关键词： ADAMS   打捆机   运动学   动力学  

摘要： 采用虚拟仿真技术,对打捆机进行3D建模,通过Adams软件对打捆机进行运动与动力学仿真分析,检验打捆机在运动过程是否出现干涉现象,得到其主要零部件相应的运动与动力学变化曲线。分析了打捆机的结构设计与受力强度是否满足设计要求,为整台机器的设计提供了依据。

关键词： 机械通气   呼气末正压   低血容量   血流动力学  

摘要： 危重患者机械通气过程中需经常调整呼气末正压（positive end- expiratory pressure ，PEEP）参数，PEEP水平过高，可使肺内压升高，甚至引起气压伤和恶性心律失常，造成相关性心脏损伤。重症监护室患者由于创伤、手术等原因，往往存在低血容量状态，而实施机械通气后又可使胸腔内压力升高，心排血量进一步下降，因此研究呼气末正压对低血容量患者的临床影响有重要意义。本文针对低血容量状态下机械通气患者，探讨呼气末正压（PEEP）水平对心脏血流动力学的影响。

关键词： 呼吸窘迫综合征   成人   通气机   机械   俯卧位   血流动力学  

摘要： 目的探讨俯卧位机械通气(PPV)治疗对急性肺损伤(ALI)/急性呼吸窘迫综合征(ARDS)患者动脉氧合及血流动力学的影响。方法选择2009年7月—2011年6月云南省第一人民医院急诊科收治的肺内和/或肺外因素所致的ALI/ARDS患者67例,在一定肌松剂和镇静剂条件下进行PPV治疗。分别检测俯卧位(PP)前、PP 1h、PP 2 h、仰卧位(SP)1 h、SP 2 h时的血气分析指标〔包括酸碱度(pH)值、动脉血氧分压(PaO2)、二氧化碳分压(PaCO2)及氧合指数(PaO2/FiO2)〕及血流动力学指标〔包括心率(HR)、平均动脉压(MAP)、中心静脉压(CVP)、心排血量(CO)、每搏量(SV)及每搏量变异率(SVV)〕;观察患者皮肤黏膜损伤、血压下降、呕吐胃内容物等不良反应的发生情况。结果以PaO2升高>10 mm Hg(1 mm Hg=0.133 kPa)为改善患者氧合状态的有效指标,其中59例(88.1%)有效。不同时间点的PaO2、PaO2/FiO2比较,差异有统计学意义(P<0.05);PP 1 h、PP 2 h、SP 1 h、SP 2 h的PaO2、PaO2/FiO2均高于PP前(P<0.05)。不同时间点的pH值、PaCO2、HR、MAP、CVP、CO、SV、SVV比较,差异均无统计学意义(P>0.05)。PPV后29例(43.3%)ALI/ARDS患者出现受压部位皮肤潮红,但没有皮肤黏膜的损伤;11例(16.4%)出现皮下水肿加重;5例(7.5%)出现血压下降;6例(9.0%)出现呕吐胃内容物;其余患者均未观察到并发症的发生。67例患者中有8例(11.9%)对PPV治疗无反应。结论 PPV可改善ALL/ARDS患者动脉氧合情况,对血流动力学无明显影响,且无明显不良反应发生,近期临床疗效较好,为今后临床研究提供了参考依据。

关键词： Digestion   Food structure   Processing   Dairy products   Modelling   Computer simulation  

