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  • Analytical Chemistry and Spectroscopy  (7,072)
  • Animals
  • 1990-1994  (9,341)
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  • 1
    Electronic Resource
    Electronic Resource
    New molecular descriptors for 2D and 3D structures. Theory (1994)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 8 (1994), S. 263-272 
    Details
    ISSN: 0886-9383
    Keywords: Molecular descriptors ; Principal component analysis ; Chemometrics ; Pattern recognition ; Total surface area ; PCDD PCDF ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New theoretical molecular indices are defined. They contain information about the whole molecular structure in terms of size, shape, symmetry and atom distribution. These indices are calcualted from the (x, y, z) co-ordinates of a molecule within different weighting schemes in a straightforward manner and represent a very general approach to describe molecules, molecular fragments, macromolecules and molecular conformations in a unitary conceptual framework. Their interpretability is quite evident and is defined by the same mathematical properties as the algorithm used for their calculation. Examples on the total surface area, toxicity of PCDD and PCDF and reaction rate of catalysed reactions show a high modelling power of these indices.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180080405
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  • 2
    Electronic Resource
    Electronic Resource
    Generalized rank annihilation method. III: Practical implementation (1994)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 8 (1994), S. 273-285 
    Details
    ISSN: 0886-9383
    Keywords: GRAM ; Least-squares problem ; Eigenvalue problem ; NIPALS ; Performance index ; Condition number ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we discuss the practical implementation of the generalized rank annihilation method (GRAM). The practical implementation comes down to developing a computer program where two critical steps can be distinguished: the construction of the factor space and the oblique rotation of the factors. The construction of the factor space is a least-squares (LS) problem solved by singular value decomposition (SVD), whereas the rotation of the factors is brought about by solving an eigenvalue problem. In the past several formulations for GRAM have been published. The differences essentially come down to solving either a standard eigenvalue problem or a generalized eigenvalue problem. The first objective of this paper is to discuss the numerical stability of the algorithms resulting from these formulations. It is found that the generalized eigenvalue problem is only to be preferred if the construction of the factor space is not performed with maximum precision. This is demonstrated for the case where the dominant factors are calculated by the non-linear iterative partial least-squares (NIPALS) algorithm. Several performance measures are proposed to investigate the numerical accuracy of the computed solution. The previously derived bias and variance are proposed to estimate the number of physically significant digits in the computed solution. The second objective of this paper is to discuss the relevance of theoretical considerations for application of GRAM in the presence of model errors.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180080406
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  • 3
    Electronic Resource
    Electronic Resource
    Comments on the DATa ANalysis (DATAN) algorithm and rank annihilation factor analysis for the analysis of correlated spectral data (1994)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 8 (1994), S. 287-292 
    Details
    ISSN: 0886-9383
    Keywords: Rank annihilation ; Principal components ; Procrustes rotation ; Multivariate analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that the DATa ANalysis (DATAN) algorithm can be expressed in terms of rank annihilation factor analysis (RAFA). Subsequent advances in RAFA are applied to DATAN to eliminate the problems and restrictions associated with DATAN. The extension of DATAN in terms of the trilinear decomposition algorithm is discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180080407
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  • 4
    Electronic Resource
    Electronic Resource
    Computational methods in the chemical sciences, A. F. Carley and P. H. Morgan, Ellis Horwood, Ltd, Chichester, U.K., 1989. ISBN 0-85312-746-8 (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 68-69 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050108
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  • 5
    Electronic Resource
    Electronic Resource
    Comments on the power method (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. 331-334 
    Details
    ISSN: 0886-9383
    Keywords: Power method ; NIPALS algorithm ; Singular value decomposition ; Experimental design ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a recent short communication, Miyashita et al. have commented on the weakness of the NIPALS algorithm (equivalently the power method) for calculating the eigenvalues out of order. They offer a diagnostic to ascertain when this may have occurred and suggested a modification to the NIPALS algorithm to avoid this situation. Further comments regarding the use of the power method and Miyashita's presentation of its weakness are warranted. The general inadequacies of methods for decomposing a matrix with degenerate eigenvalues and their relationship to the orthogonal design of experiments are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040407
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  • 6
    Electronic Resource
    Electronic Resource
    Diary (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. i 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040502
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  • 7
    Electronic Resource
    Electronic Resource
