Low Gradient Research Articles

Isotope-derived young water fractions in streamflow across the tropical Andes mountains and Amazon floodplain

Abstract. The role of topography in determining water transit times and pathways through catchments is unclear, especially in mountainous environments – yet these environments play central roles in global water, sediment, and biogeochemical fluxes. Since the vast majority of intensively monitored catchments are at northern latitudes, the interplay between water transit, topography, and other landscape and climatic characteristics is particularly underexplored in tropical environments. To address this gap, here we present the results of a multiyear hydrologic sampling campaign (twice-monthly and storm sampling) to quantify water transit in seven small catchments (<1.3 km2 area) across the transition from the Andes mountains to the Amazon floodplain in southern Peru. We use the stable isotope composition of water (δ18O) to calculate the fraction of streamflow comprised of recent precipitation (“young water fraction”) for each of the seven small catchments. Flow-weighted young water fractions (Fyw) are 5 %–26 % in the high-elevation mountains, 22 %–52 % in the mid-elevation mountains, and 7 % in the foreland floodplain. Across these catchments, topography does not exert a clear control on water transit; instead, stream Fyw is apparently controlled by a combination of hydroclimate (precipitation regime) and bedrock permeability. Mid-elevation sites are posited to have the highest Fyw due to more frequent and intense rainfall; less permeable bedrock and poorly developed soils may also facilitate high Fyw at these sites. Lowland soils have low Fyw due to very low flow path gradients despite low permeability. The data presented here highlight the complexity of factors that determine water transit in tropical mountainous catchments, particularly highlighting the role of intense orographic precipitation at mountain fronts in driving rapid conveyance of water through catchments. These results have implications for the response of Earth's montane “water towers” to climate change and for water–rock reactions that control global biogeochemical cycles.

Integrating of electrocoagulation process with submerged membrane bioreactor for wastewater treatment under low voltage gradients

Treating and reusing wastewater has become an essential aspect of water management worldwide. However, the increase in emerging pollutants such as polycyclic aromatic hydrocarbons (PAHs), which are presented in wastewater from various sources like industry, roads, and household waste, makes their removal difficult due to their low concentration, stability, and ability to combine with other organic substances. Therefore, treating a low load of wastewater is an attractive option. The study aimed to address membrane fouling in the submerged membrane bioreactor (SMBR) used for wastewater treatment. An aluminum electrocoagulation (EC) device was combined with SMBR as a pre-treatment to reduce fouling. The EC-SMBR process was compared with a conventional SMBR without EC, fed with real grey water. To prevent impeding biological growth, low voltage gradients were utilized in the EC deviceThe comparison was conducted over 60 days with constant transmembrane pressure and infinite solid retention time (SRT). In phase I, when the EC device was operated at a low voltage gradient (0.64 V/cm), no significant improvement in the pollutants removal was observed in terms of color, turbidity, and chemical oxygen demand (COD). Nevertheless, during phase II, a voltage gradient of 1.26 V/cm achieved up to 100%, 99.7%, 92%, 94.1%, and 96.5% removals in the EC-SMBR process in comparison with 95.1%, 95.4%, 85%, 91.7% and 74.2% removals in the SMBR process for turbidity, color, COD, ammonia nitrogen (NH3–N), total phosphorus (TP), respectively. SMBR showed better anionic surfactant (AS) removal than EC-SMBR. A voltage gradient of 0.64 V/cm in the EC unit significantly reduced fouling by 23.7%, while 1.26 V/cm showed inconsistent results. Accumulation of Al ions negatively affected membrane performance. Low voltage gradients in EC can control SMBR fouling if Al concentration is controlled. Future research should investigate EC-SMBR with constant membrane flux for large-scale applications, considering energy consumption and operating costs.

