The Beijing 325 m meteorological tower stands as a pivotal research platform for exploring atmospheric boundary layer physics and atmospheric chemistry.With a legacy spanning 45 years,the tower has played a crucial ro...The Beijing 325 m meteorological tower stands as a pivotal research platform for exploring atmospheric boundary layer physics and atmospheric chemistry.With a legacy spanning 45 years,the tower has played a crucial role in unraveling the complexities of urban air pollution,atmospheric processes,and climate change in Beijing,China.This review paper provides a comprehensive overview of the measurements on the tower over the past two decades.Through long-term comprehensive observations,researchers have elucidated the intricate relationships between anthropogenic emissions,meteorological dynamics,and atmospheric composition,shedding light on the drivers of air pollution and its impacts on public health.The vertical measurements on the tower also enable detailed investigations into boundary layer dynamics,turbulent mixing,and pollutant dispersion,providing invaluable data for validating chemical transport models.Key findings from the tower’s research include the identification of positive feedback mechanisms between aerosols and the boundary layer,the characterization of pollutant sources and transport pathways,the determination of fluxes of gaseous and particulate species,and the assessment of the effectiveness of pollution control measures.Additionally,isotopic measurements have provided new insights into the sources and formation processes of particulate matter and reactive nitrogen species.Finally,the paper outlines future directions for tower-based research,emphasizing the need for long-term comprehensive measurements,the development of innovative tower platforms,and integration of emerging technologies.展开更多
Proton exchange membrane fuel cells(PEMFCs)have gained increasing interests as promising power sources due to their ability to convert hydrogen and oxygen directly into electricity with high efficiency and zero greenh...Proton exchange membrane fuel cells(PEMFCs)have gained increasing interests as promising power sources due to their ability to convert hydrogen and oxygen directly into electricity with high efficiency and zero greenhouse gas emissions.Bipolar plates(BPs)are considered as a critical component of PEMFCs,serving to collect current,separate gases,distribute the flow field,and conduct heat.This paper reviews the technical status and advancements in BP materials,with special focus on strategies for enhancing interfacial contact resistance(ICR)and corrosion resistance through conductive polymer(CP)coatings.First,commonly used BP materials in PEMFCs are summarized.Then,the advantages and limitations of various coatings for metallic BPs are discussed.Finally,recent progress in CP coatings for metallic BPs,aimed at achieving high corrosion resistance and low ICR,is comprehensively reviewed.展开更多
The occurrence of maize diseases was systematically studied at different growth stages of maize in different areas of Anhui Province. It was found that maize has a long optimal growth period in Anhui Province, and the...The occurrence of maize diseases was systematically studied at different growth stages of maize in different areas of Anhui Province. It was found that maize has a long optimal growth period in Anhui Province, and the maize planting structure is complex. The northern region is mainly planted with summer maize in large scale, while the southern region is mainly planted with spring maize in scattered pattern. In terms of diseases, the south spring maize suffered from more diverse diseases than the north summer maize. The main maize disease in Suzhou, Bozhou, Fuyang and Bengbu areas was southern rust, which was common with the highest diseased plant rate of 76%. The main maize diseases in Lu'an, Anqing, Chizhou, Tongling and Xuancheng were rust, maize rough dwarf virus(MRDV), southern leaf blight and sheath blight. Other diseases such as northern leaf blight, stalk rot and maize smut occurred commonly. The diseased plant rate of maize rust was in the range of 25%-47%.展开更多
Seismic migration and inversion are closely related techniques to portray subsurface images and identify hydrocarbon reservoirs.Seismic migration aims at obtaining structural images of subsurface geologic discontinuit...Seismic migration and inversion are closely related techniques to portray subsurface images and identify hydrocarbon reservoirs.Seismic migration aims at obtaining structural images of subsurface geologic discontinuities.More specifically,seismic migration estimates the reflectivity function(stacked average reflectivity or pre-stack angle-dependent reflectivity)from seismic reflection data.On the other hand,seismic inversion quantitatively estimates the intrinsic rock properties of subsurface formulations.Such seismic inversion methods are applicable to detect hydrocarbon reservoirs that may exhibit lateral variations in the inverted parameters.Although there exist many differences,pre-stack seismic migration is similar with the first iteration of the general linearized seismic inversion.Usually,seismic migration and inversion techniques assume an acoustic or isotropic elastic medium.Unconventional reservoirs such as shale and tight sand formation have notable anisotropic property.We present a linearized waveform inversion(LWI)scheme for weakly anisotropic elastic media with vertical transversely isotropic(VTI)symmetry.It is based on two-way anisotropic elastic wave equation and simultaneously inverts for the localized perturbations(ΔVp_(0)/Vp_(0)/Vs_(0)/Vs_(0)/,Δ∈,Δδ)from the long-wavelength reference model.Our proposed VTI-elastic LWI is an iterative method that requires a forward and an adjoint operator acting on vectors in each iteration.We derive the forward Born approximation operator by perturbation theory and adjoint operator via adjoint-state method.The inversion has improved the quality of the images and reduces the multi-parameter crosstalk comparing with the adjoint-based images.We have observed that the multi-parameter crosstalk problem is more prominent in the inversion images for Thomsen anisotropy parameters.Especially,the Thomsen parameter is the most difficult to resolve.We also analyze the multi-parameter crosstalk using scattering radiation patterns.The linearized waveform inversion for VTI-elastic media presented in this article provides quantitative information of the rock properties that has the potential to help identify hydrocarbon reservoirs.展开更多
