Self-stabilization with r-operators

This paper describes a parameterized distributed algorithm applicable to any directed graph topology. The function parameter of our algorithm is instantiated to produce distributed algorithms for both fundamental and high level applications, such as shortest path calculus and depth-first-search tree construction. Due to fault resilience properties of our algorithm, the resulting protocols are self-stabilizing at no additional cost. Self-stabilizing protocols can resist transient failures and guarantee system recovery in a finite time. Since the condition on the function parameter (being a strictly idempotent r-operator) permits a broad range of applications to be implemented, the solution presented in our paper can be useful for a large class of distributed systems. Received: August 1999 / Accepted: January 2001     

The filtering problem for continuous-time linear systems with Markovian switching coefficients

The stochastic model under consideration is a Markovian jump process θ, with finite state space, feeding the parameters of a linear diffusion process x. The processes y and z observe linearly and separately x and θ in independent white noises. Some properties of the finite optimal filter for the x and θ processes given the history of measurements z are investigated. Apart from their theoretical interest, these results have an interesting practical bearing on the general filtering problem, by providing a natural finite suboptimal solution. Preliminary experimental results show the effectiveness of our approach to estimate the state trajectory, even with a relatively low signal-to-noise ratio on the measurement processes.     

The S-kernel: A measure of symmetry of objects

In this paper we introduce a new symmetry feature named “symmetry kernel” (SK) to support a measure of symmetry. Given any symmetry transform S, SK of a pattern P is the maximal included symmetric sub-set of P for all directions and shifts. We provide a first algorithm to exhibit this kernel where the centre of symmetry is assumed to be the centre of mass. Then we prove that, in any direction, the optimal axis corresponds to the maximal correlation of a pattern with its symmetric version. That leads to a second algorithm. The associated symmetry measure is a modified difference between the respective surfaces of a pattern and its kernel. A series of experiments supports the actual algorithm validation.     

Cocontraction changes in muscular fatigue at different levels of isometric contraction

Ten normal subjects participated in a study designed to contrast results obtained in pre- and post-fatigue states. The measures contrasted were the IEMG ratios of agonist/antagonist pairs of muscles. The experimental task was an 8 s ramp isometric elbow flexion ranging from 0 to 100% of a maximal voluntary contraction (MVC). IEMG ratios were obtained at levels of 20, 40, 60 and 80% MVC. Records from the following muscles were obtained with surface electrodes: biceps brachii (BB), brachioradialis (BR), triceps brachii (TB) and anconeus (SU). The torque at the elbow joint was measured by a Cybex II dynamometer. Fatigue was induced using a 60% MVC of elbow flexion maintained during 5 minutes. The data were collected on-line at a sampling rate of 1 kHz. The results indicated that the IEMG ratios (BB/TB and BR/SU) presented a tendency, across subjects, toward a decrease at the levels of 40%, 60% and 80% MVC at the post- relative to the pre-fatigue state. The BB/BR ratios remained stable. These changes in the post-fatigue ratios disclose a tendency toward a saturation of the agonist occurring concomitantly with an increased level of contraction of the antagonists.     

An active microphotodiode array of oscillating pixels for retinal stimulation

We have developed an active microphotodiode array (MPDA) for retinal stimulation. The unique feature of the device is that each pixel acts as an independent oscillator, whose frequency is controlled by the incident light intensity. The design is based on a double inverter relaxation oscillator, and the photodiodes are of PIN-type. These oscillating pixels stimulate the nervous tissue with bipolar pulses. The prototype stimulator chips are realized in standard 0.35 μm CMOS technology. The reported preliminary data and performance demonstrate the potential of the new concept for future retinal prostheses.     

A two-machine flowshop problem with processing time-dependent buffer constraints—An application in multimedia presentations

To have a quality multimedia presentation through networks, its presentation lag needs to be controlled. One way to reduce the lag is to prefetch the media objects before their due dates. This paper explores techniques for optimizing the object sequence in a prefetch-enabled TV-like presentation. An optimal solution is the one with which the presentation lag is minimized. We formulate the problem into a two-machine flowshop scheduling problem with a single chain precedence constraint and a player-side buffer constraint. The player-side buffer is “processing time-dependent” and distinguished from the conventional item-based intermediate buffer constraints discussed in previous flowshop studies. We prove the problem to be strongly NP-hard. A branch and bound algorithm equipped with four lower bounds and an NEH-based upper bound is developed. The simulation results show that the average gaps between the overall lower bounds and the NEH-based upper bound are less than 3% for problems with a large buffer size, and less than 13% for problems with a small buffer size and high density of precedence constraints. For applications where the media objects are delivered through extremely busy servers with which only very restricted CPU resources can be allocated for computation, the CDS-based algorithm provides better sequences than the NEH-based algorithm.     

On Topological Watersheds

In this paper, we investigate topological watersheds (Couprie and Bertrand, 1997). One of our main results is a necessary and sufficient condition for a map G to be a watershed of a map F, this condition is based on a notion of extension. A consequence of the theorem is that there exists a (greedy) polynomial time algorithm to decide whether a map G is a watershed of a map F or not. We introduce a notion of separation between two points of an image which leads to a second necessary and sufficient condition. We also show that, given an arbitrary total order on the minima of a map, it is possible to define a notion of degree of separation of a minimum relative to this order. This leads to a third necessary and sufficient condition for a map G to be a watershed of a map F. At last we derive, from our framework, a new definition for the dynamics of a minimum.Gilles Bertrand received his Ingénieurs degree from the École Centrale des Arts et Manufactures in 1976. Until 1983 he was with the Thomson-CSF company, where he designed image processing systems for aeronautical applications. He received his Ph.D. from the École Centrale in 1986. He is currently teaching and doing research with the Laboratoire Algorithmique et Architecture des Systémes Informatiques, ESIEE, Paris, and with the Institut Gaspard Monge, Université de Marne-la-Vallée. His research interests are image analysis, discrete topology and mathematical morphology.     

Explicit reference modeling methodology in parametric CAD system

Today parametric associative CAD systems must help companies to create more efficient virtual development processes. While dealing with complex parts (e.g. the number of surfaces of the solid) no CAD modeling methodology is existing. Based on the analysis of industrial designers' practices as well as student practices on CAD, we identified key factors that lead to better performance. Our objective in this article is to propose a practical method for complex parts modeling in parametric CAD system. An illustration of the performances and the results obtained by this method are presented comparing the traditional method with the proposed one while using an academic case and then an industrial case.     

Anisotropie de la decomposition d'un solide. II-mise en evidence d'un gradient thermique dans la phase solide a l'aide d'un thermographe infra-rouge

Monocrystalline platelets of pentahydrate Copper sulfate are submitted to temperature and pressure conditions such that they cause this salt to be converted into a trihydrated salt. Thermal equilibrium of these platelets is ensured before the reaction starts. Temperature is recorded as moving away from the superficial domain undergoing conversion, by means of an I.R. scanning camera fitted with a cooled detecting device. The occurence of a thermal gradient from the reactive solid-solid interface can, thus, be shown. It seems, therefore necessary to take into account the physical properties of the crystal, which are involved in the occurence of thermal gradients in the solid, to explain the anisotropy of this interface displacement during a conversion where a gas is removed.