Pairing Quantum Dots With Fullerenes for Nanoscale Photovoltaics

"This is the first demonstration of a hybrid inorganic/organic, dimeric (two-particle) material that acts as an electron donor-bridge-acceptor system for converting light to electrical current," said Brookhaven physical chemist Mircea Cotlet, lead author of a paper describing the dimers and their assembly method inAngewandte Chemie.

By varying the length of the linker molecules and the size of the quantum dots, the scientists can control the rate and the magnitude of fluctuations in light-induced electron transfer at the level of the individual dimer."This control makes these dimers promising power-generating units for molecular electronics or more efficient photovoltaic solar cells," said Cotlet, who conducted this research with materials scientist Zhihua Xu at Brookhaven's Center for Functional Nanomaterials (CFN).

Scientists seeking to develop molecular electronics have been very interested in organic donor-bridge-acceptor systems because they have a wide range of charge transport mechanisms and because their charge-transfer properties can be controlled by varying their chemistry. Recently, quantum dots have been combined with electron-accepting materials such as dyes, fullerenes, and titanium oxide to produce dye-sensitized and hybrid solar cells in the hope that the light-absorbing and size-dependent emission properties of quantum dots would boost the efficiency of such devices. But so far, the power conversion rates of these systems have remained quite low.

"Efforts to understand the processes involved so as to engineer improved systems have generally looked at averaged behavior in blended or layer-by-layer structures rather than the response of individual, well-controlled hybrid donor-acceptor architectures," said Xu.

The precision fabrication method developed by the Brookhaven scientists allows them to carefully control particle size and interparticle distance so they can explore conditions for light-induced electron transfer between individual quantum dots and electron-accepting fullerenes at the single molecule level.

The entire assembly process takes place on a surface and in a stepwise fashion to limit the interactions of the components (particles), which could otherwise combine in a number of ways if assembled by solution-based methods. This surface-based assembly also achieves controlled, one-to-one nanoparticle pairing.

To identify the optimal architectural arrangement for the particles, the scientists strategically varied the size of the quantum dots -- which absorb and emit light at different frequencies according to their size -- and the length of the bridge molecules connecting the nanoparticles. For each arrangement, they measured the electron transfer rate using single molecule spectroscopy.

"This method removes ensemble averaging and reveals a system's heterogeneity -- for example fluctuating electron transfer rates -- which is something that conventional spectroscopic methods cannot always do," Cotlet said.

The scientists found that reducing quantum dot size and the length of the linker molecules led to enhancements in the electron transfer rate and suppression of electron transfer fluctuations.

"This suppression of electron transfer fluctuation in dimers with smaller quantum dot size leads to a stable charge generation rate, which can have a positive impact on the application of these dimers in molecular electronics, including potentially in miniature and large-area photovoltaics," Cotlet said.

"Studying the charge separation and recombination processes in these simplified and well-controlled dimer structures helps us to understand the more complicated photon-to-electron conversion processes in large-area solar cells, and eventually improve their photovoltaic efficiency," Xu added.

A U.S. patent application is pending on the method and the materials resulting from using the technique, and the technology is available for licensing. This work was funded by the DOE Office of Science.

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A Simple, Mildly Invasive Solution for Conserving Historic Buildings

Her European doctoral thesis, undertaken at the Tecnalia Construction Unit and presented at the University of the Basque Country (UPV/EHU), is entitledRehabilitation of masonry arches by a compatible and minimally invasive strengthening system.

The solution proposed is based on a composite material known as BTRM (Basalt Textile-Reinforced Mortar). This involves a series of tissues of basalt embedded in an inorganic matrix (cement-free mortar modified with polymers). With her research, Ms Garmendia aimed at contributing greater knowledge on the behaviour of masonry arches, as well as on the efficaciousness of the BTRM system applied to such arches.

BTRM system

The researcher was able to show that, thanks to the physicochemical characteristics of BTRM components (resistance to high temperatures, permeability water vapour, flexibility, etc.), this composite material is compatible with the elements to be reinforced in arches. Moreover, it involves an easy-to-apply technology for buildings and especially for those with complex geometries like arches or vaulting. Also notable is its competitive cost compared to the more usual reinforcement methods employed to date.

The work carried out to arrive at these conclusions used a comprehensive, integral approach, with this reinforcement solution applied to stone buildings and, more specifically, to stonemasonry. First, mineralogical and mechanical characterisation tests were carried out on the materials making up the construction, both at the level of each constituent material and also for the overall structure; for the latter, 24 medium-scale, prismatic concrete test pieces were made, varying the material type (mortar and stone) and its bonding. Then the proposed reinforcement system put forward was looked at in more detail; carrying out physicochemical tests on the basalt tissue, the inorganic matrix and the tissue-matrix compound.

A third stage involved carrying out trials on twelve arches -- technical control of displacement to the point of reaching collapse. These arches were built and reinforced according to different criteria, both in terms of their typology (stonemasonry with or without mortar between the keystones/voussoirs) and in terms of reinforcement (without BTRM either with piers -- the lower surfaces of the arches -- , or with extrados -- the upper surfaces of the arches -- , or with both). Finally, various calculation methods were employed to mathematically evaluate the effect of the reinforcement solution proposed.

In conclusion, the experimental results reached with the PhD have shown the physicochemical compatibility between the BTRM system and the corresponding substrate of the stone construction to be reinforced, as well as validating its mechanical effectiveness in the reinforcement of arched structures. Thus, it was verified that this reinforcement solution could be the optimum alternative to traditional methods.

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Origami Not Just for Paper Anymore: DNA, Folded Into Complex Shapes, Could Have a Big Impact on Nanotechnology

Trying to build DNA structures on a large scale was once considered unthinkable. But about five years ago, Caltech computational bioengineer Paul Rothemund laid out a new design strategy called DNA origami: the construction of two-dimensional shapes from a DNA strand folded over on itself and secured by short"staple" strands. Several years later, William Shih's lab at Harvard Medical School translated this concept to three dimensions, allowing design of complex curved and bent structures that opened new avenues for synthetic biological design at the nanoscale.

A major hurdle to these increasingly complex designs has been automation of the design process. Now a team at MIT, led by biological engineer Mark Bathe, has developed software that makes it easier to predict the three-dimensional shape that will result from a given DNA template. While the software doesn't fully automate the design process, it makes it considerably easier for designers to create complex 3-D structures, controlling their flexibility and potentially their folding stability.

"We ultimately seek a design tool where you can start with a picture of the complex three-dimensional shape of interest, and the algorithm searches for optimal sequence combinations," says Bathe, the Samuel A. Goldblith Assistant Professor of Applied Biology."In order to make this technology for nanoassembly available to the broader community -- including biologists, chemists, and materials scientists without expertise in the DNA origami technique -- the computational tool needs to be fully automated, with a minimum of human input or intervention."

Bathe and his colleagues described their new software in the Feb. 25 issue ofNature Methods. In that paper, they also provide a primer on creating DNA origami with collaborator Hendrik Dietz at the Technische Universitaet Muenchen."One bottleneck for making the technology more broadly useful is that only a small group of specialized researchers are trained in scaffolded DNA origami design," Bathe says.

Programming DNA

DNA consists of a string of four nucleotide bases known as A, T, G and C, which make the molecule easy to program. According to nature's rules, A binds only with T, and G only with C."With DNA, at the small scale, you can program these sequences to self-assemble and fold into a very specific final structure, with separate strands brought together to make larger-scale objects," Bathe says.

Rothemund's origami design strategy is based on the idea of getting a long strand of DNA to fold in two dimensions, as if laid on a flat surface. In his first paper outlining the method, he used a viral genome consisting of approximately 8,000 nucleotides to create 2-D stars, triangles and smiley faces.

That single strand of DNA serves as a"scaffold" for the rest of the structure. Hundreds of shorter strands, each about 20 to 40 bases in length, combine with the scaffold to hold it in its final, folded shape.

"DNA is in many ways better suited to self-assembly than proteins, whose physical properties are both difficult to control and sensitive to their environment," Bathe says.

Bathe's new software program interfaces with a software program from Shih's lab called caDNAno, which allows users to manually create scaffolded DNA origami from a two-dimensional layout. The new program, dubbed CanDo, takes caDNAno's 2-D blueprint and predicts the ultimate 3-D shape of the design. This resulting shape is often unintuitive, Bathe says, because DNA is a flexible object that twists, bends and stretches as it folds to form a complex 3-D shape.

According to Rothemund, the CanDo program should allow DNA origami designers to more thoroughly test their DNA structures and tweak them to fold correctly."While we have been able to design the shape of things, we have had no tools to easily design and analyze the stresses and strains in those shapes or to design them for specific purposes," he says.

At the molecular-level, stress in the double helix of DNA decreases the folding stability of the structure and introduces local defects, both of which have hampered progress in the scaffolded DNA origami field.

Postdoctoral researcher Do-Nyun Kim and graduate student Matthew Adendorff, both of the Bathe lab, are now furthering CanDo's capabilities and optimizing the scaffolded DNA origami design process.

Building nanoscale tools

Once scientists have a reliable way to assemble DNA structures, the next question is what to do with them. One application scientists are excited about is a"DNA carrier" that can transport drugs to specific destinations in the body such as tumors, where the carrier would release the cargo based on a specific chemical signal from the target cancer cell.

Another possible application of scaffolded DNA origami could help reproduce part of the light-harvesting apparatus of photosynthetic plant cells. Researchers hope to recreate that complex series of about 20 protein subunits, but to do that, components must be held together in specific positions and orientations. That's where DNA origami could come in.

