Showing papers by "Mines ParisTech published in 2001"

Segmentation of vessel-like patterns using mathematical morphology and curvature evaluation

Abstract: This paper presents an algorithm based on mathematical morphology and curvature evaluation for the detection of vessel-like patterns in a noisy environment. Such patterns are very common in medical images. Vessel detection is interesting for the computation of parameters related to blood flow. Its tree-like geometry makes it a usable feature for registration between images that can be of a different nature. In order to define vessel-like patterns, segmentation is performed with respect to a precise model. We define a vessel as a bright pattern, piece-wise connected, and locally linear, mathematical morphology is very well adapted to this description, however other patterns fit such a morphological description. In order to differentiate vessels from analogous background patterns, a cross-curvature evaluation is performed. They are separated out as they have a specific Gaussian-like profile whose curvature varies smoothly along the vessel. The detection algorithm that derives directly from this modeling is based on four steps: (1) noise reduction; (2) linear pattern with Gaussian-like profile improvement; (3) cross-curvature evaluation; (4) linear filtering. We present its theoretical background and illustrate it on real images of various natures, then evaluate its robustness and its accuracy with respect to noise.

Towards Design Theory and Expandable Rationality: The Unfinished Program of Herbert Simon

Abstract: It is said that Herbert Simon would have described himself as follows : «I am a monomaniac. What I am a monomaniac about is decision making ». In spite of its shares of legend and humour, this self-portrait deeply reflects the main logic of Herbert Simon’s works. From his early papers on administrative behaviour to his last investigations on thought and learning, Simon kept a same goal : to explain complex and mysterious human behaviour by simple and constrained, yet informed, decision rules. « Bounded rationality » was the name he gave to a research orientation wich rejected the maximizing behaviour assumed by classic economics. But beyond this critical aim, Simon attempted to build an empirically grounded theory of human problem solving. A theory that was intended to settle the foundation stone of « behavioural economics ».

Plastic potentials for anisotropic porous solids

Abstract: The aim of this paper is to incorporate plastic anisotropy into constitutive equations of porous ductile metals. It is shown that plastic anisotropy of the matrix surrounding the voids in a ductile material could have an influence on both effective stress–strain relation and damage evolution. Two theoretical frameworks are envisageable to study the influence of plastic flow anisotropy: continuum thermodynamics and micromechanics. By going through the Rousselier thermodynamical formulation, one can account for the overall plastic anisotropy, in a very simple manner. However, since this model is based on a weak coupling between plasticity and damage dissipative processes, it does not predict any influence of plastic anisotropy on cavity growth, unless a more suitable choice of the thermodynamical force associated with the damage parameter is made. Micromechanically-based models are then proposed. They consist of extending the famous Gurson model for spherical and cylindrical voids to the case of an orthotropic material. We derive an upper bound of the yield surface of a hollow sphere, or a hollow cylinder, made of a perfectly plastic matrix obeying the Hill criterion. The main findings are related to the so-called ‘scalar effect’ and ‘directional effect’. First, the effect of plastic flow anisotropy on the spherical term of the plastic potential is quantified. This allows a classification of sheet materials with regard to the anisotropy factor h ; this is the scalar effect. A second feature of the model is the plasticity-induced damage anisotropy. This results in directionality of fracture properties (‘directional effect’). The latter is mainly due to the principal Hill coefficients whilst the scalar effect is enhanced by ‘shear’ Hill coefficients. Results are compared to some micromechanical calculations using the finite element method.

Ultra-fast aliasing analysis using CLA: a million lines of C code in a second

Abstract: We describe the design and implementation of a system for very fast points-to analysis. On code bases of about million lines of unpreprocessed C code, our system performs field-based Andersen-style points-to analysis in less than a second and uses less than 10MB of memory. Our two main contributions are a database-centric analysis architecture called compile-link-analyze (CLA), and a new algorithm for implementing dynamic transitive closure. Our points-to analysis system is built into a forward data-dependence analysis tool that is deployed within Lucent to help with consistent type modifications to large legacy C code bases.

