Fatigue crack propagation in rocker and roller–rocker bearings of railway steel bridges

In this work, a method is proposed for rolling contact fatigue crack propagation analysis using contact and fracture theories in conjunction with fatigue laws. The proposed method is used in the fatigue analysis of rocker and roller–rocker bearings of a railway open web girder bridge which is instrumented with strain gages. Using a contact algorithm based on the minimum energy principle for bodies in rolling contact with dry friction, the normal and tangential pressure distribution are computed. It is seen that the most critical location of a crack in bearings is at a point very close to the contact region, as expected.

Fatigue crack propagation in rocker and roller-rocker bearings of railway steel bridges

In this work, a method is proposed for rolling contact fatigue crack propagation analysis using contact and fracture theories in conjunction with fatigue laws. The proposed method is used in the fatigue analysis of rocker and roller-rocker bearings of a railway open web girder bridge which is instrumented with strain gages. Using a contact algorithm based on the minimum energy principle for bodies in rolling contact with dry friction, the normal and tangential pressure distribution are computed. It is seen that the most critical location of a crack in bearings is at a point very close to the contact region, as expected. (C) 2010 Elsevier Ltd. All rights reserved.

Optimal synthesis of adjustable planar four-bar crank-rocker type mechanisms for approximate multi-path generation

This paper deals with an optimization based method for synthesis of adjustable planar four-bar, crank-rocker mechanisms. For multiple different and desired paths to be traced by a point on the coupler, a two stage method first determines the parameters of the possible driving dyads. Then the remaining mechanism parameters are determined in the second stage where a least-squares based circle-fitting procedure is used. Compared to existing formulations, the optimization method uses less number of design variables. Two numerical examples demonstrate the effectiveness of the proposed synthesis method. (C) 2013 Elsevier Ltd. All rights reserved.

Effect of a rocker non-heeled shoe on EMG and ground reaction forces during gait without previous training

Unstable shoes have been designed to promote "natural instability" and during walking they should simulate barefoot gait, enhancing muscle activity and, thus, attributing an advantage over regular tennis shoes. Recent studies showed that, after special training on the appropriate walking pattern, the use of the Masai Barefoot Technology (MBT) shoe increases muscle activation during walking. Our study presents a comparison of muscle activity as well as horizontal and vertical forces during gait with the MBT, a standard tennis shoe and barefoot walking of healthy individuals without previous training. These variables were compared in 25 female subjects and gait conditions were compared using ANOVA repeated measures (effect size:0.25). Walking with the MBT shoe in this non-instructed condition produced higher vertical forces (first vertical peak and weight acceptance rate) than walking with a standard shoe or walking barefoot, which suggests an increase in the loads received by the musculoskeletal system, especially at heel strike. Walking with the MBT shoe did not increase muscle activity when compared to walking with the standard shoe. The barefoot condition was more effective than the MBT shoe at enhancing muscle activation. Therefore, in healthy individuals, no advantage was found in using the MBT over a standard tennis shoe without a special training period. Further studies using the MBT without any instruction over a longer period are needed to evaluate if the higher loads observed in the present study would return to their baseline values after a period of adaptation, and if the muscle activity would increase over time. (C) 2012 Elsevier B.V. All rights reserved.

Auriferous Tertiary Gravels Near Rocker, in Silver Bow County, Montana

Between the villages of Rocker and Silver Bow, in south­western Montana, are found an interesting group of placers. Gold occurs in Tertiary gravel beds that are interstratified with beds of rhyolitic volcanic ash. With the aid of a plane table and open-sight alidade, a small portion of the lake-bed area near Rocker was mapped; all distances were paced, but numerous checks assure a fairly accurate map.

A pilot study in different unstable designs on the biomechanical effect of gait characteristics

The purpose of this study was to compare kinematics and kinetics during walking for healthy subjects using unstable shoes with different designs. Ten subjects participated in this study, and foot biomechanical data during walking were quantified using motion analysis system and a force plate. Data were collected for unstable shoes condition after accommodation period of one week. With soft material added in the heel region, the peak impact force was effectively reduced when compared among similar shapes. In addition, the soft material added in the rocker bottom showed more to be in dorsiflexed position during the initial stance. The shoe with three rocker curves design reduced the contact area in the heel strike, which may result in increasing human body forward speed. Further studies shall be carried out after adapting to long periods of wearing unstable shoes.

