Monday, August 17, 2009

PLASTICS THAT CONVERT LIGHT TO ELECTRICITY COULD HAVE A BIG IMPACT

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Researchers the world over are striving to develop organic solar cells that can be produced easily and inexpensively as thin films that could be widely used to generate electricity.

But a major obstacle is coaxing these carbon-based materials to reliably form the proper structure at the nanoscale (tinier than 2 millionths of an inch) to be highly efficient in converting light to electricity. The goal is to develop cells made from low-cost plastics that will transform at least 10 percent of the sunlight that they absorb into usable electricity and can be easily manufactured.

A research team headed by David Ginger, a University of Washington associate professor of chemistry, has found a way to make images of tiny bubbles and channels, roughly 10,000 times smaller than a human hair, inside plastic solar cells. These bubbles and channels form within the polymers as they are being created in a baking process, called annealing, that is used to improve the materials' performance.

The researchers are able to measure directly how much current each tiny bubble and channel carries, thus developing an understanding of exactly how a solar cell converts light into electricity. Ginger believes that will lead to a better understanding of which materials created under which conditions are most likely to meet the 10 percent efficiency goal.

As researchers approach that threshold, nanostructured plastic solar cells could be put into use on a broad scale, he said. As a start, they could be incorporated into purses or backpacks to charge cellular phones or mp3 players, but eventually they could make in important contribution to the electrical power supply.

Most researchers make plastic solar cells by blending two materials together in a thin film, then baking them to improve their performance. In the process, bubbles and channels form much as they would in a cake batter. The bubbles and channels affect how well the cell converts light into electricity and how much of the electric current actually gets to the wires leading out of the cell. The number of bubbles and channels and their configuration can be altered by how much heat is applied and for how long.

The exact structure of the bubbles and channels is critical to the solar cell's performance, but the relationship between baking time, bubble size, channel connectivity and efficiency has been difficult to understand. Some models used to guide development of plastic solar cells even ignore the structure issues and assume that blending the two materials into a film for solar cells will produce a smooth and uniform substance. That assumption can make it difficult to understand just how much efficiency can be engineered into a polymer, Ginger said.

For the current research, the scientists worked with a blend of polythiophene and fullerene, model materials considered basic to organic solar cell research because their response to forces such as heating can be readily extrapolated to other materials. The materials were baked together at different temperatures and for different lengths of time.

Ginger is the lead author of a paper documenting the work, published online July 9 by the American Chemical Society journal Nano Letters and scheduled for a future print edition. Coauthors are Liam Pingree and Obadiah Reid of the UW. The research was funded by the National Science Foundation and the U.S. Department of Energy.

Ginger noted that the polymer tested is not likely to reach the 10 percent efficiency threshold. But the results, he said, will be a useful guide to show which new combinations of materials and at what baking time and temperature could form bubbles and channels in a way that the resulting polymer might meet the standard.

Such testing can be accomplished using a very small tool called an atomic force microscope, which uses a needle similar to the one that plays records on an old-style phonograph to make a nanoscale image of the solar cell. The microscope, developed in Ginger's lab to record photocurrent, comes to a point just 10 to 20 nanometers across (a human hair is about 60,000 nanometers wide). The tip is coated with platinum or gold to conduct electrical current, and it traces back and forth across the solar cell to record the properties.

As the microscope traces back and forth over a solar cell, it records the channels and bubbles that were created as the material was formed. Using the microscope in conjunction with the knowledge gained from the current research, Ginger said, can help scientists determine quickly whether polymers they are working with are ever likely to reach the 10 percent efficiency threshold.

Making solar cells more efficient is crucial to making them cost effective, he said. And if costs can be brought low enough, solar cells could offset the need for more coal-generated electricity in years to come.

"The solution to the energy problem is going to be a mix, but in the long term solar power is going to be the biggest part of that mix," he said.

(Photo: Mary Levin/UW)

University of Washington

COMPUTERS UNLOCK MORE SECRETS OF THE MYSTERIOUS INDUS VALLEY SCRIPT

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Four-thousand years ago, an urban civilization lived and traded on what is now the border between Pakistan and India. During the past century, thousands of artifacts bearing hieroglyphics left by this prehistoric people have been discovered. Today, a team of Indian and American researchers are using mathematics and computer science to try to piece together information about the still-unknown script.

