Faculty Profiles - OHIRA Toru

Papers - OHIRA Toru

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Balancing with positive feedback: the case for discontinuous control Reviewed

John Milton, Jennifer L. Townsend, Meredith A. King, Toru Ohira

PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES Vol. 367 ( 1891 ) page： 1181 - 1193 2009.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC

Experimental observations indicate that positive feedback plays an important role for maintaining human balance in the upright position. This observation is used to motivate an investigation of a simple switch-like controller for postural sway in which corrective movements are made only when the vertical displacement angle exceeds a certain threshold. This mechanism is shown to be consistent with the experimentally observed variations in the two-point correlation for human postural sway. Analysis of first-passage times for this model suggests that this control strategy may slow escape by taking advantage of two intrinsic properties of a stochastic unstable first-order delay differential equation: (i) time delay and (ii) the possibility that the dynamics can be 'temporarily confined' near the origin.

DOI： 10.1098/rsta.2008.0257

Web of Science

PubMed

Temporal stochasticity and non-locality Reviewed

Toru Ohira

JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT 2009.1

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

We attempt to consider concepts of 'stochasticity' and 'non-locality' on the time axis. Even though these concepts are more familiar on the space axis, delayed dynamics, for example, can be interpreted as dynamics with temporal non-locality. Along these lines, we present anticipative dynamics as another example of non-locality on the time axis. Two directions are discussed for temporal stochasticity. The first introduces fluctuations at the location of time points, which affects the dynamics. The second takes into consideration the stochasticity in the time flow or variable itself. Through these examples, we show that the combination of stochasticity and non-locality both on the space and time axes can produce rather complex phenomena.

DOI： 10.1088/1742-5468/2009/01/P01032

Web of Science

Resonance with Temporal Stochasticity and Non-locality Reviewed

Toru Ohira

NOISE AND FLUCTUATIONS Vol. 1129 page： 49 - 52 2009

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

We present here a simple model which shows a "resonant" phenomena through stochasticity and non-locality on the time axis. This model incorporates "stochastic time" and "delayed feedback" into its dynamics. We argue that a combination of temporal stochasticity and non-locality can provide rather complex behaviors.

Web of Science

J-GLOBAL

Delayed random walks: Investigating the interplay between delay and noise Reviewed

Toru Ohira, John Milton

Delay Differential Equations: Recent Advances and New Directions page： 305 - 335 2009

Language：English Publishing type：Part of collection (book) Publisher：Springer US

A model for a 1-dimensional delayed random walk is developed by generalizing the Ehrenfest model of a discrete random walk evolving on a quadratic, or harmonic, potential to the case of non-zero delay. The Fokker-Planck equation derived from this delayed random walk (DRW) is identical to that obtained starting from the delayed Langevin equation, i.e. a first-order stochastic delay differential equation (SDDE). Thus this DRW and SDDE provide alternate, but complimentary ways for describing the interplay between noise and delay in the vicinity of a fixed point. The DRW representation lends itself to determinations of the joint probability function and, in particular, to the auto-correlation function for both the stationary and the transient states. Thus the effects of delay are manisfested through experimentally measurable quantities such as the variance, the correlation time, and the power spectrum. Our findings are illustrated through applications to the analysis of the fluctuations in the center of pressure that occur during quiet standing. © 2009 Springer-Verlag US.

DOI： 10.1007/978-0-387-85595-0_11

Scopus

Non-locality on the time axis Reviewed

Toru Ohira

FRONTIERS OF FUNDAMENTAL AND COMPUTATIONAL PHYSICS Vol. 1018 page： 21 - 26 2008

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

We consider the question of introducing the concept of "non-locality" in a time variable, which is opposite to the normal description of the concept in space. Simple delayed and anticipative dynamical models are proposed as representatives of non-locality in time. These models show rather complex behaviors as we increase the level of temporal non-locality. We further demonstrate that these models can induce a "resonance" when combined with spatial or temporal noise. Applications to physical and bio-physiological systems are also discussed.

Web of Science

Human and machine stick balancing Reviewed

Shigeru Tajima, Toru Ohira, Yukinori Tonosaki

PROCEEDINGS OF THE ASME INTERNATIONAL DESIGN ENGINEERING TECHNICAL CONFERENCES AND COMPUTERS AND INFORMATION IN ENGINEERING CONFERENCE 2007, VOL 5, PTS A-C, page： 721 - 727 2008

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER SOC MECHANICAL ENGINEERS

We compared the similarities and differences in stick balancing for the human fingertip and that by a servo-controlled machine. The motion of the stick in both cases exhibited a swinging or hunting behavior, which appears to be related to feedback delay. However, human stick balancing appears also to be affected by psychological factors, such as attention, which are not present in machine control systems. We discuss how machine control systems compare with human stick balancing. We also discuss about the repulsive delayed random walk as a simplified model of the stick balancing.

Web of Science

Unstable dynamical systems: Delays, noise and control Reviewed

J. G. Milton, J. L. Cabrera, T. Ohira

EPL Vol. 83 ( 4 ) 2008

Language：English Publishing type：Research paper (scientific journal) Publisher：EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY

Escape from an unstable fixed point in a time-delayed dynamical system in the presence of additive white noise depends on both the magnitude of the time delay, tau, and the initial function. In particular, the longer the delay the smaller the variance and hence the slower the rate of escape. Numerical simulations demonstrate that the distribution of first passage times is bimodal, the longest first passage times are associated with those initial functions that cause the greatest number of delayed zero crossings, i.e. instances where the deviations of the controlled variable from the fixed point at times t and t - tau have opposite signs. These observations support the utility of control strategies using pulsatile stimuli triggered only when variables exceed certain thresholds. Copyright (C) EPLA, 2008.

