2,736 research outputs found
Interplay between structure and density anomaly for an isotropic core-softened ramp-like potential
Using molecular dynamics simulations and integral equations we investigate
the structure, the thermodynamics and the dynamics of a system of particles
interacting through a continuous core- softened ramp-like interparticle
potential. We found density, dynamic and structural anomalies similar to that
found in water. Analysis of the radial distribution function for several
temperatures at fixed densities show a pattern that may be related to the
origin of density anomaly.Comment: 7 pages, 3 figure
A Framework for the Design and Implementation of Learning Objects: a Competence-based Approach
This paper presents a framework for the design and implementation of learning objects using a competence-based approach. This framework is illustrated by the development of a standalone Windows application (Trilho GOA) whose primary purpose is to create standardized pedagogical contents trough the aggregation and standardization of instructional resources in several formats that can be used later on a Learning Management System (LMS) supporting SCORM 1.2. The paper contains a brief introduction to the developed software, its system architecture, main features and several pedagogical advantages for its users
Structural anomalies for a three dimensional isotropic core-softened potential
Using molecular dynamics simulations we investigate the structure of a system
of particles interacting through a continuous core-softened interparticle
potential. We found for the translational order parameter, t, a local maximum
at a density and a local minimum at . Between and , the parameter
anomalously decreases upon pressure. For the orientational order parameter,
, was observed a maximum at a density . For densities between and , both the
translational (t) and orientational () order parameters have anomalous
behavior. We know that this system also exhibits density and diffusion anomaly.
We found that the region in the pressure-temperature phase-diagram of the
structural anomaly englobes the region of the diffusion anomaly that is larger
than the region limited by the temperature of maximum density. This cascade of
anomalies (structural, dynamic and thermodynamic) for our model has the same
hierarchy of that one observed for the SPC/E water.Comment: 19 pages, 8 figure
IBI: Targeting cumulative coordination within an iterative protocol to derive coarse-grained models of (multi-component) complex fluids
We present a coarse-graining strategy that we test for aqueous mixtures. The
method uses pair-wise cumulative coordination as a target function within an
iterative Boltzmann inversion (IBI) like protocol. We name this method
coordination iterative Boltzmann inversion (IBI). While the
underlying coarse-grained model is still structure based and, thus, preserves
pair-wise solution structure, our method also reproduces solvation
thermodynamics of binary and/or ternary mixtures. Additionally, we observe much
faster convergence within IBI compared to IBI. To validate the
robustness, we apply IBI to study test cases of solvation
thermodynamics of aqueous urea and a triglycine solvation in aqueous urea
Water-like hierarchy of anomalies in a continuous spherical shouldered potential
We investigate by molecular dynamics simulations a continuous isotropic
core-softened potential with attractive well in three dimensions, introduced by
Franzese [cond-mat/0703681, to appear on Journal of Molecular Liquids], that
displays liquid-liquid coexistence with a critical point and water-like density
anomaly. Here we find diffusion and structural anomalies. These anomalies occur
with the same hierarchy that characterizes water. Yet our analysis shows
differences with respect to the water case. Therefore, many of the anomalous
features of water could be present in isotropic systems with soft-core
attractive potentials, such as colloids or liquid metals, consistent with
recent experiments showing polyamorphism in metallic glasses.Comment: 27 pages, 9 figures. to appear in J. Chem. Phy
An ubiquitous mechanism for waterlike anomalies
Using collision driven molecular dynamics a system of spherical particles
interacting through an effective two length scales potential is studied. The
potential can be tuned by means of a single parameter, , from a ramp
to a square-shoulder potential representing a
family of two length scales potential in which the shortest interaction
distance has higher potential energy than the largest interaction distance. For
all the potentials, ranging between the ramp and the square-shoulder, density
and structural anomalies were found, while the diffusion anomaly is found in
all but in the square-shoulder potential. The presence anomalies in
square-shoulder potential, not observed in previous simulations, confirm the
assumption that the two length scales potential is an ubiquitous ingredient for
a system to exhibit water-like anomaliesComment: 6 pages, 7 figure
Liquid crystal phase and waterlike anomalies in a core-softened shoulder-dumbbells system
Using molecular dynamics we investigate the thermodynamics, dynamics and
structure of 250 diatomic molecules interacting by a core-softened potential.
This system exhibits thermodynamics, dynamics and structural anomalies: a
maximum in density-temperature plane at constante pressure and maximum and
minimum points in the diffusivity and translational order parameter against
density at constant temperature. Starting with very dense systems and
decreasing density the mobility at low temperatures first increases, reach a
maximum, then decreases, reach a minimum and finally increases. In the
pressure-temperature phase diagram the line of maximum translational order
parameter is located outside the line of diffusivity extrema that is enclosing
the temperature of maximum density line. We compare our results with the
monomeric system showing that the anisotropy due to the dumbbell leads to a
much larger solid phase and to the appearance of a liquid crystal phase. the
double ranged thermodynamic and dynamic anomalies.Comment: 14 pages, 5 figure
Thermodynamic and dynamic anomalies for a three dimensional isotropic core-softened potential
Using molecular dynamics simulations and integral equations (Rogers-Young,
Percus-Yevick and hypernetted chain closures) we investigate the thermodynamic
of particles interacting with continuous core-softened intermolecular
potential. Dynamic properties are also analyzed by the simulations. We show
that, for a chosen shape of the potential, the density, at constant pressure,
has a maximum for a certain temperature. The line of temperatures of maximum
density (TMD) was determined in the pressure-temperature phase diagram.
Similarly the diffusion constant at a constant temperature, , has a maximum
at a density and a minimum at a density .
In the pressure-temperature phase-diagram the line of extrema in diffusivity is
outside of TMD line. Although in this interparticle potential lacks
directionality, this is the same behavior observed in SPC/E water.Comment: 16 page
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