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951.
Sylwia Basąg František Kovanda Zofia Piwowarska Andrzej Kowalczyk Katarzyna Pamin Lucjan Chmielarz 《Journal of Thermal Analysis and Calorimetry》2017,129(3):1301-1311
The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H2-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO2, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co3+ cations, formed during high-temperature treatment of the hydrotalcite-like precursor. 相似文献
952.
František Kačík Jana Luptáková Pavel Šmíra Adriana Eštoková Danica Kačíková Andrea Nasswettrová Tatiana Bubeníková 《Journal of Thermal Analysis and Calorimetry》2017,128(2):755-764
Glasses having composition 5Li2O–5ZnO– xBi2O3 –(90 ? x) P2O5 (x = 5, 10, 15, 20 and 25 mol%) were prepared by the normal melt quenching technique. Nanocomposite glass containing bismuth phosphate BiPO4 nanocrystals was obtained, which can be attributed to homogeneous nucleation process. The formation of BiPO4 nanocrystals was confirmed and characterized by X-ray diffraction patterns (XRD), transmission electron microscopy (TEM), differential scanning calorimetry, optical absorption (UV–Vis) and micro-hardness studies. The morphological analysis by XRD and TEM microscopy showed the formation of hexagonal BiPO4 nanocrystals, and its estimated nanocrystalline sizes were found to be varying from 5.35 to 11.53 nm depending on the Bi2O3 concentrations. The density (ρ) and molar volume (V m) were also determined and found to be in compositional dependence. Glass transition temperature (T g) and glass crystallization temperature (T c) were obtained and found to be increased (from 240.0 to 337.2 °C) with increasing Bi2O3 up to 20 mol% and then decreased (from 337.2 to 331.8 °C) due to the structural changes in the glass network. Effect of BiPO4 content on the optical properties had been investigated. From the UV–Vis spectra, it was observed that the fundamental absorption edge shifts toward lower wavelengths, i.e., blueshifts with increasing Bi2O3 mol% up to 20 mol%, and then shifts toward higher wavelengths, i.e., redshifts beyond 20 mol%. It was also observed that the obtained E opt (for indirect and direct transitions) increases with gradual increase in Bi2O3 content up to 20 mol% and then decreases beyond 20 mol%. This may be due to the introduction of Bi cations into the glass network as a network former up to 20 mol% causing a decrease in ΔE values, beyond 20 mol%, the introduction of Bi ions into the glass network interstitially leads to increase the values of ΔE. The optical properties of the present nanocrystallized glasses showed a quantum size dependence, in which the optical band gap energy (E opt) was changed as a function of BiPO4 nanocrystalline sizes. 相似文献
953.
954.
Andrej Zlatoš 《纯数学与应用数学通讯》2017,70(5):884-949
Consider reaction‐diffusion equation u t =Δ u + f (x,u ) with and general inhomogeneous ignition reaction f ≥ 0 vanishing at u = 0,1. Typical solutions 0 ≤ u ≤ 1 transition from 0 to 1 as time progresses, and we study them in the region where this transition occurs. Under fairly general qualitative hypotheses on f we show that in dimensions d ≤ 3, the Hausdorff distance of the superlevel sets {u ≥ ε } and {u ≥ 1‐ε} remains uniformly bounded in time for each ε ? (0,1). Thus, u remains uniformly in time close to the characteristic function of in the sense of Hausdorff distance of superlevel sets. We also show that each {u ≥ ε} expands with average speed (over any long enough time interval) between the two spreading speeds corresponding to any x ‐independent lower and upper bounds on f . On the other hand, these results turn out to be false in dimensions d ≥ 4, at least without further quantitative hypotheses on f . The proof for d ≤ 3 is based on showing that as the solution propagates, small values of u cannot escape far ahead of values close to 1. The proof for d ≥ 4 is via construction of a counterexample for which this fails. Such results were before known for d =1 but are new for general non‐periodic media in dimensions d ≥ 2 (some are also new for homogeneous and periodic media). They extend in a somewhat weaker sense to monostable, bistable, and mixed reaction types, as well as to transitions between general equilibria of the PDE and to solutions not necessarily satisfying . © 2016 Wiley Periodicals, Inc. 相似文献
955.
