8,158 research outputs found
Nonlinear Breathing-like Localized Modes in C60 Nanocrystals
We study the dynamics of nanocrystals composed of C60 fullerene molecules. We
demonstrate that such structures can support long-lived strongly localized
nonlinear oscillatory modes, which resemble discrete breathers in simple
lattices. We reveal that at room temperatures the lifetime of such nonlinear
localized modes may exceed tens of picoseconds; this suggests that C60
nanoclusters should demonstrate anomalously slow thermal relaxation when the
temperature gradient decays in accord to a power law, thus violating the
Cattaneo-Vernotte law of thermal conductivity.Comment: 6 pages, 6 figure
Heat Conduction in One-Dimensional chain of Hard Discs with Substrate Potential
Heat conduction of one-dimensional chain of equivalent rigid particles in the
field of external on-site potential is considered. Zero diameters of the
particles correspond to exactly integrable case with divergent heat conduction
coefficient. By means of simple analytical model it is demonstrated that for
any nonzero particle size the integrability is violated and the heat conduction
coefficient converges. The result of the analytical computation is verified by
means of numerical simulation in a plausible diapason of parameters and good
agreement is observedComment: 14 pages, 7 figure
Non-stationary heat conduction in one-dimensional chains with conserved momentum
The Letter addresses the relationship between hyperbolic equations of heat
conduction and microscopic models of dielectrics. Effects of the non-stationary
heat conduction are investigated in two one-dimensional models with conserved
momentum: Fermi-Pasta-Ulam (FPU) chain and chain of rotators (CR). These models
belong to different universality classes with respect to stationary heat
conduction. Direct numeric simulations reveal in both models a crossover from
oscillatory decay of short-wave perturbations of the temperature field to
smooth diffusive decay of the long-wave perturbations. Such behavior is
inconsistent with parabolic Fourier equation of the heat conduction. The
crossover wavelength decreases with increase of average temperature in both
models. For the FPU model the lowest order hyperbolic Cattaneo-Vernotte
equation for the non-stationary heat conduction is not applicable, since no
unique relaxation time can be determined.Comment: 4 pages, 5 figure
Normal heat conductivity in two-dimensional scalar lattices
The paper revisits recent counterintuitive results on divergence of heat
conduction coefficient in two-dimensional lattices. It was reported that in
certain lattices with on-site potential, for which one-dimensional chain has
convergent conductivity, for the 2D case it turns out to diverge. We
demonstrate that this conclusion is an artifact caused by insufficient size of
the simulated system. To overcome computational restrictions, a ribbon of
relatively small width is simulated instead of the square specimen. It is
further demonstrated that the heat conduction coefficient in the "long"
direction of the ribbon ceases to depend on the width, as the latter achieves
only 10 to 20 interparticle distances. So, one can consider the dynamics of
much longer systems, than in the traditional setting, and still can gain a
reliable information regarding the 2D lattice. It turns out that for all
considered models, for which the conductivity is convergent in the 1D case, it
is indeed convergent in the 2D case. In the same time, however, the length of
the system, necessary to reveal the convergence in the 2D case, may be much
bigger than in its 1D counterpart.Comment: 6 pages, 6 figure
Lattice stretching bistability and dynamic heterogeneity
A simple one-dimensional lattice model is suggested to describe the
experimentally observed plateau in force-stretching diagrams for some
macromolecules. This chain model involves the nearest-neighbor interaction of a
Morse-like potential (required to have a saturation branch) and an harmonic
second-neighbor coupling. Under an external stretching applied t o the chain
ends, the intersite Morse-like potential results in the appearance of a
double-well potential within each chain monomer, whereas the interaction
between the second neighbors provide s a homogeneous bistable (degenerate)
ground state, at least within a certain part of the chain.
As a result, different conformational changes occur in the chain under the
external forcing. The transition regions between these conformations are
described as topological solitons. With a strong second-neighbor interaction,
the solitons describe the transition between the bistable ground states.
However, the key point of the model is the appearance of a heterogenous
structure, when the second-neighbor coupling is sufficiently weak. In this
case, a part of the chain has short bonds with a single-well potential, whereas
the complementary part admits strongly stretched bonds with a double-well
potential. This case allows us to explain the existence of a plateau in the
force-stretching diagram for DNA and alpha-helix protein. Finally, the soliton
dynamics are studied in detail.Comment: Submitted to Phys. Rev. E, 13 figure
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