Regime shifts from submersed macrophyte dominance to phytoplankton dominance have been widely reported in small-to medium-sized shallow lakes.However,alternative stable states in large shallow lakes(surface area>50...Regime shifts from submersed macrophyte dominance to phytoplankton dominance have been widely reported in small-to medium-sized shallow lakes.However,alternative stable states in large shallow lakes(surface area>500 km^(2))remain unconfirmed.To understand the alternative stable states and the main influencing factors of submersed macrophytes in large lakes,the ecosystem states from monitoring data from 1959 to 2019 in large shallow Taihu Lake(2338 km^(2)in average depth of 2.12 m)in China were examined.Changes in submersed macrophyte coverage(C_(Mac))and phytoplankton chlorophyll a(Chl a)in the time series and their relationships with environmental factors were analyzed.During the field investigation from August 2018 to May 2019,nutrients and Chl a showed obvious heterogeneity across the lake,being generally higher in the western and northern areas and lower in the southeast area,while C_(Mac)was only observed in the eastern areas,e.g.,East Taihu Lake,Xukou Bay,and Gonghu Bay.During the long-term monitoring from 1959 to 2019 in the Central Region,Meiliang Bay,and East Taihu Lake,Chl a increased significantly in the time series.C_(Mac)varied slightly among different subareas,always at low levels(<10%)in the Central Region and Meiliang Bay but at relatively high levels in East Taihu Lake(10%–90%).Frequency distributions of response variables had no multimodality except for C_(Mac)in East Taihu Lake,with two peaks between 15%and 20%and between 55%and 60%.A dual relationship was found between Chl a and total phosphorus(TP)in the areas with and without macrophytes,while C_(Mac)showed no relationship with TP,and submersed macrophytes did not flourish in the Central Region and Meiliang Bay even when TP was at very low levels(≈10 mg/m3).Taihu Lake had similar algal turbidity(TurbAlg)as small-to mediumsized lakes but generally presented with higher values of nonalgal turbidity(TurbNonAlg),as did their contribution to total turbidity as a percentage.This study suggested that large shallow Taihu Lake may have no alternative stable states,but more evidence is needed for East Taihu Lake,which was dominated by macrophytes,as it remains unknown whether hysteresis occurs between the processes of eutrophication and oligotrophication.Unfavorable conditions caused by wind might be the main reason due to the absence of submersed macrophytes in Taihu Lake.These results demonstrate that stricter nutrient control is needed to maintain a healthy state or to recover from a decayed state for large lakes.展开更多
Fractures are widely present in geomaterials of civil engineering and deep underground engineering.Given that geomaterials are usually brittle,the fractures can significantly affect the evaluation of underground engin...Fractures are widely present in geomaterials of civil engineering and deep underground engineering.Given that geomaterials are usually brittle,the fractures can significantly affect the evaluation of underground engineering construction safety and the early warning of rock failure.However,the crack initiation and propagation in brittle materials under composite loading remain unknown so far.In this study,a three-dimensional internal laser-engraved cracking technique was applied to produce internal cracks without causing damage to the surfaces.The uniaxial compression tests were performed on a brittle material with internal cracks to investigate the propagation of these internal cracks at different dip angles under compression and shear.The test results show that the wing crack propagation mainly occurs in the specimen with an inclined internal crack,which is a mixed-ModeⅠ–Ⅱ–Ⅲfracture;in contrast,ModeⅠfracture is present in the specimen with a vertical internal crack.The fractography characteristics of ModeⅢfracture display a lance-like pattern.The fracture mechanism in the brittle material under compression is that the internal wing cracks propagate to the ends of the whole sample and cause the final failure.The initial deflection angle of the wing crack is determined by the participation ratio of stress intensity factors KII to KI at the tip of the internal crack.展开更多
In this paper the spatio-temporal variation of vegetation cover in northwest China during the period of 1982-2006 and its driving factors were analyzed using GIMMS/NDVI data. The annual average NDVI was increased with...In this paper the spatio-temporal variation of vegetation cover in northwest China during the period of 1982-2006 and its driving factors were analyzed using GIMMS/NDVI data. The annual average NDVI was increased with a rate of 0.0005/a in northwest China and there was an obvious difference between regions. The trend line slopes of NDVI were higher than 0.0005 in the Tianshan Moutains and Altay Mountains of Xinjiang, the Qilian Mountains of Gansu and the eastern part of Qinghai, which indicated the vegetation cover was significantly increased in these areas. The trend line slopes of NDVI were lower than -0.0005 in the southern region of Qinghai, the border regions of Shaanxi and Ningxia, the parts of Gansu and Tarim Basin, Turpan and Tuoli in Xinjiang, which indicated the vegetation cover was declined in these areas. The NDVI of woodland, grassland and cultivated land had an ascending tendency during the study period. The study shows that the vegetation cover change was caused by both natural factors and human activities in northwest China. The natural vegetation change, such as forests was influenced by climate change, while human activities were the main reason to the change of planting vegetation. The changes of vegetation covers for different elevations, slopes and slope aspects were quite different. When the eleva- tion is exceeded to 4,000 m, the NDVI increasing trend was very low; the NDVI at the slope of less than 25~ was increased by the ecological construction; the variation of NDVI on sunny slope was stronger than that on shady slope. The temperature rose significantly in recent 25 years in northwest China by an average rate of 0.67^-C/10a, and precipitation increased by an average rate of 8.15 mm/10a after 1986. There was positive correlation between vegetation cover and temperature and annual precipitation changes. Rising temperature increased the evaporation and drought of soils, which is not conducive to plant growth, and the irrigation in agricultural areas reduced the correlation between agricultural vegetation NDVI and precipita- tion. The improvement of agricultural production level and the projects of ecological construction are very important causes for the NDVI increase in northwest China, and the ecological effect of large-scale ecological construction projects has appeared.展开更多
