713 research outputs found

    Coupling a model of human thermoregulation with computational fluid dynamics for predicting human-environment interaction

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    This paper describes the methods developed to couple a commercial CFD program with a multi-segmented model of human thermal comfort and physiology. A CFD model is able to predict detailed temperatures and velocities of airflow around a human body, whilst a thermal comfort model is able to predict the response of a human to the environment surrounding it. By coupling the two models and exchanging information about the heat transfer at the body surface the coupled system can potentially predict the response of a human body to detailed local environmental conditions. This paper presents a method of exchanging data, using shared files, to provide a means of dynamically exchanging simulation data with the IESD-Fiala model during the CFD solution process. Additional code is used to set boundary conditions for the CFD simulation at the body surface as determined by the IESD-Fiala model and to return information about local environmental conditions adjacent to the body surface as determined by the CFD simulation. The coupled system is used to model a human subject in a naturally ventilated environment. The resulting ventilation flow pattern agrees well with other numerical and experimental work

    Union railways: Ad spot pricing dilemma? (B)

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    Faced with considerable losses and increased pressure to generate alternative sources of funding, Union Railways (UR) twice attempted to auction ad spots at their flagship trains and stations. On both the occasions, the market responded with substantially lower bids than management’s expectation. Surprised by the lackluster response, the management decided to conduct a detailed analysis of the ad spot market and engaged a team of advisers. They were tasked to help UR decide the base price for different types of ad spots (e.g. billboards, window skins, bogie door skins) and to recommend whether the ad spots be sold to either one or multiple intermediaries. Equipped with data (e.g. prevalent market rates and industry best practices) from multiple sources, the advisors faced the daunting task of designing a simple pricing mechanism that can work for multiple types of ad spots

    Collapsing dynamics of relativistic fluid in modified gravity admitting a conformal Killing vector

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    The collapsing dynamics of relativistic fluid are explored in f(R)f(R) gravity in a detailed systematic manner for the non-static spherically symmetric spacetime satisfying the equation of the conformal Killing vector. With quasi-homologous condition and diminishing complexity factor condition, exact solutions for dissipative as well as for non-dissipative systems are found and the astrophysical applications of these exact solutions are discussed. Furthermore, it is demonstrated that f(R)=Rf(R)=R, which is the extensive restriction of f(R)f(R) gravity, prior solutions of the collapsing fluid in general relativity, can be retrieved.Comment: 26 pages, version accepted for publication in the European Physical Journal

    Chandra Observations of the Gamma-ray Binary LSI+61303: Extended X-ray Structure?

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    We present a 50 ks observation of the gamma-ray binary LSI+61303 carried out with the ACIS-I array aboard the Chandra X-ray Observatory. This is the highest resolution X-ray observation of the source conducted so far. Possible evidence of an extended structure at a distance between 5 and 12 arcsec towards the North of LSI+61303 have been found at a significance level of 3.2 sigma. The asymmetry of the extended emission excludes an interpretation in the context of a dust-scattered halo, suggesting an intrinsic nature. On the other hand, while the obtained source flux, of F_{0.3-10 keV}=7.1^{+1.8}_{-1.4} x 10^{-12} ergs/cm^2/s, and hydrogen column density, N_{H}=0.70+/-0.06 x 10^{22} cm^{-2}, are compatible with previous results, the photon index Gamma=1.25+/-0.09 is the hardest ever found. In light of these new results, we briefly discuss the physics behind the X-ray emission, the location of the emitter, and the possible origin of the extended emission ~0.1 pc away from LSI+61303.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letter

    Jet-Induced Nucleosynthesis in Misaligned Microquasars

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    The jet axes and the orbital planes of microquasar systems are usually assumed to be approximately perpendicular, eventhough this is not currently an observational requirement. On the contrary, in one of the few systems where the relative orientations are well-constrained, V4641Sgr, the jet axis is known to lie not more than ~36 degrees from the binary plane. Such a jet, lying close to the binary plane, and traveling at a significant fraction of the speed of light may periodically impact the secondary star initiating nuclear reactions on its surface. The integrated yield of such nuclear reactions over the age of the binary system (less the radiative mass loss) will detectably alter the elemental abundances of the companion star. This scenario may explain the anomalously high Li enhancements (roughly ~20-200 times the sun's photospheric value; or, equivalently, 0.1-1 times the average solar system value) seen in the companions of some black-hole X-ray binary systems. (Such enhancements are puzzling since Li nuclei are exceedingly fragile - being easily destroyed in the interiors of stars - and Li would be expected to be depleted rather than enhanced there.) Gamma-ray line signatures of the proposed process could include the 2.22 MeV neutron capture line as well as the 0.478 MeV 7Li* de-excitation line, both of which may be discernable with the INTEGRAL satellite if produced in an optically thin region during a large outburst. For very energetic jets, a relatively narrow neutral pion gamma-decay signature at 67.5 MeV could also be measurable with the GLAST satellite. We argue that about 10-20% of all microquasar systems ought to be sufficiently misaligned as to be undergoing the proposed jet-secondary impacts.Comment: ApJ, accepted. Includes referee's suggestions and some minor clarifications over previous versio

    Compact relativistic geometries in f(R,G)f(R,G) gravity

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    One of the possible potential candidates for describing the universe's rapid expansion is modified gravity. In the framework of the modified theory of gravity f(R,G)f(R,G), the present work features the materialization of anisotropic matter, such as compact stars. Specifically, to learn more about the physical behavior of compact stars, the radial, and tangential pressures as well as the energy density of six stars namely HerX1Her X-1, SAXJ1808.43658SAXJ1808.4-3658, 4U1820304U1820-30, PSRJ16142230PSR J 1614 2230, VELAX1VELA X-1, and CenX3Cen X-3 are calculated. Herein, the modified theory of gravity f(R,G)f(R,G) is disintegrated into two parts i.e. the tanh\tanh hyperbolic f(R)f(R) model and the three different f(G)f(G) model. The study focuses on graphical analysis of compact stars wherein the stability aspects, energy conditions, and anisotropic measurements are mainly addressed. Our calculation revealed that, for the positive value of parameter n of the model f(G)f(G), all the six stars behave normally.Comment: Some changes have been made. " To appear in International Journal of Geometric Methods in Modern Physics

    A simplified modal-based method to quantify delamination in carbon fibre-reinforced plastic beam

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    This study contributes to our knowledge about the detection and recognition of carbon fibre-reinforced plastic (CFRP) composites by using a modal analysis technique. Delamination was artificially induced during the manufacturing process of CFRP beams so that the dimension and location of the artificial delamination were known. The first three longitudinal bending modes were considered for detecting, locating, and evaluating the delamination. Contrary to what is commonly practised, the sensor placed on the CFRP structure had a large mass in order to contribute actively to restricting the delamination and hence modifying the structure’s natural frequencies, thus making it much easier to monitor its health condition. The technique was implemented on a beam with a delamination gap of 9% of the beam’s length, positioned within the span of the beam. The results demonstrate that the proposed technique can be effective not only to locate the delamination but also to measure its extent accurately.Scopu
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