A “Logic-Constrained” Knapsack Formulation and a Tabu Algorithm for the Daily Photograph Scheduling of an Earth Observation Satellite

Abstract: The daily photograph scheduling problem of earth observation satellites such as Spot 5 consists of scheduling a subset of mono or stereo photographs from a given set of candidates to different cameras. The scheduling must maximize a profit function while satisfying a large number of constraints. In this paper, we first present a formulation of the problem as a generalized version of the well-known knapsack model, which includes large numbers of binary and ternary “logical” constraints. We then develop a tabu search algorithm which integrates some important features including an efficient neighborhood, a dynamic tabu tenure mechanism, techniques for constraint handling, intensification and diversification. Extensive experiments on a set of large and realistic benchmark instances show the effectiveness of this approach.

Common‐angle migration: A strategy for imaging complex media

Abstract: Complex velocity models characterized by strong lateral variations are certainly a great motivation, but also a great challenge, for depth imaging. In this context, some unexpected results can occur when using depth imaging algorithms. In general, after a common shot or common offset migration, the resulting depth images are sorted into common‐image gathers (CIG), for further processing such as migration‐based velocity analysis or amplitude‐variation‐with‐offset analysis. In this paper, we show that CIGs calculated by common‐shot or common‐offset migration can be strongly affected by artifacts, even when a correct velocity model is used for the migration. The CIGs are simply not flat, due to unexpected curved events (kinematic artifacts) and strong lateral variations of the amplitude (dynamic artifacts). Kinematic artifacts do not depend on the migration algorithm provided it can take into account lateral variations of the velocity model. This can be observed when migrating the 2‐D Marmousi dataset either with a wave‐equation migration or with a multivalued Kirchhoff migration/inversion. On the contrary, dynamic artifacts are specific to multi‐arrival ray‐based migration/inversion. This approach, which should provide a quantitative estimation of the reflectivity of the model, provides in this context dramatic results. In this paper, we propose an analysis of these artifacts through the study of the ray‐based migration/inversion operator. The artifacts appear when migrating a single‐fold subdata set with multivalued ray fields. They are due to the ambiguous focusing of individual reflected events at different locations in the image. No information is a priori available in the single‐fold data set for selecting the focusing position, while migration of multifold data would provide this information and remove the artifacts by the stack of the CIGs. Analysis of the migration/inversion operator provides a physical condition, the imaging condition, for insuring artifact free CIGs. The specific cases of common‐shot and common‐offset single‐fold gathers are studied. It appears clearly that the imaging condition generally breaks down in complex velocity models for both these configurations. For artifact free CIGs, we propose a novel strategy: compute CIGs versus the diffracting/reflecting angle. Working in the angle domain seems the natural way for unfolding multivalued ray fields, and it can be demonstrated theoretically and practically that common‐angle imaging satisfies the imaging condition in the great majority of cases. Practically, the sorting into angle gathers can not be done a priori over the data set, but is done in the inner depth migration loop. Depth‐migrated images are obtained for each angle range. A canonical example is used for illustrating the theoretical derivations. Finally, an application to the Marmousi model is presented, demonstrating the relevance of the approach.

Demand-driven pointer analysis

Abstract: Known algorithms for pointer analysis are “global” in the sense that they perform an exhaustive analysis of a program or program component In this paper we introduce a demand-driven approach for pointer analysis Specifically, we describe a demand-driven flow-insensitive, subset-based, con text-insensitive points-to analysis Given a list of pointer variables (a query), our analysis performs just enough computation to determine the points-to sets for these query variables Using deductive reachability formulations of both the exhaustive and the demand-driven analyses, we prove that our algorithm is correct We also show that our analysis is optimal in the sense that it does not do more work than necessary We illustrate the feasibility and efficiency of our analysis with an implementation of demand-driven points-to analysis for computing the call-graphs of C programs with function pointers The performance of our system varies substantially across benchmarks - the main factor is how much of the points-to graph must be computed to determine the call-graph For some benchmarks, only a small part of the points-to graph is needed (eg pouray emacs and gcc), and here we see more than a 10x speedup For other benchmarks (eg burlap and gimp), we need to compute most (> 95%) of the points-to graph, and here the demand-driven algorithm is considerably slower, because using the demand-driven algorithm is a slow method of computing the full points-to graph

