We study an initial boundary value problem for the Navier-Stokes equations of compressible viscous heat-conductive fluids in a 2-D periodic domain or the unit square domain. We establish a blow-up criterion for the lo...We study an initial boundary value problem for the Navier-Stokes equations of compressible viscous heat-conductive fluids in a 2-D periodic domain or the unit square domain. We establish a blow-up criterion for the local strong solutions in terms of the gradient of the velocity only, which coincides with the famous Beale-Kato-Majda criterion for ideal incompressible flows.展开更多
A one-dimensional quantum hydrodynamic model （or quantum Euler-Poisson system） for semiconductors with initial boundary conditions is considered for general pressure-density function. The existence and uniqueness of...A one-dimensional quantum hydrodynamic model （or quantum Euler-Poisson system） for semiconductors with initial boundary conditions is considered for general pressure-density function. The existence and uniqueness of the classical solution of the corresponding steady-state quantum hydrodynamic equations is proved. Furthermore, the global existence of classical solution, when the initial datum is a perturbation of t he steadystate solution, is obtained. This solution tends to the corresponding steady-state solution exponentially fast as the time tends to infinity.展开更多
In this article, the globally bounded in-time pointwise estimate of solutions to the simplified Keller-Segel system modelling chemotaxis are derived. Moreover, a local existence theorem is obtained.
In this paper, the decomposition of SU(2) gauge potential in terms of Pauli spinor is studied. Using this decomposition, the spinor structures of Chern Simons form and the Chern density are obtained. Furthermore, the ...In this paper, the decomposition of SU(2) gauge potential in terms of Pauli spinor is studied. Using this decomposition, the spinor structures of Chern Simons form and the Chern density are obtained. Furthermore, the knot quantum number of non-Abelian gauge theory can be expressed by the Chern-Simons spinor structure, and the second Chern number is characterized by the Hopf indices and the Brouwer degrees of Φ-mapping.展开更多
Future changes in the 50-yr return level for temperature and precipitation extremes over China's Mainland are investigated based on a CMIP5 multi-model ensemble for RCP2.6, RCP4.5 and RCP8.5 scenarios. The followi...Future changes in the 50-yr return level for temperature and precipitation extremes over China's Mainland are investigated based on a CMIP5 multi-model ensemble for RCP2.6, RCP4.5 and RCP8.5 scenarios. The following indices are analyzed： TXx and TNn （the annual maximum and minimum of daily annual maximum consecutive 5-day precipitation） and CDD maximum and minimum surface temperature）, RX5day （the （maximum annual number of consecutive dry days）. After first validating the model performance, future changes in the 50-yr return values and return periods for these indices are investigated along with the inter-model spread. Multi-model median changes show an increase in the 50-yr return values of TXx and a decrease for TNn, more specifically, by the end of the 21st century under RCP8.5, the present day 50-yr return period of warm events is reduced to 1.2 yr, while extreme cold events over the country are projected to essentially disappear. A general increase in RX5day 50-yr return values is found in the future. By the end of the 21st century under RCP8.5, events of the present RX5day 50-yr return period are projected to reduce to 〈 10 yr over most of China. Changes in CDD-50 show a dipole pattern over China, with a decrease in the values and longer return periods in the north, and vice versa in the south. Our study also highlights the need for further improvements in the representation of extreme events in climate models to assess the future risks and engineering design related to large-scale infrastructure in China.展开更多
In this article, we prove the local existence and uniqueness of the classical solution to the Cauchy problem of the 3-D compressible Navier-Stokes equations with large initial data and vacuum, if the shear viscosity ...In this article, we prove the local existence and uniqueness of the classical solution to the Cauchy problem of the 3-D compressible Navier-Stokes equations with large initial data and vacuum, if the shear viscosity μ is a positive constant and the bulk viscosity λ（ρ） = ρ^β with β≥0. Note that the initial data can be arbitrarily large to contain vacuum states.展开更多
Iron and Manganese contents and parameters including pH, conductivity, and organic matter contents were determined in the sediments of the Okpara dam in Northern Benin. Fifteen samples were collected during a one-mont...Iron and Manganese contents and parameters including pH, conductivity, and organic matter contents were determined in the sediments of the Okpara dam in Northern Benin. Fifteen samples were collected during a one-month period and analysed in laboratory using the method of sequential extraction of Tessier. The analyses indicated that sediments contained high concentrations in reducible fraction of Iron and relatively high contents of exchangeable fraction, acidhydrolysable fraction and residual fraction of Manganese. The findings of this study confirmed the hypotheses that the meal contents of the sediments were relatively high and varied according to the geochemical phases.展开更多
