星空体育频道: 2013-07-21

2013年7月26日星期五

NASA's Van Allen Probes discover particle accelerator in the heart of Earths radiation belts

The discovery that the particles are accelerated by a local energy source is akin to the discovery that hurricanes grow from a local energy source, such as a region of warm ocean water. In the case of the radiation belts, the source is a region of intense electromagnetic waves, tapping energy from other particles located in the same region. Knowing the location of the acceleration will help scientists improve space weather predictions, because changes in the radiation belts can be risky for satellites near Earth. The results were published in Science magazine on July 25, 2013.

In order for scientists to understand the belts better, the Van Allen Probes were designed to fly straight through this intense area of space. When the mission launched in August 2012, it had top-level goals to understand how particles in the belts are accelerated to ultra-high energies, and how the particles can sometimes escape. By determining that this superfast acceleration comes from these local kicks of energy, as opposed to a more global process, scientists have been able to definitively answer one of those important questions for the first time.

"This is one of the most highly anticipated and exciting results from the Van Allen Probes," said David Sibeck, Van Allen Probes project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It goes to the heart of why we launched the mission."

The radiation belts were discovered upon the launch of the very first successful U.S. satellites sent into space, Explorers I and III. It was quickly realized that the belts were some of the most hazardous environments a spacecraft can experience. Most satellite orbits are chosen to duck below the radiation belts or circle outside of them, and some satellites, such as GPS spacecraft, must operate between the two belts. When the belts swell due to incoming space weather, they can encompass these spacecraft, exposing them to dangerous radiation. Indeed, a significant number of permanent failures on spacecraft have been caused by radiation. With enough warning, we can protect technology from the worst consequences, but such warning can only be achieved if we truly understand the dynamics of what's happening inside these mysterious belts.

"Until the 1990s, we thought that the Van Allen belts were pretty well-behaved and changed slowly," said Geoff Reeves, the first author on the paper and a radiation belt scientist at Los Alamos National Laboratory in Los Alamos, N.M. "With more and more measurements, however, we realized how quickly and unpredictably the radiation belts changed. They are basically never in equilibrium, but in a constant state of change."

In fact, scientists realized that the belts don't even change consistently in response to what seem to be similar stimuli. Some solar storms caused the belts to intensify; others caused the belts to be depleted, and some seemed to have almost no effect at all. Such disparate effects from apparently similar events suggested that this region is much more mysterious than previously thought. To understand -- and eventually predict -- which solar storms will intensify the radiation belts, scientists want to know where the energy that accelerates the particles comes from.

The twin Van Allen Probes were designed to distinguish between two broad possibilities on what processes accelerate the particles to such amazing speeds: radial acceleration or local acceleration. In radial acceleration, particles are transported perpendicular to the magnetic fields that surround Earth, from areas of low magnetic strength far from Earth to areas of high magnetic strength nearer Earth. The laws of physics dictate that the particle speeds in this scenario will speed up when the magnetic field strength increases. So the speed would increase as the particles move toward Earth, much the way a rock rolling down hill gathers speed simply due to gravity. The local acceleration theory posits that the particles gain energy from a local energy source more similar to the way hot ocean water spawns a hurricane above it.

To help distinguish between these possibilities, the Van Allen Probes consist of two spacecraft. With two sets of observations, scientists can measure the particles and energy sources in two regions of space simultaneously, which is crucial to distinguish between causes that occur locally or come from far away. Also, each spacecraft is equipped with sensors to measure particle energy and position and determine pitch angle -- that is, the angle of movement with respect to Earth's magnetic fields. All of these will change in different ways depending on the forces acting on them, thus helping scientists distinguish between the theories.

Equipped with such data, Reeves and his team observed a rapid energy increase of high-energy electrons in the radiation belts on Oct. 9, 2012. If the acceleration of these electrons was occurring due to radial transport, one would measure effects starting first far from Earth and moving inward due to the very shape and strength of the surrounding fields. In such a scenario, particles moving across magnetic fields naturally jump from one to the next in a similar cascade, gathering speed and energy along the way -- correlating to that scenario of rocks rolling down a hill.

But the observations didn't show an intensification that formed further away from Earth and gradually moved inward. Instead they showed an increase in energy that started right in the middle of the radiation belts and gradually spread both inward and outward, implying a local acceleration source.

