Subtle electronic effect in magnetite discovered: Long-standing puzzle in study of magnetism finally solved

ScienceDaily (Dec. 21, 2011) — A fundamental problem that has long puzzled scientists has been solved after more than 70 years. An international team of researchers has discovered a subtle electronic effect in magnetite, the most magnetic of all naturally occurring minerals. The effect causes a dramatic change to how this material conducts electricity at very low temperatures.

The discovery gives new insight into the mineral in which magnetism was discovered, and it may enable magnetite and similar materials to be exploited in new ways.

Ancient knowledge

Magnetite's properties have been known for more than 2000 years and gave rise to the original concepts of magnets and magnetism. The mineral has formed the basis for decades of research into magnetic recording and information storage materials.

The research was led by the University in collaboration with the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, where the experiments were conducted. Their results were published in Nature.

Unexplained behaviour

In 1939, Dutch scientist Evert Verwey discovered that the electrical conductivity of magnetite decreases abruptly and dramatically at low temperatures. At about 125 Kelvin, or minus 150 degrees Celsius, the metallic mineral turns into an insulator.

Despite many efforts, until now the reason for this transition has been debated and remained controversial.

X-ray experiment

The team of scientists fired an intense X-ray beam at a tiny crystal of magnetite at very low temperatures. Their results enabled them to understand a subtle rearrangement of the mineral's chemical structure. Electrons are trapped within groups of three iron atoms, where they can no longer transport an electrical current.

"We have solved a fundamental problem in understanding the original magnetic material, upon which everything we know about magnetism is built," said Professor Paul Attfield, Centre for Science at Extreme Conditions. "This vital insight into how magnetite is constructed and how it behaves will help in the development of future electronic and magnetic technologies."

The research was funded by the Science and Technology Facilities Council, the Engineering and Physical Sciences Research Council, and the Leverhulme Trust.

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The above story is reprinted from materials provided by University of Edinburgh.

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Journal References:

Mark S. Senn, Jon P. Wright, J. Paul Attfield. Charge order and three-site distortions in the Verwey structure of magnetite. Nature, 2011; DOI: 10.1038/nature10704J. Paul Attfield. Condensed-matter physics: A fresh twist on shrinking materials. Nature, 2011; 480 (7378): 465 DOI: 10.1038/480465a

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Early research on cellphone conversations likely overestimated crash risk, study suggests

ScienceDaily (Dec. 14, 2011) — A Wayne State University study published in the January 2012 issue of the journal Epidemiology points out that two influential early studies of cellphone use and crash risk may have overestimated the relative risk of conversation on cellphones while driving.

In this new study, Richard Young, Ph.D., professor of research in Wayne State University's Department of Psychiatry and Behavioral Neurosciences in the School of Medicine, examined possible bias in a 1997 Canadian study and a 2005 Australian study. These earlier studies used cellphone billing records of people who had been in a crash and compared their cellphone use just before the crash to the same time period the day (or week) before -- the control window.

Young said the issue with these studies is that people may not have been driving during the entire control window period, as assumed by the earlier study investigators.

"Earlier case-crossover studies likely overestimated the relative risk for cellphone conversations while driving by implicitly assuming that driving during a control window was full time when it may have been only part time," said Young. "This false assumption makes it seem like cellphone conversation is a bigger crash risk than it really is."

In Young's new study, his research team used Global Positioning Satellite (GPS) data to track day-to-day driving of more than 400 drivers during a 100-day period. He then divided the days into pairs, with the first day representing the "control" day and the second day representing the "crash" day in the earlier studies. Overall, the team found little driving consistency in any given clock time period between the two days -- driving time on the control day was only about one-fourth of the driving time on the crash day, during any specific clock time period.

"This underestimation of the amount of driving in the control windows by nearly four times could reduce cellphone conversation time in that control period," Young said. "It makes it appear that there is less cellphone conversation in control periods than in the time just before a crash, making the relative risk estimate appear greater than it really is."

