Tuesday, June 29, 2010

DURHAM ASTRONOMERS DOUBTS ABOUT THE DARK SIDE

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New research by astronomers in the Physics Department at Durham University suggests that the conventional wisdom about the content of the Universe may be wrong. Graduate student Utane Sawangwit and Professor Tom Shanks looked at observations from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite to study the remnant heat from the Big Bang. The two scientists find evidence that the errors in its data may be much larger than previously thought, which in turn makes the standard model of the Universe open to question. The team publish their results in a letter to the journal Monthly Notices of the Royal Astronomical Society.

Launched in 2001, WMAP measures differences in the Cosmic Microwave Background (CMB) radiation, the residual heat of the Big Bang that fills the Universe and appears over the whole of the sky. The angular size of the ripples in the CMB is thought to be connected to the composition of the Universe. The observations of WMAP showed that the ripples were about twice the size of the full Moon, or around a degree across.

With these results, scientists concluded that the cosmos is made up of 4% ‘normal’ matter, 22% ‘dark’ or invisible matter and 74% ‘dark energy’. Debate about the exact nature of the ‘dark side’ of the Universe – the dark matter and dark energy – continues to this day.

Sawangwit and Shanks used astronomical objects that appear as unresolved points in radio telescopes to test the way the WMAP telescope smoothes out its maps. They find that the smoothing is much larger than previously believed, suggesting that its measurement of the size of the CMBR ripples is not as accurate as was thought. If true this could mean that the ripples are significantly smaller, which could imply that dark matter and dark energy are not present after all.

Prof. Shanks comments “CMB observations are a powerful tool for cosmology and it is vital to check for systematic effects. If our results prove correct then it will become less likely that dark energy and exotic dark matter particles dominate the Universe. So the evidence that the Universe has a ‘Dark Side’ will weaken!”

In addition, Durham astronomers recently collaborated in an international team whose research suggested that the structure of the CMB may not provide the robust independent check on the presence of dark energy that it was thought to.

If dark energy does exist, then it ultimately causes the expansion of the Universe to accelerate. On their journey from the CMB to the telescopes like WMAP, photons (the basic particles of electromagnetic radiation including light and radio waves) travel through giant superclusters of galaxies. Normally a CMB photon is first blueshifted (its peak shifts towards the blue end of the spectrum) when it enters the supercluster and then redshifted as it leaves, so that the two effects cancel. However, if the supercluster galaxies are accelerating away from each other because of dark energy, the cancellation is not exact, so photons stay slightly blueshifted after their passage. Slightly higher temperatures should appear in the CMB where the photons have passed through superclusters.

However, the new results, based on the Sloan Digital Sky Survey which surveyed 1 million luminous red galaxies, suggest that no such effect is seen, again threatening the standard model of the Universe.

Utane Sawangwit says, “If our result is repeated in new surveys of galaxies in the Southern Hemisphere then this could mean real problems for the existence of dark energy.”

If the Universe really has no ‘dark side’, it will come as a relief to some theoretical physicists. Having a model dependent on as yet undetected exotic particles that make up dark matter and the completely mysterious dark energy leaves many scientists feeling uncomfortable. It also throws up problems for the birth of stars in galaxies, with as much ‘feedback’ energy needed to prevent their creation as gravity provides to help them form.

Prof. Shanks concludes “Odds are that the standard model with its enigmatic dark energy and dark matter will survive - but more tests are needed. The European PLANCK satellite, currently out there collecting more CMB data will provide vital new information and help us answer these fundamental questions about the nature of the Universe we live in.”

Royal Astronomical Society

FLOWER POWER MAKES TROPICS COOLER, WETTER

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The world is a cooler, wetter place because of flowering plants, according to new climate simulation results published in the journal Proceedings of the Royal Society B. The effect is especially pronounced in the Amazon basin, where replacing flowering plants with non–flowering varieties would result in an 80 percent decrease in the area covered by ever–wet rainforest.

The simulations demonstrate the importance of flowering–plant physiology to climate regulation in ever–wet rainforest, regions where the dry season is short or non–existent, and where biodiversity is greatest.

“The vein density of leaves within the flowering plants is much, much higher than all other plants,” said the study’s lead author, C. Kevin Boyce, Associate Professor in Geophysical Sciences at the University of Chicago. “That actually matters physiologically for both taking in carbon dioxide from the atmosphere for photosynthesis and also the loss of water, which is transpiration. The two necessarily go together. You can’t take in CO2 without losing water.”

This higher vein density in the leaves means that flowering plants are highly efficient at transpiring water from the soil back into the sky, where it can return to Earth as rain.

“That whole recycling process is dependent upon transpiration, and transpiration would have been much, much lower in the absence of flowering plants,” Boyce said. “We can know that because no leaves throughout the fossil record approach the vein densities seen in flowering plant leaves.”

