关键词： Graphe nanoribbons   Single walled carbon nanotubes   Mechanical property   Molecular dynamics simulation  

摘要： We perform molecular dynamics (MD) simulations of nanoindentation to study the mechanical properties of a graphene nanoribbon encapsulated in a single-walled carbon nanotube (GNR@SWCNT). The effects of different temperatures, nanotube diameters, and slenderness ratios on the properties of the GNR@SWCNT are examined. Results show that the maximum load and contact stiffness increase with an increase of temperature. But the adhesion force and ratio of springback are low at a high temperature of 1200 K. The maximum load and contact stiffness are high for the nanoindentation of the GNR@SWCNT with a low slenderness ratio. In addition, the GNR@SWCNT has a more than 15% rate of springback exhibiting a superelastic nanocomposite behavior. The results are useful for engineering applications of nanocomposites composed of carbon nanotubes and graphene materials. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Hydrated lime   Mortar   Strength   Water transport kinetics  

摘要： The purpose of this paper is an investigation of the possible role of zeolite and powdered Bayburt stones on the fresh and hardened properties of hydrated lime (CL90) mortars. Parameters studied in this paper form the main barriers to the use of hydrated lime in construction practice. Enhancement of these parameters is vital for mortar/substrate optimisation in masonry construction. The major concern of this paper therefore is the combination of wet mortar and brick substrate and most significantly the interaction between them at fresh and hardened states. The results show that transfer sorptivity and time to dewater hydrated lime mortars can be manipulated when zeolite and powdered Bayburt stones are used as replacement materials to the binder. Long setting time of CL90 mortars is decreased with the increasing replacement levels of both zeolite and powdered Bayburt stones. Experimental results also showed that the increasing replacement levels of zeolite and powdered Bayburt stones resulted in a dramatic increase in compressive strength and these results are also supported with the microstructural images. The ability to enhance water transport kinetics and mechanical properties of hydrated lime mortars with zeolite and powdered Bayburt stones should not be underestimated as this enables such materials to be used in construction practice more competently. These results have important practical consequences, not only in the initial adhesion of the mortar to the substrate but also in the strength of the set material and therefore the use of hydrated lime mortars may be encouraged if zeolite and Bayburt stones can improve the fresh and hardened state properties of these mortars. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Silicon nitride   Thin layer   Shear mechanical property   Fracture mechanism   Molecular dynamics  

摘要： Molecular dynamics simulations are performed to clarify the shear mechanical property of beta-Si3N4 nano-thin layer in the basal plane with different extreme strain rates and loading temperatures. The thin layer displays nonlinear and linear response stress-strain relationships, and fracture stresses and strains increase gradually with increasing the strain rates, which is attributed to the appearance of a great quantity of single nitrogen atom and "turtle-like" hexagon defects. With increasing loading temperature, there is a noticeable drop in both fracture stress and fracture strain. In the higher loading temperature range, the lower fracture stresses are obtained owing to the disappearance of defects mentioned above, which can be also elaborated by a combination of factors such as the appeared N-6h-Si bond breaking alone in configuration evolution and the accompanied lower total energy. (C) 2015 Elsevier B.V. All rights reserved.

关键词： 机械功   热能   动力工程  

摘要： 现阶段,科学技术水平的提高对经济社会发展有很大的促进作用,在经济社会发展中,能源的需求量越来越大,尤其是工业生产中,为此,越来越多的人对热能与动力工程的研究产生了很大的兴趣,因为只有更好的发展热能与动力工程,才能更好的促进工业产业发展。在热能与动力工程研究中存在着很多的问题,这些问题的出现一定要找到解决的方法,这样才能更好的实现能源建设。基于此,本文就机械功在热能与动力工程中的应用与优化进行分析与研究。

关键词： MOLECULAR dynamics   SINGLE crystals   CRYOGENICS   NANOINDENTATION   DEFORMATIONS (Mechanics)   PHASE transformations (Physics)  

摘要： Molecular dynamics simulations of nanoindentation tests on monocrystalline silicon (010) surface were conducted to investigate the mechanical properties and deformation mechanism from cryogenic temperature being 10 K to room temperature being 300 K. Furthermore, the load-displacement curves were obtained and the phase transformation was investigated at different temperatures. The results show that the phase transformation occurs both at cryogenic temperatures and at room temperature. By searching for the presence of the unique non-bonded fifth neighbour atom, the metastable phases (Si-III and Si-XII) with fourfold coordination could be distinguished from Si-I phase during the loading stage of nanoindentation process. The Si-II, Si-XIII, and amorphous phase were also found in the region beneath the indenter. Moreover, through the degree of alignment of the metastable phases along specific crystal orientation at different temperatures, it was found that the temperature had effect on the anisotropy of the monocrystalline silicon, and the simulation results indicate that the anisotropy of monocrystalline silicon is strengthened at low temperatures.

