Engineers Solve Longstanding Problem in Photonic Chip Technology: Findings Help Pave Way for Next Generation of Computer Chips

Engineers Solve Longstanding Problem in Photonic Chip Technology: Findings Help Pave Way for Next Generation of Computer Chips

  1:00:00 AM    Science Lover

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Stretching for thousands of miles beneath oceans, optical fibers now connect every continent except for Antarctica. With less data loss and higher bandwidth, optical-fiber technology allows information to zip around the world, bringing pictures, video, and other data from every corner of the globe to your computer in a split second. But although optical fibers are increasingly replacing copper wires, carrying information via photons instead of electrons, today's computer technology still relies on electronic chips.

Caltech engineers have developed a new way to 
isolate light on a photonic chip, allowing light to 
travel in only one direction. This finding can lead 
to the next generation of computer-chip technology: 
photonic chips that allow for faster computers 
and less data loss. (Credit: Caltech/Liang Feng)

Now, researchers led by engineers at the California Institute of Technology (Caltech) are paving the way for the next generation of computer-chip technology: photonic chips. With integrated circuits that use light instead of electricity, photonic chips will allow for faster computers and less data loss when connected to the global fiber-optic network.

"We want to take everything on an electronic chip and reproduce it on a photonic chip," says Liang Feng, a postdoctoral scholar in electrical engineering and the lead author on a paper to be published in the August 5 issue of the journal Science. Feng is part of Caltech's nanofabrication group, led by Axel Scherer, Bernard A. Neches Professor of Electrical Engineering, Applied Physics, and Physics, and co-director of the Kavli Nanoscience Institute at Caltech.

In that paper, the researchers describe a new technique to isolate light signals on a silicon chip, solving a longstanding problem in engineering photonic chips.

An isolated light signal can only travel in one direction. If light weren't isolated, signals sent and received between different components on a photonic circuit could interfere with one another, causing the chip to become unstable. In an electrical circuit, a device called a diode isolates electrical signals by allowing current to travel in one direction but not the other. The goal, then, is to create the photonic analog of a diode, a device called an optical isolator. "This is something scientists have been pursuing for 20 years," Feng says.

Normally, a light beam has exactly the same properties when it moves forward as when it's reflected backward. "If you can see me, then I can see you," he says. In order to isolate light, its properties need to somehow change when going in the opposite direction. An optical isolator can then block light that has these changed properties, which allows light signals to travel only in one direction between devices on a chip.

"We want to build something where you can see me, but I can't see you," Feng explains. "That means there's no signal from your side to me. The device on my side is isolated; it won't be affected by my surroundings, so the functionality of my device will be stable."

To isolate light, Feng and his colleagues designed a new type of optical waveguide, a 0.8-micron-wide silicon device that channels light. The waveguide allows light to go in one direction but changes the mode of the light when it travels in the opposite direction.

A light wave's mode corresponds to the pattern of the electromagnetic field lines that make up the wave. In the researchers' new waveguide, the light travels in a symmetric mode in one direction, but changes to an asymmetric mode in the other. Because different light modes can't interact with one another, the two beams of light thus pass through each other.



Previously, there were two main ways to achieve this kind of optical isolation. The first way -- developed almost a century ago -- is to use a magnetic field. The magnetic field changes the polarization of light -- the orientation of the light's electric-field lines -- when it travels in the opposite direction, so that the light going one way can't interfere with the light going the other way. "The problem is, you can't put a large magnetic field next to a computer," Feng says. "It's not healthy."

The second conventional method requires so-called nonlinear optical materials, which change light's frequency rather than its polarization. This technique was developed about 50 years ago, but is problematic because silicon, the material that's the basis for the integrated circuit, is a linear material. If computers were to use optical isolators made out of nonlinear materials, silicon would have to be replaced, which would require revamping all of computer technology. But with their new silicon waveguides, the researchers have become the first to isolate light with a linear material.

Although this work is just a proof-of-principle experiment, the researchers are already building an optical isolator that can be integrated onto a silicon chip. An optical isolator is essential for building the integrated, nanoscale photonic devices and components that will enable future integrated information systems on a chip. Current, state-of-the-art photonic chips operate at 10 gigabits per second (Gbps) -- hundreds of times the data-transfer rates of today's personal computers -- with the next generation expected to soon hit 40 Gbps. But without built-in optical isolators, those chips are much simpler than their electronic counterparts and are not yet ready for the market. Optical isolators like those based on the researchers' designs will therefore be crucial for commercially viable photonic chips.

In addition to Feng and Scherer, the other authors on the Science paper, "Non-reciprocal light propagation in a silicon photonic circuit," are Jingqing Huang, a Caltech graduate student; Maurice Ayache of UC San Diego and Yeshaiahu Fainman, Cymer Professor in Advanced Optical Technologies at UC San Diego; and Ye-Long Xu, Ming-Hui Lu, and Yan-Feng Chen of the Nanjing National Laboratory of Microstructures in China. This research was done as part of the Center for Integrated Access Networks (CIAN), one of the National Science Foundation's Engineering Research Centers. Fainman is also the deputy director of CIAN. Funding was provided by the National Science Foundation, and the Defense Advanced Research Projects Agency.