摘要： Beyond the individual content in nutrients, it is now established that the matrix structure is also to consider when evaluating the nutritional properties and possible health effects of a food material. The objective of this study was to gain knowledge on the effect of the structure of dairy products on the digestion of milk proteins as inferred from a mathematical modelling of mini-pig in vivo data. Six dairy matrices of the same composition but differing by their physicochemical and structural properties were investigated. They were manufactured using technological processes commonly used in the industry (heat treatment, rennet gelation, acid gelation and mixing). The experimental results cover a 7-h postprandial period and consist of plasmatic amino acid concentrations as well as dry matter contents and chromium concentrations (a marker of the liquid phase of the meal) of samples collected at the stomach exit. The model developed not only accounts for the main digestive events but also for phenomena that can occur within the stomach (milk clotting and aggregate syneresis). It provides a good fitting of all the experimental data and allows estimating parameter values that can be explained by considering the properties of the matrices investigated. The model has also been used to estimate quantities that cannot be observed experimentally (stomach volumes, endogenous secretions, gastric emptying half-time, etc.) in order to recover a better picture of all the results and validate the model predictions against the literature. It even appears that our simulations of gastric emptying and aminoacidemia superimpose very well with previously published data obtained using similar matrices and the same mini-pig species. This study shows that the great differences in the kinetics of amino acid absorption that were observed experimentally can be fully understood by considering the behaviour of the dairy matrices within the stomach. It therefore offers interesting perspectives

关键词： Calcium silicate hydrate (C-S-H)   Water/Ca ratio   Molecular dynamics   Uniaxial tension/compression test  

摘要： Calcium silicate hydrate (C-S-H) is the most important hydration product of cement-based materials. In the nanostructure of C-S-H, structural water molecules are distributed in the interlayer region and determine the mechanical performance of C-S-H gel. In this study, C-S-H gels with different water contents expressed as the water/Ca ratio are characterized in the light of molecular dynamics. In order to study the influence of the water molecules, the structures of 12 C-S-H gel samples with water/Ca ratios from 0 to 0.95 are investigated. It is found that the penetration of water molecules transforms the C-S-H gel from an amorphous to a layered structure by silicate depolymerization as the water content gradually increases. The structures are then tested for mechanical properties by simulated uniaxial tension and compression. The mechanical tests associated with structural analysis reveal that the structural water molecules can greatly weaken the stiffness and the cohesive force by replacing the ionic covalent bond with unstable H-bond connections. By studying the tensile failure mechanism of C-S-H gels at different humidity levels, the disconnecting role of the structural water molecules is comprehensively interpreted. Because the interlayer water molecules prevent reconstruction of the bonds between the Ca-w and the silicate chains, the plasticity of the C-S-H gels is reduced significantly in the change from a dry state to a saturated state. In addition, the compressive strength of a C-S-H gel in the saturated state is much larger than the tensile strength. This provides molecular evidence for the tensile weakness of cement paste. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Nanocomposites   Polybenzoxazine   Glass transition   Kinetics  

摘要： In this study, we used a singly azido-functionalized polyhedral oligomeric silsesquioxane (FOSS) derivative and a montmorillonite intercalated by propargyldimethylstearylammonium bromide to prepare an exfoliated montmorillonite through click chemistry. This exfoliated montmorillonite was then introduced into a benzoxazine matrix prepared from paraformaldehyde, aniline, and phenol to form polybenzoxazine/exfoliated clay nanocomposites. Dynamic mechanical analysis, differential scanning calorimetry, and Agrawal integral equation revealed that the glass transition kinetics had a close relationship to the structure, assembly process, and anchoring effect of montmorillonite layers, the compatibility between polybenzoxazine and intercalator, and the methods of dynamic mechanical analysis and differential scanning calorimetry. The polybenzoxazine/exfoliated clay nanocomposites presented the same mechanism function at different weight ratios between polybenzoxazine and exfoliated clay, and the kinetic compensation effect equations revealed the nature of glass transition. (C) 2014 Elsevier *** rights reserved.

关键词： Inverse dynamics control   Robust H-infinity control   Adaptive fuzzy control   Robot manipulator with uncertain dynamics  

摘要： On the basis of inverse dynamics controller as a nominal control portion, two types of novel robust adaptive inverse dynamics control schemes are proposed for the trajectory tracking control of robot manipulator with uncertain dynamics. They are composed of an adaptive fuzzy control algorithm and a nonlinear tracking control model. The adaptive fuzzy control algorithm is employed to approximate the structured uncertainties, and the nonlinear robust control model is designed to eliminate the effects of the unstructured uncertainties and approximation errors. The tuning parameters in the adaptive fuzzy control algorithm are derived through the Lyapunov method. Comparison studies of their control performances with the conventional inverse dynamics controller are carried out, and their validity is demonstrated by numerical simulations of a two-link rotary robot manipulator.

