1,746 research outputs found
Partnerships Form the Basis for Implementing a National Space Weather Plan
The 2017 Space Weather Enterprise Forum, held June 27, focused on the vital role of partnerships in order to establish an effective and successful national space weather program. Experts and users from the many government agencies, industry, academia, and policy makers gathered to discuss space weather impacts and mitigation strategies, the relevant services and supporting infrastructure, and the vital role cross-cutting partnerships must play for successful implementation of the National Space Weather Action Plan
Differentiating EDRs from the Background Magnetopause Current Sheet: A Statistical Study
The solar wind is a continuous outflow of charged particles from the Sun's
atmosphere into the solar system. At Earth, the solar wind's outward pressure
is balanced by the Earth's magnetic field in a boundary layer known as the
magnetopause. Plasma density and temperature differences across the boundary
layer generate the Chapman-Ferraro current which supports the magnetopause.
Along the dayside magnetopause, magnetic reconnection can occur in electron
diffusion regions (EDRs) embedded into the larger ion diffusion regions (IDRs).
These diffusion regions form when opposing magnetic field lines in the solar
wind and Earth's magnetic field merge, releasing magnetic energy into the
surrounding plasma. While previous studies have given us a general
understanding of the structure of the diffusion regions, we still do not have a
good grasp of how they are statistically differentiated from the non-diffusion
region magnetopause. By investigating 251 magnetopause crossings from NASA's
Magnetospheric Multiscale (MMS) Mission, we demonstrate that EDR magnetopause
crossings show current densities an order of magnitude higher than regular
magnetopause crossings - crossings that either passed through the reconnection
exhausts or through the non-reconnecting magnetopause, providing a baseline for
the magnetopause current sheet under a wide range of driving conditions.
Significant current signatures parallel to the local magnetic field in EDR
crossings are also identified, which is in contrast to the dominantly
perpendicular current found in the regular magnetopause. Additionally, we show
that the ion velocity along the magnetopause is highly correlated with a
crossing's location, indicating the presence of magnetosheath flows inside the
magnetopause
Structure of the Current Sheet in the 11 July 2017 Electron Diffusion Region Event.
The structure of the current sheet along the Magnetospheric Multiscale (MMS) orbit is examined during the 11 July 2017 Electron Diffusion Region (EDR) event. The location of MMS relative to the X-line is deduced and used to obtain the spatial changes in the electron parameters. The electron velocity gradient values are used to estimate the reconnection electric field sustained by nongyrotropic pressure. It is shown that the observations are consistent with theoretical expectations for an inner EDR in 2-D reconnection. That is, the magnetic field gradient scale, where the electric field due to electron nongyrotropic pressure dominates, is comparable to the gyroscale of the thermal electrons at the edge of the inner EDR. Our approximation of the MMS observations using a steady state, quasi-2-D, tailward retreating X-line was valid only for about 1.4Â s. This suggests that the inner EDR is localized; that is, electron outflow jet braking takes place within an ion inertia scale from the X-line. The existence of multiple events or current sheet processes outside the EDR may play an important role in the geometry of reconnection in the near-Earth magnetotail
The temperate Burkholderia phage AP3 of the Peduovirinae shows efficient antimicrobial activity against B. cenocepacia of the IIIA lineage
Burkholderia phage AP3 (vB_BceM_AP3) is a temperate virus of the Myoviridae and the Peduovirinae subfamily (P2likevirus genus). This phage specifically infects multidrug-resistant clinical Burkholderia cenocepacia lineage IIIA strains commonly isolated from cystic fibrosis patients. AP3 exhibits high pairwise nucleotide identity (61.7 %) to Burkholderia phage KS5, specific to the same B. cenocepacia host, and has 46.7–49.5 % identity to phages infecting other species of Burkholderia. The lysis cassette of these related phages has a similar organization (putative antiholin, putative holin, endolysin, and spanins) and shows 29–98 % homology between specific lysis genes, in contrast to Enterobacteria phage P2, the hallmark phage of this genus. The AP3 and KS5 lysis genes have conserved locations and high amino acid sequence similarity. The AP3 bacteriophage particles remain infective up to 5 h at pH 4–10 and are stable at 60 °C for 30 min, but are sensitive to chloroform, with no remaining infective particles after 24 h of treatment. AP3 lysogeny can occur by stable genomic integration and by pseudo-lysogeny. The lysogenic bacterial mutants did not exhibit any significant changes in virulence compared to wild-type host strain when tested in the Galleria mellonella moth wax model. Moreover, AP3 treatment of larvae infected with B. cenocepacia revealed a significant increase (P < 0.0001) in larvae survival in comparison to AP3-untreated infected larvae. AP3 showed robust lytic activity, as evidenced by its broad host range, the absence of increased virulence in lysogenic isolates, the lack of bacterial gene disruption conditioned by bacterial tRNA downstream integration site, and the absence of detected toxin sequences. These data suggest that the AP3 phage is a promising potent agent against bacteria belonging to the most common B. cenocepacia IIIA lineage strains
Observational evidence of magnetic reconnection in the terrestrial bow shock transition region
We report evidence of magnetic reconnection in the transition region of the
terrestrial bow shock when the angle between the shock normal and the immediate
upstream magnetic field is 65 degrees. An ion-skin-depth-scale current sheet
exhibits the Hall current and field pattern, electron outflow jet, and enhanced
energy conversion rate through the nonideal electric field, all consistent with
a reconnection diffusion region close to the X-line. In the diffusion region,
electrons are modulated by electromagnetic waves. An ion exhaust with energized
field-aligned ions and electron parallel heating are observed in the same shock
transition region. The energized ions are more separated from the inflowing
ions in velocity above the current sheet than below, possibly due to the shear
flow between the two inflow regions. The observation suggests that magnetic
reconnection may contribute to shock energy dissipation
Energy Conversion and Partition in the Asymmetric Reconnection Diffusion Region
We investigate the energy conversion and partition in the asymmetric reconnection diffusion region using two-dimensional particle-in-cell simulations and Magnetosphere Multiscale (MMS) mission observations. Under an upstream condition with equal temperatures in the two inflow regions, the simulation analysis indicates that the energy partition between ions and electrons depends on the distance from the X-line. Within the central electron diffusion region (EDR), nearly all dissipated electromagnetic field energies are converted to electrons. From the EDR to the ion diffusion region (IDR) scales, the rate of the electron energy gain decreases to be lower than that of ions. A magnetopause reconnection event inside the IDR observed by MMS shows comparable ion and electron energy gains, consistent with the simulation result in the transition region from EDR to IDR. At the EDR scale, the electron energization is mainly by the reconnection electric field (E(sub r)); in-plane electric fields (E(sub xz)) provide additional positive contributions near the X-line and do negative work on electrons beyond the EDR. The guide field reduces the electron energization by both E(sub r) and E(sub xz) in the EDR. For ion energization, E(sub r) and E(sub xz) have comparable contributions near the time of the peak reconnection rate, while E(sub xz) dominants at later time. At the IDR scale, the guide field causes asymmetry in the amount of the energy gain and energization mechanisms between two exhausts but does not have significant effects on energy partition. Our study advances understanding of ion and electron energization in asymmetric reconnect IDRs
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