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Effectiveness of Sentinel-1-2 Multi-Temporal Composite Images for Land-Cover Monitoring in the Indochinese Peninsula

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Journal of Geoscience and Environment Protection 2020年第9期8卷 24-32页

作者： Nguyen Thanh Hoan Ram C. Sharma Nguyen Van Dung dang xuan tung Institute of Geography Vietnam Academy of Science and Technology Hanoi Vietnam Graduate University of Science and Technology Vietnam Academy of Science and Technology Hanoi Vietnam Department of Informatics Tokyo University of Information Sciences Chiba Japan Institute of Geological Sciences Vietnam Academy of Science and Technology Hanoi Vietnam

The Indochinese Peninsula, which contains two thirds of the world’s tropical forests, however, is one of the world’s most threatened habitat with some of the highest rates of deforestation and land use changes. Availability of higher resolution satellite data collected by the likes of Landsat 8 and Sentinel-1-2 has brought new opportunities for precise land cover monitoring in recent years. However, utilizing a massive volume of high spatial and temporal resolution data for ecological applications is challenging. One approach is to employ composite images generated from the multi-temporal satellite data. The research was conducted in two study sites located in the Indochinese Peninsula, Laos-Thailand and Vietnam-Cambodia, vulnerable to deforestation and land use changes. We assessed the potential of recently available composite images, such as Biophysical Image Composite (BIC), Forest Cover Composite (FCC), Enhanced Forest Cover Composite (EFCC), and Water Cover Composite (WCC) for the classification and mapping of land cover types. Three machine learning classifiers, k-Nearest Neighbors (KNN), Support Vector Machines (SVM) and Random Forests (RF) were employed and the performance of composite images was evaluated quantitatively with the support of ground truth data. The overall accuracies (Kappa coefficient) obtained from the combination of composite images were 0.92 (0.89) and 0.90 (0.86) for Laos-Thailand, and Vietnam sites respectively. These results highlight effectiveness of the composite images for the classification and mapping of land cover types.

关键词： Satellite Remote Sensing Machine Learning Optical Radar

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Iterative Method for Solving a Problem with Mixed Boundary Conditions for Biharmonic Equation

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Advances in Applied Mathematics and Mechanics 2009年第5期1卷 683-698页

作者： dang Quang A Le tung Son Institute of Information Technology 18 Hoang Quoc Viet Cau giayHanoiVietnam Pedagogic College Thai Nguyen UniversityVietnam

The solution of boundary value problems(BVP)for fourth order differential equations by their reduction to BVP for second order equations,with the aim to use the available efficient algorithms for the latter ones,attracts attention from many *** this paper,using the technique developed by the authors in recent works we construct iterative method for a problem with complicated mixed boundary conditions for biharmonic equation which is originated from nanofluidic *** convergence rate of the method is proved and some numerical experiments are performed for testing its dependence on a parameter appearing in boundary conditions and on the position of the point where a transmission of boundary conditions occurs.

关键词： Iterative method biharmonic equation mixed boundary conditions

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Visualization Investigation on Flowing Condensation in Horizontal Small Channels with Liquid Separator

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Journal of Thermal Science 2018年第1期27卷 48-54页

作者： ZHANG xuan JIA Li dang Chao PENG Qi Institude of Thermal Engineering School of MechanicalElectronic and Control EngineeringBeijing Jiaotong UniversityBeijing 100044China Beijing key laboratory of flow and heat transfer of phase changing in micro and small scale Beijing 100044China

