1 On a casual afternoon,I opened an enlightening book called How the Steel Was Tempered written by a writer called Nikolai Ostrovsky.Immediately,I was lost in the immortal(不朽的)work.Reading the book was an eye⁃openi...1 On a casual afternoon,I opened an enlightening book called How the Steel Was Tempered written by a writer called Nikolai Ostrovsky.Immediately,I was lost in the immortal(不朽的)work.Reading the book was an eye⁃opening experience for me.As a middle school student,I initially thought this book would be just another historical novel,but it turned out to be so much more.The book tells the story about the journey of a young man who is called Pavel Korchagin.展开更多
Root tips are the main components of absorptive fine roots,but their seasonal dynamics and relationship to environmental factors remain unclear due to the difficulties in methodology.In this study,we explored the temp...Root tips are the main components of absorptive fine roots,but their seasonal dynamics and relationship to environmental factors remain unclear due to the difficulties in methodology.In this study,we explored the temporal patterns of root-tip production and mortality in monoculture plantations of five temperate tree species at a common site in northeastern China,and identified the general environmental controls on such processes.We made monthly in-situ assessments of root tip length(RTL)production and mortality in two hardwood and three coniferous species with a minirhizotron(MR)method during the growing seasons of 2008 and 2009.Air temperature,rainfall,soil temperature and water content at 10 cm depth were determined concurrently.RTL production in all species exhibited consistent peaks in summer(June–August)in two growing seasons.RTL mortality showed substantial interannual and interspecific variability,with peaks in autumn and winter in 2008,but various patterns in 2009.RTL production positively correlated with monthly soil and air temperature across all species,and with monthly rainfall in three coniferous species.However,there was no significant correlation between RTL production and soil water content.By contrast,RTL mortality was weakly related to environmental factors,showing positive correlations with soil temperature in Korean spruce,and with rainfall in Korean pine and Korean spruce.Our findings suggest that the seasonal patterns of RTL production are convergent across the five temperate tree species due to the overlapped distribution of heat and rainfall,which can conduce roots to maximizing the acquisition of nutrient resources in the soil.展开更多
Prescribed burning is commonly used to maintain forest ecosystem functions and reduce the risk of future wildfires.Although many studies have investigated the response of microbial community to wildfires in forest eco...Prescribed burning is commonly used to maintain forest ecosystem functions and reduce the risk of future wildfires.Although many studies have investigated the response of microbial community to wildfires in forest ecosystems,the effects of prescribed burnings on soil microbial community structure are less studied.It is also unclear that how post-fire soil physiochemical properties changes affected soil microbial communities.Here,we studied the impacts of prescribed burning on soil microbiome in three typical temperate forests of northern China by collecting soil physicochemical and high-throughput sequencing for 16S rRNA and 18S rRNA was applied to analyze the diversity and community composition of soil microbes(bacteria and fungi).Compared with pre-fire condition,prescribed burning significantly decreased Chaol index and altered soil bacterial communities(P<0.05),whereas it had no significant effect on fungal diversity and community structure of the(P>0.05).Planctomycetes and Actinobacteria made the greatest contributions to the bacterial community dissimilarity between the pre-fire and post-fire conditions.The main variables influencing the post-fire soil microbial community structure are soil pH,available phosphorus,total nitrogen,and the ratio of soil total carbon to soil total nitrogen,which could account for 73.5% of the variation in the microbial community structure in these stands.Our findings demonstrated a great discrepancy in the responses of bacteria and fungi to prescribed burning.Prescribed burning altered the soil microbial structure by modifying the physicochemical properties.Our results pointed that it is essential to evaluate the impact of prescribed burnings on forest ecosystem functions.These findings provide an important baseline for assessing post-fire microbial recovery in the region and offer critical guidance for restoration efforts.展开更多
The microstructure evolution and mechanical properties of a Fe-0.12C-0.2Si-1.6Mn-0.3Cr-0.0025B(wt.%)steel with different initial microstructures,i.e.,hot rolled(HR)and cold rolled-annealed(CRA),were studied through op...The microstructure evolution and mechanical properties of a Fe-0.12C-0.2Si-1.6Mn-0.3Cr-0.0025B(wt.%)steel with different initial microstructures,i.e.,hot rolled(HR)and cold rolled-annealed(CRA),were studied through optical microscopy,scanning electron microscopy,electron channeling contrast imaging,microhardness and room temperature uniaxial tensile tests.After water quenching from 930℃ to room temperature,a fully martensitic microstructure was obtained in both as-quenched HR and CRA specimens,which shows a microhardness of 480±5 HV,and no significant difference in microstructure and microhardness was observed.Tensile test results show that the product of tensile strength and total elongation(UTS×TE)of the as-quenched HR specimen,i.e.,24.1 GPa%,is higher than that of the as-quenched CRA specimen,i.e.,18.9 GPa%.While,after being tempered at 300℃,the martensitic microstructures and mechanical properties of the two as-quenched specimens change significantly due to the synergy role of the matrix phase softening and the precipitation strengthening.Concerning the maximum UTS×TE,it is 18.9 GPa%obtained in the as-quenched CRA one,while that is 24.4 GPa%obtained in the HR specimen after tempered at 300℃ for 5 min.展开更多
High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here...High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here we investigated the effect of matrix and precipitates on mechanical properties of Cr-Ni-Mo-V/Nb steel after water quenching and tempering(150-500℃).The results showed that the microstructure of the present steel is noticeably tuned by changing the tempering temperature.An excellent combination of strength(a yield strength of 1308 MPa with a total elongation of 8.2%)and toughness(Charpy V-notch impact toughness of 40.5 J/cm^(2))is obtained upon tempering at 200℃.This is attributed to the lath martensite containing high dislocation density,the martensite-twin substructure,and the strengthening effects of the precipitated needle-likeε-carbides and spherical VC particles.The acicularε-carbides are replaced by the rod-shaped Fe_(3)C at the tempering temperature of 350℃,resulting in the remarkable deterioration in strength,hardness,and elongation.Spheroidized carbides formed at a tempering temperature of 500℃ are beneficial to the enhancement of the elongation and toughness,but the strength decreases due to the matrix softening caused by the recovery of dislocation.展开更多
