Water Pore Research Articles

Experimental investigation into effects of material and energy regulation of debris flow by using check dams with different porosities

The design of check dam openings for debris flow control has been identified as a longstanding challenge, with no definitive solution yet identified. In this study, a quantitative analysis of the control efficacy of check dams with varying opening rates is presented. Field investigation data of 67 check dams located in Wenxian County, Gansu Province, were utilized to gain a preliminary understanding of their running state and damage situation. Building upon this, five check dams with opening rates ranging from 2.1% to 10.4% were designed and subjected to testing. Parameters including volumetric water content, pore water pressure, deposit morphology, and particle size distribution were analyzed to investigate the effect of varying opening rates on debris flow control. The results showed that: 1) As the opening rate of the check dams increased, the peaks of volumetric water content and pore water pressure behind the dam first decreased and then stabilized. When the opening rate was increased to 6.3% or higher, these parameters reached stable values. 2) Check dams with different opening rates all demonstrated good effects in retaining the coarse and sluicing the fine, resulting in the average particle size behind dams was coarsened by 2.65 times. This coarsening was primarily attributed to an increase in the proportion of retained particles within the 2–5 mm size range. 3) An optimal opening range of 4.2%–6.3% was identified for effective debris flow control. Compared with other dams, Dam II with opening rate 4.2% exhibited superior performance in mitigating flow energy and intercepting coarse particles, but it imposed stringent strength-related requirements.

Study on the physical mechanical properties and freeze-thaw resistance of energy storage concrete with artificial phase change aggregate

As the main material for major infrastructure in cold regions, the mechanical properties and freeze-thaw resistance of concrete have become key scientific issues affecting the safety and normal operation and maintenance of infrastructure in cold regions. Energy storage concrete with phase change materials (PCM) has high thermal storage performance, which is beneficial to improving the frost resistance of concrete. In our preliminary research work, the artificial phase change aggregate (APCA) containing PCM with high latent heat, good mechanical properties and frost resistance were made and tested. The APCA was added to the concrete and replaced with natural coarse aggregate in different proportions, resulting in several energy storage concrete schemes with different APCA contents. The water absorption characteristics, microstructure and pore characteristics of energy storage concrete with different APCA contents were tested and analyzed through negative pressure saturation test, SEM and MIP. The effects of APCA replacement on the composition, mechanical properties, failure morphology characteristics and frost resistance durability of energy storage concrete at various ages were analyzed through XRD test, strength test and freeze-thaw cycle test. The results showed that replacing natural coarse aggregates with APCA changed the pore characteristics of concrete, reduced its saturation water absorption rate, but did not change the composition of hydration products at various ages of concrete. Replacing with an appropriate amount of APCA in concrete is beneficial for reducing the total porosity, the number of more-harmful pores and harmful pores. APCA reduce the compressive strength and splitting tensile strength of energy storage concrete at various ages. The early splitting strength of energy storage concrete increases rapidly, while the later growth is relatively slow. APCA are beneficial for suppressing the expansion of pores and cracks under freeze-thaw action of concrete. APCA is helpful to improve the freeze–thaw resistance of the energy storage concrete. After 100 freeze-thaw cycles, their strength is still 96% of the 28 day strength, and their compressive strength is about 35 MPa. This study provides a reliable experimental and theoretical basis for improving the freezing resistance of concrete in cold area.

Multi-plateau water adsorption of pyrene-based covalent organic frameworks for potential humidity control

Indoor air humidity significantly influences air quality, human health, and work performance. Covalent organic frameworks (COFs) have been proven effective in humidity regulation; however, challenges remain in broadening their range of humidity control. This study designs and synthesizes a series of pyrene-based crystalline COFs as humidity control materials, investigating the moisture adsorption–desorption characteristics under structural modulation. Among these, PY-3,3′-BPY-COF exhibits unique multi-step adsorption isotherms, achieving the highest water uptake capacity (1 g/g) and efficient water uptake-release cycles. Theoretical and experimental analyses reveal a linear relationship between the maximum water uptake rate and the specific surface area, while the adsorption inflection points are influenced by the water binding energy and pore size distribution. Importantly, the introduction of strong binding sites promotes multi-step adsorption phenomena, significantly enhancing the humidity control capabilities of COFs across a wide range of humidity levels. This research introduces an innovative approach for broad-spectrum indoor humidity control and reveals the fundamental relationship between the structure characteristics of COFs and their capabilities in water adsorption and release.

