Mantis shrimp eye could improve high-definition CDs, DVDs

ScienceDaily (June 24, 2011) — The eye of the peacock mantis shrimp has led an international team of researchers to develop a two-part waveplate that could improve CD, DVD, blu-ray and holographic technology, creating even higher definition and larger storage density.

Peacock mantis shrimp are one of only a few animal species that can see circularly polarized light -- like the light used to create 3-D movies. Some researchers believe the mantis shrimp's eyes are better over the entire visual spectrum than any artificial waveplates.

A waveplate is a transparent slab that can alter the polarization of light because it is birefringent -- exhibits double refraction. The mineral calcite, which is sometimes used as a waveplate, is birefringent. This print viewed through a calcite lens appears as doubled and slightly offset letters.

"We want to change the polarization without affecting the amount of light that gets through," said Akhlesh Lakhtakia, Charles Godfrey Binder Professor of Engineering Science and Mechanics, Penn State. " We want both transmittance and changing polarization to occur quite independent of frequency. In other words, we do not want to affect the color."

Waveplates restore polarization in devices that require only one polarization of light, but lose polarization within the process. They can also separate light into separate polarizations to carry specific information and can filter light for optical devices.

Typically, waveplates are made from minerals like quartz, calcite or birefringent polymers. In some cases, to create the range and transparency required, two different materials are stacked or joined, but this type of construction sometimes delaminates, coming apart at the seams.

A team of engineers from the National Taipei University of Technology and Lakhtakia developed a method to produce periodically multilayered materials, similar to the lens in the peacock mantis shrimp, that are suitable for waveplates in the visual light spectrum and cannot delaminate because they are manufactured as one piece. The researchers report their work in the current online issue of Nature Communications.

The research team's waveplate is made of two layers of nanorods that are structurally similar to those in the eye of the peacock mantis shrimp. The researchers begin with tantalum pentoxide, but deposit the two layers using different deposition processes creating a multilayered thin film. One method produces a layer of needle-like nanorods that are all parallel to each other and all slanted in the same direction. The second method produces nanorods that are also parallel to each other but are upright.

"The two separate layers are needed so that we can play off one against the other to achieve the desired polarization without significantly reducing transmittance over a broad range of frequencies," said Lakhtakia.

The waveplates consist of a layer of slanted nanorods sandwiched between two layers of upright nanorods. Multiple sandwiches are then stacked to make the required waveplate. Because the size of the nanorods is much less than the wavelengths of visible light, the waveplate is birefringent. Because of the two materials, the waveplate can polarize or repolarize light over the visual spectrum.

The researchers report that "the fabrication technique of the periodically multilayered structures is a workhorse technique in the thin-film industry, does not require expensive lithography equipment and is compatible with … technology commonplace in electronics and optoelectronics industries."

Other researchers on this project were Professor Yi-Jun Jen, post-doctoral researcher Ching-Wei Yu and graduate students Chia-Feng Lin, Meng-Jie Lin, Shih-Hao Wang and Jyun-Rong Lai, Department of Electro-optical Engineering, National Taipei University of Technology.

The National Taipei University of Technology, the National Science Council of the Republic of China and the Charles Godfrey Binder Endowment at Penn State supported this research.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Penn State.

Journal Reference:

Yi-Jun Jen, Akhlesh Lakhtakia, Ching-Wei Yu, Chia-Feng Lin, Meng-Jie Lin, Shih-Hao Wang, Jyun-Rong Lai. Biologically inspired achromatic waveplates for visible light. Nature Communications, 2011; 2: 363 DOI: 10.1038/ncomms1358

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'Catch and release' program could improve nanoparticle safety assessment

ScienceDaily (June 8, 2011) — Depending on whom you ask, nanoparticles are, potentially, either one of the most promising or the most perilous creations of science. These tiny objects can deliver drugs efficiently and enhance the properties of many materials, but what if they also are hazardous to your health in some way? Now, scientists at the National Institute of Standards and Technology (NIST) have found a way to manipulate nanoparticles so that questions like this can be answered.

