Magnetic cavities (sometimes referred to as magnetic holes) at electron kinetic scale are thought to be one of the extremely small intermittent structures formed in magnetized turbulent plasmas, ...where the turbulence energy cascaded down to electron scale may finally be dissipated and consequently energize the electrons. However, the geometry and formation of these structures remain not definitively resolved. Here we discuss an electron scale magnetic cavity embedded in a proton scale magnetic cavity observed by the MMS spacecraft in the magnetosheath. By applying an innovative particle sounding technique, we directly depict the boundary of the electron scale magnetic cavity and uncover the geometry. We find that this structure is nearly circular with a radius of 10.0 km and its formation is due to the diamagnetic current. Investigation of the electron scale structure is only recently made possible by the high spatial and temporal resolution provided by MMS observations.
We present X-ray timing results of the new black hole candidate MAXI J1535−571 during its 2017 outburst from Hard X-ray Modulation Telescope (Insight-HXMT) observations taken from 2017 September 6 to ...23. Following the definitions given by Belloni, we find that the source exhibits transitions from the low/hard state to the hard intermediate state, and eventually to the soft intermediate state. Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of Insight-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV, which has rarely been explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lag) and strongly correlated with the centroid frequency. Assuming a geometrical origin of type-C QPOs, the source is consistent with being a high-inclination system.
The Beishan orogenic collage is located in the southernmost part of the Altaids, and connects the Southern Tien Shan suture to the west with the Solonker suture to the east. The orogen was previously ...regarded as early Paleozoic in age in contrast to the surrounding southern Altaid collages, which are Late Paleozoic or even Early Mesozoic. This paper reviews the tectonic units of the Beishan orogen, which along a north-south traverse consists of several arcs and ophiolitic melanges. These tectonic units were thrust imbricated and overprinted by strike-slip faulting during Permian-Triassic times, and the youngest strata involved in the deformation are Permian. Stitching plutons are Late Permian in age. Peaks of magmatic-metamorphic-tectonic activity, and paleomagnetic and paleogeographic data indicate that the Beishan orogenic collage evolved by development of several, Early to Mid-Paleozoic arcs in different parts of the Paleoasian Ocean. The Late Paleozoic collage is characterized by three active continental margins or island arcs that are separated by two ophiolitic melanges. The northernmost active margin is represented by the Queershan arc, which may have lasted until the Permian. The Shibanshan unit is the southernmost, subduction-related continental arc along the northern margin of the Dunhuang block. In the Late Carboniferous to Permian the eastern end (promontory) of the Tarim Craton probably collided with the Chinese eastern Tien Shan arc, forming a new active continental margin, which interacted with the Beishan Late Paleozoic archipelago, generating a complicated subduction-accretionary orogen; this is suggested to be one of the last phases in the development of the long-lived Altaid accretionary orogenesis. The new model for this orogen bridges the gap between the western and eastern ends of the southern Altaids. The modern Timor-Australia collision zone with its many surrounding arcs is an appropriate analog for the Altaids in the Late Paleozoic. PUBLICATION ABSTRACT
The generation of kinetic‐scale flux ropes (KSFRs) is closely related to magnetic reconnection. Both flux ropes and reconnection sites are detected in the magnetosheath and can impact the dynamics ...upstream of the magnetopause. In this study, using the Magnetospheric Multiscale satellite, 12,623 KSFRs with a scale <20 RCi are statistically studied in the Earth's dayside magnetosheath. It is found that they are mostly generated near the bow shock (BS), and propagate downstream in the magnetosheath. Their quantity significantly increases as the scale decreases, consistent with a flux rope coalescence model. Moreover, the solar wind parameters can control the occurrence rate of KSFRs. They are more easily generated at high Mach number, large proton density, and weak magnetic field strength of the solar wind, similar to the conditions that favor BS reconnection. Our study shows a close connection between KSFR generation and BS reconnection.
Plain Language Summary
Kinetic‐scale flux ropes (KSFRs) exist widely in near‐earth space and play an important role in mass transport, energy conversion, and dissipation during magnetic field reconnection. The KSFR in the magnetosheath can be generated by reconnection in three regions: the magnetopause, the magnetosheath, and the BS. The spatial distribution of KSFRs can indirectly reflect the reconnection situation in the magnetosheath. We use various methods to select the KSFRs and study their spatial distribution and generation in the magnetosheath. Our results show that BS reconnection plays an important role in generating the KSFR in the magnetosheath.
Key Points
Kinetic‐scale flux ropes observed in the magnetosheath are primarily generated near the bow shock (BS) and travel to downstream magnetosheath
The quantity of flux ropes significantly increases as their scale decreases, which is in accordance with the FR coalescence model
The occurrence of flux ropes is influenced by solar wind parameters, and could strongly correlate with BS reconnection
Current densities associated with dipolarization fronts (DFs) have been calculated in the geomagnetic tail using the curlometer technique applied to high‐resolution magnetic field B→ data obtained by ...the four Cluster spacecraft. We then use the relation b→·∇×B→ to characterize the behavior of field‐aligned current (FAC) during 25 DF events. Our results show that the magnitude of FAC density (J//) ranges from 5 to 20 nA/m2, and they are observed in Northern and Southern Hemispheres flowing along both directions of the B→‐field. The FACs have dimensions characteristic of the DFs and with region‐1 current sense flowing inside the DFs and region‐2 sense just in front of DF (in the Bz dips). Most of our observations come from 15 to 20 RE in the tail, different from previous statistical studies based mainly on observations made around 9–12 RE. We suggest that DFs can sustain significant FACs and appear as “wedgelets” in the early stage.
