36 results on '"Hutchings, Michael"'
Search Results
2. Abiotic stress tolerance can explain range size and filling in temperate woody plants
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Puglielli, Giacomo, Tordoni, Enrico, Laanisto, Lauri, Kalwij, Jesse M., Hutchings, Michael J., Humphreys, Aelys M., Puglielli, Giacomo, Tordoni, Enrico, Laanisto, Lauri, Kalwij, Jesse M., Hutchings, Michael J., and Humphreys, Aelys M.
- Abstract
Efforts to understand the mechanisms explaining the relationship between abiotic stress tolerance and range size and filling have hitherto yielded contradictory results. Unlike previous studies that have focused on single stress factors, we here examine the extent to which range size and filling can be explained by tolerance of multiple abiotic stressors (cold, shade, drought and waterlogging). As range metrics, we used range size and filling (the ratio between actual and potential range) for 331 European and North American temperate woody plant species. Stress tolerance strategies were expressed as a multivariate axis reflecting a cold/waterlogging-drought tolerance trade-off. We used mixed models to evaluate the relationship between range size/filling and this multivariate stress tolerance axis, using latitude as a covariate, and phylogeny and plant functional type as random effects. Range size and stress tolerance were negatively correlated, mostly independently of latitude and continent. Thus, cold/wet-tolerant species had the largest range sizes and cold-sensitive/drought-tolerant species the smallest. In contrast, range filling mostly depended on latitude. Our results show that abiotic stress tolerance can explain interspecific differences in range size, and to a lesser extent range filling, which sets up predictions for range size variation in plants that go beyond latitude.
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- 2023
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3. Comparative analysis of the anthelmintic efficacy of European heather extracts on Teladorsagia circumcincta and Trichostrongylus colubriformis egg hatching and larval motility
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Shepherd, Francesca, Chylinski, Caroline, Hutchings, Michael R, Lima, Joana, Davidson, Ross, Kelly, Robert, Macrae, Alastair, Salminen, Juha-Pekka, Engström, Marica T, Maurer, Veronika, Steinshamn, Håvard, Fittje, Susanne, Morell Perez, Angela, García, Rocío, Athanasiadou, Spiridoula, Shepherd, Francesca, Chylinski, Caroline, Hutchings, Michael R, Lima, Joana, Davidson, Ross, Kelly, Robert, Macrae, Alastair, Salminen, Juha-Pekka, Engström, Marica T, Maurer, Veronika, Steinshamn, Håvard, Fittje, Susanne, Morell Perez, Angela, García, Rocío, and Athanasiadou, Spiridoula
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Background Gastrointestinal nematode (GIN) control is traditionally achieved with the use of anthelmintic drugs, however due to regulations in organic farming and the rise in anthelmintic resistance, alternatives are sought after. A promising alternative is the use of bioactive plant feeding due to the presence of plant secondary metabolites (PSMs) such as proanthocyanidins (PAs). This study focussed on the perennial shrub heather (Ericaceae family), a plant rich in PAs, highly abundant across Europe and with previously demonstrated anthelmintic potential. Methods In vitro assays were used to investigate heather’s anthelmintic efficacy against egg hatching and larval motility. Heather samples were collected from five European countries across two seasons, and extracts were tested against two GIN species: Teladorsagia circumcincta and Trichostrongylus colubriformis. Polyphenol group-specific ultraperformance liquid chromatography-tandem mass spectrometry analysis was performed to identify relevant polyphenol subgroups present, including the PA concentration and size and ratio of the subunits. Partial least squares analysis was performed to associate efficacy with variation in PSM composition. Results Heather extracts reduced egg hatching of both GIN species in a dose-dependent manner by up to 100%, while three extracts at the highest concentration (10 mg/ml) reduced larval motility to levels that were not significantly different from dead larvae controls. PAs, particularly the procyanidin type, and flavonol derivatives were associated with anthelmintic activity, and the particular subgroup of polyphenols associated with the efficacy was dependent on the GIN species and life stage. Conclusions Our results provide in vitro evidence that heather, a widely available plant often managed as a weed in grazing systems, has anthelmintic properties attributed to various groups of PSMs and could contribute to sustainable GIN control in ruminant production systems across Europe.
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- 2022
4. Convexity In Contact Geometry And Reeb Dynamics
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Chaidez, Julian C, Hutchings, Michael L1, Chaidez, Julian C, Chaidez, Julian C, Hutchings, Michael L1, and Chaidez, Julian C
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Reeb flows are a rich, ubiquitous class of dynamical systems arising in symplectic geometry, which include billiard systems, many-body orbital systems, geodesic flows and many Hamiltonian flows. Convexity hypotheses play an important, albeit mysterious, role in the study of these flows. In this thesis, we discuss several new results in the study of convexity in symplectic geometry and Reeb dynamics.In Chapter 1, we resolve a longstanding open problem on the intrinsic characterization of Reeb flows arising from Hamiltonian flows on the convex boundaries. Namely, we prove that dynamically convex Reeb flows, introduced by Hofer-Wysocki-Zehnder, are not all convex. Our proof uses a novel relation between Riemannian geometry and Reeb dynamics, and uses constructions of Abbondandolo-Bramham-Hryniewicz-Salomao.In Chapter 2, we describe a powerful new framework for computationally modelling Reeb dynamics on the boundaries of convex polytopes. We apply this framework to provide new evidence and examples relating to the Viterbo conjecture, a major open problem in Reeb dynamics and quantitative symplectic geometry.In Chapter 3, we study convex toric domains and toric surfaces. A longstanding conjecture in toric geometry states that the Gromov width is monotonic under inclusion of moment polytopes of closed toric varieties. We use methods from toric geometry and ECH to prove a generalization of this conjecture in dimension 4.
