In Situ TEM Observation of the Behavior of an Individual Fullerene-Like MoS<Subscript>2</Subscript> Nanoparticle in a Dynamic Contact

Inorganic fullerene-(IF)-like nanoparticles made of metal dichalcogenides (IF-MoS₂, IF-WS₂) have been known to be effective as anti-wear and friction modifier additives under boundary lubrication. The lubrication mechanism of these nanoparticles has been widely investigated in the past and even if the exfoliation and third body transfer of molecular sheets onto the asperities constitute the prevalent mechanism for the improved tribological behavior of IF nanoparticles, it has also been suggested that a rolling friction process could also play a role for well crystallized and spherical particles. In this study, in situ Transmission Electron Microscopy (TEM) observations of the behavior of single IF-MoS₂ nanoparticles were conducted using a sample holder that combines TEM and Atomic Force Microscopy (AFM) which simultaneously can apply normal and shear loads. It was shown that depending on the test conditions, either a rolling process or a sliding of the fullerenes could be possible. These in situ TEM observations are the first carried out with IF nanoparticles.     

Kinetics of phase separation in polyurethane/polystyrene semi-1 interpenetrating polymer networks. 1. Light transmission studies

The phase separation of different in-situ semi-1 interpenetrating polymer networks (IPNs) based on polyurethane and polystyrene has been followed by light transmission. The effect of the presence ab initio of small amounts of homopolystyrene in the initial reaction mixture on the phase separation process has also been examined. If gelation of the polyurethane occurs before the onset of phase separation, the latter is impeded or strongly limited, and transparent semi-1 IPNs are obtained. In the opposite case, phase separation is macroscopic and the material is turbid.     

Estimation of parameters of a multifractal process

Multifractal functions are widely used to model irregular signals such as turbulence, data stream or road traffic. Here, we consider multifractal functions defined as lacunar wavelet series observed in a white noise model. These random functions are statistically characterized by two parameters. The first parameter governs the intensity of the wavelet coefficients while the second one governs its sparsity. We construct estimators of these two parameters and discuss statistical properties of this important model: the rate of the Fisher information and a testing procedure to check the multifractal feature of an observed noisy signal.      

Solving agreement problems with failure detectors: a survey

This paper surveys problems related to achieving agreement in distributed systems. Various agreement problems can be specified as a variant of the basic consensus problem. Unfortunately, this fundamental problem cannot be solved in asynchronous systems if crash failures can occur. In order to overcome this impossibility result, Chandra and Toueg have augmented the asynchronous system model with the notion of failure detectors. A failure detector is associated with each process of the distributed computation and is responsible for detecting external failures. Suspicions are essentially implemented using time-out mechanisms, which means that (1) the detection of a real failure is usually delayed and (2) a failure detector can make mistakes by incorrectly suspecting a process to have crashed. In this paper, various classes of failure detectors are presented. All are specified by a completeness property and an accuracy property. A completeness property puts a condition on the detection of crashed processes, while an accuracy property restricts the possible mistakes made by a failure detector. After reviewing the hierarchy of failure detector classes, two particular solutions to the consensus problem are examined. In each case, a different class of failure detectors is used. The proposed solutions have liveness properties and deliver their expected results provided that a minimal set of well-defined conditions is satisfied. After a detailed presentation of the consensus problem, various agreement problems are reviewed and their relationship with the consensus problem are underlined. Finally, for each agreement problem, we indicate under which minimum assumptions a solution can be found.     

Une note sur le cylindre des langages déterministes

La famille des langages déterministes constitue un cylindre non principal. Nous redémontrons ce résultat de S.A. Greibach en décrivant cette famille comme l'union d'une infinité de cylindres emboîtés qui constituent une hiérarchie stricte, chacun d'entre eux étant ici un cylindre principal.     

Le diagnostic des circuits intégrés par faisceau d’électrons

The purpose of this synthetic article is to show how the electron beam testing technique of prototype integrated circuits after a first run has now reached maturity. Firstly the physics of measurement has been the subject of many improvements which means that results, both more reliable and more precise (in voltage and in time) can be obtained more quickly. Moreover this improved performance has led to the development of fully comprehensive diagnosis stations so ergonomic that the user forgets his scanning electron microscope, stations which become the final link in the chain of computer aided design.     

Kinetics of phase separation in polyurethane/polystyrene semi-1 interpenetrating polymer networks. 2. Microscopy observations and theoretical approach

The phase separation process of in-situ polyurethane/polystyrene semi-1 interpenetrating polymer networks has been followed by optical microscopy completed by image analysis. The final morphology has been examined by scanning electron microscopy, and its relation to the phase separation process has been established. When phase separation occurs before gelation of the medium, polystyrene is dispersed both as large and small noduli in the polyurethane network; a polyurethane-rich interphase separates the noduli from the matrix. These observations explain the previous results on the turbidity of such systems measured by light transmission. In the opposite cases, no visible phase separation is observed on the micrographs. The thermodynamics of the phase separation process has also been examined.     

Evolution structurale par substitution cationique dans les perovskites hexagonales fluorees: II - Les systèmes Cs1−xRbxMF3 (M = Mg,Co, Ni,Zn)

The substitution of rubidium for cesium in CsMF₃ phases has the same influence as pressure. While no phase transformation is observed if M is magnesium or zinc, the sequences 2H → 9R → 6H and 9R → 6H → 3C are respectively observed in the case of nickel and cobalt with increasing rubidium concentration. The 9R-Cs_0.70 Rb_0.30 NiF₃ phase is antiferromagnetic and the 6H-Cs_0.50 Rb_0.50 CoF₃ compound is a ferrimagnet (T_C = 62 K).     

An A Contrario Decision Method for Shape Element Recognition

Shape recognition is the field of computer vision which addresses the problem of finding out whether a query shape lies or not in a shape database, up to a certain invariance. Most shape recognition methods simply sort shapes from the database along some (dis-)similarity measure to the query shape. Their main weakness is the decision stage, which should aim at giving a clear-cut answer to the question: “do these two shapes look alike?” In this article, the proposed solution consists in bounding the number of false correspondences of the query shape among the database shapes, ensuring that the obtained matches are not likely to occur “by chance”. As an application, one can decide with a parameterless method whether any two digital images share some shapes or not.     

Facteur de couplage phase-amplitude des diodes lasers avec absorbant saturable

The phase-amplitude coupling factor (α-factor) is one of the fundamental parameters of semiconductor lasers. We show that this factor can be evaluated by time-resolved spectroscopic measurements in pulsed regime. Experiments are carried out with injectionseeded single-mode GaAs lasers whose active stripe includes regions of saturable absorption made by ion implantation. We show that the measured pulse downchirp is proportional to pulse energy. The downchirp amplitude is found to approach four laser cavity intermode spacings at the highest energies. Correspondingly, the ±-values can be five times higher than those reported to date in litterature. High a-values are confirmed in pulse compression experiments. Several mechanisms are proposed to interprete these new results.