In recent years,research investigations have focused on the substantial freshwater storage in the Beaufort Gyre(BG)region due to climate change.Despite active mesoscale eddies in the area,a notable gap in understandin...In recent years,research investigations have focused on the substantial freshwater storage in the Beaufort Gyre(BG)region due to climate change.Despite active mesoscale eddies in the area,a notable gap in understanding the three-dimensional structure and induced transport has been observed.This study concentrates on the Canada Basin in the western Arctic Ocean,specifically examining a subsurface anticyclonic eddy(SAE)sampled by a Mooring A in the BG region.Hybrid Coordinate Ocean Model(HYCOM)analysis data reveal its lifecycle from February 15 to March 15,2017,marked by initiation,development,maturity,decay,and termination stages.This work extends the finding of SAE passing through Mooring A by examining its overall effects,spatiotemporal variations,and swirl transport.SAE generation through baroclinic instability,which contributes to the westward tilt of the vertical axis,is also confirmed in this study.Swirl transport induced by SAE is predominantly eastward and downward due to its trajectory and background flow.SAE temporarily weakens stratification and extends the subsurface depth but demonstrates transient effects.Moreover,SAE transports upper-layer freshwater,Pacific Winter Water,and Atlantic Water downward,emphasizing its potential influence on freshwater redistribution in the Canadian Basin.This research provides valuable insights into mesoscale eddy dynamics,revealing their role in modulating the upper water mass in the BG region.展开更多
This paper explores the construction methods of“Same Course with Different Structures”curriculum resources based on knowledge graphs and their applications in the field of education.By reviewing the theoretical foun...This paper explores the construction methods of“Same Course with Different Structures”curriculum resources based on knowledge graphs and their applications in the field of education.By reviewing the theoretical foundations of knowledge graph technology,the“Same Course with Different Structures”teaching model,and curriculum resource construction,and integrating existing literature,the paper analyzes the methods for constructing curriculum resources using knowledge graphs.The research finds that knowledge graphs can effectively integrate multi-source data,support personalized teaching and precision education,and provide both a scientific foundation and technical support for the development of curriculum resources within the“Same Course with Different Structures”framework.展开更多
This article aims to develop a head pursuit （HP） guidance law for three-dimensional hypervelocity interception, so that the effect of the perturbation induced by seeker detection can be reduced. On the basis of a no...This article aims to develop a head pursuit （HP） guidance law for three-dimensional hypervelocity interception, so that the effect of the perturbation induced by seeker detection can be reduced. On the basis of a novel HP three-dimensional guidance model, a nonlinear variable structure guidance law is presented by using Lyapunov stability theory. The guidance law positions the interceptor ahead of the target on its tlight trajectory, and the speed of the interceptor is required to be lower than that of the target, A numerical example of maneuvering ballistic target interception verifies the rightness of the guidance model and the effectiveness of the proposed method.展开更多
Microseismic/acoustic emission(MS/AE)source localization method is crucial for predicting and controlling of potentially dangerous sources of complex structures.However,the locating errors induced by both the irregula...Microseismic/acoustic emission(MS/AE)source localization method is crucial for predicting and controlling of potentially dangerous sources of complex structures.However,the locating errors induced by both the irregular structure and pre-measured velocity are poorly understood in existing methods.To meet the high-accuracy locating requirements in complex three-dimensional hole-containing structures,a velocity-free MS/AE source location method is developed in this paper.It avoids manual repetitive training by using equidistant grid points to search the path,which introduces A*search algorithm and uses grid points to accommodate complex structures with irregular holes.It also takes advantage of the velocity-free source location method.To verify the validity of the proposed method,lead-breaking tests were performed on a cubic concrete test specimen with a size of 10 cm10 cm10 cm.It was cut out into a cylindrical empty space with a size of/6cm10 cm.Based on the arrivals,the classical Geiger method and the proposed method are used to locate lead-breaking sources.Results show that the locating error of the proposed method is 1.20 cm,which is less than 2.02 cm of the Geiger method.Hence,the proposed method can effectively locate sources in the complex three-dimensional structure with holes and achieve higher precision requirements.展开更多
As in-situ observations are sparse,targeted observations of a specific mesoscale eddy are rare.Therefore,it is difficult to study the three-dimensional structure of moving mesoscale eddies.From April to September 2014...As in-situ observations are sparse,targeted observations of a specific mesoscale eddy are rare.Therefore,it is difficult to study the three-dimensional structure of moving mesoscale eddies.From April to September 2014,an anticyclonic eddy located at 135°E-155°E,26°N-42°N was observed using 17 rapidsampling Argo floats,and the spatiotemporal variations in the three-dimensional structure were studied.The results are as follows:(1)the eddy was identified and tracked using satellite altimeter data.It had a lifetime of 269 days and an average radius of 91.5 km.The lifetime of the eddy can be divided into three phases,i.e.,the initiation,maturity,and termination phases.The depth of its influence reached 1000 m;(2)the Argo profiles were divided into seven periods(approximately 20 days in each)for composite analysis,and the composite Argo profiles and CARS2009(CSIRO Atlas of Regional Seas)climatology data were merged following the data-interpolating variational analysis(DIVA)method to reconstruct the three-dimensional structure.The temperature and salinity anomaly cores of the anticyclonic mesoscale eddy are located from 400 to 600 m.From 800 to 900 m,there is an area of low salinity at the center of the eddy.A high concentration anomaly of dissolved oxygen was located at approximately 250 m;(3)to better understand the features of the eddy and its interaction with the surroundings,we calculated the anomalous velocity of the geostrophic flow and the heat,salt,dissolved oxygen transport anomaly,and discussed the eddy's origin and its adjustments to topography.The maximum heat,salt,and oxygen transport caused by eddy were 9.37×10^11 W,3.08×10^3 kg/s,and 2.70×10^2 kg/s,which all occurred during the termination phase.This study highlights the applicability of using Argo floats to understand the three-dimensional structure thermohaline features of eddies in the North Pacific.展开更多
