147 research outputs found
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
Simulation modeling of the curvilinear motion of an industrial tractor with a differential rotation mechanism and tracking trajectory stabilization system
The article is devoted to the investigation of the transient processes in the hydrodynamic transmission and hydro-hydraulic turning mechanism at the entrance to the turn and turning on the spot. Boundary ground conditions are determined for the tractor to perform stepless maneuvering while performing technological operations. The algorithm of the tracking system has been formulated, which made it possible to keep the radius of the trajectory fixed by the handwheel as the external resistance to movement changes
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