Silicon carbide increases energy efficiency

Illustration of the fill port of a silicon single crystal bar which has been prepared by the zone melting process. (Photo: TRUMPF Hüttinger)
To increase the efficiency of the power supply in industrial processes, thereby saving energy and CO2, the aim of the new joint "MMPSiC": Researchers at the Light Technology Institute (LTI) at the Karlsruhe Institute of Technology (KIT) examine together with the industrial partners TRUMPF Hüttinger and IXYS Semiconductor the use of power semiconductor switches of silicon carbide. The Federal Research Ministry is supporting the project with around 800,000 euros.

Of the semiconductor manufacturing over the coating of displays to processes in the automotive industry: Many industrial processes consume large amounts of electrical energy. Among these are technologies that will play an important role in the energy transition, as the zone melting method (float zone method) for producing high purity crystalline materials: The substance is electrically fused in a narrow zone; the melting zone is gradually continued. Behind the melting zone crystallized substance purer than before. The zone melting method provides, among other high-purity silicon single crystals for the manufacture of solar cells.

Power supply of zone melting systems based on tube technology systems are used to now having an electrical efficiency of up to 65 percent. By switching to power semiconductor silicon carbide, the efficiency of the process power supply could be increased to over 80 percent. This would save large amounts of electrical energy and reduce greenhouse gas emissions. For example, for a single float-zone scale plant would result consisting of 20 x 150 kW-process power supplies, with an annual duration of 4800 hours, a savings of more than 200,000 kWh of electrical energy and 109 tonnes of CO2 (Umweltbundesamt, as of July 2013).

The feasibility of such a process power supplies, researchers at the Light Technology Institute (LTI) of KIT together with the partners TRUMPF Hüttinger GmbH + Co. KG (Freiburg) and IXYS Semiconductor GmbH (Lampertheim) in the joint project "Modular medium frequency process power supply with silicon carbide semiconductor power switches" (MMPSiC) , As the semiconductor material Silicon Carbide offers several advantages: Thanks to the larger electronic band gap allows much higher operating temperatures than conventional semiconductors. Power electronics with silicon carbide is characterized by higher energy efficiency and compactness.

"When the power of energy-intensive industrial applications such as the zone melting method, it is necessary to switch at high frequencies," says the project director, Dr. Rainer Kling from LTI of KIT. "Silicon carbide is not yet tested for these high frequencies; so that we are breaking new ground. "In addition to examining the long-term stability include the control and the layout of the circuit to the tasks of the KIT researchers in the joint project MMPSiC.

The Federal Ministry of Education and Research (BMBF) supports MMPSiC project on the basis of the program "Information and Communication Technology 2020" (ICT 2020) as part of the funding program "Power electronics to increase energy efficiency" (LES 2) with around 800,000 euros. Of which receives the LTI KIT around 439,000 euros. Overall, the project volume is 1.3 million euros. The joint project started in 2014 and is planned for three years.

Source: KIT

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How an innovative grants program (and Belgian beer mixers) at Johns Hopkins fuels discoveries about the human brain

A neuroscientist, an electrical engineer, a surgeon, and an education researcher walk up to a bar.

This could be the start of a joke, or it could be a scene from a recent Science of Learning Institute event at Johns Hopkins University. At the institute's four-times-yearly Belgian Beer Events, scientists from far-flung fields—and often from far-flung parts of the university itself—present their research to each other in short, digestible chunks. Their creativity and conviviality stimulated by a cup of ale or lager, the researchers strike up conversations and form connections that range widely across disciplinary boundaries, from classroom learning to machine learning, from recovery from stroke to memory formation in the brain.

Such conversations can be all too rare at a university where faculty are spread not just across a campus but throughout a large city and beyond. The result, for an inherently interdisciplinary subject like the science of learning, is that projects that could address fundamental and important questions can be hard to conceive and get off the ground. And too often, promising basic research doesn't get translated into the settings where it could help real-world learners.

