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O processo sucessório em associações produtivas no Brasil: estrutura, desafios e oportunidades; The succession process in productive associations in Brazil: structure, challenges and opportunities

Sousa, Edileusa Godoi de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 15/12/2010 PT
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26.43%
O propósito desta tese foi investigar como tem ocorrido o processo de sucessão em empreendimentos sociais no Brasil, com foco no associativismo produtivo, identificando quais fatores limitam e quais facilitam esse processo a partir das dimensões Indivíduo, Organização e Ambiente. Trata-se de uma pesquisa de caráter exploratório e descritivo, desenvolvida em duas etapas complementares. Na primeira etapa, o grupo amostral compôs-se de 378 empreendimentos, que foram objeto de um survey, para identificar as associações produtivas. Destas foram selecionadas para constituírem a amostra aquelas que já passaram ou estão passando por processo sucessório e cujos dirigentes demonstraram disposição em participar da pesquisa. Na segunda etapa, composta por uma amostra com 32 empreendimentos, buscou-se analisar como interagem as dimensões Indivíduo, Organização e Ambiente na configuração do processo sucessório, identificando quais os fatores que, em cada uma dessas dimensões, podem facilitar e aqueles que podem limitar o processo sucessório. Para analisar a estrutura e as principais características do processo sucessório, tomou-se por base os seguintes eixos orientadores: dimensão Indivíduo - papéis da liderança, habilidade da liderança e estilos de liderança; dimensão Organização - estrutura...

Associations between microsatellite markers and traits related to performance, carcass and organs in chickens

Boschiero, C.; Rosário, M. F.; Ledur, M. C.; Campos, R. L. R.; Ambo, M.; Coutinho, L. L.; Moura, A. S. A. M. T.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 615-620
ENG
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Associations between four microsatellite markers on chromosome 11 and five on chromosome 13 with performance, carcass and organs traits were investigated in chickens using a least-squares approach applied to single-marker analysis. Three hundred and twenty seven F 2 chickens from the EMBRAPA broiler×layer experimental population were evaluated for 16 traits: five related to performance, five to carcass and five to organs, plus the hematocrit. Two significance thresholds were considered: p<0.05 and p<0.0056; the last value resulted from the application of a multiple tests analyses correction. On chromosome 11, six associations (p<0.05) between the genotypes of two markers with four growth related and one carcass trait were found. On chromosome 13, six associations (p<0.05) between marker genotypes and three performance traits, eight associations (p<0.05) between marker genotypes and two carcass traits and eight associations (p<0.05) between marker genotypes and four organs traits were detected. These associations were indications of the presence of quantitative trait loci on these chromosomes, especially on chromosome 13. In this chromosome, the strongest evidence was for body weight at 41 days of age and percentage of carcass because the p-values exceeded the multiple test threshold (p<0.0056)...

Automatic and Deliberate Affective Associations with Sexual Stimuli in Women with Superficial Dyspareunia

Brauer, Marieke; de Jong, Peter J.; Huijding, Jorg; Laan, Ellen; ter Kuile, Moniek M.
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
EN
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Current views suggest that in women with superficial dyspareunia the prospect of penile–vaginal intercourse automatically activates fear-related associations. The automatic activation of negative associations is assumed to interfere with the development of sexual arousal. In turn, this may further aggravate the dyspareunia-related complaints. To assess whether automatic negative associations are involved in this sexual pain disorder, women with superficial dyspareunia (n = 35) and a control group (n = 35) completed a modified pictorial Affective Simon Task (AST). Questioning the role of dysfunctional automatic associations in superficial dyspareunia, the AST indicated that symptomatic women displayed relatively positive rather than negative automatic associations with sexual stimuli. At the self-report level, however, affective associations with sex cues were significantly more negative for women with dyspareunia than for controls. This discrepancy between “reflective” and “reflexive” affective associations with sexual stimuli in women with dyspareunia points to the relevance of conscious appraisal and deliberate rather than automatic processes in the onset and maintenance of dyspareunia.

Do Automatic Self-Associations Relate to Suicidal Ideation?

