Cumulative Frequency Curves Research Articles

Ecosystem service supply–demand ratio zoning and thresholds of the key influencing factors in the Pearl River Delta, China

ContextHuman demand for natural resources continues to increase owing to climate change and population growth. The supply capacity of ecosystem services has also declined drastically, posing a severe threat to the long-term sustainability of human society.ObjectivesTaking the fast-urbanized Pearl River Delta (PRD) as the study area, the specific research objectives of this study were to intuitively reveal the spatial distribution of ecosystem service supply–demand relationships in rapid urbanization and explore the dominant influencing factors and their impact process on ecosystem service supply–demand relationships.MethodsIt zoned the ecological space based on the ecosystem service supply–demand ratio (ESSDR) evaluated by six typical ecosystem services. And then, the Geographical Detector model, Structural Equation Modeling and regression analysis were used to explore the ranking and threshold effects of influencing factors of ESSDR.Results(1) From 2000 to 2020, the ESSDR in the central PRD deteriorated, whereas the ESSDR in the remote areas of the PRD was further optimized. Stable grading eigenvalues of the ESSDR were found based on cumulative frequency curves from 2000 to 2020. (2) Green density (GD) and land development size (LDS) were the dominant natural and social factors influencing ESSDR in the PRD, respectively. (3) There were two thresholds in the impact process of GD (21% and 66%) and LDS (8% and 54%) on the ESSDR, which matched the gradients of urban, developing urban, and rural areas.ConclusionsThere are certain thresholds in the ESSDR responding to land use change. The focus should be on the imbalance in areas with GD < 21% or LDS > 54% and protective measures should be strengthened in areas with GD > 66% or LDS < 8%.

Two synergistic types of muscles were detected during forearm rotation exercise by T2 cumulative frequency curves using 0.2T magnetic resonance imaging.

The purpose of this study was the detection and characterization of synergistic muscle activity. Using T2-map MRI, T2 values for 10 forearm muscles in 11 healthy adult volunteers were obtained in the resting state and after isotonic forearm supination and pronation exercises with the elbow extended. T2 was normalized by Z = (T2e-T2r)/SDr, where T2e was T2 after exercise, while T2r and SDr were the reference values of 34ms and 3ms, respectively. Using the cumulative frequency curves of Z values (CFZ), we detected 2 and 3 synergistic muscles for supination and pronation, respectively, and divided these into 2 types, one activated by exercise strength dependently, and the other, independent of exercise strength, activated by only a smaller fraction of the participants. We also detected co-contraction for the supination. Thus, CFZ is a useful visualization tool to detect and characterize not only synergistic muscle, but also co-contraction muscle.

A laboratory investigation into tyre-pavement contact behaviour of passenger car

ABSTRACT Understanding tyre-pavement contact behaviour helps to address pavement skid resistance which is highly related to traffic safety. In this study, a pressure distribution measurement system was employed to investigate the tyre-pavement contact behaviour of a passenger car in laboratory. The pavement macrotexture was characterised by a 3D scanner and the sand patch method. It was shown that the asphalt pavement gradation, the vertical force, the tyre inclination angle and the tyre pressure significantly have effects on tyre-pavement contact behaviour. The cumulative frequency curve of tyre-pavement contact stress can be well fitted by the Boltzmann model. Under the vertical force of 4 kN, the average contact stress increases significantly when the inclination angle exceeds 3.2°, while an inclination angle within 3.2° has almost no effect. The force on the rib on the side that the tyre leans to changes the most with the inclination angle. As the tyre pressure increases, the average contact stress increases linearly and the contact area decreases linearly. With the increase of tyre pressure, the contact region gradually shrinks towards the middle and the contact force slightly increases in the middle and decreases at the edges.

