Saturation Depth Research Articles

Verbal memory is linked to average oxygen saturation during sleep, not the apnea-hypopnea index nor novel hypoxic load variables

IntroductionThe apnea-hypopnea index (AHI) is the current diagnostic parameter for diagnosing and estimating the severity of obstructive sleep apnea (OSA). It is, however, poorly associated with the main clinical symptom of OSA, excessive daytime sleepiness, and with the often-seen cognitive decline among OSA patients. To better evaluate OSA severity, novel hypoxic load parameters have been introduced that consider the duration and depth of oxygen saturation drops associated with apneas or hypopneas. The aim of this paper was to compare novel hypoxic load parameters and traditional OSA parameters to verbal memory and executive function in OSA patients. MethodA total of 207 adults completed a one-night polysomnography at sleep laboratory and two neuropsychological assessments, the Rey Auditory Verbal Learning Test and Stroop test. Results: Simple linear regression analyses were used to evaluate independent associations between each OSA parameter and cognitive performance. Associations were found between immediate recall and arousal index, hypoxia <90 %, average SpO2 during sleep, and DesSev100+RevSev100. Total recall was associated with all OSA parameters, and no associations were found with the Stroop test. Subsequently, sex, age, and education were included as covariates in multiple linear regression analyses for each OSA parameter and cognitive performance. The main findings of the study were that average SpO2 during sleep was a significant predictor of total recall (p < .007, β = −.188) with the regression model explaining 21.2 % of performance variation. Average SpO2 during sleep was also a significant predictor of immediate recall (p < .022, β = −.171) with the regression model explaining 11.4 % of performance variation. Neither traditional OSA parameters nor novel hypoxic load parameters predicted cognitive performance after adjustment for sex, age, and education. ConclusionThe findings validate that the AHI is not an effective indicator of cognitive performance in OSA and suggest that average oxygen saturation during sleep may be the strongest PSG predictor of cognitive decline seen in OSA. The results also underline the importance of considering age when choosing neurocognitive tests, the importance of including more than one test for each cognitive domain as most tests are not pure measures of a single cognitive factor, and the importance of including tests that cover all cognitive domains as OSA is likely to have diffuse cognitive effects.

Influence of cnoidal wave-induced seepage force on shields number in shallow water

Sediment incipient motion in shallow water is a major concern for coastal engineers. Wave-induced seepage force has reportedly had an important impact on the sediment incipience. The effect of wave asymmetry and skewness is important for defining nearshore wave motions and the resulting sediment movement, but it has been discounted in most previous studies considering seepage. Using analytical and numerical models, this study examines the influence of two-dimensional nonlinear wave-induced seepage forces on sediment incipient motions in shallow water. A new modified Shields number was derived, which better addresses the problem of seepage. The results indicate that seepage force could stabilize the sand particles by lowering the maximum Shields number by up to 38.0%; in the linear wave cases, the opposite is true. This discrepancy is subject to the nonlinearity and asymmetry of shallow wave motions, as well as the decreasing “suction” force and increasing “injection” force. Besides, disregarding horizontal seepage would greatly underestimate the contribution of seepage to sediment incipient motions, especially in situations with steeper waves or an unsaturated and less permeable seabed. A lower Young's modulus, larger saturation, permeability, and water depth would all considerably decrease the maximum Shields number.

Geospatial insights into Alphonso mango cultivation: a comprehensive land suitability study in the coastal belt of Maharashtra, India.

Land suitability assessment is integral to the advancement of precision agriculture. This inquiry is focused on identifying optimal regions for cultivating Alphonso mango in the coastal belt of Maharashtra, spanning across Palghar, Raigad, Thane, Ratnagiri, and Sindhudurg districts. Employing a GIS-based Analytic Hierarchy Process (AHP) methodology, 10 crucial parameters have been considered, encompassing climatic, physical, and chemical soil characteristics: cation exchange capacity, organic carbon, slope, rainfall, soil pH, soil texture, mean annual soil temperature, base saturation, soil drainage, and soil depth. Weights are assigned to these parameters based on expert opinions and existing literature to determine their significance in developing a soil suitability map. The study reveals distinct land suitability zones for Alphonso mango cultivation. The land suitability map designates 25.78% of the study area as highly suitable, while 9.18% is considered unsuitable for Alphonso mango cultivation. To validate the study, the Receiver Operating Characteristic (ROC) curve has been employed, indicating an 83% approval rate for the reliability and performance of the soil suitability. The results categorise soil suitability classes, providing valuable insights for farmers and agricultural planners to make informed decisions regarding Alphonso mango cultivation in similar geoenvironmental regions.

