Delay-induced multistability near a global bifurcation

We study the effect of a time-delayed feedback within a generic model for a saddle-node bifurcation on a limit cycle. Without delay the only attractor below this global bifurcation is a stable node. Delay renders the phase space infinite-dimensional and creates multistability of periodic orbits and the fixed point. Homoclinic bifurcations, period-doubling and saddle-node bifurcations of limit cycles are found in accordance with Shilnikov's theorems.Comment: Int. J. Bif. Chaos (2007), in prin

Fabrication and test of lightweight honeycomb sandwich structures Final report

Fabrication and testing of lightweight honeycomb sandwich structure

Potential utilization of the NASA/George C. Marshall Space Flight Center in earthquake engineering research

Earthquake engineering research capabilities of the National Aeronautics and Space Administration (NASA) facilities at George C. Marshall Space Flight Center (MSFC), Alabama, were evaluated. The results indicate that the NASA/MSFC facilities and supporting capabilities offer unique opportunities for conducting earthquake engineering research. Specific features that are particularly attractive for large scale static and dynamic testing of natural and man-made structures include the following: large physical dimensions of buildings and test bays; high loading capacity; wide range and large number of test equipment and instrumentation devices; multichannel data acquisition and processing systems; technical expertise for conducting large-scale static and dynamic testing; sophisticated techniques for systems dynamics analysis, simulation, and control; and capability for managing large-size and technologically complex programs. Potential uses of the facilities for near and long term test programs to supplement current earthquake research activities are suggested

Application of advanced technologies to small, short-haul transport aircraft (STAT)

The benefits of selected advanced technologies for 19 and 30 passenger, short-haul aircraft were identified. Advanced technologies were investigated in four areas: aerodynamics, propulsion, structures, and ride quality. Configuration sensitivity studies were conducted to show design tradeoffs associated with passenger capacity, cabin comfort level, and design field length

Best Legume for Permanent Pasture

No other pasture legume now available compares with birdsfoot trefoil in abiliity to withstand continuous grazing once it is established. Trefoil does, however, need more attention than other legumes in getting established. Here are some tips from Iowa State College agronomists

Texas Honey Plants

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Quantum theory of impact ionization in coherent high-field semiconductor transport

Generation of carriers in semiconductors by impact ionization is studied under the influence of a constant, arbibrarily high electric field. Using the density-matrix approach a system of equations for the coherent dynamics of electrons and holes in the presence of impact ionization and Auger recombination is derived, which extends the semiconductor Bloch equations by the inclusion of impact-ionization density-correlation functions as additional dynamic variables. From these equations we recover the pure (Zener) and the photon-induced (Franz-Keldysh) carrier tunneling rate and derive an expression for the field-assisted impact-ionization scattering rate. Different levels of approximation of the kinetic equations are discussed. It is shown that in contrast to the semiclassical treatment in the presence of an electric field, a fixed impact-ionization threshold does no longer exist, and the impact-ionization scattering rate is drastically enhanced around the semiclassical threshold by the intracollisional field effect. The close connection of field-assisted impact ionization to the Franz-Keldysh effect is emphasized