Spatial Distribution of Arsenic in the Aksu River Basin, Xinjiang, China: The Cumulative Frequency Curve and Geostatistical Analysis

The quality of drinking water is crucial for human health and the sustainable development of societies. The Aksu River Basin, a typical inland river system, has areas where groundwater arsenic levels exceed safe drinking water standards (i.e., arsenic concentrations greater than 10 μg/L). Identifying the causes of high arsenic levels in the basin’s groundwater requires further study. Analyzing the hydrogeochemical composition of the Aksu River basin helps us to understand the spatial distribution of groundwater environments and locate areas with dangerously high arsenic levels. In this research, we collected 196 groundwater samples from along the river. Out of these, 38 samples had arsenic levels above 10 μg/L, which represents 19.4% of the total samples collected. By examining the slope changes in the cumulative frequency curves of major ion ratios and employing geostatistics (specifically, the Kriging interpolation), and taking into account the environmental characteristics of the entire basin, we divided the study area into five sub-regions (Zone I through Zone V). The geostatistical analysis showed a significant spatial variability in groundwater arsenic levels, with a clear spatial correlation. Our findings demonstrate that arsenic concentrations in the Aksu River basin’s groundwater vary widely, with Zones II and III—mainly located in the northeastern part of the basin and in Awat County—being hotspots for high-arsenic water. Factors such as a weak reducing environment, intense evaporation, strong cation exchange, and the low-permeability recharge of surface water contribute to the accumulation of arsenic in the basin’s groundwater. The results of this study are vital for assessing the risk of arsenic contamination in groundwater in similar basins and for identifying critical areas for further investigation and research.

Textural Characteristics and Depositional Regime of the Shitalakshya River Sediments, Bangladesh

This study analyzes the depositional regime and textural properties of the sediments from the Shitalakshya River in Bangladesh, enabling us to comprehend how these sediments evolved in a river environment. For this investigation, 30 representative samples were taken from the Shitalakshya River, and their textures were analyzed. The cumulative frequency curve is obtained by using semilog graph paper to plot particle size (in phi scale) against cumulative percent. The statistical parameters such as median (Md), mode (Mo), mean (MZ), standard deviation (σi), skewness (SKi), and kurtosis (KG) were calculated using the percentile of phi values (1%, 5%, 16%, 25%, 50%, 75%, 84%, and 95%). The cumulative curves show that the sediments are deposited through the traction population (1.90%), saltation population (75.64%), and suspension population (22.46%). The median value varies between 0.7Ø and 4.85Ø, with an average of 2.738Ø indicating coarse sand to coarse silt. The analyzed samples have unimodal, bimodal, and polymodal distribution, which indicates the sediments are carried by different tributaries and distributaries in the Sitalakshya River system. The range of 1.46Ø–4.05Ø represented by the observed mean value suggests sand with medium to extremely fine grains. Most of the sediments indicate moderate sorting, which is shown by the standard deviation (sorting), which ranges from 0.399Ø to 1.48Ø. The skewness value ranges between −0.01Ø and 0.66Ø, suggesting near symmetrical skewed, while the kurtosis value ranges from 0.54Ø to 1.87Ø, indicating the sediments are 20% leptokurtic, 20% mesokurtic, and 60% platykurtic. According to the CM plot, the Shitalakshya River is mostly deposited in the area between the rolling and suspension fields, indicating a transportation regime of saltation. The scatter plots of skewness versus sorting and graphic mean versus sorting indicate that the sediments fall within the river sand zone. The energy process discriminant functions of the sediments show that they were deposited by a fluvial process.

Identification of the Sediment Movement Mechanism via Grain Size and Shape: A Case Study of a Beach in Eastern Hainan Island in South China

This paper used dynamic image analysis (DIA) to analyze the grain size and shape data of beach surface sediments in Bao’ding Bay, eastern Hainan Island, China, and explored the effects of sediment transport modes and beach morphology on the grain size–shape trend curves. This paper adopted a method of combining grain size cumulative frequency curves and grain size–shape trend curves to identify three sediment transport modes: suspension, saltation, and traction, and analyzed the characteristics of the grain size–shape trend curves under different beach morphologies (reflective, intermediate, and dissipative). This paper found that the grain size–shape trend curves can effectively indicate the sediment transport modes and improve the accuracy of subpopulation division; the grain size–shape trend curves showed different distribution characteristics in the cross-shore and longshore directions, which are closely related to the beach’s morphology and sediment transport direction. This paper provides a new method and idea for studying beach sediment transport and sedimentary environment using sediment grain size and shape data.

