Saturation State Research Articles

Comparative Analysis of Analogue and Digital Methods for Magnetic Flux Estimation in the Core of a Medium-Voltage Voltage Transformer Operating Under Ferroresonance Conditions

The main objective of the research described in the article was to determine the following: Is it possible to estimate the magnetic flux linkage in the core of a voltage transformer using analogue or digital methods? Will it be possible to estimate it approximately both in the normal state and in the state of deep core saturation (ferroresonant state)? The research aimed to identify the advantages and disadvantages of both proposed estimation methods. As part of the research described in this paper, a simulation model was developed and executed in the MATLAB/Simulink environment to generate a series of secondary voltage and flux waveforms in voltage transformers. The secondary voltage and flux waveforms were modelled under ground fault conditions, initiating ferroresonance oscillations in the medium-voltage network. To determine the associated flux from the simulated secondary voltages of the voltage transformers, an analogue integration circuit, a voltage analogue input circuit and a numerical integration algorithm with offset elimination were developed and implemented in an STM32 microcontroller. The obtained reference flux waveforms were used to verify the accuracy of the estimation of flux waveforms obtained using the analogue and digital methods. As a result, it was determined that both methods allow for a relatively accurate estimation of the periodic component of the magnetic flux. It also presented how both methods respond to the presence of slowly changing (aperiodic) components. Possible applications were proposed in order to create an innovative criterion for detecting ferroresonance oscillations.

Differential impacts of pH on growth, physiology, and elemental stoichiometry across three coccolithophore species

AbstractCoccolithophores are pivotal players in ocean biogeochemistry, yet the impact of changing pH on the physiology of different species remains unclear as there has been a dominant focus on Gephyrocapsa huxleyi. Meta‐analyses of existing experimental data are challenging due to the differences in multidimensional culture conditions. This study investigated the response of three species—Gephyrocapsa huxleyi, Coccolithus braarudii, and Chrysotila carterae—under varying CO2 conditions (via pH). The sensitivity to pH differed between species, but all species showed reduced growth rates under the highest CO2 (lowest pH) treatment possibly due to high [H+]‐related inhibition. Low pH impacted cellular physiology and elemental stoichiometry, while the impact of high pH was less adverse. The changes in elemental production induced by low pH could exert a negative influence on the contribution of coccolithophores to nutrient and carbon export, especially for biogeochemically relevant open‐ocean species. pH also affected coccolith formation, especially in C. braarudii, through CO2 limitation at high pH and low calcite saturation state at low pH. Contrasting species‐specific pH sensitivities highlighted the potential for species like G. huxleyi to further outperform others like C. braarudii in an acidic ocean. Literature synthesis showed that coccolithophores show a broad CO2 optimum, although growth rates and particulate inorganic carbon to particulate organic carbon ratios consistently declined with increasing CO2. Strain‐specific CO2 optima partly contributed to the variability within responses of individual species, giving the misleading perception of a broad species‐level CO2 optimum. Strain‐specific optima exist possibly due to their adaptation to carbonate chemistry conditions at the place of origin.

Reduced-Order Modeling for Subsurface Flow Simulation in Fractured Reservoirs

Summary Reservoir simulation for fractured reservoirs is often challenging and time-consuming due to the strong heterogeneity and complex flow dynamics introduced by fracture-matrix interactions. In this study, we introduce a novel reduced-order modeling procedure to speed up the flow simulation of fractured reservoirs. The reduced-order model (ROM) is developed based on proper orthogonal decomposition (POD) in conjunction with the embedded discrete fracture model (EDFM) that provides full-order simulation results. With the full-order training simulation, snapshots of reservoir pressure and saturation state at different timesteps are captured and assembled into separate data matrices. Singular value decomposition (SVD) is then applied to these data matrices to obtain a reduced set of orthogonal base vectors for pressure and saturation solutions, respectively. These base vectors enable the projection of high-dimensional linear equations into much lower-dimensional spaces, which significantly accelerates the process of solving nonlinear governing equations under the EDFM approach. The developed reduced-order modeling procedure is implemented in the MATLAB reservoir simulation toolbox (MRST) and tested via multiple cases for both 2D and 3D fractured reservoirs under different boundary and well control scenarios. In certain challenging cases, the use of multiple training simulations is explored and is shown to provide improved predictions. Overall, the proposed ROM approach is able to provide simulation results that are very consistent with those obtained from the full-order simulations while achieving computational speedups of about an order of magnitude for large-scale cases. These observations indicate that the proposed ROM exhibits satisfactory generalization performance, making it suitable for problems that require many flow simulations under different settings, such as production optimization.

