997 resultados para climatic environment
Resumo:
We used mitochondrial cyt b sequences to investigate the phylogenetic relationships of Crocidura russula (sensu lato) populations across the Strait of Gibraltar, western Europe, Maghreb, and the Mediterranean and Atlantic islands. This revealed very low genetic divergence between European and Moroccan populations. The application of a molecular clock previously calibrated for shrews suggested that the separation of European from Moroccan lineages occurred less than 60 000 bp, which is at least 5 million years (Myr) after the reopening of the Strait of Gibraltar. This means that an overwater dispersal event was responsible for the observed phylogeographical structure. In contrast, genetic analyses revealed that Moroccan populations were highly distinct from Tunisian ones. According to the molecular clock, these populations separated about 2.2 million years ago (Ma), a time marked by sharp alternations of dry and humid climates in the Maghreb. The populations of the Mediterranean islands Ibiza, Pantelleria, and Sardinia were founded from Tunisian populations by overwater dispersal. In conclusion, overwater dispersal across the Strait of Gibraltar, probably assisted by humans, is possible for small terrestrial vertebrates. Moreover, as in Europe, Quaternary climatic fluctuations had a major effect on the phylogeographical structure of the Maghreb biota.
Resumo:
This paper is inspired by articles in the last decade or so that have argued for more attention to theory, and to empirical analysis, within the well-known, and long-lasting, contingency framework for explaining the organisational form of the firm. Its contribution is to extend contingency analysis in three ways: (a) by empirically testing it, using explicit econometric modelling (rather than case study evidence) involving estimation by ordered probit analysis; (b) by extending its scope from large firms to SMEs; (c) by extending its applications from Western economic contexts, to an emerging economy context, using field work evidence from China. It calibrates organizational form in a new way, as an ordinal dependent variable, and also utilises new measures of familiar contingency factors from the literature (i.e. Environment, Strategy, Size and Technology) as the independent variables. An ordered probit model of contingency was constructed, and estimated by maximum likelihood, using a cross section of 83 private Chinese firms. The probit was found to be a good fit to the data, and displayed significant coefficients with plausible interpretations for key variables under all the four categories of contingency analysis, namely Environment, Strategy, Size and Technology. Thus we have generalised the contingency model, in terms of specification, interpretation and applications area.
Resumo:
In order to investigate a possible method of biological control of schistosomiasis, we used the fish Geophagus brasiliensis (Quoy & Gaimard, 1824) which is widely distributed throughout Brazil, to interrupt the life cycle of the snail Biomphalaria tenagophila (Orbigny, 1835), an intermediate host of Schistosoma mansoni. In the laboratory, predation eliminated 97.6% of the smaller snails (3-8 mm shell diameter) and 9.2% of the larger ones (12-14 mm shell diameter). Very promising results were also obtained in a seminatural environment. Studies of this fish in natural snail habitats should be further encouraged.
Resumo:
This paper considers the role which selfish, moral and social incentives and pressures play in explaining the extent to which stated choices over pro-environment behaviours vary across individuals. The empirical context is choices over household waste contracts and recycling actions in Poland. A theoretical model is used to show how cost-based motives and the desire for a positive self- and social image combine to determine the utility from alternative choices of recycling behaviour. We then describe a discrete choice experiment designed to empirically investigate the effects such drivers have on stated choices. Using a latent class model, we distinguish three types of individual who are described as duty-orientated recyclers, budget recyclers and homo oeconomicus. These groups vary in their preferences for how frequently waste is collected, and the number of categories into which household waste must be recycled. Our results have implications for the design of future policies aimed at improving participation in recycling schemes.
Resumo:
In line with global changes, the UK regulatory regime for audit and corporate governance has changed significantly since the Enron scandal, with an increased role for audit committees and independent inspection of audit firms. UK listed company chief financial officers (CFOs), audit committee chairs (ACCs) and audit partners (APs) were surveyed in 2007 to obtain views on the impact of 36 economic and regulatory factors on audit quality. 498 usable responses were received, representing a response rate of 36%. All groups rated various audit committee interactions with auditors among the factors most enhancing audit quality. Exploratory factor analysis reduces the 36 factors to nine uncorrelated dimensions. In order of extraction, these are: economic risk; audit committee activities; risk of regulatory action; audit firm ethics; economic independence of auditor; audit partner rotation; risk of client loss; audit firm size; and, lastly, International Standards on Auditing (ISAs) and audit inspection. In addition to the activities of the audit committee, risk factors for the auditor (both economic and certain regulatory risks) are believed to most enhance audit quality. However, ISAs and the audit inspection regime, aspects of the ‘standards-surveillance compliance’ regulatory system, are viewed as less effective. Respondents commented that aspects of the changed regime are largely process and compliance driven, with high costs for limited benefits, supporting psychological bias regulation theory that claims there is overconfidence that a useful regulatory intervention exists.
