关键词： 大型养路机械   自有动力源   掉道紧急起复救援  

摘要： 结合铁路大型养路机械掉道紧急起复救援的问题,本文提出了利用大型养路机械自有动力源实现掉道紧急起复救援的方案,并对方案实施问题进行了探讨,从而为关注这一话题的人们提供参考。

关键词： 旋翼飞行机械臂   动力学建模   耦合前馈补偿   Lyapunov指数  

摘要： 旋翼飞行机械臂(rotor-flying manipulator, RFM)以旋翼无人机作为基座，可以实现一些空中操作。然而机械臂运动或是载荷的变化都会导致整个系统的重心产生偏移，给系统的动力学建模带来很大困难。此外，旋翼无人机、机械臂和交互环境之间的耦合效应，以及旋翼无人机本质不稳定的特性，也给系统的稳定性控制提出很大挑战。针对这些问题，本文充分协调动力学建模效率与模型精度的关系，深入分析模型的动力学特性，量化机械臂与旋翼无人机之间的耦合特性，以及在控制器设计时进行耦合前馈补偿，提高了控制性能。具体将从如下几个方面展开深入研究:\n (1)采用基于伪速度的建模方法，研究RFM的动力学建模问题。利用整体建模策略，采用基于欧拉-庞卡莱方程的伪速度建模方法，通过计算机符号推导，得到RFM在3维空间的动力学模型，并基于Lyapunov指数理论，分析所建模型的动力学特性，为后续稳定性控制提供指导。\n (2)采用参数自整定滑模控制算法，研究在机械臂运动耦合影响下，旋翼无人机的姿态稳定控制问题。首先，利用滑模控制算法的强鲁棒和抗干扰特性，对旋翼无人机的姿态设计滑模控制器，以抑制机械臂运动的耦合影响。然后，采用权重自适应改进粒子群算法，对设计的控制器进行参数自整定，以提高参数整定的效率。\n (3)采用前馈补偿PID控制算法，研究在机械臂运动耦合影响下，机械臂末端执行器的位姿控制问题。首先，利用Jacobian矩阵建立RFM的运动学反解模型。然后，推导RFM的耦合前馈补偿PID控制律。最后，采用分层控制策略，设计RFM的轨迹跟踪控制器，以抑制机械臂运动的耦合影响，实现末端执行器的轨迹跟踪功能。\n (4)采用阻抗控制算法，研究在机械臂和环境接触的耦合影响下，RFM的稳定接触控制问题。采用独立控制策略，对旋翼无人机设计前馈补偿PID控制器，对机械臂设计阻抗控制器，实现与环境的稳定交互，以及机械臂的位置和接触力控制功能。

关键词： 移动并联机械手   移动双串联机械手   多体动力学建模   加权初值法   数值仿真  

摘要： 提出一种用于验证移动并联机械手动力学建模及数值仿真正确性与有效性的方法。该方法先将移动并联系统某处运动副打开,用关节支反力替代运动副约束,从而形成移动双串联机械手,并以多体动力学理论为指导,在笛卡尔坐标系下分别进行移动并联、双串联机械手动力学建模,采用加权初值法对移动双串联机械手系统进行数值仿真。最后通过对移动并联、双串联机械手动力学数值仿真比较,验证系统动力学模型构建和数值仿真的正确性和有效性。

关键词： Disturbance   Fire management   Functional traits   Habitat accommodation model   Pyrodiversity  

摘要： Models based on functional traits have limited power in predicting how animal populations respond to disturbance because they do not capture the range of demographic and biological factors that drive population dynamics, including variation in trophic interactions. I tested the hypothesis that successional changes in vegetation structure, which affected invertebrate abundance, would influence growth rates and body condition in the early-successional, insectivorous gecko Nephrurus stellatus. I captured geckos at 17 woodland sites spanning a succession gradient from 2 to 48 years post-fire. Body condition and growth rates were analysed as a function of the best-fitting fire-related predictor (invertebrate abundance or time since fire) with different combinations of the co-variates age, sex and location. Body condition in the whole population was positively affected by increasing invertebrate abundance and, in the adult population, this effect was most pronounced for females. There was strong support for a decline in growth rates in weight with time since fire. The results suggest that increased early-successional invertebrate abundance has filtered through to a higher trophic level with physiological benefits for insectivorous geckos. I integrated the new findings about trophic interactions into a general conceptual model of mechanisms underlying post-fire population dynamics based on a long-term research programme. The model highlights how greater food availability during early succession could drive rapid population growth by contributing to previously reported enhanced reproduction and dispersal. This study provides a framework to understand links between ecological and physiological traits underlying post-fire population dynamics.

关键词： POLYMERIC nanocomposites   POLYURETHANES   METHACRYLATES   MULTIWALLED carbon nanotubes   X-ray scattering  

摘要： Nanocomposites based on polyurethane-poly(2-hydroxyethyl methacrylate) semi-interpenetrating polymer network (PU-PHEMA semi-IPN) doped with 0.01, 0.05, 0.1, or 0.25 wt% of non-functionalized multi-walled carbon nanotubes (MWCNTs) were synthesized. Their nanostructure was studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) techniques, and their dynamics and properties were characterized over the temperature range from -100 degrees C to 180 degrees C using dynamic mechanical analysis (DMA) and laser-interferometric creep rate spectroscopy (CRS). It was shown that ultra-low MWCNT contents (0.01%-0.1%) substantially modified matrix nanostructure due to the influence of nanofiller on the processes of micro-phase separation and mixing of matrix components, the changes in the molecular packing density, and good dispersion of MWCNTs. The structural changes were somewhat smaller at 0.25% nanotubes where tendency to formation of their aggregates was observed. Accordingly, the strong changes in dynamic behavior, elastic properties and creep resistance in the studied materials were caused by ultra-low MWCNT additives. The strong effect of extraordinary broadening of the PHEMA relaxation peak in the nanocomposites and, simultaneously, the strongly improved creep resistance over the 80 degrees C-160 degrees C temperature range (at 0.1% MWCNTs) were shown that is of importance for the application of these nanocomposites as perspective damping materials. POLYM. COMPOS., 39:263-273, 2018. (c) 2016 Society of Plastics Engineers

