A new kind of metal in the deep Earth
The crushing pressures and intense temperatures in Earth's deep interior squeeze atoms and electrons so closely together that they interact very differently. With depth materials change. New experiments and supercomputer computations have revealed that iron oxide undergoes a new kind of transition under deep Earth conditions. Iron oxide, FeO, is a component of the second most abundant mineral at Earth's lower mantle, ferropericlase. The finding, published in an upcoming issue of Physical Review Letters, could alter our understanding of deep Earth dynamics and the behavior of the protective magnetic field, which shields our planet from harmful cosmic rays.
Ferropericlase contains both magnesium and iron oxide. To imitate the extreme conditions in the lab, the team including coauthor Ronald Cohen of Carnegie's Geophysical Laboratory, studied the electrical conductivity of iron oxide to pressures and temperatures up to 1.4 million times atmospheric pressure and 4000°F -- on par with conditions at the core-mantle boundary. They also used a new computational method that uses only fundamental physics to model the complex many-body interactions among electrons. The theory and experiments both predict a new kind of metallization in FeO.
Compounds typically undergo structural, chemical, electronic, and other changes under these extremes. Contrary to previous thought, the iron oxide went from an insulating (non-electrical conducting) state to become a highly conducting metal at 690,000 atmospheres and 3000°F, but without a change to its structure. Previous studies had assumed that metallization in FeO was associated with a change in its crystal structure. This result means that iron oxide can be both an insulator and a metal depending on temperature and pressure conditions.
"At high temperatures, the atoms in iron oxide crystals are arranged with the same structure as common table salt, NaCl," explained Cohen. "Just like table salt, FeO at ambient conditions is a good insulator -- it does not conduct electricity. Older measurements showed metallization in FeO at high pressures and temperatures, but it was thought that a new crystal structure formed. Our new results show, instead, that FeO metallizes without any change in structure and that combined temperature and pressure are required. Furthermore, our theory shows that the way the electrons behave to make it metallic is different from other materials that become metallic."
"The results imply that iron oxide is conducting in the whole range of its stability in Earth's lower mantle." Cohen continues, "The metallic phase will enhance the electromagnetic interaction between the liquid core and lower mantle. This has implications for Earth's magnetic field, which is generated in the outer core. It will change the way the magnetic field is propagated to Earth's surface, because it provides magnetomechanical coupling between the Earth's mantle and core."
"The fact that one mineral has properties that differ so completely -- depending on its composition and where it is within the Earth -- is a major discovery," concluded Geophysical Laboratory director Russell Hemley
Scientists identify an innate function of vitamin E
Published: Tuesday, December 20, 2011 - 15:34 in Health & Medicine
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It's rubbed on the skin to reduce signs of aging and consumed by athletes to improve endurance but scientists now have the first evidence of one of vitamin E's normal body functions. The powerful antioxidant found in most foods helps repair tears in the plasma membranes that protect cells from outside forces and screen what enters and exits, Georgia Health Sciences University researchers report in the journal Nature Communications.
Everyday activities such as eating and exercise can tear the plasma membrane and the new research shows that vitamin E is essential to repair. Without repair of muscle cells, for example, muscles eventually waste away and die in a process similar to what occurs in muscular dystrophy. Muscle weakness also is a common complaint in diabetes, another condition associated with inadequate plasma membrane repair.
"Without any special effort we consume vitamin E every day and we don't even know what it does in our bodies," said Dr. Paul McNeil, GHSU cell biologist and the study's corresponding author. He now feels confident about at least one of its jobs.
Century-old animal studies linked vitamin E deficiency to muscle problems but how that happens remained a mystery until now, McNeil said. His understanding that a lack of membrane repair caused muscle wasting and death prompted McNeil to look at vitamin E.
Vitamin E appears to aid repair in several ways. As an antioxidant, it helps eliminate destructive byproducts from the body's use of oxygen that impede repair. Because it's lipid-soluble, vitamin E can actually insert itself into the membrane to prevent free radicals from attacking. It also can help keep phospholipids, a major membrane component, compliant so they can better repair after a tear.
For example, exercise causes the cell powerhouse, the mitochondria, to burn a lot more oxygen than normal. "As an unavoidable consequence you produce reactive oxygen species," McNeil said. The physical force of exercise tears the membrane. Vitamin E enables adequate plasma membrane repair despite the oxidant challenge and keeps the situation in check.
