To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hyb...To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hybrid modular multilevel converter–capacitor-commutated line-commutated converter(MMC-CLCC)HVDC transmission system and its corresponding control strategy.First,the system topology is constructed,and a submodule configuration method for the MMC—combining full-bridge submodules(FBSMs)and half-bridge submodules(HBSMs)—is proposed to enable direct power flow reversal.Second,a hierarchical control strategy is introduced,includingMMCvoltage control,CLCC current control,and a coordinationmechanism,along with the derivation of the hybrid system’s power flow reversal characteristics.Third,leveraging the CLCC’s fast current regulation and theMMC’s negative voltage control capability,a coordinated power flow reversal control strategy is developed.Finally,an 800 kV MMC-CLCC hybrid HVDC system is modeled in PSCAD/EMTDC to validate the power flow reversal performance under a high proportion of full-bridge submodule configuration.Results demonstrate that the proposed control strategy enables rapid(1-s transition)and smooth switching of bidirectional power flow without modifying the structure of primary equipment:the transient fluctuation ofDC voltage from the rated value(UdcN)to themaximumreverse voltage(-kUdcN)is less than 5%;the DC current strictly follows the preset characteristic curve with a deviation of≤3%;the active power reverses continuously,and the system maintains stable operation throughout the reversal process.展开更多
Membrane electrode assembly(MEA)is widely considered to be the most promising type of electrolyzer for the practical application of electrochemical CO_(2) reduction reaction(CO_(2)RR).In MEAs,a square-shaped cross-sec...Membrane electrode assembly(MEA)is widely considered to be the most promising type of electrolyzer for the practical application of electrochemical CO_(2) reduction reaction(CO_(2)RR).In MEAs,a square-shaped cross-section in the flow channel is normally adopted,the configuration optimization of which could potentially enhance the performance of the electrolyzer.This paper describes the numerical simulation study on the impact of the flow-channel cross-section shapes in the MEA electrolyzer for CO_(2)RR.The results show that wide flow channels with low heights are beneficial to the CO_(2)RR by providing a uniform flow field of CO_(2),especially at high current densities.Moreover,the larger the electrolyzer,the more significant the effect is.This study provides a theoretical basis for the design of high-performance MEA electrolyzers for CO_(2)RR.展开更多
CO_(2)reduction reaction(CO_(2)RR)electrolyzers based on gas diffusion electrode(GDE)enable the direct mass transfer of CO_(2)to the catalyst surface for participation in the reaction,thereby establishing an efficient...CO_(2)reduction reaction(CO_(2)RR)electrolyzers based on gas diffusion electrode(GDE)enable the direct mass transfer of CO_(2)to the catalyst surface for participation in the reaction,thereby establishing an efficient three-phase reaction interface that significantly enhances current density.However,current hydrophobic modification methods face difficulties in achieving precise and substantial control over wettability,and the hydrophobic modifiers tend to significantly impair the conductivity of the electrode and ion transport capabilities.This study employs Nafion ionomers to hydrophobically modify the threedimensional catalyst layer,revealing the bifunctionality of Nafion.The fluorinated backbone of Nafion ensures the hydrophobicity of the entire catalyst layer,while its sulfonic acid groups promote ion transport,without significantly affecting the conductivity of the electrode.Furthermore,by employing modifiers with distinct wettability characteristics,a highly efficient and large-scale manipulation of the hydrophilic/hydrophobic properties of the catalyst layer was successfully realized.The electrode,constructed with silver nanopowder as a representative catalyst and modified with the hydrophobic ionomer Nafion,exhibits a substantial enhancement in both catalytic activity and durability.The optimized electrode exhibited exceptional electrocatalytic performance in both flow cell and membrane electrode assembly(MEA)configurations.Notably,in the MEA,the electrode achieved a remarkable CO Faradaic efficiency(FE)of 93.3%at a total current density of 200 mA cm^(-2),while maintaining stable operation for over 62 h.展开更多
The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely asso...The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.展开更多
Detecting oriented targets in remote sensing images amidst complex and heterogeneous backgrounds remains a formidable challenge in the field of object detection.Current frameworks for oriented detection modules are co...Detecting oriented targets in remote sensing images amidst complex and heterogeneous backgrounds remains a formidable challenge in the field of object detection.Current frameworks for oriented detection modules are constrained by intrinsic limitations,including excessive computational and memory overheads,discrepancies between predefined anchors and ground truth bounding boxes,intricate training processes,and feature alignment inconsistencies.To overcome these challenges,we present ASL-OOD(Angle-based SIOU Loss for Oriented Object Detection),a novel,efficient,and robust one-stage framework tailored for oriented object detection.The ASL-OOD framework comprises three core components:the Transformer-based Backbone(TB),the Transformer-based Neck(TN),and the Angle-SIOU(Scylla Intersection over Union)based Decoupled Head(ASDH).By leveraging the Swin Transformer,the TB and TN modules offer several key advantages,such as the capacity to model long-range dependencies,preserve high-resolution feature representations,seamlessly integrate multi-scale features,and enhance parameter efficiency.These improvements empower the model to accurately detect objects across varying scales.The ASDH module further enhances detection performance by incorporating angle-aware optimization based on SIOU,ensuring precise angular consistency and bounding box coherence.This approach effectively harmonizes shape loss and distance loss during the optimization process,thereby significantly boosting detection accuracy.Comprehensive evaluations and ablation studies on standard benchmark datasets such as DOTA with an mAP(mean Average Precision)of 80.16 percent,HRSC2016 with an mAP of 91.07 percent,MAR20 with an mAP of 85.45 percent,and UAVDT with an mAP of 39.7 percent demonstrate the clear superiority of ASL-OOD over state-of-the-art oriented object detection models.These findings underscore the model’s efficacy as an advanced solution for challenging remote sensing object detection tasks.展开更多
