Friday, August 6, 2010

NANOTECHNOLOGY FOR WATER PURIFICATION

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Nanotechnology refers to a broad range of tools, techniques and applications that simply involve particles on the approximate size scale of a few to hundreds of nanometers in diameter. Particles of this size have some unique physicochemical and surface properties that lend themselves to novel uses. Indeed, advocates of nanotechnology suggest that this area of research could contribute to solutions for some of the major problems we face on the global scale such as ensuring a supply of safe drinking water for a growing population, as well as addressing issues in medicine, energy, and agriculture.

Writing in the International Journal of Nuclear Desalination, researchers at the D.J. Sanghvi College of Engineering, in Mumbai, India, explain that there are several nanotechnology approaches to water purification currently being investigated and some already in use. "Water treatment devices that incorporate nanoscale materials are already available, and human development needs for clean water are pressing," Alpana Mahapatra and colleagues Farida Valli and Karishma Tijoriwala, explain.

Water purification using nanotechnology exploits nanoscopic materials such as carbon nanotubes and alumina fibers for nanofiltration, it also utilizes the existence of nanoscopic pores in zeolite filtration membranes, as well as nanocatalysts and magnetic nanoparticles. Nanosensors, such as those based on titanium oxide nanowires or palladium nanoparticles are used for analytical detection of contaminants in water samples.

The impurities that nanotechnology can tackle depend on the stage of purification of water to which the technique is applied, the team adds. It can be used for removal of sediments, chemical effluents, charged particles, bacteria and other pathogens. They explain that toxic trace elements such as arsenic, and viscous liquid impurities such as oil can also be removed using nanotechnology.

"The main advantages of using nanofilters, as opposed to conventional systems, are that less pressure is required to pass water across the filter, they are more efficient, and they have incredibly large surface areas and can be more easily cleaned by back-flushing compared with conventional methods," the team says.

For instance, carbon nanotube membranes can remove almost all kinds of water contaminants including turbidity, oil, bacteria, viruses and organic contaminants. Although their pores are significantly smaller carbon nanotubes have shown to have an equal or a faster flow rate as compared to larger pores, possibly because of the smooth interior of the nanotubes. Nanofibrous alumina filters and other nanofiber materials also remove negatively charged contaminants such as viruses, bacteria, and organic and inorganic colloids at a faster rate than conventional filters.

"While the current generation of nanofilters may be relatively simple, it is believed that future generations of nanotechnology-based water treatment devices will capitalize on the properties of new nanoscale materials," the team says.

The researchers point out that several fundamental aspects of nanotechnology have raised concerns among the public and activist groups. They concede that the risks associated with nanomaterials may not be the same as the risks associated with the bulk versions of the same materials because the much greater surface area to volume ratio of nanoparticles can make them more reactive than bulk materials and lead to so far unrecognized and untested interactions with biological surfaces. Water purification based on nanotechnology has not yet led to any human health or environmental problems but the team echoes the sentiment of others that further research into the biological interactions of nanoparticles should be carried out.

Inderscience Publishers

ARTIFICIALLY CONTROLLING WATER CONDENSATION LEADS TO 'ROOM-TEMPERATURE ICE'

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Earth's climate is strongly influenced by the presence of particles of different shapes and origins -- in the form of dust, ice and pollutants -- that find their way into the lowest portion of the atmosphere, the troposphere. There, water adsorbed on the surface of these particles can freeze at higher temperatures than pure water droplets, triggering rain and snow.

Researchers at Spain's Centre d'Investigació en Nanociència i Nanotecnologia (CIN2) have studied the underlying mechanisms of water condensation in the troposphere and found a way to make artificial materials to control water condensation and trigger ice formation at room temperature. Described in the Journal of Chemical Physics, which is published by the American Institute of Physics, their work may lead to new additives for snowmaking, improved freezer systems, or new coatings that help grow ice for skating rinks.

"Several decades ago, scientists predicted that materials with crystal faces exhibiting a structure similar to that of hexagonal ice, the form of all natural snow and ice on Earth, would be an ideal agent to induce freezing and trigger rain," explains Dr. Albert Verdaguer. "This explanation has since proven to be insufficient."

The research team chose to study barium fluoride (BaF2), a naturally occurring mineral, also known as "Frankdicksonite," as an option. They examined water adsorption on BaF2 (111) surfaces under ambient conditions using different scanning force microscopy modes and optical microscopy to zoom in on the role atomic steps play in the structure of water films, which can affect the stabilization of water bilayers and, ultimately, condensation.

