The near-horizon metric for a black brane in Anti-de Sitter (AdS) space and the metric near the AdS boundary both exhibit hydrodynamic behavior. We demonstrate the equivalence of this pair of hydrodynamic systems for the sound mode of a conformal theory. This is first established for Einstein’s gravity, but we then show how the sound damping constant will be modified, from its Einstein form, fo...

Damping of ship whipping vibrations following a slam due to wave impact is traditionally assumed to be primarily of material or structural origin. However, several mechanisms of energy dissipation to the surrounding water exist, including gravity and acoustic waves. Neither transports much energy for the lowest frequency modes, in which the acoustic wavelength may be an order or magnitude great...

A numerical model is developed to simulate fully nonlinear transient waves in a semiinfinite, two-dimensional wave tank. A mixed Eulerian-Lagrangian formulation is adopted and a high-order boundary element method is used to solve for the fluid motion at each time step. Input wave characteristics are specified at the upstream boundary of the computational domain using an appropriate wave theory....

We construct a theory of spin wave excitations in the bilayer manganite La1.2Sr1.8Mn2O7 based on the simplest possible double–exchange model, but including leading quantum corrections to the spin wave dispersion and damping. Comparison is made with recent inelastic neutron scattering experiments. We find that quantum effects account for some part of the measured damping of spin waves, but canno...

Eigenvalues of a potential dynamical system with damping forces that are described by an indefinite real symmetric matrix can behave as those of a Hamiltonian system when gain and loss are in a perfect balance. This happens when the indefinitely damped system obeys parity-time ( ) symmetry. How do pure imaginary eigenvalues of a stable -symmetric indefinitely damped system behave when variation...

We show local existence of solutions to the initial boundary value problem corresponding to a semilinear wave equation with interior damping and source terms. The difficulty in dealing with these two competitive forces comes from the fact that the source term is not a locally Lipschitz function from H1(Ω) into L2(Ω) as typically assumed in the literature. The strategy behind the proof is based ...

In this paper we show local existence of solutions to the initial boundary value problem corresponding to a semilinear wave equation with interior damping and source terms. The difficulty in dealing with these two competitive forces comes from the fact that the source term is not a locally Lipschitz function from H1(Ω) into L2(Ω) as typically assumed in the literature. The strategy behind the p...

In the present work the change in natural frequencies, damping and mode shapes of a prefabricated timber floor element have been investigated when it was integrated into a building structure. The timber floor element was first subjected to modal testing in laboratory with ungrounded and simply supported boundary conditions, and then in situ at different stages of building construction. The firs...

We consider the problem of oscillation damping in air of a thermally actuated microlever as it gradually approaches an infinite wall in parallel geometry. As the gap is decreased from 20 microm down to 400 nm, we observe the increasing damping of the lever Brownian motion in the fluid laminar regime. This manifests itself as a linear decrease in the lever quality factor accompanied by a dramati...

The optimal damping control for nonlinear time-delay systems with persistent disturbances is considered. Based on successive approximation approach (SAA), the optimal damping control (ODC) law is achieved by solving a decoupled sequence of inhomogeneous linear two-point boundary value (TPBV) problems without time-delay and time-advance terms. The ODC law of the original problem consists of accu...