4,554 research outputs found

    Evolutionary Optimization of Centrifugal Nozzles for Organic Vapours

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    This paper discusses the shape-optimization of non-conventional centrifugal turbine nozzles for Organic Rankine Cycle applications. The optimal aerodynamic design is supported by the use of a non-intrusive, gradient-free technique specifically developed for shape optimization of turbomachinery profiles. The method is constructed as a combination of a geometrical parametrization technique based on B-Splines, a high-fidelity and experimentally validated Computational Fluid Dynamic solver, and a surrogate-based evolutionary algorithm. The non-ideal gas behaviour featuring the flow of organic fluids in the cascades of interest is introduced via a look-up-table approach, which is rigorously applied throughout the whole optimization process. Two transonic centrifugal nozzles are considered, featuring very different loading and radial extension. The use of a systematic and automatic design method to such a non-conventional configuration highlights the character of centrifugal cascades; the blades require a specific and non-trivial definition of the shape, especially in the rear part, to avoid the onset of shock waves. It is shown that the optimization acts in similar way for the two cascades, identifying an optimal curvature of the blade that both provides a relevant increase of cascade performance and a reduction of downstream gradients

    Internal ratings and bank opacity: evidence from analysts’ forecasts

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    We document that reliance on internal ratings-based (IRB) models to compute credit risk and capital requirements reduces bank opacity. Greater reliance on IRB models is associated with lower absolute forecast error and reduced disagreement among analysts regarding expected bank earnings per share. These results are stronger for banks that apply internal ratings to the most opaque loans and adopt the advanced version of IRB models, which entail a more granular risk assessment and greater disclosure of risk parameters. The results stem from the higher earnings informativeness and the more comprehensive disclosure of credit risk in banks adopting internal ratings. We employ an instrumental variables approach to validate our findings

    Plant nanobionic materials with a giant temperature response mediated by pectin-Ca^(2+)

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    Conventional approaches to create biomaterials rely on reverse engineering of biological structures, on biomimicking, and on bioinspiration. Plant nanobionics is a recent approach to engineer new materials combining plant organelles with synthetic nanoparticles to enhance, for example, photosynthesis. Biological structures often outperform man-made materials. For example, higher plants sense temperature changes with high responsivity. However, these properties do not persist after cell death. Here, we permanently stabilize the temperature response of isolated plant cells adding carbon nanotubes (CNTs). Interconnecting cells, we create materials with an effective temperature coefficient of electrical resistance (TCR) of −1,730% K^(−1), ∼2 orders of magnitude higher than the best available sensors. This extreme temperature response is due to metal ions contained in the egg-box structure of the pectin backbone, lodged between cellulose microfibrils. The presence of a network of CNTs stabilizes the response of cells at high temperatures without decreasing the activation energy of the material. CNTs also increase the background conductivity, making these materials suitable elements for thermal and distance sensors

    Risk of temporomandibular joint effusion related to magnetic resonance imaging signs of disc displacement

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    Background: It has been suggested that TMJ effusion may represent an inflammatory response to a dysfunctional disc-condyle relationship. The purpose of the present study was to evaluate whether the status of the disc in the temporomandibular joint, as depicted in magnetic resonance (MR) images, is predictive of the presence of temporomandibular joint (TMJ) effusion. Methods: The relationship between disc displacement and TMJ effusion was analyzed in MR images of 154 TMJs in 77 patients complaining for pain and/or dysfunction in the TMJ area and referred from medical practitioners to specialist consultation. Logistic regression analysis was used to identify the significant correlation between presence/absence of joint effusion and disc displacement. Results: Significant correlation (P<0.01) between disc displacement and joint effusion was found. OR for all type of disc displacement was 3.1, and the odds that a joint had magnetic resonance imaging findings of effusion was greater for anterior disc displacement without reduction. Conclusions: The status of the disc could represent a factor involved in the development of temporomandibular joint oedema. However, these findings suggest that disc displacement may not be regarded as the dominant factor in defining the occurrence of TMJ effusion. Certain local or systemic conditions other than the disc-condyle relationship must be considered

    Use of RELAP50MOD3.3 Code to Get Fluid Dynamic Stability Maps

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    The analysis that has been carried out in the present paper shows the possibility to predict the onset of density wave oscillations by means of RELAP5/MOD3.3 code for simple geometry systems, whereas the difference between 1D and 3D approximations is not relevant for the purpose of the analysis; the shape of the boundary line in the stability maps is in agreement with the other authors prediction. The approximation used for helically coiled pipes in the multichannel systems seems not to affect the instability onset and the classical shape of the instability maps, that seem a powerful tool for the fluid dynamic instability predictio

    GRMHD simulations of accretion flows onto massive binary black hole mergers embedded in a thin slab of gas

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    We present general relativistic magnetohydrodynamic simulations of merging equal-mass, spinning black holes embedded in an equatorial thin slab of magnetized gas. We evolve black holes either non-spinning, with spins aligned to the orbital angular momentum, and with misaligned spins. The rest-mass density of the gas slab follows a Gaussian profile symmetric relative to the equatorial plane and it is initially either stationary or with Keplerian rotational support. As part of our diagnostics, we follow the accretion of matter onto the black hole horizons and the Poynting luminosity. Throughout the inspiral phase, the configurations with non-zero spins display modulations in the mass accretion rate that are proportional to the orbital frequency and its multiples. Our frequency analysis suggests that these modulations are influenced by the initial geometry and angular momentum of the gas distribution. In contrast to binary models evolved in the gas cloud scenario, we do not observe a significant increase in the mass accretion rate after the merger in any of our simulations. This observation brings attention to a potential link between the electromagnetic signatures of massive binary black hole mergers and the geometrical distribution of the surrounding gas. It also suggests the possibility of not detecting a peak luminosity at the time of merger in future electromagnetic observations.Comment: 14 pages, 7 figures, submitted to PR
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