22,967 research outputs found
Sliding Blocks Revisited: A simulational Study
A computational study of sliding blocks on inclined surfaces is presented.
Assuming that the friction coefficient is a function of position, the
probability for the block to slide down over a length is
numerically calculated. Our results are consistent with recent experimental
data suggesting a power-law distribution of events over a wide range of
displacements when the chute angle is close to the critical one, and suggest
that the variation of along the surface is responsible for this.Comment: 6 pages, 4 figures. submitted to Int. J. Mod. Phys. (Proc. Brazilian
Wokshop on Simulational Physics
Análise da estrutura de uma vegetação ciliar do rio São Francisco no Projeto de Irrigação Bebedouro, Petrolina-PE.
O presente trabalho foi realizado na vegetação ciliar do Rio S ão Francisco, no Projeto de I rrigação Bebedouro, em Petrolina-PE
Persistence in the zero-temperature dynamics of the -states Potts model on undirected-directed Barab\'asi-Albert networks and Erd\"os-R\'enyi random graphs
The zero-temperature Glauber dynamics is used to investigate the persistence
probability in the Potts model with , ,..., states on {\it directed} and {\it
undirected} Barab\'asi-Albert networks and Erd\"os-R\'enyi random graphs. In
this model it is found that decays exponentially to zero in short times
for {\it directed} and {\it undirected} Erd\"os-R\'enyi random graphs. For {\it
directed} and {\it undirected} Barab\'asi-Albert networks, in contrast it
decays exponentially to a constant value for long times, i.e, is
different from zero for all values (here studied) from ; this shows "blocking" for all these values. Except that for
in the {\it undirected} case tends exponentially to zero;
this could be just a finite-size effect since in the other "blocking" cases you
may have only a few unchanged spins.Comment: 14 pages, 8 figures for IJM
Monitoring strategies for “Ponta da Ferraria e Pico das Camarinhas” geosite (S. Miguel Island, Azores)
This paper presents an ongoing work that is being developed under the scope of a master thesis. “Ponta da Ferraria e Pico das Camarinhas” is a protected area and a geosite with high geological relevance in S. Miguel Island, Azores archipelago, Portugal. Because of its importance for the Azores Geopark geoconservation strategy, a monitoring work has been under development during the last year in order to assure that the main geological features of the geosite are preserved, even considering its present use. Among the many geological features of the geosite the littoral cone (or pseudocrater) is the most endangered due to its uniqueness and high vulnerability. The monitoring strategy also intends to assess how visitors evaluate the interpretative panel located in the geosite based on visitors’ opinions. The number of visitors is being determined by direct counting and the visitors’ profile is being outlined based on data obtained with short questionnaires
Dynamical complexity of discrete time regulatory networks
Genetic regulatory networks are usually modeled by systems of coupled
differential equations and by finite state models, better known as logical
networks, are also used. In this paper we consider a class of models of
regulatory networks which present both discrete and continuous aspects. Our
models consist of a network of units, whose states are quantified by a
continuous real variable. The state of each unit in the network evolves
according to a contractive transformation chosen from a finite collection of
possible transformations, according to a rule which depends on the state of the
neighboring units. As a first approximation to the complete description of the
dynamics of this networks we focus on a global characteristic, the dynamical
complexity, related to the proliferation of distinguishable temporal behaviors.
In this work we give explicit conditions under which explicit relations between
the topological structure of the regulatory network, and the growth rate of the
dynamical complexity can be established. We illustrate our results by means of
some biologically motivated examples.Comment: 28 pages, 4 figure
Clustering, Angular Size and Dark Energy
The influence of dark matter inhomogeneities on the angular size-redshift
test is investigated for a large class of flat cosmological models driven by
dark energy plus a cold dark matter component (XCDM model). The results are
presented in two steps. First, the mass inhomogeneities are modeled by a
generalized Zeldovich-Kantowski-Dyer-Roeder (ZKDR) distance which is
characterized by a smoothness parameter and a power index ,
and, second, we provide a statistical analysis to angular size data for a large
sample of milliarcsecond compact radio sources. As a general result, we have
found that the parameter is totally unconstrained by this sample of
angular diameter data.Comment: 9 pages, 7 figures, accepted in Physical Review
Validity of the N\'{e}el-Arrhenius model for highly anisotropic Co_xFe_{3-x}O_4 nanoparticles
We report a systematic study on the structural and magnetic properties of
Co_{x}Fe_{3-x}O_{4} magnetic nanoparticles with sizes between to nm,
prepared by thermal decomposition of Fe(acac)_{3} and Co(acac)_{2}. The large
magneto-crystalline anisotropy of the synthesized particles resulted in high
blocking temperatures ( K \leqq K for d nm ) and large coercive fields ( kA/m for K).
The smallest particles ( nm) revealed the existence of a magnetically
hard, spin-disordered surface. The thermal dependence of static and dynamic
magnetic properties of the whole series of samples could be explained within
the N\'{e}el-Arrhenius relaxation framework without the need of ad-hoc
corrections, by including the thermal dependence of the magnetocrystalline
anisotropy constant through the empirical Br\"{u}khatov-Kirensky
relation. This approach provided values very similar to the bulk
material from either static or dynamic magnetic measurements, as well as
realistic values for the response times ( s).
Deviations from the bulk anisotropy values found for the smallest particles
could be qualitatively explained based on Zener\'{}s relation between
and M(T)
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