This study aims to develop a chloride diffusion simulation method that considers the hydration microstructure and pore solution properties during the hydration of tricalcium silicate(C3S).The method combines the hydra...This study aims to develop a chloride diffusion simulation method that considers the hydration microstructure and pore solution properties during the hydration of tricalcium silicate(C3S).The method combines the hydration simulation,thermodynamic calculation,and finite element analysis to examine the effects of pore solution,including effect of electrochemical potential,effect of chemical activity,and effect of mechanical interactions between ions,on the chloride effective diffusion coefficient of hydrated C3S paste.The results indicate that the effect of electrochemical potential on chloride diffusion becomes stronger with increasing hydration age due to the increase in the content of hydrated calcium silicate;as the hydration age increases,the effect of chemical activity on chloride diffusion weakens when the number of diffusible elements decreases;the effect of mechanical interactions between ions on chloride diffusion decreases with the increase of hydration age.展开更多
In this research,we focus on the free-surface deformation of a one-dimensional elastic semiconductor medium as a function of magnetic field and moisture diffusivity.The problem aims to analyze the interconnection betw...In this research,we focus on the free-surface deformation of a one-dimensional elastic semiconductor medium as a function of magnetic field and moisture diffusivity.The problem aims to analyze the interconnection between plasma and moisture diffusivity processes,as well as thermo-elastic waves.The study examines the photothermoelasticity transport process while considering the impact of moisture diffusivity.By employing Laplace’s transformation technique,we derive the governing equations of the photo-thermo-elastic medium.These equations include the equations for carrier density,elastic waves,moisture transport,heat conduction,and constitutive relationships.Mechanical stresses,thermal conditions,and plasma boundary conditions are used to calculate the fundamental physical parameters in the Laplace domain.By employing numerical techniques,the Laplace transform is inverted to get complete time-domain solutions for the primary physical domains under study.Referencemoisture,thermoelastic,and thermoelectric characteristics are employed in conjunction with a graphical analysis that takes into consideration the effects of applied forces on displacement,moisture concentration,carrier density,stress due to forces,and temperature distribution.展开更多
In this study,the fluid flow and mixing process in an impinging stream-rotating packed bed(IS-RPB)is simulated by using a new three-dimensional computational fluid dynamics model.Specifically,the gaseliquid flow is si...In this study,the fluid flow and mixing process in an impinging stream-rotating packed bed(IS-RPB)is simulated by using a new three-dimensional computational fluid dynamics model.Specifically,the gaseliquid flow is simulated by the Euler-Euler model,the hydrodynamics of the reactor is predicted by the RNG k-εmethod,and the high-gravity environment is simulated by the sliding mesh model.The turbulent mass transfer process is characterized by the concentration variance c^(2) and its dissipation rateεc formulations,and therefore the turbulent mass diffusivity can be directly obtained.The simulated segregation index Xs is in agreement with our previous experimental results.The simulated results reveal that the fringe effect of IS can be offset by the end effect at the inner radius of RPB,so the investigation of the coupling mechanism between IS and RPB is critical to intensify the mixing process in IS-RPB.展开更多
Alumina is one of the crucial and extensively utilized refractory components.As the refractory wear due to dissolution at elevated temperatures during operation is a major threat to refractory lifespan,quantifying dis...Alumina is one of the crucial and extensively utilized refractory components.As the refractory wear due to dissolution at elevated temperatures during operation is a major threat to refractory lifespan,quantifying dissolution is important for developing cost-effective and resource-efficient refractories.This study investigated the dissolution of alumina particles in two silicate and one calcium aluminate slags at 1450,1500,and 1550°C using high-temperature confocal laser scanning microscopy(HT-CLSM).Dissolution was quantified in terms of diffusivity,with all influencing factors,including Stefan flow and bath movement,incorporated into the determination process.The trends observed in total dissolution time and diffusivity in three slags at three experimental temperatures could not be explained solely on the basis of slag basicity.Two parameters,considering the influencing factors,were introduced to explain these trends.Furthermore,the linear trend observed in Arrhenius plots of diffusivities supports the diffusivity results.Additionally,good agreement between the diffusivities of alumina in one silicate slag obtained via CLSM and rotating finger test investigations verified the reliability of the results.展开更多
From viewpoint of chemical element and microstructure of wood, this paper makes a discussion on thermal diffusivity of wood and two theoretical expressions of thermal diffusivity for the choral and radial directions w...From viewpoint of chemical element and microstructure of wood, this paper makes a discussion on thermal diffusivity of wood and two theoretical expressions of thermal diffusivity for the choral and radial directions were derived. The thermal diffusivities of the choral and radial directions for about 20 species of trees were calculated with the derived theoretical expressions and compared with the experimental values. The average error of the theoretical values of thermal diffusivity was 7.5% for choral direction and 6.2% for radial direction.展开更多
A simple method was developed to relate soil sorptivity to hydraulic diffusivity and water absorption experiments were conducted utilizing one-dimensional horizontal soil columns to validate the relationship. In addit...A simple method was developed to relate soil sorptivity to hydraulic diffusivity and water absorption experiments were conducted utilizing one-dimensional horizontal soil columns to validate the relationship. In addition, an estimation method for hydraulic diffusivity with disc infiltrometer was developed. The results indicated a favorable fit of the theoretical relation to the experimental data. Also, the experiment with disc infiltrometer for estimating the diffusivity showed that the new method was feasible.展开更多
