Tetsuya Iwasaki

• Osaka National Hospital

This paper develops a design method for the interconnections of a network of Andronov–Hopf oscillators such that the system exhibits a desired strange attractor. Because of the structure of the oscillators, the desired behavior can be achieved via weak linear coupling, which destabilizes the oscillators’ phase difference. First, a set of sufficient...

Aim To investigate the efficacy and safety of all oral direct acting antiviral (DAA) treatment in hepatitis C patients coinfected with HIV. Methods In all, 35 patients with hepatitis C virus (HCV)/human immunodeficiency virus (HIV) coinfection (22 patients with HCV genotype 1 infection, 6 with genotype 2, and 7 with genotype 3) were treated with s...

82 Background: Recently, the proportion of elderly patients (pts) with metastatic gastric cancer (mGC) has increased in Japan. Survival benefits of salvage treatment after second-line chemotherapy (CTX) for mGC were shown in several prospective studies. However, the role of salvage treatment in elderly pts remains controversial. Methods: We reviewe...

Restorative proctocolectomy with ileal pouch-anal anastomosis (IPAA) is widely accepted as the operation of choice for refractory ulcerative colitis (UC), UC with dysplasia or cancer, or familial adenomatous polyposis. Pouchitis is the most frequent complication after IPAA for UC. Although the pathogenesis of pouchitis remains unclear, current evid...

143 Background: Recently, the proportion of elderly patients (pts) with advanced gastric cancer has increased in Japan. Survival benefits of second-line chemotherapy (CTX) such as weekly paclitaxel (PTX)±Ramucirumab (RAM) or irinotecan (CPT) were shown in several phase 3 trials for metastatic gastric cancer (mGC). However, efficacy and prognostic f...

The prevalence of Crohn's disease (CD) in Japan is increasing, and so is the incidence of colorectal and small bowel cancers associated with CD. However, few reports have described the malignant transformation of duodenal lesions; moreover, such a diagnosis is rarely possible preoperatively. We present a case of malignant degeneration in the duoden...

Animal locomotion can be viewed as mechanical rectification due to the dynamics that convert periodic body movements to a positive average thrust, resulting in a steady locomotion velocity. This paper considers a general multibody mechanical rectifier under continuous interactions with the environment, with full rotation and translation in 3-D spac...

An 89-year-old woman with abdominal pain and vomiting was admitted to our hospital. Ab-dominal computed tomography showed food-induced ileus caused by a plum species that the pa-tient had eaten. Although an ileus tube was inserted, the ileus did not improve and the food resi-due remained in the bowel. Using double balloon enteroscopy (DBE), the foo...

This article has no abstract.

We consider a class of multibody robotic systems inspired by dynamics of animal locomotion, such as swimming and crawling. Distinctive properties of such systems are that the stiffness matrix is asymmetric due to skewed restoring force from the environment, and the damping matrix is a scalar multiple of the inertia matrix when the body is flat like...

This paper provides analytical insights into the hypothesis that fish exploit resonance to reduce the mechanical cost of swimming. A simple body-fluid fish model, representing carangiform locomotion, is developed. Steady swimming at various speeds is analysed using optimal gait theory by minimizing bending moment over tail movements and stiffness,...

A class of large-scale, multi-agent systems with decentralized information structures can be represented by a linear system with a generalized frequency variable. In this paper, we investigate fundamental properties of such systems, stability, and ${cal D}$-stability, exploiting the dynamical structure. Specifically, we first show that such system...

Significance Animals can adapt the frequency and shape of their oscillatory body movements during locomotion in response to changes in the environment. Although central pattern generators (CPGs) are known to be the basic neuronal circuits responsible for generation of rhythmic movements, no conclusive evidence has so far been found to attribute ada...

We consider a class of multilink mechanical systems arising from undulatory locomotion of multisegmental slender animals. All the body joints are assumed to have actuators, but the system is underactuated because of the lack of direct control over the position and orientation within the inertial frame. Yet, the system is controllable through intera...

Anemia frequently develops in patients given pegylated-interferon, ribavirin (RBV), telaprevir (TVR) triple therapy and restricts treatment by forcing reduction or discontinuation of RBV administration. We investigated whether erythropoietin (EPO) could alleviate RBV-induced anemia to help maintain the RBV dose during the first 12 weeks, the triple...

