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Wednesday, December 12, 2012
Monday, December 10, 2012
Water, water everywhere, and Silas Mariner may have been right
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Public release date: 10-Dec-2012[ | E-mail |
Share ] Contact: Lynn Nystrom
tansy@vt.edu
540-231-4371
Virginia Tech
Eighty billion metric tons is an unfathomable amount to the human brain. Yet that number is the estimation of the global amount of sediment eroded on a yearly basis over the continental surface of the earth. An estimated 20 billion of these metric tons end up in the ocean water via rivers.
The action of water and wind is responsible for this massive redistribution of materials, leading to significant water pollution and a variety of ecological problems.
"This redistribution of material over the surface of the earth affects most of its physical, chemical, and biological processes in ways that are not well understood and which are exceedingly difficult to comprehend," Panos Diplas professor of civil and environmental engineering (CEE) at Virginia Tech, said.
Farmers familiar with the flow of a small stream on their property can tell you tales of when that seemingly innocent body of water reacts to heavy downpours and becomes two, three, or even 10 times its normal size. It can move culverts, change course, and wash away low-lying areas adjacent to the stream, including gravel roads. Agricultural run-off is a huge problem in farming.
Diplas has spent part of his career studying river mechanics, improving the understanding of erosion processes and sediment transport. His multiple research findings over more than two decades earned him the 2012 Hans Albert Einstein Award, a lifetime achievement award. He was also a member of a team that received the 2012 Karl Emil Hilgard Hydraulic Prize for the best paper, and both awards came from the American Society of Civil Engineers.
At Virginia Tech, Diplas directs the Kelso Baker Hydraulics Laboratory considered the best such facility in Virginia and the surrounding states. Civil engineering alumnus Kelso Baker of Sewickley, Pa., Class of 1951, provided the support to create this lab that enables researchers to study phenomena related to the movement of water, sediment, and pollutants through wetlands and waterways. The lab also provides the means for modeling the behavior of stream flow during floods, simulating ecological aspects of channel flows, and developing measures to control scour around bridge foundations and other structures.
The uniqueness of this university laboratory can provide Diplas and his colleagues a strong competitive advantage when applying for research project funding. For example, he currently is an investigator on several projects, including: two National Cooperative Highway Research program grants ($600,000 and $500,000 respectively); two National Science Foundation awards ($380,000 and $74,000 respectively); a $210,000 Defense University Research Instrumentation Program investigation; a $247,000 Army Research Office project; and a $258,000 Virginia Uranium, Inc. study. These projects support work on bridge foundation scour, design of in-stream structures, movement of contaminants through a riverine system, role of turbulent flow on particle movement, and dam decommissioning.
Why so many different types of grants? As Diplas explained, the impact of flow in such areas as streams, rivers, floodplains, and in the vicinity of infrastructure, such as bridge crossings, has broad-reaching implications. It can "influence the hydrosphere, the pedosphere (the outer most layer of the earth composed of soil), the biosphere, and the atmosphere in profound ways," he said.
An overview of Diplas' expertise that garnered him the Einstein Award can be found in a book chapter he authored with Clinton Dancey, a faculty member and collaborator from the mechanical engineering department. The book, Coherent Flow Structures at the Earth's Surface, to be published in 2013, contains their chapter "Initiation of motion, sediment transport, and morphological feedbacks in rivers."
In it, they wrote, "Determining the minimum, or critical, force necessary to dislodge a particle out of its pocket, arguably constitutes one of the most fundamental and elementary problems in mechanics, regardless of the type of movement. When it comes to flow-induced forces, identifying this critical condition has confounded scientists and engineers for several hundred years.
"The main culprit for this problem is the fluctuating nature of the applied fluid forces, due to the turbulent nature of the flow, while the resistance to particle movement remains the same."
Diplas pointed to "coherent flow structure characteristics typically encountered in turbulent flows which dominate natural phenomena" and how they impact particle entrainment in water. He believes that particle dislodging in waterways is due to more than just force magnitude. The duration of the applied hydrodynamic forces is "relevant in predicting grain removal from the channel bed surface," he wrote in his book chapter.
