Faculty Profiles - OHIRA Toru

Papers - OHIRA Toru

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Random Walks with Delay Reviewed

OHIRA Toru

Vol. 32 ( 1 ) page： 55-57 2013.3

Ranking and Winning in Tournaments Reviewed

TOKUYAMA Kichi, MAEMURA Ryuta, YOKOUCHI Kengo, OHIRA Toru

Vol. 19th page： 41-43 2013

Delayed pursuit-escape as a model for virtual stick balancing Reviewed

MILTON John G, FUERTE Andres, BELAIR Christophe, LIPPAI Joshua, KAMIMURA Atsushi, OHIRA Toru

Nonlinear Theory Its Appl IEICE (Web) Vol. 4 ( 2 ) page： 129-137 (J-STAGE)-137 - 137 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

The process of pursuit and escape underlies many biological phenomena ranging from predator-prey interactions, combat and sporting activities. Time delays, &tau;, arise as a consequence of the time taken to identify the opponent, formulate a strategy, and then act upon it. Here we consider virtual stick balancing (VSB) as a delayed pursuit-escape task. The movements of the target in VSB are programmed to resemble those of balancing a stick at the fingertip. A model of delayed pursuit-escape is developed by assuming that the target movements are governed by a simple random walk and the movements of the pursuer by a delayed random walk biased towards the target when &tau;=0. When &tau; > 0 the movements can become transiently biased away from the target. The model reproduces the oscillatory dynamics and statistical properties of VSB. For both model and VSB, transients occur in which the pursuer moves inappropriately causing increases in tracking error. The presence of a signature, or trigger, for impending escape suggests the possibility that escapes can be predicted before they occur.

DOI： 10.1587/nolta.4.129

J-GLOBAL

Group chase and escape with conversion from targets to chasers Reviewed

Ryosuke Nishi, Atsushi Kamimura, Katsuhiro Nishinari, Toru Ohira

PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS Vol. 391 ( 1-2 ) page： 337 - 342 2012.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We study the effect of converting caught targets into new chasers in the context of the recently proposed 'group chase and escape' problem. Numerical simulations have shown that this conversion can substantially reduce the lifetimes of the targets when a large number of them are initially present. At the same time, it also leads to a non-monotonic dependence on the initial number of targets, resulting in the existence of a maximum lifetime. As a counter-effect for this conversion, we further introduce self-multiplying abilities to the targets. We found that the longest lifetime exists when a suitable combination of these two effects is created. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physa.2011.08.010

Web of Science

Collective Motions of Chases and Escapes Reviewed

Ohira Toru

PROCEEDINGS OF THE SEVENTEENTH INTERNATIONAL SYMPOSIUM ON ARTIFICIAL LIFE AND ROBOTICS (AROB 17TH '12) page： 538-540 2012

Collective Motions of Chases and Escapes Reviewed

Toru Ohira

PROCEEDINGS OF THE SEVENTEENTH INTERNATIONAL SYMPOSIUM ON ARTIFICIAL LIFE AND ROBOTICS (AROB 17TH '12) page： 538 - 540 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ALIFE ROBOTICS CO, LTD

We discuss a new take on an old mathematical problem of chase and escape. We consider one group chases another, called "group chase and escape", by presenting simple models. We have found that even a simple model can exhibit rich and complex behavior. The model has been extended to investigate the effects of (1) fluctuations in chasing and escaping movements, (2) reaction delays when chasing, and (3) the conversion of caught escapees to new chasers. We show that these effects can add further complexity and result in unexpected behaviors.