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- 2021
5. International Biological Flora: Nervilia nipponica
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Gale, Stephan W., Maeda, Ayako, Miyashita, Ayana, Sugiura, Daisuke, Ogura-Tsujita, Yuki, Kinoshita, Akihiko, Fujimori, Shohei, Hutchings, Michael J., Yukawa, Tomohisa, Gale, Stephan W., Maeda, Ayako, Miyashita, Ayana, Sugiura, Daisuke, Ogura-Tsujita, Yuki, Kinoshita, Akihiko, Fujimori, Shohei, Hutchings, Michael J., and Yukawa, Tomohisa
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- 2021
6. Some properties of magnetic ions and their interaction
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Hutchings, Michael
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530.4 - Abstract
Introduction: The techniques of electron paramagnetic resonance (E.P.R.) have been used to investigate the interaction of rare earth ions with (a) their crystalline environment, by measuring their effective g tensor, and, (b) each other, by observing their pair spectra. The experiments have been carried out in host lattices which, when magnetically concentrated, show interesting ordering properties. The Apparatus: Measurements have been made at both X and K Band frequencies. The X Band spectrometer, originally constructed by Drs. A.H. Cooke and J.G. Park, was modified by the addition of a 115 Ke/s, and 50 c/s, phase sensitive detection system to give greater sensitivity. The K Band spectrometer was designed with a tuneable cylindrical H
011 transmission cavity, and incorporated an improved system of cryogenics. E.P.R. of rare earth ions in diamagnetic garnets: The investigation of the properties or rare earth ions la diamagnetic garnets is of importance in connection with their profound influence on the ferrimagnetism of the iron garnets (for example see Dillon et al. 1960). The results of Ryan (1960) on the E.P.R. of rare earth lone in yttrium aluminium garnet (YAG) and yttrium gallium garnet (YGG) have shown a considerable difference of their g tensor in the two lattices, particularly for the case of Kr3+ . In order to investigate further this variation, in particular the dependence on the host ion in the rare earth site, measurements have been made of the g tensors in the lutetium garnets LAG and LGG. The results, obtained mainly at X Band and 4.2°K, are given in Table 1 together with that for Dy3+ in YAG where no resonance had previously been observed. They indicate that the variation between lutetium and yttrium lattices is not so great as that between the aluminium and gallium lattices.- Published
- 1963
7. Drivers of vegetative dormancy across herbaceous perennial plant species
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Shefferson, Richard P., Kull, Tiiu, Hutchings, Michael J., Selosse, Marc-Andre, Jacquemyn, Hans, Kellett, Kimberly M., Menges, Eric S., Primack, Richard B., Tuomi, Juha, Alahuhta, Kirsi, Hurskainen, Sonja, Alexander, Helen M., Anderson, Derek S., Brys, Rein, Brzosko, Emilia, Dostalik, Slavomir, Gregg, Katharine, Ipser, Zdenek, Jakalaniemi, Anne, Jersakova, Jana, Kettle, W. Dean, McCormick, Melissa K., Mendoza, Ana, Miller, Michael T., Moen, Asbjorn, Oien, Dag-Inge, Puttsepp, Ulle, Roy, Melanie, Sather, Nancy, Sletvold, Nina, Stipkova, Zuzana, Tali, Kadri, Warren, Robert J., II, Whigham, Dennis F., Shefferson, Richard P., Kull, Tiiu, Hutchings, Michael J., Selosse, Marc-Andre, Jacquemyn, Hans, Kellett, Kimberly M., Menges, Eric S., Primack, Richard B., Tuomi, Juha, Alahuhta, Kirsi, Hurskainen, Sonja, Alexander, Helen M., Anderson, Derek S., Brys, Rein, Brzosko, Emilia, Dostalik, Slavomir, Gregg, Katharine, Ipser, Zdenek, Jakalaniemi, Anne, Jersakova, Jana, Kettle, W. Dean, McCormick, Melissa K., Mendoza, Ana, Miller, Michael T., Moen, Asbjorn, Oien, Dag-Inge, Puttsepp, Ulle, Roy, Melanie, Sather, Nancy, Sletvold, Nina, Stipkova, Zuzana, Tali, Kadri, Warren, Robert J., II, and Whigham, Dennis F.
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Vegetative dormancy, that is the temporary absence of aboveground growth for 1year, is paradoxical, because plants cannot photosynthesise or flower during dormant periods. We test ecological and evolutionary hypotheses for its widespread persistence. We show that dormancy has evolved numerous times. Most species displaying dormancy exhibit life-history costs of sprouting, and of dormancy. Short-lived and mycoheterotrophic species have higher proportions of dormant plants than long-lived species and species with other nutritional modes. Foliage loss is associated with higher future dormancy levels, suggesting that carbon limitation promotes dormancy. Maximum dormancy duration is shorter under higher precipitation and at higher latitudes, the latter suggesting an important role for competition or herbivory. Study length affects estimates of some demographic parameters. Our results identify life historical and environmental drivers of dormancy. We also highlight the evolutionary importance of the little understood costs of sprouting and growth, latitudinal stress gradients and mixed nutritional modes.
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- 2018
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8. Symplectic capacities from positive S-1-equivariant symplectic homology
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Gutt, Jean, Hutchings, Michael, Gutt, Jean, and Hutchings, Michael
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We use positive S-1-equivariant symplectic homology to define a sequence of symplectic capacities c(k) for star-shaped domains in R-2n. These capacities are conjecturally equal to the Ekeland-Hofer capacities, but they satisfy axioms which allow them to be computed in many more examples. In particular, we give combinatorial formulas for the capacities c(k) of any convex toric domain or concave toric domain. As an application, we determine optimal symplectic embeddings of a cube into any convex or concave toric domain We also extend the capacities c(k) to functions of Lionville domains which are almost but not quite symplectic capacities.
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- 2018
9. Vulnerability of a specialized pollination mechanism to climate change revealed by a 356-year analysis
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Hutchings, Michael J., Robbirt, Karen M., Roberts, David L., Davy, Anthony J., Hutchings, Michael J., Robbirt, Karen M., Roberts, David L., and Davy, Anthony J.
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Pollination of Ophrys sphegodes by sexual deception of male Andrena nigroaenea bees depends on male bees emerging before female bees and before flowering, and on the orchid flowering before female bee emergence, so that competition for the services of naïve male bees is avoided. Using previously established relationships between the timing of these phenological events and spring temperature, we model flowering and bee emergence dates from 1659 to 2014, using central England temperature records. All phenological events were predicted to advance significantly over this period, accompanying a trend towards warmer springs. The interval between male and female flight decreased over time, whereas that between male flight and flowering increased. In addition, female flight preceded orchid flowering after warm springs and it preceded flowering and male bee flight following the warmest springs. Such reversals in phenology have increased in frequency over the last 356 years. In most years, the Ophrys/Andrena pollination system achieves limited pollination success. The results presented here suggest that climate warming has changed the timing of the phenological events that are critical to reproductive success in O. sphegodes and that continuing warming will increase the frequency of years in which this rare orchid suffers complete reproductive failure.
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- 2018
10. Interactions between four species in a complex wildlife: livestock disease community: implications for Mycobacterium bovis maintenance and transmission
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Scottish Government, Economic and Social Research Council (UK), Natural Environment Research Council (UK), Ministerio de Economía y Competitividad (España), Cowie, Catherine E., Hutchings, Michael R., Barasona, José A., Gortázar, Christian, Vicente, Joaquín, White, Piran C. L., Scottish Government, Economic and Social Research Council (UK), Natural Environment Research Council (UK), Ministerio de Economía y Competitividad (España), Cowie, Catherine E., Hutchings, Michael R., Barasona, José A., Gortázar, Christian, Vicente, Joaquín, and White, Piran C. L.