Also, in the article that won him the Hilgard Prize, Diplas argued that "flow and turbulence are more influenced by the vegetation density" than by other factors.
Vegetation in aquatic environments "considerably alters the turbulent flow in streams, rivers, and floodplains. The additional drag exerted by plants largely influencesthe transport of sediments" and dissolved substances, Diplas said. This research was already substantiated.
Diplas' new contribution in this area of study is the result of his large-eddy simulation studies of turbulent flow. He was able to show through analysis that flow and turbulence are more influenced by vegetation density than by the cylinder-based diameter Reynolds number. In fluid mechanics the Reynolds number is used to characterize different flow regimes. When forces resistant to change dominate turbulent flow, it is likely to create eddies, vortices, and other flow instabilities.
###
Diplas' work in this area was supported by the National Science Foundation and eventually led to a publication in an issue of Science in 2008, "Analysis of impulse events associated to entrainment of coarse particles." Several more publications have followed the Science article, and several more are currently in press. The book chapter provides a summary of this work. A less technical discussion will appear in the 2014 issue of the McGraw-Hill Yearbook of Science & Technology.
"Your recent work published in Science is amongst the most important contributions to the sediment entrainment literature since the pioneering work of A.J. Grass in the early 1970s," wrote the editors of the book, Coherent Flow Structures at the Earth's Surface, in their letter inviting Diplas to contribute a book chapter. This book is part of a series published every 15 years summarizing the most important developments in river mechanics and related phenomena.
[ | E-mail | Share ] ?
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
Public release date: 10-Dec-2012[ | E-mail |
Share ] Contact: Lynn Nystrom
tansy@vt.edu
540-231-4371
Virginia Tech
Eighty billion metric tons is an unfathomable amount to the human brain. Yet that number is the estimation of the global amount of sediment eroded on a yearly basis over the continental surface of the earth. An estimated 20 billion of these metric tons end up in the ocean water via rivers.
The action of water and wind is responsible for this massive redistribution of materials, leading to significant water pollution and a variety of ecological problems.
"This redistribution of material over the surface of the earth affects most of its physical, chemical, and biological processes in ways that are not well understood and which are exceedingly difficult to comprehend," Panos Diplas professor of civil and environmental engineering (CEE) at Virginia Tech, said.
Farmers familiar with the flow of a small stream on their property can tell you tales of when that seemingly innocent body of water reacts to heavy downpours and becomes two, three, or even 10 times its normal size. It can move culverts, change course, and wash away low-lying areas adjacent to the stream, including gravel roads. Agricultural run-off is a huge problem in farming.
Diplas has spent part of his career studying river mechanics, improving the understanding of erosion processes and sediment transport. His multiple research findings over more than two decades earned him the 2012 Hans Albert Einstein Award, a lifetime achievement award. He was also a member of a team that received the 2012 Karl Emil Hilgard Hydraulic Prize for the best paper, and both awards came from the American Society of Civil Engineers.
At Virginia Tech, Diplas directs the Kelso Baker Hydraulics Laboratory considered the best such facility in Virginia and the surrounding states. Civil engineering alumnus Kelso Baker of Sewickley, Pa., Class of 1951, provided the support to create this lab that enables researchers to study phenomena related to the movement of water, sediment, and pollutants through wetlands and waterways. The lab also provides the means for modeling the behavior of stream flow during floods, simulating ecological aspects of channel flows, and developing measures to control scour around bridge foundations and other structures.
The uniqueness of this university laboratory can provide Diplas and his colleagues a strong competitive advantage when applying for research project funding. For example, he currently is an investigator on several projects, including: two National Cooperative Highway Research program grants ($600,000 and $500,000 respectively); two National Science Foundation awards ($380,000 and $74,000 respectively); a $210,000 Defense University Research Instrumentation Program investigation; a $247,000 Army Research Office project; and a $258,000 Virginia Uranium, Inc. study. These projects support work on bridge foundation scour, design of in-stream structures, movement of contaminants through a riverine system, role of turbulent flow on particle movement, and dam decommissioning.
Why so many different types of grants? As Diplas explained, the impact of flow in such areas as streams, rivers, floodplains, and in the vicinity of infrastructure, such as bridge crossings, has broad-reaching implications. It can "influence the hydrosphere, the pedosphere (the outer most layer of the earth composed of soil), the biosphere, and the atmosphere in profound ways," he said.
