lunes, 22 de marzo de 2010
A new sensor technology promises to make cellphone cameras good enough to use for wedding photos.
InVisage Technologies, a Menlo Park, California-based company, has developed an image sensor using quantum dots instead of silicon. The company claims its technology increases sensor performance by more than four times.
“We have all heard ‘Gee, I wish the camera on my iPhone was better,’” says InVisage’s President and CEO Jess Lee. “But the heart of the problem is in the heart of the camera, which is the sensor.”
Most cameras today used either a CCD (charged-couple device) sensor or a CMOS (complementary metal-oxide-semiconductor)-based sensor. The silicon in current image sensors has a light absorbing efficiency of only about 50 percent, says Lee.
Reducing efficiency still further are the layers of copper or aluminum circuitry laid on top of the silicon. The metal blocks the light, so only a fraction of a sensor’s silicon is exposed to light.
Replacing silicon with quantum dots could change all that. A quantum dot is a nanocrystal made of a special class of semiconductors. It allows manufacturers to have a very high degree of control over its conductive properties, and is about 90% efficient at absorbing light, according to Lee.
The quantum dots are usually suspended in fluid. InVisage takes a vial of these and spins it onto a layer of silicon, then adds the required metal circuitry to create a new type of sensor that it is calling QuantumFilm.
invisage-chart3In addition to the increased sensitivity, InVisage’s technology allows the metal circuits to be placed underneath the quantum film, where they don’t block the light.
“This is entirely different from the type of image sensors that we have right now,” says Tom Hausken, director with market research firm Strategies Unlimited. “Usually you see incremental improvements in sensor design, but these guys have made a a significant change in the process.”
Quantum dots can be made from silicon, tellurides or sulphides. InVisage won’t reveal exactly which material it is using.
As opposed to silicon’s indirect band gap, quantum dots have a direct band gap. Lee says Invisage can tune the Dots’ band gap much more efficiently than silicon so it is more sensitive to visible light, ultraviolet and even infrared waves.
In the last few years, manufacturers have been touting megapixels as the measure of a camera’s prowess. But the true measure of picture quality is not as much in the megapixels but in the size of the sensor used in the device.
To capture the light, imaging sensors need to have as much as area as possible. Powerful DSLR cameras have an imaging sensor that’s about a third of the size of a business card, while camera phones sport sensors that are only about a quarter inch wide (see top photo). Smaller sensors mean less light sensitivity for each pixel on the sensor, and that translates into lower-quality images.
Quantum dot-based sensors won’t be more expensive than traditional CMOS-based sensors, promises Lee. InVisage says it will have samples ready for phone manufacturers by the end of the year and the sensors could be in phones by mid next-year.
Though quantum dots are commercially produced by other manufacturers, they have never been used on image sensors before, says Hausken.
“Mostly people have looked to use it in displays, solar cells and as identification markers,” he says. “So we will have to see how effective and reliable it is as a sensor.”
Towers that help carry electricity from one place to another, like these in France, are not a pretty sight. But there’s also an invisible problem--the power lost due to electrical resistance. Superconducting technology may be a solution.
Few people welcome the sight of those steel lattice towers that help carry electricity from one place to another, but there’s a deeper problem on the lines that’s invisible.
Conventional aluminum or copper power lines have a certain amount of natural resistance to the flow of electricity, so some energy is lost as heat during transmission. About 7 to 10 percent of the power put on the U.S. grid is wasted due to electrical resistance. That may not sound like much, but it’s enough juice to run 14 cities the size of New York.
So experts and entrepreneurs are looking at the potential of superconducting materials. These materials would allow power to zip along for miles with zero electrical resistance, but there’s a catch. The super-cables would have to be super-chilled--kept at a temperature of about -350 degrees Fahrenheit (-212 degrees Celsius)--in order to work their magic.
Scientists at the Electric Power Research Institute (EPRI), an electric industry-funded nonprofit focused on technology, said in a new report that a superconducting cable system could be ready for commercial development within a decade. Moreover, they said it’s an important technology to consider, given the challenge of greater reliance on renewable energy. Areas with great potential for wind and solar power are often in remote regions far from population centers. Super-chilled wires could efficiently shuttle thousands of megawatts of electricity from distant sites to cities, said the EPRI report.
"The reason the superconductor [system] is beautiful is it likes big,” explained Steven Eckroad, a co-author of the report. “It likes high power."
Another advantage of such a system is it would be buried underground. Proponents say that out-of-sight transmission projects would face less opposition than the traditional power towers. This month, for example, the Los Angeles Department of Water and Power dropped plans for an 85-mile, U.S.$800 million transmission line designed to convey electricity from remote solar, geothermal and nuclear plants in the southeastern California desert and Arizona. The project faced fierce opposition from environmentalists opposed to erecting 16-foot (5-meter) pylons across the Big Morongo Canyon Preserve, the San Bernardino National Forest and other preservation areas.
