Growth of high-quality Nb_(3)Sn thin films for superconducting radiofrequency(SRF)applications using the vapor diffusion method requires a uniform distribution of tin nuclei on the niobium(Nb)surface.This study examin...Growth of high-quality Nb_(3)Sn thin films for superconducting radiofrequency(SRF)applications using the vapor diffusion method requires a uniform distribution of tin nuclei on the niobium(Nb)surface.This study examines the mechanism underlying the observed non-uniform distribution of tin nuclei with tin chloride SnCl_(2).Electron backscatter diffraction(EBSD)analysis was used to examine the correlation between the nucleation behavior and orientation of niobium grains in the substrate.The findings of the density functional theory(DFT)simulation are in good agreement with the experimental results,showing that the non-uniform distribution of tin nuclei is the result of the adsorption energy of SnCl_(2)molecules by varied niobium grain orientations.Further analysis indicated that the surface roughness and grain size of niobium also played significant roles in the nucleation behavior.This study provides valuable insights into enhancing the surface pretreatment of niobium substrates during the growth of Nb_(3)Sn thin films using the vapor diffusion method.展开更多
To investigate the influence of non-uniform water distribution on the mechanical properties and failure behavior of red sandstone,we designed five immersion heights and durations to achieve varying non-uniform water d...To investigate the influence of non-uniform water distribution on the mechanical properties and failure behavior of red sandstone,we designed five immersion heights and durations to achieve varying non-uniform water distribution states.Uniaxial compression tests were conducted on red sandstone under these conditions.The effects of non-uniform water distribution on deformation,failure,strength,and energy characteristics of red sandstone were analyzed.The impact of non-uniform water distribution on the intensity of rock failure was discussed,and the failure mechanism under non-uniform water distribution was revealed.The hazards of low immersion heights on underground rock structures were analyzed.The results demonstrate that peak strength and elastic modulus of red sandstone exhibit high sensitivity to immersion height,with reductions of 38%and 23%respectively even at L=1/50H.Water immersion reduces both energy storage capacity and energy dissipation capability of red sandstone.The immersion height and duration influence the failure mode of red sandstone by controlling the migration and separation of dry-wet interfaces.Low immersion height poses significant risks to underground rock structures(e.g.,a 38%strength reduction when L=1/50H),and the concentration degree of water non-uniform distribution is the key factor in assessing the weakening effect of water on rocks.展开更多
Cooling system design applicable to more than one photovoltaic(PV)unit may be challenging due to the arrangement and geometry of the modules.Different cooling techniques are provided in this study to regulate the temp...Cooling system design applicable to more than one photovoltaic(PV)unit may be challenging due to the arrangement and geometry of the modules.Different cooling techniques are provided in this study to regulate the temperature of conductive panels that are arranged perpendicular to each other.The model uses two vented cavity systems and one L-shaped channel with ternary nanofluid enhanced non-uniform magnetic field.Their cooling performances and comparative results between different systems are provided.The finite element method is used to conduct a numerical analysis for a range of values of the following:the strength of themagnetic field(Hartmann number(Ha)between 0 and 50),the inclination of the magnetic field(γbetween 0 and 90),and the loading of nanoparticles in the base fluid(ϕbetween 0 and 0.03),taking into account both uniformand non-uniformmagnetic fields.For the L-shaped channel and vented cavities,vortex size is controlled by imposing magnetic field and adjusting its strength.Whether uniform or non-uniform magnetic field is applied affects the cooling performances for different cooling configurations.Temperature drops of the horizontal panel with different magnetic field strengths by using channel cooling,vented cavity-1 and vented cavity-2 systems for uniformmagnetic are 11℃,21.5℃,and 3℃when the reference case of Ha=0 is considered for the same cooling systems.However,they become 9.5℃,13.5℃,and 12.5℃when nonuniform magnetic field is used.In the presence of uniform magnetic field effects and changing its magnitude,the use of cooling channel in vented cavity-1 and vented cavity-2 systems results in temperature drops of 4℃,10.8℃,and 3.8℃for vertical panels.On the other hand,when non-uniform magnetic field effects are present,they become 0.5℃,2.1℃,and 9℃.For L-channel cooling,the average Nu for the horizontal panel is more affected byγ,andNu rises asγrises.With increasing nanoparticle loading of ternary nanofluid,the average panel surface temperature shows a linear drop.For the horizontal panel,the temperature declines for nanofluid at the highest loading are 4℃,10℃,and 12℃as compared to using only base fluid.The values of 5℃,7℃,and 11℃are obtained for the vertical panel.Different cooling systems’performance is estimated using artificial neural networks.The method captures the combined impact of applying non-uniformmagnetic field and nanofluid together on the cooling performancewhile accounting for varied cooling strategies for both panels.展开更多
In low-light image enhancement,prevailing Retinex-based methods often struggle with precise illumina-tion estimation and brightness modulation.This can result in issues such as halo artifacts,blurred edges,and diminis...In low-light image enhancement,prevailing Retinex-based methods often struggle with precise illumina-tion estimation and brightness modulation.This can result in issues such as halo artifacts,blurred edges,and diminished details in bright regions,particularly under non-uniform illumination conditions.We propose an innovative approach that refines low-light images by leveraging an in-depth awareness of local content within the image.By introducing multi-scale effective guided filtering,our method surpasses the limitations of traditional isotropic filters,such as Gaussian filters,in handling non-uniform illumination.It dynamically adjusts regularization parameters in response to local image characteristics and significantly integrates edge perception across different scales.This balanced approach achieves a harmonious blend of smoothing and detail preservation,enabling more accurate illumination estimation.Additionally,we have designed an adaptive gamma correction function that dynamically adjusts the brightness value based on local pixel intensity,further balancing enhancement effects across different brightness levels in the image.Experimental results demonstrate the effectiveness of our proposed method for non-uniform illumination images across various scenarios.It exhibits superior quality and objective evaluation scores compared to existing methods.Our method effectively addresses potential issues that existing methods encounter when processing non-uniform illumination images,producing enhanced images with precise details and natural,vivid colors.展开更多
Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds nu...Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.展开更多
The intrusion of obstacles onto railway tracks presents a significant threat to train safety,characterized by sudden and unpredictable occurrences.With China leading the world in high-speed rail mileage,ensuring railw...The intrusion of obstacles onto railway tracks presents a significant threat to train safety,characterized by sudden and unpredictable occurrences.With China leading the world in high-speed rail mileage,ensuring railway security is paramount.The current laser monitoring technologies suffer from high false alarm rates and unreliable intrusion identification.This study addresses these issues by investigating high-resolution laser monitoring technology for railway obstacles,focusing on key parameters such as monitoring range and resolution.We propose an enhanced non-uniform laser scanning method,developing a laser monitoring system that reduces the obstacle false alarm rate to 2.00%,significantly lower than the 20%standard(TJ/GW135-2015).This rate is the best record for laser monitoring systems on China Railway.Our system operates seamlessly in all weather conditions,providing superior accuracy,resolution,and identification efficiency.It is the only 3D LiDAR system certified by the China State Railway Group Co.,Ltd.(Certificate No.[2023]008).Over three years,our system has been deployed at numerous points along various lines managed by the China State Railway Group,accumulating a dataset of 300,000 observations.This extensive deployment has significantly enhanced railway safety.The development and implementation of our railway laser monitoring system represent a substantial advancement in railway safety technology.Its low false alarm rate(2.00%),high accuracy(20 cm×20 cm×20 cm),and robust performance in diverse conditions underscore its potential for widespread adoption,promising to enhance railway safety in China and internationally.展开更多
To analyze a multibody system composed of non-uniform beam and spring-mass subsystems, the model discretization is carried on by utilizing the finite element method（FEM）, the dynamic model of non-uniform beam is dev...To analyze a multibody system composed of non-uniform beam and spring-mass subsystems, the model discretization is carried on by utilizing the finite element method（FEM）, the dynamic model of non-uniform beam is developed by using the transfer matrix method of multibody system（MS-TMM）, the transfer matrix of non-u- niform beam is derived, and the natural frequencies are computed. Compared with the numerical assembly method （NAM）, the results by MS-TMM have good agreement with the results by FEM, and are better than the results by NAM. When using the high precision method, the global dynamic equations of the complex multibody system are not needed and the orders of involved system matrices are decreased greatly. For the investigation on the re- verse problem of the physical parameter identification of multibody system, MS-TMM and the optimization tech- nology based on genetic algorithms（GAs） are combined and extended. The identification problem is exchanged for an optimization problem, and it is formulated as a global minimum solution of the objective function with respect to natural frequencies of multibody system. At last, the numerical example of non-uniform beam with attach- ments is discussed, and the identification results indicate the feasibility and the effectivity of the proposed aop- proach.展开更多
Array configuration of multiple-input multiple-output （MIMO） radar with non-uniform linear array （NLA） is proposed. Unlike a standard phased-array radar where NLA is used to generate thinner beam patterns, in MIMO...Array configuration of multiple-input multiple-output （MIMO） radar with non-uniform linear array （NLA） is proposed. Unlike a standard phased-array radar where NLA is used to generate thinner beam patterns, in MIMO radar the property of NLA is exploited to get more distinct virtual array elements so as to improve pa- rameter identifiability, which means the maximum number of targets that can be uniquely identified by the radar. A class of NLA called minimum redundancy linear array （MRLA） is employed and a new method to construct large MRLAs is descrihed. The numerical results verify that compared to uniform linear array （ULA） MIMO radars, NLA MIMO radars can retain the same parameter identifiability with fewer physical antennas and achieve larger aperture length and lower Cramer-Rao bound with the same number of the physical antennas.展开更多
To reveal the principles of human thermal responses and find out the effects of body parts on whole-body thermal sensation,through a subjective survey,experimental investigations on human responses are carried out whe...To reveal the principles of human thermal responses and find out the effects of body parts on whole-body thermal sensation,through a subjective survey,experimental investigations on human responses are carried out when a single body part is thermally stimulated.Cooling airflow is sent to seven body parts,respectively.Totally 94 samples are tested.To eliminate the obvious multicollinearity of thermal sensation among different body parts,the principal component regression approach is adopted to obtain the principal components for the body parts under different experimental conditions.Through regression and analysis of principal components,the weighting factors of the seven body parts are obtained.A predictive model on whole-body thermal sensation is obtained based on the weighting factors.The results show that the different characteristics of trunk and limbs are clearly seen.The weighting factors of local thermal sensation are integrated values,and there is little difference among values of different body parts.展开更多
A novel approximation of the two-dimensional （2D） potential function perpendicular to the channel is proposed,and then an analytical threshold voltage model for a fully depleted SOI-MOSFET with a non-uniform Gaussia...A novel approximation of the two-dimensional （2D） potential function perpendicular to the channel is proposed,and then an analytical threshold voltage model for a fully depleted SOI-MOSFET with a non-uniform Gaussian distribution doping profile is given based on this approximation. The model agrees well with numerical simulation by MEDICI. The result represents a new way and some reference points in analyzing and controlling the threshold voltage of non-uniform fully depleted （FD） SOI devices in practice.展开更多
In this study,an image binarization optimization algorithm,based on local threshold algorithms,is proposed because global and traditional local threshold segmentation algorithms cannot effectively address the problems...In this study,an image binarization optimization algorithm,based on local threshold algorithms,is proposed because global and traditional local threshold segmentation algorithms cannot effectively address the problems of nonuniform backgrounds of wood defect images.The proposed algorithm calculates the threshold by the mean,standard deviation and the extreme value of the window.The results indicate that this modified algorithm enhances the image segmentation for wood defect images on a complex background,which is much superior to the global threshold algorithm and the Bernsen algorithm,and slightly better than the Niblack algorithm and Sauvola algorithm.Compared with similar models,the algorithm proposed in this paper has higher segmentation accuracy,as high as 92.6%for wood defect images with a complex background.展开更多