Online teaching in colleges and universities has developed rapidly in recent years.This paper explores the online teaching implementation effect and online teaching influencing factors of college students by using cro...Online teaching in colleges and universities has developed rapidly in recent years.This paper explores the online teaching implementation effect and online teaching influencing factors of college students by using cross-analysis method,and the study shows that;college students are more satisfied with the online teaching effect as a whole,and the main influencing factors of undergraduate online teaching are the class status and external environment,while the main influencing factors of graduate students’online teaching are the teacher’s academic level and the class status.In addition,undergraduate students and graduate students have big differences in evaluation indexes such as equipment,platform,interaction frequency and course mode.Based on the research results,this paper puts forward corresponding countermeasure suggestions in four aspects:students,teachers,teaching platforms,and online course mechanism.展开更多
A series of environmental and energy issues,such as global warming,water pollution,acid rain,and energy shortage,have to be settled urgently.Metal-organic frameworks(MOFs)are compounds consisting of metal ions or clus...A series of environmental and energy issues,such as global warming,water pollution,acid rain,and energy shortage,have to be settled urgently.Metal-organic frameworks(MOFs)are compounds consisting of metal ions or clusters coordinated to organic ligands,which show great promise for alleviating or mitigating these challenges owing to their outstanding physical and chemical properties.In this review,we summarize the recent advances of MOFs in the fields of green applications,including carbon capture,harmful gas removal,sewage treatment,and green energy storage.In addition,the challenges and prospects of the large-scale commercialized use of MOFs in handling environmental issues are also discussed.展开更多
In this paper, we use fluctuation analysis to study statistical correlations in wind speed time series. Each time series used here was recorded hourly over 40 years. The fluctuation functions of wind speed time series...In this paper, we use fluctuation analysis to study statistical correlations in wind speed time series. Each time series used here was recorded hourly over 40 years. The fluctuation functions of wind speed time series were found to scale with a universal exponent approximating to 0.7, which means that the wind speed time series are long-term correlated. In the classical method of extreme estimations, data are commonly assumed to be independent (without correlations). This assumption will lead to an overestimation if data are long-term correlated. We thus propose a simple method to improve extreme wind speed estimations based on correlation analysis. In our method, extreme wind speeds are obtained by simply scaling the mean return period in the classical method. The scaling ratio is an analytic function of the scaling exponent in the fluctuation analysis.展开更多
A variety of dust control methods are often applied in coal mines,among which the application of wet scrubbers has proven to be an efficient technology for the removal of dust in airstreams,rather than diluting or con...A variety of dust control methods are often applied in coal mines,among which the application of wet scrubbers has proven to be an efficient technology for the removal of dust in airstreams,rather than diluting or confining the dust.In this paper,a wet scrubber design was developed.Based on a self-designed experimental test platform,the total dust concentration,respirable dust concentration,air volume,and average pressure drops of wet scrubbers with 12,16,20,and 24 blades were measured under different water intake conditions.The results show that the different water intake levels have only minimal effects on the air volume of the wet scrubbers.However,increased water intake had improved the dust removal efficiency of the wet scrubbers with the same number of blades.The wet scrubber with 16 blades was found to have the best dust removal efficiency at a water intake level of 1.35 m^(3)/h.Its total dust and respirable dust removal efficiency reached 96.81%and 95.59%,respectively.The air volume was 200.4 m^(3)/min,and the average pressure drop was determined to be 169.4 Pa.In addition,when the wet scrubber with 16 blades was applied in a coal preparation plant in China's Shanxi Province,it was observed that the total dust concentration had fallen below 8.1 mg/m^(3),and the respirable dust concentration had fallen below 5.9 mg/m^(3).Therefore,the results obtained in this research investigation provide important references for the use of wet scrubbers to improve coal production environmental conditions.展开更多
Skewness(S) and kurtosis(K) of temperature in the surface layer over a grassland are investigated under unstable thermal stratifications. We find that both skewness and kurtosis generally obey Monin–Obukhov similarit...Skewness(S) and kurtosis(K) of temperature in the surface layer over a grassland are investigated under unstable thermal stratifications. We find that both skewness and kurtosis generally obey Monin–Obukhov similarity theory and tend to be constant values(1.5 and 5.3, respectively) when the stability parameter z/L <-2. Quantitative formulas of the similarity functions are proposed. The temperature probability density function(PDF) is close to Gaussian in near neutral stratification and non-Gaussian in unstable stratification. The influence of coherent motions on the PDF behavior is analyzed using the quadrant analysis technique. It shows that PDF behaviors are controlled by ejections and sweeps. The results also indicate that the PDF type of the ejections always follows a Gaussian distribution, while the PDF of the sweeps changes with stability.展开更多
