Friday, August 8, 2008

Clumps And Streams Of Dark Matter May Lie In Inner Regions Of Milky Way

In this image of local dark matter densities in the inner regions of the Milky Way galaxy, lines indicate the directions in which particles are moving. (Credit: M. Zemp)

Using one of the most powerful supercomputers in the world to simulate the halo of dark matter that envelopes our galaxy, researchers found dense clumps and streams of the mysterious stuff lurking in the inner regions of the halo, in the same neighborhood as our solar system.

"In previous simulations, this region came out smooth, but now we have enough detail to see clumps of dark matter," said Piero Madau, professor of astronomy and astrophysics at the University of California, Santa Cruz.

The results, reported in the August 7 issue of the journal Nature, may help scientists figure out what the dark matter is. So far, it has been detected only through its gravitational effects on stars and galaxies. According to one theory, however, dark matter consists of weakly interacting massive particles (WIMPs), which can annihilate each other and emit gamma rays when they collide. Gamma rays from dark matter annihilation could be detected by the recently launched Gamma-ray Large Area Space Telescope (GLAST), which UCSC physicists helped build.

"That's what makes this exciting," Madau said. "Some of those clumps are so dense they will emit a lot of gamma rays if there is dark matter annihilation, and it might easily be detected by GLAST."

Juerg Diemand, a postdoctoral fellow at UCSC and first author of the Nature paper, said the simulation is based on the assumptions of "cold dark matter" theory, the leading explanation for how the universe evolved after the Big Bang. In a separate paper that has been accepted for publication in the Astrophysical Journal, the researchers used their findings to make specific predictions about the gamma-ray signals that would be detectable by GLAST. The lead author of this paper is Michael Kuhlen, a former UCSC graduate student now at the Institute for Advanced Study in Princeton, N.J.

"There are several candidate particles for cold dark matter, and our predictions for GLAST depend on the assumed particle type and its properties," Diemand said. "For typical WIMPs, anywhere from a handful to a few dozen clear signals should stand out from the gamma-ray background after two years of observations. That would be a big discovery for GLAST."

Although the nature of dark matter remains a mystery, it appears to account for about 82 percent of the matter in the universe. As a result, the evolution of structure in the universe has been driven by the gravitational interactions of dark matter. The ordinary matter that forms stars and planets has fallen into the "gravitational wells" created by clumps of dark matter, giving rise to galaxies in the centers of dark matter halos.

According to the cold dark matter theory of cosmological evolution, gravity acted initially on slight density fluctuations present shortly after the Big Bang to pull together the first clumps of dark matter. These grew into larger and larger clumps through the hierarchical merging of smaller progenitors.

This is the process that Diemand and Madau's team simulated on the Jaguar supercomputer at Oak Ridge National Laboratory. The simulation took about one month to run and followed the gravitational interactions of more than a billion parcels of dark matter over 13.7 billion years. Running on up to 3,000 processors in parallel, the computations used about 1.1 million processor-hours.

"It simulates the dark matter distribution from near the time of the Big Bang until the present epoch, so practically the entire age of the universe, and focuses on resolving the halo around a galaxy like the Milky Way," Diemand said. "We see a lot of substructure, even in the inner part of the halo where the solar system is."

The simulation revealed numerous subhalos and streams of dark matter within the halo of the Milky Way, and more substructure appears within each subhalo, Madau said. "Every substructure has its own sub-substructure, and so on. There are lumps on all scales," he said.

The most massive of the subhalos would be likely to host dwarf galaxies such as those observed orbiting the Milky Way. By studying the motions of stars within dwarf galaxies, astronomers can calculate the density of the dark matter in the subhalos and compare that with the densities predicted by the simulation.

"We can make comparisons with the dwarf galaxies and stellar streams associated with the Milky Way. The appearance of these stellar systems is closely linked to the substructure of the dark matter halo," Diemand said.

The central densities in the simulated dark matter subhalos are consistent with the observations of stellar motions in dwarf galaxies, he said. But there remains a discrepancy between the number of dark matter subhaloes in the simulation and the number of dwarf galaxies that have been observed around the Milky Way. Some subhalos may remain dark if, for example, they are not sufficiently massive to support star formation, Madau said.

In addition to Diemand and Madau, the coauthors of the Nature paper include Michael Kuhlen of the Institute for Advanced Study; Marcel Zemp, a postdoctoral fellow at UCSC, who developed a time-stepping algorithm that made the simulation remarkably accurate; and Ben Moore, Doug Potter, and Joachim Stadel at the University of Zurich. This research was supported by the U.S. Department of Energy, NASA, and the Swiss National Science Foundation.