The past decade has witnessed the substantial growth in research interests and progress on the subject of coupled hydro-mechanical processes in rocks and soils,driven mainly by the surge of research in unconventional ...The past decade has witnessed the substantial growth in research interests and progress on the subject of coupled hydro-mechanical processes in rocks and soils,driven mainly by the surge of research in unconventional hydrocarbon reservoirs and associated hazards.Many coupling techniques have been developed to include the effects of fluid flow in the discrete element method(DEM),and the techniques have been applied to a variety of geomechanical problems.Although these coupling methods have been successfully applied in various engineering fields,no single fluid/DEM coupling method is universal due to the complexity of engineering problems and the limitations of the numerical methods.For researchers and engineers,the key to solve a specific problem is to select the most appropriate fluid/DEM coupling method among these modeling technologies.The purpose of this paper is to give a comprehensive review of fluid flow/DEM coupling methods and relevant research.Given their importance,the availability or unavailability of best practice guidelines is outlined.The theoretical background and current status of DEM are introduced first,and the principles,applications,and advantages and disadvantages of different fluid flow/DEM coupling methods are discussed.Finally,a summary with speculation on future development trends is given.展开更多
In order to improve the mechanical properties of Mg-Li alloy with single β phase structure, Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) alloy was prepared. Subsequently, the as-cast microstructure and mechanical proper...In order to improve the mechanical properties of Mg-Li alloy with single β phase structure, Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) alloy was prepared. Subsequently, the as-cast microstructure and mechanical properties were observed and tested. The results showed that the structure of Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) as-cast alloy was composed of β phase matrix and Al_2Nd, Al_(11)Nd_3, MgLiAl_2, Al_4Li_9 and AlLi phases. With the increase of Nd content in the alloy, the Al-Nd intermetallic compounds have a trend to change from needle-like Al_(11)Nd_3 to granular Al_2Nd. The hardness of as-cast Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) alloy was stable at room temperature. The tensile strength of Mg-12Li-3Al-1.1Nd was as high as 180 MPa, the elongation rate of Mg-12Li-3Al-0.7Nd reached 53.7%, and the comprehensive mechanical properties of Mg-12Li-3Al-2.0Nd was the best. PLC phenomenon occurred during the tensile process of the alloys at room temperature. Therefore, the β-based Mg-Li alloy with good plasticity as well as enhanced strength can be obtained by a moderate addition of Nd and Al.展开更多
Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards.Previous studies of it have mainly focused on suffusion in homogeneous soil specimens.In this study,the coupled ...Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards.Previous studies of it have mainly focused on suffusion in homogeneous soil specimens.In this study,the coupled discrete element method(DEM)and computational fluid dynamics(CFD)approach is adopted to model suffusion in multi-layered soils with different fines contents,and soils with one or more impermeable zones.The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained.Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed.The simulation results show that,for soils with multiple layers,the cumulative eroded mass is mainly determined by the fines content of the bottom layer.In general,the higher the fines content of the bottom soil layer,the higher the cumulative eroded mass.In addition,suffusion is more severe if the fines content of the layer above is decreased.Impermeable zones inside soil specimens can increase the flow velocity around those zones,facilitating the migration of fine particles and intensifying suffusion.展开更多
This paper describes the combinational surface kinetics enhancement and surface states passivation of nickel-borate(Ni-Bi)co-catalyst for a hematite(Fe_(2)O_(3))photoanode.The Ni-Brmodified Fe_(2)O_(3) photoanode exhi...This paper describes the combinational surface kinetics enhancement and surface states passivation of nickel-borate(Ni-Bi)co-catalyst for a hematite(Fe_(2)O_(3))photoanode.The Ni-Brmodified Fe_(2)O_(3) photoanode exhibits a cathodic onset potential shift of 230 mV and a 2.3-fold enhancement of the photocurrent at 1.23 V,versus the reversible hydrogen electrode(RHE).The borate(Bi)in the Ni-Bi film promotes the release of pro-tons for the oxygen evolution reaction(OER).展开更多
As one of the world’s most produced chemicals, ammonia(NH3) is synthesized by Haber-Bosch process. This century-old industry nourishes billions of people and promotes social and economic development. In the meantime,...As one of the world’s most produced chemicals, ammonia(NH3) is synthesized by Haber-Bosch process. This century-old industry nourishes billions of people and promotes social and economic development. In the meantime, 3%-5% of the world’s natural gas and 1%-2% of the world’s energy reserves are consumed, releasing millions of tons of carbon dioxide annually to the atmosphere. The urgency of replacing fossil fuels and mitigating climate change motivates us to progress toward more sustainable methods for N2 reduction reaction based on clean energy. Herein, we overview the emerging advancement for sustainable N2 fixation under mild conditions, which include electrochemical, photo-, plasma-enabled and homogeneous molecular NH3 productions. We focus on NH3 generation by electrocatalysts and photocatalysts. We clarify the features and progress of each kind of NH3 synthesis process and provide promising strategies to further promote sustainable ammonia production and construct state-of-the-art catalytic systems.展开更多
