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1

Phenotypically heterogeneous populations in spatially heterogeneous environments  

NASA Astrophysics Data System (ADS)

The spatial expansion of a population in a nonuniform environment may benefit from phenotypic heterogeneity with interconverting subpopulations using different survival strategies. We analyze the crossing of an antibiotic-containing environment by a bacterial population consisting of rapidly growing normal cells and slow-growing, but antibiotic-tolerant persister cells. The dynamics of crossing is characterized by mean first arrival times and is found to be surprisingly complex. It displays three distinct regimes with different scaling behavior that can be understood based on an analytical approximation. Our results suggest that a phenotypically heterogeneous population has a fitness advantage in nonuniform environments and can spread more rapidly than a homogeneous population.

Patra, Pintu; Klumpp, Stefan

2014-03-01

2

Specialization and Bet Hedging in Heterogeneous Populations  

NASA Astrophysics Data System (ADS)

Phenotypic heterogeneity is a strategy commonly used by bacteria to rapidly adapt to changing environmental conditions. Here, we study the interplay between phenotypic heterogeneity and genetic diversity in spatially extended populations. By analyzing the spatiotemporal dynamics, we show that the level of mobility and the type of competition qualitatively influence the persistence of phenotypic heterogeneity. While direct competition generally promotes persistence of phenotypic heterogeneity, specialization dominates in models with indirect competition irrespective of the degree of mobility.

Rulands, Steffen; Jahn, David; Frey, Erwin

2014-09-01

3

Eradication of infectious diseases in heterogeneous populations  

SciTech Connect

A model is presented of infectious disease in heterogeneous populations, which allows for variable intra- to intergroup contact ratios. The authors give necessary and sufficient conditions for disease eradication by means of vaccination. Smallpox is used as an illustrative example.

Travis, C.C.; Lenhart, S.M.

1987-04-01

4

Population dynamics on heterogeneous bacterial substrates  

NASA Astrophysics Data System (ADS)

How species invade new territories and how these range expansions influence the population's genotypes are important questions in the field of population genetics. The majority of work addressing these questions focuses on homogeneous environments. Much less is known about the population dynamics and population genetics when the environmental conditions are heterogeneous in space. To better understand range expansions in two-dimensional heterogeneous environments, we employ a system of bacteria and bacteriophage, the viruses of bacteria. Thereby, the bacteria constitute the environment in which a population of bacteriophages expands. The spread of phage constitutes itself in lysis of bacteria and thus formation of clear regions on bacterial lawns, called plaques. We study the population dynamics and genetics of the expanding page for various patterns of environments.

Mobius, Wolfram; Murray, Andrew W.; Nelson, David R.

2012-02-01

5

Range Expansion of Heterogeneous Populations  

NASA Astrophysics Data System (ADS)

Risk spreading in bacterial populations is generally regarded as a strategy to maximize survival. Here, we study its role during range expansion of a genetically diverse population where growth and motility are two alternative traits. We find that during the initial expansion phase fast-growing cells do have a selective advantage. By contrast, asymptotically, generalists balancing motility and reproduction are evolutionarily most successful. These findings are rationalized by a set of coupled Fisher equations complemented by stochastic simulations.

Reiter, Matthias; Rulands, Steffen; Frey, Erwin

2014-04-01

6

Heterogeneity in the muscle satellite cell population  

PubMed Central

Satellite cells, the adult stem cells responsible for skeletal muscle regeneration, are defined by their location between the basal lamina and the fiber sarcolemma. Increasing evidence suggests that satellite cells represent a heterogeneous population of cells with distinct embryological origin and multiple levels of biochemical and functional diversity. This review focuses on the rich diversity of the satellite cell population based on studies across species. Ultimately, a more complete characterization of the heterogeneity of satellite cells will be essential to understand the functional significance in terms of muscle growth, homeostasis, tissue repair, and aging. PMID:20849971

Biressi, Stefano; Rando, Thomas A.

2010-01-01

7

Optical metabolic imaging quantifies heterogeneous cell populations  

PubMed Central

The genetic and phenotypic heterogeneity of cancers can contribute to tumor aggressiveness, invasion, and resistance to therapy. Fluorescence imaging occupies a unique niche to investigate tumor heterogeneity due to its high resolution and molecular specificity. Here, heterogeneous populations are identified and quantified by combined optical metabolic imaging and subpopulation analysis (OMI-SPA). OMI probes the fluorescence intensities and lifetimes of metabolic enzymes in cells to provide images of cellular metabolism, and SPA models cell populations as mixed Gaussian distributions to identify cell subpopulations. In this study, OMI-SPA is characterized by simulation experiments and validated with cell experiments. To generate heterogeneous populations, two breast cancer cell lines, SKBr3 and MDA-MB-231, were co-cultured at varying proportions. OMI-SPA correctly identifies two populations with minimal mean and proportion error using the optical redox ratio (fluorescence intensity of NAD(P)H divided by the intensity of FAD), mean NAD(P)H fluorescence lifetime, and OMI index. Simulation experiments characterized the relationships between sample size, data standard deviation, and subpopulation mean separation distance required for OMI-SPA to identify subpopulations. PMID:25780745

Walsh, Alex J.; Skala, Melissa C.

2015-01-01

8

The Oldest Old and the Population Heterogeneity  

NASA Astrophysics Data System (ADS)

We have simulated the effect of the diversity of the late expressed genes in the genetic pool of population on the phenotypes of individuals in the late ages. Using Penna model based on the Monte Carlo method we have obtained for the oldest fractions of populations lower mortality rates than predicted by the exponential Gompertz function. Such deviations from the expected exponential increase of mortality are the characteristic for populations which are not in equilibrium with the environment, or if a relatively high probability of reversions was assumed, or if the population is heterogeneous. In such populations, the genes expressed in the late ages, are under the very weak selection pressure and thus, highly-polymorphic. As an effect, the probability of the genetically-determined death of the oldest organisms does not grow as fast as predicted by the Gompertz exponential curve describing mortality during earlier periods of life.

?aszkiewicz, A.; Szymczak, Sz.; Cebrat, S.

9

Population turnover and adaptation in heterogeneous environments  

NASA Astrophysics Data System (ADS)

We study adaptive dynamics in a structured population model of asexual individuals which takes into account environmental heterogeneity among the subpopulations. The key purpose of the present work is to address how population turnovers, i.e. extinction events followed by recolonization, affect the rate of fixation of advantageous mutations. This model is a generalization of our previous model to address the interplay between environmental correlation and evolutionary forces on the adaptive process. The incorporation of population turnovers into the model enables us to make a direct correspondence between the model and host-parasite dynamics (epidemiological models). Strikingly, contrary to the intuitive and usual deleterious effect associated to extinction events, it is observed that population turnovers can in fact speed up adaptation as heterogeneity rises. On the other side, in nearly homogeneous population turnovers have a neutral effect on fixation rates, but a detrimental outcome is also achieved when extinction events become very common. In resume, population turnover outcomes on fixation rates of advantageous mutations are strongly influenced by the selective correlation among the subpopulations (demes).

Campos, Paulo R. A.; de Oliveira, Viviane M.

2012-02-01

10

Stochastic population growth in spatially heterogeneous environments.  

PubMed

Classical ecological theory predicts that environmental stochasticity increases extinction risk by reducing the average per-capita growth rate of populations. For sedentary populations in a spatially homogeneous yet temporally variable environment, a simple model of population growth is a stochastic differential equation dZ(t) = ?Z(t)dt + ?Z(t)dW(t), t ? 0, where the conditional law of Z(t+?t)-Z(t) given Z(t) = z has mean and variance approximately z ??t and z²?²?t when the time increment ?t is small. The long-term stochastic growth rate lim(t??) t?¹ log Z(t) for such a population equals ? ? ?²/2 . Most populations, however, experience spatial as well as temporal variability. To understand the interactive effects of environmental stochasticity, spatial heterogeneity, and dispersal on population growth, we study an analogous model X(t) = (X¹(t) , . . . , X(n)(t)), t ? 0, for the population abundances in n patches: the conditional law of X(t+?t) given X(t) = x is such that the conditional mean of X(i)(t+?t) ? X(i)(t) is approximately [x(i)?(i) + ?(j) (x(j) D(ji) ? x(i) D(i j) )]?t where ?(i) is the per capita growth rate in the ith patch and D(ij) is the dispersal rate from the ith patch to the jth patch, and the conditional covariance of X(i)(t+?t)? X(i)(t) and X(j)(t+?t) ? X(j)(t) is approximately x(i)x(j)?(ij)?t for some covariance matrix ? = (?(ij)). We show for such a spatially extended population that if S(t) = X¹(t)+· · ·+ X(n)(t) denotes the total population abundance, then Y(t) = X(t)/S(t), the vector of patch proportions, converges in law to a random vector Y(?) as t ? ?, and the stochastic growth rate lim(t??) t?¹ log S(t) equals the space-time average per-capita growth rate ?(i)?(i)E[Y(i)(?)] experienced by the population minus half of the space-time average temporal variation E[?(i,j) ?(i j)Y(i)(?) Y(j)(?)] experienced by the population. Using this characterization of the stochastic growth rate, we derive an explicit expression for the stochastic growth rate for populations living in two patches, determine which choices of the dispersal matrix D produce the maximal stochastic growth rate for a freely dispersing population, derive an analytic approximation of the stochastic growth rate for dispersal limited populations, and use group theoretic techniques to approximate the stochastic growth rate for populations living in multi-scale landscapes (e.g. insects on plants in meadows on islands). Our results provide fundamental insights into "ideal free" movement in the face of uncertainty, the persistence of coupled sink populations, the evolution of dispersal rates, and the single large or several small (SLOSS) debate in conservation biology. For example, our analysis implies that even in the absence of density-dependent feedbacks, ideal-free dispersers occupy multiple patches in spatially heterogeneous environments provided environmental fluctuations are sufficiently strong and sufficiently weakly correlated across space. In contrast, for diffusively dispersing populations living in similar environments, intermediate dispersal rates maximize their stochastic growth rate. PMID:22427143

Evans, Steven N; Ralph, Peter L; Schreiber, Sebastian J; Sen, Arnab

2013-02-01

11

Spreading of persistent infections in heterogeneous populations  

NASA Astrophysics Data System (ADS)

Up to now, the effects of having heterogeneous networks of contacts have been studied mostly for diseases which are not persistent in time, i.e., for diseases where the infectious period can be considered very small compared to the lifetime of an individual. Moreover, all these previous results have been obtained for closed populations, where the number of individuals does not change during the whole duration of the epidemics. Here, we go one step further and analyze, both analytically and numerically, a radically different kind of diseases: those that are persistent and can last for an individual’s lifetime. To be more specific, we particularize to the case of tuberculosis’ (TB) infection dynamics, where the infection remains latent for a period of time before showing up and spreading to other individuals. We introduce an epidemiological model for TB-like persistent infections taking into account the heterogeneity inherent to the population structure. This sort of dynamics introduces new analytical and numerical challenges that we are able to sort out. Our results show that also for persistent diseases the epidemic threshold depends on the ratio of the first two moments of the degree distribution so that it goes to zero in a class of scale-free networks when the system approaches the thermodynamic limit.

Sanz, J.; Floría, L. M.; Moreno, Y.

2010-05-01

12

Habitat heterogeneity affects population growth in goshawk Accipiter gentilis  

Microsoft Academic Search

Summary 1. The concept of site-dependent population regulation combines the ideas of Ideal Free Distribution-type of habitat settlement and density dependence in a vital rate mediated by habitat heterogeneity. The latter is also known as habitat heterogeneity hypothesis. Site-dependent population regulation hypothesis predicts that increasing population density should lead to inhabitation of increasingly poor territories and decreasing per capita population

Oliver Kruger; Jan Lindstrom

2001-01-01

13

Are Heterogeneous or Homogeneous Groups More Beneficial to Students?  

Microsoft Academic Search

This study investigated the relative benefits to the student of working in homogeneous versus heterogeneous classroom groups. Correlation analysis of 18 desirable outcomes versus 8 personality-based heterogeneity variables reveals that heterogeneity associates with advantages as well as disadvantages. Ways in which group composition might be customized to benefit students with particular needs or to emphasize particular goals are described, along

Nancy M. Schullery; Stephen E. Schullery

2006-01-01

14

Adaptive Dynamics in Games Played by Heterogeneous Populations  

Microsoft Academic Search

Consider a population of agents who play a game through repeated interactions, and adapt their behavior based on information about other agents' previous behavior. The standard way of modeling such a process is to assume that everyone in the population is governed by the same adaptive rule, e.g., best response, imitation, or the replicator dynamic. This paper studies heterogeneous populations

Yuri M. Kaniovski; Arkadii V. Kryazhimskii; H. Peyton Young

2000-01-01

15

Are Heterogeneous or Homogeneous Groups More Beneficial to Students?  

ERIC Educational Resources Information Center

This study investigated the relative benefits to the student of working in homogeneous versus heterogeneous classroom groups. Correlation analysis of 18 desirable outcomes versus 8 personality-based heterogeneity variables reveals that heterogeneity associates with advantages as well as disadvantages. Ways in which group composition might be…

Schullery, Nancy M.; Schullery, Stephen E.

2006-01-01

16

The Adult Student Population.  

ERIC Educational Resources Information Center

This study is concerned with the following topics on adult student attendance at Harrisburg Area Community College (HACC) during the 1969-70 academic year: student background, reason for attendance, enrollment in programs or courses, academic success, evidence of personal and occupational development. The report is based on the useable…

Snyder, Fred A.; Blocker, Clyde E.

17

DEMOGRAPHIC PROCESSES: POPULATION DYNAMICS IN HETEROGENEOUS LANDSCAPES  

EPA Science Inventory

Few topics have attracted the attention of ecologists more than fluctuations in the numbers of plants and animals through time and their variation in abundance through space. nderstanding population fluctuations, and thus population conservation, requires understanding the links ...

18

Heterogeneous Heterozygosities in Mus musculus Populations  

Microsoft Academic Search

Both chance and adaptation have effects in determining the genetical constitution of local populations of any organism, but opinions differ widely over their relative importance. This study describes the frequencies of electrophoretically detected alleles at 22 loci in 1538 house mice (Mus musculus L.) from 27 population samples collected from the Faroe, Shetland and Orkney archipelagoes; the mainland of Great

R. J. Berry; Josephine Peters

1977-01-01

19

Tit for tat in heterogeneous populations  

Microsoft Academic Search

THE 'iterated prisoner's dilemma' is now the orthodox paradigm for the evolution of cooperation among selfish individuals. This viewpoint is strongly supported by Axelrod's computer tournaments, where 'tit for tat' (TFT) finished first1. This has stimulated interest in the role of reciprocity in biological societies1-8. Most theoretical investigations, however, assumed homogeneous populations (the setting for evolutionary stable strategies9,10) and programs

Martin A. Nowak; Karl Sigmund

1992-01-01

20

Stochastic adaptation in finite games played by heterogeneous populations  

Microsoft Academic Search

We analyze stochastic adaptation in finite n-player games played by heterogeneous populations containing best repliers, better repliers, and imitators. Individuals select strategies by applying a personal learning rule to a sample from a finite history of past play. We give sufficient conditions for convergence to minimal closed sets under better replies and selection of a Pareto dominant such set. Finally,

Jens Josephson

2009-01-01

21

Growth rate determination of heterogeneous microbial population in swine manure.  

PubMed

The effect of manure concentration on the growth of the heterogeneous microbial population under batch condition was studied. Four manure concentrations were used in the study. The dehydrogenase activity was used as a measure of the active biomass in the manure. The chemical oxygen demand test was used to measure the change in organic material caused by biological activities. The growth curve of the heterogeneous microbial population in swine manure was essentially similar to that of a pure culture grown batchwise in that it had the four principle phases: lag, exponential growth, stationary, and death. The exponential growth phase followed a diauxic growth pattern. High concentration of manure had an inhibitory effect on the microbial growth. Manure diluted less than 1:3 (manure:water) depressed the specific growth rate of the microbial population. PMID:2802598

Ghaly, A E; Kok, R; Ingrahm, J M

1989-10-01

22

Group testing in heterogeneous populations by using halving algorithms  

PubMed Central

Summary Group (pooled) testing is often used to reduce the total number of tests that are needed to screen a large number of individuals for an infectious disease or some other binary characteristic. Traditionally, research in group testing has assumed that each individual is independent with the same risk of positivity. More recently, there has been a growing set of literature generalizing previous work in group testing to include heterogeneous populations so that each individual has a different risk of positivity. We investigate the effect of acknowledging population heterogeneity on a commonly used group testing procedure which is known as ‘halving’. For this procedure, positive groups are successively split into two equal-sized halves until all groups test negatively or until individual testing occurs. We show that heterogeneity does not affect the mean number of tests when individuals are randomly assigned to subgroups. However, when individuals are assigned to subgroups on the basis of their risk probabilities, we show that our proposed procedures reduce the number of tests by taking advantage of the heterogeneity. This is illustrated by using chlamydia and gonorrhoea screening data from the state of Nebraska. PMID:25035521

Black, Michael S.; Bilder, Christopher R.; Tebbs, Joshua M.

2014-01-01

23

Networks and Models with Heterogeneous Population Structure in Epidemiology  

Microsoft Academic Search

\\u000a Heterogeneous population structure can have a profound effect on infectious disease dynamics, and is particularly important\\u000a when investigating “tactical” disease control questions. At times, the nature of the network involved in the transmission\\u000a of the pathogen (bacteria, virus, macro-parasite, etc.) appears to be clear; however, the nature of the network involved is\\u000a dependent on the scale (e.g. within-host, between-host, or

R. R. Kao

2010-01-01

24

Population regulation by habitat heterogeneity or individual adjustment?  

PubMed

1. The habitat heterogeneity (HHH) and individual adjustment (IAH) hypotheses are commonly proposed to explain a decrease in reproduction rate with increasing population density. Higher numbers of low-quality territories with low reproductive success as density increases lead to a decrease in reproduction under the HHH, while more competition at high density decreases reproduction across all territories under the IAH. 2. We analyse the influence of density and habitat heterogeneity on reproductive success in eight populations of long-lived territorial birds of prey belonging to four species. Sufficient reliability in distinguishing between population-wide, site-specific and individual quality effects on reproduction was granted through the minimal duration of 20 years of all data sets and the ability to control for individual quality in five of them. 3. Density increased in five populations but reproduction did not decrease in these. Territory occupancy as a surrogate of territory quality correlated positively with reproductive success but only significantly so in large data sets with more than 100 territories. 4. Reproductive success was always best explained by measures of territory quality in multivariate models. Direct or delayed (t-1) population density entered very few of the best models. Mixed models controlling for individual quality showed an increasing reproductive performance in older individuals and in those laying earlier, but measures of territory quality were also always retained in the best models. 5. We find strong support for the habitat heterogeneity hypothesis but weak support for the individual adjustment hypothesis. Both individual and site characteristics are crucial for reproductive performance in long-lived birds. Proportional occupancy of territories enables recognition of high-quality territories as preferential conservation targets. PMID:21950339

Krüger, Oliver; Chakarov, Nayden; Nielsen, Jan T; Looft, Volkher; Grünkorn, Thomas; Struwe-Juhl, Bernd; Møller, Anders P

2012-03-01

25

The Heterogeneous HLA Genetic Makeup of the Swiss Population  

PubMed Central

This study aims at investigating the HLA molecular variation across Switzerland in order to determine possible regional differences, which would be highly relevant to several purposes: optimizing donor recruitment strategies in hematopoietic stem cell transplantation (HSCT), providing reliable reference data in HLA and disease association studies, and understanding the population genetic background(s) of this culturally heterogeneous country. HLA molecular data of more than 20,000 HSCT donors from 9–13 recruitment centers of the whole country were analyzed. Allele and haplotype frequencies were estimated by using new computer tools adapted to the heterogeneity and ambiguity of the data. Non-parametric and resampling statistical tests were performed to assess Hardy-Weinberg equilibrium, selective neutrality and linkage disequilibrium among different loci, both in each recruitment center and in the whole national registry. Genetic variation was explored through genetic distance and hierarchical analysis of variance taking into account both geographic and linguistic subdivisions in Switzerland. The results indicate a heterogeneous genetic makeup of the Swiss population: first, allele frequencies estimated on the whole national registry strongly deviate from Hardy-Weinberg equilibrium, by contrast with the results obtained for individual centers; second, a pronounced differentiation is observed for Ticino, Graubünden, and, to a lesser extent, Wallis, suggesting that the Alps represent(ed) a barrier to gene flow; finally, although cultural (linguistic) boundaries do not represent a main genetic differentiation factor in Switzerland, the genetic relatedness between population from south-eastern Switzerland and Italy agrees with historical and linguistic data. Overall, this study justifies the maintenance of a decentralized donor recruitment structure in Switzerland allowing increasing the genetic diversity of the national—and hence global—donor registry. It also indicates that HLA data of local donor recruitment centers can be used as reference data in both epidemiological and population genetic studies focusing on the genetic history of present European populations. PMID:22848484

Buhler, Stéphane; Nunes, José Manuel; Nicoloso, Grazia; Tiercy, Jean-Marie; Sanchez-Mazas, Alicia

2012-01-01

26

Confounding and heterogeneity in genetic association studies with admixed populations.  

PubMed

Association studies among admixed populations pose many challenges including confounding of genetic effects due to population substructure and heterogeneity due to different patterns of linkage disequilibrium (LD). We use simulations to investigate controlling for confounding by indicators of global ancestry and the impact of including a covariate for local ancestry. In addition, we investigate the use of an interaction term between a single-nucleotide polymorphism (SNP) and local ancestry to capture heterogeneity in SNP effects. Although adjustment for global ancestry can control for confounding, additional adjustment for local ancestry may increase power when the induced admixture LD is in the opposite direction as the LD in the ancestral population. However, if the induced LD is in the same direction, there is the potential for reduced power because of overadjustment. Furthermore, the inclusion of a SNP by local ancestry interaction term can increase power when there is substantial differential LD between ancestry populations. We examine these approaches in genome-wide data using the University of Southern California's Children's Health Study investigating asthma risk. The analysis highlights rs10519951 (P = 8.5 × 10(-7)), a SNP lacking any evidence of association from a conventional analysis (P = 0.5). PMID:23334005

Liu, Jinghua; Lewinger, Juan Pablo; Gilliland, Frank D; Gauderman, W James; Conti, David V

2013-02-15

27

Extent of heterogeneity in mitochondrial DNA of European populations.  

PubMed

Variation in the mitochondrial DNA (mtDNA) control region as detected by sequence-specific oligonucleotide (SSO) probes is described for 595 individuals from six European or European-derived populations. Estimates of diversity for mtDNA types exceed 0.91 in all populations, while 50% of the 158 types which were observed occur only once. Of 68 shared types, most occur rarely (< 3% of the total population); only one type occurs at a frequency greater than 10%, and it is present at comparable frequencies in all six populations (18-29%). An analysis of molecular variance (AMOVA) incorporating genetic distances between types shows that 100% of the variation present in the total sample is attributable to within-population diversity, while there are essentially no between-population differences. Another AMOVA was performed for the first hypervariable region SSO sites only, which included this sample plus an additional 537 SSO types from mine more European populations that were inferred from published mtDNA control region sequence data. Similar results were obtained, with over 99% of the variation overall attributable to within-population differences, and less than 1% of the variation attributable to between-population differences. The Saami were the most different from other populations, which had been observed in an earlier study of nucleotide sequence data. Overall, there is no statistically significant heterogeneity for European populations (p > 0.001), and these groups are virtually indistinguishable with respect to mtDNA SSO types. These results demonstrate the utility of mtDNA typing for forensic investigations. PMID:9144933

Melton, T; Wilson, M; Batzer, M; Stoneking, M

1997-05-01

28

Stochastic and deterministic simulations of heterogeneous cell population dynamics.  

PubMed

A Monte Carlo algorithm, which can accurately simulate the dynamics of entire heterogeneous cell populations, was developed. The algorithm takes into account the random nature of cell division as well as unequal partitioning of cellular material at cell division. Moreover, it is general in the sense that it can accommodate a variety of single-cell, deterministic reaction kinetics as well as various stochastic division and partitioning mechanisms. The validity of the algorithm was assessed through comparison of its results with those of the corresponding deterministic cell population balance model in cases where stochastic behavior is expected to be quantitatively negligible. Both algorithms were applied to study: (a) linear intracellular kinetics and (b) the expression dynamics of a genetic network with positive feedback architecture, such as the lac operon. The effects of stochastic division as well as those of different division and partitioning mechanisms were assessed in these systems, while the comparison of the stochastic model with a continuum model elucidated the significance of cell population heterogeneity even in cases where only the prediction of average properties is of primary interest. PMID:16487980

Mantzaris, Nikos V

2006-08-01

29

A Diffusion?Based Theory of Organism Dispersal in Heterogeneous Populations  

Microsoft Academic Search

We develop a general theory of organism movement in heterogeneous populations that can explain the leptokurtic move- ment distributions commonly measured in nature. We describe pop- ulation heterogeneity in a state-structured framework, employing advection-diffusion as the fundamental movement process of indi- viduals occupying different movement states. Our general analysis shows that population heterogeneity in movement behavior can be defined as

2003-01-01

30

Explicit kinetic heterogeneity: mechanistic models for interpretation of labeling data in heterogeneous populations  

SciTech Connect

Estimation of division and death rates of lymphocytes in different conditions is vital for quantitative understanding of the immune system. Deuterium, in the form of deuterated glucose or heavy water, can be used to measure rates of proliferation and death of lymphocytes in vivo. Inferring these rates from labeling and delabeling curves has been subject to considerable debate with different groups suggesting different mathematical models for that purpose. We show that the three models that are most commonly used are in fact mathematically identical and differ only in their interpretation of the estimated parameters. By extending these previous models, we here propose a more mechanistic approach for the analysis of data from deuterium labeling experiments. We construct a model of 'kinetic heterogeneity' in which the total cell population consists of many sub-populations with different rates of cell turnover. In this model, for a given distribution of the rates of turnover, the predicted fraction of labeled DNA accumulated and lost can be calculated. Our model reproduces several previously made experimental observations, such as a negative correlation between the length of the labeling period and the rate at which labeled DNA is lost after label cessation. We demonstrate the reliability of the new explicit kinetic heterogeneity model by applying it to artificially generated datasets, and illustrate its usefulness by fitting experimental data. In contrast to previous models, the explicit kinetic heterogeneity model (1) provides a mechanistic way of interpreting labeling data; (2) allows for a non-exponential loss of labeled cells during delabeling, and (3) can be used to describe data with variable labeling length.

Ganusov, Vitaly V [Los Alamos National Laboratory

2008-01-01

31

A mathematical and computational approach for integrating the major sources of cell population heterogeneity  

Microsoft Academic Search

Several approaches have been used in the past to model heterogeneity in bacterial cell populations, with each approach focusing on different source(s) of heterogeneity. However, a holistic approach that integrates all the major sources into a comprehensive framework applicable to cell populations is still lacking.In this work we present the mathematical formulation of a cell population master equation (CPME) that

Michail Stamatakis; Kyriacos Zygourakis

2010-01-01

32

Teaching the Growing Population of Nontraditional Students.  

ERIC Educational Resources Information Center

This document contains three articles on teaching the growing population of nontraditional students. "The Changing Demographics of the Classroom" defines "nontraditional students"; reviews the characteristics, risk factors, and special needs of nontraditional students; and identifies the following services as particularly important to…

Wagner, June G.

2002-01-01

33

Estimation of multiple transmission rates for epidemics in heterogeneous populations  

PubMed Central

One of the principal challenges in epidemiological modeling is to parameterize models with realistic estimates for transmission rates in order to analyze strategies for control and to predict disease outcomes. Using a combination of replicated experiments, Bayesian statistical inference, and stochastic modeling, we introduce and illustrate a strategy to estimate transmission parameters for the spread of infection through a two-phase mosaic, comprising favorable and unfavorable hosts. We focus on epidemics with local dispersal and formulate a spatially explicit, stochastic set of transition probabilities using a percolation paradigm for a susceptible–infected (S–I) epidemiological model. The S–I percolation model is further generalized to allow for multiple sources of infection including external inoculum and host-to-host infection. We fit the model using Bayesian inference and Markov chain Monte Carlo simulation to successive snapshots of damping-off disease spreading through replicated plant populations that differ in relative proportions of favorable and unfavorable hosts and with time-varying rates of transmission. Epidemiologically plausible parametric forms for these transmission rates are compared by using the deviance information criterion. Our results show that there are four transmission rates for a two-phase system, corresponding to each combination of infected donor and susceptible recipient. Knowing the number and magnitudes of the transmission rates allows the dominant pathways for transmission in a heterogeneous population to be identified. Finally, we show how failure to allow for multiple transmission rates can overestimate or underestimate the rate of spread of epidemics in heterogeneous environments, which could lead to marked failure or inefficiency of control strategies. PMID:18077378

Cook, Alex R.; Otten, Wilfred; Marion, Glenn; Gibson, Gavin J.; Gilligan, Christopher A.

2007-01-01

34

Effects of Population Heterogeneity on Accuracy of DIF Detection  

ERIC Educational Resources Information Center

Heterogeneity within English language learners (ELLs) groups has been documented. Previous research on differential item functioning (DIF) analyses suggests that accurate DIF detection rates are reduced greatly when groups are heterogeneous. In this simulation study, we investigated the effects of heterogeneity within linguistic (ELL) groups on…

Oliveri, María Elena; Ercikan, Kadriye; Zumbo, Bruno D.

2014-01-01

35

Functional heterogeneity of side population cells in skeletal muscle  

SciTech Connect

Skeletal muscle regeneration has been exclusively attributed to myogenic precursors, satellite cells. A stem cell-rich fraction referred to as side population (SP) cells also resides in skeletal muscle, but its roles in muscle regeneration remain unclear. We found that muscle SP cells could be subdivided into three sub-fractions using CD31 and CD45 markers. The majority of SP cells in normal non-regenerating muscle expressed CD31 and had endothelial characteristics. However, CD31{sup -}CD45{sup -} SP cells, which are a minor subpopulation in normal muscle, actively proliferated upon muscle injury and expressed not only several regulatory genes for muscle regeneration but also some mesenchymal lineage markers. CD31{sup -}CD45{sup -} SP cells showed the greatest myogenic potential among three SP sub-fractions, but indeed revealed mesenchymal potentials in vitro. These SP cells preferentially differentiated into myofibers after intramuscular transplantation in vivo. Our results revealed the heterogeneity of muscle SP cells and suggest that CD31{sup -}CD45{sup -} SP cells participate in muscle regeneration.

Uezumi, Akiyoshi [Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502 (Japan); Ojima, Koichi [Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502 (Japan); Fukada, So-ichiro [Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502 (Japan); Ikemoto, Madoka [Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502 (Japan); Masuda, Satoru [Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502 (Japan); Miyagoe-Suzuki, Yuko [Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502 (Japan); Takeda, Shin'ichi [Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502 (Japan)]. E-mail: takeda@ncnp.go.jp

2006-03-17

36

Phenotypic heterogeneity is a selected trait in natural yeast populations subject to environmental stress  

PubMed Central

Populations of genetically uniform microorganisms exhibit phenotypic heterogeneity, where individual cells have varying phenotypes. Such phenotypes include fitness-determining traits. Phenotypic heterogeneity has been linked to increased population-level fitness in laboratory studies, but its adaptive significance for wild microorganisms in the natural environment is unknown. Here, we addressed this by testing heterogeneity in yeast isolates from diverse environmental sites, each polluted with a different principal contaminant, as well as from corresponding control locations. We found that cell-to-cell heterogeneity (in resistance to the appropriate principal pollutant) was prevalent in the wild yeast isolates. Moreover, isolates with the highest heterogeneity were consistently observed in the polluted environments, indicating that heterogeneity is positively related to survival in adverse conditions in the wild. This relationship with survival was stronger than for the property of mean resistance (IC50) of an isolate. Therefore, heterogeneity could be the major determinant of microbial survival in adverse conditions. Indeed, growth assays indicated that isolates with high heterogeneities had a significant competitive advantage during stress. Analysis of yeasts after cultivation for ??500 generations additionally showed that high heterogeneity evolved as a heritable trait during stress. The results showed that environmental stress selects for wild microorganisms with high levels of phenotypic heterogeneity. PMID:24000788

Holland, Sara L; Reader, Tom; Dyer, Paul S; Avery, Simon V

2014-01-01

37

Modelling Heterogeneous Location Habits in Human Populations for Location Prediction Under Data Sparsity  

E-print Network

Modelling Heterogeneous Location Habits in Human Populations for Location Prediction Under Data of population mobility (i.e., in groups without spa- tial or social overlap) has been limited in three impo. However, development of such approaches has been limited by the requirement of personal semantic labels

Anderson, Jim

38

Observed-Score Equating with a Heterogeneous Target Population  

ERIC Educational Resources Information Center

Test equating is a statistical procedure for adjusting for test form differences in difficulty in a standardized assessment. Equating results are supposed to hold for a specified target population (Kolen & Brennan, 2004; von Davier, Holland, & Thayer, 2004) and to be (relatively) independent of the subpopulations from the target population (see…

Duong, Minh Q.; von Davier, Alina A.

2012-01-01

39

SOURCES OF HETEROGENEITY BIAS WHEN DNA MARK-RECAPTURE SAMPLING METHODS ARE APPLIED TO GRIZZLY BEAR (URSUS ARCTOS) POPULATIONS  

Microsoft Academic Search

One of the challenges in estimating grizzly bear (Ursus arctos) population size using DNA methods is heterogeneity of capture probabilities. This study developed general tools to explore heterogeneity variation using data from a DNA mark-recapture project in which a proportion of the bear population had GPS collars. The Huggins closed population mark-recapture model was used to determine if capture probability

John Boulanger; Gordon Stenhouse; Robin Munro

2004-01-01

40

Follow the Leader: Herding Behavior in Heterogeneous Populations  

E-print Network

Here we study the emergence of spontaneous leadership in large populations. In standard models of opinion dynamics, herding behavior is only obeyed at the local scale due to the interaction of single agents with their neighbors; while at the global scale, such models are governed by purely diffusive processes. Surprisingly, in this paper we show that the combination of a strong separation of time scales within the population and a hierarchical organization of the influences of some agents on the others induces a phase transition between a purely diffusive phase, as in the standard case, and a herding phase where a fraction of the agents self-organize and lead the global opinion of the whole population.

Mosquera-Donate, Guillem

2014-01-01

41

A Mathematical and Computational Approach for Integrating the Major Sources of Cell Population Heterogeneity  

PubMed Central

Several approaches have been used in the past to model heterogeneity in bacterial cell populations, with each approach focusing on different source(s) of heterogeneity. However, a holistic approach that integrates all the major sources into a comprehensive framework applicable to cell populations is still lacking. In this work we present the mathematical formulation of a cell population master equation (CPME) that describes cell population dynamics and takes into account the major sources of heterogeneity, namely stochasticity in reaction, DNA-duplication, and division, as well as the random partitioning of species contents into the two daughter cells. The formulation also takes into account cell growth and respects the discrete nature of the molecular contents and cell numbers. We further develop a Monte Carlo algorithm for the simulation of the stochastic processes considered here. To benchmark our new framework, we first use it to quantify the effect of each source of heterogeneity on the intrinsic and the extrinsic phenotypic variability for the well-known two-promoter system used experimentally by Elowitz et al. (2002). We finally apply our framework to a more complicated system and demonstrate how the interplay between noisy gene expression and growth inhibition due to protein accumulation at the single cell level can result in complex behavior at the cell population level. The generality of our framework makes it suitable for studying a vast array of artificial and natural genetic networks. Using our Monte Carlo algorithm, cell population distributions can be predicted for the genetic architecture of interest, thereby quantifying the effect of stochasticity in intracellular reactions or the variability in the rate of physiological processes such as growth and division. Such in silico experiments can give insight into the behavior of cell populations and reveal the major sources contributing to cell population heterogeneity. PMID:20685607

Stamatakis, Michail; Zygourakis, Kyriacos

2010-01-01

42

Measures of human population structure show heterogeneity among genomic regions  

Microsoft Academic Search

Estimates of genetic population structure (FST) were constructed from all autosomes in two large SNP data sets. The Perlegen data set contains genotypes on ?1 million SNPs segregating in all three samples of Americans of African, Asian, and European descent; and the Phase I HapMap data set contains genotypes on ?0.6 million SNPs segregating in all four samples from specific

Bruce S. Weir; Lon R. Cardon; Amy D. Anderson; Dahlia M. Nielsen; William G. Hill

2005-01-01

43

Evolutionary conservation advice for despotic populations: habitat heterogeneity  

E-print Network

Sciences, University of Jyva¨skyla¨, Jyva¨skyla¨, Finland 4 Department of Evolution, Ecology and Genetics preferences for good habitat are often thought to have a beneficial stabilizing effect for populations of conflict. We show that, in an endangered species, this process decreases the productivity of favoured

44

Slow epidemic extinction in populations with heterogeneous infection rates  

NASA Astrophysics Data System (ADS)

We explore how heterogeneity in the intensity of interactions between people affects epidemic spreading. For that, we study the susceptible-infected-susceptible model on a complex network, where a link connecting individuals i and j is endowed with an infection rate ?ij=?wij proportional to the intensity of their contact wij, with a distribution P(wij) taken from face-to-face experiments analyzed in Cattuto [PLoS ONE1932-620310.1371/journal.pone.0011596 5, e11596 (2010)]. We find an extremely slow decay of the fraction of infected individuals, for a wide range of the control parameter ?. Using a distribution of width a we identify two large regions in the a-? space with anomalous behaviors, which are reminiscent of rare region effects (Griffiths phases) found in models with quenched disorder. We show that the slow approach to extinction is caused by isolated small groups of highly interacting individuals, which keep epidemics alive for very long times. A mean-field approximation and a percolation approach capture with very good accuracy the absorbing-active transition line for weak (small a) and strong (large a) disorder, respectively.

Buono, C.; Vazquez, F.; Macri, P. A.; Braunstein, L. A.

2013-08-01

45

A heterogeneous population model for the analysis of bacterial growth kinetics  

Microsoft Academic Search

A two-compartment, heterogeneous population model (HPM) was derived using the simulation software SB ModelMaker© to describe the growth of Listeria monocytogenes in bacteriological media at 5–35 °C. The model assumed that, at time t = 0, the inoculum was distributed between two distinct compartments, Non-Growing and Growing, and that growth could be described by four parameters: initial total cell population

R. C. McKellar

1997-01-01

46

Anomalous diffusion of heterogeneous populations characterized by normal diffusion at the individual level  

PubMed Central

The characterization of the dispersal of populations of non-identical individuals is relevant to most ecological and epidemiological processes. In practice, the movement is quantified by observing relatively few individuals, and averaging to estimate the rate of dispersal of the population as a whole. Here, we show that this can lead to serious errors in the predicted movement of the population if the individuals disperse at different rates. We develop a stochastic model for the diffusion of heterogeneous populations, inspired by the movement of the parasitic nematode Phasmarhabditis hermaphrodita. Direct observations of this nematode in homogeneous and heterogeneous environments reveal a large variation in individual behaviour within the population as reflected initially in the speed of the movement. Further statistical analysis shows that the movement is characterized by temporal correlations and in a heterogeneously structured environment the correlations that occur are of shorter range compared with those in a homogeneous environment. Therefore, by using the first-order correlated random walk techniques, we derive an effective diffusion coefficient for each individual, and show that there is a significant variation in this parameter among the population that follows a gamma distribution. Based on these findings, we build a new dispersal model in which we maintain the classical assumption that individual movement can be described by normal diffusion, but due to the variability in individual dispersal rates, the diffusion coefficient is not constant at the population level and follows a continuous distribution. The conclusions and methodology presented are relevant to any heterogeneous population of individuals with widely different diffusion rates. PMID:18708322

Hapca, Simona; Crawford, John W; Young, Iain M

2008-01-01

47

The Innovation Diffusion Process in a Heterogeneous Population: A Micromodeling Approach  

Microsoft Academic Search

A model of the innovation diffusion process is developed using a micromodeling approach that explicitly considers the determinants of adoption at the individual level in a decision analytic framework, and incorporates heterogeneity in the population with respect to initial perceptions, preference characteristics, and responsiveness to information. The micromodelling approach provides a behavioral basis for explaining adoption at the disaggregate level

Rabik Ar Chatterjee; Jehoshua Eliashberg

1990-01-01

48

Modelling Lipid Competition Dynamics in Heterogeneous Protocell Populations  

NASA Astrophysics Data System (ADS)

Recent experimental work in the field of synthetic protocell biology has shown that prebiotic vesicles are able to `steal' lipids from each other. This phenomenon is driven purely by asymmetries in the physical state or composition of the vesicle membranes, and, when lipid resource is limited, translates directly into competition amongst the vesicles. Such a scenario is interesting from an origins of life perspective because a rudimentary form of cell-level selection emerges. To sharpen intuition about possible mechanisms underlying this behaviour, experimental work must be complemented with theoretical modelling. The aim of this paper is to provide a coarse-grain mathematical model of protocell lipid competition. Our model is capable of reproducing, often quantitatively, results from core experimental papers that reported distinct types vesicle competition. Additionally, we make some predictions untested in the lab, and develop a general numerical method for quickly solving the equilibrium point of a model vesicle population.

Shirt-Ediss, Ben; Ruiz-Mirazo, Kepa; Mavelli, Fabio; Solé, Ricard V.

2014-07-01

49

Modelling Lipid Competition Dynamics in Heterogeneous Protocell Populations  

PubMed Central

Recent experimental work in the field of synthetic protocell biology has shown that prebiotic vesicles are able to ‘steal’ lipids from each other. This phenomenon is driven purely by asymmetries in the physical state or composition of the vesicle membranes, and, when lipid resource is limited, translates directly into competition amongst the vesicles. Such a scenario is interesting from an origins of life perspective because a rudimentary form of cell-level selection emerges. To sharpen intuition about possible mechanisms underlying this behaviour, experimental work must be complemented with theoretical modelling. The aim of this paper is to provide a coarse-grain mathematical model of protocell lipid competition. Our model is capable of reproducing, often quantitatively, results from core experimental papers that reported distinct types vesicle competition. Additionally, we make some predictions untested in the lab, and develop a general numerical method for quickly solving the equilibrium point of a model vesicle population. PMID:25024020

Shirt-Ediss, Ben; Ruiz-Mirazo, Kepa; Mavelli, Fabio; Solé, Ricard V.

2014-01-01

50

Student Populations Served by College of Business Degree Programs  

E-print Network

students are male and over 40% are Hispanic with small percentages of Black, Asian, and American IndianCollege of Business Student Populations Served by College of Business Degree Programs Updated: Jan to the population through integration of quality national and international students. The PGA Golf Management

Johnson, Eric E.

51

A score-type test for heterogeneity in zero-inflated models in a stratified population.  

PubMed

We propose a score-type statistic to evaluate heterogeneity in zero-inflated models for count data in a stratified population, where heterogeneity is defined as instances in which the zero counts are generated from two sources. Evaluating heterogeneity in this class of models has attracted considerable attention in the literature, but existing testing procedures have primarily relied on the constancy assumption under the alternative hypothesis. In this paper, we extend the literature by describing a score-type test to evaluate homogeneity against general alternatives that do not neglect the stratification information under the alternative hypothesis. The limiting null distribution of the proposed test statistic is a mixture of chi-squared distributions that can be well approximated by a simple parametric bootstrap procedure. Our numerical simulation studies show that the proposed test can greatly improve efficiency over tests of heterogeneity that ignore the stratification information. An empirical application to dental caries data in early childhood further shows the importance and practical utility of the methodology in using the stratification profile to detect heterogeneity in the population. PMID:24488881

Cao, Guanqun; Hsu, Wei-Wen; Todem, David

2014-05-30

52

Evolution of cooperation in a heterogeneous population with influential individuals  

NASA Astrophysics Data System (ADS)

Influential individuals are introduced and integrated with the public goods game (PGG) to investigate their influence on the emergence and evolution of cooperation. In the model, some influential individuals whose behaviors can be controlled by us are introduced into a homogeneous population on a square lattice. The influential individuals can play three kinds of roles: I. exemplar, II. supervisor with the power to punish defectors, and III. supervisor with the power to reward cooperative co-players. It is found that the existence of influential individuals who play Role I turns out to be detrimental to cooperation and that the larger the number of influential individuals is, the more difficult it is for cooperation to be maintained. For those playing supervisory roles, both punishment and reward are found to be effective ways for the influential individuals to promote and stabilize cooperative behavior. By comparing the critical costs and the mean payoffs for a low multiplication factor under the role of punishment and the role of reward, it is found that reward is a more effective intervention measure than punishment for influential individuals seeking to improve cooperation and that reward leads to a higher mean payoff.

Zhuang, Qian; Wang, Dong; Fan, Ying; Di, Zengru

2012-02-01

53

Distinct Allelic Patterns of Nanog Expression Impart Embryonic Stem Cell Population Heterogeneity  

PubMed Central

Nanog is a principal pluripotency regulator exhibiting a disperse distribution within stem cell populations in vivo and in vitro. Increasing evidence points to a functional role of Nanog heterogeneity on stem cell fate decisions. Allelic control of Nanog gene expression was reported recently in mouse embryonic stem cells. To better understand how this mode of regulation influences the observed heterogeneity of NANOG in stem cell populations, we assembled a multiscale stochastic population balance equation framework. In addition to allelic control, gene expression noise and random partitioning at cell division were considered. As a result of allelic Nanog expression, the distribution of Nanog exhibited three distinct states but when combined with transcriptional noise the profile became bimodal. Regardless of their allelic expression pattern, initially uniform populations of stem cells gave rise to the same Nanog heterogeneity within ten cell cycles. Depletion of NANOG content in cells switching off both gene alleles was slower than the accumulation of intracellular NANOG after cells turned on at least one of their Nanog gene copies pointing to Nanog state-dependent dynamics. Allelic transcription of Nanog also raises issues regarding the use of stem cell lines with reporter genes knocked in a single allelic locus. Indeed, significant divergence was observed in the reporter and native protein profiles depending on the difference in their half-lives and insertion of the reporter gene in one or both alleles. In stem cell populations with restricted Nanog expression, allelic regulation facilitates the maintenance of fractions of self-renewing cells with sufficient Nanog content to prevent aberrant loss of pluripotency. Our findings underline the role of allelic control of Nanog expression as a prime determinant of stem cell population heterogeneity and warrant further investigation in the contexts of stem cell specification and cell reprogramming. PMID:23874182

Wu, Jincheng; Tzanakakis, Emmanuel S.

2013-01-01

54

Physiological heterogeneities in microbial populations and implications for physical stress tolerance  

PubMed Central

Background Traditionally average values of the whole population are considered when analysing microbial cell cultivations. However, a typical microbial population in a bioreactor is heterogeneous in most phenotypes measurable at a single-cell level. There are indications that such heterogeneity may be unfavourable on the one hand (reduces yields and productivities), but also beneficial on the other hand (facilitates quick adaptation to new conditions - i.e. increases the robustness of the fermentation process). Understanding and control of microbial population heterogeneity is thus of major importance for improving microbial cell factory processes. Results In this work, a dual reporter system was developed and applied to map growth and cell fitness heterogeneities within budding yeast populations during aerobic cultivation in well-mixed bioreactors. The reporter strain, which was based on the expression of green fluorescent protein (GFP) under the control of the ribosomal protein RPL22a promoter, made it possible to distinguish cell growth phases by the level of fluorescence intensity. Furthermore, by exploiting the strong correlation of intracellular GFP level and cell membrane integrity it was possible to distinguish subpopulations with high and low cell membrane robustness and hence ability to withstand freeze-thaw stress. A strong inverse correlation between growth and cell membrane robustness was observed, which further supports the hypothesis that cellular resources are limited and need to be distributed as a trade-off between two functions: growth and robustness. In addition, the trade-off was shown to vary within the population, and the occurrence of two distinct subpopulations shifting between these two antagonistic modes of cell operation could be distinguished. Conclusions The reporter strain enabled mapping of population heterogeneities in growth and cell membrane robustness towards freeze-thaw stress at different phases of cell cultivation. The described reporter system is a valuable tool for understanding the effect of environmental conditions on population heterogeneity of microbial cells and thereby to understand cell responses during industrial process-like conditions. It may be applied to identify more robust subpopulations, and for developing novel strategies for strain improvement and process design for more effective bioprocessing. PMID:22799461

2012-01-01

55

Extreme heterogeneity in parasitism despite low population genetic structure among monarch butterflies inhabiting the Hawaiian Islands.  

PubMed

Host movement and spatial structure can strongly influence the ecology and evolution of infectious diseases, with limited host movement potentially leading to high spatial heterogeneity in infection. Monarch butterflies (Danaus plexippus) are best known for undertaking a spectacular long-distance migration in eastern North America; however, they also form non-migratory populations that breed year-round in milder climates such as Hawaii and other tropical locations. Prior work showed an inverse relationship between monarch migratory propensity and the prevalence of the protozoan parasite, Ophryocystis elektroscirrha. Here, we sampled monarchs from replicate sites within each of four Hawaiian Islands to ask whether these populations show consistently high prevalence of the protozoan parasite as seen for monarchs from several other non-migratory populations. Counter to our predictions, we observed striking spatial heterogeneity in parasite prevalence, with infection rates per site ranging from 4-85%. We next used microsatellite markers to ask whether the observed variation in infection might be explained by limited host movement and spatial sub-structuring among sites. Our results showed that monarchs across the Hawaiian Islands form one admixed population, supporting high gene flow among sites. Moreover, measures of individual-level genetic diversity did not predict host infection status, as might be expected if more inbred hosts harbored higher parasite loads. These results suggest that other factors such as landscape-level environmental variation or colonization-extinction processes might instead cause the extreme heterogeneity in monarch butterfly infection observed here. PMID:24926796

Pierce, Amanda A; de Roode, Jacobus C; Altizer, Sonia; Bartel, Rebecca A

2014-01-01

56

Extreme Heterogeneity in Parasitism Despite Low Population Genetic Structure among Monarch Butterflies Inhabiting the Hawaiian Islands  

PubMed Central

Host movement and spatial structure can strongly influence the ecology and evolution of infectious diseases, with limited host movement potentially leading to high spatial heterogeneity in infection. Monarch butterflies (Danaus plexippus) are best known for undertaking a spectacular long-distance migration in eastern North America; however, they also form non-migratory populations that breed year-round in milder climates such as Hawaii and other tropical locations. Prior work showed an inverse relationship between monarch migratory propensity and the prevalence of the protozoan parasite, Ophryocystis elektroscirrha. Here, we sampled monarchs from replicate sites within each of four Hawaiian Islands to ask whether these populations show consistently high prevalence of the protozoan parasite as seen for monarchs from several other non-migratory populations. Counter to our predictions, we observed striking spatial heterogeneity in parasite prevalence, with infection rates per site ranging from 4–85%. We next used microsatellite markers to ask whether the observed variation in infection might be explained by limited host movement and spatial sub-structuring among sites. Our results showed that monarchs across the Hawaiian Islands form one admixed population, supporting high gene flow among sites. Moreover, measures of individual-level genetic diversity did not predict host infection status, as might be expected if more inbred hosts harbored higher parasite loads. These results suggest that other factors such as landscape-level environmental variation or colonization-extinction processes might instead cause the extreme heterogeneity in monarch butterfly infection observed here. PMID:24926796

Pierce, Amanda A.; de Roode, Jacobus C.; Altizer, Sonia; Bartel, Rebecca A.

