Monday, September 7, 2009

MAP CHARACTERIZES ACTIVE LAKES BELOW ANTARCTIC ICE

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Lakes in Antarctica, concealed under miles of ice, require scientists to come up with creative ways to identify and analyze these hidden features. Now, researchers using space-based lasers on a NASA satellite have created the most comprehensive inventory of lakes that actively drain or fill under Antarctica's ice. They have revealed a continental plumbing system that is more dynamic than scientists thought.

"Even though Antarctica's ice sheet looks static, the more we watch it, the more we see there is activity going on there all the time," said Benjamin Smith of the University of Washington in Seattle, who led the study.

Unlike most lakes, Antarctic lakes are under pressure from the ice above. That pressure can push melt water from place to place like water in a squeezed balloon. The water moves under the ice in a broad, thin layer, but also through a linked cavity system. This flow can resupply other lakes near and far.

Understanding this plumbing is important, as it can lubricate glacier flow and send the ice speeding toward the ocean, where it can melt and contribute to sea level change. But figuring out what's happening beneath miles of ice is a challenge.

Researchers led by Smith analyzed 4.5 years of ice elevation data from NASA's Ice, Cloud and land Elevation satellite (ICESat) to create the most complete inventory to date of changes in the Antarctic plumbing system. The team has mapped the location of 124 active lakes, estimated how fast they drain or fill, and described the implications for lake and ice-sheet dynamics in the Journal of Glaciology.

For decades, researchers flew ice-penetrating radar on airplanes to "see" below the ice and infer the presence of lakes. In the 1990s, researchers began to combine airborne- and satellite-based data to observe lake locations on a continent-wide scale.

Scientists have since established the existence of about 280 "subglacial" lakes, most located below the East Antarctic ice sheet. But those measurements were a snapshot in time, and the question remained as to whether lakes are static or dynamic features. Were they simply sitting there collecting water?

In 2006 Helen Fricker, a geophysicist at the Scripps Institution of Oceanography, La Jolla, Calif., used satellite data to first observe subglacial lakes on the move. Working on a project to map the outline of Antarctica's land mass, Fricker needed to differentiate floating ice from grounded ice. This time it was laser technology that was up to the task. Fricker used ICESat's Geoscience Laser Altimeter System and measured how long it took a pulse of laser light to bounce of the ice and return to the satellite, from which she could infer ice elevation. Repeating the measurement over a course of time revealed elevation changes.

Fricker noticed, however, a sudden dramatic elevation change -- over land. It turned out this elevation change was caused by the filling and draining of some of Antarctica's biggest lakes.

"Sub-ice-sheet hydrology is a whole new field that opened up through the discovery of lakes filling and draining on relatively short timescales and involving large volumes of water," said Robert Bindschadler, a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Md., who has used ICESat data in other studies of Antarctica. "ICESat gets the credit for enabling that discovery."

But were active lakes under the ice a common occurrence or a fluke?

To find out, Ben Smith, Fricker and colleagues extended their elevation analysis to cover most of the Antarctic continent and 4.5 years of data from ICESat's Geoscience Laser Altimeter System (GLAS). By observing how ice sheet elevation changed between the two or three times the satellite flew over a section every year, researchers could determine which lakes were active. They also used the elevation changes and the properties of water and ice to estimate the volume change.

Only a few of the more than 200 previously identified lakes were confirmed active, implying that lakes in East Antarctica's high-density "Lakes District" are mostly inactive and do not contribute much to ice sheet changes.

Most of the 124 newly observed active lakes turned up in coastal areas, at the head of large drainage systems, which have the largest potential to contribute to sea level change.

"The survey identified quite a few more subglacial lakes, but the locations are the intriguing part," Bindschadler said. "The survey shows that most active subglacial lakes are located where the ice is moving fast, which implies a relationship."

Connections between lakes are apparent when one lake drains and another simultaneously fills. Some lakes were found to be connected to nearby lakes, likely through a network of subglacial tunnels. Others appeared to be linked to lakes hundreds of miles away.

The team found that the rate at which lake water drains and fills varies widely. Some lakes drained or filled for periods of three to four years in steady, rather than episodic, changes. But water flow rates beneath the ice sheet can also be as fast as small rivers and can rapidly supply a lubricating film beneath fast-flowing glaciers.

"Most places we looked show something happening on short timescales," Smith said. "It turns out that those are fairly typical examples of things that go on under the ice sheet and are happening all the time all over Antarctica."

(Photo: Ben Smith, University of Washington)

NOSTRILS ALTERNATE TO PROCESS COMPETING ODORS

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When the nose encounters two different scents simultaneously, the brain processes them separately through each nostril in an alternating fashion.

