For the first time a mathematical modelling of porous catalyst particles subject to both internal mass concentration gradients as well as temperature gradients, in endothermic or exothermic reactions has been reported...For the first time a mathematical modelling of porous catalyst particles subject to both internal mass concentration gradients as well as temperature gradients, in endothermic or exothermic reactions has been reported. This model contains a non-linear mass balance equation which is related to rate expression. This paper presents an approximate analytical method (Modified Adomian decomposition method) to solve the non-linear differential equations for chemical kinetics with diffusion effects. A simple and closed form of expressions pertaining to substrate concentration and utilization factor is presented for all value of diffusion parameters. These analytical results are compared with numerical results and found to be in good agreement.展开更多
Theoretical studies of the diffusionalisotope effect in solids are still stuck in the 1960s and 1970s.With the development of high spatial resolution mass spectrometers,isotopic data of mineral grains are rapidly accu...Theoretical studies of the diffusionalisotope effect in solids are still stuck in the 1960s and 1970s.With the development of high spatial resolution mass spectrometers,isotopic data of mineral grains are rapidly accumulated.To dig up information from these data,molecularlevel theoretical models are urgently needed.Based on the microscopic definition of the diffusion coe fficient(D),a new theoretical framework for calculating the diffusional isotope effect(DIE(v))(intermsofD*/D)forvacancy-mediated impurity diffusion in solids is provided based on statistical mechanics formalism.The newly derived equation shows that theDIE(v)can be easily calculated as long as the vibration frequencies of isotope-substituted solids are obtained.The calculatedDIE(v)values of^(199)Au/^(195)Au and^(60)Co/^(57)Co during diffusion in Cu and Au metals are all within 1%of errors compared to the experimental data,which shows that this theoretical model is reasonable and precise.展开更多
This paper presents a theoretical method for predicting the effective diffusion coefficient of macromolecules in the microporous membrfines in view of the effects of molecular dimension and configuration. On the basi...This paper presents a theoretical method for predicting the effective diffusion coefficient of macromolecules in the microporous membrfines in view of the effects of molecular dimension and configuration. On the basis of the hindered diffusion theory of spherical neutral macromolecules in a micropore of a long cylinder, the effects of molecular dimension and configuration are studied by defining two molecular dimensions:the mean projected radius to predict the concentration partition and the ' hydrodynamically equivalent sphere' radius to evaluate the hydrodynamic reverse drag force. The quantitative comparison shows that the effective diffusion coefficients for different macromolecules predicted by the present method are more consistent with the available published experimental data.展开更多
The safety assessment of high-level radioactive waste repositories requires a high predictive accuracy for radionuclide diffusion and a comprehensive understanding of the diffusion mechanism.In this study,a through-di...The safety assessment of high-level radioactive waste repositories requires a high predictive accuracy for radionuclide diffusion and a comprehensive understanding of the diffusion mechanism.In this study,a through-diffusion method and six machine-learning methods were employed to investigate the diffusion of ReO_(4)^(−),HCrO_(4)^(−),and I−in saturated compacted bentonite under different salinities and compacted dry densities.The machine-learning models were trained using two datasets.One dataset contained six input features and 293 instances obtained from the diffusion database system of the Japan Atomic Energy Agency(JAEA-DDB)and 15 publications.The other dataset,comprising 15,000 pseudo-instances,was produced using a multi-porosity model and contained eight input features.The results indicate that the former dataset yielded a higher predictive accuracy than the latter.Light gradient-boosting exhibited a higher prediction accuracy(R2=0.92)and lower error(MSE=0.01)than the other machine-learning algorithms.In addition,Shapley Additive Explanations,Feature Importance,and Partial Dependence Plot analysis results indicate that the rock capacity factor and compacted dry density had the two most significant effects on predicting the effective diffusion coefficient,thereby offering valuable insights.展开更多
The pan-Arctic is confronted with air pollution transported from lower latitudes.Observations have shown that aerosols help increase plant photosynthesis through the diffuse radiation fertilization effects(DRFEs).Whil...The pan-Arctic is confronted with air pollution transported from lower latitudes.Observations have shown that aerosols help increase plant photosynthesis through the diffuse radiation fertilization effects(DRFEs).While such DRFEs have been explored at low to middle latitudes,the aerosol impacts on pan-Arctic ecosystems and the contributions by anthropogenic and natural emission sources remain less quantified.Here,we perform regional simulations at 0.2o×0.2ousing a well-validated vegetation model(Yale Interactive terrestrial Biosphere,YIBs)in combination with multi-source of observations to quantify the impacts of aerosol DRFEs on the net primary productivity(NPP)in the pan-Arctic during 2001-19.Results show that aerosol DRFEs increase pan-Arctic NPP by 2.19 Pg C(12.8%)yr^(-1)under clear-sky conditions,in which natural and anthropogenic sources contribute to 8.9% and 3.9%,respectively.Under all-sky conditions,such DRFEs are largely dampened by cloud to only 0.26 Pg C(1.24%)yr^(-1),with contributions of 0.65% by natural and 0.59% by anthropogenic species.Natural aerosols cause a positive NPP trend of 0.022% yr^(-1)following the increased fire activities in the pan-Arctic.In contrast,anthropogenic aerosols induce a negative trend of-0.01% yr^(-1)due to reduced emissions from the middle latitudes.Such trends in aerosol DRFEs show a turning point in the year of 2007 with more positive NPP trends by natural aerosols but negative NPP trends by anthropogenic aerosols thereafter.Though affected by modeling uncertainties,this study suggests a likely increasing impact of aerosols on terrestrial ecosystems in the pan-Arctic under global warming.展开更多