Web of Science

Vulnerability to paroxysmal oscillations in delayed neural networks: A basis for nocturnal frontal lobe epilepsy? Reviewed

Austin Quan, Ivan Osorio, Toru Ohira, John Milton

CHAOS Vol. 21 ( 4 ) page： 047512 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Resonance can occur in bistable dynamical systems due to the interplay between noise and delay (tau) in the absence of a periodic input. We investigate resonance in a two-neuron model with mutual time-delayed inhibitory feedback. For appropriate choices of the parameters and inputs three fixed-point attractors co-exist: two are stable and one is unstable. In the absence of noise, delay-induced transient oscillations (referred to herein as DITOs) arise whenever the initial function is tuned sufficiently close to the unstable fixed-point. In the presence of noisy perturbations, DITOs arise spontaneously. Since the correlation time for the stationary dynamics is similar to tau, we approximated a higher order Markov process by a three-state Markov chain model by rescaling time as t -> 2s tau, identifying the states based on whether the sub-intervals were completely confined to one basin of attraction (the two stable attractors) or straddled the separatrix, and then determining the transition probability matrix empirically. The resultant Markov chain model captured the switching behaviors including the statistical properties of the DITOs. Our observations indicate that time-delayed and noisy bistable dynamical systems are prone to generate DITOs as switches between the two attractors occur. Bistable systems arise transiently in situations when one attractor is gradually replaced by another. This may explain, for example, why seizures in certain epileptic syndromes tend to occur as sleep stages change. (C) 2011 American Institute of Physics. [doi:10.1063/1.3664409]

DOI： 10.1063/1.3664409

Web of Science

PubMed

Group Chase and Escape Problems Reviewed

KAMIMURA Atsushi, OHIRA Toru

Butsuri Vol. 66 ( 3 ) page： 205-208 - 208 2011.3

A team approach to undergraduate research in biomathematics: Balance control Reviewed

J. Milton, A. Radunskaya, W. Ou, T. Ohira

Mathematical Modelling of Natural Phenomena Vol. 6 page： 260-277 2011.1

Language：English Publishing type：Research paper (scientific journal)

The question, how does an organism maintain balance? provides a unifying theme to introduce undergraduate students to the use of mathematics and modeling techniques in biological research. The availability of inexpensive high speed motion capture cameras makes it possible to collect the precise and reliable data that facilitates the development of relevant mathematical models. An in-house laboratory component ensures that students have the opportunity to directly compare prediction to observation and motivates the development of projects that push the boundaries of the subject. The projects, by their nature, readily lend themselves to the formation of inter-disciplinary student research teams. Thus students have the opportunity to learn skills essential for success in today's workplace including productive team work, critical thinking, problem solving, project management, and effective communication. © EDP Sciences, 2011.

DOI： 10.1051/mmnp/20116614

Scopus

Stochastic Resonance with Group Chase and Escape Reviewed

Atsushi Kamimura, Shigenori Matsumoto, Tomoaki Nogawa, Nobuyasu Ito, Toru Ohira

2011 21ST INTERNATIONAL CONFERENCE ON NOISE AND FLUCTUATIONS (ICNF) page： 200 - 203 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

We describe a simple model developed under the new idea of one group chasing another called, "group chase and escape". We will demonstrate that even a simple model can exhibit rather rich and complex behavior. In particular, we show that the appropriate level of fluctuation in each step of the process for chase and escape can minimize the time taken for the entire catch.

Web of Science

Visuomotor tracking tasks with delayed pursuit and escape Reviewed

John Milton, Joshua Lippai, Rachel Bellows, Andrew Blomberg, Atsushi Kamimura, Toru Ohira

Proceedings of the ASME Design Engineering Technical Conference Vol. 4 page： 419 - 425 2011

Language：English Publishing type：Research paper (international conference proceedings)

Virtual stick balancing (VSB) is a manual visuomotor tracking task that involves interplay between a human and a computer in which the movements are programmed to resemble those of balancing a stick at the fingertip. Since time delays and random perturbations ("noise") are intrinsic properties of this task, we modeled VSB as a delayed pursuit-escape process: the target movements are described by a simple random walk and those movements controlled by the computer mouse by a delayed random walk biased towards the target. As subjects become more skilled, a stereotyped and recurring pursuit-escape pattern develops in which the mouse pursues the target until it overtakes it, causing the target to move in a different direction, followed, after a lag, by the pursing mouse. The delayed pursuit-escape random walk model captured the qualitative nature of this tracking task and provided insights into why this tracking task always fails at some point in time, even for the most expert subjects. Copyright © 2011 by ASME.