"DNA origami enables the nanoscale construction of very precise architectural arrangements. Researchers are exploiting this unique property to pursue a number of applications at the nanoscale, including a synthetic photocell," Bathe says."While applications such as this are still quite far off on the horizon, we believe that predictive engineering software tools are essential for progress in this direction."

Novel applications may also grow out of a new competition being held at Harvard this summer, called BIOMOD. Undergraduate teams from about a dozen schools, including MIT, Harvard and Caltech, will try to design nanoscale biomolecules for robotics, computing and other applications.

In the meantime, Bathe is focusing on further developing CanDo to enable automated DNA origami design."Once you have an automated computational tool that allows you to design complex shapes in a precise way, I think we're in a much better position to exploit this technology for interesting applications," he says.

For DNA origami to have a broad impact, it needs to become routine to simply order up DNA parts to build any configuration you can dream up, Bathe says. He notes:"Once non-specialists can design arbitrary 3-D nanostructures using DNA origami, their imaginations can run free."

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Functioning Synapse Created Using Carbon Nanotubes: Devices Might Be Used in Brain Prostheses or Synthetic Brains

The team, which was led by Professor Alice Parker and Professor Chongwu Zhou in the USC Viterbi School of Engineering Ming Hsieh Department of Electrical Engineering, used an interdisciplinary approach combining circuit design with nanotechnology to address the complex problem of capturing brain function.

In a paper published in the proceedings of the IEEE/NIH 2011 Life Science Systems and Applications Workshop in April 2011, the Viterbi team detailed how they were able to use carbon nanotubes to create a synapse.

Carbon nanotubes are molecular carbon structures that are extremely small, with a diameter a million times smaller than a pencil point. These nanotubes can be used in electronic circuits, acting as metallic conductors or semiconductors.

"This is a necessary first step in the process," said Parker, who began the looking at the possibility of developing a synthetic brain in 2006."We wanted to answer the question: Can you build a circuit that would act like a neuron? The next step is even more complex. How can we build structures out of these circuits that mimic the function of the brain, which has 100 billion neurons and 10,000 synapses per neuron?"

Parker emphasized that the actual development of a synthetic brain, or even a functional brain area is decades away, and she said the next hurdle for the research centers on reproducing brain plasticity in the circuits.

The human brain continually produces new neurons, makes new connections and adapts throughout life, and creating this process through analog circuits will be a monumental task, according to Parker.

She believes the ongoing research of understanding the process of human intelligence could have long-term implications for everything from developing prosthetic nanotechnology that would heal traumatic brain injuries to developing intelligent, safe cars that would protect drivers in bold new ways.

For Jonathan Joshi, a USC Viterbi Ph.D. student who is a co-author of the paper, the interdisciplinary approach to the problem was key to the initial progress. Joshi said that working with Zhou and his group of nanotechnology researchers provided the ideal dynamic of circuit technology and nanotechnology.

"The interdisciplinary approach is the only approach that will lead to a solution. We need more than one type of engineer working on this solution," said Joshi."We should constantly be in search of new technologies to solve this problem."

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Fat Turns Into Soap in Sewers, Contributes to Overflows

"We found that FOG deposits in sewage collection systems are created by chemical reactions that turn the fatty acids from FOG into, basically, a huge lump of soap," says Dr. Joel Ducoste, a professor of civil, construction and environmental engineering at NC State and co-author of a paper describing the research. Collection systems are the pipes and pumping stations that carry wastewater from homes and businesses to sewage-treatment facilities.

These hardened FOG deposits reduce the flow of wastewater in the pipes, contributing to sewer overflows -- which can cause environmental and public-health problems and lead to costly fines and repairs.

The research team used a technique called Fourier Transform Infrared (FTIR) spectroscopy to determine what the FOG deposits were made of at the molecular level. FTIR spectroscopy shoots a sample material with infrared light at various wavelengths. Different molecular bonds vibrate in response to different wavelengths. By measuring which infrared wavelengths created vibrations in their FOG samples, researchers were able to determine each sample's molecular composition.

Using this technique, researchers confirmed that the hardened deposits were made of calcium-based fatty acid salts -- or soap.

"FOG itself cannot create these deposits," Ducoste says."The FOG must first be broken down into its constituent parts: glycerol and free fatty acids. These free fatty acids -- specifically, saturated fatty acids -- can react with calcium in the sewage collection system to form the hardened deposits.

"Until this point we did not know how these deposits were forming -- it was just a hypothesis," Ducoste says."Now we know what's going on with these really hard deposits."

The researchers are now focused on determining where the calcium in the collection system is coming from, and how quickly these deposits actually form. Once they've resolved those questions, Ducoste says, they will be able to create numerical models to predict where a sewage system may have"hot spots" that are particularly susceptible to these blockages.

Ultimately, Ducoste says,"if we know how -- and how quickly -- these deposits form, it may provide scientific data to support policy decisions related to preventing sewer overflows."

The research was funded by the Water Resources Research Institute and the U.S. Environmental Protection Agency.

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Pier Review: Comparing Ultra High-Resolution Photographs from the Past and the Present Could Hold the Key to Restoring Hastings' Fire-Damaged Pier

Prior to the fire, NPL, the UK's National Measurement Institute, had been surveying the pier to support redevelopment plans and to monitor long-term changes in the pier. The project was part of the development of a world leading low-cost technique to assess long-term degradation of structures.

The technique is called Digital Image Correlation. It has been used in the laboratory for some time but NPL have recently been pioneering its use for looking at civil engineering structures. It involves taking ultra high-resolution panoramic photos -- images up to 1.4 Giga Pixels in size -- at two different times to identify structural changes. Advanced mathematical programs then analyse the pair of images to identify changes in the structure pixel by pixel. Using this information, engineers can understand how large structures change over time.

Following the devastating fire, NPL scientists returned to Hastings to take their second set of photos. They were then required to develop more advanced analysis techniques, which could deal with the much larger than anticipated changes to the Pier, and produce meaningful information about the structure. This work is proving more valuable than expected as considerable change has now taken place. In addition, the large panoramic images provide a snapshot of the structure in time, which is useful for archival purposes.

Up to 45 images were stitched together to produce an ultra high-resolution final image 80,000 pixels wide -- 300-400 times more detailed than a typical camera-phone photograph. Processing a pair of these images, one before the fire and one after, can help highlight where the structure has apparently changed because of the fire.

Results have been very positive. Whilst the super-structure has been severely damaged and there are large visual changes, the cast iron framework -- or sub-structure -- seems much less affected. The sub-structure on the west side of the Pier appears to be remarkably similar pre and post fire. On the East side there are small areas where there are some changes, and one localised area of the sub-structure about half way along showing significant distortion. But the vast majority of the sub-structure seems largely unchanged. The area showing the most distortion -- presumably caused by the extreme heat -- was at a downwind point where anecdotally the fire was seen to be fiercest.

Digital Image Correlation allows the computer to effectively carry out the laborious checking of the whole structure. This means quicker and cheaper identification of areas which have been deformed or damaged, and hence may need closer inspection. This is important on large structures such as piers as it allows civil engineers to focus their efforts on the parts that most need attention, dramatically speeding the inspection process and reducing the cost of repair.

The project has also helped prove the concept of Digital Image Correlation for the measurement of changes in large structures, by providing NPL with a real-life case study enabling development of key analysis software.

Nick McCormick, Principle Research Scientist at NPL, said:"It was fortunate that we began the project before the fire, as the results will be invaluable in regenerating the pier when restoration funding is secured. From a scientific point of view, the scale of the changes actually proved very interesting, although challenging, and required us to develop far more advanced analysis techniques than originally intended. These will be hugely important in our work to develop low cost monitoring solutions for other structures. Obviously we hope the next one won't be so badly damaged part way through our study. For most applications we work on we would expect to monitor much less significant changes over time -- for example small cracks appearing in bridges or building subsidence -- so that problems can be remedied before they escalate to cause such serious damage."

Digital Image Correlation is one of a number of techniques that NPL is developing for low-cost examination of large civil engineering structures such as bridges, buildings, tunnels and piers.

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Carbon Fiber Used to Reinforce Buildings; Protect from Explosion

Sarah Orton, assistant professor of civil engineering in the MU College of Engineering, has focused on using carbon fiber reinforced polymer (CFRP), a fabric that can carry 143,000 pounds of force per square inch and has various applications to strengthen reinforced concrete buildings. CFRP has been used previously to strengthen buildings for earthquakes.

"CFRP has been used in places like California since the 1980s to protect buildings from earthquakes, but it has so many applications," Orton said."Now, we have to worry about damage caused by attacks. This fabric can be a great tool to protect people in threatened buildings."

To protect a building from an extreme event, CFRP can be used to increase the bending capacity of walls or columns. Previously, Orton invented an anchor that can be embedded in the column or joint to make CFRP more effective. In that work, Orton found that the anchors allow the CFRP to reach its full tension strength rather than separating from the concrete at only about half its strength.

CFRP can be used to protect an entire wall from an explosion. To study the effectiveness of different ways of applying CFRP, Orton worked with the U.S. Army Engineer Research and Development Center (ERDC) to detonate explosives near CFRP-reinforced concrete slabs. She found that CFRP, when layered and anchored, provided a significant amount of protection. However, she said that applying additional protection to the front of the concrete slab, such as a steel plate, would enhance the slab's performance.

Orton says the high costs of approximately$30 per square foot have kept CFRP from being widely implemented in non-earthquake prone areas.