For most of biological history there were no flowering plants—known scientifically as angiosperms. They evolved about 120 million years ago, during the Cretaceous Period, and took another 20 million years to become prevalent. Flowering species were latecomers to the world of vascular plants, a group that includes ferns, club mosses and confers. But angiosperms now enjoy a position of world domination among plants.

“They’re basically everywhere and everything, unless you’re talking about high altitudes and very high latitudes,” Boyce said.

Dinosaurs walked the Earth when flowering plants evolved, and various studies have attempted to link the dinosaurs’ extinction or at least their evolutionary paths to flowering plant evolution. “Those efforts are always very fuzzy, and none have gained much traction,” Boyce said.

Boyce and Lee are, nevertheless, working toward simulating the climatic impact of flowering plant evolution in the prehistoric world. But simulating the Cretaceous Earth would be a complex undertaking because the planet was warmer, the continents sat in different alignments and carbon– dioxide concentrations were different.

“The world now is really very different from the world 120 million years ago,” Boyce said.

So as a first step, Boyce and co–author with Jung–Eun Lee, Postdoctoral Scholar in Geophysical Sciences at UChicago, examined the role of flowering plants in the modern world. Lee, an atmospheric scientist, adapted the National Center for Atmospheric Research Community Climate Model for the study.

Driven by more than one million lines of code, the simulations computed air motion over the entire globe at a resolution of 300 square kilometers (approximately 116 square miles). Lee ran the simulations on a supercomputer at the National Energy Research Scientific Computing Center in Berkeley, Calif.

“The motion of air is dependent on temperature distribution, and the temperature distribution is dependent on how heat is distributed,” Lee said. “Evapo–transpiration is very important to solve this equation. That’s why we have plants in the model.”

The simulations showed the importance of flowering plants to water recycling. Rain falls, plants drink it up and pass most of it out of their leaves and back into the sky.

In the simulations, replacing flowering plants with non–flowering plants in eastern North America reduced rainfall by up to 40 percent. The same replacement in the Amazon basin delayed onset of the monsoon from Oct. 26 to Jan. 10.

“Rainforest deforestation has long been shown to have a somewhat similar effect,” Boyce said. Transpiration drops along with loss of rainforest, “and you actually lose rainfall because of it.”

Studies in recent decades have suggested a link between the diversity of organisms of all types, flowering plants included, to the abundance or rainfall and the vastness of tropical forests. Flowering plants, it seems, foster and perpetuate their own diversity, and simultaneously bolster the diversity of animals and other plants generally. Indeed, multiple lineages of plants and animals flourished shortly after flowering plants began dominating tropical ecosystems.

The climate–altering physiology of flowering plants might partly explain this phenomenon, Boyce said. “There would have been rainforests before flowering plants existed, but they would have been much smaller,” he said.

(Photo: Dan Dry)

University of Chicago

DESPERATE FEMALE SPIDERS FIGHT BY DIFFERENT RULES

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If you thought women's pro wrestling was a cutthroat business, jumping spiders may have them beat.

In most animals the bigger, better fighter usually wins. But a new study of the jumping spider Phidippus clarus suggests that size and skill aren't everything – what matters for Phidippus females is how badly they want to win.

Found in fields throughout North America, nickel-sized Phidippus clarus is a feisty spider prone to picking fights. In battles between males, the bigger, heavier spider usually wins. Males perform an elaborate dance before doing battle to size up the competition. "They push each other back and forth like sumo wrestlers," said lead author Damian Elias of the University of California at Berkeley.

This fancy footwork allows males to gauge how closely matched they are before escalating into a full-blown fight. "Males rarely get to the point where they solve things by fighting," said co-author Carlos Botero of the National Evolutionary Synthesis Center in Durham, NC. "Before the actual fight there's a lot of displaying. This allows them to resolve things without injuring themselves."

But when the researchers watched female fights, they found that females fight by different rules. They skip the preliminaries and go straight for the kill. "Males have a more gentlemanly form of combat, whereas in females it's an all-out fight," said Elias. "At the drop of a hat they start bashing and biting each other."

And unlike male combat, female feuds were often fatal. "They don't give up, even when their opponent is beating them to a pulp," said Botero. "They keep going until one of them is dead, or severely injured."

The researchers were unable to predict which female would win based on size or strength. "Nothing we could measure predicted which one would come out on top. That was really unexpected," said Elias.

At first, the researchers wondered if victory went not to the bigger fighter, but to the owner of the battlefield. "In a lot of animals one of the things that determines whether they win a fight is whether they're on their own territory," Elias said.

Phidippus clarus spiders live in nests they build from silk and rolled up leaves. While males are nomads, wandering from nest to nest in search of mates, females generally stick to one nest and guard it against intruders.

