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PubMed1980

The influence of sexual and larval selection on the maintenance of polymorphism at the sepia locus in Drosophila melanogaster.

Sexual selection is measured between two strains of Drosophila melanogaster: a wild strain and a strain mutant at the sepia locus. Frequency-dependent male mating was found to successful, whereas the female genotype exerted no influence. The rarer the male genotype becomes, the greater is its mating success. A selection model is build for this behavior characteristic in which selection operates differently in the two sexes. The genetic consequencies of this odel upon the maintenance of genetic polymorphism at the sepia locus are compared to experimental data from previous population cage studies. The fit obtained with this sexual selection model is compared to that of the larval selection model previously investigated. A model composed of both sexual and larval components of fitness is presented. The role that each major selection component is expected to play in experimental populations as the gene frequency changes is discussed. Sexual selection leads to an equilibrium level higher than larval selection, and the combined model is very close to the experimental values.

Animals↗
PubMed2006

Bootstrap model averaging in time series studies of particulate matter air pollution and mortality.

The consensus from time series studies that have investigated the mortality effects of particulate matter air pollution (PM) is that increases in PM are associated with increases in daily mortality. However, recently concerns have been raised that the observed positive association between PM and mortality may be an artefact of model selection due to multiple hypothesis testing. This problem arises when a number of models are investigated, but only the "best" model is reported and all subsequent inference is based on this model, ignoring the model selection process. In this paper, we introduce the use of the bootstrap as a means of addressing the problems of model selection in PM mortality time series studies. Using the bootstrap to perform inference about the effect of PM on mortality is a process based on a set of models rather than on a single model. It is shown that using the bootstrap to overcome the problems of model selection is competitive with the existing methodology of Bayesian model averaging.

Air Pollutants↗
PubMed1986

A neural network model for selective attention in visual pattern recognition.

A neural network model of the mechanism of selective attention in visual pattern recognition is proposed and simulated on a digital computer. When a complex figure consisting of two patterns or more is presented to the model, it is segmented into individual patterns, and each pattern is recognized separately. Even if one of the patterns to which the model is paying selective attention is affected by noise or defects, the model can recall the complete pattern from which the noise has been eliminated and the defects corrected. It is not necessary for perfect recall that the stimulus pattern should be identical in shape to the training pattern. Even though the pattern is distorted in shape or changed in size, it can be correctly recognized and the missing portions restored. The model consists of a hierarchical neural network which has efferent as well as afferent connections between cells. The afferent and the efferent signals interact with each other in the network: the efferent signals, that is, the signals for selective attention, have a facilitating effect on the afferent ones, and, at the same time, the afferent signals gate efferent signal flow. When some feature in the stimulus is not extracted in the afferent paths, the threshold for detection of that feature is automatically lowered by decreasing the efficiency of inhibition, and the model tries to extract even vague traces of the undetected feature.

Afferent Pathways↗
PubMed1989

[Effects of longterm selection on the genetic structure of populations--a simulation study. I. Simulation models and selection responses].

Monte Carlo method has been utilized to investigate responses to longterm selection. The simulation involves 3 gene effect models (additive, dominant, and over-dominant), two population sizes, three linkage intensities, and three heritability levels, thus making 54 combinations. For each combination, 5 replicate populations are selected over 49 consecutive non-overlapping generations. The results demonstrate that under all the gene effect models, linkage is important only in the case of small populations and intense linkage, when it reduces responses significantly due to hampering the fixation of favourable alleles and accelerating their loss. Linkage has no apparent effect if it is not very tight or if the population is large. Much greater responses are achieved in the large populations than in the small ones, especially for traits with low heritability. Among those discussed are problems of crossing selected lines to obtain extra responses, and discrepancy of some theoretic results on selection limits.

Computer Simulation↗
PubMed2000

Akaike's Information Criterion and Recent Developments in Information Complexity.

In this paper we briefly study the basic idea of Akaike's (1973) information criterion (AIC). Then, we present some recent developments on a new entropic or information complexity (ICOMP) criterion of Bozdogan (1988a, 1988b, 1990, 1994d, 1996, 1998a, 1998b) for model selection. A rationale for ICOMP as a model selection criterion is that it combines a badness-of-fit term (such as minus twice the maximum log likelihood) with a measure of complexity of a model differently than AIC, or its variants, by taking into account the interdependencies of the parameter estimates as well as the dependencies of the model residuals. We operationalize the general form of ICOMP based on the quantification of the concept of overall model complexity in terms of the estimated inverse-Fisher information matrix. This approach results in an approximation to the sum of two Kullback-Leibler distances. Using the correlational form of the complexity, we further provide yet another form of ICOMP to take into account the interdependencies (i.e., correlations) among the parameter estimates of the model. Later, we illustrate the practical utility and the importance of this new model selection criterion by providing several real as well as Monte Carlo simulation examples and compare its performance against AIC, or its variants. Copyright 2000 Academic Press.