2014-01-01

57

Evaluating binding avidities of populations of heterogeneous multivalent ligand-functionalized nanoparticles.  

PubMed

Ligand-functionalized, multivalent nanoparticles have been extensively studied as targeted carriers in biomedical applications for drug delivery and imaging. The chemical synthesis method used, however, generates nanoparticles that are heterogeneous with respect to the number of ligands on each nanoparticle. This article examines the role this heterogeneity in ligand number plays in multivalent interactions between nanoparticle ligands and targeted receptors. We designed and synthesized a model heterogeneous multivalent nanoparticle system and developed a unique kinetic analysis to quantify the avidity interactions. This system used mono-dispersed poly(amidoamine) (PAMAM) dendrimers that were then chemically functionalized with ssDNA oligonucleotides as to yield the heterogeneous nanoparticle platform (ligand valencies n = 1.7, 3.1, 6), and employed complementary oligonucleotides as targeted receptors on a surface plasmon resonance (SPR) biosensor to evaluate the multivalent binding of the nanoparticle population. Kinetic analysis of both parallel initial rate and dual-Langmuir analyses of SPR binding curves was performed to assess avidity distributions. We found that batches of multivalent nanoparticles contain both fast- and slow-dissociation subpopulations, which can be characterized as having "weak" and "strong" surface interactions ("binding"), respectively. Furthermore, we found that the proportion of "strong" binders increased as a function of the mean oligonucleotide valence of the nanoparticle population. These analyses allowed an assessment of how avidity distributions are modulated by the number of functionalized ligands and suggested that there are threshold valences that differentiated fast- and slow-dissociation nanoparticles. PMID:24810868

Li, Ming-Hsin; Choi, Seok Ki; Leroueil, Pascale R; Baker, James R

2014-06-24

58

From Single-Cell Genetic Architecture to Cell Population Dynamics: Quantitatively Decomposing the Effects of Different Population Heterogeneity Sources for a Genetic Network with Positive Feedback Architecture  

PubMed Central

Phenotypic cell-to-cell variability or cell population heterogeneity originates from two fundamentally different sources: unequal partitioning of cellular material at cell division and stochastic fluctuations associated with intracellular reactions. We developed a mathematical and computational framework that can quantitatively isolate both heterogeneity sources and applied it to a genetic network with positive feedback architecture. The framework consists of three vastly different mathematical formulations: a), a continuum model, which completely neglects population heterogeneity; b), a deterministic cell population balance model, which accounts for population heterogeneity originating only from unequal partitioning at cell division; and c), a fully stochastic model accommodating both sources of population heterogeneity. The framework enables the quantitative decomposition of the effects of the different population heterogeneity sources on system behavior. Our results indicate the importance of cell population heterogeneity in accurately predicting even average population properties. Moreover, we find that unequal partitioning at cell division and sharp division rates shrink the region of the parameter space where the population exhibits bistable behavior, a characteristic feature of networks with positive feedback architecture. In addition, intrinsic noise at the single-cell level due to slow operator fluctuations and small numbers of molecules further contributes toward the shrinkage of the bistability regime at the cell population level. Finally, the effect of intrinsic noise at the cell population level was found to be markedly different than at the single-cell level, emphasizing the importance of simulating entire cell populations and not just individual cells to understand the complex interplay between single-cell genetic architecture and behavior at the cell population level. PMID:17384073

Mantzaris, Nikos V.

2007-01-01

59

From single-cell genetic architecture to cell population dynamics: quantitatively decomposing the effects of different population heterogeneity sources for a genetic network with positive feedback architecture.  

PubMed

Phenotypic cell-to-cell variability or cell population heterogeneity originates from two fundamentally different sources: unequal partitioning of cellular material at cell division and stochastic fluctuations associated with intracellular reactions. We developed a mathematical and computational framework that can quantitatively isolate both heterogeneity sources and applied it to a genetic network with positive feedback architecture. The framework consists of three vastly different mathematical formulations: a), a continuum model, which completely neglects population heterogeneity; b), a deterministic cell population balance model, which accounts for population heterogeneity originating only from unequal partitioning at cell division; and c), a fully stochastic model accommodating both sources of population heterogeneity. The framework enables the quantitative decomposition of the effects of the different population heterogeneity sources on system behavior. Our results indicate the importance of cell population heterogeneity in accurately predicting even average population properties. Moreover, we find that unequal partitioning at cell division and sharp division rates shrink the region of the parameter space where the population exhibits bistable behavior, a characteristic feature of networks with positive feedback architecture. In addition, intrinsic noise at the single-cell level due to slow operator fluctuations and small numbers of molecules further contributes toward the shrinkage of the bistability regime at the cell population level. Finally, the effect of intrinsic noise at the cell population level was found to be markedly different than at the single-cell level, emphasizing the importance of simulating entire cell populations and not just individual cells to understand the complex interplay between single-cell genetic architecture and behavior at the cell population level. PMID:17384073

Mantzaris, Nikos V

2007-06-15

60

Impact of Small Groups with Heterogeneous Preference on Behavioral Evolution in Population Evacuation  

PubMed Central

Up to now, there have been a great number of mechanisms to explain the individual behavior and population traits, which seem of particular significance in evolutionary biology and social behavior analysis. Among them, small groups and heterogeneity are two useful frameworks to the above issue. However, vast majority of existing works separately consider both scenarios, which is inconsistent with realistic cases in our life. Here we propose the evolutionary games of heterogeneous small groups (namely, different small groups possess different preferences to dilemma) to study the collective behavior in population evacuation. Importantly, players usually face completely different dilemmas inside and outside the small groups. By means of numerous computation simulations, it is unveiled that the ratio of players in one certain small group directly decides the final behavior of the whole population. Moreover, it can also be concluded that heterogeneous degree of preference for different small groups plays a key role in the behavior traits of the system, which may validate some realistic social observations. The proposed framework is thus universally applicable and may shed new light into the solution of social dilemmas. PMID:25793637

Wang, Tao; Huang, Keke; Wang, Zhen; Zheng, Xiaoping

2015-01-01

61

Allee effects can both conserve and create spatial heterogeneity in population densities.  

PubMed

In order to determine conditions which allow the Allee effect (caused by biparental reproduction) to conserve and create spatial heterogeneity in population densities, we studied a deterministic model of a symmetric two-patch metapopulation. We proved that under certain conditions there exist stable equilibria with unequal population densities in the two patches, a situation which can be interpreted as conserved heterogeneity. Furthermore, the Allee effect can lead to instability of the equilibrium with equal population densities if some degree of competition is assumed to occur between the subpopulations (non-local competition). This indicates the potential of the Allee effect to create spatial heterogeneity. Neither of these effects appear under biologically realistic parameter values in a model where uniparental reproduction is assumed. We proved that both the between-patch migration intensity and the degree of non-local competition are decisive in determining boundaries between these types of behaviour of the spatial system with Allee effect. Therefore, we propose that the Allee effect, migration intensity, and non-local competition should be considered jointly in studies focusing on problems like pattern formation in space and invasions of spreading species. PMID:10607518

Gyllenberg, M; Hemminki, J; Tammaru, T

1999-12-01

62

FIGG: Simulating populations of whole genome sequences for heterogeneous data analyses  

PubMed Central

Background High-throughput sequencing has become one of the primary tools for investigation of the molecular basis of disease. The increasing use of sequencing in investigations that aim to understand both individuals and populations is challenging our ability to develop analysis tools that scale with the data. This issue is of particular concern in studies that exhibit a wide degree of heterogeneity or deviation from the standard reference genome. The advent of population scale sequencing studies requires analysis tools that are developed and tested against matching quantities of heterogeneous data. Results We developed a large-scale whole genome simulation tool, FIGG, which generates large numbers of whole genomes with known sequence characteristics based on direct sampling of experimentally known or theorized variations. For normal variations we used publicly available data to determine the frequency of different mutation classes across the genome. FIGG then uses this information as a background to generate new sequences from a parent sequence with matching frequencies, but different actual mutations. The background can be normal variations, known disease variations, or a theoretical frequency distribution of variations. Conclusion In order to enable the creation of large numbers of genomes, FIGG generates simulated sequences from known genomic variation and iteratively mutates each genome separately. The result is multiple whole genome sequences with unique variations that can primarily be used to provide different reference genomes, model heterogeneous populations, and can offer a standard test environment for new analysis algorithms or bioinformatics tools. PMID:24885193

2014-01-01

63

Environmental heterogeneity explains the genetic structure of Continental and Mediterranean populations of Fraxinus angustifolia Vahl.  

PubMed

Tree species with wide distributions often exhibit different levels of genetic structuring correlated to their environment. However, understanding how environmental heterogeneity influences genetic variation is difficult because the effects of gene flow, drift and selection are confounded. We investigated the genetic variation and its ecological correlates in a wind-pollinated Mediterranean tree species, Fraxinus angustifolia Vahl, within a recognised glacial refugium in Croatia. We sampled 11 populations from environmentally divergent habitats within the Continental and Mediterranean biogeographical regions. We combined genetic data analyses based on nuclear microsatellite loci, multivariate statistics on environmental data and ecological niche modelling (ENM). We identified a geographic structure with a high genetic diversity and low differentiation in the Continental region, which contrasted with the significantly lower genetic diversity and higher population divergence in the Mediterranean region. The positive and significant correlation between environmental and genetic distances after controlling for geographic distance suggests an important influence of ecological divergence of the sites in shaping genetic variation. The ENM provided support for niche differentiation between the populations from the Continental and Mediterranean regions, suggesting that contemporary populations may represent two divergent ecotypes. Ecotype differentiation was also supported by multivariate environmental and genetic distance analyses. Our results suggest that despite extensive gene flow in continental areas, long-term stability of heterogeneous environments have likely promoted genetic divergence of ashes in this region and can explain the present-day genetic variation patterns of these ancient populations. PMID:22905171

Temunovi?, Martina; Franji?, Jozo; Satovic, Zlatko; Grgurev, Marin; Frascaria-Lacoste, Nathalie; Fernández-Manjarrés, Juan F

2012-01-01

64

Grassland Management Regimens Reduce Small-Scale Heterogeneity and Species Diversity of ?-Proteobacterial Ammonia Oxidizer Populations  

PubMed Central

The impact of soil management practices on ammonia oxidizer diversity and spatial heterogeneity was determined in improved (addition of N fertilizer), unimproved (no additions), and semi-improved (intermediate management) grassland pastures at the Sourhope Research Station in Scotland. Ammonia oxidizer diversity within each grassland soil was assessed by PCR amplification of microbial community DNA with both ammonia oxidizer-specific, 16S rRNA gene (rDNA) and functional, amoA, gene primers. PCR products were analysed by denaturing gradient gel electrophoresis, phylogenetic analysis of partial 16S rDNA and amoA sequences, and hybridization with ammonia oxidizer-specific oligonucleotide probes. Ammonia oxidizer populations in unimproved soils were more diverse than those in improved soils and were dominated by organisms representing Nitrosospira clusters 1 and 3 and Nitrosomonas cluster 7 (closely related phylogenetically to Nitrosomonas europaea). Improved soils were only dominated by Nitrosospira cluster 3 and Nitrosomonas cluster 7. These differences were also reflected in functional gene (amoA) diversity, with amoA gene sequences of both Nitrosomonas and Nitrosospira species detected. Replicate 0.5-g samples of unimproved soil demonstrated significant spatial heterogeneity in 16S rDNA-defined ammonia oxidizer clusters, which was reflected in heterogeneity in ammonium concentration and pH. Heterogeneity in soil characteristics and ammonia oxidizer diversity were lower in improved soils. The results therefore demonstrate significant effects of soil management on diversity and heterogeneity of ammonia oxidizer populations that are related to similar changes in relevant soil characteristics. PMID:11772604

Webster, Gordon; Embley, T. Martin; Prosser, James I.

2002-01-01

65

Time-evolution of age-dependent mortality patterns in mathematical model of heterogeneous human population.  

PubMed

The widely-known Gompertz law of mortality states the exponential increase of mortality with age in human populations. Such an exponential increase is observed at the adulthood span, roughly after the reproductive period, while mortality data at young and extremely old ages deviate from it. The heterogeneity of human populations, i.e. the existence of subpopulations with different mortality dynamics, is a useful consideration that can explain age-dependent mortality patterns across the whole life-course. A simple mathematical model combining the heterogeneity of populations with an assumption that the mortality in each subpopulation grows exponentially with age has been proven to be capable of reproducing the entire mortality pattern in a human population including the observed peculiarities at early- and late-life intervals. In this work we fit this model to actual (Swedish) mortality data for consecutive periods and consequently describe the evolution of mortality dynamics in terms of the evolution of the model parameters over time. We have found that the evolution of the model parameters validates the applicability of the compensation law of mortality to each subpopulation separately. Furthermore, our study has indicated that the population structure changes so that the population tends to become more homogeneous over time. Finally, our analysis of the decrease of the overall mortality in a population over time has shown that this decrease is mainly due to a change in the population structure and to a lesser extent to a reduction of mortality in each of the subpopulations, the latter being represented by an alteration of the parameters that outline the exponential dynamics. PMID:25219506

Avraam, Demetris; Arnold-Gaille, Séverine; Jones, Dyfan; Vasiev, Bakhtier

2014-12-01

66

High school students' understanding and problem solving in population genetics  

NASA Astrophysics Data System (ADS)

This study is an investigation of student understanding of population genetics and how students developed, used and revised conceptual models to solve problems. The students in this study participated in three rounds of problem solving. The first round involved the use of a population genetics model to predict the number of carriers in a population. The second round required them to revise their model of simple dominance population genetics to make inferences about populations containing three phenotype variations. The third round of problem solving required the students to revise their model of population genetics to explain anomalous data where the proportions of males and females with a trait varied significantly. As the students solved problems, they were involved in basic scientific processes as they observed population phenomena, constructed explanatory models to explain the data they observed, and attempted to persuade their peers as to the adequacy of their models. In this study, the students produced new knowledge about the genetics of a trait in a population through the revision and use of explanatory population genetics models using reasoning that was similar to what scientists do. The students learned, used and revised a model of Hardy-Weinberg equilibrium to generate and test hypotheses about the genetics of phenotypes given only population data. Students were also interviewed prior to and following instruction. This study suggests that a commonly held intuitive belief about the predominance of a dominant variation in populations is resistant to change, despite instruction and interferes with a student's ability to understand Hardy-Weinberg equilibrium and microevolution.

Soderberg, Patti D.

67

World Population: Fundamentals of Growth. Student Chartbook. Third Edition.  

ERIC Educational Resources Information Center

This booklet is designed for K-12 students and educators to learn about world population growth factors. Data are shown through charts and graphs with brief explanations. The booklet contains: (1) "World Population Growth and Regional Distribution through History"; (2) "Population Growth through Natural Increase"; (3) "Effect of Migration on…

Kent, Mary Mederios

68

Power in Numbers: Student Participation in Mathematical Discussions in Heterogeneous Spaces  

ERIC Educational Resources Information Center

Mathematics classrooms are conceptualized as heterogeneous spaces in which multiple figured worlds come into contact. The study explores how a group of high school students drew upon several figured worlds as they navigated mathematical discussions. (Contains 5 excerpts and 2 footnotes.)

Esmonde, Indigo; Langer-Osuna, Jennifer M.

2013-01-01

69

Genetic Heterogeneity of the ?-Globin Gene in Various Geographic Populations of Yunnan in Southwestern China  

PubMed Central

Objectives The aim of this study was to investigate the geographic distribution of ?-globin gene mutations in different ethnic groups in Yunnan province. Methods From 2004 to 2014, 1,441 subjects with hemoglobin disorders, identified by PCR-reverse dot blot and DNA sequencing, were studied according to ethnicity and geographic origin. Haplotypes were examined among 41 unrelated thalassemia chromosomes. Results Eighteen ?-thalassemia mutations and seven hemoglobin variants were identified for 1,616 alleles in 22 different ethnic groups from all 16 prefecture-level divisions of Yunnan. The prevalence of ?-thalassemia was heterogeneous and regionally specific. CD 41-42 (-TCTT) was the most prevalent mutation in the populations of northeastern Yunnan. CD 17 (A>T) was the most common mutation in the populations of southeastern Yunnan, especially for the Zhuang minority, whereas Hb E (CD 26, G>A) was the most prevalent mutation in populations of southwestern Yunnan, especially for the Dai minority. Among the seven types of haplotypes identified, CD 17 (A>T) was mainly linked to haplotype VII (+ - - - - - +) and IVS-II-654 (C>T) was only linked to haplotype I (+ - - - - + +). Conclusion Our data underline the heterogeneity of ?-globin gene mutations in Yunnan. This distribution of ?-globin mutations in the geographic regions and ethnic populations provided a detailed ethnic basis and evolutionary view of humans in southern China, which will be beneficial for genetic counseling and prevention strategies. PMID:25849334

Zhang, Jie; He, Jing; Zeng, Xiao-Hong; Ge, Shi-Jun; Huang, Yu; Su, Jie; Ding, Xue-Mei; Yang, Ji-Qing; Cao, Yong-Jiu; Chen, Hong; Zhang, Ying-Hong; Zhu, Bao-Sheng

2015-01-01

70

Order-Disorder Phase Transition in Heterogeneous Populations of Self-propelled Particles  

NASA Astrophysics Data System (ADS)

Biological systems are typically heterogeneous as individuals vary in their characteristics, their response to the external environment and to each other. For example, cell diversity plays a crucial role in the successful survival of many biological systems. Phenotypic heterogeneity is associated with cellular response to intercellular communications, the response to external environmental cues, motility modes, and proliferation rates. Here we study the effect of phenotypic diversity on the properties of collective motion in the context of the scalar noise model of collective migration. For simplicity, we study a population that is composed of two sub-populations, each with different sensitivities to external noise. We find that the two sub-populations interact non-additively: Within a large range of parameters, the dynamics of the system can be described by an equivalent homogeneous system with an effective temperature that depends on the average circular mean of the phenotypes. However, if one of the sub-populations is sufficiently "cold", it dominates the dynamics of the group as a whole.

Ariel, Gil; Rimer, Oren; Ben-Jacob, Eshel

2015-02-01

71

Landscape heterogeneity drives intra-population niche variation and reproduction in an arctic top predator  

PubMed Central

While intra-population variability in resource use is ubiquitous, little is known of how this measure of niche diversity varies in space and its role in population dynamics. Here we examined how heterogeneous breeding environments can structure intra-population niche variation in both resource use and reproductive output. We investigated intra-population niche variation in the Arctic tundra ecosystem, studying peregrine falcon (Falco peregrinus tundrius, White) breeding within a terrestrial-marine gradient near Rankin Inlet, Nunavut, Canada. Using stable isotope analysis, we found that intra-population niches varied at the individual level; we examined within-nest and among-nest variation, though only the latter varied along the terrestrial-marine gradient (i.e., increased among-nest variability among birds nesting within the marine environment, indicating higher degree of specialization). Terrestrial prey species (small herbivores and insectivores) were consumed by virtually all falcons. Falcons nesting within the marine environment made use of marine prey (sea birds), but depended heavily on terrestrial prey (up to 90% of the diet). Using 28-years of peregrine falcon nesting data, we found a positive relationship between the proportion of terrestrial habitat surrounding nest sites and annual nestling production, but no relationship with the likelihood of successfully rearing at least one nestling reaching 25 days old. Annually, successful inland breeders raised 0.47 more young on average compared to offshore breeders, which yields potential fitness consequences for this long-living species. The analyses of niche and reproductive success suggest a potential breeding cost for accessing distant terrestrial prey, perhaps due to additional traveling costs, for those individuals with marine nest site locations. Our study indicates how landscape heterogeneity can generate proximate (niche variation) and ultimate (reproduction) consequences on a population of generalist predator. We also show that within-individual and among-individual variation are not mutually exclusive, but can simultaneously arise and structure intra-population niche variation. PMID:24101979

L'Hérault, Vincent; Franke, Alastair; Lecomte, Nicolas; Alogut, Adam; Bêty, Joël

2013-01-01

72

Landscape heterogeneity drives intra-population niche variation and reproduction in an arctic top predator.  

PubMed

While intra-population variability in resource use is ubiquitous, little is known of how this measure of niche diversity varies in space and its role in population dynamics. Here we examined how heterogeneous breeding environments can structure intra-population niche variation in both resource use and reproductive output. We investigated intra-population niche variation in the Arctic tundra ecosystem, studying peregrine falcon (Falco peregrinus tundrius, White) breeding within a terrestrial-marine gradient near Rankin Inlet, Nunavut, Canada. Using stable isotope analysis, we found that intra-population niches varied at the individual level; we examined within-nest and among-nest variation, though only the latter varied along the terrestrial-marine gradient (i.e., increased among-nest variability among birds nesting within the marine environment, indicating higher degree of specialization). Terrestrial prey species (small herbivores and insectivores) were consumed by virtually all falcons. Falcons nesting within the marine environment made use of marine prey (sea birds), but depended heavily on terrestrial prey (up to 90% of the diet). Using 28-years of peregrine falcon nesting data, we found a positive relationship between the proportion of terrestrial habitat surrounding nest sites and annual nestling production, but no relationship with the likelihood of successfully rearing at least one nestling reaching 25 days old. Annually, successful inland breeders raised 0.47 more young on average compared to offshore breeders, which yields potential fitness consequences for this long-living species. The analyses of niche and reproductive success suggest a potential breeding cost for accessing distant terrestrial prey, perhaps due to additional traveling costs, for those individuals with marine nest site locations. Our study indicates how landscape heterogeneity can generate proximate (niche variation) and ultimate (reproduction) consequences on a population of generalist predator. We also show that within-individual and among-individual variation are not mutually exclusive, but can simultaneously arise and structure intra-population niche variation. PMID:24101979

L'hérault, Vincent; Franke, Alastair; Lecomte, Nicolas; Alogut, Adam; Bêty, Joël

2013-09-01

73

Student Difficulties With Trigonometric Vector Components Persist In Multiple Student Populations  

E-print Network

Student Difficulties With Trigonometric Vector Components Persist In Multiple Student Populations 43210 Abstract: Students in introductory physics courses sometimes struggle to correctly break down, and a coordinate system. Students struggle further when asked to break down a vector in an inclined coordinate

Heckler, Andrew F.

74

Addressing population heterogeneity and distribution in epidemics models using a cellular automata approach  

PubMed Central

Background The spread of an infectious disease is determined by biological and social factors. Models based on cellular automata are adequate to describe such natural systems consisting of a massive collection of simple interacting objects. They characterize the time evolution of the global system as the emergent behaviour resulting from the interaction of the objects, whose behaviour is defined through a set of simple rules that encode the individual behaviour and the transmission dynamic. Methods An epidemic is characterized trough an individual–based–model built upon cellular automata. In the proposed model, each individual of the population is represented by a cell of the automata. This way of modeling an epidemic situation allows to individually define the characteristic of each individual, establish different scenarios and implement control strategies. Results A cellular automata model to study the time evolution of a heterogeneous populations through the various stages of disease was proposed, allowing the inclusion of individual heterogeneity, geographical characteristics and social factors that determine the dynamic of the desease. Different assumptions made to built the classical model were evaluated, leading to following results: i) for low contact rate (like in quarantine process or low density population areas) the number of infective individuals is lower than other areas where the contact rate is higher, and ii) for different initial spacial distributions of infected individuals different epidemic dynamics are obtained due to its influence on the transition rate and the reproductive ratio of disease. Conclusions The contact rate and spatial distributions have a central role in the spread of a disease. For low density populations the spread is very low and the number of infected individuals is lower than in highly populated areas. The spacial distribution of the population and the disease focus as well as the geographical characteristic of the area play a central role in the dynamics of the desease. PMID:24725804

2014-01-01

75

Policy options for alcohol price regulation: the importance of modelling population heterogeneity.  

PubMed

Context and aims Internationally, the repertoire of alcohol pricing policies has expanded to include targeted taxation, inflation-linked taxation, taxation based on alcohol-by-volume (ABV), minimum pricing policies (general or targeted), bans of below-cost selling and restricting price-based promotions. Policy makers clearly need to consider how options compare in reducing harms at the population level, but are also required to demonstrate proportionality of their actions, which necessitates a detailed understanding of policy effects on different population subgroups. This paper presents selected findings from a policy appraisal for the UK government and discusses the importance of accounting for population heterogeneity in such analyses. Method We have built a causal, deterministic, epidemiological model which takes account of differential preferences by population subgroups defined by age, gender and level of drinking (moderate, hazardous, harmful). We consider purchasing preferences in terms of the types and volumes of alcoholic beverages, prices paid and the balance between bars, clubs and restaurants as opposed to supermarkets and off-licenses. Results Age, sex and level of drinking fundamentally affect beverage preferences, drinking location, prices paid, price sensitivity and tendency to substitute for other beverage types. Pricing policies vary in their impact on different product types, price points and venues, thus having distinctly different effects on subgroups. Because population subgroups also have substantially different risk profiles for harms, policies are differentially effective in reducing health, crime, work-place absence and unemployment harms. Conclusion Policy appraisals must account for population heterogeneity and complexity if resulting interventions are to be well considered, proportionate, effective and cost-effective. PMID:19839965

Meier, Petra Sylvia; Purshouse, Robin; Brennan, Alan

2010-03-01

76

Deconstructing stem cell population heterogeneity: Single-cell analysis and modeling approaches  

PubMed Central

Isogenic stem cell populations display cell-to-cell variations in a multitude of attributes including gene or protein expression, epigenetic state, morphology, proliferation and proclivity for differentiation. The origins of the observed heterogeneity and its roles in the maintenance of pluripotency and the lineage specification of stem cells remain unclear. Addressing pertinent questions will require the employment of single-cell analysis methods as traditional cell biochemical and biomolecular assays yield mostly population-average data. In addition to time-lapse microscopy and flow cytometry, recent advances in single-cell genomic, transcriptomic and proteomic profiling are reviewed. The application of multiple displacement amplification, next generation sequencing, mass cytometry and spectrometry to stem cell systems is expected to provide a wealth of information affording unprecedented levels of multiparametric characterization of cell ensembles under defined conditions promoting pluripotency or commitment. Establishing connections between single-cell analysis information and the observed phenotypes will also require suitable mathematical models. Stem cell self-renewal and differentiation are orchestrated by the coordinated regulation of subcellular, intercellular and niche-wide processes spanning multiple time scales. Here, we discuss different modeling approaches and challenges arising from their application to stem cell populations. Integrating single-cell analysis with computational methods will fill gaps in our knowledge about the functions of heterogeneity in stem cell physiology. This combination will also aid the rational design of efficient differentiation and reprogramming strategies as well as bioprocesses for the production of clinically valuable stem cell derivatives. PMID:24035899

Wu, Jincheng; Tzanakakis, Emmanuel S.

2014-01-01

77

Deconstructing stem cell population heterogeneity: single-cell analysis and modeling approaches.  

PubMed

Isogenic stem cell populations display cell-to-cell variations in a multitude of attributes including gene or protein expression, epigenetic state, morphology, proliferation and proclivity for differentiation. The origins of the observed heterogeneity and its roles in the maintenance of pluripotency and the lineage specification of stem cells remain unclear. Addressing pertinent questions will require the employment of single-cell analysis methods as traditional cell biochemical and biomolecular assays yield mostly population-average data. In addition to time-lapse microscopy and flow cytometry, recent advances in single-cell genomic, transcriptomic and proteomic profiling are reviewed. The application of multiple displacement amplification, next generation sequencing, mass cytometry and spectrometry to stem cell systems is expected to provide a wealth of information affording unprecedented levels of multiparametric characterization of cell ensembles under defined conditions promoting pluripotency or commitment. Establishing connections between single-cell analysis information and the observed phenotypes will also require suitable mathematical models. Stem cell self-renewal and differentiation are orchestrated by the coordinated regulation of subcellular, intercellular and niche-wide processes spanning multiple time scales. Here, we discuss different modeling approaches and challenges arising from their application to stem cell populations. Integrating single-cell analysis with computational methods will fill gaps in our knowledge about the functions of heterogeneity in stem cell physiology. This combination will also aid the rational design of efficient differentiation and reprogramming strategies as well as bioprocesses for the production of clinically valuable stem cell derivatives. PMID:24035899

Wu, Jincheng; Tzanakakis, Emmanuel S

2013-11-15

78

Statewide Survey of ESL Student Populations: Overview.  

ERIC Educational Resources Information Center

In spring 1989, 25 community colleges conducted a survey of their English-as-a-Second-Language (ESL) students to project the need for ESL services at institutional and statewide levels, and to assess students' existing and desired levels of English proficiency, and the time and resources needed to achieve the desired level. In addition, the study…

Spicer, Scot L.; And Others

79

Isolation and enrichment of defined neural cell populations from heterogeneous neural stem cell progeny.  

PubMed

The renewable source of neural stem cells (NSCs) with multi-lineage differentiation capability towards neurons, astrocytes, and oligodendrocytes represent an ideal supply for cell therapy of central nervous system (CNS) diseases. In spite of this, the clinical use of NSCs is hampered by heterogeneity, poor neuronal cell yield, predominant astrocytic differentiation of NSC progeny and possible uncontrolled proliferation, and tumor formation upon transplantation. The ability to generate highly enriched and defined neural cell populations from the renewable source of NSCs might overcome many of these impediments and pave the way towards their successful clinical applications. Here, we describe a simple method for NSC differentiation and subsequent purification of neuronal progenitor cells, taking advantage of size and granularity differences between neuronal cells and other NSC progeny. This highly enriched neuronal cell population provides an invaluable source of cells for both in vitro and in vivo studies. PMID:23934837

Azari, Hassan

2013-01-01

80

Synchronization in interacting populations of heterogeneous oscillators with time-varying coupling.  

PubMed

In many networks of interest (including technological, biological, and social networks), the connectivity between the interacting elements is not static, but changes in time. Furthermore, the elements themselves are often not identical, but rather display a variety of behaviors, and may come in different classes. Here, we investigate the dynamics of such systems. Specifically, we study a network of two large interacting heterogeneous populations of limit-cycle oscillators whose connectivity switches between two fixed arrangements at a particular frequency. We show that for sufficiently high switching frequency, this system behaves as if the connectivity were static and equal to the time average of the switching connectivity. We also examine the mechanisms by which this fast-switching limit is approached in several nonintuitive cases. The results illuminate novel mechanisms by which synchronization can arise or be thwarted in large populations of coupled oscillators with nonstatic coupling. PMID:19045488

So, Paul; Cotton, Bernard C; Barreto, Ernest

2008-09-01

81

Impact of Roles Assignation on Heterogeneous Populations in Evolutionary Dictator Game  

NASA Astrophysics Data System (ADS)

The evolution of cooperation is a hot and challenging topic in the field of evolutionary game theory. Altruistic behavior, as a particular form of cooperation, has been widely studied by the ultimatum game but not by the dictator game, which provides a more elegant way to identify the altruistic component of behaviors. In this paper, the evolutionary dictator game is applied to model the real motivations of altruism. A degree-based regime is utilized to assess the impact of the assignation of roles on evolutionary outcome in populations of heterogeneous structure with two kinds of strategic updating mechanisms, which are based on Darwin's theory of evolution and punctuated equilibrium, respectively. The results show that the evolutionary outcome is affected by the role assignation and that this impact also depends on the strategic updating mechanisms, the function used to evaluate players' success, and the structure of populations.

Deng, Xinyang; Liu, Qi; Sadiq, Rehan; Deng, Yong

2014-11-01

82

Impact of Roles Assignation on Heterogeneous Populations in Evolutionary Dictator Game  

PubMed Central

The evolution of cooperation is a hot and challenging topic in the field of evolutionary game theory. Altruistic behavior, as a particular form of cooperation, has been widely studied by the ultimatum game but not by the dictator game, which provides a more elegant way to identify the altruistic component of behaviors. In this paper, the evolutionary dictator game is applied to model the real motivations of altruism. A degree-based regime is utilized to assess the impact of the assignation of roles on evolutionary outcome in populations of heterogeneous structure with two kinds of strategic updating mechanisms, which are based on Darwin's theory of evolution and punctuated equilibrium, respectively. The results show that the evolutionary outcome is affected by the role assignation and that this impact also depends on the strategic updating mechanisms, the function used to evaluate players' success, and the structure of populations. PMID:25377303

Deng, Xinyang; Liu, Qi; Sadiq, Rehan; Deng, Yong

2014-01-01

83

Understanding Sleep Disorders in a College Student Population.  

ERIC Educational Resources Information Center

College students' sleep habits are changing dramatically, and related sleep problems are increasing. Reviews the current literature on sleep problems, focusing on the college student population. The unique challenges of college settings are discussed as they apply to understanding sleep problems, and suggestions are made for professionals who work…

Jensen, Dallas R.

2003-01-01

84

Rapid estimation of genetic relatedness among heterogeneous populations of alfalfa by random amplification of bulked genomic DNA samples  

Microsoft Academic Search

A procedure which involves the use of RAPD markers, obtained from bulked genomic DNA samples, to estimate genetic relatedness among heterogeneous populations is demonstrated in this study. Bulked samples of genomic DNA from several alfalfa plants per population were used as templates in polymerase chain reactions with different random primers to produce RAPD patterns. The results show that the RAPD

Kangfu Yu; K. P. Pauls

1993-01-01

85

Full-length haplotype reconstruction to infer the structure of heterogeneous virus populations  

PubMed Central

Next-generation sequencing (NGS) technologies enable new insights into the diversity of virus populations within their hosts. Diversity estimation is currently restricted to single-nucleotide variants or to local fragments of no more than a few hundred nucleotides defined by the length of sequence reads. To study complex heterogeneous virus populations comprehensively, novel methods are required that allow for complete reconstruction of the individual viral haplotypes. Here, we show that assembly of whole viral genomes of ?8600 nucleotides length is feasible from mixtures of heterogeneous HIV-1 strains derived from defined combinations of cloned virus strains and from clinical samples of an HIV-1 superinfected individual. Haplotype reconstruction was achieved using optimized experimental protocols and computational methods for amplification, sequencing and assembly. We comparatively assessed the performance of the three NGS platforms 454 Life Sciences/Roche, Illumina and Pacific Biosciences for this task. Our results prove and delineate the feasibility of NGS-based full-length viral haplotype reconstruction and provide new tools for studying evolution and pathogenesis of viruses. PMID:24972832

Giallonardo, Francesca Di; Töpfer, Armin; Rey, Melanie; Prabhakaran, Sandhya; Duport, Yannick; Leemann, Christine; Schmutz, Stefan; Campbell, Nottania K.; Joos, Beda; Lecca, Maria Rita; Patrignani, Andrea; Däumer, Martin; Beisel, Christian; Rusert, Peter; Trkola, Alexandra; Günthard, Huldrych F.; Roth, Volker; Beerenwinkel, Niko; Metzner, Karin J.

2014-01-01

86

Application of phasor plot and autofluorescence correction for study of heterogeneous cell population.  

PubMed

Protein-protein interactions in cells are often studied using fluorescence resonance energy transfer (FRET) phenomenon by fluorescence lifetime imaging microscopy (FLIM). Here, we demonstrate approaches to the quantitative analysis of FRET in cell population in a case complicated by a highly heterogeneous donor expression, multiexponential donor lifetime, large contribution of cell autofluorescence, and significant presence of unquenched donor molecules that do not interact with the acceptor due to low affinity of donor-acceptor binding. We applied a multifrequency phasor plot to visualize FRET FLIM data, developed a method for lifetime background correction, and performed a detailed time-resolved analysis using a biexponential model. These approaches were applied to study the interaction between the Toll Interleukin-1 receptor (TIR) domain of Toll-like receptor 4 (TLR4) and the decoy peptide 4BB. TLR4 was fused to Cerulean fluorescent protein (Cer) and 4BB peptide was labeled with Bodipy TMRX (BTX). Phasor displays for multifrequency FLIM data are presented. The analytical procedure for lifetime background correction is described and the effect of correction on FLIM data is demonstrated. The absolute FRET efficiency was determined based on the phasor plot display and multifrequency FLIM data analysis. The binding affinity between TLR4-Cer (donor) and decoy peptide 4BB-BTX (acceptor) was estimated in a heterogeneous HeLa cell population. PMID:24770662

Szmacinski, Henryk; Toshchakov, Vladimir; Lakowicz, Joseph R

2014-04-01

87

Full-length haplotype reconstruction to infer the structure of heterogeneous virus populations.  

PubMed

Next-generation sequencing (NGS) technologies enable new insights into the diversity of virus populations within their hosts. Diversity estimation is currently restricted to single-nucleotide variants or to local fragments of no more than a few hundred nucleotides defined by the length of sequence reads. To study complex heterogeneous virus populations comprehensively, novel methods are required that allow for complete reconstruction of the individual viral haplotypes. Here, we show that assembly of whole viral genomes of ?8600 nucleotides length is feasible from mixtures of heterogeneous HIV-1 strains derived from defined combinations of cloned virus strains and from clinical samples of an HIV-1 superinfected individual. Haplotype reconstruction was achieved using optimized experimental protocols and computational methods for amplification, sequencing and assembly. We comparatively assessed the performance of the three NGS platforms 454 Life Sciences/Roche, Illumina and Pacific Biosciences for this task. Our results prove and delineate the feasibility of NGS-based full-length viral haplotype reconstruction and provide new tools for studying evolution and pathogenesis of viruses. PMID:24972832

Giallonardo, Francesca Di; Töpfer, Armin; Rey, Melanie; Prabhakaran, Sandhya; Duport, Yannick; Leemann, Christine; Schmutz, Stefan; Campbell, Nottania K; Joos, Beda; Lecca, Maria Rita; Patrignani, Andrea; Däumer, Martin; Beisel, Christian; Rusert, Peter; Trkola, Alexandra; Günthard, Huldrych F; Roth, Volker; Beerenwinkel, Niko; Metzner, Karin J

2014-08-01

88

Cancer research in Asian American, Native Hawaiian, and Pacific Islander populations: accelerating cancer knowledge by acknowledging and leveraging heterogeneity.  

PubMed

The Asian American, Native Hawaiian, and Pacific Islander population is large, growing, and extremely heterogeneous. Not only do they bear unique burdens of incidence and outcomes for certain cancer types, they exhibit substantial variability in cancer incidence and survival patterns across the ethnic groups. By acknowledging and leveraging this heterogeneity through investing in cancer research within these populations, we have a unique opportunity to accelerate the availability of useful and impactful cancer knowledge. See all the articles in this CEBP Focus section, "Cancer in Asian and Pacific Islander Populations." PMID:25368394

Gomez, Scarlett Lin; Glaser, Sally L; Horn-Ross, Pamela L; Cheng, Iona; Quach, Thu; Clarke, Christina A; Reynolds, Peggy; Shariff-Marco, Salma; Yang, Juan; Lee, Marion M; Satariano, William A; Hsing, Ann W

2014-11-01

89

Mitochondrial DNA from El Mirador Cave (Atapuerca, Spain) Reveals the Heterogeneity of Chalcolithic Populations  

PubMed Central

Previous mitochondrial DNA analyses on ancient European remains have suggested that the current distribution of haplogroup H was modeled by the expansion of the Bell Beaker culture (ca 4,500–4,050 years BP) out of Iberia during the Chalcolithic period. However, little is known on the genetic composition of contemporaneous Iberian populations that do not carry the archaeological tool kit defining this culture. Here we have retrieved mitochondrial DNA (mtDNA) sequences from 19 individuals from a Chalcolithic sample from El Mirador cave in Spain, dated to 4,760–4,200 years BP and we have analyzed the haplogroup composition in the context of modern and ancient populations. Regarding extant African, Asian and European populations, El Mirador shows affinities with Near Eastern groups. In different analyses with other ancient samples, El Mirador clusters with Middle and Late Neolithic populations from Germany, belonging to the Rössen, the Salzmünde and the Baalberge archaeological cultures but not with contemporaneous Bell Beakers. Our analyses support the existence of a common genetic signal between Western and Central Europe during the Middle and Late Neolithic and points to a heterogeneous genetic landscape among Chalcolithic groups. PMID:25116044

Pierini, Federica; Matas-Lalueza, Laura; Gigli, Elena; Lari, Martina; Civit, Sergi; Lozano, Marina; Vergès, Josep Maria; Caramelli, David; Ramírez, Oscar; Lalueza-Fox, Carles

2014-01-01

90

Temporal and Spatial Heterogeneity of Mtdna Polymorphisms in Natural Populations of Drosophila mercatorum  

PubMed Central

Restriction endonuclease analysis of mtDNA was used to examine the genetic relatedness of several geographically separated isolines of the Drosophila mercatorum subgroup. In addition, we examined the temporal and spatial distribution of two mtDNA restriction site polymorphisms produced by the enzymes BstEII and BstNI at a single locality—Kamuela, Hawaii. Due to small sample sizes of some collections and the undesirable dependance of the estimation of polymorphism frequency on its variance, an arcsin square root transformation of the frequency data was used. We also use an Fst estimator of our transformed frequencies to demonstrate considerable spatial and temporal differentiation within the Kamuela population. In contrast, isozyme data from the same population reveals no pattern of differentiation. The temporal and geographic heterogeneity and population subdivision detected with mtDNA analysis also is consistent with the known dispersal behavior and ecological constraints of this species. The mtDNA data in conjunction with the isozyme data show that the population structure of the Kamuela D. mercatorum is close to the boundary line separating panmixia from subdivision, a conclusion that could not be made from isozyme data alone. PMID:3038671

DeSalle, Rob; Templeton, Alan; Mori, Ikue; Pletscher, Susan; Johnston, J. Spencer

1987-01-01

91

Heterogeneity of single cell cytokine gene expression in clonal T cell populations  

PubMed Central

T helper type 0 (Th0), Th1, and Th2 CD4+ T cell clones derived from a T cell receptor alpha/beta (TCR-alpha/beta) transgenic mouse were activated by antigen presented on "artificial" antigen-presenting cells that expressed or lacked the costimulatory molecule B7-1, and were analyzed for single cell cytokine mRNA expression by in situ hybridization. There was significant heterogeneity in the frequency of T cells that expressed individual cytokine mRNAs within each clonal population, suggesting that transcriptional control of each of the cytokine genes was not coordinate within an individual cell. The majority of antigen-stimulated Th1 cells expressed mRNA for interferon gamma (IFN-gamma), but far fewer cells in the same population expressed interleukin 2 (IL-2). Similarly, the frequency of IL-4-expressing cells was greater than that of IL-5- or IL-10-expressing cells in the same Th2 population, but the difference in expression frequencies was more variable between clones. The expression frequencies of each of the cytokines was quite heterogeneous in the antigen-activated Th0 population. The principal effect of increased antigen on the activation of individual cytokine genes in each of the clonal populations was to increase recruitment of mRNA-positive cells, with little or no effect on the level of cytokine mRNA expression in individual positive cells. The effects of B7 costimulation were variable depending on the cytokine gene analyzed. B7 costimulation markedly increased the frequency and the level of IL-2 mRNA expression in individual positive cells in the Th1 and Th0 populations, with less effect on the recruitment and single cell expression level of IFN-gamma. IL-4 frequencies were modestly increased by B7 costimulation of the Th2 clones, but there was no detectable increase in single cell IL-4 expression level. The observed patterns of cytokine mRNA expression favor a model of T cell activation in which all-or-none, rather than graded, responses of cytokine genes are dominant. PMID:7523568

1994-01-01

92

Evidence That the Heterogeneity of a T4 Population Is the Result of Heritable Traits  

PubMed Central

Many bacteriophage populations display heterogeneity in their adsorption characteristics; a portion of the phage population remains free in solution throughout adsorption experiments (residual fraction). This residual fraction generally constitutes a minority of phages that exhibit significantly slower adsorption kinetics than the main phage stock (main fraction). While this phenomenon is likely the result of evolutionary driving forces, the present study demonstrates that the residual fraction is not always the result of phenotypic variations within a single genotype, as is generally thought. Experiments with phage T4 showed that two subgroups with distinct adsorption traits that were passed on to their progeny could be isolated from the original phage stock. Sequencing of genes involved in adsorption revealed two point mutations in gene 37 of residual fraction isolates, which resulted in modifications to the long tail-fiber, the organelle of attachment and host cell recognition. Adsorption studies consistently showed that T4 phage stocks amplified from residual fraction isolates had significantly lower adsorption efficiencies than those amplified from main fractions. The conducted experiments provide convincing evidence that the observed heterogeneity in T4 adsorption behavior is the result of conserved mutations to the phage genome and is not exclusively the result of phenotypic variations within the population. While it is believed high mutation rates exist to hasten phage adaptation, this study shows that this bet hedging strategy can also, in the short term, inadvertently handicap the phage's adsorption capabilities to a given host under normal infection conditions, resulting in the residual fraction observed in adsorption experiments. PMID:25551763

Storms, Zachary J.; Sauvageau, Dominic

2014-01-01

93

Deep-Sequencing of the Peach Latent Mosaic Viroid Reveals New Aspects of Population Heterogeneity  

PubMed Central

Viroids are small circular single-stranded infectious RNAs characterized by a relatively high mutation level. Knowledge of their sequence heterogeneity remains largely elusive and previous studies, using Sanger sequencing, were based on a limited number of sequences. In an attempt to address sequence heterogeneity from a population dynamics perspective, a GF305-indicator peach tree was infected with a single variant of the Avsunviroidae family member Peach latent mosaic viroid (PLMVd). Six months post-inoculation, full-length circular conformers of PLMVd were isolated and deep-sequenced. We devised an original approach to the bioinformatics refinement of our sequence libraries involving important phenotypic data, based on the systematic analysis of hammerhead self-cleavage activity. Two distinct libraries yielded a total of 3,939 different PLMVd variants. Sequence variants exhibiting up to ?17% of mutations relative to the inoculated viroid were retrieved, clearly illustrating the high level of divergence dynamics within a unique population. While we initially assumed that most positions of the viroid sequence would mutate, we were surprised to discover that ?50% of positions remained perfectly conserved, including several small stretches as well as a small motif reminiscent of a GNRA tetraloop which are the result of various selective pressures. Using a hierarchical clustering algorithm, the different variants harvested were subdivided into 7 clusters. We found that most sequences contained an average of 4.6 to 6.4 mutations compared to the variant used to initially inoculate the plant. Interestingly, it was possible to reconstitute and compare the sequence evolution of each of these clusters. In doing so, we identified several key mutations. This study provides a reliable pipeline for the treatment of viroid deep-sequencing. It also sheds new light on the extent of sequence variation that a viroid population can sustain, and which may give rise to a quasispecies. PMID:24498066

Wang, Shengrui; Najmanovich, Rafael J.; Perreault, Jean-Pierre

2014-01-01

94

Exposing medical students to expanding populations  

PubMed Central

Physicians are required to advocate for and counsel patients based on the best science and the interests of the individual while avoiding discrimination, ensuring equal access to health and mental services. Nonetheless, the communication gap between physician and patients has long been observed. To this end, the Institute for the Public Understanding of Health and Medicine of the Rutgers University New Jersey Medical School has expanded its efforts. This report describes two new programs: a legacy lecture series for medical students and an international “experience”, in Huancayo, Peru, for medical students and faculty. The MiniMed outreach program, now in its ninth year and first described in this journal in 2012, was designed to empower the powerless to communicate more effectively with clinicians, thus improving both the effectiveness of the physician–patient relationship and health care outcomes. The approach of the two new programs and their effects on patients, particularly the underserved, and medical students and faculty, are outlined in the following article. PMID:25834472

Lindenthal, JJ; DeLisa, JA; Heinrich, GF; Calderón Gerstein, WS

2015-01-01

95

Heterogeneity in genetic diversity among non-coding loci fails to fit neutral coalescent models of population history.  