The existing investigations on thermal comfort mostly focus on the thermal environment conditions, especially of the air-flow field and the temperature distributions in vehicle cabin. Less attention appears to direct ...The existing investigations on thermal comfort mostly focus on the thermal environment conditions, especially of the air-flow field and the temperature distributions in vehicle cabin. Less attention appears to direct to the thermal comfort or thermal sensation of occupants, even to the relationship between thermal conditions and thermal sensation. In this paper, a series of experiments were designed and conducted for understanding the non-uniform conditions and the occupant＇s thermal responses in vehicle cabin during the heating period. To accurately assess the transient temperature distribution in cabin in common daily condition, the air temperature at a number of positions is measured in a full size vehicle cabin under natural winter environment in South China by using a discrete thermocouples network. The occupant body is divided into nine segments, the skin temperature at each segment and the occupant＇s local thermal sensation at the head, body, upper limb and lower limb are monitored continuously. The skin temperature is observed by using a discrete thermocouples network, and the local thermal sensation is evaluated by using a seven-point thermal comfort survey questionnaire proposed by American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc（ASHRAE） Standard. The relationship between the skin temperature and the thermal sensation is discussed and regressed by statistics method. The results show that the interior air temperature is highly non-uniform over the vehicle cabin. The locations where the occupants sit have a significant effect on the occupant＇s thermal responses, including the skin temperature and the thermal sensation. The skin temperaWa-e and thermal sensation are quite different between body segments due to the effect of non-uniform conditions, clothing resistance, and the human thermal regulating system. A quantitative relationship between the thermal sensation and the skin temperature at each body segment of occupant in real life traffic is presented. The investigation result indicates that the skin temperature is a robust index to evaluate the thermal sensation. Applying the skin temperature to designing and controlling parameters of the heating, ventilation and air conditioning（HVAC） system may benefit the thermal comfort and reducing energy consumption.展开更多
The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3)aviation kerosene in a horizontal circular tube has been numerically studied,focusing mainly on the non-uniform heat transfer deteriorati...The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3)aviation kerosene in a horizontal circular tube has been numerically studied,focusing mainly on the non-uniform heat transfer deterioration along the circumferential direction.The governing equations of mass,momentum and energy have been solved using the pressure-based segregated solver based on the finite volume method.The re-normalization group(RNG)k-εturbulence model with an enhanced wall treatment was selected.Considering the heat conduction in the solid wall,the mechanism of heat transfer deterioration and the buoyancy effect on deteriorated heat transfer were discussed.The evolution of secondary flow was analyzed.Effects of the outer-wall heat flux,mass flux,pressure and tube thermal conductivity on heat transfer were investigated.Moreover,the buoyancy criterion and the heat transfer correlation were obtained.Results indicate that the poor flow performance of near-wall fluid causes the pseudo-film boiling,further leads to the heat transfer deterioration.The strong buoyancy has an effect of enhancing the heat transfer at the bottom of tube,and weakening the heat transfer at the top of tube,which results in the non-uniform inner-wall temperature and heat flux distributions.Decreasing the ratio of outer-wall heat flux and mass flux,increasing the pressure could weaken the heat transfer difference along the circumferential direction,while the effect of thermal conductivity of tube on the circumferential parameters distributions is more complicated.When the buoyancy criterion of(Grq/Grth)max≤0.8 is satisfied,the effect of buoyancy could be ignored.The new correlations work well for non-uniform heat transfer predictions.展开更多
The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. Ho...The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. However, how to establish a unified model of a non-uniform as-cast billet depicting the flow stress and microstructure evolution behaviors during hot working is the key to microstructure prediction and parameter optimization of the CPFP. In this work, hot compression tests are performed using a non-uniform as-cast 42 CrMo billet at 1123–1423 K and 0.01–1sà1. The effect laws of the non-uniform state of the as-cast billet with different initial grain sizes on the flow stress and microstructure are revealed deeply. Based on experimental results, a unified model of flow stress and grain size evolutions is developed by the internal variable modeling method. Verified results show that the model can well describe the responses of the flow stress and microstructure to deformation conditions and initial grain sizes. To further evaluate its reliability, the unified model is applied to FE simulation of the cast preformed ring rolling process.The predictions of the rolling force and grain size indicate that it could well describe the flow stress and microstructure evolutions during the process.展开更多
This paper describes the application of the variance method for flux estimation over a mixed agricultural region in China. Eddy covariance and flux variance measurements were conducted in a near-surface layer over a n...This paper describes the application of the variance method for flux estimation over a mixed agricultural region in China. Eddy covariance and flux variance measurements were conducted in a near-surface layer over a non-uniform land surface in the central plain of China from 7 June to 20 July 2002. During this period, the mean canopy height was about 0.50 m. The study site consisted of grass （10% of area）, beans （15%）, corn （15%） and rice （60%）. Under unstable conditions, the standard deviations of temperature and water vapor density （normalized by appropriate scaling parameters）, observed by a single instrument, followed the Monin-Obukhov similarity theory. The similarity constants for heat （CT） and water vapor （Cq） were 1.09 and 1.49, respectively. In comparison with direct measurements using eddy covariance techniques, the flux variance method, on average, underestimated sensible heat flux by 21% and latent heat flux by 24%, which may be attributed to the fact that the observed slight deviations （20% or 30% at most） of the similarity ＂constants＂ may be within the expected range of variation of a single instrument from the generally-valid relations.展开更多
