I’ve been a big fan of Dilbert for years now, but I recently found a great webcomic that I’ve started reading daily called XKCD. The tagline is: A webcomic of romance, sarcasm, math, and language. The drawings are simple stick figures, but it is the situations and ideas that are interesting and funny.

# Monthly Archives: May 2007

# ADS Digital Library

While googling for information on the Virial Theorem, I ran across a really cool page hosted at the Harvard ADS system. ADS stands for Astrophysics Data System, and it is primarily an abstract search engine that helps you locate journal articles mostly in the realm of Astronomy and Astrophysics, but they also have a small virtual library of books that you can freely download.

Here are the titles I found interesting:

- The Foundations of Celestial Mechanics by George W. Collins, II

(1989, 2004). - The Fundamentals of Stellar Astrophysics, by George W. Collins, II

(1989, 2003). - Fundamental Numerical Methods and Data Analysis by George W. Collins, II

(1990, 2003). - The Virial Theorem in Stellar Astrophysics, by George W. Collins, II

(1978, Pachart Publishing House, Tuscon, Arizona).

If you want to concatenate all the separate PDF chapters, I recommend using the texexec method oulined in this web page by Matthew Skala.

# Command Line Unit Conversion Utility

I found a handy tool for figuring out unit conversions quickly, and yes I am aware that Google does this, but sometimes the command line is more convenient. Here are some examples of how to use it:

$ units lightyear parsec * 0.30660139 / 3.2615638 $ units inches feet * 0.08333333 / 12 $ units 2m cm * 200 / 0.005

So the first line tells you what value to multiply the second unit by to make the conversion. And the second line is the inverse operation, that is, what you divide the second unit by to obtain the same value in the first unit.

To install this on a Debian/Ubuntu system, just run the following command:

$ sudo apt-get install units