The effects of positron diffusion on the measured S parameter have been investigated by a point-source diffusion model and a δ function method. Firstly, the theoretical analyses of the effects are presented for the s...The effects of positron diffusion on the measured S parameter have been investigated by a point-source diffusion model and a δ function method. Firstly, the theoretical analyses of the effects are presented for the samples of a homogeneous semi-infinite medium and a film of definite thickness. Then the results are used to analyze the S parameters in several composite systems and interface models.展开更多
In this article, we investigated the influence of size and initial water content on the effective diffusion coefficient of sweet potatoes samples cut into cubic and cylindrical shapes. The sizes of the cubic samples a...In this article, we investigated the influence of size and initial water content on the effective diffusion coefficient of sweet potatoes samples cut into cubic and cylindrical shapes. The sizes of the cubic samples are 0.5, 1, 1.5, 1.75, 2, 2.5 and 3 cm edge with a respective initial water content of 2.7, 3.76, 3.48, 2.68, 3.28, 2.17 and 2.29 kg/kgms. For cylindrical samples, the radius is set at 0.5 cm and sample heights are 1, 1.5, 2, 2.5, 3, 3.5 and 4 cm with respective water contents of 2.2, 3.19, 2.85, 2.1, 2.17, 2.39 and 2.03 kg/kgms. The effective diffusion coefficients of cubic samples are of the order of 10−10 and 10−9 m2∙s−1 grew with sample edge. As for the cylindrical samples, the effective diffusion coefficients were of the order of 10−9 m2∙s−1 and there was no linear correlation between cylinder height and their effective diffusion coefficient. As for the examination of the initial water content on the effective diffusion coefficient, it turned out that the initial water content had no influence on the effective diffusion coefficient of the sweet potato samples.展开更多
During nearly 200 years of development in the knowledge of Brownian motion,the Janus sphere,as a typical Brownian particle with special surface properties,has been widely studied in the past few decades.A standard Jan...During nearly 200 years of development in the knowledge of Brownian motion,the Janus sphere,as a typical Brownian particle with special surface properties,has been widely studied in the past few decades.A standard Janus sphere possesses two distinct surfaces.These two surfaces elicit different hydrodynamic interactions with ambient fluids or other interactions in response to environmental stimuli,such as chemical gradients,magnetic fields,and even light.The diffusion of Janus spheres,particularly when controlled by a remotely applied field,has inspired various applications,ranging from the design of micro-swimmers and novel procedures for probing the mechanical properties of suspensions to the fabrication of composites with enhanced performance.In this work,we report a systematic analysis of field-controlled diffusion of Janus spheres.Commencing with stochastic differential equations of motion at the microscale,we derive a coarse-grained Fokker-Planck equation at the macroscale,describing the evolution of the probability distribution function of the Janus sphere in terms of its position and orientation.Leveraging the concept of the hydrodynamic center,we derive,for the first time,explicit generalized Stokes-Einstein relations for long-time effective diffusivity,incorporating the effects of both the surface discontinuity of the Janus sphere and the external fields.The formulae enable predictions of the effective diffusivity as it varies with the slip length and characteristic angle of Janus spheres,and reveal the impact of an aligning potential field on the diffusion coefficients both parallel and perpendicular to the direction of the field.This work not only deepens the understanding of field-controlled diffusion of Janus particles,but also holds a meaningful impact on the future applications in microfluidics and related fields.展开更多
Considering both the compaction effect of pile surrounding soil and the stress diffusion effect of pile end soil,this paper theoretically investigates the torsional vibration characteristics of tapered pile.Utilizing ...Considering both the compaction effect of pile surrounding soil and the stress diffusion effect of pile end soil,this paper theoretically investigates the torsional vibration characteristics of tapered pile.Utilizing the complex stiffness transfer model to simulate compaction effect and tapered fictitious soil pile model to simulate stress diffusion,the analytical solution for the torsional impedance at tapered pile top is obtained by virtue of Laplace transform technique and impedance transfer method.Based on the present solution,a parametric study is conducted to investigate the rationality of the present solution and the influence of soil and pile properties on the torsional vibration characteristics of tapered pile embedded in layered soil.The results show that,both the compaction effect and stress diffusion effect have significant influence on the torsional vibration characteristics of tapered pile,and these two factors should be considered during the dynamic design of pile foundation.展开更多
A rotating disc column (RDC) with inner diameter 68 mm and 28 compartments is used in this study. Parameters including Sauter mean diameter, hold-up and mass transfer coefficient are measured experimentally un-der dif...A rotating disc column (RDC) with inner diameter 68 mm and 28 compartments is used in this study. Parameters including Sauter mean diameter, hold-up and mass transfer coefficient are measured experimentally un-der different operating conditions. The correlations in literature for molecular diffusion and enhancement factor equation including eddy diffusion, circulation and oscillation of drops are evaluated. A new equation for the effec-tive diffusion coefficient as a function of Reynolds number is proposed. The calculated values of mass transfer co-efficient and column height from the previous equations and present equation are compared with the experimental data. The results from the present equation are in very good agreement with the experimental results, which may be used in designing RDC columns.展开更多