Glashouwer, Klaske A.; de Jong, Peter J.; Penninx, Brenda W. J. H.; Kerkhof, Ad J. F. M.; van Dyck, Richard; Ormel, Johan
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
EN
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Dysfunctional self-schemas are assumed to play an important role in suicidal ideation. According to recent information-processing models, it is important to differentiate between ‘explicit’ beliefs and automatic associations. Explicit beliefs stem from the weighting of propositions and their corresponding ‘truth’ values, while automatic associations reflect more simple associations in memory. Both types of associations are assumed to have different functional properties and both may be involved in suicidal ideation. Thus far, studies into self-schemas and suicidal ideation focused on the more explicit, consciously accessible traces of self-schemas and predominantly relied on self-report questionnaires or interviews. To complement these ‘explicit’ findings and more directly tap into self-schemas, this study investigated automatic self-associations in a large scale community sample that was part of the Netherlands Study of Depression and Anxiety (NESDA). The results showed that automatic self-associations of depression and anxiety were indeed significantly related to suicidal ideation and past suicide attempt. Moreover, the interactions between automatic self-depressive (anxious) associations and explicit self-depressive (anxious) beliefs explained additional variance over and above explicit self-beliefs. Together these results provide an initial insight into one explanation of why suicidal patients might report difficulties in preventing and managing suicidal thoughts.

Associations of salivary cortisol levels with inflammatory markers: the Multi-Ethnic Study of Atherosclerosis

DeSantis, AS; DiezRoux, AV; Hajat, A; Aiello, AE; Golden, SH; Jenny, NS; Seeman, TE; Shea, S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
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Socioeconomic and psychosocial factors have been found to be associated with systemic inflammation. Although stress is often proposed as a contributor to these associations, no population studies have investigated the links between inflammation and biomarkers of stress. The current study examines associations between daily cortisol profiles and inflammatory markers interleukin-6 (IL-6), interleukin-10 (IL-10), and tumor necrosis factor (TNF-a) in a population-based sample of 869 adults with repeat measures of cortisol over multiple days. Persons with higher levels of IL-6 had a less pronounced cortisol awakening response, a less steep daily decline, and higher cortisol area under the curve for the day with associations persisting after controls for risk factors and other cytokines. Persons with higher levels of TNF-a had lower cortisol levels upon waking, and flatter daily decline, although associations with decline were attenuated when controlling for inflammatory risk factors. Higher levels of IL-10 were associated with marginally flatter daily cortisol decline (p < .10). This study is the first to identify associations of basal cortisol activity and inflammatory markers in a population-based sample. Findings are consistent with the possibility that HPA axis activity may mediate associations between psychosocial stressors and inflammatory processes. Additional prospective data are necessary to clarify the directionality of associations between cortisol and inflammatory markers.

Prediction of Associations between OMIM Diseases and MicroRNAs by Random Walk on OMIM Disease Similarity Network

Chen, Hailin; Zhang, Zuping
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em 20/03/2013 EN
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Increasing evidence has revealed that microRNAs (miRNAs) play important roles in the development and progression of human diseases. However, efforts made to uncover OMIM disease-miRNA associations are lacking and the majority of diseases in the OMIM database are not associated with any miRNA. Therefore, there is a strong incentive to develop computational methods to detect potential OMIM disease-miRNA associations. In this paper, random walk on OMIM disease similarity network is applied to predict potential OMIM disease-miRNA associations under the assumption that functionally related miRNAs are often associated with phenotypically similar diseases. Our method makes full use of global disease similarity values. We tested our method on 1226 known OMIM disease-miRNA associations in the framework of leave-one-out cross-validation and achieved an area under the ROC curve of 71.42%. Excellent performance enables us to predict a number of new potential OMIM disease-miRNA associations and the newly predicted associations are publicly released to facilitate future studies. Some predicted associations with high ranks were manually checked and were confirmed from the publicly available databases, which was a strong evidence for the practical relevance of our method.

Implicit Drinking Identity: Drinker + Me Associations Predict College Student Drinking Consistently

Lindgren, Kristen P.; Foster, Dawn W.; Westgate, Erin C.; Neighbors, Clayton
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.43%
Predicting hazardous drinking in college students continues to be a serious priority. Emerging evidence suggests that implicit measures may offer additional insight in predicting unique variance in alcohol outcomes. Implicit drinking identity, in particular, may be a powerful predictor of alcohol use. The current study examined the predictive validity of three alcohol-related associations (e.g., drinking identity, alcohol approach, and alcohol cope) using adaptations of the Implicit Association Test (IAT) in a sample of 243 undergraduates. Confirming previous findings, drinking identity associations were the most consistent predictor of alcohol consumption and alcohol problems. They were the only associations that were unique predictors of alcohol use after controlling for other implicit associations. In comparison, alcohol cope and alcohol approach associations were weak but consistent predictors of alcohol consumption and alcohol problems. Although positively correlated with all drinking outcomes, neither set of associations predicted unique variance in the drinking outcomes when all implicit associations were included in the same model. Collectively, these results extend previous findings that implicit drinking identity may be a uniquely powerful tool for predicting alcohol outcomes and a potential target for clinical intervention and prevention efforts.

