Characterisation of fatty acids in biological oil samples using comprehensive multidimensional gas chromatography

Comprehensive multidimensional gas chromatography can adequately resolve very complex mixtures of analytes such as the fatty acid mixtures which are contained in, e.g., fish and vegetable oils. Well-ordered patterns are obtained in the two-dimensional separation plane which can be used to tentatively identify peaks when no standard is available. The technique which can also be used for quantification, i.e., quantitative ratio analysis, should be especially useful for fingerprinting purposes. Unravelling the composition of complex mixtures such as fish oils appears to be highly rewarding.     

A stereodivergent approach to substituted 4-hydroxypiperidines

A stereodivergent route toward both diastereomeric forms of functionalized 4-hydroxypiperidines has been successfully developed. This route involves biocatalytic generation of the enantiopure starting materials followed by functionalization via N-acyliminium ion-mediated CC-bond formation.     

Snx[BPO4]1−x composites as negative electrodes for lithium ion cells: Comparison with amorphous SnB0.6P0.4O2.9 and effect of composition

A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB_0.6P_0.4O_2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn_0.72[BPO₄]_0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO₄ matrix. The electrochemical responses of ATCO and Sn_0.72[BPO₄]_0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g⁻¹, respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by ¹¹⁹Sn Mössbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous Sn^II composite oxide and shows that in the case of Sn_0.72[BPO₄]_0.28, the surface of the tin clusters is mainly formed by Sn^II in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn⁰. The determination of the recoilless free fractions f (Lamb-Mössbauer factors) leads to the effective fraction of both Sn⁰ and Sn^II species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Sn_x[BPO₄]_1−x composite materials (0.17<x<0.91). The cell using the compound Sn_0.72[BPO₄]_0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g⁻¹ at C/5 rate).     

Isochronous centers of polynomial Hamiltonian systems and a conjecture of Jarque and Villadelprat

We study the conjecture of Jarque and Villadelprat stating that every center of a planar polynomial Hamiltonian system of even degree is nonisochronous. This conjecture has already been proved for quadratic and quartic systems. Using the correction of a vector field to characterize isochronicity and explicit computations of this quantity for polynomial vector fields, we are able to describe a very large class of nonisochronous Hamiltonian systems of even arbitrarily large degree.     

Determination of iodate in rain-water

The determination of iodate in rain-water by neutron activation analysis is described. Iodate is separated by anion exchange. The determination limit of I is 0.02 μg·L⁻¹ for a 20 ml sample. The influence of the sea on the composition of rain-water is demonstrated by the analysis of coastal rain-water. The results indicate that inorganic iodine (I₂ and IO ₃ ⁻ ) is enriched in filtered coastal rain-water relative to the composition of sea-water.     

Parity- and time-reversal-violating moments of light nuclei

I present the calculation of parity- and time-reversal-violating moments of the nucleon and light nuclei, originating from the QCD $\bar \theta$ term and effective dimension-six operators. By applying chiral effective field theory these calculations are performed in a unified framework. I argue that measurements of a few light-nuclear electric dipole moments would shed light on the mechanism of parity and time-reversal violation.     

NMR evidence of LiF coating rather than fluorine substitution in Li(Ni0.425Mn0.425Co0.15)O2

A series of “Li_1+z/2(Ni_0.425Mn_0.425Co_0.15)_1−z/2O_2−zF_z” materials was prepared by a coprecipitation route and their structure was characterized using X-ray diffraction (XRD), as well as ⁷Li and ¹⁹F Magic Angle Spinning (MAS) NMR spectroscopy. Two hypotheses were considered: (i) formation of layered oxyfluoride materials and (ii) formation of a mixture between the layered material and LiF. Structural parameters were refined by the Rietveld method, using XRD diffraction data. The refinement results did not allow us to choose between these two hypotheses: no significant change in crystallinity and structural parameters was observed irrespective of the fluorine ratio. ⁷Li and ¹⁹F MAS NMR analyses showed signals with isotropic positions characteristic of LiF, but envelopes characteristic of very strong dipolar interactions with the electron spins of the material, demonstrating that LiF was not incorporated into the layered oxide structure but was instead present as a coating.     

On dual molecules and convolution-dominated operators

We show that sampling or interpolation formulas in reproducing kernel Hilbert spaces can be obtained by reproducing kernels whose dual systems form molecules, ensuring that the size profile of a function is fully reflected by the size profile of its sampled values. The main tool is a local holomorphic calculus for convolution-dominated operators, valid for groups with possibly non-polynomial growth. Applied to the matrix coefficients of a group representation, our methods improve on classical results on atomic decompositions and bridge a gap between abstract and concrete methods.     

The determination of bromine and iodine in environmental water samples by thermal neutron activation and isotope exchange

A routine-method for the determination of bromine and iodine in environmental water by neutron activation is presented. The elements are isolated by isotope exchange between the irradiated sample and a solution of Br₂ or I₂ CCl₄. The method is not sensitive to the chemical species in which the halogen is present. The lower limit of the determination is 1.0 μg Br·1⁻¹ and 0.1 μgI·1⁻¹.