Research on the diffusion characteristics of swells contributes positively to wave energy forecasting, swell monitoring, and early warning. In this work, the South Indian Ocean westerly index(SIWI) and Indian Ocean sw...Research on the diffusion characteristics of swells contributes positively to wave energy forecasting, swell monitoring, and early warning. In this work, the South Indian Ocean westerly index(SIWI) and Indian Ocean swell diffusion effect index(IOSDEI) are defined on the basis of the 45-year(September 1957–August 2002) ERA-40 wave reanalysis data from the European Centre for Medium-Range Weather Forecasts(ECMWF) to analyze the impact of the South Indian Ocean westerlies on the propagation of swell acreage. The following results were obtained: 1) The South Indian Ocean swell mainly propagates from southwest to northeast. The swell also spreads to the Arabian Sea upon reaching low-latitude waters. The 2.0-meter contour of the swell can reach northward to Sri Lankan waters. 2) The size of the IOSDEI is determined by the SIWI strength. The IOSDEI requires approximately 2–3.5 days to fully respond to the SIWI. The correlations between SIWI and IOSDEI show obvious seasonal differences, with the highest correlations found in December–January–February(DJF) and the lowest correlations observed in June–July–August(JJA). 3) The SIWI and IOSDEI have a common period of approximately 1 week in JJA and DJF. The SIWI leads by approximately 2–3 days in this common period.展开更多
To investigate the transport characteristics of chloride ions in cement-based materials, the Mori-Tanaka (M-T) prediction scheme of the effective diffusion coefficient in composites containing single-phase and multi-p...To investigate the transport characteristics of chloride ions in cement-based materials, the Mori-Tanaka (M-T) prediction scheme of the effective diffusion coefficient in composites containing single-phase and multi-phase inclusions is systematically deduced based on the theory of composite mechanics and porous medium. The volume fraction, morphology and distribution of aggregates, as well as the interfacial transition zone (ITZ) are fully taken into consideration in this proposed model. The results show that the algorithm of M-T prediction scheme with high accuracy is relatively simple.展开更多
Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diff...Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diffusion of gas in turbulent bulk flow by utilizing the tracer gas data. This paper discussed about the measurement using tracer gas technique in Cibaliung Underground Mine, Indonesia and the evaluation of effective axial diffusion coefficient, E, by numerical simulation. In addition, a scheme to treat network flow in mine ventilation system was also proposed. The effective axial diffusion coefficient for each airway was evaluated based on Taylor's theoretical equation. It is found that the evaluated diffusion coefficient agrees well with Taylor's equation by considering that the wall friction factor, f, is higher than those for smooth pipe flow. It also shows that the value of effective diffusion coefficient can be inherently determined and the value is constant when matching with other measurements. Furthermore, there are possibilities to utilize the tracer gas measurement data to evaluate the airway friction factors.展开更多
Fractal approach is used to derive a power law relation between effective diffusion coefficient of solute in porous media and the geometry parameter characterizing the media. The results are consistent with the empiri...Fractal approach is used to derive a power law relation between effective diffusion coefficient of solute in porous media and the geometry parameter characterizing the media. The results are consistent with the empirical equations analogous to Archie`s law and are expected to be applied to prediction of effective diffusion coefficient. Key words: diffusion; effective diffusion coefficient; fractal; porous media.展开更多
The diffusion and reaction phenomenon in a Fe-based catalyst pellet for Fischer-Tropsch synthesis was studied. It was considered that the pores of catalyst pellets were full of liquid wax under Fischer-Tropsch synthes...The diffusion and reaction phenomenon in a Fe-based catalyst pellet for Fischer-Tropsch synthesis was studied. It was considered that the pores of catalyst pellets were full of liquid wax under Fischer-Tropsch synthesis conditions. The re- actants diffused from the bulk gas phase to the external surface of the pellet, and then the reactants diffused through the wax inside the pellet and reacted on the internal surface formed along the pore passages of the pellet. On the basis of reaction kinetics and double a-ASF product distribution model, a diffusion and reaction model of catalyst pellet was established. The effects of diffusion and reaction interaction in a catalyst pellet, the bulk temperature, the reaction pressure and the pellet size on the reactivity were further investigated. The relationship between the internal diffusion effectiveness factor of spherical catalyst pellet and the Thiele modulus were also discussed. The bulk temperature and pellet size have significant effects on the reactivity, while the pressure shows only a slight influence on the reactivity. The internal diffusion effectiveness factor decreases with an increasing Thiele modulus.展开更多