To test the idea that in turf wars the rightful owner typically wins, the researchers set up a series of fights between resident and intruder females. But when they put pairs of females in an arena — one with a nest, and one that was homeless — the head of the household wasn't always the winner. Instead, the female most likely to win was the one closer to reproductive age.

"The ones that were closer to maturation fought harder," said Botero. "They were more motivated and valued the nest more strongly."

Why might that be?

Before a spider is ready to reproduce, she must first shed her hard outer skin and grow to adult size through a process known as molting. "They're very vulnerable to predators at that time," said Elias. "If they're really close to molting and they don't have a nest at that moment, they're unlikely to survive."

Females need the safety of their nests to molt, mate, and rear their young. "Finding a good nest becomes more critical the closer they are to maturing," said Elias.

"In female fights it's not how big or heavy they are, but how badly they want it," he added. "That trumps size and weight and whether it's her territory. They fight until they have nothing left."

The team's findings were published online in the June 4 issue of Behavioral Ecology.

(Photo: UC Berkeley)

University of California at Berkeley

DINOSAUR-CHEWING MAMMALS LEAVE BEHIND OLDEST KNOWN TOOTH MARKS

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Paleontologists have discovered the oldest mammalian tooth marks yet on the bones of ancient animals, including several large dinosaurs. They report their findings in a paper published online June 16 in the journal Paleontology.

Nicholas Longrich of Yale University and Michael J. Ryan of the Cleveland Museum of Natural History came across several of the bones while studying the collections of the University of Alberta Laboratory for Vertebrate Palaeontology and the Royal Tyrrell Museum of Palaeontology. They also found additional bones displaying tooth marks during fieldwork in Alberta, Canada. The bones are all from the Late Cretaceous epoch and date back about 75 million years.

The pair discovered tooth marks on a femur bone from a Champsosaurus, an aquatic reptile that grew up to five feet long; the rib of a dinosaur, most likely a hadrosaurid or ceratopsid; the femur of another large dinosaur that was likely an ornithischian; and a lower jaw bone from a small marsupial.

The researchers believe the marks were made by mammals because they were created by opposing pairs of teeth—a trait seen only in mammals from that time. They think they were most likely made by multituberculates, an extinct order of archaic mammals that resemble rodents and had paired upper and lower incisors. Several of the bones display multiple, overlapping bites made along the curve of the bone, revealing a pattern similar to the way people eat corn on the cob.

The animals that made the marks were about the size of a squirrel and were most likely gnawing on the bare bones for minerals rather than for meat, said Longrich. "The bones were kind of a nutritional supplement for these animals."

There are likely many other instances of mammalian tooth marks on other bones that have yet to be identified, including older examples, said Longrich. "The marks stood out for me because I remember seeing the gnaw marks on the antlers of a deer my father brought home when I was young," he said. "So when I saw it in the fossils, it was something I paid attention to."

But he points out that the Late Cretaceous creatures that chewed on these bones were not nearly as adept at gnawing as today's rodents, which developed that ability long after dinosaurs went extinct.

(Photo: Nicholas Longrich/Yale University)

Yale University

WHY DO CERTAIN DISEASES GO INTO REMISSION DURING PREGNANCY?

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During pregnancy, many women experience remission of autoimmune diseases like multiple sclerosis and uveitis. Now, scientists have described a biological mechanism responsible for changes in the immune system that helps to explain the remission.

The expression of an enzyme known as pyruvate kinase is reduced in immune cells in pregnant women compared to non-pregnant women, according to Howard R. Petty, Ph.D., biophysicist at the University of Michigan Kellogg Eye Center and Roberto Romero, M.D., of the National Institutes for Health.

The study, which appears online ahead of print in the August issue of the American Journal of Reproductive Immunology, also reports that expression of the enzyme is lower in pregnant women compared to those with pre-eclampsia, a condition with inflammatory components.

The study is significant because the newly discovered mechanism points to a pathway that could be targeted for treatment. “It may be possible to design drugs that mildly suppress pyruvate kinase activity as a means of replicating the immune status of normal pregnancy,” says Petty.

In addition to pre-eclampsia, he believes that rheumatoid arthritis, type 1 diabetes, and uveitis may eventually yield to similarly designed drugs.

In his search to explain the phenomenon, Petty knew to look for a metabolic pathway or mechanism with two characteristics. It had to “dial down” the intensity of the normal immune response, an action needed so that a pregnant woman does not reject the fetus, which has proteins from the father that are “foreign” to the mother. At the same time, such a mechanism must support cell growth needed by the developing fetus.

The activity of the enzyme pyruvate kinase—and and its product, pyruvate—fills both roles: promoting cell growth while modifying the immune response. Because pyruvate kinase activity is depressed during pregnancy, cell metabolism supports an increased production of lipids, carbohydrates, amino acids, and other substances that support cell growth.