The mass non-uniformity of hemispherical resonator is one of reasons for frequency split,and frequency split can cause gyroscope to drift.Therefore,it is of great significance to analyze the relationship between mass ...The mass non-uniformity of hemispherical resonator is one of reasons for frequency split,and frequency split can cause gyroscope to drift.Therefore,it is of great significance to analyze the relationship between mass non-uniformity and frequency split,which can provide a theoretical basis for mass balance of imperfect resonator.The starting point of error mechanism analysis for gyroscope is the motion equations of resonator.Firstly,based on the Kirchhoff-Love hypothesis in the elastic thin shell theory,the geometric deformation equations of resonator are deduced.Secondly,the deformation energy equation of resonator is derived according to the vibration mode and relationship between the stress and strain of hemispherical thin shell.Thirdly,the kinetic energy equation of resonator is deduced by the Coriolis theorem.Finally,the motion equations of resonator are established by the Lagrange mechanics principle.The theoretical values of precession factor and natural frequency are calculated by the motion equations,which are substantially consistent with the ones by the finite element method and practical measurement,the errors are within a reasonable range.Simultaneously,the varying trend of natural frequency with respect to the geometrical and physical parameters of resonator by the motion equations is consistent with that by the finite element analysis.The above conclusions prove the correctness and rationality of motion equations.Similarly,the motion equations of resonator with mass non-uniformity are established by the same modeling method in case of ignoring the input angular rate and damping,and the state equations with respect to the velocity and displacement of vibration system are derived,then twonatural frequencies are solved by the characteristic equation.It is concluded that one of reasons for frequency split is the 4 th harmonic of mass non-uniformity,and thus much attention should be paid to minimizing the 4 th harmonic of mass non-uniformity in the course of mass balancing for imperfect resonator.展开更多
An integrated coupling element considering wheel-rail interface for analyzing the dynamic responses of vehicle-rail-bridge interaction system with a non-uniform continuous bridge is presented. The governing equations ...An integrated coupling element considering wheel-rail interface for analyzing the dynamic responses of vehicle-rail-bridge interaction system with a non-uniform continuous bridge is presented. The governing equations of the interaction system are established first, and the solution procedure and assembly method of the coupling element are demonstrated. Finally, the accuracy, efficiency and function of the integrated coupling element are tested using two numerical examples. The influences of different combinations of rail and bridge element length in the coupling element on the solution are investigated, and the effects of different rail irregularities on the dynamic responses are discussed.展开更多
The asymptotic development method is applied to analyze the free vibration of non-uniform axially functionally graded(AFG) beams, of which the governing equations are differential equations with variable coefficients....The asymptotic development method is applied to analyze the free vibration of non-uniform axially functionally graded(AFG) beams, of which the governing equations are differential equations with variable coefficients. By decomposing the variable flexural stiffness and mass per unit length into reference invariant and variant parts, the perturbation theory is introduced to obtain an approximate analytical formula of the natural frequencies of the non-uniform AFG beams with different boundary conditions.Furthermore, assuming polynomial distributions of Young's modulus and the mass density, the numerical results of the AFG beams with various taper ratios are obtained and compared with the published literature results. The discussion results illustrate that the proposed method yields an effective estimate of the first three order natural frequencies for the AFG tapered beams. However, the errors increase with the increase in the mode orders especially for the cases with variable heights. In brief, the asymptotic development method is verified to be simple and efficient to analytically study the free vibration of non-uniform AFG beams, and it could be used to analyze any tapered beams with an arbitrary varying cross width.展开更多
There is a remarkable difference in stress distribution between a specimen and a plate removed from the specimen.The plate presents a uniform stress distribution whereas the specimen presents a non-uniform stress dist...There is a remarkable difference in stress distribution between a specimen and a plate removed from the specimen.The plate presents a uniform stress distribution whereas the specimen presents a non-uniform stress distribution.Firstly,the real stress distributions in plates with thickness of 30,40 and 50 mm and then in the specimens were obtained through simulation and X-ray surface stress measurement.Secondly,in order to study the impact of specimens shapes and processing ways on the results accuracy,two irregular shapes (parallelogram and trapezoid) and two processing ways (saw and electron discharge machining (EDM)) were compared and analyzed by simulation and experiment using layer removal method,then the specimen effects on measurement results were evaluated.The results show that:1) the non-uniform stress distribution characteristics of the specimen near the surface of the cut is significant,the range of non-uniform stress distribution is approximately one-thickness distance away from the cut,and it decreases gradually along the depth;2) In order to ensure the stability in the results,it is suitable to take the specimen plane size 2-3 times of its thickness;3) Conventional processing methods have little effect on experimental results and the average deviation is less than 5%.展开更多
To promote the performance of the traditional multichannel filter bank which leads to speech quality degradation,an efficient design method of the non-uniform cosine modulated filter bank（CMFB） based on the audiogra...To promote the performance of the traditional multichannel filter bank which leads to speech quality degradation,an efficient design method of the non-uniform cosine modulated filter bank（CMFB） based on the audiogram for digital hearing aids is proposed. First, a low-pass prototype filter is designed by the linear iterative algorithm. Secondly,the uniform CMFB is achieved on the basis of the principle formulas. Then, the adjacent channels of a uniform filter bank which have low or gradual slopes are merged according to the trend of audiogram of the hearing impaired person. Finally,the corresponding non-uniform CMFB is obtained. Simulation results show that the signal processed by the proposed filter bank is similar to the original signal in a time-domain waveform and spectrogram without significant distortion or difference. The speech quality results show that the personal evaluation of speech quality（PESQ） of non-uniform CMFB is 35% higher than that of the traditional design, and the hearing-aid speech quality index（HASQI） increases by about 40%.展开更多
基金supported by the National Natural Science Foundation of China(No.12175283)Youth Innovation Promotion Association of Chinese Academy of Sciences(2020410)Advanced Energy Science and Technology Guangdong Laboratory(HND20TDSPCD,HND22PTDZD).
