1,120 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
The Cosmos Project: a journey to the stars
There seems to be some agreement that âscience for allâ does not necessarily mean âone size fits allâ (Lynch, 2001). Teaching scientific disciplines in schools has been traditionally concerned with delivering science as a product with a main focus on its conceptual structure. In our research we propose to concentrate on science as a process, putting it in the societal context. We introduce the Cosmos project that aims to explore the use of narrative and performative languages, as well as new media technologies in relation to delivering complex scientific topics to pre-school children aged three to six. We created a theatrical piece and developed a set of new interactive preschool activities that enabled young learners to participate and contribute to their learning through physical engagement enhanced by modern technologies. This paper presents a critical discussion about the recent tendencies in teaching science to young learners; the rationale for the Cosmos project and its main research objectives. It will conclude with evaluation of the pre- and postperformance educational activities
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
Looking for more: the social phenomenology of play in World of Warcraft
More and more, contemporary electronic games are transcending the player-versus-machine model, incorporating to varying degrees new types of social play, where individuals can interact with each other in a state of &lsquo;telecopresence&rsquo; in immersive, three-dimensional virtual worlds. Yet we are faced with the puzzle of adequately understanding the meanings of these experiences of play in the absence of the physical body. Given that in many cases players only interact with each other indirectly through their virtual player characters, how can we interpret the meanings of play within contemporary virtual game worlds? Using the popular game World of Warcraft as a case study, this thesis attempts to answer this question via an ethnography primarily informed by a revised conception of the phenomenological sociology of Schutz (1899-1959), and drawing upon other notable technology writers such as Heidegger, Ihde, and Dreyfus, to explore the nature of mediated social action in the virtual fantasy game world of World of Warcraft. Using auto-ethnographic evidence, the thesis examines some of the experiential aspects of play-as-practice, player knowledge and expertise, and social relations, contending that play in World of Warcraft can be typically understood as a substantial commitment by the player that is multifaceted and heavily contingent upon the game&rsquo;s design in regards to the richness of social exchange in the game world
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
Is Social Psychology Really Different?
Gergen (1976), outlines a number of problems that make it difficult to apply general social psychological the ories, or to assess their validity unequivocally. These dif ficulties are not unique to social psychology, however. The application of general scientific principles has never been a simple matter, not even in the well-established physical sci ences. Moreover, there are formidable difficulties in asses sing general theoretical propositions in every field of in quiry, since empirical procedures will inevitably depend on assumptions about local field conditions, the adequacy of meas urement techniques, and the like. As a consequence, if re sults are inconsistent with theoretical expectations, there will always be some uncertainty as to where the problem lies. Social psychologists should not assume that their difficulties are totally unlike those encountered in other fields of sci entific inquiry. The problems raised by Gergen do not, con sequently, rule out the possible development and application of general social psychological theories.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69124/2/10.1177_014616727600200417.pd
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
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
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
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