Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands,primarily due to insufficient water resources and inadequate irrigation facilities.Consequently,combined salinit...Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands,primarily due to insufficient water resources and inadequate irrigation facilities.Consequently,combined salinity-drought stress poses a major threat to rice production.In this study,two salinity levels(NS,non-salinity;HS,high salinity)along with three drought treatments(CC,control condition;DJ,drought stress imposed at jointing;DH,drought stress imposed at heading)were performed to investigate their combined influences on leaf photosynthetic characteristics,biomass accumulation,and rice yield formation.Salinity,drought,and their combination led to a shortened growth period from heading to maturity,resulting in a reduced overall growth duration.Grain yield was reduced under both salinity and drought stress,with a more substantial reduction under the combined salinity-drought stress.The combined stress imposed at heading caused greater yield losses in rice compared with the stress imposed at jointing.Additionally,the combined salinity-drought stress induced greater decreases in shoot biomass accumulation from heading to maturity,as well as in shoot biomass and nonstructural carbohydrate(NSC)content in the stem at heading and maturity.However,it increased the harvest index and NSC remobilization reserve.Salinity and drought reduced the leaf area index and SPAD value of flag leaves and weakened the leaf photosynthetic characteristics as indicated by lower photosynthetic rates,transpiration rates,and stomatal conductance.These reductions were more pronounced under the combined stress.Salinity,drought,and especially their combination,decreased the activities of ascorbate peroxidase,catalase,and superoxide dismutase,while increasing the contents of malondialdehyde,hydrogen peroxide,and superoxide radical.Our results indicated a more significant yield loss in rice when subjected to combined salinity-drought stress.The individual and combined stresses of salinity and drought diminished antioxidant enzyme activities,inhibited leaf photosynthetic functions,accelerated leaf senescence,and subsequently lowered assimilate accumulation and grain yield.展开更多
The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters.In this study,we carried out biaxial compression tests on cubic granite samples of 100 mm in side le...The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters.In this study,we carried out biaxial compression tests on cubic granite samples of 100 mm in side length with different intermediate principal stress gradients in combination with acoustic emission(AE)technique.Results show that the fracture characteristics of granite samples change from‘sudden and aggregated’to‘continuous and dispersed’with the increase of the intermediate principal stress.The effect of increasing intermediate principal stress on AE amplitude is not significant,but it increases the proportions of high-frequency AE signals and shear cracks,which in turn increases the possibility of unstable rock failure.The difference of stress in different directions causes the anisotropy of rock fracture and thus leads to the obvious anisotropic characteristics of wave velocity variations.The anisotropy of wave velocity variations with stress difference is probable to identify the principal stress directions.The AE characteristics and the anisotropy of wave velocity variations of granite under two-dimensional stress are not only beneficial complements for rock fracture characteristic and principal stress direction identification,but also can provide a new analysis method for stability monitoring in practical rock engineering.展开更多
The hydraulic actuator,known as the"muscle"of military aircraft,is responsible for flight attitude adjustment,trajectory control,braking turn,landing gear retracting and other actions,which directly affect i...The hydraulic actuator,known as the"muscle"of military aircraft,is responsible for flight attitude adjustment,trajectory control,braking turn,landing gear retracting and other actions,which directly affect its flight efficiency and safety.However,the sealing assembly often has the situation of over-aberrant aperture fit clearance or critical over-aberrant clearance,which increases the failure probability and degree of movable seal failure,and directly affects the flight efficiency and safety of military aircraft.In this paper,the simulation model of hydraulic actuator seal combination is established by ANSYS software,and the sealing principle is described.The change curve of contact width and contact pressure of combination seal under the action of high-pressure fluid is drawn.The effects of different oil pressure,fit clearance and other parameters on the sealing performance are analyzed.Finally,the accelerated life test of sliding seal components is carried out on the hydraulic actuator accelerated life test rig,and the surface morphology is compared and analyzed.The research shows that the O-ring is the main sealing element and the role of the check ring is to protect and support the O-ring to prevent damage caused by squeezing into the fit clearance,so the check ring bears a large load and is prone to shear failure.Excessive fit clearance is the main factor affecting the damage of the check ring,and the damage parts are mainly concentrated at the edge of the sealing surface.This paper provides a theoretical basis for the design of hydraulic actuator and the improvement of sealing performance.展开更多
To investigate the stress response characteristics and shear stress transfer mechanism of BFRP(basalt fiber reinforced plastics)anchors under rainfall conditions and to explore the reinforcement effect of BFRP anchors...To investigate the stress response characteristics and shear stress transfer mechanism of BFRP(basalt fiber reinforced plastics)anchors under rainfall conditions and to explore the reinforcement effect of BFRP anchors,a comparative indoor physical model test was conducted in this study using loess mudstone slope as a typical case,and multi-attribute response data,such as slope displacement,BFRP anchor strain and axial force,were obtained.Based on the variation law of slope displacement,it can be concluded that the deformation displacement of the slope on the side reinforced by BFRP anchors is smaller than that of slopes reinforced with steel anchors;the bearing capacity of BFRP anchor is given priority in time,and the anchoring effect of BFRP anchor at the top of the slope is given priority,and the axial force value of anchor is characterized by a surface amplification effect in space;the axial force is higher around the anchor head and tends to decay as a negative exponential function as the anchor extends in the direction of the interior of the slope;the shear stress of BFRP anchor and anchorage body are unevenly distributed along the axial direction,with the maximum value occurring in the free section near the slope surface and decreases as the BFRP anchor extends towards the interior of the slope.These results can provide a theoretical basis for the optimal design of BFRP anchors.展开更多
To investigate the dynamic characteristics and long-term dynamic stability of the new subgrade structure of medium-low-speed(MLS)maglevs,cyclic vibration tests were performed under natural and rainfall conditions,and ...To investigate the dynamic characteristics and long-term dynamic stability of the new subgrade structure of medium-low-speed(MLS)maglevs,cyclic vibration tests were performed under natural and rainfall conditions,and the dynamic response of the subgrade structure was monitored.The dynamic response attenuation characteristics along the depth direction of the subgrade were compared,and the distribution characteristics of the dynamic stress on the surface of the subgrade along the longitudinal direction of the line were analyzed.The critical dynamic stress and cumulative deformation were used as indicators to evaluate the long-term dynamic stability of the subgrade.Results show that water has a certain effect on the dynamic characteristics of the subgrade,and the dynamic stress and acceleration increase with the water content.With the dowel steel structure set between the rail-bearing beams,stress concentration at the end of the loaded beam can be prevented,and the diffusion distance of the dynamic stress along the longitudinal direction increases.The dynamic stress measured in the subgrade bed range is less than 1/5 of the critical dynamic stress.The postconstruction settlement of the subgrade after similarity ratio conversion is 3.94 mm and 7.72 mm under natural and rainfall conditions,respectively,and both values are less than the 30 mm limit,indicating that the MLS maglev subgrade structure has good long-term dynamic stability.展开更多
