Electrodeposition of alginate with PEDOT/PSS coated MWCNTs to make an interpenetrating conducting hydrogel for neural interface

Neural interface is a critical component for the communication between the central nervous system and outside devices. But neural tissues withstand constant mechanical activity with outside devices which aggravates inflammation response. The investigation about soft interfacial modification materials for neural implants is a promising way to reduce the mechanical mismatch of neural tissues and implants. In this study, soft alginic acid gel and poly(3, 4-ethylenedioxythiophene)/poly(styrene sulfate)(PEDOT/PSS) coated multi-walled carbon nanotubes(MWCNT) was co-deposited on a microwire neural electrode, then PEDOT/PSS was electrochemically grown through the coating material to form a kind of soft interpenetrating networks (IPNs) for the improvement of neural interface. Compared to unmodified electrodes, the modified electrodes possess higher charge storage capacity (CSC) and lower electrochemical impedance, which would benefit the performance of stimulating and recording respectively. The IPNs are very soft after reswelling in brain tissue, and the cell experiment indicate its fantastic biocompatibility. Furthermore, acute neural recording experiments revealed that the IPNs reduced the noise floor. All these characteristics are greatly desired for the neural interface. Overall, we developed a soft interpenetrating conducting hydrogel coating material on the neural interface with excellent electrical and biological performance.     

Controlled structure and density of “living” polystyrene brushes on flat silica surfaces

Thin layers of polystyrene were grown from surface-grafted nitroxide initiators via controlled “living” free radical polymerization. The “reactive” Langmuir-Blodgett deposition method allowed an effective control of the initiator layer density leading to PS brushes with different and high grafting density and stretching. The influence of the grafting density on the layer structure was studied. Comparison with theoretical predictions for monodispersed brushes in bad solvent was discussed. The thickness was found to vary linearly with molecular weight and the density dependence was shown using wetting measurements. Special features of controlled radical nitroxide polymerization from a surface were discussed. A direct comparison of the molecular weight and polydispersity between surface and bulk polymers was made by de-grafting the brushes into a toluene/HF solution. Finally, some evidence of a “surface Fischer” effect was shown from re-initiated layers. Received 20 December 2001     

A review of research progress in air-to-water sound transmission

International and domestic research progress in theory and experiment and applications of the air-to-water sound transmission are presented in this paper. Four classical numerical methods of calculating the underwater sound field generated by an airborne source, i.e., the ray theory, the wave solution, the normal-mode theory and the wavenumber integration approach, are introduced. Effects of two special conditions, i.e., the moving airborne source or medium and the rough air-water interface, on the air-to-water sound transmission are reviewed. In experimental studies, the depth and range distributions of the underwater sound field created by different kinds of airborne sources in near-field and far-field, the longitudinal horizontal correlation of underwater sound field and application methods for inverse problems are reviewed.     

Atomistic–continuum interphase model for effective properties of composite materials containing nano-inhomogeneities

Classical micromechanics were revised to study the elastic properties of heterogeneous materials containing nano-inhomogeneities. Contrary to previous studies, this work introduces the concept of an interphase, in contrast to a sharp interface, to account for the interface excess stress effect at the nano-scale. The interphase's constitutive properties are derived from atomistic simulations within the continuum framework. These properties are then incorporated in a micromechanics-based interphase model to compute the effective properties of nano-composites. This scale transition approach bridges the gap between discrete systems (atomic level interactions) and continuum mechanics. An advantage of this approach is that it combines atomistic with continuum models that consider inhomogeneity and interphase morphology. It thereby enables us to account simultaneously for both the shape and the anisotropy of a nano-inhomogeneity and interphase at the continuum level when we compute a material's overall properties. In so doing, it frees us from making any assumptions about the interface characteristics between matrix and the nano-inhomogeneity.     