BACKGROUND Severe periodontitis is a major oral health concern today as it can lead to loss of teeth.Conventional periodontal therapy has numerous pitfalls as it does not address the pulp-periodontal complex in its en...BACKGROUND Severe periodontitis is a major oral health concern today as it can lead to loss of teeth.Conventional periodontal therapy has numerous pitfalls as it does not address the pulp-periodontal complex in its entirety.AIM To investigate the effect of dental pulp periodontal therapy on the levels of interleukin-1β(IL-1β)and IL-10 in gingival crevicular fluid(GCF)in patients with severe periodontitis.METHODS Eighty-six patients with severe periodontitis were randomly divided into a research group(n=43)and a control group(n=43).The control group was treated with simple periodontal therapy,and the research group was treated with dental pulp periodontal therapy.The total effective rates of the treatments;periodontal status before and after treatment through the measurement of the periodontal pocket probing depth(PPD),gingival sulcus bleeding index(SBI),mobility(MD),and plaque index(PLI);the levels of inflammatory factors IL-1βand IL-10 in the GCF;and the incidence of complications were calculated for both groups and compared using the Student’s t test and theχ^(2) test.RESULTS The total effective rate of treatment in the study group(93.02%)was higher than that in the control group(76.74%;P<0.05).While before treatment,there was no significant difference in the PLI,MD,SBI,or PPD between the two groups,the post-treatment values of PLI,MD,SBI,and PPD(4.71±0.16 mm,0.61±0.09 mm,0.96±0.17 mm,and 0.76±0.26 mm,respectively)were significantly lower(P<0.05)in the research group than in the control group(5.35±0.24 mm,0.93±0.15 mm,1.35±0.30 mm,and 1.04±0.41 mm,respectively).There was no significant difference in the level of IL-1βor IL-10 in the GCF before treatment between the two groups;after treatment,the IL-1βlevel in the research group(139.04±15.54 pg/mL)was significantly lower than that in the control group(156.35±18.10 pg/mL),and the level of IL-10 in the research group(7.98±1.01 ug/L)was higher than that in the control group(5.56±0.96 ug/L)(P<0.05).The incidence of complications in the study group(4.65%)was significantly lower than that of the control group(18.60%;P<0.05).CONCLUSION Endodontic therapy and periodontal treatment for patients with severe periodontitis can effectively reduce the levels of inflammatory factors in the GCF and the inflammatory reaction.In addition,it can improve the periodontal condition and the overall treatment effect,reduce the risk of complications,and ensure the safety of treatment.展开更多
Suffusion in gap-graded soil involves selective erosion of fine particles through the pores formed by coarse particles under seepage forces.As the fines content(FC)decreases,the hydraulic and mechanical behavior of th...Suffusion in gap-graded soil involves selective erosion of fine particles through the pores formed by coarse particles under seepage forces.As the fines content(FC)decreases,the hydraulic and mechanical behavior of the soil will change,posing a huge threat to engineering safety.In this study,we first conduct a series of experimental tests of suffusion by using gap-graded soils and then analyze the evolution process of suffusion and the effect of the hydraulic gradient.Subsequently,according to the physical model,a discrete element method(DEM)numerical model with dynamic fluid mesh(DFM)is developed to extend the experimental study to the pore scale.Our results reveal the migration process of fines and the formation of erosion zones.A parametric study is then conducted to investigate the effect of the hydraulic gradient,FC,and K_(0) pressure(which limits the lateral displacement of the sample and applies vertical pressure)on eroded weight.The results show that the eroded weight increases with the increase of the hydraulic gradient and FC but decreases with the increase of K_(0) pressure.展开更多
To improve the mechanical properties of AZ91D magnesium alloy,the submicrocrystal Al-Ti-B master alloy was prepared with copper mold inject casting method,and the influence of submicrocrystal Al-Ti-B master alloy on t...To improve the mechanical properties of AZ91D magnesium alloy,the submicrocrystal Al-Ti-B master alloy was prepared with copper mold inject casting method,and the influence of submicrocrystal Al-Ti-B master alloy on the microstructure and mechanical properties of AZ91D was investigated.Results show that,the distribution of Ti B_2 phase in submicrocrystal Al-Ti-B alloy is even and disperse,and the average size of Ti Al_3 phase is reduced from 10-30μm to～1μm.The properties of AZ91D refined with submicrocrystal Al-Ti-B master alloy are better than that with coarse-grained Al-Ti-B master alloy without copper mold inject casting.The tensile strength,elongation and Brinell hardness of AZ91D are increased by 10.6%,25%and 18.1%,respectively.Therefore,refinement of AZ91D with submicrocrystal Al-Ti-B that is obtained by copper mold inject casting is an effective method to improve its mechanical properties.展开更多
Background:For secondary cavity-nesting bird species that do not add lining materials to nests,the presence of old nest material or organic remains that have accumulated within nest cavities from previous breeding eve...Background:For secondary cavity-nesting bird species that do not add lining materials to nests,the presence of old nest material or organic remains that have accumulated within nest cavities from previous breeding events may be a cue of nest-site quality.These materials potentially contain information about past breeding success in con-and heterospecifics and may improve the thermal insulation of eggs during incubation.However,few studies have addressed whether the presence of old nest materials serves as a cue for cavity-nesting raptors when choosing specific nest sites.Methods:We conducted a 9-year nest box experiment to test whether old nest materials from con-and heterospecifics serve as informative cues to the European Kestrel(Falco tinnunculus)when making nest selection decisions,as this species uses nest boxes without adding nesting material.Results:The presence of old nest materials and entrance size best discriminated nest boxes occupied by European Kestrels from unoccupied boxes.Nest boxes containing conspecific organic remains,artificial dry leaf and branch material,and material left behind by Great Tits(Parus major)were reused at higher rates,especially those containing conspecific nest material,than nest boxes containing true or simulated nest materials from predators.In 2010,no single nest box was occupied by the same banded individual that occupied the box in the previous year(10 females and 2 males were banded in 2009).Conclusions:European Kestrels preferred nest boxes containing old nest material over empty boxes,which is consistent with previous findings that they exploit con-and heterospecific cues when deciding where to settle and breed,as old nest or organic material provides substrate for incubating females.Kestrels may be able to assess the predation risks associated with a specific nest site based on experience or the presence of prey remains.The repeated use of nest boxes across breeding seasons by kestrels cannot be entirely ascribed to philopatry.This study provides evidence that old nest materials are potentially used as informative cues when making nest-site selection decisions in European Kestrels.展开更多