Thermal property is one of the most important properties of light-emitting diode （LED）. Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly h...Thermal property is one of the most important properties of light-emitting diode （LED）. Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly having an influence on the light-emitting efficiency and the life-span of the device. In this paper, photoacoustic piezoelectric （PAPE） technique has been employed to investigate the thermal properties of polyvinyl alcohol （]？VA） and silicon dioxide, which are the new and the traditional packaging materials in white LED, respectively. Firstly, the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials; secondly, the experimental system has been set up and adjusted by measuring the reference sample; thirdly, the thermal diffusivities of PVA and silicon dioxide are measured and analysed. The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.展开更多
Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and ad vection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial hori zo...Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and ad vection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial hori zontal diffusivity/viscosity due to the incorrect alignment of the axis. Therefore, such models can smear sharp fronts and introduce other numerical artifacts. For simulation with relatively low resolution, large lateral diffusion was explicitly used in models; therefore, such numerical diffusion may not be a problem. However, with the increase of horizontal resolution, the artificial diffusivity/viscosity associated with hori zontal advection in the commonly used Eulerian coordinates may become one of the most challenging ob stacles for modeling the ocean circulation accurately. Isopycnal eddy diffusion （mixing） has been widely used in numerical models. The common wisdom is that mixing along isopycnal is energy free. However, a careful examination reveals that this is not the case. In fact, eddy diffusion can be conceptually separated into two steps： stirring and subscale diffusion. Due to the thermobaric effect, stirring, or exchanging water masses, along isopycnal surface is associated with the change of GPE in the mean state. This is a new type of instability, called the thermobaric instability. In addition, due to cabbeling subscale diffusion of water parcels always leads to the release of GPE. The release of GPE due to isopycnal stirring and subscale diffusion may lead to the thermobaric instability.展开更多
The method proposed by Stammer (1998) is modified using eddy statistics from altimeter observation to obtain more realistic eddy diffusivity (K) for the North Pacific. Compared with original estimates, the modified K ...The method proposed by Stammer (1998) is modified using eddy statistics from altimeter observation to obtain more realistic eddy diffusivity (K) for the North Pacific. Compared with original estimates, the modified K has remarkably reduced values in the Kuroshio Extension (KE) and North Equatorial Counter Current (NECC) regions, but slightly enhanced values in the Subtropical Counter Current (STCC) region. In strong eastward flow areas like the KE and NECC, owing to a large difference between mean flow velocity and propagation velocity of mesoscale eddies, tracers inside the mesoscale eddies are transported outside rapidly by advection, and mixing length L is hence strongly suppressed. The low eddy probability (P) is also responsible for the reduced K in the NECC area. In the STCC region, however, L is mildly suppressed and P is very high, so K there is enhanced. The zonally-averaged K has two peaks with comparable magnitudes, in the latitude bands of the STCC and KE. In the core of KE, because of the reduced values of P and L, the zonally-averaged K is a minimum. Zonally-integrated eddy heat transport in the KE band, calculated based on the modified K, is much closer to the results of previous independent research, indicating the robustness of our modified K. The map of modified K provides useful information for modeling studies in the North Pacific.展开更多
The nanostructured zirconia coatings were deposited by atmospherically plasma spraying. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction were used to investigate the...The nanostructured zirconia coatings were deposited by atmospherically plasma spraying. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction were used to investigate the microstructure of the zirconia coatings. Thermal diffusivity values at normal temperatures have been evaluated by laser flash technique. Effect of annealing on the microstructure evolution of the zirconia coating has been performed. The grains and thermal diffusivity are increased with increasing annealing time and temperature. The grain growth is according to the GRIGC （the grain rotation induced grain coalescence） mechanism. The increase in thermal diffusivity is attributed to the grain growth and the decrease in porosity of nanostructured zirconia coatings.展开更多
We report field measurements of vertical profiles of the turbulent diffusivity and temperature at different stations in the South China Sea(SCS).Our study shows that the measured turbulent diffusivity follows a power-...We report field measurements of vertical profiles of the turbulent diffusivity and temperature at different stations in the South China Sea(SCS).Our study shows that the measured turbulent diffusivity follows a power-law distribution with a varying exponent in water layers.Similar multiple-layer scaling regimes were also observed from the temperature fluctuations.Combining turbulent diffusivity and temperature fluctuations,the vertical structure of temperature was revealed.Furthermore,we discussed the temperature profiles in each layer.A constant function of a dimensionless temperature profile was found in water layers that have identical turbulence conditions.Our results reveal the multiple-layer structure of temperature in the SCS.This study contributes to the understanding of the vertical structure of multiple layers in the SCS and provides clues for exploring the physical mechanism for maintaining the temperature structure.展开更多