Calcium isotopes support spatial redox gradients on the Tethys European margin across the Triassic-Jurassic boundary

The end-Triassic mass extinction was among the most severe biotic crises of the Phanerozoic. It has been linked with the global expansion of marine anoxia, and the prolongation of these conditions within epeiric seas has been proposed as a cause for the suppression of biodiversity during the Hettangian. Testing this interpretation is complicated by spatially heterogeneous patterns of local marine redox conditions within the western Tethys European Epicontinental Shelf. In this study, we assess the redox state within this region by focusing on two carbonate successions in Italy, a peritidal platform at Mount Sparagio, Sicily, and an offshore ramp deposit at Val Adrara in the Southern Alps. Based on previously published I/Ca ratios, these locations record distinct local background redox conditions, with Val Adrara showing a notably lower pre-extinction oxygen saturation state than Mount Sparagio. Here, we measure δ13C and δ18O at Mount Sparagio and δ44Ca and trace element ratios at both sites to identify the roles of mineralogical and diagenetic effects on the preservation of primary redox signals. A numerical framework of multiple elemental (Sr, Mg, Mn, I) and isotopic (δ13C, δ18O, δ44Ca, δ238U, and δ34SCAS) ratios was constructed to recognize modes of carbonate diagenesis and source-mixing in the data. While diagenesis is impossible to completely rule out, our state-of-the-art approach provides robust evidence against common forms of diagenetic alteration as the main drivers of the overall paleoredox proxy trends.Where the redox signals are largely preserved, we interpret differences in pre-extinction I/Ca between the two sites to reflect distinct local oxygenation states. Drawing from published Community Earth System Model simulations, we propose that ocean circulation and hydrological regime could have been important drivers of spatial heterogeneity in paleo-redox conditions across the European Epicontinental Shelf.

Progression of ocean interior acidification over the industrial era.

Ocean acidification driven by the uptake of anthropogenic CO2 represents a major threat to ocean ecosystems, yet little is known about its progression beneath the surface. Here, we reconstruct the history of ocean interior acidification over the industrial era on the basis of observation-based estimates of the accumulation of anthropogenic carbon. Across the top 100 meters and from 1800 to 2014, the saturation state of aragonite (Ωarag) and pH = -log[H+] decreased by more than 0.6 and 0.1, respectively, with nearly 50% of the progression occurring over the past 20 years. While the magnitude of the Ωarag change decreases uniformly with depth, the magnitude of the [H+] increase exhibits a distinct maximum in the upper thermocline. Since 1800, the saturation horizon (Ωarag = 1) shoaled by more than 200 meters, approaching the euphotic zone in several regions, especially in the Southern Ocean, and exposing many organisms to corrosive conditions.

Experimental Study on Deformation and Damage Evolution of Cracked Red Sandstone Under Freeze–Thaw Cycles

Cracked rock masses in cold regions are subjected to freeze–thaw cycles over extended periods, resulting in freeze–thaw deformation. The combined effects of freeze–thaw cycling and the depth of cracks significantly influence the stability and durability of underground rock engineering in these regions. In some cold regions with minimal annual rainfall, rock masses are unable to absorb external water during freeze–thaw cycles. As freeze–thaw deformation progresses, the rock transitions naturally from a saturated state to an unsaturated state. To investigate the deformation damage mechanisms and evolution patterns of saturated red sandstone with initial non-penetrating cracks of varying depths (20 mm, 30 mm, 40 mm) under freeze–thaw cycling conditions without external water replenishment and with naturally varying saturation levels, relevant freeze–thaw cycle experiments and strain monitoring were conducted. The results indicate that cracked red sandstone experiences residual strain in each freeze–thaw cycle, which gradually accumulates, leading to irreversible freeze–thaw damage deformation. The cumulative residual strain of the rock specimen after 45 freeze–thaw cycles was 40.69 times greater than the residual strain from the first cycle. Additionally, the freeze–thaw strain characteristic values exhibited a clear correlation with crack depth. These findings provide experimental methods and data references for analyzing the deformation and failure mechanisms of cracked rock induced by freeze–thaw damage in cold regions.

