Search Of Galactic Halo Yields A Treasure Trove Of Variable Stars
Posted: Thursday, September 27, 2001
Source: National Center For Atmospheric Research/University Corporation For Atmospheric Research (http://www.ucar.edu/ucar/)
BOULDER -- According to a new data analysis, the atmosphere redistributes annually as much heat from the tropics to the poles as would be produced by five million of the world's biggest power stations, generating 1,000 megawatts each.
This is far more heat than previously estimated and much more than the oceans carry poleward. Until now scientists have been unable to reconcile observations of the atmosphere and ocean with results from global climate models. The new study establishes the role of each in total heat transport poleward.
"This new analysis makes the observations more consistent with the most stable global climate models and gives us confidence that the models are on target," says Kevin Trenberth of the National Center for Atmospheric Research.
Trenberth and NCAR colleague Julie Caron performed the analysis, which was published in a recent issue of the Journal of Climate, a publication of the American Meteorological Society. It was selected this month by the journal Science as an Editor's Choice of important new findings.
The atmosphere and oceans help to even out the planet's temperatures by moving vast amounts of solar heat from the equator toward both poles, primarily during winter in each hemisphere. Without this leveling effect, all the high latitudes would be frozen solid while the tropics would be much warmer and wetter.
Based on a reanalysis of data gathered between February 1985 and April 1989, the study shows that the atmosphere handles 78% of the total heat transport in the Northern Hemisphere and 92% in the Southern Hemisphere at 35 degrees latitude--where the total poleward transport in each hemisphere peaks. The ocean carries more heat than the atmosphere only in the tropics between 0 and 17 degrees north, according to the study.
In the past, computer models attempting to mimic the Earth's climate have required artificial fixes to match real-world observations. Only recently have NCAR and the United Kingdom's Hadley Center developed climate models stable enough to simulate centuries of climate without these fixes.
Their results now nearly match the observations. To complete the picture, recent results from ocean measurements fit well with those deduced by Trenberth and Caron from the atmospheric component and both now add up to the alreadh known total heat transport.
In the late 1970s the ocean and atmosphere were thought to be conveying about the same amount of heat globally. Scientists estimated that the atmosphere was hauling 57% of the heat load, with oceans bearing a hefty 43% at the 35-degree latitude. As analyses have improved, estimates have steadily increased the magnitude of poleward heat transport occurring in the atmospheres of both hemispheres.
The atmosphere's role may have been slighted in the past because of a lack of data over the oceans, where substantial atmospheric heat transport occurs. Satellites have helped fill that gap. Trenberth and Caron focused on the 1985-1989 period because it offers reliable top- of-the-atmosphere radiation data from satellite measurements taken during the Earth Radiation Budget Experiment.
The new study was based on two data reanalyses, one by the National Centers for Environmental Prediction and NCAR, the other by the European Centre for Medium-Range Weather Forecasts. The study was funded by the National Oceanic and Atmospheric Administration and NASA. NCAR is managed by the University Corporation for Atmospheric Research with primary sponsorship by the National Science Foundation.
Send page by E-Mail Scientists Discover How Some Viruses Take Strong Hold Of Cells
Posted: Wednesday, September 26, 2001
Source: Brookhaven National Laboratory (http://www.bnl.gov/)
UPTON, NY -- As part of an ongoing effort to understand how viruses infect cells, scientists at the U.S. Department of Energy's Brookhaven National Laboratory have deciphered the molecular-level interaction between coxsackievirus -- which infects the heart, brain, pancreas, and other organs -- and the human cell protein to which it attaches.
This work, published in the October issue of Nature Structural Biology, may lead to improved ways to thwart viral infections, and may help scientists design virus-based vehicles for gene therapy.
The study reveals that the receptor protein for coxsackievirus (known as coxsackievirus-adenovirus receptor, or CAR) forms pairs on the surface of human cells, with two adjacent CAR receptors attached to one another below the surface of the cell membrane. When coxsackievirus binds to the human cell, it forms bonds with both receptors of the pair.
"This arrangement is advantageous for the virus," says Brookhaven biologist Paul Freimuth, one of the study's authors. "The binding becomes almost irreversible, because both bonds would have to reverse simultaneously to release the virus. That increases the likelihood that the virus will infect the cell."
The structural studies also reveal that the binding sites on the coxsackievirus are "cleverly" hidden from the body's immune system, which produces antibodies to fight infections. "If you think of the virus as a golf ball, the binding sites that recognize the receptor are inside the dimples," Freimuth says. "Antibodies can't fit into the indentations, but the receptor is a slender molecule that can fit in."
Both of these features -- hidden binding sites and simultaneous binding to multiple receptors -- are shared by other viruses in the same family, including the virus that causes polio and rhinovirus, one cause of the common cold and other respiratory and gastrointestinal infections.
"It's a very clever arrangement that these viruses have worked out," Freimuth says, "and very hard to defeat." For example, scientists have tried administering single receptor-like molecules designed to tie up binding sites on a virus and block its ability to attach to cells. These haven't worked very well, Freimuth suggests, because the double hold the virus forms with the cell makes it hard for these single molecules to compete. But perhaps administering receptor-like molecules with double binding sites would be able to compete and interfere with the virus' attack.
The current work may also help scientists interested in developing viruses used in gene therapy. The idea behind gene therapy is to destroy a virus’ disease-causing genes and replace them with therapeutic genes -- ones that might fix a genetic defect that causes cancer or some other disease.
Being able to tailor-make viruses that bind to specific receptors could help deliver the genes to cells where they are needed without affecting other cells. And the knowledge that multiple binding sites help viruses gain a strong hold could help scientists to make these designer viruses more effective delivery vehicles. Tailor-made viruses may also offer insight into studies of systems biology -- for example, how added genes affect behavior see: http://www.bnl.gov/bnlweb/pubaf/pr/bnlpr090501.htm.
The structural details reported in the current study were derived by cryo-electron microscopy -- the analysis of frozen samples of the virus bound to partial and full receptor molecules. This part of the study was performed at Purdue University. Cloning and sequencing the receptor gene and producing the receptor protein were all performed at Brookhaven Lab.