The Rayleigh distillation isotope fractionation(RDIF) model is one of the most popular methods used in isotope geochemistry. Numerous isotope signals observed in geologic processes have been interpreted with this mode...The Rayleigh distillation isotope fractionation(RDIF) model is one of the most popular methods used in isotope geochemistry. Numerous isotope signals observed in geologic processes have been interpreted with this model. The RDIF model provides a simple mathematic solution for the reservoir-limited equilibrium isotope fractionation effect. Due to the reservoir effect, tremendously large isotope fractionations will always be produced if the reservoir is close to being depleted. However, in real situations, many prerequisites assumed in the RDIF model are often difficult to meet. For instance, it requires the relocated materials, which are removed step by step from one reservoir to another with different isotope compositions(i.e., with isotope fractionation), to be isotopically equilibrated with materials in the first reservoir simultaneously. This ‘‘quick equilibrium requirement’’ is indeed hard to meet if the first reservoir is sufficiently large or the removal step is fast. The whole first reservoir will often fail to re-attain equilibrium in time before the next removal starts.This problem led the RDIF model to fail to interpret isotope signals of many real situations. Here a diffusion-coupled and Rayleigh-like(i.e., reservoir-effect included) separation process is chosen to investigate this problem. We find that the final isotope fractionations are controlled by both the diffusion process and the reservoir effects via the disequilibrium separation process. Due to its complexity, we choose to use a numerical simulation method to solve this problem by developing specific computing codes for the working model.According to our simulation results, the classical RDIF model only governs isotope fractionations correctly at the final stages of separation when the reservoir scale(or thickness of the system) is reduced to the order of magnitude of the quotient of the diffusivity and the separation rate. The RDIF model fails in other situations and the isotope fractionations will be diffusion-limited when the reservoir is relatively large, or the separation rate is fast. We find that the effect of internal isotope distribution inhomogeneity caused by diffusion on the Rayleigh-like separation process is significant and cannot be ignored. This method can be applied to study numerous geologic and planetary processes involving diffusion-limited disequilibrium separation processes including partial melting,evaporation, mineral precipitation, core segregation, etc.Importantly, we find that far more information can be extracted through analyzing isotopic signals of such ‘‘disequilibrium’’processes than those of fully equilibrated ones, e.g., reservoir size and the separation rate. Such information may provide a key to correctly interpreting many isotope signals observed from geochemical and cosmochemical processes.展开更多
The generation and propagation characteristics of bright spatial bound-soliton pairs (BSPs) are investigated under the diffusion effect in photovoltaic photorefractive crystals by numerical simulation. The results sho...The generation and propagation characteristics of bright spatial bound-soliton pairs (BSPs) are investigated under the diffusion effect in photovoltaic photorefractive crystals by numerical simulation. The results show that two coherent solitons, one as the signal light and the other as the control light, can form a BSP when the peak intensity of the control light is appropriately selected. Moreover, under the diffusion effect, the BSP experiences a self-bending process during propagating and the center of the BSP moves on a parabolic trajectory. Furthermore, the lateral shift of the BSP at the output face of the crystal can be manipulated by adjusting the peak intensity of the control light. The research results provide a method for the design of all-optical switching and routing based on the manipulation of the lateral position of BSPs.展开更多
We study the stochastic motion of a Brownian particle driven by a constant force over a static periodic potential. We show that both the effective diffusion and the effective drag coefficient are mathematically well-d...We study the stochastic motion of a Brownian particle driven by a constant force over a static periodic potential. We show that both the effective diffusion and the effective drag coefficient are mathematically well-defined and we derive analytic expressions for these two quantities. We then investigate the asymptotic behaviors of the effective diffusion and the effective drag coefficient, respectively, for small driving force and for large driving force. In the case of small driving force, the effective diffusion is reduced from its Brownian value by a factor that increases exponentially with the amplitude of the potential. The effective drag coefficient is increased by approximately the same factor. As a result, the Einstein relation between the diffusion coefficient and the drag coefficient is approximately valid when the driving force is small. For moderately large driving force, both the effective diffusion and the effective drag coefficient are increased from their Brownian values, and the Einstein relation breaks down. In the limit of very large driving force, both the effective diffusion and the effective drag coefficient converge to their Brownian values and the Einstein relation is once again valid.展开更多
The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes （LEDs） is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelen...The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes （LEDs） is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law L α I^m, with smaller parameter m in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg- defect-related nonradiative centers in the active region. Furthermore, the forward current-voltage characteristics are improved.展开更多
文摘For the first time a mathematical modelling of porous catalyst particles subject to both internal mass concentration gradients as well as temperature gradients, in endothermic or exothermic reactions has been reported. This model contains a non-linear mass balance equation which is related to rate expression. This paper presents an approximate analytical method (Modified Adomian decomposition method) to solve the non-linear differential equations for chemical kinetics with diffusion effects. A simple and closed form of expressions pertaining to substrate concentration and utilization factor is presented for all value of diffusion parameters. These analytical results are compared with numerical results and found to be in good agreement.