The team led by a University of Washington researcher has used computers to extract patterns in ancient Indus symbols. The study, published this week in the Proceedings of the National Academy of Sciences, shows distinct patterns in the symbols' placement in sequences and creates a statistical model for the unknown language.

"The statistical model provides insights into the underlying grammatical structure of the Indus script," said lead author Rajesh Rao, a UW associate professor of computer science. "Such a model can be valuable for decipherment, because any meaning ascribed to a symbol must make sense in the context of other symbols that precede or follow it."

Co-authors are Nisha Yadav and Mayank Vahia of the Tata Institute of Fundamental Research and Centre for Excellence in Basic Sciences in Mumbai; Hrishikesh Joglekar of Mumbai; R. Adhikari of the Institute of Mathematical Sciences in Chennai; and Iravatham Mahadevan of the Indus Research Centre in Chennai.

Despite dozens of attempts, nobody has yet deciphered the Indus script. The symbols are found on tiny seals, tablets and amulets, left by people inhabiting the Indus Valley from about 2600 to 1900 B.C. Each artifact is inscribed with a sequence that is typically five to six symbols long.

Some people have questioned whether the symbols represent a language at all, or are merely pictograms of political or religious icons.

The new study looks for mathematical patterns in the sequence of symbols. Calculations show that the order of symbols is meaningful; taking one symbol from a sequence found on an artifact and changing its position produces a new sequence that has a much lower probability of belonging to the hypothetical language. The authors said the presence of such distinct rules for sequencing symbols provides further support for the group's previous findings, reported earlier this year in the journal Science, that the unknown script might represent a language.

"These results give us confidence that there is a clear underlying logic in Indus writing," Vahia said.

Seals with sequences of Indus symbols have been found as far away as West Asia, in the region historically known as Mesopotamia and site of modern-day Iraq. The statistical results showed that the West-Asian sequences are ordered differently from sequences on artifacts found in the Indus valley. This supports earlier theories that the script may have been used by Indus traders in West Asia to represent different information compared to the Indus region.

"The finding that the Indus script may have been versatile enough to represent different subject matter in West Asia is provocative. This finding is hard to reconcile with the claim that the script merely represents religious or political symbols," Rao said.

The researchers used a Markov model, a statistical method that estimates the likelihood of a future event (such as inscribing a particular symbol) based on patterns seen in the past. The method was first developed by Russian mathematician Andrey Markov a century ago and is increasingly used in economics, genetics, speech-recognition and other fields.

"One of the main purposes of our paper is to introduce Markov models, and statistical models in general, as computational tools for investigating ancient scripts," Adhikari said.

One application described in the paper uses the statistical model to fill in missing symbols on damaged archaeological artifacts. Such filled-in texts can increase the pool of data available for deciphering the writings of ancient civilizations, Rao said.

(Photo: J. M. Kenoyer / harappa.com)

University of Washington

NANOPARTICLES CROSS BLOOD-BRAIN BARRIER TO ENABLE 'BRAIN TUMOR PAINTING'

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Brain cancer is among the deadliest of cancers. It's also one of the hardest to treat. Imaging results are often imprecise because brain cancers are extremely invasive. Surgeons must saw through the skull and safely remove as much of the tumor as they can. Then doctors use radiation or chemotherapy to destroy cancerous cells in the surrounding tissue.

Researchers at the University of Washington have been able to illuminate brain tumors by injecting fluorescent nanoparticles into the bloodstream that safely cross the blood-brain barrier -- an almost impenetrable barrier that protects the brain from infection. The nanoparticles remained in mouse tumors for up to five days and did not show any evidence of damaging the blood-brain barrier, according to results published this week in the journal Cancer Research.

Results showed the nanoparticles improved the contrast in both MRI and optical imaging, which is used during surgery.

"Brain cancers are very invasive, different from the other cancers. They will invade the surrounding tissue and there is no clear boundary between the tumor tissue and the normal brain tissue," said lead author Miqin Zhang, a UW professor of materials science and engineering.

Being unable to distinguish a boundary complicates the surgery. Severe cognitive problems are a common side effect.

