Thursday, September 24, 2009

GRAPHITIC MEMORY TECHNIQUES ADVANCE AT RICE

0 comentarios
Advances by the Rice University lab of James Tour have brought graphite’s potential as a mass data storage medium a step closer to reality and created the potential for reprogrammable gate arrays that could bring about a revolution in integrated circuit logic design.

In a paper published in the online journal ACS Nano, Tour and postdoctoral associate Alexander Sinitskii show how they've used industry-standard lithographic techniques to deposit 10-nanometer stripes of amorphous graphite, the carbon-based, semiconducting material commonly found in pencils, onto silicon. This facilitates the creation of potentially very dense, very stable nonvolatile memory for all kinds of digital devices.

With backing from a major manufacturer of memory chips, Tour and his team have pushed the technology forward in several ways since a paper that appeared last November first described two-terminal graphitic memory. While noting advances in other molecular computing techniques that involve nanotubes or quantum dots, he said none of those have yet proved practical in terms of fabrication.

Not so with this simple-to-deposit graphite. "We're using chemical vapor deposition and lithography -- techniques the industry understands," said Tour, Rice's Chao Professor of Chemistry and a professor of mechanical engineering and materials science and of computer science. "That makes this a good alternative to our previous carbon-coated nanocable devices, which perform well but are very difficult to manufacture."

Graphite makes a good, reliable memory "bit" for reasons that aren't yet fully understood. The lab found that running a current through a 10-atom-thick layer of graphite creates a complete break in the circuit -- literally, a gap in the strip a couple of nanometers wide. Another jolt repairs the break. The process appears to be indefinitely repeatable, which provides addressable ones and zeroes, just like today's flash memory devices but at a much denser scale.

Graphite's other advantages were detailed in Tour's earlier work: the ability to operate with as little as three volts, an astoundingly high on/off ratio (the amount of juice a circuit holds when it’s on, as opposed to off) and the need for only two terminals instead of three, which eliminates a lot of circuitry. It's also impervious to a wide temperature range and radiation; this makes it suitable for deployment in space and for military uses where exposure to temperature extremes and radiation is a concern.

Tour's graphite-forming technique is well-suited for other applications in the semiconductor industry. One result of the previous paper is a partnership between the Tour group and NuPGA (for "new programmable gate arrays"), a California company formed around the research to create a new breed of reprogrammable gate arrays that could make the design of all kinds of computer chips easier and cheaper.

The Tour lab and NuPGA, led by industry veteran Zvi Or-Bach (founder of eASIC and Chip Express), have applied for a patent based on vertical arrays of graphite embedded in "vias," the holes in integrated circuits connecting the different layers of circuitry. When current is applied to a graphite-filled via, the graphite alternately splits and repairs itself (a process also described in the latest paper), just like it does in strip form. Essentially, it becomes an "antifuse," the basic element of one type of field programmable gate array (FPGA), best described as a blank computer chip that uses software to rewire the hardware.

Currently, antifuse FPGAs can be programmed once. But this graphite approach could allow for the creation of FPGAs that can be reprogrammed at will. Or-Bach said graphite-based FPGAs would start out as blanks, with the graphite elements split. Programmers could "heal" the antifuses at will by applying a voltage, and split them with an even higher voltage.

Such a device would be mighty handy to computer-chip designers, who now spend many millions to create the photolithography mask sets used in chip fabrication. If the design fails, it's back to square one.

"As a result of that, people are only hesitantly investing in new chip designs," said Tour. "They stick with the old chip designs and make modifications. FPGAs are chips that have no specific ability, but you use software to program them by interconnecting the circuitry in different ways." That way, he said, fabricators don’t need expensive mask sets to try new designs.

"The No. 1 problem in the industry, and one that gives an opportunity for a company like ours, is that the cost of masks keeps moving up as people push semiconductors into future generators," said Or-Bach. "Over the last 10 years, the cost of a mask set has multiplied almost 10 times.

"If we can really make something that will be an order of magnitude better, the markets will be happy to make use of it. That's our challenge, and I believe the technology makes it possible for us to do that."

Rice University

SCIENTISTS DISCOVER HUNGER'S TIMEKEEPER

0 comentarios

Researchers at Columbia and Rockefeller Universities have identified cells in the stomach that regulate the release of a hormone associated with appetite. The group is the first to show that these cells, which release a hormone called ghrelin, are controlled by a circadian clock that is set by mealtime patterns. The finding, published in Proceedings of the National Academy of Sciences, has implications for the treatment of obesity and is a landmark in the decades-long search for the timekeepers of hunger.

