2007年11月27日星期二
Sell High Impact Glass Bead
http://buy-or-sell.org/Chemicals/Sell-High-Impact-Glass-Bead-IAR3Y9IG/
Sell Azamethiphos
http://buy-or-sell.org/Chemicals/Sell-Azamethiphos-64mRY3Pi/
Sell Polyester chips
http://buy-or-sell.org/Chemicals/Sell-Polyester-chips-2Wt6ufSs/
Sell Pentaerythritol
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Sell Pre-Installation Service
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Sell DVD Duplication Service
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Credit Woes Send Stocks Skidding Again
The Highs And Lows of Holiday e-Commerce
Apple Agrees to Settlement Over Burst's Claims
Server Sales Healthy Despite Consolidation Trend
2007年11月25日星期日
Researchers Turn Skin Cells Into Stem Cells
By Gretchen Vogel
ScienceNOW Daily News
20 November 2007
The work builds on a study published last year by Shinya Yamanaka of Kyoto University in Japan, which showed that mouse tail cells could be transformed into ES-like cells by inserting four genes (ScienceNOW, 3 July 2006). Those genes are normally switched off after embryonic cells differentiate into the various cell types. In June this year, Yamanaka and another group reported that the cells were truly pluripotent, meaning that they had the potential to grow into any tissue in the body (ScienceNOW, 6 June).
Now the race to repeat the feat in human cells has ended in a tie: Two groups report today that they have reprogrammed human skin cells into so-called induced pluripotent cells (iPSs). In a paper published online in Cell, Yamanaka and his colleagues show that their mouse technique works with human cells as well. And in a paper published online in Science, James Thomson of the University of Wisconsin, Madison, and his colleagues report success in reprogramming human cells, again by inserting just four genes, two of which are different from those Yamanaka uses.
In the new work, Yamanaka and his colleagues used a retrovirus to ferry into adult cells the same four genes they had previously used to reprogram mouse cells: OCT3/4, SOX2, KLF4, and c-MYC. They reprogrammed cells taken from the facial skin of a 36-year-old woman and from connective tissue from a 69-year-old man. Roughly one iPS cell line was produced for every 5000 cells the researchers treated using the technique, an efficiency that enabled them to produce several cell lines from each experiment.
Thomson's team started from scratch, identifying its own list of 14 candidate reprogramming genes. Like Yamanaka's group, the team used a systematic process of elimination to identify four factors: OCT3 and SOX2, as Yamanaka used, and two different genes, NANOG and LIN28. The group reprogrammed cells from fetal skin and from the foreskin of a newborn boy. The researchers were able to transform about one in 10,000 cells, less than Yamanaka's technique achieved, Thomson says, but still enough to create several cell lines from a single experiment.
Although promising, both techniques share a downside. The retroviruses used to insert the genes could cause tumors in tissues grown from the cells. The crucial next step, everyone agrees, is to find a way to reprogram cells by switching on the genes rather than inserting new copies. The field is moving quickly toward that goal, says stem cell researcher Douglas Melton of Harvard University. "It is not hard to imagine a time when you could add small molecules that would tickle the same networks as these genes" and produce reprogrammed cells without genetic alterations, he says.
Once the kinks are worked out, "the whole field is going to completely change," says stem cell researcher Jose Cibelli of Michigan State University in East Lansing. "People working on ethics will have to find something new to worry about."
For a more in-depth news story on this topic, see this week's issue of Science, available online 22 November.
Lyme Disease's Unusual Suspects
By Martin Enserink
ScienceNOW Daily News
21 November 2007
Lyme disease can cause anything from rash to arthritic and psychiatric diseases. Borrelia burgdorferi sensu stricto, the bacterium that causes Lyme disease in the United States, is transmitted to humans by blacklegged ticks. Researchers have assumed that the vast majority of ticks become infected when, as larvae, they take their first blood meal from a white-footed mouse. Indeed, lab studies have shown that as many as 90%26#37; of ticks feeding on an infected mouse pick up the bug, an "extremely high number," says disease ecologist Dustin Brisson of the University of Pennsylvania.