Journal Article↗
PubMed1976

Some aspects of a stochastic two locus selfing genetic model with selection and computer simulation.

The present paper examines a specific genetic model as a finite Markov process, using the normal matrix approach. This model is the two locus selfing model with selection studied by Tan (1973), who used an eigenvalue approach. The properties of the process are analytically and numerically investigated and the effects of selection and cross-over on the transition from a heterozygotic parent through several generations of heterozygotic progeny are assessed. These results enlarge upon Tan's work and, in addition, present two new aspects of the model. In particular (1) the expected number of generations of heterozygotic progeny of genotype j that will descend from a heterozygotic parent of genotype i and (2) the variance of this number of generations about the mean value have not been previously considered.

Crossing Over, Genetic↗
PubMed2004

An asymptotic maximum principle for essentially linear evolution models.

Recent work on mutation-selection models has revealed that, under specific assumptions on the fitness function and the mutation rates, asymptotic estimates for the leading eigenvalue of the mutation-reproduction matrix may be obtained through a low-dimensional maximum principle in the limit N-->infinity (where N, or N(d) with d> or =1, is proportional to the number of types). In order to extend this variational principle to a larger class of models, we consider here a family of reversible matrices of asymptotic dimension N(d) and identify conditions under which the high-dimensional Rayleigh-Ritz variational problem may be reduced to a low-dimensional one that yields the leading eigenvalue up to an error term of order 1/N. For a large class of mutation-selection models, this implies estimates for the mean fitness, as well as a concentration result for the ancestral distribution of types.

Animals↗
PubMed2006

A new model of selection in women's handball.

The aim of the study was to assess the basic motor abilities that determine top performance in women's handball, and to identify test panel for primary selection at handball school. The study included 155 female attendants of the Split Handball School, mean age 12.5 years. Differences in the basic motor abilities between the subjects that developed into elite handball players after 7-year training process and those that abandoned handball for being unable to meet the competition criteria were evaluated by use of discriminative analysis. The former were found to have also been superior initially in all variables analyzed, and in arm coordination, overall body coordination, throw and jump explosive strength, arm movement frequency and repetitive trunk strength in particular. Motor superiority based on the abilities of coordination, explosive strength and speed determines performance in women's handball, qualifying these abilities as reliable selection criteria. Based on this study results, a new model of selection in women's handball, with fine arm coordination as the major limiting factor of performance, has been proposed.

Child↗
PubMed1999

The role of resource allocation models in selecting clinical preventive services.

OBJECTIVE: To demonstrate the potential value and current limitations of using resource allocation models for selecting health services. DESIGN: To identify the most efficient mix of preventive services that could be offered by a managed care organization (MCO) for a fixed budget, an optimization model (greatest number of life years saved) and a cost-effectiveness model (rank order of most to least cost effective) were developed. Because of the lack of cost-effectiveness analyses that met the study criteria, only 9 preventive services were selected to demonstrate each model. PATIENTS AND METHODS: The 2 models were applied to a hypothetical managed care population of 100,000 enrollees with age, sex, and risk distribution similar to that of the US population. Data for the input variables were obtained from cost-effectiveness studies of 9 preventive services. Model variables included the target population, percent of enrollees who received the preventive service, the cost of the preventive service, life years saved, and cost-effectiveness ratios. RESULTS: The models demonstrated that efficient allocation of finite resources can be achieved. When budgets are limited, different premises between the 2 models may yield different health consequences. However, as the budgets were increased, results from the 2 models were more closely aligned. CONCLUSIONS: Resource allocation models have the potential for assisting MCOs in selecting a set of preventive services that will maximize population health. Before this potential can be fully realized, additional methodological development and cost-effectiveness studies are needed. The use of resource allocation should be examined for selecting all healthcare services.

Budgets↗
PubMed1991

A recruitment model for selecting residents.

The process of selecting residents is an important issue in medical training. In an attempt to quantify and thereby objectify this process, a model for selection was developed. The model, using scaled scores reflective of each of the applicants' characteristics, was used to rank applicants in the Department of Physical Medicine and Rehabilitation at the Medical College of Wisconsin, Milwaukee. Data derived from the selection process were analyzed over a three-year period, 1986-1989. Statistical analysis of the data showed that as few as three experienced faculty members were needed to interview reliably. The statistically significant correlation (p less than .01) between those who interviewed and those who did not interview was necessarily influenced by the fact that those who did not interview had access to the narrative descriptors of those who did. These findings suggest that the use of this recruitment model would permit a more cost-effective approach to the selection of residents.

