Monday, January 17, 2011

“NANOSCOOPS” COULD SPARK NEW GENERATION OF ELECTRIC AUTOMOBILE BATTERIES

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An entirely new type of nanomaterial developed at Rensselaer Polytechnic Institute could enable the next generation of high-power rechargeable lithium (Li)-ion batteries for electric automobiles, as well as batteries for laptop computers, mobile phones, and other portable devices.

The new material, dubbed a “nanoscoop” because its shape resembles a cone with a scoop of ice cream on top, can withstand extremely high rates of charge and discharge that would cause conventional electrodes used in today’s Li-ion batteries to rapidly deteriorate and fail. The nanoscoop’s success lies in its unique material composition, structure, and size.

The Rensselaer research team, led by Professor Nikhil Koratkar, demonstrated how a nanoscoop electrode could be charged and discharged at a rate 40 to 60 times faster than conventional battery anodes, while maintaining a comparable energy density. This stellar performance, which was achieved over 100 continuous charge/discharge cycles, has the team confident that their new technology holds significant potential for the design and realization of high-power, high-capacity Li-ion rechargeable batteries.

“Charging my laptop or cell phone in a few minutes, rather than an hour, sounds pretty good to me,” said Koratkar, a professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer. “By using our nanoscoops as the anode architecture for Li-ion rechargeable batteries, this is a very real prospect. Moreover, this technology could potentially be ramped up to suit the demanding needs of batteries for electric automobiles.”

Batteries for all-electric vehicles must deliver high power densities in addition to high energy densities, Koatkar said. These vehicles today use supercapacitors to perform power-intensive functions, such as starting the vehicle and rapid acceleration, in conjunction with conventional batteries that deliver high energy density for normal cruise driving and other operations. Koratkar said the invention of nanoscoops may enable these two separate systems to be combined into a single, more efficient battery unit.

Results of the study were detailed in the paper “Functionally Strain-Graded Nanoscoops for High Power Li-Ion Battery Anodes,” published by the journal Nano Letters.

The anode structure of a Li-ion battery physically grows and shrinks as the battery charges or discharges. When charging, the addition of Li ions increases the volume of the anode, while discharging has the opposite effect. These volume changes result in a buildup of stress in the anode. Too great a stress that builds up too quickly, as in the case of a battery charging or discharging at high speeds, can cause the battery to fail prematurely. This is why most batteries in today’s portable electronic devices like cell phones and laptops charge very slowly – the slow charge rate is intentional and designed to protect the battery from stress-induced damage.

The Rensselaer team’s nanoscoop, however, was engineered to withstand this buildup of stress. Made from a carbon (C) nanorod base topped with a thin layer of nanoscale aluminum (Al) and a “scoop” of nanoscale silicon (Si), the structures are flexible and able to quickly accept and discharge Li ions at extremely fast rates without sustaining significant damage. The segmented structure of the nanoscoop allows the strain to be gradually transferred from the C base to the Al layer, and finally to the Si scoop. This natural strain gradation provides for a less abrupt transition in stress across the material interfaces, leading to improved structural integrity of the electrode.

The nanoscale size of the scoop is also vital since nanostructures are less prone to cracking than bulk materials, according to Koratkar.

“Due to their nanoscale size, our nanoscoops can soak and release Li at high rates far more effectively than the macroscale anodes used in today’s Li-ion batteries,” he said. “This means our nanoscoop may be the solution to a critical problem facing auto companies and other battery manufacturers – how can you increase the power density of a battery while still keeping the energy density high?”

A limitation of the nanoscoop architecture is the relatively low total mass of the electrode, Koratkar said. To solve this, the team’s next steps are to try growing longer scoops with greater mass, or develop a method for stacking layers of nanoscoops on top of each other. Another possibility the team is exploring includes growing the nanoscoops on large flexible substrates that can be rolled or shaped to fit along the contours or chassis of the automobile.

(Photo: RPI)

Rensselaer Polytechnic Institute

PREHISTORIC BIRD USED CLUB-LIKE WINGS AS WEAPON

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Long before the knights of medieval Europe wielded flails or martial artists brandished nunchucks, it appears that a flightless prehistoric bird used its own wings as a similar type of weapon in combat.