Despite having the desired hexagonal structure, BaF2 turned out to be a poor ice-nucleating material. But oddly enough, other researchers had discovered that when the mineral's surface has defects, its condensation efficiency is enhanced.

Verdaguer and his colleagues figured out why this occurs. "Under ambient conditions -- room temperature and different humidities -- we observed that water condensation is mainly induced by the formation of two-dimensional ice-like patches at surface defects," Verdaguer says. "Based on our results and previous research, we're preparing artificial materials to improve water condensation in a controllable way."

The next step? The researchers' goal now is to produce environmentally-friendly synthetic materials for efficiently inducing snow. "If water condenses in an ordered way, such as a hexagonal structure, on such surfaces at ambient conditions, the term 'room temperature ice' would be fully justified," adds Verdaguer. "The solid phase, ice, would be produced by a surface effect rather than as a consequence of temperature. In the long term, we intend to prepare smart materials, 'intelligent surfaces,' that will react to water in a predefined way."

American Institute of Physics

BACKGROUND MUSIC CAN IMPAIR PERFORMANCE

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For decades research has shown that listening to music alleviates anxiety and depression, enhances mood, and can increase cognitive functioning, such as spatial awareness. However, until now, research has not addressed how we listen to music. For instance, is the cognitive benefit still the same if we listen to music whilst performing a task, rather than before it? Further, how does our preference for a particular type of music affect performance? A new study from Applied Cognitive Psychology shows that listening to music that one likes whilst performing a serial recall task does not help performance any more than listening to music one does not enjoy.

The researchers explored the ‘irrelevant sound effect’ by requiring participants to perform serial recall (recall a list of 8 consonants in presentation order) in the presence of five sound environments: quiet, liked music (e.g., Rihanna, Lady Gaga, Stranglers, and Arcade Fire), disliked music (the track “Thrashers” by Death Angel), changing-state (a sequence of random digits such as “4, 7, 1, 6”) and steady-state (“3, 3, 3”). Recall ability was approximately the same, and poorest, for the music and changing-state conditions. The most accurate recall occurred when participants performed the task in the quieter, steady-state environments. Thus listening to music, regardless of whether people liked or disliked it, impaired their concurrent performance.

Lead researcher Nick Perham explains: “The poorer performance of the music and changing-state sounds are due to the acoustical variation within those environments. This impairs the ability to recall the order of items, via rehearsal, within the presented list. Mental arithmetic also requires the ability to retain order information in the short-term via rehearsal, and may be similarly affected by their performance in the presence of changing-state, background environments.”

Although music can have a very positive effect on our general mental health, music can, in the circumstances described, also have negative effects on cognitive performance. Perham remarks, “Most people listen to music at the same time as, rather than prior to performing a task. To reduce the negative effects of background music when recalling information in order one should either perform the task in quiet or only listen to music prior to performing the task.”

John Wiley & Sons, Inc.

GUT MOVEMENTS IN CATERPILLARS INSPIRE SOFT-BODY ROBOT DESIGN

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"Weird movements" in the abdomens of freely crawling caterpillars are making headlines in the fields of engineering and biology, says Jake Socha, Virginia Tech assistant professor of engineering science and mechanics. Beyond evolutionary implications, the findings are already contributing to the design and development of soft material robots.

The work of an interdisciplinary research team, including Socha, lead author Michael Simon of Tufts University's Department of Biology, and senior author Barry Trimmer, professor of biology at Tufts in whose laboratory the research was done, is appearing in the August 28, 2010 issue of Current Biology.

Describing their findings, the researchers said they used a type of powerful X-ray imaging to discover internal soft-tissue movements that were massively out of sync with the external body movements. The need for X-rays was because large caterpillars are entirely opaque. They then verified these findings using transmission-light microscopy to see the internal soft-tissue movements of smaller, translucent caterpillars as they slowly inched their way along a glass microscope slide. As the dissection microscope magnified the images, the researchers recorded them to a video camera, and then captured them on a computer.

This combined imaging showed that the caterpillar's gut slid forward in advance of the surrounding tissues. Seem inconsequential? Actually, it is "unlike any form of legged locomotion previously reported and represents a new feature in our emerging understanding of crawling," they reported in Current Biology.

The novelty is that the caterpillar's center of mass moves forward while the middle 'legs' are anchored to the substrate. The internal gut movements are locally decoupled from visible translations of the body. "This type of two-body mechanical system has never been seen before, and is probably unique to soft, squishy animals," Socha explained.

