The diffusion coefficients of several alloying elements（Al,Mo,Co,Ta,Ru,W,Cr,Re） in Ni are directly calculated using the five-frequency model and the first principles density functional theory.The correlation factors...The diffusion coefficients of several alloying elements（Al,Mo,Co,Ta,Ru,W,Cr,Re） in Ni are directly calculated using the five-frequency model and the first principles density functional theory.The correlation factors provided by the five-frequency model are explicitly calculated.The calculated diffusion coefficients show their excellent agreement with the available experimental data.Both the diffusion pre-factor（D 0） and the activation energy（Q） of impurity diffusion are obtained.The diffusion coefficients above 700 K are sorted in the following order：DAl〉DCr〉DCo〉DTa〉DMo〉DRu〉DW〉D Re.It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair（E 1）.The value of E 2-E 1（E 2 is the solute diffusion energy） and the correlation factor each also show a positive correlation.The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients.展开更多
The diffusion coefficient of natural gas in foamy oil is one of the key parameters to evaluate the feasibility of gas injection for enhanced oil recovery in foamy oil reservoirs. In this paper, a PVT cell was used to ...The diffusion coefficient of natural gas in foamy oil is one of the key parameters to evaluate the feasibility of gas injection for enhanced oil recovery in foamy oil reservoirs. In this paper, a PVT cell was used to measure diffusion coefficients of natural gas in Venezuela foamy oil at high pressures, and a new method for deter- mining the diffusion coefficient in the foamy oil was de- veloped on the basis of experimental data. The effects of pressure and the types of the liquid phase on the diffusion coefficient of the natural gas were discussed. The results indicate that the diffusion coefficients of natural gas in foamy oil, saturated oil, and dead oil increase linearly with increasing pressure. The diffusion coefficient of natural gas in the foamy oil at 20 MPa was 2.93 times larger than that at 8.65 MPa. The diffusion coefficient of the natural gas in dead oil was 3.02 and 4.02 times than that of the natural gas in saturated oil and foamy oil when the pressure was 20 MPa. However, the gas content of foamy oil was 16.9 times higher than that of dead oil when the dissolution time and pressure were 20 MPa and 35.22 h, respectively.展开更多
The effect of curing age on chloride diffusion coefficient of recycled aggregate concrete subjected to different compressive stresses was investigated.A compression loading setup was both designed and fabricated.The c...The effect of curing age on chloride diffusion coefficient of recycled aggregate concrete subjected to different compressive stresses was investigated.A compression loading setup was both designed and fabricated.The chloride diffusion coefficients of recycled aggregate concrete under compressive stresses were measured by the rapid chloride ion migration(RCM)method.The experimental results show that the chloride diffusion coefficients of recycled aggregate concrete(RAC)under different compressive stress ratios generally decrease with the increase of curing age.For RAC subjected to the same compressive stress ratios,the chloride diffusion coefficients approximately have power functions with curing ages and the relationship models are proposed.Moreover,the influence of curing age on chloride diffusion coefficient firstly decreases and then increases as the compressive stress ratio increases.展开更多
We present a mathematical and numerical study for a pointwise optimal control problem governed by a variable-coefficient Riesz-fractional diffusion equation.Due to the impact of the variable diffusivity coefficient,ex...We present a mathematical and numerical study for a pointwise optimal control problem governed by a variable-coefficient Riesz-fractional diffusion equation.Due to the impact of the variable diffusivity coefficient,existing regularity results for their constantcoefficient counterparts do not apply,while the bilinear forms of the state(adjoint)equation may lose the coercivity that is critical in error estimates of the finite element method.We reformulate the state equation as an equivalent constant-coefficient fractional diffusion equation with the addition of a variable-coefficient low-order fractional advection term.First order optimality conditions are accordingly derived and the smoothing properties of the solutions are analyzed by,e.g.,interpolation estimates.The weak coercivity of the resulting bilinear forms are proven via the Garding inequality,based on which we prove the optimal-order convergence estimates of the finite element method for the(adjoint)state variable and the control variable.Numerical experiments substantiate the theoretical predictions.展开更多
We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with t...We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ＊ = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T＊ = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-α, where α is an adjustable parameter and N is the number of particles. It is observed that the values of a 〈 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations fronl the literature.展开更多
