Monday, November 9, 2009

GAMMA-RAY PHOTON RACE ENDS IN DEAD HEAT; EINSTEIN WINS THIS

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Racing across the universe for the last 7.3 billion years, two gamma-ray photons arrived at NASA's orbiting Fermi Gamma-ray Space Telescope within nine-tenths of a second of one another. The dead-heat finish may stoke the fires of debate among physicists over Einstein's special theory of relativity because one of the photons possessed a million times more energy than the other.

For Einstein's theory, that's no problem. In his vision of the structure of space and time, unified as space-time, all forms of electromagnetic radiation - gamma rays, radio waves, infrared, visible light and X-rays - are reckoned to travel through the vacuum of space at the same speed, no matter how energetic. But in some of the new theories of gravity, space-time is considered to have a "shifting, frothy structure" when viewed at a scale trillions of times smaller than an electron. Some of those models predict that such a foamy texture ought to slow down the higher-energy gamma-ray photon relative to the lower energy one. Clearly, it did not.

Even in the world of high-energy particle physics, where a minute deviation can sometimes make a massive difference, nine-tenths of a second spread over more than 7 billion years is so small that the difference is likely due to the detailed processes of the gamma-ray burst rather than confirming any modification of Einstein's ideas.

"This measurement eliminates any approach to a new theory of gravity that predicts a strong energy-dependent change in the speed of light," said Peter Michelson, professor of physics at Stanford University and principal investigator for Fermi's Large Area Telescope (LAT), which detected the gamma-ray photons on May 10. "To one part in 100 million billion, these two photons traveled at the same speed. Einstein still rules."

Michelson is one of the authors of a paper that details the research, published online Oct. 28 by Nature.

Physicists have yearned for years to develop a unifying theory of how the universe works. But no one has been able to come up with one that brings all four of the fundamental forces in the universe into one tent. The Standard Model of particle physics, which was well developed by the end of the 1970s, is considered to have succeeded in unifying three of the four: electromagnetism; the "strong force" (which holds nuclei together inside atoms); and the "weak force" (which is responsible for radioactive decay, among other things.) But in the Standard Model, gravity has always been the odd man out, never quite fitting in. Though a host of theories have been advanced, none has been shown successful.

But by the same token, Einstein's theories of relativity also fail to unify the four forces.

"Physicists would like to replace Einstein's vision of gravity - as expressed in his relativity theories - with something that handles all fundamental forces," Michelson said. "There are many ideas, but few ways to test them."

The two photons provided rare experimental evidence about the structure of space-time. Whether the evidence will prove sufficient to settle any debates remains to be seen.

The photons were launched on their pan-galactic marathon during a short gamma-ray burst, an outpouring of radiation likely generated by the collision of two neutron stars, the densest known objects in the universe.

A neutron star is created when a massive star collapses in on itself in an explosion called a supernova. The neutron star forms in the core as matter is compressed to the point where it is typically about 10 miles in diameter, yet contains more mass than our sun. When two such dense objects collide, the energy released in a gamma-ray burst can be millions of times brighter than the entire Milky Way, albeit only briefly. The burst (designated GRB 090510) that sent the two photons on their way lasted 2.1 seconds.

(Photo: NASA/Sonoma State University/Aurore Simonnet)

Stanford University

WHEN ANTS ATTACK: RESEARCHERS RECREATE CHEMICALS THAT TRIGGER AGGRESSION IN ARGENTINE ANTS

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Experiments led by researchers at the University of California, Berkeley, have demonstrated that normally friendly ants can turn against each other by exploiting the chemical cues they use to distinguish colony-mates from rivals.

The new study, published in the open-access journal BMC Biology, sheds light on the factors influencing the social behavior of the Argentine ant, Linepithema humile, and provides hope for a new tactic in controlling the spread of this invasive species.

The research was conducted on the highly invasive Argentine ant, but the researchers note that the findings are likely relevant to other types of insects that rely upon chemical signals to identify each other.

"Almost all living organisms use chemical recognition cues to some degree, but it is particularly common among ants and other insects," said evolutionary biologist Neil Tsutsui, UC Berkeley associate professor of environmental science, policy and management and the study's principal investigator. "Surprisingly, it wasn't until this work that the specific chemicals used by Argentine ants to identify each other were isolated and tested."

Native to South America, the Argentine ant has taken hold in numerous countries worldwide, including Australia, Japan and the United States. In California, the ants are pervasive, pushing out native ant species and wreaking ecological havoc along the way. The Argentine ant has been blamed for exacerbating problems with some agricultural crops in the state, and for the decline of the coast horned lizard, which feeds exclusively upon the native ant species decimated by the invader.

