Is dark matter mostly 'dark atoms'?

Physicists currently believe that most of the dark matter in the universe is made up of individual particles, and the challenge is to work out what kind of particles these are. New research, however, overturns this assumption and says that observational and experimental data are better explained if dark matter exists as composite particles – atoms of dark protons and dark electrons that are acted on by the dark-matter equivalent of the electromagnetic force.

Ring of 'dark atoms'?

Dark matter is thought to make up more than 80% of the matter in the universe. As its name suggests, dark matter does not reveal itself by emitting light because it does not interact via electromagnetism. Its existence is instead inferred through its gravitational effects on normal matter.
Physicists' favourite candidate for dark matter is a broad class of so-called weakly interacting massive particles, or WIMPs, which interact via the weak nuclear force. WIMPs are in line with much of the observational evidence for dark matter, but two anomalies remain. One is the fact that WIMP models predict that dark matter ought to clump together gravitationally at all length scales, from galaxies down to much smaller sub-galactic structures. However, this is not what is observed – no dark-matter structures smaller than about 400 light-years across have been found by astronomers.

And then there's DAMA

The other problem concerns the results of experiments on Earth designed to detect dark-matter particles directly via their collision with nuclei of ordinary matter. One such experimental collaboration, DAMA in the Gran Sasso laboratory in Italy, has generated controversy by claiming to have collected extremely strong evidence for dark matter inside its detector. Unfortunately, DAMA's results cannot be interpreted as collisions of WIMPs without appearing to strongly contradict a number of other experiments around the world.
Now, David Kaplan and colleagues at Johns Hopkins University in the US say that these two problems could be overcome if dark matter consists not of individual fundamental particles but is instead largely made up of composite "atoms". These atoms would be made up of the dark matter equivalent of protons and electrons bound together by the equivalent of the electromagnetic force, and would be accompanied by a certain fraction of ionized atoms – in other words, free electrons and protons.
The researchers point out that the existence of these charged particles would have altered the evolution of dark matter in the early universe. WIMPs, being uncharged, would have decoupled from normal radiation less than 1 second after the Big Bang, whereas atomic dark matter, with its ionized fraction, would have remained in thermal equilibrium with dark radiation for about the first 20 minutes. The universe would therefore have expanded to a certain size before gravitational clumping could have occurred, dictating the size of the smallest dark-matter structure that we see today.

Inelastic collisions

To explain the discrepancy between DAMA and other experiments, Kaplan and colleagues build on an idea put forward by Neal Weiner and David Tucker-Smith in 2001. Weiner and Tucker-Smith proposed that the collisions detected by DAMA are inelastic, that some kinetic energy is lost because on collision the dark-matter particles absorb energy to become slightly more massive and that these energy-sapping collisions are far more likely to occur with the relatively heavy sodium iodide in DAMA's detector than with, say, the silicon and germanium of which CDMS detector in the US is made of. Kaplan's group, on the other hand, says that this energy loss can be explained by the incoming dark-matter atoms jumping up an energy level when they collide, rather than being due to the creation of new particles that are postulated specifically for this process.
The researchers admit that there is a "tension" within their model because the explanation of missing structure in the universe requires a higher fraction of dark atoms to be ionized than does the mismatch of experimental results. But they say that this difference can be resolved if atomic and ionized dark matter assume different halo shapes within galaxies.

Kaplan's colleague Christopher Wells admits that their proposal is speculative but that it does have the additional benefit of bringing dark matter more into line with the ordinary matter that we are familiar with. Indeed, they say that dark hydrogen atoms could bind to form hydrogen molecules and that the formation of these molecules could then lead to the creation of "dark stars" or other compact objects. They add that the interaction of dark photons with ordinary photons could lead to emission lines in the spectra of cosmic gamma rays.

Not really problems?

Daniel Hooper, an astrophysicist at Fermilab in the US, does not believe that the problems being addressed by the atomic dark-matter model are really problems at all – that the problem of structure formation is essentially solved while the DAMA results are "not very compelling". "That being said," he adds, "to those scientists who think these are issues that need solutions, the 'atomic dark matter' idea presented here does seem to resolve the problems fairly easily."

Ozone: Climate change boosts ultraviolet risk for high latitudes

Enlarge

This undated photo, released by the International Polar Foundation, shows Belgium's Princess Elisabeth base in Antartica. By century's end, UV levels in Antarctica could rise by up to 20 percent at seasonal peaks while average exposure in northern Scandinavia, Siberia and northern Canada could fall by almost a tenth.

Climate change will disrupt Earth's precious ozone layer, boosting ultraviolet (UV) radiation in the deep southern hemisphere and reducing UV in far northern latitudes, a study warned on Sunday.

