Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm in diameter （PM2.5）, ground meteorological data, vertical measurements of winds, temperature, and relative humidity ...Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm in diameter （PM2.5）, ground meteorological data, vertical measurements of winds, temperature, and relative humidity （RH）, and ECMWF reanalysis data, the major changes in the vertical structures of meteorological factors in the boundary layer （BL） during the heavy aerosol pollution episodes （HPEs） that occurred in winter 2016 in the urban Beijing area were analyzed. The HPEs are divided into two stages： the transport of pollutants under prevailing southerly winds, known as the transport stage （TS）, and the PM2.5 explosive growth and pollution accumulation period characterized by a temperature inversion with low winds and high RH in the lower BL, known as the cumulative stage （CS）. During the TS, a surface high lies south of Beijing, and pollutants are transported northwards. During the CS, a stable BL forms and is characterized by weak winds, temperature inversion, and moisture accumulation. Stable atmospheric stratifica- tion featured with light/calm winds and accumulated moisture （RH 〉 80%） below 250 m at the beginning of the CS is closely associated with the inversion, which is strengthened by the considerable decrease in near-surface air temperat- ure due to the interaction between aerosols and radiation after the aerosol pollution occurs. A significant increase in the PLAM （Parameter Linking Aerosol Pollution and Meteorological Elements） index is found, which is linearly re- lated to PM mass change. During the first 10 h of the CS, the more stable BL contributes approximately 84% of the explosive growth of PM2.5 mass. Additional accumulated near-surface moisture caused by the ground temperature de- crease, weak turbulent diffusion, low BL height, and inhibited vertical mixing of water vapor is conducive to the sec- ondary aerosol formation through chemical reactions, including liquid phase and heterogeneous reactions, which fur- ther increases the PM2.5 concentration levels. Th展开更多
近年来,基于连续时间随机游动(Continuous Time Random Walk,CTRW)理论所建立的模拟非均质多孔介质中溶质运移的方法已在大量的数值实验、室内实验、野外实验中得到了广泛的验证,为非均质多孔介质中的溶质运移行为提供了一种有效的模拟...近年来,基于连续时间随机游动(Continuous Time Random Walk,CTRW)理论所建立的模拟非均质多孔介质中溶质运移的方法已在大量的数值实验、室内实验、野外实验中得到了广泛的验证,为非均质多孔介质中的溶质运移行为提供了一种有效的模拟方法。简述了提出和发展CTRW的研究背景、基础理论以及与经典的对流-弥散方程等其他模拟方法的关系,综述了该理论在模拟溶质运移中的发展和应用,分析了实际应用中的关键问题,并展望了将其进一步发展应用于模拟反应性溶质运移的前景。展开更多
Turbulence is a thermodynamic system composed of a lot of vorticons rather than disturbance to random moving particles. The transport coefficients derived from the definition on turbulence show that the anomalous tran...Turbulence is a thermodynamic system composed of a lot of vorticons rather than disturbance to random moving particles. The transport coefficients derived from the definition on turbulence show that the anomalous transport is a natural result of present turbulence in Tokamak plasma and provides an important theoretical reference for the design and operation of Tokamak.展开更多
With the extreme drought(flood)event in southern China from July to August in 2022(1999)as the research object,based on the comprehensive diagnosis and composite analysis on the anomalous drought and flood years from ...With the extreme drought(flood)event in southern China from July to August in 2022(1999)as the research object,based on the comprehensive diagnosis and composite analysis on the anomalous drought and flood years from July to August in 1961-2022,it is found that there are significant differences in the characteristics of the vertically integrated moisture flux(VIMF)anomaly circulation pattern and the VIMF convergence(VIMFC)anomaly in southern China in drought and flood years,and the VIMFC,a physical quantity,can be regarded as an indicative physical factor for the"strong signal"of drought and flood in southern China.Specifically,in drought years,the VIMF anomaly in southern China is an anticyclonic circulation pattern and the divergence characteristics of the VIMFC are prominent,while those are opposite in flood years.Based on the SST anomaly in the typical draught year of 2022 in southern China and the SST deviation distribution characteristics of abnormal draught and flood years from 1961 to 2022,five SST high impact areas(i.e.,the North Pacific Ocean,Northwest Pacific Ocean,Southwest Pacific Ocean,Indian Ocean,and East Pacific Ocean)are selected via the correlation analysis of VIMFC and the global SST in the preceding months(May and June)and in the study period(July and August)in 1961-2022,and their contributions to drought and flood in southern China are quantified.Our study reveals not only the persistent anomalous variation of SST in the Pacific and the Indian Ocean but also its impact on the pattern of moisture transport.Furthermore,it can be discovered from the positive and negative phase fitting of SST that the SST composite flow field in high impact areas can exhibit two types of anomalous moisture transport structures that are opposite to each other,namely an anticyclonic(cyclonic)circulation pattern anomaly in southern China and the coastal areas of east China.These two types of opposite anomalous moisture transport structures can not only drive the formation of drought(flood)in southern China but also展开更多