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How Vampire Bats Find Veins

How Vampire Bats Find Veins

  12:25:00 AM    Science Lover

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Heat-sensing protein channels in vampire bats allow the flying mammals to find the best place to sink their teeth into their prey.

The common vampire bat (Desmodus rotundus)

Researchers have discovered an infrared-sensing protein channel that allows vampire bats to identify the hottest part of the animal—veins close to the skin’s surface that carry 38 degree-Celsius (100° F) blood, and presumably the best spot for feeding.

The channel is a variant of TRPV1, a heat-sensing protein channel that is triggered by high temperatures that could potentially cause injury, according to the study published today (August 3) in Nature, and is distinct from the heat sensor used by snakes—the only other non-insect animals that are known to detect heat by sensing infrared radiation.

“Infrared [detection] allows these guys, in pitch black, to hunt down warm-blooded prey,” said zoologist Bill Schutt, assistant professor at Long Island University, who was not involved in the research. Here, the researchers identified a modification in a common heat-sensing protein channel that lowered its temperature threshold so that it is more attuned to an animal’s body heat, he added.

The common vampire bat was appropriately named after the myth of Dracula—it feeds at night and lives solely on a diet of blood, every day or two consuming up to half its weight in the vital substance from large mammals, especially sleeping livestock. The bats first use echolocation to detect their prey, but once they are within 20 centimeters of their target, they use infrared sensors in specialized pits around their noses to zero in on the best place to feed.

In a previous study, physiologist David Julius at the University of California, San Francisco, and colleagues found that infrared detection by snakes—which, like bats, use nerves located in facial pits to detect their prey—is mediated by a cell-surface protein channel called transient receptor potential cation channel A1 (TRPA1). The channel is actually insensitive to heat in most organisms, but had evolved the capability in snakes, leading the group to suspect that a similar transformation may have given vampire bats their ability to sense infrared.




To see if this was the case, Julius and his collaborators at the University of California, San Francisco, the Venezuelan Institute of Scientific Investigation (IVIC), and the Carnegie Institution in Baltimore, Maryland, compared gene expression in vampire bats’ heat-sensing nerves, called trigeminal ganglia, with expression in a nerve cluster near the spine, called dorsal root ganglia (DRG). They also compared these expression patterns to those of the ganglia in four bat species that do not have infrared sensory abilities.

To their surprise, they did not observe any differences in transcription of the TRPA1-coding gene, nor of any other genes. Instead, they discovered that the protein TRPV1—a heat-sensing protein channel normally triggered by temperatures over 43° C (110° F)—existed in two different isoforms—an approximately 850-amino-acid version and one that was 62 amino acids shorter. The short form, which resulted from alternative splicing of the transcribed mRNA, made up as much as half of the TRPV1 found in the trigeminal ganglia of vampire bats, whereas it comprised only a small percentage of the TRPV1 in the DRG. It was similarly low in both types of nerve clusters in the other bat species, suggesting that the short form may play a role in infrared detection.

To test this hypothesis, the researchers expressed one of the two TRPV1 isoforms in human kidney cells and in frog oocytes grown in vitro, and measured their temperature sensitivity using calcium imaging and electrophysiological assays, respectively. As expected, cells producing the long isoform were activated at 40 degrees Celsius (104° F). Cells producing the short isoform, on the other hand, were activated at just 30 degrees (86° F)—a drop that allows the protein to respond to the warmth of the vampire bats’ prey.

“This is a big jump in understanding how these animals locate their prey,” said Brock Fenton, a biology professor at the University of Western Ontario and author of an accompanying Nature News and Views article. While the longer isoform maintains its normal function of detecting potentially harmful high temperatures, the shorter isoform in the trigeminal nerves of the common vampire bat allows the animals to detect lower temperatures, such as the body heat of their mammalian prey.

“Basically, evolution tweaked a system in vampires bats that was already being used to sense temperatures,” said Schutt, author of the 2008 book Dark Banquet: Blood and the Curious Lives of Blood-Feeding Creatures, turning it into a useful hunting tool.

This is in contrast to the pit viper, whose infrared-sensing ability evolved from a different type of channel not involved in heat detection, but in the detection of noxious smells, added Fenton. The different evolutionary strategies employed by these two lineages “is an example of how plastic our sensory systems can be,” he said.

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Sun-Free Photovoltaics Powered by Heat

Sun-Free Photovoltaics Powered by Heat

  6:24:00 PM    Science Lover

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A new photovoltaic energy-conversion system developed at MIT can be powered solely by heat, generating electricity with no sunlight at all. While the principle involved is not new, a novel way of engineering the surface of a material to convert heat into precisely tuned wavelengths of light -- selected to match the wavelengths that photovoltaic cells can best convert to electricity -- makes the new system much more efficient than previous versions.

A variety of silicon chip micro-reactors developed by the MIT team. Each of these contains photonic crystals on both flat faces, with external tubes for injecting fuel and air and ejecting waste products. Inside the chip, the fuel and air react to heat up the photonic crystals. In use, these reactors would have a photovoltaic cell mounted against each face, with a tiny gap between, to convert the emitted wavelengths of light to electricity. (Credit: Photo by Justin Knight)

The key to this fine-tuned light emission, described in the journal Physical Review A, lies in a material with billions of nanoscale pits etched on its surface. When the material absorbs heat -- whether from the sun, a hydrocarbon fuel, a decaying radioisotope or any other source -- the pitted surface radiates energy primarily at these carefully chosen wavelengths.