"This is a really useful material," Orton said."I continue to be fascinated by the material's strength and applications. Retrofitting buildings with CFRP will help protect people from attacks and potentially collapse of the building."

The study,"Use of Carbon Fiber Anchors to Improve Performance of CFRP Strengthened Concrete Structures Subjected to Blast and Impact Loads," will be published in a special publication of the American Concrete Institute.

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Rainbow-Trapping Scientist Now Strives to Slow Light Waves Even Further

In a paper published March 29 in theProceedings of the National Academy of Sciences, Qiaoqiang Gan (pronounced"Chow-Chung" and"Gone"), PhD, an assistant professor of electrical engineering at the University at Buffalo's School of Engineering and Applied Sciences, and his colleagues at Lehigh University, where he was a graduate student, described how they slowed broadband light waves using a type of material called nanoplasmonic structures.

Gan explains that the ultimate goal is to achieve a breakthrough in optical communications called multiplexed, multiwavelength communications, where optical data can potentially be tamed at different wavelengths, thus greatly increasing processing and transmission capacity.

He notes that it is widely recognized that if light could ever be stopped entirely, new possibilities would open up for data storage.

"At the moment, processing data with optical signals is limited by how quickly the signal can be interpreted," he says."If the signal can be slowed, more information could be processed without overloading the system."

Gan and his colleagues created nanoplasmonic structures by making nanoscale grooves in metallic surfaces at different depths, which alters the materials' optical properties.

These plasmonic chips provide the critical connection between nanoelectronics and photonics, Gan explains, allowing these different types of devices to be integrated, a prerequisite for realizing the potential of optical computing,"lab-on-a-chip" biosensors and more efficient, thin-film photovoltaic materials.

According to Gan, the optical properties of the nanoplasmonic structures allow different wavelengths of light to be trapped at different positions in the structure, potentially allowing for optical data storage and enhanced nonlinear optics.

The structures Gan developed slow light down so much that they are able to trap multiple wavelengths of light on a single chip, whereas conventional methods can only trap a single wavelength in a narrow band.

"Light is usually very fast, but the structures I created can slow broadband light significantly," says Gan."It's as though I can hold the light in my hand."

That, Gan explains, is because of the structures' engineered surface"plasmon resonances," where light excites the waves of electrons that oscillate back and forth on metal surfaces.

In this case, he says, light can be slowed down and trapped in the vicinity of resonances in this novel, dispersive structural material.

Gan and his colleagues also found that because the nanoplasmonic structures they developed can trap very slow resonances of light, they can do so at room temperature, instead of at the ultracold temperatures that are required in conventional slow-light technologies.

"In the PNAS paper, we showed that we trapped red to green," explains Gan."Now we are working on trapping a broader wavelength, from red to blue. We want to trap the entire rainbow."

Gan, who was hired at UB under the UB 2020 strategic strength in Integrated Nanostructured Systems, will be working toward that goal, using the ultrafast light source in UB's Department of Electrical Engineering in the laboratory of UB professor and vice president for research Alexander N. Cartwright.

"This ultrafast light source will allow us to measure experimentally just how slow is the light that we have trapped in our nanoplasmonic structures," Gan explains."Once we know that, we will be able to demonstrate our capability to manipulate light through experiments and optimize the structure to slow the light further."

Co-authors with Gan on the study are Filbert Bertoli, Yongkang Gao, Yujie Ding, Kyle Wagner and Dmitri Vezenov, all of Lehigh University.

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New Research Advances Understanding of Lead Selenide Nanowires

Now, a research team at the University of Pennsylvania's schools of Engineering and Applied Science and Arts and Sciences has shown how to control the characteristics of semiconductor nanowires made of a promising material: lead selenide.

Led by Cherie Kagan, professor in the departments of Electrical and Systems Engineering, Materials Science and Engineering and Chemistry and co-director of Pennergy, Penn's center focused on developing alternative energy technologies, the team's research was primarily conducted by David Kim, a graduate student in the Materials Science and Engineering program.

The team's work was published online in the journalACS Nanoand will be featured in the Journal's April podcast.

The key contribution of the team's work has to do with controlling the conductive properties of lead selenide nanowires in circuitry. Semiconductors come in two types,nandp, referring to the negative or positive charge they can carry. The ones that move electrons, which have a negative charge, are called"n-type." Their"p-type" counterparts don't move protons but rather the absenceof an electron -- a"hole" -- which is the equivalent of moving a positive charge.

Before they are integrated into circuitry, the semiconductor nanowire must be"wired up" into a device. Metal electrodes must be placed on both ends to allow electricity to flow in and out; however, the"wiring" may influence the observed electrical characteristics of the nanowires, whether the device appears to ben-type orp-type. Contamination, even from air, can also influence the device type. Through rigorous air-free synthesis, purification and analysis, they kept the nanowires clean, allowing them to discover the unique properties of these lead selenide nanomaterials.

Researchers designed experiments allowing them to separate the influence of the metal"wiring" on the motion of electrons and holes from that of the behavior intrinsic to the lead selenide nanowires. By controlling the exposure of the semiconductor nanowire device to oxygen or the chemical hydrazine, they were able to change the conductive properties betweenp-type andn-type. Altering the duration and concentration of the exposure, the nanowire device type could be flipped back and forth.

"If you expose the surfaces of these structures, which are unique to nanoscale materials, you can make themp-type, you can make themn-type, and you can make them somewhere in between, where it can conduct both electrons and holes," Kagan said."This is what we call 'ambipolar.'"

Devices combining onen-type and onep-type semiconductor are used in many high-tech applications, ranging from the circuits of everyday electronics, to solar cells and thermoelectrics, which can convert heat into electricity.

"Thinking about how we can build these things and take advantage of the characteristics of nanoscale materials is really what this new understanding allows," Kagan said.

Figuring out the characteristics of nanoscale materials and their behavior in device structures are the first steps in looking forward to their applications.

These lead selenide nanowires are attractive because they may be synthesized by low-cost methods in large quantities.

"Compared to the big machinery you need to make other semiconductor devices, it's significantly cheaper," Kagan said."It doesn't look much more complicated than the hoods people would recognize from when they had to take chemistry lab."

In addition to the low cost, the manufacturing process for lead selenide nanowires is relatively easy and consistent.

"You don't have to go to high temperatures to get mass quantities of these high-quality lead selenide nanowires," Kim said."The techniques we use are high yield and high purity; we can use all of them."

And because the conductive qualities of the lead selenide nanowires can be changed while they are situated in a device, they have a wider range of functionality, unlike traditional silicon semiconductors, which must first be"doped" with other elements to make them"p" or"n."

The Penn team's work is a step toward integrating these nanomaterials in a range of electronic and optoelectronic devices, such as photo sensors.

The research was conducted by Kim and Kagan, along with Materials Science and Engineering undergraduate and graduate students Tarun R. Vemulkar and Soong Ju Oh; Weon-Kyu Koh, a graduate student in Chemistry; and Christopher B. Murray, a professor in Chemistry and in Materials Science and Engineering.

This work was supported with funding from the National Science Foundation Division of Materials Research, the National Science Foundation Solar Program and the National Science Foundation Nano-Bio Interface Center.

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Invisibility Cloaks and More: Force of Acoustical Waves Tapped for Metamaterials

Metamaterials are artificial materials that are engineered to have properties not found in nature. These materials usually gain their unusual properties -- such as negative refraction that enables subwavelength focusing, negative bulk modulus, and band gaps -- from structure rather than composition.

By creating an inexpensive bench-top technique, as described in the American Institute of Physics' journalReview of Scientific Instruments, Los Alamos National Lab (LANL) researchers are making these highly desirable metamaterials more accessible.

Their technique harnesses an acoustical wave force, which causes nano-sized particles to cluster in periodic patterns in a host fluid that is later solidified, explains Farid Mitri, a Director's Fellow, and member of the Sensors& Electrochemical Devices, Acoustics& Sensors Technology Team, at LANL.

"The periodicity of the pattern formed is tunable and almost any kind of particle material can be used, including: metal, insulator, semiconductor, piezoelectric, hollow or gas-filled sphere, nanotubes and nanowires," he elaborates.

The entire process of structure formation is very fast and takes anywhere from 10 seconds to 5 minutes. Mitri and colleagues believe this technique can be easily adapted for large-scale manufacturing and holds the potential to become a platform technology for the creation of a new class of materials with extensive flexibility in terms of periodicity (mm to nm) and the variety of materialsthat can be used.

"This new class of acoustically engineered materials can lead to the discovery of many emergent phenomena, understanding novel mechanisms for the control of material properties, and hybrid metamaterials," says Mitri.

Applications of the technology, to name only a few, include: invisibility cloaks to hide objects from radar and sonar detection, sub-wavelength focusing for production of high-resolution lenses for microscopes and medical ultrasound/optical imaging probes, miniature directional antennas, development of novel anisotropic semiconducting metamaterials for the construction of effective electromagnetic devices, biological scaffolding for tissue engineering, light guide, and a variety of sensors.

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Conch Shell Gives Nano Insights Into Composite Materials

David Williamson and Bill Proud review how these organisms build such tough shells from such a seemingly weak substance. They discover that the key to conch strength lies in the small size of the calcium carbonate crystals from which it is formed by the sea snail. The crystals are below a threshold size known as the Griffith flaw size, any bigger and the crystals would be large enough for cracks to propagate through them under stress, the team explains. This makes the shells tough enough to cope, to some extent, with the crushing jaws of predatory turtles and the vice-like grip of crab claws. Weight for weight the shells are as tough as mild steel.

