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Search Results: 1 - 10 of 1464 matches for " Magnetohydrodynamic waves "
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On the coronal heating mechanism by the resonant absorption of Alfven waves
H. Y. Alkahby
International Journal of Mathematics and Mathematical Sciences , 1993, DOI: 10.1155/s0161171293001012
Abstract: In this paper, we will investigate the heating of the solar corona by the resonant absorption of Alfven waves in a viscous and isothermal atmosphere permeated by a horizontal magnetic field. It is shown that if the viscosity dominates the motion in a high (low)- 2 plasma, it creates an absorbing and reflecting layer and the heating process is acoustic (magnetoacoustic). When the magnetic field dominates the oscillatory process it creates a non-absorbing reflecting layer. Consequently, the heating process is magnetohydrodynamic. An equation for resonance is derived. It shows that resonances may occur for many values of the frequency and of the magnetic field if the wavelength is matched with the strength of the magnetic field. At the resonance frequencies, magnetic and kinetic energies will increase to very large values which may account for the heating process. When the motion is dominated by the combined effects of the viscosity and the magnetic field, the nature of the reflecting layer and the magnitude of the reflection coefficient depend on the relative strengths of the magnetic field and the viscosity.
Propagation of linear MHD waves in a hydrogen plasma: the mode crossing problem
Tremola, C;Sigalotti, L. Di G;Sira, E;
Revista mexicana de física , 2006,
Abstract: here we use linear analysis to investigate the propagation of small thermal and magnetohydrodynamic (mhd) disturbances in a heat-conducting, ionizing-recombining, hydrogen plasma threaded by an external uniform magnetic field. linearization of the governing mhd equations for this model leads to a dispersion equation for the wavenumber k as a function of the frequency ω which may be either quadratic or cubic in k2, depending on the orientation of the magnetic field. in either case, the solution of the dispersion equation is such that crossing of the roots may happen at some frequencies, implying that they may not always correspond to the same particular physical wave. the crossing of modes is merely a mathematical property of the solution and must not be interpreted as an interchange of the thermal and mhd waves' physical nature at the crossing frequency. here we find that mode crossing is a function of the wave frequency, plasma temperature, magnetic field strength and orientation.
What geometrical factors determine the in situ solar wind speed?
Bo Li,Yao Chen,LiDong Xia
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-011-4965-2
Abstract: At present it remains to address why the fast solar wind is fast and the slow wind is slow. Recently we have shown that the field line curvature may substantially influence the wind speed ν, thereby offering an explanation for the Arge et al. finding that ν depends on more than just the flow tube expansion factor. Here we show by extensive numerical examples that the correlation between ν and field line curvature is valid for rather general base boundary conditions and for rather general heating functions. Furthermore, the effect of field line curvature is even more pronounced when the proton-alpha particle speed difference is examined. We suggest that any solar wind model has to take into account the field line shape for any quantitative analysis to be made.
Steady Magnetohydrodynamic Equations for Quantum Plasmas  [PDF]
Muhammad Asif, Umar Bashir
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.312233
Abstract: Steady Magnetohydrodynamic (MHD) Equations of force, density and energy for quantum plasmas have been derived. These equations constitute our Steady Magnetohydrodynamic model for quantum plasmas. All the quantum effects are contained in the last term of quantum force equation and in the last three terms of quantum Energy Equation, so-called Bohm potential and may be valuable for the description of quantum phenomena like tunneling.
Coronal Holes
Steven R. Cranmer
Living Reviews in Solar Physics , 2009,
Abstract: Coronal holes are the darkest and least active regions of the Sun, as observed both on the solar disk and above the solar limb. Coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. This paper reviews measurements of the plasma properties in coronal holes and how these measurements are used to reveal details about the physical processes that heat the solar corona and accelerate the solar wind. It is still unknown to what extent the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wave-like fluctuations), and to what extent much of the mass and energy is input intermittently from closed loops into the open-field regions. Evidence for both paradigms is summarized in this paper. Special emphasis is also given to spectroscopic and coronagraphic measurements that allow the highly dynamic non-equilibrium evolution of the plasma to be followed as the asymptotic conditions in interplanetary space are established in the extended corona. For example, the importance of kinetic plasma physics and turbulence in coronal holes has been affirmed by surprising measurements from the UVCS instrument on SOHO that heavy ions are heated to hundreds of times the temperatures of protons and electrons. These observations point to specific kinds of collisionless Alfvén wave damping (i.e., ion cyclotron resonance), but complete theoretical models do not yet exist. Despite our incomplete knowledge of the complex multi-scale plasma physics, however, much progress has been made toward the goal of understanding the mechanisms ultimately responsible for producing the observed properties of coronal holes.
Unsteady Magnetohydrodynamic Boundary Layer Flow near the Stagnation Point towards a Shrinking Surface  [PDF]
Santosh Chaudhary, Pradeep Kumar
Journal of Applied Mathematics and Physics (JAMP) , 2015, DOI: 10.4236/jamp.2015.37112
Abstract: The unsteady two-dimensional, laminar flow of a viscous, incompressible, electrically conducting fluid towards a shrinking surface in the presence of a uniform transverse magnetic field is studied. Taking suitable similarity variables, the governing boundary layer equations are transformed to ordinary differential equations and solved numerically by a perturbation technique for a small magnetic parameter. The effects of various parameters such as unsteadiness parameter, velocity parameter, magnetic parameter, Prandtl number and Eckert number for velocity and temperature distributions along with local Skin friction coefficient and local Nusselt number have been discussed in detail through numerical and graphical representations.