The three-dimensional structure and the seasonal variation of the North Pacific meridional overturning circulation （NPMOC） are analyzed based on the Simple Ocean Data Assimilation data and Argo profiling float data....The three-dimensional structure and the seasonal variation of the North Pacific meridional overturning circulation （NPMOC） are analyzed based on the Simple Ocean Data Assimilation data and Argo profiling float data. The NPMOC displays a multi-cell structure with four cells in the North Pacific altogether. The TC and the STC are a strong clockwise meridional cell in the low latitude ocean and a weaker clockwise meridional cell between 7°N and 18°N, respectively, while the DTC and the subpolar cell are a weaker anticlockwise meridional cell between 3°N and 15°N and a weakest anticlockwise meridional cell between 35°N and 50°N, respectively. The DTC, the TC and the STC are all of very strong seasonal variations. As to the DTC, the southward transport is strongest in fall and weakest in spring. For the TC, the northward transport is strongest in winter and weakest in spring, while the southward transport is strongest in fall and weakest in spring, which is associated with the strong southward fiow of the DTC in fall. As the STC, the northward transport is strongest in winter and weakest in summer, while the southward transport is strongest in summer and weakest in spring. This seasonal difference may be associated with the DTC. The zonal wind stress and the east-west slope of sea level play important roles in the seasonal variations of the TC, the STC and the DTC.展开更多
In order to obtain high-performance electromagnetic wave absorbers,the adjustment of structure and components is essential.Based on the above requirements,this system forms a three-dimensional frame structure consisti...In order to obtain high-performance electromagnetic wave absorbers,the adjustment of structure and components is essential.Based on the above requirements,this system forms a three-dimensional frame structure consisting of MXene and transition metal oxides(TMOs)through efficient electrostatic self-assembly.This three-dimensional network structure has rich heterojunction structures,which can cause a large amount of interface polarization and conduction losses in incident electromagnetic waves.Hollow structures cause multiple reflections and scattering of electromagnetic waves,which is also an important reason for further increasing electromagnetic wave losses.When the doping ratio is 1:1,the system has the best impedance matching,the maximum effective absorption bandwidth(EAB max)can reach 5.12 GHz at 1.7 mm,and the minimum reflection loss(RL_(min))is-50.30 dB at 1.8 mm.This provides a reference for the subsequent formation of 2D-MXene materials into 3D materials.展开更多
This paper presents a three-dimensional particle-in-cell （PIC） simulation of a Ka-band relativistic Cherenkov source with a slow wave structure （SWS） consisting of metal photonic band gap （PBG） structures. In th...This paper presents a three-dimensional particle-in-cell （PIC） simulation of a Ka-band relativistic Cherenkov source with a slow wave structure （SWS） consisting of metal photonic band gap （PBG） structures. In the simulation, a perfect match layer boundary is employed to absorb passing band modes supported by the PBG lattice with an artificial metal boundary. The simulated axial field distributions in the cross section and surface of the SWS demonstrate that the device operates in the vicinity of the π point of a TM01-1ike mode. The Fourier transformation spectra of the axial fields as functions of time and space show that only a single frequency appears at 36.27 GHz, which is in good agreement with that of the intersection of the dispersion curve with the slow space charge wave generated on the beam. The simulation results demonstrate that the SWS has good mode selectivity.展开更多
Neural stem cells,which are capable of multi-potential differentiation and self-renewal,have recently been shown to have clinical potential for repairing central nervous system tissue damage.However,the theme trends a...Neural stem cells,which are capable of multi-potential differentiation and self-renewal,have recently been shown to have clinical potential for repairing central nervous system tissue damage.However,the theme trends and knowledge structures for human neural stem cells have not yet been studied bibliometrically.In this study,we retrieved 2742 articles from the PubMed database from 2013 to 2018 using "Neural Stem Cells" as the retrieval word.Co-word analysis was conducted to statistically quantify the characteristics and popular themes of human neural stem cell-related studies.Bibliographic data matrices were generated with the Bibliographic Item Co-Occurrence Matrix Builder.We identified 78 high-frequency Medical Subject Heading(MeSH)terms.A visual matrix was built with the repeated bisection method in gCLUTO software.A social network analysis network was generated with Ucinet 6.0 software and GraphPad Prism 5 software.The analyses demonstrated that in the 6-year period,hot topics were clustered into five categories.As suggested by the constructed strategic diagram,studies related to cytology and physiology were well-developed,whereas those related to neural stem cell applications,tissue engineering,metabolism and cell signaling,and neural stem cell pathology and virology remained immature.Neural stem cell therapy for stroke and Parkinson’s disease,the genetics of microRNAs and brain neoplasms,as well as neuroprotective agents,Zika virus,Notch receptor,neural crest and embryonic stem cells were identified as emerging hot spots.These undeveloped themes and popular topics are potential points of focus for new studies on human neural stem cells.展开更多
Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed...Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.展开更多
Based on patent cooperation data,this study used a range of city network analysis approaches in order to explore the structure of the Chinese city network which is driven by technological knowledge flows.The results r...Based on patent cooperation data,this study used a range of city network analysis approaches in order to explore the structure of the Chinese city network which is driven by technological knowledge flows.The results revealed the spatial structure,composition structure,hierarchical structure,group structure,and control structure of Chinese city network,as well as its dynamic factors.The major findings are:1) the spatial pattern presents a diamond structure,in which Wuhan is the central city;2) although the invention patent knowledge network is the main part of the broader inter-city innovative cooperation network,it is weaker than the utility model patent;3) as the senior level cities,Beijing,Shanghai and the cities in the Zhujiang(Pearl) River Delta Region show a strong capability of both spreading and controlling technological knowledge;4) whilst a national technology alliance has preliminarily formed,regional alliances have not been adequately established;5) even though the cooperation level amongst weak connection cities is not high,such cities still play an important role in the network as a result of their location within ′structural holes′ in the network;and 6) the major driving forces facilitating inter-city technological cooperation are geographical proximity,hierarchical proximity and technological proximity.展开更多