Measurement Method of Deeply Saturated Excitation Characteristics of Converter Transformer Under AC-DC Hybrid Excitation

During operation, converter transformers enter a saturation state, leading to phenomena such as magnetising inrush currents. Accurately measuring the excitation characteristic curve of an iron core under deep-saturation conditions is essential for analysing low-frequency transient phenomena in transformers. This paper presents a method for calculating the excitation characteristics of a converter transformer under deep iron core saturation. The method involves establishing an improved T model for the converter transformer and conducting open-circuit experiments in the linear working region to obtain the excitation characteristic curve and knee point parameters. AC-DC hybrid excitation is used to achieve deep saturation, and measurements of saturated inductance at different levels of saturation at the transformer terminals are taken. The mathematical relationship between saturated inductance and magnetic impedance is derived, allowing deduction of the magnetising characteristic curve of the converter transformer under deep-saturation conditions based on measured saturated inductance values. A finite element simulation analysis was performed on a single-phase four-column converter transformer with a capacity of 250 MVA. Additionally, a test platform for toroidal transformers and dry-type transformers has been set up to carry out excitation characteristic measurement and verification. Experimental results demonstrate that errors are maintained within 10% or less, validating this approach’s effectiveness.

Cooling potential of cement concrete pavements based on their thermophysical properties

Impermeable paving surfaces constitute one of the main causes of the aggravation of the urban heat island phenomenon. The replacement of such surfaces with cool pavements represents an innovative and promising approach to mitigate this phenomenon. In this study, the investigated cool pavements allow to restrict the rise in the surface temperature by facilitating the evaporation of water through capillary pores. This process occurs from the water-supplied base to the surface exposed to solar radiation. The pavement's cooling potential is quantified by its surface temperature, influenced by various factors, including prevailing weather conditions, thermophysical properties of the pavement, and its initial temperature and saturation state. Within the scope of this research, the pavement’s qualification for its cooling potential is carried out based on the results of an experimental thermophysical characterization. The main objective is to identify the thermophysical properties governing the surface temperature of the pavement under external climatic conditions.To achieve this objective, 21 cement concrete pavements with different formulations are initially identified. These pavements are categorized into two series: the first (denoted as BS) comprises 8 pavements made from recycled sand and containing hydrophilic materials, while the second (denoted as BI) includes 13 pavements made from structural insulating concrete. The methods employed for pavement characterization are outlined, and the corresponding results, encompassing thermophysical properties measurements and surface temperature values, are presented. Analysis of these results reveals new correlations between thermophysical properties and surface temperature. These correlations highlight the coupling between pavement properties, that dictate surface temperature under real summer conditions, contingent on whether the pavement is draining or non-draining. Furthermore, a robust negative linear correlation (R2= 0.92) is identified between surface temperature and evaporation rate under controlled conditions. This underscores the pivotal role of evaporation in substantially regulating the surface temperature of both types of pavements.

Migrating is not enough for modern planktonic foraminifera in a changing ocean.

