https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse <p>Journal of Tropical Science and Engineering is a multidisciplinary journal (chemistry and materials, biology and biomedicine) published since 2012 under the Press Operation License No.02/GP-BVHTTDL, dated January 16, 2026 issued by the Ministry of Culture, Sports and Tourism, and p-ISSN:3093-3633, e-ISSN: 3093-3803, assigned by the National Agency for Science and Technology Information and Statistics under the Ministry of Science and Technology.</p> TROPICAL SCIENCE AND TECHNOLOGY JOURNAL en-US Journal of Tropical Science and Engineering 3093-3633 https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse/article/view/762 Long-term and accurate daily and monthly streamflow data play a crucial role in understanding hydrological regimes and managing water resources; however, such records are often incomplete, particularly for reservoir inflows. This study addresses this gap by evaluating and comparing the performance of a process-based model (SWAT) and a data-driven model (Light Gradient Boosting Machine – LGBM) in simulating daily and monthly inflows to six major reservoirs in the Ba River Basin, Vietnam – a basin strongly influenced by reservoir regulation for irrigation and hydropower. Observed meteorological, hydrological, and satellite-derived datasets from 2016 to 2023 were utilized, with the period from 2017 to 2022 allocated for calibration and training, and 2016 and 2023 reserved for independent validation. SWAT calibration was performed automatically with SWAT-CUP, while the hyperparameters of LGBM were optimized using Bayesian Optimization (BOA). The results demonstrate the superior performance of LGBM in most cases, achieving higher Nash–Sutcliffe Efficiency (NSE) and Kling–Gupta Efficiency (KGE) scores, and reproducing key hydrological signatures more accurately than SWAT. Nevertheless, SWAT exhibited comparatively better performance in simulating monthly inflows to the An Khe reservoir, highlighting the potential advantages of process-based models under specific conditions. Ba Duy Dinh Duc Hanh Nguyen Huu Minh Quan Le Minh Tuan Ly Shamil Raufovich Pozdniakov Albina Iskandarovna Pozdniakova Dmitrii Vladimirovich Shilov Vu Anh Tu Dinh Copyright (c) 2026 Journal of Tropical Science and Engineering https://creativecommons.org/licenses/by/4.0 1 2 2 21 10.58334/jtse.vol.001.762 https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse/article/view/776 Dioxin contamination remains a serious and persistent environmental issue in Vietnam, especially at historical hotspots such as Phu Cat Airport. This study investigated the taxonomic and functional diversity of microorganisms inhabiting hotspots long-term dioxin-contaminated soil using metagenomic sequencing and enrichment-based isolation approaches. Shotgun metagenomic sequencing generated 50,349,630 high-quality reads, of which 12.81% were taxonomically classified, revealing 39 phyla dominated by Pseudomonadota (34.19%), Actinomycetota (14.61%), Planctomycetota, and Bacillota. Through three successive enrichments in mineral medium containing dioxin-contaminated soil extract, microbial cell density increased from 10³ CFU/g in the original soil to 10⁷ CFU/mL in enrichment cultures, while diversity decreased, reflecting selective adaptation to pollutant stress. Twenty bacterial strains were successfully isolated and grouped into nine distinct morphological types. Based on 16S rRNA gene sequencing, these isolates were assigned to eight genera within three phyla: Rhodococcus, Microbacterium, and Paenarthrobacter (Actinomycetota); Bacillus and Niallia (Bacillota); and Pseudomonas, Stenotrophomonas, and Vitreoscilla (Pseudomonadota). Among them, Rhodococcus ruber, R. phenolicus, and Pseudomonas sp. showed growth in medium containing 5% soil extract (TEQ measured prior to filtration: 604.6 pg TEQ/mL), indicating tolerance to dioxin-associated selective pressure. Comparative analysis of metagenomic and culture-based data revealed consistent dominance of Pseudomonadota and Actinomycetota, confirming their ecological importance and tolerance under long-term dioxin stress. The findings suggest that dioxin exposure may have influenced the formation of a phylogenetically diverse microbial community detected in the composite soil sample collected from the contaminated area. The combined use of culture-based and metagenomic methods offers preliminary insights into the indigenous microbial community and serves as a starting point for future studies aimed at determining whether these bacteria possess functional traits relevant to the bioremediation of persistent organic pollutants in Vietnam. ThS Thi Kim Thanh Nguyen Viet Cuong Nguyen Van Thang Le Duc Tan Phung Thi Tuyen Do Cao Cuong Ngo Copyright (c) 2026 Journal of Tropical Science and Engineering https://creativecommons.org/licenses/by/4.0 1 2 22 33 10.58334/jtse.vol.001.776 https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse/article/view/736 Petroleum pollution often involves mixtures of volatile monoaromatic compounds