26,450 research outputs found
A multistream model for quantum plasmas
The dynamics of a quantum plasma can be described self-consistently by the
nonlinear Schroedinger-Poisson system. Here, we consider a multistream model
representing a statistical mixture of N pure states, each described by a
wavefunction. The one-stream and two-stream cases are investigated. We derive
the dispersion relation for the two-stream instability and show that a new,
purely quantum, branch appears. Numerical simulations of the complete
Schroedinger-Poisson system confirm the linear analysis, and provide further
results in the strongly nonlinear regime. The stationary states of the
Schroedinger-Poisson system are also investigated. These can be viewed as the
quantum mechanical counterpart of the classical Bernstein-Greene-Kruskal modes,
and are described by a set of coupled nonlinear differential equations for the
electrostatic potential and the stream amplitudes.Comment: 20 pages, 10 figure
Variational approach for the quantum Zakharov system
The quantum Zakharov system is described in terms of a Lagrangian formalism.
A time-dependent Gaussian trial function approach for the envelope electric
field and the low-frequency part of the density fluctuation leads to a coupled,
nonlinear system of ordinary differential equations. In the semiclassic case,
linear stability analysis of this dynamical system shows a destabilizing r\^ole
played by quantum effects. Arbitrary value of the quantum effects are also
considered, yielding the ultimate destruction of the localized, Gaussian trial
solution. Numerical simulations are shown both for the semiclassic and the full
quantum cases.Comment: 6 figure
Cold-air performance of a tip turbine designed to drive a lift fan
Performance was obtained over a range of speeds and pressure ratios for a 0.4 linear scale version of the LF460 lift fan turbine with the rotor radial tip clearance reduced to about 2.5 percent of the rotor blade height. These tests covered a range of speeds from 60 to 140 percent of design equivalent speed and a range of scroll inlet total to diffuser exit static pressure ratios from 2.6 to 4.2. Results are presented in terms of equivalent mass flow, equivalent torque, equivalent specific work, and efficiency
In situ performance measurements of the mitre photovoltaic array
A data acquisition system was developed to provide more accurate and consistent measurement of the degradation of solar arrays. A technique was developed for in-situ measurement of photovoltaic panels of sufficient quality to permit evaluation of electrical performance over extended periods of several years
Cold-air performance of a 12.766-centimeter-tip-diameter axial-flow cooled turbine. 1: Design and performance of a solid blade configuration
A solid blade version of a single-stage, axial-flow turbine was investigated to determine its performance over a range of speeds from 0 to 105 percent of equivalent design speed and over a range of total to static pressure ratios from 1.62 to 5.07. The results of this investigation will be used as a baseline for comparison with those obtained from a cooled version of this turbine
- …