Showing papers by "French Institute for Research in Computer Science and Automation published in 1997"

The complete genome sequence of the Gram-positive bacterium Bacillus subtilis

Abstract: Bacillus subtilis is the best-characterized member of the Gram-positive bacteria. Its genome of 4,214,810 base pairs comprises 4,100 protein-coding genes. Of these protein-coding genes, 53% are represented once, while a quarter of the genome corresponds to several gene families that have been greatly expanded by gene duplication, the largest family containing 77 putative ATP-binding transport proteins. In addition, a large proportion of the genetic capacity is devoted to the utilization of a variety of carbon sources, including many plant-derived molecules. The identification of five signal peptidase genes, as well as several genes for components of the secretion apparatus, is important given the capacity of Bacillus strains to secrete large amounts of industrially important enzymes. Many of the genes are involved in the synthesis of secondary metabolites, including antibiotics, that are more typically associated with Streptomyces species. The genome contains at least ten prophages or remnants of prophages, indicating that bacteriophage infection has played an important evolutionary role in horizontal gene transfer, in particular in the propagation of bacterial pathogenesis.

Multiobjective output-feedback control via LMI optimization

Abstract: This paper presents an overview of a linear matrix inequality (LMI) approach to the multiobjective synthesis of linear output-feedback controllers. The design objectives can be a mix of H/sub /spl infin// performance, H/sub 2/ performance, passivity, asymptotic disturbance rejection, time-domain constraints, and constraints on the closed-loop pole location. In addition, these objectives can be specified on different channels of the closed-loop system. When all objectives are formulated in terms of a common Lyapunov function, controller design amounts to solving a system of linear matrix inequalities. The validity of this approach is illustrated by a realistic design example.

Querying Semi-Structured Data

Abstract: The amount of data of all kinds available electronically has increased dramatically in recent years. The data resides in different forms, ranging from unstructured data in the systems to highly structured in relational database systems. Data is accessible through a variety of interfaces including Web browsers, database query languages, application-specic interfaces, or data exchange formats. Some of this data is raw data, e.g., images or sound. Some of it has structure even if the structure is often implicit, and not as rigid or regular as that found in standard database systems. Sometimes the structure exists but has to be extracted from the data. Sometimes also it exists but we prefer to ignore it for certain purposes such as browsing. We call here semi-structured data this data that is (from a particular viewpoint) neither raw data nor strictly typed, i.e., not table-oriented as in a relational model or sorted-graph as in object databases. As will seen later when the notion of semi-structured data is more precisely de ned, the need for semi-structured data arises naturally in the context of data integration, even when the data sources are themselves well-structured. Although data integration is an old topic, the need to integrate a wider variety of data- formats (e.g., SGML or ASN.1 data) and data found on the Web has brought the topic of semi-structured data to the forefront of research. The main purpose of the paper is to isolate the essential aspects of semi- structured data. We also survey some proposals of models and query languages for semi-structured data. In particular, we consider recent works at Stanford U. and U. Penn on semi-structured data. In both cases, the motivation is found in the integration of heterogeneous data.

Region-based memory management

Abstract: This paper describes a memory management discipline for programs that perform dynamic memory allocation and de-allocation. At runtime, all values are put intoregions. The store consists of a stack of regions. All points of region allocation and de-allocation are inferred automatically, using a type and effect based program analysis. The scheme does not assume the presence of a garbage collector. The scheme was first presented in 1994 (M. Tofte and J.-P. Talpin,in“Proceedings of the 21st ACM SIGPLAN?SIGACT Symposium on Principles of Programming Languages,” pp. 188?201); subsequently, it has been tested in The ML Kit with Regions, a region-based, garbage-collection free implementation of the Standard ML Core language, which includes recursive datatypes, higher-order functions and updatable references L. Birkedal, M. Tofte, and M. Vejlstrup, (1996),in“Proceedings of the 23 rd ACM SIGPLAN?SIGACT Symposium on Principles of Programming Languages,” pp. 171?183. This paper defines a region-based dynamic semantics for a skeletal programming language extracted from Standard ML. We present the inference system which specifies where regions can be allocated and de-allocated and a detailed proof that the system is sound with respect to a standard semantics. We conclude by giving some advice on how to write programs that run well on a stack of regions, based on practical experience with the ML Kit.

