Prediction models were proposed to estimate the reduced Townsend ionization coefficient and ionization cross-section.A shape function of the reduced Townsend ionization coefficient curves was derived from the ionizati...Prediction models were proposed to estimate the reduced Townsend ionization coefficient and ionization cross-section.A shape function of the reduced Townsend ionization coefficient curves was derived from the ionization collision probability model.The function had three parameters:the first ionization potential energy,A_(α),and B_(α).A_(α)and B_(α)were related to the molecule symmetry and size.The polarization of molecules could characterize the molecule symmetry.The multi-layer molecular cross-section(MMCS)was proposed to describe the contributions of electrons and molecule radius on different molecule surfaces to collisions.A prediction model of the ionization cross-section was also proposed based on Aα.The molecule parameters were calculated by the Becke3–Lee–Yang–Parr(B3LYP)method and the 6–311G**basis set.We used available data of 30 and 23 gases,respectively,to build the prediction models of reduced Townsend ionization coefficients and ionization cross-sections.The relationships between the molecular parameters Aαand Bαand the ionization cross-section were built up via nonlinear fittings.The determination coefficients R^(2)of Aα,Bα,and the ionization cross-section were 0.877,0.887,and 0.838,respectively.The results showed that the accuracy of models was positively correlated with the molecule symmetry and reduced electric field.This was mainly related to the accuracy of the MMCS model in predicting Aα.The MMCS model needed to be improved to describe the collision direction selectivity caused by the molecule asymmetry.Under a high reduced electric field,that error of Aαhad less influence on the prediction results.However,the prediction results for single atoms with high symmetry were poor.This may be due to the absolute error of the model close to single atoms’reduced Townsend ionization coefficients.The models could provide the basis for gas insulation prediction and discharge calculations,especially for symmetric molecules under a high electric field.展开更多
Reeds are widely distributed in drought and high salt conditions of northwestern China. Leaf epidermal micromorphology, anatomy, chloroplast ultrastructure and physio-chemical characteristics due to long-term adaptati...Reeds are widely distributed in drought and high salt conditions of northwestern China. Leaf epidermal micromorphology, anatomy, chloroplast ultrastructure and physio-chemical characteristics due to long-term adaptation in the natural habitats of common reed （Phragmites communis Trin.） contrasted considerably among three different ecotypes： dune reed （DR）, Gobi salt reed （GSR） and swamp reed （SR）. The main objective of the present study is to determine the adapting characteristics of morphology, anatomy and physiological responses of thin roots in DR, GSR and SR. The results show that root length density was higher in SR and few root hairs were observed in DR. Cross-section anatomical features show that each ecotype has an endodermis and exodermis, while cortex thickness and proportion of root cortical aerenchyma and stele in root structure varied among the three ecotypes. The stele and xylem share a larger area in DR compared to GSR and SR. GSR has a large proportion of the cortex with radialized distribution of aerenchyma cells spacing, and the cortex has a peripheral, mechanically stiff ring in the exodermis. SEM and TEM microscope images show that GSR has a scle- renchyma ring with high lignification in the exodermis. The physio-chemical parameters show that GSR had a higher level of stress tolerance than DR. These findings indicate that developed water-absorbing tissues were largely distributed in the root structure of DR, and a main framework with supporting function spacing with aerenchyma was dominant in GSR in the long term adaptation to their natural habitats, respectively.展开更多
