Editor's Note:

Chinese people believe that letters are as valuable as gold. For thousands of years, letters, across mountains and oceans, have been delivering the writers' sentiments and conveying friendship and expectations.

Xi Jinping, general secretary of the Communist Party of China (CPC) Central Committee and Chinese president, has managed to find time to reply to some of the letters sent to him from different sectors of the society and different parts of the world despite of his busy work schedule.

Through his letters, Xi has corresponded with people from all walks of life on numerous occasions, part of a series of excellent China stories in the new era.

The Global Times traced and contacted some of the recipients of Xi's letters, to hear the inspiring stories behind the letters and their communications with the Chinese president.

In this installment, the Global Times speaks with teachers and students from Muscatine High School in Iowa, the US, who shared their experiences and insights from their visit to China for exchanges after being invited by President Xi, as well as their hopes for future youth exchanges between China and the US.

"I'm extremely thankful that President Xi spent time to write to us. It was very touching he was able to hear about the amazing times on our trip," Seinna Stonking, a freshman at Muscatine High School in the central US state of Iowa, told the Global Times.

This spring, Stoneking felt inspired and fruitful. She, together with more than 20 other students from her school, received a special gift - a letter from Chinese President Xi Jinping after they concluded their visit to China, which they considered as a "life-changing" and "eye-opening" journey.

On February 24, which marked the Chinese Lantern Festival of the Year of the Dragon, Xi replied to a letter from the students of Muscatine High School who visited China in late January and sent them New Year cards in return.

In the letter, the Chinese president encouraged the Muscatine High School students to revisit China and encouraged more American youths to come to China for exchanges and study, where they can get first-hand experience of a real China in a multi-dimensional and comprehensive manner, foster genuine friendship with the Chinese youth, and learn from each other so that they can jointly contribute to a stronger friendship between the people of the two countries.

Over the years, notwithstanding setbacks in China-US relations, Xi has consistently championed people-to-people exchanges with the US. He has written letters to Americans, stressing that the hope of the China-US relationship lies in the people, its foundation is in grass-roots connections, its future depends on the youth, and its vitality comes from subnational exchanges.

In tandem with the fervent hopes of the Chinese people, an increasing number of young Americans are immersing themselves in the vibrant tapestry of China. They're not merely visiting the nation, but also securing this chance to embrace the country's rich culture, and feel a profound connection between the two countries.

'Dear Grandpa Xi'

In an interview with the Global Times, students from Muscatine High School weren't bashful about their gratitude to President Xi.

"In my and my classmates' letter to President Xi, we wanted to highlight how eye-opening this trip truly was. To add on to this, how grateful we were to be able to have this once-in-a-lifetime opportunity," Stonking said.

With Xi's support, several Muscatine High School students paid an exchange visit to Beijing, Shanghai, and Hebei Province, among other places in China from January 24 to 30, becoming the first group of American students to visit China under a program Xi announced at Welcome Dinner by Friendly Organizations in the US, in San Francisco during his visit to the country in November 2023. The program aimed at inviting 50,000 American youths over the next five years to China for exchanges and study.

One of their gifts to Xi upon their arrival in Beijing was a school flag of Muscatine High School with the words "Grandpa Xi, Here We Are" written in Chinese.

Behind the phrase "Here We Are" was the excitement most students feel when coming to China for the first time, where they climb the Great Wall, visit the Forbidden City, and experience traditional Chinese culture such as writing Chinese calligraphy and weaving Chinese knots.

"It was a new experience for me; it was life-changing and I loved the Great Wall and Shanghai. I had a great time meeting all the teachers and students," Leo Regennitter, a sophomore at the school, told the Global Times.

"The most memorable experience for me will always be the opportunity I got to make a connection with many students I met. All the students and teachers were so unbelievably kind and hardworking. The many places I went to like the Great Wall or the Shanghai Tower took my breath away and were so beautiful," Stonking recalled.

On January 28, before the end of our visit to China, the children discussed what gifts they could give President Xi, to express their gratitude for inviting them to visit China and share with him the joy of their visit, Heidi Kuo, a Chinese language teacher at Muscatine High School, told the Global Times.

Then, a letter featuring beautifully written Chinese characters to "Dear Grandpa Xi" was born.

"Many students poured their heart into their letters, sketching the awe-inspiring highlights of their China journey. From the majestic Great Wall to the cuddly panda, each illustration breathed life into their experiences. There was also a vivid strokes of a hand-painted Chinese dragon in the letter that truly captured their belief in its symbolic representation of China," shared Kuo.

"China is really huge, just like the US. Thank you for giving us the opportunity to come to China," said the letter signed by over 20 students, with hearts drawn next to their signatures.

An 'eye-opening' trip
According to Muscatine Journal, on February 28, during their monthly work session, the Muscatine School Board had the opportunity to hear directly from some of the students and chaperones who visited China for a week, where both Regennitter and Stoneking had the chance to speak about some of their experiences.