The hierarchical MoS_(2)/CoNi composites were successfully synthesized by a two-step hydrothermal method.The large surface area of the MoS_(2) enhances the dispersivity of the CoNi nanoparticles and the formation of a...The hierarchical MoS_(2)/CoNi composites were successfully synthesized by a two-step hydrothermal method.The large surface area of the MoS_(2) enhances the dispersivity of the CoNi nanoparticles and the formation of abundant MoS_(2)/CoNi interfaces,which make an important contribution to the dielectric loss,and the introduction of the CoNi improves impedance matching and introduces magnetic loss,which can improve the absorption performance to electromagnetic waves.Through the calculation of the electromagnetic parameters,the minimum reflection loss(RL)value of the MoS_(2)/CoNi composites achieves-41.44 dB at 13.53 GHz under a thickness of 2.0 mm and the corresponding effective absorption bandwidth(RL below-10 dB)is 5.6 GHz.The MoS_(2)/CoNi composite has the potential to be applied to microwave absorption due to its strong absorption and wide bandwidth.展开更多
A fast joint probabilistic data association （FJPDA） algorithm is proposed in tiffs paper. Cluster probability matrix is approximately calculated by a new method, whose elements βi^t（K） can be taken as evaluation ...A fast joint probabilistic data association （FJPDA） algorithm is proposed in tiffs paper. Cluster probability matrix is approximately calculated by a new method, whose elements βi^t（K） can be taken as evaluation functions. According to values of βi^t（K）, N events with larger joint probabilities can be searched out as the events with guiding joint probabilities, tiros, the number of searching nodes will be greatly reduced. As a result, this method effectively reduces the calculation load and nnkes it possible to be realized on real-thne, Theoretical ,analysis and Monte Carlo simulation results show that this method is efficient.展开更多
The state-of-art Computational Fluid Dynamics （CFD） codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FL...The state-of-art Computational Fluid Dynamics （CFD） codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUENT on describing the wind field details over a complex terrain. The results of the numerical tests show that FLUENT can simulate the wind field over extremely complex terrain, which cannot be simulated by mesoscale models. The reason why FLUENT can cope with extremely complex terrain, which can not be coped with by mesoscale models, relies on some particular techniques adopted by FLUENT, such as computer-aided design （CAD） technique, unstructured grid technique and finite volume method. Compared with mesoscale models, FLUENT can describe terrain in much more accurate details and can provide wind simulation results with higher resolution and more accuracy.展开更多
Turbulence in the nocturnal boundary layer(NBL)is still not well characterized,especially over complex underlying surfaces.Herein,gradient tower data and eddy covariance data collected by the Beijing 325-m tower were ...Turbulence in the nocturnal boundary layer(NBL)is still not well characterized,especially over complex underlying surfaces.Herein,gradient tower data and eddy covariance data collected by the Beijing 325-m tower were used to better understand the differentiating characteristics of turbulence regimes and vertical turbulence structure of urban the NBL.As for heights above the urban canopy layer(UCL),the relationship between turbulence velocity scale(VTKE)and wind speed(V)was consistent with the“HOckey-Stick”(HOST)theory proposed for a relatively flat area.Four regimes have been identified according to urban nocturnal stable boundary layer.Regime 1 occurs where local shear plays a leading role for weak turbulence under the constraint that the wind speed V<VT(threshold wind speed).Regime 2 is determined by the existence of strong turbulence that occurs when V>VT and is mainly driven by bulk shear.Regime 3 is identified by the existence of moderate turbulence when upside-down turbulence sporadic bursts occur in the presence of otherwise weak turbulence.Regime 4 is identified as buoyancy turbulence,when V>VT,and the turbulence regime is affected by a combination of local wind shear,bulk shear and buoyancy turbulence.The turbulence activities demonstrated a weak thermal stratification dependency in regime 1,for which within the UCL,the turbulence intensity was strongly affected by local wind shear when V<VT.This study further showed typical examples of different stable boundary layers and the variations between turbulence regimes by analyzing the evolution of wind vectors.Partly because of the influence of large-scale motions,the power spectral density of vertical velocity for upsidedown structure showed an increase at low frequencies.The upside-down structures were also characterized by the highest frequency of the stable stratifications in the higher layer.展开更多
The turbulent standard deviations and the turbulent third-order and fourth-order moments are the key turbulence dispersion parameters in Lagrangian dispersion models.However,the characteristics of these parameters und...The turbulent standard deviations and the turbulent third-order and fourth-order moments are the key turbulence dispersion parameters in Lagrangian dispersion models.However,the characteristics of these parameters under heavy haze conditions in urban areas have not been fully investigated,and the commonly used similarity relations of these parameters in modelswere based on observations in highly flat and sparsely populated areas.In this paper,the vertical profiles of these parameters and their local similarity relations under heavy haze conditions in the wintertime of Beijing have been analyzed by using data collected at a 325-m meteorological tower.The heavy haze process has been divided into three stages:transport stage(TS),cumulative stage(CS),and dispersion stage(DS).Results show that the turbulent dispersion parameters behave differently during three stages.In the TS and DS,the maxima appear in the profiles of the turbulent standard deviations above the urban canopy;in the CS,the turbulent standard deviation are almost constant with height.The analysis of the third and fourth order moments shows that the wind velocities above the urban canopy in the TS deviate from the Gaussian distribution more significantly than those in the CS and DS.The local similarity relations of the turbulent dispersion parameters in the TS,especially for the longitudinal wind components,are normally different from those in the CS and DS.Thus,different from the common assumptions in Lagrangian models,the turbulence dispersion in horizontal directions is anisotropic and should be parameterized by multiple similarity relations under heavy haze conditions.展开更多
