Bottleneck effect on genetic variance. A theoretical investigation of the role of dominance

The phenomenon that the genetic variance of fitness components increase following a bottleneck or inbreeding is supported by a growing number of experiments and is explained theoretically by either dominance or epistasis. In this article, diffusion approximations under the infinite sites model are used to quantify the effect of dominance, using data on viability in Drosophila melanogaster. The model is based on mutation parameters from mutation accumulation experiments involving balancer chromosomes (set I) or inbred lines (set II). In essence, set I assumes many mutations of small effect, whereas set II assumes fewer mutations of large effect. Compared to empirical estimates from large outbred populations, set I predicts reasonable genetic variances but too low mean viability. In contrast, set II predicts a reasonable mean viability but a low genetic variance. Both sets of parameters predict the changes in mean viability (depression), additive variance, between-line variance and heritability following bottlenecks generally compatible with empirical results, and these changes are mainly caused by lethals and deleterious mutants of large effect. This article suggests that dominance is the main cause for increased genetic variances for fitness components and fitness-related traits after bottlenecks observed in various experiments.     

Confounding of sources of variation in factor-analytic techniques.

Illustrates a statistical model which is a 2-way analysis of variance model which requires that factor-analytic techniques be used to decompose the interaction parameters. Factor-analytic techniques are commonly applied directly to matrices which contain a grand mean and/or row and/or column effects in addition to row * column interaction. Each factor obtained from such an analysis will generally account for variation due to all sources of variation present in the initial matrix. Some ways in which such confounding of sources of variation causes difficulties in making valid interpretations of factors are discussed. Special attention is given to the problem of describing individual differences in patterns of performance on a set of measurements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Validation of Streamflow Measurements Made with Acoustic Doppler Current Profilers

The U.S. Geological Survey and other international agencies have collaborated to conduct laboratory and field validations of acoustic Doppler current profiler (ADCP) measurements of streamflow. Laboratory validations made in a large towing basin show that the mean differences between tow cart velocity and ADCP bottom-track and water-track velocities were ?0.51 and ?1.10%, respectively. Field validations of commercially available ADCPs were conducted by comparing streamflow measurements made with ADCPs to reference streamflow measurements obtained from concurrent mechanical current-meter measurements, stable rating curves, salt-dilution measurements, or acoustic velocity meters. Data from 1,032 transects, comprising 100 discharge measurements, were analyzed from 22 sites in the United States, Canada, Sweden, and The Netherlands. Results of these analyses show that broadband ADCP streamflow measurements are unbiased when compared to the reference discharges regardless of the water mode used for making the measurement. Measurement duration is more important than the number of transects for reducing the uncertainty of the ADCP streamflow measurement.     

Fluid flow in porous systems

Nuclear magnetic resonance (NMR) measurements of water velocity flowing through glass bead packs with a bead diameter of 10 mm have been made using the phi echo-planar imaging (PEPI) sequence. These results indicate that for various flow rates the flow variance is proportional to the mean flow velocity in agreement with the Mansfield-Issa equation. The velocity distributions are approximately Gaussian. Investigation of the slopes of the variance vs. velocity curves as a function of slice thickness indicate some coherence effects in the connectivity of the glass bead system. An extension of an earlier intervoxel coupling model is presented, which seems to explain the observed coherence effects.     

Application of Acoustic Doppler Velocimeters for Streamflow Measurements

The U.S. Geological Survey (USGS) principally has used Price AA and Price pygmy mechanical current meters for measurement of discharge. New technologies have resulted in the introduction of alternatives to the Price meters. One alternative, the FlowTracker acoustic Doppler velocimeter, was designed by SonTek/YSI to make streamflow measurements in wadeable conditions. The device measures a point velocity and can be used with standard midsection method algorithms to compute streamflow. The USGS collected 55 quality-assurance measurements with the FlowTracker at 43 different USGS streamflow-gaging stations across the United States, with mean depths from 0.05?to?0.67?m, mean velocities from 13?to?60?cm/s, and discharges from 0.02?to?12.4?m3/s. These measurements were compared with Price mechanical current meter measurements. Analysis of the comparisons shows that the FlowTracker discharges were not statistically different from the Price meter discharges at a 95% confidence level.     