Regennitter shared the wonderful experiences the group had at the Shijiazhuang Foreign Language School, which is Muscatine's sister school, where they played table tennis and learned to make Chinese knots. The group also had the opportunity to celebrate Chinese New Year at the Zhang Yuan Garden, where they were joined by college students from the US.

"I told so many people in my life it was an amazing experience that I'll never forget. If any student was thinking of going and was unsure, I would them to go for it and they won't regret it," Stoneking told the Global Times. "It's a completely different experience to see China in person," she emphasized.

While also citing the Chinese saying "seeing is believing" in his reply letter, Xi said the warm and friendly American people he met during his first visit to the US in 1985 have given him an indelible impression.

The same touching experience has happened after three decades, among a group of high school students.

"While in China, I've never felt safer and did not view the country as it can sometimes be portrayed in American media," Stoneking said.

Many US media outlets reported that the students' trip to China came amid increased tensions between the US and China in the wake of a series of fractious actions.

However, American students who come to China see that Chinese and American students have forged deep friendships and are eager to communicate with and learn about each other.

"From what I experienced, the people of the US and China are more similar than different and we can learn a lot from each other," Stonking stressed.

Stonking said she felt the trip to China was "so motivating," and encouraged her to learn more about the Chinese language and the culture, "If I get the opportunity I would love to go to college in China and I hope to be a fluent speaker (of Chinese) someday."

Friendship continues to flourish

Muscatine is honored to have sent the first batch of students in the youth exchange program. The encouragement of interactions between the young people of the two countries is a continuation of the nearly 40-year friendship between Xi and the people of Muscatine, American entrepreneur Gary Dvorchak told the Global Times.

In the spring of 1985, Xi, at that time a county leader in Zhengding, in China's northern province of Hebei, took his initial steps on US soil.

From then on, Xi never forgot his American friends and believes that people hold the key to state-to-state relations.

During his trip to the US in November 2023, Xi recalled the story of this friendship with his old friends, mentioning that the house number during his stay was No. 2911 Bonnie Drive.

Today, 2911 Bonnie Drive, just two kilometers from Muscatine High School, has a more familiar name among locals - Sino-US Friendship House.

Dvorchak, owner of the house, and son of Eleanor and Thomas Dvorchak, the family that hosted Xi during his 1985 visit to Muscatine, believed that President Xi's warm response to the school students shows the value he sees in having young people from both countries getting to know each other personally and better understanding the values we share as human beings.

Dvorchak believes that the 50,000 young people exchange program and the Sino-US Friendship House getting more attention shows that people-to-people exchanges are all signs of building positive momentum.

"My hopes are high that the level of interaction will grow, producing tighter bonds among the people of our two great countries. This effort is critical to improving the relations between our countries," he said.

Kuo, in her seventh year of teaching Chinese at Muscatine High School, has witnessed a remarkable shift in student interest toward China and its rich culture. From once being unfamiliar, more and more students now eagerly embrace the allure of China.

Excitingly, the school is gearing up to send more students on a trip to China this coming April.

"After returning from our trip and watching the videos we captured, many students expressed a strong desire to visit China," Kuo shared.

Some Chinese schools also expressed their interest in fostering a sister school relationship with Muscatine High School. "We are eager to see students from both countries build even stronger bonds of friendship," she said.

In ancient times, shells served as decorations, tools, religious artifacts and currency, as well as canvases for art. However, archaeological evidence of this practice has been scarce, and research in this area has been lacking.

Recently, Chinese scholars for the first time recreated images of shell paintings from over 2,000 years ago, based on findings at an archaeological site dating from the Warring States period (475BC-221BC). 

A paper authored by Professor Luo Wugan and a team from the University of Chinese Academy of Sciences and several other universities was recently published in the prestigious Journal of Cultural Heritage. It traces the history of shell paintings, a unique art form, back to at least the Warring States period in China.

Observations through three-dimensional video microscopy revealed that the production of the shell paintings began with precise delineation and positioning of images using raised lines. This technique is reminiscent of methods widely used in jade carving. The intricacy and precision of the craftsmanship on such small and fragile shells is highly impressive.

Subsequent comprehensive analysis using X-ray fluorescence and Raman spectroscopy revealed the various pigment components used in the colored decorations of the shell paintings: the vibrant red pigment was sourced from cinnabar, the fresh green hue was attributed to malachite, and the deep, mysterious black color derived from the use of charcoal.

Technological archaeological research on shell paintings also indicates that this distinctive art form seemed to flourish in northern China during the Warring States period, with its influence extending into the Han dynasty. These shell paintings also exhibit a rich variety of subjects, with lifelike characters and sophisticated compositions, making them of immense historic, scientific and artistic value.

Pakistani Ambassador to China Moin ul Haque inaugurated the Pakistan National Pavilion and attended the opening ceremony of the 9th Sichuan Agricultural Expo in Chengdu on October 28. Hu Yun, vice governor of Southwest China's Sichuan Province, presided over the opening ceremony.