"In this particular case, all of the acceleration took place in about 12 hours," said Reeves. "With previous measurements, a satellite might have only been able to fly through such an event once, and not get a chance to witness the changes actually happening. With the Van Allen Probes we have two satellites and so can observe how things change and where those changes start."

Scientists believe these new results will lead to better predictions of the complex chain of events that intensify the radiation belts to levels that can disable satellites. While the work shows that the local energy comes from electromagnetic waves coursing through the belts, it is not known exactly which such waves might be the cause. During the set of observations described in the paper, the Van Allen Probes observed a specific kind of wave called chorus waves at the same time as the particles were accelerated, but more work must be done to determine cause and effect.

"This paper helps differentiate between two broad solutions," said Sibeck. "This shows that the acceleration can happen locally. Now the scientists who study waves and magnetic fields will jump in to do their job, and find out what wave provided the push."

Luckily, such a task will also be helped along by the Van Allen Probes, which were also carefully designed to measure and distinguish between the numerous types of electromagnetic waves.

"When scientists designed the mission and the instrumentation on the probes, they looked at the scientific unknowns and said, 'This is a great chance to unlock some fundamental knowledge about how particles are accelerated,'" said Nicola J. Fox, deputy project scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "With five identical suites of instruments on board twin spacecraft -- each with a broad range of particle and field and wave detection -- we have the best platform ever created to better understand this critical region of space above Earth."

The Applied Physics Laboratory built and operates the twin Van Allen Probes for NASA's Science Mission Directorate. The Van Allen Probes comprise the second mission in NASA's Living With a Star program, managed by Goddard, to explore aspects of the connected sun-Earth system that directly affect life and society.

For more information about the Van Allen probes, visit: http://www.nasa.gov/vanallenprobes/

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Women's height linked to cancer risk, study finds

July 25, 2013 — The taller a postmenopausal woman is, the greater her risk for developing cancer, according to a study published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.

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Height was linked to cancers of the breast, colon, endometrium, kidney, ovary, rectum, and thyroid, as well as to multiple myeloma and melanoma, and these associations did not change even after adjusting for factors known to influence these cancers, in this study of 20,928 postmenopausal women, identified from a large cohort of 144,701 women recruited to the Women's Health Initiative (WHI).

"We were surprised at the number of cancer sites that were positively associated with height. In this data set, more cancers are associated with height than were associated with body mass index [BMI]," said Geoffrey Kabat, Ph.D., senior epidemiologist in the Department of Epidemiology and Population Health at Albert Einstein College of Medicine of Yeshiva University in New York, N.Y. "Ultimately, cancer is a result of processes having to do with growth, so it makes sense that hormones or other growth factors that influence height may also influence cancer risk."

Some genetic variations associated with height are also linked to cancer risk, and more studies are needed to better understand how these height-related genetic variations predispose some men and women to cancer, according to the authors.

Kabat and colleagues used data from the WHI, a large, multicenter study that recruited postmenopausal women between the ages 50 and 79, between 1993 and 1998. At study entry, the women answered questions about physical activity, and their height and weight were measured.

The researchers identified 20,928 women who had been diagnosed with one or more invasive cancers during the follow-up of 12 years. To study the effect of height, they accounted for many factors influencing cancers, including age, weight, education, smoking habits, alcohol consumption, and hormone therapy.

They found that for every 10-centimeter (3.94 inches) increase in height, there was a 13 percent increase in risk of developing any cancer. Among specific cancers, there was a 13 percent to 17 percent increase in the risk of getting melanoma and cancers of the breast, ovary, endometrium, and colon. There was a 23 percent to 29 percent increase in the risk of developing cancers of the kidney, rectum, thyroid, and blood.

Of the 19 cancers studied, none showed a negative association with height.

Because the ability to screen for certain cancers could have influenced the results, the researchers added the participants' mammography, Pap, and colorectal cancer screening histories to the analyses and found the results remained unchanged.