High ductility and corrosion resistance chromium gradient stainless steel for fuel cell bipolar plates fabricated via laser powder bed fusion

Stainless steel sheets with a higher Cr content feature better corrosion resistance but lower ductility and formability, leading to the trade-off of performance and fabrication complexity/cost in many industrial scenarios, such as fuel cell bipolar plates and microreactors. To address that, thin stainless steel (SS) plates with a Cr gradient composition are fabricated with laser powder bed fusion technology in this work. Combining a Cr-rich (30 wt% Cr content) stainless steel composition with SS 316 L along the thickness direction using a gradient transition layer, the prepared gradient sheet achieves an elongation higher than 45%, which far exceeds the 19.9 ± 1.1% of the freestanding Cr-rich composition. Furthermore, detailed mechanical tests and microstructure characterizations are performed to analyze the mechanism for significant ductility improvement. The restraining function of high ductility composition promotes the multi-axial stress state in the low ductility Cr-rich composition and gradient layers, eventually activating more slip systems and dislocation entanglement. The resulting extra-hardening is accompanied by a significant increase in plastic deformation, leading to the fracture morphology with more pronounced large deformation characteristics.

Molecular dynamics study on the thermal decomposition of 1,3,5-trinitro-1,3,5-triazinane (RDX) catalyzed by aluminum nanoparticles with different contents

The mechanism of thermal decomposition of 1,3,5-trinitro-1,3,5-triazinane (RDX) catalyzed by nano-sized aluminum powder remains unclarified. In the present study, reactive molecular dynamics simulations using the parameterized reactive force field with low gradient correction (ReaxFF-lg) were conducted to study the microscale process of the RDX thermal decomposition catalyzed by different Al contents, and the density functional theory calculations were used to analyze the initial decomposition pathways of RDX on the Al surface. The thermal disintegration and the released energy of RDX are significantly facilitated by an increase in Al concentration at a lower level and the optimal value is around 35 wt%, while a higher concentration of Al will lead to an opposite effect. The dissociation of nitro group is the most probable initial reaction pathway for RDX decomposition on the Al surface. In addition, the evolutions of Al-containing clusters, key intermediates, and final products were analyzed, providing more information about this reaction. The findings suggest that the addition of Al nanoparticles improves the properties of RDX-based explosives, but the optimal amount of Al is critical for achieving the desired effects. The detailed analysis of the reaction mechanism and intermediate products provides valuable insights into the underlying mechanisms of the Al/RDX system.

Clumped isotopes in globally distributed Holocene coccoliths reveal their habitat depth

Reliable temperature reconstructions are necessary to improve climate reconstructions and comparisons with paleoclimate model simulations. Most existing paleotemperature proxies are based on organic and inorganic remains of marine organisms. Despite the evidence that the habitat depth of coccolithophores and other phytoplankton depend on their ability to balance light, nutrients, and grazing pressure, calibrations of proxies based on photosynthesizers often assume they live in the surface ocean. Here we present the first globally distributed dataset of core top multi-species coccolith clumped isotopes (Δ47), which show a clear latitudinal thermal gradient and demonstrate coccolith Δ47 sensitivity to temperature. The application of the most recent Δ47-temperature calibration for marine biogenic carbonates yields calcification temperatures implying deep habitats of ∼50 to ∼150 m for tropical coccolithophores, which could photosynthesize with 1-10% of surface photosynthetic active radiation (PAR) levels. Because of the uncertainties of Δ47 thermometry and of the low upper ocean temperature gradient, at well-mixed high-latitude locations, coccolith Δ47 cannot be used to reliably constrain a specific habitat depth. Nevertheless, Δ47 is a good indicator of paleotemperatures of the mixed layer. We also use coccolith Δ47 to derive the first regression relating core top coccolith Δ47 and sea surface temperatures (SST). Although this formulation cannot be considered a proper coccolith-specific Δ47 calibration, since it ignores coccolithophore's potential for calcification at depth, it facilitates comparison with temperature proxies like U37k′, which are regressed to SST, rather than production temperature.

Association of atrial fibrillation with survival in patients with low-flow low-gradient aortic stenosis with preserved ejection fraction undergoing TAVI.