Mechanism of island dolostones formation in the Cretaceous calcitic ocean: Insights from the Mid-Pacific Guyots

Dolomite is common in carbonate successions. There is an ongoing debate about the origin of ancient massive dolostones. Recent studies suggest widespread syndepositional and early-burial dolomitisation by normal and near-normal seawater, in the rock record, than previously recognised. Seawater dolomitisation is ubiquitous in Cenozoic islands but Cretaceous counterparts are rare, except for Resolution and Allison guyots, Mid-Pacific Mountains. We explored their dolomitisation conditions and the implications on our understanding of Cretaceous normal seawater syndepositional and near-surface dolomitisation. Integrating geochemical and borehole data reveals temporal overlap between 87Sr/86Sr ages of dolomites, and K/Ar and 40Ar/39Ar ages of the basement. Dolomites near basaltic basement exhibit 42-times Fe-enrichment compared to normal seawater dolomites. Host-rock thermal modelling suggested that δ18Odol temperatures are ∼18–29 °C higher than concurrent temperatures. Seismic interpretation and seismic facies forward modelling demonstrate a spatial overlap between dolomites and magmatic sills in both guyots. Accordingly, magmatically driven hydrothermal dolomitisation is proposed, which promoted dolomitisation by providing high heat flow, increasing seawater circulation, and overcoming limited dolomitisation potential of Cretaceous seawater. The H2O–CO2–SO2–HCl-rich magmatic-hydrothermal acidic fluids would mix with seawater causing slight modification by leaching Mg and Fe from basaltic basement. Consequently, magmatically active Cretaceous islands had greater potential for seawater dolomitisation than counterparts with ceased magmatism, due to increased heat flux and slight increase in Mg:Ca of dolomitising fluids. Our findings imply that deep-seated island dolostones don't only form by deep cold seawater below calcite saturation depth. Instead, magmatism appears crucial in this study and potentially other locations (e.g. Xisha Islands). The absence of dolostones in other Cretaceous islands supports previous models of reduced effectiveness of massive dolomitisation by Cretaceous normal seawater, questioning interpretations of syndepositional and near-surface dolomitisation. Thus, caution is advised when interpreting these dolomites by considering additional factors (dolomite geometry, geological settings, and dolomitisation age), as they may share characteristics with syndepositional and near-surface normal seawater dolomites.

Effects of Burial Furrow Parameters on Soil Water Movement under Subsurface Stalk Composite Pipe Irrigation

Stalk composite pipe (SCP), a novel product used for subsurface irrigation, is primarily composed of crop stalks, soil, and water. In subsurface SCP irrigation (SSI), comprehending the effects of burial furrow parameters on soil water movement is critical. However, the precise effects are not known. Here, we aimed to assess the effects of varying burial furrow dimensions, including widths of 15, 20, and 25 cm, depths of 10, 15, and 20 cm, and backfilling-soil bulk densities of 1.1, 1.2, and 1.3 g cm−3, on wetted distance and soil water movement. We conducted an indoor soil bin experiment and numerical simulation using HYDRUS-2D in 2020–2021 in Zhengzhou City, Northern China. Wider burial furrows resulted in increased wetted distance and soil water content, ultimately leading to greater effect in a horizontal direction. In the horizontal profile, the average soil water content of the SSI treatments, which used burial furrow widths of 15, 20, and 25 cm, were 1.121, 1.230, and 1.280 times higher, respectively, than those of CK. The burial furrow depth had minimal effect on the wetted distance, whereas adjusting the burial furrow depth primarily affected the saturation depth. The speed of wetting-front migration was affected by the backfilling-soil bulk density. For a given soil and crop, it is advisable to determine first the burial furrow width and backfilling-soil bulk density. Subsequently, the burial furrow depth should be established based on the distribution of the crop’s roots. Our findings offer a scientific basis for using SSI.

