Aeronautical Engineering: A special bibliography, supplement 60

This bibliography lists 284 reports, articles, and other documents introduced into the NASA scientific and technical information system in July 1975

The Effects of Simplifying Assumptions in Power Analysis

In experimental research, planning studies that have sufficient probability of detecting important effects is critical. Carrying out an experiment with an inadequate sample size may result in the inability to observe the effect of interest, wasting the resources spent on an experiment. Collecting more participants than is necessary may unnecessarily put too many participants at risk and potentially detect an effect size that is not clinically meaningful. Therefore, obtaining the most accurate estimates of necessary sample size prior to applying for research funding and carrying out experiments is of utmost importance. Educational studies often select whole classrooms for participation. When clusters of individuals are assigned to experimental conditions, the design is referred to as a cluster randomized clinical trial. An over-estimation or under-estimation of the number of clusters needed can have large budgetary or logistical consequences. Accurate sample size estimates, especially in large-scale studies, can help researchers carry out high-quality research and make valid conclusions. Statistical power is the probability of rejecting a false null hypothesis so that a researcher can correctly conclude that an effect has been observed in a study. Three different methods of estimating power are examined in this study, including (a) formulaic power functions, (b) empirical simulation studies, and (c) constructing exemplary datasets. Formula-based methods make assumptions that may not be met in practice. This study assessed (a) the extent to which failure to account for practical data conditions such as attrition, unequal treatment group sizes, and unequal cluster sizes bias estimates of anticipated power and sample size; and (b) if these effects were moderated by the amount of variability that is attributable to between-cluster differences. The empirical simulation study and exemplary dataset methods showed that attrition and unequal treatment group sizes have substantial effects on estimates of power and sample size. Unequal cluster sizes did not appreciably affect power. Higher levels of bias were found when less variability was attributable to between-cluster differences. Power analyses based on a formulaic approach that fail to account for attrition or treatment group imbalance may severely overestimate power and underestimate the sample size necessary to observe important effects. Adviser: James A. Bovair

Recoil Polarization Measurements for Neutral Pion Electroproduction at Q^2=1 (GeV/c)^2 Near the Delta Resonance

We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q^2 = 1.0 (GeV/c)^2 in 10 bins of W across the Delta resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near 1.232 GeV, but variations among models is large for response functions governed by imaginary parts and for both increases rapidly with W. We performed a nearly model-independent multipole analysis that adjusts complex multipoles with high partial waves constrained by baseline models. Parabolic fits to the W dependence of the multipole analysis around the Delta mass gives values for SMR = (-6.61 +/- 0.18)% and EMR = (-2.87 +/- 0.19)% that are distinctly larger than those from Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+) = (+7.1 +/- 0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe. Finally, using a unitary isobar model (UIM), we find that excitation of the Roper resonance is dominantly longitudinal with S1/2 = (0.05 +/- 0.01) GeV^(-1/2) at Q^2=1. The ReS0+ and ReE0+ multipoles favor pseudovector coupling over pseudoscalar coupling or a recently proposed mixed-coupling scheme, but the UIM does not reproduce the imaginary parts of 0+ multipoles well.Comment: 60 pages, 54 figure

Strain comparisons in aquaculture species: a manual

When different strains or breeds of a particular species are available, the best choice is seldom immediately obvious for producers. Scientists are also interested in the relative performance of different strains because it provides a basis for recommendations to producers and it often stimulates the conduct of work aimed at unraveling the underlying biological mechanisms involved in the expression of such differences. Hence, strain or breed comparisons of some sort are frequently conducted. This manual is designed to provide general guidelines for the design of strain comparison trials in aquaculture species. Example analyzes are provided using SAS and SPSS. The manual is intended to serve a wide range of readers from developing countries with limited access to information. The users, however, are expected to have a basic knowledge of quantitative genetics and experience in statistical methods and data analysis as well as familiarity with computer software. The manual mainly focuses on the practical aspects of design and data analysis, and interpretation of results

