Scattering and leapfrogging of vortex rings in a superfluid

The dynamics of vortex ring pairs in the homogeneous nonlinear Schr\"odinger equation is studied. The generation of numerically-exact solutions of traveling vortex rings is described and their translational velocity compared to revised analytic approximations. The scattering behavior of co-axial vortex rings with opposite charge undergoing collision is numerically investigated for different scattering angles yielding a surprisingly simple result for its dependence as a function of the initial vortex ring parameters. We also study the leapfrogging behavior of co-axial rings with equal charge and compare it with the dynamics stemming from a modified version of the reduced equations of motion from a classical fluid model derived using the Biot-Savart law.Comment: 12 pages, 11 figure

van der Waals interactions of the benzene dimer: towards treatment of polycyclic aromatic hydrocarbon dimers

Although density functional theory (DFT) in principle includes even long-range interactions, standard implementations employ local or semi-local approximations of the interaction energy and fail at describing the van der Waals interactions. We show how to modify a recent density functional that includes van der Waals interactions in planar systems [Phys. Rev. Lett. 91, 126402 (2003)] to also give an approximate interaction description of planar molecules. As a test case we use this modified functional to calculate the binding distance and energy for benzene dimers, with the perspective of treating also larger, flat molecules, such as the polycyclic aromatic hydrocarbons (PAH).Comment: 7 pages, 2 figures (3 figure files) submitted to Materials Science and Engineering

Hybrid superprism with low insertion losses and suppressed cross-talk

We demonstrate with the two-dimensional finite-difference time-domain method that an adiabatic transition in a superprism with an interface along the [1 [overline 2]] direction enhances the transmission through the superprism to more than 90% (–0.5 dB) over the wavelength range 1.47–1.68 µm, including the telecommunication C and L bands. We also show that diffraction governed by a quasinegative index of refraction inside the superprism can be used to obtain nearly transform-limited beam widths at the output of the superprism. The reduction of the beam width at the output suppresses cross-talk and greatly enhances the achievable frequency resolution of the superprism

Determination of aerodynamic damping coefficients from wind-tunnel free-flight trajectories of non-axisymmetric bodies

Aerodynamic damping coefficient from wind tunnel free flight trajectories of nonaxisymmetrical bodie

Approximation of sweep surfaces by tensor product B-splines

Journal ArticleTensor product B-spline approximations to surfaces generated by sweeping a (possibly deforming) B-spline cross-section curve along a Bspline axis curve are discussed. A general form for the tensor product B-spline approximation for sweeps is derived and expressed in terms of the approximation of a set of offset curves of the axis curve. The actual algorithm used to generate the approximation depends on the nature of the desired deformation and change in orientation that the crosssection undergoes as it is swept along the axis. Several algorithms for generating tensor product B-spline approximations to sweep surfaces are presented