Resumo:
Rapport de synthèse : Cette recherche s'intéresse (1) au port et à l'utilisation d'armes chez les adolescents ainsi que (2) aux rôles des facteurs environnementaux et individuels dans la violence juvénile. Les données étaient tirés de SMASH 2002 (Swiss multicenter adolescent survey on health 2002), étude dans laquelle un échantillon représentatif de 7548 étudiants et apprentis âgés entre 16 et 20 ans vivant en Suisse ont été interrogés Dans une première étude, les adolescents ayant porté une arme (couteau, masse, coup de poing américain, pistolet/autre arme à feu, spray) durant l'année précédant l'enquête étaient comparés avec ceux n'ayant pas porté d'arme. Ensuite, dans le sous-échantillon de porteurs d'armes, ceux ayant uniquement porté l'arme étaient comparés avec ceux ayant utilisé une arme dans une bagarre. Des facteurs individuels, familiaux, scolaires et sociaux ont été étudiés à l'aide d'analyses bivariées et multivariées. 13.7% des jeunes vivant en Suisse ont porté une arme dans l'année précédant l'enquête. 6.2% des filles porteuses d'armes et 19.9% des garçons porteurs d'armes ont fait usage de l'arme dans une bagarre. Chez les garçons et chez les filles, les porteurs d'armes étaient plus souvent délinquants et victimes de violence physique. Les garçons porteurs d'armes étaient plus souvent des apprentis, à la recherche de sensations fortes, porteurs de tatouages, avaient une mauvaise relation avec leurs parents, étaient dans des bagarres sous l'influence de substances, et avaient des relations sexuelles à risque. En comparaison avec les porteuses d'armes, les filles utilisatrices d'armes étaient plus souvent fumeuses quotidiennes. Les garçons ayant utilisé leur arme étaient plus souvent nés à l'étranger, vivaient dans un milieu urbain, étaient des apprentis, avaient un mauvais contexte scolaire, avaient des relations sexuelles à risque et étaient impliqués dans des bagarres sous l'influence de substances. Nos résultats montrent que porter une arme est un comportement relativement fréquent chez les adolescents vivant en Suisse et qu'une proportion non négligeable de ces porteurs d'armes ont utilisé l'arme dans une bagarre. De ce fait, une discussion sur le port d'arme devrait être incluse dans l'entretien clinique ainsi que dans les programmes de prévention visant les adolescents. Dans une deuxième étude, la violence juvénile était définie comme présente si l'adolescent avait commis au moins un des quatre délits suivants durant l'année précédant l'enquête: attaquer un adulte, arracher ou voler quelque chose, porter une arme ou utiliser une arme dans une bagarre. Des niveaux écologiques étaient testés et résultaient en un modèle à trois niveaux pour les garçons (niveau individuel, niveau classe et niveau école) et, à cause d'une faible prévalence de la violence chez les filles, en un modèle à un niveau (individuel) pour les filles. Des variables dépendantes étaient attribuées à chaque niveau, en se basant sur la littérature. Le modèle multiniveaux des garçons montrait que le niveau école (10%) et le niveau classe (24%) comptaient pour plus d'un tiers de la variance inter-individuelle dans le comportement violent. Les facteurs associés à ce comportement chez les filles étaient être victime de violence physique et la recherche de sensations fortes. Pour les garçons, les facteurs explicatifs de la violence étaient pratiquer des relations sexuelles à risque, être à la recherche de sensations fortes, être victime de violence physique, avoir une mauvaise relation avec les parents, être déprimé et vivre dans une famille monoparentale au niveau individuel, la violence et les actes antisociaux au niveau de la classe et être apprenti au niveau de l'école. Des interventions au niveau de la classe ainsi qu'un règlement explicit en ce qui concerne la violence et d'autres comportements à risque dans des écoles devraient être prioritaires pour la prévention de la violence chez les adolescents. En outre, la prévention devrait tenir compte des différences entre les sexes.
