The crystal habit,crystalline structure,surface condition and composition of the ultrafine Al particles prepared by inert gas evaporation method were studied in detail by means of high resolution transmission electron...The crystal habit,crystalline structure,surface condition and composition of the ultrafine Al particles prepared by inert gas evaporation method were studied in detail by means of high resolution transmission electron microscope,X-ray diffraction and X-ray photo-electron spectrum.The results indicate that the ultrafine Al particles prepared in high pure inert gas are of clear crystal habits,single crystal in a large majority and fcc crystalline structure with a_0=0.405 nm.It is also found on the surface of the Al particles that there is a layer of amor- phous Al_2O_3 with 2 nm average thickness,which could protect the particles against oxidizing further.Therefore,the ultrafine Al particles prepared by the inert gas evaporation method are very stable in atmosphere.展开更多
This paper aims to design an automated Global Reporting Format’s (GRF) application in order to reduce time of manual application (on a runway) of the Global Reporting Format developed by International Civil Aviation ...This paper aims to design an automated Global Reporting Format’s (GRF) application in order to reduce time of manual application (on a runway) of the Global Reporting Format developed by International Civil Aviation Organization (ICAO). A method has been used to measure and generate Runway Condition Report (RCR) automatically. The developed computing model is an autonomous and automatic application implemented specially for West Africa (and can be extended to any rainy area). It uses Arduino materials and computing code developed by the authors. Results obtained show that using that method to retrieve the Runway Condition Report (RCR) is fast, so human presence on the runway is reduced. Even though the results obtained using this model are slightly different from those expected, the actual runway conditions are not too much affected.展开更多
This study proposes an alternative calculation mode for stresses on the slip surface(SS).The calculation of the normal stress(NS)on the SS involves examining its composition and expanding its unknown using the Taylor ...This study proposes an alternative calculation mode for stresses on the slip surface(SS).The calculation of the normal stress(NS)on the SS involves examining its composition and expanding its unknown using the Taylor series.This expansion enables the reasonable construction of a function describing the NS on the SS.Additionally,by directly incorporating the nonlinear Generalized Hoke-Brown(GHB)strength criterion and utilizing the slope factor of safety(FOS)definition,a function of the shear stress on the SS is derived.This function considers the mutual feedback mechanism between the NS and strength parameters of the SS.The stress constraints conditions are then introduced at both ends of the SS based on the spatial stress relation of one point.Determining the slope FOS and stress solution for the SS involves considering the mechanical equilibrium conditions and the stress constraint conditions satisfied by the sliding body.The proposed approach successfully simulates the tension-shear stress zone near the slope top and provides an intuitive description of the concentration effect of compression-shear stress of the SS near the slope toe.Furthermore,compared to other methods,the present method demonstrates superior processing capabilities for the embedded nonlinear GHB strength criterion.展开更多
A compact four-component two-dimensional （2-D） finite-difference frequency domain （FDFD） method with the equivalent surface impedance boundary condition is used to analyze the dispersion characteristics of multila...A compact four-component two-dimensional （2-D） finite-difference frequency domain （FDFD） method with the equivalent surface impedance boundary condition is used to analyze the dispersion characteristics of multilayer metal-coated waveguides. According to the equivalent surface impedance boundary condition,the relationship between transverse field components on the boundary can be easily depicted. Once the eigen equation is solved,the propagation constant can be obtained as the eigen value for a given frequency. Results of the proposed method agaree well with those of high frequency structure simulator（HFSS）.展开更多
A method of detecting dry, icy and wet road surface conditions based on scanniag detection of single wavelength backward power is proposed in this letter. The detector is used to receive the backward scattered power w...A method of detecting dry, icy and wet road surface conditions based on scanniag detection of single wavelength backward power is proposed in this letter. The detector is used to receive the backward scattered power which changes with the incidence angle. The relationship between backward power and incidence angle is used to find out the effective angle range and distinguish method. Experiment and simulation show that it is feasible to classifv these three conditions within incidence angle of 5.3 degree.展开更多
