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31.
A number of plane stress numerical analyses of the mode I elastoplastic fracture mechanics problem have been performed in the past using the Huber–Mises yield criterion. This study employs instead the Tresca yield condition using an incremental theory of plasticity for a stationary crack. A commercial finite element program is used to solve the opening mode of fracture problem (mode I) for a square plate containing a central crack under generalized plane stress loading conditions. A biaxial uniform tensile traction is applied to the edges of a thin plate composed of a linear elastic non-work hardening material under small strain assumptions. The finite element results are compared with the analytical predictions of the Dugdale plastic strip model for a crack in an infinite plate subject to a biaxial uniform load at infinity. 相似文献
32.
Metal-halide perovskite semiconductors are certainly one of the hottest topic in solar energy conversion. Optimization of both the absorber material and device architecture has led to an astoundingly rapid increase in the reported device efficiencies. Initially developed in the context of dye-sensitized solar cell research, metal-halide perovskite devices now reach efficiency values and hence need to be compared to more conventional photovoltaic technologies such as silicon, copper indium gallium diselenide and cadmium telluride. Strong direct band gap absorption, long charge carrier diffusion length, ease and flexibility in processing at low temperatures and facile tunability makes these materials ideal for solar energy conversion applications. This review will both reflect on favorable properties of these hybrid and ionic semiconductors as well as reflecting on lead toxicity, material and device stability as the most critical issues that need to be solved in order for these materials to become technologically viable. 相似文献
33.
Claudia Unger Martin Gruene Lothar Koch Juergen Koch Boris N. Chichkov 《Applied Physics A: Materials Science & Processing》2011,103(2):271-277
In this work, the printing mechanism of an alginate-based hydrogel via laser-induced forward transfer (LIFT) is investigated
by spatial and temporal high-resolved stroboscopic imaging. First, the generation of the liquid jet is studied at two different
laser fluences in a process without collector slide. Furthermore, the impingement process onto the collector slide at the
same fluence levels is observed. With the help of these images the development of the jet is explained. Besides the influences
of the collector slide as well as the applied laser fluence on the transfer are demonstrated. 相似文献
34.
The 1.1-complexes formed by the reaction of nickel(II) halides and substituted aminoethyl- and aminomethyl-pyridines-(2) may be divided into two groups. Compounds, which are yellow or red brown in the solid state, and violet in solution in acetone belong to the first group. The complexes of the second group are violet in solution and in the solid state. On account of the vis- and ir-spectra, the magnetic behaviour, and the molar weight a distorted tetrahedral structure is discussed for the violet compounds, and a dimeric structure with coordination number 5 of the central atom for the complexes of the first group. The factors determining the structure of the investigated compounds are stated. 相似文献
35.
W.K. Unger 《Journal of magnetism and magnetic materials》1975,1(1):88-89
Due to a partially inhomogeneous Cu concentration, CuyCr2Se4?zBrx single crystal can show a complicated temperature dependence of the wall motion threshold field which is about 0.5 kA/m near the Curie temperature. The crystals can be homogenized by means of a NH4OH treatment. 相似文献
36.
The authors implemented bipolar velocity compensated pulse techniques for T2-weighted MR imaging of the brain. Signal-to-noise (S/N) and image quality was compared for pulse sequences with standard and optimized RF pulses, low and regular bandwidth versions and cardiac triggering. Images from bipolar velocity compensated sequences allowed better visualization of vessels and basilar cisterns and improved image quality relative to standard sequences without velocity compensation. The implementation of optimized RF pulses with bipolar sequences resulted in further improvement in image quality. Single echo sequences consistently had improved image quality and signal-to-noise relative to the second echo of a double echo sequence. Low bandwidth bipolar sequences with extended sampling period had 30% higher S/N, but at the cost of slight loss in edge definition. The highest image quality was obtained with the bipolar, optimized RF, single echo sequence. Using this technique contiguous high quality image slices could be obtained with velocity compensation. The addition of cardiac triggering to bipolar sequences resulted in slight improvement in image quality, but this difference was marginal and probably rarely necessary for MR imaging of the brain. 相似文献
37.
Studies on Oxide Catalysts. XLIV. Modification of the Catalytic Behavior of Modified ZSM-5 Zeolites by Thermal Treatment The catalytic activity, the shape selectivity, and the deactivation behavior of ZSM-5 in paraffin cracking reactions can be regulated by a thermal pretreatment. A minimum of the deactivation rate as a function of zeolite pretreatment time at 600°C found in the hexane cracking could be verified in the methanol conversion reaction to gasoline. 相似文献
38.
Christiane Werner Frederik Wegener Stephan Unger Salvador Nogués Pierrick Priault 《Rapid communications in mass spectrometry : RCM》2009,23(16):2428-2438
Recent advances in understanding the metabolic origin and the temporal dynamics in δ13C of dark‐respired CO2 (δ13Cres) have led to an increasing awareness of the importance of plant isotopic fractionation in respiratory processes. Pronounced dynamics in δ13Cres have been observed in a number of species and three main hypotheses have been proposed: first, diurnal changes in δ13C of respiratory substrates; second, post‐photosynthetic discrimination in respiratory pathways; and third, dynamic decarboxylation of enriched carbon pools during the post‐illumination respiration period. Since different functional groups exhibit distinct diurnal patterns in δ13Cres (ranging from 0 to 10‰ diurnal increase), we explored these hypotheses for different ecotypes and environmental (i.e. growth light) conditions. Mass balance calculations revealed that the effect of respiratory substrates on diurnal changes in δ13Cres was negligible in all investigated species. Further, rapid post‐illumination changes in δ13Cres (30 min), which increased from 2.6‰ to 5‰ over the course of the day, were examined by positional 13C‐labelling to quantify changes in pyruvate dehydrogenase (PDH) and Krebs cycle (KC) activity. We investigated the origin of these dynamics with Rayleigh mass balance calculations based on theoretical assumptions on fractionation processes. Neither the estimated changes of PDH and KC, nor decarboxylation of a malate pool entirely explained the observed pattern in δ13Cres. However, a Rayleigh fractionation of 12C‐discriminating enzymes and/or a rapid decline in the decarboxylation rate of an enriched substrate pool may explain the post‐illumination peak in δ13Cres. These results are highly relevant since δ13Cres is used in large‐scale carbon cycle studies. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
39.
Jaan Unger Marcus Stiemer Alexander Brosius Bob Svendsen Heribert Blum Matthias Kleiner 《International Journal of Solids and Structures》2008,45(2):442-459
The purpose of this work is the development and application of strategies to identify material model parameters for metals at high strain-rates using data obtained from high-speed electromagnetic metal forming. To this end, a staggered algorithm for the finite-element-based numerical solution of the coupled electromagnetic-mechanical boundary-value problem has been developed based on mixed Eulerian–Lagrangian multigrid methods. On this basis, the parameter determination together with a sensitivity analysis and error estimation are carried out. After verifying the validity of this approach using synthetic data sets, it is applied to the identification of material parameters using experimental results from electromagnetic tube forming. 相似文献
40.