Tour into the picture: using a spidery mesh interface to make animation from a single image

Abstract: A new method called TIP (Tour Into the Picture) is presented for easily making animations from one 2D picture or photograph of a scene. In TIP, animation is created from the viewpoint of a camera which can be three-dimensionally "walked or flownthrough" the 2D picture or photograph. To make such animation, conventional computer vision techniques cannot be applied in the 3D modeling process for the scene, using only a single 2D image. Instead a spidery mesh is employed in our method to obtain a simple scene model from the 2D image of the scene using a graphical user interface. Animation is thus easily generated without the need of multiple 2D images. Unlike existing methods, our method is not intended to construct a precise 3D scene model. The scene model is rather simple, and not fully 3D-structured. The modeling process starts by specifying the vanishing point in the 2D image. The background in the scene model then consists of at most five rectangles, whereas hierarchical polygons are used as a model for each foreground object. Furthermore a virtual camera is moved around the 3D scene model, with the viewing angle being freely controlled. This process is easily and effectively performed using the spidery mesh interface. We have obtained a wide variety of animated scenes which demonstrate the efficiency of TIP. CR

Deadlock analysis of Petri nets using siphons and mathematical programming

Abstract: This paper exploits the potential of siphons for the analysis of Petri nets, It generalizes the well-known Commoner condition and is based on the notion of potential deadlocks which are siphons that eventually become empty. A linear programming based sufficient condition under which a siphon is not a potential deadlock is obtained. Based on the new sufficient condition, a mathematical programming approach and a mixed-integer programming approach are proposed for checking general Petri nets and structurally bounded Petri nets respectively without explicitly generating siphons. Stronger results are obtained for asymmetric choice nets and augmented marked graphs. In particular, we show that an asymmetric choice net is live iff it is potential-deadlock-free and an augmented marked graph is live and reversible iff it is potential-deadlock-free.

Limit Cycles in a Passive Compass GaitBiped and Passivity-Mimicking Control Laws

Abstract: It is well-known that a suitably designed unpowered mechanical biped robot can “walk” down an inclined plane with a steady periodic gait. The energy required to maintain the motion comes from the conversion of the biped‘s gravitational potential energy as it descends. Investigation of such passive natural motions may potentially lead us to strategies useful for controlling active walking machines as well as to understand human locomotion. In this paper we demonstrate the existence and the stability of symmetric and asymmetric passive gaits using a simple nonlinear biped model. Kinematically the robot is identical to a double pendulum (similar to the Acrobot and the Pendubot) and is able to walk with the so-called compass gait. Using the passive behavior as a reference we also investigate the performance of several active control schemes. Active control can enlarge the basin of attraction of passive limit cycles and can create new gaits.

Distributed and Parallel Database Systems.

Abstract: The maturation of database management system (DBMS) technology has coincided with significant developments in distributed computing and parallel processing technologies. The end result is the development of distributed database management systems and parallel database management systems that are now the dominant data management tools for highly data-intensive applications. With the emergence of cloud computing, distributed and parallel database systems have started to converge. In this chapter, we present an overview of the distributed DBMS and parallel DBMS technologies, highlight the unique characteristics of each, and indicate the similarities between them. We also discuss the new challenges and emerging solutions.