Changing how I feel about the food: experimentally manipulated affective associations with fruits change fruit choice behaviors

Walsh, Erin M.; Kiviniemi, Marc T.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Fewer than half of Americans meet current recommendations for fruit and vegetable intake. The behavioral affective associations model posits that feelings and emotions associated with a behavior are a proximal influence on decision making. Cross-sectional evidence supports the model and suggests that affective associations predict fruit and vegetable consumption. The purpose of this study was to test whether a causal relation exists between affective associations about fruits and future fruit consumption behavior, as measured by a snack selection task. Following a baseline assessment of cognitive and affective variables, participants’ (N = 161) affective associations about fruits were experimentally manipulated with an implicit priming paradigm. Images of fruits were repeatedly paired with positive, negative, or neutral affective stimuli. The key outcome measure was a behavioral choice task in which participants chose between fruit and a granola bar. Participants in the positive prime condition were three times more likely than those in the negative condition to select a piece of fruit over the granola bar alternative in the snack selection task. They were also twice as likely as those in the neutral condition to select fruit. There were no changes in self-reported affective associations or cognitive beliefs. These findings provide further evidence of the implicit and direct influence of affective associations on behavior...

Visualization of species pairwise associations: a case study of surrogacy in bird assemblages

Lane, Peter W; Lindenmayer, David B; Barton, Philip S; Blanchard, Wade; Westgate, Martin J
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.43%
Quantifying and visualizing species associations are important to many areas of ecology and conservation biology. Species networks are one way to analyze species associations, with a growing number of applications such as food webs, nesting webs, plant–animal mutualisms, and interlinked extinctions. We present a new method for assessing and visualizing patterns of co-occurrence of species. The method depicts interactions and associations in an analogous way with existing network diagrams for studying pollination and trophic interactions, but adds the assessment of sign, strength, and direction of the associations. This provides a distinct advantage over existing methods of quantifying and visualizing co-occurrence. We demonstrate the utility of our new approach by showing differences in associations among woodland bird species found in different habitats and by illustrating the way these can be interpreted in terms of underlying ecological mechanisms. Our new method is computationally feasible for large assemblages and provides readily interpretable effects with standard errors. It has wide applications for quantifying species associations within ecological communities, examining questions about particular species that occur with others...

A Longitudinal Examination of Bidirectional Associations between Subjective Sleep Characteristics and Psychosocial Functioning among University Students

Tavernier, Royette
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
26.43%
A number of studies have found a significant link between sleep and psychosocial functioning among university students. A critical examination of this literature, however, indicates that one important gap within the literature is the need for longitudinal studies that specifically test for bidirectional associations between these two constructs. The main purpose of my dissertation was to address this gap by conducting three studies that examined bidirectional associations between sleep and psychosocial functioning among a sample of university students. Participants were 942 (71.5% female) undergraduate students enrolled at a Canadian university, who completed survey assessments annually for three consecutive years, beginning in their first year of university. In the first study, I assessed bidirectional associations between two sleep characteristics (sleep quality and sleep duration) and three psychosocial functioning variables (academics, friendship quality, and intrapersonal adjustment). Results based on cross-lagged models indicated a significant bidirectional association between sleep quality and intrapersonal adjustment, such that more sleep problems predicted more negative intrapersonal adjustment over time, and vice versa. Unidirectional associations indicated that both higher academic achievement and more positive friendship quality were significant predictors of less sleep problems over time. In the second study...

The Australian cerebral palsy research study - epidemiological and genetic associations with cerebral palsy.

