关键词： Sodium carbonate   Ground granulated blast furnace slag   Fineness   Reaction kinetics   Compressive strength  

摘要： This paper evaluates the slag characteristics on the reaction kinetics, reaction products and mechanical properties of sodium carbonate activated slag (SCAS). The results show that, by reducing the slag particle size, the precipitation of strength-giving phase of SCAS can be dramatically accelerated, and the time to reach the reaction peak (TRRP) can be accelerated from 86 h to 23 h and a 3 d-compressive strength of about 34 MPa is achieved. The fresh behaviour of pastes is affected by the initial precipitation of calcium carbonate and the formation of gaylussite is also accelerated when reducing the particle sizes of slags. It is observed that the early strength development of samples is largely controlled by the fineness of slag particles, while the later strength firstly increases with the reduction of slag particles until reaching a turning point and then decreases. Furthermore, the influential factors including the alkali activator dosage and slag characteristics on the reaction kinetics of Na2CO3 activated slag are discussed. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： 运动力学   机械结构设计   应用研究  

摘要： 随着我国社会经济的高速发展,机械制造业在社会的应用范围更加广泛,我国已经成为世界机械制造生产大国,机械技术也得到了进一步改进,科学知识与技术之间的融合更加深入。而机械结构设计的革新中,更需要运用一些运动力学方面的知识。本文以运动力学为研究对象,探索运动力学在机械结构设计过程中所起的应用。

关键词： biomechanics   evolution   mantis shrimp   comparative phylogenetics   many-to-one mapping   scaling  

摘要： The influence of biophysical relationships on rates of morphological evolution is a cornerstone of evolutionary theory. Mechanical sensitivity-the correlation strength between mechanical output and the system's underlying morphological components-is thought to impact the evolutionary dynamics of form-function relationships, yet has rarely been examined. Here, we compare the evolutionary rates of the mechanical components of the four-bar linkage system in the raptorial appendage of mantis shrimp (Order Stomatopoda). This system's mechanical output (kinematic transmission (KT)) is highly sensitive to variation in its output link, and less sensitive to its input and coupler links. We found that differential mechanical sensitivity is associated with variation in evolutionary rate: KT and the output link exhibit faster rates of evolution than the input and coupler links to which KT is less sensitive. Furthermore, for KT and, to a lesser extent, the output link, rates of evolution were faster in 'spearing' stomatopods than 'smashers', indicating that mechanical sensitivity may influence trait-dependent diversification. Our results suggest that mechanical sensitivity can impact morphological evolution and guide the process of phenotypic diversification. The connection between mechanical sensitivity and evolutionary rates provides a window into the interaction between physical rules and the evolutionary dynamics of morphological diversification.

关键词： Hydride composite   Volumetric hydrogen capacity   Carbon-based materials   Melt infiltration   Solution impregnation   Hydrogen storage  

摘要： To enhance volumetric hydrogen capacity for on-board fuel cells, compaction of LiAlH4-LiBH4 nanoconfined in activated carbon nanofibers (ACNF) is for the first time proposed. Loose powders of milled and nanoconfined LiAlH4-LiBH4 samples are compacted under 976 MPa to obtain the pellet samples with thickness and diameter of similar to 1.20-1.30 and 8.0 mm, respectively. Dehydrogenation temperature of milled LiAlH4-LiBH4 increases from 415 to 434 degrees C due to compaction, while those of both compacted and loose powder samples of nanoconfined LiAlH4-LiBH4 are lower at comparable temperature of 330-335 degrees C. Hydrogen content liberated from milled LiAIH4-LiBH4 pellet is 65% of theoretical capacity in the temperature range of 80 -475 degrees C, while that of nanoconfined LiAlH4-LiBH4 pellet is up to 80% atlower temperature of 100 -400 degrees C. Besides, nanoconfined LiAlH4-LiBH4 pellet shows significant reduction of activation energy (Delta E-A up to 69 kJ/mol H-2) as compared with milled sample. Significant enhancement of volumetric hydrogen storage capacity up to 64% (from 32.5 to 53.3 gH(2)/L) is obtained from nanoconfined LiAlH4-LiBH4 pellet. Hydrogen content released and reproduced of nanoconfined LiAlH4-LiBH4 pellet are 67 and 50% of theoretical capacity, respectively, while those of milled LiAlH4-LiBH4 pellet are only 30 and 10%, respectively. Moreover, upon four hydrogen release and uptake cycles, nanoconfined LiAlH4-LiBH4 pellet can preserve its shape with slight cracks, suggesting good mechanical stability during cycling. Curvatures and fibrous structure woven on one another of ACNF in nanoconfined LiAlH4-LiBH4 pellet not only favor hydrogen permeability through pellet sample during de/rehydrogenation, resulting fast kinetics, but also reinforce the pellet shape during cycling under high temperature and pressure condition. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： 履带车辆   液压转向   差速机构   动力学分析  