Research on right-turn warning and control technology for urban intersection bus

This paper proposes a right-turn warning and control technology for urban intersection buses to address the safety issues associated with right turns. Firstly, the safety of bus-vehicle, non-motorized vehicle, and pedestrian conflicts is studied, and conflict levels are defined using the K-means clustering algorithm, trajectory smoothing, and the 85th percentile cumulative frequency curve method. Secondly, a measurement system based on the OpenCV laser triangulation method and velocity sensors, combined with YOLO v7 for target classification and recognition, is used to calculate the Time to Collision (TTC) value. A microcontroller receives the TTC signal to generate signals for vehicle deceleration or turning, thereby avoiding collisions. SUMO scene simulation is conducted for validation. The results show that the proposed system enables buses to predict traffic conflicts in advance, issue early warnings, and take evasive actions, thus reducing accident rates. This research provides inspiration for related studies on the safety of right turns for urban intersection buses both domestically and internationally.

Assessing ecosystem health of floodplain lakes using an Integrated Bioassessment Index

Lakes within river-floodplain ecosystems are key biodiversity refuges majorly threatened by eutrophication and hydrologic river-lake fragmentation. However, an integrative index, specifically designed to comprehensively assess the health of floodplain lakes, considering multiple biological taxa and major stressors, remains unavailable. Based on biological data collected from 68 isolated lakes in the eastern plain lake region of China, we constructed a reliable index for assessing floodplain lake ecosystem health: Integrated Bioassessment Index (L-IBAI). The L-IBAI consists of components of overall health and species diversity, eutrophication, and hydrological connectivity and water level regimes. To construct the L-IBAI, we firstly used the observed species (SO)-area (A) model to predict the expected species richness (SE), and then developed observed to expected indices by calculating the SO/SE ratio for fish (F-O/E-SA) and benthos (B-O/E-SA). The health level thresholds for the other four indices, namely the ratio of Secchi depth and water depth (ZSD/ZM), chlorophyll a in phytoplankton (Chl a), the percent of rheophile fish species, and emergent macrophytes coverage, were determined using cumulative frequency curves. The final L-IBAI score was obtained by summing the weighted values of the three components mentioned earlier. The L-IBAI can significantly discriminate rural from urban lakes, and is a reliable index for assessing lake ecosystem health. Moreover, we developed three simplified three-index integrated bioassessment indices, which consists of three indices belonging to the three elements are also effective. The developed L-IBAI is flexible to be extended and applied to other floodplain lakes, and outcomes of health assessments for the eastern plain lakes in China helped to identify conservation and restoration priorities.

System analysis and experimental investigation of a pendulum-based wave energy converter

Global economic development and environmental protection requirements are increasing the demand for renewable energy rapidly. Wave energy converters are a hotspot in research, and many designs have been proposed. Pendulum-based wave energy converters, because of their sealed structure and high reliability, are drawing researchers' attention. This article considers the concept of a Vertical Axis Parametric Pendulum Wave Energy Converter (VAPPWEC) and focuses mainly on the characteristics of the pendulum system. The dynamic function of the pendulum is proposed. A new evaluation indicator, Cumulative Frequency curves of Angular Velocity (CFAV) is introduced to analyze pendulum motion accurately and evaluate the harvesting performance conveniently. The model test shows the parametric resonance zone of the pendulum with a notable boundary and the pendulum's stability under power take-off (PTO) damping. Additionally, a large-range analysis method based on the Prescribed Excitation Model (PEM) is proposed, and the output power is assessed. Linear damping performs better than constant damping, with a maximum capture width ratio of 39.05%.

Environmental geochemical baseline determination and pollution assessment of heavy metals in farmland soil of typical coal-based cities: A case study of Suzhou City in Anhui Province, China

