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1

Population heterogeneity and causal inference  

PubMed Central

Population heterogeneity is ubiquitous in social science. The very objective of social science research is not to discover abstract and universal laws but to understand population heterogeneity. Due to population heterogeneity, causal inference with observational data in social science is impossible without strong assumptions. Researchers have long been concerned with two potential sources of bias. The first is bias in unobserved pretreatment factors affecting the outcome even in the absence of treatment. The second is bias due to heterogeneity in treatment effects. In this article, I show how “composition bias” due to population heterogeneity evolves over time when treatment propensity is systematically associated with heterogeneous treatment effects. A form of selection bias, composition bias, arises dynamically at the aggregate level even when the classic assumption of ignorability holds true at the microlevel.

Xie, Yu

2013-01-01

2

PUNCH: Population Characterization of Heterogeneity.  

PubMed

Neuropsychiatric disorders are notoriously heterogeneous in their presentation, which precludes straightforward and objective description of the differences between affected and typical populations that therefore makes finding reliable biomarkers a challenge. This difficulty underlines the need for reliable methods to capture sample characteristics of heterogeneity using a single continuous measure, incorporating the multitude of scores used to describe different aspects of functioning. This study addresses this challenge by proposing a general method of identifying and quantifying the heterogeneity of any clinical population using a severity measure called the PUNCH (Population Characterization of Heterogeneity). PUNCH is a decision level fusion technique to incorporate decisions of various phenotypic scores, while providing interpretable weights for scores. We provide applications of our framework to simulated datasets and to a large sample of youth with Autism Spectrum Disorder (ASD). Next we stratify PUNCH scores in our ASD sample and show how severity moderates findings of group differences in diffusion weighted brain imaging data; more severely affected subgroups of ASD show expanded differences compared to age and gender matched healthy controls. Results demonstrate the ability of our measure in quantifying the underlying heterogeneity of the clinical samples, and suggest its utility in providing researchers with reliable severity assessments incorporating population heterogeneity. PMID:24799135

Tunc, Birkan; Ghanbari, Yasser; Smith, Alex R; Pandey, Juhi; Browne, Aaron; Schultz, Robert T; Verma, Ragini

2014-09-01

3

Range expansion of heterogeneous populations.  

PubMed

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. PMID:24766021

Reiter, Matthias; Rulands, Steffen; Frey, Erwin

2014-04-11

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

Efficient coding in heterogeneous neuronal populations  

PubMed Central

A ubiquitous feature of neuronal responses within a cortical area is their high degree of inhomogeneity. Even cells within the same functional column are known to have highly heterogeneous response properties when the same stimulus is presented. Whether the wide diversity of neuronal responses is an epiphenomenon or plays a role for cortical function is unknown. Here, we examined the relationship between the heterogeneity of neuronal responses and population coding. Contrary to our expectation, we found that the high variability of intrinsic response properties of individual cells changes the structure of neuronal correlations to improve the information encoded in the population activity. Thus, the heterogeneity of neuronal responses is in fact beneficial for sensory coding when stimuli are decoded from the population response.

Chelaru, Mircea I.; Dragoi, Valentin

2008-01-01

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.

Biressi, Stefano; Rando, Thomas A.

2010-01-01

7

Evolution of altruistic punishment in heterogeneous populations.  

PubMed

Evolutionary models for altruistic behavior typically make the assumption of homogeneity: each individual has the same costs and benefits associated with cooperating with each other and punishing for selfish behavior. In this paper, we relax this assumption by separating the population into heterogeneous classes, such that individuals from different classes differ in their ability to punish for selfishness. We compare the effects of introducing heterogeneity this way across two population models, that each represents a different type of population: the infinite and well-mixed population describes the way workers of social insects such as ants are organized, while a spatially structured population is more related to the way social norms evolve and are maintained in a social network. We find that heterogeneity in the effectiveness of punishment by itself has little to no effect on whether or not altruistic behavior will stabilize in a population. In contrast, heterogeneity in the cost that individuals pay to punish for selfish behavior allows altruistic behavior to be maintained more easily. Fewer punishers are needed to deter selfish behavior, and the individuals that punish will mostly belong to the class that pays a lower cost to do so. This effect is amplified when individuals that pay a lower cost for punishing inflict a higher punishment. The two population models differ when individuals that pay a low cost for punishing also inflict a lower punishment. In this situation, altruistic behavior becomes harder to maintain in an infinite and well-mixed population. However, this effect does not occur when the population is spatially structured. PMID:21903100

de Weerd, Harmen; Verbrugge, Rineke

2011-12-01

8

Oncology Social Work with an Ethnically Heterogeneous Population  

Cancer.gov

Social Work With an Social Work With an Ethnically Heterogeneous Ethnically Heterogeneous Population of Cancer Population of Cancer Patients Patients Chanan Chanan Qassem Qassem , MSW , MSW Shaare Zedek Shaare Zedek Medical Center Medical Center Jerusalem,

9

Population robustness arising from cellular heterogeneity  

PubMed Central

Heterogeneity between individual cells is a common feature of dynamic cellular processes, including signaling, transcription, and cell fate; yet the overall tissue level physiological phenotype needs to be carefully controlled to avoid fluctuations. Here we show that in the NF-?B signaling system, the precise timing of a dual-delayed negative feedback motif [involving stochastic transcription of inhibitor ?B (I?B)-? and -?] is optimized to induce heterogeneous timing of NF-?B oscillations between individual cells. We suggest that this dual-delayed negative feedback motif enables NF-?B signaling to generate robust single cell oscillations by reducing sensitivity to key parameter perturbations. Simultaneously, enhanced cell heterogeneity may represent a mechanism that controls the overall coordination and stability of cell population responses by decreasing temporal fluctuations of paracrine signaling. It has often been thought that dynamic biological systems may have evolved to maximize robustness through cell-to-cell coordination and homogeneity. Our analyses suggest in contrast, that this cellular variation might be advantageous and subject to evolutionary selection. Alternative types of therapy could perhaps be designed to modulate this cellular heterogeneity.

Paszek, Pawel; Ryan, Sheila; Ashall, Louise; Sillitoe, Kate; Harper, Claire V.; Spiller, David G.; Rand, David A.; White, Michael R. H.

2010-01-01

10

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

11

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.

12

Evolutionary Game Dynamics in Populations with Heterogenous Structures  

PubMed Central

Evolutionary graph theory is a well established framework for modelling the evolution of social behaviours in structured populations. An emerging consensus in this field is that graphs that exhibit heterogeneity in the number of connections between individuals are more conducive to the spread of cooperative behaviours. In this article we show that such a conclusion largely depends on the individual-level interactions that take place. In particular, averaging payoffs garnered through game interactions rather than accumulating the payoffs can altogether remove the cooperative advantage of heterogeneous graphs while such a difference does not affect the outcome on homogeneous structures. In addition, the rate at which game interactions occur can alter the evolutionary outcome. Less interactions allow heterogeneous graphs to support more cooperation than homogeneous graphs, while higher rates of interactions make homogeneous and heterogeneous graphs virtually indistinguishable in their ability to support cooperation. Most importantly, we show that common measures of evolutionary advantage used in homogeneous populations, such as a comparison of the fixation probability of a rare mutant to that of the resident type, are no longer valid in heterogeneous populations. Heterogeneity causes a bias in where mutations occur in the population which affects the mutant's fixation probability. We derive the appropriate measures for heterogeneous populations that account for this bias.

Maciejewski, Wes; Fu, Feng; Hauert, Christoph

2014-01-01

13

Heterogeneous Vascular Dependence of Tumor Cell Populations  

PubMed Central

Cells within a tumor are highly heterogeneous with respect to a wide range of genotypic and phenotypic characteristics. The latter include such properties as growth, survival, invasion, and metastasis. We asked whether the degree to which individual tumor cells rely on a tumor’s vasculature might also be heterogeneous. By adapting an intravital Hoechst 33342 staining technique, we labeled and isolated tumor cells based on their relative proximity to perfused vessels. Because tumor regions distal to the vasculature are likely hypoxic, we examined cells deficient for hypoxia-inducible factor-1? (HIF-1?), a transcription factor that has been shown to mediate hypoxia-induced responses, including apoptosis. Despite reduced vascularization in HIF-1??/? embryonic stem cell-derived tumors, their growth in vivo was found to be accelerated relative to HIF-1?+/+ tumor counterparts. We hypothesized that this paradoxical observation is because of decreased apoptotic rate, resulting in diminished vascular dependence of HIF-1??/? cells. Analysis of heterogeneous tumors established from mixtures of HIF-1?+/+ with HIF-1??/? cells revealed that the proportion of cells expressing wild-type HIF-1? was increased in perivascular areas and decreased in distal tumor regions. Thus, cells expressing HIF-1? were found to be highly dependent on proximity to blood vessels for their growth and survival in vivo, whereas cells that had lost HIF-1? expression were much less so. Heterogeneity in angiogenesis dependence was also observed among cell subpopulations isolated from human melanoma xenografts. This potential for selection of less vascular-dependent tumor cell variants throughout the course of disease progression may have important implications for the long-term efficacy of anti-angiogenic therapy.

Yu, Joanne L.; Rak, Janusz W.; Carmeliet, Peter; Nagy, Andras; Kerbel, Robert S.; Coomber, Brenda L.

2001-01-01

14

Dynamics of epidemics outbreaks in heterogeneous populations  

NASA Astrophysics Data System (ADS)

The dynamics of epidemic outbreaks have been investigated in recent years within two alternative theoretical paradigms. The key parameter of mean field type of models such as the SIR model is the basic reproduction number R0, the average number of secondary infections caused by one infected individual. Recently, scale free network models have received much attention as they account for the high variability in the number of social contacts involved. These models predict an infinite basic reproduction number in some cases. We investigate the impact of heterogeneities of contact rates in a generic model for epidemic outbreaks. We present a system in which both the time periods of being infectious and the time periods between transmissions are Poissonian processes. The heterogeneities are introduced by means of strongly variable contact rates. In contrast to scale free network models we observe a finite basic reproduction number and, counterintuitively a smaller overall epidemic outbreak as compared to the homogeneous system. Our study thus reveals that heterogeneities in contact rates do not necessarily facilitate the spread to infectious disease but may well attenuate it.

Brockmann, Dirk; Morales-Gallardo, Alejandro; Geisel, Theo

2007-03-01

15

Student Heterogeneity and Diversity at Catholic Colleges  

ERIC Educational Resources Information Center

The purpose of this study was to examine structural diversity at Catholic colleges; more specifically, the variation in the student body diversity characteristics of a sample of freshman students matriculated at Catholic colleges. For the purpose of this article, diversity characteristics include background characteristics associated with student

Elliott, Diane Cardenas

2012-01-01

16

How population heterogeneity in susceptibility and infectivity influences epidemic dynamics.  

PubMed

An important concern in public health is what population group should be prioritised for vaccination. To this end, we present an epidemic model with arbitrary initial distributions for population susceptibility, and corresponding infectivity distributions. We consider four scenarios: first, a population with heterogeneous susceptibility with a uniform distribution, but homogeneous infectivity; second, a heterogeneously susceptible population with linear heterogeneous infectivity functions, where the most susceptible are either the most or least infectious; third, a bimodal distribution for susceptibility, with all combinations of infectivity functions; finally, we consider the effects of additional pre-epidemic immunity, ostensibly through vaccination, on the epidemic dynamics. For a seasonal influenza-like infectious disease, we find the smallest final size and overall number of deaths due to the epidemic to occur if the most susceptible are vaccinated, corresponding to targeting children. PMID:24444766

Hickson, R I; Roberts, M G

2014-06-01

17

Item Response Theory Scaling with Heterogeneous Populations.  

ERIC Educational Resources Information Center

Tools used in scaling proficiency scores from the Second International Assessment of Educational Progress (IAEP) are described. The second IAEP study, conducted in 1991, was an international comparative study of the mathematics and science skills of samples of 9- and 13-year-old students from 20 countries. This paper focuses on part of the second…

Blais, Jean-Guy

18

Genetic heterogeneity among Eurytemora affinis populations in Western Europe  

Microsoft Academic Search

Evolutionary diversification of the broadly distributed copepod sibling species complex Eurytemora affinis has been documented in the northern hemisphere. However, the fine scale geographic distribution, levels of genetic subdivision,\\u000a evolutionary, and demographic histories of European populations have been less explored. To gain information on genetic subdivision\\u000a and to evaluate heterogeneity among European populations, we analyzed samples from 8 locations from

Gesche Winkler; Sami Souissi; Céline Poux; Vincent Castric

19

Promoting Student Collaboration in a Detracked, Heterogeneous Secondary Mathematics Classroom  

ERIC Educational Resources Information Center

Detracking and heterogeneous groupwork are two educational practices that have been shown to have promise for affording all students needed learning opportunities to develop mathematical proficiency. However, teachers face significant pedagogical challenges in organizing productive groupwork in these settings. This study offers an analysis of one…

Staples, Megan E.

2008-01-01

20

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.

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

2014-01-01

21

Molecular heterogeneity of familial hypercholesterolemia in the St. Petersburg population  

SciTech Connect

Inheritance of Taq I, BstE II, and Nco I restriction fragment length polymorphisms (RFLP) in three families from St. Petersburg with familial hypercholesterolemia (FH) was studied. In two of these families, polymorphic markers of the low density lipoprotein receptor (LDLR) gene cosegregated with the disease. This data confirmed FH diagnosis based on the analysis of blood plasma lipid levels. Three different RFLP haplotypes were associated with the disease, suggesting the presence of at least three point mutations in the LDLR gene in the population studied, i.e., suggesting molecular heterogeneity of FH in the St. Petersburg population. 23 refs., 6 figs., 3 tabs.

Mandel`shtam, M.Yu.; Lipovetskii, B.M.; Schvartsman, A.L.; Gaitskhoki, V.S. [Institute of Experimental Medicine, St. Petersburg (Russian Federation)

1995-04-01

22

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

23

Heterogeneity of the population of command neurons in the lamprey.  

PubMed

The effects of signals transmitted from the brain to the spinal locomotor networks by a population of command neurons are determined by specific functional projections of each individual neuron. To reveal these projections, we used a simple vertebrate model, the lamprey, in which responses of the spinal networks to spikes in single reticulospinal axons were detected by using the spike-triggered averaging of the motoneuronal activity. We found that individual neurons exert a uniform effect on the segmental motor output along the whole extent of their axons. Twenty different patterns of effect, that is, combinations of influences on the segmental motoneuron pools, were found. The widespread projections and heterogeneity of the population of command neurons present a basis for formation of different gross motor synergies. PMID:11567070

Zelenin, P V; Grillner, S; Orlovsky, G N; Deliagina, T G

2001-10-01

24

Heterogeneity of apolipoprotein E polymorphism in different Mexican populations.  

PubMed

Mexico has approximately 100 million inhabitants. Most of the urban Mexican population has been considered mestizo (Indian and Spanish descent), whereas the Indian population predominates in rural areas and small towns in the countryside. In this study we analyzed the apolipoprotein E (APOE) polymorphism in Guadalajara (the second largest metropolitan area of Mexico) and its surrounding areas, two adjoining states (Nayarit and Durango), and an Indian town (Huichol Indians) from western Mexico. APOE*3 was the most common allele, and APOE*3/*3 was the most common genotype in all populations studied. Guadalajara revealed the highest frequency of the APOE*2 allele (7.8%); the frequency decreased in the rural area (4.4%), followed by Nayarit (1.6%), and was absent in Durango and in the Huichols. On the contrary, the lowest frequency of the APOE*4 allele was in Guadalajara (8.4%); the frequency increased in the rural area (9.3%), in Nayarit and Durango (11.5% and 11.7%), and reached a high frequency in the Huichol Indians (28%). The distribution of the APOE allele in the western population of Mexico is similar to those described in Mexican American migrants living in the United States but is different from those populations living in Mexico City. This study shows the heterogeneity of the Mexican population, where the frequency of the APOE*2 allele is higher in Guadalajara than in other urban areas of Mexico and is similar to frequencies described in the Caucasian population. On the contrary, the Huichols revealed the highest frequency of the APOE*4 allele in Mexico and in the Americas. This information could be useful for the study of dyslipidemias associated with chronic diseases and as markers of ethnic variation in the Americas. PMID:16900882

Aceves, Dolores; Ruiz, Bertha; Nuño, Patricia; Roman, Sonia; Zepeda, Eloy; Panduro, Arturo

2006-02-01

25

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

26

Proportional reasoning competence among different student populations  

NASA Astrophysics Data System (ADS)

A collaborative project between Western Washington University, Rutgers University, and New Mexico State University seeks to understand student's competence level on proportional reasoning. We have been collecting and analyzing data from introductory physics and science education courses using a set of assessment tasks. We utilize the notion of constructs to categorize student thinking according to repetitive patterns. Results suggest that, when students confront ratio and proportion problems, they often experience a gap between the mechanics of the mathematical operations and the conscious understanding of what they are doing. In this poster we will share results of our findings from different courses, institutions, and student populations. Supported by NSF grants DUE-1045227, DUE-1045231, DUE-1045250..

Wong, King

2012-10-01

27

Gifted Students' Perceptions of the Academic and Social/Emotional Effects of Homogeneous and Heterogeneous Grouping  

ERIC Educational Resources Information Center

This study investigated student perceptions of differences in academic and social effects that occur when gifted and talented youth are grouped homogeneously (i.e., in special classes for gifted students) as contrasted with heterogeneously (i.e., in classes with many ability levels represented). Forty-four students in grades 5-11 completed…

Adams-Byers, Jan; Whitsell, Sara Squiller; Moon, Sidney M.

2004-01-01

28

Breeding site heterogeneity reduces variability in frog recruitment and population dynamics  

USGS Publications Warehouse

Environmental stochasticity can have profound effects on the dynamics and viability of wild populations, and habitat heterogeneity provides one mechanism by which populations may be buffered against the negative effects of environmental fluctuations. Heterogeneity in breeding pond hydroperiod across the landscape may allow amphibian populations to persist despite variable interannual precipitation. We examined recruitment dynamics over 10 yr in a high-elevation Columbia spotted frog (Rana luteiventris) population that breeds in ponds with a variety of hydroperiods. We combined these data with matrix population models to quantify the consequences of heterogeneity in pond hydroperiod on net recruitment (i.e. number of metamorphs produced) and population growth rates. We compared our heterogeneous system to hypothetical homogeneous environments with only ephemeral ponds, only semi-permanent ponds, and only permanent ponds. We also examined the effects of breeding pond habitat loss on population growth rates. Most eggs were laid in permanent ponds each year, but survival to metamorphosis was highest in the semi-permanent ponds. Recruitment success varied by both year and pond type. Net recruitment and stochastic population growth rate were highest under a scenario with homogeneous semi-permanent ponds, but variability in recruitment was lowest in the scenario with the observed heterogeneity in hydroperiods. Loss of pond habitat decreased population growth rate, with greater decreases associated with loss of permanent and semi-permanent habitat. The presence of a diversity of pond hydroperiods on the landscape will influence population dynamics, including reducing variability in recruitment in an uncertain climatic future.

McCaffery, Rebecca M.; Eby, Lisa A.; Maxell, Bryce A.; Corn, Paul Stephen

2013-01-01

29

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

PubMed

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

2014-06-01

30

The impact of population heterogeneity on risk estimation in genetic counseling  

PubMed Central

Background Genetic counseling has been an important tool for evaluating and communicating disease susceptibility for decades, and it has been applied to predict risks for a wide class of hereditary disorders. Most diseases are complex in nature and are affected by multiple genes and environmental conditions; it is highly likely that DNA tests alone do not define all the genetic factors responsible for a disease, so that persons classified into the same risk group by DNA testing actually could have different disease susceptibilities. Ignorance of population heterogeneity may lead to biased risk estimates, whereas additional information on population heterogeneity may improve the precision of such estimates. Methods Although DNA tests are widely used, few studies have investigated the accuracy of the predicted risks. We examined the impact of population heterogeneity on predicted disease risks by simulation of three different heterogeneity scenarios and studied the precision and accuracy of the risks estimated from a logistic regression model that ignored population heterogeneity. Moreover, we also incorporated information about population heterogeneity into our original model and investigated the resulting improvement in the accuracy of risk estimation. Results We found that heterogeneity in one or more categories could lead to biased estimates not only in the "contaminated" categories but also in other homogeneous categories. Incorporating information about population heterogeneity into the original model greatly improved the accuracy of risk estimation. Conclusions Our findings imply that without thorough knowledge about genetic basis of the disease, risks estimated from DNA tests may be misleading. Caution should be taken when evaluating the predicted risks obtained from genetic counseling. On the other hand, the improved accuracy of risk estimates after incorporating population heterogeneity information into the model did point out a promising direction for genetic counseling, since more and more new techniques are being invented and disease etiology is being better understood.

Liu, Wenlei; Icitovic, Nikolina; Shaffer, Michele L; Chase, Gary A

2004-01-01

31

PEGylation of microspheres generates a heterogeneous population of particles with differential surface characteristics and biological performance  

Microsoft Academic Search

Surface PEGylation of polystyrene microspheres with methoxy-poly(ethylene glycol)-5000 (mPEG-5000) generated a heterogeneous population of entities that differed in surface characteristics and in vitro biological performance (phagocytosis and complement activation). Surface heterogeneity was determined by hydrophobic interaction chromatography, measurements of particle electrophoretic mobility in a defined field and adlayer thickness of the projected mPEG chains. The particle population separation by hydrophobic

J. K Gbadamosi; A. C Hunter; S. M Moghimi

2002-01-01

32

Characterizing the effect of population heterogeneity on evolutionary dynamics on complex networks.  

PubMed

Recently, the impact of network structure on evolutionary dynamics has been at the center of attention when studying the evolutionary process of structured populations. This paper aims at finding out the key structural feature of network to capture its impact on evolutionary dynamics. To this end, a novel concept called heat heterogeneity is introduced to characterize the structural heterogeneity of network, and the correlation between heat heterogeneity of structure and outcome of evolutionary dynamics is further investigated on various networks. It is found that the heat heterogeneity mainly determines the impact of network structure on evolutionary dynamics on complex networks. In detail, the heat heterogeneity readjusts the selection effect on evolutionary dynamics. Networks with high heat heterogeneity amplify the selection effect on the birth-death process and suppress the selection effect on the death-birth process. Based on the above results, an effective algorithm is proposed to generate selection adjusters with desired size and average degree. PMID:24849192

Tan, Shaolin; Lü, Jinhu

2014-01-01

33

Characterizing the effect of population heterogeneity on evolutionary dynamics on complex networks  

PubMed Central

Recently, the impact of network structure on evolutionary dynamics has been at the center of attention when studying the evolutionary process of structured populations. This paper aims at finding out the key structural feature of network to capture its impact on evolutionary dynamics. To this end, a novel concept called heat heterogeneity is introduced to characterize the structural heterogeneity of network, and the correlation between heat heterogeneity of structure and outcome of evolutionary dynamics is further investigated on various networks. It is found that the heat heterogeneity mainly determines the impact of network structure on evolutionary dynamics on complex networks. In detail, the heat heterogeneity readjusts the selection effect on evolutionary dynamics. Networks with high heat heterogeneity amplify the selection effect on the birth-death process and suppress the selection effect on the death-birth process. Based on the above results, an effective algorithm is proposed to generate selection adjusters with desired size and average degree.

Tan, Shaolin; Lu, Jinhu

2014-01-01

34

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

35

Statistical Treatment Rules for Heterogeneous Populations: With Application to Randomized Experiments  

Microsoft Academic Search

This paper uses Wald's concept of the risk of a statistical decision function to address the question: How should sample data on treatment response be used to guide treatment choices in a heterogeneous population? Statistical treatment rules (STRs) are statistical decision functions that map observed covariates of population members and sample data on treatment response into treatment choices. I propose

Charles F. Manski

1999-01-01

36

Expanding the Religious Heterogeneity of the Student Body.  

ERIC Educational Resources Information Center

Encourages church-related junior colleges to step out of denominational sectarianism in their educational missions and provide an educational environment for students from many religious backgrounds. (DMM)

Fields, George D., Jr.

1990-01-01

37

Uncovering epidemiological dynamics in heterogeneous host populations using phylogenetic methods  

PubMed Central

Host population structure has a major influence on epidemiological dynamics. However, in particular for sexually transmitted diseases, quantitative data on population contact structure are hard to obtain. Here, we introduce a new method that quantifies host population structure based on phylogenetic trees, which are obtained from pathogen genetic sequence data. Our method is based on a maximum-likelihood framework and uses a multi-type branching process, under which each host is assigned to a type (subpopulation). In a simulation study, we show that our method produces accurate parameter estimates for phylogenetic trees in which each tip is assigned to a type, as well for phylogenetic trees in which the type of the tip is unknown. We apply the method to a Latvian HIV-1 dataset, quantifying the impact of the intravenous drug user epidemic on the heterosexual epidemic (known tip states), and identifying superspreader dynamics within the men-having-sex-with-men epidemic (unknown tip states).

Stadler, Tanja; Bonhoeffer, Sebastian

2013-01-01

38

Uncovering epidemiological dynamics in heterogeneous host populations using phylogenetic methods.  

PubMed

Host population structure has a major influence on epidemiological dynamics. However, in particular for sexually transmitted diseases, quantitative data on population contact structure are hard to obtain. Here, we introduce a new method that quantifies host population structure based on phylogenetic trees, which are obtained from pathogen genetic sequence data. Our method is based on a maximum-likelihood framework and uses a multi-type branching process, under which each host is assigned to a type (subpopulation). In a simulation study, we show that our method produces accurate parameter estimates for phylogenetic trees in which each tip is assigned to a type, as well for phylogenetic trees in which the type of the tip is unknown. We apply the method to a Latvian HIV-1 dataset, quantifying the impact of the intravenous drug user epidemic on the heterosexual epidemic (known tip states), and identifying superspreader dynamics within the men-having-sex-with-men epidemic (unknown tip states). PMID:23382421

Stadler, Tanja; Bonhoeffer, Sebastian

2013-03-19

39

Slow epidemic extinction in populations with heterogeneous infection rates.  

PubMed

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)=?w(ij) proportional to the intensity of their contact w(ij), with a distribution P(w(ij)) taken from face-to-face experiments analyzed in Cattuto et al. [PLoS ONE 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. PMID:24032889

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

2013-08-01

40

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

41

Phase II Cancer Clinical Trials with Heterogeneous Patient Populations  

PubMed Central

SUMMARY The patient population for a phase II trial often consists of multiple subgroups in terms of risk level. In this case, a popular design approach is to specify the response rate and the prevalence of each subgroup, to calculate the response rate of the whole population by the weighted average of the response rates across subgroups, and to choose a standard phase II design such as Simon’s optimal or minimax design to test on the response rate for the whole population. In this case, although the prevalence of each subgroup is accurately specified, the observed prevalence among the accrued patients to the study may be quite different from the expected one because of the small sample size, which is typical in most phase II trials. The fixed rejection value for a chosen standard phase II design may be either too conservative (i.e., increasing the false rejection probability of the experimental therapy) if the trial accrues more high-risk patients than expected or too anti-conservative (i.e., increasing the false acceptance probability of the experimental therapy) if the trial accrues more low-risk patients than expected. We can avoid such problem by adjusting the rejection values depending on the observed prevalence from the trial. In this paper, we investigate the performance of the flexible designs compared with the standard design with fixed rejection values under various settings.

Jung, Sin-Ho; Chang, Myron N.; Kang, Sun J.

2012-01-01

42

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.

Stamatakis, Michail; Zygourakis, Kyriacos

2010-01-01

43

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

44

Characteristics of the General Physics student population.  

NASA Astrophysics Data System (ADS)

Are pre-medical students different than the other students in a General physics class? They often appear to be different, based on how often they seek help from the instructor or how nervous they are about 2 points on a lab report. But are these students different in a measurable characteristic? The purpose of this study is to better understand the characteristics of the students in the introductory physics classes. This is the first step toward improving the instruction. By better understanding the students the classroom, the organization and pedagogy can be adjusted to optimize student learning. The characteristics to be investigated during this study are: · student epistemological structure, · student attitudes, · science course preparation prior to this course, · study techniques used, · physics concepts gained during the class · performance in the class. The data will be analyzed to investigate differences between groups. The groups investigated will be major, gender, and traditional/nontraditional students.

Hunt, Gary L.

2006-12-01

45

Modelling lipid competition dynamics in heterogeneous protocell populations.  

PubMed

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

46

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.

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

2014-01-01

47

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.

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

2008-01-01

48

Population Heterogeneity and State Dependence: State of the Evidence and Directions for Future Research  

Microsoft Academic Search

Criminological research has consistently uncovered a positive correlationbetween past and current criminal behavior. Continuity in offending overtime can be attributed to at least two processes—populationheterogeneity and state dependence. A population heterogeneity processattributes stability in offending over time to differences in ananti-social characteristic (self-control, impulsivity, psychopathicpersonality) across persons that is established early in life andtime-stable thereafter. An implication of a population

Daniel Nagin; Raymond Paternoster

2000-01-01

49

Exploratory analysis of motorcycle holding time heterogeneity using a split-population duration model  

Microsoft Academic Search

This study integrated the samples taken in 2000 for motorcycle usage and their corresponding records registered in the Taiwan’s Vehicle Registration System to observe the survival process of motorcycle ownership. The specific heterogeneity of censored observations that failed to demonstrate actual ownership status in the registration system was corrected by employing a split-population duration model with a Weibull hazard function.

Hsin-Li Chang; Tsu-Hurng Yeh

2007-01-01

50

Coverage-adjusted estimators for mark-recapture in heterogeneous populations  

Microsoft Academic Search

Consideration of coverage yields a new class of estimators of population size for the standard mark-recapture model which permits heterogeneity of capture probabilities. Real data and simulation studies are used to assess these coverage-adjusted estimators. The simulations highlight the need for estimators that perform well for a wide range of values of the mean and coefficient of variation of the

J. Ashbridge; I. B. J. Goudie

2000-01-01

51

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

52

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

53

Assessing Heterogeneous Student Bodies Using a Methodology that Encourages the Acquisition of Skills Valued by Employers  

ERIC Educational Resources Information Center

This work compares the results of three assessment systems used in two Spanish universities (the "Universidad Politecnica de Madrid" and the "Universidad Catolica de Avila"): the traditional system based on final examinations, continuous assessment with periodic tests and a proposed system (specially designed for heterogeneous student bodies)…

Perdigones, Alicia; Garcia, Jose Luis; Valino, Vanesa; Raposo, Cecilia

2009-01-01

54

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. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24488881

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

2014-05-30

55

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.

2012-01-01

56

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

57

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.

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

2014-01-01

58

Disease-marker associations: power and heterogeneity in independent population samples.  

PubMed

We applied generalized transmission disequilibrium testing (TDT) models in combined replicates 1 through 5 from each of four simulated population samples. All analyses were conducted without knowledge of the generating models. To assess power and consistency of results within and between samples, analyses were repeated in all 25 replicates combined and in each replicate. With the exception of sample-specific findings for locus D, power was generally low to detect linkage in a genome scan or to confirm linkages detected by allele sharing in affected relatives, due to lack of linkage disequilibrium. We proposed likelihood ratio and Wald tests to detect heterogeneity among samples in disease-marker associations. Pooling data across heterogeneous populations may not improve power of the TDT method. PMID:10597484

Bull, S B; Toma, C; Mirea, L

1999-01-01

59

A methodological strategy for PAH genotyping in populations with a marked molecular heterogeneity of hyperphenylalaninemia  

Microsoft Academic Search

The elucidation of the molecular basis of hyperphenylalaninemia in various world populations (PKU Consortium Database: http:\\/\\/www.mcgill.ca\\/pahdb\\/) has revealed a remarkable molecular heterogeneity at the locus encoding for phenylalanine hydroxylase. As a consequence, genotyping of HPA patients has prompted the establishment of an impressive number of mutation detection protocols. In spite of the large variety of methods proposed so far, no

V. Romano; D. Lio; L. Scola; L. Leggio; G. De Leo; A. Salerno

2001-01-01

60

Analysis of fluorescent reporters indicates heterogeneity in glucose uptake and utilization in clonal bacterial populations  

PubMed Central

Background In this study, we aimed at investigating heterogeneity in the expression of metabolic genes in clonal populations of Escherichia coli growing on glucose as the sole carbon source. Different metabolic phenotypes can arise in these clonal populations through variation in the expression of glucose transporters and metabolic enzymes. First, we focused on the glucose transporters PtsG and MglBAC to analyze the diversity of glucose uptake strategies. Second, we analyzed phenotypic variation in the expression of genes involved in gluconeogenesis and acetate scavenging (as acetate is formed and excreted during bacterial growth on glucose), which can reveal, for instance, phenotypic subpopulations that cross-feed through the exchange of acetate. In these experiments, E. coli MG1655 strains containing different transcriptional GFP reporters were grown in chemostats and reporter expression was measured with flow cytometry. Results Our results suggest heterogeneous expression of metabolic genes in bacterial clonal populations grown in glucose environments. The two glucose transport systems exhibited different level of heterogeneity. The majority of the bacterial cells expressed the reporters for both glucose transporters MglBAC and PtsG and a small fraction of cells only expressed the reporter for Mgl. At a low dilution rate, signals from transcriptional reporters for acetyl-CoA synthetase Acs and phosphoenolpyruvate carboxykinase Pck indicated that almost all cells expressed the genes that are part of acetate utilization and the gluconeogenesis pathway, respectively. Possible co-existence of two phenotypic subpopulations differing in acs expression occurred at the threshold of the switch to overflow metabolism. The overflow metabolism results in the production of acetate and has been previously reported to occur at intermediate dilution rates in chemostats with high concentration of glucose in the feed. Conclusions Analysis of the heterogeneous expression of reporters for genes involved in glucose and acetate metabolism raises new question whether different metabolic phenotypes are expressed in clonal populations growing in continuous cultures fed on glucose as the initially sole carbon source.