Additional stress formed by postconstruction buildings in loess-filling areas affects water infiltration in soil and causes soil deformation.To investigate this effect,under constant water head,vertical infiltration t...Additional stress formed by postconstruction buildings in loess-filling areas affects water infiltration in soil and causes soil deformation.To investigate this effect,under constant water head,vertical infiltration tests on compacted loess with two initial dry densities for different applied vertical stresses were developed using vertical stresscontrollable one-dimensional soil columns.The timehistory curves of vertical deformation,wetting front depth,cumulative infiltration depth,volumetric water content(VWC)and suction were measured,and the soil-water characteristic curves(SWCCs)were determined.The results showed that:(1)the infiltration ability of the soil column weakens with increasing applied vertical stress and initial dry density;(2)vertical deformation increases rapidly at first and then tends to be stable slowly at the consolidation and wetting-induced deformation stage,and is positively correlated with applied vertical stress and is negatively correlated with initial dry density.The stability time of wetting-induced deformation and the corresponding wetting front depth increase with the increase of applied vertical stress,while they decrease obviously when initial dry density increases;(3)the influence of applied vertical stress on soilwater characteristics in soil columns with various initial dry densities is related to the deformation depth of soil column.The VG(Van Genuchten)model is suitable for fitting the SWCCs at different monitoring positions.A normalized SWCC model introducing the applied vertical stress was proposed for each initial dry density using the mathematical relationship between the fitting parameters and the applied vertical stress.展开更多
Tree peony(Paeonia suffruticosa Andr.)is a traditional Chinese flower,which prefers cool weather.However,high temperature in summer in the middle and lower reaches of the Yangtze River restricts its growth and develop...Tree peony(Paeonia suffruticosa Andr.)is a traditional Chinese flower,which prefers cool weather.However,high temperature in summer in the middle and lower reaches of the Yangtze River restricts its growth and development.In this study,osmotic regulation,antioxidant enzyme activities,and photosynthetic characteristics of tree peony in response to high-temperature stress were investigated.The results showed that high-temperature stress had destroyed the cell membrane,manifested as the increased relative electrical conductivity and malondialdehyde content.Moreover,high-temperature stress led to excessive accumulation of reactive oxygen species,thereby,activating antioxidant enzyme activities.Also,photosynthetic parameters and chlorophyll fluorescence parameters directly reflected the damage to the photosystem II reflection center under high-temperature stress.In addition,high-temperature stress led to stomatal closure and chloroplast damage.This study revealed the physiological responses of tree peony to high-temperature stress,laying a foundation for the promotion of tree peony in high-temperature areas and the improvement of high-temperature resistance.展开更多
[Objectives]To investigate the effects of different temperature and starvation stress on the expression of AaHsp90 and reveal the molecular mechanism of adaptation to environment in Antheraea assama.[Methods]Taking th...[Objectives]To investigate the effects of different temperature and starvation stress on the expression of AaHsp90 and reveal the molecular mechanism of adaptation to environment in Antheraea assama.[Methods]Taking the normal feeding group at 26℃as the control,the expression change of AaHsp90 was detected by real-time PCR in midgut,fat body and hemlymph after high temperature stress at 38℃,low temperature stress at 4℃and starvation stress separately for different time on the third day of the fifth larvae.[Results]The expression of AaHsp90 in midgut,fat body and hemlymph of Antheraea assama were increased obviously at first and then decreased sharply with the prolongation of treatment time at 38℃.There has a certain inhibitory effect on the expression of AaHsp90 in midgut,fat body and hemolymph after treatment with 4℃for different time.After treatment with starvation,the AaHsp90 expression were increased at 12 and 18 h and decreased sharply at 24 h in midgut,fat body and hemolymph of A.assama.[Conclusions]Comprehensive analysis showed that high temperature and starvation stress can induce the expression of AaHsp90,while low temperature stress mainly suppressed its expression.It was suggested that the AaHsp90 protein may play an important role in the process of adaptation to high temperature and starvation stress in A.assama.展开更多
As global temperature rise,the threat of heat stress to rapeseed production is becoming more obvious.Exploring the response characteristics of two important biological pathways,oil accumulation and photosynthesis,to h...As global temperature rise,the threat of heat stress to rapeseed production is becoming more obvious.Exploring the response characteristics of two important biological pathways,oil accumulation and photosynthesis,to heat stress during B.napus seed filling is helpful in the genetic improvement of heat-tolerant rapeseed.The effects of heat stress on seed oil accumulation and chlorophyll fluorescence characteristics of 29 B.napus germplasms with different oil content and environmental sensitivity,including 6 rapeseed varieties which exhibited environmentsensitive/insensitive and with high,medium or low oil content,were tested by whole plant heat stress or the in vitro silique culture system.Both assay exhibited similar trend on oil content of the rapeseed germplasms.The heat effect on the chlorophyll fluorescence kinetic parameters F_(v)/F_(m),ETR and Y(Ⅱ)were also consistent.Heat stress significantly decreased oil content,although there was abundant genetic variation on heat tolerance among the genotypes.Correlation analysis showed that the decrease rate of F_(v)/F_(m) of silique heat-stressed B.napus developing seed was positive correlative to the decrease rate of mature seed oil content of the whole plant heat-stressed rapeseed(R=0.9214,P-value<0.01).Overall,the results indicated that heat stress inhibited oil accumulation and photosynthesis in B.napus developing seed.The decrease rate of chlorophyll fluorescence parameter F_(v)/F_(m) of heat-stressed developing seed could be used as the index of heat tolerant rapeseed identification.Further,two heat insensitive rapeseed varieties with high oil content were identified.展开更多
Syringa species not only have good ornamental properties but also play an important role in the landscaping and environmental purification of cities.To investigate the chilling stress resistance of Syringa oblata Lind...Syringa species not only have good ornamental properties but also play an important role in the landscaping and environmental purification of cities.To investigate the chilling stress resistance of Syringa oblata Lindl.and Syringa reticulata var.mandshurica and provide theoretical grounds for the practical cultivation of Syringa species,in vitro leaves were used to study photosynthetic gas exchange parameters and chlorophyll fluorescence parameters.After nine hours of chilling,decreasing rates of net photosynthesis,stomatal conductance,and transpiration in S.reticulata var.mandshurica leaves were significantly greater than that of the S.oblata,while intercellular CO2 concentrations in S.oblata leaves were higher than those in S.reticulata var.mandshurica.The quantum yield of PSII reaction center(APSII)declined in S.reticulata and light capture efficiency(Fv 0/Fm 0)was stable.However,reduction percentages of Fv 0/Fm 0,APSII,and Fv/Fm in S.oblata were significant higher than those of S.reticulata var.mandshurica.After nine hours of chilling,the relative variable fluorescence of VJ and VI of S.oblata increased and the increasing rate of VJ was greater than VI.In contrast,the change of VJ and VI in S.reticulata var.mandshurica leaves was relatively small.This suggests that chilling primarily damaged the electron transport process of QA to QB at the receptor site of the PSII reaction center.Photosynthetic capacity of S.oblata was more sensitive to chilling stress compared to S.reticulate var.mandshurica,which the limitations were mainly due to non-stomatal factors such as the decrease in electron transport efficiency,activity in the PSII reaction center,and the destruction of the photodamage defense system.展开更多
