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951.
Machkour A Thallaj NK Benhamou L Lachkar M Mandon D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(25):6660-6668
Coordination of FeCl3 to the title ligand yields a mononuclear iron(III) complex 1, which was characterized by spectroscopic techniques and X-ray diffraction. The ligand is (kappa3-N) tridentate and the metal, which lies in a pseudo-octahedral environment, is bound to a phenolate group from the catechol substituent. The dichloroiron(II) complex 2 was easily obtained by metalation of the ligand with FeCl2 and characterized by various spectroscopic techniques. In their cyclic voltammograms both 1 and 2 display the same reversible FeII/FeIII wave at E1/2=10 mV (vs. SCE). Reduction of compound 1 with Zn/Hg yields 2', which displays identical properties to 2. Taken together, these findings indicate that in spite of the different oxidation state of the metal in 2, no major geometrical/structural change is observed at the metal center with respect to 1. The reaction of 2 with dioxygen in the absence of organic substrates proceeds extremely rapidly and yields compound 3, which is a diiron(III) derivative whose X-ray crystal structure is also reported. The possibility of a radical-based mechanism is discussed. Compound 3 displays an unusual geometry: one iron(III) center is seven-coordinate, whereas the other lies in a square-pyramidal environment. The two iron atoms are bridged by the catecholato substituents. To the best of our knowledge, 3 is the first example of a seven-coordinate iron(III) derivative with tris(2-pyridylmethyl)amine ligands. 相似文献
952.
The wavelet response as a multiscale characterization of scattering processes at granular interfaces
We perform a multiscale analysis of the backscattering properties of a complex interface between water and a layer of randomly arranged glass beads with diameter D = 1 mm. An acoustical experiment is done to record the wavelet response of the interface in a large frequency range from λ/D = 0.3 to λ/D = 15. The wavelet response is a physical analog of the mathematical wavelet transform which possesses nice properties to detect and characterize abrupt changes in signals. The experimental wavelet response allows to identify five frequency domains corresponding to different backscattering properties of the complex interface. This puts quantitative limits to the validity domains of the models used to represent the interface and which are flat elastic, flat visco-elastic, rough random half-space with multiple scattering, and rough elastic from long to short wavelengths respectively. A physical explanation based on Mie scattering theory is proposed to explain the origin of the five frequency domains identified in the wavelet response. 相似文献
953.
954.
Concentration gradients surrounding Ni4Ti3 precipitates grown by appropriate annealing in a Ni51Ti49 B2 austenite matrix are investigated by electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM). Concentration gradients of approximately 1.0-2.0 at.% in Ni within the surrounding B2 matrix can be detected by both EELS and EFTEM, revealing a Ni depleted zone in the matrix. Besides the concentration gradients, the EELS integrated cross-section of the Ni L(2,3) edges for the Ni-depleted region increased slightly, when compared with a matrix region away from the precipitate and not depleted in Ni. 相似文献
955.
Dominique Fourdrinier 《Journal of multivariate analysis》2010,101(6):1390-1399
For independently distributed observables: Xi∼N(θi,σ2),i=1,…,p, we consider estimating the vector θ=(θ1,…,θp)′ with loss ‖d−θ‖2 under the constraint , with known τ1,…,τp,σ2,m. In comparing the risk performance of Bayesian estimators δα associated with uniform priors on spheres of radius α centered at (τ1,…,τp) with that of the maximum likelihood estimator , we make use of Stein’s unbiased estimate of risk technique, Karlin’s sign change arguments, and a conditional risk analysis to obtain for a fixed (m,p) necessary and sufficient conditions on α for δα to dominate . Large sample determinations of these conditions are provided. Both cases where all such δα’s and cases where no such δα’s dominate are elicited. We establish, as a particular case, that the boundary uniform Bayes estimator δm dominates if and only if m≤k(p) with , improving on the previously known sufficient condition of Marchand and Perron (2001) [3] for which . Finally, we improve upon a universal dominance condition due to Marchand and Perron, by establishing that all Bayesian estimators δπ with π spherically symmetric and supported on the parameter space dominate whenever m≤c1(p) with . 相似文献
956.
In this article we provide an algorithm, where to escape from a local maximum y of convex function f over D, we (locally) solve piecewise convex maximization max{min{f (x) − f (y), p
y
(x)} | x ∈ D} with an additional convex function p
y
(·). The last problem can be seen as a strictly convex improvement of the standard cutting plane technique for convex maximization.
We report some computational results, that show the algorithm efficiency. 相似文献
957.
Sonodynamic toxicity has always been linked to the cavitation phenomenon. In this work, sonodynamic effect with Photofrin® was evaluated with a new ultrasound device: a regulated cavitation generator. In this way, acoustic intensity was substituted with cavitation level as ultrasound parameter. Photofrin® potentiated significantly the cavitation cytotoxicity even for low setpoints where no inertial cavitation appeared. Therefore sonodynamic mechanism was principally mechanical, facilitated by the Photofrin® insertion in cellular cytoplasmic membranes. This assertion was also supported by the fact that sonodynamic cytotoxicity was independent from the Photofrin® presence or absence in the extracellular medium. Reproducible sonodynamic efficiency was perfectly obtained with this new regulated cavitation generator. 相似文献
958.
Dominique Bazin Xavier Carpentier Olivier Traxer Dominique Thiaudière Andrea Somogyi Solenn Reguer Glenn Waychunas Paul Jungers Michel Daudon 《Journal of synchrotron radiation》2008,15(5):506-509
This very first report of an X‐ray absorption spectroscopy experiment at Synchrotron SOLEIL is part of a long‐term study dedicated to pathological calcifications. Such biological entities composed of various inorganic and/or organic compounds also contain trace elements. In the case of urinary calculi, different papers already published have pointed out that these oligo‐elements may promote or inhibit crystal nucleation as well as growth of mineral. Use of this analytical tool specific to synchrotron radiation, allowing the determination of the local environment of oligo‐elements and thus their occupation site, contributes to the understanding of the role of trace elements in pathological calcifications. 相似文献
959.
Etienne Shaffer Amr S. Helmy Dominique Drouin Jan J. Dubowski 《Applied Physics A: Materials Science & Processing》2008,93(4):869-874
We have investigated ArF (λ=193 nm) excimer laser-induced crystallization of amorphous CdSe semiconductor thin films. The crystallization has been monitored
by a related photoluminescence emission in the free-exciton and defect-band transition regions. For different irradiation
conditions, we have observed formation of nanorods, up to 2 μm long, as well as the formation of arrays of CdSe nanobeads
with a narrow size distribution and characteristic dimensions corresponding to λ/2 and λ/8. The successful crystallization has also been confirmed by confocal Raman spectroscopy. 相似文献
960.
Elastic plates or cylinders can support guided modes with zero group velocity (ZGV) at a nonzero value of the wave number. Using laser-based ultrasonic techniques, we experimentally investigate some fascinating properties of these ZGV modes: resonance and ringing effects, backward wave propagation, interference between backward and forward modes. Then, the conditions required for the existence of ZGV Lamb modes in isotropic plates are discussed. It is shown that these modes appear in a range of Poisson's ratio about the value for which the cutoff frequency curves of modes belonging to the same family intercept, i.e., for a bulk wave velocity ratio equal to a rational number. An interpretation of this phenomenon in terms of a strong repulsion between a pair of modes having a different parity in the vicinity of the cutoff frequencies is given. Experiments performed with materials of various Poisson's ratio demonstrate that the resonance spectrum of an unloaded elastic plate, locally excited by a laser pulse, is dominated by the ZGV Lamb modes. 相似文献