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
South Africa's sugarcane sector, a cornerstone of the country's agriculture, stands ready to further integrate into the vast Chinese market as the zero-tariff policy for African countries officially takes effect.
China's Customs Tariff Commission of the State Council announced Tuesday that from May 1, 2026 to April 30, 2028, the country will grant zero-tariff treatment to 20 African countries that have established diplomatic ties with China and are not classified as the least developed countries.
This follows the country's earlier decision to grant zero-tariff treatment on 100 percent of tariff lines, effective from Dec 1, 2024, for the 33 least developed African countries with which it maintains diplomatic relations.
In effect, the zero-tariff treatment has been expanded to cover all 53 African countries that maintain ties with China.
In KwaZulu-Natal province, one of South Africa's traditional agricultural powerhouses, local farmers are hopeful that their sugarcane products will soon reach Chinese consumers.
Pratish Sharma, a sugarcane grower in the province, has witnessed the industry endure an unprecedented winter of challenges, including volatile international prices and trade barriers. When he heard of China's zero-tariff policy, however, his hope returned.
"It'll make trading in China a lot easier. It will create a better revenue stream for exports of sugar to China. And agreements like these assist in rejuvenating our economy within the industry and making us more viable," the farmer said.
Official data shows that China has been South Africa's largest trading partner for 17 consecutive years, with bilateral trade exceeding 53.5 billion U.S. dollars.
Yet, the country's agricultural products currently account for only 0.4 percent of China's total agricultural imports, indicating huge growth potential.
Kulani Siweya, market and trade policy director at the South African Sugar Association, sees greater opportunity ahead for the country's roughly 25,000 registered sugarcane growers.
"Main regions or destinations are the U.S., Europe. [We are] exporting about between 35,000 to 70,000 tonnes to the China market. South Africa stands ready to give you quality sweet sugar that will satisfy the Chinese palate," said Siweya.
Beyond sugar, South African specialties such as citrus, macadamia nuts, wine, and other high-quality agricultural products are also expected to gain broader market access in China. This has encouraged farmers like Sharma to experiment with a wider range of crops.
"I've converted 18 hectares of sugar cane into macadamias. So that process of diversification has already begun. And with trade initiatives such as the zero-rated making all of us more sustainable and viable," Sharma said.
John Steenhuisen, South African Minister of Agriculture, said China's zero-tariff initiative will help reshape the agricultural sector.
"The tariff-free access that's been granted us is going to be a game changer for not only citrus but also for the entire agricultural sector. We're now going to be able to compete with excellent quality wines and other agricultural goods in that market in a far more competitive basis," said the minister.
South African sugarcane growers eye sweeter exports as China's zero-tariff policy for Africa takes effect