Cost-Benefit Analysis↗
PubMed2003

Multilevel selection in models of prebiotic evolution: compartments and spatial self-organization.

In this paper we explore the impact of new levels of selection in models of early evolution. We contrast two types of higher levels of selection. On the one hand we look at spatially explicit models of replicators in which, by a process of self-organization, new levels of selection arise as large scale spatial patterns with a dynamics of their own. Alternatively externally imposed levels of selection above the basic replicators are created by enclosing the replicators in vesicles. In this paper we first review some results on the impact of emerging higher levels of selection on the evolutionary persistence of interacting co-evolving replicator systems. Moreover, we present a vesicle model, which can potentially integrate emerging and imposed levels of selection. We use the models to examine the classical problem information integration in early evolution.

Biological Evolution↗
PubMed2001

Perfect simulation from population genetic models with selection.

We consider using the ancestral selection graph (ASG) to simulate samples from population genetic models with selection. Currently the use of the ASG to simulate samples is limited. This is because the computational requirement for simulating samples increases exponentially with the selection rate and also due to needing to simulate a sample of size one from the population at equilibrium. For the only case where the distribution of a sample of size one is known, that of parent-independent mutations, more efficient simulation algorithms exist. We will show that by applying the idea of coupling from the past to the ASG, samples can be simulated from a general K-allele model without knowledge of the distribution of a sample of size one. Furthermore, the computation involved in generating such samples appears to be less than that of simulating the ASG until its ultimate ancestor. In particular, in the case of genic selection with parent-independent mutations, the computational requirement increases only quadratically with the selection rate. The algorithm is demonstrated by simulating samples at a microsatellite locus.

Algorithms↗
PubMed2000

Development of an animal model of selective coronary atherosclerosis.

BACKGROUND: Atherosclerosis causes over 40% of all deaths in the USA and Western Europe. Although several hypotheses have been proposed, the etiology and pathogenesis of the atherosclerosis remain unknown. OBJECTIVE: To develop a model of selective coronary atherosclerosis in pigs. DESIGN: An animal model of selective coronary atherosclerosis was developed by combining a guide-wire-induced endothelial injury and cholesterol-enriched diet. METHODS: Twelve pigs were subjected to guide-wire-induced injury to endothelium of left anterior descending (LAD) coronary artery. Six animals (control group) were fed a standard pig food; the remaining six animals (cholesterol group) were fed a 6%-cholesterol-enriched diet. Three animals from the control group were killed immediately after the endothelial injury (acute control group). The other three animals in the control group (chronic control group) and all animals in the cholesterol-fed group were killed 4 weeks after the injury. RESULTS: The endothelial surface and the media of the left circumflex coronary artery LCX in all animals were intact. Long eccentric areas of endothelial injury were found in the LAD coronary arteries of animals in the acute control group. Numerous fibrous atherosclerotic plaques in LAD coronary arteries were found in animals in the chronic control group as well as in animals in the cholesterol-fed group, but were highly pronounced in animals in the last group. No accumulation of lipids was found in the plaques of animals in both groups. CONCLUSIONS: Administration of a 6%-cholesterol diet for 6 weeks is not sufficient to cause coronary atherosclerosis in pigs. Selective coronary atherosclerosis can be induced within 4 weeks with the same diet when the blood vessel has been injured with a guide wire.

Animals↗
PubMed1983

Selecting a model for use in curriculum evaluation.

In summary, our purposes have been to emphasize the importance of using a model in curriculum evaluation and to present guidelines for selecting an appropriate model. We have discussed our experience in selecting and using the Stake model only as an example. While a model does not eliminate all of the problems and frustrations of curriculum evaluation, it does make the task more manageable. It can also improve the quality of the evaluation and can even make curriculum evaluation enjoyable.

Curriculum↗
PubMed2004

Quantitative determination of low density lipoprotein oxidation by FTIR and chemometric analysis.

This study was conducted to develop a quantitative FTIR spectroscopy method to measure LDL lipid oxidation products and determine the effect of oxidation on LDL lipid and protein. In vitro LDL oxidation at 37 degrees C for 1 h produced a range of conjugated diene (CD) (0.14-0.26 mM/mg protein) and carbonyl contents (0.9-3.8 microg/g protein) that were used to produce calibration sets. Spectra were collected from the calibration set and partial least squares regression was used to develop calibration models from spectral regions 4000-650, 3750-3000, 1720-1500, and 1180-935 cm(-1) to predict CD and carbonyl contents. The optimal models were selected based on their standard error of prediction (SEP), and the selected models were performance-tested with an additional set of LDL spectra. The best models for CD prediction were derived from spectral regions 4000-650 and 1180-935 cm(-1) with the lowest SEP of 0.013 and 0.013 mM/mg protein, respectively. The peaks at 1745 (cholesterol and TAG ester C=O stretch), 1710 (carbonyl C-O stretch), and 1621 cm(-1) (peptide C=O stretch) positively correlated with LDL oxidation. FTIR and chemometrics revealed protein conformational changes during LDL oxidation and provided a simple technique that has potential for rapidly observing structural changes in human LDL during oxidation and for measuring primary and secondary oxidation products.

