Bottom Layer Research Articles

Halfa grass assembled double-layered hydrogel evaporator for sunlight-driven steam generation and selective uranium extraction

Fresh drinking water and energy are crucial for the human society to live in a sustainable way, and both of these could be attained from the seawater. Herein, we designed a double-layered hydrogel evaporator (PCG@FCG) by using calcined carbon fiber derived from halfa grass (Desmostachya bipinnata) as a light absorbing photothermal material. The bottom hydrophilic layer composed of chitosan (CS), carboxy methyl cellulose (CMC), and amidoxime-modified chitosan (AOC), which helps in water transport to the upper surface of evaporator. The amidoxime modified chitosan helps in selective binding and recovery of uranium from the seawater. Such a judiciously designed PCG@FCG evaporator shows light absorbance of 96 %, stable evaporation rate of 2.0 kg m−2 h−1, having an outstanding selective uranium recovery of 325 mg g−1 under one sun irradiation. These outcomes result from the inherent structural porosity, enhanced evaporation rate, and selectively designed uranium binding sites. In addition, excellent salt-mitigating ability to promote uninterrupted evaporation, ability to purify the organic-contaminated wastewater/seawater endow the PCG@FCG evaporator with efficient seawater desalination ability and selective adsorption of uranium from the seawater. Overall, this innovatively-designed floating evaporator offers a sustainable approach to utilize the lavish resources in the seawater.

Two-dimensional van der Waals heterostructure for ultra-sensitive nanoelectromechanical piezoresistive pressure sensing

Micro electromechanical systems (MEMS) micro-pressure sensors have wide applications in consumer electronics, industrial monitoring, and biomedicine. However, as the next-generation portable and wearable devices bloom in recent years, existing design of pressure sensors faces great challenges to break the trade-off between the sensitivity and nonlinearity in the miniaturization process. Here, we report a sandwich-like Graphene/h-BN/Graphene-resistor heterostructure sensing element for micro-pressure detection. This novel design decouples pressure-to-strain translation process and strain-to-electrical signal sensing process by the insulation of bottom graphene structure layer and top graphene piezoresistive layer. We reveal the effects of the heterostructure dimensions, layer number and pretension on the mechanical performance utilizing finite element method (FEM) simulation, and propose the design principle of the piezoresistors and patterning strategy of the heterostructure. Remarkably, the heterostructure exhibits ultra-high sensitivity per unit area, outperforming state-of-art graphene and silicon-based sensors by up to five orders of magnitude, as well as a significant reduction of the nonlinearity. Our work shows tremendous potential of 2D material heterostructure as a promising platform to break the miniaturization limitation of ultrasensitive pressure sensors.

In-Situ Atomic-Scale Observation of Brownmillerite to Ruddlesden–Popper Phase Transition Tuned by Epitaxial Strain in Cobaltites

Phase transitions involving oxygen ion extraction within the framework of the crystallographic relevance have been widely exploited for sake of superconductivity, ferromagnetism, and ion conductivity in perovskite-related oxides. However, atomic-scale pathways of phase transitions and ion extraction threshold are inadequately understood. Here we investigate the atomic structure evolution of LaCoO3 films upon oxygen extraction and subsequent Co migration, focusing on the key role of epitaxial strain. The brownmillerite to Ruddlesden–Popper phase transitions are discovered to stabilize at distinct crystal orientations in compressive- and tensile-strained cobaltites, which could be attributed to in-plane and out-of-plane Ruddlesden–Popper stacking faults, respectively. A two-stage process from exterior to interior phase transition is evidenced in compressive-strained LaCoO2.5, while a single-step nucleation process leaving bottom layer unchanged in tensile-strained situation. Strain analyses reveal that the former process is initiated by an expansion in Co layer at boundary, whereas the latter one is associated with an edge dislocation combined with antiphase boundary. These findings provide a chemo-mechanical perspective on the structure regulation of perovskite oxides and enrich insights into strain-dependent phase diagram in epitaxial oxides films.

