Effective index drift from molecular hydrogen diffusion inhydrogen-loaded optical fibres and its effect on Bragg gratingfabrication

When hydrogen loading is used to enhance the photosensitivity of silica-based optical waveguides and fibres, the presence of molecular hydrogen dissolved in the glass matrix changes the effective index of propagation of guided optical modes by as much as 0.05%. Real-time monitoring of the reflectivity spectrum of Bragg gratings written in such conditions shows that the centre wavelength follows the changes in hydrogen concentration due to diffusion and reaction with glass defects     

Comparison Between a Pt–Rh/Ba/Al2O3 and a Newly Formulated NOX-Trap Catalysts Under Alternate Lean–Rich Flows

In situ FT-IR spectroscopy coupled with mass spectrometry have been used to study the mechanism of nitrates formation and reduction over a common Pt–Rh/Ba/Al₂O₃ NO _x storage catalyst, compared with a different alumina-based compound.The experimental device used consists of a transmission reactor cell (having a very small dead volume) dedicated to the evolution of surface species, and of a mass spectrometer combined with a FT-IR micro-cell for gas analysis, allowing time resolved analysis in stationary and transient conditions.At the first time the nitration properties of the catalysts under a lean flow have been studied in the appropriate temperature window (473–673 K). The dynamics of nitrates formation has been pointed out, as well as the different coordination sites on the compounds surface. Then the catalysts have been alternatively exposed to rich and lean flows very close to the real exhaust composition. This has allowed the identification of reduction pathway, active sites, intermediate species and by-products for NO _X -trap reaction. In particular, we have differentiated the role of the support and of the noble metal in the mechanism, as well as of isocyanate adspecies and ammonia among the detected species. The very high NO _X storage properties and the selectivity (near 100%) in nitrogen of the newly designed catalyst have been pointed out.     

Co-substitution at the Mn-site in YMnO3: Structural stability and physical properties

The YMnO₃ oxide, crystallizing in the P6₃cm space group is one of the most studied multiferroic material. While these properties can be modified by substitutions at the Mn-site, the peculiar fivefold coordination appears to limit the M solubility range in YMn_1?xM_xO₃. This motivated the preparation by solid state reaction of several series of co-substituted YMn_1?x(M′,M″)_xO₃, which were studied using both powder X-ray diffraction and transmission electron microscopy. The cation pairs have been chosen for their ability to adopt a fivefold coordination similar to that of Mn³⁺ in YMnO₃, to keep a constant average trivalent oxidation state and to maintain an average cationic radius similar to that of Mn³⁺. For YMn_1?x(Cu_1/2Ti_1/2)_xO₃, a complete solid solution is observed without cation ordering. For all other studied cation pairs, the solubility range is always reaching a minimum value of 25% for the Zn containing pairs (Zn_2/3V_1/3 and Zn_3/4Mo_1/4), a maximum of 50% being reached for the Cu containing pairs (Cu_2/3V_1/3, Cu_2/3Nb_1/3 and Cu_3/4W_1/4). Interestingly, the non-centrosymmetric P6₃cm space group is retained within the solubility range without generating cation ordering phenomena. These co-substitutions at the Mn³⁺ are found to induce a decrease of the antiferromagnetic ordering temperature, the T_N variations being similar to the temperature decrease of the dielectric anomaly. Thus, these oxides are interesting candidates for the study of the multiferroic behavior of YMnO₃ derivatives.     

The effect of climate variations on glulam—an experimental study

Climate variations affect timber structures by causing moisture induced stresses which may lead to cracks in timber members. The paper presents experimentally determined moisture induced stresses that arise perpendicular to the grain of glulam specimens during exposure to 1-dimensional drying and wetting. Although to a certain extent reduced by creep effects, the determined tensile stresses can significantly exceed the characteristic tensile strength of glulam. Additional measurements of moduli of elasticity (E) and hygroexpansion coefficients (α) revealed that these parameters are strongly affected by the geometrical configuration (pith locations) of the specimens. By means of all the parameters determined here, it can be avoided that parameters have to be selected from different literature sources, which introduces large uncertainties into the numerical simulations.     