We consider linear mechanical systems with asymmetric stiffness matrices. The class of systems captures essential body dynamics of animal/robotic locomotion. In particular, rhythmic body movements similar to those observed in animals can be found as a properly defined natural oscillation of the linear system. The objective is to design a nonlinear...

The mechanism of entrainment to natural oscillations in a class of (bio)mechanical systems described by linear models is investigated. Two new nonlinear control strategies are proposed to achieve global convergence to a prescribed resonance mode of oscillation within a finite time. The effectiveness of the proposed methods for resonance entrainment...

Rhythmic motion employed in animal locomotion is ultimately controlled by neuronal circuits known as central pattern generators (CPGs). It appears that these controllers produce efficient oscillatory command signals by entraining to a resonant gait via sensory feedback. This property is of great interest in the control of autonomous vehicles. In th...

Rhythmic motion employed in animal locomotion is ultimately controlled by neuronal circuits known as central pattern generators (CPGs). It appears that these controllers produce efficient, oscillatory command signals by entraining to an efficient or economic gait via sensory feedback. This property is of great interest in the control of autonomous...

Neuronal circuits known as central pattern generators (CPG) are responsible for the rhythmic motions in animal locomotion. These circuits exploit the resonant modes of the body to produce efficient locomotion through sensory feedback. As such, the neuronal mechanisms are of interest in the control of autonomous robotic vehicles. The objective of th...

The mechanism of entrainment to natural oscillations in a class of (bio)mechanical systems described by linear models is investigated. A nonlinear control strategy (based on the speed gradient control algorithm) is analyzed providing the system oscillation in resonance mode with a natural frequency. It ensures an energy-optimal entrainment performa...

Undulatory animal locomotion arises from three closely related propagating waves that sweep rostrocaudally along the body: activation of segmental muscles by motoneurons (MNs), strain of the body wall, and muscle tension induced by activation and strain. Neuromechanical models that predict the relative propagation speeds of neural/muscle activation...

Flapping-wing rectifier systems are defined as systems which produce bulk loco-motion through the interaction of periodic wing movement with a surrounding environment. A nonlinear model is developed featuring a 6 degree-of-freedom main body (position and orientation) and wing deformation. Each wing may move independently and is described as the mot...

Mechanical systems can often be controlled efficiently by exploiting a resonance. An optimal trajectory minimizing an energy cost function is found at (or near) a natural mode of oscillation. Motivated by this fact, we consider the natural entrainment problem: the design of nonlinear feedback controllers for linear mechanical systems to achieve a p...

We have studied the dynamical properties of tension development in leech longitudinal muscle during swimming. A new method is proposed for modeling muscle properties under functionally relevant conditions where the muscle is subjected to both periodic activation and rhythmic length changes. The 'dual-sinusoid' experiments were conducted on preparat...

The essential mechanism underlying animal locomotion can be viewed as mechanical rectification that converts periodic body movements to thrust force through interactions with the environment. This paper defines a general class of mechanical rectifiers as multi-body systems equipped with such thrust generation mechanisms. A simple model is developed...

Swimming of fish and other animals results from interactions of rhythmic body movements with the surrounding fluid. This paper develops a model for the body-fluid interaction in undulatory swimming of leeches, where the body is represented by a chain of rigid links and the hydrodynamic force model is based on resistive and reactive force theories....

We consider a class of mechanical systems arising from the dynamics of multi-segmental animal locomotion. Our earlier paper has revealed that a chain of body segments oscillate in a natural mode if the head is externally forced to move at a constant velocity and the damping effect is reduced by an appropriate amount. In this paper, we further show...

For a biologically inspired mechanical system consisting of multiple segments, its natural oscillation is defined as a periodic body movement pattern conforming to the dynamics inherent to the body-environment interaction, leading to an effective locomotion of the system. In the literature, a central pattern generator based controller has been desi...

This paper introduces a mathematical tool for analyzing neuronal oscillator circuits based on multivariable harmonic balance (MHB). The tool is applied to a model of the central pattern generator (CPG) for leech swimming, which comprises a chain of weakly coupled segmental oscillators. The results demonstrate the effectiveness of the MHB method and...

This paper considers the design of feedback controllers for a class of collocated mechanical systems, aiming to achieve a natural mode of oscillation as a stable limit cycle of the closed-loop system. Motivated by recent results on central pattern generators, the controller is formed as a collection of multiple identical agents without direct commu...

