Ueber Alkalien widerstehende Gef?sse

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Eine Neuberechnung der Atomgewichte

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Arbeiten technischen Inhalts

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Sums of reciprocal Stekloff eigenvalues

Let 0 = λ₁ < λ₂ ≤ λ₃ ≤ … be the Stekloff eigenvalues of a plane domain. The paper is concerned with formulas for ∑^∞₂λ^(–2)_j in simply and doubly connected domains. In the simply connected case it is proven that the disk minimized this sum. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

From mass to structure: an aromaticity index for high‐resolution mass data of natural organic matter

Recent progress in Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) has provided extensive molecular mass data for complex natural organic matter (NOM). Structural information can be deduced solely from the molecular masses for ions with extreme molecular element ratios, in particular low H/C ratios, which are abundant in thermally altered NOM (e.g. black carbon). In this communication we propose a general aromaticity index (AI) and two threshold values as unequivocal criteria for the existence of either aromatic (AI > 0.5) or condensed aromatic structures (AI ≥ 0.67) in NOM. AI can be calculated from molecular formulae which are derived from exact molecular masses of naturally occurring compounds containing C, H, O, N, S and P, and is especially useful for substances with aromatic cores and few alkylations. In order to test the validity of our model index, AI is applied to FTICRMS data of a NOM deep‐water sample from the Weddell Sea (Antarctica), a fulvic acid standard, and an artificial dataset of all theoretically possible molecular formulae. For graphical evaluation a ternary plot is suggested for four‐dimensional data representation. The proposed aromaticity index is a step towards structural identification of NOM and the molecular identification of polyaromatic hydrocarbons in the environment. Copyright © 2006 John Wiley & Sons, Ltd.     

Bulk single crystals of β-Ga2O3 and Ga-based spinels as ultra-wide bandgap transparent semiconducting oxides

In the course of development of transparent semiconducting oxides (TSOs) we compare the growth and basic physical properties bulk single crystals of ultra-wide bandgap (UWBG) TSOs, namely β-Ga₂O₃ and Ga-based spinels MgGa₂O₄, ZnGa₂O₄, and Zn_1-xMg_xGa₂O₄. High melting points of the materials of about 1800 -1930 °C and their thermal instability, including incongruent decomposition of Ga-based spinels, require additional tools to obtain large crystal volume of high structural quality that can be used for electronic and optoelectronic devices. Bulk β-Ga₂O₃ single crystals were grown by the Czochralski method with a diameter up to 2 inch, while the Ga-based spinel single crystals either by the Czochralski, Kyropoulos-like, or vertical gradient freeze / Bridgman methods with a volume of several to over a dozen cm³. The UWBG TSOs discussed here have optical bandgaps of about 4.6 - 5 eV and great transparency in the UV / visible spectrum. The materials can be obtained as electrical insulators, n-type semiconductors, or n-type degenerate semiconductors. The free electron concentration (n_e) of bulk β-Ga₂O₃ crystals can be tuned within three orders of magnitude 10¹⁶ - 10¹⁹ cm^?3 with a maximum Hall electron mobility (μ) of 160 cm²V^?1s^?1, that gradually decreases with n_e. In the case of the bulk Ga-based spinel crystals with no intentional doping, the maximum of n_e and μ increase with decreasing the Mg content in the compound and reach values of about 10²⁰ cm^?3 and about 100 cm²V^?1s^?1 (at n_e > 10¹⁹ cm^?3), respectively, for pure ZnGa₂O₄.     

A dynamical study of the melting behavior of polypivalolactone single crystals by the X-ray diffraction method

Wide-angle and small-angle X-ray diffraction patterns of polypivalolactone single crystals were recorded as a function of temperature while heating at a constant rate. Long periods were found to increase abruptly at a certain temperature, while the degree of crystallinity decreased up to that temperature and then recovered on further heating, to an extent depending on the rate of heating. Multiple endotherms were observed in DSC measurements. The temperature at which the first endotherm peak was observed corresponded exactly to the temperature of the long period jump mentioned above. From these data, it is concluded that the original lamellar crystals melt at each peak temperature in the DSC thermogram and new lamellae are produced by subsequent crystallization. Multiple endotherms in the DSC thermogram are thus considered to represent repeated melt-recrystallization processes.