Similar to hydraulic fracturing(HF), the coalescence and fracture of cracks are induced within a rock under the action of an ultrasonic field, known as ultrasonic fracturing(UF). Investigating UF is important in both ...Similar to hydraulic fracturing(HF), the coalescence and fracture of cracks are induced within a rock under the action of an ultrasonic field, known as ultrasonic fracturing(UF). Investigating UF is important in both hard rock drilling and oil and gas recovery. A three-dimensional internal laser-engraved crack(3D-ILC) method was introduced to prefabricate two parallel internal cracks within the samples without any damage to the surface. The samples were subjected to UF. The mechanism of UF was elucidated by analyzing the characteristics of fracture surfaces. The crack propagation path under different ultrasonic parameters was obtained by numerical simulation based on the Paris fatigue model and compared to the experimental results of UF. The results show that the 3D-ILC method is a powerful tool for UF research.Under the action of an ultrasonic field, the fracture surface shows the characteristics of beach marks and contains powder locally, indicating that the UF mechanism includes high-cycle fatigue fracture, shear and friction, and temperature load. The two internal cracks become close under UF. The numerical result obtained by the Paris fatigue model also shows the attraction of the two cracks, consistent with the test results. The 3D-ILC method provides a new tool for the experimental study of UF. Compared to the conventional numerical methods based on the analysis of stress-strain and plastic zone, numerical simulation can be a good alternative method to obtain the crack path under UF.展开更多
The simulation of crack propagation processes in rock engineering has been not only a research hot spot among scholars but also a challenge.Based on this background,a new numerical method named improved kernel of smoo...The simulation of crack propagation processes in rock engineering has been not only a research hot spot among scholars but also a challenge.Based on this background,a new numerical method named improved kernel of smoothed particle hydrodynamics(IKSPH)has been put forward.By improving the kernel function in the traditional smoothed particle hydrodynamics(SPH)method,the brittle fracture characteristics of the base particles are realized.The particle domain searching method(PDSM)has also been put forward to generate the arbitrary complex fissure networks.Three numerical examples are analyzed to validate the efficiency of IKSPH and PDSM,which can correctly reveal the morphology of wing crack and the laws of crack coalescence compared with previous experimental and numerical studies.Finally,a rock slope model with complex joints is numerically simulated and the progressive failure processes are exhibited,which indicates that the IKSPH method can be well applied to rock mechanics engineering.The research results showed that IKSPH method reduces the programming difficulties and avoids the traditional grid distortion,which can provide some references for the application of IKSPH to rock mechanics engineering and the understanding of rock fracture mechanisms.展开更多
The Qilian mountain area was examined for using the Logistic-CA-Markov coupling model combined with GIS spatial analyst technology to research the transformation of LUCC, driving force system and simulate future tende...The Qilian mountain area was examined for using the Logistic-CA-Markov coupling model combined with GIS spatial analyst technology to research the transformation of LUCC, driving force system and simulate future tendency of variation. Results show that: (1) Woodland area decreased by 12.55%, while grassland, cultivated land, and settlement areas increased by 0.22%, 7.92%, and 0.03%, respectively, from 1986 to 2014. During the period of 1986 to 2000, forest degradation in the middle section of the mountain area decreased by 1,501.69 km2. Vegetation cover area improved, with a net increase of grassland area of 38.12 km2 from 2000 to 2014. (2) For constructing the system driving force, the best simulation scale was 210m×210m. Based on logistic regression analysis, the contribution (weight) of composite driving forces to land use and cover change was obtained, and the weight value was more objectively compared with AHP and MCE method. (3) In the natural scenarios, it is predicted that land use and cover distribution maps of Qilian mountain area in 2028 and 2042, and the Lee-Sallee index test was adopted. Over the next 27 years (2015-2042), farmland, woodland, grassland, settlement areas show an increasing trend, especially settlements with an obvious change of 0.56%. The area of bare land will decrease by 0.89%. Without environmental degradation, tremendous structural change of LUCC will not occur, and typical characteristic of the vertical zone of the mountain would remain. Farmland and settlement areas will increase, but only in the vicinity of Qilian and Sunan counties.展开更多
Ultrasonic fracturing(UF)can be used to form crack networks for oil or gas in the mining industry and hard rock excavation.In this paper,the three-dimensional internal laser-engraved crack method(3DILC)is introduced t...Ultrasonic fracturing(UF)can be used to form crack networks for oil or gas in the mining industry and hard rock excavation.In this paper,the three-dimensional internal laser-engraved crack method(3DILC)is introduced to make penny-shaped internal crack within the samples without any damage to the surfaces.Physical experiments were performed on the transparent samples with internal cracks at different depths.The macro-and micro-fracture fractography characteristics were focused on and analyzed in details.Based on fractography,the mechanisms of the UF were revealed.The propagation paths of cracks of different depths were simulated based on the Paris fatigue model and compared with experimental results.The results show that the 3D-ILC method is a powerful tool for the experimental research on the internal crack propagation in the UF.Under the action of ultrasonic field,fractography shows the characteristics of beach marks,lance-like pattern,rime-like pattern and glass powder.It can be judged that the mechanisms of UF include high cycle fatigue fracture,shear fracture,and friction.The results of the numerical simulation using the Paris fatigue model are consistent with the experimental results.展开更多
