April 9, 2009, 4:46 AM CT

Aerosols may drive a significant portion of arctic warming

Though greenhouse gases are invariably at the center of discussions about global climate change, new NASA research suggests that much of the atmospheric warming observed in the Arctic since 1976 appears to be due to changes in tiny airborne particles called aerosols.

Emitted by natural and human sources, aerosols can directly influence climate by reflecting or absorbing the sun's radiation. The small particles also affect climate indirectly by seeding clouds and changing cloud properties, such as reflectivity.

A newly released study, led by climate scientist Drew Shindell of the NASA Goddard Institute for Space Studies, New York, used a coupled ocean-atmosphere model to investigate how sensitive different regional climates are to changes in levels of carbon dioxide, ozone, and aerosols.

The scientists observed that the mid and high latitudes are particularly responsive to changes in the level of aerosols. Indeed, the model suggests aerosols likely account for 45 percent or more of the warming that has occurred in the Arctic during the last three decades. The results were reported in the recent issue of Nature Geoscience

Though there are several varieties of aerosols, prior research has shown that two types -- sulfates and black carbon -- play an particularly critical role in regulating climate change. Both are products of human activity......... Posted by: Beverly      Read more         Source

March 31, 2009, 3:03 PM CT

First Live Action Movie of Individual Carbon Atoms in Action

Science fiction fans still have another two months of waiting for the new Star Trek movie, but fans of actual science can feast their eyes now on the first movie ever of carbon atoms moving along the edge of a graphene crystal. Given that graphene - single-layered sheets of carbon atoms arranged like chicken wire - may hold the key to the future of the electronics industry, the audience for this new science movie might also reach blockbuster proportions.

Scientists with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), working with TEAM 0.5, the world's most powerful transmission electron microscope, have made a movie that shows in real-time carbon atoms repositioning themselves around the edge of a hole that was punched into a graphene sheet. Viewers can observe how chemical bonds break and form as the suddenly volatile atoms are driven to find a stable configuration. This is the first ever live recording of the dynamics of carbon atoms in graphene.

"The atom-by-atom growth or shrinking of crystals is one of the most fundamental problems of solid state physics, but is particularly critical for nanoscale systems where the addition or subtraction of even a single atom can have dramatic consequences for mechanical, optical, electronic, thermal and magnetic properties of the material," said physicist Alex Zettl who led this research. "The ability to see individual atoms move around in real time and to see how the atomic configuration evolves and influences system properties is somewhat akin to a biologist being able to watch as cells divide and a higher order structure with complex functionality evolves"......... Posted by: Beverly      Read more         Source

February 25, 2009, 5:35 AM CT

Graphene's edge structure affects electronic properties

Graphene, a single-atom-thick sheet of carbon, holds remarkable promise for future nanoelectronics applications. Whether graphene actually cuts it in industry, however, depends upon how graphene is cut, say scientists at the University of Illinois.

Graphene consists of a hexagonal lattice of carbon atoms. While researchers have predicted that the orientation of atoms along the edges of the lattice would affect the material's electronic properties, the prediction had not been proven experimentally.

Now, scientists at the U. of I. say they have proof.

"Our experimental results show, without a doubt, that the crystallographic orientation of the graphene edges significantly influences the electronic properties," said Joseph Lyding, a professor electrical and computer engineering.

"To utilize nanometer-size pieces of graphene in future nanoelectronics, atomically precise control of the geometry of these structures will be required".

Lyding and graduate student Kyle Ritter (now at Micron Technology Inc. in Boise, Idaho) report their findings in a paper accepted for publication in Nature Materials. The paper was posted on the journal's Web site on Sunday (Feb. 15).

To carry out their work, the scientists developed a method for cutting and depositing nanometer-size bits of graphene on atomically clean semiconductor surfaces like silicon......... Posted by: Beverly      Read more         Source

February 25, 2009, 5:32 AM CT

New Hydrogen Purification Method

President Barack Obama's pursuit of energy independence promises to accelerate research and development for alternative energy sources -- solar, wind and geothermal power, biofuels, hydrogen and biomass, to name a few.

For the hydrogen economy, one of the roadblocks to success is the hydrogen itself. Hydrogen needs to be purified before it can be used as fuel for fuel cells, but current methods are not very clean or efficient.

