Vietnam Journal of Science, Technology and Engineering

10-18

Authors: M. Peeraiah*, K. Nagamalleswara Rao, B. Balakrishna

Nanofluids are a type of emerging heat transfer fluid with great promise for thermal engineering due to its high heat transfer coefficients. Improving heat transmission remains an ongoing task in engineering fields as diverse as semiconductor technology and high-performance vehicles. This paper investigates and compares the jet impact heat transfer coefficient, thermal conductivity, and viscosity of nanofluids with those of a base fluid in an automobile radiator with nozzle plate spacing. Aluminium oxide (Al2O3) and deionised water were selected as the working fluids, and they were used in varying quantities ranging from 0 to 1 volume percent. The nanofluids were prepared using a two-step method with the aid of an ultrasonic homogeniser. The results reveal that the heat transfer coefficient increased by 11.68% at a nanofluid concentration of 1% when nanoparticles were suspended in the base fluid. Furthermore, a 45-49% improvement in the heat transfer coefficient was recorded using a nanoparticle volume concentration of 1% compared to the base fluid.

27-32

Authors: Hung Duc Nguyen*, Tan Quang Tu, Mau Hoang Chu

Saponins are naturally occurring compounds ubiquitously present in various organisms, predominantly in plants. They are noted for forming colloidal solutions in water, which foam on shaking and precipitate cholesterol. Several in vitro and in vivo tests on mixtures and individual saponins have revealed a broad spectrum of biological and pharmacological activities, including cancer-related activity, antiphlogistic and antiallergic, immunomodulating, antihepatotoxic, antiviral, hypoglycemic, antifungal and molluscicidal activities. The Dracaena genus is renowned for an abundance of steroidal saponins utilized in treating digestive and hematological disorders. Previous studies on this genus revealed the presence of steroidal saponins, some of which showed cytotoxic activities against cultured tumor cells and interesting biological activities. This study procured steroidal saponin from the foliage of D. dracoL. using various chromatographic techniques and 1D and 2D nuclear magnetic resonance (NMR) spectroscopic analysis. The structure was deduced as 26-O-β-D-glucopyranosyl-22-O-methylfurosta-5,25(27)-diene-1β,3β,22α,26-tetrol 1-O-{O-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranosyl}; a compound previously isolated from the underground parts of Ruscusaculeatus in Japan. Future evaluation of the saponin’s biological activity is imperative to enhance chemotaxonomic data concerning the chemical composition and biological functionality of D. draco L. and, by extension, the Dracaena genus.

52-60

Authors: Bhim Kumar Dahal*, Jun Jie Zheng

This study evaluates the index, microstructural, and mechanical behaviour of cement-stabilised soft soil. The marine soil dredged from Hangzhou is taken for the study. Different percentages of ordinary Portland cement (OPC)by dry mass were added to the soils during reconstitution, i.e., 5, 10, 15, and 20%. The reconstituted samples were analysed in the laboratory to determine basic properties such as moisture content, void ratio, density, specific gravity, consistency limits, and particle size distribution. The microstructures of the reconstituted samples were also evaluated through scanning electron microscopy. Results inferred a significant impact on the physical properties of the soil. An increase in cement content increases the consistency limits. Additionally, the specific gravity, plasticity index, and density of the treated soil initially decreased but increased upon further addition of cement content. The microstructure of the soil transformed from a dispersed to a flocculated structure, with larger and denser particles. The change in microstructure was also evident in the particle size distribution, with an increase in cement content leading to larger size particles. Finally, the unconfined compression test conducted on the reconstituted soil indicates a substantial enhancement in strength with higher cement content and prolonged curing periods.

69-75

Authors: Thi-Hoan Luong, Huu-Khanh-Tan Tran, Woo-Jin Jung, Van-Viet Nguyen, Dang-Minh-Chanh Nguyen*

In this study, the authors aim to determine the chemical compositions of the essential oil from Ocimum tenuiflorumleaves and to evaluate its antioxidant and antifungal activities. The essential oil used in this research, extracted by hydrodistillation, was chemically profiled using gas chromatography/mass spectrometry (GC/MS) analysis. Methyl eugenol (46.07%), caryophyllene (15.65%), eugenol (11.83%), β-elemene (4.33%), β-copaene (4.18%), caryophyllene oxide (3.18%), and α-copaene (1.95%) were identified as major components of the essential oil. The results indicated that the essential oil of O. tenuiflorum leaves possessed relatively high 2,2-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging activities with IC50 values of 53.5 and 55.1 μg/ml, respectively, compared with 67.2 and 63.2 μg/ml, respectively, for the positive control. The reducing powers of O. tenuiflorum essential oil and butylated hydroxytoluene (BHT) at a concentration of 200 μg/ml were 0.95 and 0.73, respectively. Additionally, the essential oil of O. tenuiflorum at a concentration of 200 μg/ml strongly inhibited the mycelial growth of Rhizoctonia solani.