Synthesis of path generating flexible-link mechanisms

Flexible-link mechanisms are those linkage mechanisms (or structures) which are capable of motion by virtue of elastic deformation of one or more;links. In such mechanisms a single flexible link; can replace several rigid links and joints resulting in fewer links, fewer pin joints, reduced overall weight and reduced mechanical error. In spite of such clear advantages, contributions toward flexible-link mechanisms remain very scarce. The area of flexible-link mechanisms offers much scope for further exploration. This paper attempts to show the potential of flexible-link mechanisms in accomplishing a kinematic task like path generation. Synthesis of a four-bar mechanism with a flexible rocker for circular and straight line path generation is carried out. Displacement analysis of the structure is carried out using finite element method (FEM) and synthesis is formulated and solved as an optimization problem. Several numerical examples are presented for illustration. Based on the results obtained with these examples, the flexible-link mechanism considered shows good promise for-path generation.

一种行星探索车举升机构设计

介绍了摇杆-转向架悬挂系统的收缩和展开状态,根据展开过程,分析了举升机构的任务。采用双重四杆机构设计举升机构,以满足摇杆-转向架展开过程中两大步骤的需要。详细介绍了该举升机构的工作原理和双重四杆机构的切换过程。最后对举升过程中的四杆机构参数进行了分析设计,给出了机构参数设计模型,利用该模型可以对四杆机构的受力进行优化设计。

基于摇臂-转向架结构月球车的越障能力判断准则

对轮式移动系统进行越障分析时,常以垂直越障作为评价标准。但是,月球车在凹凸不平的月面上行驶时,垂直越障模型不具有一般性。为此,本文对基于摇臂-转向架结构月球车在任意路面的越障进行了研究。一般情况下,由于任意路面越障模型相对复杂,可以建立的独立平衡方程数目少于未知变量数,因此无法得到越障能力与路面参数的函数关系式。针对上述问题,文中将最大有效牵引力假设引入越障模型中,得到了一种任意路面越障能力的判断准则。通过算例分析,表明了所提方法的有效性。

六轮摇臂式月球车环境交互动力学建模研究

目前，移动机器人被广泛应用于危险的非结构环境中，在诸如行星探测、灾难搜救、军事侦察、矿山开采等作业中， 机器人将起着越来越重要的作用。机器人在非结构环境中的运动能力和环境适应能力决定了机器人的作业性能。具备稳定性、机动性、越障能力、通过能力与可靠性的移动机器人将具有更好的环境适应能力，进而更好地完成作业任务。 本文针对中国科学院知识创新工程方向性项目“月球车月面探测作业支撑技术研究” 的实际需求， 在对国内外的同类研究深入分析综合的基础上， 对月球车移动系统与环境交互动力学的几个关键问题进行了研究与探讨。(1)研究月球车的运动稳定性和机动性问题。基于车体固定坐标系和地面固定坐标系， 分别建立了四轮转向的六轮摇臂转向架式月球车的转向动力学模型， 证明在两种坐标系下的模型转向动力学方程的一致性；分析了月球车运动的稳态特性和瞬态特性，采用机动性因子来定量地描述月球车运动的稳定性和机动性及其相互关系， 并用机动性因子来设计月球车的稳定性和机动性。(2)研究如何保持理想运动姿态的问题。建立了保持月球车运动姿态的理想模型， 模拟人驾驶汽车的过程建立月球车跟踪规划路径行驶的视觉预瞄模型，设计了保持月球车理想姿态行驶的模型参考自适应控制方案。(3)研究月球车的运动在环境扰动的干扰下会偏离规划路径的问题。利用Laplace 变换考察月球车运动动力学系统对几种典型的环境干扰力形式 的响应，研究环境干扰力对月球车运动的影响。(4)根据车辆地面力学的理论，设计月球车车轮的结构参数，使其充分利 用土壤推力，考虑纵列式月球车多轮通过土壤参数的修正，在NASA 建议的五种土壤上对月球车的支承通过性指标进行了计算； 研究刚性驱动轮在松软路面上行驶车轮滑转率和车轮结构参数对车轮挂钩牵引力、驱动力矩、车轮驱动效率等车轮驱动动力学特性的影响。(5)针对月球车在松软路面上不能正常行驶的主要原因是车轮过度下陷这个问题， 结合月球车行驶动力学模型， 设计以车轮滑转率为状态变量的滑模驱动控制器。仿真结果表明， 采用该控制器可以避免车轮的过度 滑转下陷，保证月球车能够在软质路面上正常行驶。(6)评价六轮摇臂转向架式月球车的越障能力，给出了车轮牵引系数与垂直越障高度的定量函数关系式； 针对月球车越障能力的评价以及越障时各车轮驱动力矩的协调分配的问题， 建立一种基于运动轨迹角的月球车越障能力判断准则， 引入了越障指数，用于定量地评价月球车的越障能力。(7)利用闭链坐标变换和瞬时重合坐标法，结合Kane 方程，同时考虑三维不平地形、松软路面和车轮的滑移，建立了六轮摇臂转向架式月球车的三维姿态动力学模型。

