Discrete duality finite volume schemes for Leray−Lions−type elliptic problems on general 2D meshes

Discrete duality finite volume schemes on general meshes, introduced by Hermeline and Domelevo and Omnès for the Laplace equation, are proposed for nonlinear diffusion problems in 2D with nonhomogeneous Dirichlet boundary condition. This approach allows the discretization of non linear fluxes in such a way that the discrete operator inherits the key properties of the continuous one. Furthermore, it is well adapted to very general meshes including the case of nonconformal locally refined meshes. We show that the approximate solution exists and is unique, which is not obvious since the scheme is nonlinear. We prove that, for general W^?1,p′(Ω) source term and W^1‐(1/p),p(?Ω) boundary data, the approximate solution and its discrete gradient converge strongly towards the exact solution and its gradient, respectively, in appropriate Lebesgue spaces. Finally, error estimates are given in the case where the solution is assumed to be in W^2,p(Ω). Numerical examples are given, including those on locally refined meshes. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007     

An investigation of the role of the disparate redox states of the tetrathiafulvalene unit in modulating hydrogen bonding interactions in solution

We have investigated the electrochemically controlled hydrogen bonding interactions between tetrathiafulvalene host 3 and guests 4 or 5. Stabilisation of the 3⁺ state is dependent upon the nature of the guest species, whereas both guests prevent precipitation of the electrochemically generated 3²⁺ species at the working electrode via hydrogen bonded molecular recognition processes.     

Determination of thallium in natural waters by anodic stripping voltammetry

Thallium was determined in natural waters by anodic stripping voltammetry at a hanging mercury drop electrode, in acetate buffer pH 4.6+EDTA, after preconcentration and separation on an anion exhange resin. For Pacific Ocean surface waters a mean value of 13.0±1.4 ng Tl l^?1 was found, while for freshwater samples the value was 3.7±1.0 ng Tl l^?1. Thermodynamic considerations of thallium speciation predict that both in seawater and freshwater thallium exists primarily in the trivalent state. This was confirmed by experiment.     

Iron-catalyzed homo-coupling of simple and functionalized arylmagnesium reagents

Iron-catalyzed homo-coupling of simple and functionalized arylmagnesium reagents is described. The reaction is highly chemoselective (CN, COOEt and NO(2) groups are tolerated). The procedure was used to perform intramolecular couplings. This cyclization reaction is the key step of the total synthesis of the N-methylcrinasiadine.     

Cationic lanthanide complexes of neutral tripodal N,O ligands: enthalpy versus entropy-driven podate formation in water

The cationic lanthanide complexes of two neutral tripodal N,O ligands, tpa (tris[(2-pyridyl)methyl]amine) and tpaam (tris[6-((2-N,N-diethylcarbamoyl)pyridyl)methyl]amine) are studied in water. The analysis of the proton lanthanide induced NMR shifts indicate that there is no abrupt structural change in the middle of the rare-earth series. Unexpectedly, the formation constant values of the lanthanide podates of tpaam and tpa in D2O at 298 K are similar, suggesting that the addition of the three amide groups to the ligand tpa does not lead to any increase in stability of the lanthanide complexes of tpaam in respect to tpa, even though the amide groups are coordinated to the metal in aqueous solution. The measurement of the enthalpy and entropy changes of the complexation reactions shows that the two similar ligands tpa and tpaam have different driving forces for lanthanide complexation. Indeed, the formation of tpa podates benefits from an exothermic enthalpy change associated with a small entropy change, whereas the complexation reaction with tpaam is clearly entropy-driven though opposed by a positive enthalpy change. The hydration states of the europium complexes were measured by luminescence and show the coordination of 4-5 water ligands in [Eu(tpa)]3+ whereas there are only 2 in [Eu(tpaam)]3+. Therefore the heptadentate ligand tpaam releases the translational entropy of more water molecules than does the tetradentate ligand tpa.     

Pyridylmagnesiates: generation by bromine–metal exchange and enantioselective addition to aldehydes

Butyl and dibutylmagnesiates incorporating chiral ligands have been prepared and their reactivity studied. The reagents were efficient to promote the clean bromine–magnesium exchange of azinyl bromides at room temperature and subsequent reaction with aldehydes affording pyridylcarbinols. (R,R)-TADDOL-based dibutylmagnesiate was the best reagent leading to acceptable to good enantioselectivities, depending on the substrate and on the aldehyde substitution. This is the first example of enantioselective addition of in situ generated pyridylmagnesiate to carbonyl electrophiles.     

Screening of Wood/Forest and Vine By-Products as Sources of New Drugs for Sustainable Strategies to Control Fusarium graminearum and the Production of Mycotoxins

Fusarium graminearum is a fungal pathogen that can colonize small-grain cereals and maize and secrete type B trichothecene (TCTB) mycotoxins. The development of environmental-friendly strategies guaranteeing the safety of food and feed is a key challenge facing agriculture today. One of these strategies lies on the promising capacity of products issued from natural sources to counteract crop pests. In this work, the in vitro efficiency of sixteen extracts obtained from eight natural sources using subcritical water extraction at two temperatures was assessed against fungal growth and TCTB production by F. graminearum. Maritime pine sawdust extract was shown to be extremely efficient, leading to a significant inhibition of up to 89% of the fungal growth and up to 65% reduction of the mycotoxin production by F. graminearum. Liquid chromatography/mass spectrometry analysis of this active extract revealed the presence of three families of phenolics with a predominance of methylated compounds and suggested that the abundance of methylated structures, and therefore of hydrophobic compounds, could be a primary factor underpinning the activity of the maritime pine sawdust extract. Altogether, our data support that wood/forest by-products could be promising sources of bioactive compounds for controlling F. graminearum and its production of mycotoxins.     

Acetylene-terminated resins: Mechanism of thermal polymerization and properties of cured polymers

The polymerization kinetics and mechanisms of model compounds (mono- and difunctional) characteristic of prepolymers of ATR (acetylene-terminated resins) have been studied by HPLC, FTIR, UV, NMR (liquid and solid) and HPLC in the temperature range of 150–220°C. Using monofunctional compounds, we were able to show that the thermal polymerization of acetylene functions is not a simple reaction. Initially, the majority of compounds formed have a low polymerization degree, followed by the formation of species with higher and progressive polymerization degrees. Spectroscopic techniques such as NMR and FTIR lead to the unambiguous determination of reaction conversion up to 95% in the case of bifunctional prepolymers. The understanding of network structures, on the other hand, is more delicate in polyaromatic systems, since the chains formed are very similar to the basic skeleton of the prepolymer. The kinetic curves obtained isothermally between 150–220°C have shown that while kinetic monitoring of the disappearance of the first 90% of ethynyl functions poses no particular problems, there is a considerable uncertainty for the last 10%, regardless of the technique chosen. We have demonstrated that me thermal properties are dependent on the molecular weight and the structure of the polymer.     

An analysis of over-relaxation in a kinetic approximation of systems of conservation laws

The over-relaxation approach is an alternative to the Jin–Xin relaxation method in order to apply the equilibrium source term in a more precise way. This is also a key ingredient of the lattice Boltzmann method for achieving second-order accuracy. In this work, we provide an analysis of the over-relaxation kinetic scheme. We compute its equivalent equation, which is particularly useful for devising stable boundary conditions for the hidden kinetic variables.     

Improving imprinted shape cavities of molecularly imprinted sol–gel host matrix with minimal relaxation for sensing of creatinine

Journal of Sol-Gel Science and Technology - Molecularly imprinted polymer (MIP) is of great attention in biomimetic recognition systems due to its selective molecular recognition towards any guest...