Accurate quantification of life-cycle greenhouse gas(GHG)footprints(GHG_(fp))for a crop cultivation system is urgently needed to address the conflict between food security and global warming mitigation.In this study,t...Accurate quantification of life-cycle greenhouse gas(GHG)footprints(GHG_(fp))for a crop cultivation system is urgently needed to address the conflict between food security and global warming mitigation.In this study,the hydrobiogeochemical model,CNMM-DNDC,was validated with in situ observations from maize-based cultivation systems at the sites of Yongji(YJ,China),Yanting(YT,China),and Madeya(MA,Kenya),subject to temperate,subtropical,and tropical climates,respectively,and updated to enable life-cycle GHG_(fp)estimation.The model validation provided satisfactory simulations on multiple soil variables,crop growth,and emissions of GHGs and reactive nitrogen gases.The locally conventional management practices resulted in GHG_(fp)values of 0.35(0.09–0.53 at the 95%confidence interval),0.21(0.01–0.73),0.46(0.27–0.60),and 0.54(0.21–0.77)kg CO_(2)e kg~(-1)d.m.(d.m.for dry matter in short)for maize–wheat rotation at YJ and YT,and for maize–maize and maize–Tephrosia rotations at MA,respectively.YT's smallest GHG_(fp)was attributed to its lower off-farm GHG emissions than YJ,though the soil organic carbon(SOC)storage and maize yield were slightly lower than those of YJ.MA's highest SOC loss and low yield in shifting cultivation for maize–Tephrosia rotation contributed to its highest GHG_(fp).Management practices of maize cultivation at these sites could be optimized by combination of synthetic and organic fertilizer(s)while incorporating 50%–100%crop residues.Further evaluation of the updated CNMM-DNDC is needed for different crops at site and regional scales to confirm its worldwide applicability in quantifying GHG_(fp)and optimizing management practices for achieving multiple sustainability goals.展开更多
In order to avoid poor machinability caused by excessive hardness under high-silicon conditions in the traditional free-cutting graphited steel,it is important to develop a suitable silicon-saving,aluminum-containing ...In order to avoid poor machinability caused by excessive hardness under high-silicon conditions in the traditional free-cutting graphited steel,it is important to develop a suitable silicon-saving,aluminum-containing free-cutting steel.This study investigated the microstructure and graphite precipitation behavior of Fe–0.58C–1.0Al(wt%)steels with varying silicon contents(0.55wt%–2.67wt%)after tempering at different temperatures(680℃,715℃).The tempering structure and the precipitation behavior of graphite and Fe_(3)C in Fe–0.58C–1.0Al steels were systematically studied by optical microscopy(OM),field emission scanning electron microscopy(FESEM),and electron microprobe analyzer(EPMA).The results showed that,at both tempering temperatures,the microstructure of 0.55wt%Si steel is ferrite+granular Fe_(3)C,and the microstructures of 1.38wt%–2.67wt%Si steels are ferrite+petaloid graphite+granular Fe_(3)C.With increasing Si content from 1.38wt%to 2.67wt%at constant tempering temperature,the number density of graphite particles increases,though their average size decreases.Meanwhile,the number density and average size of Fe_(3)C in experimental steels continuously decrease with the increase of Si content.For 0.55wt%Si steel without graphite precipitation,increasing tempering temperature promotes the accumulation and growth of Fe_(3)C.For 1.38wt%–2.67wt%Si steels with graphite precipitation,higher tempering temperature promotes graphite particles growth while accelerating the decomposition and refinement of Fe_(3)C.Furthermore,compared with the experimental steels containing 0.55wt%Si,1.38wt%Si,and 2.67wt%Si,the 1.89wt%Si steel exhibits significantly lower hardness.Especially,when tempered at 715℃,Fe–0.58C–1.0Al steel with 1.89wt%Si exhibits enhanced graphitization behavior and reduced hardness,which is nearly HV 20 lower than previously reported Fe–0.55C–2.33Si steel.展开更多
The failure analysis was conducted on unqualified torsion bar spring in automobile suspension system used for light vehicles during engine test.The effects of through hardening,surface induction hardening,quenching an...The failure analysis was conducted on unqualified torsion bar spring in automobile suspension system used for light vehicles during engine test.The effects of through hardening,surface induction hardening,quenching and tempering,and tempering temperature on the microstructure and fatigue life of 45CrNiMoVA steel torsion bars were also investigated.Results showed that only the torsion bar spring after through quenching and tempering is subjected to surface induction quenching and tempering to achieve the fatigue life of the qualified torsion bar.The fatigue life of torsion bar spring reaches 3×10^(5) cycles more than the required 2×10^(5) cycles.This is because the distribution of gradient microstructure was helpful to relieve the applied stress during the fatigue process.The microstructure of the non-hardened region,which consists of tempered sorbite regardless of whether it is tempered at 330 or 430℃,contributes to minimizing the impact of temper brittleness on the fatigue life of the torsion bar.Consequently,the fatigue life of the torsion bar is relatively unaffected by temper brittleness due to the presence of tempered sorbite in its non-hardened regions.And the reason for the unqualified fatigue life was that the depth and hardness of the hardened region did not meet the standard requirements of 5–7 mm and 47–52 HRC,respectively.展开更多
Temperate glaciers are highly sensitive to variations in climate and environmental conditions.Investigating the chemical composition of dissolved organic matter(DOM)in glacier snow is essential for understanding its c...Temperate glaciers are highly sensitive to variations in climate and environmental conditions.Investigating the chemical composition of dissolved organic matter(DOM)in glacier snow is essential for understanding its characteristics,sources,and transformation processes within glacial systems.This study aims to elucidate the chemical composition and transformation of DOM in snow environment by analyzing samples collected from snowpits,surface snow,and snow meltwater at Baishui Glacier No.1 on Mt.Yulong during May and June.The average concentrations of dissolved organic carbon(DOC)in snow meltwater collected in May(1.63±0.63 mg L^(-1))and June(1.54±0.35 mg L^(-1))were both significantly higher than those measured in snowpit samples from May(0.74±0.10 mg L^(-1))and June(0.54±0.10 mg L^(-1)),as well as in surface snow samples from May(0.65±0.31 mg L^(-1))and June(0.69±0.30 mg L^(-1)).However,the concentrations of DOC in samples from the same category did not show significant variation between May and June.Using excitation-emission matrix(EEM)fluorescence spectroscopy coupled with parallel factor(PARAFAC)analysis,three protein-like components(C_(1),C_(2),and C_(3))and one humic-like component(C_(4))were identified.The protein-like components accounted for more than 75%of the total DOM in all snow samples,indicating that the fluorescent DOM originated from biological or microbial sources.Significant