News on China's scientific and technological development.

Supercapacitors based on carbon nanotubes and conducting polymers have higher energy densities (amount of energy stored) than pure carbon nanotube-based ones, but they suffer from lower power densities (amount of power). This is because the polymer layers overlap, leading to poor electrical conductivity.

Now, scientists from China, Australia and Singapore have changed the design to increase the power density. The ultrathin supercapacitor could have potential uses in lightweight and flexible storage devices for portable electronic devices.

Weiya Zhou from the Chinese Academy of Sciences, and colleagues, used what they call a skeleton/skin strategy to make the improvement. The carbon nanotubes (single-walled carbon nanotubes - SWCNTs) are the skeleton and the polymer layers (polyaniline - PANI) are the skin. The skeleton/skin structure ensures that the films are better conductors than conventional SWCNT/PANI electrodes.

"Electrons can be transported continuously through the skeleton/skin architecture," says Zhou. "In the SWCNT/PANI network, interbundle junctions and continuous connections with SWCNT-SWCNT contacts ensure low resistance." So, they found that the film's conductivity was higher than that of SWCNT/PANI electrodes with overlapped PANI-PANI contact, which led to improved power density.

"Thin and flexible energy storage devices are desired in many electronic devices that require flexibility," says George Chen, an expert in electrochemical technology from the University of Nottingham, UK. Flexible phones or other personal electronic devices would make usage convenient and more reliable, he adds.

Also, ultrathin supercapacitors can help to reduce the volume of the whole device and allow installation of additional functionalities in place of a bulk battery. "There are many applications of ultrathin supercapacitors (or batteries), for example imagine just wearing them, instead of carrying them in your shoulder bag, when boarding a flight," he says.

He does caution that the work is still at the early stages of development and that improvements are needed before commercial ultrathin supercapacitors become a reality. "For example, the device as reported exhibited negative deviation from theoretical predictions, which means the actual energy capacity was likely lower than reported," he says.

"Also, the device suffers from a fast loss of stored energy, known as self-discharge. Reasons for such non-ideal behaviour are still not known and call for further research in terms of fundamental science and practical engineering."

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Chinese scientists are looking for a site for a giant solar telescope, which will be the world's largest in the next two decades with data helping to understand solar activities.

The Chinese Giant Solar Telescope (CGST), or one of "the next-generation ground-based solar telescopes," will lead a field of solar observation in 20 years, if the construction is approved and starts in 2016, according to Prof. Deng Yuanyong, director of Huairou Solar Observing Station of the National Astronomical Observatories (NAO) under the Chinese Academy of Sciences (CAS).

The national project with a budget of about 90-million U.S. dollars was proposed by the entire solar community of China.

It aims to build a very large infrared and optical solar telescope, with the spatial resolution expected to be equivalent to an 8meter-diameter telescope and light-gathering power equivalent to a 5m-diameter full aperture telescope, Deng told Xinhua at the International Astronomical Union (IAU)'s 28th General Assembly, which started in Beijing on Aug. 21 and will last two weeks.

The world's largest ground-based solar telescope currently in use is the 1m solar telescope of Sweden, with solar telescopes of 1.5m and 1.6m soon to be launched by Germany and the United States, respectively.

Deng, an initiator of the project, said the CGST will obtain precise measurements of the solar vector magnetic field with high-spatial resolution, and detect the fine structures of solar magnetic field and dynamic field.

The elemental magnetic structures play a key role in the process of all kinds of solar magnetic interactions. However, after more than 100 years of development, the nature of the solar magnetic field is still one of the most important mysteries in solar physics.

According to Deng, the CGST will surpass the capabilities of the large optical telescopes currently being planned by other countries, such as the U.S. Advanced Technology Solar Telescope (ATST), which is going to be installed in Hawaii, and the European Solar Telescope (EST). Both have a design diameter of 4m.

"From 1m and 8m and the preferred adoption of the ring structure as it has superiority in the thermal design, scientists have to conquer many key technologies," Deng said, adding the construction period is expected 10 to 15 years.

"Although solar physics has made big progress with ground-based and space-borne observations in the past decades, it seems that we do need more efforts," he continued.

He also said the detection of the fundamental structure of the magnetic field always requires resolution -- spatial, temporal, and spectral -- and sensitivity as high as possible.

As solar radiation in the infrared region is very weak, gathering more photons with a larger telescope is necessary, which is not only required for high resolution but also for the high magnetic sensitivity, Deng said.

"The results of simulation and analysis showed that the current design could meet the demand of most science cases not only in infrared band but also in near infrared band and even in visible band," he said.

At present, the best site in China for solar observations was found in Fuxian Lake of Yunnan Observatory in southwest China. "However, as the CGST will mainly work in the infrared, this site is not ideal," Deng said.

In 2010, the Chinese solar community started a four-year project called "site survey for solar observations in the western part of China," which was supported by the National Science Foundation of China to find the best site for the CGST and other solar projects.

Lin Jun, chief scientist of the CAS Yunnan Observatory, said the western part of the country, including Tibet Autonomous Region as well as Yunnan and Sichuan provinces, may provide more candidates for the site of the CGST with the right geological and weather conditions.