Two parameterization schemes for vertical eddy diffusivity were utilized to investigate their impacts on both the daily and monthly mean concentrations of ozone and NOy, which are the major fractions of the sum of all...Two parameterization schemes for vertical eddy diffusivity were utilized to investigate their impacts on both the daily and monthly mean concentrations of ozone and NOy, which are the major fractions of the sum of all reactive nitrogen species, i.e., NOy=NO＋NO2＋HNO3＋PAN. Simulations indicate that great changes in the vertical diffusivity usually occur within the planetary boundary layer （PBL）. Daily and monthly mean concentrations of NOy are much more sensitive to changes in the vertical diffusivity than those of ozone and ozone and NOy levels only at or in （relatively） clean sites and areas, where long-range transport plays a crucial role, display roughly equivalent sensitivity. The results strongly suggest that a widely-accepted parameterization scheme be selected and the refinement of the model＇s vertical resolution in the PBL be required, even for regional and long-term studies, and ozone only being examined in an effort to judge the model＇s performance be unreliable, and NOy be included for model evaluations.展开更多
Dopamine content in the basal ganglia is strongly associated with the degree of dopaminergic neuron loss in the substantia nigra pars com- pacta. Symptoms of Parkinson＇s disease might not arise until more than 50% of...Dopamine content in the basal ganglia is strongly associated with the degree of dopaminergic neuron loss in the substantia nigra pars com- pacta. Symptoms of Parkinson＇s disease might not arise until more than 50% of the substantia nigra pars compacta is lost and the dopamine content in the basal ganglia is reduced by more than 80%. Greater diagnostic sensitivity and specificity would allow earlier detection of Parkinson＇s disease. Diffusion tensor imaging is a recently developed magnetic resonance imaging technique that measures mean diffusiv- ity and fractional anisotropy, and responds to changes in brain microstructure. When the microscopic barrier （including cell membranes, microtubules and other structures that interfere with the free diffusion of water） is destroyed and extracellular fluid volume accumulates, the mean diffusivity value increases; when the integrity of the microstructure （such as myelin） is destroyed, fractional anisotropy value decreases. However, there is no consensus as to whether these changes can reflect the early pathological alterations in Parkinson＇s disease. Here, we established a rat model of Parkinson＇s disease by injecting rotenone （or sunflower oil in controls） into the right suhstantia nigra. Diffusion tensor imaging results revealed that in the stages of disease, at 1, 2, 4, and 6 weeks after rotenone injection, fiactional anisotropy value decreased, but mean diffusivity values increased in the right substantia nigra in the experimental group. Fractional anisotropy values were lower at 4 weeks than at 6 weeks in the right substantia nigra of rats from the experimental group. Mean diffusivity values were mark- edly greater at 1 week than at 6 weeks in the right corpus striatum of rats from the experimental group. These findings suggest that mean diffusivity and fractional anisotropy values in the brain of rat models of Parkinson＇s disease 4 weeks after model establishment can reflect early degeneration of dopaminergic neurons. ＇The change in fractional anisotropy values after destruction of myelin integrity is likely to be of greater early diagnostic significance than the change in mean diffusivity values.展开更多
The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity using the single beam thermal lens(TL) technique. For this purpose, the decomposition of Cu(OH)_(2...The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity using the single beam thermal lens(TL) technique. For this purpose, the decomposition of Cu(OH)_(2) into CuO is studied in a time range up to 120 h, by subjecting the sample to morphological, structural, and spectroscopic characterizations. The time evolution of thermal diffusivity can be divided into three regions for demonstrating the dynamics of the reaction. When the reaction is complete, the thermal diffusivity is also found to be saturated. In addition to the morphological modifications,from rods to flakes, the variations in the amount of hydroxyl group are attributed to be responsible for the enhancement of base fluid's thermal diffusivity by 165%. Thus the study unveils the role of hydroxyl groups in the thermal behavior of CuO.展开更多
Analyses are performed to examine the physical processes involved innonlinear oscillations of Eady baroclinic waves obtained from viscous semigeostrophic models withtwo types of boundary conditions (free-slip and non-...Analyses are performed to examine the physical processes involved innonlinear oscillations of Eady baroclinic waves obtained from viscous semigeostrophic models withtwo types of boundary conditions (free-slip and non-slip). By comparing with previous studies forthe case of the free-slip boundary condition, it is shown that the nonlinear oscillations areproduced mainly by the interaction between the baroclinic wave and zonal-mean state (totalzonal-mean flow velocity and buoyancy stratification) but the timescale of the nonlinearoscillations is largely controlled by the diffusivity. When the boundary condition is non-slip, thenonlinear oscillations are further damped and slowed by the diffusive process. Since the free-slip(non-slip) boundary condition is the zero drag (infinite drag) limit of the more realistic dragboundary condition, the nonlinear oscillations obtained with the two types of boundary conditionsare two extremes for more realistic nonlinear oscillations.展开更多
The effect of boron doping on the sensitivity to environmental embrittlement of Ni3Al-based alloys was investigated in this paper. The results show that the ductilizing effect of boron in Ni3Al is partly to suppress ...The effect of boron doping on the sensitivity to environmental embrittlement of Ni3Al-based alloys was investigated in this paper. The results show that the ductilizing effect of boron in Ni3Al is partly to suppress moisture-induced hydrogen embrittlement.The mechanism of this suppressing effect of boron relates to its severely decreasing the hydrogen diffusivity by boron segregated at the grain boundaries. The surface reaction of Fe3Al with water vapor and oxygen was experimentally confirmed by AES and XPS analysis. The kinetics of these reactions can be used to explain the different ductility behavior of aluminides in various environments.展开更多