Northwestern University chemist Mercouri G. Kanatzidis, together with postdoctoral research associate Gerasimos S. Armatas, has developed a class of new porous materials, structured like honeycomb, that is very effective at separating hydrogen from complex gas mixtures. The materials exhibit the best selectivity in separating hydrogen from carbon dioxide and methane, to the best of the researchers' knowledge.

The results, which offer a new way to separate gases not available before, is published online by the journal Nature Materials. The materials are a new family of germanium-rich chalcogenides.

"A more selective process means fewer cycles to produce pure hydrogen, increasing efficiency," said Kanatzidis, Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences and the paper's senior author. "Our materials could be used very effectively as membranes for gas separation. We have demonstrated their superior performance"......... Posted by: Beverly      Read more         Source

January 15, 2009, 7:39 PM CT

Organic solar cells a step closer

Inexpensive solar cells, vastly improved medical imaging techniques and lighter and more flexible television screens are among the potential applications envisioned for organic electronics.

Recent experiments conducted by Greg Scholes and Elisabetta Collini of University of Toronto's Department of Chemistry may bring these within closer reach thanks to new insights into the way molecules absorb and move energy. Their findings would be reported in the prestigious international journal Science on January 16.

The U of T team -- whose work is devoted to investigating how light initiates physical processes at the molecular level and how humans might take better advantage of that fact -- looked specifically at conjugated polymers which are thought to beone of the most promising candidates for building efficient organic solar cells.

Conjugated polymers are very long organic molecules that possess properties like those of semiconductors and so can be used to make transistors and LEDs. When these conductive polymers absorb light, the energy moves along and among the polymer chains before it is converted to electrical charges.

"One of the biggest obstacles to organic solar cells is that it is difficult to control what happens after light is absorbed: whether the desired property is transmitting energy, storing information or emitting light," explains Collini. "Our experiment suggests it is possible to achieve control using quantum effects, even under relatively normal conditions." ......... Posted by: Beverly      Read more         Source

January 15, 2009, 6:28 PM CT

Biofuel carbon footprint not as big

Publications ranging from the journal Science to Time magazine have blasted biofuels for significantly contributing to greenhouse gas emissions, calling into question the environmental benefits of making fuel from plant material. But a new analysis by Michigan State University researchers says these dire predictions are based on a set of assumptions that may not be correct.

"Greenhouse gas release from changes in land use - growing crops that could be used for biofuels on previously unfarmed land - has been identified as a negative contributor to the environmental profile of biofuels," said Bruce Dale, MSU University Distinguished Professor of chemical engineering and materials science. "Other analyses have estimated that it would take from 100 to 1,000 years before biofuels could overcome this 'carbon debt' and start providing greenhouse gas benefits".

But as Dale and his co-authors point out in their research, reported in the January online edition of the journal Environmental Science & Technology, earlier analyses didn't consider many variables that might influence the greenhouse gas emissions linked to biofuels.

"Our analysis shows that crop management is a key factor in estimating greenhouse gas emissions linked to land use change linked to biofuels," Dale said. "Sustainable management practices, such as no-till farming and planting cover crops, can reduce the time it takes for biofuels to overcome the carbon debt to three years for grassland conversion and 14 years for temperate zone forest conversion"......... Posted by: Beverly      Read more         Source

January 14, 2009, 6:25 AM CT

Stability testing of soy-based biofuel

The National Institute of Standards and Technology (NIST) has developed a method to accelerate stability testing of biodiesel fuel made from soybeans and also identified additives that enhance stability at high temperatures. The results, described in a new paper,* could help overcome a key barrier to practical use of biofuels.

Both oxidation and heating can cause biodiesel to break down, adversely affecting performance. These two effects commonly are analyzed separately, but NIST chemists developed a method to approximate both effects at the same time while also analyzing fluid composition. NISTs advanced distillation curve method could accelerate and simplify testing of biodiesels, as per main author Tom Bruno. NIST scientists used the new method to demonstrate the effectiveness of three additives in reducing oxidation of biodiesel at high temperatures, as would occur in aviation fuels.

