Showing papers by "École normale supérieure de Cachan published in 1996"

Regulation of a PWM rectifier in the unbalanced network state using a generalized model

Abstract: This study concerns the modeling and control of a pulse-width-modulated (PWM) rectifier in the case of network variations. The aim is to limit and stabilize variations of DC output voltage and line currents in such circumstances. Network variations can result in costly damage to power converters and their loads but a power converter such as the PWM rectifier, using cascade digital control, offers many capabilities to stabilize the system with optimized control. A generalized model of the PWM rectifier is first presented using the Clarke notation in order to separate the positive and negative sequences. The model is also extended to the harmonics. The cases of harmonic disturbance and an unbalanced network are then analyzed and an optimized regulation is presented for the latter case, validating the generalized model. Experimental results are proposed. The line current compensation loop method coupled with identification of network parameters offers a good solution to stabilize the PWM rectifier in an unbalanced network.

Mechanical properties of reactive powder concretes

Abstract: Reactive Powder Concretes (RPC) are a set of ultrahigh-strength concretes reinforced with steel fibers. Their compressive strength is between 200 and 800MPa, and their flexural strength can reach 140MPa.RPC200 has been studied with respect to compressive strength and two-point loading strength to define its mechanical behavior.RPC800, which has been mostly studied from the point of view of compressive strength, displays hardening elastic non-linear behavior at low stress. This behavior is similar to that of some natural rocks. The critical stress intensity factorKIc, and the average fracture energy,\(\bar G_F \), ofRPC200 andRPC800 have been studied experimentally by applying the theory of linear fracture mechanics (compliance method). The fracture energy, which is a measurement of ductility, can reach 40,000 J/m2 forRPC200, as compared to 100 to 150 J/m2 for ordinary concretes. Fracture energy depends on the volume of fibers added to the concrete. The optimum content is between 2 and 3% by volume.

Unreliable Channels Are Easier to Verify Than Perfect Channels

Abstract: We consider the problem of verifying correctness of finite state machines that communicate with each other over unbounded FIFO channels that are unreliable Various problems of interest in verification of FIFO channels that can lose messages have been considered by Finkel and by Abdulla and Jonsson We consider, in this paper, other possible unreliable behaviors of communication channels, viz, (a) duplication and (b) insertion errors Furthermore, we also consider various combinations of duplication, insertion, and lossiness errors Finite state machines that communicate over unbounded FIFO buffers are a model of computation that forms the backbone of the ISO standard protocol specification languages Estelle and SDL While the assumption of a perfect communication medium is reasonable at the higher levels of the OSI protocol stack, the lower levels have to deal with an unreliable communication medium; hence our motivation for the present work The verification problems that are of interest arereachability,unboundedness,deadlock, andmodel-checking against CTL* All of these problems are undecidable for machines communicating over reliable unbounded FIFO channels So it is perhaps surprising that some of these problems become decidable when unreliable channels are modeled The contributions of this paper are (a) an investigation of solutions to these problems for machines with insertion errors, duplication errors, or a combination of duplication, insertion, and lossiness errors, and (b) a comparison of the relative expressive power of the various errors

On global existence of solutions to coupled matrix Riccati equations in closed-loop Nash games

Abstract: Presents comparison and global existence results for solutions of coupled matrix Riccati differential equations appearing in closed loop Nash games and in mixed H/sub 2//H/sub /spl infin//-type problems. Convergence of solutions is established for the diagonal case, solutions of the corresponding algebraic equations are discussed using numerical examples.

Progressive damage in discrete models and consequences on continuum modelling

Abstract: In phenomenological damage models, damage is very often understood as a degradation of the elastic stiffness of the material. The unrealistic features of damage localisation as a result of strain softening are usually circumvented by the introduction of an internal length in the continuum description that scales the localisation process and controls the size of the damage/strain localisation zone. This paper focuses on the motivation for introducing such an internal length. It is based on the analysis of failure in lattice models presenting an initial disorder in strength. The simple model introduced here and studied numerically, should be amenable to a continuum description for large enough lattice sizes. In the lattice modelling, an internal length appears as a correlation length owing to spatial redistributions and interactions during the failure process. The variations of this length with the system size are studied numerically and theoretically with an original model based on percolation theory, which accounts for the spatial interactions. The analysis shows that the internal length increases with the damage of the system, and finally reaches a finite (lattice size independent) value at the peak load. A full statistical analysis of the local stress is provided and discussed in the formalism of multifractals, so as to extract the salient scaling features of the model.