differences in the relative proportions of the four fluorescent components were observed between snowpit samples from May and June,whereas no significant variations were noted in the other sample types.Furthermore,a clear transformation from protein-like to humic-like components was observed during the transition from snowpits to snow meltwater.Further analysis using Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)revealed that DOM in these snow samples was predominantly composed of aliphatic and peptide-like compounds(30.9%-50.9%),suggesting a substantial microbial contribution.FT-ICR MS data also demonstrated compositional shifts in DOM among snowpit,surface snow,and meltwater samples.Specifically,aliphatic and peptide-like compounds were progressively transformed into unsaturated compounds with high oxygen content,polyphenolic species,and condensed aromatic compounds during their transition from snowpit to meltwater.Therefore,the relative contribution of terrestrial-derived DOM increased during the transition from snowpit to snowmelt.Furthermore,an increase in heteroatom content in the DOM of meltwater samples indicated continuous chemical transformations likely driven by biological activity and/or photochemical processes during snowmelt and leaching.展开更多
Tree growth synchrony serves as a valuable ecological indicator of forest resilience to climate stress and disturbances.However,our understanding of how increasing temperature affects tree growth synchrony during rapi...Tree growth synchrony serves as a valuable ecological indicator of forest resilience to climate stress and disturbances.However,our understanding of how increasing temperature affects tree growth synchrony during rapidly and slowly warming periods in ecosystems with varying climatic conditions remains limited.By using tree-ring data from temperate broadleaf(Fraxinus mandshurica,Phellodendron amurense,Quercus mongolica,and Juglans mandshurica)and Korean pine(Pinus koraiensis)mixed forests in northeast China,we investigated the effects of climate change,particularly warming,on the growth synchrony of five dominant temperate tree species across contrasting warm-dry and cool-wet climate conditions.Results show that temperature over water availability was the primary factor driving the growth and growth synchrony of the five species.Growth synchrony was significantly higher in warm-dry than in cool-wet areas,primarily due to more uniform climate conditions and higher climate sensitivity in the former.Rapid warming from the 1960s to the 1990s significantly enhanced tree growth synchrony in both areas,followed by a marked reversal as temperatures exceeded a certain threshold or warming slowed down,particularly in the warm-dry area.The growth synchrony variation patterns of the five species were highly consistent over time,although broadleaves exhibited higher synchrony than conifers,suggesting potential risks to forest resilience and stability under future climate change scenarios.Growing season temperatures and non-growing season temperatures and precipitation had a stronger positive effect on tree growth in the cool-wet area compared to the warm-dry area.High relative humidity hindered growth in the cool-wet area but enhanced it in the warm-dry area.Overall,our study highlights that the diversity and sensitivity of climate-growth relationships directly determine spatiotemporal growth synchrony.Temperature,along with water availability,shape long-term forest dynamics by affecting tree growth and synchrony.These results provide crucial insights for forest management practice to enhance structural diversity and resilience capacity against climate changeinduced synchrony shifts.展开更多
The demand for oil casing steel with ultra-high strength and excellent impact toughness for safe application in ultra-deep wells is pressing.In improving the combination of strength,ductility,and impact toughness,the ...The demand for oil casing steel with ultra-high strength and excellent impact toughness for safe application in ultra-deep wells is pressing.In improving the combination of strength,ductility,and impact toughness,the designed Cr-Mo-V micro-alloyed oil casing steel was quenched at 800,900,and 1000℃,followed by tempering at 600,680,and 760℃,respectively,to obtain distinct microstruc-tures.The results showed that the microstructure of the samples quenched at 800℃ followed by tempering comprised untransformed ferrite and large undissolved carbides,which considerably deteriorated tensile strength and impact toughness.For other conditions,the nuc-leated carbides and the boundaries are key factors that balance the tensile strength from 1226 to 971 MPa and the impact toughness from 65 to 236 J.From the perspective of carbide,optimal precipitation strengthening is achieved with a smaller carbide size obtained by a low tempering temperature of 600℃,while larger-sized carbides would remarkably soften the matrix to improve the toughness but deteriorate the tensile strength.Additionally,an increase in prior austenite grain size with the corresponding enlarged sub-boundaries obtained by high quenching temperatures substantially diminishes grain refinement strengthening,dislocation strengthening,and the energy absorbed in the crack propagation process,which is unfavorable to strength and toughness.展开更多
The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results sh...The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.展开更多
Tracking the sap flux of woody plants in savannas is essential for understanding their response to climate change and human management.Solar-induced fluorescence(SIF)has potential to predict transpiration yet its appl...Tracking the sap flux of woody plants in savannas is essential for understanding their response to climate change and human management.Solar-induced fluorescence(SIF)has potential to predict transpiration yet its applicability for estimating savanna sap flux is unclear.Using three years of tower-based far-red SIF observations and groundbased sap flow monitoring in a temperate savanna of Otindag Sandy Land,China,we investigated the relationship between far-red SIF and sap flux density and developed linear and random forest models for estimating.The results show a variable correlation between SIF and sap flux density for Ulmus pumila var.sabulosa(J.H.Xin)G.H.Zhu&D.H.Bian(U.pumila.)at an hourly scale.The strongest correlations were during the mid-growth period July and August when considering the time lag between SIF and sap flux(0-0.5 h).Photosynthetically active radiation was the primary factor driving the SIF and sap flux density relationship.Soil moisture,vapor pressure deficit,and air temperature also influenced this relationship on daily and monthly scales.Compared to SIF-based linear regression models,the SIF-based random forest model performed better in tracking the seasonal sap flux density.The results suggest the feasibility of accurately monitoring vegetation sap flux using SIF,woody fractional vegetation cover,and environmental factors in a temperate savanna.This method could also be used in modeling land surface processes in savanna-type ecosystems.展开更多
