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.
(Left) Mammillaria elongata, or golden star cactus, displays a helical morphology. (Right) A magnetic cactus of dipole magnets on stacked bearings assumes phyllotactic spirals, similar to the biological cactus. With the magnetic cactus, physicists have investigated the dynamics of phyllotaxis.
One of humanity’s earliest mathematical inquiries might have involved the geometric patterns in plants. The arrangement of leaves on a branch, seeds in a sunflower, and spines on a cactus appear with an intriguing regularity, providing a simple demonstration of mathematically complex patterns.
In a recent study, researchers have experimentally demonstrated for the first time a celebrated model of “phyllotaxis,” the study of mathematical regularities in plants. In 1991, S.L. Levitov proposed a model of phyllotaxis suggesting that the appearance of the Fibonacci sequence and golden mean in the pattern of spines on a cactus can be replicated for cylindrically constrained, repulsive objects. Now, researchers have constructed a “magnetic cactus” with 50 outward-pointing magnets acting as spines, which are mounted on bearings and free to rotate on a vertical axis acting as the plant stem. With this setup, the researchers, from Los Alamos National Laboratory in New Mexico; Cornell University in Ithaca, New York; and The Pennsylvania State University (PSU), have verified Levitov’s model, and their study has been published in a recent issue of Physical Review Letters.
Blavatsky’s masterwork on theosophy, covering cosmic, planetary, and human evolution, as well as science, religion, and mythology. Based on the Stanzas of Dzyan, with corroborating testimony from over 1,200 sources.
PROEM.
PAGES FROM A PRE-HISTORIC PERIOD.
An Archaic Manuscript — a collection of palm leaves made impermeable to water, fire, and air, by some specific unknown process — is before the writer’s eye. On the first page is an immaculate white disk within a dull black ground. On the following page, the same disk, but with a central point. The first, the student knows to represent Kosmos in Eternity, before the re-awakening of still slumbering Energy, the emanation of the Word in later systems. The point in the hitherto immaculate Disk, Space and Eternity in Pralaya, denotes the dawn of differentiation. It is the Point in the Mundane Egg (see Part II., “The Mundane Egg”), the germ within the latter which will become the Universe, the all, the boundless, periodical Kosmos, this germ being latent and active, periodically and by turns. The one circle is divine Unity, from which all proceeds, whither all returns. Its circumference — a forcibly limited symbol, in view of the limitation of the human mind — indicates the abstract, ever incognisablepresence, and its plane, the Universal Soul, although the two are one. Only the face of the Disk being white and the ground all around black, shows clearly that its plane is the only knowledge, dim and hazy though it still is, that is attainable by man. It is on this plane that the Manvantaric manifestations begin; for it is in this soul that slumbers, during the Pralaya, the Divine Thought,* wherein lies concealed the plan of every future Cosmogony and Theogony.
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.
