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Archive for the ‘Uncategorized’ Category

We’ve moved

Posted by slayton on July 29, 2009

I’ve moved this blog to:

I know it isn’t a big change but technexus sounds better to me than nexus172.


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What are moments and products of inertia?

Posted by Mark on April 8, 2009

I saw this question today on the internet at a forum, and nobody seemed to have an answer. Some people thought they knew what they were talking about, but had absolutely no clue. I have a clue, as I’m responsible for keeping track of these properties for over a hundred components on a developmental rocket program.

Question: Do the moments and products of inertia represent anything in the physical world?

Answer: In short, yes. But not intuitively.

It’s best to think of moments and products of inertia in terms of the inertia tensor, which is a mathematical concept – it’s a matrix of inertias for a given 3D object.

The moments are the diagonal values of the inertia tensor and the products are the off-axis values. Keeping the tensor in mind, you can think of an object’s moments of inertia to be the rotational equivalents of the general concept of inertia. Ie, as inertia is the resistance to change in motion, moment of inertia is an object’s resistance to change in rotational motion about some axis. As there are three dimensions, any physical object’s rotation can be defined about 3 axes. It is these axes that form the basis of the inertia tensor. If it took 4 axes to define rotation, the matrix would be 4×4, not 3×3.

In the real 3D world rotation is quite complex – for most real-life objects, you are not going to be able to find 3 axes about which the object will rotate in a stable manner. Ie, most objects don’t have mass distributed symmetrically about all 3 axes at once. Thus, you get off-axis moments of inertia, also known as products of inertia. POI’s can be thought of as measurements of dynamic imbalance of an object and basically represent asymmetrically distributed mass. Note that mass can be distributed symmetrically about one axis but not another, leaving you with products of inertia.

If you see an inertia tensor and the products are zero, there is no dynamic imbalance – the object will rotate perfectly about the defined axes. In such a case, you can call these the principle axes.

Ugh. This is complicated stuff and is often not covered in undergrad engineering or science. What I’ve written is only going to be a piece of the puzzle to understanding, but I hope it has helped. Let me know if any of you see errors in what I’m saying.

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The Halloween Documents

Posted by slayton on October 11, 2008

The following link contains a Microsoft Internal Memo about the real threat posed by Open Source Software (OSS) and more specifically Linux.  I’d suggest you read it as it points out from a very critical source the strengths of both Linux and the OSS development community.

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Linux is not Windows

Posted by slayton on October 11, 2008

The following work is copyright and belongs to Dominic Humphries. It may be redistributed under a Creative Commons License: The original URL of this article is: which must supplied in attribution.

Linux is NOT Windows

If you’ve been pointed at this page, then the chances are you’re a relatively new Linux user who’s having some problems making the switch from Windows to Linux. This causes many problems for many people, hence this article was written. Many individual issues arise from this single problem, so the page is broken down into multiple problem areas.

Problem #1: Linux isn’t exactly the same as Windows.

You’d be amazed how many people make this complaint. They come to Linux, expecting to find essentially a free, open-source version of Windows. Quite often, this is what they’ve been told to expect by over-zealous Linux users. However, it’s a paradoxical hope.

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Secure Shell

Posted by slayton on October 5, 2008

Secure Shell – SSH

In my previous post I mentioned the existance of the shell.  This post is about Secure Shell(ssh) and what you can accomplish with ssh.  In a nutshell (pun intended) ssh allows you to open a shell securely on another machine that is running an ssh server.  All ssh authentication is done over the Open SSL protocol, meaning that your connection is completely encrypted and cannot be snooped or intercepted.

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Why Use Linux?

Posted by Mark on September 24, 2008

There is no way that I can list all the possible reasons to use Linux, but I can list the reasons I, a somewhat technically-inclined person, am giving it a try.

  1. I am tired of Windows giving me broken applications and incompatibility issues with no fixes available. With Windows I feel like I’m at the mercy of the companies involved (in my case Microsoft and Toshiba, primarily) for solving my hardware incompatibility issues (that should never have been issues). If they don’t feel like I’m an important enough market, they probably won’t release a fix. With Linux I am at the mercy of a community of people just like me (well, hopefully a little smarter), who respond in a much more personable way. Besides, with Linux I can edit the system myself and create a fix if one doesn’t exist. More difficult at first, but probably worth it in the long run.
  2. I want a faster, more stable, more efficient operating system. My old Toshiba Pentium 4 laptop is struggling under the weight of Windows. Linux has given it rebirth. Boot time, application load time, even the internet all seem to run more smoothly and quickly.
  3. I figure this is great practice for building a Hackintosh. This way I can get familiar with things like the command line interface, patching, and learn how to diagnose problems and find/create solutions. Since OSX is a Unix-based OS, it will be very easy to apply knowledge learned here to what will be required to build my own fully-functioning mac.
  4. It is absolutely free. Just go to for a free download or a free CD.

That said, there are some down sides, I recognize. For example:

  • Problems will come up that are difficult to fix. This is ok, though – Linux is about teaching yourself how to have more control over your system. It’s ok if problems come up – and even if MORE problems come up versus Windows – as long as there is a route to fixing it. That is the guarantee of Linux, the way I see it, and the basis of its advantages over any closed-source OS.
  • It will take more time (at first) to do things I am used to being able to do easily in Windows.

The big question is whether the time/effort investment will yield worthy returns. I am hoping the answer is a definitive yes. Expect the answer to that question to come in about 6 months.