This finding by researchers at Rice University in Houston is the first demonstration of "perceptual rivalry" in the olfactory system. The study was published online today by the journal Current Biology and will appear in the Sept. 29 print edition.

"Our discovery opens up new avenues to explore the workings of the olfactory system and olfactory awareness," said Denise Chen, assistant professor of psychology, who coauthored the research paper with graduate student Wen Zhou.

For the study, 12 volunteers sampled smells from two bottles containing distinctively different odors. One bottle had phenyl ethyl alcohol, which smells like a rose, and the other had n-butanol, which smells like a marker pen. The bottles were fitted with nosepieces so that volunteers could sample both scents simultaneously -- one through each nostril.

During 20 rounds of sampling, all 12 participants experienced switches between smelling predominantly the rose scent and smelling predominantly the marker scent. Some experienced more frequent and drastic switches than others, but there was no predictable pattern of the switch across the whole group of volunteers or within individuals.

Chen said this "binaral rivalry" between the nostrils resembles the rivalry that occurs between other pairs of sensory organs. When the eyes simultaneously view two different images -- one for each eye -- the two images are perceived in alternation, one at a time. And when alternating tones an octave apart are played out of phase to each ear, most people experience a single tone that goes back and forth from ear to ear.

In the laboratory setting in which each nostril simultaneously received a different smell, the participants experienced an "olfactory illusion," she said. "Instead of perceiving a constant mixture of the two smells, they perceive one of the smells, followed by the other, in an alternating fashion, as if the nostrils were competing with one another. Although both smells are equally present, the brain attends to predominantly one of them at a time."

"The binaral rivalry involves adaptations at the peripheral sensory neurons and in the cortex," Chen said. "Our work sets the stage for future studies of this phenomenon so we can learn more about the mechanisms by which we perceive smells."

In binaral rivalry, the tug-of-war between dominance and suppression of the olfactory perception exists only in the mind of the person who smells the odors, while the physical properties of the olfactory stimuli remain unchanged, Chen said. This gives humans the rare opportunity to dissociate olfactory perception and physical stimulation. As such, binaral rivalry may offer a unique window into consciousness and awareness in both healthy and ill people.

Human olfaction is a subject very much in its infancy. Chen said understanding the mechanisms with which people process olfactory information is not only important to basic science, but may also, over the long run, contribute to the assessment and cure of olfactory disorders in patients and, in particular, the elderly.

Rice University

LLNL RESEARCH REVEALS HOW BLAST WAVES MAY CAUSE HUMAN BRAIN INJURY EVEN WITHOUT DIRECT HEAD IMPACTS

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New research on the effects of blast waves could lead to an enhanced understanding of head injuries and improved military helmet design.

Using numerical hydrodynamic computer simulations, Lawrence Livermore scientists Willy Moss and Michael King, along with University of Rochester colleague Eric Blackman, have discovered that nonlethal blasts can induce enough skull flexure to generate potentially damaging loads in the brain, even without direct head impact.

Traumatic brain injury (TBI) results from mechanical loads in the brain, often without skull fracture, and causes complex, long-lasting symptoms.

TBI in civilians is usually caused by direct head impacts resulting from motor vehicle and sports accidents. TBI also has emerged among military combat personnel exposed to blast waves. As modern body armor has substantially reduced soldier fatalities from explosive attacks, the lower mortality rates have revealed the high prevalence of TBI.

There has been extensive research on how head impacts, for example from automobile accidents, cause traumatic brain injury. But TBIs resulting from blast waves without head impacts have not been well understood.

To tackle this puzzle, the team used three-dimensional hydrodynamic simulations to prove that direct action of the blast wave on the head causes skull flexure, producing mechanical loads in brain tissue comparable to those in an injury-inducing impact, even at nonlethal blast pressures as low as 1 bar above atmospheric pressure.

In particular, the team showed that blast waves affect the brain very differently from direct impacts.

The primary source of injury from direct impacts is the force resulting from the bulk acceleration of the head. In contrast, a blast wave squeezes the skull, creating pressures as large as an injury-inducing impact and pressure gradients in the brain that are much larger. This occurs even when the bulk head accelerations induced by a blast wave are much smaller than from a direct impact.

“The blast wave sweeps over the skull like a rolling pin going over dough,” said King, LLNL co-principal investigator.

Although the simulations show that the skull is deformed only about 50 microns (the width of a human hair), “this is large enough to generate potentially damaging loads in the brain,” according to Moss.

Because blast waves and direct impact affect the head in fundamentally different ways, armor systems that are designed to protect soldiers from impacts and projectiles may not be optimal for blast wave protection.

The team studied how helmets and their suspension systems influence the blast-induced mechanical loads in the brain.

