L'émergence d'une migration féminine autonome du milieu rural vers le milieu urbain au Burkina FASO ?

Dans cet article, nous utilisons les données de l’enquête nationale "Dynamique migratoire, insertion urbaine et environnement au Burkina Faso – 2000" pour vérifier l'hypothèse de l'émergence d'une migration féminine autonome du milieu rural vers le milieu urbain au Burkina Faso. La migration "autonome" est définie comme une migration visant à satisfaire des objectifs économiques individuels. Nous montrons que la migration autonome n’explique que partiellement la recrudescence des migrations de femmes célibataires du milieu rural vers le milieu urbain. Les migrations de femmes mariées, qui restent prépondérantes entre le milieu rural et le milieu urbain au Burkina Faso, répondent essentiellement, quant à elles, à des impératifs familiaux. Cependant, on observe que le mariage avec un migrant peut, dans certains cas, répondre à des objectifs économiques individuels. Finalement, les changements relevés apparaissent assez subtiles et s’inscrivent plutôt dans la continuité.

As ilhas, os arquivos e a história : o caso dos Açores

Nos Açores, a força da geografia define o carácter da história, que evidencia expressões bem diferenciadas. Por um lado, as ilhas agem como meio de aproximação dos continentes, equivalendo a um sinónimo de universalidade, que resulta de um privilegiado posicionamento no Atlântico Norte, movido pelo determinismo do mar e pelas condições da navegação à vela. Por outro lado, as ilhas figuram como factor de cristalização de comportamentos, correspondendo a um sinónimo de isolamento, motivado pelo afastamento do mundo e pela descontinuidade territorial interna. Nestas circunstâncias, os planos insulares de pesquisa histórica primam naturalmente pela pluralidade dos objectivos. Assim, demonstram uma participação muito activa na construção do mundo atlântico, que obriga à integração das investigações açorianas nas categorias mais universais do saber, mas aconselham também à realização de estudos de incidência local, conducentes à individualização de idiossincracias, que derivam da divisão do arquipélago em nove parcelas muito desiguais. Em 1979, por altura da publicação do seu livro O Arquipélago dos Açores no Século XVII: aspectos sócio-económicos (1575-1675), Maria Olímpia da Rocha Gil reconhece precisamente a indispensabilidade do desenvolvimento da investigação histórica açoriana de acordo com duas linhas ao mesmo tempo dissemelhantes e convergentes: “... em primeiro, aquela que nos leva a considerar que a história do arquipélago se integra no longo processo da história do Atlântico; em segundo lugar, a que se orienta para o estudo da evolução histórica local tendo em conta as características que lhe são próprias”. No entanto, desde tempos quase imemoriais, diversos cronistas e historiadores evidenciam um entendimento muito semelhante, que certifica a complexidade dos estudos históricos insulares. A comprová-lo, atentemos nas Saudades da Terra do Doutor Gaspar Frutuoso, redigidas logo no termo do século XVI, que relevam de uma assentada as especificidades locais, as correlações com os demais arquipélagos da Macaronésia e o envolvimento nas dinâmicas do Atlântico. [...

Effect of thermal poling in sodium tantalum phosphate glass-ceramics

Eu3+-doped sodium tantalum phosphate glass-ceramics containing bronze -like perovskite crystalline phase Na2Ta8O21 were obtained with different crystalline states (degree of crystallinity and average crystallite size) by a suitable control of the heat-treatment time and temperature of the precursor glass. Luminescence properties of Eu3+ in these materials are in agreement with a progressive insertion of the rare earth ions in the sodium tantalate Na2Ta8O21 phase, as probed by a clear decrease of the intensity ratio between transitions [5D0 →] 7F2/7F1 and narrowing of characteristic emission bands. Thermal poling insights were performed on these glassy and glass-ceramic materials and the experimental conditions had to be carefully optimized in the glass-ceramics to avoid electrical sparks and sample break associated with dielectric breakdown of the samples. Suitable and stable thermal poling treatments could be performed at 250 °C and 900 V under N2 atmosphere on both glass and glass-ceramics. These first insights pointed out a lower migration kinetic of sodium ions when compared to the precursor glass as well as a lower content of depleted ions, since part of sodium is supposed to be “frozen” inside the crystalline phase in glass-ceramics. Despite these lower kinetic poling conditions, a poled sodium depleted layer whose thickness depends on the poling time was successfully formed at the anode side. Reflectance infrared spectroscopy was also used to investigate the structural changes in the poled layer. These IR data pointed out that structural changes induced by thermal poling are mainly promoted in the phosphate network rather than tantalate units in both glass and glass-ceramics in agreement with a selective sodium migration from the remaining glassy phase. Macroscopic induced SHG measured by the Maker fringes technique is also consistent with the EFISH model and quantitative simulations of these data allowed to estimate second order nonlinear optical susceptibilities χ(2) ten to twenty times lower in the glass-ceramics than in the precursor glass. Such electric behavior is discussed in terms of dielectric properties of heterogeneous materials and interfacial polarization mechanisms between crystallites and glassy phase.Centre for functional and surface-functionalized glasse

