102 research outputs found

    A photopolymerizable glass with diffraction efficiency near 100% for holographic storage

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    Permanent holographic storage has been demonstrated in a photopolymerizable organically modified silica glass. The glass was prepared by dispersing a titanocene photoinitiator and a high refractive index acrylic monomer in a porous silica matrix. This glass exhibits unprecedented sensitivity and refractive index change upon a moderate exposure to green light and can be fabricated in thickness up to several millimeters. A photopolymerizable storage medium of such a thickness with good holographic properties is needed for practical holographic storage devices. Lack of such medium has been considered the main obstacle in development of write-once holographic memories. In our glass, we have stored permanent volume holograms of diffraction efficiency approaching 100% and refractive index modulation up to 4.5 x 10(-3), making this photopolymerizable material suitable for use in holographic data storage

    Modulation of Riverine Concentration‐Discharge Relationships by Changes in the Shape of the Water Transit Time Distribution

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    The concentrations of weathering-derived solutes in rivers and their covariance with discharge are thought to reflect reactive-transport processes in hillslopes and to reveal the sensitivity of solute fluxes to climatic change. It is expected that discharge-driven changes in water transit times play some role in setting concentration-discharge (C-Q) relationships, but knowledge gaps remain. To explore the specific role of changes in the shape of the transit time distribution with discharge, we combine models to simulate C-Q relationships for major cations and Si as example solutes with contrasting affinities to partition into secondary phases. The model results are compared with an analysis of C-Q relationships using the Global River Chemistry Database. We find that changes in the shape of the transit time distribution with discharge can produce a range of cation-Q and Si-Q relationships that encompasses most of the range observed in real catchments, including positive Si-Q relationships and variable cation to Si ratios. We find that C-Q relationships (characterized by power law exponents) can remain approximately constant, even as the Damköhler Number (ratio of transport time scale to reaction time scale) is varied over 3 orders of magnitude. So, in our model analysis, C-Q relationships are as sensitive to hydrologic variability as they are to reaction rates. Additionally we find that, depending on the storage-discharge relationship, changes in rainfall patterns can influence C-Q relationships. Altogether, our results suggest ways in which C-Q relationships may be nonstationary in response to climatic change and/or vary in space and time due to catchment hydrologic properties

    Über Kobaltmagnesium-Rot

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    Sol-gel processes

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