An unrealistic image of science

Many UK secondary schools (ages 11-18) host Open Days for pupils in their final year of primary school education (age 10). At these events science teachers try, through the judicious use of a select number of practical tasks, to portray science as being a fun, exciting and essentially a „hands on‟ activity. Whilst this approach generates short-term situational interest amongst pupils it is ultimately an unrealistic, and arguably unsustainable, image of science

Strong Correlations and Magnetic Frustration in the High Tc Iron Pnictides

We consider the iron pnictides in terms of a proximity to a Mott insulator. The superexchange interactions contain competing nearest-neighbor and next-nearest-neighbor components. In the undoped parent compound, these frustrated interactions lead to a two-sublattice collinear antiferromagnet (each sublattice forming a Neel ordering), with a reduced magnitude for the ordered moment. Electron or hole doping, together with the frustration effect, suppresses the magnetic ordering and allows a superconducting state. The exchange interactions favor a d-wave superconducting order parameter; in the notation appropriate for the Fe square lattice, its orbital symmetry is $d_{xy}$. A number of existing and future experiments are discussed in light of the theoretical considerations.Comment: (v2) 4+ pages, 4 figures, discussions on several points expanded; references added. To appear in Phys. Rev. Let

Toward an anisotropic atom-atom model for the crystalline phases of the molecular S8 compound

We analize two anisotropic atom-atom models used to describe the crystalline alpha,beta and gamma phases of S8 crystals, the most stable compound of elemental sulfur in solid phases, at ambient pressure and T<=400 K. The calculations are performed via a series of classical molecular dynamics (MD) simulations, with flexible molecular models and using a constant pressure-constant temperature algorithm for the numerical simulations. All intramolecular modes that mix with lattice modes, and are therefore relevant on the onset of structural phase transitions, are taken into account. Comparisons with experimental data and previous results obtained with an isotropic atom-atom molecular model are also performed.Comment: Major changes, new simulations and figures added, revtex4, to appear in J. Chem. Phy

Ground state of a partially melted Wigner molecule

We consider three spinless fermions free to move on 2d square lattice with periodic boundary conditions and interacting via a U/r Coulomb repulsion. When the Coulomb energy to kinetic energy ratio r_s is large, a rigid Wigner molecule is formed. As r_s decreases, we show that melting proceeds via an intermediate regime where a floppy two particle molecule coexists with a partially delocalized particle. A simple ansatz is given to describe the ground state of this mesoscopic solid-liquid regime.Comment: to appear in Europhysics Letter

Two-dimensional Anderson-Hubbard model in DMFT+Sigma approximation

Density of states, dynamic (optical) conductivity and phase diagram of paramagnetic two-dimensional Anderson-Hubbard model with strong correlations and disorder are analyzed within the generalized dynamical mean-field theory (DMFT+Sigma approximation). Strong correlations are accounted by DMFT, while disorder is taken into account via the appropriate generalization of the self-consistent theory of localization. We consider the two-dimensional system with the rectangular "bare" density of states (DOS). The DMFT effective single impurity problem is solved by numerical renormalization group (NRG). Phases of "correlated metal", Mott insulator and correlated Anderson insulator are identified from the evolution of density of states, optical conductivity and localization length, demonstrating both Mott-Hubbard and Anderson metal-insulator transitions in two-dimensional systems of the finite size, allowing us to construct the complete zero-temperature phase diagram of paramagnetic Anderson-Hubbard model. Localization length in our approximation is practically independent of the strength of Hubbard correlations. However, the divergence of localization length in finite size two-dimensional system at small disorder signifies the existence of an effective Anderson transition.Comment: 10 pages, 10 figures, improve phase diagra

Exploring effort–reward imbalance and professional quality of life among health workers in Cape Town, South Africa: a mixed-methods study

Background In the context of a growing appreciation for the wellbeing of the health workforce as the foundation of high-quality, sustainable health systems, this paper presents findings from two complementary studies to explore occupational stress and professional quality of life among health workers that were conducted in preparation for a task-shifting intervention to improve antenatal mental health services in Cape Town. Methods This mixed-methods, cross-sectional study was conducted in public sector Midwife Obstetric Units and associated Non-Profit Organisations in Cape Town. Semi-structured interviews and a quantitative survey were conducted among facility-and community-based professional and lay health workers. The survey included demographic as well as effort–reward imbalance (ERI) and professional quality of life (PROQOL) questionnaires to examine overall levels of work-related psychosocial stress and professional quality of life, as well as differences between lay and professional health workers. Qualitative data was analysed using a thematic content analysis approach. Quantitative data was analysed using STATA 12. Results Findings from 37 qualitative interviews highlighted the difficult working conditions and often limited reward and support structures experienced by health workers. Corroborating these findings, our quantitative survey of 165 professional and lay health workers revealed that most health workers experienced a mismatch between efforts spent and rewards gained at work (61.1% of professional and 70.2% of lay health workers; p = 0.302). There were few statistically significant differences in ERI and PROQOL scores between professional and lay health workers. Although Compassion Satisfaction was high for all health worker groups, lay health workers also showed elevated levels of burnout and compassion fatigue, with community-based health workers particularly affected. Conclusions Findings of this study add to the existing evidence base on adverse working conditions faced by South African public-sector health workers that should be taken into consideration as national and local governments seek to ‘re-engineer’ South Africa’s Primary Health Care system. Furthermore, they also highlight the importance of taking into consideration the wellbeing of health workers themselves to develop interventions that can sustainably foster resilient and high-quality health systems

Measurement of the Probability Distribution of Total Transmission in Random Waveguides

Measurements have been made of the probability distribution of total transmission of microwave radiation in waveguides filled with randomly positioned scatterers which would have values of the dimensionless conductance g near unity. The distributions are markedly non-Gaussian and have exponential tails. The measured distributions are accurately described by diagrammatic and random matrix calculations carried out for nonabsorbing samples in the limit g >> 1 when g is expressed in terms of the variance of the distribution, which equals the degree of long-range intensity correlation across the output face of the sample.Comment: 5 pages, 5 post script figures, RevTe

Hall effect in the marginal Fermi liquid regime of high-Tc superconductors

The detailed derivation of a theory for transport in quasi-two-dimensional metals, with small-angle elastic scattering and angle-independent inelastic scattering is presented. The transport equation is solved for a model Fermi surface representing a typical cuprate superconductor. Using the small-angle elastic and the inelastic scattering rates deduced from angle-resolved photoemission experiments, good quantitative agreement with the observed anomalous temperature dependence of the Hall angle in optimally doped cuprates is obtained, while the resistivity remains linear in temperature. The theory is also extended to the frequency-dependent complex Hall angle