Climate Change Causing Ice Melts Unveils Ancient Tools

Home of "Ice Giants" thaws, shows pre-Viking hunts

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• Slideshow:Ancient Reindeer Hunting Gear
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Reuters – The Juvfonna ice field at 1,850 metres (6070 feet) above sea level is seen in the Jotunheimen mountains …

By Alister Doyle, Environment Correspondent Alister Doyle, Environment Correspondent – Tue Sep 14, 6:04 am ET

JUVFONNA, Norway (Reuters) – Climate change is exposing reindeer hunting gear used by the Vikings' ancestors faster than archaeologists can collect it from ice thawing in northern Europe's highest mountains.

"It's like a time machine...the ice has not been this small for many, many centuries," said Lars Piloe, a Danish scientist heading a team of "snow patch archaeologists" on newly bare ground 1,850 meters (6,070 ft) above sea level in mid-Norway.

Specialized hunting sticks, bows and arrows and even a 3,400-year-old leather shoe have been among finds since 2006 from a melt in the Jotunheimen mountains, the home of the "Ice Giants" of Norse mythology.

As water streams off the Juvfonna ice field, Piloe and two other archaeologists -- working in a science opening up due to climate change -- collect "scare sticks" they reckon were set up 1,500 years ago in rows to drive reindeer toward archers.

But time is short as the Ice Giants' stronghold shrinks.

"Our main focus is the rescue part," Piloe said on newly exposed rocks by the ice. "There are many ice patches. We can only cover a few...We know we are losing artefacts everywhere."

Freed from an ancient freeze, wood rots in a few years. And rarer feathers used on arrows, wool or leather crumble to dust in days unless taken to a laboratory and stored in a freezer.

Jotunheimen is unusual because so many finds are turning up at the same time -- 600 artefacts at Juvfonna alone.

Other finds have been made in glaciers or permafrost from Alaska to Siberia. Italy's iceman "Otzi," killed by an arrow wound 5,000 years ago, was found in an Alpine glacier in 1991. "Ice Mummies" have been discovered in the Andes.

Click image to see photos of the ancient hunting gear

Reuters/Photo courtesy of Vegard Vike

RESCUE

Patrick Hunt, of Stanford University in California who is trying to discover where Carthaginian general Hannibal invaded Italy in 218 BC with an army and elephants, said there was an "alarming rate" of thaw in the Alps.

"This is the first summer since 1994 when we began our Alpine field excavations above 8,000 ft that we have not been inundated by even one day of rain, sleet and snow flurries," he said.

"I expect we will see more 'ice patch archaeology discoveries'," he said. Hannibal found snow on the Alpine pass he crossed in autumn, according to ancient writers.

Glaciers are in retreat from the Andes to the Alps, as a likely side-effect of global warming caused by human emissions of greenhouse gases, the U.N. panel of climate experts says.

The panel's credibility has suffered since its 2007 report exaggerated a thaw by saying Himalayan glaciers might vanish by 2035. It has stuck to its main conclusion that it is "very likely" that human activities are to blame for global warming.

"Over the past 150 years we have had a worldwide trend of glacial retreat," said Michael Zemp, director of the Swiss-based World Glacier Monitoring Service. While many factors were at play, he said "the main driver is global warming."

In Norway, "some ice fields are at their minimum for at least 3,000 years," said Rune Strand Oedegaard, a glacier and permafrost expert from Norway's Gjoevik University College.

The front edge of Jovfunna has retreated about 18 meters (60 ft) over the past year, exposing a band of artefacts probably from the Iron Age 1,500 years ago, according to radiocarbon dating. Others may be from Viking times 1,000 years ago.

Juvfonna, about 1 km across on the flank of Norway's highest peak, Galdhoepiggen, at 2,469 meters, also went through a less drastic shrinking period in the 1930s, Oedegaard said.

REINDEER

Inside the Juvfonna ice, experts have carved a cave to expose layers of ice dating back 6,000 years. Some dark patches turned out to be ancient reindeer droppings -- giving off a pungent smell when thawed out.

Ice fields like Juvfonna differ from glaciers in that they do not slide much downhill. That means artefacts may be where they were left, giving an insight into hunting techniques.

