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Benford's distribution. Source: Wikipedia.org

Issue no. 32, 2010 Published: Oct 15, 2010
Curious mathematical law is rife in nature
Phonons tunnel across the vacuum
Electrified nano filter promises cheaper clean drinking water
Microbial hair - it's electric
Researchers crack the nanocrystal challenge
Key component contract for ITER fusion reactor

Curious mathematical law is rife in nature
What do earthquakes, spinning stellar remnants, bright space objects and other natural phenomena have in common? Some of their properties conform to a little known mathematical law, which could now find new uses. Benford's law states that for many sets of numbers, the first or 'leading' digit of each number is not random. Instead, there is a 30.1 per cent chance that a number's leading digit is a 1. Progressively higher leading digits get increasingly unlikely, and a number has just a 4.6 per cent chance of beginning with a 9. Not all sets of numbers obey this law, but it crops up surprisingly often. As a result, mathematicians have put it to work, using deviations from it to detect cases of tax fraud, voter fraud and even digital image manipulation. Now researchers of the Australian National University in Canberra have extended the list of natural phenomena with properties that follow Benford's law. Their new list includes the depths of almost 250,000 earthquakes that occurred worldwide between 1989 and 2009, the brightness of gamma rays that reach Earth as recorded by the Fermi space telescope, the rotation rates of pulsars, and 987 infectious disease numbers reported to the Wold Health Organization in 2007. As well as using Benford's law to detect mild earthquakes, the team think it could find other uses. Just how widespread the law is in nature is not known. When the team looked at the masses of 400 extrasolar planets, there was an anomalous bump in numbers starting with 6. This may be an artefact of a small sample, a problem with the measurement technique or a sign that exoplanet masses do not fit Benford's law.
New Scientist Oct 14, 2010	back to top

Phonons tunnel across the vacuum
Heat can be conducted across a nanometre-sized vacuum gap - something that was deemed impossible until now. So say researchers at the Air Force Research Laboratory in the US, who have found that the heat is transferred via an effect called 'phonon tunnelling' in which quantized molecular vibrations, called phonons, appear to traverse the forbidden zone. The finding could be important for improving thermoelectric devices and for future nanoscale electronic circuits. Heat flow between two objects via conduction can normally only occur when the objects are in contact with each other. This process occurs when phonons - quanta of vibrational energy - are transferred from the hotter object to the cooler one. Until now, such transfer was thought to be impossible between non-touching objects in a vacuum because the vacuum is a forbidden zone for phonons. The US team has now turned this idea on its head by actually measuring the heat flow between the tip of a scanning tunnelling microscope held at room temperature and a cold surface made of gold. The two objects were separated in a vacuum by a 0.3 nm thin gap. The tip was held at room temperature while the gold surface was cooled to 90, 150 or 210 K. The team found that the thermal energy transmitted through the tiny gap exceeds the Planck's radiation by c2/v2 = 1010 (where c is the speed of light and v the speed of sound). According to their measurements, this means that the last atom at the nanosized tip dissipates heat an astonishing 1010 times faster than normal by generating phonons inside the gold. And, contrary to earlier hypotheses, the heat transfer is not due to the tip emitting radiation into the vacuum. The team say the phonon tunnelling is driven by electric fields between the two objects.
Physical Review Letters Oct 14, 2010	back to top

Electrified nano filter promises cheaper clean drinking water
With almost one billion people lacking access to clean, safe drinking water, scientists are reporting development and successful initial tests of an inexpensive new filtering technology that kills up to 98% of disease-causing bacteria in water in seconds without clogging. Most water purifiers work by trapping bacteria in tiny pores of filter material. Pushing water through those filters requires electric pumps and consumes a lot of energy. In addition, the filters can get clogged and must be changed periodically. The new material, in contrast, has relatively huge pores, which allow water to flow through easily. And it kills bacteria outright, rather than just trapping them. Yi Cui and colleagues knew that contact with silver and electricity can destroy bacteria, and decided to combine both approaches. They spread sub-microscopic silver nanowires onto cotton, and then added a coating of carbon nanotubes, which give the filter extra electrical conductivity. Tests of the material on E. coli-tainted water showed that the silver/electrified cotton killed up to 98% of the bacteria. The filter material never clogged, and the water flowed through it very quickly without any need for a pump.
NanoTechWeb / Nano Letters Oct 13, 2010	back to top

