Wireless transmission using cooperation on demand

Mobile users with single antennas can still take advantage of spatial diversity through repetition based cooperative transmission. In this paper, we consider a scheme in which the cooperation is triggered only if the source–destination channel is of an unacceptable quality. Therefore, the destination selects one relay out of a decoding set of relays for cooperation. We analyze the end-to-end outage probability in slow and fast fading environments and we evaluate the usefulness of relaying when the source acts blindly and ignores the decision of the selected relay whether it may cooperate or not. The performance in both environments are evaluated through analysis and simulations in terms of end-to-end outage probability and the number of active relays. Some selected performance results show that some selected computer simulation based results coincide with our analytical results.     

Weak solutions for immiscible compressible multifluid flows in porous media

We consider a multifluid flow model describing evolution of pressures and relative saturations of non-miscible and compressible phases in porous media. This model is obtained by a macroscopic representation of the flow. It takes into account capillary effects and velocity fields are described by Darcy laws. Global weak solutions for such a model is introduced. To cite this article: C. Galusinski, M. Saad, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Cyclic poly(pyridine ether)s by the polycondensation of 2,6‐difluoropyridine with various diphenols

The bistrimethylsilyl derivatives of six different diphenols were polycondensed with 2,6‐difluoropyridine in N‐methylpyrrolidone in the presence of K₂CO₃. On the basis of previous studies, the reaction conditions were optimized for almost quantitative conversions. The feed ratio was systematically varied to optimize the molecular weight. A 2 mol % excess of 2,6‐difluoropyridine was needed to obtain maximum molecular weights. In the matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectra of the optimized polyethers, only cycles were found (detectable up to 5000 Da). Obviously, the relatively low molecular weights obtained under optimized conditions resulted from a limitation of the chain growth by cyclization, indicating a high cyclization tendency for poly(pyridine ether)s. The size exclusion chromatography measurements not only proved low molecular weights but also demonstrated the existence of bimodal mass distributions and high polydispersities. Protonation of the poly(pyridine ether)s required strong acids such as methane or trifluoromethane sulfonic acid. The solubilities of the neutral and protonated polyethers derived from bisphenol A were studied in various solvents. The MALDI‐TOF mass spectra proved that protonation at 20–25 °C did not cause cleavage of ether bonds. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4781–4789, 2005     

Mathematical Analysis and Pattern Formation for a Partial Immune System Modeling the Spread of an Epidemic Disease

Our motivation is a mathematical model describing the spatial propagation of an epidemic disease through a population. In this model, the pathogen diversity is structured into two clusters and then the population is divided into eight classes which permits to distinguish between the infected/uninfected population with respect to clusters. In this paper, we prove the weak and the global existence results of the solutions for the considered reaction-diffusion system with Neumann boundary. Next, mathematical Turing formulation and numerical simulations are introduced to show the pattern formation for such systems.     

On a fully nonlinear degenerate parabolic system modeling immiscible gas–water displacement in porous media

In this paper, we are interested in the simultaneous flow of two immiscible fluid phases within a porous medium. We consider a two-phase flow model where the fluids are immiscible and there is no mass transfer between the phases. The medium is saturated by compressible/incompressible phase flows. We study the gas–water displacement without simplified assumptions on the state law of gas density. We establish an existence result for the nonlinear degenerate parabolic system based on new energy estimate on pressures.     

Hafnium Chloride Catalyzed Polycondensation of α,ω-Alkanediol with Dicarboxylic Acids or Succinic Anhydride

Three different kinds of polycondensation were preformed and the usefulness of HfCl₄.2THF as estrification and polycondensation catalyst was evaluated. It was compared with HfCl₄, BiCl₃, LaCl₃ and SnCl₂. In polycondensations of 1,6-hexandiol, and 1,10-decandiol with various dicarboxylic acids all catalysts failed to give satisfactory results. However, in polycondensations of 1,4-butanediol with succinic anhydride in refluxing decalin good results were obtained, and HfCl₄.2THF was the most effective catalyst after SnCl₂. The MALDI-TOF mass spectra revealed that cyclization made a significant contribution to the limitation of the chain growth.     

Effects of pH and Ionic Salts on the Emulsifying and Rheological Properties of Acorn Protein Isolate

This study was designed to evaluate the emulsifying and rheological properties of acorn protein isolate (API) in different pH mediums (pH 3, 7 and 9) and in the presence of ionic salts (1 M NaCl and 1 M CaCl₂). API shows higher solubility in distilled water at pH 7, while at the same pH, a decrease in solubility was observed for API in the presence of CaCl₂ (61.30%). A lower emulsifying activity index (EAI), lower stability index (ESI), larger droplet sizes and slight flocculation were observed for API in the presence of salts at different pHs. Importantly, CaCl₂ treated samples showed relevantly higher EAI (252.67 m²/g) and ESI (152.67 min) values at all pH as compared to NaCl (221.76 m²/g), (111.82 min), respectively. A significant increase in interfacial protein concentration (4.61 mg/m²) was observed for emulsion at pH 9 with CaCl₂, while the major fractions of API were observed in an interfacial layer after SDS-PAGE analysis. All of the emulsion shows shear thinning behavior (τ_c > 0 and n < 1), while the highest viscosity was observed for emulsion prepared with CaCl₂ at pH 3 (11.03 ± 1.62). In conclusion, API, in the presence of ionic salts at acidic, neutral and basic pH, can produce natural emulsions, which could be substitutes for synthetic surfactants for such formulations.     

Site-Selective C−H Functionalization of Carbazoles

Carbazole alkaloids hold great potential in pharmaceutical and material sciences. However, the current approaches for C1 functionalization of carbazoles rely on the use of a pre-installed directing group, severely limiting their applicability and hindering their overall efficiency. Herein, we report for the first time the development of direct Pd-catalyzed C−H alkylation and acylation of carbazoles assisted by norbornene (NBE) as a transient directing mediator. Notably, the involvement of a six-membered palladacycle intermediate was suggested in this case, representing the first example of such intermediacy within the extensively studied Pd/norbornene reactions realm.