14,358 research outputs found

    Magnetic structure of Ba(TiO)Cu4_4(PO4_4)4_4 probed using spherical neutron polarimetry

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    The antiferromagnetic compound Ba(TiO)Cu4_4(PO4_4)4_4 contains square cupola of corner-sharing CuO4_4 plaquettes, which were proposed to form effective quadrupolar order. To identify the magnetic structure, we have performed spherical neutron polarimetry measurements. Based on symmetry analysis and careful measurements we conclude that the orientation of the Cu2+^{2+} spins form a non-collinear in-out structure with spins approximately perpendicular to the CuO4_4 motif. Strong Dzyaloshinskii-Moriya interaction naturally lends itself to explain this phenomenon. The identification of the ground state magnetic structure should serve well for future theoretical and experimental studies into this and closely related compounds.Comment: 9 pages, 4 figure

    Southern Sky Redshift Survey: Clustering of Local Galaxies

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    We use the two-point correlation function to calculate the clustering properties of the recently completed SSRS2 survey. The redshift space correlation function for the magnitude-limited SSRS2 is given by xi(s)=(s/5.85 h-1 Mpc)^{-1.60} for separations between 2 < s < 11 h-1 Mpc, while our best estimate for the real space correlation function is xi(r) = (r/5.36 h-1 Mpc)^{-1.86}. Both are comparable to previous measurements using surveys of optical galaxies over much larger and independent volumes. By comparing the correlation function calculated in redshift and real space we find that the redshift distortion on intermediate scales is small. This result implies that the observed redshift-space distribution of galaxies is close to that in real space, and that beta = Omega^{0.6}/b < 1, where Omega is the cosmological density parameter and b is the linear biasing factor for optical galaxies. We also use the SSRS2 to study the dependence of xi on the internal properties of galaxies. We confirm earlier results that luminous galaxies (L>L*) are more clustered than sub-L* galaxies and that the luminosity segregation is scale-independent. We find that early types are more clustered than late types, but that in the absence of rich clusters, the relative bias between early and late types in real space, is not as strong as previously estimated. Furthermore, both morphologies present a luminosity-dependent bias, with the early types showing a slightly stronger dependence on luminosity. We also find that red galaxies are significantly more clustered than blue ones, with a mean relative bias stronger than that seen for morphology. Finally, we find that the relative bias between optical and iras galaxies in real space is b_o/b_I \sim 1.4.Comment: 43 pages, uses AASTeX 4.0 macros. Includes 8 tables and 16 Postscript figures, updated reference

    Design of crystal-like aperiodic solids with selective disorder--phonon coupling

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    Functional materials design normally focuses on structurally-ordered systems because disorder is considered detrimental to many important physical properties. Here we challenge this paradigm by showing that particular types of strongly-correlated disorder can give rise to useful characteristics that are inaccessible to ordered states. A judicious combination of low-symmetry building unit and high-symmetry topological template leads to aperiodic "procrystalline" solids that harbour this type of topological disorder. We identify key classes of procrystalline states together with their characteristic diffraction behaviour, and establish a variety of mappings onto known and target materials. Crucially, the strongly-correlated disorder we consider is associated with specific sets of modulation periodicities distributed throughout the Brillouin zone. Lattice dynamical calculations reveal selective disorder-phonon coupling to lattice vibrations characterised by these same periodicities. The principal effect on the phonon spectrum is to bring about dispersion in energy rather than wave-vector, as in the poorly-understood "waterfall" effect observed in relaxor ferroelectrics. This property of procrystalline solids suggests a mechanism by which strongly-correlated topological disorder might allow new and useful functionalities, including independently-optimised thermal and electronic transport behaviour as required for high-performance thermoelectrics.Comment: 4 figure

    Lunar Flight Study Series: Volume 8. Earth-Moon Transit Studies Based on Ephemeris Data and Using Best Available Computer Program. Part 3: Analysis of Some Lunar Landing Site Problems Utilizing Two Fundamental Principles

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    This report presents two fundamental properties of lunar trajectories and makes use of these properties to solve various lunar landing site problems. Not only are various problems treated and solved but the properties and methods are established for use in the solution of other problems. This report presents an analysis of lunar landing site problems utilizing the direct mission mode as well as the orbital mission mode. A particular landing site is then specified and different flight profiles are analyzed for getting an exploration vehicle to that landing site. Rendezvous compatible lunar orbits for various stay-times at the landing site are treated. Launch opportunities are discussed for establishing rendezvous compatible lunar orbits without powered plane changes. Then, the minimum required plane changes for rendezvous in the lunar orbit are discussed for launching from earth on any day. On days that afford rendezvous compatible opportunities, there are no powered plane change requirements in the operations from launch at AMR through the rendezvous in lunar orbit, after the stay at the lunar site

    SPATIOTEMPORAL AND JOINT KINEMATIC DIFFERENCES BETWEEN FOOTSTRIKE PATTERNS IN MALE AND FEMALE 10,000M ATHLETES

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    The aim of this study was to examine biomechanical differences between footstrike patterns in elite 10,000m racing. Video data of 53 men and 33 women were recorded in competition and used to compare spatiotemporal and joint kinematic variables between rearfoot, midfoot and forefoot strikers, and to find associations. There were no differences between footstrike patterns for speed, step length or cadence, but rearfoot strikers had longer contact times than forefoot and midfoot strikers by 0.017 and 0.014 s, respectively, and shorter flight times by 0.023 and 0.021 s, respectively. The main causes of different footstrike patterns were the ankle and foot angles at initial contact; thigh, knee and shank angles differed little. In women, longer hip-ankle “overstriding” distances were associated with faster running speeds (r = 0.58), and so were a positive contributor to performance

    Inter-University International Collaboration for an Online Course: A Case Study

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    This paper is a practical account of the experience of collaboration between two international partners – one in Europe and the other in the United States. This collaboration experience is a lens through which the authors outline the origin, design and implementation of an inter-university teaching experience. The processes, strengths and difficulties are outlined and the rationale for utilising a virtual world is given, along with the participants’ perspectives of the experience. No institutional changes or formal agreements were needed. The same course was validated and accredited by each institution and designed to address the requirements of each with the responsibility for participant progress and assessment remaining with the home institution. The paper discusses issues of coordination and makes recommendations for developing similar collaborations
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