文摘Growth of high-quality Nb_(3)Sn thin films for superconducting radiofrequency(SRF)applications using the vapor diffusion method requires a uniform distribution of tin nuclei on the niobium(Nb)surface.This study examines the mechanism underlying the observed non-uniform distribution of tin nuclei with tin chloride SnCl_(2).Electron backscatter diffraction(EBSD)analysis was used to examine the correlation between the nucleation behavior and orientation of niobium grains in the substrate.The findings of the density functional theory(DFT)simulation are in good agreement with the experimental results,showing that the non-uniform distribution of tin nuclei is the result of the adsorption energy of SnCl_(2)molecules by varied niobium grain orientations.Further analysis indicated that the surface roughness and grain size of niobium also played significant roles in the nucleation behavior.This study provides valuable insights into enhancing the surface pretreatment of niobium substrates during the growth of Nb_(3)Sn thin films using the vapor diffusion method.
基金supported by the National Natural Science Foundation of China(Nos.52474133,52304227,52304091,and 52374095)the Natural Science Foundation of Hunan Province(Nos.2025JJ50316 and 2023JJ40548).
文摘To investigate the influence of non-uniform water distribution on the mechanical properties and failure behavior of red sandstone,we designed five immersion heights and durations to achieve varying non-uniform water distribution states.Uniaxial compression tests were conducted on red sandstone under these conditions.The effects of non-uniform water distribution on deformation,failure,strength,and energy characteristics of red sandstone were analyzed.The impact of non-uniform water distribution on the intensity of rock failure was discussed,and the failure mechanism under non-uniform water distribution was revealed.The hazards of low immersion heights on underground rock structures were analyzed.The results demonstrate that peak strength and elastic modulus of red sandstone exhibit high sensitivity to immersion height,with reductions of 38%and 23%respectively even at L=1/50H.Water immersion reduces both energy storage capacity and energy dissipation capability of red sandstone.The immersion height and duration influence the failure mode of red sandstone by controlling the migration and separation of dry-wet interfaces.Low immersion height poses significant risks to underground rock structures(e.g.,a 38%strength reduction when L=1/50H),and the concentration degree of water non-uniform distribution is the key factor in assessing the weakening effect of water on rocks.
基金funded by the Deanship of Scientific Research and Libraries,Princess Nourah bint Abdulrahman University,through the Program of Research Project Funding after Publication,grant No.(RPFAP-88-1445).
文摘Cooling system design applicable to more than one photovoltaic(PV)unit may be challenging due to the arrangement and geometry of the modules.Different cooling techniques are provided in this study to regulate the temperature of conductive panels that are arranged perpendicular to each other.The model uses two vented cavity systems and one L-shaped channel with ternary nanofluid enhanced non-uniform magnetic field.Their cooling performances and comparative results between different systems are provided.The finite element method is used to conduct a numerical analysis for a range of values of the following:the strength of themagnetic field(Hartmann number(Ha)between 0 and 50),the inclination of the magnetic field(γbetween 0 and 90),and the loading of nanoparticles in the base fluid(ϕbetween 0 and 0.03),taking into account both uniformand non-uniformmagnetic fields.For the L-shaped channel and vented cavities,vortex size is controlled by imposing magnetic field and adjusting its strength.Whether uniform or non-uniform magnetic field is applied affects the cooling performances for different cooling configurations.Temperature drops of the horizontal panel with different magnetic field strengths by using channel cooling,vented cavity-1 and vented cavity-2 systems for uniformmagnetic are 11℃,21.5℃,and 3℃when the reference case of Ha=0 is considered for the same cooling systems.However,they become 9.5℃,13.5℃,and 12.5℃when nonuniform magnetic field is used.In the presence of uniform magnetic field effects and changing its magnitude,the use of cooling channel in vented cavity-1 and vented cavity-2 systems results in temperature drops of 4℃,10.8℃,and 3.8℃for vertical panels.On the other hand,when non-uniform magnetic field effects are present,they become 0.5℃,2.1℃,and 9℃.For L-channel cooling,the average Nu for the horizontal panel is more affected byγ,andNu rises asγrises.With increasing nanoparticle loading of ternary nanofluid,the average panel surface temperature shows a linear drop.For the horizontal panel,the temperature declines for nanofluid at the highest loading are 4℃,10℃,and 12℃as compared to using only base fluid.The values of 5℃,7℃,and 11℃are obtained for the vertical panel.Different cooling systems’performance is estimated using artificial neural networks.The method captures the combined impact of applying non-uniformmagnetic field and nanofluid together on the cooling performancewhile accounting for varied cooling strategies for both panels.
文摘In low-light image enhancement,prevailing Retinex-based methods often struggle with precise illumina-tion estimation and brightness modulation.This can result in issues such as halo artifacts,blurred edges,and diminished details in bright regions,particularly under non-uniform illumination conditions.We propose an innovative approach that refines low-light images by leveraging an in-depth awareness of local content within the image.By introducing multi-scale effective guided filtering,our method surpasses the limitations of traditional isotropic filters,such as Gaussian filters,in handling non-uniform illumination.It dynamically adjusts regularization parameters in response to local image characteristics and significantly integrates edge perception across different scales.This balanced approach achieves a harmonious blend of smoothing and detail preservation,enabling more accurate illumination estimation.Additionally,we have designed an adaptive gamma correction function that dynamically adjusts the brightness value based on local pixel intensity,further balancing enhancement effects across different brightness levels in the image.Experimental results demonstrate the effectiveness of our proposed method for non-uniform illumination images across various scenarios.It exhibits superior quality and objective evaluation scores compared to existing methods.Our method effectively addresses potential issues that existing methods encounter when processing non-uniform illumination images,producing enhanced images with precise details and natural,vivid colors.
