排序方式: 共有18条查询结果,搜索用时 265 毫秒
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F. Nucera A. F. Vakakis D. M. McFarland L. A. Bergman G. Kerschen 《Nonlinear dynamics》2007,50(3):651-677
In the field of seismic protection of structures, it is crucial to be able to diminish ‘as much as possible’ and dissipate
‘as fast as possible’ the load induced by seismic (vibration-shock) energy imparted to a structure by an earthquake. In this
context, the concept of passive nonlinear energy pumping appears to be natural for application to seismic mitigation. Hence, the overall problem discussed in this paper can be formulated
as follows: Design a set of nonlinear energy sinks (NESs) that are locally attached to a main structure, with the purpose of passively
absorbing a significant part of the applied seismic energy, locally confining it and then dissipating it in the smallest possible
time. Alternatively, the overall goal will be to demonstrate that it is feasible to passively divert the applied seismic energy
from the main structure (to be protected) to a set of preferential nonlinear substructures (the set of NESs), where this energy
is locally dissipated at a time scale fast enough to be of practical use for seismic mitigation. It is the aim of this work to show that the concept of nonlinear energy pumping is feasible for seismic mitigation. We consider
a two degree-of-freedom (DOF) primary linear system (the structure to be protected) and study seismic-induced vibration control
through the use of Vibro-Impact NESs (VI NESs). Also, we account for the possibility of attaching to the primary structure additional alternative NES configurations
possessing essential but smooth nonlinearities (e.g., with no discontinuities). We study the performance of the NESs through
a set of evaluation criteria. The damped nonlinear transitions that occur during the operation of the VI NESs are then studied
by superimposing wavelet spectra of the nonlinear responses to appropriately defined frequency – energy plots (FEPs) of branches
of periodic orbits of underlying Conservative systems. 相似文献
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宋光乐 《光谱学与光谱分析》2003,23(4):820-822
从Fourier级数出发 ,到任意闭区间上可积函数的Fourier分析 ,给出了数字信号Fourier分析的理论基础。以字符“b”为例 ,建立了严格的数学模型 ,严密推导了Fourier系数表达式。阐明了Fourier级数的“项”和“n阶Fourier级数”(前n项和 )的概念。详尽地分析了信道通频带B与Fourier阶数n(展开式“保留”项 )的关系。借助计算机计算了n≤ 10 0时各Fourier级数项和前n项和 ,并用Plot将计算结果绘成曲线 ,获得n≤10 0时各级Fourier展开曲线。与数字信号对照 ,Fourier级数的取项与波形的关系显而易见 ,特别是n取值较小时 ,Fourier级数取项少 ,波形失真严重 ;所以在B一定时传输速率不能过高 ,否则 ,由于波形失真而导致信号出错。 相似文献
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Dinesh Singla Prof. Vijay Luxami Prof. Kamaldeep Paul 《European journal of organic chemistry》2023,26(34):e202300531
Palladium-catalyzed [4+2] oxidative annulation of coumarin-benzimidazoles with olefins for the synthesis of polycyclic aromatic hydrocarbons have been achieved. This synthetic protocol gives access to a wide range of structurally distinct imidazo[1,2-a]chromeno[3,4-c]pyridines in moderate to good yield with wide functional group tolerance. Further, photophysical properties of annulated scaffolds have been examined, which discloses their interesting solvatochromic emission behaviors. 相似文献
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The membrane material was prepared by mixing 40% of cesium-triphenyl-cyanoborate and 60% of PVC powder. The mixture was pressed at a pressure of 20tons/cm2 for 1hours to make the membrane. Then, the membrane was mounted on a self-constructed electrode body. Nernstian slope of 60 mv/decade was obtained throughout the concentration range 10?1~2×10?5M. Selectivity coefficients were presented. The life time of the electrode is longer than 6 months. 相似文献
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Steven C. Gauci Prof. Filip E. Du Prez Dr. Joshua O. Holloway Dr. Hannes A. Houck Prof. Christopher Barner-Kowollik 《Angewandte Chemie (International ed. in English)》2023,62(40):e202310274
Exploiting the optimum wavelength of reactivity for efficient photochemical reactions has been well-established based on the development of photochemical action plots. We herein demonstrate the power of such action plots by a remarkable example of the wavelength-resolved photochemistry of two triazolinedione (TAD) substrates, i.e., aliphatic and aromatic substituted, that exhibit near identical absorption spectra yet possess vastly disparate photoreactivity. We present our findings in carefully recorded action plots, from which reaction selectivity is identified. The profound difference in photoreactivity is exploited by designing a ‘hybrid’ bisfunctional TAD molecule, enabling the formation of a dual-gated reaction manifold that demonstrates the exceptional and site-selective (photo)chemical behavior of both TAD substrates within a single small molecule. 相似文献
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Torsional vibrations transmitted from the engine to the drivetrain system induce a plethora of noise, vibration and harshness (NVH) concerns, such a transmission gear rattle and clutch in-cycle vibration, to name but a few. The main elements of these oscillations are variations in the inertial imbalance and the constituents of combustion power torque, collectively referred to as engine order vibration. To attenuate the effect of these transmitted vibrations and their oscillatory effects in the drive train system, a host of palliative measures are employed in practice, such as clutch pre-dampers, slipping discs, dual mass flywheel and others, all of which operate effectively over a narrow band of frequencies and have various unintended repercussions. These include increased powertrain inertia, installation package space and cost. This paper presents a numerical study of the use of multiple Nonlinear Energy Sinks (NES) as a means of attenuating the torsional oscillations for an extended frequency range and under transient vehicle manoeuvres. Frequency–Energy Plots (FEP) are used to obtain the nonlinear absorber parameters for multiple NES coupled in parallel to the clutch disc of a typical drivetrain configuration. The results obtained show significant reduction in the oscillations of the transmission input shaft, effective over a broad range of response frequencies. It is also noted that the targeted reduction of the acceleration amplitude of the input shaft requires significantly lower NES inertia, compared with the existing palliative measures. 相似文献