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排序方式: 共有36条查询结果,搜索用时 15 毫秒
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An approach to model the deterioration of steel structures is presented by transferring the results of a continuum damage mechanics analysis to an extended beam model which can account for the loss of structural integrity. Damage starts at the microscopic level by the initiation, growth and coalescence of voids with decreasing material resistance followed by the formation of microcracks at the mesoscale. Nevertheless, the material behavior can be sufficiently modelled on a phenomenological basis taking into account viscoplasticity, hardening effects and damage evolution. The associated model parameters are identified with the help of an evolutionary algorithm adapting numerical to experimental results. Using the finite element method a nonlocal formulation of the damage variable is required to obtain mesh-independent results by structural analysis. The maximum element size is limited by the small magnitude of the internal length. Therefore, numerical analyses of large scale 3D steel structures are computationally expensive. To reduce the effort a beam element is proposed to account for the plastic hinges and the loss of resistance in the course of damage evolution. The corresponding relationship of bending moment and curvature bases on the continuum damage mechanics model. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
S. Riechel U. Lemmer J. Feldmann T. Benstem W. Kowalsky U. Scherf A. Gombert V. Wittwer 《Applied physics. B, Lasers and optics》2000,71(6):897-900
We report on the laser modes in optically pumped solid-state lasers using an electroluminescent organic semiconductor as the
active medium. Mechanically flexible distributed-feedback lasers are fabricated by depositing a thin film of an active material
onto a nano-patterned polyester substrate either via spin-coating of a soluble ladder-type poly(p-phenylene) or via vacuum
co-sublimation of small organic molecules. The different surface texture resulting from the fabrication process causes different
feedback mechanisms. In both lasers higher lateral modes give rise to a broadening of the laser spectra at higher pumping
levels.
Received: 7 August 2000 / Revised version: 12 September 2000 / Published online: 8 November 2000 相似文献
4.
Hans-Joachim Kowalsky 《Archiv der Mathematik》1957,8(5):336-339
Ohne Zusammenfassung 相似文献
5.
Hans-Joachim Kowalsky 《Archiv der Mathematik》1954,6(1):9-12
Ohne Zusammenfassung 相似文献
6.
In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco... 相似文献
7.
D. Schneider S. Hartmann T. Benstem T. Dobbertin D. Heithecker D. Metzdorf E. Becker T. Riedl H.-H. Johannes W. Kowalsky T. Weimann J. Wang P. Hinze 《Applied physics. B, Lasers and optics》2003,77(4):399-402
We report on a wavelength-tunable organic solid-state laser based on a second-order distributed-feedback (DFB) resonator design with the guest–host system Alq3:DCM2 as the gain medium. The laser wavelength can be shifted from 608.9 to 646.5 nm by varying the grating period of the Bragg reflector. This allows the characterization of laser parameters for a large wavelength region on a single sample. The laser threshold and output characteristics are measured for different laser wavelengths. A minimum threshold for laser activity occurs at a lasing wavelength of 633 nm, giving the spectral position of the gain maximum. PACS 42.70.Jk; 78.45.+h; 78.66.Qn 相似文献
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9.
Márcio AF Belo-Filho Franklina MB Toledo Bernardo Almada-Lobo 《The Journal of the Operational Research Society》2014,65(11):1735-1747
Setup operations are significant in some production environments. It is mandatory that their production plans consider some features, as setup state conservation across periods through setup carryover and crossover. The modelling of setup crossover allows more flexible decisions and is essential for problems with long setup times. This paper proposes two models for the capacitated lot-sizing problem with backlogging and setup carryover and crossover. The first is in line with other models from the literature, whereas the second considers a disaggregated setup variable, which tracks the starting and completion times of the setup operation. This innovative approach permits a more compact formulation. Computational results show that the proposed models have outperformed other state-of-the-art formulation. 相似文献
10.
Henrik-Alexander Christ Pen Yiao Ang Fuzhao Li Hans-Hermann Johannes Wolfgang Kowalsky Henning Menzel 《Journal of polymer science. Part A, Polymer chemistry》2022,60(4):715-725
The fabrication of micron-sized poly(methyl methacrylate) (PMMA) polymer optical fibers doped with rhodamine B as an organic dye is demonstrated. Highly aligned and defect-free fibers are fabricated by using the stable jet electrospinning (SJES) method and systematically varying critical parameters such as solvent type and polymer concentration. At optimal conditions, for example, a polymer concentration of 35 wt% of PMMA in butanone, ribbon-shaped fibers with a smooth surface and diameter of about 20 μm could be spun using SJES mode and deposited on a rotating drum as target in a highly aligned manner. Photoluminescence spectra of the doped fibers excited longitudinally and transversely with a laser show an excitation peak with full-width-at-half-maximum of only 5.05 nm and a low lasing threshold at a pump energy of 0.55 μJ, indicating that SJES could become a new source of amplified optics components or organic solid-state fiber lasers. 相似文献