742 research outputs found
Geometrical frustration in the spin liquid beta'-Me3EtSb[Pd(dmit)2]2 and the valence bond solid Me3EtP[Pd(dmit)2]2
We show that the electronic structures of the title compounds predicted by
density functional theory (DFT) are well described by tight binding models. We
determine the frustration ratio, J'/J, of the Heisenberg model on the
anisotropic triangular lattice, which describes the spin degrees of freedom in
the Mott insulating phase for a range of Pd(dmit)2 salts. All of the
antiferromagnetic materials studied have J'/J 0.9, consistent
with predictions for the Heisenberg model. All salts with 0.5 < J'/J < 0.9,
where many-body theories find a number of competing ground states, are known,
experimentally, to be charge ordered, valence bond solids or spin liquids.Comment: Accepted for publication in Phys. Rev. Lett. 4+11 pages, 3+15
figures, major rewrite, added calculations of Hubbard
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
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
Rock scour in Australia: some latest Queensland experiences
From 2010, a succession of floods in eastern Australia, and particularly in Queensland, brought about spillway operation at high head dams with return periods in the region of Annual Exceedance Probabilities (AEP) of up to 1 in 2,000 years. As such, a number of spillways experienced extensive scour of rock downstream â including Boondooma Dam and Paradise Dam â the subject of the present paper. For both dams, part of the scour assessment process has been to utilise a large-scale physical model to obtain transient data which, together with the detailed geologic assessment, have been incorporated into the numerical scour modelling procedures developed by Dr Erik Bollaert. This paper will first of all describe the features of the 2011 and 2013 flood events at both dams, as well as the resulting rock scour and damage on both spillways and the geology of the rock area below. The paper will then go on to describe the computational scour modelling procedures of calibration and application, used in conjunction with a large-scale physical model of both dam and spillway, demonstrating a âsystemâ approach to spillway scour analysis for plunge pools and similar situations with energy dissipation on natural materials
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
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
Radiative decay branching ratio of the Hoyle state
The triple-alpha process is a vital reaction in nuclear astrophysics,
characterized by two consecutive reactions
() that drive
carbon formation. The second reaction occurs through the Hoyle state, a 7.65
MeV excited state in with .The rate of the
process depends on the radiative width, which can be determined by measuring
the branching ratio for electromagnetic decay. Recent measurements by Kib\'edi,
\textit{et al.} conflicted with the adopted value and resulted in a significant
increase of nearly 50\% in this branching ratio, directly affecting the
triple-alpha reaction. This work aims to utilize charged-particle spectroscopy
with magnetic selection as a means to accurately measure the total radiative
branching ratio () of the Hoyle state in . The Hoyle state in was populated via inelastic scattering. The scattered -particles
were detected using a E-E telescope, while the recoiled
ions were identified in a magnetic spectrometer. A radiative branching ratio
value of was obtained. The radiative branching ratio for
the Hoyle state obtained in this work is in agreement with the original adopted
value. Our result suggests that the proton-- spectroscopy
result reported by Kib\'edi \textit{et al.} may be excluded
Multi-Orbital Molecular Compound (TTM-TTP)I_3: Effective Model and Fragment Decomposition
The electronic structure of the molecular compound (TTM-TTP)I_3, which
exhibits a peculiar intra-molecular charge ordering, has been studied using
multi-configuration ab initio calculations. First we derive an effective
Hubbard-type model based on the molecular orbitals (MOs) of TTM-TTP; we set up
a two-orbital Hamiltonian for the two MOs near the Fermi energy and determine
its full parameters: the transfer integrals, the Coulomb and exchange
interactions. The tight-binding band structure obtained from these transfer
integrals is consistent with the result of the direct band calculation based on
density functional theory. Then, by decomposing the frontier MOs into two
parts, i.e., fragments, we find that the stacked TTM-TTP molecules can be
described by a two-leg ladder model, while the inter-fragment Coulomb energies
are scaled to the inverse of their distances. This result indicates that the
fragment picture that we proposed earlier [M.-L. Bonnet et al.: J. Chem. Phys.
132 (2010) 214705] successfully describes the low-energy properties of this
compound.Comment: 5 pages, 4 figures, published versio
'It's the other assessment that is the key': three Norwegian physical education teachers' engagement (or not) with assessment for learning
peer-reviewedThe international agenda for assessment continues to convey a growing interest in assessment for learning (AfL) as a tool to support learning and enhance teaching. Complementing this, the recent literature on assessment in physical education acknowledges the need for physical educators to integrate AfL into their teaching and assessment practice as an important part of the future development of the subject. Appreciating that physical education must be recognized as part of the larger movement culture in society and is a place to learn about movement culture, this study explores how AfL is understood and enacted by physical education teachers and the extent to which such enactment complements or challenges learning movement cultures within physical education. This study shares how three Norwegian physical education teachers used AfL to term what they were practicing with respect to assessment in physical education. We follow the interactions of the selected teachers throughout focus groups, using the empirical data as our 'dialogue partner' in reconstructing and discussing their assessment stories. We conclude that the need of embedding AfL in learning theory may well be one of the strongest challenges to enacting AfL in physical education. We acknowledge that not only are most existing theories of learning defined cognitively, but also that learning connected to physical education and activity is, to a large extent, practical and embodied, and also linked to the powerful discourses of sport and related areas such as health.PUBLISHEDpeer-reviewe
Evaluating the achievements and impacts of EC framework programme transport projects
Purpose The purpose of this paper is to present what kind of elements and evaluation methods should be included into a framework for evaluating the achievements and impacts of transport projects supported in EC Framework Programmes (FP). Further, the paper discusses the possibilities of such an evaluation framework in producing recommendations regarding future transport research and policy objectives as well as mutual learning for the basis of strategic long term planning. Methods The paper describes the two-dimensional evaluation methodology developed in the course of the FP7 METRONOME project. The dimensions are: (1) achievement of project objectives and targets in different levels and (2) research project impacts according to four impact groups. The methodology uses four complementary approaches in evaluation, namely evaluation matrices, coordinator questionnaires, lead user interviews and workshops. Results Based on the methodology testing, with a sample of FP5 and FP6 projects, the main results relating to the rationale, implementation and achievements of FP projects is presented. In general, achievement of objectives in both FPs was good. Strongest impacts were identified within the impact group of management and co-ordination. Also scientific and end-user impacts of the projects were adequate, but wider societal impacts quite modest. The paper concludes with a discussion both on the theoretical and practical implications of the proposed methodology and by presenting some relevant future research needs
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