"Although it is not a modifiable risk factor [A modifiable risk factor can be changed, controlled, or treated, e.g., diet, lifestyle. Height is a non-modifiable risk factor because it cannot be changed], the association of height with a number of cancer sites suggests that exposures in early life, including nutrition, play a role in influencing a person's risk of cancer," said Kabat. "There is currently a great deal of interest in early-life events that influence health in adulthood. Our study fits with this area."

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Neuroscientists plant false memories in mice: Location where brain stores memory traces, both false and authentic, pinpointed

In a step toward understanding how these faulty memories arise, MIT neuroscientists have shown that they can plant false memories in the brains of mice. They also found that many of the neurological traces of these memories are identical in nature to those of authentic memories.

"Whether it's a false or genuine memory, the brain's neural mechanism underlying the recall of the memory is the same," says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and senior author of a paper describing the findings in the July 25 edition of Science.

The study also provides further evidence that memories are stored in networks of neurons that form memory traces for each experience we have -- a phenomenon that Tonegawa's lab first demonstrated last year.

Neuroscientists have long sought the location of these memory traces, also called engrams. In the pair of studies, Tonegawa and colleagues at MIT's Picower Institute for Learning and Memory showed that they could identify the cells that make up part of an engram for a specific memory and reactivate it using a technology called optogenetics.

Lead authors of the paper are graduate student Steve Ramirez and research scientist Xu Liu. Other authors are technical assistant Pei-Ann Lin, research scientist Junghyup Suh, and postdocs Michele Pignatelli, Roger Redondo and Tomas Ryan.

Seeking the engram

Episodic memories -- memories of experiences -- are made of associations of several elements, including objects, space and time. These associations are encoded by chemical and physical changes in neurons, as well as by modifications to the connections between the neurons.

Where these engrams reside in the brain has been a longstanding question in neuroscience. "Is the information spread out in various parts of the brain, or is there a particular area of the brain in which this type of memory is stored? This has been a very fundamental question," Tonegawa says.

In the 1940s, Canadian neurosurgeon Wilder Penfield suggested that episodic memories are located in the brain's temporal lobe. When Penfield electrically stimulated cells in the temporal lobes of patients who were about to undergo surgery to treat epileptic seizures, the patients reported that specific memories popped into mind. Later studies of the amnesiac patient known as "H.M." confirmed that the temporal lobe, including the area known as the hippocampus, is critical for forming episodic memories.

However, these studies did not prove that engrams are actually stored in the hippocampus, Tonegawa says. To make that case, scientists needed to show that activating specific groups of hippocampal cells is sufficient to produce and recall memories.

To achieve that, Tonegawa's lab turned to optogenetics, a new technology that allows cells to be selectively turned on or off using light.

For this pair of studies, the researchers engineered mouse hippocampal cells to express the gene for channelrhodopsin, a protein that activates neurons when stimulated by light. They also modified the gene so that channelrhodopsin would be produced whenever the c-fos gene, necessary for memory formation, was turned on.

In last year's study, the researchers conditioned these mice to fear a particular chamber by delivering a mild electric shock. As this memory was formed, the c-fos gene was turned on, along with the engineered channelrhodopsin gene. This way, cells encoding the memory trace were "labeled" with light-sensitive proteins.

The next day, when the mice were put in a different chamber they had never seen before, they behaved normally. However, when the researchers delivered a pulse of light to the hippocampus, stimulating the memory cells labeled with channelrhodopsin, the mice froze in fear as the previous day's memory was reactivated.

"Compared to most studies that treat the brain as a black box while trying to access it from the outside in, this is like we are trying to study the brain from the inside out," Liu says. "The technology we developed for this study allows us to fine-dissect and even potentially tinker with the memory process by directly controlling the brain cells."

Incepting false memories

That is exactly what the researchers did in the new study -- exploring whether they could use these reactivated engrams to plant false memories in the mice's brains.

First, the researchers placed the mice in a novel chamber, A, but did not deliver any shocks. As the mice explored this chamber, their memory cells were labeled with channelrhodopsin. The next day, the mice were placed in a second, very different chamber, B. After a while, the mice were given a mild foot shock. At the same instant, the researchers used light to activate the cells encoding the memory of chamber A.

On the third day, the mice were placed back into chamber A, where they now froze in fear, even though they had never been shocked there. A false memory had been incepted: The mice feared the memory of chamber A because when the shock was given in chamber B, they were reliving the memory of being in chamber A.