Soil is the foundation of agricultural green development and human survival; the study of local environmental geochemical baselines can guide soil management and ensure the safe use of soil. In this study, a total of 100 shallow farmland soil samples were collected in each township of Yongqiao District, Suzhou City, Anhui Province, China. Herein, the contents of 10 heavy metal elements including As, Hg, Cd, Pb, Cr, Cu, Mn, Ni, Zn and Fe were determined. In addition, the geochemical baseline of heavy metals was calculated based on the relative cumulative frequency curve method, and the soil pollution status was evaluated. The results show that the average contents of As, Hg, Cd, Cu, Mn and Zn exceeded the soil background values of Anhui Province by 3.82%–64.74% (1.04–1.65 times), meanwhile, the average contents of Pb and Cr were lower than the soil background values of Anhui Province. The average contents of Cd, Cr, Cu, Mn and Ni exceeded the Chinese soil background values by 1.61%–64.74% (0.98–1.65 times). The geochemical baseline values of As, Hg, Cd, Pb, Cr, Cu, Mn, Ni, Zn and Fe were 9.585 mg/kg, 0.028 mg/kg, 0.112 mg/kg, 21.59 mg/kg, 53.66 mg/kg, 19.31 mg/kg, 543.8 mg/kg, 24.93 mg/kg, 50.57 mg/kg and 2.654%, respectively. The pollution assessment results also showed that most of the farmland soil samples in the study area were non-polluting or slightly polluted based on geochemical baselines. Hg and Cu in a few samples were moderately polluted, and Cd in only one sample was moderately intensely polluted. Combined with the distribution of pollution and field investigation, it is considered that Hg comes from atmospheric deposition and agricultural non-point source pollution of industrial pollution. Cu comes from animal husbandry and agricultural pollution. Meanwhile, Cd is related to natural sources, wood processing and agricultural fertiliser application. The study demonstrated that the calculation of soil geochemical background value should take full account of the differences between the various regions, combined with the current state, particularly the pre-consideration of the distribution of elements or pollutants. Then, reasonably select the evaluation standard value so that the evaluation results can truly reflect the state of soil pollution.

Estimation of Nitrate Background Value in Groundwater under the Long-Term Human Impact

This study demonstrates an approach to estimate the background value of nitrate as a basis for better groundwater management and protection in areas under long-term human impact. The aim was to determine the ambient background value (ABV) of nitrate in the catchment area of the Velika Gorica well field, a hydrogeologically homogeneous area within the Zagreb aquifer. ABVs are determined using four well-known model-based objective methods (the iterative 2-σ technique, IT; the calculated distribution function, CDF; the cumulative frequency curve, CFC; and the probability plot, PP), while simultaneously testing the reliability of the results of each method. If the results are not statistically significant, data selection is performed. The results show that using data without selection can lead to statistically non-significant ABVs, but with the additional selection of data, a statistically non-significant result became a statistically significant one. In summary, all final ABVs must be statistically significant and determined using as large a data set as possible. Reducing the size of the data set is acceptable only in the case of a statistically non-significant result.

Source apportionment and source-specific risk evaluation of potential toxic elements in oasis agricultural soils of Tarim River Basin

As rapidly developing area of intensive agriculture during the past half century, the oases in the source region of the Tarim River have encountered serious environmental challenges. Therefore, a comparative analysis of soil pollution characteristics and source-specific risks in different oases is an important measure to prevent and control soil pollution and provide guidance for extensive resource management in this area. In this study, the concentration of potential toxic elements (PTEs) was analyzed by collecting soil samples from the four oases in the source region of the Tarim River. The cumulative frequency curve method, pollution index method, positive matrix factorization (PMF) model, geographical detector method and health risk assessment model were used to analyze the pollution status and source-specific risk of potential toxic elements in different oases. The results showed that Cd was the most prominent PTE in the oasis agricultural soil in the source region of the Tarim River. Especially in Hotan Oasis, where 81.25% of the soil samples were moderately contaminated and 18.75% were highly contaminated with Cd. The PTEs in the Hotan Oasis corresponded to a moderate level of risk to the ecological environment, and the noncarcinogenic risk of soil PTEs in the four oases to local children exceeded the threshold (TH > 1), while the carcinogenic risk to local residents was acceptable (1E−06 < TCR < 1E−04). The research results suggested that the Hotan Oasis should be the key area for soil pollution control in the source region of the Tarim River, and agricultural activities and natural sources, industrial sources, and atmospheric dust fall are the priority sources that should be controlled in the Aksu Oasis, Kashgar Oasis and Yarkant River Oasis, respectively. The results of this study provide important decision-making support for the protection and management of regional agricultural soil and the environment.

