arXiv subjects

B. U. Felderhof

Publications and source records attributed to B. U. Felderhof.

42 records · Page 3Linked to original sources

arXiv2013

Velocity relaxation of a porous sphere immersed in a viscous incompressible fluid

Velocity relaxation of a spherically symmetric polymer, immersed in a viscous incompressible fluid, and after a sudden small impulse or a sudden twist from a state of rest, is studied on the basis of the linearized Navier-Stokes equations with an added Darcy type drag term. Explicit expressions for the translational and rotational velocity relaxation functions of the polymer and for the flow pattern of the fluid are derived for a uniform permeable sphere. Surprisingly, it is found that the added mass vanishes. For fairly large values of the ratio of sphere radius to the screening length characterizing the permeability the velocity relaxation functions in the short and intermediate time regime differ significantly from that of a sphere with no-slip boundary condition. At long times both relaxation functions show universal power law behavior.

physics.flu-dyn↗

arXiv2013

Radiation from a semi-infinite unflanged cylindrical dielectric waveguide or optical fiber

Radiative emission from a semi-infinite unflanged circular cylindrical dielectric waveguide or optical fiber is studied for the case of axisymmetric modes of TM polarization on the basis of an iterative scheme. The first step of the scheme leads to approximate values for the reflection coefficients and the electromagnetic fields inside and outside the waveguide. In a numerical example the reflection back into the waveguide is appreciable. Correspondingly the radiation pattern of the outgoing radiation differs appreciably from the lowest order approximation in which reflection is neglected.

physics.optics↗

arXiv2013

Radiation from a semi-infinite unflanged planar dielectric waveguide

Radiative emission from an open-ended unflanged planar dielectric waveguide is studied for the case of TM polarization on the basis of an iterative scheme. The first step of the scheme leads to approximate values for the reflection coefficients and electromagnetic fields inside and outside the waveguide. It is shown that for the related problems of reflection from a step potential in one-dimensional quantum mechanics and of Fresnel reflection of an electromagnetic plane wave from a half-space the iterative scheme is in accordance with the exact solution.

physics.optics↗

arXiv2013

Optimizing second harmonic generation in a circular cylindrical waveguide with embedded periodically arranged tubelets of nonlinear susceptibility

Optical second-harmonic generation (SHG) is studied for the confined geometry of a circular cylindrical waveguide or optical fiber. A model situation of high symmetry is considered where the material with nonlinear susceptibility is isotropic and distributed in radially symmetric manner about the axis. In addition it is assumed that the material of high second-order nonlinearity consists of a thin circular layer, with periodic variation in the axial direction - similar to a usual quasi-phasematched configuration. One can optimize the efficiency of SHG by choosing the period of the array such that a Bragg condition is satisfied. Depletion is studied in the framework of mode-coupling theory. ?

physics.optics↗

arXiv2013

Use of the Basset coefficient in the calculation of the velocity of a spheroid slowing down in a viscous incompressible fluid after a sudden impulse

The motion of a spheroid in a viscous incompressible fluid after a sudden small impulse in the direction of the symmetry axis is studied on the basis of the linearized Navier-Stokes equations. The time-dependence of the spheroid velocity follows by a Fourier transform from the frequency- dependence of the impedance involving friction coefficient, body mass, and added fluid mass. A term proportional to the square root of frequency in the asymptotic high frequency expansion of the impedance, with a Basset coefficient, describes the initial decay in time from the initial value determined by the effective mass. It is shown from numerical evidence based on the exact multipole expansion of the solution for the flow field in terms of spheroidal wavefunctions that the knowledge of the Basset coefficient is insufficient for a reliable estimate of the deviations from a simple two-pole approximation to the complete behavior in time. The two-pole approximation can be calculated from the effective mass and the steady state friction coefficient.

physics.flu-dyn↗

arXiv2013

Derivation of the Love equation for the charge density of a circular plate condenser

The electrostatic problem of two coaxial parallel charged disks of different radii in infinite space is solved by expansion in terms of complex potentials. For perfectly conducting disks a pair of coupled integral equations is derived for the two weight functions of the expansion. The weight function on each disk is linearly related to its radially symmetric charge density. If the radii are equal and the disks are oppositely charged the pair of equations reduce to Love's integral equation for the circular plate condenser.

physics.class-ph↗