Moreover, that false memory appeared to compete with a genuine memory of chamber B, the researchers found. These mice also froze when placed in chamber B, but not as much as mice that had received a shock in chamber B without having the chamber A memory activated.

The researchers then showed that immediately after recall of the false memory, levels of neural activity were also elevated in the amygdala, a fear center in the brain that receives memory information from the hippocampus, just as they are when the mice recall a genuine memory.

The MIT team is now planning further studies of how memories can be distorted in the brain.

"Now that we can reactivate and change the contents of memories in the brain, we can begin asking questions that were once the realm of philosophy," Ramirez says. "Are there multiple conditions that lead to the formation of false memories? Can false memories for both pleasurable and aversive events be artificially created? What about false memories for more than just contexts -- false memories for objects, food or other mice? These are the once seemingly sci-fi questions that can now be experimentally tackled in the lab."

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Novel mechanism in spinal cord injury discovered: 'See-saw' molecule may offer clues to potential therapies in the long-term

July 25, 2013 — More than 11,000 Americans suffer spinal cord injuries each year, and since over a quarter of those injuries are due to falls, the number is likely to rise as the population ages. The reason so many of those injuries are permanently disabling is that the human body lacks the capacity to regenerate nerve fibers. The best our bodies can do is route the surviving tissue around the injury site.

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"It's like a detour after an earthquake," says Kuo-Fen Lee, the Salk Institute's Helen McLoraine Chair in Molecular Neurobiology. "If the freeway is down, but you can still take the side-streets, traffic can still move. So your strategy has to be to find a way to preserve as much tissue as possible, to give yourself a chance for that rerouting."

In a paper published in this week's PLOS ONE, Lee and his colleagues describe how a protein named P45 may yield insight into a possible molecular mechanism to promote rerouting for spinal cord healing and functional recovery. Because injured mice can recover more fully than human beings, Lee sought the source of the difference. He discovered that P45 had a previously unknown neuroprotective effect.

"As a biochemist and neurobiologist, this discovery gives me hope that we can find a potential target molecule for drug treatments," says Lee. "Nevertheless, I must caution that this is only the first step in knowing what to look for."

In a human or a mouse, the success of an attempted rerouting after a spinal cord injury depends on how much healthy tissue is left. But wounds set off a cascade of reactions within cells, which if not stopped in time will result in more dead and dying tissue extending beyond the injury site. Nerve traction from the injury site leads to disconnection of the network required for normal sensory and motor functions. Lee found that P45 is the key factor determining whether the cascade continues on to its destructive end.

A complex of proteins, by sequentially interacting with each other, induces this cascade of cell death. Lee discovered that P45 is a natural antagonist to this process. Antagonists are molecules, some naturally occurring, some made in pharmaceutical laboratories, that work essentially like sticking gum in a lock. Because the antagonist is in place, no other molecule can get in. In this case, P45 prevents two other proteins in the death cascade from connecting, rendering their actions harmless and stopping cell death.

But there's more to how P45 works that gives Lee hope that he may be on to a unique approach to finding new ways to treat spinal cord injuries. In other recent findings, which are being prepared for publication, his team saw P45 also yield positive effects, specifically the encouragement of healthy tissue growth. Thus, Lee concludes its real role may be as a sort of "see-saw" molecule that tips the balance in the cascade from negative to positive.

"The great thing about P45 is that it can both inhibit the negative by blocking the conformational change that would lead to more cell death, while promoting the positive-the survival and growth of tissue-thus making it easier to foster recovery following spinal cord injury," Lee explains.

"If you can understand where you could tilt the balance of positive/negative signal, it would give you less damage while helping to promote healing," says Lee. "It could be combinatorial-maybe one molecule can do both, or maybe it's a combination of two molecules, one to negate, one to promote. The hope is if such a control switch could be found, more tissue could be preserved at the site of injury, thus increasing the chances that movement might someday be restored."

The next step for Lee's laboratory will be to seek either a gene, or a process that works in a similar see-saw way in humans, or can be made to work with therapeutic intervention. Still, Lee cautions, this remains a proof of concept experiment in mice. Even if such a mechanism were found in humans, clinical applications would be years away.