In order to quantify the characteristics of the surface of jointed rock mass,new equipment,the three-dimensional laser surface topography instrument,was used to accurately measure surface morphology of joints.Scan pic...In order to quantify the characteristics of the surface of jointed rock mass,new equipment,the three-dimensional laser surface topography instrument,was used to accurately measure surface morphology of joints.Scan pictures and parameters were obtained to describe the rock joint surface characteristics,for example,the height frequency of surface,and mean square roughness.Using the method of fractal dimension,the values of joint roughness coefficient(JRC) were calculated based on the above parameters.It could access to the joint surface rock sample morphology of the main parameters of characteristic.The maximum peak height is 2.692 mm in the test joint plane.The maximum profile height is 4.408 mm.JRC value is 6.38 by fractal dimension computing.It belongs to the smooth joint surface.The results show that it is a kind of the effective method to quantitatively evaluate the surface topography by the three-dimensional laser surface topography instrument and the fractal dimension method.According to the results,during the process of underground large-scale mining,safe measures to prevent slip failure of the joint plane by controlling surface tension and shear mechanical response were proposed.展开更多
The lack of suitable varieties is a constraint to okra production in West Africa. This study aimed to assess the magnitude of morphological diversity of 260 accessions of okra (Abelmoschus esculentus L. Moench) in Mal...The lack of suitable varieties is a constraint to okra production in West Africa. This study aimed to assess the magnitude of morphological diversity of 260 accessions of okra (Abelmoschus esculentus L. Moench) in Mali. A total of 25 qualitative and quantitative traits, including plant height, number of branches, pod length, and pod yield, were measured under field conditions. Significant variation was observed for all agronomic traits (p 2 < 60), suggesting that these traits are largely controlled by genetic factors. The pod yield was affected by the incidence of diseases. Principal component analysis (PCA) revealed four distinct clusters, indicating a broad genetic base. These findings provide valuable insights for breeding programs targeting improved okra varieties with enhanced yield and resilience, contributing to sustainable agricultural development in Mali.展开更多
A light-weight structure with sufficient mechanical strength and heat transfer performance is increasingly required for some thermal management issues.The porous structure with the skeleton supporting the ambient stre...A light-weight structure with sufficient mechanical strength and heat transfer performance is increasingly required for some thermal management issues.The porous structure with the skeleton supporting the ambient stress and the pores holding the flowing fluid is considered very promising,attracting significant scientific and industrial interest over the past few decades.However,due to complicated morphology of the porous matrices and thereby various performance of the pressure drop and heat transfer coefficients (HTC),the comprehensive comparison and evaluation between different structures are largely unclear.In this work,recent researches on the efforts of forced convection heat transfer in light-weight porous structure are reviewed;special interest is placed in the open-cell foam,lattice-frame,structured packed bed,and wire-woven structures.Their experimental apparatus,morphological of the porous structures,effect of morphology on pressure drop and HTC,and further applications are discussed.The new method which measure morphology accurately should be paid more attention to develop more accuracy correlation.Also,the most research focused on low Reynolds number and existing structure,while very few researchers investigated the property of forced convection heat transfer in high velocity region and developed new porous structure.展开更多
Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well ceme...Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient N_(c) are revealed,and the calculation method of N_(c) is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section.展开更多
Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LE...Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.展开更多
Karst fracture-cavity carbonate reservoirs,in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances,have become significant fields of oil and gas exploration and explo...Karst fracture-cavity carbonate reservoirs,in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances,have become significant fields of oil and gas exploration and exploitation.Proppant fracturing is considered as the best method for exploiting carbonate reservoirs;however,previous studies primarily focused on the effects of individual types of geological formations,such as natural fractures or cavities,on fracture propagation.In this study,true-triaxial physical simulation experiments were systematically performed under four types of stress difference conditions after the accurate prefabrication of four types of different fracture-cavity distributions in artificial samples.Subsequently,the