Tuesday, April 20, 2010


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In an analysis of the past 1.2 million years, UC Santa Barbara geologist Lorraine Lisiecki discovered a pattern that connects the regular changes of the Earth's orbital cycle to changes in the Earth's climate. The finding is reported in the scientific journal Nature Geoscience.

Lisiecki performed her analysis of climate by examining ocean sediment cores. These cores come from 57 locations around the world. By analyzing sediments, scientists are able to chart the Earth's climate for millions of years in the past. Lisiecki's contribution is the linking of the climate record to the history of the Earth's orbit.

It is known that the Earth's orbit around the sun changes shape every 100,000 years. The orbit becomes either more round or more elliptical at these intervals. The shape of the orbit is known as its "eccentricity." A related aspect is the 41,000-year cycle in the tilt of the Earth's axis.

Glaciation of the Earth also occurs every 100,000 years. Lisiecki found that the timing of changes in climate and eccentricity coincided. "The clear correlation between the timing of the change in orbit and the change in the Earth's climate is strong evidence of a link between the two," said Lisiecki. "It is unlikely that these events would not be related to one another."

Besides finding a link between change in the shape of the orbit and the onset of glaciation, Lisiecki found a surprising correlation. She discovered that the largest glacial cycles occurred during the weakest changes in the eccentricity of Earth's orbit –– and vice versa. She found that the stronger changes in the Earth's orbit correlated to weaker changes in climate. "This may mean that the Earth's climate has internal instability in addition to sensitivity to changes in the orbit," said Lisiecki.

She concludes that the pattern of climate change over the past million years likely involves complicated interactions between different parts of the climate system, as well as three different orbital systems. The first two orbital systems are the orbit's eccentricity, and tilt. The third is "precession," or a change in the orientation of the rotation axis.

(Photo: UCSB)

University of California, Santa Barbara


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Seeking a way to confirm that patients have taken their medication, University of Florida engineering researchers have added a tiny microchip and digestible antenna to a standard pill capsule. The prototype is intended to pave the way for mass-produced pills that, when ingested, automatically alert doctors, loved ones or scientists working with patients in clinical drug trials.

“It is a way to monitor whether your patient is taking their medication in a timely manner,” said Rizwan Bashirullah, UF assistant professor in electrical and computer engineering.

Such a pill is needed because many patients forget, refuse or bungle the job of taking their medication. This causes or exacerbates medical problems, spurs hospitalizations or expensive medical procedures and undercuts clinical trials of new drugs.

The American Heart Association calls patients’ failure to follow prescription regimens “the number one problem in treating illness today.” Studies have found, for example, that patients with chronic diseases normally take only about half their prescribed medications. According to the American Heart Association, 10 percent of hospital admissions result from patients not following the guidelines on their prescriptions. Other studies have found that not taking medication properly results in 218,000 deaths annually.

So-called “medication compliance” is a big problem for clinical trials, Bashirullah said, because failure to take experiment drugs skews studies’ results or renders them meaningless. As a result, researchers often require visual confirmation of participants taking pills, an extremely expensive proposition if hundreds or thousands of people are participating in the trials.

“The idea is to use technology to do this in a more seamless, much less expensive way,” Bashirullah said.

Bashirullah, doctoral student Hong Yu, UF materials science and engineering Professor Chris Batich and Neil Euliano of Gainesville-based Convergent Engineering designed and tested a system with two main parts.

One part is the pill, a standard white capsule coated with a label embossed with silvery lines. The lines comprise the antenna, which is printed using ink made of nontoxic, conductive silver nanoparticles. The pill also contains a tiny microchip, one about the size of a period.

When a patient takes the pill, it communicates with the second main element of the system: a small electronic device carried or worn by the patient – for now, a stand-alone device, but in the future perhaps built into a watch or cell phone. The device then signals a cell phone or laptop that the pill has been ingested, in turn informing doctors or family members.

Bashirullah said the pill needs no battery because the device sends it power via imperceptible bursts of extremely low-voltage electricity. The bursts energize the microchip to send signals relayed via the antenna. Eventually the patient’s stomach acid breaks down the antenna – the microchip is passed through the gastrointestinal tract — but not before the pill confirms its own ingestion.

