World's Most Powerful X-Ray Laser Creates 2-Million-Degree Matter

This photograph shows the interior of a Linac Coherent Light Source SXR experimental chamber, set up for an investigation to create and measure a form of extreme, 2-million-degree matter known as “hot, dense matter.” The central part of the frame contains the holder for the material that will be converted by the powerful LCLS laser into hot, dense matter. To the left is an XUV spectrometer and to the right is a small red laser set up for alignment and positioning. (Credit: Photo courtesy of University of Oxford/Sam Vinko)

Researchers working at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory have used the world's most powerful X-ray laser to create and probe a 2-million-degree piece of matter in a controlled way for the first time. This feat, reported inNature, takes scientists a significant step forward in understanding the most extreme matter found in the hearts of stars and giant planets, and could help experiments aimed at recreating the nuclear fusion process that powers the sun.

The experiments were carried out at SLAC's Linac Coherent Light Source (LCLS), whose rapid-fire laser pulses are a billion times brighter than those of any X-ray source before it. Scientists used those pulses to flash-heat a tiny piece of aluminum foil, creating what is known as "hot dense matter," and took the temperature of this solid plasma -- about 2 million degrees Celsius. The whole process took less than a trillionth of a second.

"The LCLS X-ray laser is a truly remarkable machine," said Sam Vinko, a postdoctoral researcher at Oxford University and the paper's lead author. "Making extremely hot, dense matter is important scientifically if we are ultimately to understand the conditions that exist inside stars and at the center of giant planets within our own solar system and beyond."

Scientists have long been able to create plasma from gases and study it with conventional lasers, said co-author Bob Nagler of SLAC, an LCLS instrument scientist. But no tools were available for doing the same at solid densities that cannot be penetrated by conventional laser beams.

"The LCLS, with its ultra-short wavelengths of X-ray laser light, is the first that can penetrate a dense solid and create a uniform patch of plasma -- in this case a cube one-thousandth of a centimeter on a side -- and probe it at the same time," Nagler said.

The resulting measurements, he said, will feed back into theories and computer simulations of how hot, dense matter behaves. This could help scientists analyze and recreate the nuclear fusion process that powers the sun.

"Those 60 hours when we first aimed the LCLS at a solid were the most exciting 60 hours of my entire scientific career," said Justin Wark, leader of the Oxford group. "LCLS is really going to revolutionize the field, in my view."

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---

Journal Reference:

1. S. M. Vinko, O. Ciricosta, B. I. Cho, K. Engelhorn, H.-K. Chung, C. R. D. Brown, T. Burian, J. Chalupský, R. W. Falcone, C. Graves, V. Hájková, A. Higginbotham, L. Juha, J. Krzywinski, H. J. Lee, M. Messerschmidt, C. D. Murphy, Y. Ping, A. Scherz, W. Schlotter, S. Toleikis, J. J. Turner, L. Vysin, T. Wang, B. Wu, U. Zastrau, D. Zhu, R. W. Lee, P. A. Heimann, B. Nagler, J. S. Wark. Creation and diagnosis of a solid-density plasma with an X-ray free-electron laser. Nature, 2012; DOI: 10.1038/nature10746

One step closer to dark matter in universe

ScienceDaily (Oct. 31, 2011) — Scientists all over the world are working feverishly to find the dark matter in the universe. Now researchers at Stockholm University have taken one step closer to solving the enigma with a new method.

The universe is still a mystery. We know what about 5 percent of the universe consists of. The rest is simply unknown. Researchers have gotten as far as knowing that a major portion, about 23 percent of the universe consists of a new kind of matter. No one has seen this matter, and no one knows what it consists of. The remaining roughly 72 percent of the universe is made up of something even more enigmatic, called dark energy. Jan Conrad and Maja Llena Garde are scientists at Fysikum, Stockholm University and the Oskar Klein Center for Cosmoparticle Physics, and they are part of the international research team that has taken a giant step toward finding dark matter with the help of a new method.

"With our new method, for the first time we have been able to exclude models regarded by many as the most natural ones. Previous attempts did not achieve the same sensitivity. What's more, our results are especially reliable," says Jan Conrad.

"We can't see dark matter because it doesn't interact with the matter we know about. Nor does it emit any light. It's virtually invisible. But we can determine that it affects the matter we're familiar with."

"We see how the rotation of galaxies is affect by something that weighs a lot but is invisible. We also see how the gas in galaxy clusters doesn't move as it would if there were only visible matter present. So we know it's there. The question is simply what it is. Many theoretical models have been developed to predict particles that meet the requirements for being identified as dark matter. But experiments are needed if we are to determine whether any of these models are correct," says Jan Conrad.

Since dark matter is invisible, we can only see traces of it, and one way to do this is to look at light with extremely high energy, so-called gamma radiation. With the help of the satellite-borne Fermi Large Area Telescope, scientists can study gamma radiation and look for traces of dark matter.

"We've looked at gamma radiation from dwarf galaxies. These galaxies are small and dim, but extremely massive, so they seem to consist largely of dark matter. Unfortunately we still haven't detected a gamma signal from the dark matter in these objects, but we are definitely getting closer. Our new method involves looking at several dwarf galaxies at the same time and combining the observations in a new way, which yields excellent results. This is an exciting time for dark matter research, because we're getting closer and closer," says Maja Llena Garde.

"This is truly a giant step forward in our pursuit of dark matter," says the director of the Oskar Klein Center, Lars Bergström. "With my colleague Joakim Edsjö, I've studied these processes theoretically for more than ten years, but this is the first time important experimental breakthroughs are being seen. Now we just hope that Jan, Maja, and the Fermi team will continue this exciting quest using their new method."

