code: def conductivity_prior_mean_3d(x):
      """Prior mean for the conductivity."""
      vol1 = x[0]  # LiNO3
      vol2 = x[1]  # Li2SO4
      vol3 = x[2]  # NaClO4
      vol4 = 10 - (vol1 + vol2 + vol3)  # Water
      return (
          0.9 * vol1
          + 0.12 * (vol2 + vol3) ** 2.05
          + 2.4 * vol4 * (vol1**1.6)
      )
  
label_desc: Use image node_id 1 for calling a global function with example usage: conductivity_prior_mean_3d(x) and returns: unknown