SHS of high-purity MAX compounds in the Ti-Al-C system

During the synthesis of MAX phases using combustion synthesis (or Self-Propagating High-temperature Synthesis), the main drawback is the presence of binary phases, and especially the simple MX carbide, when X = C. Our experiments were designed in order to check whether the cooling rate of the sample immediately after synthesis might play a key role for obtaining samples with low-level carbide contents. In the best conditions, a TiC content of about 2% only has been observed. A systematic study on the direct effect of the cooling rate on the final composition has then been conducted, and confirms that high cooling rates allow the synthesis of high-purity MAX phases in the Ti-Al-C system.      

Adaptive regulation in bimodal linear systems

This paper considers an adaptive regulation problem for switched bimodal linear systems where it is desired to achieve regulation against unknown sinusoidal exogenous inputs representing disturbance or reference signals. Switching among plant models as well as among disturbance and reference signals is defined according to a performance variable. The design of the proposed adaptive regulators involves two main steps. First, a set of observer‐based Q‐parameterized stabilizing controllers for the switched system is constructed, and a sufficient regulation condition for the resulting switched closed‐loop system is presented. Second, an adaptation algorithm is developed to tune the Q parameter in the expression of the parameterized controller and make it converge to the desired Q parameter that guarantees regulation for the switched system. The tuning of the Q parameter is performed to compensate for the lack of information on the properties of the sinusoidal exogenous inputs. Finally, a numerical example is presented to illustrate the effectiveness of the proposed method. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrodynamical modelling and multidimensional approximation of estuarian river flows

We propose a new approach for deriving hydrodynamical models, within the framework of mixed variational formulations. We thus obtain a 2D-horizontal model, as well as a 2D-vertical one and a 1D model taking into account the geometry of the river. We briefly study here the 2D-vertical and the 1D models and we propose (after time discretization) low-order conforming finite element approximations. All the variational problems are well-posed. We justify next a posteriori estimators between the models, which allow us to couple them. Numerical tests, achieved with a realistic bathymetry, are next presented.     

Redesigning an FKBP-ligand interface to generate chemical dimerizers with novel specificity

FKBP ligand homodimers can be used to activate signaling events inside cells and animals that have been engineered to express fusions between appropriate signaling domains and FKBP. However, use of these dimerizers in vivo is potentially limited by ligand binding to endogenous FKBP. We have designed ligands that bind specifically to a mutated FKBP over the wild-type protein by remodeling an FKBP-ligand interface to introduce a specificity binding pocket. A compound bearing an ethyl substituent in place of a carbonyl group exhibited sub-nanomolar affinity and 1,000-fold selectivity for a mutant FKBP with a compensating truncation of a phenylalanine residue. Structural and functional analysis of the new pocket showed that recognition is surprisingly relaxed, with the modified ligand only partially filling the engineered cavity. We incorporated the specificity pocket into a fusion protein containing FKBP and the intracellular domain of the Fas receptor. Cells expressing this modified chimeric protein potently underwent apoptosis in response to AP1903, a homodimer of the modified ligand, both in culture and when implanted into mice. Remodeled dimerizers such as AP1903 are ideal reagents for controlling the activities of cells that have been modified by gene therapy procedures, without interference from endogenous FKBP.     

Synthesis and activity of bivalent FKBP12 ligands for the regulated dimerization of proteins

The total synthesis and in vitro activities of a series of chemical inducers of dimerization (CIDs) is described. The use of small-molecule CIDs to control the dimerization of engineered FKBP12-containing fusion proteins has been demonstrated to have broad utility in biological research as well as potential medical applications in gene and cell therapies. The facility and flexibility of preparation make this new class of wholly synthetic compounds exceptionally versatile tools for the study of intracellular signaling events mediated by protein-protein interactions or protein localization. While some congeners possess potency comparable to or better than the first generation natural product-derived CID, FK1012, structure-activity relationships are complex and underscore the need for application-specific compound optimizations.     

Modification of cation-exchange membrane properties by electro-adsorption of polyethyleneimine

A cation-exchange membrane has been modified by fixation of polyethyleneimine on its surface. This fixation was carried out under an electric field effect, thus it is called electro-adsorption. The polycation formed in an acidic medium migrated toward the membrane and a charged layer was deposited on the surface, and the selectivity towards divalent ions decreased, yielding to the increase of the proton transfer. When the amount of adsorbed PEI increased, the electrical resistance ofthe membrane increased and the transport number of zinc decreased. However, suitable conditions like pH, current density and electro-adsorption time were controlled in the order to obtain membranes with better selectivity and low electrical resistance.     

Electrical and optical characterisation of CuInS2 crystals and polycrystalline coevaporated thin films

Single crystals CuInS₂ were grown by iodine vapour transport method, whereas polycrystalline thin films were obtained by coevaporation technique from three sources. The temperature dependence of the hole mobility in valence band is analysed by taking into account contributions from several scattering mechanisms of the charge carriers. To account for the temperature dependant conductivity of polycrystalline CuInS₂ thin films, grainboundary conduction process was suggested. In the low temperature region, we interpret the data in terms of the Mott law and the analysis is very consistent with the variable range hopping. However, thermionic emission is predominant at high temperatures. Photoluminescence measurements have been performed on CuInS₂ crystals and the analysis has revealed that the emission is mainly due to free-to-bound and donor–acceptor pair transitions. The band gap of that compound is derived from the excitonic emission line at 1.53 eV.     

Effect of friction coefficient and density on mixing particles in the rolling regime

In this work, optical imaging is used to quantify the mixing dynamics of granular materials. Two different methods (GLCM and Multivariate RGB analysis) are combined to extract surface information and the time to achieve a specific degree of mixing. In particular, the effect of density, friction coefficient, surface quality and particle geometry was studied. The results show that the Froude number alone is not enough to completely characterize the rolling regime. In addition, the filling ratio must be in a specific range which depends on the material properties.     

A novel method for synthesis of low-cost Ti-Al-C-based cermets

Ti²AlC-Ti³AlC²/Al²O³ samples have been successfully synthesized by aluminothermic reduction of TiO2 in the presence of C. Phase composition of resultant products obtained at different Al excess was characterized by XRD. Microstructures of the samples were observed by SEM. XRD analysis proved that it is possible to improve the yield of MAX phases using Al excess. With increasing Al excess, a major MAX phase was found to change from Ti²AlC to Ti³AlC².