Excitons tend to self-organize into an ordered array of microscopic droplets, like a miniature pearl necklace. (UCSD)

Atomic Bose-Einstein condensation occurs at temperatures near the absolute zero. However, excitons are expected to exhibit the same phenomenon at temperatures that are million times higher (although admittedly still rather low on a common scale, some hundred times lower than the room temperature). Remarkably, this is a range of temperatures where Butov and his team have observed the onset of exciton coherence.

"Excitons are particles that can be created in semiconductors, in our case, gallium arsenide, the material used to make transistors in cell phones," said Fogler. "One can make excitons, or excite them, by shining light on a semiconductor. The light kicks electrons out of the atomic orbitals they normally occupy inside of the material. And this creates a negatively charged ‘free’ electron and a positively charged ‘hole.’"

The force of electric attraction keeps these two objects close together, like an electron and proton in a hydrogen atom. It also enables the exciton to exist as a single particle rather than a non-interacting electron and hole. However, it can be the cause of the excitons’ demise. Since the electron and hole remain in close proximity, they sometimes annihilate one another in a flash of light, similar to annihilation of matter and antimatter.

The wave-like interference pattern reveals the spontaneous coherence of excitons. (UCSD)

To suppress this annihilation, Butov and his team separate electrons and their holes in different nano-sized structures called quantum wells.

"Excitons in such nano-structures can live a thousand or even a million times longer than in a regular bulk semiconductor," said Butov.

"These long-lived excitons can be prepared in large numbers and form a high density exciton gas. But whether excitons can cool down to low temperatures before they recombine and disappear has been a key question for scientists."

"What we found was the emergence of spontaneous coherence in an exciton gas," added Butov.

"This is evidenced by the behavior of the coherence length we were able to extract from the light pattern (as shown in the figure) emitted by excitons as they recombine. Below the temperature of about five degrees Kelvin above absolute zero, the coherence length becomes clearly resolved and displays a steady and rapid growth as temperature decreases. This occurs in concert with the formation of the beads of the ‘pearl necklace.’ The coherence length reaches about two microns at the coldest point available in the experiment."

Other members of the research team were UCSD students Sen Yang and Aaron Hammack and Arthur Gossard, a professor in UC Santa Barbara’s materials science department. The research project was supported by grants from the National Science Foundation, U.S. Army Research Office and the Hellman Fund.

University of California, San Diego - http://www.ucsd.edu

"While terrorism and the war in Iraq are the main issues of national concern, there's been a remarkable increase in the American public's recognition of global warming and their willingness to do something about it," said Stephen Ansolabehere, MIT's Elting R. Morison Professor of Political Science.

The survey results were released Oct. 31 at the seventh annual Carbon Sequestration Forum, an international meeting held at MIT that focuses on methods of capturing and storing emissions of carbon dioxide--a major contributor to climate change.

Ansolabehere's colleagues on the work are Howard Herzog, principal research engineer in MIT's Laboratory for Energy and the Environment (LFEE), LFEE research associates Thomas E. Curry and Mark de Figueiredo, and Professor David M. Reiner of the University of Cambridge.

The findings are a result of two surveys, the first administered in September 2003 and the follow-up in September 2006. Each survey included about 20 questions focusing on the environment, global warming and a variety of climate-change-mitigation technologies.

In designing and administering the surveys, the research team collaborated with Knowledge Networks, a company that specializes in Internet-based public opinion surveys. More than 1,200 people answered each survey (with no overlap between the two groups of respondents).

Comparing results from the two surveys provides insights into how public awareness, concern and understanding have changed--or not changed--during the past three years.

The environment continues to rank in the middle of the list of "most important issues facing the U.S. today." However, among 10 environmental problems, global warming (or climate change) now tops the list: Almost half the respondents put global warming in first or second place. In 2003, the destruction of ecosystems, water pollution and toxic waste were far higher priorities.

There is also an increased sense that global warming is an established problem. In the 2006 survey, 28 percent of the respondents agreed that it is a serious problem and immediate action is necessary--up from 17 percent in 2003.

All together, almost 60 percent of the 2006 respondents agreed that there's enough evidence to warrant some level of action.

The other big change is a substantial increase in people's willingness to spend their own money to do something about it.

In 2003, people were willing to pay on average $14 more per month on their electricity bill to "solve" global warming. In 2006 they agreed to pay $21 more per month--a 50 percent increase in their willingness to pay.