BACKGROUND Primary intracranial alveolar soft-part sarcoma(PIASPS)is a rare malignancy.We aimed to investigate the clinical profiles and outcomes for PIASPS.CASE SUMMARY We firstly reported five consecutive cases from...BACKGROUND Primary intracranial alveolar soft-part sarcoma(PIASPS)is a rare malignancy.We aimed to investigate the clinical profiles and outcomes for PIASPS.CASE SUMMARY We firstly reported five consecutive cases from our institute.Then,the cases from previous studies were pooled and analyzed to delineate the characteristics of this disease.Our cohort included two males and three females.The median age was 21-years-old(range:8-54-years-old).All the patients received surgical treatment.Gross total resection(GTR),radiotherapy,and chemotherapy were administered in 3 patients,4 patients,and 1 patient,respectively.After a median follow-up of 36 mo,tumor progression was noticed in 4 patients;and 3 patients died of the disease.Pooled data(n=14)contained 5 males and 9 females with a median age of 19 years.The log-rank tests showed that GTR(P=0.011)could prolong progression-free survival,and radiotherapy(P<0.001)resulted in longer overall survival.CONCLUSION Patients with PIASPS suffer from poor outcomes.Surgical treatment is the first choice,and GTR should be achieved when the tumor is feasible.Patients with PIASPS benefit from radiotherapy,which should be considered as a part of treatment therapies.展开更多
Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivit...Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivity KH has rarely been studied in the context of frequent urban pollution in recent years.In this study,KH under urban pollution conditions was directly calculated based on K-theory.The authors found an obvious diurnal variation in K_(H),with variations also in the vertical distributions between each case and over time.Interestingly,the height corresponding to the high occurrence frequency of negative K_(H) rises gradually after sunrise,peaks at noon,falls near sunset,and concentrates around 140 m during most of the night.The KH magnitude and fluctuation are smaller in the pollutant accumulation stage(CS)at all levels than in the pollutant transport stage and pollutant removal stage.Turbulent diffusion may greatly affect PM_(2.5) concentrations at the CS because of the negative correlation between PM_(2.5) concentrations and the absolute value of KH at the CS accompanied by weak wind speeds.The applicability of K-theory is not very good during either day or at night.These problems are inherent in K-theory when characterizing complex systems,such as turbulent diffusion,and require new frameworks or parameterization schemes.These findings may provide valuable insight for establishing a new turbulence diffusion parameterization scheme for KH and promote the study of turbulent diffusion,air quality forecasting,and weather and climate modeling.展开更多
Based on the existing plant layout and process flow,a simulation analysis was conducted using the Plant Simulation platform with the utilization efficiency of each station and production capacity of the dismantling sy...Based on the existing plant layout and process flow,a simulation analysis was conducted using the Plant Simulation platform with the utilization efficiency of each station and production capacity of the dismantling system as indicators.A problem with long-term suspension in the disassembly process was determined.Based on the two optimization directions of increasing material transportation equipment and expanding the buffer capacity,a cost-oriented optimization model is established.A genetic algorithm and model simulation were used to solve the model.An optimization scheme that satisfies the production needs and has the lowest cost is proposed.The results show that the optimized dismantling system solves the suspended work problem at the dismantling station and a significant improvement in productivity and station utilization efficiency compared with the previous system.展开更多
We report an approach of high-pressure hydrogenation to improve the performance of crystalline Si(c-Si) solar cells.As-received p-type c-Si wafer-based PN junctions were subjected to high-pressure(2.5 MPa) hydrogen at...We report an approach of high-pressure hydrogenation to improve the performance of crystalline Si(c-Si) solar cells.As-received p-type c-Si wafer-based PN junctions were subjected to high-pressure(2.5 MPa) hydrogen atmosphere at 200 ℃,followed by evaporating antireflection layers,passivation layers,and front and rear electrodes.The efficiency of the so prepared c-Si solar cell was found to increase evidently after high-pressure hydrogenation,with a maximal enhancement of 10%.The incorporation of hydrogen by Si solar cells was identified,and hydrogen passivation of dangling bonds in Si was confirmed.Compared to the regular approach of hydrogen plasma passivation,the approach of high-pressure hydrogenation reported here needs no post-hydrogenation treatment,and can be more convenient and efficient to use in improving the performances of the c-Si and other solar cells.展开更多
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0760200)the National Natural Science Foundation of China(Grant Nos.42330605 and 42377101).
