Researchers' refinement increases solar concentrator efficiency

ScienceDaily (Jan. 19, 2012) ? A team of researchers at the University of California, Merced, has redesigned luminescent solar concentrators to be more efficient at sending sunlight to solar cells.

The advancement could be an important breakthrough for solar energy harvesting, said UC Merced physics Professor Sayantani Ghosh, who led the project.

"We tweaked the traditional flat design for luminescent solar concentrators and made them into cylinders," Ghosh said. "The results of this architectural redesign surprised us, as it significantly improves their efficiency."

The main problem preventing luminescent concentrators from being used commercially is that they have high rates of self-absorption, Ghosh said, meaning they absorb a significant amount of the light they produce instead of transporting it to the solar cells.

The research team showed the problem can be addressed by changing the shape of the concentrator. They discovered a hollow cylindrical solar concentrator is a better design compared with a flat concentrator or a solid cylinder concentrator. The hollow cylinders absorb more sunlight while having lower self-absorption losses.

Luminiscent solar concentrators are designed to absorb solar radiation over a broad range of colors and re-emit it over a narrower range (for example, only red), a process known as down-converting. This light is transported to solar cells for photocurrent generation. The quantum dots embedded in the concentrator are the materials that carry out this color conversion.

The biggest advantage they offer over traditional solar cells is that they can work even in diffuse sunlight, like on cloudy days. And because of this, they do not need to directly face the sun at all times, eliminating the need for tracking mechanisms.

Ghosh said the discovery could make commercially viable luminescent solar concentrators a reality, especially because the design enhances performance while using the same number of quantum dots, therefore without being more costly.

This saves on infrastructure costs and also opens up the possibility that the collectors can be integrated onto vertical surfaces like walls and windows. The next step is to develop a large array of hollow cylindrical luminescent solar concentrators and track the efficiency of the panel.

Richard Inman, Georgiy Shcherbatyuk, Dmitri Medvedko and Ajay Gopinathan are the other members of the team that conducted this research.

Inman served as the lead researcher while he was an undergraduate at UC Merced, an example of the hands-on learning opportunities available to students. He's now a graduate student at UC San Diego. Medvedko is an undergraduate student, and Shcherbatyuk is a graduate student. Gopinathan is a physics professor.

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The above story is reprinted from materials provided by University of California, Merced.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Journal Reference:

1. R. H. Inman, G. V. Shcherbatyuk, D. Medvedko, A. Gopinathan, S. Ghosh. Cylindrical luminescent solar concentrators with near-infrared quantum dots. Optics Express, 2011; 19 (24): 24308 DOI: 10.1364/OE.19.024308

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

Source: http://feeds.sciencedaily.com/~r/sciencedaily/~3/ELIjOtEiQT0/120119153042.htm

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Romney preparing for the long haul in 2012 race (AP)

GREENVILLE, S.C. ? Preparing for the long haul, Mitt Romney said Saturday's South Carolina presidential contest "could be real close" and he agreed to two more debates with his rivals ahead of the Florida primary.

In the face of questions about releasing his tax returns and struggling with a renewed threat from Newt Gingrich, Romney lashed out at the former speaker, calling on the former House speaker to better explain his contractual ties to Freddie Mac, the quasi-government mortgage company. Gingrich served as a consultant to Freddie Mac over a period of eight years.

Romney said he would attend a debate Monday in Tampa, Fla., and his campaign confirmed he would be at one Thursday in Jacksonville, Fla., ahead of the state's primary Jan. 31. His planned appearances are an acknowledgment that the former Massachusetts governor will have to continue the battle with Gingrich longer than expected or hoped.

But Romney avoided confronting Gingrich, his chief rival in South Carolina's first-in-the South vote, at a stop at Tommy's Country Ham House.

Both men had scheduled campaign events for the same time on primary day. Romney stopped by the breakfast restaurant 45 minutes ahead of schedule. When Gingrich arrived at the restaurant ? just minutes after Romney's bus left the parking lot ? he said: "Where's Mitt?"

About an hour earlier, Romney was outside of his Greenville headquarters, launching a new attack on the speaker. He called on Gingrich to further explain his contracts with Freddie and release any advice he had provided. "I'd like to see what he actually told Freddie Mac. Don't you think we ought to see it?" Romney said.

It was another response to pressure on Romney to release his tax returns before Republican voters finish choosing a nominee. A day earlier, Romney had called on Gingrich to release information related to an ethics investigation of Gingrich in the 1990s.

Romney says he will release several years' worth of tax returns in April. Gingrich has called on him to release them much sooner. On Saturday, Romney refused to answer questions from reporters about the returns and whether his refusal to release them had hurt him with South Carolina voters.

Romney still has significant advantages over his three remaining Republican rivals, including an enormous financial edge and a well-organized campaign. But with his Iowa victory now rescinded, losing in South Carolina would be a setback that could draw the primary contest out much longer. Just 10 days ago, Romney's campaign was looking ahead to the general election as they anticipated a quick sweep in early primaries.