基金suppor ted by Chinese NSF projects(42173021,41873024,42130114)the strategic priority research program(B)of CAS(XDB41000000)+1 种基金the preresearch Project on Civil Aerospace Technologies No.D020202 funded by the Chinese National Space Administration(CNSA)Guizhou Provincial 2021 Science and Technology Subsidies(No.GZ2021SIG)。
文摘Theoretical studies of the diffusionalisotope effect in solids are still stuck in the 1960s and 1970s.With the development of high spatial resolution mass spectrometers,isotopic data of mineral grains are rapidly accumulated.To dig up information from these data,molecularlevel theoretical models are urgently needed.Based on the microscopic definition of the diffusion coe fficient(D),a new theoretical framework for calculating the diffusional isotope effect(DIE(v))(intermsofD*/D)forvacancy-mediated impurity diffusion in solids is provided based on statistical mechanics formalism.The newly derived equation shows that theDIE(v)can be easily calculated as long as the vibration frequencies of isotope-substituted solids are obtained.The calculatedDIE(v)values of^(199)Au/^(195)Au and^(60)Co/^(57)Co during diffusion in Cu and Au metals are all within 1%of errors compared to the experimental data,which shows that this theoretical model is reasonable and precise.
文摘This paper presents a theoretical method for predicting the effective diffusion coefficient of macromolecules in the microporous membrfines in view of the effects of molecular dimension and configuration. On the basis of the hindered diffusion theory of spherical neutral macromolecules in a micropore of a long cylinder, the effects of molecular dimension and configuration are studied by defining two molecular dimensions:the mean projected radius to predict the concentration partition and the ' hydrodynamically equivalent sphere' radius to evaluate the hydrodynamic reverse drag force. The quantitative comparison shows that the effective diffusion coefficients for different macromolecules predicted by the present method are more consistent with the available published experimental data.
基金the Key Program of National Natural Science Foundation of China(No.12335008),the Postgraduate Research and Innovation Project of Huzhou University(No.2023KYCX62)the Scientific Research Fund of Zhejiang Provincial Education Department(No.Y202352712)the Huzhou science and technology planning project(No.2021GZ60)。
文摘The safety assessment of high-level radioactive waste repositories requires a high predictive accuracy for radionuclide diffusion and a comprehensive understanding of the diffusion mechanism.In this study,a through-diffusion method and six machine-learning methods were employed to investigate the diffusion of ReO_(4)^(−),HCrO_(4)^(−),and I−in saturated compacted bentonite under different salinities and compacted dry densities.The machine-learning models were trained using two datasets.One dataset contained six input features and 293 instances obtained from the diffusion database system of the Japan Atomic Energy Agency(JAEA-DDB)and 15 publications.The other dataset,comprising 15,000 pseudo-instances,was produced using a multi-porosity model and contained eight input features.The results indicate that the former dataset yielded a higher predictive accuracy than the latter.Light gradient-boosting exhibited a higher prediction accuracy(R2=0.92)and lower error(MSE=0.01)than the other machine-learning algorithms.In addition,Shapley Additive Explanations,Feature Importance,and Partial Dependence Plot analysis results indicate that the rock capacity factor and compacted dry density had the two most significant effects on predicting the effective diffusion coefficient,thereby offering valuable insights.