Zonal PANS: evaluation of different treatments of the RANS–LES interface

The partially Reynolds-averaged Navier–Stokes (PANS) model can be used to simulate turbulent flows either as RANS, large eddy simulation (LES) or DNS. Its main parameter is f_k whose physical meaning is the ratio of the modelled to the total turbulent kinetic energy. In RANS f_k = 1, in DNS f_k = 0 and in LES f_k takes values between 0 and 1. Three different ways of prescribing f_k are evaluated for decaying grid turbulence and fully developed channel flow: f_k = 0.4, f_k = k^3/2 _tot/? and, from its definition, f_k = k/k_tot where k_tot is the sum of the modelled, k, and resolved, k_res, turbulent kinetic energy. It is found that the f_k = 0.4 gives the best results. In Girimaji and Wallin, a method was proposed to include the effect of the gradient of f_k. This approach is used at RANS– LES interface in the present study. Four different interface models are evaluated in fully developed channel flow and embedded LES of channel flow: in both cases, PANS is used as a zonal model with f_k = 1 in the unsteady RANS (URANS) region and f_k = 0.4 in the LES region. In fully developed channel flow, the RANS– LES interface is parallel to the wall (horizontal) and in embedded LES, it is parallel to the inlet (vertical). The importance of the location of the horizontal interface in fully developed channel flow is also investigated. It is found that the location – and the choice of the treatment at the interface – may be critical at low Reynolds number or if the interface is placed too close to the wall. The reason is that the modelled turbulent shear stress at the interface is large and hence the relative strength of the resolved turbulence is small. In RANS, the turbulent viscosity – and consequently also the modelled Reynolds shear stress – is only weakly dependent on Reynolds number. It is found in the present work that it also applies in the URANS region.     

Remarks on Sharp Interface Limit for an Incompressible Navier-Stokes and Allen-Cahn Coupled System*

The authors are concerned with the sharp interface limit for an incompressible Navier-Stokes and Allen-Cahn coupled system in this paper. When the thickness of the diffuse interfacial zone, which is parameterized by ε, goes to zero, they prove that a solution of the incompressible Navier-Stokes and Allen-Cahn coupled system converges to a solution of a sharp interface model in the L^∞(L²) ∩ L²(H¹) sense on a uniform time interval independent of the smal...     

基于界面跟踪方法的汽蚀模型和算法的有效性验证

针对两相附着汽蚀流动机理,基于界面跟踪方法发展了新的汽蚀模型和算法。所发展的汽蚀模型和算法不仅考虑了液相／气相界面处的压力差,而且考虑了耦合Reynolds-Averaged Navier-Stokes方程求解技术得到的流场压力梯度信息来迭代计算附着汽蚀形状。采用具有试验数据的半球形头部圆柱体汽蚀绕流作为算例来验证所提出的汽蚀模型和算法的有效性。采用不同的网格数和松弛因子数值验证了发展的汽蚀模型和算法的有效性。三种汽蚀数下的数值计算结果得到的压力系数分布与试验数据完全吻合。结果表明所提出的汽蚀模型和算法能够准确模拟出汽蚀发生点和汽蚀长度。     

离子辐照引起的金属／绝缘体界面混合与相变研究

载能离子穿过固体界面引起界面原子迁移使界面原子混合和物质成分变化，从而导致界面发生材料相变。简要介绍了载能离子辐照引起金属／绝缘体界面混合效应及相变现象的主要实验研究进展、低能离子和高能离子辐照引起金属／绝缘体界面现象差异，并对离子辐照引起界面混合及相变的机制进行了初步探讨。When penetrating an interface between two kind of solids, energetic ions can induce atomic diffusion at both sides of the interface and then result in intermixing, atom re-distribution or composition change, as well as phase transformation. Main progress on the study of intermixing and phase change at metal/insulator interface induced by energetic ion irradiations, the difference of phenomena occurred at metal/insulator interfaces induced by high-and low-energy ions were briefly reviewed. Furthermore, the possible mechanisms related to intermixing and phase change at metal/insulator interface produced by energetic ion irradiations were also discussed in short words.     

Self-consistent Monte Carlo simulations of the electron and ion distributions of inhomogeneous liquid alkali metals. II. Longitudinal and transverse density distributions in the liquid-vapor interface of binary metallic alloys

We present the results of Monte Carlo simulations of the liquid-vapor interface of sodium-cesium alloys. The longitudinal density profile of each alloy shows that the liquid-vapor interface consists of a well-defined monolayer of cesium sitting on top of a slab of the bulk alloy. Underneath the monolayer there is a slight excess of sodium. A comparison with a van der Waals analog of one of the alloys shows that the presence of the well-defined monolayer of cesium on the outside of the liquid-vapor interface is a feature peculiar to metallic mixtures. The transverse pair correlation functions of the cesium monolayer are insensitive to the composition of the bulk of the slab.     

脉冲激光烧蚀块状靶材的双动态界面研究

给出脉冲激光作用块状靶材的烧蚀模型.根据能量平衡原理,导出烧蚀面的位置随时间的变化关系.利用绝热近似、温度连续性条件和能量平衡原理来获得烧蚀面与固液相界面边界条件.结合热传导方程,利用精确解与积分近似法相结合的方案,给出固液两相的温度分布与时间和位置的变化关系,以及固液相界面的位置随时间的变化规律,并与已有的理论和实验结果进行比较.最后以铝靶为例计算模拟了激光烧蚀的全过程计算. 关键词： 脉冲激光 等离子体 固液相界面 烧蚀面