Increase in energy cost of running at the end of a triathlon

Abstract: The purpose of the present study was to verify the increase in energy cost of running at the end of a triathlon. A group 11 trained male subjects performed a triathlon (15-km swimming, 40-km cycling, 10-km running). At least 1 week later the subjects ran 10-km as a control at the same pace as the triathlon. Oxygen uptake (VO2), ventilation (VE) and heart rate (HR) were measured during both 10-km runs with a portable telemetry system. Blood samples were taken prior to the start of the triathlon and control run, after swimming, cycling, triathlon run and control run. Compared to the control values the results demonstrated that triathlon running elicited a significantly higher (P < 0.005) mean VO2 [51.2 (SEM 0.4) vs 47.8 (SEM 0.4) ml.min-1.kg-1] VE [86 (SEM 4.2) vs 74 (SEM 5.3) l.min-1], and HR [162 (SEM 2) vs 156 (SEM 1.9) beats.min-1)]. The triathlon run induced a greater loss in body mass than the control run [2 (SEM 0.2) vs 0.6 (SEM 0.2) kg], and a greater decrease in plasma volume [14.4% (SEM 1.5) vs 6.7% (SEM 0.9)]. The lactate concentrations observed at the end of both 10-km runs did not differ [2.9 (SEM 0.2) vs 2.5 (SEM 0.2) m.mol.l-1]. Plasma free fatty acids concentrations were higher (P < 0.01) after the triathlon than after the control run [1.53 (SEM 0.2) to 0.51 (SEM 0.07) mmol.l-1]. Plasma creatine kinase concentrations rose under both conditions from 58 (SEM 12) to 112 (SEM 14) UI.l-1 after the triathlon, and from 61 (SEM 7) to 80 (SEM 6) UI.l-1 after the control run. This outdoor study of running economy at the end of an Olympic distance triathlon demonstrated a decrease in running efficiency.

From Intercalation to Aggregation: Nonlinear Optical Properties of Stilbazolium Chromophores−MPS3 Layered Hybrid Materials

Abstract: A number of cationic chromophores derived from the stilbazolium skeleton have been synthesized and inserted into the transparent layered MPS3 compounds (M = Mn, Cd, Zn). The NLO properties of the intercalates have been studied. Some of the materials are found to be active for second harmonic generation. UV−visible spectroscopy shows that some of the chromophores, once inserted, undergo strong intermolecular interactions and form J-type aggregates along the inorganic galleries, whereas others do not. Moreover, we have found that only those intercalates which contain aggregates are NLO active. The results allow us to understand, at least partially, why the centrosymmetrical MPS3 host lattice can yield noncentrosymmetrical intercalates. The host lattice appears not so much to impose specific orientations upon the guest species as to favor chromophore aggregation.

Transparent incremental state saving in time warp parallel discrete event simulation

Abstract: Many systems rely on the ability to rollback (or restore) parts of the system state to undo or recover from undesired or erroneous computations. Examples of such systems include fault tolerant systems with checkpointing, editors with undo capabilities, transaction and data base systems and optimistically synchronized parallel and distributed simulations. An essential part of such systems is the state saving mechanism. It should not only allow efficient state saving, but also support efficient state restoration in case of roll back. Furthermore, it is often a requirement that this mechanism is transparent to the user. In this paper we present a method to implement a transparent incremental state saving mechanism in an optimistically synchronized parallel discrete event simulation system based on the Time Warp mechanism. The usefulness of this approach is demonstrated by simulations of large, detailed, realistic FCA and a DCA-like cellular phone systems.

Geometrical Behavior Laws for Computer-aided Tolerancing

Abstract: The analysis of the difficulties encountered with traditional dimension chains in the description of the behaviour of a set of parts, with variation, has led us to develop a tridimensional model of variations. It is therefore designed to treat the problem of transfer of dimensions.