This paper presents the temperature dependence of in-plane thermal diffusivity and anisotropy distribution for pitch-based carbon-fiber-reinforced polymers (CFRPs). The measurement was performed using the laser-spot p...This paper presents the temperature dependence of in-plane thermal diffusivity and anisotropy distribution for pitch-based carbon-fiber-reinforced polymers (CFRPs). The measurement was performed using the laser-spot periodic heating method. The samples were unidirectional (UD) and crossply (CP) CFRPs. All carbon fibers of the UD samples ran in one direction, while those of the CP samples ran in two directions. In both UD and CP CFRPs, from -80°C to +80°C, temperature dependence of thermal diffusivity values increased as temperature decreased. In this temperature range, the anisotropic ratio between the fiber direction and its perpendicular direction of the UD CFRP was 106 - 124. During the anisotropy distribution measurement, it was found that thermal anisotropy can be visualized by scanning the laser in a circle on the sample. The thermal diffusivity of the UD CFRP in the fiber direction was 17 times larger than that in the 15°direction, and the thermal diffusivity in the other directions was lower than that in the 15°direction. The anisotropy distribution for the CP CFRP reflected its inhomogeneous structure.展开更多
A very simple model based on the Quadrupole method was used in thetheoretical analysis of thermal diffusivity of composite materials of Cu-PVC, PVC-Cu-PVC, andCu-PVC-Cu. The use of MATLAB software with a return to rea...A very simple model based on the Quadrupole method was used in thetheoretical analysis of thermal diffusivity of composite materials of Cu-PVC, PVC-Cu-PVC, andCu-PVC-Cu. The use of MATLAB software with a return to real space using the Stehfest algorithm makesthe time of calculation very short. The thermal responses on the rear face of each consideredsample, which determine the thermal diffusivity were represented. A mathematical demonstration whichconfirmed the results was given. Thermal diffusivity determined from the rear face thermalresponses were compared with the results of the thermal diffusivity calculated by considering thecomposite materials to be homogeneous, and a discussion on the two kinds of results was provided.展开更多
Horizontal soil column method was used to determine the horizontal diffusion rate of sandy loam, loam and clay loam under the same bulk density. The results showed that the migration rates of different lithological we...Horizontal soil column method was used to determine the horizontal diffusion rate of sandy loam, loam and clay loam under the same bulk density. The results showed that the migration rates of different lithological wet fronts were different. The sandy loam had the fastest migration rate, the loam followed, and the clay loam was the slowest, but the law of change is the same among the three lithologies. The volumetric water content affects the change of Boltzmann parameter λ. When the volumetric water content is between 0.35-0.45 cm^3/cm^3,λ approaches stability. When the volumetric water content is less than 0.35 cm^3/cm^3, the λ value decreases rapidly with the decrease of water content. The water diffusion rate is related to the volumetric water content and particle size. The greater the moisture content is, the greater the diffusion rate will be. The larger the particle size, the larger the diffusion rate. The diffusivity of sandy loam is 10-30 times larger than that of loam and clay loam. The relationship between water content and diffusion rate is in accordance with the exponential function .展开更多
This paper presents a system approach of mass balance of ozone and other species under diffusion-convection-reaction processes to study the ozone layer along the altitude in the stratosphere. The ozone abundance and g...This paper presents a system approach of mass balance of ozone and other species under diffusion-convection-reaction processes to study the ozone layer along the altitude in the stratosphere. The ozone abundance and general distribution above the tropical area were calculated and compared to the published measured data. The peak ozone layer was found to be 21 mPa at 22 km or 9.7 ppm at 30 km, and the involved competing processes depicting the ozone layer were explained in details. In the entire stratosphere from 10 km to 50 km, the calculated ozone distribution displayed a similar profile and trend to the observational data, with the calculation in ppm slightly above the measurement by 12%. The standard deviation of the differences between calculated and measured data was close to 0.25. A sensitivity study of gas diffusivities of molecular ozone D<sub>3</sub> and atomic oxygen D<sub>1</sub> on changing the ozone abundance and profile in the stratosphere showed that in the upper two-third of the stratosphere, D<sub>1</sub> evidently exhibited a pronounced impact on ozone, as much as 24-fold larger than D<sub>3</sub>. The mechanism leading to this finding was also elaborated. The approach and calculations in this paper are shown to be useful for providing an initial insight into the structure and behavior of the complex ozone layer.展开更多
基金Funded by the Natural Science Foundation of Jiangsu Province(No.BK20241529)China Postdoctoral Science Foundation(No.2024M750736)。
文摘This study aims to develop a chloride diffusion simulation method that considers the hydration microstructure and pore solution properties during the hydration of tricalcium silicate(C3S).The method combines the hydration simulation,thermodynamic calculation,and finite element analysis to examine the effects of pore solution,including effect of electrochemical potential,effect of chemical activity,and effect of mechanical interactions between ions,on the chloride effective diffusion coefficient of hydrated C3S paste.The results indicate that the effect of electrochemical potential on chloride diffusion becomes stronger with increasing hydration age due to the increase in the content of hydrated calcium silicate;as the hydration age increases,the effect of chemical activity on chloride diffusion weakens when the number of diffusible elements decreases;the effect of mechanical interactions between ions on chloride diffusion decreases with the increase of hydration age.
