In Figure , "blue" and "green" clusters are most integrated into the general citation scheme. The "blue" co-citation cluster includes Harvard University (USA) and two Chinese universities -Shanghai Jiao Tong University and Zhejiang University. Interestingly, in Figure , both Chinese universities were separated in the "yellow" cluster. This fact shows potential interest in collaboration which was not yet established. Surprisingly, two Saudi Arabia universities (King Saud University and King Abdulaziz University) have neither collaborations (Figure ) nor co-citations (Figure ). In general, many universities that have co-authorships do not have co-citations. We can explain this by the fact that many scientific groups help each other with scientific equipment, but at the same time, they are engaged in entirely different research topics.