Lower Layer Research Articles

Comparison of microstructural evolution and high temperature oxidation behavior of AlCoCrFeNiTi and AlCoCrFeNiZr high-entropy alloy coatings

In this study, the isothermal oxidation behaviors of HEA coating systems with AlCoCrFeNiTi and AlCoCrFeNiZr contents were evaluated by comparing microstructurally and investigated in terms of potential applications of thermal barrier coatings (TBCs). For this reason, their oxidation resistance under isothermal conditions, as well as diffusion phenomena occurring at the bond and top coating interface, were investigated. CoNiCrAlY bond coating was applied to the surface of a Nickel-based superalloy substrate by high velocity oxygen-fuel (HVOF) spraying. HEA coating materials were produced by using the mechanical alloying (MA) process. The mechanical activated synthesized HEAs were sprayed on a CoNiCrAlY bond coating by Atmospheric Plasma Spraying (APS). The microstructural changes at the coating interface of CoNiCrAlY, AlCoCrFeNiTi and AlCoCrFeNiZr (HEAs) coatings resulting from oxidation processes at 1200 °C for 5, 25, 50 and 100 h, and the formation and growth behaviors of the thermally grown oxide (TGO) layer were investigated. The present results demonstrate a potential of HEAs in TBC applications. After oxidation tests, crystal lattice transformations took place in both coating systems. In the AlCoCrFeNiZr-HEA TBC system, an increase in diffusion rate, oxygen permeability, and consequently TGO layer thickness was observed by the transformation from the cubic lattice structure to a monoclinic lattice structure with a larger volume. In the AlCoCrFeNiTi-HEA TBC system, the transformation of a narrow rhombohedral lattice with tight planes was maintained. Therefore, the TBC system with AlCoCrFeNiTi-HEA has a lower TGO layer thickness compared to the TBC system with AlCoCrFeNiZr-HEA and has a longer service life against oxidation failure at high operating temperatures. As a result of the production, experimental studies and high temperature oxidation test studies under service conditions, it was seen that AlCoCrFeNiTi and AlCoCrFeNiZr-HEA coatings can be used in the structure of TBC systems.

Seasonal and Interannual Salinity Variability on the Northeast U.S. Continental Shelf: Insights From Satellite Sea Surface Salinity and Implications for Stratification

AbstractThe Northeast U.S. continental shelf (NEUS) is a highly productive and economically important region that has undergone substantial changes in recent years. Warming exceeds the global average and several episodes of anomalously warm, sustained temperatures have had profound impacts on regional fisheries. A majority of recent research studies focused on the analysis of temperature; however, salinity can serve as a valuable tracer as well. With now more than a decade of remote‐sensing sea surface salinity data, we shed new light onto salinity variability in the region with focus on the Mid‐Atlantic Bight and assess its role for modulating stratification on the shelf using historical hydrographic data. Local river discharge drives decreasing salinities not only in spring and summer on the shelf but also in the Slope Sea. In spring, fresher water aids the build‐up of stratification and a low salinity surface layer extends to the shelf break above the pycnocline by the beginning of summer. An observed salinification in the fall is linked to offshore forcing over the slope associated with the presence of Warm Core Rings. Coherent low‐frequency salinity variability is found over the slope and shelf, highlighting that shelf conditions are significantly impacted by offshore variability. Conditions on the NEUS in 2015 were characterized by anomalously high salinities, associated with a northerly position of the Gulf Stream. A freshening between 2015 and 2021, is in agreement with increased river cumulative discharge as well as lower offshore salinities. Overall, salinity serves as a valuable additional tracer of these multi‐variate processes.

