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

The Brillouin scattering spectra in NaNO2 have been studied using a Fabry-Perot interferometer. The observed Brillouin shifts for eighteen acoustic phonons in nine scattering geometries have been assigned to specific modes of vibration. All of nine elastic constants have been re-examined from these observations. The temperature dependence of C22D associated with the longitudinal phonon propagating along the ferroelectric b-axis has been studied with particular emphasis on the region close to the Curie and Neel points. The elastic stiffness constant C22D showed an anomalous decrease both at the Curie and at the Neel temperatures.

Brillouin scattering in sodium nitrite

The effect of optical purity on the antiferroelectric phase transition and the field-induced ferroelectric phase transition in Sm C A * were studied by means of dielectric measurements and observations of D-E hysteresis loops. The Curie-Weiss law was found to hold in Sm A and the Curie-Weiss constant to increase as the optical purity is reduced. Three types of D-E curves were obtained in the Sm C A * phase. It was found that a double hysteresis loop changed into a single one at high frequencies. The results obtained are discussed on the basis of a phenomenological theory

Experimental studies on phase ntransitions in an antiferroelectric liquid crystal

Exact Expressions for Some Dielectric Properties of Ferroelectric Thin Films Based on the Tilley-Zeks Model(Condensed matter : electronic structure and electrical, magnetic, and optical properties)

Lattice vibrations in finite discrete systems with symmetric and asymmetric boundary conditions are studied based on the Tilley-Zeks model. Two methods are adopted, i.e., one is the method utilizing analytical functions, and the other is the method of numerical solutions of an eigenvalue problem of the dynamical matrix form. It is found that, in finite systems, the normal modes, the soft-mode frequency and the transition temperature all depend strongly on the lattice constant a.

Lattice Vibrations in Finite Discrete Systems with Symmetric and Asymmetric Boundary Conditions

The phase transitions in ferroelectric KH 2 PO 4 (KDP) and antiferroelectric NH 4 H 2 PO 4 (ADP) crystals are discussed on the basis of the eight-pseudospin model of KH 2 PO 4 -type crystals previously proposed, where eight pseudospins represent protons on hydrogen bonds connecting PO 4 radicals in a unit cell. The dielectric susceptibilities along the c -axis, which is the unique ferroelectric axis, and a ( b )-axis, which is perpendicular to the unique axis, are calculated.

Yoshihiro Ishibashi

Papers

Brillouin scattering in sodium nitrite

Experimental studies on phase ntransitions in an antiferroelectric liquid crystal

Exact Expressions for Some Dielectric Properties of Ferroelectric Thin Films Based on the Tilley-Zeks Model(Condensed matter : electronic structure and electrical, magnetic, and optical properties)

Lattice Vibrations in Finite Discrete Systems with Symmetric and Asymmetric Boundary Conditions

Eight-Pseudospin Model of KH2PO4-Type Crystals: II. Phase Transitions and Dielectric Susceptibilities