Diffusion and wave behaviour in linear Voigt modelDiffusion et comportement ondulatoire dans le modèle linéaire de Voigt

A boundary value problem $\text{P}{}_{\mathrm{\epsilon }}$ related to a third order parabolic equation with a small parameter ε is analized. This equation models the one-dimensional evolution of many dissipative media as viscoelastic fluids or solids, viscous gases, superconducting materials, incompressible and electrically conducting fluids. Moreover, the third order parabolic operator regularizes various nonlinear second order wave equations. In this paper, the hyperbolic and parabolic behaviour of the solution of $\text{P}{}_{\mathrm{\epsilon }}$ is estimated by means of slow timeτ=εt and fast timeθ=t/ε. As consequence, a rigorous asymptotic approximation for the solution of $\text{P}{}_{\mathrm{\epsilon }}$ is established. To cite this article: M. De Angelis, P. Renno, C. R. Mecanique 330 (2002) 21–26     

On the initial-value problem in a cold plasma model

We study existence of solutions to elliptic systems with measure on the right hand side.     

Electrostatics in wind-blown sand

Wind-blown sand, or "saltation," is an important geological process, and the primary source of atmospheric mineral dust aerosols. Significant discrepancies exist between classical saltation theory and measurements. We show here that these discrepancies can be resolved by the inclusion of sand electrification in a physically based saltation model. Indeed, we find that electric forces enhance the concentration of saltating particles and cause them to travel closer to the surface, in agreement with measurements. Our results thus indicate that sand electrification plays an important role in saltation.     

Photoionization of highly charged ions using an ECR ion source and undulator radiation

Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series.     

Metallic waveguide mirrors in polymer film waveguides

A technology for the fabrication of metallic waveguide mirrors is developed. Plane and curved waveguide mirrors, the latter acting in the same way as cylindrical lenses, are realized in benzocyclobutene (BCB) film waveguides. The waveguide mirror structure is dry-etched into the BCB film waveguide. To enhance the reflectivity of the waveguide mirrors, the waveguide edge is metallized. The BCB film waveguide mirrors are characterized with respect to waveguide attenuation and mirror reflectivity. The waveguide attenuation of the processed BCB waveguide is 0.5 dB/cm. Ag-coated BCB waveguide mirrors show a reflectivity of 71%. The efficiency of total internal reflection (TIR, i.e. in the case without metallization) at the dry-etched waveguide edge is 74%. As an application of the BCB waveguide mirrors a hybrid integrated optical module for Fourier-optical transverse mode selection in broad area lasers (BAL) is proposed. Received: 16 May 2001 / Published online: 23 October 2001     

Small exponent asymptotics

We study the surprisingly complicated asymptotic character ofa simple first-order differential equation, which involves aterm with a low exponent of the dependent variable. While numericalsolutions and straightforward asymptotic expansions indicatea clearly defined boundary layer type transition, we find thatthe correct asymptotic structure involves a 'hidden' boundarylayer, and that a straightforward approach cannot discern this.