The Standard Model of Leptons as a Purely Vectorial Theory

We propose a way to reconcile the Standard Model of leptons with a purely vectorial theory. The observed neutrino is predicted to be massless. The unobservability of its partner and the $V-A$ structure of the weak currents are given the same origin.Comment: 10 pages. Latex, 8 postscript figures included. We have corrected 2 (cancelling) sign misprints, and made explicit that we also recover the usual couplings of the U(1) gauge field B. The conclusions are unchanged. PAR-LPTHE 93/1

Singularity, complexity, and quasi--integrability of rational mappings

We investigate global properties of the mappings entering the description of symmetries of integrable spin and vertex models, by exploiting their nature of birational transformations of projective spaces. We give an algorithmic analysis of the structure of invariants of such mappings. We discuss some characteristic conditions for their (quasi)--integrability, and in particular its links with their singularities (in the 2--plane). Finally, we describe some of their properties {\it qua\/} dynamical systems, making contact with Arnol'd's notion of complexity, and exemplify remarkable behaviours.Comment: Latex file. 17 pages. To appear in CM

SOCIAL RELATIONS AND SEED TRANSACTIONS AMONG SMALLSCALE MAIZE FARMERS IN THE CENTRAL VALLEYS OF OAXACA, MEXICO; PRELIMINARY FINDINGS

This paper explores social arrangements associated with seed transactions among small-scale maize farmers in the Central Valleys of Oaxaca, Mexico, a centre of crop genetic diversity. A formal seed distribution system has yet to develop in the region and when seed loss occurs, farmers are faced with costs and difficulties identifying, locating, and obtaining seed of desired varieties. For these reasons, it was hypothesized that there were strong incentives for collective action among farmers to facilitate seed supply. The study found, however, no evidence of collective action with regards to seed supply in the three study communities-San Pablo Huitzo, San Lorenzo Albarradas, Santa Ana Zegache. Instead, farmers acquired seed using a variety of networks of social relations and different types of seed transactions. The results suggest that seed flow among farmers in the Central Valleys of Oaxaca is a complex process of negotiation and reciprocity, influenced by a variety of agroecological, socioeconomic, and cultural factors.Farm Management,

Participatory research: a catalyst for greater impact

This paper discusses the notion of farmer empowerment as a primary objective of participatory research. The authors argue that agricultural technologies are adapted - not adopted – through a social and cultural process which includes the transformation of the technology. Farmer participation in agricultural research is important and necessary first of all to increase the efficiency and impact of agricultural research and technology development. This includes the identification of traits that can guide crop breeders’ work. Farmer empowerment is valuable and desirable, and while it can result from participatory research, direct empowerment per se should not be the main objective of participatory research conducted by research organizations. Of more importance is the empowerment of partner organizations and the identification of future research needs, i.e. the functional purposes of participatory approaches in agricultural research

Singularity confinement and algebraic integrability

Two important notions of integrability for discrete mappings are algebraic integrability and singularity confinement, have been used for discrete mappings. Algebraic integrability is related to the existence of sufficiently many conserved quantities whereas singularity confinement is associated with the local analysis of singularities. In this paper, the relationship between these two notions is explored for birational autonomous mappings. Two types of results are obtained: first, algebraically integrable mappings are shown to have the singularity confinement property. Second, a proof of the non-existence of algebraic conserved quantities of discrete systems based on the lack of confinement property is given.Comment: 18 pages, no figur

Ecologização da agricultura e das relações inovadoras com o mercado: situação atual e perspectivas no Brasil.

Este texto analisa o desenvolvimento da agricultura agroecológica e orgânica no Brasil. Apresenta uma grande diversidade social e de modelos de produção reconhecidos pela legislação brasileira: orgânica, agroecológica, ecológica, biodinâmica, permacultura, etc. Descreve sinteticamente como as políticas e os interesses sociais ligados às questões da agricultura familiar e do meio ambiente causaram a reorganização dos sistemas de produção, em termos de práticas agrícolas e de novas relações com mercados e com os recursos naturais. A análise foi baseada em entrevistas com agricultores e agentes envolvidos no desenvolvimento de vários modelos orgânicos; qualifica os modelos de produção assim como os valores socioculturais relacionados. Apresenta também alguns aspectos das raízes históricas do movimento agroecológico brasileiro e as maneiras como os agricultores familiares se adaptam aos novos interesses da produção ecológica

On the Symmetries of Integrability

We show that the Yang-Baxter equations for two dimensional models admit as a group of symmetry the infinite discrete group $A_2^{(1)}$. The existence of this symmetry explains the presence of a spectral parameter in the solutions of the equations. We show that similarly, for three-dimensional vertex models and the associated tetrahedron equations, there also exists an infinite discrete group of symmetry. Although generalizing naturally the previous one, it is a much bigger hyperbolic Coxeter group. We indicate how this symmetry can help to resolve the Yang-Baxter equations and their higher-dimensional generalizations and initiate the study of three-dimensional vertex models. These symmetries are naturally represented as birational projective transformations. They may preserve non trivial algebraic varieties, and lead to proper parametrizations of the models, be they integrable or not. We mention the relation existing between spin models and the Bose-Messner algebras of algebraic combinatorics. Our results also yield the generalization of the condition $q^n=1$ so often mentioned in the theory of quantum groups, when no $q$ parameter is available.Comment: 23 page

Thermal noise properties of two aging materials

In this lecture we review several aspects of the thermal noise properties in two aging materials: a polymer and a colloidal glass. The measurements have been performed after a quench for the polymer and during the transition from a fluid-like to a solid-like state for the gel. Two kind of noise has been measured: the electrical noise and the mechanical noise. For both materials we have observed that the electric noise is characterized by a strong intermittency, which induces a large violation of the Fluctuation Dissipation Theorem (FDT) during the aging time, and may persist for several hours at low frequency. The statistics of these intermittent signals and their dependance on the quench speed for the polymer or on sample concentration for the gel are studied. The results are in a qualitative agreement with recent models of aging, that predict an intermittent dynamics. For the mechanical noise the results are unclear. In the polymer the mechanical thermal noise is still intermittent whereas for the gel the violation of FDT, if it exists, is extremely small.Comment: to be published in the Proceedings of the XIX Sitges Conference on ''Jammming, Yielding and Irreversible Deformation in Condensed Matter'', M.-C.Miguel and M. Rubi eds.,Springer Verlag, Berli

Baxterization, dynamical systems, and the symmetries of integrability

We resolve the `baxterization' problem with the help of the automorphism group of the Yang-Baxter (resp. star-triangle, tetrahedron, \dots) equations. This infinite group of symmetries is realized as a non-linear (birational) Coxeter group acting on matrices, and exists as such, {\em beyond the narrow context of strict integrability}. It yields among other things an unexpected elliptic parametrization of the non-integrable sixteen-vertex model. It provides us with a class of discrete dynamical systems, and we address some related problems, such as characterizing the complexity of iterations.Comment: 25 pages, Latex file (epsf style). WARNING: Postscript figures are BIG (600kB compressed, 4.3MB uncompressed). If necessary request hardcopy to [email protected] and give your postal mail addres