Application of multimedia methodology for investigation of karst water in highland regions of Ha Giang Province, Vietnam

Ha Giang is one of the largest, northern border provinces of Vietnam, consisting of four districts: Yen Minh, Quan Ba, Dong Van and Meo Vac. This province features varied karst landscape of Carboniferous–Permian limestone. The region has been recognized by UNESCO as one of the 77 geological parks in the world and the second in Southeast Asia on 3 October 2012. In the dry season, little or no rain is recorded; therefore, surface water is very scarce. For this reason, proper delineation and exploitation of the groundwater resource is critical for sustainable water supply. This has been identified as an important challenge under the scientific project KC-08-10 in the national program KC-08. Remote sensing and GIS were used to decipher the signature of karst water in the highland of Ha Giang. Information layers generated were subjected to multi-criteria evaluation using analytic hierarchy process for decision making to identify ideal locations for groundwater prospecting. The study resulted in delineation of ten zones for all regions and 18 ideal drilling sites in Tam Son Town of Quan Ba District. Drilling and resistivity soundings were performed to assess the success of the interpretation. Deep resistivity survey confirmed low resistivity (200–300 Ωm) near the identified potential sites in Tam Son Town of Quan Ba District. Further, successful drilling at site LKTS1 with a discharge of 7–9 l/s is observed, proving the potential of this methodology for rapid exploration of groundwater in water-scare karst terrains of Vietnam.     

Hyper-parameter optimization of gradient boosters for flood susceptibility analysis

Properly choosing hyper-parameters improves machine learning models' performance and reduces training time and resource requirements. In this study, we investigated the uses of the Bayesian optimization algorithm for hyper-parameter searches of two classifiers, namely LightGBM and XGBoost. The models were verified with a dataset from Vietnam, including historical flood locations from satellite images and survey data, and 11 features from three groups, namely physical, hydrological, and human-related factors. The models' performance was evaluated using Area under Receiver Operating Characteristic curves (AUC-ROC). Several strategies were applied to avoid over-fitting, and the results show that two tuned Gradient boosters reached considerably high AUC values (approximately 0.98) compared with the previous study with a similar dataset. The model interpretation was also implemented using the Shapley (SHAP) values to understand better how models work and the interactions between features. The search for optimal hyper-parameters is worth investigating in the future, particularly when there is growing work for novel optimization algorithms. The verification of such an approach is scientifically sound, and the models can be used as an alternative solution for natural hazard analysis in countries prone to hazards.     

Damage identification using inverse analysis in coupled thermo‐hydro‐mechanical problems applied to masonry dams

In this paper, we propose a method to detect the damage and estimate the degree of damage by means of a multifield‐based inverse analysis. The fields being considered are displacement, temperature, and water pressure. Furthermore, the uncertainties due to the size of the damage, the errors in the measurement data, and the errors in the model parameters are also investigated. The uncertainty due to the measurements is quantified by assuming different sources of noise in the measurements. The inverse problem is solved repeatedly by a sampling process. The uncertainties in the inverse solutions can be quantified by their probability distributions. This method can be applied to identify damages in masonry dams using coupled nonlinear thermo‐hydro‐mechanical problems.     

镉诱导长江华溪蟹(Sinopotamon yangtsekiense)心肌细胞凋亡的研究

采用急性毒性实验方法,研究了不同浓度氯化镉(0、7.25、14.50、29.00、58.00和116.00mg/L)处理不同时间(1d、3d、5d和7d)对长江华溪蟹心肌细胞凋亡的影响。结果表明,低浓度组及染毒时间较短时镉对心肌的影响不明显,但随着染毒浓度的增加和时间的延长,心肌出现空泡变性、玻璃样变性、炎细胞浸润等病理现象,在染毒7d虽然观察到疑似的凋亡细胞,但凋亡率较低;荧光显微镜未观察到心肌细胞典型的凋亡细胞核形态学变化;琼脂糖凝胶电泳图谱未出现凋亡细胞所特有的梯状条带;流式细胞术检测结果显示镉处理组细胞凋亡率增加,但与对照组相比,无统计学意义(P>0.05);Caspase-3活性也没有显著性变化(P>0.05)。因此,在本实验所选取的浓度和时间范围内,镉未诱导长江华溪蟹心肌细胞发生细胞凋亡,这与本课题组前期研究中观察到的肝胰腺、精巢组织在染毒2d、7d发生细胞凋亡的情况明显不同,这可能与心脏组织的特殊性、不同组织对镉的积累量不同有关。     

Effect of alkaline solutions on bentonite properties

The influence of alkaline aqueous solutions on the properties of bentonite was investigated to evaluate the performance of bentonitic engineered barriers when contacted with alkaline groundwater. Batch and hydraulic conductivity tests were conducted on Na-bentonite using six different alkaline aqueous solutions. For the batch tests, almost no change in the montmorillonite fraction of the bentonite was observed after reacting with alkaline solutions (pH = 8.4–13.1), regardless of the solution type. On the other hand, aluminosilicate minerals (e.g., albite) were dissolved and secondary minerals (e.g., anorthite) were formed in alkaline NaOH solutions (pH > 13). The cation (Ca or Na) concentration primarily affected the swelling properties of bentonite rather than the pH of the solution, which was comparable to the results of the hydraulic conductivity tests. For the Ca solutions, the hydraulic conductivity of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ solution (6.5 × 10^?9 cm/s) was approximately an order of magnitude lower than that of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (5.0 × 10^?8 cm/s), whereas the hydraulic conductivity to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (pH = 11.3) (5.0 × 10^?8 cm/s) was slightly higher than that to the 1 mol/L CaCl₂ solution (pH_i = 8.4) (4.4 × 10^?8 cm/s). For the NaOH solutions with pH > 13, the hydraulic conductivity of the bentonite specimen decreased with increasing Na concentration, suggesting that the effect of Na concentration was more dominant than that of permeant pH.     

