Search results for "Classical physics"
showing 10 items of 190 documents
Dipole surface plasmon in large K N + clusters
1993
The dipole surface plasmon forK N + clusters is analyzed using the RPA sum-rule technique within a semiclassical Density Functional Theory and the spherical jellium model. The theoretical frequencies are blue shifted as compared to the experimental ones. The discrepancies between theory and experiment are reduced when considering non-local energy contributions in the density functional and phenomenologically including atomic lattice effects by means of an electron effective mass and a static dielectric constant.
Low-energy corrections to the eikonal description of elastic scattering and breakup of one-neutron halo nuclei in nuclear-dominated reactions
2018
Background: The eikonal approximation is a high-energy reaction model, which is very computationally efficient and provides a simple interpretation of the collision. Unfortunately, it is not valid at energies around 10 MeV/nucleon, the range of energy of HIE-ISOLDE at CERN and the future ReA12 at MSU. Fukui et al. [Phys. Rev. C 90, 034617 (2014)10.1103/PhysRevC.90.034617] have shown that a simple semiclassical correction of the projectile-target deflection could improve the description of breakup of halo nuclei on heavy targets down to 20 MeV/nucleon. Purpose: We study two similar corrections, which aim at improving the projectile-target relative motion within the eikonal approximation, wit…
High Order Harmonics from a Molecule: Evidence of the Nuclear Motion
2007
The electromagnetic spectrum emitted by a molecule driven by a laser presents harmonics and satellite lines whose separation is equal to the oscillation frequency of the nuclei. Full quantum and semiclassical calculations are presented.
Analysis of the viscous quantum hydrodynamic equations for semiconductors
2004
The steady-state viscous quantum hydrodynamic model in one space dimension is studied. The model consists of the continuity equations for the particle and current densities, coupled to the Poisson equation for the electrostatic potential. The equations are derived from a Wigner–Fokker–Planck model and they contain a third-order quantum correction term and second-order viscous terms. The existence of classical solutions is proved for “weakly supersonic” quantum flows. This means that a smallness condition on the particle velocity is still needed but the bound is allowed to be larger than for classical subsonic flows. Furthermore, the uniqueness of solutions and various asymptotic limits (sem…
Pair production due to an electric field in 1+1 dimensions and the validity of the semiclassical approximation
2021
Solutions to the backreaction equation in $1+1$-dimensional semiclassical electrodynamics are obtained and analyzed when considering a time-varying homogeneous electric field initially generated by a classical electric current, coupled to either a quantized scalar field or a quantized spin-$\frac{1}{2}$ field. Particle production by way of the Schwinger effect leads to backreaction effects that modulate the electric field strength. Details of the particle production process are investigated along with the transfer of energy between the electric field and the particles. The validity of the semiclassical approximation is also investigated using a criterion previously implemented for chaotic i…
An educational path for the magnetic vector potential and its physical implications
2013
We present an educational path for the magnetic vector potential A aimed at undergraduate students and pre-service physics teachers. Starting from the generalized Ampere–Laplace law, in the framework of a slowly varying time-dependent field approximation, the magnetic vector potential is written in terms of its empirical references, i.e. the conduction currents. Therefore, once the currents are known, our approach allows for a clear and univocal physical determination of A, overcoming the mathematical indeterminacy due to the gauge transformations. We have no need to fix a gauge, since for slowly varying time-dependent electric and magnetic fields, the ‘natural’ gauge for A is the Coulomb o…
Stability of an electromagnetically levitated spherical sample in a set of coaxial circular loops
2005
This paper presents a theoretical study of oscillatory and rotational instabilities of a solid spherical body, levitated electromagnetically in axisymmetric coils made of coaxial circular loops. We apply our previous theory to analyze the static and dynamic stability of the sample depending on the ac frequency and the position of the sample in the coils for several simple configurations. We introduce an original analytical approach employing a gauge transformation for the vector potential. First, we calculate the spring constants that define the frequency of small-amplitude oscillations. For static stability, the spring constants must be positive. Dynamic instabilities are characterized by …
Finite difference time domain simulation of soil ionization in grounding systems under lightning surge conditions
2004
This paper proposes a Maxwell’s equations finite difference time domain (FDTD) approach for electromagnetic transients in ground electrodes in order to take into account the non linear effects due to soil ionization. A time variable soil resistivity method is used in order to simulate the soil breakdown, without the formulation of an initial hypothesis about the geometrical shape of the ionized zone around the electrodes. The model has been validated by comparing the computed results with available data found in technical literature referred to concentrated earths. Some application examples referred to complex grounding systems are reported to show the computational capability of the propos…
One pendulum to run them all
2013
The analytical solution for the three-dimensional linear pendulum in a rotating frame of reference is obtained, including Coriolis and centrifugal accelerations, and expressed in terms of initial conditions. This result offers the possibility of treating Foucault and Bravais pendula as trajectories of the same system of equations, each of them with particular initial conditions. We compare them with the common two-dimensional approximations in textbooks. A previously unnoticed pattern in the three-dimensional Foucault pendulum attractor is presented.
Return to Equilibrium, Non-self-adjointness and Symmetries, Recent Results with M. Hitrik and F. Hérau
2014
In this talk we review some old and new results about the use of supersymmetric structures in semi-classical problems. Necessary and sufficient conditions are obtained for a real semiclassical partial differential operator of order two to possess a supersymmetric structure. For operators coming from a chain of oscillators, coupled to two heat baths, we show the non-existence of a smooth supersymmetric structure. The recent and new results all come from joint works with Michael Hitrik and Frederic Herau.