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The Fermi-LAT Collaboration: M. Ackermann, M. Ajello, A. Albert, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, R. D. Blandford, E. D. Bloom, E. Bonamente, A. W. Borgland, J. Bregeon, M. Brigida, P. Bruel, R. Buehler, T. H. Burnett, S. Buson, G. A. Caliandro, R. A. Cameron, B. Canadas, P. A. Caraveo, J. M. Casandjian, C. Cecchi, E. Charles, A. Chekhtman, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, S. Cutini, A. de Angelis, F. de Palma, C. D. Dermer, S. W. Digel, E. do Couto e Silva, P. S. Drell, A. Drlica-Wagner, L. Falletti, C. Favuzzi, S. J. Fegan, E. C. Ferrara, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, N. Gehrels, S. Germani, N. Giglietto, F. Giordano, M. Giroletti, T. Glanzman, G. Godfrey, I. A. Grenier, et al. Constraining dark matter models from a combined analysis of Milky Way satellites with the Fermi Large Area Telescope. Physical Review Letters, 2011 [link]

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Dark matter mystery deepens

ScienceDaily (Oct. 17, 2011) — Like all galaxies, our Milky Way is home to a strange substance called dark matter. Dark matter is invisible, betraying its presence only through its gravitational pull. Without dark matter holding them together, our galaxy's speedy stars would fly off in all directions. The nature of dark matter is a mystery -- a mystery that a new study has only deepened.

"After completing this study, we know less about dark matter than we did before," said lead author Matt Walker, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics.

The standard cosmological model describes a universe dominated by dark energy and dark matter. Most astronomers assume that dark matter consists of "cold" (i.e. slow-moving) exotic particles that clump together gravitationally. Over time these dark matter clumps grow and attract normal matter, forming the galaxies we see today.

Cosmologists use powerful computers to simulate this process. Their simulations show that dark matter should be densely packed in the centers of galaxies. Instead, new measurements of two dwarf galaxies show that they contain a smooth distribution of dark matter. This suggests that the standard cosmological model may be wrong.

"Our measurements contradict a basic prediction about the structure of cold dark matter in dwarf galaxies. Unless or until theorists can modify that prediction, cold dark matter is inconsistent with our observational data," Walker stated.

Dwarf galaxies are composed of up to 99 percent dark matter and only one percent normal matter like stars. This disparity makes dwarf galaxies ideal targets for astronomers seeking to understand dark matter.

Walker and his co-author Jorge Peñarrubia (University of Cambridge, UK) analyzed the dark matter distribution in two Milky Way neighbors: the Fornax and Sculptor dwarf galaxies. These galaxies hold one million to 10 million stars, compared to about 400 billion in our galaxy. The team measured the locations, speeds and basic chemical compositions of 1500 to 2500 stars.

"Stars in a dwarf galaxy swarm like bees in a beehive instead of moving in nice, circular orbits like a spiral galaxy," explained Peñarrubia. "That makes it much more challenging to determine the distribution of dark matter."

Their data showed that in both cases, the dark matter is distributed uniformly over a relatively large region, several hundred light-years across. This contradicts the prediction that the density of dark matter should increase sharply toward the centers of these galaxies.

"If a dwarf galaxy were a peach, the standard cosmological model says we should find a dark matter 'pit' at the center. Instead, the first two dwarf galaxies we studied are like pitless peaches," said Peñarrubia.

Some have suggested that interactions between normal and dark matter could spread out the dark matter, but current simulations don't indicate that this happens in dwarf galaxies. The new measurements imply that either normal matter affects dark matter more than expected, or dark matter isn't "cold." The team hopes to determine which is true by studying more dwarf galaxies, particularly galaxies with an even higher percentage of dark matter.

The paper discussing this research was accepted for publication in The Astrophysical Journal.

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Astronomers discover complex organic matter exists throughout the universe

ScienceDaily (Oct. 26, 2011) — Astronomers report in the journal Nature that organic compounds of unexpected complexity exist throughout the Universe. The results suggest that complex organic compounds are not the sole domain of life but can be made naturally by stars.

Prof. Sun Kwok and Dr. Yong Zhang of The University of Hong Kong show that an organic substance commonly found throughout the Universe contains a mixture of aromatic (ring-like) and aliphatic (chain-like) components. The compounds are so complex that their chemical structures resemble those of coal and petroleum. Since coal and oil are remnants of ancient life, this type of organic matter was thought to arise only from living organisms. The team's discovery suggests that complex organic compounds can be synthesized in space even when no life forms are present.

The researchers investigated an unsolved phenomenon: a set of infrared emissions detected in stars, interstellar space, and galaxies. These spectral signatures are known as "Unidentified Infrared Emission features." For over two decades, the most commonly accepted theory on the origin of these signatures has been that they come from simple organic molecules made of carbon and hydrogen atoms, called polycyclic aromatic hydrocarbon (PAH) molecules. From observations taken by the Infrared Space Observatory and the Spitzer Space Telescope, Kwok and Zhang showed that the astronomical spectra have features that cannot be explained by PAH molecules. Instead, the team proposes that the substances generating these infrared emissions have chemical structures that are much more complex. By analyzing spectra of star dust formed in exploding stars called novae, they show that stars are making these complex organic compounds on extremely short time scales of weeks.

Not only are stars producing this complex organic matter, they are also ejecting it into the general interstellar space, the region between stars. The work supports an earlier idea proposed by Kwok that old stars are molecular factories capable of manufacturing organic compounds. "Our work has shown that stars have no problem making complex organic compounds under near-vacuum conditions," says Kwok. "Theoretically, this is impossible, but observationally we can see it happening."

Most interestingly, this organic star dust is similar in structure to complex organic compounds found in meteorites. Since meteorites are remnants of the early Solar System, the findings raise the possibility that stars enriched the early Solar System with organic compounds. The early Earth was subjected to severe bombardments by comets and asteroids, which potentially could have carried organic star dust. Whether these delivered organic compounds played any role in the development of life on Earth remains an open question.

