Design of fully rotatable, roller-crank-driven, cam mechanisms for arbitrary motion specifications

The design of a non-traditional cam and roller-follower mechanism is described here. In this mechanism, the roller-crank rather than the cam is used as the continuous input member, while both complete a full rotation in each revolution and remain in contact throughout. It is noted that in order to have the cam fully rotate for every full rotation of the roller-crank, the cam cannot be a closed profile, rather the roller traverses the open cam profile twice in each cycle. Using kinematic analysis, the angular velocity of the cam when the roller traverses the cam profile in one direction, is related to the angular velocity of the cam when the roller retraces its path on the cam in the other direction. Thus, one can specify any arbitrary function relating the motion of the cam to the motion of the roller-crank for only 180 degrees of rotation in the angular velocity space. The motion of the cam in the remaining portion is then automatically determined. In specifying the arbitrary motion, many desirable characteristics such as multiple dwells, low acceleration and jerk, etc., can be obtained. Useful design equations are derived for this purpose. Using the kinematic inversion technique, the cam profile is readily obtained once the motion is specified in the angular velocity space. The only limitation to the arbitrary motion specification is making sure that the transmission angle never gets too low, so that the force will be transmitted efficiently from roller to cam. This is addressed by incorporating a transmission index into the motion specification in the synthesis process. Consequently, in this method we can specify any arbitrary motion within a permissible rone, such that the transmission index is higher than the specified minimum value. Single-dwell, double-dwell and a long hesitation motion are used as examples to demonstrate the ffectiveness of the design method. Force closure using an optimally located spring and quasi-kinetostatic analysis are also discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.

Turnout Intention and Social Networks

How can networking affect the turnout in an election? We present a simple model to explain turnout as a result of a dynamic process of formation of the intention to vote within Erdös-Renyi random networks. Citizens have fixed preferences for one of two parties and are embedded in a given social network. They decide whether or not to vote on the basis of the attitude of their immediate contacts. They may simply follow the behavior of the majority (followers) or make an adaptive local calculus of voting (Downsian behavior). So they either have the intention of voting when the majority of their neighbors are willing to vote too, or they vote when they perceive in their social neighborhood that elections are "close". We study the long run average turnout, interpreted as the actual turnout observed in an election. Depending on the combination of values of the two key parameters, the average connectivity and the probability of behaving as a follower or in a Downsian fashion, the system exhibits monostability (zero turnout), bistability (zero turnout and either moderate or high turnout) or tristability (zero, moderate and high turnout). This means, in particular, that for a wide range of values of both parameters, we obtain realistic turnout rates, i.e. between 50% and 90%.

Proceso de internacionalización y estrategia de marketing de Batz Sociedad Cooperativa

El presente trabajo analiza el proceso de internacionalización y la estrategia de marketing llevados a cabo por la cooperativa industrial vizcaína Batz. Mediante ello se ha tratado de evaluar la forma en que ha actuado la empresa en relación a ambos aspectos a lo largo de su trayectoria. El trabajo comienza con unos breves apuntes dedicados a presentar algunos aspectos teóricos sobre la internacionalización de empresas y las estrategias de marketing. Una vez analizados los rasgos principales de la cooperativa objeto de estudio en el segundo capítulo, los capítulos tercero y cuarto abordan el análisis del proceso de internacionalización y la estrategia de marketing seguidos por la empresa, respectivamente. Del estudio realizado se concluye que la empresa ha seguido un proceso de internacionalización en el que destaca la coherencia entre los retos planteados en cada momento y las respuestas dadas, las cuales han sido acompañadas y respaldadas por decisiones de marketing acertadas.

Aplicación de ROS: Sistema Operativo Robótico sobre Lego Mindstorms NXT

[ES]El objetivo de este Trabajo de Fin de Grado es estudiar el programa llamado ROS, un entorno para la programación de robots. Proporciona una serie de herramientas, librerías, drivers… que facilitan en gran medida la programación de sistemas robóticos. Para realizar este estudio se utilizará ROS para crear una aplicación para un robot LEGO Mindstorms NXT. Estos robots son pequeños y versátiles, y son adecuados para la investigación. La aplicación que se llevará a cabo será un seguidor de línea, un robot capaz de seguir una pista dibujada sobre una superficie de otro color. Para programar la aplicación, se utilizarán en la medida de lo posible las herramientas proporcionadas por ROS. De esta manera, se espera alcanzar una mayor comprensión de ROS y de su funcionamiento, con sus fortalezas y sus debilidades.

