Comparaison des cinetiques de formation de la couche passivante de WO3 sur des electrodes monocristallines de tungstene orientees (100) et (110) en milieu H2SO4 1 M*

A detailed study of chronoamperometric curves, associated with a direct measurement of coverage through inhibiting properties of WO₃ allowed us to compare the formation processes of such oxide on (100) and (110) orientated tungsten single crystals in H₂SO₄ 1 M medium. This comparison shows that the chemical dissolution of WO₃ and the number of atoms ‘in depth’ of the inhibiting limiting layer does not depend on the crystallographic orientation of the metal. On the contrary the number of superficial atoms taken into account to form this layer and the kinetic parameters of last step of oxidation in the over all process are strongly dependent on the tungsten crystallographic orientation.     

Derivatives of Di-O-octanoylglycerol and mono-O-octylglycerol as modulators of protein kinase C and diacylglycerol kinase activities

Twelve analogs of 1,2-di-O-octanoylglycerol modified at C-3 and three quaternaryN-alkyl-ammonium derivatives of glycerol were synthesized. The compounds were testedin vitro as potential modulators of the calcium activated, phospholipid dependent protein kinase C (PKC) and diacylglycerol (DAG) kinase activities in order to understand the molecular interactions of these enzymes with their natural activators, inhibitors, or substrates. PKC activity was assayed by measuring histone H₁ phosphorylation, and the compounds synthesized were tested either in the presence (inhibitors) or in the absence (activators) of 1,2-di-O-octanoyglycerol analogs with the phosphatidylserine/Ca²⁺ mixture. DAG kinase activity was measured by the incorporation of phosphate into 1,2-di-O-oleoyl-sn-glycerol in the presence of the various analogs synthesized. In regard to PKC activity, the assays revealed that 1,2-di-O-octanoylglycerol analogs are inactive when modified at C-3 with groups which do not permit hydrogen bonding. Under our conditions, di-O-octanoylthioglycerol, which has been reported as inactive, was able to activate PKC in the presence of phosphatidylserine. It has been shown to give a synergistic activation with diacylglycerol and had no affinity for the phorbol ester receptor binding site, suggesting thatO-octanoylthioglycerol interacts with the enzyme at a different site from the phorbol ester receptor binding site. PKC and DAG kinase activities are inhibited byN-alkyl-ammonium compounds (IC₅₀ 24 μM) only when either two 8-carbon alkyl or acyl chains are present at the 1- and 2-positions of the glycerol backbone. The fact that these compounds have a strong effect on the binding of [³H]phorbol 12,13-dibutyrate to protein kinase C, and also inhibit DAG kinase, may suggest binding to the DAG site of the regulatory domain of PKC.     

GC sniffing analysis: olfactive intensity measurement by two methods

The intensity perceived by sniffing after GC elution of six volatile compounds was measured by ten judges using two pieces of apparatus: a PC mouse which is moved on a 60-cm length scale and a rheostat apparatus which measures the finger span. The choice of the components mixed was influenced by purity, elution time, presence in food and known Steven's slopes. The histograms obtained by summing the responses (determined by measuring the areas under the peaks) of ten people show no significant differences between the two pieces of apparatus. Histograms realised in parallel by Charm analysis with three other judges showed great differences between subjects. However, the mean of the three Charm analysis histograms was very similar to those histograms obtained with the two previously described pieces of apparatus. The same concentrations of ethyl butyrate, 3-methyl butanoic acid and 2,3,5-trimethyl pyrazine had the greatest odour intensity and thiophene, 2,6-dimethyl pyrazine and acetophenone had the lowest odour intensity.     

Aerodynamic Modelling and Experimental Identification of a Coaxial-Rotor UAV

A comprehensive design of a Gun Launched Micro Air Vehicle (GLMAV) is presented. The GLMAV rotorcraft is a new Micro Air Vehicle (MAV) concept using two-bladed coaxial contra-rotating rotors and a cyclic swashplate. The MAV packaged in a projectile is launched using the energy delivered by a portable weapon. When it reaches the apogee, the projectile is transformed in such a way that the MAV becomes operational over the zone to be observed. A detailed GLMAV nonlinear mathematical model is presented for hover and near-hover flight conditions and identified from experimental load data using a strain-gage aerodynamic balance. Simplifications brought to the aerodynamic submodel have permitted its linearization in the parameter space. The parameter estimation was based on the Kalman filter estimation method applied to the simplified aerodynamic model and using the input-output data from the experiment. The persistently exciting condition is given in terms of physical variables of the GLMAV through two simple expressions. The identification results are presented and validated through comparisons between the model output and real load data.     