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Nasa insists perchlorate doesn't rule out life on Mars

Samples containing perchlorate were found in and around the "Snow White" trench dug by Phoenix's robotic arm. NASA/JPL-Caltech/University of Arizona

Martian soil appears to contain perchlorate salts, according to the latest twitterings from Nasa's Phoenix Mars Lander. The presence of perchlorate generated rumours this week because of suggestions that it meant that the soil is less friendly to life than previously thought.

Not so, according to Michael Hecht of Nasa's Jet Propulsion Laboratory, who said that "finding perchlorates is neither good nor bad for life". However, he said different perchlorate salts have different properties that could "make us reassess how we think about life on Mars" if the finding were confirmed and perchlorate was found at other sites.

One possibility, for example, is that the soil samples were contaminated by perchlorates transported from Earth on the lander. Although the fuel of Phoenix itself contains no perchlorates, they were used in the boosters during launch.

Perchlorates are ions consisting of an atom of chlorine surrounded by four oxygen atoms. They are weak oxidants meaning that they tend to transfer oxygen atoms in chemical reactions. On Earth, organisms coexist with perchlorates in arid places such as Chile's Atacama desert.

Another Mars Phoenix scientist, Samuel Kounaves, confirmed that "it's a benign chemical in terms of most organisms". Some even use it to generate energy.

Last week, the Wet Chemistry Laboratory on the Mars lander found water in the soil by "tasting" it. Perchlorate was detected by Phoenix's Thermal and Evolved-Gas Analyzer (TEGA) "which has the ability to sniff it, and we hadn't done that yet", said Hecht.

Nasa has some animations of the laboratory and the analyser.

The Phoenix project took the unusual step of releasing these intermediate results: "We decided to show the public science in action because of the extreme interest in the Phoenix mission, which is searching for a habitable environment on the northern plains of Mars," said principal investigator Peter Smith.

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CERN announces start-up date for LHC

Geneva, 7 August 2008. CERN has today announced that the first attempt to circulate a beam in the Large Hadron Collider (LHC) will be made on 10 September. This news comes as the cool down phase of commissioning CERN's new particle accelerator reaches a successful conclusion. Television coverage of the start-up will be made available through Eurovision.

The LHC is the world's most powerful particle accelerator, producing beams seven times more energetic than any previous machine, and around 30 times more intense when it reaches design performance, probably by 2010. Housed in a 27-kilometre tunnel, it relies on technologies that would not have been possible 30 years ago. The LHC is, in a sense, its own prototype.

Starting up such a machine is not as simple as flipping a switch. Commissioning is a long process that starts with the cooling down of each of the machine's eight sectors. This is followed by the electrical testing of the 1600 superconducting magnets and their individual powering to nominal operating current. These steps are followed by the powering together of all the circuits of each sector, and then of the eight independent sectors in unison in order to operate as a single machine.

By the end of July, this work was approaching completion, with all eight sectors at their operating temperature of 1.9 degrees above absolute zero (-271°C). The next phase in the process is synchronization of the LHC with the Super Proton Synchrotron (SPS) accelerator, which forms the last link in the LHC's injector chain. Timing between the two machines has to be accurate to within a fraction of a nanosecond. A first synchronization test is scheduled for the weekend of 9 August, for the clockwise-circulating LHC beam, with the second to follow over the coming weeks. Tests will continue into September to ensure that the entire machine is ready to accelerate and collide beams at an energy of 5 TeV per beam, the target energy for 2008. Force majeure notwithstanding, the LHC will see its first circulating beam on 10 September at the injection energy of 450 GeV (0.45 TeV).

Once stable circulating beams have been established, they will be brought into collision, and the final step will be to commission the LHC's acceleration system to boost the energy to 5 TeV, taking particle physics research to a new frontier.

'We're finishing a marathon with a sprint,' said LHC project leader Lyn Evans. 'It's been a long haul, and we're all eager to get the LHC research programme underway.'

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Are We Really Separated by Six Degrees of Separation? Microsoft Research Says "Yes"

734pxsix_degrees_of_separation_2 Microsoft has studied a total of 30 billion instant messages sent by over 250 million people in June of 2006, and determined that we are in fact, all linked by only 6.6 degrees of separation.

"We've been able to put our finger on the social pulse of human connectivity - on a planetary scale - and we've confirmed that it's indeed a small world." Microsoft researcher Eric Horvitz told AFP on Monday. "Over the next few decades, new kinds of computing applications, from smart networks to automated translation systems, will help make the world even smaller, with closer social connections and deeper understanding among people."