The temperature-dependent coefficients of self-diffusion for liquid metals are simulated by molecular dynamics meth ods based on the embedded-atom-method （EAM） potential function. The simulated results show that a g...The temperature-dependent coefficients of self-diffusion for liquid metals are simulated by molecular dynamics meth ods based on the embedded-atom-method （EAM） potential function. The simulated results show that a good inverse linear relation exists between the natural logarithm of self-diffusion coefficients and temperature, though the results in the litera ture vary somewhat, due to the employment of different potential functions. The estimated activation energy of liquid metals obtained by fitting the Arrhenius formula is close to the experimental data. The temperature-dependent shear-viscosities obtained from the Stokes-Einstein relation in conjunction with the results of molecular dynamics simulation are generally consistent with other values in the literature.展开更多
The static and dynamic diffusion coefficients are important coefficients to describe the moisture transfer processes in particleboard. In this paper, the formula of culculating the static and dynamic diffusion coeffic...The static and dynamic diffusion coefficients are important coefficients to describe the moisture transfer processes in particleboard. In this paper, the formula of culculating the static and dynamic diffusion coefficients were deduced. At first, the static diffusion coefficients of four kinds of particleboards were determined by using diffusion cup method. The results demonstrated that the static diffusion coefficients parallel to panel surface were 10-20 times as large as that of perpendicular to panel surface for test boards. To determine both dynamic diffusion coefficients and surface emission coefficients of moisture in particleboards in one experimental period, specimens in four different thicknesses of each kind of particleboard were used in the experiment. Then the method of regression was used and the dynamic diffusion coefficients and surface emission coefficients were determined based on the slope and intercept of the regressive line.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 coefficient and dynamics of water diffusion in adhesive-graphite joints were calculated in-situ with energy dispersive X-ray (EDX) analysis, a method that is significantly simpler than elemental analysis. Water di...The coefficient and dynamics of water diffusion in adhesive-graphite joints were calculated in-situ with energy dispersive X-ray (EDX) analysis, a method that is significantly simpler than elemental analysis. Water diffusion coefficient and dynamics of adhesive-graphite joints treated by different surface treatment methods were also investigated. Calculation results indicated that the water diffusion rate in adhesive-graphite joints treated by sandpaper was higher than that treated by chemical oxidation or by silane couple agent. Also the durability of graphite joints treated by coupling agent is superior to that treated by chemical oxidation or sandpaper burnishing.展开更多
Optical fibers are seen in the optical sensing and optical fiber communication. Simultaneous propagation of optical pulses in an inhomogeneous optical fiber is described by a coupled time-dependent coefficient fourth-...Optical fibers are seen in the optical sensing and optical fiber communication. Simultaneous propagation of optical pulses in an inhomogeneous optical fiber is described by a coupled time-dependent coefficient fourth-order nonlinear Schr?dinger system, which is discussed in this paper. For such a system, we work out the Lax pair, Darboux transformation, and corresponding vector semi-rational nonautonomous rogue wave solutions. When the group velocity dispersion(GVD) and fourth-order dispersion(FOD) coefficients are the constants, we exhibit the first-and second-order vector semirational rogue waves which are composed of the four-petalled rogue waves and eye-shaped breathers. Both the width of the rogue wave along the time axis and temporal separation between the adjacent peaks of the breather decrease with the GVD coefficient or FOD coefficient. With the GVD and FOD coefficients as the linear, cosine, and exponential functions, we respectively present the first-and second-order periodic vector semi-rational rogue waves, first-and second-order asymmetry vector semi-rational rogue waves, and interactions between the eye-shaped breathers and the composite rogue waves.展开更多
Ray tracing method is used to study the propagation of collimated beams in a liquid-core cylindrical lens(LCL),which has dual functions of diffusion cell and image formation.The diffusion images on the focal plane of ...Ray tracing method is used to study the propagation of collimated beams in a liquid-core cylindrical lens(LCL),which has dual functions of diffusion cell and image formation.The diffusion images on the focal plane of the used LCL are simulated by establishing and solving both linear and nonlinear ray equations,the calculated results indicate that the complex imaging results of LCL in inhomogeneous media can be treated by the law of ray propagation in homogeneous media under the condition of small refractive index gradient of diffusion solution.Guided by the calculation conditions,the diffusion process of triethylene glycol aqueous solution is experimentally studied at