Morphology and optical absorption of Bi2Fe4O9 crystals via mineralizer-assisted hydrothermal synthesis

Submicron-sized Bi₂Fe₄O₉ crystals were successfully synthesized via the hydrothermal method, while micron-sized Bi₂Fe₄O₉ crystals with rod-like morphologies were obtained in the presence of the mineralizer KNO₃. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were employed to characterize the products. According to a series of time-dependent experiments, it was concluded that the likeliest formation mechanism for the microrods was the Ostwald ripening process. It was proposed that the blocking effect of NO₃^? contributed to the formation of the rod-like powders. Moreover, the optical absorption of the prepared Bi₂Fe₄O₉ crystals was measured using an UV–vis spectrophotometer, indicating that Bi₂Fe₄O₉ powders can be used as effective photocatalysts under visible light.     

A facile strategy to modify TiO2 nanoparticles via surface‐initiated ATRP of styrene

A core‐shell hybrid nanocomposites, possessing a hard core of nano titanium dioxide (n‐TiO₂) and a soft shell of brushlike polystyrene (PS), were successfully prepared by surface‐initiated atom transfer radical polymerization (ATRP) at 90 °C in anisole solution using CuBr/PMDETA as the catalyst, in the presence of sacrificial initiator. FTIR, ¹H NMR, XPS, TEM, SEM, TGA, and DSC were used to determine the chemical structure, morphology, thermal properties, and the grafted PS quantities of the resulting products. TEM images of the samples provided direct evidence for the formation of a core‐shell structure. The thermal stabilities of the grafted polymers were dramatically elevated relative to that of pristine PS according to TGA results. DSC results demonstrated that the TiO₂‐PS nanocomposites exhibited higher glass transition temperature (T_g) compared with pristine PS. The molecular weights of the free polymers formed by sacrificial initiator, which were similar to that of surface‐attached polymers were measured by GPC instrument which showed that the molecular weights of PS were well controlled with a relatively narrow polydispersity index (PDI < 1.2). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1782–1790, 2010     

Minimizing the weighted number of tardy jobs on parallel processors

We present a branch-and-bound algorithm to minimize the weighted number of tardy jobs on either identical or non-identical processors. Bounds come from a surrogate relaxation resulting in a multiple-choice knapsack. Extensive computational experiments indicate problems with 400 jobs and several machines can be solved quickly. The results also indicate what parameters affect solution difficulty for this algorithmic approach.     

Liquid phase epitaxial growth and optical property of flower-like ZnO nanosheets on Zinc foil

Large scale flower-like ZnO nanosheets have been synthesized on Zinc foil by a simple hydrothermal method. Their morphology and microstructures were characterized and analyzed by X-ray spectroscopy (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). The as-synthesized flower-like nanosheets are hexagonal phase single crystal with 200-300 nm in width, 50 nm in thickness. The growth process follows the liquid phase epitaxial growth mechanism. In this approach, the ZnO buffer is used as substrate for the growth of flower-like ZnO nanosheets. The growth direction of the nanosheets is the preferential [0 0 0 1] growth direction of ZnO. The photoluminescence spectrum of the sample exhibits only a sharp and strong UV emission centered at 386 nm, which indicates that the flower-like ZnO nanosheets on Zn foil are of good optical property.     

Consistency of change point estimators for symmetrical stable distribution with parameters shift

Assume that the characteristic indexαof stable distribution satisfies 1<α<2,and that the distribution is symmetrical about its mean.We consider the change point estimators for stable distribution withαor scale parameterβshift.For the one case that mean is a known constant,ifαorβchanges,then density function will change too.To this end,we suppose the kernel estimation for a change point.For the other case that mean is an unknown constant,we suppose to apply empirical characteristic function to estimate the change-point location.In the two cases,we consider the consistency and strong convergence rate of estimators.Furthermore,we consider the mean shift case.If mean changes,then corresponding characteristic function will change too.To this end,we also apply empirical characteristic function to estimate change point.We obtain the similar convergence rate.Finally,we consider its application on the detection of mean shift in financial market.     

跳扩散模型下的欧式障碍期权的定价

本文在标的资产价格服从跳扩散模型的假设下,运用Girsanov定理获得了价格过程的等价鞅测度,用期权定价的鞅方法得出障碍期权的定价公式.     

Copper(I) Oxide Catalyzed Formation of C?S Bond Mediated by N,N′‐Type Ligand

1,10‐Phenanthroline, a simple and cheap N,N′‐type ligand, was found to work well as the ligand of C? S coupling catalyzed by Cu₂O. The corresponding coupling products were synthesized in good to excellent yields (75%–99%) in DMSO at 80°C. A variety of aryl halides and thiols were investigated and satisfactory results were obtained.     

Novel approaches for the preparation of silica-based zwitterionic hybrid copolymers

Two novel routes for the preparation of silica-based zwitterionic hybrid copolymers were proposed. A series of zwitterionic hybrid copolymers were prepared by the sulfonation of phenyl groups and the quaternary amination of tertiary amine groups alternately. Both FT-IR and ¹H NMR spectra confirm the step products. TGA and DrTGA analyses indicate that the thermal stability of these zwitterionic hybrid copolymers is higher than 400 °C. The determination of sulfonation degree reveals that the zwitterionic hybrid copolymer (c) from sulfonation-quarteramination (Route I) has the minimal value; meanwhile the anion-exchange capacity exhibits that the zwitterionic hybrid copolymer (e) from quarteramination-sulfonation (Route II) has the minimal value. These findings demonstrate the impact of electrostatic effect on the charge content of ionic groups. MALDI-TOF mass spectra exhibit that the decrease in the stability of the charged hybrid copolymers can be ascribed to the electrostatic effect between the molecular chains. The surface SEM images demonstrate that the surface of zwitterionic hybrid copolymer (e) from quarteramination-sulfonation (Route II) has some aggregated particles and form clusters regions in the hybrid matrix, which can also be attributed to the ionic interactions between those charged groups.     

高频金融数据的标度分析

高频金融数据通常具有尖峰厚尾的非正态特征，常用稳定分布来拟合。本文采用稳定分布的性质对高频上证指数收益率的分布作了标度分析，求得特征指数为1．48，说明我们在分析证券指数分布时可以用稳定分布，而非正态分布。