Simple Coherent Polarization Manipulation Scheme for Generating High Power Radially Polarized Beam

We present a simple novel scheme that converts a Gaussian beam into an approximated radially polarized beam using coherent polarization manipulation together with Poynting walk-off in birefringent crystals. Our scheme alleviates the interferometric stability required by previous schemes that implemented this coherent mode summation using Mach-Zehnder-like interferometers. A symmetrical arrangement of two walk-off crystals with a half-wave plate, allows coherence control even when the laser has short temporal coherence length. We generated 14 watts of radially polarized beam from an Ytterbium fiber laser, only limited by the available fiber laser power.Comment: Submitting for publicatio

Dispersal and noise: Various modes of synchrony in\ud ecological oscillators

We use the theory of noise-induced phase synchronization to analyze the effects of dispersal on the synchronization of a pair of predator-prey systems within a fluctuating environment (Moran effect). Assuming that each isolated local population acts as a limit cycle oscillator in the deterministic limit, we use phase reduction and averaging methods to derive a Fokker–Planck equation describing the evolution of the probability density for pairwise phase differences between the oscillators. In the case of common environmental noise, the oscillators ultimately synchronize. However the approach to synchrony depends on whether or not dispersal in the absence of noise supports any stable asynchronous states. We also show how the combination of correlated (shared) and uncorrelated (unshared) noise with dispersal can lead to a multistable\ud steady-state probability density

On the Implementation of Efficient Channel Filters for Wideband Receivers by Optimizing Common Subexpression Elimination Methods

No abstract availabl

Fluidized-bed reactor modeling for production of silicon by silane pyrolysis

An ideal backmixed reactor model (CSTR) and a fluidized bed bubbling reactor model (FBBR) were developed for silane pyrolysis. Silane decomposition is assumed to occur via two pathways: homogeneous decomposition and heterogeneous chemical vapor deposition (CVD). Both models account for homogeneous and heterogeneous silane decomposition, homogeneous nucleation, coagulation and growth by diffusion of fines, scavenging of fines by large particles, elutriation of fines and CVD growth of large seed particles. At present the models do not account for attrition. The preliminary comparison of the model predictions with experimental results shows reasonable agreement. The CSTR model with no adjustable parameter yields a lower bound on fines formed and upper estimate on production rates. The FBBR model overpredicts the formation of fines but could be matched to experimental data by adjusting the unkown jet emulsion exchange efficients. The models clearly indicate that in order to suppress the formation of fines (smoke) good gas-solid contacting in the grid region must be achieved and the formation of the bubbles suppressed

Nonlinear dynamics of quantum dot nuclear spins

We report manifestly nonlinear dependence of quantum dot nuclear spin polarization on applied magnetic fields. Resonant absorption and emission of circularly polarized radiation pumps the resident quantum dot electron spin, which in turn leads to nuclear spin polarization due to hyperfine interaction. We observe that the resulting Overhauser field exhibits hysteresis as a function of the external magnetic field. This hysteresis is a consequence of the feedback of the Overhauser field on the nuclear spin cooling rate. A semi-classical model describing the coupled nuclear and electron spin dynamics successfully explains the observed hysteresis but leaves open questions for the low field behaviour of the nuclear spin polarization.Comment: 7 pages, 4 figure

Effects of demographic noise on the synchronization of a metapopulation in a fluctuating environment

We use the theory of noise-induced phase synchronization to analyze the effects of demographic noise on the synchronization of a metapopulation of predator-prey systems within a fluctuating environment (Moran effect). Treating each local predator–prey population as a stochastic urn model, we derive a Langevin equation for the stochastic dynamics of the metapopulation. Assuming each local population acts as a limit cycle oscillator in the deterministic limit, we use phase reduction and averaging methods to derive the steady state probability density for pairwise phase differences between oscillators, which is then used to determine the degree of synchronization of\ud the metapopulation