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  • Analytical Chemistry and Spectroscopy  (3)
  • principal component analysis  (1)
  • 1
    ISSN: 1573-4943
    Keywords: Β-Lactoglobulin ; structure ; sol-gel transition ; infrared ; principal component analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Fourier transform infrared spectroscopy has been applied to investigate the secondary structural changes ofΒ-lactoglobulin in water/ethanol mixtures. The studies were carried out at two differentpHs and at high protein concentrations. The spectra were recorded using an attenuated total reflection cell. The amide I band ofΒ-lactoglobulin in water reveals large amounts of intra extendedΒ-sheet structure. About 20% ethanol,Β-lactoglobulin unfolds andΒ-strand formation is observed.α-Helices are built up by increasing the ethanol concentration up to 30%. In 50% ethanol,Β-lactoglobulin gels providing the apparent pH are neutral. The secondary structural changes ofΒ-lactoglobulin were observed on the similarity maps obtained by Principal Component Analysis.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0886-9383
    Keywords: NIR ; Fast Fourier transform ; Principal component analysis ; Discrimination ; Baking quality ; Wheat ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Digitalized continuous near infra-red reflectance (NIR) spectra are composed of a great number of data which must be reduced for microcomputer mathematical treatment. The sequence ‘fast Fourier transform preceding principal component analysis’ was tested to perform data size reduction without a large loss of information. The method was applied on a collection of wheat spectra composed of 351 data. Ten resulting data, which described 99.5% of the total variance, were kept. The relevance of the method was estimated by the ability of the resulting data (i) to regenerate the original signal, and (ii) to discriminate the baking quality of the wheat by stepwise multiple discriminant analysis. The average difference between initial and regenerated spectra was -2.4 × 10-3 log (1/R) units and the standard deviation was 1.16 × 10-3 log (1/R) units. The discrimination treatments gave 89.9% of well classified samples for the calibration test and 90.5% for the prediction test. The application of these mathematical treatments to other continuous signals is discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0886-9383
    Keywords: NIR reflectance ; Multivariate analysis ; Principal component analysis ; Stepwise multiple linear regression ; Silage quality ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calibrations to predict crude protein (CP) and in vitro dry matter digestibility (IVDMD) in dried grass silage from reflectance data collected at 19 wavelengths on an InfraAlyzer 400R have been developed using stepwise multiple linear (SML) and principal component (PC) regression techniques. A direct comparison of the efficacy of each multivariate technique in this applications has been possible by using identical calibration development and evaluation sample sets. The effect of two data transformation steps prior to PC regression was also investigated. PC regression of raw reflectance data yielded no significant improvement in the standard errors of prediction (SEP) for CP and IVDMD over those obtained by SMLR, viz. 0·61 vs 0·63 and 2·9 vs 3·0 respectively. Computation time for development and evaluation of the PC regression equation was less than for selection of the best SMLR equation, and PCR equations may be more robust. Data transformation to reduce granularity effects prior to PCR did not produce any improvement in predictive accuracy for either IVDMD or CP.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0886-9383
    Keywords: Discriminant analysis ; Size-exclusion chromatography ; Wheat proteins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Continuous digitalized signals such as spectra, electrophoregrams or chromatograms generally have a large number of data points and contain redundant information. It is therefore troublesome performing discriminant analysis without any preliminary selection of variables. A procedure for the application of canonical discriminant analysis (CDA) on this kind of data is studied. CDA can be presented as a succession of two principal component analyses (PCAs). The first is performed directly on the raw data and gives PC scores. The second is applied on the gravity centres of each qualitative group assessed on the normalized PC scores. A stepwise procedure for selection of the relevant PC scores is presented. The method has been tested on an illustrative collection of 165 size-exclusion high-performance (SE-HPLC) chromatograms of proteins of wheat belonging to 55 genotypes and grown in three locations. The discrimination of the growing locations was performed using seven to nine PC scores and gave more than 86% accurate classifications of the samples both in the training sets and the verification sets. The genotypes were also rather well identified, with more than 85% of the samples correctly classified. The studied method gives a way of assessing relevant mathematical distances between digitalized signals according to qualitative knowledge of the samples.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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