Intrinsic resistivity and the SO(5) theory of high-temperature superconductors

The topological structure of the order parameter in Zhang's SO(5) theory of superconductivity allows for an unusual type of dissipation mechanism via which current-carrying states can decay. The resistivity due to this mechanism, which involves orientation rather than amplitude order-parameter fluctuations, is calculated for the case of a thin superconducting wire. The approach is a suitably modified version of that pioneered by Langer and Ambegaokar for conventional superconductors.Comment: 4 pages, including 1 figure (REVTEX); references added, minor corrections mad

Topological phases of topological insulator thin films

We study the properties of a thin film of topological insulator material. We treat the coupling between helical states at opposite surfaces of the film in the properly-adapted tunneling approximation, and show that the tunneling matrix element oscillates as function of both the film thickness and the momentum in the plane of the film for Bi$_2$Se$_3$ and Bi$_2$Te$_3$. As a result, while the magnitude of the matrix element at the center of the surface Brillouin Zone gives the gap in the energy spectrum, the sign of the matrix element uniquely determines the topological properties of the film, as demonstrated by explicitly computing the pseudospin textures and the Chern number. We find a sequence of transitions between topological and non-topological phases, separated by semimetallic states, as the film thickness varies. In the topological phase the edge states of the film always exist but only carry a spin current if the edge potentials break particle-hole symmetry. The edge states decay very slowly away from the boundary in Bi$_2$Se$_3$, making Bi$_{2}$Te$_{3}$, where this scale is shorter, a more promising candidate for the observation of these states. Our results hold for free-standing films as well as heterostructures with large-gap insulators

Pairing correlations in a trapped one-dimensional Fermi gas

We use a BCS-type variational wavefunction to study attractively-interacting quasi one-dimensional (1D) fermionic atomic gases, motivated by cold-atom experiments that access the 1D regime using an anisotropic harmonic trapping potential (with trapping frequencies $\omega_x = \omega_y \gg \omega_z$) that confines the gas to a cigar-shaped geometry. To handle the presence of the trap along the $z$-direction, we construct our variational wavefunction from the harmonic oscillator Hermite functions that are the eigenstates of the single-particle problem. Using an analytic determination of the effective interaction among harmonic oscillator states along with a numerical solution of the resulting variational equations, we make specific experimental predictions for how pairing correlations would be revealed in experimental probes like the local density and the momentum correlation function.Comment: 8 pages, 6 figures. Published in Phys. Rev.

A systematic review of interactions in pedagogical approaches with reported outcomes for the academic and social inclusion of pupils with special educational needs

From the introduction/background: The growing demand for inclusive practices within mainstream schools has resulted in classroom teachers having to take direct responsibility for the individual learning needs of all pupils within the setting, and reduced the expectation that support staff should be the primary practitioners for children with special educational needs (SEN). The belief in a need for special pedagogical approaches for these children has also been widely critiqued (e.g. Norwich and Lewis, 2001; Hart, 1996) and there has been a growing focus upon the teaching practices that can be, and are, more broadly used by mainstream practitioners. Central to all these approaches are the interactions that both create the learning context and operate within it

Supported Employment in Maine: Youth in Foster Care

This report describes the employment experiences of 35 Maine youth in foster care. The study methods used included a quantitative analysis of the employment experiences of youth in care and a qualitative component that included interviews with five youth from the sample and four adults (a program job coach, a vocational case manager, a foster/adoptive parent, and a representative from a First Jobs business partner

Differences in Nursing Home Utilization and Clinical Outcome in Veterans Administration Nursing Home Patients