Mesoscale eddies play an important role in modulating the ocean circulation.Many previous studies on the threedimensional structure of mesoscale eddies were mainly based on composite analysis,and there are few targete...Mesoscale eddies play an important role in modulating the ocean circulation.Many previous studies on the threedimensional structure of mesoscale eddies were mainly based on composite analysis,and there are few targeted observations for individual eddies.A cyclonic eddy surveyed during an oceanographic cruise in the Northwest Pacific Ocean is investigated in this study.The three-dimensional structure of this cyclonic eddy is revealed by observations and simulated by the four-dimensional variational data assimilation(4 DVAR)system combined with the Regional Ocean Modeling System.The observation and assimilation results together present the characteristics of the cyclonic eddy.The cold eddy has an obvious dual-core structure of temperature anomaly.One core is at 50–150 m and another is at 300–550 m,which both have the average temperature anomaly of approximately-3.5℃.The salinity anomaly core is between 250 m and 500 m,which is approximately-0.3.The horizontal velocity structure is axis-asymmetric and it is enhanced on the eastern side of the cold eddy.In the assimilation experiment,sea level anomaly,sea surface temperature,and in situ measurements are assimilated into the system,and the results of assimilation are close to the observations.Based on the high-resolution assimilation output results,the study also diagnoses the vertical velocity in the mesoscale eddy,which reaches the maximum of approximately 10 m/d.The larger vertical velocity is found to be distributed in the range of 0.5 to 1 time of the normalized radius of the eddy.The validation of the simulation result shows that the 4 DVAR method is effective to reconstruct the three-dimensional structure of mesoscale eddy and the research is an application to study the mesoscale eddy in the Northwest Pacific by combining observation and assimilation methods.展开更多
A comprehensive safety evaluation system taking the most influential factors into account has been developed to evaluate the reliability of hydraulic metal structures. Applying the techniques of AI and DB, the idea of...A comprehensive safety evaluation system taking the most influential factors into account has been developed to evaluate the reliability of hydraulic metal structures. Applying the techniques of AI and DB, the idea of a one-machine and three-base system is proposed. The framework of the three-base system has been designed and the structural framework constructed in turn. A practical example is given to illustrate the process of using this system and it can be used for comparison and analysis purposes. The key technology of the system is its ability to reorganize and improve the expert system＇s knowledge base by establishing the expert system. This system utilizes the computer technology inference process, making safety evaluation conclusions more reasonable and applicable to the actual situation. The system is not only advanced, but also feasible, reliable, artificially intelligent, and has the capacity to constantly grow.展开更多
The bis(tributyltin) ester of succinic acid was synthesized by the reaction of disodium salt of succinic acid with tributyltin chloride in a molar ratio of 1:2. The crystal structure was determined by X-ray single-cry...The bis(tributyltin) ester of succinic acid was synthesized by the reaction of disodium salt of succinic acid with tributyltin chloride in a molar ratio of 1:2. The crystal structure was determined by X-ray single-crystal diffraction. It belongs to orthorhombic with space group Pccn, a = 20.949(3), b = 17.470(3), c = 20.345(3) Angstrom, V = 7446(2) Angstrom(3), Z = 8, D-c = 1.242 g/cm(3), mu = 1.365 mm(-1), F(000) = 2864, R = 0.0544 and wR = 0.1417. The tin atom is of five-coordination in a trigonal bipyramidal structure by bridging two carboxylate groups in different directions and the resulting structure which contains straight twist large ring channels along the axes of a, b and c is a three-dimensional framework polymer containing two different tin atoms.展开更多
A magnitude 5.5 earthquakes occurred in Eryuan County,Dali Bai Autonomous Prefecture,Yunnan Province,China,on March 3.And a magnitude 5.0 earthquake occurred in the same place on April 17,2013,i.e.,45 days later.Then,...A magnitude 5.5 earthquakes occurred in Eryuan County,Dali Bai Autonomous Prefecture,Yunnan Province,China,on March 3.And a magnitude 5.0 earthquake occurred in the same place on April 17,2013,i.e.,45 days later.Then,on May 21,2021,multiple earthquakes,one with magnitude 6.4 and several at 5.0 or above,occurred in Yangbi County,Dali Bai Autonomous Prefecture,Yunnan Province,China.All of these occurred in the Weixi-QiaohouWeishan fault zone.In this study,1,874 seismic events in Yangbi and Eryuan counties were identified by automatic micro-seismic identification technology and the first arrivals were picked up manually.Following this,a total of 11,968 direct P-wave absolute arrivals and 73,987 high-quality Pwave relative arrivals were collected for joint inversion via the double difference tomography method.This was done to obtain the regional three-dimensional fine crustal P-wave velocity structure.The results show that the travel time residuals before and after inversion decreased from the initial–0.1–0.1 s to–0.06–0.06 s.The upper crust in the study area,which exhibited a low-velocity anomaly,corresponded to the basin region;this indicated that the low-velocity anomaly in the shallow part of the study area was affected by the basin.Results also showed some correlation between the distribution of the earthquakes and velocity structure,as there was a lowvelocity body Lv1 with a wide distribution at depths ranging from 15–20 km in the Yangbi and Eryuan earthquake regions.In addition,earthquakes occurred predominantly in the highlow velocity abnormal transition zone.The low-velocity body in the middle and lower crust may be prone to concentrating upper crustal stress,thus leading to the occurrence of earthquakes.展开更多