关键词： 油酸兔   正压机械通气   膈肌起搏  

摘要： 目的通过膈肌起搏联合机械通气观察对油酸型兔急性呼吸窘迫综合征血流动力学和氧动力学影响。方法选取健康成年家兔20只,耳缘静脉注射油酸法制备兔ARDS模型,行气管切开机械通气,采用自身前后对照法,作为对照组(单纯机械通气组),实验组为膈肌起搏联合机械通气组。使用Swan-Ganz导管及相关仪器观察两组血流动力学、血气分析等变化。结果与对照组比较,实验组HR、PaO_2、OI对比,P>0.05,差异不具有统计学意义,MAP、CVP、MPAP、PAWP、CO在实验组对比,P<0.05,差异具有统计学意义。结论膈肌起搏联合机械通气可以增加心脏前负荷,增加心排血量,提高平均动脉压,改善灌注,从而降低机械通气对血流动力学的副作用。

关键词： 刚柔耦合   等效元素集成法   转换张量   等效质量阵   5R机械臂  

摘要： 为分析复杂机械系统动力学特性,将系统划分为含有限刚性构件的刚柔耦合系统,基于等效元素集成法,对构件自身的动力学特性进行等效,组建成等效系统。将建模的关键归结为系统中二阶转换张量和相应的三阶转换张量的求解以及系统质量阵的组装,然后,按多柔体动力学的方式建立方程。建立了港口起重机5R机械臂刚柔耦合动力学模型,给出了动力响应曲线,并与刚性解进行了比较。结果表明,采用EFEM方法,动力学方程维数减少,系统质量阵阶数降低,模型建立简单快捷,规范化、程式化,解题效率和精度较高。

关键词： 农业机械动力   基尼系数   空间自相关   探索性空间数据分析  

摘要： 以全国省级行政区为基本研究单元,利用基尼系数与ESDA空间分析技术,分析了近10年全国农机总动力的区域差异时空特征。结果表明:全国省域平均单位农机动力投入存在明显的空间差异,整体呈现东部大于西部、北部大于南部、由东部沿海向西递减的空间分布格局,但这种区域差异在研究期内呈现明显缩小趋势。近10年,全国省域农机动力投入在全局水平表现出显著的空间正相关性,同时又存在明显的局域空间自相关特征。其中,高高聚集区主要分布于京津冀地区,而低低聚集则分布于西南地区,并且随着时间的推移其空间聚集程度在不断减弱,各省域农机动力投入趋向均衡发展。

关键词： Inverse dynamic analysis   Hill-type muscle model   Rehabilitation   Functional electrical stimulation   Hybrid orthoses  

摘要： The objective of this work is to validate a mechanistic muscle model by using inverse dynamics analysis. To do so, an artificially activated Hill-type muscle model is used. Compared to the traditional physiologically activated muscle model, an artificially activated model must take into account an additional set of parameters and dynamics that can affect the resulting force. To validate the model, the ankle dorsiflexion activated by functional electrical stimulation (FES) is subjected to an inverse dynamic analysis (IDA). The resulting values of the net joint torques are used to estimate first the muscle forces, and second, by inversion of the proposed artificially activated model, the stimulation profile that produces the recorded motion. The results are then compared with the stimulation profile applied to the subject, and the model parameters are adjusted correspondingly. Once the model has been validated, the methodology could be used to design rehabilitation programs based on electrical stimulation or to prescribe FES actuation in the design of hybrid orthoses or neuroprostheses to achieve a given movement. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Dividing wall column   Mechanical design   Hydrodynamics   CFD analysis  

摘要： Distillation is one of the most widely used separation processes, mainly because it allows obtaining products with high purities. However, it has high energy requirements due to its low thermodynamic efficiency. Among the alternatives to reduce these energy requirements, the dividing wall column (DWC) is one of the most promising technologies, also allowing savings in capital costs compared to conventional distillation sequences. Even so, there is only little information about the physical design of dividing wall columns, and most of the recent developments on this area have been achieved by private industry. Moreover, most of the reported information is for packed columns. Nevertheless, the design of dividing wall columns with trays is important for systems with high vapor loads. Thus, a strategy for the mechanical design of sieve trays for the separation of a hydrocarbon mixture in a dividing wall column is presented in this work. Furthermore, an operational analysis of the trays using Computational Fluid Dynamics (CFD) is reported. Designed trays are tested in terms of weir flooding, active zone flooding and flow regime. Reported strategy allows obtaining operational designs for the trays of the whole column. (C) 2015 Elsevier B.V. All rights reserved.