New method for enhancing thermal conductivity could cool computer chips, lasers and other devices

ScienceDaily (Dec. 14, 2011) — The surprising discovery of a new way to tune and enhance thermal conductivity -- a basic property generally considered to be fixed for a given material -- gives engineers a new tool for managing thermal effects in smart phones and computers, lasers and a number of other powered devices.

The finding was made by a group of engineers headed by Deyu Li, associate professor of mechanical engineering at Vanderbilt University, and published online in the journal Nature Nanotechnology on Dec. 11.

Li and his collaborators discovered that the thermal conductivity of a pair of thin strips of material called boron nanoribbons can be enhanced by up to 45 percent depending on the process that they used to stick the two ribbons together. Although the research was conducted with boron nanoribbons, the results are generally applicable to other thin film materials.

An entirely new way to control thermal effects

"This points at an entirely new way to control thermal effects that is likely to have a significant impact in microelectronics on the design of smart phones and computers, in optoelectronics on the design of lasers and LEDs, and in a number of other fields," said Greg Walker, associate professor of mechanical engineering at Vanderbilt and an expert in thermal transport who was not directly involved in the research.

According to Li, the force that holds the two nanoribbons together is a weak electrostatic attraction called the van der Waals force. (This is the same force that allows the gecko to walk up walls.)

"Traditionally, it is widely believed that the phonons that carry heat are scattered at van der Waals interfaces, which makes the ribbon bundles' thermal conductivity the same as that of each ribbon. What we discovered is in sharp contrast to this classical view. We show that phonons can cross these interfaces without being scattered, which significantly enhances the thermal conductivity," said Li. In addition, the researchers found that they could control the thermal conductivity between a high and a low value by treating the interface of the nanoribbon pairs with different solutions.

The enhancement is completely reversible

One of the remarkable aspects of the effect Li discovered is that it is reversible. For example, when the researchers wetted the interface of a pair of nanoribbons with isopropyl alcohol, pressed them together and let them dry, the thermal conductivity was the same as that of a single nanoribbon. However, when they wetted them with pure alcohol and let them dry, the thermal conductivity was enhanced. Then, when they wetted them with isopropyl alcohol again, the thermal conductivity dropped back to the original low value.

"It is very difficult to tune a fundamental materials property such as thermal conductivity and the demonstrated tunable thermal conductivity makes the research especially interesting," Walker said.

One of the first areas where this new knowledge is likely to be applied is in thermal management of microelectronic devices like computer chips. Today, billions to trillions of transistors are jammed into chips the size of a fingernail. These chips generate so much heat that one of the major factors in their design is to prevent overheating. In fact, heat management is one of the major reasons behind today's multi-core processor designs.

"A better understanding of thermal transport across interfaces is the key to achieving better thermal management of microelectronic devices," Li said.

Discovery may improve design of nanocomposites

Another area where the finding will be important is in the design of "nanocomposites" -- materials made by embedding nanostructure additives such as carbon nanotubes to a host material such as various polymers -- that are being developed for use in flexible electronic devices, structural materials for aerospace vehicles and a variety of other applications.

Collaborators on the study were post-doctoral research associate Juekan Yang, graduate students Yang Yang and Scott Waltermire from Vanderbilt; graduate students Xiaoxia Wu and Youfei Jiang, post-doctoral research associate Timothy Gutu, research assistant professor Haitao Zhang, and Associate Professor Terry T. Xu from the University of North Carolina; Professor Yunfei Chen from the Southeast University in China; Alfred A. Zinn from Lockheed Martin Space Systems Company; and Ravi Prasher from the U.S. Department of Energy.

The research was performed with financial support from the National Science Foundation, Lockheed Martin's Engineering and Technology University Research Initiatives program and the Office of Naval Research.

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The above story is reprinted from materials provided by Vanderbilt University. The original article was written by David Salisbury.

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Journal Reference:

Juekuan Yang, Yang Yang, Scott W. Waltermire, Xiaoxia Wu, Haitao Zhang, Timothy Gutu, Youfei Jiang, Yunfei Chen, Alfred A. Zinn, Ravi Prasher, Terry T. Xu, Deyu Li. Enhanced and switchable nanoscale thermal conduction due to van der Waals interfaces. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.216

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New method for enhancing thermal conductivity could cool computer chips, lasers and other devices

ScienceDaily (Dec. 14, 2011) — The surprising discovery of a new way to tune and enhance thermal conductivity -- a basic property generally considered to be fixed for a given material -- gives engineers a new tool for managing thermal effects in smart phones and computers, lasers and a number of other powered devices.

