1,036 research outputs found
Dissipative Interaction and Anomalous Surface Absorption of Bulk Phonons at a Two-Dimensional Defect in a Solid
We predict an extreme sensitivity to the dissipative losses of the resonant
interaction of bulk phonons with a 2D defect in a solid. We show that the total
resonant reflection of the transverse phonon at the 2D defect, described
earlier without an account for dissipation, occurs only in the limit of
extremely weak dissipation and is changed into almost total transmission by
relatively weak bulk absorption. Anomalous surface absorption of the transverse
phonon, when one half of the incident acoustic energy is absorbed at the 2D
defect, is predicted for the case of "intermediate" bulk dissipation.Comment: 11 preprint pages, no figure
Deeply Penetrating Elastic and Coupled Surface Waves in Crystals
Deeply penetrating elastic and coupled surface waves (DPSW) in crystals are treated. It is
shown that the parameters of the DPSW are very sensitive to near-surface disturbances of the
acoustic and electromagnetic paraipeters of the crystal, which is essential for the technical
applications of DPSW.Zadanie pt. Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej naukę
On modulational instability and energy localization in anharmonic lattices at finite energy density
The localization of vibrational energy, induced by the modulational
instability of the Brillouin-zone-boundary mode in a chain of classical
anharmonic oscillators with finite initial energy density, is studied within a
continuum theory. We describe the initial localization stage as a gas of
envelope solitons and explain their merging, eventually leading to a single
localized object containing a macroscopic fraction of the total energy of the
lattice. The initial-energy-density dependences of all characteristic time
scales of the soliton formation and merging are described analytically. Spatial
power spectra are computed and used for the quantitative explanation of the
numerical results.Comment: 12 pages, 7 figure
Wandering breathers and self-trapping in weakly coupled nonlinear chains: classical counterpart of macroscopic tunneling quantum dynamics
We present analytical and numerical studies of phase-coherent dynamics of
intrinsically localized excitations (breathers) in a system of two weakly
coupled nonlinear oscillator chains. We show that there are two qualitatively
different dynamical regimes of the coupled breathers, either immovable or
slowly-moving: the periodic transverse translation (wandering) of low-amplitude
breather between the chains, and the one-chain-localization of high-amplitude
breather. These two modes of coupled nonlinear excitations, which involve large
number of anharmonic oscillators, can be mapped onto two solutions of a single
pendulum equation, detached by a separatrix mode. We also study two-chain
breathers, which can be considered as bound states of discrete breathers with
different symmetry and center locations in the coupled chains, and bifurcation
of the anti-phase two-chain breather into the one-chain one. Delocalizing
transition of 1D breather in 2D system of a large number of parallel coupled
nonlinear chains is described, in which the breather, initially excited in a
given chain, abruptly spreads its vibration energy in the whole 2D system upon
decreasing breather frequency or amplitude below the threshold one. The
threshold breather frequency is above the cut off phonon frequency in 2D
system, and the threshold breather amplitude scales as square root of the
inter-chain coupling constant. Delocalizing transition of discrete vibrational
breather in 2D and 3D systems of coupled nonlinear chains has an analogy with
delocalizing transition for Bose-Einstein condensates in 2D and 3D optical
lattices.Comment: 33 pages, 16 figure
Nano-wires with surface disorder: Giant localization lengths and dynamical tunneling in the presence of directed chaos
We investigate electron quantum transport through nano-wires with one-sided
surface roughness in the presence of a perpendicular magnetic field.
Exponentially diverging localization lengths are found in the
quantum-to-classical crossover regime, controlled by tunneling between regular
and chaotic regions of the underlying mixed classical phase space. We show that
each regular mode possesses a well-defined mode-specific localization length.
We present analytic estimates of these mode localization lengths which agree
well with the numerical data. The coupling between regular and chaotic regions
can be determined by varying the length of the wire leading to intricate
structures in the transmission probabilities. We explain these structures
quantitatively by dynamical tunneling in the presence of directed chaos.Comment: 15 pages, 12 figure
Excitation of travelling multibreathers in anharmonic chains
We study the dynamics of the "externally" forced and damped Fermi-Pasta-Ulam
(FPU) 1D lattice. The forcing has the spatial symmetry of the Fourier mode with
wavenumber p and oscillates sinusoidally in time with the frequency omega. When
omega is in the phonon band, the p-mode becomes modulationally unstable above a
critical forcing, which we determine analytically in terms of the parameters of
the system. For omega above the phonon band, the instability of the p-mode
leads to the formation of a travelling multibreather, that, in the
low-amplitude limit could be described in terms of soliton solutions of a
suitable driven-damped nonlinear Schroedinger (NLS) equation. Similar
mechanisms of instability could show up in easy-axis magnetic structures, that
are governed by such NLS equations.Comment: To appear in Physica D (2002
Numerical Simulation of an Electroweak Oscillon
Numerical simulations of the bosonic sector of the
electroweak Standard Model in 3+1 dimensions have demonstrated the existence of
an oscillon -- an extremely long-lived, localized, oscillatory solution to the
equations of motion -- when the Higgs mass is equal to twice the boson
mass. It contains total energy roughly 30 TeV localized in a region of radius
0.05 fm. A detailed description of these numerical results is presented.Comment: 12 pages, 8 figures, uses RevTeX4; v2: expanded results section,
fixed typo
- …