Analyse du processus d'élaboration d'un projet de simulation

International audienceNous présentons dans cet article une étude orientée sur l'analyse du processus d'élaboration d'un projet de simulation de système de production. Après avoir présenté un état de l'art traitant de cette problématique, nous détaillons le cadre d'élaboration d'un processus de simulation à travers la présentation des différentes étapes le constituant ainsi que celle des délivrables qui lui sont associés. Nous donnons ainsi la vision que nous avons de ce processus. L'accent est en particulier mis sur le rôle déterminant de la première étape qui vise à identifier et caractériser le besoin à l'origine du projet de simulation, généralement un problème à résoudre, et à évaluer la capacité de l'outil de simulation à évènements discrets à répondre efficacement à ce besoin. Nous proposons ensuite une classification des outils de simulation actuellement présents sur le marché en fonction de l'approche de modélisation utilisée, à savoir les outils orientés " fonction " ou " processus " et les outils orientés " composant " ou " objet ". Ainsi, après une description assez brève de ces approches de modélisation, nous présentons certains des avantages et des inconvénients de chaque type d'outil par rapport à un point de vue de l'utilisateur potentiel

dartR v2: An accessible genetic analysis platform for conservation, ecology and agriculture

Innumerable approaches to analyse genetic data are now available to guide conservation, ecological and agricultural projects. However, streamlined and accessible tools are needed to bring these approaches within the reach of a broader user base. dartR was released in 2018 to lessen the intrinsic complexity of analysing single nucleotide polymorphisms (SNPs) and dominant markers (presence/absence of amplified sequence tags) by providing user-friendly data quality control and marker selection functions. dartR users have grown steadily since its release and provided valuable feedback on their interaction with the package allowing us to enhance dartR capabilities. Here, we present Version 2 of dartR. In this version, we substantially increased the number of available functions from 45 to 144. In addition to improved functionality, we focused on enhancing the user experience by extending plot customisation, function standardisation, increasing user support and function speed. dartR provides functions for various stages in analysing genetic data, from data manipulation to reporting. dartR provides many functions for importing, exporting and linking to other packages, to provide an easy-to-navigate conduit between data generation and analysis options already available via other packages. We also implemented simulation functions whose results can be analysed seamlessly with several other dartR functions. As more methods and approaches mature to inform conservation, we envision that accessible platforms to analyse genetic data will play a crucial role in translating science into practice

A note on cluster methods for strongly correlated electron systems

We develop, clarify and test various aspects of cluster methods dynamical mean field methods using a soluble toy model as a benchmark. We find that the Cellular Dynamical Mean Field Theory (C-DMFT) converges very rapidly and compare its convergence properties with those of the Dynamical Cluster Approximation (DCA). We propose and test improved estimators for the lattice self energy within C-DMFT.Comment: 5 pages, 3 figures; major change

L'amélioration du zébu malgache : création d'une race à viande par métissage

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Quantum phase transitions in the Bose-Fermi Kondo model

We study quantum phase transitions in the Bose-Fermi Kondo problem, where a local spin is coupled to independent bosonic and fermionic degrees of freedom. Applying a second order expansion in the anomalous dimension of the Bose field we analyze the various non-trivial fixed points of this model. We show that anisotropy in the couplings is relevant at the SU(2) invariant non Fermi liquid fixed points studied earlier and thus the quantum phase transition is usually governed by XY or Ising-type fixed points. We furthermore derive an exact result that relates the anomalous exponent of the Bose field to that of the susceptibility at any finite coupling fixed point. Implications on the dynamical mean field approach to locally quantum critical phase transitions are also discussed.Comment: 13 pages, 9 figures, some references added/correcte

Quantum impurity solvers using a slave rotor representation

We introduce a representation of electron operators as a product of a spin-carry ing fermion and of a phase variable dual to the total charge (slave quantum rotor). Based on this representation, a new method is proposed for solving multi-orbital Anderson quantum impurity models at finite interaction strength U. It consists in a set of coupled integral equations for the auxiliary field Green's functions, which can be derived from a controlled saddle-point in the limit of a large number of field components. In contrast to some finite-U extensions of the non-crossing approximation, the new method provides a smooth interpolation between the atomic limit and the weak-coupling limit, and does not display violation of causality at low-frequency. We demonstrate that this impurity solver can be applied in the context of Dynamical Mean-Field Theory, at or close to half-filling. Good agreement with established results on the Mott transition is found, and large values of the orbital degeneracy can be investigated at low computational cost.Comment: 18 pages, 15 figure

Ferromagnetic transition in a double-exchange system

We study ferromagnetic transition in three-dimensional double-exchange model. The influence of strong spin fluctuations on conduction electrons is described in coherent potential approximation. In the framework of thermodynamic approach we construct for the system "electrons (in a disordered spin configuration) + spins" the Landau functional, from the analysis of which critical temperature of ferromagnetic transition is calculated.Comment: 4 pages, 1 eps figure, LaTeX2e, RevTeX. References added, text change