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851.
D. E. Appelbe R. A. E. Austin G. C. Ball J. A. Cameron B. Djerroud T. E. Drake S. Flibotte C. D. O’Leary A. Melarangi C. E. Svensson J. C. Waddington D. Ward 《The European Physical Journal A - Hadrons and Nuclei》2000,8(2):153-155
The decays of 2557Mn32 and 2558Mn33 have been studied with the 8π Spectrometer following the reaction 48Ca(13C,pxn)60 − x
Mn at a beam energy of 40 MeV. The level schemes of these two nuclei have been extended, and the multipolarities of the observed
transitions have been determined. 相似文献
852.
Huajiang Ouyang 《Journal of the mechanics and physics of solids》2005,53(5):1000-1014
Centrifugal atomisation using a spinning disc is an effective means of producing high quality metal powder. The atomising disc frequently experiences severe vibration and produces noise. The vibration adversely affects the production of metal powder. This paper presents the first study of the dynamics of atomising discs. The disc is modelled as a plate under the excitation of a growing mass, which represents the metal stream flowing down to and spreading out on the disc. The influence of the rotating speed of the disc and the growing mass on the dynamics of the disc is investigated. It is found that the disc vibration is non-stationary with multiple frequencies that vary with time and its magnitude increases with mass flow rate of the model metal and decreases with the disc speed. One interesting finding is that the disc vibration grows like flutter in the period before the metal flow on the disc becomes steady, due to the radially growing mass. 相似文献
853.
854.
Shu Karube Wataru HoshinoTatsuo Soutome Keijin Sato 《International Journal of Non》2002,37(3):541-564
It is well-known that vibration cutting is an effective method to cut materials with accuracy. However, it often suffers from unevenness of surface roughness caused by the non-linear vibration phenomena in tool-work vibration system. To solve this problem, we propose a vibration cutting model described by two-dimensional differential equations to analyze the non-linear phenomena. This non-linear model reproduces the basic features of the real vibration cutting systems, that is, the reduction of the cutting force and the displacement of work by pulsing of the cutting force. In this report, our experiment shows that various non-linear phenomena exist in the vibration cutting system. Our non-linear model for the vibration cutting produce behaviors which qualitatively agree with these various non-linear phenomena. These behaviors can be classified by the Lyapunov exponents. 相似文献
855.
Aleš Tondl 《International Journal of Non》2004,39(5):821-832
This contribution deals with the quenching of self-excited vibrations by means of parametric excitation due to periodic variation of spring stiffness. A three-mass chain system is investigated in detail. It is shown that the self-excitation can be fully or partly suppressed in a particular frequency interval. 相似文献
856.
Andrew K. Mitchell 《Experimental Mechanics》2005,45(3):250-258
This paper describes a non-contacting optical technique for vibration measurement, which can be used to determine the magnitude
and phase of every point of a continuous surface under steady-state conditions. In this method, the vibrating surface to be
studied is illuminated by a white-light, sinusoidal grating projected from an oblique angle. A series of precisely timed digital
images of the vibrating object is recorded as the grid is moved across the surface. An automated analysis then extracts magnitude
and phase data at each pixel in the recorded images. The use of white light makes it possible to study the motion of larger
surfaces than might be conveniently possible with more conventional Moiré or holographic techniques, and the optical arrangement
used seems relatively insensitive to external disturbances. The method seems particularly well suited to the study of structures
undergoing relatively low-frequency, large-amplitude vibrations. 相似文献
857.
