Set up Apache Ant on WinXP

  1. Download version 1.8.4 of Apache Ant as a ZIP file.
  2. Extract this file to C:\Ant\. Don’t use the Program Files folder, since Ant doesn’t cope well with spaces.
  3. Add the bin folder of your installation to the Path environment variable. Click Start – Control Panel – System – Advanced – Environment Variables. Select Path from the list of system variables and click Edit. In the text box, type a semicolon behind the last entry and add the path,
    C:\Ant\apache-ant-1.8.4\bin
  4. Verify your installation by opening a console and running
    ant -version

    On success, the output isOutput of running ant -version on WinXP.
    and you are set.

You may get an error like

Unable to locate tools.jar.
Expected to find it in C:\Program Files\Java\jre6\lib\tools.jar
Buildfile: build.xml does not exist! Build failed

This is most likely caused by the space or a missing Java Development Kit. Install the Java Development Kit, the most recent version being Java SE 6 Update 37. Create a new environment variable JAVA_HOME along the lines of step three above. The value is the path to your JDK,

C:\Java\jdk1.6.0_37

Let me know your questions and comments.

Craft a Möbius strip

Here is a step by step guide on how I made a Möbius strip from paper. A short video shows how to fold a paper strip up into Möbius shape. It takes only a few minutes to complete the tutorial.

Make it

  1. Take a blank sheet of paper (US letter / European A4), a pair of scissors and glue.
  2. Cut a 1” / 3cm wide strip off of the sheet.3cm wide paper strip
  3. Mark the up side with a horizontal red line, as shown in the picture.
  4. Grab each end with one hand. Twist the right end along the red line, so that the blank side comes on top.
  5. Turn both ends of the strip by 180 degrees in opposite directions, the left end clockwise, the right end counterclockwise, until they meet and overlap.
  6. Glue both ends together at the overlap.Möbius strip with overlap region marked
  7. Finished!

Have fun with it

FolIowing these steps, I made a clockwise and a counterclockwise strip, and cut them in half along the red line. Instead of splitting, the strips just became twice as long and got doubly twisted, as you can see in the gallery.

Then I cut another Möbius strip. This time the starting point was one-third away from the edge. The cut didn’t come full circle, but was two-thirds away from the edge after one round. I went on cutting. After the second round I finally returned to the starting point. The strip separated in two intertwined pieces, a small Möbius strip and a long doubly twisted strip.

Create a self-signed certificate on WinXP

Here is a step by step guide on how I created and signed a X.509 certificate on a WinXP machine, where IIS tools like makecert.exe are not available. You can use the certificate to establish a SSL connection to your Windows Azure server and test your web site.

Generate the certificate

  1. Download and install the FileZilla Server.
  2. Start the FileZilla Server Interface. Open the Server Options window by choosing the menu point Edit → Settings.screenshot filezilla edit settings
  3. In the left column, choose SSL/TLS Settings entry. Click on the button Generate new certificate.screenshot filezilla ssl tls settings
  4. Fill in the form, choose a folder to save the file and click on the button Generate certificate.screenshot filezilla generate cert

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Zahlensysteme

Im einfachsten denkbaren Zahlensystem symbolisiert ein senkrechter Strich die Eins, und die Anzahl der Striche entspricht der dargestellten natürlichen Zahl. Die Position eines Striches hat keinen Einfluss auf seinen Wert. Die Vier sieht dann so aus:

     ||||

Will man große Zahlen darstellen, muss man viele Striche zeichnen. Wie sollte man zum Beispiel die Tausend aufschreiben?

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