In the early twentieth century, engineers were preoccupied with the premature failure of materials used in shipping and railways. Concepts such as stress magnification and the propagation of tiny cracks that grow to form big cracks were beginning to be understood. Civil engineer Charles Edward Inglis Inglis devised a mathematical equation to help explain the process. And, in 1920, Alan Arnold Griffith built on the Inglis work to explain for the first time that the reason materials in the real world are not as strong as theoretical calculations would suggest is that the presence of tiny flaws magnify the applied stress in a manner according to the Inglis analysis leading to premature failure.

"Griffith pointed out that the effective strength of technical materials might be increased many tens of times if these flaws could be eliminated," explain Williamson and Proud. Little was known at the time of biomaterials and how their properties might one day copied to create biomimetic materials of much greater strength than their industrial counterparts. Griffith's work has now been used to improve our understanding of conch shells and other biomaterials to allow scientists to produce novel composite biomimetic materials. Research in this area has seen almost exponential growth in the last decade.

The team explains that in the archetypal conch shell material, the queen conch (Strombus gigas) uses a crossed layered, or lamellar, structure. At the smallest length scale the shell is made from tiny crystals of calcium carbonate in the so-called orthorhombic polymorphic form of aragonite. Each single crystal is a mere 60 to 130 nanometres thick and about 100 to 380 nanometres across, although they can be several micrometres long. A nanometre is a billionth of a metre; a micrometre is a thousand times bigger, a millionth of a metre. These dimensions, the Cambridge team explains are below the critical flaw size described by Griffith almost a century ago.

To make a biomimetic material, researchers might first adopt the small crystal size for their composites as well as the crossed layered structure of the conch shell. However, to be truly biomimetic, such materials will also have to incorporate another critical feature of the living material: the ability to self-heal. Attacked by a hungry turtle the shell of a queen conch might be strong enough to deter the predator, but damage will occur, but living tissue can carry out repairs. Materials scientists have discovered that certain polymers can be heat treated so that they undergo self-healing, extended research might allow crystalline composites that mimic conch shell to be made that have the same property.

The team concludes that, it is important to treat these biomaterials as sources of inspiration, rather than prototypes to be replicated in exquisite detail. After all, if nature had access to a modern, high-tech material like the extremely tough ceramic titanium boride used in aluminium smelting equipment and electrical discharge machining, would seashells look the same as they do now?

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Only the Weak Survive? Self-Healing Materials Strengthened by Adding More 'Give'

Conventional rules of survival tend to favor the strongest, but University of Pittsburgh-based researchers recently found that in the emerging world of self-healing materials, it is the somewhat frail that survive.

The team presents in the journalLangmuira new model laying out the inner workings of self-healing materials made of nanoscale gel particles that can regenerate after taking damage and are being pursued as a coating or composite material. Moreover, the researchers discovered that an ideal amount of weak bonds actually make for an overall stronger material that can withstand more stress.

Although self-healing nanogel materials have already been realized in the lab, the exact mechanical nature and ideal structure had remained unknown, explained Anna Balazs, corresponding author and Distinguished Professor of Chemical Engineering in Pitt's Swanson School of Engineering. The team's findings not only reveal how self-healing nanogel materials work, but also provide a blueprint for creating more resilient designs, she said. Balazs worked with lead author and Pitt postdoctoral researcher Isaac Salib; Chet Gnegy, a Pitt chemical and petroleum engineering sophomore; German Kolmakov, a postdoctoral researcher in Balazs' lab; and Krzysztof Matyjaszewski, a chemistry professor at Carnegie Mellon University with an adjunct appointment in Pitt's Department of Chemical and Petroleum Engineering.

The team worked from a computational model Gnegy, Kolmakov, and Salib created based on a self-healing material Matyjaszewski developed known as nanogel, a composition of spongy, microscopic polymer particles linked to one another by several tentacle-like bonds. The nanogel particles consist of stable bonds -- which provide overall strength -- and labile bonds, highly reactive bonds that can break and easily reform, that act as shock absorbers.

The computer model allowed the researchers to test the performance of various bond arrangements. The polymers were first laid out in an arrangement similar to that in the nanogel, with the tentacles linked end-to-end by a single strong bond. Simulated stress tests showed, however, that though these bonds could recover from short-lived stress, they could not withstand drawn out tension such as stretching or pulling. Instead, the team found that when particles were joined by several parallel bonds, the nanogel could absorb more stress and still self-repair.

The team then sought the most effective concentration of parallel labile bonds, Balazs said. According to the computational model, even a small number of labile bonds greatly increased resilience. For instance, a sample in which only 30 percent of the bonds were labile -- with parallel labile bonds placed in groups of four -- could withstand pressure up to 200 percent greater than what could fracture a sample comprised only of stable bonds. A film shows that as this sample is stretched, the labile bonds (red) rearrange themselves to hold the material together.

On the other hand, too many labile linkages were so collectively strong that the self-healing ability was cancelled out and the nanogel became brittle, the researchers report.

The Pitt model is corroborated by nature, which engineered the same principle into the famously tough abalone shell, Balazs said. An amalgamation of microscopic ceramic plates and a small percentage of soft protein, the abalone shell absorbs a blow by stretching and sliding rather than shattering.

"What we found is that if a material can easily break and reform, the overall strength is much better," she said."In short, a little bit of weakness gives a material better mechanical properties. Nature knows this trick."

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High-Tech Concrete Technology Has a Famous Past

Almost 1,900 years ago, the Romans built what continues to be the world's largest unreinforced solid concrete dome in the world -- the Pantheon. The secret, probably unknown to the Emperor Hadrian's engineers at the time, was that the lightweight concrete used to build the dome had set and hardened from the inside out. This internal curing process enhanced the material's strength, durability, resistance to cracking, and other properties so that the Pantheon continues to be used for special events to this day.

But it is only within the last decade or so that internally cured concrete has begun to have an impact on modern world infrastructure. Increasingly, internally cured concrete is being used in the construction of bridge decks, pavements, parking structures, water tanks, and railway yards, according to a review of the current status of the new (or old) concrete technology just published by the National Institute of Standards and Technology (NIST).

The virtues of internally cured concrete stem from substituting light-weight, pre-wetted absorbent materials for some of the sand and/or coarse aggregates (stones) that are mixed with cement to make conventional concrete. Dispersed throughout the mixture, the water-filled lightweight aggregates serve as reservoirs that release water on an as-needed basis to nearby hydrating cement particles.

According to one study cited in the review, bridge decks made with internally cured, high-performance concrete were estimated to have a service life of 63 years, as compared with 22 years for conventional concrete and 40 years for high-performance concrete without internal curing.

"As with many new technologies, the path from research to practice has been a slow one, but as of 2010, hundreds of thousands of cubic meters" of the lighter and more durable material have been successfully used in U.S. construction, write the report's co-authors, NIST chemical engineer Dale Bentz and Jason Weiss, Purdue University civil engineering professor.

Compared with conventional varieties, internally cured concrete increases the cost of a project by 10 to 12 percent, Bentz and Weiss estimate on the basis of bridge-building projects in New York and Indiana. The increased front-end cost, they write, must be evaluated against the reduced risk of cracking, better protection against salt damage, and other improved properties that"should contribute to a more durable structure that has a longer life and lower life-cycle costs," they write."Further, this could have substantial benefits in a reduced disruption to the traveling public, generally producing a more sustainable solution."

The 82-page report summarizes the current practice and theory of internal curing, reviews project experiences and material performance in the field, and describes opportunities for research that could lead to enhancements in the material.

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Materials Identified That May Deliver More 'Bounce'

The alloys could be used in springier blood vessel stents, sensitive microphones, powerful loudspeakers, and components that boost the performance of medical imaging equipment, security systems and clean-burning gasoline and diesel engines.

While these nanostructured metal alloys are not new -- they are used in turbine blades and other parts demanding strength under extreme conditions -- the Rutgers researchers are pioneers at investigating these new properties.

"We have been doing theoretical studies on these materials, and our computer modeling suggests they will be super-responsive," said Armen Khachaturyan, professor of Materials Science and Engineering in the Rutgers School of Engineering. He and postdoctoral researcher Weifeng Rao believe these materials can be a hundred times more responsive than today's materials in the same applications.

Writing in the March 11 issue of the journalPhysical Review Letters, the researchers describe how this class of metals with embedded nanoparticles can be highly elastic, or"springy," and can convert electrical and magnetic energy into movement or vice-versa. Materials that exhibit these properties are known among scientists and engineers as"functional" materials.

One class of functional materials generates an electrical voltage when the material is bent or compressed. Conversely, when the material is exposed to an electric field, it will deform. Known as piezoelectric materials, they are used in ultrasound instruments; audio components such as microphones, speakers and even venerable record players; autofocus motors in some camera lenses; spray nozzles in inkjet printer cartridges; and several types of electronic components.

In another class of functional materials, changes in magnetic fields deform the material and vice-versa. These magnetorestrictive materials have been used in naval sonar systems, pumps, precision optical equipment, medical and industrial ultrasonic devices, and vibration and noise control systems.

The materials that Khachaturyan and Rao are investigating are technically known as"decomposed two-phase nanostructured alloys." They form by cooling metals that were exposed to high temperatures at which the nanosized particles of one crystal structure, or phase, are embedded into another type of phase. The resulting structure makes it possible to deform the metal under an applied stress while allowing the metal to snap back into place when the stress is removed.