Climate change is a pressing global environmental issue^([1]).The gradual rise in global surface temperature is the most immediate and direct among its public health impacts.Influenza,the leading cause of human respir...Climate change is a pressing global environmental issue^([1]).The gradual rise in global surface temperature is the most immediate and direct among its public health impacts.Influenza,the leading cause of human respiratory viral infections,remains a substantial public health concern owing to its considerable disease burden,particularly in highrisk groups.Mounting epidemiological evidence has linked influenza to extreme heat and cold weather^([2–4]).展开更多
Investigating the spatial distribution of vegetation in monsoonal-climate-dominated high mountain area and detecting its changes that occurred in paraglacial areas is crucial for understanding the cascading environmen...Investigating the spatial distribution of vegetation in monsoonal-climate-dominated high mountain area and detecting its changes that occurred in paraglacial areas is crucial for understanding the cascading environmental effects of shrinking glaciers.We used Landsat images from 1994 to 2022,obtained landscape distribution patterns of glaciers and vegetation in Mt.Gongga,and detected paraglacial vegetation changes under deglaciating environments.We observed there is a pronounced difference in glacier and vegetation coverage between the eastern and western slopes in Mt.Gongga,the eastern slope occupies 78.68% of vegetation area and 61.02% of glacier area,whilst the western slope occupies lower area.Exaggerate warming accelerated glacier retreat,and proglacial areas are generally characterized by very fast primary succession,resulting in an increase of 0.32 km^(2)in vegetation area within two typical glacier forefields on the eastern slope.The phenomenon of paraglacial slope failure following glacier thinning is widespread in Mt.Gongga,resulting in vegetation area decreased by 0.34 km^(2).Concurrently,the fast retreat of glaciers and changes in ice surface geomorphology have caused rapid dynamics in supraglacial vegetation developed on its lower debris-covered sections.We suggested that rapid changes of temperate glaciers can significantly influence paraglacial landform,leading to rapid dynamic changes of vegetation in a balance between colonization and destruction.展开更多
Droughts pose significant threats to forest ecosystems globally.Effective forest management strategies,adapted to local conditions,are needed to mitigate negative drought impacts.One proposed strategy is competition r...Droughts pose significant threats to forest ecosystems globally.Effective forest management strategies,adapted to local conditions,are needed to mitigate negative drought impacts.One proposed strategy is competition reduction to increase water availability and,as a result,alleviate drought stress.This study investigates the effect of competition intensity on drought stress and tree growth in European beech(Fagus sylvatica)and pedunculate oak(Quercus robur).We deployed 72 point dendrometers,placed along a competition intensity gradient,in National Park Brabantse Wouden(Belgium),to measure daily minimum tree water deficit(TWD_(min))as a drought stress proxy and daily radial growth at tree level.Our results revealed species-dependent effects of competition intensity(CI).For European beech,competition reductions positively influenced growth and alleviated(1<CI<2)or aggravated(CI<0.5)drought stress.For pedunculate oak,competition intensity did not affect drought stress or growth along the investigated gradient.Environmental variables consistently affected TWDmin and growth of both species.Precipitation reduced TWDmin and increased growth,while vapor pressure deficit led to opposite trends.Thus,environmental conditions and competition can play a critical role in forest dynamics,especially in light of climate change.However,reducing competition through increased management efforts does not seem to be a one-size-fits-all solution to alleviating drought stress.Additionally,there seems to be a trade-off between reducing drought stress and improving tree growth in European beech:tree growth continuously benefited from competition reductions,while under low competition(CI<0.5)drought stress increased.Revisiting or reviving long-term thinning intensity trials encompassing various regions,species,and soil types will be needed to gain comprehensive insights into mitigating drought stress through management interventions under different local stand conditions.展开更多
Increasing human activity is altering the struc-ture of forests,which affects the composition of communi-ties,including birds.However,little is known about the key forest structure variables that determine the richnes...Increasing human activity is altering the struc-ture of forests,which affects the composition of communi-ties,including birds.However,little is known about the key forest structure variables that determine the richness of bird communities in European temperate oak forests.We,there-fore,aimed to identify key variables in these habitats that could contribute to the design of management strategies for forest conservation by surveying 11 oak-dominated forest sites throughout the mid-mountain range of Hungary at 86 survey points to reveal the role of different compositional and structural variables for forest stands that influence the breeding bird assemblages in the forests at the functional group and individual species levels.Based on decision tree modelling,our results showed that the density of trees larger than 30 cm DBH was an overall important variable,indi-cating that large-diameter trees were essential to provide diverse bird communities.The total abundance of birds,the foliage-gleaners,primary and secondary cavity nest-ers,residents,and five specific bird species were related to the density of high trunk diameter trees.The abundance of shrub nesters was negatively influenced by a high density of trees over 10 cm DBH.The density of the shrub layer positively affected total bird abundance and the abundance of foliage gleaners,secondary cavity nesters and residents.Analysis of the co-dominant tree species showed that the presence of linden,beech,and hornbeam was important in influencing the abundance of various bird species,e.g.,Eur-asian Treecreeper(Certhia familiaris),Marsh Tit(Poecile palustris)and Wood Warbler(Phylloscopus sibilatrix).Our results indicated that large trees,high tree diversity,and dense shrub layer were essential for forest bird communities and are critical targets for protection to maintain diverse and abundant bird communities in oak-dominated forest habitats.展开更多
In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition...In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.展开更多
The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by c...The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.展开更多
文摘1 On a casual afternoon,I opened an enlightening book called How the Steel Was Tempered written by a writer called Nikolai Ostrovsky.Immediately,I was lost in the immortal(不朽的)work.Reading the book was an eye⁃opening experience for me.As a middle school student,I initially thought this book would be just another historical novel,but it turned out to be so much more.The book tells the story about the journey of a young man who is called Pavel Korchagin.
基金supported by the National Natural Science Foundation of China(32071749)。
文摘Root tips are the main components of absorptive fine roots,but their seasonal dynamics and relationship to environmental factors remain unclear due to the difficulties in methodology.In this study,we explored the temporal patterns of root-tip production and mortality in monoculture plantations of five temperate tree species at a common site in northeastern China,and identified the general environmental controls on such processes.We made monthly in-situ assessments of root tip length(RTL)production and mortality in two hardwood and three coniferous species with a minirhizotron(MR)method during the growing seasons of 2008 and 2009.Air temperature,rainfall,soil temperature and water content at 10 cm depth were determined concurrently.RTL production in all species exhibited consistent peaks in summer(June–August)in two growing seasons.RTL mortality showed substantial interannual and interspecific variability,with peaks in autumn and winter in 2008,but various patterns in 2009.RTL production positively correlated with monthly soil and air temperature across all species,and with monthly rainfall in three coniferous species.However,there was no significant correlation between RTL production and soil water content.By contrast,RTL mortality was weakly related to environmental factors,showing positive correlations with soil temperature in Korean spruce,and with rainfall in Korean pine and Korean spruce.Our findings suggest that the seasonal patterns of RTL production are convergent across the five temperate tree species due to the overlapped distribution of heat and rainfall,which can conduce roots to maximizing the acquisition of nutrient resources in the soil.
基金financially supported by the National Natural Science Foundation(No.32471868,No.32001324)Youth Lift Project of China Association for Science and Technology(No.YESS20210370)+1 种基金Fundamental Research Funds for the Central Universities(2572023CT01)We thank the Grassland Bureau and the National Innovation Alliance of Wildland Fire Prevention and Control Technology of China for supporting this research.
文摘Prescribed burning is commonly used to maintain forest ecosystem functions and reduce the risk of future wildfires.Although many studies have investigated the response of microbial community to wildfires in forest ecosystems,the effects of prescribed burnings on soil microbial community structure are less studied.It is also unclear that how post-fire soil physiochemical properties changes affected soil microbial communities.Here,we studied the impacts of prescribed burning on soil microbiome in three typical temperate forests of northern China by collecting soil physicochemical and high-throughput sequencing for 16S rRNA and 18S rRNA was applied to analyze the diversity and community composition of soil microbes(bacteria and fungi).Compared with pre-fire condition,prescribed burning significantly decreased Chaol index and altered soil bacterial communities(P<0.05),whereas it had no significant effect on fungal diversity and community structure of the(P>0.05).Planctomycetes and Actinobacteria made the greatest contributions to the bacterial community dissimilarity between the pre-fire and post-fire conditions.The main variables influencing the post-fire soil microbial community structure are soil pH,available phosphorus,total nitrogen,and the ratio of soil total carbon to soil total nitrogen,which could account for 73.5% of the variation in the microbial community structure in these stands.Our findings demonstrated a great discrepancy in the responses of bacteria and fungi to prescribed burning.Prescribed burning altered the soil microbial structure by modifying the physicochemical properties.Our results pointed that it is essential to evaluate the impact of prescribed burnings on forest ecosystem functions.These findings provide an important baseline for assessing post-fire microbial recovery in the region and offer critical guidance for restoration efforts.
基金Chongqing Natural Science Foundation(No.CSTB2022NSCQ-MSX1394)Graduate Research and Innovation Foundation of Chongqing,China(Grant No.CYS22008)+2 种基金Open Project of State Key Laboratory of Advanced Special Steel,Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University(SKLASS 2023-10)the Science and Technology Commission of Shanghai Municipality(No.19DZ2270200)the Open Project of the Large Casting and Forging Manufacturing Technology Engineering Center of Shanghai Institute of Mechanical and Electrical Engineering,State Key Laboratory of Vanadium and Titanium Resources Open Fund(No.2022P4FZG04A).
文摘The microstructure evolution and mechanical properties of a Fe-0.12C-0.2Si-1.6Mn-0.3Cr-0.0025B(wt.%)steel with different initial microstructures,i.e.,hot rolled(HR)and cold rolled-annealed(CRA),were studied through optical microscopy,scanning electron microscopy,electron channeling contrast imaging,microhardness and room temperature uniaxial tensile tests.After water quenching from 930℃ to room temperature,a fully martensitic microstructure was obtained in both as-quenched HR and CRA specimens,which shows a microhardness of 480±5 HV,and no significant difference in microstructure and microhardness was observed.Tensile test results show that the product of tensile strength and total elongation(UTS×TE)of the as-quenched HR specimen,i.e.,24.1 GPa%,is higher than that of the as-quenched CRA specimen,i.e.,18.9 GPa%.While,after being tempered at 300℃,the martensitic microstructures and mechanical properties of the two as-quenched specimens change significantly due to the synergy role of the matrix phase softening and the precipitation strengthening.Concerning the maximum UTS×TE,it is 18.9 GPa%obtained in the as-quenched CRA one,while that is 24.4 GPa%obtained in the HR specimen after tempered at 300℃ for 5 min.
基金supported by the National Natural Science Foundation of China(Grant Nos.51904278,51974288 and 52071300)the Special Funding Projects for Local Science and Technology Development guided by the Central Committee(YDZJSX2021C007,YDZJSX2021B020 and YDZX20191400004587)+4 种基金the Key Research and Development Project of Shanxi Province(202102050201004,202102150401002,202202050201015)the Scientific and Technological Innovation Talent Team Project of Shanxi Province(202204051002020)the Basic Research Program of Shanxi Province(20210302123218,202203021212126,202203021221096)the Foundation of the State Key Laboratory of Advanced Metallurgy,USTB(K22-11)the Special Project for Transformation of Scientific Achievements(202204021301025).
文摘High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here we investigated the effect of matrix and precipitates on mechanical properties of Cr-Ni-Mo-V/Nb steel after water quenching and tempering(150-500℃).The results showed that the microstructure of the present steel is noticeably tuned by changing the tempering temperature.An excellent combination of strength(a yield strength of 1308 MPa with a total elongation of 8.2%)and toughness(Charpy V-notch impact toughness of 40.5 J/cm^(2))is obtained upon tempering at 200℃.This is attributed to the lath martensite containing high dislocation density,the martensite-twin substructure,and the strengthening effects of the precipitated needle-likeε-carbides and spherical VC particles.The acicularε-carbides are replaced by the rod-shaped Fe_(3)C at the tempering temperature of 350℃,resulting in the remarkable deterioration in strength,hardness,and elongation.Spheroidized carbides formed at a tempering temperature of 500℃ are beneficial to the enhancement of the elongation and toughness,but the strength decreases due to the matrix softening caused by the recovery of dislocation.
