arXiv subjects

Keisuke Yoshida

Publications and source records attributed to Keisuke Yoshida.

10 recordsLinked to original sources

arXiv2026

Diffusional earthquakes and their slip-distance scaling

The final size of an earthquake typically cannot be predicted from its ongoing seismic radiation. Expanding observations reveal distinct exceptions, such as slow earthquakes, injection-induced seismicity, and earthquake swarms, in which fault slip has an upper bound. A common thread among these anomalies is the diffusive migration of their active areas. Here, we report a unified scaling relation for these diffusional earthquakes. By tracking prolonged earthquake swarms in Northeast Japan, we constrained the time evolution of their active seismicity areas and cumulative seismic moments. Their moment-duration trajectories coincide with the final states documented for global swarms and induced seismicity across various scales. When plotted as seismic moment versus seismicity area, their trajectories collapse onto those of slow earthquakes, uniformly explained by a diffusional constant-slip model. This constant-slip scaling carves out a unique class of diffusional earthquakes, where the final available seismic energy is predetermined by slip distance.

physics.geo-ph↗

arXiv2026

Wrinkles, rucks, and folds formed in a heavy sheet on a frictional surface

Soft elastic sheets resting on rigid surfaces develop wrinkles, rucks, and folds due to the combined influence of elasticity, gravity, and contact interactions. Despite their ubiquity, the principles governing their morphology and transitions remain unclear. We introduce a minimal experiment in which the center of a gravity-loaded sheet is gradually lifted from the supporting plane. This operation generates a clear sequence of shapes: an axisymmetric uplift, a finite number of wrinkles, system-spanning rucks produced by global buckling, and folded states that can arise from ruck collapse upon unloading at larger lifts. Combining experiments, finite-element simulations, and F\"oppl-von K\'arm\'an theory, we establish a unified physical picture of this morphology sequence. In the frictionless case, elasticity and gravity alone govern the response, leading to a universal wrinkling threshold: the wrinkle number is fixed and the onset displacement scales linearly with the sheet thickness. With interfacial friction, the wrinkled state is described by introducing an additional nondimensional parameter that compares frictional and elastic-gravitational forces. These results suggest a simple route to programmable sheet morphogenesis via friction and gravity.

cond-mat.soft↗

arXiv2025

Sliding of cylindrical shell into a rigid hole

Fitting two different materials is a versatile methodology in manufacturing complex structures. One of the canonical models for fitting is the snap-fit model, in which flexible materials and rigid structures are assembled by pushing their interlocking components together. The assembly via snap-fit is often accompanied by large deformations of flexible structures and abrupt force drops, highlighting the role of elasticity, geometry, and contact friction. Despite several model studies revealing fundamental mechanics for snap-fit, the current snap-fit design relies on prototyping and empirical rules. In this paper, we analyze a snap-fit model in which a naturally curved beam slips into a rigid hole. We construct an analytical model based on the theory of elastica with contact friction and demonstrate that its predictions are in excellent quantitative agreement with both simulations and experiments. We find three distinct sliding modes: Folding, Pinning, and Unfolding. The classification is systematically organized in a phase diagram based on the geometric parameters of the shells and the hole. Our study complements existing approaches by providing a predictive framework for contact-based structures that involve friction, elasticity, and geometry, and sheds light on a unified understanding of the interactions between an elastic and a rigid body.

cond-mat.soft↗

arXiv2023

Indentation of an elastic arch on a frictional substrate: Pinning, unfolding and snapping

We investigate the morphology and mechanics of a naturally curved elastic arch loaded at its center and frictionally supported at both ends on a flat, rigid substrate. Through systematic numerical simulations, we classify the observed behaviors of the arch into three distinct types of configurations in terms of the arch geometry and the coefficient of static friction with the substrate. A linear theory is developed based on a planar elastica model combined with Amontons-Coulomb's frictional law, which quantitatively explains the numerically constructed phase diagram. The snapping transition of a loaded arch in a sufficiently large indentation regime, which involves a discontinuous force jump, is numerically observed. The proposed model problem allows a fully analytical investigation and demonstrates a rich variety of mechanical behaviors owing to the interplay between elasticity, geometry, and friction. This study provides a basis for understanding more common but complex systems, such as a cylindrical shell subjected to a concentrated load and simultaneously supported by frictional contact with surrounding objects.