基金funded by Taif University,Taif,Saudi Arabia(TU-DSPP-2024-172).
文摘In this research,we focus on the free-surface deformation of a one-dimensional elastic semiconductor medium as a function of magnetic field and moisture diffusivity.The problem aims to analyze the interconnection between plasma and moisture diffusivity processes,as well as thermo-elastic waves.The study examines the photothermoelasticity transport process while considering the impact of moisture diffusivity.By employing Laplace’s transformation technique,we derive the governing equations of the photo-thermo-elastic medium.These equations include the equations for carrier density,elastic waves,moisture transport,heat conduction,and constitutive relationships.Mechanical stresses,thermal conditions,and plasma boundary conditions are used to calculate the fundamental physical parameters in the Laplace domain.By employing numerical techniques,the Laplace transform is inverted to get complete time-domain solutions for the primary physical domains under study.Referencemoisture,thermoelastic,and thermoelectric characteristics are employed in conjunction with a graphical analysis that takes into consideration the effects of applied forces on displacement,moisture concentration,carrier density,stress due to forces,and temperature distribution.
基金supported by the National Natural Science Foundation of China (22208328, 22378370 and 22108261)Fundamental Research Program of Shanxi Province(20210302124618)
文摘In this study,the fluid flow and mixing process in an impinging stream-rotating packed bed(IS-RPB)is simulated by using a new three-dimensional computational fluid dynamics model.Specifically,the gaseliquid flow is simulated by the Euler-Euler model,the hydrodynamics of the reactor is predicted by the RNG k-εmethod,and the high-gravity environment is simulated by the sliding mesh model.The turbulent mass transfer process is characterized by the concentration variance c^(2) and its dissipation rateεc formulations,and therefore the turbulent mass diffusivity can be directly obtained.The simulated segregation index Xs is in agreement with our previous experimental results.The simulated results reveal that the fringe effect of IS can be offset by the end effect at the inner radius of RPB,so the investigation of the coupling mechanism between IS and RPB is critical to intensify the mixing process in IS-RPB.
基金funded by the COMET program within the K2 Center “Integrated Computational MaterialProcess and Product Engineering (IC-MPPE)”, Project No. 859480+7 种基金supported by the Austrian Federal Ministries for TransportInnovationand Technology (BMVIT)Digital and Economic Affairs (BMDW)represented by the Austrian Research Funding Association (FFG)the federal states of StyriaUpper Austriaand Tyrol
文摘Alumina is one of the crucial and extensively utilized refractory components.As the refractory wear due to dissolution at elevated temperatures during operation is a major threat to refractory lifespan,quantifying dissolution is important for developing cost-effective and resource-efficient refractories.This study investigated the dissolution of alumina particles in two silicate and one calcium aluminate slags at 1450,1500,and 1550°C using high-temperature confocal laser scanning microscopy(HT-CLSM).Dissolution was quantified in terms of diffusivity,with all influencing factors,including Stefan flow and bath movement,incorporated into the determination process.The trends observed in total dissolution time and diffusivity in three slags at three experimental temperatures could not be explained solely on the basis of slag basicity.Two parameters,considering the influencing factors,were introduced to explain these trends.Furthermore,the linear trend observed in Arrhenius plots of diffusivities supports the diffusivity results.Additionally,good agreement between the diffusivities of alumina in one silicate slag obtained via CLSM and rotating finger test investigations verified the reliability of the results.
基金Natural Science Foundation of Fujian Province. "Theoretical Research on Wood Thermal Property".
文摘From viewpoint of chemical element and microstructure of wood, this paper makes a discussion on thermal diffusivity of wood and two theoretical expressions of thermal diffusivity for the choral and radial directions were derived. The thermal diffusivities of the choral and radial directions for about 20 species of trees were calculated with the derived theoretical expressions and compared with the experimental values. The average error of the theoretical values of thermal diffusivity was 7.5% for choral direction and 6.2% for radial direction.
