Semi‐interpenetrating polymer networks composed of poly(N‐isopropyl acrylamide) and polyacrylamide hydrogels

Three series of semi‐interpenetrating polymer networks, based on crosslinked poly(N‐isopropyl acrylamide) (PNIPA) and 1 wt % nonionic or ionic (cationic and anionic) linear polyacrylamide (PAAm), were synthesized to improve the mechanical properties of PNIPA gels. The effect of the incorporation of linear polymers into responsive networks on the temperature‐induced transition, swelling behavior, and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with various molar ratios (25:1 to 100:1) of the monomer (N‐isopropyl acrylamide) to the crosslinker (methylenebisacrylamide). The hydrogels were characterized by the determination of the equilibrium degree of swelling at 25 °C, the compression modulus, and the effective crosslinking density, as well as the ultimate hydrogel properties, such as the tensile strength and elongation at break. The introduction of cationic and anionic linear hydrophilic PAAm into PNIPA networks increased the rate of swelling, whereas the presence of nonionic PAAm diminished it. Transition temperatures were significantly affected by both the crosslinking density and the presence of linear PAAm in the hydrogel networks. Although anionic PAAm had the greatest influence on increasing the transition temperature, the presence of nonionic PAAm caused the highest dimensional change. Semi‐interpenetrating polymer networks reinforced with cationic and nonionic PAAm exhibited higher tensile strengths and elongations at break than PNIPA hydrogels, whereas the presence of anionic PAAm caused a reduction in the mechanical properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3987–3999, 2004     

Thermoelastoplastic deformation of complexly reinforced shells

The problem on the elastoplastic deformation of reinforced shells of variable thickness under thermal and force loadings is formulated. A qualitative analysis of the problem is carried out and its linearization is indicated. Calculations of isotropic and metal composite cylindrical shells have shown that the load-carrying capacity of shell structures under elastoplastic deformations is several times (sometimes by an order of magnitude) higher than under purely elastic ones; the heating of shells with certain patterns of reinforcement sharply reduces their resistance to elastic deformations, but only slightly affects their resistance to elastoplastic ones; not always does the reinforcement in the directions of principal stresses and strains provide the greatest load-carrying capacity of a shell; there are reinforcement schemes that ensure practically the same resistance of shells at different types of their fastening. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 707–728, November–December, 2006.     

Rational Profiling of Equal-Stress-Reinforced Plates Subjected to Elastoplastic Transverse Bending

The problem of rational profiling of equal-stress-reinforced Kirchhoff plates subjected to purely elastic and elastoplastic transverse bending is formulated. A qualitative analysis of the systems of resolving equations is carried out. It is found that the problem can have two possible solutions, which can be controlled. By particular calculations, it is shown that, through rational profiling of the bent plates, the consumption of phase materials in them can be reduced greatly compared with that in traditional ones, or the load-carrying capacity of the plates can be raised significantly at a fixed consumption of phase materials.     

Nanocellulose reinforced as green agent in polymer matrix composites applications

Owing to their abundance, high strength and stiffness, and low weight and biodegradability, nanocellulose (NC) is regarded as a promising candidate for the preparation of green composites. The high reinforcing effect assigned to the mechanical percolation phenomenon of NC is due to the stiff continuous networks of cellulosic nanoparticles linked via hydrogen bonding. Compared to nanocrystalline cellulose, NC fibers result in more significant improvement to the modulus, stiffness, and strength as aspect ratio NC fiber is higher compared to NC crystal. Indeed, in the case of biopolymer composites, the reinforcement effect of NC is attributed to the NC‐polymer interactions and the reinforcing effect occurring through effective stress transfer at the NC‐polymer interface. The NC‐reinforced composites tend to become more brittle as the concentration of the reinforcing particles increase up to the saturated level, due to the reduction in surface adhesion between filler and matrix. Due to its promising mechanical and structural stability, NC composites have been used widely in many industrial applications such as food packaging, electronic applications, and tissue engineering.     