Two Job’s tears cultivars, yy18-1 (high resistance to drought stress) and yy12-7 (susceptible to drought stress) were used to investigate the responses of seed germination, root and seedling growth, and seedling anti...Two Job’s tears cultivars, yy18-1 (high resistance to drought stress) and yy12-7 (susceptible to drought stress) were used to investigate the responses of seed germination, root and seedling growth, and seedling antioxidant characteristics to drought stress simulated by polyethylene glycol (PEG) 6000 solutions with 0, -0.05, -0.1, -0.15, and -0.2 MPa osmotic potentials. The results showed that the germination energy, germination rate, germination index, root and seedling lengths, root and seedling diameters, root and seedling fresh masses, root and seedling dry masses, and seedling relative water content (RWC) decreased with the decrease of the osmotic potential of PEG 6000 solution. The contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline in seedling increased with the decrease of the osmotic potential of PEG 6000 solution. The activities of peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in seedling increased and then decreased with the decrease of osmotic potential of PEG 6000 solution. -0.1 MPa was the optimal osmotic potential of PEG 6000 solution simulated drought stress at germination stage for Job’s tears. The proline content and activities of POD and CAT were important mechanisms for the maintenance of drought resistance in Job’s tears seedling.展开更多
Many of the abandoned mining and industrial land in villages and towns are seriously polluted by heavy metals in China,it is necessary for sustainable development to adopt efficient and economical ways to restore the ...Many of the abandoned mining and industrial land in villages and towns are seriously polluted by heavy metals in China,it is necessary for sustainable development to adopt efficient and economical ways to restore the ecology of abandoned mining and industrial land.Pollution level of topsoil contaminated with metallurgical slag from nonferrous metal smelting waste site in Baoding,North China and the heavy metals(HMs)accumulation behavior of Bidens pilosa L.(B.pilosa,native pioneer plant)were studied.Two selected study sites were mainly contaminated by As(270~434 mg/kg),Cd(63~95 mg/kg),Pb(5496~24504 mg/kg)and Zn(4500~21300 mg/kg),which exceed the national standard severely.Investigation of multi-metal accumulation in different parts of B.pilosa indicated that the absorption of toxic metals varied by types,concentration and species of HMs under stress conditions,soil property and plant tissues.The results showed that B.pilosa had excellent ability to accumulate HMs under different HMs stress condition,with the highest accumulation concentration of 85 mg/kg for As,380 mg/kg for Cd,4000 mg/kg for Pb,and 7500 mg/kg for Zn in roots under experimental conditions,respectively.The growth trend of B.pilosa declined with the increase of HMs stress concentration in tested soils.HMs stress led to different degrees of plant toxicity and obstruction of physiological metabolism.Among the plant physiological index,Chla and ChlT decreased 28.0%and 28.1%,37.3%and 35.5%under different stress treatments,respectively.Indicators related to physiological metabolic strength and stress resistance of plant,such as MDA(Malondiadehyde),CAT(catalase),SOD(superoxide dismutase)and SP(soluble protein),all increased with the increase of HMs stress concentration.展开更多
To characterize long-term nonprogressors (LTNPs) and viremia controllers (VCs), infected with HIV-1 through contaminated blood donation or transfusion between 1992 and 1996 in Henan, China. LTNPs and VCs were defi...To characterize long-term nonprogressors (LTNPs) and viremia controllers (VCs), infected with HIV-1 through contaminated blood donation or transfusion between 1992 and 1996 in Henan, China. LTNPs and VCs were defined by CD4+T lymphocyte (CD4) count and viral load (VL). Of 29,294 patients infected with HIV-1 via contaminated blood donation or transfusion that had conducted for more than 20 years, 92 were LTNPs/VCs. There were 70 LTNPs (0.24%), 43 VCs (0.15%), and 48 LTNPs+VCs- (0.16%).展开更多
The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve...The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve (SWCC) that represents the relationship between matric suction and moisture content. In this study, a full-automatic rapid stress-dependent SWCC pressure-plate extractor was developed. Then, the influences of overburden stress and degree of compaction on the SWCC of subgrade soil such as high liquid limit silt (MH) and low liquid limit clay (CL) were analyzed. Accordingly, a new model taking into account the influences of overburden stress and degree of compaction based on the well-known Van Genuchten (VG) SWCC fitting model was presented and validated. The results show that with the increase of the degree of compaction and overburden stress, the saturated moisture content of subgrade soil decreases, while the air-entry value increases and the transition section curve becomes flat. The influences of the degree of compaction and overburden stress on the SWCC of MH is greater than that of CL. Meanwhile, there was a satisfactory agreement between the prediction and measurement, indicating a good performance of the new model for predicting the SWCC.展开更多
To better understand the stress-corrosion behavior of friction stir welding(FSW),the effects of the microstructure on the stress-corrosion behavior of the FSW in a 2198-T34 aluminum alloy were investigated.The experim...To better understand the stress-corrosion behavior of friction stir welding(FSW),the effects of the microstructure on the stress-corrosion behavior of the FSW in a 2198-T34 aluminum alloy were investigated.The experimental results show that the low-angle grain boundary(LABs)of the stir zone(SZ)of FSW is significantly less than that of heated affected zone(HAZ),thermo-mechanically affected zone(TMAZ),and parent materials(PM),but the grain boundary precipitates(GBPs)T1(Al2CuLi)were less,which has a slight effect on the stress corrosion.The dislocation density in SZ was greater than that in other regions.The residual stress in SZ was+67 MPa,which is greater than that in the TMAZ.The residual stress in the HAZ and PM is-8 MPa and-32 MPa,respectively,and both compressive stresses.The corrosion potential in SZ is obviously less than that in other regions.However,micro-cracks were formed in the SZ at low strain rate,which indicates that the grain boundary characters and GBPs have no significant effect on the crack initiation in the stress-corrosion process of the AA2198-T34.Nevertheless,the residual tensile stress has significant effect on the crack initiation during the stress-corrosion process.展开更多