These nanostructured alloys might be more effective than traditional metals in applications such blood vessel stents, which have to be flexible but can't lose their"springiness." In the piezoelectric and magnetorestrictive components, the alloy's potential to snap back into shape after deforming -- a property known as non-hysteresis -- could improve energy efficiency over traditional materials that require energy input to restore their original shapes.

In addition to potentially showing responses far greater than traditional materials, the new materials may be tunable; that is, they may exhibit smaller or larger shape changes and output force based on varying mechanical, electrical or magnetic input and the material processing.

The researchers hope to test the results of their computer simulations on actual metals in the near future.

The Rutgers team collaborated with Manfred Wittig, professor of Materials Science and Engineering at the University of Maryland. Their research was funded by the National Science Foundation and the U.S. Department of Energy.

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NASA Readies for World's Largest Can Crusher Test

It's similar to what a team of NASA engineers will do to an immense aluminum-lithium rocket fuel tank in late March; their hope is to use data from the test to generate new"shell-buckling design factors" that will enable light-weight, safe and sturdy"skins" for future launch vehicles.

Testing for this innovative study is under way at NASA's Marshall Space Flight Center in Huntsville, Ala., where engineers are supporting the test led by the NASA Engineering and Safety Center, or NESC, based at NASA's Langley Research Center in Hampton, Va.

The aerospace industry's shell buckling knockdown factors are a complex set of engineering data that dates back to Apollo-era studies of rocket structures -- well before modern composite materials, manufacturing processes and advanced computer modeling. The hope is for the new test data to update essential calculations that are typically a significant cost, performance, and safety driver in designing large structures like the main fuel tank of a future heavy-lift launch vehicle.

The large-scale test follows a series of smaller scale tests, all aimed at reducing the time and money spent designing and testing future rockets. And by incorporating more modern, lighter high-tech materials into the design and manufacturing process, rockets will save weight and carry more payload.

This week, technicians moved a 27.5-foot-diameter and 20-foot-tall space shuttle external tank barrel-shaped test article into place at Marshall's Engineering Test Laboratory. Once installed, the section will be sandwiched between two massive loading rings that will press down with almost one-million pounds of force on the central cylindrical test article forcing it to buckle.

"Spacecraft structures, especially fuel tanks, are designed to be as thin as possible, as every pound of vehicle structure sacrifices valuable payload weight and can dramatically increase the cost of flying a rocket," said Mark Hilburger, a senior research engineer in the Structural Mechanics and Concepts Branch at Langley and the principal investigator of the NESC's Shell Buckling Knockdown Factor project."Looking toward future heavy-lifters, our goal is to provide designers greater confidence in how buckling happens in structures so we can develop lighter-weight tanks."

Research to date suggests a potential weight savings of as much as 20 percent.

Leading up to the big crush in late March, the shell buckling team has previously tested four, 8-foot-diameter aluminum-lithium cylinders to failure. In preparation for the upcoming test, hundreds of sensors have been placed on the barrel section to measure strain, local deformations and displacement. In addition, advanced optical measurement techniques will be used to monitor tiny deformations over the entire outer surface of the test article.

"This unique test rig was essential to developing the lightweight space shuttle external tank that is flying today. Our sophisticated testing capability is back in action to better understand design factors for next-generation metallic launch vehicle structures," said Mike Roberts, an engineer in Marshall's Structural Strength Test branch and the center lead for this test activity."Months of preparation for the facility, test article, high-speed cameras and data systems are all in place and ready to support this major test."

The Shell Buckling Knockdown Factor Project is led and funded by the NESC; Marshall is responsible for the test including the engineering, the equipment design, the hardware facilities and safety assurance. Lockheed Martin Space Systems Company fabricated the test article at Marshall's Advance Weld Process Development Facility using state of the art welding and inspection techniques.

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Catalogue of Sustainable Design Resources Developed

From insulation made from mushrooms to kitchen tops created from recycled glass, Kingston University has catalogued more than 1,000 different sustainable materials for use in the construction industry. The result is a materials library, Rematerialise, which is being launched at EcoBuild, the world's largest event for showcasing sustainable design and construction practices.

Reader in sustainable design, Jakki Dehn has been developing Rematerialise at Kingston University's Faculty of Art, Design and Architecture for 17 years and believes designers will find it invaluable when planning new products."They can come and touch and feel a whole range of materials all in one place -- materials which, otherwise, they might have to spend weeks investigating themselves," she said.

Several firms have already drawn on Dehn's expertise to help with ongoing projects. Product design company Jedco, based in Weybridge in Surrey, has developed a scaffolding board made from recycled polymers and a solar-powered bus-stop."The scaffolding boards have proved useful on oil rigs, because unlike wood, they don't absorb water. So, in this case, the sustainable product is actually better than the material it's replacing," Dehn said.

Dehn began her research into sustainable materials in 1994 and received Arts and Humanities Research Council funding in 2003. Rematerialise now houses more than 1,200 materials from 15 different countries. It contains recycled materials, products made from resources that are very plentiful and easy to re-grow and products made from resources that are not generally used very much. The University hopes eventually to put the entire library online so planners can do initial research before making an appointment to view the materials themselves at Kingston University's Knights Park campus.

As word about the resource has spread, new products have started arriving on an almost daily basis."We recently received a new type of insulation material made from mushrooms. The piece we were sent was only an inch thick but, apparently, you could put your hand on one side of it and take a blow-torch to the other side and you wouldn't be able to feel the heat," said Dehn, who admitted she was yet to put it to the test. Another eye-catching material is resilica, which is used to make kitchen worktops as an alternative to granite or formica. It's made mainly of glass recycled from cars and building sites.

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Plants That Can Move Inspire New Adaptive Structures

Mechanical engineering professor Kon-Well Wang presented the team's latest work Feb. 19 at the American Association for the Advancement of Science's 2011 Annual Meeting in Washington D.C. Wang is the Stephan P. Timoshenko Collegiate Professor of Mechanical Engineering and chair of the Department of Mechanical Engineering.

"This is quite different from other traditional adaptive materials approaches," Wang said."In general, people use solid-state materials to make adaptive structures. This is really a unique concept inspired by biology."

Researchers at U-M and Penn State University are studying how plants like the Mimosa can change shape, and they're working to replicate the mechanisms in artificial cells. Today, their artificial cells are palm-size and larger. But they're trying to shrink them by building them with microstructures and nanofibers. They're also exploring how to replicate the mechanisms by which plants heal themselves.

"We want to put it all together to create hyper-cellular structures with circulatory networks," Wang said.

The Mimosa is among the plant varieties that exhibit specialized"nastic motions," large movements you can see in real time with the naked eye, said Erik Nielsen, assistant professor in the U-M Department of Molecular, Cellular and Developmental Biology.

The phenomenon is made possible by osmosis, the flow of water in and out of plants' cells. Triggers such as touch cause water to leave certain plant cells, collapsing them. Water enters other cells, expanding them. These microscopic shifts allow the plants to move and change shape on a larger scale.

It's hydraulics, the researchers say.

"We know that plants can deform with large actuation through this pumping action," Wang said."This and several other characteristics of plant cells and cell walls have inspired us to initiate ideas that could concurrently realize many of the features that we want to achieve for adaptive structures."

Nielsen believes nastic movements might be a good place to start trying to replicate plant motions because they don't require new growth or a reorganization of cells.

"These rapid, nastic motions are based on cells and tissues that are already there," Nielsen said."It's easy for a plant to build new cells and tissues during growth, but it's not as easy to engineer an object or machine to completely change the way it's organized. We hope studying these motions can inform us about how to make efficient adaptive materials that display some of the same types of flexibility that we see in biological systems."

When this technology matures, Wang said it could enable robots that change shape like elephant trunks or snakes to maneuver under a bridge or through a tunnel, but then turn rigid to grab a hold of something. It also could lead to morphing wings that would allow airplanes to behave more like birds, changing their wing shape and stiffness in response to their environment or the task at hand.

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Better Way to Diagnose Pneumonia

Called PneumoniaCheck, the device created at Georgia Tech is a solution to the problem of diagnosing pneumonia, which is a major initiative of the U.S. Centers for Disease Control and Prevention (CDC).

Pneumonia, an inflammation of the lungs, kills about 2.4 million people each year. The problem is particularly devastating in Africa, Southeast Asia and the Eastern Mediterranean, where a child dies of pneumonia every 15 seconds.

Developed by mechanical engineering students, graduate business students and faculty at Georgia Tech, PneumoniaCheck will be commercially launched this month to healthcare professionals through the startup company, MD Innovate Inc.

"Georgia Tech created a simple and new device to detect the lung pathogens causing pneumonia," said David Ku, Georgia Tech Regents' Professor of Mechanical Engineering, Lawrence P. Huang Chair Professor for Engineering Entrepreneurship in the College of Management, and Professor of Surgery at Emory University."It has the potential to save more lives than any other medical device."

Last year, Ku was asked by the head of virology at the CDC to develop a quick and economical way to diagnose pneumonia, particularly in developing nations where it is a leading cause of death among children.

Ku challenged a group of mechanical engineering and bioengineering graduate students to develop an accurate device for diagnosing pneumonia. Current sampling methods using the mouth and nose are only 40 percent effective. The samples are typically contaminated by bacteria in the mouth, which leads to misdiagnosis and an incorrect prescription of antibiotics.

