This is a simple oscillator using a 555 timer chip. It is similar to the square wave example, but has a very short duty cycle.
A timing interval starts when the trigger input ("tr") goes lower than 1/3 Vin, or 3.33V. When this happens, the 555 output goes high. This causes the capacitor to be quickly charged through the diode until it reaches 6.67V. Then, the timing interval ends, the output goes low, and the capacitor is discharged through the "dis" input.
When the capacitor is discharged enough so that the trigger reaches 3.33V, then a new timing interval begins. The end result is a series of short pulses.
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