Macrocycles as components of gas-chromatographic phases

The use of crown compounds (18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6, benzo-15-crown-5, dibenzo-24-crown-8, 4,13-diaza-18-crown-6,4,13-dibenzyl-diaza-18-crown-6, and cryptand [2.2.2]) as components of stationary phases in the determination of organic compounds by gas chromatography is studied. The polarity, selectivity, efficiency, and working temperature ranges of stationary phases based on crown ethers and cryptand as well as conventional stationary phases for gas chromatography are compared. The influence of the type and number of heteroatoms, the conformational lability of the cavity, and the presence of substituents on the polarity and selectivity of the stationary phases under study is revealed. Preferable types of interactions of stationary phases containing crown compounds with organic compounds of different classes are discussed. It is concluded that phases of the mixed type based on crown ethers are promising for improving the selectivity and efficiency of gas-chromatographic separation     

Interrelated functionalities of hierarchically CNT/CeO2/Pt nanostructured layers: synthesis, characterization, and electroactivity

We present a free-standing catalyst layer comprising current collector/CNTs (catalyst support)/CeO(2)/Pt (catalyst) nanostructured layers, each layer constructed upon the one below it. FESEM and TEM showed that a CeO(2) layer has a fluffy morphology recalling the texture of cotton, whereas Pt nanoparticles assemble into cauliflower or broccoli-like arrangement. New insights have been gained into the effect of CeO(2) on the structural properties of the beneath CNTs layer and on the above Pt layer. First, by means of Raman analysis, it was found that interaction of CeO(2) with CNTs induced a decrease in the crystallinity of the latter. Second, by TEM and XPS analyses, it was observed that the size of Pt nanoparticles in the CNT/CeO(2)/Pt structure was inferior to that in the CNT/Pt, implying that CeO(2) influenced the dispersion quality of Pt nanoparticles. For the first time, it is observed that CeO(2) supported CNTs undergo oxidation/reduction reactions at low potentials in the ethanol electrolyte. The electrochemical analysis showed that entities produced from those redox processes are surface adsorbed/desorbed species most likely hydroxides. This unexpected electroactivity is due to the beneath CNTs that boosted the conductivity of CeO(2). Such improved conductivity of CeO(2) has fostered the electron-transfer kinetics of ethanol at Pt as demonstrated by the decreased overpotential required to oxidize ethanol and by the specific mass activity, which was greater than that of CNT/Pt.     

On steady motions of a rigid body bearing three-degree-of-freedom control momentum gyroscopes and their stability

Equations of motion are obtained for a rigid body bearing N three-degree-of-freedom control momentum gyroscopes in gimbals and the entire set of steady motions in a homogeneous external field is determined. The steady motion dependence on the magnitude of the system angular momentum is studied and a detailed analysis of the secular stability is performed.     

Missing boundary data reconstruction by the factorization method

We consider the data completion problem for the Laplace equation in a cylindrical domain. The Neumann and Dirichlet boundary conditions are given on one face of the cylinder while there is no condition on the other face. This Cauchy problem has been known since Hadamard (1953) to be ill-posed. Here it is set as an optimal control problem with a regularized cost function. We use the factorization method for elliptic boundary value problems. For each set of Cauchy data, to obtain the estimate of the missing data one has to solve a parabolic Cauchy problem in the cylinder and a linear equation. The operator appearing in these problems satisfy a Riccati equation that does not depend on the data. To cite this article: A. Ben Abda et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Solvent effects on the initial and transition states upon solvolysis oftrans-dichlorotetra(4-ethylpyridine)cobalt(III) perchlorate in water+methanol mixtures