An overview of Diplas' expertise that garnered him the Einstein Award can be found in a book chapter he authored with Clinton Dancey, a faculty member and collaborator from the mechanical engineering department. The book, Coherent Flow Structures at the Earth's Surface, to be published in 2013, contains their chapter "Initiation of motion, sediment transport, and morphological feedbacks in rivers."
In it, they wrote, "Determining the minimum, or critical, force necessary to dislodge a particle out of its pocket, arguably constitutes one of the most fundamental and elementary problems in mechanics, regardless of the type of movement. When it comes to flow-induced forces, identifying this critical condition has confounded scientists and engineers for several hundred years.
"The main culprit for this problem is the fluctuating nature of the applied fluid forces, due to the turbulent nature of the flow, while the resistance to particle movement remains the same."
Diplas pointed to "coherent flow structure characteristics typically encountered in turbulent flows which dominate natural phenomena" and how they impact particle entrainment in water. He believes that particle dislodging in waterways is due to more than just force magnitude. The duration of the applied hydrodynamic forces is "relevant in predicting grain removal from the channel bed surface," he wrote in his book chapter.
Also, in the article that won him the Hilgard Prize, Diplas argued that "flow and turbulence are more influenced by the vegetation density" than by other factors.
Vegetation in aquatic environments "considerably alters the turbulent flow in streams, rivers, and floodplains. The additional drag exerted by plants largely influencesthe transport of sediments" and dissolved substances, Diplas said. This research was already substantiated.
Diplas' new contribution in this area of study is the result of his large-eddy simulation studies of turbulent flow. He was able to show through analysis that flow and turbulence are more influenced by vegetation density than by the cylinder-based diameter Reynolds number. In fluid mechanics the Reynolds number is used to characterize different flow regimes. When forces resistant to change dominate turbulent flow, it is likely to create eddies, vortices, and other flow instabilities.
###
Diplas' work in this area was supported by the National Science Foundation and eventually led to a publication in an issue of Science in 2008, "Analysis of impulse events associated to entrainment of coarse particles." Several more publications have followed the Science article, and several more are currently in press. The book chapter provides a summary of this work. A less technical discussion will appear in the 2014 issue of the McGraw-Hill Yearbook of Science & Technology.
"Your recent work published in Science is amongst the most important contributions to the sediment entrainment literature since the pioneering work of A.J. Grass in the early 1970s," wrote the editors of the book, Coherent Flow Structures at the Earth's Surface, in their letter inviting Diplas to contribute a book chapter. This book is part of a series published every 15 years summarizing the most important developments in river mechanics and related phenomena.
[ | E-mail | Share ] ?
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
Source: http://www.eurekalert.org/pub_releases/2012-12/vt-wwe121012.php
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Sunday, December 9, 2012
Why In The World Should Instagram Allow Twitter ... - Business Insider
YouTube/kevinrose
Let me get this straight. All Instagram has is photos. And you want me to give them to you for?free?
?
It used to be that when an Instagram user took a photo and then shared it with Twitter, that photo would show up in the Twitter user's tweet on Twitter.com and Twitter's various apps.Then, last week, Instagram crippled this feature, only allowing Twitter to display cropped photos.
Today, Instagram seems to have turned this feature off.?
(Intagram users can still share their photos to Twitter, but now other users have to click a link in a tweet to see the photo.)
Some users are whining about the change.
TechCrunch's Michael Arrington's post on the topic is headlined: "They Screwed Us. Right Before They Screwed Us Again.?#poohead."
But why in the world should Instagram allow Twitter to scrape its photos?
Imagine if the New York Times were to allow Twitter to scrape its entire articles and republish them in Twitter apps.?
That'd be nuts!
The only way the Times would do it is if Twitter were paying it.
That's how cable works, after all.
To get ESPN channels on its distribution platforms, Time Warner Cable pays Disney?$4.69 per cable subscriber, per month.
Maybe what we're witnessing in this fight between Twitter and Instagram is a first step toward that kind of cable model.