Prof. Sun Kwok is the Dean of Science and Chair Professor of Physics of the University of Hong Kong. He serves as Vice President of Division VI (interstellar matter) of the International Astronomical Union, and is the incoming Vice President of Commission 51 (bioastronomy) of the International Astronomical Union. He has published many books, including the recent book "Organic Matter in the Universe" (Wiley, 2011). Dr. Yong Zhang is a Research Assistant Professor at the University of Hong Kong. This work was supported by the Research Grants Council of Hong Kong.

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Sun Kwok, Yong Zhang. Mixed aromatic–aliphatic organic nanoparticles as carriers of unidentified infrared emission features. Nature, 2011; DOI: 10.1038/nature10542

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2011 Nobel Prize in Chemistry: 'Quasicrystals' once thought impossible have changed understanding of solid matter

ScienceDaily (Oct. 5, 2011) — The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Chemistry for 2011 to Daniel Shechtman of the Technion -- Israel Institute of Technology in Haifa, Israel, for the discovery of quasicrystals: non-repeating regular patterns of atoms that were once thought to be impossible.

A remarkable mosaic of atoms

In quasicrystals, we find the fascinating mosaics of the Arabic world reproduced at the level of atoms: regular patterns that never repeat themselves. However, the configuration found in quasicrystals was considered impossible, and Daniel Shechtman had to fight a fierce battle against established science. The Nobel Prize in Chemistry 2011 recognizes a breakthrough that has fundamentally altered how chemists conceive of solid matter.

On the morning of April 8, 1982, an image counter to the laws of nature appeared in Daniel Shechtman's electron microscope. In all solid matter, atoms were believed to be packed inside crystals in symmetrical patterns that were repeated periodically over and over again. For scientists, this repetition was required in order to obtain a crystal.

Shechtman's image, however, showed that the atoms in his crystal were packed in a pattern that could not be repeated. Such a pattern was considered just as impossible as creating a football using only six-cornered polygons, when a sphere needs both five- and six-cornered polygons. His discovery was extremely controversial. In the course of defending his findings, he was asked to leave his research group. However, his battle eventually forced scientists to reconsider their conception of the very nature of matter.

Aperiodic mosaics, such as those found in the medieval Islamic mosaics of the Alhambra Palace in Spain and the Darb-i Imam Shrine in Iran, have helped scientists understand what quasicrystals look like at the atomic level. In those mosaics, as in quasicrystals, the patterns are regular -- they follow mathematical rules -- but they never repeat themselves.

When scientists describe Shechtman's quasicrystals, they use a concept that comes from mathematics and art: the golden ratio. This number had already caught the interest of mathematicians in Ancient Greece, as it often appeared in geometry. In quasicrystals, for instance, the ratio of various distances between atoms is related to the golden mean.

Following Shechtman's discovery, scientists have produced other kinds of quasicrystals in the lab and discovered naturally occurring quasicrystals in mineral samples from a Russian river. A Swedish company has also found quasicrystals in a certain form of steel, where the crystals reinforce the material like armor. Scientists are currently experimenting with using quasicrystals in different products such as frying pans and diesel engines.

Daniel Shechtman, Israeli citizen. Born 1941 in Tel Aviv, Israel. Ph.D. 1972 from Technion -- Israel Institute of Technology, Haifa, Israel. Distinguished Professor, The Philip Tobias Chair, Technion -- Israel Institute of Technology, Haifa, Israel.

The Prize amount: SEK 10 million.

For further information, including backgrounders for the public and scientists and links for further reading, see: http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2011/press.html

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Hubble survey carries out a dark matter census

ScienceDaily (Oct. 13, 2011) — Cluster MACS J1206.2-0847 (or MACS 1206 for short) is one of the first targets in a Hubble survey that will allow astronomers to construct the highly detailed dark matter maps of more galaxy clusters than ever before. These maps are being used to test previous but surprising results that suggest that dark matter is more densely packed inside clusters than some models predict. This might mean that galaxy cluster assembly began earlier than commonly thought.

The Cluster Lensing And Supernova survey with Hubble (CLASH) probes, with unparalleled precision, the distribution of dark matter in 25 massive clusters of galaxies. So far, the CLASH team has observed six of the 25 clusters.

Dark matter makes up the bulk of the Universe's mass, yet it can only be detected by measuring how its gravity tugs on visible matter and warps the fabric of space-time like a fairground mirror so that the light from distant objects is distorted.

Galaxy clusters like MACS 1206 are perfect laboratories for studying dark matter's gravitational effects because they are the most massive structures in the Universe to be held together by gravity. Because of their immense gravitational pull, the clusters act like giant cosmic lenses, amplifying, distorting and bending any light that passes through them -- an effect known as gravitational lensing.

Lensing effects can also produce multiple images of the same distant object, as is evident in this Hubble picture. In particular, the apparent numbers and shapes of the distant galaxies far beyond a galaxy cluster become distorted as the light passes through, yielding a visible measurement of how much mass there is in the intervening cluster, and how it is distributed. The substantial lensing distortions seen are proof that the dominant mass component of the clusters is dark matter. The distortions would be far weaker if the clusters' gravity came only from visible matter.

MACS 1206 lies four billion light-years from Earth. Hubble's keen vision helped CLASH astronomers to uncover 47 multiple images of 12 newly identified faraway galaxies. Finding so many multiple images in a cluster is a unique capability of Hubble, and the CLASH survey is optimised to find them. The new observations build on earlier work by Hubble and ground-based telescopes.

Among the observations which complement Hubble's is a major project using the European Southern Observatory's Very Large Telescope. Unlike Hubble, which is making images of the clusters, the VLT is carrying out spectroscopic observations, where instruments split up the galaxies' light into their component colours letting the scientists draw inferences about many of the properties of the cluster galaxies, including their distance and chemical makeup.

Taking advantage of two of Hubble's powerful cameras, the Advanced Camera for Surveys and the Wide Field Camera 3, the CLASH survey covers a broad wavelength range, from ultraviolet to near-infrared.