Taking the Paleogene salt strata in the west of Kuqa foreland thrust belt as study object, the deformation features of salt structure in the compression direction and perpendicular to the compression direction were ex...Taking the Paleogene salt strata in the west of Kuqa foreland thrust belt as study object, the deformation features of salt structure in the compression direction and perpendicular to the compression direction were examined to find out the control factors and formation mechanisms of the salt structures. By using the three-dimensional discrete element numerical simulation method, the formation mechanisms of typical salt structures of western Kuqa foreland thrust belt in Keshen and Dabei work areas were comprehensively analyzed. The simulation results show that the salt deformation in Keshen and Dabei work areas is of forward spread type, with deformation concentrated in the piedmont zone;the salt deformation is affected by the early uplift near the compression end, pre-existing basement faults, synsedimentary process and the initial salt depocenter;in the direction perpendicular to the compression direction, salt rocks near the compression end have strong lateral mobility with the velocity component moving towards the middle part, and the closer to the middle, the larger the velocity will be, so that salt rocks will aggregate towards the middle and deform intensely, forming complex folds and separation of salt structures from salt source, and local outcrop with thrust faults. Compared with 2 D simulation, 3 D simulation can analyze salt structures in the principal stress direction and direction perpendicular to the principal stress, give us a full view of the formation mechanisms of salt structures, and guide the exploration of oil and gas reservoirs related to salt structures.展开更多
The geometric and spatial characteristics of pore structures determine the permeability and water retention of soils, which have important effects on soil functional diversity and ecological restoration. Until recentl...The geometric and spatial characteristics of pore structures determine the permeability and water retention of soils, which have important effects on soil functional diversity and ecological restoration. Until recently, there have not been tools and methods to visually and quantitatively describe the characteristics of soil pores. To solve this problem, this research reconstructs the geometry and spatial distribution of soil pores by the marching cubes method, texture mapping method and the ray casting method widely used in literature. The objectives were to explore an optimal method for three-dimensional visualization of soil pore structure by comparing the robustness of the three methods on soil CT images with single pore structure and porosity ranging from low (2–5%) to high (12–18%), and to evaluate the reconstruction performance of the three methods with different geometric features. The results demonstrate that there are aliases (jagged edges) and deficiency at the boundaries of the model reconstructed by the marching cubes method and pore volumes are smaller than the ground truth, whereas the results of the texture mapping method lack the details of pore structures. For all the soil images, the ray casting method is preferable since it better preserves the pore characteristics of the ground truth. Furthermore, the ray casting method produced the best soil pore model with higher rendering speed and lower memory consumption. Therefore, the ray casting method provides a more advanced method for visualization of pore structures and provides an optional technique for the study of the transport of moisture and the exchange of air in soil.展开更多
Point bars are well developed on the Yellow River delta, an~ which theShengli I point bar is the most typical. The point bar, being about 4 km in length and several tensto more than 100 meters in width, is located on ...Point bars are well developed on the Yellow River delta, an~ which theShengli I point bar is the most typical. The point bar, being about 4 km in length and several tensto more than 100 meters in width, is located on the south side of the Shengli Bridge in KenliCounty, Dongying, Shandong. It is a typical fine-grained point bar with silt, which is predominant,some clay and minor plant debris and clay boulders. The Shengli I Point bar has complicated 3-Dstructures. Firstly, in a plane view, it comprises mainly eight sedimentary units, bar edge, baredge, bar platform, bar plain, bar channel, bar gully, bar pond and bar bay, developing side by sideand superimposed one by one m a complex way. Secondly, its vertical structures are very complex dueto the partial superimposition of the 8 sedimentary units. Besides hydatogenesis, very intensivewind erosion, eolian, ice and meltwater actions are also visible on the Shengli I point bar. Thecomplex form is made even more complicated because of the above co-actions.展开更多
A detail three-dimensional P wave velocity structure of Beijing, Tianjin and Tangshan area (BTT area) was deter-mined by inverting local earthquake data. In total 16 048 P wave first arrival times from 16048 shallow a...A detail three-dimensional P wave velocity structure of Beijing, Tianjin and Tangshan area (BTT area) was deter-mined by inverting local earthquake data. In total 16 048 P wave first arrival times from 16048 shallow and mid-depth crustal earthquakes, which occurred in and around the BTT area from 1992 to 1999 were used. The first arrival times are recorded by Northern China United Telemetry Seismic Network and Yanqing-Huailai Digital Seismic Network. Hypocentral parameters of 1 132 earthquakes with magnitude ML=1.7~6.2 and the three-dimensional P wave velocity structure were obtained simultaneously. The inversion result reveals the com-plicated lateral heterogeneity of P wave velocity structure around BTT area. The tomographic images obtained are also found to explain other seismological observations well.展开更多
2D nanosheets such as graphene, silicene, phosphorene, metal dichalcogenides and MXenes are emerging and promising for lithium storage due to their ultrathin nature and corresponding chemical/physical properties. Howe...2D nanosheets such as graphene, silicene, phosphorene, metal dichalcogenides and MXenes are emerging and promising for lithium storage due to their ultrathin nature and corresponding chemical/physical properties. However, the serious restacking and aggregation of the 2D nanosheets are still hampering their applications. To circumvent the issues of 2D nanosheets, one efficient strategy is to construct 3D structures with hierarchical porous structures, good chemical/mechanical stabilities and tunable electrical conductivities. In this review, we firstly focus on the available synthetic approaches of 3D structures from 2D nanosheets, and then summarize the relationships between the microstructures of 3D structures built from 2D nanosheets and their electrochemical behaviors for lithium storage. On the basis of above results, some challenges are briefly discussed in the perspective of the development of various functional 3D structures.展开更多
基金support of the Fundamental Research Funds for the Central Universities(No.E2ET0411X2).