Based on that technology, MIT researchers have made a button-sized power generator fueled by butane that can run three times longer than a lithium-ion battery of the same weight; the device can then be recharged instantly, just by snapping in a tiny cartridge of fresh fuel. Another device, powered by a radioisotope that steadily produces heat from radioactive decay, could generate electricity for 30 years without refueling or servicing -- an ideal source of electricity for spacecraft headed on long missions away from the sun.

According to the U.S. Energy Information Administration, 92 percent of all the energy we use involves converting heat into mechanical energy, and then often into electricity -- such as using fuel to boil water to turn a turbine, which is attached to a generator. But today's mechanical systems have relatively low efficiency, and can't be scaled down to the small sizes needed for devices such as sensors, smartphones or medical monitors.

"Being able to convert heat from various sources into electricity without moving parts would bring huge benefits," says Ivan Celanovic ScD '06, research engineer in MIT's Institute for Soldier Nanotechnologies (ISN), "especially if we could do it efficiently, relatively inexpensively and on a small scale."

It has long been known that photovoltaic (PV) cells needn't always run on sunlight. Half a century ago, researchers developed thermophotovoltaics (TPV), which couple a PV cell with any source of heat: A burning hydrocarbon, for example, heats up a material called the thermal emitter, which radiates heat and light onto the PV diode, generating electricity. The thermal emitter's radiation includes far more infrared wavelengths than occur in the solar spectrum, and "low band-gap" PV materials invented less than a decade ago can absorb more of that infrared radiation than standard silicon PVs can. But much of the heat is still wasted, so efficiencies remain relatively low.

An ideal match

The solution, Celanovic says, is to design a thermal emitter that radiates only the wavelengths that the PV diode can absorb and convert into electricity, while suppressing other wavelengths. "But how do we find a material that has this magical property of emitting only at the wavelengths that we want?" asks Marin Soljačić, professor of physics and ISN researcher. The answer: Make a photonic crystal by taking a sample of material and create some nanoscale features on its surface -- say, a regularly repeating pattern of holes or ridges -- so light propagates through the sample in a dramatically different way.



"By choosing how we design the nanostructure, we can create materials that have novel optical properties," Soljačić says. "This gives us the ability to control and manipulate the behavior of light."

The team -- which also includes Peter Bermel, research scientist in the Research Laboratory for Electronics (RLE); Peter Fisher, professor of physics; and Michael Ghebrebrhan, a postdoc in RLE -- used a slab of tungsten, engineering billions of tiny pits on its surface. When the slab heats up, it generates bright light with an altered emission spectrum because each pit acts as a resonator, capable of giving off radiation at only certain wavelengths.

This powerful approach -- co-developed by John D. Joannopoulos, the Francis Wright Davis Professor of Physics and ISN director, and others -- has been widely used to improve lasers, light-emitting diodes and even optical fibers. The MIT team, supported in part by a seed grant from the MIT Energy Initiative, is now working with collaborators at MIT and elsewhere to use it to create several novel electricity-generating devices.

Mike Waits, an electronics engineer at the Army Research Laboratory in Adelphi, Md., who was not involved in this work, says this approach to producing miniature power supplies could lead to lighter portable electronics, which is "critical for the soldier to lighten his load. It not only reduces his burden, but also reduces the logistics chain" to deliver those devices to the field. "There are a lot of lives at stake," he says, "so if you can make the power sources more efficient, it could be a great benefit."

The button-like device that uses hydrocarbon fuels such as butane or propane as its heat source -- known as a micro-TPV power generator -- has at its heart a "micro-reactor" designed by Klavs Jensen, the Warren K. Lewis Professor of Chemical Engineering, and fabricated in the Microsystems Technology Laboratories. While the device achieves a fuel-to-electricity conversion efficiency three times greater than that of a lithium-ion battery of the same size and weight, Celanovic is confident that with further work his team can triple the current energy density. "At that point, our TPV generator could power your smartphone for a whole week without being recharged," he says.

Celanovic and Soljačić stress that building practical systems requires integrating many technologies and fields of expertise. "It's a really multidisciplinary effort," Celanovic says. "And it's a neat example of how fundamental research in materials can result in new performance that enables a whole spectrum of applications for efficient energy conversion."

Note: The full version of the MITEI story is available at: http://web.mit.edu/mitei/research/spotlights/making-electricity-with-photovoltaics.html

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Brain Cap Technology Turns Thought Into Motion; Mind-Machine Interface Could Lead to New Life-Changing Technologies for Millions of People

Brain Cap Technology Turns Thought Into Motion; Mind-Machine Interface Could Lead to New Life-Changing Technologies for Millions of People

  3:10:00 PM    Science Lover

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"Brain cap" technology being developed at the University of Maryland allows users to turn their thoughts into motion. Associate Professor of Kinesiology José 'Pepe' L. Contreras-Vidal and his team have created a non-invasive, sensor-lined cap with neural interface software that soon could be used to control computers, robotic prosthetic limbs, motorized wheelchairs and even digital avatars.