The analysis of undulatory swimming gaits requires knowledge of the fluid forces acting on the animal body during swimming. In his classical 1952 paper, Taylor analysed this problem using a 'resistive-force' theory. The theory was used to characterize the undulatory gaits that result in the smallest energy dissipation to the fluid for a given swim...

Animal locomotion results from muscle contraction and relaxation cycles that are generated within the central nervous system and then are relayed to the periphery by motoneurons. Thus, motoneuron function is an essential element for understanding control of animal locomotion. This paper presents motoneuron input-output relationships, including impu...

We consider a class of linear flexible mechanical systems arising from the dynamics of animal locomotion. A distinctive property of such systems is that the stiffness matrix is asymmetric. Extending the standard notion to this class, we define the natural oscillation as a free response under the damping compensation to achieve marginal stability. A...

Tensegrity structures, which consist of struts and cables, have high strength to mass ratio and high energetic efficiency in deforming its shapes. This structure is sometimes observed in biological systems, which consists of muscles and skeletons, and this structure is adopted to a simplified model of animal body dynamics. From the aspect of engine...

A class of large-scale systems with decentralized information structures such as multi-agent systems can be represented by a linear system with a generalized frequency variable. In this paper, we investigate stability of such systems, which is the most fundamental property from the view point of control. Specifically, we first present a systematic...

Rhythmic movements in animal locomotion appear to exploit a resonance of the body-environment dynamics to maintain high efficiency. To gain insights into the locomotion mechanism, this paper studies a simple three-link undulatory locomotor model that swims through a single joint torque actuator. We have found that, when the locomotor is driven by a...

This paper first formally defines a general class of three dimensional rectifier systems which capture the essential aspects of animal locomotion, then formulates an optimal gait problem, and finally solves an approximation of the problem to obtain a globally optimal solution. The approximation assumes small-amplitude harmonic oscillations of mecha...

This paper considers the control synthesis problem for linear time invariant (LTI) continuous-time systems with actuator saturation nonlinearities. The control architecture is standard; a nominal LTI output feedback with an anti-windup (AW) mechanism. Traditional approaches have focused on AW synthesis where the nominal controller is first designed...

The Kalman-Yakubovich-Popov (KYP) lemma establishes the equivalence between a frequency domain inequality (FDI) of a proper rational function and a linear matrix inequality (LMI). A recent result generalized the KYP lemma to characterize an FDI of a possibly nonproper rational function on a portion of a curve on the complex plane. This note examine...

The central pattern generator for controlling animal locomotion is generally not a single oscillator but a group of interconnected oscillators. Although the whole group can be analyzed as a bulky single oscillator, it is difficult with such an approach to reveal the essential mechanism of phase coordination among oscillators. In this paper, a new a...

Rhythmic movements during animal locomotion are controlled by the neuronal circuits called central pattern generators (CPGs). The intrinsic frequency of a CPG in isolation is often different from that of observed movements, but appears to entrain to a natural mode of body oscillation through sensory feedback to achieve efficient locomotion. The obj...

A class of large-scale systems with decentralized information structures such as multi-agent dynamical systems can be represented by a linear system with a generalized frequency variable. In this paper, we propose efficient ℌ2 and ℌ∞ norm computations based on the generalized frequency variable. Specifically, we first derive a way of ℌ2 norm comput...

The central pattern generator (CPG) is a nonlinear oscillator formed by a group of neurons, providing a fundamental control mechanism underlying rhythmic movements in animal locomotion. We consider a class of CPGs modeled by a set of interconnected identical neurons. Based on the idea of multivariable harmonic balance, we show how the oscillation p...

Rhythmic movements associated with animal locomotion are controlled by neuronal circuits known as central pattern generators (CPG). These biological control systems appear to entrain to the natural frequencies of the mechanical systems they control, taking advantage of the resonance of the structure, resulting in efficient control. The ultimate goa...

The neuronal circuit controlling the rhythmic movements in animal locomotion is called the central pattern generator (CPG). The biological control mechanism appears to exploit mechanical resonance to achieve efficient locomotion. The objective of this paper is to reveal the fundamental mechanism underlying entrainment of CPGs to resonance through s...

Biological systems, and particularly neuronal circuits, embody a very high level of complexity. Mathematical modeling is therefore essential for understanding how large sets of neurons with complex multiple interconnections work as a functional system. With the increase in computing power, it is now possible to numerically integrate a model with ma...

