Archive for November, 2013

Have you read Detective Comics 763? Gotham Central? Then you probably know about Detective Josie Mac.


Josie has this unique gift, she can talk to objects. Well, in fact, she mostly feels the emotion of objects, but you get the idea. The cool thing about this is that objects may, indeed, talk nowadays, courtesy of Radio Frequency IDentification (RFID) technology. Have you ever walked out of a shop through one of those arcs just to get alarms going? And, assuming you were not planning to make a run for it, someone in the shop passed whatever made it go through a gadget and it was a go. Eventually, you’d find a dead sticker somewhere in the purchased object that looked like a flat copper spiral. Yep, that was an RFID tag!


The best about RFID is that, actually, tags do not require batteries. Instead, they feed on the tag reader, the other part of the communication link. Tags are just sticked to an objects and they work! As long as there is a reader -like Josie Mac- around, but they work 🙂

Let’s imagine that a communication device is like old light signals, that could send data in Morse code by opening and closing a lid in front of the lantern. The lantern should be on, of course, in order to send light. The alternative would be to remove the lantern and use a mirror. As long as you get a light source nearby, we could use it exactly like the lantern! We would not need energy to feed the light in that case, so the lid-mirror would work like a passive tag. That’s why that sticker in your book may trigger an alarm when you walk through the bookshop door: if you check your sides at the point, you’ll notice two large transmitters feeding the thing.


Indeed, RFID transmits digital information, so it is very much like the light-based system, only that lid-ons and offs would be gathered into a “word” of n-activations (n bits, in our case). Thus, we could transmit as much as 2^n different tags. These tags are written at some point by a reader and, after that, they simply transmit their n-bits each time they are activated.

Let’s just think about it. If we wanted to identify uniquely every person on Earth, currently 6.300.000.000 persons, we would need just 33 bits to binarize that quantity, as 2 power 33 is equal to 8.589.934.592 , more than enough to give a single unique number to each of our neighbors. This basically means that an RFID label would be enough to make every single passport on the world. However, it is things we were talking about. If we assume that every thing in the world belongs to someone, as a typical EPC code presents 96 bits, we still have 96-33, i.e. 63 bits to identify all the items of a given person. That is 9.223.372.036.854.775.808 items per person!!

Of course, it is more advisable to just provide more information than identification in an RFID label. Like, let’s say, when were they manufactured. That means a date (day, month, year). 31 days fit within 5 bits, 12 months fit within 4 and up to year 3000 can be fit within 12. Hence, we would require 21 additional bits to encode a date, along with who do the item belongs to. We still have 63-21 bits (42) to, for example, explain what kind of item we are.

There are far nicer applications to RFID than commerce. For example, sea turtles can be tagged with RFID to check how frequently they return to a given beach to lay eggs and such. Until turtles decide to speak with us, RFID is what you get. And you can tag any animal instead of branding them Far West style, too!



At the moment, in fact, there are small, low power consumption circuits that actually feed on induction, too. That’s really handy when you need to put them in places where it would be hard to replace the batteries, like a pressure sensor on a tire. In this case, passive thingies do not only provide previously stored information, but actually capture and even process it for you.


We have seen quicksand in enough movies to have a general idea about how it works: you struggle, you sink, right? At least until you ultimately grab the usual branch to plug yourself out of the trap.

Quicksand, in fact, is basically solid ground -either sand or any similar grainy soil- oversaturated in water. This usually happens when damp soil is agitated due, for example, to an earthquake. If the water in the soil can’t escape, the whole thing liquifies and the surface can not support weight anymore. Water and vibration reduce friction between solid particles and the combined material starts to behave like a viscous liquid. Another usual explanation is an underground water flow fighting gravity on the surface.


Typically, quicksand is easier to find in humid places like riverbanks, beaches or marches. Indeed, the phenomenon can be appreciated in small scale when one is standing on the sea shore.

In any case, drowning in quicksand is actually quite difficult. First, deposits are not that deep, just a few feet tops. Second, quicksand density approximately doubles water density, meaning that it is actually easier to float in quicksand than in water, in the same way that it is easier to float in salty water than in sweet water.

Actually, the problem comes when quicksand is very dense, since moving out of there would be like trying to get out of a concrete pit. In this case, movies are correct: the more you struggle, the deeper you go. The key idea would be to move out through slow movements -to reduce friction- and to spread -to increase the body surface area to float easier-. In brief, to try to swim slowly out of the pit.

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