“The vision of this project has always been that you have an antenna that is biocompatible, and that essentially dissolves a little while after entering the body,” Bashirullah said.

The team has successfully tested the pill system in artificial human models, as well as cadavers. Researchers have also simulated stomach acids to break down the antenna to learn what traces it leaves behind. Bashirullah said those tests had determined the amount of silver retained in the body is tiny, less than what people often receive from common tap water.

(Photo: Ray Carson, UF News Bureau)

University of Florida


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For the first time, a team of astronomers has imaged the eclipse of the star Epsilon Aurigae by its mysterious, less luminous companion star. Very high-resolution images, never before possible, have been published online today in the journal Nature Letters. Epsilon Aurigae has been known since 1821 as an eclipsing double star system, but astronomers have struggled for many decades trying to decipher the clues to what was causing these eclipses, which happen every 27 years. The new image largely settles the matter: the eclipse is caused by a disk of material, probably similar to the state of our solar system 4.5 billion years ago as the planets began to form around our own infant sun.

The research team includes astronomers from the University of Denver, the University of Michigan, and Georgia State University with Denver graduate student Brian Kloppenborg serving as the first author on the Nature Letters paper.

Seeing this eclipse in detail has only now become possible. Kloppenborg's research advisor, University of Denver Professor Robert Stencel, describes this long-awaited discovery, "Having studied this star on and off since my postdoctoral days in the 1980s during its last eclipse, it is very satisfying to finally resolve some of the long-standing questions associated with this famous star."

The image was obtained using the interferometric technique, an old idea that incorporates computer control and laser connections among multiple telescopes to achieve signal equivalent to one giant telescope.

"To capture the detail on Epsilon Aurigae, we've made use of the biggest optical telescope on earth, the 330-meter (1,083 feet) diameter CHARA Array atop Mount Wilson, California," said Stencel. To comprehend its size, note that 100 meters (328 feet) is roughly the length of a football field.

The CHARA Array is a collection of six telescopes, spread out over the grounds of Mount Wilson Observatory, in which individual beams of light are brought together using extraordinarily precise beam combiners to synthesize a giant telescope hundreds of meters across. The array is owned by Georgia State University (GSU) and operated by GSU's Center for High Angular Resolution Astronomy. In routine operations since 2005, the CHARA Array has already produced a number of astronomical "firsts" though its ability to produce images of unprecedented resolution.

CHARA Director and GSU Regents' Professor Harold McAlister noted, "The size of Epsilon Aurigae in these amazing new images is equivalent to the angular size of an 11-point font letter 'o' seen from a distance of more than 150 kilometers (93 miles)."

Key to the imaging success of the CHARA Array is the Michigan Infrared Combiner (MIRC), created by University of Michigan Professor John Monnier. MIRC enables the type of multi-telescope linkage that is required to produce such images and enables more of the potential of CHARA to be used in parallel for image reconstruction. The combination of MIRC at CHARA has already produced the first image ever made of a normal star other than the sun, as well as the first images of a double star system in which one component is shedding matter to its companion star.

The images of Epsilon Aurigae show the intrusion of an apparently wedge-shaped structure across the face of a huge star, nearly 150 times the size of our sun. The images of the star and wedge-shaped structure show the direct motion over a month, yielding a measurement of the relative masses of the components. The primary star itself is thought to be in a very interesting phase of its own evolution, turning out to be less massive than the eclipsing disk and the star hidden at the center of that disk.

Independently, Stencel and collaborators from the California Institute of Technology and Kitt Peak National Observatory had assembled data to show the disk contains a large, hot star known as a B5V object, describing its mass and temperature. This prior work set the stage to then evaluate the mass of the disk itself, based on the CHARA images.

It turns out the disk is as wide as the orbit of Jupiter, nearly as tall as the orbit of Earth, but contains a little less than the mass of Earth altogether. "This is a fairly direct measurement of characteristics of a disk, in contrast to the usual disk studies where indirect evidence and lots of assumptions are the only means of characterization available. With some luck, we can obtain more CHARA images this year and develop the equivalent of an MRI scan of the entire disk through eclipse," noted Stencel.

