ALBERT

Description: The influence of magnetic field intensity and process parameters on the transient fluidization behaviors of magnetically stable fluidized beds (MSFBs) was studied. The local solid holdup distribution and magnetically stabilized regimes were carried out by experimental measurements in MSFBs. The scaling approach for MSFB hydrodynamics based on magnetic field and dynamic similitude with a limited number of dimensionless groups was tested. A dimensionless number for magnetic field has been developed. An experimental criterion for the magnetically stabilized fluidization is established based on random analysis of the void fluctuation signal. It includes two characteristic parameters of the main frequency of voidage fluctuation signals, i.e., the self-correlation function and variance. A dimensionless correlation to calculate the stable zone with three dimensionless groups of Er, Ar, and Re was proposed using dimensionless analysis. The influence of magnetic field intensity and process parameters on the transient fluidization behaviors of magnetically stable fluidized beds was investigated. A dimensionless correlation to calculate the stable zone with the three dimensionless groups, i.e., Archimedes number, Reynolds number, and ratio of magnetic potential and gravity potential energy, is proposed.

Description: Magnetohydrodynamics (MHD) predicts that lunar wake expands outward at magnetosonic velocities in all directions perpendicular to background solar wind; however, fluid theories emphasize that lunar wake expands outward at sound speeds mainly along the interplanetary magnetic field (IMF). Early observations supported the MHD predictions in the near-moon region despite lack of solar wind and IMF observations. Thanks to the special orbit design of the ARTEMIS mission, the solar wind conditions are well determined at the time of concurrent observations in the lunar wake. 164 wake crossings made by ARTEMIS are statistically studied in this paper. Observations indicated that, in either distant or near-Moon regions, the lunar wake expands outward at the fast MHD wave velocities. This simple model provides a powerful way to determine wake boundaries, particularly at large distances where the boundary signatures are indistinct, thus allowing further studies on the Moon-solar wind/crustal field-solar wind interactions.

Description: The effects of swirls on the mass flow rates and on the natural gas velocity and temperature in a supersonic separator were numerically studied using the Reynolds stress model. An experimental system was set up with moist air as working fluid. The results showed that high swirl strengths decreased the mass flow rates through the supersonic separator. An increase in swirl strength resulted in a reduction and non-uniform radial distribution of the gas Mach number at the nozzle exit. With moderate swirls, low temperature (–60 °C) and a strong centrifugal field (5 · 10 6  m s –2 ) are obtained to condense and separate water and heavy hydrocarbons from natural gas. The experimental results agreed with the simulations demonstrating that strong swirls decreased the mass flow rate. The effects of swirls on the natural gas flow fields in a supersonic separator were numerically simulated, including the mass flow rates through the nozzle throat, the Mach number and the temperature at the nozzle exit. An experimental system was set up to test the effects of the swirls on the mass flow with moist air as working fluid.

Description: With high-resolution data of the recently launched Magnetospheric Multiscale (MMS) mission, we report a magnetic reconnection event at the dayside magnetopause. This reconnection event, having a density asymmetry N high /N low ≈2 on the two sides of the reconnecting current sheet and a guide field B g ≈0.4B 0 in the ‘out-of-plane’ direction, exhibit all the two-fluid features: Alfvenic plasma jets in the outflow region, bipolar Hall electric fields toward the current sheet center, quadrupolar Hall magnetic fields in the ‘out-of-plane’ direction, and the corresponding Hall currents. Obviously, the density asymmetry N high /N low ≈2 and the guide field B g ≈0.4B 0 are not sufficient to dismiss the quadrupolar pattern of Hall reconnection. This is different from previous simulations, where the bipolar pattern of Hall reconnection was suggested.

