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 ‘science for all’ does not necessarily mean ‘one size fits all’ (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

Towards the parameterisation of the Hubbard model for salts of BEDT-TTF: A density functional study of isolated molecules

We calculate the effective Coulomb repulsion between electrons/holes, U, and site energy for an isolated BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene] molecule in vacuo. U=4.2 \pm 0.1 eV for 44 experimental geometries taken from a broad range of conformations, polymorphs, anions, temperatures, and pressures (the quoted `error' is one standard deviation). Hence we conclude that U is essentially the same for all of the compounds studied. This shows that the strong (hydrostatic and chemical) pressure dependence observed in the phase diagrams of the BEDT-TTF salts is not due to U. Therefore, if the Hubbard model is sufficient to describe the phase diagram of the BEDT-TTF salts there must be significant pressure dependence on the intramolecular terms in the Hamiltonian and/or the reduction of the Hubbard U due to the interaction of the molecule with the polarisable crystal environment. The renormalised value of U is significantly smaller than the bare value of the Coulomb integral: F_0=5.2\pm0.1 eV across the same set of geometries, emphasising the importance of using the renormalised value of U. The site energy (for holes), xi=5.0\pm0.2 eV, varies only a little more than U across the same set of geometries. However, we argue that this plays a key role in understanding the role of disorder in ET salts in general and in explaining the difference between the beta_L and beta_H phases of beta-(BEDT-TTF)_2I_3 in particular.Comment: 13 pages, 6 figures, also see animations at http://www.youtube.com/watch?v=3K2kP8hWpZI, http://www.youtube.com/watch?v=wIz1cRsSdEs and http://www.youtube.com/watch?v=bNzUBAS6AFM, Expanded discussion of renormalisation effects. To appear in J. Chem. Phy

The Logic of Evaluation

A sketch of the arguments for adding the logic of evaluation to the areas of argumentation that have been partly mapped and are worth further work by workers in rhetoric, argumentation, communication, critical thinking, and informal logic. Brief coverage of: (i) the arguments that there cannot be any legitimate logic of evaluation; of (ii) the nature of evaluation (conceptions and misconceptions); and of (iii) the technical apparatus of evaluation logic

The Jim Crow craze in London's press and streets, 1836–39

In 1836, American actor Thomas D. Rice first arrived in Great Britain to tour the creation that had made him famous in the USA, Jim Crow. This blackface depiction of a raggedy, runaway slave, with his infectious songs, eccentric dancing and demotic appeal soon took London by storm. The Jim Crow craze lasted for three years, with Rice finding fame, fortune and success and his imitators becoming ubiquitous in the capital's theatres and on its streets. Although the act and its character have been acknowledged as a precursor to the evolution of British minstrelsy and blackface traditions throughout the Victorian period, the craze itself has not been substantially studied in its British context. This essay will look beyond Rice's act and the performance of Jim Crow in the theatres to look instead at Jim Crow's appropriation in print satire and street performance. It will argue that these requisitions of Jim Crow illustrate how Georgian traditions of carnival and grotesque humour were redeveloped for the early Victorian context. In print, Jim Crow was widely utilized in caustic bodily humour that attacked insincere politicians. On the streets, this same humour was seen as obscene and was repressed and contained, paving the way for the respectable, mainstream Victorian blackface act. However, integral to both appropriations of Jim Crow was the figure of the black buffoon, and the act rapidly provided an archetype for the belittling and persecution of London's black population