Experimental evidence of flutter and divergence instabilities induced by dry friction

Flutter and divergence instabilities have been advocated to be possible in elastic structures with Coulomb friction, but no direct experimental evidence has ever been provided. Moreover, the same types of instability can be induced by tangential follower forces, but these are commonly thought to be of extremely difficult, if not impossible, practical realization. Therefore, a clear experimental basis for flutter and divergence induced by friction or follower-loading is still lacking. This is provided for the first time in the present article, showing how a follower force of tangential type can be realized via Coulomb friction and how this, in full agreement with the theory, can induce a blowing-up vibrational motion of increasing amplitude (flutter) or an exponentially growing motion (divergence). In addition, our results show the limits of a treatment based on the linearized equations, so that nonlinearities yield the initial blowing-up vibration of flutter to reach eventually a steady state. The presented results give full evidence to potential problems in the design of mechanical systems subject to friction, open a new perspective in the realization of follower-loading systems and of innovative structures exhibiting 'unusual' dynamical behaviors. © 2011 Elsevier Ltd.

两种线程池的实现和性能评价

线程池被广泛地应用在中间件如Web应用服务器、事务监控器等的实现中。实现线程池的方法主要有半同步/半异步(Half-Sync/Half-Asyn)模式和领导者/跟随者(Leader/Follower)模式。实现了这两种线程池,从理论上分析了它们的性能,并进行了性能实验。实验数据表明Leader/Follower模式具有较高的性能优势。

A one-way MOS analog switch

In this paper, a one-way NMOS analog switch featuring a low plug-in consumption is presented. The performances of analog switch, especially the performances of source follower are simulated under different conditions with PSPICE. Simulation results and factors affecting the deviation between input and output are analyzed, some advice on how to reduce the deviation between input and output is given. Ar the end of the paper, voltage relationship between input and output of the analog switch is obtained. Function of first degree, Vout = kVin + V0, is used to approximate the voltage relationship. The simulation results anti the value achieved from the approximation equation are given as well.

多对一供应链收入共享契约中的采购优化

为研究多对一供应链结构中基于契约协商的采购优化策略问题及其对改善供应链绩效的影响,针对该供应链结构中零售商具有内生保留利润的特点,建立了以制造商为主方、零售商为从方的Stackelberg主从对策模型;给出了在制造商提供契约条款的对称博弈中,零售商采购策略存在唯一最优解、制造商间的博弈存在唯一对称纳什均衡最优解的证明;讨论了收入共享契约下分散供应链决策同集中供应链决策的关系,限定了该结构中供应链协调的条件。最后,通过仿真实验分析验证了契约参数及产品的可替代性对供应链绩效的影响。

