Hybrid modeling for carbon monoxide gas-phase catalytic coupling to synthesize dimethyl oxalate process

Ethylene glycol(EG)plays a pivotal role as a primary raw material in the polyester industry,and the syngas-to-EG route has become a significant technical route in production.The carbon monoxide(CO)gas-phase catalytic coupling to synthesize dimethyl oxalate(DMO)is a crucial process in the syngas-to-EG route,whereby the composition of the reactor outlet exerts influence on the ultimate quality of the EG product and the energy consumption during the subsequent separation process.However,measuring product quality in real time or establishing accurate dynamic mechanism models is challenging.To effectively model the DMO synthesis process,this study proposes a hybrid modeling strategy that integrates process mechanisms and data-driven approaches.The CO gas-phase catalytic coupling mechanism model is developed based on intrinsic kinetics and material balance,while a long short-term memory(LSTM)neural network is employed to predict the macroscopic reaction rate by leveraging temporal relationships derived from archived measurements.The proposed model is trained semi-supervised to accommodate limited-label data scenarios,leveraging historical data.By integrating these predictions with the mechanism model,the hybrid modeling approach provides reliable and interpretable forecasts of mass fractions.Empirical investigations unequivocally validate the superiority of the proposed hybrid modeling approach over conventional data-driven models(DDMs)and other hybrid modeling techniques.

Integrating remote sensing and 3-PG model to simulate the biomass and carbon stock of Larix olgensis plantation

Accurate estimations of biomass and its temporal dynamics are crucial for monitoring the carbon cycle in forest ecosystems and assessing forest carbon sequestration potentials.Recent studies have shown that integrating process-based models(PBMs)with remote sensing data can enhance simulations from stand to regional scales,significantly improving the ability to simulate forest growth and carbon stock dynamics.However,the utilization of PBMs for large-scale simulation of larch carbon storage distribution is still limited.In this study,we applied the parameterized 3-PG(Physiological Principles Predicting Growth)model across the Mengjiagang Forest Farm(MFF)to make broad-scale predictions of the biomass and carbon stocks of Larix olgensis plantation.The model was used to simulate average diameter at breast height(DBH)and total biomass,which were later validated with a wide range of observation data including sample plot data,forest management inventory data,and airborne laser scanning data.The results showed that the 3-PG model had relatively high accuracy for predicting both DBH and total biomass at stand and regional scale,with determination coefficients ranging from 0.78 to 0.88.Based on the estimation of total biomass,we successfully produced a carbon stock map of the Larix olgensis plantation in MFF with a spatial resolution of 20 m,which helps with relevant management advice.These findings indicate that the integration of 3-PG model and remote sensing data can well predict the biomass and carbon stock at regional and even larger scales.In addition,this integration facilitates the evaluation of forest carbon sequestration capacity and the development of forest management plans.

Recent Advances in Mechanistic Understanding of Metal-Free Carbon Thermocatalysis and Electrocatalysis with Model Molecules

Metal-free carbon,as the most representative heterogeneous metal-free catalysts,have received considerable interests in electro-and thermo-catalytic reac-tions due to their impressive performance and sustainability.Over the past decade,well-designed carbon catalysts with tunable structures and heteroatom groups coupled with various characterization techniques have proposed numerous reaction mechanisms.However,active sites,key intermediate species,precise structure-activity relationships and dynamic evolution processes of carbon catalysts are still rife with controversies due to the monotony and limitation of used experimental methods.In this Review,we sum-marize the extensive efforts on model catalysts since the 2000s,particularly in the past decade,to overcome the influences of material and structure limitations in metal-free carbon catalysis.Using both nanomolecule model and bulk model,the real contribution of each alien species,defect and edge configuration to a series of fundamentally important reactions,such as thermocatalytic reactions,electrocatalytic reactions,were systematically studied.Combined with in situ techniques,isotope labeling and size control,the detailed reaction mechanisms,the precise 2D structure-activity relationships and the rate-determining steps were revealed at a molecular level.Furthermore,the outlook of model carbon catalysis has also been proposed in this work.

Predicting carbon storage of mixed broadleaf forests based on the finite mixture model incorporating stand factors,site quality,and aridity index

The diameter distribution function(DDF)is a crucial tool for accurately predicting stand carbon storage(CS).The current key issue,however,is how to construct a high-precision DDF based on stand factors,site quality,and aridity index to predict stand CS in multi-species mixed forests with complex structures.This study used data from70 survey plots for mixed broadleaf Populus davidiana and Betula platyphylla forests in the Mulan Rangeland State Forest,Hebei Province,China,to construct the DDF based on maximum likelihood estimation and finite mixture model(FMM).Ordinary least squares(OLS),linear seemingly unrelated regression(LSUR),and back propagation neural network(BPNN)were used to investigate the influences of stand factors,site quality,and aridity index on the shape and scale parameters of DDF and predicted stand CS of mixed broadleaf forests.The results showed that FMM accurately described the stand-level diameter distribution of the mixed P.davidiana and B.platyphylla forests;whereas the Weibull function constructed by MLE was more accurate in describing species-level diameter distribution.The combined variable of quadratic mean diameter(Dq),stand basal area(BA),and site quality improved the accuracy of the shape parameter models of FMM;the combined variable of Dq,BA,and De Martonne aridity index improved the accuracy of the scale parameter models.Compared to OLS and LSUR,the BPNN had higher accuracy in the re-parameterization process of FMM.OLS,LSUR,and BPNN overestimated the CS of P.davidiana but underestimated the CS of B.platyphylla in the large diameter classes(DBH≥18 cm).BPNN accurately estimated stand-and species-level CS,but it was more suitable for estimating stand-level CS compared to species-level CS,thereby providing a scientific basis for the optimization of stand structure and assessment of carbon sequestration capacity in mixed broadleaf forests.

Simulation study of supercritical carbon dioxide jet fracturing for carbonate geothermal reservoir based on fluid-thermo-mechanical coupling model

Geothermal energy is a kind of renewable,sustainable and clean energy resource.Geothermal energy is abundant in carbonate reservoirs.However,low matrix permeability limits its exploitation.The super-critical carbon dioxide(SC-CO_(2))jet fracturing is expected to efficiently stimulate the carbonate geothermal reservoirs and achieve the storage of CO_(2) simultaneously.In this paper,we established a transient seepage and fluid-thermo-mechanical coupled model to analyze the impact performance of sc-CO_(2) jet fracturing.The mesh-based parallel code coupling interface was employed to couple the fluid and solid domains by exchanging the data through the mesh interface.The physical properties change of sC-CO_(2) with temperature were considered in the numerical model.Results showed that SC-CO_(2) jet frac-turing is superior to water-jet fracturing with respect to jetting velocity,particle trajectory and pene-trability.Besides,stress distribution on the carbonate rock showed that the tensile and shear failure would more easily occur by SC-CO_(2) jet than that by water jet.Moreover,pressure and temperature control the jet field and seepage field of sC-CO_(2) simultaneously.Increasing the jet temperature can effectively enhance the impingement effect and seepage process by decreasing the viscosity and density of SC-CO_(2).The key findings are expected to provide a theoretical basis and design reference for applying SC-CO_(2) jet fracturing in carbonate geothermal reservoirs.

Model investigation of the low-carbon MgO-treated soil foundation based on CO_(2) overall carbonation

The overall carbonation of MgO-admixed soil provides not only an efficient and environmentally friendly technique for improving soft ground but also a permanently safe solution for CO_(2) sequestration.To evaluate the carbon sequestration potential and promote the carbonation application in soil improvement,a laboratory-scale model investigation is designed under pressurized carbonation considering the influences of MgO dosage and CO_(2) ventilation mode(way).The temperature,dynamic resilience modulus,and dynamic cone penetration(DCP)were tested to assess the carbonation treatment effect.The physical,strength,and microscopic tests were also undertaken to reveal the evolution mechanisms of CO_(2) migration in the MgO-carbonated foundation.The results indicate that the temperature peaks of MgO-treated foundation emerge at w20 h during hydration,but occur at a distance of 0e25 cm from the gas source within 6 h during carbonation.The dynamic resilience moduli of the model foundation increase by more than two times after carbonation and the DCP indices reduce dramatically.As the distance from the gas inlet increases,the bearing capacity,strength,and carbon sequestration decrease,whereas the moisture content increases.Compared to the end ventilation,the middle ventilation produces a higher carbonation degree and a wider carbonation area.The cementation and filling of nesquehonite and dypingite/hydromagnesite are verified to be critical factors for carbonation evolution and enhancing mechanical performances.Finally,the overall carbonation model is described schematically in three stages of CO_(2) migration.The outcomes would help to facilitate the practical application of CO_(2) sequestration in soil treatment.

Lateral downslope transport and tentative sedimentary organic carbon box model in the southern Yap Trench,western Pacific Ocean

Sediment collapse and subsequent lateral downslope migration play important roles in shaping the habitats and regulating sedimentary organic carbon(SOC)cycling in hadal trenches.In this study,three sediment cores were collected using a human-occupied vehicle across the axis of the southern Yap Trench(SYT).The total organic carbon(TOC)and total nitrogen(TN)contents,δ13C,radiocarbon ages,specific surface areas,and grain size compositions of sediments from three cores were measured.We explored the influence of the lateral downslope transport on the dispersal of the sediments and established a tentative box model for the SOC balance.In the SYT,the surface TOC content decreased with water depth and was decoupled by the funneling effect of the V-shaped hadal trench.However,the sedimentation(0.0025 cm/a)and SOC accumulation rates(∼0.038 g/(m^(2)·a)(in terms of OC))were approximately 50%higher in the deeper hadal region than in the abyssal region(0.0016 cm/a and∼0.026 g/(m^(2)·a)(in terms of OC),respectively),indicating the occurrence of lateral downslope transport.The fluctuating variations in the prokaryotic abundances and the SOC accumulation rate suggest the periodic input of surficial sediments from the shallow region.The similar average TOC(0.31%–0.38%),TN(0.06%–0.07%)contents,and SOC compositions(terrestrial OC(11%–18%),marine phytoplanktonic OC(45%–53%),and microbial OC(32%–44%))of the three sites indicate that the lateral downslope transport has a significant mixing effect on the SOC composition.The output fluxes of the laterally transported SOC(0.44–0.56 g/(m^(2)·a)(in terms of OC))contributed approximately(47%–73%)of the total SOC input,and this proportion increased with water depth.The results of this study demonstrate the importance of lateral downslope transport in the spatial distribution and development of biomes.

Effect of Ultra-low Temperature on Carbonation Performance of SFRRC and Prediction Model

Through the rapid carbonation test of SFRRC with different fiber volume fractions at ultralow temperature,the influence of ultra-low temperature damage on the carbonation resistance of SFRRC was analyzed,which provides a theoretical basis for the application of SFRRC in ultra-low temperature engineering.The experimental results show that ultra-low temperatures can significantly weaken the carbonization resistance of SFRRC.When the temperature reaches 160℃,the carbonization depth increases by 67.66%compared with the normal state.The proper amount of steel fiber has an evident influence on the carbonation resistance of the material.However,when the addition amount exceeds the optimum content,the carbonation resistance of the material decreases.The grey prediction model established by constructing the original sequence can reasonably predict the carbonation resistance of SFRRC after ultra-low temperatures.

A study on the simulation of carbon and water fluxes of Dangxiong alpine meadow and its response to climate change

The alpine meadow ecosystem accounts for 27%of the total area of the Tibetan Plateau and is also one of the most important vegetation types.The Dangxiong alpine meadow ecosystem,located in the south-central part of the Tibetan Plateau,is a typical example.To understand the carbon and water fluxes,water use efficiency(WUE),and their responses to future climate change for the alpine meadow ecosystem in the Dangxiong area,two parameter estimation methods,the Model-independent Parameter Estimation(PEST)and the Dynamic Dimensions Search(DDS),were used to optimize the Biome-BGC model.Then,the gross primary productivity(GPP)and evapotranspiration(ET)were simulated.The results show that the DDS parameter calibration method has a better performance.The annual GPP and ET show an increasing trend,while the WUE shows a decreasing trend.Meanwhile,ET and GPP reach their peaks in July and August,respectively,and WUE shows a“dual-peak”pattern,reaching peaks in May and November.Furthermore,according to the simulation results for the next nearly 100 years,the ensemble average GPP and ET exhibit a significant increasing trend,and the growth rate under the SSP5–8.5 scenario is greater than that under the SSP2–4.5 scenario.WUE shows an increasing trend under the SSP2–4.5 scenario and a significant increasing trend under the SSP5–8.5 scenario.This study has important scientific significance for carbon and water cycle prediction and vegetation ecological protection on the Tibetan Plateau.

Modelling the impacts of cover crop management strategies on the water use,carbon exchange and yield of olive orchards

Cover crops have long been proposed as an alternative soil management for minimizing erosion rates in olive stands while providing additional ecosystem services.However,the trade-off between these benefits and the competition for water with the trees makes the definition of optimal management practices a challenging task in semiarid climates.This work presents an improved version of OliveCan,a process-based simulation model of olive orchards that now can simulate the main impacts of cover crops on the water and carbon balances of olive orchards.Albeit simple in its formulation,the new model components were developed to deal with different cover crop management strategies.Examples are presented for simulation runs of a traditional olive orchard in the conditions of southern Spain,evaluating the effects of different widths for the strip occupied by the cover crop(Fcc)and two contrasting mowing dates.Results revealed that high Fccresulted in lower olive yields,but only when mowing was applied at the end of spring.In this regard,late mowing and high Fccwas associated with lower soil water content from spring to summer,coinciding with olive flowering and the earlier stages of fruit growth.Fccwas also negatively correlated with surface runoff irrespective of the mowing date.On the other hand,net ecosystem productivity(NEP)was substantially affected by both Fccand mowing date.Further simulations under future climate scenarios comparing the same management alternatives are also presented,showing substantial yield reductions by the end of the century and minor or negligible changes in NEP and seasonal runoff.

Mangrove wetlands distribution status identification, changing trend analyzation and carbon storage assessment of China

This research investigates the ecological importance,changes,and status of mangrove wetlands along China’s coastline.Visual interpretation,geological surveys,and ISO clustering unsupervised classification methods are employed to interpret mangrove distribution from remote sensing images from 2021,utilizing ArcGIS software platform.Furthermore,the carbon storage capacity of mangrove wetlands is quantified using the carbon storage module of InVEST model.Results show that the mangrove wetlands in China covered an area of 278.85 km2 in 2021,predominantly distributed in Hainan,Guangxi,Guangdong,Fujian,Zhejiang,Taiwan,Hong Kong,and Macao.The total carbon storage is assessed at 2.11×10^(6) t,with specific regional data provided.Trends since the 1950s reveal periods of increase,decrease,sharp decrease,and slight-steady increases in mangrove areas in China.An important finding is the predominant replacement of natural coastlines adjacent to mangrove wetlands by artificial ones,highlighting the need for creating suitable spaces for mangrove restoration.This study is poised to guide future mangroverelated investigations and conservation strategies.

Fixed-Bed Column Adsorption Modeling of MnO4- Ions from Acidic Aqueous Solutions on Activated Carbons Prepared with the Biomass

Activated carbons calcined at 400˚C and 600˚C (AC-400 and AC-600), prepared using palm nuts, collected in the town of Franceville in Gabon, were used to study the dynamic adsorption of MnO4- ions in acidic media on fixed bed column and on the kinetic modeling of experimental data of breakthrough curves of MnO4- ions obtained. Results on the adsorption of MnO4- ions in fixed-bed dynamics obtained on AC-400 and AC-600 adsorbents beds indicated that the AC-400 bed appears to be the most efficient in removing MnO4- ions in acidic media. Indeed, the adsorbed amounts, the adsorbed capacities at saturation and the elimination percentage of MnO4- ions obtained with AC-400 (31.24 mg;52.06 mg·g-1 and 41.65% respectively) were higher compared to those obtained with AC-600 (9.87 mg;16.45 mg·g-1 and 17.79% respectively). The breakthrough curves kinetic modeling revealed that the Thomas model and the pseudo-first-order kinetic model were the most suitable models to describe the adsorption of MnO4- ions on adsorbents studied in our experimental conditions. The results of the intraparticle diffusion model showed that intraparticle diffusion was involved in the adsorption mechanism of MnO4- ions on investigated adsorbents and was not the limiting step and the only process controlling MnO4- ions adsorption. In contrast to AC-400, the intraparticle diffusion on AC-600 bed plays an important role in the adsorption mechanism of MnO4- ions.

The AVO Effect of Formation Pressure on Time-Lapse Seismic Monitoring in Marine Carbon Dioxide Storage

The phase change of CO_(2) has a significant bearing on the siting, injection, and monitoring of storage. The phase state of CO_(2) is closely related to pressure. In the process of seismic exploration, the information of formation pressure can be response in the seismic data. Therefore, it is possible to monitor the formation pressure using time-lapse seismic method. Apart from formation pressure, the information of porosity and CO_(2) saturation can be reflected in the seismic data. Here, based on the actual situation of the work area, a rockphysical model is proposed to address the feasibility of time-lapse seismic monitoring during CO_(2) storage in the anisotropic formation. The model takes into account the formation pressure, variety minerals composition, fracture, fluid inhomogeneous distribution, and anisotropy caused by horizontal layering of rock layers(or oriented alignment of minerals). From the proposed rockphysical model and the well-logging, cores and geological data at the target layer, the variation of P-wave and S-wave velocity with formation pressure after CO_(2) injection is calculated. And so are the effects of porosity and CO_(2) saturation. Finally, from anisotropic exact reflection coefficient equation, the reflection coefficients under different formation pressures are calculated. It is proved that the reflection coefficient varies with pressure. Compared with CO_(2) saturation, the pressure has a greater effect on the reflection coefficient. Through the convolution model, the seismic record is calculated. The seismic record shows the difference with different formation pressure. At present, in the marine CO_(2) sequestration monitoring domain, there is no study involving the effect of formation pressure changes on seismic records in seafloor anisotropic formation. This study can provide a basis for the inversion of reservoir parameters in anisotropic seafloor CO_(2) reservoirs.

Carbon stock estimation in halophytic wooded savannas of Uruguay:An ecosystem approach

Savannas constitute a mixture of trees and shrub patches with a more continuous herbaceous understory.The contribution of this biome to the soil organic carbon(SOC)and above-ground biomass(AGB)carbon(C)stock globally is significant.However,they are frequently subjected to land use changes,promoting increases in CO_(2) emissions.In Uruguay,subtropical wooded savannas cover around 100,000 ha,of which approximately 28%is circumscribed to sodic soils(i.e.,subtropical halophytic wooded savannas).Nevertheless,there is little background about the contribution of each ecosystem component to the C stock as well as site-specific allometric equations.The study was conducted in 5 ha of subtropical halophytic wooded savannas of the national protected area Esteros y Algarrobales del Rio Uruguay.This work aimed to estimate the contribution of the main ecosystem components(e.g.,soil,trees,shrubs,and herbaceous plants)to the C stock.Site-specific allometric equations for the most frequent tree species and shrub genus were fitted based on basal diameter(BD)and total height(H).The fitted equations accounted for between 77%and 98%of the aerial biomass variance of Netuma affinis and Vachellia caven.For shrubs(Baccharis sp.),the adjusted equation accounted for 86%of total aerial biomass.C stock for the entire system was 116.71±11.07 Mg·ha^(-1),of which 90.7%was allocated in the soil,8.3%in the trees,0.8%in the herbaceous plants,and 0.2%in the shrubs.These results highlight the importance of subtropical halophytic wooded savannas as C sinks and their relevance in the mitigation of global warming under a climate change scenario.

Stochastic seismic inversion and Bayesian facies classification applied to porosity modeling and igneous rock identification

We apply stochastic seismic inversion and Bayesian facies classification for porosity modeling and igneous rock identification in the presalt interval of the Santos Basin. This integration of seismic and well-derived information enhances reservoir characterization. Stochastic inversion and Bayesian classification are powerful tools because they permit addressing the uncertainties in the model. We used the ES-MDA algorithm to achieve the realizations equivalent to the percentiles P10, P50, and P90 of acoustic impedance, a novel method for acoustic inversion in presalt. The facies were divided into five: reservoir 1,reservoir 2, tight carbonates, clayey rocks, and igneous rocks. To deal with the overlaps in acoustic impedance values of facies, we included geological information using a priori probability, indicating that structural highs are reservoir-dominated. To illustrate our approach, we conducted porosity modeling using facies-related rock-physics models for rock-physics inversion in an area with a well drilled in a coquina bank and evaluated the thickness and extension of an igneous intrusion near the carbonate-salt interface. The modeled porosity and the classified seismic facies are in good agreement with the ones observed in the wells. Notably, the coquinas bank presents an improvement in the porosity towards the top. The a priori probability model was crucial for limiting the clayey rocks to the structural lows. In Well B, the hit rate of the igneous rock in the three scenarios is higher than 60%, showing an excellent thickness-prediction capability.

The potential for an old-growth forest to store carbon in the topsoil:A case study at Sasso Fratino,Italy

There is considerable interest devoted to oldgrowth forests and their capacity to store carbon(C)in biomass and soil.Inventories of C stocks in old-growth forests are carried out worldwide,although there is a lack of information on their actual potential for C sequestration.To further understand this,soil organic carbon(SOC)was measured in one of Italy's best-preserved old-growth forests,the Sasso Fratino Integral Nature Reserve.This reserve is on the World Heritage List along with other ancient beech forests of Europe,and it is virtually untouched due to the steepness of the terrain,even before legal constraints were imposed.Although the sandstone-derived soils are often shallow,they are rich in organic matter.However,no quantification had been carried out.By systematically sampling the topsoil across the forest,we accurately determined the average amount of SOC(62.0±16.9 Mg ha^(–1))and nitrogen(4.0±1.2 Mg ha^(–1))in the top 20 cm.Using the CENTURY model,future dynamics of SOC stocks were predicted to 2050 according to two climate scenarios,A1F1 and B2,the first of high concern and the second more optimistic.The model projected an increase of 0.2 and 0.3 Mg ha^(–1)a^(–1)by 2030 under the A1F1 and B2 scenarios,respectively,suggesting that the topsoil in old-growth forests does not reach equilibrium but continues accumulating SOC.However,from 2030 to 2050,a decline in SOC accumulation is predicted,indicating SOC net loss at high altitudes under the worst-case scenario.This study confirms that soils in oldgrowth forests play a significant role in carbon sequestration.It also suggests that climate change may affect the potential of these forests to store SOC not only in the long term but also in the coming years.

Acid-rock reaction kinetics in a two-scale model based on reaction order correction

The reaction order plays a crucial role in evaluating the response rate of acid-rock.However,the conventional two-scale model typically assumes that the reaction order is constant as one,which can lead to significant deviations from reality.To address this issue,this study proposes a novel multi-order dynamic model for acid-rock reaction by combining rotating disk experimental data with theoretical derivation.Through numerical simulations,this model allows for the investigation of the impact of acidification conditions on different orders of reaction,thereby providing valuable insights for on-site construction.The analysis reveals that higher response orders require higher optimal acid liquid flow rates,and lower optimal H+diffusion coefficients,and demonstrate no significant correlation with acid concentration.Consequently,it is recommended to increase the displacement and use high-viscosity acid for reservoirs with high calcite content,while reducing the displacement and using low-viscosity acid for reservoirs with high dolomite content.

