Dynamics of conduction blocks in a model of paced cardiac tissue

We study numerically the dynamics of conduction blocks using a detailed electrophysiological model. We find that this dynamics depends critically on the size of the paced region. Small pacing regions lead to stationary conduction blocks while larger pacing regions can lead to conduction blocks that travel periodically towards the pacing region. We show that this size-dependence dynamics can lead to a novel arrhythmogenic mechanism. Furthermore, we show that the essential phenomena can be captured in a much simpler coupled-map model.Comment: 8 pages 6 figure

Bootstrap Technique to Study Correlation Between Neutron Skin Thickness and the Slope of Symmetry Energy in Atomic Nuclei

We examine the proposed correlation between the neutron skin thickness and the slope of the symmetry energy for two doubly-magic nuclei (Sn-100 and Sn-132) and find that a statistically significant correlation appears to exist for Sn-132 whilst no such correlation appears to exist for Sn-100. Additionally, we present a new statistical tool based on random sampling to assess the confidence interval of Pearson's and Spearman's correlation coefficients in order to examine the aforementioned correlation. These estimators are then used to quantify the statistical correlations among the neutron skin thickness of atomic nuclei and the slope of the symmetry energy in the infinite nuclear medium.Peer reviewe

Phase diagram and structural properties of a simple model for one-patch particles

We study the thermodynamic and structural properties of a simple, one-patch fluid model using the reference hypernetted-chain (RHNC) integral equation and specialized Monte Carlo simulations. In this model, the interacting particles are hard spheres, each of which carries a single identical, arbitrarily-oriented, attractive circular patch on its surface; two spheres attract via a simple square-well potential only if the two patches on the spheres face each other within a specific angular range dictated by the size of the patch. For a ratio of attractive to repulsive surface of 0.8, we construct the RHNC fluid-fluid separation curve and compare with that obtained by Gibbs ensemble and grand canonical Monte Carlo simulations. We find that RHNC provides a quick and highly reliable estimate for the position of the fluid-fluid critical line. In addition, it gives a detailed (though approximate) description of all structural properties and their dependence on patch size.Comment: 27 pages, 10 figures, J. Chem. Phys. in pres

Effects of patch size and number within a simple model of patchy colloids

We report on a computer simulation and integral equation study of a simple model of patchy spheres, each of whose surfaces is decorated with two opposite attractive caps, as a function of the fraction $\chi$ of covered attractive surface. The simple model explored --- the two-patch Kern-Frenkel model --- interpolates between a square-well and a hard-sphere potential on changing the coverage $\chi$. We show that integral equation theory provides quantitative predictions in the entire explored region of temperatures and densities from the square-well limit $\chi = 1.0$ down to $\chi \approx 0.6$. For smaller $\chi$, good numerical convergence of the equations is achieved only at temperatures larger than the gas-liquid critical point, where however integral equation theory provides a complete description of the angular dependence. These results are contrasted with those for the one-patch case. We investigate the remaining region of coverage via numerical simulation and show how the gas-liquid critical point moves to smaller densities and temperatures on decreasing $\chi$. Below $\chi \approx 0.3$, crystallization prevents the possibility of observing the evolution of the line of critical points, providing the angular analog of the disappearance of the liquid as an equilibrium phase on decreasing the range for spherical potentials. Finally, we show that the stable ordered phase evolves on decreasing $\chi$ from a three-dimensional crystal of interconnected planes to a two-dimensional independent-planes structure to a one-dimensional fluid of chains when the one-bond-per-patch limit is eventually reached.Comment: 26 pages, 11 figures, J. Chem. Phys. in pres

Partial wave decomposition of the N3LO equation of state

By means of a partial wave decomposition, we separate their contributions to the equation of state (EoS) of symmetric nuclear matter for the N3LO pseudo-potential. In particular, we show that although both the tensor and the spin-orbit terms do not contribute to the EoS, they give a non-vanishing contribution to the separate (JLS) channels

Are there localized saddles behind the heterogeneous dynamics of supercooled liquids?

We numerically study the interplay between heterogeneous dynamics and properties of negatively curved regions of the potential energy surface in a model glassy system. We find that the unstable modes of saddles and quasi-saddles undergo a localization transition close to the Mode-Coupling critical temperature. We also find evidence of a positive spatial correlation between clusters of particles having large displacements in the unstable modes and dynamical heterogeneities.Comment: 7 pages, 3 figures, submitted to Europhys. Let

Coletânea de trabalhos sobre a Embrapa.

POLITICA AGRICOLA DO BRASIL E HIPOTESE DA INOVAÇAO INDUZIDA; O PAPEL DA TECNOLOGIA NA EXPANSAO AGRÍCOLA; REFORMING THE BRAZILIAN AGRICULTURAL FIESEARCH SYSTEM; NOVA ABORDAGEM PARA A PESQUISA AGRÍCOLA.bitstream/item/159154/1/Coletanea-de-trabalhos-1980-.pdfNa publicação: Eliseu Alves

Model nuclear energy density functionals derived from ab initio calculations

We present the first application of a new approach, proposed in (2016J.Phys.G:Nucl.Part.Phys.4304LT01) to derive coupling constants of the Skyrme energy density functional (EDF) fromab initioHamiltonian. By perturbing theab initioHamiltonian with several functional generators defining the Skyrme EDF, we create a set of metadata that is then used to constrain the coupling constants of the functional. We use statistical analysis to obtain such anab initio-equivalent Skyrme EDF. We find that the resulting functional describes properties of atomic nuclei and infinite nuclear matter quite poorly. This may point to the necessity of building up theab initio-equivalent functionals from more sophisticated generators. However, we also indicate that the current precision of theab initiocalculations may be insufficient for deriving meaningful nuclear EDFs.Peer reviewe

Compaction Grouting for Seismic Mitigation of Sensitive Urban Sites

For moderately loaded structures founded on liquefiable soils, spread footings on improved ground can provide considerable cost savings over deep foundation options. Liquefaction mitigation by ground improvement must be properly designed and executed; and should include a field verification program. Although densification is the most effective method of achieving verifiable mitigation of liquefaction susceptible soils, vibro-densification methods are often disregarded for urban sites due to concern for adjacent structures and utilities. An alternative to vibratory methods is compaction grouting, which can achieve densification of cohesionless materials while avoiding excessive vibration of adjacent structures. Recently, compaction grouting was successfully applied to densify a thick loose sand layer (up to 40 feet) for a large development site in an urban environment. This densification significantly increased the factor of safety against liquefaction and reduced potential liquefaction-induced settlement to under 0.5 inch. The compaction grouting program included automated data acquisition and processing and three-dimensional visualization components to ensure quality control and assurance. In addition, the site improvement program was fully verifiable, as the ground improvement program included a comparison of cone penetrometer tests (CPT) conducted prior to and following treatment. Although compaction grouting has been well utilized for several years, the potential for liquefaction mitigation in urban environments is not well established. However, ground improvement through compaction grouting can be a cost-effective alternative to drilled shafts or driven piles on liquefiable sites. This paper includes a description of the site conditions, the compaction grouting program (including automated data acquisition instrumentation and visualization), site instrumentation, post-treatment evaluation of the mitigation procedures, and analysis of the response of adjacent structures