Wave-number-explicit bounds in time-harmonic scattering

In this paper we consider the problem of scattering of time-harmonic acoustic waves by a bounded sound soft obstacle in two and three dimensions, studying dependence on the wave number in two classical formulations of this problem. The first is the standard variational/weak formulation in the part of the exterior domain contained in a large sphere, with an exact Dirichletto-Neumann map applied on the boundary. The second formulation is as a second kind boundary integral equation in which the solution is sought as a combined single- and double-layer potential. For the variational formulation we obtain, in the case when the obstacle is starlike, explicit upper and lower bounds which show that the inf-sup constant decreases like k −1 as the wave number k increases. We also give an example where the obstacle is not starlike and the inf-sup constant decreases at least as fast as k −2. For the boundary integral equation formulation, if the boundary is also Lipschitz and piecewise smooth, we show that the norm of the inverse boundary integral operator is bounded independently of k if the coupling parameter is chosen correctly. The methods we use also lead to explicit bounds on the solution of the scattering problem in the energy norm when the obstacle is starlike in which the dependence of the norm of the solution on the wave number and on the geometry are made explicit

Review of pulsed power for efficient hydrogen production

Pulsed power applied to electrolysis offers a potential method for efficient hydrogen production which has not been comprehensively studied to date. Pulsed and plasma electrolysis are introduced and previous research assessed. Electrolysis use in potential space or aerospace applications is substantially weight and volume sensitive. Pulsed plasma electrolysis is able to far exceed the Faradaic limit on electrolysis at very high surface current densities presenting the opportunity to reduce electrode mass and volume. Pulse generation technology is introduced and challenges inherent in application to electrolysis outlined

Development of an optimized converter layer for silicon carbide based neutron sensor for the detection of fissionable materials

Here, we describe the early stage design, construction and testing of a miniature silicon carbide diode neutron sensing instrument. It is intended that a more mature version of this instrument will be used as part of a robotic manipulator to investigate various parts of the stricken Fukushima nuclear power plant. Here, three such silicon carbide based proto-type sensors have been created, two of which have differing thicknesses of boron-10 deposited on, with the final one left bare. The thicknesses and materials chosen have been informed via Monte Carlo software (MCNP 6.2) which was also used to assess the suitability of two other potential converter materials – Lithium-6 and gadolinium-157. The work goes on to describe the design, construction and testing of the prototype device at two sites around the UK. The project is part of a UK/Japanese collaboration between Lancaster University and Kyoto University and is supported by an EPSRC grant via the UK Japan Civil nuclear research program

When the guns stopped roaring: Acholi ngec ma gwoko lobo

This article calls attention to the responsibility of universities to transform, through partnership, the community in which they are embedded. The authors suggest that, to find solutions to the various community challenges and achieve the UN Sustainable Development Goals (SDGs), universities need to engage in partnerships of knowledge co-creation with the community in ways that value local knowledge and experience. The article elaborates on the efforts of Gulu University Centre for Community Based Participatory Research and Lifelong Learning, located in Northern Uganda, to show the potential of co-constructing knowledge for community transformation. The centre is part of the Knowledge for Change (K4C) global consortium, which is a growing network for community-based research. The authors share three research stories of community-based research that reflect distinct challenges faced in Northern Uganda and effective community-engaged solutions. Through an exploration of the Acholi ontology and epistemology of interconnection, the authors demonstrate that local communities have the knowledge and experience to define and address local problems

Development of an Optimized Converter Layer for a Silicon-Carbide-Based Neutron Sensor for the Detection of Fissionable Materials

We describe the early stage development of a miniature silicon carbide neutron sensor, for applications including robotic monitoring at the Fukushima Daiichi nuclear power plant, specifically, within the primary containment vessel for fuel debris detection and retrieval. Monte Carlo simulations using MCNP 6.2 and Geant4 10.05.01 are used to investigate and optimize converter layers for thermal neutron detection. Performance of a 10B4C:SiC detector system is investigated in detail and a neutron detection efficiency ∼4% is predicted, with a gamma discrimination ratio of the order of 105