Description: Deciphering the flow below the cloud-level of Jupiter remains a critical milestone in understanding Jupiter's internal structure and dynamics. The expected high-precision Juno measurements of both the gravity field and the magnetic field might help to reach this goal. Here we propose a method that combines both fields to constrain the depth dependent flow field inside Jupiter. This method is based on a mean-field electrodynamic balance that relates the flow field to the anomalous magnetic field, and geostrophic balance that relates the flow field to the anomalous gravity field. We find that the flow field has two distinct regions of influence - an upper region in which the flow affects mostly the gravity field, and a lower region in which the flow affects mostly the magnetic field. An optimization procedure allows to reach a unified flow structure that is consistent with both the gravity and the magnetic fields.

Description: The pitch angle distribution (PAD) of suprathermal electrons can have both spatial and temporal evolution in the magnetotail and theoretically can be an indication of electron energization/cooling processes there. So far, the spatial evolution of PAD has been well studied, leaving the temporal evolution as an open question. To reveal the temporal evolution of electron PAD, spacecraft should monitor the same flux tube for a relatively long period, which is not easy in the dynamic magnetotail. In this study, we present such an observation by Cluster spacecraft in the magnetotail behind a dipolarization front (DF). We find that the PAD of suprathermal electrons can evolve from pancake-type to butterfly-type during 〈4 s, and then to cigar-type during 〈8 s. During this process, the flow velocity is nearly zero and the plasma entropy is constant, meaning that the evolution is temporal. We interpret such temporal evolution using the betatron cooling process, which is driven by quasi-adiabatic expansion of flux tubes, and the magnetic mirror effect, which possibly exists behind the DF as well.

Description: 〈span〉〈div〉Abstract〈/div〉Although previous studies have performed finite‐fault simulations of actual or hypothetical earthquakes to generate time histories of near‐fault ground strains and rotations, no systematic attempt has been made to assess the sensitivity of these motions to variations in seismic source parameters (e.g., fault type, magnitude, rupture velocity, slip velocity, hypocenter location, burial depth). Such a parametric investigation is presented in this article by generating time histories of ground strains and rotations at near‐fault stations and at a dense grid of observation points extending over the causative fault for a suite of hypothetical strike‐slip and dip‐slip earthquakes. The simulation results show that strike‐slip earthquakes produce large shear strain and torsion, whereas dip‐slip earthquakes generate large axial strain and rocking. The time histories of specific components of displacement gradient, strain, and rotation at near‐fault stations may be estimated from those of ground velocities using a simple scaling relation, whereas peak rotational motions in the near‐fault region may be reasonably estimated from peak translational motions using a properly selected scaling factor. The parametric analysis results show that near‐fault ground strains and rotations exhibit strong sensitivity to variations in rupture velocity, slip velocity, and burial depth, whereas a change in hypocenter location significantly alters the spatial distributions of peak ground strains (PGSs) and rotations (PGRs). The presence of a low‐velocity surface layer increases the amplitude and duration of ground strains and rotations, whereas their static offsets are also amplified. Distinct attenuation characteristics are observed for PGSs and PGRs depending on the component of interest, the earthquake magnitude, and the rupture distance. Finally, the spatial distributions of PGSs and PGRs obtained from a stochastically generated variable slip distribution are overall similar to those obtained from a tapered uniform slip distribution, whereas the spatial distributions of the respective static offsets differ significantly.〈/span〉

Description: Using MMS high-resolution measurements, we present the first observation of fast electron jet ( V e ~ 2000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale comparable to the DF thickness (~ 0.9 d i ), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E×B drift motion; it contributes significantly to the current system at the DF, including a localized ring-current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift (LHD) waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron-jet-driven current (E⋅j e ≈ 2 E⋅j i ), rather than the ion current suggested in previous studies.

Description: In this paper, we established a Hall-FLR MHD model by including Hall and finite Larmor radius (FLR) effects to study the dipolarization fronts (DFs) produced by the interchange instability in the magnetotail. The results indicate that the Hall effect on the scale of inertial length determines the distributions of electric field at DFs. The FLR effect can not only cause a dawn-dusk asymmetry of the DF structure, but also can make the DF drift dawnward. The dawnward drifting of DF can be attributed to the ion diamagnetic velocity, which also causes alteration in the direction of the high-speed flow near the DF.