China Science & Technology Forum

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Researchers Reveal Molecular Mechanism of Type III CRISPR-Cas System
Dec 01, 2018

Type III CRISPR-Cas systems are characterized by the presence of Cas10 protein and are subdivided into four (III A-D) subtypes.

Types III-A system comprises a Csm effector complex which contains five different Csm proteins (Csm1-5) and one CRISPR RNA (crRNA). The crRNA-guided complexes recognize complementary RNA targets and cleave them via the Csm3 subunit.

In a recent study published in Cell, Prof. WANG Yanli's group and Prof. ZHANG XinZheng's group at Institute of Biophysics of Chinese Academy of Sciences reported the crystal structure of Csm and a series of cryo-EM structures of Csm in complex either with cognate or non-cognate RNA targets.

They revealed that Csm complex is composed of five Csm subunits (Csm1-5) and one crRNA with a protein stoichiometry of Csm1122334151.

The spacer region of the crRNA form base was revealed to pair with the complementary target RNA, forming crRNA-target RNA duplex with every sixth base being flipped out, and Csm3 proteins was showed to cleave the target RNA periodically.

By comparing cognate RNA and non-cognate RNA bound Csm complexes, researchers showed that the 3' anti-tag region of target RNA has two distinct binding channels depending on complementarity between the 5'-tag of crRNA and 3' anti-tag of target RNA.

Csm1 subunit undergoes a conformational change upon the cognate target RNA binding, allosterically activating the DNA cleavage and cOA synthesis.

The results provided insights into the mechanistic processes required for both crRNA-meditated, sequence-specific RNA cleavage, as well as transcription-dependent, non-specific DNA cleavage and cOAs generation, which will facilitate the research on type III CRISPR-Cas system.

CRISPR-Cas are RNA-guided adaptive immune systems that protect most archaea and approximately half of bacteria against invading foreign nucleic acids.

All the cryo electron microscopy work was performed in Center for Biological Imaging, Institute of Biophysics of Chinese Academy of Sciences. The X-ray diffraction data were collected at the BL-17U1, and BL-19U1 beamlines at the Shanghai Synchrotron Radiation Facility.



Researchers Reveal Molecular Mechanism of Type III CRISPR-Cas System---Chinese Academy of Sciences

 

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China Focus: Chinese scientists aim for world's most detailed 3D map of human brain
Source: Xinhua| 2018-12-06 11:49:06|Editor: Chengcheng

by Yu Fei, Han Song, Hu Zhe

NANJING, Dec. 6 (Xinhua) -- Why do some brains discover the laws of universe, while others create soul-stirring music or paintings? How is memory and consciousness generated?

We can observe billions of stars and detect ripples in space, but we still barely understand our brains, which can fathom the universe.

Their sophisticated structure and the number of neurons are only estimates.

Now Chinese scientists are planning to draw the clearest yet three-dimensional map of the intricate neurons and blood vessels in the human brain.

This ambitious project is like taking 3D photos of a huge forest of nearly 100 billion trees, seeing not only the whole forest, but also every twig and leaf on each tree.

"Our current methods cannot see both the trees and the forest. We aim to develop new methods to obtain a high-resolution map to see clearly how the neural network is connected," said Luo Qingming, leader of the research.

Luo, president of Hainan University and chief scientist of the Suzhou Institute for Brainsmatics of the Huazhong University of Science and Technology (HUST), in east China's Jiangsu Province, said the research will help in analyzing the mechanisms of brain diseases, and promote the development of artificial intelligence.

"The continuous changes of neural networks and brain activities pose great challenges to the analysis of brain functions. But we believe that brain functions and activities depend on the basic cells, just as a circuit network depends on its basic unit - the electronic components," said Luo.

"Different types of neurons are the basis for the analysis of brain functions and for the diagnosis and treatment of brain diseases," he said.

INNOVATIVE METHOD

Luo, 52, was born in rural Qichun County, central China's Hubei Province. At middle school, he had to study by the light of a kerosene lamp. He still has a scar on his hand from an accident of chopping firewood after school to help feed his family.

In the 1990s, Luo was a photoelectron researcher in the United States and was the first-ever person to succeed in measuring brain activity by means of near-infrared optical imaging. His technology was awarded a U.S. patent.

However, he left the high-quality research conditions abroad and returned to China to work in his alma mater, HUST, in 1997.

"I feel that I should contribute to my country," said Luo, who launched his project with a starting budget of just 200,000 yuan (about 30,000 U.S. dollars) and a lab of 25 square meters.

Brain imaging is extremely difficult, as it requires expertise in different disciplines.

"The brain is as soft as bean curd. It is difficult to fix brain samples and mark the nerves and blood vessels inside. It took us three years to solve that problem," Luo said.

"We need researchers with different academic backgrounds, such as biologists and chemists to prepare brain samples, engineers and technicians with optical, mechanical and control technology to develop the imaging instruments, and computer talents to process data and display the results."

The team took eight years to develop a brain-imaging instrument with independent intellectual property rights.

The achievement was published on the journal, Science, at the end of 2010, and was ranked as one of the top 10 scientific advances in China in 2011.

MAPPING BRAINS

"If we compare the imaging system to a camera, we first made a black-and-white camera and took black-and-white pictures of a mouse brain," Luo explained.

Since then, his team has made a series of breakthroughs to take pictures in rich colors showing amazing details of the mouse brain.

In 2016, the team received an investment of 450 million yuan to set up the Suzhou Institute for Brainsmatics, a development reported in the journal, Nature.

In the spotless lab at the institute, a mouse brain sample, wrapped in resin like a piece of amber, is sliced into layers just one micron thick.

Each layer is scanned and imaged. About 10,000 layers are sliced to get a map of the whole mouse brain.

The images of the colorful neural and vascular systems shown on the computer look like intricate highway networks. This is the world's clearest map of a mammal brain.

"We have achieved success with mice, and are making efforts to map the brains of primates which are more advanced and complicated," said Li.

"Our ultimate goal is to lead the world to get a precise map of the human brain, which will help us uncover its secrets."

TECHNICAL CHALLENGES

Scientists estimate a mouse brain has tens of millions of neurons, and a monkey brain has billions, while a human brain has about 86 billion.

"We cannot map a human brain by just adding more instruments. The huge amount of data after imaging would pose great challenges for storage and analysis," Li said.

It's estimated that the data generated from imaging a human brain would be equivalent to 200,000 movies of 4K ultra-high-definition, which would fill all the storage space of the Sunway TaihuLight, China's most powerful supercomputer.

Computing is the biggest technical bottleneck, and mapping the human brain must wait for the development of IT technology, Luo said.

Human brain scanning and imaging also faces ethical challenges. "We mark the neurons in a mouse brain with transgenic technology and virus labeling technology, which cannot be applied to a human brain," Li said.

"There are countless technical problems to overcome, but we believe that with the development of technology, these problems will be solved."

The team cooperates with labs and institutes in the United States and provides data for brain research in Europe and other countries. But Luo is looking forward to the launch of China's own brain science program.

Brain science is listed as one of the major scientific and technological projects of China's 13th five-year plan (2016-2020).