基金Project supported by the Hundred Talents Program of the Chinese Academy of Sciences, the National Basic Research Program of China (No. 2005CB121103) and the National Natural Science Foundation of China (Nos. 40371057 and 50479065).
文摘A simple method was developed to relate soil sorptivity to hydraulic diffusivity and water absorption experiments were conducted utilizing one-dimensional horizontal soil columns to validate the relationship. In addition, an estimation method for hydraulic diffusivity with disc infiltrometer was developed. The results indicated a favorable fit of the theoretical relation to the experimental data. Also, the experiment with disc infiltrometer for estimating the diffusivity showed that the new method was feasible.
基金Project supported by the National Nature Science Foundation of China (Grant No. 50506006)the National High Technology Research and Development Program of China (Grant No. 2006AA03A116)the Youth Foundation of University of Electronic Science and Technology of China (Grant No. JX05024)
文摘Thermal property is one of the most important properties of light-emitting diode （LED）. Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly having an influence on the light-emitting efficiency and the life-span of the device. In this paper, photoacoustic piezoelectric （PAPE） technique has been employed to investigate the thermal properties of polyvinyl alcohol （]？VA） and silicon dioxide, which are the new and the traditional packaging materials in white LED, respectively. Firstly, the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials; secondly, the experimental system has been set up and adjusted by measuring the reference sample; thirdly, the thermal diffusivities of PVA and silicon dioxide are measured and analysed. The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.
文摘Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and ad vection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial hori zontal diffusivity/viscosity due to the incorrect alignment of the axis. Therefore, such models can smear sharp fronts and introduce other numerical artifacts. For simulation with relatively low resolution, large lateral diffusion was explicitly used in models; therefore, such numerical diffusion may not be a problem. However, with the increase of horizontal resolution, the artificial diffusivity/viscosity associated with hori zontal advection in the commonly used Eulerian coordinates may become one of the most challenging ob stacles for modeling the ocean circulation accurately. Isopycnal eddy diffusion （mixing） has been widely used in numerical models. The common wisdom is that mixing along isopycnal is energy free. However, a careful examination reveals that this is not the case. In fact, eddy diffusion can be conceptually separated into two steps： stirring and subscale diffusion. Due to the thermobaric effect, stirring, or exchanging water masses, along isopycnal surface is associated with the change of GPE in the mean state. This is a new type of instability, called the thermobaric instability. In addition, due to cabbeling subscale diffusion of water parcels always leads to the release of GPE. The release of GPE due to isopycnal stirring and subscale diffusion may lead to the thermobaric instability.
基金Supported by the Major Program of the National Natural Science Foundation of China (No.40890153)the National High Technology Research and Development Program of China (863 Program) (No.2008AA09A402)
文摘The method proposed by Stammer (1998) is modified using eddy statistics from altimeter observation to obtain more realistic eddy diffusivity (K) for the North Pacific. Compared with original estimates, the modified K has remarkably reduced values in the Kuroshio Extension (KE) and North Equatorial Counter Current (NECC) regions, but slightly enhanced values in the Subtropical Counter Current (STCC) region. In strong eastward flow areas like the KE and NECC, owing to a large difference between mean flow velocity and propagation velocity of mesoscale eddies, tracers inside the mesoscale eddies are transported outside rapidly by advection, and mixing length L is hence strongly suppressed. The low eddy probability (P) is also responsible for the reduced K in the NECC area. In the STCC region, however, L is mildly suppressed and P is very high, so K there is enhanced. The zonally-averaged K has two peaks with comparable magnitudes, in the latitude bands of the STCC and KE. In the core of KE, because of the reduced values of P and L, the zonally-averaged K is a minimum. Zonally-integrated eddy heat transport in the KE band, calculated based on the modified K, is much closer to the results of previous independent research, indicating the robustness of our modified K. The map of modified K provides useful information for modeling studies in the North Pacific.
基金This work was supported by the program for New Century Excellent Talents in University(NCET)the National Natural Science Foundation of China under the contact 50176005.
文摘The nanostructured zirconia coatings were deposited by atmospherically plasma spraying. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction were used to investigate the microstructure of the zirconia coatings. Thermal diffusivity values at normal temperatures have been evaluated by laser flash technique. Effect of annealing on the microstructure evolution of the zirconia coating has been performed. The grains and thermal diffusivity are increased with increasing annealing time and temperature. The grain growth is according to the GRIGC （the grain rotation induced grain coalescence） mechanism. The increase in thermal diffusivity is attributed to the grain growth and the decrease in porosity of nanostructured zirconia coatings.