The scientists, led by Rae Silver, head of Columbia’s Laboratory of Neurobiology and Behavior and Helene L. and Mark N. Kaplan Professor at Barnard College, showed that ghrelin’s release whets the appetite of mice, spurring them to actively search for and consume food, even when they are not hungry. In addition to Silver, the researchers involved in the study include Barnard College senior research scientist Joseph LeSauter and collaborator Donald Pfaff at The Rockefeller University.

“Circadian clocks allow animals to anticipate daily events rather than just react to them,” said LeSauter, who ran and supervised the study’s experiments. “The cells that produce ghrelin have circadian clocks that presumably synchronize the anticipation of food with metabolic cycles.”

According to previous studies, people given ghrelin injections feel voraciously hungry and eat more at a buffet than they otherwise would. The new research suggests that the stomach tells the brain when to eat and that establishing a regular schedule of meals will regulate the stomach’s release of ghrelin. “If you eat all the time, ghrelin secretion will not be well controlled,” said Silver, the paper’s lead author and the principal investigator of the study. “It’s a good thing to eat meals at a regularly scheduled time of day.”

The scientists show that stomach cells in mice release ghrelin into the general circulation before meal time. The hormone triggers a flurry of food seeking behavior associated with hunger and stimulates eating.

LeSauter studied genetically engineered mice lacking the ghrelin-recognizing receptor and compared them with normal mice on identical feeding schedules. He found that the mice lacking the ghrelin receptor began to forage for food much later and to a lesser extent than their normal counterparts.

Pfaff believes ghrelin, which travels from the stomach through the bloodstream to the brain, influences a decision-making process in brain cells. These brain cells are constantly deciding whether or not to eat, and as mealtime draws near, the presence of ghrelin increases the proportion of “yes” decisions.

The research underscores that ghrelin, the only known natural appetite stimulant made outside the brain, is a promising target for drug developers. Unlike drugs that focus on satiety, those that target ghrelin could help curb appetite before dieters take their first bite.

(Photo: Rae Silver, Joseph LeSauter and Donald Pfaff)

Columbia University

TORNADO THREAT INCREASES AS GULF HURRICANES GET LARGER

0 comentarios

Tornadoes that occur from hurricanes moving inland from the Gulf Coast are increasing in frequency, according to researchers at the Georgia Institute of Technology. This increase seems to reflect the increase in size and frequency among large hurricanes that make landfall from the Gulf of Mexico. The findings can be found in Geophysical Research Letters online and in print in the September 3, 2009 issue.

“As the size of landfalling hurricanes from the Gulf of Mexico increases, we’re seeing more tornadoes than we did in the past that can occur up to two days and several hundred miles inland from the landfall location,” said James Belanger, doctoral student in the School of Earth and Atmospheric Sciences at Georgia Tech and lead author of the paper.

Currently, it’s well known that when hurricanes hit land, there’s a risk that tornadoes may form in the area. Until now, no one has quantified that risk because observations of tornadoes were too sporadic prior to the installation of the NEXRAD Doppler Radar Network in 1995. Belanger along with co-authors Judith Curry, professor and chair of the School of Earth and Atmospheric Sciences at Tech and research scientist Carlos Hoyos, decided to see if they could create a model using the more reliable tornado record that’s existed since 1995.

The model that they developed for hurricane-induced tornadoes uses four factors that serve as good predictors of tornado activity: size, intensity, track direction and whether there’s a strong gradient of moisture at midlevels in the storm's environment.

“The size of a tropical cyclone basically sets the domain over which tornadoes can form. So a larger storm that has more exposure over land has a higher propensity for producing tornadoes than a smaller one, on average,” said Belanger.

The team looked at 127 tropical cyclones from 1948 up to the 2008 hurricane season and went further back to 1920 modifying their model to account for the type of data collected at that time. They found that since 1995 there has been a 35 percent percent increase in the size of tropical cyclones from the Gulf compared to the previous active period of storms from 1948-1964, which has lead to a doubling in the number of tornadoes produced per storm. The number of hurricane-induced tornadoes during the 2004 and 2005 hurricane seasons is unprecedented in the historical record since 1920, according to the model.

“The beauty of the model is that not only can we use it to reconstruct the observational record, but we can also use it as a forecasting tool,” said Belanger.