Esterification is an important process in the food industry and can be carried out via homogeneous or heterogeneous catalysis.The homogeneous catalyst,despite providing high conversion,can cause corrosion in reactors,...Esterification is an important process in the food industry and can be carried out via homogeneous or heterogeneous catalysis.The homogeneous catalyst,despite providing high conversion,can cause corrosion in reactors,which is not observed with the use of heterogeneous catalysts.However,some of these catalysts require a high process temperature and may lose their catalytic activity with reuse.Thus,catalytic membranes have been proposed as a promising alternative.The combination of catalysis and separation in a single module provides greater conversion,reduction of excess reagents,compact industrial plant,making the process more efficient.Within this context,this work aims to present a literature review on the catalytic membrane for the synthesis of esters,improving the understanding of the production and development.This review examines the materials,catalysts used,and synthetic pathways.A comparison between the methods,as well as limitations and gaps in the literature,are highlighted.展开更多
We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh-Taylor instability （ARTI） experiments by numerical simulations. A preheating model k（T） = KSH[1＋f（T）], where KS...We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh-Taylor instability （ARTI） experiments by numerical simulations. A preheating model k（T） = KSH[1＋f（T）], where KSH is the Spitzer Harm （SH） electron conductivity and f（T） interprets the preheating tongue effect in the cold plasma ahead of the ablative front [Phys. Rev. E 65 （2002） 57401], is introduced in simulations. The simulation results of the nonlinear evolution of the ARTI are in general agreement with the experiment results. It is found that two factors, i.e., the suppressing of ablative Kelvin Helmholtz instability （AKHI） and the heat flow cone in the spike tips, contribute to the formation of jet-like long spike in the nonlinear evolution of the ARTI.展开更多
The RE-Fe-B permanent magnets have a complex microstructure and they are susceptible to corrosion process. In this paper, the commercial nickel coatings adhesion was investigated. The microstructure of the RE-Fe-B wit...The RE-Fe-B permanent magnets have a complex microstructure and they are susceptible to corrosion process. In this paper, the commercial nickel coatings adhesion was investigated. The microstructure of the RE-Fe-B without coating was analyzed by scanning electronic microscopy and electrochemical techniques. The interface magnet/coating was studied by scanning electron microscopy and the nickel-plated Nd-Fe-B commercial magnets were tested in a salt spray chamber. The ferromagnetic and RE-rich phases were observed. After the anodic polarization curve, a strong intergranular corrosion was observed and the RE-rich phase was preferentially attacked. The interface magnet/Ni coating presented inter-granular corrosion that can affect the nickel coating adherence. This attack had probably occurred during the electrodeposition process. Not all the samples suffered localized corrosion during the salt spray tests and the Ni triple-layer coating presented a few corrosion points. RE-Fe-B alloy magnets need to be protected with appropriate coatings to each environment to which they will be exposed and the protective coating must not be damaged.展开更多
The structural, mechanical and electronic properties of W_(1-x)Zr_x(x=0.0625, 0.125, 0.1875, 0.25, 0.5) are systematically investigated by means of first-principles calculation. The total-energy calculations demonstra...The structural, mechanical and electronic properties of W_(1-x)Zr_x(x=0.0625, 0.125, 0.1875, 0.25, 0.5) are systematically investigated by means of first-principles calculation. The total-energy calculations demonstrate that the W–Zr binary substitutional solid solution remaining bcc structure can be formed at an atom level. In addition, the derived bulk modulus(B), shear modulus(G), Young's modulus(E) for each of W–Zr alloys decrease gradually with the increase of Zr concentration, suggesting that W alloying with higher Zr concentration becomes softer than pure W metal. Based on the mechanical characteristic B/G ratio, Poisson's ratio υ and Cauchy pressure C, all W_(1-x)Zr_x alloys are regarded as ductile materials. The ductility for each of those materials is improved with the increase of Zr concentration. The calculated density of states indicates that the ductility of W_(1-x)Zr_x is due to the fact that the bonding in the alloy becomes more metallic through increasing the Zr concentration in tungsten. These results provide incontrovertible evidence for the fact that Zr has a significant influence on the properties of W.展开更多
