2,421 research outputs found
Group analysis and renormgroup symmetries
An original regular approach to constructing special type symmetries for
boundary value problems, namely renormgroup symmetries, is presented. Different
methods of calculating these symmetries, based on modern group analysis are
described. Application of the approach to boundary value problems is
demonstrated with the help of a simple mathematical model.Comment: 17 pages, RevTeX LATeX file, to appear in Journal of Mathematical
Physic
On the internal modes in sine-Gordon chain
We address the issue of internal modes of a kink of a discrete sine-Gordon
equation. The main point of the present study is to elucidate how the
antisymmetric internal mode frequency dependence enters the quasicontinuum
spectrum of nonlocalized waves. We analyze the internal frequency dependencies
as functions of both the number of cites and discreteness parameter and explain
the origin of spectrum peculiarity which arises after the frequency dependence
of antisymmetric mode returns back to the continuous spectrum at some nonzero
value of the intersite coupling.Comment: 5 pages, 3 figure
Spin-transfer in diffusive ferromagnet-normal metal systems with spin-flip scattering
The spin-transfer in biased disordered ferromagnet (F) - normal metal (N)
systems is calculated by the diffusion equation. For F1-N2-F2 and
N1-F1-N2-F2-N3 spin valves, the effect of spin-flip processes in the normal
metal and ferromagnet parts are obtained analytically. Spin-flip in the center
metal N2 reduces the spin-transfer, whereas spin-flip in the outer normal
metals N1 and N3 can increase it by effectively enhancing the spin polarization
of the device.Comment: 9 pages, 3 figure
Radiation Pressure Quantization
Kepler's observation of comets tails initiated the research on the radiation
pressure of celestial objects and 250 years later they found new incarnation
after the Maxwell's equations were formulated to describe a plethora of
light-matter coupling phenomena. Further, quantum mechanics gave birth to the
photon drag effect. Here, we predict a novel universal phenomenon which can be
referred to as quantization of the radiation pressure. We develop a microscopic
theory of this effect which can be applied to a general system containing
Bose-Einstein-condensed particles, which possess an internal structure of
quantum states. By analyzing the response of the system to an external
electromagnetic field we find that such drag results in a flux of particles
constituting both the condensate and the excited states. We show that in the
presence of the condensed phase, the response of the system becomes quantized
which manifests itself in a step-like behavior of the particle flux as a
function of electromagnetic field frequency with the elementary quantum
determined by the internal energy structure of the particles.Comment: Manuscript: 4 pages, 3 figure
Exact and approximate symmetries for light propagation equations with higher order nonlinearity
For the first time exact analytical solutions to the eikonal equations in
(1+1) dimensions with a refractive index being a saturated function of
intensity are constructed. It is demonstrated that the solutions exhibit
collapse; an explicit analytical expression for the self-focusing position,
where the intensity tends to infinity, is found. Based on an approximated Lie
symmetry group, solutions to the eikonal equations with arbitrary nonlinear
refractive index are constructed. Comparison between exact and approximate
solutions is presented. Approximate solutions to the nonlinear Schrodinger
equation in (1+2) dimensions with arbitrary refractive index and initial
intensity distribution are obtained. A particular case of refractive index
consisting of Kerr refraction and multiphoton ionization is considered. It is
demonstrated that the beam collapse can take place not only at the beam axis
but also in an off-axis ring region around it. An analytical condition
distinguishing these two cases is obtained and explicit formula for the
self-focusing position is presented.Comment: 25 pages, 5 figure
Magnetomechanical Torques in Small Magnetic Cantilevers
We study the dnamics of small magnetic cantilevers, either made from Si
covered by a magnetic film or entirely ferromagnetic ones. The
magnetomechanical torques are found to cause line splittings in ferromagnetic
resonance spectra and magnetization reversal facilitated by mechanical degrees
of freedom. We show that the magnetomechanical torques can extend the limits of
detecting and exciting motion at the nanoscale. A "nanomotor" described here
effectively transforms rf magnetic fields into mechanical oscillations. We
furthermore propose to integrate mechanical oscillators into magnetoelectronic
devices that make use of current-induced spin-transfer torques. This opens new
possibilities for electric transducers of nanomechanical motion.Comment: 20 pages, 12 figures; submitted to a special issue of JJAP:
Magnetization Dynamics in Spintronic Structures and Device
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