Anomalous transport in magnetically confined plasmas is investigated using temporal fractional transport equations.The use of temporal fractional transport equations means that the order of the partial derivative with...Anomalous transport in magnetically confined plasmas is investigated using temporal fractional transport equations.The use of temporal fractional transport equations means that the order of the partial derivative with respect to time is a fraction. In this case, the Caputo fractional derivative relative to time is utilized, because it preserves the form of the initial conditions. A numerical calculation reveals that the fractional order of the temporal derivative α(α ∈(0, 1), sub-diffusive regime) controls the diffusion rate. The temporal fractional derivative is related to the fact that the evolution of a physical quantity is affected by its past history, depending on what are termed memory effects. The magnitude of α is a measure of such memory effects. When α decreases, so does the rate of particle diffusion due to memory effects. As a result,if a system initially has a density profile without a source, then the smaller the α is, the more slowly the density profile approaches zero. When a source is added, due to the balance of the diffusion and fueling processes, the system reaches a steady state and the density profile does not evolve. As α decreases, the time required for the system to reach a steady state increases. In magnetically confined plasmas, the temporal fractional transport model can be applied to off-axis heating processes. Moreover, it is found that the memory effects reduce the rate of energy conduction and hollow temperature profiles can be sustained for a longer time in sub-diffusion processes than in ordinary diffusion processes.展开更多
As the basic of a deeper investigation on the turbulent transport, the fluctuation property in the boundary of the newly-reconstructed Joint Texas Experimental Tokamak （J- TEXT） is studied experimentally using the r...As the basic of a deeper investigation on the turbulent transport, the fluctuation property in the boundary of the newly-reconstructed Joint Texas Experimental Tokamak （J- TEXT） is studied experimentally using the reciprocating Langmuir four-tip probe, which has been built and operated as the primary diagnostic tool in the boundary of J-TEXT tokamak. In this paper, spatial profiles of the plasma-edge parameters are obtained, such as electron temperature, plasma density, plasma potential, poloidal electric field and their fluctuations. The results indicate the existence of a Er ×BT shear layer at the vicinity of last closed flux surface （LCFS）, with the fluctuations suppressed in varying degrees. The turbulence-induced particle and energy fluxes can be calculated by the local plasma parameters above. Convection dominates the cross-field turbulent transport in boundary plasma. Electrostatic fluctuations properties are also studied in detail with the help of numerical analysis. Statistical analysis on density fluctuation shows that, the intermittency can affect the turbulence in the scrape-off layer （SOL）.展开更多
The quantum anomalous Hall effect is characterized by a quantized Hall resistance with a vanishing longitudinal resistance.Many experiments reported the quantization of the Hall resistance,which is always accompanied ...The quantum anomalous Hall effect is characterized by a quantized Hall resistance with a vanishing longitudinal resistance.Many experiments reported the quantization of the Hall resistance,which is always accompanied by a non-vanishing longitudinal resistance that is several k?.Meanwhile,the non-vanishing longitudinal resistance exhibits a universal exponential decay with the increase in magnetic field.We propose that the coupling of chiral edge states,which has not been properly evaluated in the previous theories,can give rise to the non-vanishing longitudinal resistance.The coupling between the chiral edges states along the opposite boundaries can be assisted by magnetic domains or defects inside the sample bulk,which has been already identified in recent experiments.Our theory provides a potential mechanism to understand the experimental result in both magnetic topological insulator and moirésuperlattice systems.展开更多