University of Maryland associate professor of 
kinesiology Jose "Pepe" Contreras-Vidal wears his 
Brain Cap, a noninvasive, sensor-lined cap with neural 
interface software that soon could be used to control 
computers, robotic prosthetic limbs, motorized 
wheelchairs and even digital avatars. (Credit: John 
Consoli, University of Maryland)

"We are on track to develop, test and make available to the public- within the next few years -- a safe, reliable, noninvasive brain computer interface that can bring life-changing technology to millions of people whose ability to move has been diminished due to paralysis, stroke or other injury or illness," said Contreras-Vidal of the university's School of Public Health.

The potential and rapid progression of the UMD brain cap technology can be seen in a host of recent developments, including a just published study in the Journal of Neurophysiology, new grants from the National Science Foundation (NSF) and National Institutes of Health, and a growing list of partners that includes the University of Maryland School of Medicine, the Veterans Affairs Maryland Health Care System, the Johns Hopkins University Applied Physics Laboratory, Rice University and Walter Reed Army Medical Center's Integrated Department of Orthopaedics & Rehabilitation.

"We are doing something that few previously thought was possible," said Contreras-Vidal, who is also an affiliate professor in Maryland's Fischell Department of Bioengineering and the university's Neuroscience and Cognitive Science Program. "We use EEG [electroencephalography] to non-invasively read brain waves and translate them into movement commands for computers and other devices.

Peer Reviewed

Contreras-Vidal and his team have published three major papers on their technology over the past 18 months, the latest a just released study in the Journal of Neurophysiology in which they successfully used EEG brain signals to reconstruct the complex 3-D movements of the ankle, knee and hip joints during human treadmill walking. In two earlier studies they showed (1) similar results for 3-D hand movement and (2) that subjects wearing the brain cap could control a computer cursor with their thoughts.

Alessandro Presacco, a second-year doctoral student in Contreras-Vidal's Neural Engineering and Smart Prosthetics Lab, Contreras-Vidal and co-authors write that their Journal of Neurophysiology study indicated "that EEG signals can be used to study the cortical dynamics of walking and to develop brain-machine interfaces aimed at restoring human gait function."

There are other brain computer interface technologies under development, but Contreras-Vidal notes that these competing technologies are either very invasive, requiring electrodes to be implanted directly in the brain, or, if noninvasive, require much more training to use than does UMD's EEG-based, brain cap technology.

Partnering to Help Sufferers of Injury and Stroke

Contreras-Vidal and his team are collaborating on a rapidly growing cadre projects with researchers at other institutions to develop thought-controlled robotic prosthetics that can assist victims of injury and stroke. Their latest partnership is supported by a new $1.2 million NSF grant. Under this grant, Contreras-Vidal's Maryland team is embarking on a four-year project with researchers at Rice University, the University of Michigan and Drexel University to design a prosthetic arm that amputees can control directly with their brains, and which will allow users to feel what their robotic arm touches.



"There's nothing fictional about this," said Rice University co-principal investigator Marcia O'Malley, an associate professor of mechanical engineering. "The investigators on this grant have already demonstrated that much of this is possible. What remains is to bring all of it -- non-invasive neural decoding, direct brain control and [touch] sensory feedback -- together into one device."

In a NIH-supported project underway, Contreras-Vidal and his colleagues are pairing their brain cap's EEG-based technology with a DARPA-funded next-generation robotic arm designed by researchers at the Johns Hopkins Applied Physics Laboratory to function like a normal limb. And the UMD team is developing a new collaboration with the New Zealand's start-up Rexbionics, the developer of a powered lower-limb exoskeleton called Rex that could be used to restore gait after spinal cord injury.

Two of the earliest partnerships formed by Contreras-Vidal and his team are with the University of Maryland School of Medicine in Baltimore and the Veterans Affairs Medical Center in Baltimore. A particular focus of this research is the use of the brain cap technology to help stroke victims whose brain injuries affect their motor-sensory control. Originally funded by a seed grant from the University of Maryland, College Park and the University of Maryland, Baltimore, the work now also is supported by a VA merit grant (anklebot BMI) and an NIH grant (Stroke).

"There is a big push in brain science to understand what exercise does in terms of motor learning or motor retraining of the human brain," says Larry Forrester, an associate professor of physical therapy and rehabilitation science at the University of Maryland School of Medicine.

For the more than a year, Forrester and the UMD team have tracked the neural activity of people on a treadmill doing precise tasks like stepping over dotted lines. The researchers are matching specific brain activity recorded in real time with exact lower-limb movements.

This data could help stroke victims in several ways, Forrester says. One is a prosthetic device, called an "anklebot," or ankle robot, that stores data from a normal human gait and assists partially paralyzed people. People who are less mobile commonly suffer from other health issues such as obesity, diabetes or cardiovascular problems, Forrester says, "so we want to get [stroke survivors] up and moving by whatever means possible."

The second use of the EEG data in stroke victims is more complex, yet offers exciting possibilities. "By decoding the motion of a normal gait," Contreras-Vidal says, "we can then try and teach stroke victims to think in certain ways and match their own EEG signals with the normal signals." This could "retrain" healthy areas of the brain in what is known as neuroplasticity.

