Avaliação inicial de algumas leguminosas herbáceas perenes para utilização como cobertura viva permanente de solo.

bitstream/CNPAB-2010/27141/1/cot016.pd

Replica symmetry breaking in mean field spin glasses trough Hamilton-Jacobi technique

During the last years, through the combined effort of the insight, coming from physical intuition and computer simulation, and the exploitation of rigorous mathematical methods, the main features of the mean field Sherrington-Kirkpatrick spin glass model have been firmly established. In particular, it has been possible to prove the existence and uniqueness of the infinite volume limit for the free energy, and its Parisi expression, in terms of a variational principle, involving a functional order parameter. Even the expected property of ultrametricity, for the infinite volume states, seems to be near to a complete proof. The main structural feature of this model, and related models, is the deep phenomenon of spontaneous replica symmetry breaking (RSB), discovered by Parisi many years ago. By expanding on our previous work, the aim of this paper is to investigate a general frame, where replica symmetry breaking is embedded in a kind of mechanical scheme of the Hamilton-Jacobi type. Here, the analog of the "time" variable is a parameter characterizing the strength of the interaction, while the "space" variables rule out quantitatively the broken replica symmetry pattern. Starting from the simple cases, where annealing is assumed, or replica symmetry, we build up a progression of dynamical systems, with an increasing number of space variables, which allow to weaken the effect of the potential in the Hamilton-Jacobi equation, as the level of symmetry braking is increased. This new machinery allows to work out mechanically the general K-step RSB solutions, in a different interpretation with respect to the replica trick, and lightens easily their properties as existence or uniqueness.Comment: 24 pages, no figure

Interpolating the Sherrington-Kirkpatrick replica trick

The interpolation techniques have become, in the past decades, a powerful approach to lighten several properties of spin glasses within a simple mathematical framework. Intrinsically, for their construction, these schemes were naturally implemented into the cavity field technique, or its variants as the stochastic stability or the random overlap structures. However the first and most famous approach to mean field statistical mechanics with quenched disorder is the replica trick. Among the models where these methods have been used (namely, dealing with frustration and complexity), probably the best known is the Sherrington-Kirkpatrick spin glass: In this paper we are pleased to apply the interpolation scheme to the replica trick framework and test it directly to the cited paradigmatic model: interestingly this allows to obtain easily the replica-symmetric control and, synergically with the broken replica bounds, a description of the full RSB scenario, both coupled with several minor theorems. Furthermore, by treating the amount of replicas $n\in(0,1]$ as an interpolating parameter (far from its original interpretation) this can be though of as a quenching temperature close to the one introduce in off-equilibrium approaches and, within this viewpoint, the proof of the attended commutativity of the zero replica and the infinite volume limits can be obtained.Comment: This article is dedicated to David Sherrington on the occasion of his seventieth birthda

A multiple-indicator latent growth mixture model to track courses with low-quality teaching

This paper describes a multi-indicator latent growth mixture model built on the data collected by a large Italian university to track students’ satisfaction over time. The analysis of the data involves two steps: first, a pre-processing of data selects the items to be part of the synthetic indicator that measures students’ satisfaction; the second step then retrieves heterogeneity that allows the identification of a clustering structure with a group of university courses (outliers) which underperform in terms of students’ satisfaction over time. Regression components of the model identify courses in need of further improvement and that are prone to receiving low classifications from students. Results show that it is possible to identify a large group of didactic activities with a high satisfaction level that stays constant over time; there is also a small group of problematic didactic activities with low satisfaction that decreases over the period under analysis.info:eu-repo/semantics/acceptedVersio

An Extended Variational Principle for the SK Spin-Glass Model

The recent proof by F. Guerra that the Parisi ansatz provides a lower bound on the free energy of the SK spin-glass model could have been taken as offering some support to the validity of the purported solution. In this work we present a broader variational principle, in which the lower bound, as well as the actual value, are obtained through an optimization procedure for which ultrametic/hierarchal structures form only a subset of the variational class. The validity of Parisi's ansatz for the SK model is still in question. The new variational principle may be of help in critical review of the issue.Comment: 4 pages, Revtex

Decomposição e liberação de nitrogênio, fósforo e potássio de resíduos da cultura do feijoeiro.

Este trabalho teve como objetivo mensurar a velocidade de decomposição e de liberação de nutrientes in situ de resíduos da cultura do feijoeiro (Phaseolus vulgaris L.). Em condições de campo, foram coletadas as folhas senescentes durante o ciclo da cultura, bem como os caules e a palhada de vagens após trilhagem dos grãos, de cultivares de feijoeiro. Esses resíduos continham 2,3 Mg ha-l de massa, 31 kg ha-l de N e 2,4 kg ha-1 de P, que correspondiam a 63, 41 e 28 % do total de massa, N e P, respectivamente, acumulados durante 0 ciclo da cultura. Foram realizados dois ensaios, nos períodos de inverno-primavera e primavera-verão, quando os caules, as vagens e as folhas senescentes foram colocados separadamente em litterbags, dispostos sobre 0 solo, e coletados entre 2 e 120 dias. As quantidades de matéria seca e nutrientes remanescentes em cada tipo de resíduo foram ajustadas a um modelo exponencial simples. O tempo de meia-vida dos resíduos foi de, no primeiro e segundo ensaios, respectivamente, 133 e 179 dias para caules, 70 e 80 dias para folhas e 64 dias para vagens. A relativamente lenta decomposição dos resíduos pode ser associada a sua alta relação C:N - acima de 60 para caule e palhada de vagens. A liberação de N e P pelos resíduos foi similar á dinâmica de decomposição, enquanto a liberação de K foi mais rápida. Os resultados indicam que as folhas senescentes e os resíduos produzidos após trilhagem dos grãos podem restituir parte da demanda de nutrientes do feijoeiro, assumindo relevância para sistemas de agricultura sustentável. The objective of this study was to measure the speed of decomposition and nutrient release in situ from residues of common bean (Phaseolus vulgaris L.) crop. In field conditions, leaves of common bean cultivars senesced during the growth cycle and stems and podwal ls after pod threshing were collected. These residues contained 2.3 Mg ha-l of mass, 31 kg ha-l of Nand 2.4 kg ha-l of P that corresponded to 63, 41 and 28 % of total mass, Nand P, respectively accumulated during the crop growth cycle. Two experiments were conducted, during winter-spring and spring-summer. Stems, podwalls and sene seed leaves were placed separately in litterbags on the ground and collected, from the 2nd to the 120th day. The dry matter and nutrient amounts found in each residue type were adjusted to a simple exponential model. The half-life of the residues was, in the first and second trial respectively, 133 and 179 days for stems, 70 and 80 days for leaves, and 64 days for podwalls. The relatively slow residue decomposition may be associated with the high C:N ratio (C:N> ao in stems and podwalls). Nitrogen and P release by residues was similar to the decomposition pattern, while K release was faster. The results indicate that senescent leaves and residues produced after pod threshing can cover part of the nutrient demand of common bean crop, which is relevant for sustainable agricultural systems.Parceria: IDAF; UFRRJ