The data were also correlated with a previous study of a portion of the CAR protein bound to adenovirus, performed at Brookhaven’s National Synchrotron Light Source and published by Freimuth and others in 1999 see: http://www.bnl.gov/bnlweb/pubaf/pr/bnlpr111899.html.
Brookhaven Lab just received $750 thousand from the U.S. Department of Energy to purchase its own cryo-electron microscope, so that this kind of complementary approach to the study of biological molecules can now take place entirely at the Lab.
This research was funded by the National Institutes of Health, the Keck Foundation, Purdue University, and the U.S. Department of Energy, which supports basic research in a variety of scientific fields.
The U.S. Department of Energy's Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists.
The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.
Send page by E-Mail Researchers Find Enzyme Crucial To Preservation Of Memories
Posted: Monday, September 24, 2001
Source: Howard Hughes Medical Institute (http://www.hhmi.org/)
Using a technique to eliminate the function of one enzyme in a restricted memory-related region in the brains of mice, researchers have shown that the enzyme is important in consolidating long-term memories.
According to the researchers, their experiments -- which showed that defects in a key biochemical signaling pathway were responsible for the animals’ inability to improve their long-term memory in a series of maze tests -- constitute a powerful approach to understanding molecules involved in learning and memory.
In an article published in the September 21, 2001, issue of Cell, Howard Hughes Medical Institute investigator Susumu Tonegawa and colleagues at the Massachusetts Institute of Technology (MIT) and the Vollum Institute reported that elimination of the enzyme, calcium-calmodulin dependent kinase (CaMKIV), in the forebrains of mice had profound effects on signaling pathways in the brain and learning behavior.
The scientists began their studies to clarify the enzyme’s role in late long-term potentiation (L-LTP), the process by which enduring memories are established through a mechanism of activating genes that trigger protein synthesis. This protein synthesis, in turn, alters the synapses -- connections between neurons -- and "etches" permanent memory pathways.
"CaMKIV had been implicated in long-term memory pathways in the past, but previous studies had involved global knockout of the enzyme in the entire animal," said Tonegawa. "Such knockouts gave inconsistent results because they affected the whole brain throughout development. We decided to use a technique to inhibit the protein only in the forebrain, which is more involved in higher brain function."
Tonegawa said that other research groups had attempted to knock out a protein called CREB, which is involved in turning on gene transcription in L-LTP, and which was believed to be activated by CaMKIV. The results of these studies were inconclusive, Tonegawa said, because there appeared to be multiple forms of CREB that could compensate for any knockout.
Tonegawa and his colleagues used a genetic technique that allowed them to replace the normal CaMKIV with a "dominant negative" mutant enzyme that would be produced only in the forebrains of the mice. Dominant negative enzymes have all of the characteristics of the functioning enzyme -- such as an ability to bind normally to other molecules -- but they lack the ability to carry out an appropriate enzymatic reaction.
The scientists first studied the molecular details of the lack of CaMKIV activity in brain slices from the transgenic mice. They discovered that the base level of CaMKIV activity in the mouse brains was normal, but when chemicals were added that mimicked the conditions of neuronal activity, as in memory formation, the enzyme function was significantly lower. The brain slice studies also revealed that CREB activation by phosphorylation in the transgenic mice was suppressed, strongly implicating a role for the CaMKIV in normal CREB activation as a result of neuronal activity.
Experiments with brain slices also revealed that the transmission of nerve impulses in the transgenic mice was normal, except under conditions mimicking protein-synthesis-dependent L-LTP.
"These results pinpointed for us the role of CaMKIV in the protein-synthesis-dependent type of LTP," emphasized Tonegawa. "This is very important, because in the past people have published studies implicating another enzyme, called protein kinase A, in LTP. However, that enzyme was not specific to the protein-synthesis-dependent type of LTP."
With clear physiological evidence that they had specifically disrupted the CaMKIV pathway, the researchers next tested how well the transgenic mice could consolidate memories of a water maze. The mice were placed in a pool of water made opaque by floating beads, and required to find a platform submerged just beneath the surface. The transgenic mice initially learned the task as well as normal mice, but as training continued, they became significantly less able to find the platform.
"Thus, while these mice have a normal ability to acquire memories, they have problems converting those memories into a long-term form," said Tonegawa. However, he noted, maze experiments still present problems in interpretation. "This training takes place over a two-week period, so the memory acquisition and consolidation processes are superimposed," said Tonegawa. "Thus, it is difficult to know whether the deficit is primarily in the acquisition phase or the consolidation phase."
In an additional set of experiments, the scientists compared normal and transgenic animals’ ability to acquire and consolidate the memory that involves associating a mild shock to the footpads to the specific context of the chamber in which the shock is administered. In these experiments, memory acquisition could be more clearly separated from memory consolidation, said Tonegawa. These experiments demonstrated that the CaMKIV-deficient mice could learn to associate the shocks to the chamber context, but they had difficulties in converting such memories to long lasting memories, said Tonegawa. "Our conclusion from these tests was that the CaMKIV pathway was primarily involved in memory consolidation and retention," he said.
Tonegawa noted that memory consolidation in the transgenic animals was not completely extinguished, suggesting that there may be parallel signaling pathways involved in consolidation, or that there may have been incomplete knockout of CaMKIV activity.
"However, we believe that further studies using this technique will allow us to dissect in greater detail the differential roles and interactions of these signal transduction pathways, and how they contribute to this very complex mechanism of memory consolidation," he said. "Also, we want to know which genes are activated in this process and how these gene products helps establish these long-term changes in synaptic strengths."
Send page by E-Mail Life's Origins In Supernovae
Posted: Thursday, September 20, 2001
Source: Oak Ridge National Laboratory (http://www.ornl.gov/)
Life's Origins In Supernovae: Oak Ridge National Laboratory Heads Department Of Energy Project That Looks To The Stars
OAK RIDGE, Tenn., – Through a newly funded Department of Energy project, astrophysicists at Oak Ridge National Laboratory and around the United States hope to gain a better understanding of what happens when stars die in spectacular explosions called core collapse supernovae.