基金jointly supported by the National Key Research and Development Program of China(Grant No.2022YFE0106500)Jiangsu Science Fund for Distinguished Young Scholars(Grant No.BK20200040)。
文摘The pan-Arctic is confronted with air pollution transported from lower latitudes.Observations have shown that aerosols help increase plant photosynthesis through the diffuse radiation fertilization effects(DRFEs).While such DRFEs have been explored at low to middle latitudes,the aerosol impacts on pan-Arctic ecosystems and the contributions by anthropogenic and natural emission sources remain less quantified.Here,we perform regional simulations at 0.2o×0.2ousing a well-validated vegetation model(Yale Interactive terrestrial Biosphere,YIBs)in combination with multi-source of observations to quantify the impacts of aerosol DRFEs on the net primary productivity(NPP)in the pan-Arctic during 2001-19.Results show that aerosol DRFEs increase pan-Arctic NPP by 2.19 Pg C(12.8%)yr^(-1)under clear-sky conditions,in which natural and anthropogenic sources contribute to 8.9% and 3.9%,respectively.Under all-sky conditions,such DRFEs are largely dampened by cloud to only 0.26 Pg C(1.24%)yr^(-1),with contributions of 0.65% by natural and 0.59% by anthropogenic species.Natural aerosols cause a positive NPP trend of 0.022% yr^(-1)following the increased fire activities in the pan-Arctic.In contrast,anthropogenic aerosols induce a negative trend of-0.01% yr^(-1)due to reduced emissions from the middle latitudes.Such trends in aerosol DRFEs show a turning point in the year of 2007 with more positive NPP trends by natural aerosols but negative NPP trends by anthropogenic aerosols thereafter.Though affected by modeling uncertainties,this study suggests a likely increasing impact of aerosols on terrestrial ecosystems in the pan-Arctic under global warming.
文摘The effects of positron diffusion on the measured S parameter have been investigated by a point-source diffusion model and a δ function method. Firstly, the theoretical analyses of the effects are presented for the samples of a homogeneous semi-infinite medium and a film of definite thickness. Then the results are used to analyze the S parameters in several composite systems and interface models.
基金National Natural Science Foundation of China !under Grant No. 59671039.
文摘The effects of distribution of induced defects on the positron diffusion was studied by using the point-source diffusion model and 6 function method.
文摘In this article, we investigated the influence of size and initial water content on the effective diffusion coefficient of sweet potatoes samples cut into cubic and cylindrical shapes. The sizes of the cubic samples are 0.5, 1, 1.5, 1.75, 2, 2.5 and 3 cm edge with a respective initial water content of 2.7, 3.76, 3.48, 2.68, 3.28, 2.17 and 2.29 kg/kgms. For cylindrical samples, the radius is set at 0.5 cm and sample heights are 1, 1.5, 2, 2.5, 3, 3.5 and 4 cm with respective water contents of 2.2, 3.19, 2.85, 2.1, 2.17, 2.39 and 2.03 kg/kgms. The effective diffusion coefficients of cubic samples are of the order of 10−10 and 10−9 m2∙s−1 grew with sample edge. As for the cylindrical samples, the effective diffusion coefficients were of the order of 10−9 m2∙s−1 and there was no linear correlation between cylinder height and their effective diffusion coefficient. As for the examination of the initial water content on the effective diffusion coefficient, it turned out that the initial water content had no influence on the effective diffusion coefficient of the sweet potato samples.
基金Project supported by the National Natural Science Foundation of China(Nos.12302079 and 11521202)the National Natural Science Foundation of U.S.A.(No.DMS-2306254)。
文摘During nearly 200 years of development in the knowledge of Brownian motion,the Janus sphere,as a typical Brownian particle with special surface properties,has been widely studied in the past few decades.A standard Janus sphere possesses two distinct surfaces.These two surfaces elicit different hydrodynamic interactions with ambient fluids or other interactions in response to environmental stimuli,such as chemical gradients,magnetic fields,and even light.The diffusion of Janus spheres,particularly when controlled by a remotely applied field,has inspired various applications,ranging from the design of micro-swimmers and novel procedures for probing the mechanical properties of suspensions to the fabrication of composites with enhanced performance.In this work,we report a systematic analysis of field-controlled diffusion of Janus spheres.Commencing with stochastic differential equations of motion at the microscale,we derive a coarse-grained Fokker-Planck equation at the macroscale,describing the evolution of the probability distribution function of the Janus sphere in terms of its position and orientation.Leveraging the concept of the hydrodynamic center,we derive,for the first time,explicit generalized Stokes-Einstein relations for long-time effective diffusivity,incorporating the effects of both the surface discontinuity of the Janus sphere and the external fields.The formulae enable predictions of the effective diffusivity as it varies with the slip length and characteristic angle of Janus spheres,and reveal the impact of an aligning potential field on the diffusion coefficients both parallel and perpendicular to the direction of the field.This work not only deepens the understanding of field-controlled diffusion of Janus particles,but also holds a meaningful impact on the future applications in microfluidics and related fields.
基金Projects(51578164,51678547,51878634,51878185,41807262)supported by the National Natural Science Foundation of China。
文摘Considering both the compaction effect of pile surrounding soil and the stress diffusion effect of pile end soil,this paper theoretically investigates the torsional vibration characteristics of tapered pile.Utilizing the complex stiffness transfer model to simulate compaction effect and tapered fictitious soil pile model to simulate stress diffusion,the analytical solution for the torsional impedance at tapered pile top is obtained by virtue of Laplace transform technique and impedance transfer method.Based on the present solution,a parametric study is conducted to investigate the rationality of the present solution and the influence of soil and pile properties on the torsional vibration characteristics of tapered pile embedded in layered soil.The results show that,both the compaction effect and stress diffusion effect have significant influence on the torsional vibration characteristics of tapered pile,and these two factors should be considered during the dynamic design of pile foundation.
