Discrete chaos induced by heteroclinic cycles connecting repellers in Banach spaces

This paper is concerned with chaos induced by heteroclinic cycles connecting repellers for maps in Banach spaces. Several criteria of chaos are established in general Banach spaces and finite-dimensional spaces, respectively, by employing the coupled-expansion theory. All the maps presented in this paper are proved to be chaotic in the sense of both Li-Yorke and Devaney or in the sense of both Li-Yorke and Wiggins or in the sense of Li-Yorke. An illustrative example is provided with computer simulations.     

FDTD法对二维正方格子光子晶体带隙的数值计算

通过optiFDTD模拟软件对二维椭圆柱构造的正方格子光子晶体的禁带特性进行了数值模拟。分别研究了在空气中椭圆介质(Ge,Si,GaAs)柱和在介质(Ge,Si,GaAs)中椭圆空气柱构造的二维正方格子光子晶体中椭圆柱的横轴半径和纵轴半径的大小,以及椭圆柱的不同旋转角度对光子禁带的影响;并计算出了在上述两种情况下的空气和介质中的最优结构参数。     

Dynamics of a delayed predator–prey model with predator migration

Based on the availability of prey and a simple predator–prey model, we propose a delayed predator–prey model with predator migration to describe biological control. We first study the existence and stability of equilibria. It turns out that backward bifurcation occurs with the migration rate as bifurcation parameter. The stability of the trivial equilibrium and the boundary equilibrium is delay-independent. However, the stability of the positive equilibrium may be delay-dependent. Moreover, delay can switch the stability of the positive equilibrium. When the positive equilibrium loses stability, Hopf bifurcation can occur. The direction and stability of Hopf bifurcation is derived by applying the center manifold method and the normal form theory. The main theoretical results are illustrated with numerical simulations.     

Global existence,asymptotic behavior,and uniform attractor for a nonautonomous equation

In this paper, we establish the global existence, asymptotic behavior, and uniform attractor for a nonautonomous viscoelastic equation with a delay term. Under some suitable assumptions, we firstly prove the global well‐posedness of the problem by using the Faedo–Galerkin approximations together with some energy estimates and then obtain the general decay results of the energy via suitable Lyapunov functionals. Finally, we prove the existence of uniform attractors. Copyright © 2013 John Wiley & Sons, Ltd.     

Encapsulated ultrafine and highly dispersed molybdenum dioxide nanoparticles in hollow mesoporous silica spheres as an efficient epoxidation catalyst for alkenes

A facile post-synthetic strategy was developed to functionalize the preformed hollow mesoporous silica spheres by encapsulating the molybdenum dioxide (MoO₂) nanoparticles inside the interior cavity. Hollow mesoporous silica spheres were prepared and employed as carriers, and the encapsulation of MoO₂ nanoparticles was achieved through a one-pot hydrothermal protocol. After characterization, the encapsulated MoO₂ nanoparticles were certified to be ultrafine and highly dispersed, which greatly promoted the catalytic activity. The as-prepared catalysts were utilized in epoxidation of alkenes and exhibited as a promising catalyst in this reaction. After reacting for 10 h, the optimal catalyst MoO₂@SiO₂-1 achieved a conversion above 95% and selectivity above 95%, respectively. Moreover, the catalysts also exhibited good reusability, conversion of 78% and selectivity of 89% (reaction time 4 h) were still obtained after recycling for 5 times. Meanwhile, the employed facial and efficient hydrothermal approach could be expanded to other molybdenum modified heterogeneous catalysts in various applications.     

Hydrocarbon-generated potential of bark coal components from Southern China

Barkinite is only found in Chinese coal and it has not been recognized by the International Committee for Coal and Organic Petrology. The hydrocarbon-generated ability of barkinite is still vague. In this work, the hydrocarbon-generated potential of barkinite and vitrinite from Mingshan coal mine in the South of China was investigated by Rock–Eval pyrolysis and solvent extraction analysis. Barkinite and vitrinite were separated by the density gradient centrifugation method. The results showed that barkinite had high hydrocarbon generation potential, as reflected by evidently high hydrogen index (HI) values (607.0 mg HC g^?1 TOC), S₁?+?S₂ values (297.4–475.7 mg HC g^?1), total hydrocarbon yield (23.55–30.20 mass%), and H/C atomic ratio (1.01). Both the S₁?+?S₂ and HI values of barkinite are higher than those of vitrinite. For barkinite, the range values of the temperature at which the S₂ peak is at its maximum (T_max) are from 437 to 446 °C, and for vitrinite are 436 °C. The extraction results represented that the total hydrocarbon yield of barkinite is from 23.55 to 30.20 mass%, while that of vitrinite is 23.99 mass%. This indicated that the high hydrocarbon generation ability of bark coal is greatly controlled by high barkinite content and followed by vitrinite content.

