摘要 :
Ionospheric phenomena as thermal radiation noise, propagation of naturally occurring radio noise through ionosphere, and generation of very low frequency emissions
摘要 :
Narrowband analyses revealed grossly similar sound pressure level spectra in each facility. Blade passing frequency (BPF) noise and multiple pure tone (MPT) noise were superimposed on a broadband (BB) base noise. From one-third oc...
展开
Narrowband analyses revealed grossly similar sound pressure level spectra in each facility. Blade passing frequency (BPF) noise and multiple pure tone (MPT) noise were superimposed on a broadband (BB) base noise. From one-third octave bandwidth sound power analyses the BPF noise (harmonics combined), and the MPT noise (harmonics combined, excepting BPF's) agreed between facilities within 1. 5 dB or less over the range of speeds and flows tested. De¬tailed noise and aerodynamic performance is also presented.
收起
摘要 :
Experimental measurements of low frequency preamplifiers show that a type LM394 bipolar input stage has less internal input noise than the popular PAR-113 commercial amplifier for source resistances under 1000 ohms. A type 2N6483 ...
展开
Experimental measurements of low frequency preamplifiers show that a type LM394 bipolar input stage has less internal input noise than the popular PAR-113 commercial amplifier for source resistances under 1000 ohms. A type 2N6483 JFET design shows similar input noise to the PAR-113. The input current noise of the JFET design is insignificant compared with the Nyquist noise of the source resistance. (Author)
收起
摘要 :
A possible approach to image segmentation is first to perform a low-level segmentation. This then allows an original image to be described in terms of a set of simple regions or primitives. Objects in the image may be subsequently...
展开
A possible approach to image segmentation is first to perform a low-level segmentation. This then allows an original image to be described in terms of a set of simple regions or primitives. Objects in the image may be subsequently recognized by matching these primitives to patterns of primitives in a data base. It is found that current techniques for low-level image segmentation fail when applied to high noise images. An algorithm is presented which overcomes the problems associated with high noise and succeeds in generating low-level segmentations of noisy imagery. The algorithm is shown also to work on low noise data. (Author)
收起
摘要 :
Predictions of the prevalence of annoyance associated with aircraft noise exposure are heavily influenced by field studies conducted in urban airport neighborhoods. Flyovers heard in such relatively high ambient noise environments...
展开
Predictions of the prevalence of annoyance associated with aircraft noise exposure are heavily influenced by field studies conducted in urban airport neighborhoods. Flyovers heard in such relatively high ambient noise environments are composed in large part of high absolute level, broadband noise. In contrast, noise exposure created en route by aircraft powered by unducted fan engines is expected to be relatively low in level, but to contain prominent low frequency tonal energy. These tones will be readily audible in rural and other low ambient noise environments. The annoyance of noise intrusions of low absolute level has been shown to be closely related to their audibility. Thus, one way to predict the annoyance of en route noise generated by unducted fan engines is to estimate its audibility relative to that of conventionally powered aircraft in different ambient noise environments. This may be accomplished by computing the audibility of spectra produced by an aircraft powered by unducted fan engines and comparing predicted probabilities of annoyance for them with those of conventionally powered transport aircraft.
收起
摘要 :
A forward-swept, low-noise rotor blade includes an inboard section, an aft-swept section and a forward-swept outboard section. The rotor blade reduces the noise of rotorcraft, including both standard helicopters and advanced syste...
展开
A forward-swept, low-noise rotor blade includes an inboard section, an aft-swept section and a forward-swept outboard section. The rotor blade reduces the noise of rotorcraft, including both standard helicopters and advanced systems such as tiltrotors. The primary noise reduction feature is the forward sweep of the planform over a large portion of the outer blade radius. The rotor blade also includes an aft-swept section. The purpose of the aft-swept region is to provide a partial balance to pitching moments produced by the outboard forward-swept portion of the blade. The rotor blade has a constant chord width; or has a chord width which decreases linearly along the entire blade span; or combines constant and decreasing chord widths, wherein the blade is of constant chord width from the blade root to a certain location on the rotor blade, then decreases linearly to the blade tip thereafter. The noise source showing maximum noise reduction is blade-vortex interaction (BVI) noise. Also reduced are thickness, noise, high speed impulsive noise, cabin vibration and loading noise.
收起