Rising carbon dioxide emissions are provoking ocean warming and acidification1,2, altering plankton habitats and threatening calcifying organisms3, such as the planktonic foraminifera (PF). Whether the PF can cope with these unprecedented rates of environmental change, through lateral migrations and vertical displacements, is unresolved. Here we show, using data collected over the course of a century as FORCIS4 global census counts, that the PF are displaying evident poleward migratory behaviours, increasing their diversity at mid- to high latitudes and, for some species, descending in the water column. Overall foraminiferal abundances have decreased by 24.2 ± 0.1% over the past eight decades. Beyond lateral migrations5, our study has uncovered intricate vertical migration patterns among foraminiferal species, presenting a nuanced understanding of their adaptive strategies. In the temperature and calcite saturation states projected for 2050 and 2100, low-latitude foraminiferal species will face physicochemical environments that surpass their current ecological tolerances. These species may replace higher-latitude species through poleward shifts, which would reduce low-latitude foraminiferal diversity. Our insights into the adaptation of foraminifera during the Anthropocene suggest that migration will not be enough to ensure survival. This underscores the urgent need for us to understand how the interplay of climate change, ocean acidification and other stressors will impact the survivability of large parts of the marine realm.

Investigation aspects of the geogenic radon potential on Bulgarian territory

Radon (222Rn) is a radioactive gas formed as a result of the radioactive decay of radium (226Ra). Radon is identified as one of the dominant sources of population exposure that could lead to lung cancer, accounting for between 3% and 14% of all lung cancers. Rocks in the Earth’s crust are a primary source of radon in the atmosphere. In this context, the geogenic radon potential (GRP) of a terrain refers to the probability of high radon concentrations being present in a building. The radon index is a concept used to characterize the geogenic potential of the terrain, providing the likelihood of radon concentration in a building, which is directly related to the influence of the Earth's surface. One approach to quantifying the radon index is based on multivariate cross-tabulation, involving two parameters: radon concentration in soil gas and the gas permeability of the earth layer, both measured at 80 cm below the surface. In Bulgaria, focused investigations on the connection between radon gas and geology, resp. on GRP have begun in the last five. As a result of the accumulated experience from field studies conducted so far related to the characterization of GRP, two important aspects have been identified that impact field measurements and the determination of radon gas in the soil, thus the methodology for calculating the radon index. The first aspect is connected with the theoretical and model-based investigations about possible state of soil saturation. The second aspect is about the GRP and fault systems in Sofia. This article makes an attempt to summarize all the studies concerning these two aspects and to suggest some further steps in the geogenic radon potential studies.

Influence of carboxyl functionalized MWCNT loading on the thermal stability and long-term water uptake behavior in tri-layered jute FRCs

Investigations on the influence of carboxyl functionalized MWCNTs on epoxy composites solely reinforced by jute fiber are very scarce. Therefore, an attempt has been made to analyze the long-term moisture absorption behavior and thermal stability at the high-temperature range (30 °C-1200 °C) in jute FRC filled with varying amounts of functionalized MWCNTs (wt. %). Jute fibers derived from needle-punched jute mats were chemically pre-treated and were studied using Fourier Transform Infrared Spectroscopy (FT-IR). The MWCNTs were ultrasonicated to ensure uniform dispersion in the epoxy matrix. Scanning Electron Microscopy (SEM) was performed to observe the fiber, matrix, and filler interactions. As the composites were fabricated using the hand layup technique, air bubbles got entrapped into the specimens for which the void content was also reported. At a substantial saturation state (weight change <5 mg), the composite with 1 % MWCNT absorbed the most water. However, at higher CNT loadings, MWCNT agglomeration stopped water uptake. These results suggest that careful adjustment of MWCNT loading is necessary to balance hydrophilicity and porosity, thereby fine-tuning the water absorption of jute FRC. Thermogravimetric analysis (TGA) has been used in the study to assess the thermal behavior of the composites, indicating that adding MWCNTs at about 1 wt. % CNT loading can increase the thermal stability of jute fiber composites. An elevated concentration of CNTs facilitates agglomeration, impeding moisture absorption, whereas the incorporation of 1 % CNTs improves thermal stability. Consequently, a CNT concentration of 1.5 % is recommended.