多移动机器人主—从编队控制研究

多机器人编队控制是多移动机器人自主协调控制领域中的关键技术。这篇论文在基于局部测量和局部控制的框架下，研究具有主—从跟踪结构的移动机器人编队系统的建模和控制问题。论文的主要研究内容可分为如下三个方面：针对一阶运动学和二阶运动学模型的编队控制器设计；将基于运动学的编队控制器与基于从机器人动力学的载体控制器相结合；将队形反馈信息融入主机器人的轨迹跟踪控制器，给出了主机器人的协调编队控制器的设计。具体内容可概括为如下几个方面：（1）以主—从机器人编队中从机器人的固联视觉传感器的观察角度出发，用视觉等效相对速度建立了主—从机器人编队系统的运动学模型。同时，在该模型中考虑了由视觉传感器时间延迟所导致的模型误差对编队系统的影响。在基于该运动学模型的编队控制器的设计过程中结合了基于从机器人载体的动力学的速度控制器。这种基于编队运动学和机器人本体动力学相结合的控制方法，避免了以往文献中速度跟踪响应无限快的假设。使得对编队控制系统的分析和设计更趋于实际。用Lyapunov稳定性理论证明了主—从机器人之间的编队跟踪误差和从机器人载体的速度跟踪误差都可以收敛到零--整体系统的渐进稳定性。（2）结合上述编队控制律，提出了一种编队系统中从机器人主动避障的方法，该方法能够令从机器人在避开动态障碍物的同时，与主机器人保持期望的相对距离或相对方位。这种方法的实质是由主机器人来引导从机器人的避障过程，主—从机器人之间通过相互协作来完成避障任务。这就使得从机器人即使在避障的过程中也能够与主机器人保持部分的协作。这样，当避障过程结束之后，主—从机器人之间可以迅速的恢复队形。（3）导出了一种新的基于相对运动学的主—从跟踪系统的二阶运动学模型。利用这个运动学模型，我们设计了一个由反馈线性化控制器和一个滑模控制器组成的复合控制器，来实现机器人主—从跟踪系统的控制。运用Lyapunov理论证明了所设计的队形控制器能够镇定包括内部动力学系统在内的整个主—从跟踪系统。同时，该控制器使得队形跟踪系统对主机器人的绝对加速度具有鲁棒性。此外，在前述控制器的基础上，我们设计了一个自适应队形控制器来处理主—从跟踪系统中存在的参数不确定性。（4）将上述基于二阶运动学的编队控制方法与从机器人的载体动力学控制系统相结合，给出了将编队运动学与载体动力学相结合的编队控制器设计方法。同时，针对载体动力学模型中含有参数不确定性的情况，设计了基于自适应控制方法的编队控制器。同时，利用Lyapunov理论给出了保证整体系统稳定性的条件。（5）基于主—从编队系统的二阶运动学模型，将队形反馈信息引入主机器人的轨迹跟踪控制器中，形成了主—从机器人协调编队的辅助控制律。该辅助控制律所对应的虚拟协调力通过主机器人的动力学系统形成了真实的协作控制力。该控制器与前一章中的从机器人的鲁棒编队跟踪控制器共同形成了主—从编队系统的协调控制器。应用Lyapunov理论给出了在主—从机器人分别采用协调编队控制器的作用下所形成的闭环系统的稳定性条件。进一步地，我们将主机器人的面向轨迹跟踪任务的协调控制器转换为面向路径跟踪任务的协调控制器。分别利用了基于MATLAB的仿真平台和实际的多移动机器人系统，验证了以上各方法的有效性。

基于时延Petri网的多UUV系统的任务分配策略

针对多水下机器人(unmanned underwater vehicle,UUV)系统动态任务分配问题展开研究,在对系统的体系结构和任务分配机制进行分析的基础上,利用时延 Petri 网理论对系统的任务分配进行建模,提出了一种新的任务分配策略:群体协调层采用集中式任务分配策略,由主 UUV 将任务实时下达给各从 UUV;监控规划层采用基于适应度的分布式任务分配方式,充分发挥各异构 UUV 自身的智能。仿真结果验证了模型的合理性和任务分配策略的有效性。

基于跟随领航者法的多UUV队形控制方法研究

本文主要研究基于跟随领航者法的多 UUV(unmanned underwater vehicle)队形控制。在 UUV 载体坐标系下建立系统的运动学模型,该模型是对笛卡尔坐标系下的运动学模型的改进,避免了极坐标系下奇异点的出现。该模型经过输入输出反馈线性化,获得稳定的队形控制器。同时,为了缩小队形控制律中的控制参数的调整范围,本文提出了辅助算法,在此基础上分析参数的有效范围。将队形控制律在多 UUV 数字仿真平台上验证,证实了改进的运动学模型和控制律的有效性。

空间对接缓冲试验台对接环重力平衡技术

在空间对接机构地面缓冲实验平台上,为了模拟空间失重状态,研制了一种高精度、高响应速度的主动对接环重力平衡装置。介绍了对接环重力平衡装置的机构原理。对对接过程随动装置的随动性对系统的干扰进行了详细分析。进行了重力平衡器相关实验,从实验数据和理论分析可以得出:所设计的重力平衡装置完全满足对摩擦阻力和惯性阻力设计指标的要求,重力平衡达到1.1%的精度。