interaction mechanism between the hydraulic fractures and fracture-cavity structures was systematically analyzed in combination with the stress distribution,cross-sectional morphology of the main propagation path,and three-dimensional visualization of the overall fracture network.It was found that the propagation of hydraulic fractures near the cavity was inhibited by the stress concentration surrounding the cavity.In contrast,a natural fracture with a smaller approach angle(0°and 30°)around the cavity can alleviate the stress concentration and significantly facilitate the connection with the cavity.In addition,the hydraulic fracture crossed the natural fracture at the 45°approach angle and bypassed the cavity under higher stress difference conditions.A new stimulation effectiveness evaluation index was established based on the stimulated reservoir area(SRA),tortuosity of the hydraulic fractures(T),and connectivity index(CI)of the cavities.These findings provide new insights into the fracturing design of carbonate reservoirs.展开更多
Multiple morphologies of colloidal perovskite nanocrystals(NCs)diversify their optical and electronic properties.Among them,the linear absorption cross-section(σ)is a primary parameter to determine their intrinsic ph...Multiple morphologies of colloidal perovskite nanocrystals(NCs)diversify their optical and electronic properties.Among them,the linear absorption cross-section(σ)is a primary parameter to determine their intrinsic photophysical features,and consequently,application potential.Herein,three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr_(3)NCs,nanocubes(NBs),nanoplatelets(NLs),and nanowires(NWs),were targeted,and their linearσvalues were obtained through femtosecond transient absorption(TA)spectroscopy analysis.At high excitation energy well above the bandgap,theσper particle of all CsPbBr3 NCs linearly increased with the particle volume(VNC)regardless of the morphology with the value ofσ400=9.45×10^(4)cm^(−1)×VNC(cm^(2)).Density functional theory(DFT)calculation confirmed the negligible influence of shapes on the optical selection rules.The Einstein spontaneous emission coefficients calculated from theσvalues define the intrinsic radiative recombination rate.However,reduced size dependence is observed when the excitation energy is close to the bandgap(i.e.,at 460 nm)with the value ofσ460=2.82×10^(8)cm0.65×(VNC)0.45(cm^(2)).This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs.These results provide in-depth insight into the optical characteristics for perovskite NCs.展开更多
基金supported by National Natural Science Foundation of China(No.U1966211)National Key R&D Program of China(No.2021YFB2401400)。
文摘Prediction models were proposed to estimate the reduced Townsend ionization coefficient and ionization cross-section.A shape function of the reduced Townsend ionization coefficient curves was derived from the ionization collision probability model.The function had three parameters:the first ionization potential energy,A_(α),and B_(α).A_(α)and B_(α)were related to the molecule symmetry and size.The polarization of molecules could characterize the molecule symmetry.The multi-layer molecular cross-section(MMCS)was proposed to describe the contributions of electrons and molecule radius on different molecule surfaces to collisions.A prediction model of the ionization cross-section was also proposed based on Aα.The molecule parameters were calculated by the Becke3–Lee–Yang–Parr(B3LYP)method and the 6–311G**basis set.We used available data of 30 and 23 gases,respectively,to build the prediction models of reduced Townsend ionization coefficients and ionization cross-sections.The relationships between the molecular parameters Aαand Bαand the ionization cross-section were built up via nonlinear fittings.The determination coefficients R^(2)of Aα,Bα,and the ionization cross-section were 0.877,0.887,and 0.838,respectively.The results showed that the accuracy of models was positively correlated with the molecule symmetry and reduced electric field.This was mainly related to the accuracy of the MMCS model in predicting Aα.The MMCS model needed to be improved to describe the collision direction selectivity caused by the molecule asymmetry.Under a high reduced electric field,that error of Aαhad less influence on the prediction results.However,the prediction results for single atoms with high symmetry were poor.This may be due to the absolute error of the model close to single atoms’reduced Townsend ionization coefficients.The models could provide the basis for gas insulation prediction and discharge calculations,especially for symmetric molecules under a high electric field.