PubMed

Inferring aspects of the population histories of species using coalescent analyses of non-coding nuclear DNA has grown in popularity. These inferences, such as divergence, gene flow, and changes in population size, assume that genetic data reflect simple population histories and neutral evolutionary processes. However, violating model assumptions can result in a poor fit between empirical data and the models. We sampled 22 nuclear intron sequences from at least 19 different chromosomes (a genomic transect) to test for deviations from selective neutrality in the gadwall (Anas strepera), a Holarctic duck. Nucleotide diversity among these loci varied by nearly two orders of magnitude (from 0.0004 to 0.029), and this heterogeneity could not be explained by differences in substitution rates alone. Using two different coalescent methods to infer models of population history and then simulating neutral genetic diversity under these models, we found that the observed among-locus heterogeneity in nucleotide diversity was significantly higher than expected for these simple models. Defining more complex models of population history demonstrated that a pre-divergence bottleneck was also unlikely to explain this heterogeneity. However, both selection and interspecific hybridization could account for the heterogeneity observed among loci. Regardless of the cause of the deviation, our results illustrate that violating key assumptions of coalescent models can mislead inferences of population history. PMID:22384117

Peters, Jeffrey L; Roberts, Trina E; Winker, Kevin; McCracken, Kevin G

2012-01-01

96

The genetic structure of a Venturia inaequalis population in a heterogeneous host population composed of different Malus species  

PubMed Central

Background Adaptation, which induces differentiation between populations in relation to environmental conditions, can initiate divergence. The balance between gene flow and selection determines the maintenance of such a structure in sympatry. Studying these two antagonistic forces in plant pathogens is made possible because of the high ability of pathogens to disperse and of the strong selective pressures exerted by their hosts. In this article, we analysed the genetic structure of the population of the apple scab fungus, Venturia inaequalis, in a heterogeneous environment composed of various Malus species. Inferences were drawn from microsatellite and AFLP data obtained from 114 strains sampled in a single orchard on nine different Malus species to determine the forces that shape the genetic structure of the pathogen. Results Using clustering methods, we first identified two specialist subpopulations: (i) a virulent subpopulation sampled on Malus trees carrying the Rvi6 resistance gene; and (ii) a subpopulation infecting only Malus trees that did not carry this resistance gene. A genome scan of loci on these two subpopulations did not detect any locus under selection. Additionally, we did not detect any other particular substructure linked to different hosts. However, an isolation-by-distance (IBD) pattern at the orchard scale revealed free gene flow within each subpopulation. Conclusions Our work shows a rare example of a very strong effect of a resistance gene on pathogen populations. Despite the high diversity of Malus hosts, the presence of Rvi6 seems sufficient to explain the observed genetic structure. Moreover, detection of an IBD pattern at the orchard scale revealed a very low average dispersal distance that is particularly significant for epidemiologists and landscape managers for the design of scab control strategies PMID:23497223

2013-01-01

97

Population Genomics Reveals Chromosome-Scale Heterogeneous Evolution in a Protoploid Yeast  

PubMed Central

Yeast species represent an ideal model system for population genomic studies but large-scale polymorphism surveys have only been reported for species of the Saccharomyces genus so far. Hence, little is known about intraspecific diversity and evolution in yeast. To obtain a new insight into the evolutionary forces shaping natural populations, we sequenced the genomes of an expansive worldwide collection of isolates from a species distantly related to Saccharomyces cerevisiae: Lachancea kluyveri (formerly S. kluyveri). We identified 6.5 million single nucleotide polymorphisms and showed that a large introgression event of 1 Mb of GC-rich sequence in the chromosomal arm probably occurred in the last common ancestor of all L. kluyveri strains. Our population genomic data clearly revealed that this 1-Mb region underwent a molecular evolution pattern very different from the rest of the genome. It is characterized by a higher recombination rate, with a dramatically elevated A:T ? G:C substitution rate, which is the signature of an increased GC-biased gene conversion. In addition, the predicted base composition at equilibrium demonstrates that the chromosome-scale compositional heterogeneity will persist after the genome has reached mutational equilibrium. Altogether, the data presented herein clearly show that distinct recombination and substitution regimes can coexist and lead to different evolutionary patterns within a single genome. PMID:25349286

Friedrich, Anne; Jung, Paul; Reisser, Cyrielle; Fischer, Gilles; Schacherer, Joseph

2015-01-01

98

Microselection – affinity selecting antibodies against a single rare cell in a heterogeneous population  

PubMed Central

Abstract Rare cells not normally present in the peripheral bloodstream, such as circulating tumour cells, have potential applications for development of non-invasive methods for diagnostics or follow up. Obtaining these cells however require some means of discrimination, achievable by cell type specific antibodies. Here we have generated a microselection method allowing antibody selection, by phage display, targeting a single cell in a heterogeneous population. One K562 cell (female origin) was positioned on glass slide among millions of lymphocytes from male donor, identifying the K562 cell by FISH (XX). Several single cell selections were performed on such individual slides. The phage particles bound to the target cell is protected by a minute disc, while inactivating all remaining phage by UV-irradiation; leaving only the phage bound to the target cell viable. We hereby retrieved up to eight antibodies per single cell selection, including three highly K562 cell type specific. PMID:20726925

Sørensen, Morten Dræby; Agerholm, Inge Errebo; Christensen, Britta; Kølvraa, Steen; Kristensen, Peter

2010-01-01

99

Light Microscopic Analysis of Mitochondrial Heterogeneity in Cell Populations and Within Single Cells  

Microsoft Academic Search

\\u000a \\u000a Abstract  Heterogeneity in the shapes of individual multicellular organisms is a daily experience. Likewise, even a quick glance through\\u000a the ocular of a light microscope reveals the morphological heterogeneities in genetically identical cultured cells, whereas\\u000a heterogeneities on the level of the organelles are much less obvious. This short review focuses on intracellular heterogeneities\\u000a at the example of the mitochondria and their

Stefan Jakobs; Stefan Stoldt; Daniel Neumann

100

Population-level thermal performance of a cold-water ectotherm is linked to ontogeny and local environmental heterogeneity  

USGS Publications Warehouse

5. Our experiments with a cold-water species show that population-level performance varies across small geographic scales and is linked to local environmental heterogeneity. This variation could influence the rate and mode of species-level responses to climate change, both by facilitating local persistence in the face of change

Hossack, Blake R.; Corn, P. Stephen; , Winsor H. Lowe; , Molly A. H. Webb; , Mariah J. Talbott; , Kevin M. Kappenman

2013-01-01

101

Parasite strain coexistence in a heterogeneous host population Darren M. Green, Istvan Z. Kiss and Rowland R. Kao  

E-print Network

Parasite strain coexistence in a heterogeneous host population Darren M. Green, Istvan Z. Kiss and Rowland R. Kao Green, D. M., Kiss, I. Z. and Kao, R. R. 2006. Parasite strain coexistence to parasite attack allows a lower transmission rate to sustain an epidemic than is required in homogeneous

Kiss, Istvan Zoltan

102

Single-Cell Behavior and Population Heterogeneity: Solving an Inverse Problem to Compute the Intrinsic Physiological State Functions  

PubMed Central

The dynamics of isogenic cell populations can be described by cell population balance models that account for phenotypic heterogeneity. To utilize the predictive power of these models, however, we must know the rates of single-cell reaction and division and the bivariate partition probability density function. These three intrinsic physiological state (IPS) functions can be obtained by solving an inverse problem that requires knowledge of the phenotypic distributions for the overall cell population, the dividing cell subpopulation and the newborn cell subpopulation. We present here a robust computational procedure that can accurately estimate the IPS functions for heterogeneous cell populations. A detailed parametric analysis shows how the accuracy of the inverse solution is affected by discretization parameters, the type of non-parametric estimators used, the qualitative characteristics of phenotypic distributions and the unknown partitioning probability density function. The effect of finite sampling and measurement errors on the accuracy of the recovered IPS functions is also assessed. Finally, we apply the procedure to estimate the IPS functions of an E. coli population carrying an IPTG-inducible genetic toggle network. This study completes the development of an integrated experimental and computational framework that can become a powerful tool for quantifying single-cell behavior using measurements from heterogeneous cell populations. PMID:21930163

Spetsieris, Konstantinos; Zygourakis, Kyriacos

2011-01-01

103

Culture History and Population Heterogeneity as Determinants of Bacterial Adaptation: the Adaptomics of a Single Environmental Transition  

PubMed Central

Summary: Diversity in adaptive responses is common within species and populations, especially when the heterogeneity of the frequently large populations found in environments is considered. By focusing on events in a single clonal population undergoing a single transition, we discuss how environmental cues and changes in growth rate initiate a multiplicity of adaptive pathways. Adaptation is a comprehensive process, and stochastic, regulatory, epigenetic, and mutational changes can contribute to fitness and overlap in timing and frequency. We identify culture history as a major determinant of both regulatory adaptations and microevolutionary change. Population history before a transition determines heterogeneities due to errors in translation, stochastic differences in regulation, the presence of aged, damaged, cheating, or dormant cells, and variations in intracellular metabolite or regulator concentrations. It matters whether bacteria come from dense, slow-growing, stressed, or structured states. Genotypic adaptations are history dependent due to variations in mutation supply, contingency gene changes, phase variation, lateral gene transfer, and genome amplifications. Phenotypic adaptations underpin genotypic changes in situations such as stress-induced mutagenesis or prophage induction or in biofilms to give a continuum of adaptive possibilities. Evolutionary selection additionally provides diverse adaptive outcomes in a single transition and generally does not result in single fitter types. The totality of heterogeneities in an adapting population increases the chance that at least some individuals meet immediate or future challenges. However, heterogeneity complicates the adaptomics of single transitions, and we propose that subpopulations will need to be integrated into future population biology and systems biology predictions of bacterial behavior. PMID:22933562

Ryall, Ben; Eydallin, Gustavo

2012-01-01

104

Evidence of a sophisticatedly heterogeneous population of human umbilical vein endothelial cells.  

PubMed

Induction and promotion of angiogenesis play a role in a diverse range of physiologic and pathophysiologic processes that are especially relevant to the field of regenerative medicine. For assessing vasculogenesis and neo-angiogenesis, identifying angiogenic factors, angiocrine factors, and vascular niche, facilitating tissue-repair and tumor growth, efficiently generating induced pluripotent stem cells, and coculturing with organ-specific stem cells, isolation and characterization of the subpopulation of human umbilical vein endothelial cells (HUVECs) and their endothelial progenitor cells (EPCs) are needed. In this study, primary HUVECs were collected from fresh umbilical cords and fractionated and characterized with the use of flow cytometry. Clonal colony assay showed that endothelial colony-forming units in culture frequently existed in fresh HUVECs. Antigenic profiling demonstrated that undifferentiated EPCs in HUVECs had normal endothelial marker CD31 with a subpopulation of cells positive for hematopoietic stem cell marker CD34 and c-Kit. With continuing passages, EPC markers CD34 and vascular endothelial growth factor receptor 2 expression decreased dramatically. Moreover, a distinct subpopulation with different proliferative capability and angiogenesis from the early-passage HUVECs was shown. In conclusion, it is possible to isolate accurately and to enrich EPCs or hematoangioblast-like cells from a heterogeneous population of HUVECs, and to explore the differential process with flow cytometry for further investigations. PMID:24815173

Zheng, Y-W; Nie, Y-Z; Tsuchida, T; Zhang, R-R; Aoki, K; Sekine, K; Ogawa, M; Takebe, T; Ueno, Y; Sakakibara, H; Hirahara, F; Taniguchi, H

2014-05-01

105

Joint Effects of Habitat Heterogeneity and Species’ Life-History Traits on Population Dynamics in Spatially Structured Landscapes  

PubMed Central

Both habitat heterogeneity and species’ life-history traits play important roles in driving population dynamics, yet there is little scientific consensus around the combined effect of these two factors on populations in complex landscapes. Using a spatially explicit agent-based model, we explored how interactions between habitat spatial structure (defined here as the scale of spatial autocorrelation in habitat quality) and species life-history strategies (defined here by species environmental tolerance and movement capacity) affect population dynamics in spatially heterogeneous landscapes. We compared the responses of four hypothetical species with different life-history traits to four landscape scenarios differing in the scale of spatial autocorrelation in habitat quality. The results showed that the population size of all hypothetical species exhibited a substantial increase as the scale of spatial autocorrelation in habitat quality increased, yet the pattern of population increase was shaped by species’ movement capacity. The increasing scale of spatial autocorrelation in habitat quality promoted the resource share of individuals, but had little effect on the mean mortality rate of individuals. Species’ movement capacity also determined the proportion of individuals in high-quality cells as well as the proportion of individuals experiencing competition in response to increased spatial autocorrelation in habitat quality. Positive correlations between the resource share of individuals and the proportion of individuals experiencing competition indicate that large-scale spatial autocorrelation in habitat quality may mask the density-dependent effect on populations through increasing the resource share of individuals, especially for species with low mobility. These findings suggest that low-mobility species may be more sensitive to habitat spatial heterogeneity in spatially structured landscapes. In addition, localized movement in combination with spatial autocorrelation may increase the population size, despite increased density effects. PMID:25232739

Ye, Xinping; Skidmore, Andrew K.; Wang, Tiejun

2014-01-01

106

Use of posterior predictive checks as an inferential tool for investigating individual heterogeneity in animal population vital rates  

PubMed Central

The investigation of individual heterogeneity in vital rates has recently received growing attention among population ecologists. Individual heterogeneity in wild animal populations has been accounted for and quantified by including individually varying effects in models for mark–recapture data, but the real need for underlying individual effects to account for observed levels of individual variation has recently been questioned by the work of Tuljapurkar et al. (Ecology Letters, 12, 93, 2009) on dynamic heterogeneity. Model-selection approaches based on information criteria or Bayes factors have been used to address this question. Here, we suggest that, in addition to model-selection, model-checking methods can provide additional important insights to tackle this issue, as they allow one to evaluate a model's misfit in terms of ecologically meaningful measures. Specifically, we propose the use of posterior predictive checks to explicitly assess discrepancies between a model and the data, and we explain how to incorporate model checking into the inferential process used to assess the practical implications of ignoring individual heterogeneity. Posterior predictive checking is a straightforward and flexible approach for performing model checks in a Bayesian framework that is based on comparisons of observed data to model-generated replications of the data, where parameter uncertainty is incorporated through use of the posterior distribution. If discrepancy measures are chosen carefully and are relevant to the scientific context, posterior predictive checks can provide important information allowing for more efficient model refinement. We illustrate this approach using analyses of vital rates with long-term mark–recapture data for Weddell seals and emphasize its utility for identifying shortfalls or successes of a model at representing a biological process or pattern of interest. We show how posterior predictive checks can be used to strengthen inferences in ecological studies. We demonstrate the application of this method on analyses dealing with the question of individual reproductive heterogeneity in a population of Antarctic pinnipeds. PMID:24834335

Chambert, Thierry; Rotella, Jay J; Higgs, Megan D

2014-01-01

107

Spatial invasion dynamics on random and unstructured meshes: implications for heterogeneous tumor populations.  

PubMed

In this work we discuss a spatial evolutionary model for a heterogeneous cancer cell population. We consider the gain-of-function mutations that not only change the fitness potential of the mutant phenotypes against normal background cells but may also increase the relative motility of the mutant cells. The spatial modeling is implemented as a stochastic evolutionary system on a structured grid (a lattice, with random neighborhoods, which is not necessarily bi-directional) or on a two-dimensional unstructured mesh, i.e. a bi-directional graph with random numbers of neighbors. We present a computational approach to investigate the fixation probability of mutants in these spatial models. Additionally, we examine the effect of the migration potential on the spatial dynamics of mutants on unstructured meshes. Our results suggest that the probability of fixation is negatively correlated with the width of the distribution of the neighborhood size. Also, the fixation probability increases given a migration potential for mutants. We find that the fixation probability (of advantaged, disadvantaged and neutral mutants) on unstructured meshes is relatively smaller than the corresponding results on regular grids. More importantly, in the case of neutral mutants the introduction of a migration potential has a critical effect on the fixation probability and increases this by orders of magnitude. Further, we examine the effect of boundaries and as intuitively expected, the fixation probability is smaller on the boundary of regular grids when compared to its value in the bulk. Based on these computational results, we speculate on possible better therapeutic strategies that may delay tumor progression to some extent. PMID:24462897

Manem, V S K; Kohandel, M; Komarova, N L; Sivaloganathan, S

2014-05-21

108

Genomic Heterogeneity in a Natural Archaeal Population Suggests a Model of tRNA Gene Disruption  

PubMed Central

Understanding the mechanistic basis of the disruption of tRNA genes, as manifested in the intron-containing and split tRNAs found in Archaea, will provide considerable insight into the evolution of the tRNA molecule. However, the evolutionary processes underlying these disruptions have not yet been identified. Previously, a composite genome of the deep-branching archaeon Caldiarchaeum subterraneum was reconstructed from a community genomic library prepared from a C. subterraneum–dominated microbial mat. Here, exploration of tRNA genes from the library reveals that there are at least three types of heterogeneity at the tRNAThr(GGU) gene locus in the Caldiarchaeum population. All three involve intronic gain and splitting of the tRNA gene. Of two fosmid clones found that encode tRNAThr(GGU), one (tRNAThr-I) contains a single intron, whereas another (tRNAThr-II) contains two introns. Notably, in the clone possessing tRNAThr-II, a 5? fragment of the tRNAThr-I (tRNAThr-F) gene was observed 1.8-kb upstream of tRNAThr-II. The composite genome contains both tRNAThr-II and tRNAThr-F, although the loci are >500 kb apart. Given that the 1.8-kb sequence flanked by tRNAThr-F and tRNAThr-II is predicted to encode a DNA recombinase and occurs in six regions of the composite genome, it may be a transposable element. Furthermore, its dinucleotide composition is most similar to that of the pNOB8-type plasmid, which is known to integrate into archaeal tRNA genes. Based on these results, we propose that the gain of the tRNA intron and the scattering of the tRNA fragment occurred within a short time frame via the integration and recombination of a mobile genetic element. PMID:22403667

Sugahara, Junichi; Fujishima, Kosuke; Nunoura, Takuro; Takaki, Yoshihiro; Takami, Hideto; Takai, Ken; Tomita, Masaru; Kanai, Akio

2012-01-01

109

Mindfulness-based stress reduction and health-related quality of life in a heterogeneous patient population  

Microsoft Academic Search

This study examined the effects of mindfulness-based stress reduction (MBSR) on health-related quality of life and physical and psychological symptomatology in a heterogeneous patient population. Patients (n=136) participated in an 8-week MBSR program and were required to practice 20 min of meditation daily. Pre- and post-intervention data were collected by using the Short-Form Health Survey (SF-36), Medical Symptom Checklist (MSCL)

Diane K Reibel; Jeffrey M Greeson; George C Brainard; Steven Rosenzweig

2001-01-01

110

Spatial Heterogeneity of Bacterial Populations along an Environmental Gradient at a Shallow Submarine Hydrothermal Vent near Milos Island (Greece)  

Microsoft Academic Search

The spatial heterogeneity of bacterial populations at a shallow-water hydrothermal vent in the Aegean Sea close to the island of Milos (Greece) was examined at two different times by using acridine orange staining for total cell counts, cultivation-based techniques, and denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA gene fragments. Concurrent with measurements of geochemical parameters, samples were

STEFAN M. SIEVERT; THORSTEN BRINKHOFF; GERARD MUYZER; WIEBKE ZIEBIS; JAN KUEVER

1999-01-01

111

Populations  

NSDL National Science Digital Library

This chapter introduces population as a group of the same kind of organisms in a given space at a given time. The activities in this section will provide students with the opportunity to define population, estimate populations in a community, and count and compare populations within a community. Students will gain the knowledge in describing plant and animal populations living in a community. They will also experiment with plant populations to control growth and development, not to mention discuss the effects of abiotic conditions on a community.

Janet R. Galle

2005-01-01

112

Environmental heterogeneity generates opposite gene-by-environment interactions for two fitness-related traits within a population.  

PubMed

Theory predicts that environmental heterogeneity offers a potential solution to the maintenance of genetic variation within populations, but empirical evidence remains sparse. The live-bearing fish Xiphophorus variatus exhibits polymorphism at a single locus, with different alleles resulting in up to five distinct melanistic "tailspot" patterns within populations. We investigated the effects of heterogeneity in two ubiquitous environmental variables (temperature and food availability) on two fitness-related traits (upper thermal limits and body condition) in two different tailspot types (wild-type and upper cut crescent). We found gene-by-environment (G × E) interactions between tailspot type and food level affecting upper thermal limits (UTL), as well as between tailspot type and thermal environment affecting body condition. Exploring mechanistic bases underlying these G × E patterns, we found no differences between tailspot types in hsp70 gene expression despite significant overall increases in expression under both thermal and food stress. Similarly, there was no difference in routine metabolic rates between the tailspot types. The reversal of relative performance of the two tailspot types under different environmental conditions revealed a mechanism by which environmental heterogeneity can balance polymorphism within populations through selection on different fitness-related traits. PMID:25496554

Culumber, Zachary W; Schumer, Molly; Monks, Scott; Tobler, Michael

2015-02-01

113

Using heterogeneity of the patient-derived xenograft model to identify the chemoresistant population in ovarian cancer  

PubMed Central

A cornerstone of preclinical cancer research has been the use of clonal cell lines. However, this resource has underperformed in its ability to effectively identify novel therapeutics and evaluate the heterogeneity in a patient's tumor. The patient-derived xenograft (PDX) model retains the heterogeneity of patient tumors, allowing a means to not only examine efficacy of a therapy, but also basic tenets of cancer biology in response to treatment. Herein we describe the development and characterization of an ovarian-PDX model in order to study the development of chemoresistance. We demonstrate that PDX tumors are not simply composed of tumor-initiating cells, but recapitulate the original tumor's heterogeneity, oncogene expression profiles, and clinical response to chemotherapy. Combined carboplatin/paclitaxel treatment of PDX tumors enriches the cancer stem cell populations, but persistent tumors are not entirely composed of these populations. RNA-Seq analysis of six pair of treated PDX tumors compared to untreated tumors demonstrates a consistently contrasting genetic profile after therapy, suggesting similar, but few, pathways are mediating chemoresistance. Pathways and genes identified by this methodology represent novel approaches to targeting the chemoresistant population in ovarian cancer PMID:25209969

Dobbin, Zachary C.; Katre, Ashwini A.; Steg, Adam D.; Erickson, Britt K.; Shah, Monjri M.; Alvarez, Ronald D.; Conner, Michael G.; Schneider, David; Chen, Dongquan; Landen, Charles N.

2014-01-01

114

Comparative Microsatellite Typing of New World Leishmania infantum Reveals Low Heterogeneity among Populations and Its Recent Old World Origin  

PubMed Central

Leishmania infantum (syn. L. chagasi) is the causative agent of visceral leishmaniasis (VL) in the New World (NW) with endemic regions extending from southern USA to northern Argentina. The two hypotheses about the origin of VL in the NW suggest (1) recent importation of L. infantum from the Old World (OW), or (2) an indigenous origin and a distinct taxonomic rank for the NW parasite. Multilocus microsatellite typing was applied in a survey of 98 L. infantum isolates from different NW foci. The microsatellite profiles obtained were compared to those of 308 L. infantum and 20 L. donovani strains from OW countries previously assigned to well-defined populations. Two main populations were identified for both NW and OW L. infantum. Most of the NW strains belonged to population 1, which corresponded to the OW MON-1 population. However, the NW population was much more homogeneous. A second, more heterogeneous, population comprised most Caribbean strains and corresponded to the OW non-MON-1 population. All Brazilian L. infantum strains belonged to population 1, although they represented 61% of the sample and originated from 9 states. Population analysis including the OW L. infantum populations indicated that the NW strains were more similar to MON-1 and non-MON-1 sub-populations of L. infantum from southwest Europe, than to any other OW sub-population. Moreover, similarity between NW and Southwest European L. infantum was higher than between OW L. infantum from distinct parts of the Mediterranean region, Middle East and Central Asia. No correlation was found between NW L. infantum genotypes and clinical picture or host background. This study represents the first continent-wide analysis of NW L. infantum population structure. It confirmed that the agent of VL in the NW is L. infantum and that the parasite has been recently imported multiple times to the NW from southwest Europe. PMID:21666787

Kuhls, Katrin; Alam, Mohammad Zahangir; Cupolillo, Elisa; Ferreira, Gabriel Eduardo M.; Mauricio, Isabel L.; Oddone, Rolando; Feliciangeli, M. Dora; Wirth, Thierry; Miles, Michael A.; Schönian, Gabriele

2011-01-01

115

A Novel Staining Protocol for Multiparameter Assessment of Cell Heterogeneity in Phormidium Populations (Cyanobacteria) Employing Fluorescent Dyes  

PubMed Central

Bacterial populations display high heterogeneity in viability and physiological activity at the single-cell level, especially under stressful conditions. We demonstrate a novel staining protocol for multiparameter assessment of individual cells in physiologically heterogeneous populations of cyanobacteria. The protocol employs fluorescent probes, i.e., redox dye 5-cyano-2,3-ditolyl tetrazolium chloride, ‘dead cell’ nucleic acid stain SYTOX Green, and DNA-specific fluorochrome 4?,6-diamidino-2-phenylindole, combined with microscopy image analysis. Our method allows simultaneous estimates of cellular respiration activity, membrane and nucleoid integrity, and allows the detection of photosynthetic pigments fluorescence along with morphological observations. The staining protocol has been adjusted for, both, laboratory and natural populations of the genus Phormidium (Oscillatoriales), and tested on 4 field-collected samples and 12 laboratory strains of cyanobacteria. Based on the mentioned cellular functions we suggest classification of cells in cyanobacterial populations into four categories: (i) active and intact; (ii) injured but active; (iii) metabolically inactive but intact; (iv) inactive and injured, or dead. PMID:23437052

Tashyreva, Daria; Elster, Josef; Billi, Daniela

2013-01-01

116

Explaining Spatial Heterogeneity in Population Dynamics and Genetics from Spatial Variation in Resources for a Large Herbivore  

PubMed Central

Fine-scale spatial variation in genetic relatedness and inbreeding occur across continuous distributions of several populations of vertebrates; however, the basis of observed variation is often left untested. Here we test the hypothesis that prior observations of spatial patterns in genetics for an island population of feral horses (Sable Island, Canada) were the result of spatial variation in population dynamics, itself based in spatial heterogeneity in underlying habitat quality. In order to assess how genetic and population structuring related to habitat, we used hierarchical cluster analysis of water sources and an indicator analysis of the availability of important forage species to identify a longitudinal gradient in habitat quality along the length of Sable Island. We quantify a west-east gradient in access to fresh water and availability of two important food species to horses: sandwort, Honckenya peploides, and beach pea, Lathyrus japonicas. Accordingly, the population clusters into three groups that occupy different island segments (west, central, and east) that vary markedly in their local dynamics. Density, body condition, and survival and reproduction of adult females were highest in the west, followed by central and east areas. These results mirror a previous analysis of genetics, which showed that inbreeding levels are highest in the west (with outbreeding in the east), and that there are significant differences in fixation indices among groups of horses along the length of Sable Island. Our results suggest that inbreeding depression is not an important limiting factor to the horse population. We conclude that where habitat gradients exist, we can anticipate fine-scale heterogeneity in population dynamics and hence genetics. PMID:23118900

Contasti, Adrienne L.; Tissier, Emily J.; Johnstone, Jill F.; McLoughlin, Philip D.

2012-01-01

117

Explaining spatial heterogeneity in population dynamics and genetics from spatial variation in resources for a large herbivore.  

PubMed

Fine-scale spatial variation in genetic relatedness and inbreeding occur across continuous distributions of several populations of vertebrates; however, the basis of observed variation is often left untested. Here we test the hypothesis that prior observations of spatial patterns in genetics for an island population of feral horses (Sable Island, Canada) were the result of spatial variation in population dynamics, itself based in spatial heterogeneity in underlying habitat quality. In order to assess how genetic and population structuring related to habitat, we used hierarchical cluster analysis of water sources and an indicator analysis of the availability of important forage species to identify a longitudinal gradient in habitat quality along the length of Sable Island. We quantify a west-east gradient in access to fresh water and availability of two important food species to horses: sandwort, Honckenya peploides, and beach pea, Lathyrus japonicas. Accordingly, the population clusters into three groups that occupy different island segments (west, central, and east) that vary markedly in their local dynamics. Density, body condition, and survival and reproduction of adult females were highest in the west, followed by central and east areas. These results mirror a previous analysis of genetics, which showed that inbreeding levels are highest in the west (with outbreeding in the east), and that there are significant differences in fixation indices among groups of horses along the length of Sable Island. Our results suggest that inbreeding depression is not an important limiting factor to the horse population. We conclude that where habitat gradients exist, we can anticipate fine-scale heterogeneity in population dynamics and hence genetics. PMID:23118900

Contasti, Adrienne L; Tissier, Emily J; Johnstone, Jill F; McLoughlin, Philip D

2012-01-01

118

Texas Community Colleges and Characteristics of a Growing Undocumented Student Population  

ERIC Educational Resources Information Center

In this study, the researchers examine the undocumented student population in Texas community colleges. The data indicate steady yearly increases in the number of undocumented students and in their percentage of the total student enrollment. The relationships between undocumented student enrollment, college size, and overall Hispanic student

Jauregui, John A.; Slate, John R.; Brown, Michelle Stallone

2008-01-01

119

Heterogeneous Catalysis.  

ERIC Educational Resources Information Center

Described is a heterogeneous catalysis course which has elements of materials processing embedded in the classical format of catalytic mechanisms and surface chemistry. A course outline and list of examples of recent review papers written by students are provided. (MVL)

Miranda, R.

1989-01-01

120

Mechanisms of population genetic heterogeneity among molting common mergansers on Kodiak Island, Alaska: implications for assessments of migratory connectivity  

USGS Publications Warehouse

Quantifying population genetic heterogeneity within nonbreeding aggregations can inform our understanding of patterns of site fidelity, migratory connectivity, and gene flow between breeding and nonbreeding areas. However, characterizing mechanisms that contribute to heterogeneity, such as migration and dispersal, is required before site fidelity and migratory connectivity can be assessed accurately. We studied nonbreeding groups of Common Mergansers (Mergus merganser) molting on Kodiak Island, Alaska, from 2005 to 2007, using banding data to assess rates of recapture, mitochondrial (mt) DNA to determine natal area, and nuclear microsatellite genotypes to assess dispersal. Using baseline information from differentiated mtDNA haplogroups across North America, we were able to assign individuals to natal regions and document population genetic heterogeneity within and among molting groups. Band-recovery and DNA data suggest that both migration from and dispersal among natal areas contribute to admixed groups of males molting on Kodiak Island. A lack of differentiation in the Common Merganser's nuclear, bi-parentally inherited DNA, observed across North America, implies that dispersal can mislead genetic assessments of migratory connectivity and assignments of nonbreeding individuals to breeding areas. Thus multiple and independent data types are required to account for such behaviors before accurate assessments of migratory connectivity can be made.

Pearce, John M.; Zwiefelhofer, Denny; Maryanski, Nate

2009-01-01

121

Cellular heterogeneity in the mouse esophagus implicates the presence of a non-quiescent epithelial stem cell population  

PubMed Central

SUMMARY Because the esophageal epithelium lacks a defined stem cell niche, it is unclear whether all basal epithelial cells in the adult esophagus are functionally equivalent. In this study, we showed that basal cells in the mouse esophagus contained a heterogeneous population of epithelial cells, similar to other rapidly cycling tissues such as the intestine or skin. Using a combination of cell surface markers, we separated primary esophageal tissue into distinct cell populations that harbored differences in stem cell potential. We also utilized an in vitro 3-D organoid assay to demonstrate that Sox2, Wnt, and bone morphogenetic protein (BMP) signaling regulate esophageal self-renewal. Finally, we labeled proliferating basal epithelial cells in vivo to show differing cell cycle profiles and proliferation kinetics. Based on our results, we propose that a non-quiescent stem cell population resides in the basal epithelium of the mouse esophagus. PMID:25373907

DeWard, Aaron D.; Cramer, Julie; Lagasse, Eric

2014-01-01

122

Niche-Dependent Gene Expression Profile of Intratumoral Heterogeneous Ovarian Cancer Stem Cell Populations  

PubMed Central

Intratumoral heterogeneity challenges existing paradigms for anti-cancer therapy. We have previously demonstrated that the human embryonic stem cells (hESC)-derived cellular microenvironment in immunocompromised mice, enables functional distinction of heterogeneous tumor cells, including cells which do not grow into a tumor in a conventional direct tumor xenograft platform. We have identified and characterized six cancer cell subpopulations each clonally expanded from a single cell, derived from human ovarian clear cell carcinoma of a single tumor, to demonstrate striking intratumoral phenotypic heterogeneity that is dynamically dependent on the tumor growth microenvironment. These cancer cell subpopulations, characterized as cancer stem cell subpopulations, faithfully recapitulate the full spectrum of histological phenotypic heterogeneity known for human ovarian clear cell carcinoma. Each of the six subpopulations displays a different level of morphologic and tumorigenic differentiation wherein growth in the hESC-derived microenvironment favors growth of CD44+/aldehyde dehydrogenase positive pockets of self-renewing cells that sustain tumor growth through a process of tumorigenic differentiation into CD44-/aldehyde dehydrogenase negative derivatives. Strikingly, these derivative cells display microenvironment-dependent plasticity with the capacity to restore self-renewal markers and CD44 expression. In the current study, we delineate the distinct gene expression and epigenetic profiles of two such subpopulations, representing extremes of phenotypic heterogeneity in terms of niche-dependent self-renewal and tumorigenic differentiation. By combining Gene Set Enrichment, Gene Ontology and Pathway-focused array analyses with methylation status, we propose a suite of robust differences in tumor self-renewal and differentiation pathways that underlie the striking intratumoral phenotypic heterogeneity which characterize this and other solid tumor malignancies. PMID:24358304

Abelson, Sagi; Shamai, Yeela; Berger, Liron; Skorecki, Karl; Tzukerman, Maty

2013-01-01

123

Student Engagement in Higher Education: Theoretical Perspectives and Practical Approaches for Diverse Populations  

Microsoft Academic Search

STUDENT ENGAGEMENT IN HIGHER EDUCATION is an important volume that fills a longstanding void in the higher education and student affairs literature. The editors and authors make clear that diverse populations of students experience college differently and encounter group-specific barriers to success. Informed by relevant theories, each chapter focuses on a different population for whom research confirms that engagement and

Quaye

2009-01-01

124

Genetic heterogeneity of severe von Willebrand disease type III in the German population  

Microsoft Academic Search

The genetic heterogeneity of severe von Willebrand disease (vWd) type III was estimated by analysing extended haplotypes of eleven intragenic restriction fragment length polymorphisms and one variable number of tandem repeat polymorphism in 32 patients from 28 families from Germany or of German origin. All patients were screened for gross deletions and for mutations at potential “hot spot” regions of

Reinhard Schneppenheim; Sonja Krey; Frauke Bergmann; Dietrich Bock; Ulrich Budde; Malte Lange; Richard Linde; Uwe Mittler; Esther Meili; Günter Mertes; Klaus Olek; Hansjörg Plendl; Eva Simeoni

1994-01-01

125

Rate response of neurons subject to fast or frozen noise: From stochastic and homogeneous to deterministic and heterogeneous populations  

NASA Astrophysics Data System (ADS)

The response of a neuronal population to afferent drive can be expected to be sensitive to both the distribution and dynamics of membrane voltages within the population. Voltage fluctuations can be driven by synaptic noise, neuromodulators, or cellular inhomogeneities: processes ranging from millisecond autocorrelation times to effectively static or “frozen” noise. Here we extend previous studies of filtered fluctuations to the experimentally verified exponential integrate-and-fire model. How fast or frozen fluctuations affect the steady-state rate and firing-rate response are both examined using perturbative solutions and limits of a 1 + 2 dimensional Fokker-Planck equation. The central finding is that, under conditions of a more-or-less constant population voltage variance, the firing-rate response is only weakly dependent on the fluctuation filter constant: The voltage distribution is the principal determinant of the population response. This result is unexpected given the nature of the systems underlying the extreme limits of fast and frozen fluctuations; the first limit represents a homogeneous population of neurons firing stochastically, whereas the second limit is equivalent to a heterogeneous population of neurons firing deterministically.

Alijani, Azadeh Khajeh; Richardson, Magnus J. E.

2011-07-01

126

Opinion dynamics of modified Hegselmann-Krause model in a group-based population with heterogeneous bounded confidence  

NASA Astrophysics Data System (ADS)

Continuous opinion dynamics in a group-based population with heterogeneous bounded confidences is considered in this paper. A slightly modified Hegselmann-Krause model is proposed, and agents are classified into three categories: open-minded-, moderate-minded-, and closed-minded-agents, while the whole population is divided into three subgroups accordingly. We study how agents of each category and the population size can affect opinion dynamics. It is observed that the number of final opinion clusters is dominated by the closed-minded agents; open-minded agents cannot contribute to forming opinion consensus and the existence of open-minded agents may diversify the final opinions instead; for the fixed population size and proportion of closed-minded agents, the relative size of the largest final opinion cluster varies along concave-parabola-like curve as the proportion of open-minded agents increases, and there is a tipping point when the number of open-minded agents is almost equal to that of moderate-minded agents; for the fixed proportion of the three categories in the population, as the population size becomes larger, the number of final opinion clusters will reach a plateau. Some of the results are different from the previous studies.

Fu, Guiyuan; Zhang, Weidong; Li, Zhijun

2015-02-01

127

Between-airport heterogeneity in air toxics emissions associated with individual cancer risk thresholds and population risks  

PubMed Central

Background Airports represent a complex source type of increasing importance contributing to air toxics risks. Comprehensive atmospheric dispersion models are beyond the scope of many applications, so it would be valuable to rapidly but accurately characterize the risk-relevant exposure implications of emissions at an airport. Methods In this study, we apply a high resolution atmospheric dispersion model (AERMOD) to 32 airports across the United States, focusing on benzene, 1,3-butadiene, and benzo [a]pyrene. We estimate the emission rates required at these airports to exceed a 10-6 lifetime cancer risk for the maximally exposed individual (emission thresholds) and estimate the total population risk at these emission rates. Results The emission thresholds vary by two orders of magnitude across airports, with variability predicted by proximity of populations to the airport and mixing height (R2 = 0.74–0.75 across pollutants). At these emission thresholds, the population risk within 50 km of the airport varies by two orders of magnitude across airports, driven by substantial heterogeneity in total population exposure per unit emissions that is related to population density and uncorrelated with emission thresholds. Conclusion Our findings indicate that site characteristics can be used to accurately predict maximum individual risk and total population risk at a given level of emissions, but that optimizing on one endpoint will be non-optimal for the other. PMID:19426510

2009-01-01

128

Cell population heterogeneity in expression of a gene-switching network with fluorescent markers of different half-lives.  

PubMed

We studied the distribution of expression levels amongst the cells of an Escherichia coli population carrying a gene-switching network, known as the genetic toggle. We employed two green fluorescent protein (GFP) reporter proteins with different half-lives and characterized the effect of isopropyl-beta-D-thiogalactopyranoside (IPTG) inducer concentration on fluorescence distribution characteristics. Our flow cytometric measurements indicated that there is a spread of fluorescence phenotypes of one to three orders of magnitude, due to the highly heterogeneous nature of the cell populations under investigation. Moreover, the shape of the distribution at a specific quasi-time-invariant reference state, defined for comparison purposes, strongly depended on inducer concentration. For very low and very high inducer concentrations, the distributions at the reference state are unimodal. On the contrary, for intermediate IPTG concentrations, two distinct subpopulations were formed below and above a single-cell threshold, resulting in distributions with a bimodal shape. The region of inducer concentrations where bimodality is observed is the same and independent of GFP half-life. Bimodal number density functions are not only obtained at the reference state. Transient studies revealed that even in cases where the distribution at the reference state is unimodal, the distribution becomes bimodal for a period of time required for the population to pass through the single-cell induction threshold. However, this feature was only captured by the system with the reduced half-life GFP. A simple single-cell model was used to shed light into the effect of inducer concentration and GFP half-life on the shape of the experimentally measured number density functions. The wide range of fluorescent phenotypes and the inability of the average population properties to fully characterize network behavior, indicate the importance of taking into account cell population heterogeneity when designing such a gene-switching network for biotechnological and biomedical applications. PMID:17092594

Portle, Stephanie; Causey, Thomas B; Wolf, Kim; Bennett, George N; San, Ka-Yiu; Mantzaris, Nikos

2007-02-01

129

Special Populations: Migrant Students with Disabilities; Native Pacific Basin and Native Hawaiian Students with Disabilities. Appendix G.  

ERIC Educational Resources Information Center

This appendix to the 14th annual report on implementation of the Individuals with Disabilities Education Act contains reports on progress in addressing the needs of two special populations: migrant students with disabilities and Native Pacific Basin and Native Hawaiian students with disabilities. Migrant students with disabilities tend to have…

Office of Special Education and Rehabilitative Services (ED), Washington, DC. Div. of Innovation and Development.

130

Flow cytometry and cell sorting of heterogeneous microbial populations: the importance of single-cell analyses.  

PubMed Central

The most fundamental questions such as whether a cell is alive, in the sense of being able to divide or to form a colony, may sometimes be very hard to answer, since even axenic microbial cultures are extremely heterogeneous. Analyses that seek to correlate such things as viability, which is a property of an individual cell, with macroscopic measurements of culture variables such as ATP content, respiratory activity, and so on, must inevitably fail. It is therefore necessary to make physiological measurements on individual cells. Flow cytometry is such a technique, which allows one to analyze cells rapidly and individually and permits the quantitative analysis of microbial heterogeneity. It therefore offers many advantages over conventional measurements for both routine and more exploratory analyses of microbial properties. While the technique has been widely applied to the study of mammalian cells, is use in microbiology has until recently been much more limited, largely because of the smaller size of microbes and the consequently smaller optical signals obtainable from them. Since these technical barriers no longer hold, flow cytometry with appropriate stains has been used for the rapid discrimination and identification of microbial cells, for the rapid assessment of viability and of the heterogeneous distributions of a wealth of other more detailed physiological properties, for the analysis of antimicrobial drug-cell interactions, and for the isolation of high-yielding strains of biotechnological interest. Flow cytometric analyses provide an abundance of multivariate data, and special methods have been devised to exploit these. Ongoing advances mean that modern flow cytometers may now be used by nonspecialists to effect a renaissance in our understanding of microbial heterogeneity. PMID:8987359

Davey, H M; Kell, D B

1996-01-01

131

Heterogeneity in stable isotope profiles predicts coexistence of populations of barn swallows Hirundo rustica differing in morphology and reproductive performance.  

PubMed Central

Population studies assume that individuals belonging to a study population are homogeneous for natal and breeding origin, although this assumption is rarely tested. We tested for heterogeneity in stable-isotope profiles (delta15N, delta13C, deltaD) of feathers grown in the African winter quarters from a Danish breeding population of adult barn swallows, Hirundo rustica. Deuterium isotope values did not provide useful information on population segregation of wintering swallows in Africa. However, both delta15N and delta13C values showed a clearly bimodal distribution with 6% belonging to one category and the remaining birds belonging to another category, resulting in this population comprising three categories of birds. Adults belonging to the two categories of delta13C isotope profiles differed weakly in morphology for several different characters. The frequency and the size of second broods differed between categories of delta13C isotope profiles. Phenotypes of nestlings from the first brood in terms of tarsus length, body mass and T-cell response differed significantly between the two delta15N isotope categories, suggesting that conditions during winter carried over to the breeding season at least as late as the first brood. Polymorphism can be maintained only if fitness is similar for birds from categories of isotope profiles. We suggest that fluctuating selection or migration-selection balance may maintain the observed polymorphism. PMID:15306333

Møller, Anders Pape; Hobson, Keith A.

2004-01-01

132

Combined effects between temporal heterogeneity of water supply, nutrient level, and population density on biomass of four broadly distributed herbaceous species.  

PubMed

Temporal heterogeneity of water supply affects grassland community productivity and it can interact with nutrient level and intraspecific competition. To understand community responses, the responses of individual species to water heterogeneity must be evaluated while considering the interactions of this heterogeneity with nutrient levels and population density. We compared responses of four herbaceous species grown in monocultures to various combinations of water heterogeneity, nutrient level, and population density: two grasses (Cynodon dactylon and Lolium perenne), a forb (Artemisia princeps), and a legume (Trifolium repens). Treatment effects on shoot and root biomass were analyzed. In all four species, shoot biomass was larger under homogeneous than under heterogeneous water supply. Shoot responses of L. perenne tended to be greater at high nutrient levels. Although root biomass was also larger under homogeneous water supply, effects of water heterogeneity on root biomass were not significant in the grasses. Trifolium repens showed marked root responses, particularly at high population density. Although greater shoot and root growth under homogeneous water supply appears to be a general trend among herbaceous species, our results suggested differences among species could be found in the degree of response to water heterogeneity and its interactions with nutrient level and intraspecific competition. PMID:21327692

Hagiwara, Yousuke; Kachi, Naoki; Suzuki, Jun-Ichirou

2012-01-01

133

The dynamic balance of import and export of zinc in Escherichia coli suggests a heterogeneous population response to stress.  

PubMed

Zinc is essential for life, but toxic in excess. Thus all cells must control their internal zinc concentration. We used a systems approach, alternating rounds of experiments and models, to further elucidate the zinc control systems in Escherichia coli. We measured the response to zinc of the main specific zinc import and export systems in the wild-type, and a series of deletion mutant strains. We interpreted these data with a detailed mathematical model and Bayesian model fitting routines. There are three key findings: first, that alternate, non-inducible importers and exporters are important. Second, that an internal zinc reservoir is essential for maintaining the internal zinc concentration. Third, our data fitting led us to propose that the cells mount a heterogeneous response to zinc: some respond effectively, while others die or stop growing. In a further round of experiments, we demonstrated lower viable cell counts in the mutant strain tested exposed to excess zinc, consistent with this hypothesis. A stochastic model simulation demonstrated considerable fluctuations in the cellular levels of the ZntA exporter protein, reinforcing this proposal. We hypothesize that maintaining population heterogeneity could be a bet-hedging response allowing a population of cells to survive in varied and fluctuating environments. PMID:25808337

Takahashi, Hiroki; Oshima, Taku; Hobman, Jon L; Doherty, Neil; Clayton, Selina R; Iqbal, Mudassar; Hill, Philip J; Tobe, Toru; Ogasawara, Naotake; Kanaya, Shigehiko; Stekel, Dov J

2015-05-01

134

Relation Between Near Work and Myopia Progression in Student Population  

PubMed Central

Aim To determine relation between near work and myopia progression in student population. Causes of myopia occurrence are not sufficiently explained. Methods This retrospective-prospective, descriptive research included 100 students with verified myopia up to -3 Dsph. Ophthalmological examination and measurement diopter-hours variable (Dh) were done twice, in the period from January 2011 until January 2012. Results A multivariate regression analysis of impact on the difference of distance visual acuity without correction to the right and left eye and difference of automatic computer refractometry in cycloplegia of both eyes indicates that, diopter-hours variable (Dh) had statistically significant impact on increase of distance visual acuity difference (right eye OR: I measurement–Dh 1.489, II measurement–Dh 1.544, p<0.05; left eye OR: I measurement–Dh 1.602, II measurement–Dh 1.538, p<0.05) and automatic computer refractometry in cycloplegia (right eye OR: I measurement 1.361, II measurement 1.493, p<0.05; left eye OR: I measurement 0.931, II measurement 1.019, p<0.05) during both measurements. Conclusion Near work cause the increase of myopia. This research opened a perspective for other researches on the impact of near work on myopia. PMID:24944532

Muhamedagic, Lejla; Muhamedagic, Belma; Halilovic, Emina Alimanovic; Halimic, Jasmina Alajbegovic; Stankovic, Aleksa; Muracevic, Bedrana

2014-01-01

135

Integrating Collaborative Population Health Projects into a Medical Student Curriculum at Stanford  

Microsoft Academic Search

The authors describe the population health curriculum at the Stanford University School of Medicine from 2003 to 2007 that includes a requirement for first-year medical students to engage in community- based population health projects. The new curriculum in population health comprises classroom and experiential teaching methods. Population health projects, a key component of the curriculum, are described and classified by

Lisa J. Chamberlain; N. Ewen Wang; Evelyn T. Ho; Ann W. Banchoff; Clarence H. Braddock III; Neil Gesundheit

2008-01-01

136

Pooled testing procedures for screening high volume clinical specimens in heterogeneous populations  

PubMed Central

Pooled testing is a procedure commonly used to reduce the cost of screening a large number of individuals for infectious diseases. In its simplest form, pooled testing works by compositing a set of individual specimens (e.g., blood or urine) into a common pool. If the pool tests negative, all individuals within it are diagnosed as negative. If the pool tests positive, retesting is needed to decode the positive individuals from the negative individuals. Traditionally, pooled testing has assumed that each individual has the same probability of being positive. However, this assumption is often unrealistic, especially when known risk factors can be used to measure distinct probabilities of positivity for each individual. In this paper, we investigate new pooled testing algorithms that exploit the heterogeneity among individual probabilities and subsequently reduce the total number of tests needed, while maintaining accuracy levels similar to standard algorithms that do not account for heterogeneity. We apply these algorithms to data from the Infertility Prevention Project, a nationally implemented program supported by the Centers for Disease Control and Prevention. PMID:22415972

Bilder, Christopher R.; Tebbs, Joshua M.

2012-01-01

137

Genetic heterogeneity of limb-girdle muscular dystrophy in Amish populations  

SciTech Connect

The autosomal recessive form of limb-girdle muscular dystrophy (LGMD2) is characterized by onset in childhood, progressive weakness predominantly of shoulder, pelvic and trunk muscles with sparing of facial muscles. A gene for LGMD2 was localized to chromosome 15q by Beckmann et al. in 1991 in Isle La Reunion families, subsequently confirmed in Amish families and in Brazilian families where genetic heterogeneity has been demonstrated. Analysis of LGM2 families for recombination events permitted the gene region to be restricted to an interval of about 7 cM defined by flanking markers D15S129 and D15S143. Extended haplotypes were established in the families on the basis of the segregation of multiple markers within this interval. Although the nine northern Indiana Amish families showed linkage of the gene to chromosome 15 markers (maximum lod score of 7.58 at {theta}=0.06 for D15S129 and 12.57 at {theta}=0.046 for D15S143), six large southern Indiana families with LGMD2, clinically indistinguishable from the LGMD2 in northern Indiana, were found to have a disease neither linked to chromosome 15 nor to chromosome 2 where a second localization has been reported. Although these two Indiana Amish LGMD2 kindreds contain some common ancestors and are clinically similar, the LGMD2 appears to be genetically heterogeneous.

Beckmann, J.S.; Allamand, V.; Broux, O. [CEPH, Paris (France)] [and others

1994-09-01

138

Paucity of class I MHC gene heterogeneity between individuals in the endangered Hawaiian monk seal population  

Microsoft Academic Search

The Hawaiian monk seal population has experienced precipitous declines in the last 50 years. In this study, we provide evidence that individuals from remaining endangered population exhibit alarming uniformity in class I major histocompatibility (MHC) genes. The peripheral blood leukocyte-derived mRNA of six captive animals rescued from a stranding incident on the French frigate shoals in the Hawaiian archipelago was used

Brian M. Aldridge; Lizabeth Bowen; Brett R. Smith; George A. Antonelis; Frances Gulland; Jeffrey L. Stott

2006-01-01

139

Distress and Psychosocial Needs of a Heterogeneous High Risk Familial Cancer Population  

Microsoft Academic Search

In order to assess the levels of distress and psychosocial support needs of a high risk population, we undertook a study to\\u000a look at both the objective and subjective levels of distress and the wants and needs of individuals from a high familial cancer\\u000a risk population. Three hundred and eighteen individuals (160 affected, 158 unaffected) completed several distress and psychosocial

Tara E. Power; John W. Robinson; Peter Bridge; Francois P. Bernier; Dawna M. Gilchrist

2011-01-01

140

High Levels of Heterogeneity in the HIV Cascade of Care across Different Population Subgroups in British Columbia, Canada  

PubMed Central

Background The HIV cascade of care (cascade) is a comprehensive tool which identifies attrition along the HIV care continuum. We executed analyses to explicate heterogeneity in the cascade across key strata, as well as identify predictors of attrition across stages of the cascade. Methods Using linked individual-level data for the population of HIV-positive individuals in BC, we considered the 2011 calendar year, including individuals diagnosed at least 6 months prior, and excluding individuals that died or were lost to follow-up before January 1st, 2011. We defined five stages in the cascade framework: HIV ‘diagnosed’, ‘linked’ to care, ‘retained’ in care, ‘on HAART’ and virologically ‘suppressed’. We stratified the cascade by sex, age, risk category, and regional health authority. Finally, multiple logistic regression models were built to predict attrition across each stage of the cascade, adjusting for stratification variables. Results We identified 7621 HIV diagnosed individuals during the study period; 80% were male and 5% were <30, 17% 30–39, 37% 40–49 and 40% were ?50 years. Of these, 32% were MSM, 28% IDU, 8% MSM/IDU, 12% heterosexual, and 20% other. Overall, 85% of individuals ‘on HAART’ were ‘suppressed’; however, this proportion ranged from 60%–93% in our various stratifications. Most individuals, in all subgroups, were lost between the stages: ‘linked’ to ‘retained’ and ‘on HAART’ to ‘suppressed’. Subgroups with the highest attrition between these stages included females and individuals <30 years (regardless of transmission risk group). IDUs experienced the greatest attrition of all subgroups. Logistic regression results found extensive statistically significant heterogeneity in attrition across the cascade between subgroups and regional health authorities. Conclusions We found that extensive heterogeneity in attrition existed across subgroups and regional health authorities along the HIV cascade of care in B.C., Canada. Our results provide critical information to optimize engagement in care and health service delivery. PMID:25541682

Lourenço, Lillian; Colley, Guillaume; Nosyk, Bohdan; Shopin, Dmitry; Montaner, Julio S. G.; Lima, Viviane D.

2014-01-01

141

A population-based study of hereditary non-polyposis colorectal cancer: evidence of pathologic and genetic heterogeneity.  

