|Coherent Excitons! |
Global Warming, A3G and AIDS,
NASA's Bison, New Math Worlds,
Babar's Missing Link?
By Kim McDonald
November 1, 2006 - Physicists at UC San Diego have for the first time observed the spontaneous production of coherence within "excitons," the bound pairs of electrons and holes that enable semiconductors to function as novel electronic devices.
Scientists working in the emerging field of nanotechnology, which is finding commercial applications for ultra-small material objects, believe that this newly discovered property could eventually help the development of novel computing devices and provide them with new insights into the quirky quantum properties of matter.
Details of the new finding appear in a paper published in the November 3 issue of the journal Physical Review Letters by a team of four physicists at UCSD working in collaboration with a materials scientist at UC Santa Barbara.
The effort was headed by Leonid Butov, a professor of physics at UCSD who in 2002 led a similar team at the Lawrence Berkeley National Laboratory to the discovery that excitons, when made sufficiently cold, tend to self-organize into an ordered array of microscopic droplets, like a miniature pearl necklace (shown in figure).
"What is coherence and why is it so important?" said Butov. "To start with, modern physics was born by the discovery that all particles in nature are also waves. Coherence means that such waves are all ‘in sync.’ The spontaneous coherence of the matter waves is the reason behind some of the most exciting phenomena in nature such as superconductivity and lasing."
"A simple way to visualize coherence is to imagine cheering spectators at a stadium making ‘a wave’," added Michael Fogler, an assistant professor of physics at UCSD and a co-author of the paper. "If the top rows get up and down at the same time as the bottom ones, the rows are mutually coherent. In turn, coherence is spontaneous when the cheering is done on the spectator’s own initiative and is not orchestrated by the directions of an external announcer."
A famous example of spontaneous coherence of matter waves is the Bose-Einstein condensate, which is a state predicted by Einstein some 80 years ago. This new form of matter was eventually created in 1995 by University of Colorado physicists and regarded as so noteworthy the scientists were awarded the 2001 Nobel Prize in Physics. The Bose-Einstein condensate is a gas of atoms so dense and cold that their matter waves lose their individuality and condense into a "macroscopic coherent superatom wave."
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.
To suppress this annihilation, Butov and his team separate electrons and their holes in different nano-sized structures called quantum wells.
"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."
"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."
|Global Warming Worries Americans - At Last!|
|Massachusetts Institute of Technology News Release |
by Nancy Stauffer
CAMBRIDGE November 1, 2006 - According to a recent MIT survey, Americans now rank climate change as the country's most pressing environmental problem--a dramatic shift from three years ago, when they ranked climate change sixth out of 10 environmental concerns.
Almost three-quarters of the respondents felt the government should do more to deal with global warming, and individuals were willing to spend their own money to help.
"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 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.
All together, almost 60 percent of the 2006 respondents agreed that there's enough evidence to warrant some level of action.
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.
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.
|A3G and AIDS|
|University of Rochester Medical Center News Release |
November 1, 2006 - For years researchers have been trying to understand how a few HIV-infected patients naturally defeat a virus that otherwise overwhelms the immune system. Last year, a research team at the University of Rochester Medical Center confirmed that such patients, called long-term non-progressors, maintain higher than normal levels of the enzyme called APOBEC-3G (A3G) in their white blood cells, which function to stave off infections.
Now, the same group has teamed up with a structural biologist to provide the first look at the A3G structure. Such information represents an early step toward the design of a new class of drugs that could afford to all the same natural protection enjoyed by few, according to a study published today in The Journal of Biological Chemistry.
Researchers believe that A3G works by mutating or "editing" the HIV genetic code every time the virus copies itself. Editing introduces errors until the virus can no longer reproduce. At the same time, HIV has also evolved to counter A3G with its own defense protein, the viral infectivity factor (Vif), which holds firmly to A3G and tricks the white blood cell into destroying it. The results of the current study suggest how the physical form of A3G leads to its role in the immune system, and what parts of it may need to be protected so that it can continue to protect the body.
"Keeping A3G in action represents a new way to attack HIV," said Joseph E. Wedekind, Ph.D., associate professor in the Department of Biochemistry and Biophysics at the University of Rochester Medical Center. Wedekind, along with Harold C. Smith, Ph.D., professor in the same department, led the study. "This first, rough glimpse of A3G's physical structure gives us a map to follow in the search for a new class of AIDS treatments," Wedekind said.