Could $21 make a real difference? Assuming 100 million U.S. households, total payments would be $25 billion per year. "That's real money," said Herzog. "While it cannot solve the whole problem, it can certainly make significant strides."

For context, Ansolabehere pointed out that the U.S. Department of Energy's budget for energy R&D is now about $2 billion per year. "Another reading of this outcome is that people want not a little bit more spent but rather a lot more spent to solve this problem--and they're willing to pay," he said.

The MIT team undertook the original survey in 2003 to find out what the public thought about carbon capture and storage (CCS), an approach that Herzog and his LFEE colleagues had been studying for more than a decade. The team was not surprised to find that more than 90 percent of the respondents had never heard of CCS. The 2006 survey showed similar results.

In general, the respondents' understanding of climate change and possible mitigation technologies showed little change between 2003 and 2006. In terms of their technology preferences, in 2006 most still recommended using more wind and solar energy and increasing efficiency, but more were willing to consider CCS and nuclear energy as possible approaches.

"It's not that people have learned something fundamental about the science, but they've come to understand that this problem is real," said Ansolabehere. "It takes a prolonged discussion of a complex topic like this really to move public concern, and what's happened over the past three years has got to continue."

The researchers plan to analyze the survey results in more depth, in particular to test for correlations between answers to questions and the economic, political, geographical and other demographic characteristics of the respondents.

More details about the surveys and their results - http://sequestration.mit.edu/research/survey2006.html

Massachusetts Institute of Technology - http://web.mit.edu/newsoffice

To achieve immediate results, the researchers elicited the help of Richard Gillilan, Ph.D., staff scientist at the Cornell High-Energy Synchrotron Source (CHESS) in Ithaca, N.Y., and second author on the JBC manuscript. Gillian has expertise in an imaging method called small-angle X-ray scattering (SAXS), which does not require the sample analyzed to be crystalline. While less detailed than crystallography, SAXS provides the general shape of a molecule, the spatial relationship of its parts to one another and hints about the function of each part.

Implications of Shape

Within infected human cells, viral DNA chains must temporarily unzip their two attached chains into single strands to be read and copied, and they must be copied if the virus is to infect more cells. Past work had established that A3G edits single strands of HIV DNA exposed while the virus copies itself. The newly determined structure of A3G suggests how it is able to crawl down HIV DNA chains, introducing mistakes wherever the chains are unzipped and skipping over zipped-up, double stranded regions. Researchers now believe A3G is capable of this because its structure is surprisingly different from other enzymes in its class.

The study also confirmed that A3G has two forms -- one that actively disrupts viral reproduction by editing as a free protein, and another in which the enzyme is inactive due to the presence of mRNA. The new SAXS results show what both forms look like, and suggest new ways in which HIV or the cell itself may turn off A3G.

HIV, along with deploying Vif, may also create a surplus of molecules that force A3G into its inactive form, researchers said. The theory is that HIV infection disrupts the normal process of making proteins, creating a surplus of free messenger RNAs that force A3G to become inactive. Messenger RNAs, copies of DNA that serve as a templates for the building of proteins, thus, may be natural regulators of whether A3G remains active or not. Preventing this mRNA interaction with A3G may represent yet another new avenue of attack on HIV.

"We are the first group to be able to say 'here are the parts of the molecule that need to be protected to keep A3G active in its age-old, ongoing war against viruses" Smith said. "We believe this work will lead to the development of a new treatments that enable patients to better harness their own natural defense mechanisms."

University of Rochester Medical Center - http://www.urmc.rochester.edu

An adult bison during the winter season in Yellowstone National Park. (National Park Service)

Now, NASA satellite data and computer modeling and U.S. Department of Agriculture (USDA) information are helping track the remnants of this once mighty herd in Yellowstone National Park as they migrate with the melting snowpack.

The Yellowstone bison are the only herd in lower North America to survive since prehistoric times.

Hunting and later poaching dwindled their number down to fewer than 50 animals by 1902.

Prior to 1700, millions of bison roamed through Montana, Wyoming and Idaho in areas that later became Yellowstone National Park, the world's first national park.

The bison herd at Yellowstone has grown to about 3,900 animals thanks to creative initiatives at the park to restore and maintain the population.

Scientists at California State University Monterey Bay (CSUMB) and Montana State University at Bozeman, and the National Park Service (NPS) have collaborated on a five-year, NASA-funded project that uses NASA satellite data and computer modeling to help park officials better understand the relationship between snow accumulation and the way it melts during the period when bison migrate between habitats at lower and higher elevations.