文摘In recent years,research investigations have focused on the substantial freshwater storage in the Beaufort Gyre(BG)region due to climate change.Despite active mesoscale eddies in the area,a notable gap in understanding the three-dimensional structure and induced transport has been observed.This study concentrates on the Canada Basin in the western Arctic Ocean,specifically examining a subsurface anticyclonic eddy(SAE)sampled by a Mooring A in the BG region.Hybrid Coordinate Ocean Model(HYCOM)analysis data reveal its lifecycle from February 15 to March 15,2017,marked by initiation,development,maturity,decay,and termination stages.This work extends the finding of SAE passing through Mooring A by examining its overall effects,spatiotemporal variations,and swirl transport.SAE generation through baroclinic instability,which contributes to the westward tilt of the vertical axis,is also confirmed in this study.Swirl transport induced by SAE is predominantly eastward and downward due to its trajectory and background flow.SAE temporarily weakens stratification and extends the subsurface depth but demonstrates transient effects.Moreover,SAE transports upper-layer freshwater,Pacific Winter Water,and Atlantic Water downward,emphasizing its potential influence on freshwater redistribution in the Canadian Basin.This research provides valuable insights into mesoscale eddy dynamics,revealing their role in modulating the upper water mass in the BG region.
基金Educational and Teaching Reform Project of Beihua University:Research on the Construction of“Same Course with Different Structures”Course Resources Based on Knowledge Graphs。
文摘This paper explores the construction methods of“Same Course with Different Structures”curriculum resources based on knowledge graphs and their applications in the field of education.By reviewing the theoretical foundations of knowledge graph technology,the“Same Course with Different Structures”teaching model,and curriculum resource construction,and integrating existing literature,the paper analyzes the methods for constructing curriculum resources using knowledge graphs.The research finds that knowledge graphs can effectively integrate multi-source data,support personalized teaching and precision education,and provide both a scientific foundation and technical support for the development of curriculum resources within the“Same Course with Different Structures”framework.
文摘This article aims to develop a head pursuit （HP） guidance law for three-dimensional hypervelocity interception, so that the effect of the perturbation induced by seeker detection can be reduced. On the basis of a novel HP three-dimensional guidance model, a nonlinear variable structure guidance law is presented by using Lyapunov stability theory. The guidance law positions the interceptor ahead of the target on its tlight trajectory, and the speed of the interceptor is required to be lower than that of the target, A numerical example of maneuvering ballistic target interception verifies the rightness of the guidance model and the effectiveness of the proposed method.
基金The authors wish to acknowledge financial support from the National Natural Science Foundation of China(51822407 and 51774327)Natural Science Foundation of Hunan Province in China(2018JJ1037)Innovation Driven project of Central South University(2020CX014).
文摘Microseismic/acoustic emission(MS/AE)source localization method is crucial for predicting and controlling of potentially dangerous sources of complex structures.However,the locating errors induced by both the irregular structure and pre-measured velocity are poorly understood in existing methods.To meet the high-accuracy locating requirements in complex three-dimensional hole-containing structures,a velocity-free MS/AE source location method is developed in this paper.It avoids manual repetitive training by using equidistant grid points to search the path,which introduces A*search algorithm and uses grid points to accommodate complex structures with irregular holes.It also takes advantage of the velocity-free source location method.To verify the validity of the proposed method,lead-breaking tests were performed on a cubic concrete test specimen with a size of 10 cm10 cm10 cm.It was cut out into a cylindrical empty space with a size of/6cm10 cm.Based on the arrivals,the classical Geiger method and the proposed method are used to locate lead-breaking sources.Results show that the locating error of the proposed method is 1.20 cm,which is less than 2.02 cm of the Geiger method.Hence,the proposed method can effectively locate sources in the complex three-dimensional structure with holes and achieve higher precision requirements.
基金Supported by the National Key R&D Program of China(No.2018YFC1406202)the National Natural Science Foundation of China(Nos.41830964,41976188,41605051)。
文摘As in-situ observations are sparse,targeted observations of a specific mesoscale eddy are rare.Therefore,it is difficult to study the three-dimensional structure of moving mesoscale eddies.From April to September 2014,an anticyclonic eddy located at 135°E-155°E,26°N-42°N was observed using 17 rapidsampling Argo floats,and the spatiotemporal variations in the three-dimensional structure were studied.The results are as follows:(1)the eddy was identified and tracked using satellite altimeter data.It had a lifetime of 269 days and an average radius of 91.5 km.The lifetime of the eddy can be divided into three phases,i.e.,the initiation,maturity,and termination phases.The depth of its influence reached 1000 m;(2)the Argo profiles were divided into seven periods(approximately 20 days in each)for composite analysis,and the composite Argo profiles and CARS2009(CSIRO Atlas of Regional Seas)climatology data were merged following the data-interpolating variational analysis(DIVA)method to reconstruct the three-dimensional structure.The temperature and salinity anomaly cores of the anticyclonic mesoscale eddy are located from 400 to 600 m.From 800 to 900 m,there is an area of low salinity at the center of the eddy.A high concentration anomaly of dissolved oxygen was located at approximately 250 m;(3)to better understand the features of the eddy and its interaction with the surroundings,we calculated the anomalous velocity of the geostrophic flow and the heat,salt,dissolved oxygen transport anomaly,and discussed the eddy's origin and its adjustments to topography.The maximum heat,salt,and oxygen transport caused by eddy were 9.37×10^11 W,3.08×10^3 kg/s,and 2.70×10^2 kg/s,which all occurred during the termination phase.This study highlights the applicability of using Argo floats to understand the three-dimensional structure thermohaline features of eddies in the North Pacific.
