A note on the breathing mode of an elastic sphere in Newtonian and complex fluids

Experiments on the acoustic vibrations of elastic nanostructures in fluid media have been used to study the mechanical properties of materials, as well as for mechanical and biological sensing. The medium surrounding the nanostructure is typically modeled as a Newtonian fluid. A recent experiment however suggested that high-frequency longitudinal vibration of bipyramidal nanoparticles could trigger a viscoelastic response in water-glycerol mixtures [M. Pelton et al., "Viscoelastic flows in simple liquids generated by vibrating nanostructures," Phys. Rev. Lett. 111, 244502 (2013)]. Motivated by these experimental studies, we first revisit a classical continuum mechanics problem of the purely radial vibration of an elastic sphere, also called the breathing mode, in a compressible viscous fluid, and then extend our analysis to a viscoelastic medium using the Maxwell fluid model. The effects of fluid compressibility and viscoelasticity are discussed. Although in the case of longitudinal vibration of bipyramidal nanoparticles, the effects of fluid compressibility were shown to be negligible, we demonstrate that it plays a significant role in the breathing mode of an elastic sphere. On the other hand, despite the different vibration modes, the breathing mode of a sphere triggers a viscoelastic response in water-glycerol mixtures similar to that triggered by the longitudinal vibration of bipyramidal nanoparticles. We also comment on the effect of fluid viscoelasticity on the idea of destroying virus particles by acoustic resonance

Vibrational modes of metal nanoshells and bimetallic core-shell nanoparticles

We study theoretically spectrum of radial vibrational modes in composite metal nanostructures such as bimetallic core-shell particles and metal nanoshells with dielectric core in an environment. We calculate frequencies and damping rates of fundamental (breathing) modes for these nanostructures along with those of two higher-order modes. For metal nanoshells, we find that the breathing mode frequency is always lower than the one for solid particles of the same size, while the damping is higher and increases with reduction of the shell thickness. We identify two regimes that can be characterized as weakly damped and overdamped vibrations in the presence of external medium. For bimetalllic particles, we find periodic dependence of frequency and damping rate on the shell thickness with period determined by mode number. For both types of nanostructures, the frequency of higher modes is nearly independent of the environment, while the damping rate shows strong sensitivity to outside medium.Comment: 7 pages, 8 figure

Simple model for the vibrations of embedded elastically cubic nanocrystals

The purpose of this work is to calculate the vibrational modes of an elastically anisotropic sphere embedded in an isotropic matrix. This has important application to understanding the spectra of low-frequency Raman scattering from nanoparticles embedded in a glass matrix. First some low frequency vibrational modes of a free cubically elastic sphere are found to be nearly independent of one combination of elastic constants. This is then exploited to obtain an isotropic approximation for these modes which enables to take into account the surrounding isotropic matrix. This method is then used to quantatively explain recent spectra of gold and copper nanocrystals in glasses.Comment: 6 pages, 5 figure

Policy Challenges Faced by Low-Income CIS Economies

In the 1990s, the CIS region experienced a painful transformation following the collapse of the USSR and the command economy. For the less developed republics of the former USSR, this process was even more dramatic as they lost subsidies from the Union's budget and some of them suffered devastating conflicts. In the 2000s, after overcoming the adaptation output decline and the consequences of the 1998-1999 financial crises, these economies started to grow rapidly, reducing poverty and macroeconomic imbalances. However, their future growth prospects are increasingly vulnerable due to their strong dependence on commodity exports, a poor business and investment climate, endemic corruption and weak governance. Quite recently, fighting high inflation has returned to the policy agenda. The modernization and diversification of the low-income CIS economies requires further market and institutional reforms aimed at overcoming the Soviet legacy of a repressive and inefficient state. The international community can help by resolving regional conflicts, assisting with trade and economic integration, and offering well-targeted development assistance

Design technique system of automatic control tent-bed test

A design technique system of automatic control is presented. And the example of application of this method is described on creation of the system of automatic control on a stand

Application CAE-systems in scientific researches and educational process

It is devoted a technique of application САE of system (APM Structure 3D) in educational process and scientific researches applied on chair