Signal-to-noise ratio enhancement

Enke, C. G., and Nieman, T. A., Signal-to-Noise Ratio Enhancement by Least-Squares Polynomial Smoothing, Ana/. Chem. 48, 1976, 705A-712A. 

C.G. Enke and T.A. Nieman, Signal-to-noise ratio enhancement by least-squares polynomial smoothing. Anal. Chem., 48 (1976) 705A-712A. 

Taavitsamen, V. M. (2009). Denoising and signal-to-noise ratio enhancement Derivatives. In "Comprehensive Chemometrics", (S. D. Brown, R. Tauler, and B. Walczak, Eds), Vol. 2, pp. 57-66. Elsevier, Amsterdam. 

A signal processing scheme to enhance the signal to noise ratio,... 

The pulse sequence (stages 2-3) can be repeated hundreds of times to enhance the signal to noise ratio The duration of time for stage 2 is on the order of milliseconds and that for stage 3 is about 1 second... 

A study was conducted to measure the concentration of D-fenfluramine HCl (desired product) and L-fenfluramine HCl (enantiomeric impurity) in the final pharmaceutical product, in the possible presence of its isomeric variants (57). Sensitivity, stabiUty, and specificity were enhanced by derivatizing the analyte with 3,5-dinitrophenylisocyanate using a Pirkle chiral recognition approach. Analysis of the caUbration curve data and quaUty assurance samples showed an overall assay precision of 1.78 and 2.52%, for D-fenfluramine HCl and L-fenfluramine, with an overall intra-assay precision of 4.75 and 3.67%, respectively. The minimum quantitation limit was 50 ng/mL, having a minimum signal-to-noise ratio of 10, with relative standard deviations of 2.39 and 3.62% for D-fenfluramine and L-fenfluramine. 

Another technique for improving the signal-to-noise ratio is to repeat scans over a frequency interval and signal averaging with a computer. In general, the signal-to-noise ratio is enhanced by the square root of the... 

The process of exponential multiplication just described produces a rapid decay of the FID and the production of broad lines suppressing the decay of the FID gives narrow lines and better resolution, with increased noise level. An alternative approach to resolution enhancement is to reduce the intensity of the earlier part of the FID. Ideally, we should use a function that reduces the early part of the FID, to give sharper lines, as well as reduces the tail of the FID, to give a better signal-to-noise ratio. 

Heteronuclear-shift-correlation spectra, which are usually presented in the absolute-value mode, normally contain long dispersive tails that are suppressed by applying a Gaussian or sine-bell function in the F domain. In the El dimension, the choice of a weighting function is less critical. If a better signal-to-noise ratio is wanted, then an exponential broadening multiplication may be employed. If better resolution is needed, then a resolution-enhancing function can be used. 

The interferometer assembly has been modified to provide acoustic isolation from both building vibrations and airborne noise (7). These improvements have greatly enhanced the signal to noise. The spectra presented here show a signal to noise ratio in excess of 500 for silica samples and in excess of 100 for the alumina samples the differences are due to different sample porosities. No smoothing of the spectra has been performed, and all spectra reported are direct reproductions of the plotter output from the spectrometer. 

The reflectance, R, is defined as the ratio of the reflected light intensity to the intensity of the incident beam. Usually, one determines the change in reflectance, A/ , induced by some parameter, such as the electrode potential. Experimentally, one measures only the intensity of the reflected beam, 4. So if the incident intensity remains constant, the reflected beam gives hJl/R = A4/4. Experimental results are presented as plots of A/J/R vs. the parameter of interest, such as the frequency of the incident light or electrode potential. Modulation schemes, wherein the beam is chopped or the potential is modulated, are used to enhance the signal-to-noise ratio. 

The fourth-order coherent Raman spectrum of a liquid surface was observed by Fujiyoshi et al. [28]. The same authors later reported a spectrum with an improved signal-to-noise ratio and different angle of incidence [27]. A water solution of oxazine 170 dye was placed in air and irradiated with light pulses. The SH generation at the oxazine solution was extensively studied by Steinhurst and Owrutsky [24]. The pump and probe wavelength was tuned at 630 nm to be resonant with the one-photon electronic transition of the dye. The probability of the Raman transition to generate the vibrational coherence is enhanced by the resonance. The efficiency of SH generation is also enhanced. 

As said before, there are two main applications of Fourier transforms the enhancement of signals and the restoration of the deterministic part of a signal. Signal enhancement is an operation for the reduction of the noise leading to an improved signal-to-noise ratio. By signal restoration deformations of the signal introduced by imperfections in the measurement device are corrected. These two operations can be executed in both domains, the time and frequency domain. 

The advantage of employing periodic perturbation of light intensity, e.g., using a chopper, and phase-sensitive detection are beyond a simple enhancement of the signal-to-noise ratio. For photoinduced electron-transfer mechanisms, as schematized in Fig. 11, the... 

Multiple receive systems with multi-coil arrays have become widely distributed in medical MRI. The benefit is the enhancement of the signal-to-noise ratio per time or a reduction of the acquisition time. This technique is not used in NMR microscopy for objects of intermediate size in standard bore (52-mm id) and wide bore (89-mm id) magnets, which are the most widely distributed magnet types for NMR microscopy. The main reason is the restricted space in such magnets for the shim... 

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