In our previous work,we endowed a new physical meaning of self-diffusion coefficient in Fick’s law,which proposed that the diffusion coefficient can be described as the product of the characteristic length and the di...In our previous work,we endowed a new physical meaning of self-diffusion coefficient in Fick’s law,which proposed that the diffusion coefficient can be described as the product of the characteristic length and the diffusion velocity.To testify this simple theory,in this work,we further investigated the underlying mechanism of the characteristic length and the diffusion velocity at the molecular level.After a complete dynamic run,the statistical average diffusion velocity and the characteristic length of molecules can be obtained by scripts,and subsequently the diffusion coefficient was determined by our proposed theory.The diffusion processes in 35 systems with a wide range of pressure and concentration variations were simulated using this model.From the simulated results,diffusion coefficients from our new model matched well with the experimental results from literatures.The total average relative deviation of predicted values with respect to the experimental results is 8.18%,indicating that the novel model is objective and rational.Compared with the traditional MSD-t model,this novel diffusion coefficient model provides more reliable results,and the theory is simple and straightforward in concept.Additionally,the effect of gas pressure and liquid concentration on the diffusion behavior were discussed,and the microscopic diffusion mechanism was elucidated through the distribution of diffusion velocity and the characteristic length analysis.Moreover,we suggested new distribution functions,providing more reliable data theoretical foundations for the future research about the diffusion coefficient.展开更多
The characteristics of adsorption, desorption, and diffusion of gas in tectonic coal are important for the prediction of coal and gas outbursts. Three types of coal samples, of which both metamorphic grade and degree ...The characteristics of adsorption, desorption, and diffusion of gas in tectonic coal are important for the prediction of coal and gas outbursts. Three types of coal samples, of which both metamorphic grade and degree of damage is different, were selected from Tongchun, Qilin, and Pingdingshan mines. Using a series of experiments in an electrostatic field, we analyzed the characteristics of gas adsorption and diffusion in tectonic coal. We found that gas adsorption in coal conforms to the Langmuir equation in an electrostatic field. Both the depth of the adsorption potential well and the coal molecular electroneg- ativity increases under the action of an electrostatic field. A Joule heating effect was caused by changing the coal-gas system conductivity in an electrostatic field. The quantity of gas adsorbed and AP result from competition between the depth of the adsorption potential well, the coal molecular electronegativ- ity, and the Joule heating effect. △P peaks when the three factors control behavior equally. Compared with anthracite, the impact of the electrostatic field on the gas diffusion capacity of middle and high rank coals is greater. Compared with the original coal, the gas adsorption quantity,△P, and the gas diffusion capacity of tectonic coal are greater in an electrostatic field. In addition, the smaller the particle size of tectonic coal, the larger the△P.展开更多
Based on the method of in situ polymerization synthesis combined with two-step sinter- ing process, LiFel-xVx（PO4）（3-y）/3Fy/C was prepared. The effects of V and F co-doping on the structure, morphology, and electr...Based on the method of in situ polymerization synthesis combined with two-step sinter- ing process, LiFel-xVx（PO4）（3-y）/3Fy/C was prepared. The effects of V and F co-doping on the structure, morphology, and electrochemical performances of LiFePO4/C were in- vestigated by X-ray diffraction, Fourier transform infrared spectra, scanning electron mi- croscope, charge/discharge tests, and electrochemical impedance spectroscopy, respectively. The results indicated that the V and F co-doping did not destroy the olivine structure of LiFePO4/C, but it can stabilize the crystal structure, decrease charge transfer resistance, enhance Li ion diffusion velocity, further improve its cycling and high-rate capabilities of LiFePO4/C.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
