164 resultados para Perturbation Problems


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It is often assumed that membership in a stigmatized group has negative consequences for the self-concept. However, this relationship is neither straightforward nor inevitable, and there is evidence suggesting that negative consequences may not necessarily occur (Psychol. Rev. 96(4) (1989) 608). This paper argues that the relationship has not been sufficiently theorized, and that a more detailed analysis is called for in order to understand the relationship between stigma and the self. The paper presents a critical examination of modified labeling theory (Am. Sociol. Rev. 52 (1987) 96), with examples from a study examining perceptions of stigma and their relationship to self-evaluation in women with chronic mental health problems. Open-ended interviews and qualitative analyses were used in preference to global measures of self-esteem. It was found that although the women were aware of society's unfavorable representations of mental illness, and the effects this had on their lives, they did not accept these representations as valid and therefore rejected them as applicable to the self. The participants did not deny their mental health problems, but their acceptance of labels was critical and pragmatic. Labels were rejected when they were perceived as carrying an unrealistic and negative stereotype, or when the women felt that their symptoms did not fit with the diagnostic criteria. The research illustrates the importance of considering people's subjective understandings of stigmatized conditions and societal reactions in order to understand the relation between stigma and the self. (C) 2002 Elsevier Science Ltd. All rights reserved.

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In the perceived hierarchy of research designs, the results from randomized controlled trials are considered to provide the highest level of evidence. Indeed these trials have been upheld as the gold standard in research. The benefits and limitations of the randomized controlled trial as a method of evaluating the effectiveness of healthcare interventions are presented. The article then examines the different levels of complexity within healthcare interventions and the problems this poses in determining effectiveness. In an effort to provide a solution to this problem, the Medical Research Council produced a framework to assist investigators to develop and evaluate complex healthcare interventions. The framework is described with reference to an example of implementing and evaluating protocols for weaning patients in the intensive care unit. The framework is critiqued on the basis that it involves an ambiguous or contradictory ontology, which fails to articulate the relationship between the positivism of randomized controlled trials with the relativism of qualitative approaches. It is concluded that the use of realist strategies in combination with randomized controlled trials provides the most coherent solution to this quandary

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Goldstone's idea of slow dynamics resulting from spontaneously broken symmetries is applied to Hubbell's neutral hypothesis of community dynamics, to efficiently simplify stage-structured multi-species models-introducing the quasi-neutral approximation (QNA). Rather than assuming population-dynamical neutrality in the QNA, deviations from ideal neutrality, thought to be small, drive dynamics. The QNA is systematically derived to first and second order in a two-scale singular perturbation expansion. The total reproductive value of species, as computed from the effective life-history parameters resulting from the non-linear interactions with the surrounding community, emerges as the new dynamic variables in this aggregated description. Using a simple stage-structured community-assembly model, the QNA is demonstrated to accurately reproduce population dynamics in large, complex communities. Further, the utility of the QNA in building intuition for management problems is illustrated by estimating the responses of a fish stock to harvesting and variations in fecundity.

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A growing literature has emerged on employee silence, located within the field of organisational behaviour. Scholars have investigated when and how employees articulate voice and when and how they will opt for silence. While offering many insights, this analysis is inherently one-sided in its interpretation of silence as a product of employee motivations. An alternative reading of silence is offered which focuses on the role of management. Using the non-union employee representation literature for illustrative purposes, the significance of management in structuring employee silence is considered. Highlighted are the ways in which management, through agenda-setting and institutional structures, can perpetuate silence over a range of issues, thereby organising employees out of the voice process. These considerations are redeployed to offer a dialectical interpretation of employee silence in a conceptual framework to assist further research and analysis.

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Connectivity mapping is a recently developed technique for discovering the underlying connections between different biological states based on gene-expression similarities. The sscMap method has been shown to provide enhanced sensitivity in mapping meaningful connections leading to testable biological hypotheses and in identifying drug candidates with particular pharmacological and/or toxicological properties. Challenges remain, however, as to how to prioritise the large number of discovered connections in an unbiased manner such that the success rate of any following-up investigation can be maximised. We introduce a new concept, gene-signature perturbation, which aims to test whether an identified connection is stable enough against systematic minor changes (perturbation) to the gene-signature. We applied the perturbation method to three independent datasets obtained from the GEO database: acute myeloid leukemia (AML), cervical cancer, and breast cancer treated with letrozole. We demonstrate that the perturbation approach helps to identify meaningful biological connections which suggest the most relevant candidate drugs. In the case of AML, we found that the prevalent compounds were retinoic acids and PPAR activators. For cervical cancer, our results suggested that potential drugs are likely to involve the EGFR pathway; and with the breast cancer dataset, we identified candidates that are involved in prostaglandin inhibition. Thus the gene-signature perturbation approach added real values to the whole connectivity mapping process, allowing for increased specificity in the identification of possible therapeutic candidates.

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A unitary operator V and a rank 2 operator R acting on a Hilbert space H are constructed such that V + R is hypercyclic. This answers affirmatively a question of Salas whether a finite rank perturbation of a hyponormal operator can be supercyclic.