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Author: Bauer, Johannes × Has files: Yes ×

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Now showing 1 - 4 of 4
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    Validation of a mathematical glass tank model
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Bauer, Johannes; Roger, Ulrich; Simons, Philip
    In the past mathematical modelling of glass furnaces concentrated on the redesign and optimization of such aggregates. For the future, it is conceivable that such models will also be used for the control of glass furnaces. The present study showed that an increased occurrence of bubbles due to increased glass pull can be found in the results of the model, while a corresponding link between model and practice could not be found for solid inclusions. As a main cause for the limited correspondence between modelling and practice the dominating influence of recycled cullet and the frequent changes of the glass pull could be identified.
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    Redox behavior of selenium in industrial soda-lime-silica glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Müller-Simon, Hayo; Bauer, Johannes; Baumann, Patrick
    Α thermodynamic model for the calculation of the redox distributions of polyvalent elements which is based on the balance of chemically bonded oxygen in glass melts has been applied to the redox reactions of selenium. Α set of reliable thermodynamic data of the selenium oxidation reactions has been derived using results of electrochemical, optical and wet-chemical investigations. Calculation results showed that selenium is reduced during cooling by iron as well as by sulfur. Due to the small selenium/sulfur ratio in selenium-decolorized flint glasses under industrial conditions selenium is completely reduced to the selenide state. Obviously, in industrially melted flint glasses selenium decolorization is not provided by the pink color of elemental selenium as assumed so far but by the amber color of iron selenide, which is supported by the fact that selenium decolorization always causes an additional yellow tint besides the required red tint and a considerable shift of the UV edge to larger wavelengths.
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    Measurement of convective heat transfer for various checker systems
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Bauer, Johannes; Hofmann, Otto-R.; Giese, Sabine
    The heat transfer properties of six different checkerworks were studied using a special test equipment. The temperature was deliberately limited to 300 C in order to measure the local temperature distribution of the air for the first time. The flow in the regenerator channels shows a considerable non-symmetrical appearance and local strands. Its enthalpy can not be determined by the measurement of only one temperature. The heat transfer depends not only on the velocity of the flow (forced convection) but also on the temperature differences and resulting density differences of the fluid (free convection). In consequence of the low operating temperature and the necessity to measure the air temperature at many points, sufficiently accurate values for the coefficient of heat transfer could only be achieved for a part of the parameter range of industrial regenerators.
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    Loss spectroscopy of molecular solids: Combining experiment and theory
    (Milton Park : Taylor & Francis, 2013) Roth, Friedrich; Cudazzo, Pierluigi; Mahns, Benjamin; Gatti, Matteo; Bauer, Johannes; Hampel, Silke; Nohr, Markus; Berger, Helmuth; Knupfer, Martin; Rubio, Angel
    The nature of the lowest-energy electronic excitations in prototypical molecular solids is studied here in detail by combining electron energy loss spectroscopy (EELS) experiments and state-of-the-art many-body calculations based on the Bethe–Salpeter equation. From a detailed comparison of the spectra in picene, coronene and tetracene we generally find a good agreement between theory and experiment, with an upshift of the main features of the calculated spectrum of 0.1–0.2 eV, which can be considered the error bar of the calculation. We focus on the anisotropy of the spectra, which illustrates the complexity of this class of materials, showing a high sensitivity with respect to the three-dimensional packing of the molecular units in the crystal. The differences between the measured and the calculated spectra are explained in terms of the small differences between the crystal structures of the measured samples and the structural model used in the calculations. Finally, we discuss the role played by the different electron–hole interactions in the spectra. We thus demonstrate that the combination of highly accurate experimental EELS and theoretical analysis is a powerful tool to elucidate and understand the electronic properties of molecular solids.