文摘The Beijing 325 m meteorological tower stands as a pivotal research platform for exploring atmospheric boundary layer physics and atmospheric chemistry.With a legacy spanning 45 years,the tower has played a crucial role in unraveling the complexities of urban air pollution,atmospheric processes,and climate change in Beijing,China.This review paper provides a comprehensive overview of the measurements on the tower over the past two decades.Through long-term comprehensive observations,researchers have elucidated the intricate relationships between anthropogenic emissions,meteorological dynamics,and atmospheric composition,shedding light on the drivers of air pollution and its impacts on public health.The vertical measurements on the tower also enable detailed investigations into boundary layer dynamics,turbulent mixing,and pollutant dispersion,providing invaluable data for validating chemical transport models.Key findings from the tower’s research include the identification of positive feedback mechanisms between aerosols and the boundary layer,the characterization of pollutant sources and transport pathways,the determination of fluxes of gaseous and particulate species,and the assessment of the effectiveness of pollution control measures.Additionally,isotopic measurements have provided new insights into the sources and formation processes of particulate matter and reactive nitrogen species.Finally,the paper outlines future directions for tower-based research,emphasizing the need for long-term comprehensive measurements,the development of innovative tower platforms,and integration of emerging technologies.
基金supported by the National Natural Science Foundation of China under Grant Nos.12102310 and U21A20113the Guangdong Basic and Applied Basic Research Foundation under Grant No.2020A1515110818+2 种基金the Inovation Team Project for Colleges and Universities of Guangdong Province under Grant No.2023KCXTD030the Key Project of Biomedicine and Health in Colleges and Universities of Guangdong Province under Grant No.2021ZDZX2055the Medical Science and Technology Research Fund of Guangdong Province under Grant No.A2022004.
文摘Proton exchange membrane fuel cells(PEMFCs)have gained increasing interests as promising power sources due to their ability to convert hydrogen and oxygen directly into electricity with high efficiency and zero greenhouse gas emissions.Bipolar plates(BPs)are considered as a critical component of PEMFCs,serving to collect current,separate gases,distribute the flow field,and conduct heat.This paper reviews the technical status and advancements in BP materials,with special focus on strategies for enhancing interfacial contact resistance(ICR)and corrosion resistance through conductive polymer(CP)coatings.First,commonly used BP materials in PEMFCs are summarized.Then,the advantages and limitations of various coatings for metallic BPs are discussed.Finally,recent progress in CP coatings for metallic BPs,aimed at achieving high corrosion resistance and low ICR,is comprehensively reviewed.
基金Supported by Discipline Construction of Anhui Academy of Agricultural Sciences(16A1133)
文摘The occurrence of maize diseases was systematically studied at different growth stages of maize in different areas of Anhui Province. It was found that maize has a long optimal growth period in Anhui Province, and the maize planting structure is complex. The northern region is mainly planted with summer maize in large scale, while the southern region is mainly planted with spring maize in scattered pattern. In terms of diseases, the south spring maize suffered from more diverse diseases than the north summer maize. The main maize disease in Suzhou, Bozhou, Fuyang and Bengbu areas was southern rust, which was common with the highest diseased plant rate of 76%. The main maize diseases in Lu'an, Anqing, Chizhou, Tongling and Xuancheng were rust, maize rough dwarf virus(MRDV), southern leaf blight and sheath blight. Other diseases such as northern leaf blight, stalk rot and maize smut occurred commonly. The diseased plant rate of maize rust was in the range of 25%-47%.
文摘Seismic migration and inversion are closely related techniques to portray subsurface images and identify hydrocarbon reservoirs.Seismic migration aims at obtaining structural images of subsurface geologic discontinuities.More specifically,seismic migration estimates the reflectivity function(stacked average reflectivity or pre-stack angle-dependent reflectivity)from seismic reflection data.On the other hand,seismic inversion quantitatively estimates the intrinsic rock properties of subsurface formulations.Such seismic inversion methods are applicable to detect hydrocarbon reservoirs that may exhibit lateral variations in the inverted parameters.Although there exist many differences,pre-stack seismic migration is similar with the first iteration of the general linearized seismic inversion.Usually,seismic migration and inversion techniques assume an acoustic or isotropic elastic medium.Unconventional reservoirs such as shale and tight sand formation have notable anisotropic property.We present a linearized waveform inversion(LWI)scheme for weakly anisotropic elastic media with vertical transversely isotropic(VTI)symmetry.It is based on two-way anisotropic elastic wave equation and simultaneously inverts for the localized perturbations(ΔVp_(0)/Vp_(0)/Vs_(0)/Vs_(0)/,Δ∈,Δδ)from the long-wavelength reference model.Our proposed VTI-elastic LWI is an iterative method that requires a forward and an adjoint operator acting on vectors in each iteration.We derive the forward Born approximation operator by perturbation theory and adjoint operator via adjoint-state method.The inversion has improved the quality of the images and reduces the multi-parameter crosstalk comparing with the adjoint-based images.We have observed that the multi-parameter crosstalk problem is more prominent in the inversion images for Thomsen anisotropy parameters.Especially,the Thomsen parameter is the most difficult to resolve.We also analyze the multi-parameter crosstalk using scattering radiation patterns.The linearized waveform inversion for VTI-elastic media presented in this article provides quantitative information of the rock properties that has the potential to help identify hydrocarbon reservoirs.
