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

Dielectric Properties of (NH4)2SnBr6

The temperature dependences of the dielectric constants of Bi4-xGdxTi3O12 (BGT-x) single crystals (x≤0.4) were measured. It was found that the paraelectric–ferroelectric phase transition temperature near 680 °C remains almost unchanged in the concentration range of 0≤x ≤0.4. Below the transition point at about 680 °C, another dielectric anomaly showing the phase transition was observed in BGT-x, where the transition temperature depends on the concentration x. We confirmed that the triggered transition from the tetragonal phase to the monoclinic phase, observed in Bi4Ti3O12, splits into two phase transitions with the addition of Gd cations, i.e., from the tetragonal phase to the orthorhombic phase and eventually to the monoclinic phase. The temperature-concentration phase diagram in BGT-x was clarified.

Phase Diagram in Bi$_{4-x}$Gd$_{x}$Ti$_{3}$O$_{12}$

Curie constant in relaxor ferroelectrics Pb(Zn

A Landau free energy proposed for the phase transitions in phospholipid bilayers has been reexamined, and the phase diagram in the adopted parameter space is presented. The temperature dependences of specific heat and the elastic stiffness constant associated with the order parameter derived from the given free energy function are shown.

A Phase Diagram Including the Intermediate Rippled Phase of Phospholipid Bilayers

The composition dependence of the structure and dielectric properties of solid solutions Sr2-x Pb x Bi4Ti5O18(0≦ x ≦ 2) (abbreviated as SPBT) was investigated. The unit cell volume of SPBT increases with increasing x. The phase below the transition temperature Tc is confirmed to be ferroelectric by the observation of P–E hysteresis loops. With increasing x, Tc decreases for x 1. Tc increases with increasing pressure. The relaxor behavior appears for x > 1.

Yoshihiro Ishibashi

Papers

Dielectric Properties of (NH4)2SnBr6

Phase Diagram in Bi$_{4-x}$Gd$_{x}$Ti$_{3}$O$_{12}$

Curie constant in relaxor ferroelectrics Pb(Zn

A Phase Diagram Including the Intermediate Rippled Phase of Phospholipid Bilayers

Dielectric properties and pressure effects in layer-type bismuth solid solution of Sr2-x Pb x Bi4Ti5O18(0≤x≤2)