VNUHCM Journal of Natural Sciences

Water quality of lak lake in dak lak province in 2020 and fluctuations of the water quality over some years

Bui Thi Hoa — 2025-12-29

Lak Lake (Dak Lak) plays an important role in regulating the flow of the Sêrêpôk River, providing domestic water, irrigation, and hydropower for the region. A study was conducted to assess the current water environment status through hydrochemical indicators in 2020, while also evaluating the lake's water quality variations during the period 2001-2020. Ten samples of water were collected in 2 seasons: rainy season August 2020 and dry season November 2020. The research results show that the water quality of Lak Lake in 2020 was poor due to low dissolved oxygen concentration. The DO parameter ranged from 3.76 to 5.07 mg/l, with an average of 4.42 mg/l across both seasons, which was the level C of the QCVN 08:2023/BTNMT standard. In particular, DO level at HL-01 site was (3.76 mg/L) in accordance with standard D of QCVN 08: 2023/BTNMT. The average BOD₅ index of the lake was (1.50±0.81 mg/L) the level A of QCVN 08: 2023/BTNMT, except for HL-03 site in the dry season with BOD5 level was in accordance with standard B of QCVN 08: 2023/BTNMT. The water quality of Lak Lake has also deteriorated over time, as parameters such as NO₃^-, PO₄^3-, BOD₅, and COD tend to increase, while DO tends to decrease. In that NO₃^- concentration in 2020 was higher 9.57 times than in 2006; The average PO₄^3- concentration in 2020 was higher 1.86 times than in 2006; The COD index in 2009 was higher 1.9 times than in 2006 but the BOD₅ in 2009 was higher 3.1 times than 2001 and in 2020 was higher 1.68 times than in 2001. The dissolved oxygen content in water decreased from 6.6 mg/l in 2001 to 4.42 mg/l in 2020 (decrease 1.49 times).

The pick-off annihilation process of ortho-positronium in zeolite ZSM-5 and Silicalite-1 under the influence of gas environment and adsorbed water

Luu Anh Tuyen — 2025-12-07

This study evaluates the influence of gas environments and adsorbed water on the pick-off annihilation process of ortho-positronium (o-Ps) lifetime in zeolite Silicalite-1 and ZSM-5. The results indicate that short-lifetime components (τ₁, τ₂, τ₃) are minimally affected, whereas long-lifetime components (τ₄, τ₅) and annihilation intensity (I₄, I₅) vary significantly depending on the gas environment. Vacuum conditions are optimal for analyzing pore structures, while air significantly reduces o-Ps lifetime due to quenching by O₂. Inert gases such as Ar and N₂ have a lesser impact and can serve as alternatives when vacuum conditions are not available. The effect of adsorbed water is categorized into three drying temperature stages, primarily influencing the τ₅ and I₅ components. Below 200°C, retained water decreases o-Ps lifetime. Between 200°C and 250°C, rapid water desorption from the pores leads to a notable increase in τ₅ and I₅. Beyond 250°C, water is nearly eliminated, and these parameters reach a saturation state. Additionally, Silicalite-1 exhibits higher o-Ps lifetime and annihilation intensity than ZSM-5, reflecting differences in pore size and density between the two materials. These findings highlight the crucial role of environmental conditions in zeolite structure analysis. Vacuum remains the optimal choice for ensuring measurement accuracy, while the influence of adsorbed water must be controlled to prevent measurement deviations.

Effect of storage temperature on the printability of the gelatin - alginate bioink

Nghia Thi Hieu Phan — 2025-12-22

Bioink is a fundamental component of three-dimensional (3D) printing technology, exerting a direct influence on the overall quality, precision, and structural integrity of printed biological constructs. Among various factors influencing printing outcomes, printability is a key determinant for success, as it impacts the precision of printed structures, the consistency of filament formation, and the ability to maintain the correct shape throughout the printing process. The printability of bioink is influenced not only by its composition but also by external conditions, particularly the storage temperature. Therefore, evaluating the impact of storage temperature on bioink printability is essential. This paper presents the evaluation of the effects of three different storage temperature conditions on the printability of gelatin-alginate B-GA bioink over a period of 21 days. These conditions included freezing at -20 ± 1°C, refrigeration at 4 ± 1°C and storage at room temperature of 25 ± 2°C. The printability was assessed by examining various parameters, including the state of the bioink, the ability to form continuous filaments, the uniformity factor (U), the diffusion rate (Df) and the effectiveness of pore formation (Pr). The results showed that the printability of B-GA bioink remained stable during the first 14 days under all three tested storage conditions. However, after 21 days, a significant decline in printability was observed in the cases of freezing and room temperature conditions, proven by the decrease in Pr values of 0.8469 ± 0.0056 and 0.8630 ± 0.0074, respectively. In contrast, refrigeration at 4 ± 1°C allowed the B-GA bioink to retain its printability consistently throughout the entire 21-day period, with a Pr value of 0.908 ± 0.0227. Therefore, in the test, storing B-GA bioink at 4 ± 1°C was the most effective condition for preserving its printability over 21 days.