Stationary Flow of Blood in a Rigid Vessel in the Presence of an External Magnetic Field: Considerations about the Forces and Wall Shear Stresses  [PDF]
Agnès Drochon, Vincent Robin, Odette Fokapu, Dima Abi-Abdallah Rodriguez
Applied Mathematics (AM) , 2016, DOI: 10.4236/am.2016.72012
Abstract: The magnetohydrodynamics laws govern the motion of a conducting fluid, such as blood, in an externally applied static magnetic field B0. When an artery is exposed to a magnetic field, the blood charged particles are deviated by the Lorentz force thus inducing electrical currents and voltages along the vessel walls and in the neighboring tissues. Such a situation may occur in several biomedical applications: magnetic resonance imaging (MRI), magnetic drug transport and targeting, tissue engineering… In this paper, we consider the steady unidirectional blood flow in a straight circular rigid vessel with non-conducting walls, in the presence of an exterior static magnetic field. The exact solution of Gold (1962) (with the induced fields not neglected) is revisited. It is shown that the integration over a cross section of the vessel of the longitudinal projection of the Lorentz force is zero, and that this result is related to the existence of current return paths, whose contributions compensate each other over the section. It is also demonstrated that the classical definition of the shear stresses cannot apply in this situation of magnetohydrodynamic flow, because, due to the existence of the Lorentz force, the axisymmetry is broken.
Magnetohydrodynamic Calculations of Toroidal Fusion Reactor to Ensure Stable Control  [PDF]
Aybaba Han?erlio?ullari, Asli Kurnaz, Yosef G. Ali Madee
Open Journal of Applied Sciences (OJAppS) , 2016, DOI: 10.4236/ojapps.2016.67041
Abstract: The development of magnetic configurations to confine the stability fluid plasmas for fusion energy is a challenge that is a mixture of basic fusion engineering and invention. In order to keep the fusion reactions in the plasma to be continuing in the fusion reactors, the speed of tritium breeding (TBR) should be kept above a certain value. At the Apex fusion reactor, a fast flowing thin liquid wall has replaced the solid first wall concept of the traditional reactors. Behind the fast flowing thin liquid wall, a slower and thicker second liquid wall (coat) is present. Monte Carlo Random method (MCRS) is the general name for the solution of experimental and statistical problems with a random approach. This method is dependent upon the theory of probability. In the present work, Mhd impacts are investigated quite unimportant for Flibe salt solutions. In this study, the fissile fuel production calculations are done for a neutron wall load of 10 MW/m2 fissile fuel production rates of 238U(n, γ)239Pu and 232Th(n,γ)233U increases almost linearly with increased heavy metal content.
Impact of an External Magnetic Field on the Shear Stresses Exerted by Blood Flowing in a Large Vessel  [PDF]
Agnès Drochon, Manon Beuque, Dima Abi-Abdallah Rodriguez
Journal of Applied Mathematics and Physics (JAMP) , 2017, DOI: 10.4236/jamp.2017.57122
Abstract: The aim of this paper is to provide an advanced analysis of the shear stresses exerted on vessel walls by the flowing blood, when a limb or the whole body, or a vessel prosthesis, a scaffold… is placed in an external static magnetic field B0. This type of situation could occur in several biomedical applications, such as magnetic resonance imaging (MRI), magnetic drug transport and targeting, tissue engineering, mechanotransduction studies… Since blood is a conducting fluid, its charged particles are deviated by the Hall effect, and the equations of motion include the Lorentz force. Consequently, the velocity profile is no longer axisymmetric, and the velocity gradients at the wall vary all around the vessel. To illustrate this idea, we expand the exact solution given by Gold (1962) for the stationary flow of blood in a rigid vessel with an insulating wall in the presence of an external static magnetic field: the analytical expressions for the velocity gradients are provided and evaluated near the wall. We demonstrate that the derivative of the longitudinal velocity with respect to the radial coordinate is preponderant when compared to the θ-derivative, and that elevated values of B0 would be required to induce some noteworthy influence on the shear stresses at the vessel wall.
A Review of Some Reference Analytic Solutions for the Magnetohydrodynamic Flow of Blood  [PDF]
Agnès Drochon, Manon Beuque, Dima Abi-Abdallah Rodriguez
Applied Mathematics (AM) , 2018, DOI: 10.4236/am.2018.910078
Abstract:
A short review of some reference solutions for the magnetohydrodynamic flow of blood is proposed in this paper. We present in details the solutions of Hartmann (1937), of Vardanyan (1973) and of Sud et al. (1974). In each case, a comparison is provided with the corresponding solution for the flow without any external magnetic field, namely Poiseuille (plane or cylindrical) and Womersley. We also present a synopsis of some other solutions for people who would like to go further in this topic. The interest in MHD flow of blood may be motivated by many reasons, such as Magnetic Resonance Imaging (MRI), Pulse Wave Velocity measurement, magnetic drug targeting, tissue engineering, mechanotransduction studies, and blood pulse energy harvesting… These fundamental solutions should also be used as particular limiting cases to validate any proposed more elaborated solutions or to validate computer codes.
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