425 research outputs found
Developing frameworks for protocol implementation
This paper presents a method to develop frameworks for protocol implementation. Frameworks are software structures developed for a specific application domain, which can be reused in the implementation of various different concrete systems in this domain. The use of frameworks support a protocol implementation process connected with formal design methods and produce an implementation code easy to extend and to reuse
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
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
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
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
Entropy, diffusivity and the energy landscape of a water-like fluid
Molecular dynamics simulations and instantaneous normal mode (INM) analysis
of a fluid with core-softened pair interactions and water-like liquid-state
anomalies are performed to obtain an understanding of the relationship between
thermodynamics, transport properties and the poten- tial energy landscape.
Rosenfeld-scaling of diffusivities with the thermodynamic excess and pair
correlation entropy is demonstrated for this model. The INM spectra are shown
to carry infor- mation about the dynamical consequences of the interplay
between length scales characteristic of anomalous fluids, such as bimodality of
the real and imaginary branches of the frequency distribu- tion. The INM
spectral information is used to partition the liquid entropy into two
contributions associated with the real and imaginary frequency modes; only the
entropy contribution from the imaginary branch captures the non-monotonic
behaviour of the excess entropy and diffusivity in the anomalous regime of the
fluid
Postmenopausal Osteoporosis reference genes for qPCR expression assays
Osteoporosis (OP) is a multifactorial disease influenced by genetic factors in more than half of the cases. In spite of the efforts to clarify the relationship among genetic factors and susceptibility to develop OP, many genetic associations need to be further functionally validated. Besides, some limitations as the choice of stably expressed reference genes (RG) should be overcome to ensure the quality and reproducibility of gene expression assays. To our knowledge, a validation study for RG in OP is still missing. We compared the expression levels, using polymerase chain reaction quantitative real time (qPCR) of 10 RG (G6PD, B2M, GUSB, HSP90, EF1A, RPLP0, GAPDH, ACTB, 18 S and HPRT1) to assess their suitability in OP analysis by using GeNorm, Normfinder, BestKeeper and RefFinder programs. A minimal number of two RG was recommended by GeNorm to obtain a reliable normalization. RPLP0 and B2M were identified as the most stable genes in OP studies while ACTB, 18 S and HPRT1 were inadequate for normalization in our data set. Moreover, we showed the dramatic effects of suboptimal RG choice on the quantification of a target gene, highlighting the importance in the identification of the most appropriate reference gene to specific diseases. We suggest the use of RPLP0 and B2M as the most stable reference genes while we do not recommend the use of the least stable reference genes HPRT1, 18 S and ACTB in OP expression assays using PBMC as biological source. Additionally, we emphasize the importance of individualized and careful choice in software and reference genes selection
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