Improved p-GaN/AlGaN/GaN HEMTs with magnetronsputtered AlN cap layer

In this paper, a low temperature sputtered AlN cap-layer p-GaN HEMT with high gate breakdown and improved reliability is realized. XPS test shows that the valence band offset of p-GaN and low-temperature magnetron sputtered AlN is 1.2 eV, which successfully suppresses the gate leakage current and greatly improves the gate reliability. Low capacitance–voltage hysteresis and small pulsed threshold voltage shift predict good AlN/p-GaN interface quality. The threshold voltage of the AlN/p-GaN HEMT is improved from 0.61 V to 0.82 V compared to the conventional p-GaN HEMT with tungsten Schottky gate (W/p-GaN HEMT), the DIBL decrease from 34.4 mV/V in W/p-GaN HEMT to 1.1 mV/V in AlN/p-GaN HEMT. The gate forward and reverse leakage is significantly suppressed, and the gate forward breakdown voltage is improved to 17 V. The gate operating range is improved from 7 V to 12 V, and the ID/IG under saturation state is improved from 104 to 107. In addition, a smaller on-resistance of 67.5 Ω·mm was obtained, which is 15.3 % lower than that of the W/p-GaN HEMT, minimizing on-state loss. The gate leakage mechanism of the AlN/p-GaN HEMT is mainly dominated by the PF emission in the medium gate voltage range. Based on this leakage mechanism, the maximum forward VG for a ten-year lifetime was extracted as 6.8 V at room temperature at a failure level of 63.2 % for the AlN/p-GaN HEMT, while this value for W/p-GaN HEMT is 5.4 V. In addition, the AlN cap layer attenuates the depletion region of metal/p-GaN by the gate Schottky metal, which keeps the GaN channel better depleted, thus keeping a higher off-state breakdown voltage. These results demonstrate the good potential of magnetron sputtering AlN as a low-cost, methodologically simple growth method for the commercial use of p-GaN HEMTs.

Effects of water content on the corrosion behavior of NiCu low alloy steel embedded in compacted GMZ bentonite

Buffer material and metal disposal containers are the key engineering barriers in the geological disposal of high-level radioactive waste. The durability of disposal containers largely depends on the water content in buffer material. This work focused on investigating the corrosion evolution of NiCu low alloy steel in compacted GMZ bentonite with different water contents for 270 d by using weight loss, electrochemical measurements, and various methods for analyzing corrosion products. As the water content increased from 13% to 20%, the water in the bentonite transformed from an unsaturated to a critical saturated state, and the corrosion rate of NiCu steel clearly increased. In these two systems, the oxygen could migrate to the thin liquid film on the steel surface through the air pores in the bentonite in the gas phase and undergo cathodic reduction. Meanwhile, it oxidized the ferrous hydrolysis products into ferric corrosion products and formed a rust layer, which could block the diffusion of oxygen. At that moment, the cathodic process of NiCu steel corrosion changed to rust reduction. When the water content continually increased to 30% and 40%, the compacted bentonite was in a saturation state, and the corrosion rate of NiCu steel was significantly decreased. This was because most pores among the bentonite particles were occupied by a large amount of free water, which hindered the diffusion of oxygen and inhibited its cathodic reduction. Furthermore, it restrained the oxidation of ferrous corrosion products, which greatly weakened the cathodic depolarization of rust, leading to the cathodic process being dominated by the hydrogen evolution reaction.

Carbonate dissolution fluxes in deep-sea sediments as determined from in situ porewater profiles in a transect across the saturation horizon

