天体物理学与航空航天技术

An array of formations resembling the fossilized remains of Ediacaran and Cambrian fauna and other marine organisms have been observed embedded atop sediments in the dried lake beds of Gale Crater, Mars. Specimens similar and diverse in morphology have been found together and upon adjacent and nearby rocks and mudstone. These include forms morphologically similar to polychaete and segmented annelids, tube worms, "Kimberella,” crustaceans, lobopods, chelicerates, Haplophrentis carinatus, and the “ice-cream-cone-shaped” “Namacalathus” and “Lophophorates” and other biomineralized metazoans. All specimens may have dwelled in a large body of water and fossilized/mineralized following the rapid receding of these waters. Statistical quantitative micro- and macro- morphological comparisons with analog organisms from Earth support the fossil-hypothesis. It is not likely so many similar and diverse specimens, side by side, oriented differently, some on top of each other, were fashioned via abiogenic forces such as wind, mineralization, crystallization, dried mud, or water-erosion scenarios as there are no terrestrial abiogenic analogs. Interplanetary transfer of life may explain the parallels with Earth. Collectively these putative fossils may represent the equivalent of a “Cambrian Explosion” and the remnants of Martian organisms that long ago flourished in the lakes and inland seas of Gale Crater.

The European Space Agency's astronomical observatory known as INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) has been responsible for numerous significant scientific discoveries over the past few decades. Since 2002, it has been in an extremely elliptical orbit around Earth, passing through the Van Allen belts, which contain high-energy ionized particles that have the potential to harm the spacecraft's onboard equipment. Thus, predicting the entry and exit times of its radiation belts is an essential component of INTEGRAL's mission planning and operation. Using a variety of machine learning techniques, we evaluate the potential of a novel, compact data representation. Gradient-boosted trees with quantile loss are found to be the most effective approach in the experimental validation. With uncertainty adjusted to the 95th percentile, our method allows INTEGRAL to carry out two additional hours of scientific measurements per orbit. INTEGRAL is shielded from harm and sees an increase in its scientific return as a result of this strategy. It is simple to apply it to other spacecraft with similar orbits and easily extend it.

Military applications and the aeronautic industry are increasingly interested in aluminum lithium alloys (Al–Li) because of the properties required due to the presence of Lithium, which provides a very considerable gain concerning the mechanical properties compared to conventional aluminum alloys. The research and development departments are interested in improving these alloys especially in additive manufacturing process, which leads today to focus on the 3rd generation of Al–Li in terms of part quality - low density compared to the 1st and the 2nd generation. The objectives of this paper is to present a review of Al–Li alloys applications, its carachetrization, the precipitations and their impact on mechanical properties and grain refinement. The various manufacturing processes, methods and tests used are then deeply investigated and presented. The last investigations that have been gotten by scientists over the previous few years on Al–Li for different processes are also reviewed in this research.