Two-layer multi-state SPH modelling of momentum growth and its feedback in viscous debris flow on wet bed sediment

Flow-momentum growth and resultant feedback from bed-sediment entrainment significantly influence the mobility of debris flows and valley topography. Existing models inadequately capture the mass and momentum growth regulated by scale-sensitive, time-dependent pore water pressure in erodible beds, which exhibit pronounced anisotropy and nonlinearity. In this study, we propose a three-dimensional, two-layer, multi-state smooth particle hydrodynamics (TLMS-SPH) model to assess the flow-momentum growth of debris flows on wet beds. Herein, an enhanced Drucker-Prager (DP) yield criterion is integrated into the Herschel-Bulkley-Papanastasiou (HBP) rheology to mitigate particle collapse induced by gravitational perturbations in steep terrains. Particularly, an efficient hydro-poro-mechanics-based pore water pressure algorithm is presented and embedded in the SPH scheme to simulate the pore pressure response. To address the size effect, we rigorously tested the method through a series of full-scale, well-documented entrainment experiments. The results demonstrate that the model effectively captures and reproduces the complex dynamics of flow-momentum growth, manifesting in erosion-induced excessive volume and mobility changes. Our method establishes a clear link between volumetric water content and pore pressure response, further underscoring its capability to delineate levee-channel and deposition morphology. This study represents the first attempt to model debris flow on beds of varying wetness from a particulate perspective.

Triggering mechanics and early warning for snowmelt-rainfall-induced loess landslide.

Loess landslides represent a significant natural hazard, especially in arid and semi-arid regions where slopes are exposed to prolonged snowmelt and rainfall infiltration. To analyze landslide stability and conduct early warning evaluations effectively, a robust monitoring system and appropriate equipment are crucial. This study utilizes historical data from the Kalahaisu landslide in Xinyuan County, Ili region, which was monitored using various techniques. The research assesses the time resolution, spatial resolution, and data accuracy of these monitoring methods. Additionally, the study explores the landslide disaster patterns and early warning indicators for the Kalahaisu landslide. It suggested that the deformation of the rainfall- and snowmelt- landslide is not only affected by the seasonal climates but also closely related to the internal structures of the loess. The other observation is that the respective time and spatial resolution of monitoring instrument would significantly affect the the interpretation time of the landslide deformation. Instruments with higher spatial resolution can more effectively identify unstable areas within a landslide, while instruments with higher temporal resolution can provide detailed time-series deformation data. Therefore, real-time and comprehensive monitoring of landslides using a suitable combination of monitoring equipment can provide strong data support for landslide stability evaluation and deformation trend prediction. Full-area monitoring techniques, such as Synthetic Aperture Radar (SAR) and equipment that measures changes in internal properties like deep water content, deep displacement, and pore pressure, offer a more comprehensive and effective approach to monitoring and interpreting landslide deformation. The insights gained from this research may enhance the prediction and prevention of loess landslides in the Ili River valley.

Investigation of the pore structure characteristics and fluid components of Quaternary mudstone biogas reservoirs: a case study of the Qaidam Basin in China

Quaternary mudstone biogas reservoirs in the Qaidam Basin have shown great potential. However, complex pore structures with high clay contents and high heterogeneity limit the understanding of the storage and migration principles of these reservoirs. In this paper, HPMI and nitrogen adsorption experiments, in combination with NMR experiments under water saturation, centrifugation, various drying temperatures and other conditions, were adopted to determine the pore structure characteristics. Specifically, the reservoir space types and pore radius distribution characteristics were clarified. The cutoff values for different types of pores were identified based on the water-saturated mudstone NMR T2 spectra for full aperture distribution scales jointly characterized by mercury injection and nitrogen adsorption experiments. Furthermore, the three pore components and the saturation of different fluids were obtained. The research results indicate that the mudstone biogas reservoir has developed various reservoir spaces, and the pore size is primarily in the micronanometer range. The average total porosity reaches 27.28%, but the proportion of movable water pores is only 9.23% with poor fluid mobility, and the fluids in the pores are mostly capillary-bound water and clay-bound water. Among the different lithologies, argillaceous sand is more likely to become a good production layer.