Of course, buried superconducting transmission lines would face their own challenges. The wires would be encased in liquid-nitrogen filled tubes to keep them cool. Refrigerators also would have to be interspersed every few miles.
Then, there’s the power conversion issue. A superconducting line would use direct current (DC), good for transmitting power over long distances. But the nation’s power system now relies on alternating current (AC) for safe low-voltage transmission of power to homes and businesses. Improvements in AC-DC power conversion make long-distance DC transmission more feasible, the EPRI report said. Some power, however, would be lost at the terminals as electricity is converted from AC to DC and back again.
But the amount of power lost when transmitting electricity on a DC superconducting system would be less than 3 percent, according to Jack McCall, director of business development at American Superconductor, a Devens, Massachusetts firm that has been working to develop a system very similar to the one EPRI envisions.
Although the EPRI study cites cost as an obstacle to deploying superconducting technology as a competitive alternative to conventional power lines, McCall said that his company’s system will cost between $8 to $13 million per mile — or about the same as a conventional overhead power line today.
American Superconductor aims to prove the technology, and at the same time tackle a vexing U.S. power grid problem. Electricity can’t go cross-country because the nation has three separate power grids—one for the East, one for the West and one for Texas. American Superconductor’s proposed Tres Amigas project, on a 22.5-square-mile (58-square-kilometer) site in Clovis, New Mexico, would unite the three grids. The project, which could cost more than $1 billion, would be privately financed and is awaiting federal approval. If it goes forward, it would be the first large-scale test of superconducting transmission technology.
"By the end of 2014, the U.S. will have a 5,000-megawatt superconductor cable running in DC that utility companies can come and look at and touch and feel and poke and prod and say, ‘Yeah, this actually works,’" McCall said.
But there are other ideas for moving power. Electric Pipeline, a start-up company in Cambridge, New York, says it has a technology for moving DC power long distances underground without superconducting material. Instead, it would use wires that contain up to 50 times more aluminum as conventional overhead wires.
Roger Faulkner, Electric Pipeline chief executive, said there would be some electricity lost, but less than on conventional power lines, and at a price that makes it a competitive alternative.
Another option, of course, is to try to get by without moving power at all. The Los Angeles power department, having abandoned its cross-desert transmission plan, is looking at constructing a huge 80-square-mile (207-square-kilometer) solar array in the dry bed of Owens Lake—the body of water drained early last century by the city aqueduct. Among the advantages city officials cite: It is close to existing power transmission.
Like a zombie clawing its way out of the grave, a new dinosaur species was discovered when scientists spotted a hand bone protruding from a cliff in the Gobi desert of Inner Mongolia, paleontologists have announced.
Called Linheraptor exquisitus, the new dinosaur is a raptor, a type of two-legged meat-eater, that lived during the late Cretaceous period in what is now northeastern China .
"We were looking at these very tall red sandstone walls that were all abraded by the wind, and I saw this claw sticking out of the side of the cliff," recalls Jonah Choiniere, a grad student at George Washington University in Washington D.C. who found the fossil on a dig in 2008.
The claw wasn't protruding much: Less than a fingertip's worth of the bone was exposed. But further investigation revealed "bone after bone," Choiniere said, until the team had unearthed a nearly complete skeleton—one of the most complete raptor fossils ever found.
It was fortunate the team found the fossil when they did, Choiniere added, because once exposed, the dinosaur would have been rapidly lost to the elements.
"Erosion is very quick there," Choiniere said. "The whole specimen could have been turned to powdered bone dust in a few years, easily."
New Dinosaur Had Killer Claw
Stretching about 8 feet (2.5 meters) and weighing 55 pounds (25 kilograms), Linheraptor would have been a fast, agile animal that preyed on small horned dinosaurs related to Triceratops, which also lived the area.
It's unclear how this particular Linheraptor died, but one idea is that it suffocated beneath a sand avalanche.
Sand dunes in the region are notoriously unstable, Choiniere said, and an earthquake, a storm, or the minute shifting of sand grains could have been enough to trigger a collapse.
"It's great for paleontologists, but it must have been terrible to be trapped in it," said Choiniere, whose study of the fossil appears online today in the journal Zootaxa.
Finding such a well-preserved new raptor is important, because it helps reveal the evolution of raptors from smaller, birdlike dinosaurs, said Tom Holtz, a paleontologist at the University of Maryland who was not involved in the study. (Take a dinosaur quiz.)