But other species that transmit B. burgdorferi to ticks less efficiently might also spread the disease if they are more numerous or if they are bitten by a large number of ticks. And some studies had suggested this to be the case. For instance, a field trial published in 2004 showed that vaccinating mice against Lyme disease and then releasing them led to only a small decrease in the number of infected ticks.
To get a fuller picture, Brisson and his colleagues pulled together data from their own studies in the Hudson Valley in New York state and from other papers. The team looked at an outer surface protein of B. burgdorferi found in ticks--which can give clues about the vertebrate host--as well as the probabilities that different host species transmit the microbe during a tick bite, the number of larvae feeding on the animals, and population densities. Then they calculated the importance of each of the host species.
White-footed mice account for only a quarter of the total number of infected ticks, the team found. Short-tailed shrews and masked shrews were responsible for another quarter each, and chipmunks for as much as 13%26#37;. That means that mice aren't the "dominant" host at all, says Brisson, and vaccination strategies aimed at mice alone are unlikely to bring Lyme disease under control. Brisson speculates that mice have received a lot of attention in part because they're conspicuous, easy to catch, and ideal lab subjects.
"It's a nice paper," says Durland Fish of Yale University School of Medicine, a co-author of the 2004 vaccination study. However, he believes there are even more culprits. In particular, the team barely looked at birds, he notes, even though one study has shown that robins, which often live close to humans, are very good at transmitting B. burgdorferi to ticks in the lab. "The situation is probably even more complex than we think," Fish says.
Odd Little Stars
By Phil Berardelli
ScienceNOW Daily News
21 November 2007
White dwarfs earn their moniker by being quite small, astronomically speaking. They start out as normal stars, but over billions of years, they expand into red giants before exhausting their energy and collapsing into objects not much bigger than Earth. Until this year, all known white dwarfs followed this pattern, and they all boasted atmospheres consisting of either hydrogen or helium, which can be easily identified by the spectral lines of their respective light.
Not so the nine discovered by an international team and reported in tomorrow's issue of Nature. Plucked from millions of stars and galaxies analyzed over the past 7 years by the Sloan Digital Sky Survey, this bunch burns considerably cooler than normal and contains atmospheres made entirely of carbon, with no traces of hydrogen or helium. Astronomers don't have a clue why. Usually, a star produces excess carbon when it is about to shut down the nuclear-fusion cycle that keeps it burning. No fusion means gravitational collapse followed by a supernova explosion that splashes the star all over its galaxy.
So why are these white dwarfs still around? One possibility, notes astronomer and lead author Patrick Dufour of the University of Arizona, Tucson, is that the stars simply might not have grown massive enough--about 10 times heavier than the sun--to explode but are so close to the limit that they might be harboring abnormally high amounts of carbon. The unique chemical signature of the stars may provide clues to what's going on. "It tells us that nature has found a way that we didn't know to make white dwarf stars without the usual hydrogen or helium surface layers," Dufour says.
A whole new class of carbon-dominated white dwarf stars is a "major discovery," says astronomer Pierre Bergeron of the University of Montreal in Canada. It's something that occurs only once in a decade or so, he says, and the underlying process governing these white dwarfs "will launch an entirely new field of research." Astronomer Klaus Werner of the Institute for Astronomy and Astrophysics in T?bingen, Germany, agrees. "There is currently no explanation how such stars can be formed," he says. "It's a real challenge to stellar-evolution theory."
2007年11月23日星期五
Sell Single Side Supermarket Shelf with Iron Backboard (New Style)
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Sell Railing Stands
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2007年11月11日星期日
First Penryn Chips With 'Reinvented Transistor'
2007年11月10日星期六
Sell Duster Vehicle
http://buy-or-sell.org/Automobile/Sell-Duster-Vehicle-KDdruwmh/
2007年11月9日星期五
Sell shade nets
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barbour
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Sell Ceramic frog
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2007年11月8日星期四
HP To Focus On Partner For Its Camera Biz
2007年11月6日星期二
Vontu Buy Puts Symantec At Head Of DLP Field
2007年11月5日星期一
Symantec Snaps Up Vontu
2007年11月2日星期五
Sell CNC Cutting
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Sell PKG H Beam Copying Cutting Machine (ISO, I Beam, Box Beam)
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