文摘Online teaching in colleges and universities has developed rapidly in recent years.This paper explores the online teaching implementation effect and online teaching influencing factors of college students by using cross-analysis method,and the study shows that;college students are more satisfied with the online teaching effect as a whole,and the main influencing factors of undergraduate online teaching are the class status and external environment,while the main influencing factors of graduate students’online teaching are the teacher’s academic level and the class status.In addition,undergraduate students and graduate students have big differences in evaluation indexes such as equipment,platform,interaction frequency and course mode.Based on the research results,this paper puts forward corresponding countermeasure suggestions in four aspects:students,teachers,teaching platforms,and online course mechanism.
基金from the National Natural Science Foundation of China(21776097,21802103,and 22008032)the Guangdong Natural Science Foundation(2017A030313052)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(2019A1515110706)the Guangdong Natural Science Foundation(2017A030313052)。
文摘A series of environmental and energy issues,such as global warming,water pollution,acid rain,and energy shortage,have to be settled urgently.Metal-organic frameworks(MOFs)are compounds consisting of metal ions or clusters coordinated to organic ligands,which show great promise for alleviating or mitigating these challenges owing to their outstanding physical and chemical properties.In this review,we summarize the recent advances of MOFs in the fields of green applications,including carbon capture,harmful gas removal,sewage treatment,and green energy storage.In addition,the challenges and prospects of the large-scale commercialized use of MOFs in handling environmental issues are also discussed.
基金supported by the National Key R&D Program of China (Grant No. 2016YFC0208802)the National Natural Science Foundation of China (Grant Nos. 41675012 and 11472272)
文摘In this paper, we use fluctuation analysis to study statistical correlations in wind speed time series. Each time series used here was recorded hourly over 40 years. The fluctuation functions of wind speed time series were found to scale with a universal exponent approximating to 0.7, which means that the wind speed time series are long-term correlated. In the classical method of extreme estimations, data are commonly assumed to be independent (without correlations). This assumption will lead to an overestimation if data are long-term correlated. We thus propose a simple method to improve extreme wind speed estimations based on correlation analysis. In our method, extreme wind speeds are obtained by simply scaling the mean return period in the classical method. The scaling ratio is an analytic function of the scaling exponent in the fluctuation analysis.
基金supported by the Shanxi Province Colleges and Universities Science and Technology Achievement Transformation and Cultivation Project(2020CG008).
文摘A variety of dust control methods are often applied in coal mines,among which the application of wet scrubbers has proven to be an efficient technology for the removal of dust in airstreams,rather than diluting or confining the dust.In this paper,a wet scrubber design was developed.Based on a self-designed experimental test platform,the total dust concentration,respirable dust concentration,air volume,and average pressure drops of wet scrubbers with 12,16,20,and 24 blades were measured under different water intake conditions.The results show that the different water intake levels have only minimal effects on the air volume of the wet scrubbers.However,increased water intake had improved the dust removal efficiency of the wet scrubbers with the same number of blades.The wet scrubber with 16 blades was found to have the best dust removal efficiency at a water intake level of 1.35 m^(3)/h.Its total dust and respirable dust removal efficiency reached 96.81%and 95.59%,respectively.The air volume was 200.4 m^(3)/min,and the average pressure drop was determined to be 169.4 Pa.In addition,when the wet scrubber with 16 blades was applied in a coal preparation plant in China's Shanxi Province,it was observed that the total dust concentration had fallen below 8.1 mg/m^(3),and the respirable dust concentration had fallen below 5.9 mg/m^(3).Therefore,the results obtained in this research investigation provide important references for the use of wet scrubbers to improve coal production environmental conditions.
基金supported by the National Key Research and Development Program of China (2017YFC0209605)the National Natural Science Foundation of China (Grant Nos. 11472272, 41605010 and 41675012)
文摘Skewness(S) and kurtosis(K) of temperature in the surface layer over a grassland are investigated under unstable thermal stratifications. We find that both skewness and kurtosis generally obey Monin–Obukhov similarity theory and tend to be constant values(1.5 and 5.3, respectively) when the stability parameter z/L <-2. Quantitative formulas of the similarity functions are proposed. The temperature probability density function(PDF) is close to Gaussian in near neutral stratification and non-Gaussian in unstable stratification. The influence of coherent motions on the PDF behavior is analyzed using the quadrant analysis technique. It shows that PDF behaviors are controlled by ejections and sweeps. The results also indicate that the PDF type of the ejections always follows a Gaussian distribution, while the PDF of the sweeps changes with stability.