Review of Electrical Parameters Influence on Characteristics of Plasma Electrolytic Oxide Coating on Zircaloy

<p>Zircaloy-4 (Zr-4) is used as a fuel cladding material in Pressurized Water Reactor (PWR). Zr-4 as a cladding material works in extreme conditions in pressurized water up to 150 atm at 325 ˚C. In addition, the refuelling process in the reactor requires surface protection of the clay material to minimize corrosion and wear. One of the raising methods to enhance the corrosion resistance of the Zr-4 is by plasma electrolytic oxidation (PEO). Characteristics of the ceramic oxide layer produced by PEO are influenced by current density, type and composition of the electrolyte, and voltage mode. One of the challenges in the PEO development on the Zr-4 substrate is a high porosity with a range of 5%-20% and the low number (below 6%) of t-ZrO<sub>2</sub> phases in the inner and outer layers. Optimizing the electrical parameters is necessary to overcome this problem. The results of the literature study show that the cathodic current at the AC voltage plays an important role in determining the resulting plasma characteristics. Low duty cycle (cathodic current> 50%) produce plasma with high density, resulting in a low porosity layer. Oppositely, high duty cycle (cathodic current <50%) produced high content of t-ZrO<sub>2</sub> increase the mechanical resistance. Two-step PEO is beneficial in combining the low and high duty cycle to obtain the benefit of each step. </p>

Joint scheduling of hybrid flow-shop with limited automatic guided vehicles: A hierarchical learning-based swarm optimizer

Transportation system in workshop is essential for high-efficient production scheduling. Due to the limited transportation resources, the joint scheduling of production and transportation has emerged as a pivotal issue in modern manufacturing. This paper investigates a joint scheduling of hybrid flow-shop with limited automatic guided vehicles (HFSP-LAGV), which extends the classical hybrid flow-shop scheduling by considering the limited number of the AGVs on the transportation resources. To solve such problem, a mixed integer linear programming (MILP) model is firstly built to formulate HFSP-LAGV. Then, a hierarchical learning-based swarm optimizer (HLSO) is proposed. An encoding and decoding method based on three dispatch rules is proposed. The framework of HLSO comprises a pyramid-based layering strategy, an inter-layer learning and an intra-layer learning. The pyramid-based layering strategy divides the swarm into several layers. In the inter-layer learning, the individuals in higher layers guide the evolution of individuals in lower layers to achieve the exploration of global area. In the intra-layer learning, an offline Q-learning-based local search is designed to implement the self-learning of elite individuals in higher layer to intensify the exploitation of the local area. A Q-learning model that has been pre-trained offline is used to guide the selection of appropriate operator of local search. Experimental results reveal the effectiveness of the designs and the superiority of HLSO over several well-performing methods on solving HFSP-LAGV.

Developing Liquefaction Prediction Equations for Gravels Based on DPT Blow Count and Shear Wave Velocity at Field Case History Sites

Gravelly soils have liquefied at multiple sites in at least 20 earthquakes over the past 130 years. These gravels typically contain more than 25% sand which lowers the permeability and makes them susceptible to liquefaction. In other cases, a low permeability layer at the surface impedes drainage and causes liquefaction. Typical SPT- or CPT-based liquefaction correlations can be affected by large gravel particles and lead to erroneous results. To deal with these problems, we have developed liquefaction triggering curves for gravelly soils based on (1) shear wave velocity (Vs) and (2) a 74-mm diameter dynamic cone penetrometer (DPT), that are less affected by gravel particles. These correlations are based on case histories where gravel did and did not liquefy in past earthquakes. The VS-based liquefaction triggering curves for gravels shift to the right relative to similar curves based on sands. Good agreement has been obtained with liquefaction resistance from the DPT and the CPT when these methods could all penetrate the gravel in Wellington New Zealand. Correlations are developed between Vs and blow count from the DPT.