To people like ORNL astrophysicist Tony Mezzacappa, this work is about more than just satisfying their curiosity. The project is aimed at answering some basic questions about the origin of life.
"Life as we know it would not exist if not for these incredible explosions of stars," said Mezzacappa, a member of ORNL’s Physics Division. "When stars die in these explosions that generate billions upon billions of watts of energy, elements necessary for life are strewn throughout the galaxy and become part of the ‘soup’ from which our solar system formed."
The five-year $9.2 million Scientific Discovery through Advanced Computing (SciDAC) project headed by Mezzacappa will focus on several areas, but a major thrust will be on developing a standard model for core collapse supernovae. Modeling requirements for this work are severe.
"The advent of computing resources capable of trillions of calculations per second makes it possible to carry out the necessary large-scale three-dimensional simulations to understand the supernova explosion mechanism and all the phenomena that accompany the explosion of stars," Mezzacappa said.
While it takes millions of years for a star to evolve, the core collapse supernova explosion takes place in just hours. These events occur about two to three times each century in our galaxy.
Aside from the significant computational challenges of the project, Mezzacappa notes that this work, which draws from scientists at eight universities and the National Center for Supercomputer Applications, has strong ties to basic research missions of DOE.
"DOE has long been involved in both neutrino astrophysics and accelerator-based neutrino physics," Mezzacappa said. "This work will make important progress toward a standard model of supernovae similar to the development of the standard model for the sun. It also ties together much of DOE’s efforts in the areas of high-energy and nuclear physics."
With accurate supernovae models, neutrinos from supernovae can tell scientists about the properties of the dense matter in a supernova.
"We want to learn about the explosion mechanism and then the composition of the star and what that can tell us about fundamental particle and nuclear physics," Mezzacappa said.
Another important aspect of the work includes learning more about how stable heavy elements are created. With this information, scientists hope to understand the chain of events leading to the formation of life on Earth.
Also of particular interest to DOE is a collaboration with NASA and new observations of the Earth’s cosmic ray environment. Supernovae are likely the principal source and one of the acceleration mechanisms for cosmic rays.
"Our work addresses very broad themes important to DOE’s national mission," Mezzacappa said. "The ability to model the movement of radiation through matter and its interaction with that matter is a concern not only for supernovae models but also for people who model internal combustion engines, climate patterns and to researchers seeking better tools for radiation therapy."
One of the collaborators is the University of Tennessee, where distinguished scientist Jack Dongarra and colleagues will be working on mathematical solutions (algorithms) to help solve the equations that govern the motion of neutrinos through the stellar material. Dongarra is also a member of a SciDAC team of computer scientists who specialize in measuring and optimizing the performance of computer programs.
Mezzacappa also said ORNL will be collaborating with members of the University of Tennessee’s Joint Institute for Computational Sciences, whose expertise spans a number of areas of interest to ORNL.
SciDAC is an integrated program that will help create a new generation of scientific simulation computer programs. The programs will take full advantage of the extraordinary computing capabilities of computers capable of performing trillions of calculations per second to address increasingly complex problems.
The recently announced 51 DOE SciDAC projects will receive a total of $57 million this fiscal year to advance fundamental research in several areas related to the department’s missions, including climate modeling, fusion energy sciences, chemical sciences, nuclear astrophysics, high-energy physics and high-performance computing.
In addition to the University of Tennessee and the National Center for Supercomputer Applications, collaborators for the project are North Carolina State University, Florida Atlantic University, the University of California-San Diego, the University of Washington, State University of New York at Stony Brook, Clemson and the University of Illinois at Urbana-Champaign. Individuals involved in the project from ORNL are David Dean and Mike Strrayer of the Physics Division and Ross Toedte of the Computer Science and Mathematics Division.
ORNL is a DOE multiprogram facility operated by UT-Battelle.
Send page by E-Mail Chandra Examines Quadrillion-Volt Pulsar
Posted: Monday, September 17, 2001
Source: NASA/Marshall Space Flight Center (http://www.msfc.nasa.gov)
The high-voltage environment of one of the most energetic and strongly magnetized pulsars known has been surveyed by NASA's Chandra X-ray Observatory. A team of astronomers found a powerful jet of high-energy particles extending over a distance of 20 light years and bright arcs believed to be due to particles of matter and anti-matter generated by the pulsar.
The team of US, Canadian, and Japanese scientists pointed Chandra at the rapidly spinning neutron star B1509-58, located 19,000 light years away in the constellation of Circinus, for over five hours. These results were announced at the "Two Years of Science with Chandra" symposium in Washington, D.C.
“Jets and arcs on this vast scale have never been seen in any other pulsar,” said Bryan Gaensler of the Smithsonian Astrophysical Observatory. “The spectacular images we have obtained of this source are letting us test theories as to how pulsars unleash so much energy.”
The features seen with Chandra give the scientists insight into the process by which voltages of more than 7000 trillion volts are created around rotating neutron stars (the dense remnants of supernova explosions) and how these extreme voltages affect their environment. B1509-58 is of particular interest because it has a much stronger magnetic field than the Crab Nebula pulsar, which exhibits similar features on a much smaller scale.
The general picture emerging from these results is that high-energy particles of matter and antimatter are streaming away from the neutron star along its poles and near its equator. The particles leaving the poles produce the jets; astronomers speculate that only one side of the jet is apparent in B1509-58, indicating that this one side is beamed in our direction, while the other is rushing away.
"Until this observation, no one knew for sure whether such tremendous voltages and energy outputs were a trademark of all pulsars, or if the Crab was an oddball," said Vicky Kaspi of McGill University in Montreal. "Now thanks to Chandra, it is becoming clear that pulsars are stupendous cosmic power plants."