Using powerful x-rays generated by the Advanced Photon Source at Argonne National Laboratory in Argonne, Illinois, they were actually able to track the tracheae of the caterpillars. These gas-filled tubes inside the slow-moving insects supply all the tissues of their bodies with oxygen and vent carbon dioxide to the exterior via spiral openings in their body walls. The tracheae proved to be reliable markers that connected to both the body walls and the guts of the caterpillars.

Socha said they "quantified the relative timing of the gut, body wall, and proleg movements during the individual crawls. Each crawl began with a step by the rear 'legs' followed by a forward-moving wave of overlapping contractions and middle 'leg' steps in successive segments.

"Remarkably, at the start of each crawl, the gut in mid-body segments moved in advance of the body wall and prior to the middle 'leg' swing phases."

This movement meant the abdomen typically advanced an entire step forward before the body wall caught up. The researchers described it as "a unique phenomenon of gut sliding."

Since the research team is also interested in engineering applications, they moved from considering the biological implications of an internally pistoning gut to potential uses in soft-bodied robots.

Their findings are already finding their way into designing maneuverable and orientation-independent soft material robots. The next step for these 'softbots' includes a diverse array of potential uses, such as shape-changing robots capable of engaging in search-and-rescue operations, space applications for which a 'gravity-agnostic' crawler would be highly valued, and medical applications in which a biocompatible, soft robot would reduce incidental tissue damage and discomfort.

(Photo: Virginia Tech)

Virginia Tech

GRAPHENE ORGANIC PHOTOVOLTAICS, OR, WILL JOGGERS' T-SHIRTS SOMEDAY POWER THEIR CELL PHONES?

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A University of Southern California team has produced flexible transparent carbon atom films that the researchers say have great potential for a new breed of solar cells.

"Organic photovoltaic (OPV) cells have been proposed as a means to achieve low cost energy due to their ease of manufacture, light weight, and compatibility with flexible substrates," wrote Chongwu Zhou, a professor of electrical engineering in the USC Viterbi School of Engineering, in a paper recently published in the journal ACS Nano.

The technique described in the article describes progress toward a novel OPV cell design that has significant advantages, particularly in the area of physical flexibility.

A critical aspect of any OPV photo-electronic device is a transparent conductive electrode through which light can couple with active materials to create electricity. The new work indicates that graphene, a highly conductive and highly transparent form of carbon made up of atoms-thick sheets of carbon atoms, has high potential to fill this role.

While graphene's existence has been known for decades, it has only been studied extensively since 2004 because of the difficulty of manufacturing it in high quality and in quantity.

The Zhou lab reported the large scale production of graphene films by chemical vapor deposition three years ago. In this process, the USC engineering team creates ultra thin graphene sheets by first depositing carbon atoms in the form of graphene films on a nickel plate from methane gas.

Then they lay down a protective layer of thermo plastic over the graphene layer, and then dissolve the nickel underneath in an acid bath. In the final step they attach the plastic-protected graphene to a very flexible polymer sheet, which can then be incorporated into a OPV cell.

The USC team has produced graphene/polymer sheets ranging in sizes up to 150 square centimeters that in turn can be used to create dense arrays of flexible OPV cells.

These OPV devices convert solar radiation to electricity, but not as efficiently as silicon cells. The power provided by sunlight on a sunny day is about 1000 watts per meter square. "For every 1000 watts of sunlight that hits a one square meter area of the standard silicon solar cell, 14 watts of electricity will be generated," says Lewis Gomez De Arco, a doctoral student and a member of the team that built the graphene OPVs. "Organic solar cells are less efficient; their conversion rate for that same one thousand watts of sunlight in the graphene-based solar cell would be only 1.3 watts."

But what graphene OPVs lack in efficiency, they can potentially more than make for in lower price and, greater physical flexibility. Gomez De Arco thinks that it may eventually be possible to run printing presses laying extensive areas covered with inexpensive solar cells, much like newspaper presses print newspapers.

"They could be hung as curtains in homes or even made into fabric and be worn as power generating clothing. I can imagine people powering their cellular phone or music/video device while jogging in the sun," he said.

The USC researchers say graphene OPVs would be major advance in at least one crucial area over a rival OPV design, one based on Indium–Tin–Oxide (ITO). In the USC team's tests, ITO cells failed at a very small angle of bending, while the graphene-based cells remained operational after repeated bending at much larger stress angles. This would give the graphene solar cells a decided advantage in some uses, including the printed-on-fabric applications proposed by the USC team.