One potential method for retraining comes from one of the Maryland research team's newest members, Steve Graff, a first-year bioengineering doctoral student. He envisions a virtual reality game that matches real EEG data with on-screen characters. "It gives us a way to train someone to think the right thoughts to generate movement from digital avatars. If they can do that, then they can generate thoughts to move a device," says Graff, who brings a unique personal perspective to the work. He has congenital muscular dystrophy and uses a motorized wheelchair. The advances he's working on could allow him to use both hands -- to put on a jacket, dial his cell phone or throw a football while operating his chair with his mind.

No Surgery Required

During the past two decades a great deal of progress has been made in the study of direct brain to computer interfaces, most of it through studies using monkeys with electrodes implanted in their brains. However, for use in humans such an invasive approach poses many problems, not the least of which is that most people don't' want holes in their heads and wires attached to their brains. "EEG monitoring of the brain, which has a long, safe history for other applications, has been largely ignored by those working on brain-machine interfaces, because it was thought that the human skull blocked too much of the detailed information on brain activity needed to read thoughts about movement and turn those readings into movement commands for multi-functional high-degree of freedom prosthetics," said Contreras-Vidal. He is among the few who have used EEG, MEG or other sensing technologies to develop non-invasive neural interfaces, and the only one to have demonstrated decoding results comparable to those achieved by researchers using implanted electrodes.

A paper Contreras-Vidal and colleagues published in the Journal of Neuroscience in March 2010 showed the feasibility of Maryland's EEG-based technology to infer multidimensional natural movement from noninvasive measurements of brain activity. In their two latest studies, Contreras-Vidal and his team have further advanced the development of their EEG brain interface technology, and provided powerful new evidence that it can yield brain computer interface results as good as or better than those from invasive studies, while also requiring minimal training to use.

In a paper published in April in the Journal of Neural Engineering, the Maryland team demonstrated that people wearing the EEG brain cap, could after minimal training control a computer cursor with their thoughts and achieve performance levels comparable to those by subjects using invasive implanted electrode brain computer interface systems. Contreras-Vidal and his co-authors write that this study also shows that compared to studies of other noninvasive brain control interface systems, training time with their system was substantially shorter, requiring only a single 40-minute session.

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New Invisibility Cloak Hides Objects from Human View

New Invisibility Cloak Hides Objects from Human View

  2:26:00 PM    Science Lover

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For the first time, scientists have devised an invisibility cloak material that hides objects from detection using light that is visible to humans. The new device is a leap forward in cloaking materials, according to a report in the ACS journal Nano Letters.

A real-life invisibility cloak, shown in this cross- sectional 
illustration, can hide objects from human view. (Credit: ACS)

Xiang Zhang and colleagues note that invisibility cloaks, which route electromagnetic waves around an object to make it undetectable, "are still in their infancy." Most cloaks are made of materials that can only hide things using microwave or infrared waves, which are just below the threshold of human vision. To remedy this, the researchers built a reflective "carpet cloak" out of layers of silicon oxide and silicon nitride etched in a special pattern. The carpet cloak works by concealing an object under the layers, and bending light waves away from the bump that the object makes, so that the cloak appears flat and smooth like a normal mirror.

Although the study cloaked a microscopic object roughly the diameter of a red blood cell, the device demonstrates that it may be "capable of cloaking any object underneath a reflective carpet layer. In contrast to the previous demonstrations that were limited to infrared light, this work makes actual invisibility for the light seen by the human eye possible," the scientists write.



The authors acknowledge funding from the U.S. Army Research Office, the Natural Sciences and Engineering Research Council of Canada, and the NSF Graduate Research Fellowship Program.

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Southampton engineers fly the world's first 'printed' aircraft

Southampton engineers fly the world's first 'printed' aircraft

  10:10:00 AM    Science Lover

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Engineers at the University of Southampton have designed and flown the world's first 'printed' aircraft, which could revolutionise the economics of aircraft design.

SULSA is the world's first "printed" aircraft.
Credit: University of Southampton

The SULSA (Southampton University Laser Sintered Aircraft) plane is an unmanned air vehicle (UAV) whose entire structure has been printed, including wings, integral control surfaces and access hatches. It was printed on an EOS EOSINT P730 nylon laser sintering machine, which fabricates plastic or metal objects, building up the item layer by layer.

No fasteners were used and all equipment was attached using 'snap fit' techniques so that the entire aircraft can be put together without tools in minutes.

The electric-powered aircraft, with a 2-metres wingspan, has a top speed of nearly 100 miles per hour, but when in cruise mode is almost silent. The aircraft is also equipped with a miniature autopilot developed by Dr Matt Bennett, one of the members of the team.

Laser sintering allows the designer to create shapes and structures that would normally involve costly traditional manufacturing techniques. This technology allows a highly-tailored aircraft to be developed from concept to first flight in days. Using conventional materials and manufacturing techniques, such as composites, this would normally take months. Furthermore, because no tooling is required for manufacture, radical changes to the shape and scale of the aircraft can be made with no extra cost.

This project has been led by Professors Andy Keane and Jim Scanlan from the University's Computational Engineering and Design Research group.

Professor Scanlon says: "The flexibility of the laser sintering process allows the design team to re-visit historical techniques and ideas that would have been prohibitively expensive using conventional manufacturing. One of these ideas involves the use of a Geodetic structure. This type of structure was initially developed by Barnes Wallis and famously used on the Vickers Wellington bomber which first flew in 1936. This form of structure is very stiff and lightweight, but very complex. If it was manufactured conventionally it would require a large number of individually tailored parts that would have to be bonded or fastened at great expense."



