Amplitude noise spectra

Fig. 12. Amplitude noise spectra for a matrix line in glow discharge source (GDS) atomic emission spectrometry. Steel standard sample 218A (Research Institute CKD, Czech Republic) / 50 mA argon pressure 600 Pa burning voltage 900 V 0.35 m McPherson monochromator line Fe I 371.9 nm. (a) Without needle valve between the vacumm pump and the GDS, (b) with needle valve between the pump and the GDS. (Reprinted with permission from Ref. [40].)...

Fig. 12. Amplitude noise spectra for a matrix line in glow discharge source (CDS) atomic emission spectrometry. Steel standard sample 218A (Research Institute CKD, Czech Republic) / 50 mA argon pressure 600 Pa burning voltage 900 V ...

Fig. 1. Comparison of amide V VCD for an identical sample of poly-L-lysine in D20 as measured on the UIC dispersive instrument (top) and on the ChirallRFT-VCD instrument (at Vanderbilt University, kindly made available by Prof. Prasad Polavarapu). Sample spectra were run at the same resolution for the same total time ( 1 h) in each case. The FTIR absorbance spectrum of the sample is shown below. VCD spectra are offset for sake of comparison. Each ideal baseline is indicated by a thin line, the scale providing a measure of amplitude. Noise can be estimated as the fluctuation in the baseline before and after the amide V, which indicates the S/N advantage of the single band dispersive measurement.

All data sets are analysed using global analysis [[3],[4]]. Since part of the noise is correlated, i.e. baseline noise or amplitude noise of the whole spectrum, this kind of analysis is excellently suited to extract more reliable information from the data than a single-trace analysis. If the data contains sufficient information, or extra information is available, a target analysis is applied (i.e. a specific model is fitted to the data) from which spectra of physical states result. 

The period of the pinning SDW potential has been derived from two sets of NMR experiments which have been performed recently in a sliding SDW state. First, measurement of the SDW velocity from the proton spin echo amplitude of (TMTSF)2PF6 [119] (Fig. 37) as a function of the dc current (above threshold field) and comparison with the SDW noise spectrum lead to a pinning potential period that is half the SDW wavelength (namely, a = 2). Second, the result a = 1 is inferred from a study of the amplitude of the motionally narrowed 13C spectrum in (TMTSF)2PF6 and of a SDW current and noise spectrum [111] (Fig. 38). 

Landauer studied the behavior of a bistable system consisting of a tunnel diode and focused his attention on the activation jump between the two states resulting from thermal fluctuations. Later, Matsuno ° analyzed the power spectrum of the noise affecting the electric conductivity of a Gunn diode. Diode oscillations were proven to be accompanied by modulation of both amplitude and frequency. The noise spectrum was shown to exhibit typical 1// characteristics, and fluctuations were found to appear in the region close to the critical threshold with an increasing relaxation time as the threshold was approached. This behavior is largely reminiscent of that ex-... 

In a so-called noise spectrum (Fig. 8) the noise amplitude is plotted as a function of the frequency [see Ref. [36]). Here one distinguishes between white noise ,... 

Specifically = l/vH should be proportional to 3m. Further, if the particle distribution dominates the noise spectrum, the slope of /w(v) at i amplitude should correlate with the particle distribution spread as represented by o . The slope, designated as In o, of the form y... 

The mutual interference of the two UV-llght beams perpendicular to one another was determined with detection at 254 nm for both channels, with the filter placed at the detector side, amounted to less than 1%. This Interference was completely eliminated when two different filters were placed before each detector. The noise level of each channel was measured with the DACs at 12 bits (0.025%). As the 1-Hz region of the noise spectrum of the detector signal is most important in isotachophoresls (with respect to the detector response time required), the amplitude of both detector signals was measured ten times at 1-sec Intervals. Prom these values the average baseline (offset) and noise were calculated. The average noise level was ca. 0.1% (0.0004 a.u.) for 206, 254 and 280 nm. 

Fig. 3 Peak amplitude, noise level, and signal-to-noise ratio for spectrum of non-decaying signal of frequency 10 Hz, sampled with (a) 512, (b) 256, (c) 128 pts. Noise is white and Gaussian...

Signals with continuous spectra. Amplitude (autopower) spectrum approaches smooth distribution in long time limit. Phase spectrum randomized. Bandwidth-limited in any practicallly-obtainable signal. "Noise response admittance analysis"... 

In a so-called noise spectrum (Fig. 8) the noise amplitude is plotted as a function... 

In a noise spectrum (Fig. 5) the noise amplitude is plotted as a function of frequency [31]. White noise (Fig. 5 A) occurs over all frequencies and is almost always fundamental in origin, whereas for Mf noise (Fig. 5B) the amplitude decreases with the frequency and it is nonfundamental in origin. Discrete noise bands with well-defined causes may also occur (Fig. 5 C). These may stem from the source, caused by gas flow dynamics or contributions from the vacuum line, etc. Noise spectra are a powerful diagnostic tool to trace the sources of noise, and to study instrumental limitations to the power of detection. In atomic. spectrometry, it is important to determine if noise from the detector is predominant if so. it can be described by a Poisson distribution ... 

