Mines ParisTech

About: Mines ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Microstructure. The organization has 6564 authors who have published 11676 publications receiving 359898 citations. The organization is also known as: École nationale supérieure des mines de Paris & École des mines de Paris.

Topology Optimization of Heat and Mass Transfer Problems: Laminar Flow

Abstract: The design of efficient structures for heat and mass transfer problems involves the implementation of an appropriate topology optimization strategy in order to fully take into account the bi-objective nature of the problem. This article couples the finite-volume method (FVM), for the direct solver, with the discrete adjoint approach, for the sensitivity analysis, in order to tackle both fluid dynamic and heat transfer optimization in the frame of laminar flows. Details are provided about the sparsity pattern of the discrete adjoint system, which requires special attention to select a suitable matrix iterative solver. Several examples underline the adequacy of topology optimization in conjunction with the FVM for the minimization of the power dissipated by the fluid. Then, a bi-objective problem aiming at minimizing the pressure drop while maximizing the recoverable thermal power is solved by the identification of its Pareto frontier, thanks to an aggregate objective function (AOF) method. The main conclus...

Minimal and Optimal Computations of Recursive Programs

Abstract: Procedure call mechanisms have mainly been studied in the framework of recursive programs without assignments, for the simplicity of their operational and denotational semantics (See Scott [16], Nivat [14], Vuillemin [17]). According to operational semantics, procedure calls act as textual rewritings ; "computation rules" select at each computation step the occurrences of unknown functions to be rewritten. A computation rule is called correct if the value it computes is the one given by the denotational semantics. Correctness and efficiency of computation rules have been studied in Vuillemin [17,18], Montangero-Pacini-Turini [13], Downey-Sethi [7]. The main results are well-known: innermost evaluation (call by value) is not correct, parallel outermost or full substitution are correct. Vuillemin [17,18] gives a sufficient condition for a rule to be correct, (safety), later extended by Downey-Sethi [7] into a necessary and sufficient one (security). Vuillemin also studies particular implementation of call-by-name, the delay rule ; he shows its optimality with respect to a reasonable implementation cost, provided interpretations satisfy a sequentiality condition. This result is in fact twofold : sequentiality allows elimination of useless steps, and optimality follows by using sharing mechanisms in term implementation. The basis of all these studies is the following theorem (Vuillemin [17,18]) : provided some restrictive conditions on programs are satisfied, the set of terms derivable from a given term is a lattice under the derivation ordering. Our aim is to extend these results, for the three following reasons : first, though every program can be transformed to match Vuillemin's conditions, the transformations may affect the costs of computations : a more direct proof can be investigated. Second, a direct generalization to the e-calculus is not straightforward, since e-terms definitely do not form lattices. Third, the symbolic (or Herbrand) interpretation [5] is not sequential in the sense of Vuillemin, and no optimality result is known for it. Our point of view will be purely syntactic : we reconstruct the lattice property in derivations. We study minimal computations (i.e. finite or infinite derivations)in the symbolic interpretation, and transform them into optimal ones. Eventually, we characterize interpretations to which similar results apply. Extension towards the e-calculus is done in [10]. The lattice property of terms breaks down in general : two very different derivations may lead to the same term by syntactical accidents, which collapse two a priori different terms. In section I, we take care of this fact by introducing an equivalence and a preorder on derivations. We give three characterizations of these relations. For the main one, we extend the classical notion of residuals [4] by defining residuals of derivations by derivations. We show that derivation classes form a lattice. In section II, we study the "simple derivations" defined by Vuillemin with use of labels (named here complete derivations). We give two characterizations of them in the usual formalism. Section III, is devoted to minimality and optimality results. Ordering infinite derivations as well as finite one, we construct least computations of every syntactic approximation of the infinite tree determined by the program. The associated complete derivation are optimal with respect to Vuillemin's cost. Extension to interpretations is then straightforward, as soon as they satisfy a syntactic condition. All classes of sequential interpretations considered in [2,6,11,17] do satisfy this condition. The "computation rule" we use for constructing the optimal computations is very inefficient in general, but reduces to the usual delay rules in sequential interpretations.

Public perceptions and governance of controversial technologies to tackle climate change: nuclear power, carbon capture and storage, wind, and geoengineering

Abstract: The role carbon emissions play in contributing to climate change makes clear the necessity for a global reconsideration of current modes of energy production. In recent years, as concerns over the threats of climate change (CC) have become more acute, four technologies have notably risen to the forefront of academic and public discourse: nuclear power, carbon capture and storage (CCS), wind power, and geoengineering. The particular interest of these four approaches lies in the fact that they reflect both energy production and climate control technologies, are often socially controversial, and present complex challenges of governance. Nuclear and wind power both deserve an important place among the variety of low-carbon energy options. In countries where public acceptance is evaluated, although, support for nuclear energy appears to be conditional upon simultaneous development of other renewable energies alongside a feasible plan to address the disposal of nuclear waste. The Fukushima accident sharply increased public concern about the safety and vulnerability of nuclear reactors. While wind power receives general public support, issues of accommodation can arise when it comes to siting wind farms. Persistent dependency upon carbon-producing energy has made favorable the option of CCS. However, in addition to technical and geological factors, social resistance to the placement of carbon storage units remains a key obstacle. Geoengineering offers the technological capacity to directly act on the climate should levels of atmospheric CO2 become dangerously high. Public perception regarding the risk of climate change can be labile, and the alternatives reviewed here share the characteristic that their technical and political dimensions are intertwined. The variety of options for combining and implementing these technologies, coupled with the inherently time-sensitive nature of CC, underscore the complexity of the endeavor. In order to bridge these various levels of analysis and decision making, and to better understand and integrate people's involvement, exercises in risk governance could be developed at both the national and international levels. WIREs Clim Change 2011 2 712–727 DOI: 10.1002/wcc.134 This article is categorized under: Perceptions, Behavior, and Communication of Climate Change > Social Amplification/Attenuation of Climate Risks The Carbon Economy and Climate Mitigation > Policies, Instruments, Lifestyles, Behavior

Solving geometric constraints by homotopy

Abstract: Numerous methods have been proposed in order to solve geometric constraints, all of them having their own advantages and drawbacks. In this article, we propose an enhancement to the classical numerical methods, which, up to now, are the only ones that apply to the general case.