Experimental characterization of friction coefficients at the tool-chip-workpiece interface in cutting: Evaluation of lubrication efficiency of mineral oil

Collaboration avec le LTDS/ENISEThe characterization of friction coefficients at the tool-chip-workpiece interface remains an issue. This paper presents a new experimental set-up able to simulate similar tribological phenomena as the ones occurring at the tool-chip-workpiece interface. Especially, this system aims to reach contact pressures up to 3 GPa and sliding velocities between 0 to 1000 m/min, and to obtain an open-tribosystem (continuous regeneration of the tool-workmaterial contact). This system has been applied to the characterization of the tool-chip-workpiece interface during the cutting of an AISI4142 treated steel with TiN coated tools. Two environments have been tested: dry cutting, lubrication with a basic mineral oil. The effect of the mineral oil has been investigated

Polynomials over the reals are safe for program interpretations

In the field of implicit computational complexity, we are con- sidering in this paper the fruitful branch of interpretation methods. Due to their good intensional properties, they have been widely developped. Among usual issues is the synthesis problem which has been solved by the use of Tarski's decision procedure, and consequently interpretations are usually chosen over the reals rather than over the integers. Doing so, one cannot use anymore the (good) properties of the natural (well-) ordering of N employed to bound the complexity of programs. We show that, actually, polynomials over the reals benefit from some properties that allows their safe use for complexity. We illustrate this by two char- acterizations, one of PTIME and one of PSPACE

On simulation in automata networks

An automata network is a finite graph where each node holds a state from some finite alphabet and is equipped with an update function that changes its state according to the configuration of neighboring states. More concisely, it is given by a finite map $f:Q^n\rightarrow Q^n$. In this paper we study how some (sets of) automata networks can be simulated by some other (set of) automata networks with prescribed update mode or interaction graph. Our contributions are the following. For non-Boolean alphabets and for any network size, there are intrinsically non-sequential transformations (i.e. that can not be obtained as composition of sequential updates of some network). Moreover there is no universal automaton network that can produce all non-bijective functions via compositions of asynchronous updates. On the other hand, we show that there are universal automata networks for sequential updates if one is allowed to use a larger alphabet and then use either projection onto or restriction to the original alphabet. We also characterize the set of functions that are generated by non-bijective sequential updates. Following Tchuente, we characterize the interaction graphs $D$ whose semigroup of transformations is the full semigroup of transformations on $Q^n$, and we show that they are the same if we force either sequential updates only, or all asynchronous updates

Minimum Mosaic Inference of a Set of Recombinants

International audienceIn this paper, we investigate the central problem of finding recombination events (Kececioglu & Gusfield 1998, Ukkonen 2002, Schwartz et al. 2002, Koivisto et al. 2004, Rastas & Ukkonen 2007, Wu & Gusfield 2007). It is commonly assumed that a present population is a descendent of a small number of specific sequences called founders. Due to recombination, a present sequence (called a recombinant ) is thus composed of blocks from the founders. A major question related to founder sequences is the so-called Minimum Mosaic problem: using the natural parsimony criterion for the number of recombinations, find the best founders. In this article, we prove that the Minimum Mosaic problem given haplotype recombinants with no missing values is hard for an unbounded number of founders and propose some exact exponential-time algorithms for the problem. Notice that, in (Rastas & Ukkonen 2007), Rastas et al. proved that the Minimum Mosaic problem is hard using a somewhat unrealistic mutation cost function (details provided afterwards). The aim of this paper is to provide a better complexity insight of the problem

Complexity Insights of the Minimum Duplication Problem

International audienceThe Minimum Duplication problem is a well-known problem in phylogenetics and comparative genomics. Given a set of gene trees, the Minimum Duplication problem asks for a species tree that induces the minimum number of gene duplications in the input gene trees. Recently, a variant of the Minimum Duplication problem, called Minimum Duplication Bi-partite, has been introduced, where the goal is to find all pre-duplications, that is duplications that in the evolution precede the first speciation with respect to a species tree. In this paper, we investigate the complexity of both Minimum Duplication and Minimum Duplication Bipartite. First of all, we prove that the Minimum Duplication problem is APX-hard, even when the input consists of five uniquely leaf-labelled gene trees (improving upon known results on the complexity of the problem). Then, we show that the Minimum Duplication Bipartite problem can be solved efficiently with a randomized algorithm when the input gene trees have bounded depth. An extended abstract of this paper appeared in SOFSEM 2012

Vaporization of bi-component droplets in a turbulent over-heated flow : Experiments and Numerical Simulation

This paper deals with an experimental study of bi-component droplets evaporation in a turbulent over-heated channel flow. Droplets are made of a mixture of n-octane and 3-pentanone (15% in volume). Planar Laser Induced Fluorescence (PLIF) of 3-pentanone is used to derive both concentration of this molecule in liquid and gas phases. Concomitant dispersion of the liquid droplets and evaporation can be clearly observed with a trend to homogenisation of the 3-pentanone vapour in the flowfield due to high turbulence rate, on the order of 40%. The experimental results, in term of concentration of 3-pentanone in both liquid and gas phases have been compared to a simplified numerical simulation based on the discrete component model, taking into account the droplet composition, associated to the isolated droplet model. It appears that the measurements performed on the liquid phase overestimate the calculated evaporation, as the gas phase measurements performed far from the injection point are in correct agreement with the calculations. One of the explanations is that the PLIF CCD camera dynamic is not sufficient to detect simultaneously the biggest and smallest droplets. In the present cases, most of the numerous smallest droplets seem to be ignored by the measurement, which tends to overestimate the droplet evaporation. The second important cause of discrepancy between experimental and numerical results is linked to the strong extinction of the fluorescence signal issuing from the liquid phase, due to the absorptio