| 2012-02-10 | Fri | Giuseppe Colantuono (Sheffield) | SP2RC Friday Seminars |
| 13:05 | Lecture Theatre 9 | A simple model to evaluate photovoltaics with energy storage: initial results and ideas | |
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Abstract: Energy storage can be a means of smoothing out the unpredictability of "green" energy sources and increase the availability of power at times of peak demand. Efforts for integrating photovoltaics (PV) with batteries are already going on, even if they still suffer from high costs. A possible metric to evaluate the impact of storage coupled to a PV array is "Loss Of Load Hours" (LOLH). LOLH represents the total amount of time, for a given period (e.g one month), during which the demand (e.g. the power usage of the home where the PV array is installed) cannot be satisfied and electricity must be drawn from the grid. An analogous measure is the total time during which the battery is fully charged, energy cannot be stored any longer and is therefore uploaded to the grid. A simple model for the computation of LOLH will be presented . The inputs of the model are given by the timeseries of the solar irradiance incident on the PV array and the timeseries of the power load. Some preliminary results and possible developments for both real-world and idealized loads will be discussed. |
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| 2012-02-09 | Thu | Vanessa Didelez (University of Bristol) | Probability and Statistics Seminar |
| 14:00 | LT-6 | Mendelian Randomisation as an Instrumental Variable Approach to Causal Inference | |
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Abstract: In epidemiology we often want to estimate the causal effect of an exposure on a health outcome based on observational data, where the possibility of unobserved confounding cannot be excluded. To deal with this problem, it has recently become popular to use a technique called Mendelian randomisation, where it is exploited that the exposure is associated with a genetic variant, which can be assumed to be unaffected by the same confounding factors and which makes it suitable as a so-called instrumental variable. In my talk, this technique is illustrated with various examples, in particular with the effect of alcohol consumption on blood pressure / hypertension. Different methods of using an instrumental variable to estimate the causal effect on a binary outcome are compared based on their theoretical properties as well as by simulation. Finally, it will be discussed if a Bayesian approach is useful in the context of Mendelian randomisation. References:Didelez and Sheehan (2007). Mendelian randomisation as an instrumental variable approach to causal inference, Statistical Methods in Medical Research, 16, 309-330. Didelez, Meng and Sheehan (2010). Assumptions of IV methods for observational epidemiology, Statistical Science, 25, 22-40. Palmer, Sterne, Harbord, Lawlor, Sheehan, Meng, Granell, Davey Smith, Didelez (2011). Instrumental variable estimation of causal risk ratios and causal odds ratios in Mendelian randomization analyses, The American Journal of Epidemiology, 173 (12). Jones, Thompson, Didelez and Sheehan (2012). On the choice of parameterisation and priors for the Bayesian analyses of Mendelian randomisation studies. To appear in Statistics in Medicine. |
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| 2012-02-09 | Thu | David Barnes (Sheffield) | Topology seminar |
| 15:00 | Hicks Room J11 | Stable Model Categories | |
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Abstract: A model category is a way of giving a category a notion of homotopy. Hence in a model category we can talk of maps being homotopic or objects being homotopy equivalent. The two basic examples of model categories are topological spaces and chain complexes. Hence model categories are of interest to both topologists and algebraists. One condition that a model category may satisfy is that of stability. This is where there is a shift functor or suspension functor which is an equivalence on the homotopy category. Chain complexes are such an example, however the category of topological is not a stable model category. In this talk I will define the notion of stability more carefully, and try to describe how one may alter a category to make it stable. In particular, we will see that spectra are the stabilisation of spaces. |
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| 2012-02-08 | Wed | Paul Linden (Cambridge) | Applied Maths Colloquium |
| 14:20 | LT6 | Gravity-driven flows in stratified fluids | |
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Abstract: This talk will describe experiments on flows driven by horizontal density gradients in fluids which are stably stratified. Examples are intrusions on density interfaces or in stratified ambient fluids, and cases where the intruding fluid is also stably stratified. Traditional approaches that have been applied to unstratified fluids have been to use ideas of energy conversion from available potential energy to kinetic energy to predict the speeds of the gravity-driven flows, which in this simple case are gravity currents. I will explore how well these approaches work in systems which can support internal waves and discuss the resulting dynamics. |
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| 2012-02-08 | Wed | Tom Bridgeland (Oxford) | Pure Maths Colloquium |
| 16:00 | J11 | Hall algebras and quantum groups | |
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Abstract: Quantized enveloping algebras are Hopf algebras that are q-deformations of universal enveloping algebras. Despite being defined by a bunch of peculiar looking relations, they have found applications in many parts of maths and physics. Twenty years ago Ringel showed how to give a conceptual description of the positive half of a quantized enveloping algebra using Hall algebras of quiver representations. I'll attempt to explain why introducing Z2 graded complexes into the picture leads to a similar description of the whole thing. |
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| 2012-02-02 | Thu | Mohammad Al-Boshmki (Sheffield) | Pure Maths Postgraduate Seminar |
| 13:00 | Hicks Room J11 | Classifying spaces | |
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Abstract: Classifying spaces have played a central role in homotopy theory over the last fifty years. The classifying space of a group G is a path-connected space with fundamental group G and no other non-trivial homotopy groups. In this talk we will give a construction of classifying spaces for any topological group G, showing that classifying spaces always exist and are unique up to homotopy. We will illustrate this with examples such as Z, Z_2 and S^1. |
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| 2012-02-02 | Thu | James Cranch (Sheffield ) | |
| 15:00 | G22 Regent Court | Dependently Typed Programming and Proof in Agda | |
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Abstract: James will show some more realistic examples of datatypes (including ordered list maps) and some portions of his work with categories. |
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| 2012-01-19 | Thu | Simon Foster (Sheffield Computer Science) | |
| 15:00 | G22 Regent Court | Dependently Typed Programming and Proof in Agda | |
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Abstract: Agda is a dependently typed programming language in the style of the functional programming language Haskell. What sets it apart from Haskell is its inclusion of dependent types which allow much finer grained constraints on data and functionality to be specified. Furthermore Agda doubles as a powerful ITP, in which properties about implemented programs can be proved. In this tutorial I will introduce the Agda interface and demonstrate the key features of the language. I will create some datatypes, functions and show how to build some proofs about them, some of which will be (semi-)automated. |
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School of Mathematics and Statistics (SoMaS)
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