Delicious LiveJournal Links for 4-5-2009

[andrewducker]

• Physicist develops battery using new source of energy
  Would someone care to let me know if this article makes any sense at all?
  (tags: energy physics tech)
• The Art of DeTouch
  Very nice Java applet that shows before/after of photoshop jobs in a variety of different ways.
  (tags: photography photoshop retouch processing retouching)
• Obama Action Figures
  You have always wanted one, right?
  (tags: Obama toys japan)
• Revealed: why we need a good night's sleep
  A study into slumber has found that the nerve connections built up in the brain during a busy day are pruned back during the night in an attempt to keep the mind from overloading on junk information.
  (tags: brain health science sleep biology)

Comments

[pisica.livejournal.com]

*adds Obama action figure to list of things to buy in Japan*

[pisica.livejournal.com]

Or I could just order one:

http://www.toywiz.com/barackobama.html

[mouflonmatt.livejournal.com]

#puts on science teacher hat#
The new battery power source thing is neither new nor that exciting. You simply charge it by using magnets rather than electromagnetic induction. You still have to provide a power source to spin the magnet. It is good in that it will charge fast, eg seconds not hours.

The computer drive thingy looks interesting, but theres not much info in the article.

[kurosau.livejournal.com]

It looks to me to be a very very tiny magnetic version of a flywheel battery. Is that right?

[martling.livejournal.com]

Would someone care to let me know if this article makes any sense at all?

The article, no. But later on I will pull the actual Nature paper and have a look. Fast charging isn't that interesting - we can do that with capacitors. But if the energy density is higher than existing techniques, that gets very exciting.

[martling.livejournal.com]

Found this lurking in my todo list.

I read the Nature article. It's primarily a set of results supporting the hypothesis that in magnetic nanostructures, Faraday's law of induction gives rise to an electromotive force (EMF) which acts on the spin of an electron in a static magnetic field.

The device they use to demonstrate this is a quite exotic thing; "a magnetic tunnel junction containing zinc-blende-structured MnAs quantum nanomagnets". It's 200um in diameter, the thickness isn't clearly given but I get the impression it's of the order of 100nm.

There are two interesting effects demonstrated that arise from this spin-origin EMF. One is a very high magnetoresistance; i.e. the resistance of the device changes massively for small differences in magnetic field. This could be used as an ultra high sensitivity sensor for measuring magnetic fields. The other effect is that the device will act as a "spin battery", charged by magnetic energy which is then slowly transformed into electrical energy in the presence of a static magnetic field. The results show the device sourcing a current of ~10uA at 2V into a 200kOhm load for 10 minutes. However, this requires a 10kGauss magnetic field to achieve, which in practice must come from an electromagnet rather than a permanent magnet - iron magnets give around 100 Gauss, neodymium around 2kGauss.

It's hard to do an energy density calculation for this without more details of the structure, overhead for providing the static field, etc. But a quick back-of-the-envelope estimate based on the above figures gives an estimate of 2250MJ per liter, assuming you can manufacture, produce and operate these devices tightly packed, which you probably can't. But then, lithium ion batteries are about 0.9MJ per liter...

[andrewducker]

Thanks - that was very interesting! I hope it is something that they can mass produce.

[xquiq.livejournal.com]

Loving the utterly random & slightly nuts 'god vs evolution' debate in the comments section on the sleep article. Some of the comments are priceless...