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Naoki Sakata

Publications and source records attributed to Naoki Sakata.

8 recordsLinked to original sources

Characterization of non-self OU sequences of two-component link diagrams

A non-self OU sequence is a cyclic sequence of crossing information of non-self crossings that is obtained by traversing a knot component of an oriented link diagram. In this paper, we investigate what information can be derived from non-self OU sequences, and we completely characterize pairs of non-self OU sequences of diagrams of two-component links. We also characterize the pairs for specific prime links with crossing number up to five.

math.GT

Reducing Total Trip Time and Vehicle Emission through Park-and-Ride -- methods and case-study

This study addresses important issues of traffic congestion and vehicle emissions in urban areas by developing a comprehensive mathematical framework to evaluate Park-and-Ride (PnR) systems. The proposed approach integrates queueing theory and emissions modeling to simultaneously assess waiting times, travel times, and vehicle emissions under various PnR usage scenarios. The methodology employs a novel combination of Monte Carlo simulation and matrix geometric analytic methods to analyze a queueing network representing PnR facilities and road traffic. A case study of Tsukuba, Japan demonstrates the model's applicability, revealing potential reductions in social costs related to total trip time and emissions through optimized PnR policies. Specifically, the study found that implementing optimal bus frequency and capacity policies could reduce total social costs by up to 30\% compared to current conditions. This research contributes to the literature by providing a unified framework for evaluating PnR systems that considers both time and environmental costs, offering valuable insights for urban planners and policymakers seeking to improve transportation sustainability. The proposed model utilizes a single server queue with a deterministic service time and multiple arrival streams to represent traffic flow, incorporating both private cars and public buses. Emissions are calculated using the Methodologies for Estimating Air Pollutant Emissions from Transport (MEET) framework. The social cost of emissions and total trip time (SCETT) is introduced as a comprehensive metric for evaluating PnR system performance.

stat.CO

A mathematical approach to mechanical properties of networks in thermoplastic elastomers

We employ a mathematical model to analyze stress chains in thermoplastic elastomers (TPEs) with a microphase-separated spherical structure composed of triblock copolymers. The model represents stress chains during uniaxial and biaxial extensions using networks of spherical domains connected by bridges. We advance previous research and discuss permanent strain and other aspects of the network. It explores the dependency of permanent strain on the extension direction, using the average of tension tensors to represent isotropic material behavior. The concept of deviation angle is introduced to measure network anisotropy and is shown to play an essential role in predicting permanent strain when a network is extended in a specific direction. The paper also discusses methods to create a new network structure using various polymers.

cond-mat.soft

Stable configurations of entangled systems with repulsive interactions

Entangled systems are prevalent in both biological and synthetic materials. This study examines the stable configurations of weaves consisting of two families of intertwined threads, such as warp and weft threads. By analyzing the steepest descent flow of an energy functional featuring repulsive interactions, we develop a framework for identifying stable states in ${\mathbb R}^3$. Although a weave consists of one-dimensional threads that do not intersect each other, it behaves collectively like a two-dimensional object. To describe this phenomenon, we define a non-separable component of a weave as a ``layer'' and establish the existence and uniqueness of its stable configuration. Furthermore, we show that two distinct layers drift apart with an asymptotic growth rate of $t^{1/3}$ as $t \to \infty$.

math.DG

Passivity-based sliding mode control for mechanical port-Hamiltonian systems

In this work, we propose a new passivity-based sliding mode control method for mechanical port-Hamiltonian systems. Passivity-based sliding mode control (PBSMC) is unification of sliding mode control and passivity-based control. It achieves sliding mode control and Lyapunov stability simultaneously by employing an energy based Lyapunov function. The proposed method gives a family of stabilizing controllers which smoothly interpolates passivity-based control and sliding mode control with free parameters. The freedom is useful to adjust the trade-off between robustness against external disturbances and undesired chattering vibration. In addition, this paper relaxes the restrictive condition which is required in the authors' former result. As a result, we can apply the proposed PBSMC method to trajectory tracking control problems. Furthermore, the robustness of the proposed controller against matched and unmatched disturbances is investigated. Numerical examples demonstrate the effectiveness of the proposed method.

eess.SY

Handlebody decompositions of 3-manifolds and polycontinuous patterns

We introduce the concept of a handlebody decomposition of a 3-manifold, a generalization of a Heegaard splitting, or a trisection. We show that two handlebody decompositions of a closed orientable 3-manifold are stably equivalent. As an application to materials science, we consider a mathematical model of polycontinuous patterns and discuss a topological study of microphase separation of a block copolymer melt.

math.GT