Science and Technology Development Journal 2021-07-12T16:10:36+00:00 Phuc Van Pham Open Journal Systems The efficiency of short sintering time on thermoelectric properties of delafossite CuCr0:85Mg0:15O2 ceramics 2021-07-12T16:10:35+00:00 Dung Van Hoang Truong Huu Nguyen Anh Tuan Thanh Pham Thu Bao Nguyen Le Vinh Cao Tran Thang Bach Phan <p><strong>Introduction</strong>: Harvesting the waste heat emitted from the activities of humanity based on thermoelectric devices is an appropriate way to reduce the overconsumption of fossil fuel nowadays.</p> <p><strong>Methods</strong>: In this work, CuCr0:85Mg0:15O2 compounds prepared by conventional solid-state reaction method were investigated to find out that the short sintering time is enough for thermoelectric applications, directly low the cost of the devices.</p> <p><strong>Results and Conclusion</strong>: We find out that there is a significant change in the crystal structure, the chemical state, and thermoelectric properties along with the increase of the sintering time, but eventually, the dimensionless figure of merit ZT is almost constant regardless of the long or short sintering time which means that the increase of electrical conductivity will compromise the increase of thermal conductivity. The highest ZT value is 0.03 measured at 500 oC for both samples prepared at the sintering time of 3 and 12 hours.</p> 2021-05-12T00:00:00+00:00 ##submission.copyrightStatement## Dynamics of a contracting fluid compound filament with a variable density ratio 2021-07-12T16:10:34+00:00 Truong V. Vu Vinh T. Nguyen Phan H. Nguyen Nang X. Ho Binh D. Pham Hoe D. Nguyen Hung V. Vu <p><strong>Introduction</strong>: Compound fluid filaments appear in many applications, e.g., drug delivery and processing or microfluidic systems. This paper focuses on the numerical simulation of an incompressible, immiscible, and Newtonian fluid for the contraction process of a fluid compound filament by solving the Navier-Stokes equations. The front-tracking method is used to solve this problem, which uses connected segments (Lagrangian grid) that move on a fixed grid (Eulerian grid) to represent the interface between the liquids.</p> <p><strong>Methods</strong>: The interface points are advected by the velocity interpolated from those of the fixed grid using the area weighting function. The coordinates of the interface points are used to construct the indicators specifying the different fluids and compute the interfacial tension force.</p> <p><strong>Results</strong>: The simulation results show that under the effects of the interfacial tension, the capsuleshaped filament can transform into a spherical compound droplet (i.e., non-breakup) or can break up into smaller spherical compound and simple droplets (i.e., breakup). When the density ratio of the outer to middle fluids increases, the filament changes from non-breakup to breakup upon contraction.</p> <p><strong>Conclusion</strong>: Increasing the density ratio enhances the breakup of the compound filament during contraction. The breakup is also promoted by increasing the initial length of the filament.</p> 2021-05-12T00:00:00+00:00 ##submission.copyrightStatement## A computational fluid dynamics study on the design optimization of an autonomous underwater vehicle 2021-07-12T16:10:32+00:00 Thanh Long Le Thuy Hang Vuong Trung Nghia Tran <p>In this study, numerical computation is used to develop a physical model representing all important features of the Autonomous Underwater Vehicle's (AUV) shape using the finite element methods. Because the shape of the AUV is an essential factor in determining the application and the vehicle's capability, investigating the effect of the environment on this profile is needed. This paper illustrates using Computational Fluid Dynamics (CFD) to investigate the effect of fluid flow on the AUV's profile at different velocities. The results obtained from the numerical computation demonstrate some of the hydrodynamic values of the AUV's shape, such as drag force and stress. It is necessary for optimizing the design of an AUV. When the AUV moves, the maximum pressure occurs at the nose of an AUV.