12,257 research outputs found
Density of states of a binary Lennard-Jones Glass
We calculate the density of states of a binary Lennard-Jones glass using a
recently proposed Monte Carlo algorithm. Unlike traditional molecular
simulation approaches, the algorithm samples distinct configurations according
to self-consistent estimates of the density of states, thereby giving rise to
uniform internal-energy histograms. The method is applied to simulate the
equilibrium, low-temperature thermodynamic properties of a widely studied glass
former consisting of a binary mixture of Lennard-Jones particles. We show how a
density-of-states algorithm can be combined with particle identity swaps and
configurational bias techniques to study that system. Results are presented for
the energy and entropy below the mode coupling temperature.Comment: 6 pages, 3 figures, accepted by J Chem Phy
Constant Pressure Hybrid Molecular Dynamics-Monte Carlo Simulations
New hybrid Molecular Dynamics-Monte Carlo methods are proposed to increase
the efficiency of constant-pressure simulations. Two variations of the isobaric
Molecular Dynamics component of the algorithms are considered. In the first, we
use the extended-ensemble method of Andersen [H. C. Andersen J. Chem. Phys.
{\bf 72},2384 (1980)]. In the second, we arrive at a new constant-pressure
Monte Carlo technique based on the reversible generalization of the
weak-coupling barostat [H. J. C. Berendsen et. al J. Chem. Phys. {\bf 81},
3684(1984)]. This latter technique turns out to be highly effective in
equilibrating and maintaining a target pressure. It is superior to the
extended-ensemble method, which in turn is superior to simple volume-rescaling
algorithms. The efficiency of the proposed methods is demonstrated by studying
two systems. The first is a simple Lennard-Jones fluid. The second is a mixture
of polyethylene chains of 200 monomers.Comment: 10 pages, 4 figure
Lyapunov-type Inequalities for Partial Differential Equations
In this work we present a Lyapunov inequality for linear and quasilinear
elliptic differential operators in dimensional domains . We also
consider singular and degenerate elliptic problems with coefficients
involving the Laplace operator with zero Dirichlet boundary condition.
As an application of the inequalities obtained, we derive lower bounds for
the first eigenvalue of the Laplacian, and compare them with the usual ones
in the literature
A Reformulation of Matrix Graph Grammars with Boolean Complexes
Prior publication in the Electronic Journal of Combinatorics.Graph transformation is concerned with the manipulation of graphs by means of rules. Graph grammars have been traditionally studied using techniques from category theory. In previous works, we introduced Matrix Graph Grammars (MGG) as a purely algebraic approach for the study of graph dynamics, based on the representation of simple graphs by means of their adjacency matrices.
The observation that, in addition to positive information, a rule implicitly defines negative conditions for its application (edges cannot become dangling, and cannot be added twice as we work with simple digraphs) has led to a representation of graphs as two matrices encoding positive and negative information. Using this representation, we have reformulated the main concepts in MGGs, while we have introduced other new ideas. In particular, we present (i) a new formulation of productions together with an abstraction of them (so called swaps), (ii) the notion of coherence, which checks whether a production sequence can be potentially applied, (iii) the minimal graph enabling the applicability of a sequence, and (iv) the conditions for compatibility of sequences (lack of dangling edges) and G-congruence (whether two sequences have the same minimal initial graph).This work has been partially sponsored by the Spanish Ministry of Science and Innovation, project METEORIC (TIN2008-02081/TIN)
Argentina: Debt and Macroeconomic Instability
The paper reviews the Argentine debt experience in the past ten years. The emphasis is on the interaction between relative prices, financial instability, budget .deficits, inflation and debt accumulation. A longer run perspective shows that the continuing fiscal problems have stood in the way of investment and growth.
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