Structural instabilities in soft electro-magneto-elastic cylindrical membranes

Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects

We carried out global three-dimensional resistive magnetohydrodynamic simulations of galactic gaseous disks to investigate how the galactic magnetic fields are amplified and maintained. We adopt a steady axisymmetric gravitational potential given by \cite*{Miy80}. As the initial condition, we assume a warm ($T\sim10^{5} \mathrm{K}$) rotating gas torus centered at $\varpi=10 \mathrm{kpc}$ threaded by weak azimuthal magnetic fields. Numerical results indicate that in differentially rotating galactic gaseous disks, magnetic fields are amplified due to magneto-rotational instability and magnetic turbulence develops. After the amplification of magnetic energy saturates, the disk stays in a quasi-steady state. The mean azimuthal magnetic field increases with time and shows reversals with period of 1Gyr (2Gyr for a full cycle). The amplitude of $B_{\phi}$ near the equatorial plane is $B_{\phi}\sim1.5\mu \mathrm{G}$ at $\varpi=5 \mathrm{kpc}$. The magnetic fields show large fluctuations whose standard deviation is comparable to the mean field. The mean azimuthal magnetic field in the disk corona has direction opposite to the mean magnetic field inside the disk. The mass accretion rate driven by the Maxwell stress is $\sim10^{-3}M_{\odot}/ \mathrm{yr}$ at $\varpi=2.5 \mathrm{kpc}$ when the mass of the initial torus is $\sim5\times10^{8}M_{\odot}$.

We use a full-wave approach based on the finite-element method solution to Maxwell's equations for the evaluation of the effect of an ocean-land mixed propagation path on the above-ground lightning electromagnetic fields and their induced voltages on overhead lines. Two cases of normal and oblique strikes are studied. For normal strike, it is shown that neither the vertical electric field nor the azimuthal magnetic field is affected by the considered mixed propagation path. For an oblique strike, however, the azimuthal magnetic field is slightly affected when the observation point is close to the ocean-land interface (i.e., 5 m or so), while the vertical electric field remains unchanged. For both normal and oblique strikes, at moderate and far distances from the channel base and when the observation point is located in the vicinity of the ocean-land interface, the radial electric field is markedly affected by this interface. For the calculation of lightning-induced voltages, two cases, namely, the ocean-side and the river-crossing transmission lines are studied. For the ocean-side transmission line, as the overhead line gets closer to the ocean, the induced voltages on the line midpoint decrease while increasing behavior is observed in the voltages induced on the line terminations. For the river-crossing transmission line, the lightning-induced voltages along the line experience a significant change in terms of their peak values and waveshapes. In some cases, the enhancement in induced voltages can be as high as a factor of 2 with respect to that obtained by assuming a homogeneous propagation path characterized by the electrical properties of the land.

Similarity solution for magnetogasdynamic shock wave in a perfectly conducting dusty gas with axial or azimuthal magnetic field in rotating medium under the influence of radiative and conductive heat fluxes

A Nine-Electrode Probe (NEP) has been developed for simultaneous measurement of all terms in the ideal Ohm’s law E+U×B=0 in the radial (r̂) direction in cylindrical geometry, where E is the electric field, U is the plasma flow velocity, and B is the magnetic field. The probe consists of two pairs of directional Langmuir probes (“Mach” probes) to measure the axial (ẑ) and azimuthal (θ̂) plasma flows, two pairs of floating Langmuir probes at different radial positions to measure the radial electric field, and two B-dot coils to measure the axial and azimuthal magnetic field. The measurement is performed in the Flowing Magnetized Plasma (FMP) experiment. Two flow patterns are identified in the FMP experiment by the NEP. The peak-to-peak values of radial electric field fluctuation is 1.5–4 times of the mean values. Comparisons of ∣U×B∣r and Er show that Er+ ∣U×B∣r is not zero within some periods of discharge. This deviation suggests non-ideal effects in Ohm’s law can not be neglected.

The onset of electrohydrcdynamic instability in an uniformly aligned nematic Liquid crystal under a steady magnetic field and a low frequency electric field has been theoretically investigated, taking into account the boundary conditions. The result shows that the threshold voltage for the onset of instability and the ratio of wavelength of Williams domain to the sample thickness are functions of the product of the magnetic field intensity and the sample thickness, defined here as β, as well as on the direction of the applied magnetic field.