The finding was made by a group of engineers headed by Deyu Li, associate professor of mechanical engineering at Vanderbilt University, and published online in the journal Nature Nanotechnology on Dec. 11.

Li and his collaborators discovered that the thermal conductivity of a pair of thin strips of material called boron nanoribbons can be enhanced by up to 45 percent depending on the process that they used to stick the two ribbons together. Although the research was conducted with boron nanoribbons, the results are generally applicable to other thin film materials.

An entirely new way to control thermal effects

"This points at an entirely new way to control thermal effects that is likely to have a significant impact in microelectronics on the design of smart phones and computers, in optoelectronics on the design of lasers and LEDs, and in a number of other fields," said Greg Walker, associate professor of mechanical engineering at Vanderbilt and an expert in thermal transport who was not directly involved in the research.

According to Li, the force that holds the two nanoribbons together is a weak electrostatic attraction called the van der Waals force. (This is the same force that allows the gecko to walk up walls.)

"Traditionally, it is widely believed that the phonons that carry heat are scattered at van der Waals interfaces, which makes the ribbon bundles' thermal conductivity the same as that of each ribbon. What we discovered is in sharp contrast to this classical view. We show that phonons can cross these interfaces without being scattered, which significantly enhances the thermal conductivity," said Li. In addition, the researchers found that they could control the thermal conductivity between a high and a low value by treating the interface of the nanoribbon pairs with different solutions.

The enhancement is completely reversible

One of the remarkable aspects of the effect Li discovered is that it is reversible. For example, when the researchers wetted the interface of a pair of nanoribbons with isopropyl alcohol, pressed them together and let them dry, the thermal conductivity was the same as that of a single nanoribbon. However, when they wetted them with pure alcohol and let them dry, the thermal conductivity was enhanced. Then, when they wetted them with isopropyl alcohol again, the thermal conductivity dropped back to the original low value.

"It is very difficult to tune a fundamental materials property such as thermal conductivity and the demonstrated tunable thermal conductivity makes the research especially interesting," Walker said.

One of the first areas where this new knowledge is likely to be applied is in thermal management of microelectronic devices like computer chips. Today, billions to trillions of transistors are jammed into chips the size of a fingernail. These chips generate so much heat that one of the major factors in their design is to prevent overheating. In fact, heat management is one of the major reasons behind today's multi-core processor designs.

"A better understanding of thermal transport across interfaces is the key to achieving better thermal management of microelectronic devices," Li said.

Discovery may improve design of nanocomposites

Another area where the finding will be important is in the design of "nanocomposites" -- materials made by embedding nanostructure additives such as carbon nanotubes to a host material such as various polymers -- that are being developed for use in flexible electronic devices, structural materials for aerospace vehicles and a variety of other applications.

Collaborators on the study were post-doctoral research associate Juekan Yang, graduate students Yang Yang and Scott Waltermire from Vanderbilt; graduate students Xiaoxia Wu and Youfei Jiang, post-doctoral research associate Timothy Gutu, research assistant professor Haitao Zhang, and Associate Professor Terry T. Xu from the University of North Carolina; Professor Yunfei Chen from the Southeast University in China; Alfred A. Zinn from Lockheed Martin Space Systems Company; and Ravi Prasher from the U.S. Department of Energy.

The research was performed with financial support from the National Science Foundation, Lockheed Martin's Engineering and Technology University Research Initiatives program and the Office of Naval Research.

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The above story is reprinted from materials provided by Vanderbilt University. The original article was written by David Salisbury.

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

Journal Reference:

Juekuan Yang, Yang Yang, Scott W. Waltermire, Xiaoxia Wu, Haitao Zhang, Timothy Gutu, Youfei Jiang, Yunfei Chen, Alfred A. Zinn, Ravi Prasher, Terry T. Xu, Deyu Li. Enhanced and switchable nanoscale thermal conduction due to van der Waals interfaces. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.216

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Physicists move one step closer to quantum computer

ScienceDaily (Oct. 4, 2011) — Rice University physicists have created a tiny "electron superhighway" that could one day be useful for building a quantum computer, a new type of computer that will use quantum particles in place of the digital transistors found in today's microchips.

In a recent paper in Physical Review Letters, Rice physicists Rui-Rui Du and Ivan Knez describe a new method for making a tiny device called a "quantum spin Hall topological insulator." The device, which acts as an electron superhighway, is one of the building blocks needed to create quantum particles that store and manipulate data.