In this paper, based on the theories of smoke ring, current lines in the Earth, induced by transmitting source on the Earths surface, are regarded as downward moving and outward expanding current filaments which are c...In this paper, based on the theories of smoke ring, current lines in the Earth, induced by transmitting source on the Earths surface, are regarded as downward moving and outward expanding current filaments which are called as images of transmitting source. By comparing the magnetic field of the current filaments with that measured near the source, we can determine the image depth which can be used for estimating the downward vertical velocity of the image by using a cubic spline interpolation method. Then the resistivities varying with depth can be approximately estimated through a comparison between the estimated velocity of the image and the downward diffusing velocity in a homogeneous half space. We discussed the case of a circular transmitting loop, and developed a corresponding approximate inversion program which has been tested for 1-D layered-Earth models and real data.展开更多
The bump-on-tail(BOT)instability is generally caused by a beam of energetic particles existing in relatively cold background plasma.The employment of second-stage wave-driven module in the variable specific impulse ma...The bump-on-tail(BOT)instability is generally caused by a beam of energetic particles existing in relatively cold background plasma.The employment of second-stage wave-driven module in the variable specific impulse magnetoplasma rocket(VASIMR)yields the production of energetic ions,which could drive the BOT instability.The present work explores this possibility for the first time via numerical simulations based on the experimental data on the VASIMR,i.e.,referring to VX-50.It is found that the BOT instability does exist even in the plume region away from antenna.The results indicate that velocity space diffusion provides a stabilizing effect on the nonlinear evolution of waves,while dissipation in the bulk plasma essentially impedes it.To show the practical values implied by these computations,the influences of this BOT instability on the power coupling and thrust are investigated particularly.These findings are valuable for VASIMR,as well as other plasma thrusters that yield energetic particles inside relatively cold background plasma,to suppress BOT instability and thus increase the power coupling efficiency and thrust performance.展开更多
The periodic one-dimensional hopping model is useful for studying the motion of microscopic particles in the thermal noise environment. Based on the explicit formulations of mean velocity, mean first passage time and ...The periodic one-dimensional hopping model is useful for studying the motion of microscopic particles in the thermal noise environment. Based on the explicit formulations of mean velocity, mean first passage time and effective diffusion constant, a general N internal states or even infinite internal states model can be approximated by a one state model that retains the basic properties of the original process. This effective description aids the analysis of biochemical and biophysical problems. This effective description also implies that, to some extent, many processes can be well described by simple two-state models, or even one-state models.展开更多
基金supported by the National Natural Science Foundation of China(21776264 and 21376231).
文摘In our previous work,we endowed a new physical meaning of self-diffusion coefficient in Fick’s law,which proposed that the diffusion coefficient can be described as the product of the characteristic length and the diffusion velocity.To testify this simple theory,in this work,we further investigated the underlying mechanism of the characteristic length and the diffusion velocity at the molecular level.After a complete dynamic run,the statistical average diffusion velocity and the characteristic length of molecules can be obtained by scripts,and subsequently the diffusion coefficient was determined by our proposed theory.The diffusion processes in 35 systems with a wide range of pressure and concentration variations were simulated using this model.From the simulated results,diffusion coefficients from our new model matched well with the experimental results from literatures.The total average relative deviation of predicted values with respect to the experimental results is 8.18%,indicating that the novel model is objective and rational.Compared with the traditional MSD-t model,this novel diffusion coefficient model provides more reliable results,and the theory is simple and straightforward in concept.Additionally,the effect of gas pressure and liquid concentration on the diffusion behavior were discussed,and the microscopic diffusion mechanism was elucidated through the distribution of diffusion velocity and the characteristic length analysis.Moreover,we suggested new distribution functions,providing more reliable data theoretical foundations for the future research about the diffusion coefficient.
