2,274 research outputs found

    Role of insulin-like growth factor binding protein-3 in 1, 25-dihydroxyvitamin-d 3 -induced breast cancer cell apoptosis.

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    Insulin-like growth factor I (IGF-I) is implicated in breast cancer development and 1, 25-dihydroxyvitamin D3 (1, 25-D3) has been shown to attenuate prosurvival effects of IGF-I on breast cancer cells. In this study the role of IGF binding protein-3 (IGFBP-3) in 1, 25-D3-induced apoptosis was investigated using parental MCF-7 breast cancer cells and MCF-7/VD(R) cells, which are resistant to the growth inhibitory effects of 1, 25-D3. Treatment with 1, 25-D3 increased IGFBP-3 mRNA expression in both cell lines but increases in intracellular IGFBP-3 protein and its secretion were observed only in MCF-7. 1, 25-D3-induced apoptosis was not associated with activation of any caspase but PARP-1 cleavage was detected in parental cells. IGFBP-3 treatment alone produced cleavage of caspases 7, 8, and 9 and PARP-1 in MCF-7 cells. IGFBP-3 failed to activate caspases in MCF-7/VD(R) cells; however PARP-1 cleavage was detected. 1, 25-D3 treatment inhibited IGF-I/Akt survival signalling in MCF-7 but not in MCF-7/VD(R) cells. In contrast, IGFBP-3 treatment was effective in inhibiting IGF-I/Akt pathways in both breast cancer lines. These results suggest a role for IGFBP-3 in 1, 25-D3 apoptotic signalling and that impaired secretion of IGFBP-3 may be involved in acquired resistance to vitamin D in breast cancer

    Effective dielectric constant of periodic composite materials

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    We present computer simulation data for the effective permittivity (in the quasistatic limit) of a system composed of discrete inhomogeneities of permittivity e1, embedded in a three-dimensional homogeneous matrix of permittivity e2. The primary purpose of this paper is to study the related issue of the effect of the geometric shape of the components on the dielectric properties of the medium. The secondary purpose is to analyse how the spatial arrangement in these two-phase materials affects the effective permittivity. The structures considered are periodic lattices of inhomogeneities. The numerical method proceeds by an algorithm based upon the resolution of boundary integral equations. Finally, we compare the prediction of our numerical simulation with the effective medium approach and with results of previous analytical works and numerical experiments

    Effective dielectric constant of random composite materials

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    The randomness in the structure of two-component dense composite materials influences the scalar effective dielectric constant, in the quasistatic limit. A numerical analysis of this property is developed in this paper. The computer-simulation models used are based on both the finite element method and the boundary integral equation method for two-and three-dimensional structures, respectively. Owing to possible anisotropy the orientation of spatially fixed inhomogeneities of permittivity e1, embedded in a matrix of permittivity e2, affects the effective permittivity of the composite material sample. The primary goal of this paper is to analyze this orientation dependence. Second, the effect of the components geometry on the dielectric properties of the medium is studied. Third the effect of inhomogeneities randomly distributed within a matrix is investigated. Changing these three parameters provides a diverse array of behaviors useful to understand the dielectric properties of random composite materials. Finally, the data obtained from this numerical simulation are compared to the results of previous analytical wor

    Complex effective permittivity of a lossy composite material

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    In recent work, boundary integral equations and finite elements were used to study the (real) effective permittivity for two-component dense composite materials in the quasistatic limit. In the present work, this approach is extended to investigate in detail the role of losses. We consider the special but important case of the axisymmetric configuration consisting of infinite circular cylinders (assumed to be parallel to the z axis and of permittivity e1) organized into a crystalline arrangement (simple square lattice) within a homogeneous background medium of permittivity e2=1. The intersections of the cylinders with the x – y plane form a periodic two-dimensional structure. We carried out simulations taking e15320.03i or e1=3-0.03i and e2=1. The concentration dependence of the loss tangent of the composite material can be fitted very well, at low and intermediate concentrations of inhomogeneities, with a power law. In the case at hand, it is found that the exponent parameter depends significantly on the ratio of the real part of the permittivity of the components. We argue, moreover, that the numerical results discussed here are consistent with the Bergman and Milton theory