"If we can inject these nanoparticles with infrared dye, they will increase the contrast between the tumor tissue and the normal tissue," Zhang said. "So during the surgery, the surgeons can see the boundary more precisely.

"We call it 'brain tumor illumination or brain tumor painting,'" she said. "The tumor will light up."

Nano-imaging could also help with early cancer detection, Zhang said. Current imaging techniques have a maximum resolution of 1 millimeter (1/25 of an inch). Nanoparticles could improve the resolution by a factor of 10 or more, allowing detection of smaller tumors and earlier treatment.

Until now, no nanoparticle used for imaging has been able to cross the blood-brain barrier and specifically bind to brain-tumor cells. With current techniques doctors inject dyes into the body and use drugs to temporarily open the blood-brain barrier, risking infection of the brain.

The UW team surmounted this challenge by building a nanoparticle that remains small in wet conditions. The particle was about 33 nanometers in diameter when wet, about a third the size of similar particles used in other parts of the body.

Crossing the blood-brain barrier depends on the size of the particle, its lipid, or fat, content, and the electric charge on the particle. Zhang and colleagues built a particle that can pass through the barrier and reach tumors. To specifically target tumor cells they used chlorotoxin, a small peptide isolated from scorpion venom that many groups, including Zhang's, are exploring for its tumor-targeting abilities. On the nanoparticle's surface Zhang placed a small fluorescent molecule for optical imaging, and binding sites that could be used for attaching other molecules.

Future research will evaluate this nanoparticle's potential for treating tumors, Zhang said. She and colleagues already showed that chlorotoxin combined with nanoparticles dramatically slows tumors' spread. They will see whether that ability could extend to brain cancer, the most common solid tumor to affect children.

Merely improving imaging, however, would improve patient outcomes.

"Precise imaging of brain tumors is phenomenally important. We know that patient survival for brain tumors is directly related to the amount of tumor that you can resect," said co-author Richard Ellenbogen, professor and chair of neurological surgery at the UW School of Medicine. "This is the next generation of cancer imaging," he said. "The last generation was CT, this generation was MRI, and this is the next generation of advances."

(Photo: University of Washington)

University of Washington

'GREEN' ENERGY FROM ALGAE

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Microalgae are monocellular, plant-like organisms engaged in photosynthesis and converting carbon dioxide (CO2) into biomass. From this biomass, both potential resources and active substances as well as fuels like biodiesel may be produced. While growing, algae take up the amount of CO2 that is later released again when they are used for energy production. Hence, energy from algae can be produced in a CO2-neutral manner contrary to conventional energy carriers.

Apart from CO2-neutral closed loop management, algae have an-other advantage: Industrial CO2 emissions may be used as a "re-source", as algae grow faster at high carbon dioxide concentrations and, hence, produce more biomass for energy production.

However, this is not their only advantage: "Compared to land plants, algae produce five times as much biomass per hectare and contain 30 to 40% oil usable for energy production", says Professor Clemens Posten, who directs this research activity at the KIT Institute of Life Science Engineering. As the algae may also be cultivated in arid i.e. dry, areas not suited for agriculture, there is hardly any competition with agricultural areas. There, however, closed systems are required.

Presently, algae are being produced in open ponds in southern countries of relatively small productivity. This is where Posten's new technology starts. "In terms of process technology, our approach is completely different, as we are working with closed photobioreactors", underlines the scientist. "Our plants convert solar energy into biomass, the efficiency being five times higher than that in open ponds." The plates in usual photo-bioreactors are arranged vertically. "Every alga sees a little bit less light, but the plant is operated at increased efficiency", emphasizes the biologist and electrical engineer. Modern designs under investigation will find more intelligent ways to light distribution.

Consequently, algae production does not only work in countries with an extremely high solar irradiation. Most algae need a maximum of ten percent of the incident sunlight intensity. According to Posten, the remaining fraction would just be wasted, if light management in the photobioreactor would not be optimum. Posten points out that the Sahara offers just twice as much sun as Central Europe. But there, the reactor contents would have to be cooled. Other advantages of the closed system are drastic savings of water and fertilizers. Double use of algae for the production of food or fine chemicals and subsequent energy production from the residualbiomass may also be conceivable.

Posten's institute hosts one of the two KIT working groups focusing on research in the field of algae biotechnology. "As far as the development of photobioreactors is concerned, we are among the three locations worldwide, where considerable progress is being achieved in both process technology and biology", explains Posten.