2013-01-01

61

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.

2014-01-01

62

Transport of Escherichia coli in saturated porous media: dual mode deposition and intra-population heterogeneity.  

PubMed

Because of heterogeneity among members of a bacteria population, deposition rates of bacteria may decrease upon the distance bacteria are transported in an aquifer. Such deposition rate decreases may result in retained bacteria concentrations, which decrease hyper-exponentially as a function of transport distance, and may therefore significantly affect the transport of colloids in aquifers. We investigated the occurrence of hyper-exponential deposition of Escherichia coli, an important indicator for fecal contamination, and the causes for such behavior. In a series of column experiments with glass beads of various sizes, we found that attachment of E. coli decreased hyper-exponentially, or, on logarithmic scale in a bimodal way, as a function of the transported distance from the column inlet. From data fitting of the retained bacteria concentration profiles, the sticking efficiency of 40% of the E. coli population was high (alpha=1), while the sticking efficiency of 60% was low (alpha=0.01). From the E. coli total population, an E. coli subpopulation consisting of slow attachers could be isolated by means of column passage. In subsequent column experiments this subpopulation attached less than the E. coli total population, consisting of both slow and fast attachers. We concluded that the main driver for the observed dual mode deposition was heterogeneity among members of the bacteria population. Intra-population may result in some microbes traveling surprisingly high distances in the subsurface. Extending the colloid filtration theory with intra-population variability may provide a valuable framework for assessing the transport of bacteria in aquifers. PMID:17346767

Foppen, Jan Willem; van Herwerden, Manon; Schijven, Jack

2007-04-01

63

Heterogenous Population Coding of a Short-Term Memory and Decision Task  

PubMed Central

We examined neural spike recordings from prefrontal cortex (PFC) while monkeys performed a delayed somatosensory discrimination task. In general, PFC neurons displayed great heterogeneity in response to the task. That is, though individual cells spiked reliably in response to task variables from trial-to-trial, each cell had idiosyncratic combinations of response properties. Despite the great variety in response types, some general patterns held. We used linear regression analysis on the spike data to both display the full heterogeneity of the data and classify cells into categories. We compared different categories of cells and found little difference in their ability to carry information about task variables or their correlation to behavior. This suggests a distributed neural code for the task rather than a highly modularized one. Along this line, we compared the predictions of two theoretical models to the data. We found that cell types predicted by both models were not represented significantly in the population. Our study points to a different class of models that should embrace the inherent heterogeneity of the data, but should also account for the non-random features of the population.

Jun, Joseph K.; Miller, Paul; Hernandez, Adrian; Zainos, Antonio; Lemus, Luis; Brody, Carlos D.; Romo, Ranulfo

2010-01-01

64

Effect of distance-related heterogeneity on population size estimates from point counts  

USGS Publications Warehouse

Point counts are used widely to index bird populations. Variation in the proportion of birds counted is a known source of error, and for robust inference it has been advocated that counts be converted to estimates of absolute population size. We used simulation to assess nine methods for the conduct and analysis of point counts when the data included distance-related heterogeneity of individual detection probability. Distance from the observer is a ubiquitous source of heterogeneity, because nearby birds are more easily detected than distant ones. Several recent methods (dependent double-observer, time of first detection, time of detection, independent multiple-observer, and repeated counts) do not account for distance-related heterogeneity, at least in their simpler forms. We assessed bias in estimates of population size by simulating counts with fixed radius w over four time intervals (occasions). Detection probability per occasion was modeled as a half-normal function of distance with scale parameter sigma and intercept g(0) = 1.0. Bias varied with sigma/w; values of sigma inferred from published studies were often 50% for a 100-m fixed-radius count. More critically, the bias of adjusted counts sometimes varied more than that of unadjusted counts, and inference from adjusted counts would be less robust. The problem was not solved by using mixture models or including distance as a covariate. Conventional distance sampling performed well in simulations, but its assumptions are difficult to meet in the field. We conclude that no existing method allows effective estimation of population size from point counts.

Efford, M. G.; Dawson, D.K.

2009-01-01

65

Student understanding in mechanics: A large population survey  

NSDL National Science Digital Library

There has recently been a considerable growth in research probing student understanding in mechanics. Questions based on four such research probes were included in the end-of-high-school physics examination undertaken by some 5500 students. The results obtained give an indication of the extent to which various interpretations of some physical situations are held in a whole population. The possibilities of using research probes as a basis for assessment questions are also illustrated.

Gunstone, Richard

2005-10-20

66

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.

2014-01-01

67

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

68

Heterogeneity of intrinsic biophysical properties among cochlear nucleus neurons improves the population coding of temporal information.  

PubMed

Reliable representation of the spectrotemporal features of an acoustic stimulus is critical for sound recognition. However, if all neurons respond with identical firing to the same stimulus, redundancy in the activity patterns would reduce the information capacity of the population. We thus investigated spike reliability and temporal fluctuation coding in an ensemble of neurons recorded in vitro from the avian auditory brain stem. Sequential patch-clamp recordings were made from neurons of the cochlear nucleus angularis while injecting identical filtered Gaussian white noise currents, simulating synaptic drive. The spiking activity in neurons receiving these identically fluctuating stimuli was highly correlated, measured pairwise across neurons and as a pseudo-population. Two distinct uncorrelated noise stimuli could be discriminated using the temporal patterning, but not firing rate, of the spike trains in the neural ensemble, with best discrimination using information at time scales of 5-20 ms. Despite high cross-correlation values, the spike patterns observed in individual neurons were idiosyncratic, with notable heterogeneity across neurons. To investigate how temporal information is being encoded, we used optimal linear reconstruction to produce an estimate of the original current stimulus from the spike trains. Ensembles of trains sampled across the neural population could be used to predict >50% of the stimulus variation using optimal linear decoding, compared with ?20% using the same number of spike trains recorded from single neurons. We conclude that heterogeneity in the intrinsic biophysical properties of cochlear nucleus neurons reduces firing pattern redundancy while enhancing representation of temporal information. PMID:24623512

Ahn, J; Kreeger, L J; Lubejko, S T; Butts, D A; MacLeod, K M

2014-06-01

69

Wide proteolytic activity survey reinforces heterogeneity among Trypanosoma cruzi TCI and TCII wild populations.  

PubMed

Chagas disease, caused by the flagellate protozoan Trypanosoma cruzi, is characterized by considerable variation in both incidence and infection severity. This variation has been attributed to a set of complex features including the host genetic background, environmental and social factors, and the genetic heterogeneity of parasite populations. Using biochemical and molecular markers these populations can be divided into two major groups (TCI and TCII). In a previous work, our group identified cysteine and metalloprotease activities as good markers for differentiating TCI from TCII wild isolates, with a higher level of heterogeneity observed among TCII isolates. In this investigation, we applied the protease activity assay to a sample of 49 sylvatic T. cruzi isolates that had been previously assessed in terms of their Swiss mice infection patterns. Protease activity profiles were determined at pH 5.5 and 10.0 and was compared with the original host species, phylogenetic lineage, and mice infection characteristics. Substantial variability, with molecular weights ranging from 35 to 220 kDa for active proteases at pH 5.5, and of 30 to 90 kDa for active proteases at pH 10.0, was observed in gelatin substrate gels, with no phenetic separation between TCI and TCII groups or original hosts. The combinatorial expression of proteases recorded among individual isolates may account for the diverse behavior observed for parasite populations in nature. PMID:20420537

Fampa, Patrícia; Lisboa, Cristiane Varella; Zahner, Viviane; Jansen, Ana Maria; Ramirez, Marcel Ivan

2010-11-01

70

Cluster detection of diseases in heterogeneous populations: an alternative to scan methods.  

PubMed

Cluster detection has become an important part of the agenda of epidemiologists and public health authorities, the identification of high- and low-risk areas is fundamental in the definition of public health strategies and in the suggestion of potential risks factors. Currently, there are different cluster detection techniques available, the most popular being those using windows to scan the areas within the studied region. However, when these areas are heterogeneous in populations' sizes, scan window methods can lead to inaccurate conclusions. In order to perform cluster detection over heterogeneously populated areas, we developed a method not based on scanning windows but instead on standard mortality ratios (SMR) using irregular spatial aggregation (ISA). Its extension, i.e. irregular spatial aggregation with covariates (ISAC), includes covariates with residuals from Poisson regression. We compared the performance of the method with the flexible shaped spatial scan statistic (FlexScan) using mortality data for stomach and bladder cancer for 8,098 Spanish towns. The results show a collection of clusters for stomach and bladder cancer similar to that detected by ISA and FlexScan. However, in general, clusters detected by FlexScan were bigger and include towns with SMR, which were not statistically significant. For bladder cancer, clusters detected by ISAC differed from those detected by ISA and FlexScan in shape and location. The ISA and ISAC methods could be an alternative to the traditional scan window methods for cluster detection over aggregated data when the areas under study are heterogeneous in terms of population. The simplicity and flexibility of the methods make them more attractive than methods based on more complicated algorithms. PMID:24893029

Ramis, Rebeca; Gómez-Barroso, Diana; López-Abente, Gonzalo

2014-05-01

71

The performance of mixture models in heterogeneous closed population capture-recapture.  

PubMed

Dorazio and Royle (2003, Biometrics 59, 351-364) investigated the behavior of three mixture models for closed population capture-recapture analysis in the presence of individual heterogeneity of capture probability. Their simulations were from the beta-binomial distribution, with analyses from the beta-binomial, the logit-normal, and the finite mixture (latent class) models. In this response, simulations from many different distributions give a broader picture of the relative value of the beta-binomial and the finite mixture models, and provide some preliminary insights into the situations in which these models are useful. PMID:16135042

Pledger, Shirley

2005-09-01

72

Which spatial heterogeneity framework? Consequences for conclusions about patchy population distributions.  

PubMed

Patches, gradients, and hierarchies are three common organizational frameworks for assessing the effects of spatial heterogeneity on species distributions. Since these frameworks are often chosen a priori, without knowledge of study systems, they may not correspond to the empirical heterogeneity present and may result in partial or erroneous conclusions about the forces structuring species distributions. I tested the consequences of choosing particular frameworks and whether patch heterogeneity structured patchily distributed populations of the valley elderberry longhorn beetle (Desmocerus californicus dimorphus) along four rivers in California's Central Valley (USA). A comparison of the three approaches revealed that each led to incomplete conclusions about controls on the beetle's distribution and populations. Patch analysis revealed weak effects of patch size and quality, and high unexplained variance, which likely reveals large amounts of stochasticity since replication was high. The patch analysis therefore concluded that distributions consistent with patch dynamic structures like classic metapopulation, source-sink, and mainland-island models existed in the different rivers. Conversely, gradient analyses revealed a gradient-distribution pattern responding to continuous and often large-scale variables, such as host-plant age or size, water availability, and the presence of an invasive leguminous tree; again most variance in beetle occurrence remained unexplained. Hierarchical analysis identified the natural spatial patterns of the system but gave no indication of causal processes. The combination of all three approaches explained the maximum variance in beetle occurrence, through inclusion of a comprehensive list of explanatory variables, multiple spatial scales, various types of heterogeneity, and a focus on the scales at which beetle-environment interactions were strongest. Surprisingly, these results still supported the notion that the beetle exists as a metapopulation, a structure thought to be rare because it ignores habitat quality and landscape conditions. These analyses exemplify the simultaneous importance of local patch attributes and broad-scale and/or gradient variables that are commonly overlooked in patch studies. Importantly, some patch attributes acted over inter-patch scales, affecting the perception of patch distances and distributional extents. Only through the integration of frameworks was I able to decipher the system's complexity and see that all three types of heterogeneity were acting in the system, sometimes over unexpected scales. PMID:17601140

Talley, Theresa Sinicrope

2007-06-01

73

The Malthusian parameter and R0 for heterogeneous populations in periodic environments.  

PubMed

Since the classical stable population theory in demography by Sharpe and Lotka, the sign relation sign(?0)=sign(R0-1) between the basic reproduction number R0 and the Malthusian parameter (the intrinsic rate of natural increase) ?0 has played a central role in population theory and its applications, because it connects individual's average reproductivity described by life cycle parameters to growth character of the whole population. Since R0 is originally defined for linear population evolution process in a constant environment, it is an important extension if we could formulate the same kind of threshold principle for population growth in time-heterogeneous environments. Since the mid-1990s, several authors proposed some ideas to extend the definition of R0 so that it can be applied to population dynamics in periodic environments. In particular, the definition of R0 in a periodic environment by Bacaer and Guernaoui (J. Math. Biol. 53, 2006) is most important, because their definition of R0 in a periodic environment can be interpreted as the asymptotic per generation growth rate, so from the generational point of view, it can be seen as a direct extension of the most successful definition of R0 in a constant environment by Diekmann, Heesterbeek and Metz ( J. Math. Biol. 28, 1990). In this paper, we propose a new approach to establish the sign relation between R0 and the Malthusian parameter ?0 for linear structured population dynamics in a periodic environment. Our arguments depend on the uniform primitivity of positive evolutionary system, which leads the weak ergodicity and the existence of exponential solution in periodic environments. For typical finite and infinite dimensional linear population models, we prove that a positive exponential solution exists and the sign relation holds between the Malthusian parameter, which is defined as the exponent of the exponential solution, and R0 given by the spectral radius of the next generation operator by Bacaer and Guernaoui's definition. PMID:22901067

Inaba, Hisashi

2012-04-01

74

Asymptomatic Volunteers with a Polycystic Ovary Are a Functionally Distinct but Heterogeneous Population  

PubMed Central

Context/Objective: Our objective was to determine the ovarian function of asymptomatic volunteers with a polycystic ovary (V-PCO). Participants: Non-hirsute eumenorrheic V-PCO (n = 32) and volunteers with ultrasonographically normal ovaries (V-NO) (n = 21) were compared with one another and with polycystic ovary syndrome (PCOS) patients who met National Institute of Health criteria (n = 90). Design/Setting/Interventions: GnRH agonist (GnRHag), ACTH, and oral glucose tolerance tests were prospectively performed in a General Clinical Research Center. Results: The distribution of 17-hydroxyprogesterone (17OHP) responses to GnRHag of V-PCO formed a distinct population intermediate between that of V-NO, the reference population, and PCOS. Nevertheless, the V-PCO population was heterogeneous. There were 53% (seventeen of 32) that were functionally normal, with 17OHP responses and free testosterone levels like V-NO. A total of 25% (eight of 32) had an elevated free testosterone, thus meeting Rotterdam criteria for PCOS; one third of these had 17OHP hyperresponsiveness to GnRHag testing. The remaining 22% (seven of 32) had 17OHP hyperresponsiveness to GnRHag, but normal free testosterone. Of PCOS, 69% had elevated 17OHP hyperresponsiveness to GnRHag. Ovarian volume correlated significantly with 17OHP responses only in PCOS, accounting for just 10% of the variance. Conclusions: Many asymptomatic volunteers have a PCO. They are a distinct, but heterogeneous, population with respect to ovarian function, ranging from normal (53%) to occult PCOS by Rotterdam criteria (25%). Nearly one quarter (22%) had the typical PCOS type of ovarian dysfunction without hyperandrogenemia, termed a “dysregulated PCO”; they or their offspring may be at risk for PCOS. Ovarian ultrasonographic characteristics must be considered when establishing norms for ovarian function.

Mortensen, Monica; Ehrmann, David A.; Littlejohn, Elizabeth; Rosenfield, Robert L.

2009-01-01

75

Bone marrow as a home of heterogenous populations of nonhematopoietic stem cells.  

PubMed

Evidence is presented that bone marrow (BM) in addition to CD45(positive) hematopoietic stem cells contains a rare population of heterogenous CD45(negative) nonhematopoietic tissue committed stem cells (TCSC). These nonhematopoietic TCSC (i) are enriched in population of CXCR4(+) CD34(+) AC133(+) lin(-) CD45(-) and CXCR4(+) Sca-1(+) lin(-) CD45(-) in humans and mice, respectively, (ii) display several markers of pluripotent stem cells (PSC) and (iii) as we envision are deposited in BM early in development. Thus, since BM contains versatile nonhematopoietic stem cells, previous studies on plasticity trans-dedifferentiation of BM-derived hematopoietic stem cells (HSC) that did not include proper controls to exclude this possibility could lead to wrong interpretations. Therefore, in this spotlight review we present this alternative explanation of 'plasticity' of BM-derived stem cells based on the assumption that BM stem cells are heterogenous. We also discuss a potential relationship of TCSC/PSC identified by us with other BM-derived CD45(negative) nonhematopoietic stem cells that were recently identified by other investigators (eg MSC, MAPC, USSC and MIAMI cells). Finally, we discuss perspectives and pitfalls in potential application of these cells in regenerative medicine. PMID:15902288

Kucia, M; Reca, R; Jala, V R; Dawn, B; Ratajczak, J; Ratajczak, M Z

2005-07-01

76

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

77

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

78

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.

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

2014-01-01

79

Deep-sequencing of the peach latent mosaic viroid reveals new aspects of population heterogeneity.  

PubMed

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

Glouzon, Jean-Pierre Sehi; Bolduc, François; Wang, Shengrui; Najmanovich, Rafael J; Perreault, Jean-Pierre

2014-01-01

80

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

2013-01-01

81

IL12B expression is sustained by a heterogenous population of myeloid lineages during tuberculosis.  

PubMed

IL12B is required for resistance to Mycobacterium tuberculosis (Mtb) infection, promoting the initiation and maintenance of Mtb-specific effector responses. While this makes the IL12-pathway an attractive target for experimental tuberculosis (TB) therapies, data regarding what lineages express IL12B after infection is established are limited. This is not obvious in the lung, an organ in which both hematopoietic and non-hematopoietic lineages produce IL12p40 upon pathogen encounter. Here, we use radiation bone marrow chimeras and Yet40 reporter mice to determine what lineages produce IL12p40 during experimental TB. We observed that hematopoietic IL12p40-production was sufficient to control Mtb, with no contribution by non-hematopoietic lineages. Furthermore, rather than being produced by a single subset, IL12p40 was produced by cells that were heterogenous in their size, granularity, autofluorescence and expression of CD11c, CD11b and CD8?. While depending on the timepoint and tissue examined, the surface phenotype of IL12p40-producers most closely resembled macrophages based on previous surveys of lung myeloid lineages. Importantly, depletion of CD11c(hi) cells during infection had no affect on lung IL12p40-concentrations. Collectively, our data demonstrate that IL12p40 production is sustained by a heterogenous population of myeloid lineages during experimental TB, and that redundant mechanisms of IL12p40-production exist when CD11c(hi) lineages are absent. PMID:23491716

Reeme, Allison E; Miller, Halli E; Robinson, Richard T

2013-05-01

82

The benefits of diversity: Heterogenous DC populations allow for both immunity and tolerance.  

PubMed

The immune system must simultaneously mount a response against foreign antigens while tolerating self. How this happens is still unclear as many mechanisms of immune tolerance are antigen non-specific. Antigen specific immune cells called T-cells must first bind to Immunogenic Dendritic Cells (iDCs) before activating and proliferating. These iDCs present both self and foreign antigens during infection, so it is unclear how the immune response can be limited to primarily foreign reactive T-cells. Regulatory T-cells (Tregs) are known to play a key role in self-tolerance. Although they are antigen specific, they also act in an antigen non-specific manner by competing for space and growth factors as well as modifying DC behavior to help kill or deactivate other T-cells. In prior models, the lack of antigen specific control has made simultaneous foreign-immunity and self-tolerance extremely unlikely. We include a heterogeneous DC population, in which different DCs present antigens at different levels. In addition, we include Tolerogenic DC (tDCs) which can delete self-reactive T-cells under normal physiological conditions. We compare different mathematical models of immune tolerance with and without Tregs and heterogenous antigen presentation. For each model, we compute the final number of foreign-reactive and self-reactive T-cells, under a variety of different situations. We find that even if iDCs present more self-antigen than foreign antigen, the immune response will be primarily foreign-reactive as long as there is sufficient presentation of self-antigen on tDCs. Tregs are required primarily for rare or cryptic self-antigens that do not appear frequently on tDCs. We also find that Tregs can only be effective when we include heterogenous antigen presentation, as this allows Tregs and T-cells of the same antigen-specificity to colocalize to the same set of DCs. Tregs better aid immune tolerance when they can both compete for space and growth factors and directly eliminate other T-cells. Our results show the importance of the structure of the DC population in immune tolerance as well as the relative contribution of different cellular mechanisms. PMID:24816181

Moore, James R

2014-09-21

83

Diagnostic testing for ?-globin gene disorders in a heterogeneous North American population.  

PubMed

Adult hemoglobin is a heterotetramer composed of two ?-globin chains and two ?-globin chains (?2 ?2 ), each of which contains a heme molecule capable of binding oxygen and facilitating oxygen transport. The ?-globin chains are expressed from duplicated genes within a tandem gene cluster located on chromosome region 16p13.3. High-level expression of the ?-globin genes commences early in fetal development and continues throughout life. The ?-thalassemia syndromes are among the most single-gene disorders, resulting from decreased synthesis of ?-globin chains or synthesis of functionally abnormal ?-globin chains. These disorders are most common in South East Asia, but also occur in many other populations. The most common cause of ?-thalassemia is gene deletions, of which more than seventy have been reported. In addition, a small but significant proportion of cases involve point mutations of the ?-globin genes. Ideally, the diagnostic strategy should include allele-specific assays for commonly occurring deletions, as well as methods for detection of rare or novel deletions and point mutations. Here we provide an overview of the diagnostic methods available and our experience using these assays in a reference laboratory serving a heterogeneous at-risk population. PMID:23590659

Waye, J S; Eng, B

2013-06-01

84

Effect of reproductive modes and environmental heterogeneity in the population dynamics of a geographically widespread clonal desert cactus  

Microsoft Academic Search

The dynamics of plant populations in arid environments are largely affected by the unpredictable environmental conditions\\u000a and are fine-tuned by biotic factors, such as modes of recruitment. A single species must cope with both spatial and temporal\\u000a heterogeneity that trigger pulses of sexual and clonal establishment throughout its distributional range. We studied two populations\\u000a of the clonal, purple prickly pear

María C. Mandujano; Jordan Golubov; Laura F. Huenneke

2007-01-01

85

Toxicity of Increased Amounts of Chemicals and the Dose–Response Curves for Heterogeneous Microbial Populations in Soil  

Microsoft Academic Search

The paper deals with the interpretation and classification of dose–response curves in order to understand the way in which the heterogeneous soil microbial population behaves under chemical stress. The evaluation is based on a set of about 500 toxicity tests, in which geometrically increasing doses of toxicants were applied to soil samples. The responses of the microflora were measured by

Gerhard Welp; Gerhard W. Brümmer

1997-01-01

86

A comprehensive molecular characterization of beta thalassemia in a highly heterogeneous population.  

PubMed

In Iran, the prevalence of beta-thalassemia trait is approximately 4-8% in most areas, and in Mazandaran province 10% of the population are carriers. Twenty four beta-globin gene mutations were identified in 1635 persons with beta-thalassemia trait using reverse dot blot and restriction fragment length polymorphism analysis. The predominant mutations included IVSII-1 (G-A) (61%), codon 30 (G-C) (7.5%), codon 22 (-7bp) (6.2%), codon 8 (-AA) (5.4%) and IVSI-5 (G-C) (3.6%). These mutations were in different haplotypes, with IVSII-1 being the most heterogeneous. Other less frequent mutations included IVS-II-745 (C-G), codon 44 (-C), codon 39 (C-T), codon 5 (-CT), IVS I-110 (G-A), IVSI-130 (G-C), Fr8/9 (+G), IVSI-1 (G-A), and IVSI (-25bp). All rare mutations except IVSI-130 were encountered in a unique haplotype. The diversity of these mutations reflects the historical admixture of genes in the region. The high prevalence of IVSII-1 (G-A) compared to other parts of the country and the world suggests a founder effect. Our data provide a basis for genetic counseling and prenatal diagnosis. PMID:21493114

Akhavan-Niaki, Haleh; Derakhshandeh-Peykar, Poupak; Banihashemi, Ali; Mostafazadeh, Amrollah; Asghari, Beheshteh; Ahmadifard, Mohammad-Reza; Azizi, Mandana; Youssefi, Ali; Elmi, Maryam Mitra

2011-06-15

87

Normative data for vestibular evoked myogenic potential in different age groups among a heterogeneous Indian population.  

PubMed

To establish normative data of vestibular evoked myogenic potential in different age groups among a heterogeneous Indian population. Prospective study design using a sample of convenience. Eighty five normal controls ranging between the ages 7 and 71 years were asked to provide a written signed consent for the study. Demographic characteristics of the patients were summarized using descriptive statistical methods using SPSS-17 analysing software. The outcome variable (VEMP recording) was expressed in percentiles as function of age. In all patients the stimulus which gave the best response was 95 dB (97.7 %) and 100 dB (95 %). The mean of wave latencies (p1 & n1) for 95-VEMP were, 11.2 ± 3.2 and 17.3 ± 4.7 ms on the right and 11.0 ± 2.8 and 17.0 ± 4.2 ms on the left respectively. The amplitude was 45.1 ± 54 mV on right and 46.9 ± 61.6 mV on the left. The mean of latency difference was 0.87 ms. The VEMP is a relatively simple test. The VEMP response rate was maximum in the younger age group; the optimum intensity was 95 dB. The asymmetry ratio interpretation should be done according to the age specific values. PMID:24822153

Khan, Feroze K; Balraj, Achamma; Lepcha, Anjali

2014-06-01

88

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

89

Hispanics: A Diverse Population of Students to Influence the Landscape of Higher Education  

ERIC Educational Resources Information Center

Hispanic students are a growing and pervasive population within higher education. This position paper examines population characteristics and educational patterns of Hispanic students that underscore failures of the higher education system in serving these students, in addition to institutional issues and cultural values that further complicate…

Page, Jill

2013-01-01

90

The effects of spatial and temporal heterogeneity on the population dynamics of four animal species in a Danish landscape  

PubMed Central

Background Variation in carrying capacity and population return rates is generally ignored in traditional studies of population dynamics. Variation is hard to study in the field because of difficulties controlling the environment in order to obtain statistical replicates, and because of the scale and expense of experimenting on populations. There may also be ethical issues. To circumvent these problems we used detailed simulations of the simultaneous behaviours of interacting animals in an accurate facsimile of a real Danish landscape. The models incorporate as much as possible of the behaviour and ecology of skylarks Alauda arvensis, voles Microtus agrestis, a ground beetle Bembidion lampros and a linyphiid spider Erigone atra. This allows us to quantify and evaluate the importance of spatial and temporal heterogeneity on the population dynamics of the four species. Results Both spatial and temporal heterogeneity affected the relationship between population growth rate and population density in all four species. Spatial heterogeneity accounted for 23–30% of the variance in population growth rate after accounting for the effects of density, reflecting big differences in local carrying capacity associated with the landscape features important to individual species. Temporal heterogeneity accounted for 3–13% of the variance in vole, skylark and spider, but 43% in beetles. The associated temporal variation in carrying capacity would be problematic in traditional analyses of density dependence. Return rates were less than one in all species and essentially invariant in skylarks, spiders and beetles. Return rates varied over the landscape in voles, being slower where there were larger fluctuations in local population sizes. Conclusion Our analyses estimated the traditional parameters of carrying capacities and return rates, but these are now seen as varying continuously over the landscape depending on habitat quality and the mechanisms of density dependence. The importance of our results lies in our demonstration that the effects of spatial and temporal heterogeneity must be accounted for if we are to have accurate predictive models for use in management and conservation. This is an area which until now has lacked an adequate theoretical framework and methodology.

Sibly, Richard M; Nabe-Nielsen, Jacob; Forchhammer, Mads C; Forbes, Valery E; Topping, Christopher J

2009-01-01

91

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.

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

2014-01-01

92

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

PubMed

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

2014-04-01

93

Heterogeneous inbred populations are useful as sources of near-isogenic lines for RAPD marker localization.  

PubMed

The development and use of RAPD markers for applications in crop improvement has recently generated considerable interest within the plant breeding community. One potential application of RAPDs is their use for "tagging" simply-inherited (monogenic) pest-resistance genes and enabling more efficient identification and selection of genotypes carrying specific combinations of resistance genes. In this report, we propose and describe the use of heterogeneous inbred populations as sources of near-isogenic lines (NILs) for targeting RAPD markers linked to major pest resistance genes. The development of these NILs for RAPD marker analyses involved a sequence of line and mass selection during successive generations of inbreeding. DNA bulks derived from the NILs were used to identify a RAPD marker (designated OK14620, generated by 5'-CCCGCTACAC-3' decamer) that was tightly linked (2.23±1.33 centiMorgans) to an important rust [Uromyces appendiculatus (Pers.) Unger var. appendiculatus] resistance gene (Ur-3) in common bean (Phaseolus vulgaris L.). The efficiency of this approach was demonstrated by a low rate of false-positives identified, the tightness of the linkage identified, and the ability to detect polymorphism between genomic regions that are representative of the same gene pool of common bean. This method of deriving NILs should find application by researchers interested in utilizing marker-assisted selection for one or more major pest resistance genes. The identification of OK14620 should help to facilitate continued use of the Ur-3 resistance source and will now enable marker-assisted pyramiding of three different bean rust resistance sources (two previously tagged) to provide effective and stable resistance to this important pathogen. PMID:24186016

Haley, S D; Afanador, L K; Miklas, P N; Stavely, J R; Kelly, J D

1994-06-01

94

The intolerance of uncertainty scale: measurement invariance, population heterogeneity, and its relation with worry among self-identifying White and Black respondents.  

PubMed

Although it is understood that assessment tools require evaluation using diverse samples, such evaluations are relatively rare. There are obstacles to such work, but it remains important to pursue psychometric data in broad samples. As such, we evaluated measurement invariance and population heterogeneity of two versions of a widely used measure in the anxiety literature--the Intolerance of Uncertainty Scale (IUS)--among self-identifying White (N = 1,185) and Black (N = 301) students. Data from multiple-groups confirmatory factor analysis supported the equivalence of the equal form and factor loadings of both IUS versions in White and Black respondents. However, specific IUS items functioned differently in the two groups, with more IUS items appearing biased in the full-length relative to the short-form version. Correlations between IUS factors and worry were equivalent among White and Black respondents. We discuss the implications of these results for future research. PMID:22984142

Fergus, Thomas A; Wu, Kevin D

2013-10-01

95

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.

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

2014-01-01

96

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

97

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

98

Heterogeneity of the HIV epidemic in the general population of Karnataka state, south India  

PubMed Central

Background In the context of AVAHAN, the India AIDS Initiative of the Bill & Melinda Gates Foundation, general population surveys (GPS) were carried out between 2006 and 2008 in Belgaum (northern), Bellary (mid-state) and Mysore (southern) districts of Karnataka state, south India. Data from these three surveys were analysed to understand heterogeneity in HIV risk. Methods Outcome variables were the prevalence of HIV and sexually transmitted infections (STIs). Independent variables included age, district, place of residence, along with socio-demographic, medical and behavioural characteristics. Multivariate logistic regression was undertaken to identify characteristics associated with HIV and differences between districts, incorporating survey statistics to consider weights and cluster effects. Results The participation rate was 79.0% for the interview and 72.5% for providing a blood or urine sample that was tested for HIV. Belgaum had the highest overall HIV (1.43%) and Herpes simplex type-2 (HSV-2) (16.93%) prevalence, and the lowest prevalence of curable STIs. In Belgaum, the HIV epidemic is predominantly rural, and among women. In Bellary, the epidemic is predominantly in urban areas and among men, and HIV prevalence was 1.18%. Mysore had the lowest prevalence of HIV (0.80%) and HSV-2 (10.89%) and the highest prevalence of curable STIs. Higher HIV prevalence among men was associated with increasing age (p<0.001), and with history of STIs (AOR=2.44,95%CI:1.15-5.17). Male circumcision was associated with lower HIV prevalence (AOR=0.33,95%CI:0.13-0.81). Higher HIV prevalence among women was associated with age (AOR25-29years=11.22,95%CI:1.42-88.74, AOR30-34years=13.13,95%CI:1.67-103.19 and AOR35-39years=11.33,95%CI:1.32-96.83), having more than one lifetime sexual partner (AOR=4.61,95%CI:1.26-16.91) and having ever used a condom (AOR=3.32,95%CI:1.38-7.99). Having a dissolved marriage (being widowed/divorced/separated) was the strongest predictor (AOR=10.98,95%CI: 5.35-22.57) of HIV among women. Being a muslim woman was associated with lower HIV prevalence (AOR=0.27,95%CI:0.08-0.87). Conclusion The HIV epidemic in Karnataka shows considerable heterogeneity, and there appears to be an increasing gradient in HIV prevalence from south to north. The sex work structure in the northern districts may explain the higher prevalence of HIV in northern Karnataka. The higher prevalence of HIV and HSV-2 and lower prevalence of curable STIs in Belgaum suggests a later epidemic phase. Similarly, higher prevalence of curable STIs and lower HIV and HSV-2 prevalence in Mysore suggests an early phase epidemic.

