STRUCTURE OF THE THESIS The main part of the thesis is 113 pages long, consisting of the following sections: Introduction: 2 pages; Chapter 1 - Overview: 29 pages; Chapter 2 - Research Object and Method: 18 pages; Chapter 3 - Research Results: 32 pages; Chapter 4 - Discussion: 29 pages; Conclusions and recommendations: 3 pages The thesis has 124 references, of which 31 are in Vietnamese and 93 are in English.