There is limited evidence on the prognostic significance of atrial fibrillation (AF) in patients with low flow, low-gradient aortic stenosis with preserved ejection fraction (LFLG-pEF AS). We aimed to evaluate the recovery of stroke volume after transcatheter aortic valve implantation (TAVI) and clinical outcomes in patients with LFLG-pEF AS stratified by presence or absence of AF. In a prospective TAVI registry, patients with preserved left ventricular ejection fraction (LVEF≥50%) were stratified according to flow-gradient status and presence of AF. Among 2259 TAVI patients with preserved LVEF between August 2007 and June 2021, 765 had high-gradient AS (HG AS) and 444 had LFLG-pEF AS. AF was observed in 199 patients with HG AS (26.0%) and 190 patients with LFLG-pEF AS (42.8%). At 1 year, stroke volume index (SVi) was significantly improved in LFLG-pEF AS patients without AF, while SVi remained low in patients with AF (from 25.9±8.5mL/m2 to 37.2±9.9mL/m2 and from 26.8±5.1mL/m2 to 26.1±9.1mL/m2, respectively). LFLG-pEF AS patients with AF had an increased risk of 1-year all-cause mortality compared with those without AF (adjusted hazard ratio (HRadjusted) 2.57; 95% confidence interval [CI] 1.44-4.59). LFLG-pEF AS patients without AF had similar mortality compared with HG AS patients without AF (HRadjusted 0.85; 95% CI 0.49-1.46). Patients with LFLG-pEF AS and AF experienced no relevant recovery of stroke volume after TAVI, but a more than two-fold increased risk of death compared to patients with HG AS or LFLG-pEF AS without AF. https://www.clinicaltrials.gov. NCT01368250.

Efficient Table-based Function Approximation on FPGAs Using Interval Splitting and BRAM Instantiation

This article proposes a novel approach for the generation of memory-efficient table-based function approximation circuits for edge devices in general and FPGAs in particular. Given a function f(x) to be approximated in a given interval [ x 0 , x 0+a ) and a maximum approximation error E a , the goal is to determine a function table implementation with a minimized memory footprint, i.e., number of entries that need to be stored. Rather than state-of-the-art work performing an equidistant sampling of the given interval by so-called breakpoints and using linear interpolation between two adjacent breakpoints to determine f(x) at the maximum error bound, we propose and compare three algorithms for splitting the given interval into sub-intervals to reduce the required memory footprint drastically based on the observation that in sub-intervals of low gradient, a coarser sampling grid may be assumed while guaranteeing the maximum interpolation error bound E a . Experiments on elementary mathematical functions show that a large fraction in memory footprint may be saved. Second, a hardware architecture implementing the sub-interval selection, breakpoint lookup, and interpolation at a latency of just 9 clock cycles is introduced. Third, for each generated circuit design, BRAMs are automatically instantiated rather than synthesizing the reduced footprint function table using LUT primitives, providing an additional degree of resource efficiency. The approach presented here for FPGAs can equally be applied to other circuit technologies for fast and, at the same time, memory-optimized function approximation at the edge.

Detrital garnet petrology challenges Paleoproterozoic ultrahigh-pressure metamorphism in western Greenland

Abstract. Modern-style plate tectonics is characterised by the global operation of cold and deep subduction involving blueschist facies and ultrahigh-pressure metamorphism. This has been a common process since the Neoproterozoic, but a couple of studies indicate similar processes were active in the Paleoproterozoic, at least on the local scale. Particularly conspicuous are extreme ultrahigh-pressure conditions of ∼ 7 GPa at thermal gradients < 150 ∘C GPa−1 proposed for metamorphic rocks of the Nordre Strømfjord shear zone in the western part of the Paleoproterozoic Nagssugtoqidian Orogen of Greenland. By acquiring a large dataset of heavy minerals (n = 52 130) and garnet major-element composition integrated with mineral inclusion analysis (n=2669) from modern sands representing fresh and naturally mixed erosional material from the metamorphic rocks, we here intensely screened the area for potential occurrences of ultrahigh-pressure rocks and put constraints on the metamorphic evolution. Apart from the absence of any indications pointing to ultrahigh-pressure and low-temperature–high-pressure metamorphism, the results are well in accordance with a common Paleoproterozoic subduction–collision metamorphic evolution along a Barrovian-type intermediate temperature and pressure gradient with a pressure peak at the amphibolite–granulite–eclogite-facies transition and a temperature peak at medium- to high-pressure granulite-facies conditions. In addition, we discuss that all “evidence” for ultrahigh-pressure metamorphism proposed in the literature for rocks of this area is equivocal. Accordingly, the Nordre Strømfjord shear zone is not an example of modern-style plate tectonics in the Paleoproterozoic or of very low thermal gradients and extreme pressure conditions in general.

