SCIENCE

Physicists May Have Found New Way To Turn Earth's Radiation Into Energy

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PLEASE VISIT www.ansiklopedika.org (Explore: 447 on Wednesday, September 30, 2009) Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the last century. The Intergovernmental Panel on Climate Change (IPCC) concludes that increasing greenhouse gas concentrations resulting from human activity such as fossil fuel burning and deforestation are responsible for most of the observed temperature increase since the middle of the 20th century. The IPCC also concludes that natural phenomena such as solar variation and volcanoes produced most of the warming from pre-industrial times to 1950 and had a small cooling effect afterward. These basic conclusions have been endorsed by more than 40 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. Climate model projections summarized in the latest IPCC report indicate that global surface temperature will probably rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century. The uncertainty in this estimate arises from the use of models with differing sensitivity to greenhouse gas concentrations and the use of differing estimates of future greenhouse gas emissions. Some other uncertainties include how warming and related changes will vary from region to region around the globe. Most studies focus on the period up to 2100. However, warming is expected to continue beyond 2100 even if emissions stop, because of the large heat capacity of the oceans and the long lifetime of carbon dioxide in the atmosphere. Increasing global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably including expansion of subtropical deserts.The continuing retreat of glaciers, permafrost and sea ice is expected, with the Arctic region being particularly affected. Other likely effects include shrinkage of the Amazon rainforest and Boreal forests, increases in the intensity of extreme weather events, species extinctions and changes in agricultural yields. Political and public debate continues regarding what actions (if any) to take in response to global warming. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions. ansiklopedika.org

Our planet is warm. Outer space is cold. Can we take that heat difference and turn it into electricity?

Physicists at Harvard University may have found a way to do just that. They've proposed in a new study how to harvest the Earth's thermal infrared radiation, and convert it into direct-current (DC) power.

“It’s not at all obvious, at first, how you would generate DC power by emitting infrared light in free space toward the cold,” study co-author Dr. Federico Capasso, a professor of applied physics and senior research fellow in electrical engineering at the university, said in a written statement. “To generate power by emitting, not by absorbing light, that’s weird. It makes sense physically once you think about it, but it’s highly counterintuitive. We’re talking about the use of physics at the nanoscale for a completely new application.”

One method in the study involves putting a hot plate (at the temperature of the Earth) beneath a cooler plate made from emissive material that gets colder by radiating heat toward the sky. The researchers said, based on a separate study they did on infrared emissions, that during the day or night such a contraption could produce a few watts of electricity for every square meter of the device, depending on the size of the plates.

That approach is "fairly intuitive," study co-author Steven J. Byrnes, a postdoc researcher at Harvard, said in the statement. But a second proposed method is a little more complex.

It involves making many tiny electric circuits that would have two parts: "resistors" (or antennas) that emit the Earth's infrared radiation, and mini electronic components called "diodes" that conduct a resistor's electric current in a single direction. Keeping the diode warmer than the resistor will create voltage, the researchers said, and by covering a flat device with thousands or perhaps millions of these circuits and pointing it at the sky, you could get a significant amount of electricity using the Earth's radiation as its source.

But there are still complications to figure out, the researchers said, one of which is that it's hard to build and manipulate a diode with the low voltage levels created by the infrared emissions. A possible solution may lie in the manufacture of molecular-sized devices.

"People have been working on infrared diodes for at least 50 years without much progress," Byrnes said. "But recent advances such as nanofabrication are essential to making them better, more scalable, and more reproducible."

This new research was published this week in the journal Proceedings Of The National Academy Of Sciences.

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