DOI： 10.1209/0295-5075/83/48001

Web of Science

Scopus

Non-locality on the time axis Reviewed

Ohira Toru

FRONTIERS OF FUNDAMENTAL AND COMPUTATIONAL PHYSICS Vol. 1018 page： 21-26 2008

Human and machine stick balancing Reviewed

PROCEEDINGS OF THE ASME INTERNATIONAL DESIGN ENGINEERING TECHNICAL CONFERENCES AND COMPUTERS AND INFORMATION IN ENGINEERING CONFERENCE 2007, VOL 5, PTS A-C, page： 721-727 2008

Stochasticity and non-locality of time Reviewed

Toru Ohira

PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS Vol. 379 ( 2 ) page： 483 - 490 2007.6

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

We present simple classical dynamical models to illustrate the idea of introducing a stochasticity with non-locality into the time variable. For stochasticity in time, these models include noise in the time variable but not in the "space" variable, which is opposite to the normal description of stochastic dynamics. Similarly with respect to non-locality, we discuss the delayed and predictive dynamics which involve two points separated on the time axis. With certain combinations of fluctuations and non-locality in time, we observe a "resonance" effect. This is an effect similar to stochastic resonance, which has been discussed within the normal context of stochastic dynamics, but with different mechanisms. We discuss how these models may be developed to fit a broader context of generalized dynamical systems where fluctuations and nonlocality are present in both space and time. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physa.2007.01.015

Web of Science

Stochasticity and Non-Locality of Time Reviewed

OHIRA Toru

Butsuri Vol. 62 ( 4 ) page： 260-264 - 264 2007.4

Stochastic time Reviewed

Toru Ohira

Frontiers of Fundamental Physics Vol. 905 page： 191 - 194 2007

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

We presenta simple dynamical model to addres the question of introducing a stochastic nature in a time variable. This model includes noise in the time variable but not in the "space" variable, which is opposite to the normal description of stochastic dynamics. The notable feature is that these models can induce a "resonance" with varying noise strength in the time variable. Thus, they provide a different mechanism for stochastic resonance, which has been discussed within the normal context of stochastic dynamics.

Web of Science

Predictive dynamical and stochastic systems Reviewed

Toru Ohira

Cooperative Behavior in Neural Systems Vol. 887 page： 182 - 189 2007

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

We study a system whose dynamics are governed by predictions of its future states. A general formalism and concrete examples are presented. We find that the dynamical characteristics depend on how to shape the predictions as well as on how far ahead in time to make them. We also report that noise can induce oscillatory behavior, which we call "predictive stochastic resonance".

Web of Science

Stochastic time Reviewed

Ohira Toru

Frontiers of Fundamental Physics Vol. 905 page： 191-194 2007

Predictive dynamical and stochastic systems Reviewed

Ohira Toru

Cooperative Behavior in Neural Systems Vol. 887 page： 182-189 2007

Balancing the sticks with fluctuation and delay:Human vs machine Reviewed

Yukinori Tonosaki, Toru Ohira, Shigeru Tajima

2007 IEEE SYMPOSIUM ON FOUNDATIONS OF COMPUTATIONAL INTELLIGENCE, VOLS 1 AND 2 page： 95 - + 2007

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

DOI： 10.1109/FOCI.2007.372153

Web of Science

Delayed random walks and control Reviewed

Tadaaki Hosaka, Toru Ohira

FLOW DYNAMICS Vol. 832 page： 487 - + 2006

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

Issues of resonance that appear in non-standard random walk models are discussed. The first walk is called repulsive delayed random walk, which is described in the context of a stick balancing experiment. It win be shown that a type of "resonant" effect takes place to keep the stability of the fixed point better with tuned bias and delay. We also briefly discuss the second model called sticky random walk, which is introduced to model string entanglement. Peculiar resonant effects with respect to these random walks are presented.

Web of Science

Balancing with noise and delay Reviewed

T Hosaka, T Ohira, C Luciani, JL Cabrera, JG Milton

PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT ( 161 ) page： 314 - 319 2006

Language：English Publishing type：Research paper (scientific journal) Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE

Motivated by recent studies in human balance control, we study a delayed random walk with an unstable fixed point. It is observed that the random walker moves away from the unstable fixed point more slowly than is observed in the absence of delay. It is shown that, for given a noise level, there exists an optimal delay to achieve the longest first passage time. Our observations support recent demonstrations that noise has a beneficial role for balance control and emphasize that predicitive strategies are not necessary to transiently control balance.

Web of Science

J-GLOBAL

Balancing with noise and delay Reviewed

T Hosaka, T Ohira, C Luciani, JL Cabrera, JG Milton

PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT Vol. 161 ( 161 ) page： 314 - 319 2006

Language：English Publishing type：Research paper (scientific journal) Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE

DOI： 10.1143/PTPS.161.314

Web of Science

Scopus

Delayed random walks and control Reviewed

Hosaka Tadaaki, Ohira Toru

FLOW DYNAMICS Vol. 832 page： 487-+ 2006

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