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261.
An analytical model describing the nonlinear interaction between global and local buckling modes in long thin-walled rectangular hollow section struts under pure compression founded on variational principles is presented. A system of nonlinear differential and integral equations subject to boundary conditions is formulated and solved using numerical continuation techniques. For the first time, the equilibrium behaviour of such struts with different cross-section joint rigidities is highlighted with characteristically unstable interactive buckling paths and a progressive change in the local buckling wavelength. With increasing joint rigidity within the cross-section, the severity of the unstable post-buckling behaviour is shown to be mollified. The results from the analytical model are validated using a nonlinear finite element model developed within the commercial package Abaqus and show excellent comparisons. A simplified method to calculate the local buckling load of the more compressed web undergoing global buckling and the corresponding global mode amplitude at the secondary bifurcation is also developed. Parametric studies on the effect of varying the length and cross-section aspect ratio are also presented that demonstrate the effectiveness of the currently developed models. 相似文献
262.
The strain gradient exists near a crack tip may significantly influence the near-tip stress field. In this paper, the strain gradient and the internal length scales are introduced into the basic equations of mode III crack by the modified gradient elasticity (MGE). By using a complex function approach, the analytical solution of stress fields for mode III crack problem is derived within MGE. When the internal length scales vanish, the stress fields can be simplified to the stress fields of classical linear elastic fracture mechanics. The results show that the singularity of the shear stress is made up of two parts, r−1/2 part and r−3/2 part, and the sign of the stress σyz changes. With the increase of lx, the peak value of σyz decrease and its location moves farther from the fracture vertex. The influence of strain gradient for mode III crack problem cannot be ignored. 相似文献
263.
264.
Zhisheng Lin Zhengmi Du Shener Chen 《International Journal of Infrared and Millimeter Waves》1996,17(10):1749-1760
A 4MM-Wave composite mode multimode conical feedhorn has been developed. Its mode-ratios are calculated and its formulas of the radiation patterns are derived. The measurement results of one and two dimension radiation patterns, measured by the automatic measurement system which we had researched, and the properties of band width and sidelobe are given. Theoretical analyses and measurements show that at the centre frequency 69.1GHZ, down to -23dB, the radiation pattern is rotationally symmetric, in this range there is not any sidelobe existing, the band width is 4.5 GHZ. The multimode feedhorn is thus of certain practical using value. 相似文献
265.
对现代教育思想下“双主模式”的课堂网络教学系统的功能作了分析,提出了本系统基于“双主模式”教学思想的功能模块和实现此系统功能的软件模型以及实现课堂网络教学智能化的一种思路。 相似文献
266.
缪旭红 《无锡职业技术学院学报》2004,3(3):22-23
借助于计算机和网络技术的进步,传统的教学模式将发生巨大的变革。该文针对网络的特点,阐述了网络教学模式的优势所在,并提出了网络教学模式的发展与推广中存在的问题和相应的解决措施。 相似文献
267.
Fahmy AS El-Beih FM Mohamed SA Abdel-Gany SS Abd-Elbaky EA 《Applied biochemistry and biotechnology》2008,149(3):205-217
Polygalacturonase (PGI) from Aspergillus niger NRRL3 was purified about 12.0-fold from the cell-free broth using diethylaminoethyl-Sepharose and Sephacryl S-200 columns. The molecular weight of the PGI was 32,000 Da as estimated by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. PGI had an isoelectric point of 7.6 and an optimum pH of 5.0. PGI was active on polygalacturonic acid and esterified pectins, but the activity on pectin decreased with an increase in degree of esterification. PGI had higher affinity (low Km) and turnover number (Vmax/Km and Kcat/Km) toward polygalacturonic acid. PGI was found to have a temperature optimum at 40 degrees C and was approximately stable up to 30 degrees C. All the examined metal cations had partial inhibitory effects on PGI, while Mn+2 at 5 mM caused a complete inhibition for the enzyme. Comparison of viscosity reduction rates with release of reducing sugars indicated that the enzyme from A. niger is exoacting. The storage stability study of PGI showed that the enzyme in powder form retained 56% of its activity after 9 months of storage at 4 degrees C. The above properties of PGI may be suitable for food processing. 相似文献
268.
The Northern Hemisphere Annular Mode(NAM) represents the zonally symmetric planetary-scale atmospheric mass fluctuations between middle and high latitudes, whose variations have shown a large impact on other components of the climate system. Previous studies have indicated that the NAM is correlated with the Ferrel cell in their monthly or longer timescale variability.However, there have been few studies investigating their connections at daily timescale, though daily variability of NAM has been suggested to be an important component and has significant implication for weather forecast. The results from this study demonstrate that variability of the Ferrel cell leads that of the NAM by about 1–2 days. This statistically identified temporal phase difference between NAM and Ferrel cell variability can be elucidated by meridional mass redistribution. Intensified(weakened)Ferrel cell causes anomalously smaller(larger) poleward mass transport from the middle to the high latitudes,resulting in an increase(a decrease) in mass in the middle latitudes and a decrease(an increase) in the high latitudes.As a consequence, anomalously higher(lower) poleward pressure gradient forms and the NAM subsequently shifts to a positive(negative) phase at a time lag of 1–2 days. The findings here would augment the existing knowledge for better understanding the connection between the Ferrel Cell and the NAM, and may provide skillful information for improving NAM as well as daily scale weather prediction. 相似文献
269.
Structural and computational biologists often need to measure the similarity of ligand binding conformations. The commonly used root-mean-square deviation (RMSD) is not only ligand-size dependent, but also may fail to capture biologically meaningful binding features. To address these issues, we developed the Contact Mode Score (CMS), a new metric to assess the conformational similarity based on intermolecular protein-ligand contacts. The CMS is less dependent on the ligand size and has the ability to include flexible receptors. In order to effectively compare binding poses of non-identical ligands bound to different proteins, we further developed the eXtended Contact Mode Score (XCMS). We believe that CMS and XCMS provide a meaningful assessment of the similarity of ligand binding conformations. CMS and XCMS are freely available at http://brylinski.cct.lsu.edu/content/contact-mode-score and http://geaux-computational-bio.github.io/contact-mode-score/. 相似文献
270.
刘佳萍 《萍乡高等专科学校学报》2008,25(4):36-38
目前,高校在商务英语教学中仍多重视课堂教学,而忽略了实践教学这一重要环节。只有真正贯彻理论联系实际的原则,充分认识实践教学在商务英语理论教学中的重要作用,才能真正有效地发挥商务英语服务于我国外贸的作用。本文结合商务英语专业建设实际和商务英语的市场需求,对在商务英语教学中如何培养学生实践能力进行了探索。 相似文献