Devising a method for determining the moisture conductivity coefficient of subgrade soils taking into account European approaches and standards

The object of this study is the theoretical and methodological approaches to determining the coefficient of moisture conductivity of subgrade soils. The work focuses on considering the European approaches and standards when devising a method for determining the coefficient of moisture conductivity of soils. In the course of the research, a method was developed for determining the coefficient of moisture conductivity of soils K1, which characterizes the diffusion movement of water, through the filtration coefficient K0, calculated in accordance with European requirements based on laboratory test data. The proposed method is based on a mathematical model built on the basis of the differential equation of changes in soil moisture. The model is special in that, unlike existing ones, the movement of water was modeled from the bottom up, which reflects the process of moisture accumulation in the lower layers of the subgrade from groundwater or topwater. A good agreement of the mathematical model with the data by other authors was obtained (the relative error did not exceed 12.98 %). A direct relationship between the moisture conductivity coefficient of soils K1 and their initial moisture content W0 and an inverse relationship between K1 and the total moisture capacity of soils WFH were established in the paper. Dependences were derived in the range of changes in initial soil moisture W0 from 0.08 to 0.15 and WFH from 0.15 to 0.5. It was found that the values of the moisture conductivity coefficient of soils K1 increase from 4.64·10-6 to 3.81·10-5 m2/h with an increase in their initial moisture content and with a decrease in total moisture capacity. From the point of view of engineering practice of road construction, the proposed method makes it possible to predict seasonal changes in soil moisture in the subgrade, to determine the strength of the road structure. This makes it possible to make sound design decisions on the installation of drainage systems on roads in order to extend their service life

Three-dimensional numerical study on reservoir sediment flushing through an initially covered bottom tunnel

Sediment flushing through bottom tunnels has been widely applied in engineering practice to alleviate reservoir sedimentation. However, there is limited understanding of whether flushing can be accomplished once the tunnel intake is covered by deposited sediment. Here, a three-dimensional model is used to resolve the hydro-sediment-morphodynamic processes and reveal the physical mechanism for the occurrence of reservoir sediment flushing through an initially covered bottom tunnel. The results demonstrate that the reservoir water level and initial cover layer thickness have a significant impact on the pressure difference between tunnel inlet and outlet and the resistance of tunnel walls, determining the momentum of the water-sediment mixture. If water level is low or cover layer is thick, the pressure is not sufficient to overcome the resistance. The momentum tends to zero, and tunnel blockage occurs. If water level is high or cover layer thickness is small, the scour hole depth will exceed the cover layer thickness and the sediment concentration in tunnel decreases. The resistance is reduced significantly, and sediment flushing is accomplished. The present work facilitates enhanced understanding of sediment flushing, thereby informing reservoir engineers and managers of potential approaches to benefit maximization and sustainable sediment management.

3D printable earth-based alkali activated “ink”: Effect of alkali concentration and binder-to-aggregate ratio

This research attempts to investigate the effect of activator concentration (4 mol/L (M) and 8M) and binder-to-aggregate (B:A) ratio (ranging from 1:1 to 1:3 by weight) on extrudability and buildability of 3D printable natural earth-based alkali-activated materials (EAAM). It is found that natural clay in soil, used to replace 25 % of M-sand, imparts higher thixotropy, evident from 90 to 100 % recovery in viscosity compared to 65–80 % for corresponding control (containing only M-sand and no soil). Presence of clay increases the dynamic yield stress than control but reduces the plastic viscosity by 80 – 90 % in EAAM compared to corresponding control where interlocking between sand particles resists smooth extrusion of the material. EAAMs made with 8M NaOH have higher flow retention and maintain 95–100 % recovery in viscosity for longer duration than 4M EAAM. This contributes to superior extrusion quality of 8M EAAM than 4M EAAM. The findings suggest that binder content can be reduced as concentration of NaOH is increased from 4M to 8M. This is evident from lower layer deformation (0.09 % of original height) under self-weight and higher 3D printed buildable height of at least 457 mm in 8M EAAM with B:A of 1:2 compared to a maximum of 375 mm for 4M EAAM at higher B:A of 1:1. Ratios of wet compressive strength to dry compressive strength vary between 0.92 and 1.09 in 8M EAAM compared to 0.79 – 0.85 for 4M EAAM at 28-day age, suggesting lower sensitivity to moisture due to improved clay stabilization. Based on the strength and moisture sensitivity, the developed material can serve as a low-carbon and durable alternative to Portland cement in the construction of masonry elements in buildings, including cavity walls, panels, flooring tiles and façade members.