In order to provide a good practice platform for the program design contestants and algorithm enthusiasts,this paper designs and implements a programming online evaluation system based on cloud platform,which is a web...In order to provide a good practice platform for the program design contestants and algorithm enthusiasts,this paper designs and implements a programming online evaluation system based on cloud platform,which is a web system that can return the test results of the program source codes submitted by users in real time.It realizes the automatic evaluation of the program design training questions.The system is implemented by the way of front-end and back-end separation and modular programming.The front-end of the web is implemented by Vue framework,the back-end is implemented by Django framework.The judgment core is written in C language for the sake of improving the efficiency of the system.Sandbox technology is used to ensure the security of the judgment system.Experimental results show that the system can meet the need of daily teaching and competition.展开更多
Photoelectrochemical(PEC)seawater splitting is a promising method for the direct utilization of solar energy and abundant seawater resources for hydrogen production.Photoelectrodes are susceptible to various ions in s...Photoelectrochemical(PEC)seawater splitting is a promising method for the direct utilization of solar energy and abundant seawater resources for hydrogen production.Photoelectrodes are susceptible to various ions in seawater and complicated competitive reactions,resulting in the failure of photoelectrodes.This paper proposes the design and fabrication of diff erent sputtered stainless steel(SS)fi lms deposited on silicon photoanodes,completely isolating the electrolytes and semiconductor substrate.Upon coupling with the PEC flow cell,the back-illuminated photoanode coated with 316 SS cocatalyst achieves stable operation for 70 h in natural seawater with a highly alkaline KOH(30 wt.%,7.64 mol/L)electrolyte due to the remarkable protection eff ect of the substrate from stainless steel,while the PEC seawater splitting system achieves a record hydrogen production rate of 600μmol/(h·cm^(2)).An appropriate Ni/Fe ratio in the SS ensures remarkable oxygen evolution activity,while chromic oxide ensures the effective anticorrosion effect by adjusting the microenvironment of the photoanodes.Moreover,fabricating PEC flow cells with photoanodes coated with SS cocatalysts are a viable strategy for PEC seawater splitting.展开更多
Patterns in species geographic range size are relatively well-known for vertebrates,but still poorly known for plants.Contrasts of these patterns between groups have rarely been investigated.With a detailed flora and ...Patterns in species geographic range size are relatively well-known for vertebrates,but still poorly known for plants.Contrasts of these patterns between groups have rarely been investigated.With a detailed flora and fauna distribution database of Xinjiang,China,we used regression methods,redundancy analysis and random forests to explore the relationship of environment and body size with the geographic range size of plants,mammals and birds in Xinjiang and contrast these patterns between plants and animals.We found positive correlations between species range size and body size.The range size of plants was more influenced by water variables,while that of mammals and birds was largely influenced by temperature variables.The productivity variable,i.e.,Enhanced Vegetation Index(EVI)was far more correlated with range size than climatic variables for both plants and animals,suggesting that vegetation productivity inferred from remote sensing data may be a good predictor of species range size for both plants and animals.展开更多
Voltage source converter based high voltage direct current(VSC-HVDC)can participate in voltage regulation by flexible control to help maintain the voltage stability of the power grid.In order to quantitatively evaluat...Voltage source converter based high voltage direct current(VSC-HVDC)can participate in voltage regulation by flexible control to help maintain the voltage stability of the power grid.In order to quantitatively evaluate its influence on the voltage interaction between VSC-HVDC and line commutated converter based high voltage direct current(LCC-HVDC),this paper proposes a hybrid multi-infeed interaction factor(HMIIF)calculation method considering the voltage regulation control characteristics of VSC-HVDC.Firstly,for a hybrid multi-infeed high voltage direct current system,an additional equivalent operating admittance matrix is constructed to characterize HVDC equipment characteristics under small disturbance.Secondly,based on the characteristic curve between the reactive power and the voltage of a certain VSC-HVDC project,the additional equivalent operating admittance of VSC-HVDC is derived.The additional equivalent operating admittance matrix calculation method is proposed.Thirdly,the equivalent bus impedance matrix is obtained by modifying the alternating current(AC)system admittance matrix with the additional equivalent operating admittance matrix.On this basis,the HMIIF calculation method based on the equivalent bus impedance ratio is proposed.Finally,the effectiveness of the proposed method is verified in a hybrid dual-infeed high voltage direct current system constructed in Power Systems Computer Aided Design(PSCAD),and the influence of voltage regulation control on HMIIF is analyzed.展开更多
基金supported by Science and Technology Project of the headquarters of the State Grid Corporation of China(No.5500-202324492A-3-2-ZN).
