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
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|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
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|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
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|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.
Oct 11, 2010
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|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
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|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
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