基金Supported by the National Basic Research Development Program of China(973 Program)under contract Nos 2007CB816002,2007CB816005the innovative key project of Chinese Academy of Sciences under contract No.KZCXZ-YW-201
文摘The three-dimensional structure and the seasonal variation of the North Pacific meridional overturning circulation （NPMOC） are analyzed based on the Simple Ocean Data Assimilation data and Argo profiling float data. The NPMOC displays a multi-cell structure with four cells in the North Pacific altogether. The TC and the STC are a strong clockwise meridional cell in the low latitude ocean and a weaker clockwise meridional cell between 7°N and 18°N, respectively, while the DTC and the subpolar cell are a weaker anticlockwise meridional cell between 3°N and 15°N and a weakest anticlockwise meridional cell between 35°N and 50°N, respectively. The DTC, the TC and the STC are all of very strong seasonal variations. As to the DTC, the southward transport is strongest in fall and weakest in spring. For the TC, the northward transport is strongest in winter and weakest in spring, while the southward transport is strongest in fall and weakest in spring, which is associated with the strong southward fiow of the DTC in fall. As the STC, the northward transport is strongest in winter and weakest in summer, while the southward transport is strongest in summer and weakest in spring. This seasonal difference may be associated with the DTC. The zonal wind stress and the east-west slope of sea level play important roles in the seasonal variations of the TC, the STC and the DTC.
基金supported by the National Natural Science Foundation of China(Nos.51407134,52002196)Natural Science Foundation of Shandong Province(Nos.ZR2019YQ24,ZR2020QF084)+1 种基金Taishan Scholars and Young Experts Program of Shandong Province(No.tsqn202103057)the Qingchuang Talents Induction Program of Shandong Higher Education Institution(Research and Innovation Team of Structural-Functional Polymer Composites)and Special Financial of Shandong Province(Structural Design of High-efficiency Electromagnetic Wave-absorbing Composite Materials and Construction of Shandong Provincial Talent Teams(No.37000022P990304116449)).
文摘In order to obtain high-performance electromagnetic wave absorbers,the adjustment of structure and components is essential.Based on the above requirements,this system forms a three-dimensional frame structure consisting of MXene and transition metal oxides(TMOs)through efficient electrostatic self-assembly.This three-dimensional network structure has rich heterojunction structures,which can cause a large amount of interface polarization and conduction losses in incident electromagnetic waves.Hollow structures cause multiple reflections and scattering of electromagnetic waves,which is also an important reason for further increasing electromagnetic wave losses.When the doping ratio is 1:1,the system has the best impedance matching,the maximum effective absorption bandwidth(EAB max)can reach 5.12 GHz at 1.7 mm,and the minimum reflection loss(RL_(min))is-50.30 dB at 1.8 mm.This provides a reference for the subsequent formation of 2D-MXene materials into 3D materials.
基金Project supported by the National Key Basic Research Program of China (Grant No 2007CB31040)the National Natural Science Foundation of China (Grant No 60571020)
文摘This paper presents a three-dimensional particle-in-cell （PIC） simulation of a Ka-band relativistic Cherenkov source with a slow wave structure （SWS） consisting of metal photonic band gap （PBG） structures. In the simulation, a perfect match layer boundary is employed to absorb passing band modes supported by the PBG lattice with an artificial metal boundary. The simulated axial field distributions in the cross section and surface of the SWS demonstrate that the device operates in the vicinity of the π point of a TM01-1ike mode. The Fourier transformation spectra of the axial fields as functions of time and space show that only a single frequency appears at 36.27 GHz, which is in good agreement with that of the intersection of the dispersion curve with the slow space charge wave generated on the beam. The simulation results demonstrate that the SWS has good mode selectivity.
基金supported by the National Natural Science Foundation of China,No.81471308(to JL)the Stem Cell Clinical Research Project in China,No.CMR-20161129-1003(to JL)the Innovation Technology Funding of Dalian in China,No.2018J11CY025(to JL)
文摘Neural stem cells,which are capable of multi-potential differentiation and self-renewal,have recently been shown to have clinical potential for repairing central nervous system tissue damage.However,the theme trends and knowledge structures for human neural stem cells have not yet been studied bibliometrically.In this study,we retrieved 2742 articles from the PubMed database from 2013 to 2018 using "Neural Stem Cells" as the retrieval word.Co-word analysis was conducted to statistically quantify the characteristics and popular themes of human neural stem cell-related studies.Bibliographic data matrices were generated with the Bibliographic Item Co-Occurrence Matrix Builder.We identified 78 high-frequency Medical Subject Heading(MeSH)terms.A visual matrix was built with the repeated bisection method in gCLUTO software.A social network analysis network was generated with Ucinet 6.0 software and GraphPad Prism 5 software.The analyses demonstrated that in the 6-year period,hot topics were clustered into five categories.As suggested by the constructed strategic diagram,studies related to cytology and physiology were well-developed,whereas those related to neural stem cell applications,tissue engineering,metabolism and cell signaling,and neural stem cell pathology and virology remained immature.Neural stem cell therapy for stroke and Parkinson’s disease,the genetics of microRNAs and brain neoplasms,as well as neuroprotective agents,Zika virus,Notch receptor,neural crest and embryonic stem cells were identified as emerging hot spots.These undeveloped themes and popular topics are potential points of focus for new studies on human neural stem cells.
基金Supported by the Major State Basic Research Development Program of China(2011CB706501)the National Natural Science Foundation of China(51276157)
文摘Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.
