December 2009 Archives

Sun Dec 27 16:44:09 PST 2009

PETN (PentaErythritol TetraNitrate) A Molecule of Death

PETN, or PentaErythritol TetraNitrate, crops up in the news from time to time as a high explosive, often used by terrorists.

PETN's molecular structure is shown above. A central carbon atom supports four identical chains, each of which ends in a nitrate group. The resulting structure has the formula C(CH2NO3)4. This form of the formula emphasizes the four identical chains which the molecule contains. You can also write the formula at C(CO2)4(N2)24(H2O)4, which emphasizes the fact the PETN molecule contains just the right ratios of carbon, nitrogen, and oxygen to form many gas molecules from each molecule of explosive.

Not only do PETN's constuents contain a host of small stable combustion products ready to be released by the appropriate detonator, the molecule is also somewhat strained, with four identical large side chains terminating at the central carbon atom.

So when suitably triggered, PETN rearranges rapidly, releasing CO2, H2O, and N2, and plenty of heat, as these products are more stable than the PETN molecule itself. The result can be a devastating explosion.

Hence, PETN has been emplolyed by several terrorists, including Abdulfarouk Umar Muttalab.

Rather chillingly, when you look at the PETN molecule in three dimensions, as is shown above, at a certain orientation of the central tetrahedral carbon, the molecule takes on the shape of a swastika.

Posted by ZFS | Permanent link

Sat Dec 5 20:42:05 PST 2009


About a year ago I was talking with a scientist that I had known for many years, and was surprised to find, that he himself was surprised, that I accepted without question the concept of manmade global warming. 'You believe that global warming is manmade?', he said. 'Yes', says I, 'It's on the news!'. Global warming was and is not one of my day to day concerns, and I had blithely assumed that what was reported by the Al Gore, the BBC, Science, Nature, et al was to be believed.

The conversation induced me to check the usual sources, Wikipedia, Google, more attentive reading of the newspapers. I was hoping for a definitive answer. Rapidly, and sadly, I was forced to conclude that the situation was muddy. It was clear that there was room for debate, and it was clear that scientists themselves were not in agreement.

I was disappointed, there was no well thought through description of the situation. Instead, there was a disconcerting, and acrimonious debate. This seemed a different situation to CFCs and ozone, or acid rain, to name some recent examples where theories have been publicly analyzed, debated and confirmed.

It was surprising to see journals and magazines apparently taking sides. For example, for some reason, Bjorn Lomborg, the author of The Skepitcal Environmentalist (Robert Boyle the author of 'The Sceptical Chymist' would be flattered) and The Scientific American had somehow or other fallen out. Normally this does not happen in science. Theories are proposed and tested, scientists can reproduce each other's work (or cannot), and fairly soon, assuming a theory has merit, a consensus emerges, upon which new predictions theories can be built. Debates tend to be spirited but good natured.

What was (and is) the problem? Scientists are trying to find discernable information in a noisy and incomplete record. That is a very difficult thing to do, and assumptions can play havoc with the interpretation. Added to this is the problem that if calamity is imminent, we would like to avoid it if at all possible. These problems afflict both sides of the discussion. Uncertainty makes the trend hard to prove or disprove, and its dire consequences either in terms of environmental or financial disaster inject the same sense of impending disaster guaranteed to cement religious fervor into both camps.

So, I remained disappointed, the situation was far from clear, as my friend had suggested. The recent Climate Research Unit (CRU) 'Climategate' leaks have been an interesting addition to the discussion, however. At first I thought, these emails probably don't amount to much. I took a look at the file, though. (It is readily available on the internet: is the string to search for). And I found that it is quite an explosive cache of information. There is discussion of massaging charts by combining information from different sources, which unsurprisingly greatly improves their agreement, there is discussion of deleting data, there is discussion of interfering with the independence of scientific refereeing, and a great reluctance to release information publicly. Added to this, there are sets of poorly written filtering or massaging programs and a description of a frustrating attempt to reproduce a long forgotten massaging recipe. It has to be said that this is more than a few email lines out of context. All in all, not science at its best.

So, although I am no expert in climate matters, and am therefore not really qualified to comment, I have to say that I am becoming slightly doubtful of the quality of the work that leads to the alarm over manmade global warming. The effect may very well be real, but the case has been made to seem more faith based than science based by the leak.

Open information, process, and discussion would help immensely. The raw data, upon which conclusions are based, should be freely available, along with the manipulation algorithms, with all the information and algorithms stored in a revision control system, with suitable backup archiving, so that data and histories are never lost. It would also be interesting to see how predictions of the effects of global warming, which have been made since the late 1980s have faired in comparison with actual measurements.

Posted by ZFS | Permanent link