Mean stress in a granular medium in dynamics

In this paper we propose to construct a mean stress tensor for a granular medium, valid in static and in dynamics, which takes into account the contact reactions and the body forces acting at the grain level. A simple analytical example shows that taking account of inertia forces is essential to insure the symmetry of the mean stress tensor in dynamics. Finally, numerical simulations illustrating this definition of the mean stress tensor are presented for a granular medium ensiled.     

Synthesis and spectral studies on some tetrahydrobenzoxanthen-11-ones: crystal and molecular structure of 9,9-dimethyl-12-(2-nitrophenyl)-8,9,10,12-tetrahydrobenzo[<Emphasis Type="Italic">a</Emphasis>]xanthen-11-one

A series of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones have been synthesized by the multicomponent reaction (MCR) of β-naphthol, aryl aldehydes, and dimedone by using BF₃:OEt₂ as a catalyst. The derived compounds have been analyzed by IR, NMR (1D and 2D), and mass spectra. The single crystal X-ray structural analysis of 9,9-dimethyl-12-(2-nitrophenyl)-8,9,10,12-tetrahydrobenzo[a]-xanthen-11-one evidences the envelope conformation of the cyclohexane ring and the pyran ring tends to adopt flattened-boat conformation.     

Optimization of extraction procedure and chromatographic separation of glyphosate, glufosinate and aminomethylphosphonic acid in soil

Analysing herbicides in soil is a complex issue that needs validation and optimization of existing methods. An extraction and analysis method was developed to assess concentrations of glyphosate, glufosinate and aminomethylphophonic acid (AMPA) in field soil samples. After testing extractions by accelerated solvent extraction and ultrasonic extraction, agitation was selected with the best recoveries. Water was preferred as solvent extraction because it resulted in a cleaner chromatogram with fewer impurities than was the case with alkaline solvents. Analysis was performed by FMOC pre-column derivatization followed by high-performance liquid chromatography (HPLC) on a 300 mm C(18) column which permitted enhanced separation and sensitivity than a 250 mm C(18) column and increased resistance than the NH(2) column for soil samples. This extraction and analysis method allowing a minimum of steps before the injection in the HPLC with fluorescence detection is efficient and sensitive for a clay-loamy soil with detection limits of 103 μg kg(-1) for glyphosate, 15 μg kg(-1) for glufosinate and 16 μg kg(-1) for AMPA in soil samples.     

Selective conversion of {Mo132} Keplerate ion into 4-electron reduced crown-capped Keggin derivative [Te5Mo15O57](8-). A key intermediate to single-phase M1 multielement MoVTeO light-alkanes oxidation catalyst

{Mo(132)} Keplerate anion reacts with tellurites to give a soluble precursor to produce in hydrothermal conditions single-phase M1 MoVTeO light-alkanes oxidation catalyst. Characterization of this Te-containing intermediate by single-crystal X-ray diffraction, (125)Te NMR, UV-visible and redox titration reveals a molybdotellurite anion as a crown-capped Keggin derivative.     

Quantum mechanics: cleaning up metaphysical baggage

The dynamic electronic structure of atoms and molecules can be directly observed by means of the (e, 2e) reaction, which measures the distribution of energies and momenta of two electrons in coincidence after a knockout reaction initiated by an electron beam of known momentum incident on a molecular gas target. The molecular state for each event is identified by the electron separation energy. The recoil momentum for each event is known from the difference of measured initial and final momenta. It has been verified that values of this momentum are equal under suitable conditions to the momentum of the electron in the target immediately before knockout. Thus the spherically-averaged electron momentum distribution for each molecular orbital is measured. This is directly related to molecular orbitals calculated by the methods of quantum chemistry. Properties obtained by this method for different types of molecules are discussed.     

An asymptotic non-linear model for thin-walled rods with strongly curved open cross-section

In this paper, we present a non-linear one-dimensional model for thin-walled rods with open strongly curved cross-section, obtained by asymptotic methods. A dimensional analysis of the non-linear three-dimensional equilibrium equations lets appear dimensionless numbers which reflect the geometry of the structure and the level of applied forces. For a given force level, the order of magnitude of the displacements and the corresponding one-dimensional model are deduced by asymptotic expansions.     

Mössbauer spectroscopic study of synthetic lipscombite and barbosalite at room temperature

Barbosalite and lipscombite hydroxyphosphates have been prepared and characterized by Mössbauer spectroscopy. These phases have been shown to be constituted of chains of Fe—oxygen octahedra sharing faces. The principal difference in the arrangement of the ions in these structures is the organization of the octahedra in the chains. In barbosalite, the chains are composed only of trimeric groups (Fe₃O₁₂) separated by a vacant octahedral site, while lipscombite chains are composed of groups of (2n + 1) iron cations,n varying from 0 to 5 or 6. The relative abundance of the different groups was calculated from published X-ray diffraction data and used to attribute the three ferric and the two ferrous doublets observed in the Mössbauer spectrum of lipscombite. This attribution is confirmed by the comparison with the results obtained on barbosalite.     

A 100-kW three-phase AC plasma furnace for spheroidization of aluminum silicate particles

A 100-kW three-phase ac plasma furnace with sheathed copper electrodes (sheathing gas: air) is presented. It is used for spheroidizing chamotte (refractory-fired clay) particles having a smooth, pore-free surface. A simple, one-dimensional numerical model for the heat transfer to the particles explains the maximum processing rate and the detrimental influence of an inhomogeneous particle size distribution.     

Ermittlung des Gehaltes der gewaschenen Wolle an organisch-l?slichen Stoffen

Ohne Zusammenfassung     

Sur le théorème en moyenne d'Akcoglu-Sucheston

Sans résumé