The exhibition hall introduced famous tourist attractions in Pakistan and more than 10 Pakistani companies showcased some agricultural products. The exhibition hall attracted great interest from participants.

Pakistan is the guest of honor of this expo. The ambassador emphasized in his speech that Pakistan and China have established a solid bilateral relationship based on political mutual trust, strategic communication and practical cooperation. He also stressed the close cooperation between Pakistan and Sichuan, including through their sister cities.

Pakistan's participation in the 2023 CIIE will inject new impetus into the ongoing agricultural cooperation between Pakistan and China. Recently, the two sides reached five important agricultural agreement on the application of sanitary and phytosanitary measures, granting Pakistan access to the $30 billion market for cooked beef, dairy products, chili peppers, cherries and other livestock products, which will help Pakistan expand its exports to China.

Chinese Foreign Minister Wang Yi on Saturday night local time arrived in Egypt, the first leg of his four-nation Africa tour this week. This is the 34th consecutive year when a Chinese foreign minister has visited Africa as their first overseas trip at the beginning of the year.

Coming shortly after Egyptian President Abdel-Fattah al-Sisi's successful reelection in December 2023, and amid the already 100-day Palestinian-Israeli conflict in the Middle East, Wang's visit is of great significance, Chinese analysts said. They predicted that further coordinating their positions concerning hot-spot issues, especially the Palestinian-Israeli conflict in the Gaza Strip, and its spillover in the region such as the Red Sea turmoil, will be high on the agenda during Wang's exchanges with Egyptian officials.

China and Egypt are to explore the potentials of their bilateral and multilateral cooperation in a variety of fields under multilateral frameworks that include the China-proposed Belt and Road Initiative and BRICS, analysts said on Sunday.

On Sunday, President Sisi met with Wang Yi in Cairo. The Egyptian president expressed gratitude for China's strong support for Egypt's social and economic development, noting significant achievements in jointly building the Belt and Road Initiative.

He reaffirmed Egypt's commitment to the one-China principle and opposition to interference in China's internal affairs.

Wang Yi thanked Egypt for supporting China's rightful stance. China appreciates Egypt's active response to the Belt and Road Initiative and will remain to be a long-term, reliable strategic partner in Egypt's development and revitalization. China aims to strengthen the alignment of development strategies and practical cooperation for greater achievements, working together toward modernization, Wang said.

Both sides agreed to continue strengthening communication and collaboration within frameworks such as BRICS and the United Nations. Wang Yi stated that Egypt, as an Arab, African, Islamic, and developing major country, is congratulated on becoming a new member of BRICS.

They also exchanged views on the Palestinian-Israeli situation, agreeing on the need for an immediate cease-fire and preventing further conflict escalation. A joint statement regarding the situation was issued.

During the visit, Wang Yi and Egyptian Foreign Minister Shoukry also discussed and signed the second five-year plan for the China-Egypt comprehensive strategic partnership.

Wang Yi, in a joint press conference with Shoukry after their talks, expressed deep concern over the recent rapid escalation of the situation in the Red Sea, and called for an end to attacks on civilian ships.

At the same time, China believes that the UN Security Council has never authorized any country to use force against Yemen, and actions should be avoided that would add fuel to the tension in the Red Sea and increase the overall security risks in the region. It must be emphasized that the tension in the Red Sea is a prominent manifestation of the spillover of the Gaza conflict, Wang said.

The urgent task is to quickly quell the war in Gaza to prevent the conflict from further expanding or even getting out of control. All parties need to jointly maintain the safety of the Red Sea waterway in accordance with the law, while genuinely respecting the sovereignty and territorial integrity of the Red Sea coastal countries, including Yemen, he noted.

Egypt is the first African nation Wang would visit during his current Africa trip, which is of significance, coming so soon after President Abdel-Fattah al-Sisi's successful reelection. The Egyptian government has launched development plans and targets, including attracting investment and boosting tourism, to tackle the country's economic challenges, He Wenping, a director with the Institute of West Asian and African Studies under the Chinese Academy of Social Sciences, told the Global Times on Sunday.

Regarding bilateral and multilateral cooperation, Zhu Yongbiao, executive director of the Research Center for the Belt and Road at Lanzhou University, told the Global Times that the conversation will be carried out within the framework of the China-proposed Belt and Road Initiative, as well as under the BRICS framework.

BRICS inducted five new member countries - Saudi Arabia, the United Arab Emirates, Egypt, Iran and Ethiopia - into the bloc in early January 2024. The integration of new member states marked a major expansion for the bloc originally founded by Russia, Brazil, China, and India in 2006, and later joined by South Africa in 2011.

Wang's visit seeks to implement the outcomes of the China-Africa Leaders' Dialogue held in August, 2023 in Johannesburg, South Africa, according to Zhu.

China announced at the 2023 Leaders' Dialogue it would launch the Initiative on Supporting Africa's Industrialization, the Plan for China Supporting Africa's Agricultural Modernization and the Plan for China-Africa Cooperation on Talent Development, as part of the efforts to chart the course for China-Africa practical cooperation in the next stage and help Africa bring its integration and modernization into a fast track, according to the Xinhua News Agency.

