Search results for "Deute"
showing 10 items of 549 documents
Gas–solid chromatographic separation of hydrogen isotopes: a comparison between two palladium bearing materials – alumina and kieselguhr
1998
The separation of hydrogen isotopes (H, D, T) is performed by displacement gas chromatography on palladium. A large isotopic effect is associated with the reversible adsorption of hydrogen by palladium. Two Pd support materials have been compared: alpha-alumina and kieselguhr. The study includes a physicochemical characterization and a set of functional tests. The Van Deemter model gives a fairly good analysis of the process but to get more information, thermoregulated separations are needed. For both supports, palladium is impregnated as small dispersed particles in the 0.1 to 0.3 μm range diameter. For the same palladium loading, alumina is more efficient than kieselguhr.
Phenylene motion in polycarbonate and polycarbonate/additive mixtures
1987
Pulsed deuteron NMR line shapes have been analysed to characterize type and time scale of the phenylene group motion in glassy bisphenol-A polycarbonate. The motional mechanism involvesπ-flips about theC1C4 axis augmented by small angle fulctuations about the same axis, reaching a rms amplitude of ±35‡ at 380 K. The distribution of correlation times for theπ-flips is heterogeneous in nature and can be described either by a log-Gaussian or an asymmetric distribution with a more rapid decay at high correlation times comparable to the Williams-Watts distribution. From both distributions essentailly the same mean activation energy of 37 kJ/mol is obtained, whereas the temperature dependent widt…
On the 'expanded local mode' approach applied to the methane molecule: isotopic substitution CH2D2 <--- CH4
2011
International audience; On the basis of a compilation of the 'expanded local mode' model and the general isotopic substitution theory, sets of simple analytical relations between different spectroscopic parameters (harmonic frequencies, anharmonic coefficients, ro-vibrational coefficients, different kinds of Fermi- and Coriolis-type interaction parameters) of the CH2D2 molecule are derived. All of them are expressed as simple functions of a few initial spectroscopic parameters of the mother, CH4, molecule. Test calculations with the derived isotopic relations show that, in spite of a total absence of initial information about the CH2D2 species, the numerical results of the calculations have…
The proton radius puzzle
2017
High-precision measurements of the proton radius from laser spectroscopy of muonic hydrogen demonstrated up to six standard deviations smaller values than obtained from electron-proton scattering and hydrogen spectroscopy. The status of this discrepancy, which is known as the proton radius puzzle will be discussed in this paper, complemented with the new insights obtained from spectroscopy of muonic deuterium.
Caractères moisi-terreux des vins : origine et prévention
2005
Note de synthèse du groupe national de travail ONIVINS - juillet 2005; National audience
Sequential Iron-Catalyzed C(sp2)–C(sp3) Cross-Coupling of Chlorobenzamides/Chemoselective Amide Reduction and Reductive Deuteration to Benzylic Alcoh…
2023
Benzylic alcohols are among the most important intermediates in organic synthesis. Recently, the use of abundant metals has attracted significant attention due to the issues with the scarcity of platinum group metals. Herein, we report a sequential method for the synthesis of benzylic alcohols by a merger of iron catalyzed cross-coupling and highly chemoselective reduction of benzamides promoted by sodium dispersion in the presence of alcoholic donors. The method has been further extended to the synthesis of deuterated benzylic alcohols. The iron-catalyzed Kumada cross-coupling exploits the high stability of benzamide bonds, enabling challenging C(sp2)–C(sp3) cross-coupling with alkyl Grign…
Beyond Subsidies: A Study of Sustainable Public Subordinated Debt in Spain
2019
Evidence from business shows that small- and medium-sized enterprises (SMEs) are fragile. They suffer from a high mortality rate that primarily owes to difficulties in securing financing as a result of major information asymmetries. Despite these difficulties, SMEs provide the economic backbone of all economically developed countries. Aware of the key role of SMEs in national economic stability and of the financial problems that SMEs face, governments have designed a range of financial and tax measures to protect them. These financial measures include a highly specific form of public financing called subordinated debt. This concept refers to debt with the lowest credit seniority, just befor…
The glass transition in (KI)0.5(ND4I)0.5 mixed crystals as studied by deuteron spin-lattice relaxation
1993
Abstract Nuclear spin resonance has been used to study the deuteron magnetization recovery in (KI)0.5(ND4I)0.5 mixed crystals. At high temperatures the spin-lattice-relaxation is exponential. For T ⪅ 45 K deviations from this simple behaviour occur, signalling the onset of spatial inhomogeneities due to the formation of an orientational glass. The results demonstrate that the transition of (KI)0.5(ND4I)0.5 into the glassy state is driven by the freezing of random bonds.
Pseudo-solid echoes of proton and deuteron NMR in polyethvlene melts
1981
The solid echo technique is applied to determining residual dipolar and quadrupolar couplings in molten polyethylene (PE) and deuterated PE, respectively. The residual coupling defined by the square root of the second moment is about 1% of the corresponding quantity in the solid. It increases with molecular weight, and decreases with rising temperature. A theoretical treatment of time dependent residual couplings yields a decay time that is found experimentally to be about 0.1 ms in molten PE, and independent of molecular weight and temperature within our limits of accuracy. The residual coupling is discussed in relation with chain entanglement in PE. Measurements of the spin-lattice and sp…
Neutron Scattering of Poly(ethylene terephthalate)
1986
Through the use of deuterium labeling, small angle neutron scattering (SANS) has been found to be an extremely effective tool for elucidating the structure of polymer molecules in the condensed matter state. In this study, the molecular morphology of poly(ethylene terephthalate) (PET) has been determined under four different conditions: (1) in the glassy state, (2) in the semicrystalline state, (3) after cold-drawing, and (4) after undergoing partial transesterification.