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Centaurs: NASA's WISE finds mysterious centaurs may be comets

Until now, astronomers were not certain whether centaurs are asteroids flung out from the inner solar system or comets traveling in toward the sun from afar. Because of their dual nature, they take their name from the creature in Greek mythology whose head and torso are human and legs are those of a horse.

"Just like the mythical creatures, the centaur objects seem to have a double life," said James Bauer of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Bauer is lead author of a paper published online July 22 in The Astrophysical Journal. "Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system."

"Cometary origin" means an object likely is made from the same material as a comet, may have been an active comet in the past, and may be active again in the future.

The findings come from the largest infrared survey to date of centaurs and their more distant cousins, called scattered disk objects. NEOWISE, the asteroid-hunting portion of the WISE mission, gathered infrared images of 52 centaurs and scattered disk objects. Fifteen of the 52 are new discoveries. Centaurs and scattered disk objects orbit in an unstable belt. Ultimately, gravity from the giant planets will fling them either closer to the sun or farther away from their current locations.

Although astronomers previously observed some centaurs with dusty halos, a common feature of outgassing comets, and NASA's Spitzer Space Telescope also found some evidence for comets in the group, they had not been able to estimate the numbers of comets and asteroids.

Infrared data from NEOWISE provided information on the objects' albedos, or reflectivity, to help astronomers sort the population. NEOWISE can tell whether a centaur has a matte and dark surface or a shiny one that reflects more light. The puzzle pieces fell into place when astronomers combined the albedo information with what was already known about the colors of the objects. Visible-light observations have shown centaurs generally to be either blue-gray or reddish in hue. A blue-gray object could be an asteroid or comet. NEOWISE showed that most of the blue-gray objects are dark, a telltale sign of comets. A reddish object is more likely to be an asteroid.

"Comets have a dark, soot-like coating on their icy surfaces, making them darker than most asteroids," said the study's co-author, Tommy Grav of the Planetary Science Institute in Tucson, Ariz. "Comet surfaces tend to be more like charcoal, while asteroids are usually shinier like the moon."

The results indicate that roughly two-thirds of the centaur population are comets, which come from the frigid outer reaches of our solar system. It is not clear whether the rest are asteroids. The centaur bodies have not lost their mystique entirely, but future research from NEOWISE may reveal their secrets further.

JPL, managed by the California Institute of Technology in Pasadena, managed and operated WISE for NASA's Science Mission Directorate. The NEOWISE portion of the project was funded by NASA's Near Earth Object Observation Program. WISE completed its key mission objective, two scans of the entire sky, in 2011 and has been hibernating in space since then.

For more information about the WISE mission, visit: http://www.nasa.gov/wise .

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Broad-scale genome tinkering with help of an RNA guide: Biotechnology tool borrowed from pathogenic bacteria

July 25, 2013 — Duke researchers have devised a way to quickly and easily target and tinker with any gene in the human genome. The new tool, which builds on an RNA-guided enzyme they borrowed from bacteria, is being made freely available to researchers who may now apply it to the next round of genome discovery.

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The new method also has obvious utility for gene therapy and for efforts to reprogram stem or adult cells into other cell types -- for example, to make new neurons from skin cells.

"We have the genome sequence and we know what all the parts are, but we are still in need of methods to manipulate it easily and precisely," says assistant professor Charles Gersbach, of Duke's Pratt School of Engineering and the Duke Institute for Genome Sciences & Policy. "That's where this engineering tool comes in."

Gersbach's team had already been in the business of tinkering with the genome using specially engineered proteins, but the process was difficult and slow. It was hard to imagine how to scale it up for the investigation of hundreds or even thousands of genes in the way genome scientists really wanted to do. "That's where the conversation always broke down," he says.

Then, he and post-doctoral researcher Pablo Perez-Pinera found out about an RNA-guided protein called Cas9 found in a Streptococcus bacteria. The bacteria rely on Cas9 as part of an adaptive immune system to defend themselves against infection by viruses, cutting out a piece of the viral DNA and inserting it into their own genome for recognition of future infection. Other scientists then showed that those immune system components could function inside human cells.

Gersbach's team recognized the RNA-guided nature of this system as a potential game-changer for the gene engineering work they do.

