Monthly Archives: March 2015

New kind of “tandem” solar cell developed: MIT Research

Researchers combine two types of photovoltaic material to make a cell that harnesses more sunlight.

By David Chandler


 

CAMBRIDGE, Mass–Researchers at MIT and Stanford University have developed a new kind of solar cell that combines two different layers of sunlight-absorbing material in order to harvest a broader range of the sun’s energy. The development could lead to photovoltaic cells that are more efficient than those currently used in solar-power installations, the researchers say.

The new cell uses a layer of silicon — which forms the basis for most of today’s solar panels — but adds a semi-transparent layer of a material called perovskite, which can absorb higher-energy particles of light. Unlike an earlier “tandem” solar cell reported by members of the same team earlier this year — in which the two layers were physically stacked, but each had its own separate electrical connections — the new version has both layers connected together as a single device that needs only one control circuit.

The new findings are reported in the journal Applied Physics Letters by MIT graduate student Jonathan Mailoa; associate professor of mechanical engineering Tonio Buonassisi; Colin Bailie and Michael McGehee at Stanford; and four others.

“Different layers absorb different portions of the sunlight,” Mailoa explains. In the earlier tandem solar cell, the two layers of photovoltaic material could be operated independently of each other and required their own wiring and control circuits, allowing each cell to be tuned independently for optimal performance.

By contrast, the new combined version should be much simpler to make and install, Mailoa says. “It has advantages in terms of simplicity, because it looks and operates just like a single silicon cell,” he says, with only a single electrical control circuit needed.

One tradeoff is that the current produced is limited by the capacity of the lesser of the two layers. Electrical current, Buonassisi explains, can be thought of as analogous to the volume of water passing through a pipe, which is limited by the diameter of the pipe: If you connect two lengths of pipe of different diameters, one after the other, “the amount of water is limited by the narrowest pipe,” he says. Combining two solar cell layers in series has the same limiting effect on current.

To address that limitation, the team aims to match the current output of the two layers as precisely as possible. In this proof-of-concept solar cell, this means the total power output is about the same as that of conventional solar cells; the team is now working to optimize that output.

Perovskites have been studied for potential electronic uses including solar cells, but this is the first time they have been successfully paired with silicon cells in this configuration, a feat that posed numerous technical challenges. Now the team is focusing on increasing the power efficiency — the percentage of sunlight’s energy that gets converted to electricity — that is possible from the combined cell. In this initial version, the efficiency is 13.7 percent, but the researchers say they have identified low-cost ways of improving this to about 30 percent — a substantial improvement over today’s commercial silicon-based solar cells — and they say this technology could ultimately achieve a power efficiency of more than 35 percent.

They will also explore how to easily manufacture the new type of device, but Buonassisi says that should be relatively straightforward, since the materials lend themselves to being made through methods very similar to conventional silicon-cell manufacturing.

One hurdle is making the material durable enough to be commercially viable: The perovskite material degrades quickly in open air, so it either needs to be modified to improve its inherent durability or encapsulated to prevent exposure to air — without adding significantly to manufacturing costs and without degrading performance.

This exact formulation may not turn out to be the most advantageous for better solar cells, Buonassisi says, but is one of several pathways worth exploring. “Our job at this point is to provide options to the world,” he says. “The market will select among them.”

The research team also included Eric Johlin PhD ’14 and postdoc Austin Akey at MIT, and Eric Hoke and William Nguyen of Stanford. It was supported by the Bay Area Photovoltaic Consortium and the U.S. Department of Energy.

Source: News Office

Better debugger

System to automatically find a common type of programming bug significantly outperforms its predecessors.

By Larry Hardesty


CAMBRIDGE, Mass. – Integer overflows are one of the most common bugs in computer programs — not only causing programs to crash but, even worse, potentially offering points of attack for malicious hackers. Computer scientists have devised a battery of techniques to identify them, but all have drawbacks.

This month, at the Association for Computing Machinery’s International Conference on Architectural Support for Programming Languages and Operating Systems, researchers from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) will present a new algorithm for identifying integer-overflow bugs. The researchers tested the algorithm on five common open-source programs, in which previous analyses had found three bugs. The new algorithm found all three known bugs — and 11 new ones.

The variables used by computer programs come in a few standard types, such as floating-point numbers, which can contain decimals; characters, like the letters of this sentence; or integers, which are whole numbers. Every time the program creates a new variable, it assigns it a fixed amount of space in memory.

If a program tries to store too large a number at a memory address reserved for an integer, the operating system will simply lop off the bits that don’t fit. “It’s like a car odometer,” says Stelios Sidiroglou-Douskos, a research scientist at CSAIL and first author on the new paper. “You go over a certain number of miles, you go back to zero.”

In itself, an integer overflow won’t crash a program; in fact, many programmers use integer overflows to perform certain types of computations more efficiently. But if a program tries to do something with an integer that has overflowed, havoc can ensue. Say, for instance, that the integer represents the number of pixels in an image the program is processing. If the program allocates memory to store the image, but its estimate of the image’s size is off by several orders of magnitude, the program will crash.