Photochromic properties of tungstate-based glasses

Vitreous samples were prepared in the NaPO(3)-BaF(2)WO(3) ternary system with high WO(3) concentrations. These glasses exhibit a strong absorption in the visible due to the presence of reduced tungsten species and the use of oxidizing species is required. The couple Sb(2)O(3)/NaNO(3) was introduced in the composition and allowed to obtain transparent glasses. These oxidized samples were illuminated by visible laser radiation and showed an efficient volumetric photochromic effect. The photosensitive effect appeared as a dark spot throughout the entire volume of the glasses. The effect was investigated by several techniques such as, U-V-visible absorption, Raman and XANES at the L(1) and L(3) tungsten absorption edges. The results suggest a photoreduction of tungsten atoms without structural changes of the viteous network. Finally, the photochromic effect can be erased by thermal treatment at 200 degrees C for a few minutes. (C) 2007 Published by Elsevier B.V

Thermal and structural study of glasses in the binary system TeO2-Pb(PO3)(2)

The main objective of this work has been to prepare and characterize the thermal and structural properties of glasses in the pseudo binary system TeO2-Pb(PO3)(2) with respect to the composition. Homogeneous and transparent glass samples were obtained by the melt-quenching method in a large glass forming range in the pseudo binary system (100 - x)TeO2-xPb(PO3)(2) with x varying from 5 to 100. Thermal properties investigated by DSC pointed out an increase of the glass transition temperature from x 5 to x = 40 and further decrease of Tg for higher Pb(PO3)(2) concentrations. A similar tendency has been observed for the thermal stability against devitrification measured using the stability parameter Tx-Tg. FTIR together with Raman spectroscopies allowed building a structural model for these glasses with the contribution of distinct phosphate and tellurite units depending on the composition. Identification of crystalline phases obtained after the glasses heat-treatments obtained by X-ray diffraction support the structural evolution suggested by vibrational spectroscopies. These data suggest that incorporation of TeO2 in the lead metaphosphate glass results in tellurium conversion from TeO4 seesaw geometry to TeO3 trigonal pyramids and consequent conversion of well-known metaphosphate units Q(2) to modified pyrophosphate units Q(1Te)(2) in which the phosphorus PO4 tetrahedron is linked to another PO4 unit and one TeO3 pyramid. These tellurite trigonal units cross-link the modified metaphosphate chains with a resulting increase of the glass network connectivity. For high TeO2 concentrations, all Q(2) were converted to Q(1Te)(2) and the additional tellurium atoms are incorporated in the glass network as TeO4 seesaw units with a glass network built from a tridimensionalnetwork of TeO3, TeO4, and Q(1Te)(2). Finally, this work pointed out the possibility to use this pseudobinary system for the preparation of phosphate glass-ceramics containing a TeO2 crystalline phase or tellurite glass-ceramics containing a pyrophosphate or metaphosphate crystalline phase. (C) 2013 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Crystallization of monoclinic WO3 in tungstate fluorophosphate glasses

Tungstate fluorophosphate glass compositions with high WO3 concentration were prepared in the ternary system (80-0.8x)NaPO3-(20-0.2x)BaF2-xWO(3) with x = 40,50 and 60 mol%. Transparency decreases as WO3 concentration increases but can be improved by addition of oxidizing systems such as CeO2 or Sb2O3/NaNO3. Characterizations by thermal analysis (DSC) point out that an increase in the amount of WO3 results in a higher glass transition temperature. In addition, such compositions are very stable against devitrification since samples containing 40% and 50% of WO3 donot even exhibit the expected crystallization event. In these samples, the stability against crystallization decreases with the WO3 content and vitreous sample containing 60% of WO3 exhibits an endothermic event around 620 degrees C due to crystallization of monoclinic WO3 phase. In these glasses, it was shown that the nucleation stage can be induced by thermal-treatment when external nucleating agents such as Ti or Sb are used. Finally, gold-doped samples exhibit a higher crystallization tendency and monoclinic WO3 phase can be grown in such glasses. (C) 2009 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Bulk photochromism in a tungstate-phosphate glass: A new optical memory material?

In this work, we present a new photochromic tungstate based glass which have both absorption coefficient and refractive index modified under laser exposure. The photosensitive effect is superficial under ultraviolet (UV) irradiation but occurs in the entire volume of the glass under visible irradiation. The effect can be obtained in any specific point inside the volume using an infrared femtosecond laser. In addition, the photosensitive phenomenon can be erased by specific heat treatment. This glass can be useful to substitute actual data storage supports and is a promising material for 3-dimensional (3D) and holographic optical storage

Microscaled design of the linear and non-linear optical properties of tantalum germanate glasses by thermal poling

Sodium tantalum germanate glasses were thermally poled using microstructured metallic anodes of two distinct geometries. The topological, structural and optical characterization studies of micro-imprinted structures revealed an accurate reproducibility of the electrode patterns on the glass surface with strong edge effects between the poled and unpoled areas. Spatial reliefs of 100 nm depth were achieved and associated with glass network rearrangements due to sodium departure in the conductive anodic patterns. Second harmonic signals originating from both longitudinal and in-plane static electric fields were identified mainly near the borders of imprinted structures and related to a specific charge distribution model. Spatially controlled positive refractive index changes around 7 to 9 × 10−3 could be induced, opening opportunities for microscaled active optical devices operating in the middle infrared region.Centre for functional and surface-functionalized glasse