基金Under the auspices of Major Project of National Social Science Foundation of China(No.13&ZD027)National Natural Science Foundation of China(No.41201128,71433008)
文摘Based on patent cooperation data,this study used a range of city network analysis approaches in order to explore the structure of the Chinese city network which is driven by technological knowledge flows.The results revealed the spatial structure,composition structure,hierarchical structure,group structure,and control structure of Chinese city network,as well as its dynamic factors.The major findings are:1) the spatial pattern presents a diamond structure,in which Wuhan is the central city;2) although the invention patent knowledge network is the main part of the broader inter-city innovative cooperation network,it is weaker than the utility model patent;3) as the senior level cities,Beijing,Shanghai and the cities in the Zhujiang(Pearl) River Delta Region show a strong capability of both spreading and controlling technological knowledge;4) whilst a national technology alliance has preliminarily formed,regional alliances have not been adequately established;5) even though the cooperation level amongst weak connection cities is not high,such cities still play an important role in the network as a result of their location within ′structural holes′ in the network;and 6) the major driving forces facilitating inter-city technological cooperation are geographical proximity,hierarchical proximity and technological proximity.
基金The National Key R&D Program of China under contract No.2018YFC1406202the National Natural Science Foundation of China under contract Nos 41811530301,41830964 and 41976188。
文摘Mesoscale eddies play an important role in modulating the ocean circulation.Many previous studies on the threedimensional structure of mesoscale eddies were mainly based on composite analysis,and there are few targeted observations for individual eddies.A cyclonic eddy surveyed during an oceanographic cruise in the Northwest Pacific Ocean is investigated in this study.The three-dimensional structure of this cyclonic eddy is revealed by observations and simulated by the four-dimensional variational data assimilation(4 DVAR)system combined with the Regional Ocean Modeling System.The observation and assimilation results together present the characteristics of the cyclonic eddy.The cold eddy has an obvious dual-core structure of temperature anomaly.One core is at 50–150 m and another is at 300–550 m,which both have the average temperature anomaly of approximately-3.5℃.The salinity anomaly core is between 250 m and 500 m,which is approximately-0.3.The horizontal velocity structure is axis-asymmetric and it is enhanced on the eastern side of the cold eddy.In the assimilation experiment,sea level anomaly,sea surface temperature,and in situ measurements are assimilated into the system,and the results of assimilation are close to the observations.Based on the high-resolution assimilation output results,the study also diagnoses the vertical velocity in the mesoscale eddy,which reaches the maximum of approximately 10 m/d.The larger vertical velocity is found to be distributed in the range of 0.5 to 1 time of the normalized radius of the eddy.The validation of the simulation result shows that the 4 DVAR method is effective to reconstruct the three-dimensional structure of mesoscale eddy and the research is an application to study the mesoscale eddy in the Northwest Pacific by combining observation and assimilation methods.
基金supported by the National Natural Science Foundation of China (Grant No. 50539010)
文摘A comprehensive safety evaluation system taking the most influential factors into account has been developed to evaluate the reliability of hydraulic metal structures. Applying the techniques of AI and DB, the idea of a one-machine and three-base system is proposed. The framework of the three-base system has been designed and the structural framework constructed in turn. A practical example is given to illustrate the process of using this system and it can be used for comparison and analysis purposes. The key technology of the system is its ability to reorganize and improve the expert system＇s knowledge base by establishing the expert system. This system utilizes the computer technology inference process, making safety evaluation conclusions more reasonable and applicable to the actual situation. The system is not only advanced, but also feasible, reliable, artificially intelligent, and has the capacity to constantly grow.
基金the National Natural Science Foundation of China (No. 20271025)the Natural Science Foundation of Shandong province (No. Z2001B02)the State Key Laboratory of Crystal Materials,Shandong University
文摘The bis(tributyltin) ester of succinic acid was synthesized by the reaction of disodium salt of succinic acid with tributyltin chloride in a molar ratio of 1:2. The crystal structure was determined by X-ray single-crystal diffraction. It belongs to orthorhombic with space group Pccn, a = 20.949(3), b = 17.470(3), c = 20.345(3) Angstrom, V = 7446(2) Angstrom(3), Z = 8, D-c = 1.242 g/cm(3), mu = 1.365 mm(-1), F(000) = 2864, R = 0.0544 and wR = 0.1417. The tin atom is of five-coordination in a trigonal bipyramidal structure by bridging two carboxylate groups in different directions and the resulting structure which contains straight twist large ring channels along the axes of a, b and c is a three-dimensional framework polymer containing two different tin atoms.
基金funded by the general project of National Natural Science Foundation of China(No.41774072).
文摘A magnitude 5.5 earthquakes occurred in Eryuan County,Dali Bai Autonomous Prefecture,Yunnan Province,China,on March 3.And a magnitude 5.0 earthquake occurred in the same place on April 17,2013,i.e.,45 days later.Then,on May 21,2021,multiple earthquakes,one with magnitude 6.4 and several at 5.0 or above,occurred in Yangbi County,Dali Bai Autonomous Prefecture,Yunnan Province,China.All of these occurred in the Weixi-QiaohouWeishan fault zone.In this study,1,874 seismic events in Yangbi and Eryuan counties were identified by automatic micro-seismic identification technology and the first arrivals were picked up manually.Following this,a total of 11,968 direct P-wave absolute arrivals and 73,987 high-quality Pwave relative arrivals were collected for joint inversion via the double difference tomography method.This was done to obtain the regional three-dimensional fine crustal P-wave velocity structure.The results show that the travel time residuals before and after inversion decreased from the initial–0.1–0.1 s to–0.06–0.06 s.The upper crust in the study area,which exhibited a low-velocity anomaly,corresponded to the basin region;this indicated that the low-velocity anomaly in the shallow part of the study area was affected by the basin.Results also showed some correlation between the distribution of the earthquakes and velocity structure,as there was a lowvelocity body Lv1 with a wide distribution at depths ranging from 15–20 km in the Yangbi and Eryuan earthquake regions.In addition,earthquakes occurred predominantly in the highlow velocity abnormal transition zone.The low-velocity body in the middle and lower crust may be prone to concentrating upper crustal stress,thus leading to the occurrence of earthquakes.