Trust, leadership and economic necessity in post-compulsory education

Trust is a complex concept that has increasingly been debated in academic research (Kramer and Tyler, 1996). Research on 'trust and leadership' (Caldwell and Hayes, 2007) has suggested, unsurprisingly, that leadership behaviours influence 'follower' perceptions of leaders' trustworthiness. The development of 'ethical stewardship' amongst leaders may foster high trust situations (Caldwell, Hayes, Karri and Bernal, 2008), yet studies on the erosion of teacher professionalism in UK post-compulsory education have highlighted the distrust that arguably accompanies 'new managerialism', performativity and surveillance within a climate of economic rationalisation established by recent deterministic skills-focused government agendas for education (Avis, 2003; Codd, 1999, Deem, 2004, DFES, 2006). Given the shift from community to commercialism identified by Collinson and Collinson (2005) in a global economic environment characterised by uncertainty and rapid change, trust is, simultaneously, increasingly important and progressively both more fragile and limited in a post compulsory education sector dominated by skills-based targets and inspection demands. Building on such prior studies, this conference paper reports on the analysis of findings from a 2007-8 funded research study on 'trust and leadership' carried out in post-compulsory education. The research project collected and analysed case study interview and survey data from the lifelong learning sector, including selected tertiary, further and higher education (FE and HE) institutions. We interviewed 18 UK respondents from HE and FE, including principals, middle managers, first line managers, lecturers and researchers, supplementing and cross-checking this with a small number of survey responses (11) on 'trust and leadership' and a larger number (241) of survey responses on more generalised leadership issues in post-compulsory education. A range of facilitators and enablers of trust and their relationship to leadership were identified and investigated. The research analysed the ways in which interviewees defined the concept of 'trust' and the extent to which they identified that trust was a mediating factor affecting leadership and organisational performance. Prior literature indicates that trust involves a psychological state in which, despite dependency, risk and vulnerability, trustors have some degree of confident expectation that trustees will behave in benevolent rather than detrimental ways. The project confirmed the views of prior researchers (Mayer, Davis and Schoorman, 1995) that, since trust inevitably involves potential betrayal, estimations of leadership 'trustworthiness' are based on followers' cognitive and affective perceptions of the reliability, competence, benevolence and reputation of leaders. During the course of the interviews it also became clear that some interviewees were being managed in more or less transaction-focused, performative, audit-dominated cultures in which trust was not regarded as particularly important: while 'cautious trust' existed, collegiality flourished only marginally in small teams. Economic necessity and survival were key factors influencing leadership and employee behaviours, while an increasing distance was reported between senior managers and their staff. The paper reflects on the nature of the public sector leadership and management environment in post-compulsory education reported by interviewees and survey respondents. Leadership behaviours to build trust are recommended, including effective communication, honesty, integrity, authenticity, reliability and openness. It was generally felt that building trust was difficult in an educational environment largely determined by economic necessity and performativity. Yet, despite this, the researchers did identify a number of examples of high trust leadership situations that are worthy of emulation.

'Not Forsworn with Pink Ribbons': Hannah More, Thomas De Quincey, and the Literature of Power

De Quincey's conception of the literature of "power" as opposed to that of "knowledge," has proved to be one of the most influential of romantic theories of literature, playing no small part in the canonization of Wordsworth. De Quincey's early acquaintance with the Lyrical Ballads was made through the Evangelical circles of his mother, who was a follower of Hannah More and a member of the Clapham sect. In later years, however, De Quincey repudiated his early Evangelical upbringing and wrote quite scathingly of the literary pretensions of Hannah More. This paper attempts to uncover the revisionary nature of De Quincey's later reminiscences of More and to indicate thereby the covert influence of Evangelical thinking on his literary theorizing. Far from absolving literature of politics, however, colonialist and nationalist imperatives typical of Evangelical thinking may be seen to operate within the spiritualized and aesthetic sphere to which literary power is arrogated by De Quincey.

From 'trailing wives' to the emergence of a 'trailing husbands' phenomenon: Retirement migration to rural areas

Migration and gender studies have focused on economically active heterogeneous couples and traditionally highlight a dominant male role in migration decision-making. The female partner is commonly portrayed as a 'trailing wife' or 'trailing mother' with the move found to have a negative effect on her employment prospects. Much less is known about if or how the balance of power shifts between husbands and wives when employment or career-motivated moves are removed from the decision-making process. This is analysed with reference to retirement migration to rural areas of the UK and involved interviews with both partners present. For this cohort of retired couples, and in common with the literature, migration during economically active life course stages demonstrates strong 'trailing wife' and 'trailing mother' tendencies. The male's decision to retire signalled the commencement of a retirement life course stage for the couple. However, in contrast to the earlier male dominated decision-making, retirement migration saw the emergence of a 'trailing husband' phenomenon. Wives appear to adapt most successfully to the new rural environment while many husbands found it difficult to adjust (at least initially) to the multiple life changes: moving from largely urban areas to a rural setting alongside exiting the workforce. The findings suggest that the role of leader/ follower changed during the course of these couples' lives together and in relation to their reasons for moving.