2011-01-01

99

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.

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

2011-01-01

100

Grouped to Achieve: Are There Benefits to Assigning Students to Heterogeneous Cooperative Learning Groups Based on Pre-Test Scores?  

NASA Astrophysics Data System (ADS)

Cooperative learning has been one of the most widely used instructional practices around the world since the early 1980's. Small learning groups have been in existence since the beginning of the human race. These groups have grown in their variance and complexity overtime. Classrooms are getting more diverse every year and instructors need a way to take advantage of this diversity to improve learning. The purpose of this study was to see if heterogeneous cooperative learning groups based on student achievement can be used as a differentiated instructional strategy to increase students' ability to demonstrate knowledge of science concepts and ability to do engineering design. This study includes two different groups made up of two different middle school science classrooms of 25-30 students. These students were given an engineering design problem to solve within cooperative learning groups. One class was put into heterogeneous cooperative learning groups based on student's pre-test scores. The other class was grouped based on random assignment. The study measured the difference between each class's pre-post gains, student's responses to a group interaction form and interview questions addressing their perceptions of the makeup of their groups. The findings of the study were that there was no significant difference between learning gains for the treatment and comparison groups. There was a significant difference between the treatment and comparison groups in student perceptions of their group's ability to stay on task and manage their time efficiently. Both the comparison and treatment groups had a positive perception of the composition of their cooperative learning groups.

Werth, Arman Karl

101

Susceptible-infected-recovered epidemics in populations with heterogeneous contact rates  

NASA Astrophysics Data System (ADS)

Heterogeneity of contact patterns is recognized as an important feature for realistic modeling of many epidemics. During an outbreak, the frequency of contacts can vary a great deal from person to person and period to period. Contact heterogeneity has been shown to have a large impact on epidemic thresholds and the final size of epidemics. We develop and apply a model which incorporates an arbitrary distribution of contact rates. The model consists of a low-dimensional system of ordinary differential equations which incorporates arbitrary heterogeneity by making use of generating functions of the contact rate distribution. We show further how this model can be applied to the study of simple intervention strategies, such as quarantine of public venues with probability proportional to size. The dynamic model allows us to investigate the effects of gradually implementing such strategies in response to an ongoing epidemic, and we investigate these strategies using data on the contact patterns within a large US city.

Volz, E.

2008-06-01

102

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.

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

2013-01-01

103

Catalog of Exemplary Vocational Education Programs for California Community Colleges' Special Student Populations.  

ERIC Educational Resources Information Center

This directory contains abstracts of 30 model programs for special population students at California community colleges. Programs are divided into four categories corresponding to the type of special population served. The seven programs for disadvantaged students are as follows: "Career Beginnings"; "Center for Computer Assisted Instruction and…

Evaluation and Training Inst., Los Angeles, CA.

104

Fiscal Policy Effects in a Heterogeneous-Agent Overlapping-Generations Economy with an Aging Population  

National Technical Information Service (NTIS)

Among the models that the Congressional Budget Office uses to analyze the economic effects of changes in federal fiscal policy is a life-cycle growth model with overlapping generations of heterogeneous households. In this paper, we extend a similar dynami...

S. Nishiyama

2013-01-01

105

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

106

Recognising Language Impairment in Secondary School Student Populations  

ERIC Educational Resources Information Center

Up to 16% of students in mainstream secondary schools present with language impairment (LI). As with other learning difficulties, students with LI experience many academic, social, emotional and behavioral problems. Associated presenting behaviors may, however, be masking the primary language impairment. As a result, secondary school students with…

Starling, Julia; Munro, Natalie; Togher, Leanne; Arciuli, Joanne

2011-01-01

107

Implications of interacting microscale habitat heterogeneity and disturbance events on Folsomia candida (Collembola) population dynamics: A modeling approach.  

PubMed

The authors implemented a fractal algorithm in a spatially explicit individual-based model to generate landscapes with different microscale patterns of habitat fragmentation and disturbance events and studied their effects on population dynamics of the collembolan Folsomia candida. Among human activities that may cause habitat destruction, the present study focused on agricultural practices. Soil organisms living in a cultivated field are subjected to habitat loss and fragmentation as well as disturbance events generated by the application of agrochemicals and related activities. In addition, they are exposed to natural stressors, which might influence the effects of chemicals on populations. The authors designed simulation experiments that incorporate these 3 factors and investigated their effects on populations of F. candida in the presence or absence of behavioral avoidance of contaminated habitat. Simulation results show that spatial autocorrelation of contamination has different effects on population growth and equilibrium size according to the percentage of clean habitat. This pattern changes when avoidance behavior is excluded from the model, as does population recovery after a series of disturbance events. The model suggests that a combination of heterogeneous contamination and multiple stressors can lead to unexpected effects of toxicants at the population level. Individual-based models can help to understand these effects and therefore add ecological realism to environmental risk assessment of chemicals and can help to explore the effects of different risk management options. Environ Toxicol Chem 2014;33:1508-1516. © 2014 SETAC. PMID:24549590

Meli, Mattia; Palmqvist, Annemette; Forbes, Valery E

2014-07-01

108

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.

2009-01-01

109

Homeless and highly mobile students: A population-level description of the status of homeless students from three school districts  

Microsoft Academic Search

An increasing number of school-age children lack fixed, permanent housing, which negatively affects their school engagement, jeopardizing long-term school success. Much of the previous research on this problem has focused on specific interventions in specific jurisdictions on targeted populations, but seldom have researchers attempted to study homeless and highly mobile students at a population level. This descriptive study combined statewide

Anita M. Larson; Danielle M. Meehan

2011-01-01

110

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.

Davey, H M; Kell, D B

1996-01-01

111

Major Mitochondrial DNA Haplotype Heterogeneity in Highland and Lowland Amerindian Populations from Bolivia  

Microsoft Academic Search

This study provides the frequencies of four mitochondrial DNA (mtDNA) haplogroups of 233 native South Amerindians in eight populations living in the Beni Department of Bolivia, including six populations not previously studied. Linguistically, these populations belong to the three principal South Amerindian language stocks, Andean, Equatorial-Tucanoan, and Ge-Pano-Carib. Frequency analyses under geographic, historic, linguistic, and genetic configurations using the e

Francesc Bert; Alfons Corella; MANEL GENE ´; Alejandro Pérez-Pérez; Daniel Turbón

2001-01-01

112

The Effects of Homogeneous versus Heterogeneous Reading-Style Grouping on EFL Students' Non-Preferred Reading Style and Reading Comprehension  

ERIC Educational Resources Information Center

The purpose of this study was to investigate the effects of homogeneous versus heterogeneous reading-style grouping on EFL students' non-preferred reading style and reading comprehension. The study used a pretest-posttest experimental design. The original subjects of the study (N=86) were Egyptian English major senior students during the 2005/2006…

El-Koumy, Abdel Salam Abdel Khalek

2009-01-01

113

Multilocus genotyping reveals high heterogeneity and strong local population structure of the Plasmodium vivax population in the Peruvian Amazon  

Microsoft Academic Search

BACKGROUND: Peru is one of the Latin American countries with the highest malaria burden, mainly due to Plasmodium vivax infections. However, little is known about P. vivax transmission dynamics in the Peruvian Amazon, where most malaria cases occur. The genetic diversity and population structure of P. vivax isolates collected in different communities around Iquitos city, the capital of the Peruvian

Peter Van den Eede; Gert Van der Auwera; Christopher Delgado; Tine Huyse; Veronica E Soto-Calle; Dionicia Gamboa; Tanilu Grande; Hugo Rodriguez; Alejandro Llanos; Jozef Anné; Annette Erhart; Umberto D'Alessandro

2010-01-01

114

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

PubMed

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

2012-11-30

115

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.

Bilder, Christopher R.; Tebbs, Joshua M.

2012-01-01

116

The genetic heterogeneity of deer mouse populations ( Peromyscus maniculatus ) in an insular landscape  

Microsoft Academic Search

A survey of the genetic variability in deer mouse populations was performed using specimens collected from six different\\u000a islands on a lake covering approximately 50 km2. Random amplified polymorphic DNA (RAPD) was used to measure the extent of the genetic differences in this insular system.\\u000a An analysis of molecular variance (AMOVA) revealed that populations are clearly separated at this microgeographic

Pierre-Alexandre Landry; François-Joseph Lapointe

1999-01-01

117

Organizational Factors Affecting the Continuation of an Instructional Innovation for Heterogeneous Populations.  

ERIC Educational Resources Information Center

This paper investigates the elementary school principal's role in helping to sustain implementation of a complex math and science program designed to foster the development of higher order thinking skills, particularly for language minority students. The study predicted a positive relationship between coordination and program continuation; if the…

Dahl, Rene Fukuhara

118

The Heterogeneous Second-Language Population in US Colleges and the Impact on Writing Program Design  

ERIC Educational Resources Information Center

To effectively address the needs of second language (L2) learners in college writing courses, many postsecondary institutions, especially those located in cities with high concentrations of immigrants, offer college-level courses for L2 students. Such courses include noncredit English language courses in an intensive English program, developmental…

di Gennaro, Kristen

2012-01-01

119

Are New Generations of Female College-Student Populations Meeting Calcium Requirements: Comparison of American and Croatian Female Students  

PubMed Central

We compared calcium (Ca) sources and intake, as well as multivitamin/mineral supplement use between female students with nutrition/health background and those from general-student-populations. 314 participants 18–37 y, including 57 African-Americans and 54 Caucasian-Americans recruited from Nutrition and/or other Health Sciences departments (NHS), and 100 African-American and 103 Croatian women representing general-student-population (GSP), completed food frequency questionnaire assessing their usual Ca intake and supplement use. NHS populations met recommendations and consumed significantly more Ca, particularly from dairy sources, and were more likely to take supplements than GSP groups, suggesting that health education may influence Ca intake.

Douglas, Crystal C.; Rumbak, Ivana; Baric, Irena Colic; Kovacina, Marinela; Piasek, Martina; Ilich, Jasminka Z.

2010-01-01

120

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

121

Nurturing Gifted Students' Metacognitive Awareness: Effects of Training in Homogeneous and Heterogeneous Classes.  

ERIC Educational Resources Information Center

A study of six gifted elementary students found that students in the homogeneous gifted class showed a greater increase in the number of control functions performed by the mind-machines they proposed, offered descriptions of their machines which were longer, more sophisticated, and more creative, and leap-frogged off of each others' ideas.…

Sheppard, Shelby; Kanevsky, Lannie S.

1999-01-01

122

Person Perception among American and Indian Students and Creative Problem Solving in Culturally Heterogeneous Groups.  

National Technical Information Service (NTIS)

The generality of the analyses reported by Triandis (1964b), in which the behavioral differential was employed with American students, was checked with a sample of American as well as a sample of Indian students, and with a different set of stimulus perso...

H. C. Triandis M. Fishbein E. R. Hall

1964-01-01

123

Measuring the effectiveness of research-based curriculum at a university serving a diverse student population  

NSDL National Science Digital Library

California State University Fullerton is a regional comprehensive university that serves a diverse student population. Over half of the undergraduate students at CSUF are members of minority groups, and just under half spoke a language other than English at home while growing up. We have tested research-based curricular materials, including in courses at CSUF. In some cases, these materials are successful. However, in many cases student outcomes are significantly different from those reported at large research universities. Informally, many faculty believe that the student population at CSUF is significantly different from those at more selective universities. In what ways can the tools of PER be used to measure, describe, and understand the differences between student populations? Are the standard methods of PER suitable for answering questions of this type?

Loverude, Michael E.

2005-10-27

124

Measures of life stress and social support specific to an Asian student population  

Microsoft Academic Search

We designed two new measures—the Index of Life Stress (ILS) and the Index of Social Support (ISS)—to assist in the prediction of cultural adjustment for an Asian international student population. In the present study, these two measures were administered to 101 Asian international students. Stability estimates over 1 month were high: .97 for the ILS and .81 for the ISS.

Bin Yang; George A. Clum

1995-01-01

125

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

126

A Three-Sample Multiple-Recapture Approach to Census Population Estimation with Heterogeneous Catchability  

Microsoft Academic Search

A central assumption in the standard capture-recapture approach to the estimation of the size of a closed population is the homogeneity of the “capture” probabilities. In this article we develop an approach that allows for varying susceptibility to capture through individual parameters using a variant of the Rasch model from psychological measurement situations. Our approach requires an additional recapture. In

John N. Darroch; Stephen E. Fienberg; Gary F. V. Glonek; Brian W. Junker

1993-01-01

127

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

128

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

129

The mutation spectrum of the phenylalanine hydroxylase (PAH) gene and associated haplotypes reveal ethnic heterogeneity in the Taiwanese population.  

PubMed

Phenylalanine hydroxylase (PAH) deficiency is responsible for most cases of phenylketonuria (PKU). In this study of the PAH mutation spectrum in the Taiwanese population, 139 alleles were identified including 34 different mutations. The V190G, Q267R and F392I mutations are first reported in this study. The most common mutations, R241C, R408Q and Ex6-96A>G, account for 23.2%, 12.0% and 9.2%, of the mutant alleles, respectively. Haplotype analysis shows that R241C and Ex6-96A>G are exclusively associated with haplotype 4.3 to suggest founder effects. On the other hand, R408Q is found on two distinct haplotypes suggesting recurrent mutations. The spectrum of PAH mutations in Taiwan shows various links to those of other Asian regions, yet remarkable differences exist. Notably, R408Q, E286K and -4173_-407del, accounting for 21% of all mutant alleles in Taiwan, are very rare or are undetected among PKU cohorts of other Asian regions to suggest local founder effects. Moreover, the low homozygosity value of 0.092 hints at a high degree of ethnic heterogeneity within the Taiwanese population. Our study of PAH mutation spectrum and the associated haplotypes is useful for subsequent study on the origin and migration pattern via Taiwan, an island at the historical crossroad of migration of ancient populations. PMID:24401910

Liang, Ying; Huang, Miao-Zeng; Cheng, Cheng-Yi; Chao, Hung-Kun; Fwu, Victor Tramjay; Chiang, Szu-Hui; Hsiao, Kwang-Jen; Niu, Dau-Ming; Su, Tsung-Sheng

2014-03-01

130

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.

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

2010-01-01

131

Re-activated adult epicardial progenitor cells are a heterogeneous population molecularly distinct from their embryonic counterparts.  

PubMed

Cardiovascular disease remains the major cause of mortality, and cardiac cell therapy has recently emerged as a paradigm for heart repair. The epicardium is a layer of mesothelial cells covering the heart that during development contributes to different cardiovascular lineages, including cardiomyocytes, but which becomes quiescent after birth. We previously revealed that the peptide thymosin beta 4 (T?4) can reactivate adult epicardium-derived cells (EPDCs) after myocardial infarction (MI), to proliferate, and differentiate into cardiovascular derivatives. The aim of this study was to provide a lineage characterization of the adult EPDCs relative to the embryonic epicardial lineage and to determine prospective cell fate biases within the activated adult population during cardiovascular repair. Wt1(GFPCre/+) mice were primed with T?4 and MI induced by ligation of the left anterior descending coronary artery. Adult WT1(+) GFP(+) EPDCs were fluorescence-activated cell sorted (FACS) at 2, 4, and 7 days after MI. Embryonic WT1(+) GFP(+) EPDCs were isolated from embryonic hearts (E12.5) by FACS, and sorted cells were characterized by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) and immunostaining. Adult WT1(+) GFP(+) EPDCs were highly heterogeneous, expressing cardiac progenitor and mesenchymal stem markers. Based on the expression of stem cell antigen-1 (Sca-1), CD44, and CD90, we identified different subpopulations of EPDCs of varying cardiovascular potential, according to marker gene profiles, with a molecular phenotype distinct from the source embryonic epicardial cells at E12.5. Thus, adult WT1(+) GFP(+) cells are a heterogeneous population that when activated can restore an embryonic gene programme, but do not revert entirely to adopt an embryonic phenotype. Potential biases in cardiovascular cell fate suggest that discrete subpopulations of EPDCs might be clinically relevant for regenerative therapy. PMID:24702282

Bollini, Sveva; Vieira, Joaquim Miguel Nunes; Howard, Sara; Dubè, Karina Natasha; Balmer, Gemma Mary; Smart, Nicola; Riley, Paul Richard

2014-08-01

132

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.

2012-01-01

133

Genetic Diversity in Normal Cell Populations is the Earliest Stage of Oncogenesis Leading to Intra-Tumor Heterogeneity.  

PubMed

Random mutations and epigenetic alterations provide a rich substrate for microevolutionary phenomena to occur in proliferating epithelial tissues. Genetic diversity resulting from random mutations in normal cells is critically important for understanding the genetic basis of oncogenesis. However, evaluation of the cell-specific role of individual (epi-)genetic alterations in living tissues is extremely difficult from a direct experimental perspective. For this purpose, we have developed a single cell model to describe the fate of every cell in the uterine epithelium and to simulate occurrence of the first cancer cell. Computational simulations have shown that a baseline mutation rate of two mutations per cell division is sufficient to explain sporadic endometrial cancer as a rare evolutionary consequence with an incidence similar to that reported in SEER data. Simulation of the entire oncogenic process has allowed us to analyze the features of the tumor-initiating cells and their clonal expansion. Analysis of the malignant features of individual cancer cells, such as de-differentiation status, proliferation potential, and immortalization status, permits a mathematical characterization of malignancy at the single cell level and a comparison of intra-tumor heterogeneity between individual tumors. We found, under the conditions specified, that cancer stem cells account for approximately 7% of the total cancer cell population. Therefore, our mathematical modeling describes the genetic diversity and evolution in a normal cell population at the early stages of oncogenesis and characterizes intra-tumor heterogeneity. This model has explored the role of accumulation of a large number of genetic alterations in oncogenesis as an alternative to traditional biological approaches emphasizing the driving role of a small number of genetic mutations. A quantitative description of the contribution of a large set of genetic alterations will allow the investigation of the impact of environmental factors on the growth advantage of and selection pressure on individual cancer cells for tumor progression. PMID:23577323

Howk, Cory L; Voller, Zachary; Beck, Brandon B; Dai, Donghai

2013-01-01

134

Heterogeneous population growth, parental effects and genotype–environment interactions of a marine oligochaete  

Microsoft Academic Search

Cultures of asexually reproducing populations of the oligochaete Paranaislitoralis (Müller) collected from six different patches (3 to 50?m apart) on an intertidal mud flat in Flax Pond, New York, on two\\u000a occasions, June and October 1993, showed significant differences among lines in life span, number of offspring produced, and\\u000a in finite rate of increase (?). Although growth rates were significantly

P. Nilsson; J. P. Kurdziel; J. S. Levinton

1997-01-01

135

The population health performance of medical students at two medical schools  

Microsoft Academic Search

Public Health and medicine are complimentary disciplines dedicated to the health and well-being of humankind. Worldwide, medical school accreditation bodies require the inclusion of population health in medical education. In 2003, the Institutes of Medicine (IOM) recommended that all medical students receive basic public health training in population-based prevention. The purpose of this study was to (1) examine the public

Anne C Gill

2007-01-01

136

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

137

Changing Patterns of Cervical Disease in a Student Population.  

ERIC Educational Resources Information Center

The Cytology Service at the University of California at Los Angeles (UCLA) Center for Health Sciences has examined about 4000 pap smears (each year) from the UCLA Student Health Service between 1973-1978. An apparently significant increase in abnormal pap smears in young college-age women is reported. (Authors/CJ)

Rosenthal, Dorothy L.; And Others

1982-01-01

138

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

139

Differing effects of attention in single-units and populations are well predicted by heterogeneous tuning and the normalization model of attention.  

PubMed

Single-unit measurements have reported many different effects of attention on contrast-response (e.g., contrast-gain, response-gain, additive-offset dependent on visibility), while functional imaging measurements have more uniformly reported increases in response across all contrasts (additive-offset). The normalization model of attention elegantly predicts the diversity of effects of attention reported in single-units well-tuned to the stimulus, but what predictions does it make for more realistic populations of neurons with heterogeneous tuning? Are predictions in accordance with population-scale measurements? We used functional imaging data from humans to determine a realistic ratio of attention-field to stimulus-drive size (a key parameter for the model) and predicted effects of attention in a population of model neurons with heterogeneous tuning. We found that within the population, neurons well-tuned to the stimulus showed a response-gain effect, while less-well-tuned neurons showed a contrast-gain effect. Averaged across the population, these disparate effects of attention gave rise to additive-offsets in contrast-response, similar to reports in human functional imaging as well as population averages of single-units. Differences in predictions for single-units and populations were observed across a wide range of model parameters (ratios of attention-field to stimulus-drive size and the amount of baseline response modifiable by attention), offering an explanation for disparity in physiological reports. Thus, by accounting for heterogeneity in tuning of realistic neuronal populations, the normalization model of attention can not only predict responses of well-tuned neurons, but also the activity of large populations of neurons. More generally, computational models can unify physiological findings across different scales of measurement, and make links to behavior, but only if factors such as heterogeneous tuning within a population are properly accounted for. PMID:24600380

Hara, Yuko; Pestilli, Franco; Gardner, Justin L

2014-01-01

140

Differing effects of attention in single-units and populations are well predicted by heterogeneous tuning and the normalization model of attention  

PubMed Central

Single-unit measurements have reported many different effects of attention on contrast-response (e.g., contrast-gain, response-gain, additive-offset dependent on visibility), while functional imaging measurements have more uniformly reported increases in response across all contrasts (additive-offset). The normalization model of attention elegantly predicts the diversity of effects of attention reported in single-units well-tuned to the stimulus, but what predictions does it make for more realistic populations of neurons with heterogeneous tuning? Are predictions in accordance with population-scale measurements? We used functional imaging data from humans to determine a realistic ratio of attention-field to stimulus-drive size (a key parameter for the model) and predicted effects of attention in a population of model neurons with heterogeneous tuning. We found that within the population, neurons well-tuned to the stimulus showed a response-gain effect, while less-well-tuned neurons showed a contrast-gain effect. Averaged across the population, these disparate effects of attention gave rise to additive-offsets in contrast-response, similar to reports in human functional imaging as well as population averages of single-units. Differences in predictions for single-units and populations were observed across a wide range of model parameters (ratios of attention-field to stimulus-drive size and the amount of baseline response modifiable by attention), offering an explanation for disparity in physiological reports. Thus, by accounting for heterogeneity in tuning of realistic neuronal populations, the normalization model of attention can not only predict responses of well-tuned neurons, but also the activity of large populations of neurons. More generally, computational models can unify physiological findings across different scales of measurement, and make links to behavior, but only if factors such as heterogeneous tuning within a population are properly accounted for.

Hara, Yuko; Pestilli, Franco; Gardner, Justin L.

2014-01-01

141

Dynamic phase microscopy, a new method to detect viable and killed spores and to estimate the heterogeneity of spore populations  

NASA Astrophysics Data System (ADS)

One of the challenging tasks in monitoring studies is to estimate heterogeneity of microbial populations by the physiological state and potential viability of individual cells, especially with regard of their ability to withstand various environmental assaults. Previously, we described some approaches based on electron microscopy methods to discriminate vegetative, dormant, and dead cells in both aged microbial cultures and environmental samples, including permafrost. We propose to extend the arsenal of microscopy methods for monitoring studies by a new non-invasive and informative method - dynamic phase microscopy (DPM). The substantial advantage of DPM is that it gives quantitative (digitized) data of undestroyed (living) microscopic objects, exemplified in our work by Bacillus licheniformis spores. Using DPM made it possible to record interference images of objects (spores) and to produce picture of their "phase thickness" (PT) that is the optical path difference in nm. Thus, it was demonstrated the remarkable difference in the PT of spores at different physiological states: dormant, germinating, and heat-killed spores had PT values of 80, 40-50, and 20 nm, respectively. The other found criterion to distinguish between spores was the PT fluctuations. In contrast to dormant and killed spores, the PT of germinating spores oscillated with amplitude of up to 7 nm, with typical frequencies of 1.3 and 3.4 Hz. A combination of the recorded PT values and PT fluctuations gave a key to detect viable and dead cells. Under the conditions that did not support germination (the lack of nutrients), we were able to follow the response of a single dormant spore and a spore population to heating from 25 °C to 70 °C. Thus, a very small temperature change (from 40 °C to 42 °C) under conditions non-favorable for germination, caused a drastic decrease in the spores' PT; the second drop in the PT values was observed during heating from 60 °C to 70 °C. These changes were reversible: after cessation of heating, PT values became similar to dormant spores. So, DPM allowed us to track the first, reversible stage of activation, when a spore maintains the attributes of the dormant state. Under the conditions that favor germination (in the presence of nutrients), irreversible changes in the PT and spore diameter, d, were detectable in a single germinating spore and spore population. In addition, DPM allowed an easy estimation of the heterogeneity of spore populations. It is a great advantage of DPM that it makes possible to reveal the ability of spores to respond to various stimuli with or without further germination and outgrowth - the salient feature of a living cell. DPM may have a high potential in general microbiology and astrobiology, enabling to: (1) estimate the heterogeneity of spore populations either under standard conditions and subjected to solar radiation and simulated extraterrestrial factors; (2) to track a response of spores to changing conditions at the early germination stage, even if they do not enter further outgrowth; (3) to develop some approaches for monitoring studies and appraisal of the physiological state of dormant cells in situ, in samples of dry soils, permafrost, etc. regarded as models for searching life beyond the Earth.

Tychinsky, Vladimir P.; Mulyukin, Andrey L.; Lisovskii, Vitalii V.; Nikolaev, Yury A.; Kretushev, Aleksander V.; Vyshenskaya, Tatyana V.; Suzina, Nataliya E.; Duda, Vitalii I.; El-Registan, Galina I.

142

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.

Alves, Joao M.; Chikhi, Lounes; Amorim, Antonio; Lopes, Alexandra M.

2014-01-01

143

Sample Heterogeneity and the Measurement Structure of the Multidimensional Students' Life Satisfaction Scale  

ERIC Educational Resources Information Center

Several measurement assumptions were examined with the goal of assessing the validity of the Multidimensional Students' Life Satisfaction Scale (MSLSS), a measure of adolescents' satisfaction with their family, friends, living environment, school, self, and general quality of life. The data were obtained via a cross-sectional survey of 8,225…

Sawatzky, Richard; Ratner, Pamela A.; Johnson, Joy L.; Kopec, Jacek A.; Zumbo, Bruno D.

2009-01-01

144

Forms of Self-Concept in Gifted High School Students Enrolled in Heterogeneous Classes  

ERIC Educational Resources Information Center

Prior research has been devoted to understanding how to facilitate the integration of gifted young people (Intelligence Quotient, greater than or equal to 130) into classroom settings. This study investigated a typology of self-concept in gifted French high school students. Eighty-four participants, between the ages of 13 and 18 (mean age, 15.5;…

Villatte, Aude; Hugon, Mandarine; de Leonardis, Myriam

2011-01-01

145

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

146

Heterogeneous atypical cell populations are present in blood of metastatic breast cancer patients  

PubMed Central

Introduction Circulating tumor cells (CTCs) are commonly isolated from the blood by targeting the epithelial cell adhesion molecule (EpCAM) through positive selection. However, EpCAM can be downregulated during metastatic progression, or it can be initially not present. We designed the present prospective trial to characterize CTCs as well as other circulating cell populations in blood samples from women with metastatic breast cancer without EpCAM-dependent enrichment and/or isolation technology. Methods A total of 32 patients with metastatic breast cancer were enrolled, and blood samples were processed using a previously described negative depletion immunomagnetic methodology. Samples from healthy volunteers were run as controls (n?=?5). Multistep sequential labeling was performed to label and fix cell-surface markers followed by permeabilization for cytokeratins (CK) 8, 18 and 19. Multiparametric flow cytometry (FCM) analysis was conducted using a BD LSR II flow cytometer or a BD FACSAria II or FACSAria III cell sorter. Immunocytochemical staining on postenrichment specimens for DAPI, EpCAM, CD45, CK, epidermal growth factor receptor and vimentin was performed. Expression of these markers was visualized using confocal microscopy (CM). Results CD45-negative/CK-positive (CD45? CK+) populations with EpCAM?+?and EpCAM???expression were identified with both FCM and CM from the negatively enriched patient samples. In addition, EpCAM?+?and EpCAM???populations that were CK?+?and coexpressing the pan-hematopoietic marker CD45 were also noted. There were more CK?+?EpCAM???events/ml than CK?+?EpCAM?+?events/ml in both the CD45? and CD45+ fractions (both statistically significant at P???0.0005). The number of CK?+?CD45? and CK?+?CD45+ events per milliliter in blood samples (regardless of EpCAM status) was higher in patient samples than in normal control samples (P???0.0005 and P???0.026, respectively). Further, a significant fraction of the CK?+?CD45+ events also expressed CD68, a marker associated with tumor-associated macrophages. Higher levels of CD45-CK?+?EpCAM???were associated with worse overall survival (P?=?0.0292). Conclusions Metastatic breast cancer patients have atypical cells that are CK?+?EpCAM???circulating in their blood. Because a substantial number of these patients do not have EpCAM?+?CTCs, additional studies are needed to evaluate the role of EpCAM???circulating cells as a prognostic and predictive marker.

2014-01-01

147

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.

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

1987-01-01

148

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

PubMed

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, X; Michel, M F; Digat, B

1987-04-01

149

Activity-dependent heterogeneous populations of nitric oxide synthase neurons in the rat dorsal raphe nucleus.  

PubMed

The brainstem dorsal raphe nucleus (DRN) contains an abundant distribution of nitric oxide (NO) synthase (NOS)-containing neuronal profiles in two distinct populations: faint- and intense-immunoreactive cells in midline (ventromedial and dorsomedial) and lateral wing subregions, respectively. This study tested the hypothesis that different functional dynamics underlie the topography of NOS-containing cells in the DRN rostrocaudal and mediolateral neuraxis by using a capsaicin challenge paradigm (50 mg/kg, subcutaneous). Compared with vehicle, capsaicin significantly and preferentially increased nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d, an index of constitutive NOS) reactivity in the rostral midline and caudal lateral wing subregions. Furthermore, capsaicin activated more Fos-positive cells than vehicle within all subregions of the DRN but with a caudal versus rostral predominance in activation pattern. In addition, a high proportion of capsaicin-induced Fos cells in the midline but almost none in lateral wing stained for NADPH-d. These observations suggest the existence of two functionally distinct populations of NOS neurons in the DRN. Furthermore, capsaicin increased galanin immunoreactivity with predominant staining in cell soma and fiber processes in midline and lateral wing subregions of the nucleus, respectively. The total capsaicin-induced galanin immunoreactivity was higher in rostral versus caudal DRN, and a high proportion of galanin-positive cells in the midline also contained NADPH-d and neuronal NOS, thus suggesting a potential NO-galanin interaction in these neurons. The differential pattern of Fos/NADPH-d colocalization across the nucleus suggests that midline and lateral wing NOS neurons of the DRN express their neuromodulatory actions on discrete efferent targets via different intracellular mechanisms. PMID:16616732

Okere, Chuma O; Waterhouse, Barry D

2006-05-01

150

Sample Heterogeneity and the Measurement Structure of the Multidimensional Students’ Life Satisfaction Scale  

Microsoft Academic Search

Several measurement assumptions were examined with the goal of assessing the validity of the Multidimensional Students’ Life\\u000a Satisfaction Scale (MSLSS), a measure of adolescents’ satisfaction with their family, friends, living environment, school,\\u000a self, and general quality of life. The data were obtained via a cross-sectional survey of 8,225 adolescents in British Columbia,\\u000a Canada. Confirmatory factor and factor mixture analyses of

Richard Sawatzky; Pamela A. Ratner; Joy L. Johnson; Jacek A. Kopec; Bruno D. Zumbo

2009-01-01

151

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

152

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.

