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711.
We generalize the BM-local time fractional symmetric α-stable motion introduced in Cohen and Samorodnitsky (2006) by replacing the local time with a general continuous additive functional (CAF). We show that the resulting process is again symmetric α-stable with stationary increments. Depending on the CAF, the process is either self-similar or lies in the domain of attraction of the BM-local time fractional symmetric α-stable motion. We also show that the process arises as a weak limit of a discrete “random rewards scheme” similar to the one described by Cohen and Samorodnitsky. 相似文献
712.
Marwène Oumezzine Octavio Peña Sami Kallel Nabil Kallel Thierry Guizouarn Francis Gouttefangeas Mohamed Oumezzine 《Applied Physics A: Materials Science & Processing》2014,114(3):819-828
The effects of non-magnetic Ti4+ substitution on the structural, electrical and magnetic properties of La0.67Ba0.33Mn1?x Ti x O3 (0≤x≤0.1) are investigated and compared to those existing in La0.67Ba0.33Mn1?x Cr x O3 (magnetic Cr3+). The structural refinement by the Rietveld method revealed that Ti-doped samples crystallize in the cubic lattice with space group $\mathrm{Pm}\bar{3}\mathrm{m}$ , while samples with Cr crystallize in the hexagonal setting of the rhombohedral $\mathrm{R}\bar{3}\mathrm{C}$ space group for identical contents of dopant. The most relevant structural features are an increase of the lattice parameters, of the cell volume and of the inter-ionic distances with increasing Ti doping level. Both series of samples show a decrease of the paramagnetic–ferromagnetic transition temperature when the amount of chromium or titanium increases. Transport measurements show that when increasing the metal doping, the resistivity increases whereas the metallic behavior of the parent compound La0.67Ba0.33MnO3 is destroyed. For a substitution higher than 5 at.% of Ti and 10 at.% of Cr, the samples exhibit a semiconducting behavior in the whole range of temperature, for which the electronic transport can be explained by variable range hopping and/or small polaron hopping models. 相似文献
713.
Sonia Ben AbdelkhalekNabil Kallel Sami KallelThierry Guizouarn Octavio PeñaMohamed Oumezzine 《Physica B: Condensed Matter》2011,406(21):4060-4067
The electrical properties and the mechanism of conduction of the simultaneously substituted La0.7−xYxBa0.3Mn1−xFexO3 perovskite (0≤x≤0.30) have been studied. The insertion of Y3+ and Fe3+ ions in the parent compound La0.7Ba0.3MnO3 leads to an increase of the resistivity. The undoped sample (x=0) shows a metallic behavior, which can be fitted by the relation ρ(T)=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of electron-magnon scattering effects in this material. All the other samples (x≥0.10) are semiconductors throughout the studied temperature range (80-290 K). Several models have been used to fit their temperature-dependent resistivity: thermal activation, adiabatic nearest-neighbor hopping of small polarons (Holstein theory) and variable range hopping (VRH) models. The fits show that the electronic transport in semiconducting La0.7−xYxBa0.3Mn1−xFexO3 is well described and dominated by the VRH mechanism, for which the hopping distance (a) grows with increasing Fe3+ doping, thus increasing the average hopping energy W. 相似文献
714.
Bacterial biofilms constitute an extremely resistant form of bacterial colonization with dire health and economical implications. Towards achieving polymeric composites capable of resisting bacterial adhesion and biofilm formation, we prepared five 2,6-pyridinedicarboxylate-based polyesters employing five different diol monomers. The resulting polyesters were complexed with copper (II) or silver (I). The new polymers were characterized by proton and carbon nuclear magnetic resonance spectroscopy, inherent viscosity, infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The corresponding metal complexes were characterized by differential scanning calorimetry and infrared spectroscopy. The amounts of complexed copper and silver were determined by atomic absorption spectrophotometry. Finally, the resulting composites were tested for their antibacterial potential and were found to effectively resist bacterial attachment and growth. 相似文献
715.
Two at a time: α,β-Unsaturated iminium ions can be generated by laser flash photolysis of enaminophosphonium ions. The rate constants of their reactions with nucleophiles provide the first direct comparison of the electrophilicities of iminium ions derived from MacMillan's first- and second-generation catalysts. 相似文献
716.
717.
Electrophilic substitution of pyrroles by α,β-unsaturated iminium ions is slow in acetonitrile when only weakly basic counterions are present. When the reactions are carried out in the presence of KCF(3)CO(2), fast deprotonation of the intermediate σ-adducts occurs, and the rate constant for the rate-determining CC bond-forming step can be predicted from the electrophilicity parameter E of the iminium ion and the N and s parameters of the pyrroles. 相似文献
718.
Bercu Bernard Capderou Sami Durrieu Gilles 《Statistical Inference for Stochastic Processes》2019,22(1):17-40
This paper is devoted to the nonparametric estimation of the derivative of the regression function in a nonparametric regression model. We implement a very efficient and easy to handle statistical procedure based on the derivative of the recursive Nadaraya–Watson estimator. We establish the almost sure convergence as well as the asymptotic normality for our estimates. We also illustrate our nonparametric estimation procedure on simulated data and real life data associated with sea shores water quality and valvometry.
相似文献719.
A [4+4] annulation strategy for the synthesis of eight-membered carbocycles is reported that proceeds via a cascade involving two pericyclic processes. In the first step, the [4+2] cycloaddition of a conjugated enyne with an electron-deficient cyclobutene generates a strained six-membered cyclic allene that isomerizes to the corresponding 1,3-cyclohexadiene. In the second step, this bicyclo[4.2.0]octa-2,4-diene intermediate undergoes thermal or acid-promoted 6-electron electrocyclic ring opening to furnish a 2,4,6-cyclooctatrienone. The latter transformation represents the first example of the promotion of 6-electron electrocyclic ring opening reactions by acid. 相似文献
720.
In this Letter we have investigated the cosmological dynamics of non-locally corrected gravity involving a function of the inverse d'Alembertian of the Ricci scalar, f(□−1R). Casting the dynamical equations into local form, we derive the fixed points of the dynamics and demonstrate the existence and stability of a one parameter family of dark energy solutions for a simple choice, f(□−1R)∼exp(α□−1R). The effective EoS parameter is given by, weff=(α−1)/(3α−1) and the stability of the solutions is guaranteed provided that 1/3<α<2/3. For 1/3<α<1/2 and 1/2<α<2/3, the underlying system exhibits phantom and non-phantom behavior respectively; the de Sitter solution corresponds to α=1/2. For a wide range of initial conditions, the system mimics dust like behavior before reaching the stable fixed point. The late time phantom phase is achieved without involving negative kinetic energy fields. A brief discussion on the entropy of de Sitter space in non-local model is included. 相似文献