Noise techniques, structured

The structured noise method stems from the elegant work of Smith and coworkers (Smith [1966]), who developed a multifrequency technique for ac polarog-raphy. Subsequently, structured noise techniques have been used in corrosion studies by Smyrl and coworkers (Smyrl [ 9%5a,b]> Smyrl and Stephenson [1985]) and by Pound and Macdonald [1985], In all cases, the perturbation applied to the system is of the form... 

A novel approach for suppression of grain noise in ultrasonic signals, based on noncoherent detector statistics and signal entropy, is presented. The performance of the technique is demonstrated using ultrasonic B-scans from samples with coarse material structure. 

However unlike H which is the most abundant of the hydrogen isotopes (99 985%) only 1 1% of the carbon atoms m a sample are Moreover the intensity of the signal produced by nuclei is far weaker than the signal produced by the same number of H nuclei In order for NMR to be a useful technique in structure deter mination a vast increase in the signal to noise ratio is required Pulsed FT NMR pro vides for this and its development was the critical breakthrough that led to NMR becoming the routine tool that it is today... 

However, several hours of measurement are typically needed to achieve good signal-to-noise and high resolution, especially for 2D techniques. Other 2D techniques were used for structure elucidation of carotenoids from guava and annatto seeds. ... 

In order to apply RBL or GRAFA successfully some attention has to be paid to the quality of the data. Like any other multivariate technique, the results obtained by RBL and GRAFA are affected by non-linearity of the data and heteroscedast-icity of the noise. By both phenomena the rank of the data matrix is higher than the number of species present in the sample. This has been demonstrated on the PCA results obtained for an anthracene standard solution eluted and detected by three different brands of diode array detectors [37]. In all three cases significant second eigenvalues were obtained and structure is seen in the second principal component. 

Limits of Time-Resolved and Simultaneous Measurements. Structure evolution studies are based on the ability to carry out time-resolved scattering experiments. The power of this scattering technique is a function of the minimum cycle time during which a scattering pattern with sufficient signal-to-noise ratio can be recorded. As cycle times for anisotropic 2D SAXS patterns have fallen below a value... 

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