28,707 research outputs found
Integration of an object formalism within a hybrid dynamic simulation environment
PrODHyS is a general object-oriented environment which provides common and reusable components designed for the development and the management of dynamic simulation of systems engineering. Its major characteristic is its ability to simulate processes described by a hybrid model. In this framework, this paper focuses on the "Object Differential Petri Net" (ODPN) formalism integrated within PrODHyS. The use of this formalism is illustrated through a didactic example relating to the field of Chemical Process System Engineering (PSE)
Systematic Microcanonical Analyses of Polymer Adsorption Transitions
In detailed microcanonical analyses of densities of states obtained by
extensive multicanonical Monte Carlo computer simulations, we investigate the
caloric properties of conformational transitions adsorbing polymers experience
near attractive substrates. For short chains and strong surface attraction, the
microcanonical entropy turns out to be a convex function of energy in the
transition regime, indicating that surface-entropic effects are relevant.
Albeit known to be a continuous transition in the thermodynamic limit of
infinitely long chains, the adsorption transition of nongrafted finite-length
polymers thus exhibits a clear signature of a first-order-like transition, with
coexisting phases of adsorbed and desorbed conformations. Another remarkable
consequence of the convexity of the microcanonical entropy is that the
transition is accompanied by a decrease of the microcanonical temperature with
increasing energy. Since this is a characteristic physical effect it might not
be ignored in analyses of cooperative macrostate transitions in finite systems.Comment: 8 pages, 6 figure
General approach for studying first-order phase transitions at low temperatures
By combining different ideas, a general and efficient protocol to deal with
discontinuous phase transitions at low temperatures is proposed. For small
's, it is possible to derive a generic analytic expression for appropriate
order parameters, whose coefficients are obtained from simple simulations. Once
in such regimes simulations by standard algorithms are not reliable, an
enhanced tempering method, the parallel tempering -- accurate for small and
intermediate system sizes with rather low computational cost -- is used.
Finally, from finite size analysis, one can obtain the thermodynamic limit. The
procedure is illustrated for four distinct models, demonstrating its power,
e.g., to locate coexistence lines and the phases density at the coexistence.Comment: 5 page
Giant Magnetoelastic Effects in BaTiO3-based Extrinsic Multiferroic Hybrids
Extrinsic multiferroic hybrid structures consisting of ferromagnetic and
ferroelectric layers elastically coupled to each other are promising due to
their robust magnetoelectric effects even at room temperature. For a
quantitative analysis of these magnetoelectric effects, a detailed knowledge of
the piezoelectric and magnetoelastic behavior of both constituents as well as
their mutual elastic coupling is mandatory. We here report on a theoretical and
experimental study of the magnetic behavior of BaTiO3-based extrinsic
multiferroic structures. An excellent agreement between molecular dynamics
simulations and the experiments was found for Fe50Co50/BaTiO3 and Ni/BaTiO3
hybrid structures. This demonstrates that the magnetic behavior of extrinsic
multiferroic hybrid structures can be determined by means of ab-initio
calculations, allowing for the design of novel multiferroic hybrids
The Ising model in a Bak-Tang-Wiesenfeld sandpile
We study the spin-1 Ising model with non-local constraints imposed by the
Bak-Tang-Wiesenfeld sandpile model of self-organized criticality (SOC). The
model is constructed as if the sandpile is being built on a (honeycomb) lattice
with Ising interactions. In this way we combine two models that exhibit
power-law decay of correlation functions characterized by different exponents.
We discuss the model properties through an order parameter and the mean energy
per node, as well as the temperature dependence of their fourth-order Binder
cumulants. We find (i) a thermodynamic phase transition at a finite T_c between
paramagnetic and antiferromagnetic phases, and (ii) that above T_c the
correlation functions decay in a way typical of SOC. The usual thermodynamic
criticality of the two-dimensional Ising model is not affected by SOC
constraints (the specific heat critical exponent \alpha \approx 0), nor are
SOC-induced correlations affected by the interactions of the Ising model. Even
though the constraints imposed by the SOC model induce long-range correlations,
as if at standard (thermodynamic) criticality, these SOC-induced correlations
have no impact on the thermodynamic functions.Comment: 9 page
Contact-Density Analysis of Lattice Polymer Adsorption Transitions
By means of contact-density chain-growth simulations, we investigate a simple
lattice model of a flexible polymer interacting with an attractive substrate.
The contact density is a function of the numbers of monomer-substrate and
monomer-monomer contacts. These contact numbers represent natural order
parameters and allow for a comprising statistical study of the conformational
space accessible to the polymer in dependence of external parameters such as
the attraction strength of the substrate and the temperature. Since the contact
density is independent of the energy scales associated to the interactions, its
logarithm is an unbiased measure for the entropy of the conformational space.
By setting explicit energy scales, the thus defined, highly general
microcontact entropy can easily be related to the microcanonical entropy of the
corresponding hybrid polymer-substrate system.Comment: 5 pages, 3 figures, Proceedings of the 23nd Workshop on Recent
Developments in Computer Simulation Studies in Condensed Matter Physics, Feb
22-26, 2010, Athens, Georgia, US
Explosive Percolation: Unusual Transitions of a Simple Model
In this paper we review the recent advances on explosive percolation, a very
sharp phase transition first observed by Achlioptas et al. (Science, 2009).
There a simple model was proposed, which changed slightly the classical
percolation process so that the emergence of the spanning cluster is delayed.
This slight modification turns out to have a great impact on the percolation
phase transition. The resulting transition is so sharp that it was termed
explosive, and it was at first considered to be discontinuous. This surprising
fact stimulated considerable interest in "Achlioptas processes". Later work,
however, showed that the transition is continuous (at least for Achlioptas
processes on Erdos networks), but with very unusual finite size scaling. We
present a review of the field, indicate open "problems" and propose directions
for future research.Comment: 27 pages, 4 figures, Review pape
Unraveling the thermodynamic conditions for negative gas adsorption in soft porous crystals
Soft porous crystals (SPCs) are widely known for their intriguing properties and various counterintuitive phenomena such as negative linear compression, negative thermal expansion and negative gas adsorption (NGA). An intriguing case is the adsorption of methane in DUT-49 for which experimentally a drop in the amount of adsorbed particles was observed under increasing vapor pressure. It is yet unknown which specific systems can exhibit NGA under which thermodynamic conditions. Herein, a semi-analytical thermodynamic model is applied to determine the conditions required for NGA, including their sensitivity towards various system-specific parameters, and investigate the correlation with pressure-induced breathing. As such, it is found that certain non-breathing materials may exhibit breathing with NGA under application of a fixed mechanical pressure. Such meticulous control of multiple triggers for NGA can open the way to new applications such as tunable gas detection and pressure amplification
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