January 7, 2008, 11:06 PM CT

Researchers bend light through waveguides

Scientists at the University of Illinois are the first to achieve optical waveguiding of near-infrared light through features embedded in self-assembled, three-dimensional photonic crystals. Applications for the optically active crystals include low-loss waveguides, low-threshold lasers and on-chip optical circuitry.

Key to the fabrication technique which uses multi-photon polymerization and a laser scanning confocal microscope is a self-assembled, colloidal material that exhibits a photonic band gap, said Paul Braun, a University Scholar and professor of materials science and engineering.

In prior work, reported in 2002, Brauns research group was the first to show that through multi-photon polymerization they could embed a polymer feature inside a silicon dioxide, self-assembled colloidal crystal.

Now, in a paper accepted for publication in Nature Photonics, and posted on the journals Web site, Braun and his team demonstrate actual optical activity in waveguides and cavities created in their colloidal crystals.

Taking our earlier work as a starting point, we built upon recent advances in theory and computation, improvements in materials growth techniques, and better colloidal crystallization capabilities to produce this new photonic material, said Braun, who also is affiliated with the universitys Beckman Institute, Frederick Seitz Materials Research Laboratory, and Micro and Nanotechnology Laboratory......... Posted by: Kevin      Read more         Source

January 7, 2008, 10:54 PM CT

'Electrospray' droplet research

Chemical engineers at Purdue University are the first to mathematically describe precisely how droplets form when liquids are exposed to electric fields, an advance that could have applications in areas ranging from manufacturing to medical diagnostics.

The technique of using small droplets created by subjecting liquids to electric fields is vital for a variety of applications, from a type of industrial painting called electrospraying, to a method for analyzing molecules in analytical chemistry, to manufacturing tiny micro- and nanoparticles for research and industry.

"Despite its importance, industry doesn't really understand exactly how the drops form," said Osman Basaran, the Reilly Professor of Fluid Mechanics in Purdue's School of Chemical Engineering.

New findings showed that a liquid's viscosity plays a vital role in drop formation and size, a discovery that contradicts conventional wisdom, Basaran said.

The scientists first created simulations to describe droplet formation mathematically, and then they performed experiments to support the computational work.

"Computational simulations are now making it possible to understand such phenomena," he said. "But you always want to back up simulations with experimental data if at all possible"......... Posted by: Kevin      Read more         Source

January 3, 2008, 9:41 PM CT

Life at the jolt

Scientists at the Biodesign Institute are using the tiniest organisms on the planet 'bacteria' as a viable option to make electricity. In a new study featured in the journal Biotechnology and Bioengineering, lead author Andrew Kato Marcus and his colleagues Cesar Torres and Bruce Rittmann have gained critical insights that may lead to commercialization of a promising microbial fuel cell (MFC) technology.

"We can use any kind of waste, such as sewage or pig manure, and the microbial fuel cell will generate electrical energy," said Marcus, a Civil and Environmental Engineering graduate student and a member of the institute's Center for Environmental Biotechnology. Unlike conventional fuel cells that rely on hydrogen gas as a fuel source, the microbial fuel cell can handle a variety of water-based organic fuels.

"There is a lot of biomass out there that we look at simply as energy stored in the wrong place," said Bruce Rittmann, director of the center. "We can take this waste, keeping it in its normal liquid form, but allowing the bacteria to convert the energy value to our society's most useful form, electricity. They get food while we get electricity."



Waste not

Bacteria have such a rich diversity that scientists can find a bacterium that can handle almost any waste compound in their daily diet. By linking bacterial metabolism directly with electricity production, the MFC eliminates the extra steps necessary in other fuel cell technologies. "We like to work with bacteria, because bacteria provide a cheap source of electricity," said Marcus......... Posted by: Kevin      Read more         Source

January 3, 2008, 9:35 PM CT

Shape-memory polymers designed

Researchers at the Georgia Institute of Technology are developing unique polymers, which change shape upon heating, to open blocked arteries, probe neurons in the brain and engineer a tougher spine.

These so-called shape-memory polymers can be temporarily stretched or compressed into forms several times larger or smaller than their final shape. Then heat, light or the local chemical environment triggers a transformation into their permanent shape.