关键词： Poly(butylene terephthalate)   Attapulgite   Crystallization   Differential scanning calorimetry (DSC)   Dynamic mechanical analysis (DMA)  

摘要： Poly(butylene terephthalate) (PBT)/attapulgite (AT) nanocomposites were prepared by in situ polymerization. Morphology of the PBT/AT nanocomposites was observed by scanning electron microscope and polarizing optical microscope. Thermogravimetric analyses were used to examine the thermal stability. The melting behaviors, equilibrium melting temperature, isothermal crystallization behavior of pure PBT and PBT/AT nanocomposites were studied by differential scanning calorimetry. The results show that PBT/AT nanocomposites possess higher thermal stability than pure PBT, and AT nanoparticles play a heterogeneous nucleating agent in PBT crystallization that accelerated the crystallization rate. The PBT/AT nanocomposite with higher AT content could retard the transport of polymer chains to the growing crystals compared with that of PBT/AT nanocomposite in lower AT content. According to dynamic mechanical analysis results, the storage modulus of PBT/AT nanocomposites was markedly improved and the addition of AT nanoparticles promotes the crystallization of PBT, which decreases the amorphous area. Meanwhile, the well-dispersed AT nanoparticles also retard the movement of polymer chain segment and increase the proportion of rigid amorphous region.

关键词： Machinery foundation   design optimization   forced vibration   vibration isolation  

摘要： This paper deals with the problem of optimum design of a foundation for rotating machinery with a view to minimize vibration transmission from a machine source to its supporting structure. The problem of analysis and optimization of the installation systems of machinery has been extensively researched on the assumption of a rigid supporting structure. The design based on a rigid supporting structure model is reasonable for the installation of machinery in many real engineering situations. However, this rigid support based model may not be appropriate for the problem studied herein where the machinery is to be installed on a relatively flexible supporting plate. Thus, a generalized mathematical model of mobility power flow is developed in this paper, with a rotating machine as vibration source, resilient mounts as isolator, and a flexible supporting plate as receiver. The objective of minimizing vibration transmission is realized by optimization of stiffness coefficients of resilient mounts with a constraint on the vibration level of the machine. The design objective is chosen as the minimization of the power flow transmitted to the flexible supporting plate through the resilient mounts at the excitation frequency of the machinery. Both a single excitation frequency and a range of excitation frequencies are considered. A gradient-based mathematical programing method is selected for its advantage of efficiently solving the current type of optimization problem with multiple mounts and multi-degree-of-freedom vibration transmission. The sensitivities of the objective and the constraint functions with respect to the design variables are derived analytically. The design and performance of the optimized machinery foundation is illustrated and discussed using several numerical examples. The optimized mounting system is suitable for the installation case of a rotating machine with a low or medium service speed on a flexible supporting plate structure.

关键词： 空间柔性机械臂   动力学建模   数值求解   仿真验证  

摘要： 针对综合考虑臂杆柔性和关节柔性的空间机械臂刚柔耦合动力学建模,以双连杆机械臂为研究对象,采用假设模态法对柔性臂杆离散化,将柔性关节等效为扭转弹簧,基于Lagrange方程和虚功原理推导模型方程。利用Maple和Matlab软件基于Newmark-β法原理联合求解方程数值解,并用ANSYS和ADAMS软件联合设计仿真模型验证动力学模型的正确性,结果表明:无论在阶跃力矩还是正弦力矩驱动下,动力学模型的输出和ADAMS模型输出的结果一致,很好的证明了动力学仿真程序的正确性。