"This research could help promote children's education, and facilitate the diagnosis and treatment of brain-related diseases such as depression, Parkinson's disease and Alzheimer's disease," said Luo.

"Once we have sufficient financial support and concentrate our efforts, it will be possible to get a high-resolution map of the human brain in five to 10 years."

(Xinhua reporters Xia Peng and Li Bo also contributed to the story.)

 

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Focus: Twisted Light in a Photonic Chip
December 7, 2018• Physics 11, 125

Light waves capable of storing quantum information can propagate through a photonic chip waveguide and potentially be used for on-chip computation.

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Y. Chen et al., Phys. Rev. Lett. (2018)
Transmitting light, with a twist. Twisted light, with a helical wave front, can be sent through on-chip transparent glass waveguides while preserving its state of “twistedness.” In principle, each waveguide could carry several modes at once; each could represent a distinct data stream. Show less

A light beam with a corkscrew-shaped wave front can encode information based on the tightness and direction of the helix. This “twisted light” has potential uses in optical telecommunications and computing, but it is difficult to direct such light within chip-based photonic circuitry. A team in China has now demonstrated an optical waveguide that can carry twisted light efficiently on a chip and even “purify” its quantum state in the process.

Twisted light is characterized by an integer quantum number, l, that indicates (in units of Planck’s constant h) the orbital angular momentum (OAM) of each photon. Positive and negative values of l correspond to light twisted in opposite directions, like left- and right-handed corkscrews.

The possibilities for information technologies come from using these discrete quantum states to encode information, much as two-state quantum entities can act as quantum bits (qubits) encoding 1’s and 0’s. But for twisted light, l can take any integer value, so beams can encode more information. For example, three optical modes with l=−1,0, and +1 can act as a “qutrit,” with three encoding states. In principle, well-defined modes up to approximately l=300 can be produced by photonic devices [1]. Such light can also be placed in quantum combinations (superpositions) of these states, which means that it can be used for optical quantum computing.

Twisted light has previously been generated by chip-based optical devices and emitted into free space [2–4]. But keeping such light in a chip and moving it around in waveguides has proven challenging. The problem is that ordinary, fiber-optic-style channels won’t support “pure” OAM modes, in effect blurring any information encoded in them. Xian-Min Jin and co-workers from Shanghai Jiao Tong University have now made a new kind of waveguide that allows such modes to propagate cleanly.

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Y. Chen et al., Phys. Rev. Lett. (2018)
Sending light through a doughnut. A glass fiber waveguide having this pattern of refractive index will support twisted light with a helical wave front, in which quantum information can be encoded for communication and computation. The waveguide is about 10 micrometers across; yellow areas indicate regions of high refractive index. Show less

The key is to vary the waveguide’s refractive index in a “doughnut” pattern, as seen in cross section—lower index in the core and higher index in the surrounding ring. This principle has been known for some time [5]; the difficulty is in making such structures. “The conventional fabrication methods are unable to produce the necessary, arbitrary, three-dimensional structure,” says Jin.

The researchers used a laser-writing method in which ultrashort (few-hundred-femtosecond) pulses of green light are focused at a precisely controlled shallow depth within a borosilicate glass wafer. Absorption of the light locally transforms the transparent material and modifies its refractive index, while the shortness of the pulses ensures that the change is highly localized. The doughnut cross section was produced by fabricating 12 separate but overlapping, narrow, high-index channels arranged in a ring around the low-index core to generate a continuous cylindrical channel. In some of the waveguides, the team added an additional high-index central channel within the low-index core to improve the transmission.

The resulting waveguides were about 10 micrometers in diameter and almost 20 mm long. Jin and colleagues tested them with twisted light having l=+1,−1,0, and superpositions of those three states. They measured the intensity profiles of the beams entering and exiting the waveguides, as well as the interference between the transmitted beam and a reference beam identical to the input beam that was sent through free space. This interference revealed the helicity of the beams.

These measurements showed that the waveguides can support twisted modes and can also filter out “impure” components, leaving only photons with well-defined values of l. There was some loss of intensity within a waveguide, but the exiting beam was still 60% as bright as the input. The losses were greater still for higher values of l, but Jin says that his team is developing waveguides better suited to carrying these higher-order modes. The waveguides were also able to faithfully transmit twisted light that was so dim that just one photon at a time was sent through.

“This chip for transmitting twisted light is a significant advance, which may find applications in future on-chip optical and quantum computing,” says Haoran Ren, who works on chip-based optical technologies at RMIT University in Australia.

Jin says he hopes to see the first applications in high-capacity optical communications. But Kishan Dholakia, a specialist in optical manipulation at the University of St. Andrews, UK, warns that there is still some debate about whether twisted light can deliver on its promise of high data density [6]. However, he thinks this new chip design could potentially open up applications in quantum photonics and imaging.

This research is published in Physical Review Letters.

Mapping Twisted Light into and out of a Photonic Chip
Yuan Chen, Jun Gao, Zhi-Qiang Jiao, Ke Sun, Wei-Guan Shen, Lu-Feng Qiao, Hao Tang, Xiao-Feng Lin, and Xian-Min Jin
Phys. Rev. Lett. 121, 233602 (2018)
Published December 7, 2018​

–Philip Ball
Philip Ball is a freelance science writer in London; his latest book is Beyond Weird, a survey of quantum mechanics (University of Chicago Press, 2018).


Physics - Focus: Twisted Light in a Photonic Chip

 

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China Focus: Chinese scientists eye transforming Mars after successful sand-control
Source: Xinhua| 2018-12-10 15:30:39|Editor: Liangyu

by Xinhua writers: Yu Fei, Hu Zhe, Tan Yuanbin

WUHAN, Dec. 10 (Xinhua) -- Herdsmen in Dalad Banner of the Inner Mongolia Autonomous Region, north China, have long suffered from sandstorms. A gust of wind could force people to close their eyes. Sand buried large areas of pasture.

During the worst desertification in the 1980s, more than 100 families had to leave their homes in Jiefangtan Town at the edge of the desert in Dalad Banner.

More than a decade ago, scientists came and started spraying a green liquid on the desert step by step every summer. Gradually, the landscape changed. First came a crust-like cover. This grew thicker, and then the sand stopped moving.

The sand gradually turned into soil, attracting moss, lichens, grass and animals. The soil became thicker, and the vegetation returned.

The hero of this transformation was algae, one of the earliest plant forms to emerge on earth more than 3 billion years ago.

Algae can withstand temperatures up to 60 degrees centigrade, and ultraviolet radiation and drought, said Liu Yongding, a researcher at the Wuhan-based Institute of Hydrobiology of the Chinese Academy of Sciences, who has studied algae for over 40 years.

SAVING LAND

The ability of algae to live in the desert inspired Liu to fix the drifting sand.

Under natural conditions, it would take more than 10 years for desert algae to form a crust.

Liu led his team to select the best algae species from samples collected across China, and innovated technologies that could generate a crust in one year.

Almost 400 million Chinese are affected by desertification, which accounts for 27.3 percent of China's total land area. More than 7.72 million hectares of arable land have been degraded by desertification, and 670,000 hectares of farmland and 235 hectares of grassland have become drift sand or desert.