We investigate the transport of a deterministic Brownian particle theoretically, which moves in simple onedimensional, symmetric periodic potentials under the influence of both a time periodic and a static biasing for...We investigate the transport of a deterministic Brownian particle theoretically, which moves in simple onedimensional, symmetric periodic potentials under the influence of both a time periodic and a static biasing force. The physical system employed contains a friction coefficient that is speed-dependent. Within the tailored parameter regime, the absolute negative mobility, in which a particle can travel in the direction opposite to a constant applied force, is observed.This behavior is robust and can be maximized at two regimes upon variation of the characteristic factor of friction coefficient. Further analysis reveals that this uphill motion is subdiffusion in terms of localization（diffusion coefficient with the form D（t） -t-（-1） at long times）. We also have observed the non-trivially anomalous subdiffusion which is significantly deviated from the localization; whereas most of the downhill motion evolves chaotically, with the normal diffusion.展开更多
Topological insulators (TIs) host robust edge or surface states protected by time-reversal symmetry (TRS), which makes them prime candidates for applications in spintronic devices. A promising avenue of research for t...Topological insulators (TIs) host robust edge or surface states protected by time-reversal symmetry (TRS), which makes them prime candidates for applications in spintronic devices. A promising avenue of research for the development of functional TI devices has involved doping of three-dimensional (3D) TI thin film and bulk materials with magnetic elements. This approach aims to break the TRS and open a surface band gap near the Dirac point. Utilizing this gapped surface state allows for a wide range of novel physical effects to be observed, paving a way for applications in spintronics and quantum computation. This review focuses on the research of 3D TIs doped with manganese (Mn). We summarize major progress in the study of Mn doped chalcogenide TIs, including Bi2Se3, Bi2Te3, and Bi2(Te,Se)3. The transport properties, in particular the anomalous Hall effect, of the Mn-doped Bi2Se3 are discussed in detail. Finally, we conclude with future prospects and challenges in further studies of Mn doped TIs.展开更多
Natural aquifers usually exhibit complex physical and chemical heterogeneities,which are key factors complicating kinetic processes,such as contaminant transport and transformation,posing a great challenge in the reme...Natural aquifers usually exhibit complex physical and chemical heterogeneities,which are key factors complicating kinetic processes,such as contaminant transport and transformation,posing a great challenge in the remediation of contaminated groundwater.Aquifer heterogeneity usually leads to a distinct feature,the so-called“anomalous transport”in groundwater,which deviates from the phenomenon described by the classical advection-dispersion equation(ADE)based on Fick’s Law.Anomalous transport,also known as non-Fickian dispersion or“anomalous dispersion”in a broad sense,can explain the hydrogeological mechanism that leads to the temporally continuous deterioration of water quality and rapid spatial expansion of pollutant plumes.Contaminants enter and then are retained in the low-permeability matrix from the high-permeability zone via molecular diffusion,chemical adsorption,and other mass exchange effects.This process can be reversed when the concentration of pollutants in high-permeability zones is relatively low.The contaminants slowly return to the high-permeability zones through reverse molecular diffusion,resulting in sub-dispersive anomalous transport leading to the chronic gradual deterioration of water quality.Meanwhile,some contaminants are rapidly transported along the interconnected preferential flow paths,resulting in super-dispersive anomalous transport,which leads to the rapid spread of contaminants.Aquifer heterogeneity is also an important factor that constrains the efficacy of groundwater remediation,while the development,application,and evaluation of groundwater remediation technologies are usually based on the Fickian dispersion process predicted by the ADE equation.Comprehensive studies of the impacts of non-Fickian dispersion on contaminant transport and remediation are still needed.This article reviews the non-Fickian dispersion phenomenon caused by the heterogeneity of geological media,summarizes the processes and current understanding of contaminant migration and transformation in hi展开更多
An analytical algorithm for fast calculation of the Abel inversion for density profile measurement in tokamak is developed. Based upon the assumptions that the particle source is negligibly small in the plasma core re...An analytical algorithm for fast calculation of the Abel inversion for density profile measurement in tokamak is developed. Based upon the assumptions that the particle source is negligibly small in the plasma core region, density profiles can be approximated by an asymmetrical Gaussian distribution controlled only by one parameter VoID and VoID is constant along the radial direction, the analytical algorithm is presented and examined against a testing profile. The validity is confirmed by benchmark with the standard Abel inversion method and the theoretical profile. The scope of application as well as the error analysis is also discussed in detail.展开更多