A simultaneous visualization and measurement experiment was carried out to investigate condensation flow pat- terns and condensing heat transfer characteristics of refrigerant R14 lb in parallel horizontal multi-channels with liquid-vapor separator. The hydraulic diameter of each channel was 1.5 mm and the channel length was 100 ram. The refrigerant vapor flowing in the small channels was cooled by cooling water. The parallel horizontal mul- ti-channels were covered with a transparent silica glass for visualization of flow patterns. Experiments were per- formed at different inlet superheat temperatures （ranging from 3~C to 7~C）. Mass velocity was in the range of 82.37 kg mZs1 to 35.56 kg m-2s1. It was found that there were three different flow patterns through the mul- ti-channels with the increase of mass velocity. The flow patterns in each channel pass almost tended to be same and all of them were annular flows.＇ The efficiency of the liquid-vapor separator with U-type was related to vapor mass velocity and the pressure in the small channels. It was also found that the heat transfer coefficient increased with the increase of the mass velocity while the cooling water mass flow rate increased. It increased to a top point and then decreased. It increased with the increase of superheat in the low superheat temperature region.

关键词： condensation visualization multi-channels liquid-vapor separation

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Gait Optimization of a Quadruped Robot Using Evolutionary Computation

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Journal of Bionic Engineering 2021年第2期18卷 306-318页

作者： Jihoon Kim dang xuan Ba Hoyeon Yeom Joonbum Bae Mechanical Engineering Ulsan National Institute of Science and Technology(UNIST)Ulsan 44919South Korea Automatic Control HoChiMinh City University of Technology and Education(HCMUTE)HoChiMinh City 71307Vietnam

Evolutionary Computation(EC)has strengths in terms of computation for gait ***,conventional evolutionary algorithms use typical gait parameters such as step length and swing height,which limit the trajectory deformation for optimization of the foot ***,the quantitative index of fitness convergence is *** this paper,we perform gait optimization of a quadruped robot using foot placement perturbation based on *** proposed algorithm has an atypical solution search range,which is generated by independent manipulation of each placement that forms the foot trajectory.A convergence index is also introduced to prevent premature cessation of *** conventional algorithm and the proposed algorithm are applied to a quadruped robot;walking performances are then compared by gait *** the two algorithms exhibit similar computation rates,the proposed algorithm shows better fitness and a wider search *** evolutionary tendency of the walking trajectory is analyzed using the optimized results,and the findings provide insight into reliable leg trajectory design.

关键词： bionic robot evolutionary computation genetic algorithm gait optimization parameter perturbation convergence index

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Progress in developing self-consolidating concrete(SCC)constituting recycled concrete aggregates:A review

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International Journal of Minerals,Metallurgy and Materials 2021年第4期28卷 522-537页

作者： Yu-xuan Liu tung-Chai Ling Kim-Hung Mo Key Laboratory for Green&Advanced Civil Engineering Materials and Application Technology of Hunan Province College of Civil EngineeringHunan UniversityChangsha 410082China Department of Civil Engineering Faculty of EngineeringUniversity of MalayaMalaysia

Recycled concrete aggregate(RCA)derived from demolition waste has been widely explored for use in civil engineering *** of the promising strategies globally is to incorporate RCA into concrete ***,the use of RCA in high-performance concrete,such as self-consolidating concrete(SCC),has only been studied in the past *** paper summarizes recent publications on the use of coarse and/or fine RCA in *** expected,the high-water absorption and porous structure of RCA have posed challenges in producing a high-fluidity *** to an analysis of published data,a lower strength reduction(within 23%regardless of coarse RCA content)is observed in SCC compared with vibrated concrete,possibly due to the higher paste content in the SCC matrix,which enhances the weak surface layer of RCA and interfacial transition ***,SCC tends to become less durable with RCA substitution although the deterioration can be minimized by using treated RCA through removing or strengthening the adhered *** date,the information reported on the role of RCA in the long-term performance of SCC is still limited;thus,a wide range of research is needed to demonstrate the feasibility of RCA–SCC in field applications.