Key Points
The DFs sustain significant FACs and appear as wedgelets in the early stage
Only the DFs with magnetic dips correspond with the region‐2 sense FACs
This work is case study and the calculations are more accurate
Solar wind parameters play a dominant role in reconnection rate, which controls the solar wind‐magnetosphere coupling efficiency at Earth's magnetopause. Besides, low‐energy ions from the ionosphere, ...frequently detected on the magnetospheric side of the magnetopause, also affect magnetic reconnection. However, the specific role of low‐energy ions in reconnection is still an open question under active discussion. In the present work, we report in situ observations of a multiscale, multi‐type magnetopause reconnection in the presence of low‐energy ions using NASA's Magnetospheric Multiscale data on September 11, 2015. This study divides ions into cold (10–500 eV) and hot (500–30,000 eV) populations. The observations can be interpreted as a secondary reconnection dominated by electrons and cold ions (mainly in XYGSE plane) located at the edge of an ion‐scale reconnection (mainly in XZGSE plane). This analysis demonstrates a dominant role of cold ions in the secondary reconnection without hot ions' response. Cold ions and electrons are accelerated and heated by the secondary process. The case study provides observational evidence for the simultaneous operation of antiparallel and component reconnection. Our results imply that the pre‐accelerated and heated cold ions and electrons in the secondary reconnection may participate in the primary ion‐scale reconnection affecting the solar wind‐magnetopause coupling and the complicated magnetic field topology could affect the reconnection rate.
Key Points
We report Magnetospheric Multiscale observations of a multiscale, multi‐type magnetopause reconnection in the presence of low‐energy ions
An electron‐cold ion reconnection, dominated by low‐energy ions and electrons, is located at the edge of an ion‐scale reconnection
The multiscale reconnection provides observational evidence for the simultaneous operation of antiparallel and component reconnection
Abstract
The fast transitions between different types of quasi-periodic oscillations (QPOs) are generally observed in black hole transient sources (BHTs). We present a detailed study of the timing ...and spectral properties of the transitions of type-B QPOs in MAXI J1348–630, observed by Insight-HXMT. The fractional rms variability–energy relationship and energy spectra reveal that type-B QPOs probably originate from jet precession. Compared to a weak power-law dominated power spectrum, when type-B QPOs are present, the corresponding energy spectrum shows an increase in the Comptonization component and the need for the
xillverCp
component, and a slight increase in the height of the corona when using the
relxilllp
model. Therefore, we suggest that a coupled inner disk-jet region is responsible for the observed type-B QPO transitions. The timescale for the appearance/disappearance of type-B QPOs is either long or short (seconds), which may indicate instability of the disk-jet structure. For these phenomena, we hypothesize that the Bardeen–Petterson effect causes the disk-jet structure to align with the BH spin axis or that the disappearance of small-scale jets bound by the magnetic flux tubes leads to the disappearance of type-B QPOs. We observed three events regarding the B/C transitions, one of which occurred over a short time period from ∼9.2 Hz (C) to ∼4.8 Hz (B). The energy spectral analysis for the other two transitions shows that when type-C QPO is present, the Comptonization flux is higher, the spectrum is harder, and the inner radius of the disk changes insignificantly. We suggest that type-C QPOs probably originate from relatively stronger jets or the corona.
Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic ...energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. Our results demonstrate that the ULF waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of radiation belt relativistic electrons.
HIAF (High Intensity heavy ion Accelerator Facility), a new facility planned in China for heavy ion related researches, consists of two ion sources, a high intensity Heavy Ion Superconducting Linac ...(HISCL), a 45 Tm Accumulation and Booster Ring (ABR-45) and a multifunction storage ring system. The key features of HIAF are unprecedented high pulse beam intensity and versatile operation mode. The HIAF project aims to expand nuclear and related researches into presently unreachable region and give scientists possibilities to conduct cutting-edge researches in these fields. The general description of the facility is given in this article with a focus on the accelerator design.
•A dynamic approach for simulating debonding in FRP-strengthened RC beams is presented.•Convergence difficulties are effectively overcome.•Overall static structural responses can be accurately ...predicted.•Dynamic responses due to cracking and/or debonding can be appropriately captured.
This paper is concerned with the finite element simulation of debonding failures in FRP-strengthened concrete beams. A key challenge for such simulations is that common solution techniques such as the Newton–Raphson method and the arc-length method often fail to converge. This paper examines the effectiveness of using a dynamic analysis approach in such FE simulations, in which debonding failure is treated as a dynamic problem and solved using an appropriate time integration method. Numerical results are presented to show that an appropriate dynamic approach effectively overcomes the convergence problem and provides accurate predictions of test results.
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