In this work, we study the regional dependence of transport behavior of microalgae Chlorella vulgaris inside microflu- idic channel on applied fluid flow rate. The microalgae are treated as spherical naturally buoyant...In this work, we study the regional dependence of transport behavior of microalgae Chlorella vulgaris inside microflu- idic channel on applied fluid flow rate. The microalgae are treated as spherical naturally buoyant particles. Deviation from the normal diffusion or Brownian transport is characterized based on the scaling behavior of the mean square displacement （MSD） of the particle trajectories by resolving the displacements in the streamwise （flow） and perpendicular directions. The channel is divided into three different flow regions, namely center region of the channel and two near-wall boundaries and the particle motions are analyzed at different flow rates. We use the scaled Brownian motion to model the transitional characteristics in the scaling behavior of the MSDs. We find that there exist anisotropic anomalous transports in all the three flow regions with mixed sub-diffusive, normal and super-diffusive behavior in both longitudinal and transverse directions.展开更多
Anomalous transport in magnetically confined plasmas is investigated by radial fractional transport equations.It is shown that for fractional transport models,hollow density profiles are formed and uphill transports c...Anomalous transport in magnetically confined plasmas is investigated by radial fractional transport equations.It is shown that for fractional transport models,hollow density profiles are formed and uphill transports can be observed regardless of whether the fractional diffusion coefficients(FDCs)are radially dependent or not.When a radially dependent FDC<D_(α)(r)1 is imposed,compared with the case under=D_(α)(r)1.0,it is observed that the position of the peak of the density profile is closer to the core.Further,it is found that when FDCs at the positions of source injections increase,the peak values of density profiles decrease.The non-local effect becomes significant as the order of fractional derivative a 1 and causes the uphill transport.However,as a 2,the fractional diffusion model returns to the standard model governed by Fick’s law.展开更多
There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, such as the formation of charge density wave or polaron...There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, such as the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe5. It is found that a three-dimensional topological Dirac semimetal state emerges only at around Tp （at which the resistivity shows a pronounced peak）, as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe5. Our work not only provides the first evidence of a temperature-induced critical topological phase transition inHfTe5 but also gives a reasonable explanation on the long-lasting question.展开更多
We analyze the well-posedness of an anisotropic,nonlocal diffusion equation.Establishing an equivalence between weighted and unweighted anisotropic nonlocal diffusion operators in the vein of unified nonlocal vector c...We analyze the well-posedness of an anisotropic,nonlocal diffusion equation.Establishing an equivalence between weighted and unweighted anisotropic nonlocal diffusion operators in the vein of unified nonlocal vector calculus,we apply our analysis to a class of fractional-order operators and present rigorous estimates for the solution of the corresponding anisotropic anomalous diffusion equation.Furthermore,we extend our analysis to the anisotropic diffusion-advection equation and prove well-posedness for fractional orders s∈[0.5,1).We also present an application of the advection-diffusion equation to anomalous transport of solutes.展开更多
基金Supported by the National Key Project of the Ministry of Science and Technology of China(2016YFC0203306)Basic Scientific Research Project of the Chinese Academy of Meteorological Sciences(2016Z001)