Zirconia encrusted ceramic composite membrane for uremic toxins removal: Fabrication and assessment of biocompatibility

In this study, tubular zirconia composite membranes (ZM1-ZM3) were developed using low-cost tubular substrate which was prepared utilizing naturally available clay materials by an extrusion approach. The zirconia nanoparticles were encrusted on a low-cost tubular substrate using spray pyrolysis technique. The membranes were investigated for their biocompatibility in addition to pore size, chemical stability, water permeability, porosity, contact angle, thermogravimetric (TGA), and X-ray diffraction (XRD). Water permeability, pore size and porosity of optimized membrane (ZM3) were 3.05 × 10–4 ± 0.03 L.m-2.h-1.Pa-1, 119 ± 0.57 nm and 36 ± 0.12 %, respectively. Platelets adhesion and protein adsorption were measured to be 4630 ± 46 platelets.mm-2, and 1.05 ± 0.02 μg.cm-2 respectively, while the activated partial thromboplastin time (APTT) and prothrombin time (PT) were 80 ± 0.51 s and 27 ± 0.26 s, respectively. Complement activation C3 and C4 concentrations were assessed to be 76.2 ± 0.88 mg.dL-1 and 21.57 ± 0.80 mg.dL-1, respectively and hemolysis ratio was 0.31 ± 0.01 %. Moreover, the membrane had a considerable antifouling nature with a flux recovery ratio of 89.22 ± 0.58 %. Protein retention was found to be 81.14 ± 0.58 %, in addition to outstanding sieving coefficients of uremic toxins like urea (0.95 ± 0.005), creatinine (0.93 ± 0.004), and phosphate (0.90 ± 0.004). These findings suggest that the produced tubular zirconia composite membrane has the potency for hemofiltration.

Insight into failure mechanisms of rainfall induced mudstone landslide controlled by structural planes: From laboratory experiments

The role of structural planes in controlling mudstone landslides is a key issue in the study of geo-disasters in the Loess Plateau of China. In this study, the effects of sliding-control structures on the mechanisms of mudstone landslides are investigated via three model experiments with different slope structures. The results show that the hydrological response and failure mode of the experimental slope vary with the structural conditions. The vertical joints serve as preferential seepage paths, which accelerate rainfall infiltration, resulting in earlier responses of volumetric water content and pore water pressure. With the incorporation of vertical joints, the slope failure mode tends to transform from shallow failure to deep-seated failure. The presence of a weak interlayer leads to significant increases in the velocity and runout of the sliding mass. The variation in the slope failure extent and deformation characteristics with varying sliding-control structures further changes the temporal and spatial distributions of volumetric water content and pore water pressure. The different slope failure modes correspond to different sliding-control mechanisms, which are dominated by the types of structural planes and their interactions with hydrological responses. In the action of these mechanisms, pore water pressure and seepage force play significant roles in the reduction of effective stress and shear strength.

Insights into Translocation of Arginine-Rich Cell-Penetrating Peptides across a Model Membrane.

It is well-known that membrane deformation and water pores contribute to the spontaneous translocation of arginine-rich cell-penetrating peptides (CPPs). We confirm this through the observation of the spontaneous translocation of single R9 (nona-arginine) and Tat (48-60) peptides across a model membrane using the weighted ensemble (WE) method within all-atom molecular dynamics (MD) simulations. Furthermore, we demonstrate that membrane deformation and the presence of a water pore reduce the effective charge of the CPP and the bending rigidity of the model membrane during translocation. We find that R9 disturbs the model membrane more than Tat (48-60), leading to more efficient translocation of R9 across the model membrane.