Charting a course

Any program can be represented as a flow chart — or, more technically, a graph, with boxes that represent operations connected by line segments that represent the flow of data between operations. Any given program input will trace a single route through the graph. Prior techniques for finding integer-overflow bugs would start at the top of the graph and begin working through it, operation by operation.

For even a moderately complex program, however, that graph is enormous; exhaustive exploration of the entire thing would be prohibitively time-consuming. “What this means is that you can find a lot of errors in the early input-processing code,” says Martin Rinard, an MIT professor of computer science and engineering and a co-author on the new paper. “But you haven’t gotten past that part of the code before the whole thing poops out. And then there are all these errors deep in the program, and how do you find them?”

Rinard, Sidiroglou-Douskos, and several other members of Rinard’s group — researchers Eric Lahtinen and Paolo Piselli and graduate students Fan Long, Doekhwan Kim, and Nathan Rittenhouse — take a different approach. Their system, dubbed DIODE (for Directed Integer Overflow Detection), begins by feeding the program a single sample input. As that input is processed, however — as it traces a path through the graph — the system records each of the operations performed on it by adding new terms to what’s known as a “symbolic expression.”

“These symbolic expressions are complicated like crazy,” Rinard explains. “They’re bubbling up through the very lowest levels of the system into the program. This 32-bit integer has been built up of all these complicated bit-level operations that the lower-level parts of your system do to take this out of your input file and construct those integers for you. So if you look at them, they’re pages long.”

Trigger warning

When the program reaches a point at which an integer is involved in a potentially dangerous operation — like a memory allocation — DIODE records the current state of the symbolic expression. The initial test input won’t trigger an overflow, but DIODE can analyze the symbolic expression to calculate an input that will.

The process still isn’t over, however: Well-written programs frequently include input checks specifically designed to prevent problems like integer overflows, and the new input, unlike the initial input, might fail those checks. So DIODE seeds the program with its new input, and if it fails such a check, it imposes a new constraint on the symbolic expression and computes a new overflow-triggering input. This process continues until the system either finds an input that can pass the checks but still trigger an overflow, or it concludes that triggering an overflow is impossible.

If DIODE does find a trigger value, it reports it, providing developers with a valuable debugging tool. Indeed, since DIODE doesn’t require access to a program’s source code but works on its “binary” — the executable version of the program — a program’s users could run it and then send developers the trigger inputs as graphic evidence that they may have missed security vulnerabilities.

Source: News Office

This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions.

New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.

Credit:
Royal Society

Colliding Stars Explain Enigmatic Seventeenth Century Explosion

APEX observations help unravel mystery of Nova Vulpeculae 1670


New observations made with APEX and other telescopes reveal that the star that European astronomers saw appear in the sky in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. The results appear online in the journal Nature on 23 March 2015.

This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions. New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. Credit: Royal Society
This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions.
New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.
Credit:
Royal Society

Some of seventeenth century’s greatest astronomers, including Hevelius — the father of lunar cartography — and Cassini, carefully documented the appearance of a new star in the skies in 1670. Hevelius described it as nova sub capite Cygni — a new star below the head of the Swan — but astronomers now know it by the name Nova Vulpeculae 1670 [1]. Historical accounts of novae are rare and of great interest to modern astronomers. Nova Vul 1670 is claimed to be both the oldest recorded nova and the faintest nova when later recovered.

The lead author of the new study, Tomasz Kamiński (ESO and the Max Planck Institute for Radio Astronomy, Bonn, Germany) explains: “For many years this object was thought to be a nova, but the more it was studied the less it looked like an ordinary nova — or indeed any other kind of exploding star.”

When it first appeared, Nova Vul 1670 was easily visible with the naked eye and varied in brightness over the course of two years. It then disappeared and reappeared twice before vanishing for good. Although well documented for its time, the intrepid astronomers of the day lacked the equipment needed to solve the riddle of the apparent nova’s peculiar performance.

During the twentieth century, astronomers came to understand that most novae could be explained by the runaway explosive behaviour of close binary stars. But Nova Vul 1670 did not fit this model well at all and remained a mystery.

Even with ever-increasing telescopic power, the event was believed for a long time to have left no trace, and it was not until the 1980s that a team of astronomers detected a faint nebula surrounding the suspected location of what was left of the star. While these observations offered a tantalising link to the sighting of 1670, they failed to shed any new light on the true nature of the event witnessed over the skies of Europe over three hundred years ago.

This picture shows the remains of the new star that was seen in the year 1670. It was created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (green) and finally a map of the molecular emission from APEX and the SMA (red). The star that European astronomers saw in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. Credit: ESO/T. Kamiński
This picture shows the remains of the new star that was seen in the year 1670. It was created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (green) and finally a map of the molecular emission from APEX and the SMA (red).
The star that European astronomers saw in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.
Credit:
ESO/T. Kamiński

 

Tomasz Kamiński continues the story: “We have now probed the area with submillimetre and radio wavelengths. We have found that the surroundings of the remnant are bathed in a cool gas rich in molecules, with a very unusual chemical composition.”

