Vietnam Journal of Science, Technology and Engineering

3-16

Authors: P.N. Diep*, D.T. Hoai, N.B. Ngoc, P.T. Nhung, N.T. Phuong, T.T. Thai, P. Tuan-Anh

HD 163296 is one of the few protoplanetary discs displaying rings in the dust component. The present work uses ALMA observations of the 0.9 mmcontinuum emission, which have significantly better spatial resolution (~8 au) than previously available, to provide new insight into the morphology of the dust disc and its double ring structure. The disc is shown to be thin, and its position angle and inclination with respect to the sky plane are accurately measured as are the locations and shapes that characterise the observed ring-gap structure. Significant modulation of the intensity of the outer ring emission is revealed and discussed. In addition, earlier ALMA observations of the emission of three molecular lines, CO(2-1), C18O(2-1), and DCO+(3-2) with a resolution of ~70 au are used to demonstrate the Keplerian motion of the gas, which is found to be consistent with a central mass of 2.3 solar masses. An upper limit of ~9% of the rotation velocity is placed on the in-fall velocity. The beam size is shown to give the dominant contribution to the line widths, accounting for both their absolute values and their dependence on the distance to the central star

23-28

Authors: Thi Lan Nguyen, Tri Tin Nguyen, Hoang Tu Tran, Minh Dat Nguyen, Huu Hieu Nguyen*

In this research, graphene aerogel (GA) was fabricated by chemical reduction method, in which ethylenediamine (EDA) was used as a reducing and functionalising agent. The characterisation of GA was studied by density, field-emission scanning electron microscope, Brunauer-Emmett-Teller (BET) specific surface area, Fourier transform infrared spectroscopy, and X-ray diffraction. The results of the analysis showed that GA exhibits low density, ranging from 4-8 mg/cm3, high porosity, and BET specific surface area changes from 176 to 1845 m2/g. It was found that the suitable content of EDA on the synthesis of GA is 30 μl. The obtained GA was used as an adsorbent for removal of oils and methylene blue (MB) from aqueous solutions. The maximum adsorption capacities of GA for lubricant and crude oils are 160 g/g and 110 g/g respectively. The effecting factors including pH, contact time, and initial concentrations on the adsorption capacity of GA for MB were investigated. The adsorption process of MB onto GA followed the pseudo-second-order kinetic and well-fitted to Langmuir isotherm model. The maximum adsorption capacity for MB from linear Langmuir model was calculated to be 212.76 mg/g at pH 7. Accordingly, GA could be used as a potential adsorbent for removal of oils and MB from water

35-41

Authors: Nguyen Thi Hong Diep*, Thitinat Korsem, Nguyen Trong Can, Walaiporn Phonphan, Vo Quang Minh

Aquaculture is an important economic activity in the coastal zone of Vietnam. Thanh Phu is one the coastal districts in Ben Tre province that rears brackish aquaculture. In recent years, farmers could not grow shrimp because of salinity intrusion and market price fluctuation. This study aims to determine aquaculture and fallow aquaculture pond distribution by using the three indices of NDVI (Normalized Difference Vegetation Index), MNDWI (Modified Normalized Difference Water Index) and NDBaI (Modified Difference Bareness Index) on Landsat 8 imagery. The results reveal that remote sensing can support the detection of aquaculture and fallow ponds with a high accuracy of 77%. The total aquaculture area is approximately 13,093.65 ha, of which the total fallow area is 581.49 ha (roughly 4.44% of the total aquaculture area). Moreover, the fallow ponds are randomly distributed in all four ecological zones and mostly in the fourth ecological region (about 73.92%). In the fourth region, saline concentration in water is from 20 to 30‰, which directly influences cultured shrimp farms. The results also indicate the spatial distribution of aquaculture ponds and ineffective aquaculture locations using Landsat 8 imagery via index image analysis. The findings support the local management’s decision making on further aquaculture planning.

47-51

Authors: Duong Thi Nguyen*, Nguyen Thi Nhu Hoa, Le Thi Kieu Oanh, Dang Kim Tuyen, Nguyen Chi Hieu, Duong Son Ha, To Thi Ngan

Fusarium proliferatum has been identified as the causal pathogen of Fusarium root rot of Ba kich (Morinda officinalis) (FRRBK). No studies are available regarding the effectiveness of chemical treatments on the disease incidence of FRRBK. The efficacy of five active ingredients (metconazole, prochloraz, tebuconazole, kresoxim-methyl, and pyraclostrobin) from two chemical groups (demethylation inhibitors and quinone outside inhibitors) in reducing three isolates (BKVN, BKDT, and BKPL) of F. proliferatum mycelial growth was tested in vitro. The results indicate that only metconazole, prochloraz, and tebuconazole are highly effective in inhibiting the mycelial growth of F. proliferatum. These were selected for investigation of their efficacy with regard to the disease incidence of FRRBK in pot and in field conditions. Prochloraz and metconazole showed the highest efficacy and significantly suppressed the disease incidence of FRRBK in pot and in field conditions.