We perform a first-principles computational tensile test on PuO_(2)based on density-functional theory within a local density approximation(LDA)+U formalism to investigate its structural,mechanical,magnetic and intrins...We perform a first-principles computational tensile test on PuO_(2)based on density-functional theory within a local density approximation(LDA)+U formalism to investigate its structural,mechanical,magnetic and intrinsic bonding properties in four representative directions:[001],[100],[110]and[111].The stress-strain relations show that the ideal tensile strengths in the four directions are 81.2,80.5,28.3 and 16.8 GPa at strains of 0.36,0.36,0.22 and 0.18,respectively.The[001]and[100]directions are prominently stronger than the other two directions since more Pu-0 bonds participate in the pulling process.By charge and density of state analysis along the[001]direction,we find that the strong mixed ioni%ovalent character of the Pu-0 bond is weakened by tensile strain and PuO_(2)will exhibit an insulator-to-metal transition after tensile stresses exceeding about 79 GPa.展开更多
The elastic anisotropy and superconductivity upon hydrostatic compression ofα,ω,and β Hf are investigated using first-principle methods.The results of elastic anisotropies show that they increase with increasing pr...The elastic anisotropy and superconductivity upon hydrostatic compression ofα,ω,and β Hf are investigated using first-principle methods.The results of elastic anisotropies show that they increase with increasing pressure for α and ω phases,while decrease upon compression forβphase.The calculated superconducting transition temperatures are in excellent agreement with experiments.Electron-phonon coupling constants(λ)are increasing with pressure for α and ω phases,while decreasing for β phase.For β phase,the large values ofλare mainly due to the obvious TA1 soft mode.Under further compression,the TA1 soft vibrational mode will disappear gradually.展开更多
Using first-principles calculations, we systematically study the potential energy surfaces and dissociation processes of the hydrogen molecule on the Mg（0001） surface. It is found that during the dissociative adsorp...Using first-principles calculations, we systematically study the potential energy surfaces and dissociation processes of the hydrogen molecule on the Mg（0001） surface. It is found that during the dissociative adsorption process with the minimum energy barrier, the hydrogen molecule first orients perpendicularly, and then rotates tobecome parallel to the surface. It is also found that the orientation of the hydrogen molecule in the transition state is neither perpendicular nor parallel to the surface. Most importantly we find that the rotation causes a reduction of the calculated dissociation energy barrier for the hydrogen molecule. The underlying electronic mechanism for the rotation of the hydrogen molecule is also discussed in the paper.展开更多
In order to calculate the electronic structure of correlated materials, we propose implementation of the LDA＋Gutzwiller method with Newton＇s method. The self-consistence process, efficiency and convergence of calcul...In order to calculate the electronic structure of correlated materials, we propose implementation of the LDA＋Gutzwiller method with Newton＇s method. The self-consistence process, efficiency and convergence of calculation are improved dramatically by using Newton＇s method with golden section search and other improvement approaches.We compare the calculated results by applying the previous linear mix method and Newton＇s method. We have applied our code to study the electronic structure of several typical strong correlated materials, including SrVO3, LaCoO3, and La2O3Fe2Se2. Our results fit quite well with the previous studies.展开更多
Quantum molecular dynamic (QMD) simulations have been applied to study the thermophysical properties of liquid xenon under dynamic compressions. The equation of state (EOS) obtained from QMD calculations are corrected...Quantum molecular dynamic (QMD) simulations have been applied to study the thermophysical properties of liquid xenon under dynamic compressions. The equation of state (EOS) obtained from QMD calculations are corrected according to Saha equation, and contributions from atomic ionization, which are of predominance in determining the EOS at high temperature and pressure, are considered. For the pressures below 160 GPa, the necessity in accounting for the atomic ionization has been demonstrated by the Hugoniot curve, which shows excellent agreement with previous experimental measurements, and three levels of ionization have been proved to be sufficient at this stage.展开更多
基金supported by the China Postdoctoral Science Foundation (20090450333)supported by the National Basic Research Program (2005CB321700)NSFC (40890154)
文摘We study an initial boundary value problem for the Navier-Stokes equations of compressible viscous heat-conductive fluids in a 2-D periodic domain or the unit square domain. We establish a blow-up criterion for the local strong solutions in terms of the gradient of the velocity only, which coincides with the famous Beale-Kato-Majda criterion for ideal incompressible flows.