The composition and morphology of a passive film formed on Ni-based alloy 690 with different surface conditions exposed to high-temperature,high-pressure aerated and deaerated deionized water vapor with different time...The composition and morphology of a passive film formed on Ni-based alloy 690 with different surface conditions exposed to high-temperature,high-pressure aerated and deaerated deionized water vapor with different time were characterized by using X-ray photoelectron spectroscopy(XPS)and atomic force microscopy(AFM)in this study.Shot peened,mechanical polishing and electro polishing were used to obtain different surface conditions.The film thickness remained constant after different exposure treatments,while the film layered structures were different.On specimens exposed to aerated water for 2 min and deaerated water for 1 h,Ni-rich oxide was identified in the outmost oxide films while Cr-rich oxide existed in inner layers.On specimens exposed to aerated water for 1 h,Cr-rich oxide with participating of Ni-and Fe-oxide was identified in all layers,while on specimens exposed to deaerated water for 2 min,Cr-rich oxide in all layers with participating of Ni-oxide was identified.Large oxide particles with a low density were found.The oxide particles were the biggest and least dense for electro polished specimen,whilest smallest and most dense for shot peened specimen.Oxidation for the same time,the surface was oxidized more pronounced in aerated water than in deaeated water.展开更多
This study investigates the trends in the mean state and the day-to-day variability （DDV） of the surface weather conditions over northern and northeastern China （NNEC） during 1961-2014 using CN05.1 observational d...This study investigates the trends in the mean state and the day-to-day variability （DDV） of the surface weather conditions over northern and northeastern China （NNEC） during 1961-2014 using CN05.1 observational data. In this study, we show that the surface temperature （wind speed） has increased （decreased） over NNEC and that the DDV of the surface temperatures and wind speeds has decreased, indicating a trend towards a stable warm and windless state of the surface weather conditions over NNEC. This finding implies a trend towards more persistent hot and windless episodes, which threaten human health and aggravate environmental problems. The trends are also examined in reanalysis data. Both the ERA-40 and the NCEP data show an increasing （decreasing） trend in the mean state of the surface temperatures （wind speeds）. However, the reanalysis data show a consistent decreasing trend in the DDV of the surface weather conditions only in the spring. The underlying reason for the decreased DDV of the surface weather conditions is further analyzed, focusing on the spring season. Essentially, the decreased DDV of the surface weather conditions can be attributed to a decrease in synoptic-scale wave activity, which is caused by a decrease in the baroclinic instability. There is a contrasting change in the baroclinic instability over East Asia, showing a decreasing （increasing） trend north （south） of 40°N. This contrasting change in the baroclinic instability is primarily caused by a tropospheric cooling zone over East Asia at approximately 40°N, which influences the meridional temperature gradient over East Asia.展开更多
Land surface hydrothermal conditions(LSHCs) reflect land surface moisture and heat conditions, and play an important role in energy and water cycles in soil-plant-atmosphere continuum. Based on comparison of four eval...Land surface hydrothermal conditions(LSHCs) reflect land surface moisture and heat conditions, and play an important role in energy and water cycles in soil-plant-atmosphere continuum. Based on comparison of four evaluation methods(namely, the classic statistical method, geostatistical method, information theory method, and fractal method), this study proposed a new scheme for evaluating the spatial heterogeneity of LSHCs. This scheme incorporates diverse remotely sensed surface parameters, e.g., leaf area index-LAI, the normalized difference vegetation index-NDVI, net radiation-Rn, and land surface temperature-LST. The LSHCs can be classified into three categories, namely homogeneous, moderately heterogeneous and highly heterogeneous based on the remotely sensed LAI data with a 30 m spatial resolution and the combination of normalized information entropy(S’) and coefficient of variation(CV). Based on the evaluation scheme, the spatial heterogeneity of land surface hydrothermal conditions at six typical flux observation stations in the Heihe River Basin during the vegetation growing season were evaluated. The evaluation results were consistent with the land surface type characteristics exhibited by Google Earth imagery and spatial heterogeneity assessed by high resolution remote sensing evapotranspiration data. Impact factors such as precipitation and irrigation events, spatial resolutions of remote sensing data, heterogeneity in the vertical direction, topography and sparse vegetation could also affect the evaluation results. For instance, short-term changes(precipitation and irrigation events) in the spatial heterogeneity of LSHCs can be diagnosed by energy factors, while long-term changes can be indicated by vegetation factors. The spatial heterogeneity of LSHCs decreases when decreasing the spatial resolution of remote sensing data. The proposed evaluation scheme would be useful for the quantification of spatial heterogeneity of LSHCs over flux observation stations toward the global scale, and also contribute to the improvement of the accuracy of estimation and validation for remotely sensed(or model simulated) evapotranspiration.展开更多
An algorithm based on the Boundary Element Method(BEM)is presented for designing the High Skew Propeller(HSP)used in an Underwater Vehicle(UV).Since UVs operate under two different kinds of working conditions(i.e.surf...An algorithm based on the Boundary Element Method(BEM)is presented for designing the High Skew Propeller(HSP)used in an Underwater Vehicle(UV).Since UVs operate under two different kinds of working conditions(i.e.surface and submerged conditions),the design of such a propeller is an unwieldy task.This is mainly due to the fact that the resistance forces as well as the vessel efficiency under these conditions are significantly different.Therefore,some factors are necessary for the design of the opti-mum propeller to utilize the power under the mentioned conditions.The design objectives of the optimum propeller are to obtain the highest possible thrust and efficiency with the minimum torque.For the current UV,the main dimensions of the propeller are pre-dicted based on the given required thrust and the defined operating conditions.These dimensions(number of blades,pitch,diameter,expanded area ratio,thickness and camber)are determined through iterative procedure.Because the propeller operates at the stern of the UV where the inflow velocity to the propeller is non-uniform,a 5-blade HSP is preferred for running the UV.Finally,the propel-ler is designed based on the numerical calculations to acquire the improved hydrodynamic efficiency.展开更多