Foam Mortar Layer in Soft Subgrade Embankment: A Review

Soils are the basis of the construction of civil engineering structures that are designed to support and withstand the weight of the structures above them. The main problems of soft soil include low bearing capacity and large settlement. In road pavements, the sub grade as the bottom layer of the road must have a good bearing capacity. Subgrade is a part that must be considered because of the weight of the pavement structure and the embankment above it. Soft soil conditions cause the need for reinforcement of the sub grade layer. Solving the problem of road construction is done by engineering so that the sub grade as the bottom layer of the road is safe and stable and has a good bearing capacity. The effort made to increase the bearing capacity of the subgrade is by reinforcing the soil (soil improvement). One of them is with lightweight material mortar-foam is an alternative construction material in soil reinforcement for road construction. Mortar-foam is formed from a mixture of foam, cement, sand and water. Research on foam mortars has been conducted in various places and countries in various ways and methods. This article will discuss the latest developments in the use of foam mortars as backfill in soft soils in the subgrade layer presented based on information provided by the author.

Resource diversity disturbs marine Vibrio diversity and community stability, but loss of Vibrio diversity enhances community stability.

Vibrio is a salt-tolerant heterotrophic bacterium that occupies an important ecological niche in marine environments. However, little is known about the contribution of resource diversity to the marine Vibrio diversity and community stability. In this study, we investigated the association among resource diversity, taxonomic diversity, phylogenetic diversity, and community stability of marine Vibrio in the Beibu Gulf. V. campbellii and V. hangzhouensis were the dominant groups in seawater and sediments, respectively, in the Beibu Gulf. Higher alpha diversity was observed in the sediments than in the seawater. Marine Vibrio community assembly was dominated by deterministic processes. Pearson's correlation analysis showed that nitrite (-N), dissolved inorganic nitrogen (DIN), ammonium (-N), and pH were the main factors affecting marine Vibrio community stability in the surface, middle, and bottom layers of seawater and sediment, respectively. Partial least-squares path models (PLS-PM) demonstrated that resource diversity, water properties, nutrients, and geographical distance had important impacts on phylogenetic and taxonomic diversity. Regression analysis revealed that the impact of resource diversity on marine Vibrio diversity and community stability varied across different habitats, but loss of Vibrio diversity increases community stability. Overall, this study provided insights into the mechanisms underlying the maintenance of Vibrio diversity and community stability in marine environments.

Numerical Simulation of Tunnel Face Support Pressure in Layered Soft Ground

In shield construction, the limit support pressure of the tunnel face has an important influence on ground settlement and construction safety. In this study, MIDAS GTS NX software was used to conduct a series of three-dimensional finite element simulations to investigate variations in excavation face support pressure under different layered ground conditions. By changing the shear strength parameters of the top or bottom layers, the influence of composite layers with different formation boundaries on the support pressure of the excavation face was studied. It was observed that when the formation boundary is placed above the axis, the support pressure of the excavation face is more sensitive to a change in the parameters in the lower part of the formation than in the upper part. Conversely, when the formation boundary lies below the axis, this sensitivity becomes reversed. Additionally, we derived a robust and accurate equation to estimate the limiting face support pressure in layered soft ground based on numerical modeling.

Interfacial polymerization of self-standing ABC-stacking Covalent organic framework membranes for dye separation

Covalent organic framework (COF)-based membranes are burgeoning candidates for separation technologies owing to their well-ordered channel structures. However, it is still a significant challenge to obtain high-quality COF membranes with a mild and convenient preparation strategy. In this paper, we adopted a simple liquid-liquid interfacial polymerization method to manufacture a self-standing COF membrane with decent crystallinity at room temperature. Aldehyde monomer and catalyst were dissolved in water as the bottom layer and the amine monomer was dissolved in ethyl acetate as the top layer, while new COF membranes were obtained by interfacial polymerization in the two-phase interface. The synthetic conditions including precursor and catalyst dosage were further optimized, and thus-synthesized PDA-TAPB-ABC membrane displayed a stable rejection to MB of 97.57% with a high water permeance of up to 101. 32 L m−2h−1bar−1. Its dyes separation performance was much better than their AA-stacking counterpart. Moreover, the prepared membrane endowed favorable chemical stability and long-term durability.