The team has developed a method of attracting and capturing metal-based nanoparticles on a surface and releasing them at the desired moment. The method, which uses a mild electric current to influence the particles' behavior, could allow scientists to expose cell cultures to nanoparticles so that any lurking hazards they might cause to living cells can be assessed effectively.

The method also has the advantage of collecting the particles in a layer only one particle thick, which allows them to be evenly dispersed into a fluid sample, thereby reducing clumping -- a common problem that can mask the properties they exhibit when they encounter living tissue. According to NIST physicist Darwin Reyes, these combined advantages should make the new method especially useful in toxicology studies.

"Many other methods of trapping require that you modify the surface of the nanoparticles in some way so that you can control them more easily," Reyes says. "We take nanoparticles as they are, so that you can explore what you've actually got. Using this method, you can release them into a cell culture and watch how the cells react, which can give you a better idea of how cells in the body will respond."

Other means of studying nanoparticle toxicity do not enable such precise delivery of the particles to the cells. In the NIST method, the particles can be released in a controlled fashion into a fluid stream that flows over a colony of cells, mimicking the way the particles would encounter cells inside the body -- allowing scientists to monitor how cells react over time, for example, or whether responses vary with changes in particle concentration.

For this particular study, the team used a gold surface covered by long, positively charged molecules, which stretch up from the gold like wheat in a field. The nanoparticles, which are also made of gold, are coated with citrate molecules that have a slight negative charge, which draws them to the surface covering, an attraction that can be broken with a slight electric current. Reyes says that because the surface covering can be designed to attract different materials, a variety of nanoparticles could be captured and released with the technique.

Story Source:

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

Journal Reference:

Darwin R. Reyes, Geraldine I. Mijares, Brian Nablo, Kimberly A. Briggman, Michael Gaitan. Trapping and Release of Citrate-Capped Gold Nanoparticles. Applied Surface Science, 2011; DOI: 10.1016/j.apsusc.2011.04.030

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Robotics: A tiltable head could improve the ability of undulating robots to navigate disaster debris

ScienceDaily (May 10, 2011) — Search and rescue missions have followed each of the devastating earthquakes that hit Haiti, New Zealand and Japan during the past 18 months. Machines able to navigate through complex dirt and rubble environments could have helped rescuers after these natural disasters, but building such machines is challenging.

Researchers at the Georgia Institute of Technology recently built a robot that can penetrate and "swim" through granular material. In a new study, they show that varying the shape or adjusting the inclination of the robot's head affects the robot's movement in complex environments.

"We discovered that by changing the shape of the sand-swimming robot's head or by tilting its head up and down slightly, we could control the robot's vertical motion as it swam forward within a granular medium," said Daniel Goldman, an assistant professor in the Georgia Tech School of Physics.

Results of the study will be presented on May 10 at the 2011 IEEE International Conference on Robotics and Automation in Shanghai. Funding for this research was provided by the Burroughs Wellcome Fund, National Science Foundation and Army Research Laboratory.

The study was conducted by Goldman, bioengineering doctoral graduate Ryan Maladen, physics graduate student Yang Ding and physics undergraduate student Andrew Masse, all from Georgia Tech, and Northwestern University mechanical engineering adjunct professor Paul Umbanhowar.

"The biological inspiration for our sand-swimming robot is the sandfish lizard, which inhabits the Sahara desert in Africa and rapidly buries into and swims within sand," explained Goldman. "We were intrigued by the sandfish lizard's wedge-shaped head that forms an angle of 140 degrees with the horizontal plane, and we thought its head might be responsible for or be contributing to the animal's ability to maneuver in complex environments."

For their experiments, the researchers attached a wedge-shaped block of wood to the head of their robot, which was built with seven connected segments, powered by servo motors, packed in a latex sock and wrapped in a spandex swimsuit. The doorstop-shaped head -- which resembled the sandfish's head -- had a fixed lower length of approximately 4 inches, height of 2 inches and a tapered snout. The researchers examined whether the robot's vertical motion could be controlled simply by varying the inclination of the robot's head.