The Belgian Beer Events, conceived shortly after the institute launched in 2013, are helping change that. They provide an informal space where basic researchers can meet translators, where machine-learning experts can meet early-childhood educators, where cognitive scientists can meet smartphone app developers. The events rotate between locations: October's was at the School of Education, and December's was hosted by the Department of Biomedical Engineering; previous ones were held at the School of Medicine and in Homewood's Levering Hall. Computer scientist Greg Hager likens the events to "an intellectual mixing bowl."

Beyond generating lively conversation, the gatherings are sparking collaborations between researchers who otherwise might never have met. At an event in 2013, neurologist Bonnie Nozari presented her work on speech and language processing disorders. Computer scientist Raman Arora then spoke about his work on machine learning and speech recognition. Recognizing a mutual interest in speech, the two chatted. The next day, they began planning a joint project to see if computers can predict how humans will pronounce words, and then provide feedback to people seeking to learn a new language, or to relearn how to speak after a stroke.

It sounds like a lucky encounter, but in fact electrical engineer Sanjeev Khudanpur, a member of the institute's steering committee, was at work behind the scenes. He conceived the Belgian Beer Events, and he made sure that Arora, his colleague in the Whiting School of Engineering, would be speaking on the same day as Nozari, of the School of Medicine. Later, when the two were ready to apply for funding, Khudanpur encouraged their ultimately successful proposal for one of the institute's research grants. "I see myself as a matchmaker," he says.

"It's that kind of really innovative, different seeding of projects that I think we've done really well," says Barbara Landau, the institute's director and the Dick and Lydia Todd Professor of Cognitive Science in the Krieger School of Arts and Sciences. The institute funded eight projects in 2013 and eight more in 2014, with projects receiving an average of $140,000 spread over two years. Funding goes to hiring graduate students and postdoctoral researchers, developing software, purchasing equipment, and supplying other research needs. The grants are competitive; the review committee has received around 30 proposals a year. The funded projects address a broad range of learning settings, from the classroom to the operating room to distance learning that can take place anywhere. The learners are not limited to humans, either; many of the projects include a strong component of "machine learning"—harnessing computers to recognize patterns in data and use them to develop new human learning applications. Other projects focus on developing animal models that can be used to study human learning.

The grant program allows researchers to get support for projects that might not be quite ready for a proposal to a traditional funding agency like the National Science Foundation or the National Institutes of Health, says Landau. Almost without exception, an NSF or NIH review panel will want to see at least preliminary data demonstrating that an idea is viable. With Science of Learning Institute funding, scientists can do exploratory research that will provide the data needed to support a larger proposal to a more traditional funding agency. "It allows people to do things that they wouldn't necessarily be able to accomplish by a standard grant," says Landau. "The granting agencies tend to be somewhat conservative, and we're looking for innovation."

Like Arora and Nozari's collaboration, many of the funded projects harness existing technological applications to improve learning, often in novel ways. For example, Khudanpur and Hager are working with Gyusung Lee, an instructor of surgery in the School of Medicine, to develop computer software that can help teach surgeons how to use the da Vinci robotic surgical platform. The project grew out of an existing effort called the Language of Surgery, developed by researchers in the Whiting School of Engineering's Laboratory for Computational Sensing and Robotics.

Through this effort, which began in 2006, Hager, Khudanpur, and colleagues program computers to record and analyze the different kinds of movements that surgeons make while performing certain tasks with surgical robots. The researchers' goal was to find movements that could consistently be classified as either expertlike or novicelike. Novice surgeons are more likely to break a suture, for example, or to push or pull on tissue while using the robot to manipulate a surgical needle. The researchers were able to train computer software to recognize such expert and novice movements much as a surgical trainer would.

The next step is to have the assessment tool provide real-time feedback to surgical trainees. With the kind of application the researchers are envisioning, trainees could, in theory, receive an unlimited amount of individualized feedback on what skills they have mastered and where more work is needed. "We're putting the computer in the human learning loop," Khudanpur says. "The computer has certain abilities that are complementary to humans. [For example,] the computer doesn't get tired. The computer usually doesn't charge by the hour."

A few years ago, when the researchers applied for an NIH grant to develop such a learning application, the proposal was rejected because they had no data showing the idea had promise. Thanks to their Science of Learning Institute research award, the scientists are starting to collect that data. Backed by some preliminary results, they recently put in a new NIH proposal and are waiting to hear back.

