magnetic field

摘要： In this research,a numerical study of mixed convection of non-Newtonian fluid and magnetic field effect along a vertical wavy surface was investigated.A simple coordinate transformation to transform wavy surface to a flat surface is employed.A cubic spline collocation numerical method is employed to analyze transformed equations.The effect of various parameters such as Reynolds number,volume fraction 0-,Hartmann number,and amplitude of wave length was evaluated in improving the performance of a wavy microchannel.According to the presented results,the sinusoidal shape of the microchannel has a direct impact on heat transfer.By increasing the microchannel wave amplitude,the Nusselt number has risen.On the other hand,increasing the heat transfer in the higher wavelength ratio corrugated channel is seen as an effective method of increasing the heat transfer,especially at higher Reynolds numbers.The results showed that with increasing Hartmann numbers,the flow line near thewall becomesmore regular and,according to the temperature gradient created,theNusselt number growth.

摘要： The Earth’s magnetosphere is a magnetic shield that protects Earth from high-energy particles and is subject to a series of internal processes caused by jets of the solar wind (SW) that destabilize it. These disturbances affect health as well as technology and become more extreme when SW is more accelerated. Thus, to better understand the impact of high-speed solar wind (HSSW) invasion on the dynamics of the magnetospheric system, a statistical study of HSSW populations was conducted for even (20 and 22) and odd (21 and 23) solar cycles. The regression analysis using the solar-derived fields from all solar cycles, indicates three states of the inner magnetosphere: 1) the 00:00UT-15:00UT period marked by a magnetic reconnection on the day side of the Earth closest to the Sun with the interplanetary magnetic field (IMF) facing South;2) the 15:00UT-21:00UT period where IMF changes from South to North and remains there until 21:00UT;and 3) the 21:00UT-24:00UT period where there is a reconnection on the night side with stretched field lines. Observations made at different phases of solar activity lead us to suggest that the magnetospheric electric field (EM) and the Bz component of IMF (IMF-Bz) are strongly correlated not only at a particular time scale, but at different time scales. We believe that the daily fluctuations of the electrical and magnetic effects of magnetospheric origin currents play a very important role in the dayside magnetic reconnection rate. Moreover, examination of the cycles with different parities shows important amplitudes of the solar causes for the even cycles compared to the odd solar cycles. Therefore, even solar cycles have a strong influence on our socio-economic system compared to odd cycles.

摘要： This study aims to investigate the influential role of space weather parameters on the transmission of COVID-19. Solar radio flux, interplanetary magnetic field, Dst index, sunspot number, and solar wind speed were utilized to represent the space weather variables. The association of the considered variables to the number of the confirmed COVID-19 cases worldwide along with five geographical categories, i.e. Asia, Europe, Africa, South, and North America, were investigated for a period ranging from 20 January 2020 to 5 August 2021 using Pearson linear tests as well as the non-parametric Spearman’s and Kendall’s rank correlation tests. Pearson linear tests showed that the number of confirmed COVID-19 cases worldwide and the chosen geographical categories have a significant correlation to interplanetary magnetic strength, solar radio flux F10.7, and sunspot number. When the confirmed COVID-19 cases reported in the Asia continent were excluded, the solar wind speed correlated significantly with the number of COVID-19 cases reported elsewhere in the world and the other geographical categories. The non-parametric Kendall and Pearson tests showed that the world’s COVID-19 cases and the other geographical categories had significant correlations with the interplanetary magnetic field, radio flux F10.7, sunspot number, and the solar wind speed, but not with the Dst index.

摘要： An extensive analysis of iron-nitrogen-carbon(Fe-N-C)electrocatalysts synthesis and activity is presented concerning synthesis conditions such as initial Fe content,pyrolysis temperature and atmosphere(inert N_(2),reducing NH_(3),oxidizing Cl_(2) and their sequential combinations)and the influence of an external magnetic field on their performance in oxygen reduction reaction(ORR).Thermosetting porous polymers doped with FeCl_(3) were utilized as the Fe-N-C catalysts precursors.The pyrolysis temperature was varied within a 700-900°Crange.The temperature and atmosphere of pyrolysis strongly affect the porosity and compositi on of the resultant Fe-N-C catalysts,while the in itial amount of Fe precursor shows much weaker impact.Pyrolysis under NH_(3) yields materials similar to those pyrolyzed under an inert atmosphere(N_(2)).In contrast,pyrolysis under Cl_(2) yields carbon of peculiar character with highly disordered structure and extensive microporosity.The application of a static external magnetic field strongly enhances the ORR process(herein studied in an alkaline environment)and the enhancement correlates with the Fe content in the Fe-N-C catalysts.The Fe-N-C materials containing ferromagnetic iron phase embedded in N-doped microporous carbon constitute attractive catalysts for magnetic field-aided anion exchange membrane fuel cell technology.

摘要： An upper atmospheric phenomenon i.e., sprites can be thought to be mainly caused by the propagation of positive corona streamers. This research presents the formulation for the calculation of radiation power received from the propagating corona streamers responsible for the origination of the sprites. The produced magnetic field variation using the calculated electromagnetic radiation power is found to be similar with the previous observation-based research work.

摘要： This paper presents a theoretical model for the size-dependent band structure of magneto-elastic phononic crystal(PC)nanoplates according to the Kirchhoff plate theory and Gurtin-Murdoch theory,in which the surface effect and magneto-elastic coupling are considered.By introducing the nonlinear coupling constitutive relation of magnetostrictive materials,Terfenol-D/epoxy PC nanoplates are carried out as an example to investigate the dependence of the band structure on the surface effect,magnetic field,pre-stress,and geometric parameters.The results show that the surface effect has promotive influence on dispersion curves of the band structure,and the band gaps can be improved gradually with the increase in the material intrinsic length.Meanwhile,the band gaps exhibit obvious nonlinear coupling characteristics owing to the competition between the magnetic field and the pre-stress.By considering the surface effect and magneto-elastic coupling,the open and closed points of band gaps are found when the lattice constant to thickness ratio increases.The study may provide a method for flexible tunability of elastic wave propagation in magneto-elastic PC nanoplates and functional design of highperformance nanoplate-based devices.

摘要： The present study concerns the modelization and numerical simulation for the heat and flow exchange characteristics in a novel configuration saturated with a nonNewtonian Ag-MgO hybrid nanofluid.The wavy shaped enclosure is equipped with onequarter of a conducting solid cylinder.The system of equations resulting from the mathematical modeling of the physical problem in its dimensionless form is discretized via the higher-order Galerkin-based finite element method(GFEM).The dependency of various factors and their interrelationships affecting the hydro-thermal behavior and heat exchange rate are delineated.The numerical experiments reveal that the best heat transfer rate is achieved for the pseudo-plastic hybrid nanoliquid with high Rayleigh number and thermal conductivity ratio and low Hartmann number.Besides,the power-law index has a major effect in deteriorating the heat convection at high Rayleigh number.

摘要： This paper addresses the 3-D Cauchy problem of a fluid-particle system with a magnetic field.First,the local classical solutions of the linearized model on the sphere Br are obtained by some a priori estimates that do not depend on the radius r.Second,the classical solutions of the linearized model in R^(3) are obtained by combining the continuation and compactness methods.Finally,the classical solutions of the original system are proved by use of the picard iteration argument and the energy method.

摘要： Magnetic induction-free abrasive wire sawing(MIFAWS)is a method that combines magnetic fields with traditional free abrasive wire sawing technologies.Magnetic abrasive particles(MAPs)are attracted on a magnetized wire,thus leading to an increase in their number into the cutting zone.The number of instantaneous-effective abrasive particles(IEAPs)adsorbed on the wire surface has a great influence on the cutting efficiency of the saw wire.In this study,a mathematic model of the movement of the MAP is presented,and the factors influencing the IEAPs number,including slurry-supply speed and slurry dynamic viscosity,are investigated both by means of simulation analysis and experiments.The results indicate that the number of IEAPs decreases with an increase in the slurry supply speed.The cutting efficiency increases gradually with the increase of slurry supply speed,but the growth rate of wire saw cutting efficiency slows down when the slurry supply speed exceeds a given threshold.The number of IEAPs adsorbed by saw wire increases with a decrease in the dynamic viscosity of the cutting fluid,while the cutting efficiency first increases and then decreases.The cutting efficiency attains its highest value when the dynamic viscosity of the cutting fluid is 0.0047 Pa⋅s.The experimental results agree with the simulation results,and provide some guidance for the practical application of the MIFAWS process.

摘要： The present investigation is intended to demonstrate the magnetic field,relaxation time,hydrostatic initial stress,and two temperature on the thermal shock problem.The governing equations are formulated in the context of Lord-Shulman theory with the presence of bodily force,two temperatures,thermal shock,and hydrostatic initial stress.We obtained the exact solution using the normal mode technique with appropriate boundary conditions.The field quantities are calculated analytically and displayed graphically under thermal shock problem with effect of external parameters respect to space coordinates.The results obtained are agreeing with the previous results obtained by others when the new parameters vanish.The results indicate that the effect of magnetic field and initial stress on the conductor temperature,thermodynamic temperature,displacement and stress are quite pronounced.In order to illustrate and verify the analytical development,the numerical results of temperature,displacement and stress are carried out and computer simulated results are presented graphically.This study helpful in the development of piezoelectric devices.