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Mechanisms of airfoil noise near stall conditions
The focus of this paper is on investigating the noise produced by an airfoil at high angles of attack over a range of Reynolds number
Reâ2Ă10â”â4Ă10â”. The objective is not modeling this source of noise but rather understanding the mechanisms of generation for surface pressure fluctuations, due to a separated boundary layer, that are then scattered by the trailing edge. To this aim, we use simultaneous noise and surface pressure measurement in addition to velocimetric measurements by means of hot wire anemometry and time-resolved particle image velocimetry. Three possible mechanisms for the so-called âseparation-stall noiseâ have been identified in addition to a clear link between far-field noise, surface pressure, and velocity fields in the noise generation
Noise enhancing the classical information capacity of a quantum channel
We present a simple model of quantum communication where a noisy quantum
channel may benefit from the addition of further noise at the decoding stage.
We demonstrate enhancement of the classical information capacity of an
amplitude damping channel, with a predetermined detection threshold, by the
addition of noise in the decoding measurement.Comment: 4 pages, 2 figure
Noise-Induced Transitions in Optomechanical Synchronization
We study how quantum and thermal noise affects synchronization of two
optomechanical limit-cycle oscillators. Classically, in the absence of noise,
optomechanical systems tend to synchronize either in-phase or anti-phase.
Taking into account the fundamental quantum noise, we find a regime where
fluctuations drive transitions between these classical synchronization states.
We investigate how this "mixed" synchronization regime emerges from the
noiseless system by studying the classical-to-quantum crossover and we show how
the time scales of the transitions vary with the effective noise strength. In
addition, we compare the effects of thermal noise to the effects of quantum
noise
Noise and Equivalent Circuit of Double Injection
Measurements of the highâfrequency noise of a silicon doubleâinjection diode result in ăi^2ă = αâ
4kT(1/r)Îf with α=1.04 and in agreement with the literature. A new interpretation demands Nyquist noise with αâĄ1 in these devices at high frequencies. This is in accord with an equivalent circuit derived for the doubleâinjection process. Speculations are made on the general validity of Nyquist noise in nonlinear devices at high frequencies. In addition, generationârecombination noise is suggested as the prime source of the lowâfrequency noise
Influence of turbulence on the dynamo threshold
We use direct and stochastic numerical simulations of the magnetohydrodynamic
equations to explore the influence of turbulence on the dynamo threshold. In
the spirit of the Kraichnan-Kazantsev model, we model the turbulence by a
noise, with given amplitude, injection scale and correlation time. The addition
of a stochastic noise to the mean velocity significantly alters the dynamo
threshold. When the noise is at small (resp. large) scale, the dynamo threshold
is decreased (resp. increased). For a large scale noise, a finite correlation
time reinforces this effect
Minimal Noise-Induced Stabilization of One-Dimensional Diffusions
The phenomenon of noise-induced stabilization occurs when an unstable deterministic system of ordinary differential equations is stabilized by the addition of randomness into the system. In this paper, we investigate under what conditions one-dimensional, autonomous stochastic differential equations are stable, where we take the notion of stability to be that of global stochastic boundedness. Specifically, we find the minimum amount of noise necessary for noise-induced stabilization to occur when the drift and noise coefficients are power, polynomial, exponential, or logarithmic functions
Low-noise top-gate graphene transistors
We report results of experimental investigation of the low-frequency noise in
the top-gate graphene transistors. The back-gate graphene devices were modified
via addition of the top gate separated by 20 nm of HfO2 from the single-layer
graphene channels. The measurements revealed low flicker noise levels with the
normalized noise spectral density close to 1/f (f is the frequency) and Hooge
parameter below 2 x 10^-3. The analysis of the noise spectral density
dependence on the top and bottom gate biases helped us to elucidate the noise
sources in these devices and develop a strategy for the electronic noise
reduction. The obtained results are important for all proposed graphene
applications in electronics and sensors.Comment: 9 pages, 4 figure
Noise-Induced Building Vibrations Caused by Concorde and Conventional Aircraft Operations at Dulles and Kennedy International Airports
Outdoor and indoor noise levels resulting from aircraft flyovers and certain nonaircraft events were recorded, as were the associated vibration levels in the walls, windows, and floors at building test sites. In addition, limited subjective tests were conducted to examine the human detection and annoyance thresholds for building vibration and rattle caused by aircraft noise. Representative peak levels of aircraft noise-induced building vibrations are reported and comparisons are made with structural damage criteria and with vibration levels induced by common domestic events. In addition, results of a pilot study are reported which indicate the human detection threshold for noise-induced floor vibrations
Effect of Noise on Patterns Formed by Growing Sandpiles
We consider patterns generated by adding large number of sand grains at a
single site in an abelian sandpile model with a periodic initial configuration,
and relaxing. The patterns show proportionate growth. We study the robustness
of these patterns against different types of noise, \textit{viz.}, randomness
in the point of addition, disorder in the initial periodic configuration, and
disorder in the connectivity of the underlying lattice. We find that the
patterns show a varying degree of robustness to addition of a small amount of
noise in each case. However, introducing stochasticity in the toppling rules
seems to destroy the asymptotic patterns completely, even for a weak noise. We
also discuss a variational formulation of the pattern selection problem in
growing abelian sandpiles.Comment: 15 pages,16 figure
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