In developing nations, many children with respiratory infections fail to receive adequate care, and the overuse of antibiotics has led to an increase in drug-resistant bacteria. An accurate, easy-to-use and widely available new diagnostic test could improve identification of bacterial respiratory infection in children, reducing the inappropriate use of antibiotics and the long-term negative impacts of drug resistance, according to a recent article inNaturetitled"Reducing the global burden of acute lower respiratory infections in children: The contributions of new diagnostics."

As a Tech graduate student, Tamera Scholz and her peers developed the solution -- PneumoniaCheck.

The device contains a plastic tube with a mouthpiece. A patient coughs into the device to fill up a balloon-like upper airway reservoir before the lung aerosols go into a filter. Using fluid mechanics, PneumoniaCheck separates the upper airway particles of the mouth from the lower airway particles coming from the lungs.

"It's interesting because it's so simple," said Scholz (M.S. '10 Mechanical Engineering), who is now an engineer for Newell Rubbermaid."It's not a fancy contraption. It's a device that patients cough into and through fluid mechanics it separates upper and lower airway aerosols. Through each iteration, it got simpler.… I like that I will be able to see it make a difference in my lifetime."

Once the device was developed, Taylor Bronikowski and a group of Georgia Tech M.B.A. students from the College of Management started developing a business plan for PneumoniaCheck that starts locally and grows globally. They used the device as a test case to develop a Triple Bottom Line company in India that could result in financial profits, environmental sustainability and social benefits, such as jobs and healthcare.

"Our goal is to provide better medicine at a cost savings to patients and hospitals," Bronikowski said."We wanted a worldwide solution, so patients in developing nations can afford it."

Bronikowksi, Ku and Sarah Ku formed the startup company, MD Innovate Inc., in 2010 to manufacture the device in large quantities and organize distribution and commercialization. The device is now being used in pneumonia studies at Grady Memorial Hospital in downtown Atlanta and the Atlanta Veterans Administration Medical Center, Ku said.

The FDA has cleared PneumoniaCheck for sale in the U.S. The device is licensed but its patent is pending. The company will start selling PneumoniaCheck in the U.S. in January and it could hit other countries in two years, Ku said.

"It's a great feeling, working on something that has the potential to save thousands of lives," Bronikowski said.

On the horizon, Ku and future Georgia Tech graduate students will be developing a simple and effective method for diagnosing pneumonia in regions without healthcare facilities or basic infrastructure.

For more information, visit:http://www.mdinnov8.com/

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Welders Can Breathe Easier With Chromium-Free Alloy, Research Suggests

The new nickel alloy consumable is more expensive compared to those already on the market, but worth the cost in situations where adequate ventilation is a problem.

That's why two Ohio State University engineers invented the alloy -- specifically to aid military and commercial welding personnel who work in tight spaces.

In tests, welds made with the new consumable proved just as strong and corrosion-resistant as welds made with commercial stainless steel consumables. When melted, however, the new alloy does not produce fumes of hexavalent chromium, a toxic form of the element chromium which has been linked to cancer.

All stainless steels contain chromium, but Gerald Frankel and John Lippold, both professors of materials science and engineering at Ohio State, determined that the consumable alloy that joins stainless steel parts together doesn't have to contain the metal.

Use of the new alloy essentially eliminates hexavalent chromium in the welding fumes.

The university has three issued US patents and a pending European patent application covering a series of alloys -- based on nickel and copper but with no chromium -- all of which can be used with standard welding equipment.

The new alloy is expensive, however. The engineers estimated that it would cost five to 10 times more than standard welding consumables, depending on metal prices.

The Occupational Safety and Health Administration sets limits on workers' exposure to hexavalent chromium in welding fumes, which affect welders themselves and their surrounding coworkers. Reduced exposure to such toxic fumes requires either extreme ventilation or use of a chromium-free consumable.

Frankel said that the high cost of the alloy would be justified in situations where ample ventilation may be impossible.

"I always think of someone welding a steel pipe, deep inside a ship at sea," he said."Ventilation might not be possible, and a breathing appartus for the welder would make working in a confined space even more difficult. In that case, using our alloy would lower the amount of ventilation needed, and help reduce costs overall."

Frankel is a corrosion expert; Lippold is a welding expert. Lippold was already looking for ways to limit the amount of another metal -- manganese, which can cause neurological damage -- in welding consumables, when Frankel approached him about chromium.

"We came up with an alloy that is compatible with stainless steel from a corrosion perspective, and a welding process that results in high quality welds," Lippold said."It is a drop-in replacement for stainless steel comsumables welders use now."

Sometimes welders use a consumable as a bare metal wire, and other times they need to use an electrode made from a metal core coated with flux -- a chemical agent that removes impurities from the weld. The Ohio State alloy works for either application.

In the laboratory, the researchers performed electrochemical tests to optimize the composition for corrosion resistance. They also performed mechanical tests of the weld joint to test the alloy's strength. The new alloy's performance was comparable to standard commercial welding consumables for stainless steel.

Frankel and Lippold have begun further testing of their alloy with Euroweld, Ltd., a manufacturer of specialty welding materials headquartered in Mooresville, North Carolina.

The engineers are now working on ways to lower the cost of the consumable.

The university will license the alloy and its applications for commercial development.

The Strategic Environmental Research and Development Program -- a partnership of the Department of Defense, the Environmental Protection Agency, and the Department of Energy -- funded this research.

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Gas Stations Pollute Their Immediate Surroundings, Spanish Study Finds

"Some airborne organic compounds -- such as benzene, which increases the risk of cancer -- have been recorded at petrol stations at levels above the average levels for urban areas where traffic is the primary source of emission," Marta Doval, co-author of the study and a researcher at the UM, said.

The study, which has been published in theJournal of Environmental Management, shows that the air at petrol stations and in their immediate surroundings is affected by emissions stemming from evaporated vehicle fuels (unburnt fuels from fuel loading and unloading operations, refuelling and liquid spillages).

The research team measured the levels of"typical traffic" pollutants in different parts of the urban area of Murcia, and calculated the quotients for the levels of an aromatic compound (benzene) and a hydrocarbon (n-hexane) at three Murcia petrol stations (near the petrol pumps and surrounding areas) to find the distance at which the service stations stop having an impact.

"In the three cases studied we obtained maximum distances of influence of close to 100 metres, although the average distance over which this contamination has an effect is around 50 metres," Enrique González, the UM researcher who led the research team, said.

However, the distances depend on the number of petrol pumps, the amount of fuel drawn from them, traffic intensity, the structure of the surroundings, and weather conditions.

According to the researcher,"the more contaminated the zone surrounding the petrol station as a result of other causes (traffic), the lower the impact of the two pollutants at the service station." If traffic in the area surrounding the petrol station is very intense, and exceeds the emissions from the station itself, pollution at the service station is"overlapped and goes unnoticed" over short distances.

Advice for new constructions

The research study shows that a"minimum" distance of 50 metres should be maintained between petrol stations and housing, and 100 metres for"especially vulnerable" facilities such as hospitals, health centres, schools and old people's homes."Ideally, the 100 metre distance should be respected in plans for building new houses," says Doval.

The researchers propose carrying out this study at new construction areas in which it is planned to build these kinds of facilities. However, petrol stations are not the only source of emission of these pollutants.

"There is not much use in protecting people from petrol stations if the other sources of emission (above all traffic and industries near population hubs) are not controlled or reduced," stresses González.

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Engineers Predict How Fire Spreads in Warehouses

Results of this research were recently published in the journalCombustion and Flame.

Despite many years of research, including the development of analytical and numerical models and extensive experimentation, the complexity of the process of upward flame spread continues to confound the fire-research community.

"Warehouse fires are definitely a big problem," said Michael Gollner, co-author of the paper and a UC San Diego mechanical and aerospace engineering Ph.D. student."It has been recently found that fully protected warehouses have burned down and that the sprinkler systems can't always control the fires. We still don't understand all the intricacies of this problem."

In their research, Gollner and his team are focusing on the most commonly used packaging material in warehouses -- corrugated cardboard -- which has been found to affect predictions of upward flame spread by current descriptions. As part of the study of the combustion of boxes of commodities, rates of upward flame spread during early-stage burning were observed during experiments on wide samples of corrugated cardboard. The research stems from previous experiments Gollner performed focused on the burning of cardboard in collaboration with Ali Rangwala, a professor in the Department of Fire Protection Engineering at the Worcester Polytechnic Institute and a UC San Diego graduate.

"The flame didn't spread exactly as was assumed so we did some further analysis on how the flame spread on a small scale," Gollner said."What we found is that the cardboard, while in the past was assumed to be a solid material, is actually not. There are different layers, and when it burns some of the cardboard actually peels up, so it slows the rate at which fire spreads. This is very important when you are determining how long it takes a fire to reach a sprinkler and trigger a water spray. At the initial phase, that's when you can actually extinguish a fire most easily. Calculating the sprinkler activation times is really important in designing a warehouse protection system."

Forman Williams, a UC San Diego mechanical and aerospace engineering professor and co-author of the paper, said the ultimate objective of this research is to help create better classifications of fire hazards in storing commodities and materials in warehouses.

"The density and the number of sprinklers they use in a warehouse and the flow rates of sprinklers are determined by the classifications and categories of the packaging material. So we are trying to help determine what the criteria should be," Williams said.

The engineers' warehouse fire research, Gollner said, is appealing to the insurance industry and the national regulatory industry, including the National Fire Protection Association, all of which have a big priority in making sure warehouses are safe.

