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

Lattice vibrations in finite systems with the boundary conditions given as the extrapolation lengths are studied on the basis of the continuum model The system may be symmetric or asymmetric regarding the extrapolation lengths, which can be positive, negative, or of mixed signs In general, even cosine modes and odd sine modes appear alternately from the low-frequency side, but the lowest cosine mode changes to the cosh mode and the second-lowest sine mode may change to the sinh mode when the extrapolation lengths at both boundaries are negative On the other hand, it is not possible to assign the sin (sinh) mode or cos (cosh) mode to the lowest-frequency mode in the case of mixed-sign extrapolation lengths Orthogonality between the normal modes can be proved using the boundary conditions in spite of the fact that the wavenumbers K i of the normal modes are mutually incommensurate

Lattice Vibrations in Finite Systems with Boundary Conditions Given as the Extrapolation Lengths: I. Continuum Model

Brillouin scattering spectra and the thermal expansion of SnCl 2 ·2H 2 O were experimentaly studied over a temperature range covering the isomorphous transition at -55°C ( T c ). The frequency shifts of the longitudinal phonon show an anomaly at the phase transition temperature for q //[100], [001] and [101] but not for q //[010]. The thermal expansions along the crystalline axes a * , b and c show discontinuity at T c .

Brillouin Scattering and Thermal Expansion of SnCl2·2H2O

Second-order Raman spectra of CsCl single crystals

An order-disorder theory of the tetragonal-monoclinic phase transition of squaric acid (H 2 C 4 O 4 ) crystal is developed where the ice rule of proton configurations on hydrogen-bonds is respected. It is shown that the model adopted previously for the antiferroelectric transition of NH 4 H 2 PO 4 can be applied, only with a slight modification, and it gives rise to a first order transition. The coupling between the transition parameters and the strain component affects the order of the transition.

A Statistical Theory of the Phase Transition of Squaric Acid (H 2 C 4 O 4 ) Crystal

A theory of 90° domain walls in tetragonal ferroelectrics is proposed. It is argued that the depolarizing field discerns the stable head-to-tail wall from the unstable head-to-head wall energetically. The relation between the free energy function and the effect of the depolarizing field is discussed.

Yoshihiro Ishibashi

Papers

Lattice Vibrations in Finite Systems with Boundary Conditions Given as the Extrapolation Lengths: I. Continuum Model

Brillouin Scattering and Thermal Expansion of SnCl2·2H2O

Second-order Raman spectra of CsCl single crystals

A Statistical Theory of the Phase Transition of Squaric Acid (H 2 C 4 O 4 ) Crystal

Theoretical consideration on the 90° domain walls in tetragonal ferroelectrics