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31.
The crystal structure, the 13C NMR spectroscopy and the complex impedance have been carried out on [Cd3(SCN)2Br6(C2H9N2)2]n. Crystal structure shows a 2D polymeric network built up of two crystallographically independent cadmium atoms with two different octahedral coordinations. This compound exhibits a phase transition at (T=355±2 K) which has been characterized by differential scanning calorimetry (DSC), X-rays powder diffraction, AC conductivity and dielectric measurements. Examination of 13C CP/MAS line shapes shows indirect spin–spin coupling (14N and 13C) with a dipolar coupling constant of 1339 Hz. The AC conductivity of this compound has been carried out in the temperature range 325–376 K and the frequency range from 10−2 Hz to 10 MHz. The impedance data were well fitted to two equivalent electrical circuits. The results of the modulus study reveal the presence of two distinct relaxation processes. One, at low frequency side, is thermally activated due to the ionic conduction of the crystal and the other, at higher frequency side, gradually disappears when temperature reaches 355 K which is attributed to the localized dipoles in the crystal. Moreover, the temperature dependence of DC-conductivity in both phases follows the Arrhenius law and the frequency dependence of σ(ω,T) follows Jonscher's universal law. The near values of activation energies obtained from the conductivity data and impedance confirm that the transport is through the ion hopping mechanism. 相似文献
32.
Gérard Ben Arous Kay Kirkpatrick Benjamin Schlein 《Communications in Mathematical Physics》2013,321(2):371-417
We study the many body quantum evolution of bosonic systems in the mean field limit. The dynamics is known to be well approximated by the Hartree equation. So far, the available results have the form of a law of large numbers. In this paper we go one step further and we show that the fluctuations around the Hartree evolution satisfy a central limit theorem. Interestingly, the variance of the limiting Gaussian distribution is determined by a time-dependent Bogoliubov transformation describing the dynamics of initial coherent states in a Fock space representation of the system. 相似文献
33.
I. Ben Amor H. Rekik H. Kaddami M. Raihane M. Arous A. Kallel 《Journal of Electrostatics》2009,67(5):717-722
Polymer composites of a polyester resin matrix filled with short palm tree lignocellulosic fibers were studies by means of dielectric spectroscopy in the frequency range 0, 1–100 kHz and temperature interval from 40 °C to 200 °C. Three relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in Palm fiber, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and the interfacial relaxation that is attributable to the accumulation of charges at the Palm fibers/polyester interfaces. 相似文献
34.
Three iron species were detected in FeMo sulfide hydrodesulfurization catalysts:FeS2(pyrite),Fe1–xS and the mixed Fe-Mo-S structure.High temperature reduction in hydrogen and resulfidation cause a partial transformation of the above phases into FeS (troilite) and Fe7S8(pyrrhotite), respectively. 相似文献
35.
Summary A strong synergy between separate oxide phases A and B is observed in the oxidation of isobutylene to methacrolein. This is explained by the continuous activation of potential centers on A by spill-over oxygen emitted by B (remote control). This activation corresponds to the creation of Brönsted sites in the case where A is MoO3. We discuss some details of the mechanism and the consequences with respect to catalyst design and process. 相似文献
36.
Ohne Zusammenfassung 相似文献
37.
Summary. We study the spectral measure of Gaussian Wigner's matrices and prove that it satisfies a large deviation principle. We show
that the good rate function which governs this principle achieves its minimum value at Wigner's semicircular law, which entails
the convergence of the spectral measure to the semicircular law. As a conclusion, we give some further examples of random
matrices with spectral measure satisfying a large deviation principle and argue about Voiculescu's non commutative entropy.
Received: 3 April 1995 / In revised form: 14 December 1996 相似文献
38.
We study here a detailed conjecture regarding one of the most important cases of anomalous diffusion, i.e., the behavior of the “ant in the labyrinth.” It is natural to conjecture that the scaling limit for random walks on large critical random graphs exists in high dimensions and is universal. This scaling limit is simply the natural Brownian motion on the integrated super-Brownian excursion. We give here a set of four natural, sufficient conditions on the critical graphs and prove that this set of assumptions ensures the validity of this conjecture. The remaining future task is to prove that these sufficient conditions hold for the various classical cases of critical random structures, like the usual Bernoulli bond percolation, oriented percolation, and spread-out percolation in high enough dimension. In a companion paper, we do precisely that in a first case, the random walk on the trace of a large critical branching random walk. We verify the validity of these sufficient conditions and thus obtain the scaling limit mentioned above in dimensions larger than 14. © 2019 Wiley Periodicals, Inc. 相似文献
39.
The removal and separation of Cu(II), Zn(II) and Ni(II) from nitrate aqueous solutions were studied by competitive transport across cellulose triacetate plasticized membranes modified with polyelectrolytes: polyethyleneimine (PEI) and polyethyleneglycol (PEG). Competitive transport of trace ions from aqueous solutions across polymer inclusion membranes containing a mixture of the three polymers (cellulose triacetate as the support) and tris(2-ethylhexyl-phosphate) (TEHP) as the plasticizer provide the selectivity order: Cu(II) > Ni(II) > Zn(II). A long-term transport experiment was carried out to demonstrate the durability of polymer inclusion membranes. A separation of bivalents cations (Cu2+, Ni2+, Zn2+) and monovalent cations (K+ and Na+) is achieved. 相似文献
40.
Gérard Ben Arous Jiří Černý Thomas Mountford 《Probability Theory and Related Fields》2006,134(1):1-43
Let E
x
be a collection of i.i.d. exponential random variables. Symmetric Bouchaud's model on ℤ2 is a Markov chain X(t) whose transition rates are given by w
xy
= ν exp (−βE
x
) if x, y are neighbours in ℤ2. We study the behaviour of two correlation functions: ℙ[X(t
w
+t) = X(t
w
)] and ℙ[X(t') = X(t
w
) ∀ t'∈ [t
w
, t
w
+ t]]. We prove the (sub)aging behaviour of these functions when β > 1. 相似文献