Mechanisms Underlying the Overturning Failure of Terraced Field Side Walls Due to Expansive Soil Swelling During Layer‐By‐Layer Saturation

The stability of side walls in terraced fields constructed within expansive soil regions represents a critical challenge, often leading to structural failure due to the unique wetting–swelling behavior of the soil. This study employs a comprehensive approach, integrating analytical and numerical methods to elucidate the mechanism of overturning failure attributed to the swelling effect of expansive soil under conditions of layer‐by‐layer saturation. Initially, the earth pressure acting on side walls, constructed from fiber ecological bags, is assessed in their natural, unsaturated state using Bishop’s formula for unsaturated shear strength. The study further explores the failure mode through one‐dimensional analytical analysis, focusing on the horizontal and unrestrained expansion of expansive soil during progressive saturation. Subsequently, the deformation of the side wall and the swelling effect of the soil are numerically evaluated. This is achieved by analogizing the wetting–swelling deformation field in expansive soil to an equivalent temperature field, thereby facilitating the use of finite element numerical simulation to investigate the overturning failure mechanism. Findings indicate that in the natural unsaturated state, the side walls remain stable under no earth pressure. However, as saturation depth attains a critical depth of 1.4 m during layer‐by‐layer saturation, the upper wall rotates outward in the form of local overturning failure, and the corresponding infiltration saturation depth is the critical depth for the local instability of the side wall. The investigation identifies the wetting–swelling effect as the predominant factor leading to the structural failure of side walls in terraced fields situated in expansive soil areas. Moreover, a critical infiltration saturation depth of 2.6 m is determined, beyond which the stability of the side walls is compromised. This research contributes significantly to the understanding of the failure mechanisms affecting terraced agricultural infrastructures in expansive soil regions, offering a theoretical foundation for the development of more resilient construction strategies.

Fretting wear assessment in PHWR pressure tubes using transient dynamic FEA and Archard’s wear model

In Pressurized Heavy Water Reactors (PHWRs), the fuel bundles are placed in a pressure tube (PT). These bundles rest on inside of pressure tubes through the bearing pads. The pressure tubes are part of the primary pressure boundary of the reactor, and are crucial from functionality and safety point of view. Any phenomena/ factors that may cause structural degradation of PT and may affect its structural integrity, requires thorough investigation. The fretting of pressure tube at bearing pad locations is one such phenomenon, wherein the local material removal due to fretting may lead to stress concentration and associated structural degradations. Therefore, a detailed assessment of the PT fretting damage incurred during its intended life is required. Present paper covers the premise and methodology based on Archard’s wear model for evaluation of the volumetric wear rate of pressure tube. A case study has been done to evaluate the fretting wear in pressure tubes of a large Indian PHWR. 3D transient computational fluid dynamic analysis and finite element analysis with contact modelled between the fuel bundle bearing pads and pressure tube are carried out to evaluate the contact force and sliding distance time histories. Based on the analyses results, the work rate and average saturated fret depth are evaluated. The assessment revealed insignificant concern owing to the fretting of pressure tube for the considered cases.

Research of the vacuum thermocyclic nitrogen process in a plasma pulsing glow discharge

As a result of the studies, the regularities of the influence of vacuum thermocyclic nitriding in a pulsating glow discharge plasma parameters on the microhardness, the diffusion saturation depth, the magnitude and distribution of residual stresses in the hardened layers of steel surfaces are established. Based on the use of expert assessment methods and the results of a series of screening experiments, optimization criteria (endurance limit and corrosion resistance) and controlled factors for mathematical modeling of the formation of strengthened ion-nitrated surface layers are determined. A mathematical model of the technology of the formation of reinforced surfaces of the vacuum thermocyclic nitriding in a pulsating glow discharge plasma according to the criteria of endurance and corrosion resistance is obtained. An analysis of the studies showed that there are no general conclusions and recommendations on the selection of optimal technological parameters of the vacuum thermocyclic nitriding in a pulsating glow discharge plasma that would be used for the practical application of this technology. These circumstances confirm the need for further study of the vacuum thermocyclic nitriding in a plasma of a pulsating glow discharge of vacuum thermocyclic nitriding in a pulsating glow discharge plasma technology and the feasibility of its optimization.