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Livestock diseases such as bovine tuberculosis can have considerable negative effects on human health and economic activity. Wildlife reservoirs often hinder disease eradication in sympatric livestock populations. Therefore, quantifying interactions between wildlife and livestock is an important aspect of understanding disease persistence. This study was conducted on an extensive cattle farm in southwest Spain, where cattle, domestic pigs, wild boar and red deer are considered to be part of a tuberculosis host community. We tested the hypothesis that the frequency of both types of interactions would be greater at food and water sites, due to the aggregation of individuals from multiple species at these locations. We measured direct and indirect interactions between individuals using GPS and proximity loggers. Over 57,000 direct interactions were recorded over a 2-year period, of which 875 (1.5 %) occurred between different species and 216 (0.38 %) occurred between wildlife and livestock. Most direct and indirect interactions occurred at water sites. Over 90 % of indirect interactions between wildlife and livestock took place within the estimated 3-day environmental survival time of Mycobacterium bovis in this habitat. Red deer home ranges and daily activity patterns revealed significant spatial and temporal overlaps with cattle, particularly in autumn. Suids and red deer also cross the farm boundary regularly, introducing a between-farm interaction risk. The infrequent occurrence of direct interactions between individuals from different species suggests that they are unlikely to be the sole mode of disease transmission and that indirect interactions may play an important role.
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- 2016
11. Potential disruption of pollination in a sexually deceptive orchid by climatic change
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Robbirt, Karen M., Roberts, David L., Hutchings, Michael J., Davy, Anthony J., Robbirt, Karen M., Roberts, David L., Hutchings, Michael J., and Davy, Anthony J.
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Warmer springs advance many phenological events, including flowering time in plants and the flight time of insects [ 1 ]. Pollination by insects, an ecosystem service of immense economic and conservation importance [ 2 ], depends on synchrony between insect activity and flowering time. If plants and their pollinators show different phenological responses to climate warming, pollination could fail. Information about the effects of warming on specific plant-insect mutualisms is difficult to obtain from complex pollination networks [ 3 ]. In contrast, the extraordinarily specific deceptions evolved by orchids [ 4 ] that attract a very narrow range of pollinators allow direct examination of the potential for climatic warming to disrupt synchrony. Here we show that a sexually deceptive orchid and the solitary bee on which it depends for pollination will diverge in phenology with increasing spring temperature. Male bees inadvertently pollinate the orchid flowers during pseudocopulation. Analysis of museum specimens (1893–2007) and recent field-based records (1975–2009) showed that flight date of the solitary bee Andrena nigroaenea is advanced more by higher temperatures than is flowering date in the deceptive orchid Ophrys sphegodes. Male bees emerged slightly earlier than females, which attract male copulatory attentions away from the deceptive flowers. Warming by as little as 2°C increased both the probability of male flight and the proportion of females flying in the bee population before orchid flowering; this would reduce the frequency of pseudocopulation and thus lower pollination success rate in the orchid. Our results demonstrate a significant potential for coevolved plant-pollinator relationships to be disrupted by climatic warming.
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- 2014
12. Identification of 100 fundamental ecological questions
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Sutherland, William J., Freckleton, Robert P., Godfray, H. Charles J., Beissinger, Steven R., Benton, Tim, Cameron, Duncan D., Carmel, Yohay, Coomes, David A., Coulson, Tim, Emmerson, Mark C., Hails, Rosemary S., Hays, Graeme C., Hodgson, Dave J., Hutchings, Michael J., Johnson, David, Jones, Julia P.G., Keeling, Matt J., Kokko, Hanna, Kunin, William E., Lambin, Xavier, Lewis, Owen T., Malhi, Yadvinder, Mieszkowska, Nova, Milner-Gulland, E.J., Norris, Ken, Phillimore, Albert B., Purves, Drew W., Reid, Jane M., Reuman, Daniel C., Thompson, Ken, Travis, Justin M.J., Turnbull, Lindsay A., Wardle, David A., Wiegand, Thorsten, Sutherland, William J., Freckleton, Robert P., Godfray, H. Charles J., Beissinger, Steven R., Benton, Tim, Cameron, Duncan D., Carmel, Yohay, Coomes, David A., Coulson, Tim, Emmerson, Mark C., Hails, Rosemary S., Hays, Graeme C., Hodgson, Dave J., Hutchings, Michael J., Johnson, David, Jones, Julia P.G., Keeling, Matt J., Kokko, Hanna, Kunin, William E., Lambin, Xavier, Lewis, Owen T., Malhi, Yadvinder, Mieszkowska, Nova, Milner-Gulland, E.J., Norris, Ken, Phillimore, Albert B., Purves, Drew W., Reid, Jane M., Reuman, Daniel C., Thompson, Ken, Travis, Justin M.J., Turnbull, Lindsay A., Wardle, David A., and Wiegand, Thorsten
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1. Fundamental ecological research is both intrinsically interesting and provides the basic knowledge required to answer applied questions of importance to the management of the natural world. The 100th anniversary of the British Ecological Society in 2013 is an opportune moment to reflect on the current status of ecology as a science and look forward to high-light priorities for future work. 2. To do this, we identified 100 important questions of fundamental importance in pure ecology. We elicited questions from ecologists working across a wide range of systems and disciplines. The 754 questions submitted (listed in the online appendix) from 388 participants were narrowed down to the final 100 through a process of discussion, rewording and repeated rounds of voting. This was done during a two-day workshop and thereafter. 3. The questions reflect many of the important current conceptual and technical pre-occupations of ecology. For example, many questions concerned the dynamics of environmental change and complex ecosystem interactions, as well as the interaction between ecology and evolution. 4. The questions reveal a dynamic science with novel subfields emerging. For example, a group of questions was dedicated to disease and micro-organisms and another on human impacts and global change reflecting the emergence of new subdisciplines that would not have been foreseen a few decades ago. 5. The list also contained a number of questions that have perplexed ecologists for decades and are still seen as crucial to answer, such as the link between population dynamics and life-history evolution. 6. Synthesis. These 100 questions identified reflect the state of ecology today. Using them as an agenda for further research would lead to a substantial enhancement in understanding of the discipline, with practical relevance for the conservation of biodiversity and ecosystem function.
