Unsaturated Regions Research Articles

Determination of the geophysical signature of soft-clay and hard lateritic soils and the implications on geotechnical works using electrical resistivity imaging

Understanding the geophysical signature of subsurface is quite essential in mapping site conditions for geotechnical engineering and simulating geophysical surveys, especially in coastal areas. This article presents a comparative geophysical study of topsoil (often refer as engineering layer) of soft clay deposit and hard lateritic soil to evaluate the implications on geotechnical work using electrical resistivity imaging (ERI). The results of the 2D ERI show that the hard lateritic soil produces three distinctive geological layers with the topsoil having high apparent electrical resistivity (AER) values varying between 300 Ωm–1000 Ωm and a thickness between 2.0 m – 10.0 m. The layer between the unsaturated and saturated regions has a moderate layer AER and thickness values ranging from 100 Ωm–300 Ωm and 2.5 m–9.5 m, respectively. In contrast, the saturated (weathered) layer has a low AER value (< 100Ω m), which represents the regional groundwater unit, located beneath the subsurface of a depth > 6.0 m. However, the soft clay soil shows no distinctive subsurface layers, as it is characterized by a nearly homogeneity subsurface of poor AER variability. The top-soft clay deposit has very AER values ranging from 11.0 Ωm–80 Ωm, which extends beyond 6.5 m. Higher and lower AER values noted within the overburdened topsoil of lateritic and clay extractions, respectively, were due to the accumulations of compacted clay and lateritic soil, which are very essential for geotechnical works. In addition, the geophysical signal was conspicuously attenuated in soft clay soil, which shows that soft clay soil is not a favourite target of geophysical investigation. However, the geophysical signals in hard lateritic generate a fine geo-electrical layer pattern. It was also noted that the existence of soft clay and lateritic soil decreases with depth. This kind of information is very essential in geotechnical works.

Attention-Based Deep Learning Model for Image Desaturation of SDO/AIA

The Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) captures full-disk solar images in seven extreme ultraviolet wave bands. As a violent solar flare occurs, incoming photoflux may exceed the threshold of an optical imaging system, resulting in regional saturation/overexposure of images. Fortunately, the lost signal can be partially retrieved from non-local unsaturated regions of an image according to scattering and diffraction principle, which is well consistent with the attention mechanism in deep learning. Thus, an attention augmented convolutional neural network (AANet) is proposed to perform image desaturation of SDO/AIA in this paper. It is built on a U-Net backbone network with partial convolution and adversarial learning. In addition, a lightweight attention model, namely criss-cross attention, is embedded between each two convolution layers to enhance the backbone network. Experimental results validate the superiority of the proposed AANet beyond state-of-the-arts from both quantitative and qualitative comparisons.

Enhancing the production of small molecular products from pubescens via stepwise pyrolysis process

Pyrolysis of pubescens pretreated by torrefaction was investigated by one-step and stepwise processes. The cumulative yield of small molecular compounds reached up to 19.6 wt% via stepwise processing, yielding monosaccharides (1.49 wt%), carboxylic acids (5.20 wt%), furans (3.97 wt%) and monophenols (8.94 wt%), which is higher than the corresponding value of 12.39 wt%, with 0.65 wt%, 6.15 wt%, 1.05 wt% and 4.54 wt% of the four kinds of species obtained respectively, from one-step pyrolysis. Production of carboxylic acids could be enhanced in the temperature range of 200–320 °C via dehydration of holocellulose and cleavage of acetyl group in lignin, while the acquisition of furans could be promoted in the range of 240–360 °C via further dehydration of the units of holocellulose. In the temperature range of 240–440 °C, the cleavage of β-1,4-glycosidic linkages in cellulose and glycosidic bonds in hemicellulose enhanced the yield of monosaccharides. Furthermore, the formation of monophenols from the decomposition of H, G, and S units of lignin was enhanced via cleavage of C1-Cα, Cα-Cβ, Cβ-Cγ, Cα-OH, C-O-H(R), etc. in saturated and unsaturated regions, accompanied by elimination, dehydration reactions. With stepwise processing, the corresponding carbon content in the pyrolyzed residue was enriched, resembling the elemental composition of Bituminous coal. Moreover, the relationship between small molecular weight compounds and oligomers has been probed.

Parameter identification of unsaturated seepage model of core rockfill dams using principal component analysis and multi-objective optimization

The seepage behavior of core walls is an important aspect of safety monitoring of core rockfill dams. The permeability coefficient of unsaturated soil of the core wall is a nonlinear function not a constant. Since there are many seepage monitoring points in the core wall, parameter identification of unsaturated seepage model of soil core wall based on the data of these points is a high-dimensional multi-objective optimization problem. In this paper, a parameter identification method of unsaturated seepage in the core wall is proposed, in which an unsaturated seepage model, principal component analysis (PCA), and elitist non-dominated sorting genetic algorithm (NSGA-II) are combined. The seepage monitoring sequence of measuring points in saturated and unsaturated regions of the core wall is synthesized to a few comprehensive variables by PCA respectively. The NSGA- II is adopted to optimize the objective functions established by these comprehensive variables to obtain the Pareto-optimal solutions. The efficiency, accuracy, and robustness to the error of the proposed method have been confirmed in a fictitious dam and an actual dam. The predicted seepage pressure with the Brooks-Corey (BC) model is in best agreement with the measured data, and the simulated seepage field is more in line with the actual situation.

Discovery of recurrent flares of 6.7 GHz methanol maser emission in Cepheus A HW2

Context.Class II methanol masers at 6.7 GHz originate close to high-mass young stellar objects (HMYSOs). Their high sensitivity to local condition variations makes them a useful marker of the activity of the emerging massive stars.Aims.We aim to closely examine the variability of the 6.7 GHz CH3OH masers in Cep A HW2 using the new and archival single-dish and high-resolution Very-Long-Baseline Interferometry (VLBI) datasets.Methods.We monitored 6.7 GHz methanol masers towards the target between 2009 and 2021 using the Torun 32m radio telescope, and analysed nine datasets of VLBI observations taken over 16 yr.Results.Faint, extremely redshifted maser emission located close to the presumed central star position and coincident with the radio jet shows flaring activity with a period of ~5 yr. Flares have an asymmetric profile with a rise-to-decay time ratio of 0.18 and relative amplitude higher than 10. The velocity of the flaring cloudlets drifts at a rate of 3–4 × 10−5km s−1d−1for about 11.5 yr of the monitoring. The time-lag between the peaks of the two flaring features implies a propagation speed of the exciting factor of ~1000 km s−1. Synchronised and anticorrelated variations of the flux density of blue- and redshifted features begin ~2.5 yr after flares of the extremely redshifted emission.Conclusions.Our observations suggest that the recurrent flares are the response of low-gain unsaturated maser regions to a relatively low increase in luminosity, which has little effect on the behaviour of most maser regions of higher gain.

Hurricane‐Like Vortices in Conditionally Unstable Moist Convection

AbstractThis study investigates the emergence of hurricane‐like vortices in idealized simulations of rotating moist convection. A Boussinesq atmosphere with simplified thermodynamics for phase transitions is forced by prescribing the temperature and humidity at the upper and lower boundaries. The governing equations are solved numerically using a variable‐density incompressible Navier‐Stokes solver with adaptive mesh refinement to explore the behavior of moist convection under a broad range of conditions. In the absence of rotation, convection aggregates into active patches separated by large unsaturated regions. Rotation modulates this statistical equilibrium state so that the self‐aggregated convection organizes hurricane‐like vortices. The warm and saturated air converges to the center of the vortices, and the latent heat released through the upwelling, forms the warm core structure. These hurricane‐like vortices share characteristics similar to tropical cyclones in the earth's atmosphere. The hurricane‐like vortices occur under conditionally unstable conditions where the potential energy given at the boundaries is large enough, corresponding to a moderate rate of rotation. This regime shares many similar characteristics to the tropical atmosphere indicating that the formation of intense meso‐scale vortices is a general characteristic of rotating moist convection. The model used here does not include any interactions with radiation, wind‐evaporation feedback, or cloud microphysics, indicating that, while these processes may be relevant for tropical cyclogenesis in the Earth atmosphere, they are not its primary cause. Instead, our results confirm that the formation and maintenance of hurricane‐like vortices involve a combination of atmospheric dynamics under the presence of rotation and of phase transitions.

Three-dimensional tunnel face stability considering the steady-state seepage in saturated and unsaturated regions with changing water levels

For tunnels excavated in the unsaturated soils with changing water levels, there may be steady-state unsaturated flow above the water table and saturated flow below the water table toward the tunnel face due to the excavation. Changing water levels affect the adverse effect of the underwater saturated flow and the contribution of the unsaturated flow to the shear strength. To figure out the regularity concerning the region and magnitude of unsaturated and saturated flow effects, an analytical framework is developed within the kinematic approach of limit analysis combined with the numerical simulation. A suction stress-based equation is employed to express the contribution of unsaturated flow to shear strength. The development of the saturated flow below the water table is numerically simulated, and the resulting pore pressure distribution is extracted and interpolated on a 3D discrete rotational failure mechanism. The work rate balance equation incorporating the apparent cohesion due to unsaturated flow and the pore pressure affected by the saturated flow is established to optimize the critical face pressure. The proposed analytical framework is verified by comparisons with previous literature and numerical simulations of hydromechanical analysis. A parametric analysis is conducted to investigate the effect of groundwater levels, flow types, unsaturated properties, and hydraulic hysteresis on the tunnel face stability. The results show that it is only necessary to consider the effect of unsaturated flow and the differences caused by various unsaturated characteristics when the unsaturated zone is large enough. This work can provide a good reference for the design of face supports in the initial stage for tunnels excavated in unsaturated soils with changing groundwater levels.

Strain-Assisted Single Pt Sites on High-Curvature MoS 2 Surface for Ultrasensitive H 2 S Sensing

Strain-Assisted Single Pt Sites on High-Curvature MoS ₂ Surface for Ultrasensitive H ₂ S Sensing

Partitioning of a Hybrid Lipid in Domains of Saturated and Unsaturated Lipids in a Model Cellular Membrane.

The cellular membranes are composed of hundreds of components such as lipids, proteins, and sterols that are chemically and physically distinct from each other. The lipid–lipid and lipid–protein interactions form domains in this membrane, which play vital roles in membrane physiology. The hybrid lipids (HLs) with one saturated and one unsaturated chain can control the shape and size of these domains, ensuring the thermodynamic stability of a membrane. In this study, the thermodynamics of mixing of a HL and its structural effects on the phase separated domains in a model membrane composed of a saturated and an unsaturated lipid have been investigated. The HL is observed to mix into an unsaturated lipid reducing the Gibbs free energy, whereas the mixing is unfavorable in a saturated lipid. The presence of an HL in an unsaturated lipid tends to increase its area fraction, which is reflected in the enhanced correlation length across the bilayers in a multilayered sample. There is a feeble effect on the domain structure of the saturated lipid due to the presence of the HLs at the phase boundary. This study concludes that the HLs preferentially participate in the unsaturated lipid regions compared to that of a saturated lipid.

Moisture Distribution during Water Absorption of Ordinary Portland Cement Mortars Obtained with Low-Field Unilateral Magnetic Resonance.

Moisture distribution in cement-based materials is important from the durability point of view. In the present study, a portable three-magnet array with an elliptical surface radio frequency coil was used to undertake magnetic resonance measurements of moisture content in ordinary Portland cement mortar and concrete samples. Measurements along the length of the samples during capillary water absorption produced moisture content profiles that were compared with reference profiles acquired using a magnetic resonance imaging instrument. Profiles obtained with the three-magnet array were similar in shape and in penetration depth to those acquired with magnetic resonance imaging. The correlation coefficient between the moisture content measured with both techniques was r2 = 0.97. Similar values of saturated permeability of the mortars with identical w/c ratio were computed with the Hydrus 1D software based on the moisture content profiles. Additionally, inverse Laplace transformation of the signal decays provided the water-filled pore size distribution in saturated and unsaturated regions of the samples. The three-magnet array was successfully used to acquire nuclear magnetic resonance signal from a concrete sample, which was not possible with the magnetic resonance imaging instrument using the single-point imaging technique.

On the Poroelastic Biot Coefficient for a Granitic Rock

The Biot coefficient is a parameter that is encountered in the theory of classical poroelasticity, dealing with the mechanics of a fluid-saturated porous medium with elastic grains and an elastic skeletal structure. In particular, the coefficient plays an important role in the partitioning of externally applied stresses between the pore fluid and the porous skeleton. The conventional approach for estimating the Biot coefficient relies on the mechanical testing of the poroelastic solid, in both a completely dry and a fully saturated state. The former type of tests to determine the skeletal compressibility of the rock can be performed quite conveniently. The latter tests, which determine the compressibility of the solid material constituting the porous skeleton, involve the mechanical testing of the fully saturated rock. These tests are challenging when the rock has a low permeability, since any unsaturated regions of the rock can influence the interpretation of the compressibility of the solid phase composing the porous rock. An alternative approach to the estimation of the solid grain compressibility considers the application of the multi-phasic theories for the elasticity of composite materials, to estimate the solid grain compressibility. This approach requires the accurate determination of the mineralogical composition of the rock using XRD, and the estimation of the elasticity characteristics of the minerals by appealing to published literature. This procedure is used to estimate the Biot coefficient for the Lac du Bonnet granite obtained from the western region of the Canadian Shield.

Simulation of gas transport in a landfill with layered new and old municipal solid waste

Average biodegradation rate of newly filled municipal solid waste (MSW) in landfills is relatively fast, and the landfill gas produced by the new MSW biodegradation can cause great variations in gas pressure. To predict the gas pressure distribution in the MSW layer, a one-dimensional gas transport model is established in this study. The following factors are considered in this model: (1) the variation of gas permeability with depth; (2) the anisotropy ratio of gas permeability; (3) the settlement caused by waste biodegradation. Furthermore, a single peak model for gas production is applied as the source term of gas production. The equation for settlement caused by waste biodegradation is presented, and the time of peak gas production rate is obtained by fitting the settlement of the newly filled layer. The stratification of the unsaturated and saturated regions is taken into account by distinguishing the difference in gas saturation. The layering of the new and old waste layers is considered by distinguishing the difference in the length of time that waste has been degraded to produce gas. Based on the method of numerical calculation, the gas pressure distribution in the landfill with layered new and old MSW is well simulated. The position where the maximum gas pressure occurs is found. The sensitivity analysis shows that the influence of the anisotropy ratio on gas pressure distribution is more significant.

Drying of capillary porous media simulated by coupling of continuum-scale and micro-scale models

In this work, we recall an isothermal version of the broadly accepted macroscopic continuum model of drying, and we impose flux boundary conditions at two interfaces, i.e., at the interface between the (gas-side) boundary layer and the (medium-side) dry region, as well as the interface between the dry and unsaturated regions which evolves freely during drying. Local relative humidity, local saturation as well as local transport parameters are computed from microscopic pore network simulations. This dataset is then employed to compute fluxes that couple the internal and external mass transfer in the continuum model. Decisive advantages of this approach over the classical method are that the continuity of the mass flux at the drying front and the porous medium surface is ensured and that the continuum model parameters are computed directly from pore network simulations – no need for any empirical correlation. Derivation of the macroscopic parameter functions from the pore network simulations for use in the continuum model raises issues of averaging intervals and treatment of the dataset. Operation of the continuum model is very sensitive upon the moisture transport coefficient in the totally or partially saturated zone of the porous medium. A hybrid method is introduced to control the effect of the sensitivity of the continuum model on the macroscopic parameters. By punctually adjusting the dataset in the high saturation period, the continuum model provides a stronger agreement with pore network simulations, which shows that the underlying transport phenomena are better preserved in the scattered dataset that the new hybrid method provides.

Magnetically controlled reactors design for weak grids

Power system (PS) requires new flexible AC transmission systems, new solutions for voltage instability problems with simple design and fast response and its equipment, should allow reactive control, short-circuit capacity, dynamic behavior, flexibility and more efficiency control for the grid associated to reliability and security. This research develops a magnetically controlled reactor (MCR) design for a weak system. A methodology for design is proposed with a primary winding connected to the PS and the secondary winding connected to voltage control, the magnetic flux is modified by the direct current, therefore, the equivalent impedance is modified. This proposal is validated in a case study for Peruvian grid with low short circuit and reactive power. Our findings are: (i) A dynamic model in failure condition regarding the error signal. (ii) The MCR can assume reactive compensation in the unsaturated and saturated regions, (iii) it can be scalable into several stages with banks.

Solubility determination and thermodynamic modeling of solid−liquid equilibria in the LiBO2−Li2B4O7−H2O system at 298.15 K and 323.15 K

The solubilities and the refractive indices in the ternary system LiBO2−Li2B4O7−H2O at 298.15 K and 323.15 K were determined with the isothermal dissolution method. The phase diagrams and refractive index diagrams were drawn with the experimental values. The phase diagrams at 298.15 K and 323.15 K consist of one invariant point, two univariant curves and two crystallization regions corresponding to Li2B4O7·3H2O, LiBO2·8H2O (at 298.15 K) and LiBO2·2H2O (at 323.15 K). Based on the Pitzer model, the mixing ion-interaction parameters (θB(OH)4−,B4O5(OH)42− and ΨLi+,B(OH)4−,B4O5(OH)42−) at 298.15 K and 323.15 K were fitted with the solubility data. A comparison shows that the calculated solubilities in the ternary system at 298.15 and 323.15 K agree well with the experimental data. The phase diagram and Pitzer model for the ternary system were then used to conduct isothermal evaporation simulation. Different salt will be obtained if the original solution point in different unsaturated regions.