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

2014-01-01

153

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 3days but had lost viability by 6days 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

154

Large-scale heterogeneous representation of sound attributes in rat primary auditory cortex: from unit activity to population dynamics.  

PubMed

Recent evidence indicates the existence of pyramidal cells (PCs) and interneurons with nontrivial tuning characteristics for sound attributes in the primary auditory cortex (A1) of mammals. These neurons are functionally distributed into layers and sparsely organized at a small scale. However, their topological locations at a large scale in A1 have not yet been investigated. Furthermore, these neurons are usually classified from fine maps of attribute-dependent spiking activity, and not much attention is paid to population postsynaptic potentials related to their activity. We used extracellular recordings obtained from multiple sites in A1 of adult rats to determine neuronal codifiers for sound attributes defined by coarse representations of the population dose-response curves. We demonstrated that these codifiers, majorly involving PCs, are heterogeneously distributed along A1. Spiking activity in these neurons during stimulation was correlated to ? (12-25 Hz) and low ? (25-70 Hz) postsynaptic oscillations in the infragranular layer, whereas in the supragranular layer, better correlations were found with high ? (70-170 Hz) oscillations. The time-frequency analysis of the postsynaptic potentials showed a transient broadband power increase in all layers after the stimulus onset that was followed by a sustained high ? oscillation in the supragranular layer, fluctuations in the laminar content of the low-frequency oscillations, and a global attenuation in the low-frequency powers after the stimulus offset that happened together with a long-lasting strengthening of the ? oscillations. We concluded that, for rats, sounds are codified in A1 by segregated networks of specialized PCs whose postsynaptic activity impinges on the emergence of sparse/dense spiking patterns. PMID:21994380

Ogawa, Takeshi; Riera, Jorge; Goto, Takakuni; Sumiyoshi, Akira; Nonaka, Hiroi; Jerbi, Karim; Bertrand, Olivier; Kawashima, Ryuta

2011-10-12

155

Dynamic phase microscopy, a new method to detect viable and killed spores and to estimate the heterogeneity of spore populations  

NASA Astrophysics Data System (ADS)

One of the challenging tasks in monitoring studies is to estimate heterogeneity of microbial populations by the physiological state and potential viability of individual cells especially with regard of their ability to withstand various environmental assaults Previously we described some approaches based on electron microscopy methods to discriminate vegetative dormant and dead cells in both aged microbial cultures and environmental samples including permafrost In this communication we propose to extend the arsenal of microscopy methods for monitoring studies by a new non-invasive and informative method - dynamic phase microscopy DPM The substantial advantage of DPM is that it gives quantitative digitized data of un-destroyed living microscopic objects exemplified in our work by Bacillus licheniformis spores Using DPM made it possible to record interference images of objects spores and to produce picture of their phase thickness PT that is the optical path difference in nm Thus it was demonstrated the remarkable difference in the PT of spores at different physiological states dormant germinating and heat-killed spores had PT values of 80 nm 40-50 nm and 20 nm respectively The other found criterion to distinguish between spores was the PT fluctuations In contrast to dormant and killed spores the PT of germinating spores oscillated with amplitude of up to 7 nm with typical frequencies of 1 3 and 3 4 Hz A combination of the recorded PT values and PT fluctuations gave a key to detect viable and dead cells Under the conditions that did not

Tychinsky, V. P.; Mulyukin, A. L.; Lisovskii, V. V.; Nikolaev, Yu. A.; Kretushev, A. V.; Vyshenskaya, T. V.; Suzina, N. E.; Duda, V. I.; El-Registan, G. I.

156

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

157

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

158

Generalizing in Interaction: Middle School Mathematics Students Making Mathematical Generalizations in a Population-Modeling Project  

ERIC Educational Resources Information Center

Generalizing or making claims that extend beyond particular situations is a central mathematical practice and a focus of classroom mathematics instruction. This study examines how aspects of generality are produced through the situated activities of a group of middle school mathematics students working on an 8-week population-modeling project. The…

Jurow, A. Susan

2004-01-01

159

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

160

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

161

Genetic heterogeneity in populations of the Mediterranean shore crab, Carcinus aestuarii (Decapoda, Portunidae), from the Venice Lagoon  

NASA Astrophysics Data System (ADS)

Heterogeneity in genetic composition among recruits, mostly due to a large variance in reproductive success mediated by oceanographic processes, has been reported for marine species but is less understood in coastal lagoons' organisms. Temporal genetic variation in natural populations of the Mediterranean shore crab Carcinus aestuarii was quantified over a multi-year sample. A total of 486 adult crabs were collected at eight different sites of the Venice Lagoon during the period 2005-2007 and screened for genetic variation using 11 microsatellite loci. Two additional samples (N = 115) from neighbouring sites, located approximately 100 km North and South to the Venice Lagoon, were included for the sake of comparison. Our results show significant differences in allelic frequencies at the micro-geographic scale of the Venice Lagoon, observed between sites of collection, typologies of habitat, and areas with different class of ecological risk or pattern of hemocyanin expression. However, this pattern was not constant between years, with significant differences observed mainly in 2005 and 2006, but not in 2007. Our results indicate significant temporal differences suggesting the existence of dynamic processes that act on the genetic pool of this species. Although natural selection and gene flow might play a role, we suggest that genetic drift linked to large variation in the reproductive success of individuals is the most probable scenario to explain the local genetic patterns of differentiation in the Mediterranean shore crab. Our study, by providing the first evidence for the existence of genetic differences in this species at the micro-geographic scale, suggests that a better comprehension of the link between reproduction, recruitment and oceanography is critical to understand how colonization and maintenance of genetic variation is achieved in ephemeral and vulnerable environments such as coastal lagoons.

Marino, Ilaria Anna Maria; Barbisan, Federica; Gennari, Micol; Giomi, Folco; Beltramini, Mariano; Bisol, Paolo Maria; Zane, Lorenzo

2010-03-01

162

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

163

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

164

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.

165

Two Test Items to Explore High School Students' Beliefs of Sample Size When Sampling from Large Populations  

ERIC Educational Resources Information Center

Two test items that examined high school students' beliefs of sample size for large populations using the context of opinion polls conducted prior to national and state elections were developed. A trial of the two items with 21 male and 33 female Year 9 students examined their naive understanding of sample size: over half of students chose a…

Bill, Anthony; Henderson, Sally; Penman, John

2010-01-01

166

Global Longitudinal Pathway: Has Medical Education Curriculum Influenced Medical Students’ Skills and Attitudes Toward Culturally Diverse Populations?  

Microsoft Academic Search

Background: The Pathway represents a longitudinal program for medical students, consisting of both domestic and international experiences with poor populations. A previous study reported no significant attitudinal changes toward the medically indigent between Pathway and non-Pathway students. Purpose: The purpose of this study was to investigate and differentiate the skills and attitudes of Pathway and non-Pathway students in working with

Mary L. Zanetti; Michael A. Godkin; Joshua P. Twomey; Michele P. Pugnaire

2011-01-01

167

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.

168

The Inventory of Personality Organisation: its psychometric properties among student and clinical populations in Japan  

PubMed Central

Background The Inventory of Personality Organisation (IPO) is a self-report measure that reflects personality traits, as theorised by Kernberg. Methods In study 1, the Japanese version of the IPO was distributed to a population of Japanese university students (N = 701). The students were randomly divided into two groups. The factor structure derived from an exploratory factor analysis among one subsample was tested using a confirmatory factor structure among another subsample. In study 2, the factor-driven subscales of the IPO were correlated with other variables that would function as external criteria to validate the scale in a combined population of the students used in study 1 and psychiatric outpatients (N = 177). Results In study 1 the five-factor structure presented by the original authors was replicated in exploratory factor analyses in one subgroup of students. However, this was through reduction of the number of items (the number of the primary items was reduced from 57 to 24 whereas the number of the additional items was reduced from 26 to 13) due to low endorsement frequencies as well as low factor loadings on a designated factor. The new factor structure was endorsed by a confirmatory factor analysis in the other student subgroup. In study 2 the new five subscales of the Japanese IPO were likely to be correlated with younger age, more personality psychopathology (borderline and narcissistic), more dysphoric mood, less psychological well-being, more insecure adult attachment style, lower self-efficacy, and more frequent history of childhood adversity. The IPO scores were found to predict the increase in suicidal ideation in a week's time in a longitudinal follow-up. Conclusion Although losing more than 40% of the original items, the Japanese IPO may be a reliable and valid measure of Kernberg's personality organisation for Japanese populations.

Igarashi, Hiromi; Kikuchi, Hiroyoshi; Kano, Rikihachiro; Mitoma, Hiroshi; Shono, Masahiro; Hasui, Chieko; Kitamura, Toshinori

2009-01-01

169

Addressing the Needs of Racially/Culturally Diverse Student Populations in Higher Education: An Analysis of Educational Practices for Disadvantaged Youth  

ERIC Educational Resources Information Center

The recent growth in the racial and cultural heterogeneity of college students in the United States has increased the demand for higher educational policies that will accommodate the needs of an increasingly diverse collective student body (Kao & Thompson, 2003). Traditionally, underrepresented minority students (i.e., African American, Hispanic…

Pender, Matea

2010-01-01

170

A heterogeneous population model for contagious bovine pleuropneumonia transmission and control in pastoral communities of East Africa  

Microsoft Academic Search

Pastoral cattle live in highly structured communities characterized by complex contact patterns. The present paper describes a spatially heterogeneous model for the transmission of contagious bovine pleuropneumonia (CBPP) developed specifically for pastoral communities of East Africa. The model is validated against serological data on the prevalence of CBPP infection in several communities of southern Sudan and against livestock owner information

J. C. Mariner; J. McDermott; J. A. P. Heesterbeek; G. Thomson; P. L. Roeder; S. W. Martin

2006-01-01

171

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.

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

2013-01-01

172

Sexual behaviour and condom use as a protection against sexually transmitted infections in student population.  

PubMed

The aim of the study was to determine the differences in sexual behaviour and condom use as a protection against sexually transmitted infections (STI) between the first-year and the last-year students. Data were collected by filling anonymous and consented questionnaire in June of 2011 at University of Josip Juraj Strossmayer in Osijek, Croatia. Out of 857 students in the planned sample, 462 (53.9%) filled out the questionnaire, and 353/462 (76.4%) were sexually active. Data from sexually active students were processed and statistically significant results between first-year and the last-year students were presented. Studied sample consisted of 192/353 (54.4%) first-year students and 161/353 (45.6%) last-year students. Average age of sexual initiation for the first-year students was 17.28 +/- 1.29 years, a for the last-year students 18.45 +/- 2.14 years, and the difference is significant (Man-Whitney test = 10335.00, p < 0.01). First-year students have lower number of sexual partners (chi2 = 28.005, p < 0.01), during relationship they had lower number of intercourses with the third person (2 = 17.947, p < 0.01), and feel that lower number of their friends were already sexually active at the time of their own sexual initiation (chi2 = 18.350, p < 0.01). First-year students more often inform their partners about existing or previous STI (chi2 = 14.476, p < 0.01) and curiosity significantly influenced their decision regarding sexual initiation (chi2 = 8.689, p < 0.05). First-year students more often used condom at their first sexual intercourse (chi2 = 7.275, p < 0.01), and more rarely used withdrawal (chi2 = 6.380, p < 0.05). At their last sexual intercourse, first-year students more often used any kind of protection (chi2 = 3.853, p < 0.05),more often used condom (chi2 = 11.110, p < 0.01) and withdrawal (chi2 = 5.156, p < 0.05), and more rarely used contraceptive pills (chi2 = 4.405, p < 0.05). First-year students more often use condom in a permanent relationship (chi2 = 13.384, p < 0.05), and also plan to use it during following intercourse in the permanent relationship (chi2 = 17.575, p < 0.01). Growing condom use and decreasing risky sexual behaviour among students, as well as other adolescents and young adults needs to be maintained. Youth should learn before sexual initiation that only correct condom use at every sexual intercourse protects them against STI and human immunodeficiency virus (HIV). Sexual education and STI/HIV prevention programmes, positive role of media (television) and civil organisations that communicate with the youth can help that. Such changes among adolescents and young adults should have to be seen in student population as well. PMID:24851594

Dijani?, Tomislav; Kozul, Karlo; Miskulin, Maja; Medi?, Alan; Jurcev-Savicevi?, Anamarija; Burazin, Jelena

2014-03-01

173

Noncognitive Predictors of Academic Performance and Persistence in Horizontal and Vertical Transfer Students by Academic Level  

ERIC Educational Resources Information Center

College students increasingly are transferring among institutions of higher education in pursuit of their educational goals. The existing research on transfer students, however, does not adequately explore the unique characteristics of this heterogeneous population. The literature on transfer students suggests that transfer students are at-risk…

Davis, Christopher A.

2010-01-01

174

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

175

Knowledge and attitudes toward Tay-Sachs disease among a college student population.  

PubMed Central

To assess the feasibility of screening the single Jewish population for Tay-Sachs disease (TSD), a questionnaire examining the knowledge of and attitudes toward TSD and genetic screening was sent to 348 Yale University Jewish undergraduates. Of those students responding (63 percent), 78 percent were able to answer general genetic questions correctly while only 1.9 percent could answer specific Tay-Sachs questions correctly. A majority of the students (93.9 percent) indicated some concern about being a carrier for TSD, believed that carrier status would affect future social and reproductive behavior, and expressed an interest in having TS carrier status determined while still single (77.4 percent). Strong correlations were found between knowledge and attitudes, but no significant differences appeared between male and female respondents. In addition to leading to improvements in Tay-Sachs screening programs, the observations have led to suggestions that may be generalized to other genetic screening programs.

Austein, C. F.; Seashore, M. R.; Mick, S. S.

1981-01-01

176

Knowledge and attitudes toward Tay-Sachs disease among a college student population.  

PubMed

To assess the feasibility of screening the single Jewish population for Tay-Sachs disease (TSD), a questionnaire examining the knowledge of and attitudes toward TSD and genetic screening was sent to 348 Yale University Jewish undergraduates. Of those students responding (63 percent), 78 percent were able to answer general genetic questions correctly while only 1.9 percent could answer specific Tay-Sachs questions correctly. A majority of the students (93.9 percent) indicated some concern about being a carrier for TSD, believed that carrier status would affect future social and reproductive behavior, and expressed an interest in having TS carrier status determined while still single (77.4 percent). Strong correlations were found between knowledge and attitudes, but no significant differences appeared between male and female respondents. In addition to leading to improvements in Tay-Sachs screening programs, the observations have led to suggestions that may be generalized to other genetic screening programs. PMID:7336765

Austein, C F; Seashore, M R; Mick, S S

1981-01-01

177

Cord Blood Lin?CD45? Embryonic-Like Stem Cells Are a Heterogeneous Population That Lack Self-Renewal Capacity  

PubMed Central

Human umbilical cord blood (hUCB) has been proposed to contain not only haematopoietic stem cells, but also a rare pluripotent embryonic-like stem cell (ELSc) population that is negative for hematopoietic markers (Lin?CD45?) and expresses markers typical of pluripotent cells. The aim of this work was to isolate, characterise and expand this ELSc fraction from hUCB, as it may provide a valuable cell source for regenerative medicine applications. We found that we could indeed isolate a Lin?CD45? population of small cells (3–10 µm diameter) with a high nucleus to cytoplasm ratio that expressed the stem cell markers CD34 and CXCR4. However, in contrast to some previous reports, this fraction was not positive for CD133. Furthermore, although these cells expressed transcripts typical of pluripotent cells, such as SOX2, OCT3/4, and NANOG, they were not able to proliferate in any of the culture media known to support stem cell growth that we tested. Further analysis of the Lin?CD45? population by flow cytometry showed the presence of a Lin?CD45?Nestin+ population that were also positive for CD34 (20%) but negative for CXCR4. These data suggest that the Lin?CD45? stem cell fraction present in the cord blood represents a small heterogeneous population with phenotypic characteristics of stem cells, including a Lin?CD45?Nestin+ population not previously described. This study also suggests that heterogeneity within the Lin?CD45? cell fraction is the likely explanation for differences in the hUCB cell populations described by different groups that were isolated using different methods. These populations have been widely called “embryonic-like stem cell” on the basis of their phenotypical similarity to embryonic stem cells. However, the fact they do not seem to be able to self-renew casts some doubt on their identity, and warns against defining them as “embryonic-like stem cell” at this stage.

Alvarez-Gonzalez, Cesar; Duggleby, Richard; Vagaska, Barbora; Querol, Sergio; Gomez, Susana G.; Ferretti, Patrizia; Madrigal, Alejandro

2013-01-01

178

Cord blood Lin(-)CD45(-) embryonic-like stem cells are a heterogeneous population that lack self-renewal capacity.  

PubMed

Human umbilical cord blood (hUCB) has been proposed to contain not only haematopoietic stem cells, but also a rare pluripotent embryonic-like stem cell (ELSc) population that is negative for hematopoietic markers (Lin(-)CD45(-)) and expresses markers typical of pluripotent cells. The aim of this work was to isolate, characterise and expand this ELSc fraction from hUCB, as it may provide a valuable cell source for regenerative medicine applications. We found that we could indeed isolate a Lin(-)CD45(-) population of small cells (3-10 µm diameter) with a high nucleus to cytoplasm ratio that expressed the stem cell markers CD34 and CXCR4. However, in contrast to some previous reports, this fraction was not positive for CD133. Furthermore, although these cells expressed transcripts typical of pluripotent cells, such as SOX2, OCT3/4, and NANOG, they were not able to proliferate in any of the culture media known to support stem cell growth that we tested. Further analysis of the Lin(-)CD45(-) population by flow cytometry showed the presence of a Lin(-)CD45(-)Nestin(+) population that were also positive for CD34 (20%) but negative for CXCR4. These data suggest that the Lin(-)CD45(-) stem cell fraction present in the cord blood represents a small heterogeneous population with phenotypic characteristics of stem cells, including a Lin(-)CD45(-)Nestin(+) population not previously described. This study also suggests that heterogeneity within the Lin(-)CD45(-) cell fraction is the likely explanation for differences in the hUCB cell populations described by different groups that were isolated using different methods. These populations have been widely called "embryonic-like stem cell" on the basis of their phenotypical similarity to embryonic stem cells. However, the fact they do not seem to be able to self-renew casts some doubt on their identity, and warns against defining them as "embryonic-like stem cell" at this stage. PMID:23840798

Alvarez-Gonzalez, Cesar; Duggleby, Richard; Vagaska, Barbora; Querol, Sergio; Gomez, Susana G; Ferretti, Patrizia; Madrigal, Alejandro

2013-01-01

179

Assessment of heterogeneity between European Populations: a Baltic and Danish replication case-control study of SNPs from a recent European ulcerative colitis genome wide association study  

PubMed Central

Background Differences in the genetic architecture of inflammatory bowel disease between different European countries and ethnicities have previously been reported. In the present study, we wanted to assess the role of 11 newly identified UC risk variants, derived from a recent European UC genome wide association study (GWAS) (Franke et al., 2010), for 1) association with UC in the Nordic countries, 2) for population heterogeneity between the Nordic countries and the rest of Europe, and, 3) eventually, to drive some of the previous findings towards overall genome-wide significance. Methods Eleven SNPs were replicated in a Danish sample consisting of 560 UC patients and 796 controls and nine missing SNPs of the German GWAS study were successfully genotyped in the Baltic sample comprising 441 UC cases and 1156 controls. The independent replication data was then jointly analysed with the original data and systematic comparisons of the findings between ethnicities were made. Pearson's ?2, Breslow-Day (BD) and Cochran-Mantel-Haenszel (CMH) tests were used for association analyses and heterogeneity testing. Results The rs5771069 (IL17REL) SNP was not associated with UC in the Danish panel. The rs5771069 (IL17REL) SNP was significantly associated with UC in the combined Baltic, Danish and Norwegian UC study sample driven by the Norwegian panel (OR = 0.89, 95% CI: 0.79-0.98, P = 0.02). No association was found between rs7809799 (SMURF1/KPNA7) and UC (OR = 1.20, 95% CI: 0.95-1.52, P = 0.10) or between UC and all other remaining SNPs. We had 94% chance of detecting an association for rs7809799 (SMURF1/KPNA7) in the combined replication sample, whereas the power were 55% or lower for the remaining SNPs. Statistically significant PBD was found for OR heterogeneity between the combined Baltic, Danish, and Norwegian panel versus the combined German, British, Belgian, and Greek panel (rs7520292 (P = 0.001), rs12518307 (P = 0.007), and rs2395609 (TCP11) (P = 0.01), respectively). No SNP reached genome-wide significance in the combined analyses of all the panels. Conclusions This replication study supports an important role for the studied rs5771069 (IL17REL) SNP, but not for rs7809799 (SMURF1/KPNA7), in UC etiology in the Danish, Baltic, and Norwegian populations. Significant genetic heterogeneity was suggested for rs7520292, rs12518307, and rs2395609 (TCP11) in UC etiology between the Nordic and the other European populations.

2011-01-01

180

Transition and Students with Twice Exceptionality  

ERIC Educational Resources Information Center

"Twice exceptional" is one of the terms used to describe students who have giftedness and a disability. This is a small heterogeneous population of individual learners who are underserved in special, gifted, and mainstream education settings. Despite the availability of research on transition for students with disabilities, there is…

Prior, Susan

2013-01-01

181

Education on Population Matters in Europe: Results from a Comparative Survey among Students in Five European Countries  

ERIC Educational Resources Information Center

In 1996-1997, within the framework of the European Observatory for Population Education and Information, a comparative survey was conducted among students in final classes of secondary education in several European countries. On the one hand, the survey attempted to assess the effects of education on population in terms of knowledge acquired; the…

Van Peer, Christine

2006-01-01

182

Dental students' regard for patients from often-stigmatized populations: findings from an Indian dental school.  

PubMed

The aim of this study was to evaluate and compare a group of Indian dental students' attitudes toward HIV-positive status, substance misuse, intellectual disability, acute mental illness, and lesbian, gay, bisexual, transgender (LGBT) orientation. Two hundred and twelve students at various stages in the dental curriculum anonymously completed the Medical Condition Regard Scale (MCRS) for these conditions. Friedman and Kruskal-Wallis tests were used, respectively, to analyze the intrastage and interstage differences in MCRS scores. The results revealed that the regard of dental students was considerably positive for all the conditions except LGBT, for which it was just borderline positive. Intellectual disability received the highest regard among all the conditions and LGBT the least. An intermediary and comparable regard was noted for acute mental illness and HIV-positive status followed by substance misuse. While the regard for LGBT remained consistent throughout the curriculum, those for other conditions showed a marginal decrease at the completion of the clinical training. Active curricular reforms are required to ensure a more inclusive and nondiscriminatory dental care environment for patients from such often-stigmatized populations, especially those with LGBT orientation and substance misuse. PMID:22319086

Madhan, Balasubramanian; Gayathri, Haritheertham; Garhnayak, Lokanath; Naik, Eslavath Seena

2012-02-01

183

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.

2014-01-01

184

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

185

A COMPARISON OF A.C.T. SCORES OF TECHNOLOGY STUDENTS OF GLENDALE COMMUNITY COLLEGE WITH THE COLLEGE POPULATION IN GENERAL.  

ERIC Educational Resources Information Center

IN 1966-67, AMERICAN COLLEGE TESTING PROGRAM SCORES EARNED BY 67 GLENDALE COLLEGE (ARIZONA) TECHNICAL STUDENTS WERE COMPARED WITH SCORES OF THE COLLEGE'S POPULATION AS A WHOLE, NUMBERING 693 STUDENTS. THE SCORES OF TECHNOLOGY STUDENTS TENDED TO BE LOWER IN ENGLISH AND SOCIAL SCIENCE, ABOUT THE SAME AS THOSE OF THE GENERAL POPULATION IN NATURAL…

FROST, RONALD A.; SPECTOR, IRWIN L.

186

Recruitment in a heterogeneous population of motor neurons that innervates the depressor muscle of the crayfish walking leg muscle.  

PubMed

According to the size principle the fine control of muscle tension depends on the orderly recruitment of motor neurons from a heterogeneous pool. We took advantage of the small number of excitatory motor neurons (about 12) that innervate the depressor muscle of the crayfish walking leg to determine if the size principle applies to this muscle. We found that in accordance with the size principle, when stimulated by proprioceptive input, neurons with small extracellular spikes were recruited before neurons with medium or large spikes. Because only a small fraction of the motor neurons responded strongly enough to sensory input to be recruited in this way, we extended our analysis to all neurons by characterizing properties that have classically been associated with recruitment order such as speed of axonal conduction and extracellular spike amplitude. Through a combination of physiological and anatomical criteria we were able to identify seven classes of excitatory depressor motor neurons. The majority of these classes responded to proprioceptive input with a resistance reflex, while a few responded with an assistance reflex, and yet others did not respond. Our results are in general agreement with the size principle. However, we found qualitative differences between neuronal classes in terms of synaptic input and neuronal structure that would in theory be unnecessary, according to a strict interpretation of the size principle. We speculate that the qualitative heterogeneity observed may be due to the fact that the depressor is a complex muscle, consisting of two muscle bundles that share a single insertion but have multiple origins. PMID:18245639

Hill, Andrew A V; Cattaert, Daniel

2008-02-01

187

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.

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

188

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

189

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

190

Identification of functionally relevant populations in enhanced biological phosphorus removal processes based on intracellular polymers profiles and insights into the metabolic diversity and heterogeneity.  

PubMed

This study proposed and demonstrated the application of a new Raman microscopy-based method for metabolic state-based identification and quantification of functionally relevant populations, namely polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), in enhanced biological phosphorus removal (EBPR) system via simultaneous detection of multiple intracellular polymers including polyphosphate (polyP), glycogen, and polyhydroxybutyrate (PHB). The unique Raman spectrum of different combinations of intracellular polymers within a cell at a given stage of the EBPR cycle allowed for its identification as PAO, GAO, or neither. The abundance of total PAOs and GAOs determined by Raman method were consistent with those obtained with polyP staining and fluorescence in situ hybridization (FISH). Different combinations and quantities of intracellular polymer inclusions observed in single cells revealed the distribution of different sub-PAOs groups among the total PAO populations, which exhibit phenotypic and metabolic heterogeneity and diversity. These results also provided evidence for the hypothesis that different PAOs may employ different extents of combination of glycolysis and TCA cycle pathways for anaerobic reducing power and energy generation and it is possible that some PAOs may rely on TCA cycle solely without glycolysis. Sum of cellular level quantification of the internal polymers associated with different population groups showed differentiated and distributed trends of glycogen and PHB level between PAOs and GAOs, which could not be elucidated before with conventional bulk measurements of EBPR mixed cultures. PMID:22471394

Majed, Nehreen; Chernenko, Tatyana; Diem, Max; Gu, April Z

2012-05-01

191

LoFreq: a sequence-quality aware, ultra-sensitive variant caller for uncovering cell-population heterogeneity from high-throughput sequencing datasets  

PubMed Central

The study of cell-population heterogeneity in a range of biological systems, from viruses to bacterial isolates to tumor samples, has been transformed by recent advances in sequencing throughput. While the high-coverage afforded can be used, in principle, to identify very rare variants in a population, existing ad hoc approaches frequently fail to distinguish true variants from sequencing errors. We report a method (LoFreq) that models sequencing run-specific error rates to accurately call variants occurring in <0.05% of a population. Using simulated and real datasets (viral, bacterial and human), we show that LoFreq has near-perfect specificity, with significantly improved sensitivity compared with existing methods and can efficiently analyze deep Illumina sequencing datasets without resorting to approximations or heuristics. We also present experimental validation for LoFreq on two different platforms (Fluidigm and Sequenom) and its application to call rare somatic variants from exome sequencing datasets for gastric cancer. Source code and executables for LoFreq are freely available at http://sourceforge.net/projects/lofreq/.

Wilm, Andreas; Aw, Pauline Poh Kim; Bertrand, Denis; Yeo, Grace Hui Ting; Ong, Swee Hoe; Wong, Chang Hua; Khor, Chiea Chuen; Petric, Rosemary; Hibberd, Martin Lloyd; Nagarajan, Niranjan

2012-01-01

192

Enrichment of live unlabelled cardiomyocytes from heterogeneous cell populations using manipulation of cell settling velocity by magnetic field.  

PubMed

The majority of available cardiomyocyte markers are intercellular proteins, limiting our ability to enrich live cardiomyocytes from heterogeneous cell preparations in the absence of genetic labeling. Here, we describe enrichment of live cardiomyocytes from the hearts of adult mice in a label-free microfluidic approach. The separation device consisted of a vertical column (15?mm long, 700??m diameter), placed between permanent magnets resulting in a field strength of 1.23?T. To concentrate the field at the column wall, the column was wrapped with 69??m diameter nickel wire. Before passing the cells through the column, the cardiomyocytes in the cell suspension had been rendered paramagnetic by treatment of the adult mouse heart cell preparation with sodium nitrite (2.5?mM) for 20?min on ice. The cell suspension was loaded into the vertical column from the top and upon settling, the non-myocytes were removed by the upward flow from the column. The cardiomyocytes were then collected from the column by applying a higher flow rate (144??l/min). We found that by applying a separation flow rate of 4.2??l/min in the first step, we can enrich live adult cardiomyocytes to 93%?±?2% in a label-free manner. The cardiomyocytes maintained viability immediately after separation and upon 24?h in culture. PMID:24404002

Sofla, Aarash; Cirkovic, Bojana; Hsieh, Anne; Miklas, Jason W; Filipovic, Nenad; Radisic, Milica

2013-01-01

193

Gustatory expression pattern of the human TAS2R bitter receptor gene family reveals a heterogenous population of bitter responsive taste receptor cells.  

PubMed

Human bitter taste is mediated by approximately 25 members of the human TAS2 receptor (hTAS2R) gene family. The hTAS2R genes are expressed in taste buds of gustatory papillae on the tongue surface. Because many naturally occurring bitter compounds are toxic, bitter taste receptors are believed to serve as warning sensors against the ingestion of toxic food compounds. An important question is whether bitter taste receptor cells are a homogeneous, broadly tuned population of cells, which uniformly express all bitter taste receptor genes, or not. Gene expression analyses in rodents demonstrated an essentially overlapping expression of TAS2R genes indicating a broad tuning, whereas functional in vivo analyses suggest a narrow tuning. The present study demonstrates the expression of all 25 human TAS2R genes in taste receptor cells of human circumvallate papillae. As shown by in situ hybridization experiments, the expression of hTAS2R genes differs in both the apparent level of expression and the number of taste receptor cells expressing these genes, suggesting a heterogeneous bitter taste receptor cell population. Differences in gene expression levels were verified by quantitative reverse transcription-PCR experiments for a subset of hTAS2R genes. Direct evidence for the heterogeneity of bitter taste receptor cells is provided by dual-labeling in situ hybridizations with selected pairs of hTAS2R gene-specific probes. Functional coexpression experiments in heterologous cells show competition among hTAS2Rs, indicating a possible biological reason for the observed expression pattern. From the data, we conclude that human bitter taste receptor cells are tuned to detect a limited subset of bitter stimuli. PMID:18003842

Behrens, Maik; Foerster, Susann; Staehler, Frauke; Raguse, Jan-Dirk; Meyerhof, Wolfgang

2007-11-14

194

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

195

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

PubMed Central

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 strongest balancing selection and DPB1 being compatible with neutrality. Comparisons of the allelic spectra reported by studies since 1990 suggest 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.

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

2008-01-01

196

Occlusal dental caries incidence and implications for sealant programs in a US college student population.  

PubMed

Given the decline in dental caries incidence in preteens and young teenagers in the United States, a study of the incidence of dental caries in young adults (17-23 years) was conducted to provide a descriptive epidemiologic picture of this "new" natural history of dental caries in the late and post-teenage years. A retrospective study was performed analyzing the detailed dental records of the four-year college experience in the class of 1989, US Coast Guard Academy. Occlusal caries incidence, in the absence of associated proximal caries, was shown to be moderately common in molars (11.9%) and rare in premolars (0.8%). In contrast to previous studies' findings, demographic indicators, socioeconomic status indicators, and prior caries experience were poor predictors of occlusal caries incidence; targeting a universal sealant policy in this population therefore would be done best by tooth type rather than patient type. A preliminary cost-comparison model, projected over a 40-month period, suggests that the cost of initiating a universal molar sealant policy in this population would be 92 cents per year per student greater than the cost of restoring occlusal caries in the presence of sound proximal surfaces. This cost comparison suggests that it would be advantageous to initiate such a policy. PMID:8258782

Stahl, J W; Katz, R V

1993-01-01

197

Genetic Variability at the Esterase-6 Locus in Natural Populations of DROSOPHILA SIMULANS in Relation to Environmental Heterogeneity  

PubMed Central

The allozymic variation at the esterase-6 locus was examined in fourteen samples of natural populations of Drosophila simulans collected in two different localities. The samples were collected from different species of fruits in the two localities and from banana baits located some meters apart from the fruits. The analysis was done by sequential electrophoresis, using varied gel concentrations and buffers. By this technique, we detected 27 alleles at the esterase-6 locus, where only five alleles were detected by the usual method. The results obtained suggest that habitat choice alone may not be a selective factor, but may be selective in combination with other environmental factors.

