Rare-earth elements in Luochuan loess section,Shaanxi province     

Qizhong Wen  Suhua Yu  Fuqing Sun  Yuqi Wang  Bingru Chen  Shude Tu  Jingxin Sun 《中国地球化学学报》1985,4(2):172-180

TheΣ REE in loesses of different ages in the Luochuan section shows a narrow range of variation, indicating the homogeneity of loessic materials in chemical composition. The REEs in loess are concentrated mainly in silt-sized detrital minerals. Loesses and paleosols of different ages all are relatively enriched in rare-earth elements of the Ce family, and show similar REE distribution patterns. The fractionation among various REEs in the loess is different from that in morainic, marine and lacustrine sediments, but is similar to that in sand samples from deserts in Northwest China. The ratios of Ce/Ce* and Eu/Eu* reflect that the provenance of loessic materials and their accumulating area are all in an oxidation environment with weakly basic mediums under arid or semi-arid climate.  相似文献   

The influence of residual stresses on rock hardness     

P. Habib  Nguyen Minh Duc 《Rock Mechanics and Rock Engineering》1974,6(1):15-24

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Photometric separation of the bulge and disc components of spirals using CCD imaging     

M. Prieto  J. Cepa  C. Muñoz Tuñon  J. E. Beckman  A. M. Varela 《Astrophysics and Space Science》1990,170(1-2):225-229

We present high-resolution CCD images of a sample of spiral galaxies, in infrared photometric bands, obtained at the Cassegrain focus of the 1 m Jacobus Kapteyn Telescope, La Palma. A decisive advantage of the linearity in these images is that we can effect a reliable separation of the light from bulge and disc. We describe possible applications of the results to determine the structure of the bulges.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

Soil salinity and sodicity in a shrimp farming coastal area of the Mekong Delta,Vietnam     

Nguyen Tho  N. Vromant  Nguyen Thanh Hung  L. Hens 《Environmental Geology》2008,54(8):1739-1746

Soil salinity and sodicity are environmental problems in the shrimp farming areas of the Cai Nuoc district, Ca Mau province, Vietnam. In 2000, farmers in the district switched en masse from rice cropping to shrimp culture. Due to recent failure in shrimp farming, many farmers wish to revert to a rotational system with rice in the wet season and shrimps in the dry season. So far, all their attempts to grow rice have failed. To assess soil salinity and sodicity, 25 boreholes in shrimp ponds were analysed in four consecutive seasons from 2002 to 2004. The results showed that soil salinity was quite serious (mean EC_e 29.25 dS m⁻¹), particularly in the dry season (mean EC_e 33.44 dS m⁻¹). In the wet season, significant amounts of salts still remained in the soil (mean EC_e 24.65 dS m⁻¹) and the highest soil salinity levels were found near the sea. Soil sodicity is also a problem in the district (exchangeable sodium percentage range 9.63–72.07%). Sodicity is mainly a phenomenon of topsoils and of soils near the sea. Both soil salinity and sodicity are regulated by seasonal rainfall patterns. They could together result in disastrous soil degradation in the Cai Nuoc district.  相似文献   

Modification of the Bouwer and Rice Method to a Cutoff Wall with a Filter Cake     

The-Bao Nguyen  Chulho Lee  Sewon Kim  Hangseok Choi 《Ground water》2010,48(6):898-902

The Bouwer and Rice method is a line-fitting method used to estimate the hydraulic conductivity of an aquifer by means of a slug test. When considering a relatively impermeable layer, called a filter cake, which may form at the interface between a cutoff wall and the natural soil formation, the assumptions of the Bouwer and Rice method are violated. A modification of the Bouwer and Rice method is proposed that incorporates the concept of a flow net, whereby the geometry of the cutoff wall and filter cake is effectively considered in estimating the hydraulic conductivity of a vertical cutoff wall.  相似文献   

An Improved Formula of Fundamental Resonance Frequency of a Layered Half-Space Model Used in H/V Ratio Technique     

Tran Thanh Tuan  Pham Chi Vinh  Matthias Ohrnberger  Peter Malischewsky  Abdelkrim Aoudia 《Pure and Applied Geophysics》2016,173(8):2803-2812

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Space–time changes in hydrological processes in response to human activities and climatic change in the south China     

Xinjun Tu  Qiang Zhang  Vijay P. Singh  Xiaohong Chen  Chun-Ling Liu  Shao-Bo Wang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(6):823-834

Due to the influence of climate change and human activities, more and more regions around the world are nowadays facing serious water shortages. This is particularly so with the Guangdong province, an economically prosperous region in China. This study aims at understanding the abrupt behavior of hydrological processes by analyzing monthly precipitation series from 257 rain gauging stations and monthly streamflow series from 25 hydrological stations using the likelihood ratio statistic and schwarz information criterion (SIC). The underlying causes of the changing properties of hydrological processes are investigated by analyzing precipitation changes and information of water reservoirs. It is found that (1) streamflow series in dry season seems to exhibit abrupt changes when compared to that in the flood season; (2) abrupt changes in the values of mean and variance of hydrological variables in the dry season are more common than those in the streamflow series in the flood season, which implies that streamflow in the dry season is more sensitive to human activities and climate change than that in the flood season; (3) no change points are identified in the annual precipitation and precipitation series in the flood season. Annual streamflow and streamflow in the flood season exhibit no abrupt changes, showing the influence of precipitation on streamflow changes in the flood season. However, streamflow changes in the dry season seem to be heavily influenced by hydrological regulations of water reservoirs. The results of this study are of practical importance for regional water resource management in the Guangdong province.  相似文献   

