In-situ TEM observation of the evolution of helium bubbles in Mo during He^(+)irradiation and post-irradiation annealing

The evolution of helium bubbles in purity Mo was investigated by in-situ transmission electron microscopy(TEM)during 30 keV He^(+)irradiation(at 673 K and 1173 K)and post-irradiation annealing(after 30 keV He^(+)irradiation with the fluence of 5.74×10^(16)He^(+)/cm^(2)at 673 K).Both He^(+)irradiation and subsequently annealing induced the initiation,aggregation,and growth of helium bubbles.Temperature had a significant effect on the initiation and evolution of helium bubbles.The higher the irradiation temperature was,the larger the bubble size at the same irradiation fluence would be.At 1173 K irradiation,helium bubbles nucleated and grew preferentially at grain boundaries and showed super large size,which would induce the formation of microcracks.At the same time,the geometry of helium bubbles changed from sphericity to polyhedron.The polyhedral bubbles preferred to grow in the shape bounded by{100}planes.After statistical analysis of the characteristic parameters of helium bubbles,the functions between the average size,number density of helium bubbles,swelling rate and irradiation damage were obtained.Meanwhile,an empirical formula for calculating the size of helium bubbles during the annealing was also provided.

Co-culture of oligodendrocytes and neurons can be used to assess drugs for axon regeneration in the central nervous system

We present a novel in vitro model in which to investigate the efficacy of experimental drugs for the promotion of axon regeneration in the central nervous system. We co-cultured rat hippocampal neurons and cerebral cortical oligodendrocytes, and tested the co-culture system using a Nogo-66 receptor antagonist peptide（NEP1–40）, which promotes axonal growth. Primary cultured oligodendrocytes suppressed axonal growth in the rat hippocampus, but NEP1–40 stimulated axonal growth in the co-culture system. Our results confirm the validity of the neuron-oligodendrocyte co-culture system as an assay for the evaluation of drugs for axon regeneration in the central nervous system.

Numerical simulation of fracture propagation in Russia carbonate reservoirs during refracturing

Refracturing treatment is often performed on Russian carbonate reservoirs because of the quick production decline of reservoirs.The traditional refracturing model assumes that a refracture initiates in the normal direction relative to the initial hydro-fracture.This assumption is inconsistent with oilfield measurements of refracture propagation trajectories.Indeed,the existing model is not based on an indepth understanding of initiation and propagation mechanisms of the second hydraulic fractures during refracturing.In this study,we use the extended finite element method to investigate refracture propagation paths at different initiation angles.Both the enriched function approach and phantom mode technique are incorporated into the refracturing model,thereby ensuring that the refracture can freely extend on the structured mesh without any refinement near the crack tips.Key factors including production time,stress anisotropy and initiation angle,and the propped mechanical effect are analyzed in detail.This study provides new insight into the mechanism of refracture propagation in unconventional reservoirs.

In-situ transmission electron microscopy observation of the evolution of dislocation loops and gas bubbles in tungsten during H2+and He+dual-beam irradiation

Dislocation loop and gas bubble evolution in tungsten were in-situ investigated under 30 keV H_(2)^(+)and He^(+)dual-beam irra-diation at 973 K and 1173 K.The average size and number density of dislocation loops and gas bubbles were obtained as a function of irradiation dose.The quantitative calculation and analysis of the migration distance of 1/2<111>loops at low irradiation dose indicated that the main mechanism of the formation of<100>loops should be attributed to the high-density helium cluster inducement mechanism,instead of the 1/2<111>loop reaction mechanism.H2+and He+dual-beam irradiation induced the formation of<100>loops and 1/2<111>loops,while increasing the irradiation temperature would increase<100>loop percentage.The percentage of<100>loops was approximately 18.6%at 973 K and increased to 22.9%at 1173 K.The loop reaction between two 1/2<111>loops to form a large-sized 1/2<111>loop was in-situ observed,which induced not only the decrease of the number of 1/2<111>loops but also the significant increase of their sizes.The<100>loops impeded the movement of dislocation line and tended to escape from it instead of being absorbed.With the increase of irradiation dose,the yield strength increment(Δ_(σloop))caused by the change of loop size and density increased first and then decreased slightly,while the yield strength increment(Δ_(σbubble))caused by the change of bubble size and density always increased.Meanwhile,within the current irradiation dose range,Δ_(σloop)was much larger thanΔ_(σbubble).