The arcs are thought to be due to shock waves in matter flowing away from the equator of the pulsar. By measuring the position and width of these arcs, the team estimated the intensity of the magnetic field, and the rate at which the pulsar is pumping high-energy particles into the space around it.
"The X-ray images give us evidence that the pulsar not only accelerates particles efficiently,” said Jonathan Arons of the University of California at Berkeley, “but it gives them energy comparable to the highest energies found in the cosmic rays which continuously bombard the Earth."
In addition, the team determined that a bright cloud of X-ray emission about 25 light years from the pulsar is due to multi-million degree gas. This hot cloud was probably produced as material ejected by the supernova collided with cooler gas in interstellar space.
Other members of the B1509-58 research team included Michael Pivovaroff (ThermaWave Inc), Nobuyuki Kawai (Tokyo Institute of Technology) and Keisuke Tamura (Nagoya University).
Chandra observed B1509-58 with its Advanced CCD Imaging Spectrometer (ACIS) instrument, which was developed for NASA by Pennsylvania State University, University Park, and Massachusetts Institute of Technology, Cambridge. NASA's Marshall Space Flight Center in Huntsville, Ala, manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.
Images associated with this release are available on the World Wide Web at:
Editor's Note: The original news release can be found at http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2001/01-299.html
Send page by E-Mail Chandra Probes Nature Of Dark Matter
Posted: Friday, September 14, 2001
Source: NASA/Marshall Space Flight Center (http://www.msfc.nasa.gov)
Scientists have precisely determined the distribution of dark matter in a distant galaxy cluster with NASA's Chandra X-ray Observatory. These new measurements serve to narrow the field of candidates that explain "dark matter," the invisible and unknown material that comprises most the Universe.
John Arabadjis and Mark Bautz of the Massachusetts Institute of Technology in Cambridge, Mass., and Gordon Garmire of Penn State University in University Park, announced their results today at the "Two Years of Science with Chandra" symposium in Washington, D.C. Their observations enabled them to trace the distribution of dark matter the galaxy cluster EMSS 1358+6245.
Previous evidence from radio, optical and X-ray observations convinced astronomers that most of the matter in the universe is in some dark, as yet undetected, form that makes its presence felt only through gravity. "The new Chandra observations are providing new clues about the nature of this mysterious stuff,'' said Bautz.
"When combined with data from the Hubble Space Telescope, we are able to place restrictions on the cross section, or size, of the dark matter particles,'' said Arabadjis. "The larger the particles, the more strongly they interact, and the more they alter the dark matter distribution."
In galaxy clusters, the amount of dark matter can be inferred by measuring the pressure in the X-ray emitting hot gas and determining how much dark matter is required to provide the gravity necessary to keep the gas from escaping the cluster. In the cluster EMSS 1358+6245, the mass of the dark matter is found to be about 4 times that of the "normal" matter (matter not comprised of exotic particles), typical of large galaxy clusters. The distribution of dark matter holds the key to understanding its composition.
The most popular model for dark matter invokes slowly moving particles called cold dark matter, which interact with "normal" matter only through gravity. Recent optical observations of galaxies and galaxy clusters have suggested that dark matter particles may interact more vigorously than simple cold dark matter. The problem is that galaxies composed primarily of cold dark matter should have a greater central concentration of dark matter than the optical data suggest.
One solution has been to introduce self-interacting dark matter, or SIDM. By comparing the Chandra data with theoretical simulations, scientists can place strict constraints on the SIDM particles. Chandra observations show there is no evidence for an excessively spread-out dark matter distribution at distances larger than 150,000 light years from the cluster's center. Inside that distance the dark matter may rather uniformly distributed, so some collisions between dark matter particles may still be needed. These results over a range of distances from the cluster center place the strongest observational limits yet on the dark matter interaction rate in galaxy cluster cores.
EMSS 1358+6245, about 4 billion light years away in the constellation Draco, was observed by Chandra for 15.3 hours on Sept. 3-4, 2000 using the ACIS detector.
The ACIS instrument was developed for NASA by Penn State and MIT. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.
Images associated with this release are available on the World Wide Web at:
http://chandra.harvard.edu AND http://chandra.nasa.gov
Editor's Note: The original news release can be found at http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2001/01-298.html
Send page by E-Mail Young Stars In Orion May Solve Mystery Of Our Solar System
Posted: Wednesday, September 12, 2001
Source: Penn State (http://www.psu.edu/)
Scientists may have to give the Sun a little more credit. Exotic isotopes present in the early Solar System--which scientists have long-assumed were sprinkled there by a powerful, nearby star explosion--may have instead been forged locally by our Sun during the colossal solar-flare tantrums of its baby years.
The isotopes--special forms of atomic nuclei, such as aluminum-26, calcium-41, and beryllium-10--can form in the X-ray solar flares of young stars in the Orion Nebula, which behave just like our Sun would have at such an early age. The finding, based on observations by the Chandra X-ray Observatory, has broad implications for the formation of our own Solar System.
Eric Feigelson, professor of astronomy and astrophysics at Penn State, led a team of scientists on this Chandra observation and presents these results in Washington, D.C., today at a conference entitled "Two Years of Science with Chandra".
"The Chandra study of Orion gives us the first chance to study the flaring properties of stars resembling the Sun when our solar system was forming," said Feigelson. "We found a much higher rate of flares than expected, sufficient to explain the production of many unusual isotopes locked away in ancient meteorites. If the young stars in Orion can do it, then our Sun should have been able to do it too."
Scientists who study how our Solar System formed from a collapsed cloud of dust and gas have been hard pressed to explain the presence of these extremely unusual chemical isotopes. The isotopes are short-lived and had to have been formed no earlier than the creation of the Solar System, some five billion years ago. Yet these elements cannot be produced by a star as massive as our Sun under normal circumstances. (Other elements, such as silver and gold, were created long before the creation of the solar system.)
The perplexing presence of these isotopic anomalies, found in ancient meteoroids orbiting the Earth, led to the theory that a supernova explosion occurred very close to the Solar System's progenitor gas cloud, simultaneously triggering its collapse and seeding it with short-lived isotopes.
