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

Using the theory of Hilbert and Schmidt, spectrum can be reconstructed from the multiplebeam interferogram obtained with the Fabry-Perot interferometer . The resolution of this spectroscopic method is studied by the computer simulation. The effect of noise involved in the interferogram can be reduced by discarding the high frequency terms in eigenf unction expansion. The resolving power of this method turned out to be several millions and is about ten times larger than that obtained with conventional method . Results obtained by the method of Hilbert and Schmidt are compared with those obtained with the direct method. In the direct method, reconstructed spectrum using the interferogram involving noise is usually distorted. But it can be improved to some extent by applying the Fourier analysis.

High resolution spectroscopy by analysis of multiple-beam interferogram.

Phase diagrams possible in successive phase transitions in BaTiO3-type oxides are presented for the cases where the transition from the cubic phase is of the first order. Critical points may appear when the model parameters change.

Phase diagrams in successive phase transitions in BaTiO3-type oxides : Cases of the first order transitions from the cubic phase

Temperature dependences of the third-order nonlinear dielectric constant in the mixed crystals of Rb 1- x (NH 4 ) x H 2 PO 4 with x =0.25, 0.3, 0.4, 0.5, 0.6 and 0.7 were measured in the temperature range between 4 and 50 K. It was observed that the nonlinear dielectric constant in these crystals increases near the glass transition point and it is strongly dispersive at low frequencies. It was found that the third-order nonlinear dielectric constant is proportional to the imaginary part of the linear dielectric constant when measured under changing temperature at a fixed frequency.

Measurement of Nonlinear Dielectric Constant in Rb 1-x(NH 4)xH 2PO 4 Mixed Crystals

On the Lattice Instability in Incommensurate Phase Transition of K2SeO4

The electrostrictions in KH 2 PO 4 are discussed. It is shown that both the spontaneous strain in the ferroelectric phase and the field-induced strain in the paraelectric phase can be interpreted in a unified fashion even in terms of the simplest Slater model by taking into account the coupling between the strain and the fraction of sideway H 2 PO 4 - radicals, r . The order parameter θ, previously introduced by other workers, may not be necessary for the explanation of the peculiar nateur of the electrostrictions in this material.

Yoshihiro Ishibashi

Papers

High resolution spectroscopy by analysis of multiple-beam interferogram.

Phase diagrams in successive phase transitions in BaTiO3-type oxides : Cases of the first order transitions from the cubic phase

Measurement of Nonlinear Dielectric Constant in Rb 1-x(NH 4)xH 2PO 4 Mixed Crystals

On the Lattice Instability in Incommensurate Phase Transition of K2SeO4

Comments on Electrostrictions in KH2PO4