Civil rights movement

The civil rights movement was a nonviolent social movement and campaign from 1954 to 1968 in the United States to abolish legalized racial segregation, discrimination, and disenfranchisement in the country. The movement had its origins in the Reconstruction era during the late 19th century and had its modern roots in the 1940s, although the movement made its largest legislative gains in the 1960s after years of direct actions and grassroots protests. The social movement's major nonviolent resistance and civil disobedience campaigns eventually secured new protections in federal law for the civil rights of all Americans. After the American Civil War and the subsequent abolition of slavery in the 1860s, the Reconstruction Amendments to the United States Constitution granted emancipation and constitutional rights of citizenship to all African Americans, most of whom had recently been enslaved. For a short period of time, African-American men voted and held political office, but as time

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Reflexive stability control framework for humanoid robots

Tadej Petric

In this paper we propose a general control framework for ensuring stability of humanoid robots, determined through a normalized zero-moment-point (ZMP). The proposed method is based on the modified prioritized kinematic control, which allows smooth and continuous transition between priorities. This, as long as the selected criterion is met, allows arbitrary joint movement of a robot without any regard of the consequential movement of the ZMP. On the other hand, it constrains the movement when the criterion approaches a critical condition. The critical condition thus triggers a reflexive, subconscious behavior, which has a higher priority than the desired, conscious movement. The transition between the two is smooth and reversible. Furthermore, the switching is encapsulated in a single modified prioritized task control equation. We demonstrate the properties of the algorithm on two human-inspired robots developed in our laboratory; a human-inspired leg-robot used for imitating human movement and a skiing robot.

2013

Motion capture and reinforcement learning of dynamically stable humanoid movement primitives

Tadej Petric

Direct transfer of human motion trajectories to humanoid robots does not result in dynamically stable robot movements due to the differences in human and humanoid robot kinematics and dynamics. We developed a system that converts human movements captured by a low-cost RGB-D camera into dynamically stable humanoid movements. The transfer of human movements occurs in real-time. As need arises, the developed system can smoothly transition between unconstrained movement imitation and imitation with balance control, where movement reproduction occurs in the null space of the balance controller. The developed balance controller is based on an approximate model of the robot dynamics, which is sufficient to stabilize the robot during on-line imitation. However, the resulting movements cannot be guaranteed to be optimal because the model of the robot dynamics is not exact. The initially acquired movement is therefore subsequently improved by model-free reinforcement learning, both with respect to the accuracy of reproduction and balance control. We present experimental results in simulation and on a real humanoid robot.

IEEE2013

Hammering Does Not Fit Fitts' Law

Auke Ijspeert, Tadej Petric, Cole Stewart Simpson

While movement is essential to human wellbeing, we are still unable to reproduce the deftness and robustness of human movement in automatons or completely restore function to individuals with many types of motor impairment. To better understand how the human nervous system plans and controls movements, neuromechanists employ simple tasks such as upper extremity reaches and isometric force tasks. However, these simple tasks rarely consider impacts and may not capture aspects of motor control that arise from real-world complexity. Here we compared existing models of motor control with the results of a periodic targeted impact task extended from Bernstein's seminal work: hammering a nail into wood. We recorded impact forces and kinematics from 10 subjects hammering at different frequencies and with hammers with different physical properties (mass and face area). We found few statistical differences in most measures between different types of hammer, demonstrating human robustness to minor changes in dynamics. Because human motor control is thought to obey optimality principles, we also developed a feedforward optimal simulation with a neuromechanically inspired cost function that reproduces the experimental data. However, Fitts' Law, which relates movement time to distance traveled and target size, did not match our experimental data. We therefore propose a new model in which the distance moved is a logarithmic function of the time to move that yields better results (R-2 >= 0.99 compared to R-2 >= 0.88). These results support the argument that humans control movement in an optimal way, but suggest that Fitts' Law may not generalize to periodic impact tasks.

Frontiers Research Foundation2017

African Americans

African Americans (also referred to as Afro-Americans or Black Americans) are an ethnic group consisting of Americans with partial or total ancestry from any of the black racial groups of Africa. The

United States

The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America and consisting of 50 states, a federal distr

Democratic Party (United States)

The Democratic Party is one of two major contemporary political parties in the United States. Founded in 1828, it was predominantly built by Martin Van Buren, who assembled politicians in every state

BIO-311: Neuroscience

The course starts with fundamentals of electrical - and chemical signaling in neurons. Students then learn how neurons in the brain receive and process sensory information, and how other neurons control the behavior of an animal. Furthermore, memory, learning, and brain disorders will be introduced.

PHYS-100: Advanced physics I (mechanics)

La Physique Générale I (avancée) couvre la mécanique du point et du solide indéformable. Apprendre la mécanique, c'est apprendre à mettre sous forme mathématique un phénomène physique, en modélisant la situation et appliquant les lois de la physique.