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排序方式: 共有1149条查询结果,搜索用时 31 毫秒
91.
Susanne Liemersdorf Ralf Riedel Jürgen Oberle 《Journal of the American Ceramic Society》2008,91(1):325-328
Silicon oxycarbide (SiOC)-based ceramics were synthesized by pyrolysis of a commercial polysiloxane containing MoSi2 and ceramic filler particles. The influence of different gas atmospheres on the chemical composition and on the phase formation of the filled Si–O–C ceramic during the pyrolysis process up to elevated temperatures of above 1200°C has been studied. The pyrolysis gas composition in the furnace during pyrolysis was measured with an in situ gas analyzer. Both the core and the surface of bulk samples were investigated with respect to composition in order to take the changes on the rim area of the specimens into account. The influence of hydrogen gas on the compositional gradient of the resulting ceramic material was derived from samples investigated by polarization microscopy, X-ray diffraction (XRD), and micro-XRD (μ-XRD). 相似文献
92.
The pyrolytic conversion of bis-Lewis base adducts of decaborane(14), L·B10H12·L (L=neutral monophosphine) and phosphonium salts of the [B10H10]2– anion (e.g. [Ph4P+]2, etc.), to ceramic materials has been studied. All species examined served as binders for a variety of non-oxide refractory ceramic powders (e.g. B4C, BN, BP, B13P2, SiC, Si3N4, B, C, AIN). 相似文献
93.
Temperature‐dependent coefficient of thermal expansion (CTE) of injection molded,short‐glass‐fiber‐reinforced polymers 下载免费PDF全文
A deep understanding of the anisotropic, composite‐, geometry‐, and temperature‐dependent coefficient of thermal expansion (CTE) of short‐fiber‐reinforced polymers is often needed in material development and at early stages of the design process of injection molded parts. Usually, the data available does not reflect the complex behavior and the knowledge about the influences and interactions are missing. This paper deals with a method for calculating the composite‐, geometry‐, and temperature‐dependent anisotropic CTE of parts made from short‐fiber reinforced polymers without respectively low preload to create an understanding of its origins and influential factors. Here, a good accordance between the measurements and calculations was achieved. POLYM. ENG. SCI., 55:2661–2668, 2015. © 2015 Society of Plastics Engineers 相似文献
94.
Catalysis of an Essential Step in Vitamin B2 Biosynthesis by a Consortium of Broad Spectrum Hydrolases 下载免费PDF全文
Sonja Sarge Dr. Ilka Haase Dr. Boris Illarionov Dr. Dietmar Laudert Dr. Hans‐Peter Hohmann Prof. Adelbert Bacher Prof. Markus Fischer 《Chembiochem : a European journal of chemical biology》2015,16(17):2466-2469
An enzyme catalysing the essential dephosphorylation of the riboflavin precursor, 5‐amino‐6‐ribitylamino‐2,4(1H,3H)‐pyrimidinedione 5′‐phosphate ( 6 ), was purified about 800‐fold from a riboflavin‐producing Bacillus subtilis strain, and was assigned as the translation product of the ycsE gene by mass spectrometry. YcsE is a member of the large haloacid dehalogenase (HAD) superfamily. The recombinant protein was expressed in Escherichia coli. It catalyses the hydrolysis of 6 (vmax, 12 μmol mg?1 min?1; KM, 54 μm ) and of FMN (vmax, 25 μmol mg?1 min?1; KM, 135 μm ). A ycsE deletion mutant of B. subtilis was not riboflavin dependent. Two additional proteins (YwtE, YitU) that catalyse the hydrolysis of 6 at appreciable rates were identified by screening 13 putative HAD superfamily members from B. subtilis. The evolutionary processes that have resulted in the handling of an essential step in the biosynthesis of an essential cofactor by a consortium of promiscuous enzymes require further analysis. 相似文献
95.
Gtz Hüsken Stephan Pirskawetz Dietmar Meinel Veronika Babski Hans‐Carsten Kühne 《Bautechnik》2016,93(10):711-716
Methods for analyzing the fracture behavior of high‐strength steel fiber‐reinforced concretes High‐strength and ultra‐high strength fiber‐reinforced concretes are most suitable for applications with extreme mechanical loads. These extreme conditions require a ductile behavior under tensile loading, which is obtained solely by the addition of steel fibers and their working mechanism. Profound know ledge on the working mechanism of the steel fibers is necessary for optimizing this material. Usually, this knowledge is obtained by means of classical measuring techniques of destructive tests. Adopting measuring techniques from non‐destructive material testing helps to analyze and to identify the different stages of the fracture mechanism of high‐strength and ultra‐high strength fiber‐reinforced concretes in detail. The application of different non‐destructive measuring techniques is shown exemplary on tensile tests conducted on an ultra‐high strength fiber‐reinforced concrete and its applicability for analyzing the fracture behavior is discussed. The main focus is on the characterization of the relevant failure modes under tensile loading by the different measuring techniques and the comparison with classical measuring techniques (e. g. extensometer). The tensile tests have been analyzed by optical deformation measurements using digital image correlation (DIC), acoustic emission analysis (AE), and 3D computed tomography (CT). 相似文献
96.
