Vortex Lines or Vortex-Line Chains at the Lower Critical Field in Anisotropic Superconductors?

The vortex state at the lower critical field, H_{c1}, in clean anisotropic superconductors placed in an external field tilted with respect to the axis of anisotropy (c-axis) is considered assuming two possible arrangements: dilute vortex-lines or dilute vortex-line chains. By minimizing the Gibbs free energies in the London limit for each possibility we obtain the corresponding lower critical fields as a function of the tilt angle. The equilibrium configuration at H_{c1} for a given tilt angle is identified with that for which H_{c1} is the smallest. We report results for parameter values typical of strong and moderate anisotropy. We find that for strong anisotropy vortex-line chains are favored for small tilt angles (< 7.9^o) and that at 7.9^o there is coexistence between this configuration and a vortex-line one. For moderate anisotropy we find that there is little difference between the vortex-line and the vortex-chain lower critical fields.Comment: 5 pages, 4 figures, accepted to appear on Physica

SAFT-γ force field for the simulation of molecular fluids: 8. hetero-group coarse-grained models of perfluoroalkylalkanes assessed with new vapour-liquid interfacial tension data

The air-liquid interfacial behaviour of linear perfluoroalkylalkanes (PFAAs) is reported through a combined experimental and computer simulation study. The surface tensions of seven liquid PFAAs (perfluorobutylethane, F4H2; perfluorobutylpentane, F4H5; perfluorobutylhexane, F4H6, perfluorobutyloctane, F4H8; perfluorohexylethane, F6H2; perfluorohexylhexane, F6H6; and perfluorohexyloctane, F6H8) are experimentally determined over a wide temperature range (276 to 350 K). The corresponding surface thermodynamic properties and the critical temperatures of the studied compounds are estimated from the temperature dependence of the surface tension. Experimental density and vapour pressure data are employed to parameterize a generic heteronuclear coarse-grained intermolecular potential of the SAFT- γ family for PFAAs. The resulting force field is used in direct molecular dynamics simulations to predict with quantitative agreement the experimental tensions and to explore the conformations of the molecules in the interfacial region revealing a preferential alignment of the PFAA molecules towards the interface and an enrichment of the perfluoro-groups at the outer interface region

Supporting the Voice of People with Disabilities in Kenya, Uganda and Jordan

Research methods need to be adapted to the cultural context and traditions with which participants are familiar. Limited work has been attempted to explore ways to engage people with disabilities in low resource settings. In this paper we present methods used in two research projects that engage and actively support the voice of people with disabilities living in low resource settings. We discuss which methods have worked well and which not, with recommendations based on our experience and the research results

Individuality over function: the role of technology in disability identity

When designing or investigating technology use among people with disabilities, researchers often overstate the importance of functional aspects at the expenses of identity. We present three case studies that showcase how people with disabilities use, or aspire to use, technology to advertise, reframe or hide their identities

Super collimation of the radiation by a point source in a uniaxial wire medium

We investigate the radiation properties of a short horizontal dipole embedded in a uniaxial wire medium. It is shown that the uniaxial wire medium enables a super-collimation of the dipole radiation such that the radiation pattern has a singularity and the radiated fields are non-diffractive in the broadside direction. We derive a closed analytical formula for the power radiated by the dipole. Our theory demonstrates that as a consequence of the ultrahigh density of photonic states of the nanowire array, the power radiated by the dipole is strongly enhanced as compared to that emitted in the dielectric host material