"We started this research more than 20 years ago without any financial support, but we persisted because we see the potential and the need of the country," said Liu, 74.

"We can't turn all deserts into oases, as deserts play a role in keeping the earth's heat balanced. We aim to control desertification and restore the soil," he said.

SAND RETREAT

Liu's team has collected desert algae samples from Hulunbuir, in Inner Mongolia, to the Taklimakan Desert, in Xinjiang Uygur Autonomous Region. They also compared samples from different times over the past six decades. From a small sample of mature algae crust, they found more than 700 types of organism.

Their desertification control technology has been widely applied in the Inner Mongolia Autonomous Region.

In areas where it was applied, the area of shifting sand fell from 60 percent to 10 percent, and the fixed sandy area rose to 90 percent. The plant coverage area rose from less than 15 percent to more than 80 percent.

"It takes 100 years to form a centimeter of fertile soil and 2,000 years to form 20 cm. It would take many generations to recover if a piece of arable land was lost. We are happy that we found a way to turn sand into soil several centimeters thick that can grow plants in a few years," Liu said.

Liu believes his technology can be used in desert areas outside China, including countries participating the Belt and Road initiative. His research has attracted scientists from Europe and the United States.

EARTH TO SPACE

Liu has also set his sights on the sky.

Since 1987, his team has studied algae to support astronauts' long stay in space.

They have carried out experiments on six of China's returnable satellites, and biological experiments on the Shenzhou spacecraft. They have worked with German scientists to research the life support system on the Shenzhou-8 spacecraft. They will also carry out experiments on China's future space station.

The research can be traced back to the 1970s. "We did an experiment to find out how much algae can keep a person alive in a closed submarine environment," Liu said.

Wang Gaohong, another researcher at the Institute of Hydrobiology, said algae have significant advantages in building a life support system. The oxygen generated by higher plants of about 15 square meters is equivalent to that produced by just a square meter of algae. It can also provide protein for astronauts.

"On the other hand, in near space, at an altitude of about 20 to 100 km, the environment is similar to that of Mars. Our space biology research will also help us understand possible life forms on Mars," Wang said.

TRANSFORMING MARS

Liu has an ambitious goal: letting algae pioneer human migration to Mars.

He first publicly proposed using algae to transform the environment of Mars about 15 years ago. "The deserts on earth have a similar environment to the Martian environment. We might use our knowledge of desert algae to transform the environment and help construct a human base on the red planet."

Science fiction writers and scientists put forward the idea of transforming Mars a long time ago, but there was no practical way to realize it. Liu's research made the idea conceivable, said Wang.

The intense radiation, low air pressure, dramatic temperature changes and bleak environment on Mars are similar to early earth. Algae are primary producers of the earth's biosphere, accounting for 30 percent to 40 percent of the global total, and playing an important role in maintaining biosphere stability, said Wang.

Algae have changed the environment of earth. Now humans are also changing the earth, but for the worse.

"If one day we have to leave earth, and build another home on another planet, algae might be our pioneer," Wang said.

 

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NATURE INDEX | 12 DECEMBER 2018
Strong spending compounds chemistry prowess | Nature
The discipline’s historic prominence in China is underpinned by its crucial value to industrial processes. Committed funding sees it leading the way in emerging areas, such as nanomaterials.

Hepeng Jia

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The science behind even basic chemical reactions is hard to prove: a silver chromate precipitation reaction recorded with a macro lens.Credit: Yan Liang/Beauty of Science/USTC

There were no research labs and no chemical testing devices when Lu Wei and colleagues joined the chemistry department of the new Southern University of Science and Technology (SUSTech) in Shenzhen in 2012. Their only teaching demonstration labs were in a makeshift building; equipment had to be set up and dismantled for each class. “Our graduate students had to cycle for several kilometres to test our samples in partner labs nearby,” says Lu, founding head of the department.

As their labs took shape around them, lively discussions stretching into the evenings, sometimes with beer, sparked ideas between young faculty members, recalls Lu. Teams rearranged themselves in new combinations to stretch limited resources further by simplifying logistics.

Nature Index 2018 China​

When state-of-the-art labs were built two years later, with generous funding from the Shenzhen municipal government, the young chemists at SUSTech quickly made breakthroughs, rising to be among the top 50 in China for high-quality chemistry research with a fractional count (FC) of 83.41 for 2015–17 in the Nature Index.

One recent study in Science, lead by SUSTech chemist, Tan Bin, identified a catalyst that improves the efficiency of the chemical reaction known as Ugi, which has been widely used to synthesize compounds, especially in the search for new pharmaceuticals.

From 2012 to 2017, China’s FC in the Nature Index for chemistry grew by 84% from 2,712 to 4,993, ranking it as the world’s second after the United States. By contrast, the US saw a decline of 10% from 6,026 to 5,451.

Among the chemistry sub-disciplines, China surpassed the US for top position in organic chemistry in 2015. It has run second to the US in most other chemistry sub-disciplines in recent years.

“The solid scientific foundation built by Chinese chemists over many years, the nurturing of young talent, and the state’s surging investment in research have combined to contribute to this significant growth,” says Chen Xiaoming, a chemist at Guangzhou-based Sun Yat-sen University(SYSU), who is also a member of the Chinese Academy of Sciences (CAS).

Chemistry has long been China’s top-performing discipline in terms of international research publications. Its crucial importance to many industrial processes has guaranteed it sustained attention since modern science was introduced to the country, says Lu.

Organic growth
Organic chemistry, which studies compounds and materials containing carbon, is the strongest sub-discipline, due to its “wide application, easier operation and huge number of researchers,” says Lu, adding that it is very cheap and quick to set up an organic chemistry lab.

There has been rapid growth in studies on organic synthesis methods, nano-catalysts, synthetic organofluorine chemistry, visible-light-driven organic reactions, and natural product chemistry. So said a May 2017 special edition dedicated to organic chemistry of China’s most prestigious multidisciplinary journal, National Science Review.

Ma Shengming, guest editor of the edition and a leading chemist at CAS Shanghai Institute of Organic Chemistry(SIOC), pointed out the great industrial and environmental benefits of many of these studies which involved interdisciplinary collaboration with emerging areas such as nanomaterials.

For example, according to Hu Jinbo of SIOC, which topped the Nature Index in organic chemistry with an FC of 139.17 for 2015–17, Chinese chemists have made significant progress in improving synthetic organofluorine chemistry, which can reduce chemical pollution. In another example, visible-light-driven organic reactions greatly lower the energy needed for industrial organic chemical synthesis, wrote Wu Lizhu of the CAS Technical Institute of Physics and Chemistry in the special issue.

The large recruitment of chemists particularly through the Young Thousand Talents Plan has provided a fresh boost to the booming study of chemistry in China, says Zhao Dongbing, a chemist at Tianjin-based Nankai University, who was enrolled as a scholar under the plan after completing his postdoctoral research at Cornell University and the University of Washington in Seattle. China launched the plan in 2008 to attract established scientists and high-tech entrepreneurs to return to China. In 2011, the programme was extended to young scholars, mostly targeting highly productive postdocs. By early 2018, China had recruited 3,535 young scientists through the programme.

