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61.
62.
S. Charpentier A. Kassiba S. Fusil X. Armand M. Cauchetier J. C. Fayet J. Emery 《Applied magnetic resonance》1997,12(2-3):255-267
EPR investigations are performed in SiC and SiOC nanometric powders annealed between 1200 and 1800°C. By using different EPR frequency bands and a suitable spectra analysis, three quite different paramagnetic defects with well defined $\tilde g_i $ (i=1, 2, 3) and hyperfine $\tilde A_i $ (i=1, 2) tensors account for the EPR signal in these materials. The defects are characterized by $\tilde g_1 $ (g 1 ‖ =2.0046(3), g 1 ? =2.0023(3)), $\tilde g_2 $ (g 2 ‖ =2.0037(3), g 2 ? =2.0028(3)) and isotropic $\tilde g_3 $ (2.0030(3)) tensors. In SiC powders, the defects assignment is discussed with respect to the different SiC forms, namely α-SiC and β-SiC polytypes as well as amorphous SiC and carbon present in minor concentration in the network. In SiOC powders, the above defects are evidenced only at high annealing temperature (T a≥1200°C) when the oxygen contained is highly reduced. 相似文献
63.
Elevations of diffusion anisotropy are associated with hyper-acute stroke: a serial imaging study 总被引:1,自引:0,他引:1
Bhagat YA Hussain MS Stobbe RW Butcher KS Emery DJ Shuaib A Siddiqui MM Maheshwari P Al-Hussain F Beaulieu C 《Magnetic resonance imaging》2008,26(5):683-693
Diffusion tensor imaging (DTI) studies of human ischemic stroke within 24 h of symptom onset have reported variable findings of changes in diffusion anisotropy. Serial DTI within 24 h may clarify these heterogeneous results. We characterized longitudinal changes of diffusion anisotropy by analyzing discrete ischemic white matter (WM) and gray matter (GM) regions during the hyperacute (2.5-7 h) and acute (21.5-29 h) scanning phases of ischemic stroke onset in 13 patients. Mean diffusivity (MD), fractional anisotropy (FA) and T2-weighted signal intensity were measured for deep and subcortical WM and deep and cortical GM areas in lesions outlined by a > or =30% decrease in MD. Average reductions of approximately 40% in relative (r) MD were observed in all four brain regions during both the hyperacute and acute phases post stroke. Overall, 9 of 13 patients within 7 h post symptom onset showed elevated FA in at least one of the four tissues, and within the same cohort, 11 of 13 patients showed reduced FA in at least one of the ischemic WM and GM regions at 21.5-29 h after stroke. The fractional anisotropy in the lesion relative to the contralateral side (rFA, mean+/-S.D.) was significantly elevated in some patients in the deep WM (1.10+/-0.11, n=4), subcortical WM (1.13+/-0.14, n=4), deep GM (1.07+/-0.06, n=1) and cortical GM (1.22+/-0.13, n=5) hyperacutely (< or =7 h); however, reductions of rFA at approximately 24 h post stroke were more consistent (rFA= 0.85+/-0.12). 相似文献
64.
Claisen Rearrangement of Hydroxynaphthoquinones: Selectivity toward Naphthofuran or α‐Xiloidone Using Copper Salts and Iodine 下载免费PDF全文
Paulo Eliandro da Silva Júnior Natlia Maria de Araujo Flavio da Silva Emery 《Journal of heterocyclic chemistry》2015,52(2):518-521
α‐xiloidone is an interesting chromene that are structurally related to lapachones; in this work, we selectively synthesized α‐xiloidone from the reaction of lawsone 1 with 3,3‐chloro‐3‐methylbut‐1‐yne under copper/I2 catalysis via propargyl Claisen rearrangement. 相似文献
65.
B. Deveaud J.Y. Emery A. Chomette B. Lambert M. Baudet 《Superlattices and Microstructures》1985,1(3):205-208
The observation of single monolayer well size fluctuations in a superlattice is reported. Luminescence experiments show that several free exciton peaks occur, each of them corresponding, in the same layers, to a discreet well width differing by one monolayer from the next one. This attribution is confirmed by the intentional introduction of larger wells in the structure. Photoluminescence excitation experiments confirm this interpretation. 相似文献
66.
V. J. Emery 《Hyperfine Interactions》1991,63(1-4):13-21
Some implications of μSR experiments on high temperature superconductors are discussed. The possible relationship between the observation of spin freezing and the tendency of mobile holes to phase separate is considered. Measurements of the magnetic penetration depth as a function of doping are shown to imply that a non-retarded, or high energy scale pairing interaction is responsible for high temperature superconductivity. The depression of the transition temperature at high doping is associated with a crossover away from the regime in which a charge-transfer gap is relevant. 相似文献
67.
R.V.F. Janssens J.F.W. Jansen G.T. Emery D.C.J.M. Hageman J. Łukasiak 《Physics letters. [Part B]》1980,90(3):209-213
The ground-state rotational band of 232U is established up to Iπ = 16+ (tentatively 18+) through a study of the 232Th(α, 4nγ) reaction. Conversion electron spectroscopy is found to be especially useful in circumventing the difficulties caused by strong fission competition. 相似文献
68.
A.D. Bacher G.T. Emery W.P. Jones D.W. Miller G.S. Adams F. Petrovich W.G. Love 《Physics letters. [Part B]》1980,97(1):58-62
Differential cross sections for the excitation of states at 6.42, 6.73 and 7.04 MeV in 208Pb by 135 MeV protons are reported. Both the excitation energies and the backward peaked angular distributions observed in this experiment and in a recent (e, e′) experiment strongly suggest that these states are predominantly one-particle-one-hole excitations with Jπ = 12?, 14? and 12?, respectively. The present (p, p′) data are interpreted using a distorted wave impluse approximation and the effect of configuration mixing between the two 12? states is investigated. 相似文献
69.
70.
We apply a simplified Hartree-Fock-Roothaan Hamiltonian to the calculation of the superhyperfine interaction for [VF6]4- and [CrF6]3- in KZnF3. We obtain a satisfactory agreement with EPR measurements. 相似文献