Petty explains that our normal robust immune response depends upon pyruvate to promote calcium signaling, which, in turn, stimulates the production of messenger molecules called cytokines. When pyruvate is decreased during pregnancy, calcium signaling is also reduced, and the immune response is different than that in non-pregnant individuals. Says Petty, “Modification of signaling along this pathway allows the pregnant woman to maintain an immune response, but at a level that will not harm the fetus.”

The study included 21 women in their third trimester of a normal pregnancy, 25 women with pre-eclampsia, and a control group of non-pregnant women. Petty and colleagues used a variety of methods to confirm their findings, including fluorescence microscopy and flow cytometry, which are used to study cell signaling.

The higher levels of the enzyme seen in women with pre-eclampsia bolster the study’s findings, says Petty. “Pre-eclampsia has features of inflammatory disease. If you don’t reduce these pyruvate levels, you heighten inflammatory disease,” he adds. Petty wonders whether one day enzyme levels could be tested early in pregnancy to predict the likelihood of developing pre-eclampsia or other complications.

It is possible, says Petty, that the general mechanisms described in the current study may apply to more than one complication of pregnancy. This possibility—and that of designing drugs to suppress pyruvate kinase activity—is the focus of future research. “I have a long list of things I’d like to see developed for the clinic in the next five years,” adds Petty.

(Photo: U. Michigan)

University of Michigan

STORING CARBON DIOXIDE DEEP UNDERGROUND IN ROCK FORM

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As carbon dioxide continues to burgeon in the atmosphere causing the Earth's climate to warm, scientists are trying to find ways to remove the excess gas from the atmosphere and store it where it can cause no trouble.

Sigurdur Gislason of the University of Iceland has been studying the possibility of sequestration of carbon dioxide (CO2) in basalt and presented his findings to several thousand geochemists from around the world at the Goldschmidt Conference hosted by the University of Tennessee, Knoxville, and Oak Ridge National Laboratory.

Carbon sequestration is currently the most promising way to reduce greenhouse gases. Gislason leads an international team of scientists on the Carbfix Project, which aims at pumping carbon deep underground in southwest Iceland where it will mix with minerals and become rock. The project's goal is to find a storage solution that is long lasting, thermodynamically stable and environmentally benign.

An Icelandic geothermal plant is now hosting the pilot program. Gislason's project involves capturing and separating flue gases at the Hellisheidi Geothermal Power Plant, transporting the gas, dissolving it in water, and injecting it at high pressures to a depth between 400 and 800 meters into a thick layer of basalt. Then he and his coworkers will verify and monitor the storage.

Carbon dioxide mixed with water forms carbonic acid (also known as carbonated water or soda water), which percolates through the rocks, dissolving some minerals and forming solid carbonates with them, thereby storing the carbon dioxide in rock form, said Gislason.

If successful, Gislason said, the experiment will be scaled up and can be used wherever carbon dioxide is emitted. Currently, carbon may be captured as a byproduct in processes such as petroleum refining. It can be stored in reservoirs, ocean water and mature oilfields. However, many experts fear that CO2 may leak over time. Storage of CO2 as solid magnesium carbonates or calcium carbonates deep underground in basaltic rocks may provide a long-term and thermodynamically stable solution.

University of Tennessee

NEW CU-BOULDER STUDY INDICATES AN ANCIENT OCEAN MAY HAVE COVERED ONE-THIRD OF MARS

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A vast ocean likely covered one-third of the surface of Mars some 3.5 billion years ago, according to a new study conducted by University of Colorado at Boulder scientists.

The CU-Boulder study is the first to combine the analysis of water-related features including scores of delta deposits and thousands of river valleys to test for the occurrence of an ocean sustained by a global hydrosphere on early Mars. While the notion of a large, ancient ocean on Mars has been repeatedly proposed and challenged over the past two decades, the new study provides further support for the idea of a sustained sea on the Red Planet during the Noachian era more than 3 billion years ago, said CU-Boulder researcher Gaetano Di Achille, lead author on the study.

A paper on the subject authored by Di Achille and CU-Boulder Assistant Professor Brian Hynek of the geological sciences department appeared in the June 13 issue of Nature Geoscience. Both Di Achille and Hynek are affiliated with CU-Boulder's Laboratory for Atmospheric and Space Physics.

More than half of the 52 river delta deposits identified by the CU researchers in the new study -- each of which was fed by numerous river valleys -- likely marked the boundaries of the proposed ocean, since all were at about the same elevation. Twenty-nine of the 52 deltas were connected either to the ancient Mars ocean or to the groundwater table of the ocean and to several large, adjacent lakes, Di Achille said.

The study is the first to integrate multiple data sets of deltas, valley networks and topography from a cadre of NASA and European Space Agency orbiting missions of Mars dating back to 2001, said Hynek. The study implies that ancient Mars probably had an Earth-like global hydrological cycle, including precipitation, runoff, cloud formation, and ice and groundwater accumulation, Hynek said.

