code: def merge_particle_emission(SS):
      
      # Merge all the particles
      P = reduce(lambda x, y: x + y, [Si.particles for Si in SS])
      s = SS[0]
      S = ParticlesSimulation(t_step=s.t_step, t_max=s.t_max,
                              particles=P, box=s.box, psf=s.psf)
      S.em = np.zeros(s.em.shape, dtype=np.float64)
      for Si in SS:
          S.em += Si.em
      return S
docs: Returns a sim object summing the emissions and particles in SS (list).