Resumo:
The STEP HIV vaccine trial, which evaluated a replication-defective adenovirus type 5 (Ad5) vector vaccine, was recently stopped. The reasons for this included lack of efficacy of the vaccine and a twofold increase in the incidence of HIV acquisition among vaccinated recipients with increased Ad5-neutralizing antibody titers compared with placebo recipients. To model the events that might be occurring in vivo, the effect on dendritic cells (DCs) of Ad5 vector alone or treated with neutralizing antiserum (Ad5 immune complexes [IC]) was compared. Ad5 IC induced more notable DC maturation, as indicated by increased CD86 expression, decreased endocytosis, and production of tumor necrosis factor and type I interferons. We found that DC stimulation by Ad5 IC was mediated by the Fcgamma receptor IIa and Toll-like receptor 9 interactions. DCs treated with Ad5 IC also induced significantly higher stimulation of Ad5-specific CD8 T cells equipped with cytolytic machinery. In contrast to Ad5 vectors alone, Ad5 IC caused significantly enhanced HIV infection in DC-T cell cocultures. The present results indicate that Ad5 IC activates a DC-T cell axis that, together with the possible persistence of the Ad5 vaccine in seropositive individuals, may set up a permissive environment for HIV-1 infection, which could account for the increased acquisition of HIV-1 infection among Ad5 seropositive vaccine recipients.
Development of an optimized methodology for tensile testing of carbon steels in hydrogen environment
Resumo:
The study was performed at OCAS, the Steel Research Centre of ArcelorMittal for the Industry market. The major aim of this research was to obtain an optimized tensile testing methodology with in-situ H-charging to reveal the hydrogen embrittlement in various high strength steels. The second aim of this study has been the mechanical characterization of the hydrogen effect on hight strength carbon steels with varying microstructure, i.e. ferrite-martensite and ferrite-bainite grades. The optimal parameters for H-charging - which influence the tensile test results (sample geometry type of electrolyte, charging methods effect of steel type, etc.) - were defined and applied to Slow Strain Rate testing, Incremental Step Loading and Constant Load Testing. To better understand the initiation and propagation of cracks during tensile testing with in-situ H-charging, and to make the correlation with crystallographic orientation, some materials have been analyzed in the SEM in combination with the EBSD technique. The introduction of a notch on the tensile samples permits to reach a significantly improved reproducibility of the results. Comparing the various steel grades reveals that Dual Phase (ferrite-martensite) steels are more sensitive to hydrogen induced cracking than the FB (ferritic-bainitic) ones. This higher sensitivity to hydrogen was found back in the reduced failure times, increased creep rates and enhanced crack initiation (SEM) for the Dual Phase steels in comparison with the FB steels.
Resumo:
The assumption that climatic niche requirements of invasive species are conserved between their native and invaded ranges is key to predicting the risk of invasion. However, this assumption has been challenged recently by evidence of niche shifts in some species. Here, we report the first large-scale test of niche conservatism for 50 terrestrial plant invaders between Eurasia, North America, and Australia. We show that when analog climates are compared between regions, fewer than 15% of species have more than 10% of their invaded distribution outside their native climatic niche. These findings reveal that substantial niche shifts are rare in terrestrial plant invaders, providing support for an appropriate use of ecological niche models for the prediction of both biological invasions and responses to climate change.
Resumo:
Trichuris eggs were observed in Kerodon rupestris coprolites dated 9,000 years before present, collected in archeological sites of São Raimundo Nonato, northeastern Brazil. However, present day local rodents seem not to be infected by the parasite, suggesting its disappearence due to climatic changes.
Resumo:
El canvi climàtic és una realitat i té efectes, tant directes com indirectes, sobre la salut. Són necessàries actuacions concertades per abordar aquestes qüestions de salut pública plantejades pel canvi climàtic, així com també disposar de mecanismes per predir quina serà la seva evolució. En aquest projecte es discuteixen les malalties infeccioses adquirides a través de diferents vies (artròpodes vectors, rosegadors, aigua, aliments i aire) en referència al canvi climàtic al món i també a Catalunya. Basat en una extensa revisió dels treballs i articles publicats, i de comentaris d’experts, es presenta una avaluació dels canvis de les malalties infeccioses: incidència, prevalença i distribució dels patògens i vehicles transmissors en un entorn canviant. En el present estudi es detallen alguns dels casos més estudiats i demostrats d’emergència i reemergència de brots infecciosos a diferents zones del planeta associats a certes variacions en les variables climàtiques. Degut a l’alt nivell d’incertesa sobre el ritme del canvi climàtic i el seu impacte sobre les malalties infeccioses, es proposa un seguit de línies de futur. Una de les propostes és crear una xarxa integrada de dades ambientals i epidemiològiques, amb capacitat de connectar aquestes dades amb la vigilància dels patògens, vectors i de la qualitat de l’aigua, entre d’altres factors. Aquestes anàlisis podrien orientar les estratègies d’actuació en un futur per la protecció de la salut de la població.