Perhaps big, beloved Web brands like YouTube, the Times, and Instagram will eventually agree to share all of their content inside tweets in Twitter apps for small, per user carriage fees.
Of course, Twitter will only be able to pay content brands like YouTube, the Times, and Instagram if it is making money itself.
So far it's not. Not really. (A few hundred million dollars in revenue.)
So, maybe what Twitter will eventually do is turn around and charge the Internet Service Providers (AT&T/Verizon/Time Warner) its?own carriage fee.?
And then that fee would get passed onto users in a big bundled package.?
Just like cable. Which everyone ALSO loves to whine about. (Even?though they keep paying $150/month for it.)
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Saturday, December 8, 2012
Five questions that will be answered by UFC on Fox 5
The UFC's fifth appearance on Fox goes down on Saturday night, with one of the more stacked cards to air on the network since. What will come from the card? Read on.
Who will walk away with the lightweight belt? The biggest question of the evening goes to the main event. Benson Henderson will have the chance to show off his skills against someone other than Frankie Edgar. Diaz thinks he can't win a judges' decision, so will he be able to stop Henderson, who hasn't loss by a stoppage since 2007? Or will Henderson hold onto the championship?
Is this B.J. Penn's last stand? Penn is a legend in the UFC. His first fight was was in 2001 at UFC 31. He even dabbled with retirement until young buck Rory MacDonald called him out. Will Penn be able to stop the 13-1 MacDonald, or will the young fighter's star continue to rise?
Who will fight for the UFC light heavyweight belt after Chael Sonnen? Jon Jones is scheduled to put his championship on the line against Sonnen in April, after their season of "The Ultimate Fighter" airs. The bout between Maurico "Shogun" Rua and Alexander Gustaffson will decide who fights for the belt after Sonnen.
Will the next bantamweight star stand up? Men's bantamweight champion Dominick Cruz will be on the shelf for a while because of a reinjury to his knee. Renan Barao will put his interim title up against Michael McDonald. The next challenger may show himself on Saturday during Mike Easton vs. Raphael Assuncao.
Will fans tune in extra early on a Saturday afternoon? The Facebook prelims for UFC on Fox start at 4:20 p.m. ET. Prelims on FX (a change from when Fuel aired Fox prelims) are at 5 p.m. ET. The early start time is due to the Fox broadcast, which is expected to end in time for the 11 p.m. local news. It's a Saturday during the Christmas shopping season. Will it affect how many fans tune in for the early fights?
Want to make predictions for Saturday night? Do it in the comments, on Facebook or Twitter.
Source: http://sports.yahoo.com/blogs/mma-cagewriter/five-questions-answered-ufc-fox-5-164929730--mma.html
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Friday, December 7, 2012
Boehner says Obama pushing country toward 'fiscal cliff'
WASHINGTON (Reuters) - Republican House Speaker John Boehner accused President Barack Obama of pushing the country toward the "fiscal cliff" Friday and of wasting another week without progress in talks.
With three weeks left before a combination of steep tax hikes and spending cuts kicks in unless Congress intervenes, Boehner said the administration had adopted a "my way or the highway" approach and was engaging in "reckless talk" about going over the cliff.
"This isn't a progress report because there is no progress to report," Boehner told reporters at the Capitol. "The president has adopted a deliberate strategy to slow walk our economy right to the edge of the fiscal cliff."
Obama has insisted that tax cuts set to expire on December 31 be extended for middle-class taxpayers, but not for the wealthiest Americans. Boehner and Republicans oppose his plan to raise tax rates for the wealthiest 2 percent of Americans, preferring to find new revenues by closing loopholes and reducing deductions.
Boehner characterized as "reckless talk" Treasury Secretary Tim Geithner's comment this week that the administration was prepared to go over the cliff if tax rates for the rich were not increased.
The downbeat assessment was in line with what Boehner has offered for weeks as the two sides hold their ground on Obama's call for raising tax rates and Republican calls for cuts in entitlements like the Medicare and Medicaid healthcare programs for the elderly and the poor.
Capitol Hill aides said the budget talks would be limited to Boehner and Obama and their staffs as the deadline approached, but Boehner said a telephone call between two on Wednesday and renewed staff talks on Thursday had not made progress.