A coupled atmosphere-ocean model developed at the Institute for Space Studies at NASA Goddard Space Flight Center (Russell et al., 1995) was used to verify the validity of Haney-type surface thermal boundary condition...A coupled atmosphere-ocean model developed at the Institute for Space Studies at NASA Goddard Space Flight Center (Russell et al., 1995) was used to verify the validity of Haney-type surface thermal boundary condition, which linearly connects net downward surface heat fluxQ to air/sea temperature difference ΔT by a relaxation coefficientk. The model was initiated from the National Centers for Environmental Prediction (NCEP) atmospheric observations for 1 December 1977, and from the National Ocean Data Center (NODC) global climatological mean December temperature and salinity fields at 1°x 1° resolution. The time step is 7.5 minutes. We integrated the model for 450 days and obtained a complete model-generated global data set of daily mean downward net surface fluxQ, surface air temperatureT A, and sea surface temperatureT O. Then, we calculated the cross-correlation coefficients (CCC) betweenQ and ΔT. The ensemble mean CCC fields show (a) no correlation betweenQ and ΔT in the equatiorial regions, and (b) evident correlation (CCC≥0.7) betweenQ and ΔT in the middle and high latitudes. Additionally, we did the variance analysis and found that whenk=120 W m?2K?1, the two standard deviations, σQ and σκδT , are quite close in the middle and high latitudes. These results agree quite well with a previous research (Chu et al., 1998) on analyzing the NCEP re-analyzed surface data, except that a smaller value ofk (80 W m?2K?1) was found in the previous study. Key words Air-sea coupled system - Ocean surface fluxes - Surface thermal boundary condition展开更多
The aim of the present paper is to study the numerical solutions of the steady MHD two dimensional stagnation point flow of an incompressible nano fluid towards a stretching cylinder.The effects of radiation and conve...The aim of the present paper is to study the numerical solutions of the steady MHD two dimensional stagnation point flow of an incompressible nano fluid towards a stretching cylinder.The effects of radiation and convective boundary condition are also taken into account.The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis.The resulting nonlinear momentum,energy and nano particle equations are simplifed using similarity transformations.Numerical solutions have been obtained for the velocity,temperature and nanoparticle fraction profles.The influence of physical parameters on the velocity,temperature,nanoparticle fraction,rates of heat transfer and nanoparticle fraction are shown graphically.展开更多
By using IAP 9L AGCM, two sets of long-term climatological integration have been performed with the two different interpolation procedures for generating the daily surface boundary conditions. One interpolation proced...By using IAP 9L AGCM, two sets of long-term climatological integration have been performed with the two different interpolation procedures for generating the daily surface boundary conditions. One interpolation procedure is the so-called “traditional” scheme, for which the daily surface boundary conditions are obtained by linearly interpolating between the observed monthly mean values, however the observed monthly means cannot be preserved after interpolation. The other one is the “new” scheme, for which the daily surface boundary conditions are obtained by linearly interpolating between the “artificial” monthly mean values which are based on, but are different from the observed ones, after interpolating with this new scheme, not only the observed monthly mean values are preserved, the time series of the new generated daily values is also more consistent with the observation. Comparison of the model results shows that the differences of the globally or zonally averaged fields between these two integrations are quite small, and this is due to the compensating effect between the different regions. However, the differences of the two patterns (the global or regional geographical distributions), are quite significant, for example, the magnitude of the difference in the JJA mean rainfall between these two integrations can exceed 2 mm/ day over Asian monsoon regions, and the difference in DJF mean surface air temperature can also exceed 2?C over this region. The fact that the model climatology depends quite strongly on the method of prescribing the daily surface boundary conditions suggests that in order to validate the climate model or to predict the short-term climate anomalies, either the “new? interpolation scheme or the high frequency surface boundary conditions (e.g., daily or weekly data instead of the monthly data) should be introduced. Meanwhile, as for the coupled model, the daily coupling scheme between the different component climate models ( e.g., atmospheric and oceanic general circulation models) is preferred in order to partly eliminate the “climate drift” problem which may appear during the course of direct coupling.展开更多
