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Sunday, October 14, 2007
Tuesday, March 20, 2007
No Sex For 40 Million Years? No Problem
Science Daily — A group of organisms that has never had sex in over 40 million years of existence has nevertheless managed to evolve into distinct species, says new research published today. The study challenges the assumption that sex is necessary for organisms to diversify and provides scientists with new insight into why species evolve in the first place.
Scanning electron micrographs showing morphological variation of bdelloid rotifers and their jaws. Have these asexual animals really diversified into evolutionary species? (Credit: Diego Fontaneto / Courtesy of PLoS Biology)
The research, published in PLoS Biology, focuses on the study of bdelloid rotifers, microscopic aquatic animals that live in watery or occasionally wet habitats including ponds, rivers, soils, and on mosses and lichens. These tiny asexual creatures multiply by producing eggs that are genetic clones of the mother -- there are no males. Fossil records and molecular data show that bdelloid rotifers have been around for over 40 million years without sexually reproducing, and yet this new study has shown that they have evolved into distinct species.
Using a combination of DNA sequencing and jaw measurements taken using a scanning electron microscope, the research team examined bdelloid rotifers living in different aquatic environments across the UK, Italy and other parts of the world. They found genetic and jaw-shape evidence that the rotifers had evolved into distinct species by adapting to differences in their environment.
Dr Tim Barraclough from Imperial College London's Division of Biology explained: "We found evidence that different populations of these creatures have diverged into distinct species, not just because they become isolated in different places, but because of the differing selection pressures in different environments.
"One remarkable example is of two species living in close proximity on the body of another animal, a water louse. One lives around its legs, the other on its chest, yet they have diverged in body size and jaw shape to occupy these distinct ecological niches. Our results show that, over millions of years, natural selection has caused divergence into distinct entities equivalent to the species found in sexual organisms."
Previously, many scientists had thought that sexual reproduction was necessary for speciation because of the importance of interbreeding in explaining speciation in sexual organisms. Asexual creatures like the bdelloid rotifers were known not to be all identical, but it had been argued that the differences might arise solely through the chance build-up of random mutations that occur in the 'cloning' process when a new rotifer is born. The new study proves that these differences are not random and are the result of so-called 'divergent selection', a process well known to cause the origin of species in sexual organisms.
Dr Barraclough adds: "These really are amazing creatures, whose very existence calls into question scientific understanding, because it is generally thought that asexual creatures die out quickly, but these have been around for millions of years.
"Our proof that natural selection has driven their divergence into distinct species is another example of these miniscule creatures surprising scientists -- and their ability to survive and adapt to change certainly raises interesting questions about our understanding of evolutionary processes."
Note: This story has been adapted from a news release issued by Imperial College London.
(c) www.sciencedaily.com
248-dimension maths puzzle solved
An international team of mathematicians has detailed a vast complex numerical "structure" which was invented more than a century ago.
Mapping the 248-dimensional structure, called E8, took four years of work and produced more data than the Human Genome Project, researchers said.
The structure is described in the form of a vast matrix
E8 is a "Lie group", a means of describing symmetrical objects.
The team said their findings may assist fields of physics which use more than four dimensions, such as string theory.
Lie groups were invented by the 19th Century Norwegian mathematician Sophus Lie (pronounced "Lee").
Familar structures such as balls and cones have symmetry in three dimensions, and there are Lie groups to describe them. E8 is much bigger.
"What's attractive about studying E8 is that it's as complicated as symmetry can get", observed David Vogan from the Massachussetts Institute of Technology (MIT) in the US.
"Mathematics can almost always offer another example that's harder than the one you're looking at now, but for Lie groups, E8 is the hardest one."
Professor Vogan is presenting the results at MIT in a lecture entitled The Character Table for E8, or How We Wrote Down a 453,060 x 453,060 Matrix and Found Happiness.
Fundamental force
Conceptualising, designing and running the calculations took a team of 19 mathematicians four years. The final computation took more than three days' solid processing time on a Sage supercomputer.
Lie groups were invented by the Norwegian Sophus Lie
What came out was a matrix of linked numbers, which together describe the structure of E8. It contains more than 60 times as much data as the human genome sequence.
Each of the 205,263,363,600 entries on the matrix is far more complicated than a straightforward number; some are complex equations.
The team calculated that if all the numbers were written out in small type, they would cover an area the size of Manhattan.
In addition to facilitating further understanding of symmetry and related areas of mathematics, the team hopes its work will contribute to areas of physics, such as string theory, which involve structures possessing more than the conventional four dimensions of space and time.