摘要： 履带车辆因其通过性能、牵引性能较好，被广泛应用于农业、军事、矿山和建筑等领域。转向性能反映了履带车辆的行驶灵活性和准确性，并对履带车辆的动力性及作业效率有一定影响，是重要的履带车辆性能评价指标。液压机械差速转向机构结合了液压无级调速特性和机械高效率传动的优点，是履带车辆越来越广泛应用的转向机构，其通过液压机构实现履带车辆无级转向，通过机械机构实现履带车辆转向功率的高效利用。随着对液压机械差速转向研究和优化的不断深入，只单一研究该机构得到的成果对该机构的进一步优化和性能提高的贡献已出现瓶颈，因此，有必要把路面因素以及车辆因素看作一个整体的车辆地面系统来进行研究，以便使履带车辆获得更好的转向动力学特性。本文在研究履带车辆差速转向特性的基础上，考虑履带车辆结构参数与地面特性参数，建立基于液压机械差速的履带车辆转向运动学及动力学模型，对履带车辆的转向动力学特性进行研究。\n 本研究首先根据履带车辆差速转向的特性建立其液压机械差速转向数学模型，并进行优化；其次通过研究不同土壤的性质和履带车辆履带板与土壤相互接触的特性，建立履带板与土壤的接触数学模型，使之相互作用并进行不同土壤接触模型之间的研究对比。采用 Matlab软件进行液压机械差速转向仿真模型的建立；采用 RecurDyn软件进行履带板与土壤接触仿真模型以及履带车辆仿真模型的建立。通过 RecurDyn/control技术接口进行液压机械差速转向仿真模型与所建立履带车辆几何仿真模型相联合，并在不同土壤地面模型上进行联合仿真，得到履带车辆模型的仿真位移曲线和履带板与土壤相互作用力的变化，以分析履带车辆的转向特点。本研究可为液压机械差速转向履带车辆动力学特性研究提供研究方法，使在不同土壤条件下该项研究变得方便快捷，对履带车辆研究发展有积极作用。

关键词： 工程机械臂   系统结构   动力学   特性  

摘要： 现如今计算机和产品设计相关方面的技术发展迅速,机械产品逐渐朝着高速、精确、环保的方向发展,对机械产品特性的研究成为如今设计机械产品的关键,国内外相关领域都对其投入了较大的关注力度。工程机械臂是工程机械中十分重要的元件,它的动力学性能对整个工程机械的作用发挥都有着极其重要的作用。工程机械的工作环境往往十分恶劣,因此工程机械臂所受的负荷情况十分复杂,为了保证机械臂工作的安全性与可靠性,本文对工程机械臂的结构动力学及特性进行了简要分析。

关键词： 粮食产出   面板模型   自然灾害   机械动力   河北省  

摘要： 为了探究农业生产投入要素对粮食产出的效应,选取国家农业主产省份河北省11个地级市的面板数据,运用固定效应回归和变系数回归分析方法,主要得出以下结论:1劳动力、机械动力投入对粮食产出起到正面效应,而自然灾害导致粮食减产;2机械动力的投入对粮食增产的作用显著,大部分地区对机械投入积极性较大;3不同的地区因地理环境、气候差异导致自然灾害对粮食产出的影响也不同;4农村人力资源对粮食产出的作用不容小觑。最后,基于提高农业机械化程度、抗灾保产、重视农业人力资本投入3个方面提出相关建议。

关键词： 机械臂   动力学   ADAMS   拉格朗日法  

摘要： 为了提高三维空间助力机械臂的设计效率,运用拉格朗日方法建立机械臂的动力学模型,利用SolidWorks建立三维空间助力机械臂的构件模型,将装配后三维实体模型导入A D A M S中进行动力学仿真分析,得到相关性能曲线图,为空间助力机械臂的结构设计和最优控制提供依据。

关键词： 沙棘   机械化采收   有限元方法   模态分析   谐响应分析  

摘要： 沙棘在西部广泛种植,用于水土保持和防风固沙。其果实有较高价值,但采收非常困难,影响其经济价值开发。机械振动使果实分离是可行的方式之一。为了正确合理地设计开发装备,利用有限元方法对沙棘的机械振动采收机制进行动力学研究。首先,沙棘树的3D模型由Pro/E建立并导入ANSYS,再用模态分析确定沙棘树的自然振动属性,最后采用谐响应分析观察模型在正弦谐波载荷下的稳态响应。模态分析表明:沙棘树的前2 0阶固有频率为8.7 9 0~3 1.2 2 4 Hz。谐响应分析表明:振动载荷应用于侧枝比应用于主干更加优越,且对沙棘树枝条的破坏性更小。此外,14Hz和180~280N的振动载荷可以确保大多数沙棘果实从树上分离。为此,对沙棘振动采收进行有限元仿真分析,为振动装备的开发提供了理论基础。