    L’architecture de la géographie scolaire québécoise : 1804-1960

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    L'article propose une reconstitution de l'évolution de l'architecture de la géographie scolaire à partir d'une analyse des manuels de géographie publiés au Québec entre 1804 et 1960. Ces quelques jalons s'appuient sur une analyse interne du contenu des manuels et accordent une importance particulière à la composition et aux réaménagements successifs du champ des préoccupations géographiques à travers les époques (ce qui constitue l'objet de la discipline). On cherchera aussi à élucider les modes de raisonnement ou principes d'organisation qui confèrent une unité relative à ces « architectures » disciplinaires successives. Sensible aux continuités et aux ruptures, cette reconstitution identifie trois périodes dans l'évolution de la géographie scolaire québécoise : 1) 1804-1868; 2) 1868- 1912; 3) 1912-1960 (elle-même découpée en deux sous-périodes, 1912-1938 et 1938-1960).This paper traces the evolution of school geography through an analysis of geography textbooks published in Québec between 1804 and 1960. These historical highlights are based on an internal analysis of textbook content with an emphasis on the make-up and successive reorganizations of the areas of geographical interest through time (e.g. what constitutes the object of the discipline). It also describes the modes of thought or organizing principles which provide these disciplinary "architectures" with some internal cohesiveness. Taking into account both ongoing trends and ruptures, this historical reconstruction identifies three periods in the evolution of Québec school geography: 1) 1804-1868; 2) 1868-1912; 3) 1912-1960 (which is further divided into two sub-periods, 1912-1938 and 1938-1960)

    Dificultades de los estudiantes con el papel específico del campo eléctrico en la Óptica

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    This paper deals with the difficulties of the understanding of tlie specific role of the electric field in Optics among students enrolled in undergraduate physics courses. Wiener's experiment along with symmetry arguments provide the basis for an instructional strategy designed to address this specific difficulty

    Régions et régionalisation dans les manuels de géographie : l’exemple de l’Outaouais, 1804-1957

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    L'auteur retrace quatre étapes dans l'évolution de la division régionale du Québec dans les manuels de géographie utilisés au Québec entre 1804 et 1957. L'étude de l'Outaouais illustre la séquence et les modalités du découpage régional mis en oeuvre par la littérature scolaire. On peut y suivre l'émergence de l'idée d'une région outaouaise et son impact sur la population. L'article tente d'établir le rapport qui existe entre la trame de l'exposé régional, l'idée générale de région qu'il suggère et l'image particulière de celle-ci au fil des années. L'étude des manuels souligne ainsi quelques aspects de la fonction sociale de la géographie scolaire.The four major phases of the evolution of regional divisions of Québec is defined through the analysis of geography textbooks produced in Québec from 1804 to 1957. The study of the Outaouais region provides an illustration of the sequence and implications of those regional divisions in the literature. The emerging idea of an Outaouais region is thus reconstituted. This idea has certainly had a significant impact because of the public nature of the textbook. The article further examines the existing links between the regional divisions and the regional concept through time. The study of textbooks reveals some aspects of the social function of school geography

    Réflexion sur l’influence éventuelle de la géographie française dans l’évolution de la géographie scolaire au Québec

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    À partir d'une reconstitution de révolution de la discipline dans les manuels de géographie québécois entre 1920 et i960, l'auteur examine certains indices de la diffusion des idées de la géographie française classique dans les manuels. L'auteur met en lumière le rôle important qu'a joué la première génération de géographes professionnels dans la redéfinition de l'architecture générale de la discipline à l'intérieur du matériel scolaire. Il suggère, en cours de route, quelques filiations possibles avec la géographie française par l'entremise de certains grands thèmes qui l'ont caractérisée à pareille époque (analyse des processus en géographie physique; examen des relations homme/nature, des genres de vie et de la notion de paysage en géographie humaine).Reconstituting the evolution of the discipline in Québec geography textbooks published between 1920 and 1960, the author examines various « traces » of « classic » French geography. The author highlights the important role played by the first generation of professional geographers in redefining the general « architecture » of the discipline in school material. He hints at the possible influence of the French school in discussing general themes which characterized French geography of the period (analysis of processes in physical geography; the study of man/nature relationship, « genre de vie » and the notion of landscape in human geography)
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