De Albuquerque, Cleide M. R.; Napp, Marly

1981-01-01

198

Heterogeneous populations of bone marrow stem cells--are we spotting on the same cells from the different angles?  

PubMed

Accumulated evidence suggests that in addition to hematopoietic stem cells (HSC), bone marrow (BM) also harbors endothelial stem cells (ESC), mesenchymal stem cells (MSC), multipotential adult progenitor cells (MAPC), pluripotent stem cells (PCS) as well as tissue committed stem cells (TCSC) recently identified by us. In this review we discuss the similarities and differences between these cell populations. Furthermore, we will present the hypothesis that all of these versatile BM derived stem cells are in fact different subpopulations of TCSC. These cells accumulate in bone marrow during ontogenesis and being a mobile population of cells are released from BM into peripheral blood after tissue injury to regenerate damaged organs. Furthermore, since BM is a "hideout" for TCSC, their presence in preparations of bone marrow derived mononuclear cells should be considered before experimental evidence is interpreted simply as trans-differentiation or plasticity of HSC. Finally, our observation that the number of TCSC accumulate in the bone marrow of young animals and their numbers decrease during senescence provides a new insight into aging and may explain why the regeneration processes becomes less effective in older individuals. PMID:15493574

Ratajczak, Mariusz Z; Kucia, Magda; Majka, Marcin; Reca, Ryan; Ratajczak, Janina

2004-01-01

199

Evolution of aging: individual life history trade-offs and population heterogeneity account for mortality patterns across species.  

PubMed

A broad range of mortality patterns has been documented across species, some even including decreasing mortality over age. Whether there exist a common denominator to explain both similarities and differences in these mortality patterns remains an open question. The disposable soma theory, an evolutionary theory of aging, proposes that universal intracellular trade-offs between maintenance/lifespan and reproduction would drive aging across species. The disposable soma theory has provided numerous insights concerning aging processes in single individuals. Yet, which specific population mortality patterns it can lead to is still largely unexplored. In this article, we propose a model exploring the mortality patterns which emerge from an evolutionary process including only the disposable soma theory core principles. We adapt a well-known model of genomic evolution to show that mortality curves producing a kink or mid-life plateaus derive from a common minimal evolutionary framework. These mortality shapes qualitatively correspond to those of Drosophila melanogaster, Caenorhabditis elegans, medflies, yeasts and humans. Species evolved in silico especially differ in their population diversity of maintenance strategies, which itself emerges as an adaptation to the environment over generations. Based on this integrative framework, we also derive predictions and interpretations concerning the effects of diet changes and heat-shock treatments on mortality patterns. PMID:24925106

Le Cunff, Y; Baudisch, A; Pakdaman, K

2014-08-01

200

Subjective Evaluations of Intelligence and Academic Self-Concept Predict Academic Achievement: Evidence from a Selective Student Population  

ERIC Educational Resources Information Center

The study examined the relationship between implicit theories, goal orientations, subjective and test estimates of intelligence, academic self-concept, and achievement in a selective student population (N=300). There was no direct impact of implicit theories of intelligence and goal orientations on achievement. However, subjective evaluations of…

Kornilova, Tatiana V.; Kornilov, Sergey A.; Chumakova, Maria A.

2009-01-01

201

Process-Oriented Guided-Inquiry Learning in an Introductory Anatomy and Physiology Course with a Diverse Student Population  

ERIC Educational Resources Information Center

Process-oriented guided-inquiry learning (POGIL), a pedagogical technique initially developed for college chemistry courses, has been implemented for 2 yr in a freshman-level anatomy and physiology course at a small private college. The course is populated with students with backgrounds ranging from no previous college-level science to junior and…

Brown, Patrick J. P.

2010-01-01

202

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.

203

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

204

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

205

Medical Student Indebtedness and Career Plans, 1974-1975.  

National Technical Information Service (NTIS)

With the decreasing availability of financial aid to medical students and the need for a more heterogeneous physician population to deliver the kind of health care that is needed, policy makers require information if they are to plan for student financing...

R. E. Mantovani T. L. Gordon D. G. Johnson

1976-01-01

206

Heterogeneous pattern of selective pressure for PRRT2 in human populations, but no association with autism spectrum disorders.  

PubMed

Inherited and de novo genomic imbalances at chromosome 16p11.2 are associated with autism spectrum disorders (ASD), but the causative genes remain unknown. Among the genes located in this region, PRRT2 codes for a member of the synaptic SNARE complex that allows the release of synaptic vesicles. PRRT2 is a candidate gene for ASD since homozygote mutations are associated with intellectual disability and heterozygote mutations cause benign infantile seizures, paroxysmal dyskinesia, or hemiplegic migraine. Here, we explored the contribution of PRRT2 mutations in ASD by screening its coding part in a large sample of 1578 individuals including 431 individuals with ASD, 186 controls and 961 individuals from the human genome Diversity Panel. We detected 24 nonsynonymous variants, 1 frameshift (A217PfsX8) and 1 in-frame deletion of 6 bp (p.A361_P362del). The frameshift mutation was observed in a control with no history of neurological or psychiatric disorders. The p.A361_P362del was observed in two individuals with autism from sub-Saharan African origin. Overall, the frequency of PRRT2 deleterious variants was not different between individuals with ASD and controls. Remarkably, PRRT2 displays a highly significant excess of nonsynonymous (pN) vs synonymous (pS) mutations in Asia (pN/pS?=?4.85) and Europe (pN/pS?=?1.62) compared with Africa (pN/pS?=?0.26; Asia vs Africa: P?=?0.000087; Europe vs Africa P?=?0.00035; Europe vs Asia P?=?P?=?0.084). We also showed that whole genome amplification performed through rolling cycle amplification could artificially introduce the A217PfsX8 mutation indicating that this technology should not be performed prior to PRRT2 mutation screening. In summary, our results do not support a role for PRRT2 coding sequence variants in ASD, but provide an ascertainment of its genetic variability in worldwide populations that should help researchers and clinicians to better investigate the role of PRRT2 in human diseases. PMID:24594579

Huguet, Guillaume; Nava, Caroline; Lemière, Nathalie; Patin, Etienne; Laval, Guillaume; Ey, Elodie; Brice, Alexis; Leboyer, Marion; Szepetowski, Pierre; Gillberg, Christopher; Depienne, Christel; Delorme, Richard; Bourgeron, Thomas

2014-01-01

207

Dentists' comfort in treating underserved populations after participating in community-based clinical experiences as a student.  

PubMed

The purpose of this project was to determine new dentists' comfort levels in treating traditionally underserved populations after participating in two consecutive five-week community-based clinical experiences while in dental school. A written survey was mailed to all known University of Iowa alumni (1992-2002; N=745). Respondents were asked to rank their comfort levels in treating twelve underserved populations on a five-point Likert type scale (5=no problem; 1=will not). Bivariate and logistic regression model analyses were performed to examine associations (p<0.05) among comfort and six predictor variables. Alumni (n=372) were most comfortable treating other ethnic, low-income, non-English-speaking, and HIV+/AIDS populations and least comfortable treating incarcerated and homebound populations. The following variables were significantly associated with comfort: 1) perception that the community experiences had great/much value; 2) practice located in larger communities; 3) non-solo practitioners; and 4) dentist's gender. As more dental schools utilize community-based clinical experiences to increase students' exposure to underserved populations, it is important that these experiences provide exposure to a variety of populations. Additionally, dental schools should continuously monitor the short- and long-term value of these programs for their students and recent graduates. PMID:18381848

McQuistan, Michelle R; Kuthy, Raymond A; Heller, Keith E; Qian, Fang; Riniker, Katharine J

2008-04-01

208

Secondary school students: a safer blood donor population in an urban with high HIV prevalence in east Africa.  

PubMed

We evaluated the enrollment of secondary school students as voluntary unremunerated blood donors in a city where the HIV-1 prevalence among the adult population is 11.8%. Between 1st July, 1992 and 1st December, 1993, consecutive blood donors were screened for anti-HIV-1, TPHA, HBsAg and anti-HBc. Test results were related to age, sex, voluntary or relative donor status. 525 (22.4%) of 2345 were voluntary donors aged 24 years or less and 529 (29.6%) of 1820 of the relative donors were of the same age group. Voluntary donors had statistically significant lower prevalence rates of anti-HIV-1, TPHA, and anti-HBc, 1.5%, 2.1% and 50.2% respectively, compared to relative donors of the same age group, 4.7%, 9.0% and 70.3% respectively. We conclude that secondary school students constituted a safer donor population. The student population offered the additional advantage of being easily accessible for donation and lesser blood units needed to be discarded. For a blood transfusion centre in an urban settlement, recruitment of secondary school students as voluntary unremunerated blood donors should be considered as a cost-effective strategy. PMID:7859656

Jacobs, B; Berege, Z A; Schalula, P J; Klokke, A H

1994-11-01

209

A Comparison of Alcohol and Illicit Drug Use between Pharmacy Students and the General College Population.  

ERIC Educational Resources Information Center

A study of substance use and abuse habits and attitudes of pharmacy students in eight institutions found substances used, in descending order of frequency, were alcohol, marijuana, amphetamines, and then all other drugs. Except for tranquilizers and heroin, all substances were used less by pharmacy students than by other students. (Author/MSE)

Miller, Christina Jarvis; And Others

1990-01-01

210

Teacher's Understanding, Perceptions, and Experiences of Students in Foster Care: A Forgotten Population  

ERIC Educational Resources Information Center

The purpose of this study is to examine elementary teacher's understanding, perceptions, and experiences of working with students in foster care. The researcher examined whether teachers are informed about students in foster care, determined teacher's understanding of the foster care system, and how their students are affected. The results…

Watson-Davis, Darneika

2010-01-01

211

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

212

Trans-ethnic fine-mapping of lipid loci identifies population-specific signals and allelic heterogeneity that increases the trait variance explained.  

PubMed

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; Boehnke, Michael; Haiman, Christopher A; Chen, Yii-Der I; Kooperberg, Charles; Assimes, Themistocles L; Crawford, Dana C; Hsiung, Chao A; North, Kari E; Mohlke, Karen L

2013-03-01

213

Population Expanding with the Phalanx Model and Lineages Split by Environmental Heterogeneity: A Case Study of Primula obconica in Subtropical China  

PubMed Central

Background Current and historical events have both affected the current distribution patterns and intraspecific divergence of plants. While numerous studies have focused on the Qinghai-Tibetan Plateau (QTP), the impacts of such events on the flora of subtropical China remain poorly understood. Subtropical China is famous for its highly complex topography and the limited impact from glaciation during the Pleistocene; this may have resulted in a different genetic legacy for species in this region compared to fully glaciated areas. Methodology/Principal Findings We used plastid and nuclear DNA sequence data and distribution modeling to analyze the divergence patterns and demographic history of Primula obconica Hance, a widespread herbaceous montane species in subtropical China. The phylogenetic analysis revealed two major lineages (lineage A and lineage B), representing a west-east split into the Yunnan and Eastern groups, and the Sichuan and Central groups, respectively. The Eastern and Central groups comprised relatively new derived haplotypes. Nested Clade Analysis and Bayesian Skyline Plot analyses both indicated that P. obconica mainly experienced a gradual expansion of populations. In addition, the simulated distribution of P. obconica during the Last Glacial Maximum was slightly larger than its present-day distribution. Conclusion/Significance Our results are the first to identify a west-east migration of P. obconica. The gradual expansion pattern and a larger potential distribution range in cold periods detected for P. obconica indicate that the population expansion of this species is consistent with the phalanx model. In addition, the current patterns of genetic differentiation have persisted as a result of the extensive environmental heterogeneity that exists in subtropical China.

Yan, Hai-Fei; Zhang, Cai-Yun; Wang, Feng-Ying; Hu, Chi-Ming; Ge, Xue-Jun; Hao, Gang

2012-01-01

214

The Use of a Heterogeneously Controlled Mouse Population Reveals a Significant Correlation of Acute Phase Parasitemia with Mortality in Chagas Disease  

PubMed Central

Chagas disease develops upon infection with the protozoan parasite Trypanosoma cruzi and undergoes an acute phase characterized by massive parasite replication and the presence of parasites in the blood. This condition is known as acute phase parasitemia. This initial stage may result in a cure, in the development of the chronic stages of the disease or in the death of the infected host. Despite intensive investigation related to the characterization of the acute and chronic phases of the disease, the cause-effect relationship of acute phase parasitemia to the outcome of the disease is still poorly understood. In this study, we artificially generated a heterogeneously controlled mouse population by intercrossing F1 mice obtained from a parental breeding of highly susceptible A/J with highly resistant C57BL/6 mouse strains. This F2 population was infected and used to assess the correlation of acute phase parasitemia with the longevity of the animals. We used nonparametric statistical analyses and found a significant association between parasitemia and mortality. If males and females were evaluated separately, we found that the former were more susceptible to death, although parasitemia was similar in males and females. In females, we found a strong negative correlation between parasitemia and longevity. In males, however, additional factors independent of parasitemia may favor mouse mortality during the development of the disease. The correlations of acute phase parasitemia with mortality reported in this study may facilitate an appropriate prognostic approach to the disease in humans. Moreover, these results illustrate the complexity of the mammalian genetic traits that regulate host resistance during Chagas disease.

Sanches, Tiago L. M.; Cunha, Larissa D.; Silva, Grace K.; Guedes, Paulo M. M.; Silva, Joao Santana; Zamboni, Dario S.

2014-01-01

215

The use of a heterogeneously controlled mouse population reveals a significant correlation of acute phase parasitemia with mortality in Chagas disease.  

PubMed

Chagas disease develops upon infection with the protozoan parasite Trypanosoma cruzi and undergoes an acute phase characterized by massive parasite replication and the presence of parasites in the blood. This condition is known as acute phase parasitemia. This initial stage may result in a cure, in the development of the chronic stages of the disease or in the death of the infected host. Despite intensive investigation related to the characterization of the acute and chronic phases of the disease, the cause-effect relationship of acute phase parasitemia to the outcome of the disease is still poorly understood. In this study, we artificially generated a heterogeneously controlled mouse population by intercrossing F1 mice obtained from a parental breeding of highly susceptible A/J with highly resistant C57BL/6 mouse strains. This F2 population was infected and used to assess the correlation of acute phase parasitemia with the longevity of the animals. We used nonparametric statistical analyses and found a significant association between parasitemia and mortality. If males and females were evaluated separately, we found that the former were more susceptible to death, although parasitemia was similar in males and females. In females, we found a strong negative correlation between parasitemia and longevity. In males, however, additional factors independent of parasitemia may favor mouse mortality during the development of the disease. The correlations of acute phase parasitemia with mortality reported in this study may facilitate an appropriate prognostic approach to the disease in humans. Moreover, these results illustrate the complexity of the mammalian genetic traits that regulate host resistance during Chagas disease. PMID:24651711

Sanches, Tiago L M; Cunha, Larissa D; Silva, Grace K; Guedes, Paulo M M; Silva, João Santana; Zamboni, Dario S

2014-01-01

216

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.

Pickard, Dawn M.; Pyle, Eric; Fetters, Marcia; Marcia Fetters, Dawn M. Pickard, and Eric Pyle

2003-02-01

217

Underachieving Gifted Students and Ways to Improve School Performance of at Risk Student Population Who Have High Potential: Improving Writing Performance in Underachieving Gifted Students  

ERIC Educational Resources Information Center

Giftedness has often been equated with being academically talented or being a high achiever in school. However, there is often concern about the gifted students who could be described as unmotivated and underachieving in one or many academic areas. At the Jones Street School, a school for gifted elementary students, the location of this study,…

Brown-Anfelouss, Marjorie

2012-01-01

218

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).

219

A pilot investigation of "metaphor blindness" in a college student population.  

PubMed

Previous research from our group suggests that patients with lesions in the left inferior parietal lobule (IPL)-which is concerned with abstract numerical cognition and cross-modal association (which is consistent with its strategic location at the crossroads between the temporal, parietal and occipital lobes) have difficulty understanding proverbs and metaphors (Ramachandran and Hubbard, 2001). In the current pilot investigation, we report "metaphor blindness" in a college student population; that is, either the complete inability or difficulty for otherwise intellectually non-challenged individuals to comprehend metaphors of language. Participants (N=205) read 12 metaphorical ("The detective jumped at the clue") and 12 literal ("The accident was a fall") sentences and had to decide whether the sentences conveyed a metaphorical or literal meaning. The mean accuracy for these metaphorical sentences was 11.0 (SD=2.3; RNG=0-12); the mean accuracy for literal sentences was 7.2 (SD=1.8; RNG=2-10). We found that 5% of participants (11/205) were unable or had difficulty understanding metaphors (i.e., were statistical outliers), while their score for literal sentences felt within a normal statistical range M=8.3 (SD=2.3; RNG=5-10). Follow-up control procedures were conducted in order to help ascertain that the results were not due to low verbal IQ and task difficulty. Likewise, none of the "metaphor blind" participants reported any psychiatric or neurological histories that would impair language comprehension, including strokes, brain injuries, language problems dyslexia, and signs of late language onset. The results are very preliminary and future studies are needed to confirm these findings. We suggest that brain modules may be specialized even for subtle functions like metaphor and their formation in embryogenesis may be controlled by small handfuls of genes whose expression can go awry-as in "metaphor blindness". PMID:24661940

Jalal, Baland; Ramachandran, Vilayanur S

2014-06-01

220

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.

2013-01-01

221

Cascade Effects in Heterogeneous Populations  

Microsoft Academic Search

We present a model of sequential choice which explains the emer- gence and persistence of unpopular, inefficient behavioral norms in society. We model individuals as naive Bayesian norm followers, rational agents whose subjective expected utility is increased by adherence to an established norm. Agents use Bayesian reasoning to combine their private preferences and prior beliefs with empirical observations of others'

Daniel B. Neill

2005-01-01

222

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

223

Rethinking Policy for At-Risk Students.  

ERIC Educational Resources Information Center

As the school-age population in the United States becomes increasingly culturally diverse and economically heterogeneous, public schools are confronted with issues of program specialization and social integration. Programs designed for students with special needs often take the form of discrete instructional structures. One consequence of targeted…

Wong, Kenneth K., Ed.; Wang, Margaret C., Ed.

224

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

225

Smoking Cessation Delivered by Medical Students Is Helpful to Homeless Population  

ERIC Educational Resources Information Center

Objective: The authors pilot a smoking-cessation outreach for the homeless that extends medical students' tobacco cessation education. Method: In this prospective study, second-year medical students administered cognitive behavior therapy or unstructured support to homeless subjects to help them quit smoking. Self-report and biological measures…

Spector, Andrew; Alpert, Hilary; Karam-Hage, Maher

2007-01-01

226

CHARACTERISTICS OF THE STUDENT POPULATION, UNIVERSITY OF ALABAMA RESIDENT CENTER, HUNTSVILLE, ALABAMA.  

ERIC Educational Resources Information Center

THE MAIN PURPOSE OF THIS 1959 SURVEY WAS TO ANALYZE SOME OF THE BASIC CHARACTERISTICS OF STUDENTS AT THE UNIVERSITY OF ALABAMA RESIDENT CENTER, HUNTSVILLE. FINDINGS WERE TABULATED IN SUMMARY FORM AND BY MAJOR FIELDS OF ACADEMIC INTEREST. OF THE STUDENTS (LARGELY YOUNG ADULTS), 51 PERCENT WERE IN ENGINEERING. ONLY 16 PERCENT WERE FEMALE. MOST…

FRANKLIN, ELTON

227

Student as Institutional Mirror: What Campuses Can Learn from Nontraditional Populations  

ERIC Educational Resources Information Center

College campuses look different today, at the beginning of the twenty-first century, than they did 50 years ago. The buildings and signage may look almost the same, but the students who learn in those buildings definitely do not. Increased access and the diversity movement have resulted in younger and older students sitting side by side in the…

Davis, Jeff

2011-01-01

228

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

229

Factorial and Structural Validity of Holland's Hexagonal Model for an Asian Student Population.  

ERIC Educational Resources Information Center

A study examined the utility of Holland's hexagonal model as a culturally appropriate theoretical framework for U.S. career psychologists working with Asian international students. Chinese-descent international students enrolled in three Southeastern universities (n=170) completed three instruments: Holland's Self-Directed Search (SDS), an…

Tay, Kenneth Kim; Hill, Joseph A.; Ward, Connie M.

230

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.

231

Writing to learn ecology: a study of three populations of college students  

Microsoft Academic Search

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 dead zones around the world. We explored how undergraduate students (42

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

2012-01-01

232

Writing to learn ecology: a study of three populations of college students  

Microsoft Academic Search

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 dead zones around the world. We explored how undergraduate students (42

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

2011-01-01

233

Assessing the Validity and Reliability of a Questionnaire on Dietary Fibre-related Knowledge in a Turkish Student Population  

PubMed Central

This study aimed to validate a questionnaire on dietary fibre (DF)-related knowledge in a Turkish student population. Participants (n=360) were either undergraduate students who have taken a nutrition course for 14 weeks (n=174) or those in another group who have not taken such a nutrition course (n=186). Test-retest reliability, internal reliability, and construct validity of the questionnaire were determined. Overall internal reliability (Cronbach's alpha=0.90) and test-retest reliability (0.90) were high. Significant differences (p<0.001) between the scores of the two groups of students indicated that the questionnaire had satisfactory construct validity. It was found that one-fifth of the students were unsure of the correct answer for any item, and 52.5% of them were not aware that DF had to be consumed on a daily basis. Only 36.4 to 44.2% of the students were able to correctly identify the food sources of DF.

Deniz, Melike S.

2013-01-01

234

Political Jurisdictions in Heterogeneous Communities.  

ERIC Educational Resources Information Center

We investigate whether political jurisdictions form in response to the trade-off between economies of scale and the costs of a heterogeneous population. We consider heterogeneity in income, race, ethnicity, and religion, and we test the model using American school districts, school attendance areas, municipalities, and special districts. We find…

Alesina, Alberto; Baqir, Reza; Hoxby, Caroline

2004-01-01

235

Political Jurisdictions in Heterogeneous Communities  

Microsoft Academic Search

We investigate whether political jurisdictions form in response to the trade-off between economies of scale and the costs of a heterogeneous population. We consider heterogeneity in income, race, ethnicity, and religion, and we test the model using American school districts, school attendance areas, municipalities, and special districts. We find strong evidence of a trade-off between economies of scale and racial

Alberto Alesina

2004-01-01

236

[Assignment of students for the Royal School of Medicine on the basis of ethnic minority population in the Ottoman Empire].  

PubMed

Tibhane-i Amire (Royal School of Medicine) was founded in 1827 in order to train Muslim physicians and surgeons equipped with modern medical knowledge ("novel medicine"). Following the Declaration of Tanzimat (Imperial Decree of Reformation) Non-Muslims were permitted to enroll to the School of Medicine just after the decree on January 16, 1841. At the beginning, to room, board and educate students of different religions and sects were not approved. But the Chief Physician and the Dean of the School of Medicine solved the problem by undertaking all the responsibilities. The first year following the afore-mentioned decree, 38 Christian students were enrolled and their number increased to 76 in the next year. In 1847, 29 students from the Jewish community were accepted to the School, for whom all the facilities covering their religious deeds, needs and customs were provided. The same year some Serbian students were accepted and special treatment was requested, since they were kins to the Serbian Prince. Greeks and Walachians were also accepted to the School, as there had not been any political restriction. In 1851 the total student number was 459, among whom there were 14 Non-Muslims. The same year, day students were also admitted as boarders, since it was hard to go to school in winter. In 1857, the Armenian Patriarch was given an audience by the Grand Vizier on an official demand stating that the assignment to them was not in proportion with their population, so it should be increased. This was approved by the Superior Council of Tanzimat. In 1855 the Greek Patriarch demanded officially that this decree should be withdrawn by stating that the Greek population was much larger than the Armenian's. Upon this, the council rearranged the assignment based on a reliable source and determined that it ought to be 30 for Armenians, 46 for Jews and Latin community, 74 for Greeks (including 15 Bulgarians) and totally 150 Non-Muslims. Together with 300 Muslim students, the student number reached up to 450. ... PMID:11625086

Altinta?, A

1995-01-01

237

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.

238

Students.  

ERIC Educational Resources Information Center

A review of 1977 cases that involved students and institutions of higher education indicates that students seem to be more concerned with their rights as educational consumers. The majority of cases concern controversies focusing on classroom and academic evaluation and treatment of students; receipt of various forms of financial aid; use of…

Gehring, Donald D.; Young, D. Parker

239

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

240

Heterogeneous voter models  

NASA Astrophysics Data System (ADS)

We introduce the heterogeneous voter model (HVM), in which each agent has its own intrinsic rate to change state, reflective of the heterogeneity of real people, and the partisan voter model (PVM), in which each agent has an innate and fixed preference for one of two possible opinion states. For the HVM, the time until consensus is reached is much longer than in the classic voter model. For the PVM in the mean-field limit, a population evolves to a preference-based state, where each agent tends to be aligned with its internal preference. For finite populations, discrete fluctuations ultimately lead to consensus being reached in a time that scales exponentially with population size.

Masuda, Naoki; Gibert, N.; Redner, S.

2010-07-01

241

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

242

Serological studies in a student population prone to infection with human papilloma virus  

PubMed Central

Four hundred and sixty-seven serum specimens from the female students at a residential college were examined for the presence of circulating antibody to human wart virus using the technique of counter-current immunoelectroosmophoresis. A significantly higher incidence of antibodies was found in students with a past history of plantar warts than in any other group. Antibody took several months to develop and was detectable in 20-30% of the students up to 9 years after infection. From a few cases of multiple infection, it was shown that reinfection could occur in spite of the presence of circulating antibodies probably of the IgG class. The sensitivity of the test was compared with two recognized techniques for detection of wart virus antibodies, namely gel diffusion and passive haemagglutination. ImagesPlate 1

Cubie, Heather A.

1972-01-01

243

Positive Mental Health and Well-Being among a Third Level Student Population  

PubMed Central

Introduction Much research on the health and well-being of third level students is focused on poor mental health leading to a dearth of information on positive mental health and well-being. Recently, the Warwick Edinburgh Mental Well-being scale (WEMWBS) was developed as a measurement of positive mental health and well-being. The aim of this research is to investigate the distribution and determinants of positive mental health and well-being in a large, broadly representative sample of third level students using WEMWBS. Methods Undergraduate students from one large third level institution were sampled using probability proportional to size sampling. Questionnaires were distributed to students attending lectures in the randomly selected degrees. A total of 2,332 self-completed questionnaires were obtained, yielding a response rate of 51% based on students registered to relevant modules and 84% based on attendance. One-way ANOVAs and multivariate logistic regression were utilised to investigate factors associated with positive mental health and well-being. Results The sample was predominantly female (62.66%), in first year (46.9%) and living in their parents’ house (42.4%) or in a rented house or flat (40.8%). In multivariate analysis adjusted for age and stratified by gender, no significant differences in WEMWBS score were observed by area of study, alcohol, smoking or drug use. WEMWBS scores were higher among male students with low levels of physical activity (p=0.04). Men and women reporting one or more sexual partners (p<0.001) were also more likely to report above average mental health and well-being. Conclusion This is the first study to examine positive mental health and well-being scores in a third level student sample using WEMWBS. The findings suggest that students with a relatively adverse health and lifestyle profile have higher than average mental health and well-being. To confirm these results, this work needs to be replicated across other third level institutions.

Davoren, Martin P.; Fitzgerald, Eimear; Shiely, Frances; Perry, Ivan J.

2013-01-01

244

Heterogeneity, Stability, and Efficiency in Distributed Systems  

Microsoft Academic Search

This paper explores the increasing the heterogeneity of an agent population to stabilize decentralized systems by adding bias terms to each agent's expected payoffs. Two approaches are evaluated, corresponding to heterogeneous preferences and heterogeneous transaction costs; empiri- cally, the transaction cost case provides stability with near optimal payoffs under certain conditions. Theoretically, in the idealized case of an infinite number

James D. Thomas; Katia P. Sycara

1998-01-01

245

Preparing English Teachers To Teach Diverse Student Populations: Beliefs, Challenges, Proposals for Change.  

ERIC Educational Resources Information Center

Argues a need for in-depth consideration of principles and practices to prepare teachers for classrooms they will face in the future. Notes problems created by the disparity between increasing student diversity and their overwhelmingly white, female English/language arts teachers. Provides an overview of the issues involved and practical ideas for…

Rosen, Lois Matz; Abt-Perkins, Dawn

2000-01-01

246

Analysis of the Learning Styles of Diverse Student Populations and Implications for Higher Education Instructional Change  

ERIC Educational Resources Information Center

Higher education is one of the last institutions of learning to embrace the challenge of learner diversity that exists everywhere today (Dunn & Griggs, 2000; Rowley, Lujan, Dolence, 1998). This investigation explored the relationships between perceived preferred instructional strategies and student learning styles of learning-style aware…

Novogrodsky, Dorothy

2012-01-01

247

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

248

Profile of the Graduate Student Population in U.S. Medical Schools.  

ERIC Educational Resources Information Center

Medical school surveys in 1994-95 and 1995-96 (n=104 schools) found that PhDs accounted for 25-30% of medical school enrollments; in some institutions, it was about half. Trend is toward interdisciplinary rather than departmental degrees. Number of student supported by National Institutes of Health (NIH) research grants was nearly twice that for…

Ammons, Stanley W.; Kelly, Douglas E.

1997-01-01

249

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

250

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

251

Migraine Prevalence in Adolescents Aged 13–15: A Student Population?Based Study in Taiwan  

Microsoft Academic Search

To estimate the lifetime migraine prevalence in school adolescents aged 13–15 in Taiwan, we conducted a self?administered questionnaire survey in four sampled public junior high schools. Migraine was diagnosed according to the diagnostic criteria of the International Headache Society. A total of 4064 students (1983 boys, 2081 girls) completed the questionnaire (response rate 91.6%). The lifetime prevalence of migraine was

2000-01-01

252

Money Attitude, Self-esteem, and Compulsive Buying in a Population of Medical Students  

PubMed Central

This study tried to determine the prevalence of compulsive buying (CB) and to identify among compulsive buyers a specific relation to money, a different buying style, and a lowered level of self-esteem. We included 203 medical students and diagnosed CB with the Mc Elroy criteria and a specific questionnaire. The money attitude was characterized by the Yamauchi and Templer's scale and self-esteem with the Rosenberg scale. 11% of the medical students presented compulsive buying (CB+). Sex ratio and mean ages were comparable in the CB+ and control groups. CB+ students drank less alcohol and smoked an equivalent number of cigarettes. Compulsive buyers had higher scores of distress (tendency to be hesitant, suspicious, and doubtful attitude toward situations involving money) and bargain missing (fear of missing a good opportunity to buy an item). They bought more often gifts for themselves, items they use less than expected and choose goods increasing their self-esteem. Their score of self-esteem was not different from the one from controls.

Lejoyeux, Michel; Richoux-Benhaim, Charlotte; Betizeau, Annabelle; Lequen, Valerie; Lohnhardt, Hannah

2011-01-01

253

Special education and education reform in Mexico: providing quality education to a diverse student population  

Microsoft Academic Search

This paper discusses the reform of basic education in Mexico and the restructuring of special education services that is occurring within the context of that reform. Recent developments in the transformation of educational services for diverse populations are identified and discussed. The activities of the General Directorate of Special Education of the Public Education Secretariat in the Federal District of

Eliseo Guajardo Ramos; Todd V. Fletcher

1998-01-01

254

Increasing Accessibility: Lessons Learned in Retaining Special Population Students in Canada  

ERIC Educational Resources Information Center

In Canada, changing demographics and increased competition--as well as social values based on equity--have inspired efforts to increase the postsecondary education (PSE) participation rates of youths from under-represented/under-served groups. Despite its population having the highest level of educational attainment among those of OECD countries,…

Smith, Clayton; Gottheil, Susan

2011-01-01

255

An Action Research Project on Preparing Teachers to Meet the Needs of Underserved Student Populations  

ERIC Educational Resources Information Center

The focus of this action research study was on the initial stage in reforming our teacher preparation programs. We designed, conducted, evaluated, and revised the components of our teacher preparation programs that were aimed at providing preservice teachers with the confidence and knowledge needed to meet the needs of youth populations

Buck, Gayle A.; Cordes, Jeanene G.

2005-01-01

256

An Action Research Project on Preparing Teachers to Meet the Needs of Underserved Student Populations  

Microsoft Academic Search

The focus of this action research study was on the initial stage in reforming our teacher preparation programs. We designed, conducted, evaluated, and revised the components of our teacher preparation programs that were aimed at providing preservice teachers with the confidence and knowledge needed to meet the needs of youth populations underserved in science education. The conceptual framework of this

Gayle A. Buck; Jeanene G. Cordes

2005-01-01

257

Effects of Student Population Density on Academic Achievement in Georgia Elementary Schools.  