In the frequency range below 10 Hz the amplitude of the noise power strongly depends on the time elapsed after cooling the sample (no field is applied ). The noise power measured for example at 3 x 10 Hz in the first five hours is 10 times above the value measured after 50 h. There seems to exist a characteristic frequency (which decreases with t ), above which the l/Spectra recorded for waiting times longer than 70h are stationary and present a 1/w dependence between 2 x 10 Hz and 2 x 10 Hz. 

Since a nuclear reactor is a statistical system, it will show fluctuations in neutron intensity. These fluctuations, or pile noise, are not commonly considered of interest in themselves, but only as interference to other experiments. However, since the nature of the pile noise depends strongly on important reactor parameters, its study can enable the determination of quantities less easily accessible by other means. In particular, Moore (f) points out that the noise spectrum of such a system, that is, the mean square noise amplitude per unit band width, is proportional to the square modulus of the transfer function or to the Fourier cosine transform of the autocorrelation function. Thus, observation of the noise spectrum of a reactor could yield information about the shape of its transfer function. To test this technique, pile noise analyses were done on various low-power experimental reactors at Argonne National J aboratory. Since these reactors operate at such a low level that power effects on reactivity do not appear, the shape of the low-frequency portions of their transfer functions would depend only on fairly well-known delayed neutron parameters, and thus would be of little interest. However, the high-frequency rolloff portion of the transfer function is strongly dependent on the quotient of the effective delayed neutron fraction over the prompt neutron... 

Ideally, any procedure for signal enhancement should be preceded by a characterization of the noise and the deterministic part of the signal. Spectrum (a) in Fig. 40.18 is the power spectrum of white noise which contains all frequencies with approximately the same power. Examples of white noise are shot noise in photomultiplier tubes and thermal noise occurring in resistors. In spectrum (b), the power (and thus the magnitude of the Fourier coefficients) is inversely proportional to the frequency (amplitude 1/v). This type of noise is often called 1//... 

The most fundamental aspect of a sensitivity discussion of remote detection is the fact that it is inherently a point-by-point technique. Each spectrum recorded by the detector does not contain any information other than its amplitude. Conceptually, a remote NMR experiment is very similar to a 2D NMR experiment with a z filter between encoding and detection, which causes all transverse magnetization to dephase. For 2D NMR experiments, it has been shown that the signal-to-noise ratio (SNR) per square root time, which will be denominated as sensitivity in the following, is the same as in the ID case when neglecting T2 relaxation [20, 21]. To compare the sensitivity of a remotely detected spectrum [Figure 2.6.4(b)] with an equivalent experiment with direct detection [Figure 2.6.4(a)], we can use an expression similar to the discussion in Ref. [20] ... 

The first term measures the difference between the data and the fit, KF. The second term is a Tikhonov regularization and its amplitude is controlled by the parameter a. The effect of this regularization term is to select a solution with a small 2-norm 11 F 2 and as a result a solution that is smooth and without sharp spikes. However, it may cause a bias to the result. When a is chosen such that the two terms are comparable, the bias is minimized and the result is stable in the presence of noise. When a is much smaller, the resulting spectrum F can become unstable. 

Fig. 1.1 The regions for transient cavitation bubbles and stable cavitation bubbles when they are defined by the shape stability of bubbles in the parameter space of ambient bubble radius (R0) and the acoustic amplitude (p ). The ultrasonic frequency is 515 kHz. The thickest line is the border between the region for stable cavitation bubbles and that for transient ones. The type of bubble pulsation has been indicated by the frequency spectrum of acoustic cavitation noise such as nf0 (periodic pulsation with the acoustic period), nfo/2 (doubled acoustic period), nf0/4 (quadrupled acoustic period), and chaotic (non-periodic pulsation). Any transient cavitation bubbles result in the broad-band noise due to the temporal fluctuation in the number of bubbles. Reprinted from Ultrasonics Sonochemistry, vol. 17, K.Yasui, T.Tuziuti, J. Lee, T.Kozuka, A.Towata, and Y. Iida, Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles, pp. 460-472, Copyright (2010), with permission from Elsevier...

The cantilever is excited into resonance by electrically exciting the piezoelectric cantilever mount. The frequency of the excitation wave is scanned in a given frequency range, and the frequency of maximum cantilever amplitude is taken as the resonance frequency. The frequency spectrum of the cantilever response shows the fundamental frequency as well as the harmonics of cantilever vibration. The cantilevers, however, also resonate in response to ambient conditions such as room temperature or acoustic noise without requiring any external power. 

---