60-64

Authors: Ha Van Thieu*

Background: childhood overweight is increasingly common worldwide as are its consequences, which include increased risk of later cardiovascular disease and diabetes. Although metabolic syndrome (MetS) has been extensively studied in adults, not much is known about the condition in children and adolescents. MetS and its individual components are detectable during childhood, and both commonly persist throughout adolescence and adulthood.Objective: to determine the prevalence of MetS and cut-off values of waist circumference (WC) and body mass index (BMI) for predicting MetS in children with overweight and obesity. Methods: we conducted cross-sectional analysis of 510 children with overweight and obesity aged 10 to 15 years in Bien Hoa city, Dong Nai province (2012-2014). MetS diagnosis was defined according to the 2007 International Diabetes Federation definition. Results: a relationship existed between BMI and dyslipidaemia (p<0.05). Among all participants, 31.37% met the criteria for MetS (female>male, p>0.05). The most common manifestation of MetS in this study was WC-blood pressure-triglyceride (41.15%). The cut-off anthropometry values for predicting MetS were as follows: BMI of 25.00 in boys and 24.50 in girls, and WC of 82 cm in boys and 80 cm in girls. Conclusions: the prevalence of MetS was 31.37% among children with overweight and obesity. The cut-off values of WC and BMI in this study could be the optimal threshold for predicting MetS in such children aged 10 to 15 years.

71-78

Authors: Nguyen Van Thang, Vu Van Thang, Tran Dinh Trong*, Jerome Faucet

This paper explores the maximum amount of rainfall in the Central coastal provinces of Vietnam (Quang Binh case study) for return periods of 5 years, 10 years, 20 years, 50 years, and 100 years, which correspond to frequencies of 20%, 10%, 5%, 2%, and 1%, respectively. The results show that at a frequency of 20%, the maximum intensity of rain during a heavy rain spell can range from 636.6 to 696.0 mm, while the maximum one-day amount received was over 300 mm, which can occur many times in 5 years. At a frequency of 1%, the intensity of rain during a heavy rain spell can range from 1,197.9 to 1,268.3 mm, while the maximum one-day amount ranged from 487.4 to 521.9 mm. However, such values are very rare over the course of 100 years. In addition, in terms of annual rainfall, the spatial distribution of heavy rainfall in coastal areas was significantly smaller than that in mountainous areas. The highest one-day and five-day rainfall have the same pattern of spatial distribution as annual rainfall.

84-89

Authors: Dao Minh Trang, Huynh Thi Lan Huong*, Mai Van Trinh

This study aims to develop a method for calculating the carbon footprint of rice during its life cycle by combining Life Cycle Assessment (LCA) and the 2006 Guideline of the Intergovernmental Panel on Climate Change (IPCC) for National Greenhouse Gas Inventories (GL 2006) for paddy rice grown in Phu Luong commune, Dong Hung district, Thai Binh province, Vietnam. In the course of the study, a LCA survey that included activities in the upstream processes, the agricultural process, and the post-farm stage was conducted based on interviews with three groups of 30 farmer households that apply the conventional practice of rice production, the system of rice intensification (SRI), or the wide-narrow row method. These cultivation practices are applied for both the winter-spring crop and summer-autumn crop seasons. The emissions were calculated by multiplying the activity data by the default emission factors in GL 2006 or in other relevant studies. The emission factors of methane (CH4) from rice cultivation and nitrous oxide (N2O) from agricultural soil were adjusted using actual measurement results from the Institute of Agricultural Environment (IAE) in 2016. The results of the calculations show that the main sources of the emissions that constitute the carbon footprint of rice include: (i) CH4 emissions from rice cultivation; (ii) electricity generation for irrigation; (iii) diesel combustion for the operation of agricultural machinery, and (iv) fertiliser production. Emissions from other activities were negligible. The carbon footprint of spring rice is 2.69kgCO2e/kg of rice grown using the conventional paddy cultivation method, 2.35 kgCO2e/kg for rice grown using the SRI method, and 2.29 kgCO2e/kg for rice grown using the wide-narrow row method. In summer, the carbon footprint for rice grown using the conventional method is 3.72kgCO2e/kg of rice, 3.56 kgCO2e/kg of rice using SRI, and 3.3kgCO2e/kg of rice using the wide-narrow row method. Three mitigation options are proposed: integrated crop management for rice; alternate wetting and drying; and the substitution of urea fertiliser (CO(NH2)2) with ammonium sulphate ((NH4)2SO4).