Hi, I searched about Lagrangian Particle Tracking subject in history texts and I found that "hemi" example relates to it. After a review of this example, some questions are: - How can I have a constant number of particles in the domain? It needs that the number of particles which come to the domain should be equal to the number of particles exit the domain. - How about the particles which contact to the wall? How do they come back? - How can I attach some information (for example Temperature) to any particle and change it each time step according to the flow properties and then have ensemble average of the magnitude of these information particles? Thank you Arash