Influence of aspect ratio and arrangement direction on the shear behavior of ellipsoids

This work studies the macroscopic and microscopic behaviors of ellipsoids under triaxial tests using 3D discrete element method (DEM) simulation. To avoid the boundary effect, a novel stress servo-controlled periodic boundary condition is proposed to maintain the confining pressure of samples during testing. The shape features of ellipsoids are investigated, including the aspect ratio of elongated/oblate ellipsoids and the initial arrangement directions of ellipsoids. The macroscopic properties of ellipsoidal particle samples, such as the deviatoric stress, volumetric strain, internal friction angle, as well as dilatancy angles are explored. Elongated and oblate ellipsoids with varying aspect ratios are investigated for the occurrence of stick-slips. In addition, it is demonstrated that the initial arrangement direction has a significant impact on the coordination number and contact force chains. The corresponding anisotropy coefficients of the entire contact network are analyzed to probe the microscopic roots of macroscopic behavior.     

Theoretical investigation on submicron particle penetration through circular tubes inside a porous medium

The analytical infinite series solution of submicron particle transport in a circular tube bounded by a porous wall, such as a pinhole, is determined under the slip velocity boundary condition, and the solution is verified by using the experimental data in the previous studies for the specific cases. The results show that particle penetration rate increases with the increase of the porous parameter, the axial pressure drop, and the pinhole radius, whereas it decreases with increasing the pinhole length. The penetration rate of nano-particles are more sensitive to the variation of these parameters. However, the differences between the penetrations of particles ranging from 0.3 μm to 1 μm are not evident because the diffusion becomes weak gradually in this size range. In addition, a further comparison is performed between the analytical solution and the existing studies, and approximate expressions are presented for accurate calculation of particle penetration rate through pinholes appearing in porous materials including filter devices and masks.     

同轴电喷法制备PCL-蛋清体系复合微胶囊

以鸡蛋的卵清蛋白作为蛋白质药物模板、生物可降解材料聚己内酯(PCL)为药物载体模板,采用同轴电喷法制备PCL-蛋清体系的复合微球.研究了电导率、黏度对于电喷微球成型的影响.核壳溶液推进速率比、电压、溶液质量分数和接收距离等对于所得微球表面形态和结构的影响.利用扫描电子显微镜(SEM)研究了微球的表面形态,用荧光显微镜表征了微球的包覆模式.结果表明:同轴电喷法可以制备PCL-蛋清体系的复合结构微胶囊,其中推进速率比对微球形貌、粒径及其分布的影响比较明显,当PCL与蛋清溶液推进速率比大于10时,将出现具有包覆结构的微球.     

Nonbiofouling surface based on amphiphilic alkanethiol self‐assembled monolayers

A series of novel amphiphilic alkanethiols used for preparation of nonbiofouling surfaces have been synthesized and characterized. Surface properties of the resultant self assembled layers have been studied by multiple characterization techniques, such as XPS, Grazing angle infrared spectroscopy (GA‐FTIR) and contact angle measurements. The antifouling performance of surfaces grafted with terminally fluorinated alkanethiols were assayed employing the fouling diatom Nitzschia and ubiquitous Staphylococcus aureus. The results indicated that amphiphilic alkanethiol‐grafted surfaces could effectively reduce the bacterial adhesion and settlement of the fouling diatom. Copyright © 2010 John Wiley & Sons, Ltd.     

Superabsorbent materials derived from hydroxyethyl cellulose and bentonite: Preparation,characterization and swelling capacities

Superabsorbent polymers (SAPs) and composites (SAPCs) were prepared entirely by graft copolymerization of polyacrylamide (PAM) onto hydroxyethyl cellulose (HEC), using potassium persulfate (KPS) as an initiator, and N,N′-methylenebisacrylamide (MBA) as a crosslinker, in an aqueous solution. The extent of grafting was evaluated from % grafting efficiency (%GE) for various HEC/AM ratios, and a near optimal ratio was determined. Influences of various preparation parameters, i.e., the ratio of HEC/AM, amount of initiator and crosslinker, reaction temperature and time, and amount of filler on water swelling capacity of SAPs and SAPCs were studied. An FT-IR determination confirmed that the PAM was successfully grafted onto the HEC backbone, by showing absorption bands of the HEC backbone and new absorption bands from the grafted copolymer. The swelling capacity of SAPs and SAPCs depended strongly on different parameters, and the maximum swelling capacity was over 426 g/g and 538 g/g for the SAPs and SAPCs, respectively.     

