Fix error in scientific publication links

publications.html

@@ -27,12 +27,12 @@ layout: default_orekit
   </li>
   -->
   <li>
-    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="">Automatic differentiation for propagation of orbit uncertainties in Orekit</a><br/>
+    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="doc/Antolino-2016-automatic-diff-for-prop-of-orbit-uncertainties.pdf">Automatic differentiation for propagation of orbit uncertainties in Orekit</a><br/>
       Andrea Antolino (CS), Luc Maisonobe (CS)<br/>
       November 2016 – Stardust Conference</p>
   </li>
   <li>
-    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="https://www.researchgate.net/publication/283292056_VALIDATING_SHORT_PERIODICS_CONTRIBUTIONS_IN_A_DRAPER_SEMI-ANALYTICAL_SATELLITE_THEORY_IMPLEMENTATION_THE_OREKIT_EXAMPLE">Validating short periodics contributions in a draper semi-analytical satellite theory implementation: the Orekit example</a><br/>
+    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="https://www.researchgate.net/publication/283292056_VALIDATING_SHORT_PERIODICS_CONTRIBUTIONS_IN_A_DRAPER_SEMI-ANALYTICAL_SATELLITE_THEORY_IMPLEMENTATION_THE_OREKIT_EXAMPLE">Validating short periodics contributions in a Draper semi-analytical satellite theory implementation: the Orekit example</a><br/>
       Nicolas Bernard, Luc Maisonobe (CS), Lucian Barbulescu (University of Craiova), Petre Bazavan (CS)<br/>
       October 2015 – 25th International Symposium on Space Flight Dynamics (ISSFD)</p>
   </li>
@@ -47,12 +47,12 @@ layout: default_orekit
       April 2014 – Key topics in Propagation applied to Space Situational Awareness (KePASSA)</p>
   </li>
   <li>
-    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="">Revisiting the DSST Standalone Orbit Propagator</a><br/>
+    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="https://www.researchgate.net/publication/289898859_Revisiting_the_DSST_Standalone_Orbit_Propagator">Revisiting the DSST standalone orbit propagator</a><br/>
       Paul Cefola (University at Buffalo), Romain Di Costanzo (CS), Z. J. Folcik, Nicolas Bernard<br/>
       January 2014 – Advances in the Astronautical Sciences journal 152:2891-2914</p>
   </li>
   <li>
-    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="">Verification of the Orekit Java implementation of the Draper semi-analytical satellite theory</a><br/>
+    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="https://www.researchgate.net/publication/273132999_Verification_of_the_Orekit_Java_implementation_of_the_Draper_semi-analytical_satellite_theory">Verification of the Orekit Java implementation of the Draper semi-analytical satellite theory</a><br/>
       Paul Cefola (University at Buffalo), Barry Bentley (University of Cambridge), Luc Maisonobe (CS), Pascal Parraud (CS)<br/>
       February 2013 – 23rd AAS/AIAA Spaceflight Mechanics Meeting</p>
   </li>