They looked at two common systems: a nylon web system formerly used in the Personnel Armor Systems Ground Troops infantry helmet and viscoelastic foam pads like those in advanced combat helmets. Both helmets were modeled as hemi-ellipsoidal Kevlar shells.
In the first case, the 1.3 centimeter gap between the webbing and the shell allows the blast wave to “wash” under the helmet. In this case, the blast wave is focused by the shape of the helmet and the pressures under the helmet exceed those outside, so the helmet doesn't prevent the rippling deformation of the skull and pressure gradients in the brain.

In the second case, this “under wash” effect is mostly prevented by the presence of the foam pads, but under blast loading, the pads can become stiffer so that the blast wave-induced motion or deformation of the helmet is transferred to the skull. This can result in dangerous loads in the brain.

“The possibility that blasts may contribute to traumatic brain injury has implications for injury diagnosis and improved armor design,” Moss said.

Blackman added, “By comparing the effect of blasts on the head with the effect of head impacts we'd be able to make some sense of the distinct mechanisms of injury, the damage a solider might incur, and how a helmet might be designed to minimize both.”

(Photo: U.S. Marine Corps Base Quantico/Lance Cpl. Sha'ahn Williams)

Lawrence Livermore National Laboratory

IRIDESCENCE FOUND IN 40-MILLION-YEAR-OLD FOSSIL BIRD FEATHER

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Known for their wide variety of vibrant plumage, birds have evolved various chemical and physical mechanisms to produce these beautiful colors over millions of years. A team of paleontologists and ornithologists has now discovered evidence of vivid iridescent colors in fossil feathers more than 40 million years old.

The finding, published online August 26 in the journal Biology Letters, signifies the first evidence of a preserved color-producing nanostructure in a fossilized feather.

Iridescence is the quality of changing color depending on the angle of observation, such as the rainbow of colors seen in an oil slick.

The simplest iridescent feather colors are produced by light scattering off the feather's surface and a smooth surface of melanin pigment granules within the feather protein.

Examining feather fossils from the Messel Shale in Germany with an electron microscope, scientists funded by the National Science Foundation (NSF) have documented this smooth layer of melanin structures, called melanosomes.

"Although fossil feathers have been known for many years, determining their original color has not been done," said H. Richard Lane, a paleontologist and program director in NSF's Division of Earth Sciences.

"Discovery of a color-producing nanostructure in a fossil feather opens up the possibility that we someday be able to determine such colors in fossil birds, as well as in feathered dinosaurs."

For more than 25 years, paleontologists have found microscopic tubular structures on fossilized feathers and hair. These were long interpreted as bacteria that had digested the feathers at the time they were fossilized.

The team had previously discovered that these structures were in fact not bacteria but melanosomes; this information allowed the scientists to document the original color patterns.

"The feathers produced a black background with a metallic greenish, bluish or coppery color at certain angles--much like the colors we see in starlings and grackles today," said Richard Prum, a scientist at Yale and one of the paper's authors.

Following up on the new finding, he and colleagues are racing to discover what additional coloration features may be found in fossil feathers.

"The discovery of ultra-structural detail in feather fossils opens up remarkable possibilities for the investigation of other features in soft-bodied fossils, like fur and even internal organs," said scientist Derek Briggs of Yale, a co-author of the paper.

"The 'Holy Grail' is reconstructing the colors of feathered dinosaurs," said Yale graduate student and paper lead author Jakob Vinther. "We are working hard to determine if this will be possible."

(Photo: Richard Prum)

National Science Foundation

TROPICAL STORMS ENDURE OVER WET LAND, FIZZLE OVER DRY

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If it has already rained, it's going to continue to pour, according to a Purdue University study of how ocean-origin storms behave when they come ashore.

More than 30 years of monsoon data from India showed that ground moisture where the storms make landfall is a major indicator of what the storm will do from there. If the ground is wet, the storm is likely to sustain, while dry conditions should calm the storm.

"Once a storm comes overland, it was unclear whether it would stall, accelerate or fizzle out," said Dev Niyogi, Indiana state climatologist and associate professor of agronomy and earth and atmospheric sciences. "We found that whether a storm becomes more intense or causes heavy rains could depend on the land conditions - something we'd not considered. Thus far we've looked at these storms based mainly on ocean conditions or upper atmosphere."

Niyogi said tropical storms gain their strength from warm ocean water evaporation.

"The same phenomenon - the evaporation from the ocean that sustains the storms - could be the same phenomenon that sustains that storm over land with moisture in the soil," he said. "The storm will have more moisture and energy available over wet soil than dry."

Niyogi's team's findings were published in the August edition of the journal Geophysical Research Letters.

