558 research outputs found

### 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

### Motion of vortices in ferromagnetic spin-1 BEC

The paper investigates dynamics of nonsingular vortices in a ferromagnetic
spin-1 BEC, where spin and mass superfluidity coexist in the presence of
uniaxial anisotropy (linear and quadratic Zeeman effect). The analysis is based
on hydrodynamics following from the Gross-Pitaevskii theory. Cores of
nonsingular vortices are skyrmions with charge, which is tuned by uniaxial
anisotropy and can have any fractal value between 0 and 1. There are
circulations of mass and spin currents around these vortices. The results are
compared with the equation of vortex motion derived earlier in the
Landau-Lifshitz-Gilbert theory for magnetic vortices in easy-plane
ferromagnetic insulators. In the both cases the transverse gyrotropic force
(analog of the Magnus force in superfluid and classical hydrodynamics) is
proportional to the charge of skyrmions in vortex cores.Comment: 19 pages, 2 figures, to be published in the special issue of Fizika
Nizkikh Temperatur dedicated to A.M.Kosevich. arXiv admin note: substantial
text overlap with arXiv:1801.0109

### Numerical Simulation of an Electroweak Oscillon

Numerical simulations of the bosonic sector of the $SU(2)\times U(1)$
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 $W^\pm$ 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

### Multiphonon anharmonic decay of a quantum mode

A nonperturbative theory of multiphonon anharmonic transitions between energy
levels of a local mode is presented. It is shown that the rate of transitions
rearranges near the critical level number $n_{cr}$: at smaller $n$ the process
slows down, while at larger $n$ it accelerates in time, causing a jump-like
loss of energy followed by the generation of phonon bursts. Depending on
parameters, phonons are emitted in pairs, triplets etc.Comment: submitted to Europhys.Let

### Nano-wires with surface disorder: Giant localization lengths and quantum-to-classical crossover

We investigate electronic quantum transport through nano-wires with one-sided
surface roughness. A magnetic field perpendicular to the scattering region is
shown to lead to exponentially diverging localization lengths in the
quantum-to-classical crossover regime. This effect can be quantitatively
accounted for by tunneling between the regular and the chaotic components of
the underlying mixed classical phase space.Comment: 4 pages, 3 figures; final version (including added references

### Model mass spectrometric study of competitive interactions of antimicrobial bisquaternary ammonium drugs and aspirin with membrane phospholipids

The aim of the study is to reveal molecular mechanisms of possible activity modulation of antimicrobial bis-quaternary ammonium compounds (BQAC) and aspirin (ASP) through noncovalent competitive complexation under their combined introduction into the model systems with membrane phospholipids. Methods. Binary and triple systems containing either decamethoxinum or ethonium, or thionium and aspirin, as well as dipalmitoyl-phosphatidylcholine (DPPC) have been investigated by electrospray ionization mass spectrometry. Results. Basing on the analysis of associates recorded in the mass spectra, the types of nonocovalent complexes formed in the systems studied were determined and the supposed role of the complexation in the BQAC and ASP activity modulation was discussed. The formation of associates of BQAC dications with ASP anion is considered as one of the possible ways of deactivation of ionic forms of the medications. The formation of stable complexes of BQAC with DPPC and ASP with DPPC in binary systems as well as the complexes distribution in triple-components systems BQAC:ASP:DPPC point to the existence of competition between drugs of these two types for the binding to DPPC. Conclusions. The results obtained point to the competitive complexation in the model molecular systems containing the BQAC, aspirin and membrane phospholipids. The observed phenomenon testifies to the possibility of modulating the activity of bisquaternary antimicrobial agents and aspirin under their combined usage, due to the competition between the drugs for binding to the target membrane phospholipid molecules and also due to the formation of stable noncovalent complexes between BQAC and ASP

### Anomalous Defects and Their Quantized Transverse Conductivities

Using a description of defects in solids in terms of three-dimensional
gravity, we study the propagation of electrons in the background of
disclinations and screw dislocations. We study the situations where there are
bound states that are effectively localized on the defect and hence can be
described in terms of an effective 1+1 dimensional field theory for the low
energy excitations. In the case of screw dislocations, we find that these
excitations are chiral and can be described by an effective field theory of
chiral fermions. Fermions of both chirality occur even for a given direction of
the magnetic field. The ``net'' chirality of the system however is not always
the same for a given direction of the magnetic field, but changes from one sign
of the chirality through zero to the other sign as the Fermi momentum or the
magnitude of the magnetic flux is varied. On coupling to an external
electromagnetic field, the latter becomes anomalous, and predicts novel
conduction properties for these materials.Comment: New material added. ReVTeX , 31 pgs., 4 figs.(uses epsf

### Conductance of a tunnel point-contact of noble metals in the presence of a single defect

In paper [1] (Avotina et al. Phys. Rev. B,74, 085411 (2006)) the effect of
Fermi surface anisotropy to the conductance of a tunnel point contact, in the
vicinity of which a single point-like defect is situated, has been investigated
theoretically. The oscillatory dependence of the conductance on the distance
between the contact and the defect has been found for a general Fermi surface
geometry. In this paper we apply the method developed in [1] to the calculation
of the conductance of noble metal contacts. An original algorithm, which
enables the computation of the conductance for any parametrically given Fermi
surface, is proposed. On this basis a pattern of the conductance oscillations,
which can be observed by the method of scanning tunneling microscopy, is
obtained for different orientations of the surface for the noble metals.Comment: 8 pages, 5 figure

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