Yingxia Wei

Deformation mechanisms of face-centered-cubic metal nanowires with twin boundaries

This letter addresses the issue of deformation mechanisms and mechanical tensile behavior of the twinned metal nanowires using atomistic simulations. Free surfaces are always the preferential dislocation nucleation sites in the initial inelastic deformation stage, while with further plastic deformation, twin boundary interfaces will act as sources of dislocations with the assistance of the newly formed defects. The smaller the twin boundary spacing, the higher the yielding stresses of the twinned nanowires. Twin boundaries, which serve both as obstacles to dislocation motion and dislocation sources, can lead to hardening effects and contribute to the tensile ductility. This work illustrates that the mechanical properties of metal nanowires could be controlled by tailoring internal growth twin structures. (c) 2007 American Institute of Physics.

Formation of fivefold deformation twins in nanocrystalline face-centered-cubic copper based on molecular dynamics simulations

Fivefold deformation twins were reported recently to be observed in the experiment of the nanocrystalline face-centered-cubic metals and alloys. However, they were not predicted previously based on the molecular dynamics (MD) simulations and the reason was thought to be a uniaxial tension considered in the simulations. In the present investigation, through introducing pretwins in grain regions, using the MD simulations, the authors predict out the fivefold deformation twins in the grain regions of the nanocrystal grain cell, which undergoes a uniaxial tension. It is shown in their simulation results that series of Shockley partial dislocations emitted from grain boundaries provide sequential twining mechanism, which results in fivefold deformation twins.

Direct observation of laser guided corona discharges

Laser based lightning control holds a promising way to solve the problem of the long standing disaster of lightning strikes. But it is a challenging project due to insufficient understanding of the interaction between laser plasma channel and high voltage electric filed. In this work, a direct observation of laser guided corona discharge is reported. Laser filament guided streamer and leader types of corona discharges were observed. An enhanced ionization took place in the leader (filament) through the interaction with the high voltage discharging field. The fluorescence lifetime of laser filament guided corona discharge was measured to be several microseconds, which is 3 orders of magnitude longer than the fluorescence lifetime of laser filaments. This work could be advantageous towards a better understanding of laser assisted leader development in the atmosphere.

Longitudinally resolved measurement of plasma density along femtosecond laser filament via terahertz spectroscopy

We report on a longitudinally resolved measurement of plasma density along femtosecond laser filament in air via terahertz (THz) spectroscopy. By applying a needlelike high-voltage direct current (DC) electric field on the laser filament and scanning it along filament, the longitudinal evolution of amplified THz emission has been demonstrated. The peak frequency of the DC electric field biased THz emission is proportional to the plasma density inside the laser filament. This latter phenomenon was used to characterize the plasma density. Longitudinal distribution of plasma density of ∼1015 cm−3 along laser filament has been experimentally recorded. The technique demonstrated is very simple and helpful for understanding the THz generation process through laser filamentation.