China and Africa will host the ninth ministerial conference of the Forum on China-Africa Cooperation (FOCAC) in China in 2024, which will likely take place in Beijing towards the end of the year.

FOCAC is hailed by the international community as an epitome of an efficient and effective platform for South-South cooperation and is a springboard for Africa and China to firmly support each other in strengthening development interests and collaboration in international affairs, as well as at multilateral occasions.

China-Egypt cooperation covers various fields, including infrastructure like development of the new Egyptian capital, railway projects and space collaboration with the launch of Egypt's second satellite. There is also cooperation in oil development, with new oil fields discovered in Egypt, as well as in aviation and technology, He Wenping said.

Wang's visit will further align the China-proposed Belt and Road Initiative with Egypt's 2030 development vision. Egypt's new government has many plans in motion, including tourism cooperation and dealing with their foreign exchange shortage, which might involve trade and import of non-Egyptian agricultural products. All these areas are expected to feature in the bilateral discussions and potential cooperation agreements, He explained.

The Xihoumen Highway and Railway Bridge in East China's Zhejiang Province marked phased progress when 18 drill piles belonging to pier No 5 of the bridge, each with a diameter of 6.3 meters - the world's largest - were injected with cement on Sunday, state broadcaster CCTV reported.

The final cement injection was completed on Sunday, according to CCTV.

Since drilling work began in July last year, workers overcame technological challenges in the construction of the drill piles, which have the world's largest diameter, measuring 84 meters in length, of which a 37-meter-section is plunged firmly into bedrock beneath choppy water at a maximum depth of 60 meters in the area. 

The completion of the cement injection at pier No 5 was completed ahead of schedule, according to the report.

The Xihoumen Highway and Railway Bridge, dubbed the world's longest super sea-crossing bridge with a total length of 3,118 meters, and connecting Zhoushan's Jintang and Cezi islands, is among a total of 10 landmark projects Zhejiang Province is undertaking to boost regional connectivity. 

The bridge will allow trains travel at speeds of up to 250 kilometers per hour and will link up with Zhoushan, Zhejiang's last city not connected by rail.

The bridge has a main span of 1,488 meters. Its width, at 68 meters, is also the world's widest for a dual-purpose sea bridge. 

As China rings in 2024 with a bang, a number of Chinese localities including East China's Anhui and Central China's Hunan provinces have launched a new round of major projects, reflecting a robust start to the new year, which Chinese experts describes as an encouraging sign for economic growth.

With a smart wristband and a mobile phone, Amaris Malfa, a young Bostonian, "walked" into the ancient Chinese painting An Era in Jinling, and even interacted with the people depicted therein. 

"This is amazing! It is so vivid and vibrant, like a moving painting," Malfa said. "I really wish my fiancé could have seen it!"

The digital artwork An Era in Jinling, which enables visitors to physically immerse themselves in the dynamic city scape of Jinling, the ancient name of Nanjing, and wander in real time through the historical city from China's Song Dynasty (960-1279), has wowed many US visitors at the See Nanjing cultural exhibition at the Faneuil Hall Marketplace in Boston, Massachusetts.

The exhibition features Chinese garden arts and Nanjing's intangible cultural heritage, as well as Global Smile Delivery, a display of Nanjing's best wishes to the world that highlights the historical and modern elements of the 2,500-year-old Chinese city near the Yangtze River. 

"Seeing is believing and being part of it allows the overseas audiences to have a better and deeper understanding of the cultural heritage of Jinling and what people's lives looked like dating back 1,000 years ago," Ai Lin, the director of the Deji Art Museum in Nanjing who has led her team to develop this digital exhibition inspired by the ancient painting of the same name, told the Global Times on Wednesday..

According to Ai, the handscroll, magnified and projected onto a 110-meter by 3.6-meter screen, depicts a total of 533 figures, 90 animals, and over two dozen carriages, horses and sedans. Audiences can wander the streets and interact with these figures in real time. 

"The Deji Art Museum hopes to encourage visitors to explore and interact with history and art across time with the assistance of advanced technology, making each an ambassador of Chinese culture," said Ai. 

Before the US tour, Ai and her team members completed a lot of research in order to ensure every detail is close to locals' understanding of Chinese culture. 

"We managed to make it easy for them to access Chinese culture even if some of them may have little knowledge about China. We have an over 5,000-year-old culture, but how to show it and its stories to overseas audiences still remains a topic that we all need to explore," she said. 

"As a city that served as the capital of six dynasties in Chinese history, Nanjing is one of the cradles of Chinese civilization and produced a myriad of great people in history," Chinese Consul General in New York Huang Ping said in his opening address. 

"Like the Charles River in Boston, the Qinhuai River running through Nanjing has witnessed numerous major historical events."