"The site must stay far away from the hustle and bustle of cities, as well as modern industrialization," Lin said, adding the telescope could also monitor the solar energy and the change of the local environment.

The CGST was selected and recommended by the CAS to the National Development and Reform Commission (NDRC), China's economic planner that approved major infrastructure projects, as the "National major basic scientific project for 2016-2030" in January 2010.

In November that year, the CGST was selected by the NDRC as a National 14-15th Five-Year planning project for astronomy (2021-2025, or 2026-2030).The long-term astronomical project was proposed in 2009 by the NAO, Yunnan Observatory, Purple Mountain Observatory in Nanjing, Nanjing University, Nanjing Institute of Astronomical Optical Technology and Beijing Normal University, which are the six major solar research groups in China.

"As the CGST is still in its very early stage, we are looking forward to more international collaboration," Deng said.

Meanwhile, some large-scale astronomical projects in China, including the Large Sky Multi-Object Fiber Spectroscopic Telescope (LAMOST) completed in 2008 in Xinglong, north China's Hebei Province, and the 500m Aperture Spherical Radio Telescope (FAST) to be completed in 2016 in Pingtang County of southwestern Guizhou Province, will provide experience for the building of the CGST.

There are also more ambitious plans for China to build telescopes in space. "We are planning both ground-based and space solar telescopes," Deng said, adding China is planning to launch the Space Solar Telescope (SST) project, which was first proposed in mid-1990s.

A 1m optical telescope equipped with a two-dimensional real-time spectrograph and high-accuracy polarimeter will be sent into space to observe the basic structures and understand the solar magnetic field, he said.

The 1m-diameter Chinese SST will surpass the 0.5m space telescope of the Japanese Hinode solar mission launched in 2006 with the collaboration of the United States and Britain, Deng said.

"Astronomical observation through space telescopes avoids disturbance from the earth's atmosphere," said Lin Jun.

However, due to the difficulty and risks of space missions, working from the ground is a better way to develop the technology and the approach to use later for space mission, he said

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Chinese astronomers are actively searching for Earth-like planets using survey instruments in Antarctica, as they believe efforts to seek an extra-solar planet that may sustain life will soon be paid back.

"It's highly possible that human beings might find such a planet in the coming few years," said Wang Lifan, a researcher at the Purple Mountain Observatory and director of the Chinese Center for Antarctic Astronomy.

"Such planets likely exist in the Milky Way, with a possible distance of thousands of light years from us," Wang said.

Chinese astronomers installed the first of three Antarctic Survey Telescopes (AST3-1) at Dome Argus, located at the highest elevation on the Antarctic continent, at the beginning of the year. One of its primary missions is to search for extra-solar planets suitable for life.

"We will send people there to retrieve observation data next spring. I hope we can find some likely candidates. It's hard to say precisely how many, but I hope there are no less than 10," Wang said.

Chinese astronomers now rely on an Iridium satellite phone to give orders to and receive data from their survey instruments in Antarctica, which only allows them to send and receive a small amount of data at a time.

However, Wang revealed that his team is considering building a supercomputer system in Antarctica. "The new system could help us analyze the massive amounts of data gathered at the site and transmit small amounts of processed data back via satellite."

Astronomers around the world have been looking for Earth-like planets for years, a feat that has proven difficult, as it would require finding a planet with a very specific size, temperature and atmosphere.

"So far, humans have yet to find an exact twin of the Earth," Wang said.

"We search through a wide range of main sequence stars, mainly sun-like stars, and then look for planets within a suitable distance around them. Stars that are smaller and darker than the sun, such as dwarfs, are also in our survey scope," he said.

"If the stars are particularly large, they are inclined to evolve faster. Some will explode soon, and their planets will go missing after the explosion," he added.

Scientists have been trying to find signs of life in the universe by looking for habitable planets first. "We know too little about life. Maybe there are new forms of life that do not need exactly the same environment as we have on Earth. Some can survive in very harsh environments," Wang said.

The second AST3 will be installed in Antarctica between late 2013 and early 2014, while the third one will be installed between late 2014 and early 2015. "These telescopes are expected to help us find at least 100 sun-like stars. We will work with Australian scientists to further study the movement of the stars to calculate their size," Wang said.

Chinese scientists are also planning to set up an Antarctic observatory to further boost their research and broaden the search for habitable planets. If approved and included in the 12th Five-Year Plan, the observatory should go into operation by 2020.

"Antarctica has the best conditions on Earth for astronomical observation, as it has very flat ground, a transparent atmosphere and little turbulence. The ground-based telescopes here will bring us precious information from the universe," he said. (Xinhua)

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An increasing number of science and technology international conferences are being held in China, as the country's scientific research and innovation capabilities and influence continue to grow.

The latest example is the 28th General Assembly of the International Astronomical Union, which is being held in Beijing from Monday to Aug 31. This is the first time China has hosted the triennial event since joining the organization in 1935.

"Over the past 30 years, since China adopted the reform and opening-up policies, it has not only opened its door for economic development, but also for exchanges in science and technology...