基金financially supported by the Key Scientific Research Projects of the Southwest University of Science and Technology(No.17zx910201)the Longshan Academic Talent Research Supporting Program of SWUST(Nos.18LZX437 and 18LZXT09)+1 种基金the Sichuan Science and Technology Program(No.2017TD0020)。
文摘The hierarchical MoS_(2)/CoNi composites were successfully synthesized by a two-step hydrothermal method.The large surface area of the MoS_(2) enhances the dispersivity of the CoNi nanoparticles and the formation of abundant MoS_(2)/CoNi interfaces,which make an important contribution to the dielectric loss,and the introduction of the CoNi improves impedance matching and introduces magnetic loss,which can improve the absorption performance to electromagnetic waves.Through the calculation of the electromagnetic parameters,the minimum reflection loss(RL)value of the MoS_(2)/CoNi composites achieves-41.44 dB at 13.53 GHz under a thickness of 2.0 mm and the corresponding effective absorption bandwidth(RL below-10 dB)is 5.6 GHz.The MoS_(2)/CoNi composite has the potential to be applied to microwave absorption due to its strong absorption and wide bandwidth.
文摘A fast joint probabilistic data association （FJPDA） algorithm is proposed in tiffs paper. Cluster probability matrix is approximately calculated by a new method, whose elements βi^t（K） can be taken as evaluation functions. According to values of βi^t（K）, N events with larger joint probabilities can be searched out as the events with guiding joint probabilities, tiros, the number of searching nodes will be greatly reduced. As a result, this method effectively reduces the calculation load and nnkes it possible to be realized on real-thne, Theoretical ,analysis and Monte Carlo simulation results show that this method is efficient.
基金supported by the National Natural Science Foundation of China(40805004, 40705039 and 90715031)the "Mini-projecton detailed survey and evaluation of wind energy resources"supported by National Climate Center of Chinese Meteoro-logical Administration (CWERA2010002)
文摘The state-of-art Computational Fluid Dynamics （CFD） codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUENT on describing the wind field details over a complex terrain. The results of the numerical tests show that FLUENT can simulate the wind field over extremely complex terrain, which cannot be simulated by mesoscale models. The reason why FLUENT can cope with extremely complex terrain, which can not be coped with by mesoscale models, relies on some particular techniques adopted by FLUENT, such as computer-aided design （CAD） technique, unstructured grid technique and finite volume method. Compared with mesoscale models, FLUENT can describe terrain in much more accurate details and can provide wind simulation results with higher resolution and more accuracy.
基金supported by the National Natural Science Foundation of China (Grant No. 42105093 and 41975018)the China Postdoctoral Science Foundation (Grant No. 2020M670420)the Special Research Assistant Project。
文摘Turbulence in the nocturnal boundary layer(NBL)is still not well characterized,especially over complex underlying surfaces.Herein,gradient tower data and eddy covariance data collected by the Beijing 325-m tower were used to better understand the differentiating characteristics of turbulence regimes and vertical turbulence structure of urban the NBL.As for heights above the urban canopy layer(UCL),the relationship between turbulence velocity scale(VTKE)and wind speed(V)was consistent with the“HOckey-Stick”(HOST)theory proposed for a relatively flat area.Four regimes have been identified according to urban nocturnal stable boundary layer.Regime 1 occurs where local shear plays a leading role for weak turbulence under the constraint that the wind speed V<VT(threshold wind speed).Regime 2 is determined by the existence of strong turbulence that occurs when V>VT and is mainly driven by bulk shear.Regime 3 is identified by the existence of moderate turbulence when upside-down turbulence sporadic bursts occur in the presence of otherwise weak turbulence.Regime 4 is identified as buoyancy turbulence,when V>VT,and the turbulence regime is affected by a combination of local wind shear,bulk shear and buoyancy turbulence.The turbulence activities demonstrated a weak thermal stratification dependency in regime 1,for which within the UCL,the turbulence intensity was strongly affected by local wind shear when V<VT.This study further showed typical examples of different stable boundary layers and the variations between turbulence regimes by analyzing the evolution of wind vectors.Partly because of the influence of large-scale motions,the power spectral density of vertical velocity for upsidedown structure showed an increase at low frequencies.The upside-down structures were also characterized by the highest frequency of the stable stratifications in the higher layer.
