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  • 1990-1994  (4)
  • 1950-1954
  • Intraclass correlation  (2)
  • second harmonic generation  (2)
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  • 1990-1994  (4)
  • 1950-1954
Year
Keywords
  • 1
    Electronic Resource
    Electronic Resource
    The dilemma of negative analysis of variance estimators of intraclass correlation (1992)
    Springer
    Theoretical and applied genetics 85 (1992), S. 79-88 
    Details
    ISSN: 1432-2242
    Keywords: Intraclass correlation ; Negative estimate ; Restricted maximum likelihood
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary At least two common practices exist when a negative variance component estimate is obtained, either setting it to zero or not reporting the estimate. The consequences of these practices are investigated in the context of the intraclass correlation estimation in terms of bias, variance and mean squared error (MSE). For the one-way analysis of variance random effects model and its extension to the common correlation model, we compare five estimators: analysis of variance (ANOVA), concentrated ANOVA, truncated ANOVA and two maximum likelihood-like (ML) estimators. For the balanced case, the exact bias and MSE are calculated via numerical integration of the exact sample distributions, while a Monte Carlo simulation study is conducted for the unbalanced case. The results indicate that the ANOVA estimator performs well except for designs with family size n = 2. The two ML estimators are generally poor, and the concentrated and truncated ANOVA estimators have some advantages over the ANOVA in terms of MSE. However, the large biases may make the concentrated and truncated ANOVA estimators objectionable when intraclass correlation (ϱ) is small. Bias should be a concern when a pooled estimate is obtained from the literature since ϱ〈0.05 in many genetic studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223848
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Bias of maximum likelihood estimator of intraclass correlation (1991)
    Springer
    Theoretical and applied genetics 82 (1991), S. 421-424 
    Details
    ISSN: 1432-2242
    Keywords: Intraclass correlation ; Maximum likelihood estimator ; Bias
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A bias correction was derived for the maximum likelihood estimator (MLE) of the intraclass correlation. The bias consisted of two parts: a correction from MLE to the analysis of variance estimator (ANOVA) and the bias of ANOVA. The total possible bias was always negative and depended upon both the degree of correlation and the design size and balance. The first part of the bias was an exact algebraic expression from MLE to ANOVA, and the corrected estimator by this part was ANOVA. It was also shown that the first correction term was equivalent to Fisher's reciprocal bias correction on hisZ scores. The total possible bias of MLE was large for small and moderate samples. Relative biases were larger for small parametric values and vice versa. To ensure a relative bias less than 10% assuming an intraclass correlation of 0.025, which is not unusual in most of the animal genetic studies, the total number of observations (N) should be not less than 500. From a design point of view, minimum bias occurred atn = 2, the minimum family size possible, underN fixed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588594
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Investigation of dipolar reorientation dynamics of pure bulk polymers using second harmonic generation (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2615-2624 
    Details
    ISSN: 0887-6266
    Keywords: second harmonic generation ; correlated dipolar orientation ; trapped charges ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Second harmonic generation (SHG) in three corona-poled, pure, bulk polymers is studied as a function of temperature. It is found that this technique readily yields dynamical information that is complementary to that obtained from the technique of dielectric relaxation (DR). The SHG results are compared to those from DR in the same temperature ranges above Tg. It is found that in the temperature ranges examined, the relaxation times obtained from SHG are several orders fo magnitude longer than those measured by dielectric relaxation. This is explained as being due to the strong correlation between oriented dipoles and to trapped charges injected by the poling process. Fitting measured data to the Williams-Landau-Ferry (WLF) equation indicates that more free volume is needed in SHG for dipolar reorientation than is needed in DR. An SHG relaxation elongation phenomenon at constant temperature is found to occur in the pure bulk polymers and is similar to that found in chromophore-doped polymers previously studied. The SHG technique is developed as a new tool to directly study the reorientational dynamics of polar polymer segments. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321607
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Second harmonic generation and optical anisotropy of a spin-cast polymer film (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1983-1988 
    Details
    ISSN: 0887-6266
    Keywords: second harmonic generation ; optical anisotropy ; spin-cast polymer film ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The nonlinear susceptibilities (χ(2)33, χ(2)31), and the refractive index anisotropy, of a main chain accordion polymer, BCSC (see the text for the complete chemical formula), have been measured by the techniques of second harmonic generation (SHG) and waveguiding. A large birefringence, which is induced in the BCSC film by the spin-coating process, is almost removed by electric field poling. Our results demonstrate the fundamental difference between the birefringence associated with quadrupolar orientational order and the dipolar order associated with SHG. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090311310
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    Paper (German National Licenses)
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