文摘Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm in diameter （PM2.5）, ground meteorological data, vertical measurements of winds, temperature, and relative humidity （RH）, and ECMWF reanalysis data, the major changes in the vertical structures of meteorological factors in the boundary layer （BL） during the heavy aerosol pollution episodes （HPEs） that occurred in winter 2016 in the urban Beijing area were analyzed. The HPEs are divided into two stages： the transport of pollutants under prevailing southerly winds, known as the transport stage （TS）, and the PM2.5 explosive growth and pollution accumulation period characterized by a temperature inversion with low winds and high RH in the lower BL, known as the cumulative stage （CS）. During the TS, a surface high lies south of Beijing, and pollutants are transported northwards. During the CS, a stable BL forms and is characterized by weak winds, temperature inversion, and moisture accumulation. Stable atmospheric stratifica- tion featured with light/calm winds and accumulated moisture （RH 〉 80%） below 250 m at the beginning of the CS is closely associated with the inversion, which is strengthened by the considerable decrease in near-surface air temperat- ure due to the interaction between aerosols and radiation after the aerosol pollution occurs. A significant increase in the PLAM （Parameter Linking Aerosol Pollution and Meteorological Elements） index is found, which is linearly re- lated to PM mass change. During the first 10 h of the CS, the more stable BL contributes approximately 84% of the explosive growth of PM2.5 mass. Additional accumulated near-surface moisture caused by the ground temperature de- crease, weak turbulent diffusion, low BL height, and inhibited vertical mixing of water vapor is conducive to the sec- ondary aerosol formation through chemical reactions, including liquid phase and heterogeneous reactions, which fur- ther increases the PM2.5 concentration levels. Th
文摘近年来,基于连续时间随机游动(Continuous Time Random Walk,CTRW)理论所建立的模拟非均质多孔介质中溶质运移的方法已在大量的数值实验、室内实验、野外实验中得到了广泛的验证,为非均质多孔介质中的溶质运移行为提供了一种有效的模拟方法。简述了提出和发展CTRW的研究背景、基础理论以及与经典的对流-弥散方程等其他模拟方法的关系,综述了该理论在模拟溶质运移中的发展和应用,分析了实际应用中的关键问题,并展望了将其进一步发展应用于模拟反应性溶质运移的前景。
文摘Turbulence is a thermodynamic system composed of a lot of vorticons rather than disturbance to random moving particles. The transport coefficients derived from the definition on turbulence show that the anomalous transport is a natural result of present turbulence in Tokamak plasma and provides an important theoretical reference for the design and operation of Tokamak.
基金The Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(2019QZKK0105)the Science and Technology Development Fund of the Chinese Academy of Meteorological Sciences(2022KJ022)+2 种基金Special Fund for the Basic Scientific Research Expenses of the Chinese Academy of Meteorological Sciences(2021Z013)the Science and Technology Development Fund of the Chinese Academy of Meteorological Sciences(2022KJ021)Major Projects of the Natural Science Foundation of China(91337000)。
文摘With the extreme drought(flood)event in southern China from July to August in 2022(1999)as the research object,based on the comprehensive diagnosis and composite analysis on the anomalous drought and flood years from July to August in 1961-2022,it is found that there are significant differences in the characteristics of the vertically integrated moisture flux(VIMF)anomaly circulation pattern and the VIMF convergence(VIMFC)anomaly in southern China in drought and flood years,and the VIMFC,a physical quantity,can be regarded as an indicative physical factor for the"strong signal"of drought and flood in southern China.Specifically,in drought years,the VIMF anomaly in southern China is an anticyclonic circulation pattern and the divergence characteristics of the VIMFC are prominent,while those are opposite in flood years.Based on the SST anomaly in the typical draught year of 2022 in southern China and the SST deviation distribution characteristics of abnormal draught and flood years from 1961 to 2022,five SST high impact areas(i.e.,the North Pacific Ocean,Northwest Pacific Ocean,Southwest Pacific Ocean,Indian Ocean,and East Pacific Ocean)are selected via the correlation analysis of VIMFC and the global SST in the preceding months(May and June)and in the study period(July and August)in 1961-2022,and their contributions to drought and flood in southern China are quantified.Our study reveals not only the persistent anomalous variation of SST in the Pacific and the Indian Ocean but also its impact on the pattern of moisture transport.Furthermore,it can be discovered from the positive and negative phase fitting of SST that the SST composite flow field in high impact areas can exhibit two types of anomalous moisture transport structures that are opposite to each other,namely an anticyclonic(cyclonic)circulation pattern anomaly in southern China and the coastal areas of east China.These two types of opposite anomalous moisture transport structures can not only drive the formation of drought(flood)in southern China but also
基金supported by the National Key R&D Program of China (Grant No. 2022YFE03090000)the National Natural Science Foundation of China (Grant No. 11925501)the Fundamental Research Fund for the Central Universities (Grant No. DUT22ZD215)。