Before each experimental run in a test chamber filled with quarter-inch-diameter plastic spheres, the researchers submerged the robot a couple inches into the granular medium and leveled the surface. Then they tracked the robot's position until it reached the end of the container or swam to the surface.

The researchers investigated the vertical movement of the robot when its head was placed at five different degrees of inclination. They found that when the sandfish-inspired head with a leading edge that formed an angle of 155 degrees with the horizontal plane was set flat, negative lift force was generated and the robot moved downward into the media. As the tip of the head was raised from zero to 7 degrees relative to the horizontal, the lift force increased until it became zero. At inclines above 7 degrees, the robot rose out of the medium.

"The ability to control the vertical position of the robot by modulating its head inclination opens up avenues for further research into developing robots more capable of maneuvering in complex environments, like debris-filled areas produced by an earthquake or landslide," noted Goldman.

The robotics results matched the research team's findings from physics experiments and computational models designed to explore how head shape affects lift in granular media.

"While the lift forces of objects in air, such as airplanes, are well understood, our investigations into the lift forces of objects in granular media are some of the first ever," added Goldman.

For the physics experiments, the researchers dragged wedge-shaped blocks through a granular medium. Blocks with leading edges that formed angles with the horizontal plane of less than 90 degrees resembled upside-down doorstops, the block with a leading edge equal to 90 degrees was a square, and blocks with leading edges greater than 90 degrees resembled regular doorstops.

They found that blocks with leading edges that formed angles with the horizontal plane less than 80 degrees generated positive lift forces and wedges with leading edges greater than 120 degrees created negative lift. With leading edges between 80 and 120 degrees, the wedges did not generate vertical forces in the positive or negative direction.

Using a numerical simulation of object drag and building on the group's previous studies of lift and drag on flat plates in granular media, the researchers were able to describe the mechanism of force generation in detail.

"When the leading edge of the robot head was less than 90 degrees, the robot's head experienced a lift force as it moved forward, which resulted in a torque imbalance that caused the robot to pitch and rise to the surface," explained Goldman.

Since this study, the researchers have attached a wedge-shaped head on the robot that can be dynamically modulated to specific angles. With this improvement, the researchers found that the direction of movement of the robot is sensitive to slight changes in orientation of the head, further validating the results from their physics experiments and computational models.

Being able to precisely control the tilt of the head will allow the researchers to implement different strategies of head movement during burial and determine the best way to wiggle deep into sand. The researchers also plan to test the robot's ability to maneuver through material similar to the debris found after natural disasters and plan to examine whether the sandfish lizard adjusts its head inclination to ensure a straight motion as it dives into the sand.

This material is based on research sponsored by the Burroughs Wellcome Fund, the National Science Foundation (NSF) under Award Number PHY-0749991, and the Army Research Laboratory (ARL) under Cooperative Agreement Number W911NF-08-2-0004.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Georgia Institute of Technology Research News.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Robotics: A tiltable head could improve the ability of undulating robots to navigate disaster debris

ScienceDaily (May 10, 2011) — Search and rescue missions have followed each of the devastating earthquakes that hit Haiti, New Zealand and Japan during the past 18 months. Machines able to navigate through complex dirt and rubble environments could have helped rescuers after these natural disasters, but building such machines is challenging.

Researchers at the Georgia Institute of Technology recently built a robot that can penetrate and "swim" through granular material. In a new study, they show that varying the shape or adjusting the inclination of the robot's head affects the robot's movement in complex environments.

"We discovered that by changing the shape of the sand-swimming robot's head or by tilting its head up and down slightly, we could control the robot's vertical motion as it swam forward within a granular medium," said Daniel Goldman, an assistant professor in the Georgia Tech School of Physics.

Results of the study will be presented on May 10 at the 2011 IEEE International Conference on Robotics and Automation in Shanghai. Funding for this research was provided by the Burroughs Wellcome Fund, National Science Foundation and Army Research Laboratory.

The study was conducted by Goldman, bioengineering doctoral graduate Ryan Maladen, physics graduate student Yang Ding and physics undergraduate student Andrew Masse, all from Georgia Tech, and Northwestern University mechanical engineering adjunct professor Paul Umbanhowar.

