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March 1, 2007, 10:03 PM CT

Atomic Processes In Nanomaterials

Atomic Processes In Nanomaterials Image courtesy / Subra Suresh
Scientists from MIT, Georgia Institute of Technology and Ohio State University have developed a new computer modeling approach to study how materials behave under stress at the atomic level, offering insights that could help engineers design materials with an ideal balance between strength and resistance to failure.

When designing materials, there is often a tradeoff between strength and ductility (resistance to breaking)--properties that are critically important to the performance of materials.

Recent advances in nanotechnology have allowed scientists to manipulate a material's nanostructure to make it both strong and ductile. Now, the MIT-related team has figured out why some nano-designed metals behave with that desirable compromise between strength and ductility.

The team, led by Subra Suresh, the Ford Professor of Engineering in the Department of Materials Science and Engineering, developed a simulation method derived from experimental data that allows them to visualize the deformation of materials on a timescale of minutes. Prior methods allowed for only a nanosecond-scale glimpse at the atomic-level processes.

"It's a method to look at mechanical properties at the atomic scale of real experiments without being bogged down by limitations of nanosecond timescales of the simulation methods such as molecular dynamics," said Suresh, the senior author of a paper on the work that appears as the cover story in the Feb. 27 issue of the Proceedings of the National Academy of Sciences.........

Posted by: John      Read more         Source


February 21, 2007, 9:25 PM CT

Biologically inspired sensors

Biologically inspired sensors
o find prey and avoid being preyed upon, fish rely on a row of specialized sensory organs along the sides of their bodies, called the lateral line. Now, a research team led by Chang Liu at the University of Illinois at Urbana-Champaign has built an artificial lateral line that can provide the same functions in underwater vehicles.

"Our development of an artificial lateral line is aimed at enhancing human ability to detect, navigate and survive in the underwater environment," said Liu, a Willett Scholar and a professor of electrical and computer engineering at Illinois. "Our goal is to develop an artificial device that mimics the functions and capabilities of the biological system".

In fish, the lateral line provides guidance for synchronized swimming, predator and obstacle avoidance, and prey detection and tracking. Equipped with an artificial lateral line, a submarine or underwater robot could similarly detect and track moving underwater targets, and avoid collisions with moving or stationary objects.

The artificial lateral line consists of an integrated linear array of micro fabricated flow sensors, with the sizes of individual sensors and spacings between them matching those of their biological counterpart.

"By detecting changes in water pressure and movement, the device can supplement sonar and vision systems in submarines and underwater robots," said Liu, who also is affiliated with the universitys Beckman Institute for Advanced Science and Technology, the Institute for Genomic Biology, and the Micro and Nanotechnology Laboratory.........

Posted by: John      Read more         Source


February 21, 2007, 9:22 PM CT

Creates Metallic Interconnects, Nanostructures

Creates Metallic Interconnects, Nanostructures
reating high-resolution metallic interconnects is an essential part of the fabrication of microchips and other nanoscale devices. Scientists at the University of Illinois at Urbana-Champaign have developed a simple and robust electrochemical process for the direct patterning of metallic interconnects and other nanostructures.

"Solid-state superionic stamping offers a new approach, both as a stand-alone process and as a complement to other nanofabrication techniques, for creating chemical sensors, photonic structures and electrical interconnects," said Nicholas X. Fang, a professor of mechanical science and engineering, and corresponding author of a paper reported in the Feb. 14 issue of the journal Nano Letters.

The S4 process uses a patterned superionic material as a stamp, and etches a metallic film by an electrochemical reaction. In superionic materials, metal ions can move almost freely around the crystal lattice. These mobile materials can also be used in batteries and fuel cells.

Unlike conventional processing in which patterns are first placed on photoresist, followed by metal deposition and subsequent etching the S4 process creates.

high-resolution metallic nanopatterns in a single step, potentially reducing manufacturing costs and increasing yields.........

Posted by: John      Read more         Source


February 19, 2007, 7:56 PM CT

Using Nano-Magnets to Enhance Medical Imaging

Using Nano-Magnets to Enhance Medical Imaging NIST studies show that molecular nanomagnets create concentration-dependent contrast in magnetic resonance imaging (MRI).
Nanoscale magnets in the form of iron-containing molecules might be used to improve the contrast between healthy and diseased tissue in magnetic resonance imaging (MRI)-as long as the concentration of nanomagnets is carefully managed-as per a new report* by scientists at the National Institute of Standards and Technology (NIST) and collaborators. Molecular nanomagnets are a new class of MRI contrast agents that may offer significant advantages, such as versatility in design, over the compounds used today.