文摘A rotating disc column (RDC) with inner diameter 68 mm and 28 compartments is used in this study. Parameters including Sauter mean diameter, hold-up and mass transfer coefficient are measured experimentally un-der different operating conditions. The correlations in literature for molecular diffusion and enhancement factor equation including eddy diffusion, circulation and oscillation of drops are evaluated. A new equation for the effec-tive diffusion coefficient as a function of Reynolds number is proposed. The calculated values of mass transfer co-efficient and column height from the previous equations and present equation are compared with the experimental data. The results from the present equation are in very good agreement with the experimental results, which may be used in designing RDC columns.
基金supported by the National Key R&D Program (No.2017YFC1405103)the Joint Funds of the National Natural Science Foundation of China (No.U170 6220)+1 种基金the National Natural Science Foundation of China (Nos.41901006, 41471005, and 41271016)the Natural Science Foundation of Shandong Province (No.ZR 2019BD005)。
文摘Research on the diffusion characteristics of swells contributes positively to wave energy forecasting, swell monitoring, and early warning. In this work, the South Indian Ocean westerly index(SIWI) and Indian Ocean swell diffusion effect index(IOSDEI) are defined on the basis of the 45-year(September 1957–August 2002) ERA-40 wave reanalysis data from the European Centre for Medium-Range Weather Forecasts(ECMWF) to analyze the impact of the South Indian Ocean westerlies on the propagation of swell acreage. The following results were obtained: 1) The South Indian Ocean swell mainly propagates from southwest to northeast. The swell also spreads to the Arabian Sea upon reaching low-latitude waters. The 2.0-meter contour of the swell can reach northward to Sri Lankan waters. 2) The size of the IOSDEI is determined by the SIWI strength. The IOSDEI requires approximately 2–3.5 days to fully respond to the SIWI. The correlations between SIWI and IOSDEI show obvious seasonal differences, with the highest correlations found in December–January–February(DJF) and the lowest correlations observed in June–July–August(JJA). 3) The SIWI and IOSDEI have a common period of approximately 1 week in JJA and DJF. The SIWI leads by approximately 2–3 days in this common period.
基金Funded by the National Natural Science Foundations of China(Nos.51778378,51478278)。
文摘To investigate the transport characteristics of chloride ions in cement-based materials, the Mori-Tanaka (M-T) prediction scheme of the effective diffusion coefficient in composites containing single-phase and multi-phase inclusions is systematically deduced based on the theory of composite mechanics and porous medium. The volume fraction, morphology and distribution of aggregates, as well as the interfacial transition zone (ITZ) are fully taken into consideration in this proposed model. The results show that the algorithm of M-T prediction scheme with high accuracy is relatively simple.
基金the financial support of this work by Japan Ministry of Education, Culture, Sport, Science and Technology and Kyushu University’s Global COE program
文摘Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diffusion of gas in turbulent bulk flow by utilizing the tracer gas data. This paper discussed about the measurement using tracer gas technique in Cibaliung Underground Mine, Indonesia and the evaluation of effective axial diffusion coefficient, E, by numerical simulation. In addition, a scheme to treat network flow in mine ventilation system was also proposed. The effective axial diffusion coefficient for each airway was evaluated based on Taylor's theoretical equation. It is found that the evaluated diffusion coefficient agrees well with Taylor's equation by considering that the wall friction factor, f, is higher than those for smooth pipe flow. It also shows that the value of effective diffusion coefficient can be inherently determined and the value is constant when matching with other measurements. Furthermore, there are possibilities to utilize the tracer gas measurement data to evaluate the airway friction factors.
文摘Fractal approach is used to derive a power law relation between effective diffusion coefficient of solute in porous media and the geometry parameter characterizing the media. The results are consistent with the empirical equations analogous to Archie`s law and are expected to be applied to prediction of effective diffusion coefficient. Key words: diffusion; effective diffusion coefficient; fractal; porous media.
基金Financial support from the National Basic Research Program of China(973 Program,2010CB736203)
文摘The diffusion and reaction phenomenon in a Fe-based catalyst pellet for Fischer-Tropsch synthesis was studied. It was considered that the pores of catalyst pellets were full of liquid wax under Fischer-Tropsch synthesis conditions. The re- actants diffused from the bulk gas phase to the external surface of the pellet, and then the reactants diffused through the wax inside the pellet and reacted on the internal surface formed along the pore passages of the pellet. On the basis of reaction kinetics and double a-ASF product distribution model, a diffusion and reaction model of catalyst pellet was established. The effects of diffusion and reaction interaction in a catalyst pellet, the bulk temperature, the reaction pressure and the pellet size on the reactivity were further investigated. The relationship between the internal diffusion effectiveness factor of spherical catalyst pellet and the Thiele modulus were also discussed. The bulk temperature and pellet size have significant effects on the reactivity, while the pressure shows only a slight influence on the reactivity. The internal diffusion effectiveness factor decreases with an increasing Thiele modulus.