Localization of cholecystokinin-like peptide in neuroendocrine cells of mammalian lungs: a light and electron microscopic immunohistochemical study

Mixing of starved cells of complementary mating types of Tetrahymena thermophila induces shortening of their longitudinal length within 10 min of mixing. This early morphogenetic transformation in preconjugant sexual interaction (costimulation period) was named "costimulation-induced rounding" (CIR). CIR is the earliest morphological change that has ever been found in the costimulation period and differs from "synchronous rounding" in the vegetative cell cycle, because CIR cells are still able to form food vacuoles, while cells in synchronous rounding do not have this ability. When sexual cell-to-cell collisions between two mating types were hampered by unidirectional stirring for 20 min after mixing of the two mating types, both CIR and conjugation were delayed by 20 min. When secreted materials needed for the onset of costimulation were removed by washing the cells with 10 mM Tris-HCl, pH 7.4, before mixing the two mating types, both CIR and conjugation were delayed by about 30 min. CIR-like rounding was not induced by cell-free medium either from the opposite mating type or from mixed costimulated cells. These results indicated that CIR is induced when cells are activated to form conjugating pairs by cell-to-cell collisions between complementary mating types in the presence of secreted molecules.     

Erythrocyte Na+/Li+ countertransport and Na+/K+-2Cl- co-transport measurement in essential hypertension: useful diagnostic tools or failure? A meta-analysis of 17 years of literature

1.A meta-analysis of 17 years of literature on erythrocyte Na+/Li+ countertransport (NLCT) and Na+/K+ co-transport (COT) measurements in relation to essential hypertension is presented. The analysis aimed to answer two questions: (i) Which clinical or laboratory variables influence NLCT and COT flux values? (ii) How useful are NLCT and COT measurements as a diagnostic aid in essential hypertension?2. Regression analysis was performed on the mean flux values and relevant clinical and laboratory values. Studies in both normotensive and hypertensive subjects were stratified for variables which showed a significant association with the measured flux. For hypertensive subjects the studies were also stratified for medication. Means of strata were calculated after weighing the mean of a study by the inverse of its own variance and were compared in normotensive as well as hypertensive subjects using a t-test.3.The analysis did not demonstrate systematic effects of laboratory variables for either NLCT or COT. It was found that essential hypertension, family history of hypertension, gender and antihypertensive medication are main determinants for the flux values of both transport systems. After stratification for these determinants, significant differences in weighed mean flux values between normotensive and hypertensive subjects were demonstrated. However, these differences are much smaller than the variance in the weighed mean flux values, suggesting the existence of other unknown variables that strongly affect the flux rates.4.In conclusion, NLCT and COT measurements cannot be of diagnostic use in essential hypertension.     

Multivariate analysis of variance by multiple regression methods.

Discusses multivariate analysis of variance as a general case of familiar multiple regression analysis. A consequence of this approach is a unified treatment of multivariate analysis of variance which can be used by psychologists who are generally familiar with multiple regression approaches to univariate analysis of variance. It is suggested that the generality of the approach permits solutions consistent with any of the several available strategies for dealing with problems of unequal and disproportionate cell frequencies. Inherent in the multiple regression formulation is the otherwise not so obvious fact that univariate analysis of variance results are an integral part of the multivariate solution and that both are important for understanding complex data. Methods of interpreting multivariate analysis of variance results in complex factorial experimental designs are discussed. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Regularized reconstruction in electrical impedance tomography using a variance uniformization constraint