Solar flares could produce such isotopes, but the flares would have to be hundreds of thousands of times more powerful and hundreds of times more frequent than those our Sun generates.
Enter the stars in the Orion Nebula. This star-forming region has several dozen new stars nearly identical to our Sun, only much younger. Feigelson's team used Chandra to study the flaring in these analogs of the early Sun and found that nearly all exhibit extremely high levels of X-ray flaring--powerful and frequent enough to forge many of the kinds of isotopes found in the ancient meteorites from the early solar system.
"This is a very exciting result for space X-ray astronomy," said Donald Clayton, Centennial Professor of Physics and Astronomy at Clemson University. "The Chandra Penn State team has shown that stellar-flare acceleration produces radioactive nuclei whether we want them or not. Now the science debate can concentrate on whether such irradiation made some or even all of the extinct radioactivities that were present when our solar system was formed, or whether some contamination of our birth molecular cloud by external material is also needed."
"This is an excellent example of how apparently distant scientific fields, like X-ray astronomy and the origins of solar systems, can in fact be closely linked," said Feigelson.
### The Orion observation was made with Chandra's Advanced CCD Imaging Spectrometer, which was conceived and developed for NASA by Penn State and Massachusetts Institute of Technology under the leadership of Gordon Garmire, the Evan Pugh Professor of Astronomy and Astrophysics at Penn State. The Penn State observation team includes Pat Broos, James Gaffney, Gordon Garmire, Leisa Townsley and Yohko Tsuboi. Collaborators also include Lynne Hillenbrand of CalTech and Steven Pravdo of the NASA Jet Propulsion Laboratory.
Isotopes are atoms whose nuclei have different numbers of neutrons. Many isotopes are unstable, or radioactive, and decay into other elements. A famous example is carbon-14 whose decay gives scientists the opportunity to date organic materials over thousands of years.
A rare type of ancient meteorite called carbonaceous chondrites, which are rocks from the Asteroid Belt whose orbits are perturbed and fall to the Earth, date back to the formation of our Solar System 4.55 billion years ago. Studying carbonaceous chondrites gives us a unique window on conditions in the solar nebula when the Sun and Solar System were forming. Certain portions of carbonaceous chondrites, small melted pebbles called Calcium-Aluminum-rich Inclusions or CAIs, have unusually high abundances of decay products of rare, short-lived isotopes. These include beryllium-10, calcium-41, 26-aluminum and 53-manganese, among others.
Explaining the presence of these short-lived isotopes, which do not appear anywhere else in solar system material, has been one of the toughest challenges of solar system science. The favored explanation has been that a star exploded in a supernova and triggered a nearby cloud of dust and gas to collapse to form our Sun and planetary system. But conditions have to be carefully adjusted for this model, and it cannot be widely applied to all stars. The principal alternative model is that energetic particles from violent flares hit particles in the solar nebula and transformed some of their atoms to radioactive isotopes. A drawback to this model has been that the level of flaring needed, around 100,000 times the flaring level of the Sun today, was thought to be impossibly high. However, the X-ray observations reported here give direct evidence for just this high level of flaring. In addition, this model readily applied to all young stars and solar systems, not just a few.
Send page by E-Mail A Previously Unknown Role For Antibodies
Posted: Friday, September 7, 2001
Source: Scripps Research Institute (http://www.scripps.edu/)
Scientists At The Scripps Research Institute Discover A Previously Unknown Role For Antibodies
La Jolla, CA, September 7, 2001 -- A team of scientists lead by Professor Richard Lerner, Ph.D., President of The Scripps Research Institute (TSRI) have discovered that antibodies have a novel catalytic ability—unique among proteins—which could possibly mean they do more to protect our bodies than scientists had previously thought.
In the current issue of the journal Science, the team demonstrates that antibodies can catalyze the formation of hydrogen peroxide from singlet oxygen.
All antibodies have the ability to do this," says Professors Paul Wentworth Jr., Ph.D. and Kim Janda, Ph.D., two of the lead authors on the paper. "Singlet oxygen is not something you want around."
Singlet oxygen is an electronically excited form of oxygen that forms spontaneously during normal metabolic processes or when oxygen is subjected to visible or ultraviolet light in the presence of a sensitizer. Singlet oxygen is highly reactive, making it potentially dangerous to an organism. Throughout evolution, animals have developed various mechanisms for removing singlet oxygen in order to survive. Also called immunoglobins, antibodies are produced by the immune system's B cells. The body has a large pool of B cells that recognize a wide range of foreign proteins, and after a pathogen enters the bloodstream, B cells produce specific antibodies that circulate through the blood and track down, bind to, and help eliminate the viral or bacterial invaders.
In the report, the team speculates that before this antibody-mediated immune response evolved in vertebrates hundreds of millions of years ago, an ancient form of antibodies may have existed—molecules whose role was to catalyze singlet oxygen destruction.
"Antibodies could have played a role as ancient proteins whose function was to remove singlet oxygen," says Janda.
The ability to convert oxygen into hydrogen peroxide may also be part of a previously unrecognized killing mechanism that would enhance the defensive role of antibodies by allowing them to subject pathogens to hydrogen peroxide and participate directly in their killing.
Lerner and Wentworth comment, "This heretofore unknown and intrinsic capacity of antibodies opens up exciting possibilities for new antibody-mediated therapies for conditions ranging from bacterial and viral infection to cancer. Furthermore, the ability of antibodies to generate toxic compounds may be linked to a number of autoimmune disease states, such as lupus."
Based on their examination of antibody and T-cell receptor x-ray crystal structures, the authors propose a conserved site within the antibody structure where they believe the singlet oxygen binds and where the catalytic process is initiated.
Another interesting finding is that the antibodies carry the reaction through an unusual intermediate called dihydrogen trioxide that is formed from the addition of water and oxygen. Dihydrogen trioxide has never before been observed in biological systems. "Although its presence has been a source of considerable speculation," says Wentworth.