Despite their importance for long-term climate regulation, the rates and mechanisms of seafloor carbonate dissolution are poorly understood, especially with respect to calcite saturation and the role of sedimentary metabolic CO2 production. Here, we present results from an in situ porewater sampler deployed at the Cocos Ridge in the eastern equatorial Pacific, where we examine seafloor carbonate dissolution in locations with bottom water Ωcalcite ranging from 1.0 to 0.84 (1600–3200 m). With cm-scale resolution from the sediment–water interface to 35 cm, we present porewater profiles of total alkalinity, pH, dissolved inorganic carbon (DIC), δ13C of DIC, Ωcalcite, [Mn], [Ca], and [Sr], as well as solid phase porosity, % CaCO3, and % organic C. These profiles provide evidence that deep-sea sedimentary carbonate dissolution occurs via sediment-side control, wherein dissolution is dominated by sedimentary processes rather than strictly bottom water saturation state. We estimate dissolution fluxes using three independent approaches: alkalinity fluxes, δ13C of DIC combined with DIC fluxes, and [Ca] fluxes. We report seafloor dissolution fluxes with uncertainties < 38 %: 40 ± 15, 98 ± 20, 100 ± 32, and 89 ± 27 μmol CaCO3/m2/day at sites 3200, 2900, 2700, and 1600 m deep, respectively. The magnitude of dissolution fluxes is a function of bottom water saturation state (Ωcalcite), bottom water dissolved oxygen, and sedimentary CaCO3 content, but not correlated with any of these parameters independently. We observe dissolution occurring at all stations, including where bottom water is saturated with respect to calcite, and present evidence that this occurs through respiration-driven dissolution within the sediment. At all sites, porewater Ωcalcite decreases below bottom water values before increasing toward saturation deeper in the sediment. Using the δ13C of DIC, we partition the DIC fluxes across the sediment–water interface and find 21–48 % of DIC is sourced from CaCO3 dissolution, with the remainder sourced from organic matter respiration. We present a sedimentary mass balance, assembled with dissolution rates and mass accumulation rates obtained through Δ14C of foraminiferal calcite, and calculate CaCO3 burial efficiencies between 2 and 67 %, inversely correlating with water depth. Our results also provide evidence that net chemical erosion of 5,000––10,000 year old carbonate is occurring at the deepest site. Aerobic organic C respiration coupled with sedimentary CaCO3 dissolution, as documented here, will provide more alkalinity to bottom waters than from undersaturation-driven dissolution alone. This process can neutralize anthropogenic CO2 at the seafloor in a larger range of saturation states than previously estimated.

A stochastic precipitating quasi-geostrophic model

Efficient and effective modeling of complex systems, incorporating cloud physics and precipitation, is essential for accurate climate modeling and forecasting. However, simulating these systems is computationally demanding since microphysics has crucial contributions to the dynamics of moisture and precipitation. In this paper, appropriate stochastic models are developed for the phase-transition dynamics of water, focusing on the precipitating quasi-geostrophic (PQG) model as a prototype. By treating the moisture, phase transitions, and latent heat release as integral components of the system, the PQG model constitutes a set of partial differential equations (PDEs) that involve Heaviside nonlinearities due to phase changes of water. Despite systematically characterizing the precipitation physics, expensive iterative algorithms are needed to find a PDE inversion at each numerical integration time step. As a crucial step toward building an effective stochastic model, a computationally efficient Markov jump process is designed to randomly simulate transitions between saturated and unsaturated states that avoids using the expensive iterative solver. The transition rates, which are deterministic, are derived from the physical fields, guaranteeing physical and statistical consistency with nature. Furthermore, to maintain the consistent spatial pattern of precipitation, the stochastic model incorporates an adaptive parameterization that automatically adjusts the transitions based on spatial information. Numerical tests show the stochastic model retains critical properties of the original PQG system while significantly reducing computational demands. It accurately captures observed precipitation patterns, including the spatial distribution and temporal variability of rainfall, alongside reproducing essential dynamic features such as potential vorticity fields and zonal mean flows.

The effect of carbonate chemistry on trace elements incorporation in a high-Mg calcitic foraminifera

