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Dive into the research topics where Shai Revzen is active.

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Featured researches published by Shai Revzen.


Proceedings of the National Academy of Sciences of the United States of America | 2008

Active tails enhance arboreal acrobatics in geckos.

Ardian Jusufi; Daniel I. Goldman; Shai Revzen; Robert J. Full

Geckos are natures elite climbers. Their remarkable climbing feats have been attributed to specialized feet with hairy toes that uncurl and peel in milliseconds. Here, we report that the secret to the geckos arboreal acrobatics includes an active tail. We examine the tails role during rapid climbing, aerial descent, and gliding. We show that a geckos tail functions as an emergency fifth leg to prevent falling during rapid climbing. A response initiated by slipping causes the tail tip to push against the vertical surface, thereby preventing pitch-back of the head and upper body. When pitch-back cannot be prevented, geckos avoid falling by placing their tail in a posture similar to a bicycles kickstand. Should a gecko fall with its back to the ground, a swing of its tail induces the most rapid, zero-angular momentum air-righting response yet measured. Once righted to a sprawled gliding posture, circular tail movements control yaw and pitch as the gecko descends. Our results suggest that large, active tails can function as effective control appendages. These results have provided biological inspiration for the design of an active tail on a climbing robot, and we anticipate their use in small, unmanned gliding vehicles and multisegment spacecraft.


The Journal of Experimental Biology | 2010

Insects running on elastic surfaces

Andrew J. Spence; Shai Revzen; Justin Seipel; Chris Mullens; Robert J. Full

SUMMARY In nature, cockroaches run rapidly over complex terrain such as leaf litter. These substrates are rarely rigid, and are frequently very compliant. Whether and how compliant surfaces change the dynamics of rapid insect locomotion has not been investigated to date largely due to experimental limitations. We tested the hypothesis that a running insect can maintain average forward speed over an extremely soft elastic surface (10 N m−1) equal to 2/3 of its virtual leg stiffness (15 N m−1). Cockroaches Blaberus discoidalis were able to maintain forward speed (mean ± s.e.m., 37.2±0.6 cm s−1 rigid surface versus 38.0±0.7 cm s−1 elastic surface; repeated-measures ANOVA, P=0.45). Step frequency was unchanged (24.5±0.6 steps s−1 rigid surface versus 24.7±0.4 steps s−1 elastic surface; P=0.54). To uncover the mechanism, we measured the animals centre of mass (COM) dynamics using a novel accelerometer backpack, attached very near the COM. Vertical acceleration of the COM on the elastic surface had a smaller peak-to-peak amplitude (11.50±0.33 m s−2, rigid versus 7.7±0.14 m s−2, elastic; P=0.04). The observed change in COM acceleration over an elastic surface required no change in effective stiffness when duty factor and ground stiffness were taken into account. Lowering of the COM towards the elastic surface caused the swing legs to land earlier, increasing the period of double support. A feedforward control model was consistent with the experimental results and provided one plausible, simple explanation of the mechanism.


Journal of the Royal Society Interface | 2012

Finding the dimension of slow dynamics in a rhythmic system

Shai Revzen; John Guckenheimer

Dynamical systems with asymptotically stable periodic orbits are generic models for rhythmic processes in dissipative physical systems. This paper presents a method for reconstructing the dynamics near a periodic orbit from multivariate time-series data. It is used to test theories about the control of legged locomotion, a context in which time series are short when compared with previous work in nonlinear time-series analysis. The method presented here identifies appropriate dimensions of reduced order models for the deterministic portion of the dynamics. The paper also addresses challenges inherent in identifying dynamical models with data from different individuals.


IEEE Transactions on Automatic Control | 2015

Model Reduction Near Periodic Orbits of Hybrid Dynamical Systems

Samuel A. Burden; Shai Revzen; Shankar Sastry

We show that, near periodic orbits, a class of hybrid models can be reduced to or approximated by smooth continuous-time dynamical systems. Specifically, near an exponentially stable periodic orbit undergoing isolated transitions in a hybrid dynamical system, nearby executions generically contract super exponentially to a constant-dimensional subsystem. Under a non-degeneracy condition on the rank deficiency of the associated Poincaré map, the contraction occurs in finite time regardless of the stability properties of the orbit. Hybrid transitions may be removed from the resulting subsystem via a topological quotient that admits a smooth structure to yield an equivalent smooth dynamical system. We demonstrate reduction of a high-dimensional underactuated mechanical model for terrestrial locomotion, assess structural stability of deadbeat controllers for rhythmic locomotion and manipulation, and derive a normal form for the stability basin of a hybrid oscillator. These applications illustrate the utility of our theoretical results for synthesis and analysis of feedback control laws for rhythmic hybrid behavior.


Automatica | 2012

A control-theoretic approach to disseminating values and overcoming malicious links in wireless networks

Shreyas Sundaram; Shai Revzen; George J. Pappas

We consider a network in which every node has a value that it wishes to disseminate to all other nodes, despite an attack by an adversary that can falsify messages on a number of the links. To achieve this objective, we study a class of linear iterative strategies in which, at each time-step, each node in the network broadcasts a value to its neighbors that is a linear combination of its previous value and the values received from its neighbors. We take the number of unreliable links to be bounded, in that the number of incoming unreliable links to any node plus the total number of other nodes with incoming unreliable links is no greater than some nonnegative integer f . We show that the linear iterative strategy will be resilient to the unreliable links if and only if the vertex connectivity is at least 2 f + 1 . If this condition is satisfied, we show that almost any choice of weights in the linear combinations will suffice to provide resilience. We further show that each node can identify the exact set of unreliable links that directly enter that node, and can communicate this information to the other nodes via the linear strategy.


Biological Cybernetics | 2013

Instantaneous kinematic phase reflects neuromechanical response to lateral perturbations of running cockroaches

Shai Revzen; Samuel A. Burden; Talia Y. Moore; Jean-Michel Mongeau; Robert J. Full

Instantaneous kinematic phase calculation allows the development of reduced-order oscillator models useful in generating hypotheses of neuromechanical control. When perturbed, changes in instantaneous kinematic phase and frequency of rhythmic movements can provide details of movement and evidence for neural feedback to a system-level neural oscillator with a time resolution not possible with traditional approaches. We elicited an escape response in cockroaches (Blaberus discoidalis) that ran onto a movable cart accelerated laterally with respect to the animals’ motion causing a perturbation. The specific impulse imposed on animals (0.50


conference on decision and control | 2011

Dimension reduction near periodic orbits of hybrid systems

Samuel A. Burden; Shai Revzen; Shankar Sastry


Ecology | 2015

Thermal adaptation and phosphorus shape thermal performance in an assemblage of rainforest ants

Michael Kaspari; Natalie A. Clay; Jane Lucas; Shai Revzen; Adam D. Kay; Stephen P. Yanoviak

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Advances in Experimental Medicine and Biology | 2009

Towards Testable Neuromechanical Control Architectures for Running

Shai Revzen; Daniel E. Koditschek; Robert J. Full


Journal of the Royal Society Interface | 2014

Constructing predictive models of human running

Horst Moritz Maus; Shai Revzen; John Guckenheimer; Christian Ludwig; Johann Reger; Andre Seyfarth

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Robert J. Full

University of California

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Shankar Sastry

University of California

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