We study here robust stability of linear systems with several uncertain incommensurate delays, more precisely the property usually called delay-dependent stability. The main result of this paper consists in establishing that the latter is equivalent to the feasibility of some Linear Matrix Inequality (LMI), a convex optimization problem whose numer...

While regulations around an equilibrium point or a reference trajectory have been the focus of recent feedback control theories, generation of autonomous oscillations with a specific pattern plays a crucial role in important control applications such as robotics. The central pattern generator (CPG) is the fundamental neuronal mechanism underlying r...

We investigated passive properties of leech body wall as part of a larger project to understand better mechanisms that control locomotion and to establish mathematical models that predict such dynamical behavior. In tests of length-tension relationships in 2-segment-long preparations of body wall through step-stretch manipulations (step size = 1 mm...

We consider the class of discrete-time nonlinear/uncertain systems described by the feedback connection of a linear time-invariant system and a “troublesome component,” i.e. either a static nonlinearity or a time-varying parametric uncertainty. We propose a generalized quadratic Lyapunov function for stability analysis of such systems. In particula...

This paper considers a control synthesis problem for linear systems to meet design specifications in terms of multiple frequency domain inequalities in (semi)finite ranges. Our approach is based on the generalized Kalman–Yakubovich–Popov (GKYP) lemma, and dynamic output feedback controllers of order equal to the plant are considered. A new multipli...

This paper describes a mathematical model of the neuronal central pattern generator (CPG) that controls the rhythmic body motion of the swimming leech. The systems approach is employed to capture the neuronal dynamics essential for generating coordinated oscillations of cell membrane potentials by a simple CPG architecture with a minimal number of...

We study here robust stability of linear systems with several uncertain incommensurate delays, more precisely delay-dependent stability. The main result of this paper consists in establishing that this property is equivalent to the feasibility of some linear matrix inequality (LMI), a convex optimization problem. The method is based on two main ide...

The neuronal circuit controlling the rhythmic movements in animal locomotion is called the central pattern generator (CPG). The biological control mechanism appears to exploit mechanical resonance to achieve efficient locomotion. The objective of this paper is to reveal the fundamental mechanism underlying entrainment of CPGs to resonance through s...

Rhythmic body motions observed in animal locomotion are known to be controlled by neuronal circuits called central pattern generators (CPGs). It appears that CPGs are energy efficient controllers that cooperate with biomechanical and environmental constraints through sensory feedback. In particular, the CPGs tend to induce rhythmic motion of the bo...

The Manta Ray, Manta birostris , is an amazing creature, propelling itself through the water with the elegant and complex flapping of its wings. Achieving outstanding efficiencies, engineers are looking for ways to mimic its flight through the water and harness its propulsive techniques. This study combines two biologically inspired aspects to a...

The Manta Ray, Manta birostris, is an amazing creature, propelling itself through the water with the elegant and complex flapping of its wings. Achieving outstanding efficiencies, engineers are looking for ways to mimic its flight through the water and harness its propulsive techniques. This study combines two biologically inspired aspects to achie...

This paper considers linear time invariant systems with sector type nonlinearities and proposes regional ℒ2 performance analysis and synthesis methods based on the circle criterion. In particular, we consider the effect of non-zero initial states and/or an ℒ2 disturbance inputs on the ℒ2 norm of a selected performance output. We show that both anal...

In this paper we show that the class of polynomially parameter-dependent quadratic (PPDQ) Lyapunov functions of specified degree characterizes the stability of single-parameter dependent linear, time-invariant, (s-PDLTI) systems. Using PPDQ Lyapunov functions we provide necessary and sufficient conditions for the stability of s-PDLTI systems. Check...

Many of the significant results in systems and control literature rely on characterizations of system properties in terms of frequency domain inequalities (FDIs) and/or time domain inequalities (TDIs). Classical FDIs, required to hold on the entire frequency range, have been interpreted by equivalent TDIs so that satisfaction of one implies that of...

The celebrated Kalman-Yakubovicˇ-Popov (KYP) lemma establishes the equivalence between a frequency domain inequality (FDI) and a linear matrix inequality, and has played one of the most fundamental roles in systems and control theory. This paper first develops a necessary and sufficient condition for an S-procedure to be lossless, and uses th...

A variety of powerful tools and results in systems and control theory rely on classical Kalman-Yakubovich-Popov-Zames results establishing equivalence between special frequency domain inequalities (FDIs), linear matrix inequalities (LMIs) and time domain inequalities (TDIs). Recent developments have addressed FDIs within (semi)finite frequency rang...

