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： 机械设计   动力学   研究  

摘要： 近年来,随着我国现代工业的不断发展,机械行业也在不断的进步,这对于机械产品质量提出了更高的要求。作为影响机械产品质量的重要因素,应当对其予以充分重视。在进行机械结构设计时,动力学作为连接物理学与机械科学的重要内容,其对机械结构设计的提高与改进有着积极的引导作用,并且还有利于提升机械结构产品质量。基于此,本文将对机械设计中的动力学问题进行分析研究。

关键词： 热能   动力机械   现状   发展  

摘要： 我国于2013年将新专业目录进行整合,全国目前共计百余所有热能动力工程专业的大学。因为热动研究热能和动能,属于跨专业的工程研究类型,所以对其进行研究的难度略大。热动专业需要学习机械工程、热能动力以及工程热物理等方面的知识,专业涵盖的知识面比较广泛。能源动力产业属于我国经济发展的基础性支援产业,可以在各个行业中得到良好的运营,是国家科技发展基础方向之一。

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： 铁路机务系统   机械动力设备   优化管理对策  

摘要： 科学技术的发展带动着各个行业的进步,许多先进技术及设备在铁路机务系统中的应用,对机械动力设备提出更高的要求。为保证机械动力设备的正常运行,就需要对其进行优化管理,以提高铁路部门工作效率,从而使铁路部门能够创造更多的经济效益。本文对铁路机务系统机械动力设备的优化维修方法进行分析,并就其优化管理对策进行探讨。

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。