code: public static Structure getBiologicalAssembly(String pdbId, int biolAssemblyNr) throws IOException, StructureException {
  		return getBiologicalAssembly(pdbId, biolAssemblyNr, AtomCache.DEFAULT_BIOASSEMBLY_STYLE);
  	}
docs: Returns the biological assembly for the given PDB id and bioassembly identifier,
  using multiModel={@value AtomCache#DEFAULT_BIOASSEMBLY_STYLE}
  @param pdbId
  @param biolAssemblyNr - the ith biological assembly that is available for a PDB ID (we start counting at 1, 0 represents the asym unit).
  @return a Structure object or null if that assembly is not available
  @throws StructureException if there is no bioassembly available for given biolAssemblyNr or some other problems encountered while loading it
  @throws IOException