Voder-Vocoder

I hate unnecessarily long URLs. One of the things I always try to figure out how to leave out is the file name extension. As Tim Berners-Lee says:

"cgi", even ".html" is something which will change. You may not be using HTML for that page in 20 years time, but you might want today's links to it to still be valid. The canonical way of making links to the W3C site doesn't use the extension

Here are two ways of doing this with Apache.

1) Insert this line into your ".htaccess" file:

DefaultType text/html

Then when you create any new html pages, call them "foobar" instead of "foobar.html" and then your URL will be:

http://example.com/directory/foobar

and not

http://example.com/directory/foobar.html

Which makes more sense. Now you can at some later point in time change the default to .shtml or .php

2) Put this in your ".htaccess" file:

Options All MultiViews

Then put a file called "foobar.html" in the directory "directory/" and the URL:

http://example.com/directory/foobar

will automagically work.

3) Here's a third way:

RewriteEngine on
RewriteCond %{REQUEST_FILENAME}.html  -f
RewriteRule ^(.*)$           $1.html

Favorite Firefox Addons:

Go Up

Lets you go "up" a level in the current website via the provided toolbar button, or by pressing Alt+Up arrow. The "up" is determined by trimming the last section of the URL, e.g. example.org/foo/somepage.html becomes example.org/foo/

I don't use this much, but it does come in handy every so often.

Flashblock

Flashblock is an extension for the Mozilla, Firefox, and Netscape browsers that takes a pessimistic approach to dealing with Macromedia Flash content on a webpage and blocks ALL Flash content from loading. It then leaves placeholders on the webpage that allow you to click to download and then view the Flash content.

This is a lifesaver. Try moving your mouse cursor over a piece of flash, then hitting the page-down key. Nothing happens, unless the flash is blocked.

MM3-ProxySwitch

In the Firefox Browser (and other Mozilla programs) you can per default configure only the setting for one internet connection. With the MM3-ProxySwitch you can manage different configurations and simply switch over between these.

I use this one on my laptop for managing proxies.

FullerScreen

This extension enhances the Full Screen mode into a really full screen mode, hiding the remaining toolbars and statusbar and making them visible again when the mouse pointer hits an edge of the screen.

It also offers a slideshow mode, enabling @projection CSS rules in a document when full screen mode is turned on. Navigation between slides in implemented in the extension and a slide manager showing thumbnails for the slides is available through shift-F11.

I'm still trying this out, but it seems like a good idea.

What is the tension in a spinning ring, for example Bank's orbitals or a Niven Ring?

Let us brake the ring into N sections. The angle (in radians) subtended by each section, dθ, is 2π / N. Suppose the radius of the ring is R and the mass-per-unit-length of the ring is λ; then the mass of a section is λRdθ and the mass of the whole ring M = 2πRλ.

Ignoring gravity, there are two forces pulling on each small section: tension pulling to the left and tension pulling to the right. Because the ring is circularly symmetric, the magnitude of the two tensions are equal. The directions of the two forces are dθ from being opposite.

If at some moment in time, the left tension is pointing in the direction, then the right tension will be

where T is the magnatude of either tension.

As N gets large and dθ gets small, and . So:

Consequently, the centripital force on the small section is Tdθ. From Newton's second law:

Tdθ = (λRdθ)a

where a is the centripetal acceleration.

T = λRa

Part B: Plug in some numbers.

Let P be the period of revolution. P = 2π√(R/a).

If the ring is made of solid steel, T / λ = 154000 N·m/kg. Setting our centripetal acceleration to an earthly 10 m/s², we find that the maximum radius for a ring of steel is 15 kilometers. Period of revolution = 243 seconds = 4 minutes. If you assume that half of the mass of your ring is structural material and the other half is nonstructural, then you get a diameter of 15 km. Multiply the period by 1/√2.

Carbon nanotubes: maximum size of 4800 kilometers. Period of revolution = 4353 seconds = 1.2 hours

The period of revolution for a Culture Orbital is a convenient 24 hours. The radius of a Niven Ring is 1 AU. Neither of these is feasible with today's understanding of physics.

On the other hand, a Stanford Torus with a radius of 893 meters and an orbital period of 60 seconds would need to have an average specific strength of 8745 N·m/kg, so at least 6% of the mass would need to be steel structure. (You would probably want a 4x fudge factor. Say 25% structural steel. Then sections of the ring could be replaced if they show signs of wear.)

Yesterday I cut off about four inches of hair, down to a #6 buzz.

Today I got contacts.

They are not going to recognize me at work.

Ahh! There's something in my eyes! Oh. Right.

I got my Kill-A-Watt electricity usage monitor in the mail today. So far I have discovered:

1) When completely powered off, the computer power supply and the television consume 5 watts each.

2) The computer speakers/subwoofer consumes around seven watts if the power is off and around seven watts if the power is on.

3) The 19 inch LCD monitor consumes very little power when off and around 26 watts when on. (Most of which is radiated as visible light.)

4) The CPU consumes around 99 watts when running smoothly and not spinning the drives much.

This page collects several of the scripts I've written for Linux over the years.

Maybe someone else will find them useful.