The PML for rough surface scattering

In this paper we investigate the use of the perfectly matched layer (PML) to truncate a time harmonic rough surface scattering problem in the direction away from the scatterer. We prove existence and uniqueness of the solution of the truncated problem as well as an error estimate depending on the thickness and composition of the layer. This global error estimate predicts a linear rate of convergence (under some conditions on the relative size of the real and imaginary parts of the PML function) rather than the usual exponential rate. We then consider scattering by a half-space and show that the solution of the PML truncated problem converges globally at most quadratically (up to logarithmic factors), providing support for our general theory. However we also prove exponential convergence on compact subsets. We continue by proposing an iterative correction method for the PML truncated problem and, using our estimate for the PML approximation, prove convergence of this method. Finally we provide some numerical results in 2D.(C) 2008 IMACS. Published by Elsevier B.V. All rights reserved

How are normal sleeping controls selected? A systematic review of cross-sectional insomnia studies, and a standardised method to select healthy controls for sleep research

There appears to be some inconsistency in how normal sleepers (controls) are selected and screened for participation in research studies for comparison with insomnia patients. The purpose of the current study is to assess and compare methods of identifying normal sleepers in insomnia studies, with reference to published standards. We systematically reviewed the literature on insomnia patients which included control subjects. The resulting 37 articles were systematically reviewed with reference to the five criteria for normal sleep specified by Edinger et al. (2004). In summary, these criteria are: evidence of sleep disruption; sleep scheduling; general health; substance/medication use; and other sleep disorders. We found sleep diaries, PSG, and clinical screening examinations to be widely used with both control subjects and insomnia participants. However, there are differences between research groups in the precise definitions applied to the components of normal sleep. We found that none of reviewed studies applied all of the Edinger et al. criteria, and 16% met four criteria. In general, screening is applied most rigorously at the level of a clinical disorder, whether physical, psychiatric, or sleep. While the Edinger et al. criteria seem to be applied in some form by most researchers, there is scope to improve standards and definitions in this area. Ideally, different methods such as sleep diaries and questionnaires would be used concurrently with objective measures to ensure normal sleepers are identified, and descriptive information for control subjects would be reported. Here, we have devised working criteria and methods to be used for assessment of normal sleepers. This would help clarify the nature of the control group, in contrast to insomnia subjects and other patient groups

Thermal neutron absorption in printed circuit boards

Measurements and simulations of thermal neutron attenuation by printed circuit boards are compared. Attenuation coefficients in typical epoxy-resin/glass-fibre substrate material can be as high as 2 cm-1, corresponding to 27% attenuation by 1.6 mm of substrate. Attenuation is attributed to neutron scattering off hydrogen in the resin acting in synergy with absorption by boron in the glass; this effect is substantially greater than that estimated from absorption by boron alone. Design of thermal neutron detector assemblies should take this attenuation into account and may require board thickness to be minimised or specialised substrate materials to be used

I will leave you now and this loudspeaker will take my place

Notions of ‘presence’ and ‘liveness’ run through academic theories and popular conceptions of sound mediation generally, and mediation of voice in particular. This article looks at experimental video that engages with these questions, particularly around the notion of the ‘authentic’ voice and vocal ‘presence’. We will demonstrate how these different experimental approaches explore the interaction between voice, vocal technique and audio-visual technology, thus challenging and interrogating conventions of how the soundtrack represents the voice and (in conjunction with the moving image) the audio-visually mediated body. Presenting Anneke Kampman's work as an experimental practice-led research response to seminal theories of sound and the film soundtrack, we provide further context through engagement with key examples of earlier video art and sound art by Vladan Radovanović, Richard Serra, and Meredith Monk. Overall, the article intervenes by demonstrating how video art and sound art can address key theoretical questions concerning voice and body in a broader sound and moving image context, as well as adopting a sound-focussed approach to aesthetic analysis of video art