The research article, "Antibodies Catalyze the Oxidation of Water" is authored by Paul Wentworth, Jr., Lyn H. Jones, Anita D. Wentworth, Xueyong Zhu, Nicholas A. Larsen, Ian A. Wilson, Xin Xu, William A. Goddard III, Kim D. Janda, Albert Eschenmoser, and Richard A. Lerner, and appears in the September 7, 2001 issue of the journal Science.
The research was funded in part by the National Institutes of Health and The Skaggs Institute for Chemical Biology.
Send page by E-Mail Stellar Winds In Evolution Of Milky Way Galaxy
Posted: Friday, September 7, 2001
Source: Penn State (http://www.psu.edu/)
Scientists Find X Rays From Stellar Winds That
May Play Significant Role In Evolution Of Milky Way Galaxy
Colorful star-forming regions that have captivated stargazers since the advent of the telescope 400 years ago contain gas thousands of times more energetic than previously recognized, powered by colliding stellar winds. This multimillion-degree gas radiated as X rays is one of the long-sought sources of energy and elements in the Milky Way galaxy's interstellar medium.
A team led by Leisa Townsley, a senior research associate in astronomy and astrophysics at Penn State University, uncovered this wind phenomenon in the Rosette Nebula, a stellar nursery. With the Chandra X-ray Observatory, the team found that the most massive stars in the nebula produce winds that slam into each other, create violent shocks, and infuse the region with 6-million-degree gas.
The findings are presented in Washington, D.C., today at a conference entitled "Two Years of Science with Chandra."
"A ghostly glow of diffuse X-ray emission pervades the Rosette Nebula and perhaps many other similar star-forming regions throughout the Galaxy," said Townsley. "We now have a new view of the engine lighting the beautiful Rosette Nebula and new evidence for how the interstellar medium may be energized."
Townsley and her colleagues created a striking X-ray panorama of the Rosette Molecular Cloud from four images with Chandra's Advanced CCD Imaging Spectrometer. This is a swath of the sky nearly 100 light-years across sprayed with hundreds of X-ray-emitting young stars. In one corner of the Rosette Molecular Cloud lies the Rosette Nebula, called an "H II region" because the hydrogen gas there has been stripped of its electrons due to the strong ultraviolet radiation from its young stars. This region, about 5,000 light years away in the constellation Monoceros, the Unicorn, has long been a favorite among amateur astronomers. The wispy, colorful display is visible with small telescopes.
The Chandra survey reveals, for the first time, 6-million-degree gas at the center of the Rosette Nebula, occupying a volume of about 3,000 cubic light years. Fueling the fury are a handful of massive type-O and type-B stars at the core of the nebula, the most massive members of a populous "OB association" that also includes hundreds of lower-mass stars.
"Until this observation, no one really knew where the energy of the powerful OB stellar winds goes," said Eric Feigelson, professor of astronomy and astrophysics at Penn State and a co-investigator in the study. "Theorists have speculated about this for decades, and we now see with Chandra the heat from the winds slamming into the cooler gas."
Earlier X-ray telescopes did not have the resolution to differentiate between point sources and diffuse emission in the Rosette Nebula to the extent that Chandra has. Chandra imaged over 300 individual young stars in the Rosette Nebula, plus hundreds more in the Rosette Molecular Cloud. "We were able to identify the faint, diffuse radiation by subtracting out these point sources and looking at what was left over," explains team member Patrick Broos, a research assistant in astronomy and astrophysics at Penn State.
The diffuse emission is not likely to be from supernova remnants left over from exploded stars because the Rosette Nebula is too young to have produced these, according to You-Hua Chu, of the University of Illinois at Urbana-Champaign. Rather, the diffuse emission must be related to the way the stellar winds from OB associations dissipate their energy. Understanding the detailed processes involved will rely on front-line research done in the laboratory on energy transport in very hot gases, according to Thierry Montmerle, of the Centre d'Etudes de Saclay in France. Chu and Montmerle have joined the research team to help interpret the Chandra results.
The observations were made with Chandra's Advanced CCD Imaging Spectrometer, which was conceived and developed for NASA by Penn State and Massachusetts Institute of Technology under the leadership of Gordon Garmire, the Evan Pugh Professor of Astronomy and Astrophysics at Penn State.
IMAGES: Images are available on the web at http://www.science.psu.edu/alert/Townsley9-2001.htm
Send page by E-Mail Mothers Transmit Mitochondrial DNA Through Daughters Only
Posted: Friday, September 7, 2001
Source: Uppsala University (http://www.uu.se/)
Scientists have argued whether or not the often-studied mitochondrial DNA molecule is clonally inherited. It is with assuming clonal inheritance this type of DNA has been used to track the origin of modern human as well as to draw pictures of genetic relationships among other animals and plants. The conflict has now been solved by two evolutionary geneticists from Uppsala University in Sweden, who present the new evidence in this week’s issue of Nature. Their results show that mitochondrial DNA is stably transmitted from mothers to their offspring only. This clonal inheritance indeed makes mitochondrial DNA suitable for use in evolutionary studies.
The genetic material in humans and other animals is arranged in chromosomes that are inherited both from the mother and the father. A small fraction of the genetic material is also assembled in the mitochondria and has been assumed to only be inherited from mothers to offspring. A belief that often has been challenged. If there is stable maternal inheritance of mitochondrial DNA, distinct maternal lineages would be created and these can be used for evolutionary and phylogenetic studies. Examples are the origin of modern humans and the link between humans and apes.
Recent findings suggest that mitochondrial DNA is not entirely inherited from mother to offspring; instead paternal mitochondrial DNA occasionally slips through with sperm. Also, genetic changes may occur in mothers mitochondrial DNA, similar to what happen with our chromosomes when egg and sperm are formed. There is therefore an ongoing debate whether or not mitochondrial DNA can be used for phylogenetic analyses.
To test the hypotheses that mitochondrial DNA is entirely transmitted through females one would have to follow its inheritance for hundreds or thousands of generations. In practice, this proves impossible. A new idea posits to compare the inheritance of mitochondria with some other genetic material that is transmitted through females only. If the pattern of inheritance is identical, this evidence stable maternal inheritance of the mitochondrial DNA.