In the study now reported in Nature Methods on July 25, Gersbach and his colleagues modified Cas9 to turn genes on rather than cut them. They showed that their tool could turn on very specific genes in human cells. They went on to demonstrate use of the tool to modify targets of interest for fighting inflammation and activating gene networks for making neurons, muscle cells or stem cells. They showed they could induce a gene known to alleviate symptoms of sickle cell disease, too.

In other words, it works, and it works on genes that matter from a clinical perspective. In principle, the RNA-guided tool could be used to modify or influence any gene anywhere in the genome.

Gersbach now hopes to apply the new tool along with collaborators in the IGSP to investigate the functions of thousands of sites across the genome. With tissue engineer Farshid Guilak, a professor of engineering and orthopaedic surgery, he will continue to work on its application in the fight against inflammatory and autoimmune diseases such as arthritis.

"This simple and versatile tool makes it easy for anyone to do this," Gersbach says.

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Behavior of turbulent flow of superfluids is opposite that of ordinary fluids

Think of the assassin T-1000 in the movie "Terminator 2: Judgment Day" -- a robotic shape-shifter made of liquid metal. Or better yet, consider a real-world example: liquid helium. When cooled to extremely low temperatures, helium exhibits behavior that is otherwise impossible in ordinary fluids. For instance, the superfluid can squeeze through pores as small as a molecule, and climb up and over the walls of a glass. It can even remain in motion years after a centrifuge containing it has stopped spinning.

Now physicists at MIT have come up with a method to mathematically describe the behavior of superfluids -- in particular, the turbulent flows within superfluids. They publish their results this week in the journal Science.

"Turbulence provides a fascinating window into the dynamics of a superfluid," says Allan Adams, an associate professor of physics at MIT. "Imagine pouring milk into a cup of tea. As soon as the milk hits the tea, it flares out into whirls and eddies, which stretch and split into filigree. Understanding this complicated, roiling turbulent state is one of the great challenges of fluid dynamics. When it comes to superfluids, whose detailed dynamics depend on quantum mechanics, the problem of turbulence is an even tougher nut to crack."

To describe the underlying physics of a superfluid's turbulence, Adams and his colleagues drew comparisons with the physics governing black holes. At first glance, black holes -- extremely dense, gravitationally intense objects that pull in surrounding matter and light -- may not appear to behave like a fluid. But the MIT researchers translated the physics of black holes to that of superfluid turbulence, using a technique called holographic duality.

Consider, for example, a holographic image on a magazine cover. The data, or pixels, in the image exist on a flat surface, but can appear three-dimensional when viewed from certain angles. An engineer could conceivably build an actual 3-D replica based on the information, or dimensions, found in the 2-D hologram.

"If you take that analogy one step further, in a certain sense you can regard various quantum theories as being a holographic image of a world with one extra dimension," says Paul Chesler, a postdoc in MIT's Department of Physics.

Taking this cosmic line of reasoning, Adams, Chesler and colleagues used holographic duality as a "dictionary" to translate the very well-characterized physics of black holes to the physics of superfluid turbulence.

To the researchers' surprise, their calculations showed that turbulent flows of a class of superfluids on a flat surface behave not like those of ordinary fluids in 2-D, but more like 3-D fluids, which morph from relatively uniform, large structures to smaller and smaller structures. The result is much like cigarette smoke: From a burning tip, smoke unfurls in a single stream that quickly disperses into smaller and smaller eddies. Physicists refer to this phenomenon as an "energy cascade."

"For superfluids, whether such energy cascades exist is an open question," says Hong Liu, an associate professor of physics at MIT. "People have been making all kinds of claims, but there hasn't been any smoking-gun type of evidence that such a cascade exists. In a class of superfluids, we produced very convincing evidence for the direction of this kind of flow, which would otherwise be very hard to obtain. "

The power of duality

Holographic duality is a mathematical principle first proposed in 1997 by physicist Juan Maldacena. The theory can be described by envisioning a theoretical lake that's split into two layers: an overlying 2-D surface and a 3-D interior. Maldacena's theory posits that on the lake's surface, there is no gravity -- an environment that can best be described by particle theory. On the other hand, the underlying interior is thought to consist of tiny strings that vibrate, fuse and break apart to create matter and gravity -- an environment that can be mathematically explained by string theory.