DOI： 10.1115/DETC2011-47312

Scopus

Stochastic Resonance with Group Chase and Escape Reviewed

Kamimura Atsushi, Matsumoto Shigenori, Nogawa Tomoaki, Ito Nobuyasu, Ohira Toru

2011 21ST INTERNATIONAL CONFERENCE ON NOISE AND FLUCTUATIONS (ICNF) page： 200-203 2011

Dynamical aspect of group chase and escape Reviewed

Shigenori Matsumoto, Tomoaki Nogawa, Atsushi Kamimura, Nobuyasu Ito, Toru Ohira

NON-EQUILIBRIUM STATISTICAL PHYSICS TODAY Vol. 1332 page： 226 - + 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Recently, a new concept is proposed for chasing and evading in crowds, called "group chase and escape" through a simple model. In this model, two kinds of players, chasers and escapees, play tag on a two-dimensional square lattice. Each chaser approaches its nearest escapee. On the other hand, each escapee steps away from its nearest chaser. Although there are no communications within each group, players appear to cooperate among themselves to chase or escape. We found relation between this cooperative behavior and group formations depend on the density of chasers and targets.

DOI： 10.1063/1.3569508

Web of Science

J-GLOBAL

A Team Approach to Undergraduate Research in Biomathematics: Balance Control Reviewed

J. Milton, A. Radunskaya, W. Ou, T. Ohira

MATHEMATICAL MODELLING OF NATURAL PHENOMENA Vol. 6 ( 6 ) page： 260 - 277 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：EDP SCIENCES S A

DOI： 10.1051/mmmp/20116614

Web of Science

Group chase and escape Reviewed

Atsushi Kamimura, Toru Ohira

NEW JOURNAL OF PHYSICS Vol. 12 2010.5

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We describe here a new concept of one group chasing another, called 'group chase and escape', by presenting a simple model. We will show that even a simple model can demonstrate rather rich and complex behavior. In particular, there are cases where an optimal number of chasers exists for a given number of escapees (or targets) to minimize the cost of catching all targets. We have also found an indication of self-organized spatial structures formed by both groups.

DOI： 10.1088/1367-2630/12/5/053013

Web of Science

Resonance with Stochastic Time Reviewed

Toru Ohira

FRONTIERS OF FUNDAMENTAL AND COMPUTATIONAL PHYSICS Vol. 1246 page： 154 - 159 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

We introduce a resonant phenomenon using a model incorporating delay (temporal non-locality) and stochastic time (temporal stochasticity). Although this model is a very simple linear dynamical differential equation, the addition of these elements makes it very rich. As an illustrative example, we describe a human stick balancing experiment that includes added fluctuations. We discuss how these concepts of temporal non-locality and stochasticity could play a role in characterizing biological and physiological systems, as well as in physics.

DOI： 10.1063/1.3460193

Web of Science

Chase and Escape in Groups Reviewed

Atsushi Kamimura, Shigenori Matsumoto, Nobuyasu Ito, Toru Ohira

CELLULAR AUTOMATA Vol. 6350 page： 570 - 579 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPRINGER-VERLAG BERLIN

We study here a recently proposed theme of one group chasing another, called "group chase and escape". Rather rich and complex behavior such as self-organized structures can arise from a model with simple rules. We discuss models with various cases of different speeds between the two groups, search ranges, and motion fluctuations.

DOI： 10.1007/978-3-642-15979-4_62

Web of Science

J-GLOBAL

Delay, noise, and resonance: Human balancing and temporal non-locality Reviewed

Toru Ohira

Artificial Life and Robotics Vol. 15 ( 4 ) page： 436 - 438 2010

Language：English Publishing type：Research paper (scientific journal)

A rather peculiar phenomenon has been observed while a human was balancing a stick on a fingertip. The balancing time improved when the subject moved another object with the other hand. This was particularly so for many subjects with medium stick balancing skills. On the basis of this example, I consider how this seemingly simple task is composed of intricate mixtures of feedback delay, fluctuations, and predictions. I present some simple models of dynamics in which these factors lead to complex behaviors. From these examples, I infer that the concept of "nonlocality" could play an important role in characterizing biological and physiological systems. © 2010 International Symposium on Artificial Life and Robotics (ISAROB).

