1,383 research outputs found
Does the bonding rule break down in AsSe glass?
The local coordination numbers of AsSe glass were determined by a
combination of anomalous x-ray scattering experiments, reverse Monte Carlo
calculations, and {\it ab initio} molecular dynamics simulations. The
well-known `8- bonding rule' proposed by Mott breaks down around the As
atoms, exceeding the rule by 7--26%. An experimental prediction based on
mean-field theory agrees with the present experimental and theoretical results.
The fourfold coordinated As atoms likely form As-As wrong bond chains rather
than ethan-like configurations, which is identified as the origin for the
breakdown of the `8- bonding rule'.Comment: 6 pages, 6figures, 1table, submitted to Europhysics Letter
Evaluation of an innovative programme for training teachers of children with learning and behavioural difficulties in New Zealand
Thurston equivalence of topological polynomials
We answer Hubbard's question on determining the Thurston equivalence class of
``twisted rabbits'', i.e. images of the ``rabbit'' polynomial under n-th powers
of the Dehn twists about its ears.
The answer is expressed in terms of the 4-adic expansion of n. We also answer
the equivalent question for the other two families of degree-2 topological
polynomials with three post-critical points.
In the process, we rephrase the questions in group-theoretical language, in
terms of wreath recursions.Comment: 40 pages, lots of figure
Transformer Oil Passivation and Impact of Corrosive Sulphur
In recent years a significant volume of research has been undertaken in order to understand the recent failures in oil insulated power apparatus due to deposition of copper sulphide on the conductors and in the insulation paper. Dibenzyl Disulfide (DBDS) has been found to be the leading corrosive sulphur compound in the insulation oil [1]. The process of copper sulphide formation and the deposition in the paper is still being investigated, but a recently proposed method seems to be gaining some confidence [1]. This method suggests a two-step process; initially the DBDS and some oil soluble copper complexes are formed. Secondly the copper complexes are absorbed in the paper insulation, where they then decompose into copper sulphide [2]. The most commonly used mitigating technique for corrosive sulphur contaminated oil is passivation, normally using Irgamet 39 or 1, 2, 3-benzotriazole (BTA). The passivator is diluted into the oil to a concentration of around 100ppm, where it then reacts with the copper conductors to form a complex layer around the copper, preventing it from interacting with DBDS compounds and forming copper sulphide. This research project will investigate the electrical properties of HV transformers which have tested positive for corrosive sulphur, and the evolution of those properties as the asset degrades due to sulphur corrosion. Parallel to this the long term properties of transformers with passivated insulation oil will be analysed in order to understand the passivator stability and whether it is necessary to keep adding the passivator to sustain its performance. Condition monitoring techniques under investigation will include dielectric spectroscopy, frequency response analysis, recovery voltage method (aka interfacial polarisation) amongst others. Partial discharge techniques will not be investigated, as the voltage between the coil plates is low and therefore it will not contribute significantly to the overall insulation breakdown, in corrosive oil related faults [3]. The goal of this research is to establish key electrical properties in both passivated and non-passivated power transformers that demonstrate detectable changes as the equipment degrades due to the insulation oil being corrosive
Thurston's pullback map on the augmented Teichm\"uller space and applications
Let be a postcritically finite branched self-cover of a 2-dimensional
topological sphere. Such a map induces an analytic self-map of a
finite-dimensional Teichm\"uller space. We prove that this map extends
continuously to the augmented Teichm\"uller space and give an explicit
construction for this extension. This allows us to characterize the dynamics of
Thurston's pullback map near invariant strata of the boundary of the augmented
Teichm\"uller space. The resulting classification of invariant boundary strata
is used to prove a conjecture by Pilgrim and to infer further properties of
Thurston's pullback map. Our approach also yields new proofs of Thurston's
theorem and Pilgrim's Canonical Obstruction theorem.Comment: revised version, 28 page
Structural and dynamical properties of liquid Si. An orbital-free molecular dynamics study
Several static and dynamic properties of liquid silicon near melting have
been determined from an orbital free {\em ab-initio} molecular dynamics
simulation. The calculated static structure is in good agreement with the
available X-ray and neutron diffraction data. The dynamical structure shows
collective density excitations with an associated dispersion relation which
closely follows recent experimental data. It is found that liquid silicon can
not sustain the propagation of shear waves which can be related to the power
spectrum of the velocity autocorrelation function. Accurate estimates have also
been obtained for several transport coefficients. The overall picture is that
the dynamic properties have many characteristics of the simple liquid metals
although some conspicuous differences have been found.Comment: 12 pages, 11 figure
Angiographic complexity of coronary artery disease according to SYNTAX score and clinical outcomes after revascularisation with newer-generation drug-eluting stents: a substudy of the BIOSCIENCE trial
The impact of smart grid technology on dielectrics and electrical insulation
Delivery of the Smart Grid is a topic of considerable interest within the power industry in general, and the IEEE specifically. This paper presents the smart grid landscape as seen by the IEEE Dielectrics and Electrical Insulation Society (DEIS) Technical Committee on Smart Grids. We define the various facets of smart grid technology, and present an examination of the impacts on dielectrics within power assets. Based on the trajectory of current research in the field, we identify the implications for asset owners and operators at both the device level and the systems level. The paper concludes by identifying areas of dielectrics and insulation research required to fully realize the smart grid concept. The work of the DEIS is fundamental to achieving the goals of a more active, self-managing grid
Probing the Sensitivity of Electron Wave Interference to Disorder-Induced Scattering in Solid-State Devices
The study of electron motion in semiconductor billiards has elucidated our
understanding of quantum interference and quantum chaos. The central assumption
is that ionized donors generate only minor perturbations to the electron
trajectories, which are determined by scattering from billiard walls. We use
magnetoconductance fluctuations as a probe of the quantum interference and show
that these fluctuations change radically when the scattering landscape is
modified by thermally-induced charge displacement between donor sites. Our
results challenge the accepted understanding of quantum interference effects in
nanostructures.Comment: 8 pages, 5 figures, Submitted to Physical Review
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