79,565 research outputs found

    Fourier's law on a one-dimensional optical random lattice

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    We study the transport properties of a one-dimensional hard-core bosonic lattice gas coupled to two particle reservoirs at different chemical potentials which generate a current flow through the system. In particular, the influence of random fluctuations of the underlying lattice on the stationary-state properties is investigated. We show analytically that the steady-state density presents a linear profile. The local steady-state current obeys the Fourier law j=κ(τ)nj=-\kappa(\tau)\nabla n where τ\tau is a typical timescale of the lattice fluctuations and n\nabla n the density gradient imposed by the reservoirs.Comment: 9 pages, 2 figure

    Symmetry Analysis of Multiferroic Co_3TeO_6

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    A phenomenological explanation of the magnetoelectric behavior of Co_3TeO_6 is developed. We explain the second harmonic generation data and the magnetic field induced spontaneous polarization in the magnetically ordered phase below 20K.Comment: Phys rev B Rapids, to appea

    Forcing anomalous scaling on demographic fluctuations

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    We discuss the conditions under which a population of anomalously diffusing individuals can be characterized by demographic fluctuations that are anomalously scaling themselves. Two examples are provided in the case of individuals migrating by Gaussian diffusion, and by a sequence of L\'evy flights.Comment: 5 pages 2 figure

    Visual scanning behavior and pilot workload

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    An experimental paradigm and a set of results which demonstrate a relationship between the level of performance on a skilled man-machine control task, the skill of the operator, the level of mental difficulty induced by an additional task imposed on the basic control task, and visual scanning performance. During a constant, simulated piloting task, visual scanning of instruments was found to vary as a function of the level of difficulty of a verbal mental loading task. The average dwell time of each fixation on the pilot's primary instrument increased as a function of the estimated skill level of the pilots, with novices being affected by the loading task much more than the experts. The results suggest that visual scanning of instruments in a controlled task may be an indicator of both workload and skill

    Towards Additive Manufacture of Next Generation Prosthetics, Assessing Emerging CAD Strategies for Improving the Existing CAD Process

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    The research project that this work comes from aims to address the issues and inefficiencies of current CAD systems in regards to working on multiple scales, with a particular focus on improving prosthetic design. Working from the micron scale to the macro scale and following on from work that defined a criteria of necessary material properties, this paper is a continuation of previous work that attempts to answer the research question ‘How can new CAD strategies be applied to improve the efficiency of producing parts with these necessary material properties?’ A selection of emerging CAD strategies from the last five years have been selected with a view of improving the hybrid process order created in the previous study. Each of these processes is introduced, and their pros and cons compared before identifying the areas of the CAD criteria that they can improve efficiency. Testing was performed using the software if it is available to see areas of improvement first-hand

    Energy and width measurements of low-Z pionic X-ray transitions

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    High resolution spectrometric measurement of energy and natural line widths of 2p-1s pionic X ray transitions, as well as muonic transition energies in Li, Be, B, and C isotope

    Entropy, instrument scan and pilot workload

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    Correlation and information theory which analyze the relationships between mental loading and visual scanpath of aircraft pilots are described. The relationship between skill, performance, mental workload, and visual scanning behavior are investigated. The experimental method required pilots to maintain a general aviation flight simulator on a straight and level, constant sensitivity, Instrument Landing System (ILS) course with a low level of turbulence. An additional periodic verbal task whose difficulty increased with frequency was used to increment the subject's mental workload. The subject's looppoint on the instrument panel during each ten minute run was computed via a TV oculometer and stored. Several pilots ranging in skill from novices to test pilots took part in the experiment. Analysis of the periodicity of the subject's instrument scan was accomplished by means of correlation techniques. For skilled pilots, the autocorrelation of instrument/dwell times sequences showed the same periodicity as the verbal task. The ability to multiplex simultaneous tasks increases with skill. Thus autocorrelation provides a way of evaluating the operator's skill level

    Extreme 18O-enrichment in majorite constrains a crustal origin of transition zone diamonds

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    The fate of subducted oceanic lithosphere and its role in the planet-scale geochemical cycle is a key problem in solid Earth studies. Asthenospheric and transition zone minerals included in diamond have been interpreted as representing subducted oceanic crust based on inclusion REE patterns and strong 13C depletion of their host diamond (δ13C as low as -23 ‰). This view/explanation, however, has been challenged by alternative interpretations that variable carbon isotopic compositions either result from high temperature fractionation involving carbides, or reflect primordial, unhomogenised mantle reservoirs. Here, we present the first oxygen isotope analyses of inclusions in such ultradeep diamonds – majoritic garnets in diamond from Jagersfontein (South Africa). The oxygen isotope compositions provide unambiguous evidence for derivation of the inclusions from subducted crustal materials. The δ18OVSMOW values of the majorites range from +8.6 ‰ to +10.0 ‰, well outside that of ambient mantle (+5.5 ±0.4 ‰) and indicate that the protoliths were very heavily weathered at relatively low temperatures. When this information is combined with the broadly eclogitic composition of the majoritic garnets, a derivation from subducted sea-floor basalts is implied. Based on the association between the heavy oxygen and light carbon, the light carbon isotope composition cannot relate to deep mantle processes and is also ultimately derived from the crust
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