For instance, like its more famous relative the Velociraptor, Linheraptor possessed a large "killing claw" on each foot, which it may have used to bring down prey. (Related: "Jurassic Park Raptors Had Feathers, Fossil Suggests.")
This claw "is fairly big in Linheraptor, but it's not as big as in Velociraptor and Deinoychus," another famous raptor, Holtz noted. The claw that Choiniere initially spotted, however, was not Linheraptor's killing claw, but another claw on the dinosaur's hand.
Linheraptor also stands out from its raptor relatives because it has an unusually large lobe in a sinus cavity called the antorbital fenestra, a unique feature that will require further study to explain.
"It's not a missing link," Holtz added of Linheraptor. "But it does represent a grade of raptor between the earliest forms, such as those we know from early Cretaceous China, and the classic late forms, such as Velociraptor."
The find is also remarkable, he said, since "the team gave it the species name exquisitus, and it certainly fits that, because it's a wonderful specimen."
More than three million years ago, the ancestors of modern humans were still spending a considerable amount of their lives in trees, but something new was happening.
David Raichlen, an assistant professor in the University of Arizona School of Anthropology, and his colleagues at the University at Albany and City University of New York's Lehman College have developed new experimental evidence indicating that these early hominins were walking with a human-like striding gait as long as 3.6 million years ago.
The results of their research appears in PLoS ONE, a journal from the Public Library of Science.
A trackway of fossil footprints preserved in volcanic ash deposited 3.6 million years ago was uncovered in Laetoli, Tanzania, more than 30 years ago. The significance of those prints for human evolution has been debated ever since. The most likely individuals to have produced these footprints, which show clear evidence of bipedalism, or walking on two legs, would have been members of the only bipedal species alive in the area at that time, Australopithecus afarensis. That species includes "Lucy," whose skeletal remains are the most complete of any individual A. afarensis found to date.
A number of features in the hips, legs, and back of this group indicate that they would have walked on two legs while on the ground. But the curved fingers and toes as well as an upward-oriented shoulder blade provide solid evidence that Lucy and other members of her species also would have spent significant time climbing in trees.
This morphology differs distinctly from our own genus, Homo, who abandoned arboreal life around 2 million years ago and irrevocably committed to human-like bipedalism. Since the Laetoli tracks were discovered, scientists have debated whether they indicate a modern human-like mode of striding bipedalism, or a less-efficient type of crouched bipedalism more characteristic of chimpanzees whose knees and hips are bent when walking on two legs.
To resolve this, Raichlen and his colleagues devised the first biomechanical experiment explicitly designed to address this question. The team built a sand trackway in Raichlen's motion capture lab at the UA and filmed human subjects walking across the sand. The subjects walked both with normal, erect human gaits and then with crouched, chimpanzee-like gaits. Three-dimensional models of the footprints were collected by biological anthropologist Adam Gordon using equipment brought from his Primate Evolutionary Morphology Laboratory at the University at Albany.
The researchers examined the relative depth of footprints at the heel and toe, and found that depths are about equal when made by a person walking with an erect gait. In contrast, the toe print is much deeper than the heel print when produced by a crouched gait, a product of the timing of weight transfer over the length of the foot.
"Based on previous analyses of the skeletons of Australopithecus afarensis, we expected that the Laetoli footprints would resemble those of someone walking with a bent knee, bent hip gait typical of chimpanzees, and not the striding gait normally used by modern humans," Raichlen said. "But to our surprise, the Laetoli footprints fall completely within the range of normal human footprints."
The fossil footprints at Laetoli preserve a remarkably even depth at the toe and heel, just like those of modern humans. "This more human-like form of walking is incredibly energetically efficient, suggesting that reduced energy costs were very important in the evolution of bipedalism prior to the origins of our own genus, Homo," Raichlen said.
If the Laetoli footprints were made by Lucy's species, as most scientists agree to be the case, these experimental results have interesting implications for the timing of evolutionary events.
"What is fascinating about this study is that it suggests that, at a time when our ancestors had an anatomy well-suited to spending a significant amount of time in the trees, they had already developed a highly efficient, modern human-like mode of bipedalism," said Adam Gordon.
"The fossil record indicates that our ancestors did not make a full-time commitment to leaving the trees and walking on the ground until well over a million years after these (Laetoli) prints were made. The fact that partially tree-dwelling animals, like Lucy, had such a remarkably modern gait is a testament to the importance of energetic efficiency in moving around on two legs," Gordon said.
martes, 16 de marzo de 2010
The sharpest images yet taken by the Mars Express spacecraft of Mars’ tiny moon Phobos reveal features as small as 14.5 feet across, the European Space Agency announced March 15.