O’Callaghan, Michael E.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2011
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Introduction Twenty two mostly small studies have reported associations between cerebral palsy (CP) and specific single nucleotide polymorphisms (SNPs). These data require prospective confirmation in a large cohort. Only one study has examined maternal genetic risk factors for CP. The current large study of mothers and children examines the contributions of genetic and epidemiological factors to CP and their interactions. Methods Caucasian children aged between five and 18 years who were born in Australia were recruited with their mothers. Results from 587 case pairs and 1,154 control pairs were analysed. Each mother and child provided DNA using buccal swabs. Multiplex PCR was used to genotype individuals and 35 specific SNPs were included in the analysis. These candidate SNPs have been putatively associated with thrombophilia, inflammation and preterm birth. Mothers completed a health, pregnancy and delivery questionnaire. State perinatal data for each participant provided further epidemiological data, while CP registers provided cerebral palsy diagnosis data. Univariable analysis examined each epidemiological and genetic risk factor individually with Bonferroni correction for multiple testing. Subsequent multivariable analyses were performed combining risks and examining interactions. Odds ratio (OR) and 95% confidence intervals are reported. Results Univariable analysis of SNP associations with CP did not confirm the majority of associations reported in the literature after correction for multiple testing. Prothrombin gene mutation in the child remained associated with hemiplegia in term delivered infants where a maternal infection during pregnancy was reported (OR 4.52...

Interessenverbände in der IT-Branche - erste empirische Ergebnisse zur Organisationsfähigkeit von Arbeitgeberverbänden; Interest federations in the IT branch - the first empiric results to the organization ability of employers' associations

Menez, Raphael
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: ResearchPaper; info:eu-repo/semantics/other
DE_DE
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Gegenstand des Forschungsprojektes „Interessenverbände in der IT-Branche“ ist die Organisationsfähigkeit von Arbeitgeberverbänden und Gewerkschaften in dieser Querschnittsbranche. Die vorliegende Studie markiert das erste Teilprojekt in diesem Rahmen und beschäftigt sich mit den Organisationsbedingungen von Arbeitgeberverbänden in der IT-Branche. Folgende Ergebnisse werden in dem Bericht präsentiert: Arbeitgeberverbände schätzen den Organisationsbedarf von IT-Unternehmen als eher gering ein, da erstens die Nachfrage nach tariflicher Regulierung gering ist und zweitens die Gewerkschaften noch keine hinreichende Mitgliederbasis in den IT-Unternehmen aufgebaut haben. Als Reaktion darauf verstärken einige der untersuchten Verbände den Ausbau von Beratungs- und Serviceleistungen und die Einrichtung von OT-Strukturen. Die OT-Strukturen führen bei den Arbeitgeberverbänden allerdings zu einer Entkopplung von Tariforientierung und Dienstleistungsorientierung und einer Redefinition des verbandlichen Selbstverständnisses in Richtung Arbeitgeberdienstleistungsverband. Dabei scheint die Etablierung einer verbandlichen Ordnung in der IT-Branche in der aktuellen Situation aus zwei Gründen eher unwahrscheinlich zu sein: Weil erstens diejenigen Verbände...

Les impacts de la dispersion historique sur la variabilité génétique à différentes échelles spatiales : connaître l'histoire pour mieux comprendre le présent.

Cyr, Frédéric
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
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La variabilité génétique actuelle est influencée par une combinaison complexe de variables historiques et contemporaines. Dès lors, une interprétation juste de l’impact des processus actuels nécessite une compréhension profonde des processus historiques ayant influencé la variabilité génétique. En se basant sur la prémisse que des populations proches devraient partager une histoire commune récente, nombreuses études, effectuées à petite échelle spatiale, ne prennent pas en considération l’effet potentiel des processus historiques. Cette thèse avait pour but de vérifier la validité de cette prémisse en estimant l’effet de la dispersion historique à grande et à petite échelle spatiale. Le premier volet de cette thèse avait pour but d’évaluer l’impact de la dispersion historique sur la répartition des organismes à grande échelle spatiale. Pour ce faire, les moules d’eau douce du genre flotteurs (Pyganodon spp.) ont servies de modèle biologique. Les moules d'eau douce se dispersent principalement au stade larvaire en tant que parasites des poissons. Une série de modèles nuls ont été développés pour évaluer la co-occurrence entre des parasites et leurs hôtes potenitels. Les associations distinctes du flotteur de Terre-Neuve (P. fragilis) avec des espèces de poissons euryhalins permettent d’expliquer sa répartition. Ces associations distinctes ont également pu favoriser la différenciation entre le flotteur de Terre-Neuve et son taxon soeur : le flotteur de l’Est (P. cataracta). Cette étude a démontré les effets des associations biologiques historiques sur les répartitions à grande échelle spatiale. Le second volet de cette thèse avait pour but d’évaluer l’impact de la dispersion historique sur la variabilité génétique...