Self-Calibration of a Moving Camera from PointCorrespondences and Fundamental Matrices

Abstract: We address the problem of estimating three-dimensional motion, and structure from motion with an uncalibrated moving camera We show that point correspondences between three images, and the fundamental matrices computed from these point correspondences, are sufficient to recover the internal orientation of the camera (its calibration), the motion parameters, and to compute coherent perspective projection matrices which enable us to reconstruct 3-D structure up to a similarity In contrast with other methods, no calibration object with a known 3-D shape is needed, and no limitations are put upon the unknown motions to be performed or the parameters to be recovered, as long as they define a projective camera The theory of the method, which is based on the constraint that the observed points are part of a static scene, thus allowing us to link the intrinsic parameters and the fundamental matrix via the absolute conic, is first detailed Several algorithms are then presented, and their performances compared by means of extensive simulations and illustrated by several experiments with real images

Stochastic geometry and architecture of communication networks

Abstract: This paper proposes a new approach for communication networks planning based on stochastic geometry. We first summarize the state of the art in this domain, together with its economic implications, before sketching the main expectations of the proposed method. The main probabilistic tools are point processes and stochastic geometry. We show how several performance evaluation and optimization problems within this framework can actually be posed and solved by computing the mathematical expectation of certain functionals of point processes. We mainly analyze models based on Poisson point processes, for which analytical formulae can often be obtained, although more complex models can also be analyzed, for instance via simulation.

Collision and self-collision handling in cloth model dedicated to design garments

Abstract: This article presents a method for collision handling applied to the semi-rigid mass-spring cloth model formerly described in [Pro95].

Multipoint communication: a survey of protocols, functions, and mechanisms

Abstract: Group communication supports information transfer between a set of participants. It is becoming more and more relevant in distributed environments. For distributed or replicated data, it provides efficient communication without overloading the network. For some types of multimedia applications, it is the only way to control data transmission to group members. This paper surveys protocol functions and mechanisms for data transmission within a group, from multicast routing problems up to end-to-end multipoint transmission control. We provide a bibliography which is organized by topic.

Anisotropic unstructured mesh adaption for flow simulations

Abstract: SUMMARY Three new ideas for anisotropic adaption of unstructured triangular grids are presented, with particular emphasis on fluid flow computations. # 1997 by John Wiley & Sons, Ltd.

On computing four-finger equilibrium and force-closure grasps of polyhedral objects

Abstract: This article addresses the problem of computing stable grasps of three-dimensional polyhedral objects. We consider the case of a hand equipped with four hard fingers and assume point contact with friction. We prove new necessary and sufficient conditions for equilibrium and force closure, and present a geometric characterization of all possible types of four-finger equilibrium grasps. We then focus on concurrent grasps, for which the lines of action of the four contact forces all intersect in a point. In this case, the equilibrium conditions are linear in the unknown grasp parameters, which reduces the problem of computing the stable grasp regions in configuration space to the problem of constructing the eight-dimensional projec tion of an ll-dimensinnal polytope. We present two projection methods: the first one uses a simple Gaussian elimination ap proach, while the second one relies on a novel output-sensitive contour-tracking algorithm. Finally, we use linear optimization within the valid configuration...

Querying Documents in Object Databases

Abstract: that consist in grammars annotated with database programs. To query documents, we introduce an extension of OQL, the ODMG standard query language for object databases. Our extension (named OQL-doc) allows us to query documents without a precise knowledge of their structure using in particular generalized path expressions and pattern matching. This allows us to introduce in a declarative language (in the style of SQL or OQL), navigational and information retrieval styles of accessing data. Query processing in the context of documents and path expressions leads to challenging implementation issues. We extend an object algebra with new operators to deal with generalized path expressions. We then consider two essential complementary optimization techniques. We show that almost standard database optimization techniques can be used to answer queries without having to load the entire document into the database. We also consider the interaction of full-text indexes (e.g., inverted files) with standard database collection indexes (e.g., B-trees) that provide important speed-up.

The Zipper

Abstract: Almost every programmer has faced the problem of representing a tree together with a subtree that is the focus of attention, where that focus may move left, right, up or down the tree. The Zipper is Huet's nifty name for a nifty data structure which fulfills this need. I wish I had known of it when I faced this task, because the solution I came up with was not quite so efficient or elegant as the Zipper.