"One of the biggest concerns is that these systems are designed for firefighter response; they are not made to put themselves out," Gollner explained."They are made to contain themselves until firefighters can enter.…Hopefully this will help become a part of new commodity classification standards in the future and in the way warehouses are designed. We hope to allow them to design warehouses safer not only to protect the goods in these warehouses but also the people who work in them and the firefighters who have to respond."

Next on the researchers' agenda is to conduct follow-on experiments looking at how fire spreads on surfaces at different angles, a project currently sponsored by the Society of Fire Protection Engineers, Educational and Scientific Foundation.

"We would like to understand better what controls the fire spread in different situations," Williams said."There are lots of things we really don't understand, although fire has been around for a very long time."

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An Ice-Bar Made from Pure Ice

Building structures from ice and snow is probably something everyone has tried in their youth. Today, using ice as a building material is also something which is being discussed by scientists. The research group supervised by Prof. Kollegger of the Institute of Structural Engineering is looking into ways of building large-scale, stable domes made of ice. Following a thorough preparatory and research phase, a new ice dome construction method is now being put to the test in Obergurgl -- a world first. This structure, showing more than 10 metres free span, is now home to a bar -- for as long as the temperatures are low enough.

Using ice as a building material has actually been done before: entire ice hotels have been built in e.g. Scandinavia."In most cases though the spans of the structures are small or the ice is not a load-bearing component and merely acts as cladding for the actual construction," explains Prof. Kollegger. The team of Vienna University of Technology has developed an ice dome which presents a stable and free-standing safe structure, and does not require additional support using other building materials. Theoretical calculations and several experiments have been carried out in this area over the past few years and, thanks to the latest technology, ice structures which are large and stable enough to actually be used as serviceable buildings can now be built.

Slow deformation process - like a glacier

First, a 20 cm-thick plate of ice is cut into 16 segments. These two-dimensional segments have then to be transformed into a three-dimensional structure. The University research team takes advantage of one property of ice, known as"creep behaviour." If pressure is applied to the ice, it can slowly change its shape without breaking. Glacial creep functions similarly."The segments of ice are placed on stacks of wood. Then, under the load of its own weight, the ice begins to change shape all by itself, resulting in a curved dome segment," explains Sonja Dallinger, research assistant at the Institute of Structural Engineering and on-site manager of the Obergurgl construction experiment.

The greatest challenge that had to be faced was the prevention of any breakage of the individually curved segments when assembling the dome. To solve this issue, a wooden tower was erected and the dome segments were held together by means of steel chains. The wooden tower could only be removed once all the segments had been positioned correctly and the ice dome stood on its own.

Austria's coolest bar

The ice dome was constructed in front of the spa area of the Hotel Alpina in Obergurgl and is presently being used as an ice bar. The drinks are definitely pretty cool -- and of course it's up to you whether or not to wear a cocktail dress!

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Nanoscale Rope: Complex Nanomaterials That Assemble Themselves

Berkeley Lab scientists have developed a nanoscale rope that braids itself, as seen in this atomic force microscopy image of the structure at a resolution of one-millionth of a meter.

Their work is the latest development in the push to develop self-assembling nanoscale materials that mimic the intricacy and functionality of nature's handiwork, but which are rugged enough to withstand harsh conditions such as heat and dryness.

Although still early in the development stage, their research could lead to new applications that combine the best of both worlds. Perhaps they'll be used as scaffolds to guide the construction of nanoscale wires and other structures. Or perhaps they'll be used to develop drug-delivery vehicles that target disease at the molecular scale, or to develop molecular sensors and sieve-like devices that separate molecules from one another.

Specifically, the scientists created the conditions for synthetic polymers called polypeptoids to assemble themselves into ever more complicated structures: first into sheets, then into stacks of sheets, which in turn roll up into double helices that resemble a rope measuring only 600 nanometers in diameter (a nanometer is a billionth of a meter).

"This hierarchichal self assembly is the hallmark of biological materials such as collagen, but designing synthetic structures that do this has been a major challenge," says Ron Zuckermann, who is the Facility Director of the Biological Nanostructures Facility in Berkeley Lab's Molecular Foundry.

In addition, unlike normal polymers, the scientists can control the atom-by-atom makeup of the ropy structures. They can also engineer helices of specific lengths and sequences. This"tunability" opens the door for the development of synthetic structures that mimic biological materials' ability to carry out incredible feats of precision, such as homing in on specific molecules.

"Nature uses exact length and sequence to develop highly functional structures. An antibody can recognize one form of a protein over another, and we're trying to mimic this," adds Zuckermann.

Zuckermann and colleagues conducted the research at The Molecular Foundry, which is one of the five DOE Nanoscale Science Research Centers premier national user facilities for interdisciplinary research at the nanoscale. Joining him were fellow Berkeley Lab scientists Hannah Murnen, Adrianne Rosales, Jonathan Jaworski, and Rachel Segalman. Their research was published in a recent issue of theJournal of the American Chemical Society.

The scientists worked with chains of bioinspired polymers called a peptoids. Peptoids are structures that mimic peptides, which nature uses to form proteins, the workhorses of biology. Instead of using peptides to build proteins, however, the scientists are striving to use peptoids to build synthetic structures that behave like proteins.

The team started with a block copolymer, which is a polymer composed of two or more different monomers.

"Simple block copolymers self assemble into nanoscale structures, but we wanted to see how the detailed sequence and functionality of bioinspired units could be used to make more complicated structures," says Rachel Segalman, a faculty scientist at Berkeley Lab and professor of Chemical and Biomolecular Engineering at University of California, Berkeley.

With this in mind, the peptoid pieces were robotically synthesized, processed, and then added to a solution that fosters self assembly.

The result was a variety of self-made shapes and structures, with the braided helices being the most intriguing. The hierarchical structure of the helix, and its ability to be manipulated atom-by-atom, means that it could be used as a template for mineralizing complex structures on a nanometer scale.

"The idea is to assemble structurally complex structures at the nanometer scale with minimal input," says Hannah Murnen. She adds that the scientists next hope is to capitalize on the fact that they have minute control over the structure's sequence, and explore how very small chemical changes alter the helical structure.

Says Zuckermann,"These braided helices are one of the first forays into making atomically defined block copolymers. The idea is to take something we normally think of as plastic, and enable it to adopt structures that are more complex and capable of higher function, such as molecular recognition, which is what proteins do really well."

X-ray diffraction experiments used to characterize the structures were conducted at beamlines 8.3.1 and 7.3.3 of Berkeley Lab's Advanced Light Source, a national user facility that generates intense x-rays to probe the fundamental properties of substances. This work was supported in part by the Office of Naval Research.

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Self-Assembling Structures Open Door to New Class of Materials

The helical"supermolecules" are made of tiny colloid balls instead of atoms or molecules. Similar methods could be used to make new materials with the functionality of complex colloidal molecules. The team publishes its findings in the Jan. 14 issue of the journalScience.

"We can now make a whole new class of smart materials, which opens the door to new functionality that we couldn't imagine before," said Steve Granick, Founder Professor of Engineering at the University of Illinois and a professor of materials science and engineering, chemistry, and physics.

Granick's team developed tiny latex spheres, dubbed"Janus spheres," which attract each other in water on one side, but repel each other on the other side. The dual nature is what gives the spheres their ability to form unusual structures, in a similar way to atoms and molecules.

In pure water, the particles disperse completely because their charged sides repel one another. However, when salt is added to the solution, the salt ions soften the repulsion so the spheres can approach sufficiently closely for their hydrophobic ends to attract. The attraction between those ends draws the spheres together into clusters.

At low salt concentrations, small clusters of only a few particles form. At higher levels, larger clusters form, eventually self-assembling into chains with an intricate helical structure.

"Just like atoms growing into molecules, these particles can grow into supracolloids," Granick said."Such pathways would be very conventional if we were talking about atoms and molecules reacting with each other chemically, but people haven't realized that particles can behave in this way also."

The team designed spheres with just the right amount of attraction between their hydrophobic halves so that they would stick to one another but still be dynamic enough to allow for motion, rearrangement, and cluster growth.

"The amount of stickiness really does matter a lot. You can end up with something that's disordered, just small clusters, or if the spheres are too sticky, you end up with a globular mess instead of these beautiful structures," said graduate student Jonathan Whitmer, a co-author of the paper.

One of the advantages of the team's supermolecules is that they are large enough to observe in real time using a microscope. The researchers were able to watch the Janus spheres come together and the clusters grow -- whether one sphere at a time or by merging with other small clusters -- and rearrange into different structural configurations the team calls isomers.

"We design these smart materials to fall into useful shapes that nature wouldn't choose," Granick said.

Surprisingly, theoretical calculations and computer simulations by Erik Luijten, Northwestern University professor of materials science and engineering and of engineering sciences and applied mathematics, and Whitmer, a student in his group, showed that the most common helical structures are not the most energetically favorable. Rather, the spheres come together in a way that is the most kinetically favorable -- that is, the first good fit that they encounter.

Next, the researchers hope to continue to explore the colloid properties with a view toward engineering more unnatural structures. Janus particles of differing sizes or shapes could open the door to building other supermolecules and to greater control over their formation.

"These particular particles have preferred structures, but now that we realize the general mechanism, we can apply it to other systems -- smaller particles, different interactions -- and try to engineer clusters that switch in shape," Granick said.

The team also included University of Illinois graduate students Qian Chen and Shan Jiang and research scientist Sung Chul Bae. The U.S. Department of Energy and the National Science Foundation supported this work.

