Variational bounds on the energy dissipation rate in body-forced shear flow

A new variational problem for upper bounds on the rate of energy dissipation in body-forced shear flows is formulated by including a balance parameter in the derivation from the Navier-Stokes equations. The resulting min-max problem is investigated computationally, producing new estimates that quantitatively improve previously obtained rigorous bounds. The results are compared with data from direct numerical simulations.Comment: 15 pages, 7 figure

Exponentially growing solutions in homogeneous Rayleigh-Benard convection

It is shown that homogeneous Rayleigh-Benard flow, i.e., Rayleigh-Benard turbulence with periodic boundary conditions in all directions and a volume forcing of the temperature field by a mean gradient, has a family of exact, exponentially growing, separable solutions of the full non-linear system of equations. These solutions are clearly manifest in numerical simulations above a computable critical value of the Rayleigh number. In our numerical simulations they are subject to secondary numerical noise and resolution dependent instabilities that limit their growth to produce statistically steady turbulent transport.Comment: 4 pages, 3 figures, to be published in Phys. Rev. E - rapid communication

Fuel quality/processing study. Volume 4: On site processing studies

Fuel treated at the turbine and the turbine exhaust gas processed at the turbine site are studied. Fuel treatments protect the turbine from contaminants or impurities either in the upgrading fuel as produced or picked up by the fuel during normal transportation. Exhaust gas treatments provide for the reduction of NOx and SOx to environmentally acceptable levels. The impact of fuel quality upon turbine maintenance and deterioration is considered. On site costs include not only the fuel treatment costs as such, but also incremental costs incurred by the turbine operator if a turbine fuel of low quality is not acceptably upgraded

Phase space dynamics of overdamped quantum systems

The phase space dynamics of dissipative quantum systems in strongly condensed phase is considered. Based on the exact path integral approach it is shown that the Wigner transform of the reduced density matrix obeys a time evolution equation of Fokker-Planck type valid from high down to very low temperatures. The effect of quantum fluctuations is discussed and the accuracy of these findings is tested against exact data for a harmonic system.Comment: 7 pages, 2 figures, to appear in Euro. Phys. Let

Subdiffusion-limited reactions

We consider the coagulation dynamics A+A -> A and A+A A and the annihilation dynamics A+A -> 0 for particles moving subdiffusively in one dimension. This scenario combines the "anomalous kinetics" and "anomalous diffusion" problems, each of which leads to interesting dynamics separately and to even more interesting dynamics in combination. Our analysis is based on the fractional diffusion equation

CalMagNet ? an array of search coil magnetometers monitoring ultra low frequency activity in California

International audienceThe California Magnetometer Network (CalMagNet) consists of sixty-eight triaxial search-coil magnetometer systems measuring Ultra Low Frequency (ULF), 0.001?16 Hz, magnetic field fluctuations in California. CalMagNet provides data for comprehensive multi-point measurements of specific events in the Pc 1?Pc 5 range at mid-latitudes as well as a systematic, long-term study of ULF signals in active fault regions in California. Typical events include geomagnetic micropulsations and spectral resonant structures associated with the ionospheric Alfvén resonator. This paper provides a technical overview of the CalMagNet sensors and data processing systems. The network is composed of ten reference stations and fifty-eight local monitoring stations. The primary instruments at each site are three orthogonal induction coil magnetometers. A geophone monitors local site vibration. The systems are designed for future sensor expansion and include resources for monitoring four additional channels. Data is currently sampled at 32 samples per second with a 24-bit converter and time tagged with a GPS-based timing system. Several examples of representative magnetic fluctuations and signals as measured by the array are given