46,317 research outputs found
A boundary element method for the solution of a class of steady-state problems for anisotropic media
No full textD. L. Clements and W. S. Budh
A hypersingular boundary integral equation for a class of antiplane multiple crack problems for inhomogeneous elastic materials
No full textW. T. Ang, D. L. Clements, T. Cook
An approximate formula for the stress intensity factor for the pressurized star crack
No full textCopyright © 2003 Published by Elsevier Science Ltd.An elementary approximate formula for the stress intensity factor for the pressurized star crack is established. The formula is sufficiently accurate to be used in practical applications in place of the more complex formulas derived by Westmann [1] and Williams [2].D. L. Clements and N. Widanahttp://www.elsevier.com/wps/find/journaldescription.cws_home/623/description#descriptio
Spatial heterogeneity of parasite co-infection: Determinants and geostatistical prediction at regional scales.
No full textMultiple parasite infections are widespread in the developing world and understanding their geographical distribution is important for spatial targeting of differing intervention packages. We investigated the spatial epidemiology of mono- and co-infection with helminth parasites in East Africa and developed a geostatistical model to predict infection risk. The data used for the analysis were taken from standardised school surveys of Schistosoma mansoni and hookworm (Ancylostoma duodenale/Necator americanus) carried out between 1999 and 2005 in East Africa. Prevalence of mono- and co-infection was modelled using satellite-derived environmental and demographic variables as potential predictors. A Bayesian multi-nominal geostatistical model was developed for each infection category for producing maps of predicted co-infection risk. We show that heterogeneities in co-infection with S. mansoni and hookworm are influenced primarily by the distribution of S. mansoni, rather than the distribution of hookworm, and that temperature, elevation and distance to large water bodies are reliable predictors of the spatial large-scale distribution of co-infection. On the basis of these results, we developed a validated geostatistical model of the distribution of co-infection at a scale that is relevant for planning regional disease control efforts that simultaneously target multiple parasite species
Bayesian spatial analysis of a national urinary schistosomiasis questionnaire to assist geographic targeting of schistosomiasis control in Tanzania, East Africa.
No full textSpatial modelling was applied to self-reported schistosomiasis data from over 2.5 million school students from 12,399 schools in all regions of mainland Tanzania. The aims were to derive statistically robust prevalence estimates in small geographical units (wards), to identify spatial clusters of high and low prevalence and to quantify uncertainty surrounding prevalence estimates. The objective was to permit informed decision-making for targeting of resources by the Tanzanian national schistosomiasis control programme. Bayesian logistic regression models were constructed to investigate the risk of schistosomiasis in each ward, based on the prevalence of self-reported schistosomiasis and blood in urine. Models contained covariates representing climatic and demographic effects and random effects for spatial clustering. Degree of urbanisation, median elevation of the ward and median normalised difference vegetation index (NDVI) were significantly and negatively associated with schistosomiasis prevalence. Most regions contained wards that had >95% certainty of schistosomiasis prevalence being >10%, the selected threshold for bi-annual mass chemotherapy of school-age children. Wards with >95% certainty of schistosomiasis prevalence being >30%, the selected threshold for annual mass chemotherapy of school-age children, were clustered in north-western, south-western and south-eastern regions. Large sample sizes in most wards meant raw prevalence estimates were robust. However, when uncertainties were investigated, intervention status was equivocal in 6.7-13.0% of wards depending on the criterion used. The resulting maps are being used to plan the distribution of praziquantel to participating districts; they will be applied to prioritising control in those wards where prevalence was unequivocally above thresholds for intervention and might direct decision-makers to obtain more information in wards where intervention status was uncertain
Pooling of Forecasts
No full textWe consider forecasting using a combination, when no model coincides with a non-constant data generation process (DGP). Practical experience suggests that combining forecasts adds value, and can even dominate the best individual device. We show why this can occur when forecasting models are differentially mis-specified, and is likely to occur when the DGP is subject to deterministic shifts. Moreover, averaging may then dominate over estimated weights in the combination. Finally, it cannot be proved that only non-encompassed devices should be retained in the combination. Empirical and Monte Carlo illustrations confirm the analysis.
