Vietnam Journal of Science, Technology and Engineering

3-7

Authors: Nhu-Quynh Luc*, Duc-Huy Quach, Chi-Hung Vu, Hong-Truong Nguyen, Thanh-Long Vo-Khac

The authors initially employs the fast Fourier transform (FFT) approach to transforming voice inputs into digital signals before integrating a speech recognition solution (which includes two models: the hidden Markov model (HMM) and the artificial neural network (ANN)). To achieve standard-tone identification of voice signals and digitally store speech, the authors then incorporated a 2048-bit Rivest-Shamir-Adleman (RSA) encryption method to encrypt and decrypt digital speech. The authors’ building team constructed the program using a 256-bit advanced encryption standard - Galois counter mode (AES-GCM) encryption method to assure the application’s effectiveness. The authors successfully created a voice recognition application according to the HMM of ANN. The collected findings suggest that the authors’ secure speech recognition program (named soft voice - RSA) has improved in terms of safety, keeping speech material secret, and speed. It takes roughly 0.2 s to generate a 2048-bit RSA key pair that exceeds the National Institute of Standards and Technology (NIST) standard, 700-1070 ms to process speech, 1-4 ms to encrypt 2048-bit RSA, 6-8 ms to decrypt 2048-bit RSA.

14-20

Authors: Thi Minh Dinh, Khac Khoi Tran, Anh Trung Le, Thi Minh Nguyet Nguyen, Thi Hue Do*, Ian Liau

Mentha crispa L. is one of Vietnam’s most precious folk medicines and is also a spice used in many delicious dishes in Vietnam and around the world. The use of Mentha crispa L. leaf extract as a reducing agent for Ag+ ions to synthesize silver nanoparticles is discussed in this paper. Single silver nanospheres were dispersed in biological media and their sizes were controlled in the range of 20-80 nm. Factors affecting particle size and shape such as extract concentration, AgNO3 concentration, reaction time, and temperature were investigated to determine the optimal parameters for particle synthesis. The optical properties, dispersion, crystal structure, morphology, and sizes of silver nanoparticles were investigated through UV-Vis absorption spectroscopy, dynamic light scattering (DLS) measurements, X-ray diffraction, and transmission electron microscopy (TEM). The functional groups on the L.AgNPs were determined by Fourier-transform infrared (FTIR) transmittance spectra. The synthesised silver nanoparticles were used to treat methylene blue (MB) dye, the main component of dye wastewater, based on their photocatalytic properties. The results show that in the presence of L.AgNPs, the photodegradation efficiency of NaBH4 or H2O2 reducing agents is much higher, up to 95% of illumination.

27-31

Authors: Tien Dat Doan, Nhung Hac Thi, Ho Thi Oanh,Tuyen Nguyen Duc, Dong Hoon Choi, Mai Ha Hoang*

Transparent flexible electrodes based on silver nanowires (AgNWs) have great potential for practical applications and many studies have been carried out to improve their conductivity, transparency, and surface roughness. In this study, we demonstrate a new approach for the fabrication of high-performance transparent flexible electrodes based on AgNWs and graphene oxide (GO) on polymer substrates using the pressing method. The surface morphology of the pressed AgNW/GO electrode was characterised by atomic force microscopy (AFM) and observed by scanning electron microscope (SEM). The electrode had a low surface roughness with the root mean square (Rq) of 7 nm. The electrode exhibits a low sheet resistance of 22 Ω/sq, a high transmittance of ~88%, resulted in a figures-of-merit (FoM) value of ~12.6. The optical and electrical properties of the electrode are comparable to that of the flexible ITO electrode. In addition, the electrodes also displayed outstanding durability and mechanical stability. This simple and scalable fabrication method is expected to contribute to future studies on flexible transparent conductive electrodes.

39-43

Authors: Duc Thien Dao, Hoang Sa Nguyen, Huu Thu Do, Thanh Tam Nguyen*

Pteris multifida Poir. is an evergreen herbaceous fern that is distributed in temperate and tropical regions of East Asia and cultivated in many other countries. It is an ethnomedicinal plant used for detoxicating, cooling, reducing pain, and as a treatment for many diseases like dysentery, typhoid, cholecystitis, diarrhoea, enteritis, jaundice, and eczema among others. Several compounds including flavonoids, sesquiterpenoids, diterpenoids, coumarins, lignans, and sterols with anti-spasmodic, anti-bacterial, anti-hyperlipidemic, anti-oxidative, and cytotoxic activities have been isolated from this plant. In the present study, three sesquiterpenoids, (2S,3S)-pretosin Q (1), (2R,3S)-pterosin C (2), (2S,3S)-pterosin C (3); two lignans, pinoresinol (4); lariciresinol 9-O-β-glucopyranoside (5), three flavonoids, naringenin (6), apigenin (7), and luteolin (8) were obtained from the ethyl acetate extract of the whole of P. multifida collected in Nam Dinh province, Vietnam. The chemical structures were elucidated by various spectroscopic means including one- and two-dimensional (1D, 2D)-NMR, mass spectrometry, and comparison with published data. Compounds 4-6 were isolated from P. multifida for the first time.