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Chemists Develop Fully Biodegradable and Recyclable Synthetic Resin

Most plastic products for domestic or construction use consist of three-dimensional networks of cross-linked polymers. These are thermosetting plastics. A classic example is the Bakelite resin produced from the reaction of phenol with formaldehyde. This material is still used to bind wood fibers in pressed wood such as medium density fiberboard (MDF) and formica. Synthetic resins are widely used in the construction industry. The resin of urea / formaldehyde is used in Medium Density Overlay (MDO), a combination of concrete and plywood, used in concrete molds.

Completely biodegradable bioplastics

By selecting the right raw materials and process conditions for the cross-linking reaction the scientists, who work for the UvA'sHeterogeneous Catalysis and Sustainable Chemistryresearch group, were able to make a range of bio-plastics ranging from hard foam material to flexible thin sheet materials. These are non-toxic and biodegradable. The process requires no toxic ingredients and no harmful substances are released from combustion. Moreover, the raw materials are readily available at competitive prices on the world market.

The new plastic could replace polyurethane and polystyrene in the construction and packaging industries. This also applies to the epoxy resins used for panels such as MDF. The follow-up research will focus on new applications and process development and upscaling.

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No Left Turn: 'Superstreet' Traffic Design Improves Travel Time, Safety

Superstreets are surface roads, not freeways. It is defined as a thoroughfare where the left-hand turns from side streets are re-routed, as is traffic from side streets that needs to cross the thoroughfare. In both instances, drivers are first required to make a right turn and then make a U-turn around a broad median. While this may seem time-consuming, the study shows that it actually results in a significant time savings since drivers are not stuck waiting to make left-hand turns or for traffic from cross-streets to go across the thoroughfare.

"The study shows a 20 percent overall reduction in travel time compared to similar intersections that use conventional traffic designs," says Dr. Joe Hummer, professor of civil, construction and environmental engineering at NC State and one of the researchers who conducted the study."We also found that superstreet intersections experience an average of 46 percent fewer reported automobile collisions -- and 63 percent fewer collisions that result in personal injury."

The researchers assessed travel time at superstreet intersections as the amount of time it takes a vehicle to pass through an intersection from the moment it reaches the intersection -- whether traveling left, right or straight ahead. The travel-time data were collected from three superstreets located in eastern and central North Carolina, all of which have traffic signals. The superstreet collision data were collected from 13 superstreets located across North Carolina, none of which have traffic signals.

The superstreet concept has been around for over 20 years, but little research had been done to assess its effectiveness under real-world conditions. The NC State study is the largest analysis ever performed of the impact of superstreets in real traffic conditions.

A paper on the travel time research is being presented Jan. 24 at the Transportation Research Board Annual Meeting in Washington, D.C. The paper is co-authored by Hummer, former NC State graduate students Rebecca Haley and Sarah Ott, and three researchers from NC State's Institute for Transportation Research and Education: Robert Foyle, associate director; Christopher Cunningham, senior research associate; and Bastian Schroeder, research associate.

The collision research was part of an overarching report of the study submitted to the North Carolina Department of Transportation (NCDOT) last month, and is the subject of a forthcoming paper. The study was funded by NCDOT.

NC State's Department of Civil, Construction and Environmental Engineering is part of the university's College of Engineering.

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Coiled Nanowires May Hold Key to Stretchable Electronics

"In order to create stretchable electronics, you need to put electronics on a stretchable substrate, but electronic materials themselves tend to be rigid and fragile," says Dr. Yong Zhu, one of the researchers who created the new nanowire coils and an assistant professor of mechanical and aerospace engineering at NC State."Our idea was to create electronic materials that can be tailored into coils to improve their stretchability without harming the electric functionality of the materials."

Other researchers have experimented with"buckling" electronic materials into wavy shapes, which can stretch much like the bellows of an accordion. However, Zhu says, the maximum strains for wavy structures occur at localized positions -- the peaks and valleys -- on the waves. As soon as the failure strain is reached at one of the localized positions, the entire structure fails.

"An ideal shape to accommodate large deformation would lead to a uniform strain distribution along the entire length of the structure -- a coil spring is one such ideal shape," Zhu says."As a result, the wavy materials cannot come close to the coils' degree of stretchability." Zhu notes that the coil shape is energetically favorable only for one-dimensional structures, such as wires.

Zhu's team put a rubber substrate under strain and used very specific levels of ultraviolet radiation and ozone to change its mechanical properties, and then placed silicon nanowires on top of the substrate. The nanowires formed coils upon release of the strain. Other researchers have been able to create coils using freestanding nanowires, but have so far been unable to directly integrate those coils on a stretchable substrate.

While the new coils' mechanical properties allow them to be stretched an additional 104 percent beyond their original length, their electric performance cannot hold reliably to such a large range, possibly due to factors like contact resistance change or electrode failure, Zhu says."We are working to improve the reliability of the electrical performance when the coils are stretched to the limit of their mechanical stretchability, which is likely well beyond 100 percent, according to our analysis."

A paper describing the research was published online Dec. 28 byACS Nano. The paper is co-authored by Zhu, NC State Ph.D. student Feng Xu and Wei Lu, an assistant professor at the University of Michigan. The research was funded by the National Science Foundation.

NC State's Department of Mechanical and Aerospace Engineering is part of the university's College of Engineering.

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Recycled Haitian Concrete Can Be Safe, Strong and Less Expensive, Researchers Say

In a paper published in theBulletin of the American Ceramic Society, researchers Reginald R. DesRoches, Kimberly E. Kurtis and Joshua J. Gresham say that they have made new concrete, from recycled rubble and other indigenous raw materials using simple techniques, which meets or exceeds the minimum strength standards used in the United States.

Most of the damaged areas of Haiti are still in ruins. The trio says their work points to a successful and sustainable strategy for managing an unprecedented amount of waste, estimated to be 20 million cubic yards.

"The commodious piles of concrete rubble and construction debris form huge impediments to reconstruction and are often contaminated," says DesRoches, professor and Associated Chair of Civil and Environmental Engineering at Georgia Tech."There are political and economic dilemmas as well, but we have found we can turn one of the dilemmas -- the rubble -- into a solution via some fairly simple methods of recycling the rubble and debris into new concrete."

DesRoches, who was born in Haiti, traveled several times in 2010 to Port-au-Prince to gather samples of typical concrete rubble and additionally collect samples of two readily available sand types used as fine aggregates in some concrete preparation.

He and Gresham also studied the methods, tools and raw materials used by local laborers to make concrete mixes. DesRoches recalls they encountered no mixing trucks."Instead, all of the construction crews were manually batching smaller amounts of concrete. Unfortunately, they were mixing volumes of materials 'by eye,' an unreliable practice that probably caused much of the poor construction and building failure during the earthquake," he says.

Before leaving, DesRoches and Gresham manually cast an initial set of standard 3-inch by 6-inch concrete test blocks using mixes from several different construction sites.

They returned to Georgia Tech with their cast blocks, sand samples and notes, where they were joined by Kurtis, also a professor and Chair of the American Concrete Institute's Materials Science of Concrete Committee.

They quickly discovered that the concrete test samples cast in Haiti were of poor quality."The Haitian-made concrete had an average compressive strength of 1,300 pounds per square inch," says Kurtis."In comparison, concrete produced in the U.S. would be expected to have a minimum strength of 3,000 pounds per square inch.

They then manually crushed the samples with a hammer to provide course aggregate for a second round of tests. In this round, they made concrete samples from mixes that combined the course aggregate with one of the two types of sands they had collected. However, instead of"eye-balling" the amounts of materials, in this round of tests they carefully measured volumes using methods prescribed by the American Concrete Institute. The materials were still mixed by hand to replicate the conditions in Haiti.

Subsequent tests of samples made from each type of sand provided good news: The compressive strength of both of the types of new test blocks, still composed of Haitian materials, dramatically increased, showing an average over 3,000 pounds per square inch.

"Based upon these results, we now believe that Haitian concrete debris, even of inferior quality, can be effectively used as recycled course aggregate in new construction," says Kurtis."It can work effectively, even if mixed by hand. The key is having a consistent mix of materials that can be easily measured. We are confident are results can be scaled up mix procedure where quantities can be measured using common, inexpensive construction equipment."

DesRoches is pleased because recycling eliminates two hurdles to reconstruction."First, removing the remaining debris is nearly impossible because there are few, if any, safe landfill sites near Port-au-Prince, and the nation lacks the trucks and infrastructure to haul it away. It is better to use it than to move it."Second," DesRoches says,"Finding fresh aggregate is more difficult than getting rid of the debris. It is costly to find, mine and truck in."

The trio notes recycled concrete aggregate has been used worldwide for roadbeds, drainage, etc., and that many European Union countries commonly use 20 percent recycled aggregates in structural concrete. Published research by others has also demonstrated that the use of local-sourced recycled aggregate concrete production can be more sustainable.

Because of the urgency of quick and safe reconstruction, the researchers urge that recycling the debris quickly move from proof-of-concept to large scale testing."More work must be done to characterize the recycled materials, test additional performance parameters and gauge the safest ways to crush the rubble. Seismic behavior and building codes must be studied. But, these tests can and should be done dynamically, during reconstruction, because the benefits can be so immediate and significant," says DesRoches.

DesRoches, Kurtis and Gresham say they plan on sharing their research with Haitian government officials and nongovernmental organizations working on reconstruction projects. DesRoches is hopeful that a debris strategy and infrastructure will eventually emerge from the government once the disputed presidential elections in Haiti are resolved."Some think that many rebuilding projects have on hold for the past few months because of distraction from the elections. The next round of elections is this month, so it soon may be possible to accelerate reconstruction."

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