The evolution of the coronal loop structure due to the phase mixing of high and low-frequency Alfvén waves

ABSTRACT Coronal loops are known to host Alfvén waves propagating in the corona from the lower layers of the solar atmosphere and because of their internal structure, phase mixing is likely to occur. The structure of the coronal loop could be significantly affected by the thermodynamic feedback of the heating generated by phase mixing. However, this phenomenon can be sensitive to the period of the propagating Alfvén waves due to how short period waves can be easily dissipated and the way long-period waves may accumulate considerable energy in resonating coronal loops. Using the Lare2d code, a coronal loop model of a field-aligned thermodynamic equilibrium and a cross-field background heating profile is created, with an additional forcing term added to drive Alfvén waves with coronal amplitudes between $5{\!-\!}30 \, \mathrm{km} \, \mathrm{s}^{-1}$. We show that high-frequency waves can generate heating corresponding to a ${\sim} 10~{{\ \rm per\ cent}}$ increase of the initial coronal shell temperature, chromospheric upflows of up to $0.6 \, \mathrm{km} \, \mathrm{s}^{-1}$ and a coronal shell mass increase of ${\sim} 15~{{\ \rm per\ cent}}$. These changes are sufficient to alter and maintain a new coronal loop density structure, broadening the region where efficient phase mixing (and therefore heating) occurs. In contrast, low-frequency waves are unable to be effectively dissipated, resulting in minimal changes to the loop structure. We see little evidence of wave energy accumulation in the corona and are unable to conclude that the dissipation of low-frequency Alfvén waves can be an effective heating mechanism in coronal loops in the setup used in this study.

The Re-Crushing Spatiotemporal Evolution Law of Broken Coal in the Goaf for Sustainable Utilization of Abandoned Mines

The broken coal samples’ (BCS) re-crushing characteristics in the goaf during roof compaction directly affect the mechanics and seepage characteristics of the caving zone. This will further affect the safety of coal mining and the sustainable utilization of abandoned mines. Thus, the experiment of BCS compaction is carried out with the help of an acoustic emission (AE) monitoring system. The Hurst exponent changes of the AE counts at different stages were obtained using the R/S analysis method. The results indicate that the compaction and re-crushing of the BCS at the laboratory scale have long-term memory. When providing sufficient stress, the AE activity of BCS will continue to develop according to the current trend. Based on the AE breakage location technology, the spatial distribution re-crushing characteristics of the BCS are obtained. Re-crushing of the BCS demonstrates uniform breakage in the horizontal direction and layered breakage in the vertical direction. In the horizontal direction, the boundary area first began to break, and the damage gradually spread evenly to the central area. In the vertical direction, the upper layer was the first to be broken, and then the damage began to shift to the middle and lower layers.

Heteroepitaxy of ε‐Ga2O3 thin film for artificial synaptic device

AbstractEmerging‐wide bandgap semiconductor Ga2O3 shows distinct characteristics for optoelectronic applications and a stable crystal phase of Ga2O3 is highly desired. Herein, we have first reported a metal‐semiconductor‐metal structure photonic synaptic device based on the ε‐Ga2O3 thin film. The ε‐Ga2O3 epilayer is grown on the c‐sapphire with a low temperature nucleation layer, which presents a crystal orientation relationship with the c‐sapphire (ε‐Ga2O3 <010> // c‐sapphire <1–100> and ε‐Ga2O3 <001> // c‐sapphire <0001>). The ε‐Ga2O3 photonic device was stimulated by UV pulses at different pulse widths, pulse intervals, and reading voltages. Under the UV pulse excitation, the photonic device exhibits primary synaptic functions including excitatory postsynaptic current, short term memory, pair pulse facilitation, long term memory, and STM‐to‐LTM conversion. In addition, stronger and repeated stimuli can naturally contribute to the higher learning capability, thus prolonging the memory time.