Integrating EMR-Linked and In Vivo Functional Genetic Data to Identify New Genotype-Phenotype Associations

Mosley, Jonathan D.; Van Driest, Sara L.; Weeke, Peter E.; Delaney, Jessica T.; Wells, Quinn S.; Bastarache, Lisa; Roden, Dan M.; Denny, Josh C.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 20/06/2014 EN
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26.43%
The coupling of electronic medical records (EMR) with genetic data has created the potential for implementing reverse genetic approaches in humans, whereby the function of a gene is inferred from the shared pattern of morbidity among homozygotes of a genetic variant. We explored the feasibility of this approach to identify phenotypes associated with low frequency variants using Vanderbilt's EMR-based BioVU resource. We analyzed 1,658 low frequency non-synonymous SNPs (nsSNPs) with a minor allele frequency (MAF)<10% collected on 8,546 subjects. For each nsSNP, we identified diagnoses shared by at least 2 minor allele homozygotes and with an association p<0.05. The diagnoses were reviewed by a clinician to ascertain whether they may share a common mechanistic basis. While a number of biologically compelling clinical patterns of association were observed, the frequency of these associations was identical to that observed using genotype-permuted data sets, indicating that the associations were likely due to chance. To refine our analysis associations, we then restricted the analysis to 711 nsSNPs in genes with phenotypes in the On-line Mendelian Inheritance in Man (OMIM) or knock-out mouse phenotype databases. An initial comparison of the EMR diagnoses to the known in vivo functions of the gene identified 25 candidate nsSNPs...

Associations Between Sperm Competition and Natural Variation in Male Reproductive Genes on the Third Chromosome of Drosophila melanogaster

Fiumera, Anthony C.; Dumont, Bethany L.; Clark, Andrew G.
Fonte: Copyright © 2007 by the Genetics Society of America Publicador: Copyright © 2007 by the Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /06/2007 EN
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26.43%
We applied association analysis to elucidate the genetic basis for variation in phenotypes affecting postcopulatory sexual selection in a natural population of Drosophila melanogaster. We scored 96 third chromosome substitution lines for nine phenotypes affecting sperm competitive ability and genotyped them at 72 polymorphisms in 13 male reproductive genes. Significant heterogeneity among lines (P < 0.01) was detected for all phenotypes except male-induced refractoriness (P = 0.053). We identified 24 associations (8 single-marker associations, 12 three-marker haplotype associations, and 4 cases of epistasis revealed by single-marker interactions). Fewer than 9 of these associations are likely to be false positives. Several associations were consistent with previous findings [Acp70A with the male's influence on the female's refractoriness to remating (refractory), Esterase-6 with a male's remating probability (remating) and a measure of female offspring production (fecundity)], but many are novel associations with uncharacterized seminal fluid proteins. Four genes showed evidence for pleiotropic effects [CG6168 with a measure of sperm competition (P2′) and refractory, CG14560 with a defensive measure of sperm competition (P1′) and a measure of female fecundity...

Inflammation and Immune-Related Candidate Gene Associations with Acute Lung Injury Susceptibility and Severity: A Validation Study

O'Mahony, D. Shane; Glavan, Bradford J.; Holden, Tarah D.; Fong, Christie; Black, R. Anthony; Rona, Gail; Tejera, Paul; Christiani, David C.; Wurfel, Mark M.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
26.43%
Introduction: Common variants in genes related to inflammation, innate immunity, epithelial cell function, and angiogenesis have been reported to be associated with risks for Acute Lung Injury (ALI) and related outcomes. We tested whether previously-reported associations can be validated in an independent cohort at risk for ALI. Methods: We identified 37 genetic variants in 27 genes previously associated with ALI and related outcomes. We prepared allelic discrimination assays for 12 SNPs from 11 genes with MAF>0.05 and genotyped these SNPs in Caucasian subjects from a cohort of critically ill patients meeting criteria for the systemic inflammatory response syndrome (SIRS) followed for development of ALI, duration of mechanical ventilation, and in-hospital death. We tested for associations using additive and recessive genetic models. Results: Among Caucasian subjects with SIRS (n = 750), we identified a nominal association between rs2069832 in IL6 and ALI susceptibility (OR\(_{adj}\) 1.61; 95% confidence interval [CI], 1.04–2.48, P = 0.03). In a sensitivity analysis limiting ALI cases to those who qualified for the Acute Respiratory Distress Syndrome (ARDS), rs61330082 in NAMPT was nominally associated with risk for ARDS. In terms of ALI outcomes...

