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.

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

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.

Statistical physics of social dynamics

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.

Traffic and related self-driven many-particle systems

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.

Perspective on the Development of Lead-free Piezoceramics

Statistical physics of vehicular traffic and some related systems

The electro-hydrodynamic instability was investigated in a nematic liquid crystal cell with the free boundary condition on the sides and with a small aspect ratio. In such a free lateral boundary cell, a transition from quasi-periodicity to chaos was observed by measuring the angle-deflective oscillation when the applied voltage was increased. The correlation dimension in the chaotic state was obtained from the time sequence of the transmission intensity.

The Transition from Quasi-Periodicity to Chaos in the Electro-Hydrodynamic Instability of a Nematic Liquid Crystal

The spontaneous polarization and dielectric susceptibility of relaxors have been calculated for the second and the first order transition cases on the basis of the assumed Gaussian distribution of the transition temperatures. Dispersion of the susceptibility is obtained on the effective medium approximation. The obtained frequency dependences of the temperatures, where the susceptibility attains peak values, are found to agree qualitatively with the experimental results.

Considerations on Dielectric Properties of Relaxors

The experimental results of the Brillouin scattering in several scheelite-type crystals are briefly reviewed. The high pressure Raman scattering studies of LaNbO 4 and NdNbO 4 crystals were recently carried out and have revealed that the behavior of their lowest frequency optical modes is quite different from the one reported for BiVO 4 . A lattice model for the ferroelastic transition from a tetragonal phase is presented and discussed.

The ferroelastic transition in some scheelite-type crystals

Domain structures formed by quench in the NaNO 2 -type crystals, whose incommensurate phase transition can be reproduced by the thermodynamic potential with no Lifshitz invariant, have been studied by solving the kinetic equation numerically, adopting a two-dimensional model. The temporal evolution of domain structures, consisting of positive and negative domains, is shown and analyzed. It has turned out that in the early stage the amplitude of the modulation wave with a specific wavenumber grows up and then the phase approaches the stable state.

Growth Kinetics of Domain Structures of Crystal with an Incommensurate Phase –The Case of No Lifshitz Invariant–

Landau potential functional is derived for type-I commensurate- incommensurate phase transitions that appear in the phase diagram of a simple discrete model with fourth order anharmonicity (DIFFOUR model) Coefficients of the lowest order terms (including the usual Lifshitz and lock-in terms) are given explicitly for the rippled (polar) phases with the period p = 3, 5 and 7 sites

Yoshihiro Ishibashi

Papers

The Transition from Quasi-Periodicity to Chaos in the Electro-Hydrodynamic Instability of a Nematic Liquid Crystal

Considerations on Dielectric Properties of Relaxors

The ferroelastic transition in some scheelite-type crystals

Growth Kinetics of Domain Structures of Crystal with an Incommensurate Phase –The Case of No Lifshitz Invariant–

Rippled Commensurate Phases in DIFFOUR Model: Continuum Approximation.