Developmentally controlled subcellular remodeling and VND-initiated vacuole-executed PCD module shape xylem-like cells in peat moss

Peat moss (Sphagnum) is a non-vascular higher plant with unique xylem-like hyaline (H) cells that are accompanied by photosynthetic chlorophyllous cells. These cellular structures play crucial roles in water storage and carbon sequestration. However, it is largely unknown how peat moss develops the H cells. This study systematically explored the Sphagnum Developmental Cell Atlas and Lineage and classified leaf cell development into two lineages with six stages (S0-S5) based on changes in key cellular traits, including the formation of spiral secondary cell walls (S4) and the presence of water pores (S5). Cell lineage-specific subcellular remodeling was transcriptionally regulated during leaf development, and vacuole-mediated clearance of organelles and cell death led to mature dead H cells. Interestingly, expression of land plant conserved Vascular-related NAC Domain (VND) genes correlated with H cell formation. Overall, these results suggest that the origination of xylem-like H cells is related to VND, likely through the neofunctionalization of vacuole-mediated cell death to attempt xylem formation in peat moss, suggesting potential uncoupling of xylem and phloem cell origins. This study positions peat moss as a potential model organism for studying integrative evolutionary cell biology.

An operational IoT-based slope stability forecast using a digital twin

The paper investigates the combined use of real-time hydrological monitoring, publicly available meteorological data and hydrological and geotechnical numerical modelling, to develop data-driven models to forecast the stability of a slope. This study showcases a first attempt to integrate these critical aspects into a fully automatic Internet of Thing (IoT)-based local landslide early warning system (Lo-LEWS).The paper uses a validated hydrological numerical model, back-calculated over real monitored conditions, to evaluate the slope stability. The factor of safety (FoS) was computed coupling the commercial package GeoStudio, using transient SEEP/W and Slope. The analyses were conducted for 5 different 1-year datasets encompassing both historical (2019–2020, 2021–2022, 2022–2023) and future projections (2064–2065, 2095–2096) of meteorological variables. Daily variation of hydrological and meteorological variables, along with vegetation indicators were used as inputs to train data-driven models, using polynomial regression (PR) and Random Forest (RF), to forecast daily FoS values. The trained models proved to be effective and were employed to forecast slope stability for the rolling three days. To accurately forecast the FoS, it was essential to incorporate forecasted hydrological, meteorological and vegetation variables into the analysis. The hydrological variables used as inputs for the data-driven models are forecasted using an open-source Python package for the analysis of hydrogeological time series, called Pastas (Collenteur et al., 2019). This model uses historical and forecasted meteorological and vegetation conditions to, specifically, replicate and forecast the time series of volumetric water content (VWC) and pore water pressure (PWP). The forecasted hydrological variables from Pastas, the forecasted meteorological variables as well as Leaf Area Index (LAI) are used as inputs for the trained data-driven models to forecast the FoS values.Finally, a web-based platform (WBP) has been created that automatically runs once a day and perform the following actions: 1) fetches measured and forecasted data using APIs, 2) runs rolling three days forecast based on collected hydrological, meteorological and vegetation variables, and 3) sends the forecasted values back to the Norwegian Geotechnical Institute (NGI) data platform, NGI Live, making them available for real-time visualization in online dashboards. If FoS, VWC or PWP threshold values are exceeded, text messages and emails are sent to the system managers, enabling them to take appropriate actions. The successful implementation of this framework is the result of a collaborative effort across diverse expertise areas, including geotechnics, hydrology, meteorology, instrumentation, and informatics.

