In situ observation of the phase transformation kinetics of bismuth during shock release

A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-Ⅳphase during the shock release,instead of the thermodynamically stable Bi-Ⅲphase.The emergence of the metastable Bi-Ⅳphase is understood by the competitive interplay between two transformation pathways towards the Bi-Ⅳand Bi-Ⅲ,respectively.The former is more rapid than the latter because the Bi-Ⅴto B-Ⅳtransformation is driven by interaction between the closest atoms while the Bi-Ⅴto B-Ⅲtransformation requires interaction between the second-closest atoms.The nucleation time for the Bi-Ⅴto Bi-Ⅳtransformation is determined to be 5.1±0.9 ns according to a classical nucleation model.This observation demonstrates the importance of the formation of the transient metastable phases,which can change the phase transformation pathway in a dynamic process.

Direct visualization of laser-driven dynamic fragmentation in tin by in situ x-ray diffraction

We present a novel method for investigating laser-driven dynamic fragmentation in tin using in situ X-ray diffraction.Our experimental results demonstrate the feasibility of the method for simultaneously identifying the phase and temperature of fragments through analysis of the diffraction pattern.Surprisingly,we observe a deviation from the widely accepted isentropic release assumption,with the temperature of the fragments being found to be more than 100 K higher than expected,owing to the release of plastic work during dynamic fragmentation.Our findings are further verified through extensive large-scale molecular dynamics simulations,in which strain energies are found to be transferred into thermal energies during the nucleation and growth of voids,leading to an increase in temperature.Our findings thus provide crucial insights into the impact-driven dynamic fragmentation phenomenon and reveal the significant influence of plastic work on material response during shock release.

Integrated slipper retainer mechanism to eliminate slipper wear in high-speed axial piston pumps

he power density of axial piston pumps can greatly benefit from increasing the speed level.However,traditional slippers in axial piston pumps are exposed to continuous sliding on the swash plate,suffering from serious wear at high rotational speeds.Therefore,this paper presents a new integrated slipper retainer mechanism for high-speed axial piston pumps,which can avoid direct contact between the slippers and the swash plate and thereby eliminate slipper wear under severe operating conditions.A lubrication model was developed for this specific slipper retainer mechanism,and experiments were carried out on a pump prototype operating at high rotational speed up to 10000 r/min.Experimental results qualitatively validated the theoretical model and confirmed the effectiveness of the new slipper design.

Visualization of MicrotubuleOrganization and Dynamics in Living Arabidopsis Embryonic Cells

Dear Editor, Embryogenesis is a critical developmental stage during the life cycle of flowering plants. During embryogenesis, the first round of asymmetric cell division in the zygote is followed by a series of cellular events, including cell division （symmetric or asymmetric） and directional cell expan- sion to generate the apical-basal axis, radial and lateral symmetry, and patterns of different cell fates for initiation of different organ primordia, which lay the foundation for post-embryonic development （Jurgens, 2001; Wendrich and Weijers, 2013）.