Strontium‐Substituted Hydroxyapatite‐Gelatin Biomimetic Scaffolds Modulate Bone Cell Response

Strontium has a beneficial role on bone remodeling and is proposed for the treatment of pathologies associated to excessive bone resorption, such as osteoporosis. Herein, the possibility to utilize a biomimetic scaffold as strontium delivery system is explored. Porous 3D gelatin scaffolds containing about 30% of strontium substituted hydroxyapatite (SrHA) or pure hydroxyapatite (HA) are prepared by freeze‐drying. The scaffolds display a very high open porosity, with an interconnectivity of 100%. Reinforcement with further amount of gelatin provokes a modest decrease of the average pore size, without reducing interconnectivity. Moreover, reinforced scaffolds display reduced water uptake ability and increased values of mechanical parameters when compared to as‐prepared scaffolds. Strontium displays a sustained release in phosphate buffered saline: the quantities released after 14 d from as‐prepared and reinforced scaffolds are just 14 and 18% of the initial content, respectively. Coculture of osteoblasts and osteoclasts shows that SrHA‐containing scaffolds promote osteoblast viability and activity when compared to HA‐containing scaffolds. On the other hand, osteoclastogenesis and osteoclast differentiation are significantly inhibited on SrHA‐containing scaffolds, suggesting that these systems could be usefully applied for local delivery of strontium in loci characterized by excessive bone resorption.     

Co-Evolution of Predator-Prey Ecosystems by Reinforcement Learning Agents

The problem of finding adequate population models in ecology is important for understanding essential aspects of their dynamic nature. Since analyzing and accurately predicting the intelligent adaptation of multiple species is difficult due to their complex interactions, the study of population dynamics still remains a challenging task in computational biology. In this paper, we use a modern deep reinforcement learning (RL) approach to explore a new avenue for understanding predator-prey ecosystems. Recently, reinforcement learning methods have achieved impressive results in areas, such as games and robotics. RL agents generally focus on building strategies for taking actions in an environment in order to maximize their expected returns. Here we frame the co-evolution of predators and preys in an ecosystem as allowing agents to learn and evolve toward better ones in a manner appropriate for multi-agent reinforcement learning. Recent significant advancements in reinforcement learning allow for new perspectives on these types of ecological issues. Our simulation results show that throughout the scenarios with RL agents, predators can achieve a reasonable level of sustainability, along with their preys.     

含噁嗪环硅烷偶联剂对石英纤维/含硅芳炔复合材料性能的影响

从石英纤维(QF)、含硅芳炔树脂(PSA)分子结构特点出发,设计并合成了一种含有噁嗪环和端炔的新型硅烷偶联剂(BCA),并以BCA改善QF/PSA复合材料的界面性能。采用差示扫描量热分析(DSC)、红外光谱分析(FT-IR)、X-射线电子能谱(XPS)及扫描电镜(SEM)等测试手段表征了BCA与QF/PSA复合材料的相互作用和界面改性效果。结果表明:BCA能够分别与PSA和QF形成良好的化学键合,改善复合材料的界面黏结;经w=2.0%的BCA处理后,QF/PSA复合材料的层间剪切强度、弯曲强度分别较未处理前提高了69.1%和68.8%。     

广州开发区SDK-D-2地块砌石挡土墙灌浆处理试验工程施工总结

针对广州开发区SDK-D-2地块砌石挡土墙软弱地层,采用单液静力注浆进行灌浆加固。详细论述了灌浆处理工程中的材料及工艺设备、工艺参数、工艺流程,异常情况技术处理及检测措施,分析了灌浆效果。实践表明处理方法有效,达到了工程设计标准。     

基于最小二乘法的均匀扩声技术研究

针对目前室外及超大型室内空间的扩声应用中声场分布不均匀的问题,本文提出了一种基于最小二乘法声场重建方法的扩声技术。该技术通过对目标声场的逼近来计算线性扬声器阵列各通道的输入参数,实现扩声区域内声压级的均匀分布,同时约束非扩声区域的声能量以获得较好指向性。本文通过仿真研究算法各参数的改变对控制结果的影响,探讨不同扩声区域和目标所对应参数的选取方法。仿真和实验比较了该算法以及未经控制的声场、相移法波束控制的效果,证明该方法可以获得更好的声场均匀度。