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June 16th, 2006 - Adventures in Engineering — LiveJournal
The wanderings of a modern ronin.

Ben Cantrick
  Date: 2006-06-16 05:54
  Subject:   Email was dead; back now.
Public
My ISP's user machine ate itself in a spectacular fashion about two weeks ago, and took my ability to receive email straight to hell with it. I haven't had a working email account since the 3rd. This afternoon I logged in to see if it was fixed. It was, finally. And I had 824 unread emails!

Almost all of them were spam. In fact, I only saw three that needed replying to. But if you've sent me an important email in the last two weeks and haven't gotten a reply yet, please re-send it and I'll get back to you.

I need to remember the password to my GMail account so I have a backup in case this happens again...
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Ben Cantrick
  Date: 2006-06-16 19:12
  Subject:   Guess what, humanity? The Earth does not need you.
Public

Face facts here, people. Global warming, however disasterous it may be for the human race, is hardly a ten second warm flash in the geological history of life on earth. Do you think that some smart Tyrannosarus, 165 million years ago, saw that big meteor come down from the sky and went into hysterical dramatics: "Oh no! That's the END OF ALL LIFE ON EARTH?" I imagine one probably did. Well, the big lizards all eventually took the eternal dirt-nap, and the clever monkeys (that's us) will too. And when we're tens of millions of years dead and gone, the earth will find something else. Perhaps higher life forms will evolve from racoons. (Planet of the Furries - AAAHHHHHHHH!!!) It could easily happen.

When we talk about environmental protection, let's get it straight what we're talking about: OUR OWN SURVIVAL as the dominant life form on the planet. We're at the top of the food chain right now, which is an agreeable position to be in, and I'd like us to continue our good run here for as long as possible. But the Earth... DOES NOT NEED US. Never has, never will. This little blue mudball will continue its happy piroutte around the sun for hundreds of millions of years after the human race has been reduced to a few poorly calcified fossils. Fossils that will be dug up by whatever sentient animal evolves after we are thousands of millenia dead and gone.

So don't talk about "Saving the Earth" - it's hubris to imply that humanity has the ability to save or destroy the earth. We don't, not any more than a dust mite can save or destroy the house whose door-mat it lives in. Talk about "saving our own asses." Because that's what taking care of the environment really is.


- http://www.mrcranky.com/movies/inconvenienttruth/2/5.html
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Ben Cantrick
  Date: 2006-06-16 20:19
  Subject:   Today we learn about CRCs.
Public
A cyclic redundancy check (CRC) is a type of hash function used to produce a checksum (a small, fixed number of bits) against a block of data, such as a packet of network traffic or a block of a computer file. The checksum is used to detect errors after transmission or storage. A CRC is computed and appended before transmission or storage, and verified afterwards by recipient to confirm that no changes occurred on transit. CRCs are popular because they are simple to implement in binary hardware, are easy to analyze mathematically, and are particularly good at detecting common errors caused by noise in transmission channels.

http://en.wikipedia.org/wiki/Cyclic_redundancy_check

The Wikipedia article doesn't lack for technical correctness, but until I go back to school and get that graduate level math degree, I think my understanding of "division in the ring of polynomials over the finite field GF(2)" is going to be hazy at best.


A better resource for learning about CRCs is Ross Williams' "Painless Guide To CRC Error Detection Algorithms":

The basic idea of CRC algorithms is simply to treat the message as an enormous binary number, to divide it by another fixed binary number, and to make the remainder from this division the checksum. Upon receipt of the message, the receiver can perform the same division and compare the remainder with the "checksum" (transmitted remainder). The quotient, or normal result of the division, is simply thrown away.

The polynomials are the tricky bit, but they turn out to be mathematically equivalent to doing binary math with no carries.Collapse )

A summary of the operation of the class of CRC algorithms:

1. Choose divisor polynomial, G, of width W.
2. Append W zero bits to the message. Call this M'.
3. Divide M' by G, using CRC arithmetic. The remainder is the checksum.

That's all there is to it.


There's also an excellent section on optimizing CRC implementations.
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Ben Cantrick
  Date: 2006-06-16 22:48
  Subject:   Twilight for the F-14 Tomcat
Public


Hundreds of former Grumman employees and aviation buffs paid their last respects yesterday to a soon-to-retire jet that, for decades, defined Long Island industry. "Pound for pound, it is the best aircraft that the United States ever had," said John Lampasone, who worked at Grumman for 24 years. "And it's a shame that they're taking it out of service."

http://www.newsday.com/news/local/longisland/ny-bzgrumm16,0,5658213.story

A fly-by that got the pilot grounded for 30 days.Collapse )

No insult to F-14's replacement, the F-22, which is an amazing aircraft. But I think ol' swing-wings will always be my favorite fighter jet.
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