"While mathematicians have known for a long time about the beauty and the uniqueness of E8, we physicists have come to appreciate its exceptional role only more recently," commented Hermann Nicolai, director of the Max Planck Institute for Gravitational Physics (the Albert Einstein Institute) in Germany.
"Yet, in our attempts to unify gravity with the other fundamental forces into a consistent theory of quantum gravity, we now encounter it at almost every corner."
(c) http://news.bbc.co.uk
Monday, February 26, 2007
Searching for Signs of Life on Mars
by Guy Webster, Dwayne Brown
Urey Instrument. Credit: NASA/JPL
NASA-funded researchers are refining a tool that could not only check for the faintest traces of life's molecular building blocks on Mars, but could also determine whether they have been produced by anything alive.
The instrument, called Urey: Mars Organic and Oxidant Detector, has already shown its capabilities in one of the most barren climes on Earth, the Atacama Desert in Chile. The European Space Agency has chosen this tool from the United States as part of the science payload for the ExoMars rover planned for launch in 2013. Last month, NASA selected Urey for an instrument-development investment of $750,000.
Artist's concept of ExoMars. Credit: European Space Agency
The European Space Agency plans for the ExoMars rover to grind samples of Martian soil to fine powder and deliver them to a suite of analytical instruments, including Urey, that will search for signs of life. Each sample will be a spoonful of material dug from underground by a robotic drill.
"Urey will be able to detect key molecules associated with life at a sensitivity roughly a million times greater than previous instrumentation," said Dr. Jeffrey Bada of Scripps Institution of Oceanography at the University of California, San Diego. Bada is the principal investigator for an international team of scientists and engineers working on various components of the device.
To aid in interpreting that information, part of the tool would assess how rapidly the environmental conditions on Mars erase those molecular clues.
Dr. Pascale Ehrenfreund of the University of Leiden in the Netherlands, said, "The main objective of ExoMars is to search for life. Urey will be a key instrument for that because it is the one with the highest sensitivity for organic chemicals." Ehrenfreund, one of two deputy principal investigators for Urey, coordinates efforts of team members from five other European countries.
Urey can detect several types of organic molecules, such as amino acids, at concentrations as low as a few parts per trillion.
All life on Earth assembles chains of amino acids to make proteins. However, amino acids can be made either by a living organism or by non-biological means. This means it is possible that Mars has amino acids and other chemical precursors of life but has never had life. To distinguish between that situation and evidence for past or present life on Mars, the Urey instrument team will make use of the knowledge that most types of amino acids can exist in two different forms. One form is referred to as "left-handed" and the other as "right-handed." Just as the right hand on a human mirrors the left, these two forms of an amino acid mirror each other.
Amino acids from a non-biological source come in a roughly 50-50 mix of right-handed and left-handed forms. Life on Earth, from the simplest microbes to the largest plants and animals, makes and uses only left-handed amino acids, with rare exceptions. Comparable uniformity -- either all left or all right -- is expected in any extraterrestrial life using building blocks that have mirror-image versions because a mixture would complicate biochemistry.
"The Urey instrument will be able to distinguish between left-handed amino acids and right-handed ones," said Allen Farrington, Urey project manager at NASA's Jet Propulsion Laboratory, which will build the instrument to be sent to Mars.
If Urey were to find an even mix of the mirror-image molecules on Mars, that would suggest life as we know it never began there. All-left or all-right would be strong evidence that life now exists on Mars, with all-right dramatically implying an origin separate from Earth life. Something between 50-50 and uniformity could result if Martian life once existed, because amino acids created biologically gradually change toward an even mixture in the absence of life.
The 1976 NASA Viking mission discovered that strongly oxidizing conditions at the Martian surface complicate experiments to search for life. The Urey instrument has a component, called the Mars oxidant instrument, for examining those conditions.
The oxidant instrument has microsensors coated with various chemical films. "By measuring the reaction of the sensor films with chemicals present in the Martian soil and atmosphere, we can establish if organisms could survive and if evidence of past life would be preserved," said Dr. Richard Quinn, a co-investigator on Urey from the SETI Institute, Mountain View, Calif., who also works at NASA Ames Research Center, Moffett Field, Calif.
"In order to improve our chances of finding chemical evidence of life on Mars, and designing human habitats and other equipment that will function well on Mars' surface, we need to improve our understanding of oxidants in the planet's surface environment," said Dr. Aaron Zent, a Urey co-investigator at NASA Ames.
A Urey component called the sub-critical water extractor handles the task of getting any organic compounds out of each powdered sample the ExoMars rover delivers to the instrument. "It's like an espresso maker," explained JPL's Dr. Frank Grunthaner, a deputy principal investigator for Urey. "We bring the water with us. It is added to the sample, and different types of organic compounds dissolve into the liquid as the temperature increases. We keep it under pressure the whole time."
