Search results for "fluids"

Fundamentals of metastability exchange optical pumping in helium

2010

21 pages; International audience; Advances in metastability exchange optical pumping (MEOP) at high laser powers, but also at high gas pressures and high magnetic field strengths, has provided strong motivation for revisiting the understanding of the limitations of this powerful technique. A comprehensive model has been developped for improved description of the combined effects of OP, ME, and relaxation, and of detailed MEOP features observed over the broad range of operating conditions. A brief description is provided, with illustrative comparisons of computed and experimental results. This improved tool is used to explain the excellent photon efficiency of OP obtained at all field streng…

In search for a canonical design ABL stability class for wind farm turbines

2016

Production as well as loading of wake exposed wind turbines is known to depend significantly on stability of the Atmospheric Boundary Layer (ABL), which adds a new dimension to design of wind farm turbines. Adding this new aspect in wind turbine design makes the number of design cycle computations to blow up with a factor equal to the number of representative stability bin classes. The research question to be answered in this paper is: Can an ABL stability probability distribution in a meaningful way be collapsed into a representative design stability class as based on a (predefined) confidence level.

The strange case of Paul Appell's last memoir on Monge's problem: "sur les déblais et remblais"

2016

International audience; We analyze a case of plagiarism that appears in a work published in 1928 by Paul Appell (1855–1930) in the collection Mémorial des sciences mathématiques. Appell's memoir entitled Le problème géométrique des déblais et remblais contains a verbatim copy of several pages from a memoir published in 1886 by Albert de Saint-Germain (1839–1914). By tracing back Appell's last years, we have found historical evidences that might cast a shadow of doubt on Appell's full responsibility by the plagiarism that appeared under his name.

Molecular ND Band Spectroscopy in the Divertor Region of Nitrogen Seeded JET Discharges

2018

In this contribution we present OES measurements in the JET tokamak of the deuterated NH (ND) radical and the correlation between results of those experiments and measurement of ammonia production. The observation region covers most of the divertor and its outer throat. Measurements are performed in different magnetic configurations. The results include temporal and spatial dependence of the molecular emission intensity and study of the emission band shape (vibrational and rotational temperatures) during different JET pulses, with or without nitrogen seeding. Results are a step towards the understanding of nitrogen-containing molecule creation and destruction in the divertor plasma. For com…

Toward a scientific and personal biography of Tullio Levi-Civita (1873–1941)

2005

International audience; Tullio Levi-Civita was one of the most important Italian mathematicians in the early part of the 20th century, contributing significantly to a number of research fields in mathematics and physics. In addition, he was involved in the social and political life of his time and suffered severe political and racial persecution during the period of Fascism. He tried repeatedly and in several cases successfully to help colleagues and students who were victims of anti-Semitism in Italy and Germany. His scientific and private life is well documented in the letters and documents contained in his Archive. The authors' aim is to illustrate the events of his life by means of his …

Parametric thermal analysis for the optimization of Double Walled Tubes layout in the Water Cooled Lithium Lead inboard blanket of DEMO fusion reactor

2019

Abstract Within the roadmap that will lead to the nuclear fusion exploitation for electric energy generation, the construction of a DEMOnstration (DEMO) reactor is, probably, the most important milestone to be reached since it will demonstrate the technological feasibility and economic competitiveness of an industrial-scale nuclear fusion reactor. In order to reach this goal, several European universities and research centres have joined their efforts in the EUROfusion action, funded by HORIZON 2020 UE programme. Within the framework of EUROfusion research activities, ENEA and University of Palermo are involved in the design of the Water-Cooled Lithium Lead Breeding Blanket (WCLL BB), that …

Dry deposition models for radionuclides dispersed in air: a new approach for deposition velocity evaluation schema

2017

In the framework of a National Research Program funded by the Italian Minister of Economic Development, the Department of Energy, Information Engineering and Mathematical Models (DEIM) of Palermo University and ENEA Research Centre of Bologna, Italy is performing several research activities to study physical models and mathematical approaches aimed at investigating dry deposition mechanisms of radioactive pollutants. On the basis of such studies, a new approach to evaluate the dry deposition velocity for particles is proposed. Comparisons with literature experimental data show that the proposed dry deposition scheme allows to capture the main phenomena involved in the dry deposition process…

Medium fidelity modelling of loads in wind farms under non-neutral ABL stability conditions – a full-scale validation study

2017

An accurate optical technique for measuring the nuclear polarisation of 3He gas

2010

12 pages; International audience; In the metastability exchange optical pumping cells of our on-site production unit and of our other experimental set-ups, we use a light absorption technique to measure the 3He nuclear polarisation. It involves weak probe beams at 1083 nm, that are either perpendicular or parallel to the magnetic field and cell axis, with suitable light polarisations. When metastability exchange collisions control the populations of the sublevels in the 23S state, absolute values of the 3He ground state nuclear polarisation are directly inferred from the ratio of the absorption rates measured for these probe beams. Our report focuses on the transverse detection scheme for w…

Generalized Camassa-Holm Equations: Symmetry, Conservation Laws and Regular Pulse and Front Solutions

2021

In this paper, we consider a member of an integrable family of generalized Camassa–Holm (GCH) equations. We make an analysis of the point Lie symmetries of these equations by using the Lie method of infinitesimals. We derive nonclassical symmetries and we find new symmetries via the nonclassical method, which cannot be obtained by Lie symmetry method. We employ the multiplier method to construct conservation laws for this family of GCH equations. Using the conservation laws of the underlying equation, double reduction is also constructed. Finally, we investigate traveling waves of the GCH equations. We derive convergent series solutions both for the homoclinic and heteroclinic orbits of the…