In their native habitat, Argentine ants use their aggression to engage in inter-colony warfare with each other as they compete for resources, a behavioral trait that biologists credit for keeping the ants' numbers in check. Colonies tend to be small, typically measuring a few meters to a couple of hundred meters wide.

Biologists say that part of what makes the Argentine ants such successful invaders is that outside their home turf in South America, the fighting among them largely stops, allowing Argentine ant colonies from different regions to band together into a formidable group. Previous research conducted by Tsutsui and others provided evidence that the reason behind this relatively peaceful co-existence is the ants' genetic similarity, suggesting that they are part of the same, vast family. This lack of diversity falls in line with the theory that the invasive ants descended from a few individuals introduced to the new region.
"The striking thing about these Argentine ants in introduced ranges is that – with few exceptions – they are essentially functioning as a single, geographically huge supercolony," said Tsutsui. "If you take ants from San Diego and put them next to those from San Francisco, they'll act like they've known each other all their lives. They are part of a massive supercolony that extends hundreds of miles, nearly the entire length of California."

The UC Berkeley researchers worked with study co-authors Robert Sulc and Kenneth Shea from UC Irvine to narrow down and synthesize seven chemical molecules that trigger aggressive behavior among the Argentine ants. They also used two "control" chemicals not linked to fighting behavior. The "enemy" compounds were similar in that they were all long chains of hydrocarbons with one to three methyl groups attached.

Researchers then coated individual worker ants from the same colony with the purified substance. The researchers matched each of the chemically disguised ants with 10 untreated ants, one by one for five minutes each, in a petri dish.

"The 'enemy' chemicals generated significantly greater instances of flared mandibles, biting and other attacking behavior than did the control chemicals," said study co-lead author Ellen van Wilgenburg, a post-doctoral researcher in Tsutsui's lab at UC Berkeley. "We also saw higher levels of aggression when we increased the concentration of the chemicals and when we combined some of the chemicals together."

Despite this finding, Tsutsui cautions that significant barriers must be overcome before a pest-control substance based upon these chemicals is ready for the market. "We are still in the process of understanding how these chemicals control social behaviors in ants," he said. "These are custom chemicals that are very costly to synthesize at this stage. We are still a long way off from having large enough quantities to deploy in the field, or even knowing if these chemicals can control populations in the field."

(Photo: Sarah Yang/UC Berkeley)

UC Berkeley

FIGHTING SLEEP, PENN RESEARCHERS REVERSE THE COGNITIVE IMPAIRMENT CAUSED BY SLEEP DEPRIVATION

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A research collaboration led by biologists and neuroscientists at the University of Pennsylvania has found a molecular pathway in the brain that is the cause of cognitive impairment due to sleep deprivation. Just as important, the team believes that the cognitive deficits caused by sleep deprivation, such as an inability to focus, learn or memorize, may be reversible by reducing the concentration of a specific enzyme that builds up in the hippocampus of the brain.

It is known that sleep deprivation can have cognitive consequences, including learning and memory deficits, but the mechanisms by which sleep deprivation affects brain function remain unknown. A particular challenge has been to develop approaches to reverse the impact of sleep deprivation on cognitive function.

The findings, reported in the journal Nature, could present a new approach to treating the memory and learning deficits of insomnia. A molecular mechanism by which brief sleep deprivation alters hippocampal function is now identified in mice, involving the impairment of cyclic-AMP- and protein-kinase-A-dependent forms of synaptic plasticity, or readiness for cognitive function.

Ted Abel, principal investigator and professor of biology in the School of Arts and Sciences at the University of Pennsylvania, led the international team of researchers that found that sleep deprivation in mice affects an important molecular pathway in the hippocampus, a region of the brain known to be important for memory and learning.

The study showed that mice deprived of sleep had increased levels of the enzyme PDE4 and reduced levels of the molecule cAMP, the latter of which is crucial in forming new synaptic connections in the hippocampus, a physiological hallmark of learning.

Researchers then treated the mice with PDE inhibitors, which rescued the sleep deprivation-induced deficits in cAMP signaling, synaptic plasticity and hippocampus dependent memory. This reversal also helped to rescue deficits in synaptic connections in the hippocampus and therefore counteract some of the memory consequences of sleep deprivation.

“Millions of people regularly obtain insufficient sleep,” Abel said. “Our work has identified a treatment in mice that can reverse the cognitive impact of sleep deprivation. Further, our work identifies specific molecular changes in neurons caused by sleep deprivation, and future work on this target protein promises to reveal novel therapeutic approaches to treat the cognitive deficits that accompany sleep disturbances seen in sleep apnea, Alzheimer’s disease and schizophrenia.”

University of Pennsylvania

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