Source: Nature Index/Dimensions from Digital Science

Zhao believes chemistry accounted for the second largest category of recruits under the plan, after the life sciences, though official numbers are no longer available due to political sensitivities over the recruitment of scholars from the US. Many of the returning postdocs “have good competency, smart ideas and can readily join hot research areas,” says Zhao.

These Young Thousand Talent Scholars, including Zhao, Lu and Tan, contribute a large portion of papers from China published in top chemistry journals. For example Xiong Yujie, a chemist at Hefei-based University of Science and Technology of China, who was recruited in the first batch of Young Thousand Talent Scholars in 2011, has since published more than 100 papers, including a dozen in journals tracked by the Nature Index such as ACS Nano, Advanced Materials,and Angewandte Chemie International Edition.

It is not clear whether the plan will continue to be of as much benefit to chemistry and other disciplines in China, given US accusations that it is a channel for the theft of US technology and intellectual property.

Chinese authorities and universities have removed the name lists of Thousand Talents recruits from websites and some US-based Chinese scientists who might previously have applied have shied away from the scheme.

Although figures for individual research disciplines are not available, China’s research and development expenditure has been growing, from 1.03 trillion yuan (US$150 billion) in 2012 to 1.76 trillion yuan in 2017, accounting for 2.1% of its GDP. China’s R&D surpasses that of many industrial countries in both absolute and relative terms. For example, in 2016 the R&D/GDP ratio of the United Kingdom was 1.67% when China’s was 2.08%.

Surging research investment means that expensive devices, such as infrared and nuclear magnetic resonance spectrometers and elemental analysers, though unaffordable to many chemistry labs in the West, are standard equipment in Chinese research universities.

Sustainability worries
Chinese chemistry attracts the same criticism as Chinese science overall: that in the race to publish, China focuses on areas with international traction and quick results.

Zhao acknowledges that the heavy pressure on young principal investigators to publish stops them from delving into the mechanisms underlying basic chemistry, because proving the science behind even very conventional chemical reactions is a long and arduous process.

But, Lu of SUSTech is more optimistic. “An original innovation does not start from scratch, but from following others. Major breakthroughs need gradual accumulations. I have seen more and more Chinese innovative studies that can change our chemistry textbooks.”

Nature 564, S68-S69 (2018)

doi: 10.1038/d41586-018-07693-3

This article is part of Nature Index 2018 China, an editorially independent supplement. Advertisers have no influence over the content.

 

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PUBLIC RELEASE: 13-DEC-2018
Chinese scientists get first look at geometric phase effect in a chemical reaction
CHINESE ACADEMY OF SCIENCES HEADQUARTERS

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This is a schematic illustration of the geometric phase effect arising in the H+HD reaction: the different interference of two reaction path. CREDIT: SUN Zhigang

In the simplest chemical reaction in nature, the H + H2 reaction, a well-known conical intersection exists between the ground and first excited state. Therefore, the H + H2 reaction and its isotopic variants have long been the benchmark system in the study of the geometric phase (GP) effect in chemical reactions.

Previously, efforts were made to observe and understand the GP effect in the H+H2 reaction. However, no convincing experimental evidence of the GP effect in any chemical reaction has been detected until now.

Recently, researchers from the University of Science and Technology of China and the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences carried out a combined experimental and theoretical investigation of the H+HD to H2+D reaction.

The experimental team, which was led by Prof. WANG Xingan and Prof. YANG Xueming, performed a crossed molecular beams study using the high-resolution velocity map ion imaging technique. Rapid forward-scattering oscillations of H2 (v', j') products were observed in differential cross sections at a collision energy in the vicinity of the H3 conical intersection.

Prof. SUN Zhigang developed a unique quantum theoretical approach for considering the GP effect in a chemical reaction. Based upon a newly developed accurate potential energy surface by Prof. ZHANG Donghui, the researchers found that the experimentally observed oscillation structures in the forward scatterings could only be reproduced by theoretical calculations including the geometric phase effect.

Through this study, a new reaction mechanism has also been discovered for this benchmark reaction at high collision. This investigation clearly answered a long- standing question in chemical reaction dynamics, i.e., how the GP effect profoundly influences chemical reactivity. The study certainly has important implications for dynamics studies of molecular systems with conical intersections in general.

This research, entitled "Observation of the geometric phase effect in the H+HD to H2+D reaction," was published in Science.

The Born-Oppenheimer approximation (BOA) is the foundation for understanding the quantum nature of molecular systems and leads to the development of important concepts such as electronic states and molecular orbits. In a molecule, non-adiabatic interactions between electronic states are ubiquitous. However, because of the complicated nature of non-adiabatic couplings, molecular systems are often treated without considering non-adiabatic couplings and the effect of excited states.

However, in the presence of conical interactions in molecular systems, such approximations could break down. Half a century ago, scientists found that by introducing a geometric phase, one could properly treat these systems quantum mechanically. Introducing a GP effect, however, could have a profound effect on the quantum systems. For example, one of the quantum Hall effects results from an electronic geometric phase effect. Therefore, the effect of the geometric phase is a fundamental question in both physics and chemistry.


Chinese scientists get first look at geometric phase effect in a chemical reaction | EurekAlert! Science News

Daofu Yuan, Yafu Guan, Wentao Chen, Hailin Zhao, Shengrui Yu, Chang Luo, Yuxin Tan, Ting Xie, Xingan Wang, Zhigang Sun, Dong H. Zhang & Xueming Yang. Observation of the geometric phase effect in the H + HD → H2 + D reaction. Science (2018). DOI: 10.1126/science.aav1356​

 

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Two Stalagmites Found in Chinese Cave Are a 'Holy Grail' for Accurate Radiocarbon Dating
George Dvorsky
Today 2:09pm

The stalagmites from Hulu Cave, with sampling etch marks.
Image: Hai Cheng et al., 2018/Science

Since its inception in the 1950s, radiocarbon dating has proven indispensable to archaeologists and climate scientists, who rely on the technique to accurately date organic compounds. But a good thing just got better, owing to the discovery of two stalagmites in a Chinese cave containing a seamless chronological atmospheric record dating back to the last Ice Age.

An unbroken, high-resolution record of atmospheric carbon-12 and carbon-14 was found in a pair of stalagmites located within Hulu Cave near Nanjing, China, according to new research published today in Science. Because this record extends back to the last glacial period, to around 54,000 years ago, scientists are now equipped with a more accurate standard for use in radiocarbon calibration.

There’s no question that radiocarbon dating has revolutionized archaeology. Armed with this technique, scientists can date organic compounds, such as bone, hair, wood, seeds, and shells. The further back in time we go, however, the less reliable carbon dating becomes, as the technique is reliant upon accurate historical measurements of atmospheric carbon, specifically the ratio of carbon-12 to carbon-14.

