Rocket measurements of cosmic noise intensities below 5 mc/s
Rocket measurements of cosmic radio noise intensities below five Mc/s
COSMIC NOISE↗
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Origin of high-intensity noise in the area of a large protuberance on a launch vehicle
Origin of high intensity noise in area of large protuberance on Atlas-Agena-Mariner C model tested in supersonic wind tunnel
SCALE MODEL↗
Rocket measurements of cosmic-noise intensities below 5 Mc/s.
Cosmic radio-noise intensities below 5 mc measured by rocket probe
ROCKET SOUNDING↗
A Theoretical Basis for the Scaling Law of Broadband Shock Noise Intensity in Supersonic Jets
A theoretical basis for the scaling of broadband shock noise intensity In supersonic jets was formulated considering linear shock-shear wave interaction. Modeling of broadband shock noise with the aid of shock-turbulence interaction with special reference to linear theories is briefly reviewed. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process with the noise generation contribution from off-peak incident angles being relatively unimportant. The proposed hypothesis satisfactorily explains the well-known scaling law for the broadband shock-associated noise in supersonic jets.
Kandula, Max↗
On the Scaling Law for Broadband Shock Noise Intensity in Supersonic Jets
A theoretical model for the scaling of broadband shock noise intensity in supersonic jets was formulated on the basis of linear shock-shear wave interaction. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process rather than the noise generation contribution from off-peak incident angles. The proposed theory satisfactorily explains the well-known scaling law for the broadband shock -associated noise in supersonic jets.
Kanudula, Max↗
Free-field propagation of high intensity noise
Research on high intensity (finite amplitude) acoustic waves shows that nonlinear distortion effects generally result in a shift of energy to higher frequencies. The higher intensities associated with supersonic jets would therefore indicate that high frequency enhancement of the spectrum should occur, resulting in the differences observed between subsonic and supersonic jets. A 10,000 acoustic watt source installed in an anechoic chamber generates sound levels such that acoustic shocks are readily observable. Dual frequency excitation of the source produces a strong parametric effect with a difference frequency comparable in level to the primary frequency. The test set up and recording equipment being used to determine the finite amplitude noise representative of an actual supersonic jet are described as well as the development of a computer program based on Burger's equation. The spectra of 1/2 octave band, 1 kHz sine wave, and dual frequency input and output are presented in graphs along with waveforms at Z = .025, 0.1, and 1.0.
Mcdaniel, O. H.↗
Cosmic radio noise intensity from 0.45 to 3.0 MHz observed by the ATS II satellite.
Cosmic radio noise intensity measurements by ATS 2 satellite-borne radiometer
Somerlock, C. R.↗
Free-field propagation of high intensity noise
Observed spectral data from supersonic jet aircraft are known to contain much more high frequency energy than can be explained by linear acoustic propagation theory. It is believed that the high frequency energy is an effect of nonlinear distortion due to the extremely high acoustic levels generated by the jet engines. The objective, to measure acoustic waveform distortion for spherically diverging high intensity noise, was reached by using an electropneumatic acoustic source capable of generating sound pressure levels in the range of 140 to 160 decibels (re 20 micro Pa). The noise spectrum was shaped to represent the spectra generated by jet engines. Two microphones were used to capture the acoustic pressure waveform at different points along the propagation path in order to provide a direct measure of the waveform distortion as well as spectral distortion. A secondary objective was to determine that the observed distortion is an acoustic effect. To do this an existing computer prediction code that deals with nonlinear acoustic propagation was used on data representative of the measured data. The results clearly demonstrate that high intensity jet noise does shift the energy in the spectrum to the higher frequencies along the propagation path. In addition, the data from the computer model are in good agreement with the measurements, thus demonstrating that the waveform distortion can be accounted for with nonlinear acoustic theory.
Welz, Joseph P.↗
Intensity noise in diode-pumped single-frequency Nd:YAG lasers and its control by electronic feedback
The power spectrum of the relative intensity noise (RIN) of single-frequency diode-pumped Nd:YAG lasers is observed to be shot-noise limited at frequencies above 20 MHz for a photocurrent of up to 4.4 mA. Relaxation oscillations result in noise 60-70 dB above shot noise at a few hundred kHz. These relaxation oscillations have been suppressed using electronic feedback.
