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It has been confirmed that dipolarization fronts (DFs) can be a result from the existence of interchange instability in the magnetotail. In this paper, we used a Hall MHD model to simulate the evolution of the interchange instability, which produces DFs on the leading edge. A test particle simulation was performed to study the physical phenomenon of ion acceleration on DF. Numerical simulation indicates that almost all particles move towards the earthward and dawnward and then drift to the tail. The DF-reflected ion population on the duskside appears earlier as a consequence of the asymmetric Hall electric field. Ions, with dawn-dusk asymmetric semicircle behind the DF, may tend to be accelerated to a higher energy (> 13.5 keV). These high-energy particles are eventually concentrated in the dawnside. Ions experience effective acceleration by the dawnward electric field Ey while they drift through the dawn flank of the front towards the tail.

A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X line; while using the MITS and FOTE methods, we find it is a magnetic island (O line). We compare the efficiency and accuracy of these three methods and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide and nonguide field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forthcoming Magnetospheric Multiscale (MMS) mission.

This paper studies the effective polytropic index in the central plasma sheet (CPS) by using the method of Kartalev et al. (2006), which adopts the denoising technique of Haar wavelet to identify the homogeneous MHD Bernoulli integral (MBI) and has been frequently used to study the polytropic relation in the solar wind. We chose the quiet CPS crossing by Cluster C1 during the interval 08:51:00–09:19:00 UT on 03 August 2001. In the central plasma sheet, thermal pressure energy per unit mass is the most important part in MBI, and kinetic energy of fluid motion and electromagnetic energy per unit mass are less important. In the MBI, there are many peaks, which correspond to isothermal or near isothermal processes. The interval lengths of homogenous MBI regions are generally less than 1 min. The polytropic indexes are calculated by linearly fitting the data of lnp and lnn within a 16 s window, which is shifted forward by 8 s step length. Those polytropic indexes with |R|⩾0.8 (R is the correlation coefficient between lnp and lnn) and p-value⩽0.1 in the homogeneous regions are almost all in the range of [0, 1]. The mean and median effective polytropic indexes with high R and low p-value in homogeneous regions are 0.34 and 0.32 respectively, which are much different from the polytropic index obtained by traditional method ( α trad=−0.15). This result indicates that the CPS is not uniform even during quiet time and the blanket applications of polytropic law to plasma sheet may return misleading value of polytropic index. The polytropic indexes in homogeneous regions with a high correlation coefficient basically have good regression significance and are thus credible. These results are very important to understand the energy transport in magnetotail in the MHD frame.

This paper uses the data of Cluster from 2001 to 2009 to study the polytropic processes of central plasma sheet (CPS) ions. We first adopt the approach of MHD Bernoulli integral (MBI) to identify homogeneous streamflow tubes (quasi-invariant MBI regions) and then calculate the polytropic index of ions for those streamflow tubes whose outward electromagnetic energy ratios δ

During reconnection, a flux pileup region (FPR) is formed behind a dipolarization front in an outflow jet. Inside the FPR, the magnetic field magnitude and Bz component increase and the whistler-mode waves are observed frequently. As the FPR convects toward the Earth during substorms, it is obstructed by the dipolar geomagnetic field to form a near-Earth FPR. Unlike the structureless emissions inside the tail FPR, we find that the whistler-mode waves inside the near-Earth FPR can exhibit a discrete structure similar to chorus. Both upper band and lower band chorus are observed, with the upper band having a larger propagation angle (and smaller wave amplitude) than the lower band. Most chorus elements we observed are “rising-tone” type, but some are “falling-tone” type. We notice that the rising-tone chorus can evolve into falling-tone chorus within

Mycotaxon is pleased to add a new annotated species distribution list to our 133 previously posted free-access fungae. The 9-page "Diversity of macrofungi in Yushan, Jiangsu, China" by Bing Xu, Haoyu Lu, Donglei Zhao, Wei Wang, and Hong Ji may be downloaded from our website via http://www.mycotaxon.com/mycobiota/index.html