room temperature by using the LCL in this paper.The spatial and temporal concentration profile Ce(z,t)of diffusion solution is obtained by analyzing diffusion image appearing on the focal plane of the LCL;Then,the concentration-dependent diffusion coefficient is assumed to be a polynomial D(C)=D0×(1+α1C+α2C2+α3C3+…).The finite difference method is used to solve the Fick diffusion equation for calculating numerically the concentration profiles Cn(z,t).The D(C)of triethylene glycol aqueous solution is obtained by comparing the Cn(z,t)with Ce(z,t).Finally,the obtained polynomial D(C)is used to calculate the refractive index profiles nn(z,t)s of diffusion solution in the used LCL.Based on the ray propagation law in inhomogeneous media and the calculated n(z,t),the ray tracing method is used again to simulate the dynamic images of the whole experimental diffusion process to varify the correctness of the calculated D(C).The method presented in this work opens up a new way for both measuring and verifying the concentration-dependent liquid diffusion coefficients.展开更多
The investigation of runaway electrons is expanded by different methods. The aim of this study is to show sawtooth oscillations of hard x-ray emission and with the help of sawtooth oscillations to obtain radial diffus...The investigation of runaway electrons is expanded by different methods. The aim of this study is to show sawtooth oscillations of hard x-ray emission and with the help of sawtooth oscillations to obtain radial diffusion coefficient and magnetic fluctuations. In the same way, the hard x-ray spectral evaluation is compared in several time intervals and it is shown that during discharge, the energy of the runaway electrons is less than 200？keV. Also, for typical plasmas, population of runaway electrons is measured at seven time intervals of 5ms and temporal evaluation of runaway electron mean energy. The sawtooth-like shape is observed in the hard x-ray range （10–1000？keV）. By the sawtooth oscillation method, the RE diffusion coefficient in radial transport in the IR-T1 plasma is Dr～0.5Dr～0.5m^2s^-1. The magnetic field fluctuation due to magnetic diffusion DmDm is given as br/Bt～10^-4.展开更多
The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa i...The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa in a frequency range of 10-1 Hz–106 Hz. The measured electrical conductivity along the ⊥ [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ± 0.06 e V and 2.51 ± 0.19 cm~3/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the⊥ [001] axis is approximately three times higher than that along the ⊥ [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst–Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.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
Objective To assess the clinical feasibility of diagnosing and staging liver fibrosis by apparent diffusion coefficient (ADC). Methods Totally, 43 patients (mean age 29.3 years) with chronic hepatitis by liver biopsy ...Objective To assess the clinical feasibility of diagnosing and staging liver fibrosis by apparent diffusion coefficient (ADC). Methods Totally, 43 patients (mean age 29.3 years) with chronic hepatitis by liver biopsy and 7 healthy controls (mean age 39.9 years) underwent liver diffusion weighted imaging (DWI) with four b values: 0, 200, 500, and 1000 s/mm2 respectively. The liver fibrosis was staged according to Ishak fibrosis stage. The ADC value of liver fibrosis patients and healthy controls was compared. The correlation of ADC value and liver fibrosis staging was analyzed. Result The histological staging showed 8 stage 1 patients, 10 stage 2 patients, 6 stage 3 patients, 9 stage 4 patients, 8 stage 5 patients and 2 stage 6 patients. The mean ADC value of liver fibrosis patients was significantly lower than that of healthy controls except for stage 1 group (P < 0.05). There was a negative correlation between liver fibrosis staging and ADC value (r = -0.697 with b=500 s/mm2, P < 0.01). Receiver operating characteristic (ROC) curve of ADC value of advanced liver fibrosis (Ishak stage F3 and higher) showed that area under curve = 0.913, 0.825, and 0.794 with b = 500, 1000, and 200 s/mm2, respectively (95% confidence interval: 83.6%-99.0%, 70.7%-94.3%, 66.5%- 92.4%; P < 0.05). When b value was 500 s/mm2, the sensitivity (84%) and specificity (80%) of DWI for diagnosis of advanced liver fibrosis were the highest. Conclusion DWI is proved to be a useful clinical tool in the quantitative evaluation of liver fibrosis and in the prediction of the process of liver fibrosis with the recommendable b value (500 s/mm2).展开更多
Objective To investigate the feasibility of whole body diffusion weighted imaging (WB-DWI) in screening metastasis. Methods WB-DWI was performed in 24 patients diagnosed with various types of primary tumors. The three...Objective To investigate the feasibility of whole body diffusion weighted imaging (WB-DWI) in screening metastasis. Methods WB-DWI was performed in 24 patients diagnosed with various types of primary tumors. The three-dimensional maximum intensity projection reconstruction and black-and-white flip technique were used to observe metastatic lesions, and the results were compared with those of bone scintigraphy. Results By WB-DWI scanning sequence at b = 800 s/mm2, all the bone lesions found by bone scintigraphy in the cohort were well identified, and other lesions of soft tissue and organs were also well demonstrated. Its screening capability was equivalent with bone scintigraphy in screening metastases in bones (P = 0.062). Conclusion WB-DWI was practicable with the parameter settings attempted in metastases screening.展开更多
