Thermodynamic and rheological properties of rhyolite and andesite melts

The heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative-enthalpy measurements made between 400 and 1800 K. For the glass phases, the experimental data agree with empirical models of calculation of the heat capacity. For the liquid phases, the agreement is less good owing to strong interactions between alkali metals and aluminum, which are not currently accounted for by empirical heat capacity models. The viscosity of both liquids has been measured from the glass transition to 1800 K. The temperature dependence of the viscosity is quantitatively related to the configurational heat capacity (determined calorimetrically) through the configurational entropy theory of relaxation processes. For both rhyolite and andesite melts, the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions

Multiple isoform recovery (MIR)-PCR: a simple method for the isolation of related mRNA isoforms

We present a rapid and efficient method for the detection of related transcripts with different expression levels. This approach combines the rapid amplification of cDNA ends (RACE) method with a cDNA subtractive technique. The strategy is based on successive subtractions of prevalent isoforms resulting in enrichment of less expressed transcripts. For each subtraction, a biotinylated primer specific for the prevalent isoform is hybridized on the total cDNA and the hybrid is retained on a streptavidin affinity column. The unbound cDNA serves as a template for subsequent isoform identification. To illustrate its application we describe the isolation of three new actin cDNA isoforms in the freshwater planarian Dugesia (S) polychro

Hydro-thermal flows in a rough fracture

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Glass, an ubiquitous material

Glasses play a fundamental role in our daily lives at the economic, cultural, societal, energy and geological levels. Geological glasses testify to igneous activity of the Earth and represent an important material for tools and ornamental objects from the Paleolithic to the present day. Glasses are also used to manufacture technical materials, such as containers (dishes, glasses, jars, bottles ...), screens (television, computer, smartphone ...), fibers with multiple applications (reinforcement, information, transport, energy, health ...), to ensure the storage of domestic or nuclear waste and, more recently, biomaterials (dental or bone implants ...). Thus, silica-based glasses are at the heart of the history of the Earth and humanity. The variation in composition of natural and industrial glasses is vast but its structure is generally based on a tetrahedral frame of $\mathrm{SiO}_{4}$ units, the backbone of more than 90% of the glasses that surround us in our daily lives. Around this silica frame, other chemical elements are well constrained to form to form a single unit structure for use as network modifying elements, charge compensator, dyes, volatiles, and other substances. This article is a short introduction on glass

Glass, an ubiquitous material

Glasses play a fundamental role in our daily lives at the economic, cultural, societal, energy and geological levels. Geological glasses testify to igneous activity of the Earth and represent an important material for tools and ornamental objects from the Paleolithic to the present day. Glasses are also used to manufacture technical materials, such as containers (dishes, glasses, jars, bottles ...), screens (television, computer, smartphone ...), fibers with multiple applications (reinforcement, information, transport, energy, health ...), to ensure the storage of domestic or nuclear waste and, more recently, biomaterials (dental or bone implants ...). Thus, silica-based glasses are at the heart of the history of the Earth and humanity. The variation in composition of natural and industrial glasses is vast but its structure is generally based on a tetrahedral frame of $\mathrm{SiO}_{4}$ units, the backbone of more than 90% of the glasses that surround us in our daily lives. Around this silica frame, other chemical elements are well constrained to form to form a single unit structure for use as network modifying elements, charge compensator, dyes, volatiles, and other substances. This article is a short introduction on glass

Anisotropie structurelle induite par l'étirage à chaud d'une préforme en silice pure - Etude par dynamique moléculaire et par spectrométrie Raman

National audienceCette étude révèle un nouvel aspect sur la structure de la silice à l'échelle nanométrique. L'orientation acquise par les petits anneaux (Si-O) n pour n ≤ 5 suite à la déformation à chaud persiste à froid et induit une anisotropie structurale dont la forme « isotropie transverse » est vérifiée par spectrométrie Raman

Deformation of silica glass studied by molecular dynamics: Structural origin of the anisotropy and non-Newtonian behavior

International audienceA novel aspect of the medium-range structure of silica drawn into fibers is studied. The network of silica glass structure is composed of corner-shared SiO 4 tetrahedra, and it can be seen as a structure of interconnected rings (Si-O) n of various size, denoted nMR (n-Membered Ring). Molecular Dynamics simulations show that small-sized silica rings get a preferential orientation during the drawing, either during the high-temperature stage for 3MR, or during the cooling for 4MR and 5MR, and they persist in this state in the fiber at ambient temperature. This leads to a structural anisotropy, more specifically a " transverse isotropy " , because of different longitudinal and transversal physical properties. This anisotropic structural rearrangement during the drawing process induces a non-Newtonian behavior of the modeled glass melt, with strain-rate dependent properties. Highlights: Anisotropy in silica glass comes from the orientation that small silica rings acquire during the deformation. The model is in agreement with experiments (non-Newtonian behavior of the melt, anisotropic elasticity of the fiber). The anisotropy in silica fiber is a " transverse isotropy "

Thermodynamic and rheological properties of rhyolite and andesite melts

The heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative-enthalpy measurements made between 400 and 1800 K. For the glass phases, the experimental data agree with empirical models of calculation of the heat capacity. For the liquid phases, the agreement is less good owing to strong interactions between alkali metals and aluminum, which are not currently accounted for by empirical heat capacity models. The viscosity of both liquids has been measured from the glass transition to 1800 K. The temperature dependence of the viscosity is quantitatively related to the configurational heat capacity (determined calorimetrically) through the configurational entropy theory of relaxation processes. For both rhyolite and andesite melts, the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions