The classical phase field model has wide applications for brittle materials,but nonlinearity and inelasticity are found in its stress-strain curve.The degradation function in the classical phase field model makes it a...The classical phase field model has wide applications for brittle materials,but nonlinearity and inelasticity are found in its stress-strain curve.The degradation function in the classical phase field model makes it a linear formulation of phase field and computationally attractive,but stiffness reduction happens even at low strain.In this paper,generalized polynomial degradation functions are investigated to solve this problem.The first derivative of degradation function at zero phase is added as an extra constraint,which renders higher-order polynomial degradation function and nonlinear formulation of phase field.Compared with other degradation functions(like algebraic fraction function,exponential function,and trigonometric function),this polynomial degradation function enables phase in[0,1](should still avoid the first derivative of degradation function at zero phase to be 0),so there is noconvergence problem.The good and meaningful finding is that,under the same fracture strength,the proposed phase field model has a larger length scale,which means larger element size and better computational efficiency.This proposed phase field model is implemented in LS-DYNA user-defined element and user-defined material and solved by the Newton-Raphson method.A tensile test shows that the first derivative of degradation function at zero phase does impact stress-strain curve.Mode I,mode II,and mixed-mode examples show the feasibility of the proposed phase field model in simulating brittle fracture.展开更多
Background The invasiveness of Spartina alterniflora Loisel.into the estuarine coastal wetlands has impacted the stability of soil organic carbon,as well as the functional genes of soil microorganisms.However,the mech...Background The invasiveness of Spartina alterniflora Loisel.into the estuarine coastal wetlands has impacted the stability of soil organic carbon,as well as the functional genes of soil microorganisms.However,the mechanisms by which S.alterniflora invasion affects soil organic carbon,especially at the micro-level,is still unclear.Therefore,this study compared the differences in soil carbon cycling(C-cycling)functional genes between invaded and native areas during the cold season,as well as the changes in microbial communities involved in differential functional genes'expression.Results Our results showed that in salt marsh wetlands dominated by Suaeda salsa(L.)Pall.,invasion by S.alterniflora negatively impacts soil microbial biomass carbon(MBC)and reduces the diversity of C-cycling functional genes.The invasion species significantly increased the relative abundance of carbon fixation genes,while decreasing the relative abundance of carbon degradation genes.Additionally,the differential genes-expressing microbial communities exhibited notable differences across groups.At the class level,both generalist taxa(e.g.,Gammaproteobacteria,Deltaproteobacteria)and specialist taxa(e.g.,Nitrospiria,Flavobacteriia)collectively influenced the abundance of C-cycling functional genes.Correlation and hierarchical partitioning analyses revealed that the increased soil carbon fixation capacity was closely associated with increased soil organic carbon(SOC)and decreased MBC,whereas the decline in soil carbon degradation capacity was linked to higher soil electrical conductivity(EC)and a lower C:P ratio.Conclusions Our study filled a gap in research during the cold season and revealed that the invasion of S.alterniflora significantly impacts both soil C-cycling functional genes and their expressing microbial communities,thereby potentially affecting the soil organic carbon of salt marsh wetland ecosystems.展开更多
The effects of brine addition on the dynamic changes in nitrogen transformation,and bacterial community of fermented Allium chinense(A.chinense)bulbs,as well as screening and identification of lactic acid bacteria(LAB...The effects of brine addition on the dynamic changes in nitrogen transformation,and bacterial community of fermented Allium chinense(A.chinense)bulbs,as well as screening and identification of lactic acid bacteria(LAB)with nitrite degradation function were explored in this work.In contrast with natural fermentation(NC)group,supplementation with aged pickle brine(PBa)declined the pH value.In terms of nitrogen metabolism,PBa fermentation could enhance the degradation of nitrite via activating nitrite reductase(NIR).Besides,the ammonium contents showed a small fluctuation without significant difference during fermentation.Furthermore,PBa could alter the microbial diversity of A.chinense bulbs to modulate nitrogen metabolism-related genes including nirA/B/D and narK/G/H.Correlation analysis confirmed that the LAB abundances exhibited significant negative relationships with the levels of nitrite.These results inferred that the microbial pathways of nitrite degradation in A.chinense bulbs might be attributed to denitrification.Accordingly,the present findings suggested that brine fermentation could promote the nitrogen metabolism in A.chinense bulbs via regulating the microbial community and expression of denitrification-related genes,thus shortening the fermentation time compared to the NC group.Moreover,one strain of LAB(L7)was isolated from PBa group by pure culture method,which showed high similarity to Lactiplantibacillus argentoratensis HBUAS570840,and strong nitrite-lowering ability,high salt tolerance,and strong antibacterial activity.Therefore,the addition of brine can be utilized as an effective strategy to modulate the nitrogen metabolism of A.chinense bulbs.展开更多
文摘The classical phase field model has wide applications for brittle materials,but nonlinearity and inelasticity are found in its stress-strain curve.The degradation function in the classical phase field model makes it a linear formulation of phase field and computationally attractive,but stiffness reduction happens even at low strain.In this paper,generalized polynomial degradation functions are investigated to solve this problem.The first derivative of degradation function at zero phase is added as an extra constraint,which renders higher-order polynomial degradation function and nonlinear formulation of phase field.Compared with other degradation functions(like algebraic fraction function,exponential function,and trigonometric function),this polynomial degradation function enables phase in[0,1](should still avoid the first derivative of degradation function at zero phase to be 0),so there is noconvergence problem.The good and meaningful finding is that,under the same fracture strength,the proposed phase field model has a larger length scale,which means larger element size and better computational efficiency.This proposed phase field model is implemented in LS-DYNA user-defined element and user-defined material and solved by the Newton-Raphson method.A tensile test shows that the first derivative of degradation function at zero phase does impact stress-strain curve.Mode I,mode II,and mixed-mode examples show the feasibility of the proposed phase field model in simulating brittle fracture.
基金supported by the Key R&D Program of Zhejiang Province(2023C02004,2023C02015)the National Natural Science Foundation of China(42277283,42090060)+1 种基金the Fundamental Research Funds for the Central Universities(226-2022-00139)Ningbo Welfare Science and Technology Plan Project(No.2022S118)
文摘Background The invasiveness of Spartina alterniflora Loisel.into the estuarine coastal wetlands has impacted the stability of soil organic carbon,as well as the functional genes of soil microorganisms.However,the mechanisms by which S.alterniflora invasion affects soil organic carbon,especially at the micro-level,is still unclear.Therefore,this study compared the differences in soil carbon cycling(C-cycling)functional genes between invaded and native areas during the cold season,as well as the changes in microbial communities involved in differential functional genes'expression.Results Our results showed that in salt marsh wetlands dominated by Suaeda salsa(L.)Pall.,invasion by S.alterniflora negatively impacts soil microbial biomass carbon(MBC)and reduces the diversity of C-cycling functional genes.The invasion species significantly increased the relative abundance of carbon fixation genes,while decreasing the relative abundance of carbon degradation genes.Additionally,the differential genes-expressing microbial communities exhibited notable differences across groups.At the class level,both generalist taxa(e.g.,Gammaproteobacteria,Deltaproteobacteria)and specialist taxa(e.g.,Nitrospiria,Flavobacteriia)collectively influenced the abundance of C-cycling functional genes.Correlation and hierarchical partitioning analyses revealed that the increased soil carbon fixation capacity was closely associated with increased soil organic carbon(SOC)and decreased MBC,whereas the decline in soil carbon degradation capacity was linked to higher soil electrical conductivity(EC)and a lower C:P ratio.Conclusions Our study filled a gap in research during the cold season and revealed that the invasion of S.alterniflora significantly impacts both soil C-cycling functional genes and their expressing microbial communities,thereby potentially affecting the soil organic carbon of salt marsh wetland ecosystems.
基金funded by Hunan Provincial Science Fund for Distinguished Young Scholars,China(2021JJ10007)the Research and Development Program in Key Areas of Hunan Province,China(2021NK2015,2019SK2121)Hunan Scientific Talents Promotion Program supported by Hunan Association for Science and Technology,China(2019TJ-Q01).
文摘The effects of brine addition on the dynamic changes in nitrogen transformation,and bacterial community of fermented Allium chinense(A.chinense)bulbs,as well as screening and identification of lactic acid bacteria(LAB)with nitrite degradation function were explored in this work.In contrast with natural fermentation(NC)group,supplementation with aged pickle brine(PBa)declined the pH value.In terms of nitrogen metabolism,PBa fermentation could enhance the degradation of nitrite via activating nitrite reductase(NIR).Besides,the ammonium contents showed a small fluctuation without significant difference during fermentation.Furthermore,PBa could alter the microbial diversity of A.chinense bulbs to modulate nitrogen metabolism-related genes including nirA/B/D and narK/G/H.Correlation analysis confirmed that the LAB abundances exhibited significant negative relationships with the levels of nitrite.These results inferred that the microbial pathways of nitrite degradation in A.chinense bulbs might be attributed to denitrification.Accordingly,the present findings suggested that brine fermentation could promote the nitrogen metabolism in A.chinense bulbs via regulating the microbial community and expression of denitrification-related genes,thus shortening the fermentation time compared to the NC group.Moreover,one strain of LAB(L7)was isolated from PBa group by pure culture method,which showed high similarity to Lactiplantibacillus argentoratensis HBUAS570840,and strong nitrite-lowering ability,high salt tolerance,and strong antibacterial activity.Therefore,the addition of brine can be utilized as an effective strategy to modulate the nitrogen metabolism of A.chinense bulbs.
