Vietnam Academy of Science and Technology: Journals Online
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FORECAST ON WATER QUALITY OF TO LICH RIVER BASED BY SCENES OF HA NOI SEWERAGE PLANNING BY MODEL QUAL2K
No full textTo Lich River is well-known as a main drainage river and plays a vital role to the landscape distribution of Hanoi city, which is currently polluted due to improperly untreated wastewater flow. Thanks to QUAL2K model, the variation of river water quality has been forecasted by 4 particular scenarios. For the first scenario, the whole generated wastewater along To Lich River is not totally collected and treated. For the second one, it occurs as the former one with an addition of diluted water of 5m3/s from Red river. Next, wastewater is mostly well managed but minor sources are not collected. Finally, the whole generated wastewater is properly treated and added with a diluted amount of 5m3/s from Red river. The study indicated that in order to meet standard of column B1, QCVN 08-MT:2015/BTNMT (Vietnam National Regulation), centralized and decentralized generated sewerage is required the appropriate treatment to reach column B National Standard 02:2014/BTNMT, with the BOD5 is lower than 20 mg/L before discharging into the nature
TWO-STREAM CONVOLUTIONAL NETWORK FOR DYNAMIC HAND GESTURE RECOGNITION USING CONVOLUTIONAL LONG SHORT-TERM MEMORY NETWORKS
Full text linkHuman action and gesture recognition provides important and worth information for interaction between human and device ambient that monitors living, healthcare facilities or entertainment activities in smart homes. Recent years, there were many machine learning model application studies to recognize human action and gesture. In this paper, we propose a dynamic hand gesture recognition system in video based on two stream-convolution network (ConvNet) architecture. Specifically, we research the state-of-the-art approaches using to recognize dynamic hand gesture in video and propose an improvement method to enhance performance of model which is suitable for uses such as indoor environment in this paper. Our contribution is improvement of two stream ConvNet to achieve better performance. The results show that the proposal model improves execution speed and memory resource usage comparing to existing models
NGHIÊN CỨU XU THẾ BIẾN ĐỘNG TRƯỜNG NHIỆT ĐỘ BỀ MẶT BIỂN VÀ ẢNH HƯỞNG CỦA ENSO ĐẾN VÙNG BIỂN TÂY NAM VIỆT NAM SỬ DỤNG DỮ LIỆU VIỄN THÁM VÀ GIS
No full textIn this article, the sea surface temperature trends and the influence of ENSO on the southwest sea of Vietnam were analyzed using the continuous satellite-acquired data sequence of SST in the period of 2002–2018. GIS and average statistical methods were applied to calculate the average monthly and seasonal sea surface temperature, the seasonal sea surface temperature anomalies for each year and for the whole study period. Subsequently, the changing trends of sea surface temperature in the northeast and southwest monsoon seasons were estimated using linear regression analysis. Research results indicated that the sea surface temperature changed significantly throughout the calendar year, in which the maximum and minimum sea surface temperature are 31oC in May and 26oC in January respectively. Sea surface temperature trends range from 0oC/year to 0.05oC/year during the Northeast monsoon season and from 0.025oC/year to 0.055oC/year during the southwest monsoon season. Results based on the Oceanic Niño Index (ONI) analysis also show that the sea surface temperature in the study area and adjacent areas is strongly influenced and significantly fluctuates during El Niño and La Niña episodes.Bài báo giới thiệu kết quả nghiên cứu xu thế biến động trường nhiệt độ bề mặt biển và ảnh hưởng của hiện tượng ENSO đến vùng biển Tây Nam Việt Nam dựa trên phân tích chuỗi số liệu nhiệt độ bề mặt biển từ vệ tinh trong giai đoạn 2002-2018. Các phương pháp GIS và trung bình thống kê được áp dụng để tính toán nhiệt độ bề mặt biển trung bình tháng, trung bình mùa và dị thường trung bình mùa cho từng năm và cho cả giai đoạn nghiên cứu. Trên cơ sở đó, xu thế biến động trường nhiệt mặt biển theo hai mùa gió đông bắc và tây nam được ước tính bằng phương pháp phân tích hồi quy tuyến tính. Kết quả nghiên cứu cho thấy nhiệt độ bề mặt biển có sự thay đổi đáng kể giữa các tháng trong năm, đạt cực đại là 31°C vào tháng 5 và cực tiểu là 26°C vào tháng 1. Xu thế biến động của trường nhiệt độ bề mặt biển vào mùa gió đông bắc dao động trong khoảng từ 0°C/năm đến 0,05°C/năm và mùa gió tây nam khoảng từ 0,025°C/năm đến 0,055°C/năm. Kết quả nghiên cứu dựa vào chỉ số Nino đại dương (ONI) cũng cho thấy rằng trường nhiệt độ bề mặt biển vùng biển Tây Nam và lân cận chịu tác động mạnh và có sự biến động rõ rệt trong các thời kỳ xuất hiện El Nino và La Nin
