Yoshihiro Ishibashi

Bio: Yoshihiro Ishibashi is an academic researcher from Nagoya University. The author has contributed to research in topics: Phase transition & Ferroelectricity. The author has an hindex of 46, co-authored 577 publications receiving 9700 citations. Previous affiliations of Yoshihiro Ishibashi include Kyushu University & Aichi Shukutoku University.

Note on Ferroelectric Domain Switching

Abstract: A phenomenological theory is given for ferroelectric domain switching. It takes into account the initial size of a reversed nucleus and also the shape of domains. It is shown that the Avrami theorem can be easily derived if we utilize Kolmogorov's method. We solved the problems under two assumptions: one is the constant nucleation rate throughout the switching period and the order is the assumption of latent nuclei of a given definite number and no further nucleations, The i max t max / P s values of several ferroelectrics reported so far summarized and discussed in the light of the present theory.

Traffic Flow in 1D Cellular Automaton Model Including Cars Moving with High Speed

Abstract: Traffic flow is simulated by one-dimensional cellular automaton (CA) model including cars moving with high speed. The simulation shows a phase transition between the moving phase and the jamming phase at p =1/( m +1) ( p : density of cars, m : the maximum number of sites by which cars advance at each time step). A mean-field theory can reproduce the average velocity found by simulations.

A Theory of D-E Hysteresis Loop Based on the Avrami Model

Abstract: The D - E hysteresis loop of ferroelectrics is theoretically studied on the basis of the extended Avrami theory. If the sideway velocity depends only on the instant value of the applied field, the volume fraction of the reversed area is expressed as q ( E )=1-exp (- f - d Φ( E )), where f and d are, respectively, the frequency of the applied field and the growth dimension of domains, and Φ is a function of E . This result is obtained irrespective of the waveform of the applied field and the field dependence of the sideway velocity, if the nucleation event is deterministic. For the stochastic nucleation due to thermal fluctuation, on the other hand, the above result is modified as q ( E )=1-exp (- f -( d +1) Φ( E )). The effect of the delay of wall motion is also discussed.

Self-Organized Phase Transitions in Cellular Automaton Models for Pedestrians

Abstract: Cellular automaton models for walking of pedestrians are studied in a system where one pedestrian and many pedestrians walk in the opposite direction and encounter each other on a passageway. Two models have been studied for the behavior avoiding from collision when the pedestrians meet with each other. Phase transitions on the walking behavior occur by self-organization with the critical density on the pedestrians.

Morphotropic phase boundary in solid solution systems of perovskite-type oxide ferroelectrics

Abstract: The origin of the appearance of the morphotropic phase boundary in the perovskite-type oxide solid solution systems and the increase in the dielectric susceptibilities in the vicinity of the boundary is theoretically clarified on the basis of a Landau-type free energy function. The dielectric susceptibilities are concretely expressed in terms of the model parameters, and found to diverge at the morphotropic phase boundary within the present model.

VESTA: a three-dimensional visualization system for electronic and structural analysis

Abstract: A cross-platform program, VESTA, has been developed to visualize both structural and volumetric data in multiple windows with tabs. VESTA represents crystal structures by ball-and-stick, space-filling, polyhedral, wireframe, stick, dot-surface and thermal-ellipsoid models. A variety of crystal-chemical information is extractable from fractional coordinates, occupancies and oxidation states of sites. Volumetric data such as electron and nuclear densities, Patterson functions, and wavefunctions are displayed as isosurfaces, bird's-eye views and two-dimensional maps. Isosurfaces can be colored according to other physical quantities. Translucent isosurfaces and/or slices can be overlapped with a structural model. Collaboration with external programs enables the user to locate bonds and bond angles in the `graphics area', simulate powder diffraction patterns, and calculate site potentials and Madelung energies. Electron densities determined experimentally are convertible into their Laplacians and electronic energy densities.

Statistical physics of social dynamics

Abstract: Statistical physics has proven to be a fruitful framework to describe phenomena outside the realm of traditional physics. Recent years have witnessed an attempt by physicists to study collective phenomena emerging from the interactions of individuals as elementary units in social structures. A wide list of topics are reviewed ranging from opinion and cultural and language dynamics to crowd behavior, hierarchy formation, human dynamics, and social spreading. The connections between these problems and other, more traditional, topics of statistical physics are highlighted. Comparison of model results with empirical data from social systems are also emphasized.

Traffic and related self-driven many-particle systems

Abstract: Since the subject of traffic dynamics has captured the interest of physicists, many surprising effects have been revealed and explained. Some of the questions now understood are the following: Why are vehicles sometimes stopped by ``phantom traffic jams'' even though drivers all like to drive fast? What are the mechanisms behind stop-and-go traffic? Why are there several different kinds of congestion, and how are they related? Why do most traffic jams occur considerably before the road capacity is reached? Can a temporary reduction in the volume of traffic cause a lasting traffic jam? Under which conditions can speed limits speed up traffic? Why do pedestrians moving in opposite directions normally organize into lanes, while similar systems ``freeze by heating''? All of these questions have been answered by applying and extending methods from statistical physics and nonlinear dynamics to self-driven many-particle systems. This article considers the empirical data and then reviews the main approaches to modeling pedestrian and vehicle traffic. These include microscopic (particle-based), mesoscopic (gas-kinetic), and macroscopic (fluid-dynamic) models. Attention is also paid to the formulation of a micro-macro link, to aspects of universality, and to other unifying concepts, such as a general modeling framework for self-driven many-particle systems, including spin systems. While the primary focus is upon vehicle and pedestrian traffic, applications to biological or socio-economic systems such as bacterial colonies, flocks of birds, panics, and stock market dynamics are touched upon as well.

Perspective on the Development of Lead-free Piezoceramics

Abstract: A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.