文摘Anomalous transport in magnetically confined plasmas is investigated using temporal fractional transport equations.The use of temporal fractional transport equations means that the order of the partial derivative with respect to time is a fraction. In this case, the Caputo fractional derivative relative to time is utilized, because it preserves the form of the initial conditions. A numerical calculation reveals that the fractional order of the temporal derivative α(α ∈(0, 1), sub-diffusive regime) controls the diffusion rate. The temporal fractional derivative is related to the fact that the evolution of a physical quantity is affected by its past history, depending on what are termed memory effects. The magnitude of α is a measure of such memory effects. When α decreases, so does the rate of particle diffusion due to memory effects. As a result,if a system initially has a density profile without a source, then the smaller the α is, the more slowly the density profile approaches zero. When a source is added, due to the balance of the diffusion and fueling processes, the system reaches a steady state and the density profile does not evolve. As α decreases, the time required for the system to reach a steady state increases. In magnetically confined plasmas, the temporal fractional transport model can be applied to off-axis heating processes. Moreover, it is found that the memory effects reduce the rate of energy conduction and hollow temperature profiles can be sustained for a longer time in sub-diffusion processes than in ordinary diffusion processes.
基金supported by Open Research Program from Key Laboratory of Geospace Environment, Chinese Academy of Sciences
文摘As the basic of a deeper investigation on the turbulent transport, the fluctuation property in the boundary of the newly-reconstructed Joint Texas Experimental Tokamak （J- TEXT） is studied experimentally using the reciprocating Langmuir four-tip probe, which has been built and operated as the primary diagnostic tool in the boundary of J-TEXT tokamak. In this paper, spatial profiles of the plasma-edge parameters are obtained, such as electron temperature, plasma density, plasma potential, poloidal electric field and their fluctuations. The results indicate the existence of a Er ×BT shear layer at the vicinity of last closed flux surface （LCFS）, with the fluctuations suppressed in varying degrees. The turbulence-induced particle and energy fluxes can be calculated by the local plasma parameters above. Convection dominates the cross-field turbulent transport in boundary plasma. Electrostatic fluctuations properties are also studied in detail with the help of numerical analysis. Statistical analysis on density fluctuation shows that, the intermittency can affect the turbulence in the scrape-off layer （SOL）.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074108,and 12147102)Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQ-MSX0568)+4 种基金supported by the National Natural Science Foundation of China(Grant No.12074107)the Program of Outstanding Young and Middle-aged Scientific and Technological Innovation Team of Colleges and Universities in Hubei Province(Grant No.T2020001)the Innovation Group Project of the Natural Science Foundation of Hubei Province of China(Grant No.2022CFA012)supported by the Würzburg-Dresden Cluster of Excellence ct.qmat,EXC2147(Grant No.390858490)the Deutsche Forschungsgemeinschaft(Grant No.SFB 1170)。
文摘The quantum anomalous Hall effect is characterized by a quantized Hall resistance with a vanishing longitudinal resistance.Many experiments reported the quantization of the Hall resistance,which is always accompanied by a non-vanishing longitudinal resistance that is several k?.Meanwhile,the non-vanishing longitudinal resistance exhibits a universal exponential decay with the increase in magnetic field.We propose that the coupling of chiral edge states,which has not been properly evaluated in the previous theories,can give rise to the non-vanishing longitudinal resistance.The coupling between the chiral edges states along the opposite boundaries can be assisted by magnetic domains or defects inside the sample bulk,which has been already identified in recent experiments.Our theory provides a potential mechanism to understand the experimental result in both magnetic topological insulator and moirésuperlattice systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.11547027 and 11505149)the Program for Innovative Research Team(in Science and Technology)in University of Yunnan Province,China+2 种基金the Science Foundation of Kunming University,China(Grant Nos.YJL15005 and XJL15016)the Academic Rewards for Outstanding Young Doctoral Candidate in Yunnan Province,Chinathe Cultivation Foundation for Outstanding Doctoral Dissertation of Yunnan University,China
文摘We investigate the transport of a deterministic Brownian particle theoretically, which moves in simple onedimensional, symmetric periodic potentials under the influence of both a time periodic and a static biasing force. The physical system employed contains a friction coefficient that is speed-dependent. Within the tailored parameter regime, the absolute negative mobility, in which a particle can travel in the direction opposite to a constant applied force, is observed.This behavior is robust and can be maximized at two regimes upon variation of the characteristic factor of friction coefficient. Further analysis reveals that this uphill motion is subdiffusion in terms of localization（diffusion coefficient with the form D（t） -t-（-1） at long times）. We also have observed the non-trivially anomalous subdiffusion which is significantly deviated from the localization; whereas most of the downhill motion evolves chaotically, with the normal diffusion.