Paleontologists at Yale University and the Smithsonian Institution have discovered that Xenicibis, a member of the ibis family that lived about ten thousand years ago and was found only in Jamaica, most likely used its specialized wings like a flail, swinging its upper arm and striking its enemies with its thick hand bones.

"No animal has ever evolved anything quite like this," said Nicholas Longrich of Yale, who led the research. "We don't know of any other species that uses its body like a flail. It's the most specialized weaponry of any bird I've ever seen."

As part of the new study, the researchers analyzed a number of recently discovered partial skeletons of Xenicibis and found that the wings were drastically different from anything they'd seen before. "When I first saw it, I assumed it was some sort of deformity," Longrich said. "No one could believe it was actually that bizarre."

The bird, which was the size of a large chicken, is anatomically similar to other members of the ibis family except for its wings, which include thick, curved hand bones unlike those of any other known bird. Xenicibis also had a much larger breastbone and longer wings than most flightless birds. "That was our first clue that the wings were still being used for something," Longrich said.

While other birds are known to punch or hammer one another with their wings, Xenicibis is the only known animal to have used its hands, hinged at the wrist joint, like two baseball bats to swing at and strike its opponents. Although modern day ibises do not strike one another in this fashion, they are very territorial, with mates often fighting other pairs over nesting and feeding rights.

It's also possible that the birds used their club-like wings to defend themselves against other species that might have preyed on the birds' eggs or young. Xenicibis is unusual in that it became flightless even in the midst of a number of predators, including the Jamaican yellow boa, a small extinct monkey and over a dozen birds of prey.

The team found that two of the wing bones in the collection showed evidence of combat, including a fractured hand bone and a centimeter-thick upper arm bone that was broken in half. The damage is proof of the extreme force the birds were able to wield with their specialized wings, Longrich said.

(Photo: Nicholas Longrich/Yale University)

Yale University

DETECTING ESOPHAGEAL CANCER WITH LIGHT

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A tiny light source and sensors at the end of an endoscope may provide a more accurate way to identify pre-cancerous cells in the lining of the esophagus.

Developed by biomedical engineers at Duke University and successfully tested on patients during a clinical trial at the University of North Carolina at Chapel Hill, the device holds the promise of being a less invasive method for testing patients suspected of having Barrett's esophagus, a change in the lining of the esophagus due to acid reflux. Acid reflux occurs when stomach acid splashes, or refluxes, up into the esophagus.

Long periods of acid reflux can change the cells that line the esophagus, making them appear more like intestinal cells than esophageal cells. These cellular changes can also be a precursor to cancer. As in most cancers, early identification of these pre-cancerous cells often leads to better outcomes for patients. Barrett's esophagus afflicts more than one percent of the U.S. population, with most patients above the age of 50.

Using an endoscope to reach the esophagus via the nose, physicians shine short bursts of this light at locations of suspected disease and sensors capture and analyze the light as it is reflected back. In particular, they are trying to spot characteristic changes within the layer of cells known as the epithelium, which line cavities and surfaces throughout the body.

"By interpreting the way the light scatters after we shine it at a location on the tissue surface, we can the spot the tell-tales signs of cells that are changing from their healthy, normal state to those that may become cancerous," said Neil Terry, a Ph.D. student working in the laboratory of Adam Wax, associate professor of biomedical engineering at Duke's Pratt School of Engineering, who developed the device.

The team published their findings online in the January issue of the journal Gastroenterology.

"Specifically, the nuclei of pre-cancerous cells are larger than typical cell nuclei, and the light scatters back from them in a characteristic manner," Terry continued. "When we compared the findings from our system with an actual review by pathologists, we found they correlated in 86 percent of the samples."

UNC gastroenterologist Nicholas Shaheen, M.D., conducted the preliminary clinical trial of the device on 46 patients with Barrett's esophagus.

"Currently, we take many random tissue samples from areas we where we think abnormal cells may be located," Shaheen said. "This new system may make our biopsies smarter and more targeted. Early detection is crucial, because the cure rate for esophageal cancer that is caught early is quite high, while the cure rate for advanced disease is dismal, with a 15 percent survival rate after five years."

The technology that Wax and his team developed for cancer detection is known as angle-resolved low coherence interferometry (a/LCI). The technique is able to separate the unique patterns of the nucleus from the other parts of the cell and provide representations of its changes in shape in real time.

