Tuesday, June 15, 2010

DISCREPANT FEATURES FOUND IN COSMIC RAY ENERGY SPECTRA

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In May a University of Maryland-led team of scientists reported some previously unknown features in the energy spectra of cosmic ray nuclei, which have been studied for almost 100 years. Cosmic rays were discovered in 1912 with an electroscope carried on a manned hot air balloon.

The current observations were made with a NASA-funded balloon-borne instrument that has flown for 156 days above 99.5% of the atmosphere in five separate long-duration flights high over Antarctica, the first for a record-breaking 42 days. Researchers from the Cosmic Ray Energetics And Mass (CREAM) collaboration have reported a difference between spectra of protons and helium and a hardening (flattening) of all nuclei spectra at about 200 GeV/nucleon. These new observations contradict the current paradigm for the origin of cosmic rays in supernovae, which in its simplest form leads to a simple power law spectrum for all elements. Details of the cosmic ray origin and acceleration mechanism are not yet completely understood.

"Whether or not the proton spectrum is the same as that of heavier nuclei has long been a tantalizing question, but the spectral flattening was a surprise," said Eun-Suk Seo, Principal Investigator for the CREAM project and professor at the University of Maryland. "We were looking for a spectral cut off, evidence of the supernova acceleration limit, but instead found a relative increase in flux with energy." Such features could not be observed before, because the energy ranges of previous experiments were limited, and cosmic-ray particles are very scarce at high energies. Different types of sources or acceleration sites could explain the observed difference in protons and helium spectra.

The observed hardening of nuclei spectra could result from a nearby source, analogous to one explanation for the electron excess. The hardening of nuclei spectra at the rigidity (momentum per charge) similar to the onset of previously reported electron enhancements indicates that a single mechanism might be responsible for both electrons and nuclei. The pervasive discrepant hardening in elemental spectra provides important constraints on cosmic-ray acceleration and propagation. It must be accounted for in any explanation of the mysterious cosmic ray "knee", the steepening, rather than flattening, of the all-particle spectrum near 1015 eV observed in ground based air shower measurements.

The 2,500-pound CREAM instrument was conceived to measure the detailed energy dependence of elemental spectra to the highest energy possible with a balloon-borne instrument. It has been flown above some 128,000 feet altitude over Antarctica using a helium-filled balloon about as large as a football stadium. Its measurements in near space bridge the energy gap between similar lower-energy data and abundant ground-based air shower measurements at higher energies.

University of Maryland

NEW DISCOVERY INTO CAUSES OF TREMOR

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Scientists at Newcastle University have made a discovery which could help around 1 million people in the UK who suffer from shakes and tremors.

Mild tremor is a feature of daily life in healthy individuals – we have all experienced it, especially when nervous, tired or hungry. But more severe tremors are a symptom of nervous diseases, such as Parkinson’s, Multiple Sclerosis and Essential Tremor. Essential tremor is common in old age, but younger people can also be affected, and in severe cases it can leave patients unable to walk unaided.

Now scientists have discovered a mechanism in the spine which works to counteract the brain waves which produce tremor, meaning they are a step closer to treating these shakes and transforming lives.

Research leader Prof. Stuart Baker, professor of movement neuroscience, said: “We don’t fully understand the brain systems causing these tremors but they can really have a massive impact on someone’s quality of life. They lose their independence and can’t do something as simple as make a cup of tea.

“Our approach was that instead of looking at why people suffer from tremors, we started to look at why most people don’t suffer from them. The brain waves from the parts of the brain controlling movement work at 10 cycles per second, so really, everyone should have a tremor at that frequency. In fact we do, but for most of us - most of the time – tremor is so small as to be hardly noticeable. We reasoned that there is something in the body which counters the tremor, cancelling it out, and we wanted to find out what it was."

The research, which is published in the American Journal Proceedings of the National Academy of Sciences and is funded by the Wellcome Trust, involved teaching macaque monkeys to move their index finger slowly backwards and forwards. This exacerbated the natural minor tremors that both primates and humans experience. Sensors were used to record the activity of nerve cells from the brain and the spinal cord as the animals moved. The brain and spinal cord both showed rhythmic activity at the same frequency as the tremor. But crucially the spinal cord was active alternately with the brain, counteracting the oscillations and reducing the size of the tremor.

Prof. Baker continued: “There are many different sorts of disease which produce tremor. In some, maybe the controller in the spine malfunctions, and that is what actually causes the tremor. In other diseases, we already know that the problem is in the brain: particular brain regions produce abnormally high oscillations. But even then, the spinal system we have discovered will reduce tremors, making the symptoms much less severe than they would otherwise be.

“Understanding more about how the spinal controller works could open the way to adjusting it to work better, reducing the levels of tremors patients suffer and improving their lives.”

Newcastle University

THE DILEMMA OF PLANTS FIGHTING INFECTIONS

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Scientists from Tübingen reveal an evolutionary dilemma: plants that are more resistant to disease grow more slowly and are less competitive than susceptible relatives when enemies are rare.