Astronomers need the diverse colours to estimate the distances to the lensed galaxies and to study them in more detail. Hubble's unique capabilities allow astronomers to estimate distances to galaxies that are four times fainter than those that ground-based telescopes can see.

The era when the first clusters formed is not precisely known, but is estimated to be at least nine billion years ago and possibly as far back as twelve billion years ago. If most of the clusters in the CLASH survey are found to have excessively high accumulations of dark matter in their central cores, then it may yield new clues about the early stages of the origin of structure in the Universe.

Future telescopes like the NASA/ESA/CSA James Webb Space Telescope (JWST), a space-based infrared observatory now being built, will be able to study the fainter lensed galaxies in clusters like MACS 1206 in greater detail. JWST will be powerful enough to observe the spectra of some of the magnified galaxies and study their early chemical composition.

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Physicists localize 3-D matter waves for first time

ScienceDaily (Oct. 7, 2011) — University of Illinois physicists have experimentally demonstrated for the first time how three-dimensional conduction is affected by the defects that plague materials. Understanding these effects is important for many electronics applications.

Led by physics professor Brian DeMarco, the researchers achieved complete localization of quantum matter waves in three dimensions, first theorized roughly half a century ago. The group published its findings in the Oct. 7 issue of the journal Science.

Defects in materials are inevitable, but their effects are poorly understood. Understanding how disorder in a material affects waves traveling through it has implications for many applications, including ultrasonic waves in medical imaging, lasers for imaging and sensing, and electron waves for electronics and superconductors.

"The physics behind disorder is fundamental to understanding the impact of unavoidable material imperfections on these kinds of applications," DeMarco said.

Scientists have long theorized, but never observed, that strong disorder causing interference on all sides can trap a matter wave in one place, a phenomenon known as Anderson localization.

According to DeMarco, this is analogous to a trumpeter playing in a concert hall filled with randomly placed barriers that reflect sound waves. Instead of traveling in all directions, the sound stays at its source, never propagating outward because of destructive interference.

"The result? Perfect silence everywhere in the concert hall. The trumpeter blows into his instrument, but the sound never leaves the trumpet," DeMarco said. "That's exactly the case in our experiment, although we use quantum matter waves instead of sound, and the barriers are created using a speckled green laser beam."

To simulate electrons moving in waves through a metal, DeMarco's group uses ultra-cold atoms moving as matter waves in a disordered laser beam. Using laser light as an analogy for a material allows the researchers to completely characterize and control the disorder -- a feat impossible in solids, which has made understanding and testing theories of Anderson localization difficult.

The researchers demonstrated that the laser light could completely localize the atoms -- the first direct observation of three-dimensional Anderson localization of matter.

"This means that we can study Anderson localization in a way that is relevant to materials," DeMarco said. "Now, theories of Anderson localization in 3-D can be compared to our 'material' and tested for the first time."

The team also measured the energy a particle needs to escape localization, known as the mobility edge. Waves with energy higher than the mobility edge are free to propagate throughout the disorder, but waves with energy lower than the mobility edge are completely localized -- even when there is a path through the barriers.

By tuning the power of the speckled green laser beam, the researchers measured the relationship between the mobility edge and disorder strength. They found that as disorder increased, so did the mobility edge, meaning that materials with high concentrations of defects induce more localization.

DeMarco hopes to use the quantum-matter analogues to better understand and manipulate materials.

Eventually, he plans to use his measurements of Anderson localization and the mobility edge along with future work exploring other parameters to engineer materials to better perform specific applications -- in particular, high-temperature superconductors.

"Comparing measurements on a solid to theory are complicated by our lack of knowledge of the disorder in the solid and our inability to remove it," DeMarco said. "But, that's exactly what we can do with our experiment, and what makes it so powerful and exciting."

The Defense Advanced Research Projects Agency, the Office of Naval Research and the National Science Foundation supported this work.

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S. S. Kondov, W. R. McGehee, J. J. Zirbel, B. DeMarco. Three-Dimensional Anderson Localization of Ultracold Matter. Science, 2011; 334 (6052): 66 DOI: 10.1126/science.1209019

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Hubble survey carries out a dark matter census

ScienceDaily (Oct. 13, 2011) — Cluster MACS J1206.2-0847 (or MACS 1206 for short) is one of the first targets in a Hubble survey that will allow astronomers to construct the highly detailed dark matter maps of more galaxy clusters than ever before. These maps are being used to test previous but surprising results that suggest that dark matter is more densely packed inside clusters than some models predict. This might mean that galaxy cluster assembly began earlier than commonly thought.

The Cluster Lensing And Supernova survey with Hubble (CLASH) probes, with unparalleled precision, the distribution of dark matter in 25 massive clusters of galaxies. So far, the CLASH team has observed six of the 25 clusters.

Dark matter makes up the bulk of the Universe's mass, yet it can only be detected by measuring how its gravity tugs on visible matter and warps the fabric of space-time like a fairground mirror so that the light from distant objects is distorted.

Galaxy clusters like MACS 1206 are perfect laboratories for studying dark matter's gravitational effects because they are the most massive structures in the Universe to be held together by gravity. Because of their immense gravitational pull, the clusters act like giant cosmic lenses, amplifying, distorting and bending any light that passes through them -- an effect known as gravitational lensing.

Lensing effects can also produce multiple images of the same distant object, as is evident in this Hubble picture. In particular, the apparent numbers and shapes of the distant galaxies far beyond a galaxy cluster become distorted as the light passes through, yielding a visible measurement of how much mass there is in the intervening cluster, and how it is distributed. The substantial lensing distortions seen are proof that the dominant mass component of the clusters is dark matter. The distortions would be far weaker if the clusters' gravity came only from visible matter.

MACS 1206 lies four billion light-years from Earth. Hubble's keen vision helped CLASH astronomers to uncover 47 multiple images of 12 newly identified faraway galaxies. Finding so many multiple images in a cluster is a unique capability of Hubble, and the CLASH survey is optimised to find them. The new observations build on earlier work by Hubble and ground-based telescopes.

