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1.
We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation. 相似文献
2.
Pedro Ribeiro 《International journal for numerical methods in engineering》2004,61(15):2696-2715
A p‐version, hierarchical finite element for curved, moderately thick, elastic and isotropic beams is introduced. The convergence properties of the element are analysed and some results are compared with results published elsewhere or calculated using a commercial finite element package. It is verified that, with the proposed element, shear locking does not affect the computation of the natural frequencies and that low dimensional, accurate models are obtainable. Geometrically non‐linear vibrations due to finite deformations, which occur for harmonic excitations with frequencies close to the first three natural frequencies of vibration, are investigated using Newmark's method. The influence of the thickness, longitudinal inertia and curvature radius on the dynamic behaviour of curved beams are studied. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
3.
Hakan Boyaci 《Sadhana》2006,31(1):1-8
A simply supported damped Euler-Bernoulli beam with immovable end conditions are considered. The concept of non-ideal boundary
conditions is applied to the beam problem. In accordance, the boundaries are assumed to allow small deflections and moments.
Approximate analytical solution of the problem is found using the method of multiple scales, a perturbation technique. 相似文献
4.
参数强迫激励下非线性振子尖点型奇点的分叉 总被引:2,自引:0,他引:2
本文首先研究了不具有Z_2—对称性时的规范形理论和退化向量场的普适开折理论。然后利用这些理论研究了参数激励与强迫激励联合作用下非线性振动系统的尖点型奇点的余维2退化分叉。 相似文献
5.
6.
提出了引起星型活塞式压缩机振动这一宏观现象发生的根源.在一阶惯性力机器内完全平衡的情形下,对二阶惯性力因目前无法在机器内平衡,分析其形成的机理.在机器向大排量方向发展时,二阶惯性力引起机器振动不可忽略,容易引起机器在水平面内移动,所以需采取与基础紧固的措施. 相似文献
7.
E. Zafari 《先进材料力学与结构力学》2017,24(9):725-736
In the present study, transverse vibrations of nanobeams with manifold concentrated masses, resting on Winkler elastic foundations, are investigated. The model is based on the theory of nonlocal elasticity in the presence of concentrated masses applied to Euler–Bernoulli beams. A closed-form expression for the transverse vibration modes of Euler–Bernoulli beams is presented. The proposed expressions are provided explicitly as the function of two integrated constants, which are determined by the standard boundary conditions. The utilization of the boundary conditions leads to definite terms of natural frequency equations. The natural frequencies and vibration modes of the concerned nanobeams with different numbers of concentrated masses in different positions under some typical boundary conditions (simply supported, cantilevered, and clamped–clamped) have been analyzed by means of the proposed closed–form expressions in order to show their efficiency. It is worth mentioning that the effect of various nonlocal length parameters and Winkler modulus on natural frequencies and vibration modes are also discussed. Finally, the results are compared with those corresponding to a classical local model. 相似文献
8.
9.
LIU Yanping~ LIU Dongqing~ .Key Laboratory of Condition Monitoring Control for Power Plant Equipment of Ministry of Education North China Electric Power University Beijing China .Beijing University of Science Technology Beijing China 《武汉理工大学学报》2006,28(Z2)
In order to understand the vibration characteristic of system structure of electronic equipment cabinet within the particular vibration frequency,the finite element analysis software-ANSYS is used to simulate the tests of random vibrations of the cabinet system and obtain the isopleths graph of deformation and stress of the cabinet.It can confirm maximum of deformation and stress of the cabinet and position happened.Through more analysis of the frequency response curve,which can confirm harm- ful consequences random vibrations caused and weak link of the cabinet structure.The numerical simulation results are in good a- greement with the experimental results.It shows that this research provides an efficient method for the anti-seismic design and the dynamic optimization design. 相似文献
10.
给出了梁大挠度强迫振动响应灵敏度分析的新方法,讨论了灵敏度分析方程中的长期项处理方法,使响应灵敏度得到一个合理的结果。 相似文献