Biodieselwhich can be prepared from vegetable oil, animal fats, used cooking oil, or microalgaeis a potential replacement or extender for petroleum-based diesel fuel. Biodiesel offers several advantages, including renewability, the potential for domestic production, biodegradability, and decreased emissions of carbon monoxide and particulate matter. Biodiesel also has several serious disadvantages, including increased nitrogen oxide emissions and chemical instability, particularly at higher temperatures......... Posted by: Beverly      Read more         Source

January 14, 2009, 6:23 AM CT

Ultra sensitive gas detectors

When cells are under stress, they blow off steam by releasing minute amounts of nitrogen oxides and other toxic gases. In a recent paper,* scientists at the National Institute of Standards and Technology (NIST) described a new method for creating gas detectors so sensitive that some day they appears to be able to register these tiny emissions from a single cell, providing a new way to determine if drugs or nanoparticles harm cells or to study how cells communicate with one another. Based on metal oxide nanotubes, the new sensors are a hundred to 1,000 times more sensitive than current devices based on thin films and are able to act as multiple sensors simultaneously.

Gas sensors often operate by detecting the subtle changes that deposited gas molecules make in the way electricity moves through a surface layer. Thus, the more surface available, the more sensitive the sensor will be. Researchers are interested in developing gas sensors based on nanotubes because, having walls that are only a few nanometers thick, they are almost all surface.

Eventhough nanotubes have proven to be well suited for gas sensing applications, fabricating the devices themselves is a difficult, imprecise and time-consuming process, as per Kurt Benkstein, an author of the paper. Older methods include randomly scattering free nanotubes on a surface with preformed electrical contacts (the hope being that a least a few of the nanotubes would tumble into place) or laying contacts over the top of the nanotubes after they had been dispersed, among others. These methods, though they can result in functional devices, preclude scientists from knowing where exactly the reactions are happening on the substrate. This makes it impossible to do multiple simultaneous tests. Also, these sensors are not as sensitive as they could be because there is no way to ensure that the gas is reacting with the interior of the tube......... Posted by: Beverly      Read more         Source

January 14, 2009, 6:20 AM CT

Understand polymer film instability

While exploring the properties of polymer formation, a team of researchers at the National Institute for Standards and Technology (NIST) has made a fundamental discovery* about these materials that could improve methods of creating the stable crystalline films that are widely used in electronics applicationsand also offer insight into a range of other phenomena.

The team has determined that temperature can play a decisive role in determining which of two competing processescalled crystallization and dewettingwill take the lead when a semicrystalline polymer film hardens, thereby granting qualitatively different properties to the finished film. The findings could lead to better control of these two processes, which can cause imperfections in polymer films during their formation.

Such imperfections can hinder the performance of potential new technologies, such as solar cells or thin film transistors, that employ organic polymer films on their surfaces, as per research chemist Christopher Soles. At this point, he said, the organic semiconductor industry is being hindered by a lack of understanding of crystal formation in thin polymer films.

If organic photovoltaicsto take just one exampleare ever to be realized and marketed, we need to understand how the film formation process works, said Soles. You have to know the properties of these materials first in order to control their stability......... Posted by: Beverly      Read more         Source

January 8, 2009, 7:54 PM CT

Nano "Tractor Beam" Traps DNA

View a video of DNA molecules suspended in a stream of water flowing through a nanoscale channel.

Using a beam of light shunted through a tiny silicon channel, scientists have created a nanoscale trap that can stop free floating DNA molecules and nanoparticles in their tracks. By holding the nanoscale material steady while the fluid around it flows freely, the trap may allow scientists to boost the accuracy of biological sensors and create a range of new 'lab on a chip' diagnostic tools.

The Cornell University research team reports its findings in the Jan. 1, 2009, issue of the journal Nature.

"For this research to emerge in the marketplace in a device such as a 'lab on a chip', it is essential for engineers to be able to manipulate matter at the scale of molecules and atoms, especially while the matter is contained within a fluid stream only slightly larger than the particles themselves," says William Schultz, the National Science Foundation (NSF) program officer who oversaw the researchers' grant. "NSF and other funding agencies have made nano-science and -technology a high priority. The Cornell scientists have made an important step in realizing the full potential of these devices".

Light has been used to manipulate cells and even nanoscale objects before, but the new technique allows scientists to manipulate the particles more precisely and over longer distances......... Posted by: Beverly      Read more         Source