This paper proposes a mathematical model of the neuronal central pattern generator (CPG) for leech swimming. The model is developed through the "systems approach" where dynamical components and their connections are first identified through input/output data from physiological experiments and then integrated into a chain of nonlinear oscillators. O...

In this paper, we propose a class of parameter-dependent Lyapunov functions which can be used to assess the stability properties of linear, time-invariant, single-parameter dependent (LTIPD) systems in a non-conservative manner. It is shown that stability of LTIPD systems is equivalent to the existence of a Lyapunov function of a polynomial type (i...

This paper proposes a generalized version of the Kalman-Yakubovic-Popov (KYP) lemma that establishes the equivalence between a frequency domain inequality (FDI) and a linear matrix inequality (LMI). Our new result allows us to treat (semi)finite frequency ranges and possibly nonproper transfer functions. We study implications of this generalization...

This paper considers a robust control synthesis problem for uncertain linear systems to meet design specifications given in terms of multiple frequency domain inequalities in (semi)finite ranges. We restrict our attention to static gain feedback controllers. We develop a new multiplier method that allows for reduction of synthesis conditions to lin...

This paper proposes a prototype mechanical rectifier (PMR) that captures essential dynamics underlying animal locomotion by a simple pendulum-disk configuration. We use the PMR to study the control mechanism of animal locomotion. In particular, we verify via numerical experiments the prediction from biological observations that a central pattern ge...

This paper considers a robust control synthesis problem for uncertain linear systems to meet design specifications given in terms of multiple frequency domain inequalities in (semi)finite ranges. In this paper, we restrict our attention to static (gain feedback) controllers. We will develop a new multiplier method that allows for reduction of synth...

The cerebrated Kalman-Yakubovi c-Popov (KYP) lemma establishes the equivalence between a frequency domain inequality (FDI) and a linear matrix inequality (LMI), and has played one of the most fundamental roles in systems and control theory. This paper generalizes the KYP lemma in two aspects --- the frequency range and the class of systems --- and...

Nonminimum phase zeros are well known to limit the best achievable control performance when the control gain is allowed to be arbitrarily high. On the other hand, the phase crossover appears to be a limiting factor for performance when high-gain controllers are not allowed. In particular, the positive-realness in a finite frequency range seems cruc...

The celebrated Kalman-Yakubovic-Popov (KYP) lemma converts frequency domain inequalities to linear matrix inequalities in the state space, suitable for development of systems theory and for numerical computations. This paper generalizes the KYP lemma to treat conditions on restricted frequency intervals. Conditions for both continuous-time and disc...

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This paper summarizes the authors’ recent results on finite frequency characterization of easily controllable plants under control effort constraint, the aim being the development of a new approach for plant/control design integration. We first show by a motivating example that the closed-loop bandwidth achievable with a reasonable control effort i...

The vast majority of literature on control theory has focused on stability and certain regulation performances with respect to equilibrium points of dynamical systems. On the other hand, there are many practically important problems that are concerned with control specifications described by periodic motions. This paper makes an initial attempt to...

A snake robot without wheels that has potential for adapting to the environment is considered. The model of this snake robot is developed based on the directional friction coefficients. After the model transformation that decouples the inertial locomotion from the internal shape motion, an optimally efficient serpentine locomotion is examined. Base...

This paper considers a class of linear systems containing time-varying parameters whose behavior is not known exactly. We assume that the parameters vary within known intervals and there are known bounds on their rates of variation. Our objective is to give a computationally verifiable condition that guarantees stability of the system for all possi...

Proposes regional L₂ performance analysis and synthesis methods for linear time invariant systems with sector type nonlinearities using the circle criterion. The methods can treat both nonzero initial state vectors of systems belonging to a bounded set and disturbance inputs belonging to a set of signals having bounded L₂ nor...

This paper deals with regional stabilization of linear time-invariant systems by dynamic output feedback controllers subject to known bounds on the magnitudes of the control inputs. Specifically, we consider the achievable region of attraction, i.e., the set of vectors with the following property: there exists a (nonlinear) controller such that any...

This paper provides an overview of the authors' recent developments on a generalization of the Kalman-Yakubovich-Popov (KYP) lemma that provides a unified linear matrix inequality (LMI) characterization of frequency domain inequalities (FDIs) in (semi)finite frequency ranges for both continuous-and discrete-time systems and its application to dynam...