Chinese scientists have observed the reverse "Brazil nut effect" for the first time during a space experiment aboard China Space Station in orbit, uncovering how gravity affects granular materials, with findings offering valuable insights for handling regolith and supporting future space exploration.
Since the completion of construction of the China Space Station two years ago, scientists have conducted numerous groundbreaking experiments.
Among them is the discovery of the reverse "Brazil nut effect" during a granular dynamics study, where particles of different sizes were vibrated at varying gravity levels in the station’s variable gravity cabinet.
The study revealed that in microgravity, larger particles sink -- contrary to their behavior on the Earth, where they rise to the surface in what is known as the "Brazil nut effect."
"We discovered that gravity plays a crucial role in this process. On the Earth, we observe the 'Brazil nut effect,' [where larger particles rise to the top]. But in a low-gravity, horizontal environment, we found the reverse 'Brazil nut effect,' where larger particles sink. This behavior shows a clear dependence on the gravity level -- when gravity increases, larger particles start rising again. This finding is the most significant result of our experiment," said Hou Meiying, a researcher at the Institute of Physics, the Chinese Academy of Sciences (CAS).
The experiment was enabled by a set of hybrid granular equipment delivered to China Space Station in November 2022 aboard the Tianzhou-5 cargo spacecraft.
Installed in the Wentian module's variable gravity cabinet, the equipment allowed researchers to systematically study the vibration and segregation of granular mixtures under various gravity conditions.
Over 18 months, the team of scientists uncovered the transformation mechanisms of granular behavior in microgravity, marking a pioneering achievement in this field.
Previously, such experiments were limited to computer simulations on the Earth. The study confirmed the pivotal role of gravity in granular material dynamics and offered theoretical support for addressing challenges in managing granular materials, such as lunar dust and soil, in extraterrestrial environments.
"This research lays a theoretical foundation for managing granular materials, such as lunar dust and soil, which will be critical when establishing bases in space, on the Moon, or on Mars," said Zhang Wei, researcher at the CAS's Technology and Engineering Center for Space Utilization.
China space station experiment reveals reverse "Brazil nut effect" in microgravity
President Xi Jinping has extended Spring Festival greetings to Chinese people of all ethnic groups, compatriots in Hong Kong, Macao and Taiwan, as well as overseas Chinese during an inspection trip to the northeastern province of Liaoning from Wednesday to Friday.
Xi, also general secretary of the Communist Party of China (CPC) Central Committee and chairman of the Central Military Commission (CMC), wished all Chinese people happiness and good health, and the country peace and prosperity in the upcoming Year of the Snake.
The Spring Festival, or the Chinese New Year, falls on Jan. 29 this year. It is the most important holiday on the Chinese calendar and an occasion for family reunions.
For more than a decade, Xi, as the Party and the state's top leader, has made it a tradition to spend time with ordinary people, especially those in difficulties, during the holiday season.
On Wednesday afternoon, Xi made his first stop at Zhujiagou Village, administered by the city of Huludao. Having suffered severe flooding in August last year, the village launched post-disaster reconstruction and 41 affected households moved into new residences before the start of winter.
At the entrance to the village, Xi looked at the affected areas, asking in detail about the summer flooding and the relocation of villagers at that time, as well as the subsequent relief work. He urged local officials to ensure the villagers stay warm throughout the winter.
During visits to two village households, the president inspected the structural integrity of their homes, checked their preparations for holiday celebrations, and asked whether government subsidies for rebuilding had been adequately provided. He also inquired about the villagers' main sources of income.
Noting that natural disasters had hit a number of regions across China during the past year, Xi said: "As the Spring Festival draws near, on behalf of the Party Central Committee, I extend sincere regards and festive greetings to all those affected and those working on the frontlines of post-disaster reconstruction!"
On Thursday morning, Xi went to the provincial capital Shenyang, where he talked with merchants and customers at a food market to learn about the market supply during the holiday season.
He later visited a residential community in Shenyang, and acknowledged the significant improvements in living conditions following a general revamping there.
At the community service center, Xi joined residents who were writing Spring Festival couplets, while children were tying Chinese knots that symbolize auspiciousness. He also enjoyed a Chinese bamboo flute performance, encouraging the performers to further promote fine traditional Chinese culture.
Before leaving, Xi waved to the crowd and extended festive greetings. "Having a good Spring Festival means a great start to the new year," he told the residents.
While inspecting a cold rolling mill of Bensteel Group in the city of Benxi on Thursday afternoon, Xi said that the manufacturing sector should keep pursuing higher-standard, smarter, and more eco-friendly development, and make more technology-intensive products with higher added value.
On Friday morning, Xi met with officers and soldiers of the Chinese People's Liberation Army (PLA) Northern Theater Command and spoke to representatives of troops across the military via video link.
Xi expressed sincere regards to service personnel of the PLA and the People's Armed Police Force, civilian personnel posted in the armed forces, and members of militia and reserve forces, on behalf of the CPC Central Committee and the CMC.
After listening to the work report from local officials of Liaoning on Friday morning, Xi urged the province, which already has a relatively complete industrial system, to accelerate the modernization of this system.
Traditional industries should strengthen industrial foundation reengineering and seek breakthroughs on major technologies and equipment to continuously boost core competitiveness, he said, while also highlighting the importance of ecological protection.
The full revitalization of northeast China relies fundamentally on reform and opening up, and more efforts should be made to strengthen the rule of law in government operations and optimize the business environment, Xi added, urging officials to improve their capabilities and performance in line with the country's further opening up.
Noting that Liaoning is rich in agricultural resources and has a solid foundation for development, Xi said the province should adhere to the integrated development of urban and rural areas.
He also stressed enhancing cultural confidence and strength, unswervingly upholding the leadership of the Party and exercising full and rigorous Party self-improvement.
Xi urged more efforts to care for disadvantaged groups, ensure smooth transportation, provide sufficient market supplies, enrich people's cultural life, and strengthen workplace safety during the holiday season.
Xi extends Spring Festival greetings to all Chinese during inspection tour