To test how well it predicted the number of tornadoes associated with a given hurricane, they input the intensity of the storm at landfall, it’s size, track and moisture at mid-levels, and were able to generate a forecast of how many tornadoes formed from the hurricane. They found that for Hurricane Ike in 2008, their model predicted exactly the number of tornadoes that occurred, 33. For Hurricane Katrina in 2005, the model predicted 56 tornadoes, and 58 were observed.

The team’s next steps are to take a look to see how hurricane size, not just intensity (as indicated by the Safir-Simpson scale), affects the damage experienced by residents.

“Storm surge, rain and flooding are all connected to the size of the storm,” said Curry. “Yet, size is an underappreciated factor associated with damage from hurricanes. So it’s important to develop a better understanding of what controls hurricane size and how size influences hurricane damage. The great damage in Galveston from Hurricane Ike in 2008 was inconsistent with Category 2 wind speeds at landfall, but it was the large size that caused the big storm surge that did most of the damage.”

(Photo: NOAA)

Georgia Institute of Technology

SCIENTISTS DISCOVER NEW GENETIC VARIATION THAT CONTRIBUTES TO DIABETES

0 comentarios

Scientists have identified a genetic variation in people with type 2 diabetes that affects how the body's muscle cells respond to the hormone insulin, in a new study published in Nature Genetics. The researchers, from Imperial College London and other international institutions, say the findings highlight a new target for scientists developing treatments for diabetes.

Previous studies have identified several genetic variations in people with type 2 diabetes that affect how insulin is produced in the pancreas. Today's study shows for the first time a genetic variation that seems to impair the ability of the body's muscle cells to use insulin to help them make energy.

People with type 2 diabetes can have problems with the body not producing enough insulin and with cells in the muscles, liver and fat becoming resistant to it. Without sufficient insulin, or if cells cannot use insulin properly, cells are unable to take glucose from the blood and turn it into energy. Until now, scientists had not been able to identify the genetic factors contributing to insulin resistance in type 2 diabetes.

In the new research, scientists from international institutions including Imperial College London, McGill University, Canada, CNRS, France, and the University of Copenhagen, Denmark, looked for genetic markers in over 14,000 people and identified four variations associated with type 2 diabetes. One of these was located near a gene called IRS1, which makes a protein that tells the cell to start taking in glucose from the blood when it is activated by insulin. The researchers believe that the variant they have identified interrupts this process, impairing the cells' ability to make energy from glucose. The researchers hope that scientists will be able to target this process to produce new treatments for type 2 diabetes.

Professor Philippe Froguel, one of the corresponding authors of today's study from the Department of Genomic Medicine at Imperial College London, said: "We are very excited about these results - this is the first genetic evidence that a defect in the way insulin works in muscles can contribute to diabetes. Muscle tissue needs to make more energy using glucose than other tissues. We think developing a treatment for diabetes that improves the way insulin works in the muscle could really help people with type 2 diabetes.

"It is now clear that several drugs should be used together to control this disease. Our new study provides scientists developing treatments with a straightforward target for a new drug to treat type 2 diabetes," added Professor Froguel.

The researchers carried out a multistage association study to identify the new gene. First, they looked at genome-wide association data from 1,376 French individuals and identified 16,360 single-nucleotide polymorphisms (SNPs), or genetic variations, associated with type 2 diabetes. The researchers then studied these variations in 4,977 French individuals.

Next, the team selected the 28 most strongly associated SNPs and looked for them in 7,698 Danish individuals. Finally, the researchers identified four SNPs strongly associated with type 2 diabetes. The most significant of these variations was located near the insulin receptor substrate 1, or IRS1, gene.

To test their findings, the team analysed biopsies of skeletal muscle from Danish twins, one of whom had type 2 diabetes. They found that the twin with diabetes had the variation near IRS1 and this variation resulted in insulin resistance in the muscle. They also noted that the variation affected the amount of protein produced by the gene IRS1, suggesting that the SNP controls the IRS1 gene.

(Photo: ICL)

Imperial College London

NEW CLUES IN EASTER ISLAND HAT MYSTERY

0 comentarios

A team of archaeologists has come one step closer to unravelling the mystery of how the famous statues dotting the landscape of a tiny Pacific island acquired their distinctive red hats.

Dr Sue Hamilton from University College London and Dr Colin Richards from The University of Manchester are the first archaeologists ever to have excavated Easter Island’s statue hat quarry, known to the locals as 'Puna Pau'.

