Glasses Tech

March 8, 2010

Anomalous uplift and subsidence of the Ontong Java Plateau inferred from CO2 contents of submarine basaltic glasses

Filed under: Glasses 2005 — admin @ 9:52 am

Eyeglasses

The Ontong Java Plateau in the western Pacific is anomalous compared to other oceanic large igneous provinces in that it appears to have never formed a large subaerial plateau. Paleoeruption depths (at 122 Ma) estimated from dissolved H2O and CO2 in submarine basaltic glass pillow rims vary from ∼1100 m below sea level (mbsl) on the central part of the plateau to 2200–3000 mbsl on the northeastern edge. Our results suggest maximum initial uplift for the plateau of 2500–3600 m above the surrounding seafloor and 1500 ± 400 m of postemplacement subsidence since 122 Ma. Our estimates of uplift and subsidence for the plateau are significantly less than predictions from thermal models of oceanic lithosphere, and thus our results are inconsistent with formation of the plateau by a high-temperature mantle plume. (more…)

Application of video glasses for sustained affective picture presentations: A comparison with video projector presentations

Filed under: Glasses 2005 — admin @ 9:52 am

Video glasses have previously been reported to be an effective instrument for emotion induction or for reducing pain perception. In the present study, we assessed the application of video glasses within the affective picture viewing paradigm. Possible advantages of this new method were tested by a comparison with a commonly used video projector. Twenty-four participants viewed sustained picture series of pleasant, neutral, and unpleasant valence with video glasses and with a projector on different days. Affective report, heart rate (HR), and skin conductance level were measured. (more…)

Evaporative differentiation of impact-produced melts: Laser-simulation experiments and comparison with impact glasses from the Logoisk crater

Filed under: Glasses 2005 — admin @ 9:51 am

Evaporative modification of silicates during impacts by large meteorites is the result of high-temperature processing of colliding silicate materials. There are still unresolved questions about the influence of vaporization on the chemical compositions of impact glasses. Here we present the results of experimental modeling of impact-related high-temperature pulse heating of silicates with compositions representative of Earth’s crust. Trends involving differential volatilization of the main rock-forming elements were determined experimentally and compared with those predicted by thermodynamic equilibrium calculations. Our results indicate that impact-induced vaporization is significant for melts at temperatures of 3000–5000 K. As vaporization begins, melts lose Si, Fe, and alkalis and are enriched in Mg, Ca, Al, and Ti. (more…)

Randomised clinical trial of the effectiveness of base-in prism reading glasses versus placebo reading glasses for symptomatic convergence insufficiency in children

Filed under: Glasses 2005 — admin @ 9:51 am

Purpose: To compare base-in prism reading glasses with placebo reading glasses for the treatment of symptomatic convergence insufficiency (CI) in children aged 9 to <18 years.

Methods: In a randomised clinical trial, 72 children aged 9 to <18 years with symptomatic CI were assigned to either base-in prism glasses or placebo reading glasses. Symptom level, measured with a quantitative symptom questionnaire (CI Symptom Survey-V15), was the primary outcome measure. Near point of convergence and positive fusional vergence at near were secondary outcomes. (more…)

Aluminum coordination and the densification of high-pressure aluminosilicate glasses

Filed under: Glasses 2005 — admin @ 9:50 am

To better understand the relationship between atomic-scale structures and densities of aluminosilicate glasses and liquids, we used 27Al MAS NMR to determine the speciation of aluminum ions in K3AlSi3O9, Na3AlSi3O9, and Ca3Al2Si6O18 glasses quenched from melts at 3 to 10 GPa. These data are a first approximation of high-pressure melt structure and illustrate the effects of the type of modifier cation. High field strength modifier cations (e.g., Ca) clearly induce more high-coordinated Al than lower field strength cations (e.g., Na and K). (more…)

Structure and the extent of disorder in quaternary (Ca-Mg and Ca-Na) aluminosilicate glasses and melts

Filed under: Glasses 2005 — admin @ 9:49 am

The structure of multi-component silicate melts and glasses (e.g., Ca-Mg and Ca-Na aluminosilicates) can provide insight into the properties of natural silicate melts and has implications for relevant magmatic processes. In spite of its importance, the atomic and molecular structure of most multi-components (e.g., quaternary) melts and glasses has not been fully described, primarily because of insufficient resolution obtained with conventional spectroscopic and scattering methods; the information obtained by these methods is compromised by severe inhomogeneous peak broadening due to structural complexity. Here we report the first 17O and 27Al 3QMAS NMR spectra for quaternary, (more…)

The effect of fictive temperature on Al coordination in high-pressure (10 GPa) sodium aluminosilicate glasses

Filed under: Glasses 2005 — admin @ 9:49 am

Typical liquidus temperatures can be over 1000 °C greater than the glass transition temperatures for high-pressure aluminosilicate melts so the effect of temperature must be determined if glass data is to be used to approximate the structural speciation present in geologic melts. This study has investigated the effect of fictive temperature (Tf, taken as the temperature where the melt structure is the same as that of the glass) on the percentage of [5]Al and [6]Al species in two high-pressure (10 GPa) Na-aluminosilicate glasses (Na3AlSi7O17 and NaAlSi3O8) where one glass of each composition was quenched from the high-pressure melt while the other was annealed near the glass transition temperature. (more…)

Effect of current density on the electron microprobe analysis of alkali aluminosilicate glasses

Filed under: Glasses 2005 — admin @ 7:22 am

In a previous work (Morgan and London 1996), we proposed an optimized procedure for electron microprobe analysis (EMPA) of rhyolitic glasses using a broad (20 µm diameter), low-current (2 nA) fixed beam. Some important applications for EMPA of glass, such as vitreous inclusions in minerals and experimental run products, require smaller beam diameters that produce greater areal current densities (expressed as nA/µm2). For these situations, we have assessed the effect of areal current density on the migration of Na and its concomitant effects on other elements and their ratios during EMPA of granitic glasses. Anhydrous and hydrous glasses of a haplogranite composition (Ab38.23Or29.31Qtz33.37C0.10) were analyzed at 20 kV accelerating potential, using 2–50 nA beam currents, fixed beam diameters of 2–20 µm, and counting times scaled to yield similar analytical uncertainty at each condition (~2.6% relative for Na2O). (more…)

Quantification of Anion and Cation Release from a Range of Ternary Phosphate-based Glasses with Fixed 45 mol% P2O5

Filed under: Glasses 2005 — admin @ 7:15 am

This article reports on the use of ion chromatography (IC) to investigate extensively the release profiles of both cations and anions and characterize the relationship between composition and degradation for a ternary-based Na2O-CaO-P2O5 glass system developed as biomaterials. Studies are carried out on glasses with the formula 45P2O5-55(xCaO-Na2O) in deionized water, where x = 30, 35, and 40 mol%, using a cumulative release method, where the solution is changed at regular intervals. (more…)

Stability and dynamics of crystals and glasses of motorized particles

Filed under: Glasses 2004 — admin @ 7:02 am

Many of the large structures of the cell, such as the cytoskeleton, are assembled and maintained far from equilibrium. We study the stabilities of various structures for a simple model of such a far-from-equilibrium organized assembly in which spherical particles move under the influence of attached motors. From the variational solutions of the many-body master equation for Brownian motion with motorized kicking we obtain a closed equation for the order parameter of localization. (more…)

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