Membranes,minerals, and proteins of developing vertebrate enamel

Developing tooth enamel is formed as organized mineral in a specialized protein matrix. In order to analyze patterns of enamel mineralization and enamel protein expression in species representative of the main extant vertebrate lineages, we investigated developing teeth in a chondrichthyan, the horn shark, a teleost, the guppy, a urodele amphibian, the Mexican axolotl, an anuran amphibian, the leopard frog, two lepidosauria, a gecko and an iguana, and two mammals, a marsupial, the South American short-tailed gray opossum, and the house mouse. Electron microscopic analysis documented the presence of a distinct basal lamina in all species investigated. Subsequent stages of enamel biomineralization featured highly organized long and parallel enamel crystals in mammals, lepidosaurians, the frog, and the shark, while amorphous mineral deposits and/or randomly oriented crystals were observed in the guppy and the axolotl. In situ hybridization using a full-length mouse probe for amelogenin mRNA resulted in amelogenin specific signals in mouse, opossum, gecko, frog, axolotl, and shark. Using immunohistochemistry, amelogenin and tuftelin enamel proteins were detected in the enamel organ of many species investigated, but tuftelin epitopes were also found in other tissues. The anti-M179 antibody, however, did not react with the guppy and axolotl enameloid matrix. We conclude that basic features of vertebrate enamel/enameloid formation such as the presence of enamel proteins or the mineral deposition along the dentin-enamel junction were highly conserved in vertebrates. There were also differences in terms of enamel protein distribution and mineral organization between the vertebrates lineages. Our findings indicated a correlation between the presence of amelogenins and the presence of long and parallel hydroxyapatite crystals in tetrapods and shark.     

Hyperthermostable mutants of Bacillus licheniformis {alpha}-amylase: multiple amino acid replacements and molecular modelling

We have identified previously two critical positions for thethermostability of the highly thermostable -amylase from Bacilluslicheniformis. We have now introduced all 19 possible aminoacid residues to these two positions, His 133 and Ala209. Themost favourable substitutions were to Ile and Val, respectively,which both increased the half-life of the enzyme at 80°Cby a factor of 3. At both positions a stabilizing effect ofhydrophobic residues was observed, although only in the caseof position 133 could a clear correlation be drawn between thehydrophobicity of the inserted amino acid and the gain in proteinstability. The construction of double mutants showed a cumulativeeffect of the most favourable and/or deleterious substitutions.Computer modelling was used to generate a 3-D structure of thewild-type protein and to model substitutions at position 209,which lies in the conserved (/ß)₈ barrel domain of-amylase; Ala209 would be located at the beginning of the thirdhelix of the barrel, in the bottom of a small cavity facingthe fourth helix. The model suggests that replacement by, forexample, a valine could fill this cavity and therefore increaseintra- and interhelical compactness and hydrophobic interactions.     

Le programme d’admissibilité avec contraintes de sécurité et coûts de mutations: application aux réseaux de transmission mixtes (analogiques et numériques)

This paper presents a second version of the «feasibility program» (securad)developed by the cnet.This program enables the routing at minimal cost of several thousands of requirements (expressed in circuits or groups of circuits) on very large mixed (analogue and digital) transmission networks, while respecting given capacities and taking into account security constraints and network-rearrangement costs. The authors also describe a procedure for determining lower bounds for the cost of the optimal solution by solving a dual problem, and thus checking the quality of the approximate solutions obtained. This program has already been widely applied to the long-distance transmission network and to large digital metropolitan networks for both short term and medium to long term planning purposes.     

Improving trochoidal tool paths generation and implementation using process constraints modelling

With the emergence of high dynamic machine tools equipped with performing NC controllers, new types of strategies have risen to meet the demands associated to high-speed milling process. Among them, trochoidal tool paths are applied in rough machining applications. In this paper several improvements for their implementation are proposed. First, maximal radial depth of cut calculation according to tool path parameterization is made. Two interpolation models are tested and compared. The aim is to select the best tool path parameters according to the process constraints. Then, improved tool path generation for pocket milling applications is proposed. An experimental study is performed to validate the proposed approach and study the efficiency of trochoidal tool path implementation for pocket milling applications. The impact of the dynamics of the machine tool is evaluated in particular. The work presented here leads consequently to enhancement of implementation of trochoidal tool paths according to process constraints.     

Ion transport in CLIP: Investigation through conductivity and NMR measurements

The study deals with the electrochemical and physico-chemical characterizations of new proton-conducting ionic liquids. Through the use of several amines and perfluorinated acids, it attempts to define the most appropriate ionic liquids for use in high temperature PEMFCs. In addition to the usual characterizations based on Pulsed Field Gradient NMR and conductivity measurements, NMR correlation techniques NOESY, HOESY and COSY experiments are used to characterize the interactions and spatial proximities of ionic liquid species.     

Risk and threat factors in prior representations of driving situations among powered two-wheeler riders and car drivers

Our research objective is to contribute to gaining a better understanding of the difficulties inherent to managing interactions between power two-wheeler riders and car drivers. 132 power two-wheeler riders and 94 car drivers have been asked what they perceive as being riskiest in driving situations for the representatives of their generic reference group. From all the answers produced, only those which provide information on risk factors related to the other and the occurrence of interferences due to the dynamic situation have been retained and analysed. The results provide a partial explanation of the difficulties related to the two types of users’ taking each other into account. On the one hand, the frequency with which the other is mentioned as a source of risk is linked to the concept of conspicuity. This interpretation is related to the relative frequency of the interactions and the difference of real and perceived vulnerability between the users. On the other hand, the specific risk factors attributed to the other illustrates a mutual misunderstanding or ignorance of the driving situation's determinants. These include various practices among users which can be related to the physical and dynamic characteristics of their vehicle and their level of familiarity with other users. The potential road safety consequences of prior representations of risk factors among users are presented and suggestions for improving road user safety are proposed.     

Polyethersulfone containing sulfonimide groups as proton exchange membrane fuel cells

In this publication a new synthesis approach of polyethersulfone containing sulfonimide groups (SI-PES), by chemical modification of sulfonated polyethersulfone (S-PES), was developed. The synthesis protocol was optimized in order to turn all the sulfonic function into sulfonimide. The effect of replacing arylsulfonic acid function with a more acidic one, i.e. aryl trifluoromethanesulfonimide, was evaluated through thermal, dynamic mechanical analysis, water uptake and conductivity. For similar ionic exchange capacity (IEC), i.e. 1.8 H⁺/dm³, at 60 °C and 95% relative humidity, the conductivity of SI-PSF is 9.5 mS/cm while that of S-PSF is only 3.5 mS/cm. However, at 60 °C the water uptake is 3 times higher for SI-PSF membranes as compare with S-PSF. An important change is observed in the slope of the conductivity and water uptake plots of SI-PES membranes, at different temperatures, depending of IEC. This could be explained by an important change in membrane morphology.