69,807 research outputs found
The Modelling of Primary Alkaline Battery Cathodes: A Simplified Model for porous manganese oxide particle discharge
No full textA simplified model, to that produced previously by the authors, for the galvanostatic discharge of primary alkaline battery cathodes is presented. Laplace transform and perturbation methods are employed to obtain the leading order spatial and temporal behaviour of the porous cathode over two distinct size scales. It is shown that for a wide range of industrially relevant discharge conditions the time taken for KOH electrolyte to diffuse into a porous electrolytic manganese dioxide particle is fast compared with the cathodic discharge time and that ohmic losses within the graphite phase of the cathode can be considered to be negligible. Numerical solution of the simplified model equations is discussed and the results are validated against relevant experimental data
A recovery-based error estimator for anisotropic mesh adaptation in CFD
No full textWe provide a unifying framework that generalizes the 2D and 3D
settings proposed in [32] and [17], respectively. In these two works
we propose a gradient recovery type a posteriori error estimator for
finite element approximations on anisotropic meshes. The novelty is the
inclusion of the geometrical features of the computational mesh (size,
shape and orientation) in the estimator itself. Moreover, we preserve the
good properties of recovery based error estimators, in particular their
computational cheapness and ease of implementation. A metric-based
optimization procedure, relying on the estimator, drives the anisotropic
adaptation of the mesh. The focus of this work then moves to a goaloriented
framework. In particular, we extend the idea proposed in [32, 17]
to the control of a goal functional. The preliminary results are promising,
since it is shown numerically to yield quasi-optimal triangulations with
respect to the error-vs-number of elements behaviour
Pulse-pumping of cascaded Raman fibre amplifiers
No full textIn this thesis, I investigate cascaded Raman fibre amplifiers (RFAs) pumped with shaped optical pulses delivered from a Yb doped fibre MOPA source. RFAs offer the potential to generate gain at any arbitrary wavelength with an appropriate pump source, limited only by the fibre’s transparency range. The use of a counter-propagating signal and pump creates a continuous gain, despite the instantaneous nature of stimulated Raman scattering (SRS). A high power Yb doped fibre source emitting around the 1050 to 1100 nm region offers a flexible pump source that can in principle be used to generate gain for any signal from ~1100 to 2000 nm in a silica-based fibre via cascaded SRS. This opens up opportunities for an ultrabroadband amplifier with unmatched spectral width. Furthermore, by using a pump source that is in a MOPA configuration there is a high degree of control over the output characteristics which offers the potential of near-instantaneous electronic control of ultra-broadband Raman gain spectra. In the simplest configuration, cascaded Raman wavelength shifting across a wide range of wavelengths using single-level pump pulses (i.e., approximate super-Gaussian pulses) is investigated. Using a silica-based highly nonlinear fibre (HNLF), cascaded Raman wavelength shifting up to seven Stokes orders is demonstrated and counter-propagating gain measurements are made across all seven Stokes orders. From a pump wavelength of 1064 nm, the peak gain of the 7th Stokes order was ~1575 nm which demonstrated the potential for gain covering more than 500 nm. I believe this is the first time such a measurement has been undertaken. Other fibre types were also studied for comparison. Furthermore, the noise performance and gain saturation properties of cascaded RFAs were investigated, as well. In a more advanced configuration, the Raman gain spectra produced from pumping the HNLF with step-shaped pump pulses are investigated. Such pulses consist of multiple levels with different, controllable, instantaneous powers. By adjusting the power of each step appropriately I show that different parts of the pulse transfer their energy to different Stokes orders, leading to a controllable gain spectrum covering multiple Stokes orders at the same time. I further study how the gain spectrum can be controlled by manipulating the individual duty cycle of each section of the step-shaped pump pulses as well as using multiple pump wavelengths in a time-division multiplexed pumping scheme. Single and dual wavelength pumping of various fibres with step-shaped pulses was experimentally demonstrated. Raman gain spectra spanning two and three Stokes orders and covering over 100 nm were realised. Computer simulations are also carried out for pumping with more than two pump wavelengths and for gain spectra targeting gain simultaneously up to seven Stokes orders and covering up to ~500 nm. This shows that the use of step-shaped pulses and multiple pump wavelengths allow for further increase and control of the useable bandwidth
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
It's not me, it's you: Examining the print media's approach to 'Europe' in Brexit Britain
No full textDespite declining sales, the UK print media remains a powerful actor in British political debate. In recent times, nowhere has this seemed more evident than in the run-up to the UK referendum on European Union membership, during which a predominantly Eurosceptic press lent its backing to an ultimately victorious Leave campaign. Through qualitative analysis of reports by two pro-Remain and two Leave-supporting newspapers, during pre- and post-referendum periods, this chapter scrutinises not only the extent of the print media’s influence over the broader discourse about ‘Europe’, but also what this signifies for meaningful democratic debate on emotive but highly complex issues such as Brexit. Crucially, the research establishes three pertinent findings. First, though the Leave press was extremely vocal during the referendum campaign, its influence stems from a far longer-term shaping of the UK’s EU-related debates. Second, the significant role played by newspapers in setting the parameters of wider dialogue about the EU raises critical questions as to whether sufficient checks and balances are operating across the democratic landscape to ensure a diversity of discussion. Third, while one might have expected the Leave vote to create the elbow room for all quarters of the British press to examine the Brexit process with rigour, the Eurosceptic press has instead chosen further to entrench the ‘us versus them’ narrative that has always dominated its coverage of Europe. This arguably has repercussions beyond Brexit, including the issue of whether stepping back from Europe also means distancing the UK from the separate European Convention on Human Rights
Lois Andison : Autobody
No full textFarrell comments on the interface of biology and technology in Andison’s kinetic sculptures, which caution against reliance on technology and offer a humorous critique of society’s desire to engineer perfection based on myths of an invulnerable, immortal body. She finds that the artist destabilises patriarchal ideology by enumerating inculcated behaviours which masquerade as “natural” gender attributes and by illustrating the pressures on women to conform to beauty ideals. Biographical notes. Bibl. 2 p. 10 bibl. ref. List of works
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A Raman fibre amplifier generating simultaneous gain across multiple Stokes orders by using step shaped optical pulses
No full textOptical amplification based on stimulated Raman scattering (SRS) in optical fibres offers the potential to generate gain at any arbitrary wavelength with an appropriate pump source. This has proved a very effective and successful way of providing gain at those wavelengths not directly available with rare-earth doped fibres. However most of this success has been achieved using CW pump sources, but in recent years there has been renewed interest in the pulsed pumping of Raman amplifiers
Modelling of primary alkaline battery cathodes: a simplified model
No full textA simplified model, to that produced previously by the authors, for the galvanostatic discharge of primary alkaline battery cathodes is presented. Laplace transform and perturbation methods are employed to obtain the leading order spatial and temporal behaviour of the porous cathode over two distinct size scales. It is shown that for a wide range of industrially relevant discharge conditions the time taken for KOH electrolyte to diffuse into a porous electrolytic manganese dioxide particle is fast compared with the cathodic discharge time and that ohmic losses within the graphite phase of the cathode can be considered to be negligible. Numerical solution of the simplified model equations is discussed and the results are validated against relevant experimental dat
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