被动柔顺式月面巡视探测器轮-地交互及运动控制研究

月面巡视探测器（简称月球车）是一类在月面环境下执行巡视探测、科学考察及样品采样等任务的空间机器人，是我国月球探测二期工程中执行月面探测任务的关键载体。月球车行走能力事关我国探月二期工程的成败，开展在复杂地形下移动能力和地形通过能力的研究，是目前移动机器人研究中的前沿课题，是月面巡视任务的关键技术之一。本论文的选题具有重要的理论意义和应用价值。 月面环境的特殊性使月球车进行长距离、大范围的巡视任务面临一系列问题，包括地形对月球车移动性的影响、移动能力、地形通过能力、地形适应能力、安全性等。本文以月球车保持复杂地形下的高移动能力和地形通过能力为研究目标，以一种典型的被动柔顺式月球车为对象，从月球车与环境地形具有整体不可分离性的角度，将机器人与环境地形看成是相互作用的整体，深入研究了轮-地交互关系、软硬地形上的轮-地接触模型、环境地形给月球车带来的影响、软硬地形上的月球车建模、参数估计及运动控制等问题。根据对月球车移动性能影响程度之不同，本文从硬质地形与松软地形两个方面来考察环境地形的物理属性和轮-地交互关系。在硬质地形上，主要考虑地形平坦与不平坦对机器人移动的影响及其控制，六个驱动轮的速度协调控制，车轮打滑（前滑、侧滑、转向滑移）对机器人的建模、分析及控制的影响。在松软地形上，主要考虑轮-地接触关系，土壤特性对移动的影响及其控制。在大量阅读国内外文献并归纳总结的基础上，重点开展了如下几方面的研究： （1）在硬质不平坦地形下，引入轮-地几何接触角概念以反映地形不平坦时轮-地接触点在轮缘上位置的变化，去掉了通常采用的车轮纯滚动假设，考虑车轮滑移（包括侧滑、侧滑以及转向滑移），并结合月球车被动柔顺式移动机构的特点，提出了一种基于速度闭链的运动学建模方法，进行了基于整车模型的月球车速度协调控制研究。该运动学建模方法基于轮心处的速度投影建立整体运动学模型，物理概念清晰、便于实时运动学正反解计算。 （2）针对运动学模型中轮-地几何接触角难以直接测量的问题，提出了两种在线估计方法：误差计算法和卡尔曼滤波估计法。这两种方法均基于月球车整体运动学模型，只需要车轮内部传感器的测量信息，就能在线估计轮-地几何接触角。 （3）由于车轮滑移的影响，采用航位推算方法进行月球车状态估计以及里程计计算存在较大误差。本文提出了基于整体运动学模型的车体运动状态估计方法，并在月球车样机上对车体速度估计、航向角估计、里程计实时计算等方法进行了大量实验研究，验证了算法的有效性。 （4）针对松软地形上刚性轮与地形的交互建模问题，提出了一种基于Guass-Legendre数值积分和Newton-Raphson数值解法的地形参数实时估计方法。以月壤参数的变化范围为参考空间，通过数值仿真将不同地形参数对轮-地接触力的影响进行比较，进而选取对轮-地接触力有较大影响的地形参数进行在线估计，仿真和实验结果均表明估计算法是有效的。 （5）松软地形上常规的速度控制效果差，本文开展了月球车准静力学建模及牵引力控制算法研究，提出了两种牵引力控制算法。对月球车准静力学模型进行简化，提出了一种基于目标优化、考虑车体姿态变化的牵引力控制算法。利用上一章在线估计出的地形参数，对车轮滑移率进行最优估计，提出了一种基于最优滑移率的牵引力控制算法，并进行了仿真验证。

