Search results for "semiclassical"
showing 10 items of 111 documents
Line broadening coefficient calculations for methane perturbed by nitrogen
2010
Abstract We report semiclassical line broadening calculations for methane perturbed by nitrogen at room temperature. For this, we have developed a symmetrized version of the Robert and Bonamy theory. The interaction potential was built from electrostatic (octopole and hexadecapole for methane, quadrupole for nitrogen) and atom–atom contributions. The relative (classical) trajectories of the molecules were computed in the frame of the usual parabolic model, through analytical formula. High orders of developments had to be used for the short range molecular interactions. As a consequence, a combination of symbolic computation and source code generation was employed to implement practical calc…
Calculated line broadening parameters for methane perturbed by diatomic molecules
2013
International audience; We report semiclassical line broadening calculations for methane perturbed by diatomic molecules: nitrogen, N2, oxygen, O2 and hydrogen, H2, at room temperature. For this, we have developed a symmetrized version of the Robert and Bonamy theory. The interaction potential was built from electrostatic (octopole and hexadecapole for methane, quadrupole for the diatomic molecules) and atom-atom contributions. The relative (classical) trajectories of the molecules were computed in the frame of the usual parabolic model, through analytical formula. High orders of developments had to be used for the short range molecular interactions in the case of N2 and O2. For H2, a lower…
Giant piezoelectricity in B/N doped 4,12,2-graphyne
2020
Abstract The effects of boron (B) and nitrogen (N) substitutions in 4,12,2-graphyne on its geometric structure and mechanical as well as electronic properties have been systematically investigated with the aid of density functional theory (DFT). The trend in the elastic properties of the substituted systems is determined by the doping positions and the type of the dopants. The Bader charge analysis reveals that the N dopant at the sp-site destroys the acetylenic linkage in 4,12,2-graphyne, but instead tends to form a polar bond, or even possibly a charge-shift bond. In particular, an obvious in-plane piezoelectricity is induced by foreign atom substitutions owing to the deformation of the p…
Spectra for Semiclassical Operators with Periodic Bicharacteristics in Dimension Two
2014
We study the distribution of eigenvalues for selfadjoint $h$--pseudodifferential operators in dimension two, arising as perturbations of selfadjoint operators with a periodic classical flow. When the strength $\varepsilon$ of the perturbation is $\ll h$, the spectrum displays a cluster structure, and assuming that $\varepsilon \gg h^2$ (or sometimes $\gg h^{N_0}$, for $N_0 >1$ large), we obtain a complete asymptotic description of the individual eigenvalues inside subclusters, corresponding to the regular values of the leading symbol of the perturbation, averaged along the flow.
Tunnel effect and symmetries for Kramers–Fokker–Planck type operators
2011
AbstractWe study operators of Kramers–Fokker–Planck type in the semiclassical limit, assuming that the exponent of the associated Maxwellian is a Morse function with a finite number n0 of local minima. Under suitable additional assumptions, we show that the first n0 eigenvalues are real and exponentially small, and establish the complete semiclassical asymptotics for these eigenvalues.
Population of neutron-rich nuclei around 48ca with deep inelastic collisions
2009
The deep inelastic reaction 48Ca+64Ni at 6 MeV/A has been studied using the CLARA–PRISMA setup. Angular distributions for pure elastic scattering and total cross-sections of the most relevant transfer channels have been measured. The experimental results are compared with predictions from a semiclassical model, showing good agreement for the presently analyzed few neutrons transfer channels. The decay of the most intense reaction products has also been studied, giving indications of the population of states with very short lifetimes. Gadea Raga, Andrés, Gadea.Andres@ific.uv.es
Numerical study of the long wavelength limit of the Toda lattice
2014
We present the first detailed numerical study of the Toda equations in $2+1$ dimensions in the limit of long wavelengths, both for the hyperbolic and elliptic case. We first study the formal dispersionless limit of the Toda equations and solve initial value problems for the resulting system up to the point of gradient catastrophe. It is shown that the break-up of the solution in the hyperbolic case is similar to the shock formation in the Hopf equation, a $1+1$ dimensional singularity. In the elliptic case, it is found that the break-up is given by a cusp as for the semiclassical system of the focusing nonlinear Schr\"odinger equation in $1+1$ dimensions. The full Toda system is then studie…
Plasma effects on neutrino-antineutrino synchrotron radiation in dense matter
2000
Abstract We consider plasma effects on ν ν synchroton radiation from ultrarelativistic, degenerate electrons in neutron stars with strong magnetic fields. Under typical conditions for such stars, a semiclassical calculation can be performed, in which electrons are considered to move along classical paths. We show that collective effects in the plasma lead to an essential enhancement (about three times) of the vector weak-current contributions to neutrino pair emissivity.
Spectral properties of random non-self-adjoint operators
2015
In this thesis we are interested in the spectral properties of random non-self-adjoint operators. Weare going to consider primarily the case of small random perturbations of the following two types of operators: 1. a class of non-self-adjoint h-differential operators Ph, introduced by M. Hager [32], in the semiclassical limit (h→0); 2. large Jordan block matrices as the dimension of the matrix gets large (N→∞). In case 1 we are going to consider the operator Ph subject to small Gaussian random perturbations. We let the perturbation coupling constant δ be e (-1/Ch) ≤ δ ⩽ h(k), for constants C, k > 0 suitably large. Let ∑ be the closure of the range of the principal symbol. Previous results o…
Large angular-momentum changing in a short half-cycle pulse interaction with a Rydberg atom
1999
We show that, in contrast to multiphoton absorption in atoms, the remote region from a nucleus is dominant in the process of a half-cycle pulse interaction with a Rydberg atom, and that this interaction produces a very large change in the angular momentum of the electron. We have found good agreement between classical trajectory Monte Carlo, semiclassical, and quantum-mechanical calculations for the energy distribution of the electron.