979 resultados para Fonction cumulative


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Research on Processing Instruction has so far investigated the primary effects of Processing Instruction. In this book, the results of a series of experimental studies investigating possible secondary and cumulative effects of Processing Instruction on the acquisition of French, Italian and English as a second language will be presented. The results of the three experiments have demonstrated that Processing Instruction not only provides learners the direct or primary benefit of learning to process and produce the morphological form on which they received instruction, but also a secondary benefit in that they transferred that training to processing and producing another morphological form on which they had received no instruction.

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Background: There has been relatively little research into health inequalities in older populations. This may be partly explained by the difficulty in identifying appropriate indicators of socio-economic status for older people. Ideally, indicators of socio-economic status to be used in studies of health inequalities in older populations should incorporate some measure of life-time socio-economic standing, and house value may fill this role. This study examined whether an indicator of accumulated wealth based on a combination of housing tenure and house value was a strong predictor of ill-health in older populations.
Methods: A total of 191 848 people aged =65 years and not living in communal establishments were identified from the 2001 Northern Ireland Census and followed for 5 years. Self-reported health and mortality risk by housing tenure/house value groupings were examined while controlling for a range of other demographic and socio-economic characteristics.
Results: Housing tenure/house value was highly correlated with other indicators of socio-economic status. Public-sector renters had worse self-reported health and higher mortality rates than owner occupiers but significant gradients were also found between those living in the highest-and lowest-valued owner-occupier properties. The relationship between housing tenure and value was unchanged by adjustment for indicators of social support and quality of the physical environment. Adjustment for limiting long-term illness and self-reported health at baseline narrowed but did not eliminate the health gains associated with living in more expensive housing.
Conclusions: House value of residence is an accessible and powerful indicator of accumulated wealth that is highly correlated with current health status and predictive of future mortality risk in older populations.

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Agonistic interactions between animals are often settled by the use of repeated signals which advertise the resource-holding potential of the sender. According to the sequential assessment game this repetition increases the accuracy with which receivers may assess the signal, but under the cumulative assessment model the repeated performances accumulate to give a signal of stamina. These models may be distinguished by the temporal pattern of signalling they predict and by the decision rules used by the contestants. Hermit crabs engage in shell fights over possession of the gastropod shells that they inhabit. During these interactions the two roles of signaller and receiver may be examined separately because they are fixed for the duration of the encounter. Attackers rap their shell against that of the defender in a series of bouts whereas defenders remain tightly withdrawn into their shells for the duration of the contest. At the end of a fight the attacker may evict the defender from its shell or decide to give up without first effecting an eviction; the decision for defenders is either to maintain a grip on its shell or to release the shell and allow itself to be evicted. We manipulated fatigue levels separately for attackers and defenders, by varying the oxygen concentration of the water that they are held in prior to fighting, and examined the effects that this has on the likelihood of each decision and on the temporal pattern of rapping. We show that the vigour of rapping and the likelihood of eviction are reduced when the attacker is subjected to low oxygen but that this treatment has no effect on rates of eviction when applied to defenders. We conclude that defenders compare the vigour of rapping with an absolute threshold rather than with a relative threshold when making their decision. The data are compatible with the cumulative assessment model and with the idea that shell rapping signals the stamina of attackers, but do not fit the predictions of the sequential assessment game.

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Empirical support for ‘invasional meltdown’, where the presence of one invading species facilitates another and compounds negative impacts on indigenous species, is equivocal with few convincing studies. In Ireland, the bank vole was introduced 80 years ago and now occupies a third of the island. The greater white-toothed shrew arrived more recently within the invasive range of the bank vole. We surveyed the abundance of both invasive species and two indigenous species, the wood mouse and pygmy shrew, throughout their respective ranges. The negative effects of invasive on indigenous species were strong and cumulative bringing about species replacement. The greater white-toothed shrew, the second invader, had a positive and synergistic effect on the abundance of the bank vole, the first invader, but a negative and compounding effect on the abundance of the wood mouse and occurrence of the pygmy shrew. The gradual replacement of the wood mouse by the bank vole decreased with distance from the point of the bank vole’s introduction whilst no pygmy shrews were captured where both invasive species were present. Such interactions may not be unique to invasions but characteristic of all multispecies communities. Small mammals are central in terrestrial food webs and compositional changes to this community in Ireland are likely to reverberate throughout the ecosystem. Vegetation composition and structure, invertebrate communities and the productivity of avian and mammalian predators are likely to be affected. Control of these invasive species may only be effected through landscape and habitat management.

