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

Computer analyses have been performed of the vibration of monatomic linear chains where each atom is in double minimum potential and is connected to nearest neighbor atoms by springs. It has shown that the increase of spring constant induces many low frequency vibrations in the small wave number region and then the system seems to become overdamped, with a frequency dependent loss factor.

Computer analysis of vibration of linear chain of atoms lying in a double minimum potential

A new mechanism of incommensurate (INC) phase transition will be mentioned. The INC phase may be stabilized by freezing of a soft mode on the [k, k, 0] or [k, k, 1/2] branch induced by the parabolic splitting of the doubly degenerate modes at the Brillouin zone boundary (1/2, 1/2, 0) or (1/2, 1/2, 1/2). A simple model theory of the incommensurate phase transition of this type is proposed, which easily reproduces a special feature for the INC phase that the macroscopic symmetry changes at the INC phase transition.

A New Mechanism of the Incommensurate Phase Transition

Ferroelectric hysteresis loops are discussed in terms of free energy expanded to the eighth order in polarization. For suitable choice of the coefficients, deformed triple hysteresis loops will be observed. There is a possibility that such deformed loops are utilized for nondestructive readout memory.

Hysteresis Loops in Ferroelectrics Undergoing an Isomorphous Phase Transition

We investigated the switching behavior of a ferroelectric liquid crystal with negative dielectric anisotropy in a high-applied-voltage region at various temperatures. It has been found that the switching time decreases with increasing applied voltage, but in higher-voltage regions it attains a minimum and then increases. By furthur increasing the applied voltage, the switching time attains a maximum and then decreases. The minimum of the switching time shifts towards a higher voltage with increasing temperature. It has been disclosed that the switching time falls on a universal curve when the switching time and the applied voltage are suitably scaled. The equation of motion with respect to the azimuthal angle φ of the n-director was introduced, and its analyses show qualitative agreement with the experimental findings.

Anomalous Applied Voltage Dependence of the Switching Time in a Ferroelectric Liquid Crystal with Negative Dielectric Anisotropy

The p - T phase diagram of Hg 2 Cl 2 was obtained through the measurements of strains carried out under various pressures up to about 5 kbar. Pressure derivative, d T c /d p , for the tetragonal-orthorhombic transition was found to be 44 K/kbar.

Yoshihiro Ishibashi

Papers

Computer analysis of vibration of linear chain of atoms lying in a double minimum potential

A New Mechanism of the Incommensurate Phase Transition

Hysteresis Loops in Ferroelectrics Undergoing an Isomorphous Phase Transition

Anomalous Applied Voltage Dependence of the Switching Time in a Ferroelectric Liquid Crystal with Negative Dielectric Anisotropy

Effect of Pressure on Phase Transition in Hg 2 Cl 2 Crystals