When he mimicked what happens with exercise by using hydrogen peroxide to produce free radicals, he found that tears in skeletal muscle cells would not heal unless pretreated with vitamin E.
Next steps, which will be aided by two recent National Institutes of Health grants, include examining membrane repair in vitamin E-deficient animals.
McNeil also wants to further examine membrane repair failure in diabetes. Former GHSU graduate student Dr. Amber C. Howard showed in a recent paper in the journal Diabetes that cells taken from animal models of types 1 and 2 diabetes have faulty repair mechanisms. Howard found high glucose was a culprit by soaking cells in a high-glucose solution for eight to 12 weeks, during which time they developed a repair defect. It's also well documented that reactive oxygen species levels are elevated in diabetes.
The Nature Communications paper showed that vitamin E treatment in an animal model of diabetes restored some membrane repair ability. Also, an analogue of the most biologically active form of vitamin E significantly reversed membrane repair deficits caused by high glucose and increased cell survival after tearing cells in culture.
Now McNeil wants to know if he can prevent the development of advanced glycation end products -- a sugar that high glucose adds to proteins that his lab has shown can also impede membrane repair -- in the animal models of diabetes. The researchers have a drug that at least in cultured animal cells, prevents repair defects from advanced glycation end products.
Howard, first author on the Nature Communications paper, is an instructor at Husson University in Bangor, Maine. McNeil is a faculty member in GHSU's Medical College of Georgia and College of Graduate Studies
Self-healing electronics could work longer and reduce waste
Published: Wednesday, December 21, 2011 - 01:32 in Physics & Chemistry
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L. Brian Stauffer
Scott R. White
When one tiny circuit within an integrated chip cracks or fails, the whole chip -- or even the whole device -- is a loss. But what if it could fix itself, and fix itself so fast that the user never knew there was a problem? A team of University of Illinois engineers has developed a self-healing system that restores electrical conductivity to a cracked circuit in less time than it takes to blink. Led by aerospace engineering professor Scott White and materials science and engineering professor Nancy Sottos, the researchers published their results in the journal Advanced Materials.
"It simplifies the system," said chemistry professor Jeffrey Moore, a co-author of the paper. "Rather than having to build in redundancies or to build in a sensory diagnostics system, this material is designed to take care of the problem itself."
As electronic devices are evolving to perform more sophisticated tasks, manufacturers are packing as much density onto a chip as possible. However, such density compounds reliability problems, such as failure stemming from fluctuating temperature cycles as the device operates or fatigue. A failure at any point in the circuit can shut down the whole device.
"In general there's not much avenue for manual repair," Sottos said. "Sometimes you just can't get to the inside. In a multilayer integrated circuit, there's no opening it up. Normally you just replace the whole chip. It's true for a battery too. You can't pull a battery apart and try to find the source of the failure."
Most consumer devices are meant to be replaced with some frequency, adding to electronic waste issues, but in many important applications -- such as instruments or vehicles for space or military functions -- electrical failures cannot be replaced or repaired.
The Illinois team previously developed a system for self-healing polymer materials and decided to adapt their technique for conductive systems. They dispersed tiny microcapsules, as small as 10 microns in diameter, on top of a gold line functioning as a circuit. As a crack propagates, the microcapsules break open and release the liquid metal contained inside. The liquid metal fills in the gap in the circuit, restoring electrical flow.
"What's really cool about this paper is it's the first example of taking the microcapsule-based healing approach and applying it to a new function," White said. "Everything prior to this has been on structural repair. This is on conductivity restoration. It shows the concept translates to other things as well."
A failure interrupts current for mere microseconds as the liquid metal immediately fills the crack. The researchers demonstrated that 90 percent of their samples healed to 99 percent of original conductivity, even with a small amount of microcapsules.
The self-healing system also has the advantages of being localized and autonomous. Only the microcapsules that a crack intercepts are opened, so repair only takes place at the point of damage. Furthermore, it requires no human intervention or diagnostics, a boon for applications where accessing a break for repair is impossible, such as a battery, or finding the source of a failure is difficult, such as an air- or spacecraft.
"In an aircraft, especially a defense-based aircraft, there are miles and miles of conductive wire," Sottos said. "You don't often know where the break occurs. The autonomous part is nice -- it knows where it broke, even if we don't."
Next, the researchers plan to further refine their system and explore other possibilities for using microcapsules to control conductivity. They are particularly interested in applying the microcapsule-based self-healing system to batteries, improving their safety and longevity.