ERIC Educational Resources Information Center

The purpose of this study was to determine the relationship between school density and achievement test scores. The study utilized a bipolar sample in order to include schools whose achievement scores were at the top and bottom of the population spectrum when considering Iowa Tests of Basic Skills (ITBS) scores. Based on comparing test scores and…

Swift, Diane O'Rourke

258

Modelling of the substrate heterogeneities experienced by a limited microbial population in scale-down and in large-scale bioreactors  

Microsoft Academic Search

A methodology based on stochastic modelling is presented to describe the influence of the bioreactor heterogeneity on the microorganisms growth and physiology. The stochastic model is composed of two sub-models: a microorganism circulation sub-model and a fluid mixing sub-model used for the characterization of the concentration gradient. The first one is expressed by a classical stochastic model (with random number

F. Delvigne; A. Lejeune; J. Destain; P. Thonart

2006-01-01

259

Simulating Population Growth.  

ERIC Educational Resources Information Center

Presents a strategy to help students grasp the important implications of population growth. Involves an interactive demonstration that allows students to experience exponential and logistic population growth followed by a discussion of the implications of population-growth principles. (JRH)

Byington, Scott

1997-01-01

260

An Action Research Project on Preparing Teachers to Meet the Needs of Underserved Student Populations  

NASA Astrophysics Data System (ADS)

The focus of this action research study was on the initial stage in reforming our teacher preparation programs. We designed, conducted, evaluated, and revised the components of our teacher preparation programs that were aimed at providing preservice teachers with the confidence and knowledge needed to meet the needs of youth populations underserved in science education. The conceptual framework of this study predicted that providing preservice teachers with experiences in teaching science to at-risk youth in a nonformal educational setting and that exploring these experiences in a seminar setting will increase the teachers confidence and knowledge in regard to teaching science to children from underserved populations. The community-based experience allowed for an experience in which 20 preservice teachers taught in a situation in which at-risk youth were the majority, thus spotlighting their needs in a manner traditionally not experienced by these prospective teachers. A two-phase methodological design (J. Creswell, 1994) was utilized to answer the questions: (a) Did the plan lead to the desired outcomes? and (b) What strategies fostered or hindered progress toward the desired outcomes? The findings of this study were utilized to develop our next action step in preparing teachers to foster science literacy for All Americans.

Buck, Gayle A.; Cordes, Jeanene G.

2005-02-01

261

Heterogeneity within the native range: population genetic analyses of sympatric invasive and noninvasive clades of the freshwater invading copepod Eurytemora affinis  

Microsoft Academic Search

Invasive species are often composed of highly differentiated populations or sibling species distributed across their native ranges. This study analysed patterns of distribution and the evolutionary and demographic histories of populations within the native range of the copepod species complex Eurytemora affinis. Genetic structure was analysed for samples from 17 locations from both the invaded and native ranges in the

GESCHE WINKLER; JULIAN J. DODSON; CAROL EUNMI LEE

2007-01-01

262

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

263

Spatial heterogeneity and the persistence of infectious diseases  

Microsoft Academic Search

The endemic persistence of infectious diseases can often not be understood without taking into account the relevant heterogeneities of host mixing. Here, we consider spatial heterogeneity, defined as ‘patchiness’ of the host population. After briefly reviewing how disease persistence is influenced by population size, reproduction number and infectious period, we explore its dependence on the level of spatial heterogeneity. Analysis

T. J. Hagenaars; C. A. Donnelly; N. M. Ferguson

2004-01-01

264

A Study To Determine How the Office of Student Affairs Can Better Serve the Student Population at Arizona State University at Tempe.  

ERIC Educational Resources Information Center

In 1985, the Office of Student Affairs (OSA) at Arizona State University offered 10 major categories of services to students. Its austere budget allocation was noted as a significant obstacle to an increase in its professional office staff; this led to a concern that the provision of student services was not being optimized. A study was conducted…

Campbell, Charles R.

265

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

266

Rationale and Development of a General Population Well-Being Measure: Psychometric Status of the GP-CORE in a Student Sample  

ERIC Educational Resources Information Center

This paper presents the rationale, development, and psychometric status of a non-clinical self-report measure for the general population (GP) ? including students ? derived from the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM) and hence termed the GP-CORE. In contrast to the CORE-OM, the GP-CORE does not comprise items…

Sinclair, Alice; Barkham, Michael; Evans, Chris; Connell, Janice; Audin, Kerry

2005-01-01

267

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

268

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

269

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

270

Modeling Heterogeneity in Susceptibility and Infectivity for HIV Infection.  

National Technical Information Service (NTIS)

The paper discusses the dynamics of heterogeneity in HIV spread and develops a theory of heterogeneity in susceptibility and infectivity within a population that allows a simple representation of key phenomena within an epidemic model. It is suggested tha...

N. S. Cardell D. E. Kanouse

1991-01-01

271

Evolutionary Dynamics of Intratumor Heterogeneity  

PubMed Central

Intraneoplastic diversity in human tumors is a widespread phenomenon of critical importance for tumor progression and the response to therapeutic intervention. Insights into the evolutionary events that control tumor heterogeneity would be a major breakthrough in our comprehension of cancer development and could lead to more effective prevention methods and therapies. In this paper, we design an evolutionary mathematical framework to study the dynamics of heterogeneity over time. We consider specific situations arising during tumorigenesis, such as the emergence of positively selected mutations (“drivers”) and the accumulation of neutral variation (“passengers”). We perform exact computer simulations of the emergence of diverse tumor cell clones over time, and derive analytical estimates for the extent of heterogeneity within a population of cancer cells. Our methods contribute to a quantitative understanding of tumor heterogeneity and the impact of heritable alterations on this tumor trait.

Iwasa, Yoh; Michor, Franziska

2011-01-01

272

'Pragmatic randomized controlled trial of individually prescribed exercise versus usual care in a heterogeneous cancer survivor population': A feasibility study PEACH Trial: Prescribed exercise after chemotherapy  

Microsoft Academic Search

BACKGROUND: Many cancer survivors suffer a range of physical and psychological symptoms which may persist for months or years after cessation of treatment. Despite the known benefits of exercise and its potential to address many of the adverse effects of treatment, the role of exercise as well as optimum duration, frequency, and intensity in this population has yet to be

Julie M Walsh; Juliette Hussey; Emer Guinan; Dearbhaile O' Donnell

2010-01-01

273

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.

Program, The W.

274

Individual vs. population plastic responses to elevated CO 2 , nutrient availability, and heterogeneity: a microcosm experiment with co-occurring species  

Microsoft Academic Search

We conducted an experiment to evaluate the plastic phenotypic responses of individuals, growing under intra-specific competition,\\u000a and populations of three co-occurring grassland species (Lolium\\u000a perenne, Plantago lanceolata, and Holcus lanatus) to joint variations in atmospheric CO2 partial pressure (P\\u000a CO2; 37.5 vs. 70 Pa), nutrient availability (NA; 40 vs. 120 mg N added as organic material), and the spatial pattern of nutrient

Fernando T. Maestre; José L. Quero; Fernando Valladares; James F. Reynolds

2007-01-01

275

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.

2014-01-01

276

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

277

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

278

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.

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

2012-01-01

279

Pricing Strategies Under Heterogeneous Service Requirements.  

National Technical Information Service (NTIS)

This paper analyzes a communication network, used by customers with heterogeneous service requirements. We investigate priority queueing as a way to establish service differentiation. It is assumed that there is an infinite population of customers, who jo...

M. R. H. Mandjes

2004-01-01

280

Distribution and gender effects of the subscales of a German version of the temperament autoquestionnaire briefTEMPS-M in a university student population  

Microsoft Academic Search

Background: This paper examines the distribution of the temperamental characteristics and gender effects of a new autoquestionnaire developed by Akiskal et al. (TEMPS-A) in its German briefTEMPS-M version. Methods: As described in a companion article [J. Affect. Disord. 85 (2005), 53, this issue], based on a study population of 1056 students of the Westfälische-Wilhelms-Universität in Münster, Germany, we constructed the

Andreas Erfurth; Alexander L. Gerlach; Nikolaus Michael; Ines Boenigk; Inga Hellweg; Salvatore Signoretta; Kareen Akiskal; Hagop S. Akiskal

2005-01-01

281

Integration of the K-12 LGBTQI Student Population in School Counselor Education Curricula: The Current State of Affairs  

Microsoft Academic Search

A national survey of 123 school counselor educators investigated how participants integrated K–12 lesbian, gay, bisexual, transgender, questioning, intersex (LGBTQI) students’ needs and concerns into school counseling curricula. Results indicated 91.9% of participants integrated the K–12 LGBTQI students’ needs and concerns for a median pedagogical duration of one, 3-hour session within a single course, focusing on students’ knowledge and awareness

Melissa Luke; Kristopher M. Goodrich; Janna L. Scarborough

2011-01-01

282

Heterogeneous pumice populations in the 2.08-Ma Cerro Gal??n 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 Gal??n 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 Gal??n eruption, grey pumice provides evidence not only for cryptic silicic recharge in a large caldera system but also a probable trigger for the eruption. ?? 2011 Springer-Verlag.

Wright, H. M. N.; Folkes, C. B.; Cas, R. A. F.; Cashman, K. V.

2011-01-01

283

The Strategies and Struggles of Graduate Diversity Officers in the Recruitment of Doctoral Students of Color  

ERIC Educational Resources Information Center

The growing heterogeneity of American society is increasingly reflected in the undergraduate student population, yet there has been less change within graduate education. As graduate education is the pipeline to the professoriate, we must have a better understanding of how to promote institutional change toward greater graduate diversity. This…

Griffin, Kimberly A.; Muniz, Marcela M.

2011-01-01

284

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

285

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

286

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.

School, Maryland V.

287

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

288

Characteristics and Predictors of Health Problems from Use among High-Frequency Cannabis Users in a Canadian University Student Population  

ERIC Educational Resources Information Center

Aims: Assess key cannabis use, risk and outcome characteristics among high-frequency cannabis users within a university student sample in Toronto, Canada. Methods: N = 134 active universities students (ages of 18-28) using cannabis at least three times per week were recruited by mass advertisement, telephone-screened and anonymously assessed by an…

Fischer, Benedikt; Dawe, Meghan; Mcguire, Fraser; Shuper, Paul A; Jones, Wayne; Rudzinski, Katherine; Rehm, Jurgen

2012-01-01

289

Places to Avoid: Population-Based Study of Student Reports of Unsafe and High Bullying Areas at School  

ERIC Educational Resources Information Center

Students' perceptions of school safety and experiences with bullying were examined in a large Canadian cohort of 5,493 girls and 5,659 boys in Grades 4 to 12. Results indicate notable differences in when and where students felt safe based on their own perceptions of safety and their own experiences with bullying, particularly across elementary and…

Vaillancourt, Tracy; Brittain, Heather; Bennett, Lindsay; Arnocky, Steven; McDougall, Patricia; Hymel, Shelley; Short, Kathy; Sunderani, Shafik; Scott, Carol; Mackenzie, Meredith; Cunningham, Lesley

2010-01-01

290

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

291

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.

Kun, Adam; Dieckmann, Ulf

2013-01-01

292

Do Your Homework! Investigating the Role of Culturally Relevant Pedagogy in Comprehensive School Reform Models Serving Diverse Student Populations  

Microsoft Academic Search

Like the African proverb, ‘It takes a village to raise a child’, many educational researchers charge that it takes a comprehensive\\u000a school reform to raise student achievement. With the passing of the No Child Left Behind legislation in 2002, national officials\\u000a authorized the Comprehensive School Reform program to support low performing schools as they struggled to improve student\\u000a achievement. As

Tonia Durden

2008-01-01

293

Heterogeneous Crystal Populations: Signatures, Genesis and Chronologies  

NASA Astrophysics Data System (ADS)

The ongoing development of accessory phase-based techniques helps to illuminate possible scenarios for the physical state of magmatic systems between eruptions. These, in turn, may aid in the detection of magmas in the crust. At Long Valley caldera, eastern California, ion microprobe analyses of 238U-230Th in zircon from the youthful Inyo Dome rhyolites show that even though their ages are mainly younger than the 760 k.y. old caldera-forming Bishop Tuff, they are significantly older than eruption (up to 200 k.y. and more). Do these ages date the timing of magma emplacement and show that liquid was present in the system for at least 200 k.y.? Or do the ages represent sampling by the ion beam of bimodal age domains, meaning that they could have been rapidly mobilized from voluminous crystal mushes residual after the Bishop Tuff (e.g., Hildreth, 2004)? Additionally or alternatively, could the "old" zircons be derived via assimilation of young, hydrothermally altered intrusive rocks (Schmitt and Simon, 2004)? The majority of 238U-206Pb analyses of zircons from Deer Mountain (13 of 20) are consistent with a single crystallization age that is somewhat older than previously obtained by 238U-230Th disequilibrium dating; the remaining zircon ages are younger and range to within error of the eruption age. The absence of Bishop Tuff-aged zircons indicates that if crystal mush contributes to the Inyo Dome rhyolites, its remobilization must have involved reheating to temperatures in excess of zircon saturation conditions (T>~800°C). Ion microprobe U-Th ages of allanites from South Deadman Dome range from 150 to <10 ka, in contrast to virtually all of the zircon ages which are >100 ka. The ca. 2-fold ranges in MnO/MgO and La/Nd in the same allanites overlap and extend the range of compositions we obtained for rhyolites from Toba caldera (Vazquez and Reid, 2005). The South Deadman Dome allanites could, by analogy to experimental results for a Toba rhyolite, have crystallized between the temperature interval of ~765°C to ~745°C. Taken at face value, the temperature-age distributions of allanite and zircon are therefore suggestive of a broad cooling trend. In detail, however, the T-t evolution defined by the allanites is one of a protracted interval of INCREASING temperature before eruption. We infer that intrusions of hotter, less evolved magma progressively hybridized the magma reservoir. Given the rarity with which zircons contemporary with the allanites have (as yet) been detected, the thermochemical conditions of that reservoir were sufficiently well buffered so that extensive (re)crystallization of zircon did not occur. Repose of a crystal-rich magma is indicated. This abstract is dedicated to the pioneering work of Stan Hart and Nobu Shimizu who showed how the Cameca 3f, Serial No. 1, could be used to investigate the isotopic and chemical evolution of crystals.

Reid, M. R.; Vazquez, J. A.

2005-12-01

294

Identifying subgroup markers in heterogeneous populations  

PubMed Central

Traditional methods that aim to identify biomarkers that distinguish between two groups, like Significance Analysis of Microarrays or the t-test, perform optimally when such biomarkers show homogeneous behavior within each group and differential behavior between the groups. However, in many applications, this is not the case. Instead, a subgroup of samples in one group shows differential behavior with respect to all other samples. To successfully detect markers showing such imbalanced patterns of differential signal, a different approach is required. We propose a novel method, specifically designed for the Detection of Imbalanced Differential Signal (DIDS). We use an artificial dataset and a human breast cancer dataset to measure its performance and compare it with three traditional methods and four approaches that take imbalanced signal into account. Supported by extensive experimental results, we show that DIDS outperforms all other approaches in terms of power and positive predictive value. In a mouse breast cancer dataset, DIDS is the only approach that detects a functionally validated marker of chemotherapy resistance. DIDS can be applied to any continuous value data, including gene expression data, and in any context where imbalanced differential signal is manifested.

de Ronde, Jorma J.; Rigaill, Guillem; Rottenberg, Sven; Rodenhuis, Sjoerd; Wessels, Lodewyk F. A.

2013-01-01

295

Synovial Tissue Heterogeneity and Peripheral Blood Biomarkers  

Microsoft Academic Search

Rheumatoid arthritis is characterized by multiple pathobiological processes and heterogeneous clinical phenotypes. Not surprisingly,\\u000a the inflamed synovium harbors an equally complex pathology. This includes variability in infiltrating and resident cell populations,\\u000a spatial arrangements, and cell–cell interactions, as well as gene expression profiles. Remarkable progress in our understanding\\u000a of the many facets of tissue heterogeneity has been facilitated by the increasing

Serena Bugatti; Antonio Manzo; Michele Bombardieri; Barbara Vitolo; Frances Humby; Stephen Kelly; Carlomaurizio Montecucco; Costantino Pitzalis

296

The Use of Conceptual versus Physical Models in Teaching Action Research to Culturally Diverse Student Populations: A Preliminary Analysis.  

ERIC Educational Resources Information Center

Graduate business administration students (n=55) were asked which model they used for action research projects: conceptual or a physical model visually depicting action research. The physical model was favored by 69%; most agreed that it helped them understand the process of action research, was easy to use, and flexibly applied to various…

McMurray, Adela J.

2002-01-01

297

The Impact of Rapid Automatized Naming and Phonological Awareness on the Reading Fluency of a Minority Student Population  

ERIC Educational Resources Information Center

The purpose of this study was to explore the relationship between phonological awareness (PA) and rapid automatized naming (RAN) on the reading fluency (RF) of students from traditionally underrepresented groups. The study included 86 participants attending 1st through 4th grade within an inner-city charter school located in a high-poverty, urban…

Taub, Gordon E.; Szente, Judit

2012-01-01

298

Financing the Future: Postsecondary Students, Costs, and Financial Aid 1993-1994. Household Economic Studies. Current Populations Reports.  

National Technical Information Service (NTIS)

Finding a way to finance postsecondary schooling (that is, schooling beyond high school), may be as much of a challenge as the course material. Fortunately, many students though not all are able to obtain financial assistance. The ability to pay for, or f...

J. C. Day K. Witkowski

1999-01-01

299

Relationship between perfectionism and domains of worry in a college student population: Considering the role of BIS\\/BAS motives  

Microsoft Academic Search

The present study examined whether perfectionism dimensions were unique predictors of worry when behavioral inhibition system (BIS) and behavioral activation system (BAS) motives are also considered in the model in a sample of 254 college students. Results indicated that, although BIS\\/BAS motives accounted for variance in different domains of worry, perfectionism dimensions were found to account for additional variance in

Edward C. Chang; Kathryn M. Zumberg; Lawrence J. Sanna; Laura P. Girz; Allison M. Kade; Sarah R. Shair; Nicole B. Hermann; Kavita Srivastava

2007-01-01

300

Preparing Elementary Pre-Service Teachers from a Non-Traditional Student Population to Teach with Technology  

ERIC Educational Resources Information Center

This article documents the development of a two-stage curriculum intended to improve elementary teacher candidates' understanding of technology integration. Most students in the program came from low-income districts and lacked technology experience. The first stage of the curriculum consisted of a prerequisite basic technology skills course…

An, Heejung; Wilder, Hilary; Lim, Keol

2011-01-01

301

An Examination of the Substance Abuse Subtle Screening Inventory-3 Correctional Scale in a College Student Population  

ERIC Educational Resources Information Center

In this study, the authors examined the Substance Abuse Subtle Screening Inventory-3 Correctional scale's sensitivity and specificity at detecting college students' illegal behaviors. Sensitivity was strong, but specificity was weak. Implications for counseling and suggestions for future research are included. (Contains 3 tables.)

Burck, Andrew M.; Laux, John M.; Ritchie, Martin; Baker, David

2008-01-01

302

Telomere heterogeneity: Taking advantage of stochastic events  

PubMed Central

Various means employed to solve problems associated with the ends (telomeres) of linear DNA chromosomes exhibit one common feature: generation of both intra- and intercellular heterogeneity of telomeres at the level of their structural and functional states. We argue that this heterogeneity is not a simple by-product of molecular pathways mediating telomere maintenance. Instead, we propose that these mechanisms were selected because they generate heterogeneity. Similarly as noise in gene expression, stochastic events at telomeres may have an adaptive value allowing cells to sustain viable and flexible populations, with implications for fields ranging from evolutionary biology to molecular medicine.

Tomaska, Lubomir; Nosek, Jozef

2009-01-01

303

Gender differences in alcohol-related non-consensual sex; cross-sectional analysis of a student population  

PubMed Central

Background Sexual offences are a global public health concern. Recent changes in the law in England and Wales have dramatically altered the legal landscape of sexual offences, but sexual assaults where the victim is voluntarily intoxicated by alcohol continue to have low conviction rates. Worldwide, students are high consumers of alcohol. This research aimed to compare male and female students in relation to their knowledge and attitudes about alcohol and sexual activity and to identify factors associated with being the victim of alcohol-related non-consensual sex. Methods 1,110 students completed an online questionnaire. Drinking levels were measured using the Alcohol Use Disorder Identification Test. Non-consensual sexual experiences were measured using the Sexual Experience Survey. Univariate and multivariate analyses were undertaken using chi square and backwards stepwise logistic regression respectively. Results A third of respondents had experienced alcohol-related non-consensual sex. Male and female students differed in the importance they gave to cues in deciding if a person wished to have sex with them and their understanding of the law of consent. 82.2% of women who had experienced alcohol-related non-consensual sex were hazardous drinkers compared to 62.9% who drank at lower levels (P < 0.001). Differences existed between men and women, and between those who had and had not experienced alcohol-related non-consensual sex, in relation to assessments of culpability in scenarios depicting alcohol-related intercourse. A third of respondents believed that a significant proportion of rapes were false allegations; significantly more men than women responded in this way. Conclusions Alcohol-related coerced sexual activity is a significant occurrence among students; attitudinal and knowledge differences between males and females may explain this. Educational messages that focus upon what is deemed acceptable sexual behaviour, the law and rape myths are needed but are set against a backdrop where drunkenness is commonplace.

2012-01-01

304

What else are psychotherapy trainees learning? A qualitative model of students' personal experiences based on two populations.  

PubMed

After an introductory course in experiential-integrative psychotherapy, 21 graduate students provided personal narratives of their experiences, which were analyzed using the grounded theory method. Results produced 37 hierarchically organized experiences, revealing that students perceived multiple changes in both professional (i.e., skill acquisition and learning related to the therapeutic process) and personal (i.e., self growth in a more private sphere) domains. Analysis also highlighted key areas of difficulties in training. By adding the personal accounts of graduate trainees, this study enriches and extends Pascual-Leone et al.'s (2012) findings on undergraduates' experiences, raising the number of cases represented in the model to 45. Findings confirm the model of novice trainee experiences while highlighting the unique experiences of undergraduate vs. graduate trainees. PMID:23964814

Pascual-Leone, Antonio; Rodriguez-Rubio, Beatriz; Metler, Samantha

2013-01-01

305

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

306

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

307

Psychometric Properties of the Arabic Version of the Obsessive Compulsive Beliefs Questionnaire-44 in a Student Population  

PubMed Central

Objective We examined the psychometric properties of the Arabic version of the Obsessive Compulsive Beliefs Questionnaire-44 (OBQ-44) in a sample of Kuwait University students. This questionnaire was developed by the Obsessive Compulsive Cognitions Working Group in order to assess belief domains believed to be crucial in the development of obsessive compulsive symptoms. Method The Arabic version of the OBQ-44 was developed according to the standard translation and back-translation methods. The Arabic versions of the OBQ-44, the Maudsley Obsessive - Compulsive Inventory (MOCI), and Beck Depression Inventory-Revised (BDI-II) were then administered on a sample of 200 Kuwait University students from the faculty of humanities chosen through random cluster sampling. Retest was administered within a 4 week time period. Results The results of principle component factor analysis with varimax rotation indicated 6 factors which overlapped to a high degree. A 3 factor solution was chosen based on the scree plot and factor loadings which explained 36.12% of the variance. The factors were labeled as responsibility and threat estimation (RT), importance and control of thought (ICT) and perfectionism/Certainty (PC). The reliability coefficient of the three factors and the total score were assessed using three methods: Internal consistency, Test-retest reliability and Split-half reliability. Results showed an acceptable internal consistency for the Arabic version of the OBQ-44. Regarding the validity of OBQ-44, the instrument correlated with the total score of MOCI and most of its subscales. Conclusion These data support the reliability and validity of the OBQ-44 in a sample of Kuwait University students.

Rahat, Maryam; Mohamadi, Norolah

2012-01-01

308

Validity and reliability of portfolio assessment of student competence in two dental school populations: a four-year study.  

PubMed

The purpose of this study was to empirically investigate the validity and reliability of portfolio assessment in two U.S. dental schools using a unified framework for validity. In the process of validation, it is not the test that is validated but rather the claims (interpretations and uses) about test scores that are validated. Kane's argument-based validation framework provided the structure for reporting results where validity claims are followed by evidence to support the argument. This multivariate generalizability theory study found that the greatest source of variance was attributable to faculty raters, suggesting that portfolio assessment would benefit from two raters' evaluating each portfolio independently. The results are generally supportive of holistic scoring, but analytical scoring deserves further research. Correlational analyses between student portfolios and traditional measures of student competence and readiness for licensure resulted in significant correlations between portfolios and National Board Dental Examination Part I (r=0.323, p<0.01) and Part II scores (r=0.268, p<0.05) and small and non-significant correlations with grade point average and scores on the Western Regional Examining Board (WREB) exam. It is incumbent upon the users of portfolio assessment to determine if the claims and evidence arguments set forth in this study support the proposed claims for and decisions about portfolio assessment in their respective institutions. PMID:24789826

Gadbury-Amyot, Cynthia C; McCracken, Michael S; Woldt, Janet L; Brennan, Robert L

2014-05-01

309

Endothelial Cell Heterogeneity  

PubMed Central

The endothelial lining of blood vessels shows remarkable heterogeneity in structure and function, in time and space, and in health and disease. An understanding of the molecular basis for phenotypic heterogeneity may provide important insights into vascular bed-specific therapies. First, we review the scope of endothelial heterogeneity and discuss its proximate and evolutionary mechanisms. Second, we apply these principles, together with their therapeutic implications, to a representative vascular bed in disease, namely, tumor endothelium.

Aird, William C.

2012-01-01

310

On the relationship between autistic traits and executive functioning in a non-clinical Dutch student population.  

PubMed

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 examined by means of a random number generation test and a phonemic fluency test. Using appropriate dependent measures, the following EF components were examined: 1) inhibition of prepotent responding, 2) simple output inhibition, 3) working memory monitoring and updating, and 4) switching. No significant relationship was found between the AQ and each of the four components of EF. However, two TCI subscales were reliably correlated with either the working memory or the shifting component. These results were discussed in view of the concept of an autism spectrum with respect to executive abilities. PMID:22700989

Maes, Joseph H R; Vissers, Constance Th W M; Egger, Jos I M; Eling, Paul A T M

2013-07-01

311

Optimal Heterogeneity for Coding in Spiking Neural Networks  

NASA Astrophysics Data System (ADS)

The effect of cellular heterogeneity on the coding properties of neural populations is studied analytically and numerically. We find that heterogeneity decreases the threshold for synchronization, and its strength is nonlinearly related to the network mean firing rate. In addition, conditions are shown under which heterogeneity optimizes network information transmission for either temporal or rate coding, with high input frequencies leading to different effects for each coding strategy. The results are shown to be robust for more realistic conditions.

Mejias, J. F.; Longtin, A.

2012-06-01

312

Heterogeneity of FFA responses or multiplexing?  

PubMed

Recent work using cluster analysis of brain activity during movies revealed distinct clusters that respond to faces and different non-face categories in the fusiform face area (FFA). Because of the limited heterogeneity observed, these results could mean that the FFA contains one population of cells capable of representing multiple categories. PMID:24360882

Ross, David A; McGugin, Rankin W; Gauthier, Isabel

2014-04-01

313

Heterogeneous Collaboration Using XML  

Microsoft Academic Search

The recent proliferation of computing devices and use contexts demand equivalent diversity in collaborative applications. Our work on the DISCIPLE and Manifold frameworks supports the development of collaborative applications for these heterogeneous environments. Using eXtensible Markup Language (XML) for the communication medium provides for the heterogeneity. Collaborators share the same data or a subset of the data, represented in XML,

Ivan Marsic; Allan Krebs; Helmuth Trefftz; Bogdan Dorohonceanu; Marilyn Tremaine

2000-01-01

314

Microbial cell individuality and the underlying sources of heterogeneity  

Microsoft Academic Search

Single cells in genetically homogeneous microbial cultures exhibit marked phenotypic individuality, a biological phenomenon that is considered to bolster the fitness of populations. Major phenotypes that are characterized by heterogeneity span the breadth of microbiology, in fields ranging from pathogenicity to ecology. The cell cycle, cell ageing and epigenetic regulation are proven drivers of heterogeneity in several of the best-known

Simon V. Avery

2006-01-01

315

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.

2010-01-01

316

The competing benefits of noise and heterogeneity in neural coding.  

PubMed

Noise and heterogeneity are both known to benefit neural coding. Stochastic resonance describes how noise, in the form of random fluctuations in a neuron's membrane voltage, can improve neural representations of an input signal. Neuronal heterogeneity refers to variation in any one of a number of neuron parameters and is also known to increase the information content of a population. We explore the interaction between noise and heterogeneity and find that their benefits to neural coding are not independent. Specifically, a neuronal population better represents an input signal when either noise or heterogeneity is added, but adding both does not always improve representation further. To explain this phenomenon, we propose that noise and heterogeneity operate using two shared mechanisms: (1) temporally desynchronizing the firing of neurons in the population and (2) linearizing the response of a population to a stimulus. We first characterize the effects of noise and heterogeneity on the information content of populations of either leaky integrate-and-fire or FitzHugh-Nagumo neurons. We then examine how the mechanisms of desynchronization and linearization produce these effects, and find that they work to distribute information equally across all neurons in the population in terms of both signal timing (desynchronization) and signal amplitude (linearization). Without noise or heterogeneity, all neurons encode the same aspects of the input signal; adding noise or heterogeneity allows neurons to encode complementary aspects of the input signal, thereby increasing information content. The simulations detailed in this letter highlight the importance of heterogeneity and noise in population coding, demonstrate their complex interactions in terms of the information content of neurons, and explain these effects in terms of underlying mechanisms. PMID:24877735

Hunsberger, Eric; Scott, Matthew; Eliasmith, Chris

2014-08-01

317

Students' Attitude Towards Mathematics  

ERIC Educational Resources Information Center

Students' success in mathematics depends upon attitude towards mathematics. It also influences the participation rate of learners. This study was based on a survey of high school students about their attitudes towards mathematics. Students of both the gender constitute the population of this study. Sample of the study was 685 students (male = 379…

Farooq, Muhammad Shahid; Shah, Syed Zia Ullah

2008-01-01

318

A Student Profile.  

ERIC Educational Resources Information Center

A survey of graduates and students from the University of Maine at Augusta (UMA) was conducted in Spring 1980 to provide a profile of new and continuing students and to assess the vocational success of recent UMA graduates. The survey sample included: (1) 461 students selected from the entire UMA population; (2) 49 students enrolled in UMA's…

Maine Univ., Augusta.

319

Challenging Student Behaviour  

ERIC Educational Resources Information Center

The issue of poor student behaviour within higher education institutions (HEIs) has been well documented in recent years. Although the number of reported cases constitutes a very small percentage of the overall student population in the UK, the impact of student misconduct on the rest of the student body and staff in HEIs can be substantial. For…

Jones, Glyn; Philp, Clare

2011-01-01

320

Dynamic heterogeneity and life histories.  

PubMed

Biodemography is increasingly focused on the large and persistent differences between individuals within populations in fitness components (age at death, reproductive success) and fitness-related components (health, biomarkers) in humans and other species. To study such variation we propose the use of dynamic models of observable phenotypes of individuals. Phenotypic change in turn determines variation among individuals in their fitness components over the life course. We refer to this dynamic accumulation of fitness differences as dynamic heterogeneity and illustrate it for an animal population in which longitudinal data are studied using multistate capture-mark-recapture models. Although our approach can be applied to any characteristic, for our empirical example we use reproduction as the phenotypic character to define stages. We indicate how our stage-structured model describes the nature of the variation among individual characteristics that is generated by dynamic heterogeneity. We conclude by discussing our ongoing and planned work on animals and humans. We also discuss the connections between our work and recent work on human mortality, disability and health, and life course theory. PMID:20738276

Tuljapurkar, Shripad; Steiner, Ulrich K

2010-08-01

321

Transcription factor heterogeneity in pluripotent stem cells: a stochastic advantage  

PubMed Central

When pluripotent cells are exposed to a uniform culture environment they routinely display heterogeneous gene expression. Aspects of this heterogeneity, such as Nanog expression, are linked to differences in the propensity of individual cells to either self-renew or commit towards differentiation. Recent findings have provided new insight into the underlying causes of this heterogeneity, which we summarise here using Nanog, a key regulator of pluripotency, as a model gene. We discuss the role of transcription factor heterogeneity in facilitating the intrinsically dynamic and stochastic nature of the pluripotency network, which in turn provides a potential benefit to a population of cells that needs to balance cell fate decisions.

