Characteristics of groundwater in karstic region in northeastern Vietnam     

Lam Van Nguyen  Ngoc Kim Nguyen  Hoan Van Hoang  Tuan Quang Tran  Nga Trong Vu 《Environmental Earth Sciences》2013,70(2):501-510

The groundwater in the karst region of northeastern Vietnam is found in various structural zones such as the Ha Lang, Song Hien, Hon Gai, Song Lo, Song Gam, and Hoang Lien Son Zones, etc. Results from this study show that groundwater in this region is at different depths: ~120 m deep at Quang Ninh, ~100 m at Lang Son, ~80 m at Cao Bang (The most water-abundant depth observed at Cao Bang varies from 40 to 45 m) while it varies from 18–25 to 80 m deep at Quan Ba (Ha Giang), especially at Meo Vac (Ha Giang), where groundwater is observed at 700–800 m deep (equivalent to local base level of the Nho Que River). Overall, groundwater in the region is fresh with total minerals varying from 250 to 400 mg/l; except for the coastal area of Quang Ninh, where groundwater is characterized by much higher total minerals (M = 3–18 g/l) due to the mixing with the saline sea water. The chemistry of water in the region demonstrates that the water is mainly bicarbonate with a [HCO₃ ^?] concentration varying from 150 to 265 mg/l, pH is of 6.5–8.1, and its hardness is of 3.7–6.0 meq/l.  相似文献   

Active fault segmentation and seismic hazard in Hoa-Binh reservoir, Vietnam     

Phan Trong Trinh  Hoang Quang Vinh  Nguyen Van Huong  Ngo Van Liem 《Central European Journal of Geosciences》2013,5(2):223-235

Based on remote sensing, geological data, geomorphologic analysis, and field observations, we determine the fault system which is a potential source of earthquakes in Hoa-Binh reservoir. It is the sub-meridian fault system composed of fault segments located in the central part of the eastern and western flanks of the Quaternary Hoa-Binh Graben: the Hoa-Binh 1 fault is east-dipping (75–80°), N-S trending, 4 km long, situated in the west of the Hoa-Binh Graben, and the Hoa-Binh 2 is a west-dipping (75–80°), N-S trending; 8.4 km long fault, situated in the east of the Hoa-Binh Graben. The slip rate of normal fault in Hoa-Binh hydropower dam was estimated at 0.3–1.1 mm/yr. The Maximum Credible Earthquake (MCE) and Peak Ground Acceleration (PGA) in the Hoa-Binh hydropower dam have been assessed. The estimated MCE of HB.1 and HB.2 is 5.6 and 6.1 respectively, and the maximum PGA at Hoa-Binh dam is 0.30 g and 0.40 g, respectively. The assessment of seismic hazard in Hoa-Binh reservoir is a typical example of seismic hazards of a large dam constructed in an area of low seismicity and lack of law of seismic attenuation.  相似文献   

Quasi-Thermal Noise Diagnostics in Space Plasmas     

K. Issautier  M. Moncuquet  N. Meyer-Vernet  S. Hoang  R. Manning 《Astrophysics and Space Science》2001,277(1-2):309-311

We present the method of plasma diagnostics by quasi-thermal noise spectroscopy and show examples of application in the solar wind and the Earth's plasmasphere. Using only an electric antenna and a radio receiver, diagnostics of various space environments (magnetized or not) can be obtained in situ. Because of its accuracy, this technique can be used to cross-check other plasma sensors. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Spatial prediction of rainfall-induced shallow landslides using hybrid integration approach of Least-Squares Support Vector Machines and differential evolution optimization: a case study in Central Vietnam     

Dieu Tien Bui  Binh Thai Pham  Quoc Phi Nguyen  Nhat-Duc Hoang 《International Journal of Digital Earth》2016,9(11):1077-1097

This study represents a hybrid intelligence approach based on the differential evolution optimization and Least-Squares Support Vector Machines for shallow landslide prediction, named as DE–LSSVM_SLP. The LSSVM is used to establish a landslide prediction model whereas the DE is adopted to search the optimal tuning parameters of the LSSVM model. In this research, a GIS database with 129 historical landslide records in the Quy Hop area (Central Vietnam) has been collected to establish the hybrid model. The receiver operating characteristic (ROC) curve and area under the curve (AUC) were used to assess the performance of the newly constructed model. Experimental results show that the proposed model has high performances with approximately 82% of AUCs on both training and validating datasets. The model’s results were compared with those obtained from other methods, Support Vector Machines, Multilayer Perceptron Neural Networks, and J48 Decision Trees. The result comparison demonstrates that the DE–LSSVM_SLP deems best suited for the dataset at hand; therefore, the proposed model can be a promising tool for spatial prediction of rainfall-induced shallow landslides for the study area.  相似文献   

Pan-sharpening quality investigation of PLÉIADES-1A images     

Mustafa Ozendi  Huseyin Topan  Murat Oruc  Ali Cam 《国际地球制图》2016,31(8):881-890

Optical remote sensing satellites obtain MS and Pan images simultaneously over the same coverage area. Remote sensing and image processing communities are working on different pan-sharpening methods capable of taking advantage of MS and Pan images. Each remote sensing system has its own advantages and disadvantages, leading to the question ‘Which pan-sharpening method should be used for which type of imagery?’ The aim of this research is to investigate the pan-sharpening performance of PLÉIADES-1A images. For this purpose, pan-sharpened images were generated using PCA, IHS and Brovey Transform which are the most popular pan-sharpening methods. Then, the pan-sharpened images were evaluated quantitatively using Correlation Coefficient, Root Mean Square Error, Relative Average Spectral Error, Spectral Angle Mapper and Erreur Relative Globale Adimensionnelle de Synthése. In addition, pan-sharpened images were evaluated qualitatively by taking object availability and completeness into consideration.  相似文献   