Synchronization of stochastically hybrid coupled neural networks with coupling discrete and distributed time-varying delays

A general model of linearly stochastically coupled identical connected neural networks with hybrid coupling is proposed, which is composed of constant coupling, coupling discrete time-varying delay and coupling distributed timevarying delay. All the coupling terms are subjected to stochastic disturbances described in terms of Brownian motion, which reflects a more realistic dynamical behaviour of coupled systems in practice. Based on a simple adaptive feedback controller and stochastic stability theory, several sufficient criteria are presented to ensure the synchronization of linearly stochastically coupled complex networks with coupling mixed time-varying delays. Finally, numerical simulations illustrated by scale-free complex networks verify the effectiveness of the proposed controllers.     

Seasonal variability of cloud optical depth over northwestern China derived from CERES/MODIS satellite measurements

The seasonal variability of cloud optical depth over northwestern China derived from Clouds and the Earth＇s Radiant Energy System （CERES） Single Scanner Footprint （SSF） Aqua Moderate Resolution Imaging Spectroradiometer （MODIS） Edition IB data from July 2002 to June 2004 is presented. The regions of interest are those with Asia monsoon influence, the Tianshan and Qilian Mountains, and the Taklimakan Desert. The results show that the instantaneous measurements presented here are much higher than the previous results derived from International Satellite Cloud Climatology Project （ISCCP） D2 monthly mean data. Generally the measurements of cloud optical depth are the highest in summer and the lowest in winter, however, Taklimakan Desert has the lowest measurements in autumn. The regional variation is quite significant over northwestern China.     

Characterization of the surface properties of xylan by FT-Raman spectroscopy and wicking technique

Using FT-Raman spectroscopy, column wicking technique and the equations of Washburn as well as van Oss et al., the surface properties of xylan, the main component in hemicelluloses, has been characterized and estimated. Raman spectrum showed that xylan has been structured by acetyl group and methyl-bonded glucurono group. Obtained results show that the surface free energy of xylan is higher in comparison with literature reported values for cellulose because the former has a larger Lifshitz–van der Waals component than the latter. However, xylan has been found to have very smaller polarity and orientation data than that of cellulose.     

A simplified approach for evaluation of the polarity parameters for polymer using the K coefficient of the Mark-Houwink-Sakurada equation

Since two solvent polarity parameters, e.g., the Et(30) defined by Reichardt and the pi* defined by Kamlet and Taft, respectively, plotted with the K coefficient of the Mark-Houwink-Sakurada equation, presented good linear fits, this paper suggests applying the extrapolating method in the same way as the Zisman plot to obtain similar polarity parameters for polymers. In order to verify those obtained polarity parameter values for various polymers, literature-reported polarity values determined using other techniques are referenced and indicate that this paper introduced a simplified approach that can be applied to evaluate the polarity parameters for polymers. In this paper, since we observe that various polymers are of interest to present absolutely different slope tendencies, e.g., positive and negative, it is also suggested that polarity properties of polymers may be reinterpreted.     

First-Principles Study of Electronic Properties in PbS（1^-00） with Vacancy Defect

Electronic properties of both Pb and S vacancy defects in PbS（1^-00） have been studied using the first-principles density functional theory （DFT） calculations with the plane-wave pseudopotentials. It is found that the density of states （DOS） near the top of the valence band and the bottom of the conduction band is significantly modified by these defects. Our calculation indicates that in the case of S vacancy defects the Fermi energy shifts to the conduction band making it as an n-type PbS （donor）. However, in the case of Pb vacancy, because of the appreciable change of the DOS, the system acts as a p-type PbS （accepter）. In addition, the structural relaxation shows that the defect leads to outward relaxation of the nearest-neighbouring atoms and inward relaxation of the next-nearest neighbouring atoms.