Search results for "Linear"
showing 10 items of 7165 documents
On the convexity of relativistic ideal magnetohydrodynamics
2015
We analyze the influence of the magnetic field in the convexity properties of the relativistic magnetohydrodynamics system of equations. To this purpose we use the approach of Lax, based on the analysis of the linearly degenerate/genuinely non-linear nature of the characteristic fields. Degenerate and non-degenerate states are discussed separately and the non-relativistic, unmagnetized limits are properly recovered. The characteristic fields corresponding to the material and Alfv\'en waves are linearly degenerate and, then, not affected by the convexity issue. The analysis of the characteristic fields associated with the magnetosonic waves reveals, however, a dependence of the convexity con…
Transition cancellations of 87Rb and 85Rb atoms in a magnetic field
2020
We have analyzed the magnetic field dependencies of the intensities of all the optical transitions between magnetic sublevels of hyperfine levels, excited with σ + , π , and σ − polarized light, for the D 1 and D 2 lines of 87 R b and 85 R b atoms. Depending on the type of transition and the quantum numbers of the involved levels, the Hamiltonian matrices are of 1 × 1 , 2 × 2 , 3 × 3 , or 4 × 4 dimension. As an example, analytical expressions are presented for the case of 2 × 2 dimension matrices for the D 1 line of both isotopes. Eigenvalues and eigenkets are given, and the expression for the transition intensity as a function of B has been determined. It is found that some π transitions o…
Isotropic Chiral Acoustic Phonons in 3D Quasicrystalline Metamaterials.
2020
International audience; The elastic properties of three-dimensional (3D) crystalline mechanical metamaterials, unlike those of amorphous structures, are generally strongly anisotropic—even in the long-wavelength limit and for highly symmetric crystals. Aiming at isotropic linear elastic wave propagation, we therefore study 3D periodic approximants of 3D icosahedral quasicrystalline mechanical metamaterials consisting of uniaxial chiral metarods. Considering the increasing order of the approximants, we approach nearly isotropic effective speeds of sound and isotropic acoustical activity. The latter is directly connected to circularly polarized 3D metamaterial chiral acoustic phonons—for all …
Exact Solutions of the Two Dimensional Boussinesq and Dispersive Water Waves Equations
2010
In this paper two-dimensional Boussinesq and dispersive water waves equations are investigated in exact solutions. The Exp-function method is used for seeking exact solutions of the equations through symbolic computation.
Direct theoretical evidence of nuclear motion in H+2by means of high harmonic generation
2007
The numerical solution of the time-dependent Schro ̈dinger equation for vibrating hydrogen molecular ions in many-cycle laser pulses shows that high- order harmonic generation is sensitive to laser-induced molecular vibrations. In particular, the odd harmonic lines in the emitted spectra are surrounded by additional regular peaks whose spacing is given by the vibrational frequency of the nuclei motion. Analytical theory relates these satellite peaks to the molecular vibrations in terms of an approximated effective potentials. These results are not affected by the dimensionality of the system.
Laser driven parametric amplification of xuv and soft-x-rays in neutral gases
2010
We present the first theoretical description and also experimental evidence for the amplification of XUV and soft-X-ray radiation by parametric stimulated emission in neutral gases driven by near-IR laser pulses reaching small-signal-gain up to 8000.
Laser-driven amplification of soft X-rays by parametric stimulated emission in neutral gases
2010
The high-order harmonics of short laser pulses created in a nonlinear medium are a useful source of extreme-ultraviolet and soft-X-ray radiation. A newly discovered phenomenon that amplifies this emission even further could improve the efficiency of short-wavelength light sources.
Dipole soliton-vortices
2007
On universal symmetry grounds, we analyze the existence of a new type of discrete-symmetry vortex solitons that can be considered as coherent states of dipole solitons carrying a nonzero topological charge. Remarkably, they can be also interpreted as excited angular Bloch states. The stability of new soliton states is elucidated numerically.
Radiation dose distribution around a mobile linear accelerator Mobetron using Monte Carlo simulation
2016
The aim of this work is to analyze the scattered radiation produced by the mobile accelerator Mobetron. To do so detailed Monte Carlo simulation using two different codes, Penelope2011 and Geant4, were performed. Experimental measurements were also done to validate them. To quantify the attenuation of the internal structures present in the accelerator head on the scattered radiation produced, some of the main structural shielding in the Mobetron has been incorporated into the simulation. Results are compared with experimental measurements. Some discrepancies between the calculated and measured dose values were found. These differences can be traced back to the importance of the radiation co…