Carbon-14, or C14, is a rare form of carbon that, unlike carbon-12 (so-called “normal” carbon), is radioactive. C14 is an isotope consisting of six protons and eight neutrons, and it’s in a perpetual state of decay, featuring a generous half-life of 5,370 years. Like normal carbon, C14 combines with oxygen to create carbon dioxide, which is absorbed by all living creatures, whether they’re animals or plants. Consequently, the ratio of C12 to C14 in all living organisms is always the same as the ratio in the atmosphere.

Because atmospheric levels of C12 and C14 change over time, the specific ratio in an organic sample (e.g. bones, wood) serves as a timestamp for a living creature’s death. When an organism dies, it stops acquiring new carbon. As time passes, the C14 decays like a ticking clock, but it’s not replaced. By measuring the amount of radioactive decay, scientists can determine when a formerly living organism died.

But there are limits to this dating approach, and it has to do with the C14 half-life. Organic objects can only be dated up to around 55,000 to 60,000 years ago, after which time the amount of C14 in a sample dwindles down to negligible proportions. What’s more, calibration is critical to this technique; changes in the amount of atmospheric radiocarbon over time means that radiocarbon dates have to calibrated against a chronological, or calendrical, timescale.

Building these calendars is easier said than done. Ideally, scientists would like to have an accurate and unbroken chronological record of changing C12 and C14 atmospheric concentrations over time. This can be done, for example, by counting tree rings (also known as dendrochronology), which, as any 8-year-old will happily tell you, is a reliable way of determining the age of a tree. Unfortunately, few calibrated datasets that directly sample atmospheric carbon exist further back in time than the Holocene tree ring record, at approximately 12,600 to 14,000 years ago (obviously, trees don’t live to be tens of thousands of years old, but ancient, fossilized trees can be dated using other methods). Radiocarbon dating is thus limited by the ability of a given material to provide an absolute age, while also preserving a record of changing atmospheric conditions.

But now, with the discovery and analysis of two special stalagmites in Hulu Cave, scientists have stumbled upon an unbroken record of atmospheric carbon dating back some 54,000 years. Instead of counting tree rings or studying coral reefs(another technique used to infer absolute dates), the researchers, led by Hai Cheng from the Institute of Global Environmental Change, at Xi’an Jiaotong University, analyzed the mineral composition inside the stalagmites. By dating hundreds of layers within these structures, which was done by using a highly reliable isotopic dating technique known as thorium-230 dating, the researchers were able to establish an unprecedented chronological baseline that can now be used for radiocarbon dating.

“Up to now, different approaches for C14 calibration have their own constraints,” Hai told Gizmodo. “For instance, it remains difficult [to use] tree-rings to calibrate the atmospheric C14 beyond the current limit of around 14,000 years before present. Corals do not accumulate continuously over thousands of years and are difficult to collect since those in the time range of interest are now largely submerged. Stalagmites, which can be excellent choices for thorium-230 dating, typically contain a significant fraction of carbon ultimately derived from limestone bedrock.”

UC Berkeley geologist Larry Edwards, a co-author of the new study, helped to develop the thorium-230 method back in the late 1980s, but he wasn’t able to find ideal cave deposits to perform a study like this one.

“In addition to carbon from the atmosphere, cave deposits contain carbon from the limestone around the cave,” Edwards told Gizmodo. “We thus needed to make a correction for the limestone-derived carbon. We discovered that the Hulu Cave samples contain very little limestone-derived carbon, and are therefore nearly ideal for this kind of study—hence our ability to complete a precise calibration of the C-14 timescale, a goal of the scientific community for the last nearly seven decades.”

In the study, Hai and his colleagues present around 300 paired carbon 14 and thorium-230 dates extracted from the thin calcite layers within the Hulu Cave stalagmites. The average temporal resolution between each pair is about 170 years. These particular stalagmites, said Hai, are very special, containing “dead carbon” that’s remarkably stable and reliable.

“As such, the C14 in the Hulu samples are mainly derived from atmospheric sources, which allows us to make a milestone contribution towards the refinement of the C14 calibration curve through the paired measurements of the C12/C14 and thorium-230 ages,” said Hai, adding: “The new Hulu record has less uncertainty and resolves previously unknown fine-scale structure.”

As the researchers write in their paper, the new calendrical record represents a “holy grail” for scientists, offering a high-resolution and continuous record of atmospheric C14 that covers the full range of the radiocarbon dating method. For archaeologists, it also means they can now date organic compounds between 14,000 to 54,000 years with greater confidence, especially the older samples.

“For a sample that is actually 40,000 years old, the nominal C14 age would be about 35,000 years, and the age you would calculate from previous calibration data would be about 38,000 years, with a large uncertainty,” explained Edwards. “So a difference of 2,000 to 5,000 years, depending upon how you chose to calibrate your age, prior to our work.”

Excitingly, this research will also be of interest to climate scientists, who can use this data to study atmospheric changes over time.

It’s a very cool result from a very cool and unlikely source—the slow drip, drip, dripping within a dark cave in eastern China.

[Science]



Two Stalagmites Found in Chinese Cave Are a 'Holy Grail' for Accurate Radiocarbon Dating | Gizmodo

Hai Cheng, R. Lawrence Edwards, John Southon, Katsumi Matsumoto, Joshua M. Feinberg, Ashish Sinha, Weijian Zhou, Hanying Li, Xianglei Li, Yao Xu, Shitao Chen, Ming Tan, Quan Wang, Yongjin Wang, Youfeng Ning. Atmospheric 14C/12C changes during the last glacial period from Hulu Cave. Science (2018). DOI: 10.1126/science.aau0747​

 

[JSCh]

Fu Wei, Qiao Jie and Tang Fuchou Teams publish their collaborative research findings in Science
DEC . 11 2018

Peking University, Dec. 11, 2018: On November 30, Science, the international top academic journal (IF= "41.058), published the collaborative research findings by Fu Wei and Qiao Jie research teams from PKU Third Hospital and Tang Fuchou research team from Biomedical Pioneering Innovation Center of Peking University School of Life Sciences, titled “Single-Cell Multiomics Sequencing and Analyses of Human Colorectal Cancer.”

Professor Fu Wei’s research team has long been devoted to the clinical treatment and applied basic research of gastrointestinal tumors. Academician Qiao Jie’s research team has a long-term collaboration with Professor Tang Fuchou’s team and they have been dedicated to using single-cell sequencing to explore the epigenetic modifications of germ cells and embryos and the molecular mechanism of gene expression regulation during human early development so as to provide important data for understanding the characteristics of human early embryonic development.

Overview of the workflow
​

For the first time in the world, the research made an in-depth analysis of gene copy number variation, DNA methylation heterogeneity, features of gene expression changes, and their interrelationship during the onset and metastasis of human colorectal cancer (CRC) at the level of single-cell resolution and multi-omics. It pointed out a new direction for the study of the CRC metastasis mechanism and provided new theoretical evidence for the clinical treatment of metastatic CRC.