Critical motion sequences for monocular self-calibration and uncalibrated Euclidean reconstruction

Abstract: In this paper sequences of camera motions that lead to inherent ambiguities in uncalibrated Euclidean reconstruction or self-calibration are studied. Our main contribution is a complete, detailed classification of these critical motion sequences (CMS). The practically important classes are identified and their degrees of ambiguity are derived. We also discuss some practical issues, especially concerning the reduction of the ambiguity of a reconstruction.

Methods and Applications of (MAX, +) Linear Algebra

Abstract: Exotic semirings such as the “(max, +) semiring” (ℝ ∪ {−∞},max,+), or the “tropical semiring” (ℕ ∪ {+∞}, min, +), have been invented and reinvented many times since the late fifties, in relation with various fields: performance evaluation of manufacturing systems and discrete event system theory; graph theory (path algebra) and Markov decision processes, Hamilton-Jacobi theory; asymptotic analysis (low temperature asymptotics in statistical physics, large deviations, WKB method); language theory (automata with multiplicities).

Using geometric corners to build a 2D mosaic from a set of images

Abstract: The main problem for building a mosaic is the computation of the warping functions (homographies) In fact two cases are to be distinguished The first is when the homography is mainly a translation (ie The rotation around the optical axis and the zooming factor are small) The second is the general case (when the rotation around the optical axis and zooming are arbitrary) Some efficient methods have been developed to solve the first case But the second case is more difficult, in particular, when the rotation around the optical axis is very large (90 degrees or more) Often in this case human interaction is needed to provide a first approximation of the transformation that will bring one back to the first case The authors present a method to solve this problem without human interaction for any rotation around the optical axis and fairly large zooming factors

Explicit/implicit fluid/structure staggered procedures with a structural predictor and fluid subcycling for 2D inviscid aeroelastic simulations

Abstract: Field time integrators with second-order-accurate numerical schemes for both the fluid and the structure are considered for unsteady Euler aeroelastic computations. We show that if these schemes are simply coupled and used straightforwardly with subcycling, then accuracy and stability properties may be lost. We present new coupling staggered procedures where momentum conservation is enforced at the interface. This is done by using a structural predictor. Continuity of structural and fluid grid displacements is not satisfied at the fluid/structure interface. However, we show on a two-degree-of-freedom aerofoil that this new type of method has many advantages, e.g. accuracy of conservation at the interface and extended stability. The supersonic flutter of a flat panel is simulated in order to numerically prove that the algorithm gives accurate results with arbitrary subcycling for the fluid in the satisfying limit of 30 time steps per period of coupled oscillation. © 1997 John Wiley & Sons, Ltd.

Inference in model-based cluster analysis

Abstract: A new approach to cluster analysis has been introduced based on parsimonious geometric modelling of the within-group covariance matrices in a mixture of multivariate normal distributions, using hierarchical agglomeration and iterative relocation. It works well and is widely used via the MCLUST software available in S-PLUS and StatLib. However, it has several limitations: there is no assessment of the uncertainty about the classification, the partition can be suboptimal, parameter estimates are biased, the shape matrix has to be specified by the user, prior group probabilities are assumed to be equal, the method for choosing the number of groups is based on a crude approximation, and no formal way of choosing between the various possible models is included. Here, we propose a new approach which overcomes all these difficulties. It consists of exact Bayesian inference via Gibbs sampling, and the calculation of Bayes factors (for choosing the model and the number of groups) from the output using the Laplace–Metropolis estimator. It works well in several real and simulated examples.