The discovery of a road and a ceremonial axe by the team, who are the first British archaeologists to work on the island since 1914, has thrown new light on the mystery.

At around 2,500 miles off the coast of Chile, the Island is the world’s most remote place inhabited by people.

“We now know that the hats were rolled along the road made from a cement of compressed red scoria dust with a raised pavement along one side,” said Dr Richards.

“It is likely that they were moved by hand but tree logs could also have been used,” he added.

Dr Hamilton said: “The hat quarry is inside the crater of an ancient volcano and on its outer lip. A third of the crater has been quarried away by hat production.

“So far we have located more than 70 hats at the ceremonial platforms and in transit. Many more may have been broken up and incorporated into the platforms.

“The mint condition of the obsidian adze - a seven inch long axe like tool used for squaring up logs or hollowing out timber, perhaps in canoe construction - suggests that it was not a quarry tool but an offering left by a worker.”

The team examined the way the hats, each weighing several tons and made of red scoria, a volcanic rock like pumice, were moved by Polynesians between 500 and 750 years ago.

They were placed on the heads of carved stone human figures known as moai which stand on ceremonial platforms which encircle the island's coastline. The way the hats were raised and attached is unknown.

The adze and the way the road is lined with hats along one side suggests, say the team, that the road was a ceremonial avenue leading to the quarry itself.

Dr Richards said: “It is clear that the quarry had a sacred context as well as an industrial one.

“The Polynesians saw the landscape as a living thing and after they carved the rock the spirits entered the statues.

“Initially, the Polynesians built the moai out of various types of local stone, including the Puna Pau scoria, but between 1200 to 1300 AD Puna Pau switched from producing statues to hats.

“The change correlated with an increase in the overall size of the statues across the island.”

Because of this long period of use, the team's investigations at Puna Pau provide evidence for the earliest monumentality in the Eastern Pacific.

Dr Hamilton said: “The quarry is in a secret place which is invisible from other parts of the island and the noise of production would have been contained by the crater.

“These people lived in a successful and well-organised society - the Easter Island of 500 years ago was a managed living environment.

“70 per cent of the island was transformed into open gardens and agriculture using a sophisticated stone mulching system to conserve moisture - we are mapping these plantation areas as part of our landscape survey.

“The presence of discrete quarry bays at Rano Raraku statue quarry meant that different - and possibly competing groups were likely to have their own areas of production in Puna Pau too,“ Dr Richards explained.

Dr Hamilton and Dr Richards are joint directors of the 'Rapa Nui (Easter Island) Landscapes of Construction Project'. They will be working on the Island over the next five years.

(Photo: U. Manchester)

University of Manchester

WHY BEING BIG LIKE AN ELEPHANT PUTS A SPRING IN YOUR STEP...

0 comentarios
Large, lumbering animals such as elephants move much more efficiently than small, agile ones such as mice, University of Manchester scientists have shown.

Dr Robert Nudds and colleagues Drs Jonathan Codd and Bill Sellers at the Faculty of Life Sciences have found that bigger animals move three and a half times more efficiently than smaller ones.

"The difference is down to having a more upright posture," says Dr Nudds.

"We believe the tendons in the legs of larger animals have better elastic storage than those in smaller ones. Tendons act as a spring. In larger animals such as an elephant, the tendons may be springier returning more energy into the next step, by pinging the leg off the floor.

"In addition efficiency doesn't increase continuously with body size. There is a step change between large animals such as elephants and small animals such as mice. This is down to their posture - elephants are 'uprights', while mice are 'crouchers'.

"Standing up straight does have an impact."

He and the team, whose results are published in PLoS ONE (Monday 7th September), analysed existing data to contribute to a larger study on animal locomotion. They compared efficiency values (the amount of movement achieved compared to metabolic energy consumed) across a range of body sizes. Instead of finding a steady increase in efficiency as animals got larger, they found a step-change, whereby all small animals are 7% efficient and all larger animals 26% efficient.

Humans, which are also upright walkers, also have an efficiency rating of around 26%.

While it was known that large animals moved more efficiently than smaller ones, the step change and the impact of posture was a revelation.

"The big difference is that posture rather than body size determines the efficiency of locomotion," says Dr Nudds, whose study was funded by the Leverhulme Trust. "So your mother was right when she told you to stand up straight and stop slouching!"

University of Manchester

Followers

Archive

 

Selected Science News. Copyright 2008 All Rights Reserved Revolution Two Church theme by Brian Gardner Converted into Blogger Template by Bloganol dot com