Professor Keane adds: "Another design benefit that laser sintering provides is the use of an elliptical wing planform. Aerodynamicists have, for decades, known that elliptical wings offer drag benefits. The Spitfire wing was recognised as an extremely efficient design but it was notoriously difficult and expensive to manufacture. Again laser sintering removes the manufacturing constraint associated with shape complexity and in the SULSA aircraft there is no cost penalty in using an elliptical shape."

SULSA is part of the EPSRC-funded DECODE project, which is employing the use of leading edge manufacturing techniques, such as laser sintering, to demonstrate their use in the design of UAVs.

The University of Southampton has been at the forefront of UAV development since the early 1990s, when work began on the Autosub programme at its waterfront campus at the National Oceanography Centre, Southampton. A battery powered submarine travelled under sea ice in more than 300 voyages to map the North Sea, and assess herring stocks.

Now, the University is launching a groundbreaking course which enables students to take a Master's Degree in unmanned autonomous vehicle (UAV) design.

Provided by University of Southampton

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New Way to Measure Expansion of Universe

New Way to Measure Expansion of Universe

  12:38:00 AM    Science Lover

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Using a measurement of the clustering of the galaxies surveyed, plus other information derived from observations of the early universe, researchers have measured the Hubble constant with an uncertainly of less than 5 percent. The new work draws on data from a survey of more than 125,000 galaxies.

The 6df Galaxy Survey data, each dot is a galaxy and 
Earth is at the center of the sphere. (Credit: Image courtesy 
of International Centre for Radio Astronomy Research)

A PhD student from The International Centre for Radio Astronomy Research (ICRAR) in Perth has produced one of the most accurate measurements ever made of how fast the Universe is expanding.

Florian Beutler, a PhD candidate with ICRAR at the University of Western Australia, has calculated how fast the Universe is growing by measuring the Hubble constant.

"The Hubble constant is a key number in astronomy because it's used to calculate the size and age of the Universe," said Mr Beutler.

As the Universe swells, it carries other galaxies away from ours. The Hubble constant links how fast galaxies are moving with how far they are from us.

By analysing light coming from a distant galaxy, the speed and direction of that galaxy can be easily measured. Determining the galaxy's distance from Earth is much more difficult. Until now, this has been done by observing the brightness of individual objects within the galaxy and using what we know about the object to calculate how far away the galaxy must be.

This approach to measuring a galaxy's distance from Earth is based on some well-established assumptions but is prone to systematic errors, leading Mr Beutler to tackle the problem using a completely different method.



Published July 26 in the Monthly Notices of the Royal Astronomical Society, Mr Beutler's work draws on data from a survey of more than 125,000 galaxies carried out with the UK Schmidt Telescope in eastern Australia. Called the 6dF Galaxy Survey, this is the biggest survey to date of relatively nearby galaxies, covering almost half the sky.

Galaxies are not spread evenly through space, but are clustered. Using a measurement of the clustering of the galaxies surveyed, plus other information derived from observations of the early Universe, Mr Beutler has measured the Hubble constant with an uncertainly of less than 5%.*

"This way of determining the Hubble constant is as direct and precise as other methods, and provides an independent verification of them," says Professor Matthew Colless, Director of the Australian Astronomical Observatory and one of Mr Beutler's co-authors. "The new measurement agrees well with previous ones, and provides a strong check on previous work."

The measurement can be refined even further by using data from larger galaxy surveys.

"Big surveys, like the one used for this work, generate numerous scientific outcomes for astronomers internationally," says Professor Lister Staveley-Smith, ICRAR's Deputy Director of Science.

* The new measurement of the Hubble constant is 67.0 ± 3.2 km s-1 Mpc-1

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Scientists Discover Tipping Point for the Spread of Ideas

Scientists Discover Tipping Point for the Spread of Ideas

  9:46:00 AM    Science Lover

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Scientists at Rensselaer Polytechnic Institute have found that when just 10 percent of the population holds an unshakable belief, their belief will always be adopted by the majority of the society. The scientists, who are members of the Social Cognitive Networks Academic Research Center (SCNARC) at Rensselaer, used computational and analytical methods to discover the tipping point where a minority belief becomes the majority opinion. The finding has implications for the study and influence of societal interactions ranging from the spread of innovations to the movement of political ideals.

In this visualization, we see the tipping point where minority opinion (shown in red) quickly becomes majority opinion. Over time, the minority opinion grows. Once the minority opinion reached 10 percent of the population, the network quickly changes as the minority opinion takes over the original majority opinion (shown in green). (Credit: SCNARC/Rensselaer Polytechnic Institute)

"When the number of committed opinion holders is below 10 percent, there is no visible progress in the spread of ideas. It would literally take the amount of time comparable to the age of the universe for this size group to reach the majority," said SCNARC Director Boleslaw Szymanski, the Claire and Roland Schmitt Distinguished Professor at Rensselaer. "Once that number grows above 10 percent, the idea spreads like flame."

As an example, the ongoing events in Tunisia and Egypt appear to exhibit a similar process, according to Szymanski. "In those countries, dictators who were in power for decades were suddenly overthrown in just a few weeks."