and recalcitrant PAHs, but the isolation and characterization of native hydrocarbon‑degrading microbes in Vietnam are still underexplored. In this study, we isolated and characterized an autochthonous hydrocarbon‑oxidizing bacterium, Rhodococcus ruber KHA5.2, from oil‑impacted coastal sands in Khanh Hoa Province, Vietnam. Species assignment was supported by full‑length 16S rRNA similarity > 99.8% to Rhodococcus spp. and confirmed by digital DNA–DNA hybridization of 99.08% to R. ruber NBRC 15591. Short‑read de novo assembly yielded a 5.43‑Mb draft genome (GC 70.1%) across 981 contigs with 94.72% completeness, consistent with typical Rhodococcus genomes in terms of size and GC content. Experimentally, KHA5.2 oxidized crude oil and representative aromatics spanning BTX constituents (benzene, toluene, xylene) and the low‑molecular‑weight PAH naphthalene. The strain was able to grow at NaCl concentrations up to 5% and across pH 3–11 and 20–40°C; however, hydrocarbon-oxidizing activity, as assessed by the DCPIP reduction assay, was only observed optimally at 0–3% NaCl, indicating that the range of salt tolerance for growth is broader than that for effective oxidative activity. In minimal mineral medium supplemented with 1% (v/v) crude oil, optical density increased to its maximum value on day 6 and then declined, consistent with depletion of readily utilizable fractions and/or accumulation of inhibitory intermediates. The diversity of aromatic compounds oxidized by KHA5.2 matched that observed in closely related Rhodococcus species.. However, these results are based on qualitative assays, and further quantitative evaluation of degradation rates and field trials are needed to fully confirm the strain’s bioremediation capabilities. Taken together, genome-based taxonomy, salinity-tolerant physiology, and qualitative evidence of aromatic substrate oxidation suggest that R. ruber KHA5.2 represents a promising candidate for further bioremediation-oriented investigations in brackish and intertidal settings. To translate laboratory indicators into field‑level performance, standardized experimental conditions and quantitative, mass‑balance measurements (GC–FID/GC–MS) across salinity gradients and environmental matrices will be essential. Thu Hang Bui Thi Tuyen Do Thi Thanh Thuy Tran Viet Cuong Nguyen Thi Kim Thanh Nguyen Cao Cuong Ngo Copyright (c) 2026 Journal of Tropical Science and Engineering https://creativecommons.org/licenses/by/4.0 1 2 34 44 10.58334/jtse.vol.001.736 https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse/article/view/795 This paper presents the first study of the corrosion behavior of nickel-aluminum bronze CuAl9Ni5 produced by the wire-arc additive manufacturing (WAAM-CMT) method in tropical seawater, and the effect of heat treatment on it. To improve the mechanical properties, a two-stage heat treatment was performed: quenching at 900°C followed by aging at 400°C. Metallographic analysis revealed that this treatment results in a refined and uniform distribution of phase formations, compared to the original Widmanstätten structure. This resulted in a significant increase in hardness and strength. In parallel, laboratory electrochemical tests were conducted in synthetic seawater, and long-term field tests were performed at the Nha Trang offshore station (Vietnam) for 2544 hours (approximately 106 days). All samples, including heat-treated ones, demonstrated high corrosion resistance, with a corrosion rate in the laboratory of below 0.04 mm/year. The damage was only superficial. The obtained results prove that the combination of WAAM technology and heat treatment modes makes it possible to create large-sized products (e.g., propellers) from CuAl9Ni5 bronze with an optimal combination of mechanical properties and exceptional resistance to marine corrosion. Zhanna Sergeevna Shabunina Tigran Vladimirovich Uglunts Alexey Olegovich Silkin Ruslan Valisovich Mendagaliev Sofia Sergeevna Shabunina Nhat Linh Cao Van Chi Nguyen Vyacheslav Vyacheslavovich Khalaman Marina Yurievna Gazizova Olga Gennadievna Klimova-Korsmik Copyright (c) 2026 Journal of Tropical Science and Engineering https://creativecommons.org/licenses/by/4.0 1 2 45 59 10.58334/jtse.vol.001.795 https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse/article/view/849 In this study, indirubin with a purity exceeding 97% was synthesized from Strobilanthes cusia leaf extract and isatin. Subsequently, this was used as the starting material for the synthesis of eight new indirubin-3’-oxime derivatives. These compounds, bearing substituents containing a bromine atom (3b, 3c), an azide group (4a–c), or 2-amino-1,3,4-thiadiazole moiety (5a–c), were successfully synthesized in yields ranging from 75% to 88%. The chemical structures of all compounds were elucidated using modern spectroscopic techniques, including 1H and 13C NMR spectroscopy, High-Resolution Electrospray Ionization Mass Spectrometry (HR-MS (ESI)), and Infra Red (IR) spectroscopy. The cytotoxic activity of the synthesized compounds was evaluated against the HT29 