SummaryMicrofibril angle (MfA) of the trachcid cell wall of conifers influences the performance and properties of forest products. For instance a high MfA has been found detrimental for solid wood properties. Although it is assumed that there is a correlation between MfA and the growth conditions a tree experiences. there are few studies on how growth conditions influence MfA. In this study mean MfA of the cell walls was determined for 646 early wood samples, from pith and outwards, of Picea abies trees using automated double gaussian curve fitting of the 002 arcs generated by X-Ray diffraction and recorded using a area detector. The determinations of mean MfA were based on appr. 500-2000 tracheids per wood sample. It was indicated that a determination of mean MfA would require less than 3 minutes, if the curve fitting program is included already at the time of data acquisition. In an attempt to model the dependency of MfA on factors related to wood formation, the age effect was Found most descriptive and a simple model based on 1/cambial age gave an r 2 = 0.69. Only a slightly higher correlation (r 2 = 0.73) was reached when additional variables significant at p ≤ 0.001 were used, although they, together with the age effect, supported the assumption that growth conditions affect MfA. The study suggests that to concentrate and minimize the volume of wood with high MfA, in an individual tree, juvenile growth suppression in combination with an extended rotation period should be used.
In the course of studying a biological phenomenon thought to be a precursor to chromosome breakage, researchers have found that treatments sometimes produce a higher proportion of "outliers" than do controls. Our examples pertain to smokers and patients undergoing chemotherapy, although the statistical methods developed here would apply to subjects exposed to any other health hazard. We formulate the problem in a nonparametric setting. Locally most powerful rank tests are obtained for mixture alternatives. In one instance, the approximate scores test has the simple form of counting the number of treatment responses above a combined sample percentile. Our test statistics are compared to the Wilcoxon and normal scores tests using empirical power studies and asymptotic efficiencies.
Two important wood properties are stiffness (modulus of elasticity or MOE) and bending strength (modulus of rupture or MOR). In the past, MOE has often been modeled as a Gaussian and MOR as a lognormal or a two or three parameter Weibull. It is well known that MOE and MOR are positively correlated. To model the simultaneous behavior of MOE and MOR for the purposes of wood system reliability calculations, we introduce a bivariate Gaussian-Weibull distribution and the associated pseudotruncated Weibull. We use asymptotically efficient likelihood methods to obtain an estimator of the parameter vector of the bivariate Gaussian-Weibull, and then obtain the asymptotic distribution of this estimator.
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