Slope Scaling Effect and Slope-Conversion-Atlas for Typical Water Erosion Regions in China

Slope has obvious scale-dependent characteristics and it changes with the change in DEM resolution, which brings uncertainty to the evaluation process of regional resource and environment. In this paper, one typical county in each of the six water erosion regions in China was selected as the sample area, respectively. Based on DEM data of ALOS DEM, ASTER GDEM and SRTM DEM with different spatial resolutions, slope characteristics, such as gradient, eigenvalue, frequency and cumulative frequency curves, were calculated by using the third-order inverse distance square weighted difference algorithm, to explore the ability of depicting terrain by these three DEM data. Based on the idea of geo-information map, the “surface-slope conversion atlas” under different resolutions was constructed to achieve the grading correction of slope extraction under low resolution. The results showed that: (1) with the resolution of DEM decreases, the slope information of each area tends to be more generalized and gradually concentrated. The slope frequency curve gradually changed from “tall and thin” to “short and fat”, and the peak of the cumulative frequency curve moved to the low-slope area. Six sample areas showed different degrees of slope reduction. (2) In the process of slope grading correction, except for Maoxian, the proportion of low-resolution results converted to medium and low slope grades (0°–25°) is large. (3) The slope spectrum conversion method has a good correction effect on the errors generated by the slope extraction results of DEM90 and DEM30, and the correction rates reached 80% and 90%, respectively. A slope conversion atlas can effectively improve the expression ability of low-resolution DEM data on topography, which can provide a basis for regional resource and environment evaluation, and territorial space optimization.

Pre-quake frequency characteristics of Ms ≥7.0 earthquakes in mainland China

In this study, natural orthogonal expansion was performed on earthquake frequencies to compute the pre-quake frequency fields of 9 Ms ≥7.0 earthquakes in mainland China from 1980 to 2020. The temporal and spatial pre-quake anomalies of these earthquakes were extracted from their frequency fields. We found that the majority of pre-quake temporal anomalies (i.e., variations exceeding two-times the absolute mean square error) of a strong earthquake are condensed within the first four frequency fields, and typically comprise multiple components. The temporal factor of the first frequency field usually accounts for the largest proportion of these anomalies (40%–60% of the entire field). Most Ms ≥7.0 earthquakes exhibited long-term anomalies 5–8 years before their occurrence; some presented medium-term anomalies 1–2 years prior to the quake, and only a few presented short-term and imminent anomalies (≤3 months before the quake). Anomalous seismic hazard zones have high-gradient turning points in regional frequency-field contour maps, and the epicenters of strong earthquakes are often located in areas containing active faults that have contour values. Through the comparison of seismic frequency field and the traditional method of regional seismic activity frequency (3 months), it is shown that the frequency-field time factor has the advantages of diversified and rich abnormal information. The slope comparison between the frequency field and the cumulative frequency curve shows that the frequency anomaly time of the two is consistent, and the conclusion is reliable. Therefore, the seismic frequency method can predict the occurrence time and location of strong earthquakes, which is closer to the predictable seismic model.

Source Apportionment of Chemical Elements and Their Geochemical Baseline Values in Surface Water of the Parauapebas River Basin, Southeast Amazon, Brazil

The present work aims to evaluate the chemical quality and establish the geochemical baseline values of elements in the surface waters of the Parauapebas River basin (PRB), which is one of the major subbasins in the Itacaiúnas River watershed (IRW) located in the Brazilian Amazon. A total of 327 surface water samples were collected during the rainy and dry seasons in 2017. Results indicate that waters are slightly acidic to alkaline (pH 6 to 8), and there was a strong influence of the seasonal variation on water quality, with higher values of turbidity, Fe, Al, Mn, TDS, etc. in the rainy season. Two geochemical baseline types for the PRB were defined, i.e., ‘conservative baseline’ (CB), represented by the cumulative frequency curve, and the ‘environmental baseline’ (EB), comprising the sum of natural and diffuse anthropogenic contributions, represented by the 98th percentile. Except Fe, Mn and Al, the CB and EB values of various trace elements (Ba, Co, Cr, Cu, Ni, Rb, Sn, Sr, Ti, V and Zn) were lower than the recommended limits of CONAMA 357/05—class 2. The principal component analysis (PCA) identified the major geochemical association (Al-Ti-Cu-Cr-Ni-V), which is an imprint of the local geological setting. Ni and Cr showed enrichment at sites where mafic and ultramafic rocks are concentrated, while Cu concentration is mainly associated with the north and south mineralization belts. High concentrations of Fe and Mn are characteristic of the waters of this region and this is mostly influenced by specific land use activities and intense weathering/erosion of catchment materials. At the upper Parauapebas, anthropogenic contributions associated with soil use and occupation were also important along with the geogenic effects. The obtained results regarding sources of contaminants in some microbasins can be taken as a starting point for future studies on the environmental quality of the region’s water resources.

