Resistance of pure and mixed rare earth silicates against calcium-magnesium-aluminosilicate (CMAS): A comparative study

Rare earth silicate environmental barrier coatings (EBCs) are state of the art for protecting SiC ceramic matrix composites (CMCs) against corrosive media. The interaction of four pure rare earth silicate EBC materials Yb₂SiO₅, Yb₂Si₂O₇, Y₂SiO₅, Y₂Si₂O₇ and three ytterbium silicate mixtures with molten calcium-magnesium-aluminosilicate (CMAS) were studied at high temperature (1400°C). The samples were characterized by SEM and XRD in order to evaluate the recession of the different materials after a reaction time of 8 hours. Additionally, the coefficient of thermal expansion (CTE) was determined to evaluate the suitability of Yb silicate mixtures as EBC materials for SiC CMCs. Results show that monosilicates exhibit a lower recession in contact with CMAS than their disilicate counterparts. The recession of the ytterbium silicates is far lower than the recession of the yttrium silicates under CMAS attack. Investigation of the ytterbium silicate mixtures exposes their superior resistance to CMAS, which is even higher than the resistance of the pure monosilicate. Also their decreased CTE suggests they will display better performance than the pure monosilicate.     

Further Exploration of Controlled and Automatic Memory Processes in Early Alzheimer's Disease.

The authors' aim in this study was to explore automatic and controlled processes in Alzheimer's disease (AD) by using a variant of the word-stem completion task that applies the process-dissociation procedure. Several methodological precautions were taken in order to limit problems observed in previous studies (e.g., poor task sensitivity, ceiling and/or floor effects, no control over comprehension of instructions). Our results (a) confirmed the marked deterioration in controlled processes and (b) showed that when psychometric constraints were limited, automatic memory processes were preserved in AD. These data are in line with those from more global studies in suggesting that AD is characterized by an early deterioration in controlled processes and an initial preservation of automatic processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Finite elements for microwave device simulation: application tomicrowave dielectric resonator filters

The two-dimensional (2-D) and three-dimensional (3-D) finite element methods (FEMs) are applied to compute the exact scattering parameters (taking into account the transmission lines) of dielectric resonator (DR) filters. These filters act in TM or hybrid modes. A sensitivity analysis is also performed to predict the influence of the geometrical parameters on the devices responses. Examples of one, two, and three DR filters are given. Experimental results are in good agreement with theoretical ones     

Modelling of multiple-mechanism agglomeration in a crystallization process

A three-level agglomeration model coupled with crystal growth is developed. It accounts for Brownian, laminar, and turbulent agglomeration. The desupersaturation profiles, the particle size distributions, the average sizes, and variances (or standard deviations), as well as the instantaneous agglomeration degrees for each mechanism, can be calculated as functions of time. The model is applied to the crystallization of an amorphous solid into a crystalline polymorph in a batch crystallizer. A runaway phenomenon is detected for agglomeration when crystals are switching over from the Brownian regime to the laminar one: this switchover significantly affects the desupersaturation curve and the crystal shapes.     

Self-propagating combustion synthesis of intermetallic matrix composites in the ISS

Combustion Synthesis experiments have been performed on the ISS (International Space Station) during the Belgian taxi-flight mission ODISSEA in November 2002, in the framework of the ESA-coordinated project COSMIC (Combustion Synthesis under Microgravity Conditions). The main objective of the experiments was to investigate the general physico-chemical mechanisms of combustion synthesis processes and the formation of products microstructure. Within the combustion zone, a number of gravity-dependent phenomena occur, while other phenomena are masked by gravity. Under certain conditions, gravity-dependent secondary processes may also occur in the heat-affected zone after combustion. To study the influence of gravity, a specially dedicated reactor ensemble was designed and used in the Microgravity Science Glovebox (MSG) onboard the ISS. In this work, the experiment design is first discussed in terms of the experimental functionality and reactor ensemble integration in the MSG. To investigate microstructure formation, a sample constituted by a cylindrical portion followed by a conical one, the latter being inserted inside a massive copper block, is used. The experiment focused on the synthesis of intermetallic matrix composites (IMCs) based on the Al-Ti-B system. Depending on the composition, different intermetallic compounds (TiAl and TiAl₃) can be formed as matrix phase while TiB2 represents the reinforcing particulate phase. During the ISS mission, six samples with a relatively high green density of 65%TD have successfully been processed. The influence of the composition on the combustion process will be examined.     

Physico-chemical characterization, preparation and performance of poly (methylidene malonate 2.1.2) nanoparticles

The present investigation confirms that initially implemented procedure to produce poly(methylidene malonate 2.1.2) (PMM 2.1.2) nanoparticles (Lescure et al. Pharm Res 1994;11:1270-77) lead to products mostly containing plasticizing oligomers which strongly lowered glass-transition temperature (Tg), dramatically reduced nanoparticle consistency and rendered them too sensitive to solubilization when diluted in an aqueous medium. From MALDI-TOF spectroscopy analysis, performed on intact colloids, emerged some structural information about these oligomeric species which could result from an intramolecular cyclization mechanism occurring soon in the course of the polymerization process. Thus, with the objective of overcoming these drawbacks, this contribution deals with the variations of manufacturing specifications such as pH and magnetic stirring speed to try and modulate molecular weight (MW) of nanoparticle constituents and reduce oligomer concentration. Although the analyses performed on these new nanoparticles were rather encouraging, the colloid formation yield became so low that it required the development of other methodologies, excluding a previous emulsion step, and allowing a controlled production of PMM 2.1.2-made nanoparticles having better physico-chemical characteristics while keeping good pharmaceutical capabilities.     

Scattering matrix of dielectric resonator coupled with twomicrostrip lines

A lumped equivalent circuit is proposed to model the coupling of a dielectric resonator with two microstrip lines terminated by any impedance. A three-dimensional finite-element method is used to determine the resonant frequency, quality factor, and coupling coefficients as functions of the electromagnetic parameters of the structure. Scattering parameters are computed. Methods are presented to evaluate these coefficients from a field analysis. They are shown to give good agreement between computed and experimental results     

Increased biological activity of a recombinant factor IX variant carrying alanine at position +1

In attempts to improve the post-translational modification andprocessing of recombinant factor IX (FIX) we have altered thecDNA sequence encoding pre-pro-FIX using site-directed mutagenesisand have expressed the variant cDNAs in BHK21 cells using avaccinia-virus-derived vector. We find that substitution ofthe tyrosine residue at +1 for an alanine increases the biologicalactivity of the recombinant molecules 2–fold. On the otherhand, substitution of the proline at –3 for a valine resultsin no significant change to the specific activity of the protein.Other alterations to the N-terminus of the FIX proteins, inattempts to mimic other vitamin-K-dependent proteins, resultin the failure to produce a secreted polypeptide. N-terminalsequence analysis of purified recombinant molecules revealsa correlation between specific activity and the efficiency ofcorrect pro-sequence cleavage. -Carboxylation analysis of purifiedrecombinant proteins indicates that each molecule includingunmutated FIX is completely -carboxylated in this system. Thusthe observed increase in biological activity of FIX variantscontaining an alanine at position +1 is not due to increased-carboxylation but, at least in part, to more efficient pro-peptidecleavage.