Dutch Robotics 2011 adult-size team description

This document presents the 2011 edition of the team Dutch Robotics from The Netherlands. Our team gathers three Dutch technical universities, namely Delft University of Technology, Eindhoven University of Technology and University of Twente, and the commercial company Philips. We contribute an adult-size humanoid robot TUlip, which is designed based on theory of the limit cycle walking developed in our earlier research. The key of our theory is that stable periodic walking gaits can be achieved even without high-bandwidth robot position control. Our control approach is based on simultaneous position and force control. For accurate force control, we make use of the Series Elastic Actuation. The control software of TUlip is based on the Darmstadt’s RoboFrame, and it runs on a PC104 computer with Linux Xenomai. The vision system consists of two wide-angle cameras, each interfaced with a dedicated Blackfin processor running vision algorithms, and a wireless networking interface

Dutch Robotics 2010 adult-size team description

This document presents the 2010 edition of the team Dutch Robotics from The Netherlands. Our team gathers three Dutch technical universities, namely Delft University of Technology, Eindhoven University of Technology and University of Twente, and the commercial company Philips. We contribute an adult-size humanoid robot TUlip, which is designed based on theory of the limit cycle walking developed in our earlier research. The key of our theory is that stable periodic walking gaits can be achieved even without high-bandwidth robot position control. Our control approach is based on simultaneous position and force control. For accurate force control, we make use of the Series Elastic Actuation. The control software of TUlip is based on the Darmstadt’s RoboFrame, and it runs on a PC104 computer with Linux Xenomai. The vision system consists of two wide-angle cameras, each interfaced with a dedicated Blackfin processor running vision algorithms, and a wireless networking interface

Transition from Persistent to Anti-Persistent Correlations in Postural Sway Indicates Velocity-Based Control

The displacement of the center-of-pressure (COP) during quiet stance has often been accounted for by the control of COP position dynamics. In this paper, we discuss the conclusions drawn from previous analyses of COP dynamics using fractal-related methods. On the basis of some methodological clarification and the analysis of experimental data using stabilogram diffusion analysis, detrended fluctuation analysis, and an improved version of spectral analysis, we show that COP velocity is typically bounded between upper and lower limits. We argue that the hypothesis of an intermittent velocity-based control of posture is more relevant than position-based control. A simple model for COP velocity dynamics, based on a bounded correlated random walk, reproduces the main statistical signatures evidenced in the experimental series. The implications of these results are discussed

Non-linear stimulus-response behavior of the human stance control system is predicted by optimization of a system with sensory and motor noise

We developed a theory of human stance control that predicted (1) how subjects re-weight their utilization of proprioceptive and graviceptive orientation information in experiments where eyes closed stance was perturbed by surface-tilt stimuli with different amplitudes, (2) the experimentally observed increase in body sway variability (i.e. the “remnant” body sway that could not be attributed to the stimulus) with increasing surface-tilt amplitude, (3) neural controller feedback gains that determine the amount of corrective torque generated in relation to sensory cues signaling body orientation, and (4) the magnitude and structure of spontaneous body sway. Responses to surface-tilt perturbations with different amplitudes were interpreted using a feedback control model to determine control parameters and changes in these parameters with stimulus amplitude. Different combinations of internal sensory and/or motor noise sources were added to the model to identify the properties of noise sources that were able to account for the experimental remnant sway characteristics. Various behavioral criteria were investigated to determine if optimization of these criteria could predict the identified model parameters and amplitude-dependent parameter changes. Robust findings were that remnant sway characteristics were best predicted by models that included both sensory and motor noise, the graviceptive noise magnitude was about ten times larger than the proprioceptive noise, and noise sources with signal-dependent properties provided better explanations of remnant sway. Overall results indicate that humans dynamically weight sensory system contributions to stance control and tune their corrective responses to minimize the energetic effects of sensory noise and external stimuli

A rigorous model of reflex function indicates that position and force feedback are flexibly tuned to position and force tasks

This study aims to quantify the separate contributions of muscle force feedback, muscle spindle activity and co-contraction to the performance of voluntary tasks (“reduce the influence of perturbations on maintained force or position”). Most human motion control studies either isolate only one contributor, or assume that relevant reflexive feedback pathways during voluntary disturbance rejection tasks originate mainly from the muscle spindle. Human ankle-control experiments were performed, using three task instructions and three perturbation characteristics to evoke a wide range of responses to force perturbations. During position tasks, subjects (n = 10) resisted the perturbations, becoming more stiff than when being relaxed (i.e., the relax task). During force tasks, subjects were instructed to minimize force changes and actively gave way to imposed forces, thus becoming more compliant than during relax tasks. Subsequently, linear physiological models were fitted to the experimental data. Inhibitory, as well as excitatory force feedback, was needed to account for the full range of measured experimental behaviors. In conclusion, force feedback plays an important role in the studied motion control tasks (excitatory during position tasks and inhibitory during force tasks), implying that spindle-mediated feedback is not the only significant adaptive system that contributes to the maintenance of posture or force