Because astronomers hadn't observed much light from the faint companion, the prevailing opinion labeled it a smaller star orbited edge-on by a thick disk of dust. The theory held that the disk's orbit must be in precisely the same plane as the dark object's orbit around the brighter star, and all of this had to be occurring in the same plane as Earth's vantage point. This would be an unlikely alignment, but it explained observations. The new images show that this is indeed the case. A geometrically-thin, dark, dense, but partially-translucent cloud can be seen passing in front of Epsilon Aurigae.

"This really shows that the basic paradigm was right, despite the slim probability," Monnier said. "It kind of blows my mind that we could capture this. There's no other system like this known. On top of that, it seems to be in a rare phase of stellar life. And it happens to be so close to us! It's extremely fortuitous."

The star began its current eclipse during late summer 2009, seemingly affecting us on Earth as well. Stencel and Kloppenborg had applied for CHARA observing time earlier that year. While waiting for the star to become well-placed in the nighttime sky, Mother Nature had other plans: the Station Fire broke out in the San Gabriel Mountains around Mount Wilson in late August 2009, consuming hundreds of thousands of acres of National Forest over several weeks and shutting down operations at the observatory.

For weeks thereafter, access to Mount Wilson was closed to all, and only with great fortune were the November and December 2009 observations accomplished. Not long after that, in early 2010, with the arrival of the rainy season, extensive mudslides destroyed sections of the access road to Mount Wilson. Despite the challenges, with road repairs underway, there is hope for more observations during this rare but long eclipse, which will last for the rest of 2010.

"We have witnessed the initial phases of this eclipse, and we certainly don't want to miss the rest of the show," said Kloppenborg.

(Photo: Robert Stencel, University of Denver)

The National Science Foundation


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A team of archaeologists from the University of Chicago's Oriental Institute, along with a team of Syrian colleagues, is uncovering new clues about a prehistoric society that formed the foundation of urban life in the Middle East prior to invention of the wheel.

The mound of Tell Zeidan in the Euphrates River Valley near Raqqa, Syria, which had not been built upon or excavated for 6,000 years, is revealing a society rich in trade, copper metallurgy and pottery production. Artifacts recently found there are providing more support for the view that Tell Zeidan was among the first societies in the Middle East to develop social classes according to power and wealth.

Tell Zeidan dates from between 6000 and 4000 B.C., and immediately preceded the world's first urban civilizations in the ancient Middle East. It is one of the largest sites of the Ubaid culture in northern Mesopotamia.

Thus far, archaeologists have unearthed evidence of this society's trade in obsidian and production and development of copper processing, as well as the existence of a social elite that used stone seals to mark ownership of goods and culturally significant items.

"The project addresses questions not only of how such societies emerged but how they were sustained and flourished," said John Yellen, program director for archaeology in the National Science Foundation's (NSF) Social, Behavioral & Economic Sciences directorate. NSF supports the University of Chicago's research.

Covering about 31 acres, Tell Zeidan was situated where the Balikh River joins the Euphrates River in modern-day Syria. The location was at the crossroads of major, ancient trade routes in Mesopotamia that followed the course of the Euphrates River valley. The Ubaid period lasted from about 5300 to 4000 B.C.

"This enigmatic period saw the first development of widespread irrigation, agriculture, centralized temples, powerful political leaders and the first emergence of social inequality as communities became divided into wealthy elites and poorer commoners," said Gil Stein, director of the Oriental Institute and a leader of the expedition.

"The research also is important because it provides insight into how complex societies, based on linkages which extended across hundreds of miles, developed," said Yellen, noting the distance travelled for raw materials needed for many of the Tell Zeidan artifacts.

For example, copper ore was carried by workers from sources near modern-day Diyarbakir, Turkey, about 185 to 250 miles away, then smelted at Tell Zeidan to produce metal tools and other implements.

One of the most remarkable finds was a stone stamp seal depicting a deer, Stein said. The seal was about two inches by two-and-a-half inches and was carved from a red stone not native to the area. A similar seal design was found 185 miles to the east near Mosul in northern Iraq.

"The existence of very elaborate seals with near-identical motifs at such widely distant sites suggests that in this period, high-ranking elites were assuming leadership positions across a very broad region, and those dispersed elites shared a common set of symbols and perhaps even a common ideology of superior social status," said Stein.

Stein said the location's potential for further discoveries is so great the project is likely to last for decades.