It has been demonstrated that Kelvin–Helmholtz (KH) instability is an essential large-scale mechanism to generate plasma waves along the boundary layers of Venus. In this paper, evolution of KH instability on the Venusian ionopause with the influence of the Hall effect was investigated under Hall magnetohydrodynamic (MHD) simulations. Linear and nonlinear physical behaviors of KH instability with different wavelengths of perturbation, magnetic field configurations, and ion inertial lengths were studied. Numerical results indicate that, for perturbation with short wavelength, the circulation area of matter becomes small and the driving force is weakened. The combined effect of short wavelength and the antiparallel magnetic field leads to longer linear growth time, while the antiparallel magnetic field tends to enlarge the pressure gradient. As for the moderate wavelength of perturbation, the growth rate reaches its peak value, whereas the maximal y component of total kinetic energy increases significantly with the wavelength. Hall MHD simulations indicate that the Hall effect does not change the growth rates for different ion inertial lengths at all. However, the Hall effect has a depression effect on small structures at the nonlinear stage of KH instability.

Ultra high-voltage direct current (UHVDC) transmission projects of ±1100kV have been in design and construction in China, recently. The electromagnetic environment with corona discharge phenomenon of UHVDC transmission lines has been of interest for engineers. It is necessary to control the electric field strength of the sub-conductors of the power lines because the field on the lines has significant impacts on radio interference (RI), audible noise (AN) and ionized electric field on the ground. In this paper, the electric field on the sub-conductor surfaces are analyzed by the charge simulation method (CSM). The configuration of ±1100kV UHVDC power lines are suggested in order to limit the electromagnetic environment nearby, which may provide useful reference for the design of ±1100kV UHVDC transmission lines.

In this research effort, numerical simulation of two-dimensional magnetohydrodynamic (MHD) channel is performed and Hall effect is studied. The computational model consists of the Navier-Stokes (N-S) equations coupled with electrical-magnetic source terms, Maxwell equations and the generalized Ohm's law. Boundary conditions for the electrical potential equation considering Hall effect are derived. To start with, the MHD channel with single-pair electrodes is studied and flow of the electric current is in accordance with physical principle. Then the MHD channel with five-pair electrodes is numerically simulated. The results show that the electrical current concentrates on the downstream of the anode and the upstream of the cathode due to Hall effect, and the flow field becomes asymmetrical. At the current value of the magnetic interaction parameter, the electrical-magnetic force affects the flow remarkably, decreasing the outlet Mach number and increasing the outlet pressure; what's more, the flow structure in the channel becomes extremely complex. Performances of MHD channels with continual electrodes and segmented electrodes are compared. The results show that performance of the MHD channel with segmented electrodes is better than that with continual electrodes with the increase of Hall parameter.

A numerical procedure based on a five-wave model associated with non-ideal, low magnetic Reynolds number magnetohydrodynamic (MHD) flows was developed. It is composed of an entropy conditioned scheme for solving the non-homogeneous Navier-Stokes equations, in conjunction with an SOR method for solving the elliptic equation governing the electrical potential of flow field. To validate the developed procedure, two different test cases were used which included MHD Rayleigh problem and MHD Hartmann problem. The simulations were performed under the assumption of low magnetic Reynolds number. The simulated results were found to be in good agreement with the closed form analytical solutions deduced in the present study, showing that the present algorithm could simulate engineering MHD flow at low magnetic Reynolds number effectively. In the end, a flow field between a pair of segmented electrodes in a three dimensional MHD channel was simulated using the present algorithm with and without including Hall effects. Without the introduction of Hall effects, no distortion was observed in the current and potential lines. By taking the Hall effects into account, the potential lines distorted and clustered at the upstream and downstream edges of the cathode and anode, respectively.