Contrast agents are used to highlight different tissues in the body or to help distinguish between healthy and diseased tissue. NIST is working with two universities and a hospital to design, produce and test nanomolecules that might make MRI imaging more powerful and easier to perform. The new paper resolves a debate in the literature by showing that iron-containing magnets just two nanometers wide, dissolved in water, do provide reasonable contrast in non-clinical MRI images-as long as the nanomagnet concentration is below a certain threshold. (A nanometer is one billionth of a meter.) Prior studies by other research groups had reached conflicting conclusions on the utility of molecular nanomagnets for MRI, but without accounting for concentration. NIST scientists, making novel magnetic measurements, were able to monitor the molecules' decomposition and magnetic properties as the composition was varied.........

Posted by: John      Read more         Source


February 19, 2007, 7:53 PM CT

High-Frequency Cryocooler Is Tiny

High-Frequency Cryocooler Is Tiny
new cryogenic refrigerator has been demonstrated at the National Institute of Standards and Technology (NIST) that operates at twice the usual frequency, achieving a long-sought combination of small size, rapid cooling, low temperatures and high efficiency. The cryocoooler could be used to chill instruments for space and military applications, and is a significant step toward even smaller, higher-frequency versions for integrated circuits and microelectromechanical (MEM) systems.

The new cryocooler, described in the current issue of Applied Physics Letters,* is a "pulse tube" design that uses oscillating helium gas to transport heat, achieving very cold temperatures (-223 degrees C or -370 degrees F) in a matter of minutes without any cold moving parts. With cold components about 70 by 10 millimeters in size, the device operates at 120 cycles per second (hertz), in comparison to the usual 60 Hz, which enables use of a much smaller oscillator to generate gas flow, as well as faster cool-down. Because changing the size of one component can negatively affect others, the scientists used a NIST-developed computer model to find the optimal combination of frequency, pressure and component geometry.

The new cryocooler is as efficient as the low-frequency version because it uses a higher average pressure and a finer screen mesh in the regenerator-a stainless steel tube packed with screening that provides a large surface area for transfer of heat between the gas and the steel. This is a key part of the cooling process. The helium gas is pre-cooled by the screen in the regenerator before entering the pulse tube, where the gas is expanded and chilled. The cold gas reverses its direction and carries heat away from the object to be cooled before it enters the regenerator again and picks up stored heat from the screen. Then it is compressed again for a new cycle. In comparison to a prototype NIST mini-cryocooler flown on a space shuttle in 2001, the new version is about the same size but gets much colder.........

Posted by: John      Read more         Source


February 19, 2007, 7:08 PM CT

Recast Usual View of Elusive Force

Recast Usual View of Elusive Force JILA scientists measured how temperature affects the Casimir-Polder force using an apparatus that holds four small squares of glass inside a vacuum chamber.
Physicists at JILA have demonstrated that the warmer a surface is, the stronger its subtle ability to attract nearby atoms, a finding that could affect the design of devices that rely on small-scale interactions, such as atom chips, nanomachines, and microelectromechanical systems (MEMS).

The research highlights an underappreciated aspect of the elusive Casimir-Polder force, one of the stranger effects of quantum mechanics. The force arises from the ever-present random fluctuation of microscopic electric fields in empty space. The fluctuations get stronger near a surface, and an isolated neutral atom nearby will feel them as a subtle pull-a flimsy, invisible rubber band between bulk objects and atoms that may be a source of friction, for example, in tiny devices. The JILA group previously made the most precise measurement ever of Casimir-Polder, measuring forces hundreds of times weaker than ever before and at greater distances (more than 5 micrometers). JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder.

Now, as reported in last week's Physical Review Letters*, the JILA team has made the first measurement of the temperature dependence of this force. By using a combination of temperatures at opposite extremes-making a glass surface very hot while keeping the environment neutral and using ultracold atoms as a measurement tool-the new research underscores the power of surfaces to influence the Casimir-Polder force. That is, electric fields within the glass mostly reflect inside the surface but also leak out a little bit to greatly strengthen the fluctuations in neighboring space. As a result, says group leader and NIST Fellow Eric Cornell, "warm glass is stickier than cold glass".........

Posted by: John      Read more         Source


February 15, 2007, 6:17 AM CT

Trackstick Pro GPS

Trackstick Pro GPS
Katherine reviewed the original TrackStick GPS, but now the company has come out with the improved Pro, with 4 times the memory.

What is it? A tiny GPS recorder which, unlike real time tracking devices, records histories; it doesn't tell you where you are but where you've been. For example, it could tell you where your kids have been, verify employee driving routes, and watch large shipment routes.

How does it work? The Track Stick receives signals from twenty-four satellites orbiting the earth. With this information, the Track Stick can precisely calculate its own position anywhere on the planet to within fifteen meters. That's comforting.

When I asked the inventor, Richard Haberkern, why he came up with the Trackstick, he explained that he was intrigued with the new GPS systems years ago and came up with Trackstick as a low cost alternative for individuals and was surprised when it was snapped up by the FBI, CIA and Homeland Security.

