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排序方式： 共有216条查询结果，搜索用时 15 毫秒
71.
Ch. Ludwig T. Sekinger J. Kuhl H.-U. Habermeier M. Tani K. Sakai M. Hangyo S. Miyazawa M. Mukaida 《physica status solidi b》1999,213(2):405-413
Using coherent THz pulse spectroscopy, we have analyzed the electrodynamic properties of thin YBa2Cu3O7—δ films in the temperature range between 10 and 300 K. The temperature dependence of the London penetration depth in c-axis direction determined from the complex conductivity yields clear evidence for d-wave symmetry of the order parameter. 相似文献
72.
The photoluminescence (PL) dynamics of InGaN/GaN quantum wells with different In concentrations xIn have been measured. The PL emission forms a broad band consisting of two parts with dramatically different dynamics. The high energy part (QWH) is present only under higher excitation densities (>103 W/cm2), it has fast decay (of a few tens of ps) and changes only slightly with temperature. Its relative amplitude and the PL lifetime τ increase with the xIn. The second, low energy part (QWL) has slow decay (of the order of 10 ns), its amplitude saturates under higher excitation densities and quickly vanishes when the temperature increases. At 10 K the QWL lifetimes change from τ = 1.8 ± 0.2 ns (xIn = 0.11) up to 20 ± 4 ns (xIn = 0.4) while the thermal activation energy (Ea = 18 ± 3 meV) is not sensitive for the In concentration. We propose that QWH and QWL come from nonlocalised and localised carrier recombination, respectively. 相似文献
73.
J. Frstner A. Knorr S. Kuckenburg T. Meier S.W. Koch H. Giessen S. Linden J. Kuhl 《physica status solidi b》2000,221(1):453-457
Nonlinear propagation of optical pulses through an extended bulk semiconductor is investigated using the coupled semiconductor Maxwell‐Bloch equations including excitation induced correlations. For short pulse excitation around the exciton resonance, the theory describes the development of polariton beats and their suppression at increasing input pulse intensities due to the coupling of single exciton states to the Coulomb‐correlated continuum of two‐exciton states. A comparison of the theoretical results with experimental observations for CdSe bulk material is presented. 相似文献
74.
A technique for fitting a free-form scattering length density profile to reflectivity data via least-squares minimization is presented. The approach combines aspects of simulated annealing with a parametrized representation of the scattering length density profile. The ability of the algorithm to accurately recover the scattering length density profile from arbitrary initial parameter values is demonstrated for simulated and experimental data. 相似文献
75.
Peter Kuhl Nina P. Zapevalova Andreas Könnecke Hans-Dieter Jakubke 《Monatshefte für Chemie / Chemical Monthly》1983,114(3):343-347
Carboxypeptidase Y catalyzes in a biphasic system containing carbon tetrachloride and carbonate buffer the reaction ofZ-Phe-OMe and variousZ-andBoc-protected dipeptide methyl esters with Val-NH2 and Leu-NH2, respectively. This method has been applied to the synthesis of the corresponding N-protected tripeptide amides on a preparative scale. Using a substrate—nucleophile ratio of only 1:2 or 1:3 the peptide derivatives are obtained in yields of 56–97%.Abbreviations: IUPAC-IUB rules for peptides are followed, see Eur. J. Biochem.27, 201 (1972).Boc=tert-butyloxycarbonyl,Z=benzyloxycarbonyl,-OMe=methyl ester, HPLC=high performance liquid chromatography, TLC=thin layer chromatography,CPD-Y=carboxypeptidase Y. 相似文献
76.
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78.
Justin Felix Hofmann Claudia von Boyneburgk Sophie Tunger Hans-Peter Heim Detlef Kuhl 《PAMM》2019,19(1)
This contribution focuses on an innovative composite material consisting of textile layers made from continuous wooden fibers embedded in a thermoplastic matrix. A finite element simulation of potential use‐cases is planned to support the development process and to study the suitability of the material in an architectural context. The simulation is based on a constitutive model assuming homogenous orthotropic elastic behavior and will be expanded to include multiscale modeling in future research. The material parameters used in such models can often be determined based on a small number of local measurements during experiments like tensile tests, which assume classical one dimensional load scenaria at least in parts of the specimen. However, this is not sufficient for non‐homogeneous materials, especially when dealing with non‐isotropic materials in off‐axis configurations and the need for full‐field measurements like digital image correlation (DIC) arises. Experimental results of uniaxial on‐ and off‐axis tensile tests using DIC are presented and used in the identification of the material parameters of the given model. Results of simulations and experiments are compared and the suitability of the material model is discussed. 相似文献
79.
While long underestimated, more and more evidence confirms that mechanics play a critical role for brain function and dysfunction. Therefore, computational simulations based on the field equations of nonlinear continuum mechanics can provide important insights into the underlying mechanisms of brain injury and disease. Realistic numerical predictions, however, require models capable of capturing the complex and unique mechanical behavior of this ultrasoft, highly heterogeneous and adaptive tissue. In recent years, contradictory experimental results have retarded progress in this field. Here, we summarize the key characteristics of brain tissue behavior on different length and time scales and propose application‐specific modeling approaches, which are as complex as necessary but as simple as possible. The presented considerations will, on the one hand, facilitate well‐designed future experiments and, on the other hand, help to choose the appropriate constitutive law for a specific application. 相似文献
80.
The development of the human brain with its characteristically folded surface morphology remains an intensively discussed topic. Impressive advancements in different fields of research have enhanced the understanding of the brain. However, the mechanism that underlies the folding process in healthy and diseased brains remains undetermined. Here, we hypothesize that growth induced mechanical instabilities drive folding. Using the nonlinear field theories of continuum mechanics supplemented by the theory of finite growth [1], we model the human brain as a bi-material with the cerebral cortex, a morphogenetically growing outer layer of gray matter, and the subcortex, a strain-driven growing inner core of white matter [2]. This approach integrates the two popular but competing hypotheses that cortical folding is either driven by differential growth or by axon elongation. Through systematic sensitivity analyses, we identify the critical process parameters of cortical folding and quantify their impact on brain morphology. We further simulate phenomena causing malformations like lissencephaly and polymicrogyria [3], which are associated with neurological disorders, including severe retardation, epilepsy, schizophrenia, and autism. Understanding the mechanisms of cortical folding during brain development might facilitate the diagnostics and treatment of malformed brains. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献