Humans↗
PubMed2003

Mechanisms and models for anaerobic granulation in upflow anaerobic sludge blanket reactor.

Upflow anaerobic sludge blanket (UASB) reactor has been employed in industrial and municipal wastewater treatment for decades. However, the long start-up period required for the development of anaerobic granules seriously limits the application of this technology. In order to develop the strategy for rapid UASB start-up, the mechanisms for anaerobic granulation should be understood. This paper attempts to provide a up-to-date review on the existing mechanisms and models for anaerobic granulation in the UASB reactor, which include inert nuclei model, selection pressure model, multi-valence positive ion-bonding model, synthetic and natural polymer-bonding model, Capetown's model, spaghetti theory, syntrophic microcolony model, multi-layer model, secondary minimum adhesion model, local dehydration and hydrophobic interaction model, surface tension model, proton translocation-dehydration theory, cellular automaton model and cell-to-cell communication model. Based on those previous works, a general model for anaerobic granulation is also proposed. It is expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of the UASB granules.

Bacteria, Anaerobic↗
PubMedDate not supplied

Evaluation of polyvinyl acetate dispersion as a sustained release polymer for tablets.

Kollicoat SR 30D is a unique 30% aqueous dispersion of polyvinvyl acetate stabilized by polyvinyl-pyrrolidone intended for preparation of sustained release products. Detailed evaluation of this polymer dispersion as a sustained release coating for active pharmaceutical ingredients of two diverse classes of drugs was studied. A water insoluble drug (ibuprofen) and a water soluble drug (ascorbic acid) were selected as model active drugs. Ibuprofen was granulated using a GPCG-1 fluid bed processor prior to tableting, to improve the particle size and particle flow properties. In this process a 2(3) factorial design was implemented to evaluate the optimum process parameters such as spray rate, inlet air temperature and the inlet air velocity. The statistical model selected was Y(ijkl) = mu + tau(i) + beta(j) + theta(k) + (taubeta)ij + (betatheta)jk + (tautheta)ik + (taubetatheta)ijk + epsilon(ijkl). The factorial design showed that the spray rate, inlet air temperature, and inlet air velocity had a significant effect (p value <0.05) on the particle size. Significant improvement was observed in the flow properties of the granules. The granules were coated with Kollicoat SR30D dispersion using top spray method in the fluid bed processor. The dissolution studies showed that the release of ibuprofen decreased with an increase in the coating levels of Kollicoat SR 30 D. In the case of ascorbic acid, preparation of sustained release coated commercial granules was not possible due to the difficulty in coating a highly soluble drug particle. However, the coated granules when compressed into tablets showed some sustainability. Ibuprofen tablets manufactured with coated granules with a 15 g polymer for 300 g batch showed dissolution parameters of t50 and t90 at 4.2 hr and 7.5 hr, respectively. An approximate zero-type of release was observed when the polymer content was increased to 45 g for 300 g batch. Ascorbic acid tablets made with coated commercial granules having a total polymer content of 45 g per a 500 g batch showed an average dissolution t50 and t90 at 1.0 hr and 4.55 hr, respectively. When the total polymer content was increased to 60 g, per 500 g, the average dissolution t50 and t90 delayed to 1.40 hr and 7.20 hr, respectively.

Analysis of Variance↗
PubMed2004

How can statistical approaches enhance transdisciplinary study of drug misuse prevention?

Application of statistical techniques in transdisciplinary research includes statistical model selection and model specification. This paper presents statistical models used in drug misuse prevention research. The historical roots of these models are discussed to illustrate the numerous disciplines from which different techniques originated. Single and multilevel approaches are described to illustrate methods of synthesizing perspectives from different scientific arenas. Using single-level approaches in transdisciplinary research, these models can easily incorporate broader theoretical considerations and more integrated hypotheses by representing each discipline with a set of variables. Simultaneous testing of every set of variables obtained from different disciplines may provide more comparable results to identify critical factors associated with substance-use behavior. Using multilevel approaches, more powerful syntheses across disciplines can be achieved by representing each discipline at a different level.

Biomedical Research↗