关键词： Calcium   Sodium aluminosilicate hydrate (NASH) gel   Molecular structure   Mechanical properties   Molecular dynamics simulation  

摘要： The effects of calcium content on the molecular structure and mechanical properties of sodium aluminosilicate hydrate (NASH) gels were studied by molecular dynamics simulations. NASH gels with different calcium content were constructed, followed by optimization, equilibration, and production runs of molecular dynamics simulation. Properties such as energy profile, radial distribution function (RDF), distribution of bond length and bond angle, mean square displacement (MSD), elastic modulus and density were obtained. The results indicated that with the increase of Ca/Al, average bond lengths and total energy decreased monotonically, and the distributions of bond lengths and bond angles became narrower. Results from the MSD analysis showed that diffusion degree of both Si and Al in the gels decreased with the increase of the Ca/Al ratio. Furthermore, the elastic modulus, compressive strength and density of the gel systems increased monotonically with the increase of calcium content, and the trend is consistent with experimental findings.

关键词： 机械系统动力学   研究生教育   创新性科研人才   教学改革方法  

摘要： 机械系统动力学是各高校机械工程、力学、动力工程及工程热物理等机械类专业硕士研究生的一门重要的学位课,不仅是本科生材料力学、理论力学等课程的延伸,还是博士研究生高等动力学、非线性动力学等课程的基础,提高该门课程的教学质量是确保机械类研究生培养质量的关键课程之一.基于国内"双一流"学科建设的要求,以培养创新性科研人才为目标,分析目前课程教学存在的不足,提出面向工程实际的教学改革方法,并以西南石油大学机电工程学院2019级和2020级研究生为实践对象,开展教学改革方法的现场实践,发现:通过本课程的教学改革,提高

关键词： 体位交换   危重症专职管理   呼吸窘迫综合征   机械通气   呼吸动力学   血气分析  

摘要： 目的观察分析体位交换及危重症专职管理对呼吸窘迫综合征患儿机械通气呼吸动力学、血气分析指标的影响。方法选取该院2018年1月至2019年10月收治的28例呼吸窘迫综合征患儿为研究对象,按照随机数字表法分为试验组和对照组,每组14例。试验组采用体位交换及危重症专职管理护理方法进行护理,对照组采用常规仰卧位机械通气护理方法进行护理。分析两组患儿护理前后的血气分析指标和呼吸动力学指标以及并发症发生率、呼吸支持时间、住院时间、家长对护理总满意度评分。结果护理前两组患儿的氧分压、酸碱度、二氧化碳分压等血气分析指标和气道阻力、胸肺顺应性等呼吸动力学指标比较差异无统计学意义(P>0.05),护理后试验组患儿的气道阻力、胸肺顺应性等呼吸动力学指标明显高于对照组,差异有统计学意义(P<0.05),试验组患儿的氧分压、酸碱度等水平高于对照组,试验组患儿的二氧化碳分压明显低于对照组,差异有统计学意义(P<0.05);试验组患儿的败血症、腹胀、颅内出血以及肺出血等并发症发生率明显低于对照组,差异有统计学意义(P<0.05);试验组患儿的呼吸支持时间、住院时间明显短于对照组,差异有统计学意义(P<0.05);试验组患儿家长的护理态度、护理管理、健康教育等护理总满意度评分明显高于对照组,差异有统计学意义(P<0.05)。结论体位交换及危重症专职管理可积极改善呼吸窘迫综合征患儿机械通气的呼吸动力学、血气分析指标,有效提高患儿家长总满意度,缩短患儿的呼吸支持时间和住院时间,值得临床推广应用。

关键词： 农机跨区服务   劳动力转移   空间效应   环境效率  

摘要： 采用SBM-DEA模型、Moran’s I指数和PSDM模型,以较有代表性的粮食作物小麦为研究对象,依据2001—2018年15个省的面板数据,基于农机跨区服务和劳动力空间转移的视角,分析了农业机械替代劳动力对粮食生产环境效率的空间影响,并对影响机制进行了甄别。结果表明:①2001—2018年中国粮食生产环境效率总体递增,地区间环境效率和变动率的发展虽不平衡,但不平衡的局面正在逐渐改善。②农业机械对劳动力的替代程度和粮食生产环境效率分别在2004年和2005年以后出现明显的空间正相关关系。③农业机械对劳动力的替代程度可以提高粮食生产环境效率,且存在空间溢出效应,但不如预期般显著,在剔除2001—2004年的样本后发现,替代程度对环境效率的改善作用主要来源于2005年以后,而作用路径主要通过提高单产水平和降低非期望产出实现。据此,本文提出了促进农业机械替代劳动力与粮食生产环境效率之间协调发展的政策启示。

