Wave noise

The way how the spectroscopic informations (number, position, intensities, and shapes of peaks) changes with decreasing number of coefficients taken into the account can be seen clearly. The FT introduces the noise waves in the flat area of spectra very early (64 FCs in Fig. 5.3), while the use of the HT causes the intensity cut-offs (128 HCs in Fig. 5.3). The loss of resolution is about the same for both transformations the neighboring peaks are melted into one in all cases at the same stage of coefficient reduction in both transforms. Because the spectral resolution depends on the terms with the highest frequency present in the FT or HT, the reduction of the representation for the same percentage of high frequency coefficients will have the same effect on the resolution for both transformations. 

In Figure 5.4 two examples for reproduction of discrete spectra using different degrees of reduction are shown. In order to retain all the peaks the coefficients must not be cut off above the frequency corresponding to the difference of two closest peaks. This holds true for both FFT and FHT, but the latter gives better reproductions because it does not introduce noise waves around the peaks as FFT does. 

Any sound can be visualized as a waveform, like the cross section of a ripple on a pond. When in the 64 mode, the Commodore 128 is capable of reproducing four different waveforms. Three of them (the triangle, sawtooth, and pulse waves) produce clear tones, and the fourth (the noise wave) makes a rushing or hissing sound. Figure 1 represents each of these waveforms. You can assign any one of the four waveforms to any of the 128 s three sound channels, or voices. 

Figure 4. Loading sequence of the shaking table test (the arrows indicate the time when the White Noise wave excites the models).

T. NOMURA, S. GOTOH, and K. YAMAKI, Reactivity Measurements by the Two-Detector Cross-Correlation Method and Siqpercritical Reactor-Noise Analysis, Neutron Noise, Waves and Pulse Propagation, ABC Symp. Ser. 9, CONF-660206 (May 1967). 

Recent experiments to cancel the effects of noise electronically by emitting a signal that effectively flattens the noise wave shape have achieved some success in low-frequency operation and situations where the receiver position and the source emission are well-defined. However, the industrial application of this technique is still in its infancy. 

Noise is generally measured in decibels weighted to the A scale which approximates the ear s response to noise. Therefore, most readings are given as dB(A) or dBA. This single number covers a wide range of frequencies. A decibel is a logarithmic value to the base 10. Therefore, if the decibel value is increased by 10 the noise exposure has doubled. More sophisticated noise analyses will consider the actual pressure on a person s eardrum and will consider the frequency of the noise waves. 

Noise problems offshore are often compounded by the fact that the noise waves can be reflected off walls and other surfaces and may actually be amplified. 

Nanolibre nonwovens are lightweight, porous, have a high surface area-to-volume ratio to maximise the reflection of noise waves, and can absorb high, medium, and low frequencies [48]. 

The tidal component of water level measurements can be separated from the non-tidal component by means of harmonic analysis. The tidal component is translated in sets of tidal constituents, of which the most important are M2, S2,01 and Kl. The non-tidal component, or residual, may include tidal noise, wave set-up and positive or negative water level surge heights as a result of meteorological (wind and barometric) variations. 

The described approach is suitable for the reconstruction of complicated dielectric profiles of high contrast and demonstrates good stability with respect to the noise in the input data. However, the convergence and the stability of the solution deteriorate if the low-frequency information is lacking. Thus, the method needs to be modified before using in praetiee with real microwave and millimeter wave sourees and antennas, whieh are usually essentially band-limited elements. 

The second example shows results obtained with an angle beam probe for transverse waves in coarse grained grey cast iron. Two commercially available probes are compared the composite design SWK 60-2 and the standard design SWB 60-2. The reflector in this example is a side-drilled hole of 5 mm diameter. The A-scans displayed below in Fig. 5 and 6 show that the composite probe has a higher sensitivity by 12 dB and that the signal to noise ratio is improved by more than 6 dB. 

The transducers discussed above were designed to propagate waves in both directions normal to the direction of the fingers. It has been shown [17] that they produce a roughly collimated beam so they can be used to inspect a band of structure whose width is the transducer finger length the maximum distance away from the transducer covered by the beam is dependent on the attenuation of the wave and the signal-noise ratio, but is typically around 1-2 m in a... 

As any conventional probe, acoustic beam pattern of ultrasound array probes can be characterized either in water tank with reflector tip, hydrophone receiver, or using steel blocks with side-drilled holes or spherical holes, etc. Nevertheless, in case of longitudinal waves probes, we prefer acoustic beam evaluation in water tank because of the great versatility of equipment. Also, the use of an hydrophone receiver, when it is possible, yields a great sensitivity and a large signal to noise ratio. 

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

Kapral R and Wu X-G Internal noise, osoillations, ehaos and ehemieal waves Chemical M/aves and Patterns eds R Kapral and K Showalter (Dordreoht Kluwer) eh 18, pp 609-34... 

A connnon teclmique used to enliance the signal-to-noise ratio for weak modes is to inject a local oscillator field polarized parallel to the RIKE field at the detector. This local oscillator field is derived from the probe laser and will add coherently to the RIKE field [96]. The relative phase of the local oscillator and the RIKE field is an important parameter in describing the optical heterodyne detected (OHD)-RIKES spectrum. If the local oscillator at the detector is in phase with the probe wave, the heterodyne mtensity is proportional to... 

The pyrolysis of CR NH (<1 mbar) was perfomied at 1.3 atm in Ar, spectroscopically monitoring the concentration of NH2 radicals behind the reflected shock wave as a fiinction of time. The interesting aspect of this experiment was the combination of a shock-tube experiment with the particularly sensitive detection of the NH2 radicals by frequency-modulated, laser-absorption spectroscopy [ ]. Compared with conventional narrow-bandwidth laser-absorption detection the signal-to-noise ratio could be increased by a factor of 20, with correspondingly more accurate values for the rate constant k T). 

Noise Control Sound is a fluctuation of air pressure that can be detected by the human ear. Sound travels through any fluid (e.g., the air) as a compression/expansion wave. This wave travels radially outward in all directions from the sound source. The pressure wave induces an oscillating motion in the transmitting medium that is superimposed on any other net motion it may have. These waves are reflec ted, refracted, scattered, and absorbed as they encounter solid objects. Sound is transmitted through sohds in a complex array of types of elastic waves. Sound is charac terized by its amplitude, frequency, phase, and direction of propagation. 

Cavitation has three negative side effects in valves—noise and vibration, material removal, and reduced flow. The bubble-collapse process is a violent asymmetrical implosion that forms a high-speed microjet and induces pressure waves in the fluid. This hydrodynamic noise and the mechanical vibration that it can produce are far stronger than other noise-generation sources in liquid flows. If implosions occur adjacent to a solid component, minute pieces of material can be removed, which, over time, will leave a rough, cinderlike surface. 

Acoustic Coupling When the shell-side fluid is a low-density gas, acoustic resonance or coupling develops when the standing waves in the shell are in phase with vortex shedding from the tubes. The standing waves are perpendicular to the axis of the tubes and to the direction of cross-flow. Damage to the tubes is rare. However, the noise can be extremely painful. 

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