Carex brunnescens(Pers.)Poir.is considered to be the only clonal herb found to date that can develop and form fixed dunes in Maqu alpine degraded grasslands of northwestern China.However,due to strong dormant characte...Carex brunnescens(Pers.)Poir.is considered to be the only clonal herb found to date that can develop and form fixed dunes in Maqu alpine degraded grasslands of northwestern China.However,due to strong dormant characteristics of C.brunnescens seeds,the sand-fixing effect of the plant is severely limited.This study explores a technique that can rapidly promote the seed germination of C.brunnescens,and also investigates the adaptation and sand-fixing effect by cultivating C.brunnescens seedlings to establish living sand barriers in the sand ridges of moving sand dunes.Results show that the seed germination rate obtained a maximum of 63.7%or 65.1%when seeds were treated with 150 mg/L gibberellic acid(GA3)for 24 h followed by soaking in sulfuric acid(98%H2SO4)for 2.5 min or sodium hydroxide(10%NaOH)for 3.5 h,and then germinated(25°C in daytime and 5°C at nighttime)in darkness for 10 d.After breaking seed dormancy of C.brunnescens,the living sand barrier of C.brunnescens(plant spacing 15−20 cm;sand barrier spacing 10−20 m)was established in the perpendicular direction to the main wind in the middle and lower parts of the sand ridges on both sides of the moving sand dunes.When the sand ridges were leveled by wind erosion,the living sand barrier(plant spacing 15−20 cm;sand barrier spacing 0.5−1.0 m)of C.brunnescens was reestablished on the wind-eroded flat ground.Finally,a stable sand-fixing surface can be formed after connecting the living sand barriers on both sides,thus achieving a good sand-fixing effect.These findings suggest that rapid seed germination technology combined with the sand−fixing method of C.brunnescens can shorten the seed germination period and make the seedling establishment become much easier which may be an effective strategy to restore and reconstruct Maqu degraded grasslands.展开更多
Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers.Compared to mechanical processing,laser polish...Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers.Compared to mechanical processing,laser polishing with moving beam spot is a noncontact processing method,which is able to form a defect-free surface.This work aims to explore the mechanism of forming a smooth,defect-free fused silica surface by high-power density laser polishing with coupled multiple beams.The underlying mechanisms of laser polishing was revealed by numerical simulations and the theoretical results were verified by experiments.The simulated polishing depth and machined surface morphology were in close agreement with the experimental results.To obtain the optimized polishing quality,the effects of laser polishing parameters(e.g.overlap rate,pulse width and polishing times)on the polishing quality were experimentally investigated.It was found that the processing efficiency of fused silica materials by carbon dioxide(CO2)laser polishing could reach 8.68 mm2 s−1,and the surface roughness(Ra)was better than 25 nm.Besides,the cracks on pristine fused silica surfaces introduced by initial grinding process were completely removed by laser polishing to achieve a defect-free surface.The maximum laser polishing rate can reach 3.88μm s−1,much higher than that of the traditional mechanical polishing methods.The rapid CO2 laser polishing can effectively achieve smooth,defect-free surface,which is of great significance to improve the surface quality of fused silica optics applied in high-power laser facilities.展开更多
Identifying the ecological environment suitable for the growth of Thuja sutchuenensis and predicting other potential distribution areas are essential to protect this endangered species. After selecting 24 environmenta...Identifying the ecological environment suitable for the growth of Thuja sutchuenensis and predicting other potential distribution areas are essential to protect this endangered species. After selecting 24 environmental factors thatcould affect the distribution of T. sutchuenensis, including climate, topography, soil and Normalized DifferenceVegetation Index (NDVI), we adopted the Random Forest-MaxEnt integrated model to analyze our data. Basedon the Random Forest study, the contribution of the mean temperature of the warmest quarter, mean temperatureof the coldest quarter, annual mean temperature and mean temperature of the driest quarter was large. Based onMaxEnt model prediction outputs, the potential distribution map not only identified areas that originallyrecorded T. sutchuenensis, such as Xuanhan County, Kai County and Chengkou County, but also identified highlysuitable distribution areas where T. sutchuenensis may exist, including Wanyuan County, Sichuan Province, andthe junction of Chongqing and Hubei Province. This provides a more explicit geographic range for ex situ conservation and reintroduction of T. sutchuenensis. Our results also indicate that, in addition to climate factors,topography and soil factors are also important environmental factors that affect distribution. This provides a theoretical basis for subsequent laboratory construction to simulate the indoor growth of T. sutchuenensis.展开更多
Based on the free-energy average method,an area-weighted effective potential is derived for rectangular corrugated nano-pore.With the obtained potential,classical density functional theory is employed to investigate t...Based on the free-energy average method,an area-weighted effective potential is derived for rectangular corrugated nano-pore.With the obtained potential,classical density functional theory is employed to investigate the structural and thermodynamic properties of confined Lennard-Jones fluid in rectangular corrugated slit pores.Firstly,influence of pore geometry on the adsorptive potential is calculated and analyzed.Further,thermodynamic properties including excess adsorption,solvation force,surface free energy and thermodynamic response functions are systematically investigated.It is found that pore geometry can largely modulate the structure of the confined fluids,which in turn influences other thermodynamic properties.In addition,the results show that different geometric elements have different influences on the confined fluids.The work provides an effective route to investigate the effect of roughness on confined fluids.It is expected to shed light on further understanding about interfacial phenomena near rough walls,and then provide useful clues for the design and characterization of novel materials.展开更多