Meanwhile, thanks to a talk Hager gave last fall, his team's research may soon spawn another effort, which would take Language of Surgery technology out of the operating room and into the classroom. Hager's presentation inspired Landau and Amy Shelton, a professor in the School of Education, who is also on the institute's steering committee, to wonder whether motion-tracking software could recognize the movements that young children make when learning to build toy towers out of blocks. Spatial skills like tower building, in addition to being important in their own right, are of interest to researchers because they often predict children's future abilities in math and other areas. Hager, Landau, and Shelton are now discussing a potential project to put motion sensors on blocks and use computers to track how children acquire manipulation skills, a tactic similar to the one Hager's team uses to assess the skills of aspiring surgeons.

Institute-funded collaborations between computer scientists and education researchers are also reaching far beyond traditional education settings like medical training. In a project funded in 2014, computer scientists Philipp Koehn and Jason Eisner are teaming with Chadia Abras in the School of Education's Center for Technology Education to develop a radically new way to learn a foreign language. The idea is based on macaronic language—a kind of text that mixes two languages into a Spanglish-like hybrid. While such mixing has traditionally been employed by novice speakers or for satirical purposes, Eisner realized that coupled with recent advances in machine translation, it could also help introduce learners to foreign vocabulary and syntax in a gentle and piecemeal way rather than all at once, as in a typical foreign text read laboriously with the aid of a dictionary.

To implement the idea, the researchers are developing software that translates a text progressively, with more and more of the text appearing in the foreign language as the reader's comprehension improves. For an English-to-German learner, for instance, the English phrase "a loaf of bread" could start to appear as "ein Loaf of Bread." When the reader is comfortable with reading the German word "ein" instead of the English "a," the program could progress to "ein Breadloaf," resembling German in syntax but retaining English words. The text would then become "ein Brot loaf," and finally the fully German "ein Brotlaib*." The program will intermittently assess the student's reading comprehension and ability, and tune the amount of foreign language presented to the reader's progress; readers also can direct the program to make the translation easier or harder.

Since the concept still needs to be proved, it makes an ideal Science of Learning Institute project, says Koehn. Eisner adds, "It's a bet that this will work out and will not, for example, confuse people or give them bad habits." The researchers plan to develop an English-to-German application and test it on the Web and in Johns Hopkins classes in combination with more traditional classroom and textbook instruction. If successful, the software could also be made available on the Internet for independent learners.

The project exemplifies how interdisciplinary teams can merge cutting-edge research in machine and human learning, says Kelly Fisher, the institute's assistant director and an assistant professor in the School of Education. "It's a software program that is learning itself, learning about the learner."

Institute-funded research also targets learners far beyond those who are acquiring skills for the first time. Learning is critical for the millions of people who lose skills when they suffer strokes and other neurological conditions and then need to regain them, often through lengthy and complex rehabilitation processes. Research on how to more efficiently relearn lost skills could make a huge difference in how quickly such people can return to work and fully participate in society again.

Cognitive scientist Michael McCloskey recently discovered a new, debilitating, and apparently very rare reading deficit known as alphanumeric visual awareness deficit, or AVAD. McCloskey, a professor in Cognitive Science, identified the condition based on two cases that came to him in one year. One of them, a 61-year-old Baltimore geologist with a neurological disease, could see fine in general, but when looking at letters or numbers, he saw only blurs. McCloskey and his colleagues found, however, that by teaching the patient new characters to use in place of the digits, they could restore his recognition abilities. The researchers developed a smartphone calculator app and modified the geologist's laptop to allow him to do math with the new symbols.

Seeking to build on this work, McCloskey assembled a team of neurologists and cognitive scientists to look for more people with AVAD in order to study the condition using brain imaging and other techniques, and to develop apps and other technology that would help affected people make sense of letters and numbers again. But the researchers have run into a roadblock: They haven't found a single other case of AVAD beyond the original two. A woman in North Carolina who seemed to have the deficit turned out to have a somewhat different condition. "On the one hand, it's interesting that [AVAD is] so rare; on the other hand, it's not what we were hoping for," McCloskey says.