</p> 2021-05-13T00:00:00+00:00 ##submission.copyrightStatement## Comparison of moss bag and native moss technique in monitoring airborne particulate and toxic elements 2021-07-12T16:10:24+00:00 Nguyen Thi Minh Sang Le Hong Khiem Son An Nguyen <p><strong>Introduction</strong>: In Vietnam, the government has invested in monitoring stations in a few big cities like Hanoi and Ho Chi Minh City, which have transportation centers and industrial zones, to assess and predict levels of air pollution. However, the main disadvantage of installing monitoring stations is the cost of investment for operations, maintenance, and equipment. It is also time-consuming to collect and analyze the results. Therefore, it is generally not suitable for the country as a whole.</p> <p><strong>Methods</strong>: Using mosses to monitor air quality brings qualitative and quantitative data with simple, environmentally-friendly economic methods. Mosses have particular biological characteristics that make them very suitable adsorbents for a wide variety of chemical elements. When used as transplants like moss bags, allow them to monitor a highly dense sampling network of any site easily. Mosses are bioindicators, plants with artificial roots.</p> <p><strong>Results</strong>: In this study, moss bag and native moss were the two methods used to evaluate the accumulation of trace elements in air through Barbula Indica. Observations showed that both methods could detect the same elements: Al, Si, P, S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Y, Sb, Ba, Pb, and U. However, the accumulation of the elements in native moss is higher than in moss bag. The main reason is that the absorption efficiency of native moss in air-deposited elements is higher than in moss bags.</p> <p><strong>Conclusion</strong>: Moss bags have been used most extensively and successfully in urban areas, where vegetation samples are either unobtainable or are poorly located to the source. These areas can lack moss, or the native moss simply does not grow during the dry season.</p> 2021-05-15T00:00:00+00:00 ##submission.copyrightStatement## P2- a2=3Mn2=3M1=3O2 (M = Fe, Co, Ni) cathode materials in localized high concentration electrolyte for the long-cycling performance of sodium-ion batteries 2021-07-12T16:10:36+00:00 Kha Minh Le Huynh Thi Kim Tuyen Thanh Duy Vo Hoang Van Nguyen Nhan Thanh Tran Man Van Tran Phung My Loan Le <p><strong>Introduction</strong>: Localized high concentration electrolytes (LHCE) have been intensively studied due to their unique properties, especially in suppressing the Na dendrite formation and long-term cycling. Therefore, the low electrochemical performance of the P2-type cathode can be overcome by using LHCE.</p> <p><strong>Methods</strong>: P2-type sodium layered oxides Na2=3Mn2=3M1=3O2 (M = Fe, Co, Ni) cathode materials were synthesized via a simple co-precipitation following a supported solid-state reaction. XRD and Rietveld method analyzed the phase composition and lattice parameters. SEM images observed the morphology of materials. The half-cell of three cathode were performed in LHCE consisting of 2.1 M sodium bis(fluorosulfonyl)imide (NaFSI) dissolved in 1,2-dimethoxyethane (DME) and bis(2,2,2-trifluoroethyl) ether (BTFE) (solvent molar ratio 1:2). The galvanostatic charge-discharge, striping-plating, and linear sweep voltage tests were carried out to investigate the electrochemical behaviors.</p> <p><strong>Results</strong>: As-prepared electrode materials exhibited discharge capacities of 94.5, 147.1, and 142.9 mAh/g at C/10 in the potential range of 1.5-4.2 V for Na2=3Mn2=3Fe1=3O2 (MFO), Na2=3Mn2=3Co1=3O2 (MCO) and Na2=3Mn2=3Ni1=3O2 (MNO), respectively. Interestingly, the MNO cathode material has a superior cycling performance with 86.5% capacity retention after 100 cycles than MCO and MFO.</p> <p><strong>Conclusion</strong>: Such superior electrochemical performance of synthesized MNO could be ascribed to the combined synergistic effects between the nickel partially substituted MNO cathode structure and using LHCE 2.1 M NaFSI/DME-BTFE (1:2). Nickel substituted MNO cathode exhibited the enhancement of discharge capacity and the long cycling stability in LHCE due to the mitigation of dendrite formation on sodium metal anode.