Di Achille and Hynek used a geographic information system, or GIS, to map the Martian terrain and conclude the ocean likely would have covered about 36 percent of the planet and contained about 30 million cubic miles, or 124 million cubic kilometers, of water. The amount of water in the ancient ocean would have formed the equivalent of a 1,800-foot, or 550-meter-deep layer of water spread out over the entire planet.

The volume of the ancient Mars ocean would have been about 10 times less than the current volume of Earth's oceans, Hynek said. Mars is slightly more than half the size of Earth.

The average elevation of the deltas on the edges of the proposed ocean was remarkably consistent around the whole planet, said Di Achille. In addition, the large, ancient lakes upslope from the ancient Mars ocean likely formed inside impact craters and would have been filled by the transport of groundwater between the lakes and the ancient sea, according to the researchers.

A second study headed by Hynek and involving CU-Boulder researcher Michael Beach of LASP and CU-Boulder doctoral student Monica Hoke being published in the Journal of Geophysical Research–Planets -- which is a publication of the American Geophysical Union -- detected roughly 40,000 river valleys on Mars. That is about four times the number of river valleys that have previously been identified by scientists, said Hynek.

The river valleys were the source of the sediment that was carried downstream and dumped into the deltas adjacent to the proposed ocean, said Hynek. "The abundance of these river valleys required a significant amount of precipitation," he said. "This effectively puts a nail in the coffin regarding the presence of past rainfall on Mars." Hynek said an ocean was likely required for the sustained precipitation.

"Collectively, these results support the existing theories regarding the extent and formation time of an ancient ocean on Mars and imply the surface conditions during the time probably allowed the occurrence of a global and active hydrosphere integrating valley networks, deltas and a vast ocean as major components of an Earth-like hydrologic cycle," Di Achille and Hynek wrote in Nature Geoscience.

"One of the main questions we would like to answer is where all of the water on Mars went," said Di Achille. He said future Mars missions -- including NASA's $485 million Mars Atmosphere and Volatile Evolution mission, or MAVEN, which is being led by CU-Boulder and is slated to launch in 2013 -- should help to answer such questions and provide new insights into the history of Martian water.

The river deltas on Mars are of high interest to planetary scientists because deltas on Earth rapidly bury organic carbon and other biomarkers of life and are a prime target for future exploration. Most astrobiologists believe any present indications of life on Mars will be discovered in the form of subterranean microorganisms.

"On Earth, deltas and lakes are excellent collectors and preservers of signs of past life," said Di Achille. "If life ever arose on Mars, deltas may be the key to unlocking Mars' biological past."

Hynek said long-lived oceans may have provided an environment for microbial life to take hold on Mars.

The study was funded by NASA's Mars Data Analysis Program.

(Photo: University of Colorado)

University of Colorado

SOME PEOPLE DO NOT TASTE SALT LIKE OTHERS

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Low-salt foods may be harder for some people to like than others, according to a study by a Penn State College of Agricultural Sciences food scientist. The research indicates that genetics influence some of the difference in the levels of salt we like to eat.

Those conclusions are important because recent, well-publicized efforts to reduce the salt content in food have left many people struggling to accept fare that simply does not taste as good to them as it does to others, pointed out John Hayes, assistant professor of food science, who was lead investigator on the study.

Diets high in salt can increase the risk of high blood pressure and stroke. That is why public health experts and food companies are working together on ways to help consumers lower salt intake through foods that are enjoyable to eat. This study increases understanding of salt preference and consumption.

The research involved 87 carefully screened participants who sampled salty foods such as broth, chips and pretzels, on multiple occasions, spread out over weeks. Test subjects were 45 men and 42 women, reportedly healthy, ranging in age from 20 to 40 years. The sample was composed of individuals who were not actively modifying their dietary intake and did not smoke cigarettes. They rated the intensity of taste on a commonly used scientific scale, ranging from barely detectable to strongest sensation of any kind.

The study, a collaboration between Hayes and Valerie Duffy, professor of allied health science and Bridget S. Sullivan, Master's graduate, University of Connecticut, appeared in June 16 issue of Physiology & Behavior.

"Most of us like the taste of salt. However, some individuals eat more salt, both because they like the taste of saltiness more, and also because it is needed to block other unpleasant tastes in food," said Hayes. "Supertasters, people who experience tastes more intensely, consume more salt than do nontasters. Snack foods have saltiness as their primary flavor, and at least for these foods, more is better, so the supertasters seem to like them more."

However, supertasters also need higher levels of salt to block unpleasant bitter tastes in foods such as cheese, Hayes noted. "For example, cheese is a wonderful blend of dairy flavors from fermented milk, but also bitter tastes from ripening that are blocked by salt," he said. "A supertaster finds low-salt cheese unpleasant because the bitterness is too pronounced."

