Rapidly rotating plane layer convection with zonal flow

The onset of convection in a rapidly rotating layer in which a thermal wind is present is studied. Diffusive effects are included. The main motivation is from convection in planetary interiors, where thermal winds are expected due to temperature variations on the core-mantle boundary. The system admits both convective instability and baroclinic instability. We find a smooth transition between the two types of modes, and investigate where the transition region between the two types of instability occurs in parameter space. The thermal wind helps to destabilise the convective modes. Baroclinic instability can occur when the applied vertical temperature gradient is stable, and the critical Rayleigh number is then negative. Long wavelength modes are the first to become unstable. Asymptotic analysis is possible for the transition region and also for long wavelength instabilities, and the results agree well with our numerical solutions. We also investigate how the instabilities in this system relate to the classical baroclinic instability in the Eady problem. We conclude by noting that baroclinic instabilities in the Earth's core arising from heterogeneity in the lower mantle could possibly drive a dynamo even if the Earth's core were stably stratified and so not convecting.Comment: 20 pages, 7 figure

Correlation Induced Insulator to Metal Transitions

We study a spinless two-band model at half-filling in the limit of infinite dimensions. The ground state of this model in the non-interacting limit is a band-insulator. We identify transitions to a metal and to a charge-Mott insulator, using a combination of analytical, Quantum Monte Carlo, and zero temperature recursion methods. The metallic phase is a non-Fermi liquid state with algebraic local correlation functions with universal exponents over a range of parameters.Comment: 12 pages, REVTE

Band Narrowing and Mott Localization in Iron Oxychalcogenides La2O2Fe2O(Se,S)2

Bad metal properties have motivated a description of the parent iron pnictides as correlated metals on the verge of Mott localization. What has been unclear is whether interactions can push these and related compounds to the Mott insulating side of the phase diagram. Here we consider the iron oxychalcogenides La2O2Fe2O(Se,S)2, which contain an Fe square lattice with an expanded unit cell. We show theoretically that they contain enhanced correlation effects through band narrowing compared to LaOFeAs, and we provide experimental evidence that they are Mott insulators with moderate charge gaps. We also discuss the magnetic properties in terms of a Heisenberg model with frustrating J1-J2-J2' exchange interactions on a "doubled" checkerboard lattice.Comment: 4 pages, 5 eps figures. Version to appear in Phys. Rev. Let

Kosterlitz-Thouless Transition and Short Range Spatial Correlations in an Extended Hubbard Model

We study the competition between intersite and local correlations in a spinless two-band extended Hubbard model by taking an alternative limit of infinite dimensions. We find that the intersite density fluctuations suppress the charge Kondo energy scale and lead to a Fermi liquid to non-Fermi liquid transition for repulsive on-site density-density interactions. In the absence of intersite interactions, this transition reduces to the known Kosterlitz-Thouless transition. We show that a new line of non-Fermi liquid fixed points replace those of the zero intersite interaction problem.Comment: 11 pages, 2 figure

Brînzeni: A Multidisciplinary Study of an Upper Palaeolithic site in Moldova

Brînzeni cave occupies an important place in the Palaeolithic of Moldova. Its significance is reconsidered in the light of work carried out at the site in 1992–1993 and subsequently, and the opportunity is taken to bring together both published and previously unpublished reports about it, to shed light on its environmental history and archaeological characterisation. On current evidence, the principal occupation layer occupies a chronologically intermediate position between the Aurignacian and the Gravettian in the region, and the archaeological assemblage is certainly distinctive, although probably not ‘transitional’ in the sense previously claimed.McDonald Institute for Archaeological Research, Cambridg

Developments in Correlated Fermions

This manuscript is based on the Summary and Overview talk given at the "The International Conference of Strongly Correlated Electronic Systems" (SCES '04), July 26-30, at Karlsruhe, Germany. After highlighting some of the principal new experimental developments in heavy fermions presented at the conference, I turn to two kinds of theoretical questions. (1) What is understood of the fermi-liquid state of the heavy fermions and what is not, but may reasonably well be understood by systematic calculations. (2) The profound issues raised by the observed correlations near the quantum critical points in the heavy fermions. The numbers and letters in the parenthesis in the text refer to the listing of the talks in the "Program and Abstracts" book of the conference