The findings were published in the July 22, 2011, early online edition of the journal Physical Review E in an article titled "Social consensus through the influence of committed minorities."

An important aspect of the finding is that the percent of committed opinion holders required to shift majority opinion does not change significantly regardless of the type of network in which the opinion holders are working. In other words, the percentage of committed opinion holders required to influence a society remains at approximately 10 percent, regardless of how or where that opinion starts and spreads in the society.

To reach their conclusion, the scientists developed computer models of various types of social networks. One of the networks had each person connect to every other person in the network. The second model included certain individuals who were connected to a large number of people, making them opinion hubs or leaders. The final model gave every person in the model roughly the same number of connections. The initial state of each of the models was a sea of traditional-view holders. Each of these individuals held a view, but were also, importantly, open minded to other views.

Once the networks were built, the scientists then "sprinkled" in some true believers throughout each of the networks. These people were completely set in their views and unflappable in modifying those beliefs. As those true believers began to converse with those who held the traditional belief system, the tides gradually and then very abruptly began to shift.



"In general, people do not like to have an unpopular opinion and are always seeking to try locally to come to consensus. We set up this dynamic in each of our models," said SCNARC Research Associate and corresponding paper author Sameet Sreenivasan. To accomplish this, each of the individuals in the models "talked" to each other about their opinion. If the listener held the same opinions as the speaker, it reinforced the listener's belief. If the opinion was different, the listener considered it and moved on to talk to another person. If that person also held this new belief, the listener then adopted that belief.

"As agents of change start to convince more and more people, the situation begins to change," Sreenivasan said. "People begin to question their own views at first and then completely adopt the new view to spread it even further. If the true believers just influenced their neighbors, that wouldn't change anything within the larger system, as we saw with percentages less than 10."

The research has broad implications for understanding how opinion spreads. "There are clearly situations in which it helps to know how to efficiently spread some opinion or how to suppress a developing opinion," said Associate Professor of Physics and co-author of the paper Gyorgy Korniss. "Some examples might be the need to quickly convince a town to move before a hurricane or spread new information on the prevention of disease in a rural village."

The researchers are now looking for partners within the social sciences and other fields to compare their computational models to historical examples. They are also looking to study how the percentage might change when input into a model where the society is polarized. Instead of simply holding one traditional view, the society would instead hold two opposing viewpoints. An example of this polarization would be Democrat versus Republican.

The research was funded by the Army Research Laboratory (ARL) through SCNARC, part of the Network Science Collaborative Technology Alliance (NS-CTA), the Army Research Office (ARO), and the Office of Naval Research (ONR).

The research is part of a much larger body of work taking place under SCNARC at Rensselaer. The center joins researchers from a broad spectrum of fields -- including sociology, physics, computer science, and engineering -- in exploring social cognitive networks. The center studies the fundamentals of network structures and how those structures are altered by technology. The goal of the center is to develop a deeper understanding of networks and a firm scientific basis for the newly arising field of network science. More information on the launch of SCNARC can be found at http://news.rpi.edu/update.do?artcenterkey=2721&setappvar=page(1)

Szymanski, Sreenivasan, and Korniss were joined in the research by Professor of Mathematics Chjan Lim, and graduate students Jierui Xie (first author) and Weituo Zhang.

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Researchers develop prototype to detect fake websites

Researchers develop prototype to detect fake websites

  10:16:00 AM    Science Lover

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Do you go online to pay bills, shop, transfer funds, sign up for classes, send email or instant messages or search for medical information? If so, then this pertains to you.

It seems logical that a more Internet-driven world would translate into a heightened awareness of fake websites. But it isn't so. The vast majority of people still are unable to determine the authenticity of websites, resulting in tremendous monetary loses. That is what is driving the work of UA Artificial Intelligence Lab members who, along with a UA alumnus, have earned a top honor from MIS Quarterly for their research.

Members of a University of Arizona Eller College of Management team and a UA alumnus developed a prototype system to detect fake websites. When tested against other existing commercial systems, the team found that its system resulted in effective and more accurate detections of spoof sites – better than a human can.

The team's subsequent article, “Detecting Fake Websites: The Contribution of Statistical Learning Theory" was published last year in an issue of MIS Quarterly, or MISQ. A preeminent peer-reviewed journal in the field of management information systems, MISQ has since been named the article its top paper for 2010.

"Even to get into MISQ is very difficult, and this is probably the first technical paper to receive the Best Paper award," said Hsinchun Chen, the UA Artificial Intelligence Lab director, one of the paper's five authors.

MISQ will formally honor the researchers in Shanghai, China later this year during the International Conference on Information Systems.

"The topic of detecting fake websites and also our computational approach are both considered major contributions. This topic has great relevance to the industry, the society and the citizens in general," said Chen, also the McClelland Professor of Management Information Systems.

"This award is not something just for me, or my lab, but also for our department," he said, adding that the team's eventual goal is technology transfer.

UA alumnus Ahmed Abbasi, now a University of Virginia assistant professor of information technology, is lead author on the paper. Chen served as his dissertation adviser. Other co-authors are UA Eller College's department of management information systems faculty members Zhu Zhang and Jay F. Nunamaker Jr.; and David Zimbra, a doctoral student in the Artificial Intelligence Lab.