The dissolved compounds are highly concentrated by stripping away water in a tiny oven. Then a detector checks for fluorescent glowing, which would indicate the presence of amino acids, some components of DNA and RNA, or other organic compounds that bind to a fluorescing chemical added by the instrument.
A Urey component called the micro-capillary electrophoresis unit has the critical job of separating different types of organic compounds from one another for identification, including separation of mirror-image amino acids from each other. "We have essentially put a laboratory onto a single wafer," said Dr. Richard Mathies of the University of California, Berkeley, a Urey co-investigator. The device for sending to Mars will be a small version incorporating this detection technology, which is already in use for biomedical procedures such as law-enforcement DNA tests and checking for hazardous microbes.
Switzerland will provide electronics design and packaging expertise for Urey. Micro-Cameras and Space Exploration S.A., Neuchatel, will collaborate with JPL and the European Space Agency to accomplish this significant contribution to the heart of the instrument. Dr. Jean-Luc Josset, Urey co-investigator at the University of Neuchatel will coordinate this effort and help provide detector selection and support.
(c) www.physorg.com
New Engine Helps Satellites Blast Off With Less Fuel
Georgia Tech researchers have developed a new protoype engine that allows satellites to take off with less fuel, opening the door for deep space missions, lower launch costs and more payload in orbit.
Dr. Mitchell Walker, an assistant professor in the Daniel Guggenheim School of Aerospace Engineering, tests an engine. (Credit: Image courtesy of Georgia Institute of Technology)
The efficient satellite engine uses up to 40 percent less fuel by running on solar power while in space and by fine-tuning exhaust velocity. Satellites using the Georgia Tech engine to blast off can carry more payload thanks to the mass freed up by the smaller amount of fuel needed for the trip into orbit. Or, if engineers wanted to use the reduced fuel load another way, the satellite could be launched more cheaply by using a smaller launch vehicle.
The fuel-efficiency improvements could also give satellites expanded capabilities, such as more maneuverability once in orbit or the ability to serve as a refueling or towing vehicle.
The Georgia Tech project, lead by Dr. Mitchell Walker, an assistant professor in the Daniel Guggenheim School of Aerospace Engineering, was funded by a grant from the U.S. Air Force. The project team made significant experimental modifications to one of five donated satellite engines from aircraft engine manufacturer Pratt & Whitney to create the final prototype.
The key to the engine improvements, said Walker, is the ability to optimize the use of available power, very similar to the transmission in a car. A traditional chemical rocket engine (attached to a satellite ready for launch) runs at maximum exhaust velocity until it reaches orbit, i.e. first gear.
The new Georgia Tech engine allows ground control units to adjust the engine’s operating gear based on the immediate propulsive need of the satellite. The engine operates in first gear to maximize acceleration during orbit transfers and then shifts to fifth gear once in the desired orbit. This allows the engine to burn at full capacity only during key moments and conserve fuel.
“You can really tailor the exhaust velocity to what you need from the ground,” Walker said.
The Georgia Tech engine operates with an efficient ion propulsion system. Xenon (a noble gas) atoms are injected into the discharge chamber. The atoms are ionized, (electrons are stripped from their outer shell), which forms xenon ions. The light electrons are constrained by the magnetic field while the heavy ions are accelerated out into space by an electric field, propelling the satellite to high speeds.
Tech’s significant improvement to existing xenon propulsion systems is a new electric and magnetic field design that helps better control the exhaust particles, Walker said. Ground control units can then exercise this control remotely to conserve fuel.
The satellite engine is almost ready for military applications, but may be several years away from commercial use, Walker added.
Note: This story has been adapted from a news release issued by Georgia Institute of Technology.
(c) www.sciencedaily.com
Milky Way Black Hole May Be a Colossal 'Particle Accelerator'
by Lori Stiles
This graphic illustrates the idea that the black hole at the center of the Milky Way is like an extremely powerful particle accelerator, revving up protons in the surrounding magnetic plasma and slinging them into lower-energy protons with such energy that high-energy gamma rays result from the collision. The yellow line depicts a high-energy proton flung into a lower-energy proton in the hydrogen gas cloud. The green arrow represents the high-energy gamma ray that results from the proton collision. (Art credit: Sarah Ballantyne)
Scientists were startled when they discovered in 2004 that the center of our galaxy is emitting gamma rays with energies in the tens of trillions of electronvolts. Now astrophysicists at The University of Arizona, Los Alamos National Laboratory and the University of Adelaide (Australia) have discovered a mechanism that might produce these high-energy gamma rays.
