The mechanism of superconductivity in cuprates remains one of the big challenges of condensed matter physics. High-Tc
cuprates crystallize into a layered perovskite structure featuring copper oxygen ...octahedral coordination. Due to the Jahn Teller effect in combination with the strong static Coulomb interaction, the octahedra in high-Tc
cuprates are elongated along the c axis, leading to a 3dx²-y² orbital at the top of the band structure wherein the doped holes reside. This scenario gives rise to 2D characteristics in high-Tc
cuprates that favor d-wave pairing symmetry. Here, we report superconductivity in a cuprate Ba₂CuO4-y, wherein the local octahedron is in a very exceptional compressed version. The Ba₂CuO4-y compound was synthesized at high pressure at high temperatures and shows bulk superconductivity with critical temperature (Tc
) above 70 K at ambient conditions. This superconducting transition temperature is more than 30 K higher than the Tc
for the isostructural counterparts based on classical La₂CuO₄. X-ray absorption measurements indicate the heavily doped nature of the Ba₂CuO4-y superconductor. In compressed octahedron, the 3d3z²-r² orbital will be lifted above the 3dx²-y² orbital, leading to significant 3D nature in addition to the conventional 3dx²-y² orbital. This work sheds important light on advancing our comprehensive understanding of the superconducting mechanism of high Tc
in cuprate materials.
The South Atlantic Anomaly (SAA) refers to a region where the strength of the magnetic field is notably weaker compared to a dipole field. While previous studies have primarily focused on its effects ...on the inner radiation belt, this study investigates its impact on the aurora system. By analyzing 2 years' worth of data obtained by the Fengyun‐3E/ACMag instrument, we discover that magnetic fluctuations within the auroral oval are significantly weaker in the longitude sector corresponding to the SAA, as compared to those outside this area. This characteristic remains permanent and independent of seasons and geomagnetic activities. Additional investigation using Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager (DMSP/SSUSI) observations reveals a similar phenomenon in the auroral intensity. Therefore, our results demonstrate that the SAA substantially weakens the aurora system, shedding new light on the effects of magnetic anomalies on planetary auroras and magnetosphere‐ionosphere‐thermosphere coupling.
Plain Language Summary
The South Atlantic Anomaly (SAA) is a unique location on Earth where the magnetic field is weaker than normal. This region has drawn a lot of attention because its weakened magnetic field brings the inner Van Allen radiation belt unusually close to the Earth's surface, which poses a threat to satellites passing through it. Here, we uncovered another interesting aspect of the SAA: its impact on the aurora system. To investigate this, we first examined 2 years' worth of data from the ACMag instruments on the Fengyun‐3E satellite, which orbits the Earth at an altitude of 836 km in a dawn‐dusk, Sun‐synchronous orbit. Our findings reveal that the magnetic fluctuations within the southern auroral oval are significantly weaker in the region that aligns with the SAA. This weakening effect is consistently present, regardless of the season or the level of geomagnetic activity. To reinforce our results, we also analyzed auroral intensity from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on the Defense Meteorological Satellite Program (DMSP) satellite, and it corroborated the same weakening trend in this data set. In conclusion, our observations demonstrate that the SAA has a substantial impact on weakening the aurora system. This discovery deepens our understanding of how magnetic anomalies can influence planetary auroras.
Key Points
The effects of the South Atlantic Anomaly (SAA) on the terrestrial aurora system are examined using multiple instruments
Observations reveal a substantial weakening of auroral magnetic fluctuations and auroral intensity in the SAA longitude sector
The results indicate considering magnetic anomalies like the SAA is essential for comprehensively understanding planetary aurora systems
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.
Free-electron lasers have been successfully operated with ultrahigh brightness and excellent transverse coherence at X-ray wavelengths. One of the next goals for further improvements is full ...coherence. An obvious approach is to seed the free-electron laser interaction using a conventional source that has good temporal coherence. Here, we show the first lasing of a free-electron laser with an echo-enabled harmonic generation scheme, which shows great promise for producing coherent lasing at short wavelengths, even in the X-ray regime. The experiment was conducted at a test facility that combines a 135.4 MeV electron accelerator with an amplifier consisting of a series of undulator magnets. Lasing was achieved at the third harmonic of the seed with a gain of ∼100,000 over spontaneous radiation. The measurements show typical exponential growth and excellent spectral characteristics, as well as good intensity stability.
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.
Composite structures made of 2 mm-thick titanium and 10 mm-thick carbon steel are widely used in infrastructures such as long-distance gas transportation. However, cracking, which is caused by ...intermetallic compounds (ICs), is a dominate failure mode in welds of this structure. Thus, a common way to improve the in-service life of is reduce the number of ICs. In this paper, we employ a novel hybrid welding method to fabricate composite structures of TA
titanium and Q235 carbon steel. Specifically, Ti and carbon steel is welded by laser and double Cold Metal Transfer (CMT) welding, respectively. The microstructure near the interface of Ti and steel is then examined using SEM, EBSD, EDS, with emphasis on the ICs in terms of chemical elements and morphologies. Results show that FeTi and Fe
Ti are the main ICs near the interface, and responsible for the failure of the welds. The effect of welding heat input on the formation of ICs is investigated as well. Results show that ICs are smaller when the heat input is low. Under low heat input circumstance, the tensile strength of the weld can reach up to 420 MPa.