So he and his team have reoriented their project, broadening the scope to include more-common character recognition disorders. For example, some people cannot recognize a number or letter when it is presented to them whole but can recognize a character if they watch it being drawn. Perhaps, says McCloskey, a smartphone app could be developed to read signs and other important text, and draw each character in sequence for people with this deficit. His team is also starting to collaborate with a software developer, MicroBLINK, to make an app that would identify characters and then read the text aloud.

In addition to potentially helping people regain lost abilities, many institute-funded projects such as McCloskey's are aimed at teasing apart the different brain regions and processes responsible for seemingly coherent learned skills like reading. Along these lines but focusing on an entirely different brain function, psychologist Marina Bedny, of the Krieger School's Department of Psychological and Brain Sciences, is heading a team that received an institute grant to study how the brain can retool its hardware when the original purpose of one of its regions is no longer needed. In sighted people, around a quarter of the brain is devoted to visual processing; in blind people, these brain regions get repurposed. How does this work? Bedny wondered.

To investigate this question, she and colleagues in the Krieger School's Department of Cognitive Science and in the Department of Physical Medicine and Rehabilitation at the School of Medicine are combining language comprehension assessments with a technique called transcranial magnetic stimulation, or TMS. They hope to learn whether brain regions normally devoted to sight are needed for language processing in blind people. The researchers recently collected data at a National Federation of the Blind convention and are in the process of testing a control group of sighted people. This effort would have been impossible without a source of support for interdisciplinary projects, Bedny says. "You just can't do this kind of research without an interdisciplinary team because you need so many different kinds of expertise," from linguistics to neuroimaging to TMS. "We really needed the whole team to make it happen."

In another example of institute-funded brain research, neuroscientist David Foster, of the School of Medicine, is taking on perhaps the most basic of all aspects of learning: memory formation. Specifically, Foster is interested in how certain kinds of memories are formed in a brain region called the hippocampus. He has studied this process in detail in rat brains, using dozens of implanted electrodes to precisely record electrical signals as the rats' neurons fire in sequences that represent stored memories. Foster would like to carry out similar studies in humans, but he cannot just go sticking electrodes deep into people's brains. So he first needs to develop less-invasive procedures.

Foster and William Anderson, an associate professor of neurosurgery in the School of Medicine, are now developing such techniques, piggybacking on research that Anderson's group does on epilepsy patients wherein they collect and analyze electrical data gathered from the surface of the brain. By piloting their study on a small sample of patients, the researchers hope to strengthen their position for applying for a larger grant, possibly from the NIH.

Bedny and Foster, both assistant professors, say that institute funding has allowed them to take on projects that might have otherwise been too risky and uncertain for an untenured faculty member. "I probably would not do too much looking outside of my own area to collaborate if I wasn't pushed and incentivized to do so by this kind of mechanism," Foster says. "This allows me, and pays me, to invest in thinking outside of my own small area."

The research grant program is the Science of Learning Institute's first major initiative, and many of the projects from the initial funding round are close to reporting results. The institute plans to continue awarding grants for at least three more years, and possibly more, depending on funding. To assess the program's success, Landau and Fisher are tracking metrics such as publications that awardees produce and external awards that leverage institute-funded work.

The institute also just launched its second big initiative: the Distinguished Science of Learning Fellowship Program. This program will award around five postdoctoral and predoctoral fellowships annually to students wanting to pursue interdisciplinary research in learning. Each fellow will have two advisers from different disciplines.

The fellows also will play a key role in the third prong of the institute's mission: translating and disseminating results beyond academia. Traditionally, much of the learning that occurs in the nation's formal classrooms and more informal settings is not as informed by research as it could be, says Fisher. To help change that, the Science of Learning Institute recently launched partnerships with the Port Discovery Children's Museum in Baltimore and the Children's Museum of Manhattan in New York to develop exhibits that are based on the research into the science of learning. The institute also plans to hire a dissemination expert to help translate research results into classrooms and other learning settings.

