322,942 research outputs found

    Instrumentation for Millimeter-wave Magnetoelectrodynamic Investigations of Low-Dimensional Conductors and Superconductors

    Full text link
    We describe instrumentation for conducting high sensitivity millimeter-wave cavity perturbation measurements over a broad frequency range (40-200 GHz) and in the presence of strong magnetic fields (up to 33 tesla). A Millimeter-wave Vector Network Analyzer (MVNA) acts as a continuously tunable microwave source and phase sensitive detector (8-350 GHz), enabling simultaneous measurements of the complex cavity parameters (resonance frequency and Q-value) at a rapid repetition rate (approx. 10 kHz). We discuss the principal of operation of the MVNA and the construction of a probe for coupling the MVNA to various cylindrical resonator configurations which can easily be inserted into a high field magnet cryostat. We also present several experimental results which demonstrate the potential of the instrument for studies of low-dimensional conducting systems.Comment: 20 pages including fig

    T-Parity Violation by Anomalies

    Full text link
    Little Higgs theories often rely on an internal parity ("T-parity'') to suppress non-standard electroweak effects or to provide a dark matter candidate. We show that such a symmetry is generally broken by anomalies, as described by the Wess-Zumino-Witten term. We study a simple SU(3) x SU(3)/SU(3) Little Higgs scheme where we obtain a minimal form for the topological interactions of a single Higgs field. The results apply to more general models, including [SU(3) x SU(3)/SU(3)]^4, SU(5)/SO(5), and SU(6)/Sp(6).Comment: 17 page

    Valley symmetry breaking and gap tuning in graphene by spin doping

    Get PDF
    We study graphene with an adsorbed spin texture, where the localized spins create a periodic magnetic flux. The latter produces gaps in the graphene spectrum and breaks the valley symmetry. The resulting effective electronic model, which is similar to Haldane's periodic flux model, allows us to tune the gap of one valley independently from that of the other valley. This leads to the formation of two Hall plateaux and a quantum Hall transition. We discuss the density of states, optical longitudinal and Hall conductivities for nonzero frequencies and nonzero temperatures. A robust logarithmic singularity appears in the Hall conductivity when the frequency of the external field agrees with the width of the gap.Comment: 14 pages, 7 figure

    Thinking about audience and agency in the museum: models from historical research

    Get PDF
    This paper examines a current trend within museum studies to conceptualise the contemporary museum as democratic, open, and working in partnership with its community, which is seen as a fundamental change from museums at some point in the past, when they were didactic and produced or encouraged a passive audience. This trend, it maintains, is not just produced by museums needing to fit into various agendas for social inclusivity, but also by some of the most important texts in museum history, which look at the ways in which various forms of agency worked to deny agency to the public. It argues that such a view radically understates the forms of agency available to ‚Äėoutsiders‚Äô to museums in the past; and that as a corollary, analyses of the contemporary museum need to be wary of seeing shared agency as already achieved. By exploring the forces which work to distribute agency widely inside and beyond the museum, alongside those which worked to centralise agency in the institution of the museum and its curators, we can gain a much fuller understanding of museums past and present

    Prototype Environmental Assessment of the impacts of siting and construction of an SPS ground receiving station

    Get PDF
    A prototype assessment of the environmental impacts of siting and constructing a Satellite Power System (SPS) Ground Receiving Station (GRS) is reported. The objectives of the study were: (1) to develop an assessment of the nonmicrowave related impacts of the reference system SPS GRS on the natural environment; (2) to assess the impacts of GRS construction and operations in the context of actual baseline data for a site in the California desert; and (3) to identify critical GRS characteristics or parameters that are most significant in terms of the natural environment

    Making Upper Division Mathematics Courses Relevant for Pre-Service Teachers

    Get PDF
    This article addresses the disconnect that in-service and pre-service secondary school teachers feel between the material presented in upper division mathematics courses and high school classroom practice. Two examples are given from an abstract algebra course in which this problem is addressed

    Hitting The Fan

    Get PDF
    • ‚Ķ
    corecore