Background:To perform anatomical anterior cruciate ligament reconstruction(ACLR),tunnels should be placed relatively higher in the femoral anterior cruciate ligament(ACL)footprint based on the findings of direct and i...Background:To perform anatomical anterior cruciate ligament reconstruction(ACLR),tunnels should be placed relatively higher in the femoral anterior cruciate ligament(ACL)footprint based on the findings of direct and indirect femoral insertion.But the clinical results of higher femoral tunnels(HFT)in double-bundle ACLR(DB-ACLR)remain unclear.The purpose was to investigate the clinical results of HFT and lower femoral tunnels(LFT)in DB-ACLR.Methods:From September 2014 to February 2016,83 patients who underwent DB-ACLR and met the inclusion and exclusion criteria were divided into HFT-ACLR(group 1,n=37)and LFT-ACLR(group 2,n=46)according to the position of femoral tunnels.Preoperatively and at the final follow-up,clinical scores were evaluated with International Knee Documentation Committee(IKDC),Tegner activity,and Lysholm score.The stability of the knee was evaluated with KT-2000,Lachman test,and pivot-shift test.Cartilage degeneration grades of the International Cartilage Repair Society(ICRS)were evaluated on magnetic resonance imaging(MRI).Graft tension,continuity,and synovialization were evaluated by second-look arthroscopy.Return-to-sports was assessed at the final follow-up.Results:Significantly better improvement were found for KT-2000,Lachman test,and pivot-shift test postoperatively in group 1(P>0.05).Posterolateral bundles(PL)showed significantly better results in second-look arthroscopy regarding graft tension,continuity,and synovialization(P<0.05),but not in anteromedial bundles in group 1.At the final follow-up,cartilage worsening was observed in groups 1 and 2,but it did not reach a stastistically significant difference(P>0.05).No statistically significant differences were found in IKDC subjective score,Tegner activity,and Lysholm score between the two groups.Higher return-to-sports rate was found in group 1 with 86.8%(32/37)vs.65.2%(30/46)in group 2(P=0.027).Conclusion:The HFT-ACLR group showed better stability results,better PL,and higher return-to-sports rate compared to the LFT-ACLR group.展开更多
A novel melting infiltration by ultrasonic vibration was investigated and applied to fabricate Ti6Al4V(TC4)lattice structure-reinforced Mg-10Gd-2Y-1Zn-xZr(refer to VW92 hereafter,x=0,0.5 wt%)alloy matrix composites.Th...A novel melting infiltration by ultrasonic vibration was investigated and applied to fabricate Ti6Al4V(TC4)lattice structure-reinforced Mg-10Gd-2Y-1Zn-xZr(refer to VW92 hereafter,x=0,0.5 wt%)alloy matrix composites.The edge-to-edge matching model indicates that the well-matching and possible orientation relationships(ORs)between theα-Mg andα-Ti,[10-10]_(α-Mg)//[11-23]_(α-Ti) in(0002)_(α-Mg)//(10-10)_(α-Ti) possesses the smallest misfit of 0.4%(f_(r)),and thus theα-Mg grains can nucleate on the TC4 lattice structure.Interfacial reaction occurred in the TC4/VW92+0.5 wt%Zr composites,and the reaction product was confirmed to be Al_(2)Zr_(3),AlZr_(2) andα-Ti(Zr)particles formed by continuous solution of Zr-Ti.Among the interfacial products,the AlZr_(2) phase is a brittle phase with high-volume fraction,which is not conducive to the load transfer.But generally speaking,theα-Ti(Zr)and theα-Mg tend to form a coherent interface,which is beneficial for improving the interfacial bonding strength of composites.展开更多
Many circular RNAs(circRNAs)are reported to be abnormally expressed during the progression of various tumors,and these circRNAs can be used as anti-tumor targets.Therefore,it is important to identify circRNAs that can...Many circular RNAs(circRNAs)are reported to be abnormally expressed during the progression of various tumors,and these circRNAs can be used as anti-tumor targets.Therefore,it is important to identify circRNAs that can be used effectively for the clinical diagnosis and treatment of colorectal cancer(CRC).Here,we report that hsa_Circ_0000826(Circ_0000826),a circ RNA with significantly reduced expression level in CRC tissues,is associated with a poor prognosis in patients.The silencing of Circ_0000826 promotes the proliferation of CRC cells.Conversely,the overexpression of Circ_0000826 restricted CRC cell proliferation both in vitro and in vivo.Furthermore,Circ_0000826 could target AU-rich element RNA-binding protein 1(AUF1).AUF1,known as heterogeneous nuclear ribonucleoprotein D(hnRNP D),could bind to the c-MYC 3’-UTR and promote c-MYC expression.When Circ_0000826 binds to AUF1,it competitively inhibits the binding of AUF1 to the c-MYC 3’-UTR,which inhibits the c-MYC expression and cell proliferation.These results provide novel insights into the functional mechanism of Circ_0000826 action in CRC progression and indicate its potential use as a therapeutic target in CRC.展开更多
Summary What is already known about this topic?Joint effects of gestational weight gain(GWG)and hyperglycemia on adverse pregnancy outcomes suggest that lower optimal GWG is optimal for women with gestational diabetes...Summary What is already known about this topic?Joint effects of gestational weight gain(GWG)and hyperglycemia on adverse pregnancy outcomes suggest that lower optimal GWG is optimal for women with gestational diabetes mellitus(GDM).However,there is still a lack of guidelines.What is added by this report?Optimal weekly GWG range after diagnosis of GDM for underweight,normal-weight,overweight,and obese women was 0.37–0.56 kg/week,0.26–0.48 kg/week,0.19–0.32 kg/week,and 0.12–0.23 kg/week,respectively.What are the implications for public health practice?The findings may be used to inform prenatal counseling regarding optimal gestational weight gain for women with gestational diabetes mellitus,and suggest the need for weight gain management.展开更多
What is already known about this topic?Elevated gestational weight gain(GWG)during pregnancy among women diagnosed with gestational diabetes mellitus(GDM)is correlated with an increased instance of large for gestation...What is already known about this topic?Elevated gestational weight gain(GWG)during pregnancy among women diagnosed with gestational diabetes mellitus(GDM)is correlated with an increased instance of large for gestational age(LGA)and macrosomia.However,it remains uncertain whether managing weekly GWG following a GDM diagnosis positively impacts fetal birth weight.What is added by this report?Our study found that GWG following GDM diagnosis correlates positively with the risk of LGA and macrosomia among all body mass index(BMI)subgroups,especially for overweight and obese women.What are the implications for public health practice?The results of this research highlight the importance of enforcing a more stringent regulation on GWG on a weekly basis for overweight and obese women diagnosed with GDM,particularly when considering neonatal growth.展开更多
基金Supported by the National Key Research and Development Program of China(No.2021YFC3200103)the Major Science and Technology Program for Water Pollution Control and Treatment of China(No.2017ZX07302-002)+2 种基金the State Key Laboratory of Freshwater Ecology and Biotechnology(No.2019FBZ01)the Wuhan Science and Technology Plan Project(No.2020020602012152),the Research Project of Wuhan Municipal Construction Group Co.,Ltd.(No.wszky202014)Haijun WANG was supported by the Youth Innovation Association of Chinese Academy of Sciences as an excellent member(No.Y201859)。