The Science of Learning Institute's stated mission is "to understand and optimize the most essential part of our human capital: the ability to learn." The mission makes the institute a crucial catalyst at a university—a place dedicated to learning—where all the pieces are already in place to make major progress on one of the most important scientific questions of our time, says Landau. "One of the goals of the Science of Learning Institute," she says, "is really to sew together the parts of the university that haven't yet interacted—to make it, in President Daniels' words, one university."

Source: JHU

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New technique could lead to cheaper, more efficient solar power and LEDs

Researchers Valerio Adinolfi (left) and Riccardo Comin examine a perovskite crystal. Perovskites are attracting growing interest in the context of thin-film solar technologies, but had never been studied in their purest form: as perfect single crystals. Credit; Toronto

U of T experts are shining new light on an emerging family of solar-absorbing materials that could lead to cheaper and more efficient solar panels and LEDs.

The materials, called perovskites, are particularly good at absorbing visible light, but had never been studied in their purest form: as perfect single crystals.

Using a new technique, researchers grew large, pure perovskite crystals and studied how electrons move through the material as light is converted to electricity.

Led by Professor Ted Sargent of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto in collaboration with Professor Osman Bakr of the King Abdullah University of Science and Technology (KAUST), the team used a combination of laser-based techniques to measure selected properties of the perovskite crystals.

By tracking down the ultrafast motion of electrons in the material, they have been able to measure the diffusion length – how far electrons can travel without getting trapped by imperfections in the material – as well as mobility – how fast the electrons can move through the material. Their work was published this week in the journal Science.

“Our work sets the bar for the ultimate solar energy-harvesting performance of perovskites,” says Riccardo Comin, a post-doctoral fellow with the Sargent Group. “With these materials it’s been a race to try to get record efficiencies, and there are no signs of stopping or slowing down.”

In recent years, perovskite efficiency has soared to over 20 per cent, very close to the current best performance of commercial-grade silicon-based solar panels you see mounted in Spanish deserts and on Californian roofs.

“In terms of efficiency, perovskites are perfectly comparable or better than materials that have already been commercialized,” says Valerio Adinolfi, a PhD candidate in the Sargent Group and co-first author on the paper. “The challenge is to make solar attractive from the business side. It’s not just matter of making it efficient – the point is to make it efficient and cheap.”

The study has obvious implications for green energy, but may also enable innovations in lighting.

Think of a solar panel made of perovskite crystals as a fancy slab of glass: light hits the crystal surface and gets absorbed, exciting electrons in the material. Those electrons travel easily through the crystal to electrical contacts on its underside, where they are collected in the form of electric current.

Now imagine the sequence in reverse – power the slab with electricity, inject electrons and release energy as light. A more efficient electricity-to-light conversion means perovskites could open new frontiers for energy-efficient LEDs.

Parallel work in the Sargent Group focuses on improving nano-engineered solar-absorbing particles called colloidal quantum dots. “Perovskites are great visible-light harvesters, and quantum dots are great for infrared,” said Sargent.

“In future, we will explore the opportunities for stacking together complementary absorbent materials,” says Dr. Comin. “There are very promising prospects for combining perovskite work and quantum dot work for further boosting the efficiency.”

Source: U of T

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Electric eels deliver taser-like shocks

News research has discovered that the electric eel delivers Taser-like shocks. Credit: Kenneth Catania, Vanderbilt University

The electric eel -- the scaleless Amazonian fish that can deliver an electrical jolt strong enough to knock down a full-grown horse -- possesses an electroshock system uncannily similar to a Taser.

That is the conclusion of a nine-month study of the way in which the electric eel uses high-voltage electrical discharges to locate and incapacitate its prey. The research was conducted by Vanderbilt University Stevenson Professor of Biological Sciences Kenneth Catania and is described in the article "The shocking predatory strike of the electric eel" published in the Dec. 5 issue of the journal Science.

People have known about electric fish for a long time. The ancient Egyptians used an electric marine ray to treat epilepsy. Michael Faraday used eels to investigate the nature of electricity and eel anatomy helped inspire Volta to create the first battery. Biologists have determined that a six-foot electric eel can generate about 600 volts of electricity -- five times that of a U.S. electrical outlet. This summer scientists at the University of Wisconsin-Madison announced that they had sequenced the complete electric eel genome.

