1,721,037 research outputs found
ARES: A fast and accurate tool for the identification of plasma stationary points and separatrix
No full textIn this work, triangular C 1 interpolation based on Argyris element (AE) is used to develop the ARgyris element based searching (ARES) algorithm, an efficient tool for the accurate identification of stationary points (SPs), e.g. X-point, magnetic axis, snowflake point, etc and separatrix in magnetic confinement fusion application. AE-based interpolation allows the formulation of the nonlinear problem of SP identification on the triangle as a vectorial root-finding problem, addressed via different Newton-like algorithms. The proposed method is able to detect both first-order SP (e.g. X-points and magnetic axis, where the norm of the gradient vanishes) and second-order SP (e.g. snowflake points, where both the norm of the gradient and of the second derivatives vanishes). The separatrix is detected inside the triangles via the novel zero line searching algorithm, and is described by means of quintic spline interpolant of its components. Thanks to its modularity and efficiency, ARES is suitable to run on structured and unstructured triangular meshes, and can be readily integrated with any kind of Grad-Shafranov solver based on 2D triangular finite element method, or used for real-time SP and separatrix identification for control oriented purposes
Efficient FEM-BEM Coupling Based on Argyris Element for Axi-Symmetric Open Boundary Magnetostatic Problems
No full textThis article describes a novel and accurate implementation of finite element method-boundary element method (FEM-BEM) coupling based on Argyris element (AE), for the C1 solution of axi-symmetric magnetostatic problems in open boundary domains. The aim of the work is twofold: 1) to provide novel, easy, and accurate way to compute the basis functions that is strongly not affected by accuracy errors and 2) to give a clear mathematical and numerical description of the FEM-BEM coupling based on AE. The first goal is achieved by shifting to the origin the physical triangular elements and computing the basis function in the shifted coordinate system. Second, AE-based FEM-BEM coupling relies on the boundary integral equations (BIEs) for poloidal flux and its partial derivatives of both first and second order, accurately computed by combining the analytical formula based on elliptic integrals together with high degree Gaussian cubature. The application of the proposed method to an advanced plasma equilibrium magnetic configuration, typical of magnetic confinement fusion (MCF) (i.e., snowflake configuration), highlights that, even in case of coarse triangulation, satisfactory results can be achieved, and the error on the boundary conditions (BCs) is well below machine working precision
A Coupled FEM-BEM Approach for the Solution of the Free-Boundary Axi-Symmetric Plasma Equilibrium Problem
No full textIn this paper we present a coupled Finite Element Method - Boundary Element Method (FEM-BEM) approach for the solution of the free-boundary axi-symmetric plasma equilibrium problem. The proposed method, obtained from an improvement of the Hagenow-Lackner coupling method, allows to efficiently model the equilibrium problem in unbounded domains by discretizing only the plasma region; the external conductors can be modelled either as 2D or 3Dmodels, according to the problem of interest. The paper explores different iterative methods for the solution of the nonlinear Grad-Shafranov equation, such as Picard, Newton-Raphson and Newton-Krylov, in order to provide a robust and reliable tool, able to handle large-scale problems (e.g. high resolution equilibria). This method has been implemented in the FRIDA code (FReeboundary Integro-Differential Axisimmetric - https://github.om/matteobonotto/ FRIDA), together with a suitable Adaptive Integration Technique (AIT) for the computation of the source term. FRIDA has been successfully tested and validated against experimental data from RFX-mod device, and numerical equilibria of an ITER-like device
A Service Station Location Model to Explore Prospects and Policies for Alternative Transport Fuels: A Case of CNG Distribution in Italy
Full text linkCNG is an example of alternative gaseous fuel whose market development
requires supply infrastructure (pipelines), refuelling stations and alternative
vehicles to exist at the same time, which is known as the ‘‘chicken and egg
dilemma’’. In this chapter, a case study of limited or locally nonexistent market
development for CNG in an Italian frontier region is analyzed and a mixed integer
non linear programming model is introduced to evaluate the effect of incentive
measures envisaged by the regional government to foster refuelling station
development. It is found that, taking an entrepreneurs’ perspective of maximizing
profits, even with substantial capital grants investors are more likely to choose
higher demand areas, in spite of fiercer competition, rather than areas without
stations. Subsidies should be more specifically targeted to critical areas to be
efficient
CombiNeRF: A Combination of Regularization Techniques for Few-Shot Neural Radiance Field View Synthesis
Full text linkNeural Radiance Fields (NeRFs) have shown impressive results for novel view synthesis when a sufficiently large amount of views are available. When dealing with few-shot settings, i.e. with a small set of input views, the training could overfit those views, leading to artifacts and geometric and chromatic inconsistencies in the resulting rendering. Regularization is a valid solution that helps NeRF generalization. On the other hand, each of the most recent NeRF regularization techniques aim to mitigate a specific rendering problem. Starting from this observation, in this paper we propose CombiNeRF, a framework that synergically combines several regularization techniques, some of them novel, in order to unify the benefits of each. In particular, we regularize single and neighboring rays distributions and we add a smoothness term to regularize near geometries. After these geometric approaches, we propose to exploit Lipschitz regularization to both NeRF density and color networks and to use encoding masks for input features regularization. We show that CombiNeRF outperforms the state-of-the-art methods with few-shot settings in several publicly available datasets. We also present an ablation study on the LLFF and NeRF-Synthetic datasets that support the choices made. We release with this paper the open-source implementation of our framework
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Sensitivity analysis of low-order plasma moments reconstruction for RFX-mod2 tokamak operations
No full textThe reconstruction of total plasma current and plasma centroid position from low-order moments of toroidal current density is presented for RFX-mod2 shaped tokamak equilibria. DEMO-like shape conditions and negative triangularity plasmas are considered in the analysis. The impact of a single sensor failure on the reconstruction is investigated by performing a sensitivity analysis at each possible poloidal position of the faulty sensor. The effects of using mono-axial or bi-axial sensors are also quantified. The minimum number of sensors necessary to estimate both the total plasma current and the centroid position within a certain level of accuracy has been assessed for the wide plasma shape conditions of the considered equilibria
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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