Glasses Tech – Prescription Glasses, Prescription Eyeglasses

March 8, 2010

The first three minutes: smooth muscle contraction, cytoskeletal events, and soft glasses

Filed under: Glasses 2003 — admin @ 6:02 am

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Smooth muscle exhibits biophysical characteristics and physiological behaviors that are not readily explained by present paradigms of cytoskeletal and cross-bridge mechanics. There is increasing evidence that contractile activation of the smooth muscle cell involves an array of cytoskeletal processes that extend beyond cross-bridge cycling and the sliding of thick and thin filaments. We review here the evidence suggesting that the biophysical and mechanical properties of the smooth muscle cell reflect the integrated interactions of an array of highly dynamic cytoskeletal processes that both react to and transform the dynamics of cross-bridge interactions over the course of the contraction cycle. (more…)

The origin of the boson peak and thermal conductivity plateau in low-temperature glasses

Filed under: Glasses 2003 — admin @ 6:00 am

We argue that the intrinsic glassy degrees of freedom in amorphous solids giving rise to the thermal conductivity plateau and the “boson peak” in the heat capacity at moderately low temperatures are directly connected to those motions giving rise to the two-level-like excitations seen at still lower temperatures. These degrees of freedom can be thought of as strongly anharmonic transitions between the local minima of the glassy energy landscape that are accompanied by ripplon-like domain wall motions of the glassy mosaic structure predicted to occur at T g by the random first-order transition theory. (more…)

Physics and chemistry of silicate glasses and melts

Filed under: Glasses 2003 — admin @ 5:41 am

Property and structure data from binary and ternary silicate and aluminosilicate melts and glasses often reveal simple and systematic relationships to composition and temperature. Properties whose dominant structural control is the abundance of fully polymerized Q4-species, exhibit smooth variations with silica content. Such properties include activation energies associated with transport. Properties that depend on the type and abundance of coexisting structural species in depolymerized melts, either show smooth functional relationships to melt polymerization, NBO/T, or exhibit pronounced minimum or maximum values at intermediate NBO/T-values. (more…)

Determination of molar absorptivity of IR fundamental OH-stretching vibration in rhyolitic glasses

Filed under: Glasses 2003 — admin @ 5:41 am

Molar absorptivity of the infrared (IR) fundamental OH-stretching vibration band at 3550 cm–1 was determined for rhyolitic glasses. Five obsidian samples, unheated and heated at 500–700 °C using an internally heated pressure vessel, were used to evaluate the dependence of the molar absorptivity and final quenched H2O speciation on H2O contents and temperature. Water contents of the obsidians were measured by Karl-Fischer titration first, then the amount of unextracted H2O was calibrated by IR (more…)

Evidence for rhenium enrichment in the mantle wedge from submarine arc–like volcanic glasses (Papua New Guinea)

Filed under: Glasses 2003 — admin @ 5:40 am

AbstractThe low Re abundance in arc-type volcanic rocks characterized by high 187Os/188Os ratios is an unsolved puzzle of the 187Re-187Os isotope system, leaving a significant gap in our understanding of the evolution of the upper mantle–continental crust system. Here we report new observations of high Re concentrations in fresh, submarine-erupted—i.e., relatively undegassed—island arc–like volcanic glasses dredged from the eastern Manus Basin, offshore Papua New Guinea. (more…)

Titanium coordination in silicate glasses investigated using O K-edge X-ray absorption spectroscopy

Filed under: Glasses 2003 — admin @ 5:38 am

A series of titanium silicate glasses along the composition joins TiO2–SiO2, TiO2–Na2SiO3, TiO2–K2SiO3 and TiO2–CaSiO3, has been examined using oxygen K-edge X-ray absorption near edge structure spectroscopy (XANES) confined to the near-surface region. Sharp pre-edge features in the spectra can be used to determine the Ti coordination in the glasses. The presence of [4]Ti is indicated by a pre-edge peak at ~534 eV while [5]Ti is indicated by a peak at ~533 eV. Titanium exists in all these glasses as [4]Ti and [5]Ti with no [6]Ti being present. For alkali-containing glasses the [5]Ti site becomes more prevalent with increasing TiO2. TiO2-K2SiO3 compositions contain a greater proportion of [4]Ti than comparable (more…)

Glasses Tech – Prescription Glasses, Prescription Eyeglasses