Ivan's weblog

It is often said that general chemistry students tend to have trouble with the proper use of significant figures. However, it turns out that they are in good company–quantum chemists have been doing the same mistake for years (and yes, I’m one of them!).

This article discusses the problem:

Uncertainties in Scaling Factors for ab Initio Vibrational Frequencies
Karl K. Irikura, Russell D. Johnson III, and Raghu N. Kacker
J. Phys. Chem. A; 2005; 109 pp 8430 - 8437;

http://dx.doi.org/10.1021/jp052793n

As you may know (if you do quantum chemistry), the vibrational frequencies from ab initio calculations are systematically wrong, so they are often fudged by multiplying them by a “scaling factor". This factor is usually reported with four figures (something like 0.8982).

The authors of this article estimated the uncertainty of the scaling factor itself, and concluded:

The uncertainties presented in Table 1 reveal that the scaling factors are accurate to only two significant figures. The common practice of reporting four significant figures overstates the precision of vibrational scaling factors.

Figure 2 is especially revealing. It also shows that the basis set hardly affects the scaling factor, once the error bars are taken into consideration.

So, if this article is right, it turns out that generations of quantum chemists are sometimes no better than undergrads when it comes to reporting their results with “honest” precision!

Ok, this is not really news, and I’m not even sure if it’s true, but it sounds all too plausible. Coca-Cola had a campaign in 2001 for teaching restaurants how not to give (free) tap water to consumers. While it is obviously in the best interest of both the Coca-Cola company and the restaurant to sell as many drinks as possible, the weasel language is what makes it funny:

Water. It’s necessary to sustain life, but to many Casual Dining restaurant chains it contributes to a dull dining experience for the customer. Many customers choose tap water not because they enjoy it, but because it is what they always have drunk in the past. In response, some restaurant chains are implementing programs to help train crews to sell alternative choices to tap water, like soft drinks and noncarbonated beverages, with the goal of increasing overall guest satisfaction. Because of its own successful campaign against water, the Olive Garden has recently sent a powerful message to the entire restaurant industry — less water and more beverage choices mean happier customers.

See the screenshots from Coca-Cola’s website. It seems they took the page down after getting too much attention, so I can’t verify their accuracy.

…you start writing “two” instead of “too". I’ve been making that kind of silly mistake more often lately.

I learned English mostly by reading and writing, so I suspect that I thought of words as sequences of letters. Since “two” and “too” are different sequences with different meanings, I could never confuse them. But they sound the same, so now, after speaking English for a few years, I must be thinking of words a bit more phonetically, because I’m starting to make some of the strange mistakes that the native speakers make.

I just hope that I never write “principle” when I mean “principal", because if that happens, I’ll eat my hat!

Today, which is Labor Day in the U.S., we ran the 2005 New Haven 5K Road Race. I did 28:54 net time, and Fabiola did 29:28. This is pretty similar (or even greater) to the time we made in previous races; we’ll have to train more if we want to improve our time. ;-)

You have to see it to believe it: http://www.neilgaiman.com/journal/2005/09/satanic-tomato.asp.

Episode IV (or currently about half of it), as animated ASCII, via telnet:
telnet towel.blinkenlights.nl

Added: originally available as a Java applet, at http://www.asciimation.co.nz/.