36,493 research outputs found
Powerful jets from accreting black holes: evidence from the optical and infrared
A common consequence of accretion onto black holes is the formation of
powerful, relativistic jets that escape the system. In the case of supermassive
black holes at the centres of galaxies this has been known for decades, but for
stellar-mass black holes residing within galaxies like our own, it has taken
recent advances to arrive at this conclusion. Here, a review is given of the
evidence that supports the existence of jets from accreting stellar-mass black
holes, from observations made at optical and infrared wavelengths. In
particular it is found that on occasion, jets can dominate the emission of
these systems at these wavelengths. In addition, the interactions between the
jets and the surrounding matter produce optical and infrared emission on large
scales via thermal and non-thermal processes. The evidence, implications and
applications in the context of jet physics are discussed. It is shown that many
properties of the jets can be constrained from these studies, including the
total kinetic power they contain. The main conclusion is that like the
supermassive black holes, the jet kinetic power of accreting stellar-mass black
holes is sometimes comparable to their bolometric radiative luminosity. Future
studies can test ubiquities in jet properties between objects, and attempt to
unify the properties of jets from all observable accreting black holes, i.e. of
all masses.Comment: 26 pages, 4 figures, 1 table. Invited chapter for the edited book
"Black Holes and Galaxy Formation", Nova Science Publishers, Inc., at pres
Experimental determination of turbulence in a GH2-GOX rocket combustion chamber
The intensity of turbulence and the Lagrangian correlation coefficient for a gaseous rocket combustion chamber have been determined from the experimental measurements of the tracer gas diffusion. A combination of Taylor's turbulent diffusion theory and Spalding's numerical method for solving the conservation equations of fluid mechanics was used to calculate these quantities. Taylor's theory was extended to consider the inhomogeneity of the turbulence field in the axial direction of the combustion chamber. An exponential function was used to represent the Lagrangian correlation coefficient. The results indicate that the maximum value of the intensity of turbulence is about 15% and the Lagrangian correlation coefficient drops to about 0.12 in one inch of the chamber length
Lidar measurements of stratospheric aerosols over Menlo Park, California, October 1972 - March 1974
During an 18-month period, 30 nighttime observations of stratospheric aerosols were made using a ground based ruby lidar located near the Pacific coast of central California (37.5 deg. N, 122.2 deg. W). Vertical profiles of the lidar scattering ratio and the particulate backscattering coefficient were obtained by reference to a layer of assumed negligible particulate content. An aerosol layer centered near 21 km was clearly evident in all observations, but its magnitude and vertical distribution varied considerably throughout the observation period. A reduction of particulate backscattering in the 23- to 30-km layer during late January 1973 appears to have been associated with the sudden stratospheric warming which occurred at that time
Crew appliance concepts. Volume 2, appendix B: Shuttle orbiter appliances supporting engineering data
Technical data collected for the food management and personal hygiene appliances considered for the shuttle orbiter are presented as well as plotted and tabulated trade study results for each appliance. Food storage, food operation, galley cleanup, waste collection/transfer, body cleansing, and personal grooming were analyzed
Lidar measurements of the post-fuego stratospheric aerosol
Fifteen lidar observations of the stratospheric aerosol were made between February and November 1975. All observations revealed the greatly increased particulate backscattering that followed the eruption of the volcano Fuego in October 1974. Vertical structure consisted initially of multiple layers, which later merged to form a single, broader peak. Essentially all of the increased scattering was confined to altitudes below 20 km. Hence, aerosol layer centroids in 1975 were typically several km below their altitude prior to the eruption. Radiative and thermal consequences of the measured post-Fuego layer were computed using several recently published models. The models predict a temperature increase of several K at the altitude of the layer, caused by the infrared absorption bands of the sulfuric acid particles. The surface temperature decrease predicted by the models is considerably smaller than 1 K, partly because of the small optical thickness of the volcanic layer, and partly because of its short residence time relative to the earth-ocean thermal response time
Crew appliance concepts. Volume 4, appendix C: Modular space station appliances supporting engineering data
Data collected for the appliances considered for the space station are presented along with plotted and tabulated trade study results for each appliance. The food management, and personal hygiene data are applicable to a six-man mission of 180-days
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