With Hemerocallis fulva‘Golden Doll'as an experimental material,the effects of different concentrations of neutral salt( NaCl) and alkaline salt( NaHCO3) stresses on photosynthesis and chlorophyll fluorescence ch...With Hemerocallis fulva‘Golden Doll'as an experimental material,the effects of different concentrations of neutral salt( NaCl) and alkaline salt( NaHCO3) stresses on photosynthesis and chlorophyll fluorescence characteristics in H. fulva seedlings were studied. The results showed that salt stress treatment significantly reduced the photosynthetic capacity of H. fulva. Under the NaCl and NaHCO3 stresses,the photosynthetic characteristics and chlorophyll fluorescence parameters of H. fulva seedlings were basically the same,but the photosynthetic characteristics and chlorophyll fluorescence parameter values of H. fulva seedlings were significantly different under different salt types and salt concentrations. With the extension of days of salt stress and the increase of salt concentration,the initial fluorescence yield( Fo) and non-photochemical quenching coefficient( NPQ) increased;the maximum fluorescence yield( Fm),maximum photochemical efficiency( Fv/Fm),PSII actual photosynthetic quantum yield( Y) and apparent quantum efficiency( AQY) all showed a downward trend;and moreover,with the extension of days of salt stress and the increase of salt concentration,the net photosynthetic rate( Pn) decreased and the intercellular CO2 concentration( Ci) increased. It was speculated that under salt stress,the photosynthetic characteristics of H. fulva leaves were inhibited. On the one hand,the non-stomatal limiting factor,i. e.,the chlorophyll content decreased,which led to the inhibition of photosynthetic characteristics. On the other hand,the decrease in the photosynthetic performance of mesophyll cells led to a decrease in the net photosynthetic rate of H. fulva. The changes of photosynthetic characteristics and chlorophyll fluorescence parameters in H. fulva caused by salt stress were closely related to the types of salts and salt concentration. High salt stress significantly inhibited the photosynthetic capacity of H. fulva‘Golden Doll',and the effect of NaHCO3 on H. fulva seedlings was significantly greater than that of NaCl.展开更多
To gain insight into the flow mechanisms and stress sensitivity for fractured-vuggy reservoirs,several core models with different structural characteristics were designed and fabricated to investigate the impact of ef...To gain insight into the flow mechanisms and stress sensitivity for fractured-vuggy reservoirs,several core models with different structural characteristics were designed and fabricated to investigate the impact of effective stress on permeability for carbonate fractured-vuggy rocks(CFVR).It shows that the permeability performance curves under different pore and confining pressures(i.e.altered stress conditions)for the fractured core models and the vuggy core models have similar change patterns.The ranges of permeability variation are significantly wider at high pore pressures,indicating that permeability reduction is the most significant during the early stage of development for fractured-vuggy reservoirs.Since each obtained effective stress coefficient for permeability(ESCP)varies with the changes in confining pressure and pore pressure,the effective stresses for permeability of four representative CFVR show obvious nonlinear characteristics,and the variation ranges of ESCP are all between 0 and 1.Meanwhile,a comprehensive ESCP mathematical model considering triple media,including matrix pores,fractures,and dissolved vugs,was proposed.It is proved theoretically that the ESCP of CFVR generally varies between 0 and 1.Additionally,the regression results showed that the power model ranked highest among the four empirical models mainly applied in stress sensitivity characterization,followed by the logarithmic model,exponential model,and binomial model.The concept of“permeability decline rate”was introduced to better evaluate the stress sensitivity performance for CFVR,in which the one-fracture rock is the strongest,followed by the fracture-vug rock and two-horizontalfracture rock;the through-hole rock is the weakest.In general,this study provides a theoretical basis to guide the design of development and adjustment programs for carbonate fractured-vuggy reservoirs.展开更多
The stress,strain as well as resistivity of coal during uniaxial compression process were tested based on self-built real-time testing system of loaded coal resistivity.Furthermore,the coal resistivity regularity and ...The stress,strain as well as resistivity of coal during uniaxial compression process were tested based on self-built real-time testing system of loaded coal resistivity.Furthermore,the coal resistivity regularity and mechanism were analyzed at different stages of complete stress-strain process,which includes the two kinds of coal body with typical conductive characteristics.The results indicate that coal resistivity with different conductive characteristics has different change rules in complete stress-strain process.It is mainly represented at the densification and flexibility phases before dilatation occurs.The variation of resistivity can be divided into two kinds,named down and up.Dilatation of coal samples occurred between 66%σ_(max) and 87%σ_(max).Because of dilatation,coal resistivity involves sudden change.The overall representation is shifting from reducing into improving or from slow improving into accelerated improving.Thus,coal resistivity always shows an increasing tendency at the plastic stage.After peak stress,coal body enters into failure stage.The expanding and communicating of macro fracture causes further improvement of coal resistivity.The maximum value of resistivity rangeability named λ reached 3.49.Through making real-time monitoring on coal resistivity,variation rules of resistivity can be deemed as precursory information so as to reflect the dilatation and sudden change before coal body reaches buckling failure,which can provide a new technological means for forecasting the dynamic disaster of coal petrography.展开更多
The microscopic and ultrastructural characteristics of mesophyll cells in flag leaves of two rice lines (a thermo-sensitive line 4628 and a thermo-resistant line 996) under high temperature stress (37°C during 8:...The microscopic and ultrastructural characteristics of mesophyll cells in flag leaves of two rice lines (a thermo-sensitive line 4628 and a thermo-resistant line 996) under high temperature stress (37°C during 8:00-17:00 and 30°C during 17:00-8:00) were investigated using an optical and a transmission electron microscopy. The membrane permeability and malondialdehyde content increased under the high temperature stress, and the increase of both variables was greater in the line 4628 than in the line 996. Under the high temperature stress, the line 996 showed tightly arranged mesophyll cells in flag leaves, fully developed vascular bundles and some closed stomata, whereas the line 4628 suffered from injury because of undeveloped vascular bundles, loosely arranged mesophyll cells and opened stomata. The mesophyll cells in flag leaves of the line 4628 were severely damaged under the high temperature stress, i.e. the chloroplast envelope became blurred, the grana thylakoid layer was arranged loosely and irregularly, the stroma layer disappeared, many osmiophilic granules appeared within the chloroplast, the outer membrane of mitochondria and the nucleus disintegrated and became blurred, the nucleolus disappeared, and much fibrillar-granular materials appeared within the nucleus. In contrast, the mesophyll cells in flag leaves of the line 996 maintained an intact ultrastructure under the high temperature stress. From these results, it is suggested that the ultrastructural modification of the cell membrane system is the primary plant response to high temperature stress and can be used as an index to evaluate the crop heat tolerance.展开更多
Using the finite element method, this paper investigates lateral stress-induced propagation characteristics in a photonic crystal fibre of hexagonal symmetry. The results of simulation show the strong stress dependenc...Using the finite element method, this paper investigates lateral stress-induced propagation characteristics in a photonic crystal fibre of hexagonal symmetry. The results of simulation show the strong stress dependence of effective index of the fundamental guided mode, phase modal birefringence and confinement loss. It also finds that the contribution of the geometrical effect that is related only to deformation of the photonic crystal fibre and the stress-related contribution to phase modal birefringence and confinement loss are entirely different. Furthermore, polarization-dependent stress sensitivity of confinement loss is proposed in this paper.展开更多
基金financed by the National Key Research and Development Program,China(Grant Nos.2022YFE0113400 and 2022YFD1500402)National Natural Science Foundation of China(Grant No.32001466)+3 种基金Scientific and Technological Innovation Fund of Carbon Emissions Peak and Neutrality of Jiangsu Provincial Department of Science and Technology,China(Grant Nos.BE2022304 and BE2022305)Joints Funds of the National Natural Science Foundation of China(Grant No.U20A2022)Postdoctoral Research Foundation of China(Grant No.2020M671628)the Priority Academic Program Development of Jiangsu Higher Education Institutions,China.
