6,702 research outputs found

    Convective mass transfer from a submerged drop in a thin falling film

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    We study the fluid mechanics of removing a passive tracer contained in small, viscous drops attached to a flat inclined substrate using thin gravity-driven film flows. A convective mass transfer establishes across the drop-film interface and the tracer in the drop diffuses into the film flow. The Peclet number for the tracer in the film is large. The Peclet number Pe_d in the drop varies from 0.01 to 1. The characteristic transport time in the drop is much larger than in the film. We model the mass transfer of the tracer from the drop bulk into the film using an empirical model based on Newton's law of cooling. This model is supported by a theoretical model solving the quasi-steady 2D advection-diffusion equation in the film coupled with a time-dependent 1D diffusion equation in the drop. We find excellent agreement between our experimental data and the 2 models, which predict an exponential decrease in time of the tracer concentration in the drop. The results are valid for all drop and film Peclet numbers studied. The transport characteristic time is related to the drop diffusion time scale, as diffusion within the drop is the limiting process. Our theoretical model predicts the well-known relationship between the Sherwood and Reynolds numbers in the case of a well-mixed drop Sh~Re_L^{1/3}=\gamma L^2/\nu_f, based on the drop length L, film shear rate \gamma and film kinematic viscosity \nu_f. We show that this relationship is mathematically equivalent to a more physically intuitive relationship Sh~Re_\delta, based on the diffusive boundary layer thickness \delta. The model also predicts a correction in the case of a non-uniform drop concentration, which depends on Re_\delta, the Schmidt number, the drop aspect ratio and the diffusivity ratio. This prediction is in agreement with experiments at low Pe_d. It also agrees as Pe_d approaches 1, although the influence of Re_\delta increases.We wish to thank D. Page-Croft and the technicians of the GK Batchelor Laboratory at the Department of Applied Mathematics and Theoretical Physics, Cambridge. We are grateful to F. Bartholomew, F. Yuen and M. Etzold from the BP Institute, Cambridge, for their help in conducting contact angle and viscosity measurements. J. R. L. wishes to thank his colleagues P. Luzzatto-Fegiz and F. Peaudecerf for fruitful discussions. J. R. L. acknowledges financial support from Magdalene College, Cambridge, through a Nevile Research Fellowship in Applied Mathematics. This material is based upon work supported by the Defense Threat Reduction Agency under Contract No. HDTRA1-12-D-0003-0001.This is the author accepted manuscript. The final version is available from Cambridge University Press via http://dx.doi.org/10.1017/jfm.2015.742

    HIV Prevalence Study and Costing Analysis undertaken for the development of an HIV/AIDS Workplace Strategy for Buffalo City Municipality

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    In contrast to most private sector employers in South Africa, local government has been slow to put in place HIV workplace strategies. While general workplace policies are available, there is an absence of specific guidelines for local authorities in their response as employers and as service delivery agencies to HIV/AIDS. The Buffalo City Municipality (BCM) embarked upon an innovative approach involving research and an inclusive process to develop a response to HIV/AIDS. This response is advocated as good practice. The report outlines the steps taken towards the development and adoption of a Buffalo City Municipality HIV strategy in late 2004. Lessons learned are documented for the benefit of other local authorities in the development of their own HIV strategies. The success in the development of the Buffalo City Municipality HIV/AIDS strategy is based on two important legs. Firstly, the process adopted and secondly the research initiative to provide the data to inform the HIV strategy. The process: BCM is to be commended for its innovative and proactive stance. Key to the success has been the leadership of the initiative where political councillors, departmental heads, and all levels of managers have supported the process. The outcome of the political support has been shown in the high rate of HIV testing in the sampled group, the enthusiastic take-up of Voluntary Counseling and Testing (VCT) by the employees, and the commitment to the resultant BCM HIV/AIDS Cross-cutting Strategy. Further, the involvement of staff from human resources and engineering through to finance and planning in the development of the BCM strategy again attests to the recognition that addressing HIV in the workforce and the broader community must be treated as an inter-sectoral and cross-cutting issue. The success of the process added considerably to the value and accomplishment of the research. The SA Medical Research Council (MRC) (an external group) was commissioned to undertake an HIV prevalence study, as they were seen to be independent and authoritive, as well as to carry out a Knowledge, Attitudes and Practice study (KAP) and to facilitate a VCT process. In addition, a health economist was requested to assess the cost implications of HIV for BCM as an employer. A team of external researchers worked closely with a BCM staff team in the design and setting up of the studies. The fieldwork took place in June 2004 and the overall BCM strategy was completed within two months, in August 2004. From a sample of 20% of the employees, the study found that 10.3% were HIV infected. Key findings are that temporary employees had a higher prevalence (7.7%) than permanent staff (9.3%). Women had a higher prevalence rate than men (10,2 and 9% respectively). The highest prevalence was in the 20-29 year age group. All job bands were infected but levels of infection were highest amongst the lower skill levels (11.7%) and black Africans (12.6%). There was no difference in infection level between employees with different educational levels

    Machine learning for automatic prediction of the quality of electrophysiological recordings

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    The quality of electrophysiological recordings varies a lot due to technical and biological variability and neuroscientists inevitably have to select “good” recordings for further analyses. This procedure is time-consuming and prone to selection biases. Here, we investigate replacing human decisions by a machine learning approach. We define 16 features, such as spike height and width, select the most informative ones using a wrapper method and train a classifier to reproduce the judgement of one of our expert electrophysiologists. Generalisation performance is then assessed on unseen data, classified by the same or by another expert. We observe that the learning machine can be equally, if not more, consistent in its judgements as individual experts amongst each other. Best performance is achieved for a limited number of informative features; the optimal feature set being different from one data set to another. With 80–90% of correct judgements, the performance of the system is very promising within the data sets of each expert but judgments are less reliable when it is used across sets of recordings from different experts. We conclude that the proposed approach is relevant to the selection of electrophysiological recordings, provided parameters are adjusted to different types of experiments and to individual experimenters

    p53 suppresses type II endometrial carcinomas in mice and governs endometrial tumour aggressiveness in humans

