VMCA- Minimum control speed on the ground. It Drecreases with increased pressure alt.
V1- A take off safety speed. At a point before V1 if the critical engine fails the take off should be aborted, if at or above V1 the aircraft should continue the take off on one engine (After this point there will not be enough runway left to bring the aircraft to a halt safely, hence the take off must be contuinued). Just as a note all multi aircraft perf calcs are based on one engine out.