关键词： Redox reactions   Oscillation   Catalysts   Hydrogels   Polymers  

摘要： We show experimentally that chemical and mechanical self-oscillations in Belousov-Zhabotinsky hydrogels are inherently asynchronous, that is, there is a detectable delay in swelling-deswelling response after a change in the chemical redox state. This phenomenon is observable in many previous experimental studies and potentially has far-reaching implications for the functionality and response time of the material in future applications;however, so far, it has not been quantified or reported systematically. Here, we provide a comprehensive qualitative and quantitative description of the chemical-to-mechanical delay, and we propose to explain it as a consequence of the slow nonequilibrium swelling-deswelling dynamics of the polymer material. Specifically, standard hydrogel pieces are large enough that transport processes, for example, counterion migration and water diffusion, cannot occur instantaneously throughout the entire gel piece, as opposed to previous theoretical considerations. As a result, the volume response of the polymer to a chemical change may be governed by a characteristic response time, which leads to the emergence of delay in mechanical oscillation. This is supported by our theoretical calculations.

关键词： Silicene   C-S-H   Molecular dynamics   Surface structure   Mechanical performance  

摘要： As the silicon counterpart of graphene, silicene has a great potential in reinforcing cement-based materials due to its outstanding physical properties. In this paper, the surface structure, bonding, mechanical performance and failure mechanism of silicene reinforced calcium-silicate-hydrate composite (C-S-H/ silicene) with different humidity were investigated by molecular dynamics simulations. It has been demonstrated that the incorporation of silicene nanosheet can effectively bridge the upper and lower layers of C-S-H and enhance the strength and stability of the interlayer region of C-S-H via various chemical bonds (e.g. Si-Os-Si covalent bonds). This bridging effect provided by silicene nanosheet significantly improves the strength and plasticity of C-S-H. However, the penetration of water molecules may weaken the stability of these chemical bonds, leading to the degradation of tensile strength. Besides, C-S-H/ silicene breaks in the internal area rather than interlayers in a dry state during the failure process. This can be explained that Si-Os-Si bonds are strong enough to connect the silicene sheet and C-S-H layers and hinder the propagation of cracks. Hopefully, the reinforce mechanism of silicene on C-S-H could provide new insights on understanding and predicting performance of silicene under specific conditions. (c) 2021 Elsevier Ltd. All rights reserved.

关键词： Dehydration of C-S-H   Reactive molecular dynamics   Interlayer spacing collapse   Structural ordering   Stiffness and toughness   Packing density  

摘要： The dehydration and dehydroxylation of C-S-H gel ubiquitously occurs in the thermal destruction or recycle of the concrete materials, and the latter is closely related to the sustainability in the construction industry. Utilizing reactive molecular dynamics simulation, this paper presents an investigation on the structure, dynamics and mechanical properties evolution of the C-S-H with decreasing water content, at the molecular level. Dynamically, it is found that the dehydration and dehydroxylation are successively occurred as the hydration degree of C-S-H decreases. At the dehydration stage, water molecules are dis-sociated to maintain the number of hydroxyls. The C-S-H structure does not change much at this stage. At the dehydroxylation stage, the number of hydroxyl groups sharply decreases, along with large structural transformation in the C-S-H, including fast decreasing interlayer spacing, merging of interlayer calcium layers and disordering of the primary calcium silicate layers. With respect to the mechanical properties, the interlayer spacing collapse significantly increases the stiffness and toughness of the C-S-H structure. On the other hand, drastic volume shrinkage of the C-S-H structure due to dehydroxylation can lead to decreasing contact points between C-S-H nano-globules. This means an increase in the mechanical prop-erties of C-S-H matrix but a decrease in the packing density of C-S-H gel. Eventually, the indentation modulus of C-S-H gel monotonously decreases during dehydration and dehydroxylation. (c) 2021 Published by Elsevier Ltd.

关键词： molecular dynamics simulations   PEGylated pH-sensitive liposomes   cholesteryl hemisuccinate   phase transition   bilayer hydrophilicity  

摘要： Liposome-based drug delivery systems composed of DOPE stabilized with cholesteryl hemisuccinate (CHMS) have been proposed as a drug delivery mechanism with pH-triggered release as the anionic form (CHSa) is protonated (CHS) at reduced pH;PEGylation is known to decrease this pH sensitivity. In this manuscript, we set out to use molecular dynamics (MD) simulations with a model with all-atom resolution to provide insight into why incorporation of poly(ethyleneglycol) (PEG) into DOPE-CHMS liposomes reduces their pH sensitivity;we also address two additional questions: (1) How CHSa stabilizes DOPE bilayers into a lamellar conformation at a physiological pH of 7.4? and (2) how the change from CHSa to CHS at acidic pH triggers the destabilization of DOPE bilayers? We found that (A) CHSa stabilizes the DOPE lipid membrane by increasing the hydrophilicity of the bilayer surface, (B) when CHSa changes to CHS by pH reduction, DOPE bilayers are destabilized due to a reduction in bilayer hydrophilicity and a reduction in the area per lipid, and (C) PEG stabilizes DOPE bilayers into the lamellar phase, thus reducing the pH sensitivity of the liposomes by increasing the area per lipid through penetration into the bilayer, which is our main focus.