《International Journal of Non》2002,37(7):1181-1198
The non-linear vibration of simply supported, circular cylindrical shells is analysed. Geometric non-linearities due to finite-amplitude shell motion are considered by using Donnell's non-linear shallow-shell theory; the effect of viscous structural damping is taken into account. A discretization method based on a series expansion of an unlimited number of linear modes, including axisymmetric and asymmetric modes, following the Galerkin procedure, is developed. Both driven and companion modes are included, allowing for travelling-wave response of the shell. Axisymmetric modes are included because they are essential in simulating the inward mean deflection of the oscillation with respect to the equilibrium position. The fundamental role of the axisymmetric modes is confirmed and the role of higher order asymmetric modes is clarified in order to obtain the correct character of the circular cylindrical shell non-linearity. The effect of the geometric shell characteristics, i.e., radius, length and thickness, on the non-linear behaviour is analysed: very short or thick shells display a hardening non-linearity; conversely, a softening type non-linearity is found in a wide range of shell geometries. 相似文献
858.
区域非稳定动力学环境下,长期的构造变形、重力卸荷以及地震动力作用的共同影响,可以导致岩体发生大范围变形、松动。松动岩体内发育大量的软弱结构面,且表现出整体破碎、松弛严重、透水强烈,张性节理裂隙发育、地表裂缝较发育、岩体地震动力破坏信息反映明显等特征。岩体的变形松动可以分为卸荷变形松动、倾倒变形松动、顺层滑移松动、断层控制松动、节理裂隙控制松动等5种模式。岩体的物理振动试验结果表明,地震动力是造成岩体松动的主因。数值模拟结果表明,在单纯自重应力影响作用下,松动岩体不会出现大面积的失稳破坏现象,但在地震动力作用下,松动岩体会发生大面积屈服破坏。 相似文献
859.
Attilio Maccari 《International Journal of Non》2003,38(1):123-131
We investigate the primary resonance of an externally excited van der Pol oscillator under state feedback control with a time delay. By means of the asymptotic perturbation method, two slow-flow equations on the amplitude and phase of the oscillator are obtained and external excitation-response and frequency-response curves are shown. We discuss how vibration control and high amplitude response suppression can be performed with appropriate time delay and feedback gains. Moreover, energy considerations are used in order to investigate existence and characteristics of limit cycles of the slow-flow equations. A limit cycle corresponds to a two-period modulated motion for the van der Pol oscillator. We demonstrate that appropriate choices for the feedback gains and the time delay can exclude the possibility of modulated motion and reduce the amplitude peak of the primary resonance. Analytical results are verified with numerical simulations. 相似文献
860.
Rumyana Simeonova Dimitrina Zheleva Iva Valkova Georgi Stavrakov Irena Philipova Mariyana Atanasova Irini Doytchinova 《Molecules (Basel, Switzerland)》2021,26(7)
The acetylcholinesterase (AChE) inhibitors are the main drugs for symptomatic treatment of neurodegenerative disorders like Alzheimer’s disease. A recently designed, synthesized and tested hybrid compound between the AChE inhibitor galantamine (GAL) and the antioxidant polyphenol curcumin (CU) showed high AChE inhibition in vitro. Here, we describe tests for acute and short-term toxicity in mice as well as antioxidant tests on brain homogenates measured the levels of malondialdehide (MDA) and glutathione (GSH) and in vitro DPPH, ABTS, FRAP and LPO inhibition assays. Hematological and serum biochemical analyses were also performed. In the acute toxicity tests, the novel AChE inhibitor given orally in mice showed LD50 of 49 mg/kg. The short-term administration of 2.5 and 5 mg/kg did not show toxicity. In the ex vivo tests, the GAL-CU hybrid performed better than GAL and CU themselves; in a dose of 5 mg/kg, it demonstrates 25% reduction in AChE activity, as well as a 28% and 73% increase in the levels of MDA and GSH, respectively. No significant changes in blood biochemical data were observed. The antioxidant activity of 4b measured ex vivo was proven in the in vitro tests. In the ABTS assay, 4b showed radical scavenging activity 10 times higher than the positive control butylhydroxy toluol (BHT). The GAL-CU hybrid is a novel non-toxic AChE inhibitor with high antioxidant activity which makes it a prospective multitarget drug candidate for treatment of neurodegenerative disorders. 相似文献