The aim of the paper is to highlight the necessity of applying the concept of constrained fuzzy arithmetic instead of the concept of standard fuzzy arithmetic in a fuzzy extension of Analytic Hierarchy Process (AHP). Emphasis is put on preserving the reciprocity of pairwise comparisons during the computations. For deriving fuzzy weights from a fuzzy pairwise comparison matrix, we consider a fuzzy extension of the geometric mean method and simplify the formulas proposed by Enea and Piazza (Fuzzy Optim Decis Mak 3:39–62, 2004). As for the computation of the overall fuzzy weights of alternatives, we reveal the inappropriateness of applying the concept of standard fuzzy arithmetic and propose the proper formulas where the interactions among the fuzzy weights are taken into account. The advantage of our approach is elimination of the false increase of uncertainty of the overall fuzzy weights. Finally, we advocate the validity of the proposed fuzzy extension of AHP; we show by an illustrative example that by neglecting the information about uncertainty of intensity of preferences we lose an important part of knowledge about the decision making problem which can cause the change in ordering of alternatives. 相似文献
956.
In this paper, we introduce a unifying approach to option pricing under continuous‐time stochastic volatility models with jumps. For European style options, a new semi‐closed pricing formula is derived using the generalized complex Fourier transform of the corresponding partial integro‐differential equation. This approach is successfully applied to models with different volatility diffusion and jump processes. We also discuss how to price options with different payoff functions in a similar way. In particular, we focus on a log‐normal and a log‐uniform jump diffusion stochastic volatility model, originally introduced by Bates and Yan and Hanson, respectively. The comparison of existing and newly proposed option pricing formulas with respect to time efficiency and precision is discussed. We also derive a representation of an option price under a new approximative fractional jump diffusion model that differs from the aforementioned models, especially for the out‐of‐the money contracts. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
957.
In this paper, we study pseudo-Riemannian submanifolds of a pseudo-hyperbolic space \(\mathbb H^{m-1}_s (-1) \subset \mathbb E^m_{s+1}\) with 2-type pseudo-hyperbolic Gauss map. We give a characterization of proper pseudo-Riemannian hypersurfaces in \(\mathbb H^{n+1}_s (-1) \subset \mathbb E^{n+2}_{s+1}\) with non-zero constant mean curvature and 2-type pseudo-hyperbolic Gauss map. For \(n=2\), we prove classification theorems. In addition, we show that the hyperbolic Veronese surface is the only maximal surface fully lying in \(\mathbb H^4_2 (-1) \subset \mathbb H^{m-1}_2 (-1)\) with 2-type pseudo-hyperbolic Gauss map. Moreover, we prove that a flat totally umbilical pseudo-Riemannian hypersurface \(M^n_t\) of the pseudo-hyperbolic space \(\mathbb {H}^{n+1}_t(-1) \subset \mathbb E^{n+2}_{t+1}\) has biharmonic pseudo-hyperbolic Gauss map. 相似文献
958.
Tom Alberts Jeremy Clark Saša Kocić 《Stochastic Processes and their Applications》2017,127(10):3291-3330
We study a directed polymer model defined on a hierarchical diamond lattice, where the lattice is constructed recursively through a recipe depending on a branching number and a segment number . When it is known that the model exhibits strong disorder for all positive values of the inverse temperature , and thus weak disorder reigns only for (infinite temperature). Our focus is on the so-called intermediate disorder regime in which the inverse temperature vanishes at an appropriate rate as the size of the system grows. Our analysis requires separate treatment for the cases and . In the case we prove that when the inverse temperature is taken to be of the form for , the normalized partition function of the system converges weakly as to a distribution and does so universally with respect to the initial weight distribution. We prove the convergence using renormalization group type ideas rather than the standard Wiener chaos analysis. In the case we find a critical point in the behavior of the model when the inverse temperature is scaled as ; for an explicitly computable critical value the variance of the normalized partition function converges to zero with large when and grows without bound when . Finally, we prove a central limit theorem for the normalized partition function when . 相似文献
959.
Vladimir Piterbarg Goran Popivoda Siniša Stamatović 《Lithuanian Mathematical Journal》2017,57(1):128-141
Let ξ(t), t ∈ [0, T],T > 0, be a Gaussian stationary process with expectation 0 and variance 1, and let η(t) and μ(t) be other sufficiently smooth random processes independent of ξ(t). In this paper, we obtain an asymptotic exact result for P(sup t∈[0,T](η(t)ξ(t) + μ(t)) > u) as u→∞. 相似文献
960.
For most values of parameters λ and α, the zeros of the Lerch zeta-function L(λ, α, s) are distributed very chaotically. In this paper, we consider the particular case of equal parameters L(λ, λ, s) and show by calculations that the nontrivial zeros either lie extremely close to the critical line σ = 1/2 or are distributed almost symmetrically with respect to the critical line. We also investigate this phenomenon theoretically. 相似文献