13,578 research outputs found
Electrochemical sintering process for producing electrodes from cadmium felt and a nickel or silver grid
Electrochemical sintering process produces cadmium felt electrodes. Two pieces of cadmium felt are sandwiched around a nickel screen or silver expanded metal grid, held together by mold compression, and electrochemically sinitered by being put through several charge and discharge cycles at low current density
The role of freestream turbulence scale in subsonic flow separation
The ojective of this work is the clarification of the role of freestream turbulence scale in determining the location of boundary layer separation. An airfoil in subsonic wind tunnel flow is the specific case studied. Hot-film and hot-wire anemometry, liquid-film visualization and pressure measurements are the principal diagnostic techniques in use. The Vanderbilt University subsonic wind tunnel is the flow facility being used
The role of freestream turbulence scale in subsonic flow separation
The clarification of the role of freestream turbulence scale in determining the location of boundary layer separation is discussed. Modifications to the test facility were completed. Wind tunnel flow characteristics, including turbulence parameters, were determined with two turbulence generating grids, as well as no grid. These results are summarized. Initial results on the role of scale on turbulent boundary layer separation on the upper surface of an airfoil model are also discussed
Solar sail capture trajectories at Mercury
Mercury is an ideal environment for future planetary exploration by solar sail since it has proved difficult to reach with conventional propulsion and hence remains largely unexplored. In addition, its proximity to the Sun provides a solar sail acceleration of order ten times the sail characteristic acceleration at 1 AU. Conventional capture techniques are shown to be unsuitable for solar sails and a new method is presented. It is shown that capture is bound by upper and lower limits on the orbital elements of the approach orbit and that failure to be within limits results in a catastrophic collision with the planet. These limits are presented for a range of capture inclinations and sail characteristic accelerations. It is found that sail hyperbolic excess velocity is a critical parameter during capture at Mercury, with only a narrow allowed band in order to avoid collision with the planet. The new capture methodis demonstrated for a Mercury sample return mission
The Peak Brightness and Spatial Distribution of AGB Stars Near the Nucleus of M32
The bright stellar content near the center of the Local Group elliptical
galaxy M32 is investigated with 0.12 arcsec FWHM H and K images obtained with
the Gemini Mauna Kea telescope. Stars with K = 15.5, which are likely evolving
near the tip of the asymptotic giant branch (AGB), are resolved to within 2
arcsec of the nucleus, and it is concluded that the peak stellar brightness
near the center of M32 is similar to that in the outer regions of the galaxy.
Moreover, the projected density of bright AGB stars follows the visible light
profile to within 2 arcsec of the nucleus, indicating that the brightest stars
are well mixed throughout the galaxy. Thus, there is no evidence for an age
gradient, and the radial variations in spectroscopic indices and ultraviolet
colors that have been detected previously must be due to metallicity and/or
some other parameter. We suggest that either the bright AGB stars formed as
part of a highly uniform and coherent galaxy-wide episode of star formation, or
they originated in a separate system that merged with M32.Comment: 9 pages of text, 3 figures. ApJ (Letters) in pres
Computational studies of light acceptance and propagation in straight and curved multimodal active fibres
A Monte Carlo simulation has been performed to track light rays in
cylindrical multimode fibres by ray optics. The trapping efficiencies for skew
and meridional rays in active fibres and distributions of characteristic
quantities for all trapped light rays have been calculated. The simulation
provides new results for curved fibres, where the analytical expressions are
too complex to be solved. The light losses due to sharp bending of fibres are
presented as a function of the ratio of curvature to fibre radius and bending
angle. It is shown that a radius of curvature to fibre radius ratio of greater
than 65 results in a light loss of less than 10% with the loss occurring in a
transition region at bending angles of pi/8 rad.Comment: 21 pages, 13 figure
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