Effect of Printing Parameters on the Surface Roughness of 3D-Printed Melt-Cast Explosive Substitutes Based on Melt Extrusion Technology.

In recent years, the application of 3D printing technology in the energetic materials field has proved its ability to innovate traditional charging methods and fabricate complex structures to improve combustion/detonation performance. The melt extrusion technology is the most promising way to fabricate complex structures and multiple components of melt-cast explosives. In this study, a paraffine-based composite was used to substitute melt-cast explosives, and a Design of Experiments approach based on central composite design was adopted to investigate the influence of layer thickness, percent infill, extrusion temperature, and printing velocity on the roughness of printed samples. The results showed that layer thickness and printing velocity could significantly influence the roughness of printed specimens, and no obvious voids or cracks inside the specimens can be detected in computed tomography. In addition, a composite-shaped grain was successfully fabricated via the EAM-D-1 printer, which proved the feasibility of 3D printing melt-cast explosives with complex structures. This work will greatly help to achieve 3D printing melt-cast explosives with complex structures and higher accuracy.

Variation in bill surface area is associated with local climatic factors across populations of the plain laughingthrush.

Recent studies have found that avian bill and tarsus morphology may have evolved in response to climatic conditions, and these organs play important roles in thermoregulation and water retention in extreme environments. Here, we examined whether bill surface area and tarsus length were associated with climatic conditions in the plain laughingthrush, Garrulax davidi, which mainly occurs in north China and occupies several climatic zones from east to west. We measured bill surface area and tarsus length in 321 adults from 11 populations, almost encompassing all habitat types of the species. We analyzed the relationships among these morphological traits and local climatic factors. Bill surface area was positively correlated with maximum temperature, indicating that bill surface area tended to be larger in hotter environments. Furthermore, we found a negative relationship among bill surface area and winter precipitation, indicating that bill surface area tended to be larger in arid areas. However, we did not find any relationships between tarsus length and climatic factors. These results suggest that local climates may shape the evolution of bill morphology divergence, and summer seems to be the critical season for thermoregulation in this temperate zone passerine.