Self-propulsion is a characteristic mechanical feature of living organisms. A flagellum or cilium, a hair-like appendage of eukaryotic cellular swimming, has been a central research topic in biophysical studies. In this review article, we aim to provide a comprehensive summary of the continuum mechanics governing such living matter, with a specific emphasis on self-propelled objects moving through viscous, low-Reynolds-number fluids. As the scallop theorem asserts, self-propulsion is only attainable through a non-reciprocal path in shape space. We present an overview of the underlying theories behind this non-reciprocity, drawing on recent advances in the gauge-theoretic formulation and the odd-elasticity framework of active matter.

Growth of ice crystals is ubiquitous around us. However, despite its importance in nature and technology, we still do not know what is occurring at the forefront in the melt growth of ice. Here, using extensive molecular dynamics simulations, we comprehensively explore how supercooled water molecules are incorporated into the ice basal face. Structural and dynamic characterizations of the ice-water interface demonstrate that the ice basal face is sharp at the molecular level and its growth proceeds layer-by-layer through two-dimensional nucleation without any intermediate structures. We further quantify the crossover from layerwise to adhesive growth, called kinetic roughening, with the height difference correlation and the normal growth rate analysis. Moreover, we identify the presence of an ultra-low density water layer in contact with the structural interface, which assists two-dimensional nucleation at a small amount of supercooling without involving any triggers, such as dislocations.

The ultrahigh-magnetic-field phase of solid oxygen, θ phase, has been discovered by applying 130 T. We discuss the phase transition mechanism and the proposed crystal structure of the θ phase. We also discuss the scenario of the magnetic-field-induced liquid-liquid transition of oxygen.

On 2021 May 27, an extremely energetic particle dubbed “Amarterasu particle” was detected by the surface detector array of the Telescope Array experiment which is the largest cosmic ray detector in the northern hemisphere located in Utah, USA. We report on the detection of this particle, reconstruction method, possible interpretations, and future perspectives including ongoing upgrades dubbed TA×4 and TALE experiments.