基金The first author was supported by the China Postdoctoral Science Foundation(2005037318)The second author acknowledges partial support from the Austrian-Chinese Scientific-Technical Collaboration Agreement, the CTS of Taiwanthe Wittgenstein Award 2000 of P.A. Markowich, funded by the Austrian FWF, the Grants-in-Aid of JSPS No.14-02036the NSFC(10431060)the Project-sponsored by SRF for ROCS, SEM
文摘A one-dimensional quantum hydrodynamic model （or quantum Euler-Poisson system） for semiconductors with initial boundary conditions is considered for general pressure-density function. The existence and uniqueness of the classical solution of the corresponding steady-state quantum hydrodynamic equations is proved. Furthermore, the global existence of classical solution, when the initial datum is a perturbation of t he steadystate solution, is obtained. This solution tends to the corresponding steady-state solution exponentially fast as the time tends to infinity.
基金Supported by the NSF of Jiangxi Province, the NSFC (10225105, 10671023) and a CAEP grant
文摘In this article, the globally bounded in-time pointwise estimate of solutions to the simplified Keller-Segel system modelling chemotaxis are derived. Moreover, a local existence theorem is obtained.
文摘In this paper, the decomposition of SU(2) gauge potential in terms of Pauli spinor is studied. Using this decomposition, the spinor structures of Chern Simons form and the Chern density are obtained. Furthermore, the knot quantum number of non-Abelian gauge theory can be expressed by the Chern-Simons spinor structure, and the second Chern number is characterized by the Hopf indices and the Brouwer degrees of Φ-mapping.
基金supported by the National Key R&D Program of China (Grant No. 2017YF0605004)the National Natural Science Foundation of China (Grant No. 41675069)the Climate Change Specific Fund of China (Grant No. CCSF201731)
文摘Future changes in the 50-yr return level for temperature and precipitation extremes over China's Mainland are investigated based on a CMIP5 multi-model ensemble for RCP2.6, RCP4.5 and RCP8.5 scenarios. The following indices are analyzed： TXx and TNn （the annual maximum and minimum of daily annual maximum consecutive 5-day precipitation） and CDD maximum and minimum surface temperature）, RX5day （the （maximum annual number of consecutive dry days）. After first validating the model performance, future changes in the 50-yr return values and return periods for these indices are investigated along with the inter-model spread. Multi-model median changes show an increase in the 50-yr return values of TXx and a decrease for TNn, more specifically, by the end of the 21st century under RCP8.5, the present day 50-yr return period of warm events is reduced to 1.2 yr, while extreme cold events over the country are projected to essentially disappear. A general increase in RX5day 50-yr return values is found in the future. By the end of the 21st century under RCP8.5, events of the present RX5day 50-yr return period are projected to reduce to 〈 10 yr over most of China. Changes in CDD-50 show a dipole pattern over China, with a decrease in the values and longer return periods in the north, and vice versa in the south. Our study also highlights the need for further improvements in the representation of extreme events in climate models to assess the future risks and engineering design related to large-scale infrastructure in China.
基金supported by China Postdoctoral Science Foundation(2012M520205)supported by National Natural SciencesFoundation of China(11171229,11231006)Project of Beijing Chang Cheng Xue Zhe
文摘In this article, we prove the local existence and uniqueness of the classical solution to the Cauchy problem of the 3-D compressible Navier-Stokes equations with large initial data and vacuum, if the shear viscosity μ is a positive constant and the bulk viscosity λ（ρ） = ρ^β with β≥0. Note that the initial data can be arbitrarily large to contain vacuum states.
