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Population Used (population + used)
Selected AbstractsDifferences between European birthweight standards: impact on classification of ,small for gestational age'DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 11 2006K Hemming PhD We describe a quantitative and comparative review of a selection of European birthweight standards for gestational age for singletons, to enable appropriate choices to be made for clinical and research use. Differences between median values at term across standards in 10 regions and misclassification of 'small for gestational age'(SGA), were studied. Sex and parity differences, exclusion criteria, and methods of construction were considered. There was wide variation between countries in exclusion criteria, methods of calculating standards, and median birthweight at term. The lightest standards (e.g. France's medians are 255g lower than Norway's medians) were associated with fewer exclusion criteria. Up to 20% of the population used in the construction of the Scottish standard would be classified as SGA using the Norwegian standard. Substantial misclassification of SGA is possible. Assumptions about variation used in the construction of some standards were not justified. It is not possible to conclude that there are real differences in birthweight standards between European countries. Country-based standards control for some population features but add misclassification due to the differing ways in which standards are derived. Standards should be chosen to reflect clinical or research need. If standards stratified by sex or parity are not available, adjustments should be made. In multinational studies, comparisons should be made between results using both a common standard and country-based standards. [source] Crystal fingerprint space , a novel paradigm for studying crystal-structure setsACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010Mario Valle The initial aim of the crystal fingerprint project was to solve a very specific problem: to classify and remove duplicate crystal structures from the results generated by the evolutionary crystal-structure predictor USPEX. These duplications decrease the genetic diversity of the population used by the evolutionary algorithm, potentially leading to stagnation and, after a certain time, reducing the likelihood of predicting essentially new structures. After solving the initial problem, the approach led to unexpected discoveries: unforeseen correlations, useful derived quantities and insight into the structure of the overall set of results. All of these were facilitated by the project's underlying idea: to transform the structure sets from the physical configuration space to an abstract, high-dimensional space called the fingerprint space. Here every structure is represented as a point whose coordinates (fingerprint) are computed from the crystal structure. Then the space's distance measure, interpreted as structure `closeness', enables grouping of structures into similarity classes. This model provides much flexibility and facilitates access to knowledge and algorithms from fields outside crystallography, e.g. pattern recognition and data mining. The current usage of the fingerprint-space model is revealing interesting properties that relate to chemical and crystallographic attributes of a structure set. For this reason, the mapping of structure sets to fingerprint space could become a new paradigm for studying crystal-structure ensembles and global chemical features of the energy landscape. [source] Comparing the accuracy and precision of three techniques used for estimating missing landmarks when reconstructing fossil hominin craniaAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009Rudolph Neeser Abstract Various methodological approaches have been used for reconstructing fossil hominin remains in order to increase sample sizes and to better understand morphological variation. Among these, morphometric quantitative techniques for reconstruction are increasingly common. Here we compare the accuracy of three approaches,mean substitution, thin plate splines, and multiple linear regression,for estimating missing landmarks of damaged fossil specimens. Comparisons are made varying the number of missing landmarks, sample sizes, and the reference species of the population used to perform the estimation. The testing is performed on landmark data from individuals of Homo sapiens, Pan troglodytes and Gorilla gorilla, and nine hominin fossil specimens. Results suggest that when a small, same-species fossil reference sample is available to guide reconstructions, thin plate spline approaches perform best. However, if no such sample is available (or if the species of the damaged individual is uncertain), estimates of missing morphology based on a single individual (or even a small sample) of close taxonomic affinity are less accurate than those based on a large sample of individuals drawn from more distantly related extant populations using a technique (such as a regression method) able to leverage the information (e.g., variation/covariation patterning) contained in this large sample. Thin plate splines also show an unexpectedly large amount of error in estimating landmarks, especially over large areas. Recommendations are made for estimating missing landmarks under various scenarios. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source] Calculation of conformational energies and optical rotation of the most simple chiral alkane,CHIRALITY, Issue 9 2008Stefan Grimme Abstract Quantum chemical calculations have been performed to investigate the conformer distribution of 4-ethyl-4-methyloctane and its optical rotation. With the reference methods MP2 and SCS-MP2, the energies of seven conformers are found within a range of about 1.5 kcal mol,1. It is demonstrated that the relative energies cannot be reliably predicted with conventional GGA or hybrid density functionals, Hartree-Fock, semiempirical AM1, and classical force field (MM3) calculations. An empirical dispersion correction to GGA (PBE-D), hybrid (B3LYP-D), or double hybrid (B2PLYP-D) functionals corrects these errors and results in very good agreement with the reference energies. Optical rotations have been calculated for all seven conformers at the TDDFT(BHLYP/aTZV2P) level. The computed macroscopic rotation is derived from a classical Boltzmann average. The result (1.9,3.2 deg dm,1 (g/mL),1) is very close to the experimental value of 0.2 deg dm,1 (g/mL),1 for the (R)-enantiomer and has the right sign. Because six conformers are significantly populated at room temperature and the rotations of individual conformers differ in sign and magnitude, the calculated average rotation is rather sensitive to the conformer population used. From the electronic structure point of view, this example emphasizes the effect of long-range dispersion effects for the evaluation of population averaged quantities in large molecules. Computations based on free enthalpies are in worse agreement with experiment that is attributed to artefacts of the harmonic approximation used to compute the vibrational entropy terms. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source] Recurrent selection of cocoa populations in Côte d'Ivoire: comparative genetic diversity between the first and second cyclesPLANT BREEDING, Issue 5 2009N. D. Pokou Abstract In Côte d'Ivoire, the cocoa breeding programme has been based on the creation of hybrids between different genetic groups. From 1990 onward, a reciprocal recurrent selection programme has been set up with the purpose of improving simultaneously the characteristics of the two main genetic groups: Upper Amazon Forastero (UA) and a mixture of Lower Amazon Forastero (LA) and Trinitario (T). Based on data obtained from 12 microsatellite primers, the genetic diversity and genetic distances of the parental populations used in the first and second selection cycles are presented. The results revealed that the diversity of populations UA0 and UA1 on the one hand and (LA+T)0 and (LA+T)1 on the other is similar. The genetic distances were small between the parental populations used for the first and second cycles. Genetic diversity was greater in the UA group than in the LA+T group. The number of rare and of private alleles was reduced for both genetic groups, as well as the number of the frequent alleles in the LA+T group. [source] Human cranial anatomy and the differential preservation of population history and climate signaturesTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 12 2006Katerina Harvati Abstract Cranial morphology is widely used to reconstruct evolutionary relationships, but its reliability in reflecting phylogeny and population history has been questioned. Some cranial regions, particularly the face and neurocranium, are believed to be influenced by the environment and prone to convergence. Others, such as the temporal bone, are thought to reflect more accurately phylogenetic relationships. Direct testing of these hypotheses was not possible until the advent of large genetic data sets. The few relevant studies in human populations have had intriguing but possibly conflicting results, probably partly due to methodological differences and to the small numbers of populations used. Here we use three-dimensional (3D) geometric morphometrics methods to test explicitly the ability of cranial shape, size, and relative position/orientation of cranial regions to track population history and climate. Morphological distances among 13 recent human populations were calculated from four 3D landmark data sets, respectively reflecting facial, neurocranial, and temporal bone shape; shape and relative position; overall cranial shape; and centroid sizes. These distances were compared to neutral genetic and climatic distances among the same, or closely matched, populations. Results indicate that neurocranial and temporal bone shape track neutral genetic distances, while facial shape reflects climate; centroid size shows a weak association with climatic variables; and relative position/orientation of cranial regions does not appear correlated with any of these factors. Because different cranial regions preserve population history and climate signatures differentially, caution is suggested when using cranial anatomy for phylogenetic reconstruction. Anat Rec Part A, 2006. © 2006 Wiley-Liss, Inc. [source] | |||||||||||||