Electropolymerized manganese porphyrin films as catalytic electrode materials for biomimetic oxidations with molecular oxygen

Abstract: Some recently published results on the electrocatalytic oxidation of hydrocarbons, olefins and a thioacetamide derivative by molecular oxygen are described. The catalytic process involves electropolymerized manganese porphyrin films as electrode materials in acetonitrile or dichloromethane solution containing 1-methylimidazole and benzoic (or acetic) anhydride, with acceptable catalytic efficiency (up to 500 turnovers of the catalyst per hour) and faradaic yield (up to 98%). Confinement of the catalyst on the electrode surface markedly improves its stability compared with that of homogeneous electrocatalytic systems and makes the supported porphyrin stable and reusable.

Resolutions of the prescribed volume form equation

Abstract: For a given volume formfdx on a bounded regular domain Ω in IR n , we are looking for a transformationu of Ω, keeping the boundary fixed and which sends the Lebesgue measuredx intofdx (i.e. we solve det (Δu)=f. Forf in various spaces, we propose two different constructions which ensure the existence ofu with some gain of regularity. Our methods permit the recovery Dacorogna and Moser's results [4], but also, we prove the existence of suchu in Holder spaces forf inC 0, or even inL ∞.

Some properties of ordered eigenvalues of a Wishart matrix: application in detection test and model order selection

Abstract: High resolution methods for estimation of parameters in signal processing (bearing angles in array processing or frequencies in spectral analysis for example) can suffer from a bad selection of the model order. This paper proposes an algorithm based on the properties of the eigenvalues of the covariance matrix. In the noise only case, this matrix is a Wishart matrix. For white noise the profile of ordered eigenvalues fits an exponential law. The proposed algorithm uses this property and looks for a mismatch between the observed profile and the model in order to detect the presence of a signal. Under estimation may result from the occurrence of small signal eigenvalues. Performances is greatly improved by the use of deflation for recursive detection-estimation test. Results of simulations are provided in order to show the capabilities of the algorithm.

'Crush-crack' : a non-local damage model for concrete

Abstract: SUMMARY A model is presented based on the non-local damage theory. It sets out to describe the behavior of concrete under free-variable loads, which are constant in sign. Its purpose is to analyze shear behavior and high strain-gradient localized problems, and it takes Mazar’s model as a starting point with reference to the basic idea of a scalar isotropic non-local damage controlled by principal tensile strains. In addition, the other two main features are an internal variable denoted to the control or reversible volumetric expansion in compression, and irreversible strains aimed at modelling crushing in compression and cracks both in tension and compression. As a consequence, induced-anisotropy, dilatancy and path-dependency can be reproduced. In particular, the modelling of micro- and macrocracks makes it possible to capture mixed-mode cracking as well as aggregate interlock, which requires a residual stiffness to guarantee the transmission of transversal and normal stresses for assigned slips.The model requires the knowledge of the material response in uniaxial tension and compression, and biaxial compression tests which can be introduced directly by adopting experimental curves, or by means of a reduced number of parameters. The effectiveness of the model is shown through comparisons with several sets of experimental tests on both small specimens, assumed to be homogeneous, and boundary value problems.

Photon-photon elastic scattering in the visible domain

Abstract: We are investigating the direct detection of photon-photon elastic scattering at optical energies. In a first experiment using two high-intensity pulsed laser beams, we have explored the feasibility of the method, and in particular the rejection of back-ground noise. We obtained an upper limit of the photon-photon elastic scattering cross section at 95% confidence level of 10−39 cm2. This limit can be lowered by twenty orders of magnitude by stimulating the scattering by a third beam, and by using high repetition rate existing lasers.

Stabilization of controllable systems

Abstract: The goal of this paper is to present a partial survey on the local stabilizability of locally controllable systems.