As well as APEX, the team also used the Submillimeter Array (SMA) and the Effelsberg radio telescope to discover the chemical composition and measure the ratios of different isotopes in the gas. Together, this created an extremely detailed account of the makeup of the area, which allowed an evaluation of where this material might have come from.

What the team discovered was that the mass of the cool material was too great to be the product of a nova explosion, and in addition the isotope ratios the team measured around Nova Vul 1670 were different to those expected from a nova. But if it wasn’t a nova, then what was it?

The answer is a spectacular collision between two stars, more brilliant than a nova, but less so than a supernova, which produces something called a red transient. These are a very rare events in which stars explode due to a merger with another star, spewing material from the stellar interiors into space, eventually leaving behind only a faint remnant embedded in a cool environment, rich in molecules and dust. This newly recognised class of eruptive stars fits the profile of Nova Vul 1670 almost exactly.

Co-author Karl Menten (Max Planck Institute for Radio Astronomy, Bonn, Germany) concludes: “This kind of discovery is the most fun: something that is completely unexpected!”

Notes
[1] This object lies within the boundaries of the modern constellation of Vulpecula (The Fox), just across the border from Cygnus (The Swan). It is also often referred to as Nova Vul 1670 and CK Vulpeculae, its designation as a variable star.

Source: ESO News

 

A cartoon illustration of a levitated drop of superfluid helium. A single photon circulating inside the drop (red arrow) will be used to produce the superposition. The drop's gravitational field (illustrated schematically in the background) may play a role in limiting the lifetime of such a superposition.

Credit: Yale News

Opening a window on quantum gravity

Yale University has received a grant from the W. M. Keck Foundation to fund experiments that researchers hope will provide new insights into quantum gravity. Jack Harris, associate professor of physics, will lead a Yale team that aims to address a long-standing question in physics — how the classical behavior of macroscopic objects emerges from microscopic constituents that obey the laws of quantum mechanics.

Very small objects like photons and electrons are known for their odd behavior. Thanks to the laws of quantum mechanics, they can act as particles or waves, appear in multiple places at once, and mysteriously interact over great distances. The question is why these behaviors are not observed in larger objects.

A cartoon illustration of a levitated drop of superfluid helium. A single photon circulating inside the drop (red arrow) will be used to produce the superposition. The drop's gravitational field (illustrated schematically in the background) may play a role in limiting the lifetime of such a superposition. Credit: Yale News
A cartoon illustration of a levitated drop of superfluid helium. A single photon circulating inside the drop (red arrow) will be used to produce the superposition. The drop’s gravitational field (illustrated schematically in the background) may play a role in limiting the lifetime of such a superposition.
Credit: Yale News

Scientists know that friction plays an important part in producing classical behavior in macroscopic objects, but many suspect that gravity also suppresses quantum effects. Unfortunately, there has been no practical way to test this possibility, and in the absence of a full quantum theory of gravity, it is difficult even to make any quantitative predictions.

To address this problem, Harris will create a novel instrument that will enable a drop of liquid helium to exhibit quantum mechanical effects. “A millimeter across,” Harris said, “our droplet will be five orders of magnitude more massive than any other object in which quantum effects have been observed. It will enable us to explore quantum behavior on unprecedentedly macroscopic scales and to provide the first experimental tests of leading models of gravity at the quantum level.”

Game-changing research

The W.M. Keck Foundation grant will fund five years of activity at the Harris lab, which is part of Yale’s Department of Physics. In the first year, Harris and his team will construct their apparatus, and in subsequent years they will use it to perform increasingly sophisticated experiments.

“We are extremely grateful to the W.M. Keck Foundation for this generous support,” said Steven Girvin, the Eugene Higgins Professor of Physics and deputy provost for research. “This is a forward-looking grant that will advance truly ground-breaking research.”

Girvin, whose own research interests include quantum computing, described the Harris project as a possible game-changer. “Truly quantum mechanical behaviors have been observed in the flight of molecules through a vacuum and in the flow of electrons through superconductive circuits, but nothing has been accomplished on this scale. If Jack succeeds, this would be the first time that an object visible to the naked eye has bulk motion that exhibits genuine quantum mechanical effects.”

Into the whispering gallery

To explain his project, Harris invokes an architectural quirk of St. Paul’s cathedral, a London landmark with a famous “whispering gallery.” High up in its main dome, a whisper uttered against one wall is easily audible at great distances, as the sound waves skim along the dome’s interior. Harris plans to create his own whispering gallery, albeit on a smaller scale, using a droplet of liquid helium suspended in a powerful magnetic field. Rather than sound waves, Harris’ gallery will bounce a single photon.

This approach is closely related to an idea proposed by Albert Einstein in the 1920s, but until now, it has remained beyond the technical capabilities of experimentalists. To complete the experiment, Harris will need to combine recent advances in three different areas of physics: the study of optical cavities (objects that can capture photons), magnetic levitation, and the strange, frictionless world of superfluid helium. “Superfluid liquid helium has particular properties, like absence of viscosity and near-absence of optical absorption,” Harris explained. “In our device, a drop of liquid helium will be made to capture a single photon, which will bounce around inside. We expect to see the drop respond to the photon. “A photon always behaves quantum mechanically,” he added. “If you have a macroscopic object — our helium drop — that responds appreciably to a photon, the quantum mechanical behavior can be transferred to the large object. Our device will be ideally suited to studying quantum effects in the drop’s motion.” Potential applications for Harris’ research include new approaches to computing, cryptography, and communications. But Harris is most excited about the implications for fundamental physics: “Finding a theory of quantum gravity has been an outstanding challenge in physics for several decades, and it has proceeded largely without input from experiments. We hope that our research can provide some empirical data in this arena.”