Today's computers use binary bits of data that are either ones or zeros. Quantum computers would use quantum bits, or "qubits," which can be both ones and zeros at the same time, thanks to the quirks of quantum mechanics.

This quirk gives quantum computers a huge edge in performing particular types of calculations, said Du, professor of physics and astronomy at Rice. For example, intense computing tasks like code-breaking, climate modeling and biomedical simulation could be completed thousands of times faster with quantum computers.

"In principle, we don't need many qubits to create a powerful computer," he said. "In terms of information density, a silicon microprocessor with 1 billion transistors would be roughly equal to a quantum processor with 30 qubits."

In the race to build quantum computers, researchers are taking a number of approaches to creating qubits. Regardless of the approach, a common problem is making certain that information encoded into qubits isn't lost over time due to quantum fluctuations. This is known as "fault tolerance."

The approach Du and Knez are following is called "topological quantum computing." Topological designs are expected to be more fault-tolerant than other types of quantum computers because each qubit in a topological quantum computer will be made from a pair of quantum particles that have a virtually immutable shared identity. The catch to the topological approach is that physicists have yet to create or observe one of these stable pairs of particles, which are called "Majorana fermions" (pronounced MAH-yor-ah-na FUR-mee-ons).

The elusive Majorana fermions were first proposed in 1937, although the race to create them in a chip has just begun. In particular, physicists believe the particles can be made by marrying a two-dimensional topological insulator -- like the one created by Du and Knez -- to a superconductor.

Topological insulators are oddities; although electricity cannot flow through them, it can flow around their narrow outer edges. If a small square of a topological insulator is attached to a superconductor, Knez said, the elusive Majorana fermions are expected to appear precisely where the materials meet. If this proves true, the devices could potentially be used to generate qubits for quantum computing, he said.

Knez spent more than a year refining the techniques to create Rice's topological insulator. The device is made from a commercial-grade semiconductor that's commonly used in making night-vision goggles. Du said it is the first 2-D topological insulator made from a material that physicists already know how to attach to a superconductor.

"We are well-positioned for the next step," Du said. "Meanwhile, only experiments can tell whether we can find Majorana fermions and whether they are good candidates for creating stable qubits."

The research was funded by the National Science Foundation, Rice University, the Hackerman Advanced Research Program, the Welch Foundation and the Keck Foundation.

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Journal Reference:

Ivan Knez, Rui-Rui Du, Gerard Sullivan. Evidence for Helical Edge Modes in Inverted InAs/GaSb Quantum Wells. Physical Review Letters, 2011; 107 (13) DOI: 10.1103/PhysRevLett.107.136603

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New material can enhance energy, computer, lighting technologies

ScienceDaily (Nov. 16, 2011) — Arizona State University researchers have created a new compound crystal material that promises to help produce advances in a range of scientific and technological pursuits.

ASU electrical engineering professor Cun-Zheng Ning says the material, called erbium chloride silicate, can be used to develop the next generations of computers, improve the capabilities of the Internet, increase the efficiency of silicon-based photovoltaic cells to convert sunlight into electrical energy, and enhance the quality of solid-state lighting and sensor technology.

Ning's research team of team of students and post-doctoral degree assistants help synthesize the new compound in ASU's Nanophotonics Lab in the School of Electrical, Computer and Energy Engineering, one of the university's Ira A. Fulton Schools of Engineering.

The lab's erbium research is supported by the U.S. Army Research Office and U.S. Air Force Office of Scientific Research. Details about the new compound are reported in the Optical Materials Express on the website of the Optical Society of America.

The breakthrough involves the first-ever synthesis of a new erbium compound in the form of a single-crystal nanowire, which has superior properties compared to erbium compounds in other forms.

Erbium is one of the most important members of the rare earth family in the periodic table of chemical elements. It emits photons in the wavelength range of 1.5 micrometers, which are used in the optical fibers essential to high-quality performance of the Internet and telephones.

Erbium is used in doping optical fibers to amplify the signal of the Internet and telephones in telecommunications systems. Doping is the term used to describe the process of inserting low concentrations of various elements into other substances as a way to alter the electrical or optical properties of the substances to produce desired results. The elements used in such processes are referred to as dopants.

"Since we could not dope as many erbium atoms in a fiber as we wish, fibers had to be very long to be useful for amplifying an Internet signal. This makes integrating Internet communications and computing on a chip very difficult," Ning explains.

"With the new erbium compound, 1,000 times more erbium atoms are contained in the compound. This means many devices can be integrated into a chip-scale system," he says. "Thus the new compound materials containing erbium can be integrated with silicon to combine computing and communication functionalities on the same inexpensive silicon platform to increase the speed of computing and Internet operation at the same time."