A Fabrication Method for Memristors with Graphene Top Electrodes and their Characterization

In recent years, there has been extensive research on the memristor, a non-volatile memory device that demonstrates effective emulation of biological synapses. The implementation of graphene as a top electrode in memristive switching systems presents an intriguing alternative to conventional materials such as Platinum. Graphene, as a carbon-derived material, possesses a remarkable area- to-volume ratio, biocompatibility, adsorption capabilities, and high electrical conductivity and thereby offers a promising avenue for the fabrication of biosensors with superior characteristics. This study reports a novel fabrication method of utilizing graphene as a top electrode in memristive devices. Characterization results of micrometric devices as well as larger memristive devices are also discussed. Larger devices show promising results to be used as memristive sensors. Microstructures have been fabricated successfully through developing a process flow and patterning graphene using photolithography and lift-off. E-beam evaporation and sputtering were used for depositing bottom metal electrodes and active layer respectively. Graphene was produced using the chemical vapor deposition (CVD) method and subsequently transferred using the fishing technique. Ultimately Pt/TiO2/TiOx/Graphene memristive devices were fabricated.

Integrated preparation of B4C–TiB2 multilayer graded ceramics with high hardness and high toughness

AbstractThe enhancement in the comprehensive performance of hardness, toughness, and strength is significant for ceramic materials. In this study, the B4C–TiB2 multilayer graded ceramics were designed and integrally manufactured by spark plasma sintering method using B4C and TiB2 as raw materials. The B4C–TiB2 multilayer graded ceramics feature a transition from the top layer with high hardness to the bottom layer with high toughness, passing through an intermediate layer. The gradient change of this material is observed in both the hardness and fracture toughness, reaching values of 36.2–28.4 GPa and 2.2–6.2 MPa m.5. The compressive strength reaches up to 2960 MPa, whereas the bending strength gets to 677 MPa in the appropriate loading direction. The structure forms a gradient pattern with high hardness on the front side, high toughness on the back side, and overall low density and high strength. This study may facilitate the development of impact‐resistant performance of lightweight materials.

Controls on terrigenous sediment supply to northwestern South China Sea based on a sediment trap record at Xisha Trough

The South China Sea (SCS) is the largest marginal sea in the western Pacific and comprises an ideal natural laboratory for studying deep-sea processes. Previous investigations in the region have primarily focused on surface currents and to a lesser extent on intermediate currents, while observations of bottom currents are scarce, hindering our understanding of deep ocean sediment transport and deposition mechanisms. Here, we carried out grain size measurement and end-member modelling analysis (EMMA) on samples collected by a sediment trap at a water depth of 1500 m in the Xisha Trough in the northwestern South China Sea. Grain size data shows that terrigenous material has particle sizes ranging from 0.3 μm to 745.9 μm and a peak at 4–11 μm. The EMMA result suggests that finer sediment accounting for an average of 48.2% of the sediment represents material transported by deep water currents (End-member 1; EM1), and this is primary sediment source in the region. Coarser sediment contributing to 32.9% of the sediment is the second most significant source (EM3), representing the deposits of surface currents influenced by monsoons and deposited close to the source. A third sediment type (EM2) constituting approximately 18.9% of the sediment exhibits a wide range of grain sizes and rapid changes, indicating transport in the bottom nepheloid layer triggered by anticyclonic eddies. Our study identifies three primary sediment transport mechanisms to the northwestern SCS, bridging present-day observations with paleoceanography and providing a crucial basis for future research on paleoceanographic reconstructions.

Peat Ground Improvement with GeoPolySoilS

Peat soil is frequently seen as a soil foundation concern which normally required soil stabilization work. This study is conducted to assess the strength of peat soil mixed with GeoPolySoilS as a proposed ground improvement work for peat soil in Kampung Johan Setia in Klang Selangor, Malaysia. In order to look into the strength improvement of this peat soil, laboratory tests were conducted namely Unconfined Compressive Strength Test (UCT) and Calfornia Bearing Ratio Test (CBR). The highest strength of UCT for the uncured soils with 14% GeoPolySoilS is 161 kPa whilst for the sample that was cured for 7,14,28 and 50 days, the highest value of UCT with 20% GeoPolySoilS are 58.08 kPa,61.66 kPa, 95.62 kPa and 80.04 kPa respectively. For the CBR value, the highest top layer value is 8.12% for peat soil mixed with 14% GeoPolySoilS whilst the highest value for the bottom layer is 62.25% for unsoaked CBR. For soaked CBR, the highest top layer value is 5.82% for 20% GeoPolySoilS and the highest value for bottom layer is 43.07%. The strength of the modified peat increased with the increased of curing time and the percentage of GeoPolySoilS.

