关键词： 混合动力   工程机械   动力系统   机电一体化  

摘要： 文章从力学的角度分析了曲轴两种耦合振动产生的机理,根据牛顿定律得到轴系耦合振动相互作用的关系表达式,然后针对混合动力工程机械系统的结构特殊性,通过对混合动力系统轴系的简化。对于实际的混合动力系统,由于存在多动力元件给系统主轴结构带来更多的复杂性,轴系因此而产生的振动情况要复杂的多,而且针对上述建立的耦合方程的求解也十分不便。由此,建立实际轴系的几何模型,运用有限元技术和多体动力学方法具体分析混合动力轴系的振动性。

关键词： 多体动力学   机械工程领域   运用  

摘要： 多体系统属于一门综合性课程,涵盖的学科较多,包括计算力学、工程力学等,是机械领域发展的新型课程。近年来,互联网技术也与其良好融合。通过实践证明显示,多动体力学对机械工程领域的推动作用较大,引起了社会的广泛重视。

关键词： 机械通气   呼吸末正压   血流动力学   影响  

摘要： 目的:分析研究机械通气时呼吸末正压对血流动力学的影响。方法:选取我院收治的90例呼吸衰竭并行机械通气的患者作为研究对象,回顾不同呼吸末正压水平下患者各项血流动力学指标(HR、MAP、CI、CVP)的变化情况。结果:随着呼吸末正压通气(PEEP)的升高,患者的MAP、CI水平整体呈下降趋势,而CVP则呈上升趋势,HR基本位置恒定,当PEEP从0变化至5cmH_2O时,各项指标均未见较大变化,CI、CVP从PEEP改变至10cmH_2O后开始明显降低或升高,而MAP在PEEP变至15cmH_2O后方开始显著升高。结论:机械通气时的呼吸末正压影响患者的血流动力学变化,治疗中应根据实际情况进行调整,改善肺通气功能的同时,维持有效的心排血量,保证组织供血。

关键词： 电动汽车   上海交通大学   博士生导师   工程学院   机械   “十五”时期   新能源汽车   产业竞争力  

摘要： 从第一个五年建设计划到“十五”时期，我国走过了近50年的历程。如今，新能源汽车特别是电动汽车已被确立为我国“十三五”规划的重点支持方向之一，而发展电动汽车也早已被确定为提高我国汽车产业竞争力、保障能源安全和发展低碳经济的重要途径。

关键词： 右美托咪定   丙泊酚   血流动力学   心脏瓣膜手术   机械通气   镇静  

摘要： 目的比较右美托咪定与丙泊酚对心脏瓣膜术后机械通气患者的镇静效果及血流动力学的影响。方法选取60例心脏瓣膜术后机械通气患者,随机分为右美托咪定组(D组)30例和丙泊酚组(P组)30例,D组给予右美托咪定0.2~0.7μg/(kg·h)+舒芬太尼0.15μg/(kg·h),P组给予丙泊酚1.2~3.0 mg/(kg·h)+舒芬太尼0.15μg/(kg·h)。以脑电双频指数(BIS)值为70~85、Richmond躁动镇静评分(RASS)-2^-3分为镇静目标。分别于术前(T_1)、心肺转流(CPB)结束后2 h(T_2)、术后4 h(T_3)和术后12 h(T_4)测定患者血流动力学相关指标。比较两组患者各观察时间点的BIS值、RASS评分以及平均动脉压(MAP)下降、心动过缓、躁动或谵妄等不良反应发生率。结果两组患者镇静后的BIS值与RASS评分差异无统计学意义(P>0.05)。两组患者镇静后血流动力学变化存在差异,MAP有不同程度的下降,在T_2时间点,P组的MAP小于D组(P<0.05);在T_3、T_4时间点,D组心指数(CI)高于P组(P<0.05,P<0.01)。在T_2、T_3、T_4时间点,P组的动脉血乳酸含量较D组升高明显(P<0.05,P<0.01)。两组间T_1~T_4各时点的全身血管阻力指数(SVRI)、每搏输出量(SV)、右心室射血分数(RVEF)、混合静脉血氧饱和度(Sv O2)差异无统计学意义(P>0.05)。两组各血管活性药物用量差异无统计学意义(P>0.05)。两组患者术后MAP下降、心动过缓发生率差异无统计学意义(P>0.05),D组镇静过程中躁动及谵妄发生率低于P组(P<0.05)。结论两组患者均可取得较好的镇静效果。右美托咪定对血流动力学影响较小,且其用于术后镇静可降低躁动或谵妄的发生率。右美托咪定更适合用于心脏瓣膜术后镇静。

关键词： Biomechanics   Elastic exoskeleton   Muscle-tendon mechanics   Unconstrained work loops   Biorobotics  