Every winter, the deep snow in Yellowstone drives most bison to lower elevations as they embark on their quest for food. In this search, some bison will migrate beyond the Park's borders. When bison are outside the boundaries of Yellowstone, the management authority on the northern boundaries of Yellowstone shifts to the State of Montana. Conflicts can arise between people who value conservation of the bison and the ranch owners and others who concerned about the possible risk to nearby cattle from Brucellosis-infected bison.

An inter-agency partnership has developed a management plan to address this issue, requiring Yellowstone officials to move the animals off of private property, back onto public land, and sometimes capturing bison to prevent them from commingling with neighboring livestock.

"Our goal is to provide the latest snowpack information to park officials," said landscape dynamics expert Fred Watson, principal investigator of the project and an assistant professor of science and environmental policy at CSUMB. "Ecologists try to best understand how animal populations respond to the changing conditions of the landscape where they live. Snow is a very important factor in the livelihood of all wildlife species in the ecosystem, including the Yellowstone bison population," said Watson.

The release of captive bison is timed to ensure a higher likelihood the animals will remain in the park. Knowing when and where the snow will melt is key to whether the bison will stay within park boundaries. To better inform the management team, park officials use a model of snowpack dynamics developed by Watson and his staff to provide the most up-to-date projections on snowpack distribution throughout Yellowstone's winter range areas.

The snowpack model provides daily maps of snowpack depth and density throughout the Yellowstone landscape, in near-real time. It uses data from NASA's Landsat satellite to describe how the snowpack is influenced by patterns of vegetation, geothermal features, and wind. Daily measurements of precipitation and temperature from USDA Snowpack Telemetry system are used to drive the model through time.

"Bison have one of the longest migrations of any large mammal in the country. The fact that they are moving to low-elevation winter ranges outside the park is actually a sign of how successful our restoration efforts have been," said Rick Wallen, leader of the Park's Bison Ecology and Management team. "The modeling of snowpack conditions on winter ranges provides managers a measure of how quickly a snow-covered area becomes clear during the spring melting period. We now have a much better idea when to release wild bison and expect winter ranges to become accessible for the bison during the critical late winter period."

"The National Park Service is not a traditional user of NASA information," said Watson. "But this is a great opportunity to use NASA technology to help the folks at Yellowstone. This project lets them know what capabilities we have and enables us to try different ways to incorporate NASA data and technology into their whole bison management program. It's a wonderful chance to aid in wildlife management."

NASA/Goddard Space Flight Center - http://www.nasa.gov/goddard

Fibration (Etienne Ghys/Jos Leys)

Providence RI November 1, 2006 - A collaboration between a mathematician and an artist-geometer has resulted in some of the most mathematically sophisticated and aesthetically gripping animations ever seen in the field.

Their visualizations of cutting-edge research in dynamical systems theory not only provide a dramatic new way of visiting mathematical worlds once seen only in the mind's eye, but also point to a new era for the use of computer graphics in communicating and carrying out mathematical research.

The two collaborators are Etienne Ghys, a mathematician at the Ecole Normale Sup´rieure in Lyon, France, and Jos Leys, a Belgian graphic artist and engineer with strong mathematical interests. They have written an online animated exposition of an important new theorem Ghys has proved in dynamical systems theory. The exposition will appear as the November 2006 installment of the Feature Column on the web site of the American Mathematical Society.

Ghys's Theorem: A Deep Connection in Dynamical Systems Theory

Ghys was preparing a lecture for the Bibliothèque National de France when he found some intriguing mathematical pictures on Leys's web site. Soon the two were discussing making illustrations of a theorem that Ghys had recently proved, which gives a deep connection between two seemingly unrelated phenomena in dynamical systems theory: Lorenz attractors and modular flows. A dynamical system is a system that evolves over time, like the weather or the stock market. Mathematicians study the differential equations that describe how dynamical systems change over time.

Lorenz attractors: The Lorenz attractor has become the paradigmatic image of chaos theory. In the 1960s the meteorologist Edward Lorenz stumbled on this "strange attractor" in his research examining a particular dynamical system that modeled weather patterns. As that system evolves, the points in it trace out trajectories that return back to their original locations, forming periodic orbits that accumulate around the attractor (hence the name). The orbits are knots: closed loops in 3-dimensional space. Out of the infinite universe of mathematical knots, only a small set of very special knots appear in the Lorenz attractor. The animations of Ghys and Leys display these special Lorenz knots and show how the knots determine the shape of the Lorenz attractor.