human colon cancer cell line. Indirubin derivatives 5b and 5c exhibited potent cytotoxic activity, with IC50 values of 3.2 ± 0.1 µM and 6.2 ± 0.2 µM, respectively. Both compounds were more potent than the parent indirubin (1a) and the positive control, 5-fluorouracil. Overall, the synthesized indirubin derivatives represent a valuable synthetic platform for the further development of novel indirubin-based bioactive compounds in medicinal chemistry and anticancer drug discovery. Dr. Trong Dan Nguyen Duy Nam Pham Dinh Duy Vu Duy Nhan Vu Thi Hoai Thu Vo Quang Cuong Hoang Duc Quang Hoang Dimitri Igorevich Fomenkov Alexey Igorevich Ilovaisky Ivan Andreevich Yaremenko Alexander Olegovich Terent'ev Thi Thu Trang Bui Copyright (c) 2026 Journal of Tropical Science and Engineering https://creativecommons.org/licenses/by/4.0 1 2 60 72 10.58334/jtse.vol.001.849 https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse/article/view/760 Protective adhesive coatings are critical for stabilizing black powder charges in humid tropical climates. In this study, we investigated the effects of maleic rosin ether and alkyd resin additives on the properties of nitrocellulose adhesives. Initially, maleic rosin ether was incorporated at varying concentrations (10% - 20% relative to the mass of nitrocellulose NC1/4) to determine the optimal ratio for enhancing adhesion. The optimal concentration of maleic rosin ether was determined to be 15%, which resulted in desirable adhesive properties. Based on the optimal maleic rosin ether concentration of 15%, alkyd resin was subsequently added at concentrations ranging from 5% to 20% to evaluate its contribution to adhesive properties. The incorporation of 13% alkyd resin significantly improved film performance, enhancing viscosity, non-volatile content, drying time, and adhesion strength. Specifically, the prepared adhesives were directly applied to black powder charges and evaluated under cyclic thermal-humidity conditions in accordance with the TCVN 7699-2-30:2007 standard. Among the tested formulations, the adhesive containing 15% maleic rosin ether and 13% alkyd resin exhibited superior performance, demonstrating excellent resistance to moisture and temperature fluctuations. These findings underscore its potential as a highly effective protective coating for use in tropical climate environments. These results highlight its potential as a highly effective protective coating for applications in tropical climates. Van Tuynh Luu Van Truong Phan Van Thanh Nguyen Copyright (c) 2026 Journal of Tropical Science and Engineering https://creativecommons.org/licenses/by/4.0 1 2 73 84 10.58334/jtse.vol.001.760 https://jtse.tapchikhcnnd.mod.gov.vn/index.php/jtse/article/view/839 The problem of biofouling remains relevant for the maritime industry and shipping. The most effective method of combating it is the use of antifouling coatings. Antifouling coatings with metallic biocidal additivesare the most effective today. Such coatings suppress biofouling, but at the same time have a negative effect on the environment due to the leaching of heavy metal ions into seawater. At the same time, the ban on highly toxic compounds in coating formulations stimulated the need to develop new, environmentally friendly and effective solutions. Today, self-polishing coatings are one of the most promising. Due to the low surface energy and adhesion, microorganisms are easily washed away by streams of water. To do this, the ship needs to increase its speed. To minimize the primary attachment of organisms to the surface, self-polishing coatings use biocides. Coatings based on quaternary ammonium salts (QACs) are one of the most promising areas of biocides in this field. Such coatings combine such qualities as efficiency, environmental friendliness, and durability. In this article, we describe the production of new biocidal coatings based on MT resins (silsesquioxanes based on mono-(M) and trifunctional (T) alkoxysilanes) modified with quaternary ammonium salts. We have developed a method for the synthesis of organosilicon derivatives of tetramethylethylenediamine and the further production of MT resins based on them. A technique for coating metallic substrates has been developed. The antibacterial properties of the compounds obtained were studied, as well as tests for marine fouling. Studies of the obtained samples for antibacterial properties have established that the coatings inhibit the growth of both gram-positive and gram-negative bacteria, as well as inhibit the process of marine fouling. Marine fouling was assessed by increasing biomass on coated steel plates immersed in tropical waters near Dam-Bay Island (Nha Trang). The coatings were exhibited for a total of 1 year. The self-polishing properties of the coatings were evaluated by surface treatment with strong water pressure. Marina Shagidanova Petr Shkinev Inna Kholoshenko Tran Duong Vu Fedor Drozdov Copyright (c) 2026 Journal of Tropical Science and Engineering https://creativecommons.org/licenses/by/4.0 1 2 85 91 10.58334/jtse.vol.001.839