An antiplane crack between bonded dissimilar functionally graded isotropic elastic materials
No full textThis is a pre-copyedited, author-produced PDF of an article accepted for publication in The Quarterly Journal of Mechanics and Applied Mathematics following peer review. The definitive publisher-authenticated version Clements, David Laurence, An antiplane crack between bonded dissimilar functionally graded isotropic elastic materials, The Quarterly Journal of Mechanics and Applied Mathematics, 2013; 66(3):333-349 is available online at: http://qjmam.oxfordjournals.org/content/66/3/333.The problem of a plane crack along the interface of two dissimilar functionally graded isotropic half-spaces under antiplane strain is considered. The materials exhibit quadratic variation in the shear modulus. Numerical values for the stress intensity factors and crack displacement are obtained for some particular materials.D. L. Clement
Axisymmetric loading of a class of inhomogeneous transversely isotropic half-spaces with quadratic elastic moduli
No full textSome axisymmetric problems are considered for a class of inhomogeneous anisotropic elastic materials for which the elastic moduli vary continuously as a quadratic function of the spatial coordinates. For a restricted class of transversely isotropic materials, loading of a half-space and a layer on a rigid foundation are considered and integral expressions for the displacement and stress are obtained. Particular attention is given to cases when the values of the elastic moduli near to the plane boundary of the half-space and the layer approach zero. Numerical results are obtained for some example transversely isotropic and isotropic materials.D. L. Clements and J. Kusum
(1)H NMR studies of enantioselective host-guest complexation by modified beta-cyclodextrins and their europium(III) complexes
No full textThe enantioselectivity of mono-substituted β-cyclodextrins 6A-[bis(carboxylatomethyl)amino]-6A-deoxy-β-cyclodextrin, 6βCDidaH2, (2AS,3AS)-3A-[bis(carboxylatomethyl)amino]-3A-deoxy-β-cyclodextrin, 3βCDidaH2, 6A-[tris(carboxylatomethyl)(2-aminoethyl)amino]-6A-deoxy-β-cyclodextrin, 6βCDedtaH3, and their Eu3+ complexes in the formation of host-guest complexes with six enantiomeric guests in D2O have been studied by 1H NMR 600 MHz spectroscopy. The guests are d/l-tryptophanate, d/l-Trp-, d/l-4hydroxyphenylglycinate, d/l-4HOPhg-, d/l-histidinate, d/l-His-, d/l-pheniramine, d/l-Phm/d/l-PhmH+, d/l-phenylglycinate, d/l-Phg-, and d/l-β-phenylserinate, d/l-βPhs-. Enantioselective host-guest complexation occurs between [Eu(3βCDida)]+, [Eu(6βCDida)]+, and [Eu(6βCDedta)] and d/l-Trp-, [Eu(3βCDida)]+ and [Eu(6βCDida)]+ and d/l-4HOPhg-, and βCD, 3βCDida2-, 6βCDida2-, 6βCDedta3-, [Eu(3βCDida)]+, [Eu(6βCDida)]+, and [Eu(6βCDedta)] and d/l-Phm/d/l-PhmH+. While host-guest complexation occurs for d/l-His- and d/l-Phg-, no enantioselectivity is apparent. Host-guest complexation occurs in the d/l-βPhs- systems but their spectra are too complex for reliable analysis. The preparation of 3βCDidaH2 and 6βCDedtaH3 and the determination of their pKas are also reported. © 2007 Elsevier Ltd. All rights reserved.Duc-Truc Pham, Philip Clements, Christopher J. Easton and Stephen F. Lincolnhttp://www.sciencedirect.com/science/journal/0957416
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