By century's end, UV levels in Antarctica could rise by up to 20 percent at seasonal peaks while average exposure in northern Scandinavia, Siberia and northern Canada could fall by almost a tenth.

The shift could have worrying impacts on human health, as high exposure to UV is linked to cancer, cataracts and crop damage just as low exposure causes vitamin D insufficiency.

"Our study is showing that there is a new threat to the ozone layer, and this is climate change, which will either increase or decrease UV depending on the region," said atmospheric physicist Michaela Hegglin of Canada's University of Toronto.

"And while too much UV exposure is known to be a bad thing, too little UV exposure can also have detrimental effects, though these are much less explored."

The ozone layer refers to the thin sandwich of triple-atom oxygen molecules in the stratosphere, between 10 and 50 kilometers (six and 30 miles) in altitude, which filter harmful UVB light from the Sun.

Awareness of the layer's importance emerged in the 1970s, when scientists discovered it was being depleted by chlorofluorocarbon (CFC) chemicals used in aerosols and refrigeration.

An international treaty, the Montreal Protocol, set down measures to phase out these chemicals, and the ozone "hole" over Antarctica caused by CFCs is expected to recover by the latter half of the century.

The new study, published in the journal Nature Geoscience, points to an unforeseen peril -- not from depletion but from the way the ozone layer is distributed by high-altitude winds.

Hegglin and co-author Theodore Shepherd put together a computer model simulating the consequences of warmer surface temperatures on an atmospheric pump called the Brewer-Dobson circulation, which drives ozone around the world.

Under it, air is moved upwards from the tropics -- where most ozone is produced -- and then shifts polewards before descending to the lower part of the stratosphere.

There it lingers for a long time before eventually entering the troposphere, the lower part of the atmosphere that includes ground level.

The computer model suggests that between 1965 and 2095, changes in convention mean the flow of ozone from the stratosphere to the troposphere will rise by 23 percent.

The figure is derived from a modest increase in carbon emissions in a scenario also used by the UN's Intergovernmental Panel on Climate Change (IPCC) computer models. It also incorporates the trend towards ozone recovery after CFCs are withdrawn.

The shifting layer leads to big changes in UV exposure for those living at Earth's extremities.

Above 60 degrees latitude north, a line roughly giving the location of Stockholm, Helsinki, Saint Petersburg and Anchorage, Alaska, clear-sky levels of UV will fall by 9.1 percent by 2095 compared with 1965 levels.

In the northern mid-latitudes, there will be a fall of 3.6 percent.

In the tropics, UV exposure will rise by 3.8 percent. The southern mid-latitudes will be unchanged.

Below 60 degrees latitude south -- essentially Antarctica -- there will be a UV increase of an average 3.2 percent, although this figure masks huge swings.

In the southern hemisphere's late spring and early summer, UV levels in Antarctica could rise by up to 20 percent, equivalent to nearly half of the ozone hole caused by CFCs.

Another concern is that a rise in ozone levels in the troposphere could have an effect on air quality and stoke the warming cycle.

Ozone in the troposphere becomes both a greenhouse gas and a potential health problem. At ground level, ozone formed by the reaction between sunlight and road pollution is a notorious irritant for people with respiratory problems.

Two more genetic risk factors for Alzheimer's disease found

Two more genetic risk factors for Alzheimer's disease found

An international team of scientists has identified two more genetic risk factors for Alzheimer's disease. The findings are reported in the online edition of the journal Nature Genetics.

The group, led by investigators from the School of Medicine at Cardiff in the United Kingdom and including scientists from Washington University School of Medicine in St. Louis, completed the largest genome-wide association study ever involving patients with Alzheimer's disease. The study pooled DNA samples from more than 19,000 older European and U.S. residents. Seven thousand had Alzheimer's disease, and the others had no clinical symptoms of the disorder.

Prior to this study, only four genes had been definitively associated with Alzheimer's disease. Three genetic mutations have been identified as causes of rare, inherited forms of early-onset Alzheimer's. The fourth gene, APOE4, is the only one previously linked to the more common late-onset form of the disease.

By looking at more than 600,000 common DNA markers, researchers on the current study were able to identify two new genes that appeared to be involved in elevated risk for Alzheimer's and confirmed the importance of APOE4.

"There's good evidence that these new genes may be novel risk factors, the first discovered since APOE in 1993," says Washington University researcher and co-author Alison M. Goate, D.Phil. "So it's a very important observation because this study is the first to provide such significant evidence of novel genetic risk factors for the most common form of Alzheimer's disease."

Goate, who in 1991 led a team in England that identified the first early-onset Alzheimer's mutation in the APP gene on chromosome 21, is now the Samuel and Mae S. Ludwig Professor of Genetics in Psychiatry and professor of neurology at Washington University. She says the new genes identified in this study are APOJ, also called clustrin on chromosome 8, and PICALM on chromosome 11.