Until now, however, no one had figured out how the eel's electroshock system actually worked. In order to do so, Catania equipped a large aquarium with a system that can detect the eel's electric signals and obtained several eels, ranging up to four feet in length.

As he began observing the eels' behavior, the biologist discovered that their movements are incredibly fast. They can strike and swallow a worm or small fish in about a tenth of a second. So Catania rigged up a high-speed video system that ran at a thousand frames per second so he could study the eel's actions in slow motion.

Catania recorded three different kinds of electrical discharges from the eels: low-voltage pulses for sensing their environment; short sequences of two or three high-voltage millisecond pulses (called doublets or triplets) given off while hunting; and volleys of high-voltage, high-frequency pulses when capturing prey or defending themselves from attack.

He found that the eel begins its attack on free-swimming prey with a high-frequency volley of high-voltage pulses about 10 to 15 milliseconds before it strikes. In the high-speed video, it became apparent that the fish were completely immobilized within three to four milliseconds after the volley hit them. The paralysis was temporary: If the eel didn't immediately capture a fish, it normally regained its mobility after a short period and swam away.

"It's amazing. The eel can totally inactivate its prey in just three milliseconds. The fish are completely paralyzed," said Catania.

These observations raised an obvious question: How do the eels do it? For that, there was no clear answer in the scientific literature.

"I have some friends in law enforcement, so I was familiar with how a Taser works," said Catania. "And I was struck by the similarity between the eel's volley and a Taser discharge. A Taser delivers 19 high-voltage pulses per second while the electric eel produces 400 pulses per second."

The Taser works by overwhelming the nerves that control the muscles in the target's body, causing the muscles to involuntarily contract. To determine if the eel's electrical discharge had the same effect, Catania walled off part of the aquarium with an electrically permeable barrier. He placed a pithed fish on other side of the barrier from the eel and then fed the eel some earthworms, which triggered its electrical volleys. The volleys that passed through the barrier and struck the fish produced strong muscle contractions.

To determine whether the discharges were acting on the prey's motor neurons -- the nerves that control the muscles -- or on the muscles themselves, he placed two pithed fish behind the barrier: one injected with saline solution and other injected with curare, a paralytic agent that targets the nervous system. The muscles of the fish with the saline continued to contract in response to the eel's electrical discharges but the muscle contractions in the fish given the curare disappeared as the drug took effect. This demonstrated that the eel's electrical discharges were acting through the motor neurons just like Taser discharges.

Next Catania turned his attention to the way in which the eel uses electrical signals for hunting. The eel is nocturnal and doesn't have very good eyesight. So it needs other ways to detect hidden prey.

The biologist determined that the closely space doublets and triplets that the eel emits correspond to the electric signal that motor neurons send to muscles to produce an extremely rapid contraction.

"Normally, you or I or any other animal can't cause all of the muscles in our body to contract at the same time. However, that is just what the eel can cause with this signal," Catania said.
Putting together the fact that the eels are extremely sensitive to water movements with the fact that the whole-body muscle contraction causes the prey's body to twitch, creating water movements that the eel can sense, Catania concluded that the eel is using these signals to locate hidden prey.

To test this hypothesis, Catania connected a pithed fish to a stimulator.. He put the fish in a clear plastic bag to protect it from the eel's emissions. He found that when he stimulated the fish to twitch right after the eel emitted one of its signals, the eel would attack. But, when the fish failed to respond to its signal, the eel did not attack. The result supports the idea that the eel uses its electroshock system to force its prey to reveal their location.

"If you take a step back and think about it, what the eel can do is extremely remarkable," said Catania. "It can use its electrical system to take remote control of its prey's body. If a fish is hiding nearby, the eel can force it to twitch, giving away its location, and if the eel is ready to capture a fish, it can paralyze it so it can't escape."

The research was funded by a Pradel Award from the National Academy of Sciences, a Guggenheim fellowship and National Science Foundation grant 0844743.

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Source: Vanderbilt University

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