Due to the popularity of Microsoft Messenger, Horvitz and colleague Jure Leskovec believe that the amount of chats that they studied amount to approximately half of the instant message sent worldwide during that period. The pair stress, of course, that they were not privy to the contents of the messages.

"To me, it was pretty shocking. What we're seeing suggests there may be a social connectivity constant for humanity," said Eric Horvitz, a Microsoft researcher who conducted the study with colleague Jure Leskovec. "People have had this suspicion that we are really close. But we are showing on a very large scale that this idea goes beyond folklore."

The origin of the six degrees of separation theory spawns from a study by Stanley Milgram and Jeffrey Travers in 1969. They tasked 300 people in the US state of Nebraska to send a letter to someone in Boston, through acquaintances. Though most of the letters did not reach their intended recipient, those letters that did arrive were found to arrive with an average of 6.2 degrees of separation from the sender.

Though the study was not considered scientific, it went on to inspire a multitude of children, including a play and film, and a charitable website, launched by Kevin Bacon in 2007, Through the website, “you can support your favorite charities by donating or creating fundraising badges — as well as check out the favorite causes of other people, including celebrities.”

But though this original study was less than scientific, the study by Horvitz and Leskovec definitely has credibility. "We used a population sample that is more than two million times larger than the group studied earlier and confirmed the classic finding," Horvitz and Leskovec concluded.

Posted by Josh Hill.

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the physics arXiv blog News and views from the coal face of science * Home * About * Bookstore * Quantum communication: when 0 + 0

One of the lesser known cornerstones of modern physics is Claude Shannon’s mathematical theory of communication which he published in 1948 while juggling and unicycling his way around Bell Labs.

Shannon’s theory concerns how a message created at one point in space can be reproduced at another point in space. He calls the conduit for such a process a channel and the limits imposed by the universe on this process the channel capacity.

The capacity of a communications channel is hugely important idea. It tells you, among other things, the rate at which you can send information from one location to another, without loss. If you’ve ever made a phone call, watched television or surfed the internet you’ll have benefited from the work associated with this idea.

In recent years, our ideas about communication have been transformed by the possibility of using quantum particles to carry information. When that happens the strange rules of quantum mechanics govern what can and cannot be sent from one region of space to another. This kind of thinking has has spawned the entirely new fields of quantum communication and quantum computing.

But ask a physicist what the capacity is of a quantum information channel and she’ll stare at the floor and shuffle her feet. Despite years of trying, nobody has been able to update Shannon’s theory of communication with a quantum version.

Which is why a paper today on the arXiv is so exciting. Graeme Smith at the IBM Watson Research Center in Yorktown Heights NY (a lab that has carried the torch for this problem) and Jon Yard from Los Alamos National Labs have made what looks to be an important breakthrough by calculating that two zero-capacity quantum channels can have a nonzero capacity when used together.

That’s interesting because it indicates that physicists may have been barking up the wrong tree with this problem: perhaps the quantum capacity of a channel does not uniquely specify its ability for transmitting quantum information. And if not, what else is relevant?

That’s going to be a stepping stone to some interesting new thinking in the coming months and years. Betcha!

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Quantum chaos unveiled?

A University of Utah study is shedding light on an important, unsolved physics problem: the relationship between chaos theory – which is based on 300-year-old Newtonian physics – and the modern theory of quantum mechanics.

The study demonstrated a fundamental new property – what appears to be chaotic behavior in a quantum system – in the magnetic "spins" within the nuclei or centers of atoms of frozen xenon, which normally is a gas and has been tested for making medical images of lungs.

The new study – published in the Aug. 8 issue of the journal Physical Review Letters – was led by Brian Saam, an associate professor of physics and associate dean of the University of Utah's College of Science.

Quantum mechanics – which describes the behavior of molecules, atoms electrons and other subatomic particles – "plays a key role in understanding how electronics work, how all sorts of interesting materials behave, how light behaves during communication by optical fibers," Saam says.

"When you look at all the technology governed by quantum physics, it's not unreasonable to assume that if one can apply chaos theory in a meaningful way to quantum systems, that will provide new insights, new technology, new solutions to problems not yet known."

A Chaotic Dance of Nuclear Spins

Just as atomic nuclei and their orbiting electrons can have electrical charges, they also have another property known as "spin." The spin within an atomic nucleus or electron is like a spinning bar magnet that points either up or down.

Saam and graduate student Steven Morgan zapped xenon atoms with a strong magnetic field, laser beam and radio-wave pulse so the nuclear spins were aligned in four different configurations in four samples of frozen xenon, each containing about 100 billion billion atoms [billion twice is correct].