Young found that when the cellphone conversation time in the control window was adjusted for the amount of driving, the amount of cellphone usage in the control window was about the same as in the minutes before a crash. He concluded that the crash risk for cellphone conversation while driving is one-fourth of what was claimed in previous studies, or near that of normal baseline driving.

Young added that many well-controlled studies with real driving show that the primary increase in crash risk from portable electronic devices comes from tasks that require drivers to look at the device or operate it with their hands, such as texting while driving. Five other recent real-world studies concur with his conclusion that the crash risk from cellular conversations is not greater than that of driving with no conversation.

"Tasks that take a driver's eyes off the road or hands off the steering wheel are what increase crash risk," said Young. "Texting, emailing, manual dialing and so forth -- not conversation -- are what increase the risk of crashes while driving."

The National Transportation Safety Board has recommended that all 50 states and the District of Columbia ban the non-emergency use of portable electronic devices for all drivers. Young said this recommendation goes beyond the data from newer studies, including his, because it would ban cellphone conversations while driving.

"Recent real-world studies show that cellphone conversations do not increase crash risk beyond that of normal driving -- it is the visual-manual tasks that take the eyes off the road and the hands off the wheel that are the real risk," said Young.

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Journal Reference:

Richard A. Young. Cell Phone Use and Crash Risk. Epidemiology, 2012; 23 (1): 116 DOI: 10.1097/EDE.0b013e31823b5efc

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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.

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Arctic ice near all-time low, 2nd study confirms

Arctic sea ice on Sept. 9, seen by satellite, had retreated 35 per cent from its median 1979-to- 2000 low (indicated by the orange line), U.S. data says. National Snow and Ice Data Center

A second major scientific body has said Arctic sea ice is about as low as it's ever been since satellites began monitoring it.

And a researcher at the U.S.-based National Snow and Ice Data Center said that open water at the top of the globe may already be affecting weather in more southern reaches of North America.

The amount of ice in the North is almost at the all-time low of 2007 and could drop further in coming weeks, the centre said Thursday. That assessment came days after German researchers concluded ice cover is already less than it was four years ago, which was the lowest since satellite monitoring began in 1979.

There is now about one-third less ice in the Arctic than the 1979-2000 average.

Northern sea ice is considered a leading indicator of global warming.

Although the National Snow and Ice Data Center suggests the ice level could still drop below the all-time low, this year's result is more worrisome because it happened in a summer that didn't have the same kind of unusual weather as in 2007.

Walter Meier, a researcher at the centre, said that year was marked by remarkably sunny skies and winds that tended to bunch the ice together. This year had none of those special conditions.

'We haven't seen ice cover this low probably for the last several thousand years'—Researcher Walter Meier

This year "has more to do with the changing long-term climate of the Arctic rather than just a single one-year extreme event," said James Overland, an oceanographer with the U.S. National Oceanic and Atmospheric Administration.

Although satellite data only exists for the last 32 years, there's ample other evidence that the extent of modern sea ice is at historic lows, Meier said.

"We haven't seen ice cover this low probably for the last several thousand years."

Much has been made of the possibility of faster shipping routes and greater access to resources in an increasingly ice-free Arctic, but Overland said there are also implications for weather in the rest of North America that are starting to emerge.

"There is some evidence that warming in the Arctic will bring cooling to some of the weather further south," he said.

Air warms up more over dark open water than it does over white, reflective sea ice and some scientists believe that the warmer air is starting to disrupt wind patterns that normally keep Arctic air bottled up in the North. Overland theorizes that disruption may have helped create the cold, snowy winters of 2008 and 2009 in Eastern Canada, as well as the cold weather along the U.S. east coast in 2009 and 2010.

"We're not sure about this," said Overland. "It's very controversial."

It is expected that as early as 2030, the Arctic will be ice-free for part of the year.

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