Zhou and the other researchers on the USC team – which included Yi Zhang, Cody W. Schlenker, Koungmin Ryu, and Mark E. Thompson in addition to Gomez de Arco — are excited by the potential for this technology.

Their paper concludes that their approach constitutes a significant advance toward the production of transparent conductive electrodes in solar cells. "CVD graphene meets the most important criteria of abundance, low cost, conductivity, stability, electrode/organic film compatibility, and flexibility that are necessary to replace ITO in organic photovoltaics, which may have important implications for future organic optoelectronic devices."

(Photo: USC Viterbi School of Engineering)

University of Southern California

TRAVELING MICROORGANISMS

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Every day, millions of microorganisms reach Spain from the Sahara Desert and the Sahel region – by flying. Louis Pasteur demonstrated back in 1861 that germs can move through the air, but it was only recently discovered that bacteria, funguses and viruses can travel thousands of kilometers stuck onto dust particles.

Satellite images show clouds that come close to the size of the Iberian Peninsula. For the first time, the international team on the Ecosensor project, funded by the BBVA Foundation, have analyzed these traveling microorganisms using molecular biology techniques. As well as identifying the species, they have found that they colonize high-mountain lakes in the Sierra Nevada and the Pyrenees, and that the phenomenon is escalating with climate change.

The "migration" of these microorganisms on African dust is most intense in spring and summer, and has been gathering momentum in recent years; at times multiplying their numbers ten times over. This is due, researchers say, to the drought afflicting the Sahel region for the last thirty years, itself a product of our changing climate. An added spur is the loss of plant cover in Africa driven by changes in farming practices. It is reckoned that between 60 and 200 million tons of dust rise up from the Sahara every year; a material rich in nitrogen, phosphorous and iron with an important role in the growth of marine plankton, and even the fertilization of tropical forests.

Ecosensor brings together an international team of atmospheric physicists and biologists led by Isabel Reche, of the University of Granada, and Emilio O. Casamayor, from the Blanes Center for Advanced Studies. The molecular biology techniques these researchers use allow them to detect almost all the organisms present in a given sample, in contrast to earlier methods which Reche explains revealed "a good deal less than there really is".

That is why until now we could not even identify 0.1 percent of the 500 bacteria present in a liter of air, and had no inkling of how they might affect their "destination" ecosystems. The Saharan dust spreads across the whole planet, but the prevailing winds – from the east – mean the regions most affected are the Canary Islands and the Caribbean (see satellite photos).

Ecosensor researchers have taken air samples in the places where it is easiest to detect the rain of microorganisms, such as high-mountain lakes. "Such spots have barely been altered by local human activity" Reche remarks, " so they are invaluable for studying the incidence of invading airborne microorganisms blown in from remote sources".

The lakes chosen are located in Sierra Nevada and the Pyrenees, as well as the Alps (Austria), Argentinean Patagonia, the Bylot Islands in the Arctic (Canada), and the South Shetland archipelago (Antarctica).

The researchers suck out air, filter it and extract the DNA of the organisms present. "By analyzing the genes we can tell what microorganism they belong to," Reche continues. They also separate the microorganisms to ascertain which can reach the lakes alive.

Their results, which have recently appeared in various scientific publications, show that Sierra Nevada and Pyrenean lakes harbor microorganisms "that we have also found in the soil in Mauritania", says Reche. "It is truly amazing". Among the microorganisms identified are Pseudomonas – a Bacillus genus capable of colonizing a wide range of niches; Staphylococci – a genus that includes microorganisms present in human skin, and Acinetobacter, which contribute to the mineralization of the soil. In general terms, they are considered to be non-pathogenic for humans.

But how might the advent of these new microorganisms affect local ecosystems? "The increase in dust load in pristine ecosystems, like high-mountain lakes, has major repercussions" explains Reche, "because with it come nutrients that fertilize the lakes and alter their microbial communities". Some of these changes have harmful effects; indeed the dust may already be damaging the fauna and flora of some ecosystems. Caribbean corals, for instance, are suffering decline due to excess dust deposition.

Another big question is, how do microorganisms manage to stay biologically active after their journey? The dust travels at between 2000 and 4000 meters altitude, exposed to severe dryness and harmful radiation; not all the organisms found form spores, so they must have other defense mechanisms at their command. One hypothesis mentioned by Reche is "an increase in the quantity of protective pigments, which adhere to the mineral particles, conferring a degree of protection".

(Photo: BBVA)

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