基金supported by the Strategic Priority Research Program (B) of CAS (No. XDB41000000)Pre-research Project on Civil Aerospace Technologies No. D020202 funded by the Chinese National Space Administration (CNSA) and Chinese NSF projects (No. 42130114)。
文摘The Rayleigh distillation isotope fractionation(RDIF) model is one of the most popular methods used in isotope geochemistry. Numerous isotope signals observed in geologic processes have been interpreted with this model. The RDIF model provides a simple mathematic solution for the reservoir-limited equilibrium isotope fractionation effect. Due to the reservoir effect, tremendously large isotope fractionations will always be produced if the reservoir is close to being depleted. However, in real situations, many prerequisites assumed in the RDIF model are often difficult to meet. For instance, it requires the relocated materials, which are removed step by step from one reservoir to another with different isotope compositions(i.e., with isotope fractionation), to be isotopically equilibrated with materials in the first reservoir simultaneously. This ‘‘quick equilibrium requirement’’ is indeed hard to meet if the first reservoir is sufficiently large or the removal step is fast. The whole first reservoir will often fail to re-attain equilibrium in time before the next removal starts.This problem led the RDIF model to fail to interpret isotope signals of many real situations. Here a diffusion-coupled and Rayleigh-like(i.e., reservoir-effect included) separation process is chosen to investigate this problem. We find that the final isotope fractionations are controlled by both the diffusion process and the reservoir effects via the disequilibrium separation process. Due to its complexity, we choose to use a numerical simulation method to solve this problem by developing specific computing codes for the working model.According to our simulation results, the classical RDIF model only governs isotope fractionations correctly at the final stages of separation when the reservoir scale(or thickness of the system) is reduced to the order of magnitude of the quotient of the diffusivity and the separation rate. The RDIF model fails in other situations and the isotope fractionations will be diffusion-limited when the reservoir is relatively large, or the separation rate is fast. We find that the effect of internal isotope distribution inhomogeneity caused by diffusion on the Rayleigh-like separation process is significant and cannot be ignored. This method can be applied to study numerous geologic and planetary processes involving diffusion-limited disequilibrium separation processes including partial melting,evaporation, mineral precipitation, core segregation, etc.Importantly, we find that far more information can be extracted through analyzing isotopic signals of such ‘‘disequilibrium’’processes than those of fully equilibrated ones, e.g., reservoir size and the separation rate. Such information may provide a key to correctly interpreting many isotope signals observed from geochemical and cosmochemical processes.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61875058, 11874018, 11974006, and 61378036).
文摘The generation and propagation characteristics of bright spatial bound-soliton pairs (BSPs) are investigated under the diffusion effect in photovoltaic photorefractive crystals by numerical simulation. The results show that two coherent solitons, one as the signal light and the other as the control light, can form a BSP when the peak intensity of the control light is appropriately selected. Moreover, under the diffusion effect, the BSP experiences a self-bending process during propagating and the center of the BSP moves on a parabolic trajectory. Furthermore, the lateral shift of the BSP at the output face of the crystal can be manipulated by adjusting the peak intensity of the control light. The research results provide a method for the design of all-optical switching and routing based on the manipulation of the lateral position of BSPs.
文摘We study the stochastic motion of a Brownian particle driven by a constant force over a static periodic potential. We show that both the effective diffusion and the effective drag coefficient are mathematically well-defined and we derive analytic expressions for these two quantities. We then investigate the asymptotic behaviors of the effective diffusion and the effective drag coefficient, respectively, for small driving force and for large driving force. In the case of small driving force, the effective diffusion is reduced from its Brownian value by a factor that increases exponentially with the amplitude of the potential. The effective drag coefficient is increased by approximately the same factor. As a result, the Einstein relation between the diffusion coefficient and the drag coefficient is approximately valid when the driving force is small. For moderately large driving force, both the effective diffusion and the effective drag coefficient are increased from their Brownian values, and the Einstein relation breaks down. In the limit of very large driving force, both the effective diffusion and the effective drag coefficient converge to their Brownian values and the Einstein relation is once again valid.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61505197 and 61334009the National High-Technology Research and Development Program of China under Grant No 2014AA032604
文摘The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes （LEDs） is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law L α I^m, with smaller parameter m in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg- defect-related nonradiative centers in the active region. Furthermore, the forward current-voltage characteristics are improved.