"This optical approach of sampling allows us to cover more tissue sites in less time and has the potential to significantly improve our ability to spot and monitor these pre-cancerous cells," Wax said. "This type of approach could be used to improve and perhaps one day supplant the physical biopsies currently being used."

Wax pointed out that since approximately 85 percent of all cancers begin within the layers of the epithelium in various parts of the body, he believes that the new system could also work in such cancers as those of the colon, trachea, cervix or bladder.

(Photo: Duke University)

Duke University

NEURONAL MIGRATION ERRORS: RIGHT CELLS, WRONG PLACE

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Normally, cortical nerve cells or neurons reside in the brain's gray matter with only a few scattered neurons in the white matter, but some people with schizophrenia have a higher number of neurons in the white matter. Neuronal migration errors may arise in schizophrenia as a consequence of both genetic and environmental factors.

The phenomenon of aberrant cellular localization has now been studied in detail in a paper by Yang and colleagues, published in the current issue of Biological Psychiatry.

Using a specialized technique that involves staining cells, the researchers were able to determine the distribution of nerve cells in brain tissue from people who had been diagnosed with schizophrenia in comparison to tissue from people who did not carry this diagnosis prior to their death.

Their results linked two main findings emerging from analyses of brain tissue in schizophrenia: abnormalities in the inhibitory neurons within the cortex and increases in neurons in white matter below the cortex.

"Our observations challenge the long held theory that increased neurons in the white matter might be remaining from a transient layer of cells," explained Prof. Cyndi Shannon Weickert and Dr. Samantha Fung. "We suggest that, in schizophrenia, inhibitory neurons that were travelling to the cortex might actually be stuck at some stage in their development."

This study's findings highlight the importance of brain development for the emergence of symptoms associated with schizophrenia. As noted by Dr. John Krystal, Editor of Biological Psychiatry, "this study highlights the importance for schizophrenia of better understanding the molecular switches that control the migration of nerve cells and the development of the connections between nerve cells."

If scientists understood the molecular factors that prevented the neurons from migrating into the cortex, they might be able to develop treatments that prevented the inhibitory neurons from getting "stuck" in the white matter.

Elsevier

PREGNANT, CONSTIPATED AND BLOATED? FLY POO MAY TELL YOU WHY

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Clues about how the human gut helps regulate our appetite have come from a most unusual source – fruit fly faeces. Scientists at the University of Cambridge are using the fruit fly to help understand aspects of human metabolism, including why pregnant women suffer from bloating and constipation, and even the link between a low calorie diet and longevity.

Although scientists have known for some time that there are as many as 500 million nerve cells in our gut, the sheer complexity that this presents means that little is known about the different types of nerve cell and their functions.

Now, researchers led by Dr Irene Miguel-Aliaga, with funding from the Wellcome Trust and the Biotechnology and Biological Sciences Research Council, have used the fruit fly, Drosophila melanogaster, to investigate the function of these intestinal neurons. The fly has simpler versions of our nervous and digestive systems, which lend it to genetic manipulation. Their findings are published today in the journal Cell Metabolism.

"We reasoned that what comes out of the gut may be able to tell us about what is going on inside," explains Dr Miguel-Aliaga. "So, we devised a method to extract information about several metabolic features from the flies' faecal deposits – which are actually rather pretty and don't smell bad. Then we turned specific neurons on and off and examined what came out."

Dr Miguel-Aliaga and colleagues found that these intestinal neurons have very important and specialised functions, such as regulating appetite or adjusting intestinal water balance during reproduction.

Female flies in their reproductive stage get constipated – their gut emptying rate is reduced even though they are eating more food; at the same time, they retain more water and the contents of their intestines become more concentrated. The researchers showed that these intestinal changes are triggered by the sex peptide, a hormone that males inject into the female during copulation, which activates of a small group of gut neurons. This shares the same function as the sex hormones found in humans, such as progesterone, oxytocin and oestrogen.

"Humans and fruit flies reproduce in very different ways, yet the associated symptoms of constipation and bloating and their cause – a reproductive hormone – are the same," explains Dr Miguel-Aliaga. "This suggests that this mechanism has been conserved through evolution. These intestinal changes may provide a benefit at a time of high nutritional demand by maximizing nutrient absorption."