It always adopts the direct hierarchy analysis to value the exploitation conditions of surface mining areas. This way has some unavoidable shortcomings because it is mainly under the aid of experts and it is affected ...It always adopts the direct hierarchy analysis to value the exploitation conditions of surface mining areas. This way has some unavoidable shortcomings because it is mainly under the aid of experts and it is affected by the subjective thinking of the experts. This paper puts forwards a new approach that divides the whole exploitation conditions into sixteen subsidiary systems and each subsidiary system forms a neural network system. The whole decision system of exploitation conditions of surface mining areas is composed of sixteen subsidiary neural network systems. Each neural network is practiced with the data of the worksite, which is reasonable and scientific. This way will be a new decision approach for exploiting the surface mining areas.展开更多
The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce th...The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce the risk of anastomotic thrombosis due to the size mismatch。展开更多
Mixed convection flow of magnetohydrodynamic(MHD) Jeffrey nanofluid over a radially stretching surface with radiative surface is studied. Radial sheet is considered to be convectively heated. Convective boundary condi...Mixed convection flow of magnetohydrodynamic(MHD) Jeffrey nanofluid over a radially stretching surface with radiative surface is studied. Radial sheet is considered to be convectively heated. Convective boundary conditions through heat and mass are employed. The governing boundary layer equations are transformed into ordinary differential equations. Convergent series solutions of the resulting problems are derived. Emphasis has been focused on studying the effects of mixed convection, thermal radiation, magnetic field and nanoparticles on the velocity, temperature and concentration fields. Numerical values of the physical parameters involved in the problem are computed for the local Nusselt and Sherwood numbers are computed.展开更多
In this paper, equivalent surface impedance boundary condition （ESIBC）, which takes fractal parameters （D, G） into SIBC, is implemented in the 4-component 2-D compact finite difference frequency domain （2-D CFDFD...In this paper, equivalent surface impedance boundary condition （ESIBC）, which takes fractal parameters （D, G） into SIBC, is implemented in the 4-component 2-D compact finite difference frequency domain （2-D CFDFD） method to an- alyze the propagation characteristics of lossy circular waveguide with fractal rough surface based on Weierstrass-Mandelbrot （W-M） function. Fractal parameters’ effects on attenuation constant are presented in the 3 mm lossy circular waveguide, and the attenuation constants of the first three modes vary monotonically with scaling constant （G） and decrease as the fractal dimension （D） increasing.展开更多
To deal with the staircase approximation problem in the standard finite-difference time-domain（FDTD） simulation,the two-dimensional boundary condition equations（BCE） method is proposed in this paper.In the BCE met...To deal with the staircase approximation problem in the standard finite-difference time-domain（FDTD） simulation,the two-dimensional boundary condition equations（BCE） method is proposed in this paper.In the BCE method,the standard FDTD algorithm can be used as usual,and the curved surface is treated by adding the boundary condition equations.Thus,while maintaining the simplicity and computational efficiency of the standard FDTD algorithm,the BCE method can solve the staircase approximation problem.The BCE method is validated by analyzing near field and far field scattering properties of the PEC and dielectric cylinders.The results show that the BCE method can maintain a second-order accuracy by eliminating the staircase approximation errors.Moreover,the results of the BCE method show good accuracy for cylinder scattering cases with different permittivities.展开更多
This article manages Darcy-Forchheimer 3D flow of water based carbon nanomaterial(CNTs).A bidirectional nonlinear stretchable surface has been utilized to make the flow.Disturbance in permeable space has been represen...This article manages Darcy-Forchheimer 3D flow of water based carbon nanomaterial(CNTs).A bidirectional nonlinear stretchable surface has been utilized to make the flow.Disturbance in permeable space has been represented by Darcy Forchheimer(DF)expression.Heat transfer mechanism is explored through convective heating.Outcomes for SWCNT and MWCNT have been displayed and compared.The reduction of partial differential framework into nonlinear common differential framework is made through reasonable variables.Optimal series scheme is utilized for arrangements advancement of associated flow issue.Optimal homotopic solution expressions for velocities and temperature are studied through graphs by considering various estimations of physical variables.Moreover surface drag coefficients and heat transfer rate are analyzed through plots.展开更多
Wind turbine blades are prone to failure due to high tip speed,rain,dust and so on.A surface condition detecting approach based on wind turbine blade aerodynamic noise is proposed.On the experimental measurement data,...Wind turbine blades are prone to failure due to high tip speed,rain,dust and so on.A surface condition detecting approach based on wind turbine blade aerodynamic noise is proposed.On the experimental measurement data,variational mode decomposition filtering and Mel spectrogram drawing are conducted first.The Mel spectrogram is divided into two halves based on frequency characteristics and then sent into the convolutional neural network.Gaussian white noise is superimposed on the original signal and the output results are assessed based on score coefficients,considering the complexity of the real environment.The surfaces of Wind turbine blades are classified into four types:standard,attachments,polishing,and serrated trailing edge.The proposed method is evaluated and the detection accuracy in complicated background conditions is found to be 99.59%.In addition to support the differentiation of trained models,utilizing proper score coefficients also permit the screening of unknown types.展开更多