Geological Hazards of Housing Development of a Pliocene Terrace Land Plot in the City of Rostov-on-Don

Introduction. In Rostov-on-Don the industrial and civil construction is carried out under a number of geological hazards: soils subsiding deformations, landslides, underfloodings, suffusions. Building up the new urban districts has always led to the groundwater surge. The Pliocene terrace building conditions in the eastern part of the city are characterised by the high risk of underflooding due to the shallow groundwater, low hydraulic gradients and water permeability of soils. The data on the present state of the groundwater level is not published in the media. Based on the materials on the territory geological structure and hydrogeological conditions, as well as on the numerical hydrogeological modeling, the present paper aims to investigate the groundwater balance determining factors and to develop the geofiltration monitoring recommendations for constraining the underflooding.Materials and methods. The geological structure and hydrogeological conditions of the territory were analysed using the published reading and graphical materials, as well as the engineering and geological survey results. The aquifers’ geometrical parameters analysis and the spatial data visualisation were made by means of the QGIS geographic information system. For creating and analysing the numerical geofiltration models, the Visual Modflow software product of Aquaveo company was used.Research results. The natural and technogenic geofiltration state of the territory under investigation had been forming for many years. The study of the designed numerical hydrogeological model indicates on the high risk of local underflooding as well as defines the conditions of its spreading throughout the entire territory. The role of the ravine-gully system that drains the aquifer and constrains the underflooding has been assessed. To control the territory groundwater balance and to specify the aquifers’ parameters, the layout of the observational hydrogeological wells network has been developed. Discussion and conclusion. The existing groundwater balance is vulnerable. Building up the territory is highly likely to cause additional infiltration of technogenic water and to lead to underflooding. The territory development project should envisage the geofiltration process monitoring and groundwater draining solutions.

Numerical Investigation of the Effect of Modified Heat Exchanger Block on Thermal Stress and Dislocation Density of DS‐Grown mc‐Si Ingot

AbstractThe present work is based on the numerical investigation of thermal stress and the dislocation density of the directional solidification (DS) grown multi‐crystalline silicon (mc‐Si) ingot. The heat exchanger block (HEB) plays the main role in the growth process, which decides the thermal stress and melt‐crystal interface of the mc‐Si ingot. The conventional furnace is modified to increase the quality of the mc‐Si ingot. The modification on the conventional furnace is done in the insulation block replaced by 1/3rd of the HEB. The HEB enhances the huge amount of heat extraction from the bottom of the crucible. The von Mises stress, dislocation density, and thermal gradient are analyzed. The thermal stress is reduced by the low thermal gradient influenced by the modified HEB. The modified HEB reduces the von Mises stress and dislocation density. The modified furnace system overcomes the conventional case ingot. The result shows that the modified furnace grown mc‐Si ingot improves the efficiency of the solar cell.

Runoff required to drive postimpact gully development on the walls of Meteor Crater (Arizona, USA)

Since the impact ∼50,000 yr ago, surface runoff has entrained and transported sediment from the walls to the floor of Meteor Crater (Arizona, USA). Previous work interpreted this erosion and deposition to be due to predominantly fluvial (i.e., dilute water transport) processes. However, light detection and ranging (LiDAR)−derived topographic data and field observations indicate that debris flows dominated, which were likely generated by runoff that entrained the talus that borders bedrock cliffs high on the crater walls. The low gradient of the crater floor caused debris flows to stop, leaving lobate deposits, while fluvial processes delivered sediment toward the center of the crater. Cosmogenic radionuclide dating of levee deposits suggests that debris-flow activity ceased in the late Pleistocene, synchronous with regional drying. Assuming a rock-to-water ratio of 0.3 at the time of transport by mass flows, it would have taken ∼2 × 106 m3 of water to transport the estimated ∼6.8 × 106 m3 of debris-flow deposits found at the surface of the crater floor. This extensive erosion would require ∼6 m of total runoff over the 0.35 km2 upslope source area of the crater, or ∼18 mm of runoff per debris-flow event. Much more runoff did occur, as evidenced by crater lake deposits, Holocene fluvial activity (which produced little erosion), and contemporary rainfall rates. Rarely on Earth is the total amount of water that creates and runs through a landscape estimated, yet such calculations are commonly done on Mars. Our analysis suggests that erosional and depositional landforms may record only a small fraction of the total runoff.