‘This is my garden’: justice claims and struggles over forests in Vietnam’s REDD+     

Cam Hoang  Poshendra Satyal  Esteve Corbera 《Climate Policy》2019,19(6):S23-S35

ABSTRACT

This paper explores dynamics of conflict over forests in Vietnam, as the country lays the groundwork for Reducing Emissions from Deforestation and Forest Degradation (REDD+). Drawing on a case study in Lam Dong province and applying an environmental justice lens, we examine how various social actors assert claims over forests and how these claims invoke different notions of justice, authority and identity. Our analysis highlights that the development and implementation of the project has generated renewed competing claims and conflicts over forests among social actors. Underlying these conflicts there are incompatible notions of justice and associated rights, which lead different actors to accord legitimacy variously to the global norms brought about by REDD+, the customary resource practices of indigenous people, or to the state’s laws. We show that the negotiations over forests in REDD+ reflect the influence of the specific historical and political-economic settings in which REDD+ activities take place, including pre-existing conflicts over forests and power relations underpinning forest management. From a policy perspective, our research suggests that any attempts to introduce simplified and uniform regulations for forest governance in REDD+ should be avoided, since local institutions and conceptions of justice will significantly influence what is regarded as legitimate policy and can thus be endorsed as inspiration for sustainable forest governance.

Key policy insights

• REDD+ in Vietnam has spurred contestations over who is legitimately entitled to govern and manage forests.

• Claims and conflicts over forests can be explained by incompatible and distinct notions of justice, authority and identity.

• Contestations over justice pose radical challenges to any global and national efforts that attempt to implement simplified rules and ideas for forest based-climate change mitigation.

• Attention to justice, especially to compatibility and differences in ideas about justice, is crucial for sustainable forest governance.

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Comparative evaluation of freeze and thaw effect on strength of BEICP-stabilized silty sands and cement- and fly ash-stabilized soils     

Hoang  Tung  Do  Huyen  Alleman  James  Cetin  Bora  Dayioglu  Asli Y. 《Acta Geotechnica》2023,18(2):1073-1092

Acta Geotechnica - This paper addresses a soil bio-stabilization technique using bacterial enzyme-induced calcium carbonate precipitation (BEICP) as an alternative to previous conventional methods...  相似文献   

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Radio Flux Density Variations with Frequency     

V. Krupar  M. Maksimovic  O. Santolik  E. P. Kontar  B. Cecconi  S. Hoang  O. Kruparova  J. Soucek  H. Reid  A. Zaslavsky 《Solar physics》2014,289(8):3121-3135

We have performed a statistical study of 152 Type III radio bursts observed by Solar TErrestrial RElations Observatory (STEREO)/Waves between May 2007 and February 2013. We investigated the flux density between 125 kHz and 16 MHz. Both high- and low-frequency cutoffs were observed in 60 % of events, suggesting an important role of propagation. As already reported by previous authors, we observed that the highest flux density occurs at 1 MHz on both spacecraft. We developed a simplified analytical model of the flux density as a function of radial distance and compared it with the STEREO/Waves data.  相似文献   

Evaluating the performance of an explicit dynamic relaxation technique in analyzing non-linear geotechnical engineering problems     

Hoang K. Dang  Mohamed A. Meguid 《Computers and Geotechnics》2010,37(1-2):125-131

Explicit dynamic relaxation is an efficient tool that has been used to solve problems involving highly non-linear differential equations. The key feature of this method is the ability to use explicit dynamic algorithms in solving static problems. Few attempts have been made to date to apply this technique in conventional geotechnical engineering. In this study, an algorithm that incorporates the application of a stiffness dependent time step scheme is proposed. The algorithm has been successfully used to solve 2D and 3D non-linear geotechnical engineering problems. To calibrate the developed algorithm, numerical simulations have been conducted for a strip and square footings supported by Mohr–Coulomb material. Performance of four different types of brick elements used in collapse load calculation is examined in terms of convergence speed and accuracy. In addition, the role of employing adaptive time steps in reducing the number of iterations needed for convergence is also evaluated.  相似文献   

Present-day stress and pore pressure fields in the Cuu Long and Nam Con Son Basins, offshore Vietnam   总被引：1，自引：0，他引：1  

Nguyen Thi Thanh Binh  Tomochika Tokunaga  Hoang Phuoc Son  Mai Van Binh 《Marine and Petroleum Geology》2007,24(10):607-615

Knowledge of the in situ, or contemporary stress field is vital for planning optimum orientations of deviated and horizontal wells, reservoir characterization and a better understanding of geodynamic processes and their effects on basin evolution.This study provides the first documented analysis of in situ stress and pore pressure fields in the sedimentary formations of the Cuu Long and Nam Con Son Basins, offshore Vietnam, based on data from petroleum exploration and production wells.In the Cuu Long Basin, the maximum horizontal stress is mainly oriented in NNW–SSE to N–S in the northern part and central high. In the Nam Con Son Basin, the maximum horizontal stress is mainly oriented in NE–SW in the northern part and to N–S in the central part of the basin.The magnitude of the vertical stress has a gradient of approximately 22.2 MPa/km at 3500 m depth. Minimum horizontal stress magnitude is approximately 61% of the vertical stress magnitude in normally pressured sequences.The effect of pore pressure change on horizontal stress magnitudes was estimated from pore pressure and fracture tests data in depleted zone caused by fluid production, and an average pore pressure–stress coupling ratio (ΔS_h/ΔP_p) obtained was 0.66. The minimum horizontal stress magnitude approaches the vertical stress magnitude in overpressured zones of the Nam Con Son Basin, suggesting that an isotropic or strike-slip faulting stress regime may exist in the deeper overpressured sequences.  相似文献