Glasses Tech

The Fine Art of Prescribing Glasses: Without Making a Spectacle of Yourself, Third Edition

admin — Mon, 08 Mar 2010 09:56:35 +0000

Once again, Drs Milder and Rubin have provided an invaluable text for all who deal with refractive correction of the eye. The Fine Art of Prescribing Glasses: Without Making a Spectacle of Yourself, Third Edition, has been thoughtfully updated and revised by the authors.

The text’s 22 chapters thoroughly cover the necessary subjects that allow ophthalmologists and optometrists to excel in refractions and in prescribing lenses. Throughout this book, case examples and discussions illustrate and emphasize important points. As in previous editions, the style of writing makes concepts easy to understand. The chapter lengths allow for a comfortable review of specific topics, without the necessity of reading earlier chapters to understand any one section. The result is a book of great value for the office or clinic. Everyone who prescribes glasses or contacts or performs refractive surgery should read this text.

by Benjamin Milder, MD; Melvin L. Rubin, MD, MS; 494 pp, with illus, $88, ISBN 0-937404-66-7, Gainesville, Fla, Triad Publishing Company, 2004.

Arch Ophthalmol. 2005;123:712.

THE STRUCTURE OF LITHIUM-CONTAINING SILICATE AND GERMANATE GLASSES

admin — Mon, 08 Mar 2010 09:54:29 +0000

The addition of alkali oxides to silicate glasses results in the disruption of the silicate network and the formation of non-bridging oxygen atoms and Qn species. Lithium-containing silicate glasses behave differently than other alkali-containing silicate glasses. Addition of Li2O to silicate and germanate glasses generates Q2 species at low Li contents. Furthermore, the preference for Q2 formation is enhanced in Li-germanate relative to Li-silicate glasses. The proposed mechanism for incorporation of the Li involves its bonding to pairs of non-bridging atoms of oxygen on adjacent Q2 tetrahedra, resulting in a Li coordination of 4 in a square-planar configuration.

Leonie G. Soltay and Grant S. Henderson

Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada

E-mail address: granth@geology.utoronto.ca

Keywords: glasses, structure, lithium, alkalis, germanates, melts, Q species, silicates.

Structural Relaxation of Polymer Glasses at Surfaces, Interfaces, and In Between

admin — Mon, 08 Mar 2010 09:53:48 +0000

We analyzed the glassy-state structural relaxation of polymers near surfaces and interfaces by monitoring fluorescence in multilayer films. Relative to that of bulk, the rate of structural relaxation of poly(methyl methacrylate) is reduced by a factor of 2 at a free surface and by a factor of 15 at a silica substrate interface; the latter exhibits a nearly complete arresting of relaxation. The distribution in relaxation rates extends more than 100 nanometers into the film interior, a distance greater than that over which surfaces and interfaces affect the glass transition temperature.

1 Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208, USA.
2 Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.

* To whom correspondence should be addressed. E-mail: broadbelt@northwestern.edu; j-torkelson@northwestern.edu
Rodney D. Priestley,1 Christopher J. Ellison,1 Linda J. Broadbelt,1* John M. Torkelson1,2*

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

admin — Mon, 08 Mar 2010 09:52:53 +0000

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. Two controversial possibilities to explain the anomalous uplift and subsidence are that the plateau (1) formed as a result of a giant bolide impact, or (2) formed from a mantle plume but has a lower crust of dense garnet granulite and/or eclogite; neither of these possibilities is fully consistent with all available geological, geophysical, and geochemical data. The origin of the largest magmatic event on Earth in the past 200 m.y. thus remains an enigma.

Julie Roberge1, Paul J. Wallace1, Rosalind V. White2 and Millard F. Coffin3
+ Author Affiliations

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

admin — Mon, 08 Mar 2010 09:52:24 +0000

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. The results showed that the video glasses presentation mode is not generally superior to the projector mode. Instead, typical responses to prolonged presentations of emotional pictures were obtained across both modalities with valence-modulated pleasure ratings and with an arousal modulation for arousal ratings, skin conductance level, and HR. These results suggest that video glasses are as useful for presenting prolonged affective picture series as are projectors. Specific contexts in which the application of video glasses is preferential are discussed.

Author Affiliations

University of Hamburg, Hamburg, Germany
The authors thank Thomas Ritz for his helpful comments on a previous draft of this article. The authors declare that they have no competing or financial interests in products that are referred to in this article. Reprint requests and correspondence concerning this article should be addressed to A. von Leupoldt, Psychological Institute III, University of Hamburg, Von-Melle-Park 5, 20146 Hamburg, Germany (e-mail: andreas.vonleupoldt@uni-hamburg.de).

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

admin — Mon, 08 Mar 2010 09:51:46 +0000

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. With increased mass loss, melts start to lose Mg while Si and even Na can still be present. Still greater mass loss produces melts enriched in Ca, Al, and Ti. We then attempted to use the experimentally determined trends to look for signs of evaporative differentiation in impact glasses from the Logoisk structure (Byelorussia). Fresh impact glasses from suevites in the Logoisk crater have compositions that are in good agreement with the differentiation trends obtained both experimentally and via thermodynamic calculations in the range of 3000–5000 K. The most useful methods for recognizing evaporative differentiation in the natural glasses are the conservation of the initial Ca/Al ratio and the anti-correlation of Si and Al.