New observations of the total electron content and ionospheric scintillations over Ho Chi Minh City
No full textIn January 2018, a Trimble NetR9 GNSS receiver was installed at International University - Vietnam National University (IU-VNU), which is located at 10°52'N, 106°48'E in Ho Chi Minh City (HCMC). The GNSS signals recorded from the receiver are useful for studying the ionospheric variations over this station as well as the magnetosphere-ionosphere coupling effects, therefore, we aim to preliminarily process and evaluate data recorded from this new station. Based on the data obtained with this GNSS receiver, we first estimated the total electron content (TEC) using the carrier-phase method which is a combination of code and phase measurements. We then calculated the rate of change of TEC index (ROTI) with respect to time and investigated its day-to-day variations. Our results show some typical features in the diurnal and seasonal TEC and ionospheric scintillation variations during 2018-2019. The distributions of ROTI over these two years of solar minimum show significant occurrences of scintillation, which are caused by small-scale ionospheric irregularities in the equatorial ionosphere. In addition, we found a significant increase of TEC in the latest strong geomagnetic storm in August 2018. The disturbance dynamo appears to have suppressed plasma bubbles after sunset and enhanced their formation at midnight. Thus, the disturbance dynamo effectively caused a delay of ionospheric scintillations. The TEC observed in HCMC also contributes to the data of ground-based observational receiver systems along 105o E longitude for studying ionospheric variations in low-latitude and equatorial regions. Our preliminary results indicate that the GNSS data collected at IU-VNU station is a valuable reference dataset for further research of the ionosphere
High-order Harmonic Generation from Hydrogen Molecular Ion in Coherent Superposition State
Full text linkAtom in a coherent superposition state reveals an advantage in the enhancement conversion efficiency of high-order harmonic generation (HHG), which is meaningful in producing attosecond pulses. In this study, we expand to investigate a more complicated system, H molecule in the superposition of the ground and second excited states, exposed to an ultrashort intense laser pulse by numerically solving the time-dependent Schrödinger equation. Firstly, we examine the enhancement of HHG from this system. Then, we study the depletion effect on the cutoff energy of HHG spectra with the coherent superposition state. We found that these effects on the HHG from molecules are similar to those from atoms. Finally, we study the signature of the interesting effect, which is absent for atoms -- two-center interference effect in the HHG from H in the coherent superposition state. We recognize that the minimum positions in HHG from molecules in the superposition state, and in the pure ground state are the same. Especially, for weak laser intensity, in the HHG with the superposition state, the minimum due to the interference effect is apparent, while it is invisible in the HHG from pure ground state. As a result, in comparison with the ground-state molecule, the coherent molecule can be used as a more accurate tool to determine the internuclear distance of molecule
Valance Band Maximum and Thermoelectric Properties of BiOSe: First-Principles Calculations
Full text linkBi2O2Se has been known as a promising thermoelectric material with low thermal conductivity. Detail understanding of band structure is therefore important. In this report, by employing first-principles density functional theory and using primitive unit cell, the electronic band structure of Bi2O2Se is examined. The compound is found to be a narrow band gap semiconductor with very flat bands at the valence band maximum (VBM). Nevertheless, the curvature of energy surface at VBM is directional dependent. Overall, the heavy bands at VBM do not reduce drastically electrical conductivity. It is demonstrated by utilizing the solution of Boltzmann Transport Equation to compute the transport coefficients, i.e. the Seebeck coefficient, the electrical conductivity thereby the power factor and the electronic thermal conductivity. The figure of merit of the compound is also estimated and discussed. The p-type doping is suggested increasing the thermoelectric performance of the compound. All results are in good agreement with experiments and calculations reported earlier