With this Chinese art program and "the cultural feast" at the Faneuil Hall Marketplace, "I have no doubt that the 'Nanjing Week' will offer audiences totally new and multiple perspectives of this wonderful part of China," he said. 

He also released a tweet to recommend the exhibition: "The digital exhibition of an ancient painting, letters and paintings drawn by animals and insects will show you a perfect combination of culture, nature and urban development."

For Deji Art Museum, An Era in Jinling not only provides a window for the people of the US to get to know China's cultural treasures, but also raises their interest in China and Chinese civilization. Among the figures in the painting is a waiter being called "Tea Doctor," not because they had a doctoral degree, but because they are good at making and serving tea.

They are tea professionals from 1,000 years ago. Their amazing skills were not only popular in China, but were also introduced to other Asian countries like Japan, which was highly influenced by China's tea culture. 

"Things like that are interesting information that they want to learn and makes them want to learn more," Ai added. 

"The display and interaction of a single ancient painting is far from enough. The most important thing is to open a door for them into Chinese culture. A figure in the painting will say, 'Hello, Boston! Welcome to Nanjing,' inviting them to visit China to have a close look at this friendly country and people," added Ai, who said she hopes this creative digital artwork of Deji Art Museum can tour to more places and show more people "how wonderful Chinese art is and how cool China's technology is."

Boston Council President Ed Flynn said that the exhibition "is serving as a remarkable symbol of cultural understanding and exchanges, fostering goodwill, and strengthening the bonds of friendship between our two cities."

Besides this, the exhibition also features unique "Insect Poetry" and "Insect Painting," which represent a beautiful land of dreams and harmonious coexistence between mankind and nature.

As a renowned Chinese city with a long history and rich culture, Nanjing boasts a wealth of intangible cultural heritage, including Pingtan, a form of storytelling and singing in a local dialect, and Kunqu Opera, known as a living fossil of Chinese theatrical art.

Kunqu Opera, known as a living fossil of Chinese theatrical art.

Some dinosaurs liked to cheat on their vegetarian diet.

Based on the shape of their teeth and jaws, large plant-eating dinosaurs are generally thought to have been exclusively herbivorous. But for one group of dinosaurs, roughly 75-million-year-old poop tells another story. Their fossilized droppings, or coprolites, contained tiny fragments of mollusk and other crustacean shells along with an abundance of rotten wood, researchers report September 21 in Scientific Reports. Eating the crustaceans as well as the wood might have given the dinosaurs an extra dose of nutrients during breeding season to help form eggs and nourish the embryos.
“Living herd animals do occasionally turn carnivore to fulfill a particular nutritional need,” says vertebrate paleontologist Paul Barrett of the Natural History Museum in London. “Sheep and cows are known to eat carcasses or bone when they have a deficiency in a mineral such as phosphorus or calcium, or if they’re pregnant or ill.” But the discovery that some plant-eating dinos also ate crustaceans is the first example of this behavior in an extinct herbivore, says Barrett, who was not involved in the new study.

Ten years ago, paleoecologist Karen Chin of the University of Colorado Boulder described finding large pieces of rotted wood in dino dung. The coprolites were within a layer of rock in Montana, known as the Two Medicine Formation, dating to between 80 million and 74 million years ago. That layer also contained numerous fossils of Maiasaura, a type of large, herbivorous duck-billed dinosaur, or hadrosaur (SN: 8/9/14, p. 20).
Chin wondered whether the wood itself was the dino’s real dietary target. “The coprolites in Montana were associated with the nesting grounds of the Maiasaura ,” she says. “I suspected that the dinosaurs were after insects in the wood. But I never found any insects in the coprolites there.”

Her hunch wasn’t too far off. Now she’s found evidence of some kind of crustaceans in dino poop. The new evidence comes from an 860-meter-thick layer of rock in Utah known as the Kaiparowits Formation, which dates to between 76.1 million and 74 million years ago. Ten of the 15 coprolites that Chin and her team examined contained tiny fragments of shell that were scattered throughout the dung. They were too small to identify by species, and may have been crabs, insects or some other type of shelled animal, Chin says. Based on the scattering of shell fragments, the animals were certainly eaten along with the wood rather than being later visitors to the dung heap.

Since bones from hadrosaurs are especially abundant in the Kaiparowits Formation, Chin suspects those kinds of dinos deposited the dung. Other large herbivores, such as three-horned ceratopsians and armored ankylosaurs, also roamed the area (SN: 6/24/17, p. 4).

The crustacean diet cheat may have been a seasonal event, related perhaps to breeding to obtain extra nutrients, Chin and colleagues say.

But how often — or why — the dinosaurs ate the shelled critters is hard to prove from the fossil dung alone, Barrett says. Herbivore coprolites are rare in the fossil record because a diet of leaves and other green plant material doesn’t leave a lot of hard material to preserve (unlike bones in carnivore dung). Coprolites with crustaceans, on the other hand, are more likely to get fossilized — and that preferential preservation might make it appear that this behavior was more frequent than it actually was. “These kinds of things give neat snapshots of specific behaviors that those animals are doing at any one time,” he adds. “But it’s difficult to build that into a bigger picture.”