关键词： self-consolidating concrete construction and demolition waste recycled concrete aggregate(RCA) durability property enhancement

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Thermal Performance Prediction in the Air Gap of a Rotor-Stator Configuration: Effects of Numerical Models

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Journal of Thermal Science 2020年第1期29卷 206-218页

作者： dang Dinh-Dong PHAM xuan-Tan NGUYEN Chi-Cong Department of Mechanical Engineering École de technologie supérieureMontrealQCCanada Hydro-Québec’s research institute VarennesQCCanada

This study is dedicated to a numerical investigation of convective heat transfer on the rotor surfaces of a rotor-stator configuration that is typically found in large *** computational fluid dynamics calculations with two turbulence modelling approaches are used to predict the flow structure and heat transfer in the air gap of the rotor-stator *** steady state mixing plane approach is employed at the interface to couple the rotor and stator *** show that the location of mixing plane interface in the air gap plays an important role in the prediction of heat transfer on the pole ***,it is indicated that the prediction of temperature distribution on the pole face is greatly affected by the turbulence models ***,through a comparison between the pure convective and conjugate heat transfer methodologies,it is shown that the inclusion of solid domain into the numerical model significantly improves the thermal prediction of the solid components of the machine.

关键词： hydro-generators electrical cooling mixing plane windage loss conjugate heat transfer

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Characterization of random stress fields obtained from polycrystalline aggregate calculations using multi-scale stochastic finite elements

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Frontiers of Structural and Civil Engineering 2015年第2期9卷 121-140页

作者： Bruno SUDRET Hung xuan dang Marc BERVEILLER Asmahana ZEGHADI Thierry YALAMAS Risk Safety and Uncertainty Quantification ETH Zurich Stefano-Franscini-Platz 5 Zurich CH-8093 Switzerland Phimeca Engineering S.A. Centre d'affaires du Zenith 34 rue de Sarlieve Cournon F-63800 France EDF R&D Dept. of Materials and Mechanics of Components Site des Renardieres Moret-sur-Loing Cedex 77250 France

The spatial variability of stress fields resulting from polycrystalline aggregate calculations involving random grain geometry and crystal orientations is investigated. A periodogram-based method is proposed to identify the properties of homogeneous Gaussian random fields (power spectral density and related covariance structure). Based on a set of finite element polycrystalline aggregate calculations the properties of the maximal principal stress field are identified. Two cases are considered, using either a fixed or random grain geometry. The stability of the method w.r.t the number of samples and the load level (up to 3.5% macroscopic deformation) is investigated.

关键词： polycrystalline aggregates crystal plasticity random fields spatial variability correlation structure

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Effects of Stress Level and Stress State on Creep Ductility:Evaluation of Different Models

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Journal of Materials Science & Technology 2016年第8期32卷 695-704页

作者： Jian-Feng Wen Shan-tung Tu Fu-Zhen xuan Xue-Wei Zhang Xin-Lin Gao Key Laboratory of Pressure Systems and Safety (Ministry of Education) School of Mechanical and Power Engineering East China University of Science and Technology Department of Materials Science and Engineering Texas A&M UniversityCollege Station Department of Mechanical Engineering Southern Methodist University

The last few decades have witnessed an increasing emphasis on the development of strain-based ap- proach for predicting the creep life or damage of components operating at elevated temperatures. Creep ductility, as a key parameter in this approach, may vary with a number of factors including strain rate, state of stress, operating temperature, material microstructure, etc. The present paper, however, is focused on reviewing the state-of-the-art understanding of the effects of stress level and stress state on the creep ductility. Mechanisms involving the void growth and coalescence are presented to describe the role of stress level in the variation of uniaxial creep ductility. The prediction capacity of existing empirical duc- tility models is also assessed in light of uniaxial test data. On the other hand, a vast body of multiaxial creep test data, collected from open literature, is utilized to examine the influence of the state of stress on the creep ductility. Then, a variety of multiaxial ductility factor models are introduced and evaluated with the available experimental data. Finally, a brief discussion on the dependence of creep ductility on the stress triaxiality and Lode parameter, predicted by numerical methods, is provided.