基金jointly supported by the National Key R&D Program of China(Grant No.2022YFE0209200)the National Natural Science Foundation of China(Grant Nos.U22A20562,42330607 and 41761144054)the National Large Scientific and Technological Infrastructure“Earth System Science Numerical Simulator Facility”(Earth-Lab)(https://cstr.cn/31134.02.EL)。
文摘Accurate quantification of life-cycle greenhouse gas(GHG)footprints(GHG_(fp))for a crop cultivation system is urgently needed to address the conflict between food security and global warming mitigation.In this study,the hydrobiogeochemical model,CNMM-DNDC,was validated with in situ observations from maize-based cultivation systems at the sites of Yongji(YJ,China),Yanting(YT,China),and Madeya(MA,Kenya),subject to temperate,subtropical,and tropical climates,respectively,and updated to enable life-cycle GHG_(fp)estimation.The model validation provided satisfactory simulations on multiple soil variables,crop growth,and emissions of GHGs and reactive nitrogen gases.The locally conventional management practices resulted in GHG_(fp)values of 0.35(0.09–0.53 at the 95%confidence interval),0.21(0.01–0.73),0.46(0.27–0.60),and 0.54(0.21–0.77)kg CO_(2)e kg~(-1)d.m.(d.m.for dry matter in short)for maize–wheat rotation at YJ and YT,and for maize–maize and maize–Tephrosia rotations at MA,respectively.YT's smallest GHG_(fp)was attributed to its lower off-farm GHG emissions than YJ,though the soil organic carbon(SOC)storage and maize yield were slightly lower than those of YJ.MA's highest SOC loss and low yield in shifting cultivation for maize–Tephrosia rotation contributed to its highest GHG_(fp).Management practices of maize cultivation at these sites could be optimized by combination of synthetic and organic fertilizer(s)while incorporating 50%–100%crop residues.Further evaluation of the updated CNMM-DNDC is needed for different crops at site and regional scales to confirm its worldwide applicability in quantifying GHG_(fp)and optimizing management practices for achieving multiple sustainability goals.
基金supports by the National Natural Science Foundation of China(No.52274311)the Natural Science Research Project of Anhui Educational Committee,China(No.2023AH051081).
文摘In order to avoid poor machinability caused by excessive hardness under high-silicon conditions in the traditional free-cutting graphited steel,it is important to develop a suitable silicon-saving,aluminum-containing free-cutting steel.This study investigated the microstructure and graphite precipitation behavior of Fe–0.58C–1.0Al(wt%)steels with varying silicon contents(0.55wt%–2.67wt%)after tempering at different temperatures(680℃,715℃).The tempering structure and the precipitation behavior of graphite and Fe_(3)C in Fe–0.58C–1.0Al steels were systematically studied by optical microscopy(OM),field emission scanning electron microscopy(FESEM),and electron microprobe analyzer(EPMA).The results showed that,at both tempering temperatures,the microstructure of 0.55wt%Si steel is ferrite+granular Fe_(3)C,and the microstructures of 1.38wt%–2.67wt%Si steels are ferrite+petaloid graphite+granular Fe_(3)C.With increasing Si content from 1.38wt%to 2.67wt%at constant tempering temperature,the number density of graphite particles increases,though their average size decreases.Meanwhile,the number density and average size of Fe_(3)C in experimental steels continuously decrease with the increase of Si content.For 0.55wt%Si steel without graphite precipitation,increasing tempering temperature promotes the accumulation and growth of Fe_(3)C.For 1.38wt%–2.67wt%Si steels with graphite precipitation,higher tempering temperature promotes graphite particles growth while accelerating the decomposition and refinement of Fe_(3)C.Furthermore,compared with the experimental steels containing 0.55wt%Si,1.38wt%Si,and 2.67wt%Si,the 1.89wt%Si steel exhibits significantly lower hardness.Especially,when tempered at 715℃,Fe–0.58C–1.0Al steel with 1.89wt%Si exhibits enhanced graphitization behavior and reduced hardness,which is nearly HV 20 lower than previously reported Fe–0.55C–2.33Si steel.
基金support from the National Natural Science Foundation of China(No.52174351).
文摘The failure analysis was conducted on unqualified torsion bar spring in automobile suspension system used for light vehicles during engine test.The effects of through hardening,surface induction hardening,quenching and tempering,and tempering temperature on the microstructure and fatigue life of 45CrNiMoVA steel torsion bars were also investigated.Results showed that only the torsion bar spring after through quenching and tempering is subjected to surface induction quenching and tempering to achieve the fatigue life of the qualified torsion bar.The fatigue life of torsion bar spring reaches 3×10^(5) cycles more than the required 2×10^(5) cycles.This is because the distribution of gradient microstructure was helpful to relieve the applied stress during the fatigue process.The microstructure of the non-hardened region,which consists of tempered sorbite regardless of whether it is tempered at 330 or 430℃,contributes to minimizing the impact of temper brittleness on the fatigue life of the torsion bar.Consequently,the fatigue life of the torsion bar is relatively unaffected by temper brittleness due to the presence of tempered sorbite in its non-hardened regions.And the reason for the unqualified fatigue life was that the depth and hardness of the hardened region did not meet the standard requirements of 5–7 mm and 47–52 HRC,respectively.