文摘To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hybrid modular multilevel converter–capacitor-commutated line-commutated converter(MMC-CLCC)HVDC transmission system and its corresponding control strategy.First,the system topology is constructed,and a submodule configuration method for the MMC—combining full-bridge submodules(FBSMs)and half-bridge submodules(HBSMs)—is proposed to enable direct power flow reversal.Second,a hierarchical control strategy is introduced,includingMMCvoltage control,CLCC current control,and a coordinationmechanism,along with the derivation of the hybrid system’s power flow reversal characteristics.Third,leveraging the CLCC’s fast current regulation and theMMC’s negative voltage control capability,a coordinated power flow reversal control strategy is developed.Finally,an 800 kV MMC-CLCC hybrid HVDC system is modeled in PSCAD/EMTDC to validate the power flow reversal performance under a high proportion of full-bridge submodule configuration.Results demonstrate that the proposed control strategy enables rapid(1-s transition)and smooth switching of bidirectional power flow without modifying the structure of primary equipment:the transient fluctuation ofDC voltage from the rated value(UdcN)to themaximumreverse voltage(-kUdcN)is less than 5%;the DC current strictly follows the preset characteristic curve with a deviation of≤3%;the active power reverses continuously,and the system maintains stable operation throughout the reversal process.
基金the National Key R&D Program of China(No.2021YFA1501503)the National Natural Science Foundation of China(Nos.22250008,22121004,22108197)+3 种基金the Haihe Laboratory of Sustainable Chemical Transformations(No.CYZC202107)the Natural Science Foundation of Tianjin City(No.21JCZXJC00060)the Program of Introducing Talents of Discipline to Universities(No.BP0618007)the Xplorer Prize for financial support。
文摘Membrane electrode assembly(MEA)is widely considered to be the most promising type of electrolyzer for the practical application of electrochemical CO_(2) reduction reaction(CO_(2)RR).In MEAs,a square-shaped cross-section in the flow channel is normally adopted,the configuration optimization of which could potentially enhance the performance of the electrolyzer.This paper describes the numerical simulation study on the impact of the flow-channel cross-section shapes in the MEA electrolyzer for CO_(2)RR.The results show that wide flow channels with low heights are beneficial to the CO_(2)RR by providing a uniform flow field of CO_(2),especially at high current densities.Moreover,the larger the electrolyzer,the more significant the effect is.This study provides a theoretical basis for the design of high-performance MEA electrolyzers for CO_(2)RR.
基金National Key R&D Program of China(2023YFA1507902,2021YFA1500804)the National Natural Science Foundation of China(22121004,22038009,22250008)+2 种基金the Haihe Laboratory of Sustainable Chemical Transformations(CYZC202107)the Program of Introducing Talents of Discipline to Universities,China(No.BP0618007)the Xplorer Prize,China,for their financial support。
文摘CO_(2)reduction reaction(CO_(2)RR)electrolyzers based on gas diffusion electrode(GDE)enable the direct mass transfer of CO_(2)to the catalyst surface for participation in the reaction,thereby establishing an efficient three-phase reaction interface that significantly enhances current density.However,current hydrophobic modification methods face difficulties in achieving precise and substantial control over wettability,and the hydrophobic modifiers tend to significantly impair the conductivity of the electrode and ion transport capabilities.This study employs Nafion ionomers to hydrophobically modify the threedimensional catalyst layer,revealing the bifunctionality of Nafion.The fluorinated backbone of Nafion ensures the hydrophobicity of the entire catalyst layer,while its sulfonic acid groups promote ion transport,without significantly affecting the conductivity of the electrode.Furthermore,by employing modifiers with distinct wettability characteristics,a highly efficient and large-scale manipulation of the hydrophilic/hydrophobic properties of the catalyst layer was successfully realized.The electrode,constructed with silver nanopowder as a representative catalyst and modified with the hydrophobic ionomer Nafion,exhibits a substantial enhancement in both catalytic activity and durability.The optimized electrode exhibited exceptional electrocatalytic performance in both flow cell and membrane electrode assembly(MEA)configurations.Notably,in the MEA,the electrode achieved a remarkable CO Faradaic efficiency(FE)of 93.3%at a total current density of 200 mA cm^(-2),while maintaining stable operation for over 62 h.
基金supported by the National Key Research and Development Project(Grant No.2023YFE0110900)the National Natural Science Foundation of China(Grant Nos.42320104003 and 42077247).
文摘The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.
基金supported by the Key Research and Development Program of Shaanxi Province(2024GX-YBXM-010).