About the W.M. Keck Foundation

The W.M. Keck Foundation was established in 1954 by William Myron Keck, founder of the Superior Oil Company. The foundation supports pioneering research in science, engineering, and medicine and has provided generous funding for numerous research initiatives at Yale University. In 2014, the Keck Foundation awarded a separate grant to a team of scientists led by Corey O’Hern, associate professor of mechanical engineering at Yale, to explore the physics of systems composed of macro-sized particles. Source : Yale News

Fully experimental image of a nanoscaled and ultrafast optical rogue wave retrieved by Near-field Scanning Optical Microscope (NSOM). The flow lines visible in the image represent the direction of light energy. 
Credit: KAUST

Tsunami on demand: the power to harness catastrophic events

A new study published in Nature Physics features a nano-optical chip that makes possible generating and controlling nanoscale rogue waves. The innovative chip was developed by an international team of physicists, led by Andrea Fratalocchi from KAUST (Saudi Arabia), and is expected to have significant applications for energy research and environmental safety.

Can you imagine how much energy is in a tsunami wave, or in a tornado? Energy is all around us, but mainly contained in a quiet state. But there are moments in time when large amounts of energy build up spontaneously and create rare phenomena on a potentially disastrous scale. How these events occur, in many cases, is still a mystery.

To reveal the natural mechanisms behind such high-energy phenomena, Andrea Fratalocchi, assistant professor in the Computer, Electrical and Mathematical Science and Engineering Division of King Abdullah University of Science and Technology (KAUST), led a team of researchers from Saudi Arabia and three European universities and research centers to understand the dynamics of such destructive events and control their formation in new optical chips, which can open various technological applications. The results and implications of this study are published in the journal Nature Physics.

“I have always been fascinated by the unpredictability of nature,” Fratalocchi said. “And I believe that understanding this complexity is the next frontier that will open cutting edge pathways in science and offer novel applications in a variety of areas.”

Fratalocchi’s team began their research by developing new theoretical ideas to explain the formation of rare energetic natural events such as rogue waves — large surface waves that develop spontaneously in deep water and represent a potential risk for vessels and open-ocean oil platforms.”

“Our idea was something never tested before,” Fratalocchi continued. “We wanted to demonstrate that small perturbations of a chaotic sea of interacting waves could, contrary to intuition, control the formation of rare events of exceptional amplitude.”

Fully experimental image of a nanoscaled and ultrafast optical rogue wave retrieved by Near-field Scanning Optical Microscope (NSOM). The flow lines visible in the image represent the direction of light energy.  Credit: KAUST
Fully experimental image of a nanoscaled and ultrafast optical rogue wave retrieved by Near-field Scanning Optical Microscope (NSOM). The flow lines visible in the image represent the direction of light energy.
Credit: KAUST

A planar photonic crystal chip, fabricated at the University of St. Andrews and tested at the FOM institute AMOLF in the Amsterdam Science Park, was used to generate ultrafast (163 fs long) and subwavelength (203 nm wide) nanoscale rogue waves, proving that Fratalocchi’s theory was correct. The newly developed photonic chip offered an exceptional level of controllability over these rare events.

Thomas F. Krauss, head of the Photonics Group and Nanocentre Cleanroom at the University of York, UK, was involved in the development of the experiment and the analysis of the data. He shared, “By realizing a sea of interacting waves on a photonic chip, we were able study the formation of rare high energy events in a controlled environment. We noted that these events only happened when some sets of waves were missing, which is one of the key insights our study.”

Kobus Kuipers, head of nanophotonics at FOM institute AMOLF, NL, who was involved in the experimental visualization of the rogue waves, was fascinated by their dynamics: “We have developed a microscope that allows us to visualize optical behavior at the nanoscale. Unlike conventional wave behavior, it was remarkable to see the rogue waves suddenly appear, seemingly out of nowhere, and then disappear again…as if they had never been there.”

Andrea Di Falco, leader of the Synthetic Optics group at the University of St. Andrews said, “The advantage of using light confined in an optical chip is that we can control very carefully how the energy in a chaotic system is dissipated, giving rise to these rare and extreme events. It is as if we were able to produce a determined amount of waves of unusual height in a small lake, just by accurately landscaping its coasts and controlling the size and number of its emissaries.”

The outcomes of this project offer leading edge technological applications in energy research, high speed communication and in disaster preparedness.

