972 research outputs found
Radio-frequency reflectometry on an undoped AlGaAs/GaAs single electron transistor
Radio frequency reflectometry is demonstrated in a sub-micron undoped
AlGaAs/GaAs device. Undoped single electron transistors (SETs) are attractive
candidates to study single electron phenomena due to their charge stability and
robust electronic properties after thermal cycling. However these devices
require a large top-gate which is unsuitable for the fast and sensitive radio
frequency reflectometry technique. Here we demonstrate rf reflectometry is
possible in an undoped SET.Comment: Four pages, three figures, one supplementary fil
From coinductive proofs to exact real arithmetic: theory and applications
Based on a new coinductive characterization of continuous functions we
extract certified programs for exact real number computation from constructive
proofs. The extracted programs construct and combine exact real number
algorithms with respect to the binary signed digit representation of real
numbers. The data type corresponding to the coinductive definition of
continuous functions consists of finitely branching non-wellfounded trees
describing when the algorithm writes and reads digits. We discuss several
examples including the extraction of programs for polynomials up to degree two
and the definite integral of continuous maps
Self-gravitating fluid shells and their non-spherical oscillations in Newtonian theory
We summarize the general formalism describing surface flows in
three-dimensional space in a form which is suitable for various astrophysical
applications. We then apply the formalism to the analysis of non-radial
perturbations of self-gravitating spherical fluid shells.
Spherically symmetric gravitating shells (or bubbles) have been used in
numerous model problems especially in general relativity and cosmology. A
radially oscillating shell was recently suggested as a model for a variable
cosmic object. Within Newtonian gravity we show that self-gravitating static
fluid shells are unstable with respect to linear non-radial perturbations. Only
shells (bubbles) with a negative mass (or with a charge the repulsion of which
is compensated by a tension) are stable.Comment: 20 pages, to be published in the Astrophysical Journal, typos
correcte
On the principal bifurcation branch of a third order nonlinear long-wave equation
We study the principal bifurcation curve of a third order equation which
describes the nonlinear evolution of several systems with a long--wavelength
instability. We show that the main bifurcation branch can be derived from a
variational principle. This allows to obtain a close estimate of the complete
branch. In particular, when the bifurcation is subcritical, the large amplitude
stable branch can be found in a simple manner.Comment: 11 pages, 3 figure
Discrete exterior calculus (DEC) for the surface Navier-Stokes equation
We consider a numerical approach for the incompressible surface Navier-Stokes
equation. The approach is based on the covariant form and uses discrete
exterior calculus (DEC) in space and a semi-implicit discretization in time.
The discretization is described in detail and related to finite difference
schemes on staggered grids in flat space for which we demonstrate second order
convergence. We compare computational results with a vorticity-stream function
approach for surfaces with genus 0 and demonstrate the interplay between
topology, geometry and flow properties. Our discretization also allows to
handle harmonic vector fields, which we demonstrate on a torus.Comment: 21 pages, 9 figure
Self-Assembled Triply Periodic Minimal Surfaces as moulds for Photonic Band Gap Materials
We propose systems with structures defined by self-assembled triply periodic
minimal surfaces (STPMS) as candidates for photonic bandgap materials. To
support our proposal we have calculated the photonic bands for different STPMS
and we have found that, at least, the double diamond and gyroid structures
present full photonic bandgaps. Given the great variety of systems which
crystalize in these structures, the diversity of possible materials that form
them and the range of lattice constants they present, the construction of
photonic bandgap materials with gaps in the visible range may be presently
within reach.Comment: 3 pages, 2 figures, RevTe
Planform selection in two-layer Benard-Marangoni convection
Benard-Marangoni convection in a system of two superimposed liquids is
investigated theoretically. Extending previous studies the complete
hydrodynamics of both layers is treated and buoyancy is consistently taken into
account. The planform selection problem between rolls, squares and hexagons is
investigated by explicitly calculating the coefficients of an appropriate
amplitude equation from the parameters of the fluids. The results are compared
with recent experiments on two-layer systems in which squares at onset have
been reported.Comment: 17 pages, 7 figures, oscillatory instability included, typos
corrected, references adde