Dual-Band Frequency Selective Surface-Backed Reflectarray for High-Speed Ka-Band Satellites

A dual-band, dual-polarized frequency selective surface (FSS)-backed multilayer reflectarray antenna is designed for 5G high-speed satellites operating at Ka-band uplink and downlink frequencies (20/30 GHz). A reflectarray antenna system consists of two reflectarrays that are separated from each other by an FSS layer that behaves as a planar bandpass filter at Ka-band satellite uplink frequencies. Each reflectarray antenna is designed with dual-polarized unit cells. In order to achieve a uniform phase distribution across the reflectarray surface, physical dimensions and positions of the unit cells with a fixed periodicity are carefully chosen. The FSS conductor is etched to the bottom layer of the 30 GHz reflectarray substrate to save cost and weight. The reflectarray performance is analyzed by using CST Microwave Studio and array theory. A prototype is fabricated, and the results are experimentally verified. The gain of the reflectarray is measured as 21.13 dBi and 26.94 dBi at 20 and 30 GHz, respectively. A crosspol level of more than 35 dB is observed at both frequencies. The simulated and measured results show that the proposed reflectarray is suitable for high-speed Ka-band satellites.

Constraints of Sedimentary Environment on Shale Organic Matter Enrichment: Insights from Elemental Geochemistry and Multiple Factor Analysis.

The organic-rich shale of the Wufeng-Longmaxi formation is an important section for shale gas exploration. The traditional univariate or bivariate analysis causes researchers to have great controversy about its enrichment mechanism. This study explores the combination of multiple factor analysis (MFA) and element geochemistry to calculate the contribution rate of a paleoenvironment to organic matter enrichment and clarify the main controlling factors of organic matter enrichment. Research has shown that there is generally high productivity from the Wufeng (O3w)-Longmaxi formation (S1l) deposition. The degree of terrigenous clastic input and weathering during the period of the O3w is relatively low, and sedimentary water restriction is strong, mainly developing an anoxic-dysoxic sedimentary environment. During the deposition of S1l1, the input intensity and weathering of terrigenous debris were slightly enhanced, and the increase of the water column led to the development of an anoxic environment at the bottom of the water layer. During the S1l2+3 period, the degree of terrigenous debris and weathering is the largest, and the high oxygen content of the water column is mainly a normal oxic environment. An MFA calculation shows that the paleoproductivity and paleoredox environment of the organic-rich shale section have the highest contribution rate of about 59.57% to the enrichment of organic matter, which is higher than that of paleoclimate conditions and terrigenous clastic input, indicating that the enrichment of organic matter is mainly controlled by paleoproductivity and the preservation environment. This study provides a basis for the application of MFA in element geochemistry and can serve as a model for other studies.

Interannual-decadal variations in the Yellow Sea Cold Water Mass in summer during 1958–2016 using an eddy-resolving hindcast simulation based on OFES2

In the Yellow Sea, a large volume of cold water with temperature below 10 °C exists in the bottom layer in summer and affects the regional circulation, climate and marine ecosystem. Here, we investigated in detail the interannual-decadal variations in the summer Yellow Sea Cold Water Mass (YSCWM) using six decades (1958–2016) of a quasi-global eddy-resolving hindcast simulation, which was validated with observations. Results indicated that volume and mean temperature of the YSCWM were 0.52 × 1012–4.10 × 1012 m3 (2.22 × 1012 m3 on average) and 8.53–9.32 °C (8.94 °C on average). The YSCWM was dominated by interannual-decadal variations with a weakly warming and shrinking trend. The YSCWM volume (mean temperature) had larger (smaller) average values and varied more significantly during the two periods of 1958–1988 and 2005–2016 than during 1989–2004. Interannual-decadal variations in the summer YSCWM agreed with those in February temperature in the Yellow Sea, which were primarily caused by net surface heat flux variations, with a minor but negative contribution from heat exchange with the East China Sea through the northward Yellow Sea warm current and southward coastal currents. Winter net surface heat flux variations were dominated by latent heat flux and sensible heat flux, both of which resulted from combined effects of the Siberia High, Western Pacific pattern and Arctic Oscillation through controlling sea surface wind speed and air temperature over the Yellow Sea. The current study provided a more complete picture and in-depth understanding of changes in the summer YSCWM responding to large-scale climate change and variabilities during the past six decades.