Erbium materials can also be used to increase the energy-conversion efficiency of silicon solar cells.

Silicon does not absorb solar radiation with wavelengths longer than 1.1 microns, which results in waste of energy -- making solar cells less efficient.

Erbium materials can remedy the situation by converting two or more photons carrying small amounts of energy into one photon that is carrying a larger amount of energy. The single, more powerful photon can then be absorbed by silicon, thus increasing the efficiency of solar cells.

Erbium materials also help absorb ultraviolet light from the sun and convert it into photons carrying small amounts of energy, which can then be more efficiently converted into electricity by silicon cells. This color-conversion function of turning ultraviolet light into other visible colors of light is also important in generating white light for solid-state lighting devices.

While erbium's importance is well-recognized, producing erbium materials of high quality has been challenging, Ning says.

The standard approach is to introduce erbium as a dopant into various host materials, such as silicon oxide, silicon, and many other crystals and glasses.

"One big problem has been that we have not been able to introduce enough erbium atoms into crystals and glasses without degrading optical quality, because too many of these kinds of dopants would cluster, which lowers the optical quality," he says.

What is unique about the new erbium material synthesized by Ning's group is that erbium is no longer randomly introduced as a dopant. Instead, erbium is part of a uniform compound and the number of erbium atoms is a factor of 1,000 more than the maximum amount that can be introduced in other erbium-doped materials.

Increasing the number of erbium atoms provides more optical activity to produce stronger lighting. It also enhances the conversion of different colors of light into white light to produce higher-quality solid-state lighting and enables solar cells to more efficiently convert sunlight in electrical energy.

In addition, since erbium atoms are organized in a periodic array, they do not cluster in this new compound. The fact that the material has been produced in a high-quality single-crystal form makes the optical quality superior to the other doped materials, Ning says.

Like many scientific discoveries, the synthesis of this new erbium material was made somewhat by accident.

"Similar to what other researchers are doing, we were originally trying to dope erbium into silicon nanowires. But the characteristics demonstrated by the material surprised us," he says. "We got a new material. We did not know what it was, and there was no published document that described it. It took us more than a year to finally realize we got a new single-crystal material no one else had produced."

Ning and his team are now trying to use the new erbium compound for various applications, such as increasing silicon solar cell efficiency and making miniaturized optical amplifiers for chip-scale photonic systems for computers and high-speed Internet.

"Most importantly," he says, "there are many things we have yet to learn about what can be achieved with use of the material. Our preliminary studies of its characteristics show it has many amazing properties and superior optical quality. More exciting discoveries are waiting to be made."

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Mimicking the brain -- in silicon: New computer chip models how neurons communicate with each other at synapses

ScienceDaily (Nov. 15, 2011) — For decades, scientists have dreamed of building computer systems that could replicate the human brain's talent for learning new tasks.

MIT researchers have now taken a major step toward that goal by designing a computer chip that mimics how the brain's neurons adapt in response to new information. This phenomenon, known as plasticity, is believed to underlie many brain functions, including learning and memory.

With about 400 transistors, the silicon chip can simulate the activity of a single brain synapse -- a connection between two neurons that allows information to flow from one to the other. The researchers anticipate this chip will help neuroscientists learn much more about how the brain works, and could also be used in neural prosthetic devices such as artificial retinas, says Chi-Sang Poon, a principal research scientist in the Harvard-MIT Division of Health Sciences and Technology.

Poon is the senior author of a paper describing the chip in the Proceedings of the National Academy of Sciences the week of Nov. 14. Guy Rachmuth, a former postdoc in Poon's lab, is lead author of the paper. Other authors are Mark Bear, the Picower Professor of Neuroscience at MIT, and Harel Shouval of the University of Texas Medical School.

Modeling synapses

There are about 100 billion neurons in the brain, each of which forms synapses with many other neurons. A synapse is the gap between two neurons (known as the presynaptic and postsynaptic neurons). The presynaptic neuron releases neurotransmitters, such as glutamate and GABA, which bind to receptors on the postsynaptic cell membrane, activating ion channels. Opening and closing those channels changes the cell's electrical potential. If the potential changes dramatically enough, the cell fires an electrical impulse called an action potential.

All of this synaptic activity depends on the ion channels, which control the flow of charged atoms such as sodium, potassium and calcium. Those channels are also key to two processes known as long-term potentiation (LTP) and long-term depression (LTD), which strengthen and weaken synapses, respectively.

