibull distribution. Studies are carried out as a function of the fraction of inhomogeneities, p.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasUniversidad de Buenos Aire

Non-linear properties of <i>R–R</i> distributions as a measure of heart rate variability

We analyze the dynamic quality of the R–R interbeat intervals of electrocardiographic signals from healthy people and from patients with premature ventricular contractions (PVCs) by applying different measure algorithms to standardised public domain data sets of heart rate variability. Our aim is to assess the utility of these algorithms for the above mentioned purposes. Long and short time series, 24 and 0.50 h respectively, of interbeat intervals of healthy and PVC subjects were compared with the aim of developing a fast method to investigate their temporal organization. Two different methods were used: power spectral analysis and the integral correlation method. Power spectral analysis has proven to be a powerful tool for detecting long-range correlations. If it is applied in a short time series, power spectra of healthy and PVC subjects show a similar behavior, which disqualifies power spectral analysis as a fast method to distinguish healthy from PVC subjects. The integral correlation method allows us to study the fractal properties of interbeat intervals of electrocardiographic signals. The cardiac activity of healthy and PVC people stems from dynamics of chaotic nature characterized by correlation dimensions df equal to 3:40 ± 0:50 and 5:00 ± 0:80 for healthy and PVC subjects respectively. The methodology presented in this article bridges the gap between theoretical and experimental studies of non-linear phenomena. From our results we conclude that the minimum number of coupled differential equations to describe cardiac activity must be six and seven for healthy and PVC individuals respectively. From the present analysis we conclude that the correlation integral method is particularly suitable, in comparison with the power spectral analysis, for the early detection of arrhythmias on short time (0.5 h) series.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasUniversidad de Buenos Aire

A Quantum Chemistry Approach to Possible Sulfur Adsorbate Structures on the Basal Plane of Graphite Clusters

A quantum chemistry study for possible sulfur adsorbate structures on the basal plane of graphite clusters has beenmade using the MNDO method. The potential energy curves showed the possible formation of S atoms, sulfur dimer and trimer adsorbates on top and bridge substrate positions, whereas neither sulfur atom, dimer, nor trimer adsorption binding to hollow position could be formed. Results gave support to a recently reported interpretation for sulfur atom adsorption on the basal plane of graphite based upon scanning tunneling microscopy data.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Self-healing during electrical treeing: A feature of the two-phase liquid-solid nature of silicone gels

We report the results of electrical treeing tests carried out on a range of silicone dielectric gel samples made by varying the ratio of the same two components used for cross-linking a commercial silicone gel. These samples range from liquids to elastomers via two-phase gels. The extent of the curing is followed by means of FTIR spectroscopy and the samples are characterized through their dynamical mechanical properties. It is shown that the gel samples exhibit treeing behavior that includes features typical of both liquids and solids. A filamentary structure is produced that has permanence together with attached bubbles that self-heal locally during treeing, although differences in detail were found depending on the degree of curing. Removal of the treeing voltage allows a more substantial self-healing to occur. This behavior is discussed in terms of the two-phase liquid-solid nature of the silicone gels.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Oxygen assisted H2O dissociation on the Pt{110}(1 × 2) surface from first principles

Water dissociation with and without oxygen coadsorption is investigated on the Pt{110}(1 × 2) surface at low coverage from first principles. Calculations indicate that desorption of the water molecule is likely to occur fromthe clean surface ahead of partial dissociation. The assistance of coadsorbed atomic O in the H2O partial dissociation changes the picture. Several H2O+O→OH+ OH possible reactions (with no OH+ H + O intermediate step) have been analyzed. The comparison between the activation energy for the mentioned reaction and the activation energy for H2O desorption shows no strong preference for one reaction over the other one.These results predict that the partial dissociation of H2O is a likely process if it is assisted by atomic O on the Pt {110}(1 × 2) surface. Dissociation and desorption of the H2O molecule are competitive processes on the surface and is possible to predict a dynamic system.Fil: Ranea, Victor Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Mola, Eduardo Elías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Catolica Argentina; Argentin