A study of semiconductor-based atomic oxygen sensors for ground and satellite applications

Available from British Library Document Supply Centre-DSC:DXN032263 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Refocusing sustainability education: using students’ reflections on their carbon footprint to reinforce the importance of considering CO2 production in the construction industry

The construction industry is the most significant contributor to the UK’s CO2 emissions. It is responsible for an annual output of approximately 45% of the total. This figure highlights the role the industry must play in helping to achieve the UK Government’s CO2 reduction target. It is ergo incumbent on construction-related educators to emphasise this issue and explore ways in which it can be achieved. Unintentional desensitisation has resulted in the term ‘sustainability’, particularly CO2 production, being seen by students as just another concept to be studied from a theoretical perspective. Many students fail to grasp its broader implications and how it should affect strategic environmental decisions about construction processes, technologies, and products. In an attempt to address this problem, an innovative learning, teaching, and assessment strategy was used with final year undergraduate construction students to improve their level of sustainability literacy. The theory of threshold concepts in the context of transformative learning was used as the baseline philosophy to the study. The approach involved asking students to calculate their carbon footprint and to reflect upon and extrapolate their findings to the construction industry and its practice. Content analysis was performed on the reflective commentaries acquired from student portfolios collected over four academic years. The results showed how the students’ reflections on their carbon footprints proved to be an enlightening experience. Terms such as ‘shocked by my footprint’, ‘surprised at the findings’, and ‘change in attitude’ were among the contemplative comments. When students linked their findings to the construction industry, phrases such as ‘waste generation’, ‘technologies’, and ‘materials’ were some of the concepts considered. By using their personal experiences as a benchmark, students were able to gain a deeper level of understanding of the causes and consequences of CO2 production. They also found it more straightforward to relate these issues to the construction industry and its practice. Several novel recommendations are made to raise the level of sustainability literacy in the construction industry thereby facilitating a potential reduction in worldwide CO2 production

Preconditioning Kernel Matrices

The computational and storage complexity of kernel machines presents the primary barrier to their scaling to large, modern, datasets. A common way to tackle the scalability issue is to use the conjugate gradient algorithm, which relieves the constraints on both storage (the kernel matrix need not be stored) and computation (both stochastic gradients and parallelization can be used). Even so, conjugate gradient is not without its own issues: the conditioning of kernel matrices is often such that conjugate gradients will have poor convergence in practice. Preconditioning is a common approach to alleviating this issue. Here we propose preconditioned conjugate gradients for kernel machines, and develop a broad range of preconditioners particularly useful for kernel matrices. We describe a scalable approach to both solving kernel machines and learning their hyperparameters. We show this approach is exact in the limit of iterations and outperforms state-of-the-art approximations for a given computational budget

Investigating the infinite spider's web in complex dynamics

This thesis contains a number of new results on the topological and geometric properties of certain invariant sets in the dynamics of entire functions, inspired by recent work of Rippon and Stallard. First, we explore the intricate structure of the spider's web fast escaping sets associated with certain transcendental entire functions. Our results are expressed in terms of the components of the complement of the set (the 'holes' in the web). We describe the topology of such components and give a characterisation of their possible orbits under iteration. We show that there are uncountably many components having each of a number of orbit types, and we prove that components with bounded orbits are quasiconformally homeomorphic to components of the filled Julia set of a polynomial. We prove that there are singleton periodic components and that these are dense in the Julia set. Next, we investigate the connectedness properties of the set of points K( f) where the iterates of an entire function f are bounded. We describe a class of transcendental entire functions for which K( f) is to- tally disconnected if and only if each component of K (f) containing a critical point is aperiodic. Moreover we show that, for such functions, if K(f) is disconnected then it has uncountably many components. We give examples of functions for which K(f) is totally disconnected, and we use quasiconformal surgery to construct a function for which K(f) has a component with empty interior that is not a singleton. Finally we show that, if the Julia set of a transcendental entire function is locally connected, then it must take the form of a spider's web. In the opposite direction, we prove that a spider's web Julia set is always locally connected at a dense subset of buried points. We also show that the set of buried points (the residual Julia set) can be a spider's web