The MIT researchers designed their computer chip so that the transistors could mimic the activity of different ion channels. While most chips operate in a binary, on/off mode, current flows through the transistors on the new brain chip in analog, not digital, fashion. A gradient of electrical potential drives current to flow through the transistors just as ions flow through ion channels in a cell.

"We can tweak the parameters of the circuit to match specific ion channels," Poon says. "We now have a way to capture each and every ionic process that's going on in a neuron."

Previously, researchers had built circuits that could simulate the firing of an action potential, but not all of the circumstances that produce the potentials. "If you really want to mimic brain function realistically, you have to do more than just spiking. You have to capture the intracellular processes that are ion channel-based," Poon says.

The new chip represents a "significant advance in the efforts to incorporate what we know about the biology of neurons and synaptic plasticity onto CMOS [complementary metal-oxide-semiconductor] chips," says Dean Buonomano, a professor of neurobiology at the University of California at Los Angeles, adding that "the level of biological realism is impressive.

The MIT researchers plan to use their chip to build systems to model specific neural functions, such as the visual processing system. Such systems could be much faster than digital computers. Even on high-capacity computer systems, it takes hours or days to simulate a simple brain circuit. With the analog chip system, the simulation is even faster than the biological system itself.

Another potential application is building chips that can interface with biological systems. This could be useful in enabling communication between neural prosthetic devices such as artificial retinas and the brain. Further down the road, these chips could also become building blocks for artificial intelligence devices, Poon says.

Debate resolved

The MIT researchers have already used their chip to propose a resolution to a longstanding debate over how LTD occurs.

One theory holds that LTD and LTP depend on the frequency of action potentials stimulated in the postsynaptic cell, while a more recent theory suggests that they depend on the timing of the action potentials' arrival at the synapse.

Both require the involvement of ion channels known as NMDA receptors, which detect postsynaptic activation. Recently, it has been theorized that both models could be unified if there were a second type of receptor involved in detecting that activity. One candidate for that second receptor is the endo-cannabinoid receptor.

Endo-cannabinoids, similar in structure to marijuana, are produced in the brain and are involved in many functions, including appetite, pain sensation and memory. Some neuroscientists had theorized that endo-cannabinoids produced in the postsynaptic cell are released into the synapse, where they activate presynaptic endo-cannabinoid receptors. If NMDA receptors are active at the same time, LTD occurs.

When the researchers included on their chip transistors that model endo-cannabinoid receptors, they were able to accurately simulate both LTD and LTP. Although previous experiments supported this theory, until now, "nobody had put all this together and demonstrated computationally that indeed this works, and this is how it works," Poon says.

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The above story is reprinted from materials provided by Massachusetts Institute of Technology. The original article was written by Anne Trafton, MIT News Office.

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

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Mimicking the brain -- in silicon: New computer chip models how neurons communicate with each other at synapses

ScienceDaily (Nov. 15, 2011) — For decades, scientists have dreamed of building computer systems that could replicate the human brain's talent for learning new tasks.

MIT researchers have now taken a major step toward that goal by designing a computer chip that mimics how the brain's neurons adapt in response to new information. This phenomenon, known as plasticity, is believed to underlie many brain functions, including learning and memory.

With about 400 transistors, the silicon chip can simulate the activity of a single brain synapse -- a connection between two neurons that allows information to flow from one to the other. The researchers anticipate this chip will help neuroscientists learn much more about how the brain works, and could also be used in neural prosthetic devices such as artificial retinas, says Chi-Sang Poon, a principal research scientist in the Harvard-MIT Division of Health Sciences and Technology.

Poon is the senior author of a paper describing the chip in the Proceedings of the National Academy of Sciences the week of Nov. 14. Guy Rachmuth, a former postdoc in Poon's lab, is lead author of the paper. Other authors are Mark Bear, the Picower Professor of Neuroscience at MIT, and Harel Shouval of the University of Texas Medical School.

Modeling synapses

There are about 100 billion neurons in the brain, each of which forms synapses with many other neurons. A synapse is the gap between two neurons (known as the presynaptic and postsynaptic neurons). The presynaptic neuron releases neurotransmitters, such as glutamate and GABA, which bind to receptors on the postsynaptic cell membrane, activating ion channels. Opening and closing those channels changes the cell's electrical potential. If the potential changes dramatically enough, the cell fires an electrical impulse called an action potential.

All of this synaptic activity depends on the ion channels, which control the flow of charged atoms such as sodium, potassium and calcium. Those channels are also key to two processes known as long-term potentiation (LTP) and long-term depression (LTD), which strengthen and weaken synapses, respectively.