文摘Detecting oriented targets in remote sensing images amidst complex and heterogeneous backgrounds remains a formidable challenge in the field of object detection.Current frameworks for oriented detection modules are constrained by intrinsic limitations,including excessive computational and memory overheads,discrepancies between predefined anchors and ground truth bounding boxes,intricate training processes,and feature alignment inconsistencies.To overcome these challenges,we present ASL-OOD(Angle-based SIOU Loss for Oriented Object Detection),a novel,efficient,and robust one-stage framework tailored for oriented object detection.The ASL-OOD framework comprises three core components:the Transformer-based Backbone(TB),the Transformer-based Neck(TN),and the Angle-SIOU(Scylla Intersection over Union)based Decoupled Head(ASDH).By leveraging the Swin Transformer,the TB and TN modules offer several key advantages,such as the capacity to model long-range dependencies,preserve high-resolution feature representations,seamlessly integrate multi-scale features,and enhance parameter efficiency.These improvements empower the model to accurately detect objects across varying scales.The ASDH module further enhances detection performance by incorporating angle-aware optimization based on SIOU,ensuring precise angular consistency and bounding box coherence.This approach effectively harmonizes shape loss and distance loss during the optimization process,thereby significantly boosting detection accuracy.Comprehensive evaluations and ablation studies on standard benchmark datasets such as DOTA with an mAP(mean Average Precision)of 80.16 percent,HRSC2016 with an mAP of 91.07 percent,MAR20 with an mAP of 85.45 percent,and UAVDT with an mAP of 39.7 percent demonstrate the clear superiority of ASL-OOD over state-of-the-art oriented object detection models.These findings underscore the model’s efficacy as an advanced solution for challenging remote sensing object detection tasks.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41772286 and 42077247)the Fundamental Research Funds for the Central Universities, China
文摘The past decade has witnessed the substantial growth in research interests and progress on the subject of coupled hydro-mechanical processes in rocks and soils,driven mainly by the surge of research in unconventional hydrocarbon reservoirs and associated hazards.Many coupling techniques have been developed to include the effects of fluid flow in the discrete element method(DEM),and the techniques have been applied to a variety of geomechanical problems.Although these coupling methods have been successfully applied in various engineering fields,no single fluid/DEM coupling method is universal due to the complexity of engineering problems and the limitations of the numerical methods.For researchers and engineers,the key to solve a specific problem is to select the most appropriate fluid/DEM coupling method among these modeling technologies.The purpose of this paper is to give a comprehensive review of fluid flow/DEM coupling methods and relevant research.Given their importance,the availability or unavailability of best practice guidelines is outlined.The theoretical background and current status of DEM are introduced first,and the principles,applications,and advantages and disadvantages of different fluid flow/DEM coupling methods are discussed.Finally,a summary with speculation on future development trends is given.
基金financially supported by the Science and Technology Research Project for Colleges and Universities of Hebei Province(ZD2014040)
文摘In order to improve the mechanical properties of Mg-Li alloy with single β phase structure, Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) alloy was prepared. Subsequently, the as-cast microstructure and mechanical properties were observed and tested. The results showed that the structure of Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) as-cast alloy was composed of β phase matrix and Al_2Nd, Al_(11)Nd_3, MgLiAl_2, Al_4Li_9 and AlLi phases. With the increase of Nd content in the alloy, the Al-Nd intermetallic compounds have a trend to change from needle-like Al_(11)Nd_3 to granular Al_2Nd. The hardness of as-cast Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) alloy was stable at room temperature. The tensile strength of Mg-12Li-3Al-1.1Nd was as high as 180 MPa, the elongation rate of Mg-12Li-3Al-0.7Nd reached 53.7%, and the comprehensive mechanical properties of Mg-12Li-3Al-2.0Nd was the best. PLC phenomenon occurred during the tensile process of the alloys at room temperature. Therefore, the β-based Mg-Li alloy with good plasticity as well as enhanced strength can be obtained by a moderate addition of Nd and Al.
基金This work is supported by the Research Grants Council(RGC)of Hong Kong(No.15226322)the National Natu‐ral Science Foundation of China(No.42207210).
文摘Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards.Previous studies of it have mainly focused on suffusion in homogeneous soil specimens.In this study,the coupled discrete element method(DEM)and computational fluid dynamics(CFD)approach is adopted to model suffusion in multi-layered soils with different fines contents,and soils with one or more impermeable zones.The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained.Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed.The simulation results show that,for soils with multiple layers,the cumulative eroded mass is mainly determined by the fines content of the bottom layer.In general,the higher the fines content of the bottom soil layer,the higher the cumulative eroded mass.In addition,suffusion is more severe if the fines content of the layer above is decreased.Impermeable zones inside soil specimens can increase the flow velocity around those zones,facilitating the migration of fine particles and intensifying suffusion.
基金We acknowledge the National Key Research and Development Program of China(2016YFB0600901),the National Natural Science Foundation of China(21525626,U1463205,U1662111),the Special-ized Research Fund for the Doctoral Program of Higher Education(20130032120018),and the Program of Introducing Talents of Disci-pline to Universities(B06006)for financial support.
文摘This paper describes the combinational surface kinetics enhancement and surface states passivation of nickel-borate(Ni-Bi)co-catalyst for a hematite(Fe_(2)O_(3))photoanode.The Ni-Brmodified Fe_(2)O_(3) photoanode exhibits a cathodic onset potential shift of 230 mV and a 2.3-fold enhancement of the photocurrent at 1.23 V,versus the reversible hydrogen electrode(RHE).The borate(Bi)in the Ni-Bi film promotes the release of pro-tons for the oxygen evolution reaction(OER).
文摘As one of the world’s most produced chemicals, ammonia(NH3) is synthesized by Haber-Bosch process. This century-old industry nourishes billions of people and promotes social and economic development. In the meantime, 3%-5% of the world’s natural gas and 1%-2% of the world’s energy reserves are consumed, releasing millions of tons of carbon dioxide annually to the atmosphere. The urgency of replacing fossil fuels and mitigating climate change motivates us to progress toward more sustainable methods for N2 reduction reaction based on clean energy. Herein, we overview the emerging advancement for sustainable N2 fixation under mild conditions, which include electrochemical, photo-, plasma-enabled and homogeneous molecular NH3 productions. We focus on NH3 generation by electrocatalysts and photocatalysts. We clarify the features and progress of each kind of NH3 synthesis process and provide promising strategies to further promote sustainable ammonia production and construct state-of-the-art catalytic systems.
