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  • Analytical Chemistry and Spectroscopy  (15)
  • Electronic structure and strongly correlated systems
  • 1990-1994  (15)
  • 1
    Electronic Resource
    Electronic Resource
    Tensorial resolution: A direct trilinear decomposition (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. 29-45 
    Details
    ISSN: 0886-9383
    Keywords: Tensor ; Superdiagonalization ; GRAM ; Three-way ; Multilinear ; Trilinear ; PARAFAC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modern instrumentation in chemistry routinely generates two-dimensional (second-order) arrays of data. Considering that most analyses need to compare several samples, the analyst ends up with a three-dimensional (third-order) array which is difficult to visualize or interpret with the conventional statistical tools.Some of these data arrays follow the so-called trilinear model, \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm R}_{ijk} = \sum\limits_{r = 1}^N {{\rm X}_{ir} {\rm Y}_{jr} {\rm Z}_{kr} + {\rm Error}_{ijk} } $$\end{document} These trilinear arrays of data are known to have unique factor analysis decompositions which correspond to the true physical factors that form the data, i.e. given the array ∝, a unique solution can be found in many cases for each order X, Y and Z. This is in contrast to the well-known second-order bilinear data factor analysis, where the abstract solutions obtained are not unique and at best cannot be easily compared with the underlying physical factors owing to a rotational ambiguity.Trilinear decompositions have had the disadvantage, however, that a non-linear optimization with many parameters is necessary to reach a least-squares solution. This paper will introduce a method for reducing the problem to a rectangular generalized eigenvalue-eigenvector equation where the eigenvectors are the contravariant form (pseudo-inverse) of the actual factors. It is shown that the method works well when the factors are linearly independent in at least two orders (e.g. Xir and Yjr are full rank matrices).Finally, it is shown how trilinear decompositions relate to multicomponent calibration, curve resolution and chemical analysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040105
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  • 2
    Electronic Resource
    Electronic Resource
    Dependence between fusion temperatures and chemical components of a certain type of coal using classical, non-parametric and bootstrap techniques (1990)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 4 (1990), S. 429-439 
    Details
    ISSN: 0886-9383
    Keywords: Principal components ; Multiple and stepwise regression ; Non-parametric density and regression estimation ; Bootstrap inference ; Canonical correlation ; PLS regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A statistical study of the dependence between various critical fusion temperatures of a certain kind of coal and its chemical components is carried out. As well as using classical dependence techniques (multiple, stepwise and PLS regression, principal components, canonical correlation, etc.) together with the corresponding inference on the parameters of interest, non-parametric regression and bootstrap inference are also performed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180040606
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  • 3
    Electronic Resource
    Electronic Resource
    Thermospray mass spectrometry of phosphorothionate pesticides and their oxygen analogues (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 20 (1991), S. 3-10 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Positive and negative ion modes thermospray mass spectrometry were used for the characterization of the phosphorothionate pesticides parathion-ethyl, fenchlorphos, bromophos-ethyl and fenitrothion and their oxygen analogues. A convenient and easy procedure using dimethyldioxirane has been developed for the preparation of the triester phosphates from the corresponding phosphorothionates. The spectra reported from paraoxon-ethyl and fenitrooxon are compared with those of standards available. For the first time, the characterization of the oxygen analogues of fenchlorphos and bromofos-ethyl by any mass spectrometric technique is reported.By employing the positive ion mode, the base peak was [M + NH4]+ for all the studied pesticides with a second abundant ion corresponding to [M + H]+ whereas in the negative ion mode typical negative chemical ionization mechanisms involving electron capture, dissociative electron capture and anion attachment have been observed. The corresponding specific fragments were: [M - R]-, R being a methyl or ethyl; [FG]-, FG being the functional group fragment which contains the phosphorus moiety; M-, [M - Cl]-, phenolate and thiophenolate anions and adducts with the ionizing additive. Special emphasis is given to the changes in the spectra of the phosphorothionate pesticides as compared to their oxygen analogues. With the positive ion mode, sensitivity was about one and a half orders of magnitude better for the oxygen analogues than for the parent pesticides, whereas in the negative ion mode identical sensitivities were observed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200200104
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  • 4
    Electronic Resource
    Electronic Resource
    Experimental design optimization of the separation of the aromatic compounds in petroleum cuts by supercritical fluid chromatography (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 169-174 
    Details
    ISSN: 0935-6304
    Keywords: Experimental design optimization ; Supercritical fluid chromatography ; Aromatic content ; Petroleum cuts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A experimental design optimization method is demonstrated for evaluation of the resolution of the performance mixture used in the proposed ASTM test to determine the aromatic content of aviation fuels. The method uses a Doehlert experimental matrix test to optimize the resolution and analysis time by varying the pressure and temperature of the supercritical carbon dioxide mobile phase. The separation between saturated and aromatic compounds was optimized using only seven experiments. With this procedure, the analysis time required for determination of the total aromatic content of more complex samples can be reduced to less than 10 min.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160308
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of the trifluoropropyl group in polysiloxane stationary phases used for capillary gas chromatography (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 721-724 