cond-mat.soft↗

arXiv2022

Topological entropy for countable Markov shifts and Exel--Laca algebras

We show that the (Gurevich) topological entropy for the countable Markov shift associated with an infinite transition matrix $A$ coincides with the non-commutative topological entropy for the Exel--Laca algebra associated with $A$, under certain conditions on $A$. An important example satisfying the conditions is the renewal shift, which is not locally finite. We also pose interesting questions for future research on non-commutative topological entropy for non-locally finite transition matrices.

math.OA↗

arXiv2021

On the Simplicity of C$^*$-algebras Associated to Multispinal Groups

We characterize the simplicity of universal C$^*$-algebras arising from multispinal groups. Let $\mathcal{O}_{G_{\max}}$ be the universal C$^*$-algebra associated to a multispinal group $G$. We show that the invertibility of a matrix completely determines the simplicity of $\mathcal{O}_{G_{\max}}$.

math.OA↗

arXiv2020

Mechanics of a snap-fit

Snap-fits are versatile mechanical designs in industrial products, which enable the repeated assembling and disassembling of two solid parts. This important property is attributed to a fine balance between geometry, friction, and bending elasticity. In the present study, we combine theory, simulation, and experiment to reveal the fundamental physical principles of snap-fit functions in the simplest possible setup consisting of a rigid cylinder and a thin elastic shell. We construct a phase diagram using geometric parameters and identify four distinct mechanical phases. We develop analytical predictions based on the linear elasticity theory combined with the law of static friction and rationalize the numerical and experimental results. The study reveals how an operational asymmetry of snap-fits (i.e., easy to assemble but difficult to disassemble) emerges from an exquisite combination of geometry, elasticity, and friction and suggests optimization of the tunable functionalities for a range of mechanical designs.

cond-mat.soft↗

arXiv2020

A von Neumann algebraic approach to self-similar group actions

We study some relations between self-similar group actions and operator algebras. We consider KMS states on the Cuntz--Pimsner algebras constructed by Nekrashevych from self-similar actions and the GNS representations of the KMS states. The KMS states are given by the Bernoulli measure. We also consider the von Neumann algebras on the GNS spaces and show that the von Neumann algebras are type III factors.

math.OA↗

arXiv2019

Instant MPC for linear systems and dissipativity-based stability analysis

This letter is devoted to the concept of ``instant'' model predictive control (iMPC) for linear systems. An optimization problem is formulated to express the finite-time constrained optimal regulation control, like conventional MPC. Then, iMPC determines the control action based on the optimization process rather than the optimizer, unlike MPC. The iMPC concept is realized by a continuous-time dynamic algorithm of solving the optimization; the primal-dual gradient algorithm is directly implemented as a dynamic controller. On the basis of the dissipativity evaluation of the algorithm, the stability of the control system is analyzed. Finally, a numerical experiment is performed in order to demonstrate that iMPC emulates MPC and to show its less computational burden.

eess.SY↗

arXiv2014

Silica aerogel radiator for use in the A-RICH system utilized in the Belle II experiment

This paper presents recent progress in the development and mass production of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter, which will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH system is especially designed to identify charged kaons and pions. The refractive index of the installed aerogel Cherenkov radiators is approximately 1.05, and we aim for a separation capability exceeding 4$σ$ at momenta up to 4 GeV/$c$. Large-area aerogel tiles (over 18 $\times $ 18 $\times $ 2 cm$^3$) were first fabricated in test productions by pin drying in addition to conventional methods. We proposed to fill the large end-cap region (area 3.5 m$^2$) with 124 water-jet-trimmed fan-shaped dual-layer-focusing aerogel combinations of different refractive indices (1.045 and 1.055). Guided by the test production results, we decided to manufacture aerogels by the conventional method and are currently proceeding with mass production. In an electron beam test undertaken at the DESY, we confirmed that the $K$/$π$ separation capability of a prototype A-RICH counter exceeded 4$σ$ at 4 GeV/$c$.

physics.ins-det↗