PubMed

Hereditary non-polyposis colorectal cancer (HNPCC) may be the result of Lynch syndrome (LS) caused by mutations in mismatch repair (MMR) genes, a syndrome of unknown etiology called familial colorectal cancer type-X (FCCTX), or familial serrated neoplasia associated with the colorectal cancer (CRC) somatic BRAF mutation. To determine the cause of HNPCC in the founder population of the island of Newfoundland, we studied 37 families with LS and 29 families without LS who fulfilled the Amsterdam I criteria. In non-LS, four index CRCs were BRAF mutation positive, one of which was microsatellite instable. Geographic clustering of LS families caused by three different founder mutations in MSH2 was observed. Nine unique MMR mutations in four MMR genes were identified in single families distributed in different geographic isolates. The geographic distribution of non-LS was similar to LS. The coefficient of relatedness using genotype data was significantly higher for non-LS than for all CRC. Extensive genealogic investigation failed to connect non-LS families and in some clusters pathologic CRC heterogeneity was observed. We conclude that non-LS HNPCC may be a heterogeneous disorder with different pathogenic pathways, and that the geographic distribution is consistent with multiple different mutations in unknown CRC susceptibility gene(s). PMID:23278430

Warden, G; Harnett, D; Green, J; Wish, T; Woods, M O; Green, R; Dicks, E; Rahman, P; Zhai, G; Parfrey, P

2013-12-01

142

Computing Ro in a population with heterogeneity in sexual activity and proportionate mixing using a STM-solver  

NASA Astrophysics Data System (ADS)

A model to determinate the reproductive basic number, detonated Ro, for the case of population with heterogeneity in sexual activity and proportionate mixing is solved using computer algebra and SMT solvers. Specifically Maple and Z3 were used. The code for the solution of the model was written in Z3-Python, but it can also be played by Z3-SMT-Lib. Ro represents an algebraic synthesis of every epidemiological parameter. Numerical simulations were done to prove the effectiveness of the model and the code. The algebraic structure of Ro suggests the possible control measurements that should be implemented to avoid the propagation of the sexual transmitted diseases. The obtained results are important on the computational epidemiology field. As a future investigation, it is suggested to apply the STM solvers to analyze models for other kinds of epidemic diseases.

Gutierrez A., Natalia A.

2014-06-01

143

CCAST: A Model-Based Gating Strategy to Isolate Homogeneous Subpopulations in a Heterogeneous Population of Single Cells  

PubMed Central

A model-based gating strategy is developed for sorting cells and analyzing populations of single cells. The strategy, named CCAST, for Clustering, Classification and Sorting Tree, identifies a gating strategy for isolating homogeneous subpopulations from a heterogeneous population of single cells using a data-derived decision tree representation that can be applied to cell sorting. Because CCAST does not rely on expert knowledge, it removes human bias and variability when determining the gating strategy. It combines any clustering algorithm with silhouette measures to identify underlying homogeneous subpopulations, then applies recursive partitioning techniques to generate a decision tree that defines the gating strategy. CCAST produces an optimal strategy for cell sorting by automating the selection of gating markers, the corresponding gating thresholds and gating sequence; all of these parameters are typically manually defined. Even though CCAST is optimized for cell sorting, it can be applied for the identification and analysis of homogeneous subpopulations among heterogeneous single cell data. We apply CCAST on single cell data from both breast cancer cell lines and normal human bone marrow. On the SUM159 breast cancer cell line data, CCAST indicates at least five distinct cell states based on two surface markers (CD24 and EPCAM) and provides a gating sorting strategy that produces more homogeneous subpopulations than previously reported. When applied to normal bone marrow data, CCAST reveals an efficient strategy for gating T-cells without prior knowledge of the major T-cell subtypes and the markers that best define them. On the normal bone marrow data, CCAST also reveals two major mature B-cell subtypes, namely CD123+ and CD123- cells, which were not revealed by manual gating but show distinct intracellular signaling responses. More generally, the CCAST framework could be used on other biological and non-biological high dimensional data types that are mixtures of unknown homogeneous subpopulations. PMID:25078380

Anchang, Benedict; Do, Mary T.; Zhao, Xi; Plevritis, Sylvia K.

2014-01-01

144

Association of acculturation and country of origin with self-reported hypertension and diabetes in a heterogeneous Hispanic population  

PubMed Central

Background Hispanics are the fasting growing population in the U.S. and disproportionately suffer from chronic diseases such as hypertension and diabetes. Little is known about the complex interplay between acculturation and chronic disease prevalence in the growing and increasingly diverse Hispanic population. We explored the association between diabetes and hypertension prevalence among distinct U.S. Hispanic subgroups by country of origin and by degree of acculturation. Methods We examined the adult participants in the 2001, 2003, 2005, and 2007 California Health Interview Survey (CHIS). Using weighted logistic regression stratified by nativity, we measured the association between country of origin and self-reported hypertension and diabetes adjusting for participants’ demographics, insurance status, socio-economic status and degree of acculturation measured by citizenship, English language proficiency and the number of years of residence in the U.S. Results There were 33,633 self-identified Hispanics (foreign-born: 19,988; U.S.-born: 13,645). After multivariable adjustment, we found significant heterogeneity in self-reported hypertension and diabetes prevalence among Hispanic subgroups. Increasing years of U.S. residence was associated with increased disease prevalence. Among all foreign-born subgroups, only Mexicans reported lower odds of hypertension after adjustment for socioeconomic and acculturation factors. Both U.S.-born and foreign-born Mexicans had higher rates of diabetes as compared to non-Hispanic whites. Conclusions We found significant heterogeneity among Hispanics in self-reported rates of hypertension and diabetes by acculturation and country of origin. Our findings highlight the importance of disaggregation of Hispanics by country of origin and acculturation factors whenever possible. PMID:22966844

2012-01-01

145

Stage-dependent responses to emergent habitat heterogeneity: consequences for a predatory insect population in a coffee agroecosystem  

PubMed Central

Interactions among members of biological communities can create spatial patterns that effectively generate habitat heterogeneity for other members in the community, and this heterogeneity might be crucial for their persistence. For example, stage-dependent vulnerability of a predatory lady beetle to aggression of the ant, Azteca instabilis, creates two habitat types that are utilized differently by the immature and adult life stages of the beetle. Due to a mutualistic association between A. instabilis and the hemipteran Coccus viridis – which is A. orbigera main prey in the area – only plants around ant nests have high C. viridis populations. Here, we report on a series of surveys at three different scales aimed at detecting how the presence and clustered distribution of ant nests affect the distribution of the different life stages of this predatory lady beetle in a coffee farm in Chiapas, Mexico. Both beetle adults and larvae were more abundant in areas with ant nests, but adults were restricted to the peripheries of highest ant activity and outside the reach of coffee bushes containing the highest densities of lady beetle larvae. The abundance of adult beetles located around trees with ants increased with the size of the ant nest clusters but the relationship is not significant for larvae. Thus, we suggest that A. orbigera undergoes an ontogenetic niche shift, not through shifting prey species, but through stage-specific vulnerability differences against a competitor that renders areas of abundant prey populations inaccessible for adults but not for larvae. Together with evidence presented elsewhere, this study shows how an important predator is not only dependent on the existence of two qualitatively distinct habitat types, but also on the spatial distribution of these habitats. We suggest that this dependency arises due to the different responses that the predator's life stages have to this emergent spatial pattern. PMID:25473473

Liere, Heidi; Perfecto, Ivette; Vandermeer, John

2014-01-01

146

CCAST: a model-based gating strategy to isolate homogeneous subpopulations in a heterogeneous population of single cells.  

PubMed

A model-based gating strategy is developed for sorting cells and analyzing populations of single cells. The strategy, named CCAST, for Clustering, Classification and Sorting Tree, identifies a gating strategy for isolating homogeneous subpopulations from a heterogeneous population of single cells using a data-derived decision tree representation that can be applied to cell sorting. Because CCAST does not rely on expert knowledge, it removes human bias and variability when determining the gating strategy. It combines any clustering algorithm with silhouette measures to identify underlying homogeneous subpopulations, then applies recursive partitioning techniques to generate a decision tree that defines the gating strategy. CCAST produces an optimal strategy for cell sorting by automating the selection of gating markers, the corresponding gating thresholds and gating sequence; all of these parameters are typically manually defined. Even though CCAST is optimized for cell sorting, it can be applied for the identification and analysis of homogeneous subpopulations among heterogeneous single cell data. We apply CCAST on single cell data from both breast cancer cell lines and normal human bone marrow. On the SUM159 breast cancer cell line data, CCAST indicates at least five distinct cell states based on two surface markers (CD24 and EPCAM) and provides a gating sorting strategy that produces more homogeneous subpopulations than previously reported. When applied to normal bone marrow data, CCAST reveals an efficient strategy for gating T-cells without prior knowledge of the major T-cell subtypes and the markers that best define them. On the normal bone marrow data, CCAST also reveals two major mature B-cell subtypes, namely CD123+ and CD123- cells, which were not revealed by manual gating but show distinct intracellular signaling responses. More generally, the CCAST framework could be used on other biological and non-biological high dimensional data types that are mixtures of unknown homogeneous subpopulations. PMID:25078380

Anchang, Benedict; Do, Mary T; Zhao, Xi; Plevritis, Sylvia K

2014-07-01

147

Molecular identity and heterogeneity of trichomonad parasites in a closed avian population  

Microsoft Academic Search

Columbids (pigeons and doves) are the primary host of Trichomonas gallinae, the flagellate protozoon which causes avian trichomoniasis, a widespread, often lethal disease. Although predominantly apathogenic, the organism is paradigmatic for the study of strain-specific virulence, with some strains causing greater than 75% mortality and epizootic die-offs in wildlife populations. In recent years, research on this important emerging pathogen has

Daniela Gaspar da Silva; Emma Barton; Nancy Bunbury; Patricia Lunness; Diana J. Bell; Kevin M. Tyler

2007-01-01

148

Survival and competition of clonal plant populations in spatially and temporally heterogeneous habitats  

Microsoft Academic Search

Clonal populations are hierarchically organized: genetic individuals (genets) can consist of many physiological individuals (ramets). Each ramet takes up resources from its local environment, but the resource pattern can be reorganized within the clone by transport between ramets. Thus, an integrated clone is not directly subject to the pattern of resource availability in its habitat. Local shortages can be compensated,

B. Oborny; Á. Kun

2003-01-01

149

The Power of the F Test in Normal Populations with Heterogeneous Variances.  

ERIC Educational Resources Information Center

An empirical study of the power of the F test in normal populations with variances proportional to the cell means is reported. The results indicate that the power of the test can be approximated by the noncentral F distribution with a modified parameter of noncentrality. (Author/CM)

Budescu, David V.

1982-01-01

150

Heterogeneous Staining for Mismatch Repair Proteins during Population-Based Prescreening for Hereditary Nonpolyposis Colorectal Cancer  

Microsoft Academic Search

The aim of this study was to determine the fre- quency of microsatellite instability (MSI )i n tu- mors from a population-based series of young colo- rectal cancer patients and its correlation with the loss of expression of mismatch repair (MMR) pro- teins. The BAT-26 mononucleotide repeat was used to screen for MSI in all colorectal cancers diag- nosed in

Natasha Watson; Fabienne Grieu; Melinda Morris; Jennet Harvey; Colin Stewart; Lyn Schofield; Jack Goldblatt; Barry Iacopetta

2007-01-01

151

Evolutionary models of color categorization II Realistic observer models and population heterogeneity  

Microsoft Academic Search

The evolution of color categorization is investigated using computer simulations of agent population categori- zation games. Various realistic observer types are implemented based on Farnsworth-Munsell 100 Hue Test human performance data from normal and anomalous trichromats, dichromats, and humans with four retinal photopigments. Results show that (i) a small percentage of realistically modeled deficient agents greatly affects the shared categorization

Kimberly A. Jameson; Natalia L. Komarova

2009-01-01

152

1.0 SERVICES FOR SPECIAL POPULATIONS 1.1 Student Athletes  

E-print Network

, FAX x3953 · In addition to meeting University and college standards, student athletes must also meet contact in each college advising office, keeps track of the NCAA/MAC requirements and student athletes1.0 SERVICES FOR SPECIAL POPULATIONS 1.1 Student Athletes 1.1.a Athletic Advising Office 205

Viola, Ronald

153

The Impact of Multi-Dimensional Behavioral Interventions in Student Conduct Processes: Achieving Increased Learning Outcomes in Adult Student Populations  

ERIC Educational Resources Information Center

As adult students constitute nearly half of all undergraduates in the United States, college practitioners need to identify effective disciplinary strategies for this population when violations of institutional rules and regulations occur. The purpose of this quasi-experimental, action research study was to modify the student conduct process for…

Braddix, D'Andre Cortez

2012-01-01

154

Verbal Humor in Gifted Students and Students in the General Population: A Comparison of Spontaneous Mirth and Comprehension.  

ERIC Educational Resources Information Center

The reactions of 60 gifted students and 60 regular students in grades 4, 6, and 8 to an audiotape of age-appropriate riddles, jokes, puns, satire, and nonhumorous items were compared. Results indicated that gifted subjects performed significantly higher in spontaneous mirth response and comprehension of verbal humor than the general population

Shade, Rick

1991-01-01

155

Human factors involvement in bringing the power of AI to a heterogeneous user population  

NASA Technical Reports Server (NTRS)

The Human Factors involvement in developing COMPAQ QuickSolve, an electronic problem-solving and information system for Compaq's line of networked printers, is described. Empowering customers with expert system technology so they could solve advanced networked printer problems on their own was a major goal in designing this system. This process would minimize customer down-time, reduce the number of phone calls to the Compaq Customer Support Center, improve customer satisfaction, and, most importantly, differentiate Compaq printers in the marketplace by providing the best, and most technologically advanced, customer support. This represents a re-engineering of Compaq's customer support strategy and implementation. In its first generation system, SMART, the objective was to provide expert knowledge to Compaq's help desk operation to more quickly and correctly answer customer questions and problems. QuickSolve is a second generation system in that customer support is put directly in the hands of the consumers. As a result, the design of QuickSolve presented a number of challenging issues. Because the produce would be used by a diverse and heterogeneous set of users, a significant amount of human factors research and analysis was required while designing and implementing the system. Research that shaped the organization and design of the expert system component as well.

Czerwinski, Mary; Nguyen, Trung

1994-01-01

156

A heterogeneous population code for elapsed time in rat medial agranular cortex  

PubMed Central

The neural mechanisms underlying the temporal control of behavior are largely unknown. Here we recorded from the medial agranular cortex in rats trained to respond on a temporal production procedure for probabilistically available food reward. Due to variability in estimating the time of food availability, robust responding typically bracketed the expected duration, starting some time before and ending some time after the signaled delay. This response period provided an analytic “steady-state” window during which the subject actively timed their behavior. Remarkably, during these response periods, a variety of firing patterns were seen which could be broadly described as ramps, peaks, and dips, with different slopes, directions, and times at which maxima or minima occur. Regularized linear discriminant analysis indicated that these patterns provided sufficiently reliable information to discriminate the elapsed duration of responding within these response periods. Modeling this across neuron variability showed that the utilization of ramps, dips, and peaks with different slopes and minimal/maximal rates at different times led to a substantial improvement in temporal prediction errors, suggesting that heterogeneity in the neural representation of elapsed time may facilitate temporally controlled behavior. PMID:21319888

Matell, Matthew S.; Shea-Brown, Eric; Gooch, Cindy; Wilson, A. George; Rinzel, John

2010-01-01

157

Heterogeneity of genetic architecture of body size traits in a free-living population.  

PubMed

Knowledge of the underlying genetic architecture of quantitative traits could aid in understanding how they evolve. In wild populations, it is still largely unknown whether complex traits are polygenic or influenced by few loci with major effect, due to often small sample sizes and low resolution of marker panels. Here, we examine the genetic architecture of five adult body size traits in a free-living population of Soay sheep on St Kilda using 37 037 polymorphic SNPs. Two traits (jaw and weight) show classical signs of a polygenic trait: the proportion of variance explained by a chromosome was proportional to its length, multiple chromosomes and genomic regions explained significant amounts of phenotypic variance, but no SNPs were associated with trait variance when using GWAS. In comparison, genetic variance for leg length traits (foreleg, hindleg and metacarpal) was disproportionately explained by two SNPs on chromosomes 16 (s23172.1) and 19 (s74894.1), which each explained >10% of the additive genetic variance. After controlling for environmental differences, females heterozygous for s74894.1 produced more lambs and recruits during their lifetime than females homozygous for the common allele conferring long legs. We also demonstrate that alleles conferring shorter legs have likely entered the population through a historic admixture event with the Dunface sheep. In summary, we show that different proxies for body size can have very different genetic architecture and that dense SNP helps in understanding both the mode of selection and the evolutionary history at loci underlying quantitative traits in natural populations. PMID:25753777

Bérénos, Camillo; Ellis, Philip A; Pilkington, Jill G; Lee, S Hong; Gratten, Jake; Pemberton, Josephine M

2015-04-01

158

Heterogeneity of genetic architecture of body size traits in a free-living population  

PubMed Central

Knowledge of the underlying genetic architecture of quantitative traits could aid in understanding how they evolve. In wild populations, it is still largely unknown whether complex traits are polygenic or influenced by few loci with major effect, due to often small sample sizes and low resolution of marker panels. Here, we examine the genetic architecture of five adult body size traits in a free-living population of Soay sheep on St Kilda using 37 037 polymorphic SNPs. Two traits (jaw and weight) show classical signs of a polygenic trait: the proportion of variance explained by a chromosome was proportional to its length, multiple chromosomes and genomic regions explained significant amounts of phenotypic variance, but no SNPs were associated with trait variance when using GWAS. In comparison, genetic variance for leg length traits (foreleg, hindleg and metacarpal) was disproportionately explained by two SNPs on chromosomes 16 (s23172.1) and 19 (s74894.1), which each explained >10% of the additive genetic variance. After controlling for environmental differences, females heterozygous for s74894.1 produced more lambs and recruits during their lifetime than females homozygous for the common allele conferring long legs. We also demonstrate that alleles conferring shorter legs have likely entered the population through a historic admixture event with the Dunface sheep. In summary, we show that different proxies for body size can have very different genetic architecture and that dense SNP helps in understanding both the mode of selection and the evolutionary history at loci underlying quantitative traits in natural populations. PMID:25753777

Bérénos, Camillo; Ellis, Philip A; Pilkington, Jill G; Lee, S Hong; Gratten, Jake; Pemberton, Josephine M

2015-01-01

159

Unexpected genetic heterogeneity for primary ciliary dyskinesia in the Irish Traveller population.  

PubMed

We present a study of five children from three unrelated Irish Traveller families presenting with primary ciliary dyskinesia (PCD). As previously characterized disorders in the Irish Traveller population are caused by common homozygous mutations, we hypothesised that all three PCD families shared the same recessive mutation. However, exome sequencing showed that there was no pathogenic homozygous mutation common to all families. This finding was supported by histology, which showed that each family has a different type of ciliary defect; transposition defect (family A), nude epithelium (family B) and absence of inner and outer dynein arms (family C). Therefore, each family was analysed independently using homozygosity mapping and exome sequencing. The affected siblings in family A share a novel 1?bp duplication in RSPH4A (NM_001161664.1:c.166dup; p.Arg56Profs*11), a radial-spoke head protein involved in ciliary movement. In family B, we identified three candidate genes (CCNO, KCNN3 and CDKN1C), with a 5-bp duplication in CCNO (NM_021147.3:c.258_262dup; p.Gln88Argfs*8) being the most likely cause of ciliary aplasia. This is the first study to implicate CCNO, a DNA repair gene reported to be involved in multiciliogenesis, in PCD. In family C, we identified a ?3.5-kb deletion in DYX1C1, a neuronal migration gene previously associated with PCD. This is the first report of a disorder in the relatively small Irish Traveller population to be caused by >1 disease gene. Our study identified at least three different PCD genes in the Irish Traveller population, highlighting that one cannot always assume genetic homogeneity, even in small consanguineous populations. PMID:24824133

Casey, Jillian P; McGettigan, Paul A; Healy, Fiona; Hogg, Claire; Reynolds, Alison; Kennedy, Breandan N; Ennis, Sean; Slattery, Dubhfeasa; Lynch, Sally A

2015-02-01

160

Ploidy frequencies in plants with ploidy heterogeneity: fitting a general gametic model to empirical population data  

PubMed Central

Genome duplication (polyploidy) is a recurrent evolutionary process in plants, often conferring instant reproductive isolation and thus potentially leading to speciation. Outcome of the process is often seen in the field as different cytotypes co-occur in many plant populations. Failure of meiotic reduction during gametogenesis is widely acknowledged to be the main mode of polyploid formation. To get insight into its role in the dynamics of polyploidy generation under natural conditions, and coexistence of several ploidy levels, we developed a general gametic model for diploid–polyploid systems. This model predicts equilibrium ploidy frequencies as functions of several parameters, namely the unreduced gamete proportions and fertilities of higher ploidy plants. We used data on field ploidy frequencies for 39 presumably autopolyploid plant species/populations to infer numerical values of the model parameters (either analytically or using an optimization procedure). With the exception of a few species, the model fit was very high. The estimated proportions of unreduced gametes (median of 0.0089) matched published estimates well. Our results imply that conditions for cytotype coexistence in natural populations are likely to be less restrictive than previously assumed. In addition, rather simple models show sufficiently rich behaviour to explain the prevalence of polyploids among flowering plants. PMID:23193129

Suda, Jan; Herben, Tomáš

2013-01-01

161

Heterogeneous dopamine populations project to specific subregions of the primate amygdala.  

PubMed

Amygdala dysfunction has been reported among patients with various psychiatric disorders, and dopamine is critical to the amygdala's ability to mediate fear conditioning. Recent work indicates that the midbrain dopaminergic neurons have heterogeneous receptor and membrane channel profiles, as well as differential physiologic responses to discrete stimuli. To begin understanding how dopamine affects amygdala physiology and pathology in higher primates, we mapped the inputs from the midbrain dopaminergic neurons to various amygdala nuclei in the monkey using retrograde and anterograde tracing techniques, and single and double immunofluorescence histochemistry for tracer and tyrosine hydroxylase, a dopamine marker. Our results show that the primate amygdala as a whole receives broad input, mostly from the dorsal tier of the substantia nigra, pars compacta, and the A8-retrorubral field. Input from the A10-ventral tegmental area, while present, was less prominent. These results differ from data in the rat, where the midline A10-ventral tegmental area is a major source of dopamine to the amygdala "mesolimbic" pathway. Both the "amygdala proper" and the "extended amygdala" receive the majority of their input from the dorsal tier of the substantia nigra and A8-retrorubral field, but the extended amygdala receives additional modest input from the ventral tier. In addition, the "extended amygdala" structures have a denser input than the "amygdala proper," with the exception of the lateral core of the central nucleus, which receives no input. Our anterograde studies confirm these findings, and revealed fine, diffuse terminal fibers in the amygdala proper, but a denser network of fibers in the extended amygdala outside the lateral core of the central nucleus. These results indicate that the entire extent of the dorsal tier beyond the A10-ventral tegmental area may regulate the amygdala in primates, and subsequently serve as a source of dysfunction in primate psychopathology. PMID:19914353

Cho, Y T; Fudge, J L

2010-02-17

162

Isolation of a heterogeneous population of temperature-sensitive mutants of measles virus from persistently infected human lymphoblastoid cell lines.  

PubMed

Two human lymphoblastoid B-cell lines, WI-L2 and 8866, were infected with the Edmonston strain of measles virus at a multiplicity of infection of 10(-6), and stable persistent infections were established. By immunofluorescence and electron microscopy, the vast majority of cells from both cell lines were expressing viral antigens and releasing virion-like particles. However, very little infectious virus could be detected at 37 degrees C, either by an infectious centers assay or by titration of supernates from persistently infected cultures. When cultures were shifted to 31 degrees C, the cells released a population of virus that was temperature-sensitive. Clonal analysis of supernatant virus at 31 degrees C revealed a highly heterogeneous population of temperature-sensitive mutants, differing in plating efficiency ratios, thermolability, and antigen production at the nonpermissive temperature. Factors such as interferon, defective interfering particles, and extracellular virus do not appear to be important in maintaining the persistent carrier state. These studies have important implications for persistent infections of lymphoid cells in vivo, and the slow neurological diseases associated with measles, subacute sclerosing panencephalitis, and multiple sclerosis. PMID:210247

Ju, G; Udem, S; Rager-Zisman, B; Bloom, B R

1978-06-01

163

Acculturation, dietary practices and risk for childhood obesity in an ethnically heterogeneous population of Latino school children in the San Francisco bay area.  

PubMed

Previous studies have found increased acculturation to the US lifestyle increases risk for obesity in Latinos. However, methodologies differ, and results in children are inconsistent. Moreover, previous studies have not evaluated risk factors within the heterogeneous US population. We recruited 144 self-identified Latino school children and their mother or father in grades 4-6 in San Francisco parochial schools and South San Francisco public schools using an information letter distributed to all students. Children and parents had weights, heights, demographic information, dietary patterns and lifestyle variables collected in English or Spanish through an interview format. A high percentage of our children were overweight [?85th percentile body mass index (BMI)] (62.5%) and obese (?95th percentile BMI) (45.2%). Correspondingly parents also had a high percentage of overweight (BMI ? 25 & <30) (40.8%) and obesity (BMI ? 30) (45.3%). Mexico was the country of origin for 62.2% of parents, and 26.6% were from Central or South America. In multivariate logistic analysis, speaking Spanish at home was an independent risk factor for obesity [odds ratio (OR) 2.97, 95% confidence interval (CI) 1.28-6.86]. Eating breakfast daily (OR 0.34, 95% CI 0.15-0.78) and consumption of tortas (a Mexican fast food sandwich) (OR 0.45, 95% CI 0.21-1.00) were associated with decreased risk. In stratified analysis, significant differences in risk factors existed between Mexican origin versus Central/South American Latino children. The processes of acculturation likely impact eating and lifestyle practices differentially among Latino groups. Interventions should focus on ensuring that all children eat a nutritious breakfast and take into consideration ethnicity when working with Latino populations. PMID:22101726

Wojcicki, Janet M; Schwartz, Norah; Jiménez-Cruz, Arturo; Bacardi-Gascon, Montserrat; Heyman, Melvin B

2012-08-01

164

The 8p23 Inversion Polymorphism Determines Local Recombination Heterogeneity across Human Populations  

PubMed Central

For decades, chromosomal inversions have been regarded as fascinating evolutionary elements as they are expected to suppress recombination between chromosomes with opposite orientations, leading to the accumulation of genetic differences between the two configurations over time. Here, making use of publicly available population genotype data for the largest polymorphic inversion in the human genome (8p23-inv), we assessed whether this inhibitory effect of inversion rearrangements led to significant differences in the recombination landscape of two homologous DNA segments, with opposite orientation. Our analysis revealed that the accumulation of genetic differentiation is positively correlated with the variation in recombination profiles. The observed recombination dissimilarity between inversion types is consistent across all populations analyzed and surpasses the effects of geographic structure, suggesting that both structures (orientations) have been evolving independently over an extended period of time, despite being subjected to the very same demographic history. Aside this mainly independent evolution, we also identified a short segment (350 kb, <10% of the whole inversion) in the central region of the inversion where the genetic divergence between the two structural haplotypes is diminished. Although it is difficult to demonstrate it, this could be due to gene flow (possibly via double-crossing over events), which is consistent with the higher recombination rates surrounding this segment. This study demonstrates for the first time that chromosomal inversions influence the recombination landscape at a fine-scale and highlights the role of these rearrangements as drivers of genome evolution. PMID:24682157

Alves, Joao M.; Chikhi, Lounès; Amorim, António; Lopes, Alexandra M.

2014-01-01

165

A New Approach to Evaluation of University Teaching Considering Heterogeneity of Students' Preferences  

ERIC Educational Resources Information Center

Students' evaluations of teaching are increasingly used by universities to evaluate teaching performance. However, these evaluations are controversial mainly due to the fact that students value various aspects of excellent teaching differently. Therefore, in this paper we propose a new approach to students' evaluations of university…

Kuzmanovic, Marija; Savic, Gordana; Popovic, Milena; Martic, Milan

2013-01-01

166

Spatial Heterogeneity of Bacterial Populations along an Environmental Gradient at a Shallow Submarine Hydrothermal Vent near Milos Island (Greece)  

PubMed Central

The spatial heterogeneity of bacterial populations at a shallow-water hydrothermal vent in the Aegean Sea close to the island of Milos (Greece) was examined at two different times by using acridine orange staining for total cell counts, cultivation-based techniques, and denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA gene fragments. Concurrent with measurements of geochemical parameters, samples were taken along a transect from the center of the vent to the surrounding area. Most-probable-number (MPN) counts of metabolically defined subpopulations generally constituted a minor fraction of the total cell counts; both counting procedures revealed the highest cell numbers in a transition zone from the strongly hydrothermally influenced sediments to normal sedimentary conditions. Total cell counts ranged from 3.2 × 105 cells ml?1 in the water overlying the sediments to 6.4 × 108 cells g (wet weight) of sediment?1. MPN counts of chemolithoautotrophic sulfur-oxidizing bacteria varied between undetectable and 1.4 × 106 cells g?1. MPN counts for sulfate-reducing bacteria and dissimilatory iron-reducing bacteria ranged from 8 to 1.4 × 105 cells g?1 and from undetectable to 1.4 × 106 cells g?1, respectively. DGGE revealed a trend from a diverse range of bacterial populations which were present in approximately equal abundance in the transition zone to a community dominated by few populations close to the center of the vent. Temperature was found to be an important parameter in determining this trend. However, at one sampling time this trend was not discernible, possibly due to storm-induced disturbance of the upper sediment layers. PMID:10473383

Sievert, Stefan M.; Brinkhoff, Thorsten; Muyzer, Gerard; Ziebis, Wiebke; Kuever, Jan

1999-01-01

167

Molecular correlations in phenylketonuria: mutation patterns and corresponding biochemical and clinical phenotypes in a heterogeneous California population.  

PubMed

We studied 133 California phenylketonuria (PKU) patients and one obligate heterozygote to delineate the molecular basis of PKU in a population with greater ethnic diversity than in previous studies, and to determine whether a correlation exists between genotype and clinical phenotype, with the latter defined by both the diagnostic pretreatment blood phenylalanine (PHE) level and cognitive (IQ) test scores. To determine PAH genotypes, we used PCR-mediated amplification, denaturing gradient gel electrophoresis, and direct sequencing on dried whole blood samples. Where possible, mutation severity was defined according to predicted in vitro PAH enzyme activity estimated by using Cos cell expression analysis for a given mutation. We then asked whether mutation severity, as defined by such expression analysis, correlated with pretreatment PHE levels or with IQ test results. A mutation was identified in 236 (88%) of 267 mutant alleles. Seventeen new mutant alleles were found; A47E, T81P, I102T, E182G, T328D, Y343P, K371R, Y387H, A389E, E422K, IVS9nt5, IVS11nt20, delS70, del364-368/del198-220, delF299, delT323, and -1C/T. In striking contrast to a number of studies in other populations, in this study, based on predicted PAH activity, we observed no correlation between mutation severity and pretreatment PHE levels. There was also no correlation between genotype and IQ. We conclude that in samples collected from an ethnically heterogeneous population, there is no correlation of mutation severity with either pretreatment PHE levels or IQ measurement in treated patients. We caution that genetic counseling in PKU should incorporate the notion that prognosis may not be predicted with precision based on mutation analysis in a given patient. PMID:10541324

Enns, G M; Martinez, D R; Kuzmin, A I; Koch, R; Wakeem, C K; Woo, S L; Eisensmith, R C; Packman, S

1999-11-01

168

Population Heterogeneity of Agrobacterium tumefaciens in Galls of Populus L. from a Single Nursery  

PubMed Central

This study focused on the natural crown gall infections occurring in a Leuce poplar nursery. Soil effects on crown gall frequency were detected, indicating that contamination was due to a resident Agrobacterium tumefaciens population, which was present before seedling plantation. The crown gall frequency on poplar progenies varied from 3 to 67%, indicating the feasibility of improvement in crown gall resistance. Of 129 tumor isolates, 128 were pathogenic. These isolates were of biotype 1 or 2. Biochemical, serological, and antibiotic resistance typing results concurred, indicating the presence of four biotype 1 and two biotype 2 resident subpopulations. No significant change was noticed in the relative proportions of subpopulations from one year to another. Pathogenic subpopulations both in vitro and in planta were susceptible to Kerr K84 (P. B. New and A. Kerr, J. Appl. Bacteriol. 90:172-179, 1972). In addition, no serological cross-reactions were found to occur between K84 and the pathogenic subpopulations. PMID:16347314

Nesme, Xavier; Michel, Marie-France; Digat, Bernard

1987-01-01

169

Bipolar disorder in the Bulgarian Gypsies: genetic heterogeneity in a young founder population.  

PubMed

We report the results of follow-up analyses of 12 genomic regions showing evidence of linkage in a genome-wide scan (GWS) of Gypsy families with bipolar affective disorder (BPAD). The Gypsies are a young founder population comprising multiple genetically differentiated sub-isolates with strong founder effect and limited genetic diversity. The BPAD families belong to a single sub-isolate and are connected by numerous inter-marriages, resulting in a super-pedigree with 181 members. We aimed to re-assess the positive GWS findings and search for evidence of a founder susceptibility allele after the addition of newly recruited subjects, some changes in diagnostic assignment, and the use of denser genetic maps. Linkage analysis was conducted with SimWalk2, accommodating the full complexity of pedigree structure and using a conservative narrow phenotype definition (BPAD only). Six regions were rejected, while 1p36, 13q31, 17p11, 17q21, 6q24, and 4q31 produced nominally significant results in both the individual families and the super-pedigree. Haplotypes were reconstructed and joint tests for linkage and association were done for the most promising regions. No common ancestral haplotype was identified by sequencing a strong positional and functional candidate gene (GRM1) and additional STR genotyping in the top GWS region, 6q24. The best supported region was a 12 cM interval on 4q31, also implicated in previous studies, where we obtained significant results in the super-pedigree using both SimWalk2 (P = 0.004) and joint Pseudomarker analysis of linkage and linkage disequilibrium (P = 0.000056). The size of the region and the characteristics of the Gypsy population make it suitable for LD mapping. PMID:18444255

Kaneva, Radka; Milanova, Vihra; Angelicheva, Dora; MacGregor, Stuart; Kostov, Christian; Vladimirova, Rositza; Aleksiev, Spiridon; Angelova, Mina; Stoyanova, Vessela; Loh, Angeline; Hallmayer, Joachim; Kalaydjieva, Luba; Jablensky, Assen

2009-03-01

170

Analysis of biochemical genetic data on Jewish populations: II. Results and interpretations of heterogeneity indices and distance measures with respect to standards.  

PubMed Central

A nonparametric statistical methodology is used for the analysis of biochemical frequency data observed on a series of nine Jewish and six non-Jewish populations. Two categories of statistics are used: heterogeneity indices and various distance measures with respect to a standard. The latter are more discriminating in exploiting historical, geographical and culturally relevant information. A number of partial orderings and distance relationships among the populations are determined. Our concern in this study is to analyze similarities and differences among the Jewish populations, in terms of the gene frequency distributions for a number of genetic markers. Typical questions discussed are as follows: These Jewish populations differ in certain morphological and anthropometric traits. Are there corresponding differences in biochemical genetic constitution? How can we assess the extent of heterogeneity between and within groupings? Which class of markers (blood typings or protein loci) discriminates better among the separate populations? The results are quite surprising. For example, we found the Ashkenazi, Sephardi and Iraqi Jewish populations to be consistently close in genetic constitution and distant from all the other populations, namely the Yemenite and Cochin Jews, the Arabs, and the non-Jewish German and Russian populations. We found the Polish Jewish community the most heterogeneous among all Jewish populations. The blood loci discriminate better than the protein loci. A number of possible interpretations and hypotheses for these and other results are offered. The method devised for this analysis should prove useful in studying similarities and differences for other groups of populations for which substantial biochemical polymorphic data are available. PMID:380330

Karlin, S; Kenett, R; Bonné-Tamir, B

1979-01-01

171

A Millifluidic Study of Cell-to-Cell Heterogeneity in Growth-Rate and Cell-Division Capability in Populations of Isogenic Cells of Chlamydomonas reinhardtii  

PubMed Central

To address possible cell-to-cell heterogeneity in growth dynamics of isogenic cell populations of Chlamydomonas reinhardtii, we developed a millifluidic drop-based device that not only allows the analysis of populations grown from single cells over periods of a week, but is also able to sort and collect drops of interest, containing viable and healthy cells, which can be used for further experimentation. In this study, we used isogenic algal cells that were first synchronized in mixotrophic growth conditions. We show that these synchronized cells, when placed in droplets and kept in mixotrophic growth conditions, exhibit mostly homogeneous growth statistics, but with two distinct subpopulations: a major population with a short doubling-time (fast-growers) and a significant subpopulation of slowly dividing cells (slow-growers). These observations suggest that algal cells from an isogenic population may be present in either of two states, a state of restricted division and a state of active division. When isogenic cells were allowed to propagate for about 1000 generations on solid agar plates, they displayed an increased heterogeneity in their growth dynamics. Although we could still identify the original populations of slow- and fast-growers, drops inoculated with a single progenitor cell now displayed a wider diversity of doubling-times. Moreover, populations dividing with the same growth-rate often reached different cell numbers in stationary phase, suggesting that the progenitor cells differed in the number of cell divisions they could undertake. We discuss possible explanations for these cell-to-cell heterogeneities in growth dynamics, such as mutations, differential aging or stochastic variations in metabolites and macromolecules yielding molecular switches, in the light of single-cell heterogeneities that have been reported among isogenic populations of other eu- and prokaryotes. PMID:25760649

Damodaran, Shima P.; Eberhard, Stephan; Boitard, Laurent; Rodriguez, Jairo Garnica; Wang, Yuxing; Bremond, Nicolas; Baudry, Jean; Bibette, Jérôme; Wollman, Francis-André

2015-01-01

172

Population Change: A Unit for Upper Elementary Urban Students  

ERIC Educational Resources Information Center

Materials offered as a new approach for students through involvement in their own immediate urban environment. Unit contains eight lessons including a survey made of the immediate neighborhood by the students. Data cards, check-lists, and summary charts are presented. (EB)

Seymour, Lowell A.; Thompson, Adell

1975-01-01

173

Population heterogeneity and dynamics in starter culture and lag phase adaptation of the spoilage yeast Zygosaccharomyces bailii to weak acid preservatives  

PubMed Central

The food spoilage yeast Zygosaccharomyces bailii shows great resistance to weak-acid preservatives, including sorbic acid (2, 4-hexadienoic acid). That extreme resistance was shown to be due to population heterogeneity, with a small sub-population of cells resistant to a variety of weak acids, probably caused by a lower internal pH reducing the uptake of all weak acids. In the present paper, it was found that resistant cells were extremely rare in exponential cultures, but increased by up to 8000-fold in stationary phase. Inoculation of media containing sorbic acid with a population of Z. bailii cells gave rise to what appeared to be a prolonged lag phase, suggesting adaptation to the conditions before the cells entered the period of exponential growth. However, the apparent lag phase caused by sorbic acid was largely due to the time required for the resistant sub-population to grow to detectable levels. The slow growth rate of the sub-population was identical to that of the final total population. The non-resistant bulk population remained viable for 3 days but had lost viability by 6 days and, during that time, there was no indication of any development of resistance in the bulk population. The sub-population growing in sorbic acid showed very high population diversity in colony size and internal pH. After removal of sorbic acid, the population rapidly reverted back to the normal, largely non-resistant, population distribution. The data presented suggest that a reevaluation of the lag phase in microbial batch culture is required, at least for the resistance of Z. bailii to sorbic acid. Furthermore, the significance of phenotypic diversity and heterogeneity in microbial populations is discussed more broadly with potential relevance to bacterial “persisters”, natural selection and evolution. PMID:24813627

Stratford, Malcolm; Steels, Hazel; Nebe-von-Caron, Gerhard; Avery, Simon V.; Novodvorska, Michaela; Archer, David B.

2014-01-01

174

Population heterogeneity and dynamics in starter culture and lag phase adaptation of the spoilage yeast Zygosaccharomyces bailii to weak acid preservatives.  

PubMed

The food spoilage yeast Zygosaccharomyces bailii shows great resistance to weak-acid preservatives, including sorbic acid (2, 4-hexadienoic acid). That extreme resistance was shown to be due to population heterogeneity, with a small sub-population of cells resistant to a variety of weak acids, probably caused by a lower internal pH reducing the uptake of all weak acids. In the present paper, it was found that resistant cells were extremely rare in exponential cultures, but increased by up to 8000-fold in stationary phase. Inoculation of media containing sorbic acid with a population of Z. bailii cells gave rise to what appeared to be a prolonged lag phase, suggesting adaptation to the conditions before the cells entered the period of exponential growth. However, the apparent lag phase caused by sorbic acid was largely due to the time required for the resistant sub-population to grow to detectable levels. The slow growth rate of the sub-population was identical to that of the final total population. The non-resistant bulk population remained viable for 3 days but had lost viability by 6 days and, during that time, there was no indication of any development of resistance in the bulk population. The sub-population growing in sorbic acid showed very high population diversity in colony size and internal pH. After removal of sorbic acid, the population rapidly reverted back to the normal, largely non-resistant, population distribution. The data presented suggest that a reevaluation of the lag phase in microbial batch culture is required, at least for the resistance of Z. bailii to sorbic acid. Furthermore, the significance of phenotypic diversity and heterogeneity in microbial populations is discussed more broadly with potential relevance to bacterial "persisters", natural selection and evolution. PMID:24813627

Stratford, Malcolm; Steels, Hazel; Nebe-von-Caron, Gerhard; Avery, Simon V; Novodvorska, Michaela; Archer, David B

2014-07-01

175

[Dynamical electrical states of heterogeneous populations of ion channels in the membranes of excitable cells].  

PubMed

In computer models, we studied instantaneous (time-varying) current-voltage relationships (iIVs) of populations of ion channels characteristic of the membrane of different type excitable cells, of which the responses to electrical stimuli essentially differ: giant squid axon (Hodgkin-Huxley model), cardiomyocyte, dendrites of CA3 hippocampal pyramidal neurons and Purkinje neurons of the cerebellum. The membrane potential was stepped from the rest level to a certain depolarization test level that was clamped for a certain time, and the total current was measured at different moments after the step onset. For each iIV zero-current points (potentials) were determined. A set of such points, which were situated on the limb of iIV positive slop and corresponded to the state of high membrane depolarization (excitation state, upstate) at different time moments, were used to characterize the dynamics of the excitation state in time. With these indicators the axon membrane was characterized by a single excitation state that rapidly occurred (0.25 ms) and was short-lasting (decayed from -45 to 40 mV during life-time of 5.5 ms). There were two such states of the membrane of cardiomyocyte. The first one was early, rapidly occurring and short-living (rapidly relaxing). It occurred shortly after the depolarization start and lasted for 14.5 ms. The second one was late, slowly rising and long-lasting (occurred with a 7.5-ms delay, increased from 11 to 46 mV in 39 ms and then relaxed lasting for 623 ms in total). The dendritic membrane ofCA3 neurons had one long-lasting excitation state that occurred shortly after the depolarization shift, first rapidly relaxed during 3 ms from initial 30 mV level to -10 mV and then slowly, in 80 ms, stabilized at the level of -20 mV. In the Purkinje neuron membrane two short-lasting and one very long-lasting excitation states were revealed. The first state of very high (>100 mV) depolarization relaxed to 4 mV in 0.8 ms. Shortly before its vanishing, at 0.7 ms, the second short-lasting state emerged, which relaxed in 1 ms from -22 mV to -48 mV. At 1.8 ms a new excitation state emerged, which after a transient relaxation stabilized at -29.65 mV starting from 88 ms. Thus, iIVs allowed disclosing a fine organization of the states of electrical excitation of the membrane and revealing, in populations of ion channels of different content, existence of different number of the mentioned states, which differ from each other in occurrence time and life-time. PMID:22946313

Korogod, S M; Kulagina, I B

2012-01-01

176

Sleep Patterns and Predictors of Disturbed Sleep in a Large Population of College Students  

Microsoft Academic Search

PurposeTo characterize sleep patterns and predictors of poor sleep quality in a large population of college students. This study extends the 2006 National Sleep Foundation examination of sleep in early adolescence by examining sleep in older adolescents.

Hannah G. Lund; Brian D. Reider; Annie B. Whiting; J. Roxanne Prichard

2010-01-01

177

Heterogeneity in Risk of Pelvic Inflammatory Diseases After Chlamydia Infection: A Population-Based Study in Manitoba, Canada  

PubMed Central

Background.?The association between chlamydia infection and pelvic inflammatory disease (PID) is a key parameter for models evaluating the impact of chlamydia control programs. We quantified this association using a retrospective population-based cohort. Methods.?We used administrative health data sets to construct a retrospective population-based cohort of women and girls aged 12–24 years who were resident in Manitoba, Canada, between 1992 and 1996. We performed survival analysis on a subcohort of individuals who were tested for chlamydia to estimate the risk of PID diagnosed in a primary care, outpatient, or inpatient setting after ?1 positive chlamydia test. Results.?A total of 73 883 individuals contributed 625 621 person years of follow-up. Those with a diagnosis of chlamydia had an increased risk of PID over their reproductive lifetime compared with those who tested negative (adjusted hazard ratio [AHR], 1.55; 95% confidence interval [CI], 1.43–1.70). This risk increased with each subsequent infection: the AHR was 1.17 for first reinfection (95% CI, 1.06–1.30) and 1.35 for the second (95% CI, 1.04–1.75). The increased risk of PID from reinfection was highest in younger individuals (AHR, 4.55 (95% CI, 3.59–5.78) in individuals aged 12–15 years at the time of their second reinfection, compared with individuals older than 30 years). Conclusions.?There is heterogeneity in the risk of PID after a chlamydia infection. Describing the progression to PID in mathematical models as an average rate may be an oversimplification; more accurate estimates of the cost-effectiveness of screening may be obtained by using an individual-based measure of risk. Health inequalities may be reduced by targeting health promotion interventions at sexually active girls younger than 16 years and those with a history of chlamydia. PMID:25381374

Davies, Bethan; Ward, Helen; Leung, Stella; Turner, Katy M. E.; Garnett, Geoff P.; Blanchard, James F.; Yu, B. Nancy

2014-01-01

178

Class Size Effects on Student Achievement: Heterogeneity across Abilities and Fields  

ERIC Educational Resources Information Center

In this paper, we analyze class size effects on college students exploiting data from a project offering special remedial courses in mathematics and language skills to freshmen enrolled at an Italian medium-sized public university. To estimate the effects of class size, we exploit the fact that students and teachers are virtually randomly assigned…

De Paola, Maria; Ponzo, Michela; Scoppa, Vincenzo

2013-01-01

179

An exploratory study on the contribution of graduate entry students personality to the diversity of medical student populations.  

PubMed

Studies conducted in medical education show that personality influences undergraduate medical students academic and clinical performances and also their career interests. Our aims with this exploratory study were: to assess the contribution of graduate entry students to the diversity of personality in medical student populations; to assess whether eventual differences may be explained by programme structure or student age and sex. We performed a cross-sectional study underpinned by the five-factor model of personality, with students attending three medical schools in Portugal. The five personality dimensions were assessed with the Portuguese version of the NEO-Five Factor Inventory. MANOVA and MANCOVA analyses were performed to clarify the contributions of school, programme structure, age and sex. Student personality dimensions were significantly different between the three medical schools [F (10,1026)  = 3.159, p < .001, [Formula: see text] = 0.03, ? = 0.987]. However, taking sex and age into account the differences became non-significant. There were institutional differences in personality dimensions. However, those were primarily accounted for by sex and age effects and not by the medical school attended. Diversifying age and sex of the admitted students will diversify the personality of the medical student population. PMID:25410707

Marvão, Pedro; Neto, Isabel; Castelo-Branco, Miguel; Ponte, José; Portela, Miguel; Costa, Patrício; Costa, Manuel João

2014-12-01

180

Minority Student Response to the Anthropology of Asian Black Populations. Revised.  

ERIC Educational Resources Information Center

Since 1970, the University of Chicago has offered three undergraduate anthropology courses on Philippine Negrito and Malay and Thai aboriginal black populations. Between 1975 and 1981, 72 students, including American blacks, Filipinos, and other Asians, attended the courses. The instructor's observations of students' responses to the courses…

Warren, Charles P.

181

Mild Disability Students and Everyday Mathematics: Serving the Needs of This Population  

ERIC Educational Resources Information Center

No Child Left Behind requires school districts to demonstrate adequate yearly progress in mathematics for all students, including the sub-population of disabled students. Given that more than 200 Ohio school districts have implemented Everyday Mathematics (EM) to achieve this mandate, districts need to know if this standards-based program meets…

Brehe Pixler, Priscilla

2009-01-01

182

Pregnant and Parenting Students on Campus: Policy and Program Implications for a Growing Population  

ERIC Educational Resources Information Center

The number of pregnant and parenting students in higher education is increasing. Research suggests this population experiences added pressure and stress while pursuing their education. Few resources exist for these students and the universities who provide services do not adequately promulgate them to the campus community. The research presented…

Brown, Virginia; Nichols, Tracy R.

2013-01-01

183

Geography, the Integrating Discipline: Explaining China's Population-Driven Geopolitics to Students  

ERIC Educational Resources Information Center

This article demonstrates geography's role as an integrative discipline and its utility in connecting students to the world around them. A case study links China's demography and its geopolitics to the lives of U.S. students. The relationship of China's population pressures to its resulting economic growth, need for economic resources, and…

Bouchat, Clarence J.

2008-01-01

184

Working in the Margins: A Study of University Professionals Serving Marginalized Student Populations  

ERIC Educational Resources Information Center

The purpose of this research is to gain some understandings of how university professionals who work with marginalized student populations perceive their professional work as situated within a university context. The professionals in this study work in federal TRIO programs that serve first-generation, low-income students who have been…

Wallace, Dawn; Ropers-Huilman, Becky; Abel, Ron

2004-01-01

185

Changes in Student Populations and Average Test Scores of Dutch Primary Schools  

ERIC Educational Resources Information Center

This article focuses on the relation between student population characteristics and average test scores per school in the final grade of primary education from a dynamic perspective. Aggregated data of over 5,000 Dutch primary schools covering a 6-year period were used to study the relation between changes in school populations and shifts in mean…

Luyten, Hans; de Wolf, Inge

2011-01-01

186

Changes in student populations and average test scores of Dutch primary schools  

Microsoft Academic Search

This article focuses on the relation between student population characteristics and average test scores per school in the final grade of primary education from a dynamic perspective. Aggregated data of over 5,000 Dutch primary schools covering a 6-year period were used to study the relation between changes in school populations and shifts in mean test scores. Path analysis findings indicate

Hans Luyten; Inge de Wolf

2011-01-01

187

The relative influence of climate, environmental heterogeneity, and human population on the distribution of vertebrate species richness in south-eastern Spain  

NASA Astrophysics Data System (ADS)

In view of the many factors affect species richness, this study examines the relative influence of environmental heterogeneity, climate, human disturbance and spatial structure with respect to the species-richness distribution of terrestrial vertebrates in an area of south-eastern Spain with a Mediterranean climate. We show that environmental heterogeneity was the primary factor determining species richness (20.3% of variance), with the effect of temperature and precipitation being lower (11.6%). Climate had greater importance in determining the species richness of ectotherms (amphibians and reptiles) than of endotherms (mammals and birds). Species richness had less spatial autocorrelation in mammals and birds than in ectotherms. Also, a positive correlation was found between species richness and human population density, especially in reptiles and mammals. Orders and families more sensitive to human presence, such as snakes, raptors, ungulates, and carnivores, showed no relationship (or a negative one) with the human population. This study highlights the importance of environmental heterogeneity (topographic heterogeneity and habitat diversity) for vertebrate conservation in zones with a Mediterranean climate.