Chain Entanglement in Thin Freestanding Polymer Films

When a thin glassy film is strained uniaxially, a shear deformation zone (SDZ) can be observed. The ratio of the thickness of the SDZ to that of the undeformed film is related to the maximum extension ratio, which depends on the entanglement molecular weight, Me. We have measured _ as a function of film thickness in strained freestanding films of polystyrene as a probe of Me in confinement. It is found that thin films stretch further than thick films before failure, consistent with the interpretation that polymers in thin films are less entangled than bulk polymers, thus the effective value of Me in thin films is significantly larger than that of the bulk. Our results are well described by a conceptually simple model based on the probability of finding intermolecular entanglements near an interface

Spatial Correlations in Dynamical Mean Field Theory

We further develop an extended dynamical mean field approach introduced earlier. It goes beyond the standard $D=\infty$ dynamical mean field theory by incorporating quantum fluctuations associated with intersite (RKKY-like) interactions. This is achieved by scaling the intersite interactions to the same power in 1/D as that for the kinetic terms. In this approach, a correlated lattice problem is reduced to a single-impurity Anderson model with additional self-consistent bosonic baths. Here, we formulate the approach in terms of perturbation expansions. We show that the two-particle vertex functions are momentum-dependent, while the single-particle self-energy remains local. In spite of this, the approach is conserving. Finally, we also determine the form of a momentum-dependent dynamical susceptibility; the resulting expression relates it to the corresponding Weiss field, local correlation function and (momentum-dependent) intersite coupling.Comment: 28 pages, REVTEX, 8 figures include

Modelling the coefficient of thermal expansion in Ni-based superalloys and bond coatings

The coefficient of thermal expansion (CTE) of nickel-based superalloys and bond coat layers was modelled by considering contributions from their constituent phases. The equilibrium phase composition of the examined materials was determined using thermodynamic equilibrium software with an appropriate database for Ni-based alloys, whereas the CTE and elastic properties of the principal phases were modelled using published data. The CTEs of individual phases were combined using a number of approaches to determine the CTE of the phase aggregate. As part of this work, the expansion coefficients of the superalloy IN-738LC and bond coat Amdry-995 were measured as a function of temperature and compared with the model predictions. The predicted values were also validated with the published data for the single-crystal superalloy CMSX-4 and a number of other Ni-based alloy compositions at 1000 K. A very good agreement between experiment and model output was found, especially up to 800  $$^\circ$$ � C. The modelling approaches discussed in this paper have the potential to be an extremely useful tool for the industry and for the designers of new coating systems

Electrocardiographic Left Ventricular Hypertrophy Among Gambian Diabetes Mellitus Patients

Background: The global prevalence of diabetes and its complications is increasing worldwide. Its role in coronary heart disease has been linked with the presence of left ventricular hypertrophy (LVH). The present study aims to determine the prevalence of electrocardiographic left ventricular hypertrophy (ECG-LVH) in adult diabetic subjects, its epidemiological and clinical correlates.Methods: A descriptive cross-sectional study involving 534 patients was conducted at the Edward Francis Small Teaching Hospital (formerly Royal Victoria Teaching Hospital), The Gambia. Four hundred and forty patients were included using a standard questionnaire. Anthropometry, laboratory investigations and electrocardiogram were carried out. We used the Lewis, Cornell, and Sokolow-Lyon Voltage criteria to define ECG-LVH. MinitabTM statistical software version 13.20 was used for analysis.Results: 146 (35.2%) patients had ECG-LVH using all 3 criteria and this prevalence was higher among women being 116 (79.5%). A generally high prevalence of overweight (155/37.4%) and obesity (119/28.6%) was observed among study participants, and both clinic-day systolic and diastolic blood pressure (BP) were significantly higher in those with ECG-LVH. Poor diabetes control was observed in both groups.Conclusion: There was a high prevalence of ECGLVH and it is especially so with combining multiple criteria, hence the need for screening. Clinic-day hypertension was associated with ECG-LVH hence the need for diagnosing and aggressive treatment of hypertension in patients with diabetes mellitus.Keywords: Diabetes mellitus, ECG-LVH, The Gambia, voltage criteri