This paper describes a new approach to reconstruction of the conductivity field in electrical impedance tomography. Our goal is to improve the tradeoff between the quality of the images and the numerical complexity of the reconstruction method. In order to reduce the computational load, we adopt a linearized approximation to the forward problem that describes the relationship between the unknown conductivity and the measurements. In this framework, we focus on finding a proper way to cope with the ill-posed nature of the problem, mainly caused by strong attenuation phenomena; this is done by devising regularization techniques well suited to this particular problem. First, we propose a solution which is based on Tikhonov regularization of the problem. Second, we introduce an original regularized reconstruction method in which the regularization matrix is determined by space-uniformization of the variance of the reconstructed condictivities. Both methods are nonsupervised, i.e., all tuning parameters are automatically determined from the measured data. Tests performed on simulated and real data indicate that Tikhonov regularization provides results similar to those obtained with iterative methods, but with a much smaller amount of computations. Regularization using a variance uniformization constraint yields further improvements, particularly in the central region of the unknown object where attenuation is most severe. We anticipate that the variance uniformization approach could be adapted to iterative methods that preserve the nonlinearity of the forward problem. More generally, it appears as a useful tool for solving other severely ill-posed reconstruction problems such as eddy current tomography.     

Detection of the phosphorylcholine epitope in streptococci, Haemophilus and pathogenic Neisseriae by immunoblotting

Intimal-medial thickness (IMT) of the extracranial carotid arteries measured by B-mode ultrasonography has been used as a marker of systemic and coronary atherosclerosis. Previous studies have indicated that maximum and mean carotid IMT are significantly correlated with the extent and severity of coronary artery disease (CAD), but the clinical usefulness of these markers is limited because they are neither specific nor sensitive enough to identify patients with or without significant CAD. The correlation of a new IMT marker, variance of IMT, with coronary risk factors and coronary atherosclerosis was investigated in 200 patients who underwent carotid ultrasonography and coronary angiography. IMT was measured in 16 sites of the extracranial carotid arteries for the calculation of mean, maximum and variance of IMT. Univariate analysis showed that these three indexes were significantly correlated with age, serum lipoprotein (a) and hypertension. However, age was correlated weakly with variance of IMT. There were significant gender differences in the mean and maximum IMT but not in the variance. There were also significant correlations of mean IMT with smoking, and maximum and variance of IMT with high-density lipoprotein. Multiple logistic regression analysis in 100 age and sex matched patients indicated that the only significant predictor for CAD in this subgroup was variance of IMT (odds ratio = 1.6). These results indicated that each risk factor causes different morphologic manifestations in the carotid atherosclerotic lesion. Variance of IMT, which represents the irregularity of carotid IMT, was correlated well with CAD and appears to be useful for assessing systemic and coronary atherosclerosis.     

Reaeration Equations Derived from U.S. Geological Survey Database

Accurate estimation of the reaeration-rate coefficient (K2) is extremely important for waste-load allocation. Currently, available K2 estimation equations generally yield poor estimates when applied to stream conditions different from those for which the equations were derived because they were derived from small databases composed of potentially highly inaccurate measurements. A large data set of K2 measurements made with tracer-gas methods was compiled from U.S. Geological Survey studies. This compilation included 493 reaches on 166 streams in 23 states. Careful screening to detect and eliminate erroneous measurements reduced the data set to 371 measurements. These measurements were divided into four subgroups on the basis of flow regime (channel control or pool and riffle) and stream scale (discharge greater than or less than 0.556 m3∕s). Multiple linear regression in logarithms was applied to relate K2 to 12 stream hydraulic and water-quality characteristics. The resulting best-estimation equations had the form of semiempirical equations that included the rate of energy dissipation and discharge or depth and width as variables. For equation verification, a data set of K2 measurements made with tracer-gas procedures by other agencies was compiled from the literature. This compilation included 127 reaches on at least 24 streams in at least seven states. The standard error of estimate obtained when applying the developed equations to the U.S. Geological Survey data set ranged from 44 to 61%, whereas the standard error of estimate was 78% when applied to the verification data set.     