82-88

Authors: Manh Cuong Nguyen*, Thi Thuy Hang Le, Thanh Nam Do, Thai Son Pham, Hoang Long Trinh, Thi Bich Thuy Phung, Yen Thi Hoang, Quang Khai Tran

Influenza, a historical and contemporary public health challenge, is an acute respiratory infection caused mainly by influenza A or B viruses. This descriptive case series describes 194 children treated for seasonal influenza at the Department of Pediatrics, 103 Military Hospital, Vietnam Military Medical University, from May 2022 to May 2023. Influenza primarily occurred during winter and early spring, peaking in December and January, 57.2% were aged 12-60 months, boys. Vaccination coverage was limited (36.3%), especially post-COVID-19. Complications were seen in 75.3% of the cases, including febrile seizures (42.3%), bronchopneumonia (40.2%), respiratory failure (8.2%), acute myocarditis, influenza-associated encephalopathy, and septic shock. The study reveals bacterial coinfections, affected 20% of the cases, mainly by Streptococcus pneumoniae and S. aureus, and atypical bacteria Mycoplasma pneumoniae. Non-vaccinated children faced significantly higher risks of complications, oseltamivir within 48 hours reducing the risks of complications. Influenza predominantly affects 12-60 month-olds, males, and peaks annually in winter. Severe conditions stem from bacterial coinfections, emphasizing the importance of vaccination and prompt antiviral treatment to mitigate complications. The study highlights a critical need for increased vaccination, especially in the post-COVID-19 era, to manage influenza in children effectively.

101-106

Authors: Nguyen Quang Huy*, Pham Quynh Trang, Nguyen Thi Loi

This study aimed to investigate the occurrence of potential pathogenic bacteria from surface water samples collected at 30 stations along Ha Long Bay, Vietnam. Among 116 bacterial isolates identified, the composition analysis indicated 24 distinct bacterial genera, with Vibrio (29.3%), Pseudomonas (23.3%), Staphylococcus (8.6%), and Bacillus (6.0%) being the most dominant. The taxonomic analysis revealed 61/116 (52.6%) isolates as potential pathogens (risk group 2) belonging to 21 bacterial species. Potential pathogens were detected in 28/30 (93.3%) sampling stations, with the most common pathogens including Vibrio alginolyticus (n=25), Vibrioparahaemolyticus (n=5),Enterobacter cloacae (n=3), Pseudomonas mendocina (n=3), Aeromonas hydrophila (n=2), Enterobacter asburiae (n=2), Klebsiella oxytoca (n=2), Bacillus cereus (n=2),and Staphylococcus haemolyticus (n=2). The selected pathogens were highly resistant to Amoxicillin (100%), Piperacillin (100%), Amoxicillin + Clavulanate (85.7%), Ticarcillin (71.4%), Cefoxitin (54.4%), Kanamycin (50%), and Fosfomycin (50%), and less resistant to Trimethoprim + sulfamethoxazole, Fusidic Acid, Tetracycline, Erythromycin, Pristinamycin, Dalacin, and Rifampicin (<25%), and susceptible to the remaining antibiotics. Notably, 12/23 (52.2%) isolates were resistant to at least three antibiotics and were multidrug-resistant bacteria. Our findings underline that the occurrence of pathogenic antibiotic-resistant bacteria in the marine environment of Ha Long Bay presents a potential threat to human health. Further genomic surveillance studies are necessary to manage and control the emergence and spread of pathogenic-resistant bacteria in this area.

114-120

Authors: Muslim Babatunde Aminu*, Femi Ologunaye

We present the results of a multi-frequency ground-penetrating radar (GPR) survey over a university road in south-western Nigeria that has experienced persistent failures. The goal was to evaluate causes of failure to aid remediation efforts. Data was collected concurrently at 250, 500, and 1000 MHz using a UTSI electronic trivue system. Data were processed and interpreted using Reflex-Win. Visual observations of major features apparent on the road surface including failed sections were noted. Imaged features included possible bases of the surface course, base course and sub-base, subsurface projections of an outcropping and buried basement rocks, three deeply cut and back-filled sections that lie beneath sections of the road that have experienced persistent failure, and the ringing effects and rebar-associated reflection hyperbolae of two reinforced concrete drains. Indications of preferential wetting of the shallow subsurface beneath much of the failed sections suggest that failure is due to excessive moisture content in these sections. These failed sections generally correspond to regions of deep cut and backfill, and regions cut and filled for the construction of reinforced concrete drains. Apparently, the backfills at these locations have failed to prevent water influx into the subsurface and more effective remediation measures need to be deployed.