基金Supported by the China National Science and Technology Major Project(2016ZX05033002,2016ZX05033001).
文摘Taking the Paleogene salt strata in the west of Kuqa foreland thrust belt as study object, the deformation features of salt structure in the compression direction and perpendicular to the compression direction were examined to find out the control factors and formation mechanisms of the salt structures. By using the three-dimensional discrete element numerical simulation method, the formation mechanisms of typical salt structures of western Kuqa foreland thrust belt in Keshen and Dabei work areas were comprehensively analyzed. The simulation results show that the salt deformation in Keshen and Dabei work areas is of forward spread type, with deformation concentrated in the piedmont zone;the salt deformation is affected by the early uplift near the compression end, pre-existing basement faults, synsedimentary process and the initial salt depocenter;in the direction perpendicular to the compression direction, salt rocks near the compression end have strong lateral mobility with the velocity component moving towards the middle part, and the closer to the middle, the larger the velocity will be, so that salt rocks will aggregate towards the middle and deform intensely, forming complex folds and separation of salt structures from salt source, and local outcrop with thrust faults. Compared with 2 D simulation, 3 D simulation can analyze salt structures in the principal stress direction and direction perpendicular to the principal stress, give us a full view of the formation mechanisms of salt structures, and guide the exploration of oil and gas reservoirs related to salt structures.
基金supported by the National Natural Science Foundation Project(41501283)Beijing Science and Technology Plan Project(Z161100000916012)+2 种基金the National Key Research and Development Program(2017YFD0600901)Special Fund for Beijing Common Construction Projectthe Fundamental Research Funds for the Central Universities(2015ZCQ-GX-04)
文摘The geometric and spatial characteristics of pore structures determine the permeability and water retention of soils, which have important effects on soil functional diversity and ecological restoration. Until recently, there have not been tools and methods to visually and quantitatively describe the characteristics of soil pores. To solve this problem, this research reconstructs the geometry and spatial distribution of soil pores by the marching cubes method, texture mapping method and the ray casting method widely used in literature. The objectives were to explore an optimal method for three-dimensional visualization of soil pore structure by comparing the robustness of the three methods on soil CT images with single pore structure and porosity ranging from low (2–5%) to high (12–18%), and to evaluate the reconstruction performance of the three methods with different geometric features. The results demonstrate that there are aliases (jagged edges) and deficiency at the boundaries of the model reconstructed by the marching cubes method and pore volumes are smaller than the ground truth, whereas the results of the texture mapping method lack the details of pore structures. For all the soil images, the ray casting method is preferable since it better preserves the pore characteristics of the ground truth. Furthermore, the ray casting method produced the best soil pore model with higher rendering speed and lower memory consumption. Therefore, the ray casting method provides a more advanced method for visualization of pore structures and provides an optional technique for the study of the transport of moisture and the exchange of air in soil.
文摘Point bars are well developed on the Yellow River delta, an~ which theShengli I point bar is the most typical. The point bar, being about 4 km in length and several tensto more than 100 meters in width, is located on the south side of the Shengli Bridge in KenliCounty, Dongying, Shandong. It is a typical fine-grained point bar with silt, which is predominant,some clay and minor plant debris and clay boulders. The Shengli I Point bar has complicated 3-Dstructures. Firstly, in a plane view, it comprises mainly eight sedimentary units, bar edge, baredge, bar platform, bar plain, bar channel, bar gully, bar pond and bar bay, developing side by sideand superimposed one by one m a complex way. Secondly, its vertical structures are very complex dueto the partial superimposition of the 8 sedimentary units. Besides hydatogenesis, very intensivewind erosion, eolian, ice and meltwater actions are also visible on the Shengli I point bar. Thecomplex form is made even more complicated because of the above co-actions.
基金Climbing Project Continental Dynamics of East Asia (95-S-05) from Ministry of Science and Technology, P. R. China.
文摘A detail three-dimensional P wave velocity structure of Beijing, Tianjin and Tangshan area (BTT area) was deter-mined by inverting local earthquake data. In total 16 048 P wave first arrival times from 16048 shallow and mid-depth crustal earthquakes, which occurred in and around the BTT area from 1992 to 1999 were used. The first arrival times are recorded by Northern China United Telemetry Seismic Network and Yanqing-Huailai Digital Seismic Network. Hypocentral parameters of 1 132 earthquakes with magnitude ML=1.7~6.2 and the three-dimensional P wave velocity structure were obtained simultaneously. The inversion result reveals the com-plicated lateral heterogeneity of P wave velocity structure around BTT area. The tomographic images obtained are also found to explain other seismological observations well.
基金financially supported by the National Science Foundation of China(Nos.51572007 and 51622203),"Recruitment Program of Global Experts"
文摘2D nanosheets such as graphene, silicene, phosphorene, metal dichalcogenides and MXenes are emerging and promising for lithium storage due to their ultrathin nature and corresponding chemical/physical properties. However, the serious restacking and aggregation of the 2D nanosheets are still hampering their applications. To circumvent the issues of 2D nanosheets, one efficient strategy is to construct 3D structures with hierarchical porous structures, good chemical/mechanical stabilities and tunable electrical conductivities. In this review, we firstly focus on the available synthetic approaches of 3D structures from 2D nanosheets, and then summarize the relationships between the microstructures of 3D structures built from 2D nanosheets and their electrochemical behaviors for lithium storage. On the basis of above results, some challenges are briefly discussed in the perspective of the development of various functional 3D structures.