基金supported by the National Key Research and Development Program (Project No. 2016YFA0300600)the National Science, Foundation of China (Projects No. 11604374 and No. 61425015)+1 种基金the National Basic Research Program of China (Project No. 2015CB921102)the Strategic Priority Research Program of Chinese Academy of Sciences (Project No. XDB28000000)
文摘Topological insulators (TIs) host robust edge or surface states protected by time-reversal symmetry (TRS), which makes them prime candidates for applications in spintronic devices. A promising avenue of research for the development of functional TI devices has involved doping of three-dimensional (3D) TI thin film and bulk materials with magnetic elements. This approach aims to break the TRS and open a surface band gap near the Dirac point. Utilizing this gapped surface state allows for a wide range of novel physical effects to be observed, paving a way for applications in spintronics and quantum computation. This review focuses on the research of 3D TIs doped with manganese (Mn). We summarize major progress in the study of Mn doped chalcogenide TIs, including Bi2Se3, Bi2Te3, and Bi2(Te,Se)3. The transport properties, in particular the anomalous Hall effect, of the Mn-doped Bi2Se3 are discussed in detail. Finally, we conclude with future prospects and challenges in further studies of Mn doped TIs.
基金supported by the National Key R&D Program of China(Grant No.2016YFC0402806)the National Natural Science Foundation of China(Grant Nos.41931292,42007162&41722208)the Natural Science Foundation of Guangdong Province(CN)(Grant No.2020A1515010891).
文摘Natural aquifers usually exhibit complex physical and chemical heterogeneities,which are key factors complicating kinetic processes,such as contaminant transport and transformation,posing a great challenge in the remediation of contaminated groundwater.Aquifer heterogeneity usually leads to a distinct feature,the so-called“anomalous transport”in groundwater,which deviates from the phenomenon described by the classical advection-dispersion equation(ADE)based on Fick’s Law.Anomalous transport,also known as non-Fickian dispersion or“anomalous dispersion”in a broad sense,can explain the hydrogeological mechanism that leads to the temporally continuous deterioration of water quality and rapid spatial expansion of pollutant plumes.Contaminants enter and then are retained in the low-permeability matrix from the high-permeability zone via molecular diffusion,chemical adsorption,and other mass exchange effects.This process can be reversed when the concentration of pollutants in high-permeability zones is relatively low.The contaminants slowly return to the high-permeability zones through reverse molecular diffusion,resulting in sub-dispersive anomalous transport leading to the chronic gradual deterioration of water quality.Meanwhile,some contaminants are rapidly transported along the interconnected preferential flow paths,resulting in super-dispersive anomalous transport,which leads to the rapid spread of contaminants.Aquifer heterogeneity is also an important factor that constrains the efficacy of groundwater remediation,while the development,application,and evaluation of groundwater remediation technologies are usually based on the Fickian dispersion process predicted by the ADE equation.Comprehensive studies of the impacts of non-Fickian dispersion on contaminant transport and remediation are still needed.This article reviews the non-Fickian dispersion phenomenon caused by the heterogeneity of geological media,summarizes the processes and current understanding of contaminant migration and transformation in hi
基金supported by the National Natural Science Foundation of China （No. 10235010） the special fund for scientific research startup to the winner of the Chinese Academy of Sciences President Award. As well as in part by JSPS-CAS Core-University Program on Plasma and Nuclear Fusion
文摘An analytical algorithm for fast calculation of the Abel inversion for density profile measurement in tokamak is developed. Based upon the assumptions that the particle source is negligibly small in the plasma core region, density profiles can be approximated by an asymmetrical Gaussian distribution controlled only by one parameter VoID and VoID is constant along the radial direction, the analytical algorithm is presented and examined against a testing profile. The validity is confirmed by benchmark with the standard Abel inversion method and the theoretical profile. The scope of application as well as the error analysis is also discussed in detail.
