18,945 research outputs found
Magnetic field gradient effects on the magnetorotational instability
The magnetorotational instability (MRI), also known as the Balbus -- Hawley
instability, is thought to have an important role on the initiation of
turbulence and angular momentum transport in accretion discs. In this work, we
investigate the effect of the magnetic field gradient in the azimuthal
direction on MRI. We solve the magnetohydrodynamic equations by including the
azimuthal component of the field gradient. We find the dispersion relation and
calculate the growth rates of the instability numerically. The inclusion of the
azimuthal magnetic field gradient produces a new unstable region on wavenumber
space. It also modifies the growth rate and the wavelength range of the
unstable mode: the higher the magnitude of the field gradient, the greater the
growth rate and the wider the unstable wavenumber range. Such a gradient in the
magnetic field may be important in T Tauri discs where the stellar magnetic
field has an axis which is misaligned with respect to the rotation axis of the
disc.Comment: 8 pages, 3 figures, accepted for publication in A
Development of an LED display system for cross-track distance and velocity for Loran-C flight
The methodology for estimating cross-track velocity by combining rate-gyro and Loran-C data is illustrated in block diagrams. At present, preliminary analysis has established values for K sub 1, K sub 2, the parameters of the digital control loops. A computer program was written to implement a digital simulation of the system as illustrated. Given a model for the noise in the rate-gyro and Loran-C receiver, and their dynamic response, the simulation provides a working model to establish good control loop parameters. The layout of the LED display for flight testing of Loran-C approach flying, which was constructed during a visit to Langley Research Center, is shown. Four bar-graph LED displays are paired to provide cross-track distance and velocity from a Loran-C defined runway centerline. Two seven-segment LED displays are used to provide alphanumeric readout of range to touchdown and desired height. A metal case was built, a circuit board designed, and manufactured with the assistance of NASA Langley personnel
Perceived Impacts of Gambling: Integration of Two Theories
This study explores the race and educational attainment variations on resident perceptions and support for a proposed casino development. In addition, it investigates the influence of perceived benefits and costs on casino gambling support. The findings indicate that residents who are likely to receive personal benefits from gambling development tend to believe that its socioeconomic benefits outweigh the associated costs. Respondents\u27 race is found to exercise a significant influence on their perceptions of benefits and costs, and casino development support. This study integrates two separate research streams of social exchange theory and social representation theory, and in doing so makes a major theoretical contribution in tourism and gaming literature
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