基金supported by the National Natural Science Foundation of China (No.41975018)the General Financial Grant from the China Postdoctoral Science Foundation (No.2020M670420)
文摘The turbulent standard deviations and the turbulent third-order and fourth-order moments are the key turbulence dispersion parameters in Lagrangian dispersion models.However,the characteristics of these parameters under heavy haze conditions in urban areas have not been fully investigated,and the commonly used similarity relations of these parameters in modelswere based on observations in highly flat and sparsely populated areas.In this paper,the vertical profiles of these parameters and their local similarity relations under heavy haze conditions in the wintertime of Beijing have been analyzed by using data collected at a 325-m meteorological tower.The heavy haze process has been divided into three stages:transport stage(TS),cumulative stage(CS),and dispersion stage(DS).Results show that the turbulent dispersion parameters behave differently during three stages.In the TS and DS,the maxima appear in the profiles of the turbulent standard deviations above the urban canopy;in the CS,the turbulent standard deviation are almost constant with height.The analysis of the third and fourth order moments shows that the wind velocities above the urban canopy in the TS deviate from the Gaussian distribution more significantly than those in the CS and DS.The local similarity relations of the turbulent dispersion parameters in the TS,especially for the longitudinal wind components,are normally different from those in the CS and DS.Thus,different from the common assumptions in Lagrangian models,the turbulence dispersion in horizontal directions is anisotropic and should be parameterized by multiple similarity relations under heavy haze conditions.
文摘BACKGROUND Primary intracranial alveolar soft-part sarcoma(PIASPS)is a rare malignancy.We aimed to investigate the clinical profiles and outcomes for PIASPS.CASE SUMMARY We firstly reported five consecutive cases from our institute.Then,the cases from previous studies were pooled and analyzed to delineate the characteristics of this disease.Our cohort included two males and three females.The median age was 21-years-old(range:8-54-years-old).All the patients received surgical treatment.Gross total resection(GTR),radiotherapy,and chemotherapy were administered in 3 patients,4 patients,and 1 patient,respectively.After a median follow-up of 36 mo,tumor progression was noticed in 4 patients;and 3 patients died of the disease.Pooled data(n=14)contained 5 males and 9 females with a median age of 19 years.The log-rank tests showed that GTR(P=0.011)could prolong progression-free survival,and radiotherapy(P<0.001)resulted in longer overall survival.CONCLUSION Patients with PIASPS suffer from poor outcomes.Surgical treatment is the first choice,and GTR should be achieved when the tumor is feasible.Patients with PIASPS benefit from radiotherapy,which should be considered as a part of treatment therapies.
基金jointly supported by the National Natural Science Foundation of China[grant numbers 41975018 and 41675012]the National Key Research and Development Program of China[grant number 2017YFC0209605]。
文摘Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivity KH has rarely been studied in the context of frequent urban pollution in recent years.In this study,KH under urban pollution conditions was directly calculated based on K-theory.The authors found an obvious diurnal variation in K_(H),with variations also in the vertical distributions between each case and over time.Interestingly,the height corresponding to the high occurrence frequency of negative K_(H) rises gradually after sunrise,peaks at noon,falls near sunset,and concentrates around 140 m during most of the night.The KH magnitude and fluctuation are smaller in the pollutant accumulation stage(CS)at all levels than in the pollutant transport stage and pollutant removal stage.Turbulent diffusion may greatly affect PM_(2.5) concentrations at the CS because of the negative correlation between PM_(2.5) concentrations and the absolute value of KH at the CS accompanied by weak wind speeds.The applicability of K-theory is not very good during either day or at night.These problems are inherent in K-theory when characterizing complex systems,such as turbulent diffusion,and require new frameworks or parameterization schemes.These findings may provide valuable insight for establishing a new turbulence diffusion parameterization scheme for KH and promote the study of turbulent diffusion,air quality forecasting,and weather and climate modeling.
基金the Research on Key Technology of Dismantling Railway Scrap Freight Cars,No.W2021JSFW0236.
文摘Based on the existing plant layout and process flow,a simulation analysis was conducted using the Plant Simulation platform with the utilization efficiency of each station and production capacity of the dismantling system as indicators.A problem with long-term suspension in the disassembly process was determined.Based on the two optimization directions of increasing material transportation equipment and expanding the buffer capacity,a cost-oriented optimization model is established.A genetic algorithm and model simulation were used to solve the model.An optimization scheme that satisfies the production needs and has the lowest cost is proposed.The results show that the optimized dismantling system solves the suspended work problem at the dismantling station and a significant improvement in productivity and station utilization efficiency compared with the previous system.
基金Project supported by the National Natural Science Foundation of China(Grant No.62075044)the Shanghai Science and Technology Committee,China(Grant No.18JC1411500)the CIOMP–Fudan University Joint Foundation(Grant No.FC2017-001).
文摘We report an approach of high-pressure hydrogenation to improve the performance of crystalline Si(c-Si) solar cells.As-received p-type c-Si wafer-based PN junctions were subjected to high-pressure(2.5 MPa) hydrogen atmosphere at 200 ℃,followed by evaporating antireflection layers,passivation layers,and front and rear electrodes.The efficiency of the so prepared c-Si solar cell was found to increase evidently after high-pressure hydrogenation,with a maximal enhancement of 10%.The incorporation of hydrogen by Si solar cells was identified,and hydrogen passivation of dangling bonds in Si was confirmed.Compared to the regular approach of hydrogen plasma passivation,the approach of high-pressure hydrogenation reported here needs no post-hydrogenation treatment,and can be more convenient and efficient to use in improving the performances of the c-Si and other solar cells.