文摘Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands,primarily due to insufficient water resources and inadequate irrigation facilities.Consequently,combined salinity-drought stress poses a major threat to rice production.In this study,two salinity levels(NS,non-salinity;HS,high salinity)along with three drought treatments(CC,control condition;DJ,drought stress imposed at jointing;DH,drought stress imposed at heading)were performed to investigate their combined influences on leaf photosynthetic characteristics,biomass accumulation,and rice yield formation.Salinity,drought,and their combination led to a shortened growth period from heading to maturity,resulting in a reduced overall growth duration.Grain yield was reduced under both salinity and drought stress,with a more substantial reduction under the combined salinity-drought stress.The combined stress imposed at heading caused greater yield losses in rice compared with the stress imposed at jointing.Additionally,the combined salinity-drought stress induced greater decreases in shoot biomass accumulation from heading to maturity,as well as in shoot biomass and nonstructural carbohydrate(NSC)content in the stem at heading and maturity.However,it increased the harvest index and NSC remobilization reserve.Salinity and drought reduced the leaf area index and SPAD value of flag leaves and weakened the leaf photosynthetic characteristics as indicated by lower photosynthetic rates,transpiration rates,and stomatal conductance.These reductions were more pronounced under the combined stress.Salinity,drought,and especially their combination,decreased the activities of ascorbate peroxidase,catalase,and superoxide dismutase,while increasing the contents of malondialdehyde,hydrogen peroxide,and superoxide radical.Our results indicated a more significant yield loss in rice when subjected to combined salinity-drought stress.The individual and combined stresses of salinity and drought diminished antioxidant enzyme activities,inhibited leaf photosynthetic functions,accelerated leaf senescence,and subsequently lowered assimilate accumulation and grain yield.
基金This work was financially supported by the National Key Research and Development Program of China(Grant No.2021YFC2900500)the International(Regional)Cooperation and Exchange Program of National Natural Science Foundation of China(Grant No.52161135301)the Special Fund for Basic Scientific Research Operations in Universities(Grant No.2282020cxqd055).
文摘The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters.In this study,we carried out biaxial compression tests on cubic granite samples of 100 mm in side length with different intermediate principal stress gradients in combination with acoustic emission(AE)technique.Results show that the fracture characteristics of granite samples change from‘sudden and aggregated’to‘continuous and dispersed’with the increase of the intermediate principal stress.The effect of increasing intermediate principal stress on AE amplitude is not significant,but it increases the proportions of high-frequency AE signals and shear cracks,which in turn increases the possibility of unstable rock failure.The difference of stress in different directions causes the anisotropy of rock fracture and thus leads to the obvious anisotropic characteristics of wave velocity variations.The anisotropy of wave velocity variations with stress difference is probable to identify the principal stress directions.The AE characteristics and the anisotropy of wave velocity variations of granite under two-dimensional stress are not only beneficial complements for rock fracture characteristic and principal stress direction identification,but also can provide a new analysis method for stability monitoring in practical rock engineering.
基金the qualification of school-enterprise cooperation project,the project name:"Failure Mechanism Analysis and life Prediction of Hydraulic actuator sliding seal Assembly",funded by"Shijiazhuang Haishan Industrial Development Corporation",project number(AF21E20211158).
文摘The hydraulic actuator,known as the"muscle"of military aircraft,is responsible for flight attitude adjustment,trajectory control,braking turn,landing gear retracting and other actions,which directly affect its flight efficiency and safety.However,the sealing assembly often has the situation of over-aberrant aperture fit clearance or critical over-aberrant clearance,which increases the failure probability and degree of movable seal failure,and directly affects the flight efficiency and safety of military aircraft.In this paper,the simulation model of hydraulic actuator seal combination is established by ANSYS software,and the sealing principle is described.The change curve of contact width and contact pressure of combination seal under the action of high-pressure fluid is drawn.The effects of different oil pressure,fit clearance and other parameters on the sealing performance are analyzed.Finally,the accelerated life test of sliding seal components is carried out on the hydraulic actuator accelerated life test rig,and the surface morphology is compared and analyzed.The research shows that the O-ring is the main sealing element and the role of the check ring is to protect and support the O-ring to prevent damage caused by squeezing into the fit clearance,so the check ring bears a large load and is prone to shear failure.Excessive fit clearance is the main factor affecting the damage of the check ring,and the damage parts are mainly concentrated at the edge of the sealing surface.This paper provides a theoretical basis for the design of hydraulic actuator and the improvement of sealing performance.
基金the financial support by the National Key R&D Program of China(No.2018YFC1504901)Science and technology development project of China Railway 11th Bureau Group Co.,LTD(20210601)+4 种基金Science and technology development project of China Railway Lanzhou Bureau Group Co.,LTD(2021046-2)Science and technology program of Gansu Province(Grant No.21JR7RA739)Science and Technology Development Project of China Railway Research Institute Co.Ltd(2017-KJ008-Z008-XB)Science and technology development project of China Railway Ninth Bureau Group Co.,Ltd(DLF-ML-JSFW-202109)The Science and Technology Foundation of Guizhou Province(NO.ZK[2022]Key018)。
文摘To investigate the stress response characteristics and shear stress transfer mechanism of BFRP(basalt fiber reinforced plastics)anchors under rainfall conditions and to explore the reinforcement effect of BFRP anchors,a comparative indoor physical model test was conducted in this study using loess mudstone slope as a typical case,and multi-attribute response data,such as slope displacement,BFRP anchor strain and axial force,were obtained.Based on the variation law of slope displacement,it can be concluded that the deformation displacement of the slope on the side reinforced by BFRP anchors is smaller than that of slopes reinforced with steel anchors;the bearing capacity of BFRP anchor is given priority in time,and the anchoring effect of BFRP anchor at the top of the slope is given priority,and the axial force value of anchor is characterized by a surface amplification effect in space;the axial force is higher around the anchor head and tends to decay as a negative exponential function as the anchor extends in the direction of the interior of the slope;the shear stress of BFRP anchor and anchorage body are unevenly distributed along the axial direction,with the maximum value occurring in the free section near the slope surface and decreases as the BFRP anchor extends towards the interior of the slope.These results can provide a theoretical basis for the optimal design of BFRP anchors.
基金supported by the 2018 Major Science and Technology Project of China Railway Construction Corporation Limited(No.2018-A01)the National Natural Science Foundation of China(No.51978588).
文摘To investigate the dynamic characteristics and long-term dynamic stability of the new subgrade structure of medium-low-speed(MLS)maglevs,cyclic vibration tests were performed under natural and rainfall conditions,and the dynamic response of the subgrade structure was monitored.The dynamic response attenuation characteristics along the depth direction of the subgrade were compared,and the distribution characteristics of the dynamic stress on the surface of the subgrade along the longitudinal direction of the line were analyzed.The critical dynamic stress and cumulative deformation were used as indicators to evaluate the long-term dynamic stability of the subgrade.Results show that water has a certain effect on the dynamic characteristics of the subgrade,and the dynamic stress and acceleration increase with the water content.With the dowel steel structure set between the rail-bearing beams,stress concentration at the end of the loaded beam can be prevented,and the diffusion distance of the dynamic stress along the longitudinal direction increases.The dynamic stress measured in the subgrade bed range is less than 1/5 of the critical dynamic stress.The postconstruction settlement of the subgrade after similarity ratio conversion is 3.94 mm and 7.72 mm under natural and rainfall conditions,respectively,and both values are less than the 30 mm limit,indicating that the MLS maglev subgrade structure has good long-term dynamic stability.