文摘Regime shifts from submersed macrophyte dominance to phytoplankton dominance have been widely reported in small-to medium-sized shallow lakes.However,alternative stable states in large shallow lakes(surface area>500 km^(2))remain unconfirmed.To understand the alternative stable states and the main influencing factors of submersed macrophytes in large lakes,the ecosystem states from monitoring data from 1959 to 2019 in large shallow Taihu Lake(2338 km^(2)in average depth of 2.12 m)in China were examined.Changes in submersed macrophyte coverage(C_(Mac))and phytoplankton chlorophyll a(Chl a)in the time series and their relationships with environmental factors were analyzed.During the field investigation from August 2018 to May 2019,nutrients and Chl a showed obvious heterogeneity across the lake,being generally higher in the western and northern areas and lower in the southeast area,while C_(Mac)was only observed in the eastern areas,e.g.,East Taihu Lake,Xukou Bay,and Gonghu Bay.During the long-term monitoring from 1959 to 2019 in the Central Region,Meiliang Bay,and East Taihu Lake,Chl a increased significantly in the time series.C_(Mac)varied slightly among different subareas,always at low levels(<10%)in the Central Region and Meiliang Bay but at relatively high levels in East Taihu Lake(10%–90%).Frequency distributions of response variables had no multimodality except for C_(Mac)in East Taihu Lake,with two peaks between 15%and 20%and between 55%and 60%.A dual relationship was found between Chl a and total phosphorus(TP)in the areas with and without macrophytes,while C_(Mac)showed no relationship with TP,and submersed macrophytes did not flourish in the Central Region and Meiliang Bay even when TP was at very low levels(≈10 mg/m3).Taihu Lake had similar algal turbidity(TurbAlg)as small-to mediumsized lakes but generally presented with higher values of nonalgal turbidity(TurbNonAlg),as did their contribution to total turbidity as a percentage.This study suggested that large shallow Taihu Lake may have no alternative stable states,but more evidence is needed for East Taihu Lake,which was dominated by macrophytes,as it remains unknown whether hysteresis occurs between the processes of eutrophication and oligotrophication.Unfavorable conditions caused by wind might be the main reason due to the absence of submersed macrophytes in Taihu Lake.These results demonstrate that stricter nutrient control is needed to maintain a healthy state or to recover from a decayed state for large lakes.
基金National Natural Science Foundation of China,Grant/Award Numbers:51409170,51739008。
文摘Fractures are widely present in geomaterials of civil engineering and deep underground engineering.Given that geomaterials are usually brittle,the fractures can significantly affect the evaluation of underground engineering construction safety and the early warning of rock failure.However,the crack initiation and propagation in brittle materials under composite loading remain unknown so far.In this study,a three-dimensional internal laser-engraved cracking technique was applied to produce internal cracks without causing damage to the surfaces.The uniaxial compression tests were performed on a brittle material with internal cracks to investigate the propagation of these internal cracks at different dip angles under compression and shear.The test results show that the wing crack propagation mainly occurs in the specimen with an inclined internal crack,which is a mixed-ModeⅠ–Ⅱ–Ⅲfracture;in contrast,ModeⅠfracture is present in the specimen with a vertical internal crack.The fractography characteristics of ModeⅢfracture display a lance-like pattern.The fracture mechanism in the brittle material under compression is that the internal wing cracks propagate to the ends of the whole sample and cause the final failure.The initial deflection angle of the wing crack is determined by the participation ratio of stress intensity factors KII to KI at the tip of the internal crack.
基金funded by the National Natural Science Foundation of China (40961038)the Knowledge Innovation Project of the Chinese Academy of Science (KZCX2-YW-Q10-4)+1 种基金the Public Service Sector (Meteorology) Research Project (GYHY200806021-07)the Provincial Key Subjects of Ecological Economy (5001-021)
文摘In this paper the spatio-temporal variation of vegetation cover in northwest China during the period of 1982-2006 and its driving factors were analyzed using GIMMS/NDVI data. The annual average NDVI was increased with a rate of 0.0005/a in northwest China and there was an obvious difference between regions. The trend line slopes of NDVI were higher than 0.0005 in the Tianshan Moutains and Altay Mountains of Xinjiang, the Qilian Mountains of Gansu and the eastern part of Qinghai, which indicated the vegetation cover was significantly increased in these areas. The trend line slopes of NDVI were lower than -0.0005 in the southern region of Qinghai, the border regions of Shaanxi and Ningxia, the parts of Gansu and Tarim Basin, Turpan and Tuoli in Xinjiang, which indicated the vegetation cover was declined in these areas. The NDVI of woodland, grassland and cultivated land had an ascending tendency during the study period. The study shows that the vegetation cover change was caused by both natural factors and human activities in northwest China. The natural vegetation change, such as forests was influenced by climate change, while human activities were the main reason to the change of planting vegetation. The changes of vegetation covers for different elevations, slopes and slope aspects were quite different. When the eleva- tion is exceeded to 4,000 m, the NDVI increasing trend was very low; the NDVI at the slope of less than 25~ was increased by the ecological construction; the variation of NDVI on sunny slope was stronger than that on shady slope. The temperature rose significantly in recent 25 years in northwest China by an average rate of 0.67^-C/10a, and precipitation increased by an average rate of 8.15 mm/10a after 1986. There was positive correlation between vegetation cover and temperature and annual precipitation changes. Rising temperature increased the evaporation and drought of soils, which is not conducive to plant growth, and the irrigation in agricultural areas reduced the correlation between agricultural vegetation NDVI and precipita- tion. The improvement of agricultural production level and the projects of ecological construction are very important causes for the NDVI increase in northwest China, and the ecological effect of large-scale ecological construction projects has appeared.