基金supported by the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-087)and the National Key R&D Program of China(Grant No.2022YFA1204100)。
文摘Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.
基金financially supported by the National Natural Science Foundation of China(Nos.62275244,62375258,62225507,U2033211,62175230,and 62175232)the CAS Project for Young Scientists in Basic Research(No.YSBR-065)+2 种基金Scientific Instrument Developing Project of the Chinese Academy of Sciences(No.YJKYYQ20200001)National Key R&D Program of China(No.2022YFB3607800,No.2022YFB3605800,and No.2022YFB4601501)Key Program of the Chinese Academy of Sciences(ZDBS-ZRKJZ-TLC018)。
文摘The intrusion of obstacles onto railway tracks presents a significant threat to train safety,characterized by sudden and unpredictable occurrences.With China leading the world in high-speed rail mileage,ensuring railway security is paramount.The current laser monitoring technologies suffer from high false alarm rates and unreliable intrusion identification.This study addresses these issues by investigating high-resolution laser monitoring technology for railway obstacles,focusing on key parameters such as monitoring range and resolution.We propose an enhanced non-uniform laser scanning method,developing a laser monitoring system that reduces the obstacle false alarm rate to 2.00%,significantly lower than the 20%standard(TJ/GW135-2015).This rate is the best record for laser monitoring systems on China Railway.Our system operates seamlessly in all weather conditions,providing superior accuracy,resolution,and identification efficiency.It is the only 3D LiDAR system certified by the China State Railway Group Co.,Ltd.(Certificate No.[2023]008).Over three years,our system has been deployed at numerous points along various lines managed by the China State Railway Group,accumulating a dataset of 300,000 observations.This extensive deployment has significantly enhanced railway safety.The development and implementation of our railway laser monitoring system represent a substantial advancement in railway safety technology.Its low false alarm rate(2.00%),high accuracy(20 cm×20 cm×20 cm),and robust performance in diverse conditions underscore its potential for widespread adoption,promising to enhance railway safety in China and internationally.
基金Supported by the National Natural Science Foundation of China(10902051)the Natural Science Foundation of Jiangsu Province(BK2008046)~~
文摘To analyze a multibody system composed of non-uniform beam and spring-mass subsystems, the model discretization is carried on by utilizing the finite element method（FEM）, the dynamic model of non-uniform beam is developed by using the transfer matrix method of multibody system（MS-TMM）, the transfer matrix of non-u- niform beam is derived, and the natural frequencies are computed. Compared with the numerical assembly method （NAM）, the results by MS-TMM have good agreement with the results by FEM, and are better than the results by NAM. When using the high precision method, the global dynamic equations of the complex multibody system are not needed and the orders of involved system matrices are decreased greatly. For the investigation on the re- verse problem of the physical parameter identification of multibody system, MS-TMM and the optimization tech- nology based on genetic algorithms（GAs） are combined and extended. The identification problem is exchanged for an optimization problem, and it is formulated as a global minimum solution of the objective function with respect to natural frequencies of multibody system. At last, the numerical example of non-uniform beam with attach- ments is discussed, and the identification results indicate the feasibility and the effectivity of the proposed aop- proach.
基金Supported by the Aeronautic Science Foundation of China(2008ZC52026)the Innovation Foundation of Nanjing University of Aeronautics and Astronautics~~
文摘Array configuration of multiple-input multiple-output （MIMO） radar with non-uniform linear array （NLA） is proposed. Unlike a standard phased-array radar where NLA is used to generate thinner beam patterns, in MIMO radar the property of NLA is exploited to get more distinct virtual array elements so as to improve pa- rameter identifiability, which means the maximum number of targets that can be uniquely identified by the radar. A class of NLA called minimum redundancy linear array （MRLA） is employed and a new method to construct large MRLAs is descrihed. The numerical results verify that compared to uniform linear array （ULA） MIMO radars, NLA MIMO radars can retain the same parameter identifiability with fewer physical antennas and achieve larger aperture length and lower Cramer-Rao bound with the same number of the physical antennas.
基金The National Natural Science Foundation of China(No.50678030)
文摘To reveal the principles of human thermal responses and find out the effects of body parts on whole-body thermal sensation,through a subjective survey,experimental investigations on human responses are carried out when a single body part is thermally stimulated.Cooling airflow is sent to seven body parts,respectively.Totally 94 samples are tested.To eliminate the obvious multicollinearity of thermal sensation among different body parts,the principal component regression approach is adopted to obtain the principal components for the body parts under different experimental conditions.Through regression and analysis of principal components,the weighting factors of the seven body parts are obtained.A predictive model on whole-body thermal sensation is obtained based on the weighting factors.The results show that the different characteristics of trunk and limbs are clearly seen.The weighting factors of local thermal sensation are integrated values,and there is little difference among values of different body parts.
文摘A novel approximation of the two-dimensional （2D） potential function perpendicular to the channel is proposed,and then an analytical threshold voltage model for a fully depleted SOI-MOSFET with a non-uniform Gaussian distribution doping profile is given based on this approximation. The model agrees well with numerical simulation by MEDICI. The result represents a new way and some reference points in analyzing and controlling the threshold voltage of non-uniform fully depleted （FD） SOI devices in practice.