The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion ...The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and ^(99)TcO_4^- on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients(De, Da), plotting breakthrough curves and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from(1.68 ± 0.40) 9 × 10^(-11) to(2.80 ± 0.62) 9 × 10^(-11) m^2/s and from(4.61 ±1.28) 9 × 10^(-12) to (16.2 ± 2.50) 9 × 10^(-12) m^2/s, respectively.The apparent and effective diffusion coefficients of^(99)TcO_4^-ranged from(5.26 ± 0.16) 9 × 10^-12to(7.78 ± 0.43) 9× 10^-12m^2/s and from(1.49 ± 0.002) 9 × 10^(-12) to(4.16 ±0.07) 9 × 10^(-12) m^2/s, respectively. The distribution coefficients of HTO and^(99)TcO_4^-ranged from(0.70 ± 0.12) 9× 10^(-2) to(1.36 ± 0.53) 9 × 10^(-2) mL/g and from(1.12 ±0.06) 9 × 10^(-2) to(5.79 ± 2.22) 9 × 10^(-2) mL/g, respectively.The Deand Kdvalues were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and ^(99)Tc could be considered nonsorbent radionuclides. The data obtained in this studyprovide a valuable reference for the safety assessment of waste repositories.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
The electron drift velocity, electron energy distribution function （EEDF）, densitynormalized effective ionization coefficient and density-normalized longitudinal diffusion velocity are calculated in SF6-O2 and SFs-A...The electron drift velocity, electron energy distribution function （EEDF）, densitynormalized effective ionization coefficient and density-normalized longitudinal diffusion velocity are calculated in SF6-O2 and SFs-Air mixtures. The experimental results from a pulsed Townsend discharge are plotted for comparison with the numerical results. The reduced field strength varies from 40 Td to 500 Td （1 Townsend=10-17 V.cm2） and the SF6 concentration ranges from 10% to 100%. A Boltzmann equation associated with the two-term spherical harmonic expansion approximation is utilized to gain the swarm parameters in steady-state Townsend. Results show that the accuracy of the Boltzlnann solution with a two-term expansion in calculating the electron drift velocity, electron energy distribution function, and density-normalized effective ionization coefficient is acceptable. The effective ionization coefficient presents a distinct relationship with the SF6 content in the mixtures. Moreover, the E/Ncr values in SF6-Air mixtures are higher than those in SF6-O2 mixtures and the calculated value E/Ncr in SF6-O2 and SF6-Air mixtures is lower than the measured value in SFB-N2. Parametric studies conducted on these parameters using the Boltzmann analysis offer substantial insight into the plasma physics, as well as a basis to explore the ozone generation process.展开更多
Objective To assess the reproducibility of whole-body diffusion weighted imaging(WB-DWI) technique in healthy volunteers under normal breathing with background body signal suppression.Methods WB-DWI was performed on 3...Objective To assess the reproducibility of whole-body diffusion weighted imaging(WB-DWI) technique in healthy volunteers under normal breathing with background body signal suppression.Methods WB-DWI was performed on 32 healthy volunteers twice within two-week period using short TI inversion-recovery diffusion-weighted echo-planar imaging sequence and built-in body coil.The volunteers were scanned across six stations continuously covering the entire body from the head to the feet under normal breathing.The bone apparent diffusion coefficient(ADC) and exponential ADC(eADC) of regions of interest(ROIs) were measured.We analyzed correlation of the results using paired-t-test to assess the reproducibility of the WB-DWI technique.Results We were successful in collecting and analyzing data of 64 WB-DWI images.There was no significant difference in bone ADC and eADC of 824 ROIs between the paired observers and paired scans(P>0.05).Most of the images from all stations were of diagnostic quality.Conclusion The measurements of bone ADC and eADC have good reproducibility.WB-DWI technique under normal breathing with background body signal suppression is adequate.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 50971005)
文摘The diffusion coefficients of several alloying elements（Al,Mo,Co,Ta,Ru,W,Cr,Re） in Ni are directly calculated using the five-frequency model and the first principles density functional theory.The correlation factors provided by the five-frequency model are explicitly calculated.The calculated diffusion coefficients show their excellent agreement with the available experimental data.Both the diffusion pre-factor（D 0） and the activation energy（Q） of impurity diffusion are obtained.The diffusion coefficients above 700 K are sorted in the following order：DAl〉DCr〉DCo〉DTa〉DMo〉DRu〉DW〉D Re.It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair（E 1）.The value of E 2-E 1（E 2 is the solute diffusion energy） and the correlation factor each also show a positive correlation.The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients.