Evaluation of Two Low‐Cost–High‐Performance Adsorbent Materials in the Waste‐to‐Product Approach for the Removal of Pesticides from Drinking Water     

Pham Thi Thuy  Nguyen Viet Anh  Bart van der Bruggen 《洁净——土壤、空气、水》2012,40(3):246-253

This study evaluates the performance of two low cost and high performance adsorption materials, i.e., activated carbon produced from two natural waste products: Bamboo and coconut shell, in the removal of three pesticides from drinking water sources. Due to the fact that bamboo and coconut shell are abundant and inexpensive materials in many parts of the world, they respond to the “low‐cost” aspect. The adsorption capacities of two local adsorbents have been compared with commercial activated carbon to explore their potential to respond to the “high quality” aspect. Two pesticides were selected, namely dieldrin and chlorpyrifos, because they are commonly used in agriculture activities, and may remain in high concentrations in surface water used as drinking water sources. The results indicate that the adsorption of pesticides on activated carbons is influenced by physico‐chemical properties of the activated carbon and the pesticides such as the presence of an aromatic ring, and their molar mass. The activated carbon produced from bamboo can be employed as low‐cost and high performance adsorbent, alternative to commercial activated carbon for the removal of pesticides during drinking water production. The performance of activated carbon from bamboo was better due to its relatively large macroporosity and planar surface. The effect of adsorbent and pesticide characteristics on the performance was derived from batch experiments in which the adsorption behavior was studied on the basis of Freundlich isotherms.  相似文献   

Groundwater investigation on sand dunes area in southern part of Vietnam by magnetic resonance sounding     

Nguyen V. Giang  Tang D. Nam  Maksim Bano 《Acta Geophysica》2012,60(1):157-172

In the last five years, magnetic resonance sounding (MRS), as a non-invasive geophysical method, has emerged as a new technique for ground water investigation in Vietnam. In this paper, we present the general theoretical basis of this method together with acquisition, processing, and interpretation of the MRS data. We show a case study of MRS surveys in sand dunes area in order to characterize aquifers situated in the southern part of Vietnam. From the interpretation of MRS soundings we delimited an aquifer layer in the subsurface with strong lateral variations for which we determined the depth at 44 m and water content between 3% and 9.5%. The longitudinal relaxation constant T*₁ is about 250 m s, while the transverse relaxation T*₂ is between 150–200 m s. That indicates fine to medium grain size and thus low to medium hydraulic permeability. These results are confirmed by the observations from the well LK1 between 45 to 70 m. The results of other MRS measurements showed the presence of a low water bearing aquifer and were confirmed by the observations in two other wells.  相似文献   

A cross-system analysis of sedimentary organic carbon in the mangrove ecosystems of Xuan Thuy National Park, Vietnam   总被引：1，自引：0，他引：1  

Nguyen Tai Tue  Nguyen Thi NgocTran Dang Quy  Hideki HamaokaMai Trong Nhuan  Koji Omori 《Journal of Sea Research》2012,67(1):69-76

A cross-system analysis of bulk sediment composition, total organic carbon (TOC), atomic C/N ratio, and carbon isotope composition (δ¹³C) in 82 surface sediment samples from natural and planted mangrove forests, bank and bottom of tidal creeks, tidal flat, and the subtidal habitat was conducted to examine the roles of mangroves in sedimentation and organic carbon (OC) accumulation processes, and to characterize sources of sedimentary OC of the mangrove ecosystem of Xuan Thuy National Park, Vietnam. Sediment grain sizes varied widely from 5.4 to 170.2 μm (mean 71.5 μm), with the fine sediment grain size fraction (< 63 μm) ranging from 11 to 99.3% (mean 72.5%). Bulk sediment composition suggested that mangroves play an important role in trapping fine sediments from river outflows and tidal water by the mechanisms of tidal current attenuation by vegetation and the ability of fine roots to bind sediments. The TOC content ranged from 0.08 to 2.18% (mean 0.78%), and was higher within mangrove forests compared to those of banks and bottoms of tidal creeks, tidal flat, and subtidal sediments. The sedimentary δ¹³C ranged from − 27.7 to − 20.4‰ (mean − 24.1‰), and mirrored the trend observed in TOC variation. The TOC and δ¹³C relationship showed that the factors of microbial remineralization and OC sources controlled the TOC pool of mangrove sediments. The comparison of δ¹³C and C/N ratio of sedimentary OC with those of mangrove and marine phytoplankton sources indicated that the sedimentary OC within mangrove forests and the subtidal habitat was mainly composed of mangrove and marine phytoplankton sources, respectively. The application of a simple mixing model showed that the mangrove contribution to sedimentary OC decreased as follows: natural mangrove forest > planted mangrove forest > tidal flat > creek bank > creek bottom > subtidal habitat.  相似文献