A numerical procedure based on a five-wave MHD model associated with non-ideal, low magnetic Reynolds number MHD flows was developed in the present study for analyzing the flow fields in the MHD generator of a MHD bypass scramjet. The numerical procedure is composed of an entropy conditioned scheme for solving the non-homogeneous Navier-Stokes equations, in conjunction with an SOR method for solving the elliptic equation governing the electrical potential. It was found that a separation would take place near the downstream edge of the second electrode, where the local adverse pressure gradient is large, and the core of the flow field is characterized as a 2-D flow due to the Hartmann effects along the direction of the magnetic field. The electric current lines would be increasingly distorted as the magnetic interactive parameter increases, and even induce an eddy current. Induced eddy current was also found in the different cross-sections along the axial direction, all of these would definitely deteriorate the performance of the MHD generator. The cross-sectional M-shape velocity profile found along the axial direction between the insulating walls is responsible for the formation of the vortex flow at the corner of the insulator cross-section, which, in turn, induces the corner eddy current at the corner. A numerical parametric study was also performed, and the computed performance parameters for the MHD generator suggest that, in order to enhance the performance of MHD generator, the magnetic interaction parameter should be elevated.

Using an extended MHD model including the Hall effect and finite Larmor radius effect, we reproduce multiple dipolarization fronts (DFs) associated with the interchange instability in the braking region of bursty bulk flow in the plasma sheet. Our simulations reveal that the multiple DFs produced by the interchange instability are “growing” type DFs because the maximum plasma flow speeds are behind the fronts. Both the earthward and tailward moving DFs can be produced by interchange instability in the near-Earth region. The Hall electric field is the dominant electric field component in the dip region and the DF layer. The convective and the electron pressure gradient electric field components are smaller. The sharp Bz changes in both the dip region and DF layer correspond to the oppositely directed currents that are primarily associated with electrons. The ion diamagnetic current due to the strong ion pressure gradient causes an intense downward current in the dip region, which can produce the dip ahead ...

By analyzing the types, causes and the fault feature of common fault of squirrel-cage asynchronous motor, and based on the study of the principles and methods of fault detection of electromotor, the multi-channel electric power data acquisition system is designed, which can realize the online fault detection of motor. Using AT89C52 microcontroller as the core components of the controller, and data collection use a special measurement chip CS5460. The data collected is transmitted to the upper computer by RS232 bus so as to realize the electric energy data. Sampling interpolation FFT algorithm make software compensation, and then the MCU high-speed interval of multi-channel data acquisition is realized.

International audience; Dipolarization fronts (DFs) are frequently detected in the Earth's magnetotail from XGSM = −30 RE to XGSM = −7 RE. How these DFs are formed is still poorly understood. Three possible mechanisms have been suggested in previous simulations: (1) jet braking, (2) transient reconnection, and (3) spontaneous formation. Among these three mechanisms, the first has been verified by using spacecraft observation, while the second and third have not. In this study, we show Cluster observation of DFs inside reconnection diffusion region. This observation provides in situ evidence of the second mechanism: Transient reconnection can produce DFs. We suggest that the DFs detected in the near-Earth region (XGSM > −10 RE) are primarily attributed to jet braking, while the DFs detected in the mid- or far-tail region (XGSM

On 3 September 2009, the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites observed a significant intensification of chorus in response to the interplanetary shock in the Earth's dayside plasma trough. We analyze the wave-particle interaction and reveal that the chorus intensification can be caused by the gyroresonance between the chorus and the energetic electrons. When the electrons are scattered from resonance points to low-density regions along the diffusion curves, a part of their energy can be lost and then transferred to amplify the chorus. During the compression of the magnetosphere, the temperature anisotropy of electrons is enhanced. This makes the electron diffusion and chorus intensification very effective. The maximum growth rate after the shock is about 50% greater than that before the shock. The lower-energy (15-25 keV) electrons contribute more to the growth of chorus due to the larger density gradient along the diffusion curve. The < 10 keV electrons are almost isotropic, so they contribute little to the amplification of chorus. We investigate the free energy for the chorus intensification and find that it can be generated through the local betatron acceleration and radial diffusion processes. The local betatron acceleration results from the shock-induced compression of the magnetosphere. The linear and nonlinear growth rates are also compared. We find that the linear diffusion process works well for the present case.

