Majority-vote on undirected Barabasi-Albert networks

On Barabasi-Albert networks with z neighbours selected by each added site, the Ising model was seen to show a spontaneous magnetisation. This spontaneous magnetisation was found below a critical temperature which increases logarithmically with system size. On these networks the majority-vote model with noise is now studied through Monte Carlo simulations. However, in this model, the order-disorder phase transition of the order parameter is well defined in this system and this wasn't found to increase logarithmically with system size. We calculate the value of the critical noise parameter q_c for several values of connectivity $z$ of the undirected Barabasi-Albert network. The critical exponentes beta/nu, gamma/nu and 1/nu were calculated for several values of z.Comment: 15 pages with numerous figure

Constraints on Cold Dark Matter Accelerating Cosmologies and Cluster Formation

We discuss the properties of homogeneous and isotropic flat cosmologies in which the present accelerating stage is powered only by the gravitationally induced creation of cold dark matter (CCDM) particles ($\Omega_{m}=1$). For some matter creation rates proposed in the literature, we show that the main cosmological functions such as the scale factor of the universe, the Hubble expansion rate, the growth factor and the cluster formation rate are analytically defined. The best CCDM scenario has only one free parameter and our joint analysis involving BAO + CMB + SNe Ia data yields ${\tilde{\Omega}}_{m}= 0.28\pm 0.01$ ($1\sigma$) where $\tilde{{\Omega}}_{m}$ is the observed matter density parameter. In particular, this implies that the model has no dark energy but the part of the matter that is effectively clustering is in good agreement with the latest determinations from large scale structure. The growth of perturbation and the formation of galaxy clusters in such scenarios are also investigated. Despite the fact that both scenarios may share the same Hubble expansion, we find that matter creation cosmologies predict stronger small scale dynamics which implies a faster growth rate of perturbations with respect to the usual $\Lambda$CDM cosmology. Such results point to the possibility of a crucial observational test confronting CCDM with $\Lambda$CDM scenarios trough a more detailed analysis involving CMB, weak lensing, as well as the large scale structure.Comment: 12 pages, 3 figures, Accepted for publication by Physical Rev.

Nutrição do bovino de corte confinado.

Alimentacao, niveis e fontes de energia, niveis e fontes de proteina, niveis e fontes de minerais, niveis e fontes de vitaminas, antibioticos, manejo, tipo do animal.bitstream/item/43920/1/CPATC-DOCUMENTOS-2-NUTRICAO-DO-BOVINO-DE-CORTE-CONFINADO-FL-13155.pd

Thermodynamics of Decaying Vacuum Cosmologies

The thermodynamic behavior of vacuum decaying cosmologies is investigated within a manifestly covariant formulation. Such a process corresponds to a continuous irreversible energy flow from the vacuum component to the created matter constituents. It is shown that if the specific entropy per particle remains constant during the process, the equilibrium relations are preserved. In particular, if the vacuum decays into photons, the energy density $\rho$ and average number density of photons $n$ scale with the temperature as $\rho \sim T^{4}$ and $n \sim T^{3}$. The temperature law is determined and a generalized Planckian type form of the spectrum, which is preserved in the course of the evolution, is also proposed. Some consequences of these results for decaying vacuum FRW type cosmologies as well as for models with ``adiabatic'' photon creation are discussed.Comment: 21 pages, uses LATE

Interacting dark energy in f(R)f(R) gravity

The field equations in $f(R)$ gravity derived from the Palatini variational principle and formulated in the Einstein conformal frame yield a cosmological term which varies with time. Moreover, they break the conservation of the energy--momentum tensor for matter, generating the interaction between matter and dark energy. Unlike phenomenological models of interacting dark energy, $f(R)$ gravity derives such an interaction from a covariant Lagrangian which is a function of a relativistically invariant quantity (the curvature scalar $R$). We derive the expressions for the quantities describing this interaction in terms of an arbitrary function $f(R)$, and examine how the simplest phenomenological models of a variable cosmological constant are related to $f(R)$ gravity. Particularly, we show that $\Lambda c^2=H^2(1-2q)$ for a flat, homogeneous and isotropic, pressureless universe. For the Lagrangian of form $R-1/R$, which is the simplest way of introducing current cosmic acceleration in $f(R)$ gravity, the predicted matter--dark energy interaction rate changes significantly in time, and its current value is relatively weak (on the order of 1% of $H_0$), in agreement with astronomical observations.Comment: 8 pages; published versio

Higher spin vertex models with domain wall boundary conditions

We derive determinant expressions for the partition functions of spin-k/2 vertex models on a finite square lattice with domain wall boundary conditions.Comment: 14 pages, 12 figures. Minor corrections. Version to appear in JSTA

Inflationary Models Driven by Adiabatic Matter Creation

The flat inflationary dust universe with matter creation proposed by Prigogine and coworkers is generalized and its dynamical properties are reexamined. It is shown that the starting point of these models depends critically on a dimensionless parameter $\Sigma$, closely related to the matter creation rate $\psi$. For $\Sigma$ bigger or smaller than unity flat universes can emerge, respectively, either like a Big-Bang FRW singularity or as a Minkowski space-time at $t=-\infty$. The case $\Sigma=1$ corresponds to a de Sitter-type solution, a fixed point in the phase diagram of the system, supported by the matter creation process. The curvature effects have also been investigated. The inflating de Sitter is a universal attractor for all expanding solutions regardless of the initial conditions as well as of the curvature parameter.Comment: 25 pages, 2 figures(available from the authors), uses LATE