基金supported by grants from the Sichuan Natural Science Foundation Project(2024NSFSC0793)Dagu Glacier Research Institute(Center)project of Aba Normal College(AS-DTPT 2023072)the support of Youth Innovation Promotion Association CAS(2021429)。
文摘Temperate glaciers are highly sensitive to variations in climate and environmental conditions.Investigating the chemical composition of dissolved organic matter(DOM)in glacier snow is essential for understanding its characteristics,sources,and transformation processes within glacial systems.This study aims to elucidate the chemical composition and transformation of DOM in snow environment by analyzing samples collected from snowpits,surface snow,and snow meltwater at Baishui Glacier No.1 on Mt.Yulong during May and June.The average concentrations of dissolved organic carbon(DOC)in snow meltwater collected in May(1.63±0.63 mg L^(-1))and June(1.54±0.35 mg L^(-1))were both significantly higher than those measured in snowpit samples from May(0.74±0.10 mg L^(-1))and June(0.54±0.10 mg L^(-1)),as well as in surface snow samples from May(0.65±0.31 mg L^(-1))and June(0.69±0.30 mg L^(-1)).However,the concentrations of DOC in samples from the same category did not show significant variation between May and June.Using excitation-emission matrix(EEM)fluorescence spectroscopy coupled with parallel factor(PARAFAC)analysis,three protein-like components(C_(1),C_(2),and C_(3))and one humic-like component(C_(4))were identified.The protein-like components accounted for more than 75%of the total DOM in all snow samples,indicating that the fluorescent DOM originated from biological or microbial sources.Significant differences in the relative proportions of the four fluorescent components were observed between snowpit samples from May and June,whereas no significant variations were noted in the other sample types.Furthermore,a clear transformation from protein-like to humic-like components was observed during the transition from snowpits to snow meltwater.Further analysis using Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)revealed that DOM in these snow samples was predominantly composed of aliphatic and peptide-like compounds(30.9%-50.9%),suggesting a substantial microbial contribution.FT-ICR MS data also demonstrated compositional shifts in DOM among snowpit,surface snow,and meltwater samples.Specifically,aliphatic and peptide-like compounds were progressively transformed into unsaturated compounds with high oxygen content,polyphenolic species,and condensed aromatic compounds during their transition from snowpit to meltwater.Therefore,the relative contribution of terrestrial-derived DOM increased during the transition from snowpit to snowmelt.Furthermore,an increase in heteroatom content in the DOM of meltwater samples indicated continuous chemical transformations likely driven by biological activity and/or photochemical processes during snowmelt and leaching.
基金supported by the National Natural Science Foundation of China(Nos.42107476 and 42177421)the China Postdoctoral International Exchange Fellowship Program(No.PC2021099)+1 种基金the Science and Technology Innovation Program of Hunan Province(No.2020RC2058)the China Scholarship Council(CSC,No.202206600004,to D.Yuan).
文摘Tree growth synchrony serves as a valuable ecological indicator of forest resilience to climate stress and disturbances.However,our understanding of how increasing temperature affects tree growth synchrony during rapidly and slowly warming periods in ecosystems with varying climatic conditions remains limited.By using tree-ring data from temperate broadleaf(Fraxinus mandshurica,Phellodendron amurense,Quercus mongolica,and Juglans mandshurica)and Korean pine(Pinus koraiensis)mixed forests in northeast China,we investigated the effects of climate change,particularly warming,on the growth synchrony of five dominant temperate tree species across contrasting warm-dry and cool-wet climate conditions.Results show that temperature over water availability was the primary factor driving the growth and growth synchrony of the five species.Growth synchrony was significantly higher in warm-dry than in cool-wet areas,primarily due to more uniform climate conditions and higher climate sensitivity in the former.Rapid warming from the 1960s to the 1990s significantly enhanced tree growth synchrony in both areas,followed by a marked reversal as temperatures exceeded a certain threshold or warming slowed down,particularly in the warm-dry area.The growth synchrony variation patterns of the five species were highly consistent over time,although broadleaves exhibited higher synchrony than conifers,suggesting potential risks to forest resilience and stability under future climate change scenarios.Growing season temperatures and non-growing season temperatures and precipitation had a stronger positive effect on tree growth in the cool-wet area compared to the warm-dry area.High relative humidity hindered growth in the cool-wet area but enhanced it in the warm-dry area.Overall,our study highlights that the diversity and sensitivity of climate-growth relationships directly determine spatiotemporal growth synchrony.Temperature,along with water availability,shape long-term forest dynamics by affecting tree growth and synchrony.These results provide crucial insights for forest management practice to enhance structural diversity and resilience capacity against climate changeinduced synchrony shifts.
基金supported from the National Nat-ural Science Foundation of China(Nos.52274342 and 52130408)the Fundamental Research Funds for the Central Universities of Central South University,China(No.1053320213826).
文摘The demand for oil casing steel with ultra-high strength and excellent impact toughness for safe application in ultra-deep wells is pressing.In improving the combination of strength,ductility,and impact toughness,the designed Cr-Mo-V micro-alloyed oil casing steel was quenched at 800,900,and 1000℃,followed by tempering at 600,680,and 760℃,respectively,to obtain distinct microstruc-tures.The results showed that the microstructure of the samples quenched at 800℃ followed by tempering comprised untransformed ferrite and large undissolved carbides,which considerably deteriorated tensile strength and impact toughness.For other conditions,the nuc-leated carbides and the boundaries are key factors that balance the tensile strength from 1226 to 971 MPa and the impact toughness from 65 to 236 J.From the perspective of carbide,optimal precipitation strengthening is achieved with a smaller carbide size obtained by a low tempering temperature of 600℃,while larger-sized carbides would remarkably soften the matrix to improve the toughness but deteriorate the tensile strength.Additionally,an increase in prior austenite grain size with the corresponding enlarged sub-boundaries obtained by high quenching temperatures substantially diminishes grain refinement strengthening,dislocation strengthening,and the energy absorbed in the crack propagation process,which is unfavorable to strength and toughness.
基金supported by the National Key research and Development Program of China(No.2022YFB4003001).
文摘The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.
基金supported by the Fundamental Research Funds of Chinese Academy of Forestry(grants No.CAFYBB2020QD002,CAFYBB2021MC002 and CAFYBB2023ZA009)National Natural Science Foundation of China(grants 32001371,32171875 and 32371960)。
文摘Tracking the sap flux of woody plants in savannas is essential for understanding their response to climate change and human management.Solar-induced fluorescence(SIF)has potential to predict transpiration yet its applicability for estimating savanna sap flux is unclear.Using three years of tower-based far-red SIF observations and groundbased sap flow monitoring in a temperate savanna of Otindag Sandy Land,China,we investigated the relationship between far-red SIF and sap flux density and developed linear and random forest models for estimating.The results show a variable correlation between SIF and sap flux density for Ulmus pumila var.sabulosa(J.H.Xin)G.H.Zhu&D.H.Bian(U.pumila.)at an hourly scale.The strongest correlations were during the mid-growth period July and August when considering the time lag between SIF and sap flux(0-0.5 h).Photosynthetically active radiation was the primary factor driving the SIF and sap flux density relationship.Soil moisture,vapor pressure deficit,and air temperature also influenced this relationship on daily and monthly scales.Compared to SIF-based linear regression models,the SIF-based random forest model performed better in tracking the seasonal sap flux density.The results suggest the feasibility of accurately monitoring vegetation sap flux using SIF,woody fractional vegetation cover,and environmental factors in a temperate savanna.This method could also be used in modeling land surface processes in savanna-type ecosystems.