The link at Science: http://science.sciencemag.org/content/362/6418/1060

Written by: Lang Lang
Edited by: Zhang Jiang
Source: PKU Third Hospital
Link:http://bynew.bjmu.edu.cn/zhxw/2018n/200744.htm


Fu Wei, Qiao Jie and Tang Fuchou Teams publish their collaborative research findings in Science_Peking University

 

[JSCh]

Big data reveals hints of how, when and where mental disorders start
New genetic complexities emerge for schizophrenia, bipolar disorder and autism

BY LAURA SANDERS
2:49PM, DECEMBER 13, 2018

ON THE BRAIN Lab-grown brain organoids (one shown) mimic the real thing, analyses suggest. Along with other parts of a large research effort called PsychENCODE, the organoid results may offer new clues about psychiatric diseases such as schizophrenia.

VACCARINO LAB​

Psychiatric disorders’ many complexities have stymied scientists looking for clear genetic culprits. But a new giant dataset holds clues to how, when and where these brain disorders begin.

Called PsychENCODE, the project’s first large data release has revealed intricate insights into the behavior of genes and the stretches of genetic material between them in both healthy brains and those from people with schizophrenia, bipolar disorder or autism spectrum disorder.

The results, split among 10 studies published online December 13 in Science, Science Advances and Science Translational Medicine, offer some of the most detailed looks yet at the links between these genetic elements and brain health. “It’s all connected, and now we have the tools to unravel those connections,” says geneticist Thomas Lehner of the National Institute of Mental Health in Bethesda, Md., who oversaw the project but wasn’t involved in the research.

Earlier studies have pinpointed certain genes and other stretches of the genome — the genetic material that makes up cells’ instruction books — as being involved in schizophrenia, bipolar disorder and autism spectrum disorder. The new collection of work goes further, both confirming and clarifying some of these roles.

“This is a massive undertaking,” says neuroscientist Christine Denny of Columbia University who was not involved in the project. “It’s pretty phenomenal.”

In part of the new research, neuroscientist Nenad Sestan of Yale University and colleagues looked at gene behavior as brains develop. Samples of postmortem brains ranging from fetal stages through adulthood revealed two major points of genetic upheaval: early prenatal development and adolescence. Activity in groups of genes linked to psychiatric disorders suggests that these are times when important genetic behavior goes awry, the researchers say.

Similar psychENCODE analyses in rhesus macaques revealed similar developmental paths, Sestan says. Those comparisons also turned up some gene behavior that’s exclusive to humans (and others exclusive to macaques), differences that “may drive unique features of the diseases in humans,” he says.

Other PsychENCODE projects scrutinized spots in the genome that aren’t necessarily located inside genes. Researchers linked many of these genetic hot spots, which are thought to differ in people with psychiatric diseases, to genes for the first time. That information could be used to predict a person’s risk of these psychiatric disorders from genomic makeup alone.

Still more research uncovered important differences in how genes behave in brains from people with autism, bipolar disorder or schizophrenia. The researchers found that RNA, a go-between molecule that helps carry out DNA's instructions, was different in the brains of people with psychiatric disorders. Those results may ultimately lead to targeted medicines for the diseases.

Some projects also focused on how to use laboratory tools including brain organoids, clumps of neural tissue grown in dishes, to further the research. By comparing the gene activity of cells in brain organoids with that of cells taken from actual brains, researchers found that the two mirror each other at early stages of development. Those similarities mean that the organoids, good mimics of young brains, might be particularly useful in understanding brain disorders that start early.

Lehner first began advocating for a group effort aimed at understanding the genetic landscape of psychiatric disorders about a decade ago. But it wasn’t until 2015 that the National Institute of Mental Health announced plans for PsychENCODE and helped organize the 15 participating research institutions. To see the first wave of results “feels really good,” Lehner says. “I’m delighted.”

The PsychENCODE group is making progress, says Columbia University psychiatrist Jeffrey Lieberman. “But the jury is still out in terms of what it will result in,” he says. “It could produce important — and if we’re lucky, game-changing — results.”

Citations
The PsychENCODE Consortium. Revealing the brain’s molecular architecture. Science. Vol. 362, December 14, 2018, p. 1263.

M. Li et al. Integrative functional genomic analysis of human brain development and neuropsychiatric risks. Science. Vol. 362, December 14, 2018, p. 1264. doi: 10.1126/science.aat7615.

M.J. Gandal et al. Transcriptome-wide isoform-level dysregulation in ASD, schizophrenia and bipolar disorder. Science. Vol. 362, December 14, 2018, p. 1265. doi:10.1126/science.aat8127.

D. Wang et al. Comprehensive functional genomic resource and integrative model for the human brain. Science. Vol. 362, December 14, 2018, p. 1266. doi:10.1126/science.aat8464.

Y. Zhu et al. Spatiotemporal transcriptomic divergence across human and macaque brain development.Science. Vol. 362, December 14, 2018, p. 1267. doi:10.1126/science.aat8077.

A. Amiri et al. Transcriptome and epigenome landscape of human cortical development modeled in organoids. Science. Vol. 362, December 14, 2018, p. 1268. doi:10.1126/science.aat6720.

P. Rajarajan et al. Neuron-specific signatures in the chromosomal connectome associated with schizophrenia risk. Science. Vol. 362, December 14, 2018, p. 1269. doi:10.1126/science.aat4311.

J.-Y. An et al. Genome-wide de novo risk score implicates promoter variation in autism spectrum disorder. Science. Vol. 362, December 14, 2018, p. 1270. doi:10.1126/science.aat6576.

S.L. Rhie et al. Using 3D epigenomic maps of primary olfactory neuronal cells from living individuals to understand gene regulation. Science Advances. Published online December 13, 2018. doi:10.1126/sciadv.aav8550.

C. Chen et al. The transcription factor POU3F2 regulates a gene coexpression network in brain tissue from patients with psychiatric disorders. Science Translational Medicine. Vol. 10, December 19, 2018. doi:10.1126/scitranslmed.aat8178.

Q. Meng et al. The DGCR5 long noncoding RNA may regulate expression of several schizophrenia-related genes. Science Translational Medicine. Vol. 10, December 19, 2018. doi:10.1126/scitranslmed.aat6912.​

PsychENCODE hints at the genetic origins of mental disorders | Science News

 

[cirr]

Chinese researchers develop ultrahigh-voltage integrated micro-supercapacitors with alterable shapes

2018-12-18 15:59:35 Xinhua Editor : Gu Liping

Chinese researchers have developed high voltage planar integrated micro-supercapacitors with superior flexibility.

The ultrahigh-voltage micro-supercapacitors were developed by a research group made up of scientists from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences (CAS) and the Institute of Metal Research of the CAS.

The boom of portable and wearable electronics has stimulated the urgent demand for miniature electrochemical energy storage devices with high flexibility and tailored performance. But the cost-effective and scalable fabrication of integrated micro-supercapacitors is yet to be achieved.

With assistance from low-cost, industrially applicable technology, the researchers demonstrated fast and scalable fabrication of graphene-based planar integrated micro-supercapacitors with shape diversity, versatility and outstanding flexibility.

The output voltage and capacitance of the integrated micro-supercapacitors are readily adjustable. To prove the validity of the concept, a tandem energy storage pack integrating 130 individual micro-supercapacitors in series can output a recorded voltage exceeding 100 volts, said the study published in the Energy and Environmental Science journal.

