607 research outputs found
Order statistics and heavy-tail distributions for planetary perturbations on Oort cloud comets
This paper tackles important aspects of comets dynamics from a statistical
point of view. Existing methodology uses numerical integration for computing
planetary perturbations for simulating such dynamics. This operation is highly
computational. It is reasonable to wonder whenever statistical simulation of
the perturbations can be much more easy to handle. The first step for answering
such a question is to provide a statistical study of these perturbations in
order to catch their main features. The statistical tools used are order
statistics and heavy tail distributions. The study carried out indicated a
general pattern exhibited by the perturbations around the orbits of the
important planet. These characteristics were validated through statistical
testing and a theoretical study based on Opik theory.Comment: 9 pages, 12 figures, submitted for publication in Astronomy and
Astrophysic
Effects of finite curvature on soliton dynamics in a chain of nonlinear oscillators
We consider a curved chain of nonlinear oscillators and show that the
interplay of curvature and nonlinearity leads to a number of qualitative
effects. In particular, the energy of nonlinear localized excitations centered
on the bending decreases when curvature increases, i.e. bending manifests
itself as a trap for excitations. Moreover, the potential of this trap is
double-well, thus leading to a symmetry breaking phenomenon: a symmetric
stationary state may become unstable and transform into an energetically
favorable asymmetric stationary state. The essentials of symmetry breaking are
examined analytically for a simplified model. We also demonstrate a threshold
character of the scattering process, i.e. transmission, trapping, or reflection
of the moving nonlinear excitation passing through the bending.Comment: 13 pages (LaTeX) with 10 figures (EPS
Nonequilibrium electrons in tunnel structures under high-voltage injection
We investigate electronic distributions in nonequilibrium tunnel junctions
subject to a high voltage bias under competing electron-electron and
electron-phonon relaxation processes. We derive conditions for reaching
quasi-equilibrium and show that, though the distribution can still be thermal
for low energies where the rate of the electron-electron relaxation exceeds
significantly the electron-phonon relaxation rate, it develops a power-law tail
at energies of order of . In a general case of comparable electron-electron
and electron-phonon relaxation rates, this tail leads to emission of
high-energy phonons which carry away most of the energy pumped in by the
injected current.Comment: Revised versio
On the vibron dressing in the --helicoidal macromolecular chains
We present a study of the physical properties of the vibrational excitation
in --helicoidal macromolecular chains, caused by the interaction with
acoustical and optical phonon modes. The influence of the temperature and the
basic system parameters on the vibron dressing has been analyzed by employing
the simple mean--field approach based on the variational extension of the
Lang--Firsov unitary transformation. Applied approach predicts a region in
system parameter space where one takes place an abrupt transition from
partially dressed (light and mobile) to fully dressed (immobile) vibron states.
We found that the boundary of this region depends on system temperature and
type of bond among structural elements in the macromolecular chain.Comment: 22 pages, 12 figures, title changed, the interaction with optical
phonon modes jointly with acoustical ones added, consideration significantly
enlarged, references added, the paper develops the results of
arxiv:1210.3918, accepted for publication in Chinese Physics
AC conductivity of graphene: from tight-binding model to 2+1-dimensional quantum electrodynamics
We consider the relationship between the tight-binding Hamiltonian of the
two-dimensional honeycomb lattice of carbon atoms with nearest neighbor hopping
only and the 2+1 dimensional Hamiltonian of quantum electrodynamics which
follows in the continuum limit. We pay particular attention to the symmetries
of the free Dirac fermions including spatial inversion, time reversal, charge
conjugation and chirality. We illustrate the power of such a mapping by
considering the effect of the possible symmetry breaking which corresponds to
the creation of a finite Dirac mass, on various optical properties. In
particular, we consider the diagonal AC conductivity with emphasis on how the
finite Dirac mass might manifest itself in experiment. The optical sum rules
for the diagonal and Hall conductivities are discussed.Comment: 46 pages, ws-ijmpb, 7 EPS figures; final version published in IJMP
Hall-like effect induced by spin-orbit interaction
The effect of spin-orbit interaction on electron transport properties of a
cross-junction structure is studied. It is shown that it results in spin
polarization of left and right outgoing electron waves. Consequently, incoming
electron wave of a proper polarization induces voltage drop perpendicularly to
the direct current flow between source and drain of the considered
four-terminal cross-structure. The resulting Hall-like resistance is estimated
to be of the order of 10^-3 - 10^-2 h/e^2 for technologically available
structures. The effect becomes more pronounced in the vicinity of resonances
where Hall-like resistance changes its sign as function of the Fermi energy.Comment: 4 pages (RevTeX), 4 figures, will appear in Phys. Rev. Let
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