Assessment of Depth of Mud-Filtrate Invasion and Water Saturation Using Formation-Tester Measurements: Application to Deeply Invaded Tight-Gas Sandstones

Formation pressure/fluid measurements are impacted by mud-filtrate invasion, which may require long fluid pumpout durations to acquire hydrocarbon samples with minimal mud-filtrate contamination. However, unlike other well-logging instruments, formation testers do not have a fixed depth of investigation that limits their ability to pump out mud filtrate until acquiring original formation fluids (i.e., sensing the uninvaded zone). We use an in-house petrophysical and fluid-flow simulator to perform numerical simulations of mud-filtrate invasion, well logs, and formation-tester measurements to estimate the radial distance of invasion and the corresponding radial profile of water saturation. Numerical simulations are initialized with the construction of a multilayer petrophysical model. Initial guesses of volumetric concentration of shale, porosity, water saturation, irreducible water saturation, and residual hydrocarbon saturation are obtained from conventional petrophysical interpretation. Fluid-flow-dependent petrophysical properties (permeability, capillary pressure, and relative permeability), mud properties, rock mineral composition, and in-situ fluid properties are obtained from laboratory measurements. The process of mud-filtrate invasion and the corresponding resistivity and nuclear logs are numerically simulated to iteratively match the available well logs and estimate layer-by-layer formation water saturation. Next, using our multiphase formation testing simulator, we numerically simulate actual fluid sampling operations performed with a dual-packer formation tester. Finally, we estimate irreducible water saturation by minimizing the difference between the hydrocarbon breakthrough time numerically simulated and measured with formation-tester measurements. The examined sandstone reservoir is characterized by low porosity (up to 0.14), low-to-medium permeability (up to 40 md), and high residual gas saturation (between 0.4 and 0.5). The deep mud-filtrate invasion resulted from extended overbalanced exposure to high-salinity water-based mud (17 days of invasion and 1,800 psi overbalance pressure) coupled with the low mud-filtrate storage capacity of tight sandstones. Therefore, the uninvaded formation is located far beyond the depth of investigation of resistivity tools, whereby deep-sensing resistivities are lower than those of uninvaded formation resistivity. Through the numerical simulation of mud-filtrate invasion, well logs, and formation-tester measurements, we estimated radial and vertical distributions of water saturation around the borehole. Likewise, we quantified the hydrocarbon breakthrough time, which matched field measurements of 6.5 hours. The estimated radius of invasion was approximately 2.5 m, while the difference between estimated water saturation in the uninvaded zone and water saturation estimated from the deep-sensing resistivity log was approximately 0.13, therefore improving the estimation of the original gas in place.

The Montes del Plata Soil Spatial Inference System

Soil is one of the prior components of a forest site, hence determining its final productivity. Effective soil management requires an understanding of soil distribution patterns within the landscape. The ability to accurately predict and map soil properties over Montes del Plata (MDP) landholdings can improve silvicultural management decisions that can result in higher and sustainable forest productivity. Today's decisions are based mainly on interpreting conventional soil maps (discrete semi-detailed) produced from local empirical experts' knowledge. Creation of conventional soil maps is a high time-consumable non-parametrizable process which result does not represent soil heterogeneous diversity, both in location and depth. In this work, we applied Digital Soil Mapping (DSM) techniques to produce continuous soil maps showing different soil-predicted property values with a concomitant measured uncertainty grade over 1,200 hectares. We were able to produce continuous soil properties maps with an average precision accuracy of 60% by developing a DSM protocol in three representative farms of MDP landholdings, in areas to be forested with Eucalyptus on its second cycles. A set of 53 environmental covariates was developed and harmonized at 30 m2 of spatial resolution. A field sampling strategy was defined based on the Latin Hypercube sampling method, and 180 soil profiles were collected. In laboratory conditions, we perform textural and chemical analyses on 345 soil samples from A and B horizons. Vertical harmonization was applied, and properties were estimated at three standardized depths (0-30, 30-60, and 60-100). A Random Forests Model (RMF) is fitted to predict texture, organic matter, organic carbon, pH_H2O, pH_KCl, N, P, K, Ca, Mg, Al, Na, cation exchange capacity, base saturation, and profile soil depth. Our results demonstrate that DSM techniques can be successfully applied to representative MDP's landholding soils. We anticipate our preliminary work as the starting point for using DSM techniques that result in acceptable soil continuous maps in less time. However, the developed protocol performance must be tested in similar soil conditions, and an approach must be undertaken to look for a lesser sampling density. These results, in addition to focusing on only those soil parameters linked to operative silvicultural decisions (viz. P, K, Ca, and soil depth), may lead to lower final associated costs.