摘要： We present a novel biorobotic framework comprised of a biological muscle-tendon unit (MTU) mechanically coupled to a feedback controlled robotic environment simulation that mimics in vivo inertial/gravitational loading and mechanical assistance from a parallel elastic exoskeleton. Using this system, we applied select combinations of biological muscle activation (modulated with rate-coded direct neural stimulation) and parallel elastic assistance (applied via closed-loop mechanical environment simulation) hypothesized to mimic human behavior based on previously published modeling studies. These conditions resulted in constant system-level force-length dynamics (i.e., stiffness), reduced biological loads, increased muscle excursion, and constant muscle average positive power output all consistent with laboratory experiments on intact humans during exoskeleton assisted hopping. Mechanical assistance led to reduced estimated metabolic cost and MTU apparent efficiency, but increased apparent efficiency for the MTU + Exo system as a whole. Findings from this study suggest that the increased natural resonant frequency of the artificially stiffened MTU + Exo system, along with invariant movement frequencies, may underlie observed limits on the benefits of exoskeleton assistance. Our novel approach demonstrates that it is possible to capture the salient features of human locomotion with exoskeleton assistance in an isolated muscle-tendon preparation, and introduces a powerful new tool for detailed, direct examination of how assistive devices affect muscle-level neuromechanics and energetics. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Contact mechanics   Dry friction   Painleve paradox   Contact regularization   Impact without collision  

摘要： We investigate the dynamics of finite degree-of-freedom, planar mechanical systems with multiple sliding, unilateral frictional point contacts. A complete classification of systems with 2 sliding contacts is given. The contact-mode-based approach of rigid body mechanics is combined with linear stability analysis using a compliant contact model to determine the feasibility and the stability of every possible contact mode in each class. Special forms of non-stationary contact dynamics including "impact without collision" and "reverse chattering" are also investigated. Many types of solution inconsistency and indeterminacy are identified and new phenomena related to Painlev,'s non-existence and non-uniqueness paradoxes are discovered. Among other results, we show that the non-existence paradox is not fully resolvable by considering impulsive contact forces. These findings contribute to a growing body of evidence that rigid body mechanics cannot be developed into a complete and self-consistent theory in the presence of contacts and friction.

关键词： microbial interactions   methane emission   permafrost thawing   water table   soil aggregate  

摘要： The sensitivity of polar regions to raising global temperatures is reflected in rapidly changing hydrological processes associated with pronounced seasonal thawing of permafrost soil and increased biological activity. Of particular concern is the potential release of large amounts of soil carbon and stimulation of other soil-borne greenhouse gas emissions such as methane. Soil methanotrophic and methanogenic microbial communities rapidly adjust their activity and spatial organization in response to permafrost thawing and other environmental factors. Soil structural elements such as aggregates and layering affect oxygen and nutrient diffusion processes thereby contributing to methanogenic activity within temporal anoxic niches (hot spots). We developed a mechanistic individual-based model to quantify microbial activity dynamics in soil pore networks considering transport processes and enzymatic activity associated with methane production in soil. The model was upscaled from single aggregates to the soil profile where freezing/thawing provides macroscopic boundary conditions for microbial activity at different soil depths. The model distinguishes microbial activity in aerate bulk soil from aggregates (or submerged profile) for resolving methane production and oxidation rates. Methane transport pathways by diffusion and ebullition of bubbles vary with hydration dynamics. The model links seasonal thermal and hydrologic dynamics with evolution of microbial community composition and function affecting net methane emissions in good agreement with experimental data. The mechanistic model enables systematic evaluation of key controlling factors in thawing permafrost and microbial response (e.g., nutrient availability and enzyme activity) on long-term methane emissions and carbon decomposition rates in the rapidly changing polar regions.

关键词： Polyoxymethylene   CNT   composites   reinforcement   mechanical properties  

摘要： Carbon nanotube (CNT) was employed as a reinforcing material to prepare polyoxymethylene (POM)-based composite film through a simple melting extrusion. An effective approach was developed to clean and modify the surface of as-received CNT with nitric acid and then with a silane coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for POM/CNT composites due to the improved interfacial adhesion between CNT and the matrix. The thermal stabilities of the composites were also improved in the presence of CNT. The studies on crystallization behaviors showed that CNT acted as a nucleation agent for the crystallization of POM domain in composites, and therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of CNT.

关键词： DNA origami   DNA hinges   molecular dynamics simulations   coarse-grained modeling   dynamic nanostructures   compliant mechanisms   conformational fluctuations  

摘要： Structural DNA nanotechnology, the assembly of rigid 3D structures of complex yet precise geometries, has recently been used to design dynamic, mechanically compliant nanostructures with tunable equilibrium conformations and conformational distributions. Here we use coarse-grained molecular dynamics simulations to provide insights into the conformational dynamics of a set of mechanically compliant DNA nanostructures DNA hinges that use single-stranded DNA "springs" to tune the equilibrium conformation of a layered double-stranded DNA "joint" connecting two stiff "arms" constructed from DNA helix bundles. The simulations reproduce the experimentally measured equilibrium angles between hinge arms for a range of hinge designs. The hinges are found to be structurally stable, except for some fraying of the open ends of the DNA helices comprising the hinge arms and some loss of base-pairing interactions in the joint regions coinciding with the crossover junctions, especially in hinges designed to exhibit a small bending angle that exhibit large local stresses resulting in strong kinks in their joints. Principal component analysis reveals that while the hinge dynamics are dominated by bending motion, some twisting and sliding of hinge arms relative to each other also exists. Forced deformation of the hinges reveals distinct bending mechanisms for hinges with short, inextensible springs versus those with longer, more extensible springs. Lastly, we introduce an approach for rapidly predicting equilibrium hinge angles from individual force-deformation behaviors of its single- and double-stranded DNA components. Taken together, these results demonstrate that coarse-grained modeling is a promising approach for designing, predicting, and studying the dynamics of compliant DNA nanostructures, where " conformational fluctuations become important, multiple deformation mechanisms exist, and continuum approaches may not yield accurate properties.