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On the whole research has concluded that most young people navigate adolescence with few difficulties, but a minority do find this stage of life challenging, and their ways of coping may have negative consequences for both themselves and others. For some the experience of adversity in earlier childhood, and the cumulative impact of multiple adversities has the potential to compromise a young person’s natural resilience. In some cases this may result in an adolescent feeling overwhelmed, and dying through suicide or other high risk behaviours. This article explores these issues with reference to eight young people who died by suicide in Northern Ireland. The article argues that young people exposed to multiple adversities in childhood require earlier, more sustained and better co-ordinated services from professionals if their psychological and emotional well-being is to be promoted.

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BACKGROUND: "Cumulative meta-analysis" describes a statistical procedure to calculate, retrospectively, summary estimates from the results of similar trials every time the results of a further trial in the series had become available. In the early 1990 s, comparisons of cumulative meta-analyses of treatments for myocardial infarction with advice promulgated through medical textbooks showed that research had continued long after robust estimates of treatment effects had accumulated, and that medical textbooks had overlooked strong, existing evidence from trials. Cumulative meta-analyses have subsequently been used to assess what could have been known had new studies been informed by systematic reviews of relevant existing evidence and how waste might have been reduced.

METHODS AND FINDINGS: We used a systematic approach to identify and summarise the findings of cumulative meta-analyses of studies of the effects of clinical interventions, published from 1992 to 2012. Searches were done of PubMed, MEDLINE, EMBASE, the Cochrane Methodology Register and Science Citation Index. A total of 50 eligible reports were identified, including more than 1,500 cumulative meta-analyses. A variety of themes are illustrated with specific examples. The studies showed that initially positive results became null or negative in meta-analyses as more trials were done; that early null or negative results were over-turned; that stable results (beneficial, harmful and neutral) would have been seen had a meta-analysis been done before the new trial; and that additional trials had been much too small to resolve the remaining uncertainties.

CONCLUSIONS: This large, unique collection of cumulative meta-analyses highlights how a review of the existing evidence might have helped researchers, practitioners, patients and funders make more informed decisions and choices about new trials over decades of research. This would have led to earlier uptake of effective interventions in practice, less exposure of trial participants to less effective treatments, and reduced waste resulting from unjustified research.

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In recent years, the proliferation of discoveries has enabled studies of stone tools used in metal working to develop. The increasing number of tools, made mostly from Neolithic polished axes, reveals a typological and functional diversity that remained largely unsuspected. This diversity is an opportunity to understand the tools and address the technical issues relating to the plastic deformation of metals. The operations that are represented here demonstrate the techniques used by coppersmiths with specialised tools.

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Although polychlorinated biphenyls (PCBs) have been banned in many countries for more than three decades, exposures to PCBs continue to be of concern due to their long half-lives and carcinogenic effects. In National Institute for Occupational Safety and Health studies, we are using semiquantitative plant-specific job exposure matrices (JEMs) to estimate historical PCB exposures for workers (n = 24,865) exposed to PCBs from 1938 to 1978 at three capacitor manufacturing plants. A subcohort of these workers (n = 410) employed in two of these plants had serum PCB concentrations measured at up to four times between 1976 and 1989. Our objectives were to evaluate the strength of association between an individual worker's measured serum PCB levels and the same worker's cumulative exposure estimated through 1977 with the (1) JEM and (2) duration of employment, and to calculate the explained variance the JEM provides for serum PCB levels using (3) simple linear regression. Consistent strong and statistically significant associations were observed between the cumulative exposures estimated with the JEM and serum PCB concentrations for all years. The strength of association between duration of employment and serum PCBs was good for highly chlorinated (Aroclor 1254/HPCB) but not less chlorinated (Aroclor 1242/LPCB) PCBs. In the simple regression models, cumulative occupational exposure estimated using the JEMs explained 14-24% of the variance of the Aroclor 1242/LPCB and 22-39% for Aroclor 1254/HPCB serum concentrations. We regard the cumulative exposure estimated with the JEM as a better estimate of PCB body burdens than serum concentrations quantified as Aroclor 1242/LPCB and Aroclor 1254/HPCB.

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Les principales caractéristiques biomécaniques de la prothèse inversée (cupule sur le versant huméral et sphère sur le versant scapulaire), cet implant semi-contraint, consistent en une médialisation ainsi qu'un abaissement du centre de rotation. Par ce biais, le bras de levier du deltoïde est augmenté. Les fibres musculaires du deltoïde antérieur et postérieur sont ainsi également recrutées pour devenir principalement abducteur. La congruence relative des composants (semi-contrainte) confère également à la prothèse inversée une certaine stabilité primaire, importante pour pallier la déficience de la coiffe des rotateurs (sus-épineux).