基金the National Natural Science Foundation of China(No.41272177)the Henan Polytechnic University Doctor Foundation(No.WS2013A11)
文摘The characteristics of adsorption, desorption, and diffusion of gas in tectonic coal are important for the prediction of coal and gas outbursts. Three types of coal samples, of which both metamorphic grade and degree of damage is different, were selected from Tongchun, Qilin, and Pingdingshan mines. Using a series of experiments in an electrostatic field, we analyzed the characteristics of gas adsorption and diffusion in tectonic coal. We found that gas adsorption in coal conforms to the Langmuir equation in an electrostatic field. Both the depth of the adsorption potential well and the coal molecular electroneg- ativity increases under the action of an electrostatic field. A Joule heating effect was caused by changing the coal-gas system conductivity in an electrostatic field. The quantity of gas adsorbed and AP result from competition between the depth of the adsorption potential well, the coal molecular electronegativ- ity, and the Joule heating effect. △P peaks when the three factors control behavior equally. Compared with anthracite, the impact of the electrostatic field on the gas diffusion capacity of middle and high rank coals is greater. Compared with the original coal, the gas adsorption quantity,△P, and the gas diffusion capacity of tectonic coal are greater in an electrostatic field. In addition, the smaller the particle size of tectonic coal, the larger the△P.
文摘Based on the method of in situ polymerization synthesis combined with two-step sinter- ing process, LiFel-xVx（PO4）（3-y）/3Fy/C was prepared. The effects of V and F co-doping on the structure, morphology, and electrochemical performances of LiFePO4/C were in- vestigated by X-ray diffraction, Fourier transform infrared spectra, scanning electron mi- croscope, charge/discharge tests, and electrochemical impedance spectroscopy, respectively. The results indicated that the V and F co-doping did not destroy the olivine structure of LiFePO4/C, but it can stabilize the crystal structure, decrease charge transfer resistance, enhance Li ion diffusion velocity, further improve its cycling and high-rate capabilities of LiFePO4/C.
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In this paper, based on the theories of smoke ring, current lines in the Earth, induced by transmitting source on the Earths surface, are regarded as downward moving and outward expanding current filaments which are called as images of transmitting source. By comparing the magnetic field of the current filaments with that measured near the source, we can determine the image depth which can be used for estimating the downward vertical velocity of the image by using a cubic spline interpolation method. Then the resistivities varying with depth can be approximately estimated through a comparison between the estimated velocity of the image and the downward diffusing velocity in a homogeneous half space. We discussed the case of a circular transmitting loop, and developed a corresponding approximate inversion program which has been tested for 1-D layered-Earth models and real data.
基金supported by the National Natural Science Foundation of China(92271113 and 12105324)the Fundamental Research Funds for the Central Universities(2022CDJQY-003)the Chongqing Entrepreneurship and Innovation Support Program for Overseas Returnees(CX2022004).
文摘The bump-on-tail(BOT)instability is generally caused by a beam of energetic particles existing in relatively cold background plasma.The employment of second-stage wave-driven module in the variable specific impulse magnetoplasma rocket(VASIMR)yields the production of energetic ions,which could drive the BOT instability.The present work explores this possibility for the first time via numerical simulations based on the experimental data on the VASIMR,i.e.,referring to VX-50.It is found that the BOT instability does exist even in the plume region away from antenna.The results indicate that velocity space diffusion provides a stabilizing effect on the nonlinear evolution of waves,while dissipation in the bulk plasma essentially impedes it.To show the practical values implied by these computations,the influences of this BOT instability on the power coupling and thrust are investigated particularly.These findings are valuable for VASIMR,as well as other plasma thrusters that yield energetic particles inside relatively cold background plasma,to suppress BOT instability and thus increase the power coupling efficiency and thrust performance.
基金the National Natural Science Foundation of China(Grant No. 10701029)
文摘The periodic one-dimensional hopping model is useful for studying the motion of microscopic particles in the thermal noise environment. Based on the explicit formulations of mean velocity, mean first passage time and effective diffusion constant, a general N internal states or even infinite internal states model can be approximated by a one state model that retains the basic properties of the original process. This effective description aids the analysis of biochemical and biophysical problems. This effective description also implies that, to some extent, many processes can be well described by simple two-state models, or even one-state models.
