STRUCTURE OF THE THESIS The main part of the thesis is 139 pages long, consisting of the following sections: Introduction: 2 pages; Chapter 1 - Overview: 37 pages; Chapter 2 - Research Object and Method: 25 pages; Chapter 3 - Research Results: 36 pages; Chapter 4 - Discussion: 36 pages; Conclusions and recommendations: 3 pages The thesis has 124 references, of which 34 are in Vietnamese and 90 are in English.