Perovskite Films Regulation via Hydrogen-Bonded Polymer Network for Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long-term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer with abundant hydrogen bonds and carbonyl groups. The chemical bonding between polymer and perovskite could increase the growth activation energy of perovskite film and promote the preferential growth of high-quality perovskite film. Owing to the low defect density and gradient energy-level alignment, the corresponding device exhibited a champion efficiency of 23.10 %. Furthermore, due to the formation of the hydrogen-bonded polymer network in the perovskite film, the target devices demonstrated excellent air stability and enhanced flexibility for the flexible PSCs. More importantly, the polymer network could coordinate with Pb2+ ions, immobilizing lead atoms to reduce their release into the environment. This strategy paves the way for the industrialization of high-performance flexible PSCs.

Perovskite Films Regulation via Hydrogen‐Bonded Polymer Network for Efficient and Stable Perovskite Solar Cells

AbstractPerovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long‐term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer with abundant hydrogen bonds and carbonyl groups. The chemical bonding between polymer and perovskite could increase the growth activation energy of perovskite film and promote the preferential growth of high‐quality perovskite film. Owing to the low defect density and gradient energy‐level alignment, the corresponding device exhibited a champion efficiency of 23.10 %. Furthermore, due to the formation of the hydrogen‐bonded polymer network in the perovskite film, the target devices demonstrated excellent air stability and enhanced flexibility for the flexible PSCs. More importantly, the polymer network could coordinate with Pb2+ ions, immobilizing lead atoms to reduce their release into the environment. This strategy paves the way for the industrialization of high‐performance flexible PSCs.

Heating rate and ZSM-5 catalyst effects on date palm (Phœnix dactylifera L.) stones pyrolysis: Thermogravimetric analysis, production and characterization of syngases and bio-oils

In the present investigation, Date palm stones (DPS) were pyrolyzed under Nitrogen atmosphere in a laboratory scale fixed-bed reactor. Pyrolysis experiments were carried out at different heating rates (5 and 10 °C/min), both in absence and presence of ZSM-5 catalyst (20 wt%). The effects of heating rate and ZSM-5 catalyst on DPS thermal behavior, pyrolysis products yields, syngases and bio-oils proprieties were investigated. TGA results showed that adding ZSM-5 revealed no significant impact on DPS thermal behavior. However, increasing the heating rate was followed by an increase in degradation peaks temperatures and maximum mass-loss rates (in absolute terms). These same effects were found when proceeding in presence of ZSM-5. Micro-GC results showed that the heating rate rise led to a thermal shift of pyrolytic gases (CO2, CO, C2H6, CH4 and H2) release towards higher temperatures. However, the ZSM-5 addition had accelerated their release and enhanced their quality by essentially reducing CO2 contents by about 13%, for both heating rates. The produced syngases from DPS pyrolysis have proven good biofuels proprieties thanks to their important proportions of CH4 (17.19–21.74%) and H2 (12.54–18.51%). DPS pyrolysis at a heating rate of 5 °C/min and in presence of ZSM-5 (20 wt%) can be defined as the optimum operational conditions that lead to maximum production of bio-oil (43.48%) with better quality. Under these conditions, DPS bio-oil presented the highest Carbon (73.58%) and Hydrogen (10.63%) contents and the lowest Oxygen (14.89%) and Nitrogen (0.9%) contents. Moreover, it had the highest HHV of 34.37 MJ/kg and the lowest viscosity of 8.54 mPa s, comparing to other bio-oils produced at 10 °C/min with and without ZSM-5 and to the bio-oil produced at 5 °C/min without ZSM-5. GC-MS analysis revealed that Dodecanoic acid and Oleic acid were the predominant components in DPS bio-oil with the respective percentages of 17.83 and 16.49%. This experimental investigation proved the potential use of date palm stones as renewable feedstocks for bio-oil production by pyrolysis. Furthermore, the low pyrolysis gradient (5 °C/min) and the use of ZSM-5 catalyst have shown interesting results in enhancing the bio-oil quantity and quality.

