关键词： Dielectric spectroscopy   Rheology   Normal modes   Hydrogen bonding  

摘要： The present dielectric investigations of methyl-terminated poly(propylene glycol) (PPG) oligomers reveal that near the glass transition the normal modes and segmental relaxation merge in a single-process susceptibility spectrum, similar to previous observations on OH-terminated species. Moreover, the present shear-mechanical measurements demonstrate that the vanishing of chain modes can be monitored without recourse to dielectric investigations, which are able to access chain dynamics only for the relatively small fraction of type A polymers. As the normal and segmental modes merge, the viscosity displays a crossover from a polymer-like regime governed by the chain dynamics, to a simple-liquid regime governed by the structural relaxation.

关键词： aspiration   deglutition disorder   muscular failure   sepsis   swallowing disorder  

摘要： Objectives: Swallowing disorders may be associated with adverse clinical outcomes in patients following invasive mechanical ventilation. We investigated the incidence of dysphagia, its time course, and association with clinically relevant outcomes in extubated critically ill patients. Design: Prospective observational trial with systematic dysphagia screening and follow-up until 90 days or death. Settings: ICU of a tertiary care academic center. Patients: One thousand three-hundred four admissions of mixed adult ICU patients (median age, 66.0 yr [interquartile range, 54.0-74.0];Acute Physiology and Chronic Health Evaluation-II score, 19.0 [interquartile range, 14.0-24.0]) were screened for postextubation dysphagia. Primary ICU admissions (n = 933) were analyzed and followed up until 90 days or death. Patients from an independent academic center served as confirmatory cohort (n = 220). Interventions: Bedside screening for dysphagia was performed within 3 hours after extubation by trained ICU nurses. Positive screening triggered confirmatory specialist bedside swallowing examinations and follow-up until hospital discharge. Measurements and Main Results: Dysphagia screening was positive in 12.4% (n = 116/933) after extubation (18.3% of emergency and 4.9% of elective patients) and confirmed by specialists within 24 hours from positive screening in 87.3% (n = 96/110, n = 6 missing data). The dysphagia incidence at ICU discharge was 10.3% (n = 96/933) of which 60.4% (n = 58/96) remained positive until hospital discharge. Days on feeding tube, length of mechanical ventilation and ICU/hospital stay, and hospital mortality were higher in patients with dysphagia (all p < 0.001). The univariate hazard ratio for 90-day mortality for dysphagia was 3.74 (95% CI, 2.01-6.95;p < 0.001). After adjustment for disease severity and length of mechanical ventilation, dysphagia remained an independent predictor for 28-day and 90-day mortality (excess 90-d mortality 9.2%). Conclusions: Dysp

关键词： IONIC liquids   POLYMERS   IMIDAZOLES   IONIC conductivity   CALORIMETRY  

摘要： The mechanical and conductive properties of a polymeric ionic liquid (PIL) are decoupled through the addition of a fraction of trivalent anions to a chloride single-ion conductor. Trivalent phosphate ions strongly coordinate with polymer bound imidazoliums, producing an increase in both the ionic conductivity and the polymer viscosity. Both the viscosity and the ionic conductivity increase with phosphate content, and the conductivity is superior to that of the neat PIL at larger trivalent anion concentrations. The interaggregate spacing (determined by X-ray scattering), glass transition temperature (measured by calorimetry), and free volume (estimated by theology) are each sensitive to the presence of trivalent ions but not to changes in the phosphate concentration. Thus, the presence of a fraction of trivalent anions qualitatively changes the structure and interaction of ions, resulting in modified macroscopic properties of the PIL. We hypothesize that this step change in properties upon introducing phosphate ions is due to a densification of ion aggregates by the trivalent ion, which strongly binds to irnidazolium ions. This provides a new mechanism for creating PILs with tailored conductive and rheological behavior.

关键词： 多体动力学   机械工程   运用  

摘要： 多体动力学是一门涵盖了多门科学的自然科学,其包括了工程力学、计算力学等多门科学,也是机械领域中的一门新兴科学。在经过多年的发展与扩充中,多体动力学也将计算机技术吸收,并将其应用于实践中。它在机械工程中具有较大的影响,并在这一行业中的应用受到越来越多专家与学者的关注。

关键词： Polysiloxane   Hydrosilylation   Tetra-functional   Isoconversional   Curing kinetics  

