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Issue no. 14, 2008 Published: May 09, 2008
Dawn of the memristor
EU's sat-nav pioneer calls home
Dutch algorithm optimises Wi-Fi efficiency
Plastic red blood cells
Artificial mouth takes on a chewy problem
Invention: Plasma-powered flying saucer

Dawn of the memristor
Any passive circuit can be created with a combination of just three standard components: a resistor, which opposes charge flow; an inductor, which opposes any change in the flow of charge; and a capacitor, which stores charge. But the textbooks may have to be appended with a fourth standard component: a 'memristor'. In simple terms, a memristor 'remembers' the amount of charge that has flowed through it and as a result changes its resistance. The effect was predicted in 1971 by electronics engineer Leon Chua, but the only clues that it actually exists have been in the reports of strange 'hysterisis' loops in the current–voltage relationships of thin-film devices. This means that when the voltage increases the current follows a different relationship to when the voltage decreases. Now, scientists from Hewlett Packard have come up with a model of a memristor that consists of a thin piece semiconductor containing two different regions: a highly doped region, which has a low resistance, and a zero-doped region, which has a high resistance. When a voltage is applied across the semiconductor, it causes some of the dopants to drift so that the combined resistance changes, thereby producing the characteristic hysterisis effect of memristance. To put this model into practice, the team attached a layer of doped titanium dioxide to a layer of undoped titanium dioxide. Through current–voltage measurements, they found that it did indeed exhibit the hysterisis effect of memrisistance.
PhysicsWorld / Nature Apr 30, 2008	back to top

EU's sat-nav pioneer calls home
Giove-B, a test satellite for Europe's Galileo system, has sent its first navigation signals back to Earth. The European Space Agency (ESA) says the transmission is an 'historic step', showing that Galileo will be able to work alongside the US GPS system. Giove-B carries the most accurate clock ever sent into orbit, key to its intended capacity of providing location information accurate to a metre. The 30-strong Galileo fleet is intended to be fully operational by 2013. These constellation satellites will closely resemble Giove-B, which was launched atop a Russian Soyuz rocket on 26 April. The half-tonne, 2.4x1x1m box is the second demonstrator satellite to go into orbit following the launch of Giove-A in 2005. More sophisticated than its predecessor, it will test further the key Galileo technologies such as the atomic clocks that provide the precise timing underpinning all sat-nav applications. Giove-B's passive hydrogen maser clock is the most stable clock ever put in permanent orbit, and is designed to keep time with an accuracy of better than one nanosecond in 24 hours.
BBC News May 07, 2008	back to top

Dutch algorithm optimises Wi-Fi efficiency
A Dutch researcher has developed algorithms designed to optimise the efficiency of wireless networks. Peter Korteweg, a researcher at Eindhoven University of Technology, said that the algorithms focus on optimising communication to a central point in wireless networks, for example by minimising processing times and communication costs. Korteweg explained that an important problem in online networks is the communication of data to a central point in the network. The quality of the solution depends on several criteria, such as the energy cost for communication and the time needed to collect data. Korteweg studied subsidiary aspects such as minimising the maximum communication costs, the time needed to collect all data and the processing time of messages. The scientist then created an algorithm designed to ensure that the communication costs and the message delays deviate as little as possible from the best offline solution.
VNUnet UK Apr 24, 2008	back to top

Plastic red blood cells
Red blood cells travel through the bloodstream delivering vital oxygen to body tissues and taking away unwanted carbon dioxide – and they have to squeeze through blood vessels as thin as 3 micrometres across to do it. But in some diseases, such as malaria and sickle cell disease, red blood cells lose this ability to deform. Because of the small size of red blood cells and the demanding work they do, nobody has succeeded in making artificial versions to help people with such conditions. Now though Joseph DeSimone, a chemical engineer at the University of North Carolina at Chapel Hill, US, thinks he knows how. He has created tiny sacks of the polymer polyethylene glycol just 8 micrometres across – in the range of human red blood cells – that are capable of deforming in a way that allows them to pass through the tiniest capillaries. Polyethylene glycol is biologically benign, but binds easily with other substances, which makes it ideal for carrying cargo through the blood, says DeSimone. For example, a haemoglobin-type molecule carried inside the bag could deliver oxygen to the body and carry away carbon dioxide. The bags could also deliver drugs instead, or help as contrast agents for scans such as magnetic resonance imaging, PET or ultrasound.
New Scientist Apr 28, 2008	back to top

Artificial mouth takes on a chewy problem
An artificial mouth that can reproduce the mush created by a human munching on an apple has been created by French researchers. It could form part of a robotic taste-tester designed to improve food quality and our understanding of flavour. Many of the flavours we taste are generated by the release of volatile compounds from food, which pass around the back of the mouth and up into the nose. Hard foods release those compounds differently according to whether they are crushed, sliced, or liquidised. So if a robotic system is going to 'experience' the same tastes that humans do when eating, the food must undergo the same changes that occur in the mouth. The munching device mimics chewing, saliva release and food breakdown. About five times the size of a human mouth inside, the steel container is kept at a steady 37ºC. Its internal surfaces are coated with a chemically resistant plastic used for medical implants. The compression and rotation simulate the mechanical forces food undergoes in the mouth. The process is made more realistic by the addition of enzyme-containing artificial saliva through a pipe in the base of the chamber. Helium flows through the 'mouth' to reproduce the effect of breathing and carry volatile compounds away for analysis.
New Scientist / Journal of Agricultural and Food Chemistry May 06, 2008	back to top

Invention: Plasma-powered flying saucer
Pass a current or magnetic field through a conducting fluid and it will generate a force. Numerous aerospace engineers have tried and failed to exploit this phenomenon, known as magnetohydrodynamics, as an exotic form of propulsion for aircraft. But perhaps attempts so far have all been too big. A very small design could have a better chance of taking off, says Subrata Roy, an aerospace engineer at the University of Florida, Gainesville, US. With a span of less than 15 centimetres, his aircraft qualifies as a micro air vehicle (MAV), but it has an unconventional design to say the least. It is a saucer shape covered with electrodes that ionise air to create a plasma. This plasma is then accelerated by an electric field to push air around and generate lift. Roy says the machine can be filled with helium to reduce its weight, and is efficient enough to be powered by onboard batteries. Its ability to hover and generate lift electronically means that it is particularly robust against gusts of wind that send other MAVs off course, says Roy. All he needs to do now is build one and get it flying. Like other MAVs, the primary application would probably be surveillance, but a plasma flying saucer would make a great toy too.
New Scientist May 06, 2008	back to top