649 research outputs found
Discrete breathers assist energy transfer to ac driven nonlinear chains
One-dimensional chain of pointwise particles harmonically coupled with
nearest neighbors and placed in six-order polynomial on-site potentials is
considered. Power of the energy source in the form of single ac driven
particles is calculated numerically for different amplitudes and
frequencies within the linear phonon band. The results for the on-site
potentials with hard and soft nonlinearity types are compared. For the
hard-type nonlinearity, it is shown that when the driving frequency is close to
(far from) the {\em upper} edge of the phonon band, the power of the energy
source normalized to increases (decreases) with increasing . In
contrast, for the soft-type nonlinearity, the normalized power of the energy
source increases (decreases) with increasing when the driving frequency is
close to (far from) the {\em lower} edge of the phonon band. Our further
demonstrations indicate that, in the case of hard (soft) anharmonicity, the
chain can support movable discrete breathers (DBs) with frequencies above
(below) the phonon band. It is the energy source quasi-periodically emitting
moving DBs in the regime with driving frequency close to the DBs frequency,
that induces the increase of the power. Therefore, our results here support the
mechanism that the moving DBs can assist energy transfer from the ac driven
particle to the chain.Comment: 11 pages, 13 figure
Heat Treatment Condition Influence on Novokuibyshevsk Vacuum Residue Component Composition
The article presents the information about thermal degradation of Novokuibyshevsk vacuum residue and change of products composition during this process. The optimal conditions for the thermal destruction of vacuum residue components were established. The regularities of material balance composition change, Sgeneral were determined depending on cracking conditions. The basic directions of resin-asphaltene component transformations were identified, changes in their structural-group parameters in the process of initiated cracking were analyzed. Conducting of Novokuibyshevsk vacuum residue thermolysis leads to deep resins-asphaltenes average molecules structure characteristic changes. Developed alkyl and naphthenic moieties, which are presented in initial molecule, undergo degradation, amount of structural blocks in resins and asphaltenes molecules reduces, their average size decreases. Also the reduction in total content of the rings (saturated and aromatic) was established in average structural unit, at the same time decrease of rings substitution and length of the aliphatic fragments can be observed. In general the process of vacuum residue thermal cracking causes partial degradation of saturated (aliphatic and naphthenic) fragments and, partially, aromatic rings, which contain heteroatomic elements
Comment on the calculation of forces for multibody interatomic potentials
The system of particles interacting via multibody interatomic potential of
general form is considered. Possible variants of partition of the total force
acting on a single particle into pair contributions are discussed. Two
definitions for the force acting between a pair of particles are compared. The
forces coincide only if the particles interact via pair or embedded-atom
potentials. However in literature both definitions are used in order to
determine Cauchy stress tensor. A simplest example of the linear pure shear of
perfect square lattice is analyzed. It is shown that, Hardy's definition for
the stress tensor gives different results depending on the radius of
localization function. The differences strongly depend on the way of the force
definition.Comment: 9 pages, 2 figure
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