Some of the new images taken March 7 during one of several recent close flybys of the moon home in on the proposed landing site for a Russian mission, Phobos-Grunt (meaning Phobos soil), that is expected to touch down on the moon next year.
During the three flybys on March 7, 10 and 13, researchers measured the moon’s tug on Mars Express by examining changes in the frequency of radio signals beamed by the spacecraft to Earth. The frequency shifts indicate that the craft has sped up or slowed down by a few millimeters per second due to the moon’s gravity.
When combined with images, the gravity data may provide new clues about Phobos’ composition and origin. According to one theory, Mars captured the moon from the nearby asteroid belt. Alternatively, Phobos may have formed where it now resides and could be a direct leftover from the planet-making era. With dimensions of 17 by 14 by 12 miles, the moon is the larger of Mars’ two moons.
The Mars Express flybys, which happen every five months, may also determine if Phobos is a fragile pile of rocky fragments stuck together — what planetary scientists refer to as a rubble pile — or solid through and through, says Mars Express scientist Gerhard Neukum of the Free University of Berlin. He notes that due to orbital maneuvers that had to be performed on relatively short notice, scientists missed the opportunity to take even higher-resolution images with another camera on Mars Express, which would have revealed features on Phobos as small as a meter across.
The craft will make two more passes by Phobos before the end of March, but they will not come as close as the March 7 flyby.
Naked, beheaded, and tangled, the bodies of 51 young males found in the United Kingdom have been identified as brutally slain Vikings, archaeologists announced Friday.
The decapitated skeletons—their heads stacked neatly to the side—were uncovered in June 2009 in a thousand-year-old execution pit near the southern seaside town of Weymouth .
Already radio-carbon dating results released in July had shown the men lived between A.D. 910 and 1030, a period when the English fought—and often lost—battles against Viking invaders. But until now it hadn't been clear who the headless bodies had belonged to.
Analysis of teeth from ten of the dead—who were mostly in their late teens and early 20s—indicates the raiding party had been gathered from different parts of Scandinavia, including one person thought to have come from north of the Arctic Circle. The new study, led by Jane Evans of the U.K.'s NERC Isotope Geosciences Laboratory, investigated telltale chemical markers called isotopes, which can reveal a person's geographic origins.
Oxygen isotopes from drinking water, for example, become fixed in people's teeth as they age. Since isotope ratios vary with climate, Evans could tell that the had all been raised in much cooler regions than Britain.
"The values these individuals gave us could not be British," Evans said, but the ratios do match those from Norway and Sweden.
In addition, nitrogen-isotope readings showed the men enjoyed a meaty, high-protein diet—similar to readings from remains from the same period found in Sweden.
"What's fascinating about these findings is that Vikings are renowned for their pillaging, ransacking, and raping," Evans said.
"But here we've got real evidence that it was the other way round: Anglo-Saxons rounded up these Vikings and executed them."
Vikings Found With Hacked Heads, Naked Bodies
Many of the skeletons have deep cut marks to the skull, jaw, and neck. This suggests the men were war captives whose heads were savagely hacked off, said David Score of Oxford Archaeology, leader of the preconstruction survey that found the Vikings' execution pit.
"The majority seem to have taken multiple blows," he noted.
Other injuries hint that some of the slaughtered attempted to shield themselves from their executioners' blows. For instance, the hand of one victim had its fingers sliced through, Score said.
The heads were neatly piled to one side of the pit, perhaps as a victory display.
Unusually, no trace of clothing has been found, indicating the men were buried naked.
Even if only their weapons and valuables had been taken, "we should have found bone buttons and things like that, but to date we've got absolutely nothing," Score said.
Aside from their injuries, the headless Vikings "look like a healthy, robust, very strong, very masculine group of young males," he added. "It's your classic sort of warrior."
Vikings Forced to Surrender?
The burial's prominent location on a hilltop by the ancient main road to Weymouth also points to the victims being Vikings, Score said.
"Locations like this are classic sites for executions [by British-born warriors] in late Saxon and medieval times," he said. "If you're a Viking raider, you're much more likely to leave people where you killed them in the town or on the beach."
What's more, the new isotope findings suggest that the slain men had much more diverse origins than would be expected among soldiers from the Saxons' other enemies, such as ethnic Danes in northern Britain, tooth-study leader Evans noted.
Even before the new results were released, Kim Siddorn, author of Viking Weapons and Warfare, had thought the dead were Vikings.
"They had left their ship, walked inland, ran into an unusually well-organized body of Saxons, and were probably forced to surrender," Siddorn speculated in July.