The stop of his research area on the southern KIT campus marks the starting point of research conducted by the Institute for Pulsed Power and Microwave Technology on the northern campus of the KIT. Here, it is focused on extracting the valuable constituents of the algae biomass by an electric pulsed treatment. So far, Dr. Georg Müller, head of this institute's Pulsed Power Technology Division, has studied the decomposition of plant cells of olives, grapes, apples, sugar beets, and terrestrial energy plants in cooperation with partners from research and industry. Partly, large-scale facilities were constructed. "It is our objective to develop new economically efficient and sustainable extraction methods to obtain a maximum amount of cell constituents from the algae that can be used for energy production", says Müller. "The plant cells are exposed to a high electric field for a very short term. This causes a perforation of the cell membrane and the constituents are released."

Cooperation of both working groups now aims at bundling the existing know-how, with starting funds being provided by the KIT Energy Center. It is planned to establish a KIT "Algae Platform" for energy production from microalgae. In the medium term, pilot-scale and demonstration plants shall be built on the northern KIT campus, with the favorable conditions in terms of space and infrastructure being made use of. "This will represent a major node in the presently rather rapid networking of algae biotechnology", emphasizes Posten. To make energy production from algae economically efficient, it will be focused on minimizing investment and operation costs of photobioreactors and on developing highly efficient processes for the harvesting and decomposition of algae.

To close the cycle for the complete use of algae biomass for energy production, KIT researchers even go another step forwards. The biomass remaining after extraction (60 – 70%) is planned to be converted into other energy carriers like hydrogen or methane by means of the hydrothermal gasification process developed on the northern campus.

(Photo: Florian Lehr)

Helmoltz Gemeinschaft

CHICKEN-HEARTED TYRANTS

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Two titans fighting a bloody battle – that often turns fatal for both of them. This is how big predatory dinosaurs like Tyrannosaurus are often depicted while hunting down their supposed prey: even larger herbivorous dinosaurs. The fossils, though, do not account for that kind of hunting behavior but indicate that theropods, the large predatory dinosaurs, were frying much smaller fish.

Dr. Oliver Rauhut, paleontologist at Ludwig-Maximilians-Universität (LMU) in Munich, and his collegue Dr. David Hone surmise that giant carnivores like Tyrannosaurus preyed mainly on juvenile dinosaurs. "Unlike their adult and well-armed relatives these young animals hardly posed any risk to the predators," says Rauhut. "And their tender bones would have added important minerals to a theropod's diet. Now we hope for more fossils to be found that add new evidence to our hypothesis."

He's the king of tyrants: Tyrannosaurus rex is by far the most famous dinosaur. Not even recent finds of slightly bigger – and maybe even more terrifying – species like Giganotosaurus could dent the aura of "T-Rex". But what would happen if the king turned out a baby killer instead of fearless hunter of much bigger prey? "Animals such as Tyrannosaurus are often seen as the perfect 'killing machines' with extremely powerful bites, which were able to bring down even the largest possible prey," says Rauhut of the Bayerische Staatssammlung für Paläontologie und Geologie and LMU Munich. "But the very few fossils that reflect the hunt of predatory dinosaurs on large herbivores tell a tale of failure – the prey either got away, or both prey and predator were killed."

On the other hand, the also extremely sparse cases of direct evidence for the diet of predatory dinosaurs – stomach contents and coprolites – show that juveniles or much smaller prey species were ingested and the latter were swallowed whole. Rauhut and Hone, who is now at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, therefore propose as a hypothesis that large predatory dinosaurs only as an exception attacked other large dinosaurs, but mainly fed on juveniles. "Even modern predators prefer old and sick animals or unexperienced young individuals," states Hone. "These are an easy prey to bring down and the risk of injury for the predator is much lower. This strategy was probably the same in dinosaurs."

