Détection et approximation de défauts non-réguliers

This Note deals with the identifiability of non-smooth defects by boundary measurements. We prove the uniqueness of the detection by two measurements for arbitrary closed sets satisfying quasi-everywhere a conductivity assumption. This assumption is satisfied by a large class of compact sets, including all the sets which can be written as an arbitrary union of continua of positive diameter. The conductivity is a new regularity concept which is related to the thickness of the set and is to be compared to the Wiener regularity. In order to rigorously justify the numerical approach by the finite element method, we provide a stability result without any a priori smoothness assumptions. To cite this article: Z. Belhachmi, D. Bucur, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Key factor affecting the basicity of mesoporous silicas MCM-41: effect of surfactant extraction time and Si/Al ratio

Mesoporous silica Si-MCM-41 was prepared by hydrothermal method using TEOS and CTAB as the source of silica and structuring agent, respectively. The surface of the as-synthesized material was treated using HCl/ETOH solvent to remove the CTA surfactant instead of using the calcination. Characterization of the catalysts was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen sorption at 77 K, scanning and transmission electronic microscopy (SEM, TEM), and thermogravimetric analysis TGA. The catalytic properties of the prepared materials in the condensation of acetophenone with ethyl cyanoacetate were studied. The effects of the catalyst type, Si/Al ratio, reaction kinetics, and reaction temperature were also investigated to find an optimal parameter. The results show that an interesting yield was obtained (about 96%) in a short reaction time; it is found that the yields of products depend not only on the amount of surfactant inside the mesopores but also on the Si/Al ratio. The catalyst reuse shows that this catalyst can be used up to five cycles, and at temperatures higher than 50 °C, the yield of products decreases due to the slight destruction of the catalyst as confirmed by the XRD analysis. Based on the results obtained, a possible mechanism of the condensation reaction of acetophenone was proposed.     

Historical variations of Bera Lake (Malaysia) sediments geochemistry using radioisotopes and sediment quality indices

The Bera Lake basin is a lacustrine mire system and the largest natural lake in Peninsular Malaysia. Three cores were collected from the lake sediments in order to assess sediment quality and ecological risks for aquatic life and human health. An index analysis approach (C _f , C _d , E _r , and IR) and fallout ²¹⁰Pb and ¹³⁷Cs radioisotopes were applied to assess the impacts of environmental evolutionary changes. Sediment chronology was determined using the Constant Rate of Supply model with the resultant ages verified by ¹³⁷Cs horizons. Although the general contamination factors indicate low risk conditions in Bera Lake the risks associated with individual layers ranged from moderate to considerable. Five deforestation phases can be identified in the dated sediment cores with distinct variations in heavy metal influxes since 1972. These phases are in excellent agreement with the dates of land clearance and development projects undertaken over the past four decades. This study has highlighted the capability of contamination factors and chronological methods in environmental evolutionary studies where catchments have experienced extensive land use changes. The destiny of heavy metal influxes into a lake can also be revealed using this methodology.     

Synthesis and oxidation of (E)-1,2-diphenyl-2-(arylimino) ethanol derivatives

The compounds (E)-1,2-diphenyl-2-(phenylimino)ethanol, (E)-1,2-diphenyl-2-(p-tolylimino)ethanol, and (E)-2-((4-chlorophenyl)imino)-1,2-diphenylethanol) were synthesized by reaction of a p-substituted aniline with benzoin then oxidized with chromium trioxide–triethylamine in chloroform to give (E)-1,2-diphenyl-2-(phenylimino)ethanone, (E)-1,2-diphenyl-2-(p-tolylimino)ethanone, and (E)-2-((4-chlorophenyl)imino)-1,2-diphenylethanone in very high yield. The products were characterized by IR and NMR spectral analysis.     

Copper Adsorption on Chitosan-Derived Schiff Bases

The adsorption of Cu(II) ions onto the chitosan derived Schiff bases obtained from the condensation of chitosan with salicyaldehyde (polymer I), 2,4-dihydroxybenzaldehyde (polymer II) and with 4-(diethylamino) salicyaldehyde (polymer III) in aqueous solutions was investigated. Batch adsorption experiments were carried out as a function of contact time, pH, and polymer mass. The amount of metal-ion uptake of the polymers was determined by using atomic absorption spectrometry (AAS) and the highest Cu(II) ions uptake was achieved at pH 7.0 and by using sodium perchlorate as an ionic strength adjuster for polymers I, II, and III. The isothermal behavior and the kinetics of adsorption of Cu(II) ions on these polymers with respect to the initial mass of the polymer and temperature were also investigated; adsorption isothermal equilibrium data could be clearly explained by the Langmuir equation. The experimental data of the adsorption equilibrium from Cu(II) solution correlates well with the Langmuir isotherm equation.     

Thermal and sorption behavior of polyacrylonitrile supported hydrous titanium dioxide

Summary Modification of the physico-chemical properties of hydrous titanium dioxide (TiO₂) was conducted by using binding polyacrylonitrile (PAN) for the preparation of larger size particles having higher granular strength. The thermal behavior of the obtained composite has been studied by thermogravimetric and differential thermal analysis (TG/DTA). Sorption behavior of the TiO₂-PAN composite for removal of some hazardous radionuclides has been studied at different conditions such as, pH, contact time, ion concentrations and reaction temperature as well as the drying temperature. The effects of interfering ions as well as some complexing agents on the distribution ratio of the sorption process have been determined. As a result of the obtained data the optimum conditions for the removal of the studied radionuclides were recommended.