The study aims to examine the factors affecting sustainable tourism development. First, the paper presents the literature review to show the related theories and overview of the tourism sector in Vietnam. Secondly, the research model and hypotheses are represented to test the relationships between influencing factors and sustainable tourism development. Finally, 329 questionnaires had been collected from state management agencies and tourism enterprises. By using SPSS and Smart-PLS-SEM, the research shows that seven factors were affecting on sustainable tourism development in Vietnam. Specifically, social engagement has the strongest effect on sustainable tourism development, followed by state managerial competence respectively, tourism service quality, the quality of tourism human resource, infrastructure development, material tourism facilities and tourism resource.

A single crystal of Ag 12 -A (zeolite LTA) was prepared by the dynamic ion-exchange of Na 12 -A with aqueous 0.05 M AgNO 3 . It was washed with CH 3 OH and allowed to react with a stream of 0.05 M KCl in CH 3 OH at 294 K. The crystal structure of the product |K 2.35 Ag 1.1 (Ag 4 Cl 4 ) 0.45 (C 3 H 3 O 3 ) 1.1 (K 3 Cl) 3.45 (K 3 (OH) 2 ) 0.55 (H 2 O) g3.0 |-[Si 12 Al 12 O 48 ]-LTA (a ) 12.292(1) Å) was determined by single-crystal X-ray diffraction in the cubic space group Pm3 j m at 294 K. It was refined to the final error index, R 1 ) 0.052, based on the 371 reflections for which F o > 4σ(F o ). Ag 4 Cl 4 nanoclusters were found in about 45% of the sodalite cavities. Each Ag 4 Cl 4 cluster (interpenetrating tetrahedra; symmetry T d , Ag-Cl ) 3.105(17) Å) is held in place by the coordination of each of its four Ag + ions to three oxygens of the zeolite framework (Ag-O ) 2.493(5) Å) and by the coordination of each of its four Cl -ions to a K + ion through a 6-ring (Cl-K ) 2.70(3) Å). In each of the remaining 55% of the sodalite cavities, two reduced planar 1,3,5-tripyrylium cations, [(CH) 3 O 3 ] 2 2+ (C-O ) 1.52(3) Å), are found. These parallel eclipsed rings (symmetry D 3d ) have an interplanar distance of only 2.43 Å due to σ double bonding between the rings, the result of four electrons in 12-center bonding π* orbitals, and to polar attraction. Each ring makes three strong hydrogen bonds (CH · · · O ) 2.84(3) Å) to oxygens of the zeolite framework, and a Ag + ion coordinates to the three oxygens of one ring (Ag-O ) 2.68(9) Å). The large cavities are filled with K + , Cl -, Ag + , OH -, and H 2 O; the K 3 Cl 2+ unit predominates. The 1,3,5-tripyrylium ring, isoelectronic with benzene, had not been reported before.

Ensuring food safety for foodservice businesses is extremely necessary during the current complicated situation of the Covid-19 pandemic. This study has evaluated the knowledge and practices on food safety of establishment owners, food processors, and customers to prevent the Covid-19 pandemic at foodservice businesses in Son La city in 2020. The results show that over 75 % of establishment owners knew regulations to ensure food safety in the prevention of the Covid-19 pandemic, and 100 % of establishment owners were trained in disseminating and guiding pandemic prevention documents. Food processors who have good knowledge and practices of regulations of the Ministry of Health on ensuring food safety to prevent Covid-19, such as wearing masks when working, keeping contact distance with food, washing hands, disinfecting correctly, and do not gather in large numbers in production facilities have reached a high rate of over 90 %. All customers know about the 5K regulations. It is necessary to strengthen the propaganda to ensure food safety to prevent the Covid-19 pandemic so that the subjects can better understand the regulations of the Government, the Ministry of Health, Departments on ensuring food safety and prevention of the Covid-19 pandemic, and good practices of the above regulations.

The current situation of the Covid-19 epidemic is still complicated, ensuring food safety for food service businesses is very important and necessary. The study conducted to assess the facility conditions, equipment and materials to ensure food safety at 61 food service businesses to prevent Covid-19 epidemic in Son La City in 2020 showed that 100% of the processing areas of establishments with a place to wash hands, clean water and soap, fully equipped with food preservation equipment, and clean daily waste collection. However, only 29.5% of establishments arrange kitchen on the principle of one-way. 100% of establishments meet the conditions on equipment and tools. Over 80% of establishments arrange to eat in several shifts to ensure the distance and enough tables and chairs with barriers to separate and arrange the distance between customers. 100% of establishments have communication posters about Covid 19 in the dining area.

The current situation of the Covid-19 epidemic is still complicated, ensuring food safety for food service businesses is extremely necessary. Research and evaluate knowledge and practice on food safety of establishment owners, food processors and customers to prevent Covid-19 epidemic at food service establishments in Son La city in 2020 for found that the results were quite high: over 75 % of owners had knowledge of regulations to ensure food safety in the prevention of Covid-19 epidemic and 100 % were trained in disseminating and guiding epidemic prevention documents. Food processors who have knowledge and practice of regulations on ensuring food safety to prevent Covid-19 have reached a high rate of over 90 %, especially regulations of the Ministry of Health such as wearing masks when working, keep contact distance; wash hands, disinfect properly, and do not gather in large numbers in production facilities. 100 % of customers know about the 5K message. It is necessary to further strengthen the propaganda to ensure food safety to prevent Covid-19 epidemic so that the subjects can better understand the regulations of the Government, the Ministry of Health, departments and branches on ensuring food safety and prevention. Covid-19 and good practice of the above regulations.