"The biological inspiration for our sand-swimming robot is the sandfish lizard, which inhabits the Sahara desert in Africa and rapidly buries into and swims within sand," explained Goldman. "We were intrigued by the sandfish lizard's wedge-shaped head that forms an angle of 140 degrees with the horizontal plane, and we thought its head might be responsible for or be contributing to the animal's ability to maneuver in complex environments."

For their experiments, the researchers attached a wedge-shaped block of wood to the head of their robot, which was built with seven connected segments, powered by servo motors, packed in a latex sock and wrapped in a spandex swimsuit. The doorstop-shaped head -- which resembled the sandfish's head -- had a fixed lower length of approximately 4 inches, height of 2 inches and a tapered snout. The researchers examined whether the robot's vertical motion could be controlled simply by varying the inclination of the robot's head.

Before each experimental run in a test chamber filled with quarter-inch-diameter plastic spheres, the researchers submerged the robot a couple inches into the granular medium and leveled the surface. Then they tracked the robot's position until it reached the end of the container or swam to the surface.

The researchers investigated the vertical movement of the robot when its head was placed at five different degrees of inclination. They found that when the sandfish-inspired head with a leading edge that formed an angle of 155 degrees with the horizontal plane was set flat, negative lift force was generated and the robot moved downward into the media. As the tip of the head was raised from zero to 7 degrees relative to the horizontal, the lift force increased until it became zero. At inclines above 7 degrees, the robot rose out of the medium.

"The ability to control the vertical position of the robot by modulating its head inclination opens up avenues for further research into developing robots more capable of maneuvering in complex environments, like debris-filled areas produced by an earthquake or landslide," noted Goldman.

The robotics results matched the research team's findings from physics experiments and computational models designed to explore how head shape affects lift in granular media.

"While the lift forces of objects in air, such as airplanes, are well understood, our investigations into the lift forces of objects in granular media are some of the first ever," added Goldman.

For the physics experiments, the researchers dragged wedge-shaped blocks through a granular medium. Blocks with leading edges that formed angles with the horizontal plane of less than 90 degrees resembled upside-down doorstops, the block with a leading edge equal to 90 degrees was a square, and blocks with leading edges greater than 90 degrees resembled regular doorstops.

They found that blocks with leading edges that formed angles with the horizontal plane less than 80 degrees generated positive lift forces and wedges with leading edges greater than 120 degrees created negative lift. With leading edges between 80 and 120 degrees, the wedges did not generate vertical forces in the positive or negative direction.

Using a numerical simulation of object drag and building on the group's previous studies of lift and drag on flat plates in granular media, the researchers were able to describe the mechanism of force generation in detail.

"When the leading edge of the robot head was less than 90 degrees, the robot's head experienced a lift force as it moved forward, which resulted in a torque imbalance that caused the robot to pitch and rise to the surface," explained Goldman.

Since this study, the researchers have attached a wedge-shaped head on the robot that can be dynamically modulated to specific angles. With this improvement, the researchers found that the direction of movement of the robot is sensitive to slight changes in orientation of the head, further validating the results from their physics experiments and computational models.

Being able to precisely control the tilt of the head will allow the researchers to implement different strategies of head movement during burial and determine the best way to wiggle deep into sand. The researchers also plan to test the robot's ability to maneuver through material similar to the debris found after natural disasters and plan to examine whether the sandfish lizard adjusts its head inclination to ensure a straight motion as it dives into the sand.

This material is based on research sponsored by the Burroughs Wellcome Fund, the National Science Foundation (NSF) under Award Number PHY-0749991, and the Army Research Laboratory (ARL) under Cooperative Agreement Number W911NF-08-2-0004.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Georgia Institute of Technology Research News.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New material could improve safety for first responders to chemical hazards

ScienceDaily (May 2, 2011) — A new kind of sensor could warn emergency workers when carbon filters in the respirators they wear to avoid inhaling toxic fumes have become dangerously saturated.

