2,826 research outputs found
Optical ordering of nanoparticles trapped by Laguerre-Gaussian laser modes
In earlier work, it has been established that laser-induced coupling between a pair of nanoparticles can enable the generation of novel patterns, entirely determined and controlled by the frequency, intensity, and polarization of the optical input. Jn this paper, the detailed spatial disposition about the beam axis is determined for two-, three- and four-nanoparticle systems irradiated by a Laguerre-Gaussian (LG) laser mode. The range-dependent laser-induced energy shift is identified by the employment of a quantum electrodynamical description, calculations are performed to determine the distribution of absolute minima as a function of the topological charge, and the results are graphically displayed. This analysis illustrates a number of interesting features, including the fact that on increasing the LG beam's topological charge the particles increasingly cluster, i.e. the order of the structure is significantly raised - also the number of minima for which the particles can be trapped is enhanced. Finally, it is shown that similar principles apply to other kinds of radially structured optical modes
Determination of the scattering length for Rb-Cs X ground electronic state using a variational method
We performed the calculation of the scattering length for the elastic
collision between the rubidium and cesium atoms. For this we applied a
variational procedure based on the R-matrix theory for unbound states employing
the finite element method (FEM) for expansion of the wave-function in terms of
a finite set of local basis functions. The FEM presents as advantages the
possibility of the development of a efficient matrix inversion algorithm which
significantly reduces the computation time to calculate the R matrix. We also
tested a potential energy curve with spectroscopic accuracy obtained before
from a direct adjustment procedure of experimental data of the
state based on genetic algorithm. The quality of our result
was evaluated by comparing them with several ones previously published at
literature.Comment: 15 pages, 6 tables and 2 figure
Giant Faraday rotation in single- and multilayer graphene
Optical Faraday rotation is one of the most direct and practically important
manifestations of magnetically broken time-reversal symmetry. The rotation
angle is proportional to the distance traveled by the light, and up to now
sizeable effects were observed only in macroscopically thick samples and in
two-dimensional electron gases with effective thicknesses of several
nanometers. Here we demonstrate that a single atomic layer of carbon - graphene
- turns the polarization by several degrees in modest magnetic fields. The
rotation is found to be strongly enhanced by resonances originating from the
cyclotron effect in the classical regime and the inter-Landau-level transitions
in the quantum regime. Combined with the possibility of ambipolar doping, this
opens pathways to use graphene in fast tunable ultrathin infrared
magneto-optical devices
How to Identify and Separate Bright Galaxy Clusters from the Low-frequency Radio Sky?
In this work we simulate the MHz radio sky that is constrained in
the field of view ( radius) of the 21 Centimeter Array (21CMA), by
carrying out Monte-Carlo simulations to model redshifted cosmological
reionization signals and strong contaminating foregrounds, including emissions
from our Galaxy, galaxy clusters, and extragalactic point sources. As an
improvement of previous works, we consider in detail not only random variations
of morphological and spectroscopic parameters within the ranges allowed by
multi-band observations, but also evolution of radio halos in galaxy clusters,
assuming that relativistic electrons are re-accelerated in the ICM in merger
events and lose energy via both synchrotron emission and inverse Compton
scattering with CMB photons. By introducing a new approach designed on the
basis of independent component analysis (ICA) and wavelet detection algorithm,
we prove that, with a cumulative observation of one month with the 21CMA array,
about of galaxy clusters with central brightness temperatures of at 65 MHz can be safely identified and separated from the
overwhelmingly bright foreground. We find that the morphological and
spectroscopic distortions are extremely small as compared to the input
simulated clusters, and the reduced of brightness temperature profiles
and spectra are controlled to be and ,
respectively. These results robustly indicate that in the near future a sample
of dozens of bright galaxy clusters will be disentangled from the foreground in
21CMA observations, the study of which will greatly improve our knowledge about
cluster merger rates, electron acceleration mechanisms in cluster radio halos,
