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

Traverse Time in a Cellular Automaton Traffic Model

Successive phase transitions in lead-orthovanadate Pb 3 (VO 4 ) 2 are group-theoretically analyzed. The trigonal-to-monoclinic (nonpolar) transition is considered to be induced by an irreducible representation at the F point of the prototypic trigonal phase. The polar monoclinic phase is induced by simultaneous condensation of two representations at two different points both on the Brillouin zone boundary of the nonpolar monoclinic phase, which are located inside the Brillouin zone of the trigonal lattice. The reasons why the monoclinic (nonpolar)-to-monoclinic (polar) transition in Pb 3 (VO 4 ) 2 is not of the second order are pointed out.

Group-Theoretical Analyses of the Structural Phase Transitions in Lead-Orthovanadate Pb 3 (VO 4 ) 2 Crystal

Phase transitions in (1-x)Pb(In1/2Nb1/2)O3–xPbTiO3 (PIN–xPT) under two processes, i.e., zero-field heating (ZFH) after the field cooling (FC) and ZFH without FC, were investigated by dielectric constant measurement. The phase diagrams of PIN–xPT (0.2≤x≤0.45) subjected to the two processes were clarified. A new phase transition between ferroelectric phases in PIN–0.2PT on ZFH after FC was found at 113 °C. It was also revealed that the phase transition observed in PIN–0.2PT connects to the morphotropic phase boundary (MPB). We conclude that the phase transition found in PIN–0.2PT is a transition between the tetragonal and rhombohedral phases.

https://iopscience.iop.org/article/10.1143/JJAP.48.09KF07/pdf

Phase Transition under Zero-Field Heating after Field Cooling in (1-x)Pb(In1/2Nb1/2)O3–xPbTiO3

The tricritical point in temperature-electric field phase diagrams was derived for the Landau-type free energy applicable to the antiferroelectric phase transitions. The adopted free energy written in terms of two sublattice polarizations and the applied external field of the symmetry breaking nature contains three possible fourth-order terms and a sixth-order term, thus being capable of producing various types of phase diagrams. Examples of the tricritical points in the phase diagrams are presented for several parameter values.

Yoshihiro Ishibashi

Papers

Traverse Time in a Cellular Automaton Traffic Model

Group-Theoretical Analyses of the Structural Phase Transitions in Lead-Orthovanadate Pb 3 (VO 4 ) 2 Crystal

Phase Transition under Zero-Field Heating after Field Cooling in (1-x)Pb(In1/2Nb1/2)O3–xPbTiO3

Electric-Field Induced Tricritical Points in Antiferroelctric Phase Transitions

Effect of the Hydrostatic Pressure on the Transition Temperature in (NH 4 ) 2 SO 4