The nonlinear interaction of shear Alfvén waves and gradient-driven instabilities on pressure gradients in the Large Plasma Device (LAPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at UCLA is explored. Nonlinear response at the beat frequency between two shear Alfvén waves is shown to resonantly drive unstable modes as well as otherwise damped modes. Resonantly driving the damped mod...

Abstrac/-SAR surveys from separate passes show relative shifts of the ground wavcnu mber spectra thaI depend on the local slope and the off-nadir angle. We discuss the exploitation of this spectral sllift for different app] ications: I) generation of "low noise" intcrferograms benefiting phase unwrapping, 2) generation of quick-look interferograms, 3) decorrelation redllction by means of tunabl...

We study invasion fronts in a class of simple, two-species reaction-diffusion systems that occur as models for recurrent precipitation and undercooled liquids. We exhibit several different modes of front propagation: the invasion of an unstable homogeneous equilibrium can create persistent periodic patterns, transient patterns, or simply a homogeneous state. We give criteria that distinguish be...

We study mechanisms for wavenumber selection in a minimal model for run-and-tumble dynamics. We show that nonlinearity in tumbling rates induces the existence of a plethora of traveling- and standing-wave patterns, as well as a subtle selection mechanism for the wavenumbers of spatio-temporally periodic waves. We comment on possible implications for rippling patterns observed in colonies of myx...

We prove wavenumber-explicit bounds on the Dirichlet-to-Neumann map for the Helmholtz equation in the exterior of a bounded obstacle when one of the following three conditions holds: (i) the exterior of the obstacle is smooth and nontrapping, (ii) the obstacle is a nontrapping polygon, (iii) the obstacle is star-shaped and Lipschitz. We prove bounds on the Neumann-to-Dirichlet map when one of c...

As a liquid is progressively supercooled toward its glass transition temperature, an intriguing weakening of the wavenumber (q) dependence of the structural relaxation time tau(q) in the intermediate-to-large q limit is observed both in experiments and simulation studies. Neither continuous Brownian diffusive dynamics nor discontinuous activated events can alone explain the anomalous wavenumber...

A hyperhelix of order N is de­ ned to be a self-similar object consisting of a thin elastic rod wound into a helix, which is itself wound into a larger helix, until this process has been repeated N times. Wave propagation on such a structure can be discussed in a hierarchical manner, ultimately in terms of the wavenumber k de­ ning propagation on the elementary rod. It is found that the dispers...

Several relations from the Kolmogorov theory of fully-developed threedimensional turbulence are rigorously established for finite-time averages over LerayHopf weak solutions of the Navier-Stokes equations. The Navier-Stokes equations are considered with periodic or no-slip boundary conditions and an external forcing term. The main parameter is the Grashof number associated with the forcing term...

Acoustic wave propagation in a fluid with a random assortment of identical cylindrical scatterers is considered. While the leading order correction to the effective wavenumber of the coherent wave is well established at dilute areal density (n0) of scatterers, in this paper the higher order dependence of the coherent wavenumber on n0 is developed in several directions. Starting from the quasi-c...

Density fluctuation measurements covering a wavenumber range relevant to ITG, TEM and ETG type instabilities (k⊥ρi ≈ 0.2 → 10) are compared during Ohmic and neutral beam injection (NBI). These short time duration NBI perturbations modified the background temperature as well as the density fluctuation behaviour but had little effect on the background density. It is found that both the measured a...