文摘BACKGROUND Severe periodontitis is a major oral health concern today as it can lead to loss of teeth.Conventional periodontal therapy has numerous pitfalls as it does not address the pulp-periodontal complex in its entirety.AIM To investigate the effect of dental pulp periodontal therapy on the levels of interleukin-1β(IL-1β)and IL-10 in gingival crevicular fluid(GCF)in patients with severe periodontitis.METHODS Eighty-six patients with severe periodontitis were randomly divided into a research group(n=43)and a control group(n=43).The control group was treated with simple periodontal therapy,and the research group was treated with dental pulp periodontal therapy.The total effective rates of the treatments;periodontal status before and after treatment through the measurement of the periodontal pocket probing depth(PPD),gingival sulcus bleeding index(SBI),mobility(MD),and plaque index(PLI);the levels of inflammatory factors IL-1βand IL-10 in the GCF;and the incidence of complications were calculated for both groups and compared using the Student’s t test and theχ^(2) test.RESULTS The total effective rate of treatment in the study group(93.02%)was higher than that in the control group(76.74%;P<0.05).While before treatment,there was no significant difference in the PLI,MD,SBI,or PPD between the two groups,the post-treatment values of PLI,MD,SBI,and PPD(4.71±0.16 mm,0.61±0.09 mm,0.96±0.17 mm,and 0.76±0.26 mm,respectively)were significantly lower(P<0.05)in the research group than in the control group(5.35±0.24 mm,0.93±0.15 mm,1.35±0.30 mm,and 1.04±0.41 mm,respectively).There was no significant difference in the level of IL-1βor IL-10 in the GCF before treatment between the two groups;after treatment,the IL-1βlevel in the research group(139.04±15.54 pg/mL)was significantly lower than that in the control group(156.35±18.10 pg/mL),and the level of IL-10 in the research group(7.98±1.01 ug/L)was higher than that in the control group(5.56±0.96 ug/L)(P<0.05).The incidence of complications in the study group(4.65%)was significantly lower than that of the control group(18.60%;P<0.05).CONCLUSION Endodontic therapy and periodontal treatment for patients with severe periodontitis can effectively reduce the levels of inflammatory factors in the GCF and the inflammatory reaction.In addition,it can improve the periodontal condition and the overall treatment effect,reduce the risk of complications,and ensure the safety of treatment.
基金supported by the National Key Research and Development Program of China(No.2020YFC1808102)the National Natural Science Foundation of China(Nos.42077247 and 42002271)。
文摘Suffusion in gap-graded soil involves selective erosion of fine particles through the pores formed by coarse particles under seepage forces.As the fines content(FC)decreases,the hydraulic and mechanical behavior of the soil will change,posing a huge threat to engineering safety.In this study,we first conduct a series of experimental tests of suffusion by using gap-graded soils and then analyze the evolution process of suffusion and the effect of the hydraulic gradient.Subsequently,according to the physical model,a discrete element method(DEM)numerical model with dynamic fluid mesh(DFM)is developed to extend the experimental study to the pore scale.Our results reveal the migration process of fines and the formation of erosion zones.A parametric study is then conducted to investigate the effect of the hydraulic gradient,FC,and K_(0) pressure(which limits the lateral displacement of the sample and applies vertical pressure)on eroded weight.The results show that the eroded weight increases with the increase of the hydraulic gradient and FC but decreases with the increase of K_(0) pressure.
基金financially supported by the Science and Technology Research Project for Colleges and Universities of Hebei Province(ZD2014040)the Natural Science Foundation of Hebei Province(E2016202406)
文摘To improve the mechanical properties of AZ91D magnesium alloy,the submicrocrystal Al-Ti-B master alloy was prepared with copper mold inject casting method,and the influence of submicrocrystal Al-Ti-B master alloy on the microstructure and mechanical properties of AZ91D was investigated.Results show that,the distribution of Ti B_2 phase in submicrocrystal Al-Ti-B alloy is even and disperse,and the average size of Ti Al_3 phase is reduced from 10-30μm to～1μm.The properties of AZ91D refined with submicrocrystal Al-Ti-B master alloy are better than that with coarse-grained Al-Ti-B master alloy without copper mold inject casting.The tensile strength,elongation and Brinell hardness of AZ91D are increased by 10.6%,25%and 18.1%,respectively.Therefore,refinement of AZ91D with submicrocrystal Al-Ti-B that is obtained by copper mold inject casting is an effective method to improve its mechanical properties.
基金financed by the National Natural Science Foundation of China(No.31770419,31272331,30970375,30400047 to HW)the Postdoctoral Program of Agricultural Science and Technology Innovation Center in North-east China(No.150482 to WO)
文摘Background:For secondary cavity-nesting bird species that do not add lining materials to nests,the presence of old nest material or organic remains that have accumulated within nest cavities from previous breeding events may be a cue of nest-site quality.These materials potentially contain information about past breeding success in con-and heterospecifics and may improve the thermal insulation of eggs during incubation.However,few studies have addressed whether the presence of old nest materials serves as a cue for cavity-nesting raptors when choosing specific nest sites.Methods:We conducted a 9-year nest box experiment to test whether old nest materials from con-and heterospecifics serve as informative cues to the European Kestrel(Falco tinnunculus)when making nest selection decisions,as this species uses nest boxes without adding nesting material.Results:The presence of old nest materials and entrance size best discriminated nest boxes occupied by European Kestrels from unoccupied boxes.Nest boxes containing conspecific organic remains,artificial dry leaf and branch material,and material left behind by Great Tits(Parus major)were reused at higher rates,especially those containing conspecific nest material,than nest boxes containing true or simulated nest materials from predators.In 2010,no single nest box was occupied by the same banded individual that occupied the box in the previous year(10 females and 2 males were banded in 2009).Conclusions:European Kestrels preferred nest boxes containing old nest material over empty boxes,which is consistent with previous findings that they exploit con-and heterospecific cues when deciding where to settle and breed,as old nest or organic material provides substrate for incubating females.Kestrels may be able to assess the predation risks associated with a specific nest site based on experience or the presence of prey remains.The repeated use of nest boxes across breeding seasons by kestrels cannot be entirely ascribed to philopatry.This study provides evidence that old nest materials are potentially used as informative cues when making nest-site selection decisions in European Kestrels.
