Water Penetration-Its Effect on the Strength and Toughness of Silica Glass

International audienceWhen a crack forms in silica glass, the surrounding environment flows into the crack opening, and water from the environment reacts with the glass to promote crack growth. A chemical reaction between water and the strained crack-tip bonds is commonly regarded as the cause of subcritical crack growth in glass. In silica glass, water can also have a secondary effect on crack growth. By penetrating into the glass, water generates a zone of swelling and, hence, creates a compression zone around the crack tip and on the newly formed fracture surfaces. This zone of compression acts as a fracture mechanics shield to the stresses at the crack tip, modifying both the strength and subcritical crack growth resistance of the glass. Water penetration is especially apparent in silica glass because of its low density and the fact that it contains no modifier ions. Using diffusion data from the literature, we show that the diffusion of water into silica glass can explain several significant experimental observations that have been reported on silica glass, including (1) the strengthening of silica glass by soaking the glass in water at elevated temperatures, (2) the observation of permanent crack face displacements near the crack tip of a silica specimen that had been soaked in water under load, and (3) the observation of high concentrations of water close to the fracture surfaces that had been formed in water. These effects are consistent with a model suggesting that crack growth in silica glass is modified by a physical swelling of the glass around the crack tip. An implication of water-induced swelling during fracture is that silica glass is more resistant to crack growth than it would be if swelling did not occur

Fenologia reprodutiva do maracujazeiro-azedo no município de Campos dos Goytacazes, RJ Reproductive phenological of passion fruit in Campos dos Goytacazes, RJ, Brazil

Este estudo teve como objetivo caracterizar a fenologia reprodutiva do maracujazeiro-azedo no período de setembro de 2009 a setembro de 2010, nas condições do município de Campos dos Goytacazes-RJ (21° 45'W; 41°20'S). Avaliaram-se os dados referentes ao florescimento e frutificação, correlacionados com variáveis climatológicas (temperatura e pluviosidade). Uma escala para a avaliação do desenvolvimento dos estádios fenológicos reprodutivos do maracujazeiro-azedo foi proposta, com base em imagens digitalizadas de nove fenofases. Observou-se que o florescimento foi de outubro a março, meses com as maiores temperaturas médias, com pico no mês de janeiro e maior percentagem de frutos maduros no mês de fevereiro. A escala das diferentes fenofases foi útil na caracterização da fenologia reprodutiva do maracujazeiro-azedo. A variável temperatura apresentou alta correlação com o número de flores (0,87), indicando que é um agente fundamental no florescimento do maracujazeiro-azedo.<br>This research aimed to characterize the reproductive phenological of sour passion fruit from September 2009 to September 2010, in Campos dos Goytacazes city, Rio de Janeiro state, Brazil (21° 45'W; 41° 20'S). Data of flowering and fructification were evaluated and correlated with climatologic variables (temperature and rainfall). To evaluate phenological stages a scale was proposed based on digitals images of nine reproductive stages. The scale was useful in passion fruit reproductive phenological characterization. The flowering was of October to March, peak in January, and the peak fructification in February. The temperature showed high correlation with number of flowers (0.87), thus indicating that the temperature has an important effect in flowering of sour passion fruit

Mineralogy, chemistry and biological contingents of an early-middle Miocene Antarctic paleosol and its relevance as a Martian analogue

Fossil mesofauna and bacteria recovered from a paleosol in a moraine situated adjacent to the inland ice, Antarctica, and dating to the earliest glacial event in the Antarctic Dry Valleys opens several questions. The most important relates to understanding of the mineralogy and chemistry of the weathered substrate habitat in which Coleoptera apparently thrived at some point in the Early/Middle Miocene and perhaps earlier. Here, Coleoptera remains are only located in one of six horizons in a paleosol formed in moraine deposited during the alpine glacial event (>15 Ma). A tendency for quartz to decrease upward in the section may be a detrital effect or a product of dissolution in the early stage of profile morphogenesis when climate was presumably milder and the depositing glacier of temperate type. Discontinuous distributions of smectite, laumontite, and hexahydrite may have provided nutrients and water to mesofauna and bacteria during the early stage of biotic colonization of the profile. Because the mesofauna were members of burrowing Coleoptera species, future work should assess the degree to which the organisms occupied other sites in the Dry Valleys in the past. Whereas there is no reasonable expectations of finding Coleoptera/insect remains on Mars, the chemistry and mineralogy of the paleosol is within a life expectancy window for the presence of microorganisms, principally bacteria and fungi. Thus, parameters discussed here within this Antarctic paleosol could provide an analogue to identifying similar fossil or life-bearing weathered regolith on Mars

Image-based rendering of intersecting surfaces for dynamic comparative visualization

Nested or intersecting surfaces are proven techniques for visualizing shape differences between static 3D objects (Weigle and Taylor II, IEEE Visualization, Proceedings, pp. 503–510, 2005). In this paper we present an image-based formulation for these techniques that extends their use to dynamic scenarios, in which surfaces can be manipulated or even deformed interactively. The formulation is based on our new layered rendering pipeline, a generic image-based approach for rendering nested surfaces based on depth peeling and deferred shading. We use layered rendering to enhance the intersecting surfaces visualization. In addition to enabling interactive performance, our enhancements address several limitations of the original technique. Contours remove ambiguity regarding the shape of intersections. Local distances between the surfaces can be visualized at any point using either depth fogging or distance fields: Depth fogging is used as a cue for the distance between two surfaces in the viewing direction, whereas closest-point distance measures are visualized interactively by evaluating one surface’s distance field on the other surface. Furthermore, we use these measures to define a three-way surface segmentation, which visualizes regions of growth, shrinkage, and no change of a test surface compared with a reference surface. Finally, we demonstrate an application of our technique in the visualization of statistical shape models. We evaluate our technique based on feedback provided by medical image analysis researchers, who are experts in working with such models.Intelligent SystemsElectrical Engineering, Mathematics and Computer Scienc