Emission-side drivers affecting carbon neutrality based on vegetation carbon sequestration:Evidence from China

To address climate change,the world needs deep decarbonization to achieve carbon neutrality(CN),which implies net-zero human-caused CO_(2) emissions in the atmosphere.This study used emission-side drivers,including socioeconomic and net primary productivity(NPP)-based factors,to determine the changes in CN based on vegetation carbon sequestration in the case of China during 2001-2015.Spatial exploratory analysis as well as the combined use of production-theoretical decomposition analysis(PDA)and an econometric model were also utilized.We showed that CN was significantly spatially correlated over the study period;Yunnan,Heilongjiang,and Jilin presented positive spatial autocorrelations,whereas Guizhou showed a negative spatial autocorrelation.More than half of CN declined over the period during which potential energy intensity(PEIE)and energy usage technological change were the largest negative and positive drivers for increasing CN.PEIE played a significantly negative role in increasing CN.We advise policymakers to focus more on emission-side drivers(e.g.,energy intensity)in addition to strengthening NPP management to achieve CN.

Effects of landscape fragmentation of plantation forests on carbon storage in the Loess Plateau,China

Tree plantation and forest restoration are the major strategies for enhancing terrestrial carbon sequestration and mitigating climate change.The Grain for Green Project in China has positively impacted global carbon sequestration and the trend towards fragmentation of plantation forests.Limited studies have been conducted on changes in plantation biomass and stand structure caused by fragmentation,and the effect of fragmentation on the carbon storage of plantation forests remains unclear.This study evaluated the differences between carbon storage and stand structure in black locust forests in fragmented and continuous landscape in the Ansai District,China and discussed the effects of ecological significance of four landscape indices on carbon storage and tree density.We used structural equation modelling to explore the direct and indirect effects of fragmentation,edge,abiotic factors,and stand structure on above-ground carbon storage.Diameter at breast height(DBH)in fragmented forests was 53.3%thicker,tree density was 40.9%lower,and carbon storage was 49.8%higher than those in continuous forests;for all given DBH>10 cm,the trees in fragmented forests were shorter than those in continuous forests.The patch area had a negative impact on carbon storage,i.e.,the higher the degree of fragmentation,the lower the density of the tree;and fragmentation and distance to edge(DTE)directly increased canopy coverage.However,canopy coverage directly decreased carbon storage,and fragmentation directly increased carbon storage and tree density.In non-commercial forests,fragmentation reduces the carbon storage potential of plantation,and the influence of patch area,edge,and patchy connection on plantation should be considered when follow-up trees are planted and for the plantation management.Thus,expanding the area of plantation patches,repairing the edges of complex-shaped patches,enhancing the connectivity of similar patches,and applying nutrients to plantation forests at regular intervals are recommended in fragmented areas of the Loess Plateau.

Path-Dependent Progressive Failure Analysis for 3D-Printed Continuous Carbon Fibre Reinforced Composites

In order to predict the damage behaviours of 3D-printed continuous carbon fibre(CCF)reinforced composites,when additional short carbon fibre(SCF)composite components are employed for continuous printing or special functionality,a novel path-dependent progressive failure(PDPF)numerical approach is developed.First,a progressive failure model using Hashin failure criteria with continuum damage mechanics to account for the damage initiation and evaluation of 3D-printed CCF reinforced polyamide(PA)composites is developed,based on actual fibre placement trajectories with physical measurements of 3D-printed CCF/PA constituents.Meanwhile,an elastic-plastic model is employed to predict the plastic damage behaviours of SCF/PA parts.Then,the accuracy of the PDPF model was validated so as to study 3D-printed CCF/PA composites with either negative Poisson's ratio or high stiffness.The results demonstrate that the proposed PDPF model can achieve higher prediction accuracies in mechanical properties of these 3D-printed CCF/PA composites.Mechanism analyses show that the stress distribution is generally aggregated in the CCF areas along the fibre placement paths,and the shear damage and matrix tensile/compressive damage are the key damage modes.This study provides a new approach with valuable information for characterising complex 3D-printed continuous fibre-matrix composites with variable mechanical properties and multiple constituents.