Hayes cited research done more than 75 years ago by a chemist named Fox and a geneticist named Blakeslee, showing that individuals differ in their ability to taste certain chemicals. As a result, Hayes explained, we know that a wide range in taste acuity exists, and this variation is as normal as variations in eye and hair color.

"Some people, called supertasters, describe bitter compounds as being extremely bitter, while others, called nontasters, find these same bitter compounds to be tasteless or only weakly bitter," he said. "Response to bitter compounds is one of many ways to identify biological differences in food preference because supertasting is not limited to bitterness.

"Individuals who experience more bitterness also perceive more saltiness in table salt, more sweetness from table sugar, more burn from chili peppers, and more tingle from carbonated drinks."

Supertasters live in a neon food world, Hayes noted. Nontasters, on the other extreme, live in a pastel food world.

"Interestingly, nontasters may be more likely to add salt to foods at the table because they need more salt to reach the same level of perceived saltiness as a supertaster," he said. "However, most of the salt we consume comes from salt added to processed foods and not from the salt shaker."

Currently, U.S. citizens consume two to three times the amount of salt recommended for good health. Hayes advises consumers to lower their salt intake by reading the food label and looking for products that contain fewer than 480 milligrams of sodium per serving.

(Photo: PSU)

The Pennsylvania State University

NEW RESEARCH SHOWS HOW EXPERIENCE SHAPES THE BRAIN’S CIRCUITRY

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Neuroscientists once thought that the brain’s wiring was fixed early in life, during a critical period beyond which changes were impossible. Recent discoveries have challenged that view, and now, research by scientists at Rockefeller University suggests that circuits in the adult brain are continually modified by experience. The findings are reported in the June 15 issue of PLoS Biology.

The researchers, led by Charles D. Gilbert, Arthur and Janet Ross Professor and head of the Laboratory of Neurobiology, observed how neurons responsible for receiving input from a mouse’s whiskers shift their relationships with one another after single whiskers are removed. The experiments explain how the circuitry of a region of the mouse brain called the somatosensory cortex, which processes input from the various systems in the body that respond to the sense of touch, can change.

The Gilbert lab has been studying changing neuronal connections for several years. Their approach, in which scientists use a viral labeling system to attach fluorescent proteins to individual neurons and then image individual synapses in an intact, living brain with a high-resolution two-photon microscope, has provided several important clues to understanding the dynamics of the brain’s wiring.

Applying this technique, students in the Gilbert lab, Dan Stettler and Homare (Matias) Yamahachi, in collaboration with Winfried Denk at the Max Planck Institute in Heidelberg, followed the same neurons week after week in the primary visual cortex of adult monkeys. They found that the circuits of the visual cortex are highly dynamic, turning over synapses at a rate of seven percent per week. These changes occurred without any learning regimen or physical manipulations to the neurons. Last year, Yamahachi, together with Sally Marik and Justin McManus, showed that when sensory experience is altered, there are even more dramatic changes in cortical circuits, with very rapid alterations in circuitry involving an exuberant growth of new connections paralleled by a pruning of old connections. These studies and others by the Gilbert lab have begun to show that there is an underlying dynamics in the sensory cortex and it’s not a fixed system, as has long been believed.

In the new study, Marik and other members of the Gilbert lab looked at excitatory and inhibitory neurons within the cortex during periods of sensory deprivation to determine how experience shapes different components of cortical circuitry. For this study they used the whisker-barrel system in adult mice. The barrel cortex, part of the somatosensory cortex, receives sensory input from the animal’s whiskers. Scientists have shown that after a row of whiskers is removed, barrels will shift representation to adjacent intact whiskers Marik, together with Yamahachi and McManus, found after a whisker was plucked excitatory connections projecting into the deprived barrels underwent exuberant and rapid axonal sprouting. This axonal restructuring occurred rapidly -- within minutes or hours after whiskers were plucked -- and continued over the course of several weeks. At the same time that excitatory connections were invading the deprived columns, there was a reciprocal outgrowth of the axons of inhibitory neurons from the deprived to the non-deprived barrels. This suggests that the process of reshaping cortical circuits maintains the balance between excitation and inhibition that exists in the normal cortex.

“Previously we showed changes only in excitatory connections,” Gilbert says. “We’ve now demonstrated a parallel involvement of inhibitory connections, and we think that inhibition may play a role equal in importance to excitation in inducing changes in cortical functional maps.”

The new study also showed that changes in the inhibitory circuits preceded those seen in the excitatory connections, suggesting that the inhibitory changes may mediate the excitatory ones. This process, Gilbert says, mimics what happens in the brain during early postnatal development.

