def get_mass(field, data):
species_mass = data.ds.index.parameters[ptype + "_mass"]
return data["particle_weight"] * YTQuantity(species_mass, "kg")
def get_charge(field, data):
species_charge = data.ds.index.parameters[ptype + "_charge"]
return data["particle_weight"] * YTQuantity(species_charge, "C")