"This could be real close," said Romney as he chatted on the phone with a voter he called Saturday morning. He urged the man to go vote.

And as he stood on a chair inside Tommy's, where it was impossible to tell who in the tightly packed crowd was there to see him and who was there to see Gingrich, a woman shouted her thanks for buying breakfast.

"I'm happy to pay for breakfast," Romney responded, "but there's no free lunch."

Source: http://us.rd.yahoo.com/dailynews/rss/gop/*http%3A//news.yahoo.com/s/ap/20120121/ap_on_el_pr/us_romney

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Breast cancer cells targeted, then burned, by gold-filled silicon wafers

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Posted: Jan 18th, 2012

Breast cancer cells targeted, then burned, by gold-filled silicon wafers

(Nanowerk News) By shining infrared light on specially designed, gold-filled silicon wafers, scientists at The Methodist Hospital Research Institute have successfully targeted and burned breast cancer cells. If the technology is shown to work in human clinical trials, it could provide patients a non-invasive alternative to surgical ablation, and could be used in conjunction with traditional cancer treatments, such as chemotherapy, to make those treatments more effective.

The research is presented in the first issue of the new Advanced Healthcare Materials ("Cancer Therapy: Cooperative, Nanoparticle-Enabled Thermal Therapy of Breast Cancer").

"Hollow gold nanoparticles can generate heat if they are hit with a near-infrared laser," said Research Institute Assistant Member Haifa Shen, M.D., Ph.D., the report's lead author. "Multiple investigators have tried to use gold nanoparticles for cancer treatment, but the efficiency has not been very good -- they'd need a lot of gold nanoparticles to treat a tumor."

Instead, Shen and his colleagues turned to a technology developed by the study's principal investigator, Mauro Ferrari, Ph.D., The Methodist Hospital Research Institute (TMHRI) president and CEO, to amplify the gold particles' response to infrared light.

This false color image shows the embedding of hollow gold particles inside silicon wafers. The gold particles heat up quickly when harmless infrared radiation is shone upon them, causing nearby tissue (in this case, breast cancer cells) to die.

"We developed a system based on Dr. Ferrari's multi-stage vector technology platform to treat cancers with heat," Shen said. "We found that heat generation was much more efficient when we loaded gold nanoparticles into porous silicon, the carrier of the multistage vectors."

Shen and his team found that in the presence of 808 nanometer light, the gold-filled silicon particles heated up a surrounding solution by about 20 deg C (35 deg F) in seven minutes. Water particles immediately around the particles were presumed to have been hotter.

And experiments showed that tumor cell growth was lowest in the presence of gold-loaded silicon nanoparticles in three types of breast cancer cells -- MDA-MB-231 and SK-BR-3 (human), and 4T1 (mouse).

The silicon wafers the scientists are using are the result of painstaking work by Ferrari's group to design nanoparticles that preferentially bind to breast cancer cells, rather than, say, healthy liver or immune system cells. The shape and size of the silicon particles, as well as their surface chemistry, are all crucial, Ferrari's group found. Too big or the wrong shape, and the silicon nanoparticles bind to multiple cell types -- or none at all. Polyamine structures are attached to the wafers to improve their attraction to cancer cell surfaces and their solubility. The wafers are about one micrometer in diameter (one-thousandth of a millimeter). By contrast, the typical breast cancer cell is about 10 to 12 times that size.

Shen says the gold particles, too, must be designed with a specific use in mind, albeit for indirect reasons.

"The hollow gold particles we load into the porous silicon must be the right size and have the correct-sized space inside them to interact with the infrared light we are using," he said. "But the wavelength of infrared we use will have to change depending on where the tumor is. If it's close to the skin, we can use shorter wavelengths. Deeper inside the body, we have to use longer wavelengths of infrared to penetrate the tissue. The hollow space of the gold particles must be modified in response to that."

Both silicon and gold have low toxicity profiles in the human body, and are popular materials in current investigations using medical nanotechnology. Silicon is steadily broken down by physiological processes into an acid that is removed through the kidneys. And gold is chemically inert.

And infrared -- the type of light used by TV remote controls and garage door openers -- is also far less dangerous than light with shorter wavelengths, such as ultraviolet, which can cause DNA damage, and x-rays.

Understanding why hollow gold particles heat up in the presence of certain wavelengths of infrared is complex enough to require some background in physical chemistry. But the upshot is that the energy of certain wavelengths of light is largely absorbed by the particles, and that energy is released as vibrational (heat) energy. Absorption is influenced both by the diameter of the space within the hollow gold particles, and by the properties of gold itself.

Shen says he'd like to know whether the silicon-gold nanotechnology can be used to wipe out whole tumors, rather than just cancerous cells.

"We are planning pre-clinical studies to study the technology's impact on whole tissues, breast cancer cells and possibly pancreatic cancer cells," Shen said. "We would also like to see whether this approach makes chemotherapy more effective, meaning you could use less drugs to achieve the same degree of success in treating tumors. These investigations are next."

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Source: http://www.nanowerk.com/news/newsid=23989.php

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