Radio Observation of Solar-Activity-Related mHz Oscillations     

N. V. Hiep  P. T. Nhung  P. Darriulat  P. N. Diep  P. T. Anh  P. N. Dong  D. T. Hoai  N. T. Thao 《Solar physics》2014,289(3):939-950

The VATLY radio telescope, operating at 1.415 GHz in Ha Noi, has been used to track the Sun in the summer?–?autumn months in 2012. Evidence has been obtained for solar activity, including occasional flares and variable oscillations with amplitudes at the percent level and periods of about 6 min. Comparison with data collected at the same frequency by the Learmonth Observatory in Australia suggests that the observed oscillations were associated with solar activity. A joint analysis of both data sets is presented, evaluating the correlations between them. We describe the common and different main features.  相似文献   

Identification of anthropogenic radionuclides in the Song Hong (Red) and Song Da (Black) river basins of Vietnam     

Nguyen Trung Minh  L. L. Kashkarov  Cu Sy Thang  Doan Dinh Hung  Nguyen Duc Chuy  Nguyen Trung Kien  Nguyen Thi Kim Thuong  Nguyen Thi Thu  Nguyen Van Pho 《Geochemistry International》2014,52(11):925-938

The concentration and distribution of U were measured in zircon samples separated from the streambed sediments collected at different sites along the rivers of northern Vietnam using semiconductor alpha spectrometry and alpha- and fission-track autoradiography. Based on the absolute U content and distribution, we distinguished two groups of zircon grains of different origin. Group 1 zircons have relatively low and uniform U contents ranging from 280 to 440 μg/g. Group 2 zircons are characterized by heterogeneous U distribution and U contents ranging from 490 to 2040μg/g. The determination of absolute alpha activity values and alpha spectrometric characteristics for a number of group 2 zircon grains indicated the presence of relatively short-lived alpha-emitters. These radionuclides are probably ²¹⁰Po, ²³²U, ²³⁶Pu, ²⁴¹Am, and ²⁴³Am, and all of them can originate exclusively from anthropogenic sources. A comparison of the observed alpha activity values for group 2 zircons with those of group 1 zircons and zircons separated from the suspended colloids in river water samples provided conclusive evidence for traces of anthropogenic radioactive contamination in the Lao Cai, Yen Bai, Tuyen Quang, Thac Ba, Viet Tri, and Hanoi streams flowing in the Song Hong (Red) and Song Da (Black) river basins of northern Vietnam and sourced in the southern regions of the neighboring state.  相似文献   

Triggered earthquake study in Tranh River No. 2 (Vietnam) Hydropower Reservoir     

Cao Dinh Trieu  Cao Dinh Trong  Le Van Dung  Thai Anh Tuan  Dinh Quoc Van  Ha Vinh Long 《Journal of the Geological Society of India》2014,84(3):319-325

This article presents the results of investigating triggered earthquakes in the vicinity of Tranh River No.2 Hydropower Reservoir in recent years. It is found that earthquakes occurred in the vicinity of Tranh River Hydropower Reservoir, probably associated with the Trà My — Trà BÓng fault zone. It is estimated that this fault is capable of hosting an earthquake of M~6.1. The ‘b’ value for this earthquake sequence is 0.83, which is higher than the regional ‘b’ value of 0.60. We estimate that the return period of earthquakes of M=4.5, 5.0, 5.5 and 6.0 is 11, 29, 76 and 198 months respectively. On October 22, 2012 an earthquake M_S=4.6, I₀=6.0 (MSK-64) occurred at 13:41:28 hrs GMT. The epicenter of the earthquake was located at a distance of 5.5 km away from the center of the dam towards the west. The focal depth is about 4.5 km, and the rupture length is about 1.8 km.  相似文献   

Optimal choice of a surveillance operation using information theory     

Duc H. Le  Albert C. Reynolds 《Computational Geosciences》2014,18(3-4):505-518

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Holocene estuarine sediments as a source of arsenic in Pleistocene groundwater in suburbs of Hanoi,Vietnam     

Keisuke Kuroda  Takeshi Hayashi  Ayako Funabiki  An Thuan Do  Vu Duc Canh  Tran Thi Viet Nga  Satoshi Takizawa 《Hydrogeology Journal》2017,25(4):1137-1152

Groundwater pollution by arsenic is a major health threat in suburban areas of Hanoi, Vietnam. The present study evaluates the effect of the sedimentary environments of the Pleistocene and Holocene deposits, and the recharge systems, on the groundwater arsenic pollution in Hanoi suburbs distant from the Red River. At two study sites (Linh Dam and Tai Mo communes), undisturbed soil cores identified a Pleistocene confined aquifer (PCA) and Holocene unconfined aquifer (HUA) as major aquifers, and Holocene estuarine and deltaic sediments as an aquitard layer between the two aquifers. The Holocene estuarine sediments (approximately 25–40 m depth, 9.6–4.8 cal ka BP) contained notably high concentrations of arsenic and organic matter, both likely to have been accumulated by mangroves during the Holocene sea-level highstand. The pore waters in these particular sediments exhibited elevated levels of arsenic and dissolved organic carbon. Arsenic in groundwater was higher in the PCA (25–94 μg/L) than in the HUA (5.2–42 μg/L), in both the monitoring wells and neighboring household tubewells. Elevated arsenic concentration in the PCA groundwater was likely due to vertical infiltration through the arsenic-rich and organic-matter-rich overlying Holocene estuarine sediments, caused by massive groundwater abstraction from the PCA. Countermeasures to prevent arsenic pollution of the PCA groundwater may include seeking alternative water resources, reducing water consumption, and/or appropriate choice of aquifers for groundwater supply.  相似文献   

Climate change and groundwater resources in Mekong Delta,Vietnam          下载免费PDF全文

Duong D Bui  Nghia C Nguyen  Nuong T Bui  Anh T T Le  Dao T Le 《地下水科学与工程》2017,5(1):76-90

Groundwater resources have considerable influences on the human population and socioeconomic development of Vietnam and the Mekong River Delta (MRD). This paper presents an overview of the relationship between climate change and groundwater in the MRD, including the challenges, strategies and technical measures. Our results showed that groundwater levels are related to other climate and hydrological variables (i.e., rainfall, river levels, etc.); therefore, the impacts of climate change on the groundwater resources of the Mekong delta are significant, especially on groundwater recharge. Based on the results of this study, it is recommended that groundwater development in the future should focus on reducing groundwater harvesting, enhancing groundwater quantity by establishing artificial works and exploiting surface water. This study suggests that the Artificial Neural Network (ANN) model is an effective tool for forecasting groundwater levels in periods of 1 month and 3 months for aquifers in the natural and tidal regime areas of the delta.  相似文献