Since it's designed to work with Google Earth, it ended up being a very useful tool in Katrina, used for evacuation route planning, and is now being added to most search and rescue teams for mapping purposes.

It's powered by a cigarette lighter, or hard wired, or how shall we say -- covertly installed.........

Posted by: John      Read more         Source


February 13, 2007, 9:09 PM CT

Water Through Nanotube Membranes

Water Through Nanotube Membranes Precise control of water transport through a nanotube membrane is demonstrated by a novel electro-chemical approach
Credit: Rensselaer Polytechnic Institute
Troy, N.Y. By fusing wet and dry nanotechnologies, scientists at Rensselaer Polytechnic Institute have found a way to control the flow of water through carbon nanotube membranes with an unprecedented level of precision. The research, which will be described in the March 14, 2007 issue of the journal Nano Letters, could inspire technologies designed to transform salt water into pure drinking water almost instantly, or to immediately separate a specific strand of DNA from the biological jumble.

Nanotube membranes have fascinated scientists with their combination of high flow rates and high selectivity, allowing them to filter out very small impurities and other organic materials like DNA and proteins from materials with high water content. The problem is that nanotube arrays are hydrophobic, strongly repelling water.

We have, at a very fundamental level, discovered that there is a new mechanism to control water transport, said Nikhil Koratkar, associate professor of mechanical engineering at Rensselaer and lead author of the paper. This is the first time that electrochemical means can be used to control the way that the water interacts with the surface of the nanotube.

A group of Rensselaer scientists led by Koratkar has found a way to use low-voltage electricity to manipulate the flow of water through nanotubes. Control of waters movement through a nanotube with this level of precision has never been demonstrated before.........

Posted by: John      Read more         Source


February 11, 2007, 9:42 PM CT

Future Superconducting Magnet

Future Superconducting Magnet MRI machine
A research team led by a Northwestern University physicist has identified a high-temperature superconductor -- Bi-2212, a compound containing bismuth -- as a material that might be suitable for the new wires needed to one day build the most powerful superconducting magnet in the world, a 30 Tesla magnet.

The material currently used in magnetic resonance (MR) imaging machines in both hospitals and research laboratories -- a low-temperature superconducting alloy of the metallic element niobium -- has been pushed almost as far as it can go, to around 21 Tesla. (Tesla is used to define the intensity of the magnetic field.) There are no superconducting magnet wires currently available that can generate 30 Tesla.

"A new materials technology -- such as a technology based on high-temperature superconductivity -- is required to make the huge leap from 21 Tesla to 30 Tesla," said William P. Halperin, John Evans Professor of Physics and Astronomy in the Weinberg College of Arts and Sciences at Northwestern, who led the team. "We have shown that Bi-2212 could be operated at the same temperature as is presently the case for magnets made with niobium -- 4 degrees Kelvin -- and also achieve the stable state necessary for a 30 Tesla magnet".

The findings will be published online Feb. 11 by the journal Nature Physics.........

Posted by: John      Read more         Source


February 7, 2007, 9:05 PM CT

recasting usual view of elusive force

recasting usual view of elusive force JILA scientists measured how temperature affects the Casimir-Polder force using an apparatus that holds four small squares of glass inside a vacuum chamber.
Credit: E. Cornell group/JIL
Physicists at JILA have demonstrated that the warmer a surface is, the stronger its subtle ability to attract nearby atoms, a finding that could affect the design of devices that rely on small-scale interactions, such as atom chips, nanomachines, and microelectromechanical systems (MEMS).

The research highlights an underappreciated aspect of the elusive Casimir-Polder force, one of the stranger effects of quantum mechanics. The force arises from the ever-present random fluctuation of microscopic electric fields in empty space. The fluctuations get stronger near a surface, and an isolated neutral atom nearby will feel them as a subtle pulla flimsy, invisible rubber band between bulk objects and atoms that may be a source of friction, for example, in tiny devices. The JILA group previously made the most precise measurement ever of Casimir-Polder, measuring forces hundreds of times weaker than ever before and at greater distances (more than 5 micrometers). JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder.

Now, as reported in a paper scheduled for this week's issue of Physical Review Letters, the JILA team has made the first measurement of the temperature dependence of this force. By using a combination of temperatures at opposite extremesmaking a glass surface very hot while keeping the environment neutral and using ultracold atoms as a measurement toolthe new research underscores the power of surfaces to influence the Casimir-Polder force. That is, electric fields within the glass mostly reflect inside the surface but also leak out a little bit to greatly strengthen the fluctuations in neighboring space. As a result, says group leader and NIST Fellow Eric Cornell, "warm glass is stickier than cold glass".........

Posted by: John      Read more         Source


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