关键词： Creep Creep ductility Multiaxial stress state Ductility exhaustion

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Optical properties and dynamic process in metal ions doped on CdSe quantum dots sensitized solar cells

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Chinese Optics Letters 2018年第7期16卷 71-77页

作者： Ha Thanh tung dang Huu Phuc Institute of Research and Development Duy Tan University Theoretical Physics Research Group Advanced Institute of Materials Science Ton Duc Thang University Faculty of Applied Sciences Ton Duc Thang University

In recent years, the nanostructure for solar cells have attracted considerable attention from scientists as a result of a promising candidate for low cost devices. In this work, quantum dots sensitized solar cells with effective performance based on a co-sensitized Cd S∕Cd Se：Mn2＋（or Cu2＋） nanocrystal, which was made by successive ionic layer absorption and reaction, are discussed. The optical, physical, chemical, and photovoltaic properties of quantum dots sensitized solar cells were sensitized to Mn2＋and Cu2＋dopants. Therefore, the short current（JSC）of the quantum dot sensitized solar cells is boosted dramatically from 12.351 mA∕cm2 for pure Cd Se nanoparticles to 18.990 mA∕cm2 for Mn2＋ions and 19.915 mA∕cm2 for Cu2＋ions. Actually, metal dopant extended the band gap of pure Cd Se nanoparticles, reduced recombination, enhanced the efficiency of devices, and improved the charge transfer and collection. In addition, Mn2＋and Cu2＋dopants rose to the level of the conduction band of pure Cd Se nanoparticles, which leads to the reduction of the charge recombination, enhances the lightharvesting efficiency, and improves the charge diffusion and collection. The results also were confirmed by the obtained experimental data of photoluminescence decay and electrochemical impedance spectroscopy.

关键词： CdS Cu Mn FTO Optical properties and dynamic process in metal ions doped on CdSe quantum dots sensitized solar cells

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Spatiotemporal Trend Analysis of Precipitation Extremes in Ho Chi Minh City, Vietnam During 1980–2017

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International Journal of Disaster Risk Science 2021年第1期12卷 131-146页

作者： Nguyen Trong Quan Dao Nguyen Khoi Nguyen xuan Hoan Nguyen Ky Phung Thanh Duc dang Faculty of Environmental and Food Engineering Nguyen Tat Thanh UniversityHo Chi Minh City 700000Vietnam Faculty of Environment University of ScienceHo Chi Minh City 700000Vietnam Vietnam National University Ho Chi Minh City 700000Vietnam Ho Chi Minh City University of Food Industry Ho Chi Minh City 700000Vietnam Institute for Computational Science and Technology Ho Chi Minh City 700000Vietnam Engineering Systems and Design Pillar Singapore University of Technology and DesignTampines 487372Singapore

In this study,the spatiotemporal variability of trends in extreme precipitation events in Ho Chi Minh City during the period 1980–2017 was analyzed based on several core extreme precipitation indices(Rx1 day,Rx5 day,CDD,CWD,R20 mm,R25 mm,R95 p,and SDII).The nonparametric Mann–Kendall and Sen’s slope methods were used to compute the statistical strength,stability,and magnitude of trends in annual rainfall,as well as the extreme precipitation *** found that 64%of the stations had statistically significant upward trends in yearly rainfall,with high magnitudes frequently observed in the northern and southern regions of the *** the extreme precipitation indices,only SDII and R25 mm showed dominantly significant ***,there were increasing trends in the frequency and duration at the southern and central regions of the city during the study ***,El Ni?o-Southern Oscillation and Pacific Decadal Oscillation positively correlated with the duration and negatively correlated with the intensity and frequency of extreme ***,water management plans should be adjusted appropriately to reduce the severe impacts of precipitation extremes on communities and ecosystems.

关键词： Spatiotemporal trend Extreme precipitation Extreme precipitation indices Ho Chi Minh City

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