# Posts by Philip

5 posts • joined 23 Jun 2007

### The return of Killer Chlorine

#### RE: The Doctor, and the rare disease...

Right this is a long thread, so this hopefully won't get read....

There is this disease, that affects all people in equal proportion at a rate of 1 in 100 000. Assuming your a normalish human being, your chances of getting the disease is 1/100 000.

Now you go to the doctor for a routine check up (ie. the disease doesn't present any symptoms except sudden death) where he does a battery of tests. Guess what, the test comes back positive for sudden death disease.

"Lucky" for you, there is a cure, that is 100% effective, but which kills you if you don't have the disease. The doctor then tells you the test for the disease is 90% accurate. That is, if it says you don't have it, there is a 10% chance that you actually do, and if it says you don't, there is a 10% chance that actually you do.

Thus, the question is, what is the probability that you have the disease, given that the test was positive?

Applying Bayes' Theorem, hopefully correctly, gives:

(0.90*0.000 01)/(.9*0.000 01 + 0.1*0.999 9)

= 9 in 111 119 or roughly 0.0081%

or roughly 1 in 10 000.

So, no, don't take the "cure", except if your feeling really unlucky, who knows, you could be the 1 in 100 000 person who actually has the disease.

http://en.wikipedia.org/wiki/Bayes'_theorem

### God makes you stupid, researchers claim

#### Doesn't Matter

It is all good debating whether god(s) exists or not, if one does a risk analysis, then you should believe in god. If one takes risk to mean probability of occurrence multiplied by consequences, then, if there is say only a one in a billionth chance that god does indeed exist and that the consequences for not believing in him is eternity in hell.

Thus, 0.000..(add arbitrary finite amount of zeros)..0001 x eternity in hell = very big risk. So, one should believe in god, if one is willing to admit that there is a non-zero possibility that he exists. The problem is, that believing in a god for fear of eternity in hell, might not necessarily pass as believing in god, in which case you are doomed.

I have resigned myself to the fact that regardless of what any religious person says, I shall doubt whether god exists, and conclude that if he does, he is very uninterested and uninvolved in my life. If god created me, he created me to question his existence for I cannot do otherwise. All I can do is hope, that if he does exist, he won't hold the fact that he created me this way against me.

Perhaps, in a way, it could be said that I have a great deal of faith in the grace of God (if he happens to exist).

### Time Warner moots billing based on bandwidth usage

#### This is quite hilarious

Down here in South Africa, one pays approx R500 (approx 71\$) for 3GB and then about R99 (approx 14\$) per gig extra. Oh, the 70\$ is for 384kbps. The absolute fastest is 4mbps. That's 140\$.

So, you guys have it very good.

Either way, I am in favour of a tiered system. If all of the users have similar bandwidth requirements, then it is feasible to charge a flat rate amongst your customers. If your customers have a great range of requirements, with the majority using smaller amounts of data, then a tiered PAYG system should be better for the customers and the carrier overall.

Oh well, I am contempt with the 384kbps, its the fact that 3Gb really doesn't go very far that bugs me. Perhaps oneday, we might see the guided light...

### Ofcom, US senators turn on to cognitive radio

#### CR

The problem with the 2.4 GHz band is that it is very small, any very occupied. Wifi and Bluetooth free for all and whoever else cares to join. Seeing that according to some simple measurements, more than 80% of the available spectrum is unused, there is a strong case for some form of freeing up of the radio spectrum.

The current approach to Cognitive Radio, as by the IEEE 802.22 Working group, is to identify an open channel, and then to transmit on that channel for something like two seconds, and then to check that the channel is still empty before continuing to transmit. Also, the sensing requirements are very strict, something on the order of -116dBm with 95% certainty. It is also an infrastructure based standard, allowing for some planning to reduce interference with the local incumbents.

Even though Cognitve Radio faces many obstacles, it is probably one of the most promising technologies for improving radio spectrum usage. We can all only hope that they find solutions to the problems affecting Cognitive Radio, or come up with an alternative solution.

http://www.fcc.gov/sptf/files/SEWGFinalReport_1.pdf

http://www.ieee802.org/22/

### Intel chip boffins in litho brainstorm

#### RE; Reflections on Diffraction

Not really. It seems that by "drilling" a specific pattern of holes into some optical materials weird effects can be created. This is how a negative index of refraction can be obtained. I think it is therefore quite likely that they are actually using diffraction to their advantage.

I am not an expert and I hope someone with specific knowledge of photonics and photonic crystals would comment.