A Temperature Frequency Response Method for Adsorption Kinetics Measurements

A Frequency Response Method based on the infrared measurement of the sample temperature has been developed for adsorption kinetics measurements. It consists in modulating the experimental chamber volume at constant frequency. The complex ratio of the temperature response over the pressure response is independent of time but is a function of the frequency depending on all the kinetics parameters of the system. This method is accurate and allows to measure very fast kinetics. Its major drawback is that a spurious signal is observed at high pressure in absence of adsorption. The results obtained with silicalite-propane and NaX-carbon dioxide are compared with results obtained from other techniques (NMR, permeation, etc.).     

High-temperature organic reactions at room temperature using plasmon excitation: decomposition of dicumyl peroxide

Photoexcitation of gold nanoparticles in their plasmon transition around 530 nm provides the means to carry high-energy reactions at room temperature. In the case of dicumyl peroxide (with activation energy of 34.3 kcal/mol) the reaction occurs in less than 1 min under 532 nm laser excitation. The results suggest that the peroxide is exposed to temperatures of ~500 °C for submicrosecond times, and provides a guide as to which type of organic reactions may benefit from plasmon-mediated energy delivery.     

On the determination of the force distribution in overconstrained cable-driven parallel mechanisms

This paper addresses the determination of the force distribution in the cables of a redundantly actuated cable-driven parallel mechanism. First, the static model of cable-driven parallel mechanisms is derived based on the wrench matrix. Then, four performance indices are considered in order to solve the underdetermined problem associated with the distribution of the forces. A simple numerical example is then developed in order to provide insight into the problem, which leads to a geometric interpretation of the results. Based on the presented results, it is proposed to use a p-norm (e.g. a 4-norm) to optimize the distribution of the forces in a cable-driven parallel mechanism in order to minimize the largest deviations from the median forces (or other target values) while maintaining continuity in the solution. A non-iterative polynomial formulation is then proposed for the 4-norm. It is also pointed out that this formulation leads to a unique real solution.     

Highly luminescent europium(III) complexes with naphtoiltrifluoroacetone and dimethyl sulphoxide

The synthesis, luminescence properties, experimental determination and theoretical calculation of the emission quantum yield of Eu(NTA)₃.2L complexes, where NTA is naphtoiltri-fluroacetone and L denotes H₂O or DMSO (dimethyl sulphoxide), were reported. The compounds were characterized by elemental analysis (carbon, hydrogen and europium), thermal analysis, UV-visible absorption and photoluminescence spectroscopies. The experimental quantum yields were determined based on a method previously proposed by Bril and collaborators. The Eu(NTA)₃.2DMSO compound shows a high value for the Ω₂ intensity parameter (35.8 × 10^?20 cm²), reflecting the hypersensitive nature of the ⁵D₀ → ⁷F₂ transition and indicating that the lanthanide ion is in a highly polarizable chemical environment. The experimental quantum yield measured for that compound, 0.75, is one of the highest so far reported for solid-state europium complexes. The theoretical calculations of the quantum yield were carried out by solving an appropriate set of rate equations and by using empirical spectroscopic parameters and energy transfer rates. The theoretical results agree well with the experimental data for both complexes. The photostability of Eu(NTA)₃.2DMSO at 358K was evaluated in order to verify whether this complex can be applied as a phosphor for blue light emitting devices.     

Anisotropic surface melting in lyotropic cubic crystals

From experiments with metal crystals, in the vicinity of their crystal/liquid/vapor triple points, it is known that melting of crystals starts on their surfaces and is anisotropic. Recently, we have shown that anisotropic surface melting occurs also in lyotropic systems. In our previous paper (Eur. Phys. J. E 19, 223 (2006)), we have focused on the case of poor faceting at the Pn3m/L1 interface in C12EO2/water binary mixtures. There anisotropic melting occurs in the vicinity of a Pn3m/L3/L1 triple point. In the present paper, we focus on the opposite case of a rich devil's-staircase-type faceting at Ia3d/vapor interfaces in monoolein/water and phytantriol/water mixtures. We show that anisotropic surface melting takes place in these systems in a narrow humidity range close to the Ia3d-L2 transition. As whole (hkl) sets of facets disappear one after another when the transition is approached, surface melting occurs in a facet-by-facet type.     

Anisotropic surface melting in lyotropic cubic crystals

From experiments with ice or metal crystals, in the vicinity of their crystal/liquid/vapor triple points, it is known that melting of crystals starts on their surfaces and is anisotropic. It is shown here by direct observations under an optical microscope that this anisotropic surface melting phenomenon occurs also in lyotropic systems. In the case of C12EO2/water mixture, it takes place in the vicinity of the peritectic Pn3m/L3/L1 triple point. Above the peritectic triple point, where the Pn3m and L1 phases coexist in the bulk, the surface of a Pn3m-in-L1 crystal is composed of (111)-type facets surrounded by rough surfaces. The angular junction suggests that rough surfaces are wet by a L3-like layer while facets stay “dry”. This is analogous to the pre-melting at rough surfaces in solid crystals. Upon cooling below the peritectic triple point, where L3 and L1 phases coexist in the bulk, a thick layer of the L3 phase grows from the pre-melted, rough Pn3m/L1 interface. Simultaneously, facets stay dry and their radius decreases. In this tri-phasic configuration, stable in a narrow temperature range, the L3/L1 and L3/Pn3m interfaces have shapes of constant mean curvature surfaces having common borders: edges of facets.     

T2 relaxation time histograms in multiple sclerosis

An accurate measurement of the transverse relaxation time T₂, and the histogram of T₂ in the brain parenchyma can be accomplished in vivo using a multi-echo magnetic resonance imaging sequence. An estimate of the error in the T₂ measurement is derived using copper sulfate doped water phantoms. Correction factors are calculated and applied to the signal intensity of each voxel prior to the in vivo T₂ evaluation. These corrected T₂ are in good agreement with the theoretical values calculated from copper sulfate concentrations. This technique is then applied to calculate T₂ histograms of the brain. The population studied was composed of normal volunteers and multiple sclerosis patients. The corrected T₂ histogram method discriminates the normal control population from the MS population, and also discriminates between relapsing-remitting patients and primary progressive or secondary progressive patients. Moreover using this approach we are able to detect in MS patients a global shift of the T₂ of the white mater toward higher values. The results of this study showed that the method is easy to implement and may be used to characterize MS pathology.     

Reaction epoxy-amine: Suivi du mecanisme reactionnel et de la cinetique par RMN 13C, 15N et HPLC

The curing reaction of diglycidyl ether of bisphenol A (DGEBA) with metaphenylene diamine (mPDA) was investigated with high performance liquid chromatography (HPLC) and Fourier transform nuclear magnetic resonance spectroscopy (FT NMR ¹³C and ¹⁵N). With the results obtained from a series of models a mechanism was proposed and the cure kinetics were obtained at 100°C. The major conclusion is that the cure proceeded mainly by chain extension, whereas crosslinking occurred in the reaction of hydroxyl groups with epoxides and resulted in the formation of ether linkages.     

Cooperative ordering of gapped and gapless spin networks in Cu2Fe2Ge4O13

The unusual magnetic properties of a novel low-dimensional quantum ferrimagnet Cu2Fe2Ge4O13 are studied using bulk methods, neutron diffraction, and inelastic neutron scattering. It is shown that this material can be described in terms of two low-dimensional quantum spin subsystems, one gapped and the other gapless, characterized by two distinct energy scales. Long-range magnetic ordering observed at low temperatures is a cooperative phenomenon caused by weak coupling of these two spin networks.