Spectral correction

As for all absorbance-based spectral measurements, the intensity data represented in a raw (single-beam) chemical image are a combination of the spectral response of both the instrument and the sample. In order to remove the instrument response component, it is necessary to ratio the data to a background reference. For reflectance measurements, the background is a separate data cube typically acquired from a uniform. 

Further processing is also usually performed to transform the reflectance image cube to its logic (UR) form, which is effectively the sample absorbance . This results in chemical images in which brightness linearly maps to the analyte concentration, and is generally more useful for comparative as well as quantitative purposes. Note that for NIR measurements of undiluted solids the use of more rigorous functions such as those described by Kubelka and Munk are usually not required.  

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Another common treatment consists of background spectral correction by subtracting the baseline spectrum before the peak appearance. Drifts in the baseline of electropherograms can be circumvented by absorbance subtraction. Beyond these simple corrections, more sophisticated treatments for detrending and noise hltering using wavelets, artihcial neural networks, and so on can be used. 

All the spectral data presented in this chapter were taken in a spectrofluorometer that was spectrally corrected from 510 to 750 nm by a quantum counter containing tetra-f-butyl metal-ffee phthalocycanine in 1,1,2-tricholoroethan ( 1.2 x 10 M). Details of the procedures have been described in Ref. 29. 

Reported analysis of soil standard reference materials (IAEA Soil 5, IAEA SL-1 and BCR-141) indicate that about 16-20 elements may be determined with very good analytical characteristics in sediments and soils after introduction of background and spectral corrections (Liese, 1985a,b). Severson et al. (1992) reported the determination of 26 elements in soils. The accuracy and precision have been proven by analysis of NIST-SRMs. The concentration range varies between 0.1 (Se) p.g/g to %. Seventeen elements were reliably determined in soil and sediment standard reference materials without introducing any corrections (Kanda and Taira, 1988). 

Before the advent of Fourier transform spectrometers, wide-line NMR was done by sweeping the magnetic field and observing the dispersion signal, or by pulsing the radiofrequency and observing the free Induction decay without transformation. The very broad spectral widths have caused problems with baselines and faithful representations of the entire llneshapes. Various techniques, such as the quadrupole echo (lA), progressive phase alternation of the excitation pulse and detector, short spectrometer dead times, and post-acquisition spectral correction (15) have circumvented most of these. 

Figure 3. (a) black body spectra, (b) Pt holder spectra and (c) final sample spectra after blackbody and Pt holder spectral corrections... 

Extensive lists of redox indicator dyes are given in Clark [6], Kuwana[13], and the CRC Handbook of Biochemistry [16]. Some of the best indicator dyes for flavoproteins and dinuclear iron proteins are pyocyanine, indigo disulfonate (IDS), 8-chlororiboflavin, and lumiflavin acetate. Redox indicator dyes must be titrated, and their spectra and potentials determined under conditions of temperature, pH, and buffer identical to those in the enzyme experiments to allow for spectral correction. 

There are three methods of generating spectral correction curves to accoimt for these sensitivity variations. One is to measure the fluorescence spectra of standard compounds whose true fluorescence spectra have been determined and reported (3). Then the sensitivity factors could be calculated by comparing the experimentally measured spectra with the reference spectrum. 

Spectral correction involves taking the ratio of the data to a background reference in order to remove the instrument response component. Because the filter-based NIR-CI instruments operate in a true staring or DC mode, it is also necessary to subtract the dark camera response from the image cube. The correction to reflectance (R) is therefore ... 

Combination of THERMOS + GRACE + DOT into a unique code named HASOB. In this version of HASOB, we still assume no spectral correction in microscopic cross-sections for isotopes concentration calculation, fhe code HASOB is developed in such a way that users can prepare input data for neutron thermalization and fast spectral treatment in the same way just like prepare input data for THERMOS and GRACE codes as individual. This work is in progress to investigate if the absence of library of some isotopes born in U-235 and U-238 chains can be negligible in low burnup calculation. 

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