102,518 research outputs found
Radiated noise from an externally blown flap
The far field noise from subsonic jet impingement on a wing-flap with a 45 deg bend was experimentally investigated. The test parameters are jet Mach number and flap length. For long flaps, the primary source mechanisms are found to be turbulent mixing and flow impingement. For short flaps, the interaction of turbulent flow with the flap trailing edge appears to strongly influence the radiated noise
Noise generation from interacting high speed axisymmetric jet flows Semiannual status report, 1 Jun. 1968 - 31 Dec. 1969
Far field noise generation from interacting coaxial jet flows, and nozzle operational mode
LUMIS Interactive graphics operating instructions and system specifications
The LUMIS program has designed an integrated geographic information system to assist program managers and planning groups in metropolitan regions. Described is the system designed to interactively interrogate a data base, display graphically a portion of the region enclosed in the data base, and perform cross tabulations of variables within each city block, block group, or census tract. The system is designed to interface with U. S. Census DIME file technology, but can accept alternative districting conventions. The system is described on three levels: (1) introduction to the systems's concept and potential applications; (2) the method of operating the system on an interactive terminal; and (3) a detailed system specification for computer facility personnel
A compact high-flux cold atom beam source
We report on an efficient and compact high-flux Cs atom beam source based on
a retro-reflected two-dimensional magneto-optical trap (2D MOT). We realize an
effective pushing field component by tilting the 2D MOT collimators towards a
separate three-dimensional magneto-optical trap (3D MOT) in ultra-high vacuum.
This technique significantly improved 3D MOT loading rates to greater than atoms/s using only 20 mW of total laser power for the source. When
operating below saturation, we achieve a maximum efficiency of atoms/s/W
Random Scattering Matrices and the Circuit Theory of Andreev Conductances
The conductance of a normal-metal mesoscopic system in proximity to
superconducting electrode(s) is calculated. The normal-metal part may have a
general geometry, and is described as a ``circuit'' with ``leads'' and
``junctions''. The junctions are each ascribed a scattering matrix which is
averaged over the circular orthogonal ensemble, using recently-developed
techniques. The results for the electrical conductance reproduce and extend
Nazarov's circuit theory, thus bridging between the scattering and the bulk
approaches. The method is also applied to the heat conductance.Comment: 12 pages, RevTeX, including 2 figures with eps
Corotation: its influence on the chemical abundance pattern of the Galaxy
A simple theory for the chemical enrichment of the Galaxy which takes into
account the effects of spiral arms on heavy elements output was developed. In
the framework of the model with the corotation close to the position of the Sun
in the Galaxy the observed abundance features are explained.Comment: LaTeX, 6 pages, 5 jpg figures, uses aastex.sty, submitted to ApJ Let
Black holes, cuspy atmospheres, and galaxy formation
In cuspy atmospheres, jets driven by supermassive black holes (BHs) offset
radiative cooling. The jets fire episodically, but often enough that the cuspy
atmosphere does not move very far towards a cooling catastrophe in the
intervals of jet inactivity. The ability of energy released on the sub-parsec
scale of the BH to balance cooling on scales of several tens of kiloparsecs
arises through a combination of the temperature sensitivity of the accretion
rate and the way in which the radius of jet disruption varies with ambient
density. Accretion of hot gas does not significantly increase BH masses, which
are determined by periods of rapid BH growth and star formation when cold gas
is briefly abundant at the galactic centre. Hot gas does not accumulate in
shallow potential wells. As the Universe ages, deeper wells form, and
eventually hot gas accumulates. This gas soon prevents the formation of further
stars, since jets powered by the BH prevent it from cooling, and it mops up
most cold infalling gas before many stars can form. Thus BHs set the upper
limit to the masses of galaxies. The formation of low-mass galaxies is
inhibited by a combination of photo-heating and supernova-driven galactic
winds. Working in tandem these mechanisms can probably explain the profound
difference between the galaxy luminosity function and the mass function of dark
halos expected in the cold dark matter cosmology.Comment: To appear in Phil Trans Roy So
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