The development of a two dimensional numerical wave tank （NWT） with a rocker or piston type wavemaker based on the high order boundary element method （BEM） and mixed Eulerian-Lagrangian （MEL） is examined. The ca...The development of a two dimensional numerical wave tank （NWT） with a rocker or piston type wavemaker based on the high order boundary element method （BEM） and mixed Eulerian-Lagrangian （MEL） is examined. The cauchy principle value （CPV） integral is calculated by a special Gauss type quadrature and a change of variable. In addition the explicit truncated Taylor expansion formula is employed in the time-stepping process. A modified double nodes method is assumed to tackle the comer problem, as well as the damping zone technique is used to absorb the propagation of the free surface wave at the end of the tank. A variety of waves are generated by the NWT, for example; a monochromatic wave, solitary wave and irregular wave. The results confirm the NWT model is efficient and stable.展开更多
文摘The crystal habit,crystalline structure,surface condition and composition of the ultrafine Al particles prepared by inert gas evaporation method were studied in detail by means of high resolution transmission electron microscope,X-ray diffraction and X-ray photo-electron spectrum.The results indicate that the ultrafine Al particles prepared in high pure inert gas are of clear crystal habits,single crystal in a large majority and fcc crystalline structure with a_0=0.405 nm.It is also found on the surface of the Al particles that there is a layer of amor- phous Al_2O_3 with 2 nm average thickness,which could protect the particles against oxidizing further.Therefore,the ultrafine Al particles prepared by the inert gas evaporation method are very stable in atmosphere.
文摘This paper aims to design an automated Global Reporting Format’s (GRF) application in order to reduce time of manual application (on a runway) of the Global Reporting Format developed by International Civil Aviation Organization (ICAO). A method has been used to measure and generate Runway Condition Report (RCR) automatically. The developed computing model is an autonomous and automatic application implemented specially for West Africa (and can be extended to any rainy area). It uses Arduino materials and computing code developed by the authors. Results obtained show that using that method to retrieve the Runway Condition Report (RCR) is fast, so human presence on the runway is reduced. Even though the results obtained using this model are slightly different from those expected, the actual runway conditions are not too much affected.
基金Project(52278380)supported by the National Natural Science Foundation of ChinaProject(2023JJ30670)supported by the National Science Foundation of and Technology Major Project of Hunan Province,China。
文摘This study proposes an alternative calculation mode for stresses on the slip surface(SS).The calculation of the normal stress(NS)on the SS involves examining its composition and expanding its unknown using the Taylor series.This expansion enables the reasonable construction of a function describing the NS on the SS.Additionally,by directly incorporating the nonlinear Generalized Hoke-Brown(GHB)strength criterion and utilizing the slope factor of safety(FOS)definition,a function of the shear stress on the SS is derived.This function considers the mutual feedback mechanism between the NS and strength parameters of the SS.The stress constraints conditions are then introduced at both ends of the SS based on the spatial stress relation of one point.Determining the slope FOS and stress solution for the SS involves considering the mechanical equilibrium conditions and the stress constraint conditions satisfied by the sliding body.The proposed approach successfully simulates the tension-shear stress zone near the slope top and provides an intuitive description of the concentration effect of compression-shear stress of the SS near the slope toe.Furthermore,compared to other methods,the present method demonstrates superior processing capabilities for the embedded nonlinear GHB strength criterion.
基金Supported by the Project Innovation of Graduate Students of Jiangsu Province of China(CX09B-079Z)the Basic Research Items of National Key Lab of Electronic Measurement Technology~~
文摘A compact four-component two-dimensional （2-D） finite-difference frequency domain （FDFD） method with the equivalent surface impedance boundary condition is used to analyze the dispersion characteristics of multilayer metal-coated waveguides. According to the equivalent surface impedance boundary condition,the relationship between transverse field components on the boundary can be easily depicted. Once the eigen equation is solved,the propagation constant can be obtained as the eigen value for a given frequency. Results of the proposed method agaree well with those of high frequency structure simulator（HFSS）.
文摘A method of detecting dry, icy and wet road surface conditions based on scanniag detection of single wavelength backward power is proposed in this letter. The detector is used to receive the backward scattered power which changes with the incidence angle. The relationship between backward power and incidence angle is used to find out the effective angle range and distinguish method. Experiment and simulation show that it is feasible to classifv these three conditions within incidence angle of 5.3 degree.
