Short-wavelength stability analysis of thin vortex rings

The linear stability of thin vortex rings are studied by short-wavelength stability analysis. The modified Hill–Schrödinger equation for vortex rings, which incorporates curvature effect, is derived. It is used to evaluate growth rates analytically. The growth rates are also evaluated by numerical calculation and they agree well with analytical values for small which is the ratio of core radius to ring radius. Two types of vortex rings are considered: Kelvin's vortex ring and a Gaussian vortex ring. For Kelvin's vortex ring the maximum first-order growth rate is found to be 1.65/2.56. For the Gaussian vortex ring the first-order growth rate is larg

Two-Triplet-Dimer Excitation Spectra in the Shastry-Sutherland Model for SrCu_2(BO_3)_2

By using the perturbation expansion up to the fifth order, we study the two-triplet-dimer excitation spectra in the Shastry-Sutherland model, where the localized nature of a triplet-dimer, the propagation of a triplet-dimer pair by the correlated hopping and the long-range interactions between triplet-dimers play an essential role. It is found that the dispersion relations for first-neighbor triplet-dimer pair excitations with S=1 and p-type symmetry qualitatively explain the second-lowest branch observed in the neutron inelastic scattering experiment. It is also predicted that the second-lowest branch consists of two components, p_x- and p_y-states, with slightly different excitation energies. The origin of the singlet mode at 3.7meV observed in the Raman scattering experiment is also discussed.Comment: 5 pages, 3 figure

Relationship Between Gas Depth Profiles in Compost Heap and Gas Emission

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is an Invited Paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 5 (2003): Y. Fukumoto, H. Rom, and P. Dahl. Relationship Between Gas Depth Profiles in Compost Heap and Gas Emission. Vol. V. May 2003

Investigation of over-horizon VHF radio signals associated with earthquakes

International audienceThis paper presents the preliminary results on the possible reception of over-horizon VHF radio signals from a FM (frequency modulation) transmitter during abnormal situations (probably in close association with earthquakes). The transmitter is FM Sendai (frequency = 77.1 MHz) and the receiving station is our university (UEC) at Chofu, Tokyo, with the transmitter-receiver distance being about 310 km. We first show a typical example of the reception of over-horizon VHF signals in which we present the amplitude behavior, azimuthal and incident angle estimation, etc. Then, we study the correlation between a signal anomaly and an earthquake and it seems that the over-horizon VHF signals observed are probably associated with earthquakes, observed about 7 to 0 days before an earthquake. The direction finding measurements have indicated that such signals are due to favorable tropospheric (but not ionospheric) conditions attributed to the effects of earthquakes

PS-MRT Lattice Boltzmann model for direct simulation of granular soils and seepage flow

We proposed a direct numerical simulation model of granular soils and seepage flow by combining the discrete element method and the lattice Boltzmann method. The MRT model was introduced in order to obtain stable solutions of fluid flow under high Reynolds number condition. The PS model, which retains a local operation at each fluid node and keep from intensive increasing the computational costs for the calculation of collision term, was also introduced as a solid-fluid coupled model. We show the effectiveness of the PS-MRT lattice Boltzmann model through several validation tests