Early development of spiny neurons in fish and mouse: morphometric measures of dendritic spine formation pattern

Positions of spines on apical dendrites were evaluated using 4 pattern analysis techniques: spine counts, variance/mean ratio, Lloyd's patchiness index, and nearest neighbor distance matrix. Spiny tectal interneurons from jewel fish (100, 130, 160 and 1550 days old), and layer V pyramidal cells in layer IV auditory cortex of CBA/J mice (100 and 450 days old) were studied. Fish's spines became more numerous and more clumped on distal dendritic strata during development, while mice lost dendritic spines with age. Both species developed a significantly regular spacing pattern between neighboring spines during development. These changes are explained in the context of spine function and a biophysical model of dendritic spine patterns.     

Geographic variations of life history strategies in Drosophila melanogaster. III. New data

A crucial assumption of evolutionary theories of aging is that age-specific differences of life history traits may have genetic causes. The present study focuses on the existence of such differences between eight freshly caught populations of Drosophila melanogaster. A highly significant differentiation of the populations is observed, yet it accounts for a relatively small part of the variance. It is also shown that large discrepancies may be found between the estimations of fitness based, on the one hand, on data for egg production and, on the other hand, on fertility data. This stresses the need for accurate measurements of fitness for the assessment of evolutionary theories. Finally, the results suggest that neither of the current evolutionary theories of aging is generally valid. Indeed, the age-specific differences that are found between the populations match either the antagonistic pleiotropy mechanism, or the concordant pleiotropy mechanism, or none of them.     

Assessment of weighting methodology for the National Comorbidity Survey

The authors studied weighting adjustments for the National Comorbidity Survey (1990-1992), a large-scale national epidemiologic investigation of the prevalence, risk factors, and consequences of psychiatric morbidity and comorbidity in the United States. Weighting adjustments for differential selection within households, new construction, unit nonresponse, and poststratification were examined separately and in combination. Specific issues addressed included the magnitude of the bias incurred from ignoring the weights, the added variance from weighting and how well this was predicted by simple formulae, and the performance of methods for trimming the weights. Weights had quite modest effects on point estimates of prevalences but resulted in major increases in variance unless trimmed. The weights after trimming and poststratification appeared to work well. It is suggested that the added variance from weighting be carefully monitored in similar surveys. Alternatives to the use of trimming for controlling variance are worth exploring.     

Design of HIV viral dynamics studies

HIV viral dynamics studies involve repeated measurement of viral load in HIV-infected individuals, to assess short-term rates of viral load change in response to interventions such as initiation or withdrawal of antiviral therapy. Such studies are an important source of information on HIV pathogenesis. This paper concerns some statistical issues arising in their design. Using a linear random-effects model to incorporate between-patient differences in rates of viral load change, I discuss the choice of number of individuals and frequency of observation per individual. I suggest an approach for calculating the optimal sample size and observation frequency, based on minimizing the total number of viral load measurements that one needs to undertake. The conclusion, using this approach, is that over a period of linear change in viral load, three to five measurements per individual is generally appropriate. I also examine the observation frequency when the number of available individuals is limited, in which case it is shown that one can use a higher frequency of measurement per individual to achieve adequate power or precision. Finally, I consider sources of data for prior specification of variance components, together with conservative designs that are insensitive to a lack of prior information about between-patient differences.     

The Carlson Psychological Survey with adolescents: Norms and scales reliabilities.