"The power of the new Genome Wide Association Study methods is that with large datasets we can now identify genes that earlier techniques were unable to confirm," says co-author John C. Morris, M.D., of Washington University. "These new genes associated with Alzheimer's disease provide new clues about how the illness develops."

Morris, the Harvey A. and Dorismae Hacker Friedman Distinguished Professor of Neurology, is the director of Washington University's Alzheimer's Disease Research Center (ADRC). He says previous ADRC research suggests that in mice, the clustrin gene may be involved in the formation of amyloid deposits in the brain. Amyloid makes up the senile plaques that dot the brains of people with Alzheimer's.

"These genes are both significant, but their effect appears to be much smaller than that of the APOE gene," Goate says. "Using statistical methods, we've been able to estimate the amount of risk attributable to APOE at about 19 or 20 percent. The newly identified genes each come in under 10 percent, so it appears they have a much smaller effect."

But not an insignificant one, Goate says, noting that although it isn't yet clear how these new genes influence Alzheimer's disease risk, levels of clustrin tend to rise when brain tissue is injured or becomes inflamed, and some researchers have noted increased clustrin levels in the brain and cerebrospinal fluid of Alzheimer's patients.

The other gene, PICALM, appears to be involved in the breakdown of synapses, structures that allow neurons in the brain to communicate. Some scientists also hypothesize that the gene may be involved in the development of amyloid deposits, but Goate says much more work is required to identify exactly how PICALM elevates Alzheimer's risk.

She expects many more genes also are involved in Alzheimer's risk. In fact, this study identified 13 more gene variants worthy of further investigation.

More information: Harold D, et al. Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's disease. Nature Genetics,advance online publication. Sept. 6, 2009

Source: Washington University School of Medicine

Electron tunneling in carbon nanotube

Electron tunneling in carbon nanotube composites

C Gau, Cheng-Yung Kuo and H S Ko
Institute of Aeronautics and Astronautics, and Center for Micro/Nano Science and

Technology, National Cheng Kung University, Tainan, Taiwan

E-mail: gauc@mail.ncku.edu.tw

Received 2 July 2009

Published 2 September 2009


Abstract

Nanocomposites, such as polymer blending with carbon nanotubes (CNTs), have been shown to

have a drastic reduction in the resistivity and become conductive when the CNTs concentration

has reached a certain percolation threshold. The reduction could be more than a millionth of the

original polymer material. This has been realized as the formation of an infinite cluster of

connected CNTs or pathways. Therefore, the conductivity of a nanocomposite should follow

that of CNTs. Here we show that the resistivity of a nanocomposite is not governed by the

interconnected CNTs, but the polymer between neighboring CNTs. That is, polymer–CNTs

exhibit the nature of a conducting polymer, which can be explained as the tunneling of electrons

one by one from the first CNT electrode to the next-nearest CNT electrode, forming a

CNT/polymer pathway. A conduction model based on the tunneling of electrons passing, one

by one, through the polymer gap between two neighboring CNT electrodes is formulated and

derived. This model can accurately predict the significant reduction of the polymer–CNTs’

resistivity with the addition of CNTs. The temperature effect can be readily incorporated to

account for resistivity variation with the temperature of this nanocomposites.

Dreams of a quantum pioneer

Dreams of a quantum pioneer


Deciphering the Cosmic Number: The Strange Friendship of Wolfgang Pauli and Carl Jung

Arthur I Miller

2009 W W Norton

Pls visit the link (click on heading)for details

Space Science and Stuffs....

Phobos-Grunt Probe to Put Microbial Life in Mars Orbit

A tagalong to the Russian sample-return mission makes some researchers uncomfortable