The sodium-to-calcium ratio (Na/Ca) of biogenic CaCO3 has recently been introduced as a proxy for past seawater Ca2+ concentrations ([Ca2+sw]) as demonstrated by a positive correlation between seawater and shell Na/Ca with minor influence of salinity. In the present study, we investigate the effect of carbonate chemistry on the Na/Ca proxy by conducting a set of experiments independently varying pH and the concentration of dissolved inorganic carbon (DIC). In addition to Na+, the incorporation of Li+, Mg2+, and Sr2+ into the shells of the large benthic high-Mg calcitic foraminifer Operculina ammonoides was assessed by culturing under constant DIC (∼2170 µmol kg−1) with varying pH (7.5–8.4 NBS scale), and under varying DIC (830–2470 µmol kg−1) with constant pH (∼7.9). Foraminiferal growth rate correlates linearly with calcite saturation state (Ω) of the experimental seawater (SW). The lowest pH and DIC experiments show low population growth rates, and some of these specimens died and their shells partially dissolved.Na/Cashell and Li/Cashell in O. ammonoides are positively correlated with SW [CO32–] and Ω, whereas Sr/Cashell and Mg/Cashell are much less sensitive to these parameters. The relative sensitivity of Na/Cashell to Ω in O. ammonoides is ∼ 4 % per Ω unit. However, given that past changes in surface water Ω were probably small relative to changes in [Ca2+sw] the correction for this secondary effect over the Cenozoic is likely to be small. Therefore, we conclude that O. ammonoides Na/Ca sensitivity to the carbonate system is unlikely to compromise the use of this proxy to reconstruct past [Ca2+sw]. In the case of the low-Mg planktic and benthic foraminifera, a data compilation exercise indicates that no resolvable carbonate chemistry effect exists on Na/Ca. Thus, the Na/Ca proxy in benthic nummulitid and planktic foraminifera can be utilized for past [Ca2+sw] reconstructions. Furthermore, coupling this information with the distribution coefficients of other elemental and isotopic systems (e.g., Li+, Sr2+, Mg2+, K+, B, δ11B) may allow the reconstruction of wider aspects of past ocean chemistry. Finally, comparison of trace and minor element incorporation into low and high-Mg foraminiferal species, coccolithophores, inorganic calcite, and amorphous CaCO3 (ACC), we propose a modified biomineralization model for hyaline foraminifera centered on SW vacuolization. Foraminiferal data can be explained by a biomineralization process in which high-Mg species utilize a precursor phase (ACC) to produce high-Mg calcite whereas low-Mg species actively remove Mg2+ from the site of calcification.

High strain rate behaviour of cohesive soils

Soil-filled wire and geotextile gabions are essential components of defensive infrastructure in military bases, leveraging the attenuating properties of soils to safeguard personnel and critical assets against blast and fragmentation effects. However, understanding the behaviour of cohesive soils under extreme loading conditions remains largely unexplored, presenting a crucial knowledge gap for design engineers tasked with developing robust soil constitutive models to address evolving threats. This study investigates the response of cohesive soils, focusing primarily on kaolin clay due to its homogeneity, widespread availability and consistent properties. Through high strain rate experimental testing of kaolin clay specimens, using the split-Hopkinson pressure bar (SHPB) apparatus, both unconfined and confined conditions are explored across varying moisture contents, spanning the spectrum from unsaturated to fully saturated states. The analysis of the experimental results uncovers the strain rate dependence of cohesive soils and identifies distinct phase behaviour for transmitted and radial stresses influenced by factors such as strain rate, moisture content and confinement. Utilising LS-DYNA, and the finite element method (FEM), the SHPB tests are modelled for comparison against experimental findings. While LS-DYNA, supplemented by Smooth Particle Hydrodynamics (SPH) node modelling, provides valuable insights, significant disparities between modelled and practical results underscore the challenges inherent with the accuracy in simulating the behaviour of cohesive soils. Nonetheless, this comprehensive exploration of cohesive soil’s high strain rate behaviour yields critical insights for engineers, enabling them to adapt defensive strategies to diverse threats and loading scenarios effectively.

