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81.
Recently, an infinite family of chiral Virasoro vertex operators, whose exchange algebra is given by the universalR-matrix ofSL(2)
q
, has been constructed. In the present paper, the case of non-linearly (W-) extended Virasoro symmetries, related to the algebrasA
N,N>1, is considered along the same line. Contrary to the previous case (A
1) the standardR-matrix ofSL(N+1)q does not come out, and a different solution of Yang and Baxter's equations is derived. The associated quantum group structure is displayed.Unité Propre du Centre National de la Recherche Scientifique, associée à l'École Normale Supérieure et à l'Université de Paris-Sud 相似文献
82.
N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献
83.
A correlation between Szigeti effective charge and the electronic polarizability is found for the eight compounds containing divalent lead where experimental data are available. Results in Pb5Ge3O11 contribute to remove some ambiguity about the assignment of polar vibrational modes as external or internal to GeO4 and Ge2O7 entities in ferroelectric lead germanate. Complete TO-LO splittings are also deduced from infrared reflection spectra obtained at room temperature. Results are compared with previous controversial Raman measurements of the polar character of the modes including the soft mode. 相似文献
84.
85.
Dr. Thomas-Xavier Métro Prof. Christel Gervais Anthony Martinez Prof. Christian Bonhomme Dr. Danielle Laurencin 《Angewandte Chemie (International ed. in English)》2017,56(24):6803-6807
17O NMR spectroscopy has been the subject of vivid interest in recent years, because there is increasing evidence that it can provide unique insight into the structure and reactivity of many molecules and materials. However, due to the very poor natural abundance of oxygen-17, 17O labeling is generally a prerequisite. This is a real obstacle for most research groups, because of the high costs and/or strong experimental constraints of the most frequently used 17O-labeling schemes. Here, we show for the first time that mechanosynthesis offers unique opportunities for enriching in 17O a variety of organic and inorganic precursors of synthetic interest. The protocols are fast, user-friendly, and low-cost, which makes them highly attractive for a broad research community, and their suitability for 17O solid-state NMR applications is demonstrated. 相似文献
86.
A fiber-optic-based polarization control system that uses a backreflection measurement scheme at low temperatures has been developed. This provides a stringent test of the light polarization state at the output of the fiber, allowing for determination and control of the degree of circular polarization; i.e., it can generate linear, right, or left circular polarization with cryogenic fibers. This polarization controller is paving the way toward the control and manipulation of nuclear spins in semiconductors via the optical Overhauser effect and could be used, for example, for the purpose of quantum information processing with the large nuclear spins of GaAs. 相似文献
87.
Gervais C Coelho C Azaïs T Maquet J Laurent G Pourpoint F Bonhomme C Florian P Alonso B Guerrero G Mutin PH Mauri F 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,187(1):131-140
The complete set of NMR parameters for (17)O enriched phenylphosphinic acid C(6)H(5)HP( *)O(*OH) is calculated from first principles by using the Gauge Including Projected Augmented Wave (GIPAW) approach [C.J. Pickard, F. Mauri, All-electron magnetic response with pseudopotentials: NMR chemical shifts, Phys. Rev. B 63 (2001) 245101/1-245101/13]. The analysis goes beyond the successful assignment of the spectra for all nuclei ((1)H, (13)C, (17)O, (31)P), as: (i) the (1)H CSA (chemical shift anisotropy) tensors (magnitude and orientation) have been interpreted in terms of H bonding and internuclear distances. (ii) CSA/dipolar local field correlation experiments have allowed the orientation of the direct P-H bond direction in the (31)P CSA tensor to be determined. Experimental and calculated data were compared. (iii) The overestimation of the calculated (31)P CSA has been explained by local molecular reorientation and confirmed by low temperature static (1)H-->(31)P CP experiments. 相似文献
88.
Marc-André Coulombe Martin Lebeuf Neal Fairley John Walton Gervais Soucy 《Journal of Electron Spectroscopy and Related Phenomena》2012
Aluminium carbide formation and subsequent dissolution is a generally accepted mechanism to explain the cathode wear in the Hall-Héroult industry. Carbide formation is thought to occur inside the cathode pores. Being dependent upon cathodic current density, it is believed to be an electrochemical process. It is also associated with the presence of cryolitic bath species involved in the dissolution of the carbide layer and thus enabling further carbide formation. 相似文献
89.
S. Krohns J. Lu P. Lunkenheimer V. Brizé C. Autret-Lambert M. Gervais F. Gervais F. Bourée F. Porcher A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,72(2):173-182
The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu3Ti4O12 (CCTO) ceramics. For this purpose, neutron and X-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T. At low temperatures the dielectric constant shows a minor but significant dependence on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant. 相似文献
90.
A combined wall pressure/velocity analysis of the wake of a disk located in the vicinity of a flat wall is presented in this
paper. One gap ratio only is selected. In this situation, the footprint of the flow unsteadiness on the magnitude of the wall
fluctuating pressure is significant while the natural vortex shedding properties of the wake are only slightly altered. Spatio-temporal
velocity and pressure/velocity correlations are analyzed. They carry the signature of the large-scale coherence and periodicity
associated with vortex shedding and exhibit characteristic phase relations. Advanced statistical analysis techniques are adapted
and developed. A conditional phase averaging of the pressure and velocity fields is obtained. The proper orthogonal decomposition
of a spatio-temporal pressure data set on the axis of the near wake is shown to be efficient (1) to determine the phase of
the spatio-temporal pressure field projected on the two first modes and (2) to distinguish between quiescent random signatures
and more energetic phases. Conditional statistics show very clearly that the large-scale structures interact with the flat
wall. Finally, a linear stochastic estimation (LSE) of the velocity field is computed from the fluctuating pressure data.
We show the superiority of the spatio-temporal LSE over the spatial LSE in predicting the kinetic energy and the coherent
spectral properties of the fluctuating velocity field. Moreover, the linear stochastic estimation is very good in predicting
the phase-averaged conditional velocity field. 相似文献