We model a close-knit community of friends and enemies as a fully connected network with positive and negative signs on its edges. Theories from social psychology suggest that certain sign patterns are more stable than others. This notion of social “balance” allows us to define an energy landscape for such networks. Its structure is complex: numerical experiments reveal a landscape dimpled with local minima of widely varying depths. We derive rigorous bounds on the energies of these local minima and prove that they have a modular structure that can be used to classify them.
A protein called neuroligin that is implicated in some forms of autism is critical to the construction of a working synapse, locking neurons together like “molecular Velcro,” a study lead by a team of UC Davis researchers has found.
Published online in the June issue of the journal Neural Development, the study is accompanied by groundbreaking images that are the first to show two neurons coming together using neuroligin to construct a new synapse.
“Previous research has suggested that neuroligin is critical for the formation and stabilization of synapses,” said Kimberley McAllister, an associate professor of neurology in the UC Davis School of Medicine and a researcher at the UC Davis Center for Neuroscience. “Our work suggests that neuroligin is one of the first molecules to be recruited to new synapses and that it also acts as Velcro to strengthen those new connections.”
Unidentified chemical reactions taking place in some polluted air may be a source of hydroxyl radicals, data from a new field study suggest.
Hydroxyl (OH) radicals result from a series of sunlight-stimulated reactions in the atmosphere involving ozone, nitrous acid and hydrogen peroxide. The highly reactive hydroxyl radicals, which typically persist in the air no more than one second before they combine with volatile organic chemicals and other gases, help the atmosphere cleanse itself, says Franz Rohrer, an atmospheric chemist at the Jülich Research Center’s Institute for Tropospheric Chemistry in Germany.
Field data gathered in China’s Pearl River delta during the summer of 2006 hint that unknown reactions taking place in some polluted air can generate substantial — and unexpectedly large — amounts of hydroxyl radicals, Rohrer and his colleagues report online June 4 in Science.
The team took round-the-clock measurements of various atmospheric constituents in a rural yet heavily populated area about 60 kilometers northwest of Guangzhou. In that area, pollutants wafting from nearby cities mix with volatile organic chemicals produced by local trees and other vegetation, says Rohrer. Atmospheric concentrations of unburned hydrocarbons are high, but levels of various nitrogen oxides (NOx) are low.
While analyzing the data, the researchers noted an unexpected surge in hydroxyl radical levels — but without the prerequisite increase in ozone levels that should have accompanied it — around noon each day. At their peak, hydroxyl concentrations measured about 15 million radicals per cubic centimeter, between three and five times that expected according to current models of atmospheric chemistry, the team notes. All together, the unknown source or sources of hydroxyl produced enough of the chemical to have boosted its concentration about 28 parts per billion each hour.
Raytheon Company (NYSE: RTN) demonstrated the ability to communicate in real time with a submerged submarine at classified speeds and depths.
This capability, which addresses one of the most significant shortfalls in submarine communications, was exhibited for the United Kingdom’s Royal Navy during an at-sea trial of Raytheon’s Deep Siren Tactical Paging (DSTP) system.
The U.K. Ministry of Defence reported that Deep Siren demonstrated “the first step toward a transformational capability that will change the way we operate submarines in the future.”
The evaluation, which took place during the U.K. Royal Navy’s TAURUS 09 deployment, follows U.S. Navy testing conducted in 2008 that culminated with a successful military utility assessment.
Raytheon is also currently working on airborne certification of Deep Siren, which will allow the system’s buoys to be deployed via aircraft.
“The Deep Siren system is a vital command and control communications link that provides never-before available capability,” said Jerry Powlen, vice president, Network Centric Systems Integrated Communications Systems. “This system once again demonstrated its utility and reliability, proving that we are ready to move forward with production.”
We model a close-knit community of friends and enemies as a fully connected network with positive and negative signs on its edges. Theories from social psychology suggest that certain sign patterns are more stable than others. This notion of social “balance” allows us to define an energy landscape for such networks. Its structure is complex: numerical experiments reveal a landscape dimpled with local minima of widely varying depths. We derive rigorous bounds on the energies of these local minima and prove that they have a modular structure that can be used to classify them.