Despite the Vikings' brutal reputation, there was actually little to differentiate Vikings and early English warriors on the battlefield, said Siddorn, also a founder of Regia Anglorum, a historical-reenactment society.
"You would find it very difficult to tell the difference between a Viking and a Saxon if they stood in front of you in war gear," he said. Both used spears as their primary weapons, with swords and axes as backups, Siddorn added.
But Vikings usually had surprise and, in some cases, numbers on their side. "Whilst the Vikings were no better than the Saxons at fighting, they did come by the shipload," he said.
"During the height of the Viking raids, it's reasonable to say it was unsafe to live anywhere within 20 miles [32 kilometers] of the coast."
A team of researchers from Carnegie Museum of Natural History has described a new genus and species of carnivorous amphibian from western Pennsylvania. The fossil skull, found in 2004 near Pittsburgh International Airport, was recovered from rocks deposited approximately 300 million years ago during the Late Pennsylvanian Period. Named Fedexia striegeli, it is one of only a very few relatively large amphibian fossils to display evidence of a predominantly terrestrial (land-based) life history so early in geologic time.
The rocks where Fedexia was found are nearly 20 million years older than the localities of its fossil relatives, suggesting that the expansion and diversification of this group occurred much earlier than had been recognized previously. The full paper are being released in Annals of Carnegie Museum, Volume 78, Number 4, 15 March 2010.
Fedexia was described on the basis of a remarkably well-preserved fossil skull. Unlike similar discoveries, the five-inch-long (11.5 cm) fossil skull remained three-dimensional over time because it was never crushed by rocks that were deposited above it. Fedexia striegeli was named for FedEx, the corporation that owns the land on which the fossil was found, and for amateur discoverer Mr. Adam Striegel, who originally found the specimen on a geology field trip while a senior at the University of Pittsburgh.
Climate Change Likely a Factor
Fedexia represents an extinct group of amphibians called Trematopidae that lived about 70 million years before the first dinosaurs appeared. Unlike almost all other Pennsylvanian Period amphibians, which did not often venture out of the water, this rare, diverse group lived mostly on land, returning to the water perhaps only to mate or lay eggs. The trematopids also provide evidence of the earliest vertebrate life in North America adapted to a mostly terrestrial existence. Their success may have been a result of a long-term, global trend toward drier, warmer conditions that reached its climax near the end of the Pennsylvanian Period.
At the time of Fedexia's preservation, the earth's climate was in a period of transition. Immense glaciers in Earth's southern polar region produced rapidly fluctuating global climates. Western Pennsylvania, which was near the equator at that time, experienced tremendous amounts of rain. Swamps which would later develop into coal developed, and amphibians -- which are dependent on moist conditions -- flourished; in fact, the Pennsylvanian Period is known as the "Age of Amphibians."
Gradually, however, as an increasing amount of the planet's water became locked up in polar ice, the sea level dropped and more land was exposed. Vast regions of the earth became drier and warmer, including the region that would become western Pennsylvania. The coal swamps and lakes dried up, and many of the coal-forming plants became extinct. It was at this time that amphibian populations in what would become the Pittsburgh region shifted from mainly aquatic to mainly terrestrial, paralleling the change in climate from tropical to semi-arid. Vertebrates that had already begun adapting to terrestrial life -- including amphibians closely related to Fedexia striegeli -- became far more abundant, widespread, and diverse than their relatives who were still dependent upon cooler, moist environments.
The large number of trematopid amphibians appearing in the fossil record in the Permian Period suggests that climate change was a major factor in the diversification of terrestrial amphibians. The appearance of Fedexia during the Pennsylvanian Period -- 20 million years earlier than the Permian -- was an early indicator of the diversification that was to come. Co-author David Brezinski states, "The one-to-one correspondence between this early appearance of trematopids in the fossil record and the preservation of dry climate indicators in the surrounding rock units suggests that this is a climatically driven immigration and/or origination event."
Although the appearance of Fedexia and other highly terrestrial vertebrates in the fossil record seems sudden, this is undoubtedly misleading. They or their close relatives had probably already existed for a few million years, occupying upland regions where conditions for fossil preservation were not optimal. However, the climatic change to drier, warmer conditions led to an explosive dispersal of terrestrial vertebrates to coastal regions and lowlands -- including western Pennsylvania -- where accumulating sediments increased the chances for fossil preservation. Because western Pennsylvania is the "type stratigraphic sequence" -- or best record -- of sediments deposited during the Pennsylvanian geologic period, this region offers exceptional opportunities for future discoveries of terrestrial vertebrate fossils of this age.