Morphological operators on the unit circle

Abstract: Images encoding angular information are common in image analysis. Examples include the hue band of color images, or images encoding directional texture information. Applying mathematical morphology to image data distributed on the unit circle is not immediately possible, as the unit circle is not a lattice. Three approaches to solving this problem are presented. First, difference-based operators are studied (e.g., gradient, top-hat). Second, a definition of grouped circular data is suggested, and "pseudo" morphological operators, which operate only on grouped data, are introduced. Finally, processing using pixel labeling is presented, leading to the development of a cyclic opening operator. Applications for treating the hue band of color images and for finding perturbations in wood texture are given.

Metal Forming Analysis

Abstract: 1. Mathematical background 2. Introduction to the finite element method 3. Finite elements for large deformation 4. Typical finite elements 5. Classification of finite element formulations 6. Auxiliary equations: contact, friction, incompressibility 7. Thermo-mechanical principles 8. Sheet metal formability tests 9. Steady state forming problems 10. Forging analysis 11. Sheet forming analysis 12. Recent research topics.

Asymptotic stabilization via output feedback for lower triangular systems with output dependent incremental rate

Abstract: We study the global asymptotic stabilization by output feedback for systems whose dynamics are in a feedback form where the nonlinear terms admit an incremental rate depending only on the measured output. The output feedback we consider is of the observer-controller type where the design of the controller follows from standard robust backstepping. As far as we know, the novelty is in the observer which is high-gain like with a gain coming from a Riccatti equation.

The Two Pillars of New Management Research

Abstract: Ken Starkey and Paula Madan’s report, Bridging the Relevance Gap (2001), advocates the development of collaborative networks between academics and organizations. Drawing on similar experiences, this article discusses two essential conditions of such programmes: a clarification of the scientific object of management research, and the design of research-oriented partnerships. The scientific identity of management research should be distinguished from other social sciences: management sciences do not study economic or social facts, but ‘models of collective action’ which are then perceived and judged conventionally and historically as ‘economic or social phenomena’. Therefore, the essence and universality of management research is in understanding, criticizing and inventing ‘models of collective action’. In management research, as in other design sciences, the classical laboratory and field models of research are important. However, a third model of research based on partnerships is required, where knowledge does not transcend action but is integral to it. Yet research is not simply ‘doing better’ and requires theoretical and empirical control. Hence, the design of ‘research oriented partnerships’ is a crucial key of new management research. Inspired by existing experiences, the research community could lay down the rules and commitments expected from academics and companies in research-oriented partnerships. Resting on these two pillars, research could contribute to the invention of new models of collective action adapted to contemporary issues and values and reduce misleading mimetic behaviour, blind compliance to gurus or fashion in management practice.

Rheological behavior of controlled‐rheology polypropylenes obtained by peroxide‐promoted degradation during extrusion: Comparison between homopolymer and copolymer

Abstract: In the present work, experimental studies of the free-radical-initiated molecular weight degradation of polypropylene in a modular self-wiping corotating twin-screw extruder are investigated. The control of the molecular weight distribution of polypropylene resins by peroxide degradation is widely used in the polymer industry. It allows one to adjust the viscosity of these resins to the level required for processing applications. The purpose of this work was to characterize the influence of peroxide degradation on the rheological behavior of a polypropylene homopolymer and a block polypropylene/polyethylene copolymer, which includes an addition of a low percentage of polyethylene (around 7%). The homopolymer exhibits a classical behavior: When the peroxide amount is increased, we observe a decrease in the viscosity corresponding to a decreasing molecular weight and a pronounced shift toward more Newtonian behavior. The rheological behavior of the copolymer is influenced by the presence of the polyethylene phase which greatly modifies the viscoelastic properties and increases the viscosity when the polypropylene matrix is highly degraded.