(Photo: Gil Stein, Oriental Institute, University of Chicago)

National Science Foundation


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Underwater canyons have long been considered important habitats for marine life, but until recently, only canyons on continental margins had been intensively studied. Researchers from Hawaii Pacific University (HPU) and the Universtiy of Hawaii at Manoa (UHM) have now conducted the first extensive study of canyons in the oceanic Hawaiian Archipelago and found that these submarine canyons support especially abundant and unique communities of megafauna (large animals such as fish, shrimp, crabs, sea cucumbers, and sea urchins) including 41 species not observed in other habitats in the Hawaiian Islands The research is published in the March issue of the journal Marine Ecology.

The researchers used both visual and video surveys from 36 submersible dives (using UHM's Hawaii Undersea Research Laboratory submersibles Pisces IV and Pisces V) to characterize slope and canyon communities of animals at depths of 350-1500 meters along the margins of four islands of the Hawaiian Archipelago. The coastlines of Oahu and Molokai were selected as examples of high, mountainous islands with large supplies of terrestrial and marine organic matter which can be exported down slopes and canyons to provide food to deep-sea communities. Nihoa Island and Maro Reef were chosen to represent low islands and atolls that are likely to export less organic matter to feed the deep-sea fauna.

Eric Vetter, the lead author of this paper and a Professor of Marine Biology from HPU, had previously studied four canyon systems off the coast of California and found that the productive waters along southern California had resulted in the delivery and accumulation of substantial amounts of organic material. "Craig Smith (Professor of Oceanography at UHM and co-author of this study) and I wondered if the same dramatic contrast in benthic food resources between canyon and non-canyon settings seen in continental margins would also occur on tropical oceanic islands," says Vetter. "We reasoned that the low productivity in tropical regions would result in reduced source material for organic enrichment in canyons and that steep bathymetry combined with curving coastlines would limit the area over which material could be transported to individual canyons. On the other hand we thought that any amount of organic enrichment might have a measureable effect given the very low background productivity."

Canyon systems can enhance abundance and diversity of marine life by providing more varied and complex physical habitats, and by concentrating organic detritus moving along shore and downslope. On most continental margins, the continental shelf and slope are dominated by soft, low-relief sediments; in contrast, canyons crossing these margins often have steep slopes, rocky outcrops, and faster currents that can support fauna with diverse habitat requirements. The margins of oceanic islands generally are steeper than continental margins, making the physical contrast between canyon and non-canyon habitats potentially less dramatic than along continents. "We wanted to learn, given all of these differences, if tropical oceanic islands would be regions of special biological significance, particularly in terms of productivity and biodiversity," says Vetter.

To conduct the research off Oahu, Molokai, and Maro Reef, Vetter, Smith and UHM Doctoral student Fabio De Leo took turns in the submersibles counting marine life on the ocean bottom using visual transects and recording results into a voice recorder. The survey off of Nihoa Island was conducted using a video recorder attached to the submersible. The results of the 36 surveys showed that the highly mobile megafauna (like fish, sharks, shrimp and squid) were much more abundant in the canyons than on the open slopes at all depths studied. This suggests that canyons provide an especially good habitat for mobile species that are able to feed on accumulated organic matter but can escape the physical disturbances in canyons resulting from high currents and mobile sediments (e.g., migrating sand ripples).

"Perhaps the biggest surprise of this study was the large number of species, 41, that we found only in canyon habitats", says Smith. "This suggests that canyons support a substantial specialized fauna that would not exist in the Hawaiian archipelago in the absence of canyons. Thus, submarine canyons are contributing uniquely to biodiversity in the islands and merit careful attention for environmental protection and management."

The elevated abundance and biodiversity of megafauna (especially highly mobile species of fish and crustaceans) in canyons suggests that those environments experience greater food availability, and may provide critical habitat for commercially important bottom fish and invertebrate stocks. "From a conservation standpoint, these regions would be ideal candidates to become Marine Protected Areas (MPAs), especially due to the higher turnover of species diversity when compared to regular slopes", says De Leo. "If we prove that the animals are using the canyons as a feeding ground because the organic debris accumulates there and nowhere else outside the canyons, that's another argument for an MPA". Adds Smith, "if we allow the Hawaiian canyons to be overexploited or impacted by human activities such as dredge-spoil dumping, there is likely to be a significant drop in biodiversity in the deep waters of Hawaii. Clearly, canyon habitats merit special attention for inclusion in Hawaiian MPAs."