Hydrogels with Differentiated Hydrogen‐Bonding Networks for Bioinspired Stress Response

Stress response, an intricate and autonomously coordinated reaction in living organisms, holds a reversible, multi‐path, and multi‐state nature. However, existing stimuli‐responsive materials often exhibit single‐step and monotonous reactions due to the limited integration of structural components. Inspired by the cooperative interplay of extensor and flexor cells within Mimosa's pulvini, we present a hydrogel with differentiated hydrogen‐bonding (H‐bonding) networks designed to enable the biological stress response. Weak H‐bonding domains resemble flexor cells, confined within a hydrophobic network stabilized by strong H‐bonding clusters (acting like extensor cells). Under external force, strong H‐bonding clusters are disrupted, facilitating water diffusion from the bottom layer and enabling transient expansion pressure gradient along the thickness direction. Subsequently, water diffuses upward, gradually equalizing the pressure, while weak H‐bonding domains undergo cooperative elastic deformation. Consequently, the hydrogel autonomously undergoes a sequence of reversible and pluralistic motion responses, similar to Mimosa's touch‐triggered stress response. Intriguingly, it exhibits stress‐dependent color shifts under polarized light, highlighting its potential for applications in time‐sensitive "double‐lock" information encryption systems. This work achieves the coordinated stress response inspired by natural tissues using a simple hydrogel, paving the way for substantial advancements in the development of intelligent soft robots.

Hydrogels with Differentiated Hydrogen-Bonding Networks for Bioinspired Stress Response.

Stress response, an intricate and autonomously coordinated reaction in living organisms, holds a reversible, multi-path, and multi-state nature. However, existing stimuli-responsive materials often exhibit single-step and monotonous reactions due to the limited integration of structural components. Inspired by the cooperative interplay of extensor and flexor cells within Mimosa's pulvini, we present a hydrogel with differentiated hydrogen-bonding (H-bonding) networks designed to enable the biological stress response. Weak H-bonding domains resemble flexor cells, confined within a hydrophobic network stabilized by strong H-bonding clusters (acting like extensor cells). Under external force, strong H-bonding clusters are disrupted, facilitating water diffusion from the bottom layer and enabling transient expansion pressure gradient along the thickness direction. Subsequently, water diffuses upward, gradually equalizing the pressure, while weak H-bonding domains undergo cooperative elastic deformation. Consequently, the hydrogel autonomously undergoes a sequence of reversible and pluralistic motion responses, similar to Mimosa's touch-triggered stress response. Intriguingly, it exhibits stress-dependent color shifts under polarized light, highlighting its potential for applications in time-sensitive "double-lock" information encryption systems. This work achieves the coordinated stress response inspired by natural tissues using a simple hydrogel, paving the way for substantial advancements in the development of intelligent soft robots.

Mapping saltwater intrusion via Electromagnetic Induction (EMI) for planning a Managed Aquifer Recharge (MAR) facility in Maltese Island

In coastal areas, saltwater intrusion causes a depletion of the resource by reducing potable and irrigation freshwater supplies and causing severe deterioration of groundwater quality. This trend is observed in Pwales Valley, in the North part of Malta where the management of water resources plays a crucial role for the environmental sustainability of the area, given the importance of intensive agricultural activity along this valley. In order to tackle such phenomenon, actions or adaptation measures against climate change are strongly required. For example, Managed Aquifer Recharge (MAR) is an increasingly important water management strategy to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. To accurately plan a Managed Aquifer Recharge scheme, it is crucial to define a hydrogeological model of the studied area, with the use of traditional hydrogeological measurements and innovative unconventional techniques. In recent years, Electromagnetic Induction measurements, based on induction of em fields, have been increasingly used for investigating the saltwater intrusion dynamics due to their high sensitivity to the salinity. In the study area of Pwales Valley, a Managed Aquifer Recharge scheme is being planned and, for this aim, a hydrogeological model has been developed through an Electromagnetic Induction survey. More than 20,000 apparent electrical conductivity (ECa) data were collected to generate a quasi 3D high-resolution model of electrical conductivity of the Pwales Valley. The results highlighted the spatial extension of the tongue-shape salt water intrusion from east to west along the valley, as well as some geological-hydrogeological peculiarities such as the thickness of the salt wedge and the irregular top surface of the bottom impermeable layer, otherwise undetectable with other direct techniques at the field scale resolution. The approach was confirmed to be a useful tool for an effective hydrogeological characterisation, essential for planning adaptation measures to a changing climate, such as the implementation of a Managed Aquifer Recharge scheme.