The black hole at the center of our Milky Way could be working like a cosmic particle accelerator, revving up protons that smash at incredible speeds into lower energy protons and creating high-energy gamma rays, they report.
"It's similar to the same kind of particle physics experiments that the Large Hadron Collider being built at CERN will perform," UA astrophysicist David Ballantyne said.
When complete, the Large Hadron Collider in Switzerland will be able to accelerate protons to seven trillion electronvolts. Our galaxy's black hole whips protons to energies as much as 100 times higher, according to the team's new study. That's all the more impressive because "Our black hole is pretty inactive compared to massive black holes sitting in other galaxies," Ballantyne noted.
Ballantyne collaborated with UA astrophysics Professor Fulvio Melia in the new study published in Astrophysical Journal Letters.
For the last several years, Melia has been developing a theory of what may be going on very close to the Milky Way's black hole. Melia and his group find that powerful, chaotic magnetic fields accelerate protons and other particles near the black hole to extremely high energies.
"Our galaxy's central supermassive object has been a constant source of surprise ever since it's discovery some 30 years ago," Melia said. "Slowly but surely it has become the best studied and most compelling black hole in the universe. Now we're even finding that its apparent quietness over much of the spectrum belies the real power it generates a mere breath above its event horizon---the point of no return."
The Milky Way black hole "is one of the most energetic particle accelerators in the galaxy, but it does this by proxy, by cajoling the magnetized plasma haplessly trapped within its clutches into slinging protons to unearthly speeds," Melia said.
Ballantyne used detailed, realistic maps of interstellar gas extending 10 light years beyond the black hole in modeling whether accelerated protons launched from the galactic center would produce gamma rays.
"We calculated very exactly how the protons would travel in this medium, taking into account specifically the magnetic force that changes the protons' trajectories," he said. The team calculated 222,000 proton trajectories for a statistically solid study.
Even though the protons move close to the speed of light, their motion is so random that it takes several thousand years for the particles to travel beyond 10 light years of the black hole. After the high-energy protons escape the black hole environment, they fly off into the interstellar medium, where they collide with low-energy protons (hydrogen gas) in a smash-up so energetic that particles called 'pions' form. These particles of matter quickly decay into high-energy gamma rays that, like other radiation, travel in all directions.
Ballantyne, Melia and and their colleagues found that this process can explain the energy spectrum and brightness of gamma-ray emission that astronomers observe. Researchers detect the high-energy gamma-ray emission with ground-based telescopes at Namibia, Africa, at Whipple Observatory in southeastern Arizona, and elsewhere.
"Ironically, even though our galaxy's central black hole does not itself abundantly eject hyper-relativistic plasma into the surrounding medium, this discovery may indirectly explain how the most powerful black holes in the universe, including quasars, produce their enormous jets extending over intergalactic proportions. The same particle slinging almost certainly occurs in all black-hole systems, though with much greater power earlier in the universe," Melia said.
Only 31 percent of the 222,000 proton trajectories in their sample produced gamma rays within 10 light years of the black hole, Ballantyne said. The other 69 percent escape to greater distances, where presumably they, too, will interact in gamma ray-generating collisions.
"Astronomers do, indeed, observe a glow of very-high energy gamma-rays from the inner regions of the galaxy," Ballantyne said. "It's possible that this emission is also caused by protons accelerated close to the central black hole."
Ballantyne holds UA's Theoretical Astrophysics Program Prize Postdoctoral Fellowship. The university's Theoretical Astrophysics Program, organized in 1985, is an interdisciplinary program of the UA departments of physics, astronomy and planetary sciences.
(c) www.physorg.com
Wednesday, January 10, 2007
Scientist says pulsar may have four poles
SEATTLE, Jan. 10 (UPI) -- The neutron star in the Crab Nebula may have four magnetic poles, which would be a cosmic first, a Puerto Rican scientist said.
A neutron star, the remnant of a star after a supernova explosion, sometimes is called a pulsar because it emits radio waves similar to a lighthouse track of light. The profile of the Crab Nebula star's pulse suggests the magnetic field that drives its emission is different, the BBC said.
The Crab Nebula pulsar has two pulses that can be identified, Tim Hankins, from the Arecibo Observatory in Puerto Rico, said during the American Astronomical Society meeting in Seattle. The profiles of pulses from the north and south poles of a neutron star should be identical.
Profiles for these pulses weren't, which Hankins said is the first time this has been noted in a pulsar.
"What we think is that there is another pole, possibly with a partner, that is influencing and distorting the magnetic field," he said, explaining that magnetic poles always come in pairs, so the fourth pole is distinctly likely.
Copyright 2007 by United Press International. All Rights Reserved.
(c) www.physorg.com
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