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

We measured the D - E hysteresis loop of TGS (triglycine sulphate), and transformed it to the q - E hysteresis loop by a method proposed in this paper, where q is the volume fraction of reversed domains. The experimental result was compared with a theory based on the Avrami model by the present authors [H. Orihara, S. Hashimoto and Y. Ishibashi: J. Phys. Soc. Jpn. 63 (1994) 1031], in which the volume fraction 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 . We obtained a good agreement between them and confirmed the validity of our theory. The frequency dependences of the coercive field and the area inside the loop were measured and power laws were obtained with respect to them, which are discussed on the basis of the theory.

Study on D-E Hysteresis Loop of TGS Based on the Avrami-Type Model

Pattern Formation in Liquid Crystals

A Microscopic Model of a Negative Poisson's Ratio in Some Crystals

The D-E hysteresis loop of ferroelectrics is theoretically studied on the basis of the Avrami model, extended for the case of applied field dependent sidewise velocity. The exponent for the frequency dependence of the extended volume is obtained. The exponent of the area of hysteresis loop, with respect to the frequncy, is also obtained.

A theory of D-E hysteresis loop

The phase diagram of (NH 4 ) 2 SO 4 -K 2 SO 4 mixed crystal system was obtained from dielectric and pyroelectric study. It was found that the ferroelectric phase transition temperature T c decreases with the increase of concentration of K + ions, and ferroelectric phase disappears if mixed crystals contain more than 70% of K 2 SO 4 . It was also found that the spontaneous polarization of mixed crystals with low concentration of K + ion (up to 30%) increases first to maximum, and then gradually decreases as the temperature is lowered. These experimental observations suggest that in this system single homogeneous polarization may not be an order parameter and the dipole arrangements of this system may be not ferroelectric but ferrielectric as was first pointed out by Unruh.

Yoshihiro Ishibashi

Papers

Study on D-E Hysteresis Loop of TGS Based on the Avrami-Type Model

Pattern Formation in Liquid Crystals

A Microscopic Model of a Negative Poisson's Ratio in Some Crystals

A theory of D-E hysteresis loop

Ferroelectric Phase Transition in (NH4)2SO4-K2SO4 Mixed Crystals