"The phone call was pleasant, but it was just more of the same. Even the conversations the staff had yesterday were just more of the same. It's time for the president, if he's serious, to come back to us with a counter-offer," Boehner said.
Boehner and the House of Representatives leadership submitted their terms for a deal in a letter to the White House December 3.
Both sides have submitted plans that would cut deficits by more than $4 trillion over the next 10 years, but differ on how to achieve them. Republicans want drastically more spending cuts in entitlement programs, while Obama wants more in tax increases and more spending to boost the sluggish economy.
Boehner will have a challenge selling whatever agreement he might reach to conservative Tea Party sympathizers in the House, some of whom are openly critical of the concessions the speaker has already made, particularly his openness to revenue increases of any kind.
But with polling showing Americans will blame Republicans if the country goes off the "cliff," more House Republicans have been urging Boehner to get an agreement quickly, even if it means tax hikes for the wealthy.
Once the question of whether to raise tax rates is resolved, the two sides will try figure out a way to deal with the spending cuts, perhaps postponing or trimming them. They will also work toward a longer-term deficit-reduction package to be taken up after the new Congress is sworn in next month.
"It's going to require both leaders," Obama senior adviser David Axelrod told MSNBC. "Each is going to have to make sacrifices in order to get this done. I think everybody recognizes the consequences of not getting it done."
Senate Majority Leader Harry Reid and House Minority Leader Nancy Pelosi are "being kept in the loop," said an aide close to both Democratic leaders, ready to work out any details.
(Additional reporting by Susan Heavey, Rachelle Younglai, David Lawder and Richard Cowan; Writing by John Whitesides; Editing by Doina Chiacu)
Source: http://news.yahoo.com/fiscal-cliff-talks-down-obama-republican-boehner-143346673--business.html
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Thursday, December 6, 2012
They Screwed Us. Right Before They Screwed Us Again. #poohead
We just got screwed. More on this below. Nobody says “Web 2.0” anymore. The term just didn’t stand the test of time, long ago it became cliched. But a handful of years ago it had real meaning to a lot of us. It encompassed a lot of ideas, but chief among them was the notion of mashed up web services, all collaborating via APIs. Whether a service had robust APIs to allow it to collide in unexpected ways with other services was very important. Services that left out APIs, for whatever reason, were flawed. And, importantly, services at least paid lip service to the idea that data was “ours,” not “theirs,” and would be treated accordingly. So that was a really nice fantasy that lasted for a long while. But what happens in the real world is companies grow up, hire grown ups and they sit in board meetings and they fret about barriers to entry in their respective markets. And they forget about users. They all do it. Facebook screwed us (disclosure, CrunchFund owns Facebook stock). Twitter screwed us repeatedly, and comes back regularly for more (see Dave Winer’s wild ramblings over the years that all seem to come true) (disclosure, CrunchFund owns Twitter stock). And now Instagram (owned by Facebook, so see disclosure above) is screwing us. Case in point, this piece of art that I created, called Poohead, will no longer display properly on Twitter. I have to live with a flawed reproduction of the original artwork, cropped incompetently and the magic is just lost. Mostly people are saying it’s ok that Instagram is screwing us by removing our ability to properly share our pictures on Twitter. Because Twitter screwed Instagram multiple times in the recent past. Twitter, of course, only screwed Instagram because Instagram screwed Twitter right before Twitter screwed them. Because Instagram decided that they’d rather be acquired by Facebook instead of Twitter. Screw that, thought Twitter. We used to love Instagram, particularly during the time while we were trying to buy Instagram. But then we didn’t buy them and so, obviously, we now hate Instagram. We’re gonna screw them and bad. So that’s all clear now. But there are lots of civilian casualties in all this screwing. Those civilians being us users, the dopes that keep feeding these companies content in the vain hope that this time we won’t get screwed. Because these companies
Source: http://feedproxy.google.com/~r/Techcrunch/~3/zP9glp25trk/
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Wednesday, December 5, 2012
New '4-D' transistor is preview of future computers
Public release date: 5-Dec-2012[ | E-mail |
Share ] Contact: Emil Venere
venere@purdue.edu
765-494-4709
Purdue University
WEST LAFAYETTE, Ind. A new type of transistor shaped like a Christmas tree has arrived just in time for the holidays, but the prototype won't be nestled under the tree along with the other gifts.
