Scientific relatedness in solar energy: a comparative study between the USA and China
In this paper, we make use of keywords in scientific articles in solar energy during the period 2000---2013 to investigate scientific relatedness at the topic level (i.e. relatedness between topic and topic) and the country level (i.e. relatedness between topic and country). The bibliometric analyses show that both publications and knowledge topics exhibit significant rise, and China has exceeded the USA and developed into the largest scientific producer after 2010. We determine the degree of relatedness by means of the topics co-occurrence network and explore the evolving dynamic processes of scientific relatedness which indicates decreasing patterns in the two countries. The results also highlight differences between the research directions in the USA and China: in the USA "energy efficiency and environment" prove more developed, while in China "solar power" shows more central. This study assesses the extent to which the scientific relatedness exerts influence on the literature productivity at the country level. We find negative relationships between scientific relatedness and publications in both of countries. Our work has potential implications for the future policies with respect to the innovative research in the solar energy field.