1 Introduction

This article introduces the application of dynamic systems theory in second language development research, emphasizing language complexity, accuracy, and fluency as key dimensions for evaluating second language development levels. Special emphasis is placed on the importance of language complexity in the field of second language writing, and it is pointed out that current research tends to focus more on middle or undergraduate students, while there is less research on master's and doctoral dissertations. This study aims to explore the developmental characteristics of language complexity in abstracts of master's and doctoral theses, in order to provide guidance for academic writing.

2 Literature Review

This article summarizes the research background of language complexity and points out that lexical complexity and syntactic complexity are important indicators for measuring the language ability of second language learners. Domestic and foreign scholars have conducted extensive research on these two dimensions, but mainly focused on the writing texts of middle school and undergraduate students, with less research on master's and doctoral dissertations. In addition, existing research often focuses on a single dimension and lacks comprehensive analysis of both vocabulary and syntax dimensions. This study aims to address these shortcomings and comprehensively explore the developmental characteristics of language complexity in abstracts of academic dissertations from different disciplines.

3 Research Methods

This chapter introduces research methods, including two self built small corpora: Linguistics Dissertation Abstracts Corpus (LDAC) and Physics Dissertation Abstracts Corpus (PDAC), representing the disciplines of linguistics and physics, respectively. The corpus is sourced from the CNKI database, selecting abstracts of master's and doctoral dissertations from 2016 to 2020, ensuring an equal number of 200 abstracts selected each year. The research tool is Coh Metrix 3.0 software, which is used to measure the surface and deep dimensions of lexical complexity, and L2SCA is used for syntactic complexity analysis. The research focuses on the developmental characteristics and similarities and differences of language complexity in abstracts of theses in linguistics and physics at the master's to doctoral level.

4 Results and Discussion

The statistical results of vocabulary and syntactic complexity in the abstracts of master's and doctoral theses in linguistics and physics show that the diversity of textual vocabulary and the logarithmic frequency of actual meaning words in the abstracts of doctoral theses in linguistics are lower than those in the abstracts of master's theses, while the adjacent sentence latent meaning analysis and lexical semantic values are higher than those in the abstracts of master's theses, but these differences have not reached statistical significance. The lexical diversity of the text in the abstract of a doctoral thesis in physics is significantly higher than that in the abstract of a master's thesis, while there is no significant difference in the logarithmic frequency of actual words. The analysis of adjacent sentence meanings and lexical semantic values in the abstract of a physics doctoral thesis are significantly lower than those in the abstract of a master's thesis, indicating a reduction in the use of words with similar meanings for explanation by doctoral students and a higher degree of abstraction in word choice.

5 Conclusion

This study reveals the development of language complexity in abstracts of master's and doctoral theses from different disciplines in China through corpus comparative analysis. The results show that the vocabulary complexity of linguistics majors reaches its peak at the master's level, while physics majors continue to improve. In terms of syntactic complexity, students majoring in linguistics perform better than those majoring in physics, who have limited progress in their master's and doctoral studies. The study suggests that master's students strengthen their academic English writing skills, pay attention to the differences in thinking patterns between the East and the West, and suggest that universities offer targeted academic English writing courses to enhance their academic English expression abilities.