The MIT researchers designed their computer chip so that the transistors could mimic the activity of different ion channels. While most chips operate in a binary, on/off mode, current flows through the transistors on the new brain chip in analog, not digital, fashion. A gradient of electrical potential drives current to flow through the transistors just as ions flow through ion channels in a cell.

"We can tweak the parameters of the circuit to match specific ion channels," Poon says. "We now have a way to capture each and every ionic process that's going on in a neuron."

Previously, researchers had built circuits that could simulate the firing of an action potential, but not all of the circumstances that produce the potentials. "If you really want to mimic brain function realistically, you have to do more than just spiking. You have to capture the intracellular processes that are ion channel-based," Poon says.

The new chip represents a "significant advance in the efforts to incorporate what we know about the biology of neurons and synaptic plasticity onto CMOS [complementary metal-oxide-semiconductor] chips," says Dean Buonomano, a professor of neurobiology at the University of California at Los Angeles, adding that "the level of biological realism is impressive.

The MIT researchers plan to use their chip to build systems to model specific neural functions, such as the visual processing system. Such systems could be much faster than digital computers. Even on high-capacity computer systems, it takes hours or days to simulate a simple brain circuit. With the analog chip system, the simulation is even faster than the biological system itself.

Another potential application is building chips that can interface with biological systems. This could be useful in enabling communication between neural prosthetic devices such as artificial retinas and the brain. Further down the road, these chips could also become building blocks for artificial intelligence devices, Poon says.

Debate resolved

The MIT researchers have already used their chip to propose a resolution to a longstanding debate over how LTD occurs.

One theory holds that LTD and LTP depend on the frequency of action potentials stimulated in the postsynaptic cell, while a more recent theory suggests that they depend on the timing of the action potentials' arrival at the synapse.

Both require the involvement of ion channels known as NMDA receptors, which detect postsynaptic activation. Recently, it has been theorized that both models could be unified if there were a second type of receptor involved in detecting that activity. One candidate for that second receptor is the endo-cannabinoid receptor.

Endo-cannabinoids, similar in structure to marijuana, are produced in the brain and are involved in many functions, including appetite, pain sensation and memory. Some neuroscientists had theorized that endo-cannabinoids produced in the postsynaptic cell are released into the synapse, where they activate presynaptic endo-cannabinoid receptors. If NMDA receptors are active at the same time, LTD occurs.

When the researchers included on their chip transistors that model endo-cannabinoid receptors, they were able to accurately simulate both LTD and LTP. Although previous experiments supported this theory, until now, "nobody had put all this together and demonstrated computationally that indeed this works, and this is how it works," Poon says.

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New components for future computer memories

ScienceDaily (Nov. 3, 2011) — The European TRAMS (terascale reliable adaptive memory systems) consortium funded under FP7 investigates the impact of statistical NanoCMOS variability on terascale embedded static random-access memories (SRAMs) based on sub-16 nm technology generation using conventional and novel complementary metal-oxide semiconductor (CMOS) devices.

The statistical variability introduced by the discreteness of charge and matter has become a major obstacle to scaling and integration. Its impact on embedded memories is particularly dramatic, as its slows down supply voltage scaling (particularly for SRAMs) and threatens the continuation of area scaling that helps drive integration targets for systems on chip.

Concerns regarding the area of SRAM cells and power supply scaling are major drivers behind the revolutionary introduction of FinFET devices. TRAMS is striving to understand the implications of FinFET technology for the continuation of CMOS scaling as projected by Moore's law.

This year, TRAMS completed an important milestone by analysing in minute detail the statistical variability in a 10 nm-channel length FinFET on silicon-on-insulator (SOI) substrate using advanced statistical technology computer-aided design (TCAD) simulation. The FinFETs are carefully designed to meet the requirements of the International Technology Roadmap for Semiconductors (ITRS) for 11-nm CMOS technology generation. The simulations have been carried out using unique simulation technology that takes into account the major known sources of statistical variability and reliability, including random discrete dopants, the gate and the fin line edge roughness, the metal gate variability and bias temperature instability effects (e.g., NBTI/PBTI).

The results of the physical simulations have been captured in accurate statistical compact models by the TRAMS partners. These models are being used to evaluate the impact of statistical FinFET variability on the design of 11-nm embedded memories and to develop circuit and system countermeasures that will make future embedded memories resilient to statistical variability and reliability.