Climate controls on speleothem initial 234U/238U ratios in midlatitude climate over two glacial cycles

Despite early hydrological studies of 234U/238U in groundwaters, their utilization as a paleoclimatic proxy in stalagmites has remained sporadic. This study explores uranium isotope ratios in 235 datings (230Th) from six stalagmites in Ejulve cave, northeastern Iberia, covering the last 260 ka. The observed 234U enrichment is attributed to selective leaching of 234U from damaged lattice sites, linked to the number of microfractures in the drip route and wetness frequency, which under certain conditions, may result in the accumulation of 234U recoils. This selective leaching process diminishes with enhanced bedrock dissolution, leading to low δ234U. Temperature variations significantly influence bedrock dissolution intensity. During stadial periods and glacial maxima, lower temperatures likely reduced vegetation and respiration rates, thereby decreasing soil CO2 and overall rock dissolution rates. This reduction could enhance the preferential leaching of 234U from bedrock surfaces due to lower bulk rock dissolution. Additionally, the temperature regime during cold periods may have facilitated more frequent freeze–thaw cycles, resulting in microfracturing and exposure of fresh surfaces. Conversely, warmer temperatures increased soil respiration rates and soil CO2, accelerating rock dissolution rates during interstadials and interglacials, when low δ234U is consistent with high bedrock dissolution rates. The contribution of a number of variables sensitive to bedrock dissolution and wetness frequency processes successfully explains 57 % and 74 % of the variability observed in the δ234U in Andromeda stalagmite during MIS 3–4 and MIS 5b-5e, respectively. Among these variables, the growth rate has emerged as crucial to explain δ234U variability, highlighting the fundamental role of soil respiration and soil CO2 in δ234U through bedrock dissolution. I-STAL simulations provides the potential for a combination of Prior Calcite Precipitation (PCP) indicators like Mg/Ca with PCP-insensitive indicators of bedrock dissolution such as δ234U, along with growth rate data, may be useful to diagnose when PCP variations reflect predominantly changes in drip intervals and when changes in bedrock dissolution intensity contribute. The relationship between stalagmite δ234U, bedrock dissolution, and initial dripwater oversaturation suggests two significant advancements in paleoclimate proxies. First, δ234U could serve as a valuable complement to δ13C since it is significantly influenced by soil respiration and soil CO2, thereby reflecting soil and vegetation productivity sensitive to both humidity and temperature. Secondly, since PCP does not fractionate uranium isotopes, δ234U could be used in combination with Mg/Ca or δ44Ca to deconvolve PCP variations due to changing drip rates from those due to changes in initial saturation state. This study emphasizes the overriding climatic control on δ234U, regardless of the absolute 234U/238U activity ratios among samples and their proximity or distance from secular equilibrium, and advocates for its application in other cave sites.

Prograde and meandering wall modes in rotating Rayleigh–Bénard convection with conducting walls

We use direct numerical simulations to study convection in rotating Rayleigh–Bénard convection in horizontally confined geometries of a given aspect ratio, with the walls held at fixed temperatures. We show that this arrangement is unconditionally unstable to flow that takes the form of wall-adjacent convection rolls. For wall temperatures close to the temperatures of the upper or lower boundaries, we show that the base state undergoes a Hopf bifurcation to a state comprised of spatiotemporal oscillations – ‘wall modes’ – precessing in a retrograde direction. We study the saturated nonlinear state of these modes, and show that the velocity boundary conditions at the upper and lower boundaries are crucial to the formation and propagation of the wall modes: asymmetric velocity boundary conditions at the upper and lower boundaries can lead to prograde wall modes, while stress-free boundary conditions at both walls can lead to wall modes that have no preferred direction of propagation.

Why Doesn't the Observed Field‐Aligned Current Saturate With Increasing Interplanetary Electric Field?

AbstractTheoretical studies indicate that electric potential saturation in a polar cap ionosphere is regulated by the limited reconnection rate at the magnetopause associated with field‐aligned currents (FACs), predicting the possible saturation of FACs under large interplanetary electric field (IEF). However, recent statistical studies have shown that observed FACs increase linearly with IEF. To reconcile this disparity, numerical experiments are conducted to explore the response of FACs under large IEF. Results show that FACs may exhibit either linear or saturated responses, depending on the Alfvén Mach number. The magnetospheric closure paths of region 1 currents differ significantly between the linear and saturated conditions. In the linear case, essential parts of the region 1 current extend toward dayside and connect to the magnetopause currents, whereas these parts of currents almost disappear in the saturation state. Saturation usually occurs under sub‐Alfvénic solar wind conditions, so the observed FACs generally grow linearly with IEF.