In humans there is no genetic material that is only transferred through females. Hans Ellegren and Sofia Berlin therefore chose to use birds as model organisms to unravel the issue. Female birds have a unique chromosome, the W-chromosome, that is inherited from mothers to daughters in stable maternal lineages.
To be able to do the comparison between mitochondrial DNA and the W-chromosome the scientist found a fitting W-chromosome genetic type in peregrine falcons. The genetic relationships proved to be spot on identical! This shows that mitochondrial DNA must have been inherited in the same way as the W-chromosome, that is only through females.
Through calculations based on the genetic relationships, Hans Ellegren and Sofia Berlin could approximate a stable pattern of inheritance of mitochondrial DNA for at least 20.000 falcon generations, or 200.000 years. This shows that the inheritance of mitochondrial DNA really is stable even on an evolutionary time scale.
The results are important since there is evidence that parts of the genetic material are unique for females, which give rise to maternal lineages. If that had not been the case one would have had to re-evaluate many earlier findings, from the origin of humans to the relationships among extant animal and plant species. The study is also important since it for the first time compares the inheritance of a chromosome and the mitochondrial DNA.
Send page by E-Mail Chandra Catches Milky Way Monster Snacking
Posted: Thursday, September 6, 2001
Source: NASA/Marshall Space Flight Center (http://www.msfc.nasa.gov)
For the first time, a rapid X-ray flare has been observed from the direction of the supermassive black hole that resides at the center of our galaxy. This violent flare captured by NASA's Chandra X-ray Observatory has given astronomers an unprecedented view of the energetic processes surrounding this supermassive black hole.
A team of scientists led by Frederick K. Baganoff of MIT detected a sudden X-ray flare while observing Sagittarius A*, a source of radio emission believed to be associated with the black hole at the center of our Galaxy.
"This is extremely exciting because it's the first time we have seen our own neighborhood supermassive black hole devour a chunk of material," said Baganoff. "This signal comes from closer to the event horizon of our Galaxy's supermassive black hole than any that we have ever received before. It's as if the material there sent us a postcard before it fell in."
In a just few minutes, Sagittarius A* became 45 times brighter in X-rays, before declining to pre-flare levels a few hours later. At the peak of the flare, the X-ray intensity dramatically dropped by a factor of five within just a 10-minute interval. This constrains the size of the emitting region to be no larger than about 20 times the size of the "event horizon" (the one-way membrane around a black hole) as predicted by Einstein's theory of relativity.
The rapid rise and fall seen by Chandra are also compelling evidence that the X-ray emission is coming from matter falling into a supermassive black hole. This would confirm the Milky Way's supermassive black hole is powered by the same accretion process as quasars and other active galactic nuclei.
Dynamical studies of the central region of our Milky Way Galaxy in infrared and radio wavelengths indicate the presence of a large, dark object, presumably a supermassive black hole having the mass of about 3 million suns. Sagittarius A* is coincident with the location of this object, and is thought to be powered by the infall of matter into the black hole. However, the faintness of Sagittarius A* at all wavelengths, especially in X-rays, has cast some doubt on this model.
The latest precise Chandra observations of the crowded galactic center region have dispelled that doubt, confirming the results of the dynamical studies. Given the extremely accurate position, it is highly unlikely that the flare is due to an unrelated contaminating source such as an X-ray binary system.
"The rapid variations in X-ray intensity indicate that we are observing material that is as close to the black hole as the Earth is to the Sun," said Gordon Garmire of Penn State University, principal investigator of Advanced CCD Imaging Spectrometer (ACIS), which was used in these observations. "It makes Sagittarius A* a uniquely valuable source for studying conditions very near a supermassive black hole."
The energy released in the flare corresponds to the sudden infall of material with the mass equivalent to a comet. Alternatively, the scientists speculate that this flare could have been caused by the reconnection of magnetic field lines just outside the event horizon, similar to phenomenon responsible for solar flares but on a tremendous scale.
In either scenario, the energy released would be accompanied by shock waves that accelerated the electrons near the black hole to nearly the speed of light, leading to an outburst of X-rays. A longer-term increase in radio emission was also observed beginning around the time of the flare, indicating that the production of high-energy electrons was increasing.
"It's truly remarkable that we could identify and track this flare in such a crowded region of space," said Mark Bautz of MIT. "This discovery would not have been possible without the resolution and sensitivity of Chandra and the ACIS instrument."
The team first observed Sgr A* with ACIS on September 21, 1999, and again on October 26-27, 2000. The X-ray flare was detected in the second observation.
### Other members of the team are Niel Brandt, George Chartas, Eric Feigelson, Leisa Townsley (Penn State), Yoshitomo Maeda (Institute of Space and Astronautical Science, Japan), Mark Morris (UCLA), George Ricker (MIT), and Fabian Walker (CalTech).
The ACIS instrument was developed for NASA by Penn State and MIT under the leadership of Garmire. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.
Images associated with this release are available on the World Wide Web at: http://chandra.harvard.edu AND http://chandra.nasa.gov
Editor's Note: The original news release can be found at http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2001/01-296.html
Send page by E-Mail Genes That Speed Up Formation Of New Species
Posted: Thursday, September 6, 2001
Source: University Of Maryland, College Park (http://www.umd.edu)
COLLEGE PARK, MD - Like a family that splits in a feud, many species share common ancestors, but they never have much to do with their cousins. In fact, many life forms actually develop into entirely new species as they change to adapt to new environments.
Scientists have theorized that how fast one species branches out to become two, a process called speciation, is in the genes. If a couple of key genes are located close to each other on the species' genome, the theory goes, formation of a new species will move along more quickly.
By studying the genes of a common insect that appears to evolving into two separate species adapting to different environments, two University of Maryland researchers have confirmed that theory for the first time.