Identification Method for Crash-Prone Sections of Mountain Highway under Complex Weather Conditions

Mountain highway crashes usually have a weather tendency, and the crash-prone sections show obvious weather differences. However, there were few targeted quantitative analyses of the impact of weather conditions on crash-prone sections in previous studies. Aiming at the problem that traditional identification methods ignore the difference in weather, this paper proposed the time-spatial density ratio method. The method quantified the length of the road section, the period, and the influence of different weather conditions through the time-spatial density ratio. Then the time-spatial density ratios under different weather conditions were comprehensively sorted in parallel. Finally, the risk threshold was determined according to the characteristics of the cumulative frequency curve’s double inflection points, and the crash-prone sections under each weather condition were identified. This paper evaluated the crash-prone sections of the G76 Expressway. Moreover, the crash risk situation under each weather condition was characterized through kernel density analysis. The method was compared with the cumulative frequency method, a traditional method suitable for Chinese highways with similar application conditions. The effective search index was utilized as a comparison factor. The results showed that the effective search index of the time-spatial density ratio method was more than 80% greater than that of the cumulative frequency method.

P118 The use of cumulative frequency curves to analyse sedated patients

Abstract Introduction Excessive or inadequate sedation in intubated patients are both associated with increased morbidity and mortality. However, it is difficult to quantify the level of sedation accurately. Conventional sleep analysis does not quantify sedation effectively. Specific sedation analysis techniques have been developed but are labour-intensive and difficult to apply. We explored the potential of cumulative frequency curves of electroencephalograms (EEG) to quantify the level of sedation. Methods Left frontal EEG was obtained over 12-24 hours in 20 sedated and 2 non-sedated patients. Six hours of time correlated data (00:00-06:00) were analysed. Cumulative frequency curves were created for each patient. Measurements obtained were: peak (frequency in Hz occurring most often, x axis), areas under the curve at five frequencies (percentage time at the selected frequency) and average signal amplitude, at peak using a power calculation on y axis. Results For the 20 sedated patients 72±13,% (mean±SD) of study time was recorded at &amp;lt;1Hz and 91% ±5.7 at &amp;lt;4Hz (compared to 57.8 and 84.3% respectively for non-sedated patients). The peak amplitude of the signal took place at 0.45±0.32 Hz in sedated patients. The comparative amplitude determined by a comparative power determinant was 50.8±3.8 in sedated patients (c.f. 46 in non-sedated patients). Conclusion This proof of concept study shows that signal amplitude and frequency can be measured using the cumulative frequency methodology and appears to differ between sedated and non-sedated patients. This methodology has the potential to provide a useful, simple and reproducible mechanism to analyse depth of sedation in intubated patients.

Identification of arsenic spatial distribution by hydrogeochemical processes represented by different ion ratios in the Hohhot Basin, China.