Future studies by the team of the Hawaiian canyon fauna include analyses of the stable carbon and nitrogen isotopes in shrimp, urchins and other bottom feeders to identify their main food sources. Because different potential food sources, such as land plants, seafloor algae and phytoplankton, often have different stable isotope "signatures", these analyses will help the researchers to understand what exactly is fueling the rich animal assemblages in the canyons. "We need biochemical proof that the canyons are really channeling this type of material," says DeLeo. "Carbon and nitrogen isotopic signatures could tell the difference between the detrital plant material and the phytoplankton material pools, so you can see if the animal in the canyon is eating phytoplankton cells coming from pelagic production or macroalgae coming from the coast."

Vetter says that their current research is also formulating conceptual models that will allow the researchers to predict which features associated with different canyon systems act to influence biological patterns including animal abundance and diversity. "DeLeo's PhD research will include data on megafauna and macrofauna (smaller animals living in the sediments) patterns in canyons along the U.S. West Coast, Hawaii, and New Zealand, which should make important strides here."

(Photo: SOEST)

Universtiy of Hawaii at Manoa


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Obstructive sleep apnea is associated with an increased risk of stroke in middle-aged and older adults, especially men, according to new results from a landmark study supported by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health. Overall, sleep apnea more than doubles the risk of stroke in men. Obstructive sleep apnea is a common disorder in which the upper airway is intermittently narrowed or blocked, disrupting sleep and breathing during sleep.

Researchers from the Sleep Heart Health Study (SHHS) report that the risk of stroke appears in men with mild sleep apnea and rises with the severity of sleep apnea. Men with moderate to severe sleep apnea were nearly three times more likely to have a stroke than men without sleep apnea or with mild sleep apnea. The risk from sleep apnea is independent of other risk factors such as weight, high blood pressure, race, smoking, and diabetes.

They also report for the first time a link between sleep apnea and increased risk of stroke in women. Obstructive Sleep Apnea Hypopnea and Incident Stroke: The Sleep Heart Health Study, was published online March 25 ahead of print in the American Journal of Respiratory and Critical Care Medicine.

Stroke is the second leading cause of death worldwide. "Although scientists have uncovered several risk factors for stroke – such as age, high blood pressure and atrial fibrillation, and diabetes – there are still many cases in which the cause or contributing factors are unknown," noted NHLBI Acting Director Susan B. Shurin, M.D. "This is the largest study to date to link sleep apnea with an increased risk of stroke. The time is right for researchers to study whether treating sleep apnea could prevent or delay stroke in some individuals."

Conducted in nine medical centers across the United States, the SHHS is the largest and most comprehensive prospective, multi-center study on the risk of cardiovascular disease and other conditions related to sleep apnea. In the latest report, researchers studied stroke risk in 5,422 participants aged 40 years and older without a history of stroke. At the start of the study, participants performed a standard at-home sleep test, which determined whether they had sleep apnea and, if so, the severity of the sleep apnea.

Researchers followed the participants for an average of about nine years. They report that during the study, 193 participants had a stroke – 85 men (of 2,462 men enrolled) and 108 women (out of 2,960 enrolled).

After adjusting for several cardiovascular risk factors, the researchers found that the effect of sleep apnea on stroke risk was stronger in men than in women. In men, a progressive increase in stroke risk was observed as sleep apnea severity increased from mild levels to moderate to severe levels. In women, however, the increased risk of stroke was significant only with severe levels of sleep apnea.

The researchers suggest that the differences between men and women might be because men are more likely to develop sleep apnea at younger ages. Therefore, they tend to have untreated sleep apnea for longer periods of time than women. "It's possible that the stroke risk is related to cumulative effects of sleep apnea adversely influencing health over many years," said Susan Redline, M.D., MPH, professor of medicine, pediatrics, and epidemiology and biostatistics, at Case Western Reserve University in Cleveland and lead author of the paper.

"Our findings provide compelling evidence that obstructive sleep apnea is a risk factor for stroke, especially in men," noted Redline. "Overall, the increased risk of stroke in men with sleep apnea is comparable to adding 10 years to a man's age. Importantly, we found that increased stroke risk in men occurs even with relatively mild levels of sleep apnea."