Torres-Padilla, Maria-Elena; Chambers, Ian

2014-01-01

322

Dynamics of Adaptation in Spatially Heterogeneous Metapopulations  

PubMed Central

The selection pressure experienced by organisms often varies across the species range. It is hence crucial to characterise the link between environmental spatial heterogeneity and the adaptive dynamics of species or populations. We address this issue by studying the phenotypic evolution of a spatial metapopulation using an adaptive dynamics approach. The singular strategy is found to be the mean of the optimal phenotypes in each habitat with larger weights for habitats present in large and well connected patches. The presence of spatial clusters of habitats in the metapopulation is found to facilitate specialisation and to increase both the level of adaptation and the evolutionary speed of the population when dispersal is limited. By showing that spatial structures are crucial in determining the specialisation level and the evolutionary speed of a population, our results give insight into the influence of spatial heterogeneity on the niche breadth of species.

Papaix, Julien; David, Olivier; Lannou, Christian; Monod, Herve

2013-01-01

323

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

324

Heterogeneous basic catalysis  

SciTech Connect

Heterogeneous acid catalysis attracted much attention primarily because heterogeneous acidic catalysts act as catalysts in petroleum refinery and are known as a main catalyst in the cracking process which is the largest process among the industrial chemical processes. In contrast to these extensive studies of heterogeneous acidic catalysts, fewer efforts have been given to the study of heterogeneous basic catalysts. The types of heterogeneous basic catalysts are listed in Table 1. Except for non-oxide catalysts, the basic sites are believed to be surface O atoms. The studies of heterogeneous catalysis have been continuous and progressed steadily. They have never been reviewed in the chemical Reviews before. It is more useful and informative to describe the studies of heterogeneous basic catalysis performed for a long period. In the present article, therefore, the cited papers are not restricted to those published recently, but include those published for the last 25 years. The paper first describes the generation of basic sites before describing methods used in the characterization of basic surfaces. These are indicator methods, temperature programmed desorption (TPD) of CO{sub 2}, UV absorption and luminescence spectroscopies, TPD of H{sub 2}, XPS, IR of CO{sub 2}, IR of pyrrole, and oxygen exchange between CO{sub 2} and the surface. The paper then discusses studies on the catalysis by heterogeneous basic catalysts. Some of these reactions are dehydration, dehydrogenation, hydrogenation, amination, alkylation, ring transformation, and reactions of organosilanes. Catalysts discussed are single component metal oxides, zeolites, non-oxide types, and superbasic catalysts. 141 refs.

Hattori, Hideshi [Hokkaido Univ., Sapporo (Japan). Center for Advanced Research of Energy Technology

1995-05-01

325

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.

Rhinehart, Ken; Pratte, John

326

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

327

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.

328

Dynamical robustness of coupled heterogeneous oscillators  

NASA Astrophysics Data System (ADS)

We study tolerance of dynamic behavior in networks of coupled heterogeneous oscillators to deterioration of the individual oscillator components. As the deterioration proceeds with reduction in dynamic behavior of the oscillators, an order parameter evaluating the level of global oscillation decreases and then vanishes at a certain critical point. We present a method to analytically derive a general formula for this critical point and an approximate formula for the order parameter in the vicinity of the critical point in networks of coupled Stuart-Landau oscillators. Using the critical point as a measure for dynamical robustness of oscillator networks, we show that the more heterogeneous the oscillator components are, the more robust the oscillatory behavior of the network is to the component deterioration. This property is confirmed also in networks of Morris-Lecar neuron models coupled through electrical synapses. Our approach could provide a useful framework for theoretically understanding the role of population heterogeneity in robustness of biological networks.

Tanaka, Gouhei; Morino, Kai; Daido, Hiroaki; Aihara, Kazuyuki

2014-05-01

329

Synovial tissue heterogeneity and peripheral blood biomarkers.  

PubMed

Rheumatoid arthritis is characterized by multiple pathobiological processes and heterogeneous clinical phenotypes. Not surprisingly, the inflamed synovium harbors an equally complex pathology. This includes variability in infiltrating and resident cell populations, spatial arrangements, and cell-cell interactions, as well as gene expression profiles. Remarkable progress in our understanding of the many facets of tissue heterogeneity has been facilitated by the increasing availability of patients' material and the development of advanced research technologies. The next challenge is to capitalize on the large amount of data generated to elucidate the specific pathogenic pathways disparately activated in different patients and/or different phases of the disease. When tissue pathology can be reliably explored through noninvasive circulating biomarkers, then the circle will be closed. We attempt to highlight key advances in the understanding of synovial tissue heterogeneity in rheumatoid arthritis and summarize novel perspectives in synovial biomarker discovery in relation to peripheral blood. PMID:21847543

Bugatti, Serena; Manzo, Antonio; Bombardieri, Michele; Vitolo, Barbara; Humby, Frances; Kelly, Stephen; Montecucco, Carlomaurizio; Pitzalis, Costantino

2011-10-01

330

Matrix Multiplication on Heterogeneous Platforms  

Microsoft Academic Search

In this paper, we address the issue of implementing matrix multiplication on heterogeneous platforms. We target two different classes of heterogeneous computing resources: heterogeneous networks of workstations and collections of heterogeneous clusters. Intuitively, the problem is to load balance the work with different speed resources while minimizing the communication volume. We formally state this problem in a geometric framework and

Olivier Beaumont; Vincent Boudet; Fabrice Rastello; Yves Robert

2001-01-01

331

Growing heterogeneous tumors in silico  

NASA Astrophysics Data System (ADS)

An in silico tool that can be utilized in the clinic to predict neoplastic progression and propose individualized treatment strategies is the holy grail of computational tumor modeling. Building such a tool requires the development and successful integration of a number of biophysical and mathematical models. In this paper, we work toward this long-term goal by formulating a cellular automaton model of tumor growth that accounts for several different inter-tumor processes and host-tumor interactions. In particular, the algorithm couples the remodeling of the microvasculature with the evolution of the tumor mass and considers the impact that organ-imposed physical confinement and environmental heterogeneity have on tumor size and shape. Furthermore, the algorithm is able to account for cell-level heterogeneity, allowing us to explore the likelihood that different advantageous and deleterious mutations survive in the tumor cell population. This computational tool we have built has a number of applications in its current form in both predicting tumor growth and predicting response to treatment. Moreover, the latent power of our algorithm is that it also suggests other tumor-related processes that need to be accounted for and calls for the conduction of new experiments to validate the model’s predictions.

Gevertz, Jana; Torquato, S.

2009-11-01

332

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.

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

2014-01-01

333

Managing Power Heterogeneity  

NASA Astrophysics Data System (ADS)

A particularly important emergent technology is heterogeneous processors (or cores), which many computer architects believe will be the dominant architectural design in the future. The main advantage of a heterogeneous architecture, relative to an architecture of identical processors, is that it allows for the inclusion of processors whose design is specialized for particular types of jobs, and for jobs to be assigned to a processor best suited for that job. Most notably, it is envisioned that these heterogeneous architectures will consist of a small number of high-power high-performance processors for critical jobs, and a larger number of lower-power lower-performance processors for less critical jobs. Naturally, the lower-power processors would be more energy efficient in terms of the computation performed per unit of energy expended, and would generate less heat per unit of computation. For a given area and power budget, heterogeneous designs can give significantly better performance for standard workloads. Moreover, even processors that were designed to be homogeneous, are increasingly likely to be heterogeneous at run time: the dominant underlying cause is the increasing variability in the fabrication process as the feature size is scaled down (although run time faults will also play a role). Since manufacturing yields would be unacceptably low if every processor/core was required to be perfect, and since there would be significant performance loss from derating the entire chip to the functioning of the least functional processor (which is what would be required in order to attain processor homogeneity), some processor heterogeneity seems inevitable in chips with many processors/cores.

Pruhs, Kirk

334

Dynamics of heterogeneous laminates  

NASA Astrophysics Data System (ADS)

Dielectric relaxation spectroscopy (DRS) was used to assess the dynamics of molecules in the heterogeneous laminate configuration and any practical applications that the arrangement may offer. Two component systems were considered. One of the components was an insulator and served as a barrier layer between the other component and the electrode. Of particular interest was the interpretation of the anomalous polarization phenomena that occurred due to the heterogeneity of the system. It was found that the relaxation processes that manifested as a result of the system being heterogeneous were unique to the material being studied. The cautionary use of effective medium approximations to predict the behaviour of the anomalous polarization phenomena was prescribed. In developing a molecular interpretation of the anomalous polarization processes all the parameters of the Havriliak-Negami equation were employed to ascertain physical aspects of the dielectric relaxation. The anomalous relaxation processes in the heterogeneous laminate configuration was due to the migration of charge that was facilitated by associative dipoles such as hydrogen bonds or ? interactions for example. It was found that surfaces have a discernible effect on the bulk dynamics of a material because the barrier layer controlled the rate at which charge was removed from the material. The heterogeneous laminate configuration showed promise as a simple alternative to assess the effects of spatial limitations on the dynamics of a molecule. In addition to the assessment of relaxation mechanisms of the charge migration processes in a material, the heterogeneous laminate configuration is recommended for studying molecules of a highly conducting nature without the need for indirect methods of extracting molecular dynamics.

McKenzie, Ruel

335

"Pee-in-a-Pot": acceptability and uptake of on-site chlamydia screening in a student population in the Republic of Ireland  

PubMed Central

Background The aim of the study was to explore the acceptability and uptake of on-campus screening using a youth friendly approach in two Third Level higher education institutions (HEIs). This study is part of wider research exploring the optimal setting for chlamydia screening in Ireland. Methods Male and female students were given the opportunity to take a free anonymous test for chlamydia during a one week programme of "pee-in-a-pot" days at two HEI campuses in the West of Ireland. The study was set up after extensive consultation with the two HEIs and advertised on the two campuses using a variety of media in the two weeks preceding the screening days. Screening involved the provision and distribution of testing packs at communal areas and in toilet facilities. In Ireland, chlamydia notifications are highest amongst 20-29 year olds and hence the screening criterion was aimed at 18-29 year olds. Urine samples were tested using a nucleic acid amplification test (NAAT). Following the screening days, qualitative in-depth interviews were conducted with participants about their experiences of the event. Results Out of 1,249 test kits distributed in two HEIs, 592 specimens were collected giving a return rate of 47.5%. Tests excluded (54) were due to labelling errors or ineligibility of participants' age. Two thirds of those tested were females and the mean age was 21 years. Overall,3.9% (21/538) of participants tested positive, 5% (17/336) among females and 2% (4/191) among males. Participant interviews identified factors which enhanced student participation such as anonymity, convenience, accessibility of testing, and the informal and non-medical approach to testing. Conclusions Screening for chlamydia using on-campus "pee-in-a-pot" days is an acceptable strategy in this population. This model can detect and treat asymptomatic cases of chlamydia and avoid many of the barriers associated with testing for sexually transmitted infections (STIs) in clinical settings.

2010-01-01

336

Heterogeneity in statistical mechanics  

NASA Astrophysics Data System (ADS)

An overview of four studies is presented, each relating to a distinct statistical mechanical model that is at least partially characterized by some form of heterogeneity. The first concerns discreteness effects in interhelical interactions. The second relates to more general discreteness effects relevant to chemical and molecular interactions. The third is a dynamic renormalization group calculation of the fluctuations within a certain model of sedimenting elastic media - one in which the drag depends sensitively on any heterogeneities that develop in the system. Finally, the fourth is a study of the spherical model of a spin glass, which is a statistical mechanical model that is dominated by disorder effects.

Landy, Jonathan Steven

337

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

338

Liver NKT cells: an account of heterogeneity  

Microsoft Academic Search

The liver is a rich provenance of an unconventional group of T cells called natural killer T (NKT) cells that coexpress NKR-P1, a type II membrane glycoprotein of the C-type lectin superfamily (NK1.1). Accumulating evidence suggests that NKT cells comprise a far more heterogeneous population than originally thought. In addition to ‘classical’ NKT cells, which are restricted by CD1d, ‘nonclassical’

Masashi Emoto; Stefan H. E. Kaufmann

2003-01-01

339

Evaluating foam heterogeneity  

NASA Technical Reports Server (NTRS)

New analytical tool is available to calculate the degree of foam heterogeneity based on the measurement of gas diffusivity values. Diffusion characteristics of plastic foam are described by a system of differential equations based on conventional diffusion theory. This approach saves research and computation time in studying mass or heat diffusion problems.

Liou, D. W.; Lee, W. M.

1972-01-01

340

The heterogeneous home  

Microsoft Academic Search

Due to several recent trends, the domestic environment has become more homogeneous and undifferentiated. Draw- ing on concepts from environmental psychology, we critique these trends. We propose heterogeneity as a new framework for domestic design, and we present design sketches that il- lustrate how ubiquitous computing technologies can inter- act with the domestic environment to create a more varied and

Ryan Aipperspach; Ben Hooker; Allison Woodruff

2008-01-01

341

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

342

Evolutionary dynamics on degree-heterogeneous graphs.  

PubMed

The evolution of two species with different fitness is investigated on degree-heterogeneous graphs. The population evolves either by one individual dying and being replaced by the offspring of a random neighbor (voter model dynamics) or by an individual giving birth to an offspring that takes over a random neighbor node (invasion process dynamics). The fixation probability for one species to take over a population of N individuals depends crucially on the dynamics and on the local environment. Starting with a single fitter mutant at a node of degree k, the fixation probability is proportional to k for voter model dynamics and to 1/k for invasion process dynamics. PMID:16712402

Antal, T; Redner, S; Sood, V

2006-05-12

343

Modeling Mitochondrial Population Genetics  

Microsoft Academic Search

Indirect tests have detected recombination in diverse animal mitochondrial DNA (mtDNA), including mammals. These results have far reaching implications for evolution and ecology, as virtually all animal population genetics studies assume mtDTA is clonally inherited. For the first time, we demonstrated that the molecular patterns detected by these tests could alternatively be explained by mutation rate heterogeneity, or clusters of

Stephanie Sun

2009-01-01

344

Dynamic heterogeneities versus fixed heterogeneities in earthquake models  

Microsoft Academic Search

SUMMARY A debate has raged over whether fixed material and geometrical heterogeneities, or alternatively dynamic stress heterogeneities, arising through frictional instabilities dominate earthquake complexity. It may also be that both types of heterogeneities interact and are important. This paper makes a first step in examining this interaction, combining two previously separate lines of research. One line examined friction, which has

Bruce E. Shaw

2004-01-01

345

Dynamic Heterogeneities Versus Fixed Heterogeneities in Earthquake Models  

Microsoft Academic Search

A debate has raged over whether fixed material and geometrical heterogeneities or alternatively dynamic stress heterogeneities arising through frictional instabilities dominate earthquake complexity. It may also be that both types of heterogeneities interact and are important. This work makes a first step in examining this interaction, combining two previously separate lines of research. One line examined friction which have attractors

B. E. Shaw

2003-01-01

346

Managing heterogeneity in the study of neural oscillator dynamics  

PubMed Central

We consider a coupled, heterogeneous population of relaxation oscillators used to model rhythmic oscillations in the pre-Bötzinger complex. By choosing specific values of the parameter used to describe the heterogeneity, sampled from the probability distribution of the values of that parameter, we show how the effects of heterogeneity can be studied in a computationally efficient manner. When more than one parameter is heterogeneous, full or sparse tensor product grids are used to select appropriate parameter values. The method allows us to effectively reduce the dimensionality of the model, and it provides a means for systematically investigating the effects of heterogeneity in coupled systems, linking ideas from uncertainty quantification to those for the study of network dynamics.

2012-01-01

347

Conceptualizing a tool to optimize therapy based on dynamic heterogeneity  

NASA Astrophysics Data System (ADS)

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. The authors dedicate this paper to Dr Barton Kamen who inspired its initiation and enthusiastically supported its pursuit.

Liao, David; Estévez-Salmerón, Luis; Tlsty, Thea D.

2012-12-01

348

Analysis of Exploited Fish Populations.  

National Technical Information Service (NTIS)

The purpose of this text is to provide students and practicing fisheries scientists with a basic understanding of the analysis of exploited fish populations. Methods for evaluating the state of a population and techniques which lead to management options ...

R. T. Lackey W. A. Hubert

1978-01-01

349

Hispanic Student Achievement. Research Brief  

ERIC Educational Resources Information Center

What are the factors affecting the achievement of Hispanic high school youth? Hispanic Americans are the largest growing population in the United States. Currently, Hispanic students make up more than 20% of the U.S. school population and, in 23 of the 50 states, Hispanic students outnumber African American and Asian students. During the 1970s and…

Hansen, Angela L.

2005-01-01

350

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

351

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

352

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, in this lesson students work in small groups to design experiments that will determine how environmental factors affect yeast population growth.

Engineering K-Ph.d. Program

353

The Distribution of Achievement Scores in a Disadvantaged Population: Data from a National Sample of Students in Districts Receiving Emergency School Aid Act (ESAA) Funds.  

ERIC Educational Resources Information Center

This report documents,in detail, student achievement in Emergency School Aid Act (ESAA) programs. Its purpose is to provide reference or baseline data for ESAA and other compensatory program administrators and researchers working with disadvantaged students. The data tables and figures can be used to answer the following types of questions: (1)…

Cromer, Fred E.

354

Heterogeneity of Rhizobium lipopolysaccharides.  

PubMed Central

The lipopolysaccharides ( LPSs ) from strains of Rhizobium leguminosarum, Rhizobium trifolii, and Rhizobium phaseoli were isolated and partially characterized by mild acid hydrolysis and by polyacrylamide gel electrophoresis. Mild acid hydrolysis results in a precipitate which can be removed by centrifugation or extraction with chloroform. The supernatant contains polysaccharides which, in general, are separated into two fractions ( LPS1 and LPS2 ) by Sephadex G-50 gel filtration chromatography. The higher-molecular-weight LPS1 fractions among the various Rhizobium strains are highly variable in composition and reflect the variability reported in the intact LPSs (R. W. Carlson and R. Lee, Plant Physiol. 71:223-228, 1983; Carlson et al., Plant Physiol. 62:912-917, 1978; Zevenhuizen et al., Arch. Microbiol. 125:1-8, 1980). The LPS1 fraction of R. leguminosarum 128C53 has a higher molecular weight than all other LPS1 fractions examined. All LPS2 fractions examined are oligosaccharides with a molecular weight of ca. 600. The major sugar component of all LPS2 oligosaccharides is uronic acid. The LPS2 compositions are similar for strains of R. leguminosarum and R. trifolii, but the LPS2 from R. phaseoli was different in that it contained glucose, a sugar not found in the other LPS2 fractions or found only in trace amounts. Polyacrylamide gel electrophoretic analysis shows that each LPS contains two banding regions, a higher-molecular-weight heterogeneous region often containing many bands and a lower-molecular-weight band. The lower-molecular-weight bands of all LPSs have the same electrophoretic mobility, which is greater than that of lysozyme. The banding pattern of the heterogeneous regions varies among the different Rhizobium strains. In the case of R. leguminosarum 128C53 LPS, the heterogeneous region of a higher molecular weight than is this region from all other Rhizobium strains examined and consists of many bands separated from one another by a small and apparently constant molecular weight interval. When the heterogeneous region of R. Leguminosarum 128C53 LPS was cut from the gel and analyzed, its composition was found to be that of the intact LPS, whereas the lower-molecular-weight band contains only sugars found in the LPS2 oligosaccharide. In the case of R. leguminosarum 128C63 and R. trifolii 0403 LPSs, the heterogeneous regions are similar and consist of several band s separated by a large-molecular-weight interval with a the major band of these heterogeneous regions having the lowest molecular weight with an electrophoretic mobility near that of beta-lactoglobulin. The heterogeneous region from R. phaseoli 127K14 consists of several bands with electrophoretic mobilities near that of beta-lactoglobulin, whereas this region from R. trifolii 162S7 shows a continuous staining region, indicating a great deal of heterogeneity. The results described in this paper are discussed with regard to the reported properties of Escherichia coli and Salmonella LPSs. Images

Carlson, R W

1984-01-01

355

Social heterogeneity and wasteful lobbying  

Microsoft Academic Search

Using a general equilibrium model with endogenous policy, we explore how heterogeneity affects wasteful lobbying by sectoral interest groups. With the help of a simulation approach, we first investigate the impact of information heterogeneity on how lobbies react to a shift from a soft to a strict government budget constraint. Next, we examine how lobbying is influenced by heterogenous perception

Marcel Fafchamps; Alain de Janvry; Elisabeth Sadoulet

1999-01-01

356

Heterogeneous exchange of precipitates  

Microsoft Academic Search

Summary  The heterogeneous exchange of ferric ion between a labelled aqueous ferric chloride solution and the colloidal?-FeOOH, prepared by slow hydrolysis of a ferric chloride solution at 100 C, was investigated at room temperature.\\u000a \\u000a Contrary to previously described ferric (hydr)oxides, originating from freshly formed “amorphous” precipitate, the?-FeOOH showed no exchange. This was attributed to a well ordered crystal lattice related to

R. H. H. Wolf; M. Mirnik; B. Težak

1965-01-01

357

[Heterogeneity of eating disorders].  

PubMed

This paper revises the literature which has attempted to define subgroups within the umbrella category of eating disorders, taking into account the heterogeneity of the clinical picture regarding personality structure, its linkage to eating behavior disorders, and differences in emotional expression. Research conducted over the last few years, in light of the new definition of these disorders proposed by DSM IIR, reinforces the differences between patients following a restrictive pattern and patients with bulimic episodes. PMID:8213286

Ayuso Mateos, J L

1993-01-01

358

Querying Semistructured Heterogeneous Information  

Microsoft Academic Search

Semistructured data has no absolute schema fixed in advance and its structure may be irregularor incomplete. Such data commonly arises in sources that do not impose a rigid structure(such as the World-Wide Web) and when data is combined from several heterogeneous sources.Data models and query languages designed for well structured data are inappropriate in suchenvironments. Starting with a "lightweight" object

Dallan Quass; Anand Rajaraman; Yehoshua Sagiv; Jeffrey D. Ullman; Jennifer Widom

1995-01-01

359

The ESTRO Breur Lecture 2009. From population to voxel-based radiotherapy: exploiting intra-tumour and intra-organ heterogeneity for advanced treatment of non-small cell lung cancer.  

PubMed

Evidence is accumulating that radiotherapy of non-small cell lung cancer patients can be optimized by escalating the tumour dose until the normal tissue tolerances are met. To further improve the therapeutic ratio between tumour control probability and the risk of normal tissue complications, we firstly need to exploit inter patient variation. This variation arises, e.g. from differences in tumour shape and size, lung function and genetic factors. Secondly improvement is achieved by taking into account intra-tumour and intra-organ heterogeneity derived from molecular and functional imaging. Additional radiation dose must be delivered to those parts of the tumour that need it the most, e.g. because of increased radio-resistance or reduced therapeutic drug uptake, and away from regions inside the lung that are most prone to complication. As the delivery of these treatments plans is very sensitive for geometrical uncertainties, probabilistic treatment planning is needed to generate robust treatment plans. The administration of these complicated dose distributions requires a quality assurance procedure that can evaluate the treatment delivery and, if necessary, adapt the treatment plan during radiotherapy. PMID:20647155

Lambin, Philippe; Petit, Steven F; Aerts, Hugo J W L; van Elmpt, Wouter J C; Oberije, Cary J G; Starmans, Maud H W; van Stiphout, Ruud G P M; van Dongen, Guus A M S; Muylle, Kristoff; Flamen, Patrick; Dekker, André L A J; De Ruysscher, Dirk

2010-08-01

360

Molecular diversity after a range expansion in heterogeneous environments.  

PubMed

Recent range expansions have probably occurred in many species, as they often happen after speciation events, after ice ages, or after the introduction of invasive species. While it has been shown that range expansions lead to patterns of molecular diversity distinct from those of a pure demographic expansion, the fact that many species do live in heterogeneous environments has not been taken into account. We develop here a model of range expansion with a spatial heterogeneity of the environment, which is modeled as a gamma distribution of the carrying capacities of the demes. By allowing temporal variation of these carrying capacities, our model becomes a new metapopulation model linking ecological parameters to molecular diversity. We show by extensive simulations that environmental heterogeneity induces a loss of genetic diversity within demes and increases the degree of population differentiation. We find that metapopulations with low average densities are much more affected by environmental heterogeneity than metapopulations with high average densities, which are relatively insensitive to spatial and temporal variations of the environment. Spatial heterogeneity is shown to have a larger impact on genetic diversity than temporal heterogeneity. Overall, temporal heterogeneity and local extinctions are not found to leave any specific signature on molecular diversity that cannot be produced by spatial heterogeneity. PMID:17028329

Wegmann, Daniel; Currat, Mathias; Excoffier, Laurent

2006-12-01

361

Area-heterogeneity tradeoff and the diversity of ecological communities  

PubMed Central

For more than 50 y ecologists have believed that spatial heterogeneity in habitat conditions promotes species richness by increasing opportunities for niche partitioning. However, a recent stochastic model combining the main elements of niche theory and island biogeography theory suggests that environmental heterogeneity has a general unimodal rather than a positive effect on species richness. This result was explained by an inherent tradeoff between environmental heterogeneity and the amount of suitable area available for individual species: for a given area, as heterogeneity increases, the amount of effective area available for individual species decreases, thereby reducing population sizes and increasing the likelihood of stochastic extinctions. Here we provide a comprehensive evaluation of this hypothesis. First we analyze an extensive database of breeding bird distribution in Catalonia and show that patterns of species richness, species abundance, and extinction rates are consistent with the predictions of the area–heterogeneity tradeoff and its proposed mechanisms. We then perform a metaanalysis of heterogeneity–diversity relationships in 54 published datasets and show that empirical data better fit the unimodal pattern predicted by the area–heterogeneity tradeoff than the positive pattern predicted by classic niche theory. Simulations in which species may have variable niche widths along a continuous environmental gradient are consistent with all empirical findings. The area–heterogeneity tradeoff brings a unique perspective to current theories of species diversity and has important implications for biodiversity conservation.

Allouche, Omri; Kalyuzhny, Michael; Moreno-Rueda, Gregorio; Pizarro, Manuel; Kadmon, Ronen

2012-01-01

362

Prevalence of Amblyopia and Strabismus in a Population of 7th-Grade Junior High School Students in Central China: The Anyang Childhood Eye Study (ACES).  

PubMed

Abstract Purpose: To determine the prevalence of amblyopia and strabismus in 7th-grade junior high school students in central China. Methods: Using stratified cluster sampling, 2363 7th-grade students were recruited from four junior high schools in Anyang city into the cross-sectional Anyang Childhood Eye Study (ACES). All students underwent visual acuity (VA), cycloplegic autorefraction, cover test, and ocular movement examinations. Uncorrected VA and best-corrected VA (BCVA) were measured with a logarithm of the minimum angle of resolution (logMAR) chart. Cycloplegic autorefraction was performed after administration of 1.0% cyclopentolate and Mydrin-P. Strabismus was defined as heterotropia at near or distance fixation. Amblyopia was defined as BCVA?0.1 logMAR units in one or both eyes, without ocular pathology in either eye. Results: Of the 2363 eligible students, 2260 (95.6%) completed all examinations. The mean age of the students was 12.4?±?0.6 years. Amblyopia was present in 52 students (2.5%), of whom 33 (63.5%) had unilateral and 19 (36.6%) had bilateral amblyopia. Of those with unilateral amblyopia, 18 (54.5 %) had anisometropia and 7 (21.2%) had strabismus. Of those with bilateral amblyopia, 6 (31.6%) had significant refractive error. Strabismus was present in 108 students (5.0%), of whom 2 (1.9%) had esotropia, 102 (94.4%) had exotropia, 3 (2.8%) had vertical strabismus, and 1 (0.9%) had microstrabismus. Of the 108 students with strabismus, 9 (8.3%) had amblyopia. Conclusion: The cross-sectional ACES which examined the prevalence of amblyopia and strabismus in 7th-grade students in central China revealed the prevalence of strabismus, particularly the proportion of exotropia, to be higher than previously reported. PMID:24742059

Fu, Jing; Li, Shi Ming; Liu, Luo Ru; Li, Jin Ling; Li, Si Yuan; Zhu, Bi Dan; Li, He; Yang, Zhou; Li, Lei; Wang, Ning Li

2014-06-01

363

Restructuring Heterogeneous Classes for Cognitive Development: Social Interactive Perspective.  

ERIC Educational Resources Information Center

Describes a study of students in grades three, four, and five that tried an educational application derived from the social constructivism view based on theories of Vygotsky and Piaget to improve cognitive development in a heterogeneous class. Path analysis showed that complex learning techniques are related to cognitive development. (Author/LRW)

Ben-Ari, Rachel; Kedem-Friedrich, Peri

2000-01-01

364

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.

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

365

Phenotypic heterogeneity in mycobacterial stringent response  

PubMed Central

Background A common survival strategy of microorganisms subjected to stress involves the generation of phenotypic heterogeneity in the isogenic microbial population enabling a subset of the population to survive under stress. In a recent study, a mycobacterial population of M. smegmatis was shown to develop phenotypic heterogeneity under nutrient depletion. The observed heterogeneity is in the form of a bimodal distribution of the expression levels of the Green Fluorescent Protein (GFP) as reporter with the gfp fused to the promoter of the rel gene. The stringent response pathway is initiated in the subpopulation with high rel activity. Results In the present study, we characterise quantitatively the single cell promoter activity of the three key genes, namely, mprA, sigE and rel, in the stringent response pathway with gfp as the reporter. The origin of bimodality in the GFP distribution lies in two stable expression states, i.e., bistability. We develop a theoretical model to study the dynamics of the stringent response pathway. The model incorporates a recently proposed mechanism of bistability based on positive feedback and cell growth retardation due to protein synthesis. Based on flow cytometry data, we establish that the distribution of GFP levels in the mycobacterial population at any point of time is a linear superposition of two invariant distributions, one Gaussian and the other lognormal, with only the coefficients in the linear combination depending on time. This allows us to use a binning algorithm and determine the time variation of the mean protein level, the fraction of cells in a subpopulation and also the coefficient of variation, a measure of gene expression noise. Conclusions The results of the theoretical model along with a comprehensive analysis of the flow cytometry data provide definitive evidence for the coexistence of two subpopulations with overlapping protein distributions.

2011-01-01

366

Enhancing Success in Heterogeneous Classrooms and Schools: The Powers of Partnership.  

ERIC Educational Resources Information Center

A discussion of practices associated with successful schooling of students in heterogeneous groupings looks at outcomes-based instructional models, instructional models using peer power, effective use of heterogeneous and multi-age grouping, strategies for redefining school organizational structure, and teacher training content. (MSE)

Villa, Richard A.; Thousand, Jacqueline S.

1988-01-01

367

Disruption, Achievement and the Heterogeneous Benefits of Smaller Classes. NBER Working Paper No. 15812  

ERIC Educational Resources Information Center

With few exceptions, empirical research investigating the possibility of heterogeneous benefits of class size reduction lacks a conceptual framework about specific dimensions of potential heterogeneity. In this paper we develop a model of education production that incorporates disruption and student achievement and illustrates how these underlying…

McKee, Graham J.; Rivkin, Steven G.; Sims, Katharine R. E.

2010-01-01

368

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.

369

Heterogeneous differential evolution for numerical optimization.  

PubMed

Differential evolution (DE) is a population-based stochastic search algorithm which has shown a good performance in solving many benchmarks and real-world optimization problems. Individuals in the standard DE, and most of its modifications, exhibit the same search characteristics because of the use of the same DE scheme. This paper proposes a simple and effective heterogeneous DE (HDE) to balance exploration and exploitation. In HDE, individuals are allowed to follow different search behaviors randomly selected from a DE scheme pool. Experiments are conducted on a comprehensive set of benchmark functions, including classical problems and shifted large-scale problems. The results show that heterogeneous DE achieves promising performance on a majority of the test problems. PMID:24683329

Wang, Hui; Wang, Wenjun; Cui, Zhihua; Sun, Hui; Rahnamayan, Shahryar

2014-01-01

370

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

371

Fundamentals of Populations and Population Growth  

NSDL National Science Digital Library

This activity reinforces the concepts covered in the lecture presented during LESSON 3 of this unit. It takes the student through the definition of a population. Graphing skills are tested and the difference between the independent and dependent variables is explained. The S-shaped and Boom and Bust growth rate curves are next compared and contrasted. The activity then asks the student to analyze a data table and to plot its points. Students gain personal application of the lesson material. And relate the material to the grand challenge of this unit.

Vu Bioengineering Ret Program

372

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.

