关键词： 跨区作业   农业机械化   空间溢出效应  

摘要： 农业机械化是实现农业现代化的必经之路,是提高农业生产经济效益的重要途径。本研究基于2004—2018年我国23个水稻主产区的面板数据,采用空间杜宾模型深入探究农业机械化对劳动力投入的空间溢出效应。结论表明:大中型农机对劳动力投入存在显著的空间溢出效应,即本地大中型农机投入的增加将显著节约周边地区水稻生产的劳动力投入;从空间异质性来看,大中型农机对劳动力投入的空间溢出效应不仅存在于跨纬度地区,而且也显著发生于同纬度地区,但跨纬度地区的空间溢出效应明显强于同纬度地区;从时间异质性来看,大中型农机对劳动力投入的空间溢出效应呈“从无到有,先强后弱”的变化趋势。

关键词： 水下机械臂   动力学建模   RBF神经网络   滑模控制  

摘要： 本文利用切片理论与Morison方程计算了双关节水下机械臂在水中运动时受到的附加质量力、水阻力和水体流动对机械臂产生的冲击力,在传统机械臂动力学模型的基础上建立了完整的双关节水下机械臂动力学模型。基于推导的水下机械臂动力学模型提出了一种RBF滑模控制策略,采用多个RBF神经网络对水下机械臂动力学模型中的不确定项进行分块逼近,并使用饱和函数改进了控制律。本文判别了控制系统的稳定性,进行了仿真对比试验,结果表明该控制算法优于传统滑模控制和常规RBF滑模控制算法。本文所提出的算法,将水下机械臂的关节响应时间缩短至1 s,并将平均稳态误差缩小至3×10^(-6) rad,还削弱了控制系统的抖振效应,满足水下机械臂的控制要求。

关键词： 发动机   直线电机   多目标设计优化   集成设计   三维有限元模型  

摘要： 为优化永磁活塞机械电力发动机的电动力结构,在分析结构原理的基础上,建立其工作过程的三维有限元模型,并进行了试验验证。以输出电流最大和损耗最小为目标,建立了电动力结构的设计优化模型。基于ISIGHT优化设计框架集成ANSOFT Maxwell下的三维有限元模型,利用NSGA-Ⅱ遗传算法对电动力结构进行多目标设计优化。结果表明:电动力结构的输出电流和损耗值受多个尺寸影响,其中动子永磁体的尺寸影响最大,且存在最优值。优化后空载电势有效值为11.28 V,提高了27.75%;电流有效值为0.80 A,提高了26.98%;电磁力有效值为10.98 N,提高了19.14%;损耗有效值为4.17 W,降低了41.10%,发动机性能得到明显改善,验证了优化方法的有效性。

关键词： 颤碰   非线性约束   分岔   共存吸引子  

摘要： 以一类两自由度含非线性约束机械振动系统为研究对象,通过4阶变步长Runge Kutta数值算法,分析了该系统在低频激励下p/1周期运动的动力学特性及其相互转迁规律,研究了Grazing分岔和saddle node分岔在p/1周期运动中的频率迟滞特性.研究结果表明,随着激振频率减小,Grazing分岔会使p/1周期运动的碰撞次数逐步增加直至发生颤碰运动.最后,结合胞映射法研究了周期运动共存区内吸引域的分布情况及其转迁规律.

关键词： Rhodium nanowires   Molecular dynamics simulations   Tensile deformation   Embedded atom method   Surface effects  

摘要： This study comprehensively investigates the mechanical properties of rhodium (Rh) nanowires using molecular dynamics simulations in which the interactions were expressed by embedded atom method potentials and interprets their relation with the deformation process. We have observed that the stress-strain behavior of Rh nanowires is radically different from the bulk material. As the size increased, the Elastic Modulus of nanowires gradually decreases and saturates to reach bulk value. It is revealed that the mechanical response of thicker nanowires than the critical value of 2.8 nm size is characterized by the core atoms and the surface effects lose their dominance due to the stability of the core atoms. The high strain rates delay yielding and neck formation and can be used to design the strengthened thin Rh nanowires.