In this paper, a precise small 5-DOF (degree of freedom) force sensor is proposed for use in a strong EMF (electromagnetic field) environment. Detecting modules using CFPs (carbon fiber plates) and transducing modules using the optical modulation principle are adopted in order not to be affected by the EMF. For miniaturization of the multi-DOF force sensor, a 2-DOF transducing module using a spherical mirror and a 3-DOF transducing module using a plane mirror were designed and integrated. The design parameters of highly sensitive transducing modules were investigated and determined experimentally. To combine with these transducing modules, a 2-DOF detecting module using CFP single leaf springs and a 3-DOF detecting module using a CFP tripod spring were also designed. Considering the easy calibration process and convenient design change, the elastic detecting modules were designed so that they deform independently according to each input force component. A calibration test confirmed that the detecting modules deform linearly and independently of the input force. The results of the evaluation tests showed that the range and resolution of forces were ±4 N and 0.94–7.1 mN and the range and resolution of moments were ±120 N mm and 0.023–0.034 N mm, respectively. The high sensitivity and the linearity of the measuring results were also verified.

We have calculated the general dispersion relationship for surface waves on a\nferrofluid layer of any thickness and viscosity, under the influence of a\nuniform vertical magnetic field. The amplification of these waves can induce an\ninstability called peaks instability (Rosensweig instability). The expression\nof the dispersion relationship requires that the critical magnetic field and\nthe critical wavenumber of the instability depend on the thickness of the\nferrofluid layer. The dispersion relationship has been simplified into four\nasymptotic regimes: thick or thin layer and viscous or inertial behaviour. The\ncorresponding critical values are presented. We show that a typical parameter\nof the ferrofluid enables one to know in which regime, viscous or inertial, the\nferrofluid will be near the onset of instability.\n

Effects of external fields, dimension and pressure on the electromagnetically induced transparency of quantum dots

The mean-field induction equation ∂ t B ¯ − η Δ B ¯ = ∇ × F is considered in a conducting volume V , where B ¯ is the mean magnetic field, ∂ t is rate of change and η is magnetic diffusivity. Using the Green's function method and the second-order correlation approximation (SOCA), or the nearly axisymmetric methods of Braginskii [Self excitation of a magnetic field during the motion of a highly conducting fluid. Sov. Phys. JETP 1964, 20], then the electromotive force F is F = α ⋅ B ¯ . This work consists of two parts. Part I: The following antidynamo theorem (ADT) is derived: if there is no generation of azimuthal F from azimuthal B ¯ , that is 1 ϕ ⋅ α ⋅ 1 ϕ = α ϕϕ = 0 , where 1 ϕ is the unit vector in the ϕ direction, ( s , ϕ , z ) cylindrical polar coordinates, then an axisymmetric magnetic field ( B ¯ ( s , z ) ) will decay. Firstly, the magnetic field in meridional planes is shown to decay to zero. Then the azimuthal component of the magnetic field is shown to decay. As a weighted measure of the magnetic energy, ‖ b ‖ 2 = ∫ V b 2 d V , where b = B ¯ ( s , ϕ ) ⋅ 1 ϕ / s , is considered. The resulting ‖ b ‖ 2 magnetic energy analysis demonstrates that; for α = α ( s , z ) , and α ϕϕ = 0 , once the meridional field has decayed, diffusion decreases energy to more than account for the inductive contributions due to α , and, consistent with the α ϕϕ = 0 ADT, the field decays. Numerical results and field plots using the model α = s 1 z 1 ϕ , illustrate the interaction mechanisms responsible for the diffusive dominance as induction is increased. Using the SOCA and Green's function analysis, an explicit formulation for α ϕϕ is derived. Thus, physical mechanisms for the generation of α ϕϕ are established. Conditions are produced for which α ϕϕ = 0 , including a conductor filling all space with zero mean flow and co-axisymmetric perturbation flow and mean magnetic field. Part II: The Eulerian approach of Braginskii (1964), where the fields are analysed as perturbations from axisymmetry, is extended to compressible velocity fields for appropriate stellar and planetary dynamos. The hybrid Euler–Lagrange approach of Soward and Roberts [Eulerian and Lagrangian means in rotating, magnetohydrodynamic flows II. Braginsky's nearly axisymmetric dynamo. Geophys. Astrophys. Fluid Dyn. 2014, 108], following Soward [A kinematic theory of large magnetic Reynolds number dynamos. Phil. Trans. R. Soc. A 1972, 272], is continued to compressible flow and non-isochoric transformations in cylindrical polar coordinates, producing results that can be used for more general, higher-order approximations. These compressible extensions produce an α ϕϕ component and other effects for a reformulation of the problem into new effective mean, magnetic and velocity fields. Each of these approaches provides insight into mechanisms responsible for generating this critical α ϕϕ component. Common to all these approaches is the induction mechanism generated by the non-zero mean helicity of the meridional perturbation velocity field. Conclusions for non-magnetic stars are proposed and implications for hidden dynamos are drawn.

