Volume 39 first discusses clustering, a well-known problem in statistics and engineering concerning how to arrange a set of vectors (measurements) into a number of groups (clusters). The fundamental concepts of hierarchical algorithms are described, along with a review of the different linkage criterions and recent developments aimed at improving the pioneer versions. The authors presents recent developments regarding the use of water electrolysis, which results in the obtainment of syngas that may be used for power generation and the production of fuels and chemical intermediate compounds. A multi-objective optimization model for optimizing the operation of natural gas pipeline networks is developed for different network configurations, namely linear, branch and looped topologies. An overview of degummed biodiesel preparation is provided, along with a study of engine performance parameters such as brake power, brake thermal efficiency and brake specific fuel consumption of degummed biodiesel and their diesel blends. The authors go on to introduce the principles of the Distributed Reflective Denial of Service attack, discussing the threats of this kind of attack, as well as the impact on the victim server and victim network. In the closing study, a comprehensive model of a quadrotor is built with physical analysis, parameter and function identifications. The propeller and motor properties are tested in a wind tunnel in scheduled conditions in the presence of relative air flow.