    The start and early history of chemometrics: Selected interviews. Part 1 (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. 337-354 
    Details
    ISSN: 0886-9383
    Keywords: Chemometrics ; Chemometrics Society ; History of chemometrics ; Pioneers of modern chemometrics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This is a first foray into the historical start and early years of chemometrics from about 1972 onwards. We have gathered interviews with three originators (Kowalski, Wold and Massart) as well as with a selected group of six other well-known chemometricians who gradually became active in the 1970s (Christie, Clementi, Hopke, Martens, Brown and Deming). The interviews include amongst a host of subjective recollections a succinct record of the key historical literature as highlighted by the interviewees' own rankings of ‘earliest’ and ‘best’.A discussion of the most general commonalities in these interviews together with other historical material is presented in the second part of the paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040503
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  • 8
    Electronic Resource
    Electronic Resource
    U. K. usage of chemometrics and artificial intelligence in QSAR analysis (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. 355-360 
    Details
    ISSN: 0886-9383
    Keywords: Pattern recognition ; U.K. chemometrics usage ; Quantitative structure-activity relationships ; Artificial intelligence ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A survey of members of the U.K. QSAR Discussion Group has been made to determine the extent of use and development of chemometric and artificial intelligence (AI) methods in the analysis of multivariate quantitative structure-activity relationship (QSAR) data in the U.K. Chemometric methods were found to be well established in both industrial and educational establishments and there was significant method development occurring. AI methods were not employed to any great extent and the general level of interest in these techniques was low compared to chemometric methods. A requirement for more education in multivariate statistical methods and regression methods was indicated. A need for a user-friendly, comprehensive, commercially available multivariate statistical package containing multivariate stability testing and regression diagnostic methods was identified.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040504
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  • 9
    Electronic Resource
    Electronic Resource
    Factor analysis of a simulated data matrix involving aqueous complex equilibria (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. 361-377 
    Details
    ISSN: 0886-9383
    Keywords: Abstract factor analysis ; Exploratory data analysis ; Principal components ; Simulated equilibria ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract factor analyses were performed on databases consisting of simulated samples from aqueous equilbria. The program COMPLEX was used to generate equilibrium species in a system of three reactant metals and five reactant bases. Reactant concentrations and pH were drawn from random-normal distributions so that sample data vectors comprised a multivariate log-normal distribution of equilibrium concentrations. In addition, sample groups were created containing different distributions for pH and reactant concentrations.Equilibrium species were shown to contain variance contributed by change in pH among samples as well as change in reactant concentrations. Factor modelling revealed the qualitative relationships among the species and how the relationships change with pH. Factors also revealed those reactants containing variance in the data matrix. In some cases, reactant variance obscured relationships between pH and the equilibrium species.Since factor modelling of a simulated data matrix revealed the expected chemical equilibrium interactions, a potentially powerful tool exists for investigating the effects of outliers and error.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040505
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  • 10
    Electronic Resource
    Electronic Resource
    Variations in essential oils of mandarine related to processing and ripening29th paper of the series ‘On the genuineness of citrus essential oils’. (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. 379-385 
    Details
    ISSN: 0886-9383
    Keywords: PCA ; Essential oils ; Mandarine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mandarine essential oils are extracted from green unripened fruits as well as from red fruits at ripening, both oils having specific uses as natural additives in the food industry. Two processes of production, pressing and peeling, are currently adopted in their production. Capillary gas chromatography with flame ionization detection has been suggested as a sensitive method for the fractionation of volatile components of the essential oils. Principal component analysis was proposed as an exploratory chemometric method for the differentiation of essential oils from fruits at different degrees of ripening, taking into account the processes of production. Product-moment correlations between variables (concentrations of 17 components) were used as starting matrices and the explained variance was adopted as a criterion for eigenvalue selection. Bi-plots and three-dimensional plots of unrotated principal component scores were systematically used as well as those of orthogonally rotated factor scores. The 17 variables were reduced to four principal components, which explained 87% of the total variance. Projection on the first three eigenvectors of all data as unrotated component scores allowed for a tentative differentiation of 59 oils according to their degree of ripening. The two processes of production were also differentiated in a sample of 55 oils.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040506
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