基金supported by the Science Fund from the Ministry of Higher Education of Malaysia under the Fundamental Research Grant Scheme(Grant No.FRGS:FP057-2014A)the Fund from the University of Malaya Research Grant(Grant No.UMRG:RP020A-14AFR)
文摘In this work, we study the regional dependence of transport behavior of microalgae Chlorella vulgaris inside microflu- idic channel on applied fluid flow rate. The microalgae are treated as spherical naturally buoyant particles. Deviation from the normal diffusion or Brownian transport is characterized based on the scaling behavior of the mean square displacement （MSD） of the particle trajectories by resolving the displacements in the streamwise （flow） and perpendicular directions. The channel is divided into three different flow regions, namely center region of the channel and two near-wall boundaries and the particle motions are analyzed at different flow rates. We use the scaled Brownian motion to model the transitional characteristics in the scaling behavior of the MSDs. We find that there exist anisotropic anomalous transports in all the three flow regions with mixed sub-diffusive, normal and super-diffusive behavior in both longitudinal and transverse directions.
基金supported by the National MCF Energy R&D Program of China(No.2019YFE03090300)National Natural Science Foundation of China(No.11925501)Fundamental Research Funds for the Central Universities(No.DUT21GJ204)。
文摘Anomalous transport in magnetically confined plasmas is investigated by radial fractional transport equations.It is shown that for fractional transport models,hollow density profiles are formed and uphill transports can be observed regardless of whether the fractional diffusion coefficients(FDCs)are radially dependent or not.When a radially dependent FDC<D_(α)(r)1 is imposed,compared with the case under=D_(α)(r)1.0,it is observed that the position of the peak of the density profile is closer to the core.Further,it is found that when FDCs at the positions of source injections increase,the peak values of density profiles decrease.The non-local effect becomes significant as the order of fractional derivative a 1 and causes the uphill transport.However,as a 2,the fractional diffusion model returns to the standard model governed by Fick’s law.
基金Supported by the National Basic Research Program of China under Grant Nos 2015CB921303 and 2013CB921700the National Key Research Program of China under Grant No 2016YFA0300604the'Strategic Priority Research Program(B)'of the Chinese Academy of Sciences under Grant No XDB07020100
文摘There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, such as the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe5. It is found that a three-dimensional topological Dirac semimetal state emerges only at around Tp （at which the resistivity shows a pronounced peak）, as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe5. Our work not only provides the first evidence of a temperature-induced critical topological phase transition inHfTe5 but also gives a reasonable explanation on the long-lasting question.
文摘We analyze the well-posedness of an anisotropic,nonlocal diffusion equation.Establishing an equivalence between weighted and unweighted anisotropic nonlocal diffusion operators in the vein of unified nonlocal vector calculus,we apply our analysis to a class of fractional-order operators and present rigorous estimates for the solution of the corresponding anisotropic anomalous diffusion equation.Furthermore,we extend our analysis to the anisotropic diffusion-advection equation and prove well-posedness for fractional orders s∈[0.5,1).We also present an application of the advection-diffusion equation to anomalous transport of solutes.