关键词： 机械密封   动环   模态   局部磨损  

摘要： 旋转设备在运行中,传动轴的转动会导致机械密封摩擦副的接触端面发生振动。为研究接触端面振动对密封性能的影响,以某型号机械密封的摩擦副为研究对象,运用SolidWorks对机械密封的动环进行有限元建模,采用ANSYS Workbench对机械密封的动环进行结构动力学分析,分析发现:动环在1阶、2阶、3阶模态频率下会产生径向产生相对扭转;在4阶、5阶模态频率下动环两边向圆心方向发生弯曲;在6阶、7阶模态频率下密封面沿径向摆动;在8阶模态频率下端面产生相对拉伸;在9阶、10阶模态频率下端面处整体产生很大的形变。依据有限元分析结果取第1阶模态频率,通过机械密封试验台进行验证。结果表明:电机转动引起的机械密封低频共振使得动环外径处磨损严重,摩擦面大小不一且不连续;配合在轴上的静环几乎不受振动的影响,其磨损面相对均匀。机械密封动环的结构动力学分析,对减少机械密封的泄漏量,延长机械密封的使用寿命均具有重要意义。

关键词： 室间隔缺损   机械通气   脑血流速度   血流动力学  

摘要： 目的应用经颅多普勒测量大脑中动脉血流速度(cerebral blood flow velocity,CBFV),MostCare监测血流动力学,分析室间隔缺损患儿在麻醉诱导期间机械通气对CBFV和血流动力学的影响。方法选取2017年11月至2018年2月首都医科大学附属北京安贞医院择期行室间隔缺损修补术的78例患儿为研究对象。入室麻醉诱导行气管插管后,给予定容机械通气,吸入氧浓度50%。调整潮气量和呼吸频率,使呼气末二氧化碳分压从30mmHg(T1)逐渐上升至35mmHg(T2)、40mmHg(T3)、45mmHg(T4)。测量各时间点CBFV、搏动指数、阻力指数,记录脉搏氧饱和度、心率、心指数、每搏量指数、体循环阻力指数。参数相关性采用Pearson分析。结果T1~T4时刻,搏动指数和阻力指数均显著降低(P<0.05),CBFV显著增加(P<0.05);与T1相比,T4时刻体循环阻力指数显著降低(P<0.05);患儿心率、心指数、每搏量指数无明显变化(P>0.05)。T1~T4过程中CBFV与潮气量、呼吸频率和每分通气量呈负相关,搏动指数、阻力指数与潮气量、呼吸频率和每分通气量呈正相关。结论室间隔缺损患儿在麻醉诱导阶段,维持较低每分通气量可以提升CBFV和降低脑血管阻力,而对体循环血流动力学无明显影响。

关键词： 丙泊酚   右美托咪定   外科术后机械通气患者   镇静   血流动力学  

摘要： 目的探究右美托咪定与丙泊酚对外科术后机械通气患者镇静效果及血流动力学的影响。方法将我院60例外科手术后机械通气患者作为研究对象,电脑随机将其分成右美托咪定组和丙泊酚组,各30例。右美托咪定组给予右美托咪定治疗,丙泊酚组给予丙泊酚治疗,比较两种方法的镇静效果及对血流动力学的影响。结果镇静30 min后,两组的Ramsay镇静评分对比差异无统计学意义(Z=1.23,P>0.05);右美托咪定组心动过缓(6.67%)、低血压(13.33%)、低血压合并心动过缓(3.33%)发生率分别低于丙泊酚组(30.00%、36.67%、26.67%),两组间对比差异有统计学意义(χ^(2)分别为5.45、4.36、6.41,P均<0.05)。结论给予外科术后机械通气患者右美托咪定或丙泊酚,均有更好的镇静效果,但右美托咪定对于血流动力学的影响较小,更适用于机械通气患者。