Spacetime ripples from black holes are becoming routine.

For a fifth time, scientists have reported the detection of two colliding black holes via their gravitational waves, tiny vibrations that warp the fabric of spacetime. Unlike previous gravitational wave detections, which were heralded with news conferences often featuring panels of scientists squinting at journalists under bright lights, this was a low-key announcement. The event, caught on June 8, 2017, by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, was unceremoniously unveiled in a paper published online November 15 at arXiv.org.

With masses 7 and 12 times that of the sun, the pair of black holes was the lightest LIGO has spotted so far. The lack of fanfare over the detection signals a shift. Scientists are now aiming to collect data from many black hole crashes. That data can be analyzed to answer questions about the population as a whole, such as how two black holes get paired up in the first place.

Some birds of paradise really know how to work their angles. Tilted, microscopic filaments in some of the showy birds’ black feathers make that plumage look much darker than traditional black feathers, researchers report online January 9 in Nature Communications.

Dakota McCoy, an evolutionary biologist at Harvard University, and colleagues measured how much light each type of black feather absorbs. Superblack feathers absorb up to 99.95 percent of light that shines directly on them, while traditional black feathers absorb up to 96.8 percent, the researchers found.
Using scanning electron microscopy and nano-CT scanning, the team observed that ultrablack feathers have ragged, spike-studded barbules that curve upward at a roughly 30-degree angle to the tip, creating an array of deep, curved cavities. Traditional black feathers are smoother and lack such detailed microstructures. These spikes and pits scatter light multiple times, allowing for more light absorption and darker plumage, the scientists say. Even when the researchers dusted the feathers with gold, the darkest ones still retained their blackness, while traditional black plumes looked gilded in SEM images.

Superblack patches probably evolved to “exaggerate the perceived brilliance of adjacent color patches” during mating displays, the researchers write.

Like sailors and spelunkers, physicists know the power of a sturdy knot.

Some physicists have tied their hopes for a new generation of data storage to minuscule knotlike structures called skyrmions, which can form in magnetic materials. Incredibly tiny and tough to undo, magnetic skyrmions could help feed humankind’s hunger for ever-smaller electronics.

On traditional hard drives, the magnetic regions that store data are about 10 times as large as the smallest skyrmions. Ranging from a nanometer to hundreds of nanometers in diameter, skyrmions “are probably the smallest magnetic systems … that can be imagined or that can be realized in nature,” says physicist Vincent Cros of Unité Mixte de Physique CNRS/Thales in Palaiseau, France.
What’s more, skyrmions can easily move through a material, pushed along by an electric current. The magnetic knots’ nimble nature suggests that skyrmions storing data in a computer could be shuttled to a sensor that would read off the information as the skyrmions pass by. In contrast, traditional hard drives read and write data by moving a mechanical arm to the appropriate region on a spinning platter (SN: 10/19/13, p. 28). Those moving parts tend to be fragile, and the task slows down data recall. Scientists hope that skyrmions could one day make for more durable, faster, tinier gadgets.

One thing, however, has held skyrmions back: Until recently, they could be created and controlled only in the frigid cold. When solid-state physicist Christian Pfleiderer and colleagues first reported the detection of magnetic skyrmions, in Science in 2009, the knots were impractical to work with, requiring very low temperatures of about 30 kelvins (–243° Celsius). Those are “conditions where you’d say, ‘This is of no use for anybody,’ ” says Pfleiderer of the Technical University of Munich.

Skyrmions have finally come out of the cold, though they are finicky and difficult to control. Now, scientists are on the cusp of working out the kinks to create thawed-out skyrmions with all the desired characteristics. At the same time, researchers are chasing after new kinds of skyrmions, which may be an even better fit for data storage. The skyrmion field, Pfleiderer says, has “started to develop its own life.”
In a magnetic material, such as iron, each atom acts like a tiny bar magnet with its own north and south poles. This magnetization arises from spin, a quantum property of the atom’s electrons. In a ferromagnet, a standard magnet like the one holding up the grocery list on your refrigerator, the atoms’ magnetic poles point in the same direction (SN Online: 5/14/12).

Skyrmions, which dwell within such magnetic habitats, are composed of groups of atoms with their magnetic poles oriented in whorls. Those spirals of magnetization disrupt the otherwise orderly alignment of atoms in the magnet, like a cowlick in freshly combed hair. Within a skyrmion, the direction of the atoms’ poles twists until the magnetization in the center points in the opposite direction of the magnetization outside. That twisting is difficult to undo, like a strong knot (SN Online: 10/31/08). So skyrmions won’t spontaneously disappear — a plus for long-term data storage.