On Juvfonna, most finds are "scare sticks" about a meter long. Each has a separate, flapping piece of wood some 30 cm long that was originally tied at the top. The connecting thread is rarely found since it disintegrates within days of exposure.

"It's a strange feeling to be tying a string around this stick just as someone else did maybe 1,500 years ago," said Elling Utvik Wammer, a archaeologist on Piloe's team knotting a tag to a stick before storing it in a box for later study.

All the finds are also logged with a GPS satellite marker before being taken to the lab for examination.

The archaeologists reckon they were set up about two meters apart to drive reindeer toward hunters. In summer, reindeer often go onto snow patches to escape parasitic flies.

Such a hunt would require 15 to 20 people, Piloe said, indicating that Norway had an organized society around the start of the Dark Ages, 1,500 years ago. Hunters probably needed to get within 20 meters of a reindeer to use an iron-tipped arrow.

"You can nearly feel the hunter here," Piloe said, standing by a makeshift wall of rocks exposed in recent weeks and probably built by an ancient archer as a hideaway.

(Editing by Philippa Fletcher)

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MIT Researchers Develop a Way to Funnel Solar Energy

New antenna made of carbon nanotubes could make photovoltaic cells more efficient.

by Anne Trafton, MIT News Office

Published: September 13, 2010

Cambridge, MA, USA -- Using carbon nanotubes (hollow tubes of carbon atoms), MIT chemical engineers have found a way to concentrate solar energy 100 times more than a regular photovoltaic cell. Such nanotubes could form antennas that capture and focus light energy, potentially allowing much smaller and more powerful solar arrays.

"Instead of having your whole roof be a photovoltaic cell, you could have little spots that were tiny photovoltaic cells, with antennas that would drive photons into them," says Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering and leader of the research team.

Strano and his students describe their new carbon nanotube antenna, or "solar funnel," in the Sept. 12 online edition of the journal Nature Materials. Lead authors of the paper are postdoctoral associate Jae-Hee Han and graduate student Geraldine Paulus (pictured above).

Their new antennas might also be useful for any other application that requires light to be concentrated, such as night-vision goggles or telescopes.

Solar panels generate electricity by converting photons (packets of light energy) into an electric current. Strano's nanotube antenna boosts the number of photons that can be captured and transforms the light into energy that can be funneled into a solar cell.

The antenna consists of a fibrous rope about 10 micrometers (millionths of a meter) long and four micrometers thick, containing about 30 million carbon nanotubes. Strano's team built, for the first time, a fiber made of two layers of nanotubes with different electrical properties — specifically, different bandgaps.

In any material, electrons can exist at different energy levels. When a photon strikes the surface, it excites an electron to a higher energy level, which is specific to the material. The interaction between the energized electron and the hole it leaves behind is called an exciton, and the difference in energy levels between the hole and the electron is known as the bandgap.

The inner layer of the antenna contains nanotubes with a small bandgap, and nanotubes in the outer layer have a higher bandgap. That's important because excitons like to flow from high to low energy. In this case, that means the excitons in the outer layer flow to the inner layer, where they can exist in a lower (but still excited) energy state.

Therefore, when light energy strikes the material, all of the excitons flow to the center of the fiber, where they are concentrated. Strano and his team have not yet built a photovoltaic device using the antenna, but they plan to. In such a device, the antenna would concentrate photons before the photovoltaic cell converts them to an electrical current. This could be done by constructing the antenna around a core of semiconducting material.

The interface between the semiconductor and the nanotubes would separate the electron from the hole, with electrons being collected at one electrode touching the inner semiconductor, and holes collected at an electrode touching the nanotubes. This system would then generate electric current. The efficiency of such a solar cell would depend on the materials used for the electrode, according to the researchers.

Strano's team is the first to construct nanotube fibers in which they can control the properties of different layers, an achievement made possible by recent advances in separating nanotubes with different properties.

While the cost of carbon nanotubes was once prohibitive, it has been coming down in recent years as chemical companies build up their manufacturing capacity. "At some point in the near future, carbon nanotubes will likely be sold for pennies per pound, as polymers are sold," says Strano. "With this cost, the addition to a solar cell might be negligible compared to the fabrication and raw material cost of the cell itself, just as coatings and polymer components are small parts of the cost of a photovoltaic cell."