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    Type II endometrial carcinomas are a highly aggressive group of tumour subtypes that are frequently associated with inactivation of the TP53 tumour suppressor gene. We show that mice with endometrium-specific deletion of Trp53 initially exhibited histological changes that are identical to known precursor lesions of type II endometrial carcinomas in humans and later developed carcinomas representing all type II subtypes. The mTORC1 signalling pathway was frequently activated in these precursor lesions and tumours, suggesting a genetic cooperation between this pathway and Trp53 deficiency in tumour initiation. Consistent with this idea, analyses of 521 human endometrial carcinomas identified frequent mTORC1 pathway activation in type I as well as type II endometrial carcinoma subtypes. mTORC1 pathway activation and p53 expression or mutation status each independently predicted poor patient survival. We suggest that molecular alterations in p53 and the mTORC1 pathway play different roles in the initiation of the different endometrial cancer subtypes, but that combined p53 inactivation and mTORC1 pathway activation are unifying pathogenic features among histologically diverse subtypes of late stage aggressive endometrial tumours

    Smeared versus localised sources in flux compactifications

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    We investigate whether vacuum solutions in flux compactifications that are obtained with smeared sources (orientifolds or D-branes) still survive when the sources are localised. This seems to rely on whether the solutions are BPS or not. First we consider two sets of BPS solutions that both relate to the GKP solution through T-dualities: (p+1)-dimensional solutions from spacetime-filling Op-planes with a conformally Ricci-flat internal space, and p-dimensional solutions with Op-planes that wrap a 1-cycle inside an everywhere negatively curved twisted torus. The relation between the solution with smeared orientifolds and the localised version is worked out in detail. We then demonstrate that a class of non-BPS AdS_4 solutions that exist for IASD fluxes and with smeared D3-branes (or analogously for ISD fluxes with anti-D3-branes) does not survive the localisation of the (anti) D3-branes. This casts doubts on the stringy consistency of non-BPS solutions that are obtained in the limit of smeared sources.Comment: 23 pages; v2: minor corrections, added references, version published in JHE

    Patients' perceptions of the potential of breathing training for asthma: a qualitative study.

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    Poor symptom control is common in asthma. Breathing training exercises may be an effective adjunct to medication; it is therefore important to understand facilitators and barriers to uptake of breathing training exercises

    Eccrine porocarcinoma of the head: An important differential diagnosis in the elderly patient

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    Background: Eccrine porocarcinoma is a rare malignant tumor of the sweat gland, characterized by a broad spectrum of clinicopathologic presentations. Surprisingly, unlike its benign counterpart eccrine poroma, eccrine porocarcinoma is seldom found in areas with a high density of eccrine sweat glands, like the palms or soles. Instead, eccrine porocarcinoma frequently occurs on the lower extremities, trunk and abdomen, but also on the head, resembling various other skin tumors, as illustrated in the patients described herein. Observations: We report 5 cases of eccrine porocarcinoma of the head. All patients were initially diagnosed as having epidermal or melanocytic skin tumors. Only after histopathologic examination were they classified as eccrine porocarcinoma, showing features of epithelial tumors with abortive ductal differentiation. Characteristic clinical, histopathologic and immunohistochemical findings of eccrine porocarcinomas are illustrated. Conclusion: Eccrine porocarcinomas are potentially fatal adnexal malignancies, in which extensive metastatic dissemination may occur. Porocarcinomas are commonly overlooked, or misinterpreted as squamous or basal cell carcinomas as well as other common malignant and even benign skin tumors. Knowledge of the clinical pattern and histologic findings, therefore, is crucial for an early therapeutic intervention, which can reduce the risk of tumor recurrence and serious complications. Copyright (c) 2008 S. Karger AG, Basel

    Recruitment of ethnic minority patients to a cardiac rehabilitation trial: The Birmingham Rehabilitation Uptake Maximisation (BRUM) study [ISRCTN72884263]

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    Background: Concerns have been raised about low participation rates of people from minority ethnic groups in clinical trials. However, the evidence is unclear as many studies do not report the ethnicity of participants and there is insufficient information about the reasons for ineligibility by ethnic group. Where there are data, there remains the key question as to whether ethnic minorities more likely to be ineligible (e.g. due to language) or decline to participate. We have addressed these questions in relation to the Birmingham Rehabilitation Uptake Maximisation (BRUM) study, a randomized controlled trial (RCT) comparing a home-based with a hospital-based cardiac rehabilitation programme in a multi-ethnic population in the UK. Methods: Analysis of the ethnicity, age and sex of presenting and recruited subjects for a trial of cardiac rehabilitation in the West-Midlands, UK. Participants: 1997 patients presenting post-myocardial infarction, percutaneous transluminal coronary angioplasty or coronary artery bypass graft surgery. Data collected: exclusion rates, reasons for exclusion and reasons for declining to participate in the trial by ethnic group. Results: Significantly more patients of South Asian ethnicity were excluded (52% of 'South Asian' v 36% 'White European' and 36% 'Other', p < 0.001). This difference in eligibility was primarily due to exclusion on the basis of language (i.e. the inability to speak English or Punjabi). Of those eligible, similar proportions were recruited from the different ethnic groups (white, South Asian and other). There was a marked difference in eligibility between people of Indian, Pakistani or Bangladeshi origin
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