On the example Image, all particles are masked by an Age Mask.
                      This can also be achieved with a lot more options by using a 
                    Function
                    
	  Enables to use any other type of 3D mask with a Function (for advanced users)
	
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                     set as Age.
                      This mask allows to use 
                    Field
                    Defines a force-field in 3D space
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                     or 
                    3D Modifier
                    Modify a 3D geometry
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                     only on a defined period of a 
                     Particles
                    Simulate a particle system
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Particles
                    Simulate a particle system
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                     lifespan. If you want for instance for gravity to affect only dying particles, just set a function mask as Age over a 
                    Gravity
                    Apply a directional force to particles
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                     and make it work only on the end of the lifespan. Here is an example: