The purpose of this paper is to study the characteristics of the combined convection heat transfer and a micropolar nanofluid flow passing through an impermeable stretching sheet in a porous medium.The nanofluid flow ...The purpose of this paper is to study the characteristics of the combined convection heat transfer and a micropolar nanofluid flow passing through an impermeable stretching sheet in a porous medium.The nanofluid flow field is affected by a magnetic field perpendicular to the sheet.The dynamic viscosity of the micropolar nanofluid changes under the influence of the magnetic field.The continuity,linear momentum,angular momentum,and energy equations are first simplified using the order of magnitude technique that,along with the applied boundary conditions and the definition of the appropriate parameters,are transferred to the similarity space using the similarity analysis.Then the resulting equations are solved using the Runge–Kutta method.The distinction of the macroscale and microscale flow fields and temperature fields resulting from different nanoparticle shapes was clarified.Increasing the Hartmann number,the vortex viscosity parameter,the magnetic parameter,the nanoparticle volume fraction,and the permeability parameter of the porous media increased the surface friction on the sheet.Increasing the vortex viscosity parameter,the magnetic parameter,and the volume fraction of the nanoparticles increases the Nusselt number.展开更多
Electron-positron pair production in spatial inhomogeneous electric fields with sinusoidal phase modulation is studied within the Dirac-Heisenberg-Wigner formalism.The focus is on discussing the effects of the modulat...Electron-positron pair production in spatial inhomogeneous electric fields with sinusoidal phase modulation is studied within the Dirac-Heisenberg-Wigner formalism.The focus is on discussing the effects of the modulation parameters on the momentum spectrum and the reduced particle number at various spatial scales.For the momentum spectrum,the interference effect becomes more and more remarkable with the increase of modulated amplitude or frequency,while the symmetry is severely destroyed with modulated amplitude.For the reduced particle number,it is greatly enhanced by about a few times and evenly one order of magnitude when modulation parameters are applied.Moreover,the effect of spatial scales on the reduced particle number is carefully examined,and it is found that it increases rapidly at small spatial scales,while it tends to be a constant at large spatial scales.We also obtain the optimal pair production that can be achieved through different modulations.These results can provide a possibility for realizing the optimal pair production by combining the advantages of field spatial inhomogeneity with different choices of phase modulation.展开更多
基金the financial supports of the National Natural Science Foundation of China(No.51776165)supported by the China Fundamental Research Funds for the Central Universities.
文摘The purpose of this paper is to study the characteristics of the combined convection heat transfer and a micropolar nanofluid flow passing through an impermeable stretching sheet in a porous medium.The nanofluid flow field is affected by a magnetic field perpendicular to the sheet.The dynamic viscosity of the micropolar nanofluid changes under the influence of the magnetic field.The continuity,linear momentum,angular momentum,and energy equations are first simplified using the order of magnitude technique that,along with the applied boundary conditions and the definition of the appropriate parameters,are transferred to the similarity space using the similarity analysis.Then the resulting equations are solved using the Runge–Kutta method.The distinction of the macroscale and microscale flow fields and temperature fields resulting from different nanoparticle shapes was clarified.Increasing the Hartmann number,the vortex viscosity parameter,the magnetic parameter,the nanoparticle volume fraction,and the permeability parameter of the porous media increased the surface friction on the sheet.Increasing the vortex viscosity parameter,the magnetic parameter,and the volume fraction of the nanoparticles increases the Nusselt number.
基金the National Natural Science Foundation of China(NSFC)under Grant No.11875007 and No.11935008
文摘Electron-positron pair production in spatial inhomogeneous electric fields with sinusoidal phase modulation is studied within the Dirac-Heisenberg-Wigner formalism.The focus is on discussing the effects of the modulation parameters on the momentum spectrum and the reduced particle number at various spatial scales.For the momentum spectrum,the interference effect becomes more and more remarkable with the increase of modulated amplitude or frequency,while the symmetry is severely destroyed with modulated amplitude.For the reduced particle number,it is greatly enhanced by about a few times and evenly one order of magnitude when modulation parameters are applied.Moreover,the effect of spatial scales on the reduced particle number is carefully examined,and it is found that it increases rapidly at small spatial scales,while it tends to be a constant at large spatial scales.We also obtain the optimal pair production that can be achieved through different modulations.These results can provide a possibility for realizing the optimal pair production by combining the advantages of field spatial inhomogeneity with different choices of phase modulation.