Moreno-Rueda, Gregorio; Pizarro, Manuel

2007-07-01

188

The heterogeneous HLA genetic composition of the Brazilian population and its relevance to the optimization of hematopoietic stem cell donor recruitment.  

PubMed

The aim of this study was to investigate the human leukocyte antigen (HLA) molecular variation across the Brazilian population in order to determine possible regional differences, which would be highly relevant to optimizing donor recruitment strategies in hematopoietic stem cell transplantation (HSCT) and understanding the population genetic background of this heterogeneous country. HLA data of 551 HSCT donors from five Brazilian regions were characterized by high-resolution DNA alleles at the HLA-A, -B, -C, -DRB1 and -DQB1 loci and compared with other populations in Brazil and worldwide populations. Allele and haplotype frequencies were estimated. The analysis was performed to assess Hardy-Weinberg equilibrium (HWE) and linkage disequilibrium (LD) among different loci in each recruitment center. Genetic variation was explored through genetic distance analyzed by using a new algorithm based on linear algebra, taking into account geographic regions of Brazil. The results indicated a heterogeneous genetic composition of the Brazilian population, such that HLA allele and haplotype frequencies exhibit different distributions among Brazilian regions, which has important implications for donor matching. In addition, a pronounced differentiation was observed by the absence of clustering of the regional populations in the reduced-dimension space. These data may be useful for increasing donor recruitment with more genetic representativeness in the Brazilian Volunteer Bone Marrow Donors Registry (REDOME). PMID:24724906

Fabreti-Oliveira, R A; Nascimento, E; Fonseca, C G; Santos, M A

2014-08-01

189

Product News versus Advertising: An Exploration within a Student Population.  

ERIC Educational Resources Information Center

An exploratory survey (part of a larger study) examined the relative effectiveness of news versus advertising as sources of product information. Subjects, 140 undergraduate students enrolled in an introductory public speaking course or a course in visual communication, completed a 5-page media interest survey. Results indicated that news rates…

Hallahan, Kirk

190

Preparation of Agricultural Education Students to Work with Diverse Populations  

ERIC Educational Resources Information Center

This study investigated how agricultural education programs prepare teacher education students for work in diverse situations. It assessed the extent to which agricultural education programs are infusing diversity, multiculturalism, and pluralism into their curriculum as courses, field experiences, and in-service for current teachers. This census…

Talbert, B. Allen; Edwin, James

2008-01-01

191

Treatment of Bipolar Disorder in the University Student Population  

ERIC Educational Resources Information Center

University counseling centers are faced with the challenge of effectively treating bipolar students while also utilizing brief treatment frameworks and managing high patient volumes. Potential destabilization, particularly within the elevated mood phase, poses significant behavioral management issues for university clinicians and administrators,…

Federman, Russ

2011-01-01

192

Math Failure and Learning Disabilities in the Postsecondary Student Population.  

ERIC Educational Resources Information Center

This article discusses factors that contribute to the difficulties that many postsecondary students with learning disabilities have in meeting the mathematics demands, including: characteristics of learning disabilities in math, inadequate preparation for postsecondary math demands, difficulties with assessment and identification, and…

Strawser, Sherri; Miller, Susan P.

2001-01-01

193

The effect of homogeneous and heterogeneous review pairs on student achievement and attitude when utilizing computer-assisted instruction in middle-level Earth science classes  

Microsoft Academic Search

This research project investigated the influence of homogeneous (like-ability) review pairs coupled with heterogeneous (mixed-ability) cooperative learning groups using computer-assisted instruction (CAI) on academic achievement and attitude toward science in eighth grade Earth science students. Subjects were placed into academic quartiles (Hi, Med-Hi, Med-Lo, and Lo) based on achievement. Cooperative learning groups of four (one student from each academic quartile)

Ellen Beth Lyon

1998-01-01

194

Antibody responses induced by Leish-Tec®, an A2-based vaccine for visceral leishmaniasis, in a heterogeneous canine population.  

PubMed

Zoonotic visceral leishmaniasis (VL) is a widespread disease, and dogs are the main reservoirs for human parasite transmission. Hence, development of an effective vaccine that prevents disease and reduces the transmission of VL is required. As euthanasia of seropositive dogs is recommended in Brazil for VL epidemiological control, to include anti-VL canine vaccines as a mass control measure it is necessary to characterize the humoral responses induced by vaccination and if they interfere with the reactivity of vaccinated dogs in serological diagnostic tests. Leish-Tec(®) is an amastigote-specific A2 recombinant protein vaccine against canine visceral leishmaniasis (CVL) that is commercially available in Brazil. Here, we tested the immunogenicity of Leish-Tec(®) in a heterogeneous dog population by measuring A2-specific antibody responses. Healthy dogs (n=140) of various breeds were allocated to two groups: one group received Leish-Tec(®) (n=70), and the other group received a placebo (n=70). Anti-A2 or anti-Leishmania promastigote antigen (LPA) antibody levels were measured by ELISA in serum samples collected before and after vaccination. An immunochromatographic test (DPP) based on the recombinant K28 antigen was also used for serodiagnosis of CVL. Vaccinated animals, except one, remained seronegative for anti-LPA total IgG and anti-K28 antibodies. Conversely, seropositivity for anti-A2 total IgG antibodies was found in 98% of animals after vaccination. This value decreased to 81.13% at 6 months before rising again (98%), after the vaccination boost. Anti-A2 IgG2 and IgG1 titers were also increased in vaccinated animals relative to control animals. These data indicate that Leish-Tec(®) is immunogenic for dogs of different genetic backgrounds and that humoral responses induced by vaccination can be detected by A2-ELISA, but do not interfere with the LPA-ELISA and DPP diagnostic tests for CVL. PMID:24863572

Testasicca, Miriam C de Souza; dos Santos, Mariana Silva; Machado, Leopoldo Marques; Serufo, Angela Vieira; Doro, Daniel; Avelar, Daniel; Tibúrcio, Ana Maria Leonardi; Abrantes, Christiane de Freitas; Machado-Coelho, George Luiz Lins; Grimaldi, Gabriel; Gazzinelli, Ricardo Tostes; Fernandes, Ana Paula

2014-08-29

195

Dental students' attitudes toward underserved populations across four years of dental school.  

PubMed

The objective of this study was to assess dental students' attitudes toward underserved populations across their four years of dental school. Students at the Herman Ostrow School of Dentistry of the University of Southern California were invited to take part in the study. Participating students completed a questionnaire on their attitudes toward the underserved at three time points: 1) during orientation week; 2) at the end of their second year after taking part in some community dental programs; and 3) at the end of their fourth year after they had completed all their mandatory and volunteer rotations in community dental programs. Students' attitudes were measured in four categories: societal expectations, dentist/student responsibility, personal efficacy, and access to care. First-year students scored 85 out of a maximum of 115 on the questionnaire. Female students scored higher than male students (P=0.006). Age, debt, and past history of volunteer work were not related to first-year students' total attitude scores; however, students with a history of volunteer experience scored higher on the dentist/student responsibility category (P=0.04). Students' attitude scores declined across the four years of dental school (P=0.001). The same patterns were evident for all categories except societal expectations. The decline was not related to age, gender, debt, or volunteer work experience. Follow-up studies are needed to help explain the factors that may be related to this decline. PMID:21828295

Habibian, Mina; Seirawan, Hazem; Mulligan, Roseann

2011-08-01

196

The Effects of an Inquiry-Internet Research Project on Motivation, Self-Efficacy, and Academic Autonomy in Heterogenously Grouped High School Latin I Students  

ERIC Educational Resources Information Center

The purpose of this study was to analyze and induce change to lessen the achievement gap in heterogeneously grouped high school Latin classes where some students may be at academic risk, due to insufficient knowledge, inability to connect with the subject, and poor performances. The researcher engaged in action research, a branch of qualitative…

Wagman, Janet Campbell

2005-01-01

197

Circular Labor Migration and HIV in India: Exploring Heterogeneity in Bridge Populations Connecting Areas of High and Low HIV Infection Prevalence  

PubMed Central

Background.?The emerging human immunodeficiency virus (HIV) epidemics in rural areas of India are hypothesized to be linked to circular migrants who are introducing HIV from destination areas were the prevalence of HIV infection is higher. We explore the heterogeneity in potential roles of circular migrants in driving an HIV epidemic in a rural area in north India and examine the characteristics of the “sustaining bridge population”, which comprises individuals at risk of HIV acquisition at destination and of HIV transmission into networks at origin capable of sustaining an epidemic. Methods.?Results of a behavioral survey of 639 male migrants from Azamgarh district, India, were analyzed using ?2 tests and logistic regression. Results.?We estimated the size of various subgroups defined by specific sexual behaviors across different locations and over time. Only 20% fit our definition of a sustaining bridge population, with the majority making no apparent contribution to geographical connectedness between high- and low-prevalence areas. However, we found evidence of sexual contacts at origin that could potentially sustain an epidemic once HIV is introduced. Variables associated with sustaining bridge population membership were self-perceived HIV risk, current migrant status, and age. Conclusions.?Circular migrants represent a heterogeneous population in terms of their role as a bridge group. Self-perception of heightened risk could be exploited in designing prevention programs. PMID:25381375

Rai, Tanvi; Lambert, Helen S.; Borquez, Annick B.; Saggurti, Niranjan; Mahapatra, Bidhubhushan; Ward, Helen

2014-01-01

198

Who Are Our Students? Cluster Analysis as a Tool for Understanding Community College Student Populations  

ERIC Educational Resources Information Center

This study showcases cluster analysis as a useful tool for those who seek to understand the types of students their community colleges serve. Although educational goal, academic program, and demographics are often used as descriptive variables, it is unclear which, if any, of these are the best way to classify community college students. Cluster…

Ammon, Bridget V.; Bowman, Jamillah; Mourad, Roger

2008-01-01

199

Diverse levels of an inwardly rectifying potassium conductance generate heterogeneous neuronal behavior in a population of dorsal cochlear nucleus pyramidal neurons  

PubMed Central

Homeostatic mechanisms maintain homogeneous neuronal behavior among neurons that exhibit substantial variability in the expression levels of their ionic conductances. In contrast, the mechanisms, which generate heterogeneous neuronal behavior across a neuronal population, remain poorly understood. We addressed this problem in the dorsal cochlear nucleus, where principal neurons exist in two qualitatively distinct states: spontaneously active or not spontaneously active. Our studies reveal that distinct activity states are generated by the differential levels of a Ba2+-sensitive, inwardly rectifying potassium conductance (Kir). Variability in Kir maximal conductance causes variations in the resting membrane potential (RMP). Low Kir conductance depolarizes RMP to voltages above the threshold for activating subthreshold-persistent sodium channels (Nap). Once Nap channels are activated, the RMP becomes unstable, and spontaneous firing is triggered. Our results provide a biophysical mechanism for generating neural heterogeneity, which may play a role in the encoding of sensory information. PMID:22378165

Leao, Ricardo M.; Li, Shuang; Doiron, Brent

2012-01-01

200

Experiences of the Student Population at an Urban University: How Do They Use a Joint Library?  

ERIC Educational Resources Information Center

The King Library in San José, California, is a unique combination of academic and public library. It serves the diverse populations of the City of San José and San José State University (SJSU). This article provides analysis of data collected in a study on the concept of "library as place" and SJSU students' sense of belonging…

Molteni, Valeria E.; Goldman, Crystal; Oulc'hen, Enora

2014-01-01

201

Assessing Undergraduate Learning Outcomes between Accelerated Degree and Traditional Student Populations  

ERIC Educational Resources Information Center

This study investigated learning outcomes in both traditional and accelerated degree populations. Using the National Survey of Student Engagement, outcomes were examined relating to critical thinking, oral and written communication, and cultural and global understanding. Literature from life stage development and degree delivery mode areas were…

Rawls, Janita; Hammons, Stacy

2012-01-01

202

Body Dysmorphic Disorder: Gender differences and prevalence in a Pakistani medical student population  

Microsoft Academic Search

BACKGROUND: Body dysmorphic disorder (BDD) is a psychiatric disorder characterized by a preoccupation with an imagined or slight defect which causes significant distress or impairment in functioning. Few studies have assessed gender differences in BDD in a non clinical population. Also no study assessed BDD in medical students. This study was designed to determine the point prevalence of BDD in

Ather M Taqui; Mehrine Shaikh; Saqib A Gowani; Fatima Shahid; Asmatullah Khan; Syed M Tayyeb; Minahil Satti; Talha Vaqar; Saman Shahid; Afreen Shamsi; Hammad A Ganatra; Haider A Naqvi

2008-01-01

203

The Distribution of and Relationship between Autistic Traits and Social Anxiety in a UK Student Population  

ERIC Educational Resources Information Center

Traits associated with autism and social anxiety were assessed in a UK student population (n = 1325) using the Autism-spectrum Quotient and the Liebowitz Social Anxiety Scale. Clinically relevant levels of autistic traits were observed in 3.3% of the cohort; 10.1% of the cohort reported clinically relevant levels of social anxiety; 1.8% of the…

Freeth, Megan; Bullock, Tom; Milne, Elizabeth

2013-01-01

204

Integrating Vocational & Academic Education. A Handbook Featuring Four Demonstration Sites Including Students from Special Populations.  

ERIC Educational Resources Information Center

This handbook describes the processes and techniques used to develop, implement, and evaluate four integrated vocational and academic learning programs in Wisconsin that included students from special populations. The handbook contains seven chapters. Chapter 1 presents an overview of the project, including the request for proposal process and…

Tindall, Lloyd W.; And Others

205

Validity of Personal Growth Initiative Scale Scores With a Mexican American College Student Population  

Microsoft Academic Search

This study tested the validity of scores on the Personal Growth Initiative Scale (PGIS; C. Robitschek, 1998, 1999) with a Mexican American college student sample. Results indicated that the PGIS scores appear to be culturally relevant for this population, with scores on the PGIS having many similar relations with other variables that have been found in prior research with mostly

Christine Robitschek

2003-01-01

206

An Assessment of Barriers and Strategies for Recruitment and Retention of a Diverse Graduate Student Population  

ERIC Educational Resources Information Center

The purpose of this exploratory qualitative investigation was to: a) describe the barriers of recruitment and retention of diverse graduate student population at one of the predominantly white universities (PWUs) in the Midwestern US as perceived by the program coordinators and directors and b) identify successful strategies for improving the…

Quarterman, Jerome

2008-01-01

207

Teaching Population Balances for Chemical Engineering Students: Application to Granulation Processes  

ERIC Educational Resources Information Center

The population balance equation (PBE) is a useful tool to predict particle size distributions in granulation processes. When PBE is taught to advanced chemical engineering students, the internal coordinates (particle properties) are particularly hard to understand. In this paper, the flow of particles along different coordinates is carefully…

Bucala, Veronica; Pina, Juliana

2007-01-01

208

A Survey to Identify University Student Attitudes toward the Role of Government in Controlling Human Population Growth.  

ERIC Educational Resources Information Center

The purpose of this study was to obtain, measure, and evaluate the attitudes of postsecondary students on domestic population issues in order to determine the extent of support for a national government-controlled population stabilization program. A total of 125 students enrolled in either the American government or general sociology course at the…

Yost, Thomas E.

209

Determining the Effects of a Spatially Heterogeneous Selection Pressure on Bacterial Population Structure at the Submillimetre Scale  

Microsoft Academic Search

A key interest of microbial ecology is to understand the role of environmental heterogeneity in shaping bacterial diversity\\u000a and fitness. However, quantifying relevant selection pressures and their effects is challenging due to the number of parameters\\u000a that must be considered and the multiple scales over which they act. In the current study, a model system was employed to\\u000a investigate the

Frances R. Slater; Kenneth D. Bruce; Richard J. Ellis; Andrew K. Lilley; Sarah L. Turner

2010-01-01

210

[Biostatistical support for decision making in drug licensing and reimbursement exemplified by implications of heterogeneous findings in subgroups of the study population].  

PubMed

In the context of both drug licensing and reimbursement, the target population is sometimes restricted to a specific subgroup. In the setting of drug licensing the discussion concerns a negative benefit/risk assessment in a relevant subgroup. For reimbursement the debate involves the detection of an additional benefit compared with standard treatment, which can in some situations not be accepted for the overall study population. In their Methods Paper, the Institute for Quality and Efficiency in Health Care (IQWiG) refers to published articles that name criteria for the evaluation of credibility to claim a therapeutic effect on the basis of results in the subgroups of a study population (BMJ 340:850-854, 2010). A number of these criteria have found their way into the regulatory debate, which was recently published in a draft guideline of the European Medicines Agency (EMA). However, the significance of the interaction/heterogeneity test has been mentioned as one criterion for the credibility of a finding in a subgroup of the study population. This aspect is critically challenged in our paper. In our estimation, the application of this criterion hinders the critical discussion of whether a global treatment effect is applicable to relevant subgroups of a study population and the potential implications of this. We feel that biostatistical support for decision-making strategies should be the same in both worlds, even though in some instances the outcomes in a specific situation may be different, depending on the objective to be demonstrated. PMID:25566838

Gonnermann, A; Kottas, M; Koch, Armin

2015-03-01

211

Variation in DNA methylation transmissibility, genetic heterogeneity and fecundity-related traits in natural populations of the perennial herb Helleborus foetidus.  

PubMed

Inferences about the role of epigenetics in plant ecology and evolution are mostly based on studies of cultivated or model plants conducted in artificial environments. Insights from natural populations, however, are essential to evaluate the possible consequences of epigenetic processes in biologically realistic scenarios with genetically and phenotypically heterogeneous populations. Here, we explore associations across individuals between DNA methylation transmissibility (proportion of methylation-sensitive loci whose methylation status persists unchanged after male gametogenesis), genetic characteristics (assessed with AFLP markers), seed size variability (within-plant seed mass variance), and realized maternal fecundity (number of recently recruited seedlings), in three populations of the perennial herb Helleborus foetidus along a natural ecological gradient in southeastern Spain. Plants (sporophytes) differed in the fidelity with which DNA methylation was transmitted to descendant pollen (gametophytes). This variation in methylation transmissibility was associated with genetic differences. Four AFLP loci were significantly associated with transmissibility and accounted collectively for ~40% of its sample-wide variance. Within-plant variance in seed mass was inversely related to individual transmissibility. The number of seedlings recruited by individual plants was significantly associated with transmissibility. The sign of the relationship varied between populations, which points to environment-specific, divergent phenotypic selection on epigenetic transmissibility. Results support the view that epigenetic transmissibility is itself a phenotypic trait whose evolution may be driven by natural selection, and suggest that in natural populations epigenetic and genetic variation are two intertwined, rather than independent, evolutionary factors. PMID:24471446

Herrera, Carlos M; Medrano, Mónica; Bazaga, Pilar

2014-03-01

212

Analysis of survival, gene expression and behavior following chill-coma in the medfly Ceratitis capitata: effects of population heterogeneity and age.  

PubMed

The medfly Ceratitis capitata is an agricultural pest distributed worldwide thanks, in part, to its phenotypic plasticity of thermal tolerance. Cold exposure has been shown to reduce C. capitata survival, which may affect its distribution in areas with subfreezing temperatures. When insects are increasingly cooled, they attain a critical thermal threshold and enter a chill-coma state characterized by cessation of movement. It is not clear how a rapid cold exposure affects the physiological state of medflies, and how this is influenced by age and population heterogeneity. In order to approach these questions, C. capitata single-sex laboratory populations of 15 and 30 days old were subjected to a chill-coma recovery assay, and separated according to their recovery time in three subgroups: Fast-Subgroups, Intermediate-Subgroups, and Slow-Subgroups. Thereafter, we analyzed their survival, behavioral, and gene expression outputs. In female and old male populations, we found that flies with the slowest recovery time had a reduced life expectancy, a higher initial mortality rate, and a worse climbing performance compared with flies that recovered faster. Therefore, we were able to separate subgroups that developed chilling-injury from subgroups that had a reversible full recovery after cold exposure. The gene expression analysis of the heat shock protein genes hsp70 and hsp83 showed no clear association with the parameters studied. Interestingly, thorax expression levels of the Cu/Zn superoxide dismutase gene were elevated during the recovery phase in the Fast-Subgroups, but remained constant in the Slow-Subgroups that developed chilling-injury. On the other hand, none of the young male subgroups seemed to have suffered irreversible damage. Thus, we concluded that depending on age and population heterogeneity, chill-coma recovery time points out significant differences on individual cold tolerance. Moreover, the inability to properly induce the antioxidant defense system to counteract the oxidative damage caused by cold seems to contribute to the development of chilling-injury. PMID:25449902

Pujol-Lereis, Luciana Mercedes; Rabossi, Alejandro; Quesada-Allué, Luis Alberto

2014-12-01

213

Embedding Evolution: Exploring Changes in Students' Conceptual Development, Beliefs, and Motivations in a Population Ecology Unit  

NASA Astrophysics Data System (ADS)

The purpose of this study was to explore student changes in conceptual development, epistemology, and motivations when evolution concepts are embedded and explicit reflective discourse is used in a unit for population ecology. The two research problems were: (1) What changes are observed in student's conceptual development, epistemology, and motivations when there is explicit reflective discourse within a population ecology unit with embedded evolution?, and (2) In what ways does explicit reflection influence students' mental models within a population ecology unit with embedded evolution? This mixed-method, quasi-experimental study assessed two regular high school biology classes in a small, urban, Midwestern high school. Students in this study had not studied evolution within any formal chapters, but had been immersed in a curriculum with embedded evolution. The study was conducted over a four-week period in a population ecology unit near the beginning of second semester. Instruction emphasized basic conceptions in population ecology. Five key intervention activities included evolutionary concepts as part of an embedded curriculum. The independent variable was explicit reflective discourse with one or two intervention questions after completion of these activities. Data included pre- and posttest surveys measuring (a) evolutionary understanding of natural selection, (b) science beliefs, and (c) science motivations. Written artifacts included (a) explanations to scenarios, (b) pre- and post-argument reflections revealing student's science beliefs and science motivations resultant from two argumentations, and (c) three, pre-, post-, and 6-week final concept maps constructed from 12 concepts. All data sources provided descriptive data. Conceptual change was interpreted from an ontological, epistemological, and motivational perspective. The experimental class receiving explicit reflective discourse showed greater overall increases in conceptual development. Students in both classes constructed teleological and proximate explanations. Overall, the experimental class gave greater numbers of evolutionary explanations. Scored propositions from concept maps showed a mixture of synthetic and scientific conceptions in both classes, however the experimental group showed greater scientific quality. Students in both classes exhibited direct-process ontology. Both classes had high degrees of epistemological and motivational commitments demonstrated by their engagement and subsequent improvements in conceptual development in both evolutionary and ecological conceptions.

Rose, Nancy L.

214

Murine Bone Marrow Lin?Sca-1+CD45? Very Small Embryonic-Like (VSEL) Cells Are Heterogeneous Population Lacking Oct-4A Expression  

PubMed Central

Murine very small embryonic-like (VSEL) cells, defined by the Lin?Sca-1+CD45? phenotype and small size, were described as pluripotent cells and proposed to be the most primitive hematopoietic precursors in adult bone marrow. Although their isolation and potential application rely entirely on flow cytometry, the immunophenotype of VSELs has not been extensively characterized. Our aim was to analyze the possible heterogeneity of Lin?Sca+CD45? population and investigate the extent to which VSELs characteristics may overlap with that of hematopoietic stem cells (HSCs) or endothelial progenitor cells (EPCs). The study evidenced that murine Lin?Sca-1+CD45? population was heterogeneous in terms of c-Kit and KDR expression. Accordingly, the c-Kit+KDR?, c-Kit?KDR+, and c-Kit?KDR? subpopulations could be distinguished, while c-Kit+KDR+ events were very rare. The c-Kit+KDR? subset contained almost solely small cells, meeting the size criterion of VSELs, in contrast to relatively bigger c-Kit?KDR+ cells. The c-Kit?KDR?FSClow subset was highly enriched in Annexin V-positive, apoptotic cells, hence omitted from further analysis. Importantly, using qRT-PCR, we evidenced lack of Oct-4A and Oct-4B mRNA expression either in whole adult murine bone marrow or in the sorted of Lin?Sca-1+CD45?FSClow population, even by single-cell qRT-PCR. We also found that the Lin?Sca-1+CD45?c-Kit+ subset did not exhibit hematopoietic potential in a single cell-derived colony in vitro assay, although it comprised the Sca-1+c-Kit+Lin? (SKL) CD34?CD45?CD105+ cells, expressing particular HSC markers. Co-culture of Lin?Sca-1+CD45?FSClow with OP9 cells did not induce hematopoietic potential. Further investigation revealed that SKL CD45?CD105+ subset consisted of early apoptotic cells with fragmented chromatin, and could be contaminated with nuclei expelled from erythroblasts. Concluding, murine bone marrow Lin?Sca-1+CD45?FSClow cells are heterogeneous population, which do not express the pluripotency marker Oct-4A. Despite expression of some hematopoietic markers by a Lin?Sca-1+CD45?c-Kit+KDR? subset of VSELs, they do not display hematopoietic potential in a clonogenic assay and are enriched in early apoptotic cells. PMID:23696815

Nowak, Witold Norbert; Szade, Agata; Kachamakova-Trojanowska, Neli; Zukowska, Monika; Jozkowicz, Alicja; Dulak, Jozef

2013-01-01

215

Evolutionary conservation advice for despotic populations: habitat heterogeneity favours conflict and reduces productivity in Seychelles magpie robins.  

PubMed

Individual preferences for good habitat are often thought to have a beneficial stabilizing effect for populations. However, if individuals preferentially compete for better-quality territories, these may become hotspots of conflict. We show that, in an endangered species, this process decreases the productivity of favoured territories to the extent that differences in productivity between territories disappear. Unlike predictions from current demographic theory on site-dependent population regulation (ideal despotic distribution), we show that population productivity is reduced if resources are distributed unevenly in space. Competition for high-quality habitat can thus have detrimental consequences for populations even though it benefits individuals. Manipulating conflict (e.g. by reducing variation in habitat quality) can therefore prove an effective conservation measure in species with strong social or territorial conflict. PMID:20534612

López-Sepulcre, Andrés; Kokko, Hanna; Norris, Ken

2010-11-22

216

Evolutionary conservation advice for despotic populations: habitat heterogeneity favours conflict and reduces productivity in Seychelles magpie robins  

PubMed Central

Individual preferences for good habitat are often thought to have a beneficial stabilizing effect for populations. However, if individuals preferentially compete for better-quality territories, these may become hotspots of conflict. We show that, in an endangered species, this process decreases the productivity of favoured territories to the extent that differences in productivity between territories disappear. Unlike predictions from current demographic theory on site-dependent population regulation (ideal despotic distribution), we show that population productivity is reduced if resources are distributed unevenly in space. Competition for high-quality habitat can thus have detrimental consequences for populations even though it benefits individuals. Manipulating conflict (e.g. by reducing variation in habitat quality) can therefore prove an effective conservation measure in species with strong social or territorial conflict. PMID:20534612

López-Sepulcre, Andrés; Kokko, Hanna; Norris, Ken

2010-01-01

217

Modelling heterogeneity in the recoveries of marked animal populations with covariates of individual animals, groups of animals or recovery time  

USGS Publications Warehouse

A general framework is developed for modelling rates of survival and recovery of marked animal populations in terms of auxiliary information collected at the time of marking. The framework may be used to estimate differences in survival or recovery among individual animals, groups of animals, and recovery times. Analyses of the recoveries of tagged fish and banded bird populations are used to illustrate the specification and selection of various models.

Dorazio, R.M.

1997-01-01

218

"That's so gay!" Exploring college students' attitudes toward the LGBT population.  

PubMed

Traditional students are often introduced to unfamiliar subcultures for the first time on the college campus. Recent high school graduates find themselves transitioning from an atmosphere in which homophobia is likely to be tolerated and possibly even expected to an educational setting in which diversity is promoted. Research shows that the college years are influential in the re-socialization of core values, yet very little work focuses on the ideological shifts that may take place in attitudes toward the lesbian, gay, bisexual, and transgendered (LGBT) population. The research presented in this study includes a modified version of LaMar and Kite's Component Measure, which has been broken down into 6 distinctive components of tolerance. In addition to examining religion, gender, and race--factors that have been correlated in past research with differing levels of tolerance toward the LGBT community--this study adds politics, sexual orientation, academic class standing, and college of major--variables that have received little or no attention in this literature. Higher levels of LGBT tolerance are consistently observed across the indexes among women, more liberal Christian traditions, non-Christian faiths, the non-religious, and those who self-identify as LGBT. The distinctive contribution of this study is that students in the College of Arts and Sciences and students further along in their college careers are also more tolerant. Based on these findings, recommendations are made for inter-college curriculum changes that integrate students in all disciplines and students of all classifications. PMID:23469818

Holland, Laurel; Matthews, Todd L; Schott, Melinda R

2013-01-01

219

Predictors of Sexual Bother in a Population of Male North American Medical Students  

PubMed Central

Introduction The prevalence and associations of sexual bother in male medical students has not been extensively studied. Aims The aim of this study is to analyze predictors of sexual bother in a survey of male North American medical students. Methods Students enrolled in allopathic and osteopathic medical schools in North America between February 2008 and July 2008 were invited to participate in an internet-based survey of sexuality and sexual function. Main Outcome Measures The principle outcome measure was a single-item question inquiring about global satisfaction with sexual function. The survey also consisted of a questionnaire that included ethnodemographic factors, student status, sexual history, and a validated scale for the assessment of depression. Respondents completed the International Index of Erectile Function, the premature ejaculation diagnostic tool, and the Self-Esteem and Relationship Quality survey (SEAR). Descriptive statistics, analysis of variance, and multivariable logistic regression were utilized to analyze responses. Results There were 480 male subjects (mean age 26.3 years) with data sufficient for analysis. Forty-three (9%) reported sexual bother. Sexual bother was significantly more common in men with erectile dysfunction (ED), high risk of premature ejaculation (HRPE), depressive symptoms, and lower sexual frequency. However, after multivariate analysis including SEAR scores, ED, and HRPE were no longer independently predictive of sexual bother. Higher scores for all domains of the SEAR were associated with lower odds of sexual bother. Conclusions ED and HRPE are associated with sexual bother in this young and presumably healthy population. However, after controlling for relationship factors neither ED nor HRPE independently predicted sexual bother. It is plausible to hypothesize that sexual dysfunction from organic causes is rare in this population and is seldom encountered outside of relationship perturbations. Attention to relationship and psychological factors is likely of key importance in addressing sexual concerns in this population. PMID:21951580

Smith, James F.; Breyer, Benjamin N.; Shindel, Alan W.

2013-01-01

220

Selection using the alpha-1 integrin (CD49a) enhances the multipotentiality of the mesenchymal stem cell population from heterogeneous bone marrow stromal cells.  

PubMed

Bone marrow-derived mesenchymal stem cells consist of a developmentally heterogeneous population of cells obtained from colony forming progenitors. As these colonies express the alpha-1 integrin (CD49a), here we single-cell FACS sorted CD49a+ cells from bone marrow in order to create clones and then compared their colony forming efficiency and multilineage differentiation capacity to the unsorted cells. Following selection, 40% of the sorted CD49a+ cells formed colonies, whereas parental cells failed to form colonies following limited dilution plating at 1 cell/well. Following ex vivo expansion, clones shared a similar morphology to the parental cell line, and also demonstrated enhanced proliferation. Further analysis by flow cytometry using a panel of multilineage markers demonstrated that the CD49a+ clones had enhanced expression of CD90 and CD105 compared to unsorted cells. Culturing cells in adipogenic, osteogenic or chondrogenic medium for 7, 10 and 15 days respectively and then analysing them by quantitative PCR demonstrated that CD49a+ clones readily underwent multlineage differentiation into fat, bone and cartilage compared to unsorted cells. These results thus support the use of CD49a selection for the enrichment of mesenchymal stem cells, and describes a strategy for selecting the most multipotential cells from a heterogeneous pool of bone marrow mononuclear stem cells. PMID:17694277

Rider, David A; Nalathamby, Thenmozhi; Nurcombe, Victor; Cool, Simon M

2007-10-01

221

Mutational heterogeneity: a key ingredient of bet-hedging and evolutionary divergence?: The broad spectrum of mutations and their flexible frequency in populations provides a source of risk avoidance and alternative evolutionary strategies.  

PubMed

Here, we propose that the heterogeneity of mutational types in populations underpins alternative pathways of evolutionary adaptation. Point mutations, deletions, insertions, transpositions and duplications cause different biological effects and provide distinct adaptive possibilities. Experimental evidence for this notion comes from the mutational origins of adaptive radiations in large, clonal bacterial populations. Independent sympatric lineages with different phenotypes arise from distinct genetic events including gene duplication, different insertion sequence movements and several independent point mutations. The breadth of the mutational spectrum in the ancestral population should be viewed as a form of bet-hedging, reducing the risk of evolutionary dead ends and complementing the phenotypic and epigenetic heterogeneities that improve the survival capabilities of a population. Different mutational events arise from distinct cellular processes and are subject to separate environmental impacts, so the availability of any particular type of mutation may constrain or promote adaptive pathways in populations. PMID:25370372

Ferenci, Thomas; Maharjan, Ram

2015-02-01

222

Genetic Heterogeneity of Susceptibility Gene in Different Ethnic Populations: Refining Association Study of PTPN22 for Graves’ Disease in a Chinese Han Population  

PubMed Central

In our previous studies, we presumed subtypes of Graves’ disease (GD) may be caused by different major susceptibility genes or different variants of a single susceptibility gene. However, more evidence is needed to support this hypothesis. Single-nucleotide polymorphism (SNP) rs2476601 in PTPN22 is the susceptibility loci of GD in the European population. However, this polymorphism has not been found in Asian populations. Here, we investigate whether PTPN22 is the susceptibility gene for GD in Chinese population and further determine the susceptibility variant of PTPN22 in GD. We conducted an imputation analysis based on the results of our genome-wide association study (GWAS) in 1,536 GD patients and 1,516 control subjects. Imputation revealed that 255 common SNPs on a linkage disequilibrium (LD) block containing PTPN22 were associated with GD (P<0.05). Nine tagSNPs that captured the 255 common variants were selected to be further genotyped in a large cohort including 4,368 GD patients and 4,350 matched controls. There was no significant difference between the nine tagSNPs (P>0.05) in either the genotype distribution or allelic frequencies between patients and controls in the replication study. Although the combined analysis exhibited a weak association signal (Pcombined = 0.003263 for rs3811021), the false positive report probability (FPRP) analysis indicated it was most likely a false positive finding. Our study did not support an association of common SNPs in PTPN22 LD block with GD in Chinese Han population. This suggests that GD in different ethnic population is probably caused by distinct susceptibility genes. PMID:24386393

Zhao, Shuangxia; Han, Bing; Liu, Wei; Yang, Shaoying; Yu, Shasha; Sun, Yixuan; Liang, Jun; Gao, Guanqi; Zhang, Xiaomei; Yuan, Guoyue; Li, Changgui; Du, Wenhua; Chen, Gang; Chen, Jialun; Song, Huaidong

2013-01-01

223

Quantifying how fine-grained environmental heterogeneity and genetic variation affect demography in an annual plant population.  

PubMed

The ability of plant species to colonize new habitats and persist in changing environments depends on their ability to respond plastically to environmental variation and on the presence of genetic variation, thus allowing adaptation to new conditions. For invasive species in particular, the relationship between phenotypic trait expression, demography, and the quantitative genetic variation that is available to respond to selection are likely to be important determinants of the successful establishment and persistence of populations. However, the magnitude and sources of individual demographic variation in exotic plant populations remain poorly understood. How important is plasticity versus adaptability in populations of invasive species? Among environmental factors, is temperature, soil nutrients, or competition most influential, and at what scales and life stages do they affect the plants? To investigate these questions we planted seeds of the exotic annual plant Erodium brachycarpum into typical pasture habitat in a spatially nested design. Seeds were drawn from 30 inbred lines to enable quantification of genetic effects. Despite a positive population growth rate, a few plants (0.1 %) produced >50 % of the seeds, suggesting a low effective population size. Emergence and early growth varied by genotype, but as in previous studies on native plants, environmental effects greatly exceeded genetic effects, and survival was unrelated to genotype. Environmental influences shifted from microscale soil compaction and litter depth at emergence through to larger-scale soil nutrient gradients during growth and to competition during later survival and seed production. Temperature had no effect. Most demographic rates were positively correlated, but emergence was negatively correlated with other rates. PMID:22707035

Latimer, Andrew M; Jacobs, Brooke S

2012-11-01

224

Single-molecule resolution of protein dynamics on polymeric membrane surfaces: the roles of spatial and population heterogeneity.  

PubMed

Although polymeric membranes are widely used in the purification of protein pharmaceuticals, interactions between biomolecules and membrane surfaces can lead to reduced membrane performance and damage to the product. In this study, single-molecule fluorescence microscopy provided direct observation of bovine serum albumin (BSA) and human monoclonal antibody (IgG) dynamics at the interface between aqueous buffer and polymeric membrane materials including regenerated cellulose and unmodified poly(ether sulfone) (PES) blended with either polyvinylpyrrolidone (PVP), polyvinyl acetate-co-polyvinylpyrrolidone (PVAc-PVP), or polyethylene glycol methacrylate (PEGM) before casting. These polymer surfaces were compared with model surfaces composed of hydrophilic bare fused silica and hydrophobic trimethylsilane-coated fused silica. At extremely dilute protein concentrations (10(-3)-10(-7) mg/mL), protein surface exchange was highly dynamic with protein monomers desorbing from the surface within ?1 s after adsorption. Protein oligomers (e.g., nonspecific dimers, trimers, or larger aggregates), although less common, remained on the surface for 5 times longer than monomers. Using newly developed super-resolution methods, we could localize adsorption sites with ?50 nm resolution and quantify the spatial heterogeneity of the various surfaces. On a small anomalous subset of the adsorption sites, proteins adsorbed preferentially and tended to reside for significantly longer times (i.e., on "strong" sites). Proteins resided for shorter times overall on surfaces that were more homogeneous and exhibited fewer strong sites (e.g., PVAc-PVP/PES). We propose that strong surface sites may nucleate protein aggregation, initiated preferentially by protein oligomers, and accelerate ultrafiltration membrane fouling. At high protein concentrations (0.3-1.0 mg/mL), fewer strong adsorption sites were observed, and surface residence times were reduced. This suggests that at high concentrations, adsorbed proteins block strong sites from further protein adsorption. Importantly, this demonstrates that strong binding sites can be modified by changing solution conditions. Membrane surfaces are intrinsically heterogeneous; by employing single-molecule techniques, we have provided a new framework for understanding protein interactions with such surfaces. PMID:25611782

Langdon, Blake B; Mirhossaini, Roya B; Mabry, Joshua N; Sriram, Indira; Lajmi, Ajay; Zhang, Yanxia; Rojas, Orlando J; Schwartz, Daniel K

2015-02-18

225

Junior College Students on Academic Probation.  

ERIC Educational Resources Information Center

Junior college students on academic probation are as heterogeneous as the college population itself. They range from high-ability students dismissed from 4-year institutions to those with severe visual-motor handicaps. The differences should be more carefully identified so that appropriate help can be made available. Special counseling (required…

Capper, Michael R.

1969-01-01

226

Heterogeneity of breast cancer risk within the South Asian female population in England: a population-based case–control study of first-generation migrants  

Microsoft Academic Search

South Asian women in England have a lower breast cancer risk than their English-native counterparts, but less is known about variations in risk between distinct South Asian ethnic subgroups. We used the data from a population-based case–control study of first-generation South Asian migrants to assess risks by ethnic subgroup. In all, 240 breast cancer cases, identified through cancer registries, were

V A McCormack; P Mangtani; D Bhakta; A J McMichael; I dos Santos Silva

2004-01-01

227

Evaluating the Phobias, Attitudes, and Cultural Competence of Master of Social Work Students Toward the LGBT Populations  

Microsoft Academic Search

Background. Evidence suggests there is bias toward lesbian, gay, bisexual, and transgender (LGBT) persons by social workers; unfortunately, little research has been conducted to examine Master of Social Work (MSW) students' views toward these populations. The purpose of this study was to develop an assessment scale to evaluate the attitudes, phobias, and cultural competence of MSW students toward the LGBT

Carmen Logie; Tana J. Bridge; Patrick D. Bridge

2007-01-01

228

Can Welfare Mothers Hack It in College? A Comparison of Achievement between TANF Recipients and General Population Community College Students  

ERIC Educational Resources Information Center

The achievement of a group of undergraduate students enrolled in a pilot program for welfare recipients in the form of TANF (Temporary Aid to Needy Families) was compared with the achievement of general population students at an urban community college. Grades attained in a basic level, introductory Psychology course were used to measure academic…

Fenster, Judy

2004-01-01

229

The prevalence of eating disorder pathology in a cross-ethnic population of female students in South Africa  

Microsoft Academic Search

Objective: The purpose of this study was to determine the prevalence of eating disorder pathology in female students representing South Africa's ethnically diverse population. A secondary aim was to explore relationships between eating disorder pathology, Body Mass Index (BMI), and socioeconomic status (SES). Method: In a questionnaire survey of a cross-section of South African college students, the Eating Disorder Inventory

Douglas Wassenaar; Daniel le Grange; Jacquie Winship; Lance Lachenicht

2000-01-01

230

Bifurcated Commitment, Priorities, and Social Contagion: The Dynamics and Correlates of Volunteering within a University Student Population  

ERIC Educational Resources Information Center

In spite of a progressive institutionalisation of community-based learning into higher education, relatively little is known about the actual dynamics and correlates of volunteering by students. The study presented seeks a more in-depth understanding of the spontaneous, extracurricular involvement within a university student population. Data are…

Hustinx, Lesley; Vanhove, Tim; Declercq, Anja; Hermans, Koen; Lammertyn, Frans

2005-01-01

231

The Values and Attitudes of Selected College Students on Some Topics Relevant to Human Population. Monograph No. 31.  

ERIC Educational Resources Information Center

Results of a study on attitudes of Filipino college students concerning human population issues are reported. A total of 74 University of the Philippines students, half of whom were enrolled in a natural science course, answered a 15-part questionnaire on dating, friendship, premarital sex, marital expectations, and birth control. Several…

Carballo, Jose Luis O.; And Others

232

Balancing selection and heterogeneity across the classical human leukocyte antigen loci: a meta-analytic review of 497 population studies.  

PubMed

This paper presents a meta-analysis of high-resolution human leukocyte antigen (HLA) allele frequency data describing 497 population samples. Most of the datasets were compiled from studies published in eight journals from 1990 to 2007; additional datasets came from the International Histocompatibility Workshops and from the AlleleFrequencies.net database. In all, these data represent approximately 66,800 individuals from throughout the world, providing an opportunity to observe trends that may not have been evident at the time the data were originally analyzed, especially with regard to the relative importance of balancing selection among the HLA loci. Population genetic measures of allele frequency distributions were summarized across populations by locus and geographic region. A role for balancing selection maintaining much of HLA variation was confirmed. Further, the breadth of this meta-analysis allowed the ranking of the HLA loci, with DQA1 and HLA-C showing the strongest balancing selection and DPB1 being compatible with neutrality. Comparisons of the allelic spectra reported by studies since 1990 indicate that most of the HLA alleles identified since 2000 are very-low-frequency alleles. The literature-based allele-count data, as well as maps summarizing the geographic distributions for each allele, are available online. PMID:18638659

Solberg, Owen D; Mack, Steven J; Lancaster, Alex K; Single, Richard M; Tsai, Yingssu; Sanchez-Mazas, Alicia; Thomson, Glenys

2008-07-01

233

An individual-based model of the evolution of pesticide resistance in heterogeneous environments: control of Meligethes aeneus population in oilseed rape crops.  

PubMed

Preventing a pest population from damaging an agricultural crop and, at the same time, preventing the development of pesticide resistance is a major challenge in crop protection. Understanding how farming practices and environmental factors interact with pest characteristics to influence the spread of resistance is a difficult and complex task. It is extremely challenging to investigate such interactions experimentally at realistic spatial and temporal scales. Mathematical modelling and computer simulation have, therefore, been used to analyse resistance evolution and to evaluate potential resistance management tactics. Of the many modelling approaches available, individual-based modelling of a pest population offers most flexibility to include and analyse numerous factors and their interactions. Here, a pollen beetle (Meligethes aeneus) population was modelled as an aggregate of individual insects inhabiting a spatially heterogeneous landscape. The development of the pest and host crop (oilseed rape) was driven by climatic variables. The agricultural land of the landscape was managed by farmers applying a specific rotation and crop protection strategy. The evolution of a single resistance allele to the pyrethroid lambda cyhalothrin was analysed for different combinations of crop management practices and for a recessive, intermediate and dominant resistance allele. While the spread of a recessive resistance allele was severely constrained, intermediate or dominant resistance alleles showed a similar response to the management regime imposed. Calendar treatments applied irrespective of pest density accelerated the development of resistance compared to ones applied in response to prescribed pest density thresholds. A greater proportion of spring-sown oilseed rape was also found to increase the speed of resistance as it increased the period of insecticide exposure. Our study demonstrates the flexibility and power of an individual-based model to simulate how farming practices affect pest population dynamics, and the consequent impact of different control strategies on the risk and speed of resistance development. PMID:25531104

Stratonovitch, Pierre; Elias, Jan; Denholm, Ian; Slater, Russell; Semenov, Mikhail A

2014-01-01

234

An Individual-Based Model of the Evolution of Pesticide Resistance in Heterogeneous Environments: Control of Meligethes aeneus Population in Oilseed Rape Crops  

PubMed Central

Preventing a pest population from damaging an agricultural crop and, at the same time, preventing the development of pesticide resistance is a major challenge in crop protection. Understanding how farming practices and environmental factors interact with pest characteristics to influence the spread of resistance is a difficult and complex task. It is extremely challenging to investigate such interactions experimentally at realistic spatial and temporal scales. Mathematical modelling and computer simulation have, therefore, been used to analyse resistance evolution and to evaluate potential resistance management tactics. Of the many modelling approaches available, individual-based modelling of a pest population offers most flexibility to include and analyse numerous factors and their interactions. Here, a pollen beetle (Meligethes aeneus) population was modelled as an aggregate of individual insects inhabiting a spatially heterogeneous landscape. The development of the pest and host crop (oilseed rape) was driven by climatic variables. The agricultural land of the landscape was managed by farmers applying a specific rotation and crop protection strategy. The evolution of a single resistance allele to the pyrethroid lambda cyhalothrin was analysed for different combinations of crop management practices and for a recessive, intermediate and dominant resistance allele. While the spread of a recessive resistance allele was severely constrained, intermediate or dominant resistance alleles showed a similar response to the management regime imposed. Calendar treatments applied irrespective of pest density accelerated the development of resistance compared to ones applied in response to prescribed pest density thresholds. A greater proportion of spring-sown oilseed rape was also found to increase the speed of resistance as it increased the period of insecticide exposure. Our study demonstrates the flexibility and power of an individual-based model to simulate how farming practices affect pest population dynamics, and the consequent impact of different control strategies on the risk and speed of resistance development. PMID:25531104

Stratonovitch, Pierre; Elias, Jan; Denholm, Ian; Slater, Russell; Semenov, Mikhail A.

2014-01-01

235

Landscape effects of a non-native grass facilitate source populations of a native generalist bug, Stenotus rubrovittatus, in a heterogeneous agricultural landscape.  

PubMed

Non-native plant species can provide native generalist insects, including pests, with novel food and habitats. It is hypothesized that local and landscape-level abundances of non-native plants can affect the population size of generalist insects, although generalists are assumed to be less sensitive to habitat connectivity than specialists. In a heterogeneous landscape in Japan, the relationship between the density of a native pest of rice (Stenotus rubrovittatus (Matsumura) (Heteroptera: Miridae)) and the abundance of Italian ryegrass (Lolium multiflorum Lam. (Poales: Poaceae)), a non-native meadow grass known to facilitate S. rubrovittatus, was analyzed. Statistical analyses of data on bug density, vegetation, and the spatial distribution of fallow fields and meadows dominated by Italian ryegrass, obtained by field surveys, demonstrated that local and landscape-level abundances of Italian ryegrass (the unmowed meadow areas within a few hundred meters of a sampling plot) positively affected bug density before its immigration into rice fields. Our findings suggest that a generalist herbivorous insect that prefers non-native plants responds to spatial availability and connectivity of plant species patches at the metapopulation level. Fragmentation by selective mowing that decreases the total area of source populations and increases the isolation among them would be an effective and environmentally-friendly pest management method. PMID:25368057

Yoshioka, A; Takada, M B; Washitani, I

2014-01-01

236

Landscape effects of a non-native grass facilitate source populations of a native generalist bug, Stenotus rubrovittatus, in a heterogeneous agricultural landscape.  

PubMed

Non-native plant species can provide native generalist insects, including pests, with novel food and habitats. It is hypothesized that local and landscape-level abundances of non-native plants can affect the population size of generalist insects, although generalists are assumed to be less sensitive to habitat connectivity than specialists. In a heterogeneous landscape in Japan, the relationship between the density of a native pest of rice (Stenotus rubrovittatus (Matsumura) (Heteroptera: Miridae)) and the abundance of Italian ryegrass (Lolium multiflorum Lam. (Poales: Poaceae)), a non-native meadow grass known to facilitate S. rubrovittatus, was analyzed. Statistical analyses of data on bug density, vegetation, and the spatial distribution of fallow fields and meadows dominated by Italian ryegrass, obtained by field surveys, demonstrated that local and landscape-level abundances of Italian ryegrass (the unmowed meadow areas within a few hundred meters of a sampling plot) positively affected bug density before its immigration into rice fields. Our findings suggest that a generalist herbivorous insect that prefers non-native plants responds to spatial availability and connectivity of plant species patches at the metapopulation level. Fragmentation by selective mowing that decreases the total area of source populations and increases the isolation among them would be an effective and environmentally-friendly pest management method. PMID:25205015

Yoshioka, A; Takada, M B; Washitani, I

2014-01-01

237

Landscape Effects of a Non-Native Grass Facilitate Source Populations of a Native Generalist Bug, Stenotus rubrovittatus, in a Heterogeneous Agricultural Landscape  

PubMed Central

Non-native plant species can provide native generalist insects, including pests, with novel food and habitats. It is hypothesized that local and landscape-level abundances of non-native plants can affect the population size of generalist insects, although generalists are assumed to be less sensitive to habitat connectivity than specialists. In a heterogeneous landscape in Japan, the relationship between the density of a native pest of rice (Stenotus rubrovittatus (Matsumura) (Heteroptera: Miridae)) and the abundance of Italian ryegrass (Lolium multiflorum Lam. (Poales: Poaceae)), a non-native meadow grass known to facilitate S. rubrovittatus, was analyzed. Statistical analyses of data on bug density, vegetation, and the spatial distribution of fallow fields and meadows dominated by Italian ryegrass, obtained by field surveys, demonstrated that local and landscape-level abundances of Italian ryegrass (the unmowed meadow areas within a few hundred meters of a sampling plot) positively affected bug density before its immigration into rice fields. Our findings suggest that a generalist herbivorous insect that prefers non-native plants responds to spatial availability and connectivity of plant species patches at the metapopulation level. Fragmentation by selective mowing that decreases the total area of source populations and increases the isolation among them would be an effective and environmentally-friendly pest management method. PMID:25205015

Yoshioka, A.; Takada, M. B.; Washitani, I.

