Local Charge Excesses in Metallic Alloys: a Local Field Coherent Potential Approximation Theory

Electronic structure calculations performed on very large supercells have shown that the local charge excesses in metallic alloys are related through simple linear relations to the local electrostatic field resulting from distribution of charges in the whole crystal. By including local external fields in the single site Coherent Potential Approximation theory, we develop a novel theoretical scheme in which the local charge excesses for random alloys can be obtained as the responses to local external fields. Our model maintains all the computational advantages of a single site theory but allows for full charge relaxation at the impurity sites. Through applications to CuPd and CuZn alloys, we find that, as a general rule, non linear charge rearrangements occur at the impurity site as a consequence of the complex phenomena related with the electronic screening of the external potential. This nothwithstanding, we observe that linear relations hold between charge excesses and external potentials, in quantitative agreement with the mentioned supercell calculations, and well beyond the limits of linearity for any other site property.Comment: 11 pages, 1 table, 7 figure

Scaling in the Lattice Gas Model

A good quality scaling of the cluster size distributions is obtained for the Lattice Gas Model using the Fisher's ansatz for the scaling function. This scaling identifies a pseudo-critical line in the phase diagram of the model that spans the whole (subcritical to supercritical) density range. The independent cluster hypothesis of the Fisher approach is shown to describe correctly the thermodynamics of the lattice only far away from the critical point.Comment: 4 pages, 3 figure

Propriétés Physiques et Mécaniques des Graines et Amandes de Jatropha curcas L.

Cette étude a déterminé les propriétés physiques et mécaniques des graines et amandes de Jatropha curcas L. (Jatropha), originaire de l’Extrême- Nord du Cameroun. Les paramètres physiques tels que les dimensions moyennes, les caractéristiques massiques, les paramètres de forme et les caractéristiques volumiques ont été évalués. La raideur de la coque a été définie en variant la vitesse de compression de la machine d’essai de traction universel EZ 50. A grande vitesse de compression (5-40 mm/mn), les brisures d’amandes et de coques qui ont été observées ont été représentées sur les courbes de compression des graines par plusieurs points de rupture. Avec une faible vitesse de l’ordre de 1 mm/mn, les courbes de compression ont été linéaires. La valeur moyenne de la force de rupture en compression Fr(N) et la raideur K (N/mm) des coques calculées ont été respectivement 134,41 N et 105 N/mm. Les essais d’extraction d’huile de Jatropha sont réalisés à température ambiante (23-24°C) avec des charges comprises entre 1000 et 12000 N. Ce qui a permis d’obtenir les relations mathématiques entre la force de compression et la déformation relative : F(l) =8,91Exp(0,94l) -9,41 (N) ; entre la contrainte de compression et la déformation relative : ()=0,08Exp(6,89)-0,08 (MPa). L’algorithme de « Trust region » et de « Levenberg-Marquardt », ont été respectivement intégré dans l’application MATLAB R2018a pour obtenir les modèles précédents. Les points limites pour le pressage des amandes sont compris entre 0,40 et 0,85 permettant d’obtenir les limites pour une extraction optimale de l’huile. La force de compression a été comprise entre 72,71 N et 4905,70 N, pendant que la contrainte de compression varie entre 0,65 et 37,01MPa pour une consommation d’énergie allant de 0,13 à 2,83J/mm3. This study has estimated physicomechanical properties of Jatropha curcas L. (Jatropha) seeds and kernels from the Far North Region of Cameroon. Physical parameters as mean sizes, mass characteristics, morphologic and volume characteristics were evaluated. The stiffness of the husk was estimated by varying the velocity of the universal tensile testing machine EZ 50. For a high compression velocity, (5-40mm/mn), compression diagrams of seeds showed several breaking point, we observed broken seeds and kernels with low velocity of 1 mm/mn, compression diagram are linear. The means value of the compression force Fr(N) and husk stiffness K (N/mm) are respectively 134.41 N and 105 N/mm. Tensile tests of Jatropha oil were realized at 23-24°C with compression forces of 1000 and 12000N. We obtained mathematical relations between relative deformation and compression force: F(l)=8.91Exp(0.94l)-9.41 (N), compression stress and relative deformation: ()=0.08Exp(6.89)-0.08 (MPa), using respectively the “trust region” and “Levenberg-Marquardt” algorithm related to MATLAB R 2018a software. The endpoints for and optimal extraction of Jatropha oil were 0.40 and 0.85 when the compression force were between 72.71 N and 4905.5 N, the stress compression vavy between 0.65 and 37.01 MPa, therefore the consumed energy varied between 0.13 and 3.83 J/mm3

Closed Contour Fractal Dimension Estimation by the Fourier Transform

This work proposes a novel technique for the numerical calculus of the fractal dimension of fractal objects which can be represented as a closed contour. The proposed method maps the fractal contour onto a complex signal and calculates its fractal dimension using the Fourier transform. The Fourier power spectrum is obtained and an exponential relation is verified between the power and the frequency. From the parameter (exponent) of the relation, it is obtained the fractal dimension. The method is compared to other classical fractal dimension estimation methods in the literature, e. g., Bouligand-Minkowski, box-couting and classical Fourier. The comparison is achieved by the calculus of the fractal dimension of fractal contours whose dimensions are well-known analytically. The results showed the high precision and robustness of the proposed technique

Informality, Inequality and ICT in Transition economies

In this paper, we examine the role of the quality of institutional infrastructure and information and communication technology (ICT) in the relationship between the size of the informal sector (IS) and income inequality. Following our results, the sign of the relationship between IS and income inequality depends on the quality of institutions. When institutions are weak, agents invest less human capital and ICT in the formal sector (FS), thereby reducing income inequality. Utilizing panel data for sixteen transition countries we show that the relationship between the size of the IS and the level of income inequality is ambiguous. Our findings highlight the problem of measuring the relative size of the IS which is a hidden entity. We control for robustness of our findings using alternative proxies of ICT, human capital, and institutional quality and some interaction terms among these variables

Conductance fluctuations in the presence of spin scattering

Electron transport through disordered systems that include spin scatterers is studied numerically. We consider three kinds of magnetic impurities: the Ising, the XY and the Heisenberg. By extending the transfer matrix method to include the spin degree of freedom, the two terminal conductance is calculated. The variance of conductance is halved as the number of spin components of the magnetic impurities increases. Application of the Zeeman field in the lead causes a further halving of the variance under certain conditions.Comment: to be published in Phys. Rev.

In vitro development of primordial follicles after long-term culture of goat ovarian tissue

This study aims to investigate the effects of follicle stimulating hormone (FSH) and fibroblast growth factor-2 (FGF-2) on the survival and growth of caprine preantral follicles. Ovarian tissues were cultured for 1, 7, 14, 21 or 28 days in medium supplemented with FSH (FSH-2d or FSH-7d, i.e., with replacement of the culture medium every 2 or 7 days, respectively) or FSH + FGF-2 (replacement of the medium every 2 days). Non-cultured (control) and cultured ovarian fragments were processed for histological and ultrastructural analysis. After 28 days of culture, the media supplemented with FSH-2d was the most effective in maintaining the percentage of normal follicles and in promoting follicular growth. Furthermore, both treatments with FSH increased the percentage of the primary follicles. However, ultrastructural studies did not confirm follicular integrity from 14 days of culture onward. In conclusion, culturing tissue for up to 7 days in medium containing FSH alone or combined with FGF-2 maintains caprine preantral follicle integrity and promotes their growth in vitro