This work holds great potential for scalable fabrication and fast integration of other planar microscale energy storage devices, such as hybrid micro-supercapacitors and micro-batteries.

http://www.ecns.cn/news/2018-12-18/detail-ifzasznx1608884.shtml

 

[JSCh]

Fudan researchers achieve scientific breakthrough
By Lin Shujuan in Shanghai | chinadaily.com.cn | Updated: 2018-12-18 13:55

A screenshot of CCTV. ​

Researchers from Fudan University in Shanghai and Cornell University in the United States have found evidence of a new type of quantum Hall effect existent in nanostructures of three-dimensional topological semimetal.

The research, published online in Nature on Monday, represents a breakthrough in the research of the quantum Hall effect, which, discovered decades ago, remains one of the most studied phenomena in condensed matter physics. Studies of the quantum Hall effect is relevant to research areas such as topological phases, strong electron correlations and quantum computing.

Before the recent discovery, the quantum Hall effect was observed and investigated only in two-dimensional electron systems when subjected to low temperatures and strong magnetic fields.

While there has been intense interest in exploring the quantum Hall effect in higher dimensions, conditions for relevant observation are highly demanding. It took the research team three years to develop high-quality nanostructures of topological semimetals for the experiment, said Xiu Faxian, a professor in physics from Fudan University who is the corresponding author of the research paper in Nature.

Xiu's two doctoral students Zhang Cheng and Yuan Xiang, along with Zhang Yi, a Fudan alumnus and a post-doctor at Cornell University, are the co-first authors of the paper.

The team first discovered the existence of the quantum effect in three-dimensional nanostructures of semimetal last year, which was also reported in Nature Communications in November 2017. The discovery was later confirmed by another two similar research projects in Japan and the United States.

Over the past year, Xiu and his students have fine tuned their experiment with extricate designs that allow a clear observation of the underlying physics of the quantum Hall effect in three-dimensional structures.

Xiu said the discovery is only a start in the exploration of quantum Hall physics in three-dimensional materials.

"Much remains unknown and we're keen to explore further," Xiu said.

Xiu added that the team and the rest of the scientific community can tap into one legacy of their recent success.

"We have proved that nanostructures of topological semimetals provide a way of exploring quantum Hall physics in three-dimensional materials with enhanced tunability," Xiu said.

 

[JSCh]

Chinese scientist ranked in top 10
chinadaily.com.cn | Updated: 2018-12-19 11:41

Cao Yuan [Photo/nature.com]​

British science journal Nature has ranked a young Chinese scientist among its top-10 people for 2018.

The scientist received the award for his work on how the properties of two-layer graphene stacks change in certain conditions.

Cao Yuan, 22, graduated from the University of Science and Technology of China in Hefei, Anhui province, at the age of 18, and joined Pablo Jarillo-Herrero's group at the Massachusetts Institute of Technology in Cambridge, United States.

Cao has discovered that a rotation between parallel graphene sheets of around 1.1 degrees make the stack an insulator, while the stack is exposed to a small electric field and cooled to 1.7 C above absolute zero.

The twisted sheets became a superconductor, in which electricity flowed without resistance, when a slight tweak was made to the field, according to his discovery.

Nature in March published two papers from Cao and his colleagues on the unusual behaviors of the atom-thick carbon layers. His discovery is considered a major breakthrough that could act as a catalyst for a new field of physics.

He Jiankui, who has been criticized for his work on genetically modified embryos, also features in Nature's list, ranked third. He revealed in November that he used the genome editor CRISPR on two babies in an attempt to create an HIV-resistant human.

 

[JSCh]

Realising equity in maternal health: China's successes and challenges - The Lancet

Yan Guo | Yangmu Huang

China has made remarkable progress in maternal and child health since the 1990s. Mortality among children younger than 5 years dropped from 54·1 deaths per 1000 livebirths in 1990 to 12·5 per 1000 livebirths in 2015,1 meeting the Millennium Development Goal (MDG) 4 well ahead of schedule. Additionally, the maternal mortality ratio declined from 111·0 deaths per 100 000 livebirths in 1990 to 21·8 per 100 000 livebirths in 2015,1 achieving MDG 5 on target. China has also met the target for reducing the number of maternal deaths in Sustainable Development Goal (SDG) 3, but the challenge of improving equity remains.

In The Lancet, Juan Liang and colleagues 2 report an analysis of maternal mortality ratios down to the county level in China. They used data from China's national Annual Report System on Maternal and Child Health to analyse the progress made in achieving MDG 5 and the level and trends of maternal mortality ratios across China from 1996 to 2015, including inequalities. Overall, maternal mortality ratios declined substantially and rapidly, from 108·7 per 100 000 livebirths in 1996 to 21·8 per 100 000 livebirths in 2015, making the annualised rate 8·5%. As expected, substantial heterogeneity was found at the county level. However, at the provincial level, trends in inequality varied, showing much smaller inequalities within provinces than between provinces. This disparity illustrates the substantial geographical inequity of maternal health in China.

The Chinese Government has taken a series of actions to eliminate disparities in maternal health. For example, the programme Reducing Maternal Mortality and Eliminating Neonatal Tetanus, which was launched in 2000, was mainly targeted at rural areas, especially poverty-stricken areas. After years of effort, the urban–rural disparity of maternal mortality ratios in China has been greatly narrowed. In 2000, the maternal mortality ratio was 29·3 deaths per 100 000 livebirths in urban areas and 69·6 per 100 000 livebirths in rural areas, giving an urban-to-rural ratio of 1:2·37. By contrast, in 2015, the maternal mortality ratio had declined to 19·8 per 100 000 livebirths in urban areas and 20·8 per 100 000 livebirths in rural areas, reducing the urban-to-rural ratio to 1:1·05. 3

Because of socioeconomic imbalance between regions, however, health inequity is still substantial in China. 4 As noted by Liang and colleagues,2 191 counties had maternal mortality ratios greater than the target in SDG 3. Most of these counties were in poor rural areas in western China. If as well as maternal mortality ratios, the rate of decline in these ratios in the western regions is taken into account, the gap has been gradually shrinking. From 1990 to 2015, the total maternal mortality ratio in China declined by 4·42 times, while that in Tibet declined by 7·12 times, catching up with the national average maternal mortality ratio.5 Since the start of the 21st century, China has taken targeted measures to help people lift themselves out of poverty, improving women's status and education equity, which will all contribute to the improvement of maternal health.1

China's health reforms since the severe acute respiratory syndromes epidemic have greatly strengthened the health system in the western regions. However, improvements were mainly made in health financing and improving infrastructure, and development of the health workforce has lagged behind. 6 In 2016, the total number of health-care institutions was similar in the eastern (0·35 million) and western (0·31 million) regions, but the health workforce, especially the number of health technicians, was much higher in the eastern region (3·7 million) than in the western region (2·2 million). Due to the shortage of health-care workers, there is a gap in the quality of health between the two regions. 7 This is a challenge for China on the way to achieving universal health coverage.