For the research, the team used the prototype and several other detection systems to evaluate the authenticity of 900 websites.

It is easy to pick up on a site's authenticity by checking whether the URL contains "http" when it should read "https," when it was last updated, if a security key is missing or if images appear strangely pixelated.

The team found that its system – founded on statistical learning technology, which evaluates a large accumulation of data – was more apt to detect imitation sites and those that were entirely concocted, said Abbasi, who earned his doctoral degree in management information systems from the UA in 2008.

The major difference between the authors’ prototype and the other systems? Their system relied on a tremendously rich set of fraud cues.

The team developed five categories with thousands of cues, finding that the best results were attained when utilizing thousands of highly visible and also deeply embedded cues, such as placement, URL length, the number of links, characters types on the site and how thorough the site's "frequently asked questions" section is detailed, among other features.

The project's origins were born out of the Artificial Intelligence Lab, where Abbasi developed the mathematical formula the team eventually used while working as a project lead and research associate. He continued the work after having taken a faculty position at the University of Wisconsin-Milwaukee.

"It creates a greater awareness for a problem that has been around for a while yet still remains an issue as we increasingly move to the Internet for everything – online banking, online health initiatives and medical information," Abbasi said.

Given the pervasive nature of online phishing scams, being able to readily and frequently detect a site's validity is crucial, Abbasi said, also noting research that indicates people are less than 60 percent accurate in detecting fake sites, and other security issues.

"The problem we're looking at is quite big. Fake websites constitute much of the Internet fraud's multi-billion dollar industry, and that is monetary loss…we can’t even quantify the social ramifications," Abbasi said. "That's the whole motivation. It is so profitable for fraudsters, and it is slipping through the cracks."

Today, Chen and more than one dozen of his collaborators are continuing to investigate fake sites. Meanwhile, Abbasi is undertaking an investigation of peoples' abilities to detect fake sites through a grant funded by the National Science Foundation.

Today, Chen and more than one dozen of his collaborators are continuing to investigate fake sites. Meanwhile, Abbasi is undertaking an investigation of users and peoples' abilities to detect fake sites.

Abbasi said developing better detection systems requires improved statistical learning technology that utilize larger quantities of cues. It also is important to dismiss long-held perceptions about how fake sites might and should appear.

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Eat, Prey, Rain: New Model of Dynamics of Clouds and Rain Is Based On a Predator-Prey Population Model

Eat, Prey, Rain: New Model of Dynamics of Clouds and Rain Is Based On a Predator-Prey Population Model

  10:10:00 AM    Science Lover

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What do a herd of gazelles and a fluffy mass of clouds have in common? A mathematical formula that describes the population dynamics of such prey animals as gazelles and their predators has been used to model the relationship between cloud systems, rain and tiny floating particles called aerosols. This model may help climate scientists understand, among other things, how human-produced aerosols affect rainfall patterns. The research recently appeared in the Proceedings of the National Academy of Sciences (PNAS).

A new mathematical model may help climate scientists 
understand, among other things, how human-produced 
aerosols affect rainfall patterns. (Credit: © Brian 
Jackson / Fotolia)

Clouds are major contributors to the climate system. In particular the shallow marine stratocumulus clouds that form huge cloud decks over the subtropical oceans cool the atmosphere by reflecting part of the incoming solar energy back to space. Drs. Ilan Koren of the Weizmann Institute's Environmental Sciences and Energy Research Department (Faculty of Chemistry) and Graham Feingold of the NOAA Earth System Research Laboratory, Colorado, found that equations for modeling prey-predator cycles in the animal world were a handy analogy for cloud-rain cycles: Just as respective predator and prey populations expand and contract at the expense of one another, so too rain depletes clouds, which grow again once the rain runs out. And just as the availability of grass affects herd size, the relative abundance of aerosols -- which "feed" the clouds as droplets condense around them -- affects the shapes of those clouds. A larger supply of airborne particles gives rise to more droplets, but these droplets are smaller and thus remain high up in the cloud rather than falling as rain.

In previous research, Feingold and Koren had "zoomed in" to discover oscillations in convective cells in marine stratocumulus. Now they returned to their data, but from a "top down" angle to see if a generalized formula could reveal something about these systems. Using just three simple equations, they developed a model showing that cloud-rain dynamics mimic three known predator-prey modes. Like gazelles and lions, the two can oscillate in tandem, the "predator" rain cycle following a step behind peak cloud formation. Or the two can reach a sort of steady state in which the clouds are replenished at the same rate as they are diminished (as in a light, steady drizzle). The third option is chaos -- the crash that occurs when predator populations get out of hand or a strong rain destroys the cloud system.



The model shows that as the amounts of aerosols change, the system can abruptly shift from one state to another. It also reveals a bifurcation -- two scenarios at different ends of the aerosol scale that lend themselves to stable patterns. In the first, relatively low aerosol levels lead to clouds in which development depends heavily on aerosol concentrations. In the second, high levels produce saturation; these clouds depend solely on the initial environmental conditions.

Using this so-called systems approach, says Koren, "can open new windows to view and understand the emergent behavior of the complex relationships between clouds, rain and aerosols, giving us a more useful view of the big picture and helping us to understand how shifting aerosol levels can lead to different climate patterns."

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