<bibliography>
 <citation type="doi" key="10.1007/BF00872949">
  <doi>10.1007/BF00872949</doi>
 </citation>
 <citation type="doi" key="10.1017/CBO9780511815676">
  <doi>10.1017/CBO9780511815676</doi>
 </citation>
 <citation type="doi" key="10.1016/j.shpsb.2008.07.006">
  <doi>10.1016/j.shpsb.2008.07.006</doi>
 </citation>
 <citation type="doi" key="10.1007/s10701-010-9424-4">
  <doi>10.1007/s10701-010-9424-4</doi>
 </citation>
 <citation type="doi" key="10.1007/s11225-010-9246-6">
  <doi>10.1007/s11225-010-9246-6</doi>
 </citation>
 <citation type="doi" key="10.1063/1.3635841">
  <doi>10.1063/1.3635841</doi>
 </citation>
 <citation type="doi" key="10.1007/s00220-009-0865-6">
  <doi>10.1007/s00220-009-0865-6</doi>
 </citation>
 <citation type="doi" key="10.1063/1.882411">
  <doi>10.1063/1.882411</doi>
 </citation>
 <citation type="doi" key="10.1023/A:1026406502316">
  <doi>10.1023/A:1026406502316</doi>
 </citation>
 <citation type="doi" key="10.1023/A:1018716111971">
  <doi>10.1023/A:1018716111971</doi>
 </citation>
 <citation type="doi" key="10.1119/1.1975143">
  <doi>10.1119/1.1975143</doi>
 </citation>
 <citation type="doi" key="10.1119/1.10184">
  <doi>10.1119/1.10184</doi>
 </citation>
 <citation type="doi" key="10.1017/CBO9780511608216">
  <doi>10.1017/CBO9780511608216</doi>
 </citation>
 <citation type="doi" key="10.1007/BF01646746">
  <doi>10.1007/BF01646746</doi>
 </citation>
 <citation type="doi" key="10.1119/1.16104">
  <doi>10.1119/1.16104</doi>
 </citation>
</bibliography>