Geological control on carbon isotope equilibrium and kinetic fractionation of CH4-CO2-HCO3− in microbial coalbed and shale gas systems

Microbial coalbed gas (CBG) and shale gas (SG), predominately composed of methane (CH4) and carbon dioxide (CO2), are important economic resources and potent greenhouse gases. Although isotopic equilibrium of CH4 and CO2 has been observed in microbial CBG and SG basins, it is difficult to judge under what geological conditions equilibrium is achieved. Moreover, the effects of CO2 dissolution on the isotopic fractionation process need to be considered. We use data from eight microbial CBG and SG basins to discuss the geological conditions in which equilibrium and kinetic isotopic fractionation in CH4-CO2-HCO3− system is achieved. Based on isotopic equilibrium temperatures calculated using computer codes developed in MatLab software, we show that, in deep and closed reservoirs, the CH4-CO2 and CH4-HCO3− are close to carbon isotope equilibrium. In contrast, in shallow and open reservoirs, they are in disequilibrium. The CO2-HCO3− is in disequilibrium in most reservoirs. We propose that both low free energy gradients and long coexisting time of CH4 and CO2/HCO3− are necessary to attain isotopic equilibrium. However, it is difficult to accurately estimate the timescale for attaining isotope equilibrium among them. In general, a closed and deep CBG/SG reservoir is likely to be geologically and geochemically stable over long timescales, favoring isotopic equilibrium of CH4-CO2 and CH4-HCO3−. However, a shallow and open reservoir is unfavourable for their isotopic equilibrium due to shorter timescales for the coexistence of CH4-CO2-HCO3−. Using data from systems close to equilibrium, we estimated the percentage of CO2 in total CH4 and CO2 in CBG reservoirs in various basins to be from 27% to 50%, where methanogenesis is mainly by CO2 reduction. This is significantly higher than the CO2 content (1% to 15%) in gaseous CH4 and CO2 in these basins but is consistent with those (36% to 48%) from culture experiments for coal conversion by methanogenesis. Further study shows that 53–99% of the CO2 formed during CBG generation has dissolved into groundwaters to form dissolved inorganic carbon (DIC) in CBG reservoirs. We propose that CO2 dissolution likely has significantly affect the abundance and isotopic compositions of gaseous CO2 in subsurface.

Determination of the effect of milk fat on the inactivation of Listeria monocytogenes by ohmic heating

Research in recent years has focused on innovative technologies that provide pathogen inactivation without damaging the structural properties of foods. Ohmic heating (OH) is an innovative technology, that provides an effective microbial inactivation with massive and rapid heating. This study aims to determine the effects of milk fat on the inactivation of Listeria monocytogenes by OH with a low voltage gradient. L. monocytogenes (ATCC 13932) inoculated 3.1%, 1.5%, and 0.1% fat-milk samples were heated up to 62°C by OH and conventional heating (CH) process. OH treatment lead to the inactivation of L. monocytogenes in both 1.5% and 0.1% groups and led to approximately 5.30 log decrease, however, there was a 3.10 log decrease in the 3.1% group at 6 min. CH lead to a few reduction as 0.21, 0.29 and 0.39 log in 3.1%, 1.5% and 0.1% fat-milk respectively. In OH, the sublethal injury ratio was higher than CH in all milk groups. However, OH did not statistically change color and pH values at the 6th min of the process, had a significant effect on hydroxymethylfurfural value only in 3.1% fat-milk. In conclusion, the increased fat content may have important inhibitory effects on pathogen inactivation in OH. Thus, the OH conditions should be chosen carefully to sufficient inactivation of pathogens in milk with high-fat content.