Microbial hair - it's electric
Some bacteria grow electrical hair that lets them link up in big biological circuits, according to researchers at the University of Southern California. The finding suggests that microbial colonies may survive, communicate and share energy in part through electrically conducting hairs known as bacterial nanowires. To test the conductivity of bacterial nanowires, the researchers grew cultures of Shewanella oneidensis MR-1. Shewanella tend to make nanowires in times of scarcity. By manipulating growing conditions, the researchers produced bacteria with plentiful nanowires. The bacteria then were deposited on a surface dotted with microscopic electrodes. When a nanowire fell across two electrodes, it closed the circuit, enabling a flow of measurable current. When the researchers cut the nanowire, the flow of current stopped. Electricity carried on nanowires may be a lifeline. Bacteria respire by losing electrons to an acceptor - for Shewanella, a metal such as iron. In some cases, a nanowire may be a microbe's only means of dumping electrons. When an electron acceptor is scarce nearby, nanowires may help bacteria to support each other and extend their collective reach to distant sources. The researchers noted that Shewanella attach to electron acceptors as well as to each other, forming a colony in which every member should be able to respire through a chain of nanowires. Knowing how microbial communities thrive is the first step in finding ways to destroy harmful colonies, such as biofilms on teeth. Biofilms have proven highly resistant to antibiotics. The same knowledge could help to promote useful colonies, such as those in bacterial fuel cells.
PhysOrg Oct 11, 2010	back to top

Researchers crack the nanocrystal challenge
Researchers in the US are the first to use epitaxy to make nanometre-sized single crystals. Epitaxy is a standard process used in semiconductor fabrication and therefore the breakthrough could lead to the production of nanostructured thin films for a wide variety of applications, including solar cells. Most nanostructures made from inorganic materials are either amorphous or polycrystalline, and scientists have struggled to make nanostructures from single crystals that grow in a well defined way with respect to a substrate. Such crystals could be used in a host of applications in which excellent charge transport over extremely small distances is called for. Single crystals are ideal for these applications because they don't contain grain boundaries between the crystallites. These boundaries can act as trap or scattering sites for electrons and thus degrade the ability of a nanostructure to transport charge. Now, researchers at Cornell University have developed a way of making single-crystal silicon or nickel monosilicide nanostructures with the help of a block copolymer self-assembly technique. The researchers say that, as far as they know, nobody had ever succeeded in combining polymer self-assembly with inorganic single-crystal epitaxy until now. The new method could be used to make a variety of complex, nanocrystalline shapes in the future. These could either be used for fundamental studies on nanocrystals or directly in applications.
PhysicsWorld / Science Oct 08, 2010	back to top

Key component contract for ITER fusion reactor
The contract has been signed that will lead to the production of the biggest component in the ITER fusion reactor. The facility being built in France will attempt to harvest energy by exploiting the same nuclear processes that power the Sun. AMW, an Italian consortium, will construct most of the doughnut-shaped vessel at the centre of the reactor. In a fusion reaction, energy is released when light atomic nuclei - the hydrogen isotopes deuterium and tritium - are fused together to form heavier atomic nuclei. To use controlled fusion reactions on Earth as an energy source, it is necessary to heat these gases to temperatures exceeding 100 million Celsius - much hotter than the centre of the Sun. This will be done inside a vacuum vessel. AMW has now been given a 300m-euro contract to make the basic shell of this device. ITER is designed to produce 500MW of fusion power during pulses of at least 400 seconds. Critically, the machine is expected to demonstrate the principle that it possible to get far more energy out of the process than is used to initiate it. ITER is not expected to begin operations until much later this decade. Even then, these will be shake-down tests; full fusion power will not be achieved until the 2020s.
BBC News Oct 14, 2010	back to top