Fratalocchi and the team believe their research represents a major milestone for KAUST and for the field. “This discovery can change once and for all the way we look at catastrophic events,” concludes Fratalocchi, “opening new perspectives in preventing their destructive appearance on large scales, or using their unique power for ideating new applications at the nanoscale.”The title of the Nature Physics paper is “Triggering extreme events at the nanoscale in photonic seas.” The paper is accessible on the Nature Photonics website: http://dx.doi.org/10.1038/nphys3263

Source : KAUST News

A second minor planet may possess Saturn-like rings

Researchers detect features around Chiron that may signal rings, jets, or a shell of dust.

By Jennifer Chu


CAMBRIDGE, Mass. – There are only five bodies in our solar system that are known to bear rings. The most obvious is the planet Saturn; to a lesser extent, rings of gas and dust also encircle Jupiter, Uranus, and Neptune. The fifth member of this haloed group is Chariklo, one of a class of minor planets called centaurs: small, rocky bodies that possess qualities of both asteroids and comets.

Scientists only recently detected Chariklo’s ring system — a surprising finding, as it had been thought that centaurs are relatively dormant. Now scientists at MIT and elsewhere have detected a possible ring system around a second centaur, Chiron.

In November 2011, the group observed a stellar occultation in which Chiron passed in front of a bright star, briefly blocking its light. The researchers analyzed the star’s light emissions, and the momentary shadow created by Chiron, and identified optical features that suggest the centaur may possess a circulating disk of debris. The team believes the features may signify a ring system, a circular shell of gas and dust, or symmetric jets of material shooting out from the centaur’s surface.

“It’s interesting, because Chiron is a centaur — part of that middle section of the solar system, between Jupiter and Pluto, where we originally weren’t thinking things would be active, but it’s turning out things are quite active,” says Amanda Bosh, a lecturer in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

Bosh and her colleagues at MIT — Jessica Ruprecht, Michael Person, and Amanda Gulbis — have published their results in the journal Icarus.

Catching a shadow

Chiron, discovered in 1977, was the first planetary body categorized as a centaur, after the mythological Greek creature — a hybrid of man and beast. Like their mythological counterparts, centaurs are hybrids, embodying traits of both asteroids and comets. Today, scientists estimate there are more than 44,000 centaurs in the solar system, concentrated mainly in a band between the orbits of Jupiter and Pluto.

While most centaurs are thought to be dormant, scientists have seen glimmers of activity from Chiron. Starting in the late 1980s, astronomers observed patterns of brightening from the centaur, as well as activity similar to that of a streaking comet.

In 1993 and 1994, James Elliot, then a professor of planetary astronomy and physics at MIT, observed a stellar occultation of Chiron and made the first estimates of its size. Elliot also observed features in the optical data that looked like jets of water and dust spewing from the centaur’s surface.

Now MIT researchers — some of them former members of Elliot’s group — have obtained more precise observations of Chiron, using two large telescopes in Hawaii: NASA’s Infrared Telescope Facility, on Mauna Kea, and the Las Cumbres Observatory Global Telescope Network, at Haleakala.

In 2010, the team started to chart the orbits of Chiron and nearby stars in order to pinpoint exactly when the centaur might pass across a star bright enough to detect. The researchers determined that such a stellar occultation would occur on Nov. 29, 2011, and reserved time on the two large telescopes in hopes of catching Chiron’s shadow.

“There’s an aspect of serendipity to these observations,” Bosh says. “We need a certain amount of luck, waiting for Chiron to pass in front of a star that is bright enough. Chiron itself is small enough that the event is very short; if you blink, you might miss it.”

The team observed the stellar occultation remotely, from MIT’s Building 54. The entire event lasted just a few minutes, and the telescopes recorded the fading light as Chiron cast its shadow over the telescopes.

Rings around a theory

The group analyzed the resulting light, and detected something unexpected. A simple body, with no surrounding material, would create a straightforward pattern, blocking the star’s light entirely. But the researchers observed symmetrical, sharp features near the start and end of the stellar occultation — a sign that material such as dust might be blocking a fraction of the starlight.

The researchers observed two such features, each about 300 kilometers from the center of the centaur. Judging from the optical data, the features are 3 and 7 kilometers wide, respectively.  The features are similar to what Elliot observed in the 1990s.

In light of these new observations, the researchers say that Chiron may still possess symmetrical jets of gas and dust, as Elliot first proposed. However, other interpretations may be equally valid, including the “intriguing possibility,” Bosh says, of a shell or ring of gas and dust.

Ruprecht, who is a researcher at MIT’s Lincoln Laboratory, says it is possible to imagine a scenario in which centaurs may form rings: For example, when a body breaks up, the resulting debris can be captured gravitationally around another body, such as Chiron. Rings can also be leftover material from the formation of Chiron itself.

“Another possibility involves the history of Chiron’s distance from the sun,” Ruprecht says. “Centaurs may have started further out in the solar system and, through gravitational interactions with giant planets, have had their orbits perturbed closer in to the sun. The frozen material that would have been stable out past Pluto is becoming less stable closer in, and can turn into gases that spray dust and material off the surface of a body. ”

An independent group has since combined the MIT group’s occultation data with other light data, and has concluded that the features around Chiron most likely represent a ring system. However, Ruprecht says that researchers will have to observe more stellar occultations of Chiron to truly determine which interpretation — rings, shell, or jets — is the correct one.