"Research on the effects of sleep apnea not only increases our understanding of how lapses of breathing during sleep affects our health and well being, but it can also provide important insight into how cardiovascular problems such as stroke and high blood pressure develop," noted Michael J. Twery, Ph.D., director of the NIH National Center on Sleep Disorders Research, an office administered by the NHLBI.

The new results support earlier findings that have linked sleep apnea to stroke risk. SHHS researchers have also reported that untreated sleep apnea is associated with an increased risk of high blood pressure, heart attack, irregular heartbeats, heart failure, and death from any cause. Other studies have also linked untreated sleep apnea with overweight and obesity and diabetes. It is also linked to excessive daytime sleepiness, which lowers performance in the workplace and at school, and increases the risk of injuries and death from drowsy driving and other accidents.

More than 12 million American adults are believed to have sleep apnea, and most are not diagnosed or treated. Treatments to restore regular breathing during sleep include mouthpieces, surgery, and breathing devices, such as continuous positive airway pressure, or CPAP. In people who are overweight or obese, weight loss can also help.

These treatments can help improve breathing and reduce the severity of symptoms such as loud snoring and excessive daytime sleepiness, thereby improving sleep-related quality of life and performance at work or in school. Randomized clinical trials to test whether treating sleep apnea lowers the risk of stroke, other cardiovascular diseases, or death are needed.

"We now have abundant evidence that sleep apnea is associated with cardiovascular risk factors and diseases. The next logical step is to determine if treating sleep apnea can lower a person's risk of these leading killers," said Redline. "With stimulus funds, our research group is now developing the additional research and resources to begin answering this important question."

National Heart, Lung, and Blood Institute


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The vivid colors and designs animals use to interact with their environments have awed and inspired since before people learned to draw on the cave wall.

But how different creatures in the animal kingdom — from colorful birds and reef fish to butterflies and snakes — make and deploy their artful designs is one of nature's deepest secrets. Now, however, a team of researchers from the Howard Hughes Medical Institute at the University of Wisconsin-Madison has exposed the fine details of how animals make new body ornamentation from scratch. The work, the result of years-long and laborious experimentation, is published (April 7) in the journal Nature.

"How do you generate complex patterns? This is a question that has interested biologists for a really long time," says Sean Carroll, a UW-Madison molecular biologist and the senior author of the Nature report. "In this case, we at first had no clue. But now we think we've figured out all the key ingredients and we believe they are generally applicable (to many animals)."

The new study is important because it is the first to provide concrete evidence for a long-hypothesized system for generating animal color patterns, be they stripes, spots or any of the myriad designs animals use to camouflage themselves or find a mate. In particular, the Wisconsin group is the first to identify a color-inducing morphogen, a diffusible protein that tells certain cells to make pigment.

To ferret out the secret of animal ornamentation, Carroll and his UW-Madison colleagues, Thomas Werner and Shigeyuki Koshikawa, and Thomas Williams, now at the University of Dayton, pried loose the molecular details and evolutionary history of how a species of North American fruit fly, Drosophila guttifera, generates a complex pattern of 16 wing spots.

The group discovered a morphogen, a protein present in embryonic tissue and encoded by a gene known as Wingless, which seems to be a linchpin of wing decoration. Late in wing development, the Wingless morphogen is produced and diffuses through tissue where it prompts cells in certain areas of the wing to make pigment. "It acts by triggering responding cells to do things, in this case make color," Carroll explains.

In Drosophila guttifera, the morphogen acts in proximity to existing physical landmarks such as the intersections of veins and cross veins on the wing. The positioning of the spots, in short, is dictated by these pre-existing patterns, notes Carroll: "The Wingless molecule is deployed in this species at specific points in time and in specific places — the places where the spots are going to be."

The role of the Wingless morphogen was detailed by the painstaking genetic manipulation of flies that took three years and the injection of nearly 20,000 fly embryos to accomplish. Complicating the project is the fact that Drosophila guttifera is little used in research and its genome has not been sequenced.

However, by inserting the Wingless gene into different parts of the fly's genome, the team was able to successfully manipulate the decoration of the fly's wing, creating stripes instead of spots, and patterns not seen in nature. "We can make custom flies," notes Carroll. By manipulating the gene, "we can make striped flies out of spotted flies."