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Sparse microwave imaging is a novel concept in microwave imaging that is intended to deal with the problems of increasing microwave imaging system complexity caused by the requirements of the system applications, by the effort of combining the sparse signal processing theory with microwave imaging theory.

Microwave imaging is one of the two major tools of remote sensing, and has been widely used in fields such as agriculture, forestry, oceanic monitoring, topography mapping and military reconnaissance. The best known modern microwave imaging technology used in remote sensing is synthetic aperture radar (SAR), which transmits electromagnetic waves toward the scene from a platform moving in a straight line, receives the radar echoes and produces a high resolution microwave image via signal processing.

Compared with optical sensing, microwave imaging has the ability to provide all-weather all-time observation, and can be applied to deal with some special sensing requirements, including moving target detection and digital elevation model extraction.

As microwave imaging technology has been used in increasing numbers of fields, the users have of course raised demands for numerous new requirements for their microwave imaging systems. Among them, high resolution and a wide mapping swath are the basic requirements for modern microwave imaging systems. High resolution means that more details can be observed, and the wide mapping swath means larger observation areas.

Under the support of the 973 program "Study of theory, system and methodology of sparse microwave imaging", researches of Institute of Electronics, Chinese Academy of Sciences (IECAS) have conducted considerable research into most aspects of sparse microwave imaging, including its fundamental theories, system design, performance evaluation and applications.

An overview of their work can be found in the paper written by Professor WU Yirong and his research group from the Science and Technology on Microwave Imaging Laboratory at the IECAS, entitled

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Metal/semiconductor heterogeneous photocatalytic materials have been a hot topic in photocatalytic field. However, due to their structural and functional defects, the reported heterogeneous materials have certain shortcomings, such as low photon-generated carrier separation efficiency and poor visible light-driven catalytic property.

Therefore, the design and preparation of metal/semiconductor heterogeneous visible light driven photocatalysts with highly efficient electron-hole pairs separation and rapid electron transfer have been a problem to be urgently solved.

The energy and nano-catalytic materials for environment research group at Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences (LICP), has fabricated a new heterogeneous photocatalyst, namely Ag nanowire/Ag3PO4 cube necklace-like heterostructures, by a facile and efficient process.

They have prepared Ag3PO4 cube necklace-like heterostructures via selective growth of Ag3PO4 submicro-cubes on Ag nanowires. The size, morphology, position and number of the Ag3PO4 cube of the necklace-like heterostructures can all be controlled.

A detailed study of the photocatalytic activity of the heterostructures shows that Ag nanocrystals possess a favorable Fermi level and can serve as a good electron acceptor for facilitating quick electron transfer from both exterior and inner Ag3PO4 cubes under visible-light irradiation.

Thereby, the photoexcited electrons can be rapidly transferred to Ag nanowires and the photoinduced holes can still locate on Ag3PO4 cubes, which promote the effective separation of photoexcited electron–hole pairs and decrease the probability of electron–hole recombination.

More importantly, the enriched electrons on the Ag nanowires could be effectively exported due to the novel necklace heterostructure, which facilitates their participation in the multiple-electron reduction reaction of oxygen

Their photocatalytic performance studies indicate that these novel heterostructures exhibited much higher catalytic activities than pure Ag3PO4 cubes or Ag nanowires for the degradation of organic dyes under visible-light irradiation.

These demonstrations reveal that the rational design and fabrication of necklace-like metal–semiconductor heterostructures may be an effective technique to improve photocatalytic activity, and will most probably be applicable in the development of the generation of highly efficient visible-light sensitive photocatalysts.

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Diamond-like carbon (DLC) protective coatings with excellent strength and toughness properties, low friction and low environmental sensitivity has always been a challenge in the field of hard solid lubricating coatings.

The research group headed by Professor XUE Qunji and Professor WANG Liping at State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences (LICP), fabricated low friction multi-doped carbon-based nanocomposite coatings by multiple-target magnetron sputtering deposition technique.

The nanocomposite coatings were designed using First principle and finite element simulation, and fabricated via co-incorporation of strong-carbide-forming (SCF) metal weak-carbide-forming (WCF) Al.

These coatings possess typical nano-crystalline/amorphous structure, excellent strengthening and toughening properties and low environmental sensitivity. Based on Raman spectra, HRTEM analysis of focused ion beam (FIB) technique prepared coatings, thermodynamic calculation of the micro-area of worn surfaces, it has been found that the thickness of the low shear strength graphitic interlayer formed due to friction is 30nm.

In particular low friction (~0.05) of these coatings can be acquired by creating a strong thermodynamic driving force to promote phase segregation of graphitic carbon from the a-C structure so as to form a low shear strength graphitic tribo-layer on the friction contact surfaces.

This study proposes a new design for low friction carbon-based nanocomposite coatings by tailoring the microstructure and phase segregation, and thereby it contributes to better controlling the mechanical and tribological properties.

The work has been accomplished by cooperating with National Centre for Advanced Tribology at Southampton (nCATS). It has received support from National High-tech R&D Program of China (863 Program) and National Natural Science Foundation of China. The findings have been published in Journal of Materials Chemistry

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