基金The National Key R&D Program of China under contract No.2021YFC3101301the Innovative Academy of Marine Information Technology+6 种基金Chinese Academy of Sciences under contract No.CXBS202101the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract No.GML2019ZD0304the National Natural Science Foundation of China under contract Nos 41876022,41876023,11772111 and91952101the Guangdong Natural Science Foundation of China under contract Nos 1914050004866 and 2020A1515011094the Hong Kong Research Grants Council under contract Nos 16301719 and N-HKUST604/19the Science,Technology and Innovation Commission of Shenzhen Municipality under contract No.KQJSCX20180328165817522the Science and Technology Program of Guangzhou under contract No.202102020707。
文摘We report field measurements of vertical profiles of the turbulent diffusivity and temperature at different stations in the South China Sea(SCS).Our study shows that the measured turbulent diffusivity follows a power-law distribution with a varying exponent in water layers.Similar multiple-layer scaling regimes were also observed from the temperature fluctuations.Combining turbulent diffusivity and temperature fluctuations,the vertical structure of temperature was revealed.Furthermore,we discussed the temperature profiles in each layer.A constant function of a dimensionless temperature profile was found in water layers that have identical turbulence conditions.Our results reveal the multiple-layer structure of temperature in the SCS.This study contributes to the understanding of the vertical structure of multiple layers in the SCS and provides clues for exploring the physical mechanism for maintaining the temperature structure.
基金the National Natural Science Foundation of China （Grant No. 40575068） the National Key Project of Basic Research of China （Grant No. 2005CB422205） the Knowledge Innovation Project of Chinese Academy of Sciences （Grant No. KZCX2-YW-205）.
文摘Two parameterization schemes for vertical eddy diffusivity were utilized to investigate their impacts on both the daily and monthly mean concentrations of ozone and NOy, which are the major fractions of the sum of all reactive nitrogen species, i.e., NOy=NO＋NO2＋HNO3＋PAN. Simulations indicate that great changes in the vertical diffusivity usually occur within the planetary boundary layer （PBL）. Daily and monthly mean concentrations of NOy are much more sensitive to changes in the vertical diffusivity than those of ozone and ozone and NOy levels only at or in （relatively） clean sites and areas, where long-range transport plays a crucial role, display roughly equivalent sensitivity. The results strongly suggest that a widely-accepted parameterization scheme be selected and the refinement of the model＇s vertical resolution in the PBL be required, even for regional and long-term studies, and ozone only being examined in an effort to judge the model＇s performance be unreliable, and NOy be included for model evaluations.
基金supported by the Research Grant of Hebei Province Science and Technology Project of China,No.1427777118D
文摘Dopamine content in the basal ganglia is strongly associated with the degree of dopaminergic neuron loss in the substantia nigra pars com- pacta. Symptoms of Parkinson＇s disease might not arise until more than 50% of the substantia nigra pars compacta is lost and the dopamine content in the basal ganglia is reduced by more than 80%. Greater diagnostic sensitivity and specificity would allow earlier detection of Parkinson＇s disease. Diffusion tensor imaging is a recently developed magnetic resonance imaging technique that measures mean diffusiv- ity and fractional anisotropy, and responds to changes in brain microstructure. When the microscopic barrier （including cell membranes, microtubules and other structures that interfere with the free diffusion of water） is destroyed and extracellular fluid volume accumulates, the mean diffusivity value increases; when the integrity of the microstructure （such as myelin） is destroyed, fractional anisotropy value decreases. However, there is no consensus as to whether these changes can reflect the early pathological alterations in Parkinson＇s disease. Here, we established a rat model of Parkinson＇s disease by injecting rotenone （or sunflower oil in controls） into the right suhstantia nigra. Diffusion tensor imaging results revealed that in the stages of disease, at 1, 2, 4, and 6 weeks after rotenone injection, fiactional anisotropy value decreased, but mean diffusivity values increased in the right substantia nigra in the experimental group. Fractional anisotropy values were lower at 4 weeks than at 6 weeks in the right substantia nigra of rats from the experimental group. Mean diffusivity values were mark- edly greater at 1 week than at 6 weeks in the right corpus striatum of rats from the experimental group. These findings suggest that mean diffusivity and fractional anisotropy values in the brain of rat models of Parkinson＇s disease 4 weeks after model establishment can reflect early degeneration of dopaminergic neurons. ＇The change in fractional anisotropy values after destruction of myelin integrity is likely to be of greater early diagnostic significance than the change in mean diffusivity values.
文摘The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity using the single beam thermal lens(TL) technique. For this purpose, the decomposition of Cu(OH)_(2) into CuO is studied in a time range up to 120 h, by subjecting the sample to morphological, structural, and spectroscopic characterizations. The time evolution of thermal diffusivity can be divided into three regions for demonstrating the dynamics of the reaction. When the reaction is complete, the thermal diffusivity is also found to be saturated. In addition to the morphological modifications,from rods to flakes, the variations in the amount of hydroxyl group are attributed to be responsible for the enhancement of base fluid's thermal diffusivity by 165%. Thus the study unveils the role of hydroxyl groups in the thermal behavior of CuO.
