9 research outputs found
Do nonlinear waves in random media follow nonlinear diffusion equations?
Probably yes, since we find a striking similarity in the spatio-temporal
evolution of nonlinear diffusion equations and wave packet spreading in generic
nonlinear disordered lattices, including self-similarity and scaling.Comment: 6 pages, 4 figure
Nonlinear Lattice Waves in Random Potentials
Localization of waves by disorder is a fundamental physical problem
encompassing a diverse spectrum of theoretical, experimental and numerical
studies in the context of metal-insulator transition, quantum Hall effect,
light propagation in photonic crystals, and dynamics of ultra-cold atoms in
optical arrays. Large intensity light can induce nonlinear response, ultracold
atomic gases can be tuned into an interacting regime, which leads again to
nonlinear wave equations on a mean field level. The interplay between disorder
and nonlinearity, their localizing and delocalizing effects is currently an
intriguing and challenging issue in the field. We will discuss recent advances
in the dynamics of nonlinear lattice waves in random potentials. In the absence
of nonlinear terms in the wave equations, Anderson localization is leading to a
halt of wave packet spreading.
Nonlinearity couples localized eigenstates and, potentially, enables
spreading and destruction of Anderson localization due to nonintegrability,
chaos and decoherence. The spreading process is characterized by universal
subdiffusive laws due to nonlinear diffusion. We review extensive computational
studies for one- and two-dimensional systems with tunable nonlinearity power.
We also briefly discuss extensions to other cases where the linear wave
equation features localization: Aubry-Andre localization with quasiperiodic
potentials, Wannier-Stark localization with dc fields, and dynamical
localization in momentum space with kicked rotors.Comment: 45 pages, 19 figure
Quasiperiodic driving of Anderson localized waves in one dimension
We consider a quantum particle in a one-dimensional disordered lattice with Anderson localization in the
presence of multifrequency perturbations of the onsite energies. Using the Floquet representation, we transform
the eigenvalue problem into a Wannier-Stark basis. Each frequency component contributes either to a single
channel or a multichannel connectivity along the lattice, depending on the control parameters. The single-channel
regime is essentially equivalent to the undriven case. The multichannel driving increases substantially the
localization length for slow driving, showing two different scaling regimes of weak and strong driving, yet the
localization length stays finite for a finite number of frequency components. ©2016 American Physical Society1331sciescopu
Lipolytic enzymes and hydrolytic rancidity
Lipolysis, the enzymic hydrolysis of milk lipids to free fatty acids and partial glycerides, is a constant concern to the dairy industry because of the detrimental effcts it can have on the flvor and other properties of milk and milk products. However, free fatty acids also contribute to the desirable flavor of milk and milk products when present at low concentrations and, in some cheeses, when present at high concentrations. The enzymes responsible for the detrimental effects of lipolysis are of two main types: those indigenous to milk, and those of microbial origin. The major indigenous milk enzyme is lipoprotein lipase. It is active on the fat in natural milk fat globules only after their disruption by physical treatments or if certain blood serum lipoproteins are present. The major microbial lipases are produced by psychrotrophic bacteria. Many of these enzymes are heat stable and are particularly significant in stored products. Human milk differs from cows' milk in that it contains two lipases, a lipoprotein lipase and a bile salt-stimulated lipase. The ability of the latter to cause considerable hydrolysis of ingested milk lipids has important nutritional implications