“If we want to make a strong case for rings around Chiron, we’ll need observations by multiple observers, distributed over a few hundred kilometers, so that we can map the ring geometry,” Ruprecht says. “But that alone doesn’t tell us if the rings are a temporary feature of Chiron, or a more permanent one. There’s a lot of work that needs to be done.”

Nevertheless, Bosh says the possibility of a second ringed centaur in the solar system is an enticing one.

“Until Chariklo’s rings were found, it was commonly believed that these smaller bodies don’t have ring systems,” Bosh says. “If Chiron has a ring system, it will show it’s more common than previously thought.”

This research was funded in part by NASA and the National Research Foundation of South Africa.

Source: MIT News Office

Teaching programming to preschoolers: MIT Research

System that lets children program a robot using stickers embodies new theories about programming languages.

By Larry Hardesty


Researchers at the MIT Media Laboratory are developing a system that enables young children to program interactive robots by affixing stickers to laminated sheets of paper.

Not only could the system introduce children to programming principles, but it could also serve as a research tool, to help determine which computational concepts children can grasp at what ages, and how interactive robots can best be integrated into educational curricula.

Last week, at the Association for Computing Machinery and Institute of Electrical and Electronics Engineers’ International Conference on Human-Robot Interaction, the researchers presented the results of an initial study of the system, which investigated its use by children ages 4 to 8.

“We did not want to put this in the digital world but rather in the tangible world,” says Michal Gordon, a postdoc in media arts and sciences and lead author on the new paper. “It’s a sandbox for exploring computational concepts, but it’s a sandbox that comes to the children’s world.”

In their study, the MIT researchers used an interactive robot called Dragonbot, developed by the Personal Robots Group at the Media Lab, which is led by associate professor of media arts and sciences Cynthia Breazeal. Dragonbot has audio and visual sensors, a speech synthesizer, a range of expressive gestures, and a video screen for a face that can assume a variety of expressions. The programs that children created dictated how Dragonbot would react to stimuli.

“It’s programming in the context of relational interactions with the robot,” says Edith Ackermann, a developmental psychologist and visiting professor in the Personal Robots Group, who with Gordon and Breazeal is a co-author on the new paper. “This is what children do — they’re learning about social relations. So taking this expression of computational principles to the social world is very appropriate.”

Lessons that stick

The root components of the programming system are triangular and circular stickers — which represent stimuli and responses, respectively — and arrow stickers, which represent relationships between them. Children can first create computational “templates” by affixing triangles, circles, and arrows to sheets of laminated paper. They then fill in the details with stickers that represent particular stimuli — like thumbs up or down — and responses — like the narrowing or widening of Dragonbot’s eyes. There are also blank stickers on which older children can write their own verbal cues and responses.

Researchers in the Personal Robotics Group are developing a computer vision system that will enable children to convey new programs to Dragonbot simply by holding pages of stickers up to its camera. But for the purposes of the new study, the system’s performance had to be perfectly reliable, so one of the researchers would manually enter the stimulus-and-response sequences devised by the children, using a tablet computer with a touch-screen interface that featured icons depicting all the available options.

To introduce a new subject to the system, the researchers would ask him or her to issue an individual command, by attaching a single response sticker to a small laminated sheet. When presented with the sheet, Dragonbot would execute the command. But when it’s presented with a program, it instead nods its head and says, “I’ve got it.” Thereafter, it will execute the specified chain of responses whenever it receives the corresponding stimulus.

Even the youngest subjects were able to distinguish between individual commands and programs, and interviews after their sessions suggested that they understood that programs, unlike commands, modified the internal state of the robot. The researchers plan additional studies to determine the extent of their understanding.

Paradigm shift

The sticker system is, in fact, designed to encourage a new way of thinking about programming, one that may be more consistent with how computation is done in the 21st century.

“The systems we’re programming today are not sequential, as they were 20 or 30 years back,” Gordon says. “A system has many inputs coming in, complex state, and many outputs.” A cellphone, for instance, might be monitoring incoming transmissions over both Wi-Fi and the cellular network while playing back a video, transmitting the audio over Bluetooth, and running a timer that’s set to go off when the rice on the stove has finished cooking.

As a graduate student in computer science at the Weizmann Institute of Science in Israel, Gordon explains, she worked with her advisor, David Harel, on a new programming paradigm called scenario-based programming. “The idea is to describe your code in little scenarios, and the engine in the back connects them,” she explains. “You could think of it as rules, with triggers and actions.” Gordon and her colleagues’ new system could be used to introduce children to the principles of conventional, sequential programming. But it’s well adapted to scenario-based programming.

“It’s actually how we think about how programs are written before we try to integrate it into a whole programming artifact,” she says. “So I was thinking, ‘Why not try it earlier?’”

Source : MIT News Office


Stanford researchers solve the mystery of the dancing droplets

Years of research satisfy a graduate student’s curiosity about the molecular minuet he observed among drops of ordinary food coloring.

BY TOM ABATE


A puzzling observation, pursued through hundreds of experiments, has led Stanford researchers to a simple yet profound discovery: Under certain circumstances, droplets of fluid will move like performers in a dance choreographed by molecular physics.