Andreas Vetter Finn S. Babbe Bernhard Hofbeck Peter Kubis Michael Richter Stephan J. Heise Jrg Ohland Ingo Riedel Christoph J. Brabec 《Progress in Photovoltaics: Research and Applications》2016,24(7):1001-1008
Local electric defects may result in considerable performance losses in solar cells. Infrared (IR) thermography is one important tool to detect these defects on photovoltaic modules. Qualitative interpretation of IR images has been carried out successfully, but quantitative interpretation has been hampered by the lack of “calibration” defects. The aims of this study are to (i) establish methods to induce well‐defined electric defects in thin‐film solar cells serving as “calibration” defects and to (ii) assess the accuracy of IR imaging methods by using these artificially induced defects. This approach paves the way for improving quality control methods based on imaging in photovoltaic. We created ohmic defects (“shunts”) by using a focused ion beam and weak diodes (“interface shunts”) by applying a femto‐second laser at rather low power on copper indium gallium selenide cells. The defects can be induced precisely and reproducibly, and the severity of the defects on the electrical performance can be well adjusted by focused ion beam/laser parameters. The successive assessment of the IR measurement (ILIT‐Voc) revealed that this method can predict the losses in Pmpp (maximal power extractable) with a mean error of below 10%. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
97.
Emanuel Ionescu Christoph Linck Claudia Fasel Mathis Müller Hans–Joachim Kleebe Ralf Riedel 《Journal of the American Ceramic Society》2010,93(1):241-250
Polymer-derived SiOC/ZrO2 ceramic nanocomposites have been prepared using two synthetic approaches. A commercially available polymethylsilsesquioxane (MK Belsil PMS) was filled with nanocrystalline zirconia particles in the first approach. The second method involved the addition of zirconium tetra( n -propoxide), Zr(On Pr)4 , as zirconia precursor to polysilsesquioxane. The prepared materials have been subsequently cross-linked and pyrolyzed at 1100°C in argon atmosphere to provide SiOC/ZrO2 ceramics. The obtained SiOC/ZrO2 materials were characterized by means of X-ray diffraction, elemental analysis, Raman spectroscopy as well as transmission electron microscopy. Furthermore, annealing experiments at temperatures from 1300° to 1600°C have been performed. The annealing experiments revealed that the incorporation of ZrO2 into the SiOC matrix remarkably increases the thermal stability of the composites with respect to crystallization and decomposition at temperatures exceeding 1300°C. The results obtained within this study emphasize the enormous potential of polymer-derived SiOC/ZrO2 composites for high-temperature applications. 相似文献
98.
A. StephenK. Hashmi Ren Dpp Christian Lothschütz Matthias Rudolph Dominic Riedel Frank Rominger 《Advanced Synthesis \u0026amp; Catalysis》2010,352(8):1307-1314
Five different alkenylgold(I) phosphane complexes were prepared and then investigated in [1,1′‐bis(diphenylphosphino)ferrocene]palladium(II) dichloride‐catalyzed cross‐coupling reactions with different aryl halides, heterocyclic halides, an alkenyl halide, an alkynyl halide, allylic substrates, benzyl bromide and an acid chloride. With regard to the halides, the iodides were highly reactive, bromides or chlorides gave significantly reduced yields or failed, allylic acetates failed, too. The cross‐coupling partners contained a number of different functional groups, while free carboxylic acids did not deliver cross‐coupling products and o,o‐disubstituted arenes failed as well, a broad range of other functional groups like nitro groups, nitrile groups, ester groups, α,β‐unsaturated ester groups and lactones, aldehydes, alkoxy groups, pyridyl groups, thienyl groups, unprotected phenols and anilines, even aryl azides were tolerated. The structures of one alkenylgold(I) species and of four of the cross‐coupling products were proved by crystal structure analyses. 相似文献
99.
Frank Herzel Sabbir A. Osmany Kai Hu Klaus Schmalz Ulrich Jagdhold J. Christoph Scheytt Oliver Schrape Wolfgang Winkler Rüdiger Follmann Dietmar Köther Thorsten Kohl Olaf Kersten Thomas Podrebersek Heinz-Volker Heyer Frank Winkler 《Analog Integrated Circuits and Signal Processing》2010,65(1):21-32
We present an integrated fractional-N low-noise frequency synthesizer for satellite applications. By using two integrated VCOs and combining digital and analog tuning techniques, a PLL lock range from 8 to 12 GHz is achieved. Due to a small VCO fine tuning gain and optimized charge pump output biasing, the phase noise is low and almost constant over the tuning range. All 16 sub-bands show a tuning range above 900 MHz each, allowing temperature compensation without sub-band switching. This makes the synthesizer robust against variations of the device parameters with process, supply voltage, temperature and aging. The measured phase noise is ?87 dBc/Hz and ?106 dBc/Hz at 10 kHz and 1 MHz offset, respectively. In integer-N mode, phase noise values down to ?98 dBc/Hz at 10 kHz and ?111 dBc/Hz at 1 MHz offset, respectively, were measured. 相似文献
100.
Nashwa Abo Elneel Erkan Aksoy Dietmar Schroeder 《Analog Integrated Circuits and Signal Processing》2010,64(3):249-259
A novel adaptable analog/digital converter (ADC) that combines analog/digital conversion and entropy-coding for integrated
data compression and low-power operation is reported. The converter has high flexibility of operation in terms of adaptable
resolution, conversion rate and input signal statistics. This feature allows to adaptively react to changes of the situation
and to put the device in each case into the optimum configuration. The ADC has been realized in a 0.6 μm CMOS technology with
a peak resolution of 12 bit and 200 kS/s maximum sampling rate. A comprehensive power model of the converter is presented
that reflects precisely the power consumption determined from experiments. The model is very useful for optimizing the converter
configuration in the node of a wireless sensor network for specific situations. A feasible real-life application is demonstrated. 相似文献