Maldacena's theory of holographic duality demonstrates that behaviors within the gravity-bound 3-D interior can be mathematically translated into behaviors on the zero-gravity 2-D surface.

Liu and his colleagues applied equations of holographic duality to the physics of black holes -- objects that are bound by extreme gravitational forces -- and translated these forces to the behavior of zero-gravity superfluid turbulence, which is otherwise considered incredibly difficult to characterize.

"The power of this duality is that difficult questions on one side can become much easier on the other side," Liu says.

To make an accurate translation, the researchers first looked for a black hole whose surrounding matter would resemble the random turbulence of a superfluid. They eventually settled on a type of black hole surrounded by a chaotic swirl of matter and electromagnetism.

The researchers studied the complex physics of this particular type of black hole, solving equations to characterize its behavior. They then applied models of holographic duality to translate the black hole's physics to the turbulent flows of superfluids.

"It's like there exists a decoder ring that takes information about a black hole and maps it onto information about fluid mechanics," Chesler says.

From the cosmos to fluid mechanics

Through their calculations, the researchers were able to characterize how energy flows through a superfluid in turbulent flows. In ordinary fluids, energy flows differently depending on whether the fluid is flowing on a flat 2-D surface or in a deeper body, such as a river. Scientists have previously found that 2-D liquids tend to start out as relatively small structures, but as they flow, their energy combines to form larger and larger structures -- similar to the way tornadoes can merge to form hurricanes.

In contrast, liquids in 3-D behave in the opposite manner, starting as large structures and spinning out into smaller structures, much like the dispersal of cigarette smoke.

In the case of superfluids, Chesler and his colleagues found that in 2-D, superfluids behave unlike ordinary fluids in 2-D, but more like ordinary fluids in 3-D, dispersing energy at smaller and smaller scales.

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Mechanism behind squids' and octopuses' ability to change color revealed

July 25, 2013 — Color in living organisms can be formed two ways: pigmentation or anatomical structure. Structural colors arise from the physical interaction of light with biological nanostructures. A wide range of organisms possess this ability, but the biological mechanisms underlying the process have been poorly understood.

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Two years ago, an interdisciplinary team from UC Santa Barbara discovered the mechanism by which a neurotransmitter dramatically changes color in the common market squid, Doryteuthis opalescens. That neurotransmitter, acetylcholine, sets in motion a cascade of events that culminate in the addition of phosphate groups to a family of unique proteins called reflectins. This process allows the proteins to condense, driving the animal's color-changing process.

Now the researchers have delved deeper to uncover the mechanism responsible for the dramatic changes in color used by such creatures as squids and octopuses. The findings -- published in the Proceedings of the National Academy of Science, in a paper by molecular biology graduate student and lead author Daniel DeMartini and co-authors Daniel V. Krogstad and Daniel E. Morse -- are featured in the current issue of The Scientist.

Structural colors rely exclusively on the density and shape of the material rather than its chemical properties. The latest research from the UCSB team shows that specialized cells in the squid skin called iridocytes contain deep pleats or invaginations of the cell membrane extending deep into the body of the cell. This creates layers or lamellae that operate as a tunable Bragg reflector. Bragg reflectors are named after the British father and son team who more than a century ago discovered how periodic structures reflect light in a very regular and predicable manner.

"We know cephalopods use their tunable iridescence for camouflage so that they can control their transparency or in some cases match the background," said co-author Daniel E. Morse, Wilcox Professor of Biotechnology in the Department of Molecular, Cellular and Developmental Biology and director of the Marine Biotechnology Center/Marine Science Institute at UCSB.

"They also use it to create confusing patterns that disrupt visual recognition by a predator and to coordinate interactions, especially mating, where they change from one appearance to another," he added. "Some of the cuttlefish, for example, can go from bright red, which means stay away, to zebra-striped, which is an invitation for mating."

The researchers created antibodies to bind specifically to the reflectin proteins, which revealed that the reflectins are located exclusively inside the lamellae formed by the folds in the cell membrane. They showed that the cascade of events culminating in the condensation of the reflectins causes the osmotic pressure inside the lamellae to change drastically due to the expulsion of water, which shrinks and dehydrates the lamellae and reduces their thickness and spacing. The movement of water was demonstrated directly using deuterium-labeled heavy water.