“These droplets sense one another, they move and interact, almost like living cells,” said Manu Prakash, an assistant professor of bioengineering and senior author of an article published in Nature.

The unexpected findings may prove useful in semiconductor manufacturing and self-cleaning solar panels, but what truly excites Prakash is that the discovery resulted from years of persistent effort to satisfy a scientific curiosity.

Video: Stanford researchers solve the mystery of the dancing droplets

The research began in 2009 when Nate Cira, then an undergraduate at the University of Wisconsin, was doing an unrelated experiment. In the course of that experiment Cira deposited several droplets of food coloring onto a sterilized glass slide and was astonished when they began to move.

Cira replicated and studied this phenomenon alone for two years until he became a graduate student at Stanford, where he shared this curious observation with Prakash. The professor soon became hooked by the puzzle, and recruited a third member to the team: Adrien Benusiglio, a postdoctoral scholar in the Prakash Lab.

Together they spent three years performing increasingly refined experiments to learn how these tiny droplets of food coloring sense one another and move. In living cells these processes of sensing and motility are known as chemotaxis.

“We’ve discovered how droplets can exhibit behaviors akin to artificial chemotaxis,” Prakash said.

As the Nature article explains, the critical fact was that food coloring is a two-component fluid. In such fluids, two different chemical compounds coexist while retaining separate molecular identities

The droplets in this experiment consisted of two molecular compounds found naturally in food coloring: water and propylene glycol.

The researchers discovered how the dynamic interactions of these two molecular components enabled inanimate droplets to mimic some of the behaviors of living cells.

Surface tension and evaporation

Essentially, the droplets danced because of a delicate balance between surface tension and evaporation.

Evaporation is easily understood. On the surface of any liquid, some molecules convert to a gaseous state and float away.

Surface tension is what causes liquids to bead up. It arises from how tightly the molecules in a liquid bind together.

Water evaporates more quickly than propylene glycol. Water also has a higher surface tension.  These differences create a tornado-like flow inside the droplets, which not only allows them to move but also allows a single droplet to sense its neighbors.

To understand the molecular forces involved, imagine shrinking down to size and diving inside a droplet.

There, water and propylene glycol molecules try to remain evenly distributed but differences in evaporation and surface tension create turmoil within the droplet.

On the curved dome of each droplet, water molecules become gaseous and float away faster than their evaporation-averse propylene glycol neighbors.

This evaporation happens more readily on the thin lower edges of the domed droplet, leaving excess of propylene glycol there. Meanwhile, the peak of the dome has a higher concentration of water.

The water at the top exerts its higher surface tension to pull the droplet tight so it doesn’t flatten out. This tugging causes a tumbling molecular motion inside the droplet. Thus surface tension gets the droplet ready to roll.

Evaporation determines the direction of that motion. Each droplet sends aloft gaseous molecules of water like a radially emanating signal announcing the exact location of any given droplet. The droplets converge where the signal is strongest.

So evaporation provided the sensing mechanism and surface tension the pull to move droplets together in what seemed to the eye to be a careful dance.

Rule for two-component fluids

The researchers experimented with varied proportions of water and propylene glycol. Droplets that were 1 percent propylene glycol (PG) to 99 percent water exhibited much the same behavior as droplets that were two-thirds PG to just one-third water.

Based on these experiments the paper describes a “universal rule” to identify any two-component fluids that will demonstrate sensing and motility.

Adding colors to the mixtures made it easier to tell how the droplets of different concentrations behaved and created some visually striking results.

In one experiment, a droplet with more propylene glycol seems to chase a droplet with more water. In actuality, the droplet with more water exerts a higher surface tension tug, pulling the propylene droplet along.

In another experiment, researchers showed how physically separated droplets could align themselves using ever-so-slight signals of evaporation.

In a third experiment they used Sharpie pens to draw black lines on glass slides. The lines changed the surface of the slide and created a series of catch basins. The researchers filled each basin with fluids of different concentrations to create a self-sorting mechanism. Droplets bounced from reservoir to reservoir until they sensed the fluid that matched their concentration and merged with that pool.

What started as a curiosity-driven project may also have many practical implications.

The deep physical understanding of two component fluids allows the researchers to predict which fluids and surfaces will show these unusual effects. The effect is present on a large number of common surfaces and can be replicated with a number of chemical compounds.

“If necessity is the mother of invention, then curiosity is the father,” Prakash observed.

Source: Stanford News

Ant-Man possible? Scientists shrink ants to study mechanisms that control DNA expression

By shrinking ants to sizes smaller than exist in nature, biologists present a useful model for understanding how environmental factors can influence DNA expression to create a range of outcomes.

This may not be exactly what the Marvel’s Ant-Man story has but still close enough to be amazing! 

BY BJORN CAREY


In the pages of Marvel comic books, Ant-Man manipulates fictional subatomic particles in order to shrink and fight crime as one of Earth’s mightiest heroes.

In real life, a team of biologists has now achieved similar shrinking results by manipulating ants’ DNA. The work won’t produce any superpowers, but it presents a useful model for understanding how environmental factors can influence DNA expression to create a range of outcomes in a population.