In a recent issue of the journal Advanced Materials, a team of researchers from the University of California, San Diego and Tyco Electronics describe how they made the carbon nanostructures and demonstrate their potential use as microsensors for volatile organic compounds.

First responders protect themselves from such vapors, whose composition is often unknown, by breathing through a canister filled with activated charcoal -- a gas mask. Airborne toxins stick to the carbon in the filter, trapping the dangerous materials.

As the filters become saturated, chemicals will begin to pass through. The respirator can then do more harm than good by providing an illusion of safety. But there is no easy way to determine when the filter is spent. Current safety protocols base the timing of filter changes on how long the user has worn the mask.

"The new sensors would provide a more accurate reading of how much material the carbon in the filters has actually absorbed," said team leader Michael Sailor, professor of chemistry and biochemistry and bioengineering at UC San Diego. "Because these carbon nanofibers have the same chemical properties as the activated charcoal used in respirators, they have a similar ability to absorb organic pollutants."

Sailor's team assembled the nanofibers into repeating structures called photonic crystals that reflect specific wavelengths, or colors, of light. The wing scales of the Morpho butterfly, which give the insect its brilliant iridescent coloration, are natural examples of this kind of structure.

The sensors are an iridescent color too, rather than black like ordinary carbon. That color changes when the fibers absorb toxins -- a visible indication of their capacity for absorbing additional chemicals.

The agency that certifies respirators in the U.S., the National Institute of Occupational Safety and Health, has long sought such a sensor but the design requirements for a tiny, sensitive, inexpensive device that requires little power, have proved difficult to meet.

The materials that the team fabricated are very thin -- less than half the width of a human hair. Sailor's group has previously placed similar photonic sensors on the tips of optical fibers less than a millimeter across and shown that they can be inserted into respirator cartridges. And the crystals are sensitive enough to detect chemicals such as toluene at concentrations as low as one part per million.

Ting Gao, a senior researcher at the Polymers, Ceramics, and Technical Services Laboratories of Tyco Electronics in Menlo Park, California and Timothy L. Kelly, a NSERC post-doctoral fellow at UC San Diego co-authored the paper. The National Science Foundation, the Department of Homeland Security, the Natural Sciences and Engineering Research Council of Canada, and TYCO Electronics provided funding for the work.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - San Diego. The original article was written by Susan Brown.

Journal Reference:

Timothy L. Kelly, Ting Gao, Michael J. Sailor. Carbon Nanofiber Photonic Crystals: Carbon and Carbon/Silicon Composites Templated in Rugate Filters for the Adsorption and Detection of Organic Vapors (Adv. Mater. 15/2011). Advanced Materials, 2011; 23 (15): 1688 DOI: 10.1002/adma.201190052

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View the original article here

Solar power goes viral: Researchers use virus to improve solar-cell efficiency

ScienceDaily (Apr. 25, 2011) — Researchers at MIT have found a way to make significant improvements to the power-conversion efficiency of solar cells by enlisting the services of tiny viruses to perform detailed assembly work at the microscopic level.

In a solar cell, sunlight hits a light-harvesting material, causing it to release electrons that can be harnessed to produce an electric current. The new MIT research, published online in the journal Nature Nanotechnology, is based on findings that carbon nanotubes -- microscopic, hollow cylinders of pure carbon -- can enhance the efficiency of electron collection from a solar cell's surface.

Previous attempts to use the nanotubes, however, had been thwarted by two problems. First, the making of carbon nanotubes generally produces a mix of two types, some of which act as semiconductors (sometimes allowing an electric current to flow, sometimes not) or metals (which act like wires, allowing current to flow easily). The new research, for the first time, showed that the effects of these two types tend to be different, because the semiconducting nanotubes can enhance the performance of solar cells, but the metallic ones have the opposite effect. Second, nanotubes tend to clump together, which reduces their effectiveness.

And that's where viruses come to the rescue. Graduate students Xiangnan Dang and Hyunjung Yi -- working with Angela Belcher, the W. M. Keck Professor of Energy, and several other researchers -- found that a genetically engineered version of a virus called M13, which normally infects bacteria, can be used to control the arrangement of the nanotubes on a surface, keeping the tubes separate so they can't short out the circuits, and keeping the tubes apart so they don't clump.