基金supported by National Forestry Public Welfare Industry Scientific Research Special Subsidy Project(201304502)
文摘In this study,an image binarization optimization algorithm,based on local threshold algorithms,is proposed because global and traditional local threshold segmentation algorithms cannot effectively address the problems of nonuniform backgrounds of wood defect images.The proposed algorithm calculates the threshold by the mean,standard deviation and the extreme value of the window.The results indicate that this modified algorithm enhances the image segmentation for wood defect images on a complex background,which is much superior to the global threshold algorithm and the Bernsen algorithm,and slightly better than the Niblack algorithm and Sauvola algorithm.Compared with similar models,the algorithm proposed in this paper has higher segmentation accuracy,as high as 92.6%for wood defect images with a complex background.
基金supported by National Natural Science Foundation of China(Grant No.51375170)Open Fund of State Key Lab of Environmental Adaptability for Industrial Products of China
文摘The existing investigations on thermal comfort mostly focus on the thermal environment conditions, especially of the air-flow field and the temperature distributions in vehicle cabin. Less attention appears to direct to the thermal comfort or thermal sensation of occupants, even to the relationship between thermal conditions and thermal sensation. In this paper, a series of experiments were designed and conducted for understanding the non-uniform conditions and the occupant＇s thermal responses in vehicle cabin during the heating period. To accurately assess the transient temperature distribution in cabin in common daily condition, the air temperature at a number of positions is measured in a full size vehicle cabin under natural winter environment in South China by using a discrete thermocouples network. The occupant body is divided into nine segments, the skin temperature at each segment and the occupant＇s local thermal sensation at the head, body, upper limb and lower limb are monitored continuously. The skin temperature is observed by using a discrete thermocouples network, and the local thermal sensation is evaluated by using a seven-point thermal comfort survey questionnaire proposed by American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc（ASHRAE） Standard. The relationship between the skin temperature and the thermal sensation is discussed and regressed by statistics method. The results show that the interior air temperature is highly non-uniform over the vehicle cabin. The locations where the occupants sit have a significant effect on the occupant＇s thermal responses, including the skin temperature and the thermal sensation. The skin temperaWa-e and thermal sensation are quite different between body segments due to the effect of non-uniform conditions, clothing resistance, and the human thermal regulating system. A quantitative relationship between the thermal sensation and the skin temperature at each body segment of occupant in real life traffic is presented. The investigation result indicates that the skin temperature is a robust index to evaluate the thermal sensation. Applying the skin temperature to designing and controlling parameters of the heating, ventilation and air conditioning（HVAC） system may benefit the thermal comfort and reducing energy consumption.
基金support from the National Natural Science Foundation of China(No.51576027)。
文摘The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3)aviation kerosene in a horizontal circular tube has been numerically studied,focusing mainly on the non-uniform heat transfer deterioration along the circumferential direction.The governing equations of mass,momentum and energy have been solved using the pressure-based segregated solver based on the finite volume method.The re-normalization group(RNG)k-εturbulence model with an enhanced wall treatment was selected.Considering the heat conduction in the solid wall,the mechanism of heat transfer deterioration and the buoyancy effect on deteriorated heat transfer were discussed.The evolution of secondary flow was analyzed.Effects of the outer-wall heat flux,mass flux,pressure and tube thermal conductivity on heat transfer were investigated.Moreover,the buoyancy criterion and the heat transfer correlation were obtained.Results indicate that the poor flow performance of near-wall fluid causes the pseudo-film boiling,further leads to the heat transfer deterioration.The strong buoyancy has an effect of enhancing the heat transfer at the bottom of tube,and weakening the heat transfer at the top of tube,which results in the non-uniform inner-wall temperature and heat flux distributions.Decreasing the ratio of outer-wall heat flux and mass flux,increasing the pressure could weaken the heat transfer difference along the circumferential direction,while the effect of thermal conductivity of tube on the circumferential parameters distributions is more complicated.When the buoyancy criterion of(Grq/Grth)max≤0.8 is satisfied,the effect of buoyancy could be ignored.The new correlations work well for non-uniform heat transfer predictions.
基金supported by the National Natural Science Foundation of China (No’s. 51575448 and 51135007)
文摘The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. However, how to establish a unified model of a non-uniform as-cast billet depicting the flow stress and microstructure evolution behaviors during hot working is the key to microstructure prediction and parameter optimization of the CPFP. In this work, hot compression tests are performed using a non-uniform as-cast 42 CrMo billet at 1123–1423 K and 0.01–1sà1. The effect laws of the non-uniform state of the as-cast billet with different initial grain sizes on the flow stress and microstructure are revealed deeply. Based on experimental results, a unified model of flow stress and grain size evolutions is developed by the internal variable modeling method. Verified results show that the model can well describe the responses of the flow stress and microstructure to deformation conditions and initial grain sizes. To further evaluate its reliability, the unified model is applied to FE simulation of the cast preformed ring rolling process.The predictions of the rolling force and grain size indicate that it could well describe the flow stress and microstructure evolutions during the process.
文摘This paper describes the application of the variance method for flux estimation over a mixed agricultural region in China. Eddy covariance and flux variance measurements were conducted in a near-surface layer over a non-uniform land surface in the central plain of China from 7 June to 20 July 2002. During this period, the mean canopy height was about 0.50 m. The study site consisted of grass （10% of area）, beans （15%）, corn （15%） and rice （60%）. Under unstable conditions, the standard deviations of temperature and water vapor density （normalized by appropriate scaling parameters）, observed by a single instrument, followed the Monin-Obukhov similarity theory. The similarity constants for heat （CT） and water vapor （Cq） were 1.09 and 1.49, respectively. In comparison with direct measurements using eddy covariance techniques, the flux variance method, on average, underestimated sensible heat flux by 21% and latent heat flux by 24%, which may be attributed to the fact that the observed slight deviations （20% or 30% at most） of the similarity ＂constants＂ may be within the expected range of variation of a single instrument from the generally-valid relations.
