3,226 research outputs found
Nature of the collapse transition in interacting self-avoiding trails
We study the interacting self-avoiding trail (ISAT) model on a Bethe lattice
of general coordination and on a Husimi lattice built with squares and
coordination . The exact grand-canonical solutions of the model are
obtained, considering that up to monomers can be placed on a site and
associating a weight for a -fold visited site. Very rich phase
diagrams are found with non-polymerized (NP), regular polymerized (P) and dense
polymerized (DP) phases separated by lines (or surfaces) of continuous and
discontinuous transitions. For Bethe lattice with and , the collapse
transition is identified with a bicritical point and the collapsed phase is
associated to the dense polymerized phase (solid-like) instead of the regular
polymerized phase (liquid-like). A similar result is found for the Husimi
lattice, which may explain the difference between the collapse transition for
ISAT's and for interacting self-avoiding walks on the square lattice. For
and (studied on the Bethe lattice only), a more complex phase diagram is
found, with two critical planes and two coexistence surfaces, separated by two
tricritical and two critical end-point lines meeting at a multicritical point.
The mapping of the phase diagrams in the canonical ensemble is discussed and
compared with simulational results for regular lattices.Comment: 12 pages, 13 figure
Lorentz-violating Yang-Mills theory: discussing the Chern-Simons-like term generation
We analyze the Chern-Simons-like term generation in the CPT-odd
Lorentz-violating Yang-Mills theory interacting with fermions. Moreover, we
study the anomalies of this model as well as its quantum stability. The whole
analysis is performed within the algebraic renormalization theory, which is
independent of the renormalization scheme. In addition, all results are valid
to all orders in perturbation theory. We find that the Chern-Simons-like term
is not generated by radiative corrections, just like its Abelian version.
Additionally, the model is also free of gauge anomalies and quantum stable.Comment: 16 pages. No figures. Final version to appear in the Eur.Phys.J.
A State-of-the-art Integrated Transportation Simulation Platform
Nowadays, universities and companies have a huge need for simulation and
modelling methodologies. In the particular case of traffic and transportation,
making physical modifications to the real traffic networks could be highly
expensive, dependent on political decisions and could be highly disruptive to
the environment. However, while studying a specific domain or problem,
analysing a problem through simulation may not be trivial and may need several
simulation tools, hence raising interoperability issues. To overcome these
problems, we propose an agent-directed transportation simulation platform,
through the cloud, by means of services. We intend to use the IEEE standard HLA
(High Level Architecture) for simulators interoperability and agents for
controlling and coordination. Our motivations are to allow multiresolution
analysis of complex domains, to allow experts to collaborate on the analysis of
a common problem and to allow co-simulation and synergy of different
application domains. This paper will start by presenting some preliminary
background concepts to help better understand the scope of this work. After
that, the results of a literature review is shown. Finally, the general
architecture of a transportation simulation platform is proposed
Densifying the sparse cloud SimSaaS: The need of a synergy among agent-directed simulation, SimSaaS and HLA
Modelling & Simulation (M&S) is broadly used in real scenarios where making
physical modifications could be highly expensive. With the so-called Simulation
Software-as-a-Service (SimSaaS), researchers could take advantage of the huge
amount of resource that cloud computing provides. Even so, studying and
analysing a problem through simulation may need several simulation tools, hence
raising interoperability issues. Having this in mind, IEEE developed a standard
for interoperability among simulators named High Level Architecture (HLA).
Moreover, the multi-agent system approach has become recognised as a convenient
approach for modelling and simulating complex systems. Despite all the recent
works and acceptance of these technologies, there is still a great lack of work
regarding synergies among them. This paper shows by means of a literature
review this lack of work or, in other words, the sparse Cloud SimSaaS. The
literature review and the resulting taxonomy are the main contributions of this
paper, as they provide a research agenda illustrating future research
opportunities and trends
Solution on the Bethe lattice of a hard core athermal gas with two kinds of particles
Athermal lattice gases of particles with first neighbor exclusion have been
studied for a long time as simple models exhibiting a fluid-solid transition.
At low concentration the particles occupy randomly both sublattices, but as the
concentration is increased one of the sublattices is occupied preferentially.
Here we study a mixed lattice gas with excluded volume interactions only in the
grand-canonical formalism with two kinds of particles: small ones, which occupy
a single lattice site and large ones, which occupy one site and its first
neighbors. We solve the model on a Bethe lattice of arbitrary coordination
number . In the parameter space defined by the activities of both particles.
At low values of the activity of small particles () we find a continuous
transition from the fluid to the solid phase as the activity of large particles
() is increased. At higher values of the transition becomes
discontinuous, both regimes are separated by a tricritical point. The critical
line has a negative slope at and displays a minimum before reaching the
tricritical point, so that a reentrant behavior is observed for constant values
of in the region of low density of small particles. The isobaric curves
of the total density of particles as a function of (or ) show a
minimum in the fluid phase.Comment: 18 pages, 5 figures, 1 tabl
Towards a taxonomy of innovation systems
The concept of National Innovation System (NIS) has been recently applied in the context of developing nations even tough it was originally developed in relation to the more developed economies (Japan, Scandinavian countries, US etc.). This raises the methodological problem of knowing whether what was learnt in the study of more advanced NISs is relevant for all sorts of economies regardless the maturity of their actual innovation systems. With this question in mind an exploratory exercise is implemented. First a technique for mapping different NIS is put forward and next based on such mapping a taxonomy of NISs is proposed. The technique although simple in the steps it requires shows analytical potential. The cartography it generates allows one to compare directly different countries, by visualizing in bi-dimensional space the graphic pattern of the relevant dimensions of their respective NISs. This technique is applied to 69 countries (87.4% of the world population) and a set of 29 indicators is used to examine these NISs along eight major dimensions. With the resulting data, and with the help of cluster analysis, a taxonomy of innovation systems is proposed. That taxonomy which contains 6 major types of NISs indicates that what differentiates most the individual systems is their performance in three critical dimensions: innovation, diffusion and basic and applied knowledge. Country size and the natural resources endowment of the economies also emerge as important contingency factors underlying the overall dynamics of different NISs.innovation; national innovation systems; economic development.
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