Use of theoretical and estimated identity-by-descent (IBD) allele sharing measures in genome-wide linkage and association studies, with application to large pedigrees

PhD ThesisTraditionally, identity-by-descent (IBD) sharing among related individuals is estimated on the basis of the assumed pedigree structure, possibly combined with genotyping information for some or all subjects at a series of genetic markers. Recently, there has been interest in using dense SNP genotype data to estimate both average (across the genome) and local (at particular locations) IBD sharing by pairs of individuals. Although originally intended for inference of pedigree relatedness, these genetically estimated IBDs can potentially replace the traditional IBD estimates used in various genetic data analysis methods. I compared IBD estimates from various software packages (PLINK, KING and linear mixed model (LMM) packages including EMMAX, FaST-LMM, GenABEL, GEMMA and MMM) with the theoretical estimates, and examined their utility in application to LMM association analysis of real and simulated qualitative and quantitative phenotypes from a Brazilian family-based study of visceral leishmaniasis (VL) and from the 18th Genetic Analysis Workshop (GAW) data. Generally, the results from the different software packages were highly concordant. When used to model correlations between individuals in LMM analysis, these approaches achieved good control of type 1 error (well beyond that attainable using theoretical IBD estimates), while also achieving superior power to comparable non- LMM methods. Furthermore, although technically misspecified, LMM methods were also successfully applied to simulated longitudinal data. In addition, a new nonparametric linkage analysis method, Regional IBD Analysis (RIA), is proposed, where theoretical IBD estimates are replaced with the average and local genetic IBD estimates. This method was compared with traditional methods for non-parametric linkage analysis (either exact methods using small pedigrees from a study of vesicoureteral reflux disorder (VUR) or simulation-based methods using large pedigrees from the VL study) and was found to perform at least equally well while taking less time.Faculty of Medicine Ramathibodi Hospital, Mahidol Universit

A multi-trait multi-environment QTL mixed model with an application to drought and nitrogen stress trials in maize (Zea mays L.)

Despite QTL mapping being a routine procedure in plant breeding, approaches that fully exploit data from multi-trait multi-environment (MTME) trials are limited. Mixed models have been proposed both for multi-trait QTL analysis and multi-environment QTL analysis, but these approaches break down when the number of traits and environments increases. We present models for an efficient QTL analysis of MTME data with mixed models by reducing the dimensionality of the genetic variance¿covariance matrix by structuring this matrix using direct products of relatively simple matrices representing variation in the trait and environmental dimension. In the context of MTME data, we address how to model QTL by environment interactions and the genetic basis of heterogeneity of variance and correlations between traits and environments. We illustrate our approach with an example including five traits across eight stress trials in CIMMYT maize. We detected 36 QTLs affecting yield, anthesis-silking interval, male flowering, ear number, and plant height in maize. Our approach does not require specialised software as it can be implemented in any statistical package with mixed model facilities

Highlights of the SLD Physics Program at the SLAC Linear Collider

Starting in 1989, and continuing through the 1990s, high-energy physics witnessed a flowering of precision measurements in general and tests of the standard model in particular, led by e+e- collider experiments operating at the Z0 resonance. Key contributions to this work came from the SLD collaboration at the SLAC Linear Collider. By exploiting the unique capabilities of this pioneering accelerator and the SLD detector, including a polarized electron beam, exceptionally small beam dimensions, and a CCD pixel vertex detector, SLD produced a broad array of electroweak, heavy-flavor, and QCD measurements. Many of these results are one of a kind or represent the world's standard in precision. This article reviews the highlights of the SLD physics program, with an eye toward associated advances in experimental technique, and the contribution of these measurements to our dramatically improved present understanding of the standard model and its possible extensions.Comment: To appear in 2001 Annual Review of Nuclear and Particle Science; 78 pages, 31 figures; A version with higher resolution figures can be seen at http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8985.html; Second version incorporates minor changes to the tex