基金financial support from the Major Subject of National Science and Technology (2011ZX05032-001)the Fundamental Research Funds for the Central Universities(NO.11CX06022A)
文摘The diffusion coefficient of natural gas in foamy oil is one of the key parameters to evaluate the feasibility of gas injection for enhanced oil recovery in foamy oil reservoirs. In this paper, a PVT cell was used to measure diffusion coefficients of natural gas in Venezuela foamy oil at high pressures, and a new method for deter- mining the diffusion coefficient in the foamy oil was de- veloped on the basis of experimental data. The effects of pressure and the types of the liquid phase on the diffusion coefficient of the natural gas were discussed. The results indicate that the diffusion coefficients of natural gas in foamy oil, saturated oil, and dead oil increase linearly with increasing pressure. The diffusion coefficient of natural gas in the foamy oil at 20 MPa was 2.93 times larger than that at 8.65 MPa. The diffusion coefficient of the natural gas in dead oil was 3.02 and 4.02 times than that of the natural gas in saturated oil and foamy oil when the pressure was 20 MPa. However, the gas content of foamy oil was 16.9 times higher than that of dead oil when the dissolution time and pressure were 20 MPa and 35.22 h, respectively.
基金supported by the Fundamental Research Funds for the Central UniversitiesFoundation of Graduate Innovation Center in Nanjing University of Aeronautics and Astronautics (No.kfjj20150105)the National Natural Science Foundation of China (No. 51279074)
文摘The effect of curing age on chloride diffusion coefficient of recycled aggregate concrete subjected to different compressive stresses was investigated.A compression loading setup was both designed and fabricated.The chloride diffusion coefficients of recycled aggregate concrete under compressive stresses were measured by the rapid chloride ion migration(RCM)method.The experimental results show that the chloride diffusion coefficients of recycled aggregate concrete(RAC)under different compressive stress ratios generally decrease with the increase of curing age.For RAC subjected to the same compressive stress ratios,the chloride diffusion coefficients approximately have power functions with curing ages and the relationship models are proposed.Moreover,the influence of curing age on chloride diffusion coefficient firstly decreases and then increases as the compressive stress ratio increases.
基金supported by the National Natural Science Foundation of China(11971276,12171287)Natural Science Foundation of Shandong Province(ZR2016JL004)+1 种基金supported by the China Postdoctoral Science Foundation(2021TQ0017,2021M700244)International Postdoctoral Exchange Fellowship Program(Talent-Introduction Program)(YJ20210019)。
文摘We present a mathematical and numerical study for a pointwise optimal control problem governed by a variable-coefficient Riesz-fractional diffusion equation.Due to the impact of the variable diffusivity coefficient,existing regularity results for their constantcoefficient counterparts do not apply,while the bilinear forms of the state(adjoint)equation may lose the coercivity that is critical in error estimates of the finite element method.We reformulate the state equation as an equivalent constant-coefficient fractional diffusion equation with the addition of a variable-coefficient low-order fractional advection term.First order optimality conditions are accordingly derived and the smoothing properties of the solutions are analyzed by,e.g.,interpolation estimates.The weak coercivity of the resulting bilinear forms are proven via the Garding inequality,based on which we prove the optimal-order convergence estimates of the finite element method for the(adjoint)state variable and the control variable.Numerical experiments substantiate the theoretical predictions.