Composite Risk Assessment of HNS Discharged from Marine Industrial Facilities: A Case Study on Incheon Port, South Korea

This study conducted a composite risk assessment to evaluate the environmental impacts of phenol, a Hazardous and Noxious Substance (HNS) released or leaked from port facilities. The study area was designated as the vicinity of Incheon Port, South Korea, where the volume of petrochemical-related materials is substantial and various industrial facilities are located. For the composite risk assessment, various vulnerability maps were developed, incorporating the dispersion range of phenol calculated through numerical modeling. The vulnerability maps were generated by classifying socio-environment, legally protected areas, habitats, and species, followed by integrating these individual vulnerability maps to construct an integrated vulnerability map. The composite risk assessment was conducted by considering both the integrated vulnerability map and the dispersion range of phenol. The assessment results indicated that the highest risk by depth was observed in the lower layers due to the settling characteristics of phenol. Spatially, areas where islands and coastlines converge exhibited relatively higher risks. This was attributed to the high concentrations of phenol released from industrial facilities, such as crude oil refineries, petrochemical plants, and organic compound manufacturers, in regions characterized by intense human activity, sensitive habitats, and legally protected areas. Continuous monitoring of these high-risk areas is crucial for assessing the environmental impacts of HNS substances like phenol.

Flat double-layer metal-only metasurface with polarization-dependent operation in a C/X dual band

In this communication, a dual-band, orthogonal polarization transmission metasurface antenna operating at 6.5 GHz and 9.5 GHz is proposed. The element of this transmitarray is composed of only two identical layers of metal plates, with air medium filling the space between the upper and lower layers. Each layer has four sets of staggered I-slots, thus ensuring dual-frequency orthogonal polarization operation. Moreover the proposed element overcomes the challenge of achieving full 360-degree phase shift in dual-layer metal-only structures without any additional connecting elements. By altering the length of the slots, it can achieve a continuous full 360-degree phase shift while maintaining a transmission amplitude above −2 dB and exhibits co-polarized transmission in both bands. Then a prototype containing 16 × 16 elements is designed and fabricated to verify the feasibility of the design scheme. The measurement results, which are consistent with the simulation, demonstrate that the maximum gains of 24.85 and 27.64 dBi are obtained at 6.4 GHz and 9.4 GHz, with corresponding aperture efficiencies of 23.18% and 20.4% and a 3-dB gain bandwidth of 15.6% and 22.34%. The good transmission coefficients of the element and the dual-band capability make the design a competitive candidate for satellite and high-power applications.

An improved 4H-SiC trench MOS barrier Schottky diode with current spreading layer and low resistance layer

This paper investigates an improved trench MOS barrier Schottky (TMBS) structure with extra double epitaxial layers (DE-TMBS) based on the conventional TMBS (C-TMBS) featuring a high-doped N-type current spreading layer (CSL) and a high-doped low resistance layer (LRL). Compared to the C-TMBS, the CSL in the improved structure is grown on the N-type drift region, and the LRL is extended on the CSL. According to the numerical simulations and analytical models, the specific on-resistance (Ron,sp) of DE-TMBS can be significantly reduced compared to the conventional one. This is primarily due to the high doping concentration in CSL, which effectively lowers both the JFET resistance and spreading resistance. Additionally, the increased doping concentration in LRL reduces the channel resistance and JFET resistance. Moreover, the doping concentration and thickness of CSL and LRL are optimized to maximize the figure of merit (FOM), that Ron,sp is reduced by 40.9 % and the FOM (BV2/Ron,sp) is improved by 67.9 % compared to the C-TMBS structure.

Light-driven integration of diazotroph-derived nitrogen in euphotic nitrogen cycle

The bioavailable nitrogen fixed by diazotrophs is critical for sustaining productivity in the oligotrophic ocean. Despite this, understanding how diazotroph-derived nitrogen integrates into the nitrogen cycle within the euphotic zone remains unknown. Here, we investigated nitrogen fixation rates in the particulate and dissolved fractions within the euphotic zone of the North Pacific Subtropical Gyre. Our findings reveal the proportion of nitrogen fixation rates in the dissolved fraction increases with depth. Light manipulation experiments uncover that reduced light levels can stimulate the net release of diazotroph-derived nitrogen, aligning with our depth-related observations. Furthermore, we identify two distinct transfer pathways vertically associated with light-driven ecological niches. Specifically, the released diazotroph-derived nitrogen is transferred to non-diazotrophic plankton in the upper layers. Meanwhile, in the lower layers, it contributes to the nitrification process. Our results underscore the high bioavailability of diazotroph-derived nitrogen and its rapid integration into the nitrogen cycle through multiple pathways within the well-lit ocean.