基金This work is supported in part by National Natural Science Foundation of China(61373132,61872408)the Key Laboratory of informationization technology for basic education in Hunan province(2015TP1017)+1 种基金Hunan provincial higher education reform research project(2012[528])Project of research study and innovative experiment for college students in Hunan Province(2017[873]).
文摘In order to provide a good practice platform for the program design contestants and algorithm enthusiasts,this paper designs and implements a programming online evaluation system based on cloud platform,which is a web system that can return the test results of the program source codes submitted by users in real time.It realizes the automatic evaluation of the program design training questions.The system is implemented by the way of front-end and back-end separation and modular programming.The front-end of the web is implemented by Vue framework,the back-end is implemented by Django framework.The judgment core is written in C language for the sake of improving the efficiency of the system.Sandbox technology is used to ensure the security of the judgment system.Experimental results show that the system can meet the need of daily teaching and competition.
基金the National Key R&D Program of China(Nos.2021YFA1500804,2022YFA1505200)the National Natural Science Foundation of China(Nos.22121004,51861125104)+2 种基金the Natural Science Foundation of Tianjin City(Nos.18JCJQJC47500,21JCZXJC00060)Haihe Laboratory of Sustainable Chemical Transformations(No.CYZC202107)the Program of Introducing Talents of Discipline to Universities(No.BP0618007)and the Xplorer Prize for financial support。
文摘Photoelectrochemical(PEC)seawater splitting is a promising method for the direct utilization of solar energy and abundant seawater resources for hydrogen production.Photoelectrodes are susceptible to various ions in seawater and complicated competitive reactions,resulting in the failure of photoelectrodes.This paper proposes the design and fabrication of diff erent sputtered stainless steel(SS)fi lms deposited on silicon photoanodes,completely isolating the electrolytes and semiconductor substrate.Upon coupling with the PEC flow cell,the back-illuminated photoanode coated with 316 SS cocatalyst achieves stable operation for 70 h in natural seawater with a highly alkaline KOH(30 wt.%,7.64 mol/L)electrolyte due to the remarkable protection eff ect of the substrate from stainless steel,while the PEC seawater splitting system achieves a record hydrogen production rate of 600μmol/(h·cm^(2)).An appropriate Ni/Fe ratio in the SS ensures remarkable oxygen evolution activity,while chromic oxide ensures the effective anticorrosion effect by adjusting the microenvironment of the photoanodes.Moreover,fabricating PEC flow cells with photoanodes coated with SS cocatalysts are a viable strategy for PEC seawater splitting.
基金This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences(XDA26010101)the National Key Research and Development Program of China(2020YFC0832800)+1 种基金National Natural Science Foundation of China(41801366,52101405)NSFC-RS exchange project between China and UK(42011530175)。
文摘Patterns in species geographic range size are relatively well-known for vertebrates,but still poorly known for plants.Contrasts of these patterns between groups have rarely been investigated.With a detailed flora and fauna distribution database of Xinjiang,China,we used regression methods,redundancy analysis and random forests to explore the relationship of environment and body size with the geographic range size of plants,mammals and birds in Xinjiang and contrast these patterns between plants and animals.We found positive correlations between species range size and body size.The range size of plants was more influenced by water variables,while that of mammals and birds was largely influenced by temperature variables.The productivity variable,i.e.,Enhanced Vegetation Index(EVI)was far more correlated with range size than climatic variables for both plants and animals,suggesting that vegetation productivity inferred from remote sensing data may be a good predictor of species range size for both plants and animals.
基金supported by the Technology Project of the State Grid Corporation Headquarters Management(Contract No.5100-202158467A-0-0-00).
文摘Voltage source converter based high voltage direct current(VSC-HVDC)can participate in voltage regulation by flexible control to help maintain the voltage stability of the power grid.In order to quantitatively evaluate its influence on the voltage interaction between VSC-HVDC and line commutated converter based high voltage direct current(LCC-HVDC),this paper proposes a hybrid multi-infeed interaction factor(HMIIF)calculation method considering the voltage regulation control characteristics of VSC-HVDC.Firstly,for a hybrid multi-infeed high voltage direct current system,an additional equivalent operating admittance matrix is constructed to characterize HVDC equipment characteristics under small disturbance.Secondly,based on the characteristic curve between the reactive power and the voltage of a certain VSC-HVDC project,the additional equivalent operating admittance of VSC-HVDC is derived.The additional equivalent operating admittance matrix calculation method is proposed.Thirdly,the equivalent bus impedance matrix is obtained by modifying the alternating current(AC)system admittance matrix with the additional equivalent operating admittance matrix.On this basis,the HMIIF calculation method based on the equivalent bus impedance ratio is proposed.Finally,the effectiveness of the proposed method is verified in a hybrid dual-infeed high voltage direct current system constructed in Power Systems Computer Aided Design(PSCAD),and the influence of voltage regulation control on HMIIF is analyzed.