基金supported by the National Natural Science Foundation of China (Grant No. 51076128)the National High Technology Research and Development Program of China (Grant No. 2009AA05Z107)
文摘We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ＊ = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T＊ = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-α, where α is an adjustable parameter and N is the number of particles. It is observed that the values of a 〈 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations fronl the literature.
基金supported by the National Natural Science Foundation of China(Grant Nos.11032003 and 11221202)the National Basic Research Program of China(Grant No.2010CB731600)
文摘The temperature-dependent coefficients of self-diffusion for liquid metals are simulated by molecular dynamics meth ods based on the embedded-atom-method （EAM） potential function. The simulated results show that a good inverse linear relation exists between the natural logarithm of self-diffusion coefficients and temperature, though the results in the litera ture vary somewhat, due to the employment of different potential functions. The estimated activation energy of liquid metals obtained by fitting the Arrhenius formula is close to the experimental data. The temperature-dependent shear-viscosities obtained from the Stokes-Einstein relation in conjunction with the results of molecular dynamics simulation are generally consistent with other values in the literature.
文摘The static and dynamic diffusion coefficients are important coefficients to describe the moisture transfer processes in particleboard. In this paper, the formula of culculating the static and dynamic diffusion coefficients were deduced. At first, the static diffusion coefficients of four kinds of particleboards were determined by using diffusion cup method. The results demonstrated that the static diffusion coefficients parallel to panel surface were 10-20 times as large as that of perpendicular to panel surface for test boards. To determine both dynamic diffusion coefficients and surface emission coefficients of moisture in particleboards in one experimental period, specimens in four different thicknesses of each kind of particleboard were used in the experiment. Then the method of regression was used and the dynamic diffusion coefficients and surface emission coefficients were determined based on the slope and intercept of the regressive line.
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.
文摘The coefficient and dynamics of water diffusion in adhesive-graphite joints were calculated in-situ with energy dispersive X-ray (EDX) analysis, a method that is significantly simpler than elemental analysis. Water diffusion coefficient and dynamics of adhesive-graphite joints treated by different surface treatment methods were also investigated. Calculation results indicated that the water diffusion rate in adhesive-graphite joints treated by sandpaper was higher than that treated by chemical oxidation or by silane couple agent. Also the durability of graphite joints treated by coupling agent is superior to that treated by chemical oxidation or sandpaper burnishing.
基金Project supported by the BUPT Excellent Ph.D.Students Foundation(Grant No.CX2019201)the National Natural Science Foundation of China(Grant Nos.11772017 and 11805020)+1 种基金the Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications),China(Grant No.IPOC:2017ZZ05)the Fundamental Research Funds for the Central Universities of China(Grant No.2011BUPTYB02)。
文摘Optical fibers are seen in the optical sensing and optical fiber communication. Simultaneous propagation of optical pulses in an inhomogeneous optical fiber is described by a coupled time-dependent coefficient fourth-order nonlinear Schr?dinger system, which is discussed in this paper. For such a system, we work out the Lax pair, Darboux transformation, and corresponding vector semi-rational nonautonomous rogue wave solutions. When the group velocity dispersion(GVD) and fourth-order dispersion(FOD) coefficients are the constants, we exhibit the first-and second-order vector semirational rogue waves which are composed of the four-petalled rogue waves and eye-shaped breathers. Both the width of the rogue wave along the time axis and temporal separation between the adjacent peaks of the breather decrease with the GVD coefficient or FOD coefficient. With the GVD and FOD coefficients as the linear, cosine, and exponential functions, we respectively present the first-and second-order periodic vector semi-rational rogue waves, first-and second-order asymmetry vector semi-rational rogue waves, and interactions between the eye-shaped breathers and the composite rogue waves.
基金the National Natural Science Foundation of China(Grant No.11804296)the Joint Key Project of Yunnan Province,China(Grant Nos.2018FY001-020 and 2018ZI002)the Fund from the Educational Department of Yunnan Province,China(Grant No.2016CYH05).