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- 2013
13. Identification of 100 fundamental ecological questions
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Sutherland, William J, Freckleton, Robert P., Godfray, H. Charles J., Beissinger, Steven R., Benton, Tim, Cameron, Duncan D., Carmel, Yohay, Coomes, David A, Coulson, Tim, Emmerson, Mark C., Hails, Rosemary S., Hays, Graeme C., Hodgson, Dave J., Hutchings, Michael J., Johnson, David, Jones, Julia P.G., Keeling, Matt J., Kokko, Hanna, Sutherland, William J, Freckleton, Robert P., Godfray, H. Charles J., Beissinger, Steven R., Benton, Tim, Cameron, Duncan D., Carmel, Yohay, Coomes, David A, Coulson, Tim, Emmerson, Mark C., Hails, Rosemary S., Hays, Graeme C., Hodgson, Dave J., Hutchings, Michael J., Johnson, David, Jones, Julia P.G., Keeling, Matt J., and Kokko, Hanna
- Abstract
Fundamental ecological research is both intrinsically interesting and provides the basic knowledge required to answer applied questions of importance to the management of the natural world. The 100th anniversary of the British Ecological Society in 2013 is an opportune moment to reflect on the current status of ecology as a science and look forward to high-light priorities for future work. To do this, we identified 100 important questions of fundamental importance in pure ecology. We elicited questions from ecologists working across a wide range of systems and disciplines. The 754 questions submitted (listed in the online appendix) from 388 participants were narrowed down to the final 100 through a process of discussion, rewording and repeated rounds of voting. This was done during a two-day workshop and thereafter. The questions reflect many of the important current conceptual and technical pre-occupations of ecology. For example, many questions concerned the dynamics of environmental change and complex ecosystem interactions, as well as the interaction between ecology and evolution. The questions reveal a dynamic science with novel subfields emerging. For example, a group of questions was dedicated to disease and micro-organisms and another on human impacts and global change reflecting the emergence of new subdisciplines that would not have been foreseen a few decades ago. The list also contained a number of questions that have perplexed ecologists for decades and are still seen as crucial to answer, such as the link between population dynamics and life-history evolution. Synthesis. These 100 questions identified reflect the state of ecology today. Using them as an agenda for further research would lead to a substantial enhancement in understanding of the discipline, with practical relevance for the conservation of biodiversity and ecosystem function.
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- 2013
14. Validation of biological collections as a source of phenological data for use in climate change studies: a case study with the orchid Ophrys sphegodes
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Robbirt, Karen M., Davy, Anthony J., Hutchings, Michael J., Roberts, David L., Robbirt, Karen M., Davy, Anthony J., Hutchings, Michael J., and Roberts, David L.
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1.?The scarcity of reliable long-term phenological data has severely hindered the study of the responses of species to climate change. Biological collections in herbaria and museums are potential sources of long-term data for such study, but their use for this purpose needs independent validation. Here we report a rigorous test of the validity of using herbarium specimens for phenological studies, by comparing relationships between climate and time of peak flowering derived from herbarium records and from direct field-based observations, for the terrestrial orchid Ophrys sphegodes. 2.?We examined herbarium specimens of O. sphegodes collected between 1848 and 1958, and recorded peak flowering time directly in one population of O. sphegodes between 1975 and 2006. The response of flowering time to variation in mean spring temperature (March–May) was virtually identical in both sets of data, even though they covered different periods of time which differ in extent of anthropogenic temperature change. In both cases flowering was advanced by c. 6 days per °C rise in average spring temperature. 3.?The proportion of variation in flowering time explained by spring temperature was lower in the herbarium record than in direct field observations. It is likely that some of the additional variation was due to geographical variation in collection site, as flowering was significantly earlier at more westerly sites, which have had warmer springs, over their range of 3.44° of longitude. 4.?Predictions of peak flowering time based on the herbarium data corresponded closely with observed peak flowering times in the field, indicating that flowering response to temperature had not altered between the two separate periods over which the herbarium and field data were collected. 5.?Synthesis. These results provide the first direct validation of the use of herbarium collections to examine the relationships between phenology and climate when field-based observational data are not available.
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- 2011
15. Nickel(II) and Palladium(II) Complexes of Azobenzene-Containing Ligands as Dichroic Dyes
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Blackburn, Octavia A., Coe, Benjamin J., Fielden, John, Helliwell, Madeleine, McDouall, Joseph J. W., Hutchings, Michael G., Blackburn, Octavia A., Coe, Benjamin J., Fielden, John, Helliwell, Madeleine, McDouall, Joseph J. W., and Hutchings, Michael G.
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- 2010
16. Introduction to the characterization of residual stress by neutron diffraction
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Hutchings, Michael T. and Hutchings, Michael T.
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- 2005
17. Thermally induced frenkel disorder in UO//2 and ThO//2
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Macdonald, J. Emyr, Clausen, Kurt Nørgaard, Garrard, Barry, Hackett, Michael A., Hayes, William, Osborn, Raymond, Schnabel, Peter, Hutchings, Michael T., Macdonald, J. Emyr, Clausen, Kurt Nørgaard, Garrard, Barry, Hackett, Michael A., Hayes, William, Osborn, Raymond, Schnabel, Peter, and Hutchings, Michael T.
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Frenkel defect formation in the oxygen sublattice and the excitation of electronic defects in the form of small polarons are considered. A brief summary is given of the results of a recent investigation into possible oxygen lattice disorder in UO//2 and ThO//2 at temperatures up to 2930 K, using neutron scattering techniques.
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- 1985
18. Survival of Mycobacterium avium subspecies paratuberculosis in retail pasteurised milk
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Gerrard, Zara E., Swift, Benjamin M.C., Botsaris, George, Davidson, Ross S., Hutchings, Michael R., Huxley, Jonathon N., Rees, Catherine E.D., Gerrard, Zara E., Swift, Benjamin M.C., Botsaris, George, Davidson, Ross S., Hutchings, Michael R., Huxley, Jonathon N., and Rees, Catherine E.D.
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A survey of retail purchased semi-skimmed pasteurised milk (n = 368) for Mycobacterium avium subspecies paratuberculosis (MAP) was conducted between May 2014 and June 2015 across the midlands of England using the Phage-PCR assay. Overall, 10.3% of the total samples collected contained viable MAP cells, confirming that pasteurisation is not capable of fully eliminating human exposure to viable MAP through milk. Comparison of the results gained using the Phage-PCR assay with the results of surveys using either culture or direct PCR suggest that the phage-PCR assay is able to detect lower numbers of cells, resulting in an increase in the number of MAP-positive samples detected. Comparison of viable count and levels of MAP detected in bulk milk samples suggest that MAP is not primarily introduced into the milk by faecal contamination but rather are shed directly into the milk within the udder. In addition results detected an asymmetric distribution of MAP exists in the milk matrix prior to somatic cell lysis, indicating that the bacterial cells in naturally contaminated milk are clustered together and may primarily be located within somatic cells. These latter two results lead to the hypothesis that intracellular MAP within the somatic cells may be protected against heat inactivation during pasteurisation, accounting for the presence of low levels of MAP detected in retail milk.
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19. Using combined diagnostic test results to hindcast trends of infection from cross-sectional data
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Rydevik, Gustaf, Innocent, Giles T., Marion, Glenn, Davidson, Ross S., White, Piran C.L., Billinis, Charalambos, Barrow, Paul, Mertens, Peter P.C., Gavier-Widén, Dolores, Hutchings, Michael R., Rydevik, Gustaf, Innocent, Giles T., Marion, Glenn, Davidson, Ross S., White, Piran C.L., Billinis, Charalambos, Barrow, Paul, Mertens, Peter P.C., Gavier-Widén, Dolores, and Hutchings, Michael R.