Heterotopically differentiated PDLSCs-laden 3D bioprinting scaffolds for concurrent oral hard and soft tissue regeneration

Following dental extraction, the alveolar bone and gingival tissues could undergo varying degrees of resorption, affecting subsequent implant integration and aesthetic outcomes. Adequate volume of both hard and soft tissues is essential for optimal results. Three-dimensional (3D) bioprinting technology offers the advantages of biomimicry, personalization, and precise spatial distribution, which are pivotal for enhancing the success and esthetics of dental restorations. In this study, we fabricated a construct with a natural transition and varying material concentrations by 3D bioprinting, comprising an upper layer of Collagen/Alginate/periodontal ligament stem cells (PDLSCs) and a lower layer of Collagen/nano-hydroxyapatite (nHA)/Alginate/PDLSCs. Characterization of the physicochemical properties revealed that the incorporation of nHA significantly enhanced the mechanical properties of both the bioink and the construct. Flow cytometry analysis confirmed the stemness of PDLSCs. Scanning electron microscopy (SEM) revealed that the construct possesses satisfactory pore density and a natural transition at the stratification point. The construct displayed good cell viability and proliferation, with the cellular movement observed at the stratification interface after bioprinting. Differentiation staining and quantitative reverse transcription-polymerase chain reaction (RT-qPCR) results demonstrated that PDLSCs within the 3D construct are capable of both osteogenic and fibroblastic differentiations. Ectopic transplantation in mice confirmed the biocompatibility of the construct. A rat tooth extraction model validated the construct's effectiveness in the integrated regeneration of both hard and soft tissues in alveolar ridge preservation (ARP). In conclusion, this personalized, concentration-varied 3D construct exhibits excellent biocompatibility and tissue preservation effects, holding significant potential for clinical application.  

A Design Method for Road Vehicles with Autonomous Driving Control

The past three decades have witnessed extensive studies on motion-planning and tracking-control for autonomous vehicles (AVs). There is, however, a lack of studies on effective design methods for AVs, which consist of the subsystems of the mechanical vehicle, tracking-control, motion-planning, etc. To tackle this problem, this paper proposes a design approach for AVs. The proposed method features a design framework with two layers: at the upper layer, a particle swarm optimization (PSO) algorithm serves as a solver to a multi-objective optimization problem for desired AV trajectory-tracking performance; at the lower layer, a coupled dynamic analysis is conducted among the three subsystems, i.e., a nonlinear model for the mechanical vehicle, a motion-planning module, and a controller based on nonlinear model predictive control (NLMPC) for direction control. The simulation results demonstrate that the proposed method can effectively determine the desired design variables for the NLMPC controller and the mechanical vehicle to achieve optimal trajectory-tracking performance. The research findings from this work provide guidelines for designing AVs.

The long-term effect of the coronavirus pandemic on parkrun participation: an interrupted time series analysis