基金funded by the Fundamental Research Funds for the Central UniversitiesCHD(Grant No.300102262503)+2 种基金the Natural Science Basic Research Program of Shaanxi(Grants No.2022JM-167)the National Natural Science Foundation of China(Grant Nos.41790442,41772278,41877242,42072311)the Yan’an Science and Technology Plan Project(Grant No.2022SLSFGG-004)。
文摘Additional stress formed by postconstruction buildings in loess-filling areas affects water infiltration in soil and causes soil deformation.To investigate this effect,under constant water head,vertical infiltration tests on compacted loess with two initial dry densities for different applied vertical stresses were developed using vertical stresscontrollable one-dimensional soil columns.The timehistory curves of vertical deformation,wetting front depth,cumulative infiltration depth,volumetric water content(VWC)and suction were measured,and the soil-water characteristic curves(SWCCs)were determined.The results showed that:(1)the infiltration ability of the soil column weakens with increasing applied vertical stress and initial dry density;(2)vertical deformation increases rapidly at first and then tends to be stable slowly at the consolidation and wetting-induced deformation stage,and is positively correlated with applied vertical stress and is negatively correlated with initial dry density.The stability time of wetting-induced deformation and the corresponding wetting front depth increase with the increase of applied vertical stress,while they decrease obviously when initial dry density increases;(3)the influence of applied vertical stress on soilwater characteristics in soil columns with various initial dry densities is related to the deformation depth of soil column.The VG(Van Genuchten)model is suitable for fitting the SWCCs at different monitoring positions.A normalized SWCC model introducing the applied vertical stress was proposed for each initial dry density using the mathematical relationship between the fitting parameters and the applied vertical stress.
基金supported by Jiangsu Modern Agricultural Industrial Technology System(JATS[2022]489)Agricultural Science and Technology Independent Innovation Fund of Jiangsu Province(CX(22)3186)+1 种基金Policy Guidance Program of Jiangsu Province-Science and Technology Special Project of Northern Jiangsu Province(SZ-SQ2021041)the Qing Lan Project of Jiangsu Province and High-Level Talent Support Program of Yangzhou University.
文摘Tree peony(Paeonia suffruticosa Andr.)is a traditional Chinese flower,which prefers cool weather.However,high temperature in summer in the middle and lower reaches of the Yangtze River restricts its growth and development.In this study,osmotic regulation,antioxidant enzyme activities,and photosynthetic characteristics of tree peony in response to high-temperature stress were investigated.The results showed that high-temperature stress had destroyed the cell membrane,manifested as the increased relative electrical conductivity and malondialdehyde content.Moreover,high-temperature stress led to excessive accumulation of reactive oxygen species,thereby,activating antioxidant enzyme activities.Also,photosynthetic parameters and chlorophyll fluorescence parameters directly reflected the damage to the photosystem II reflection center under high-temperature stress.In addition,high-temperature stress led to stomatal closure and chloroplast damage.This study revealed the physiological responses of tree peony to high-temperature stress,laying a foundation for the promotion of tree peony in high-temperature areas and the improvement of high-temperature resistance.
基金Supported by Special Basic Cooperative Research Programs of Yunnan Provincial Undergraduate Universities Association (2021BA070001-070)Yunnan Fundamental Research Projects (202201AT070226).
文摘[Objectives]To investigate the effects of different temperature and starvation stress on the expression of AaHsp90 and reveal the molecular mechanism of adaptation to environment in Antheraea assama.[Methods]Taking the normal feeding group at 26℃as the control,the expression change of AaHsp90 was detected by real-time PCR in midgut,fat body and hemlymph after high temperature stress at 38℃,low temperature stress at 4℃and starvation stress separately for different time on the third day of the fifth larvae.[Results]The expression of AaHsp90 in midgut,fat body and hemlymph of Antheraea assama were increased obviously at first and then decreased sharply with the prolongation of treatment time at 38℃.There has a certain inhibitory effect on the expression of AaHsp90 in midgut,fat body and hemolymph after treatment with 4℃for different time.After treatment with starvation,the AaHsp90 expression were increased at 12 and 18 h and decreased sharply at 24 h in midgut,fat body and hemolymph of A.assama.[Conclusions]Comprehensive analysis showed that high temperature and starvation stress can induce the expression of AaHsp90,while low temperature stress mainly suppressed its expression.It was suggested that the AaHsp90 protein may play an important role in the process of adaptation to high temperature and starvation stress in A.assama.
基金funded by the Natural Science Foundation of Zhejiang Province(LY20C130006)the National Natural Science Foundation of China(32172018)the State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products(2010DS700124-ZZ1805).
文摘As global temperature rise,the threat of heat stress to rapeseed production is becoming more obvious.Exploring the response characteristics of two important biological pathways,oil accumulation and photosynthesis,to heat stress during B.napus seed filling is helpful in the genetic improvement of heat-tolerant rapeseed.The effects of heat stress on seed oil accumulation and chlorophyll fluorescence characteristics of 29 B.napus germplasms with different oil content and environmental sensitivity,including 6 rapeseed varieties which exhibited environmentsensitive/insensitive and with high,medium or low oil content,were tested by whole plant heat stress or the in vitro silique culture system.Both assay exhibited similar trend on oil content of the rapeseed germplasms.The heat effect on the chlorophyll fluorescence kinetic parameters F_(v)/F_(m),ETR and Y(Ⅱ)were also consistent.Heat stress significantly decreased oil content,although there was abundant genetic variation on heat tolerance among the genotypes.Correlation analysis showed that the decrease rate of F_(v)/F_(m) of silique heat-stressed B.napus developing seed was positive correlative to the decrease rate of mature seed oil content of the whole plant heat-stressed rapeseed(R=0.9214,P-value<0.01).Overall,the results indicated that heat stress inhibited oil accumulation and photosynthesis in B.napus developing seed.The decrease rate of chlorophyll fluorescence parameter F_(v)/F_(m) of heat-stressed developing seed could be used as the index of heat tolerant rapeseed identification.Further,two heat insensitive rapeseed varieties with high oil content were identified.
文摘Syringa species not only have good ornamental properties but also play an important role in the landscaping and environmental purification of cities.To investigate the chilling stress resistance of Syringa oblata Lindl.and Syringa reticulata var.mandshurica and provide theoretical grounds for the practical cultivation of Syringa species,in vitro leaves were used to study photosynthetic gas exchange parameters and chlorophyll fluorescence parameters.After nine hours of chilling,decreasing rates of net photosynthesis,stomatal conductance,and transpiration in S.reticulata var.mandshurica leaves were significantly greater than that of the S.oblata,while intercellular CO2 concentrations in S.oblata leaves were higher than those in S.reticulata var.mandshurica.The quantum yield of PSII reaction center(APSII)declined in S.reticulata and light capture efficiency(Fv 0/Fm 0)was stable.However,reduction percentages of Fv 0/Fm 0,APSII,and Fv/Fm in S.oblata were significant higher than those of S.reticulata var.mandshurica.After nine hours of chilling,the relative variable fluorescence of VJ and VI of S.oblata increased and the increasing rate of VJ was greater than VI.In contrast,the change of VJ and VI in S.reticulata var.mandshurica leaves was relatively small.This suggests that chilling primarily damaged the electron transport process of QA to QB at the receptor site of the PSII reaction center.Photosynthetic capacity of S.oblata was more sensitive to chilling stress compared to S.reticulate var.mandshurica,which the limitations were mainly due to non-stomatal factors such as the decrease in electron transport efficiency,activity in the PSII reaction center,and the destruction of the photodamage defense system.