基金supported by a Grant-inAid for Scientific Research(KAKENHI)from the Japan Society for the Promotion of Science(grant no.22J23183)。
文摘Climate change is a pressing global environmental issue^([1]).The gradual rise in global surface temperature is the most immediate and direct among its public health impacts.Influenza,the leading cause of human respiratory viral infections,remains a substantial public health concern owing to its considerable disease burden,particularly in highrisk groups.Mounting epidemiological evidence has linked influenza to extreme heat and cold weather^([2–4]).
基金Science and Technology Research Program of Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,No.IMHE-CXTD-02,No.IMHE-ZDRW-06。
文摘Investigating the spatial distribution of vegetation in monsoonal-climate-dominated high mountain area and detecting its changes that occurred in paraglacial areas is crucial for understanding the cascading environmental effects of shrinking glaciers.We used Landsat images from 1994 to 2022,obtained landscape distribution patterns of glaciers and vegetation in Mt.Gongga,and detected paraglacial vegetation changes under deglaciating environments.We observed there is a pronounced difference in glacier and vegetation coverage between the eastern and western slopes in Mt.Gongga,the eastern slope occupies 78.68% of vegetation area and 61.02% of glacier area,whilst the western slope occupies lower area.Exaggerate warming accelerated glacier retreat,and proglacial areas are generally characterized by very fast primary succession,resulting in an increase of 0.32 km^(2)in vegetation area within two typical glacier forefields on the eastern slope.The phenomenon of paraglacial slope failure following glacier thinning is widespread in Mt.Gongga,resulting in vegetation area decreased by 0.34 km^(2).Concurrently,the fast retreat of glaciers and changes in ice surface geomorphology have caused rapid dynamics in supraglacial vegetation developed on its lower debris-covered sections.We suggested that rapid changes of temperate glaciers can significantly influence paraglacial landform,leading to rapid dynamic changes of vegetation in a balance between colonization and destruction.
基金supported by the Fonds Wetenschappelijk Onderzoek(FWO)[grant number 1S16824N]the Cost Action CLEANFOREST[E-COST-GRANT-CA21138-c4968ca1].
文摘Droughts pose significant threats to forest ecosystems globally.Effective forest management strategies,adapted to local conditions,are needed to mitigate negative drought impacts.One proposed strategy is competition reduction to increase water availability and,as a result,alleviate drought stress.This study investigates the effect of competition intensity on drought stress and tree growth in European beech(Fagus sylvatica)and pedunculate oak(Quercus robur).We deployed 72 point dendrometers,placed along a competition intensity gradient,in National Park Brabantse Wouden(Belgium),to measure daily minimum tree water deficit(TWD_(min))as a drought stress proxy and daily radial growth at tree level.Our results revealed species-dependent effects of competition intensity(CI).For European beech,competition reductions positively influenced growth and alleviated(1<CI<2)or aggravated(CI<0.5)drought stress.For pedunculate oak,competition intensity did not affect drought stress or growth along the investigated gradient.Environmental variables consistently affected TWDmin and growth of both species.Precipitation reduced TWDmin and increased growth,while vapor pressure deficit led to opposite trends.Thus,environmental conditions and competition can play a critical role in forest dynamics,especially in light of climate change.However,reducing competition through increased management efforts does not seem to be a one-size-fits-all solution to alleviating drought stress.Additionally,there seems to be a trade-off between reducing drought stress and improving tree growth in European beech:tree growth continuously benefited from competition reductions,while under low competition(CI<0.5)drought stress increased.Revisiting or reviving long-term thinning intensity trials encompassing various regions,species,and soil types will be needed to gain comprehensive insights into mitigating drought stress through management interventions under different local stand conditions.
基金supported part ia l l y by LIFE4Oak Forests Project LIFE16NAT/IT/000245)the RRF 2.3.121202200008 projectthe MERLiN project funded under the European Commission H2020 Programme(101036337 MERLiN H2020 LC GD 2020)。
文摘Increasing human activity is altering the struc-ture of forests,which affects the composition of communi-ties,including birds.However,little is known about the key forest structure variables that determine the richness of bird communities in European temperate oak forests.We,there-fore,aimed to identify key variables in these habitats that could contribute to the design of management strategies for forest conservation by surveying 11 oak-dominated forest sites throughout the mid-mountain range of Hungary at 86 survey points to reveal the role of different compositional and structural variables for forest stands that influence the breeding bird assemblages in the forests at the functional group and individual species levels.Based on decision tree modelling,our results showed that the density of trees larger than 30 cm DBH was an overall important variable,indi-cating that large-diameter trees were essential to provide diverse bird communities.The total abundance of birds,the foliage-gleaners,primary and secondary cavity nest-ers,residents,and five specific bird species were related to the density of high trunk diameter trees.The abundance of shrub nesters was negatively influenced by a high density of trees over 10 cm DBH.The density of the shrub layer positively affected total bird abundance and the abundance of foliage gleaners,secondary cavity nesters and residents.Analysis of the co-dominant tree species showed that the presence of linden,beech,and hornbeam was important in influencing the abundance of various bird species,e.g.,Eur-asian Treecreeper(Certhia familiaris),Marsh Tit(Poecile palustris)and Wood Warbler(Phylloscopus sibilatrix).Our results indicated that large trees,high tree diversity,and dense shrub layer were essential for forest bird communities and are critical targets for protection to maintain diverse and abundant bird communities in oak-dominated forest habitats.
基金Project(2021YFC2801904) supported by the National Key R&D Program of ChinaProject(KY10100230067) supported by the Basic Product Innovation Research Project,China+3 种基金Projects(52271130,52305344) supported by the National Natural Science Foundation of ChinaProject(ZR2022QE073) supported by the Natural Science Foundation of Shandong Province,ChinaProject(AMGM2021F01) supported by the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai,ChinaProject(KY90200210015) supported by Leading Scientific Research Project of CNNC,China。
文摘In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.
基金supported by the Science and Technology Planning Joint Program of Liaoning Province(Applied Basic Research Project,No.2023JH2/101700054).
文摘The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.