A Remarkably Preserved Fossil
Fedexia striegeli was described on the basis of a remarkably well-preserved fossil skull. Unlike many other fossil finds, the fossil skull remained three-dimensional and did not suffer post-mortem crushing over time by the compaction of rock formations above it. The preservation of the skull is so precise that even the middle-ear bone, known as the stapes, remains perfectly intact and in its correct position, a very rare discovery in fossils.
Owing to the remarkable preservation of the skull, Fedexia was easily identified as a trematopid, mainly by the hallmark feature of the group, a greatly elongated external nasal opening that is partially subdivided into fore and aft portions. Some scientists speculate that the posterior division held a gland -- similar to that in some modern-day reptiles and marine birds -- that rid the body of excess salt, or perhaps enhanced the sense of smell; either function would have been an advantage for a terrestrial existence. Fedexia is the first trematopid to be found in Pennsylvania, and only the third in the world of Late Pennsylvanian age, the group's earliest appearance. Now that the immediate study of Fedexia striegeli is complete, the fossil has been permanently preserved for future research in the Carnegie Museum of Natural History vertebrate paleontology collection. Casts of the skull will be given to FedEx Corporation and to Mr. Striegel.
According to co-author David S Berman, "What is particularly amazing about this discovery is that it was made by an amateur who had no prior experience in recognizing vertebrate fossils in the rock, a talent that usually takes years to develop."
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An international team led by Yale University has, for the first time, measured the mass of a type of supernova thought to belong to a unique subclass and confirmed that it surpasses what was believed to be an upper mass limit. Their findings, which appear online and will be published in an upcoming issue of the Astrophysical Journal, could affect the way cosmologists measure the expansion of the universe.
Cosmologists use Type Ia supernovae -- the violent explosions of dead cores of stars called white dwarfs -- as a kind of cosmic ruler to measure distances to the supernovae's host galaxies and, as such, to understand the past and future expansion of the universe and explore the nature of dark energy. Until recently, it was thought that white dwarfs could not exceed what is known as the Chandrasekhar limit, a critical mass equaling about 1.4 times that of the Sun, before exploding in a supernova. This uniform limit is a key tool in measuring distances to supernovae.
Since 2003, four supernovae have been discovered that were so bright, cosmologists wondered whether their white dwarfs had surpassed the Chandrasekhar limit. These supernovae have been dubbed the "super-Chandrasekhar" supernovae.
Now Richard Scalzo of Yale, as part of a collaboration of American and French physicists called the Nearby Supernova Factory, has measured the mass of the white dwarf star that resulted in one of these rare supernovae, called SN 2007if, and confirmed that it exceeded the Chandrasekhar limit. They also discovered that the unusually bright supernova had not only a central mass, but a shell of material that was ejected during the explosion as well as a surrounding envelope of pre-existing material. The team hopes this discovery will provide a structural model with which to understand the other supermassive supernovae.
Using observations from telescopes in Chile, Hawaii and California, the team was able to measure the mass of the central star, the shell and the envelope individually, providing the first conclusive evidence that the star system itself did indeed surpass the Chandrasekhar limit. They found that the star itself appears to have had a mass of 2.1 times the mass of the Sun (plus or minus 10 percent), putting it well above the limit.
Being able to measure masses for all parts of the star system tells the physicists about how the system may have evolved -- a process that is currently poorly understood. "We don't really know much about the stars that lead to these supernovae," Scalzo said. "We want to know more about what kind of stars they were, and how they formed and evolved over time."
Scalzo believes there's a good chance that SN 2007if resulted from the merging of two white dwarfs, rather than the explosion of a single white dwarf and hopes to study the other super-Chandrasekhar supernovae to determine whether they, too, could have involved a merger of two white dwarfs.
Theorists continue to explore how stars with masses above the Chandrasekhar limit, which is based on a simplified star model, could exist without collapsing under their own weight. Either way, a subclass of supernovae governed by different physics could have a dramatic effect on the way cosmologists use them to measure the expansion of the universe.
"Supernovae are being used to make statements about the fate of the universe and our theory of gravity," Scalzo said. "If our understanding of supernovae changes, it could significantly impact of our theories and predictions."
Other Yale authors of the paper include Charles Baltay and David Rabinowitz.
The film "Avatar" isn't the only 3-D blockbuster making a splash this winter. A team of scientists from Houston's Texas Medical Center has unveiled a new technique for growing 3-D cell cultures, a technological leap from the flat petri dish that could save millions of dollars in drug-testing costs.
The research is reported in Nature Nanotechnology.
The 3-D technique is easy enough for most labs to set up immediately. It uses magnetic forces to levitate cells while they divide and grow. Compared with cell cultures grown on flat surfaces, the 3-D cell cultures tend to form tissues that more closely resemble those inside the body.