Kane, Thomas J.↗
Intensity noise reduction in semiconductor lasers by amplitude-phase decorrelation
Detuned operation of a laser results in coupling of field amplitude and phase fluctuations. In a semiconductor laser, this coupling is known to be very large. Here it is demonstrated that it can be used to significantly reduce intensity noise below its intrinsic limit.
Vahala, Kerry J.↗
Evaluation of simulation procedures for high intensity noise fields Final report
Response measurements of model structures to sound fields of variable intensity
Source record↗
Output beam intensity noise induced by fiber perturbations in a fiber-linked laser
The effects of acoustic perturbations on an optical fiber intended to link a laser to an optical cavity have been studied. Acoustic noise above the level of -45 dBre (1 microbar) in the frequency band of 500-1500 Hz has a measurable effect on intensity fluctuations at the fiber's output.
Hamilton, Jeffrey J.↗
Noise-intensity sensitivity in optimal stochastic systems.
Optimal stochastic control systems design, deriving sensitivity equation for analyzing optimal performance index sensitivity to variations in random signal variance parameter
Dorato, P.↗
Performance of Planar-Waveguide External Cavity Laser for Precision Measurements
A 1542-nm planar-waveguide external cavity laser (PW-ECL) is shown to have a sufficiently low level of frequency and intensity noise to be suitable for precision measurement applications. The frequency noise and intensity noise of the PW-ECL was comparable or better than the nonplanar ring oscillator (NPRO) and fiber laser between 0.1 mHz to 100 kHz. Controllability of the PW-ECL was demonstrated by stabilizing its frequency to acetylene (13C2H2) at 10(exp -13) level of Allan deviation. The PW-ECL also has the advantage of the compactness of a standard butterfly package, low cost, and a simple design consisting of a semiconductor gain media coupled to a planar-waveguide Bragg reflector. These features would make the PW-ECL suitable for precision measurements, including compact optical frequency standards, space lidar, and space interferometry
Numata, Kenji↗
Some aspects of sound discomfort caused by streetcar traffic
Streetcar noise was investigated on different lines and inside different types by sonometer measurements. The results showed variations of the total noise intensity between 88-97 db. In some squares with heavy traffic the total noise intensity reached 106 db. Noise intensity measurements inside different types of streetcars brought to light high values between 101-106 db, while in the case of the new silent type of streetcar the values were 86-87 db. The importance of the sound discomfort produced by streetcar traffic is emphasized, inasmuch as the noise intensity exceeds by far the values recommended by communal hygiene.
Ursoniu, C.↗
Quantum Noise in Laser Diodes
We have investigated the intensity noise of single mode laser diodes, either free-running or using different types of line narrowing techniques at room temperature. We have measured an intensity squeezing of 1.2 dB with grating-extended cavity lasers and 1.4 dB with injection locked lasers (respectively 1.6 dB and 2.3 dB inferred at the laser output). We have observed that the intensity noise of a free-running nominally single mode laser diode results from a cancellation effect between large anti-correlated fluctuations of the main mode and of weak longitudinal side modes. Reducing the side modes by line narrowing techniques results in intensity squeezing.
Giacobino, E.↗
Spillover stabilization and decentralized modal control of large space structures
The stabilization of the neglected dynamics of the higher modes of vibration in large space structures is studied, and the influence of the structure of the plant noise intensity matrix of the Kalman-Bucy filter on the stability margin of the residual modes is shown. An optimization procedure uses information on the residual modes to minimize spillover of known residual modes while preserving robustness with respect to the unknown dynamics, and the optimum plant noise intensity matrix is selected to maximize the stability margins of the residual modes and to properly place the observer poles. Examples for both centralized and decentralized control are considered.
Czajkowski, Eva A.↗
Shock associated noise of inverted-profile coannular jets. II - Condition for minimum noise. III - Shock structure and noise characteristic
The generation of noise by the shock-turbulence interaction with shock cells in an inverted-profile coannular jet with nozzle exit velocity aligned with the jet axis is investigated analytically, interpreting the optical measurements of Tanna et al. (1985). The noise-intensity minimum at slightly supersonic primary-flow velocities is related to the weakness of the primary-stream shock-cell structure and the lack of such a pattern in the outer fan stream. The discrepancies between this finding and those of Dosanjh et al. (1977 and 1978) are attributed to nozzle design, the definition of minimum noise, and different interpretative approaches. A first-order shock-cell model is then developed to derive formulas for the peak frequencies and the scaling of noise intensity. The results of computations using these formulas are presented in graphs and found to be in good agreement with the experimental data.
Tam, C. K. W.↗