1,705 research outputs found
Nonlinear Hysteretic Torsional Waves
We theoretically study and experimentally report the propagation of nonlinear
hysteretic torsional pulses in a vertical granular chain made of cm-scale,
self-hanged magnetic beads. As predicted by contact mechanics, the torsional
coupling between two beads is found nonlinear hysteretic. This results in a
nonlinear pulse distortion essentially different from the distortion predicted
by classical nonlinearities, and in a complex dynamic response depending on the
history of the wave particle angular velocity. Both are consistent with the
predictions of purely hysteretic nonlinear elasticity and the
Preisach-Mayergoyz hysteresis model, providing the opportunity to study the
phenomenon of nonlinear dynamic hysteresis in the absence of other type of
material nonlinearities. The proposed configuration reveals a plethora of
interesting phenomena including giant amplitude-dependent attenuation, short
term memory as well as dispersive properties. Thus, it could find interesting
applications in nonlinear wave control devices such as strong
amplitude-dependent filters
The Structure of Conserved Charges in Open Spin Chains
We study the local conserved charges in integrable spin chains of the XYZ
type with nontrivial boundary conditions. The general structure of these
charges consists of a bulk part, whose density is identical to that of a
periodic chain, and a boundary part. In contrast with the periodic case, only
charges corresponding to interactions of even number of spins exist for the
open chain. Hence, there are half as many charges in the open case as in the
closed case. For the open spin-1/2 XY chain, we derive the explicit expressions
of all the charges. For the open spin-1/2 XXX chain, several lowest order
charges are presented and a general method of obtaining the boundary terms is
indicated. In contrast with the closed case, the XXX charges cannot be
described in terms of a Catalan tree pattern.Comment: 22 pages, harvmac.tex (minor clarifications and reference corrections
added
Polariton Condensate Transistor Switch
A polariton condensate transistor switch is realized through optical
excitation of a microcavity ridge with two beams. The ballistically ejected
polaritons from a condensate formed at the source are gated using the 20 times
weaker second beam to switch on and off the flux of polaritons. In the absence
of the gate beam the small built-in detuning creates potential landscape in
which ejected polaritons are channelled toward the end of the ridge where they
condense. The low loss photon-like propagation combined with strong
nonlinearities associated with their excitonic component makes polariton based
transistors particularly attractive for the implementation of all-optical
integrated circuits
Complexity of checking whether two automata are synchronized by the same language
A deterministic finite automaton is said to be synchronizing if it has a
reset word, i.e. a word that brings all states of the automaton to a particular
one. We prove that it is a PSPACE-complete problem to check whether the
language of reset words for a given automaton coincides with the language of
reset words for some particular automaton.Comment: 12 pages, 4 figure
Microscopic Evidence of Spin State Order and Spin State Phase Separation in Layered Cobaltites RBaCo2O5.5 with R=Y, Tb, Dy, and Ho
We report muon spin relaxation measurements on the magnetic structures of
RBaCo_2O_5.5 with R=Y, Tb, Dy, and Ho. Three different phases, one
ferrimagnetic and two antiferromagnetic, are identified below 300 K. They
consist of different ordered spin state arrangements of high-, intermediate-,
and low-spin Co^3+ of CoO_6 octahedra. Phase separation into well separated
regions with different spin state order is observed in the antiferromagnetic
phases. The unusual strongly anisotropic magnetoresistance and its onset at the
FM-AFM phase boundary is explained.Comment: 4 pages, accepted for publication in Phys. Rev. Let
Photocurrent in nanostructures with asymmetric antidots
The steady current induced by electromagnetic field in a 2D system with
asymmetric scatterers is studied. The scatterers are assumed to be oriented
cuts with one diffusive and another specular sides. Besides, the existence of
isotropic impurity scatterers is assumed. This simple model simulates the
lattice of half-disk which have been studied numerically recently. The model
allows the exact solution in the framework of the kinetic equation. The static
current response in the second order of electric field is obtained. The
photogalvanic tensor contains both responses to linear and circular
polarization of electromagnetic field. The model possesses non-analyticity with
regards to the rate of impurity scattering.Comment: 9 pages, 6 figure
Acoustic Probing of the Jamming Transition in an Unconsolidated Granular Medium
Experiments with acoustic waves guided along the mechanically free surface of
an unconsolidated granular packed structure provide information on the
elasticity of granular media at very low pressures that are naturally
controlled by the gravitational acceleration and the depth beneath the surface.
Comparison of the determined dispersion relations for guided surface acoustic
modes with a theoretical model reveals the dependencies of the elastic moduli
of the granular medium on pressure. The experiments confirm recent theoretical
predictions that relaxation of the disordered granular packing through
non-affine motion leads to a peculiar scaling of shear rigidity with pressure
near the jamming transition corresponding to zero pressure. Unexpectedly, and
in disagreement with the most of the available theories, the bulk modulus
depends on pressure in a very similar way to the shear modulus
Electron beam processing of silicon carbide substrate to obtain graphene-like carbon films
This study was financially supported by Southern Federal University. The results were obtained using the equipment of the Research and Education Center "Nanotechnologies" of Southern Federal University
Cubic optical nonlinearity of free electrons in bulk gold
A fast (τresponse <90 fs) free-electron spin-flipping frequency-degenerate nonlinearity with a significant value of |χ(3)xxyy(ω,ω,ω,-ω) χ(3)xyyx(ω,ω,ω,-ω)| ~ 10-8 esu has been observed in bulk gold at 1260 nm by use of a new pump-probe polarization-sensitive technique. <br/
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