文摘Iron and Manganese contents and parameters including pH, conductivity, and organic matter contents were determined in the sediments of the Okpara dam in Northern Benin. Fifteen samples were collected during a one-month period and analysed in laboratory using the method of sequential extraction of Tessier. The analyses indicated that sediments contained high concentrations in reducible fraction of Iron and relatively high contents of exchangeable fraction, acidhydrolysable fraction and residual fraction of Manganese. The findings of this study confirmed the hypotheses that the meal contents of the sediments were relatively high and varied according to the geochemical phases.
基金support from CAPES-Coorde nação de Aperfeiçoamento de Pessoal de Nível Superior(PROEX and PrInt Programs)CNPq-Conselho Nacional de Desenvolvimento Científico e Tecnológico(307576/2018-3 and 420275/2018-5)and FAPESC-Fundação de AmparoàPesquisa do Estado de Santa Catarina.
文摘Esterification is an important process in the food industry and can be carried out via homogeneous or heterogeneous catalysis.The homogeneous catalyst,despite providing high conversion,can cause corrosion in reactors,which is not observed with the use of heterogeneous catalysts.However,some of these catalysts require a high process temperature and may lose their catalytic activity with reuse.Thus,catalytic membranes have been proposed as a promising alternative.The combination of catalysis and separation in a single module provides greater conversion,reduction of excess reagents,compact industrial plant,making the process more efficient.Within this context,this work aims to present a literature review on the catalytic membrane for the synthesis of esters,improving the understanding of the production and development.This review examines the materials,catalysts used,and synthetic pathways.A comparison between the methods,as well as limitations and gaps in the literature,are highlighted.
基金Supported by the National Basic Research Program of China under Grant No 2007CB815103, and the National Natural Science Foundation of China under Grant Nos 10935003, 10775020 and 11075024.
文摘We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh-Taylor instability （ARTI） experiments by numerical simulations. A preheating model k（T） = KSH[1＋f（T）], where KSH is the Spitzer Harm （SH） electron conductivity and f（T） interprets the preheating tongue effect in the cold plasma ahead of the ablative front [Phys. Rev. E 65 （2002） 57401], is introduced in simulations. The simulation results of the nonlinear evolution of the ARTI are in general agreement with the experiment results. It is found that two factors, i.e., the suppressing of ablative Kelvin Helmholtz instability （AKHI） and the heat flow cone in the spike tips, contribute to the formation of jet-like long spike in the nonlinear evolution of the ARTI.
文摘The RE-Fe-B permanent magnets have a complex microstructure and they are susceptible to corrosion process. In this paper, the commercial nickel coatings adhesion was investigated. The microstructure of the RE-Fe-B without coating was analyzed by scanning electronic microscopy and electrochemical techniques. The interface magnet/coating was studied by scanning electron microscopy and the nickel-plated Nd-Fe-B commercial magnets were tested in a salt spray chamber. The ferromagnetic and RE-rich phases were observed. After the anodic polarization curve, a strong intergranular corrosion was observed and the RE-rich phase was preferentially attacked. The interface magnet/Ni coating presented inter-granular corrosion that can affect the nickel coating adherence. This attack had probably occurred during the electrodeposition process. Not all the samples suffered localized corrosion during the salt spray tests and the Ni triple-layer coating presented a few corrosion points. RE-Fe-B alloy magnets need to be protected with appropriate coatings to each environment to which they will be exposed and the protective coating must not be damaged.
基金Project supported by the Beijing Municipal Natural Science Foundation,China(Grant No.2182042)the National Natural Science Foundation of China(Grant Nos.11875004,11505006,and 11604008)
文摘The structural, mechanical and electronic properties of W_(1-x)Zr_x(x=0.0625, 0.125, 0.1875, 0.25, 0.5) are systematically investigated by means of first-principles calculation. The total-energy calculations demonstrate that the W–Zr binary substitutional solid solution remaining bcc structure can be formed at an atom level. In addition, the derived bulk modulus(B), shear modulus(G), Young's modulus(E) for each of W–Zr alloys decrease gradually with the increase of Zr concentration, suggesting that W alloying with higher Zr concentration becomes softer than pure W metal. Based on the mechanical characteristic B/G ratio, Poisson's ratio υ and Cauchy pressure C, all W_(1-x)Zr_x alloys are regarded as ductile materials. The ductility for each of those materials is improved with the increase of Zr concentration. The calculated density of states indicates that the ductility of W_(1-x)Zr_x is due to the fact that the bonding in the alloy becomes more metallic through increasing the Zr concentration in tungsten. These results provide incontrovertible evidence for the fact that Zr has a significant influence on the properties of W.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51071032 and 11074155the National Basic Security Research Program of China,and the Foundations for Development of Science and Technology of China Academy of Engineering Physics under Grant No 2009B0301037.
