A recent progress on computational homology, especially, persistent homology, is summarized in this article. The persistent homology is a topological method which captures “shape of data” in multi-scale way. After brief introductions on related topological concepts, we also explain applications of these methods into glassy materials and block copolymers.

We review the interconversion phenomena between spin and mechanical angular momentum in moving bodies. In non-inertial frames, spin-dependent inertial forces emerge, which enable the conversion from mechanical angular momentum into spins. In particular, this article focuses the recent results on spin manipulation and spin-current generation from mechanical motion, including rigid rotation, elastic deformations and fluid motion.

Galactic Cosmic Rays (CRs), mostly CR protons, are accelerated up to a few PeV energies. While it is widely believed that supernova remnants (SNRs) are the sources of Galactic cosmic rays, unequivocal evidence for the acceleration of high-energy protons in SNRs lacked until recently. Inelastic collisions between high-energy protons with nuclei in the interstellar gas produce neutral pions, which in turn decay into gamma rays whose energy and spatial distributions reflect those of parent protons. This offers a compelling way to reveal the acceleration sites of protons. However, the identification of piondecay gamma rays has been tantalizingly difficult since high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. Recently, the Fermi-LAT Collaboration has reported on the detection of the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, which are known to be interacting with molecular clouds. It provides direct evidence that cosmic-ray protons are accelerated in SNRs. We describe the Fermi-LAT observations of these objects along with gamma-ray observations of some other remnants and discuss their implications to our understanding of the acceleration of the Galactic CRs.

In recent years, the relationship between thermodynamics and information has been intensively studied, leading to an emerging field of “information thermodynamics.” We have derived the second law of information thermodynamics on Bayesian networks, and applied it to biochemical information processing of E. coli chemotaxis. In this article, we review the basic concepts in information thermodynamics and our recent results.

Motivated by the colossal negative thermal expansion recently found in BiNiO₃ , the valence transition accompanied by the charge transfer between the Bi and Ni sites is theoretically studied. We introduce an effective model for Bi-6s and Ni-3d orbitals with taking into account the valence skipping of Bi cations, and investigate the ground-state and finite-temperature phase diagrams within the mean-field approximation. We find that the valence transition is caused by commensurate locking of the electron filling in each orbital associated with charge and magnetic orderings, and the critical temperature and the nature of the transitions are strongly affected by the relative energy between the Bi and Ni levels and the effective electron-electron interaction in the Bi sites. The obtained phase diagram well explains the temperature- and pressure-driven valence transitions in BiNiO₃ and the systematic variation of valence states for a series of Bi and Pb perovskite oxides. We also report recent spectroscopic experimental results in the Bi and Pb oxides.

Since the pioneering prediction of surface melting by Michael Faraday, it has been widely accepted that thin water layers, called quasi-liquid layers (QLLs), completely wet ice surfaces. Contrary to this conventional wisdom, we demonstrate that QLLs have two wetting states and that there is a first-order wetting transition between them. Furthermore, We find that QLLs are born not only under supersaturated conditions but also at undersaturation, but QLLs are absent at equilibrium. Here we propose a simple physical model that consistently explains these new aspects of surface melting of ice. We show that QLLs are a metastable transient state formed through vapour growth and sublimation of ice, which casts a serious doubt on the conventional understanding presupposing the spontaneous formation of QLLs in ice-vapor equilibrium.