A THEORETICAL MODEL FOR THERMAL-SENSITIVE MICROGEL WITH PNIPAM CORE AND ELASTIC SHELL

Poly(N-isopropylacrylamide)(PNIPAM) microgels are widely used in drug delivery due to their fast response to temperature.In order to get a better biocompatibility,PNIPAM microgels are typically coated with a layer of biocompatible material,resulting in composite microgels with core-shell structure.In a composite microgel prepared recently,for example,a microsphere of PNIPAM gel is enclosed by a phospholipid membrane,and the composite microgel exhibits a substantial volume transition in response to temperature changes.Here we develop a theoretical model to describe the thermal-responsive behavior of this composite microgel.In particular,we treat the phospholipid membrane as an elastic layer behaving like rubber-like elastomers and adopt the form of the free-energy function for nematic gels(which refer to anther species of thermalsensitive gels whose behavior has been intensively studied) as that for PNIPAM gels.We show that the thermal-responsive behavior of the composite microgel can be markedly influenced by the membrane.By investigating the state of stress on the interface,we further predict that when the coating membrane is stiff and thin,wrinkles are expected to occur on the outer surface of the composite microgel after the volume transition.     

Smart damping of laminated thin cylindrical panels using piezoelectric fiber reinforced composites

In this paper performance of a new piezoelectric fiber reinforced composite (PFRC) material has been investigated for active constrained layer damping (ACLD) of laminated thin simply supported composite cylindrical panels. The constraining layer of the ACLD treatment has been considered to be made of this PFRC material. A finite element model of smart composite panels integrated with the patches of such ACLD treatment has been developed to demonstrate the performance of these patches on enhancing the damping characteristics of thin cross-ply and angle-ply laminated composite cylindrical panels. Particular emphasis has been placed on studying the effect of variation of the piezoelectric fiber orientation in the constraining PFRC layer and the shallowness angle of the panels on the control authority of the patches.     

Convective instability of a horizontal layer of fluid between permeable membranes

The equilibrium stability is investigated of a system consisting of two semi-infinite isothermal masses of fluid divided by a horizontal layer of finite thickness of the same fluid with a vertical temperature gradient directed downwards. The transition layer is separated by thin permeable membranes. Neutral stability curves are constructed for different membrane resistances. In the case of high permeability, the equilibrium is absolutely unstable with respect to monotonic-type longwave perturbations. For low permeability membranes, instability with respect to monotonic finite-wavelength perturbations is characteristic.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 171–173, July–August, 1985.     

ADVANCES IN MICROEMULSION PHASE ON SELF-ASSEMBLY AND MICELLE EXTRACTION WITH BLOCK COPOLYMERS

In this paper we review our work on self-assembly of the system, poly（ethylene oxide）-poly（propylene oxide）-poly（elhylene oxide） （PEO-PPO-PEO） block copolymers, which is a kind of macromolecular complex fluids. The control of self-assembly could be obtained by adding inorganic salts or aliphatic alcohols. By self-assembly of amphiphilic block copelymers a microemulsion phase is formed which could be applied in micelle extraction, such as hollow-fiber membrane micelle extraction, magnetic micelle extraction and immobilized micelle extraction.     

The solution of large deflection problem of thin circular plate by the method of composite expansion

In this paper, the method of composite expansion in perturbation theory is used for the solution of large deflection problem of thin circular plate. In this method. the outer field solution and the inner boundary layer solution are combined together to satisfy all the boundary conditions. In this paper, Hencky’s membrane solution is used for the first approximation in outer field solution, and then the second approximate solution is obtained. The inner boundary layer solution is found on the bases of boundary layer coondinate. In this paper, the reciprocal ratio of maximum deflection and thickness of the plate is used as the small parameter. The results of this paper improves quite a bit in comparison with the results obtained in 1948 by Chien Wei-zang.     

Optimisation of Gas Access Through a Thin Porous Layer with a Partially Occluded Inlet Surface

Transport in Porous Media - The gas access through a thin porous layer is studied in relation to the reactant gas transfer in the gas diffusion layer (GDL) of polymer electrolyte membrane fuel...     

