Signal/Noise

An improved signal/noise ratio because all signals are seen simultaneptisiy along with the instrument s own noise (called the multiplex or Fellgett advantage). 

The actuality of researches of multi-layer objects with high density of materials for airspace technics is substantiate by several firms. The distribution of the heavier in longerons and elements of the screw of the helicopter was determined with the help of RCT. In the filler made of graphite or rubbers the layers of heavier from leaden alloys and the air stratification 1 up to 5 mm wide are revealed with the ratio signal / noise more than 3, even at presence of an external steel cover. 

In all spent researches the received ratio signal / noise and sensitivity for revealed defects, distribution of material density and the weights of high density components (tungsten, lead, uranium) are well agreed with results of alternate physics-chemical methods of analyses... 

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... 

The displacement of the spectral characteristics was 0.2 MHz, but the signal/noise ratio for the first case was 7 dB higher. 

In situ quantitation The fluorimetric analysis was made in UV light (2e,c = 313 nm, /-n > 460 nm FI 46 filter). The signal-noise ratio was better above 2 = 460 nm than when a FI 39 filter is employed. 

Program SIMCAL was expressly written to allow these sorts of what-if questions to be explored, with realistic intercepts, slopes, signal noise, digitizer characteristics, and economical factors specified, so one can get a feeling for the achieved precision and the costs this implies. 

Figure 2.15. The limit of detection LOD the minimum signal/noise-ratio necessary according to two models (ordinate) is plotted against log 0(n) under the assumption of evenly spaced calibration points. The three sets of curves are for p = 0.1 (A), 0.05 (B), and 0.02 (C). The correct statistical theory is given by the fine points, while the model presented here is depicted with coarser dots. The widely used S/N = 3. .. 6 models would be represented by horizontals at y = 3. .. 6.

Under certain combinations of instrument type and operating conditions the proceeding assumption is untenable signal noise depends on the analyte concentration. A very common form of heteroscedacity is presented in Fig. 2.17. 

Increasing the number of dimensions from two to three may result in a reduction in the signal/noise (S/N) ratio. This may be due either to the distribution of the intensity of the multiplet lines over three dimensions or to some of the coherence transfer steps being inefficient, resulting in weak 3D cross-peaks. 

Figure 35 shows the proton spectra which we obtain you can see that they are of much better quality than those we got from the on-flow experiment. The signals for acetonitrile and residual HDO have been cleanly removed using the WET sequence referred to above, and resolution and signal-noise are much better, so we can obtain coupling constants exactly. 

NMR measurements. All spectra were measured at 30 °C The spectra were taken using a Varian Unity Inova 400 spectrometer. Chemical shifts (8) are reported relative to internal TMS. 512 transients were accumulated to achieve the appropriate signal/noise ratio. 

Suppose one wanted to compare the behavior of two polymers and their blends. Let us define the signal as the difference between the logarithims of the viscoelastic quantities and the noise as the error calculated for a specific set of viscoelastic properties associated with a specific composition. The signal to noise ratio would have the appearance of the three curves shown in Figure 2 for a PMMA/Hytrel blend >3/1. Selection of the optimum conditions for comparison is apparent in that figure. Emphasis should be placed at those temperatures with high signal/noise ratios. 

Figure 2. Plot of the signal/noise ratio as defined in the text with temperature for a polyblend of PMMA and HYTRBL.

Operating at 500 or 600 MHz and using a 3 mm probe should yield an approximate threefold improvement in signal/noise which can be traded for a corresponding reduction in sample requirement. 

Of course, there is no point in overfilling your NMR tubes. This can make shimming more difficult (but certainly not impossible as in the case of too low a sample depth) but more importantly, it merely wastes materials and gives rise to unduly dilute samples giving reduced signal/noise. Any sample outside the receiver coils does not give rise to signal. 

Exponential multiplication The application of a mathematical function to an FID which has the effect of smoothing the peak shape. Signal/noise may be improved at the expense of resolution. 

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