Diffusion Nitride Coatings for Heat-Resistant Steels.

The effect of ion nitriding and nitriding in a melamine-based powder mixture on the structure and properties of AISI A290C1M steel was studied in the paper. Using ion nitriding made it possible to shorten the technological cycle's duration by 5-6 times compared to two-stage nitriding, optimize the diffusion layer's composition, provide a technologically simple process automation scheme, and improve the quality of nitride coatings. After the proposed mode of ion nitriding, a saturated layer depth of 0.25-0.32 mm, hardness up to 1000 HV, and an increase in wear resistance by 2.17 times were obtained. Using 95% melamine + 5% sodium fluoride during nitriding in a powder mixture significantly simplified the technological process. It did not require additional expensive equipment, which in turn significantly simplified the nitriding process with energy savings. The proposed technology and the composition of the mixture contributed to a significant acceleration of the nitriding process of AISI A290C1M steel, compared to traditional gas nitriding, and to obtain a hardness of the nitride layer of 970 HV and an increase in wear resistance by 2.6 times. A nitriding speed is explained by a significantly higher amount of atomic nitrogen when using melamine instead of ammonia and by the almost simultaneous disintegration of nanodispersed particles when the nitriding temperature was reached. After nitriding in a powder mixture, steel was subject to the slightest wear.

Southern ocean response to glacial and interglacial forcing

The Southern Ocean is particularly vulnerable to climate change. Atmospheric CO2 fluctuations have been highly correlated with climate on million years time scales or caused or at least amplified, the climatic change. Here we used two simulations with the UVic ESCM 2.9 model for the Last Glacial Maximum (LGM) and Marine Isotope Stage 11c (MIS11c) climate using orbital forcing and CO2 prescribed for the ages. We have clearly identified the differences between the decrease and increase inf CO2 concentration in the Southern Ocean. The LGM simulation produces a colder, saltier, and more alkaline Southern Ocean than MIS11c. The MIS11c simulations show a reduction in O2 content with respect to LGM, which may be related to less primary productivity and more CaCO3 dissolution. According to the MIS11c simulation, the surface ocean carbonate factory is expected to be more sensitive to carbon oscillations due to an increase in CO2 dissolved in sea water. As expected, it will decrease the pH due to decreased alkalinity and ion carbonate concentrations. In this scenario, the aragonite concentration in the deep sediments would be more vulnerable to dissolution as a response of shoaling of the depth of aragonite saturation. The increase in CO2 dissolved in sea water in MIS11c, decreases the pH and saturation depth of CaCO3 becomes more than 1000 m shallower than found in the LGM simulation. This implies in a negative feedback of CO2 absorption with the saturation horizon becoming shallower, less Southern Ocean capacity has to uptake atmospheric CO2. Since the CaCO3 formation in the surface ocean and the dissolution in the deeper both affect TCO2 and TA as also the pCO2. Our results indicated that, under high CO2 conditions, the surface of the Southern Ocean appears to be more sensitive to a carbon perturbation, generally due to a decrease in ion carbonate concentration that leads to changes in the carbonate buffer system that will result in a deepening more than 1000 m the aragonite depth saturation in relation to MIS11c results.

Numerical Analysis on Gas Production and Geomechanical Responses of Natural Gas Hydrate Reservoirs.