Among the observations which complement Hubble's is a major project using the European Southern Observatory's Very Large Telescope. Unlike Hubble, which is making images of the clusters, the VLT is carrying out spectroscopic observations, where instruments split up the galaxies' light into their component colours letting the scientists draw inferences about many of the properties of the cluster galaxies, including their distance and chemical makeup.

Taking advantage of two of Hubble's powerful cameras, the Advanced Camera for Surveys and the Wide Field Camera 3, the CLASH survey covers a broad wavelength range, from ultraviolet to near-infrared.

Astronomers need the diverse colours to estimate the distances to the lensed galaxies and to study them in more detail. Hubble's unique capabilities allow astronomers to estimate distances to galaxies that are four times fainter than those that ground-based telescopes can see.

The era when the first clusters formed is not precisely known, but is estimated to be at least nine billion years ago and possibly as far back as twelve billion years ago. If most of the clusters in the CLASH survey are found to have excessively high accumulations of dark matter in their central cores, then it may yield new clues about the early stages of the origin of structure in the Universe.

Future telescopes like the NASA/ESA/CSA James Webb Space Telescope (JWST), a space-based infrared observatory now being built, will be able to study the fainter lensed galaxies in clusters like MACS 1206 in greater detail. JWST will be powerful enough to observe the spectra of some of the magnified galaxies and study their early chemical composition.

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Matter shows abrupt escape from flatness: Lead made to undergo a rapid transition from 'pancake' to hemisphere

ScienceDaily (Sep. 28, 2011) — At first glance, it seems as if billions of lead atoms have mysteriously disappeared. When exposed to heat, a layer of lead coated onto a nickel surface becomes almost invisible from one moment to the next. In reality, the slightest disturbance causes these atoms to suddenly switch from a broad “flat pancake” shape to a compact hemisphere.

This remarkable phenomenon was first revealed by researchers at the University of Twente’s MESA+ Institute for Nanotechnology, who have since published their results in Physical Review Letters.

A lead coating on a nickel surface has unusual electronic properties which cause it to form flat "pancakes," consisting of billions of atoms arranged in a crystalline structure. These "pancakes" of solid lead are quantum mechanically stabilized and just a couple of dozen atoms thick. When exposed to gradual heating, nothing much changes at first. At about 520 Kelvin (247 degrees Celsius), however, the lead coating suddenly seems to disappear completely. Within the space of a few milliseconds, the lead "slivers" transform into hemispheres with a radius (or "height") of a few micrometers. Interestingly, this all takes place at a temperature below the melting point of lead. The hemispheres, too, consist of solid lead. So no mass has been lost, the material has simply taken on a different spatial configuration.

Low energy electron microscope

The technique used by the researchers to observe this process is known as Low Energy Electron Microscopy (LEEM). There are only a few such microscopes in existence, but two have recently been installed in the Netherlands. They are designed to bombard surfaces with low energy electrons. This makes them especially well suited to making accurate observations of surface phenomena and events in thin films.

Beyond the scope of our current knowledge

The abrupt transformation from flat to spherical can be explained in terms of the most energetically favourable shape. From this viewpoint, hemispheres make much more effective use of surfaces, whereas pancakes are not very stable. There has recently been a massive expansion in our understanding of atomic processes right down to the level of single atoms, facilitated by experimental techniques such as Scanning Tunnelling Microscopy (STM), together with newly developed theories. Even so, we cannot account for the sheer speed at which this transition takes place.

Group process

However, this recently discovered super-fast transition from two to three dimensions is based on a delicate interplay between several atoms, a kind of group process. In their published article, these researchers from Twente express the view that a more detailed explanation of the very rapid transition from flat to spherical will only be possible when we have a better fundamental theoretical understanding of meso-level phenomena. LEEM can be used to make direct observations of new phenomena at the meso-scale, thereby generating data crucial to our knowledge of this field. The importance of these results is that they will give us a more profound understanding of the stability of nanostructures.

This study was carried out by Prof. Harold Zandvliet's Physics of Interfaces and Nanomaterials group. Funding was provided by the FOM Institute. The group is part of the University of Twente's MESA+ Institute for Nanotechnology. The LEEM equipment used in this study was purchased with funds provided by the Dutch Technology Foundation (STW).

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Twente.

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Tjeerd Bollmann, Raoul van Gastel, Harold Zandvliet, Bene Poelsema. Anomalous Decay of Electronically Stabilized Lead Mesas on Ni(111). Physical Review Letters, 2011; 107 (13) DOI: 10.1103/PhysRevLett.107.136103

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Matter shows abrupt escape from flatness: Lead made to undergo a rapid transition from 'pancake' to hemisphere

ScienceDaily (Sep. 28, 2011) — At first glance, it seems as if billions of lead atoms have mysteriously disappeared. When exposed to heat, a layer of lead coated onto a nickel surface becomes almost invisible from one moment to the next. In reality, the slightest disturbance causes these atoms to suddenly switch from a broad “flat pancake” shape to a compact hemisphere.

This remarkable phenomenon was first revealed by researchers at the University of Twente’s MESA+ Institute for Nanotechnology, who have since published their results in Physical Review Letters.

A lead coating on a nickel surface has unusual electronic properties which cause it to form flat "pancakes," consisting of billions of atoms arranged in a crystalline structure. These "pancakes" of solid lead are quantum mechanically stabilized and just a couple of dozen atoms thick. When exposed to gradual heating, nothing much changes at first. At about 520 Kelvin (247 degrees Celsius), however, the lead coating suddenly seems to disappear completely. Within the space of a few milliseconds, the lead "slivers" transform into hemispheres with a radius (or "height") of a few micrometers. Interestingly, this all takes place at a temperature below the melting point of lead. The hemispheres, too, consist of solid lead. So no mass has been lost, the material has simply taken on a different spatial configuration.