基金supported by the National Natural Science Foundation of China (Grant Nos. 52104125, U1765204 and 51739008)
文摘Similar to hydraulic fracturing(HF), the coalescence and fracture of cracks are induced within a rock under the action of an ultrasonic field, known as ultrasonic fracturing(UF). Investigating UF is important in both hard rock drilling and oil and gas recovery. A three-dimensional internal laser-engraved crack(3D-ILC) method was introduced to prefabricate two parallel internal cracks within the samples without any damage to the surface. The samples were subjected to UF. The mechanism of UF was elucidated by analyzing the characteristics of fracture surfaces. The crack propagation path under different ultrasonic parameters was obtained by numerical simulation based on the Paris fatigue model and compared to the experimental results of UF. The results show that the 3D-ILC method is a powerful tool for UF research.Under the action of an ultrasonic field, the fracture surface shows the characteristics of beach marks and contains powder locally, indicating that the UF mechanism includes high-cycle fatigue fracture, shear and friction, and temperature load. The two internal cracks become close under UF. The numerical result obtained by the Paris fatigue model also shows the attraction of the two cracks, consistent with the test results. The 3D-ILC method provides a new tool for the experimental study of UF. Compared to the conventional numerical methods based on the analysis of stress-strain and plastic zone, numerical simulation can be a good alternative method to obtain the crack path under UF.
基金financial supports of the National Natural Science Fund(Nos.U1765204 and 51409170)。
文摘The simulation of crack propagation processes in rock engineering has been not only a research hot spot among scholars but also a challenge.Based on this background,a new numerical method named improved kernel of smoothed particle hydrodynamics(IKSPH)has been put forward.By improving the kernel function in the traditional smoothed particle hydrodynamics(SPH)method,the brittle fracture characteristics of the base particles are realized.The particle domain searching method(PDSM)has also been put forward to generate the arbitrary complex fissure networks.Three numerical examples are analyzed to validate the efficiency of IKSPH and PDSM,which can correctly reveal the morphology of wing crack and the laws of crack coalescence compared with previous experimental and numerical studies.Finally,a rock slope model with complex joints is numerically simulated and the progressive failure processes are exhibited,which indicates that the IKSPH method can be well applied to rock mechanics engineering.The research results showed that IKSPH method reduces the programming difficulties and avoids the traditional grid distortion,which can provide some references for the application of IKSPH to rock mechanics engineering and the understanding of rock fracture mechanisms.
基金supported by National Natural Science Foundation of China (No. 4961038)Natural Science Foundation of Sichuan Province Education Department (No. 16ZB0402)+1 种基金Engineering and Technical College of Chengdu University of Technology Foundation (No. C122014014)the key research projects of Science and Technology Bureau of Leshan Town
文摘The Qilian mountain area was examined for using the Logistic-CA-Markov coupling model combined with GIS spatial analyst technology to research the transformation of LUCC, driving force system and simulate future tendency of variation. Results show that: (1) Woodland area decreased by 12.55%, while grassland, cultivated land, and settlement areas increased by 0.22%, 7.92%, and 0.03%, respectively, from 1986 to 2014. During the period of 1986 to 2000, forest degradation in the middle section of the mountain area decreased by 1,501.69 km2. Vegetation cover area improved, with a net increase of grassland area of 38.12 km2 from 2000 to 2014. (2) For constructing the system driving force, the best simulation scale was 210m×210m. Based on logistic regression analysis, the contribution (weight) of composite driving forces to land use and cover change was obtained, and the weight value was more objectively compared with AHP and MCE method. (3) In the natural scenarios, it is predicted that land use and cover distribution maps of Qilian mountain area in 2028 and 2042, and the Lee-Sallee index test was adopted. Over the next 27 years (2015-2042), farmland, woodland, grassland, settlement areas show an increasing trend, especially settlements with an obvious change of 0.56%. The area of bare land will decrease by 0.89%. Without environmental degradation, tremendous structural change of LUCC will not occur, and typical characteristic of the vertical zone of the mountain would remain. Farmland and settlement areas will increase, but only in the vicinity of Qilian and Sunan counties.
基金supported by the National Natural Science Foundation of China(Nos.51739008 and 41831281)the Natural Science Foundation of Jiangsu Province(No.BK20171130).
文摘Ultrasonic fracturing(UF)can be used to form crack networks for oil or gas in the mining industry and hard rock excavation.In this paper,the three-dimensional internal laser-engraved crack method(3DILC)is introduced to make penny-shaped internal crack within the samples without any damage to the surfaces.Physical experiments were performed on the transparent samples with internal cracks at different depths.The macro-and micro-fracture fractography characteristics were focused on and analyzed in details.Based on fractography,the mechanisms of the UF were revealed.The propagation paths of cracks of different depths were simulated based on the Paris fatigue model and compared with experimental results.The results show that the 3D-ILC method is a powerful tool for the experimental research on the internal crack propagation in the UF.Under the action of ultrasonic field,fractography shows the characteristics of beach marks,lance-like pattern,rime-like pattern and glass powder.It can be judged that the mechanisms of UF include high cycle fatigue fracture,shear fracture,and friction.The results of the numerical simulation using the Paris fatigue model are consistent with the experimental results.
基金the Project of the Youth Talent Development Fund of the Northwest Institute of Eco−Environment and ResourcesChinese Academy of Science(CAREERI)(Y851C81001)+1 种基金the National Natural Science Foundation of China(41877162)the Instrument Functional Development Project from the Technology Service Center of CAREERI(Y429C51007).