By JR Minkel

In Mars exploration, of course, it's the Red Planet itself that gets top billing. But there are some good reasons to keep tabs on Phobos, the innermost and larger of Mars' two diminutive moons, which the Russian space agency plans to study with a probe set for launch next month on board a Zenit rocket. Called Phobos Grunt, the three-year mission is to land a spacecraft on the distant moon, scoop up soil samples for analysis and launch one of them back to Earth for further inspection. The probe's name means "Phobos's soil" in Russian.
If successful, Phobos Grunt would represent something of a coup for the Russian Federal Space Agency (Roscosmos). Russia has long struggled to reach Mars and has not carried out a successful interplanetary mission in decades. The nation launched Mars 96 in 1996 to explore the Red Planet, but a rocket failure occurred in Earth orbit. Phobos Grunt would also mark the first sample returned from a planetary surface since the U.S.S.R.'s Luna 24 in 1976.
As moons go, Phobos is strange. Shaped like a potato, it measures only 27 kilometers across at its widest point and orbits Mars at a distance of only about 6,000 kilometers. Researchers think Phobos and its even smaller companion Deimos started out as asteroids that were gravitationally pulled into Mars's orbit. Space agencies would like to know whether the moons' porous interiors harbor water that could be exploited by future visitors to Mars.
Russia attempted to reach Phobos before. Computer glitches sidelined the Phobos 1 and 2 craft, both launched in July 1988, before they could complete their missions. Now, for the past several months, Phobos Grunt has been subject to rumors that Roscosmos would likely have to delay the launch until 2011 at the earliest, when the flight window opens again.
Such a delay could give researchers time to get their heads around a tantalizing add-on to the probe's payload. The Planetary Society, a California-based space exploration and advocacy group, working with the Space Research Institute of the Russian Academy of Sciences, has arranged for Phobos Grunt to carry with it the Living Interplanetary Flight Experiment (LIFE), a group of samples of Earth life that will fly to Phobos and back in the Russian craft.
The goal, says Bruce Betts, the manager of the experiment for the Planetary Society, is to seek evidence for transpermia, the idea that life could have arisen on one body in the solar system and been transported via meteorites to seed life on another. For example, he says, "Could life have evolved first on Mars, been ejected off Mars, and then come to Earth?"
Although LIFE cannot test such a detailed scenario, Betts says the results will build on those of similar experiments flown on spacecraft. Bacteria have survived in low Earth orbit for up to six years but have only rarely, and briefly, left the protection of Earth's magnetosphere, which deflects the damaging cosmic rays that penetrate deep space. (When Apollo 12 returned to Earth in 1969 with the camera from the unmanned Surveyor 3 lander, which had spent more than two years on the lunar surface, scientists found Streptococcus mitis, a possible stowaway from before the probe was launched. But the bacterium's provenance is unclear, and some suspect the camera was contaminated after its return to Earth.)
The LIFE organisms were chosen with this danger in mind. Among the four bacteria to make the trip will be radiation-resistant Deinococcus radiodurans. Tardigrades, microscopic, eight-limbed invertebrates also known as water bears, were selected for their ability to repair DNA damage. Rounding out the group are three species of archaea—sometimes called "extremophiles" for their ability to thrive in conditions too harsh for other Earth life—along with yeast, plant seeds, and a soil sample collected from Israel's Negev Desert. Most of the samples will be freeze-dried and inert for the trip, to better resist the cold of space.
The LIFE menagerie will be packed in individual vials loaded into a titanium disc the width of a credit card. Betts says the packaging has been tested for acceleration forces up to 4,000 g's, or 100 times the expected acceleration during sample return.
Still, some space scientists are scratching their heads why anyone would risk putting Earthly microorganisms anywhere near Mars in the first place, especially given the relatively modest scientific payoff. "Meteorites are millions of years old—a three-year trip is really not relevant," says Daniel Glavin, an astrobiologist at the NASA Goddard Space Flight Center in Greenbelt, Md.
Strange as it may sound, the experiment satisfies international prohibitions against contaminating Mars or other bodies that might support life, says Catharine Conley, NASA's planetary protection officer. Unlike its neighboring planet, airless Phobos is surely sterile, so as long as Roscosmos provides detailed flight information confirming that Phobos Grunt is expected to reach its target moon—a safe distance from Mars—the mission should be in the clear.
"It is an uncomfortable thing," Conley says, "but we have policy. We have good policy."




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Nano Bio updates

Partial sequencing of a single DNA molecule with a scanning tunnelling microscope

Hiroyuki Tanaka¹ & Tomoji Kawai¹

Nature Nanotechnology 4, 518 - 522 (2009)
Published online: 5 July 2009 | doi:10.1038/nnano.2009.155

The scanning tunnelling microscope is capable of the real-space imaging and spectroscopy of molecules on an atomic scale. Numerous attempts have been made to use the scanning tunnelling microscope to sequence single DNA molecules, but difficulties in preparing samples of long-chain DNA molecules on surfaces, and problems in reproducing results have limited these experiments^{1, 2, 3, 4, 5, 6}. Here, we report single-molecule DNA sequencing with a scanning tunnelling microscope by using an oblique pulse-injection method to deposit the molecules onto a copper surface. First, we show that guanine bases have a distinct electronic state that allows them to be distinguished from the other nucleic acid bases. Then, by comparing data on M13mp18, a single-stranded phage DNA, with a known base sequence⁷, the 'electronic fingerprint' of guanine bases in the DNA molecule is identified. These results show that it is possible to sequence individual guanine bases in real long-chain DNA molecules with high-resolution scanning tunnelling microscope imaging and spectroscopy.

Find full paper for free on link below

http://www.nature.com/nnano/journal/v4/n8/pdf/nnano.2009.155.pdf