The work is published online in the journal Nature Communications. Sebastian Alvarado, a postdoctoral fellow at Stanford, conducted the research as a graduate student at McGill University, working alongside fellow graduate student Rajendhran Rajakumar, and professors Ehab Abouheif and Moshe Szyf, all of McGill.

 

Video : Stanford researcher explains the science behind Ant-Man

The experiment was designed as a means to study variation in quantitative traits. These are individual qualities, such as height or body weight, that can naturally vary across a defined range in a population. This variation is usually driven by the degree that environmental or other factors influence the expression of a particular gene, which makes ants an excellent test model.

In an ant colony, queens, workers and soldiers share similar genetics. But early in ant development, social, nutritional and chemical cues cause some genes to be more active, ultimately creating a wide range of body sizes, each specialized to a different task in the colony.

Many of these changes are controlled by DNA methylation, a process in which molecules are added to sections of DNA sequences. These additions affect how the DNA is interpreted and expressed, thus influencing an organism’s development or behavior.

“A lot of growth and development and sizing mechanisms that exist across the animal kingdom are found to be regulated by the same DNA methylation processes,” Alvarado said.

In the experiment, Alvarado and his colleagues at McGill exposed ant larvae to drugs that either increased or decreased the amount of DNA methylation. In doing so, they created ants that were larger within a caste and even significantly smaller than what exists in a natural population.

They then traced this size change to a specific growth factor gene, and found that across the population, varying degrees of DNA methylation to that gene directly corresponded to body size. A 20 percent modification in DNA methylation yielded a 20 percent change in body size, for example.

“This helps explain at a molecular level how continuums exist between two very discrete variables,” said Alvarado, who is now a member of biology Professor Russell Fernald’s lab at Stanford. “We can now look at diversity within a population by considering what expressions exist in between these variables and the actual molecular mechanism that controls that difference.”

Drawing a stronger connection between how environment and genetic factors influence DNA expression, Alvarado said, could have payoff in mapping the genetic basis of diseases and understanding evolutionary changes.

Source: Stanford News


 

Magnetic brain stimulation:New technique could lead to long-lasting localized stimulation of brain tissue without external connections.

By David Chandler


CAMBRIDGE, Mass–Researchers at MIT have developed a method to stimulate brain tissue using external magnetic fields and injected magnetic nanoparticles — a technique allowing direct stimulation of neurons, which could be an effective treatment for a variety of neurological diseases, without the need for implants or external connections.

The research, conducted by Polina Anikeeva, an assistant professor of materials science and engineering, graduate student Ritchie Chen, and three others, has been published in the journal Science.

Previous efforts to stimulate the brain using pulses of electricity have proven effective in reducing or eliminating tremors associated with Parkinson’s disease, but the treatment has remained a last resort because it requires highly invasive implanted wires that connect to a power source outside the brain.

“In the future, our technique may provide an implant-free means to provide brain stimulation and mapping,” Anikeeva says.

In their study, the team injected magnetic iron oxide particles just 22 nanometers in diameter into the brain. When exposed to an external alternating magnetic field — which can penetrate deep inside biological tissues — these particles rapidly heat up.

The resulting local temperature increase can then lead to neural activation by triggering heat-sensitive capsaicin receptors — the same proteins that the body uses to detect both actual heat and the “heat” of spicy foods. (Capsaicin is the chemical that gives hot peppers their searing taste.) Anikeeva’s team used viral gene delivery to induce the sensitivity to heat in selected neurons in the brain.

The particles, which have virtually no interaction with biological tissues except when heated, tend to remain where they’re placed, allowing for long-term treatment without the need for further invasive procedures.

“The nanoparticles integrate into the tissue and remain largely intact,” Anikeeva says. “Then, that region can be stimulated at will by externally applying an alternating magnetic field. The goal for us was to figure out whether we could deliver stimuli to the nervous system in a wireless and noninvasive way.”

The new work has proven that the approach is feasible, but much work remains to turn this proof-of-concept into a practical method for brain research or clinical treatment.

The use of magnetic fields and injected particles has been an active area of cancer research; the thought is that this approach could destroy cancer cells by heating them. “The new technique is derived, in part, from that research,” Anikeeva says. “By calibrating the delivered thermal dosage, we can excite neurons without killing them. The magnetic nanoparticles also have been used for decades as contrast agents in MRI scans, so they are considered relatively safe in the human body.”

The team developed ways to make the particles with precisely controlled sizes and shapes, in order to maximize their interaction with the applied alternating magnetic field. They also developed devices to deliver the applied magnetic field: Existing devices for cancer treatment — intended to produce much more intense heating — were far too big and energy-inefficient for this application.

The next step toward making this a practical technology for clinical use in humans “is to understand better how our method works through neural recordings and behavioral experiments, and assess whether there are any other side effects to tissues in the affected area,” Anikeeva says.

In addition to Anikeeva and Chen, the research team also included postdoc Gabriela Romero, graduate student Michael Christiansen, and undergraduate Alan Mohr. The work was funded by the Defense Advanced Research Projects Agency, MIT’s McGovern Institute for Brain Research, and the National Science Foundation.