"It's a preview of things to come in the semiconductor industry," said Peide "Peter" Ye, a professor of electrical and computer engineering at Purdue University. Researchers from Purdue and Harvard universities created the transistor, which is made from a material that could replace silicon within a decade. Each transistor contains three tiny nanowires made not of silicon, like conventional transistors, but from a material called indium-gallium-arsenide. The three nanowires are progressively smaller, yielding a tapered cross section resembling a Christmas tree.
The research builds on previous work in which the team created a 3-D structure instead of conventional flat transistors. The approach could enable engineers to build faster, more compact and efficient integrated circuits and lighter laptops that generate less heat than today's. New findings show how to improve the device performance by linking the transistors vertically in parallel.
"A one-story house can hold so many people, but more floors, more people, and it's the same thing with transistors," Ye said. "Stacking them results in more current and much faster operation for high-speed computing. This adds a whole new dimension, so I call them 4-D."
Findings will be detailed in two papers to be presented during the International Electron Devices Meeting on Dec. 8-12 in San Francisco. One of the papers has been highlighted by conference organizers as among "the most newsworthy topics and papers to be presented."
The work is led by Purdue doctoral student Jiangjiang Gu and Harvard postdoctoral researcher Xinwei Wang.
The newest generation of silicon computer chips, introduced this year, contain transistors having a vertical 3-D structure instead of a conventional flat design. However, because silicon has a limited "electron mobility" - how fast electrons flow - other materials will likely be needed soon to continue advancing transistors with this 3-D approach, Ye said.
Indium-gallium-arsenide is among several promising semiconductors being studied to replace silicon. Such semiconductors are called III-V materials because they combine elements from the third and fifth groups of the periodic table.
The authors of the research papers are Gu; Wang; Purdue doctoral student H. Wu; Purdue postdoctoral research associate J. Shao; Purdue doctoral student A. T. Neal; Michael J. Manfra, Purdue's William F. and Patty J. Miller Associate Professor of Physics; Roy Gordon, Harvard's Thomas D. Cabot Professor of Chemistry; and Ye.
Transistors contain critical components called gates, which enable the devices to switch on and off and to direct the flow of electrical current. Smaller gates make faster operation possible. In today's 3-D silicon transistors, the length of these gates is about 22 nanometers, or billionths of a meter.
The 3-D design is critical because gate lengths of 22 nanometers and smaller do not work well in a flat transistor architecture. Engineers are working to develop transistors that use even smaller gate lengths; 14 nanometers are expected by 2015, and 10 nanometers by 2018.
However, size reductions beyond 10 nanometers and additional performance improvements are likely not possible using silicon, meaning new materials will be needed to continue progress, Ye said.
Creating smaller transistors also will require finding a new type of insulating, or "dielectric" layer that allows the gate to switch off. As gate lengths shrink smaller than 14 nanometers, the dielectric used in conventional transistors fails to perform properly and is said to "leak" electrical charge when the transistor is turned off.
Nanowires in the new transistors are coated with a different type of composite insulator, a 4-nanometer-thick layer of lanthanum aluminate with an ultrathin, half-nanometer layer of aluminum oxide. The new ultrathin dielectric allowed researchers to create transistors made of indium-gallium- arsenide with 20-nanometer gates, which is a milestone, Ye said.
###
The work, based at the Birck Nanotechnology Center in Purdue's Discovery Park, is funded by the National Science Foundation and the Semiconductor Research Corp.
Writer: Emil Venere, 765-494-4709, venere@purdue.edu
Source: Peide Ye, 765-494-7611, yep@purdue.edu
Related websites:
Peide Ye: http://cobweb.ecn.purdue.edu/~yep/
International Electron Devices Meeting: http://www.his.com/~iedm/
Birck Nanotechnology Center: http://www.purdue.edu/discoverypark/nanotechnology/
[ | E-mail | Share ] ?
