Vibration characteristics and flutter analysis of a composite laminated plate with a store

The effects of an external store on the flutter characteristics of a composite laminated plate in a supersonic flow are investigated. The Dirac function is used to formulate the interaction between the plate and the store. The first-order piston theory is used to describe the aerodynamic load. The governing equation of the composite laminated plate with an external store is established based on the Hamilton principle. The mode shapes are constructed by the admissible functions which axe a set of characteristic orthogonal polynomials generated directly by the Gram-Schmidt process, and the boundary constraint is modeled as the artificial springs. The frequency and mode shapes of the plate under different boundaries are determined by the Rayleigh-Ritz method. The validity of the proposed approach is confirmed by comparing the results with those obtained from the finite element method （FEM）. The effects of the mounting position, the center of gravity position and the mounting points spacing of the external store on the flutter boundary are discussed for both the simply supported and cantilever plates, respectively, which correspond to the two installation sites of the external store, i.e., the belly and wings of the aircraft.

Aero-Elastic Flutter Characteristics of Laminated Composite Panel Embedded with Shape Memory Alloy Wires

The effects of shape memory alloy( SMA) wires on the natural frequency,flutter boundary and amplitude of limit cycle oscillation( LCO) of a laminated composite panel are investigated. The classical plate theory as well as von-Karman strain-displacement relation are used to formulate the nonlinear dynamic model of the smart laminated panel. The aerodynamic loadings are simulated by the third order piston theory. The thermomechanical behavior of SMA wires is estimated according to one-dimensional Brinson SMA model. The effects of SMA wires temperature,pre-strain,volume fraction and orientation on flutter boundary and amplitude of LCO of the panel are analyzed in detail.

全物理交联三重互穿网络水凝胶的制备与性能

为提升水凝胶的综合力学力学性能,设计并研究了一种全物理交联三重互穿网络水凝胶。以自由基乳液聚合法,获得疏水缔合交联的聚丙烯酰胺网络,水凝胶一步成型,依次通过冷冻-融化循环、浸没FeCl_(3)溶液分别形成微晶交联的聚乙烯醇网络及离子交联的海藻酸钠网络。获得P(AM-SMA)/PVA/SA三重互穿网络(HMITN)水凝胶。通过傅里叶变换红外对水凝胶结构进行了表征;通过电子万能试验机对水凝胶的力学性能进行了研究。结果表明,HMITN水凝胶具有良好的强度、韧性、抗疲劳及自恢复性能,强度0.45 MPa,断裂能2.48 MJ/m^(3),在200%应变下进行5次循环拉伸后仍然保持20.3%的韧性,室温下自恢复260 min后,韧性可恢复66.7%。

基于非对称PVA/墨水/PE双层膜的光驱动柔性致动器和多功能传感器

聚乙烯醇/中国墨水混合物被均匀涂覆在聚乙烯薄膜上制备了结构稳定的双层软驱动器.由于两层材料的热膨胀系数的显著差异,在氙灯照射下,驱动器能以较快的响应速度实现较大的弯曲变形.通过改变光的强度以及结合尺蠖的仿生结构设计,机器人可以在不同的表面(如纸张和树叶)上实现各种形式的运动.同时在光的驱动下,它可以实现物体的捕获、表情的改变、象鼻的收缩与卷曲以及仿生花朵的开闭等.此外,基于双层驱动器良好的光热转换和灵敏的压力传感性能,它可以实现人体运动监测(如关节弯曲、呼吸、吞咽等),还能与光电转换装置集成.这种多功能、多驱动模式软机器人在可穿戴设备、交通运输、光电转换设备等应用领域具有巨大潜力.

Sustained release of magnesium and zinc ions synergistically accelerates wound healing

Skin wounds are a major medical challenge that threaten human health.Functional hydrogel dressings demonstrate great potential to promote wound healing.In this study,magnesium(Mg)and zinc(Zn)are introduced into methacrylate gelatin(GelMA)hydrogel via low-temperature magnetic stirring and photocuring,and their effects on skin wounds and the underlying mechanisms are investigated.Degradation testing confirmed that the GelMA/Mg/Zn hydrogel released magnesium ions(Mg^(2+))and zinc ions(Zn^(2+))in a sustained manner.The Mg^(2+) and Zn^(2+)not only enhanced the migration of human skin fibroblasts(HSFs)and human immortalized keratinocytes(HaCats),but also promoted the transformation of HSFs into myofibroblasts and accelerated the production and remodeling of extracellular matrix.Moreover,the GelMA/Mg/Zn hydrogel enhanced the healing of full-thickness skin defects in rats via accelerated collagen deposition,angiogenesis and skin wound re-epithelialization.We also identified the mechanisms through which GelMA/Mg/Zn hydrogel promoted wound healing:the Mg^(2+) promoted Zn^(2+)entry into HSFs and increased the concentration of Zn^(2+)in HSFs,which effectively induced HSFs to differentiate into myofibroblasts by activating the STAT3 signaling pathway.The synergistic effect of Mg^(2+) and Zn^(2+)promoted wound healing.In conclusion,our study provides a promising strategy for skin wounds regeneration.

Development of educational attainment and gender equality in China:new evidence from the 7th National Census

This paper discusses the status and changes in educational attainment and gender inequality in education for the Chinese population based on the data from the 7th National Census of China and previous censuses since 1982.The results indicate that gender inequality in education has lessened while educational attainment has improved.However,it is necessary to continue to eradicate illiteracy in the West,further promote compulsory education rates,increase the advancement rate to high school,and reduce the urban-rural gap in education to further develop education.This paper indicates that the increased educational opportunities for women combined with their relatively superior academic abilities have resulted in a new reversed gender inequality in that males are at a disadvantage,especially in higher education.The fact that women have benefited more from the expansion of higher education than men have was an unintended consequence of China's one-child fertility policy since the family resources are less diluted by fewer children in a household and daughters are regarded as long-term family members.This paper further reveals that although women outperform men at every level of the educational system,they often voluntarily withdraw from pursuing doctoral degrees due to the increasing pressure as they age and age discrimination which drives them to enter marriage and the labor market earlier than men do.

Dynamic Response of Fractional-Order Viscoelastic High-Order Shear Beam Based on Nonlocal Strain Gradient Elasticity

The dynamic behavior of a viscoelastic high-order shear microbeam is studied based on a new constitutive model which incorporates size effects and viscoelasticity simultaneously.The size effects are modeled by the nonlocal gradient elasticity,while viscoelastic effects are modeled by fractional-order derivatives.The constitutive relation and the equations of motion are both differential equations with fractional-order derivatives.Based on the Laplace transform and inverse transform,the analytical solution of the dynamic response under a step load is obtained in terms of the Mittag–Leffler function.In order to verify the reliability of the analytical solution,a comparison with the numerical solution is also provided.Based on the numerical results,the effects of the nonlocal parameter,strain gradient parameter,fractional-order parameter,and viscosity coefficient on the dynamic response of the viscoelastic microbeam are discussed.It is found that the influences of the fractional order and the coefficient of viscosity on the dynamic response of the microbeam are very different,although both are related to the viscoelastic behavior.