Another look at recent predators reveals an additional benefit of young prey: Crocodiles, the closest living relatives of dinosaurs, have extremely strong acids in their stomachs. They can completely dissolve the poorly ossified bones of young animals which adds important nutrients to the reptiles' diet. The fossil finds of juvenile dinosaurs that have been swallowed whole by theropods support the idea that dinosaurs might have profited from this as well. Missing fossils, though, lend even more plausibility: "Finds of dinosaur nesting sites indicate that they contained large numbers of eggs which should have resulted in a high number of offspring," says Rauhut. "But little of this is reflected in the fossil record: Juvenile dinosaurs are surprisingly rare – maybe because many of them have been eaten by predators. Hopefully there will soon be more evidence to help us really understand the theropods' hunting behavior."

Ludwig-Maximilians-Universität (LMU) in Munich

VENOMOUS SEA SNAKES PLAY HEADS OR TAILS WITH THEIR PREDATORS

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In a deadly game of heads or tails venomous sea snakes in the Pacific and Indian Oceans deceive their predators into believing they have two heads, claims research published in Marine Ecology.

The discovery, made by Dr Arne Redsted Rasmussen and Dr Johan Elmberg, showed that Yellow-lipped Sea Kraits (Laticauda colubrina) use skin markings and behaviour patterns to fool predators into thinking their tail is a second head, complete with lethal venom.

There are over 65 species of sea snakes in the tropical waters of the Southern Hemisphere, ranging from Africa to the Gulf of Panama. Most spend their entire lives in the sea, inhabiting shallow water and are active predators, feeding on small fish found around coral reefs. All sea snakes have extremely potent venom which is among the most toxic known in all snake species.

When hunting for food sea snakes probe crevices and coral formations, temporarily forcing them to drop their guard to threats from the surrounding waters and making them highly vulnerable to attack. However, the Yellow-lipped Sea Krait has been found to twist its tail so that the tip corresponds with the dorsal view of the head, which combined with deceptive colouring, gives the illusion of having two heads and two loads of deadly venom.

Apart from the Yellow-lipped Sea Krait the ecology of sea snakes has largely gone understudied, due mainly to their off-shore and nocturnal behaviour. Yet, despite the number of behavioural studies devoted to this species, the discovery of this false-head-behaviour is a hitherto overlooked anti-predator adaptation.

The discovery was made while senior author Arne Redsted Rasmussen was diving off the coast of the Bunaken Island in Indonesia. A large Krait was followed for thirty minutes, swimming between corals and crevices hunting for food. Rasmussen was momentarily distracted by a second snake, but when looking back he was surprised to see the "head" was facing him while the tail probed the coral. Rasmussen's surprise grew when he saw a second head emerge from the coral instead of the expected tail. It was only when the snake swam away that the first head was clearly seen to be a paddling tail.

To build upon this discovery researchers examined 98 Sea Kraits from three major museum collections in Paris, Berlin and Copenhagen while also monitoring the behaviour of wild Sea Kraits in Solomon Islands during the Danish Galathea 3 Expedition. The research confirmed that all snakes of this species had a distinctive colouration pattern, with a bright yellow horseshoe marking on the tip of the head and the tail. The yellow was deeper than the colours on the rest of the body and the black colorations were much longer than the dark bands on the rest of the body, highlighting the similarity between the head and the tail.

The reason for this mixture of behaviour and coloration results from a developed defence strategy needed when the snake is probing for prey. Despite being extremely venomous sea snakes are susceptible to attack from several predators such as sharks, large bony fishes, and even birds.

"The value of such an adaptation is twofold; it may increase the chances of surviving predator attack by exposing a less 'vital' body part, but more importantly it may deter attack in the first place if attackers perceive the tail as the venomous snakes head," said Rasmussen.

Similar defence mechanisms have been discovered in lizards, and some land snakes have developed ingenious camouflage deterrent behaviour strategies, but this defence has never been associated with other lethally venomous predators such as sea snakes.
Traditionally the only evidence of a defence behaviour strategy in sea snakes has been documented in individual cases, when a snake was exposed to and aware of an imminent danger. This research is the first record of a combined false-head-behaviour and false-head-camouflage defence strategy used as instinct when a snake is hunting for food.

"It is intriguing that this discovery is observed in this species, as one of the key differences between the Yellow-lipped Sea Krait and other sea snakes is that they spend almost equal time on land and in the sea," said Rasmussen. "They therefore live in two worlds where two very different rules of survival apply. It remains to be confirmed whether Sea kraits use their sea defence tactic of motioning their tails when on land."

Wiley-Blackwell

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