关键词： 机械动力   环境保护   非道路移动   尾气污染  

摘要： 在非道路体系移动机械领域,呈现出丰富多样、数量多、应用广泛、难控制尾气污染等特点。在现代社会,能源和环保属于两大发展主题。伴随社会经济的增长,非道路用机械排放污染备受关注。为此,本文主要探讨了非道路移动领域机械动力控制和治理排放污染的有效途径,仅供参考。

关键词： Smart material   Artificial muscle   Bio-inspired   Self-biasing   Compliant mechanism   Thermal model   Analytical model  

摘要： Shape Memory Alloy (SMA) based actuators have become ideal candidates for use in compact and lightweight applications. These smart materials have often been referred to as artificial muscles due to their high work volume density. In this paper, a flexure-based SMA powered mechanical oscillator is developed to create an inchworm robot. Here, a novel magnetic latch system is used to create a mechanically-intelligent system that allows the abstraction of any sensors such as temperature probes. This insect robot, weighing only 9.7 g, operates without any control logic or micro-controller and is able to perform a crawling gait untethered. An analytical model of the thermal properties of the SMA coil, for the sizing of the robot speed, and an analytical model of the step length of the insect robot is presented and validated. A working prototype, with a speed of 1.55 mms(-1), is showcased in this work. (C) 2021 The Author(s). Published by Elsevier B.V.

关键词： 慢性阻塞性肺病急性发作   无创机械通气   沙丁胺醇   雾化  

摘要： 目的:探讨慢性阻塞性肺病急性发作(AECOPD)患者应用无创机械通气联合沙丁胺醇雾化吸入对机体氧代谢、胸肺顺应性及呼吸动力学的影响。方法:纳入2018年1月~2020年12月间收治的200例AECOPD患者作为研究对象,将患者采用随机数表法分为观察组和对照组,每组各100例。两组均予以无创机械通气,观察组在此基础上增加沙丁胺醇雾化吸入。比较两组恢复进程,治疗前、治疗5 d后评估患者氧代谢相关指标[氧饱和度(SpO_(2))、动脉血氧分压(PaO_(2))、二氧化碳分压(PaCO_(2))]、胸肺顺应性[总顺应性(Ct)、肺顺应性(CI)、胸廓顺应性(CTh)]、呼吸动力学[吸气峰值压(PIP)、平均气道压(MPaw)、气道阻力(Raw)]。结果:①观察组咳喘显著缓解时间、哮鸣音消失时间、住院时间均短于对照组;②治疗5d后,两组SpO_(2)、PaO_(2)、胸肺顺应性(Ct、CI、CTh)均高于治疗前,两组PaCO_(2)均低于治疗前,观察组变动幅度大于对照组;③治疗5 d后,两组PIP均高于治疗前,两组MPaw、Raw均低于治疗前,观察组变动幅度大于对照组。结论:AECOPD患者应用无创机械通气联合沙丁胺醇雾化吸入对改善其氧代谢更有利,同时也对患者胸肺顺应性和呼吸动力学产生积极影响。

关键词： 工程机械发动机   纯电动   混合动力   氢燃料电池  

摘要： 在“碳达峰、碳中和”的大背景下,新能源动力的开发应用不仅仅局限于汽车行业,工程机械行业为顺应趋势,也将加速采用新能源动力。从技术、成本及应用便携性等方面分析比较传统内燃机与新能源动力的优缺点,预测其发展趋势。

关键词： Acrylic resins   Biopolymers   Biocomposites   Phosphate ion release   Mechanical properties  

摘要： Background: The denture-base acrylic resins used by partially edentulous patients can cause local demineralization of teeth. Alkali ions released from the bioactive materials that were added to acrylic resins can increase the pH of the oral environment and slow down the demineralization process. Aim of the study: This study aimed to create a new denture-base acrylic resin that can release ions. Materials and methods: A total of 222 samples with different fillers (calcium hydrogen phosphate, hydroxyapatite, two kinds of bioactive glasses, and a product obtained by reaction between bioactive glass formed from glass ionomer cement and polyacrylic acid) were prepared for the study. All the materials were tested for mechanical properties and their use as phosphate donors for 3 weeks. The measurements were presented as mean +/- SD error of the mean. Data were analyzed by two-way analysis of variance, with a p-value of < 0.05 as statistically significant. Results: Acrylic resins obtained after the addition of a small quantity of bioactive materials (2.5-5%) showed similar mechanical properties (such as flexural strength and Izod impact resistance) as non-filled material. However, the hardness of the modified materials was higher compared to pure poly (methyl methacrylate). Samples modified with materials released phosphate ions for a short period. The materials that were identified to be most promising as an ion source were samples containing 5% calcium hydrogen phosphate (p < 0.01). Conclusions: Based on the results, it can be concluded that denture-base acrylic resins resulting after the addition of different bioactive precursors have improved mechanical properties and can release ions to the oral environment for a short period. (C) 2021 The Author. Production and hosting by Elsevier B.V. on behalf of King Saud University.