Mapping of the lunar surface by average atomic number based on positron annihilation radiation from Chang'e-1

A map of the average atomic number of lunar rock and soil can be used to differentiate lithology and soil type on the lunar surface.This paper establishes a linear relationship between the average atomic number of lunar rock or soil and the flux of position annihilation radiation(0.512-Me V gamma-ray) from the lunar surface.The relationship is confirmed by Monte Carlo simulation with data from lunar rock or soil samples collected by Luna(Russia) and Apollo(USA) missions.A map of the average atomic number of the lunar rock and soil on the lunar surface has been derived from the Gamma-Ray Spectrometer data collected by Chang'e-1,an unmanned Chinese lunar-orbiting spacecraft.In the map,the higher average atomic numbers(ZA > 12.5),which are related to different types of basalt,are in the maria region;the highest ZA(13.2) readings are associated with Sinus Aestuum.The middle ZA(~12.1) regions,in the shape of irregular oval rings,are in West Oceanus Procellarum and Mare Frigoris,which seems to be consistent with the distribution of potassium,rare earth elements,and phosphorus as a unique feature on the lunar surface.The lower average atomic numbers(ZA < 11.5)are found to be correlated with the anorthosite on the far side of the Moon.

Porous bio-high entropy alloy scaffolds fabricated by direct ink writing

Porous tantalum-titanium-niobium-zirconium(Ta-Ti-Nb-Zr)bio-high entropy alloy(bioHEA)scaffolds are fabricated using direct ink writing 3D printing technology in this study.A composite ink is prepared using four metal powders as raw materials:Ta,Ti,Nb and Zr.Ink extrusion is used to build 3D scaf-folds with interconnected porous structures at room temperature,which are then sintered in a vacuum environment.The interdiffusion of metal elements yields porous bioHEA scaffolds with a body-centered cubic(BCC)structure.The fabricated scaffolds have uniform compositions with a significant alloying ef-fect and good biocompatibility.The scaffolds have a compressive strength of 70.08-149.95 MPa and an elastic modulus of 0.18-0.64 GPa,indicating that the mechanical properties can be controlled over a wide range.The scaffolds have a compressive strength close to that of human cortical bone and thus meet the requirements for porous structure characteristics and biological and mechanical properties of orthopedic implants.