BackgroundThe growth of parkrun between 2004 and 2019 has been heralded as a success story for public health as a result of its physical activity and wellbeing benefits for participants. However, parkrun was not immune from the COVID-19 pandemic - with events in mainland England cancelled from March 2020 to July 2021. This study explores the lasting impact of the pandemic on parkrun participation to February 2023, and its implications across the socioeconomic spectrum.MethodsThe study combines aggregated parkrun weekly finisher data from 32,470 Lower Layer Super Output Areas (LSOA) in England from January 2015 to February 2023 with Office of National Statistics (ONS) data on population and deprivation. Interrupted time series analysis using segmented Poisson regression models was used to estimate the immediate change in parkrun participation and the change in the rate of growth following the pandemic. Models were fitted for each Index of Multiple Deprivation (IMD) quintile separately to assess whether this effect differed by socioeconomic deprivation.ResultsVisualisation and interrupted time series analysis showed a significant and long-term decrease in parkrun participation following the reopening of parkrun events. This was consistent across all IMD quintiles, indicating that the inequalities in parkrun participation according to IMD observed prior to the pandemic remained after the pandemic. Between March 2020 and February 2023, almost 13 million fewer parkrun finishes are estimated to have occurred relative to what would have occurred in the absence of the pandemic.ConclusionThe reduction in parkrun participation during the pandemic and following the reopening of events is likely to have negatively impacted wellbeing in would-be participants. Going forwards, policymakers must make the difficult trade-off between the long-term health and social implications of restricting outdoor physical activity events against the benefits associated with a reduction in infectious disease transmission.

A temperature tipping point in hypoxic zone size

AbstractTemperature increases will have ubiquitous effects on aquatic food webs, from microbes to consumers, and affect the quality and quantity of carbon flows within and between water layers. A decline in the biological pump moving carbon from surface to lower layers is anticipated. We reviewed 37 years of data on hypoxic zone size and water quality in the northern Gulf of Mexico to determine if air and bottom water temperature increases (0.5°C decade−1) are significantly related to variations in its areal size. There was no significant decline in important river water quality in the 24 years since the national Hypoxia Action Plan was developed to reduce its size. Changes in the ratio of km2 hypoxia per 1000 mt nitrate loading from the Mississippi River from 2000 to 2023 reveals a tipping point in the hypoxic zone size that is driven by ocean warming. Biological factors varying with temperature such as ectotherm growth rates, zooplankton grazing, cell sinking rates, and diatom sequestration of Si or N are apparently more important influences on recent hypoxic zone size than variations in physical factors. This tipping point may be common to similarly warmed and eutrophic coastal waters where warming will likely result in diminished oxygen deficiency (< 2 mgO2 L−1). Hypoxia and food web models assuming a stationary equipoise of nutrient loadings, ratios and food webs will be deficient as coastal waters warm further, coastal storm and hurricane frequency increase and land uses in the watershed are altered with climate change.

Artificial Grassland Revegetation Improves Soil Water Retention and Storage Capacity of the Degraded Hillside Alpine Meadow

ABSTRACTThe crucial role of soil water retention and storage in soil hydrology and the water cycle is well established. However, in sensitive and degraded ecosystems like alpine meadows, the effectiveness of revegetation in enhancing these critical functions remains understudied. This study investigates the effects of revegetating severely degraded hillside meadows with artificial grasslands on soil water retention and storage capacity in the Qinghai‐Tibetan Plateau. Soil analyses at a depth of 0–20 cm revealed significant improvements in soil properties after revegetation, with increases in soil organic matter content (86.8%), total porosity (11.9%), capillary porosity (31.6%), and clay content (13.5%). Both the saturated hydraulic conductivity (Ks) and field capacity (FC) increased markedly, by 9.7% and 63.7% in the upper layer (0–10 cm) and 21.7% and 69.6% in the lower layer (10–20 cm), respectively. Structural equation modeling identified bulk density, root mass density, FC, capillary porosity, and clay content as the dominant direct factors influencing Ks with path coefficients of −0.56, 0.30, −0.53, 0.57, and −0.12, respectively, while vegetation cover and aboveground biomass were found to have indirect influences. These findings demonstrate that revegetation with artificial grasslands effectively improves soil water retention and storage capacity in degraded hillside alpine meadows by regulating key soil hydraulic and physical properties. This enhanced water‐holding capacity has significant implications for understanding the dynamics of revegetation by artificial grassland establishment in improving ecosystem health and eco‐hydrological functions in these vulnerable environments. Furthermore, the study provides valuable insights and a theoretical basis for developing ecological restoration solutions for degraded hillside meadows in other alpine regions.