During the period 19-22 November 2007, the near-equatorial satellites THEMIS D (ThD) and E (ThE) traversed the Earth's morningside magnetosphere once per day and for nearly 2 h the orbits tracked c ...

When flight Mach number is lower than the design value both MHD (magneto-hydrodynamic) accelerator and generator can be used to improve the performance of the scramjet inlet. MHD controlled inlet of accelerator mode was analyzed in this paper. The magnetic field has components perpendicular and parallel to the flow direction. The computational model consists of the Euler or N-S equations coupled with the electric-magnetic source terms, ideal gas state equation, Maxwell equations and the Generalized Ohm’s law. The influence of some key parameters on the performance of the inlet was analyzed. The results show that at a proper choice of other parameters, increase of the magnitude of magnetic induction will increase mass capture and compression, due to irreversible effects total pressure will decrease. The angle of the magnetic induction and the x coordinate of the MHD interaction region have optimal values to get the maximal mass capture. The analysis also shows that the increase of mass capture and pressure is mainly due to the MHD interaction near and below the cowl lip region. A group of optimized parameters has been chosen to calculate the flow field, the results show a considerable improvement of the inlet air mass capture and pressure rise while the loss of total pressure is limited to a reasonable extend. Considering about the viscous effects the benefit of MHD controlled inlet is more obvious, the mass flow rate, pressure rise, and total pressure recovery ratio can all be increased.

[Abstract] A parametric study on the qualifications of the MHD generator inlet and the criteria for the inlet flow conditions were performed. A quasi-1D approach was utilized in the study to analyze the influences of the load factor, magnetic flux density, and the ionization power density upon the performance and the operating range of the inlet Mach number of the MHD generator. It was found that the performance of the MHD generator would increase at the cost of the reduction of the operating range of the inlet Mach number, and vice versa. Interdependencies among these parameters are investigated, and presented in the present paper. An acceptable measure to enhance the performance of the MHD generator and expand the operating range of the inlet Mach number is then proposed accordingly.

The development of the structure of symmetric reconnection layer in the presence of a shear flow parallel to the antiparallel magnetic field component is studied by using a set of one-dimensional (1D) magnetohydrodynamic (MHD) equations. The Riemann problem is simulated through a second-order conservative TVD (total variation diminishing) scheme, in conjunction with Roe’s averages for the Riemann problem. The simulation results indicate that besides the MHD shocks and expansion waves, there exist some new small-scale structures in the reconnection layer. For the case of zero initial guide magnetic field (i.e., By0 = 0), a pair of intermediate shock and slow shock (SS) is formed in the presence of the parallel shear flow. The critical velocity of initial shear flow Vzc is just the Alfven velocity in the inflow region. As Vz∞ increases to the value larger than Vzc, a new slow expansion wave appears in the position of SS in the case Vz∞

This paper presents a preliminary experimental investigation on magnetohydrodynamic (MHD) power generation using seeded supersonic argon flow as working fluid. Helium and argon are used as driver and driven gas respectively in a shock tunnel. Equilibrium contact surface operating mode is used to obtain high temperature gas, and the conductivity is obtained by adding seed K2CO3 powder into the driven section. Under the conditions of nozzle inlet total pressure being 0.32 MPa, total temperature 6 504 K, magnetic field density about 0.5 T and nozzle outlet velocity 1 959 m/s, induction voltage and short-circuit current of the segmentation MHD power generation channel are measured, and the experimental results agree with theoretical calculations; the average conductivity is about 20 S/m calculated from characteristics of voltage and current. When load factor is 0.5, the maximum power density of the MHD power generation channel reaches 4.797 1 MW/m3, and the maximum enthalpy extraction rate is 0.34%. Finally, the principle and method of indirect testing for gas state parameters are derived and analyzed.