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1.
We present a kinematically complete study of dissociative ionization of D(2) by 13.6 MeV/u S(15+) ions. The experiment allows us to unravel the competing mechanisms, namely, direct single ionization, autoionization of doubly excited states, ionization excitation, and double ionization, and to analyze the corresponding electron angular distribution from fixed-in-space molecules. The conclusions are supported by theoretical calculations in which the correlated motion of all electrons and nuclei and the interferences between them are described from first principles.  相似文献   
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3.
We display irreducible representations of the Virasoro algebra (group of diffeomorphisms of the circle) for any value of the central chargec (central extension defined by a cocycle) and of the highest weight, where the Ka determinants do not vanish. The construction is done in terms of a simple bosonic free field. The unitarity of the representation is discussed, and it is realized with non-trivial hermiticity properties of the free field if<(c-1)/24. In the particular case of the central charge (c=1/2) corresponding to the Ising model, the three unitary irreducible representations (=0, 1/16, 1/2) are realized in terms of the anticommuting oscillators of the free fields of the Neveu-Schwarz-Ramond model.  相似文献   
4.
The study of the early oeuvre of the Swiss painter Cuno Amiet (1868–1961) has revealed that, up to 1907, many of his grounds were hand applied and are mainly composed of chalk, bound in protein. These grounds are not only lean and absorbent, but also, as Synchrotron radiation X-ray microtomography has shown, porous. Our approach to the characterization of pore structure and quantity, their connectivity, and homogeneity is based on image segmentation and application of a clustering algorithm to high-resolution X-ray tomographic data. The issues associated with the segmentation of the different components of a ground sample based on X-ray imaging data are discussed. The approach applied to a sample taken from “Portrait of Max Leu” (1899) by Amiet revealed the presence of three sublayers within the ground with distinct porosity features, which had not been observed optically in cross-section. The upper and lower layers are highly porous with important connectivity and thus prone to water uptake/storage. The middle layer however shows low and nonconnected porosity at the resolution level of the X-ray tomography images, so that few direct water absorption paths through the entire sample exist. The potential of the method to characterize porosity and to understand moisture-related issues in paint layer degradation are discussed.  相似文献   
5.
Polycrystalline YMn1−xFexO3 (x=0.02-0.20) powders were synthesized by means of modified citrate method. Powder X-ray diffraction gives evidence that all the samples are single phase and exhibit hexagonal structure with P63cm space group as observed for YMnO3. The solubility limit of Fe was determined as about 6 wt.%. Cell parameter values were found to increase with Fe content, since Fe3+ and Mn3+ have the same ionic radii. This can be attributed to the increase of the tilting of MnO5 bipyramid and the buckling of Y atoms. In addition, 57Fe Mössbauer spectrometry provides evidence of two Fe3+ sites attributed to two different nearest atomic neighbours. Magnetic properties reveal a paramagnetic-to-antiferromagnetic transition, a possible increase of the magnetic anisotropy, and a competition between ferromagnetic and antiferromagnetic interactions.  相似文献   
6.
The modulated phase of (C3H7NH3)CuCl4 stable between 386 and 412 K has been analyzed by single-crystal X-ray diffraction. The structure was solved in the frame of the superspace group approach. The modulation is characterized by a wavelike displacement of the CuCl4 layer.  相似文献   
7.
In a previous paper, the quantum-group-covariant chiral vertex operators in the spin 1/2 representation were shown to act, by braiding with the other covariant primaries, as generators of the well known Uq(sl(2)) quantum group symmetry (for a single screening charge). Here, this structure is transformed to the Bloch wave/Coulomb gas operator basis, thereby establishing for the first time its quantum group symmetry properties. A Uq(sl(2)) Uq(sl(2)) symmetry of a novel type emerges: The two Cartan-generator eigenvalues are specified by the choice of matrix element (Vermamodules); the two Casimir eigenvalues are equal and specified by the Virasoro weight of the vertex operator considered; the co-product is defined with a matching condition dictated by the Hilbert space structure of the operator product. This hidden symmetry possesses a novel Hopf-like structure compatible with these conditions. At roots of unity it gives the right truncation. Its (non-linear) connection with the Uq(sl(2)) previously discussed is disentangled. Received: 25 April 1996/Accepted: 20 July 1996  相似文献   
8.
J.P. Flament  H.P. Gervais 《Tetrahedron》1980,36(13):1949-1952
Ab initio calculations for two conformers of 3-methyl cyclopentanone, with and without 3d orbitals, show that inclusion of d orbitals on the carbonyl group lower energies and is thus necessary, as follows from the variation principle; it also markedly affects rotatory strengths of the n→π* and π→π* transitions, but conformational equilibria of the cyclic skeleton and the methyl group are almost independent of the basis chosen. Internal rotation of the methyl group exerts a negligible influence on the rotatory strength of the n→π* transition, so that this group can be considered as a sphere in this respect.  相似文献   
9.
A DFT‐based molecular model for imidazolium–silica‐based nanoparticle networks (INNs) is presented. The INNs were synthesized and characterized by using small‐angle X‐ray scattering (SAXS), NMR spectroscopy, and theoretical ab initio calculations. 11B and 31P HETCOR CP MAS experiments were recorded. Calculated 19F NMR spectroscopy results, combined with the calculated anion–imidazolium (IM) distances, predicted the IM chain density in the INN, which was also confirmed from thermogravimetric analysis/mass spectrometry results. The presence of water molecules trapped between the nanoparticles is also suggested. First considerations on possible π–π stacking between the IM rings are presented. The predicted electronic properties confirm the photoluminescence emissions in the correct spectral domain.  相似文献   
10.
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