834,046 research outputs found

    Angular Momentum Transfer in Vela-like Pulsar Glitches

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    The angular momentum transfer associated to Vela-like glitches has never been calculated {\em directly} within a realistic scenario for the storage and release of superfluid vorticity; therefore, the explanation of giant glitches in terms of vortices has not yet been tested against observations. We present the first physically reasonable model, both at the microscopic and macroscopic level (spherical geometry, n=1 polytropic density profile, density-dependent pinning forces compatible with vortex rigidity), to determine where in the star the vorticity is pinned, how much of it, and for how long. For standard neutron star parameters (M=1.4M,Rs=10M=1.4 M_{\odot}, R_s=10 km, Ω˙=Ω˙Vela=1010\dot{\Omega}=\dot{\Omega}_{\rm Vela}=-10^{-10} Hz s1^{-1}), we find that maximum pinning forces of order fm1015f_m\approx10^{15} dyn cm1^{-1} can accumulate ΔLgl1040\Delta L_{\rm gl}\approx10^{40} erg s of superfluid angular momentum, and release it to the crust at intervals Δtgl3\Delta t_{\rm gl}\approx3 years. This estimate of ΔLgl\Delta L_{\rm gl} is one order of magnitude smaller than what implied indirectly by current models for post-glitch recovery, where the core and inner-crust vortices are taken as physically disconnected; yet, it successfully yields the magnitudes observed in recent Vela glitches for {\em both} jump parameters, ΔΩgl\Delta\Omega_{\rm gl} and ΔΩ˙gl\Delta\dot{\Omega}_{\rm gl}, provided one assumes that only a small fraction (<10<10%) of the total star vorticity is coupled to the crust on the short timescale of a glitch. This is reasonable in our approach, where no layer of normal matter exists between the core and the inner-crust, as indicated by existing microscopic calculation. The new scenario presented here is nonetheless compatible with current post-glitch models.Comment: 11 pages, 4 figure

    Race as Technology: From Posthuman Cyborg to Human Industry

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    Cyborg and prosthetic technologies frame prominent posthumanist approaches to understanding the nature of race. But these frameworks struggle to accommodate the phenomena of racial passing and racial travel, and their posthumanist orientation blurs useful distinctions between racialized humans and their social contexts. We advocate, instead, a humanist approach to race, understanding racial hierarchy as an industrial technology. Our approach accommodates racial passing and travel. It integrates a wide array of research across disciplines. It also helpfully distinguishes among grounds of racialization and conditions facilitating impacts of such racialization

    How advertising through the ages has shaped Christmas

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    By the 20th century, mass advertising became commonplace. Consumer messages were now broadcast to the public through billboards, magazines, radio, and later the moving image of television. Mass advertising was what allowed the slowly developing idea of Christmas as a time to give gifts to go mainstream, and eventually, to define Christmas itself

    Polarimetry in the Visible and Infrared: Application to CMB Polarimetry

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    Interstellar polarization from aligned dust grains can be measured both in transmission at visible and near-infrared wavelengths and in emission at far-infrared and sub-mm wavelengths. These observations can help predict the behavior of foreground contamination of CMB polarimetry by dust in the Milky Way. Fractional polarization in emission from aligned dust grains will be at the higher range of currently observed values of 4-10%. Away from the galactic plane, fluctuations in Q and U will be dominated by fluctuations in intensity, and less influenced by fluctuations in fractional polarization and position angle.Comment: To be published in the proceedings of "The Cosmic Microwave Background and its Polarization", New Astronomy Reviews, (eds. S. Hanany and K.A. Olive

    Hypermedia for language learning: The FREE model at Coventry University

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    Coventry University is pioneering the integration of hypermedia into the curriculum for the teaching of Italian language and society with the creation of a package based on Nerino Rossi's novel La neve nel bicchiere. The novel was already in use as a basic course text, and developing a hypermedia package was felt to be the ideal way of creating a more stimulating means of access to it. The procedure used in creating the package is described, as are its contents, the ways in which the students use it and the tasks they are given to perform, the feedback from the students, and its impact on their performance. The testing of the prototype has helped in creating a new cognitive model: the FREE (Fluid Role‐Exchange Environment) which functions as a fluid and interactive ‘pool’ where the three main actors, or act ants, ie. the learner, the lecturer and the computer, exchange roles. Within the FREE, students were involved in the construction and evaluation of the courseware, as well as testing the various versions of the prototype. The development and use of hypermedia inside and outside the classroom has made it possible to change both the students’ and the lecturer's attitude towards the material being learnt. However, the courseware does not seem to equip students sufficiently for essay writing, and this problem needs further investigation

    Self-Inverse and Exchangeable Random Variables

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    A random variable Z will be called self-inverse if it has the same distribution as its reciprocal 1/Z. It is shown that if Z is defined as a ratio, X/Y, of two rv's X and Y (with Pr[X=0]=Pr[Y=0]=0), then Z is self-inverse if and only if X and Y are (or can be chosen to be) exchangeable. In general, however, there may not exist iid X and Y in the ratio representation of Z.Comment: Statistics and Probability Letters (to appear, 6 pages

    Hydrological connectivity of soil pipes determined by ground-penetrating radar tracer detection

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    Soil pipes are common and important features of many catchments, particularly in semi-arid and humid areas, and can contribute a large proportion of runoff to river systems. They may also significantly influence catchment sediment and solute yield. However, there are often problems in finding and defining soil pipe networks which are located deep below the surface. Ground penetrating radar (GPR) has been used for non-destructive identification and mapping of soil pipes in blanket peat catchments. While GPR can identify subsurface cavities, it cannot alone determine hydrological connectivity between one cavity and another. This paper presents results from an experiment to test the ability of GPR to establish hydrological connectivity between pipes through use of a tracer solution. Sodium chloride was injected into pipe cavities previously detected by the radar. The GPR was placed downslope of the injection points and positioned on the ground directly above detected soil pipes. The resultant radargrams showed significant changes in reflectance from some cavities and no change from others. Pipe waters were sampled in order to check the radar results. Changes in electrical conductivity of the pipe water could be detected by the GPR, without data post-processing, when background levels were increased by greater than approximately twofold. It was thus possible to rapidly determine hydrological connectivity of soil pipes within dense pipe networks across hillslopes without ground disturbance. It was also possible to remotely measure travel times through pipe systems; the passing of the salt wave below the GPR produced an easily detectable signal on the radargram which required no post-processing. The technique should allow remote sensing of water sources and sinks for soil pipes below the surface. The improved understanding of flowpath connectivity will be important for understanding water delivery, solutional and particulate denudation, and hydrological and geomorphological model development
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