325 research outputs found

    The quick and the dead: when reaction beats intention

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    Everyday behaviour involves a trade-off between planned actions and reaction to environmental events.Evidence from neurophysiology, neurology and functional brain imaging suggests different neural bases for the control of different movement types. Here we develop a behavioural paradigm to test movement dynamics for intentional versus reaction movements and provide evidence for a ‘reactive advantage’ in movement execution, whereby the same action is executed faster in reaction to an opponent. We placed pairs of participants in competition with each other to make a series of button presses. Within subject analysis of movement times revealed a 10 per cent benefit for reactive actions. This was maintained when opponents performed dissimilar actions, and when participants competed against a computer, suggesting that the effect is not related to facilitation produced by action observation. Rather, faster ballistic movements may be a general property of reactive motor control, potentially providing a useful means of promoting survival

    structural analysis of transversally loaded quasi isotropic rectilinear orthotropic composite circular plates with galerkin method

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    Abstract Bending analysis of rectilinear orthotropic composite plates have been scarcely investigated taking into account the increasing use of composite materials in structural applications in the last years. This kind of plates are laminates with axisymmetric geometry and they are made up of unidirectionally reinforced layers with different orientations. Transversally loading this kind of circular plates, the deflected mid-surface is not independent from the circumferential coordinate, unlike the case of isotropic circular plate. Nevertheless, the quasi-isotropic stacking sequence makes still possible to introduce the hypothesis of axisymmetry for the mid-surface deflection under transversal load, disregarding the circumferential variation of the vertical displacement connected to the variable bending stiffness. Then, the constitutive equations for this specific family of plates were obtained finding the stress resultants-strains relations in the global cylindrical coordinate system. These expressions, along with the equilibrium equations, made it possible to derive the governing equation of the problem in the frame of Kirchhoff-Love hypothesis of the classical lamination theory. The Galerkin method was applied to solve the governing third order differential equation in terms of mid-surface deflection, introducing appropriate polynomial approximation functions compliant with the boundary conditions. In particular, fully clamped constraint conditions were considered for the outer diameter of the plate in conjunction with an internal rigid core. The characterization of this model allows to define the stiffness matrix terms of a custom composite bolted joint finite element, that is the object of future developments of this work. Results of the original proposed method are presented and compared to those obtained by means of FEA performed with a refined reference model, demonstrating a good agreement

    External Carotid Artery Shunting During Carotid Endarterectomy: An Alternative for Cerebral Protection?

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    AbstractObjectives: to assess the application of external carotid artery (ECA) shunting in cerebral protection during carotid endarterectomy (CEA). Design: prospective study. Materials and Methods: the study comprised 137 consecutive patients who underwent CEA under locoregional anaesthesia. Transcranial Doppler was used to monitor the mean velocity of the middle cerebral artery (mv-MCA): (1) before carotid clamping; (2) after clamping both the common and external carotid arteries; (3) after clamping the internal carotid artery alone (“ECA test”). The decision to shunt was based on the occurrence of neurological deficit during carotid clamping. If the ECA test revealed mv-MCA approaching the pre-clamping values ECA shunting was used, whereas the remaining patients in need of a shunt had a standard internal carotid artery (ICA) shunt. Results: shunting was necessary in 12/137 cases (9%). The ECA test indicated that in four cases – 3% of the whole series or 33% of the shunted cases. In these four patients ECA shunting reversed the neurological deficit, and CEA was successfully performed without any complications. Conclusions: ECA shunting could be considered as an alternative to standard ICA shunting. Suitable cases can be identified on the basis of the ECA test

    Punta del Lago 1: implicaciones para la arqueología de la margen norte del lago Viedma

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    Se presentan los resultados sobre aspectos cronológicos, arqueofaunísticos y de la tecnología lítica de excavaciones llevadas a cabo bajo dos paneles con motivos rupestres en el sitio Punta del Lago 1, ubicado sobre un cañadón de areniscas en la margen noreste del lago Viedma.Trabajo publicado en Gómez Otero, Julieta (comp.). X Jornadas de Arqueología de la Patagonia. Libro de resúmenes. Puerto Madryn: Instituto de Diversidad y Evolución Austral, 2017.Facultad de Ciencias Naturales y Muse