文摘We perform a first-principles computational tensile test on PuO_(2)based on density-functional theory within a local density approximation(LDA)+U formalism to investigate its structural,mechanical,magnetic and intrinsic bonding properties in four representative directions:[001],[100],[110]and[111].The stress-strain relations show that the ideal tensile strengths in the four directions are 81.2,80.5,28.3 and 16.8 GPa at strains of 0.36,0.36,0.22 and 0.18,respectively.The[001]and[100]directions are prominently stronger than the other two directions since more Pu-0 bonds participate in the pulling process.By charge and density of state analysis along the[001]direction,we find that the strong mixed ioni%ovalent character of the Pu-0 bond is weakened by tensile strain and PuO_(2)will exhibit an insulator-to-metal transition after tensile stresses exceeding about 79 GPa.
基金the National Natural Science Foundation of China(Grant Nos.11874247 and U1530258)the National Key R&D Program of China(Grant No.2017YFA0304500)+2 种基金the 111 Plan of China(Grant No.D18001)the Hundred Talent Program of the Shanxi Province(2018)the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices of China(Grant Nos.KF201703 and KF201904).
文摘The elastic anisotropy and superconductivity upon hydrostatic compression ofα,ω,and β Hf are investigated using first-principle methods.The results of elastic anisotropies show that they increase with increasing pressure for α and ω phases,while decrease upon compression forβphase.The calculated superconducting transition temperatures are in excellent agreement with experiments.Electron-phonon coupling constants(λ)are increasing with pressure for α and ω phases,while decreasing for β phase.For β phase,the large values ofλare mainly due to the obvious TA1 soft mode.Under further compression,the TA1 soft vibrational mode will disappear gradually.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10904004,10604010,60776063,50471070 and 50644041)
文摘Using first-principles calculations, we systematically study the potential energy surfaces and dissociation processes of the hydrogen molecule on the Mg（0001） surface. It is found that during the dissociative adsorption process with the minimum energy barrier, the hydrogen molecule first orients perpendicularly, and then rotates tobecome parallel to the surface. It is also found that the orientation of the hydrogen molecule in the transition state is neither perpendicular nor parallel to the surface. Most importantly we find that the rotation causes a reduction of the calculated dissociation energy barrier for the hydrogen molecule. The underlying electronic mechanism for the rotation of the hydrogen molecule is also discussed in the paper.
基金supported by the National Natural Science Foundation of China(Grant No.2011CBA00108)the National Basic Research Program of China(Grant No.2013CB921700)the Foundation of LCP
文摘In order to calculate the electronic structure of correlated materials, we propose implementation of the LDA＋Gutzwiller method with Newton＇s method. The self-consistence process, efficiency and convergence of calculation are improved dramatically by using Newton＇s method with golden section search and other improvement approaches.We compare the calculated results by applying the previous linear mix method and Newton＇s method. We have applied our code to study the electronic structure of several typical strong correlated materials, including SrVO3, LaCoO3, and La2O3Fe2Se2. Our results fit quite well with the previous studies.
基金Supported by the Foundation for Development of Science and Technology of China Academy of Engineering Physics under Grant No.2009B0301037
文摘Quantum molecular dynamic (QMD) simulations have been applied to study the thermophysical properties of liquid xenon under dynamic compressions. The equation of state (EOS) obtained from QMD calculations are corrected according to Saha equation, and contributions from atomic ionization, which are of predominance in determining the EOS at high temperature and pressure, are considered. For the pressures below 160 GPa, the necessity in accounting for the atomic ionization has been demonstrated by the Hugoniot curve, which shows excellent agreement with previous experimental measurements, and three levels of ionization have been proved to be sufficient at this stage.