Low energy electron microscope

The technique used by the researchers to observe this process is known as Low Energy Electron Microscopy (LEEM). There are only a few such microscopes in existence, but two have recently been installed in the Netherlands. They are designed to bombard surfaces with low energy electrons. This makes them especially well suited to making accurate observations of surface phenomena and events in thin films.

Beyond the scope of our current knowledge

The abrupt transformation from flat to spherical can be explained in terms of the most energetically favourable shape. From this viewpoint, hemispheres make much more effective use of surfaces, whereas pancakes are not very stable. There has recently been a massive expansion in our understanding of atomic processes right down to the level of single atoms, facilitated by experimental techniques such as Scanning Tunnelling Microscopy (STM), together with newly developed theories. Even so, we cannot account for the sheer speed at which this transition takes place.

Group process

However, this recently discovered super-fast transition from two to three dimensions is based on a delicate interplay between several atoms, a kind of group process. In their published article, these researchers from Twente express the view that a more detailed explanation of the very rapid transition from flat to spherical will only be possible when we have a better fundamental theoretical understanding of meso-level phenomena. LEEM can be used to make direct observations of new phenomena at the meso-scale, thereby generating data crucial to our knowledge of this field. The importance of these results is that they will give us a more profound understanding of the stability of nanostructures.

This study was carried out by Prof. Harold Zandvliet's Physics of Interfaces and Nanomaterials group. Funding was provided by the FOM Institute. The group is part of the University of Twente's MESA+ Institute for Nanotechnology. The LEEM equipment used in this study was purchased with funds provided by the Dutch Technology Foundation (STW).

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Twente.

Journal Reference:

Tjeerd Bollmann, Raoul van Gastel, Harold Zandvliet, Bene Poelsema. Anomalous Decay of Electronically Stabilized Lead Mesas on Ni(111). Physical Review Letters, 2011; 107 (13) DOI: 10.1103/PhysRevLett.107.136103

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

When matter melts: Scientists map phase changes in quark-gluon plasma

ScienceDaily (June 24, 2011) — In its infancy, when the universe was a few millionths of a second old, the elemental constituents of matter moved freely in a hot, dense soup of quarks and gluons. As the universe expanded, this quark-gluon plasma quickly cooled, and protons and neutrons and other forms of normal matter "froze out": the quarks became bound together by the exchange of gluons, the carriers of the color force.

"The theory that describes the color force is called quantum chromodynamics, or QCD," says Nu Xu of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), the spokesperson for the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at DOE's Brookhaven National Laboratory. "QCD has been extremely successful at explaining interactions of quarks and gluons at short distances, such as high-energy proton and antiproton collisions at Fermi National Accelerator Laboratory. But in bulk collections of matter -- including the quark-gluon plasma -- at longer distances or smaller momentum transfer, an approach called lattice gauge theory has to be used."

Until recently, lattice QCD calculations of hot, dense, bulk matter could not be tested against experiment. Beginning in 2000, however, RHIC was able to recreate the extreme conditions of the early universe in miniature, by colliding massive gold nuclei (heavy ions) at high energies.

Experimentalists at RHIC, working with theorist Sourendu Gupta of India's Tata Institute of Fundamental Research, have recently compared lattice-theory predictions about the nature of the quark-gluon plasma with certain STAR experimental results for the first time. In so doing they have established the temperature boundary where ordinary matter and quark matter cross over and change phase. Their results appear in the journal Science.

Phase diagrams

The aim of both the theoretical and experimental work is to explore and fix key points in the phase diagram for quantum chromodynamics. Phase diagrams are maps, showing, for example, how changes in pressure and temperature determine the phases of water, whether ice, liquid, or vapor. A phase diagram of QCD would map the distribution of ordinary matter (known as hadronic matter), the quark-gluon plasma, and other possible phases of QCD such as color superconductivity.

"Plotting a QCD phase diagram requires both theory calculations and experimental effort with heavy-ion collisions," says Xu, who is a member of Berkeley Lab's Nuclear Science Division and an author of the Science paper. Experimental studies require powerful accelerators like RHIC on Long Island or the Large Hadron Collider at CERN in Geneva, while calculations of QCD using lattice gauge theory require the world's biggest and fastest supercomputers. Direct comparisons can achieve more than either approach alone.

One of the basic requirements of any phase diagram is to establish its scale. A phase diagram of water might be based on the Celsius temperature scale, defined by the boiling point of water under normal pressure (i.e., at sea level). Although the boiling point changes with pressure -- at higher altitudes water boils at lower temperatures -- these changes are measured against a fixed value.

The scale of the QCD phase diagram is defined by a transition temperature at the zero value of "baryon chemical potential." Baryon chemical potential measures the imbalance between matter and antimatter, and zero indicates perfect balance.

Through extensive calculations and actual data from the STAR experiment, the team was indeed able to establish the QCD transition temperature. Before they could do so, however, they first had to realize an equally significant result, showing that the highly dynamical systems of RHIC's gold-gold collisions, in which the quark-gluon plasma winks in and out of existence, in fact achieve thermal equilibrium. Here's where theory and experiment worked hand in hand.

"The fireballs that result when gold nuclei collide are all different, highly dynamic, and last an extremely short time," says Hans Georg Ritter, head of the Relativistic Nuclear Collisions program in Berkeley Lab's Nuclear Science Division and an author of the Science paper. Yet because differences in values of the kind observed by STAR are related to fluctuations in thermodynamic values predicted by lattice gauge theory, says Ritter, "by comparing our results to the predictions of theory, we have shown that what we measure is in fact consistent with the fireballs reaching thermal equilibrium. This is an important achievement."

The scientists were now able to proceed with confidence in establishing the scale of the QCD phase diagram. After a careful comparison between experimental data and the results from the lattice gauge theory calculations, the scientists concluded that the transition temperature (expressed in units of energy) is 175 MeV (175 million electron volts).

