Complete addition laws on abelian varieties

We prove that under any projective embedding of an abelian variety A of dimension g, a complete system of addition laws has cardinality at least g+1, generalizing of a result of Bosma and Lenstra for the Weierstrass model of an elliptic curve in P^2. In contrast with this geometric constraint, we moreover prove that if k is any field with infinite absolute Galois group, then there exists, for every abelian variety A/k, a projective embedding and an addition law defined for every pair of k-rational points. For an abelian variety of dimension 1 or 2, we show that this embedding can be the classical Weierstrass model or embedding in P^15, respectively, up to a finite number of counterexamples for |k| less or equal to 5.Comment: 9 pages. Finale version, accepted for publication in LMS Journal of Computation and Mathematic

Tight binding description of the electronic response of a molecular device to an applied voltage

We analyze the effect of an external electric field on the electronic structure of molecules which have been recently studied as molecular wires or diodes. We use a self-consistent tight binding technique which provides results in good agreement with ab initio calculations and which may be applied to a large number of molecules. The voltage dependence of the molecular levels is mainly linear with slopes intimately related to the electronic structure of the molecules. We emphasize that the response to the applied voltage is an important feature which governs the behavior of a molecular device

The invariant joint distribution of a stationary random field and its derivatives: Euler characteristic and critical point counts in 2 and 3D

The full moments expansion of the joint probability distribution of an isotropic random field, its gradient and invariants of the Hessian is presented in 2 and 3D. It allows for explicit expression for the Euler characteristic in ND and computation of extrema counts as functions of the excursion set threshold and the spectral parameter, as illustrated on model examples.Comment: 4 pages, 2 figures. Corrected expansion coefficients for orders n>=5. Relation between Gram-Charlier and Edgeworth expansions is clarified

Guidelines for a Dynamic Ontology - Integrating Tools of Evolution and Versioning in Ontology

Ontologies are built on systems that conceptually evolve over time. In addition, techniques and languages for building ontologies evolve too. This has led to numerous studies in the field of ontology versioning and ontology evolution. This paper presents a new way to manage the lifecycle of an ontology incorporating both versioning tools and evolution process. This solution, called VersionGraph, is integrated in the source ontology since its creation in order to make it possible to evolve and to be versioned. Change management is strongly related to the model in which the ontology is represented. Therefore, we focus on the OWL language in order to take into account the impact of the changes on the logical consistency of the ontology like specified in OWL DL

WHICH HUMAN CAPITAL MATTERS FOR RICH AND POOR'S WAGES: EVIDENCE FROM MATCHED WORKER-FIRM DATA FROM TUNISIA

In this paper, we study the return to human capital variables for wages of workers observed in Tunisian matched worker-firm data in 1999. We develop a new method based on multivariate analysis of firm characteristics, which allows us most of the benefits obtained by introducing firm dummies in wage equations. It also provides a human capital interpretation of the effect of these dummy variables. Moreover, in the studied data, using three firm characteristics easily collectable yields results close to those obtained by using the matched structure of the data.wage, returns to human capital, matched worker-firm data, quantile regressions, factor analysis, Tunisia

Permanent and Transitory Factors Affecting the Dynamics of the Term Structure of Interest Rates

This paper proposes a novel methodology, based on the Common Principal Component analysis, allowing one to estimate the factors driving the term structure of interest rates, in the presence of time-varying covariance structure. The advantages of this method are first, that, unlike classical principal component analysis, common factors can be estimated without assuming that the volatility of the factors is constant; and second, that the factor structure can be decomposed into permanent and transitory common factors. We conclude that only permanent factors are relevant for modeling the dynamics of interest rates, and that the common principal component approach appears to be more accurate than the classical principal component one to estimate the risk factor structure.Term Structure of Interest Rates, Principal Component Analy-sis, Common Principal Component Analysis

Which Human Capital Matters for Rich and Poor’s Wages? Evidence from Matched Worker-Firm Data from Tunisia

In this paper, we study the return to human capital variables for wages of workers observed in Tunisian matched worker-firm data in 1999. This tells us how returns to human capital in a Less Developed Country like Tunisia differ from the industrial countries usually studied with matched data. We develop a new method based on multivariate analysis of firm characteristics, which allows us most of the benefits obtained by introducing firm dummies in wage equations for studying the effect of education. It also provides a human capital interpretation of the effect of these dummy variables. Moreover, in the studied data, using three firm characteristics easily collectable yields results close to those obtained by using the matched structure of the data. The workers with low wages or low conditional wages experience greater returns to human capital than workers belonging to the middle of the wage distribution, while their return to schooling is significantly lower than that of high wage workers. Wage regressions including the computed factors confirm that human capital is associated with positive intra-firm externality on wages. Therefore, a given worker would be more productive and better paid in an environment strongly endowed in human capital. However, the poorest workers do not take advantage of the human capital in the firm. Conversely, the poor benefit from working in the textile sector in terms of wages unlike the middle and high wage workers. Finally, the poorest and richest workers benefit from an innovative environment while the middle workers of the wage distribution do not.wage, returns to human capital, matched worker-firm data, quantile regressions, factor analysis, Tunisia

WAGE AND HUMAN CAPITAL IN EXPORTING FIRMS IN MOROCCO

We study the relationship of wages and education and training practices in Morocco in a context of trade and liberalisation reforms in a matched worker-firm data of eight exporting firms in two industrial sectors: Metallurgical-Electrical industries and Textile-Clothing. We find that the specific characteristics of the surveyed firms little affect worker wages. Moreover, the textile sector does not appear to be a significant channel for promoting skills in the economy. The minimal wage legislation is found to exert a positive pressure on wages. Also, some evidence of gender wage gap exists in the data. In these data, the effects of education and experience on wages are quite limited below the third quantile of wages, as well as the role of apprenticeship. In contrast, On-the-Job Training (OJT) much contributes to labour productivity as measured by wage levels. Most of the OJT is concentrated in the Metallurgical-Electrical industries. Education is positively correlated to OJT. Moreover, estimates of explanatory relationships of task organisation (chain gangs, teams, supervision and executive workers) show the powerful sector and educational determinations of job organisation in the firms. Then, our results suggest that the impact of worker education may take indirect routes and not only appear through education coefficients in wage regressions.wage, returns to human capital, matched worker-firm data, quantile regressions, Tunisia

HUMAN CAPITAL AND WAGES IN TWO LEADING INDUSTRIES OF TUNISIA: EVIDENCE FROM MATCHED WORKER-FIRM DATA

From Tunisian matched worker-firm data in 1999, we study the returns to human capital for workers observed in two leading manufacturing sectors. Workers in the mechanical and electrical industries (IMMEE) benefit from higher returns to human capital than their counterparts in the Textile-clothing industry. In the IMMEE firms, low wage workers experience greater returns to labour market experience than high wage workers. The wage premium for on-the-job training is substantial for both sectors. However, taking into account whether formal training is still ongoing at the time of the survey, our results clearly indicate that workers bear heavy costs for their training. Our analysis shows that on-the-job training (OJT) and education can be efficient channels of policies aiming at raising earnings for low wages as well as high wages workers. However, careful consideration of the industrial sector should accompany these policies since specific impact of education, experience, OJT are found in the studied sectors.wage, returns to human capital, matched worker-firm data, quantile regressions, Tunisia