The research also provides tantalising clues about the link between calorie intake and longevity. Intestinal changes which help maximize nutrient absorption would likely be active all the time, as they would provide a selective advantage when food is scarce. However, in flies – and possibly in humans – this may come at a cost: a shorter lifespan.

It has been known for some time that when female flies mate and receive the sex peptide, this shortens their lifespan; however, this is not caused entirely by their increased food intake or because they are laying many eggs, the two most obvious effects of this sex peptide. The explanation, argue the researchers, may lie in the intestinal changes triggered by the sex peptide that lead to constipation and water retention.

"A mechanism that maximises nutrient absorption by slowing the passage of food through the intestine is fine when food is scarce or during reproduction," says Dr Miguel-Aliaga, "but when we are eating a normal diet, constipation may lead to the build up of waste products produced during internal metabolism. Similarly, it could lead to changes in the composition of the gut bacteria, which are essential to regulating metabolism.

"Our research suggests that in addition to paying attention to what we eat, which has been the focus of longevity research, we may also have to consider what our body does with the food and what goes on in our guts."

(Photo: Irene Miguel-Aliaga, University of Cambridge)

Wellcome Trust

WAKE UP AND SMELL THE WILLOW

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More plant matter could be burned in coal-fired power stations if this 'green' fuel was delivered pre-roasted like coffee beans, according to researchers from the University of Leeds, UK.

Many UK power stations are now burning plant matter, or biomass, as well as coal in a bid to cut their carbon footprint. Unlike fossil fuels, plants like willow, Miscanthus and poplar are a virtually carbon-neutral source of energy: the carbon dioxide emitted when they burn is absorbed during photosynthesis by the next batch of 'energy crops' planted in their place.

But the environmental benefits of biomass are countered by some real practical and economic challenges that are forcing power stations to restrict the amount of biomass used. Biomass is moist and bulky, making it relatively expensive to transport and difficult to store for long periods without going mouldy. The fibrous plant matter is also extremely difficult to process in the mills that are used to grind dry lumps of coal into dust before they are burned.

A roasting process known as torrefaction is the answer, according to Professor Jenny Jones and colleagues from the University of Leeds' School of Process, Environmental and Materials Engineering. This process, which sees the plant matter heated to around 300 degrees centigrade in an air-free container, transforms bulky biomass into a dry, energy-rich fuel that is cheaper and easier to move around and has a much longer shelf life.

A study of two common energy crops, willow and Miscanthus, has also shown that when the plant matter is 'torrefied' it can be ground into a powder just as easily as some good quality coals. This makes it far more practical and cost-effective to replace containers of coal with biomass in existing power stations.

Team members are now exploring whether the torrefaction process can be scaled up, with a view to producing a design 'blueprint' for industrial engineers.

"If we can show that torrefaction is feasible on an industrial scale then we would hope to end up with a demonstration plant here in the UK," Professor Jones said. "We already know that many more famers would be interested in growing energy crops on areas of poorer quality soil if the economic barriers were lowered and the power companies could use more biomass without losing out financially."

The project will address outstanding questions about the safety, practicality and environmental impact of large-scale torrefaction. For example, researchers will find out what the liquid and gaseous by-products of the roasting process are made up of. They will also assess how likely it is for dust generated by the roasting and milling processes to trigger explosions.

"It is well known that fine powders can cause violent explosions under certain conditions. We will be carrying out experiments to characterise the explosibility of biomass and torrified biomass powder so that appropriate safety features can be designed into industrial-scale powder handling and power generation plants," said University of Leeds researcher Dr Roth Phylaktou, an expert on fire and explosion safety engineering and a co-investigator on the project.

The researchers will work with a range of different materials that could potentially replace coal in future. These include energy crops such as willow and Miscanthus, which are grown specifically for making 'green' fuel, as well as waste plant matter from forestry plantations and farms, such as the branches of harvested pine trees and straw.

"These are all materials that grow well in the UK but not at the expense of food crops," said Professor Jones. "We do not want farmers to have to choose between planting a field of wheat or barley and a field of willow. Ultimately, this is all about providing a secure energy supply for the future and one that is sustainable on all levels. "

(Photo: Leeds U.)

University of Leeds

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