基金financially supported by the State Key Development Program for Basic Research of China(973 Program,Grant No.2013CB429904)the National Natural Science Foundation of China(Grant No.91125029)
文摘Reeds are widely distributed in drought and high salt conditions of northwestern China. Leaf epidermal micromorphology, anatomy, chloroplast ultrastructure and physio-chemical characteristics due to long-term adaptation in the natural habitats of common reed （Phragmites communis Trin.） contrasted considerably among three different ecotypes： dune reed （DR）, Gobi salt reed （GSR） and swamp reed （SR）. The main objective of the present study is to determine the adapting characteristics of morphology, anatomy and physiological responses of thin roots in DR, GSR and SR. The results show that root length density was higher in SR and few root hairs were observed in DR. Cross-section anatomical features show that each ecotype has an endodermis and exodermis, while cortex thickness and proportion of root cortical aerenchyma and stele in root structure varied among the three ecotypes. The stele and xylem share a larger area in DR compared to GSR and SR. GSR has a large proportion of the cortex with radialized distribution of aerenchyma cells spacing, and the cortex has a peripheral, mechanically stiff ring in the exodermis. SEM and TEM microscope images show that GSR has a scle- renchyma ring with high lignification in the exodermis. The physio-chemical parameters show that GSR had a higher level of stress tolerance than DR. These findings indicate that developed water-absorbing tissues were largely distributed in the root structure of DR, and a main framework with supporting function spacing with aerenchyma was dominant in GSR in the long term adaptation to their natural habitats, respectively.
基金Project(2011QNZT087) supported by the Freedom Explore Program of Central South University of ChinaProject(51074178) supported by the National Natural Science Foundation of China+1 种基金Project(09JJ4025) supported by Hunan Provincial Natural Science Foundation of ChinaProject(2010QZZD001) supported by the Fundamental Research Funds for the Central Universities of China
文摘In order to quantify the characteristics of the surface of jointed rock mass,new equipment,the three-dimensional laser surface topography instrument,was used to accurately measure surface morphology of joints.Scan pictures and parameters were obtained to describe the rock joint surface characteristics,for example,the height frequency of surface,and mean square roughness.Using the method of fractal dimension,the values of joint roughness coefficient(JRC) were calculated based on the above parameters.It could access to the joint surface rock sample morphology of the main parameters of characteristic.The maximum peak height is 2.692 mm in the test joint plane.The maximum profile height is 4.408 mm.JRC value is 6.38 by fractal dimension computing.It belongs to the smooth joint surface.The results show that it is a kind of the effective method to quantitatively evaluate the surface topography by the three-dimensional laser surface topography instrument and the fractal dimension method.According to the results,during the process of underground large-scale mining,safe measures to prevent slip failure of the joint plane by controlling surface tension and shear mechanical response were proposed.
文摘The lack of suitable varieties is a constraint to okra production in West Africa. This study aimed to assess the magnitude of morphological diversity of 260 accessions of okra (Abelmoschus esculentus L. Moench) in Mali. A total of 25 qualitative and quantitative traits, including plant height, number of branches, pod length, and pod yield, were measured under field conditions. Significant variation was observed for all agronomic traits (p 2 < 60), suggesting that these traits are largely controlled by genetic factors. The pod yield was affected by the incidence of diseases. Principal component analysis (PCA) revealed four distinct clusters, indicating a broad genetic base. These findings provide valuable insights for breeding programs targeting improved okra varieties with enhanced yield and resilience, contributing to sustainable agricultural development in Mali.
基金This study was supported by the National Science and Technology Major Project(2017-Ⅲ-0005-0029)the National Natural Science Foundation of China(Grant Nos.51806027,U19B2005)the National Key R&D Program of China(Grant No.2018YFC0310006).
文摘A light-weight structure with sufficient mechanical strength and heat transfer performance is increasingly required for some thermal management issues.The porous structure with the skeleton supporting the ambient stress and the pores holding the flowing fluid is considered very promising,attracting significant scientific and industrial interest over the past few decades.However,due to complicated morphology of the porous matrices and thereby various performance of the pressure drop and heat transfer coefficients (HTC),the comprehensive comparison and evaluation between different structures are largely unclear.In this work,recent researches on the efforts of forced convection heat transfer in light-weight porous structure are reviewed;special interest is placed in the open-cell foam,lattice-frame,structured packed bed,and wire-woven structures.Their experimental apparatus,morphological of the porous structures,effect of morphology on pressure drop and HTC,and further applications are discussed.The new method which measure morphology accurately should be paid more attention to develop more accuracy correlation.Also,the most research focused on low Reynolds number and existing structure,while very few researchers investigated the property of forced convection heat transfer in high velocity region and developed new porous structure.