文摘Carex brunnescens(Pers.)Poir.is considered to be the only clonal herb found to date that can develop and form fixed dunes in Maqu alpine degraded grasslands of northwestern China.However,due to strong dormant characteristics of C.brunnescens seeds,the sand-fixing effect of the plant is severely limited.This study explores a technique that can rapidly promote the seed germination of C.brunnescens,and also investigates the adaptation and sand-fixing effect by cultivating C.brunnescens seedlings to establish living sand barriers in the sand ridges of moving sand dunes.Results show that the seed germination rate obtained a maximum of 63.7%or 65.1%when seeds were treated with 150 mg/L gibberellic acid(GA3)for 24 h followed by soaking in sulfuric acid(98%H2SO4)for 2.5 min or sodium hydroxide(10%NaOH)for 3.5 h,and then germinated(25°C in daytime and 5°C at nighttime)in darkness for 10 d.After breaking seed dormancy of C.brunnescens,the living sand barrier of C.brunnescens(plant spacing 15−20 cm;sand barrier spacing 10−20 m)was established in the perpendicular direction to the main wind in the middle and lower parts of the sand ridges on both sides of the moving sand dunes.When the sand ridges were leveled by wind erosion,the living sand barrier(plant spacing 15−20 cm;sand barrier spacing 0.5−1.0 m)of C.brunnescens was reestablished on the wind-eroded flat ground.Finally,a stable sand-fixing surface can be formed after connecting the living sand barriers on both sides,thus achieving a good sand-fixing effect.These findings suggest that rapid seed germination technology combined with the sand−fixing method of C.brunnescens can shorten the seed germination period and make the seedling establishment become much easier which may be an effective strategy to restore and reconstruct Maqu degraded grasslands.
基金supported by the National Natural Science Foundation of China(Grant Nos.51775147,51705105)Science Challenge Project(Grant No.TZ2016006-0503-01)+3 种基金Young Elite Scientists Sponsorship Program by CAST(Grant No.2018QNRC001)China Postdoctoral Science Foundation funded project(Grant Nos.2018T110288,2017M621260)Self-Planned Task(Grant Nos.SKLRS201718A,SKLRS201803B)of State Key Laboratory of Robotics and System(HIT)Fundamental Research Funds for the Central Universities(Grant No.HIT.NSRIF.2019053).
文摘Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers.Compared to mechanical processing,laser polishing with moving beam spot is a noncontact processing method,which is able to form a defect-free surface.This work aims to explore the mechanism of forming a smooth,defect-free fused silica surface by high-power density laser polishing with coupled multiple beams.The underlying mechanisms of laser polishing was revealed by numerical simulations and the theoretical results were verified by experiments.The simulated polishing depth and machined surface morphology were in close agreement with the experimental results.To obtain the optimized polishing quality,the effects of laser polishing parameters(e.g.overlap rate,pulse width and polishing times)on the polishing quality were experimentally investigated.It was found that the processing efficiency of fused silica materials by carbon dioxide(CO2)laser polishing could reach 8.68 mm2 s−1,and the surface roughness(Ra)was better than 25 nm.Besides,the cracks on pristine fused silica surfaces introduced by initial grinding process were completely removed by laser polishing to achieve a defect-free surface.The maximum laser polishing rate can reach 3.88μm s−1,much higher than that of the traditional mechanical polishing methods.The rapid CO2 laser polishing can effectively achieve smooth,defect-free surface,which is of great significance to improve the surface quality of fused silica optics applied in high-power laser facilities.
文摘Identifying the ecological environment suitable for the growth of Thuja sutchuenensis and predicting other potential distribution areas are essential to protect this endangered species. After selecting 24 environmental factors thatcould affect the distribution of T. sutchuenensis, including climate, topography, soil and Normalized DifferenceVegetation Index (NDVI), we adopted the Random Forest-MaxEnt integrated model to analyze our data. Basedon the Random Forest study, the contribution of the mean temperature of the warmest quarter, mean temperatureof the coldest quarter, annual mean temperature and mean temperature of the driest quarter was large. Based onMaxEnt model prediction outputs, the potential distribution map not only identified areas that originallyrecorded T. sutchuenensis, such as Xuanhan County, Kai County and Chengkou County, but also identified highlysuitable distribution areas where T. sutchuenensis may exist, including Wanyuan County, Sichuan Province, andthe junction of Chongqing and Hubei Province. This provides a more explicit geographic range for ex situ conservation and reintroduction of T. sutchuenensis. Our results also indicate that, in addition to climate factors,topography and soil factors are also important environmental factors that affect distribution. This provides a theoretical basis for subsequent laboratory construction to simulate the indoor growth of T. sutchuenensis.
基金Project supported by the National Natural Science Foundation of China(Grant No.21503077)the Fundamental Research Fund for the Central Universities of China(Grant No.2020MS147)the Science and Technology Project of Hebei Education Department,China(Grant No.QN2018119)。
文摘Based on the free-energy average method,an area-weighted effective potential is derived for rectangular corrugated nano-pore.With the obtained potential,classical density functional theory is employed to investigate the structural and thermodynamic properties of confined Lennard-Jones fluid in rectangular corrugated slit pores.Firstly,influence of pore geometry on the adsorptive potential is calculated and analyzed.Further,thermodynamic properties including excess adsorption,solvation force,surface free energy and thermodynamic response functions are systematically investigated.It is found that pore geometry can largely modulate the structure of the confined fluids,which in turn influences other thermodynamic properties.In addition,the results show that different geometric elements have different influences on the confined fluids.The work provides an effective route to investigate the effect of roughness on confined fluids.It is expected to shed light on further understanding about interfacial phenomena near rough walls,and then provide useful clues for the design and characterization of novel materials.
基金supported by the Beijing Natural Science Foundation of China(No.J210011)the National Natural Science Foundation of China(No.U22A2051)the Ministerial Commission of Science and Technology(No.JK-2022-07).