油溶性二正辛基二硫代氨基甲酸铈的合成及其摩擦化学特性研究

以二正辛胺、Ｃｅ２Ｏ３和ＣＳ２为原料合成出一种新型油溶性润滑油极压抗磨添加剂二正辛基二硫代氨基甲酸铈（Ⅲ），并在环－块式摩擦磨损试验机和四球试验机上，测定了它的减摩性能、承载能力和抗磨性能等，同时还就其添加量对这些性能的影响进行了考察；利用俄歇电子能谱仪和Ｘ射线光电子能谱仪，对边界润滑状态下形成的摩擦表面膜的元素组成和化学状态进行了分析．结果表明：在给定的试验条件下，这种添加剂可以使ＩＳＯＶＧ３２石蜡基矿物油的摩擦系数明显降低，能够使这种油的初始卡咬负荷和烧结负荷分别提高２．２倍和４．７倍，可见其减摩和抗磨性能良好；在这种添加剂作用下形成的表面层内含有有机物膜、氧化物膜、化学反应膜和Ｃｅ３＋渗透层等，这是摩擦化学作用的产物     

Experimental study of the osmotic behaviour of reverse osmosis membranes for different NaCl solutions and hydrostatic pressure differences

The osmotic behaviour of five different present-day reverse osmosis membranes was studied, using different NaCl solutions (<6 wt.%) and applying different hydrostatic pressure differences (<5.2 bar) between the high and low concentration sides. The osmotic water flux through the membranes was found to increase non-linearly with respect to the increasing concentration difference over the membrane, leading to non-constant values for apparent water permeability. The polyamide composite membranes studied resulted only in very weak osmosis for even relatively small hydrostatic pressure differences and for strong NaCl solutions. Asymmetric cellulose acetate membranes showed somewhat better osmotic behaviour. However, all the osmotic water fluxes measured were still far too small for practical application in the production of energy.     

Melting of horizontal ice layer from above by combined effect of temperature and concentration of aqua-solvent

This paper is concerned with the melting of horizontal ice layer from above by aqua-solvent with low solidification point. The solute used in this experiment are Sodium chloride NaCl, Calcium chloride CaCl₂, Magnesium chloride MgCl₂, and Urea CO(NH₂)₂- The upper surface of aqua-solvent melt layer is heated by an infrared lamp, whose temperature is in the range of about 8 ?C to 40 ?C. The ice layer located under the aqua-solvent melt layer melts greatly by a combined effect of both thermal energy and chemical reaction, and the typical temperature distribution in both aqua-solvent and ice layer is examined. The relation between melt amount of ice layer per unit temperature gradient and mean concentration in aqua-solvent melt layer was obtained.     

石墨氧化物分子沉积膜的制备及其摩擦学行为研究

采用分子沉积技术制备了石墨氧化物（GO）－聚二丙烯二甲铵（PDDA）多层超薄膜，用紫外和红外光谱对超薄膜的结构进行了分析，用原了力显微镜考察了薄膜的表面形貌及纳米摩擦学行为。结果表明：石墨氧化物分子沉积膜可以降低玻璃表面的摩擦系数；其摩擦系数随载荷增大而降低；该分子沉积薄膜良好的润滑性能归因于其较低的表面剪切强度。     

Model of spontaneous crystallization of a thin melted layer brought into contact with a massive substrate

A model of spontaneous crystallization of a thin melted metal layer brought into contact with a massive substrate is proposed. With invoking the Kolmogorov composite crystallization theory, the model allows one to predict the size distribution of crystallites across the layer, which provides a possibility of controlling the microstructure of the solidifying layer through a proper choice of substrates.     

DYNAMIC ANALYSIS OF SPINNING DEPLOYMENT OF A SOLAR SAIL COMPOSED OF VISCOELASTIC MEMBRANES

近年来, 可用于航天器推进的太阳帆自旋展开技术引起人们广泛关注. 这类太阳帆可视为由中心旋转毂轮、若干柔性绳索、太阳帆薄膜和集中质量等组成的刚柔耦合多体系统.为了对系统中的太阳帆薄膜进行建模, 提出了基于绝对节点坐标方法描述的黏弹性薄板单元, 并对其有效性进行了验证.针对简化的"IKAROS"自旋展开太阳帆系统, 采用结合自然坐标方法与绝对节点坐标方法的绝对坐标方法对其进行建模, 采用广义-α方法对大规模系统动力学方程进行求解.研究了黏弹性太阳帆薄膜自旋展开过程的动力学特性, 讨论了薄膜的黏弹性阻尼对自旋展开过程的影响规律.     

Inflation of elastomeric circular membranes using network constitutive equations

The present paper deals with the use of network-based hyperelastic constitutive equations in the context of thin membranes inflation. The study focus on the inflation of plane circular membranes and the materials are assumed to obey Gaussian and non-Gaussian statistical chains network models. The governing equations of the inflation of axisymmetric thin rubber-like membranes are briefly recalled. The material models are implemented in a numerical tool that incorporates an efficient B-spline interpolation method and a coupled Newton-Raphson/arc-length solving algorithm. Two numerical examples are studied: the homogeneous inflation of spherical balloons and the inflation of initially plane circular membranes. In the second example, the inflation profiles and the distributions of extension ratios along the membrane are extensively analysed during the inflation process. Both examples highlight the need of an accurate modelling of the strain-hardening phenomenon in elastomers.     