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
Public release date: 5-Dec-2012[ | E-mail |
Share ] Contact: Emil Venere
venere@purdue.edu
765-494-4709
Purdue University
WEST LAFAYETTE, Ind. A new type of transistor shaped like a Christmas tree has arrived just in time for the holidays, but the prototype won't be nestled under the tree along with the other gifts.
"It's a preview of things to come in the semiconductor industry," said Peide "Peter" Ye, a professor of electrical and computer engineering at Purdue University. Researchers from Purdue and Harvard universities created the transistor, which is made from a material that could replace silicon within a decade. Each transistor contains three tiny nanowires made not of silicon, like conventional transistors, but from a material called indium-gallium-arsenide. The three nanowires are progressively smaller, yielding a tapered cross section resembling a Christmas tree.
The research builds on previous work in which the team created a 3-D structure instead of conventional flat transistors. The approach could enable engineers to build faster, more compact and efficient integrated circuits and lighter laptops that generate less heat than today's. New findings show how to improve the device performance by linking the transistors vertically in parallel.
"A one-story house can hold so many people, but more floors, more people, and it's the same thing with transistors," Ye said. "Stacking them results in more current and much faster operation for high-speed computing. This adds a whole new dimension, so I call them 4-D."
Findings will be detailed in two papers to be presented during the International Electron Devices Meeting on Dec. 8-12 in San Francisco. One of the papers has been highlighted by conference organizers as among "the most newsworthy topics and papers to be presented."
The work is led by Purdue doctoral student Jiangjiang Gu and Harvard postdoctoral researcher Xinwei Wang.
The newest generation of silicon computer chips, introduced this year, contain transistors having a vertical 3-D structure instead of a conventional flat design. However, because silicon has a limited "electron mobility" - how fast electrons flow - other materials will likely be needed soon to continue advancing transistors with this 3-D approach, Ye said.
Indium-gallium-arsenide is among several promising semiconductors being studied to replace silicon. Such semiconductors are called III-V materials because they combine elements from the third and fifth groups of the periodic table.
The authors of the research papers are Gu; Wang; Purdue doctoral student H. Wu; Purdue postdoctoral research associate J. Shao; Purdue doctoral student A. T. Neal; Michael J. Manfra, Purdue's William F. and Patty J. Miller Associate Professor of Physics; Roy Gordon, Harvard's Thomas D. Cabot Professor of Chemistry; and Ye.
Transistors contain critical components called gates, which enable the devices to switch on and off and to direct the flow of electrical current. Smaller gates make faster operation possible. In today's 3-D silicon transistors, the length of these gates is about 22 nanometers, or billionths of a meter.
The 3-D design is critical because gate lengths of 22 nanometers and smaller do not work well in a flat transistor architecture. Engineers are working to develop transistors that use even smaller gate lengths; 14 nanometers are expected by 2015, and 10 nanometers by 2018.
However, size reductions beyond 10 nanometers and additional performance improvements are likely not possible using silicon, meaning new materials will be needed to continue progress, Ye said.
Creating smaller transistors also will require finding a new type of insulating, or "dielectric" layer that allows the gate to switch off. As gate lengths shrink smaller than 14 nanometers, the dielectric used in conventional transistors fails to perform properly and is said to "leak" electrical charge when the transistor is turned off.
Nanowires in the new transistors are coated with a different type of composite insulator, a 4-nanometer-thick layer of lanthanum aluminate with an ultrathin, half-nanometer layer of aluminum oxide. The new ultrathin dielectric allowed researchers to create transistors made of indium-gallium- arsenide with 20-nanometer gates, which is a milestone, Ye said.
###
The work, based at the Birck Nanotechnology Center in Purdue's Discovery Park, is funded by the National Science Foundation and the Semiconductor Research Corp.
Writer: Emil Venere, 765-494-4709, venere@purdue.edu
Source: Peide Ye, 765-494-7611, yep@purdue.edu
Related websites:
Peide Ye: http://cobweb.ecn.purdue.edu/~yep/
International Electron Devices Meeting: http://www.his.com/~iedm/
Birck Nanotechnology Center: http://www.purdue.edu/discoverypark/nanotechnology/
[ | E-mail | Share ] ?
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
Source: http://www.eurekalert.org/pub_releases/2012-12/pu-nt120512.php
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