Summary The solvolysis of trans-[Co(4-Etpy)₄Cl₂]⁺ (1) (Etpy=ethylpyridine) was investigated in water and in a wide range of water+methanol mixtures. The effect of temperature on the solvolysis was considered and the thermodynamic parameters of activation were calculated. The free energies of transfer of (1) in the initial state were calculated from the solubility of the complex [Co(4-Etpy)₄Cl₂]₂[ReCl₆]. The free energy of transfer of the cation (1) in the transition state was calculated using a free energy cycle. The effect of the solvent structure on (1) is dominant in the transition state, where –G _t ^o (1) transition >–G _t ^o (1) initial. Comparison of the present thermodynamic data with those obtained previously fortrans-[Co(4-Mepy)₄Cl₂]⁺, (2), andtrans-[Co(py₄Cl₂]⁺, (3) in the same solvent mixture, shows that the stability increases in the order: (1), (2)<(3) at low mole fraction of the co-solvent, contrary to expectation, while at high mole fraction the order of increasing stability is: (1)<(3)<(2). The results were interpreted on non-electrostatic grounds.     

Adaptive fuzzy control‐based projective synchronization of uncertain nonaffine chaotic systems

This article aims to introduce a projective synchronization approach based on adaptive fuzzy control for a class of perturbed uncertain multivariable nonaffine chaotic systems. The fuzzy‐logic systems are employed to approximate online the uncertain functions. A Lyapunov approach is used to design the parameter adaptation laws and to demonstrate the boundedness of all signals of the closed‐loop system as well as the convergence of the synchronization errors to bounded residual sets. Finally, numerical simulation results are presented to verify the feasibility and effectiveness of the proposed synchronization system based on fuzzy adaptive controller. © 2014 Wiley Periodicals, Inc. Complexity 21: 180–192, 2015     

Separation of representations with quadratic overgroups

Any unitary irreducible representation π of a Lie group G defines a moment set Iπ, subset of the dual g^? of the Lie algebra of G. Unfortunately, Iπ does not characterize π. If G is exponential, there exists an overgroup G⁺ of G, built using real-analytic functions on g^?, and extensions π⁺ of any generic representation π to G⁺ such that Iπ⁺ characterizes π.In this paper, we prove that, for many different classes of group G, G admits a quadratic overgroup: such an overgroup is built with the only use of linear and quadratic functions.     

Antioxidant Properties of Gluten-Free Pasta Enriched with Vegetable By-Products

The only therapy for coeliac disease patients is to completely avoid foods containing gluten, a protein complex common in several small-grain cereals. However, many alternative gluten-free foods available on the market present nutritional deficiencies. Therefore, the aim of this research was to evaluate the composition and the antioxidant properties of gluten-free pasta enriched with 10% or 15% of tomato waste or linseed meal, two food industry by-products. The traits analysed were protein, lipid, ash and fibre content, heat damage, tocols, carotenoids and phenolics composition (by HPLC), antioxidant capacity, and pasta fracturability. The enriched pastas contained more fibre and lipids than the control, while the protein and ash values were similar. The addition of tomato and linseed waste improved tocols concentration but had no effect on carotenoids content. The free soluble polyphenols increase was similar for both by-products and proportional to the enrichment percentage, while the bound insoluble polyphenols were higher in linseed-enriched pastas. The samples with linseed meal showed the greatest antioxidant capacity and, at 10% addition, the highest fracturability value. In conclusion, the addition of tomato and linseed by-products significantly increases the presence of bioactive compounds (particularly polyphenols), improving the nutritional value of gluten-free pasta.     

Solvent Effects on the Kinetics of Amide Bond Cleavage in p-Chloro and p-Bromo Oxazolinones in Acetonitrile–Water Mixtures

The kinetics of amide bond cleavage in p-chloro and p-bromo oxazolinone have been studied using triethylamine as a base catalyst under pseudo-first order conditions, in the temperature range (303.15?C333.15?K). The reaction rate was measured spectrophotometrically over a range of acetonitrile?Cwater mixed solvent (30?C70?%, v/v) compositions. The reaction rate was found to be faster for p-Cl than for p-Br oxazolinone. The thermodynamic parameters of activation were calculated: ?G* increased gradually as the mole fraction of the cosolvent increased due to quasi-mirror image compensation of ?H* and ?S* (entropy?Centhalpy compensation). The isokinetic temperature indicates that the reaction is enthalpy controlled. The reactivity was analyzed in the light of various simple and multiple regression equations using the Kamlet?CTaft solvatochromic parameters.