Complex-valued neural networks have many advantages over their real-valued counterparts. Conventional digital electronic computing platforms are incapable of executing truly complex-valued ...representations and operations. In contrast, optical computing platforms that encode information in both phase and magnitude can execute complex arithmetic by optical interference, offering significantly enhanced computational speed and energy efficiency. However, to date, most demonstrations of optical neural networks still only utilize conventional real-valued frameworks that are designed for digital computers, forfeiting many of the advantages of optical computing such as efficient complex-valued operations. In this article, we highlight an optical neural chip (ONC) that implements truly complex-valued neural networks. We benchmark the performance of our complex-valued ONC in four settings: simple Boolean tasks, species classification of an Iris dataset, classifying nonlinear datasets (Circle and Spiral), and handwriting recognition. Strong learning capabilities (i.e., high accuracy, fast convergence and the capability to construct nonlinear decision boundaries) are achieved by our complex-valued ONC compared to its real-valued counterpart.
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 <3 s. One of the factors that may explain why the waves are unstructured inside the tail FPR but become discrete inside the near‐Earth FPR is the spatial inhomogeneity of magnetic field: we find that such inhomogeneity is small inside the near‐Earth FPR but large inside the tail FPR.
Key Points
Near‐Earth FPR: structured chorus; midtail FPR: unstructured whistlersSpatial inhomogeneity of magnetic field can explain such phenomenonRising‐tone chorus can evolve into falling‐tone chorus within <3 s
Ionospheric oxygen outflows (IOOs) are frequently observed in Earth's inner magnetosphere. As a potential fast mass source of the inner magnetosphere, they have been extensively studied for decades. ...In this study, we identified 271 IOO events from 6‐year Van Allen Probes (VAPs) data and conducted a statistical study to reveal when, where, and how they occur. All the events are observed in the nightside magnetosphere, with the occurrence rate peaking at the L‐shells corresponding to the auroral oval. The spatial scale of IOOs in the equatorial plane is estimated from the two‐spacecraft configuration of the VAP mission. The results show that, in statistics, IOOs are 3.9‐hr wide in magnetic local time and 1.0‐Earth radius wide in L‐shell. Further investigation shows that IOOs would shift to lower L‐shells and occupy a larger L‐shell extent as the AE index increases. Analysis of the environment conditions reveals that IOOs are statistically associated with AE‐index enhancements, ultra‐low‐frequency (ULF) waves, and magnetic field dipolarization, but not with any systematic variations in the SYM‐H index and the solar wind parameters. From this observation, we suggest that geomagnetic substorms and substorm‐associated processes (e.g., ULF waves) are potential triggers of inner‐magnetosphere IOOs.
Key Points
271 ionospheric oxygen outflow events are identified from 6‐year Van Allen Probes data
All the events are observed in the nightside magnetosphere, with the occurrence rate peaking at L‐shells corresponding to the auroral oval
The outflow events are statistically associated with substorms, ultra‐low‐frequency waves, and magnetic field dipolarization
The magnetosheath is inherently complex and rich, exhibiting various kinds of structures and perturbations. It is important to understand how these structures propagate and evolve and how they relate ...to the perturbations. Here we investigate a kind of magnetosheath structure known as a magnetic dip (MD). As far as we are aware, there have been no previous studies concerning the evolution (contracting or expanding) of these types of structures, and their propagation properties cannot be unambiguously determined. In this study, using Magnetospheric MultiScale (MMS) high‐temporal resolution data and multispacecraft analysis methods, we obtain the propagation and dynamic features of a set of MDs. Four different types of MDs are identified: “frozen‐in,” “expanding,” “contracting,” and “stable‐propagating.” Significantly, a stable‐propagation event is observed with a sunward propagation component. This indicates that the source of the structure in this case is closely associated with the magnetopause, which provides strong support to the contention in earlier research. We further reveal the mechanism leading to the MD contraction or expansion. The motion of the MDs boundary is found closely related with the dynamic pressure. The scale of the contracting and expanding events are typically ~5–20 ρi (ion gyroradius), significantly smaller than that of frozen‐in events (~40 ρi). The observations could relate large‐scale (more than several tens of ρi) and kinetic‐scale (less than ρi) MDs, by revealing an evolution that spans these different scales, and help us better understand the variation and dynamics of magnetosheath structures and plasmas.
Key Points
Four different propagation properties of magnetosheath magnetic dips are identified by using several multispacecraft analysis methods
Pressure imbalance plays an important role in the evolution (contracting and expanding) of sub‐MHD scale magnetic dips
A sunward propagating magnetic dip indicates that the structure source is closely associated with the magnetopause
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