iGeoTrans – a novel iOS application for GPS positioning in geosciences

The iGeoTrans is an iOS application designed for navigation purposes for iPhone, iPad and iPod Touch. This application uses Global Positioning System (GPS), Assisted GPS system, GLONASS, Wi-Fi and Cellular Network for positioning. The iGeoTrans has included datum transformations and map projections that enable users to convert the collected data between different coordinate systems for almost all areas in the world. In addition, other features are also included such as distance, area measurements, and GPS results could be exported to the AutoCad dxf format for GIS softwares. The average horizontal and vertical root mean square errors (RMSEs) for the static test are around 4.11 and 3.51?m, respectively. The horizontal RMSE for the dynamic outdoor test is around 2.72?m. The iGeoTrans application can be used to support surveying, mapping and geosciences fieldworks for any area in the world.     

混合润湿孔隙介质中油自吸实验研究

混合润湿孔隙介质普遍存在, 使得多相流体渗流过程十分复杂, 但对其研究和认识至今仍很肤浅, 是油气运移成藏、剩余油气分布等方面研究中必须解决的关键难题。本文通过对饱和水的混合润湿模型进行油自吸实验, 观察不同混合润湿程度条件下油自吸运移过程, 分析认识混合润湿孔隙介质中多相渗流的机理。实验结果表明, 在混合润湿孔隙介质中油是否能够自发地运移与介质中亲油颗粒的比例关系密切, 但并非简单的单调变化关系。研究认为, 亲油颗粒与亲水颗粒随机分布, 导致多种与喉道配位颗粒的亲油-亲水关系, 当亲油颗粒比例占优才表现为亲油喉道。机理上, 混合润湿孔隙介质中油自吸运移的发生与否及程度取决于亲油喉道在空间上的连通程度, 后者与孔隙介质中亲油颗粒比例相当。仅有当孔隙介质中亲油颗粒足够多, 且组成的亲油喉道能够相互接触形成连续亲油通道时, 油才能够通过自吸运移进入多孔介质。     

基于GIS的移动蜂窝网络场强预测研究

利用GIS能将蜂窝网络数据库中空间与非空间数据相结合的优势,来提供必要的参数,以更准确地预测蜂窝网络的覆盖强度,研究设计了一种基于COST-231-Walfisch-Ikegami的GIS模型,用来预测越南胡志明市移动蜂窝网络的信号强度,该模型可以帮助确定无线电的视距和非视距情况。该模型对路径方向损失、多屏衍射损耗和阴影增益进行了更精确的预测。实验中采用的地图比例尺是1∶2 000,采用的平均楼层高度为3 m。统计结果表明,该GIS模型预测的路径损耗克服了每个基站的实测路径损耗,在市区可以用来预测微蜂窝覆盖范围。     

A new method for estimating driven pile static skin friction with instrumentation at the top and bottom of the pile

A numerical technique is presented to estimate ultimate skin friction of a driven pile using instrumentation installed at the top and bottom of a pile. The scheme is based on an analytical solution of the 1D wave equation with static skin friction and damping along with a genetic algorithm for solution. Specifically, acceleration and strains measured at both the top and bottom of the pile are used to develop an observed Green's function, which is matched to an analytical Green's function, which is a function of secant stiffness and viscous damping. Requiring 1–3 s of analysis time per blow, the algorithm provides a real time assessment of average skin friction along the pile. The technique was applied to four driven piles having ultimate skin frictions varying from 700 to 2000 kN, with the predicted skin frictions generally consistent with measured static load test results.     

The Cenozoic on-shore basins of Northern Vietnam: Biostratigraphy,vertebrate and invertebrate faunas

A first account of paleontological data from three Cenozoic on-shore basins in Northern Vietnam, i.e. the Na Duong, Cao Bang, and Hang Mon basins, reveals a rich fossil fauna and flora of supposed Oligocene age, offering a great potential for taxonomic, paleoenvironmental, and paleobiogeographic studies. Two excavation campaigns unearthed well-preserved fossil remains of mammals, crocodiles, at least six turtle species, some 20 fish taxa, some other 20 mollusc species, and different plant remains. The majority of these taxa are regarded as new to science. However, close affinities to modern faunas of northern Southeast Asia demonstrate the importance of these fossils for an evaluation of the biological history of this modern biodiversity hot spot. Moreover, the fossil assemblages may help to disentangle the intricate Cenozoic tectonic evolution of Southeast Asia by application of paleobiogeographic modelling. Finally, the discovery of complex paleo-food-webs and the presence of several taxa indicative of certain ecological conditions provide a solid base for autecologic, synecologic and paleoclimatic studies. The potential biostratigraphic value of the macrofauna has to be demonstrated yet, as evolutionary concepts for most of the respective groups have not been proposed to date.     