Byzantine agreement with homonyms

So far, the distributed computing community has either assumed that all the processes of a distributed system have distinct identifiers or, more rarely, that the processes are anonymous and have no identifiers. These are two extremes of the same general model: namely, $n$ processes use $\ell $ different identifiers, where $1 \le \ell \le n$ . In this paper, we ask how many identifiers are actually needed to reach agreement in a distributed system with $t$ Byzantine processes. We show that having $3t+1$ identifiers is necessary and sufficient for agreement in the synchronous case but, more surprisingly, the number of identifiers must be greater than $\frac{n+3t}{2}$ in the partially synchronous case. This demonstrates two differences from the classical model (which has $\ell =n$ ): there are situations where relaxing synchrony to partial synchrony renders agreement impossible; and, in the partially synchronous case, increasing the number of correct processes can actually make it harder to reach agreement. The impossibility proofs use the fact that a Byzantine process can send multiple messages to the same recipient in a round. We show that removing this ability makes agreement easier: then, $t+1$ identifiers are sufficient for agreement, even in the partially synchronous model, assuming processes can count the number of messages with the same identifier they receive in a round.     

Instrumental variable methods for identifying partial differential equation models

This paper presents a refined instrumental variable method for identifying partial differential equation models of distributed parameter systems directly from discrete-time sampled input–output data. The proposed method is compared with conventional least-squares and other instrumental variable-based techniques. Monte Carlo simulation analysis results are presented to illustrate the effectiveness and superiority of the proposed method in the presence of additive output measurement noise and under different spatio-temporal sampling conditions.     

Sem observations of the microstructure of frost deteriorated and self-healed concretes

The microcracking and self healing mechanisms of concrete exposed to rapid freezing and thawing in water and subsequently kept in water have been investigated by Scanning Electron Microscopy (SEM). Non air entrained concretes of water/binder ratio 0.40 with 0 and 5 % silica fume were studied. Damage was measured as loss in resonance frequency and compressive strength. After frost exposure, concrete beams were stored three months in water. During this time resonance frequency largely recovered, whereas compressive strength showed smaller recovery. On Secondary Electron Images (SEI) of fractured surfaces hydration products mainly of the C-S-H type were seen traversing cracks at several locations after self healing, but not directly after freeze/thaw. Back Scattered Electron Images (BSEI) showed that the cracks due to freeze/thaw testing were of 1–10 μm width. The cracks traversed the paste and followed the interfaces of most larger aggregate particles. On BSEI self healing was seen on 300–1000 X magnification as partly closing of several cracks smaller than 5 μm. This was most clearly seen by switching between SEI and BSEI modes. In BSEI-mode the re-hydration products appeared less dense and the cracks appeared wider than in the SEI-mode.     

Landslide damage to the board river water supply pipeline,Bromley Hill,Jamaica: Case study of a landslide caused by hurricane Gilbert (1988)

This case study highlights the importance of geotechnical investigations in the site selection, design and maintenance of life-line structures in multiple hazard prone areas. The Boar River Pipeline, carrying part of Kingston’s water supply, was damaged by a debris flow originating on the eastern slope of Bromley Hill, following the passage of hurricane Gilbert over Jamaica on September 12, 1988. Regional and site-specific geotechical investigations indicate that landslides are ubiquitous in the region, especially on east-facing slopes, and that the slide which damaged the pipelnine is a relatively shallow failure. The slide may stabilize itself in the due course of time provided there are no extreme weather events. Artificial measures of slope stabilization are recommended as a short-term solution. However, since the entire slope is involved in sliding and favourable conditions for future failures exist in the area, the better approach would be to avoid the failed slope altogether and relocate the pipeline.     

Determination of the correlation between physical measurements of roughness, optical properties, and perception of frosted glass surfaces

Chemical frosting is used as a surface decorating method by many glass package producers. After immersion in an acid frosting bath, glass items present the desired frosted effect. The perception of this particular effect is due to the formation of a microscopic crystalline pattern on the glass surface, which scatters light passing through the glass surface. The chemical composition of the frosting bath influences these properties by modifying the surface roughness, the depth, and the average slopes of the crystalline pattern. Perception of the final aspect can be modified according to the chemical composition of the frosting bath. Different correlations between all these parameters exist and have been quantified.