Despite differing initial configurations, the "dances" of the xenon spins evolved so they eventually were in sync with each other, as measured by nuclear magnetic resonance, or NMR. That took a few thousandths of a second – something physicists seriously call "long-time behavior."

"This type of common behavior has been a signature of classically chaotic (Newtonian) systems, mostly studied using a computer, but it never had been observed in an experimental system that only can be described by quantum mechanics," Saam says.

As an analogy, imagine billions of people in a huge, unfamiliar city. They start walking around in different places and directions, with little conversation among them. Yet, eventually, they all end up walking in the same direction.

Such behavior in nuclear spins had been predicted in 2005 by the study's third author, physicist Boris Fine of the University of Heidelberg in Germany. Fine had made the prediction by adapting chaos theory to quantum theory.

Order from Chaos

The evolution of disorder into order by the xenon atoms' nuclear spins is a signature of chaos theory, which, contrary to the popular notion, does not imply complete disorder. Instead, chaos theory describes how weather, certain chemical reactions, planetary orbits, subatomic particles and other dynamic systems change over time, with the changes often highly sensitive to starting conditions.

"When you have a [chaotic] system that is characterized by extreme randomness, it paradoxically can produce ordered behavior after a certain amount of time," says Saam. "There is strong evidence that is happening here in our experiment."

The sensitivity to starting conditions is known popularly as "the butterfly effect," based on the fanciful example that a butterfly flapping its wings in South America might set off subtle atmospheric changes that eventually build into a tornado in Texas.

Saam says chaos theory can make predictions about extremely complex motions of many particles that are interacting with each other. The mathematical notion of chaos first was described in the 1890s. Chaos theory was developed in the 1960s, based on classical physics developed in the late 1600s by Sir Isaac Newton. Classical physics says the motion, speed and location of any particle at any time can be determined precisely.

In contrast, quantum mechanics holds that "when things get atom small, our notions of being able to put a specific particle in a specific place with a specific speed at a specific time become blurry," Saam says. So a particle's speed and location is a matter of probability, and "the probability is the reality."

Details of the Study: 'These Guys are Dancing Together'

Technically, spin is the intrinsic angular momentum of a particle – a concept so difficult to explain in lay terms that physicists usually use the bar magnet analogy.

A nonmagnetic material normally has random spins in the nuclei of its atoms – half the spins are up and half are down, so the net spin is zero. But magnetic fields can be applied so that the spins are aligned – with more up than down, or vice versa.

Physicists can measure the alignment or "polarization" of the spins using NMR's strong magnetic field. Nuclear spins also are used medically: When a patient lies within a magnetic resonance imaging (MRI) device's large magnet, the spins within atoms in the body generate electrical signals that are used to make images of body tissues. Doctors are testing xenon as a way to enhance MRI images of the lungs.

Saam and colleagues used xenon because its spins can be aligned relatively easily.

In each experiment, Saam and Morgan used a magnetic field and a laser to align or "hyperpolarize" the spins in a sample of about 100 billion billion xenon gas atoms so a majority of the spins either were aligned "up" or "down." Then, they froze the gas into a solid at a temperature of 321 degrees below zero Fahrenheit.

Then they applied a radio wave pulse, which "flips" the spins so they all are perpendicular to the magnetic field instead of parallel to it. That makes them start circling around the magnetic field axis like spinning tops.

In this manner, the physicists created four frozen xenon samples. Within each sample, the spins were aligned, but different radio pulses were used to make the initial alignment or configuration of the spins different from one sample to the next.

The scientists then used NMR to watch the spins decay or fade over thousandths of a second.

"Although they are held in place in the crystal structure, the spins can interact with each other and change the direction in which they're pointed in much the same way that magnets interact with each other when brought close together," Saam says.

The initial configuration of spins in each xenon sample evolved in extremely complicated ways due to the presence of billions of interacting spins, and each sample rapidly "lost its memory" of where it started. Such behavior has been known for 60 years.

The surprise was that while each sample's initial NMR signal was radically different from the other, they displayed "identical long-time behavior," says Saam.

"Somehow despite the fact these spins have very complicated interactions with each other and started out in completely different orientations, they end up all moving in the same way after several milliseconds," he says. "That's never been seen before in a quantum mechanical system. These guys are dancing together."

Saam says the technical achievement was that the huge amount of polarization made it possible for NMR to measure an extremely weak spin signal – only one-thousandth as strong as the original signal by the time the samples appeared to behave chaotically.

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Algae -A Solution to Peak Oil? Virgin Airlines Says "Yes," Others Say "No"

Planet_earth "All countries must take vigorous, immediate and collective action to curb runaway energy demand. The next ten years will be crucial for all countries... We need to act now to bring about a radical shift in investment in favor of cleaner, more efficient and more secure energy technologies."