Strano's team is now working on ways to minimize the energy lost as excitons flow through the fiber, and on ways to generate more than one exciton per photon. The nanotube bundles described in the Nature Materials paper lose about 13 percent of the energy they absorb, but the team is working on new antennas that would lose only 1 percent.

Anne Trafton is a writer in the MIT news office.

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record of 17.6% on flexible CIGS solar cell

Efficiency record of 17.6% on flexible CIGS solar cell on plastic developed at EMPA

Flexible thin film solar cells on polymer film with a new record efficiency of 17.6% have been developed by the scientists at the Swiss Federal Laboratories for Material Science and Technology (EMPA). The conversion efficiency record has been independently certified by the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, Germany.

Lower thermal budget and roll-to-roll manufacturing of high efficiency flexible CIGS solar cells will pave the way for substantial reduction in production cost of next generation of solar modules produced on large industrial scale in future.

Scientists under the leadership of Dr. Ayodhya N. Tiwari at the Laboratory of Thin Film and Photovoltaics, EMPA in Switzerland have been developing thin film solar cells based on Cu(In,Ga)Se2 semiconductor material. The research group at EMPA working in close collaboration with FLISOM Company, has developed a process that resulted in a remarkably high 17.6% efficiency solar cell which is an independently certified highest efficiency record for any type of flexible solar cell on polymer film reported up to now.

This development is challenging because most of the polymer films used as substrate, lack thermal stability for growth of high electronic and structural quality CIGS solar cell layers at high temperatures. High thermal expansion coefficient of polymer causes a large stress in the layers deposited at high substrate temperature, resulting in cracks and delamination of the solar cells from the substrate. Adrian Chirila and other colleagues, working under the supervision of Dr. Tiwari have been developing a vacuum evaporation process for growth of high quality CIGS absorber layers at sufficiently low temperature of about 450 °C. This is suitable for polyimide film as a flexible substrate for roll-to-roll manufacturing.

Moving from a previous record value of 14.1% to a new record of 17.6% was achieved by reducing the optical and electronic losses in the CIGS solar cell structure. The most important factor was the optimisation of the composition gradient of Ga across the CIGS layer thickness and an appropriate incorporation of Na for doping during the final stage of the growth process. Consequently, an optimum band gap grading and larger grain size in CIGS layer resulted in a substantial increase in the efficiency of flexible solar cells.  The photovoltaic measurements performed under the standard test condition at ISE Freiburg confirmed 17.6% efficiency with Voc = 688 mV, Isc = 34.8 mA/cm2, FF = 73.6%.  

The low temperature process for CIGS deposition offers a unique advantage that the same process and equipment can be used for polymer as well as metal foils.  Flexible CIGS solar cells on metal foils with highest efficiency of ca 17.5% are generally grown at high temperatures above 550 °C, while lower efficiencies were obtained on polymer films because of lower deposition temperature. This successful development has closed the efficiency gap between the solar cells on polymer and metal foils. This solar cell processing can be adapted for roll-to-roll manufacturing of monolithically connected solar modules on polymer films. Lower thermal budget and roll-to-roll manufacturing of high efficiency flexible CIGS solar cells will pave the way for substantial reduction in production cost of next generation of solar modules produced on large industrial scale in future.

This November, Dr. Tiwari Ayodhya will be speaking at the 3^rd Thin Film Solar Summit USA about enhancing thin film efficiency and the developments that will allow the industry to go beyond the 12% mark. For more information about his participation visit www.thinfilmtoday.com/us

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photovoltaic technology can keep repairing itself

Solar Cell, Heal Thyself

New self-assembling photovoltaic technology can keep repairing itself to avoid any loss in performance.

by David L. Chandler, MIT News Office

Published: September 9, 2010

Cambridge, MA, USA -- Plants are good at doing what scientists and engineers have been struggling to do for decades: converting sunlight into stored energy, and doing so reliably day after day, year after year. Now some MIT scientists have succeeded in mimicking a key aspect of that process.

One of the problems with harvesting sunlight is that the sun's rays can be highly destructive to many materials. Sunlight leads to a gradual degradation of many systems developed to harness it. But plants have adopted an interesting strategy to address this issue: They constantly break down their light-capturing molecules and reassemble them from scratch, so the basic structures that capture the sun's energy are, in effect, always brand new.

