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

Jamming Transition in Cellular Automaton Models for Pedestrians on Passageway

It is shown that (011) and (031) twin planes can be introduced in the orthorhombic phase of K 2 SO 4 and K 2 SeO 4 , and both twin planes can be moved smoothly through crystals by appropriate external stress in the temperature range from about 300°C to the orthorhombic-hexagonal phase transition point. It is inferred from the crystal structure in the orthorhombic phase that SO 4 - (or SeO 4 - ) radicals must have two stable states (the up and down states), and change from one state to another during the passage of twin planes. It is suggested that the space group of the hexagonal phase is D 6h 4 –P6 3 /mmc, and the hexagonal-orthorhombic phase transition is essentially due to the ordering of SO 4 - (or SeO 4 - ) radicals.

Hexagonal-Orthorhombic Phase Transition and Ferroelasticity in K2SO4 and K2SeO4

A new model of the electrorheological (ER) effect for immiscible polymer blends is proposed on the basis of microscopic observations. In the absence of an electric field the polymer with high viscosity is dispersed as droplets in the other polymer with low viscosity, while in the presence of an electric field, the droplets stretch and coalesce to form bridges between electrodes, resulting in the increase of the macroscopic viscosity. A few experimental results are given to confirm the validity of this model.

Electrorheological effect in immiscible polymer blends

The temporal variation of the average velocity of cars in the Biham-Middleton-Levine (BML) model is studied The equations which govern the temporal variation of the car velocities for various densities of cars are derived By utilizing these equations, the final average velocity is approximately obtained for most self-organized states

Temporal Variations of Traffic Flow in the Biham-Middleton-Levine Model

Successive phase transition in {N(CH 3 ) 4 } 2 CuCl 4 has been studied by polarization microscopic observation and by the measurement of dielectric constant. A new phase transition is found to take place at intermediate temperature (about 8°C on cooling, about 18°C on heating) between the two phase transition points at 24°C and -9.4°C previously reported. Evidence is presented that the phase transition is the one from an incommensurate phase to a ferroelastic (commensurate) phase.

Yoshihiro Ishibashi

Papers

Jamming Transition in Cellular Automaton Models for Pedestrians on Passageway

Hexagonal-Orthorhombic Phase Transition and Ferroelasticity in K2SO4 and K2SeO4

Electrorheological effect in immiscible polymer blends

Temporal Variations of Traffic Flow in the Biham-Middleton-Levine Model

Evidence of Incommensurate-Ferroelastic (Commensurate) Phase Transition in {N(CH 3 ) 4 } 2 CuCl 4 Crystal