~Nobuo Tanaka, head of the International Energy Agency (IEA)

Big oil had better start worrying. Common algae from ponds and waste-water treatment plants has been found to produce vast amounts of burnable oil, say researchers at the University of Minnesota, algae produces an astounding 5,000 gallons of oil per acre. Corn, by comparison, produces a measly 18 gallons. Soybean yields 48 gallons. An acre of palm trees yields 635 gallons.

Algae has a clear advantage in other ways as well. Land crops use up more resources and require more manpower to grow. Algae, on the other hand, is so hardy that it grows all by itself in conditions that require little to no management.Researchers Roger Ruan and Paul Chen will start with 200 gallons of waste water, but see the potential as enormous. The only liability they have to deal with now is how to produce the fuel cheaply. They believe it will be able to be made affordable as the technology improves and starts to catch on.

Exxon claims “We're not gouging US citizens,” after raking in a record-setting quarterly profit of $11.7 billion, the largest ever profit in the history of the US.

As society gets increasingly fed up with big oil, opportunities for new energy sources are opening up.The algae production process can also take advantage of excess heat, nitrogen, carbon and phosphorus produced by coal-burning plants and waste-water incinerators, making algae pond farms a possibility for both northern and southern states.

Virgin Atlantic has become the first airline to fly with biofuel, something airline boss Richard Branson calls "a vital breakthrough" but environmentalists have derided as a "nonsensical" publicity stunt.

Virgin_branson_wideweb__470x3490Earlier this year, the Boeing 747-400 flew from London to Amsterdam, carrying in one of its four fuel tanks a 20-percent mix of biofuel derived from coconut and babassu oil. That may not sound like much, but it is the first time a commercial aircraft has flown any distance using renewable energy. Branson said the "historic" flight marks the first step toward reducing the airline industry's carbon footprint.

Pete Hardstaf, head of policy for the World Development Movement, said, "This is nothing more than a Virgin publicity stunt with dangerous consequences for the planet." Doug Parr, chief scientist for Greenpeace, told the Globe and Mail the flight is "high-altitude greenwash."

Virgin's critics offered the standard arguments against biofuels -- mainly, the environmental benefits of biofuels are negligible at best and using crops for fuel will drive up food costs, deplete arable land and contribute to deforestation.

But beyond that, the critics said any gains made through biofuels would be offset by one year's growth in the number of flights. Airline passenger growth rates are expected to rise 6 percent annually through 2009 and double by 2020. Aircraft emissions are expected to double by 2030. "The concept of using biofuels and continuing the rate of expansion in the aviation industry is nonsensical," Hardstaff said.

In stark contrast, Jon Dee, founder of Planet Ark, praised Virgin and Boeing for the effort, telling ABC Online, "I actually think it is good to show that you can fly major airliners on alternative fuels. I think that it is vital that as quickly as possible we move away from business as normal. But what we should be looking at, I think, is how we get that biofuel derived from algae. That is the best way to go when it comes to biofuel."

Branson and Boeing agree, which is why, with Virgin's fuel bill increasing by $2 billion in '08 due to rising oil prices, they're spending a lot of time and money investigating algal fuels. Billy Glover, Boeing's head of environmental strategy, says "algae looks very promising." Branson says Virgin used coconut and babassu oil for the test, "but commercial fuel will almost certainly be derived from algae."

Endangered Bighorn Sheep Get Safe Home

Today the US federal government has designated over 625 square miles of mountain range as a protected habitat for the endangered Sierra Nevada Bighorn Sheep. Conservationists had to sue the U.S. Fish and Wildlife Service in 2005 in order to have this land protected. The lawsuit stated that the Sierra Nevada bighorn sheep was threatened with extinction because this habitat wasn't protected under the Endangered Species Act as it should be.


This new habitat is located in the eastern Sierra Nevada is home to this unique subspecies of furry bighorn mountain sheep. The Fish and Wildlife Service will now have to determine whether domestic sheep and off-roading could possibly jeopardize the bighorns' future recovery.

In the early 1800's Bighorn Sheep were common and widespread throughout the western US. Their numbers were estimated at as many as at least 2 million. Due to over-hunting, domestic sheep herds eating their food, mountain lions, logging and diseases these numbers were cut down to a few thousand.

Thanks to a statewide campaign in AZ by the Boy Scouts, hard work from conservationists, the designation of National Wildlife Refuges and their endangered classification bighorn sheep stand a chance of escaping extinction.

Although the 625 square miles of mountain range is not a vast space of land, it is a start and will hopefully help these animals in the future.

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