Examined psychometric properties of the Carlson Psychological Survey by K. A. Carlson (1981) in a sample of 410 male adolescent offenders (mean age 15 yrs). The test's 4 content scales (Chemical Abuse, Thought Disturbance, Antisocial Tendencies, and Self-Depreciation) were found to be internally consistent; reliable over time; moderately intercorrelated; and generally unrelated to age, IQ, or scores on the Marlowe-Crowne Social Desirability Scale. The Carlson Psychological Survey is recommended as a personality screening test for young offenders. (French abstract) (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fluid transport in glass beads phantoms: spatial velocity measurements and confirmation of the stochastic model

A stochastic model of fluid flow in porous rocks has been previously developed to explain the measured distribution of local velocity. The theoretical predictions of this model agree well with experimental results obtained from the magnetic resonance imaging-based measurements of the spatial variation of velocity of water permeating through Bentheimer and Clashach sandstones. To further verify previous results, we have performed new velocity measurement experiments using an efficient velocity encoded pi-echo planar imaging sequence on glass bead phantoms that exhibit more regular pore size distribution than rocks. The results show that velocity distributions in glass bead phantoms also exhibit Gaussian profiles and the linear relationship between the velocity variance and the mean velocity (the Mansfield-Issa equation).     

分析测试中测量不确定度及评定 第三部分 分析测试中主要不确定度分量的评定

概述了分析测试中溶液体积测量、物质称量、长度测量、标准物质量值、工作曲线、分析方法、测量重复性、测量仪器读数的分辨力、数字修约等主要不确定度分量的评定方法,并就温度对溶液体积影响等问题进行深入讨论。     

Physique as a risk factor for ulnar variance in elite female gymnasts

The aims of this study were: 1) to determine ulnar variance variability of elite, female gymnasts; 2) to evaluate the relationship between ulnar variance and physique, maturity status, and training characteristics of these gymnasts. All 156 skeletally immature female gymnasts were participants at the World Championships Artistic Gymnastics, Rotterdam, The Netherlands, in 1987. Chronological ages varied between 13.1 and 20.6 yr (mean = 15.9 +/- 1.3 yr). A large set of anthropometric dimensions was taken and somatotype was determined by the Heath-Carter technique. Skeletal age was assessed by the Tanner-Whitehouse II method. Menarcheal status and training data were collected by questionnaire. Ulnar variance was determined according to Hafner et al. Gymnasts differ significantly from reference girls with respect to physique and maturational status: gymnasts were smaller and delayed in skeletal maturity with about 1.5 yr. For those who had attained menarche, mean age at menarche was 15.1 +/- 1.3 yr. Ulnar variance shows a normal distribution in the gymnasts, ranging from -10.5 mm to +5.9 mm, which is somewhat more positive, i.e., an ulnar overgrowth, than reference wrists. The relationship between ulnar variance and somatic and maturational features suggests that female gymnasts who are more mature and have a physique characterized as relatively tall with a high lean body mass are at greater risk for developing a positive ulnar variance. No relationship between ulnar variance and training characteristics was evident. It is concluded that the observed positive ulnar variance in this sample of elite female gymnasts is less pronounced than originally stated in most "case reports."     

A median-based test under informative dropout: the one-sample case

We consider a clinical trial in which the outcome can be assessed by a continuous measure and where dropouts tend to have poorer efficacy than completers. When each subject can act as his/her own control, efficacy is measured by the difference between the outcome measurements at two times. When all subjects complete the protocol, a paired t-test can be used to test for a treatment effect, i.e., whether or not the mean difference is zero. When a patient does not return for the final evaluation, a measure of efficacy cannot be computed for that subject. Often, data from dropouts are ignored and only the observed pairs are used to analyze the data. When the reason for dropping out is not random, the result may be misleading. In this paper, we assume that (1) the distribution of the measure of efficacy (i.e., the change between two outcome measurements) is Gaussian, (2) dropouts would have worse efficacy than the median if they were observed, and (3) the dropout rate is less than 50%. We propose a median-based t-like statistic using the sample median in place of the sample mean. The variance of the median is estimated using only data from the complete half-sample, i.e., the half-sample with better efficacy. Simulations under five patterns of dropouts are performed to compare the proposed statistic with the paired t-test. The results show that the median-based statistic provides a conservative bound for the test of significance of the treatment. In contrast, because the paired t-test does not preserve its level of significance, except when the dropout mechanism is uniform, the paired t-test should not be used for trials in which dropouts tend to have poorer efficacy than completers.