5,419 research outputs found
Common Representation of Information Flows for Dynamic Coalitions
We propose a formal foundation for reasoning about access control policies
within a Dynamic Coalition, defining an abstraction over existing access
control models and providing mechanisms for translation of those models into
information-flow domain. The abstracted information-flow domain model, called a
Common Representation, can then be used for defining a way to control the
evolution of Dynamic Coalitions with respect to information flow
The fallacy of general purpose bio-inspired computing
Bio-inspired computing comes in many flavours, inspired by biological systems from which salient features and/or organisational principles have been idealised and abstracted. These bio-inspired schemes have sometimes been demonstrated to be general purpose; able to approximate arbitrary dynamics, encode arbitrary structures, or even carry out universal computation. The generality of these abilities is typically (although often implicitly) reasoned to be an attractive and worthwhile trait. Here, it is argued that such reasoning is fallacious. Natural systems are nichiversal rather than universal, and we should expect the computational systems that they inspire to be similarly limited in their performance, even if they are ultimately capable of generality in their competence. Practical and methodological implications of this position for the use of bio-inspired computing within artificial life are outlined
Impact of Interaction Range and Curvature on Crystal Growth of Particles Confined to Spherical Surfaces
When colloidal particles form a crystal phase on a spherical template, their
packing is governed by the effective interaction between them and the elastic
strain of bending the growing crystal. For example, if growth commences under
appropriate conditions, and the circular crystal that forms reaches a critical
size, growth continues by incorporation of defects to alleviate elastic strain.
Recently it was found experimentally that, if defect formation is somehow not
possible, the crystal instead continues growing in ribbons that protrude from
the original crystal. Here we report on computer simulations in which we
observe both the formation of ribbons at short interaction ranges and packings
that incorporate defects if the interaction is longer-ranged. The ribbons only
form above some critical crystal size, below which the nucleus is roughly
spherically shaped. We find that the scaling of the critical crystal size
differs slightly from the one proposed by the Manoharan group, and reason this
is because the actual process is a two-step heterogeneous nucleation of ribbons
on top of roughly circular crystals.Comment: 24 pages, 11 figure
Competition of coarsening and shredding of clusters in a driven diffusive lattice gas
We investigate a driven diffusive lattice gas model with two oppositely
moving species of particles. The model is motivated by bi-directional traffic
of ants on a pre-existing trail. A third species, corresponding to pheromones
used by the ants for communication, is not conserved and mediates interactions
between the particles. Here we study the spatio-temporal organization of the
particles. In the uni-directional variant of this model it is known to be
determined by the formation and coarsening of ``loose clusters''. For our
bi-directional model, we show that the interaction of oppositely moving
clusters is essential. In the late stages of evolution the cluster size
oscillates because of a competition between their `shredding' during encounters
with oppositely moving counterparts and subsequent "coarsening" during
collision-free evolution. We also establish a nontrivial dependence of the
spatio-temporal organization on the system size
A three-dimensional lattice gas model for amphiphilic fluid dynamics
We describe a three-dimensional hydrodynamic lattice-gas model of amphiphilic
fluids. This model of the non-equilibrium properties of oil-water-surfactant
systems, which is a non-trivial extension of an earlier two-dimensional
realisation due to Boghosian, Coveney and Emerton [Boghosian, Coveney, and
Emerton 1996, Proc. Roy. Soc. A 452, 1221-1250], can be studied effectively
only when it is implemented using high-performance computing and visualisation
techniques. We describe essential aspects of the model's theoretical basis and
computer implementation, and report on the phenomenological properties of the
model which confirm that it correctly captures binary oil-water and
surfactant-water behaviour, as well as the complex phase behaviour of ternary
amphiphilic fluids.Comment: 34 pages, 13 figures, high resolution figures available on reques
Grid service orchestration using the Business Process Execution Language (BPEL)
Modern scientific applications often need to be distributed across grids. Increasingly
applications rely on services, such as job submission, data transfer or data
portal services. We refer to such services as grid services. While the invocation
of grid services could be hard coded in theory, scientific users want to orchestrate
service invocations more flexibly. In enterprise applications, the orchestration of
web services is achieved using emerging orchestration standards, most notably
the Business Process Execution Language (BPEL). We describe our experience
in orchestrating scientific workflows using BPEL. We have gained this experience
during an extensive case study that orchestrates grid services for the automation of
a polymorph prediction application
Perspectives of Nuclear Physics in Europe: NuPECC Long Range Plan 2010
The goal of this European Science Foundation Forward Look into the future of Nuclear Physics is to bring together
the entire Nuclear Physics community in Europe to formulate a coherent plan of the best way to develop the field in
the coming decade and beyond.<p></p>
The primary aim of Nuclear Physics is to understand the origin, evolution, structure and phases of strongly interacting matter, which constitutes nearly 100% of the visible matter in the universe. This is an immensely important and challenging task that requires the concerted effort of scientists working in both theory and experiment, funding agencies, politicians and the public.<p></p>
Nuclear Physics projects are often âbig scienceâ, which implies large investments and long lead times. They need careful forward planning and strong support from policy makers. This Forward Look provides an excellent tool to achieve this. It represents the outcome of detailed scrutiny by Europeâs leading experts and will help focus the views of the scientific community on the most promising directions in the field and create the basis for funding agencies to provide adequate support.<p></p>
The current NuPECC Long Range Plan 2010 âPerspectives of Nuclear Physics in Europeâ resulted from consultation
with close to 6 000 scientists and engineers over a period of approximately one year. Its detailed recommendations
are presented on the following pages. For the interested public, a short summary brochure has been produced to
accompany the Forward Look.<p></p>
Micelle formation, gelation and phase separation of amphiphilic multiblock copolymers
The phase behaviour of amphiphilic multiblock copolymers with a large number
of blocks in semidilute solutions is studied by lattice Monte Carlo
simulations. The influence on the resulting structures of the concentration,
the solvent quality and the ratio of hydrophobic to hydrophilic monomers in the
chains has been assessed explicitely. Several distinct regimes are put in
evidence. For poorly substituted (mainly hydrophilic) copolymers formation of
micelles is observed, either isolated or connected by the hydrophilic moieties,
depending on concentration and chain length. For more highly substituted chains
larger tubular hydrophobic structures appear which, at higher concentration,
join to form extended hydrophobic cores. For both substitution ratios gelation
is observed, but with a very different gel network structure. For the poorly
substituted chains the gel consists of micelles cross-linked by hydrophilic
blocks whereas for the highly substituted copolymers the extended hydrophobic
cores form the gelling network. The interplay between gelation and phase
separation clearly appears in the phase diagram. In particular, for poorly
substituted copolymers and in a narrow concentration range, we observe a
sol-gel transition followed by an inverse gel-sol transition when increasing
the interaction energy. The simulation results are discussed in the context of
the experimentally observed phase properties of methylcellulose, a
hydrophobically substituted polysaccharide.Comment: 14 pages, 14 figures; Soft Matter (2011
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