Synthesis of silane-modified styrene-acrylic ester emulsion and its inhibition mechanism on whitening of calcium aluminate cement mortar

A new polymer, triethoxyvinylsilane-modified styrene-acrylic ester emulsion (TMSA), was synthesized through emulsion polymerization. The effect of TMSA on the whitening of calcium aluminate cement (CAC) mortar was investigated. The results showed that TMSA had an excellent inhibition effect on the whitening of the CAC mortar with only 0.8 % - 1.6 % addition. Analysis of the micro-morphology and Raman spectra revealed that the white deposits on the surface of the mortar were C4AC(_)H11 and CaCO3, whereas TMSA addition effectively inhibited the formation of C4AC(_)H11 and reduced the occurrence of CaCO3. Through investigating the hydration, Ca2+ concentration, capillary water absorption and pore structure, it was found that the effect of the CAC hydration on the whitening of the mortars was inessential, whereas there was a strong link among whitening, capillary water absorption and macro-capillary pores. The addition of TMSA not only reduced the concentration of Ca2+ which was the source of the whitening, but also reduced the formation of macro-capillary pores in the CAC mortar that led to a significant reduction in the capillary water absorption, thus weakening the mobility of pore solution in the mortar and hindering the migration of Ca2+ to the mortar surface. Based on these two aspects, TMSA effectively inhibited the whitening of the CAC mortar.

Global transcriptional analysis for molecular responses of Alicyclobacillus acidoterrestris spores in drinking water after low- and medium-pressure ultraviolet irradiation

Ultraviolet (UV) irradiation can effectively disinfect water contaminated with pathogens. However, the biological mechanisms of inactivation by different types of UV irradiation are unknown. The present study investigated the inactivation mechanisms of Alicyclobacillus acidoterrestris spores in water by low-pressure UV (LPUV) and medium-pressure UV (MPUV) using a quasi-collimated beam apparatus. Global transcriptomic data obtained by RNA-seq revealed 291 shared differentially expressed genes (DEGs) that damaged DNA, reduced biofilm formation, and had other reactions. The individual downregulated DEGs (n = 123) mainly related to cell motility, membrane transport, and metabolism were induced by LPUV, and in turn contributed to energy-saving and metabolic activity inhibition, forcing bacteria into a viable but non-culturable (VBNC) state. The individual upregulated DEGs (n = 244) following MPUV treatment were mainly enriched in cell motility, membrane transport, metabolism, DNA replication and repair, and spore germination pathways. This results in high-energy consumption, severe damage to genetic material, and enhanced spore germination accelerated cell death. Additionally, hub genes in the protein-protein interaction network were mainly involved in transcription and translation. These findings contribute to the comprehensive understanding of the inactivation mechanisms of different types of UV irradiation, and will improve applications of UV disinfection in the treatment of water.

Characterization of water states and pore size distribution in Beijing poplar using nuclear magnetic resonance techniques

ABSTRACT This study employs nuclear magnetic resonance (NMR) techniques to elucidate the water states and pore size distribution within Beijing poplar (Populus beijingensis W. Y. Hsu) across various temperatures. By analyzing the variation in moisture content (MC) at different freezing temperatures, the proportion and distribution of cell wall pores were determined using the NMR Cryoporometry (NMR-C) method. The results show approximately 60% of the pores in both the heartwood (HW) and sapwood (SW) of Beijing poplar have diameters were 1.5 nm, while the proportion of pores with diameters greater than 4.6 nm was less than 10%. Moreover, the MC of both more freely bound water (C-water) and OH bound water (B-water) is observed to decrease exponentially with decreasing temperature. B-water in Beijing poplar is found to maintain a higher MC than C-water across the temperature range from −3 to −60°C, indicating greater resistance to freezing. The findings of this study contribute to a comprehensive understanding of water states in Beijing poplar. Also the pore size distribution of Beijing poplar provides reference data for the selection of wood chemical modification groups.