Nutrient regimes in a semi-enclosed marginal sea: The Persian Gulf

ABSTRACT In this study, the results of hydrochemical measurement aboard the RV Kavoshgar Khalij Fars in the Persian Gulf (PG) in September 2018, May, and November 2019 are discussed. Nitrate, nitrite, ammonium, phosphate, and silicate concentrations, salinity, temperature, dissolved oxygen, and pH in the water column of a 1000-km transect in the PG were studied to determine the present status of nutrient regimes of this region. Nitrate, phosphate, and silicate were more concentrated at the bottom layer and showed a maximum just below the thermocline in summer and autumn. Seasonal distribution of nutrient ratios (N:P, N:Si, Si:P) indicates P limitation in autumn, N limitation in spring, P limitation and poor Si in summer throughout the upper layer. The results of this study do not infer eutrophication in the upper layer of the PG waters in autumn and summer.

Assessment of Sensitivity and Validity Hydrodynamic Model in Cisadane Using Delft3d Flow Model

The National Capital Integrated Coastal Development (NCICD) program was prioritized as a disaster reduction technology within the annual target of BRIN in 2022. It is a part of the North Java Coastal Integrated Development Program project. A coastal reservoir development plan at the Cisadane River estuary is one of the outcomes. In this case, hydrodynamic modelling is needed to acquire hydrodynamic properties under the existing condition of Cisadane downstream, and it applied the Delft3D-FLOW model. The bathymetric data used in this simulation was obtained from the assimilation of national bathymetric data with a grid spacing of 180 m and field survey data with a horizontal resolution of 10 m and transect spacing of 200 m seaward of the Cisadane estuary. It has interpolated in a regular structured grid with 100 m and 50 m grid spacing. In addition, other data used are three hourly wind data downloaded from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the daily discharge of the Cisadane River in 2021. Astronomical water level data generated from TPXO 7.2 and TPXO 8 were used in the boundary conditions. These data are simulated using the two and three-dimensional flow model Delft3D-FLOW during November 1 – 15, 2021, using four manning coefficients (n) values, which are 0.03; 0.035; 0.04; and 0.045. The validation formulation used Normalization Root Mean Square Error (NRMSE), resulting in 5.3 - 9.6% for all the manning values and domains. The highest correlation coefficient of current velocity (u-v components) is acquired in the 10 km2 domain with 0.797 for the L3 (bottom layer).

Electrospun MoS2-CNTs-PVA/PVA Hybrid Separator for High-Performance Li/FeS2 Batteries.

As a promising candidate for high-energy-density rechargeable lithium metal batteries, Li/FeS2 batteries still suffer from the large volume change and severe shuttle effect of lithium polysulfides during cycling. To improve the electrochemical performance, great efforts have been made to modify FeS2 cathodes by constructing various nanocomposites. However, energy density is sacrificed, and these materials are not applicable at a large scale. Herein, we report that the electrochemical performance of commercial FeS2 can be greatly enhanced with the application of a double-layer MoS2-CNTs-PVA (MCP)/PVA separator fabricated by electrospinning. The assembled Li/FeS2 batteries can still deliver a high discharge capacity of 400 mAh/g after 200 cycles at a current density of 0.5 C. The improved cycling stability can be attributed to the strong affinity towards lithium polysulfides (LiPSs) of the hydroxyl-rich PVA matrix and the unique double-layer structure, in which the bottom layer acts as an electrical insulation layer and the top layer coupled with MoS2/CNTs provides catalytic sites for LiPS conversion.