"This is a critical question for privacy in the 21st century. If the courts do side with the government, that means that everywhere we go, in the real world and online, will be an open book to the government unprotected by the Fourth Amendment."
--Kevin Bankston, attorney, Electronic Frontier Foundation
In a report published in Science, a team led by Professor Sir Andre Geim shows that graphene-based membranes are impermeable to all gases and liquids (vacuum-tight). However, water evaporates through them as quickly as if the membranes were not there at all.
This newly-found property can now be added to the already long list of superlatives describing graphene. It is the thinnest known material in the universe and the strongest ever measured. It conducts electricity and heat better than any other material. It is the stiffest one too and, at the same time, it is the most ductile. Demonstrating its remarkable properties won University of Manchester academics the Nobel Prize in Physics in 2010.
Now the University of Manchester scientists have studied membranes from a chemical derivative of graphene called graphene oxide. Graphene oxide is the same graphene sheet but it is randomly covered with other molecules such as hydroxyl groups OH-. Graphene oxide sheets stack on top of each other and form a laminate.
The researchers prepared such laminates that were hundreds times thinner than a human hair but remained strong, flexible and were easy to handle.
When a metal container was sealed with such a film, even the most sensitive equipment was unable to detect air or any other gas, including helium, to leak through.
It came as a complete surprise that, when the researchers tried the same with ordinary water, they found that it evaporates without noticing the graphene seal. Water molecules diffused through the graphene-oxide membranes with such a great speed that the evaporation rate was the same independently whether the container was sealed or completely open.
MIT physicists have managed to build a light-emitting diode that has an electrical efficiency of more than 100 percent. You may ask, "Wouldn't that mean it breaks the first law of thermodynamics?" The answer, happily, is no.
The LED produces 69 picowatts of light using 30 picowatts of power, giving it an efficiency of 230 percent. That means it operates above "unity efficiency" -- putting it into a category normally occupied by perpetual motion machines.
However, while MIT's diode puts out more than twice as much energy in photons as it's fed in electrons, it doesn't violate the conservation of energy because it appears to draw in heat energy from its surroundings instead. When it gets more than 100 percent electrically-efficient, it begins to cool down, stealing energy from its environment to convert into more photons.
In slightly more detail, the researchers chose an LED with a small band gap, and applied smaller and smaller voltages. Every time the voltage was halved, the electrical power was reduced by a factor of four, but the light power emitted only dropped by a factor of two. The extra energy came instead from lattice vibrations.
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The scientists involved have detailed their discovery in a paper published in Physical Review Letters, saying: "Experiments directly confirm for the first time that this behaviour continues beyond the conventional limit of unity electrical-to-optical power conversion efficiency."
69 picowatts of light, of course, is a very small amount -- so you're not likely to be able to read in bed with one of these LEDs. However, it could have applications in low-power electronics, acting as a thermodynamic heat engine but with fast electrical control.
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