Because of increasing costs and demand for nursing home care, studies are needed that can better describe the population of users and improve prediction of clinical outcomes and program requirements. The major purpose of this study was to explore the incremental and seven month outcomes of nursing home patients using the Andersen model. The design was longitudinal. Patients from one Veterans Administration (VA) hospital-based nursing home and six freestanding. VA contract community nursing homes were studied. Functional and cognitive ability were analyzed along with socioeconomic and demographic data. and utilization patterns. A second purpose was to assess associations among variables and their interaction effects in predicting outcome. A third purpose was to assess the contribution of such independent variables as case-mix and rehospitalization rates to possible cost differences evidenced by the two nursing home types. The results of this study suggest avenues for planning and allocation of resources in the two program alternatives. The Barthel Index (BI) (Mahoney & Barthel. 1965) was used to measure functional status and the Short Portable Mental Status Questionnaire (SPMSQ) (Pfeiffer. 1975) for cognitive ability. In addition to standardized measures. sociodemographic and utilization data. perceptions of health and outcomes of care were collected on all subjects. Analytical techniques included descriptive and inferential statistics. The major hypothesis was that veterans in the hospital-based versus contract statistically significant differences in characteristics and on measures of service use and clinical outcome. Findings were evaluated for policy adequacy. adherence to program intent. federal and state cost complement and other qualitative implications. Statistically significant differences were found between patients in the two settings on predisposing, enabling and need characteristics. The hospital-based NHCU patients were more likely to be married and living with someone. They also had higher incomes, more Medicare A coverage, a greater percentage of service-connected veterans and demonstrated greater limitation in functional ability than did those in contract. The predominant outcome for both groups was continued nursing home care. Statistically significant differences were also found for outcome measures. Higher income and being 76 years or older were predictive of continued nursing home residence. The type of nursing home was not significant in explaining continued care. The total number of diagnoses. age group and type of nursing home were predictive of death as an outcome. There were significantly more deaths among those 75 years or younger. among those with lower incomes and among NHCU patients. Health service utilization did not differ significantly by nursing home type. Neither group of nursing home patients demonstrated any significant improvement in functional or mental status and self-perceived health. The only differences of note were among those 75 years or less who did improve in functional ability from the third to the sixth month. The findings suggest that the two nursing home types do have different patient population profiles. However. the continued use of nursing home care by both groups indicates some lack of fit between legislative intent and actual clinical utilization

Proximity-Induced Superconductivity at Non-Helical Topological Insulator Interfaces

We study how non-helical spin textures at the boundary between a topological insulator (TI) and a superconductor (SC) affect the proximity-induced superconductivity of the TI interface state. We consider TIs coupled to both spin-singlet and spin-triplet SCs, and show that for the spin-triplet parent SCs the resulting order parameter induced onto the interface state sensitively depends on the symmetries which are broken at the TI-SC boundary. For chiral spin-triplet parent SCs, we find that nodal proximity-induced superconductivity emerges when there is broken twofold rotational symmetry which forces the spins of the non-helical topological states to tilt away from the interface plane. We furthermore show that the Andreev conductance of lateral heterostructures joining TI-vacuum and TI-SC interfaces yields experimental signatures of the reduced symmetries of the interface states.Comment: 5 pages, 2 figure

Universal collisionless transport of graphene

The impact of the electron-electron Coulomb interaction on the optical conductivity of graphene has led to a controversy that calls into question the universality of collisionless transport in this and other Dirac materials. Using a lattice calculation that avoids divergences present in previous nodal Dirac approaches, our work settles this controversy and obtains results in quantitative agreement with experiment over a wide frequency range. We also demonstrate that dimensional regularization methods agree, as long as the scaling properties of the conductivity and the regularization of the theory in modified dimension are correctly implemented. Tight-binding lattice and nodal Dirac theory calculations are shown to coincide at low energies even when the non-zero size of the atomic orbital wave function is included, conclusively demonstrating the universality of the optical conductivity of graphene.Comment: 4+ pages,4 figures; includes Supplemental Material (18 pages, 2 figures

Elastic response of the electron fluid in intrinsic graphene: The collisionless regime

The elastic response of an electron fluid at finite frequencies is defined by the electron viscosity $\eta(\omega)$. We determine $\eta(\omega)$ for graphene at the charge neutrality point in the collisionless regime, including the leading corrections due to the electron-electron Coulomb interaction. We find interaction corrections to $\eta(\omega)$ that are significantly larger if compared to the corresponding corrections to the optical conductivity. In addition, we find comparable contributions to the dynamic momentum flux due to single-particle and many-particle effects. We also demonstrate that $\eta(\omega)$ is directly related to the nonlocal energy-flow response of graphene at the Dirac point. The viscosity in the collisionless regime is determined with the help of the strain generators in the Kubo formalism. Here, the pseudo-spin of graphene describing its two sublattices plays an important role in obtaining a viscosity tensor that fulfills the symmetry properties of a rotationally symmetric system.Comment: 18 pages, 5 figure

A systematic review of pedagogical approaches that can effectively include children with special educational needs in mainstream classrooms with a particular focus on peer group interactive approaches

The broad background to this review is a long history of concepts of special pupils and special education, and a faith in special pedagogical approaches. The rise of inclusive schools and some important critiques of special pedagogy (e.g. Hart, 1996; Norwich and Lewis, 2001; Thomas and Loxley, 2001) have raised the profile of teaching approaches that ordinary teachers can and do use to include children with special educational needs in mainstream classrooms. Inclusive education itself is increasingly conceived as being about the quality of learning and participation that goes on in inclusive schools rather than simplistic matters of where children are place