Rough Surface Effect on CO2 Displacement at the Nanoscale

CO2 injection has great potential for enhancing shale oil recovery. Understanding the CO2 displacement in nanometer pores of shale is critical for developing effective CO2 injection techniques. In this work, we applied direct numerical simulation to study the effect of the rough surface on CO2 displacement in nanometer pores of shale. By quantifying CO2 displacement in rough nanochannels, we aimed to understand how surface roughness and morphology affect displacement progress. We found that the rough surface results in shrinkage of the CO2 displacement path, slowing overall displacement rate. Additionally, the pinch-point effect in a rough nanochannel impedes the smooth progression of the interface contact line, causing periodic velocity fluctuation that further hinders CO2 displacement. We also simulated the CO2 displacement in rough nanoporous media, finding that the rough surface leads to a substantial decrease in CO2 displacement efficiency, especially under low pressure gradient conditions. Our simulation results indicate that the rough surface of a shale nanometer pore has a nonnegligible effect on CO2 displacement.

Thermal evolution and hydrocarbon generation history of the Weibei uplift in the Ordos Basin

The Weibei uplift in the Ordos Basin has a distinctive tectonic setting and intricate evolutionary history. Along these lines, we have used the stratum temperature, apatite fission track, and vitrinite reflectance data to restore the thermal and hydrocarbon generation histories of the Weibei uplift. The average value of the present geothermal gradient of the Weibei uplift was 27.9°C/km, and the heat flow was 64.9 mW/m2. The Weibei uplift exhibited a moderate geothermal field. Three uplift cooling events occurred in the Weibei uplift during the Mesozoic era: the late Jurassic-early Cretaceous (162–125 Ma), the late Cretaceous (105–65 Ma), and the Eocene-Oligocene (40–27 Ma). The uplift history indicates an early uplift in the south region and a late uplift in the later stage. The thermal evolution history simulation demonstrates that the lower Palaeozoic Ordovician source rocks began to enter the hydrocarbon generation threshold in the middle Permian-late Permian (270 Ma) era and joined the hydrocarbon generation peak in the early-middle Jurassic event (180 Ma). The upper Palaeozoic Carboniferous-Permian source rocks began to enter the hydrocarbon generation threshold in the later period of the middle Permian period (235 Ma). They joined the hydrocarbon generation peak in the late Jurassic-early Cretaceous period (150 Ma). In addition, Triassic source rocks entered the hydrocarbon generation threshold in the early Cretaceous era (135 Ma) and did not enter the hydrocarbon generation peak until now. The low geothermal gradient of the Weibei uplift in the Palaeozoic-early Mesozoic reached the maximum paleotemperature in the early Mesozoic era (100 Ma) because of tectonic thermal events. The highest geothermal gradient of the early Cretaceous reached 51.5°C/km. The peak period of the hydrocarbon generation of source rocks of the different horizons in the Weibei uplift was regulated by the geothermal field of the early Cretaceous event. Since the late Cretaceous period, the stratum has been uplifted and cooled rapidly, and the hydrocarbon generation process of the source rocks has ceased.

The diagnostic accuracy of aortic valve calcium score in patients with low gradient and high gradient aortic stenosis