Individuals of one and the same plant species often differ greatly in their ability to resist pathogens: While one rose succumbs to bacterial infection, its neighbour blissfully thrives. Scientists from the Max Planck Institute of Developmental Biology in Germany have tracked down an explanation for this common phenomenon. Their conclusion: disease resistance can incur high costs. Especially resistant plants of mouse ear cress (Arabidopsis thaliana) produce fewer and smaller leaves, and have a competitive disadvantage in the absence of enemies. Whether it is better to invest in disease resistance or biomass is thus very much dependent on the unpredictable circumstances a plant may find itself in. Therefore both large, but vulnerable plants co-exist in nature with small, but well-protected ones.

In the course of evolution, plants have invented many ways to defend themselves against enemies. Some produce smelly or bad-tasting ingredients, others develop thorns or have a particular effective immune response to viruses and bacteria. If selection pressure is sufficiently high, one would thus expect only those individuals to survive that are best protected. Pathogens, in turn, should have a difficult time. Everybody knows that this is not the case. Indeed, plants vary tremendously in their ability to defend themselves, and this is true not only for different species, but also for members of the same species.

The group of Detlef Weigel at the Max Planck Institute for Developmental Biology has now tracked down a variant of the ACD6 gene, which functions as a universal weapon in the fight against predators. With it, the plants both produce much more of a chemical that is directly toxic to microbes and more signalling molecules important in immunity. These enable mouse ear cress plants to combat a wide range of enemies, from bacteria and fungi to insects such as aphids. However, not all varieties have this variant. While it occurs throughout the area where mouse ear cress grows, from North Africa to Scandinavia, and from Central Asia to Western Europe, at any given place it is found in only about 20 percent of individuals. This already suggests that this variant might also confer some disadvantages.

"We could show that this gene makes plants resistant against pathogens, but at the same time it slows down the production of leaves and limits the size of leaves, so that these plants are always smaller than those that do not have this variant," said Detlef Weigel. "But as soon as they are being attacked, the plants with the special ACD6 variant have a leg up compared to plants with the standard version. On the down side, at places or in years where there are few enemies, they are penalized and lose out compared to the larger fellow plants." Smaller size eventually leads to reduced number of seeds and hence to fewer progeny. The conclusion of Weigel: "Just as in human society, there is no free lunch in nature."

(Photo: Jürgen Berger)

Max Planck Institute

INSPIRATORY MUSCLE TRAINING AND ENDURANCE SPORT PERFORMANCE

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An Indiana University study found that strengthening inspiratory muscles by performing daily breathing exercises for six weeks significantly reduced the amount of oxygen these same breathing muscles required during exercise, possibly making more oxygen available for other muscles.

Louise Turner, a researcher in the Department of Kinesiology, said just the act of breathing during an endurance activity, such as running, swimming or cycling performed at maximum intensity, can account for 10 to 15 percent of an athlete's total oxygen consumption. While inspiratory muscle training (IMT) has been shown to improve performance in endurance sports, Turner's study sought to shed light on how IMT does this.

"This study helps to provide further insight into the potential mechanisms responsible for the improved whole-body endurance performance previously reported following IMT," she said.

About the study:

* The double blind, placebo-controlled study involved 16 male cyclists ages 18 to 40.

* IMT involves the use of a hand-held device that provides resistance as one inhales through it, requiring greater use of inspiratory muscles. For half of the study participants, the IMT device was set to a level that provided resistance as the subjects took a fast forceful breath in. For six weeks they took 30 breaths at this setting twice a day. The cyclists in the control group did the same exercises with the IMT adjusted to a minimal level.

* After six weeks, when the study participants mimicked the breathing required for low, moderate and maximum intensity activities, the inspiratory muscles required around 1 percent less oxygen during the low intensity exercise and required 3 to 4 percent less during the high intensity exercise.

Muscles need oxygen to produce energy. Turner's research also is looking at the next component of this equation, whether more oxygen is actually available to other muscles, particularly those in the legs, because less oxygen is being used by the breathing muscles.

IMT has been used as an intervention in pulmonary diseases and conditions, such as asthma, COPD and cystic fibrosis, and also is marketed as a means for improving athletic performance in cyclists, runners and swimmers.

Indiana University

ARCTIC ICE AT LOW POINT COMPARED TO RECENT GEOLOGIC HISTORY

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Less ice covers the Arctic today than at any time in recent geologic history. That’s the conclusion of an international group of researchers, who have compiled the first comprehensive history of Arctic ice.

For decades, scientists have strived to collect sediment cores from the difficult-to-access Arctic Ocean floor, to discover what the Arctic was like in the past. Their most recent goal: to bring a long-term perspective to the ice loss we see today.

Now, in an upcoming issue of Quarternary Science Reviews, a team led by Ohio State University has re-examined the data from past and ongoing studies -- nearly 300 in all -- and combined them to form a big-picture view of the pole’s climate history stretching back millions of years.

“The ice loss that we see today -- the ice loss that started in the early 20th Century and sped up during the last 30 years -- appears to be unmatched over at least the last few thousand years,” said Leonid Polyak, a research scientist at Byrd Polar Research Center at Ohio State University. Polyak is lead author of the paper and a preceding report that he and his coauthors prepared for the U.S. Climate Change Science Program.