2014-01-01

238

Heterogeneous co-localization of AT 1A receptor and Fos protein in forebrain neuronal populations responding to acute hydromineral deficit.  

PubMed

The present study investigates co-localization of AT(1A) receptor subtype and Fos protein in neuronal populations of the lamina terminalis (LT) that have been recruited during acute Na(+) and water depletion mediated by furosemide injections. For that purpose, we combined high cellular resolution of in situ hybridization technique to reveal neurons expressing AT(1A) receptor gene (AT(1A) mRNA) with the specificity of Fos protein immunoreactivity as a marker of neuronal activation (Fos-ir). As expected, furosemide treatment dramatically increased the density of Fos-immunoreactive neuronal population in all the regions of the LT compared to control (saline-injected animals). Distribution analysis of Fos-ir neurons and AT(1A) receptor-expressing neurons performed consecutively to furosemide-induced Na(+) and water depletion indicated that double-labeled neurons (AT(1A) mRNA+Fos-ir) represented the majority (67%) of the neuronal population that expressed AT(1A) receptor in the rim of the vascular organ of the lamina terminalis (OVLT). Double-labeled neurons amounted about 60% of the neurons that expressed AT(1A) receptor in the core of the subfornical organ (SFO) and 34% in the periphery of the SFO. In the median preoptic nucleus (MnPO), the density of the double-labeled neuronal population observed in the furosemide-treated animals remained weak compared to the control group of animals. Double-labeled neuronal population estimated in the MnPO of the furosemide-treated group of animals represented 17% of the neurons that express AT(1A) receptor gene. Our results report a heterogeneous distribution of the neuronal populations that co-localize AT(1A) receptor and Fos protein in the lamina terminalis after an acute Na(+) and water depletion. This study gives anatomical support to a direct action of endogenous AngII on c-fos transcription via binding on AT(1A) receptor in specific areas of the circumventricular organs (rim of the OVLT and core of the SFO). In the MnPO, our data indicate that intracellular signaling pathways unlikely couple AT(1A) receptor with c-fos transcription. The expression of Fos protein in this nucleus might be therefore secondary to the recruitment of excitatory inputs different from AngII. This observation underlines the complexity of molecules and neurocircuits in the preoptic region that are involved in the control of acute Na(+) and water deficit. PMID:14670634

Grob, Magali; Trottier, Jean-François; Mouginot, Didier

2004-01-16

239

Effect of school environment on dental students' perceptions of cultural competency curricula and preparedness to care for diverse populations.  

PubMed

Reports of oral health disparities among racial, ethnic, and socioeconomic sectors of the U.S. population have hastened development of strategies to address this issue. Among these strategies is revising dental school curricula in order to develop more culturally competent graduates. The present study uses data from the 2003 American Dental Education Association (ADEA) survey of dental school seniors to assess students' perceptions of the adequacy of their cultural competency training. We hypothesize that these perceptions are influenced by multiple student characteristics and contextual factors, including a school's status with respect to the Pipeline, Professions, and Practice initiative of the Robert Wood Johnson Foundation and The California Endowment. Response data from ADEA survey items reflecting student perceptions of adequacy of curriculum time devoted to cultural competency and their preparedness to treat an ethnically and culturally diverse population were analyzed to assess the influence of selected student and contextual factors. Student gender, marital status, and level of educational debt were found to influence the curriculum time variable, and students at California schools reported higher perceived preparedness levels than students at dental schools nationwide. Dental school environments promoting acceptance and respect of diverse ethnicities/cultures and student race/ethnicity were significantly associated with students' perception of the adequacy of curriculum time for cultural competency and students' perception of their preparedness to provide oral health care for racially and culturally diverse groups. The findings provide insight for development of cultural competency curricula and direction for future study in this area. PMID:17554098

Hewlett, Edmond R; Davidson, Pamela L; Nakazono, Terry T; Baumeister, Sebastian E; Carreon, Daisy C; Freed, James R

2007-06-01

240

The DREEM, part 2: psychometric properties in an osteopathic student population  

PubMed Central

Background The Dundee Ready Educational Environment Measure (DREEM) is widely used to assess the educational environment in health professional education programs. A number of authors have identified issues with the psychometric properties of the DREEM. Part 1 of this series of papers presented the quantitative data obtained from the DREEM in the context of an Australian osteopathy program. The present study used both classical test theory and item response theory to investigate the DREEM psychometric properties in an osteopathy student population. Methods Students in the osteopathy program at Victoria University (Melbourne, Australia) were invited to complete the DREEM and a demographic questionnaire at the end of the 2013 teaching year (October 2013). Data were analysed using both classical test theory (confirmatory factor analysis) and item response theory (Rasch analysis). Results Confirmatory factor analysis did not demonstrate model fit for the original 5-factor DREEM subscale structure. Rasch analysis failed to identify a unidimensional model fit for the 50-item scale, however model fit was achieved for each of the 5 subscales independently. A 12-item version of the DREEM was developed that demonstrated good fit to the Rasch model, however, there may be an issue with the targeting of this scale given the mean item-person location being greater than 1. Conclusions Given that the full 50-item scale is not unidimensional; those using the DREEM should avoid calculating a total score for the scale. The 12-item ‘short-form’ of the DREEM warrants further investigation as does the subscale structure. To confirm the reliability of the DREEM, as a measure to evaluate the appropriateness of the educational environment of health professionals, further work is required to establish the psychometric properties of the DREEM, with a range of student populations. PMID:24884704

2014-01-01

241

A comparative study between Navy Junior ROTC cadets and general population students on measures of dogmatism, personality type, and self-esteem  

Microsoft Academic Search

This research investigation compared the responses of NJROTC cadets and general high school population students on measures of dogmatism, personality type, and self-esteem. The study incorporated a nonexperimental, descriptive design involving 67 NJROTC cadets and 67 general high school population students in a large urban high school. The students were matched by grade and sex and each responded to three

Daniel Franklin Machir

1991-01-01

242

An Untapped Resource for Increasing College Attainment: Estimating the Population of Potential First-Generation Students in Wisconsin. WISCAPE Policy Brief  

ERIC Educational Resources Information Center

Potential first-generation students make up a large segment of Wisconsin's teenage population. To increase the pool of educated workers in Wisconsin, policymakers must work to recruit, retain, and graduate these students. Estimates of the size of the first-generation student population in the state are crucial for these efforts. This brief…

Lazenby, Sara

2011-01-01

243

Genetic polymorphisms of 15 STR loci within Turkish student population living in Sarajevo, Bosnia and Herzegovina.  

PubMed

Allele frequencies of 15 STRs included in the PowerPlex 16 System (D3S1358, TH01, D21S11, D18S51, Penta E, D5S818, D13S317, D7S820, D16S539, CSF1PO, Penta D, VWA, D8S1179, TPOX and FGA) were calculated from the referent sample of 100 unrelated individuals of both sexes from Turkish student population living in Sarajevo, Bosnia and Herzegovina. Buccal swab, as a source of DNA, was collected from the volunteers from whom the informed consent form was obtained. DNA extraction was performed using QIAamp DNA Micro kit by Qiagen. DNA template ranging from 0.5 to 2 ng was used to amplify 15 STR loci by PCR multiplex amplification which was performed by using the PowerPlex 16 kit (Promega Corp., Madison, WI, USA) according to the manufacturer's protocol. The amplifications were carried out in a PE Gene Amp PCR System thermal cycler (Applied Biosystems) and capillary electrophoresis was carried out in an ABI PRISM 310 Genetic Analyzer (Applied Biosystems) in accordance with the manufacturer's recommendations. The frequency of each locus was calculated from the numbers of each observed genotype. Deviation from Hardy-Weinberg equilibrium and observed heterozygosity were calculated. Data were analyzed by using Microsoft Excel workbook template--Powerstats V12 and the power of discrimination (PD), power of exclusion (PE), as well as other population genetic indices for the 15 STR loci were calculated. Obtained results contribute to existing Turkish DNA database, as well as insight of differences and similarities in comparison to population of Bosnia and Herzegovina. In addition, 13 autosomal STR loci frequencies (D3S1358, TH01, D21S11, D18S51, Penta E, D5S818, D13S317, D7S820, D16S539, CSFIPO, Penta D, VWA, D8S1 179, TPOX, and FGA) were studied in 15 different worldwide populations (Turkish, Bosnian, Croatian, Serbian, Montenegrin, Macedonian, Albanian, Kosovan, Greek, Russian, Japanese, Korean, Lithuanian, Iraqi, Belarusian). For the proof of corresponding data, two different Turkish population STR data obtained from previously published articles were compared with our data and this showed that our data correspond to these 2 previously published data. Further, STR allele frequency data for 13 loci for each population were obtained from previous scientific articles and the allele frequencies and genetic diversity among the 15 sample populations were compared. In addition, even though the populations are from different nationalities, the STR data are similar among the geographically close populations. The phylogenetic tree established among worldwide populations and genetic distance values show a great affinity among the 15populations. Our data is useful for anthropological and further comparative genetic studies of populations. PMID:24611350

Dogan, Serkan; Kovacevi?, Lejla; Marjanovi?, Damir

2013-12-01

244

Investigating evolutionary trade-offs in wild populations of atlantic salmon (salmo salar): incorporating detection probabilities and individual heterogeneity.  

PubMed

Evolutionary trade-offs among demographic parameters are important determinants of life-history evolution. Investigating such trade-offs under natural conditions has been limited by inappropriate analytical methods that fail to address the bias in demographic estimates that can result when issues of detection (uncertain detection of individual) are ignored. We propose a new statistical approach to quantify evolutionary trade-offs in wild populations. Our method is based on a state-space modeling framework that focuses on both the demographic process of interest as well as the observation process. As a case study, we used individual mark-recapture data for stream-dwelling Atlantic salmon juveniles in the Scorff River (Southern Brittany, France). In freshwater, juveniles face two life-history choices: migration to the ocean and sexual maturation (for males). Trade-offs may appear with these life-history choices and survival, because all are energy dependent. We found a cost of reproduction on survival for fish staying in freshwater and a survival advantage associated with the "decision" to migrate. Our modeling framework opens up promising prospects for the study of evolutionary trade-offs when some life-history traits are not, or only partially, observable. PMID:20482614

Buoro, Mathieu; Prévost, Etienne; Gimenez, Olivier

2010-09-01

245

Expression Profiling of a Heterogeneous Population of ncRNAs Employing a Mixed DNA/LNA Microarray  

PubMed Central

Mammalian transcriptomes mainly consist of non protein coding RNAs. These ncRNAs play various roles in all cells and are involved in multiple regulation pathways. More recently, ncRNAs have also been described as valuable diagnostic tools. While RNA-seq approaches progressively replace microarray-based technologies for high-throughput expression profiling, they are still not routinely used in diagnostic. Microarrays, on the other hand, are more widely used for diagnostic profiling, especially for very small ncRNA (e.g., miRNAs), employing locked nucleic acid (LNA) arrays. However, LNA microarrays are quite expensive for high-throughput studies targeting longer ncRNAs, while DNA arrays do not provide satisfying results for the analysis of small RNAs. Here, we describe a mixed DNA/LNA microarray platform, where directly labeled small and longer ncRNAs are hybridized on LNA probes or custom DNA probes, respectively, enabling sensitive and specific analysis of a complex RNA population on a unique array in one single experiment. The DNA/LNA system, requiring relatively low amounts of total RNA, which complies with diagnostic references, was successfully applied to the analysis of differential ncRNA expression in mouse embryonic stem cells and adult brain cells. PMID:22778910

Skreka, Konstantinia; Zywicki, Marek; Karbiener, Michael; Hüttenhofer, Alexander; Scheideler, Marcel; Rederstorff, Mathieu

2012-01-01

246

Phylogenetic and clonality analysis of Bacillus pumilus isolates uncovered a highly heterogeneous population of different closely related species and clones.  

PubMed

Bacillus pumilus is a Gram-positive bacterium with a wide range of attributed applications, namely as a plant growth promoting rhizobacteria (PGPR), animal, and human probiotic. However, a rare putative role in human diseases has been reported, namely in food poisoning or as anthrax-like cutaneous infectious agent. This species is difficult to distinguish from its closely related species on the basis of phenotypic or biochemical characteristics and 16S rRNA gene sequences. In this study, the phylogenetic analysis of gyrB and rpoB gene sequences of a collection of isolates previously identified as B. pumilus, assigned most of them (93%, 38 of 41 isolates) to B. safensis or to the new recently described B. invictae. Moreover, we extended the previously reported recognized habitats of these species and unveiled a human health or biotechnological relevance (e.g. as implicated in food poisoning or PGPR) for them. Additionally, we demonstrated that both B. safensis and B. invictae species encompass a clonally diverse population, which can justify their great adaptation ability to different niches, with evidence of clonal-host specificity. PMID:25230950

Branquinho, Raquel; Meirinhos-Soares, Luís; Carriço, João A; Pintado, Manuela; Peixe, Luísa V

2014-12-01

247

Heterogeneity of breast cancer risk within the South Asian female population in England: a population-based case-control study of first-generation migrants.  

PubMed

South Asian women in England have a lower breast cancer risk than their English-native counterparts, but less is known about variations in risk between distinct South Asian ethnic subgroups. We used the data from a population-based case-control study of first-generation South Asian migrants to assess risks by ethnic subgroup. In all, 240 breast cancer cases, identified through cancer registries, were individually matched on age and general practitioner to two controls. Information on the region of origin, religious and linguistic background, and on breast cancer risk factors was obtained from participants. Breast cancer odds varied significantly between the ethnic subgroups (P=0.008), with risk increasing in the following order: Bangladeshi Muslims (odds ratio (OR) 0.33, 95% confidence interval (CI): 0.10, 1.06), Punjabi Hindu (OR 0.59, 95% CI: 0.33, 1.27), Gujarati Hindu (1=reference group), Punjabi Sikh (OR 1.23, 95% CI: 0.72, 2.11) and Pakistani/Indian Muslims (OR 1.76, 95% CI: 1.10, 2.81). The statistically significant raised risk in Pakistani/Indian Muslims increased with adjustment for socioeconomic and reproductive risk factors (OR 2.12, 95% CI: 1.25, 3.58), but was attenuated, and no longer significant, with further adjustment for waist circumference and intake of nonstarch polysaccharides and fat (OR 1.49, 95% CI: 0.85, 2.63). These findings reveal differences in breast cancer risk between South Asian ethnic subgroups, which were not fully explained by reproductive differences, but were partly accounted for by diet and body size. PMID:14710224

McCormack, V A; Mangtani, P; Bhakta, D; McMichael, A J; dos Santos Silva, I

2004-01-12

248

Trans-Ethnic Fine-Mapping of Lipid Loci Identifies Population-Specific Signals and Allelic Heterogeneity That Increases the Trait Variance Explained  

PubMed Central

Genome-wide association studies (GWAS) have identified ?100 loci associated with blood lipid levels, but much of the trait heritability remains unexplained, and at most loci the identities of the trait-influencing variants remain unknown. We conducted a trans-ethnic fine-mapping study at 18, 22, and 18 GWAS loci on the Metabochip for their association with triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C), respectively, in individuals of African American (n?=?6,832), East Asian (n?=?9,449), and European (n?=?10,829) ancestry. We aimed to identify the variants with strongest association at each locus, identify additional and population-specific signals, refine association signals, and assess the relative significance of previously described functional variants. Among the 58 loci, 33 exhibited evidence of association at P<1×10?4 in at least one ancestry group. Sequential conditional analyses revealed that ten, nine, and four loci in African Americans, Europeans, and East Asians, respectively, exhibited two or more signals. At these loci, accounting for all signals led to a 1.3- to 1.8-fold increase in the explained phenotypic variance compared to the strongest signals. Distinct signals across ancestry groups were identified at PCSK9 and APOA5. Trans-ethnic analyses narrowed the signals to smaller sets of variants at GCKR, PPP1R3B, ABO, LCAT, and ABCA1. Of 27 variants reported previously to have functional effects, 74% exhibited the strongest association at the respective signal. In conclusion, trans-ethnic high-density genotyping and analysis confirm the presence of allelic heterogeneity, allow the identification of population-specific variants, and limit the number of candidate SNPs for functional studies. PMID:23555291

Wu, Ying; Waite, Lindsay L.; Jackson, Anne U.; Sheu, Wayne H-H.; Buyske, Steven; Absher, Devin; Arnett, Donna K.; Boerwinkle, Eric; Bonnycastle, Lori L.; Carty, Cara L.; Cheng, Iona; Cochran, Barbara; Croteau-Chonka, Damien C.; Dumitrescu, Logan; Eaton, Charles B.; Franceschini, Nora; Guo, Xiuqing; Henderson, Brian E.; Hindorff, Lucia A.; Kim, Eric; Kinnunen, Leena; Komulainen, Pirjo; Lee, Wen-Jane; Le Marchand, Loic; Lin, Yi; Lindström, Jaana; Lingaas-Holmen, Oddgeir; Mitchell, Sabrina L.; Narisu, Narisu; Robinson, Jennifer G.; Schumacher, Fred; Stan?áková, Alena; Sundvall, Jouko; Sung, Yun-Ju; Swift, Amy J.; Wang, Wen-Chang; Wilkens, Lynne; Wilsgaard, Tom; Young, Alicia M.; Adair, Linda S.; Ballantyne, Christie M.; B?žková, Petra; Chakravarti, Aravinda; Collins, Francis S.; Duggan, David; Feranil, Alan B.; Ho, Low-Tone; Hung, Yi-Jen; Hunt, Steven C.; Hveem, Kristian; Juang, Jyh-Ming J.; Kesäniemi, Antero Y.; Kuusisto, Johanna; Laakso, Markku; Lakka, Timo A.; Lee, I-Te; Leppert, Mark F.; Matise, Tara C.; Moilanen, Leena; Njølstad, Inger; Peters, Ulrike; Quertermous, Thomas; Rauramaa, Rainer; Rotter, Jerome I.; Saramies, Jouko; Tuomilehto, Jaakko; Uusitupa, Matti; Wang, Tzung-Dau; Mohlke, Karen L.

2013-01-01

249

Preparing for patient-centered care: assessing nursing student knowledge, comfort, and cultural competence toward the Latino population.  

PubMed

As the Latino population continues to grow throughout the United States, cultural competence training of nursing students at the baccalaureate level has become a priority. This study aimed to explore undergraduate nursing students' attitudes and beliefs toward Latino patients and their perceived readiness to provide care to Latino patients. A cross-sectional survey was conducted at four major nursing schools in the southeastern United States, which is the region that has seen the highest percentage of growth in the Latino population. Results from multivariable regression suggest that social interaction with Latino individuals and cultural immersion in a Spanish-speaking country predict student knowledge, cultural competence, and comfort with Latino patients. Direct influence by nursing programs, such as clinical experience, coursework, and language proficiency, are positively associated with the designed outcomes, but these relationships are not statistically significant. Our findings suggest that dosage of training matters. Implications for student recruitment, selection, and training are discussed. PMID:24766083

Mayo, Rachel M; Sherrill, Windsor W; Truong, Khoa D; Nichols, Christina M

2014-06-01

250

Population.  

ERIC Educational Resources Information Center

In an effort to help meet the growing interest and concern about the problems created by the rapid growth of population, The International Planned Parenthood Federation has prepared this booklet with the aim of assisting the study of the history and future trends of population growth and its impact on individual and family welfare, national,…

International Planned Parenthood Federation, London (England).

251

Large epidemic thresholds emerge in heterogeneous networks of heterogeneous nodes  

E-print Network

One of the famous results of network science states that networks with heterogeneous connectivity are more susceptible to epidemic spreading than their more homogeneous counterparts. In particular, in networks of identical nodes it has been shown that heterogeneity can lower the epidemic threshold at which epidemics can invade the system. Network heterogeneity can thus allow diseases with lower transmission probabilities to persist and spread. Here, we point out that for real world applications, this result should not be regarded independently of the intra-individual heterogeneity between people. Our results show that, if heterogeneity among people is taken into account, networks that are more heterogeneous in connectivity can be more resistant to epidemic spreading. We study a susceptible-infected-susceptible model with adaptive disease avoidance. Results from this model suggest that this reversal of the effect of network heterogeneity is likely to occur in populations in which the individuals are aware of t...

Yang, Hui; Gross, Thilo

2015-01-01

252

Gambling and Attention Deficit Hyperactivity Disorders (ADHD) in a Population of French Students.  

PubMed

Attention deficit disorder with or without hyperactivity (ADD/ADHD) is a neurodevelopmental disorder that can be exacerbated by psychosocial factors. Various studies confirm that the severity of a psychiatric disorder, particularly when it comes to ADHD, is strongly correlated with the amount of use. This study (1) evaluated the association between ADHD and gambling among young students; (2) determined which symptom among ADHD's three symptoms (attention deficit, hyperactivity, or impulsivity) had the strongest association with video game addiction and gambling; and (3) determined the impact of the association between ADHD and video game addiction and gambling on self-esteem and academic performance of students. A total of 720 students (445 males and 274 females) were recruited from eight higher educational institutions of Ile de France. They all completed a battery of questionnaire consisting of Canadian Problem Gambling Index, UPPS Impulsive Behavior Scale, Wender Utah Rating Scale (WURS), Adult ADHD Self-Report Scale (ASRS) and Rosenberg scales, and socio-demographic data. 13.33 % of the participants had symptoms of ADHD during childhood (WURS scale score) and 40.41 % of them have symptoms of ADHD in adulthood (ASRS score). Finally, among the participants, 37.5 % had excessive gambling addiction, have positive results on WURS and ASRS scales, thus having a probable ADHD, whereas 14.55 % had no gambling addiction. The results demonstrated that adult ADHD was associated with gambling addiction. Significant associations were observed between ADHD and impulsivity, academic difficulties and gambling addiction. The association between ADHD and gambling seems to be common among vulnerable populations such as adolescents and could be related to variables such as self-esteem, which appears to potentially worsen the prognosis. Further research on this relationship is needed to optimize prevention strategies and effective treatment. PMID:25466366

Romo, L; Rémond, J J; Coeffec, A; Kotbagi, G; Plantey, S; Boz, F; Kern, L

2014-12-01

253

Training Students to Analyze Spatial and Temporal Heterogeneities in Reservoir and Seal Petrology, Mineralogy, and Geochemistry: Implications for CO{sub 2} Sequestration Prediction, Simulation, and Monitoring  

SciTech Connect

The objective of this project was to expose and train multiple students in geological tools that are essential to reservoir characterization and geologic sequestration including but not limited to advanced petrological methods, mineralogical methods, and geochemical methods; core analysis, and geophysical well-log interpretation. These efforts have included training of multiple students through geologically based curriculum and research using advanced petrological, mineralogical, and geochemical methods. In whole, over the last 3+ years, this award has supported 5,828 hours of student research, supporting the work of several graduate and undergraduate students. They have all received training directly related to ongoing CO{sub 2} sequestration demonstrations. The students have all conducted original scientific research on topics related to understanding the importance of lithological, textural, and compositional variability in formations that are being targeted as CO{sub 2} sequestration reservoirs and seals. This research was linked to the Mount Simon Sandstone reservoir and overlying Eau Claire Formation seal in the Illinois Basin- a system where over one million tons of CO{sub 2} are actively being injected with the first large-scale demonstration of anthropogenic CO{sub 2} storage in the U.S. Student projects focused specifically on 1) reservoir porosity characterization and evaluation, 2) petrographic, mineralogical, and geochemical evidence of fluid-related diagenesis in the caprock, 3) textural changes in reservoir samples exposed to experimental CO{sub 2} + brine conditions, 4) controls on spatial heterogeneity in composition and texture in both the reservoir and seal, 5) the implications of small-scale fractures within the reservoir, and 6) petrographic and stable isotope analyses of carbonates in the seal to understand the burial history of the system. The student-led research associated with this project provided real-time and hands-on experience with a relevant CO{sub 2} system, provided relevant information to the regional partnerships who are working within these formations, and provides more broadly applicable understanding and method development for other carbon capture and storage systems.

Bowen, Brenda

2013-09-30

254

The Dominance Concept Inventory: A Tool for Assessing Undergraduate Student Alternative Conceptions about Dominance in Mendelian and Population Genetics  

ERIC Educational Resources Information Center

Despite the impact of genetics on daily life, biology undergraduates understand some key genetics concepts poorly. One concept requiring attention is dominance, which many students understand as a fixed property of an allele or trait and regularly conflate with frequency in a population or selective advantage. We present the Dominance Concept…

Abraham, Joel K.; Perez, Kathryn E.; Price, Rebecca M.

2014-01-01

255

Students with Dyslexia If you have dyslexia, you are not alone. It is thought that 10% of the population  

E-print Network

Students with Dyslexia If you have dyslexia, you are not alone. It is thought that 10% of the population shows signs of dyslexia with around 4% affected severely. When applying for jobs the following organisations appear positive about dyslexia, do not limit your applications to these alone. Choose employers

Royal Holloway, University of London

256

Who Pays for Student Diversity? Population Changes and Educational Policy. Twelfth Annual Yearbook of the American Education Finance Association, 1991.  

ERIC Educational Resources Information Center

Issues of finance undergird all education policy decisions, and demographic changes have clear financial impact. This edited volume outlines demographic trends, focuses on minority and other special student populations in urban and rural settings, and relates the findings to policies. Contained in the book are the following papers: (1) "The Power…

Ward, James Gordon, Ed.; Anthony, Patricia, Ed.

257

Exploring Dual Credit Data Alignment, Student Populations, and Coursework Patterns in Texas Using a P-16 Framework  

ERIC Educational Resources Information Center

This multi-faceted study of dual credit programs in Texas was motivated by perceived discrepancies in dual credit data reporting and a lack of comprehensive, state-level information about dual credit student populations and coursework patterns. Using a P-16 framework, the author explored alignment issues that influence the delivery of dual credit…

Eklund, Julie Ann

2009-01-01

258

Population Connection: Population Education  

NSDL National Science Digital Library

Population Connection "is the national grassroots population organization that educates young people and advocates progressive action to stabilize world population at a level that can be sustained by Earth's resources." The Population Connection's Education Program develops "age-appropriate curricula to complement students' science and social science instruction about human population trends and their impacts on natural resources, environmental quality and human well-being." The Population Education website offers a variety of educational resources including downloadable classroom activities and readings, and newsletters for teachers and students. The site also provides information about professional development opportunities for educators and free population education workshops held at universities for pre-service teachers and graduate students.

259

Research Training of Students in Minority and International Settings: Lessons Learned from Cancer Epidemiology Education in Special Populations  

PubMed Central

This article describes the development and evaluation of an NCI-sponsored short-term summer cancer research education program. The study questions examined: the feasibility of conducting a cancer education program in special populations at multiple US and international field sites for masters students; the merit and worth that students and faculty attribute to the program; and students' scholarly and cancer-related career outcomes. Developing a new curriculum, increasing the pool of mentors, utilizing and increasing the number of field sites, and program dissemination were also evaluated. Evidence of the program's success included students' completion of field experiences at multiple sites and their subsequent 70% project-related publication rate, with 79% of trainees reporting themselves as likely to pursue future cancer-related careers. Evaluation-guided future plans for the program include implementing faculty development to further enhance the program outcomes. PMID:20352397

Mullan, Patricia B.; Chamberlain, Robert M.

2014-01-01

260

Second International Mathematics Study; Longitudinal, Classroom Process Surveys for Population A: Students, Teachers, and Schools, 1981-1982 [machine-readable data file].  

ERIC Educational Resources Information Center

The Second International Mathematics Study (SIMS) of the International Association for the Evaluation of Educational Achievement (IEA) was conducted in 20 countries on two sampled populations: Population A of 13-year-olds and Population B of students studying mathematics in their final year of secondary school. Mathematics achievement was measured…

Wolfe, Richard G.

261

The Impact of an Economically Disadvantaged Student Population on School Climate  

ERIC Educational Resources Information Center

The purpose of this study was to determine the relationship between student poverty levels, defined by the number of students identified as economically disadvantaged by qualifying for free and reduced lunch and school climate. The literature review examined school climate and culture, effects of student socioeconomic (SES) status on education,…

Null, Curtis F.

2012-01-01

262

Student Involvement in Learning Action Packet. Research, Strategies and Programs for Special Populations.  

ERIC Educational Resources Information Center

To improve the responsiveness of educational programs to the needs of low achieving, at risk students, Research for Better Schools (RBS) has developed an assessment procedure. This document is the portion of that procedure that addresses the involvement of students in their learning, or how low achieving students cognitively operate on content.…

Research for Better Schools, Inc., Philadelphia, PA.

263

Factors Affecting the Graduation Rates of University Students from Underrepresented Populations  

ERIC Educational Resources Information Center

One of the most pressing issues facing American universities is the number of students who fail to graduate. Nearly one out of five four-year institutions graduate fewer than one-third of its first-time, full-time degree-seeking first-year students within six years. Although there are various explanations for attrition, students often leave for…

Creighton, Linda M.

2007-01-01

264

Pluralistic Ignorance among Student-Athlete Populations: A Factor in Academic Underperformance  

ERIC Educational Resources Information Center

It is well documented that student-athletes underperform academically. Some researchers have suggested that this underperformance is because student-athletes lack motivation in academic endeavors. In contrast, we find that most student-athletes hold positive private attitudes towards academic achievement, but also believe that their peers do not.…

Levine, Joshua; Etchison, Sara; Oppenheimer, Daniel M.

2014-01-01

265

The Unique Leadership Needs of Minority Student Populations: Crafting a Leadership Identity  

ERIC Educational Resources Information Center

The purpose of this qualitative study was to determine how college-level minority student leaders make meaning of those leadership experiences. Semi-structured interviews were conducted with 12 students. Major findings noted a strong personal motivation to participate in student leadership positions. Further research on the impact of familial…

Baughman, Kristen N.; Bruce, Jacklyn

2011-01-01

266

Making Science Accessible: Strategies to Meet the Needs of a Diverse Student Population  

NSDL National Science Digital Library

Despite the sincere interest of many teachers to address the varying educational needs of their students (Scruggs and Mastropieri 1994), the current emphasis on inclusion remains a source of frustration, misunderstanding, and distrust by some teachers, parents, and students. Many regular educators are ill prepared or supported to accept the challenges of teaching students with special needs. One of the dilemmas that they often face is how to modify these activities so that they are accessible to a wider range of students. This article offers suggestions for modifying favorite activities so that they are accessible to students with hearing, visual, motor, or learning disabilities.

Dawn M. Pickard

2003-02-01

267

54 Journal of Student Research in Environmental Science at Appalachian Land Loss and Displaced Population of  

E-print Network

to storm surges, and groundwater contamination [2]. In addition to the impacts on humans, sea-level rise level but contains 10 per- cent of the world's population and 13 percent of the world's urban population

Thaxton, Christopher S.

268

Guide to Population Issues for Students and Teachers [and] Curriculum Guide.  

ERIC Educational Resources Information Center

As the world grapples with increasing environmental, social, and security problems, population is rarely considered a cause or contributing factor. The relationship of population to the human condition, and to the condition of the Earth, is often subtle and complex. But population growth affects almost every aspect of life from education to…

Facing the Future, Lopez Island, WA.

269

The Dominance Concept Inventory: A Tool for Assessing Undergraduate Student Alternative Conceptions about Dominance in Mendelian and Population Genetics  

PubMed Central

Despite the impact of genetics on daily life, biology undergraduates understand some key genetics concepts poorly. One concept requiring attention is dominance, which many students understand as a fixed property of an allele or trait and regularly conflate with frequency in a population or selective advantage. We present the Dominance Concept Inventory (DCI), an instrument to gather data on selected alternative conceptions about dominance. During development of the 16-item test, we used expert surveys (n = 12), student interviews (n = 42), and field tests (n = 1763) from introductory and advanced biology undergraduates at public and private, majority- and minority-serving, 2- and 4-yr institutions in the United States. In the final field test across all subject populations (n = 709), item difficulty ranged from 0.08 to 0.84 (0.51 ± 0.049 SEM), while item discrimination ranged from 0.11 to 0.82 (0.50 ± 0.048 SEM). Internal reliability (Cronbach's alpha) was 0.77, while test–retest reliability values were 0.74 (product moment correlation) and 0.77 (intraclass correlation). The prevalence of alternative conceptions in the field tests shows that introductory and advanced students retain confusion about dominance after instruction. All measures support the DCI as a useful instrument for measuring undergraduate biology student understanding and alternative conceptions about dominance.

Perez, Kathryn E.; Price, Rebecca M.

2014-01-01

270

Medical students' and allied health care professionals' perceptions toward the mentally retarded population  

Microsoft Academic Search

The purpose of this study was to determine if differences in expectations toward individuals with varying levels of mental\\u000a retardation exist between medical students themselves and between health care professionals involved with these individuals.\\u000a There were 136 medical students (52%) and 119 health care professionals (89%) who completed the modified Prognostic Beliefs\\u000a Scale survey. Medical students demonstrated lower expectations compared

Eric G. Handler; Ajay Bhardwaj; Dhanu Sant Jackson

1994-01-01

271

Teaching students to work with vulnerable populations through a patient advocacy course.  

PubMed

Nursing students need an in-depth understanding of how social determinants, such as poverty, unsafe housing, and illiteracy, impact the health of patients. The authors describe how a patient advocacy service-learning course increased students' awareness and proficiency in working with the challenges low-income, vulnerable individuals face as they attempt to improve their lives and health. Course learning objectives, essential requirements, and student reflections are presented. PMID:24978016

Bell, Meghan L; Buelow, Janet R

2014-01-01

272

The Roles of Population, Place, and Institution in Student Diversity in American Higher Education.  

PubMed

Student racial and ethnic diversity in higher education is an important and timely topic, as institutions, policy-makers, and economists increasingly recognize the value that accrues at many levels of having a skilled and diverse student body and workforce. Students benefit from learning in a diverse environment; firms may benefit from a diverse workforce; and more demographically diverse regions make experience higher rates of economic growth. However, the forces governing institution-level student diversity are poorly understood, as little prior research on the topic exists. This paper uses school enrollment data to parse out the contribution institutional characteristics, geographical setting, and local demographic characteristics make to student body diversity at each level of study. Results indicate that geographical location and local demographic composition play a role in student body diversity, as do the type and orientation of the institution. Institutional characteristics explain a lot of the variation in student body diversity and actual location of schools matters less than the demographic composition of young people around that location. Two broad conclusions emerge with regard to schools seeking to increase their student diversity. First, some may find their efforts hampered by circumstances outside their control (location, for example). Second, the influence of public/private status and even school size suggest further research on the ways in which these factors influence student diversity so that eventual policy action can be more effective. PMID:25425748

Franklin, Rachel S

2013-01-01

273

Inferring Program Effects for Special Populations: Does Special Education Raise Achievement for Students with Disabilities?  

Microsoft Academic Search

Most discussion of special education has centered on the costs of providing mandated programs for children with disabilities and not on their effectiveness. As in many other policy areas, inferring program effectiveness is difficult because students not in special education do not provide a good comparison group. By following students who move in and out of targeted programs, however, we

Eric A. Hanushek; John F. Kain; Steven G. Rivkin

2002-01-01

274

Ohio's At-Risk Student Population: A Decade of Rising Risk  

ERIC Educational Resources Information Center

Educators face increasing demands to raise student achievement, to improve classroom instruction, and to demonstrate accountability in an environment of high stakes testing. However, meeting these demands is challenging in the face of numerous risk factors that jeopardize the academic success of elementary and secondary students. To that end, the…

Vesely, Randall S.

2013-01-01

275

Human Population. (Student Resource Book IV in the Investigating Your Environemnt Program).  

ERIC Educational Resources Information Center

These resource papers encourage the student to discover for himself the contributions to a problem made through original literature. Since some of the papers are controversial or contradict one another, the student will need to evaluate them to determine his position. It is hoped that these papers will foster an appreciation of the work of the…

Biological Sciences Curriculum Study, Boulder, CO.

276

An Empirically Supported Program to Prevent Suicide in a College Student Population  

ERIC Educational Resources Information Center

In the fall of 1984, the University of Illinois instituted a formal program to reduce the rate of suicide among its enrolled students. At the core of the program is a policy that requires any student who threatens or attempts suicide to attend four sessions of professional assessment. The consequences for failing to comply with the program include…

Joffe, Paul

2008-01-01

277

Heterogeneous catalysis.  

PubMed

A heterogeneous catalyst is a functional material that continually creates active sites with its reactants under reaction conditions. These sites change the rates of chemical reactions of the reactants localized on them without changing the thermodynamic equilibrium between the materials. PMID:25693734

Schlögl, Robert

2015-03-01

278

Modeling Population Heterogeneity in Appearance and Performance-Enhancing Drug (APED) Use: Applications of Mixture Modeling in 400 Regular APED Users  

Microsoft Academic Search

Appearance- and performance-enhancing drugs (APEDs) constitute a wide range of substances, including anabolic–androgenic steroids, nonsteroidal anabolics, and licit and illicit ergo\\/thermogenics. A great deal of heterogeneity exists in APED use patterns among weight-lifting men, and, consequently, little is known about how these patterns are related to side effect profiles or risk potential. In the current study, a sample of 400

Thomas Hildebrandt; James W. Langenbucher; Sasha J. Carr; Pilar Sanjuan

2007-01-01

279

Lack of population genetic structuring in the marine planktonic diatom Pseudo-nitzschia pungens (Bacillariophyceae) in a heterogeneous area in the Southern Bight of the North Sea  

Microsoft Academic Search

Several marine holoplanktonic organisms show a high degree of geographically structured diversity for which it often remains\\u000a unclear to what extent this differentiation is due to the presence of cryptic taxa. For the genetically distinct diatom Pseudo-nitzschia pungens var. pungens, we used six microsatellite markers to investigate the spatial and temporal genetic composition in the heterogeneous Southern\\u000a Bight of the

Griet Casteleyn; Katharine M. Evans; Thierry Backeljau; Sofie D’hondt; Victor A. Chepurnov; Koen Sabbe; Wim Vyverman

2009-01-01

280

How Spanish Primary School Students Interpret the Concepts of Population and Species  

ERIC Educational Resources Information Center

This article presents research concerning the way in which primary school pupils in southern Spain interpret the concepts of population and species. The results show that, for the concept of population, there was an intense anthropocentrism in pupils' responses, while for the concept of species, only animals were considered as living…

Jiménez-Tejada, María-Pilar; Sánchez-Monsalve, Cristina; González-García, Francisco

2013-01-01

281

A Survey of Eating and Weight-Related Behaviors in a Medical University Student Population  

Microsoft Academic Search

The purpose of this study was to assess using a survey questionnaire the lifetime prevalence of several eating- and weight-related behaviors in medical, dental, and nursing students. The sample included 109 students: 59% were female, 67% were single, 84% were Caucasian, and average age was 26.5 years. The results indicated that the prevalence rates of food restriction, exercise, self-induced vomiting,

L. M. Varner; Jeff Crowson; Darlene Shaw

1998-01-01

282

Students delivering health care to a vulnerable Appalachian population through interprofessional service-learning.  

PubMed

Interprofessional student service-learning experiences are integrated into the preventive care of older adult residents of public housing in Appalachia. Receiving a Health Resources and Services Administration grant provided the College of Nursing at East Tennessee State University the opportunity to expand interprofessional clinical experiences for students by partnering with the College of Pharmacy, the College of Clinical & Rehabilitative Health Sciences, and the local public housing authority. Select faculty from each college met and developed a plan to form student teams from all three colleges to conduct in-home comprehensive medical and nutrition assessments and medication chart reviews of high-risk older adults. Following the in-home visit, students and faculty discuss the assessment findings at planned interprofessional meetings. Students present their findings from each discipline's perspective and collaboratively set health priorities and develop intervention strategies and an inclusive follow-up plan. Excerpts from students' reflective narratives discussing the impact of the interprofessional service-learning experiences are shared. PMID:23362854

Lee, Michelle L; Hayes, Patricia A; McConnell, Peggy; Henry, Robin M

2013-01-01

283

Predicting Population Curves.  

ERIC Educational Resources Information Center

Uses graphs to involve students in inquiry-based population investigations on the Wisconsin gray wolf. Requires students to predict future changes in the wolf population, carrying capacity, and deer population. (YDS)

Bunton, Matt

2003-01-01

284

Writing to Learn Ecology: A Study of Three Populations of College Students  

ERIC Educational Resources Information Center

Being an ecologically literate citizen involves making decisions that are based on ecological knowledge and accepting responsibility for personal actions. Using writing-to-learn activities in college science courses, we asked students to consider personal dilemmas that they or others might have in response to how human choices can impact coastal…

Balgopal, Meena M.; Wallace, Alison M.; Dahlberg, Steven

2012-01-01

285

How One University Examined Graduation Rates of Its Undergraduate Student Population  

ERIC Educational Resources Information Center

The Office of Planning and Institutional Research (OPAIR), at the University of the West Indies, Mona Campus was asked to undertake an analysis of student throughput rates as part of a University-wide initiative involving the three campuses. Each Campus was provided with a template and guidelines for reporting the data. The exercise was intended…

Paterson, Nicola; Gordon, Garvin

2010-01-01

286

Educational Policy and the Growing Latino Student Population: Problems and Prospects  

Microsoft Academic Search

In this article, the authors contend that school reform proposals in the 1980s and 1990s have ignored the changing racial and ethnic complexion of our nation. An analysis is provided of the government's school reform responses to the rapidly growing Latino student sector. The authorsfirst provide a discussion and critique offive major assumptions of 'first wave\\

Pedro Reyes; Richard R. Valencia

1993-01-01

287

Students Delivering Health Care to a Vulnerable Appalachian Population through Interprofessional Service-Learning  

ERIC Educational Resources Information Center

Interprofessional student service-learning experiences are integrated into the preventive care of older adult residents of public housing in Appalachia. Receiving a Health Resources and Services Administration grant provided the College of Nursing at East Tennessee State University the opportunity to expand interprofessional clinical experiences…

Lee, Michelle L.; Hayes, Patricia A.; McConnell, Peggy; Henry, Robin M.

2013-01-01

288

English Language Learners: Experiences of Teachers of Students with Visual Impairments Who Work with This Population  

ERIC Educational Resources Information Center

Introduction: This article presents a study that gathered data from 66 teachers of students with visual impairments about their preparation to work with children who are visually impaired and are learning English, and their knowledge of instructional strategies and methods of instruction. Methods: An online five-part survey was available to…

Topor, Irene; Rosenblum, L. Penny

2013-01-01

289

The Inventory of College Students' Recent Life Experiences: A decontaminated hassles scale for a special population  

Microsoft Academic Search

The development and validation of a new decontaminated hassles measure, the Inventory of College Students' Recent Life Experiences, are described. An initial pool of 85 items was administered to 100 undergraduates along with the Perceived Stress Scale. Forty-nine items were selected based on significant correlations against the Perceived Stress Scale. The alpha reliability of the resultant final form of the

Paul M. Kohn; Kathryn Lafreniere; Maria Gurevich

1990-01-01

290

Considerations for Changing Populations: Supporting Nontraditional Students in Acquiring Special Education Licensure.  

ERIC Educational Resources Information Center

This article describes a program at the University of Hawaii that recruits individuals with training in general education for a special education certification program. Program features include strategies for aligning course and field requirements and the infusion of cultural and linguistic considerations of the school population. (Contains…

Ornelles, Cecily; Goetz, Lori

2001-01-01

291

Evidence of hearing loss in a “normally-hearing” college-student population  

PubMed Central

We report pure-tone hearing threshold findings in 56 college students. All subjects reported normal hearing during telephone interviews, yet not all subjects had normal sensitivity as defined by well-accepted criteria. At one or more test frequencies (0.25–8 kHz), 7% of ears had thresholds ?25 dB HL and 12% had thresholds ?20 dB HL. The proportion of ears with abnormal findings decreased when three-frequency pure-tone-averages were used. Low-frequency PTA hearing loss was detected in 2.7% of ears and high-frequency PTA hearing loss was detected in 7.1% of ears; however, there was little evidence for “notched” audiograms. There was a statistically reliable relationship in which personal music player use was correlated with decreased hearing status in male subjects. Routine screening and education regarding hearing loss risk factors are critical as college students do not always self-identify early changes in hearing. Large-scale systematic investigations of college students’ hearing status appear to be warranted; the current sample size was not adequate to precisely measure potential contributions of different sound sources to the elevated thresholds measured in some subjects. PMID:21288064

Le Prell, C. G.; Hensley, B.N.; Campbell, K. C. M.; Hall, J. W.; Guire, K.

2011-01-01

292

Identification of repeat sequence heterogeneity at the polymorphic short tandem repeat locus HUMTH01[AATG][sub n] and reassignment of alleles in population analysis by using a locus-specific allelic ladder  

SciTech Connect

An allelic ladder containing amplified sequences of seven alleles of the polymorphic human tyrosine hydroxylase locus, HUMTH01, was constructed and employed as a standard marker. Sequence analysis of each ladder component indicates that fragments differ by integral multiples of the AATG core repeat sequence characteristic of this locus. Individual alles are designated [open quotes]5[close quotes] through [open quotes]11,[close quotes] according to the number of complete reiterations of the core repeat contained within them. Comparison of the HUMTH01 allelic ladder with DNA samples amplified at this locus revealed core repeat length heterogeneity (i.e., deletions or insertions shorter than one core repeat) within the human population. In particular, a common allele was identified which migrates more quickly than allele 10, but more slowly than allele 9, on electrophoresis through a denaturing polyacrylamide gel. Sequence analysis of this allele, designated [open quotes]10-1,[close quotes] reveals lack of a single adenine normally present in the seventh copy of the AATG. The allelic ladder was used to reevaluate previously published population data. Results of testing for Hardy-Weinberg equilibrium and population substructure were not altered significantly by these modifications. 29 refs., 1 fig., 3 tabs.

Puers, C. (Institute for Forensic Medicine, Muenster (Germany)); Schumm, J.W. (Promega Corp., Madison, WI (United States)); Hammond, H.A.; Caskey, C.T.; Jin, L.

1993-10-01

293

Competition for space in a heterogeneous environment  

Microsoft Academic Search

We consider effects of competition for space in a heterogeneous environment, making use of nonlinear interaction-diffusion equations. Competition for space is assumed to mean mutual repulsive interactions that force other individuals to disperse from a crowded region. In other words, we are concerned with density-dependent dispersal forced by population pressures. Spatial heterogeneity is incorporated in the growth rates, and the

T. Namba

1989-01-01

294

Host heterogeneity dominates West Nile virus transmission  

Microsoft Academic Search

Heterogeneity in host populations and communities can have large effects on the transmission and control of a pathogen. In extreme cases, a few individuals give rise to the majority of secondary infections, which have been termed super spreading events. Here, we show that transmission of West Nile virus (WNV) is dominated by extreme heterogeneity in the host community, resulting in

A. Marm Kilpatrick; Peter Daszak; Matthew J. Jones; Peter P. Marra; Laura D. Kramer

2006-01-01

295

Explanations of sleep paralysis among Egyptian college students and the general population in Egypt and Denmark.  

PubMed

This cross-cultural study compared explanations of sleep paralysis (SP) in two countries and two groups with different levels of education in one country. Comparisons were made between individuals having experienced SP at least once in a lifetime from Cairo, Egypt (n?=?89), Copenhagen, Denmark (n?=?59), and the American University in Cairo, Egypt (n?=?44). As hypothesized, participants from the general Egyptian population were more likely to endorse supernatural causal explanation of their SP compared to participants from Denmark; participants from the American University in Cairo were less likely to endorse supernatural causes of their SP compared to participants from the general Egyptian population. Moreover, participants from the American University in Cairo were marginally significantly more likely to endorse supernatural causes of their SP compared to participants from Denmark. Additionally, we explored which culturally bound explanations and beliefs about SP existed in Egypt and Denmark. We found that nearly half (48%) of the participants from the general Egyptian population believed their SP to be caused by the Jinn, a spirit-like creature with roots in Islamic tradition, which constitutes a culturally bound interpretation of the phenomenology of SP in this region of the world. Case studies are presented to illustrate these findings. PMID:24084761

Jalal, Baland; Simons-Rudolph, Joseph; Jalal, Bamo; Hinton, Devon E

2014-04-01

296

On the definition and the computation of the basic reproduction ratio R 0 in models for infectious diseases in heterogeneous populations  

Microsoft Academic Search

The expected number of secondary cases produced by a typical infected individual during its entire period of infectiousness in a completely susceptible population is mathematically defined as the dominant eigenvalue of a positive linear operator. It is shown that in certain special cases one can easily compute or estimate this eigenvalue. Several examples involving various structuring variables like age, sexual

O. Diekmann; J. A. P. Heesterbeek; J. A. J. Metz

1990-01-01

297

On the definition and the computation of the basic reproduction ratio R0 in models for infectious diseases in heterogeneous populations  

Microsoft Academic Search

The expected number of secondary cases produced by a typical infected individual during its entire period of infectiousness in a completely susceptible population is mathematically defined as the dominant eigenvalue of a positive linear operator. It is shown that in certain special cases one can easily compute or estimate this eigenvalue. Several examples involving various structuring variables like age, sexual

O. Diekmann; J. A. P. Heesterbeek; J. A. J. Metz

1990-01-01

298

Population Explosion  

NSDL National Science Digital Library

A series of experiments explore the effects of increased population growth on a population of Fast Plants. Through these inquiries, students will better understand the many substantial and pertinent issues surrounding human population explosion on Earth.These experiments can be adjusted toward middle, high school or post-secondary levels.