The system the researchers tested used a type of solar cell known as dye-sensitized solar cells, a lightweight and inexpensive type where the active layer is composed of titanium dioxide, rather than the silicon used in conventional solar cells. But the same technique could be applied to other types as well, including quantum-dot and organic solar cells, the researchers say. In their tests, adding the virus-built structures enhanced the power conversion efficiency to 10.6 percent from 8 percent -- almost a one-third improvement.

This dramatic improvement takes place even though the viruses and the nanotubes make up only 0.1 percent by weight of the finished cell. "A little biology goes a long way," Belcher says. With further work, the researchers think they can ramp up the efficiency even further.

The viruses are used to help improve one particular step in the process of converting sunlight to electricity. In a solar cell, the first step is for the energy of the light to knock electrons loose from the solar-cell material (usually silicon); then, those electrons need to be funneled toward a collector, from which they can form a current that flows to charge a battery or power a device. After that, they return to the original material, where the cycle can start again. The new system is intended to enhance the efficiency of the second step, helping the electrons find their way: Adding the carbon nanotubes to the cell "provides a more direct path to the current collector," Belcher says.

The viruses actually perform two different functions in this process. First, they possess short proteins called peptides that can bind tightly to the carbon nanotubes, holding them in place and keeping them separated from each other. Each virus can hold five to 10 nanotubes, each of which is held firmly in place by about 300 of the virus's peptide molecules. In addition, the virus was engineered to produce a coating of titanium dioxide (TiO2), a key ingredient for dye-sensitized solar cells, over each of the nanotubes, putting the titanium dioxide in close proximity to the wire-like nanotubes that carry the electrons.

The two functions are carried out in succession by the same virus, whose activity is "switched" from one function to the next by changing the acidity of its environment. This switching feature is an important new capability that has been demonstrated for the first time in this research, Belcher says.

In addition, the viruses make the nanotubes soluble in water, which makes it possible to incorporate the nanotubes into the solar cell using a water-based process that works at room temperature.

Prashant Kamat, a professor of chemistry and biochemistry at Notre Dame University who has done extensive work on dye-sensitized solar cells, says that while others have attempted to use carbon nanotubes to improve solar cell efficiency, "the improvements observed in earlier studies were marginal," while the improvements by the MIT team using the virus assembly method are "impressive."

"It is likely that the virus template assembly has enabled the researchers to establish a better contact between the TiO2 nanoparticles and carbon nanotubes. Such close contact with TiO2 nanoparticles is essential to drive away the photo-generated electrons quickly and transport it efficiently to the collecting electrode surface."

Kamat thinks the process could well lead to a viable commercial product: "Dye-sensitized solar cells have already been commercialized in Japan, Korea and Taiwan," he says. If the addition of carbon nanotubes via the virus process can improve their efficiency, "the industry is likely to adopt such processes."

Belcher and her colleagues have previously used differently engineered versions of the same virus to enhance the performance of batteries and other devices, but the method used to enhance solar cell performance is quite different, she says.

Because the process would just add one simple step to a standard solar-cell manufacturing process, it should be quite easy to adapt existing production facilities and thus should be possible to implement relatively rapidly, Belcher says.

The research team also included Paula Hammond, the Bayer Professor of Chemical Engineering; Michael Strano, the Charles (1951) and Hilda Roddey Career Development Associate Professor of Chemical Engineering; and four other graduate students and postdoctoral researchers. The work was funded by the Italian company Eni, through the MIT Energy Initiative's Solar Futures Program.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Massachusetts Institute of Technology. The original article was written by David Chandler, MIT News Office.

Journal Reference:

Xiangnan Dang, Hyunjung Yi, Moon-Ho Ham, Jifa Qi, Dong Soo Yun, Rebecca Ladewski, Michael S. Strano, Paula T. Hammond, Angela M. Belcher. Virus-templated self-assembled single-walled carbon nanotubes for highly efficient electron collection in photovoltaic devices. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.50

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