“It’s surprising that the primary visual or somatosensory cortices are involved in plasticity and capable of establishing new memories, which previously had been considered to be a specialized function of higher brain centers,” Gilbert says. “We are just beginning to tease apart the mechanisms of adult cortical plasticity. We hope to determine whether the circuit changes associated with recovery of function following lesions to the central and peripheral nervous systems also occur under normal conditions of perceptual learning.”

Rockefeller University

THE NEXT YELLOWSTONE ERUPTION COULD BE SIMILAR VOLCANIC EVENT

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Millions of years ago, volcanic eruptions in North America were more explosive and may have significantly affected the environment and the global climate. So scientists report in this week's issue of the journal Nature.

The researchers found the remains--deposited in layers of rocks--of eruptions of volcanoes located on North America's northern high plains that spewed massive amounts of sulfate aerosols into the atmosphere 40 million years ago. The scientists conducted their research at Scotts Bluff National Monument, Neb., and in surrounding areas.

"Combining measurements of the sulfate in ancient volcanic ash beds with a detailed atmospheric chemistry model, we found that the long-ago chemistry of volcanic sulfate gases is distinct from that of more modern times," says Huiming Bao, a geologist at Louisiana State University and lead author of the paper.

"This is the first example showing that the history of massive volcanic sulfate emissions, and their associated atmospheric conditions in the geologic past, may be retrieved from rock records."

Volcanic eruptions may have significant impacts on the environment, Bao says, citing the 1991 Mt. Pinatubo and more recent Iceland volcanic eruptions.

"The physical impacts of these eruptions, such as ash plumes, are relatively short-lived, but the chemical consequences of the emitted gases may have long-lasting effects on global climate," says Sonia Esperanca, program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research.

One of the most important volcanic gases is sulfur dioxide. It is oxidized in the atmosphere and turned to sulfate aerosol. This aerosol plays an important role in climate change.

"The volcanic eruptions of the last several thousand years hardly compare with some of the eruptions in the past 40 million years in western North America, especially in the amount of sulfur dioxide those eruptions spewed out," says Bao.

What's more important, he says, is that the formation of sulfate aerosol is related to atmospheric conditions at the time of a volcano's eruption.

In the Nature paper, he and colleagues show that past sulfate aerosol formed in a different way than it does today, indicating a change from atmospheric conditions then to now.

A similar volcanic event to the long-ago past likely will happen again, Bao says: in the next Yellowstone eruption.

The closest analog, Bao believes, is the 1783 Laki, Iceland, eruption and the subsequent "dry fogs" in continental Europe.

That event devastated Iceland's cattle population. People with lung problems suffered the worst, he says.

In North America, the very next year's winter, that of 1784, was the longest and one of the coldest on record. The Mississippi River froze as far south as New Orleans. The French Revolution in 1789 may have been triggered by the poverty and famine caused by the eruption, scientists believe.

"Millions of years ago, volcanic eruptions in North America were more explosive," Bao says, "and the quantity of sulfur dioxide released was probably hundreds of times more--greater even than in Laki in 1783."

(Photo: Huiming Bao)

National Science Foundation

ZOOMING IN ON INFANT PLANETARY SYSTEMS

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Using both 10-meter Keck telescopes together, astronomers at the W. M. Keck Observatory have been able to peer deeper into proto-planetary disks, swirling clouds of gas and dust that feed the growing stars in their centers and eventually coalesce into new planetary systems.

The team studied 15 young Milky Way stars varying in mass between one half and ten times that of the Sun and used the Keck Interferometer to obtain extremely fine observations to pinpoint the location of the processes that occur right at the boundary between the stars and their surrounding disks, which sit 500 light years from Earth.

The Keck Interferometer combines both 10-meter Keck telescopes to act as an 85-meter telescope, and is a project funded by NASA, in a partnership between the Jet Propulsion Laboratory, the NASA Exoplanet Science Institute and the Keck Observatory. Four years ago, with a grant from the National Science Foundation, a quest began to expand the astrometric capability of the Keck Interferometer with a specifically engineered instrument named ASTRA, or ASTrometric and phase-Referenced Astronomy.

ASTRA aims to provide extremely precise measurements of the positions and movements of stars, gas and dust. “With it in its current state, we are going for young stars and their dust disks,” said Keck Observatory scientist Julien Woillez, co-investigator of the new research and lead of the ASTRA instrument. “As we improve ASTRA, we will soon have the capability to study the motion of planets around older stars, and even the motion of stars around the black hole at the center of our Galaxy.”

The resolution achieved in this study, which will be published in the July 20 Astrophysical Journal, allowed the team to observe proto-planetary disk material within 0.1 astronomical units, or nine million miles, of the target star. One astronomical unit is roughly 93 million miles, or the distance between the Sun and Earth. The precision measurements would be similar to standing on a rooftop in San Francisco and trying to observe a Nene goose nibbling on a grain of rice in Hawai’i.

