Broad-spectrum noise

Amplifier broad-spectrum noise less than 20 nV/Hz... 

It should be noted that when relatively complex electronic systems are used to process signals, one must take into consideration the noise generated within the system itself. This is generally broad-spectrum noise of thermal origin associated with resistors and has a signal voltage of the form... 

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 removal of chromatographic analysis interference increases the reliability of the broad spectrum approach to organic analysis. The improved retention-time precision and lower background noise level make it possible to use statistical significance-level testing of the broad spectrum data (26). 

For typical geophysical data sets exhibiting a broad spectrum (i.e. a low signal to noise ratio), this study brings along important consequences Many of the patches resulting from the pointwise patches are likely to be spurious. Applying the areawise test drastically increases the reliability of the interpretation. 

The frequency spectrum of the analysed microphone signals consists of a stochastic, broad spectrum of noise contributions and of the narrow spectrum of rotation frequencies of the turbomachinery. The compressor section contributes a fundamental frequency of 2800 Hz and the turbine section a fundamental frequency of 4200 Hz. The averaged total sound power within the helium-circuit and its piping increases with the power of the drive motor up to a maximum level of 160 dB. The total sound power as dependant on the drive power at measuring point 13 is shown in Fig 28. 

Figure 1. FT NMR spectra of [(PMe2Ph)2Pt-5> -Bi8H2o] at 32 MHz (bottom trace) and at 128 MHz (top two traces some resolution enhancement). The bottom two traces were recorded with H(broad-band noise) decoupling. The 32-MHz spectrum is relatively uninformative, whereas the 128-MHz spectra permit the identification of (a) the 18 B shifts, (b) the B atoms which do not have directly bound exo-terminal H atoms (singlet peaks S), and (c) the fine structure arising from couplings 7( " Pt- B).

Figure 17. 77-MHz FT Pt- H(broad band noise) NMR spectrum of [(PMe2Ph)2PtBioHi2] (overnight accumulation, saturated solution in CD2CI2 at 2rC). In solution the compound has effective mirror-plane symmetry and the two P atoms are equivalent. The triplet structure arises from 7( Pt- P) ca. 2530 Hz (Table 6) and the broadness arises from the (unresolved) couplings 7( Pt- B) of 200-300 Hz together (presumably) with longer-range couplings V( Pt- B) spin systems from isotopomers containing °B will also contribute (Ref. 156).

Al MAS NMR has been demonstrated to be an invaluable tool for the zeoHte sdentist It provides a simple and direct way to quantify the proportions of A1 in four [Al(4)j, five [Al(5)j and six [Al(6)j coordinations. Quantitative determination of these species is an important issue in catalysis, and major effort is devoted on this topic. As mentioned already, for A1 only the central transition (-i-half to —half selective exdtation ) is detected. The central transition is unaffected by first order quadmpolar interaction, but the presence of second order effects causes broadening and complicates the quantitation of the A1 species. Usually hydrated samples and short radiofrequency pulses are employed for quantitative determination of framework and extra framework aluminum species. It is uncertain whether hydration changes the coordination of A1 species. Certain extra framework A1 can have very large quadmpolar interactions resulting in very broad lines ( NMR invisible ) [155, 202]. Unlike Si NMR, Al has a short relaxation time due to its quadmpolar nature, and the Al NMR spectrum with good signal to noise can be obtained in a relatively short time. 

The corrected free induction decay Sc t) will transform to a spectrum Sc i ) in which not only the acetone signal but also all the ethanol signals have had the instrumental contributions to their lineshapes removed. Provided that the reference region lui to wr gives a complete and accurate representation of the experimental acetone lineshape, our deconvolution process should allow us to obtain a clean corrected spectrum even when the shimming is far from ideal. There are of course limitations on this process. If the experimental lineshape is very broad, it will clearly not be possible to obtain a corrected spectrum in which the lines are very narrow without some sort of penalty. Here the limiting factor is signal-to-noise ratio since S u>) is much sharper than Se u>), the ratio of their inverse Fourier... 

UV/VIS/NIR spectroscopy and ESR spectroscopy. The UV/VIS/NIR spectrum shows a sharp peak at 983 nm and a broad peak at 846 nm. These two absorbances are attributed to allowed NIR-transitions and these values are consistent with spectra of the cation obtained with other methods [2]. EPR spectroscopy of Cgg-cations, produced by different methods, leads to a broad distribution of measured g-values. These differences are caused by the short lifetime of the cation, the usually low signal-noise ratio and the uncertainty of the purity. The most reliable value imtil now is probably the one obtained by Reed and co-workers for the salt Cgg"(CBiiHgClg)-(g= 2.0022) [2,9] (see also Section 8.5). Ex situ ESR spectroscopy of above-mentioned bulk electrolysis solutions led to a g-value of2.0027 [8], which is very close to that of the salt, whereas the ESR spectra of this electro lyticaUy formed cation shows features not observed earlier. The observed splitting of the ESR signal at lower modulation amplitudes was assigned to a rhombic symmetry of the cation radical at lower temperatures (5-200 K). 

The above procedure of the Raman spectrum retrieval exhibits an amazing robustness with respect to the noise of the data however, several empirically deduced conditions have to be satisfied for an accurate retrieval. First, the retrieved spectrum is always distorted on the edges, and, to get good precision, the CARS spectrum has to be taken in a very broad range (see, for example, Figure 6.17). Second, the presence of strong Raman lines, for which the above assumption of hn I -i- Re x ... 

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