OB Associations at the Upper End of the Milky Way Luminosity Function

Rahman, Mubdi; Matzner, Christopher D.; Moon, Dae-Sik
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/11/2012
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26.43%
The Milky Way's most luminous, young and massive (M > 10^4 Msun) star clusters and OB associations have largely evaded detection despite knowledge of their surrounding H II regions. We search for these clusters and associations within the 40 star forming complexes from Rahman & Murray in the 13 most luminous WMAP free-free emission sources of the Galaxy. Selecting for objects with the dust-reddened colors of OB stars, we identify new candidate associations using the 2MASS point source catalog. In 40 star forming complexes searched, 22 contain cluster/association candidates with sizes and masses in the range of 3' - 26' and 10^{2.3} - 10^{5} Msun. Of the 22 candidates, at least 7 have estimated masses > 10^4 Msun, doubling the number of such massive clusters known in the Galaxy. Applying our method to a statistically similar set of test locations, we estimate that 3.0 +/- 0.6 of our 22 candidate associations are unrelated to the star forming complexes. In addition, the apparent extinctions of our candidate associations correlate well with the predictions from a Galactic model. These facts, along with the clear detection of a known OB association and the previous spectral verification of one cluster found by this method, validate our method. Only one of the searched WMAP sources remains without a candidate. In 8 of the most luminous WMAP sources...

On the kinematic evolution of young local associations and the Sco-Cen complex

Fernandez, D.; Figueras, F.; Torra, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/01/2008
Relevância na Pesquisa
26.43%
Context: Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than ~100 pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations -- including an important fraction whose members are Hipparcos stars -- offer insights into the star formation process in low-density environments, shed light on the substellar domain, and could have played an important role in the recent history of the local interstellar medium. Aims: To study the kinematic evolution of young local associations and their relation to other young stellar groups and structures in the local interstellar medium, thus casting new light on recent star formation processes in the solar neighbourhood. Methods: We compiled the data published in the literature for young local associations. Using a realistic Galactic potential we integrated the orbits for these associations and the Sco-Cen complex back in time. Results: Combining these data with the spatial structure of the Local Bubble and the spiral structure of the Galaxy, we propose a recent history of star formation in the solar neighbourhood. We suggest that both the Sco-Cen complex and young local associations originated as a result of the impact of the inner spiral arm shock wave against a giant molecular cloud. The core of the giant molecular cloud formed the Sco-Cen complex...

Self-organizing patterns maintained by competing associations in a six-species predator-prey model

Szabo, G.; Szolnoki, A.; Borsos, I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/01/2008
Relevância na Pesquisa
26.43%
Formation and competition of associations are studied in a six-species ecological model where each species has two predators and two prey. Each site of a square lattice is occupied by an individual belonging to one of the six species. The evolution of the spatial distribution of species is governed by iterated invasions between the neighboring predator-prey pairs with species specific rates and by site exchange between the neutral pairs with a probability $X$. This dynamical rule yields the formation of five associations composed of two or three species with proper spatiotemporal patterns. For large $X$ a cyclic dominance can occur between the three two-species associations whereas one of the two three-species associations prevails in the whole system for low values of $X$ in the final state. Within an intermediate range of $X$ all the five associations coexist due to the fact that cyclic invasions between the two-species associations reduce their resistance temporarily against the invasion of three-species associations.; Comment: 6 pages, 8 figures

Visualization of species pairwise associations: A case study of surrogacy in bird assemblages

Lane, Peter; Lindenmayer, David; Barton, Philip; Blanchard, Wade; Westgate, Martin
Fonte: John Wiley & Sons Inc Publicador: John Wiley & Sons Inc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.43%
Quantifying and visualizing species associations are important to many areas of ecology and conservation biology. Species networks are one way to analyze species associations, with a growing number of applications such as food webs, nesting webs, plant-animal mutualisms, and interlinked extinctions. We present a new method for assessing and visualizing patterns of co-occurrence of species. The method depicts interactions and associations in an analogous way with existing network diagrams for studying pollination and trophic interactions, but adds the assessment of sign, strength, and direction of the associations. This provides a distinct advantage over existing methods of quantifying and visualizing co-occurrence. We demonstrate the utility of our new approach by showing differences in associations among woodland bird species found in different habitats and by illustrating the way these can be interpreted in terms of underlying ecological mechanisms. Our new method is computationally feasible for large assemblages and provides readily interpretable effects with standard errors. It has wide applications for quantifying species associations within ecological communities, examining questions about particular species that occur with others...