This Applet substitutes my old X-spiral program which used to run on Unix machines under X-windows.

Click the Start button to initiate a plane wave from the left.

You can click on the Reset h (reset half plane) key when the plane wave is somewhere in the middle of the tissue. This will break the front and initate a spiral wave. More instructions below.

Some buttons are not functional yet, such as R IC (read initial conditions), W IC (write initial conditions), Tip off/on (finds and plots the tip trajectory of any spiral) and Periodic Boundary Conditions (for periodicity along one of the axes) since I still need to implement them from my Fortran code (hope to get to that soon).

Things to do:

1. Record the signal at a given point in the tissue. For this use the Trace button located at the lower right end to activate it (trace on), select which traces to record ( Voltage, v-gate or both) and then click anywhere in the tissue.
   • Note 1: When you click in a new possition in the tissue, the recording automatically switch to that location.
   • Note 2: The Trace button activates and deactivates each time it is clicked (Trace on, Trace off).
3. Induce stimulus on the tissue. Click on S1 button so it says S1 on and choose the size of the stimulus in the box below. Click anywhere in the tissue to introduce a stimulus at that location. Repeat as desired to form conduction blocks and multiple waves. One can also use a really big size stimulus to "defibrillate" the tissue.
4. Visualize either the Voltage field or v-gate field in 2D (For this use the radio buttons).
5. Change the color map (three choices).
6. Change parameters
   1. Change the tissue size (lowest box on the right). The size can vary between 50 and 200 units and the tissue is always a square (enter a number and retun).
      • When changing the size, the trace recording turns off automatically.
      • As the tissue size decreases the computation time decreases and the simulation speed increases.
   2. Change parameters of the model on the fly. (Enter a number in the appropiate box and return). (See equations below for parameter's reference.)
      • Note: Use the one-cell FHN model first to see the effects of parameters on its dynamics.
   3. (For Experts) Change the integration dt and dx for the model as you change the parameters (only if you know what you are doing. Other wise you may crash the program). Note: the model is integrated using an implicit ADI so that is why dt is much larger than when using forward Euler.

These are the equations for the two-variable FHN model: