Variation Of Resistivity Research Articles

INCROP ZONE DEMARCATION OF COAL SEAM USING ELECTRICAL RESISTIVITY TOMOGRAPHY-A CASE STUDY OF A COAL BLOCK IN THE MAIN BASIN OF THE SINGRAULI COAL FIELD

Delineation of Coal seam incrop zone is necessary for mine economics and coal conservation during mining operation. In this study demarcation of the incrop zone of a coal seam has been done by using the Electrical Resistivity Tomography method of Geophysical Electrical Resistivity survey. The resistivity data acquisition of the subsurface has been carried out by a 48-channel resistivity meter in the incrop zone of coal seams of the Main basin of the Singrauli coalfield. The resistivity of the subsurface in 2D sections along the 1000m survey lines is measured and plotted with the help of inversion techniques using RES2DINV software to depict the actual lithology of the subsurface in an Electrical resistivity imaging survey. The resistivity of the subsurface varies according to the geological characteristic of the rock, porosity, saturation of water, mineral and fluid content, etc. in the rock, and the resistivity of coal seams is generally higher than sedimentary country rock. The characteristics of higher resistivity of coal seam compared to country rock are helpful to demarcate the actual position of coal seam incrop zone. Resistivity variations of the subsurface are well correlated with geological formation as provided in available borehole lithology. Electrical Resistivity Tomography is effectively used to delineate the incrop zone of coal seams. The resistivity imaging survey is more economical and environmentally friendly in comparison to the conventional drilling method to prove the incrop zone of the coal seam.

The Small-Strain Stiffness Properties of Clay-Gravel Mixture Subjected to Freeze-Thaw Cycles

Abstract In this paper, the resonant column tests were utilized to examine the small-strain stiffness and attenuation of clay-gravel mixture (CGM) under various effective consolidation pressures and freeze-thaw cycles, on the basis of investigating the electrical resistivity variation trend of CGM samples undergoing various freeze-thaw cycles. It is shown that the resistivity of CGM tends to stabilize when the freeze-thaw cycles (N) reach 9, and, thus, the samples after 0, 3, 6, 9, and 12 cycles were selected for resonance column testing. The results show that, once N > 9, the decay in dynamic shear modulus demonstrates a weakened association with N and the stiffness degradation effect of freezing-thawing would be weakened and inhibited by high effective consolidation stress. Additionally, a mathematical model was constructed to predict the maximum dynamic shear modulus (Gmax) in the basis of freeze-thaw cycles and effective consolidation stress. Microscopic analysis results suggest that the freeze-thaw effect on CGM lies in the development of soil aggregates and porosity variation within the fine-grained soil. Compared to gravel soils and frozen soil, the cementation of matrix soil and the effect of blocky structure are considered as fundamental reasons for the improved small-strain stiffness and reduced vulnerability to freeze-thaw cycles of CGM.

Geoelectrical Investigation of the Groundwater Potential in Eti-Osa, Lagos State, Nigeria

An electrical resistivity survey was conducted in Eti-Osa, Lagos State, Nigeria, to characterize the subsurface lithologic units, delineate the underlying aquifer, and assess groundwater potential. The study utilized an ABEM SAS 1000 terrameter for the data acquisition. Eight vertical electrical soundings were carried out using the Schlumberger electrode configuration. Data interpretation, both qualitative and quantitative, was presented through tables, charts, and sections. The interpreted geoelectric models revealed three to five layers with varying lithologies, including topsoil, sand, silty sand, sandy clay, silty clay, and clay. The first geoelectric layer, with resistivity values ranging from 8 Ωm to 320 Ωm, is relatively thin, with a thickness between 0.4 m and 3 m. The second layer exhibits thicknesses of 1.3 m to 15 m and resistivity variation between 1.5 Ωm to 185 Ωm. The third layer varies in thickness from 1 m to 36 m, with varying resistivity between 9 Ωm to 335 Ωm. The fourth geoelectric layer has a thickness range of 5 m to 20 m and resistivity values between 1.6 Ωm and 193 Ωm. The basement resistivity ranges from 3 Ωm to 361 Ωm. The study identified the sand layers, particularly at VES points 1, 2, 3, and 8, as the most promising for groundwater extraction. In contrast, VES points 4 and 5 are less favorable, and points 6 and 7 may yield lower-quality water. It is recommended that boreholes be drilled to depths greater than 20 meters at VES sites 1, 2, 3, and 8 for optimal water quantity and quality. However, sites 3 and 8 may be at risk of contamination due to shallower depths.

Electrospun Mats of Thermoplastic Polyurethane and Carbon Nanotubes with Piezoresistive Behavior

AbstractElectromechanical sensors obtained by electrospun mats have a high surface area and porosity, allowing superior flexibility and sensitivity of response to the sensor. Based on this context, in this work, electrospun mats based on thermoplastic polyurethane (TPU) and multi‐wall carbon nanotubes (MWCNTs) are produced by electrospinning. The electrical resistivity under different compressive stress levels is evaluated in recurring loading and unloading cycles. Incorporating MWCNT increases the elastic modulus and thermal stability but does not significantly increase the electrical conductivity. However, the electrospun mats with different concentrations of MWCNT show variation in electrical resistivity under compressive stress. The response is stable with a compressive stress of 0.25 MPa and five cycles of compression and decompression, with a variation in the relative resistivity of approximately −0.8 for all MWCNT concentrations. A similar response is observed with the increasing of the compressive stress to 0.5 MPa.

Aquifer Exploration Using the Resistivity Method with a Schlumberger Arrays in Sangubanyu Sub-Village, Banyuwangi Village, Bandongan Subdistrict, Magelang Regency

Sangubanyu sub-vilage is administratively located in Banyuwangi Village, Bandongan Subdistrict, Magelang Regency. During the dry season, it is common to find dry wells in the community, making it difficult for residents to access clean water. This situation is highly ironic, as Magelang Regency generally experiences high rainfall, is situated in the Progo and Bogowonto river basins, and is surrounded by mountains that, theoretically, act as water catchment areas. The investigation of aquifer depth was conducted using the Vertical Electrical Sounding (VES) method with a Schlumberger electrode configuration, which is used to map the vertical distribution of subsurface resistivity. VES field data collection was carried out at two measurement points using two current electrodes and two potential electrodes. The electrode spread at each measurement point was 400 meters. The sounding data from each measurement point was interpreted using IP2win software version 3.01, and the results were presented as resistivity logs showing resistivity values, depths, and the thickness of each layer. The interpretation results yielded a 1D resistivity model, showing variations in resistivity with depth. The aquifer layer was identified as sandy tuff with resistivity values ranging from 17 Ωm to 21 Ωm at depths of approximately 33 to 78 meters.

Electrical resistivity variations as a result of natural-technogenic seismicity in the Gorlovka depression of the Altai-Sayan folded region according to electrical tomography data

Relevance. In the last decade, the intensity of development of the Gorlovka coal deposit in Novosibirsk region has significantly increased, which leads to the formation of seismic activation of the subsoil of the Gorlovka depression in response to technogenic impact. Since 2019, earthquakes with a magnitude of more than 4 have been recorded in the field area, felt in Novosibirsk and its suburbs. Currently, damage from natural disasters has been rapidly growing. This happens due to many reasons, such as urbanization, population growth, man-made changes in the geological environment, construction of high-risk facilities that contribute to the activation of negative processes. Therefore, the development of trustworthy criteria for the assessment, forecast and consequences of natural and man-made hazardous phenomena is an urgent task. Timely identification of dangerous geological processes will make it possible to develop and implement measures to prevent and eliminate emergencies of a natural and man-made nature. Aim. Analysis of the results of regular observations by electrical tomography along a profile crossing the fault zone at the study site in the Gorlovka trough for further development of measurement techniques and software for automated processing and interpretation of monitoring data. Methods. Field works, quantitative interpretation Results and conclusions. The authors have obtained the first results of regular observations using electrical tomography along a profile crossing the fault zone at the study site in the Gorlovka trough, interpreting field data using the modernized DiInSo software package. It was found that the identified variations in geoelectric parameters reflect the response of the geological environment both to earthquakes occurring during the observation period and to man-made impacts (explosions). Furthermore, it is demonstrated that the fluctuations magnitude is influenced by the earthquake magnitude.

Eddy Current Measurement of Electrical Resistivity in Heat-Treated Zr-2.5%Nb Pressure Tubes.

Zr-2.5%Nb pressure tubes (PTs) house uranium fuel bundles in the fuel channels of CANDU® nuclear reactors. Preventing a failure mode caused by contact of the PT with an outer calandria tube (CT) is performed by inspection using eddy current (EC) testing and ultrasonic testing (UT) to measure the PT-CT gap. EC gap measurements are particularly sensitive to circumferential variation of the PT's electrical resistivity due to microstructural variations. A full-factorial experiment was performed to examine the statistical significance of variations in the EC test parameters and manufacturing conditions on the average circumferential electrical resistivity of as-manufactured PTs. It was found that 79% of the variance in the data could be attributed to variations caused by any of the test factors or combinations of test factors. The parameters that accounted for the majority of the variance were: (1) heat treatment (HT); (2) HT and EC frequency; (3) probe inner or outer surface placement; and (4) EC frequency. Measurements of circumferential resistivity showed up to ±2.3% variation from the average of either surface. HT caused the average PT resistivity to decrease at a rate of 1.53±0.08 μΩ·cmlog⁡hr and 1.1±0.4μΩ·cmlog⁡hr for inner and outer PT surfaces, respectively. The results are correlated with differences reported in the literature in the average βZr ribbon thickness in the axial-transverse cross-section between inner and outer PT surfaces. The results demonstrate potential for EC-based resistivity measurements to characterize variations and changes in the microstructure of Zr-2.5%Nb PT material.

Validation of four resistivity mixing models on field time lapse geoelectrical measurements from fine-grained soil undergoing freeze-thaw cycles

Resistivity mixing models relate porosity, phase composition and specific resistivities of ground materials to their bulk (effective) electrical properties. These models were typically derived for calculating hydrocarbon saturation from geophysical logs. In permafrost monitoring applications, they have been used to link ground electrical response to its phase composition, with focus on unfrozen water vs. ice content, and to derive changes in ground ice content from repeated resistivity acquisitions. Such quantitative interpretations rely on validity of the mixing models in a context different from the one they were derived in. To increase the reliability of the permafrost forecasts that are based on repeated resistivity surveys, we undertook validation of four selected resistivity mixing model formulations: i) the original Archie's law, ii) the Archie's law with an ice-content dependent cementation exponent m (Archie-M), iii) a modification of the Archie's law for multiple conducting phases (Archie-N), and iv) the geometric mean model (GM). The model application context was permafrost monitoring and fate forecasting on natural fine-grained soil undergoing cycles of freezing and thawing, based on indirect (geophysical), in-situ time-lapse resistivity measurements. The purpose of the calibrated resistivity models was to derive the phase composition of the ground from in-situ resistivity measurements, with acceptable quantitative reliability, notably with respect to the amount and changes of ice and water content. In our validation framework, daily temperature-dependent soil phase distribution was converted into an effective resistivity distribution of the ground using each of the four resistivity mixing models. From the effective resistivity model, an apparent resistivity response was forward calculated and compared to time-lapse field apparent resistivity measurements from a permafrost monitoring field site. The performance metrics were i) the root mean square error between the forward-calculated and field-measured apparent resistivities throughout the freeze-thaw season, ii) the percentage of field apparent resistivity data explained by each resistivity model, and iii) the plausibility of the calibrated model parameter estimates. We found that despite different current conducting mechanisms involved in each of the resistivity mixing model formulations, the quantitative performance of the four evaluated models was very similar. The four models typically reproduced the field-measured resistivity variations within one to two standard deviations (STD) of the field measurements, depending on the time of the year and depth in the soil profile. In the active layer, the Archie-M model most consistently reproduced the field data within 1 STD throughout the freezing and frozen periods of the year (September – May). Meanwhile, the GM best matched the actual values of resistivities during freezing. The GM also recovered porosities of the three model layers close to the true values measured on borehole samples. All the tested models were challenged by accurately simulating the thawing period – overestimating resistivities in the temperature range from −5 °C to −2 °C and underestimating them between −2 °C and thawing point. Consequently, the choice between the models should depend on the specifics of a particular application, such as available calibration data, desired parameters or ground properties to resolve, sensitivity of the modeling framework etc. An application-specific validation of several resistivity mixing models and quantification of performance of the chosen resistivity model may be called for. Additionally, the possibility of using different mixing model and water content parameterizations should be investigated, to adequately address complex ground resistivity structures and phase change processes typical of permafrost ground.

Enhancement of microstructure-based magnetic, electronic, and lattice contribution in a CoNiAl ferromagnetic shape memory alloy

In this study, a Co-Ni-Al system with nominal compositions Co42​Ni31Al27​ and Co41Ni32Al27​ was synthesized. The structural and microstructure of these confirm the presence of a non-ferromagnetic face-centered cubic (γ) phase interspersed between the grains of a ferromagnetic body-centered cubic (β) phase. Notably, γ phase is increased by 1.5 times in the Co41Ni32Al27 sample due to the 1% substitution of Co by Ni. The microstructural tuning induced a higher thermal hysteresis in the shape memory effect of Co41​Ni32Al27 with an increase in enthalpy during the phase transition (Austenitic↔Martensitic). In addition, the temperature-dependent resistivity, ρ(T) was measured to study the electron-phonon and electron-magnon scattering around the phase transition of the studied samples. The dynamic elastic properties of the studied samples were tracked by the relative change in sound velocity (δv/v) with temperature and elastic recovery was confirmed in both alloys across the 120 K to 300 K range. However, the Co41​Ni32Al27​ exhibits a high amount of lattice contribution to the shape recovery compared to the Co42​Ni31Al27​. Moreover, a larger variation in relative resistivity (Δρ/ρ) for Co41Ni32Al27 compared to Co42​Ni31Al27 during the phase transition indicates a larger shape change due to decreased Co content. Furthermore, the Co41Ni32Al27 sample shows higher temperatures of martensitic start (TMs ≈ 260K) and Austenitic finish (TAf ≈ 290K) along with high Curie temperature (Tc = 330K). Consequently, the temperature-dependent susceptibility (χ′) confirms the higher magnetoelastic recovery in the Co41Ni32Al27 sample, indicating an enhancement of magnetic field-induced strain (MFIS). Stress-induced Q−1 is lower for Co41Ni32Al27 (∼2.9×10−3) compared to Co42Ni31Al27 sample (∼5.0×10−3) signifying the enhanced mechanical strength.

Electron-lattice coupling and double exchange effects to improve TCR of La0.67-xNdxCa0.25Sr0.08MnO3 films grown on La0.3Sr0.7Al0.65Ta0.35O3 substrates

In this study, La0.67−xNdxCa0.25Sr0.08MnO3 (LNCSMO, x = 0.09, 0.10, 0.11, 0.12) films were prepared by sol-gel spin coating method. The results indicate that the LNCSMO film is oriented and grown on a La0.3Sr0.7Al0.65Ta0.35O3 (LSATO) (00l) substrate. In addition, with the increase of Nd3+ content, the Mn-O bond length (dMn-O) and Mn-O-Mn bond angle (θMn-O-Mn) decreases. The concentration ratio of Mn4+ increases firstly and then decreases, and resulting in an enhanced and then weakened double exchange (DE) effect. Measuring the variation of sample resistivity with temperature (ρ-T) using the standard four-probe method. As the content of Nd3+ increases, the metal-insulator transition temperature (Tp) gradually decreases, and the resistivity (ρ) gradually increases. The replacement of Nd3+ makes the peak temperature coefficient of resistivity value (TCRmax) of the material firstly increase and then decrease. At x = 0.11, the TCRmax reaches 34.28% K-1 at 254.72 K. This provides new insights into the impact of Nd doping on electrical transport properties.

The X-Direction Scanning of Atomic Force Microscopy to Analyze Porous Silicon P-Type Si(100) Fabricated by Electrochemical Anodization Method

This work only investigated the x-direction scanning of atomic force microscopy, which can accurately measure porous silicon's width, depth, and roughness. Pores on p-type Si (100) surfaces fabricated by electrochemical anodization method with the variation of resistivity and current density, i.e., 0.001-0.005 Ω.cm (high dopant) and 1-10 Ω.cm (low dopant), and 4, 6, 8, and 10 mA/cm2, respectively. Macroporous silicon was obtained for both high and low dopants. Pore width, pore depth, and roughness of silicon increase with increasing the current density. Characteristics of porous silicon for high dopants are smaller than that for low dopants. It indicates that large amounts of dopant in silicon can slow the etching process.

Geoelectric Joint Inversion for 3D Imaging of Vineyard Ground

Using a novel joint inversion approach, this study tackles the challenge of accurately characterizing subsurface electrical resistivity in vineyards, a critical and strategic aspect of precision viticulture. For the first time, we integrate 3D Galvanic Contact Resistivity with multi-2D Capacitively Coupled Resistivity data. Conducted in a prestigious Sangiovese vineyard in Montalcino (Tuscany, Italy), the data are analyzed utilizing a single algorithm capable of inverting Capacitively Coupled Resistivity, Galvanic Contact Resistivity, and joint datasets. This approach combines data sensitive to different depths and spatial resolutions, resulting in a comprehensive analysis of soil resistivity variations and moisture distribution, thus providing a detailed and coherent subsurface model. The joint inversion produced a high spatial resolution 3D resistivity model with a density of 20.21 data/m3. This model significantly enhances subsurface characterization, delineating root systems and correlating water distribution with resistivity patterns, showing relative variations sometimes greater than 50%. This method reduced data misfit more effectively than individual inversions and identified a low-resistivity volume (<20 Ω·m), extending from northeast to south, indicating the presence of subsurface water. The systematic alternation of high and low resistivity across vineyard rows highlights the impact of soil management activities on resistivity and supports targeted interventions for vineyard health.

Enhancing weathered slope stability assessment through the integration of slake durability index, elastic modulus of knocking ball, and electrical resistivity tomography.

This research assesses the stability of sedimentary rock slopes in Teloi, Sik, Kedah, by focusing on the mechanical properties of the rock layers and their susceptibility to weathering. Key tests include the slake durability index (SDI), elastic modulus of knocking ball (Ekb), and electrical resistivity tomography (ERT). The incorporation of electrical resistivity tomography (ERT) data through the virtual reality platform facilitates the visualization of subsurface conditions. The variability of strength characteristic of interbedded sedimentary rocks leads to the differential weathering of rock layers, which causes deterioration on the slope structure. The testing revealed significant variability in rock strength, with sandstone displaying higher durability (Id > 17.1%) and elasticity (Ekb: 0.97 to 29.31 GPa) compared to shale and siltstone, which exhibited lower durability and elasticity (Id < 2.2%, Ekb: 0.2 to 2.2 GPa). Utilizing the Wenner array setup, three distinct electrical resistivity lines were established to evaluate subsurface anomalies. The ERT profiles revealed variations in electrical resistivity among different rock types, identifying areas of weaker material, which are siltstone and shale, while high resistivity areas indicate sandstone. Kinematic analysis through the stereonet process revealed direct toppling as the primary failure mechanism, driven by the critical orientations of joint sets J1, J2, and J3. This aligns with on-site observations of hanging sandstone blocks prone to toppling failure. The findings of this research show that the slake durability index (SDI) and the elastic modulus of the knocking ball (Ekb) enhance the assessment of mechanical properties and weathering resistance of interbedded sedimentary rocks. The virtual reality platform was particularly helpful in analyzing and visualizing the sub-surface conditions and enhancing the evaluation of complex geological data. As a conclusion, this integrated method was helpful in the comprehensive geotechnical evaluation of the slopes, enabling the selection of effective stabilization measures by assessing the differential weathering of interbedded sedimentary rock and identifying potential failure zones.

One‐dimensional deep learning inversion of marine controlled‐source electromagnetic data

AbstractThis paper explores the application of machine learning techniques, specifically deep learning, to the inverse problem of marine controlled‐source electromagnetic data. A novel approach is proposed that combines the convolutional neural network and recurrent neural network architectures to reconstruct layered electrical resistivity variation beneath the seafloor from marine controlled‐source electromagnetic data. The approach leverages the strengths of both convolutional neural network and recurrent neural network, where convolutional neural network is used for recognizing and classifying features in the data, and recurrent neural network is used to capture the contextual information in the sequential data. We have built a large synthetic dataset based on one‐dimensional forward modelling of a large number of resistivity models with different levels of electromagnetic structural complexity. The combined learning of convolutional neural network and recurrent neural network is used to construct the mapping relationship between the marine controlled‐source electromagnetic data and the resistivity model. The trained network is then used to predict the distribution of resistivity in the model by feeding it with marine controlled‐source electromagnetic responses. The accuracy of the proposed approach is examined using several synthetic scenarios and applied to a field dataset. We explore the sensitivity of deep learning inversion to different electromagnetic responses produced by resistive targets distributed at different depths and with varying levels of noise. Results from both numerical simulations and field data processing consistently demonstrate that deep learning inversions reliably reconstruct the subsurface resistivity structures. Moreover, the proposed method significantly improves the efficiency of electromagnetic inversion and offers significant performance advantages over traditional electromagnetic inversion methods.

Investigation of soil resistivity impacts on the electrodes of grounding system subjected to lightning strikes

AbstractIn this paper, the study of the homogeneous resistivity and two‐layer soil influences on the performance of the electrodes of grounding systems subjected to lightning strikes is carried out considering soil ionization. The study is done on the behaviour of the ground electrodes while the resistivity of the soil is altered from small to high value in the case of homogeneous soil, while the study is obtained on two‐layer soils in the case of diverse values of the reflection factor. In the suggested algorithm for two‐layer soils, each layer has its resistivity and dielectric constant, where the dielectric constant and soil resistivity depend on the lightning frequency. The field resulting from lightning strikes, which causes soil ionization, has been studied, and the results have been used to understand the behaviour of ground rods under the influence of lightning strikes. The credibility of the results has been strengthened by comparing it with what others have obtained recently. The article's novelty can be summarized in the investigation of the performance of the electrodes of grounding grids that are installed in high soil resistivity of uniform and two‐layer soils containing the impacts of soil ionization, lightning frequency, soil resistivity, and permittivity variations.

Correlation between electrical resistivity and compressive strength of stabilized dredged sediment for early quality control

Quality control of stabilized dredged sediment (DS) presents significant challenges due to its high-water content. Nowadays, many in-situ and laboratory tests have been used to evaluate the quality of treated DS, and the dominant method is 28-day unconfined compressive strength that can be done on undisturbed samples from the field and the laboratory. Due to the waiting period to get results from the tests and the destructive nature of tests, it is desirable to use a non-destructive method to control the quality of stabilized DS at an early stage. This study suggests electrical resistivity measurement as a non-destructive and fast method for evaluating the quality of stabilized DS. Dredged sediment samples from Göta älv, Gothenburg, with different water contents, were stabilized with different water-binder ratios at the laboratory. The quality of treated sediments was evaluated by uniaxial compressive strength (UCS) after 28-day of stabilizing, while strength development during the curing period was checked with a free-free resonance test at 7, 14, and 28 days of curing, and the electrical resistivity (ER) measurement monitored on some samples during the curing period. The results indicate that a combination of UCS tests and ER measurements can be utilized early stage evaluation of the quality of stabilized DS already after 24, 48 or 72 h. According to the results, after 24 h of hydration, the electrical resistivity was less than 1 Ωm. After 72 h of hydration, the resistivity was between 1 to 2.5 Ωm, which shows the development of strength. The 28-day strength varied from 0.25 MPa to 2 MPa while the resistivity varied between 3 Ωm to 22 Ωm. The observed variations in resistivity and compressive strength can be attributed to differences in the water-to-binder ratio across the samples.This approach offers a practical, non-destructive method for detecting early quality issues of stabilized DS, enabling quicker decision-making and potentially reducing project timelines and costs while maintaining the integrity and safety of construction projects involving stabilized dredged sediments.

Gallic acid melanin pigment hydrogel as a flexible macromolecule for articular motion sensing

In this study, water-soluble melanin was synthesized through the genetic recombination of Escherichia coli using gallic acid as a substrate. The recombinant host produced 2.83 g/L of gallic acid-based melanin (GA melanin) from 20 mM gallic acid. Notably, the isolated GA melanin demonstrated exceptional antioxidant and antimicrobial activities, exhibiting a 25.7 % inhibition ratio against Candida albicans. The structure and composition of GA melanin were analyzed using Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffraction (XRD). Remarkably, GA melanin displayed high thermal stability, maintaining integrity up to 1000 °C. Additionally, it exhibited unique electrical properties in terms of conductivity and resistivity compared to other common types of melanin. Subsequently, GA melanin was cross-linked with hydrogel to create a sensing template. The resulting GA melanin hydrogel demonstrated lower resistance (80.08 ± 3.0 kohm) compared to conventional hydrogels (108.62 ± 10.4 kohm), indicating an approximately 1.77-fold improvement in adhesion. Given its physical, biological, and electrical properties, the GA melanin hydrogel was further utilized as a flexible motion-sensing material to detect resistivity changes induced by knee, wrist, and finger bending, as well as vocal cord vibrations. In all cases, the sensing module displayed notable sensitivity to motion-induced resistivity variations.

Geometric Characterization of the Mateur Plain in Northern Tunisia Using Vertical Electrical Sounding and Remote Sensing Techniques

The Mateur aquifer system in Northern Tunisia was examined using data from 19 water boreholes, 69 vertical electrical sounding (VES) stations, and a Sentinel-2 satellite image. Available boreholes and their corresponding logs were compared to define precisely the multi-layer aquifer system, including the Quaternary and Campanian aquifers of the Mateur plain. Quantitative interpretation and qualitative evaluation of VES data were conducted to define the geometry of these reservoirs. These interpretations were enhanced by remote sensing imagery processing, which enabled the identification of the Mateur plain’s superficial lineaments. Based on well log information, the lithological columns show that the Quaternary series in the Ras El Ain region contains a layer of clayey, pebbly, and gravelly limestone. Additionally, in the Oued El Tine area, a clayey lithological unit has been identified as a multi-layer aquifer. The study area, exhibiting apparent resistivity values ranging between 20 and 170 Ohm·m, appears to be rich in groundwater resources. The correlation between the lithological columns and the interpreted VES data, presented as geoelectrical cross-sections, revealed variations in depth (8–106 m), thickness (10 to 55 m), and resistivity (20–98 Ohm·m) of a coarse unit corresponding to the Mateur aquifer. Twenty-three superficial lineaments were extracted from the Sentinel-2 image. Their common superposition indicated that both of them are in a good coincidence; these could be the result of normal faults, creating an aquifer system divided into raised and sunken blocks.

Laser powder bed fusion of NbTi low-temperature superconductors

This study investigates the superconducting properties of additive manufactured in-situ NbTi alloy using laser powder bed fusion. Laser parameters were optimised for a maximum microstructural density and lowest Nb segregation fraction. These characters have been achieved at the sample built with an energy density of 3.33 J/mm2, where it shows a density value of 6.12 g/cm3, undissolved Nb fraction of 0.05 %, and randomly distributed equiaxed grains with an average size of 10–20 μm. Post-processing of the as-fabricated (AF) sample was explored as a route to collapse residual porosity and dissolve residual segregated Nb particles using hot isostatic pressing (HIP) and heat treatment, respectively. HIPing resulted in a decrease of the undissolved Nb particle fraction to 0.035 %. Heat treatment at 1250 °C for 24 h, followed by aging at 400 °C for 2 h, was found to result in the complete dissolution of Nb particles and precipitation of the ɑ-Ti phase that works as pinning centres to increase the superconducting properties. The grain size increased in both post-processes to 400–500 μm. Electrical and magnetic properties were also measured for the AF, HIP and heat-treated samples. The thermal variation of electrical resistivity showed a critical temperature (Tc) range of 9.8–9.0 K, 9.6–9.1 K and 9.9–8.8 K for the AF, HIP, and heat-treated samples, respectively, which were close to the values obtained from magnetic measurements. The critical current density (Jc) was calculated using Bean’s model employing the magnetic hysteresis loops. The AF condition showed a negligible value of Jc (5 × 10−3 kA/mm2), which improved to 0.28 kA/mm2 and 2.65 kA/mm2 for the HIPed, heat treated conditions, respectively (at 4.2 K, 5 T). Mechanical tensile testing was performed for the heat-treated sample to ensure both mechanical and superconducting properties would achieve the required performance, where achieves ultimate tensile strength value of 930 MPa, with 8 % elongation.

Assessing the effect of offline topography on electrical resistivity measurements: insights from flood embankments

Summary Electrical resistivity tomography (ERT), a geophysical imaging method, is commonly used on flood embankments (dykes or levees) to characterise their internal structure and look for defects. These surveys often use a single line of electrodes to enable 2D imaging through the embankment crest, an approach that enables rapid and efficient surveying compared to 3D surveys. However, offline variations in topography can introduce artefacts into these 2D images, by affecting the measured resistivity data. Such topographic effects have only been explored on a site-specific basis. If the topographic effects can be assessed for a distribution of embankment geometries (e.g. slope angle and crest width) and resistivity variations, it would allow for targeted correction procedures and improved survey design. To investigate topographic effects on ERT measurements, we forward-modelled embankments with different trapezoidal cross-sections sat atop a flat foundation layer with contrasting resistivity values. Each was compared to a corresponding flat model with the same vertical resistivity distribution. The modelling workflow was designed to minimise the effect of forward modelling errors on the calculation of topographic effect. We ran 1872 unique embankment forward models, representing 144 geometries, each with 13 different resistivity contrasts. Modelling results show that offline topography affects the tested array types (Wenner-Schlumberger, Dipole-Dipole, and Multiple-Gradient) in slightly different ways, but the magnitudes are similar, so all are equally suitable for embankment surveys. Three separate mechanisms are found to cause topographic effects. The dominant mechanism is caused by the offline topography confining the electrical current flow, increasing the measured transfer resistance from the embankment model. The two other mechanisms, previously unidentified, decrease the measured transfer resistances from the embankment model compared to a layered half-space but only affect embankments with specific geometries and resistivity distributions. Overall, we found that for typical embankment geometries and resistivity distributions, the resistivity distribution has a greater control on the magnitude of the topographic effect than the exact embankment geometry: the subsurface resistivity distribution cannot be neglected. 2D inversions are suitable when both the embankment is more resistive than the foundations and when the embankment's cross-sectional area is greater than 4 m2/m2 (area scaled to an embankment with a height of 1 m). Topographic corrections, 3D data acquisition or 3D forward models are required when these conditions are not met. These are demonstrated using field data from an embankment at Hexham, Northumberland, UK. Improving the accuracy of the resistivity values in ERT models will enable more accurate ground models, better integration of resistivity data with geotechnical datasets, and will improve the translation of resistivity values into geotechnical properties. Such developments will contribute to a better characterised and safer flood defence network.