滑转率对月球车车轮驱动力学特性的影响分析

应用车辆地面力学理论研究滑转率对月球车车轮挂钩牵引力、驱动效率以及功率消耗的影响。建立刚性车轮与松软月壤交互作用的动力学模型。通过实例对月球车车轮驱动动力学特性进行仿真分析。研究结果表明,车轮的挂钩牵引力、驱动效率以及驱动能耗均受到车轮滑转率的制约。存在一个最优的滑转率区间,在此区间内车轮可获得较大的挂钩牵引力、较高的驱动效率以及较低的驱动能耗。求取轮、地相对速度,对月球车车轮的地面摩擦力功率进行了估算。

A strategy to advance the evidence base in palliative medicine: formation of a palliative care research cooperative group.

BACKGROUND: Palliative medicine has made rapid progress in establishing its scientific and clinical legitimacy, yet the evidence base to support clinical practice remains deficient in both the quantity and quality of published studies. Historically, the conduct of research in palliative care populations has been impeded by multiple barriers including health care system fragmentation, small number and size of potential sites for recruitment, vulnerability of the population, perceptions of inappropriateness, ethical concerns, and gate-keeping. METHODS: A group of experienced investigators with backgrounds in palliative care research convened to consider developing a research cooperative group as a mechanism for generating high-quality evidence on prioritized, clinically relevant topics in palliative care. RESULTS: The resulting Palliative Care Research Cooperative (PCRC) agreed on a set of core principles: active, interdisciplinary membership; commitment to shared research purposes; heterogeneity of participating sites; development of research capacity in participating sites; standardization of methodologies, such as consenting and data collection/management; agile response to research requests from government, industry, and investigators; focus on translation; education and training of future palliative care researchers; actionable results that can inform clinical practice and policy. Consensus was achieved on a first collaborative study, a randomized clinical trial of statin discontinuation versus continuation in patients with a prognosis of less than 6 months who are taking statins for primary or secondary prevention. This article describes the formation of the PCRC, highlighting processes and decisions taken to optimize the cooperative group's success.

Le Sylvicole moyen ancien de l’Estrie et du Nord-Est américain : une étude descriptive et comparative de la poterie du site Vieux-Pont (BiEx-1), Lennoxville, Québec

Ce mémoire porte sur la chronologie culturelle des Amérindiens du Nord-Est américain. Il vise à documenter un des épisodes culturels de la préhistoire de l’Estrie, soit le Sylvicole moyen ancien, compris entre l’an 400 avant notre ère et 500 de notre ère. De la poterie typique de cette période a été récoltée sur le site Vieux-Pont (BiEx-1) à Lennoxville par des archéologues amateurs et professionnels depuis sa découverte. L’analyse des tessons de poterie réalisée dans ce projet a surtout révélé une forte homogénéité de l’effet basculant, une technique d’application décorative, sur la paroi interne et la panse des vases. Elle a aussi permis de proposer une occupation récente au Sylvicole moyen ancien, entre les ans 1 et 500-600 de notre ère. L’analyse comparative suggère la participation des groupes de Vieux-Pont aux mêmes réseaux d’interactions et d’échanges que ceux des régions de Montréal, de Québec, du Haut-Richelieu et de la Nouvelle-Angleterre.