Laposata, Matt

373

Heterogeneous broadband network  

NASA Astrophysics Data System (ADS)

Although the vision for the future Integrated Broadband Communication Network (IBCN) is an all optical network, it is certain that for a long period to come, the network will remain very heterogeneous, with a mixture of different physical media (fiber, coax and twisted pair), transmission systems (PDH, SDH, ADSL) and transport protocols (TCP/IP, AAL/ATM, frame relay). In the current work towards the IBCN, the ATM concept is considered the generic network protocol for both public and private network, with the ability to use different underlying transmission protocols and, through adaptation protocols, provide the appropriate services (old as well as new) to the customer. One of the major difficulties of heterogeneous network is the restriction that is usually given by the lowest common denominator, e.g. in terms of single channel capacity. A possible way to overcome these limitations is by extending the ATM concept with a multilink capability, that allows us to use separate resources as one common. The improved flexibility obtained by this protocol extension further allows a real time optimization of network and call configuration, without any impact on the quality of service seen from the user. This paper describes an example of an ATM based multilink protocol that has been experimentally implemented within the RACE project 'STRATOSPHERIC'. The paper outlines the complexity of introducing an extra network functionality compared with the added value, such as an improved ability to recover an error due to a malfunctioning network component.

Dittmann, Lars

1995-11-01

374

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.

375

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

Burton, Grace M.; Midgett, Carol

2008-01-01

376

Tumor heterogeneity: causes and consequences  

PubMed Central

With rare exceptions, spontaneous tumors originate from a single cell. Yet, at the time of clinical diagnosis, the majority of human tumors display startling heterogeneity in many morphological and physiological features, such as expression of cell surface receptors, proliferative and angiogenic potential. To a substantial extent, this heterogeneity might be attributed to morphological and epigenetic plasticity, but there is also strong evidence for the co-existence of genetically divergent tumor cell clones within tumors. In this perspective, we summarize the sources of intra-tumor phenotypic heterogeneity with emphasis on genetic heterogeneity. We review experimental evidence for the existence of both intra-tumor clonal heterogeneity as well as frequent evolutionary divergence between primary tumors and metastatic outgrowths. Furthermore, we discuss potential biological and clinical implications of intra-tumor clonal heterogeneity.

Marusyk, Andriy; Polyak, Kornelia

2009-01-01

377

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.

Liao, David

378

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.

Hense, Burkhard A.; Muller, Johannes; Kuttler, Christina; Hartmann, Anton

2012-01-01

379

Heterogeneously coupled neural oscillators  

NASA Astrophysics Data System (ADS)

The work we present in this thesis is a series of studies of how heterogeneities in coupling affect the synchronization of coupled neural oscillators. We begin by examining how heterogeneity in coupling strength affects the equilibrium phase difference of a pair of coupled, spiking neurons when compared to the case of identical coupling. This study is performed using pairs of Hodgkin-Huxley and Wang-Buzsaki neurons. We find that heterogeneity in coupling strength breaks the symmetry of the bifurcation diagrams of equilibrium phase difference versus the synaptic rate constant for weakly coupled pairs of neurons. We observe important qualitative changes such as the loss of the ubiquitous in-phase and anti-phase solutions found when the coupling is identical and regions of parameter space where no phase locked solution exists. Another type of heterogeneity can be found by having different types of coupling between oscillators. Synaptic coupling between neurons can either be exciting or inhibiting. We examine the synchronization dynamics when a pair of neurons is coupled with one excitatory and one inhibitory synapse. We also use coupled pairs of Hodgkin-Huxley neurons and Wang-Buzsaki neurons for this work. We then explore the existance of 1 : n coupled states for a coupled pair of theta neurons. We do this in order to reproduce an observed effect called quantal slowing. Quantal slowing is the phenomena where jumping between different 1 : n coupled states is observed instead of gradual changes in period as a parameter in the system is varied. All of these topics fall under the general heading of coupled, non-linear oscillators and specifically weakly coupled, neural oscillators. The audience for this thesis is most likely going to be a mixed crowd as the research reported herein is interdisciplinary. Choosing the content for the introduction proved far more challenging than expected. It might be impossible to write a maximally useful introductory portion of a thesis when it could be read by a physicist, mathematician, engineer or biologist. Undoubtedly readers will find some portion of this introduction elementary. At the risk of boring some or all of my readers we decided it was best to proceed so that enough of the mathematical (biological) background is explained in the introduction so that a biologist (mathematician) is able to appreciate the motivations for the research and the results presented. We begin with an introduction in nonlinear dynamics explaining the mathematical tools we use to characterize the excitability of individual neurons, as well as oscillations and synchrony in neural networks. The next part of the introductory material is an overview of the biology of neurons. We then describe the neuron models used in this work and finally describe the techniques we employ to study coupled neurons.

Bradley, Patrick J.

380

Population Ecology: Experiments with Protistans  

NSDL National Science Digital Library

In Part A, "Investigations in Population Ecology" students identify five different protistans, estimate the number of protistans in a culture, dilute stock cultures to achieve specific concentrations of protistans, set up and carry out a competition or predator-prey experiment of their design using one or more of the protistans available. In Part B, "Basic Population Ecology" students use mathematical models to describe exponential and logistic growth in populations of organisms and to analyze, graph, and interpret data.

Zimmerman, Melvin

2010-02-16

381

Dynamic heterogeneities versus fixed heterogeneities in earthquake models  

Microsoft Academic Search

A debate has raged over whether fixed material and geometriheterogeneities, or alternatively dynamic stress heterogeneities, arising through frictional instabilities dominate earthquake complexity. It may also be that both types of heterogeneities interact and are important. This paper makes a first step in examining this interaction, combining two previously separate lines of research. One line examined friction, which has attractors (the

Bruce E. Shaw

2004-01-01

382

Community-based participatory research to decrease smoking prevalence in a high-risk young adult population: an evaluation of the Students Against Nicotine and Tobacco Addiction (SANTA) project.  

PubMed

Students Against Nicotine and Tobacco Addiction is a community-based participatory research project that engages local medical and mental health providers in partnership with students, teachers, and administrators at the Minnesota-based Job Corps. This intervention contains multiple and synchronous elements designed to allay the stress that students attribute to smoking, including physical activities, nonphysical activities, purposeful modifications to the campus's environment and rules/policies, and on-site smoking cessation education and peer support. The intent of the present investigation was to evaluate (a) the types of stress most predictive of smoking behavior and/or nicotine dependence, (b) which activities students are participating in, and (c) which activities are most predictive of behavior change (or readiness to change). Quantitative data were collected through 5 campus-wide surveys. Response rates for each survey exceeded 85%. Stressors most commonly cited included struggles to find a job, financial problems, family conflict, lack of privacy or freedom, missing family or being homesick, dealing with Job Corps rules, and other-unspecified. The most popular activities in which students took part were physically active ones. However, activities most predictive of beneficent change were nonphysical. Approximately one third of respondents were nicotine dependent at baseline. Nearly half intended to quit within 1 month and 74% intended to quit within 6 months. Interventions perceived as most helpful toward reducing smoking were nonphysical in nature. Future efforts with this and comparable populations should engage youth in advancing such activities within a broader range of activity choices, alongside conventional education and support. PMID:24079815

Mendenhall, Tai J; Harper, Peter G; Henn, Lisa; Rudser, Kyle D; Schoeller, Bill P

2014-03-01

383

Ventilation heterogeneity in obesity.  

PubMed

Obesity is associated with important decrements in lung volumes. Despite this, ventilation remains normally or near normally distributed at least for moderate decrements in functional residual capacity (FRC). We tested the hypothesis that this is because maximum flow increases presumably as a result of an increased lung elastic recoil. Forced expiratory flows corrected for thoracic gas compression volume, lung volumes, and forced oscillation technique at 5-11-19 Hz were measured in 133 healthy subjects with a body mass index (BMI) ranging from 18 to 50 kg/m(2). Short-term temporal variability of ventilation heterogeneity was estimated from the interquartile range of the frequency distribution of the difference in inspiratory resistance between 5 and 19 Hz (R5-19_IQR). FRC % predicted negatively correlated with BMI (r = -0.72, P < 0.001) and with an increase in slope of either maximal (r = -0.34, P < 0.01) or partial flow-volume curves (r = -0.30, P < 0.01). Together with a slight decrease in residual volume, this suggests an increased lung elastic recoil. Regression analysis of R5-19_IQR against FRC % predicted and expiratory reserve volume (ERV) yielded significantly higher correlation coefficients by nonlinear than linear fitting models (r(2) = 0.40 vs. 0.30 for FRC % predicted and r(2) = 0.28 vs. 0.19 for ERV). In conclusion, temporal variability of ventilation heterogeneities increases in obesity only when FRC falls approximately below 65% of predicted or ERV below 0.6 liters. Above these thresholds distribution is quite well preserved presumably as a result of an increase in lung recoil. PMID:24651986

Pellegrino, Riccardo; Gobbi, Alessandro; Antonelli, Andrea; Torchio, Roberto; Gulotta, Carlo; Pellegrino, Giulia Michela; Dellacà, Raffaele; Hyatt, Robert E; Brusasco, Vito

2014-05-01

384

The Effect of Student Evaluations on Academic Success  

ERIC Educational Resources Information Center

This article uses longitudinal student-level data from the American University of Sharjah, a large comprehensive university in the Middle East, to examine the relationship between student evaluations of teachers and current and future student achievement. Our model strategies control for the observed and unobserved heterogeneity of students and…

Artz, Benjamin; Welsch, David M.

2013-01-01

385

Motivating Middle Grades Students Using a Cooperative Learning Approach.  

ERIC Educational Resources Information Center

Noting that lack of student motivation is one of the primary reasons students drop out of school and that lack of student motivation is particularly evident at the onset of adolescence, this study compared multidimensional motivation gains of middle school students who were heterogeneously grouped according to motivational level to gains of those…

Corder, Gregory W.

386

Postsecondary Co-Operative Education Programs and Minority Student Participation: Enrollment Patterns For Women, Veteran, Minority, and Handicapped Students; Selected Program Characteristics; and Exemplary Programs Serving Populations with Special Needs. Final Report.  

ERIC Educational Resources Information Center

The purposes of this document are: (1) to measure the participation of women, veterans, minority and handicapped students in postsecondary cooperative programs; (2) to provide a descriptive and comparative analysis of selected policies and practices of cooperative education programs, by institutional level and extent of women, veterans, minority,…

Buchanan, E. T., III; Sunnucks, George M.

387

Assessing Life Styles, Stressors and Health Status among a Predominantly African American On-Campus and Off-Campus Student Population  

ERIC Educational Resources Information Center

Students who attend college and reside on campus often have to contend with social problems such as alcohol and drug abuse, HIV/AIDS infection, courtship, sex and marriage, home and family and other social-psychological issues while trying to maintain academically and matriculate to graduation. Earlier research from the 1995 National College…

Hicks, Terence; Herndon, Michael; Hilton, Adriel; Attoh, Prince; Armstrong, Vikki

2013-01-01

388

Comparing Linear Relationships between E-Book Usage and University Student and Faculty Populations: The Differences between E-Reference and E-Monograph Collections  

ERIC Educational Resources Information Center

This paper reports the results from a quantitative study examining the strength of linear relationships between Laurentian University students and faculty members and the J. N. Desmarais Library's reference and monograph e-book collections. The number of full-text items accessed, searches performed, and undergraduate, graduate, and faculty…

Lamothe, Alain R.

2013-01-01

389

Effects of child abuse history on borderline personality traits, negative life events, and depression: A study among a university student population in Japan  

Microsoft Academic Search

To simultaneously examine the impact of childhood abuse history on borderline personality traits, negative life events, and depression, undergraduate students (N=243) were studied by questionnaire surveys with one week intervals. Neglect and emotional abuse as well as sexual maltreatment predicted borderline personality traits and baseline depression. Baseline depression as well as the impact of negative life events occurring the week

Hiromi Igarashi; Chieko Hasui; Masayo Uji; Masahiro Shono; Toshiaki Nagata; Toshinori Kitamura

2010-01-01

390

Heterogeneity of patients in clinical trials: Subgroup analysis and covariate adjustment in cardiovascular and neurosurgical trials  

Microsoft Academic Search

Randomized clinical trials (RCTs) are essential to evaluate the usefulness of \\u000atreatments and interventions, and clearly influence clinical practice. Trials are \\u000aoften performed in heterogeneous populations, such as patients with traumatic \\u000abrain injury (TBI), acute coronary syndromes (ACS), stroke and cancer. Patients \\u000aare heterogeneous regarding to their characteristics, such as age, gender, or disease severity. Heterogeneity may produce imbalance in

A. V. Hernández

2006-01-01

391

An investigation into trends in Advanced Placement test taking in science and mathematics among student sub-populations using a longitudinal growth model  

NASA Astrophysics Data System (ADS)

The lack of preparation, participation, and equal access of students in mathematics and the science education continues to afflict America's high school system (Ratliff, 2001). Additionally, gender and ethnic status have become significant factors as females and minority subgroups such as African Americans and Hispanics continue to be underrepresented in these two subject fields. Recognizing and understanding these trends is extremely important for the future of this country. As fewer minorities and females become involved in advanced mathematics and science curriculum there will be a continued lack of minorities and females in mathematics and science careers. Additionally, this insufficient representation leads to fewer numbers of females and minorities in industry and educational leadership positions in mathematics and science to promote participation and equality in these fields. According to Brainard and Carlin (2003) as trends currently stand, these two groups will be under-represented in the fields of math and science and will continue to be denied economic and social power. Thus, a better understanding of these trends in participation in mathematics and science among these groups of students is warranted. This study is intended to accomplish four objectives. The first objective is to identify the extent to which opportunities are increasing or decreasing for students in high schools taking mathematics and science Advanced Placement exams by examining six years of student testing data from the College Board. A second objective is to identify features of high schools that relate to greater expansion in Advanced Placement test taking for females and minority groups in the areas of both math and science. A third objective is to explore whether, and to what extent, any social or educational features such as economic status, regional school and living locations, and ethnic backgrounds have enhanced or reduced Advanced Placement testing in these schools. Lastly, the fourth objective is to determine which courses are showing the greatest growth rates in minority and female students among mathematics and science subject areas.

Campbell, D. Michael

392

Health Perceptions, Self and Body Image, Physical Activity and Nutrition among Undergraduate Students in Israel  

PubMed Central

Purpose This study examines health perceptions, self and body image, physical exercise and nutrition among undergraduate students. Methods A structured, self-reported questionnaire was administered to more than 1500 students at a large academic institute in Israel. The study population was heterogenic in both gender and fields of academic study. Results High correlations between health perceptions, appropriate nutrition, and positive self and body image were found. The relationships between these variables differed between the subpopulation in the sample and the different genders. Engagement in physical exercise contributed to positive body image and positive health perceptions more than engagement in healthy nutrition. Nutrition students reported higher frequencies of positive health perceptions, positive self and body image and higher engagement in physical exercise in comparison to all other students in the sample. Conclusions This study suggests, as have many before, that successful health promotion policy should reflect a collectivist rather than an individualist ethos by providing health prerequisites through a public policy of health-promotion, where the academic settings support a healthy lifestyle policy, by increasing availability of a healthy, nutritious and varied menu in the cafeterias, and offering students various activities that enhance healthy eating and exercise. Implications and contribution This study examined health perceptions, self-image, physical exercise and nutrition among undergraduate students and found high correlations between these topics. Nutrition students reported higher frequencies of positive health perceptions, and positive self and body image and engaged more in physical exercise when compared with all other students in the sample.

Korn, Liat; Gonen, Ester; Shaked, Yael; Golan, Moria

2013-01-01

393

Motivating Students To Read.  

ERIC Educational Resources Information Center

This action research project implemented a program for motivating students to read so that they would become enthusiastic, lifelong readers. The targeted population consisted of first- and second-grade students in a middle class community located in a western suburb of Chicago, Illinois. The problem of lack of motivation in reading was documented…

Kane, Roberta S.; Warner, Dori

394

Instructing African American Students.  

ERIC Educational Resources Information Center

Closing the educational achievement gap has been a schooling issue since Brown v. Board of Topeka, Kansas decision. Generally, the learning achievement of elementary and secondary African-American student has been an issue in majority school populations across the United States. And evidence of performance of these students appears to be more…

Young, Clara Y.; Wright, James V.; Laster, Joseph

2005-01-01

395

Heterogeneous geochemistry of catchment acidification  

Microsoft Academic Search

Many ions in catchment runoff are primarily controlled by heterogeneous reactions. The mass law governing heterogeneous equilibria leads directly to a simple, general expression for catchment acid buffering, which can be estimated from bulk catchment runoff composition. This analysis requires no particular assumptions or data regarding catchment minerals, water flowpaths, reaction pathways, or equilibrium constants. Thus, a catchment's vulnerability to

James W. Kirchner

1992-01-01

396

Damage in heterogeneous aluminum alloys  

Microsoft Academic Search

The role of damage on the mechanical response of a heterogeneous material was investigated through both mechanical testing and x-ray tomography. X-ray tomography was used to obtain quantitative information on the evolution of damage through processes occurring at both the local and global scale. The results indicate that heterogeneity in the spatial distribution of particles does influence the damage process.

Justin Gammage

2003-01-01

397

Damage in heterogeneous aluminum alloys  

Microsoft Academic Search

The role of damage on the mechanical response of a heterogeneous material was investigated through both mechanical testing and x-ray tomography. X-ray tomography was used to obtain quantitative information on the evolution of damage through processes occurring at both the local and global scale. The results indicate that heterogeneity in the spatial distribution of particles does influence the damage process.

Justin J. Gammage

2002-01-01

398

Query Expansion Using Heterogeneous Thesauri.  

ERIC Educational Resources Information Center

Proposes a method to improve the performance of information retrieval systems by expanding queries using heterogeneous thesauri. Experiments show that using heterogeneous thesauri with an appropriate weighting method results in better retrieval performance than using only one type of thesaurus. (Author/LRW)

Mandala, Rila; Tokunaga, Takenobu; Tanaka, Hozumi

2000-01-01

399

The Effect of Student Loan Schemes on Students Returning to Study  

ERIC Educational Resources Information Center

In this paper populations of students returning to tertiary study in the period 1997-2005 have been compared with the population of non-returning students who had the same opportunity to return. Such comparisons were conducted for students who returned after a break of 1-7 years (seven comparison groups). Students with the highest likelihood of…

Tumen, Sarah; Shulruf, Boaz

2008-01-01

400

Variance heterogeneity, transformations, and models of species abundance: a cautionary tale  

Microsoft Academic Search

Ecological systems have intrinsic heterogeneity. Counts of abundances of species often show heterogeneity of variances among observational groups or populations. This is most often dealt with by using a transformation of the data followed by a traditional statistical analysis that requires homogeneity. Such an approach is extremely useful when the mean-variance relationship is consistent across the data set. In some

Brian H. McArdle; Marti J. Anderson

2004-01-01

401

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.

Schepeler, Troels; Page, Mahalia E.; Jensen, Kim B.

2014-01-01

402

Medical Student Surgery Elective in Rural Haiti: A Novel Approach to Satisfying Clerkship Requirements While Providing Surgical Care to an Underserved Population  

Microsoft Academic Search

Background  The addition of global health programs to medical school training results in graduates with enhanced clinical skills and increased\\u000a sensitivity to cost issues. Funding from U.S. medical schools has been unable to meet student demand, and therefore it is\\u000a often a critical limiting factor to the lack of development of these programs. We describe an alternative approach for global\\u000a health

Anthony Chin-Quee; Laura White; Ira Leeds; Jana MacLeod; Viraj A. Master

2011-01-01

403

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

404

Heterogeneity in the penumbra.  

PubMed

Original experimental studies in nonhuman primate models of focal ischemia showed flow-related changes in evoked potentials that suggested a circumferential zone of low regional cerebral blood flow with normal K(+) homeostasis, around a core of permanent injury in the striatum or the cortex. This became the basis for the definition of the ischemic penumbra. Imaging techniques of the time suggested a homogeneous core of injury, while positing a surrounding 'penumbral' region that could be salvaged. However, both molecular studies and observations of vascular integrity indicate a more complex and dynamic situation in the ischemic core that also changes with time. The microvascular, cellular, and molecular events in the acute setting are compatible with heterogeneity of the injury within the injury center, which at early time points can be described as multiple 'mini-cores' associated with multiple 'mini-penumbras'. These observations suggest the progression of injury from many small foci to a homogeneous defect over time after the onset of ischemia. Recent observations with updated imaging techniques and data processing support these dynamic changes within the core and the penumbra in humans following focal ischemia. PMID:21731034

del Zoppo, Gregory J; Sharp, Frank R; Heiss, Wolf-Dieter; Albers, Gregory W

2011-09-01

405

On Heterogeneous Covert Networks  

NASA Astrophysics Data System (ADS)

Covert organizations are constantly faced with a tradeoff between secrecy and operational efficiency. Lindelauf, Borm and Hamers [13] developed a theoretical framework to determine optimal homogeneous networks taking the above mentioned considerations explicitly into account. In this paper this framework is put to the test by applying it to the 2002 Jemaah Islamiyah Bali bombing. It is found that most aspects of this covert network can be explained by the theoretical framework. Some interactions however provide a higher risk to the network than others. The theoretical framework on covert networks is extended to accommodate for such heterogeneous interactions. Given a network structure the optimal location of one risky interaction is established. It is shown that the pair of individuals in the organization that should conduct the interaction that presents the highest risk to the organization, is the pair that is the least connected to the remainder of the network. Furthermore, optimal networks given a single risky interaction are approximated and compared. When choosing among a path, star and ring graph it is found that for low order graphs the path graph is best. When increasing the order of graphs under consideration a transition occurs such that the star graph becomes best. It is found that the higher the risk a single interaction presents to the covert network the later this transition from path to star graph occurs.

Lindelauf, Roy; Borm, Peter; Hamers, Herbert

406

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

407

Human mast cell heterogeneity.  

PubMed

Mast cell neutral proteases are the most precise markers of heterogeneity among human mast cells. Two types of human mast cells have been recognized. MCTC cells contain tryptase together with chymase, cathepsin-G like protease, and mast cell carboxypeptidase; MCT cells contain tryptase, but lack the other neutral proteases present in MCTC cells. All mast cells develop from hemopoietic stem cells. In vitro procedures for studying mast cell growth have been developed, using the major human mast cell growth factor, stem cell factor (SCF, also called Kit-ligand). Cultures of hemopoietic progenitor cells in the presence of SCF alone result in selective differentiation to mast cells. The same progenitor cells can be induced to differentiate into other lineages when SCF is used with various lineage-specific colony-stimulating factors such as erythropoietin for erythrocytes. Mast cell development from hematopoietic progenitors may represent a "default pathway," occurring optimally in a permissive microenvironment such as skin, bowel, and lung. The presence or absence of certain cytokines in blood and bone marrow may create a non-permissive environment, thus the absence of granulated mast cells in such locations. PMID:7721078

Irani, A M; Schwartz, L B

1994-01-01

408

Student Services: Achieving Success for All Secondary Students.  

ERIC Educational Resources Information Center

This document, which is intended for high school student services personnel, administrators, and teachers, presents information that can be used to develop an efficient, coordinated, and comprehensive student services system to address the needs of diverse student populations. Chapter 1 contains background information on the following topics:…

Maddy-Bernstein, Carolyn; Cunanan, Esmeralda S.

409

Special Education and Student Services.  

ERIC Educational Resources Information Center

This report examines the current status and plans for special education, student services, and special projects and studies in Oregon. The first section offers an overview of special education long-range planning in secondary and transition programs, the student population with severe emotional disturbance, low incidence populations, families, the…

Brazeau, Karen; And Others

410

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.

McKeon, Sascha Naomi; Moreno, Marta; Sallum, Maria Anise; Povoa, Marinete Marins; Conn, Jan Evelyn

2013-01-01

411

Information Represented Graphically: History of Populations  

NSDL National Science Digital Library

In this lesson, students will describe and explain change of population data displayed in circle graphs and make written predictions from the information. Students will justify their explanation. Lesson 3 of a three-lesson unit.

Mathematics, Illuminations N.

2009-07-26

412

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 individualÂs genotype, and it can result in a change in phenotypeÂÂgood 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.

Program, The W.

413

Dynamic equilibrium of heterogeneous and interconvertible multipotent hematopoietic cell subsets  

PubMed Central

Populations of hematopoietic stem cells and progenitors are quite heterogeneous and consist of multiple cell subsets with distinct phenotypic and functional characteristics. Some of these subsets also appear to be interconvertible and oscillate between functionally distinct states. The multipotent hematopoietic cell line EML has emerged as a unique model to study the heterogeneity and interconvertibility of multipotent hematopoietic cells. Here we describe extensive phenotypic and functional heterogeneity of EML cells which stems from the coexistence of multiple cell subsets. Each of these subsets is phenotypically and functionally heterogeneous, and displays distinct multilineage differentiation potential, cell cycle profile, proliferation kinetics, and expression pattern of HSC markers and some of the key lineage-associated transcription factors. Analysis of their maintenance revealed that on a population level all EML cell subsets exhibit cell-autonomous interconvertible properties, with the capacity to generate all other subsets and re-establish complete parental EML cell population. Moreover, all EML cell subsets generated during multiple cell generations maintain their distinct phenotypic and functional signatures and interconvertible properties. The model of EML cell line suggests that interconvertible multipotent hematopoietic cell subsets coexist in a homeostatically maintained dynamic equilibrium which is regulated by currently unknown cell-intrinsic mechanisms.

Weston, Wendy; Zayas, Jennifer; Perez, Ruben; George, John; Jurecic, Roland

2014-01-01

414

Knowledge Discovery in Heterogeneous Environments.  

National Technical Information Service (NTIS)

This chapter addresses the topic of knowledge discovery in heterogeneous environments. It begins with an overview of the knowledge- discovery process. Because of the importance of using clean, consistent data in the knowledge-discovery process, the chapte...

M. N. Kamel M. G. Ceruti

2002-01-01

415

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...

416

Homogeneous, Heterogeneous, and Enzymatic Catalysis.  

ERIC Educational Resources Information Center

Discusses three areas of catalysis: homegeneous, heterogeneous, and enzymatic. Explains fundamentals and economic impact of catalysis. Lists and discusses common industrial catalysts. Provides a list of 107 references. (MVL)

Oyama, S. Ted; Somorjai, Gabor A.

1988-01-01

417

Population Structures and Cohorts  

NSDL National Science Digital Library

This module provides a gentle introduction to the use of StudentChip software and census data to investigate basic population issues. In the first part of this module, you will use data from the 1990 U.S. census to create population pyramids for several racial and ethnic groups. These population pyramids provide the ability to view the age and sex structure of a population. They not only allow us to view the cumulative impacts of past patterns of fertility, mortality, and migration, but also provide hints about what a particular population is likely to look like in the future. In the second part of the module you will continue our exploration of basic U.S. population structures by comparing some of the basic characteristics of a number of distinct birth cohorts.

Crowder, Kyle

2009-04-20

418

Research on Heterogeneous Database Transformation  

Microsoft Academic Search

Access, MySQL, SQL Server and Oracle9i databases are studyed in this paper. Aiming at the characteristics of data types in heterogeneous database, simple but flexible data types matching method is proposed. In the environment of C#.Net, using standard SQL language and binary text file as intermediate data file, heterogeneous database import-and-export system is developped, which is relatively independent to individual

Zhou Shudao; Zhu Guotao; Wang Yanjie; Shen Ye; Liu Zanyi

2011-01-01

419

Heterogeneous components of chitosans.  

PubMed

The main objectives of the research were to compare the components of partially N-deacetylated chitins prepared identically from native chitin and a chitin regenerated from a heavily deacetylated chitosan. Additionally, to determine if any of the water-soluble components would serve as substrates in a study of a Chitinase isolated from soy bean hull. The brief heating of suspended chitins in 20% (w/w) NaOH resulted in similar degrees of N-deacetylation, the native chitin giving DAc 0.84 and the regenerated chitin DAc 0.79-0.72, with DAc indicating the proportion of glucosamine residues that are acetylated. Evidence for the nature of the hydrolysis of acetamido groups was provided by analyses of the water-soluble and -insoluble Smith degradation products. The water-soluble fraction derived from the native chitin comprised very small amounts of erythrityl N-acetyl glucosaminoside (GlcNAc1E), erythrityl N,N'-diacetyl chitobioside (GlcNAc2E), and erythrityl N,N',N''-triacetyl chitotrioside (GlcNAc3E), each identified by MALDI-TOF mass spectrometry of the butanoyl derivative. The water-insoluble products, as analyzed by light scattering detection method of their butanoyl esters and corrected for their composition, had a molecular weight (Mw) of 25 kDa, corresponding to about 120 N-acetyl glucosaminyl repeating residues (DPw), contrasting to that of 140 kDa with DPw of 680 for the parent chitin. Much of the decrease in the molecular weight of the polymer occurs by the loss of sugar residues by alkaline peeling at reducing terminals. For the regenerated chitin (DAc 1.0), prepared by N-reacetylation of a commercial chitosan (DAc 0.15), the resulting Smith products comprised erythritol and a series of N-acetyl glucosaminyl erythritol homologues of up to at least 39 N-acetyl glucosaminyl repeating residues, reflecting greater heterogeneity in the hydrolysis of acetamido groups along the polymer chain than what was seen for the native chitin. Of the water-soluble Smith products, GlcNAc5-7E were good substrates for chitinase isolated from soybean hull. PMID:20957998

Yang, Byung Y; Ding, Qiong; Montgomery, Rex

2010-11-01

420

Writing approaches of nursing students.  

PubMed

Over the past 20years, research has focused on the writing processes of college students, however, despite recent support for writing as a tool of reflection in nursing education, little is known about how it is that nursing students go about writing papers and assignments as part of their professional education. In order to determine the writing processes of nursing students, the Inventory of Processes in College Composition, a self-response questionnaire, was administered to 169 nursing students. Results support the independence of the writing approaches that nursing students use and similarity to the writing approaches of a general college student population. PMID:22112918

Lavelle, Ellen; Ball, Susan C; Maliszewski, Genevieve

2013-01-01

421

Dealing with spatial heterogeneity  

NASA Astrophysics Data System (ADS)

Heterogeneity can be dealt with by defining homogeneous equivalent properties, known as averaging, or by trying to describe the spatial variability of the rock properties from geologic observations and local measurements. The techniques available for these descriptions are mostly continuous Geostatistical models, or discontinuous facies models such as the Boolean, Indicator or Gaussian-Threshold models and the Markov chain model. These facies models are better suited to treating issues of rock strata connectivity, e.g. buried high permeability channels or low permeability barriers, which greatly affect flow and, above all, transport in aquifers. Genetic models provide new ways to incorporate more geology into the facies description, an approach that has been well developed in the oil industry, but not enough in hydrogeology. The conclusion is that future work should be focused on improving the facies models, comparing them, and designing new in situ testing procedures (including geophysics) that would help identify the facies geometry and properties. A world-wide catalog of aquifer facies geometry and properties, which could combine site genesis and description with methods used to assess the system, would be of great value for practical applications. On peut aborder le problème de l'hétérogénéité en s'efforçant de définir une perméabilité équivalente homogène, par prise de moyenne, ou au contraire en décrivant la variation dans l'espace des propriétés des roches à partir des observations géologiques et des mesures locales. Les techniques disponibles pour une telle description sont soit continues, comme l'approche Géostatistique, soit discontinues, comme les modèles de faciès, Booléens, ou bien par Indicatrices ou Gaussiennes Seuillées, ou enfin Markoviens. Ces modèles de faciès sont mieux capables de prendre en compte la connectivité des strates géologiques, telles que les chenaux enfouis à forte perméabilité, ou au contraire les faciès fins de barrières de perméabilité, qui ont une influence importante sur les écoulement, et, plus encore, sur le transport. Les modè les génétiques récemment apparus ont la capacité de mieux incorporer dans les modèles de faciès les observations géologiques, chose courante dans l'industrie pétrolière, mais insuffisamment développée en hydrogéologie. On conclut que les travaux de recherche ultérieurs devraient s'attacher à développer les modèles de faciès, à les comparer entre eux, et à mettre au point de nouvelles méthodes d'essais in situ, comprenant les méthodes géophysiques, capables de reconnaître la géométrie et les propriétés des faciès. La constitution d'un catalogue mondial de la géométrie et des propriétés des faciès aquifères, ainsi que des méthodes de reconnaissance utilisées pour arriver à la détermination de ces systèmes, serait d'une grande importance pratique pour les applications. La heterogeneidad se puede manejar por medio de la definición de características homogéneas equivalentes, conocidas como promediar o tratando de describir la variabilidad espacial de las características de las rocas a partir de observaciones geológicas y medidas locales. Las técnicas disponibles para estas descripciones son generalmente modelos geoestadísticos continuos o modelos de facies discontinuos como los modelos Boolean, de Indicador o de umbral de Gaussian y el modelo de cadena de Markow. Estos modelos de facies son mas adecuados para tratar la conectvidad de estratos geológicos (por ejemplo canales de alta permeabilidad enterrados o barreras de baja permeabilidad que tienen efectos importantes sobre el flujo y especialmente sobre el transporte en los acuíferos. Los modelo