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Infectious disease surveillance is key to limiting the consequences from infectious pathogens and maintaining animal and public health. Following the detection of a disease outbreak, a response in proportion to the severity of the outbreak is required. It is thus critical to obtain accurate information concerning the origin of the outbreak and its forward trajectory. However, there is often a lack of situational awareness that may lead to over- or under-reaction. There is a widening range of tests available for detecting pathogens, with typically different temporal characteristics, e.g. in terms of when peak test response occurs relative to time of exposure. We have developed a statistical framework that combines response level data from multiple diagnostic tests and is able to ‘hindcast’ (infer the historical trend of) an infectious disease epidemic. Assuming diagnostic test data from a cross-sectional sample of individuals infected with a pathogen during an outbreak, we use a Bayesian Markov Chain Monte Carlo (MCMC) approach to estimate time of exposure, and the overall epidemic trend in the population prior to the time of sampling. We evaluate the performance of this statistical framework on simulated data from epidemic trend curves and show that we can recover the parameter values of those trends. We also apply the framework to epidemic trend curves taken from two historical outbreaks: a bluetongue outbreak in cattle, and a whooping cough outbreak in humans. Together, these results show that hindcasting can estimate the time since infection for individuals and provide accurate estimates of epidemic trends, and can be used to distinguish whether an outbreak is increasing or past its peak. We conclude that if temporal characteristics of diagnostics are known, it is possible to recover epidemic trends of both human and animal pathogens from cross-sectional data collected at a single point in time.
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20. The ecology of wildlife disease surveillance: demographic and prevalence fluctuations undermine surveillance
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Walton, Laura, Marion, Glenn, Davidson, Ross S., White, Piran C.L., Smith, Lesley A., Gavier-Widen, Dolores, Yon, Lisa, Hannant, Duncan, Hutchings, Michael R., Walton, Laura, Marion, Glenn, Davidson, Ross S., White, Piran C.L., Smith, Lesley A., Gavier-Widen, Dolores, Yon, Lisa, Hannant, Duncan, and Hutchings, Michael R.
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1. Wildlife disease surveillance is the first line of defence against infectious disease. Fluctuations in host populations and disease prevalence are a known feature of wildlife disease systems. However, the impact of such heterogeneities on the performance of surveillance is currently poorly understood. 2. We present the first systematic exploration of the effects of fluctuations prevalence and host population size on the efficacy of wildlife disease surveillance systems. In this study efficacy is measured in terms of ability to estimate long term prevalence and detect disease risk. 3. Our results suggest that for many wildlife disease systems fluctuations in population size and disease lead to bias in surveillance-based estimates of prevalence and over-confidence in assessments of both the precision of prevalence estimates and the power to detect disease. 4. Neglecting such ecological effects may lead to poorly designed surveillance and ultimately to incorrect assessments of the risks posed by disease in wildlife. This will be most problematic in systems where prevalence fluctuations are large and disease fade-outs occur. Such fluctuations are determined by the interaction of demography and disease dynamics and although particularly likely in highly fluctuating populations typical of fecund short lived hosts, can’t be ruled out in more stable populations of longer lived hosts. 5. Synthesis and Applications: Fluctuations in population size and disease prevalence should be considered in the design and implementation of wildlife disease surveillance and the framework presented here provides a template for conducting suitable power calculations. Ultimately understanding the impact of fluctuations in demographic and epidemiological processes will enable improvements to wildlife disease surveillance systems leading to better characterisation of, and protection against endemic, emerging and re-emerging disease threats.
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21. Use of wild bird surveillance, human case data and GIS spatial analysis for predicting spatial distributions of West Nile Virus in Greece
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Khudyakov, Yury E., Valiakos, George, Papaspyropoulos, Konstantinos, Giannakopoulos, Alexios, Birtsas, Periklis, Tsiodras, Sotirios, Hutchings, Michael R., Spyrou, Vassiliki, Pervanidou, Danai, Athanasiou, Labrini V., Papadopoulos, Nikolaos, Tsokana, Constantina, Baka, Agoritsa, Manolakou, Katerina, Chatzopoulos, Dimitrios, Artois, Marc, Yon, Lisa, Hannant, Duncan, Petrovska, Liljana, Hadjichristodoulou, Christos, Billinis, Charalambos, Khudyakov, Yury E., Valiakos, George, Papaspyropoulos, Konstantinos, Giannakopoulos, Alexios, Birtsas, Periklis, Tsiodras, Sotirios, Hutchings, Michael R., Spyrou, Vassiliki, Pervanidou, Danai, Athanasiou, Labrini V., Papadopoulos, Nikolaos, Tsokana, Constantina, Baka, Agoritsa, Manolakou, Katerina, Chatzopoulos, Dimitrios, Artois, Marc, Yon, Lisa, Hannant, Duncan, Petrovska, Liljana, Hadjichristodoulou, Christos, and Billinis, Charalambos
- Abstract
West Nile Virus (WNV) is the causative agent of a vector-borne, zoonotic disease with a worldwide distribution. Recent expansion and introduction of WNV into new areas, including southern Europe, has been associated with severe disease in humans and equids, and has increased concerns regarding the need to prevent and control future WNV outbreaks. Since 2010, 524 confirmed human cases of the disease have been reported in Greece with greater than 10% mortality. Infected mosquitoes, wild birds, equids, and chickens have been detected and associated with human disease. The aim of our study was to establish a monitoring system with wild birds and reported human cases data using Geographical Information System (GIS). Potential distribution of WNV was modelled by combining wild bird serological surveillance data with environmental factors (e.g. elevation, slope, land use, vegetation density, temperature, precipitation indices, and population density). Local factors including areas of low altitude and proximity to water were important predictors of appearance of both human and wild bird cases (Odds Ratio = 1,001 95%CI = 0,723–1,386). Using GIS analysis, the identified risk factors were applied across Greece identifying the northern part of Greece (Macedonia, Thrace) western Greece and a number of Greek islands as being at highest risk of future outbreaks. The results of the analysis were evaluated and confirmed using the 161 reported human cases of the 2012 outbreak predicting correctly (Odds = 130/31 = 4,194 95%CI = 2,841–6,189) and more areas were identified for potential dispersion in the following years. Our approach verified that WNV risk can be modelled in a fast cost-effective way indicating high risk areas where prevention measures should be implemented in order to reduce the disease incidence.
- Full Text
- View/download PDF
22. An Investigation into Creep Cavity Development in 316H Stainless Steel
- Author
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Jazaeri, Hedieh, Bouchard, P. John, Hutchings, Michael T., Spindler, Mike W., Mamun, Abdullah A., Heenan, Richard K., Jazaeri, Hedieh, Bouchard, P. John, Hutchings, Michael T., Spindler, Mike W., Mamun, Abdullah A., and Heenan, Richard K.
