The frequency-wavenumber spectra of laminated media often exhibit anomalous modes with descending branches whose group velocity is negative, and these terminate at a minimum point at which the group velocity transitions from negative to positive. These minima are associated with resonant conditions in the medium, which have been clearly observed in experiments and in the nondestructive testing ...

We suggest that the high–velocity clouds (HVCs) are large clouds, with typical diameters of 25 kpc and containing 5×107 solar masses of neutral gas and 3×108 solar masses of dark matter, falling onto the Local Group; altogether the HVCs contain 10 solar masses of neutral gas. Our reexamination of the Local–Group hypothesis for the HVCs connects their properties to the hierarchical structure for...

We present several different statistical methods to determine the transverse velocity vector of M31. The underlying assumptions are that the M31 satellites on average follow the motion of M31 through space, and that the galaxies in the outer parts of the Local Group on average follow the motion of the Local Group barycenter through space. We apply the methods to the line-of-sight velocities of ...