When the acetylcholine neurotransmitter is washed away and the cell can recover, the lamellae imbibe water, rehydrating and allowing them to swell to their original thickness. This reversible dehydration and rehydration, shrinking and swelling, changes the thickness and spacing, which, in turn, changes the wavelength of the light that's reflected, thus "tuning" the color change over the entire visible spectrum.

"This effect of the condensation on the reflectins simultaneously increases the refractive index inside the lamellae," explained Morse. "Initially, before the proteins are consolidated, the refractive index -- you can think of it as the density -- inside the lamellae and outside, which is really the outside water environment, is the same. There's no optical difference so there's no reflection. But when the proteins consolidate, this increases the refractive index so the contrast between the inside and outside suddenly increases, causing the stack of lamellae to become reflective, while at the same time they dehydrate and shrink, which causes color changes. The animal can control the extent to which this happens -- it can pick the color -- and it's also reversible. The precision of this tuning by regulating the nanoscale dimensions of the lamellae is amazing."

Another paper by the same team of researchers, published in Journal of the Royal Society Interface, with optical physicist Amitabh Ghoshal as the lead author, conducted a mathematical analysis of the color change and confirmed that the changes in refractive index perfectly correspond to the measurements made with live cells.

A third paper, in press at Journal of Experimental Biology, reports the team's discovery that female market squid show a set of stripes that can be brightly activated and may function during mating to allow the female to mimic the appearance of the male, thereby reducing the number of mating encounters and aggressive contacts from males. The most significant finding in this study is the discovery of a pair of stripes that switch from being completely transparent to bright white.

"This is the first time that switchable white cells based on the reflectin proteins have been discovered," Morse noted. "The facts that these cells are switchable by the neurotransmitter acetylcholine, that they contain some of the same reflectin proteins, and that the reflectins are induced to condense to increase the refractive index and trigger the change in reflectance all suggest that they operate by a molecular mechanism fundamentally related to that controlling the tunable color."

Could these findings one day have practical applications? "In telecommunications we're moving to more rapid communication carried by light," said Morse. "We already use optical cables and photonic switches in some of our telecommunications devices. The question is -- and it's a question at this point -- can we learn from these novel biophotonic mechanisms that have evolved over millions of years of natural selection new approaches to making tunable and switchable photonic materials to more efficiently encode, transmit, and decode information via light?"

In fact, the UCSB researchers are collaborating with Raytheon Vision Systems in Goleta to investigate applications of their discoveries in the development of tunable filters and switchable shutters for infrared cameras. Down the road, there may also be possible applications for synthetic camouflage.

Other members of the UCSB interdisciplinary research team involved in these discoveries include Elizabeth Eck, Erica Pandolfi, Aaron T. Weaver, and Mary Baum.

This research was supported by the Office of Naval Research via a Multidisciplinary University Research Initiative award and an Army Research Office grant through UCSB's Institute for Collaborative Biotechnologies. As well, use was made of UCSB Materials Research Laboratory central facilities and equipment, which are supported by a grant from the National Science Foundation.

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Asus polishes the display for Nexus 7 tablet Tablets Eyes On Android

2013/07/25

Asus Nexus 7 As well as Android 4.3, Google has announced a new Nexus tablet, the Nexus 7 to be precise. Asus is the manufacturer partnering for this release, for what is claimed to be the “world’s highest-resolution 7-inch tablet” with a 323ppi display. Google writes:

Together with ASUS, we took what you loved about the original Nexus 7 and made it even better. The first thing you’ll notice is the sharpness of the screen: the 323 pixels packed into every inch of the screen makes it the world’s highest-resolution 7-inch tablet. It’s lighter than ever, with more than nine hours of HD video playback and 10 hours of web browsing or reading. Nexus 7 now features stereo speakers and virtual surround sound from Fraunhofer (the inventors of the MP3 format), giving you rich and immersive audio.

The Nexus 7 is priced at $229, and will be available in the US from July 30 – Google says “more countries coming soon!”. An LTE version will be following.

Read more about the device, and register interest, on the Nexus website »

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