Effect of water occurrence in coal reservoirs on the production capacity of coalbed methane by using NMR simulation technology and production capacity simulation

The occurrence of gas and water is a critical factor affecting the production capacity of coalbed methane. Therefore, occurrence and dynamic interaction between gas and water in coal reservoirs need to be studied. T2 spectrum of all the samples were studied by NMR technique at 0, 5, 9, and 28 h of natural evaporation. Then, multifractal model was used to characterize water distribution heterogeneity, and a novel evaluation coefficient was proposed to characterize distribution heterogeneity of water content, the correlation among evaluation coefficient, water distribution heterogeneity and pore structure parameters was analyzed. The results are as follows. In the saturated state, the moisture distribution of three types is heterogeneous. Type A of adsorption pore-developed exhibits strong moisture variation heterogeneity of small pores, in contrast to the uniform moisture variation in large pores. Type B of fracture-developed has the highest coefficient of variation in moisture distribution. The coefficient of variation A1 for moisture content can determine the speed of moisture transport and evaporation in the pore structure. A lower A1 indicates a greater moisture transport volume and faster moisture transport rate over the same time. The coefficient of variation A2 for moisture distribution represents the heterogeneity of moisture content variation in the pore structure. That is, a smaller A2 indicates better heterogeneity in the distribution of moisture content in the pore structure. Numerical simulation indicates the average gas production and the peak gas production time increase and decrease with the initial moisture content (Sgrw) increases, respectively. These findings provide practical guidance for coalbed methane development, especially in optimizing coalbed methane production capacity prediction and improving recovery efficiency.

Exploring the Effects of Fissures on Hydraulic Parameters in Subsurface Flows from the Perspective of Energy Changes

Reynolds number (Re), pore water pressure (P), and water flow shear force (τ) are primary indicators reflecting the characteristics of subsurface flow. Exploring the calculation of these parameters will facilitate the understanding of the hydrodynamic characteristics in different subsurface flows and quantify their differences. Hence, we conducted a study to monitor soil water content, matrix potential, and pore water pressure in two typical soil profiles (with and without fissures). The distribution of Re, P, and τ in both matrix flow (MF) and preferential flow (PF) were calculated with an improved calculation method, focusing on their energy changes. Results showed that these hydrologic parameters are quite different between MF and PF. Re values in MF remained below 0.1, indicating lower water flow velocities, while the Re values ranged from 0.8 to 2 in PF, indicating higher flow velocities. The P values in PF was tens to hundreds of times higher than that in MF, which is mainly due to the rapid accumulation and leakage of water within soil fissures. Additionally, the larger hydraulic radius and gradient in PF also resulted in higher τ values in PF (2~6 N m−2) than in MF (0~1.5 N m−2). In PF, the pressure potential was the significant factor for τ, while τ in MF was dominated by the matrix potential and varies with the magnitude of the matrix potential gradient. This study suggests that Re, P, and τ could be considered as the major indexes to reflect dynamic characteristics of subsurface flow.

Occurrence of methane in organic pores with surrounding free water: A molecular simulation study

Free water contained in shale reservoirs can influence the enrichment and transportation of shale gas. To accurately assess shale gas adsorption in shale reservoirs and improve recovery, it is crucial to understand the occurrence of gas and water. In this study, the occurrence of methane occupying the organic pores surrounded by free water is investigated using Grand Canonical Monte Carlo/Molecular Dynamics simulations, considering the effects of pressure, temperature and pore size. The center of the model represents methane adsorbed/free within the organic pores, while the regions on either side depict free water. Although water does not significantly penetrate organic pores, pressure, temperature, and pore size have a notable impact on the wettability of water on organic surfaces, resulting in variations in the concave liquid surface morphology. This results in varying degrees of competitive adsorption of water and methane near the carbonyl group. At lower pressures, although the capillary pressure decreases sharply with increasing pore size, the improved water wettability increases the extent of its intrusion along the pore surface, thereby enhancing the competitive adsorption of methane and water. At higher pressures, capillary pressure acts as a resistance, preventing water from invading the organic pores in significant quantities. Due to the weak affinity of organic pores for water, the same phenomenon was observed even after increasing the pore size and temperature to improve water wettability. In addition, high temperatures can lead to more pronounced water intrusion. Finally, it is hypothesized that competitive adsorption of methane and water is more pronounced at shallower burial depths and slightly larger pore sizes. This result is expected to provide insights for the accurate evaluation of gas adsorption in water-bearing shales.