Thus the team could develop a "conjectural" phase diagram that showed the boundary between the low-temperature hadronic phase of ordinary matter and the high-temperature quark-gluon phase.

In search of the critical point

Lattice QCD also predicts the existence of a "critical point." In a QCD phase diagram the critical point marks the end of a line showing where the two phases cross over, one into the other. By changing the energy, for example, the baryon chemical potential (balance of matter and antimatter) can be adjusted.

Among the world's heavy-ion colliders, only RHIC can tune the energy of the collisions through the region of the QCD phase diagram where the critical point is most likely to be found -- from an energy of 200 billion electrons volts per pair of nucleons (protons or neutrons) down to 5 billion electron volts per nucleon pair.

Says Ritter, "Establishing the existence of a QCD critical point would be much more significant than setting the scale." In 2010, RHIC started a program to search for the QCD critical point.

Xu says, "In this paper, we compared experimental data with lattice calculations directly, something never done before. This is a real step forward and allows us to establish the scale of the QCD phase diagram. Thus begins an era of precision measurements for heavy-ion physics."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Sourendu Gupta, Xiaofeng Luo, Bedangadas Mohanty, Hans Georg Ritter and Nu Xu. Scale for the phase diagram of quantum chromodynamics. Science, 24 June 2011 DOI: 10.1126/science.1204621

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Neutrinos change flavors while crossing Japan: Findings shed light on why universe is made of matter instead of anti-matter

ScienceDaily (June 15, 2011) — By shooting a beam of neutrinos through a small slice of Earth under Japan, physicists say they've caught the particles changing their stripes in new ways. These observations may one day help explain why the universe is made of matter rather than anti-matter.

The T2K experiment has been using the Japan Proton Accelerator Research Complex, or J-PARC, located on the east coast, to shoot a beam of muon neutrinos 185 miles, or 295 kilometers, underground toward the Super-Kamiokande, or Super-K, detector in Kamioka, near Japan's west coast.

The goal of the experiment, which is part of a new generation of neutrino-tracking facilities, is to observe the particles changing "flavors" from muon neutrinos to electron neutrinos on this brief journey.

Neutrinos are elementary particles that come in three flavors -- muon, electron and tau. In past experiments, physicists have measured the change of muon neutrinos to tau neutrinos and electron neutrinos to muon neutrinos or tau neutrinos.

"But no one had seen muon neutrinos turn into electron neutrinos," said Chris Walter, a physicist at Duke who is part of the T2K collaboration, along with Duke physicist Kate Scholberg.

The T2K collaboration, a team of physicists from around the world, began observing the neutrinos for their transformations in January 2010. The group measured the neutrinos, determining their flavor near the accelerator and then again at Super-K. So far, scientists caught 88 neutrinos with their detector. Six of these likely began their lives as muon neutrinos and turned into electron neutrinos on their way to Super-K.

"As it stands, this result is extremely interesting, but we are just getting started," Walter said. He explained that the T2K team has taken a little less than two percent of the planned neutrino measurements, partly due to the East Japan earthquake that struck on March 11, 2011 and forced the shutdown of T2K.

The preliminary findings were submitted to Physical Review Letters and announced at a press conference June 15 in Japan.

"We could see as many electron neutrino candidates as we saw by chance, something, like one out of every 150 times," Walter said. "This is why the title of our paper includes the word 'indications' as opposed to observation or measurement."

If the "indications" become "measurements," these T2K results will be the first to measure a muon-electron neutrino change. Scientists want this measurement to study a fundamental parameter of physics called theta-13, which controls the muon-electron neutrino switch. Walter said there is more than one way to measure theta-13 and that several experiments are currently competing to be the first.

"It's good news that we have evidence of a relatively large theta-13, since there are even more interesting measurements that can be done if it is big enough," he said.

If theta-13 is large, it will allow scientists to measure the difference between oscillations of neutrinos and oscillation of anti-neutrinos. Walter explained that in the early universe, "something caused there to be slightly more matter than anti-matter. When the matter and anti-matter annihilated each other, only that little bit of matter was left over. That matter is everything we see around us today. But no one understands how this happened."

"The difference between neutrino and anti-neutrino properties that we might measure in future experiments might give clues to how the excess matter was generated," Walter said.

Of course that all depends on how quickly T2K can come back online after being shut down from the earthquake. Currently, the experiment is slated to re-start at the end of 2011.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Duke University.

Journal References:

The T2K Collaboration. Indication of Electron Neutrino Appearance from an Accelerator-produced O -axis Muon Neutrino Beam. Physical Review Letters, 2011; (submitted)The T2K Collaboration. The T2K Experiment. arXiv.org, 2011; [link]

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Neutrinos change flavors while crossing Japan: Findings shed light on why universe is made of matter instead of anti-matter

ScienceDaily (June 15, 2011) — By shooting a beam of neutrinos through a small slice of Earth under Japan, physicists say they've caught the particles changing their stripes in new ways. These observations may one day help explain why the universe is made of matter rather than anti-matter.

The T2K experiment has been using the Japan Proton Accelerator Research Complex, or J-PARC, located on the east coast, to shoot a beam of muon neutrinos 185 miles, or 295 kilometers, underground toward the Super-Kamiokande, or Super-K, detector in Kamioka, near Japan's west coast.

The goal of the experiment, which is part of a new generation of neutrino-tracking facilities, is to observe the particles changing "flavors" from muon neutrinos to electron neutrinos on this brief journey.

Neutrinos are elementary particles that come in three flavors -- muon, electron and tau. In past experiments, physicists have measured the change of muon neutrinos to tau neutrinos and electron neutrinos to muon neutrinos or tau neutrinos.

"But no one had seen muon neutrinos turn into electron neutrinos," said Chris Walter, a physicist at Duke who is part of the T2K collaboration, along with Duke physicist Kate Scholberg.