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How To Send A Text From Computer Consoles

Did you know it's possible to send a text from computer programs or clients and not pay a single dime to your mobile phone company? Recently, I was shocked and appalled to discover that my phone company was grossly overcharging me for my call rates and my text rates as well. Maybe it's my mistake for not reading the fine print in the contract, but considering that these days we can tweet, instant message and email for free from our smart phones, doesn't it make sense that we should be able to text for free as well? So I turned to the next best thing - sending texts from my computer so that I don't have to pay for them.

How To Send A Text From Computer Software And Save Money

Believe it or not, there are many options available to if you want to send a text from computer software instead of using your mobile network and paying through the nose for it. For example, you can use your e-mail to send text messages to any mobile user so long as you know their network and their mobile number. How nifty is that? I discovered that little trick some time ago, and so I went around and asked all the people I know what their mobile networks were. Then I just saved their numbers as e-mail addresses in my e-mail client, and now I text for free!

Another way to go about saving money when you send a text from computer software is by using an instant messaging client to text. Yahoo Messenger offers free texting to particular mobile networks, so you can give that a try and see if it works for you. Otherwise, social networks like Facebook and Twitter allow you to send a "text" from computer consoles as well, so that's another option for you and it will send an alert by means of a push button notification to an iPhone, or Android. It's just like texting, except it's free!

Stop Paying For It When You Can Send A Text From Computer Consoles Free!

Now that I've shared my secrets with you, you can now go ahead and send a text or ten from computer consoles absolutely free and not pay these mobile companies for a service that is essentially free to them and making them millions of dollars every single year. Let's make a stand for free texting today!

Further instructions on how to send a text from computer consoles and save money can be found at this website.

You'll find solutions guaranteed to deliver the best when you send a text from computer.

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Better 'photon loops' may be key to computer and physics advances

ScienceDaily (Aug. 22, 2011) — Surprisingly, transmitting information-rich photons thousands of miles through fiber-optic cable is far easier than reliably sending them just a few nanometers through a computer circuit. However, it may soon be possible to steer these particles of light accurately through microchips because of research performed at the Joint Quantum Institute of the National Institute of Standards and Technology (NIST) and the University of Maryland, together with Harvard University.

The scientists behind the effort say the work not only may lead to more efficient information processors on our desktops, but also could offer a way to explore a particularly strange effect of the quantum world known as the quantum Hall effect in which electrons can interfere with themselves as they travel in a magnetic field. The corresponding physics is rich enough that its investigation has already resulted in three Nobel Prizes, but many intriguing theoretical predictions about it have yet to be observed.

The advent of optical fibers a few decades ago made it possible for dozens of independent phone conversations to travel long distances along a single glass cable by, essentially, assigning each conversation to a different color-each narrow strand of glass carrying dramatic amounts of information with little interference.

Ironically, while it is easy to send photons far across a town or across the ocean, scientists have a harder time directing them to precise locations across short distances-say, a few hundred nanometers-and this makes it difficult to employ photons as information carriers inside computer chips.

"We run into problems when trying to use photons in microcircuits because of slight defects in the materials chips are made from," says Jacob Taylor, a theoretical physicist at NIST and JQI. "Defects crop up a lot, and they deflect photons in ways that mess up the signal."

These defects are particularly problematic when they occur in photon delay devices, which slow the photons down to store them briefly until the chip needs the information they contain. Delay devices are usually constructed from a single row of tiny resonators, so a defect among them can ruin the information in the photon stream. But the research team perceived that using multiple rows of resonators would build alternate pathways into the delay devices, allowing the photons to find their way around defects easily.

As delay devices are a vital part of computer circuits, the alternate-pathway technique may help overcome obstacles blocking the development of photon-based chips, which are still a dream of computer manufacturers. While that application would be exciting, lead author Mohammad Hafezi says the prospect of investigating the quantum Hall effect with the same technology also has great scientific appeal.

"The photons in these devices exhibit the same type of interference as electrons subjected to the quantum Hall effect," says Hafezi, a research associate at JQI. "We hope these devices will allow us to sidestep some of the problems with observing the physics directly, instead allowing us to explore them by analogy."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

Mohammad Hafezi, Eugene A. Demler, Mikhail D. Lukin, Jacob M. Taylor. Robust optical delay lines with topological protection. Nature Physics, 2011; DOI: 10.1038/NPHYS2063

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New 'FeTRAM' is promising computer memory technology

ScienceDaily (Sep. 27, 2011) — Researchers are developing a new type of computer memory that could be faster than the existing commercial memory and use far less power than flash memory devices.