关键词： Graphene oxide   Cementitious materials   Molecular dynamics modeling   Nanocomposites   Mechanical properties   Fracture  

摘要： Graphene oxide (GO) cementitious composites have recently attracted considerable interest due to their improved mechanical properties and durability. However, most research is focused on the macroscale performance of these composites with very little experimental and modelling research on the characterization of their nanoscale behavior. This makes the design of these new GO-cementitious composites challenging. In this paper, we present a novel molecular dynamics (MD) model for GO-cementitious nanocomposites to understand their behavior and predict their mechanical and fracture properties. In this model, different numbers of GO nanoplatelets were inserted into the C-S-H structure and a number of nanoscale mechanical parameters and crack bridging mechanism were obtained. The MD simulation results revealed that the addition of GO sheets increased the tensile and compressive strength of C-S-H by roughly 50% and 100%. The MD simulation results also identified a double-peak phenomenon which is an indication of additional plasticity when the intercalated GO/C-S-H structures are subjected to compressive stress. The fracture simulation results showed that the failure mode of the intercalated GO/C-S-H composites was marked by high energy release. The results of fracture simulations with different notch lengths also indicated that the addition of GO could improve the fracture performance due to a good interfacial connection between the GO and the C-S-H gel.

关键词： Glass fibre-epoxy (GF/Epoxy) composite   Diffusion mechanism   Acid   Cross-link density   Free-volume   Mechanical properties  

摘要： Glass Fibre-Epoxy (GF/Epoxy) composites are being the choice of material when exposed to inorganic acids such as sulphuric acid due to its superior corrosion resistance properties. Water diffusion into GF/Epoxy composites is well-reported. However, inter-relation between acid diffusion mechanism and its analogous influence on chemo-mechanical properties is never investigated with greater details. In this work, the transport behaviour of aqueous 10% sulphuric acid solution into GF/Epoxy composite and its complex inter-relations with the cross-linking density, morphology and mechanical properties is presented. The transport of aqueous solution of 10% sulphuric acid in the composite was quantified by gravimetric analysis and confirmed by the Energy Dispersive X-Ray Spectroscopy (EDX). The kinetic parameters were evaluated and compared using Fickian and Langmuir diffusion models, where the Langmuir model described the transport behaviour better. Analysis of thermomechanical properties such as storage modulus is characterised by dynamic mechanical thermal analysis (DMTA). The free volume distributions are estimated using positron annihilation lifetime spectroscopy (PALS). The indication of an increase in cross-link density with the acid exposure is further validated by Fourier-transform infrared spectroscopy (FT-IR) analysis. In the absence of substantial chemical degradation and with increased cross-linking density, the deterioration in the mechanical properties is attributed to the erosion of epoxy resin confirmed by the morphology performing Field Emission Scanning Electron Microscope (FE-SEM) analysis. The acid diffusion mechanism results show promising prospects of selecting and designing GF/Epoxy composites for industrial storage and manufacturing facilities containing aggressive environments (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Bimetals Co-Ce   Dry reforming   Calcium   Mechanism   Kinetic  

摘要： The mechanism and kinetic features of dry reforming with methane (DRM) over Ca promoted 1Co-1Ce/AC-N catalyst was investigated. The mechanistic pathway studies have conducted by FTIR and XPS analysis, structure-activity correlations demonstrated the CH4 and CO2 could adsorb on catalyst active sites and generate intermediate CHx, OH and CHxO, continue to generate CO and H-2 and then desorbed from active sites. Moreover, CH4 could also oxidized by Ce4+ and CO2 reduced by Ce3+, the same content of Ce4+ and Ce3+ on promoted catalyst greatly improved the reaction rate. The kinetic of dry reforming with methane was examined for temperature between 650 and 850 at 800 degrees C. The research was carried out by changing the CH4/CO2 ratios between 0.3 and 3.0. The obtained experiment data were fitted by three typical kinetic models (Power Law, Eley-Rideal and Langmuir-Hinshelwood), the fitting results demonstrated that the best prediction of reforming rates can provided by Langmuir-Hinshelwood model for the reaction temperatures between 650 and 800 degrees C. Moreover, activation energies of methane and carbon dioxide consumption were -117 and -47 kJ/mol, indicating that much higher energy barrier is needed for methane activation compared to carbon dioxide. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.