Storm data fed into a model showed that higher levels of ground moisture would sustain Indian monsoon depressions. The model's prediction was proven when compared to ground conditions for 125 Indian monsoons over 33 years, where storms sustained when the ground was wet at landfall.

Knowing the sustainability of a storm could lead to better predictions on flooding and damage inland before a monsoon or a hurricane makes landfall.

"We think the physics is such that we could see similar results more broadly, such as in the United States," Niyogi said.

The National Science Foundation and NASA funded the research. The Purdue led-team also consisted of researchers from the National Center for Atmospheric Research, NASA-GSFC/ESSIC, the University of Georgia, the Indian Space Research Organization and the Indian Institute of Technology Delhi.

Niyogi said the next step is to use the model and ground moisture data to test these theories for hurricanes in the United States.

Purdue University

DISCOVERY OF NATURAL ODORS COULD HELP DEVELOP MOSQUITO REPELLENTS

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When fruit flies undergo stress, they emit carbon dioxide (CO2) that serves as a warning to other fruit flies that danger or predators could be nearby. The fruit flies are able to detect the CO2 and escape because their antennae are equipped with specialized neurons that are sensitive to the gas.

But fruits and other important food sources for fruit flies also emit CO2 as a by-product of respiration and ripening. If the innate response of the fruit fly is to avoid CO2, how then does it find its way to these foods?

Anandasankar Ray, an assistant professor in the Department of Entomology, and Stephanie Turner, his graduate student, now provide an answer to the paradox.

They have identified a new class of odorants – chemical compounds with smells – present in ripening fruit that prevent the CO2-sensitive neurons in the antennae from functioning. In particular two odors, hexanol and 2,3- butanedione, are strong inhibitors of the CO2-sensitive neurons in the fruit fly.

The research has strong implications for control of deadly diseases transmitted by Culex mosquitoes such as West Nile virus disease and filariasis, an infectious tropical disease affecting the lymphatic system. Since 1999, nearly 29,000 people in the United States have been reported with West Nile virus disease. Lymphatic filariasis has affected more than 120 million people in the world.

"CO2 emitted in human breath is the main attractant for the Culex mosquito to find people, aiding the transmission of these deadly diseases," Ray said. "In our experiments we identified hexanol, and a related odor, butanal, as strong inhibitors of CO2-sensitive neurons in Culex mosquitoes. These compounds can now be used to guide research in developing novel repellents and masking agents that are economical and environmentally safe methods to block mosquitoes' ability to detect CO2 in our breath, thereby dramatically reducing mosquito-human contact."

Study results appear Aug. 26 in the advance online publication of Nature.

"This is a beautiful study that breaks new ground in the field of olfaction," said John Carlson, the Eugene Higgins Professor of Molecular, Cellular and Developmental Biology at Yale University, who was not involved in the research. "It shows that certain odorants can strongly inhibit the response of receptors that detect CO2. The results suggest some very interesting new strategies for the control of certain insect pests."

Besides showing that inhibitory odors can play an important role in modifying insect behavior, the research paper also illustrates how some of these odors have a long-term effect. Ray and Turner found, for example, that some odors silenced the CO2 neuron in the fruit fly well beyond the period of application.

"To our surprise, we found that exposure to a long-term CO2 response inhibitor can exert a profound and specific effect on the behavior of the insect, even after the inhibitor is no longer in the environment," Ray said. "This means this odorant could potentially be used to keep mosquitoes at bay for longer periods of time, benefiting people in areas where mosquito-transmitted diseases are prevalent."

Ray received his doctoral degree in molecular, cellular and developmental biology from Yale University in 2005. He joined UC Riverside in 2007. His awards include Yale University's John Spangler Nicholas Prize and the Polak Young Investigator Award from the Association of Chemoreception Sciences.

Originally from India, Ray contracted malaria during childhood. When his wife caught dengue fever on a trip to India a few years ago, he decided to intensify his research on mosquito-borne diseases.

Stephanie Turner, the first author of the research paper, received her bachelor's degree in biochemistry from UC Santa Cruz, where she performed research as an undergraduate. She worked for two years in biotechnology before joining the Cell, Molecular and Developmental Biology Graduate Program at UCR.

The research related to this project was conceived, initiated and carried out at UCR over the past one year, and was supported by UCR startup funds. Ray has plans to launch a startup company in the near future to take his basic science research on the odorants from the lab to applications that directly benefit people.

Ray and Turner already have begun work in the lab on mosquitoes that cause malaria and dengue fever. They also are setting up collaborations with a number of scientists from around the globe to do research on various mosquito species and tsetse flies.

The UCR Office of Technology Commercialization has filed a patent application on the discovery.

University of California

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