Seismic Network,Seismic Activity and Seismological Research of Vietnam

In this paper,a historical review of the seismic network of Vietnam and the ability of the network to monitor earthquakes is presented.The seismic activity of Vietnam as a country of high seismictiy in the last century and since the beginning of the new century is described.The current state of seismological research in Vietnam and cooperation with institutions outside of Vietnam is outlined.     

A review of methods of parameter estimation for the extreme value type-1 distribution

Four important methods of estimating the parameters of the extreme value type-1 (Gumbel) distribution, namely: (1) moments (MMM); (2) maximum likelihood (MML); (3) maximum entropy (MME); and (4) probability weighted moments (PWM), are considered, suitable solution procedures are recommended and related problems discussed. Approximate formulae for computing the variances-covariances of the estimators by each method are given in terms of the population value of the scale parameter, and these are shown to indicate very well the performance of the related method.

A simulation study to evaluate the performance of these methods in terms of commonly used criteria, i.e. the bias, root mean square error and goodness-of-fit statistic is described. It was found that the MMM is not as good as the remaining three methods, of which the PWM is best in terms of the bias, and the MML is best in terms of the root mean square error and efficiency. The MME, by all the criteria, ranks second best and follows the MML more closely than the PWM.     

Topography and landslides in weathered granitic rock areas—Hai Van landslide in central Vietnam

Many landslides occur every year during heavy rains at the Hai Van Pass and surrounding area in central Vietnam, where granitic rocks are distributed. As is common in granite areas, these landslides often occur as small-scale flow-type and slump-type landslides. However, several horseshoe-shaped loose slopes of widths and lengths of 500 to 800 m, which incorporate these landslides, are observed on slopes across the area. These topographies resemble those formed by past and present large-scale landslides. The presence of such a topography and the repeated occurrences of landslides within this topography are rare in granite areas, where shallow flow-type landslides are generally frequent. To understand the mechanism causing the landslides in the Hai Van region, and as a support for future risk assessment, the factors and processes leading to the formation of such a topography and their relationship with these landslides must be identified and assessed. This study investigated the history of past landslide movement in the Hai Van Pass and surrounding area through observations of drill cores and outcrops, and analysis of the direction of remanent magnetism in the granitic rocks. Mineral compositions, cracks, degrees of weathering, and topographic shapes of the granitic rocks and their relationship to the landslides occurring today were also investigated. The results of the study reveal no variation in the direction of remanent magnetism in the granitic rocks in the region that would indicate disturbance of the ground due to a past large-scale landslide. No evidence of such an event could also be found both in the drill cores and the rock outcrops. Further, results of the analysis of cracks and weathering pattern confirm that the topography of the region is affected by the weathering of the granitic rocks that progresses in concentric circles of various sizes. Thus, it can be concluded that these topographies were not formed by a singular large-scale landslide of the past, but rather by a composite of relatively shallow landslides occurring on the slope of dome structures unique to granite areas, which are formed by differential weathering and denudation regulated by cracks.     

Using Geomorphological Indicators to Predict Earthquake Magnitude (MOb‒Max): A Case Study from Cao Bang Province and Adjasent Areas (Vietnam)

Geotectonics - This paper presents analysis of geomorphological indices for predicting the maximum observed earthquake (MOb?Max) in research region, conducted in three steps: (i)...     

Methodology for evaluation of potential sites for large-scale riverbank filtration

Despite being a simple and inexpensive pretreatment technology, the cost-effectiveness of riverbank filtration (RBF) depends on complex hydrogeological and hydrogeochemical variables. One of the most important issues for decision makers regarding RBF is optimal site selection. Therefore, a methodology for multicriteria site evaluation for large-scale RBF schemes is offered. The methodology is primarily designed as a prescreening method, applied over a wide area, but can also serve as a guide for evaluating individual RBF sites. To facilitate further discussion about improvements on the methodology, the reasoning behind each relevant factor and its weight in the evaluation is presented. The methodology is divided into three sequential steps through which a site can be assessed. The first step is to establish the existence of connectivity between the river and aquifer. This is termed the essential criterion, and is a binary determination of site suitability. If the site is determined to be suitable, it is then assessed via a set of quantity criteria, which measure the aquifer capacity and amount of bank filtrate that can be effectively abstracted. Lastly, water quality criteria are assessed by means of surface-water and groundwater quality. The quantity and quality criteria form a result expressed as the site suitability index (SSI), which ranges from 0 to 1, where higher scores represent increased suitability. Finally, the methodology is applied to evaluate existing sites of large-scale RBF application as a demonstration of its applicability. The success of these existing sites is compared to the calculated SSI value and discussed.