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Just moved to linux, where did my desktop go?

Posted by Mark on September 24, 2008

> Mark: Stuart, one of the complaints I have so far about using Linux is that I feel like I have less “space” on my screen. The fonts used in Linux are bigger, the menus seem bigger, not to mention the fact that there is the system panel/bar thing at the top and then the panel at the bottom, too, which just ends up taking more space. Help!

> Stuart: So you feel like you have less space? Well I’m not surprised you feel that way, because you do.  If I had a list of common complaints from people migrating to linux, this would in the top 5, so your not alone.

There are two things that attribute to you having less space: your Desktop Manager, and the Font Rendering. I’ll try to address both below.

The default Desktop Manager in Ubuntu is Gnome and by default Gnome has two panels, one at the top and one at the bottom.  The layout of these panels is completely up to you. Here are a few examples of things you can do to the panel:

  • Try something out, click on the blank space of one the top panel and click and drag it to the bottom, left, or right. It will move.
  • If you want to get rid of it completely right click on it then select “Delete this Panel”
  • You make a lot of fun changes to a panel by right clicking selecting “Properties”. Now you can: Change the size of the panel, add Show/Hide buttons, add a background image, make the panel transparent, Enable/Disable Expanding panels.
  • You can also add widgets to the panel by right clicking and selecting “Add to Panel”. I think you’ll be surprised by the number of things you can add.
  • Its also really easy to move stuff around, just click it and drag it around the panel.  This won’t work if the widget is “locked”, to unlock a widget right click it and select “Lock to Panel”. By default the widgets that come with Ubuntu are locked.

I think after you’ve used the two panel system long enough you will like it.  I hated the top panel at first but now I’ve really come to rely upon it.  For me, the top panel serves the purpose of an application launcher and a quick system notifier. I look there for info such as: Email Received, Time, Weather, Network Status. The bottom panel is what I use to switch between running applications.  On my bottom panel I have: Window List, System Monitor, and Workspace Switcher. (I’ll do a post on the beauties of the workspace switcher another day).

Another option is to try a different Desktop Manager, there are quite a few with the most popular being: Gnome, KDE, XFCE.

The second point you bring up is Fonts.  Fonts are actually a huge issue in linux. Most of the fonts used in windows are covered by Copyright.  You can download the Microsoft Core True Type Fonts, the package is called msttcorefonts. However, in my experience linux fonts look better under linux than windows fonts do. You can try messing around with the fonts to see if you find a configuration that looks better.

To change the font settings click: System–>Preferences–>Appearance, then select the Font tab. All of my fonts are set to Sans, except Window Title Font which is Sans Bold and Fixed Width Font which is Monospace. All my fonts are set to size 10.

So in summary you can try tweaking with settings in an attempt to recover the lost screen real estate but I think you’ll probably be happiest with the default settings.

> Mark: So basically you’re telling me that I’m stuck with less viewing space unless I screw around with the fonts. Is there any way to decrease the padding in application menus or otherwise make things more compact? I don’t think I should have to buy a 21″ monitor to solve this problem.

> Stuart: So to give you an idea of my screen real-estate I have a resolution of 1280×800 on my laptop. I remember noticing a distinct drop in space when I switched to Ubuntu but about a week or so later I got used it.  I understand that the majority of newer laptops are all “widescreen” which is essentially more horizontal space at the cost of vertical space.  The Gnome panels eat into this precious vertical space. Looking back I would probably not buy a widescreen laptop again but I’m stuck with what I’ve got so I’ll make do.  A couple things I have done do to maximize my viewing area are:

  • Under System–>Preferences–>Appearance, select the interface tab and select: Icons Only under Toolbar Button Labels, this will remove text under buttons across the entire system. This should add a few more pixels.
  • Another solution is to try out KDE, or XFCE. You can download Kubuntu and Xubuntu liveCDs, which are Ubuntu but with a different window manager.  Try the liveCD if you like what you see, you can then install KDE or XFCE to your current installation via Synaptic Package Manager or by opening a terminal and typing sudo apt-get install kubuntu-desktop or sudo apt-get install xubuntu-desktop. Ubuntu will then download the appropriate files and install the other window manager. This is nice because it doesn’t remove Gnome or require a fresh install, and has the added bonus that you can switch from one desktop manager to another at any given time.
  • I use Firefox a lot. Is my most used application. I was able to gain a lot of real-estate in firefox by moving my Bookmarks Toolbar.  I moved my Bookmarks Toolbar next to the “File Edit View History Bookmarks Tools Help” bar. You can do this by: Right clicking on the toolbar, select customize, then move (click and drag) the Bookmarks Toolbar Items up to the top bar, then click done. You’ll notice that your bookmarks themselves moved, but the space they were originally occupying is still present. Right click on the toolbar again and uncheck the Bookmarks Toolbar. The bookmarks will stay but the space they previously occupied will go away!
  • There are a few more tweaks you can do in specific applications to maximize their real-estate which we can talk about later if you’d like.

So long story short, Explorer under Windows has a much higher resolution and uses less real-estate then Gnome does in linux.  Its a pain but you’ll get used to it and eventually you won’t notice it.  Believe me when I say that the loss of productivity from a “smaller” desktop is dwarfed by the increase in productivity from using an OS that is intuitive and empowering.

This is actually a great segway into my next topic which will be about the amazing world of the Terminal!

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