Article 82: other limitations to utility model rights The rights stemming from the utility model shall not be extended to: 1° the use of the patented invention of utility model on board a foreign aircraft and land vehicles, vessels or spacecraft which temporarily or accidentally enter the airspace, territory or waters of the Republic of Rwanda; 2° the acts relating to a patented invention of utility model carried out for scientific and technological research purposes and for public non-profit use; 3° the acts performed by any person who, in good faith and on the filing date or, where priority is claimed, on the priority date of the application on the basis of which the patent is granted, was using the invention of utility model or was making effective and serious preparations to use it, insofar as these acts do not differ, in their nature or purpose, from previous effective or envisaged use. The right of the prior user of the invention of utility model referred to in paragraph 1(3) of this article may be transferred or devolve only to the enterprise or business, or part thereof, in which the use or preparations with a view to use took place. It is not an infringement of a patent of utility model for any person where the use, manufacture, construction or sale of the patented invention of utility model is justified only insofar as it is necessary for the preparation and production of the information file which must be provided according to a domestic or foreign law governing the manufacture, construction, use or sale of a product. Article 83: Duration, renewal The utility model certificate shall expire, without the possibility of renewal, ten (10) years after the filing date of the corresponding application. At the end of the fifth year after the filing date, the owner of the utility model certificate shall pay a fee for maintenance in force for the following five (5) years. If the fee is not settled in accordance with this Law, the utility model certificate shall lapse. A grace period of six (6) months shall be accorded for payment of the fee for maintenance in force, in return for payment of the prescribed surcharge. A Ministerial Decree shall determine all fees stipulated in this article. SECTION 6: UTILITY MODEL ASSIGNMENT AND LICENSE Article 84: Utility model assignment The patent of utility model may be assigned, by contractual arrangement, by the patent owner to any interested person. The utility model assignment contract shall be drawn up in writing and shall be signed by the parties to the contracts.