The technology combines silicon nanowires with a "ferroelectric" polymer, a material that switches polarity when electric fields are applied, making possible a new type of ferroelectric transistor.

"It's in a very nascent stage," said doctoral student Saptarshi Das, who is working with Joerg Appenzeller, a professor of electrical and computer engineering and scientific director of nanoelectronics at Purdue's Birck Nanotechnology Center.

The ferroelectric transistor's changing polarity is read as 0 or 1, an operation needed for digital circuits to store information in binary code consisting of sequences of ones and zeroes. The new technology is called FeTRAM, for ferroelectric transistor random access memory.

"We've developed the theory and done the experiment and also showed how it works in a circuit," he said. Findings are detailed in a research paper that appeared this month in Nano Letters, published by the American Chemical Society.

The FeTRAM technology has nonvolatile storage, meaning it stays in memory after the computer is turned off. The devices have the potential to use 99 percent less energy than flash memory, a non-volatile computer storage chip and the predominant form of memory in the commercial market.

"However, our present device consumes more power because it is still not properly scaled," Das said. "For future generations of FeTRAM technologies one of the main objectives will be to reduce the power dissipation. They might also be much faster than another form of computer memory called SRAM."

The FeTRAM technology fulfills the three basic functions of computer memory: to write information, read the information and hold it for a long period of time.

"You want to hold memory as long as possible, 10 to 20 years, and you should be able to read and write as many times as possible," Das said. "It should also be low power to keep your laptop from getting too hot. And it needs to scale, meaning you can pack many devices into a very small area. The use of silicon nanowires along with this ferroelectric polymer has been motivated by these requirements."

The new technology also is compatible with industry manufacturing processes for complementary metal oxide semiconductors, or CMOS, used to produce computer chips. It has the potential to replace conventional memory systems.

A patent application has been filed for the concept.

The FeTRAMs are similar to state-of-the-art ferroelectric random access memories, FeRAMs, which are in commercial use but represent a relatively small part of the overall semiconductor market. Both use ferroelectric material to store information in a nonvolatile fashion, but unlike FeRAMS, the new technology allows for nondestructive readout, meaning information can be read without losing it.

This nondestructive readout is possible by storing information using a ferroelectric transistor instead of a capacitor, which is used in conventional FeRAMs.

This work was supported by the Nanotechnology Research Initiative (NRI) through Purdue's Network for Computational Nanotechnology (NCN), which is supported by National Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Purdue University. The original article was written by Emil Venere.

Journal Reference:

Saptarshi Das, Joerg Appenzeller. FETRAM. An Organic Ferroelectric Material Based Novel Random Access Memory Cell. Nano Letters, 2011; 11 (9): 4003 DOI: 10.1021/nl2023993

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New computer technologies shown to expose personal information

 A combination of facial recognition software, cloud computing and social networking can be used to learn individuals' identities from photographs (Photo: Yago Veith via Flickr)

Facial recognition software, social networking and cloud computing ... they're all technological advances that alone have thrown up questions regarding privacy. According to a recent Carnegie Mellon University study, however, the three technologies can be combined to learn peoples' identities and other personal information about them, starting with just a photograph of their face.

"A person's face is the veritable link between her offline and online identities," said Alessandro Acquisti, associate professor of information technology and public policy, and leader of the study. "When we share tagged photos of ourselves online, it becomes possible for others to link our face to our names in situations where we would normally expect anonymity."

Acquisti's team used "off-the-shelf" PittPatt face recognition software, cloud computing, and publicly-accessible information from social networking sites to identify individuals based both on photographs posted online, and on photos that the researchers took themselves in the real world.

In one experiment, they were able to accurately identify people whose pictures were posted on an online dating service, where the members only use pseudonyms to identify themselves. In a second experiment, they were able to identify students walking on the campus grounds, by taking photographs of them, then matching those up with their Facebook profile photos.

In a third experiment, they were able to predict personal interests and in some cases even the first five digits of the social security numbers of students, starting with nothing but a photograph. Apparently, knowing a student's date and place of birth was sufficient to guess their social security number "with great accuracy."

Overall, they were able to identify about one third of the people whose photos they analyzed.

The Carnegie Mellon team even created a one-off augmented reality smartphone app that displayed personal information about individuals in real time, as the phone's camera was trained on their face.

"The seamless merging of online and offline data that face recognition and social media make possible raises the issue of what privacy will mean in an augmented reality world," said Acquisti.

His team's findings will be presented this Thursday at the Black Hat Briefings security conference in Las Vegas.

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