There are many attempts to increase the germination rate of basidiospores using temperature, light or chemicals. The current study has been designed to use the magnetic and electromagnetic fields to stimulate the germination of basidiospores from Ganoderma applanatum. Mature, healthy and fresh basidiocarpe of Ganoderma applanatum (Aphyllophorales: hymenochaetaceae), causes white rot of hard wood was isolated from Alsantah city (Delta Nile region of Egypt) in autumn 2018 from Casuarina tree. Basidiospores were collected from the fruiting body and cultivated on different microbial growing media. Basidiospores were obtained and exposed to magnetic field (MF) and electromagnetic field (EMF) for different times of exposure extended for one hour. Basidiospores germination was stimulated when exposed to both fields. The electromagnetic field was more stimulating than the magnetic field in basidiospores germination where the spore’s germination rate reached 18.7% after exposure to the electromagnetic field for 40 min while the germination rate was 14.6% after exposure to magnetic field for 50 min. The fruiting body of the fungus was cultured to obtain fungal mycelium, and the resulting mycelium was exposed to the magnetic and electromagnetic field for different exposure times. The resulting mycelia was used to inoculate five different lignocellulosic substrate (Rice straw, Wheat straw, Wheat bran, Rice bran and Sawdust) using solid state fermentation in order to test its efficiency in these wastes degradation. Furthermore, Lignin degrading enzymes including (Laccase, Manganese-dependent peroxidases and Lignin peroxidase) were measured. The three tested enzymes showed a marked increase in their activity after exposure to the magnetic field for 20 minutes (laccase 17.8-unit, lignin peroxidase 11.1-unit and Mn dependent peroxidase 13.5- unit). Concerning the effect of electromagnetic field the activity of lignin degrading enzymes were enhanced after exposure to the electromagnetic field for 20 minutes (laccase 19.5- unit, lignin peroxidase 15.1-unit and Mn dependent peroxidase 27.4-unit). Therefore, the obtained data suggest that the using of both magnetic and electromagnetic fields could be used to break down the dormancy state of the basidiospores in order to increase the rate of spores germination and at the same time increase the activity of lignin degrading enzymes.

An asymptotic analysis is made of the magnetic induction equation for certain flows characterized by a large magnetic Reynolds number R. A novel feature is the hybrid approach given to the problem. Advantage is taken of a combination of Eulerian and Lagrange coordinates. Under certain conditions the problem can be reduced to solving a pair of coupled partial differential equations dependent on only two space coordinates (cf. Braginskii 1964 a). Two main cases are considered. First the case is examined, in which the production of azimuthal magnetic field from the meridional magnetic field by a shear in the aximuthal flow is negligible. It is shown that a term J (analogous to electric current) is related linearly to the vector B which determines the magnetic field. (Note that B is not the magnetic field vector: see (1.33) and (2.35 b).) The current J is likely to sustain dynamo action. Secondly, the case is considered, in which shearing of meridional magnetic field is the principal mechanism for creating the azimuthal magnetic field and the effect described above is one mechanism for creating meridional magnetic field from the azimuthal magnetic field. It is shown that the term J is not only linearly related to B, but has an additional contribution Px (V x B), where P is characterized by the flow (see (4.15)). Both these effects have been predicted previously in theories of dynamo action produced by turbulent motions. Under certain restrictive conditions the resulting equations in the second case reduce to Braginskil’s (1964 a, b) formulation for nearly symmetric dynamos. The words azimuthal and meridional are not used here in the usual sense. The difference in terminology is a consequence of a coordinate transformation.

A magnetically confined two-fluid plasma is considered in which the Ohmic heating of the electrons by a current driven parallel to an applied magnetic field is balanced by bremsstrahlung and equipartition to the ions. It is found that for a steady state the applied electric field must be below a critical value which in absence of bremsstrahlung is given by where the electrical conductivity is and the total pressure is p. Under this condition it is found that there are two /Futions for Te/Ti which satisfy the steady electron energy balance equation in a homogeneous, fully ionized plasma. One of these /Futions always has values above the critical value of Te/Ti (= 132 in absence of bremsstrahlung) for the onset of the electrothermal instability in a fully ionized gas. Inclusion of electron thermal conduction transverse to the magnetic field (with Hall parameter ) yields a wavelength for maximum growth of the instability of about , where ae is the electron Larmor radius. The steady non linear profiles showing current filamentation have been calculated. Runaway electrons and ion-acoustic instabilities can occur in the spatial maximum of the current density and electron temperature. Inclusion of bremsstrahlung loss reduces the value of Te/Ti for the onset of the instability, and at Te = Ti yields a maximum ion temperature obtainable by Ohmic heating in a stable plasma.

The transition of QGP from fluid-dynamical regime to freeze-out is\naccompanied by the onset of instabilities. In the present paper we investigate\nthe impact of the magnetic field on the Rayleigh instability. We show that\nextremely strong field generated in peripheral heavy ion collisions has an\ninsignificant influence on the Rayleigh bubble dynamics. Magnetic "friction"\nturns out to be much weaker than the viscous one.\n

Energy and hydrodynamic approaches to magnetocapillary instability of nonconducting jets