Physical constraints on impact melt properties from Lunar Reconnaissance Orbiter Camera images

Impact melt flows exterior to Copernican-age craters are observed in high spatial resolution (0.5 m/pixel) images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). Impact melt is mapped in detail around 15 craters ranging in diameter from 2.4 to 32.5 km. This survey supports previous observations suggesting melt flows often occur at craters whose shape is influenced by topographic variation at the pre-impact site. Impact melt flows are observed around craters as small as 2.4 km in diameter, and preliminary estimates of melt volume suggest melt production at small craters can significantly exceed model predictions. Digital terrain models produced from targeted NAC stereo images are used to examine the three-dimensional properties of flow features and emplacement setting, enabling physical modeling of flow parameters. Qualitative and quantitative observations are consistent with low-viscosity melts heated above their liquidii (superheated) with limited amounts of entrained solids.     

Characteristics of groundwater in karstic region in northeastern Vietnam

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.     

Complex deposits in the Lo Gam structure,northeastern Vietnam: mineralogy,geochemistry, and formation conditions

The Pb–Zn deposits in the Lo Gam structure, northeastern Vietnam, account for>80% of all the Pb and Zn resources of Vietnam. All the deposits make up four isolated ore districts (Thai Nguyen, Cho Don, Cho Dien, Na Son), which can be combined in one metallogenic zone extending for >100 km from southeast to northwest. The Pb–Zn deposits in all the ore districts show some similarity to stratiform (Mississippi-type) deposits: confinement to Devonian carbonate sediments; localization at the intersection of faults of different orientations; vein and stockwork (pocket-vein-disseminated) morphology of the mineralized zones; evidence for hydrothermal-metasomatic formation (carbonate-rock marbleization, quartz–carbonate veins, etc.); and low and moderate mineralization temperatures (<250 °C). On the other hand, some differences from stratiform deposits are observed: widespread occurrence of Permo-Triassic igneous rocks in the above ore districts; absent tabular orebodies, which are typical of stratiform deposits; large set of trace elements (In, Bi, Sb, Au, Ag, Cu, Cd) not typical of stratiform deposits; and an endogenic primary source, as evidenced by the isotope composition of sulfur (δS³⁴= 2.68‰), which is close to meteoritic, and the set of trace elements, which are mainly of deep genesis. All this indicates that the above Pb–Zn deposits within the carbonate units are low-and moderate-temperature hydrothermal-metasomatic products associated with active magmatism which took place in this region in the Permo-Triassic.The differences in the mineral composition of the deposits, as well as in the trace-element set and contents at different deposits, clearly indicate an intricate ore formation process and the relation of the deposits with magmatism of different compositions. The simple mineral composition and the limited set of trace elements (Cd, Ag, Sb, As) at the Lang Hich deposit are closer to the characteristics of stratiform deposits. Also, manifestations of magmatism are almost absent here. On the contrary, unusually high (ppm) In (75.8), Sn (307.5), Cu (1080), Ag (157.7), Bi (99), and As (13,650) contents were observed at the deposits of the Cho Don and Cho Dien districts, with widespread granitoid magmatism in the Phia Bioc complex. Rare-earth mineralization (orthite) and high Mo, Re, and Rb contents at the deposits of the Na Son district are probably due to the widespread occurrence of stratified alkaline volcanics and their subvolcanic analogs, which belong to the Pla Ma complex (ξγPZ₂ pm).     

Origin and extent of fresh groundwater, salty paleowaters and recent saltwater intrusions in Red River flood plain aquifers, Vietnam

A model has been established on the origin and extent of fresh groundwater, salty paleowaters and saltwater from recent seawater intrusions in the Red River flood plain in Vietnam. This was done with geological observations, geophysical borehole logging and transient electromagnetic methods. Salt paleowater is present up to 50–75?km from the coastline, with occurrence controlled by the Holocene transgression. A density-driven leaching of salty porewater has occurred from high-permeability Holocene sediments into underlying Pleistocene deposits, whereas diffusion has dominated in low-permeability layers. In the Pleistocene aquifer, the highest content of dissolved solids is found below two intrinsic valleys with Holocene marine sediments and along the coastline. Recent intrusion of saltwater from the South China Sea is observed in shallow groundwater 35?km inland, probably a result of transport of salty water inland in rivers or leaching of paleowaters from very young near-coast marine sediments. The observed inverted salinity profile, with high saline water overlying fresher groundwater, has been formed due to the global eustatic sea-level changes during the last 8,000–9,000?years. The proposed model may therefore be applicable to other coastal aquifers, with a proper incorporation of the local geological environments.