Environmental Impact of High Concentration Nitrate Migration in Soil System Using HYDRUS Simulation.

Nitrate is a promising heat transfer fluid in solar thermal power and nuclear power systems, but its leakage can cause serious environmental problems. The present paper investigates the deep and prolonged migration of high concentrations of nitrate into the soil system, and the associated diffusion range is studied to estimate and reduce the environmental pollution caused by nitrate leaks. The vertical nitrate contaminated range is mainly impacted by annual precipitation, soil properties and groundwater depth, while the horizontal contaminated range is mainly affected by the initial leakage area. During the process, the vertical contaminated range first continuously enlarges, and then decreases after a long time. The nitrate contaminant can exist and affect the environment for as long as 115–625 years, and the nitrate contamination time can be even longer in dry regions. Since nitrate diffuses more quickly in unsaturated regions rather than in saturated regions, the migration region and contaminated range both decrease as the groundwater depth is increased.

Scalable and multifunctional carbon nanotube-based textile as distributed sensors for flow and cure monitoring

Many manufacturing processes involve flow and cure of polymeric materials and development of sensors to detect these phenomena in situ and in real-time is important to reduce processing time and improve quality. This paper reports the development of a novel multifunctional sensor where carbon nanotubes are deposited onto a nonwoven textile to create a thin and porous areal sensor. The sensor is produced using a scalable dip-coating process and carbon nanotubes form an electrically conductive network on the fabric. Vacuum assisted resin transfer molding (VARTM) for advanced fiber composites is used to validate the sensor by using global and local distributed measurements to monitor the flow of epoxy resin. Spatial flow mapping is demonstrated using electrical impedance tomography (EIT). In a series of 2-D radial flow experiments, the EIT maps demonstrate accurate estimations for the resin flow, in terms of flow front location and shape, and is able to pinpoint dry spots and unsaturated regions. During elevated temperature cure, the sensor electrical response can be correlated directly to changes in viscosity and gelation of the epoxy. The sensor offers potential as a process sensor for flow and cure as well as for structural health monitoring.

High Dynamic Range Imaging Based on Bidirectional Structural Similarities and Weighted Low-Rank Matrix Completion

High dynamic range (HDR) imaging, aiming to increase the dynamic range of an image by merging multiexposure images, has attracted much attention. Ghosts are often observed in a resultant image, due to camera motion and object motion in the scene. Low-rank matrix completion (LRMC) provides an effective tool to remove ghosts. However, user specification of the included or excluded regions is required. In this paper, we propose a novel HDR imaging method based on bidirectional structural similarities and weighted low-rank matrix completion. In our method, we first propose the bidirectional structural similarities containing forward-projection structural similarity (FPSS) and backward-projection structural similarity (BPSS) to divide each image into four groups: motion region, saturated region in the source image, saturated region in the reference image, and static and unsaturated regions. Then, the weight maps and the motion maps constructed based on FPSS and BPSS are introduced in the weighted LRMC model to reconstruct the background irradiance maps. Experiments are conducted on several challenging image sets with complex scene, and the results show that the proposed method outperforms three current state-of-the-art methods and Photoshop cs6 and is robust to the reference image.

Seepage analysis of clay core wall dam based on ABAQUS

The seepage analysis of earth-rock dams is required to define the seepage field as a community of saturated and unsaturated regions. The two complement each other. The motion characteristics of unsaturated seepage are relatively complex, and the influence factors are more than saturated seepage. In this paper, combined with engineering examples, the finite element numerical simulation is used to simulate the variation of the seepage field of the earth-rock dam in saturated and unsaturated seepage, and the wetting line, seepage flow and stress and strain inside the dam are obtained. The data results are reasonable and correct. It has certain reference value in the construction of anti-seepage system of earth-rock dam.

Fast Detection and Compensation of Current Transformer Saturation Using Extended Kalman Filter

In this paper, an efficient method based on the Kalman filter (KF) theory is proposed for fast and accurate detection and compensation of current transformer (CT) saturation. During the unsaturated regions, the algorithm uses the current sample points together with extended Kalman filter (EKF) for obtaining a model, which suitably represents the current signal behavior. The acquired model is used to reconstruct the original current waveform during the saturated regions. The onset and end points of the CT saturation intervals are detected by defining a criterion based on the estimation error of the EKF algorithm. The proposed method is very profitable as it requires only one sample point to detect the CT saturation and it also copes with the problems of measurement noises and harmonics. These advantages are confirmed by a large number of test cases obtained using PSCAD/EMTDC software as well as by real-time hardware implementation.