Pump wavelength optimisation of erbium-doped fibre amplifier in 800 nm band

The absorption band centred around 805 nm suffers from two excited state absorption (ESA) bands which peak, respectively, at 790 nm. The difficulty in comparing the pump wavelength efficiencies comes from the fact that the optimum amplifier length depends not only on pump power but also on pump wavelength. It is shown that for high pump powers, pumping around 820 nm is most efficient, however for lower pump powers shorter wavelengths provide the highest gains.<>     

Formation pratique à la conception d’un circuit intégré spécifique

We present an example of practical works in design methodology for realizing digitalASIC circuit, at the graduate level in the microelectronics engineering program (ISIM) of the University of Montpellier II. This training program is illustrated by the design of a small project from specification to silicon manufacturing files, using a CMOS standard cell approach with theCAD softwares system Hilo (Genrad) and Solo 1400(ES2).     

Mutation of serine-46 to aspartate in the histidine-containing protein of Escherichia coli mimics the inactivation by phosphorylation of serine-46 in HPrs from gram-positive bacteria

Histidine-containing protein (HPr) is a phosphocarrier protein of the bacterial phosphoenolpyruvate:sugar phosphotransferase system. HPr is phosphorylated at the active site residue, His15, by phosphoenolpyruvate-dependent enzyme I in the first enzyme reaction in the process of phosphoryl transfer to sugar. In many Gram-positive bacterial species HPr may also be phosphorylated at Ser46 by an ATP-dependent protein kinase but not in the Gram-negative Escherichia coli and Salmonella typhimurium. One effect of the phosphorylation at Ser46 is to make HPr a poor acceptor for phosphorylation at His15. In Bacillus subtilis HPr, the mutation Ser46Asp mimics the effects of phosphorylation. A series of mutations were made at Ser46 in E. coli HPr: Ala, Arg, Asn, Asp, Glu, and Gly. The two acidic replacements mimic the effects of phosphorylation of Ser46 in HPrs from Gram-positive bacteria. In particular, when mutated to Asp46, the His 15 phosphoacceptor activity (enzyme I Km/Kcat) decreases by about 2000-fold (enzyme I Km, 4 mM HPr; Kcat, approximately 30%). The alanine and glycine mutations had near-wild-type properties, and the asparagine and arginine mutations yielded small changes to the Km values. The crystallographic tertiary structure of Ser46Asp HPr has been determined at 1.5 A resolution, and several changes have been observed which appear to be the effect of the mutation. There is a tightening of helix B, which is demonstrated by a consistent shortening of hydrogen bond lengths throughout the helix as compared to the wild-type structure. There is a repositioning of the Gly54 residue to adopt a 3(10) helical pattern which is not present in the wild-type HPr. In addition, the higher resolution of the mutant structure allows for a more definitive placement of the carbonyl of Pro11. The consequence of this change is that there is no torsion angle strain at residue 16. This result suggests that there is no active site torsion angle strain in wild-type E. coli HPr. The lack of substantial change at the active center of E. coli HPr Ser46Asp HPr suggests that the effect of the Ser46 phosphorylation in HPrs from Gram-positive bacteria is due to an electrostatic interference with enzyme I binding.     

Influence of roasting temperature on reactions between ferruginous blende and copper(II) oxide

Thermal treatment in an oxidizing atmosphere of a mixture of raw blende (ZnS) and copper(II) oxide enhanced the formation of a mixed ferrite phase at temperature about 600°C. The composition established at 900°C was approximately (0.8 ZnO · 0.2 CuO)Fe₂O₃. For the mixture ZnS–CuO, with 5 to 15% CuO by weight, less than 15% copper was involved in the formation of the spinel phase. The increasing copper content in the mixture, roasted above 1000°C, favoured solubilization of iron, even in a weakly acid medium.     

A study of the durability of boundary films

The frictional properties of solid surfaces are modified by the adsorption of organic molecular films. The lifetime of a monomolecular film of a fatty acid which was deposited on a surface to form a solid/monolayer/air interface has been investigated.The continual presence of an agglomerate has been observed during frictional contact under boundary lubrication conditions. This agglomerate is composed of several substances resulting from the deterioration and recombination of fatty acid molecules with each other and/or the surrounding media.     

Influence de la structure sur les propriétés mécaniques dynamiques de quelques polytéréphtalates de polyméthylèneglycol. Relaxations β et γ

The influence of structure, cristallinity and orientation on the β- and γ-relaxation mechanisms of several poly(α,ω-alkandiolterephthalates) has been investigated. The γ-relaxation consists of two main components involving molecular motions in the amorphous phase, and motions of CH₂ groups (glycolic residue) in the gauche or trans form. A third component involves movements of bigger groups. The β-relaxation at low frequencies can be compared with the dilatometric glass transition.     

Thermodynamic studies on the solvent effects in chromatography on molecularly imprinted polymers. 1. Nature of the organic modifier

Molecularly imprinted polymers (MIPs) are used as highly enantioselective stationary phases in liquid chromatography. To optimize the binding performance of MIPs, different types of polar modifiers are frequently used. Previous studies have shown that the hydrogen-bonding donor parameter (HBD) of the modifier has a large influence on the binding performance of MIPs in chiral separations. This possibility is addressed in a detailed thermodynamic study of a Fmoc-L-tryptophan (Fmoc-L-Trp) imprinted polymer, eluted with four different polar modifiers, i.e., THF, propan-2-ol, methanol, and acetic acid, which have different HBDs (0.00, 0.33, 0.43, and 0.61, respectively). Adsorption isotherm data for each enantiomer in each of these organic modifiers were acquired by frontal analysis over a 20 000 dynamic concentration range. Nonlinear regression of the isotherm data, along with independent calculation of the affinity energy distributions, identified four different types of binding sites coexisting for the enantiomers on the MIP. The exception was acetic acid, which has the highest HBD. In this case, three types of binding sites only coexist on the MIP. The isotherm parameters obtained from these data show the following: (1) The association energies of the two enantiomers with a given type of sites have a similar magnitude; however, the density of the sites is higher for the template than for its antipode. (2) The nature of the organic modifier has a larger influence on the density of high-energy sites than on the association constant of these sites. (3) The molecular size of the organic modifier has a larger influence on the site density (especially for Fmoc-D-Trp) than does HBD. (4) Using an organic modifier with a higher HBD reduces the enantioselectivity on each site. (5) High-energy sites are more enantioselective than low-energy ones. (6) Using an organic modifier with a high HBD causes a larger reduction in the density of high-energy sites approached by the template molecules.