Application of GIS-Base GALDIT for vulnerability assessment to saltwater intrusion of Holocene coastal aquifer: a case of Quang Nam - Da Nang city, Vietnam
No full textGroundwater is an essential resource which is influenced by salt water due to the groundwater exploitation in Holocene aquifer of Quang Nam - Da Nang. Hence, the measures for preventing saltwater intrusion and better groundwater management are required. In this study, GALDIT method was utilized to identify the salt water intrusion (SWI) vulnerability zones using monitoring data in Holocene aquifer of Quang Nam - Da Nang. The results of GALDIT method indicated that Da Nang and Hoi An cities were in the high SWI vulnerability zones. The moderate SWI zones were dominant and low vulnerability zones were at the southern part of the study area. The analysis of the monitoring data showed the occurrence of SWI far inland, up to the distance of 12.5 km from the sea shore and suggested the impact of human activities on SWI. The analysis of monitoring data together with GALDIT index indicated that the important of the groundwater abstraction depth or the occurrence of fresh-salt groundwater interface should be considered to improve the result of GALDIT method for the prevention of SWI. In short, the GALDIT used in this study is an important approach for the prevention of SWI in the study area
Comparison of lipid classes and fatty acid compositions of farmed and wild pacific oysters, Crassostrea gigas, in Nha Trang, Vietnam
No full textLipid classes and fatty acid compositions of the farmed (F-C. gigas) and wild (W-C. gigas) pacific oysters, Crassostrea gigas, in Nha Trang, Vietnam were investigated for the first time. The results indicated that the lipid classes and fatty acid components of these oysters were insignificantly different. The total lipid of both studied oysters included six lipid classes, namely phospholipid (PL), sterol (ST), free fatty acid (FFA), triacylglycerol (TG), monoalkyldiacylglycerol (MADG), and hydrocarbon-wax (HW) in which TG and PL were dominated with the values of 48.4%, 41.8% for TG and 19.0%, 20.3% for PL in F-C. gigas and W-C. gigas, respectively. The fatty acids (FAs) content of F-C. gigas and W-C. gigas was similar. The saturated fatty acids (SFAs) content was 48.2% in total fatty acids (TFAs) of the F-C. gigas and 44.7% in TFAs of W-C. gigas, in which 16:0 was dominated in SFAs of both oysters with the value of 24.2% in F-C. gigas and 22.0% in W-C. gigas. The contents of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) were 18.3%, 20.5% for MUFAs and 31.7%, 34.7% for PUFAs respectively in F-C. gigas and W-C. gigas. These MUFAs compositions contained 16:1n-7, 16:1n-5, 18:1n-9, 18:1n-7, 20:1n-11, 20:1n-9 and 20:1n-7, among them fatty acids 16:1n-7 (7.2% in F-C. gigas, 6.3% in W-C. gigas) and 18:1n-7 (6.6% in F-C. gigas, 7.4% in W-C. gigas) were the main MUFAs. PUFAs in these two oysters consisted of long-chain n-3 and n-6 fatty acids, in which 20:5n-3 (EPA) and 22:6n-3 (DHA) were dominated with the values of 12.7%, 13.9% for EPA in F-C. gigas and 6.5%, 6.0% for DHA in W-C. gigas
Accurate through-the-thickness stress distributions in thin-walled metallic structures subjected to large displacements and large rotations
No full textThe present paper presents the evaluation of three-dimensional (3D) stress distributions of shell structures in the large displacement and rotation fields. The proposed geometrical nonlinear model is based on a combination of the Carrera Unified Formulation (CUF) and the Finite Element Method (FEM). Besides, a Newton-Raphson linearization scheme is adopted to compute the geometrical nonlinear equations, which are constrained using the arc-length path-following method. Static analyses are performed using refined models and the full Green-Lagrange strain-displacement relations. The Second Piola-Kirchhoff (PK2) stress distributions are evaluated, and lower- to higher-order expansions are employed. Popular benchmarks problems are analyzed, including cylindrical isotropic shell structure with various boundary and loading conditions. Various numerical assessments for different equilibrium conditions in the moderate and large displacement fields are proposed. Results show the distribution of axial and shear stresses, varying the refinement of the proposed two-dimensional (2D) shell model. It is shown that for axial components, a lower-order expansion is sufficient, whereas a higher-order one is needed to accurately predict shear stresses
