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Nonlinear Free Vibration Analysis of Micro-beams Resting on Viscoelastic Foundation Based on the Modified Couple Stress Theory

Jam J. E., Noorabadi M., Namdaran N.

Archive of Mechanical Engineering

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2017

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Vol. LXIV, nr 2

239--256

EN

In this paper, nonlinear free vibration analysis of micro-beams resting on the viscoelastic foundation is investigated by the use of the modified couple stress theory, which is able to capture the size effects for structures in micron and sub-micron scales. To this aim, the governing equation of motion and the boundary conditions are derived using the Euler–Bernoulli beam and the Hamilton’s principle. The Galerkin method is employed to solve the governing nonlinear differential equation and obtain the frequency-amplitude algebraic equation. Finally, the effects of different parameters, such as the mode number, aspect ratio of length to height, the normalized length scale parameter and foundation parameters on the natural frequency-amplitude curves of doubly simply supported beams are studied.

2

Nano-inclusion with uniform internal strain induced by a screw dislocation

Dai M., Schiavone P., Gao C.-F.

Archives of Mechanics

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2016

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Vol. 68, nr 3

243--257

EN

This paper addresses the question of whether it is possible to design a nanoinclusion (characterized here by the incorporation of interface effects along the material interface) to achieve a screw dislocation-induced uniform internal strain field when a composite is subjected to anti-plane shear deformation. We demonstrate the existence of such an inclusion by identifying its shape via a conformal mapping with unknown coefficients obtained through a system of nonlinear equations. Our numerical examples verify that the inclusion shape is dependent on its size and the specific uniform internal strain field. We show also that the inclusion shape is available even with increasing distance between the inclusion and dislocation. This latter fact leads to the additional conclusion that non-circular nano-inclusions which achieve uniform internal strain fields do indeed exist in a composite subjected to uniform remote anti-plane shear loading.

3

Size-dependent Fluorescence Spectra of Individual Perylene Nanocrystals Studied by Far-Field Fluorescence Microspectroscopy Coupled with Atomic Force Microscope Observation

Asahi T., Matsune H., Yamashita K., Masuhara H., Kasai H., Nakanishi H.

Polish Journal of Chemistry

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2008

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Vol. 82, nr 4

687-699

EN

Single particle fluorescence spectroscopy coupled with AFM observation is reported for perylene nanocrystals. Fluorescence spectral measurement for individual nanocrystals with the size from 100 nm to 500 nm and fluorescence anisotropy analysis demonstrate that the size dependence in fluorescence is in the intrinsic nature of nanometer-sized crystal of perylene. Single nanoparticle fluorescence shows the enhanced monomer (M-) emission compared to the bulk crystal and a blue-shift of excimer (E-) emission peak wave length by decreasing the nanoparticle size. It is found for the first time that the size dependence is correlated well to the surface-to-volume ratio of nanocrystal. The size-dependent fluorescence is not attributed to a quantum confinement effect of exciton, but to a change in the elastic properties of nanocrystal with size, which in turn affects excimer formation. We discuss the decrease in elastic constant of crystal-line lattice due to large surface-to-volume ratio, and propose an empirical formula on the size-dependence of E-emission peak in the framework of the strong coupling model of exciton-phonon interaction.