My focus has been to optimize these polymers for many different biomedical applications. My lab studies how altering the chemistry and structure of the polymers affects their chemical, biological and mechanical properties, said Ken Gall, a professor in the George W. Woodruff School of Mechanical Engineering and School of Materials Science and Engineering.

The mechanical properties of these polymers make them extremely attractive for many biomedical applications, according to Gall, who described his research in this area during two presentations at the Materials Research Societys fall meeting in November.

Engineers are always searching for materials that display unconventional properties able to satisfy the severe requirements for implantation in the body. Particular attention must be paid to the biofunctionality, biostability and biocompatibility of these materials, which come into contact with tissue and body fluids......... Posted by: Kevin      Read more         Source

January 2, 2008, 10:50 PM CT

Wind Tunnel Key For 'Hypersonic Vehicles,'

By using the only wind tunnel capable of running quietly at "hypersonic" speeds, Purdue University engineers have conducted experiments to yield critical data for designing an advanced aircraft called the X-51A, powered by engines called scramjets.

The X-51A test vehicle is expected to evolve into missiles capable of flying at Mach 6 - or six times the speed of sound - enabling them to hit mobile "time-critical" targets.

Scramjets also may propel future military and civilian space planes.

The quiet wind tunnel operation is critical for collecting data to show precisely how air flows over a vehicle's surface in flight. No other wind tunnel runs quietly while conducting experiments in airstreams traveling at Mach 6, said Steven Schneider, an aerospace engineer and professor in Purdue's School of Aeronautics and Astronautics.

"A quiet wind tunnel yields more accurate data because it more closely simulates flight," he said.

Specifically, engineers need detailed information about how airflow changes from "laminar," or smooth, to turbulent as it speeds over an aircraft's surfaces. The information is essential to properly design vehicles that fly at hypersonic speeds, or faster than Mach 5, nearly 4,000 mph, Schneider said.

The X-51 project is led by the Air Force Research Laboratory and the Defense Advanced Research Projects Agency, and the vehicle is being built by Pratt & Whitney and the Boeing Co. Purdue engineers are part of a national team of scientists from government, academia and industry handling different aspects of the vehicle......... Posted by: Kevin      Read more         Source

January 2, 2008, 10:44 PM CT

Smaller is Stronger

As structures made of metal get smaller - as their dimensions approach the micrometer scale (millionths of a meter) or less - they get stronger. Researchers discovered this phenomenon 50 years ago while measuring the strength of tin "whiskers" a few micrometers in diameter and a few millimeters in length. A number of theories have been proposed to explain why smaller is stronger, but only recently has it become possible to see and record what's actually happening in tiny structures under stress.

Andrew Minor, of the Materials Sciences Division in the Department of Energy's Lawrence Berkeley National Laboratory, with colleagues from Hysitron Incorporated and the General Motors Research and Development Center, used the In Situ Microscope at the National Center for Electron Microscopy (NCEM) to record what happens when pillars of nickel with diameters between 150 and 400 nanometers (billionths of a meter) are compressed under a flat punch made of diamond. The transmission electron microscope is equipped so that samples can be stressed, measured, and videotaped while being observed under the electron beam.

"What controls the deformation of a metal object is the way that defects, called dislocations, move along planes in its crystal structure," Minor says. "The result of dislocation slip is plastic deformation. For example, bending a paper clip causes its trillions of dislocations per square centimeter to tangle up and multiply as they run into one another and slide along numerous slip planes." ......... Posted by: Kevin      Read more         Source

December 20, 2007, 9:48 PM CT

Metal Foam Has a Good Memory

In the world of commercial materials, lighter and cheaper is commonly better, particularly when those attributes are coupled with superior strength and special properties, such as a material's ability to remember its original shape after it's been deformed by a physical or magnetic force.

A new class of materials known as "magnetic shape-memory foams" has been developed by two research teams headed by Peter Müllner at Boise State University and David Dunand at Northwestern University, both funded by the National Science Foundation (NSF).