Satellites can provide detailed measures of how much ice is covering the pole right now, but sediment cores are like fossils of the ocean’s history, he explained.

“Sediment cores are essentially a record of sediments that settled at the sea floor, layer by layer, and they record the conditions of the ocean system during the time they settled. When we look carefully at various chemical and biological components of the sediment, and how the sediment is distributed -- then, with certain skills and luck, we can reconstruct the conditions at the time the sediment was deposited.”

For example, scientists can search for a biochemical marker that is tied to certain species of algae that live only in ice. If that marker is present in the sediment, then that location was likely covered in ice at the time. Scientists call such markers “proxies” for the thing they actually want to measure -- in this case, the geographic extent of the ice in the past.

While knowing the loss of surface area of the ice is important, Polyak says that this work can’t yet reveal an even more important fact: how the total volume of ice -- thickness as well as surface area -- has changed over time.

"When we look carefully at various chemical and biological components of the seafloor sediment, and how the sediment is distributed -- then, with certain skills and luck, we can reconstruct the conditions at the time the sediment was deposited.”

“Underneath the surface, the ice can be thick or thin. The newest satellite techniques and field observations allow us to see that the volume of ice is shrinking much faster than its area today. The picture is very troubling. We are losing ice very fast,” he said.

“Maybe sometime down the road we’ll develop proxies for the ice thickness. Right now, just looking at ice extent is very difficult.”

To review and combine the data from hundreds of studies, he and his cohorts had to combine information on many different proxies as well as modern observations. They searched for patterns in the proxy data that fit together like pieces of a puzzle.

Their conclusion: the current extent of Arctic ice is at its lowest point for at least the last few thousand years.

As scientists pull more sediment cores from the Arctic, Polyak and his collaborators want to understand more details of the past ice extent and to push this knowledge further back in time.

During the summer of 2011, they hope to draw cores from beneath the Chukchi Sea, just north of the Bering Strait between Alaska and Siberia. The currents emanating from the northern Pacific Ocean bring heat that may play an important role in melting the ice across the Arctic, so Polyak expects that the history of this location will prove very important. He hopes to drill cores that date back thousands of years at the Chukchi Sea margin, providing a detailed history of interaction between oceanic currents and ice.

“Later on in this cruise, when we venture into the more central Arctic Ocean, we will aim at harvesting cores that go back even farther,” he said. “If we could go as far back as a million years, that would be perfect.”

(Photo: OSU)

Ohio State University

SCIENTISTS CAPTURE SECRET DANCE OF ELECTRONS THAT CAUSES THEM TO CHANGE FORM

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Scientists have captured the first images of electrons that appear to take on extraordinary mass under certain extreme conditions, thus solving a 25-year mystery about how electrons behave in metals. The discovery could help with the design of new materials for high-temperature superconductors.

The findings by scientists from McMaster University, Cornell University, the U.S. Department of Energy's Brookhaven and Los Alamos National Laboratories, are published in the current issue of Nature.

"When electrons interact in materials unpredictable things can happen," says Graeme Luke, professor in the Department of Physics & Astronomy at McMaster University. "Heavy fermion behavior—where electrons behave as if they weigh 1,000 times or more their actual mass—is one of the most fascinating examples of these phenomena. In this case, they were doing a kind of wave-like dance that changes the form and very nature of the electrons."

Using properties in a crystal composed of uranium, ruthenium and silicon— synthesized by doctoral candidate Travis Williams and staff member Jim Garrett in Luke's group using the facilities of the Centre for Crystal Growth at McMaster's Brockhouse Institute for Materials Research — the effects of heavy fermions began to appear as the material was cooled below 55 Kelvin (-218 °C). But an even more unusual electronic phase transition occurred below 17.5K.

Using a technique developed specifically for their experiment known as spectroscopic imaging scanning tunneling microscopy (SI-STM), the team was able to track the arrangement and interactions of electrons in the crystals, and watch how they react at different temperatures and see what happens when they passed through the mysterious phase transition.

"For 25 years we have known that there's a phase transition occurring in this material but we've never been able to identify what kind of order was occurring. It wasn't magnetic order or superconductivity," says Luke. "We didn't know if it was related to the way electrons were behaving in a group or whether it was the result of interactions between individual electrons and uranium atoms. The microscope, however, allowed us to actually see a change in the microscopic electron states."

"Imagine flying over a body of water where standing waves are moving up and down, but not propagating toward the shore," said study leader Séamus Davis, a physicist at Brookhaven and the J.D. White Distinguished Professor of Physical Sciences at Cornell University. "When you pass over high points, you can touch the water; over low points, you can't. This is similar to what our microscope does. It images how many electrons can jump to the tip of our probe at every point on the surface."

Based on these wavelength and energy measurements, scientists can calculate the effective electron mass for specific electron bands.

The researchers are continuing to probe a variety of related compounds with this new approach to further their understanding of heavy fermion systems.

(Photo: McMaster University)

McMaster University

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