Julien Loiseau is a Ph.D. student in computer science at the University of Reims Champagne-Ardenne. He works in the CReSTIC laboratory in the SysSom group, which works on HPC and optimization using classical CPUs, GPUs, or Xeon Phi. Julien has worked on the Langford combinatorial problem, with the group setting a new time record to solve the last instances 27 and 28. This work shows the power of GPUs on very irregular problems despite the need of synchronization and communications. To continue the work on irregular problems and to benchmark the ROMEO supercomputer of the Reims University, the group began work on the Graph500 benchmark, the results of which are presented in this talk. Julien also worked for three months at the Los Alamos National Laboratory on astrophysics simulation problems.