The Hohhot Basin, a typical inland basin of the Yellow River Basin in China, has high concentrations of arsenic (As) in its shallow groundwater, while the factors dominating the distribution of high arsenic levels remain to be further identified. An analysis of the ratio of hydrogeochemical compositions can help to reveal the spatial characteristics of the shallow groundwater environmental conditions and the distribution of high-arsenic water (As >10 μg/L). In this study, a total of 170 samples of shallow groundwater in the Hohhot Basin were collected and water samples with As >10 μg/L accounted for 29.4% of the total. Based on the slope changes of the cumulative frequency curves of (HCO3- + CO32-)/SO42-, Ca2+/(HCO3- + CO32-), Ca2+/Mg2+, and Na+/Ca2+, the groundwater in the study area can be categorized into six different zones according to the environmental characteristics including redox condition, water recharge intensity, and cation exchange level. The result shows that the groundwater in the front of the piedmont alluvial plain and platform is in a weak reducing condition with high lateral recharge intensity, fast runoff, and weak cation exchange. In the Dahei River alluvial plain, which serves as the groundwater discharge zone, the groundwater runoff is sluggish with poor lateral recharge, sufficient exchange between cations in the groundwater and the aquifer matrix, and enhanced reducibility. The degree of oxidation increased in the groundwater near the Hasuhai Lake and the drainage canal, which adverse to the arsenic enrichment. High-arsenic groundwater is mainly distributed in aquifers of (HCO3- + CO32-)/SO42 > 10, Na+/Ca2+ > 13, and Ca2+/(HCO3- + CO32-) < 0.1, which represent the strong reducing condition, low surface water recharge intensity, and strong cation exchange condition. Reductive dissolution of iron oxide, strong evaporation and concentration process, and competition from phosphate in aquifers jointly lead to the release of arsenic into groundwater.

An Improved Method for the Evaluation and Local Multi-Scale Optimization of the Automatic Extraction of Slope Units in Complex Terrains

Slope units (SUs) are sub-watersheds bounded by ridge and valley lines. A slope unit reflects the physical relationship between landslides and geomorphological features and is especially useful for landslide sensitivity modeling. There have been significant algorithmic advances in the automatic delineation of SUs. But the intrinsic difficulties of determining input parameters and correcting for unreasonable SUs have hindered their wide application. An improved method of the evaluation and local multi-scale optimization for the automatic extraction of SUs is proposed. The Sus’ groups more consistent with the topographic features were achieved through a stepwise approach from a global optimum to a local refining. First, the preliminary subdivisions of multiple SUs were obtained based on the r.slopeunit software. The optimal subdivision scale was obtained by a collaborative evaluation approach capable of simultaneously measuring objective minimum discrepancies and seeking a global optimum. Second, under the selected optimal scale, unreasonable SUs such as over-subdivided slope units (OSSUs) and under-subdivided slope units (USSUs) were further distinguished. The local average similarity (LS) metric for each SU was designed based on calculating the SU’s area, common boundary and neighborhood variability. The inflection points of the cumulative frequency curve of LS were calculated as the distinguishing intervals for those unrealistic SUs by maximum interclass variance threshold. Third, a new effective optimization mechanism containing the re-subdivision of USSUs and merging of OSSUs was put into effect. We thus obtained SUs composed of terrain subdivisions with multiple scales, which is currently one of the few available methods for non-single scales. The statistical distributions of density, size and shapes demonstrate the excellent performance of the refined SUs in capturing the variability of complex terrains. Benefiting from the sufficient integrating approach of diverse features for each object, it is a significant advantage that the processing object can be transferred from general entirety to each precise individual.

Analysis of the Causes of Traffic Accidents and Identification of Accident-Prone Points in Long Downhill Tunnel of Mountain Expressways Based on Data Mining

China has a large vehicle base, uneven road conditions, and the highest rate of traffic accidents in the world. Particularly on the long downhill sections of expressway tunnels in mountainous areas with harsh geographical conditions, traffic accidents are densely distributed, and once a traffic accident occurs, the consequences are serious, which poses a large threat to people’s lives and property. This paper mined and analyzed the traffic accident data collected by the project on the Baoding section of Zhangshi Expressway. SPSS software was used to analyze the traffic accident data characteristics of the long downhill tunnel of the mountain expressways. The time, space, accident form, vehicle type, and road alignment distribution characteristics of the traffic accident in the long downhill tunnel section of mountain expressways were obtained. The decision tree algorithm was used to construct the cause analysis model of traffic accidents in the long downhill tunnel of mountain expressways, and the five primary influencing factors were obtained: horizontal curve radius, week, slope length, time, and cart ratio. The improved cumulative frequency curve method was used to study the accident-prone points of mountain expressways, and the accident-prone points and potential accident-prone points were obtained.