基金the Pre-Research Fund during the“13th Five-Year Plan” (No. 41417060101)。
文摘The mass non-uniformity of hemispherical resonator is one of reasons for frequency split,and frequency split can cause gyroscope to drift.Therefore,it is of great significance to analyze the relationship between mass non-uniformity and frequency split,which can provide a theoretical basis for mass balance of imperfect resonator.The starting point of error mechanism analysis for gyroscope is the motion equations of resonator.Firstly,based on the Kirchhoff-Love hypothesis in the elastic thin shell theory,the geometric deformation equations of resonator are deduced.Secondly,the deformation energy equation of resonator is derived according to the vibration mode and relationship between the stress and strain of hemispherical thin shell.Thirdly,the kinetic energy equation of resonator is deduced by the Coriolis theorem.Finally,the motion equations of resonator are established by the Lagrange mechanics principle.The theoretical values of precession factor and natural frequency are calculated by the motion equations,which are substantially consistent with the ones by the finite element method and practical measurement,the errors are within a reasonable range.Simultaneously,the varying trend of natural frequency with respect to the geometrical and physical parameters of resonator by the motion equations is consistent with that by the finite element analysis.The above conclusions prove the correctness and rationality of motion equations.Similarly,the motion equations of resonator with mass non-uniformity are established by the same modeling method in case of ignoring the input angular rate and damping,and the state equations with respect to the velocity and displacement of vibration system are derived,then twonatural frequencies are solved by the characteristic equation.It is concluded that one of reasons for frequency split is the 4 th harmonic of mass non-uniformity,and thus much attention should be paid to minimizing the 4 th harmonic of mass non-uniformity in the course of mass balancing for imperfect resonator.
基金Project supported by the National Natural Science Foundation of China(No.51078164)
文摘An integrated coupling element considering wheel-rail interface for analyzing the dynamic responses of vehicle-rail-bridge interaction system with a non-uniform continuous bridge is presented. The governing equations of the interaction system are established first, and the solution procedure and assembly method of the coupling element are demonstrated. Finally, the accuracy, efficiency and function of the integrated coupling element are tested using two numerical examples. The influences of different combinations of rail and bridge element length in the coupling element on the solution are investigated, and the effects of different rail irregularities on the dynamic responses are discussed.
基金Project supported by the National Natural Science Foundation of China(No.11672008)
文摘The asymptotic development method is applied to analyze the free vibration of non-uniform axially functionally graded(AFG) beams, of which the governing equations are differential equations with variable coefficients. By decomposing the variable flexural stiffness and mass per unit length into reference invariant and variant parts, the perturbation theory is introduced to obtain an approximate analytical formula of the natural frequencies of the non-uniform AFG beams with different boundary conditions.Furthermore, assuming polynomial distributions of Young's modulus and the mass density, the numerical results of the AFG beams with various taper ratios are obtained and compared with the published literature results. The discussion results illustrate that the proposed method yields an effective estimate of the first three order natural frequencies for the AFG tapered beams. However, the errors increase with the increase in the mode orders especially for the cases with variable heights. In brief, the asymptotic development method is verified to be simple and efficient to analytically study the free vibration of non-uniform AFG beams, and it could be used to analyze any tapered beams with an arbitrary varying cross width.
基金Project(2005CB623708) supported by the National Basic Research Program of China
文摘There is a remarkable difference in stress distribution between a specimen and a plate removed from the specimen.The plate presents a uniform stress distribution whereas the specimen presents a non-uniform stress distribution.Firstly,the real stress distributions in plates with thickness of 30,40 and 50 mm and then in the specimens were obtained through simulation and X-ray surface stress measurement.Secondly,in order to study the impact of specimens shapes and processing ways on the results accuracy,two irregular shapes (parallelogram and trapezoid) and two processing ways (saw and electron discharge machining (EDM)) were compared and analyzed by simulation and experiment using layer removal method,then the specimen effects on measurement results were evaluated.The results show that:1) the non-uniform stress distribution characteristics of the specimen near the surface of the cut is significant,the range of non-uniform stress distribution is approximately one-thickness distance away from the cut,and it decreases gradually along the depth;2) In order to ensure the stability in the results,it is suitable to take the specimen plane size 2-3 times of its thickness;3) Conventional processing methods have little effect on experimental results and the average deviation is less than 5%.
基金The National Natural Science Foundation of China(No.61375028,61673108)China Postdoctoral Science Foundation(No.2016M601696)+2 种基金Qing Lan Projectthe Program for Special Talent in Six Fields of Jiangsu Province(No.2016-DZXX-023)Jiangsu Planned Projects for Postdoctoral Research Funds(No.1601011B)
文摘To promote the performance of the traditional multichannel filter bank which leads to speech quality degradation,an efficient design method of the non-uniform cosine modulated filter bank（CMFB） based on the audiogram for digital hearing aids is proposed. First, a low-pass prototype filter is designed by the linear iterative algorithm. Secondly,the uniform CMFB is achieved on the basis of the principle formulas. Then, the adjacent channels of a uniform filter bank which have low or gradual slopes are merged according to the trend of audiogram of the hearing impaired person. Finally,the corresponding non-uniform CMFB is obtained. Simulation results show that the signal processed by the proposed filter bank is similar to the original signal in a time-domain waveform and spectrogram without significant distortion or difference. The speech quality results show that the personal evaluation of speech quality（PESQ） of non-uniform CMFB is 35% higher than that of the traditional design, and the hearing-aid speech quality index（HASQI） increases by about 40%.