Using knots of various kinds to store information has a long history. Ancient Incas used khipu, a system of knotted cord, to keep records or send messages (SN Online: 5/8/17). In a more modern example, Pfleiderer says, “if you don’t want to forget something then you put a knot in your handkerchief.” Skyrmions could continue that tradition.
On the right track
Skyrmions are a type of “quasiparticle,” a disturbance within a material that behaves like a single particle, despite being a collective of many individual particles. Although skyrmions are made up of atoms, which remain stationary within the material, skyrmions can move around like a true particle, by sliding from one group of atoms to another. “The magnetism just twists around, and thus the skyrmion travels,” says condensed matter physicist Kirsten von Bergmann of the University of Hamburg.

In fact, skyrmions were first proposed in the context of particles. British physicist Tony Skyrme, who lends his name to the knots, suggested about 60 years ago that particles such as neutrons and protons could be thought of as a kind of knot. In the late 1980s, physicists realized the math that supported Skyrme’s idea could also represent knots in the magnetization of solid materials.

Such skyrmions could be used in futuristic data storage schemes, researchers later proposed. A chain of skyrmions could encode bits within a computer, with the presence of a skyrmion representing 1 and the absence representing 0.

In particular, skyrmions might be ideal for what are known as “racetrack” memories, Cros and colleagues proposed in Nature Nanotechnology in 2013. In racetrack devices, information-holding skyrmions would speed along a magnetic nanoribbon, like cars on the Indianapolis Motor Speedway.

Solid-state physicist Stuart Parkin proposed a first version of the racetrack concept years earlier. In a 2008 paper in Science, Parkin and colleagues demonstrated the beginnings of a racetrack memory based not on skyrmions, but on magnetic features called domain walls, which separate regions with different directions of magnetization in a material. Those domain walls could be pushed along the track using electric currents to a sensor that would read out the data encoded within. To maximize the available space, the racetrack could loop straight up and back down (like a wild Mario Kart ride), allowing for 3-D memory that could pack in more data than a flat chip.
“When I first proposed [racetrack memories] many years ago, I think people were very skeptical,” says Parkin, now at the Max Planck Institute of Microstructure Physics in Halle, Germany. Today, the idea — with and without skyrmions — has caught on. Racetrack memories are being tested in laboratories, though the technology is not yet available in computers.

To make such a system work with skyrmions, scientists need to make the knots easier to wrangle at room temperature. For skyrmion-based racetrack memories to compete with current technologies, skyrmions must be small and move quickly and easily through a material. And they should be easy to create and destroy, using something simple like an electric current. Those are lofty demands: A step forward on one requirement sometimes leads to a step backward on the others. But scientists are drawing closer to reining in the magnetic marvels.

Heating up
Those first magnetic skyrmions found by Pfleiderer and colleagues appeared spontaneously in crystals with asymmetric structures that induce a twist between neighboring atoms. Only certain materials have that skyrmion-friendly asymmetric structure, limiting the possibilities for studying the quasiparticles or coaxing them to form under warmer conditions.

Soon, physicists developed a way to artificially create an asymmetric structure by depositing material in thin layers. Interactions between atoms in different layers can induce a twist in the atoms’ orientations. “Now, we can suddenly use ordinary magnetic materials, combine them in a clever way with other materials, and make them work at room temperature,” says materials scientist Axel Hoffmann of Argonne National Laboratory in Illinois.

Scientists produced such thin film skyrmions for the first time in a one-atom-thick layer of iron on top of iridium, but temperatures were still very low. Reported in Nature Physics in 2011, those thin film skyrmions required a chilly 11 kelvins (–262° C). That’s because the thin film of iron loses its magnetic properties above a certain temperature, says von Bergmann, who coauthored the study, along with nanoscientist Roland Wiesendanger of the University of Hamburg and colleagues. But thicker films can stay magnetic at higher temperatures. And so, “one important step was to increase the amount of magnetic material,” von Bergmann says.

To go thicker, scientists began stacking sheets of various magnetic and nonmagnetic materials, like a club sandwich with repeating layers of meat, cheese and bread. Stacking multiple layers of iridium, platinum and cobalt, Cros and colleagues created the first room-temperature skyrmions smaller than 100 nanometers, the researchers reported in May 2016 in Nature Nanotechnology.

By adjusting the types of materials, the number of layers and their thicknesses, scientists can fashion designer skyrmions with desirable properties. When condensed matter physicist Christos Panagopoulos of Nanyang Technological University in Singapore and colleagues fiddled with the composition of layers of iridium, iron, cobalt and platinum, a variety of skyrmions swirled into existence. The resulting knots came in different sizes, and some were more stable than others, the researchers reported in Nature Materials in September 2017.

Although scientists now know how to make room-temperature skyrmions, the heat-tolerant swirls, tens to hundreds of nanometers in diameter, tend to be too big to be very useful. “If we want to compete with current state-of-the-art technology, we have to go for skyrmionic objects [that] are much smaller in size than 100 nanometers,” Wiesendanger says. The aim is to bring warmed-up skyrmions down to a few nanometers.
As some try to shrink room-temp skyrmions down, others are bringing them up to speed, to make for fast reading and writing of data. In a study reported in Nature Materials in 2016, skyrmions at room temperature reached top speeds of 100 meters per second (about 220 miles per hour). Fittingly, that’s right around the fastest speed NASCAR drivers achieve. The result showed that a skyrmion racetrack might actually work, says study coauthor Mathias Kläui, a condensed matter physicist at Johannes Gutenberg University Mainz in Germany. “Fundamentally, it’s feasible at room temperature.” But to compete against domain walls, which can reach speeds of over 700 m/s, skyrmions still need to hit the gas.