文摘Ray tracing method is used to study the propagation of collimated beams in a liquid-core cylindrical lens(LCL),which has dual functions of diffusion cell and image formation.The diffusion images on the focal plane of the used LCL are simulated by establishing and solving both linear and nonlinear ray equations,the calculated results indicate that the complex imaging results of LCL in inhomogeneous media can be treated by the law of ray propagation in homogeneous media under the condition of small refractive index gradient of diffusion solution.Guided by the calculation conditions,the diffusion process of triethylene glycol aqueous solution is experimentally studied at room temperature by using the LCL in this paper.The spatial and temporal concentration profile Ce(z,t)of diffusion solution is obtained by analyzing diffusion image appearing on the focal plane of the LCL;Then,the concentration-dependent diffusion coefficient is assumed to be a polynomial D(C)=D0×(1+α1C+α2C2+α3C3+…).The finite difference method is used to solve the Fick diffusion equation for calculating numerically the concentration profiles Cn(z,t).The D(C)of triethylene glycol aqueous solution is obtained by comparing the Cn(z,t)with Ce(z,t).Finally,the obtained polynomial D(C)is used to calculate the refractive index profiles nn(z,t)s of diffusion solution in the used LCL.Based on the ray propagation law in inhomogeneous media and the calculated n(z,t),the ray tracing method is used again to simulate the dynamic images of the whole experimental diffusion process to varify the correctness of the calculated D(C).The method presented in this work opens up a new way for both measuring and verifying the concentration-dependent liquid diffusion coefficients.
文摘The investigation of runaway electrons is expanded by different methods. The aim of this study is to show sawtooth oscillations of hard x-ray emission and with the help of sawtooth oscillations to obtain radial diffusion coefficient and magnetic fluctuations. In the same way, the hard x-ray spectral evaluation is compared in several time intervals and it is shown that during discharge, the energy of the runaway electrons is less than 200？keV. Also, for typical plasmas, population of runaway electrons is measured at seven time intervals of 5ms and temporal evaluation of runaway electron mean energy. The sawtooth-like shape is observed in the hard x-ray range （10–1000？keV）. By the sawtooth oscillation method, the RE diffusion coefficient in radial transport in the IR-T1 plasma is Dr～0.5Dr～0.5m^2s^-1. The magnetic field fluctuation due to magnetic diffusion DmDm is given as br/Bt～10^-4.
基金Project supported by the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(Grant No.XDB 18010401)the Key Research Program of Frontier Sciences of CAS(Grant No.QYZDB-SSW-DQC009)+2 种基金the“135”Program of the Institute of Geochemistry of CASthe Hundred-Talent Program of CASthe National Natural Science Foundation of China(Grant Nos.41474078,41774099,and 41772042)
文摘The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa in a frequency range of 10-1 Hz–106 Hz. The measured electrical conductivity along the ⊥ [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ± 0.06 e V and 2.51 ± 0.19 cm~3/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the⊥ [001] axis is approximately three times higher than that along the ⊥ [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst–Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.
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a Grant from Shanghai Scientific and Technological Commission Foundation (06411952)
文摘Objective To assess the clinical feasibility of diagnosing and staging liver fibrosis by apparent diffusion coefficient (ADC). Methods Totally, 43 patients (mean age 29.3 years) with chronic hepatitis by liver biopsy and 7 healthy controls (mean age 39.9 years) underwent liver diffusion weighted imaging (DWI) with four b values: 0, 200, 500, and 1000 s/mm2 respectively. The liver fibrosis was staged according to Ishak fibrosis stage. The ADC value of liver fibrosis patients and healthy controls was compared. The correlation of ADC value and liver fibrosis staging was analyzed. Result The histological staging showed 8 stage 1 patients, 10 stage 2 patients, 6 stage 3 patients, 9 stage 4 patients, 8 stage 5 patients and 2 stage 6 patients. The mean ADC value of liver fibrosis patients was significantly lower than that of healthy controls except for stage 1 group (P < 0.05). There was a negative correlation between liver fibrosis staging and ADC value (r = -0.697 with b=500 s/mm2, P < 0.01). Receiver operating characteristic (ROC) curve of ADC value of advanced liver fibrosis (Ishak stage F3 and higher) showed that area under curve = 0.913, 0.825, and 0.794 with b = 500, 1000, and 200 s/mm2, respectively (95% confidence interval: 83.6%-99.0%, 70.7%-94.3%, 66.5%- 92.4%; P < 0.05). When b value was 500 s/mm2, the sensitivity (84%) and specificity (80%) of DWI for diagnosis of advanced liver fibrosis were the highest. Conclusion DWI is proved to be a useful clinical tool in the quantitative evaluation of liver fibrosis and in the prediction of the process of liver fibrosis with the recommendable b value (500 s/mm2).