</p> 2021-05-12T00:00:00+00:00 ##submission.copyrightStatement## Synthesis and cytotoxicity of substituted aromatic curcuminoids against human oral epidermal carcinoma-KB cell line 2021-07-12T16:10:33+00:00 Nga Thi Vo Nhan Phuoc Hoai Phan Tuyen Nguyen Kim Pham Hao Minh Hoang <p><strong>Introduction</strong>: The survival rate of oral cancer, like other types of cancers, has not been improved regardless of the early diagnosis and the introduction of advanced therapies. Treatment for oral cancer includes surgery, radiation therapy, and chemotherapy. However, the effectiveness has been limited due to recurrence and undesirable side effects. Metabolites from plant sources have been shown to be relatively less toxic and thus are considered as potential anti-cancer agents. Interestingly, curcumin isolated from the rhizome of Curcuma longa L. possesses broad-spectrum bioactivities. We focused on the synthesis of curcumin-based analogs bearing -OH/-OCH3/-F groups on the phenyl rings in our continuous efforts to search for curcumin-based anti-cancer agents. The synthesized compounds were subsequently evaluated for the cytotoxic activities against KB cancer cell line (an epidermal carcinoma of the mouth).</p> <p><strong>Methods</strong>: The desired curcuminoids were synthesized via aldol reactions between benzaldehyde derivatives and pentane-2,4-dione using n-butylamine as a catalyst. Structures were distinguished by NMR and MS spectra. The cytotoxic activity against KB was determined through the half-maximal inhibitory concentration (IC50, mM).</p> <p><strong>Results</strong>: Six curcumin analogs (1-6) were successfully synthesized in a yield of 48-76%. The 3- hydroxy/fluoro curcumin analogs (3, IC50 = 15.61 0.13 mM; 6, IC50 = 22.65 1.76 mM) exhibited better anti-cancer activities when compared to curcumin (1, IC50 = 33.35 2.66 mM), whereas the para-fluoro substitution patterns displayed lower inhibitory activities (4, 5) against KB cancer cell line.</p> <p><strong>Conclusions</strong>: The synthetic yields are dependent on the position and nature of substituents in aromatic rings. The presence of electron-donating groups gives products (1-3) in lower yields when compared to those (4-6) prepared from fluorinated benzaldehydes as starting materials. The curcuminoids bearing -OH groups at para-positions in aromatic rings (1, 2) can be responsible for better inhibition of cell growth, whereas the fluoro-substituted compounds (4, 5) make a negative contribution to inhibitory activity. Furthermore, the contributions -OH/-F groups at meta-position in aromatic rings of (3, 6) on the cytotoxicity against KB are remarkable and firstly reported in our findings.</p> 2021-05-12T00:00:00+00:00 ##submission.copyrightStatement## The effect of excitation light source and humidity to photocatalytic activity of g-C3N4 nanosheets for NO removal 2021-07-12T16:10:28+00:00 Vinh Hoang The Tran Tu Cam Huynh Viet Van Pham <p><strong>Introduction</strong>: Photocatalysis using nanostructured semiconductors is the potential strategy to solve the problem of environmental pollution. Besides traditional semiconductor materials, the novel polymeric metal-free semiconductor g-C3N4 has emerged as a potential substitute material because of its many outstanding features.</p> <p><strong>Methods</strong>: This study successfully synthesized two dimensions (2D)-structured g-C3N4 nanosheets by a simple thermal-exfoliation method with annealing route at 2 oC/min. Firstly, melamine was placed in a ceramic crucible with cover and then undergone the annealing route at 550 oC for 2 h to develop into the g-C3N4 bulk. Then the assynthesized g-C3N4 bulk was further annealed without the cover at 550 oC for 2 h to form the final product, g-C3N4 nanosheets.</p> <p><strong>Results</strong>: The results of XRD patterns and FTIR spectra show two typical diffractions peaks and chemical bonds that characterize the g-C3N4 matrix. The TEM images demonstrated that the as-prepared g-C3N4 possesses 2D-structured material, including several singly exfoliated sheets with a width of around several hundred nanometers. The photocatalytic NO removal efficiency of g-C3N4 nanosheets is highest at 48.27% under 30 min solar irradiation at 70% humidity. Meanwhile, the NO2 conversion yield is very low, only 9.44%, much smaller than the NO decomposition efficiency to form NO3 􀀀 ion products. The results of trapping tests indicated that the hole plays the most critical role in the photocatalytic process of g-C3N4 nanosheets. Especially, the photocatalytic NO removal efficiency still achieves 45.03% after the recycling test. Moreover, all characteristic peaks and chemical bonds in material remain even undergoing fifth times reuse as the results of XRD and FTIR.