Stars’ proto-planetary disks form in stellar nurseries when clouds of gas molecules and dust particles begin to collapse under the influence of gravity. Initially rotating slowly, the cloud’s growing mass and gravity cause it to become denser and more compact. Preserving rotational momentum, the cloud begins to spin faster and shrinks, similar to a figure skater spinning faster as she pulls in her arms. The centrifugal force flattens the cloud into a spinning disk of swirling gas and dust — eventually giving rise to planets orbiting their star in roughly the same plane.

Measuring the light emanating from the proto-planetary disks at different wavelengths with the Keck Interferometer and manipulating it further with ASTRA, the astronomers were able to distinguish between the distributions of gas, mostly made up of hydrogen, and dust, thereby resolving the disk’s features.

Astronomers know that stars acquire mass by incorporating some of the hydrogen gas in the disk that surrounds them, in a process called accretion. The team wants to better understand how material accretes onto the star, a process that has never been measured directly, said Joshua Eisner of the University of Arizona and lead author of the paper.

In proto-planetary disks, accretion can happen in one of two ways.

In one scenario, gas is swallowed as it washes up right to the fiery surface of the star. In the second, much more violent scenario, the magnetic fields sweeping from the star push back the approaching gas and cause it to bunch up, creating a gap between the star and its surrounding disk. Rather than lapping at the star’s surface, the hydrogen molecules travel along the magnetic field lines as if on a highway, becoming super-heated and ionized in this process.

“Once trapped in the star’s magnetic field, the gas is being funneled along the field lines arching out high above and below the disk’s plane,” Eisner explained. “The material then crashes into the star’s polar regions at high velocities.”

In this inferno, which releases the energy of millions of Hiroshima-sized atomic bombs every second, some of the arching gas flow is ejected from the disk and spews out far into space as interstellar wind.

“We could successfully discern that in most cases, the gas converts some of its kinetic energy into light very close to the stars,” he said, a tell-tale sign of the more violent accretion scenario.

“In other cases, we saw evidence of winds launched into space together with material accreting on the star,” Eisner added. “We even found an example—around a very high-mass star—in which the disk may reach all the way to the stellar surface.”

Because the disks are young, only a few million years, they will be around for a few more millions of years. “By that time, the first planets, gas giants similar to Jupiter and Saturn, may form, using up a lot of the disk material.”

More solid, rocky planets like the Earth, Venus or Mars, won’t be around until much later.

The building blocks for those more terrestrial planets could be forming now, he added, which is why this research is important for our understanding of how planetary systems form, including those with potentially habitable planets like Earth.

“We are going to see if we can make similar measurements of organic molecules and water in proto-planetary disks,” Eisner said. “Those would be the ones potentially giving rise to planets with the conditions to harbor life.”

(Photo: NASA/JPL-Caltech)

W. M. Keck Observatory

COLORS OF BUTTERFLY WING YIELD CLUES TO LIGHT-ALTERING STRUCTURES

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At the very heart of some of the most brilliant colors on the wings of butterflies lie bizarre structures, a multidisciplinary team of Yale researchers has found. These structures are intriguing the team’s scientists and engineers, who want to use them to harness the power of light.

The crystal nanostructures that ultimately give butterflies their color are called gyroids. These are “mind-bendingly weird” three-dimensional curving structures that selectively scatter light, said Richard Prum, chair and the William Robertson Coe Professor in the Department of Ornithology, Ecology and Evolutionary Biology. Prum led the Yale team, which reported its findings online in the Proceedings of the National Academy of Sciences.

Prum over the years became fascinated with the properties of the colors on butterfly wings and enlisted researchers to help study them from the Departments of Chemical Engineering, Physics and Mechanical Engineering, as well as the Yale School of Engineering and Applied Science.

Using an X-ray scattering technique at the Argonne National Laboratory in Illinois, Richard Prum, his graduate student Vinod Saranathan and their colleagues determined the three-dimensional internal structure of scales in the wings of five butterfly species.

The gyroid is made of chitin, the tough starchy material that forms the exterior of insects and crustaceans, Chitin is usually deposited on the outer membranes of cells. The Yale team wanted to know how a cell can sculpt itself into this extraordinary form, which resembles a network of three-bladed boomerangs. They found that, essentially, the outer membranes of the butterfly wing scale cells grow and fold into the interior of the cells. The membranes then form a double gyroid — or two, mirror-image networks shaped by the outer and inner cell membranes. The latter are easier to grow but are not as good at scattering light. Chitin is then deposited in the outer gyroid to create a single solid crystal. The cell then dies, leaving behind the crystal nanostructures on the butterfly wing.

Photonic engineers are using gyroid shapes to try to create more efficient solar cells and, by mimicking nature, may be able to produce more efficient optical devices as well, Prum said.

(Photo: Yale U.)

Yale University

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