Modular flows: A lattice is a collection of evenly-spaced points in the plane, like the set of dots in the Dots and Boxes game. A dynamical system, or flow, on the lattice is a rule for making the lattice points move in a uniform way across the plane. This notion of "modular flow" has been an important tool in mathematics, in particular in number theory, where its roots go back to the great German mathematician Carl Friedrich Gauss (1777-1855). Ghys showed how each modular flow can be associated in a unique way with a knot---and he discovered that the set of knots associated with modular flows is exactly the set of Lorenz knots!

This extraordinary result, and the animations illustrating it, formed the centerpiece for a plenary lecture Ghys presented at the quadrennial International Congress of Mathematicians in Madrid, Spain, in August 2006. Being invited to present an ICM plenary lecture is a coveted honor in the mathematical world. Ghys's lecture was enthusiastically received and constituted a major highlight of the Congress, which was attended by 4000 mathematicians from all over the world.

Getting the Knots to Close

Knot (Etienne Ghys/Jos Leys)

When Ghys and Leys first began working together, they intended to produce still images to illustrate Ghys's theorem. "Soon, we realized that animations are much more fun than still images," Ghys said. The two worked closely to develop numerical algorithms to carry out the animations. All of the work was done on their personal computers, and their interaction has been almost entirely through email. "It was an intense collaboration," said Leys. "We exchanged about 1,800 email messages in 4 months, a lot of them sent late at night when we were close to a breakthrough." While Leys wrote code in a program called UltraFractal that is good for pictures but not ideal for mathematics, Ghys would work in parallel using specialized mathematical software packages to provide hints about how the computations should be done.

The perfection with which the animations capture the mathematical world of dynamical systems and knots came as a result of hard work---and a great deal of back and forth between Ghys and Leys. "Almost never did our knots close!" Ghys recalled.

"Most of the time, the knots came out in several pieces not connected together." The errors were caused sometimes by wrong formulae, and sometimes because of numerical artifacts arising from the computing scheme. As Ghys and Leys worked together to find the best way to represent the mathematics, each learned about the other's area of expertise.

Their animations offer a glimpse deep into the heart of a mathematical world that few have been able to see until now. By the time they had begun collaborating, Ghys already had a mathematical proof of his theorem. But the animations brought him to a new level of understanding.

"When I saw the proof in action, I was `more convinced' that it is true!"

Link to the Riemann Hypothesis

At the end of their Feature Column, Ghys and Leys present an animation of yet another kind of dynamical system called a horocycle flow. There is a link between this flow and a question known as the Riemann Hypothesis, which is a statement about the distribution of prime numbers and is perhaps the biggest open problem in mathematics today. If one could prove a certain fact about the horocycle flow, the Riemann Hypothesis would follow as a consequence.

The Feature Column by Ghys and Leys is available at http://www.ams.org/featurecolumn

American Mathematical Society - http://www.ams.org

The teeth of the newly described Eritreum melakeghebrekristosi are a tip-off to its position as a missing link in the elephant family tree. (UMich)

The dating of the new fossil, discovered in the East African country of Eritrea, also pushes the origins of elephants and mastodons five million years farther into the past than previous records, Sanders said.

From 35 to 25 million years ago, representatives of the group known as proboscideans (which includes elephants, mastodons and their close relatives) lived only in Africa and Arabia, and most of them were palaeomastodonts. These animals were shorter and smaller than today's elephants, with short trunks and tusks and simple teeth that were all in place at the same time, as human adult teeth are.

After 25 million years ago, larger proboscideans such as mastodons and gomphotheres—the ancestors of modern elephants—dominated the scene.

Elephant-sized, with long tusks and trunks, these advanced proboscidans had more complex teeth that emerged more slowly, so that each quadrant of the mouth had only one or two functional teeth in place at a time.

"The new fossil from Eritrea is important because it shows aspects of dental anatomy in common with the advanced group, including molars with more cusps and complex crowns and the delayed maturation and emergence of molars," said Sanders, an assistant research scientist in the U-M Museum of Paleontology. But the creature that the new fossil represents also had characteristics in common with palaeomastodonts, namely smaller body size and a jaw structure that suggests shorter tusks and trunk.

"In age and anatomy it is exactly the sort of intermediate evolutionists would expect to bridge the gap between archaic and advanced proboscideans," Sanders said.

University of Michigan - http://www.ns.umich.edu