</p> <p><strong>Conclusion</strong>: From various modern analytic characterization methods and photocatalytic investigation, we can concluse that g-C3N4 nanosheets are very stable and possible to apply in practical applications to decompose NO gas at atmospheric conditions.</p> 2021-05-13T00:00:00+00:00 ##submission.copyrightStatement## The phytochemical investigation from n-hexane extract of the lichen Roccella montagnei 2021-07-12T16:10:26+00:00 Thu Thi-Hoai Nguyen Duong Thuc Huy <p><strong>Introduction</strong>: <em>Roccella montagnei</em> is widely distributed in subtropical regions. As the continuous study on the hexane extract of <em>Roccella montagnei</em> lichen, the isolation and structural determination of five compounds were addressed.</p> <p><strong>Method</strong>: The crude extract was obtained from the dried lichen powder's extraction at room temperature. The n-hexane, n-hexane-ethyl acetate, and ethyl acetate extracts were obtained by the liquid-liquid partition method. The organic compounds were isolated from n-hexane extract by silica gel and Sephadex LH-20 column chromatography. Their chemical structures were identified by the NMR and HR-ESI-MS data analysis and the comparison of their NMR data with the published data.</p> <p><strong>Results</strong>: Five compounds were isolated and chemically structural identified, consisting of 3b -hydroxy-7a-methoxystigmast-5-ene (1), sekikaic acid (2), lichenxanthone (3), (+)-6,8-dihydroxy-3-propyl-3,4-dihydroisocoumarin (4), and ar-turmerone (5).</p> <p><strong>Conclusion</strong>: To the best of our knowledge, except 3 which was reported from this species for the first time, four isolated compounds left did not known to be present in <em>Roccella genus</em> before.</p> 2021-05-13T00:00:00+00:00 ##submission.copyrightStatement## Ag-grafted on ZnO nanorod arrays using UV-assisted irradiation for enhanced SERS behavior in CV detection 2021-07-12T16:10:31+00:00 Ton Nu Quynh Trang Le To Cam Huong Thai Duong Vu Thi Hanh Thu <p><strong>Introduction</strong>: Semiconductor-based surface-enhanced Raman scattering (SERS) substrates with high stability and reproducibility have become one of the essential analytical tools in the analysis of chemical and biological at trace levels. Herein, a growth of the hexagonal-wrapped ZnO nanorod arrays decorating with Ag nanoparticles (AgNPs) at different concentrations of Ag was proposed.</p> <p><strong>Methods</strong>: The crystallinity, morphology, chemical composition, and optical properties of the prepared samples were investigated by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Raman system, respectively.</p> <p><strong>Results</strong>: The results revealed that the SERS performance of ZnO NRs incorporating with AgNPs exhibited higher detection of crystal violet (CV) probe molecules at a low concentration of 10􀀀8 M than that of the pristine ZnO NRs. This effect originates from the localized surface plasmonic resonance of AgNPs that could cause a strong electromagnetic field and synergistic effects of Ag, ZnO, and CV molecules in ZnONRs@Ag/CV SERS system.</p> <p><strong>Conclusion</strong>: These outcomes reveal that AgNPs play a crucial role in enhanced SERS performance for chemical and biological detection of ZnO substrate.</p> 2021-05-13T00:00:00+00:00 ##submission.copyrightStatement## Effect of the chemical vapor deposition condition on the electrochemically catalytic efficiency for hydrogen evolution reaction in MoS2 nanoparticles 2021-07-12T16:10:29+00:00 Quyen Le Do Duc Anh Nguyen <p><strong>Introduction</strong>: Using the metal organic chemical vapor deposition (MOCVD) method, we have synthesized the MoS<sub>2</sub> nanoparticles on graphite foil substrates employed as the electrochemical working electrodes with highly efficient electrocatalysis for hydrogen evolution reaction (HER).</p> <p><strong>Methods</strong>: The morphological and structural properties of the as-grown MoS<sub>2</sub> materials were demonstrated by field emission scanning electron microscope (FESEM) and Raman spectroscopies, while their elemental components were investigated by X-ray photoelectron spectroscopy (XPS).