基金financially supported by the National Natural Science Foundation of China(No.52073176)
文摘The composition and morphology of a passive film formed on Ni-based alloy 690 with different surface conditions exposed to high-temperature,high-pressure aerated and deaerated deionized water vapor with different time were characterized by using X-ray photoelectron spectroscopy(XPS)and atomic force microscopy(AFM)in this study.Shot peened,mechanical polishing and electro polishing were used to obtain different surface conditions.The film thickness remained constant after different exposure treatments,while the film layered structures were different.On specimens exposed to aerated water for 2 min and deaerated water for 1 h,Ni-rich oxide was identified in the outmost oxide films while Cr-rich oxide existed in inner layers.On specimens exposed to aerated water for 1 h,Cr-rich oxide with participating of Ni-and Fe-oxide was identified in all layers,while on specimens exposed to deaerated water for 2 min,Cr-rich oxide in all layers with participating of Ni-oxide was identified.Large oxide particles with a low density were found.The oxide particles were the biggest and least dense for electro polished specimen,whilest smallest and most dense for shot peened specimen.Oxidation for the same time,the surface was oxidized more pronounced in aerated water than in deaeated water.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41421004 and 41210007)the Atmosphere-Ocean Research Center (AORC)International Pacific Research Center (IPRC) at University of Hawaii
文摘This study investigates the trends in the mean state and the day-to-day variability （DDV） of the surface weather conditions over northern and northeastern China （NNEC） during 1961-2014 using CN05.1 observational data. In this study, we show that the surface temperature （wind speed） has increased （decreased） over NNEC and that the DDV of the surface temperatures and wind speeds has decreased, indicating a trend towards a stable warm and windless state of the surface weather conditions over NNEC. This finding implies a trend towards more persistent hot and windless episodes, which threaten human health and aggravate environmental problems. The trends are also examined in reanalysis data. Both the ERA-40 and the NCEP data show an increasing （decreasing） trend in the mean state of the surface temperatures （wind speeds）. However, the reanalysis data show a consistent decreasing trend in the DDV of the surface weather conditions only in the spring. The underlying reason for the decreased DDV of the surface weather conditions is further analyzed, focusing on the spring season. Essentially, the decreased DDV of the surface weather conditions can be attributed to a decrease in synoptic-scale wave activity, which is caused by a decrease in the baroclinic instability. There is a contrasting change in the baroclinic instability over East Asia, showing a decreasing （increasing） trend north （south） of 40°N. This contrasting change in the baroclinic instability is primarily caused by a tropospheric cooling zone over East Asia at approximately 40°N, which influences the meridional temperature gradient over East Asia.
基金the auspices of National Natural Science Foundation of China(No.41531174)National Basic Research Program of China(No.2015CB953702)。
文摘Land surface hydrothermal conditions(LSHCs) reflect land surface moisture and heat conditions, and play an important role in energy and water cycles in soil-plant-atmosphere continuum. Based on comparison of four evaluation methods(namely, the classic statistical method, geostatistical method, information theory method, and fractal method), this study proposed a new scheme for evaluating the spatial heterogeneity of LSHCs. This scheme incorporates diverse remotely sensed surface parameters, e.g., leaf area index-LAI, the normalized difference vegetation index-NDVI, net radiation-Rn, and land surface temperature-LST. The LSHCs can be classified into three categories, namely homogeneous, moderately heterogeneous and highly heterogeneous based on the remotely sensed LAI data with a 30 m spatial resolution and the combination of normalized information entropy(S’) and coefficient of variation(CV). Based on the evaluation scheme, the spatial heterogeneity of land surface hydrothermal conditions at six typical flux observation stations in the Heihe River Basin during the vegetation growing season were evaluated. The evaluation results were consistent with the land surface type characteristics exhibited by Google Earth imagery and spatial heterogeneity assessed by high resolution remote sensing evapotranspiration data. Impact factors such as precipitation and irrigation events, spatial resolutions of remote sensing data, heterogeneity in the vertical direction, topography and sparse vegetation could also affect the evaluation results. For instance, short-term changes(precipitation and irrigation events) in the spatial heterogeneity of LSHCs can be diagnosed by energy factors, while long-term changes can be indicated by vegetation factors. The spatial heterogeneity of LSHCs decreases when decreasing the spatial resolution of remote sensing data. The proposed evaluation scheme would be useful for the quantification of spatial heterogeneity of LSHCs over flux observation stations toward the global scale, and also contribute to the improvement of the accuracy of estimation and validation for remotely sensed(or model simulated) evapotranspiration.