The T2K collaboration, a team of physicists from around the world, began observing the neutrinos for their transformations in January 2010. The group measured the neutrinos, determining their flavor near the accelerator and then again at Super-K. So far, scientists caught 88 neutrinos with their detector. Six of these likely began their lives as muon neutrinos and turned into electron neutrinos on their way to Super-K.

"As it stands, this result is extremely interesting, but we are just getting started," Walter said. He explained that the T2K team has taken a little less than two percent of the planned neutrino measurements, partly due to the East Japan earthquake that struck on March 11, 2011 and forced the shutdown of T2K.

The preliminary findings were submitted to Physical Review Letters and announced at a press conference June 15 in Japan.

"We could see as many electron neutrino candidates as we saw by chance, something, like one out of every 150 times," Walter said. "This is why the title of our paper includes the word 'indications' as opposed to observation or measurement."

If the "indications" become "measurements," these T2K results will be the first to measure a muon-electron neutrino change. Scientists want this measurement to study a fundamental parameter of physics called theta-13, which controls the muon-electron neutrino switch. Walter said there is more than one way to measure theta-13 and that several experiments are currently competing to be the first.

"It's good news that we have evidence of a relatively large theta-13, since there are even more interesting measurements that can be done if it is big enough," he said.

If theta-13 is large, it will allow scientists to measure the difference between oscillations of neutrinos and oscillation of anti-neutrinos. Walter explained that in the early universe, "something caused there to be slightly more matter than anti-matter. When the matter and anti-matter annihilated each other, only that little bit of matter was left over. That matter is everything we see around us today. But no one understands how this happened."

"The difference between neutrino and anti-neutrino properties that we might measure in future experiments might give clues to how the excess matter was generated," Walter said.

Of course that all depends on how quickly T2K can come back online after being shut down from the earthquake. Currently, the experiment is slated to re-start at the end of 2011.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Duke University.

Journal References:

The T2K Collaboration. Indication of Electron Neutrino Appearance from an Accelerator-produced O -axis Muon Neutrino Beam. Physical Review Letters, 2011; (submitted)The T2K Collaboration. The T2K Experiment. arXiv.org, 2011; [link]

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

White matter disease: Genetic mutation causing MLC identified

ScienceDaily (May 4, 2011) — White matter disease (WMD) covers a large group of disorders that affect the white matter, or myelin. In children these disorders are commonly genetic and often go undiagnosed. In new research, a team led by Raúl Estévez, a lecturer from the Department of Physiological Sciences II, based at the UB's Bellvitge Health Sciences Campus, working with the researcher Marjo van der Knaap, from the University Medical Centre at VU University Amsterdam, have identified mutant GlialCAM as responsible for 25% of cases of megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare genetic disease affecting cerebral myelin.

Also participating in the study, which has been published and selected as a featured article in The American Journal of Human Genetics, were Tania López-Hernández, co-principal author and a postdoctoral fellow at the UB, and the researchers Albert Martínez, from the Institute of Biomedical Research (IRB Barcelona), and Virginia Nunes, a lecturer at the UB and researcher for the Bellvitge Biomedical Research Institute (IDIBELL).

Myelin is required for the correct propagation of nerve impulses between neurons, enabling the brain to send the signals that make us move. In children, diseases affecting this substance are largely genetic and affect a single gene. In adults, the diseases present as inflammatory conditions such as multiple sclerosis. "In the specific case of infant WMD, every type is rare or extremely rare, but if we consider all cases as a single group the incidence is high -- 1 patient for every 1,000 individuals," explains Raúl Estévez, ICREA Acadèmia award winner and a member of the Centre for Biomedical Network Research on Rare Diseases (CIBERER). "In addition," he adds, "in a high percentage of children with myelin disorders the diagnosis is not clear and no real conclusions can be reached."

Thanks to the identification in recent years of abnormal patterns in brain MRIs, researchers have been able to define new diseases. In 1995 experts discovered an autosomal recessive myelin disorder called megalencephalic leukoencephalopathy with subcortical cysts (MLC). In 2001 the gene responsible for 75% of the cases of this disease, MLC1, wa discovered and scientists found that other cases existed that were not caused by mutations of this gene. Of the remaining 25% of patients, two clinical phenotypes were observed: in the first case, the clinical progression, showing progressive degeneration, is the same as observed in the larger group; in the second case, the disease improves or disappears altogether. The common feature in all patients is the presence of macrocephaly, which may be accompanied by learning difficulties and autism.

The study published in The American Journal of Human Genetics takes as its starting point the genetic heterogeneity of the disease and looks for other possible mutations behind its development, combining biochemical and genetic studies. The results show that patients presenting a progressive degeneration of their condition exhibit two mutations in the GlialCAM gene, whose related protein is GlialCAM, while others exhibit only a single mutation in the same gene, which suggests a pattern of autosomal-dominant inheritance. The study, which also describes the biochemical defects observed in the disease, has revealed that mutant GlialCAM can also lead to benign familial macrocephaly and macrocephaly with mental retardation, with or without autism.

"Although we have yet to determine the exact function of GlialCAM, our research has shown that further collaborative multi-disciplinary translational studies will be required to learn more about the causes of these rare diseases and to find new treatments,"

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Universidad de Barcelona, via AlphaGalileo.

Journal Reference:

Tania López-Hernández, Margreet C. Ridder, Marisol Montolio, Xavier Capdevila-Nortes, Emiel Polder, Sònia Sirisi, Anna Duarri, Uwe Schulte, Bernd Fakler, Virginia Nunes, Gert C. Scheper, Albert Martínez, Raúl Estévez, Marjo S. van der Knaap. Mutant GlialCAM Causes Megalencephalic Leukoencephalopathy with Subcortical Cysts, Benign Familial Macrocephaly, and Macrocephaly with Retardation and Autism. The American Journal of Human Genetics, 2011; 88 (4): 422 DOI: 10.1016/j.ajhg.2011.02.009

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here