A stochastic particle method for the McKean-Vlasov and the Burgers equation

Abstract: In this paper we introduce and analyze a stochastic particle method for the McKean-Vlasov and the Burgers equation; the construction and error analysis are based upon the theory of the propagation of chaos for interacting particle systems. Our objective is three-fold. First, we consider a McKean-Vlasov equation in [0,T] x R with sufficiently smooth kernels, and the PDEs giving the distribution function and the density of the measure μ t , the solution to the McKean-Vlasov equation. The simulation of the stochastic system with N particles provides a discrete measure which approximates μkΔt for each time kΔt (where Δt is a discretization step of the time interval [0, T]). An integration (resp. smoothing) of this discrete measure provides approximations of the distribution function (resp. density) of μkΔt. We show that the convergence rate is O (1/√N+ for the approximation in L i (Ω x R) of the cumulative distribution function at time T, and of order O (e 2 +1/e) (1/√N + √Δt for the approximation in L l (Ω x R) of the density at time T (Ω is the underlying probability space, e is a smoothing parameter). Our second objective is to show that our particle method can be modified to solve the Burgers equation with a nonmonotonic initial condition, without modifying the convergence rate O (1/√N+√Δt). This part extends earlier work of ours, where we have limited ourselves to monotonic initial conditions. Finally, we present numerical experiments which confirm our theoretical estimates and illustrate the numerical efficiency of the method when the viscosity coefficient is very small.

Time-varying exponential stabilization of a rigid spacecraft with two control torques

Abstract: Rigid body models with two controls cannot be locally asymptotically stabilized by continuous feedbacks which are functions of the state only. This impossibility no longer holds when the feedback is also a function of time, and time-varying asymptotically stabilizing feedbacks have already been proposed. However, due to the smoothness of the feedbacks, the convergence rate is only polynomial. In this paper, exponential convergence is obtained by considering time-varying feedbacks which are only continuous.

Continuous-curvature path planning for car-like vehicles

Abstract: We consider path planning for a car-like vehicle. Previous solutions to this problem computed paths made up of circular arcs connected by tangential line segments. Such paths have a discontinuous curvature profile. Accordingly a vehicle following such a path has to stop at each curvature discontinuity in order to re-orientate its front wheels. To remove this limitation, we add a continuous-curvature constraint to the problem at hand. In addition, we introduce a constraint on the curvature derivative, so as to reflect the fact that a car-like vehicle can only re-orientate its front wheels with a finite velocity. We propose an efficient solution to the problem at hand that relies upon the definition of a set of paths with continuous curvature and maximum curvature derivative. These paths contain at most eight pieces, each piece being either a line segment, a circular arc of maximum curvature, or a clothoid arc. They are called simple continuous curvature paths. They are used to design a local path planner. The experimental results are presented.

A Framework for Uncertainty and Validation of 3-D RegistrationMethods Based on Points and Frames

Abstract: In this paper, we propose and analyze several methods to estimate a rigid transformation from a set of 3-D matched points or matched frames, which are important features in geometric algorithms. We also develop tools to predict and verify the accuracy of these estimations. The theoretical contributions are: an intrinsic model of noise for transformations based on composition rather than addition; a unified formalism for the estimation of both the rigid transformation and its covariance matrix for points or frames correspondences, and a statistical validation method to verify the error estimation, which applies even when no “ground truth” is available. We analyze and demonstrate on synthetic data that our scheme is well behaved. The practical contribution of the paper is the validation of our transformation estimation method in the case of 3-D medical images, which shows that an accuracy of the registration far below the size of a voxel can be achieved, and in the case of protein substructure matching, where frame features drastically improve both selectivity and complexity.

Exponential forgetting and geometric ergodicity in hidden Markov models

Abstract: We consider a hidden Markov model with multidimensional observations and with misspecification, i.e. the assumed coefficients (transition probability matrix and observation conditional densities) are possibly different from the true coefficients. Under mild assumptions on the coefficients of both the true and the assumed models, we prove that: 1) the prediction filter forgets almost surely their initial condition exponentially fast; and 2) the extended Markov chain, whose components are the unobserved Markov chain, the observation sequence and the prediction filter, is geometrically ergodic, and has a unique invariant probability distribution.