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Current Assumptions (current + assumption)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Incremental dynamic analysis for estimating seismic performance sensitivity and uncertainty ,

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2010
Dimitrios Vamvatsikos
Abstract Incremental dynamic analysis (IDA) is presented as a powerful tool to evaluate the variability in the seismic demand and capacity of non-deterministic structural models, building upon existing methodologies of Monte Carlo simulation and approximate moment-estimation. A nine-story steel moment-resisting frame is used as a testbed, employing parameterized moment-rotation relationships with non-deterministic quadrilinear backbones for the beam plastic-hinges. The uncertain properties of the backbones include the yield moment, the post-yield hardening ratio, the end-of-hardening rotation, the slope of the descending branch, the residual moment capacity and the ultimate rotation reached. IDA is employed to accurately assess the seismic performance of the model for any combination of the parameters by performing multiple nonlinear timehistory analyses for a suite of ground motion records. Sensitivity analyses on both the IDA and the static pushover level reveal the yield moment and the two rotational-ductility parameters to be the most influential for the frame behavior. To propagate the parametric uncertainty to the actual seismic performance we employ (a) Monte Carlo simulation with latin hypercube sampling, (b) point-estimate and (c) first-order second-moment techniques, thus offering competing methods that represent different compromises between speed and accuracy. The final results provide firm ground for challenging current assumptions in seismic guidelines on using a median-parameter model to estimate the median seismic performance and employing the well-known square-root-sum-of-squares rule to combine aleatory randomness and epistemic uncertainty. Copyright © 2009 John Wiley & Sons, Ltd. [source]

New labour and reform of the English NHS: user views and attitudes

HEALTH EXPECTATIONS, Issue 2 2010
Andrew Wallace PhD
Abstract Background, The British National Health Service has undergone significant restructuring in recent years. In England this has taken a distinctive direction where the New Labour Government has embraced and intensified the influence of market principles towards its vision of a ,modernized' NHS. This has entailed the introduction of competition and incentives for providers of NHS care and the expansion of choice for patients. Objectives, To explore how users of the NHS perceive and respond to the market reforms being implemented within the NHS. In addition, to examine the normative values held by NHS users in relation to welfare provision in the UK. Design and setting, Qualitative interviews using a quota sample of 48 recent NHS users in South East England recruited from three local health economies. Results, Some NHS users are exhibiting an ambivalent or anxious response to aspects of market reform such as patient choice, the use of targets and markets and the increasing presence of the private sector within the state healthcare sector. This has resulted in a sense that current reforms, are distracting or preventing NHS staff from delivering quality of care and fail to embody the relationships of care that are felt to sustain the NHS as a progressive public institution. Conclusion, The best way of delivering such values for patients is perceived to involve empowering frontline staffs who are deemed to embody the same values as service users, thus problematizing the current assumptions of reform frameworks that market-style incentives will necessarily gain public consent and support. [source]

Are cranial germ cell tumours really tumours of germ cells?

NEUROPATHOLOGY & APPLIED NEUROBIOLOGY, Issue 6 2006
P. J. Scotting
Germ cell tumours of the brain and those that occur in the gonads are believed to share a common origin from germ cell progenitors. This ,germ cell theory' rests upon similar histopathology between these tumours in different locations and the belief that endogenous somatic cells of the brain could not give rise to the range of cell types seen in germ cell tumours. An alternative ,embryonic cell theory' has been proposed for some classes of cranial germ cell tumours, but this still relies on the misplacement of cells in the brain (in this case the earliest embryonic stem cells) during early embryonic development. Recent evidence has demonstrated that neural stem cells of the brain can also give rise to many of the cell types seen in germ cell tumours. These data suggest that endogenous progenitor cells of the brain are a plausible alternative origin for these tumours. This idea is of central importance for studies aiming to elucidate the mechanisms of tumour development. The application of modern molecular analyses to reveal how tumour cells have altered with respect to their cell of origin relies on the certain identification of the cell from which the particular tumour arose. If the identity of this cell is mistaken, then studies to elucidate the mechanisms by which the progenitor cell has been subverted from its normal behaviour will not yield useful information. In addition, it will prove impossible to generate an appropriate animal model in which to study the underlying causes of those tumours. This article makes the case that current assumptions of the origins of cranial germ cell tumours are unreliable. It reviews the evidence in favour of the ,germ cell theory' and argues in favour of a ,brain cell theory' in which endogenous neural progenitor cells of the brain are the likely origin for these tumours. Thus, the case is made that cranial germ cell tumours, like other brain tumours, arise by the transformation of progenitor cells normally resident in the brain. [source]

Presence of haemocyte-like cells in coccinellid reflex blood

PHYSIOLOGICAL ENTOMOLOGY, Issue 1 2004
Alexandra Karystinou
Abstract., Contrary to current assumptions, the reflex blood of two-spot ladybirds, Adalia bipunctata, and seven-spot ladybirds, Coccinella septempunctata, contains haemocyte-like cells. Furthermore, DNA can be extracted and amplified from coccinellid reflex blood, confirming the presence of haemocyte-like cells and demonstrating a nondestructive method of DNA extraction. [source]