The Wisconsin Fast Plants Program

299

How is an Electronic Screening and Brief Intervention Tool on Alcohol Use Received in a Student Population? A Qualitative and Quantitative Evaluation  

PubMed Central

Background A previous study among Antwerp college and university students showed that more male (10.2%–11.1%) than female (1.8%–6.2%) students are at risk for problematic alcohol use. The current literature shows promising results in terms of feasibility and effectiveness for the use of brief electronic interventions to address this health problem in college and university students. We evaluated this type of intervention and cite existing literature on the topic. Objective To develop a website, www.eentjeteveel.be, to motivate college and university students with problematic alcohol use to reduce alcohol consumption and increase their willingness to seek help. Method The website contained a questionnaire (Alcohol Use Disorders Identification Test [AUDIT]) for students to test their alcohol use. According to their answers, the students immediately received personalized feedback (personal AUDIT score and additional information on risks associated with alcohol use) and a suggestion for further action. Afterward, students could send an email to a student counselor for questions, guidance, or advice. To obtain in-depth qualitative information on the opinions and experiences of students, we held 5 focus group discussions. The topics were publicity, experiences, impressions, and effects of the website. We analyzed the quantitative results of the online test in SPSS 15.0. Results More than 3500 students visited www.eentjeteveel.be; over half were men (55.0%). A total of 34 students participated in the focus group discussions. The mixture of quantitative and qualitative methods to evaluate the intervention allowed a thorough analysis and provided complementary results. The intervention was well received by the student population. However, some minor aspects should be reconsidered, such as website publicity and providing students with options that were added after intermediate evaluation. The intervention increased the motivation of students to think about their alcohol use but could not stimulate them to change their behavior. The website attracted relatively more male than female students and more students in the high-risk group than in the low-risk group. The high-risk group was more inclined to seek advice or guidance (23/400, 6%; ?2 2 = 32.4, P < .001) than the low-risk group (34/1714, 2%; ?2 2 = 32.4, P < .001). Conclusions We gained unique insight into students’ experiences, opinions, and perceptions with regard to the intervention. The results show that the intervention was positively received in the population, and the willingness to seek help was increased. However, real behavior change needs further research. The results of this study can assist health providers and researchers in better understanding college and university students’ perceptions of eHealth initiatives. PMID:22525340

Van Royen, Paul; Vriesacker, Bart; De Mey, Leen; Van Hal, Guido

2012-01-01

300

Tobacco Smoking in HIV-Infected versus General Population in France: Heterogeneity across the Various Groups of People Living with HIV  

PubMed Central

Background Although the various groups of people living with HIV (PLWHIV) considerably differ regarding socioeconomic and behavioral characteristics, their specificities regarding tobacco smoking have been poorly investigated. We aimed to assess patterns of tobacco consumption across the various groups of PLWHIV and to compare them to the general population, accounting for the specific socioeconomic profile of PLWHIV. Methods We used data of the ANRS-Vespa2 study, a national representative survey on PLWHIV conducted in France in 2011. Prevalence of past and current tobacco consumption, heavy smoking and strong nicotine dependence were assessed among the various groups of PLWHIV as defined by transmission category, gender and geographic origin, and compared to the French general population using direct standardization and multivariate Poisson regression models, accounting for gender, age, education and geographic origin. Results Among the 3,019 participants aged 18–85 years (median time since HIV diagnosis: 12 years), 37.5% were current smokers and 22.1% were past smokers, with marked differences across the various groups of PLWHIV. Compared to the general population, the prevalence of regular smoking was increased among HIV-infected men who have sex with men (MSM) (adjusted prevalence rate ratio (aPRR): 1.19, 95% confidence interval (95% CI): 1.07–1.32), French-native women (aPRR: 1.32, 95% CI: 1.10–1.57), and heterosexual French-native men (although not significantly, aPRR: 1.19, 95% CI: 0.98–1.45). Additionally, HIV-infected MSM were significantly less likely to be ex-smokers (aPRR: 0.73, 95% CI: 0.64–0.82) than the general population and similar trends were observed among heterosexual French-native men (aPRR: 0.89, 95% CI: 0.78–1.02) and women (aPRR: 0.84, 95% CI: 0.70–1.01). HIV-infected sub-Saharan African migrants were less likely to be regular smokers than the general population. Conclusions Smoking constitutes a major concern in various groups of PLWHIV in France including MSM and heterosexual French-natives, probably resulting from PLWHIV being less likely to quit smoking than their counterparts in the general population. PMID:25202968

Tron, Laure; Lert, France; Spire, Bruno; Dray-Spira, Rosemary

2014-01-01

301

Managing heterogeneity in prescription drug coverage policies.  

PubMed

Necessity and fairness require that health plans limit the products and services they cover. The basis for these decisions refers to population averages and related population parameters. However, individuals vary and may not be accurately represented by the parameters used to establish coverage policies. Health plans, therefore, are obligated to anticipate and manage heterogeneity among their member groups. This commentary offers considerations for managing heterogeneity in prescription drug benefits. PMID:24856594

Teagarden, J Russell

2014-06-01

302

Noise and Neuronal Heterogeneity  

E-print Network

We consider signal transaction in a simple neuronal model featuring intrinsic noise. The presence of noise limits the precision of neural responses and impacts the quality of neural signal transduction. We assess the signal transduction quality in relation to the level of noise, and show it to be maximized by a non-zero level of noise, analogous to the stochastic resonance effect. The quality enhancement occurs for a finite range of stimuli to a single neuron; we show how to construct networks of neurons that extend the range. The range increases more rapidly with network size when we make use of heterogeneous populations of neurons with a variety of thresholds, rather than homogeneous populations of neurons all with the same threshold. The limited precision of neural responses thus can have a direct effect on the optimal network structure, with diverse functional properties of the constituent neurons supporting an economical information processing strategy that reduces the metabolic costs of handling a broad...

Barber, Michael J

2010-01-01

303

Stoichiometry and population dynamics  

Microsoft Academic Search

Population dynamics theory forms the quantitative core from which most ecologists have developed their intuition about how species interactions, heterogeneity, and biodiversity play out in time. Throughout its development, theoretical population biology has built on variants of the Lotka-Volterra equations and in nearly all cases has taken a single-currency approach to understanding population change, abstracting populations as aggregations of individuals

Tom Andersen; James J. Elser; Dag O. Hessen

2004-01-01

304

Multi-event capture–recapture modeling of host–pathogen dynamics among European rabbit populations exposed to myxoma and Rabbit Hemorrhagic Disease Viruses: common and heterogeneous patterns  

PubMed Central

Host–pathogen epidemiological processes are often unclear due both to their complexity and over-simplistic approaches used to quantify them. We applied a multi-event capture–recapture procedure on two years of data from three rabbit populations to test hypotheses about the effects on survival of, and the dynamics of host immunity to, both myxoma virus and Rabbit Hemorrhagic Disease Virus (MV and RHDV). Although the populations shared the same climatic and management conditions, MV and RHDV dynamics varied greatly among them; MV and RHDV seroprevalences were positively related to density in one population, but RHDV seroprevalence was negatively related to density in another. In addition, (i) juvenile survival was most often negatively related to seropositivity, (ii) RHDV seropositives never had considerably higher survival, and (iii) seroconversion to seropositivity was more likely than the reverse. We suggest seropositivity affects survival depending on trade-offs among antibody protection, immunosuppression and virus lethality. Negative effects of seropositivity might be greater on juveniles due to their immature immune system. Also, while RHDV directly affects survival through the hemorrhagic syndrome, MV lack of direct lethal effects means that interactions influencing survival are likely to be more complex. Multi-event modeling allowed us to quantify patterns of host–pathogen dynamics otherwise difficult to discern. Such an approach offers a promising tool to shed light on causative mechanisms. PMID:24708296

2014-01-01

305

Psychosocial factors and reading difficulties: students with reading difficulties drawn from a representative population sample.  

PubMed

In a representative sample of 2,464 Norwegian adolescents, aged 12-15 years, 7.8% (n= 191) reported reading difficulties (RD). No gender difference was found. Adolescents with RD were compared to classmates on psychosocial variables. In univariate analysis, RD adolescents report higher levels of depressive symptoms, more school stress, worried more about going to school, had lower school grades and lower attachment to parents than those without RD. They also scored lower on Global Self-worth and on Social Acceptance scales. Further, they reported reduced levels of psycho-functioning during the previous year because of mental health problems, they had received more help and had used more medication for such problems. In a multivariate logistic regression analysis, receiving help for mental health problems and reduced psycho-functioning showed the strongest associations with student RD status. No gender interactions were found. The study demonstrated important differences between adolescents with and without RD. PMID:18466186

Undheim, Anne Mari; Sund, Anne Mari

2008-08-01

306

How two Chicago public schools are changing to meet the needs of a diverse student population  

SciTech Connect

The Chicago Public School System contains a wide range of high schools, which, even with the same funding sources and operating principles, have different levels of educational resources available to be focused on each educational activity. However, the basic curriculum objectives for each subject are the same across the system. Across all these approaches, a basic core curriculum is required to be met and outcome standards achieved. The Illinois Goal Assessment Program has forced all schools to look at their curriculum to re-evaluate what they are teaching and why. Algebra should include data analysis and statistics. Geometry is moving moving from proof writing to application. In the inner city, neighborhood, and selective schools, real efforts are being made to make mathematics accessible to all students.

Murphy, P.; Slaughter, R. (Chicago Public Schools, IL (United States))

1992-01-01

307

Bird Populations  

NSDL National Science Digital Library

In this lesson, students will study bird migratory patterns and the methods that researchers use to study them. Students will be introduced to the concepts of the study of bird movements. The lesson is given in two parts: 1) gathering data about bird populations, and 2) monitoring the movements of bird populations.To assess student learning, they will write a short answer essay explaining the differences between the four types of population movements described in the Movements of Bird Populations resource. Students should be able to describe what kinds of patterns might be observed in each type and how observing and studying each pattern gives scientists the evidence they need to understand the movement of bird populations.

American Association for the Advancement of Science (; )

2005-06-23

308

Population Growth  

NSDL National Science Digital Library

This series of activities explores the mathematical and environmental aspects of population growth. Using archived census and demographic data as well as up-to-the-minute population estimates from the U.S. Census Bureau, students learn how to model population growth and study the implications of a changing population. The project provides instructions, activities, back-up information, data links, reference materials, on-line help, and an instructor guide. Although intended for high school students, activities 1 through 5 and 9 avoid higher mathematics and offer students work on statistical and historical aspects of population growth appropriate for the middle school level. This on-line project is part of the Center for Improved Engineering and Science Education (CIESE) program, which has developed internet activities for the elementary, middle, and high school level student.

2007-12-12

309

Heterogeneity in Pseudomonas aeruginosa Biofilms Includes Expression of Ribosome Hibernation Factors in the Antibiotic-Tolerant Subpopulation and Hypoxia-Induced Stress Response in the Metabolically Active Population  

PubMed Central

Bacteria growing in biofilms are physiologically heterogeneous, due in part to their adaptation to local environmental conditions. Here, we characterized the local transcriptome responses of Pseudomonas aeruginosa growing in biofilms by using a microarray analysis of isolated biofilm subpopulations. The results demonstrated that cells at the top of the biofilms had high mRNA abundances for genes involved in general metabolic functions, while mRNA levels for these housekeeping genes were low in cells at the bottom of the biofilms. Selective green fluorescent protein (GFP) labeling showed that cells at the top of the biofilm were actively dividing. However, the dividing cells had high mRNA levels for genes regulated by the hypoxia-induced regulator Anr. Slow-growing cells deep in the biofilms had little expression of Anr-regulated genes and may have experienced long-term anoxia. Transcripts for ribosomal proteins were associated primarily with the metabolically active cell fraction, while ribosomal RNAs were abundant throughout the biofilms, indicating that ribosomes are stably maintained even in slowly growing cells. Consistent with these results was the identification of mRNAs for ribosome hibernation factors (the rmf and PA4463 genes) at the bottom of the biofilms. The dormant biofilm cells of a P. aeruginosa ?rmf strain had decreased membrane integrity, as shown by propidium iodide staining. Using selective GFP labeling and cell sorting, we show that the dividing cells are more susceptible to killing by tobramycin and ciprofloxacin. The results demonstrate that in thick P. aeruginosa biofilms, cells are physiologically distinct spatially, with cells deep in the biofilm in a viable but antibiotic-tolerant slow-growth state. PMID:22343293

Williamson, Kerry S.; Richards, Lee A.; Perez-Osorio, Ailyn C.; Pitts, Betsey; McInnerney, Kathleen; Stewart, Philip S.

2012-01-01

310

Prevalence of atopy in a population of hairdressing students and practising hairdressers in Melbourne, Australia.  

PubMed

Hairdressers are one of the largest groups affected by occupational contact dermatitis. In this population-based study, 193 trainee hairdressers and 184 practising hairdressers each completed a questionnaire and had their hands examined. Participants were asked about past or present atopy including eczema, asthma or hayfever, which occurred in 59.2%, and were individually correlated with a history of occupational skin problems. Almost 60% of hairdressers and trainees had experienced changes on their hands since commencing hairdressing, while 29% had evidence of abnormal skin on examination on the day of participation. Atopic individuals, who plan to work in a career such as hairdressing with known high rates of occupational contact dermatitis, should be advised to care for and protect their skin from the outset to prevent the development of this condition. There has been little awareness of this issue in Australia, despite longstanding knowledge of the association of hairdressing and contact dermatitis. PMID:16866997

Roberts, Hugh; Frowen, Kathryn; Sim, Malcolm; Nixon, Rosemary

2006-08-01

311

White blood cell count, sex and age are major determinants of heterogeneity of platelet indices in an adult general population: results from the MOLI-SANI project  

PubMed Central

Background The understanding of non-genetic regulation of platelet indices - platelet count, plateletcrit, mean platelet volume, and platelet distribution width - is limited. The association of these platelet indices with a number of biochemical, environmental and clinical variables was studied in a large cohort of the general population. Design and Methods Men and women (n=18,097, 52% women, 56±12 years) were randomly recruited from various villages in Molise (Italy) in the framework of the population-based cohort study “Moli-sani”. Hemochromocytometric analyses were performed using an automatic analyzer (Beckman Coulter, IL, Milan, Italy). Associations of platelet indices with dependent variables were investigated by multivariable linear regression analysis. Results Full models including age, sex, body mass index, blood pressure, smoking, menopause, white and red blood cell counts, mean corpuscular volume, D-dimers, C-reactive protein, high-density lipoproteins, low-density lipoproteins, triglycerides, glucose, and drug use explained 16%, 21%, 1.9% and 4.7% of platelet count, plateletcrit, mean platelet volume and platelet distribution width variability, respectively; variables that appeared to be most strongly associated were white blood cell count, age, and sex. Platelet count, mean platelet volume and plateletcrit were positively associated with white blood cell count, while platelet distribution width was negatively associated with white blood cell count. Platelet count and plateletcrit were also positively associated with C-reactive protein and D-dimers (P<0.0001). Each of the other variables, although associated with platelet indices in a statistically significant manner, only explained less than 0.5% of their variability. Platelet indices varied across Molise villages, independently of any other platelet count determinant or characteristics of the villages. Conclusions The association of platelet indices with white blood cell count, C-reactive protein and D-dimers in a general population underline the relation between platelets and inflammation. PMID:21546503

Santimone, Iolanda; Di Castelnuovo, Augusto; De Curtis, Amalia; Spinelli, Maria; Cugino, Daniela; Gianfagna, Francesco; Zito, Francesco; Donati, Maria Benedetta; Cerletti, Chiara; de Gaetano, Giovanni; Iacoviello, Licia

2011-01-01

312

Nerve terminals of squid photoreceptor neurons contain a heterogeneous population of mRNAs and translate a transfected reporter mRNA.  

PubMed

It is now well established that the distal structural/functional domains of the neuron contain 2a diverse population of mRNAs that program the local synthesis of protein. However, there is still a paucity of information on the composition and function of these mRNA populations in the adult nervous system. To generate empirically, hypotheses regarding the function of the local protein synthetic system, we have compared the mRNAs present in the squid giant axon and its parental cell bodies using differential mRNA display as an unbiased screen. The results of this screen facilitated the identification of 31 mRNAs that encoded cytoskeletal proteins, translation factors, ribosomal proteins, molecular motors, metabolic enzymes, nuclear-encoded mitochondrial mRNAs, and a molecular chaperone. Results of cell fractionation and RT-PCR analyses established that several of these mRNAs were present in polysomes present in the presynaptic nerve terminal of photoreceptor neurons, indicating that these mRNAs were being actively translated. Findings derived from in vitro transfection studies established that these isolated nerve terminals had the ability to translate a heterologous reporter mRNA. Based upon these data, it is hypothesized that the local protein synthetic system plays an important role in the maintenance/remodelling of the cytoarchitecture of the axon and nerve terminal, maintenance of the axon transport and mRNA translation systems, as well as contributing to the viability and function of the local mitochondria. PMID:15305855

Gioio, Anthony E; Lavina, Zeno Scotto; Jurkovicova, Dana; Zhang, Hengshan; Eyman, Maria; Giuditta, Antonio; Kaplan, Barry B

2004-08-01

313

Mentors Are from Venus and Mars: Exploring the Benefits of Homogeneous and Heterogeneous Gender Pairings in the Mentoring Relationships of Female Senior Student Affairs Officers  

ERIC Educational Resources Information Center

While the number of women entering the student affairs profession has increased, gender equity at the senior level of leadership remains elusive in the student affairs profession. In comparison to their presence in graduate preparation programs and lower levels of administration women continue to lag behind men in their rate of advancement to the…

Jarnagin, Lea Marie

2010-01-01

314

The fractionation experiment: reducing heterogeneity to investigate age-specific mortality in Drosophila  

Microsoft Academic Search

Age-specific mortality rates decelerate at older ages in both genetically homogenous and heterogeneous populations of Drosophila. One explanation proposed for deceleration is population heterogeneity. This hypothesis suggests that a population consists of sub-populations that differ in mortality characteristics and that the deceleration is the result of selective survival of stronger individuals. Here we describe an experiment that fractionates populations into

Aziz A. Khazaeli; Scott D. Pletcher; James W. Curtsinger

1998-01-01

315

The Nation's Report Card: Mega-States--An Analysis of Student Performance in the Five Most Heavily Populated States in the Nation. NCES 2013-450  

ERIC Educational Resources Information Center

California, Florida, Illinois, New York, and Texas enroll close to 40 percent of the nation's public school students. The importance of these "Mega-States" goes beyond the sheer size of their population. They now serve more than half of the nation's English language learners (ELL), as well as some of the largest concentrations of children from…

National Center for Education Statistics, 2013

2013-01-01

316

Postsecondary Educational Decision-Making among First-Generation College-Bound Students in Okinawa Prefecture, with Consideration of the Population Problem in Japan  

ERIC Educational Resources Information Center

In correspondence to an overall decline in the Japanese population, the number of young students in Japan has been dramatically decreasing to the extent that the Japanese government has predicted a situation in which as of 2009 admissions places in Japanese universities will be equal to the number of applicants. Currently, approximately fifty…

Amaki, Yuki

2010-01-01

317

The use of full-spectrum lighting to enhance academic achievement, attendance, sense of well being, and on-task behavior in the special education student population  

Microsoft Academic Search

The purpose of this study was to investigate the use of full spectrum lighting as a way of enhancing academic achievement, attendance, sense of well being, and on task behavior in the special education middle school student population.^ The study lasted thirty days and involved six resource classrooms from two middle schools located in the southeastern region of the United

Andrew Bruce Battles

2006-01-01

318

Changes in Student Populations and Teacher Workforce in Low-Performing Chicago Schools Targeted for Reform. Summary. Issues & Answers. REL 2012-No. 123  

ERIC Educational Resources Information Center

"Turning around" chronically low-performing schools is of increasing interest to educators and policymakers, as highlighted by the U.S. Department of Education's (2010) recent call to rapidly improve the nation's 5,000 lowest performing schools. Yet there is little rigorous research on changes in student populations and teacher workforce in…

de la Torre, Marisa; Allensworth, Elaine; Jagesic, Sanja; Sebastian, James; Salmonowicz, Michael; Meyers, Coby; Gerdeman, R. Dean

2012-01-01

319

Changes in Student Populations and Teacher Workforce in Low-Performing Chicago Schools Targeted for Reform. Issues & Answers. REL 2012-No. 123  

ERIC Educational Resources Information Center

"Turning around" chronically low-performing schools is of increasing interest to educators and policymakers, as highlighted by the U.S. Department of Education's (2010) recent call to rapidly improve the nation's 5,000 lowest performing schools. Yet there is little rigorous research on changes in student populations and teacher workforce in…

de la Torre, Marisa; Allensworth, Elaine; Jagesic, Sanja; Sebastian, James; Salmonowicz, Michael; Meyers, Coby; Gerdeman, R. Dean

2012-01-01

320

Resource heterogeneity can facilitate cooperation  

PubMed Central

Although social structure is known to promote cooperation, by locally exposing selfish agents to their own deeds, studies to date assumed that all agents have access to the same level of resources. This is clearly unrealistic. Here we find that cooperation can be maintained when some agents have access to more resources than others. Cooperation can then emerge even in populations in which the temptation to defect is so strong that players would act fully selfishly if their resources were distributed uniformly. Resource heterogeneity can thus be crucial for the emergence and maintenance of cooperation. We also show that resource heterogeneity can hinder cooperation once the temptation to defect is significantly lowered. In all cases, the level of cooperation can be maximized by managing resource heterogeneity. PMID:24088665

Kun, Ádám; Dieckmann, Ulf

2013-01-01

321

Heterogeneous pumice populations in the 2.08-Ma Cerro Galán Ignimbrite: Implications for magma recharge and ascent preceding a large-volume silicic eruption  

USGS Publications Warehouse

Triggering mechanisms of large silicic eruptions remain a critical unsolved problem. We address this question for the ~2.08-Ma caldera-forming eruption of Cerro Galán volcano, Argentina, which produced distinct pumice populations of two colors: grey (5%) and white (95%) that we believe may hold clues to the onset of eruptive activity. We demonstrate that the color variations correspond to both textural and compositional variations between the clast types. Both pumice types have bulk compositions of high-K, high-silica dacite to low-silica rhyolite, but there are sufficient compositional differences (e.g., ~150 ppm lower Ba at equivalent SiO2 content and 0.03 wt.% higher TiO2 in white pumice than grey) to suggest that the two pumice populations are not related by simple fractionation. Trace element concentrations in crystals mimic bulk variations between clast types, with grey pumice containing elevated Ba, Cu, Pb, and Zn concentrations in both bulk samples (average Cu, Pb, and Zn concentrations are 27, 35, and 82 in grey pumice vs. 11, 19, and 60 in white pumice) and biotite phenocrysts and white pumice showing elevated Li concentrations in biotite and plagioclase phenocrysts. White and grey clasts are also texturally distinct: White pumice clasts contain abundant phenocrysts (44–57%), lack microlites, and have highly evolved groundmass glass compositions (76.4–79.6 wt.% SiO2), whereas grey pumice clasts contain a lower percentage of phenocrysts/microphenocrysts (35–49%), have abundant microlites, and have less evolved groundmass glass compositions (69.4–73.8 wt.% SiO2). There is also evidence for crystal transfer between magma producing white and grey pumice. Thin highly evolved melt rims surround some fragmental crystals in grey pumice clasts and appear to have come from magma that produced white pumice. Furthermore, based on crystal compositions, white bands within banded pumice contain crystals originating in grey magma. Finally, only grey pumice clasts form breadcrusted surface textures. We interpret these compositional and textural variations to indicate distinct magma batches, where grey pumice originated from an originally deeper, more volatile-rich dacite recharge magma that ascended through and mingled with the volumetrically dominant, more highly crystalline chamber that produced white pumice. Shortly before eruption, the grey pumice magma stalled within shallow fractures, forming a vanguard magma phase whose ascent may have provided a trigger for eruption of the highly crystalline rhyodacite magma. We suggest that in the case of the Cerro Galán eruption, grey pumice provides evidence not only for cryptic silicic recharge in a large caldera system but also a probable trigger for the eruption.

Wright, Heather M.; Folkes, Christopher B.; Cas, Ray A.F.; Cashman, Katharine V.

2011-01-01

322

Deer Population  

NSDL National Science Digital Library

The deer population activity allows students to experiment with the factors which influence population dynamics. In their exploration, they encounter both exponential and logistic growth curves. Students should be familiar with the concepts of birth and death rates, emigration and immigration, predation, limiting factors such as food supply and habitat size, and carrying capacity. The activity is self-paced with extensions provided for those who have extra time.

Maryland Virtual High School

323

PERCEPTIONS OF THE CAPACITY FOR CHANGE AS A COMPONENT OF LEADERSHIP DEVELOPMENT AS REPORTED BY SELECT POPULATIONS OF COLLEGE STUDENTS: IMPLICATIONS FOR COLLEGE STUDENT LEADERSHIP DEVELOPMENT  

E-print Network

) were measured and analyzed to determine if any significant differences and/or interactions existed in the data. The results of this study inform the design of both Academic and Student Affairs student leadership development programs to enhance...

Durham Hynes, Sharra L.

2010-01-16

324

Academic Studies amid Violent Conflict: A Study of the Impact of Ongoing Conflict on a Student Population  

ERIC Educational Resources Information Center

This paper explores the impact of violent conflict on undergraduate students. In order to strengthen student resilience during periods of heightened insecurity, teachers and institutions must identify the difficulties that their students may be experiencing. Based on a case study of students in Israel, this paper identifies specific difficulties…

Ben-Tsur, Dalia

2009-01-01

325

Population Peril  

NSDL National Science Digital Library

Rising air temperatures have changed the extent and timing of sea ice formation in the Arctic, forcing some polar bear populations to go longer each year without food. In this activity, students assume the role of graduate students advising an intern part

Juanita Constible

2008-10-01

326

Conducting Research: Protocol for Collecting School or Student Data in a Public School System.  

ERIC Educational Resources Information Center

The Prince George's County Public School District is a multiculturally diverse district in Maryland serving a heterogeneous population of students, most of whom are black (70.3%) and many of whom qualify for free or reduced-price meals (40%). The school system welcomes the opportunity to participate in research projects, but has acknowledged its…

Reed, Jacqueline K.

327

Assessment of Cognitive Ability of Students with Severe and Low-Incidence Disabilities--Part 1  

ERIC Educational Resources Information Center

Students with severe and low-incidence disabilities comprise a heterogeneous population that often presents a challenge to the professionals charged with evaluating their skills and abilities. This is especially true in conducting a valid assessment of the cognitive ability of these children. Often, school psychologists are limited to the use of…

Crepeau-Hobson, Franci; Vujeva, Hana

2012-01-01

328

Population: Growth  

NSDL National Science Digital Library

This lesson discusses population growth, both in the United States and in the world. Topics include factors that influence population growth, such as government policy, religion, education or economic levels, energy use per capita, and whether a country is agrarian or industrial. The lesson includes an activity in which students research an online resource on population growth and answer questions as they navigate through its presentation.

Matt Laposata

329

Salience of Nationality in Students' Spontaneous Self-Concept: A Comparative Study of a Nationally Homogeneous and a Heterogeneous School Context  

ERIC Educational Resources Information Center

The study on which this article is based investigated the salience of nationality in adolescents' self-concept as a function of the diversity of the school context. According to the distinctiveness postulate, people selectively attend to and encode aspects that are most distinctive. We therefore predicted that students in the nationally…

Murdock, Elke; Hirt, Franziska S.; Ferring, Dieter

2014-01-01

330

An Evaluation of Behavioral Health Compliance and Microbial Risk Factors on Student Populations within a High-Density Campus  

ERIC Educational Resources Information Center

Objective: The aim of this Canadian study was to assess student behavioral response to disease transmission risk, while identifying high microbial deposition/transmission sites. Participants: A student survey was conducted during October 2009. Methods: The methods included a survey of students to assess use of health services, vaccination…

Decker, Jody F.; Slawson, Robin M.

2012-01-01

331

Effectiveness of the Brief Alcohol and Screening Intervention for College Students (BASICS) Program with a Mandated Population  

ERIC Educational Resources Information Center

Objective: This study evaluated the effectiveness of a large-scale intervention designed to reduce alcohol abuse among adjudicated college students. Participants: Participants were college students mandated to attend a Brief Alcohol Screening and Intervention for College Students (BASICS) program and a randomly selected comparison group of…

DiFulvio, Gloria T.; Linowski, Sally A.; Mazziotti, Janet S.; Puleo, Elaine

2012-01-01

332

The role of a student-run clinic in providing primary care for Calgary’s homeless populations: a qualitative study  

PubMed Central

Background Despite the increasing popularity of Student-Run Clinics (SRCs) in Canada, there is little existing literature exploring their role within the Canadian healthcare system. Generalizing American literature to Canadian SRCs is inappropriate, given significant differences in healthcare delivery between the two countries. Medical students at the University of Calgary started a SRC serving Calgary’s homeless population at the Calgary Drop-In and Rehabilitation Centre (CDIRC). This study explored stakeholders’ desired role for a SRC within Calgary’s primary healthcare system and potential barriers it may face. Methods Individual and group semi-structured interviews were undertaken with key stakeholders in the SRC project: clients (potential patients), CDIRC staff, staff from other stakeholder organizations, medical students, and faculty members. Convenience sampling was used in the recruitment of client participants. Interview transcripts were analyzed using a coding template which was derived from the literature. Results Participants identified factors related to the clinic and to medical students that suggest there is an important role for a SRC in Calgary. The clinic was cited as improving access to primary healthcare for individuals experiencing homelessness. It was suggested that students may be ideally suited to provide empathetic healthcare to this population. Barriers to success were identified, including continuity of care and the exclusion of some subsets of the homeless population due to location. Conclusions SRCs possess several unique features that may make them a potentially important primary healthcare resource for the homeless. Participants identified numerous benefits of the SRC to providing primary care for homeless individuals, as well as several important limitations that need to be accounted for when designing and implementing such a program. PMID:23866968

2013-01-01

333

Integrating web applications to provide an effective distance online learning environment for students  

Microsoft Academic Search

The Human Physiology online course offered by the Department of Physiology at the University of Toronto (www.physiology.utoronto.ca) offers a quality online learning experience and promotes flexibility to its students in terms of time and location, allowing self-directed learning within a semi-structured frame-work. The online course population has expanded, including a more heterogeneous group of students. In addition to the traditional

C. Perumalla; J. Mak; N. Kee; S. Matthews

2011-01-01

334

Monocyte and macrophage heterogeneity  

Microsoft Academic Search

Heterogeneity of the macrophage lineage has long been recognized and, in part, is a result of the specialization of tissue macrophages in particular microenvironments. Circulating monocytes give rise to mature macrophages and are also heterogeneous themselves, although the physiological relevance of this is not completely understood. However, as we discuss here, recent studies have shown that monocyte heterogeneity is conserved

Philip R. Taylor; Siamon Gordon

2005-01-01

335

A Mailed Diagnostic and Prescriptive Retention Intervention for Three At-Risk Populations of Students. Research Report #11-89.  

ERIC Educational Resources Information Center

Many at-risk college students fail to avail themselves of the resources provided for them by their universities. In the interest of academic retention, colleges and universities are taking an increasingly proactive stance and contacting at-risk students to offer them specific services. This study compared retention rates for at-risk freshman…

Boyd, Vivian; And Others

336

Dimensions of mental health: life satisfaction, anxiety and depression: a preventive mental health study in Ankara University students population  

Microsoft Academic Search

The main objective of this study is to investigate the interrelation between life satisfaction, anxiety, depression, and hopelessness among Ankara University students. 364 university students completed a test battery including the Beck Depression Inventory, the Beck Anxiety Inventory, the Hopelessness Scale and the Satisfaction with Life Scale. Life satisfaction was negatively and significantly correlated with the scores from depression, anxiety

Sevgi Guney; Temel Kalafat; Murat Boysan

2010-01-01

337

Are Student Veterans a Traditional, Nontraditional, or Special Population? A Study of Veterans on the Auburn University Campus  

ERIC Educational Resources Information Center

This non-experimental study used, with the Educational Testing Service's permission, an updated 1946 Student Opinion Questionnaire (originally designed to compare WWII veterans and nonveterans) to collect data regarding student backgrounds, attitudes and motives, worries and concerns, use of time, and perceptions of respect concerning nonveterans,…

Pattillo, Stephen Prescott

2011-01-01

338

Diffusion and Surface Reaction in Heterogeneous Catalysis  

ERIC Educational Resources Information Center

Ethylene hydrogenation on a platinum catalyst, electrolytically applied to a tube wall, is a good system for the study of the interactions between diffusion and surface reaction in heterogeneous catalysis. Theoretical background, apparatus, procedure, and student performance of this experiment are discussed. (BB)

Baiker, A.; Richarz, W.

1978-01-01

339

Coping with habitat heterogeneity: the story of Mediterranean blue tits  

Microsoft Academic Search

A prerequisite for understanding adaptation is to understand how populations respond to environmental heterogeneity. We chose\\u000a the blue tit Cyanistes caeruleus and Mediterranean habitat mosaics which exhibit a large diversity of habitats for analysing the effects of environmental\\u000a heterogeneity on phenotypic variation. Three main factors of heterogeneity have been considered: (1) whether dominant tree\\u000a species are deciduous or evergreen, (2)

Jacques Blondel

2007-01-01

340

Lipid rafts: heterogeneity on the high seas.  

PubMed Central

Lipid rafts are membrane microdomains that are enriched in cholesterol and glycosphingolipids. They have been implicated in processes as diverse as signal transduction, endocytosis and cholesterol trafficking. Recent evidence suggests that this diversity of function is accompanied by a diversity in the composition of lipid rafts. The rafts in cells appear to be heterogeneous both in terms of their protein and their lipid content, and can be localized to different regions of the cell. This review summarizes the data supporting the concept of heterogeneity among lipid rafts and outlines the evidence for cross-talk between raft components. Based on differences in the ways in which proteins interact with rafts, the Induced-Fit Model of Raft Heterogeneity is proposed to explain the establishment and maintenance of heterogeneity within raft populations. PMID:14662007

Pike, Linda J

2004-01-01

341

Population Projections: An Exercise for Population Geography.  

ERIC Educational Resources Information Center

Urges that college level geography students will develop greater appreciation of population projections when they are directly and systematically involved in making and using them. An exercise is described in which students are directed to make several population projections, compare their projections with published projections, and explain…

Peters, Gary L.

1980-01-01

342

Activation of a heterogeneous hepatitis B (HB) core and e antigen-specific CD4+ T-cell population during seroconversion to anti-HBe and anti-HBs in hepatitis B virus infection.  

PubMed

Overcoming hepatitis B virus infection essentially depends on the appropriate immune response of the infected host. Among the hepatitis B virus antigens, the core (HBcAg) and e (HBeAg) proteins appear highly immunogenic and induce important lymphocyte effector functions. In order to investigate the importance of HBcAg/HBeAg-specific T lymphocytes in patients with acute and chronic hepatitis B and to identify immunodominant epitopes within the HBcAg/HBeAg, CD4+ T-cell responses to hepatitis B virus-encoded HBcAg and HBcAg/HBeAg-derived peptides were studied in 49 patients with acute and 39 patients with chronic hepatitis B. The results show a frequent antigen-specific CD4+ T-cell activation during acute hepatitis B infection, a rare HBcAg/HBeAg-specific CD4+ T-cell response among HBeAg+ chronic carriers, and no response in patients with anti-HBe+ chronic hepatitis. An increasing CD4+ T-cell response to HBcAg/HBeAg coincides with loss of HBeAg and hepatitis B virus surface antigen (HBsAg). Functional analysis of peptide-specific CD4+ T-cell clones revealed a heterogeneous population with respect to lymphokine production. Epitope mapping within the HBcAg/HBeAg peptide defined amino acids (aa) 1 to 25 and aa 61 to 85, irrespective of the HLA haplotype, as the predominant CD4+ T-cell recognition sites. Other important sequences could be identified in the amino-terminal part of the protein, aa 21 to 45, aa 41 to 65, and aa 81 to 105. The immunodominant epitopes are expressed in both proteins, HBcAg and HBeAg. Our findings lead to the conclusion that activation of CD4+ T lymphocytes by HBcAg/HBeAg is a prerequisite for viral elimination, and further studies have to focus on the question of how to enhance or induce this type of T-cell response in chronic carriers. The immunodominant viral sequences identified may have relevance to synthetic vaccine design and to the use of peptide T-cell sites as immunotherapeutic agents in chronic infection. PMID:7538172

Jung, M C; Diepolder, H M; Spengler, U; Wierenga, E A; Zachoval, R; Hoffmann, R M; Eichenlaub, D; Frösner, G; Will, H; Pape, G R

1995-06-01

343

Meeting the Needs of Diverse Student Populations: Comprehensive Professional Development in Science, Math, and Technology for Teachers of Students with Disabilities.  

ERIC Educational Resources Information Center

Describes a model of professional development designed to improve the skills and knowledge of teams of special-education and regular-education teachers in science, mathematics, and technology instruction. The program led to the development of coping skills and persistence in science and mathematics teaching for all students. (Author/CCM)

Kimmel, Howard; Deek, Fadi P.; Farrell, Mary L.; O'Shea, Mark

1999-01-01

344

Interregional equilibrium with heterogeneous labor.  

PubMed

"The impact of labor migration on interregional equilibrium is studied when workers are heterogeneous in productivity and regional mobility. The skilled respond to market disequilibrium by moving into the most attractive region. The unskilled are immobile in the short-run and move with the skilled in the long-run. Both regions have a neoclassical production function affected by an externality depending on the number of skilled. Workers move according to the utility differential when regional amenities vary with population or according to the wage differential. The equilibrium pattern depends on the unskilled's mobility and on migration incentives. Typically, regional imbalance characterizes the equilibrium which is often suboptimal." PMID:12291408

Michel, P; Perrot, A; Thisse J-f

1996-02-01

345

The Evidence of Glioblastoma Heterogeneity  

PubMed Central

Cancers are composed of heterogeneous combinations of cells that exhibit distinct phenotypic characteristics and proliferative potentials. Because most cancers have a clonal origin, cancer stem cells (CSCs) must generate phenotypically diverse progenies including mature CSCs that can self-renew indefinitely and differentiated cancer cells that possess limited proliferative potential. However, no convincing evidence exists to suggest that only single CSCs are representative of patients' tumors. To investigate the CSCs' diversity, we established 4 subclones from a glioblastoma patient. These subclones were subsequently propagated and analyzed. The morphology, the self-renewal and proliferative capacities of the subclones differed. Fluorescence-activated cell sorting and cDNA-microarray analyses revealed that each subclone was composed of distinct populations of cells. Moreover, the sensitivities of the subclones to an inhibitor of epidermal growth factor receptor were dissimilar. In a mouse model featuring xenografts of the subclones, the progression and invasion of tumors and animal survival were also different. Here, we present clear evidence that a brain tumor contains heterogeneous subclones that exhibit dissimilar morphologies and self-renewal and proliferative capacities. Our results suggest that single cell-derived subclones from a patient can produce phenotypically heterogeneous self-renewing progenies in both in vitro and in vivo settings. PMID:25623281

Soeda, Akio; Hara, Akira; Kunisada, Takahiro; Yoshimura, Shin-ichi; Iwama, Toru; Park, Deric M.

2015-01-01

346

Neurobiological heterogeneity in ADHD  

Microsoft Academic Search

Attention-Deficit\\/Hyperactivity Disorder (ADHD) is a highly heterogeneous disorder clinically. Symptoms take many forms, from subtle but pervasive attention problems or dreaminess up to disruptive and unpredictable behavior. Interestingly, early neuroscientific work on ADHD assumed either a homogeneous neurobiological substrate or one that somehow mimicked clinical heterogeneity. Recent work however, has started to emphasize multiple neurobiological pathways towards ADHD, regardless of

P. de Zeeuw

2011-01-01

347

On the Relationship between Autistic Traits and Executive Functioning in a Non-Clinical Dutch Student Population  

ERIC Educational Resources Information Center

We examined the association between autistic traits and different aspects of executive functioning (EF), using non-clinical Social Science and Science students as participants. Autistic traits, and associated personality traits, were measured using the Autism Quotient (AQ) and the Temperament and Character Inventory (TCI), respectively. EF was…

Maes, Joseph HR; Vissers, Constance ThWM; Egger, Jos IM; Eling, Paul ATM

2013-01-01

348

The Paradoxes of Freedom: A Thematic Approach to Teaching a Compulsory Composition Course to a Multi-Ethnic Student Population.  

ERIC Educational Resources Information Center

A composition teacher at a New York City community college where cooperative education is stressed found that focusing the writing of his multiethnic students on the theme of freedom helped them look at their lives differently, revealing the contradictions involved in their beliefs, ideals, and prejudices. The course began with a discussion of…

Lynch, Daniel J.

349

Update of Project to Introduce Technology in Urban Schools Which Have Low Achievement and Economically Poor Student Populations  

ERIC Educational Resources Information Center

This document provides new insights into events which occurred in a project funded by a Technology Literacy Challenge Fund grant awarded by Michigan Department of Education(MDE) in 2000. One purpose of this document is to update the formal report of the project which introduced new technology for use by low achieving students who are studying in…

Smith, Gary R.

2009-01-01

350

Teaching for All--The Preparation of Student Teachers To Work with Diverse Populations in the Elementary School.  

ERIC Educational Resources Information Center

A literature review and analysis, and a case study of two "mainstream" student teachers working in a minority elementary school explored how teacher education prepares teachers to work in diverse settings. The literature review and analysis addressed both macro level issues (program policies) and micro level initiatives (specific studies of…

Valenciana, Christine

351

Genetic structure of human populations  

Microsoft Academic Search

The difficulty of extrapolating from inbred mouse strains used for the assessment of toxicological responses to the human population that may be exposed to the potentially toxic substance is discussed. Conventional risk estimation procedures assume little heterogeneity among members of the population in their response to a substance. This ignores the inherent genetic diversity present in human populations. Measurement of

William J. Schull

1979-01-01

352

Spatially correlated heterogeneous aspirations to enhance network reciprocity  

NASA Astrophysics Data System (ADS)

Perc & Wang demonstrated that aspiring to be the fittest under conditions of pairwise strategy updating enhances network reciprocity in structured populations playing 2×2 Prisoner's Dilemma games (Z. Wang, M. Perc, Aspiring to the fittest and promoted of cooperation in the Prisoner's Dilemma game, Physical Review E 82 (2010) 021115; M. Perc, Z. Wang, Heterogeneous aspiration promotes cooperation in the Prisoner's Dilemma game, PLOS one 5 (12) (2010) e15117). Through numerical simulations, this paper shows that network reciprocity is even greater if heterogeneous aspirations are imposed. We also suggest why heterogeneous aspiration fosters network reciprocity. It distributes strategy updating speed among agents in a manner that fortifies the initially allocated cooperators' clusters against invasion. This finding prompted us to further enhance the usual heterogeneous aspiration cases for heterogeneous network topologies. We find that a negative correlation between degree and aspiration level does extend cooperation among heterogeneously structured agents.

Tanimoto, Jun; Nakata, Makoto; Hagishima, Aya; Ikegaya, Naoki

2012-02-01

353

An administrative concern: Science teachers' instructional efficacy beliefs regarding racially, culturally, economically, and linguistically diverse student populations  

NASA Astrophysics Data System (ADS)

A teacher's sense of {instructional} efficacy has been considered a critical variable in student academic performance. Researchers Tschannen-Moran and Hoy Woolfolk (2001, p.783) defined teachers' {instructional} efficacy as a teacher's judgment of his or her capabilities to bring about desired outcomes of student engagement and learning, even among those students who may be difficult or unmotivated. There has been a substantial amount of research which reveals a strong correlation among teacher efficacy, teaching performance, and student achievement (Goddard & Goddard, et.al., 2000; Hackett; Hackett, 1995; Pajares, 1997 as cited in Villereal, 2005). This research study explored the content area of science and teacher's personal perception of their competency level in teaching science to all learners regardless of socio-economic, ethnicity/race or gender for grade levels Pre-K to 12. Lewthwaite states that a science teacher's personal teacher attributes or intrinsic factors such as science teaching self-efficacy, professional science knowledge, science teaching, instructional methodologies, interest in science, and motivation to teach science are critical dimensions and noted barriers in the delivery of science programs on elementary level campuses (Lewthwaite, Stableford & Fisher, 2001). This study focused on teacher instructional efficacy issues which may affect diverse learners' classroom and state-mandated assessment academic performance outcomes. A SPSS analysis of data was obtained from the following teacher survey instruments: The Bandura Teacher Efficacy Scale, the SEBEST, and the SETAKIST. Research findings revealed that a majority of science teachers surveyed believe they can effectively teach learners of diverse backgrounds, but responded with a sense of lower efficaciousness in teaching English Language Learners. There was also a statistically significant difference found between a state science organization and a national science organization's instructional efficacy beliefs in effectively teaching science content to females.

Tuck Bonner, Natalie Christine

354

Heterogeneous Atmospheric Chemistry  

NASA Astrophysics Data System (ADS)

In the past few years it has become increasingly clear that heterogeneous, or multiphase, processes play an important role in the atmosphere. Unfortunately the literature on the subject, although now fairly extensive, is still rather dispersed. Furthermore, much of the expertise regarding heterogeneous processes lies in fields not directly related to atmospheric science. Therefore, it seemed desirable to bring together for an exchange of ideas, information, and methodologies the various atmospheric scientists who are actively studying heterogeneous processes as well as other researchers studying similar processes in the context of other fields.

Schryer, David R.

355

Junior Biology, Populations.  

ERIC Educational Resources Information Center

Twenty-one studies related to populations are included in this student manual for a junior high school biology course. Each activity or study provides questions, diagrams, experiments, and/or descriptive material to which the student must respond. Population studies pertain to individual plants and animals, their physical environments, reactions…

Hamilton City Board of Education (Ontario).

356

Heterogeneous atmospheric chemistry  

NASA Technical Reports Server (NTRS)

The present conference on heterogeneous atmospheric chemistry considers such topics concerning clusters, particles and microparticles as common problems in nucleation and growth, chemical kinetics, and catalysis, chemical reactions with aerosols, electron beam studies of natural and anthropogenic microparticles, and structural studies employing molecular beam techniques, as well as such gas-solid interaction topics as photoassisted reactions, catalyzed photolysis, and heterogeneous catalysis. Also discussed are sulfur dioxide absorption, oxidation, and oxidation inhibition in falling drops, sulfur dioxide/water equilibria, the evidence for heterogeneous catalysis in the atmosphere, the importance of heterogeneous processes to tropospheric chemistry, soot-catalyzed atmospheric reactions, and the concentrations and mechanisms of formation of sulfate in the atmospheric boundary layer.

Schryer, D. R.

1982-01-01

357

Towards heterogeneous distributed debugging  

SciTech Connect

Several years of research and development in parallel debugger design have given up several techniques, though implemented in a wide range of tools for an equally wide range of systems. This paper is an evaluation of these myriad techniques as applied to the design of a heterogeneous distributed debugger. The evaluation is based on what features users perceive as useful, as well as the ease of implementation of the features using the available technology. A preliminary architecture for such a heterogeneous tool is proposed. Our effort in this paper is significantly different from the other efforts at creating portable and heterogeneous distributed debuggers in that we concentrate on support for all the important issues in parallel debugging, instead of simply concentrating on portability and heterogeneity.

Damodaran-Kamal, S.K.

1995-04-01

358

Population: Basic Statistics  

NSDL National Science Digital Library

This lesson reinforces the idea that Earth's population, including the population of the United States, is gowing at a dramatic rate. It discusses some of the basics of demography, the study of population and its changes, and introduces key terms used to describe a population. The lesson inlcudes an activity in which students use an online reference to look up some population statistics and answer questions related to them.

Ken Rhinehart

359

Characterization of Paper Heterogeneity  

NASA Astrophysics Data System (ADS)

Paper and paperboard are the most widely-used green materials in the world because they are renewable, recyclable, reusable, and compostable. Continued and expanded use of these materials and their potential use in new products requires a comprehensive understanding of the variability of their mechanical properties. This work develops new methods to characterize the mechanical properties of heterogeneous materials through a combination of techniques in experimental mechanics, materials science and numerical analysis. Current methods to analyze heterogeneous materials focus on crystalline materials or polymer-crystalline composites, where material boundaries are usually distinct. This work creates a methodology to analyze small, continuously-varying stiffness gradients in 100% polymer systems and is especially relevant to paper materials where factors influencing heterogeneity include local mass, fiber orientation, individual pulp fiber properties, local density, and drying restraint. A unique approach was used to understand the effect of heterogeneity on paper tensile strength. Additional variation was intentionally introduced, in the form of different size holes, and their effect on strength was measured. By modifying two strength criteria, an estimate of strength in the absence of heterogeneity was determined. In order to characterize stiffness heterogeneity, a novel load fixture was developed to excite full-field normal and shear strains for anisotropic stiffness determination. Surface strains were measured with digital image correlation and were analyzed with the VFM (Virtual Fields Method). This approach led to VFM-identified stiffnesses that were similar to values determined by conventional tests. The load fixture and VFM analyses were used to measure local stiffness and local stiffness variation on heterogeneous anisotropic materials. The approach was validated on simulated heterogeneous materials and was applied experimentally to three different paperboards. The analyses were used to create upper and lower stiffness bounds; the scale of the bounds were related to the coefficient of variations of stiffness and grammage variations. This work contributes to understanding of heterogeneous material behavior by characterizing strength loss due to variability and determining stiffness bounds in materials in which heterogeneity varies gradually and is complicated by several, interrelated physical properties.

Considine, John M.

360

Phylogenetic Quantification of Intra-tumour Heterogeneity  

PubMed Central

Intra-tumour genetic heterogeneity is the result of ongoing evolutionary change within each cancer. The expansion of genetically distinct sub-clonal populations may explain the emergence of drug resistance, and if so, would have prognostic and predictive utility. However, methods for objectively quantifying tumour heterogeneity have been missing and are particularly difficult to establish in cancers where predominant copy number variation prevents accurate phylogenetic reconstruction owing to horizontal dependencies caused by long and cascading genomic rearrangements. To address these challenges, we present MEDICC, a method for phylogenetic reconstruction and heterogeneity quantification based on a Minimum Event Distance for Intra-tumour Copy-number Comparisons. Using a transducer-based pairwise comparison function, we determine optimal phasing of major and minor alleles, as well as evolutionary distances between samples, and are able to reconstruct ancestral genomes. Rigorous simulations and an extensive clinical study show the power of our method, which outperforms state-of-the-art competitors in reconstruction accuracy, and additionally allows unbiased numerical quantification of tumour heterogeneity. Accurate quantification and evolutionary inference are essential to understand the functional consequences of tumour heterogeneity. The MEDICC algorithms are independent of the experimental techniques used and are applicable to both next-generation sequencing and array CGH data. PMID:24743184

Schwarz, Roland F.; Trinh, Anne; Sipos, Botond; Brenton, James D.; Goldman, Nick; Markowetz, Florian

2014-01-01

361

A Study of Adolescents Who Provide Tobacco to Other Adolescents in a Racial\\/Ethnic Diverse Population  

Microsoft Academic Search

This study examined the sources of tobacco and the adolescent provision of tobacco to other adolescents in an ethnically\\/racially diverse, large heterogeneous urban, adolescent population in Philadelphia, Pennsylvania. A stratified multistage purposive sampling procedure was used to select an ethnically\\/racially diverse sample, which consisted of 569 students in grades 8-10 in five public and nonpublic funded schools. A logistical regression

Steven E. Shive; Grace X. Ma; Patricia M. Legos; Earl S. Shive

2003-01-01

362

Motives for eating tasty foods associated with binge-eating. Results from a student and a weight-loss seeking population.  