M.V. Gerasimov15, O.I. Yakovlev2, Yu.P. Dikov3 and F. Wlotzka4
+ Author Affiliations

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

admin — Mon, 08 Mar 2010 09:51:11 +0000

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.

Results: The mean (SD) CI Symptom Survey score decreased (that is, less symptomatic) in both groups (base-in prism glasses from 31.6 (10.4) to 16.5 (9.2); placebo glasses from 28.4 (8.8) to 17.5 (12.3)). The change in the CI Symptom Survey scores (p = 0.33), near point of convergence (p = 0.91), and positive fusional vergence (p = 0.59) were not significantly different between the two groups after 6 weeks of wearing glasses.

Conclusions: Base-in prism reading glasses were found to be no more effective in alleviating symptoms, improving the near point of convergence, or improving positive fusional vergence at near than placebo reading glasses for the treatment of children aged 9 to <18 years with symptomatic CI.

M Scheiman1, S Cotter2, M Rouse2, G L Mitchell3, M Kulp3, J Cooper4, E Borsting2, and the Convergence Insufficiency Treatment Trial (CITT) Study Group*
+ Author Affiliations

1Eye Institute, Pennsylvania College of Optometry, Philadelphia, PA, USA
2Southern California College of Optometry, Fullerton, CA, USA
3Optometry Coordinating Center, The Ohio State University, Columbus, OH, USA
4College of Optometry, State University of New York, New York, NY, USA
Correspondence to: Professor M Scheiman Eye Institute, Pennsylvania College of Optometry, 1200 West Godfrey Ave, Philadelphia, PA 19141, USA; mscheiman@pco.edu
Accepted 1 March 2005

Aluminum coordination and the densification of high-pressure aluminosilicate glasses

admin — Mon, 08 Mar 2010 09:50:30 +0000

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). Measured glass densities show that, especially with rapid decompression, a significant portion of the total densification observed in-situ in melts is retained on return to ambient temperature and pressure. Observed increases in Al coordination are well correlated with decreased volume, which suggests that this structural change is a major part of the mechanism for recovered densification of high-pressure melts. Additionally, 23Na MAS NMR, combined with the 27Al MAS spectra and density determinations, reveal that other changes, such as the compression of modifier cation sites and/or decreased network bond angles, must also be significant, especially at low pressure.

Jeffrey R. Allwardt1,2,*, Jonathan F. Stebbins1, Burkhard C. Schmidt2,, Daniel J. Frost2, Anthony C. Withers3 and Marc M. Hirschmann3
1 Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, U.S.A.
2 Bayerisches Geoinstitut, Universität Bayreuth, Germany
3 Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A.

Correspondence: * E-mail: allwardt@pangea.stanford.edu

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

admin — Mon, 08 Mar 2010 09:49:55 +0000

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, Ca-Mg and Ca-Na peralkaline aluminosilicate glasses (i.e., M/Al > 1, M is one monovalent or one-half a divalent cation). These data reveal new details into the molecular structure of multi-component aluminosilicate melts, which include the presence of a substantial fraction of VAl in the Ca-Mg aluminosilicate glasses and IVAl-O-IVAl in both glasses at 1 atm. Traditional models of glass structure do not support the presence of such species given these high-silica, peralkaline compositions. These results suggest that Al avoidance is violated in the multi-component peralkaline aluminosilicate glasses, and that the presence of Mg2+ in the melts increases the extent of disorder in the melts (compared with Ca2+ and Na+). These factors lead to an increase in configurational entropy and the activity coefficients of the oxides, and may provide an explanation for the decrease in viscosity of these complex melts.

Sung Keun Lee1,2,*, George D. Cody2 and Bjorn O. Mysen2
1 School of Earth and Environmental Sciences, Seoul National University, Seoul 151-742, Korea
2 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington D.C. 20015, U.S.A.

Correspondence: * E-mail: sungklee@snu.ac.kr

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

admin — Mon, 08 Mar 2010 09:49:19 +0000

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. The 27Al MAS NMR spectra of the Na3AlSi7O17 samples show that the higher Tf (quenched) glass contains more high-coordinated Al than the lower Tf (annealed, 475 °C) glass. However, the 27Al spectra of the NaAlSi3O8 samples show the opposite temperature dependency, which in addition to the lack of NBO in this glass, may suggest differing mechanisms for the generation of high-coordinated Al.

Jeffrey R. Allwardt1,*, Brent T. Poe2 and Jonathan F. Stebbins1
1 Department of Geological and Environmental Sciences, Stanford University, Building 320, Stanford, California 94305-2115, U.S.A.
2 Istituto Nazionale di Geofisica e Vulcanologia, Rome

Correspondence: * E-mail: allwardt@pangea.stanford.edu