The political geography of religious radicalism. A compendium of selected case studies from around the globe

Religion has neither gone away nor remained irrelevant in our world today. There is no day that we do not hear news about religion in the media. The news we hear about religion and violence, however, appears to dominate the headlines. Although the history of religions and violence is not a new one, since September 11, 2001 there has been a growing concern about religious extremism and terrorism. At the same time, there is a corresponding interest in the subject of religion and violence among many disciplines. In the course GEO-83 “Political Geography of Religious Radicalism”, we offered students an excursion into the ambivalent world of religion and conflict through an exploration of different theoretical perspectives and approaches, case studies, seminal and class discussions and extensive literature review. The unique angle of interrogation that political geography offers in terms of the spatial dimensions and the power relations between different actors as well as the discursive aspects of interreligious conflicts and extremism has proved very valuable in generating insights on this subject matter. This volume is an attempt by students of the M.A. “Human Geography – Global Studies” programme of the University of Tübingen to demonstrate acquaintance with the approach of political geography to the study of religious violence and extremism. The students took on some of the most challenging conflicts and religious insurgencies confronting the world and offered insights using diverse theoretical and analytical frameworks. The analysis contained in each chapter was based on secondary data. Thus, limitations are set based on the availability of and access to data. Given the contested nature of religious conflicts and extremism, the reader is invited to consider all the articles in this volume as primarily an academic exercise with no intention to promote a certain narrative or to take sides. Knowledge is always incremental. Therefore, what is presented here is intended to increase our understanding of the phenomenon and to stimulate further research and efforts at finding solutions to the various conflicts. No doubt, this exercise has exposed the students to the rigour of scientific writing. This experience will remain invaluable to them in their continuing academic pursuit as well as in their future endeavours. The lecturers also found this experience to be highly rewarding. The process was quite daunting, but the commitment and the dedication of the students paid off

Bayesian Integration and Non-Linear Feedback Control in a Full-Body Motor Task

A large number of experiments have asked to what degree human reaching movements can be understood as being close to optimal in a statistical sense. However, little is known about whether these principles are relevant for other classes of movements. Here we analyzed movement in a task that is similar to surfing or snowboarding. Human subjects stand on a force plate that measures their center of pressure. This center of pressure affects the acceleration of a cursor that is displayed in a noisy fashion (as a cloud of dots) on a projection screen while the subject is incentivized to keep the cursor close to a fixed position. We find that salient aspects of observed behavior are well-described by optimal control models where a Bayesian estimation model (Kalman filter) is combined with an optimal controller (either a Linear-Quadratic-Regulator or Bang-bang controller). We find evidence that subjects integrate information over time taking into account uncertainty. However, behavior in this continuous steering task appears to be a highly non-linear function of the visual feedback. While the nervous system appears to implement Bayes-like mechanisms for a full-body, dynamic task, it may additionally take into account the specific costs and constraints of the task

Bursts and Isolated Spikes Code for Opposite Movement Directions in Midbrain Electrosensory Neurons

Directional selectivity, in which neurons respond strongly to an object moving in a given direction but weakly or not at all to the same object moving in the opposite direction, is a crucial computation that is thought to provide a neural correlate of motion perception. However, directional selectivity has been traditionally quantified by using the full spike train, which does not take into account particular action potential patterns. We investigated how different action potential patterns, namely bursts (i.e. packets of action potentials followed by quiescence) and isolated spikes, contribute to movement direction coding in a mathematical model of midbrain electrosensory neurons. We found that bursts and isolated spikes could be selectively elicited when the same object moved in opposite directions. In particular, it was possible to find parameter values for which our model neuron did not display directional selectivity when the full spike train was considered but displayed strong directional selectivity when bursts or isolated spikes were instead considered. Further analysis of our model revealed that an intrinsic burst mechanism based on subthreshold T-type calcium channels was not required to observe parameter regimes for which bursts and isolated spikes code for opposite movement directions. However, this burst mechanism enhanced the range of parameter values for which such regimes were observed. Experimental recordings from midbrain neurons confirmed our modeling prediction that bursts and isolated spikes can indeed code for opposite movement directions. Finally, we quantified the performance of a plausible neural circuit and found that it could respond more or less selectively to isolated spikes for a wide range of parameter values when compared with an interspike interval threshold. Our results thus show for the first time that different action potential patterns can differentially encode movement and that traditional measures of directional selectivity need to be revised in such cases