Quantitative tests revealing hydrogen enhanced dislocation motion in α-iron

Hydrogen embrittlement jeopardizes the use of high-strength steels as critical load-bearing components in energy, transportation, and infrastructure applications. However, our understanding of hydrogen embrittlement mechanism is still obstructed by the uncertain knowledge of how hydrogen affects dislocation motion, due to the lack of quantitative experimental evidence. Here, by studying the well-controlled, cyclic, bow-out movements of individual screw dislocations, the key to plastic deformation in α-iron, we find that the critical stress for initiating dislocation motion in a 2 Pa electron-beam-excited H2 atmosphere is 27~43% lower than that under vacuum conditions, proving that hydrogen lubricates screw dislocation motion. Moreover, we find that aside from vacuum degassing, dislocation motion facilitates the de-trapping of hydrogen, allowing the dislocation to regain its hydrogen-free behavior. Atomistic simulations reveal that the observed hydrogen-enhanced dislocation motion arises from the hydrogen-reduced kink nucleation barrier. These findings at individual dislocation level can help hydrogen embrittlement modelling in steels.

CAMSAP2 organizes a γ-tubulin-independent microtubule nucleation centre

Microtubules are dynamic polymers consisting of αβ-tubulin heterodimers. The initial polymerization process, called microtubule nucleation, occurs spontaneously via αβ-tubulin. Since a large energy barrier prevents microtubule nucleation in cells, the γ-tubulin ring complex is recruited to the centrosome to overcome the nucleation barrier. However, detachment of a considerable number of microtubules from the centrosome is known to contribute to fundamental processes in cells. Here, we present evidence that minus-end-binding calmodulin-regulated spectrin-associated protein 2 (CAMSAP2) serves as a strong nucleator for microtubule formation from soluble αβ-tubulin independent of γ-tubulin. CAMSAP2 significantly reduces the nucleation barrier close to the critical concentration for microtubule polymerization by stabilizing the longitudinal contacts among αβ-tubulins. CAMSAP2 clusters together with αβ-tubulin to generate nucleation intermediates, from which numerous microtubules radiate, forming aster-like structures. Our findings suggest that CAMSAP2 supports microtubule growth by organizing a nucleation centre as well as by stabilizing microtubule nucleation intermediates.

Parasitic crystallization of colloidal electrolytes: growing a metastable crystal from the nucleus of a stable phase

Despite its lower stability and higher nucleation barrier, a metastable charge-disordered colloidal phase manages to parasitically crystallize from nuclei of the stable charge-ordered phase due to its enhanced kinetic crystal growth.

Carbon dioxide and propane nucleation: the emergence of a nucleation barrier

A direct molecular level study of CO2 and C3H8 nucleation indicates a transition from barrierless to barrier-limited nucleation.