"There's a big push right now to find ways to grow cells in 3-D because the body is 3-D, and cultures that more closely resemble native tissue are expected to provide better results for preclinical drug tests," said study co-author Tom Killian, associate professor of physics at Rice. "If you could improve the accuracy of early drug screenings by just 10 percent, it's estimated you could save as much as $100 million per drug."
For cancer research, the "invisible scaffold" created by the magnetic field goes beyond its potential for producing cell cultures that are more reminiscent of real tumors, which itself would be an important advance, said co-author Wadih Arap, professor in the David H. Koch Center at The University of Texas M.D. Anderson Cancer Center.
To make cells levitate, the research team modified a combination of gold nanoparticles and engineered viral particles called "phage" that was developed in the lab of Arap and Renata Pasqualini, also of the Koch Center. This targeted "nanoshuttle" can deliver payloads to specific organs or tissues.
"A logical next step for us will be to use this additional magnetic property in targeted ways to explore possible applications in the imaging and treatment of tumors," Arap said.
The 3-D modeling raises another interesting long-term possibility. "This is a step toward building better models of organs in the lab," Pasqualini said.
The new technique is an example of the innovation that can result when experts come together from disparate fields. Killian studies ultracold atoms and uses finely tuned magnetic fields to manipulate them. He had been working with Rice bioengineer Robert Raphael for several years on methods to use magnetic fields to manipulate cells. So when Killian's friend Glauco Souza, then an Odyssey Scholar studying with Arap and Pasqualini, mentioned one day that he was developing a gel that could load cancer cells with magnetic nanoparticles, it led to a new idea.
"We wondered if we might be able to use magnetic fields to manipulate the cells after my gels put magnetic nanoparticles into them," said Souza, who left M.D. Anderson in 2009 to co-found Nano3D Biosciences (www.n3dbio.com), a startup that subsequently licensed the technology from Rice and M.D. Anderson.
The nanoparticles in this case are tiny bits of iron oxide. These are added to a gel that contains phage. When cells are added to the gel, the phage causes the particles to be absorbed into cells over a few hours. The gel is then washed away, and the nanoparticle-loaded cells are placed in a petri dish filled with a liquid that promotes cell growth and division.
In the new study, the researchers showed that by placing a coin-sized magnet atop the dish's lid, they could lift the cells off the bottom of the dish, concentrate them and allow them to grow and divide while they were suspended in the liquid.
A key experiment was performed in collaboration with Jennifer Molina, a graduate student in the laboratory of Maria-Magdalena Georgescu, an M.D. Anderson associate professor in neuro-oncology and also a co-author, in which the technique was used on brain tumor cells called glioblastomas. The results showed that cells grown in the 3-D medium produced proteins that were similar to those produced by gliobastoma tumors in mice, while cells grown in 2-D did not show this similarity.
Souza said that Nano3D Biosciences is conducting additional tests to compare how the new method stacks up against existing methods of growing 3-D cell cultures. He said he is hopeful that it will provide results that are just as good, if not better, than longstanding techniques that use 3-D scaffolds.
Raphael, a paper co-author, associate professor in bioengineering and a member of Rice's BioScience Research Collaborative, said, "The beauty of this method is that it allows natural cell-cell interactions to drive assembly of 3-D microtissue structures. The method is fairly simple and should be a good point of entry in 3-D cell culturing for any lab that's interested in drug discovery, stem cell biology, regenerative medicine or biotechnology."
Other co-authors include Daniel Stark and Jeyarama Ananta, both of Rice; Carly Levin of Nano3D Biosciences; and Michael Ozawa, Lawrence Bronk, Jami Mandelin, James Bankson and Juri Gelovani, all of M.D. Anderson.
The research was funded by M.D. Anderson's Odyssey Scholar Program, the Department of Defense's Breast Cancer Research Program, the National Science Foundation, the Packard Foundation, the Gillson-Longenbaugh Foundation, AngelWorks, the National Institutes of Health and the National Cancer Institute.
martes, 2 de marzo de 2010
A prehistoric snake is poised to make a meal of a newly hatched dinosaur in this life-size reconstruction of 67-million-year-old fossils unearthed in India.
Before the snake could strike, though, a surge of mud—washed out of a nearby channel by heavy rains—smothered the nest, killing both snake and prey and entombing them together.
The snake's interrupted meal offers a rare glimpse into the feeding behavior of ancient snakes—and the dangers newborn dinosaurs faced, said Jeffrey Wilson, a co-author of the new study on the discovery, to be published in this week's issue of the journal PLoS Biology.
"It's actually one of the very few examples that we have of anything other than a dinosaur eating a dinosaur," Wilson said.