基金supported by the marine research center of Amirkabir University of Technology
文摘An algorithm based on the Boundary Element Method(BEM)is presented for designing the High Skew Propeller(HSP)used in an Underwater Vehicle(UV).Since UVs operate under two different kinds of working conditions(i.e.surface and submerged conditions),the design of such a propeller is an unwieldy task.This is mainly due to the fact that the resistance forces as well as the vessel efficiency under these conditions are significantly different.Therefore,some factors are necessary for the design of the opti-mum propeller to utilize the power under the mentioned conditions.The design objectives of the optimum propeller are to obtain the highest possible thrust and efficiency with the minimum torque.For the current UV,the main dimensions of the propeller are pre-dicted based on the given required thrust and the defined operating conditions.These dimensions(number of blades,pitch,diameter,expanded area ratio,thickness and camber)are determined through iterative procedure.Because the propeller operates at the stern of the UV where the inflow velocity to the propeller is non-uniform,a 5-blade HSP is preferred for running the UV.Finally,the propel-ler is designed based on the numerical calculations to acquire the improved hydrodynamic efficiency.
文摘A coupled atmosphere-ocean model developed at the Institute for Space Studies at NASA Goddard Space Flight Center (Russell et al., 1995) was used to verify the validity of Haney-type surface thermal boundary condition, which linearly connects net downward surface heat fluxQ to air/sea temperature difference ΔT by a relaxation coefficientk. The model was initiated from the National Centers for Environmental Prediction (NCEP) atmospheric observations for 1 December 1977, and from the National Ocean Data Center (NODC) global climatological mean December temperature and salinity fields at 1°x 1° resolution. The time step is 7.5 minutes. We integrated the model for 450 days and obtained a complete model-generated global data set of daily mean downward net surface fluxQ, surface air temperatureT A, and sea surface temperatureT O. Then, we calculated the cross-correlation coefficients (CCC) betweenQ and ΔT. The ensemble mean CCC fields show (a) no correlation betweenQ and ΔT in the equatiorial regions, and (b) evident correlation (CCC≥0.7) betweenQ and ΔT in the middle and high latitudes. Additionally, we did the variance analysis and found that whenk=120 W m?2K?1, the two standard deviations, σQ and σκδT , are quite close in the middle and high latitudes. These results agree quite well with a previous research (Chu et al., 1998) on analyzing the NCEP re-analyzed surface data, except that a smaller value ofk (80 W m?2K?1) was found in the previous study. Key words Air-sea coupled system - Ocean surface fluxes - Surface thermal boundary condition
文摘The aim of the present paper is to study the numerical solutions of the steady MHD two dimensional stagnation point flow of an incompressible nano fluid towards a stretching cylinder.The effects of radiation and convective boundary condition are also taken into account.The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis.The resulting nonlinear momentum,energy and nano particle equations are simplifed using similarity transformations.Numerical solutions have been obtained for the velocity,temperature and nanoparticle fraction profles.The influence of physical parameters on the velocity,temperature,nanoparticle fraction,rates of heat transfer and nanoparticle fraction are shown graphically.
文摘By using IAP 9L AGCM, two sets of long-term climatological integration have been performed with the two different interpolation procedures for generating the daily surface boundary conditions. One interpolation procedure is the so-called “traditional” scheme, for which the daily surface boundary conditions are obtained by linearly interpolating between the observed monthly mean values, however the observed monthly means cannot be preserved after interpolation. The other one is the “new” scheme, for which the daily surface boundary conditions are obtained by linearly interpolating between the “artificial” monthly mean values which are based on, but are different from the observed ones, after interpolating with this new scheme, not only the observed monthly mean values are preserved, the time series of the new generated daily values is also more consistent with the observation. Comparison of the model results shows that the differences of the globally or zonally averaged fields between these two integrations are quite small, and this is due to the compensating effect between the different regions. However, the differences of the two patterns (the global or regional geographical distributions), are quite significant, for example, the magnitude of the difference in the JJA mean rainfall between these two integrations can exceed 2 mm/ day over Asian monsoon regions, and the difference in DJF mean surface air temperature can also exceed 2?C over this region. The fact that the model climatology depends quite strongly on the method of prescribing the daily surface boundary conditions suggests that in order to validate the climate model or to predict the short-term climate anomalies, either the “new? interpolation scheme or the high frequency surface boundary conditions (e.g., daily or weekly data instead of the monthly data) should be introduced. Meanwhile, as for the coupled model, the daily coupling scheme between the different component climate models ( e.g., atmospheric and oceanic general circulation models) is preferred in order to partly eliminate the “climate drift” problem which may appear during the course of direct coupling.
文摘It always adopts the direct hierarchy analysis to value the exploitation conditions of surface mining areas. This way has some unavoidable shortcomings because it is mainly under the aid of experts and it is affected by the subjective thinking of the experts. This paper puts forwards a new approach that divides the whole exploitation conditions into sixteen subsidiary systems and each subsidiary system forms a neural network system. The whole decision system of exploitation conditions of surface mining areas is composed of sixteen subsidiary neural network systems. Each neural network is practiced with the data of the worksite, which is reasonable and scientific. This way will be a new decision approach for exploiting the surface mining areas.