Can programme theory be used as a 'translational toolâ to optimise health service delivery in a national early yearsâ initiative in Scotland: a case study
Background
Theory-based evaluation (TBE) approaches are heralded as supporting formative evaluation by facilitating increased use of evaluative findings to guide programme improvement. It is essential that learning from programme implementation is better used to improve delivery and to inform other initiatives, if interventions are to be as effective as they have the potential to be. Nonetheless, few studies describe formative feedback methods, or report direct instrumental use of findings resulting from TBE. This paper uses the case of Scotlandâs, National Health Service, early yearsâ, oral health improvement initiative (Childsmile) to describe the use of TBE as a framework for providing feedback on delivery to programme staff and to assess its impact on programmatic action.<p></p>
Methods
In-depth, semi-structured interviews and focus groups with key stakeholders explored perceived deviations between the Childsmile programme 'as deliveredâ and its Programme Theory (PT). The data was thematically analysed using constant comparative methods. Findings were shared with key programme stakeholders and discussions around likely impact and necessary actions were facilitated by the authors. Documentary review and ongoing observations of programme meetings were undertaken to assess the extent to which learning was acted upon.<p></p>
Results
On the whole, the activities documented in Childsmileâs PT were implemented as intended. This paper purposefully focuses on those activities where variation in delivery was evident. Differences resulted from the stage of roll-out reached and the flexibility given to individual NHS boards to tailor local implementation. Some adaptations were thought to have diverged from the central features of Childsmileâs PT, to the extent that there was a risk to achieving outcomes. The methods employed prompted national service improvement action, and proposals for local action by individual NHS boards to address this.<p></p>
Conclusions
The TBE approach provided a platform, to direct attention to areas of risk within a national health initiative, and to agree which intervention components were 'coreâ to its hypothesised success. The study demonstrates that PT can be used as a 'translational toolâ to facilitate instrumental use of evaluative findings to optimise implementation within a complex health improvement programme.<p></p>
The purpose of mess in action research: building rigour though a messy turn
Mess and rigour might appear to be strange bedfellows. This paper argues that the purpose of mess is to facilitate a turn towards new constructions of knowing that lead to transformation in practice (an action turn). Engaging in action research - research that can disturb both individual and communally held notions of knowledge for practice - will be messy. Investigations into the 'messy area', the interface between the known and the nearly known, between knowledge in use and tacit knowledge as yet to be useful, reveal the 'messy area' as a vital element for seeing, disrupting, analysing, learning, knowing and changing. It is the place where long-held views shaped by professional knowledge, practical judgement, experience and intuition are seen through other lenses. It is here that reframing takes place and new knowing, which has both theoretical and practical significance, arises: a 'messy turn' takes place
Formative evaluation of electricity distribution utilities using data envelopment analysis
The use of Data Envelopment Analysis (DEA) in the electricity distribution sector has been prolific in the number of papers published in research journals. However, while numerous studies have been documented, they have mostly been summative. Their aim has been predominantly descriptive and
classificatory. This paper argues that evaluations of a formative nature are more effective than summative studies in promoting a better understanding of the structures and processes of electricity
distribution utilities and, consequently, are more appropriate to contribute to performance improvement.
To illustrate the use of DEA for formative evaluation, and highlight some of the difficulties of using DEA in practice, this paper compares the cost-efficiency of the Portuguese electricity distribution companies from 2002 to 2006. A dynamic analysis using Malmquist Indices is also conducted in order to evaluate the changes in productivity over this period. Our analysis shows that the application of DEA
for formative purposes meets some difficulties. In particular it shows that while the modelling of productivity/efficiency scores using DEA is relatively straightforward, it is comparatively more difficult to develop models that are economically valid and that produce results with face validity. On the basis of the insights derived from this analysis, the paper provides some recommendations regarding the successful application of DEA for performance improvement
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