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81.
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
82.
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
83.
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
84.
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
85.
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
86.
Dean CR Piot BA Hayden P Das Sarma S Gervais G Pfeiffer LN West KW 《Physical review letters》2008,100(14):146803
The fractional quantum Hall effect is observed at low magnetic field where the cyclotron energy is smaller than the Coulomb interaction energy. The nu=5/2 excitation gap at 2.63 T is measured to be 262+/-15 mK, similar to values obtained in samples with twice the electronic density. Examining the role of disorder on the 5/2 state, we find that a large discrepancy remains between theory and experiment for the intrinsic gap extrapolated from the infinite mobility limit. The observation of a 5/2 state in the low-field regime suggests that inclusion of nonperturbative Landau level mixing may be necessary to fully understand the energetics of half-filled fractional quantum Hall liquids. 相似文献
87.
A P.I.V. instrument using two synchronized CCD video cameras is described. The same field of view is imaged onto each CCD
array with an image splitter and one imaging lens. The delay between two exposures can be adjusted from 0.5 to 20 ms depending
on the flow velocity to be measured.
Received: 12 February 1999/Accepted: 20 March 1999 相似文献
88.
Y Guindon F Soucy C Yoakim W W Ogilvie L Plamondon 《The Journal of organic chemistry》2001,66(26):8992-8996
The work described herein considers the impact of stereoelectronic effects and allylic 1,3-strain in controlling the cyclofunctionalization reaction when a hydroxyl group is at the allylic position. The stereoelectronic arguments are supported by independent iodocyclization reactions performed using two secondary alcohols. The transition-state pathways involved in these reactions are established through a comparison of relative reaction rates. A bi-directional approach is used to demonstrate the potential of the iodocyclization reaction to differentiate a terminus in molecules with a pseudo C(2) axis of symmetry, showing that two-directional synthesis can be used to differentiate between alternative transition-state pathways. 相似文献
89.
N. Petit F. Gervais P. Buvat P. Hourquebie P. Topart 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):367-372
The reflectivity spectrum of a polyaniline CSA-doped in presence of m-cresol has been measured over the wide wavenumber range
of 15- 9 000 cm
-1 (0.002-1.1 eV) at room temperature. Experimental data compare well with similar experiments performed by another group. The
conductivity spectrum of this conducting polymer has been deduced from the reflectivity spectrum by means of two methods,
Kramers-Kronig transformation and best fit of an “extended Drude” model to the reflectivity spectrum. Whereas the deviation
from Drude behavior was interpreted in terms of Anderson localization or by inhomogeneous disorder by other groups, it is
shown here that a different model developed for conducting oxides that also exhibit non-Drude behavior, applies very well
to this example of conducting polymer.
Received 11 February 1999 and Received in final form 26 April 1999 相似文献
90.