Instantiating and detecting design patterns: putting bits and pieces together

Abstract: Design patterns ease the designing, understanding, and re-engineering of software. Achieving a well-designed piece of software requires a deep understanding and a good practice of design patterns. Understanding existing software relies on the ability to identify architectural forms resulting from the implementation of design patterns. Maintaining software involves spotting places that can be improved by using better design decisions, like those advocated by design patterns. Nevertheless, there is a lack of tools automatizing the use of design patterns to achieve well-designed pieces of software, to identify recurrent architectural forms, and to maintain software. We present a set of tools and techniques to help OO software practitioners design, understand, and re-engineer a piece of software using design-patterns. A first prototype tool, PATTERNS-BOX, provides assistance in designing the architecture of a new piece of software, while a second prototype tool, PTIDEJ, identifies design patterns used in an existing one. These tools, in combination, support maintenance by highlighting defects in an existing design, and by suggesting and applying corrections based on widely-accepted design pattern solutions.

Flatness of Heavy Chain Systems

Abstract: In this paper the flatness [M. Fliess, J. Levine, P. Martin, and P. Rouchon, Internat. J. Control, 61 (1995), pp. 1327--1361, M. Fliess, J. Levine, P. Martin, and P. Rouchon, IEEE Trans. Automat. Control, 44 (1999), pp. 922--937] of heavy chain systems, i.e., trolleys carrying a fixed length heavy chain that may carry a load, is addressed in the partial derivatives equations framework. We parameterize the system trajectories by the trajectories of its free end and solve the motion planning problem, namely, steering from one state to another state. When considered as a finite set of small pendulums, these systems were shown to be flat [R. M. Murray, in Proceedings of the IFAC World Congress, San Francisco, CA, 1996, pp. 395--400]. Our study is an extension to the infinite dimensional case. Under small angle approximations, these heavy chain systems are described by a one-dimensional (1D) partial differential wave equation. Dealing with this infinite dimensional description, we show how to get the explicit parameterization of the chain trajectory using (distributed and punctual) advances and delays of its free end. This parameterization results from symbolic computations. Replacing the time derivative by the Laplace variable $s$ yields a second order differential equation in the spatial variable where s is a parameter. Its fundamental solution is, for each point considered along the chain, an entire function of s of exponential type. Moreover, for each, we show that, thanks to the Liouville transformation, this solution satisfies, modulo explicitly computable exponentials of s, the assumptions of the Paley--Wiener theorem. This solution is, in fact, the transfer function from the flat output (the position of the free end of the system) to the whole state of the system. Using an inverse Laplace transform, we end up with an explicit motion planning formula involving both distributed and punctual advances and delays operators.

Strengthening of silica gels and aerogels by washing and aging processes

Abstract: Gels were prepared from a polyethoxydisiloxane precursor by using HF as a catalyst. During washing in water solution a significant increase in the permeability of the gels was observed, showing that dissolution-reprecipitation occurs. After washing, the gels were further soaked in a solution of polyethoxydisiloxane precursor to strengthen and stiffen the gel. As expected, a significant enhancement of the mechanical properties of the wet gels was observed. It is also interesting to note, however, that the permeability does not decrease below the value for the as-prepared gels. Hence, a promising process has been developed where both the stiffness and the strength have been increased as well as the permeability. The increase in permeability is of importance to facilitate the supercritical drying process. Reasonably successful scaling up of the supercritical drying of these gels to laboratory scale has been achieved, and monolithic and transparent gels are obtained. Optical properties have been measured on laboratory scale aerogels. The corresponding results have been correlated with structural characteristics measured by small-angle X-ray scattering (SAXS).