文摘Background:To perform anatomical anterior cruciate ligament reconstruction(ACLR),tunnels should be placed relatively higher in the femoral anterior cruciate ligament(ACL)footprint based on the findings of direct and indirect femoral insertion.But the clinical results of higher femoral tunnels(HFT)in double-bundle ACLR(DB-ACLR)remain unclear.The purpose was to investigate the clinical results of HFT and lower femoral tunnels(LFT)in DB-ACLR.Methods:From September 2014 to February 2016,83 patients who underwent DB-ACLR and met the inclusion and exclusion criteria were divided into HFT-ACLR(group 1,n=37)and LFT-ACLR(group 2,n=46)according to the position of femoral tunnels.Preoperatively and at the final follow-up,clinical scores were evaluated with International Knee Documentation Committee(IKDC),Tegner activity,and Lysholm score.The stability of the knee was evaluated with KT-2000,Lachman test,and pivot-shift test.Cartilage degeneration grades of the International Cartilage Repair Society(ICRS)were evaluated on magnetic resonance imaging(MRI).Graft tension,continuity,and synovialization were evaluated by second-look arthroscopy.Return-to-sports was assessed at the final follow-up.Results:Significantly better improvement were found for KT-2000,Lachman test,and pivot-shift test postoperatively in group 1(P>0.05).Posterolateral bundles(PL)showed significantly better results in second-look arthroscopy regarding graft tension,continuity,and synovialization(P<0.05),but not in anteromedial bundles in group 1.At the final follow-up,cartilage worsening was observed in groups 1 and 2,but it did not reach a stastistically significant difference(P>0.05).No statistically significant differences were found in IKDC subjective score,Tegner activity,and Lysholm score between the two groups.Higher return-to-sports rate was found in group 1 with 86.8%(32/37)vs.65.2%(30/46)in group 2(P=0.027).Conclusion:The HFT-ACLR group showed better stability results,better PL,and higher return-to-sports rate compared to the LFT-ACLR group.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030006)the National Natural Science Foundation of China (52225101)+2 种基金the Scientific Research Foundation of Chongqing University of Technology (2020ZDZ006)the Science and Technology Research Program of the Chongqing Municipal Education Commission (KJZD-K202201108)the University Innovation Research Group of Chongqing (CXQT20023).
文摘A novel melting infiltration by ultrasonic vibration was investigated and applied to fabricate Ti6Al4V(TC4)lattice structure-reinforced Mg-10Gd-2Y-1Zn-xZr(refer to VW92 hereafter,x=0,0.5 wt%)alloy matrix composites.The edge-to-edge matching model indicates that the well-matching and possible orientation relationships(ORs)between theα-Mg andα-Ti,[10-10]_(α-Mg)//[11-23]_(α-Ti) in(0002)_(α-Mg)//(10-10)_(α-Ti) possesses the smallest misfit of 0.4%(f_(r)),and thus theα-Mg grains can nucleate on the TC4 lattice structure.Interfacial reaction occurred in the TC4/VW92+0.5 wt%Zr composites,and the reaction product was confirmed to be Al_(2)Zr_(3),AlZr_(2) andα-Ti(Zr)particles formed by continuous solution of Zr-Ti.Among the interfacial products,the AlZr_(2) phase is a brittle phase with high-volume fraction,which is not conducive to the load transfer.But generally speaking,theα-Ti(Zr)and theα-Mg tend to form a coherent interface,which is beneficial for improving the interfacial bonding strength of composites.
基金supported by the National Natural Science Foundation of China(Grant Nos.81802470,31800658,and U1804173)the Department of Science and Technology,Henan Province(Grant Nos.212102310621 and 192102310362)+1 种基金Joint construction project of Henan Medical Science and technology research plan(No.LHGJ20210910)the Xinxiang Medical University research funding(Grant No.XYBSKYZZ201632)。
文摘Many circular RNAs(circRNAs)are reported to be abnormally expressed during the progression of various tumors,and these circRNAs can be used as anti-tumor targets.Therefore,it is important to identify circRNAs that can be used effectively for the clinical diagnosis and treatment of colorectal cancer(CRC).Here,we report that hsa_Circ_0000826(Circ_0000826),a circ RNA with significantly reduced expression level in CRC tissues,is associated with a poor prognosis in patients.The silencing of Circ_0000826 promotes the proliferation of CRC cells.Conversely,the overexpression of Circ_0000826 restricted CRC cell proliferation both in vitro and in vivo.Furthermore,Circ_0000826 could target AU-rich element RNA-binding protein 1(AUF1).AUF1,known as heterogeneous nuclear ribonucleoprotein D(hnRNP D),could bind to the c-MYC 3’-UTR and promote c-MYC expression.When Circ_0000826 binds to AUF1,it competitively inhibits the binding of AUF1 to the c-MYC 3’-UTR,which inhibits the c-MYC expression and cell proliferation.These results provide novel insights into the functional mechanism of Circ_0000826 action in CRC progression and indicate its potential use as a therapeutic target in CRC.
基金funded by the Medical and Health Technology Innovation Project of the Chinese Academy of Medical Sciences(2020-I2M-2-009,2021-I2M-1-023)the Project of the National Health Commission of the People’s Republic of China(20191901)the National Natural Science Foundation of China(81973053).
文摘Summary What is already known about this topic?Joint effects of gestational weight gain(GWG)and hyperglycemia on adverse pregnancy outcomes suggest that lower optimal GWG is optimal for women with gestational diabetes mellitus(GDM).However,there is still a lack of guidelines.What is added by this report?Optimal weekly GWG range after diagnosis of GDM for underweight,normal-weight,overweight,and obese women was 0.37–0.56 kg/week,0.26–0.48 kg/week,0.19–0.32 kg/week,and 0.12–0.23 kg/week,respectively.What are the implications for public health practice?The findings may be used to inform prenatal counseling regarding optimal gestational weight gain for women with gestational diabetes mellitus,and suggest the need for weight gain management.
文摘What is already known about this topic?Elevated gestational weight gain(GWG)during pregnancy among women diagnosed with gestational diabetes mellitus(GDM)is correlated with an increased instance of large for gestational age(LGA)and macrosomia.However,it remains uncertain whether managing weekly GWG following a GDM diagnosis positively impacts fetal birth weight.What is added by this report?Our study found that GWG following GDM diagnosis correlates positively with the risk of LGA and macrosomia among all body mass index(BMI)subgroups,especially for overweight and obese women.What are the implications for public health practice?The results of this research highlight the importance of enforcing a more stringent regulation on GWG on a weekly basis for overweight and obese women diagnosed with GDM,particularly when considering neonatal growth.