Crystal-Structure Matches in Solid-Solid Phase Transitions.

The exploration of solid-solid phase transition suffers from the uncertainty of how atoms in two crystal structures match. We devised a theoretical framework to describe and classify crystal-structure matches (CSM). Such description fully exploits the translational and rotational symmetries and is independent of the choice of supercells. This is enabled by the use of the Hermite normal form, an analog of reduced echelon form for integer matrices. With its help, exhausting all CSMs is made possible, which goes beyond the conventional optimization schemes. In an example study of the martensitic transformation of steel, our enumeration algorithm finds many candidate CSMs with lower strains than known mechanisms. Two long-sought CSMs accounting for the most commonly observed Kurdjumov-Sachs orientation relationship and the Nishiyama-Wassermann orientation relationship are unveiled. Given the comprehensiveness and efficiency, our enumeration scheme provide a promising strategy for solid-solid phase transition mechanism research.

Dynamic Nature of High-Pressure Ice VII.

Starting from Shannon's definition of dynamic entropy, we propose a theory to describe the rare-event-determined dynamic states in condensed matter and their transitions and apply it to high-pressure ice VII. A dynamic intensive quantity named dynamic field, rather than the conventional thermodynamic intensive quantities such as temperature and pressure, is taken as the controlling variable. The dynamic entropy versus dynamic field curve demonstrates two dynamic states in the stability region of ice VII and dynamic ice VII. Their microscopic differences were assigned to the dynamic patterns of proton transfer. This study puts a similar dynamical theory used in earlier studies of glass models on a simpler and more fundamental basis, which could be applied to describe the dynamic states of more realistic condensed matter systems.

Ferroelectric Problem beyond the Conventional Scaling Law.

Ferroelectric (FE) size effects against the scaling law were reported recently in ultrathin group-IV monochalcogenides, and extrinsic effects (e.g., defects and lattice strains) were often resorted to. Via first-principles based finite-temperature (T) simulations, we reveal that these abnormalities are intrinsic to their unusual symmetry breaking from bulk to thin film. Changes of the electronic structures result in different order parameters characterizing the FE phase transition in bulk and in thin films, and invalidation of the scaling law. Beyond the scaling law T_{c} limit, this mechanism can help predict materials that are promising for room-T ultrathin FE devices of broad interest.

Complex phase diagram and supercritical matter.

The supercritical region is often described as uniform with no definite transitions. The distinct behaviors of the matter therein, e.g., as liquidlike and gaslike, however, suggest "supercritical boundaries." Here we provide a mathematical description of these phenomena by revisiting the Yang-Lee theory and introducing a complex phase diagram, specifically a four-dimensional (4D) one with complex T and p. While the traditional 2D phase diagram with real temperature T and pressure p values (the physical plane) lacks Lee-Yang (LY) zeros beyond the critical point, preventing the occurrence of criticality, the off-plane zeros in this 4D scenario still induce critical anomalies in various physical properties. This relationship is evidenced by the correlation between the Widom line and LY edges in van der Waals, 2D Ising model, and water. The diverged supercritical boundaries manifest the high-dimensional feature of the phase diagram: e.g., when LY zeros of complex T or p are projected onto the physical plane, boundaries defined by isobaric heat capacity C_{p} or isothermal compression coefficient K_{T} emanates. These results demonstrate the incipient phase transition nature of the supercritical matter.

Effects of light illumination and the expression of wee1 on tissue regeneration in adult zebrafish.

The zebrafish exhibits an enhanced capability of regenerating most of its adult tissues. In this study, we examine the roles of light illumination and functional expression of mitosis-specific gene wee1 on adult zebrafish caudal fin regeneration after amputation. During the first 3 days post-amputation (dpa), the caudal fin regenerate rapidly in the day but slowly at night when the fish are kept in a normal light-dark cycle (LD) condition. However, this day-night rhythm of fin regeneration is not seen when the fish are kept in constant dark (DD), constant light (LL), or in fish in which the circadian rhythms are disrupted by random light (RL) exposures. The rate of fin growth reaches the peak levels at 2.5 dpa in LD, but is delayed when the fish are kept in DD, LL or RL conditions. In zebrafish in which the expression of wee1 is blocked by morpholinos, regeneration of the caudal fin is affected. Interestingly, the expression of wee1 also displays robust circadian rhythms. Together, the data suggests that fin regeneration in zebrafish is regulated by both environmental cues and functional gene expressions. Alterations in lighting conditions or inhibition of wee1 expression result in decreases in fin regeneration after injury.

Tissue regeneration after injury in adult zebrafish: the regenerative potential of the caudal fin.

The zebrafish has the potential to regenerate many of its tissues. In this study, we examined caudal fin regeneration in zebrafish that received repeated injuries (fin amputation) at different ages. In zebrafish that received repeated injuries, the potential for caudal fin regeneration, such as tissue growth and the expression of regeneration marker genes (msxb, fgf20a, bmp2b), did not decline in comparison to zebrafish that received only one amputation surgery. The process of initial fin regeneration (e.g., tissue outgrowth and the expression of regeneration marker genes at 7 days post-amputation) did not seem to correlate with age. However, slight differences in fin outgrowth were observed between young and old animals when examined in the late regeneration stages (e.g., 20 and 30 days post-amputation). Together, the data suggest that zebrafish has unlimited regenerative potential in the injured caudal fin.