Figure
Copyright © 2018 Ed Jones/Staff

Liang and colleagues provide the first estimates of the progress of maternal mortality ratios and MDG 5 and SDG 3 at the county level in China. However, a question worth exploring is whether it is appropriate to calculate and compare maternal mortality ratios by county. The population differences between provinces in China are large, and between counties are even greater. The largest county in China has a population of 2·44 million, while the smallest has a population of less than 10 000. The number of livebirths in the small counties can be less than 200 per year. 8 Many of the small counties are located in the western regions. Thus, the maternal mortality in these counties can be very unstable from year to year, which should be considered when drawing conclusions from Liang and colleagues' research.

Juan Liang; Xiaohong Li; Chuyun Kang; Yanping Wang; Xie Rachel Kulikoff; Matthew M Coates; Marie Ng; Shusheng Luo; Yi Mu; Xiaodong Wang; Rong Zhou; Xinghui Liu; Yali Zhang; Yubo Zhou; Maigeng Zhou; Qi Li; Zheng Liu; Li Dai; Mingrong Li; Yiyi Zhang; Kui Deng; Xinying Zeng; Changfei Deng; Ling Yi; Jun Zhu; Christopher J L Murray; Haidong Wang. Maternal mortality ratios in 2852 Chinese counties, 1996–2015, and achievement of Millennium Development Goal 5 in China: a subnational analysis of the Global Burden of Disease Study 2016. The Lancet (2018). DOI: 10.1016/s0140-6736(18)31712-4.​

 

[cirr]

Chinese scientists find quantum Hall effect in 3D materials

2018-12-19 16:51:30 CGTN Editor : Gu Liping

The path of the electrons in three-dimensional materials when exposed to a strong magnetic field /Screenshot from CCTV

Researchers in China have found evidence of a new type of quantum Hall Effect existent in a three-dimensional topological semimetal.

The study, published in Nature on Monday, illustrated the path of the electrons in three-dimensional materials when exposed to a strong magnetic field, marking a great step for condensed matter physics research in a higher dimension.

As one of the most important discoveries in condensed matter physics, the quantum Hall effect is considered the best example of quantization. Electrons in a quantum Hall system travel without losing their energy, thus always acting as perfect conducting systems with little energy consumption.

The discovery has shown great potential when applied in the development of low-energy consumption electron devices, and offered great insights and experience in topological quantum computing research.

While there has been intense interest in exploring the quantum Hall effect in higher dimensions, conditions for relevant observations are highly demanding.

"It took the research team three years to develop high-quality nanostructures of topological semimetals for the experiment," said Xiu Faxian, a professor in physics from Fudan University, who is the corresponding author of the research paper in Nature.

 

[JSCh]

Physics - Focus: A Home for Helium inside Earth
December 21, 2018• Physics 11, 133

Computations predict the existence of a compound that could store the primordial helium that is known to be present somewhere inside the Earth.

​

iStock.com/ademyan​

Hot helium mystery. Ancient helium can emerge from the ground along with lava (here from Kilauea Crater in Hawaii). Computational studies now show that the helium source could be the compound FeO2He in rocks close to the Earth’s core.

Primordial helium—a remnant of the early Solar System—emanates from the ground at sites of lava plumes like those found in Hawaii, Iceland, and the Galapagos. But the source of this helium deep inside the Earth remains unknown. Now researchers predict the existence of a helium-bearing compound, FeO2He, that could serve to store this enigmatic element. Their calculations indicate that the compound is stable at temperatures and pressures consistent with those found at the bottom of the Earth’s mantle—the mostly-solid layer between the crust and the molten outer core. If verified, the results would support the science behind using helium to trace the age and history of cosmological bodies, since other similar planets should contain the same material.

After hydrogen, helium is the most abundant element in the Universe, and on Earth, there are two places to find it. Helium is continuously produced through radioactive decays in the crust, and it is also found in lava and gas plumes originating from the mantle [1]. This mantle helium bears signatures showing that it was present when the Earth formed. Researchers assume that it must exist somewhere in the Earth in solid form; otherwise it would have escaped long ago, thanks to helium’s low density. However, helium-bearing rocks are rare—the inert element has limited capabilities to form compounds with other elements. And so far, such compounds are absent from measurements and predictions of rocks, leaving the hypothesis unconfirmed.

Yanming Ma of Jilin University in China and his colleagues set out to solve this conundrum by computationally searching for minerals containing iron and magnesium that might react with helium. Iron and magnesium are good starting points for such an investigation, as the elements are both abundant inside the Earth, says team member Changfeng Chen of the University of Nevada, Las Vegas.

The team used a crystal structure search algorithm called CALYPSO—developed by Ma’s group—that finds compound candidates by calculating their energies [2]. When the presence of helium in a candidate compound lowers the energy compared with the helium-free version, the helium-containing compound is considered “favorable,” and the algorithm spits out a proposed crystal. The algorithm’s search turned up empty-handed for magnesium-based compounds. But the team found one potential iron-based compound that fit their criteria— FeO2He.

The team’s calculations show that FeO2He forms a stable structure at temperatures between 3000 and 5000 K and at pressures ranging from 135 to 300 gigapascals (GPa), conditions that correspond to those found at the core-mantle boundary. The team also carried out simulations of FeO2He at a temperature of 3000 K and a pressure of 135 GPa to find the material’s acoustic properties. They found that sound waves move through the compound at speeds equivalent to those obtained in seismic-wave measurements of the core-mantle boundary, indicating that the material’s properties are consistent with observations of this region.

Recent synthesis experiments also point to FeO2He being a strong contender for housing primordial helium. Both FeO2 and the hydrogen-containing compounds FeO2Hx have been formed in laboratory settings at the temperatures and pressures found in the lower regions of the mantle [3, 4]. Chen says that the successful creation of those materials indicates that researchers could—relatively quickly and easily—confirm in the lab that FeO2He is stable in deep Earth conditions.

Helium-bearing compounds have, until very recently, been considered unlikely to exist under the physical conditions on or inside the Earth, Chen says, but in his opinion, his team’s new predictions change that view. Chen suggests that primordial helium reacted with FeO2 back when the Earth was new, forming a solid material. The compound is sufficiently heavy that it would only rise to the surface through so-called mantle plumes, which are columns of hot, solid rock that move up to the crust. When FeO2He nears the surface and experiences a drop in temperature and pressure, it should destabilize and release helium gas.

If this result is correct, it could solve the problem of where and how primordial helium is stored, says Matt Jackson, a geochemist at the University of California, Santa Barbara. Jackson studies the chemical compositions of lava plumes and has found signatures of primordial helium. “This is an exciting result,” he says, but he cautions that the predictions need to be tested with laboratory experiments. Ronald Cohen, a geophysicist at the Carnegie Institution for Science in Washington, DC, agrees. He and others thought that primordial helium was most likely stored as impurities in mantle minerals, so the prediction of a helium-containing compound is a surprise, he says.

This research is published in Physical Review Letters.

Rare Helium-Bearing Compound FeO2He Stabilized at Deep-Earth Conditions
Jurong Zhang, Jian Lv, Hefei Li, Xiaolei Feng, Cheng Lu, Simon A. T. Redfern, Hanyu Liu, Changfeng Chen, and Yanming Ma
Phys. Rev. Lett. 121, 255703 (2018)
Published December 21, 2018​

–Katherine Wright