Despite progress, there are a few more challenges to work out. One possible issue: A skyrmion’s swirling pattern makes it behave like a rotating object. “When you have a rotating object moving, it may not want to move in a straight line,” Hoffmann says. “If you’re a bad golf player, you know this.” Skyrmions don’t move in the same direction as an electric current, but at an angle to it. On the racetrack, skyrmions might hit a wall instead of staying in their lanes. Now, researchers are seeking new kinds of skyrmions that stay on track.

A new twist
Just as there’s more than one way to tie a knot, there are several different types of skyrmions, formed with various shapes of magnetic twists. The two best known types are Bloch and Néel. Bloch skyrmions are found in the thick, asymmetric crystals in which skyrmions were first detected, and Néel skyrmions tend to show up in thin films.

“The type of skyrmions you get is related to the crystal structure of the materials,” says physical chemist Claudia Felser of the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany. Felser studies Heusler compounds, materials that have unusual properties particularly useful for manipulating magnetism. Felser, Parkin and colleagues detected a new kind of skyrmion, an antiskyrmion, in a thin layer of such a material. They reported the find in August 2017 in Nature.

Antiskyrmions might avoid some of the pitfalls that their relatives face, Parkin says. “Potentially, they can move in straight lines with currents, rather than moving to the side.” Such straight-shooting skyrmions may be better suited for racetrack schemes. And the observed antiskyrmions are stable at a wide range of temperatures, including room temperature. Antiskyrmions also might be able to shrink down smaller than other kinds of skyrmions.

Physicists are now on the hunt for skyrmions within a different realm: antiferromagnetic materials. Unlike in ferromagnetic materials — in which atoms all align their poles — in antiferromagnets, atoms’ poles point in alternating directions. If one atom points up, its neighbor points down. Like antiskyrmions, antiferromagnetic skyrmions wouldn’t zip off at an angle to an electric current, so they should be easier to control. Antiferromagnetic skyrmions might also move faster, Kläui says.

Materials scientists still need to find an antiferromagnetic material with the necessary properties to form skyrmions, Kläui says. “I would expect that this would be realized in the next couple of years.”

Finding the knots’ niche
Once skyrmions behave as desired, creating a racetrack memory with them is an obvious next step. “It is a technology that combines the best of multiple worlds,” Kläui says — stability, easily accessible data and low energy requirements. But Kläui and others acknowledge the hurdles ahead for skyrmion racetrack memories. It will be difficult, these researchers say, to beat traditional magnetic hard drives — not to mention the flash memories available in newer computers — on storage density, speed and cost simultaneously.

“The racetrack idea, I’m skeptical about,” Hoffmann says. Instead, skyrmions might be useful in devices meant for performing calculations. Because only a small electric current is required to move skyrmions around, such devices might be used to create energy-efficient computer processors.

Another idea is to use skyrmions for biologically inspired computers, which attempt to mimic the human brain (SN: 9/6/14, p. 10). Brains consume about as much power as a lightbulb, yet can perform calculations that computers still can’t match, thanks to large interconnected networks of nerve cells. Skyrmions could help scientists achieve this kind of computation in the lab, without sapping much power.
A single skyrmion could behave like a nerve cell , or neuron, electrical engineer Sai Li of Beihang University in Beijing and colleagues suggest. In the human body, a neuron can add up signals from its neighbors, gradually building up a voltage across its membrane. When that voltage reaches a certain threshold, ions begin shifting across the membrane in waves, generating an electric pulse. Skyrmions could imitate this behavior: An electric current would push a skyrmion along a track, with the distance traveled acting as an analog for the neuron’s increasing voltage. A skyrmion reaching a detector at the end would be equivalent to a firing neuron, the researchers proposed in July 2017 in Nanotechnology .
By combining a large number of neuron-imitating skyrmions, the thinking goes, scientists could create a computer that operates something like a brain.

Additional ideas for how to use the magnetic whirls keep cropping up. “It’s still a growing field,” von Bergmann says. “There are several new ideas ahead.”

Whether or not skyrmions end up in future gadgets, the swirls are part of a burgeoning electronics ecosystem. Ever since electricity was discovered, researchers have focused on the motion of electric charges. But physicists are now fashioning a new parallel system called spintronics — of which skyrmions are a part — based on the motion of electron spin, that property that makes atoms magnetic (SN Online: 9/26/17). By studying skyrmions, researchers are expanding their understanding of how spins move through materials.

Like a kindergartner fumbling with shoelaces, studying how to tie spins up in knots is a learning process.