基金This research was financially supported by the National Science Fund for Distinguished Young Scholars(Grant No.51825904)the National Science and Technology Major Project from the Ministry of Science and Technology(MOST)of China(Grant No.2016ZX05058004-005).
文摘Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient N_(c) are revealed,and the calculation method of N_(c) is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section.
基金supported by the National Natural Science Foundation of China (Nos. 51179179 and 51079136)
文摘Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.
基金sponsored by the National Natural Science Foundation of China(Grants Nos.52104046 and 52104010).
文摘Karst fracture-cavity carbonate reservoirs,in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances,have become significant fields of oil and gas exploration and exploitation.Proppant fracturing is considered as the best method for exploiting carbonate reservoirs;however,previous studies primarily focused on the effects of individual types of geological formations,such as natural fractures or cavities,on fracture propagation.In this study,true-triaxial physical simulation experiments were systematically performed under four types of stress difference conditions after the accurate prefabrication of four types of different fracture-cavity distributions in artificial samples.Subsequently,the interaction mechanism between the hydraulic fractures and fracture-cavity structures was systematically analyzed in combination with the stress distribution,cross-sectional morphology of the main propagation path,and three-dimensional visualization of the overall fracture network.It was found that the propagation of hydraulic fractures near the cavity was inhibited by the stress concentration surrounding the cavity.In contrast,a natural fracture with a smaller approach angle(0°and 30°)around the cavity can alleviate the stress concentration and significantly facilitate the connection with the cavity.In addition,the hydraulic fracture crossed the natural fracture at the 45°approach angle and bypassed the cavity under higher stress difference conditions.A new stimulation effectiveness evaluation index was established based on the stimulated reservoir area(SRA),tortuosity of the hydraulic fractures(T),and connectivity index(CI)of the cavities.These findings provide new insights into the fracturing design of carbonate reservoirs.
基金supported by the National Natural Science Foundation of China (NSFC, U1862111)China Scholarship Council (201706990062)+4 种基金Independent Research Fund Denmark-Nature Sciences (DFF-7014-00302)Independent Research Fund Denmark-Sapere Aude starting grant (7026-00037A)Swedish Research Council VR starting grant (2017-05337), grants VR2018-06011, and VR201805090the Research Fund for international Young Scientists from NSFC, China (21950410515)Swedish Energy Agency
文摘Multiple morphologies of colloidal perovskite nanocrystals(NCs)diversify their optical and electronic properties.Among them,the linear absorption cross-section(σ)is a primary parameter to determine their intrinsic photophysical features,and consequently,application potential.Herein,three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr_(3)NCs,nanocubes(NBs),nanoplatelets(NLs),and nanowires(NWs),were targeted,and their linearσvalues were obtained through femtosecond transient absorption(TA)spectroscopy analysis.At high excitation energy well above the bandgap,theσper particle of all CsPbBr3 NCs linearly increased with the particle volume(VNC)regardless of the morphology with the value ofσ400=9.45×10^(4)cm^(−1)×VNC(cm^(2)).Density functional theory(DFT)calculation confirmed the negligible influence of shapes on the optical selection rules.The Einstein spontaneous emission coefficients calculated from theσvalues define the intrinsic radiative recombination rate.However,reduced size dependence is observed when the excitation energy is close to the bandgap(i.e.,at 460 nm)with the value ofσ460=2.82×10^(8)cm0.65×(VNC)0.45(cm^(2)).This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs.These results provide in-depth insight into the optical characteristics for perovskite NCs.
