code: def get_element_mfr_dictionary(self):
          
  
          element_symbols = self.material.elements
          element_mfrs = self.get_element_mfrs()
          result = dict()
          for s, mfr in zip(element_symbols, element_mfrs):
              result[s] = mfr
          return result
docs: Determine the mass flow rates of elements in the stream and return as
          a dictionary.
  
          :returns: Dictionary of element symbols and mass flow rates. [kg/h]