Abstract Funding Acknowledgements Type of funding sources: None. Introduction The gold standard imaging modality for diagnosing aortic stenosis (AS) is echocardiography (echo); the definition of severe AS is based on the transvalvular mean gradient (AMG) (>40 mmHg) and aortic valve area (AVA) (<1 cm2). However, in around one quarter of the cases echo provides discordant findings (AVA<1 cm2, despite of an AMG <40 mmHg), complicating clinical decision making. Computed tomography aortic valve calcium scoring (CT-AVC) offers an alternative diagnostic method. In cases with discordant echo measurements current guidelines recommend CT-AVC to decide on severity. Purpose Our aim was to validate the sensitivity of the recommended calcium score (CAS) thresholds within our patient population, as well as to identify any factors associated with below cut-off CAS values despite confirmed severe AS (CAS false negativity). Methods Our retrospective study included 332 consecutive patients with severe AS (AVA ≤1 cm2), who underwent CT angiography (CTA) for transcatheter aortic valve implantation (TAVI) planning. Based on the AMG the patients were classified into high gradient (HG: AMG ≥ 40 mmHg) and low gradient (LG: AMG <40 mmHg) groups. In the LG group AS severity was assessed by a multiparametric algorithm. To specify the predictors of CAS false negativity among patients with HG-AS, logistic regression analysis was used. The patients were followed for 50 months. Cox proportional hazard model was used to assess the risk of death from any cause. Results The HG-AS group consisted of 244 and the LG-AS cohort of 88 patients. In the HG-AS population the sensitivity of CAS to diagnose severe AS was 89%. Within the HG severe AS group, logistic regression analysis revealed an association between CAS false negativity and the AMG (OR 0.89, CI 0.83 – 0.95, p <0,001), whereas none of the other tested factors (age, sex, hypertension, diabetes, left ventricle function, renal function) showed a predictive value. In the LG-AS group, contrary to the HG-AS patients, the sensitivity of CAS to define severe LG AS was limited (53% in males and 67% in females). Over a median follow-up of 50 months, the prognosis of HG AS patients with low CAS (false negative group) was more favourable than that of the high CAS patient population (HR 0.41; CI 017 – 097; p = 0.04). Conclusions Our results confirmed that among patients with HG AS, the recommended CAS thresholds provide a good diagnostic sensitivity for severe AS. Nonetheless, the number of severe AS patients with low CAS is not negligible, especially within the LG-AS population, where the diagnosis is the most challenging. Our findings underline that in patients with discordant echocardiographic findings, a personalized, multiparametric diagnostic approach is needed, instead basing the final diagnosis exclusively on CAS.

Implications of methods for calculating the left ventricular outflow tract area in aortic stenosis severity grading

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): - Spanish Ministry of Economy and Competitiveness through the Carlos III Institute of Health-Fondo de Investigación Sanitaria. - Post-residency research contract. Medical Research Institute Hospital La Fe (IIS La Fe), Valencia, Spain. Introduction Aortic valve area (AVA) calculation by continuity equation is a fundamental aspect to estimate aortic stenosis (AS) severity. The estimation of the left ventricular outflow tract (LVOT) area is a source of technical variability in the calculation of AVA that can lead to errors in severity grading. Formulas for calculating LVOT diameter (LVOTd) based on body surface area (BSA) and patient height have been proposed, but their impact on reclassifying patients based on severity has not been described. Purpose To evaluate the differences in AS grading according to the LVOT area used in the calculation of the AVA. Methods We retrospectively analyzed (2019–2022) 1722 echocardiograms with a diagnosis of AS and with the following variables reported: AVA calculated using the continuity equation, height and weight of the patient. Predicted LVOTd by BSA was calculated by the formula: (5.7*BSA + 12). Predicted LVOTd by height was calculated as: (5.78 * height + 12.1). Results LVOT area and AVA from predicted LVOTd based on BSA and height showed slightly higher values. The AVA based on the LVOTd predicted by BSA was associated with a lower prevalence of severe AS, as well as a lower prevalence of discordant cases (mean gradient <40 mmHg and AVA <1 cm2) (Table). The AVA based on both methods of predicted LVOTd led to a reclassification from severe (by the standard method) to non-severe in a significant percentage of patients (13.6% for the BSA-predicted method, and 8.7% for the height-predicted method). For the AVA predicted by BSA, the "downgrade" of AS severity was more frequent (23.3%) in patients in the quartile with the highest BMI (>30 kg/m2), while the degree of obesity did not affect the method predicted by height. Conclusion Despite suppressing the potential errors derived from the LVOTd measurement, the AVA based on predicted LVOTd methods using BSA or height lead to a significant percentage of reclassification in terms of severity and prevalence of discordant severe AS due to low gradient. In obese patients, the method predicted by BSA is highly discordant and the method predicted by the patient's height is preferable.