- Abstract
Creep-induced cavitation is an important failure mechanism in steel components operating at high temperature. Robust techniques are required to observe and quantify creep cavitation. In this paper, the use of two complementary analysis techniques: small-angle neutron scattering (SANS), and quantitative metallography, using scanning electron microscopy (SEM), is reported. The development of creep cavities that is accumulated under uniaxial load has been studied as a function of creep strain and life fraction, by carrying out interrupted tests on two sets of creep test specimens that are prepared from a Type-316H austenitic stainless steel reactor component. In order to examine the effects of pre-strain on creep damage formation, one set of specimens was subjected to a plastic pre-strain of 8%, and the other set had no pre-strain. Each set of specimens was subjected to different loading and temperature conditions, representative of those of current and future power plant operation. Cavities of up to 300 nm in size are quantified by using SANS, and their size distribution, as a function of determined creep strain. Cavitation increases significantly as creep strain increases throughout creep life. These results are confirmed by quantitative metallography analysis.
23. Study of creep cavitation in a stainless steel weldment
- Author
-
Jazaeri, H., Bouchard, P. J., Hutchings, Michael, Lindner, P., Jazaeri, H., Bouchard, P. J., Hutchings, Michael, and Lindner, P.
- Abstract
A study of creep cavities near reheat cracking in AISI Type 316H austenitic stainless steel headers, removed from long-time high temperature operation in nuclear power plants, is reported. It is shown how application of scanning electron microscopy (SEM), cryogenic fractography and small angle neutron scattering (SANS) can be applied, in a complementary way, to observe and quantify creep cavitation damage. Creep cavities in the vicinity of the crack are found to be mainly surrounding inter-granular carbides. Trends in the size and area fraction of creep cavities relative to the crack path are quantified based on an optimised metallographic and image analysis procedure. Brittle fracture, with clear facets, of material remote from crack is achieved using a cryogenic procedure, and is compared with fractured facets of material within 8 mm of the crack which show evidence of large numbers of cavities. The SANS technique is found to be a very suitable method of quantifying creep cavitation averaged over a larger gauge volume. The distribution of cavities within the size range of 100 to 400 nm is quantified using SANS from positions normal to the crack line. It is shown that the cavity size distribution peaks at about 200 nm and this correlates closely with the quantitative SEM observations.
24. Study of cavities in a creep crack growth test specimen
- Author
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Jazaeri, H., Bouchard, P. J., Hutchings, Michael, Mamun, A. A., Heenan, R. K., Jazaeri, H., Bouchard, P. J., Hutchings, Michael, Mamun, A. A., and Heenan, R. K.
- Abstract
Small Angle Neutron Scattering (SANS) and Scanning Electron Microscopy (SEM) have been used to determine the degree of cavitation damage, of length scale 5-300 nm, associated with a creep crack grown in a compact tension specimen cut from a Type 316H stainless steel weldment. The specimen was supplied by EDF Energy as part of an extensive study of creep crack growth in the heat affected zone of reactor components. The creep crack propagates along a line 1.5 mm away from, and parallel to, the weld fusion line boundary before deviating away into parent material. The SANS results show a systematic increase in fractional size distribution of cavities approaching the crack, along lines normal to the crack line, and along lines parallel to the crack line approaching the crack mouth. Both SANS and quantitative metallography measurements using SEM indicate two populations of cavities: smaller cavities of less than 100 nm size having a mean diameter of about 60 nm, and a population of larger cavities of 100-300 nm size with a mean diameter of about 200 nm.
25. Neutron diffraction residual stress measurements on girth-welded 304 stainless steel pipes with weld metal deposited up to half and full pipe wall thickness
- Author
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Haigh, R.D., Hutchings, Michael, James, J. A., Ganguly, S., Mizuno, R., Ogawa, K., Okido, S., Paradowska, A.M., Fitzpatrick, M. E., Haigh, R.D., Hutchings, Michael, James, J. A., Ganguly, S., Mizuno, R., Ogawa, K., Okido, S., Paradowska, A.M., and Fitzpatrick, M. E.
- Abstract
The residual stress distribution has been measured in two girth-welded austenitic stainless steel pipe weldments using time-of-flight neutron diffraction. One had weld filler metal deposited up to half the pipe wall thickness, and one had weld metal deposited up to full pipe wall thickness. The aim of the work is to evaluate the evolution in residual stress profile on filling the weld, on which there is little experimental data, and where the selection of the correct hardening model used in finite element modelling can benefit greatly from an understanding of the intermediate residual stresses partway through the welding operation. The measured residual stresses are compared with those calculated by finite element modelling and measured using X-ray diffraction. The results show a change in the measured hoop stress at the weld toe from tension to compression between the half-and fully-filled weld. The finite element results show an overprediction of the residual stress, which may be a consequence of the simple isotropic hardening model applied. The results have implications for the likely occurrence of stress corrosion cracking in this important type of pipe-to-pipe weldment.
26. Multivariable Calculus
- Author
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Hutchings, Michael and Hutchings, Michael
- Abstract
This series of videos, created by Michael Hutching of the University of California, Berkeley, introduces parametric equations and polar coordinates. Vectors in 2- and 3-dimensional Euclidean spaces. Partial derivatives. Multiple integrals. Vector calculus. They also discuss theorems such as Green, Gauss, and Stokes.
27. An Investigation into Creep Cavity Development in 316H Stainless Steel
- Author
-
Jazaeri, Hedieh, Bouchard, P. John, Hutchings, Michael T., Spindler, Mike W., Mamun, Abdullah A., Heenan, Richard K., Jazaeri, Hedieh, Bouchard, P. John, Hutchings, Michael T., Spindler, Mike W., Mamun, Abdullah A., and Heenan, Richard K.
- Abstract
Creep-induced cavitation is an important failure mechanism in steel components operating at high temperature. Robust techniques are required to observe and quantify creep cavitation. In this paper, the use of two complementary analysis techniques: small-angle neutron scattering (SANS), and quantitative metallography, using scanning electron microscopy (SEM), is reported. The development of creep cavities that is accumulated under uniaxial load has been studied as a function of creep strain and life fraction, by carrying out interrupted tests on two sets of creep test specimens that are prepared from a Type-316H austenitic stainless steel reactor component. In order to examine the effects of pre-strain on creep damage formation, one set of specimens was subjected to a plastic pre-strain of 8%, and the other set had no pre-strain. Each set of specimens was subjected to different loading and temperature conditions, representative of those of current and future power plant operation. Cavities of up to 300 nm in size are quantified by using SANS, and their size distribution, as a function of determined creep strain. Cavitation increases significantly as creep strain increases throughout creep life. These results are confirmed by quantitative metallography analysis.
28. Study of cavities in a creep crack growth test specimen
- Author
-
Jazaeri, H., Bouchard, P. J., Hutchings, Michael, Mamun, A. A., Heenan, R. K., Jazaeri, H., Bouchard, P. J., Hutchings, Michael, Mamun, A. A., and Heenan, R. K.