Homogenisation of transport kinetic equations with oscillating potentials

Abstract: We consider the homogenisation of transport kinetic equations with a highly periodic oscillating external field. The external field, acting on the particles, consists of a sum of a field deriving from a periodic potential and a bounded periodic perturbation. For the profile function generated by the oscillating solution of the problem, we derive a kinetic model with transmission boundary conditions in the energy variable. In some cases, for example when the field is not perturbed, we deduce a transport kinetic equation with memory effect satisfied by the weak-* limit of the sequence of solutions.

A new laser range-finder based on FMCW-like method

Abstract: A synthesis on laser range-finding techniques is first presented, giving the methods, the performance and the correlated applications. Then, a research in progress in our laboratory on a new laser range-finder method is focused on: the frequency beat detection, derived from the FMCW radar ranging technique. The beam intensity is modulated by a sine-wave wobulated by a chirped waveform, and final detection after mixing the emitted and echoing waves gives a frequency beat proportional to the distance. The experimental set-up is described in details with the main functional blocks. Experimental results and performance are finally discussed to find improvements and specific applications.

The charge transfer state of excited bianthryl and a derivative: solvatochromism, emission CT spectra broadening in homogeneous solvents

Abstract: The photophysical properties of a recently synthesized molecule, the bis-9,9′-(2-ethyl-10-hexyl)anthryl (BOA), have been studied with the parent molecule, the 9,9′-bianthryl (BA), in solvents of various polarity The comparative analysis of the photophysical behaviour of these two probes has been achieved in order to emphasise environmental effects of the alkyl substituent on the aromatic chromophore The results obtained in perfluoroalkane, reported for the first time in this paper, suggest that the charge transfer state (CT) of BA or BOA contributes to the fluorescence emission even in non polar solvents like cyclohexane The fluorescence spectra of these two probes in perfluoroalkane have been introduced as standard spectra of the locally excited state form (LE) and used to obtain a new decomposition of the other overall fluorescence spectra into two emission components: one coming from the CT state and the second from the initial excited singlet state (LE) We have analysed the solute-solvent interactions not only in term of Stokes shift but also using the inhomogeneous band broadening parameter The vibrational band decomposition found its validation in the agreement observed between the thermodynamic and spectroscopic properties of both excited states A correlation between the inhomogeneous broadening and the Stokes shift of the charge transfer spectrum is exhibited The existence of up to 50% of the CT state even in non polar solvents like cyclohexane has been shown The dipole moment of the CT state of BA and of BOA can be estimated in the range of 62 to 103 D depending on the solvatochromic model used It has been shown that the alkyl substituent of BOA destabilises the CT state and only four methylene groups of each lateral chain of BOA contribute to the local environment of the aromatic chromophore

Hyperpolarisability of (donor)2‐acceptor‐type molecules determined by EFISHG

Abstract: Molecular first-order hyperpolarisabilities β of (donor)2-acceptor type molecules have been determined by electric field induced second-harmonic generation (EFISHG) experiments at 1.06 μm. The hyperpolarisability values are enhanced in these two dimensional charge transfer molecules, compared with a reference linear model molecule. One of these molecules absorbs part of the second-harmonic beam. We propose a determination method for β that takes into account this phenomenon. Crystals of the title molecules exhibit second harmonic generation by the powder test.

Rheological behaviour of a polymer-ceramic blend used for injection moulding

Abstract: Our aim is to describe the behaviour of highly filled injection moulding pastes, made of a polymer binder and fine ceramic powders. A specific rheometer has been developed to characterize this behaviour within the injection range of pressures and shear rates. As classical homogeneous models fail to describe the behaviour of the paste, we propose an original model deriving from the mixture theory, taking into account the separate contributions of binder and powder to the global behaviour of the paste. The qualitative and quantitative accuracies of this model are discussed.

Conception of an adaptative laser range finder based on phase shift measurement

Abstract: The whole concept of a laser rangefinder, based on heterodyne phase shift measurement, is presented. Next to the optical head, an HF card is built to produce the two frequencies that are combined to give the measurement and reference signals. After amplification, with automatic gain control, phase-shift is measured by direct high frequency counting, with better than 10 bit resolution. An interface card is used for the first averaging treatment and direct connection to the parallel port of a PC computer. An easy adaptation of the modulation frequency, from some MHz to some hundred of MHz, allows fitting to the required resolution and range.