    Punta del Lago 1: implicaciones para la arqueología de la margen norte del lago Viedma

    Get PDF
    Se presentan los resultados sobre aspectos cronológicos, arqueofaunísticos y de la tecnología lítica de excavaciones llevadas a cabo bajo dos paneles con motivos rupestres en el sitio Punta del Lago 1, ubicado sobre un cañadón de areniscas en la margen noreste del lago Viedma.Trabajo publicado en Gómez Otero, Julieta (comp.). X Jornadas de Arqueología de la Patagonia. Libro de resúmenes. Puerto Madryn: Instituto de Diversidad y Evolución Austral, 2017.Facultad de Ciencias Naturales y Muse

    Advances in high power short pulse fiber laser systems and technology

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    We review recent advances in Yb fiber lasers and amplifiers for high power short pulse systems. We go on to describe associated recent developments in fiber components for use in such systems. Examples include microstructured optical fibers for pulse compression and supercontinuum generation, and advanced fiber grating technology for chirped-pulse amplifier systems

    Physical limits of flight performance in the heaviest soaring bird

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    Flight costs are predicted to vary with environmental conditions, and this should ultimately determine the movement capacity and distributions of large soaring birds. Despite this, little is known about how flight effort varies with environmental parameters. We deployed bio-logging devices on the world’s heaviest soaring bird, the Andean condor (Vultur gryphus), to assess the extent to which these birds can operate without resorting to powered flight. Our records of individual wingbeats in >216 hours of flight show that condors can sustain soaring across a wide range of wind and thermal conditions, only flapping for 1 % of their flight time. This is amongst the very lowest estimated movement costs in vertebrates. One bird even flew for > 5 hours without flapping, covering ~ 172 km. Overall, > 70 % of flapping flight was associated with take-offs. Movement between weak thermal updrafts at the start of the day also imposed a metabolic cost, with birds flapping towards the end of glides to reach ephemeral thermal updrafts. Nonetheless, the investment required was still remarkably low, and even in winter conditions with weak thermals, condors are only predicted to flap for ~ 2 s per km. The overall flight effort in the largest soaring birds therefore appears to be constrained by the requirements for take-off

    Multiwavelength observations of the EUV variable metal-rich white dwarf GD 394

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    We present new Hubble Space Telescope (HST) ultraviolet and ground-based optical observations of the hot, metal-rich white dwarf GD394. Extreme-ultraviolet (EUV) observations in 1992-1996 revealed a 1.15 d periodicity with a 25 per cent amplitude, hypothesized to be due to metals in a surface accretion spot. We obtained phase resolved HST/Space Telescope Imaging Spectrograph high resolution far-ultraviolet spectra of GD394 that sample the entire period, along with a large body of supplementary data. We find no evidence for an accretion spot, with the flux, accretion rate, and radial velocity of GD394 constant over the observed time-scales at ultraviolet and optical wavelengths. We speculate that the spot may have no longer been present when our observations were obtained, or that the EUV variability is being caused by an otherwise undetected evaporating planet. The atmospheric parameters obtained from separate fits to optical and ultraviolet spectra are inconsistent, as is found for multiple hot white dwarfs. We also detect non-photospheric, high ionisation absorption lines of multiple volatile elements, which could be evidence for a hot plasma cocoon surrounding the white dwarf.European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013 / ERC Grant) [320964]; Leverhulme Trust Research Project Grant; NASA [NAS 5-26555]; NASA through a Space Telescope Science Institute [13719]; W. M. Keck FoundationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

    Bow shocks, nova shells, disc winds and tilted discs: the nova-like V341 Ara has it all

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    V341 Ara was recently recognized as one of the closest (d ≃ 150 pc) and brightest (V ≃ 10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow shock, where the system’s accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multiwavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10–16 d and typical amplitude of ≃1 mag. High-cadence photometry from theTransiting Exoplanet Survey Satellite (TESS) reveals for the first time both the orbital period and a ‘negative superhump’ period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect antiphased absorption and emission-line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white-dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [O III] emission produced in the bow shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a ‘guest star’ mentioned in Chinese historical records in AD 1240. If this marks the date of the system’s nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory
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