19,857 research outputs found
Exact Lyapunov Exponent for Infinite Products of Random Matrices
In this work, we give a rigorous explicit formula for the Lyapunov exponent
for some binary infinite products of random real matrices. All
these products are constructed using only two types of matrices, and ,
which are chosen according to a stochastic process. The matrix is singular,
namely its determinant is zero. This formula is derived by using a particular
decomposition for the matrix , which allows us to write the Lyapunov
exponent as a sum of convergent series. Finally, we show with an example that
the Lyapunov exponent is a discontinuous function of the given parameter.Comment: 1 pages, CPT-93/P.2974,late
Manejo das pastagens de quicuio-da-amazônia e andropogon em Paragominas, PA.
bitstream/item/57424/1/CPATU-ComTec59.pd
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
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
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
Analysing and controlling the tax evasion dynamics via majority-vote model
Within the context of agent-based Monte-Carlo simulations, we study the
well-known majority-vote model (MVM) with noise applied to tax evasion on
simple square lattices, Voronoi-Delaunay random lattices, Barabasi-Albert
networks, and Erd\"os-R\'enyi random graphs. In the order to analyse and to
control the fluctuations for tax evasion in the economics model proposed by
Zaklan, MVM is applied in the neighborhod of the noise critical . The
Zaklan model had been studied recently using the equilibrium Ising model. Here
we show that the Zaklan model is robust and can be reproduced also through the
nonequilibrium MVM on various topologies.Comment: 18 pages, 7 figures, LAWNP'09, 200
Chemical Potential and the Nature of the Dark Energy: The case of phantom
The influence of a possible non zero chemical potential on the nature
of dark energy is investigated by assuming that the dark energy is a
relativistic perfect simple fluid obeying the equation of state (EoS),
(). The entropy condition, ,
implies that the possible values of are heavily dependent on the
magnitude, as well as on the sign of the chemical potential. For , the
-parameter must be greater than -1 (vacuum is forbidden) while for not only the vacuum but even a phantomlike behavior () is
allowed. In any case, the ratio between the chemical potential and temperature
remains constant, that is, . Assuming that the dark energy
constituents have either a bosonic or fermionic nature, the general form of the
spectrum is also proposed. For bosons is always negative and the extended
Wien's law allows only a dark component with which includes
vacuum and the phantomlike cases. The same happens in the fermionic branch for
are permmited only if . The thermodynamics and statistical arguments constrain the
EoS parameter to be , a result surprisingly close to the maximal
value required to accelerate a FRW type universe dominated by matter and dark
energy ().Comment: 7 pages, 5 figure
On the width of the last scattering surface
We discuss the physical effects of some accelerated world models on the width
of the last scattering surface (LSS) of the cosmic microwave background
radiation (CMBR). The models considered in our analysis are X-matter (XCDM) and
a Chaplygin type gas. The redshift of the LSS does not depend on the kind of
dark energy (if XCDM of Chaplygin). Further, for a Chaplygin gas, the width of
the LSS is also only weakly dependent on the kind of scenario (if we have dark
energy plus cold dark matter or the unified picture).Comment: 10 pages, 1 figure, 2 tables, accepted to IJMP
Fruit development of three guava cultivars (Psidium guajava L.).
The knowledge of guava fruiting cycle is of great interest not only due to its biological aspects but also as an important datum for the application of cultural practices. This paper was carried out in the submedio Sao Francisco region on four-year old plants, from the germplasm bank of EMBRAPA-CPATSA. The objective was to study the fruit growth pattern of the guava cultivars Patillo, Paluma and Red Selection of Florida. Fruit length and diameter were monitored on twenty-day intervals, resulting on double sigmoidal curves, and characterizing three growth periods, for the cultivars. The results showed that, within the experimental period, the cultivars Red Selection of FLorida and Paluma had about the same diameter and length growth rate, with a mean value of 0.036 cm/day and 0.042 cm/day, respectively. However ,the biggest fruit size was observed for the cv. Red Selection of Florida. The cv. Patillo had the lowest fruit growth rate, with an increment of 0.027 cm/day in diameter and 0.033 cm/day in lenght
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