文摘Objective To investigate the feasibility of whole body diffusion weighted imaging (WB-DWI) in screening metastasis. Methods WB-DWI was performed in 24 patients diagnosed with various types of primary tumors. The three-dimensional maximum intensity projection reconstruction and black-and-white flip technique were used to observe metastatic lesions, and the results were compared with those of bone scintigraphy. Results By WB-DWI scanning sequence at b = 800 s/mm2, all the bone lesions found by bone scintigraphy in the cohort were well identified, and other lesions of soft tissue and organs were also well demonstrated. Its screening capability was equivalent with bone scintigraphy in screening metastases in bones (P = 0.062). Conclusion WB-DWI was practicable with the parameter settings attempted in metastases screening.
基金the Nuclear Backend Management Department at Taiwan Power Company for financially supporting this research
文摘The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and ^(99)TcO_4^- on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients(De, Da), plotting breakthrough curves and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from(1.68 ± 0.40) 9 × 10^(-11) to(2.80 ± 0.62) 9 × 10^(-11) m^2/s and from(4.61 ±1.28) 9 × 10^(-12) to (16.2 ± 2.50) 9 × 10^(-12) m^2/s, respectively.The apparent and effective diffusion coefficients of^(99)TcO_4^-ranged from(5.26 ± 0.16) 9 × 10^-12to(7.78 ± 0.43) 9× 10^-12m^2/s and from(1.49 ± 0.002) 9 × 10^(-12) to(4.16 ±0.07) 9 × 10^(-12) m^2/s, respectively. The distribution coefficients of HTO and^(99)TcO_4^-ranged from(0.70 ± 0.12) 9× 10^(-2) to(1.36 ± 0.53) 9 × 10^(-2) mL/g and from(1.12 ±0.06) 9 × 10^(-2) to(5.79 ± 2.22) 9 × 10^(-2) mL/g, respectively.The Deand Kdvalues were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and ^(99)Tc could be considered nonsorbent radionuclides. The data obtained in this studyprovide a valuable reference for the safety assessment of waste repositories.
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.
基金supported by National Natural Science Foundation of China(Nos.11105067 and 51366012)Jiangxi Province Young Scientists(Jinggang Star)Cultivation Plan of China(No.2013BCB23008)
文摘The electron drift velocity, electron energy distribution function （EEDF）, densitynormalized effective ionization coefficient and density-normalized longitudinal diffusion velocity are calculated in SF6-O2 and SFs-Air mixtures. The experimental results from a pulsed Townsend discharge are plotted for comparison with the numerical results. The reduced field strength varies from 40 Td to 500 Td （1 Townsend=10-17 V.cm2） and the SF6 concentration ranges from 10% to 100%. A Boltzmann equation associated with the two-term spherical harmonic expansion approximation is utilized to gain the swarm parameters in steady-state Townsend. Results show that the accuracy of the Boltzlnann solution with a two-term expansion in calculating the electron drift velocity, electron energy distribution function, and density-normalized effective ionization coefficient is acceptable. The effective ionization coefficient presents a distinct relationship with the SF6 content in the mixtures. Moreover, the E/Ncr values in SF6-Air mixtures are higher than those in SF6-O2 mixtures and the calculated value E/Ncr in SF6-O2 and SF6-Air mixtures is lower than the measured value in SFB-N2. Parametric studies conducted on these parameters using the Boltzmann analysis offer substantial insight into the plasma physics, as well as a basis to explore the ozone generation process.
文摘Objective To assess the reproducibility of whole-body diffusion weighted imaging(WB-DWI) technique in healthy volunteers under normal breathing with background body signal suppression.Methods WB-DWI was performed on 32 healthy volunteers twice within two-week period using short TI inversion-recovery diffusion-weighted echo-planar imaging sequence and built-in body coil.The volunteers were scanned across six stations continuously covering the entire body from the head to the feet under normal breathing.The bone apparent diffusion coefficient(ADC) and exponential ADC(eADC) of regions of interest(ROIs) were measured.We analyzed correlation of the results using paired-t-test to assess the reproducibility of the WB-DWI technique.Results We were successful in collecting and analyzing data of 64 WB-DWI images.There was no significant difference in bone ADC and eADC of 824 ROIs between the paired observers and paired scans(P>0.05).Most of the images from all stations were of diagnostic quality.Conclusion The measurements of bone ADC and eADC have good reproducibility.WB-DWI technique under normal breathing with background body signal suppression is adequate.