Natural gas hydrate (NGH) has attracted considerable global attention as a promising energy resource in recent years. To acquire valuable insights into regarding the interplay between mechanical properties and production outcomes during the production, in this study, a fully coupled thermo-hydro-mechanical-chemical (THMC) model based on the geological features of reservoirs in the Shenhu area of the South China Sea (SCS) was developed to analyze the response characteristics of various physical fields within the reservoir during the exploitation. Furthermore, the study examined the influence of mechanical behavior on hydrate exploitation and investigated the effects of varying initial hydrate saturation and seawater depth on production efficiency and reservoir deformation. The simulation results indicated that neglecting the impact of solid mechanics in the analysis of hydrate productivity can result in overestimated results, particularly during the initial production stage. Reservoirs with higher hydrate saturation experience lower initial production rates due to the influence of permeability and capillary force. Moreover, reservoirs with high hydrate saturation exhibit greater compression but lower wellhead subsidence during the long-term development. The impact of seawater depth on production capacity primarily arises from the pressure's influence on the gas-water ratio, where greater seawater depth corresponds to increased reservoir compression and wellhead subsidence.

Drainage, salt-leaching impacts, and the growth of Salicornia bigelovii irrigated with different saline waters

We sought to assess the impact on groundwater of using three types of saline waters to irrigate the halophyte Salicornia bigelovii Torrey in the hyper-arid United Arab Emirates. These were groundwater (GW) at 25 dS m−1, reverse-osmosis brine (RO) from a desalination unit at 40 dS m−1, and the aquabrine (AQ) effluent from land-based aquaculture in tanks filled with RO brine, also at 40 dS m−1. The three waters were applied through bubblers (BUB), pressure-compensated drippers (PCD), or subsurface irrigation tape (SUB). The yields of Salicornia fresh tips, harvest forage, and seed were greatest for AQ applied through BUB, being 650 g m−2. We found 2–2.6 kg m−2 for dry forage yield with AQ through BUB, compared with 1–2.3 kg m−2 for the other waters and emitter devices. The highest water productivities WPI (kg m−3) across all three crop-outputs came from Aquabrine applied by pressure-compensated drippers. We assessed the gross economic water productivity (GEWPI, $ m−3) based solely on gross revenue. The GEWPI was highest for AQ applied through PCD and SUB, namely 5.8–6.2 $ m−3. The value derives primarily from fresh tips. The GEWPl was well above the cost of desalination at $1.5 m−3. We measured drainage and leaching using fluxmeters. The greatest salt load to groundwater came from BUB, being 135–195 kg m−2. For PCD and SUB it was between 14 and 36 kg m−2. Mass-balance calculations of these salt loadings can predict the impact on the saline quality of aquifers. We used an exemplar loading of 75 kg m−2, and results in an annual salinity rise of 2.6 dS m−1 y−1 for an aquifer of saturated depth of 100 m. This significant rate of rise in the salinity of groundwater would represent a continuing deterioration in the utility of groundwater.

An Analytical Framework for Assessing the Unsaturated Bearing Capacity of Strip Footings under Transient Infiltration

The evaluation of the bearing capacity of strip footings generally assumes that the soil is either dry or fully saturated, which contradicts the actual condition in nature where the soil is often in a partially saturated state. Furthermore, infiltration has a significant impact on the shear strength of the soil. Following the upper bound theory of the limit analysis, this article provides a theoretical framework for assessing the bearing capacity under transient flow with linear variation in infiltration intensity for the first time. Firstly, the closed form of suction stress under linear transient infiltration is derived using Laplace transform and introduced into the Mohr–Coulomb criterion. A discrete failure mechanism with fewer variables and higher accuracy is provided to ensure kinematic admissibility. The upper bound solution for bearing capacity is obtained by solving the power balance equation. The present results are compared with results from the published literature and the finite element, confirming the validity and superiority of the theoretical framework provided. A parametric analysis is also conducted on three hypothetical soil types (fine sand, silt, and clay), and the results show that unsaturated transient infiltration has a positive influence on increasing the foundation bearing capacity. The magnitude of the influence is comprehensively controlled by factors such as soil type, saturated hydraulic conductivity, infiltration intensity, infiltration time, and water table depth. The increase in bearing capacity due to unsaturated transient infiltration can be incorporated into Terzaghi’s equation as a separate component presented in tabular form for engineering design purposes.