关键词： Cellulose nanocrystal   Liquid silicone rubber   Curing kinetics   Mechanical properties   3-Aminopropyltriethoxysilane  

摘要： To prepare liquid silicone rubber (LSR)/cellulose nanocrystal (CNC) nanocomposite, 3-aminopropyltriethoxysilane (APTES) was used to modify the surface of CNC to improve the interfacial interaction between the hydrophilic CNC and the hydrophobic LSR. Fourier transform infrared spectroscopy and energy dispersive spectrometer results demonstrated that APTES modified CNC successfully. It was found that small amount of modified CNC (M-CNC) had better reinforcement than SiO2 in LSR nanocomposites, the tensile strength and the strain at break of LSR increased over 85% and 44% by adding 1.5 wt% M-CNC. However, DSC and rheology tests indicated that APTES modified CNC increased the curing temperature of LSR and limited the addition of CNC, which was attributed to poisoning of Pt catalyst by APTES. Furthermore, small amount of M-CNC improved the thermal stability of LSR, the TGA results showed that the 10% weight loss temperature (T-10%) of LSR increased 56 degrees C with 1.0 wt% addition of M-CNC.

关键词： Monazite   Sintering kinetics   HT-ESEM   Hot pressing   Texture effects   Microhardness  

摘要： This work focuses on the effect of precursor morphology on the microstructural evolution of monazite-type lanthanum-europium phosphate ceramics during sintering, including grain growth rate, as well as correlations between microstructure, texture effects and their mechanical properties. Sintering kinetics of La0.5Eu0.5PO4 powders with two different grain morphologies (needle-shaped and spherical) was studied by an in situ HT-ESEM method at 1340 degrees C. La0.5Eu0.5PO4 pellets with high density (99% of the theoretical density) were obtained for both precursor powders by hot pressing. Analysis of XRD data collected for the hot pressed pellets obtained from needle-shaped precursors revealed preferential orientation of the grains towards the (100) direction. Mechanical properties of the hot pressed pellets were studied by the Vickers indentation method. The dependence of microhardness and fracture toughness on microstructure and texture was investigated.

关键词： Atomic force microscopy  

摘要： Single-molecule force spectroscopy by atomic force microscopy allows us to get insight into the mechanical unfolding of membrane proteins, and a typical experiment exhibits characteristic patterns on the force distance curves. The origin of these patterns, however, has not been fully understood yet. We performed coarse-grained simulation of the forced unfolding of halorodopsin, reproduced the characteristic features of the experimental force distance curves. A further examination near the membrane-water interface indicated the existence of a motif for the force peak formation, i.e., the occurrence of hydrophobic residues in the upper interface region and hydrophilic residues below the lower interface region. (C) 2017 Elsevier B.V. All rights reserved.

关键词： BVOCs   Camphene   OH radical   IRC   Rate constant   Lifetime  

摘要： Present manuscript represents the DFT studies on the oxidation reaction of camphene initiated by OH radical and fate of product radicals using M06-2X functional along with 6-31+G(d,p) basis set. Intrinsic reaction calculation is done for transition states involving OH-addition reactions which proceed via reaction complexes proceeding to the formation of transition states. The rate constant calculated by using canonical transition state theory at 298 K and 1 atm is found to be 5.67 x 10(-11) cm(3) molecule(-1) s(-1) which is in good agreement with the experimental rate constant. The atmospheric lifetime of the titled molecule has also been reported in our work.

关键词： Patient-specific simulation   Aortic hemodynamics   Aortic valve replacement   Virtual intervention   4D flow MRI  

摘要： Modeling different treatment options before a procedure is performed is a promising approach for surgical decision making and patient care in heart valve disease. This study investigated the hemodynamic impact of different prostheses through patient-specific MRI-based CFD simulations. Ten time-resolved MRI data sets with and without velocity encoding were obtained to reconstruct the aorta and set hemodynamic boundary conditions for simulations. Aortic hemodynamics after virtual valve replacement with a biological and mechanical valve prosthesis were investigated. Wall shear stress (WSS), secondary flow degree (SFD), transvalvular pressure drop (TPD), turbulent kinetic energy (TKE), and normalized flow displacement (NFD) were evaluated to characterize valve-induced hemodynamics. The biological prostheses induced significantly higher WSS (medians: 9.3 vs. 8.6 Pa, P=0.027) and SFD (means: 0.78 vs. 0.49, P=0.002) in the ascending aorta, TPD (medians: 11.4 vs. 2.7 mm Hg, P=0.002), TKE (means: 400 vs. 283 cm(2)/s(2), P=0.037), and NFD (means: 0.0994 vs. 0.0607, P=0.020) than the mechanical prostheses. The differences between the prosthesis types showed great inter-patient variability, however. Given this variability, a patient-specific evaluation is warranted. In conclusion, MRI-based CFD offers an opportunity to assess the interactions between prosthesis and patient-specific boundary conditions, which may help in optimizing surgical decision making and providing additional guidance to clinicians.