PubMed

The aim of this study was to use the Palatable Eating Motives Scale (PEMS) to determine if and what motives for eating tasty foods (e.g., junk food, fast food, and desserts) are associated with binge-eating in two diverse populations. BMI and scores on the PEMS, Yale Food Addiction Scale (YFAS), and Binge-eating Scale (BES) were obtained from 247 undergraduates at the University of Alabama at Birmingham (UAB) and 249 weight-loss seeking patients at the UAB EatRight program. Regression analyses revealed that eating tasty foods to forget worries and problems and help alleviate negative feelings (i.e., the 4-item Coping motive) was associated with binge-eating independently of any variance in BES scores due to sex, age, ethnicity, BMI, other PEMS motives, and YFAS scores in both students (R(2)?=?.57) and patients (R(2)?=?.55). Coping also was associated with higher BMI in students (p?students, the motives Conformity and Reward Enhancement were also independently associated with binge-eating. For this younger sample with a greater range of BES scores, eating for these motives, but not for Social ones, may indicate early maladaptive eating habits that could later develop into disorders characterized by binge-eating if predisposing factors are present. Thus, identifying one's tasty food motive or motives can potentially be used to thwart the development of BED and obesity, especially if the motive is Coping. Identifying one's PEMS motives should also help personalize conventional treatments for binge-eating and obesity toward improved outcomes. PMID:25169880

Boggiano, M M; Burgess, E E; Turan, B; Soleymani, T; Daniel, S; Vinson, L D; Lokken, K L; Wingo, B C; Morse, A

2014-12-01

363

Teaching about Population Issues.  

ERIC Educational Resources Information Center

This teaching guide on population issues contains 19 activities for students in grades 7-12. The objective is to analyze population issues that have resulted from human population dynamics. In this guide, four categories of activities are included: some are discussion starters, some provide factual data, some focus on thinking skills, and some are…

Otero, George G., Jr., Comp.

364

Individual heterogeneity and identifiability in capture?recapture models  

USGS Publications Warehouse

Individual heterogeneity in detection probabilities is a far more serious problem for capture?recapture modeling than has previously been recognized. In this note, I illustrate that population size is not an identifiable parameter under the general closed population mark?recapture model Mh. The problem of identifiability is obvious if the population includes individuals with pi= 0, but persists even when it is assumed that individual detection probabilities are bounded away from zero. Identifiability may be attained within parametric families of distributions for pi, but not among parametric families of distributions. Consequently, in the presence of individual heterogeneity in detection probability, capture?recapture analysis is strongly model dependent.

Link, W.A.

2004-01-01

365

Emerging heterogeneities in Italian customs  

E-print Network

Since its unification, more than a century ago, Italy has experienced strong social and economical diversities between its southern and northern regions. In the last decades, Italy has undergone a severe economical and political crisis reflecting corruption at various levels of social stratification as well as a poor involvement of its population in the number of elections that occurred. This might be explained by a lack of confidence, or interest in the country as a whole, as if the primary social and political focus of its citizens could still lay at smaller regional scales, possibly evidencing the persistence of different cultural heritages. In order to shed lights on the possible existence of such heterogeneities, we perform a statistical-mechanics-driven analysis focusing on key social quantifiers, namely the evolution of autochthonous marriages (as family still plays as a fundamental brick in the edification of social aggregates) and of mixed marriages, namely those involving a foreign-born and a native...

Agliari, Elena; Galluzzi, Andrea; Javarone, Marco Alberto; Pizzoferrato, Andrea; Tantari, Daniele

2015-01-01

366

Type I Error Control of Two-Group Multivariate Tests on Means under Conditions of Heterogeneous Correlation Structure.  

ERIC Educational Resources Information Center

A variety of approaches have been suggested by which to assess the equality of population mean vectors under conditions of population covariance matrix homogeneity and heterogeneity. The nonrobustness of commonly used multivariate tests of means to population covariance matrix heterogeneity has been long documented. However, most studies have…

Fouladi, Rachel T.

367

Mathematical analysis of epidemiological models with heterogeneity  

SciTech Connect

For many diseases in human populations the disease shows dissimilar characteristics in separate subgroups of the population; for example, the probability of disease transmission for gonorrhea or AIDS is much higher from male to female than from female to male. There is reason to construct and analyze epidemiological models which allow this heterogeneity of population, and to use these models to run computer simulations of the disease to predict the incidence and prevalence of the disease. In the models considered here the heterogeneous population is separated into subpopulations whose internal and external interactions are homogeneous in the sense that each person in the population can be assumed to have all average actions for the people of that subpopulation. The first model considered is an SIRS models; i.e., the Susceptible can become Infected, and if so he eventually Recovers with temporary immunity, and after a period of time becomes Susceptible again. Special cases allow for permanent immunity or other variations. This model is analyzed and threshold conditions are given which determine whether the disease dies out or persists. A deterministic model is presented; this model is constructed using difference equations, and it has been used in computer simulations for the AIDS epidemic in the homosexual population in San Francisco. The homogeneous version and the heterogeneous version of the differential-equations and difference-equations versions of the deterministic model are analyzed mathematically. In the analysis, equilibria are identified and threshold conditions are set forth for the disease to die out if the disease is below the threshold so that the disease-free equilibrium is globally asymptotically stable. Above the threshold the disease persists so that the disease-free equilibrium is unstable and there is a unique endemic equilibrium.

Van Ark, J.W.

1992-01-01

368

Site occupancy models with heterogeneous detection probabilities  

USGS Publications Warehouse

Models for estimating the probability of occurrence of a species in the presence of imperfect detection are important in many ecological disciplines. In these ?site occupancy? models, the possibility of heterogeneity in detection probabilities among sites must be considered because variation in abundance (and other factors) among sampled sites induces variation in detection probability (p). In this article, I develop occurrence probability models that allow for heterogeneous detection probabilities by considering several common classes of mixture distributions for p. For any mixing distribution, the likelihood has the general form of a zero-inflated binomial mixture for which inference based upon integrated likelihood is straightforward. A recent paper by Link (2003, Biometrics 59, 1123?1130) demonstrates that in closed population models used for estimating population size, different classes of mixture distributions are indistinguishable from data, yet can produce very different inferences about population size. I demonstrate that this problem can also arise in models for estimating site occupancy in the presence of heterogeneous detection probabilities. The implications of this are discussed in the context of an application to avian survey data and the development of animal monitoring programs.

Royle, J.A.

2006-01-01

369

Site occupancy models with heterogeneous detection probabilities.  

PubMed

Models for estimating the probability of occurrence of a species in the presence of imperfect detection are important in many ecological disciplines. In these "site occupancy" models, the possibility of heterogeneity in detection probabilities among sites must be considered because variation in abundance (and other factors) among sampled sites induces variation in detection probability (p). In this article, I develop occurrence probability models that allow for heterogeneous detection probabilities by considering several common classes of mixture distributions for p. For any mixing distribution, the likelihood has the general form of a zero-inflated binomial mixture for which inference based upon integrated likelihood is straightforward. A recent paper by Link demonstrates that in closed population models used for estimating population size, different classes of mixture distributions are indistinguishable from data, yet can produce very different inferences about population size. I demonstrate that this problem can also arise in models for estimating site occupancy in the presence of heterogeneous detection probabilities. The implications of this are discussed in the context of an application to avian survey data and the development of animal monitoring programs. PMID:16542234

Royle, J Andrew

2006-03-01

370

Factors associated with commencing smoking in 12-year-old students in Catalonia (Spain): a cross-sectional population-based study  

PubMed Central

Background Over the last decade notable progress has been made in developed countries on monitoring smoking although experimenting with cigarettes and smoking in young people remains a serious public health problem. This paper reports a cross-sectional study at the beginning of the 3-year follow-up community study TA_BES. The aim was to study the prevalence of smoking in addition to determining predictive factors for when smoking commences in a representative population of 12-year-old first year compulsory secondary education students. Methods Twenty-nine secondary schools (N = 29) from an area of Catalonia participated in the study. In these schools 2245 students answered a questionnaire to study the attitudes, behaviors, and tobacco consumption in the subject's surrounding circle and family in relation to smoking; carbon monoxide measurements were taken by means of co-oximetry on 2 different occasions. A smoker was defined as a student who had smoked daily or occasionally in the last 30 days. For non-smokers the criteria of not considering was set up for those who answered that in the future they would not be smokers and considering those who answered that they did not rule out becoming a smoker in the future. Results Among the total 2245 students included in the analysis 157(7%) were classified as smokers. Among non-smokers we differentiated between those not considering smoking 1757 (78.3%) and those considering smoking 288 (12.8%). Age is among the factors related to commencing smoking. The risk of becoming a smoker increases 2.27 times/year. The influence of the group of friends with a very high risk for boys OR 149.5 and lower, albeit high, in girls OR 38.1. Tobacco consumption of parents produces different effects in young people. A smoking father does not produce alterations in the smoking behavior of young people. However having a smoking mother or former smoking is a risk factor for boys and a protective factor for girls. We detected a gradual risk of becoming a smoker by means of the co-oximetry test. A boy/girl with a test between 6 p.p.m and 10 p.p.m increased the probability of smoking by 2.29 and co-oximetry values > 10 p.p.m multiplied the risk 4 times over. Conclusions Results indicate that the age of commencing smoking is maintained in spite of prevalence having decreased in the last few years. The risk factors identified should be used to involve families and the educational community by offering them tobacco weaning programmes. PMID:21044344

2010-01-01

371

From Single-Cell Genetic Architecture to Cell Population Dynamics: Quantitatively Decomposing the Effects of Different Population  

E-print Network

From Single-Cell Genetic Architecture to Cell Population Dynamics: Quantitatively Decomposing the Effects of Different Population Heterogeneity Sources for a Genetic Network with Positive Feedback, Texas ABSTRACT Phenotypic cell-to-cell variability or cell population heterogeneity originates from two

Bernard, Samuel

372

Conceptualizing a Tool to Optimize Therapy Based on Dynamic Heterogeneity  

PubMed Central

Complex biological systems often display a randomness paralleled in processes studied in fundamental physics. This simple stochasticity emerges owing to the complexity of the system and underlies a fundamental aspect of biology called phenotypic stochasticity. Ongoing stochastic fluctuations in phenotype at the single-unit level can contribute to two emergent population phenotypes. Phenotypic stochasticity not only generates heterogeneity within a cell population, but also allows reversible transitions back and forth between multiple states. This phenotypic interconversion tends to restore a population to a previous composition after that population has been depleted of specific members. We call this tendency homeostatic heterogeneity. These concepts of dynamic heterogeneity can be applied to populations composed of molecules, cells, individuals, etc. Here we discuss the concept that phenotypic stochasticity both underlies the generation of heterogeneity within a cell population and can be used to control population composition, contributing, in particular, to both the ongoing emergence of drug resistance and an opportunity for depleting drug-resistant cells. Using notions of both “large” and “small” numbers of biomolecular components, we rationalize our use of Markov processes to model the generation and eradication of drug-resistant cells. Using these insights, we have developed a graphical tool, called a metronomogram, that we propose will allow us to optimize dosing frequencies and total course durations for clinical benefit. PMID:23197078

Liao, David; Estévez-Salmerón, Luis; Tlsty, Thea D.

2012-01-01

373

Individual heterogeneity in life histories and eco-evolutionary dynamics.  

PubMed

Individual heterogeneity in life history shapes eco-evolutionary processes, and unobserved heterogeneity can affect demographic outputs characterising life history and population dynamical properties. Demographic frameworks like matrix models or integral projection models represent powerful approaches to disentangle mechanisms linking individual life histories and population-level processes. Recent developments have provided important steps towards their application to study eco-evolutionary dynamics, but so far individual heterogeneity has largely been ignored. Here, we present a general demographic framework that incorporates individual heterogeneity in a flexible way, by separating static and dynamic traits (discrete or continuous). First, we apply the framework to derive the consequences of ignoring heterogeneity for a range of widely used demographic outputs. A general conclusion is that besides the long-term growth rate lambda, all parameters can be affected. Second, we discuss how the framework can help advance current demographic models of eco-evolutionary dynamics, by incorporating individual heterogeneity. For both applications numerical examples are provided, including an empirical example for pike. For instance, we demonstrate that predicted demographic responses to climate warming can be reversed by increased heritability. We discuss how applications of this demographic framework incorporating individual heterogeneity can help answer key biological questions that require a detailed understanding of eco-evolutionary dynamics. PMID:25807980

Vindenes, Yngvild; Langangen, Øystein

2015-05-01

374

CAUSAL INFERENCE AND HETEROGENEITY BIAS IN SOCIAL SCIENCE*  

PubMed Central

Because of population heterogeneity, causal inference with observational data in social science may suffer from two possible sources of bias: (1) bias in unobserved pretreatment factors affecting the outcome even without treatment; and (2)bias due to heterogeneity in treatment effects. Even when we control for observed covariates, these two biases may occur if the classic ignorability assumption is untrue. In cases where the ignorability assumption is true, “composition bias” can occur if treatment propensity is systematically associated with heterogeneous treatment effects. PMID:23970824

Xie, Yu

2013-01-01

375

Astrocyte heterogeneity in the brain: from development to disease  

PubMed Central

In the last decades, astrocytes have risen from passive supporters of neuronal activity to central players in brain function and cognition. Likewise, the heterogeneity of astrocytes starts to become recognized in contrast to the homogeneous population previously predicted. In this review, we focused on astrocyte heterogeneity in terms of their morphological, protein expression and functional aspects, and debate in a historical perspective the diversity encountered in glial progenitors and how they may reflect mature astrocyte heterogeneity. We discussed data that show that different progenitors may have unsuspected roles in developmental processes. We have approached the functions of astrocyte subpopulations on the onset of psychiatric and neurological diseases.

Schitine, Clarissa; Nogaroli, Luciana; Costa, Marcos R.; Hedin-Pereira, Cecilia

2015-01-01

376

Student led part Introduction  

E-print Network

Overview Student led part Introduction Mathematical Biology ­ Matrix Population Projection Models;Overview Student led part Introduction The second lecture focuses on matrix (P)opulation (P)rojection (M)odels­ Stuart Townley Math Bio ­ Matrix PPMs 2/ 5 #12;Overview Student led part Introduction The second lecture

Knobloch,Jürgen

377

2, 983998, 2002 Heterogeneous  

E-print Network

-sized aircraft-induced aqueous sulfuric acid (H2SO4/H2O) particles on atmospheric ozone as a function additional ozone loss ­ mainly caused by hydrolysis of BrONO2 and N2O5 ­ scales in proportion contrail ice particles to be potentially important for heterogeneous chlorine activation and ozone

Paris-Sud XI, Université de

378

Gene expression heterogeneous  

E-print Network

Magazine R359 Gene expression becomes heterogeneous with age Mehmet Somel1*, Philipp Khaitovich1 for an age-dependent increase in variation in gene expression has yet been found [6­9]. Using eight microarray data sets from different studies in humans and rats, we find that gene expression becomes more

Khaitovich, Philipp

379

Heterogeneous waste processing  

DOEpatents

A combination of treatment methods are provided for treatment of heterogeneous waste including: (1) treatment for any organic compounds present; (2) removal of metals from the waste; and, (3) bulk volume reduction, with at least two of the three treatment methods employed and all three treatment methods emplyed where suitable.

Vanderberg, Laura A. (Los Alamos, NM); Sauer, Nancy N. (Los Alamos, NM); Brainard, James R. (Los Alamos, NM); Foreman, Trudi M. (Los Alamos, NM); Hanners, John L. (Los Alamos, NM)

2000-01-01

380

Population Issues. Resources in Technology.  

ERIC Educational Resources Information Center

Presents information about the problems caused by increasing population. Discusses the environmental impact and the ways that technology can be used to solve problems of overpopulation. Includes possible student outcomes and a student quiz. (JOW)

Technology Teacher, 1991

1991-01-01

381

The significance of biological heterogeneity  

Microsoft Academic Search

Heterogeneity of expression for a variety of characteristics is found among malignant cells in the organism and in culture. Normal cells are relatively uniform when organized in a tissue, but become heterogeneous for many characteristics when they are dispersed and grown in monolayer culture. The heterogenizing effect of growth in culture indicates that the morphology and behavior of normal cells

Harry Rubin

1990-01-01

382

World Population Activity I: Excel  

NSDL National Science Digital Library

(Activity 1 of 2) This activity is primarily intended as an introductory tutorial on using Excel. Students use Excel to explore population dynamics using the Logistic equation for (S-shaped) population growth.

Activity and Starting Point page by R.M. MacKay. Clark College, Physics and Meteorology.

383

Adventures With The Fish Pond: Population Modeling  

NSDL National Science Digital Library

This activity builds on the population decay M&M activity and will introduce students to recursive equations and uses calculators as an efficient tool for exploring population models. Students will describe what happens to the fish population from one year to another. Each pair of students will have an activity sheet to go along with the activity, and a calculator is needed.

PBS TeacherSource - Math

2010-01-01

384

Identifying and Quantifying Heterogeneity in High Content Analysis: Application of Heterogeneity Indices to Drug Discovery  

PubMed Central

One of the greatest challenges in biomedical research, drug discovery and diagnostics is understanding how seemingly identical cells can respond differently to perturbagens including drugs for disease treatment. Although heterogeneity has become an accepted characteristic of a population of cells, in drug discovery it is not routinely evaluated or reported. The standard practice for cell-based, high content assays has been to assume a normal distribution and to report a well-to-well average value with a standard deviation. To address this important issue we sought to define a method that could be readily implemented to identify, quantify and characterize heterogeneity in cellular and small organism assays to guide decisions during drug discovery and experimental cell/tissue profiling. Our study revealed that heterogeneity can be effectively identified and quantified with three indices that indicate diversity, non-normality and percent outliers. The indices were evaluated using the induction and inhibition of STAT3 activation in five cell lines where the systems response including sample preparation and instrument performance were well characterized and controlled. These heterogeneity indices provide a standardized method that can easily be integrated into small and large scale screening or profiling projects to guide interpretation of the biology, as well as the development of therapeutics and diagnostics. Understanding the heterogeneity in the response to perturbagens will become a critical factor in designing strategies for the development of therapeutics including targeted polypharmacology. PMID:25036749

Gough, Albert H.; Chen, Ning; Shun, Tong Ying; Lezon, Timothy R.; Boltz, Robert C.; Reese, Celeste E.; Wagner, Jacob; Vernetti, Lawrence A.; Grandis, Jennifer R.; Lee, Adrian V.; Stern, Andrew M.; Schurdak, Mark E.; Taylor, D. Lansing

2014-01-01

385

Accessing and Investigating Population Data  

NSDL National Science Digital Library

In this activity, students investigate population projections from 1990-2100 using data from the U.S. Census Bureau Web. Using the five specific population pyramids, students investigate population projection data for the United States over a 110-year period. They examine how the population data is distributed over time and explain what factors might contribute to these trends. An activity sheet and thoughtful questions, included in the lesson plan, guide the class investigation.

Grace M. Burton

2000-01-01

386

Population Growth in Yeasts  

NSDL National Science Digital Library

This lesson is the second of two that explore cellular respiration and population growth in yeasts. In the first lesson, students set up a simple way to indirectly observe and quantify the amount of respiration occurring in yeast-molasses cultures. Based on questions that arose during the first lesson and its associated activity, students in this lesson work in small groups to design experiments that determine how environmental factors affect yeast population growth.

Engineering K-PhD Program,

387

Heterogeneous atmospheric bromine chemistry  

Microsoft Academic Search

This paper considers the effect of heterogeneous bromine reactions on stratospheric photochemistry. We have considered reactions on both sulfate aerosols and on polar stratospheric clouds (PSCs). It is shown that the hydrolysis of BrONO2 on sulfate aerosols enhances the HOBr concentration, which in turn enhances the OH and HO2 concentrations, thereby reducing the HC1 lifetime and concentration. The hydrolysis of

D. J. Lary; M. P. Chipperfield; R. Toumi; T. Lenton

1996-01-01

388

Dressing up for School Work? Supporting a Collaborative Environment with Heterogeneous Technologies  

Microsoft Academic Search

This paper approaches heterogeneity and heterogeneous technology as assets, rather than limitations, in the development of computer supported cooperative work. We demonstrate how heterogeneous technologies sustain teachers' and students' school work by presenting four different prototypes (the HyConExplorer, the eCell, the iGameFloor and the eBag) that complement one another because they offer different functionalities and are, at the same time,

Christina Brodersen; Ole Sejer Iversen

2007-01-01

389

World Population  

NSDL National Science Digital Library

Access and visualize world population data using the user friendly MyWorld GIS software. Data includes total population, population density, projected population, male and female population, and age specific population, etc.

This starting point example compiled by R.M. MacKay. utilizes the MyWorld (more info) Geographic Information System (GIS) software created at Norhtwestern University.

390

Mathematically Gifted in the Heterogeneously Grouped Mathematics Classroom: What is a Teacher to Do?  

Microsoft Academic Search

Differentiation provides one method by which teachers can provide appropriate challenges at appropriate levels for all learners in a heterogeneously grouped mathematics classroom, where the range of abilities and interests can be wide. This article considers a heterogeneously grouped high school geometry class where differentiation is practiced. Students who demonstrated mastery of the concepts and skills still under study are

Catherine Finlayson Reed

2004-01-01

391

The World Population Dilemma.  

ERIC Educational Resources Information Center

This book is the third in a series published by the Population Reference Bureau aimed at illuminating the facts and consequences of human population dynamics for secondary and college-age students. Many illustrations, charts and graphs are included in this volume to help the reader grasp a number of the current ideas and concepts that are used in…

Population Reference Bureau, Inc., Washington, DC.

392

Population: Age Structure  

NSDL National Science Digital Library

One of the primary tools that demographers use to understand population is the age structure diagram, a graphic representation that shows the distribution by ages of females and males within a certain population. This lesson describes how these diagrams are constructed and interpreted. It includes an activity in which students use online data on Native American populations from the United States Census Bureau to construct their own diagrams.

Matt Laposata

393

Population Growth Curves  

NSDL National Science Digital Library

Using Avida-ED freeware, students control a few factors in an environment populated with digital organisms, and then compare how changing these factors affects population growth. They experiment by altering the environment size (similar to what is called carrying capacity, the maximum population size that an environment can normally sustain), the initial organism gestation rate, and the availability of resources. How systems function often depends on many different factors. By altering these factors one at a time, and observing the results, students are able to clearly see the effect of each one.

Bio-Inspired Technology and Systems (BITS) RET,

394

Thermodynamics and Human Population  

NASA Astrophysics Data System (ADS)

This paper discusses a Fermi-problem exercise through which I take students in several of my college courses. Students work in teams, determining the average daily Caloric needs per person. Then they use insolation values to determine the size of a collection area needed to absorb the previously determined daily energy requirements. Adjustments to the size of the collection area are made based on energy absorption per biological trophic level, as well as the consideration that most diets are a mixture of plant- and animal-derived elements. Finally, using the total amount of farmland available on the planet, students calculate a maximum population value. Although the maximum population values derived herewith should not be considered authoritative, the exercise has three beneficial purposes: 1) a chance to talk about the modeling process and extrapolations, 2) an unexpected application of physics to social contexts, and 3) raising student awareness of population and energy issues.

Cordry, Sean M.

2010-09-01

395

Dynamic heterogeneity for the physical oncologist  

NSDL National Science Digital Library

Biological systems (e.g. cells) can make stochastic transitions between phenotypes (e.g. states of relatively increased or decreased drug resistance). This means that an initially drug-sensitive population can generate relatively drug-resistant subpopulations. This video presents a metronomogram, which is a tool for understanding whether such stochastic transitions can provide an opportunity for therapeutic treatment. Citation: Liao D, Estevez-Salmeron L, and Tlsty TD (2012) "Conceptualizing a tool to optimize therapy based on dynamic heterogeneity," Phys. Biol. 9:065005.

David Liao

396

Spatial Heterogeneity of Autoinducer Regulation Systems  

PubMed Central

Autoinducer signals enable coordinated behaviour of bacterial populations, a phenomenon originally described as quorum sensing. Autoinducer systems are often controlled by environmental substances as nutrients or secondary metabolites (signals) from neighbouring organisms. In cell aggregates and biofilms gradients of signals and environmental substances emerge. Mathematical modelling is used to analyse the functioning of the system. We find that the autoinducer regulation network generates spatially heterogeneous behaviour, up to a kind of multicellularity-like division of work, especially under nutrient-controlled conditions. A hybrid push/pull concept is proposed to explain the ecological function. The analysis allows to explain hitherto seemingly contradicting experimental findings. PMID:22666024

Hense, Burkhard A.; Müller, Johannes; Kuttler, Christina; Hartmann, Anton

2012-01-01

397

Programmed Heterogeneity: Epigenetic Mechanisms in Bacteria  

PubMed Central

Contrary to the traditional view that bacterial populations are clonal, single-cell analysis reveals that phenotypic heterogeneity is common in bacteria. Formation of distinct bacterial lineages appears to be frequent during adaptation to harsh environments, including the colonization of animals by bacterial pathogens. Formation of bacterial subpopulations is often controlled by epigenetic mechanisms that generate inheritable phenotypic diversity without altering the DNA sequence. Such mechanisms are diverse, ranging from relatively simple feedback loops to complex self-perpetuating DNA methylation patterns. PMID:23592777

Casadesús, Josep; Low, David A.

2013-01-01

398

Heterogeneity in expected longevities.  

PubMed

We develop a new methodology to compute differences in the expected longevity of individuals of a given cohort who are in different socioeconomic groups at a certain age. We address the two main problems associated with the standard use of life expectancy: (1) that people's socioeconomic characteristics change, and (2) that mortality has decreased over time. Our methodology uncovers substantial heterogeneity in expected longevities, yet much less heterogeneity than what arises from the naive application of life expectancy formulae. We decompose the longevity differences into differences in health at age 50, differences in the evolution of health with age, and differences in mortality conditional on health. Remarkably, education, wealth, and income are health-protecting but have very little impact on two-year mortality rates conditional on health. Married people and nonsmokers, however, benefit directly in their immediate mortality. Finally, we document an increasing time trend of the socioeconomic gradient of longevity in the period 1992-2008, and we predict an increase in the socioeconomic gradient of mortality rates for the coming years. PMID:25391225

Pijoan-Mas, Josep; Ríos-Rull, José-Víctor

2014-12-01

399

Heterogeneous belief and asset returns  

NASA Astrophysics Data System (ADS)

Based on DSSW model, this paper introduces the noise traders with heterogeneous belief. With an equilibrium analysis, this paper examines the return of risky asset. The results show that the belief biases, the probability of economy state, the degree of the heterogeneous noise trader's aversion risk, the coefficient between heterogeneous noise traders are all the factors that have effects on the risky asset pricing and the return of risky asset.

Lei-Sun, Wen-Zou, Hui

2014-10-01

400

Interconnecting heterogeneous database management systems  

NASA Technical Reports Server (NTRS)

It is pointed out that there is still a great need for the development of improved communication between remote, heterogeneous database management systems (DBMS). Problems regarding the effective communication between distributed DBMSs are primarily related to significant differences between local data managers, local data models and representations, and local transaction managers. A system of interconnected DBMSs which exhibit such differences is called a network of distributed, heterogeneous DBMSs. In order to achieve effective interconnection of remote, heterogeneous DBMSs, the users must have uniform, integrated access to the different DBMs. The present investigation is mainly concerned with an analysis of the existing approaches to interconnecting heterogeneous DBMSs, taking into account four experimental DBMS projects.

Gligor, V. D.; Luckenbaugh, G. L.

1984-01-01

401

Anthropogenic Biomes ver. 1 Anthropogenic biomes represent heterogeneous  

E-print Network

Anthropogenic Biomes ver. 1 Africa Anthropogenic biomes represent heterogeneous landscape mosaics defined by population density and vegetation cover. The 21 biomes are grouped into six major categories: Ellis, E. C. and N. Ramankutty. 2008. Putting people in the map: anthropogenic biomes of the world. http

Columbia University

402

Bacterial persisters are dormant cells that arise heterogeneously in an  

E-print Network

membrane and oxidative stress and to increase antibiotic resistance, leading the authors to investigateBacterial persisters are dormant cells that arise heterogeneously in an antibiotic-susceptible population during entry into stationary phase. These cells are able to tolerate antibiotic treatment

Khalil, Ahmad S.

403

1 Evolving Heterogeneous Neural Agents by Local Selection  

Microsoft Academic Search

Evolutionary algorithms have been applied to the synthesis of neural architec- tures, but they normally lead to uniform populations. Homogeneous solutions, however, are inadequate for certain applications and models. For these cases, local selection may produce the desired heterogeneity in the evolving neural networks. This chapter describes algorithms based on local selection, and dis- cusses the main differences distinguishing them

Filippo Menczer; Melania Degeratu

2000-01-01

404

Characterizing Mutational Heterogeneity in a Glioblastoma Patient with Double Recurrence  

Microsoft Academic Search

Human cancers are driven by the acquisition of somatic mutations. Separating the driving mutations from those that are random consequences of general genomic instability remains a challenge. New sequencing technology makes it possible to detect mutations that are present in only a minority of cells in a heterogeneous tumor population. We sought to leverage the power of ultra-deep sequencing to

Gabrielle C. Nickel; Jill Barnholtz-Sloan; Meetha P. Gould; Sarah McMahon; Andrea Cohen; Mark D. Adams; Kishore Guda; Mark Cohen; Andrew E. Sloan; Thomas LaFramboise

2012-01-01

405

Understanding tumor heterogeneity as functional compartments - superorganisms revisited  

Microsoft Academic Search

Compelling evidence broadens our understanding of tumors as highly heterogeneous populations derived from one common progenitor.\\u000a In this review we portray various stages of tumorigenesis, tumor progression, self-seeding and metastasis in analogy to the\\u000a superorganisms of insect societies to exemplify the highly complex architecture of a neoplasm as a system of functional \\

Thomas GP Grunewald; Saskia M Herbst; Jürgen Heinze; Stefan Burdach

2011-01-01

406

The Influence of Student Characteristics on the Use of Adaptive E-Learning Material  

ERIC Educational Resources Information Center

Adaptive e-learning materials can help teachers to educate heterogeneous student groups. This study provides empirical data about the way academic students differ in their learning when using adaptive e-learning materials. Ninety-four students participated in the study. We determined characteristics in a heterogeneous student group by collecting…

van Seters, J. R.; Ossevoort, M. A.; Tramper, J.; Goedhart, M. J.

2012-01-01

407

State Population Projections  

NSDL National Science Digital Library

In this lesson plan students create graphs and analyze data based on the data provided by the United States Census Bureau. Students choose five states to focus on and create a bar graph for each, then students compare the data represented in the graphs and answer questions about the data. The lesson includes student activity sheet, the link to the U.S. Census Bureau is no longer active, please follow this link instead: http://www.census.gov/population/projections/files/stateproj/stpjpop.txt

Grace M. Burton

2008-01-01

408

Heterogeneity in spending change at retirement  

PubMed Central

The simple one-good model of life-cycle consumption requires that consumption be continuous over retirement; yet prior research based on partial measures of consumption or on synthetic panels indicates that spending drops at retirement, a result that has been called the retirement-consumption puzzle. Using panel data on total spending, nondurable spending and food spending, we find that spending declines at small rates at retirement, rates that could be explained by mechanisms such as the cessation of work-related expenses, unexpected retirement due to a health shock or by the substitution of time for spending. We find substantial heterogeneity in spending change at retirement: in the upper half of the wealth distribution spending increased. In the low-wealth population where spending did decline at higher rates, the main explanation for the decline appears to be early retirement due to poor health, possibly augmented by a short planning horizon by a minority of the population. PMID:24524026

Hurd, Michael D.; Rohwedder, Susann

2014-01-01

409

Heterogeneity and plasticity of epidermal stem cells  

PubMed Central

The epidermis is an integral part of our largest organ, the skin, and protects us against the hostile environment. It is a highly dynamic tissue that, during normal steady-state conditions, undergoes constant turnover. Multiple stem cell populations residing in autonomously maintained compartments facilitate this task. In this Review, we discuss stem cell behaviour during normal tissue homeostasis, regeneration and disease within the pilosebaceous unit, an integral structure of the epidermis that is responsible for hair growth and lubrication of the epithelium. We provide an up-to-date view of the pilosebaceous unit, encompassing the heterogeneity and plasticity of multiple discrete stem cell populations that are strongly influenced by external cues to maintain their identity and function. PMID:24961797

Schepeler, Troels; Page, Mahalia E.; Jensen, Kim B.

2014-01-01

410

Student Affairs STUDENT CONDUCT  

E-print Network

Student Affairs CODE OF STUDENT CONDUCT 2014-15 #12;Contents Letter from the Dean of Students ....................................................................ii Binghamton University's Code of Student Conduct Preamble...................... 1 Section I: Rules of Student Conduct.............................................................. 1 Section II: Definitions

Suzuki, Masatsugu

411

The Pegasus Heterogeneous Multidatabase System  

Microsoft Academic Search

Pegasus, a heterogeneous multidatabase management system that responds to the need for effective access and management of shared data across in a wide range of applications, is described. Pegasus provides facilities for multidatabase applications to access and manipulate multipole autonomous heterogeneous distributed object-oriented relational, and other information systems through a uniform interface. It is a complete data management system that

Rafi Ahmed; Philippe De Smedt; Weimin Du; William Kent; Mohammad A. Ketabchi; Witold Litwin; Abbas Rafii; Ming-chien Shan

1991-01-01

412

Taming heterogeneity - the Ptolemy approach  

Microsoft Academic Search

Modern embedded computing systems tend to be heterogeneous in the sense of being composed of subsystems with very different characteristics, which communicate and interact in a variety of ways-synchronous or asynchronous, buffered or unbuffered, etc. Obviously, when designing such systems, a modeling language needs to reflect this heterogeneity. Today's modeling environments usually offer a variant of what we call amorphous

Johan Eker; Jörn W. Janneck; Edward A. Lee; Jie Liu; Xiaojun Liu; JOZSEF LUDVIG; Stephen Neuendorffer; SONIA SACHS; Yuhong Xiong

2003-01-01

413

Distinct population structure for co-occurring Anopheles goeldii and Anopheles triannulatus in Amazonian Brazil  

PubMed Central

To evaluate whether environmental heterogeneity contributes to the genetic heterogeneity in Anopheles triannulatus, larval habitat characteristics across the Brazilian states of Roraima and Pará and genetic sequences were examined. A comparison with Anopheles goeldii was utilised to determine whether high genetic diversity was unique to An. triannulatus. Student t test and analysis of variance found no differences in habitat characteristics between the species. Analysis of population structure of An. triannulatus and An. goeldii revealed distinct demographic histories in a largely overlapping geographic range. Cytochrome oxidase I sequence parsimony networks found geographic clustering for both species; however nuclear marker networks depicted An. triannulatus with a more complex history of fragmentation, secondary contact and recent divergence. Evidence of Pleistocene expansions suggests both species are more likely to be genetically structured by geographic and ecological barriers than demography. We hypothesise that niche partitioning is a driving force for diversity, particularly in An. triannulatus. PMID:23903977

McKeon, Sascha Naomi; Moreno, Marta; Sallum, Maria Anise; Povoa, Marinete Marins; Conn, Jan Evelyn

2013-01-01

414

Distinct population structure for co-occurring Anopheles goeldii and Anopheles triannulatus in Amazonian Brazil.  

PubMed

To evaluate whether environmental heterogeneity contributes to the genetic heterogeneity in Anopheles triannulatus, larval habitat characteristics across the Brazilian states of Roraima and Pará and genetic sequences were examined. A comparison with Anopheles goeldii was utilised to determine whether high genetic diversity was unique to An. triannulatus. Student t test and analysis of variance found no differences in habitat characteristics between the species. Analysis of population structure of An. triannulatus and An. goeldii revealed distinct demographic histories in a largely overlapping geographic range. Cytochrome oxidase I sequence parsimony networks found geographic clustering for both species; however nuclear marker networks depicted An. triannulatus with a more complex history of fragmentation, secondary contact and recent divergence. Evidence of Pleistocene expansions suggests both species are more likely to be genetically structured by geographic and ecological barriers than demography. We hypothesise that niche partitioning is a driving force for diversity, particularly in An. triannulatus. PMID:23903977

McKeon, Sascha Naomi; Moreno, Marta; Sallum, Maria Anise; Povoa, Marinete Marins; Conn, Jan Evelyn

2013-08-01

415

Dental follicle progenitor cell heterogeneity in the developing mouse periodontium.  

PubMed

As a developmental precursor for diverse periodontal tissues, the dental follicle (DF) harbors great promise for periodontal tissue regeneration. However, development of optimal therapy awaits the answer to a key question that impinges on many issues in development-Do adult progenitor tissues form a homogeneous cell population that differentiates into target tissues when they arrive at the site, or they contain heterogeneous cell populations that are committed to specific fates? To address the homogeneity/heterogeneity question, we analyzed differentiation pathways and markers in several cloned DF cell lines. Our studies revealed that each of our cloned DF lines featured remarkably unique characteristics, indicative of a separate and distinct lineage. One line, DF1, was high in proliferative activity but did not display any mineralization behavior, suggesting that it might be related to a periodontal ligament-type lineage. DF2 was similar to DF1, but featured remarkably high alkaline phosphatase activity indicative of a highly undifferentiated state. DF3 matched the mineralization characteristics of a same stage alveolar bone line AB1 in terms of gene expression and von Kossa staining, indicating that DF3 might be of cementoblastic or alveolar bone osteoblastic lineage. To verify the multilineage potential of the DF for purposes of tissue engineering, a series of differentiation induction experiments was conducted. For identification purposes, characteristics of these heterogeneous follicular progenitor cells were compared with follicle components in tissue sections of the postnatal developing periodontium. The presence of heterogeneous cell populations in the DF mirrors individual developmental pathways in the formation of the dental integument. The profound cellular heterogeneity of the DF as an adult progenitor for tissue regeneration also suggests that heterogeneous cellular constituents might play as much of a role in tissue regeneration as the inducible characteristics of individual lineages might do. PMID:16978062

Luan, Xianghong; Ito, Yoshihiro; Dangaria, Smit; Diekwisch, Thomas G H

2006-08-01

416

Heterogeneity in background fitness acts as a suppressor of selection.  

PubMed

We introduce the concept of heterogeneity in background fitness to evolutionary dynamics in finite populations. Background fitness is specific to an individual but not linked to its strategy. It can be thought of as a property that is related to the physical or societal position of an individual, but is not dependent on the strategy that is adopted in the evolutionary process under consideration. In our model, an individual's total fitness is the sum of its background fitness and the fitness derived from using a specific strategy. This approach has important implications for the imitation of behavioural strategies: if we imitate others for their success, but can only adopt their behaviour and not their social and economic ties, we may imitate in vain. We study the effect of heterogeneity in background fitness on the fixation of a mutant strategy with constant fitness. We find that heterogeneity suppresses selection, but also decreases the time until a novel strategy either takes over the population or is lost again. We derive analytical solutions of the fixation probability in small populations. In the case of large total background fitness in a population with maximum inequality, we find a particularly simple approximation of the fixation probability. Numerical simulations suggest that this simple approximation also holds for larger population sizes. PMID:24211522

Hauser, Oliver P; Traulsen, Arne; Nowak, Martin A

2014-02-21

417

Student learning of anatomy  

Microsoft Academic Search

Relationships between student approaches to learning and learning outcomes were explored in a population of fi rst year students studying anatomy in a medical program off ered by a research intensive Australian university. An online survey version of the Study Process Questionnaire (Biggs et al, 2001), examination scripts and student results were the source data for this study. Th ese

Priti Pandey; Craig Zimitat

2005-01-01

418

Spatial heterogeneity study of vegetation coverage at Heihe River Basin  

NASA Astrophysics Data System (ADS)

Spatial heterogeneity of the animal-landscape system has three major components: heterogeneity of resource distributions in the physical environment, heterogeneity of plant tissue chemistry, heterogeneity of movement modes by the animal. Furthermore, all three different types of heterogeneity interact each other and can either reinforce or offset one another, thereby affecting system stability and dynamics. In previous studies, the study areas are investigated by field sampling, which costs a large amount of manpower. In addition, uncertain in sampling affects the quality of field data, which leads to unsatisfactory results during the entire study. In this study, remote sensing data is used to guide the sampling for research on heterogeneity of vegetation coverage to avoid errors caused by randomness of field sampling. Semi-variance and fractal dimension analysis are used to analyze the spatial heterogeneity of vegetation coverage at Heihe River Basin. The spherical model with nugget is used to fit the semivariogram of vegetation coverage. Based on the experiment above, it is found, (1)there is a strong correlation between vegetation coverage and distance of vegetation populations within the range of 0?28051.3188m at Heihe River Basin, but the correlation loses suddenly when the distance greater than 28051.3188m. (2)The degree of spatial heterogeneity of vegetation coverage at Heihe River Basin is medium. (3)Spatial distribution variability of vegetation occurs mainly on small scales. (4)The degree of spatial autocorrelation is 72.29% between 25% and 75%, which means that spatial correlation of vegetation coverage at Heihe River Basin is medium high.

Wu, Lijuan; Zhong, Bo; Guo, Liyu; Zhao, Xiangwei

2014-11-01

419

Science Education and ESL Students  

ERIC Educational Resources Information Center

The number of students who learn English as a second language (ESL) in U.S. schools has grown significantly in the past decade. This segment of the student population increased by 56% between the 1994-95 and 2004-05 school years (NCLR 2007). As the ESL student population increases, many science teachers struggle to tailor instructional materials,…

Allen, Heather; Park, Soonhye

2011-01-01

420

Systemic Equity Pedagogy in Science Education: A Mixed-Method Analysis of High Achieving High Schools of Culturally Diverse Student Populations in Texas  

E-print Network

The purpose of this study was to identify and describe the associations between systemic equity pedagogy (SEP) practices in highly diverse high schools and their students' science achievement and college readiness. This study focuses on science...

Blocker, Tyrone Dewayne

2013-08-14

421

Fractal heterogeneous media.  

PubMed

A method is presented for generating compact fractal disordered media by generalizing the random midpoint displacement algorithm. The obtained structures are invasive stochastic fractals, with the Hurst exponent varying as a continuous parameter, as opposed to lacunar deterministic fractals, such as the Menger sponge. By employing the detrending moving average algorithm [A. Carbone, Phys. Rev. E 76, 056703 (2007)], the Hurst exponent of the generated structure can be subsequently checked. The fractality of such a structure is referred to a property defined over a three-dimensional topology rather than to the topology itself. Consequently, in this framework, the Hurst exponent should be intended as an estimator of compactness rather than of roughness. Applications can be envisaged for simulating and quantifying complex systems characterized by self-similar heterogeneity across space. For example, exploitation areas range from the design and control of multifunctional self-assembled artificial nanostructures and microstructures to the analysis and modeling of complex pattern formation in biology, environmental sciences, geomorphological sciences, etc. PMID:20365674

Türk, Christian; Carbone, Anna; Chiaia, Bernardino M

2010-02-01

422

Angiotensin II receptor heterogeneity  

SciTech Connect

The possibility of receptor heterogeneity in the angiotensin II (AII) system has been suggested previously, based on differences in Kd values or sensitivity to thiol reagents. One of the authors earliest indications was the frequent observation of incomplete inhibition of the binding of AII to adrenal cortical membranes. Autoradiographic studies demonstrated that all of the labeling of the rat adrenal was blocked by unlabeled AII or saralasin, but not by DuP 753. The predominant receptor in the rat adrenal cortex (80%) is sensitive to dithiothreitol (DTT) and DuP 753, and is designated AII-1. The residual sites in the adrenal cortex and almost all of the sites in the rat adrenal medulla are insensitive to both DTT and DuP 753, but were blocked by EXP655. These sites have been confirmed by ligand binding studies and are designated AII-2. The rabbit adrenal cortex is unique in yielding a nonuniform distribution of AII-2 sites around the outer layer of glomerulosa cells. In the rabbit kidney, the sites on the glomeruli are AII-1, but the sites on the kidney capsule are AII-2. Angiotensin III appears to have a higher affinity for AII-2 sites since it inhibits the binding to the rabbit kidney capsule but not the glomeruli. Elucidation of the distribution and function of these diverse sites should permit the development of more selective and specific therapeutic strategies.

Herblin, W.F.; Chiu, A.T.; McCall, D.E.; Ardecky, R.J.; Carini, D.J.; Duncia, J.V.; Pease, L.J.; Wong, P.C.; Wexler, R.R.; Johnson, A.L. (DuPont Merck Pharmaceutical Company, Wilmington, DE (USA))

1991-04-01

423

Exploring Populations  

NSDL National Science Digital Library

This Immersion Unit provides a coherent series of lessons designed to guide students in developing deep conceptual understanding that is aligned with the standards, key science concepts, and essential features of classroom inquiry (as defined by the National Science Education Standards). Unit Overarching Concepts-Populations of living organisms change or stay the same over time as a result of the interactions between the genetic variations that are expressed by the individuals in the populations and the environment in which the population lives.-Science knowledge advances through inquiry.Unit Supporting Concepts-Individual organisms with certain variations of traits (adaptations) are more likely than others to survive and reproduce successfully.-When environmental conditions change it can affect the survival of both individual organisms and entire species.-Natural selection determines the differential survival of groups of organisms.-A small advantage in escaping a predator, resisting a drug, etc. can lead to the spread of a trait in a modest number of generations.-Mutations are a source of variation in an individual?s genotype, and it can result in a change in phenotype??good or bad.-Scientific progress is made by asking meaningful questions and conducting careful investigations, using appropriate tools and technology to perform tests, collect data, analyze relationships, and display data.-No matter how well one scientific explanation fits observations, a new explanation might fit them just as well or better, or might fit a wider range of observations. In science, thetesting, revising, and occasional discarding of explanations, new and old, never ends.This unit was developed through the large Math and Science Partnership project called System-wide Change for All Learners and Educators (SCALE), involving a collaboration among Los Angeles School District educators, California State University science and education faculty, and UW-Madison SCALE staff.

The Wisconsin Fast Plants Program

424

Chimera states in heterogeneous networks  

E-print Network

Chimera states in networks of coupled oscillators occur when some fraction of the oscillators synchronise with one another, while the remaining oscillators are incoherent. Several groups have studied chimerae in networks of identical oscillators, but here we study these states in a heterogeneous model for which the natural frequencies of the oscillators are chosen from a distribution. We obtain exact results by reduction to a finite set of differential equations. We find that heterogeneity can destroy chimerae, destroy all states except chimerae, or destabilise chimerae in Hopf bifurcations, depending on the form of the heterogeneity.

Carlo R. Laing

2008-12-17

425

Final Technical Report - Investigation into the Relationship between Heterogeneity and Heavy-Tailed Solute Transport  

SciTech Connect

The objective of this project was to characterize the influence that naturally complex geologic media has on anomalous dispersion and to determine if the nature of dispersion can be estimated from the underlying heterogeneous media. The UNM portion of this project was to provide detailed representations of aquifer heterogeneity through producing highly-resolved models of outcrop analogs to aquifer materials. This project combined outcrop-scale heterogeneity characterization (conducted at the University of New Mexico), laboratory experiments (conducted at Sandia National Laboratory), and numerical simulations (conducted at Sandia National Laboratory and Colorado School of Mines). The study was designed to test whether established dispersion theory accurately predicts the behavior of solute transport through heterogeneous media and to investigate the relationship between heterogeneity and the parameters that populate these models. The dispersion theory tested by this work was based upon the fractional advection-dispersion equation (fADE) model. Unlike most dispersion studies that develop a solute transport model by fitting the solute transport breakthrough curve, this project explored the nature of the heterogeneous media to better understand the connection between the model parameters and the aquifer heterogeneity. We also evaluated methods for simulating the heterogeneity to see whether these approaches (e.g., geostatistical) could reasonably replicate realistic heterogeneity. The UNM portion of this study focused on capturing realistic geologic heterogeneity of aquifer analogs using advanced outcrop mapping methods.

Weissmann, Gary S

2013-12-06

426

Population Genetics and Statistics  

NSDL National Science Digital Library

This website is part of the President's DNA Initiative and is devoted to past and current methods of macromolecules such as DNA. This website introduces the student to the subject of population genetics and stresses factors that can alter allele frequencies in a population and calculations associated with the Hardy-Weinberg principle. The student will learn to use acceptable statistical approaches to evaluating DNA data and how DNA databases are constructed and applied. This site is designed as an on-line short course with excellent graphic support. The user must register and secure a readily obtainable password prior to entering the site.

427

Generalized principles of stochasticity can be used to control dynamic heterogeneity  

PubMed Central

It is increasingly appreciated that phenotypic stochasticity plays fundamental roles in biological systems at the cellular level and that a variety of mechanisms generates phenotypic interconversion over a broad range of time scales. The ensuing dynamic heterogeneity can be used to understand biological and clinical processes involving diverse phenotypes in different cell populations. The same principles can be applied, not only to populations composed of cells, but also to populations composed of molecules, tissues, and multicellular organisms. Stochastic units generating dynamic heterogeneity can be integrated across various length scales. We propose that a graphical tool we have developed, called a metronomogram, will allow us to identify factors that suitably influence the restoration of homeostatic heterogeneity so as to modulate the consequences of dynamic heterogeneity for desired outcomes. PMID:23197162

Liao, David; Estévez-Salmerón, Luis; Tlsty, Thea D.

2012-01-01

428

Landscape heterogeneity shapes host-parasite interactions and results in apparent plant-virus codivergence.  

PubMed

Knowledge on how landscape heterogeneity shapes host-parasite interactions is central to understand the emergence, dynamics and evolution of infectious diseases. However, this is an underexplored subject, particularly for plant-virus systems. Here, we analyse how landscape heterogeneity influences the prevalence, spatial genetic structure, and temporal dynamics of Pepper golden mosaic and Pepper huasteco yellow vein begomoviruses infecting populations of the wild pepper Capsicum annuum glabriusculum (chiltepin) in Mexico. Environmental heterogeneity occurred at different nested spatial scales (host populations within biogeographical provinces), with levels of human management varying among host population within a province. Results indicate that landscape heterogeneity affects the epidemiology and genetic structure of chiltepin-infecting begomoviruses in a scale-specific manner, probably related to conditions favouring the viruses' whitefly vector and its dispersion. Increased levels of human management of the host populations were associated with higher virus prevalence and erased the spatial genetic structure of the virus populations. Also, environmental heterogeneity similarly shaped the spatial genetic structures of host and viruses. This resulted in the congruence between host and virus phylogenies, which does not seem to be due to host-virus co-evolution. Thus, results provide evidence of the key role of landscape heterogeneity in determining plant-virus interactions. PMID:23379795

Rodelo-Urrego, M; Pagán, I; González-Jara, P; Betancourt, M; Moreno-Letelier, A; Ayllón, M A; Fraile, A; Piñero, D; García-Arenal, F

2013-04-01

429

HETEROGENOUS DEGRADATION OF OXYGENATED INTERMEDIATES  

EPA Science Inventory

Issues surrounding the importance of including heterogeneous processes when determining the fate of oxygenated intermediates in the troposphere are discussed. esults of recent investigations are reviewed and preliminary data from a laboratory study are presented. n the laboratory...

430