Isolation effect of composite multilayer wave impeding block on P-wave in unsaturated foundation

The traditional wave impeding block (WIB) is designed as composite multilayer WIB with the same thickness to improve its vibration isolation effect. Based on the wave theory in unsaturated porous medium and elastic medium, the isolation effect of composite multilayer WIB on P-wave in unsaturated soil is investigated, and the solution of the vertical displacement at surface after setting composite multilayer WIB (as an example for triple-layer) in unsaturated foundation is obtained. The key factors such as incidence angle, frequency, saturation, thickness, and burial depth of the composite multilayer WIB are evaluated on its vibration isolation properties. The results show that the optimum vibration isolation effect can be achieved by controlling the wave impedance ratio among layers of materials. The isolation efficiency of composite multilayer WIB is 33.9% higher than homogeneous WIB with same thickness at l east, and has good vibration isolation effect for low, medium, and high frequency.

An Analysis of Landslide Risk Using the Change in the Volumetric Water Content Gradient in the Soil Layer Per Unit Time of Effective Cumulative Rainfall

The topographical characteristics of South Korea are coupled with heavy rain and typhoons concentrated from July to September, which take up two-thirds of the country’s annual precipitation, causing substantial damage from slope failures, landslides, debris flows, and other mountain disasters. This study uses the Land-Atmosphere Modeling Package (LAMP) data to study the area, which has been affected by numerous landslides in the past. Specifically, to analyze the likelihood of slope failure, this study simulates the rainfall events in the area at the time of the landslides as well as changes in the volumetric water content in the soil layer and uses the changes in the volumetric water content per unit time, which are affected by the effective cumulative rainfall within the soil layer. To that end, this study assesses the risk of landslides based on how rainwater infiltration in the saturation depth changes the saturation depth ratio and compares the results with the landslide spots in the past. Moreover, this study analyzes the landslide risk by applying the saturation depth ratio (Ht) to an infinite slope stability analysis model. The landslide threshold proposed in this study was obtained by analyzing the rainfall events that caused the landslides in the study area using the LAMP model. It can then be concluded that, when compared with the spatial information on the previous landslides, if the change in the volumetric water content per unit time during the first and second rainfall events is 0.7, a landslide may occur. These results indicated that the landslide risk increases the volumetric water content in the soil layer, along with the congruence between past landslide risk points and spatial landslide risks.

Isolation Effect of P-Wave By Double-Layer Wave Impeding Barrier in Unsaturated Foundations

Wave impeding block (WIB) barriers are often used to reduce vibration from different sources, but traditional vibration isolation of WIB has been limited to homogeneous materials and single-phase elastic or two-phase saturated foundations by many researchers. In fact, soils in nature are usually tri-phase unsaturated materials, and the propagation characteristics of elastic waves in unsaturated medium are completely different from those in single-phase elastic medium or two-phase saturated porous medium. In addition, the conventional WIB barrier has better vibration isolation only at low frequencies. Therefore, this paper improves the vibration isolation of the WIB by double-layer WIB with the same thickness on the basis of traditional WIB. Based on the wave theory of unsaturated porous media and elastic media, and according to the Helmholtz principle, we can obtain the solution of surface vertical displacement after setting double-layer WIB in unsaturated foundation, and then the isolation effect of double-layer WIB in unsaturated foundation under [Formula: see text]-wave incidence is investigated. The wave impedance ratio at the interface between WIB and unsaturated soil and wave impedance ratio at the interfaces among the layers of WIB is first analyzed on the vibration isolation effect of double-layer WIB, and the wave impedance ratio corresponding to the optimal vibration isolation effect of WIB barrier is achieved. Then the key factors such as incidence angle, incidence frequency, saturation, thickness, and burial depth of the double-layer WIB are evaluated on its vibration isolation properties. Finally, the isolation effects of single-layer homogeneous WIB and double-layer non-homogeneous WIB with the same thickness are compared. For the same thickness isolation barrier, the vibration isolation efficiency of double-layer WIB is 42.73% higher than single-layer at the incidence angle of [Formula: see text]–[Formula: see text]. The double-layer WIB has better isolation effect at low, medium and high frequencies than single-layer WIB.