and magnetic field in the ICM.Comment: 35 pages, 10 figures, Accepted for publication in The Astrophysical
Journa
Resonance Production and S-wave in at 190 GeV/c
The COMPASS collaboration has collected the currently largest data set on
diffractively produced final states using a negative pion
beam of 190 GeV/c momentum impinging on a stationary proton target. This data
set allows for a systematic partial-wave analysis in 100 bins of three-pion
mass, GeV/c , and in 11 bins of the reduced
four-momentum transfer squared, (GeV/c) . This
two-dimensional analysis offers sensitivity to genuine one-step resonance
production, i.e. the production of a state followed by its decay, as well as to
more complex dynamical effects in nonresonant production. In this paper,
we present detailed studies on selected partial waves with , , , , and . In these waves, we observe
the well-known ground-state mesons as well as a new narrow axial-vector meson
decaying into . In addition, we present the results
of a novel method to extract the amplitude of the subsystem with
in various partial waves from the
data. Evidence is found for correlation of the and
appearing as intermediate isobars in the decay of the known
and .Comment: 96 page
Magnon Landau levels and emergent supersymmetry in strained antiferromagnets
Inhomogeneous strain applied to lattice systems can induce artificial gauge
fields for particles moving on this lattice. Here we demonstrate how to
engineer a novel state of matter, namely an antiferromagnet with a Landau-level
excitation spectrum of magnons. We consider a honeycomb-lattice Heisenberg
model and show that triaxial strain leads to equally spaced pseudo-Landau
levels at the upper end of the magnon spectrum, with degeneracies
characteristic of emergent supersymmetry. We also present a particular strain
protocol which induces perfectly quantized magnon Landau levels over the whole
bandwidth. We discuss experimental realizations and generalizations.Comment: 5+7 pages, 3+5 figs; (v2)extended discussion and minor change
Phases of translation-invariant systems out of equilibrium: Iterative Green's function techniques and renormalization group approaches
We introduce a method to evaluate the steady-state non-equilibrium
Keldysh-Schwinger Green's functions for infinite systems subject to both an
electric field and a coupling to reservoirs. The method we present exploits a
physical quasi-translation invariance, where a shift by one unit cell leaves
the physics invariant if all electronic energies are simultaneously shifted by
the magnitude of the electric field. Our framework is straightaway applicable
to diagrammatic many-body methods. We discuss two flagship applications,
mean-field theories as well as a sophisticated second-order functional
renormalization group approach. The latter allows us to push the
renormalization-group characterization of phase transitions for lattice
fermions into the out-of-equilibrium realm. We exemplify this by studying a
model of spinless fermions, which in equilibrium exhibits a
Berezinskii-Kosterlitz-Thouless phase transition
Simulation of motor unit action potential recordings from intramuscular multichannel scanning electrodes
International audienceMultichannel intramuscular EMG (iEMG) recordings provide information on motor neuron behaviour, muscle fiber (MF) innervation geometry and, recently, have been proposed as means for establishing human-machine interfaces. Objective: in order to provide a reliable benchmark for computational methods applied to such recordings, we propose a simulation model for iEMG signals acquired by intramuscular multi-channel electrodes. Methods: we propose a number of modifications to the existing iEMG simulation methods, such as farthest point sampling for more uniform motor unit in-nervation centers distribution in the muscle cross-section, fiber-neuron assignment algorithm, motor neuron action potential propagation delay modelling and a linear model for multichannel recordings simulation. The proposed approach is also extended to gradually shifting (scanning) electrodes. Results: we provide representative applications of this model to the validation of methods for the estimation of motor unit territories, and for iEMG decomposition. Moreover, we extend this model to a full multichannel iEMG simulator using classical linear EMG modelling and existing approaches to the generation of motor neuron discharge sequences. Conclusions: the obtained simulation model provides physiologically accurate MUAPs across entire motor unit territories and for various electrode configurations. Significance: it can be used for the development and evaluation of mathematical methods for multichannel iEMG processing and analysis
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