For two decades, Smith and his team have worked to determine how "editing enzymes" like A3G make necessary changes to human genetic material. As the human immune system evolved, it recognized the ability of these enzymes to cause rapid genetic change and unleashed them on viral DNA. Last September, Smith's laboratory published work in the Journal of Virology that found higher levels of A3G closely correspond to lower HIV viral levels. After confirming that the A3G plays a key role in the body's fight with AIDS, Smith sought out Wedekind for a collaboration to determine its structure.
Wedekind is an expert in structural biology, the branch of molecular biology concerned with the study of the molecular shape and properties of proteins and nucleic acids, the molecules that make up the body's structures and carry out its life functions. Improved understanding of both protein and nucleic acid architecture has revolutionized medicine in recent years and has contributed to the design of current leading AIDS drugs. In seeking to determine the structure of A3G, however, the team was unable to use standard methods to start.
For instance, X-ray crystallography, Wedekind's area of expertise since 1989, involves aiming a high-energy X-ray beam at a sample of protein or nucleic acid that has been crystallized to form a repeating lattice of the molecule. The beams reflect off the atoms within a crystal, a camera records the reflected pattern and the data are reconstructed into a 3-D electron map by computers. The technique gives high-resolution images of the positions of atoms within a molecule, but only if researchers can first crystallize the molecule of interest. The team is making progress on crystallizing A3G, but wanted complementary, structural information in the meantime.
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.
|The Large Magellanic Cloud|
November1, 2006 - The infrared surveyor AKARI, a Japan Aerospace Exploration Agency (JAXA) mission with ESA participation, is nearing the completion of its first scan of the entire sky. During this phase of the mission, it has supplied the largest wavelength coverage of the Large Magellanic Cloud to date, and provided fascinating new images of this galaxy.
The Large Magellanic Cloud is a neighboring galaxy to the Milky Way, the galaxy to which our Solar System belongs. It is located extremely close by astronomical standards, at a distance of 160 000 light years and it contains about 10 thousand million stars, about one tenth of our Galaxy's stellar population.
The first image is a far-infrared view obtained by the Far-Infrared Surveyor (FIS) instrument on board AKARI. It reveals the distribution of interstellar matter – dust and gas – over the entire galaxy. Dust grains in these interstellar clouds are heated by the light from newly born stars, and subsequently re-radiate this energy in the form of infrared light. So, the infrared emission indicates that many stars are currently being formed. Such copious star formation activity across a whole galaxy is called a 'star burst'.
The nature of the Large Magellanic Cloud is further revealed by the contrasting distribution of the interstellar matter and the stars. The interstellar matter forms a disk-like structure whilst the stars are located in the 'spindle' shape in the lower half of the image. This shows that the two components are clearly displaced from one another.
Astronomers believe that the observed star formation and the displacement of these two components in the Large Magellanic Cloud were both triggered by the gravitational force generated by our own Galaxy, the Milky Way.
The bright region in the bottom-left of the image is known as the 'Tarantula Nebula'. It is a very productive factory of stars.
New data obtained by AKARI will unlock the secrets of how both the Large Magellanic Cloud and our own Galaxy have formed and evolved to their current state.
European Space Agency - http://www.esa.int
Japan Aerospace Exploration Agency - http://www.jaxa.jp/index_e.html
|NASA's Pet Bison!|
November 2, 2006 - Grainy photographs of America's Old West recall a time when large bison herds migrated across wide prairie lands, 30 million strong, with the changing seasons determining their path and destination.
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.
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.
|New Mathematical Worlds!|
|American Mathematical Society News Release |
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.
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.
"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.
"When I saw the proof in action, I was `more convinced' that it is true!"
|Babar's Missing Link?|
ANN ARBOR October 31, 2006 - A pig-sized, tusked creature that roamed the earth some 27 million years ago represents a missing link between the oldest known relatives of elephants and the more recent group from which modern elephants descended, an international team that includes University of Michigan paleontologist William J. Sanders has found.
The group's findings, to be published this week in the Proceedings of the National Academy of Sciences, suggest that mastodons and the ancestors of elephants originated in Africa, in contrast to mammals such as rhinos, giraffes and antelopes, which had their origins in Europe and Asia and migrated into Africa.
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.
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.