1,551 research outputs found

    Investigations on fluid dynamics of hydraulic accumulators

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    In state of the art hydrostatic installations accumulators of various designs are implemented to enhance the efficiency or to affect the dynamics of the hydraulic system. The advantages offered by the application of these devices are well known and their thermodynamic properties have been described well in the past. Yet the optimization of their particular performance re-garding fluid dynamics is an existing problem because of the lack of experimental and analytical investigation devices. Whilst operating hydraulic accumulators high dynamic flow rates and velocities including steep pressure gradients are oc-curring so that a special technique had to be created to detect these values. In the Fluid Power Laboratory of Trier University of Ap-plied Sciences a new self developed accumulator test rig re-cently was installed to measure the operating parameters of hy-draulic accumulators with the required high dynamic and accuracy. Special test procedures could be implemented to evaluate and improve especially the performance of the accu-mulators internal flow control valves. The experimental investigations were accompanied by modelling a hydraulic accumulator in a Computational Fluid Dynamic CFD environment where its internal flow phenomena could be simulated successfully. This presentation introduces the new test rig, the developed measuring procedures and the simulation model. Results of high dynamic flow and pressure measurements as well as flow simulations of hydraulic accumulators are shown.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

    Electron g-Factor Anisotropy in Symmetric (110)-oriented GaAs Quantum Wells

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    We demonstrate by spin quantum beat spectroscopy that in undoped symmetric (110)-oriented GaAs/AlGaAs single quantum wells even a symmetric spatial envelope wavefunction gives rise to an asymmetric in-plane electron Land\'e-g-factor. The anisotropy is neither a direct consequence of the asymmetric in-plane Dresselhaus splitting nor of the asymmetric Zeeman splitting of the hole bands but is a pure higher order effect that exists as well for diamond type lattices. The measurements for various well widths are very well described within 14 x 14 band k.p theory and illustrate that the electron spin is an excellent meter variable to map out the internal -otherwise hidden- symmetries in two dimensional systems. Fourth order perturbation theory yields an analytical expression for the strength of the g-factor anisotropy, providing a qualitative understanding of the observed effects

    Protease inhibitor 15, a candidate gene for abdominal aortic internal elastic lamina ruptures in the rat

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    The inbred Brown Norway (BN) rat develops spontaneous ruptures of the internal elastic lamina (RIEL) of the abdominal aorta (AA) and iliac arteries. Prior studies with crosses of the BN/Orl RJ (susceptible) and LOU/M (resistant) showed the presence of a significant QTL on chromosome 5 and the production of congenic rats proved the involvement of this locus. In this study, we further dissected the above-mentioned QTL by creating a new panel of LOU.BN(chr5) congenic and sub-congenic lines and reduced the locus to 5.2 Mb. Then 1002 HS rats were studied, whose phenotyping revealed a low prevalence and high variability for RIEL. High resolution mapping in the HS panel detected the major locus on chromosome 5 (log P>35) and refined it to 1.4Mb. Subsequently, RNA-seq analysis on AA of BN, congenics and LOU revealed expression differences for only protease inhibitor15 (Pi15) gene and a putative long intergenic noncoding RNA (lincRNA) within the linkage region. The high abundance of lincRNA with respect to reduced Pi15 expression, in conjunction with exertion of longitudinal strain, may be related to RIEL, indicating the potential importance of proteases in biological processes related to defective aortic IEL structure. Similar mechanisms may be involved in aneurysm initiation in the human AA

    Impact of etiology leading to abdominoperineal resection with anterolateral thigh flap reconstruction: A retrospective cohort study.

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    Large and deep perineal defects following abdominal perineal resection (APR) are a challenge for reconstructive surgeons. Even if generally performed for oncological reasons, APR can be indicated as well in extended infection-related debridement for Hidradenitis suppurativa, Fournier's gangrene, or Crohn's disease. We aimed to compare the outcomes of two groups of patients with different indications for APR (infectious vs. oncological) after pedicled anterolateral thigh (ALT) flap coverage RESULTS: Forty-four consecutive pedicled ALT flap used for coverage after APR in 40 patients were analyzed. Twenty-seven patients (67.5%) underwent APR for oncological reasons and 13 patients (32.5%) for infectious reasons. The overall postoperative complications rate was significantly higher for infectious cases (76.5% vs. 40.7%, p = 0.0304). Major complications occurred in 52.9% of infectious cases versus 11.1% of oncological cases (p = 0.0045). Obesity and infectious etiology were independent risk factors for overall and major complications, respectively. Patients undergoing APR for acute or chronic infections had significantly more overall and major complications than patients having oncological APR. Modified care might be considered, especially in obese patients, in terms of surgical debridement, antibiotic treatment modalities, and postoperative management

    Spin Fidelity for Three-qubit Greenberger-Horne-Zeilinger and W States Under Lorentz Transformations

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    Constructing the reduced density matrix for a system of three massive spin12-\frac{1}{2} particles described by a wave packet with Gaussian momentum distribution and a spin part in the form of GHZ or W state, the fidelity for the spin part of the system is investigated from the viewpoint of moving observers in the jargon of special relativity. Using a numerical approach, it turns out that by increasing the boost speed, the spin fidelity decreases and reaches to a non-zero asymptotic value that depends on the momentum distribution and the amount of momentum entanglement.Comment: 12pages, 2 figure

    The Aladin2 experiment: sensitivity study

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    Aladin2 is an experiment devoted to the first measurement of variations of Casimir energy in a rigid body. The main short-term scientific motivation relies on the possibility of the first demonstration of a phase transition influenced by vacuum fluctuations while, in the long term and in the mainframe of the cosmological constant problem, it can be regarded as the first step towards a measurement of the weight of vacuum energy. In this paper, after a presentation of the guiding principle of the measurement, the experimental apparatus and sensitivity studies on final cavities will be presented

    Numerical Analysis of an Overtopping Wave Energy Converter Subjected to the Incidence of Irregular and Regular Waves from Realistic Sea States

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    The present study aims to evaluate the difference in the fluid-dynamic behavior of an overtopping wave energy converter under the incidence of irregular waves based on a realistic sea state when compared to the incidence of regular waves, representative of this sea state. Thus, the sea data of three regions from the Rio Grande do Sul coast, Brazil, were considered. Fluent software was employed for the computational modeling, which is based on the finite volume method (FVM). The numerical generation of waves occurred through the imposition of the velocity boundary conditions using transient discrete values through the WaveMIMO methodology. The volume of fluid (VOF) multiphase model was applied to treat the water–air interaction. The results for the water amount accumulated in the device reservoir showed that the fluid-dynamic behavior of the overtopping converter has significant differences when comparing the two proposed approaches. Differences up to 240% were found for the water mass accumulated in the overtopping device reservoir, showing evidence that the results can be overestimated when the overtopping device is analyzed under the incidence of the representative regular waves. Furthermore, for all studied cases, it was possible to approximate the water volume accumulated over time in the overtopping reservoir through a first-degree polynomial function
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