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- 저자 : Bojan Cˇ as (검색결과 2 건)
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Non-linear analysis of composite steel-concrete beams with incomplete interaction
Miran Saje,Igor Planinc,Bojan Cˇ as,Sebastjan Bratina 국제구조공학회 2004 Steel and Composite Structures, An International J Vol.4 No.6
The flexibility of the connection between steel and concrete largely influences the global behaviour of the composite beam. Therefore the way the connection is modelled is the key issue in its structural analysis. Here we present a new strain-based finite element formulation in which we consider nonlinear material and contact models. The computational efficiency and accuracy of the formulation is proved with the comparison of our numerical results with the experimental results of Abdel Aziz (1986) obtained in a full-scale laboratory test. The shear connectors are assumed to follow a non-linear load−slip relationship proposed by Ollgaard et al. (1971). We introduce the notion of the generalized slip, which offers a better physical interpretation of the behaviour of the contact and gives an additional material slip parameter. An excellent agreement of experimental and numerical results is obtained, using only a few finite elements. This demonstrates that the present numerical approach is appropriate for the evaluation of behaviour of planar composite beams and perfect for practical calculations.
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Photocurrent Spectroscopy Investigations of Mg-Related Defect Levels in p-Type GaN
Chung sangjo,B. Karunagaran bojan,Hong C.-H,Lee H. J,Suh E.-K 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.3
The defect levels associated with the Mg impurity in p-type GaN films were systematically investigated in terms of doping concentration by using photocurrent spectroscopy. Mg-doped GaN samples were grown on sapphire substrates by using metal-organic chemical-vapor deposition (MOCVD) and were annealed in a nitrogen atmosphere at 850 C for 10 min. At room temperature, photocurrent (PC) spectra showed two peaks, one at 3.31 and the other at 3.15 eV, associated with acceptor levels formed at 300 and 142 meV, respectively, above the valence band in the as-grown samples. However, after thermal annealing, PC spectra exhibited various additional peaks, depending on the Mg concentration. In the GaN samples with a Mg concentration around 6 7 × 1017 cm.3, we observed PC peaks related to Mg at 3.31 and 3.02 eV and to the carbon acceptor at 3.17 eV. For moderately Mg-doped GaN samples, i.e., a hole concentration of p = 3 4 × 1017 cm.3, an additional peak was observed around 0.9 eV, which could be attributed to defects related to the Ga vacancy. For relatively low Mg-doped samples whose hole concentrations are 1 2 × 1017 cm.3, an additional broad peak was observed around 1.3 eV. This peak might be related to the yellow band luminescence. As the Mg concentration was increased, the concentration of Ga vacancies could be reduced because the Mg occupied the substitutional sites of Ga in the GaN lattice. When the hole concentration was above 6 7 × 1017 cm.3, the yellow luminescence and the Ga-vacancy-related peaks disappeared completely.
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