That process has now been imitated by Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering, and his team of graduate students and researchers. They have created a novel set of self-assembling molecules that can turn sunlight into electricity; the molecules can be repeatedly broken down and then reassembled quickly, just by adding or removing an additional solution. Their paper on the work was published on Sept. 5 in Nature Chemistry.

Strano says the idea first occurred to him when he was reading about plant biology. "I was really impressed by how plant cells have this extremely efficient repair mechanism," he says. In full summer sunlight, "a leaf on a tree is recycling its proteins about every 45 minutes, even though you might think of it as a static photocell."

One of Strano's long-term research goals has been to find ways to imitate principles found in nature using nanocomponents. In the case of the molecules used for photosynthesis in plants, the reactive form of oxygen produced by sunlight causes the proteins to fail in a very precise way. As Strano describes it, the oxygen "unsnaps a tether that keeps the protein together," but the same proteins are quickly reassembled to restart the process.

This action all takes place inside tiny capsules called chloroplasts that reside inside every plant cell — and which is where photosynthesis happens. The chloroplast is "an amazing machine," Strano says. "They are remarkable engines that consume carbon dioxide and use light to produce glucose," a chemical that provides energy for metabolism.

To imitate that process, Strano and his team, supported by grants from the MIT Energy Initiative and the Eni Solar Frontiers Center at MIT, produced synthetic molecules called phospholipids that form disks; these disks provide structural support for other molecules that actually respond to light, in structures called reaction centers, which release electrons when struck by particles of light. The disks, carrying the reaction centers, are in a solution where they attach themselves spontaneously to carbon nanotubes — wire-like hollow tubes of carbon atoms that are a few billionths of a meter thick yet stronger than steel and capable of conducting electricity a thousand times better than copper. The nanotubes hold the phospholipid disks in a uniform alignment so that the reaction centers can all be exposed to sunlight at once, and they also act as wires to collect and channel the flow of electrons knocked loose by the reactive molecules.

The system Strano's team produced is made up of seven different compounds, including the carbon nanotubes, the phospholipids, and the proteins that make up the reaction centers, which under the right conditions spontaneously assemble themselves into a light-harvesting structure that produces an electric current. Strano says he believes this sets a record for the complexity of a self-assembling system. When a surfactant — similar in principle to the chemicals that BP has sprayed into the Gulf of Mexico to break apart oil — is added to the mix, the seven components all come apart and form a soupy solution. Then, when the researchers removed the surfactant by pushing the solution through a membrane, the compounds spontaneously assembled once again into a perfectly formed, rejuvenated photocell. 

"We're basically imitating tricks that nature has discovered over millions of years" — in particular, "reversibility, the ability to break apart and reassemble," Strano says. The team, which included postdoctoral researcher Moon-Ho Ham and graduate student Ardemis Boghossian, came up with the system based on a theoretical analysis, but then decided to build a prototype cell to test it out. They ran the cell through repeated cycles of assembly and disassembly over a 14-hour period, with no loss of efficiency.

Strano says that in devising novel systems for generating electricity from light, researchers don't often study how the systems change over time. For conventional silicon-based photovoltaic cells, there is little degradation, but with many new systems being developed — either for lower cost, higher efficiency, flexibility or other improved characteristics — the degradation can be very significant. "Often people see, over 60 hours, the efficiency falling to 10 percent of what you initially saw," he says.

The individual reactions of these new molecular structures in converting sunlight are about 40 percent efficient, or about double the efficiency of today's best solar cells. Theoretically, the efficiency of the structures could be close to 100 percent, he says. But in the initial work, the concentration of the structures in the solution was low, so the overall efficiency of the device — the amount of electricity produced for a given surface area — was very low. They are working now to find ways to greatly increase the concentration. 

Philip Collins '90, associate professor of experimental and condensed-matter physics at the University of California, Irvine, who was not involved in this work, says, "One of the remaining differences between man-made devices and biological systems is the ability to regenerate and self-repair. Closing this gap is one promise of nanotechnology, a promise that has been hyped for many years. Strano's work is the first sign of progress in this area, and it suggests that 'nanotechnology' is finally preparing to advance beyond simple nanomaterials and composites into this new realm."

David Chandler is a writer in the MIT News Office.

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