1,720,971 research outputs found
Parto ¿respetado? : análisis de la jurisprudencia posterior a la reglamentación de 2015 de la ley de Parto Humanizado, ley 26.485, y sus implicancias con respecto a la situación actual de los derechos de la mujer
Full text linkFil: D'Alessandro, Maira Stefania. Universidad de San Andrés. Departamento de Derecho; Argentina
Chaoticity spectrum in Hamiltonian systems with many degrees of freedom
No full textWe present a diagnostic tool to analyze the chaoticity of single degrees of freedom: the coherence angles, which measure the angular distance between any physically relevant direction and the direction of maximum expansion in the tangent space. They allow at the same time a detailed characterization and a synoptic view of the dynamical behavior of a system with many degrees of freedom. Results are presented for two- and three-dimensional Lennard-Jones lattices, which show a nontrivial structure of the spectrum of coherence angles
Coherence angles and coherence times in Hamiltonian systems with many degrees of freedom
No full textThe coexistence of ordered and chaotic dynamics in one and the same system has been detected already several years ago. A thorough description of a complex dynamical system, both from a mechanical and from a statistical point of view, requires the determination of the level of order and chaoticity of each single degree of freedom (DOF). We have introduced in a recent paper a new diagnostic tool to analyse the chaoticity of single DOFs or groups of DOFs: the coherence angles, which measure the angular distance between any physically relevant direction and the direction of maximum expansion in the tangent space. They allow at the same time a detailed characterization and a synoptic view of the dynamical behaviour of a system with many DOFs, but lack resolution among the most ordered DOFs when their number is very large. We present here a method allowing the attribution to each DOF (or group of DOFs) of a characteristic coherence time, which overcomes this lack of resolution. In phase space regions characterized by a highly chaotic dynamics, the coherence times are similar. On the other hand, in regions where the dynamics is weakly chaotic, the coherence times show relevant differences in the dynamical behaviour of different groups of DOFs
Dynamical and statistical mechanical characterization of temperature coupling algorithms
No full textIn this article, we investigate molecular dynamics (MD) trajectories of a butane molecule, as obtained using different types of thermostats. Results show that at low temperature. where the harmonic approximation holds, the Nose'-Hoover (NH) thermostat fails to reproduce the statistical mechanical behavior, even using simulation lengths of millions of time steps, whereas the Gaussian isokinetic (IG) thermostat reproduces quite well the expected statistical mechanical values. The Berendsen's coupling (BC) provides good results for basic properties such as the average potential and kinetic energies but fails in reproducing the canonical fluctuations. Moreover, using the speed of divergence of initially nearby trajectories in phase space as a measure of the dynamical chaoticity, we found that the NH thermostat provides very slow divergence for the physical phase space degrees of freedom, concentrating most of its chaoticity in the dynamics of the thermostat virtual degree of freedom. On the contrary, the IG thermostat provides always highly diverging trajectories in phase space, characterized by a high chaoticity of each degree of freedom. Finally, the BC thermostat provides a moderate chaotic behavior for all of the degrees of freedom. Such results suggest that even assuming for both the "rigorous" algorithms (NH and IG) a full ergodic behavior the NH thermostat could require an extremely long time to achieve convergence of the time averaged properties
Coherence measure in Hamiltonian systems with many degrees of freedom
No full textWe study the phase space region of two- and three-dimensional lattices where a transition from chaotic to ordered dynamics takes place when the energy is lowered. In this region we find coexistence of degrees of freedom (DOF’s), endowed with different levels of chaos. The analysis of this complex dynamical pattern requires the introduction of diagnostic tools suitable for a characterization of single DOF’s: coherence angles and coherence times. We find that the coherence times—which give a measure of the time each DOF needs to relax to equilibrium—are roughly proportional to the inverse of the specific energy. This may be useful to evaluate the reliability of statistical results obtained in computer experiments performed on condensed matter systems at low energy
Coherent dynamics in a butane molecule
No full textWe have simulated by molecular dynamics a single molecule of butane in a thermal bath at different temperatures. We have found that the collective degrees of freedom of the essential dynamics are endowed with quite different degrees of coherence, and that those subject to the largest fluctuations are also the most coherent, that is, the least chaotic. We suggest that this pattern may be characteristic also of larger molecules. A detailed assessment of the degree of coherence has been obtained by computing in the tangent space the whole set of generalized coherence angles
Characterization of liquid behaviour by means of local density fluctuations
No full textBy means of principle component analysis of the local density fluctuations, as revealed by molecular dynamics simulations, we obtain detailed information on the relevant local density fluxes and corresponding spatial patterns
Theoretical study of the thermodynamics of a solvated peptide: Contryphan Vn
No full textIn recent papers we combined molecular dynamics (MD) simulations with the quasi Gaussian entropy (QGE) theory, in order to model the statistical mechanics and thermodynamics of simple solute molecules in water. In this paper we apply this approach to a more complex solute in water: a 9 residues peptide, Contryphan Vn. Results show that this approach can provide an accurate theoretical description of this complex solute-solvent system over a wide range of temperature
On the use of the quasi-Gaussian entropy theory in the study of simulated dilute solutions
No full textIn a recent paper [M. D'Alessandro, M. D'Abramo, G. Brancato, A. Di Nola, and A. Amadei, J. Phys. Chem. B 106, 11843 (2002)] we showed how to combine molecular dynamics simulations with the quasi-Gaussian entropy theory, in order to model the statistical mechanics and thermodynamics of ionic (water) solutions. In this paper we extend the method to treat nonspherical solutes, describe more thoroughly its theoretical basis and apply it to a set of more complex solute molecules in water (i.e., water, methane, ethane, methanol, and ethanol). Results show that this approach can really provide an excellent theoretical description of solute-solvent systems over a wide range of temperatures. (C) 2004 American Institute of Physics
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