The foam consists of a nickel-manganese-gallium alloy whose structure resembles a piece of Swiss cheese with small voids of space between thin, curvy "struts" of material. The struts have a bamboo-like grain structure that can lengthen, or strain, up to 10 percent when a magnetic field is applied. Strain is the degree to which a material deforms under load. In this instance, the force came from a magnetic field rather a physical load. Force from magnetic fields can be exerted over long range, making them advantageous for a number of applications. The alloy material retains its new shape when the field is turned off, but the magnetically sensitive atomic structure returns to its original structure if the field is rotated 90 degrees--a phenomenon called "magnetic shape-memory"......... Posted by: Kevin      Read more         Source

December 20, 2007, 9:27 PM CT

The Quest for a New Class of Superconductors

Fifty years after the Nobel-prize winning explanation of how superconductors work, a research team from Los Alamos National Laboratory, the University of Edinburgh, and Cambridge University are suggesting another mechanism for the still-mysterious phenomenon.

In a review published recently in Nature, scientists David Pines, Philippe Monthoux and Gilbert Lonzarich posit that superconductivity in certain materials can be achieved absent the interaction of electrons with vibrational motion of a material's structure.

The review, "Superconductivity without phonons," explores how materials, under certain conditions, can become superconductors in a non-traditional way. Superconductivity is a phenomenon by which materials conduct electricity without resistance, commonly at extremely cold temperatures around minus 424 degrees Fahrenheit (minus 253 degrees Celsius)-the fantastically frigid point at which hydrogen becomes a liquid. Superconductivity was first discovered in 1911.

A newer class of materials that become superconductors at temperatures closer to the temperature of liquid nitrogen-minus 321 degrees Fahrenheit (minus 196 degrees Celsius)-are known as "high-temperature superconductors".

A theory for conventional low-temperature superconductors that was based on an effective attractive interaction between electrons was developed in 1957 by John Bardeen, Leon Cooper and John Schrieffer. The explanation, often called the BCS Theory, earned the trio the Nobel Prize in Physics in 1972......... Posted by: Kevin      Read more         Source

December 18, 2007, 10:09 PM CT

CMS tracking detector successfully installed

Installation of the world's largest silicon tracking detector was today successfully completed at CERN1. In the early hours of Thursday 13 December the CMS2 Silicon Strip Tracking Detector began its journey from the main CERN site to the CMS experimental facility. Later that day it was lowered 90 metres into the CMS cavern. Installation began on Saturday 15 December and was concluded this morning.

"This achievement completes the installation of sub-detectors inside the CMS magnet, which was lowered into the cavern on 28 February," said CMS technical coordinator Austin Ball. "It's a big milestone for us."

With a total surface area of 205 square metres, about the same as a singles tennis court, the CMS Silicon Strip Tracking Detector is by far the largest semiconductor silicon detector ever constructed. Its silicon sensors are patterned to provide a total of 10 million individual sensing strips, each of which is read out by one of 80,000 custom designed microelectronics chips. Data are then transported via 40,000 optical fibres into the CMS data acquisition system.

"The complete system operating at the LHC will produce data at a higher rate than the entire global telephone system," said project manager Peter Sharp.

The silicon sensors are precision mounted onto 15,200 modules that are in turn mounted onto a very low mass carbon fibre structure that maintains the position of the sensors to less than the diameter of a human hair (100 microns)......... Posted by: Kevin      Read more         Source

December 18, 2007, 8:14 PM CT

Powerful carbon-based electronics

Bypassing decades-old conventions in making computer chips, Princeton engineers developed a novel way to replace silicon with carbon on large surfaces, clearing the way for new generations of faster, more powerful cell phones, computers and other electronics.

The electronics industry has pushed the capabilities of silicon -- the material at the heart of all computer chips -- to its limit, and one intriguing replacement has been carbon, said Stephen Chou, professor of electrical engineering. A material called graphene -- a single layer of carbon atoms arranged in a honeycomb lattice -- could allow electronics to process information and produce radio transmissions 10 times better than silicon-based devices.

Until now, however, switching from silicon to carbon has not been possible because technologists believed they needed graphene material in the same form as the silicon used to make chips: a single crystal of material eight or 12-inches wide. The largest single-crystal graphene sheets made to date have been no wider than a couple millimeters, not big enough for a single chip. Chou and scientists in his lab realized that a big graphene wafer is not necessary, as long they could place small crystals of graphene only in the active areas of the chip. They developed a novel method to achieve this goal and demonstrated it by making high-performance working graphene transistors......... Posted by: Sarah      Read more         Source