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  • 1
    Electronic Resource
    Electronic Resource
    Lower bounds for the reliability of the total score on a test composed of non-homogeneous items: I: Algebraic lower bounds (1977)
    Springer
    Psychometrika 42 (1977), S. 567-578 
    Details
    ISSN: 1860-0980
    Keywords: reliability bounds ; coefficient alpha ; non-homogeneous composites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Psychology
    Notes: Abstract Let Σ x be the (population) dispersion matrix, assumed well-estimated, of a set of non-homogeneous item scores. Finding the greatest lower bound for the reliability of the total of these scores is shown to be equivalent to minimizing the trace of Σ x by reducing the diagonal elements while keeping the matrix non-negative definite. Using this approach, Guttman's bounds are reviewed, a method is established to determine whether his λ4 (maximum split-half coefficient alpha) is the greatest lower bound in any instance, and three new bounds are discussed. A geometric representation, which sheds light on many of the bounds, is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02295979
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A note on the relation between coefficient alpha and guttman's “split-half” lower bounds (1979)
    Springer
    Psychometrika 44 (1979), S. 251-252 
    Details
    ISSN: 1860-0980
    Keywords: reliability bounds ; coefficient alpha ; split-half bounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Psychology
    Notes: Abstract Use of the same term “split-half” for division of ann-item test into two subtests containing equal [Cronbach], and possibly unequal [Guttman], numbers of items sometimes leads to a misunderstanding about the relation between Guttman's maximum split-half bound and Cronbach's coefficient alpha. Coefficient alpha is the average of split-half bounds in the Cronbach sense and so is not larger than the maximum split-half bound in either sense whenn is even. Whenn is odd, however, splithalf bounds exist only in the Guttman sense and the largest of these may be smaller than coefficient alpha.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02293977
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Use of inverse gas chromatography to quantify interactions in anhydride cured epoxy resins (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 35 (1994), S. 135-143 
    Details
    ISSN: 0959-8103
    Keywords: inverse gas chromatography ; solubility parameter ; epoxy resin ; phthalic anhydride ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Previous work has shown that the inverse gas chromatography (IGC) method combined with Flory-Huggins and solubility parameter theories could be used to quantify interactions in an amine cured epoxy resin matrix. In the present communication the same procedures have been adopted for an anhydride cured epoxy resin matrix. The solubility parameter at 298 K thereby obtained for the cured resin was 20-6 (MPa)1/2, which lies between the corresponding values of 18.8(MPa)1/2 and 22.5 (MPa)1/2 for the precursors, viz. Epikote 828 (an epoxide resin) and phthalic anhydride, respectively. It was noted that great care must be exercised regarding choice of solvent used for deposition of phthalic anhydride on a glass bead support because of reaction to phthaclic acid. Similar consderations apply to the choice of probes used.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pi.1994.210350203
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  • 4
    Electronic Resource
    Electronic Resource
    Use of inverse gas chromatography to quantify interactions in amine cured epoxy resins (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 35 (1994), S. 119-133 
    Details
    ISSN: 0959-8103
    Keywords: inverse gas chromatography ; solubility parameter ; epoxy resin ; composite ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Flory-Huggins interaction parameters, λ, were determined for a series of probes in an amine cured epoxy resin matrix (433-493 K) and its precursors (324-363 K) by inverse gas chromatography (IGC). Hildebrand-Scatchard theory was combined with Flory-Huggins theory in order to estimate infinte dilution solubility parameters (δ2) for the matrix and its precursors at 298 K. It was shown that the value of the solubility parameter for the cured resin matrix lies between those of its precursors. Compared to the majority of published work, an unusual aspect of this application of IGC is that solubility parameters have been determined when the stationery phases are (i) small molecules and (ii) a highly crosslinked polymer. Moreover, all possible attempts have been made to ensure equilibrium conditions between probe and stationary phase, and compensation for asymmetry of peak profile has been applied in determining δ2. The solubility parameters estimated by IGC are in good agreement with those calculated by other methods.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pi.1994.210350202
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    Paper (German National Licenses)
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