In a study published in the August 30 edition of the journal "Nature," Sara Via, an evolutionary biologist, and insect geneticist David Hawthorne discovered that genes involved in speciation are indeed located very close to each other.
Via and Hawthorne studied the pea aphid, a common crop pest that stems from a common ancestral aphid but that appears to be in the process of splitting into two species that infest different plants. Where the ancestors all survived on the same food, one of the new species now lives on alfalfa, the other on clover. And while the species look identical, they show little interest in meeting, either to share a meal or to reproduce.
"If one defines species as two groups that are unwilling or unable to successfully reproduce together, then these aphids are nearly separate species," says Via. "The pea aphids that we studied are now highly specialized on either alfalfa or clover, and they appear to interbreed very little.
"We knew that these aphids differed genetically in the their environmental choice and in how well they survived in that environment," says Via, "but we didn't know how many genes were involved in the difference, or the extent to which the genes for the different traits might act in concert."
Using a genetic map they made of the pea aphid genome, Hawthorne and Via found that a single gene or a few genes that increase performance and the tendency to find mates on one plant while decreasing performance on the other plant lie close together within several small chromosomal regions. Until now, no one has seen such a gene arrangement on actual organisms.
"When the genes lie close together like this, they are more likely to continue to change together, than if the genes were scattered around the genome, because they are less likely to be divided during reproduction," says Via. "This gene arrangement could cause very rapid evolution and speciation."
The term "rapid" is relative. It could mean that it may take only hundreds or thousands of generations for a new species to form, instead of the millions of generations that are typically expected.
"Speciation is often driven by natural selection and adaptation to different environments. When the genetics are right, it can happen very fast," says Via.
Hawthorne and Via expect this type of gene arrangement also will be found in other species that are thought to have speciated by adaptation to different habitats. "The aphids are a great model system for studying how genetic divergence and speciation may occur in other kinds of organisms that use different resources or environments," says Hawthorne.
Editor's Note: The original news release can be found at http://www.inform.umd.edu/CampusInfo/
Send page by E-Mail A defining difference between man and non-human primates
Posted: Wednesday, September 5, 2001
Source: Medical College Of Georgia (http://www.mcg.edu/)
A defining difference between man and non-human primates has been found in the circuitry of brain cells involved in language, according to researchers at the Medical College of Georgia.
Their findings belie the notion that the primary difference between man, monkey and chimpanzee is the size of the brain and opens up a new area of study that may explain man's capacity for complex communication, they say.
They also say this circuitry may be what goes awry in still unexplained conditions that affect language, such as schizophrenia, autism and even epilepsy.
"Language is something that makes us different from other species; now we have found a structural correlation," said Dr. Manuel F. Casanova, psychiatrist and neurologist at MCG and the Department of Veterans Affairs Medical Center in Augusta.
"We are trying to understand what makes the human brain different from non-human primates," said Dr. Daniel Buxhoeveden, physical anthropologist at MCG. "We also are trying to understand the pathology of diseases of the brain that are not understandable by classical methods. We think the difference is going to be in the way the brain is organized."
To study that organization, they have completed detailed computer analyses of a basic, functional unit of the human and non-human brain known as a minicolumn, a group of 80 to 100 cells and the wiring that connects them. Millions of these minicolumns are found throughout the brain; their studies focused on the minicolumns found in an area of the brain involved in language called the planum temporale.
There they found distinct, microscopic differences in the minicolumns of humans and non-human primates. They also found differences in the minicolumns in the right and left side of the brain in humans that weren't present in non-humans; previous studies found distinctive lateralization – or left-right differences – in humans and chimps.
"These minicolumns are different in their structure in the human brain and also different in that they are lateralized, larger on the left side than on the right side of the brain," Dr. Buxhoeveden said. "We didn't find this in the chimpanzee or the monkey." In most humans, language function is housed on the left side of the brain, which would make the left-right differences found all the more pertinent, Dr. Casanova said.
These differences may explain man's capacity for the subtleties of communication – such as understanding concepts and formulating and expressing responses – compared to the non-human primates' more fundamental communication system.
"Other species can communicate but they really don't have a language," Dr. Casanova said. "Like the bumble bee. They can't compare the pollen catch of that day to a month ago or maybe what they expect to find a day or a year from now. So, where should we look for something that makes us different from other species? Within the language regions of the brain."
Numerous previous studies have compared the individual brain cells and the brain in toto in man and animals and found that cells are essentially identical and that the brains looked – from the outside at least – very similar other than size differences.
For example, the chimpanzee is man's closest evolutionary relative; the two have about 99 percent of their DNA in common, but the human brain is about three and one-half times larger. "The question has been, what else changed besides size," Dr. Casanova said.
After examining brain tissue from humans, rhesus monkeys and chimpanzees obtained from the Yakovlev-Haleem Brain Collection at the Armed Forces Institute of Pathology in Washington, D.C., they believe that how brain cells are organized to work together is a key difference.
"We found evidence that the brain is organized differently in humans in this area of the brain, even though the outside looks the same," Dr. Buxhoeveden. "This provides an anatomical substrate, a hint that the brain is wired differently in humans in the language area than in the chimpanzee or the monkey."
"Now we will be looking at this to describe pathologies that are subtle, that don't have classical symptoms that you see in diseases such as Alzheimer's, where there are obvious, major things wrong with brain tissue," he said. "In diseases such as schizophrenia and autism, those obvious symptoms aren't there. But we believe that you will find them in the most subtle wiring of the brain."
The researchers are expanding their studies by including other species, including non-primates such as dolphins, mammals which have large, highly developed brains.
### The researchers' findings are published in the August issue of the American Journal of Physical Anthropology and scheduled for publication this fall in Brain Behavior and Evolution. Support for the research was provided by the Maryland-based Stanley Foundation, a major supporter of psychiatric research worldwide; Dr. Casanova is a Stanley Scholar, which means the foundation also provides ongoing support for his mentoring of future psychiatrists.
Other co-authors on the studies include Andrew E. Switala, computer programmer and mathematician; and Dr. Emil Roy, linguistics and computer applications expert.
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