First Fossil Evidence of Snakes Eating Dinosaurs
The snake's interrupted meal offers a rare glimpse into the feeding behavior of ancient snakes and the dangers that newborn dinosaurs faced, said study team member Jeffrey Wilson, a University of Michigan paleontologist.
"It's actually one of the very few examples that we have of anything other than a dinosaur eating a dinosaur," said Wilson, whose work was funded in part by a grant from the National Geographic Society's Committee for Research and Exploration.
Scientists have long known that some dinosaurs were egg snatchers, and recent fossil evidence suggests mammals also dined on young dinosaurs.
Dinosaur Devourer Was Lizard-like Snake
Modern large-mouthed snakes, such as boas and anacondas, can eat large prey because their jaw joints are positioned well behind their skulls, allowing the snakes to open their mouths very wide.
But the new species of prehistoric snake has a smaller mouth opening, like a lizard's. The snake's jaw joints were no farther aft than the back of the skull itself—earning it the name Sanejeh indicus, or "ancient-gaped one from India."
Even without giant jaws, though, Sanejeh "could swallow big things"—such as baby dinosaurs— simply because the snake itself was big, Wilson said.
"If the snake had evolved the machinery that modern snakes have, it would have been able to take even bigger things," he said.
Sanejeh did have a key adaptation also found in modern snakes: an upper jaw that can move independently of the lower jaw.
This jaw structure would have allowed Sanejeh to wriggle, mouth first, over struggling prey in an alternating side-to-side motion familiar to anyone who has ever tried to squeeze into a tight pair of jeans.
The snake may also have been capable of squeezing dinosaur eggs open to get to the hatchlings inside.
But because modern snakes tend not to attack inanimate objects, the researchers believe ancient snaked behaved similarly, so it's likely that the young dinosaur had already hatched before the snake arrived.
Young Dinosaurs Outgrew Snake Predators?
Due to the apparent victim's young age, the team couldn't determine the dinosaur's species. But they do know it was a sauropod—a giant long-necked plant-eater (sauropod picture). But what kind?
Previously discovered fossils suggest that titanosaurs—sauropods that grew to lengths of 65 feet (20 meters) or longer—roamed the region around the nest, leading the researchers to suggest the hatchling too was a titanosaur.
The fossils of Sanejeh and its apparent prey were discovered in western India's Gujarat Province in 1984. After being mislabeled as containing only a hatchling sauropod, the fossil trove was separated before finally being reunited in 2004 and sent to the University of Michigan for study.
To avoid being eaten by snakes and other predators, sauropods, in general, probably underwent growth spurts in their early years, the study says.
"By the time this sauropod was about a year old, we think it would have been out of the range of Sanejeh," Wilson said.
Dinosaur-Eating Snakes Not Surprising?
"The discovery is very interesting, and I think the study's conclusions are reasonable about the snake possibly feeding on hatchling dinosaurs," said Brad Moon, a herpetologist at the University of Louisiana at Lafayette, who was not involved in the new research.
Moon does think, though, that Sanejeh may have been attracted to the dinosaur nest for other reasons. For example, the snake might have simply been seeking shelter or pursuing some other animal, he said.
And while certainly spectacular, the revelation of a snake attack in progress is less than surprising, scientifically speaking, according to George Zug, curator emeritus of amphibians and reptiles at the National Museum of Natural History in Washington, D.C.
Though Zug agrees the new fossils are the first proof of snakes eating dinosaurs, he said the behavior wouldn't shock anyone familiar with the ways of modern snakes.
Snakes eat not only mammals and birds but also other reptiles, such as frogs and even other snakes, said Zug, who was not involved in the new study.
"So it's not out of the question that they would be preying on little dinosaurs."
Pictured in a January 7 satellite image—about a month before a massive collision—the Luxembourg-size iceberg B9B floats toward the hundred-mile-long (160-kilometer-long) floating "tongue" of Antarctica’s Mertz Glacier. The tongue is already weakened by growing rifts on both sides of its midsection.
The 60-mile-long (97-kilometer-long) B9B iceberg smashed into the Mertz Glacier Tongue on February 12 or 13—creating a second, 48-mile-long (78-kilometer-long) iceberg, according to a the Antarctic Climate and Ecosystems Cooperative Research Centre (ACECRC).
The two icebergs are now floating at sea, side by side, and debris from the breakup is filling the once clear waterway beside Mertz Glacier (map). Prior to the separation, iceberg B9B had spent nearly 20 years floating close to the glacier.
Some experts warn the newly floating ice could seriously impact ocean circulation—causing unknown consequences for Earth's climate and the region’s marine animals.