Frequency dispersive complex permittivity and permeability of ferromagnetic metallic granular composite at microwave frequencies

We experimentally studied the frequency dependent complex permittivity ε and permeability μ of composite composed of carbonyl iron powder (CIP) and epoxy resin in the frequency range 1-18 GHz. We found that the intrinsic ε and μ of CIP extracted from the measured ε and μ of composites follow the classical Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation, respectively. The dependences of ε and μ of composites on the volume fraction of CIP (vf_CIP) were investigated using the two-exponent phenomenological percolation equation (TEPPE). We found that the TEPPE can fit the experimental results very well. Comparing the results of percolation parameters derived by experimental data at different frequencies, we show that the TEPPE is frequency independent for the composites at microwave frequencies. The results also show that the ε and μ spectrums of composites with definite vf_CIP can be correctly calculated by combining the TEPPE with the theoretical models of intrinsic ε and μ.     

Cross-correlations in volume space: Differences between buy and sell volumes

We study the cross-correlations of buy and sell volumes on the Korean stock market in high frequency. We observe that the pulling effects of volumes are as small as that of returns. The properties of the correlations of buy and sell volumes differ. They are explained by the degree of synchronization of stock volumes. Further, the pulling effects on the minimal spanning tree are studied. In minimal spanning trees with directed links, the large pulling effects are clustered at the center, not uniformly distributed. The Epps effect of buy and sell volumes are observed. The reversal of the cross-correlations of buy and sell volumes is also detected.     

Steady flow in a deformable porous medium

A nonlinear model for a steady flow in a deformable porous medium is considered. The flow is governed by the poroelasticity system consisting of an elasticity equation for the displacement of the porous medium and Darcy's equation for the pressure in the fluid. This poroelasticity system is nonlinear when the permeability in Darcy's equation is assumed to depend on the dilatation of the porous medium. Existence and uniqueness of a weak solution of this poroelasticity system is established under rather weak assumptions on the regularity of the data. Convergence of a finite element approximation is proved and verified through numerical experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

A new fractional finite volume method for solving the fractional diffusion equation

The inherent heterogeneities of many geophysical systems often gives rise to fast and slow pathways to water and chemical movement. One approach to model solute transport through such media is by fractional diffusion equations with a space–time dependent variable coefficient. In this paper, a two-sided space fractional diffusion model with a space–time dependent variable coefficient and a nonlinear source term subject to zero Dirichlet boundary conditions is considered.Some finite volume methods to solve a fractional differential equation with a constant dispersion coefficient have been proposed. The spatial discretisation employs fractionally-shifted Grünwald formulas to discretise the Riemann–Liouville fractional derivatives at control volume faces in terms of function values at the nodes. However, these finite volume methods have not been extended to two-dimensional and three-dimensional problems in a natural manner. In this paper, a new weighted fractional finite volume method with a nonlocal operator (using nodal basis functions) for solving this two-sided space fractional diffusion equation is proposed. Some numerical results for the Crank–Nicholson fractional finite volume method are given to show the stability, consistency and convergence of our computational approach. This novel simulation technique provides excellent tools for practical problems even when a complex transition zone is involved. This technique can be extend to two-dimensional and three-dimensional problems with complex regions.     

A CENTRAL LIMIT THEOREM FOR STRONG NEAR-EPOCH DEPENDENT RANDOM VARIABLES

In this paper, a central limit theorem for strong near-epoch dependent sequences of random variables introduced in [9] is showed. Under the same moments condition, the authors essentially weaken the "size" requirement mentioned in other papers about near epoch dependence.     

On axisymmetrical problem of layer with temperature dependent properties

The paper deals with the axisymmetrical problem of thermoelastic layer with mechanical properties dependent on temperature. The boundary planes of the body are kept at constant but different temperatures. Moreover, the layer is assumed to be ideal fixed to a rigid foundation. The upper boundary plane is loaded by normal forces dependent on the radius. The considered stationary problem is solved according with the following scheme: (1⁰) firstly the distribution of temperature is found, (2⁰) secondly, assuming that the Young modulus is a power function of temperature and Poisson ratio is constant, the displacements and stress are calculated from adequate boundary value problem. The obtained results in the form of Hankel integrals are analysed numerically for the case of linear dependence of Young modulus on the temperature.     