关键词： Penta-graphene nanotubes   Mechanical properties   DFT   Reactive molecular dynamics   Nanotechnology   Fracture  

摘要： Membranes of carbon allotropes comprised solely of densely packed pentagonal rings, known as penta-graphene, exhibit negative Poisson's ratio (auxetic behavior) and a bandgap of 3.2 eV. In this work, we investigated the structural stability, mechanical and fracture properties of nanotubes formed by rolling up penta-graphene membranes, the so-called penta-graphene nanotubes (PGNTs). Single-walled PGNT of three distinct configurations: (n, 0), and two types of (n, n) (here called alpha and beta) were studied combining first-principles calculations and reactive molecular dynamics simulations. Our results showed Young's modulus values of 680-800 GPa, critical strain of 18-21%, ultimate tensile stress of 85-110 GPa, and Poisson's ratio values ranging from -0.05 to -0.30 (auxetic behavior). During stretching at room temperature, we observed a transition from beta-(n, n) to alpha-(n, n) PGNT near the critical strain. Fracture of PGNTs starts at the bonds that are mostly aligned to the stretching direction and after nanotube radial collapse.

关键词： 新工科   机械动力学课程   教学模式   课程改革  

摘要： 该研究针对机械动力学课程教学过程中存在的工程实际应用联系不紧密、学生积极主动性不够、思政教育与专业教育脱节等问题,在新工科背景下,将新媒体平台、新工程案例资源有机嵌入机械动力学课程课堂教学过程中的若干环节,介绍了以结合工程案例启发、丰富课堂教学内容、融入课堂思政教育、注重学习整体效果、强化师生互动交流为特色的教学新模式的应用实践。

关键词： 双光腔光机械系统   相变   选择性能量交换   模压缩  

摘要： 本文探究了单腔和双腔光机械装置的动力学相变和选择性能量交换.发现系统会经历类似于Dicke-Hepp-Lieb超辐射型的动力学相变,且两光场间的正交动量耦合出现一个新的动力学临界点.两光场间的正交动量耦合等价于单(双)模光机械系统的外场驱动.通过耦合参数的调控,系统可以实现任意两模间的选择性能量交换,且临界耦合点与选择性能量交换对应.模压缩是能量转换的标志,且任何两模的正交压缩由特定玻色模间的能量交换决定.

关键词： 农业动力机械   技术优化   机械化  

摘要： 随着我国农业的快速发展,农业生产过程中的机械化发展程度不断提升,农业动力机械技术是农业生产实现机械化的重要基础保障,农业动力机械技术性能直接关系农业生产的质量及效率。基于此,主要分析农业动力机械技术的发展现状及存在的问题,并探析农业动力机械技术的优化策略,以期为我国农业机械化生产的进步提供参考。

关键词： 体位交换护理   早产儿   呼吸窘迫综合征   机械通气   血气指标   呼吸动力学  

摘要： 目的探讨体位交换护理对早产儿呼吸窘迫综合征机械通气血气及呼吸动力学的影响。方法采用整群分层随机取样法选择我院2018年7月—2019年7月收治的60例呼吸窘迫综合征早产儿作为研究对象,采用随机数字法分为观察组和对照组各30例,两组患儿均给予机械通气治疗及常规护理,其中对照组均给予传统仰卧体位护理,观察组均给予体位交换护理。监测两组患儿护理干预前、干预后5 d的二氧化碳分压(PaCO_(2))、动脉血氧分压(PaO_(2))、pH值及气道阻力(R)、胸肺顺应性(TC),记录两组机械通气时间及PICU住院时间,比较两组临床并发症发生情况。结果观察组护理干预后的PaCO_(2)、PaO_(2)、pH值、R、TC等血气分析指标及呼吸动力学指标均明显优于干预前及同期对照组,差异均具有统计学意义(P<0.05);另观察组患儿机械通气时间及PICU住院时间均较对照组明显缩短,临床并发症发生率3.33%明显低于对照组的26.67%,差异均具有统计学意义(P<0.05)。结论体位交换护理能明显改善行机械通气治疗呼吸窘迫综合征早产儿的血气分析指标及呼吸动力学指标,有效降低临床并发症发生率,其对于促进患儿康复具有重要意义。

关键词： 踝关节骨折   手术   康复训练   机械动力牵拉   疼痛程度   踝关节功能  

摘要： 目的探讨康复训练联合机械动力牵拉对踝关节骨折术后患者康复效果的影响.方法选取该院2018年6月-2020年6月收治的96例踝关节骨折手术患者为研究对象,根据随机数字表法分为观察组和对照组,各48例.对照组术后行康复训练,观察组在对照组基础上联合机械动力牵拉.比较两组术后第1天、术后2个月的疼痛程度、踝关节功能,并比较两组干预期间并发症发生率.结果术后2个月,两组的视觉模拟评分(visual analogue score,VAS)较术后第1天降低,美国足踝外科协会踝-后足评分系统(American Orthopaedic Foot and Ankle Society,AOFAS)评分较术后第1天升高,且观察组的VAS评分较对照组低,AOFAS评分较对照组高,组间差异有统计学意义(P<0.05).两组并发症发生率比较,差异无统计学意义(P>0.05).结论康复训练联合机械动力牵拉应用于踝关节骨折术后患者,可减轻疼痛程度,改善踝关节功能,进一步降低并发症发生风险.