DOI： 10.1007/s10015-010-0837-0

Scopus

Balancing with Vibration: A Prelude for "Drift and Act" Balance Control Reviewed

John G. Milton, Toru Ohira, Juan Luis Cabrera, Ryan M. Fraiser, Janelle B. Gyorffy, Ferrin K. Ruiz, Meredith A. Strauss, Elizabeth C. Balch, Pedro J. Marin, Jeffrey L. Alexander

PLOS ONE Vol. 4 ( 10 ) page： e7427 2009.10

Language：English Publishing type：Research paper (scientific journal) Publisher：PUBLIC LIBRARY SCIENCE

Stick balancing at the fingertip is a powerful paradigm for the study of the control of human balance. Here we show that the mean stick balancing time is increased by about two-fold when a subject stands on a vibrating platform that produces vertical vibrations at the fingertip (0.001 m, 15-50 Hz). High speed motion capture measurements in three dimensions demonstrate that vibration does not shorten the neural latency for stick balancing or change the distribution of the changes in speed made by the fingertip during stick balancing, but does decrease the amplitude of the fluctuations in the relative positions of the fingertip and the tip of the stick in the horizontal plane, A(x, y). The findings are interpreted in terms of a time-delayed "drift and act" control mechanism in which controlling movements are made only when controlled variables exceed a threshold, i.e. the stick survival time measures the time to cross a threshold. The amplitude of the oscillations produced by this mechanism can be decreased by parametric excitation. It is shown that a plot of the logarithm of the vibration-induced increase in stick balancing skill, a measure of the mean first passage time, versus the standard deviation of the A(x, y) fluctuations, a measure of the distance to the threshold, is linear as expected for the times to cross a threshold in a stochastic dynamical system. These observations suggest that the balanced state represents a complex time-dependent state which is situated in a basin of attraction that is of the same order of size. The fact that vibration amplitude can benefit balance control raises the possibility of minimizing risk of falling through appropriate changes in the design of footwear and roughness of the walking surfaces.

DOI： 10.1371/journal.pone.0007427

Web of Science

PubMed

The time-delayed inverted pendulum: Implications for human balance control Reviewed

John Milton, Juan Luis Cabrera, Toru Ohira, Shigeru Tajima, Yukinori Tonosaki, Christian W. Eurich, Sue Ann Campbell

CHAOS Vol. 19 ( 2 ) page： 026110 2009.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The inverted pendulum is frequently used as a starting point for discussions of how human balance is maintained during standing and locomotion. Here we examine three experimental paradigms of time-delayed balance control: (1) mechanical inverted time-delayed pendulum, (2) stick balancing at the fingertip, and (3) human postural sway during quiet standing. Measurements of the transfer function (mechanical stick balancing) and the two-point correlation function (Hurst exponent) for the movements of the fingertip (real stick balancing) and the fluctuations in the center of pressure (postural sway) demonstrate that the upright fixed point is unstable in all three paradigms. These observations imply that the balanced state represents a more complex and bounded time-dependent state than a fixed-point attractor. Although mathematical models indicate that a sufficient condition for instability is for the time delay to make a corrective movement, tau(n), be greater than a critical delay tau(c) that is proportional to the length of the pendulum, this condition is satisfied only in the case of human stick balancing at the fingertip. Thus it is suggested that a common cause of instability in all three paradigms stems from the difficulty of controlling both the angle of the inverted pendulum and the position of the controller simultaneously using time-delayed feedback. Considerations of the problematic nature of control in the presence of delay and random perturbations ("noise") suggest that neural control for the upright position likely resembles an adaptive-type controller in which the displacement angle is allowed to drift for small displacements with active corrections made only when theta exceeds a threshold. This mechanism draws attention to an overlooked type of passive control that arises from the interplay between retarded variables and noise. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3141429]

DOI： 10.1063/1.3141429

Web of Science

PubMed

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