Glasses Tech – Prescription Glasses, Prescription Eyeglasses

March 8, 2010

Bulk-solvent and hydration-shell fluctuations, similar to α- and β-fluctuations in glasses, control protein motions and functions

Filed under: Glasses 2004 — admin @ 7:01 am


The concept that proteins exist in numerous different conformations or conformational substates, described by an energy landscape, is now accepted, but the dynamics is incompletely explored. We have previously shown that large-scale protein motions, such as the exit of a ligand from the protein interior, follow the dielectric fluctuations in the bulk solvent. (more…)

A simple empirical method for high-quality electron microprobe analysis of fluorine at trace levels in Fe-bearing minerals and glasses

Filed under: Glasses 2004 — admin @ 7:00 am

We present a new, high-quality electron microprobe method for analyzing F in Fe-bearing minerals and glasses down to trace levels (<1000 ppm F). This method is empirically based and corrects for the problem of overlap of the FK peak onto the “shoulder” of the FeL 1 peak that arises when using synthetic multi-layered diffraction crystals. It also achieves high precision and accuracy while maintaining low detection limits and a small beam diameter. (more…)

Coloured glasses for high dose dosimetry using the thermoluminescent technique

Filed under: Glasses 2004 — admin @ 6:58 am

Coloured glasses produced commercially by Cebracê, São Paulo, were analysed by the thermoluminescent (TL) method, to verify the possibility of their use as high-dose dosemeters or irradiation indicators in industrial areas, due to their easy handling and their low cost. The samples were exposed to different radiation doses, using the Gamma-Cell 220 system (60Co) of IPEN. (more…)

A XANES determination of the oxidation state of chromium in silicate glasses

Filed under: Glasses 2004 — admin @ 6:55 am

Cr K-edge X-ray absorption near-edge structure (XANES) spectra were recorded for silicate glasses of various compositions in the system CaO + MgO + Al2O3 + SiO2 ± TiO2, quenched from melts equilibrated as a function of oxygen fugacity (fO2) at 1400°C. The spectra vary systematically with fO2 (log fO2 ~0 to –16) indicating changes in the Cr oxidation state. The intensity of a shoulder on the absorption edge (attributed to the 1s 4s transition) was quantified using the corresponding peak in the XANES derivative spectrum and used to determine Cr2+/Cr. (more…)

Ca-Mg and K-Mg mixing around non-bridging O atoms in silicate glasses: An investigation using 17O MAS and 3QMAS NMR

Filed under: Glasses 2004 — admin @ 6:50 am

In an effort to improve the physical accuracy of models of the thermodynamics of silicate melts, we describe a systematic study of the extent of modifying cation mixing, using 17O 3QMAS NMR, in a series of Ca-Mg and K-Mg silicate glasses. (more…)

Determination of the molar absorption coefficient for the infrared absorption band of CO2 in rhyolitic glasses

Filed under: Glasses 2004 — admin @ 6:43 am

A new calibration was performed for the molecular CO2 band at 2349 cm –1 in the infrared absorption spectra of rhyolitic glasses. Glasses with varying amounts of CO2 (730–3900 ppm by weight) and H2O (0.5–7.0 wt%) were synthesized in an internally heated pressure vessel at 200–800 MPa and 1100 and 1200 °C. The CO2 content of the glasses was measured by coulometric CO2-titration after thermal extraction at 1200 °C. It is shown that the entire CO2 content cannot be extracted from a rhyolitic glass at this temperature. Using the Lambert-Beer law, and taking into account the residual CO2 still present in the glasses after extraction, we have calculated a linear molar absorption coefficient of 1214 ± 78 L · cm –1/mol for the band at 2349 cm –1 . Strictly, this value is a practical absorption coefficient because the IR band intensity is related to the total CO2 content and not to the molecular CO2 content. (more…)

V oxidation state and coordination number in silicate glasses by XAS

Filed under: Glasses 2004 — admin @ 6:40 am

The local structure of vanadium (V) in synthetic glasses of basaltic composition has been studied by means of high-resolution V K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to obtain quantitative data on distances, V coordination number (CN), and oxidation state. The compositions and experimental conditions were chosen so as to verify the effect of bulk-glass composition (using a diopside-anorthite composition, a sodium disilicate glass, and an iron-titanium-bearing basaltic glass) and V content (from 0.1 to 5 V2O5 wt%) on the structural role of V in these glasses. (more…)

Incinerator waste as secondary raw material: examples of applications in glasses, glass-ceramics and ceramics

Filed under: Glasses 2004 — admin @ 6:39 am

The recovery and beneficiation of solid waste residues (bottom and fly ash) produced during incineration of municipal wastes are very important goals from the environmental and economic point of view. Some technologies allow not only to reduce the volume of incinerator waste but also to generate products of economic value by vitrification, devitrification, and ceramic processes. (more…)

Volatiles in submarine basaltic glasses from the Ontong Java Plateau (ODP Leg 192): implications for magmatic processes and source region compositions

Filed under: Glasses 2004 — admin @ 6:38 am

Submarine basaltic glasses from five widely separated sites on the Ontong Java Plateau (OJP) were analysed for major and volatile elements (H2O, CO2, S, Cl). At four of the sites (1183, 1185, 1186, 1187) the glass is from pillow basalt rims, whereas at Site 1184 the glass occurs as non-vesicular glass shards in volcaniclastic rocks. Glassy pillow rims from Site 1187 and the upper group of flows at Site 1185 have 8.3–9.3 wt% MgO compared with values of 7.2–8.0 wt% MgO for glasses from Sites 1183, 1184 1186, and the lower group of flows at Site 1185. Low-MgO glasses have slightly higher H2O contents (average 0.22 wt% H2O) than high-MgO glasses (average 0.19 wt%), with the exception of Site 1184, where low-MgO glasses have lower H2O (average 0.16 wt%). Average S concentrations are 910 ± 60 ppm for the high-MgO glasses v. 1030 ± 60 ppm for the low-MgO glasses. When compared with mid-ocean ridge basalt (MORB), the OJP glasses have lower S at comparable FeOT. (more…)

Na K-edge XANES spectra of minerals and glasses

Filed under: Glasses 2004 — admin @ 6:36 am

Na K-edge X ray absorption near-edge structure (XANES) spectra for minerals and glasses were collected using synchrotron radiation. Na-K XANES is a good structural probe to determine the coordination state of this element in important minerals and glasses. From the XANES spectra on crystalline reference phases with different chemical environment, information can be obtained and compared with the structure of the minerals and glasses. (more…)

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Glasses Tech – Prescription Glasses, Prescription Eyeglasses