摘要： Investigation of the curing kinetics of a resin is one of the prerequisites for designing and optimization of the process parameters for the curing process which will help to control and predict the curing cycle of the materials. Non-isothermal curing kinetics for hydrosilylation of tetra-functional cyclosiloxanes was analyzed through both model-fitting and model-free methods for the first time. The conversion dependency of the activation energy (Ea) reveals the complexity of the curing process which leads to a complex kinetic behavior. The Friedman method shows the shift of a chemical control reaction to a diffusion control reaction due to the change of viscosity during the curing process. Detailed analysis of the curing kinetics at the molecular level shows that Ea dependency on conversion is a combined effect of diffusion of monomers and reaction intermedia, solidification of the reaction medium, "clicking" of chain-like structures, and steric hindrance pose by the hyper-branched molecules. We tentatively attribute the presence of shoulders on the non-isothermal curves to the delay in curing reaction due to diffusion process and high steric hindrance. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Bolboschoenus maritimus   Emergent macrophytes   Pattern-oriented modelling   Phragmites australis   Tidal marsh vegetation   Vegetative reproduction  

摘要： Tidal marsh vegetation offers important ecosystem services. However, in many estuaries, extensive embankments, artificial bank protection, river dredging and agriculture threaten tidal marshes. In this study we analysed the processes underlying the spatio-temporal patterns of tidal marsh vegetation in the Elbe estuary and quantified the influence of specific habitat factors by developing and applying the process-based dynamic habitat-macrophyte model HaMac in a pattern-oriented way. In order to develop and parameterise the model, we measured a wide range of biotic and abiotic parameters in two study sites in the Elbe estuary and compared observed and simulated patterns. The final model is able to reproduce the general patterns of vegetation zonation, development and growth and thus helps to understand the underlying processes. By considering the vegetative reproduction of marsh plants as well as abiotic influence factors and intraspecific competition, HaMac allowed to systematically analyse the significance of factors and processes for the dynamic of tidal marsh vegetation. Our results show that rhizome growth is the most important process and that flow velocity, inundation height and duration as well as intraspecific competition are the most important habitat factors for explaining spatio-temporal dynamics of brackish marshes. Future applications of HaMac could support the sustainable development and stabilisation of shore zones and thus contribute to the promotion and planning of ecosystem -based shoreline protection measures. (C) 2017 Elsevier B.V. All rights reserved.

关键词： 气动力敏机械手指   气压测微   气膜压力场   雷诺方程  

摘要： 气动力敏机械手指是利用气压测微技术和气膜柔性承载技术,将触觉传感器和普通机械手结合为一体,实现对工件无损伤抓取。芯轴与辊环之间的气膜是组成测力系统的关键部分,气膜内的气体压力分布状态直接影响气动力敏机械手指的工作性能。介绍了气动力敏机械手指的结构及工作原理,推导了气膜压力场雷诺方程,并采用FLUENT软件仿真计算了气膜压力场。得出的结果为实际气动力敏机械手指的设计提供了理论基础。

关键词： 动力机械   隔振系统   刚度   阻尼   传递率  

摘要： 采用理论分析和实验研究相结合的方法,研究了动力机械隔振系统参数对传递率的影响,获得了不同的激振力频率下,刚度和阻尼参数对传递率的影响规律,并分析了规律存在的内在机理。研究结果表明,当动力机械设备工作在低频共振区时,传递率Ta的最大值与刚度(或固有频率)无关,随阻尼比ξ增加按T_a=1/(2ξ)+1规律明显下降;当动力机械激励频率ω远高于固有频率时,传递率随隔振系统刚度减小而明显下降,同时减小阻尼比也有助于减小传递率;对于质量、刚度和阻尼均确定的系统,当激励频率远大于系统固有频率时,传递率Ta随激励频率ω增加而减小。上述结论得到了试验验证。

关键词： 机械臂   关节刚度   柔性多体动力学   拓扑优化   载重/自重比  

摘要： 针对柔性关节对工业机器人动力学特性的影响,基于"转子-扭簧"模型和有限元法,研究关节刚度对机械臂固有动力学特性的影响规律;考虑臂杆柔性和关节柔性,建立了机械臂多柔体动力学有限元模型,以机械臂轻量化为设计目标,以末端总位移量为约束条件对机械臂结构进行优化。研究结果表明,不同关节刚度对机械臂各阶固有频率的影响不同,优化后的机械臂载重/自重比增大,刚度和强度均得到提高,整体动力学性能明显提高。

关键词： 欠驱动   柔性机械臂   弹性变形   耦合分析  

摘要： 为建立柔性3R欠驱动机械臂的动力学方程,采用Euler-Bernoulli梁模型并添加经迭代计算的边界条件,对柔性机械臂进行了动力学耦合与仿真分析。在对柔性机械臂进行模态分析的基础上,将柔性机械臂视为包含边界条件的悬臂梁和简支-自由梁模型,采用假设模态法建立柔性3R欠驱动机械臂的动力学模型。仿真结果证明:添加经迭代计算的边界条件的柔性梁模型能更好地反映自由关节的加速度耦合情况。最后对柔性欠驱动机械臂与刚性欠驱动机械臂进行关节耦合指标分析,结果表明柔性欠驱动机械臂的自由关节包含更复杂的耦合情况,对柔性机械臂弹性振动的控制是对柔性欠驱动机械臂控制的关键。