Strong white light emission from a processed porous silicon and its photoluminescence mechanism

We have prepared various porous silicon (PS) structures with different surface conditions (any combination of oxidation, carbonization as well as thermal annealing) to increase the intensity of photoluminescence (PL) spectrum in the visible range. Strong white light (similar to day-light) emission was achieved by carrying out thermal annealing at 1100 °C after surface modification with 1-decene of anodic oxidized PS structures. Temperature-dependent PL measurements were first performed by gradually increasing the sample temperature from 10 to 300 K inside a cryostat. Then, we analyzed the measured spectrum of all prepared samples. After the analysis, we note that throughout entire measured spectrum, only two main peaks corresponding to blue and green-orange emission lines (which can be interpreted by quantum size effect and/or configuration coordinate model) were seem to be predominant for all temperature range. To further reveal and analysis these peaks, finally, measured data were inputted into the formula of activation energy of thermal excitation. We found that activation energies of blue and green-orange lines were approximately 49.3 and 44.6 meV, respectively.     

纳米微晶的制备及其性质研究

有机纳米微晶在纳米电子器件等方面具有应用前景, 已成为当前纳米科学的研究热点之一[1]. Nakanishi等[2,3]用再沉淀法制备出了有机纳米微晶, 但并未研究其生长机制和各种制备条件对生长过程的影响. 本文制备了不同粒径的纳米微晶, 研究了晶体结构和光谱性质的变化规律, 讨论了影响粒径大小和生长速率的因素, 为建立可行的有机微晶制备方法提供依据.     

Er3+掺杂ZBLAN非晶的激发态频率上转换

非晶ZBLAN光纤玻璃中掺杂稀土离子Er³⁺的上转换发光的研究表明,在室温、大功率半导体激光器的激发下,Er³⁺的荧光主要是通过单离子步进双光子过程发生的,而其多光子过程虽然非常微弱,但在强的半导体激光的照射下也可产生.通过对这两种不同过程的实验测量,可以为进一步深入地研究上转换机制提供新的依据.     

Theoretical investigations on the carbazole‐based conjugated polymers containing electron‐donating divinylaryl

The polycarbazoles have been proved to efficiently suppress the keto defect emission. Three carbazole‐based conjugated polymers, poly[9‐methyl‐3‐(4‐vinylstyryl)‐9H‐carbazole] (PBC), poly[9‐methyl‐3‐(2‐(5‐vinylthiophen‐2‐yl)vinyl)‐9H‐carbazole] (PBT) and poly[9‐methyl‐3‐(2‐(5‐vinylfuran‐2‐yl)vinyl)‐9H‐carbazole] (PBF), were investigated by quantum‐chemical techniques, and gain a detailed understanding of the influence of carbazole units and the introduction of electron‐donating on the electronic and optical properties. The electronic properties of the neutral molecules, HOMO‐LUMO gaps (ΔE), in addition to ionization potential (I_p) and electron affinity (E_a), are studied using B3LYP density functional theory. The lowest excitation energies (E_g) and the absorption wavelength are studied using the time dependent density functional theory (TDDFT). The calculated results show that all three series of polymers have good planarity. And the highest‐occupied molecular orbital (HOMO) energies lift about 0.36–0.61 eV and thus the I_P decrease about 0.01–0.19 eV compared to polycarbazole, suggesting the significant improved hole‐accepting and transporting abilities. By introducing the electron‐donating 1,4‐divinylphenylene or 2,5‐divinylthiophene or 2,5‐divinylfuran units in the backbone, and the lowest‐unoccupied molecular orbital (LUMO) energies decrease 0.20–0.39 eV. In addition, PBC, PBT and PBF have longer maximal absorption wavelengths than polycarbazole. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 706–714, 2009