Ion bombardment induced surface electrical degradation monitoring by means of luminescence in aluminas

Oxide ceramics for use as electrical insulators in future fusion devices, will be exposed to ionization and displacement damage (neutrons, gammas, ion bombardment). Enhanced oxygen loss due to ion bombardment increases surface electrical conductivity, and at the same time the surface emits light due to ion beam induced luminescence (IBIL). Results for 3 types of α-alumina and sapphire measuring electrical surface conductivity and IBIL as a function of dose at different temperatures between 20 and 200 °C, show a clear correlation between luminescence and surface electrical degradation. This indicates the potential to remotely monitor insulating material degradation not only in ITER and beyond, but also in the more immediate in-reactor experiments required for materials testing. Partial reduction of degradation by heating in air suggests the possibility for in situ recovery of the insulating properties.     

A novel low-loss inline bimodal-fiber tap: wavelength-selectiveproperties

The tap described is a combination of two elementary devices: a low-loss (resonant) mode converter and a special fused-taper coupler. Efficient coupling of light for a narrow wavelength band (<10 nm) is demonstrated. The center-wavelength of the band can be selected by tuning the resonant condition for intermodal coupling in the mode converter. The uncoupled (nonresonant) light passes through the tap, exhibiting low excess loss (<0.2 dB). The tap has application in linearly tapped fiber optic distribution systems     

Preform shape and operating condition optimization for the stretch blow molding process

In this work, a new design approach was developed to automatically and consecutively predict optimal preform geometry and optimal operating conditions for the stretch blow molding process. The numerical approach combines a constrained gradient‐based optimization algorithm that iterates automatically over predictive finite element software. The strategy allows for targeting a specified container thickness distribution by manipulating consecutively the preform geometry (thickness and shape) and the operating parameters subject to process and design constraints. For the preform shape optimization, the preform geometry is mathematically parameterized for simplified treatment and the corresponding sensitivities are evaluated using a finite difference technique. A finite difference technique is also employed for the operating condition optimization. The constrained optimization algorithms are solved via the use of the sequential quadratic programming method that updates the design variables accordingly. Predicted optimization results obtained on an industrial case are presented and discussed to assess the validity when compared to experimental results and the robustness of the proposed approach. POLYM. ENG. SCI., 47:289–301, 2007. © 2007 Society of Plastics Engineers.     

Selective Pharmacophore Models of Dopamine D1 and D2 Full Agonists Based on Extended Pharmacophore Features

This study is focused on the identification of structural features that determine the selectivity of dopamine receptor agonists toward D₁ and D₂ receptors. Selective pharmacophore models were developed for both receptors. The models were built by using projected pharmacophoric features that represent the main agonist interaction sites in the receptor (the Ser residues in TM5 and the Asp in TM3), a directional aromatic feature in the ligand, a feature with large positional tolerance representing the positively charged nitrogen in the ligand, and sets of excluded volumes reflecting the shapes of the receptors. The sets of D₁ and D₂ ligands used for modeling were carefully selected from published sources and consist of structurally diverse, conformationally rigid full agonists as active ligands together with structurally related inactives. The robustness of the models in discriminating actives from inactives was tested against four ensembles of conformations generated by using different established methods and different force fields. The reasons for the selectivity can be attributed to both geometrical differences in the arrangement of the features, e.g., different tilt angels of the π system, as well as shape differences covered by the different sets of excluded volumes. This work provides useful information for the design of new D₁ and D₂ agonists and also for comparative homology modeling of D₁ and D₂ receptors. The approach is general and could therefore be applied to other ligand–protein interactions for which no experimental protein structure is available.     

Evaluation of corrosion inhibitors performance using real-time monitoring methods

The implementation of real-time corrosion-monitoring techniques can provide a reliable mechanism for detecting the overall effectiveness of chemical treatment programs and contribute to the selection and implementation of an adequate corrosion inhibitor system. Inadequate corrosion monitoring can result in an increase of both uniform and localized (pitting) corrosion activities which can lead to premature material failures. The present research was undertaken to ascertain whether linear polarization resistance (LPR), harmonic analysis (HA), and electrochemical noise (EN) in combination are suitable for the study of performance of corrosion inhibitors under a wide variety of conditions; for example, in the absence and the presence of hydrocarbons with or without the addition of corrosion inhibitors. The findings showed questionable results regarding the usefulness of the pitting factor derived from EN and HA data. In addition, statistical parameters were obtained, such as skew and kurtosis, and these results were compared with the pitting factor.