文摘Analyses are performed to examine the physical processes involved innonlinear oscillations of Eady baroclinic waves obtained from viscous semigeostrophic models withtwo types of boundary conditions (free-slip and non-slip). By comparing with previous studies forthe case of the free-slip boundary condition, it is shown that the nonlinear oscillations areproduced mainly by the interaction between the baroclinic wave and zonal-mean state (totalzonal-mean flow velocity and buoyancy stratification) but the timescale of the nonlinearoscillations is largely controlled by the diffusivity. When the boundary condition is non-slip, thenonlinear oscillations are further damped and slowed by the diffusive process. Since the free-slip(non-slip) boundary condition is the zero drag (infinite drag) limit of the more realistic dragboundary condition, the nonlinear oscillations obtained with the two types of boundary conditionsare two extremes for more realistic nonlinear oscillations.
文摘The effect of boron doping on the sensitivity to environmental embrittlement of Ni3Al-based alloys was investigated in this paper. The results show that the ductilizing effect of boron in Ni3Al is partly to suppress moisture-induced hydrogen embrittlement.The mechanism of this suppressing effect of boron relates to its severely decreasing the hydrogen diffusivity by boron segregated at the grain boundaries. The surface reaction of Fe3Al with water vapor and oxygen was experimentally confirmed by AES and XPS analysis. The kinetics of these reactions can be used to explain the different ductility behavior of aluminides in various environments.
文摘This paper presents the temperature dependence of in-plane thermal diffusivity and anisotropy distribution for pitch-based carbon-fiber-reinforced polymers (CFRPs). The measurement was performed using the laser-spot periodic heating method. The samples were unidirectional (UD) and crossply (CP) CFRPs. All carbon fibers of the UD samples ran in one direction, while those of the CP samples ran in two directions. In both UD and CP CFRPs, from -80°C to +80°C, temperature dependence of thermal diffusivity values increased as temperature decreased. In this temperature range, the anisotropic ratio between the fiber direction and its perpendicular direction of the UD CFRP was 106 - 124. During the anisotropy distribution measurement, it was found that thermal anisotropy can be visualized by scanning the laser in a circle on the sample. The thermal diffusivity of the UD CFRP in the fiber direction was 17 times larger than that in the 15°direction, and the thermal diffusivity in the other directions was lower than that in the 15°direction. The anisotropy distribution for the CP CFRP reflected its inhomogeneous structure.
基金The research work is financially supported by National Natural Science Foundation of China (No.50276003).
文摘A very simple model based on the Quadrupole method was used in thetheoretical analysis of thermal diffusivity of composite materials of Cu-PVC, PVC-Cu-PVC, andCu-PVC-Cu. The use of MATLAB software with a return to real space using the Stehfest algorithm makesthe time of calculation very short. The thermal responses on the rear face of each consideredsample, which determine the thermal diffusivity were represented. A mathematical demonstration whichconfirmed the results was given. Thermal diffusivity determined from the rear face thermalresponses were compared with the results of the thermal diffusivity calculated by considering thecomposite materials to be homogeneous, and a discussion on the two kinds of results was provided.
基金financially supported by the Fundamental Research Fund of the Chinese Academy of Geological Sciences (YYFM201624)
文摘Horizontal soil column method was used to determine the horizontal diffusion rate of sandy loam, loam and clay loam under the same bulk density. The results showed that the migration rates of different lithological wet fronts were different. The sandy loam had the fastest migration rate, the loam followed, and the clay loam was the slowest, but the law of change is the same among the three lithologies. The volumetric water content affects the change of Boltzmann parameter λ. When the volumetric water content is between 0.35-0.45 cm^3/cm^3,λ approaches stability. When the volumetric water content is less than 0.35 cm^3/cm^3, the λ value decreases rapidly with the decrease of water content. The water diffusion rate is related to the volumetric water content and particle size. The greater the moisture content is, the greater the diffusion rate will be. The larger the particle size, the larger the diffusion rate. The diffusivity of sandy loam is 10-30 times larger than that of loam and clay loam. The relationship between water content and diffusion rate is in accordance with the exponential function .
文摘This paper presents a system approach of mass balance of ozone and other species under diffusion-convection-reaction processes to study the ozone layer along the altitude in the stratosphere. The ozone abundance and general distribution above the tropical area were calculated and compared to the published measured data. The peak ozone layer was found to be 21 mPa at 22 km or 9.7 ppm at 30 km, and the involved competing processes depicting the ozone layer were explained in details. In the entire stratosphere from 10 km to 50 km, the calculated ozone distribution displayed a similar profile and trend to the observational data, with the calculation in ppm slightly above the measurement by 12%. The standard deviation of the differences between calculated and measured data was close to 0.25. A sensitivity study of gas diffusivities of molecular ozone D<sub>3</sub> and atomic oxygen D<sub>1</sub> on changing the ozone abundance and profile in the stratosphere showed that in the upper two-third of the stratosphere, D<sub>1</sub> evidently exhibited a pronounced impact on ozone, as much as 24-fold larger than D<sub>3</sub>. The mechanism leading to this finding was also elaborated. The approach and calculations in this paper are shown to be useful for providing an initial insight into the structure and behavior of the complex ozone layer.