A comparison of machine learning methods to predict porosity in carbonate reservoirs from seismic-derived elastic properties

Porosity prediction from seismic data in carbonate reservoirs is challenging because the common presence of heterogeneities in carbonates makes it difficult to establish a clear physical relationship between reservoir properties and elastic responses. Regarding the strong nonlinearities underlying the relationship, machine learning is considered to be a good alternative to traditional methods. We compare several representative supervised machine learning algorithms (light gradient boosting machine [LightGBM], extreme gradient boosting, categorical boosting, random forest, multilayer perceptron, and convolutional neural network) in terms of predictive accuracy and runtime for crosswell blind tests and seismic prediction in a heterogeneous carbonate reservoir, offshore Brazil. The machine learning models are trained with the porosity and elastic parameters (P-impedance and [Formula: see text] ratio) from the smoothed and standardized logging data. Then, we apply the trained model on the inverted elastic properties to predict the porosity profile from seismic data. In the crosswell blind tests for the studied reservoir, LightGBM clearly stands out from the compared machine learning methods with the highest predictive accuracy and the shortest runtime, showing potential for fast and reliable porosity prediction from seismic data. In addition, we analyze the geologic factors (clay content, oil saturation, and relative depth) that possibly affect the predictive accuracy. We find that, with the constraints from clay content and fluids saturation, the performance of porosity prediction from elastic parameters can be further improved to a certain degree.

Elevated anthropogenic CO2 invasion and stimulated carbonate dissolution in the South China Sea Basin

Great concern has been drawn in how marginal seas respond to elevated atmospheric carbon dioxide (CO2) and changes of carbonate system during absorbing anthropogenic CO2 (Cant). Decades of Cant absorption had prominently changed the carbonate system in the South China Sea (SCS). The Cant penetrated 1200–1800 m in the SCS in 2015, deeper than it in 1997. While the inventory of Cant reached 0.66 Gt C in the entire SCS, approximately 10% higher than it in 1997.With the invasion of the Cant, the average saturated depth of aragonite and calcite became shallower. The organic carbon pump and carbonate pump in the central and southern SCS Basin were less efficient than those in the northern SCS Basin especially in the intermediate waters, which were probably caused by the different biogenic compositions and residence time from north to south. The less calcite carbonate (CaCO3) load and longer residence time in the southern SCS Basin enhanced organic matter remineralization therein and thus resulted in a less efficient organic carbon pump. The decomposition of organic matter enhanced the CaCO3 dissolution while more CaCO3 dissolution enhanced the ability of buffering the atmospheric CO2 especially in the intermediate waters. In the foreseeable future, the SCS will absorb more Cant and continue decreasing the saturation depth of CaCO3. Plain language summaryThe ocean absorbs more atmospheric carbon dioxide (CO2) and changes its carbonate system under increasing emission of anthropogenic CO2 (Cant) since the industrial evolution. Decades of Cant absorption resulted in a deeper penetration depth by several hundred meters from 1997 to 2015 in the South China Sea (SCS), and enhanced the inventory of Cant in the meantime. During the invasion of the Cant, although changes of carbonate system could not be found from the dissolved oxygen, apparent oxygen utilization (AOU), normalized dissolved inorganic carbon (NDIC) and normalized total alkalinity in the upper 1000 m between 1997 and 2015 since the discrepancies were not significant enough. But the signals of acidification in the SCS became more severe, resulting in a shallower saturated depth of aragonite and calcite.The distribution of NDIC and AOU showed distinct pattern from north to south in the SCS Basin especially in the intermediate water, indicating a less efficient organic carbon pump and carbonate pump in the central and southern SCS Basin than those in the northern SCS Basin. The composition of carbonate (CaCO3) and residence time contributed to the discrepancies of these two pumps. Under the invasion of Cant, more CaCO3 dissolved and enhanced the ability of absorbing atmospheric CO2. In the foreseeable future, the SCS will absorb more Cant and continue decreasing the saturation depth of CaCO3.