磁电复合材料中拓扑磁结构的力学调控

磁性斯格明子是在一些铁磁材料中存在的一种重要拓扑磁结构，由于其具有独特的磁-电-力-热多场耦合特性，在未来新型自旋电子器件中有着广泛的应用前景。然而，磁性斯格明子一般需要在外加磁场下才能稳定存在，极大地限制了其在自旋电子器件中的实际应用。本文基于实空间下磁电材料的相场模拟，发现铁电和铁磁复合薄膜中铁电斯格明子可以通过界面变形来稳定铁磁斯格明子。由于力电耦合效应，铁电层中铁电斯格明子的非均匀分布极化在界面产生周期性的非均匀界面变形。界面变形通过力磁耦合效应，使铁磁层中的磁性斯格明子在没有外加磁场的条件下能够稳定存在。本文的研究结果表明，基于磁电复合材料中的力-电-磁耦合效应，通过优化设计复合材料中不同组元的结构，可以实现拓扑磁结构的力学调控，从而为设计基于拓扑磁结构的新型自旋电子器件提供了新思路。     

The analysis of thin walled composite laminated helicopter rotor with hierarchical warping functions and finite element method

In the present paper, a series of hierarchical warping functions is developed to analyze the static and dynamic problems of thin walled composite laminated helicopter rotors composed of several layers with single closed cell. This method is the development and extension of the traditional constrained warping theory of thin walled metallic beams, which had been proved very successful since 1940s. The warping distribution along the perimeter of each layer is expanded into a series of successively corrective warping functions with the traditional warping function caused by free torsion or free bending as the first term, and is assumed to be piecewise linear along the thickness direction of layers. The governing equations are derived based upon the variational principle of minimum potential energy for static analysis and Rayleigh Quotient for free vibration analysis. Then the hierarchical finite element method is introduced to form a numerical algorithm. Both static and natural vibration problems of sample box beams are analyzed with the present method to show the main mechanical behavior of the thin walled composite laminated helicopter rotor. The project supported by the National Natural Science Foundation of China (19932030)     

Vibrations of shallow noncircular membranes with initial stresses

The basic relations for a geometrically nonlinear (quadratic approximation) theory of thin elastic membranes are obtained. The relations are used to develop a variational method for studying free vibrations of initially flat membranes bounded by a stationary piecewise-smooth contour. The membrane is deformed by uniform pressure. Numerical results are given for different types of vibrations of rectangular and elliptical shells. N. V. Gogol' Pedagogical Institute, Nezhin: S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 35, No. 8, pp. 78–86, August 1999.     

Computational analysis of liquid crystalline elastomer membranes: Changing Gaussian curvature without stretch energy

Liquid crystalline elastomers (LCEs) can undergo extremely large reversible shape changes when exposed to external stimuli, such as mechanical deformations, heating or illumination. The deformation of LCEs result from a combination of directional reorientation of the nematic director and entropic elasticity. In this paper, we study the energetics of initially flat, thin LCE membranes by stress driven reorientation of the nematic director. The energy functional used in the variational formulation includes contributions depending on the deformation gradient and the second gradient of the deformation. The deformation gradient models the in-plane stretching of the membrane. The second gradient regularises the non-convex membrane energy functional so that infinitely fine in-plane microstructures and infinitely fine out-of-plane membrane wrinkling are penalised. For a specific example, our computational results show that a non-developable surface can be generated from an initially flat sheet at cost of only energy terms resulting from the second gradients. That is, Gaussian curvature can be generated in LCE membranes without the cost of stretch energy in contrast to conventional materials.     

Carbonate-salt-based composite materials for medium- and high-temperature thermal energy storage

This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and a high thermal conductivity material. The ceramic material forms a microstructural skeleton for encapsulation of the PCM and structural stability of the composites; the high thermal conductivity material enhances the overall thermal conductivity of the composites. Using a eutectic salt of lithium and sodium carbonates as the PCM, magnesium oxide as the ceramic skeleton, and either graphite flakes or carbon nanotubes as the thermal conductivity enhancer, we produced composites with good physical and chemical stability and high thermal conductivity. We found that the wettability of the molten salt on the ceramic and carbon materials significantly affects the microstructure of the composites.     

Numerical implementation of composite Koiter shells including membrane/bending coupling coefficientsImplémentation numérique des coques composites de Koiter prenant en considération les coefficients de couplage membrane/flexions

We propose a way for determining the generalized coefficients of rigidity – some of which are membrane/bending coupling coefficients – which appear in the deformation energy of the Koiter model of thin shells. This is concerned with a heterogeneous material in the thickness direction. A new program to compute these coefficients is implemented in the finite element code Modulef, in order to simulate problems of thin multilayered shells with linearly elastic anisotropic layers. We propose an example of an inhibited multilayered thin shell, with hyperbolic middle surface, involving a composite material with unidirectional fibres. To cite this article: H. Ranarivelo, C. R. Mecanique 330 (2002) 273–278.