50-58

Authors: Van Long Nguyen, Minh Thanh Le, Lan Huong Nguyen*

This study successfully developed Co2SnO4@rGO nanocomposites at various composite ratios of Co2SnO4 and rGO using the sol-gel method. These nanocomposites were then used as heterogeneous catalysts to activate PMS in the heterogeneous catalytic oxidation of Co2SnO4@rGO/PMS as well as the hybrid ozonation system O3/Co2SnO4@rGO/PMS to degrade cefalexin (CFX). The physical-chemical characteristics of the fabricated catalysts were evaluated through nitrogen adsorption-deadsorption, SEM images, EDS mapping, and XRD. The catalytic activity of the nanocomposite was investigated in a degradation reaction of CFX from an aqueous solution. Besides this, CFX degradation kinetics were determined by fitting experimental data with a first-order model. The results showed that at the composite ratio of 2-Co2SnO4 and 1-rGO for CFX degradation had the highest efficiency reaching 95.07 and 99.07% for Co2SnO4@rGO/PMS and O3/Co2SnO4@rGO/PMS systems, respectively. The degradation of CFX in the O3/Co2SnO4@rGO/PMS system was higher than that of Co2SnO4@rGO/PMS. The results were due to a remarkable increase in SBET in 2-Co2SnO4@1-rGO compared to both Co2SnO4 and rGO, facilitating a catalytic reaction occurring on the catalyst’s surface. Moreover, the coupling between O3 and Co2SnO4@rGO/PMS generated a synergetic effect leading to the generation of more *SO4- and *OH radicals, which enhanced the CFX degradation rate in the hybrid ozonation system. These primary findings illustrated that the nanocomposite catalyst 2-Co2SnO4@1-rGO was feasible for the activation of PMS in hybrid ozonation to effectively degrade antibiotic residues from wastewater.

66-74

Authors: Thi Thuy Hang Vu*, Ngoc Thang Vu, Thi Tuyet Cham Le, Thi Ngoc Pham

This study determined the most appropriate and earliest soybean harvesting stage and the number of days of postharvest ripening with minimal effects on seed losses and quality when mechanical harvest and threshing were applied. Harvesting stages at four physiological maturities (60, 70, 80, and 90%) and various days of postharvest ripening treatment (1, 2, and 3 days) were applied for two soybean varieties DT12 and DT26. Harvesting at physiological maturity of 90% recorded the highest seed-shattering loss but the least seed damage (<5%) and highest seed quality, followed by a physiological maturity of 80%. There were no significant differences in seed yields between harvesting stages of 80 and 90% maturity. Harvesting soybeans at a physiological maturity of 60 and 70% resulted in no seed losses but a significant reduction in seed quality. To avoid adverse weather, an early harvest stage at a physiological maturity of 80% is suggested. Although postharvest ripening of soybeans for early harvest caused seed shattering losses (2-5%), it was necessary to ensure seed quality. These results indicate effective and practical methods for farmers at small households to use in early mechanical harvesting of soybeans.

80-84

Authors: Thi Thanh Loan Nguyen, Thi Van Anh Pham, Thi Xoan Le*

The current study was designed to investigate the anti-hypertensive effects of a standardised flavonoid extract from Diospyros kaki L.f leaves (DK extract) on cortisone acetate-induced hypertensive rats. Hypertension was induced in Wistar rats by subcutaneously injecting 2.5 mg cortisone acetate daily and by maintaining the rats on a 1% sodium chloride diet for a period of 28 days. The hypertensive rats were treated daily with DK extract (50 and 100 mg/kg of body weight; p.o.) or captopril (20 mg/kg of body weight; p.o.), a reference drug, for 14 consecutive days. The blood pressure and heart rate of awake rats were measured using a non-invasive tail-cuff method. The heart weight and left ventricular wall thickness of rats were measured. In vitro angiotensin-converting enzyme (ACE) inhibition activity of the DK extract and captopril were analysed. DK extract significantly and dose-dependently reduced systolic and diastolic blood pressure in the hypertensive rats. There were no significant changes observed in heart rate. The cortisone acetate-induced hypertensive rats had increased heart weight and left ventricular wall thickness. These actions were attenuated by the treatment of DK extract (100 mg/kg) and captopril. Moreover, DK extract inhibited ACE activity in vitro with an IC50 of 4.71±0.53 μg/ml. Our findings demonstrate that DK extract exerted anti-hypertensive effects and alleviated ventricular hypertrophy in the cortisone acetate-induced hypertensive rats and these actions occurred at least in part via ACE activity inhibition.

91-96

Authors: Thi Van Anh Mai*, Kim Loan Nguyen, Dinh Trien Dang, Thi Xuan Sam Nguyen, Thanh Hang Nguyen

This study explored the growth and fermentation capabilities of four distinct yeast strains, including Saccharomyces cerevisiae var. boulardii CNCM I-745, S. cerevisiae 7012, S. cerevisiae 7028, and S. cerevisiae var. diastaticus BE-134, with the aim of identifying the most suitable strain for the production of a fermented beverage from soybean residue hydrolysate (SRH). The results were as follows: S. cerevisiae 7012 exhibited the most efficient fermentation, with residual sugar content of 2.16 g/100 ml, an ethanol concentration of 1.39% v/v, and a favourable aroma, receiving a sensory score of 4.3/5 points. Within this sensory profile, the aromatic compound 2-phenylethanol was found to be the predominant component. Additionally, S. cerevisiae var. boulardii CNCM I-745 demonstrated superior biomass production ability, achieving a cell density of 7.71 log CFU/ml after 48 hours of fermentation solution also showed the highest antioxidant activity, equivalent to 1.63 mg of ascorbic acid per 100 ml. Consequently, these two yeast strains were selected for combined use in fermentation to leverage the probiotic characteristics of S. cerevisiae var. boulardiiCNCM I-745 and the flavouring capacity of S. cerevisiae 7012 in creating fermented beverages from SRH.