Copyright Notice The documents distributed by this server have been provided by the contributing authors as a means to ensure timely dissemination of scholarly and technical work on a noncommercial 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. Several of the documents are under the copyright of ACM, IEEE, Springer, or Elsevier. Relevant excerpts from these copyrights are presented below. ACM Copyright (c) 2000 by the Association for Computing Machinery, Inc. Permission to make digital or hard copies of part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page or intial screen of the document. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Publications Dept., ACM Inc., fax +1 (212) 869-0481, or permissions@acm.org. IEEE Copyright (c) Institute of Electrical and Electronics Engineers. Reprinted, with permission, from IEEE. This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by sending a blank email message to info.pub.permission@ieee.org. By choosing to view this document, you agree to all provisions of the copyright laws protecting it. Springer The Author may publish his/her contribution on his/her personal Web page provided that he/she creates a link to the above mentioned volume of LNCS at the Springer-Verlag server or to the LNCS series Homepage (URL: http://www.springer.de/comp/lncs/index.html) and that together with this electronic version it is clearly pointed out, by prominently adding "(c) Springer-Verlag", that the copyright for this contribution is held by Springer. Elsevier Elsevier is liberal with respect to authors and electronic preprints. Unlike some publishers, we do not consider that a preprint of an article (including a prior version as a thesis) prior to its submission to Elsevier for consideration amounts to prior publication, which would disqualify the work from consideration for re-publication in a journal. We also do not require authors to remove electronic preprints from publicly accessible servers (including the author's own home page) once an article has been accepted for publication. Further, we have announced in May 2004 a change in policy that facilitates institutional repositories by permitting authors to revise their personal versions of their papers to reflect changes made in the peer review process. This new policy permits authors to post such revised personal versions on their own web sites and the sites of their institutions, provided a link to the journal is included. Our policy however is that the final published version of the article as it appears in the journal will continue to be available only on an Elsevier site.