- Abstract
Small Angle Neutron Scattering (SANS) and Scanning Electron Microscopy (SEM) have been used to determine the degree of cavitation damage, of length scale 5-300 nm, associated with a creep crack grown in a compact tension specimen cut from a Type 316H stainless steel weldment. The specimen was supplied by EDF Energy as part of an extensive study of creep crack growth in the heat affected zone of reactor components. The creep crack propagates along a line 1.5 mm away from, and parallel to, the weld fusion line boundary before deviating away into parent material. The SANS results show a systematic increase in fractional size distribution of cavities approaching the crack, along lines normal to the crack line, and along lines parallel to the crack line approaching the crack mouth. Both SANS and quantitative metallography measurements using SEM indicate two populations of cavities: smaller cavities of less than 100 nm size having a mean diameter of about 60 nm, and a population of larger cavities of 100-300 nm size with a mean diameter of about 200 nm.
29. Neutron diffraction residual stress measurements on girth-welded 304 stainless steel pipes with weld metal deposited up to half and full pipe wall thickness
- Author
-
Haigh, R.D., Hutchings, Michael, James, J. A., Ganguly, S., Mizuno, R., Ogawa, K., Okido, S., Paradowska, A.M., Fitzpatrick, M. E., Haigh, R.D., Hutchings, Michael, James, J. A., Ganguly, S., Mizuno, R., Ogawa, K., Okido, S., Paradowska, A.M., and Fitzpatrick, M. E.
- Abstract
The residual stress distribution has been measured in two girth-welded austenitic stainless steel pipe weldments using time-of-flight neutron diffraction. One had weld filler metal deposited up to half the pipe wall thickness, and one had weld metal deposited up to full pipe wall thickness. The aim of the work is to evaluate the evolution in residual stress profile on filling the weld, on which there is little experimental data, and where the selection of the correct hardening model used in finite element modelling can benefit greatly from an understanding of the intermediate residual stresses partway through the welding operation. The measured residual stresses are compared with those calculated by finite element modelling and measured using X-ray diffraction. The results show a change in the measured hoop stress at the weld toe from tension to compression between the half-and fully-filled weld. The finite element results show an overprediction of the residual stress, which may be a consequence of the simple isotropic hardening model applied. The results have implications for the likely occurrence of stress corrosion cracking in this important type of pipe-to-pipe weldment.
- Full Text
- View/download PDF
30. Study of creep cavitation in a stainless steel weldment
- Author
-
Jazaeri, H., Bouchard, P. J., Hutchings, Michael, Lindner, P., Jazaeri, H., Bouchard, P. J., Hutchings, Michael, and Lindner, P.
- Abstract
A study of creep cavities near reheat cracking in AISI Type 316H austenitic stainless steel headers, removed from long-time high temperature operation in nuclear power plants, is reported. It is shown how application of scanning electron microscopy (SEM), cryogenic fractography and small angle neutron scattering (SANS) can be applied, in a complementary way, to observe and quantify creep cavitation damage. Creep cavities in the vicinity of the crack are found to be mainly surrounding inter-granular carbides. Trends in the size and area fraction of creep cavities relative to the crack path are quantified based on an optimised metallographic and image analysis procedure. Brittle fracture, with clear facets, of material remote from crack is achieved using a cryogenic procedure, and is compared with fractured facets of material within 8 mm of the crack which show evidence of large numbers of cavities. The SANS technique is found to be a very suitable method of quantifying creep cavitation averaged over a larger gauge volume. The distribution of cavities within the size range of 100 to 400 nm is quantified using SANS from positions normal to the crack line. It is shown that the cavity size distribution peaks at about 200 nm and this correlates closely with the quantitative SEM observations.
31. Residual stress characterization of single and triple-pass autogenously welded stainless steel pipes
- Author
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Haigh, R.D., Hutchings, Michael, Fitzpatrick, M.E.., James, J.A., Okido, S., Mizuno, R., Ogawa, K., Hughes, D.J., Haigh, R.D., Hutchings, Michael, Fitzpatrick, M.E.., James, J.A., Okido, S., Mizuno, R., Ogawa, K., and Hughes, D.J.
- Abstract
Using neutron diffraction the components of the residual stress field have been determined in the region near a mid-length groove in two identical austenitic stainless pipes in which weld beads had been laid down. One pipe sample had a single pass, and the second a triple pass, autogenous weld deposited around the groove circumference. The results show the effect on the stress field of the additional weld deposited and are compared to the results of Finite Element Modelling. The hoop stress component is found to be generally tensile, and greater in the triple pass weldment than in the single pass weldment. The hoop stresses reach peak values of around 400 MPa in tension. X-ray measurements of the residual stress components on the near inner surface of the pipe weldments are also presented, and show tensile stresses in both pipes, with a higher magnitude in the three-pass weldment.
32. Stochastic systems approaches to disease control
- Author
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Knight, Martin, Marion, Glenn, White, Piran, Hutchings, Michael, and Davidson, Ross
- Abstract
Recent developments in network theory have provided new avenues for studying the spread of disease within populations. However, there is a need to develop dynamic generative models of networks that can capture the dynamic nature of many real-world systems that typical models cannot account for. Models of the spread of livestock disease have frequently employed traditional network approaches, but with the availability of highly detailed animal movement datasets, there is unprecedented scope to develop generative models of livestock trade parameterised by these data and exploring the spread of disease modulated by trade. Livestock diseases incur significant financial burdens on farms and governments, and the presence of disease remains a constant issue, so developing new insights and novel control strategies is vital. Analytically tractable generative models of livestock trade, parameterised to the Scottish cattle trading system, are developed, incorporating dynamics such as time-varying trading partnerships that, to date, have not been accounted for. Expressions for the basic reproduction number R0 are obtained and manipulations to trading behaviour are shown to reduce $R_0$ while maintaining farm business requirements. Extended models, accounting for time-varying trading behaviours, are developed. Individual-based adaptation in response to changes in trading propensities is shown to mitigate the prevalence reducing potential of such changes, highlighting the need to account for behavioural responses when modelling disease spread. Typical disease control measures, such as post-movement testing and risk aversion are shown to be effective in controlling disease, but can perturb the trading system. When parameterised to the Scottish cattle trade system, the impact of these control measures on prevalence is explored. The models presented here are a first attempt at analysing trade and its effect on disease spread at a national scale for a highly heterogeneous system using a generative network modelling approach, and can be extended to other real-world systems.