     

Synergistic effect of silver seeds and organic modifiers on the morphology evolution mechanism of silver nanoparticles

Triangular, truncated triangular, quadrangular, hexagonal, and net-structured silver nanoplates as well as decahedral silver nanoparticles were manipulatively prepared starting from silver nitrate and silver seeds in the presence of poly(ethylene glycol) (PEG), poly(N-vinyl pyrrolidone) (PVP), and Tween 80 at room temperature, respectively. UV-vis spectroscopy, XRD, HRTEM, SAED, and FTIR were used to illustrate the crystal growth process and to characterize the resultant silver nanoparticles. It was found that the silver seeds and organic modifiers synergistically affected the morphology evolution of the silver nanoparticles. The co-presence of silver seeds and PEG was beneficial to the formation of triangular and truncated triangular silver nanoplates; the silver seeds and PVP favored the formation of polygonal silver nanoplates; the silver seeds and Tween 80 preferred to the formation of net-structured silver plates. The morphology evolution of the resultant silver nanoparticles was correlated with the crystallinity of the silver seeds and the adsorption ability of the organic modifiers on the crystal surfaces.     

提高布里渊光时域反射应变仪测量空间分辨力的等效脉冲光拟合法

由于探测光脉冲宽度受到限制,布里渊光时域反射仪(BOTDR)在对光纤上的应变进行分布式测量时,空间分辨力只能达到1 m。针对布里渊光时域反射仪单次采样接收背向布里渊散射信号(BBS)需要一定的时间,提出了基于等效脉冲光的多洛仑兹拟合法以提高其应变测量的空间分辨力。该方法将探测光脉冲在布里渊光时域反射仪完成单次采样所需的时间上进行积分,将积分函数作为等效脉冲光的表达式,再根据等效脉冲光的形状将布里渊光时域反射仪接收到的背向布里渊散射谱(BBS)细分,并对它进行多洛仑兹迭代拟合,准确求得每个细分布里渊散射谱的中心频率,进而利用光纤中布里渊频移与应变的对应关系,得到光纤中与细分布里渊散射谱对应的细分光纤单元上的应变情况。实验结果表明,利用这种方法,可使布里渊光时域反射仪应变测量的空间分辨力提高至0.05 m。     

The dimension of the core and the tail of the plasma produced by laser ablating SiC targets

Optical emission of the plasma generated on SiC samples by pulsed laser beam from an Nd:YAG laser was used to investigate the spatial evolution of the electron temperature (Te) and density (Ne) of the plasma. The range and the profile of the plasma were characterized by the electron temperature Te and the electron density Ne, as functions of the distance from the SiC surface. It was found that the characterized spatial distribution closely coincided with the spatial images of the plasma recorded by a digital camera. The results obtained from the two different experimental measurements are consistent with other data from the literature, obtained either by models or experiments. The present result may give the insight to the complex physical phenomena in the thin film preparations using the pulsed laser deposition (PLD).     

Capillary electrophoresis-acid barrage stacking online enrichment method for highly sensitive determination of four isoflavones

A capillary electrophoresis-acid barrage stacking online enrichment method has been established to detect the four isoflavones which are Daidzein, Genistein, Formononetin, and Biochanin A. The proposed method was optimized using a single factor alternative method, and the optimal conditions obtained from the optimization were: the BGE was 25 mM borax and 2 mM β-cyclodextrin, the applied separation voltage was 20 kV, and the detection wavelength was 260 nm. The time ratio of the injection of sample and the injection of acid was 150 s:20 s, and the acid used was 250 mM acetic acid. The sample solvent used was 60% v/v acetonitrile. The established method had the enrichment factor of these four isoflavones at 24.5, 32.0, 29.2, and 33.7, respectively, LOD and LOQ are as low as nanograms per milliliter. Finally, the CE-acid barrage stacking method was successfully applied to the determination of four isoflavones in rat plasma and red clover extract, verifying the applicability and feasibility of the method.