Spectral Enhancement

This same sensitivity can, however, be misleading. Even minor radical routes to a particular reaction product could give rise to intense polarized n.m.r. signals which could obscure the normal monotonic increase of the signal due to product formed by a non-radical route. This problem can be overcome in some cases by estimation of the spectral enhancement factor. Again, it is not possible to justify a firm, threshold value, but as a useful rule of thumb when enhancements fall below about 100 then the possibility of an important alternative non-radical route to the same product should be carefully investigated. 

Simpson et al., 1990] Simpson, A., Moore, B., and Glasberg, B. (1990). Spectral enhancement to improve the intelligibility of speech in noise for hearing-impaired listeners. Acta Otolaryngol. Suppl. 469, pages 101-107. 

SPECTRAL ENHANCEMENT OF RECOMBINANT PROTEINS WITH TRYPTOPHAN ANALOGS ... 

Spectral Enhancement of Proteins with Tryptophan Analogs... 

Figure 10. Spectral enhancement of rigid network. Spectra (A) obtained from the gated high power decoupling pulse sequence with a delay between repetitive pulses of 2 sec. Spectrum (B) obtained with same pulse sequence except the delay between pulsing Increased to 20 sec.

Although the analyst may be unaware of its existence in the sample, signal suppression serves to decrease system sensitivity and raises the working detection limit. Spectral enhancement, on the other hand, increases the system sensitivity and lowers the working detection limit. "Enhancement is a well known problem in atomic absorption spectroscopy ( 12). A variety of approaches, such as Zeeman effect correction have been proposed for its elimination (11). To avoid artificially high results, calibration standards must contain concentrations of the enhancing species equivalent to those in the sample. Ordinary standard solutions are not representative of the analytical situation."... 

It is possible in theory to generate an action spectrum which takes into account the effect of incremental monochromatic radiation in excess of the spectral irradiance of a source spectrum. Narrow-band, near-monochromatic radiation might be superimposed over the polychromatic spectrum from a xenon source to obtain radiation spectrally enhanced in any selected waveband. Using a series of interference filters, a series of cut-on filters, and two filtered xenon sources, it should be possible to generate an action spectrum for polymer degradation under spectrally-altered, UV-enhanced (or even visible-enhanced) source spectra. The effective radiation and dose rate in such an experiment can be written as follows ... 

This spectral enhancement method has already been shown to improve HREELS resolution from polymer spectra but other new methods are being tested . 

Thus, the infrared and SEIRA, Raman and SERS and IRRAS measurements allow us to determine the most probable orientation of the molecules onto different metal surfaces, to infer about the influence that these surfaces have onto the molecular structure and to conclude about the mechanism governing the spectral enhancement in IR and Raman. 

The SERS spectral data obtained on colloidal Ag as well as Ag island films indicate a weak macrocycle interaction and small structural modifications of the naphthalocyanine complex on the surface. An energy transfer mechanism contribution to the observed enhancement was proposed. The whole spectral data point that the naphthalocyanine complex is oriented with the naphthalocyanine plane face-on to the surface. In both vanadylnaphthalocyanine and vanadylpor-phine tetraphenyl substituted complexes the vanadyl group is perpendicular to the coordination site and opposed to the surface. In both complexes the phenyl substituents, oriented perpendicular to the macrocycle plane, are responsible of the weak adsorbate-substrate interaction. Several different experimental conditions such as scanning speed, laser power and excitation lines wavelengths, concentration and metal surfaces were intended to obtain SERS of the porphine complex without success this was interpreted in terms that the complex has no interaction with the surface. Thus, it was concluded that the extension of the whole r-system plays a significant role in the mechanism involving the spectral enhancement by surface effect. 

Nonetheless, the spectral enhancement for films on metallic substrates exists and, as demonstrated by Greenler [122], can achieve values of 5000 and greater ( ) relative to the normal-incidence transmission spectrum of the free film. Let us show that there is no contradiction with the conclusions listed above. As follows from Eq. (1.108), the spectral sensitivity depends not only on the MSEFs... 

Both causes of spectral enhancement act in the case of external reflection from transparent or low-absorbing substrates. The positive geometric effect is demonstrated in Fig. 1.15. The negative effect due to the spectrum representation is the most pronounced in the p-polarized spectra measured at [Pg.55]

The apphcation of direct covariance processing to either NMR spectra or mixed time—frequency data matrices was preferentially used for spectral enhancement with respect to resolution. As the resolution of the indirect or incremented dimension is endowed with that of the direct or acquisition dimension, homonuclear spectra were treated almost exclusively. 

Lopez-Rios [33] also used hydrogen and methane in an ultrahigh-vacuum chamber to generate diamond films (as well as diamondlike carbon) on silicon substrates. Figure 10 shows spectra before and after silver deposition. The spectral enhancement caused by SERS is clearly shown, for there was no spectrum without silver deposition. The asymmetry of the cubic diamond peak at 1332 and the structure at 1242 are attributed to phonon excitation. 

KBr pellets can be obtained by removing bound water at 110 °C for 2-3 h. [11]. Spectral enhancements have also been obtained by using photoacoustic FTIR methods, where IR radiation absorbed by analyte is detected as an acoustic wave generated in an inert gas in contact with the sample. PA-FTIR spectra of resin beads were found to be free of baseline artifacts caused by light scattering and sample inhomogeniety in typical FTIR experiments [12]. 

Oxenham, A.J., A.M. Simonson, L. Turicchia, and R. Saipeshkar. 2007. Evaluation of companding-based spectral enhancement using simulated cochlear-implant processing. Journal of the Acoustical Society of America 121(3) 1709-1716. 

Turicchia, L., and R. Saipeshkar. 2005. A bio-inspired companding strategy for spectral enhancement. IEEE Transactions on Speech and Audio Processing 13(2) 243—253. 

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