- Published
- 2021
33. Hindcasting trends of infection using crossectional test data
- Author
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Rydevik, Gustaf, White, Piran, Hutchings, Michael R., Marion, Glenn, Innocent, Giles T., and Davidson, Ross
- Subjects
333.7 - Abstract
Infectious diseases are a major threat to the wellbeing of humans, livestock, and wildlife. However, there is often a paucity of information for responding to these threats, and thus a need to make efficient use of existing data. This thesis shows how to use Bayesian analysis to maximise the information gained from already collected diagnostic test data. First, the commonly used latent class analysis of multiple binary diagnostic tests is ex- tended to account for vaccinated individuals, and used to estimate the effect of study size on sensitivity and specificity estimates of DIVA (”Distinguishing Infected and Vaccinated Animals”) tests for bovine Tuberculosis. It is then shown how quantitative test responses can be used as clocks indicating the time since infection to “hindcast” historic trends of disease incidence using cross-sectional data. This is used to determine whether an endemic disease is increasing or decreasing up to the time of sampling, enabling the tracking of trends in populations where routine surveillance data is not available. It is further demonstrated how to hindcast the rise and fall of disease outbreaks. Using the 2007 UK Bluetongue virus outbreak and a whooping cough outbreak as examples, it is shown that hindcasting can be used to determine whether an outbreak is increasing or past its peak at the time of sampling, thus informing potential outbreak responses. In the light of these methods for analysing quantitative test data, the challenges of generating data on test kinetics are discussed. Suggestions are given for how to improve on current methods by modelling the development of paired diagnostic tests as a dynamic host-pathogen system. This thesis demonstrates that multiple quantitative tests can be used to recover disease trends in a population. These methods have far-reaching consequences for the design and practice of disease surveillance in all contexts.
- Published
- 2015
34. Predicting impacts of climate change on livestock parasites
- Author
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Fox, Naomi J., White, Piran C. L., Hutchings, Michael R., and Marion, Glenn
- Subjects
636.089 - Abstract
The changing abundance and distribution of parasitic helminths has been identified as one of the greatest threats to animal health in the UK under climate change. This is due to the strong influence of abiotic conditions on parasites’ free-living stages. Planning adaptation and mitigation strategies requires predictions of parasite risk, and understanding of subtle interactions between abiotic conditions and parasite transmission. This requires development and application of a range of different modelling approaches. This thesis includes the first long-term forecast showing potential impacts of climate change on a parasitic helminth in the UK. By combining a correlative parasite risk model with UKCP09 climate projections, risk maps are generated identifying which areas of the UK are predicted to experience unprecedented levels of fasciolosis (liver fluke) risk in the future. Correlative models provide warnings of future risk, indicating where resources for monitoring and control should be targeted. To address more complex issues, and foresee consequences of subtle interactions between various components of a system under climate influence, a drive towards process-based mechanistic models is required. Consequently, a spatially explicit mechanistic model is developed, for the transmission of gastro-intestinal nematodes in a controlled grazing system. This allows investigation into how climate impacts on different elements of transmission. A non-linear relationship between climate change and parasite risk is revealed, with a distinct ‘tipping point’ in outbreaks when temperature driven processes exceed critical rates. This indicates that climate change could lead to sudden and dramatic changes in parasite risk. Through combining the models developed here with improved empirical data and a broader view of livestock systems, our understanding of future risks and opportunities can be increased. This will allow improved control of these physically and economically damaging parasites, reducing deleterious impacts on production efficiency and animal welfare.
- Published
- 2012
35. The perturbation effect in wildlife systems : an emergent property of simple models
- Author
-
Prentice, Jamie C., Marion, Glenn, Hutchings, Michael R., and White, Piran C. L.
- Subjects
591.7 - Abstract
Population reduction is often used as a control strategy when managing infectious diseases in wildlife populations, however it disrupts existing social structures and increases movement of infectives due to the vacuum effect, which may lead to enhanced disease transmission. Using a generic non-spatial model, key characteristics of disease systems are identified for which such effects reduce or even reverse the disease control benefits of population reduction. If population reduction is not sufficiently severe, then enhanced transmission can lead to the perturbation effect, whereby disease levels increase or disease can be stabilised where it would otherwise be unstable. Perturbation effects are enhanced for systems with low levels of disease, e.g. low levels of endemicity or emerging disease. Mechanisms observed in real systems are examined for their role in the perturbation effect. If population reduction is non-random and fails to target infected individuals, then vertical transmission (an important mechanism in many diseases including tuberculosis and paratuberculosis) can lead to the perturbation effect if horizontal transmission is low. The perturbation effect can also arise when population reduction preferentially targets resistant individuals, or mature individuals with low susceptibility, a factor implicated in wild boar and classical swine fever. In a stochastic spatial model of demography and disease dynamics with density dependent dispersal (implicated in the spread of rabies in foxes, and tuberculosis in badgers and wild boar due to the vacuum effect), enhanced transmission is found to arise implicitly as an emergent property of the disease-system, even when population reduction is entirely random. Culling strategies are examined, and the spatial heterogeneity of distribution of culling resources and timing of culling intervals are shown to influence the perturbation effect. Whilst the perturbation effect may not always be apparent, the various effects modelled are likely present in many disease systems, mitigating the results of population reduction.
- Published
- 2012
36. Neutron scattering studies of fluorite oxides at high temperatures
- Author
-
Macdonald, John Emyr and Hutchings, Michael T.
- Subjects
539.7 ,Neutrons ,Scattering ,Fluorspar ,High temperatures - Abstract
The high temperature behaviour of the fluorite oxides UO
2 , THO2 and Y2 O3 -stabilised ZrO2 have been investigated using a variety of neutron scattering techniques. Interest has centred on the cause of the anomalously large enthalpy of UO2 at temperatures above 15OOK, an understanding of which is important in view of its use as a fission reactor fuel. High temperature techniques have been developed which enable the performance of neutron scattering at temperatures up to 3OOOK. Bragg diffraction measurements have shown that a growing fraction of anions vacate their regular sites above 21OOK in UO2 and above 23OOK in ThO2 attaining vacancy concentrations of ~2O% at 29OOK in both materials. Quasielastic scattering investigations have confirmed the occurrence of anion Frenkel disorder in UO2 at high temperatures and have shown that the disorder is of a dynamic nature. Both sets of results may be interpreted in terms of fluctuating, dynamic clusters of vacancies and inter stitials, having lifetimes of a few phonon periods. The elastic constants of UO2 , which have been determined up to 293OK from measurements of the long wavelength acoustic phonons, show an increased rate of softening above 24OOK. The zone-centre optic phonons broaden rapidly above 2OOOK in UO2 - The full phonon dispersion relation of ThO2 , measured at 293K, resembles closely that of UO2 . The results provide the first direct, unambiguous evidence of thermally-induced Frenkel disorder in UO2 , which is analogous to the disorder observed in the fast-ion phase of the fluorite halides, such as CaF2 . Quasielastic scattering techniques have also been used to study the defect structure of Y2 O3 -stabilised ZrO2 between 293K and 2OOOK. Many general features of the scattering observed at room temperature may be explained in terms of nearest neighbour relaxations around oxygen vacancies. The diffuse scattering broadens in energy above 1OOOK, signifying that these clusters of relaxed ions have a finite lifetime of ~5ps at 15OOK. The results have been interpreted in terms of a vacancy hopping model which is consistent with the enhanced conductivity observed in this temperature range.- Published
- 1985
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