567 research outputs found
Contracts and Behavioral Patterns for SoS: The EU IP DANSE approach
This paper presents some of the results of the first year of DANSE, one of
the first EU IP projects dedicated to SoS. Concretely, we offer a tool chain
that allows to specify SoS and SoS requirements at high level, and analyse them
using powerful toolsets coming from the formal verification area. At the high
level, we use UPDM, the system model provided by the british army as well as a
new type of contract based on behavioral patterns. At low level, we rely on a
powerful simulation toolset combined with recent advances from the area of
statistical model checking. The approach has been applied to a case study
developed at EADS Innovation Works.Comment: In Proceedings AiSoS 2013, arXiv:1311.319
Attraction and ionic correlations between charged stiff polyelectrolytes
We use Molecular Dynamics simulations to study attractive interactions and
the underlying ionic correlations between parallel like-charged rods in the
absence of additional salt. For a generic bulk system of rods we identify a
reduction of short range repulsions as the origin of a negative osmotic
coefficient. The counterions show signs of a weak three-dimensional order in
the attractive regime only once the rod-imposed charge-inhomogeneities are
divided out. We also treat the case of attraction between a single pair of rods
for a few selected line charge densities and rod radii. Measurements of the
individual contributions to the force between close rods are studied as a
function of Bjerrum length. We find that even though the total force is always
attractive at sufficiently high Bjerrum length, the electrostatic contribution
can ultimately become repulsive. We also measure azimuthal and longitudinal
correlation functions to answer the question how condensed ions are distributed
with respect to each other and to the neighboring rod. For instance, we show
that the prevalent image of mutually interlocked ions is qualitatively correct,
even though modifications due to thermal fluctuations are usually strong.Comment: 14 pages, 14 figures, REVTeX4 styl
Electrostatics in Periodic Slab Geometries I
We propose a new method to sum up electrostatic interactions in 2D slab
geometries. It consists of a combination of two recently proposed methods, the
3D Ewald variant of Yeh and Berkowitz, J. Chem. Phys. 111 (1999) 3155, and the
purely 2D method MMM2D by Arnold and Holm, to appear in Chem. Phys. Lett. 2002.
The basic idea involves two steps. First we use a three dimensional summation
method whose summation order is changed to sum up the interactions in a
slab-wise fashion. Second we subtract the unwanted interactions with the
replicated layers analytically. The resulting method has full control over the
introduced errors. The time to evaluate the layer correction term scales
linearly with the number of charges, so that the full method scales like an
ordinary 3D Ewald method, with an almost linear scaling in a mesh based
implementation. In this paper we will introduce the basic ideas, derive the
layer correction term and numerically verify our analytical results.Comment: 10 pages, 7 figure
Electrostatics in Periodic Slab Geometries II
In a previous paper a method was developed to subtract the interactions due
to periodically replicated charges (or other long-range entities) in one
spatial dimension. The method constitutes a generalized "electrostatic layer
correction" (ELC) which adapts any standard 3D summation method to slab-like
conditions. Here the implementation of the layer correction is considered in
detail for the standard Ewald (EW3DLC) and the PPPM mesh Ewald (PPPMLC)
methods. In particular this method offers a strong control on the accuracy and
an improved computational complexity of O(N log N) for mesh-based
implementations. We derive anisotropic Ewald error formulas and give some
fundamental guidelines for optimization. A demonstration of the accuracy, error
formulas and computation times for typical systems is also presented.Comment: 14 pages, 7 figure
Attraction and unbinding of like-charged rods
We investigate the effective interaction between two like-charged rods in the
regime of large electrostatic coupling parameters using both Molecular Dynamics
simulation techniques and the recently introduced strong-coupling theory. We
obtain attraction between the rods for elevated Manning parameters accompanied
by an equilibrium surface-to-surface separation of the order of the
Gouy-Chapman length. A continuous unbinding between the rods is predicted at a
threshold Manning parameter of 2/3.Comment: 8 pages, 2 figure
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