文摘Two Job’s tears cultivars, yy18-1 (high resistance to drought stress) and yy12-7 (susceptible to drought stress) were used to investigate the responses of seed germination, root and seedling growth, and seedling antioxidant characteristics to drought stress simulated by polyethylene glycol (PEG) 6000 solutions with 0, -0.05, -0.1, -0.15, and -0.2 MPa osmotic potentials. The results showed that the germination energy, germination rate, germination index, root and seedling lengths, root and seedling diameters, root and seedling fresh masses, root and seedling dry masses, and seedling relative water content (RWC) decreased with the decrease of the osmotic potential of PEG 6000 solution. The contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline in seedling increased with the decrease of the osmotic potential of PEG 6000 solution. The activities of peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in seedling increased and then decreased with the decrease of osmotic potential of PEG 6000 solution. -0.1 MPa was the optimal osmotic potential of PEG 6000 solution simulated drought stress at germination stage for Job’s tears. The proline content and activities of POD and CAT were important mechanisms for the maintenance of drought resistance in Job’s tears seedling.
基金funded by National Natural Science Foundation(Grant No.42177236)Taishan Scholars Project Foundation(tsqn202211185)+1 种基金Guangdong Basic and Applied Basic Research Foundation(Grant No.2020A1515011077)Natural Science Foundation of Shandong Province(Grant No.ZR2020MD119)。
文摘Many of the abandoned mining and industrial land in villages and towns are seriously polluted by heavy metals in China,it is necessary for sustainable development to adopt efficient and economical ways to restore the ecology of abandoned mining and industrial land.Pollution level of topsoil contaminated with metallurgical slag from nonferrous metal smelting waste site in Baoding,North China and the heavy metals(HMs)accumulation behavior of Bidens pilosa L.(B.pilosa,native pioneer plant)were studied.Two selected study sites were mainly contaminated by As(270~434 mg/kg),Cd(63~95 mg/kg),Pb(5496~24504 mg/kg)and Zn(4500~21300 mg/kg),which exceed the national standard severely.Investigation of multi-metal accumulation in different parts of B.pilosa indicated that the absorption of toxic metals varied by types,concentration and species of HMs under stress conditions,soil property and plant tissues.The results showed that B.pilosa had excellent ability to accumulate HMs under different HMs stress condition,with the highest accumulation concentration of 85 mg/kg for As,380 mg/kg for Cd,4000 mg/kg for Pb,and 7500 mg/kg for Zn in roots under experimental conditions,respectively.The growth trend of B.pilosa declined with the increase of HMs stress concentration in tested soils.HMs stress led to different degrees of plant toxicity and obstruction of physiological metabolism.Among the plant physiological index,Chla and ChlT decreased 28.0%and 28.1%,37.3%and 35.5%under different stress treatments,respectively.Indicators related to physiological metabolic strength and stress resistance of plant,such as MDA(Malondiadehyde),CAT(catalase),SOD(superoxide dismutase)and SP(soluble protein),all increased with the increase of HMs stress concentration.
基金supported by grants from The National Key Science and Technology Projects on Major Infectious Disease Grant[2012ZX10001‐002 and 2017ZX10105009]Key Projects for Science and Technology Development of Henan Province[142102310076 and 162300410123]
文摘To characterize long-term nonprogressors (LTNPs) and viremia controllers (VCs), infected with HIV-1 through contaminated blood donation or transfusion between 1992 and 1996 in Henan, China. LTNPs and VCs were defined by CD4+T lymphocyte (CD4) count and viral load (VL). Of 29,294 patients infected with HIV-1 via contaminated blood donation or transfusion that had conducted for more than 20 years, 92 were LTNPs/VCs. There were 70 LTNPs (0.24%), 43 VCs (0.15%), and 48 LTNPs+VCs- (0.16%).
基金supported by the National Natural Science Foundation of China(Grant No.52208419)Science and Technology Innovation Program of Hunan Province,China(Grant No.2022RC1030)Project of Scientific Research of Hunan Provincial Department of Education,China(Grant No.21C0187).
文摘The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve (SWCC) that represents the relationship between matric suction and moisture content. In this study, a full-automatic rapid stress-dependent SWCC pressure-plate extractor was developed. Then, the influences of overburden stress and degree of compaction on the SWCC of subgrade soil such as high liquid limit silt (MH) and low liquid limit clay (CL) were analyzed. Accordingly, a new model taking into account the influences of overburden stress and degree of compaction based on the well-known Van Genuchten (VG) SWCC fitting model was presented and validated. The results show that with the increase of the degree of compaction and overburden stress, the saturated moisture content of subgrade soil decreases, while the air-entry value increases and the transition section curve becomes flat. The influences of the degree of compaction and overburden stress on the SWCC of MH is greater than that of CL. Meanwhile, there was a satisfactory agreement between the prediction and measurement, indicating a good performance of the new model for predicting the SWCC.
基金the National Natural Science Foundation of China(No.51771139)the Hunan Natural Science Foundation(No.2019JJ60062)。
文摘To better understand the stress-corrosion behavior of friction stir welding(FSW),the effects of the microstructure on the stress-corrosion behavior of the FSW in a 2198-T34 aluminum alloy were investigated.The experimental results show that the low-angle grain boundary(LABs)of the stir zone(SZ)of FSW is significantly less than that of heated affected zone(HAZ),thermo-mechanically affected zone(TMAZ),and parent materials(PM),but the grain boundary precipitates(GBPs)T1(Al2CuLi)were less,which has a slight effect on the stress corrosion.The dislocation density in SZ was greater than that in other regions.The residual stress in SZ was+67 MPa,which is greater than that in the TMAZ.The residual stress in the HAZ and PM is-8 MPa and-32 MPa,respectively,and both compressive stresses.The corrosion potential in SZ is obviously less than that in other regions.However,micro-cracks were formed in the SZ at low strain rate,which indicates that the grain boundary characters and GBPs have no significant effect on the crack initiation in the stress-corrosion process of the AA2198-T34.Nevertheless,the residual tensile stress has significant effect on the crack initiation during the stress-corrosion process.
