Search for: All records

Abstract Magnetic reconnection and the Kelvin–Helmholtz instability (KHI) are the two fundamental processes in planetary magnetospheres that can lead to plasma, momentum, and energy transport across the magnetospheric boundary. Flux Transfer Events (FTEs), being characterized by the bipolar variation of the magnetic normal component, are often considered to be generated by magnetic reconnection. However, several possible mechanisms can also give rise to FTE‐like features in the boundary layer and potentially mislead observational analysis; the KHI is one such candidate. Using two‐dimensional magnetohydrodynamics (MHD) simulations, we examine and categorize the signatures observed by several virtual satellites as they pass through the Kelvin–Helmholtz waves along different trajectories. We have shown that the bipolar signatures were identified during the satellite's passage across the spine region and the leading/trailing edge of the KH vortex. The duration of bipolar signatures was also shown to vary depending not only on where the satellite trajectory intersects with the vortices, but also on the density asymmetry on both sides of boundary which in turn affects the relative motion between the vortices and satellite. Further, slight adjustments to the projection angle of the magnetic field are also applied in the simulations, as the signatures of the KHI are very sensitive to the in‐plane magnetic field component. These results can be used as diagnostics when analyzing spacecraft data to help distinguish KHI‐created signatures from FTE. 

A RF photonic front-end using dual-differential driving scheme is reported with a 22nm CMOS FD-SOI driver co-integrated with a silicon traveling-wave Mach-Zehnder modulator. The proposed front-end achieves 15-25GHz bandwidth with 2dBm IIP3 and consumes 448mW. 

Abstract Understanding the formation of the seed population for the energetic electrons trapped within the Earth's Van Allen radiation belts has been under debate for decades. The magnetic reconnection in the Earth's magnetotail during the substorms is the main process of accelerating the electrons to the tens to hundreds of keV. These electrons are further injected toward the radiation belts, where they get further accelerated to relativistic energies. Recently, it has been suggested that another source could come from the dayside diamagnetic cavities where electrons and ions can be locally energized to hundreds of keV energies. It has been shown that the physical mechanism within the cavities can create a strong acceleration perpendicular to magnetic field, which can lead to temperature anisotropy and drift mirror instability. The electron fluxes localized within the troughs of the mirror mode waves exhibit the counter‐streaming “microinjection” signature. To investigate the origin of microinjections and their dependence on solar wind conditions, here we have performed an event search and a statistical study of their properties encompassing a total of ∼165 hr (47 microinjection events) of Magnetospheric Multiscale observations at the pre‐dusk sector high‐latitude boundary layer. The ultralow frequency range magnetic field fluctuations coincided with the counter‐streaming energetic electron fluxes. For most events, the interplanetary magnetic field was duskward and anti‐sunward; over 60% of these microinjections satisfy the criteria of the drift mirror instability, which indicates the temperature anisotropy could play an important role for the microinjection. 

Abstract The Kelvin‐Helmholtz (KH) instability can transport mass, momentum, magnetic flux, and energy between the magnetosheath and magnetosphere, which plays an important role in the solar‐wind‐magnetosphere coupling process for different planets. Meanwhile, strong density and magnetic field asymmetry are often present between the magnetosheath (MSH) and magnetosphere (MSP), which could affect the transport processes driven by the KH instability. Our magnetohydrodynamics simulation shows that the KH growth rate is insensitive to the density ratio between the MSP and the MSH in the compressible regime, which is different than the prediction from linear incompressible theory. When the interplanetary magnetic field (IMF) is parallel to the planet's magnetic field, the nonlinear KH instability can drive a double mid‐latitude reconnection (DMLR) process. The total double reconnected flux depends on the KH wavelength and the strength of the lower magnetic field. When the IMF is anti‐parallel to the planet's magnetic field, the nonlinear interaction between magnetic reconnection and the KH instability leads to fast reconnection (i.e., close to Petschek reconnection even without including kinetic physics). However, the peak value of the reconnection rate still follows the asymmetric reconnection scaling laws. We also demonstrate that the DMLR process driven by the KH instability mixes the plasma from different regions and consequently generates different types of velocity distribution functions. We show that the counter‐streaming beams can be simply generated via the change of the flux tube connection and do not require parallel electric fields. 

Abstract Current research underscores that there are only a few evidence-based programs that teach STEM (science, technology, engineering, and mathematics) as part of their curriculum, especially for autistic students. Even fewer programs focus on engineering and design learning. Hence, we developed an informal afterschool maker program to develop autistic and non-autistic students’ interests in engineering to understand their experiences learning STEM concepts and values while applying the engineering mindset to develop projects. This qualitative study aimed to explore and understand students’ experiences participating in STEM activities in the maker club. We interviewed twenty-six students (seventeen autistic and nine non-autistic), nine teachers, and thirteen parents representing diverse cultural and socio-economic backgrounds across three public middle schools in a large urban metropolitan city between 2018 and 2019. Our thematic analysis yielded four themes:(1) active participation in STEM; (2) curiosity about STEM topics, concepts, and practices, (3) capacity-building to engage in STEM learning; and 4) understanding of the importance of STEM education in daily life.The results of this study enabled us to understand that students were deeply engaged with the content and curriculum of our program, expanded their knowledge base about scientific concepts, used engineering-specific scientific terminologies, and engaged with the engineering design process to conceptualize, test, improvise, and problem-solve. Furthermore, this afterschool engineering education program created a safe, nurturing, and stimulating environment for students to build engineering readiness skills. 

We characterize heavy-traffic process and steady-state limits for systems staffed according to the square-root safety rule, when the service requirements of the customers are perfectly correlated with their individual patience for waiting in queue. Under the usual many-server diffusion scaling, we show that the system is asymptotically equivalent to a system with no abandonment. In particular, the limit is the Halfin-Whitt diffusion for the [Formula: see text] queue when the traffic intensity approaches its critical value 1 from below, and is otherwise a transient diffusion, despite the fact that the prelimit is positive recurrent. To obtain a refined measure of the congestion due to the correlation, we characterize a lower-order fluid (LOF) limit for the case in which the diffusion limit is transient, demonstrating that the queue in this case scales like [Formula: see text]. Under both the diffusion and LOF scalings, we show that the stationary distributions converge weakly to the time-limiting behavior of the corresponding process limit. Funding: This work was supported by the National Natural Science Foundation of China [Grant 72188101] and the Division of Civil, Mechanical and Manufacturing Innovation [Grants 1763100 and 2006350].