In addition to working out the molecular details of how the fly colors its wings, Carroll's group was also able to deduce the evolutionary history of wing coloring in Drosophila guttifera.

In short, says Carroll, the patterns found on the wings of Drosophila guttifera came about through the fly's manipulation of the Wingless gene: "It evolved by simply turning this gene on in places where it hadn't been on before."

Although the study was conducted in a lowly fruit fly, the principles uncovered by Carroll's group, he argues, very likely apply to many animals, everything from butterflies to boa constrictors. "This is animal color patterning, how they are generated, how they evolved."

(Photo: Nicolas Gompel and Sean Carroll)

University of Wisconsin-Madison


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Four billion years ago, our then stripling sun radiated only 70 to 75 percent as much energy as it does today. Other things on Earth being equal, with so little energy reaching the planet's surface, all water on the planet should have been frozen. But ancient rocks hold ample evidence that the early Earth was awash in liquid water – a planetary ocean of it. So something must have compensated for the reduced solar output and kept Earth's water wet.

To explain this apparent paradox, a popular theory holds there must have been higher concentrations of greenhouse gases in the atmosphere, most likely carbon dioxide, which would have helped retain a greater proportion of the solar energy that arrived.

But a team of earth scientists including researchers from Stanford have analyzed the mineral content of 3.8-billion-year-old marine rocks from Greenland and concluded otherwise.

"There is no geologic evidence in these rocks for really high concentrations of a greenhouse gas like carbon dioxide," said Dennis Bird, professor of geological and environmental sciences.

Instead, the team proposes that the vast global ocean of early Earth absorbed a greater percentage of the incoming solar energy than today's oceans, enough to ward off a frozen planet. Because the first landmasses that formed on Earth were small – mere islands in the planetary sea – a far greater proportion of the surface of was covered with water than today.

The study is detailed in a paper published in the April 1 issue of Nature. Bird and Norman Sleep, a professor of geophysics, are among the four authors. The lead author is Minik Rosing, a geology professor at the Natural History Museum of Denmark, University of Copenhagen, and a former Allan Cox Visiting Professor at Stanford's School of Earth Sciences.

The crux of the theory is that because oceans are darker than continents, particularly before plants and soils covered landmasses, seas absorb more sunlight.

"It's the same phenomenon you will experience if you drive to Wal-Mart on a hot day and step out of your car onto the asphalt," Bird said. "It's really hot walking across the blacktop until you get onto the white concrete sidewalk."

Another key component of the theory is in the clouds. "Not all clouds are the same," Bird said.

Clouds reflect sunlight back into space to a degree, cooling Earth, but how effective they are depends on the number of tiny particles available to serve as nuclei around which the water droplets can condense. An abundance of nuclei means more droplets of a smaller size, which makes for a denser cloud and a greater reflectivity, or albedo, on the part of the cloud.

Most nuclei today are generated by plants or algae and promote the formation of numerous small droplets. But plants and algae didn't flourish until much later in Earth's history, so their contribution of potential nuclei to the early atmosphere circa 4 billion years ago would have been minimal. The few nuclei that might have been available would likely have come from erosion of rock on the small, rare landmasses of the day and would have caused larger droplets that were essentially transparent to the solar energy that came in to Earth, according to Bird.

"We put together some models that demonstrate, with the slow continental growth and with a limited amount of clouds, you could keep water above freezing throughout geologic history," Bird said.

"What this shows is that there is no faint early sun paradox," said Sleep.

The modeling work was done with climate modeler Christian Bjerrum, a professor in the Department of Geography and Geology, University of Copenhagen, also a co-author of the Nature paper.

The rocks that the team analyzed are a type of marine sedimentary rock called a banded iron formation. It is characterized by thin alternating bands of quartz, magnetite, an iron-rich mineral, and siderite, a mineral with a high carbon content, but also some iron.

"Any rock carries a memory of the environment in which it formed," Rosing said. "These ancient rocks that are about 3.8 billion years old, they actually carry a memory of the composition of the ocean and atmosphere at the time when they were deposited."