Water Resistance and Pore Characteristics of Organic Silane Waterproof Membrane in Roadbed

Abstract In this paper, the inhibiting effect of organic silane waterproofing membrane on the capillary water rise height (CRH) of roadbed soil has been investigated, and the pore characteristics of the waterproof membrane have been studied. Different tests were performed to validate the resulting performance, such as CRH, contact angle (CA), and mercury intrusion porosimetry (MIP). The results showed that at 92 % compaction degree, the consumption of organic silane per unit area (OSA) of 8 g/m2 to 15 g/m2 could effectively inhibit the CRH. The CA of the waterproof membrane increased with OSA consumption and compaction degree. When the compaction degree and OSA consumption increased, the large pores were divided into small pores, resulting in a decrease in the most probable pore size of the waterproof membrane and an increase in the cumulative mesopore volume. Additionally, the specific surface area of the pores and the roughness of the pore surface of the waterproof membrane increased, the pore structure became more complex, and the fractal dimension was closer to 3.

Mechanism of pore water phase change, freezing expansion, and pore enlargement of coal samples under low-temperature liquid nitrogen action

Liquid nitrogen fracturing, a technology for enhancing coal seam permeability without water, garnering considerable attention due to the intricate network of fractures induced by the low-temperature impact of LN2 on coal reservoirs. The phase transition freezing expansion of water-ice plays a pivotal role in determining the efficacy of coal damage. As direct measurement of water signal change during freezing is impractical, studying the variation in unfrozen water content during coal sample re-warming subsequent to cold shock is beneficial. This approach aids in elucidating the phase transition expansion and pore expansion mechanisms at different pore scales. The findings reveal the sequence of pore ice melting in coal samples frozen by LN2: micropores exhibit initial water appearance, followed by medium-sized pores, with micropores reaching peak levels first. Subsequently, water migrates from micropores to medium-sized pores, leading to their peak levels, before macropores show water presence. The temperature gradient from the coal sample center to the coal wall, owing to thermal resistance, results in the part melting first also freezing first. Analysis indicates that the porosity signal of lignite and bituminous coal increased by 203 % and 467 % during medium-sized pore melting, emphasizing the prominence of the medium-sized pore melting stage. It is further inferred that the phase transition freezing expansion and pore expansion of coal sample water induced by LN2 primarily occur in medium-sized pores.

Nitrate and silicate fluxes at the sediment–water interface of the deep North Pacific Ocean illuminated by 226Ra/230Th disequilibria

By taking advantage of recent analytical advances, we herein develop the 226Ra/230Th isotope systematics as a novel tool for quantifying nitrate and dissolved silicate fluxes across the sediment–water interface of the deep-ocean floor. Sediment cores were retrieved from the seabed between 4927 m and 5951 m in the North Pacific Ocean. Downcore profiles of 230Th and both dissolved and total 226Ra were measured using a high-sensitivity inductively coupled plasma mass spectrometer. At all study sites, a marked deficit of total 226Ra with respect to 230Th was observed between 0 and 20 cm, indicating active migration of soluble 226Ra from the sediment into the overlying seawater. By constructing the mass balance of 226Ra in the sediment column, the flux of dissolved 226Ra across the sediment–water interface was estimated to range from 461 to 1320 dpm m−2 yr−1. When coupled to a diffusive transport model as developed by early investigators, these flux values of 226Ra enabled us to calculate the flux of any dissolved constituent of interest by measuring their bottom water concentrations and pore water “saturation” concentrations. Based on the 226Ra/230Th disequilibrium approach, the derived fluxes vary between 4.1 and 10.5 mmol m−2 yr−1 for nitrate and between 11 and 49 mmol m−2 yr−1 for dissolved silicate. A compilation of nitrate and silicate fluxes from the seabed in the deep Pacific Ocean shows that these values are consistent with historical flux measurements based on the conventional core incubation method in the same study region. In addition, both nitrate and silicate fluxes exhibit a clear depth-dependent trend. Overall, our results suggest that sedimentary diagenetic alterations at the North Pacific Ocean floor below ∼ 5000 m are efficient so that only < 2 % of the particulate organic carbon and < 12 % of the biogenic opal raining to the seafloor are ultimately preserved in the sediment.