3,128 research outputs found
Acoustic radiation from the end of two-dimensional duct, effects of uniform flow and duct lining
A study is presented of the radiation of acoustic modes from the end of a duct immersed in a uniformly moving medium. It is shown that the uniform flow has roughly the same effect as an increase in frequency at constant mode number: the number of lobes of the radiation pattern increases, and the radiation maximum is slightly displaced towards the duct axis. When the mode is near cut-off the forward radiation for an inlet is enhanced. The acoustic radiation characteristics of ducts with soft or absorbing walls and hard, perfectly-reflecting walls are then compared. It is shown, and this is of technological interest, that the side radiation from the end of an acoustically soft duct is greatly reduced for lower-order modes
Acoustic transmission and reflection by a shear discontinuity separating hot and cold regions
Acoustic transmission and reflection is analyzed for plane waves propagating from a hot moving medium, impinging on a plane shear discontinuity into a cold stationary region. It is shown that incident waves originating in the hot region and propagating in the flow direction are transmitted into the cold region at almost right angles to the interface. The result is employed to examine the strong side radiation of internal noise transmitted through the exhaust duct of a turbojet engine
Filosofía frente a poesía en los orígenes del saber
Frente a la célebre aproximación que Aristóteles establece entre filosofía y poesía,1 María Zambrano entiende su mutua relación en la Grecia arcaica como una heraclitiana lucha de contrarios. Dice en su artículo «La disputa entra la filosofía y la poesía sobre los dioses
Taut foliations and the actions of fundamental groups on leaf spaces and universal circles
Let be a leafwise hyperbolic taut foliation of a closed 3-manifold
and let be the leaf space of the pullback of to the universal cover of
. We show that if has branching, then the natural action of
on is faithful. We also show that if has a finite branch locus
whose stabilizer acts on nontrivially, then the stabilizer is an infinite
cyclic group generated by an indivisible element of .Comment: 16 pages, 2 figure
Acoustic Attenuation in Fans and Ducts by Vaporization of Liquid Droplets
A cloud of small water droplets in saturated air attenuates acoustic disturbances by viscous drag, heat transfer,
and vapor exchange with the ambient gas. The viscous and heat transfer phenomena attenuate at frequencies
above 104 Hz for I-J.l droplets. The processes associated with phase exchange attenuate at a much lower frequency
that may he controlled by choice of the liquid mass fraction. The strength of this attenuation is proportional to the mass of water vapor in the air, a factor controlled by air temperature. For plane waves, the attenuation
magnitude e~ceeds 5 db!m ~t a temperature of 25°C with a cloud of 0.7 J.l radius droplets constituting 1 % of the
gas mass. ThiS attenuation mcreases to more than 7 dbjm at frequencies above 1000 Hz where viscous and heat
transfer mechanisms contribute significantly. The attenuation of higher order duct modes is strongly increased over the above values, similarly to the attenuation by duct lining. When the droplet cloud occupies only a fraction of the duct height close to the walls, the droplet clond may be up to twice as elfective as the uniform cloud, and a significant saving is possible in the water required to saturate the air and furnish the water droplets
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