Comparison of the computed flow field around a bubble growing at an orifice using PIV techniques

For bubbles growing rapidly at orifices, the inertia of the liquid displacement and the resultant liquid flow field contribute to the production of an inertia force which tends to retard bubble movement. It is therefore the purpose of this paper to report on a study to examine the validity of liquid velocity fields predicted by potential flow methods and measurements made using Particle Image Velocimetry (PIV) techniques. Air bubbles are generated in water at atmospheric conditions from a 1 mm diameter orifice. The process is transient and occurs over a period of approximately 80 msecs. Therefore a combination of high speed video techniques and PIV image processing has been used to determine the liquid velocity vector fields during the bubble growth, detachment and translation periods. This paper will present a summary of the experimental techniques and the theoretical model and discuss the results of the study

Transient thermal analysis of a data centre cooling system under fault conditions

Data centres housing the IT infrastructure of large organisations constitute a considerable technical challenge to ensure 100% operational availability for mission critical IT systems. Specifying plant cooling systems to maintain suitable temperature levels and dissipate the heat generated can be carried out using industry standard design methods. However, accounting for perturbations in cooling due to failure of plant and restart of backup systems requires for faster thermal transients to be addressed than would normally be encountered in building system analysis. It is in this context that this paper describes the modelling and analysis of a 5 MW chilled water cooling system used for the cooling of a recently constructed UK data centre. The model has been developed using the TRNSYS software and includes a full model of the energy transfers for the data centre including chillers, hydraulic network, valve models and each of the 70 Room Air Conditioning Units. The coupling between the data centre air temperature levels and the cooler system has enabled a full assessment of the cooling system design in response to system perturbations. A number of scenarios are examined involving the failure of the chillers and how the inherent thermal inertia of the system plus additional inertia achieved through buffer vessels allowed a suitable design to be achieved. The detailed transient analysis model allowed the sizing of these vessels effectively and to gain a better understanding of the chilled water plant operation, both in normal conditions and in the case of failure

Massive Higher Spin Fields Coupled to a Scalar: Aspects of Interaction and Causality

We consider in detail the most general cubic Lagrangian which describes an interaction between two identical higher spin fieldsin a triplet formulation with a scalar field, all fields having the same values of the mass. After performing the gauge fixing procedure we find that for the case of massive fields the gauge invariance does not guarantee the preservation of the correct number of propagating physical degrees of freedom. In order to get the correct number of degrees of freedom for the massive higher spin field one should impose some additional conditions on parameters of the vertex. Further independent constraints are provided by the causality analysis, indicating that the requirement of causality should be imposed in addition to the requirement of gauge invariance in order to have a consistent propagation of massive higher spin fields.Comment: 34 pages, comments, references and one Appendix added. Typos corrected. Published versio

Some Aspects of Measurement Error in Linear Regression of Astronomical Data

I describe a Bayesian method to account for measurement errors in linear regression of astronomical data. The method allows for heteroscedastic and possibly correlated measurement errors, and intrinsic scatter in the regression relationship. The method is based on deriving a likelihood function for the measured data, and I focus on the case when the intrinsic distribution of the independent variables can be approximated using a mixture of Gaussians. I generalize the method to incorporate multiple independent variables, non-detections, and selection effects (e.g., Malmquist bias). A Gibbs sampler is described for simulating random draws from the probability distribution of the parameters, given the observed data. I use simulation to compare the method with other common estimators. The simulations illustrate that the Gaussian mixture model outperforms other common estimators and can effectively give constraints on the regression parameters, even when the measurement errors dominate the observed scatter, source detection fraction is low, or the intrinsic distribution of the independent variables is not a mixture of Gaussians. I conclude by using this method to fit the X-ray spectral slope as a function of Eddington ratio using a sample of 39 z < 0.8 radio-quiet quasars. I confirm the correlation seen by other authors between the radio-quiet quasar X-ray spectral slope and the Eddington ratio, where the X-ray spectral slope softens as the Eddington ratio increases.Comment: 39 pages, 11 figures, 1 table, accepted by ApJ. IDL routines (linmix_err.pro) for performing the Markov Chain Monte Carlo are available at the IDL astronomy user's library, http://idlastro.gsfc.nasa.gov/homepage.htm

A home from hospital service for older people.

Current policy and practice emphasises much more than ever before a need for purchasers and providers to reduce appropriately the length of hospital stay. Consequently, a number of early discharge "schemes" have been developed. This paper presents the findings from an evaluation of a "home from hospital" (HFH) scheme. The HFH service provides a maximum of six weeks' intensive domiciliary care for older people on their discharge from hospital. The aim of the service is to facilitate early discharge from hospital and to assist patients to regain independence. The study reported here elicited the views and perceptions of clients and professionals involved in the HFH scheme about the quality, efficiency and effectiveness of the service. Seventy-five patients were discharged from hospital to the HFH scheme during a two month period and those who consented to participate in the study were interviewed after discharge from the HFH service (n = 40). Participants had attended hospital for various conditions but the largest group were fracture patients. Hospital staff and community based professionals completed a questionnaire about the service. Overall, patients and professionals perceived the HFH scheme as a beneficial service, though some minor problems existed at an individual level. Clients' dependency levels generally decreased during their time on the scheme. Research using a controlled design is necessary in order to draw firm conclusions about the cost-effectiveness of a HFH service. Overall, home-from-hospital appears to be an effective model of an early discharge scheme worthy of further attention

Condition monitoring of an advanced gas-cooled nuclear reactor core

A critical component of an advanced gas-cooled reactor station is the graphite core. As a station ages, the graphite bricks that comprise the core can distort and may eventually crack. Since the core cannot be replaced, the core integrity ultimately determines the station life. Monitoring these distortions is usually restricted to the routine outages, which occur every few years, as this is the only time that the reactor core can be accessed by external sensing equipment. This paper presents a monitoring module based on model-based techniques using measurements obtained during the refuelling process. A fault detection and isolation filter based on unknown input observer techniques is developed. The role of this filter is to estimate the friction force produced by the interaction between the wall of the fuel channel and the fuel assembly supporting brushes. This allows an estimate to be made of the shape of the graphite bricks that comprise the core and, therefore, to monitor any distortion on them

Designing a Belief Function-Based Accessibility Indicator to Improve Web Browsing for Disabled People

The purpose of this study is to provide an accessibility measure of web-pages, in order to draw disabled users to the pages that have been designed to be ac-cessible to them. Our approach is based on the theory of belief functions, using data which are supplied by reports produced by automatic web content assessors that test the validity of criteria defined by the WCAG 2.0 guidelines proposed by the World Wide Web Consortium (W3C) organization. These tools detect errors with gradual degrees of certainty and their results do not always converge. For these reasons, to fuse information coming from the reports, we choose to use an information fusion framework which can take into account the uncertainty and imprecision of infor-mation as well as divergences between sources. Our accessibility indicator covers four categories of deficiencies. To validate the theoretical approach in this context, we propose an evaluation completed on a corpus of 100 most visited French news websites, and 2 evaluation tools. The results obtained illustrate the interest of our accessibility indicator