    Details
    ISSN: 0935-6304
    Keywords: Capillary GC ; Selectivity of stationary phases ; Poly(methyltrifluoropropyl siloxane) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four poly(methyl 3,3,3-trifluoropropyl siloxanes) with trifluoro-propyl group content (group substitution) between 8 and 35 percent have been synthesized and characterized as stationary phases for gas chromatography in borosilicate glass capillary columns. Results are compared with those from two commercial stationary phases-a polydimethylsiloxane and a poly(methyl 3,3,3-trifluoropropyl siloxane) with a fifty percent trifluoropropyl group content (group substitution).Retention index values, McReynolds constants, polarity (as defined by McReynolds) and retention polarity (as defined by Takács) increase regularly with the trifluoropropyl group content of the stationary phase. The temperature coefficient of the retention indices of the McReynolds probes, and that of the polarities, have been determined at temperatures between 60 and 180 °C. Specific retention volumes do not follow the linear dependence on trifluoropropyl group content observed for retention indices or polarities. Substances with electron-donor groups show maximum retention for a trifluoropropyl group content of ca 30%, whereas the retention of hydrocarbons, halogenated compounds, and alcohols decreases as the degree of trifluoropropyl group substitution increases from 0 to 50%. It is felt that a polysiloxane with a trifluoropropyl group content of ca 30 to 35% would be the best choice for the separation of ketones, nitro compounds or amines.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240161210
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of ωγ using the tilt of the propagation plane (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 22 (1993), S. 89-91 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The product of fluorescence yield (ω) and emission probability (Γ), was measured using a method based on the propagation plane inclination. Measurements of the Kα line of elements such as Cr, Fe and Ni on binary samples were carried out to determine the product ωΓ. The results were compared with those reported in well known compilations. The proposed procedure can be considered a new alternative to increase the available set of methods for measuring fundamental parameters.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300220207
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  • 7
    Electronic Resource
    Electronic Resource
    Dependence of XRF intensity on the tilt of the propagation plane: Experimental (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 20 (1991), S. 163-169 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The geometrical properties of the x-ray fluorescence (XRF) intensity related to the α-parameterization were confirmed experimentally. A special sample stage was built to allow the rotation of the sample with the propagation plane (the plane defined by the incident and take-off beam directions) and was coupled to an energy-dispersive spectrometer. The device and the way in which it was carefully aligned with the collimated x-ray beams are described. The fluorescence spectra of three NBS standard samples were measured for 16 different positions of the α angle. The incident and take-off angles were both 45° for sample rotations between α = 0 and the maximum angle of 86°. XRF intensities from non-enhanced lines do not show any dependence on α as predicted by theory. Enhanced lines, on the contrary, decrease in intensity when α increases, allowing the isolation of the primary emission by extrapolation to the limiting case α = π/2.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300200403
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  • 8
    Electronic Resource
    Electronic Resource
    SERS of cytosine and its methylated derivatives on metal colloids (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 23 (1992), S. 61-66 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: SERS spectra of cytosine, 1-methylcytosine, 5-methylcytosine and 1,5-dimethylcytosine on silver and on copper colloids are reported. A study of the influence of pH on the normal Raman spectra of these compounds was made in order to understand better the behaviour of these molecules on metal surfaces. The results obtained indicate remarkable changes in the type of adsorbate - metal interactions depending on the metal used as the SERS support. These interactions are also influenced by the presence of methyl groups in the cytosine molecule.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250230108
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  • 9
    Electronic Resource
    Electronic Resource
    Raman spectroscopy of oxygenated amorphous CdTe films (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 25 (1994), S. 203-207 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Oxygenated CdTe films prepared by r.f. sputtering have been shown to have band gap energies between 1.48 and 3.35 eV, depending on the amount of oxygen incorporated in the CdTe matrix. Samples with oxygen concentrations above 7 at.% are amorphous, whereas those with oxygen concentrations below 7 at.% are polycrystalline, as determined by x-ray and Raman measurements. The Raman spectra of the polycrystalline samples show that there is ca. 4 at.% Te in the form of inclusions under high pressure, which is relatively easy to detect owing to the enhanced Raman cross-section of Te. The Raman spectra of the amorphous samples is dominated by a single broad band at 159 cm -1. The fact that tellurates in general show a similar band, in spite of their different vibrational density of states, indicates that it corresponds to Te—Te bonds in the amorphous matrix.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250250303
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  • 10
    Electronic Resource
    Electronic Resource
    Surface-enhanced Raman spectroscopy of 1,5-dimethylcytosine on silver and copper sols (1990)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 21 (1990), S. 679-682 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra of 1.5-dimethylcytosine (DMC) as the solid and in aqueous solution are reported. A tentative assignment of Raman bands is made. Surface-enhanced Raman spectra obtained on silver and on copper colloids show appreciable differences from the normal unenhanced Raman spectra. The geometry of DMC-metal interactions is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250211008
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