基金Supported by Science and Technology Research Project of Institutions of Higher Education in Hebei Province (BJ2017102)Tangshan Normal University Doctoral Fund (2014A06)。
文摘With Hemerocallis fulva‘Golden Doll'as an experimental material,the effects of different concentrations of neutral salt( NaCl) and alkaline salt( NaHCO3) stresses on photosynthesis and chlorophyll fluorescence characteristics in H. fulva seedlings were studied. The results showed that salt stress treatment significantly reduced the photosynthetic capacity of H. fulva. Under the NaCl and NaHCO3 stresses,the photosynthetic characteristics and chlorophyll fluorescence parameters of H. fulva seedlings were basically the same,but the photosynthetic characteristics and chlorophyll fluorescence parameter values of H. fulva seedlings were significantly different under different salt types and salt concentrations. With the extension of days of salt stress and the increase of salt concentration,the initial fluorescence yield( Fo) and non-photochemical quenching coefficient( NPQ) increased;the maximum fluorescence yield( Fm),maximum photochemical efficiency( Fv/Fm),PSII actual photosynthetic quantum yield( Y) and apparent quantum efficiency( AQY) all showed a downward trend;and moreover,with the extension of days of salt stress and the increase of salt concentration,the net photosynthetic rate( Pn) decreased and the intercellular CO2 concentration( Ci) increased. It was speculated that under salt stress,the photosynthetic characteristics of H. fulva leaves were inhibited. On the one hand,the non-stomatal limiting factor,i. e.,the chlorophyll content decreased,which led to the inhibition of photosynthetic characteristics. On the other hand,the decrease in the photosynthetic performance of mesophyll cells led to a decrease in the net photosynthetic rate of H. fulva. The changes of photosynthetic characteristics and chlorophyll fluorescence parameters in H. fulva caused by salt stress were closely related to the types of salts and salt concentration. High salt stress significantly inhibited the photosynthetic capacity of H. fulva‘Golden Doll',and the effect of NaHCO3 on H. fulva seedlings was significantly greater than that of NaCl.
基金This work was supported by the Joint Fund of NSFC for Enterprise Innovation and Development(Grant No.U19B6003-02-06)the National Natural Science Foundation of China(Grant No.51974331)+1 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20200525)The authors would like to sincerely acknowledge these funding programs for their financial support.Particularly,the support provided by the China Scholarship Council(CSC)during a visit of Ke Sun(File No.202106440065)to the University of Alberta is also sincerely acknowledged.
文摘To gain insight into the flow mechanisms and stress sensitivity for fractured-vuggy reservoirs,several core models with different structural characteristics were designed and fabricated to investigate the impact of effective stress on permeability for carbonate fractured-vuggy rocks(CFVR).It shows that the permeability performance curves under different pore and confining pressures(i.e.altered stress conditions)for the fractured core models and the vuggy core models have similar change patterns.The ranges of permeability variation are significantly wider at high pore pressures,indicating that permeability reduction is the most significant during the early stage of development for fractured-vuggy reservoirs.Since each obtained effective stress coefficient for permeability(ESCP)varies with the changes in confining pressure and pore pressure,the effective stresses for permeability of four representative CFVR show obvious nonlinear characteristics,and the variation ranges of ESCP are all between 0 and 1.Meanwhile,a comprehensive ESCP mathematical model considering triple media,including matrix pores,fractures,and dissolved vugs,was proposed.It is proved theoretically that the ESCP of CFVR generally varies between 0 and 1.Additionally,the regression results showed that the power model ranked highest among the four empirical models mainly applied in stress sensitivity characterization,followed by the logarithmic model,exponential model,and binomial model.The concept of“permeability decline rate”was introduced to better evaluate the stress sensitivity performance for CFVR,in which the one-fracture rock is the strongest,followed by the fracture-vug rock and two-horizontalfracture rock;the through-hole rock is the weakest.In general,this study provides a theoretical basis to guide the design of development and adjustment programs for carbonate fractured-vuggy reservoirs.
基金supported by the Research Project of Chinese Ministry of Education of China(No.113031A)the Basic Scientific Research Business Expenses of Central University of China (Nos.3142015001 and 3142015020)the New Century Talent Supporting Project by Education Ministry of China(No. NCET-11-0837)
文摘The stress,strain as well as resistivity of coal during uniaxial compression process were tested based on self-built real-time testing system of loaded coal resistivity.Furthermore,the coal resistivity regularity and mechanism were analyzed at different stages of complete stress-strain process,which includes the two kinds of coal body with typical conductive characteristics.The results indicate that coal resistivity with different conductive characteristics has different change rules in complete stress-strain process.It is mainly represented at the densification and flexibility phases before dilatation occurs.The variation of resistivity can be divided into two kinds,named down and up.Dilatation of coal samples occurred between 66%σ_(max) and 87%σ_(max).Because of dilatation,coal resistivity involves sudden change.The overall representation is shifting from reducing into improving or from slow improving into accelerated improving.Thus,coal resistivity always shows an increasing tendency at the plastic stage.After peak stress,coal body enters into failure stage.The expanding and communicating of macro fracture causes further improvement of coal resistivity.The maximum value of resistivity rangeability named λ reached 3.49.Through making real-time monitoring on coal resistivity,variation rules of resistivity can be deemed as precursory information so as to reflect the dilatation and sudden change before coal body reaches buckling failure,which can provide a new technological means for forecasting the dynamic disaster of coal petrography.
基金supported by the National Natural Science Foundation of China (Grant No. 30500315)the Agricultural Technological Results Transformation Item of Ministry of Agriculture, China (Grant No. 05EFN214300193)the Educational Foundation of Hunan Province, China (Grant No. 07C360)
文摘The microscopic and ultrastructural characteristics of mesophyll cells in flag leaves of two rice lines (a thermo-sensitive line 4628 and a thermo-resistant line 996) under high temperature stress (37°C during 8:00-17:00 and 30°C during 17:00-8:00) were investigated using an optical and a transmission electron microscopy. The membrane permeability and malondialdehyde content increased under the high temperature stress, and the increase of both variables was greater in the line 4628 than in the line 996. Under the high temperature stress, the line 996 showed tightly arranged mesophyll cells in flag leaves, fully developed vascular bundles and some closed stomata, whereas the line 4628 suffered from injury because of undeveloped vascular bundles, loosely arranged mesophyll cells and opened stomata. The mesophyll cells in flag leaves of the line 4628 were severely damaged under the high temperature stress, i.e. the chloroplast envelope became blurred, the grana thylakoid layer was arranged loosely and irregularly, the stroma layer disappeared, many osmiophilic granules appeared within the chloroplast, the outer membrane of mitochondria and the nucleus disintegrated and became blurred, the nucleolus disappeared, and much fibrillar-granular materials appeared within the nucleus. In contrast, the mesophyll cells in flag leaves of the line 996 maintained an intact ultrastructure under the high temperature stress. From these results, it is suggested that the ultrastructural modification of the cell membrane system is the primary plant response to high temperature stress and can be used as an index to evaluate the crop heat tolerance.
基金supported by the National Natural Science Foundation of China (Grant No 60644004)the State Key Development Program for Basic Research of China (Grant No 2003CB314901)
文摘Using the finite element method, this paper investigates lateral stress-induced propagation characteristics in a photonic crystal fibre of hexagonal symmetry. The results of simulation show the strong stress dependence of effective index of the fundamental guided mode, phase modal birefringence and confinement loss. It also finds that the contribution of the geometrical effect that is related only to deformation of the photonic crystal fibre and the stress-related contribution to phase modal birefringence and confinement loss are entirely different. Furthermore, polarization-dependent stress sensitivity of confinement loss is proposed in this paper.