</p> <p><strong>Results</strong>: The optimum growth time was acquired to be 11 hours. Thereby such obtained electrode exhibited the maximum HER activity with onset over the potential of 220 mV versus reversible hydrogen electrode (RHE), and the Tafel slope of 66 mV per decade (mV/dec).</p> <p><strong>Conclusion</strong>: Our results suggest a good technique for the research of high-efficient HER electrocatalyst based on atomic-thickness layered materials.</p> 2021-05-13T00:00:00+00:00 ##submission.copyrightStatement## Using quantitative real-time polymerase chain reaction (qRT-PCR) for detection microcystin producing cyanobacteria 2021-07-12T16:10:27+00:00 Thanh Luu Pham Tran Thi Hoang Yen Tran Thanh Thai Ngo Xuan Quang <p><strong>Introduction</strong>: Cyanobacterial blooms (CBs) have become a growing concern worldwide. In the natural environment, potentially toxic (can produce toxins) and non-toxic (can not produce toxins) colonies often co-exist within a bloom.</p> <p><strong>Methods</strong>: The present study aimed to quantify toxic and non-toxic cells of cyanobacteria in the Tri An Reservoir (TAR) using a quantitative real-time polymerase chain reaction (qRT-PCR).</p> <p><strong>Results</strong>: Results showed that the Microcystis genus dominated the cyanobacterial communities in the TAR. Microcystis was also the primary microcystins (MC) producing cyanobacteria in the water. Total cyanobacteria and Microcystis cells ranged from 152103 to 27106 copy/L and from 105103 to 19106 copy/L, respectively. The cell number of potentially MC-producing cyanobacteria (corresponding to the Microcystis mcyD gene) varied from 27103 to 13106 copy/L. MC concentrations often present in raw water with a concentration of up to 4.8 mg/L. Our results showed that the MC concentration in raw water was positively correlated with the mcyD copy number, suggesting that Microcystis spp. are the main toxin producers in the TAR's surface water.</p> <p><strong>Conclusion</strong>: Our study suggested that qRT-PCR techniques and traditional count are comparable and could be used to quantify cyanobacteria. In addition, the qRT-PCR techniques can determine the toxic cyanobacterial cells and could be used as a tool for early monitoring of toxic cyanobacteria in lakes and reservoirs.</p> 2021-05-13T00:00:00+00:00 ##submission.copyrightStatement## Digital transformation in the business: a solution for developing cash accounting information systems and digitizing documents 2021-07-12T16:10:23+00:00 Nguyen Manh Tuan Nguyen Quoc Hung Nguyen Thi Hang <p>Digital transformation is becoming an inevitable trend, having a profound impact on business activities, processes,, and modelsands improving the operational efficiency of businesses. In enterprises, especially small and medium-sized enterprises, accounting professions are mainly still handled manually on books and documents. They have not standardized the professions, especially those that arise in the course of operation. This makes it difficult for accounting such as accounting work gradually increases, the handling of work is delayed, easily confused and errors .... Leading to limiting the development and expanding the size of the business. The problem for each business is the need to automate some accounting operations to adapt to the trend and context of digital transformation, contributing to improving the competitive efficiency of the business. Stemming from the above difficulties, the research will find solutions to help businesses approach and apply processing operations professionally towards the formation of digital businesses. The article will focus on building cash accounting modules and handling professional accounting processes to implement digital transformation in enterprises. The operations mentioned in the article include building the professional process of cash accounting, controlling cash collection - spending, the process of digitizing documents stored at the enterprise, etc... The article will propose how to process data and make reports required by managers for decision-making based on invoices and handling arising transactions.</p> 2021-05-21T00:00:00+00:00 ##submission.copyrightStatement##