基金supported by Grants-in-Aid from the National Natural Science Foundation of China No.10632010,30670517
文摘The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce the risk of anastomotic thrombosis due to the size mismatch。
文摘Mixed convection flow of magnetohydrodynamic(MHD) Jeffrey nanofluid over a radially stretching surface with radiative surface is studied. Radial sheet is considered to be convectively heated. Convective boundary conditions through heat and mass are employed. The governing boundary layer equations are transformed into ordinary differential equations. Convergent series solutions of the resulting problems are derived. Emphasis has been focused on studying the effects of mixed convection, thermal radiation, magnetic field and nanoparticles on the velocity, temperature and concentration fields. Numerical values of the physical parameters involved in the problem are computed for the local Nusselt and Sherwood numbers are computed.
文摘In this paper, equivalent surface impedance boundary condition （ESIBC）, which takes fractal parameters （D, G） into SIBC, is implemented in the 4-component 2-D compact finite difference frequency domain （2-D CFDFD） method to an- alyze the propagation characteristics of lossy circular waveguide with fractal rough surface based on Weierstrass-Mandelbrot （W-M） function. Fractal parameters’ effects on attenuation constant are presented in the 3 mm lossy circular waveguide, and the attenuation constants of the first three modes vary monotonically with scaling constant （G） and decrease as the fractal dimension （D） increasing.
基金Project supported by the National Natural Science Foundation of China(Grant No.51025622)
文摘To deal with the staircase approximation problem in the standard finite-difference time-domain（FDTD） simulation,the two-dimensional boundary condition equations（BCE） method is proposed in this paper.In the BCE method,the standard FDTD algorithm can be used as usual,and the curved surface is treated by adding the boundary condition equations.Thus,while maintaining the simplicity and computational efficiency of the standard FDTD algorithm,the BCE method can solve the staircase approximation problem.The BCE method is validated by analyzing near field and far field scattering properties of the PEC and dielectric cylinders.The results show that the BCE method can maintain a second-order accuracy by eliminating the staircase approximation errors.Moreover,the results of the BCE method show good accuracy for cylinder scattering cases with different permittivities.
文摘This article manages Darcy-Forchheimer 3D flow of water based carbon nanomaterial(CNTs).A bidirectional nonlinear stretchable surface has been utilized to make the flow.Disturbance in permeable space has been represented by Darcy Forchheimer(DF)expression.Heat transfer mechanism is explored through convective heating.Outcomes for SWCNT and MWCNT have been displayed and compared.The reduction of partial differential framework into nonlinear common differential framework is made through reasonable variables.Optimal series scheme is utilized for arrangements advancement of associated flow issue.Optimal homotopic solution expressions for velocities and temperature are studied through graphs by considering various estimations of physical variables.Moreover surface drag coefficients and heat transfer rate are analyzed through plots.
基金funded by the National Nature Science Founda-tion of China(Grant Nos.51905469 and 11672261)the National key research and development program of China under grant number(Grant No.2019YFE0192600)。
文摘Wind turbine blades are prone to failure due to high tip speed,rain,dust and so on.A surface condition detecting approach based on wind turbine blade aerodynamic noise is proposed.On the experimental measurement data,variational mode decomposition filtering and Mel spectrogram drawing are conducted first.The Mel spectrogram is divided into two halves based on frequency characteristics and then sent into the convolutional neural network.Gaussian white noise is superimposed on the original signal and the output results are assessed based on score coefficients,considering the complexity of the real environment.The surfaces of Wind turbine blades are classified into four types:standard,attachments,polishing,and serrated trailing edge.The proposed method is evaluated and the detection accuracy in complicated background conditions is found to be 99.59%.In addition to support the differentiation of trained models,utilizing proper score coefficients also permit the screening of unknown types.
基金Foundation item： Supported by the National Natural Science Foundation of China （Grant No.51009038/E091002）.
文摘The development of a two dimensional numerical wave tank （NWT） with a rocker or piston type wavemaker based on the high order boundary element method （BEM） and mixed Eulerian-Lagrangian （MEL） is examined. The cauchy principle value （CPV） integral is calculated by a special Gauss type quadrature and a change of variable. In addition the explicit truncated Taylor expansion formula is employed in the time-stepping process. A modified double nodes method is assumed to tackle the comer problem, as well as the damping zone technique is used to absorb the propagation of the free surface wave at the end of the tank. A variety of waves are generated by the NWT, for example; a monochromatic wave, solitary wave and irregular wave. The results confirm the NWT model is efficient and stable.
