Copyright notice

The documents available from this site are provided as a means to ensure timely dissemination of technical work on a non-commercial basis. Copyright and all rights therein are maintained by the authors or by other copyright holders, notwithstanding that they have offered their works here electronically. It is understood that all persons copying this information will adhere to the terms and constraints invoked by each author's copyright. These works may not be reposted without the explicit permission of the copyright holder (Springer-Verlag, ACM, IEEE, Elsevier, Academic Press, IOP, etc.). The electronic version of some of the works available from this site may differ from the definitive published version. Please refer to the publisher site for the copy-edited final manuscript.