Neutrinos and Electromagnetic Gauge Invariance

It is discussed a recently proposed connection among U(1)$_{\rm em}$ electromagnetic gauge invariance and the nature of the neutrino mass terms in the framework of \mbox {SU(3)}_C\otimes G_W \otimes {\mbox U(1)}_N, $G_W$ = SU(3)$_L$, extensions of the Standard Model. The impossibility of that connection, also in the extended case $G_W$ = SU(4)$_L$, is demonstrated.Comment: 10 pages, Revtex 3.0, no figure

Quasi-Topological Field Theories in Two Dimensions as Soluble Models

We study a class of lattice field theories in two dimensions that includes gauge theories. Given a two dimensional orientable surface of genus $g$, the partition function $Z$ is defined for a triangulation consisting of $n$ triangles of area $\epsilon$. The reason these models are called quasi-topological is that $Z$ depends on $g$, $n$ and $\epsilon$ but not on the details of the triangulation. They are also soluble in the sense that the computation of their partition functions can be reduced to a soluble one dimensional problem. We show that the continuum limit is well defined if the model approaches a topological field theory in the zero area limit, i.e., $\epsilon \to 0$ with finite $n$. We also show that the universality classes of such quasi-topological lattice field theories can be easily classified. Yang-Mills and generalized Yang-Mills theories appear as particular examples of such continuum limits.Comment: 23 pages, 16 figures, uses psbox.te

Estudo das combinação de fertilizantes orgânicos e químicos na produção da massa foliar da sacaca (Croton cajucara Benth).

Informações sobre práticas fitotécnicas para eficientizar o cultivo de sacaca e, assim, fornecer indicações agrícolas para a melhoria do nível de qualidade dos produtos fitoterápicos no Amazonas.bitstream/CPAA-2009-09/2732/1/Com_Tec_13.pd

Lattices and Their Continuum Limits

We address the problem of the continuum limit for a system of Hausdorff lattices (namely lattices of isolated points) approximating a topological space $M$. The correct framework is that of projective systems. The projective limit is a universal space from which $M$ can be recovered as a quotient. We dualize the construction to approximate the algebra ${\cal C}(M)$ of continuous functions on $M$. In a companion paper we shall extend this analysis to systems of noncommutative lattices (non Hausdorff lattices).Comment: 11 pages, 1 Figure included in the LaTeX Source New version, minor modifications (typos corrected) and a correction in the list of author

The Role of Interest Rates in the Brazilian Business Cycle

This paper offers additional insights on the relationship between interest rates and business cycles in Brazil. First, I document that Brazilian interest rates are very volatile, counter-cyclical and positively correlated with net exports, as observed in other emerging economies. Next, I present a dynamic general equilibrium model in which firms face working capital constraints and labor supply is independent of consumption. This parsimonious model, appropriately calibrated to the Brazilian economy, predicts that interest rate shocks can explain about one third of output fluctuations and generates business cycle regularities consistent with the Brazilian data.

Fitomolestias identificadas na microrregiao do litoral piauiense: 1988-1997.

bitstream/item/96085/1/CT740001.pd

Elaboração e edição de bases carto-temáticas em ambiente SIG.

Resumo