The critical part of the rocks' memory was the banding and that iron was found chemically bound to oxygen rather than CO2 in the bands. The alternating bands would only have been deposited if the carbon dioxide content of the atmosphere kept shifting back and forth across a threshold that controlled which mineral was deposited. But that also meant that the amount of carbon dioxide couldn't stray too far from that threshold. If there had been either substantially more or less carbon dioxide, only one of the minerals would have been laid down.

Another constraint on early carbon dioxide levels came from life itself.

In the days before photosynthetic organisms spread across the globe, most life forms were methanogens, single-celled organisms that consumed hydrogen and carbon dioxide and produced methane as a digestive byproduct.

But to thrive, methanogens need a balanced diet. If the concentration of either of their foodstuffs veers too far below their preferred proportions, methanogens won't survive. Their dietary restrictions, specifically the minimum concentration of hydrogen, provided another constraint on the concentration of carbon dioxide in the atmosphere, and it falls well below the level needed for a greenhouse effect sufficient to compensate for a weak early sun.

"The conclusion from all this is that we can't solve a faint sun paradox and also satisfy the geologic and metabolic constraints by having high carbon dioxide values," Bird said.

But the theory of a lower Earthly albedo meets those constraints.

"The lower albedo counterbalanced the fainter sun and provided Earth with clement conditions without the need for dramatically higher concentrations of greenhouse gasses in the atmosphere," Rosing said.

(Photo: L.A. Cicero)

Stanford University


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Physicists at Harvard University have found that a high-voltage nanotube can cause cold atoms to spiral inward under dramatic acceleration before disintegrating violently. Their experiments, the first to demonstrate something akin to a black hole at atomic scale, are described in the current issue of the journal Physical Review Letters.

"On a scale of nanometers, we create an inexorable and destructive pull similar to what black holes exert on matter at cosmic scales," says Lene Vestergaard Hau, Mallinckrodt Professor of Physics and of Applied Physics at Harvard. "As importantly for scientists, this is the first merging of cold-atom and nanoscale science, and it opens the door to a new generation of cold atom experiments and nanoscale devices."

Hau and co-authors Anne Goodsell, Trygve Ristroph, and Jene A. Golovchenko laser-cooled clouds of one million rubidium atoms to just a fraction of a degree above absolute zero. The physicists then launched this millimeter-long atomic cloud towards a suspended carbon nanotube, located some two centimeters away and charged to hundreds of volts.

The vast majority of the atoms passed right by the wire, but those that came within a micron of it -- roughly 10 atoms in every million-atom cloud -- were inescapably attracted, reaching high speeds as they spiraled toward the nanotube.

"From a start at about 5 meters per second, the cold atoms reach speeds of roughly 1,200 meters per second, or more than 2,700 miles per hour, as they circle the nanotube," says Goodsell, a graduate student on the project and now a postdoctoral researcher in physics at Harvard. "As part of this tremendous acceleration, the temperature corresponding to the atoms' kinetic energy increases from 0.1 degrees Kelvin to thousands of degrees Kelvin in less than a microsecond."

At this point, the speeding atoms separate into an electron and an ion rotating in parallel around the nanowire, completing each orbit in just a few trillionths of a second. The electron eventually gets sucked into the nanotube via quantum tunneling, causing its companion ion to shoot away -- repelled by the strong charge of the 300-volt nanotube -- at a speed of roughly 26 kilometers per second, or 59,000 miles per hour.

The entire experiment was conducted with great precision, allowing the scientists unprecedented access to both cold-atom and nanoscale processes.

"Cold-atom and nanoscale science have each provided exciting new systems for study and applications," says Golovchenko, Rumford Professor of Physics and Gordon McKay Professor of Applied Physics at Harvard. "This is the first experimental realization of a combined cold atom-nanostructure system. Our system demonstrates sensitive probing of atom, electron, and ion dynamics at the nanoscale."

The single-walled carbon nanotube used in these researchers' successful experiment was dubbed "Lucy," and its contributions are acknowledged in the Physical Review Letters paper. The nanotube was grown by chemical vapor deposition across a 10-micron gap in a silicon chip that provides the nanowire with both mechanical support and electrical contact.

"From the atom's point of view, the nanotube is infinitely long and thin, creating a singular effect on the atom," Hau says.

(Photo: Anne Goodsell and Tommi Hakala/Harvard University)

Harvard University




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