138 research outputs found
The Initiation Mechanism of the First On-disk X-Class Flare of Solar Cycle 25
In this paper we study the initiation mechanism of the first on-disk X-class
eruptive flare in solar cycle 25. Coronal magnetic field reconstructions reveal
a magnetic flux rope (MFR) with configuration highly consistent with a filament
existing for a long period before the flare, and the eruption of the whole
filament indicates that the MFR erupted during the flare. However, quantitative
analysis shows that the pre-flare MFR resides in a height too low to trigger a
torus instability (TI). The filament experienced a slow rise before the flare
onset, for which we estimate evolution of the filament height using a
triangulation method by combining the SDO and STEREO observations, and find it
is also much lower than the critical height for triggering TI. On the other
hand, the pre-flare evolution of the current density shows progressive thinning
of a vertical current layer on top of the flare PIL, which suggests that a
vertical current sheet forms before the eruption. Meanwhile, there is
continuously shearing motion along the PIL under the main branch of the
filament, which can drive the coronal field to form such a current sheet. As
such, we suggest that the event follows a reconnection-based initiation
mechanism as recently established using a high-accuracy MHD simulation, in
which an eruption is initiated by reconnection in a current sheet that forms
gradually within continuously-sheared magnetic arcade. The eruption should be
further driven by TI as the filament quickly rises into the TI domain during
the eruption
Novel MSVPWM to Reduce the Inductor Current Ripple for Z-Source Inverter in Electric Vehicle Applications
Microstructural evolution of Cu–Sn–Ni compounds in full intermetallic micro-joint and in situ micro-bending test
This study focuses on the microstructural evolution process of Cu–Sn–Ni intermetallic compounds (IMCs) interlayer in the
micro-joints, formed from the initial Ni/Sn (1.5 µm)/Cu structure through transient liquid phase (TLP) soldering. Under the
bonding temperature of 240 °C, the micro-joints evolve into Ni/(Cu, Ni)6Sn5/(Cu, Ni)3Sn/Cu structure, where the interfacial
reactions on Cu/Sn and Sn/Ni are suppressed by the atoms diffusing from the opposite side. The thickness of (Cu, Ni)3Sn
layer on plated Cu layer still increases with the prolonged dwell time. When the bonding temperature was elevated to 290 °C,
the phase transformation of (Cu, Ni)6Sn5 into (Cu, Ni)3Sn has been accelerated, thus the majority of IMCs interlayer is
constituted with (Cu, Ni)3Sn. However, a small amount of Ni-rich (Cu, Ni)6Sn5 phases still remain near the Ni substrate and
some of them close to the center-line of IMCs interlayer. The state between (Cu, Ni)6Sn5 and the adjacent (Cu, Ni)3Sn tends
to reach equilibrium in Ni content based on the observation from Transmission Electron Microscope (TEM). In addition,
the Cu–Sn–Ni IMCs micro-cantilevers were fabricated from these micro-joints using Focus Ion Beam (FIB) for the in situ
micro-bending test, the results indicate a high ultimate tensile strength as well as the brittle fracture in the inter- and transgranular modes
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A van der Waals antiferromagnetic topological insulator with weak interlayer magnetic coupling.
Magnetic topological insulators (TI) provide an important material platform to explore quantum phenomena such as quantized anomalous Hall effect and Majorana modes, etc. Their successful material realization is thus essential for our fundamental understanding and potential technical revolutions. By realizing a bulk van der Waals material MnBi4Te7 with alternating septuple [MnBi2Te4] and quintuple [Bi2Te3] layers, we show that it is ferromagnetic in plane but antiferromagnetic along the c axis with an out-of-plane saturation field of ~0.22 T at 2 K. Our angle-resolved photoemission spectroscopy measurements and first-principles calculations further demonstrate that MnBi4Te7 is a Z2 antiferromagnetic TI with two types of surface states associated with the [MnBi2Te4] or [Bi2Te3] termination, respectively. Additionally, its superlattice nature may make various heterostructures of [MnBi2Te4] and [Bi2Te3] layers possible by exfoliation. Therefore, the low saturation field and the superlattice nature of MnBi4Te7 make it an ideal system to investigate rich emergent phenomena
Breed, sex and anatomical location-specific gene expression profiling of the porcine skeletal muscles
Taking the pulse of COVID-19: A spatiotemporal perspective
The sudden outbreak of the Coronavirus disease (COVID-19) swept across the
world in early 2020, triggering the lockdowns of several billion people across
many countries, including China, Spain, India, the U.K., Italy, France,
Germany, and most states of the U.S. The transmission of the virus accelerated
rapidly with the most confirmed cases in the U.S., and New York City became an
epicenter of the pandemic by the end of March. In response to this national and
global emergency, the NSF Spatiotemporal Innovation Center brought together a
taskforce of international researchers and assembled implemented strategies to
rapidly respond to this crisis, for supporting research, saving lives, and
protecting the health of global citizens. This perspective paper presents our
collective view on the global health emergency and our effort in collecting,
analyzing, and sharing relevant data on global policy and government responses,
geospatial indicators of the outbreak and evolving forecasts; in developing
research capabilities and mitigation measures with global scientists, promoting
collaborative research on outbreak dynamics, and reflecting on the dynamic
responses from human societies.Comment: 27 pages, 18 figures. International Journal of Digital Earth (2020
A repeating fast radio burst associated with a persistent radio source
The dispersive sweep of fast radio bursts (FRBs) has been used to probe the ionized baryon content of the intergalactic medium1, which is assumed to dominate the total extragalactic dispersion. Although the host-galaxy contributions to the dispersion measure appear to be small for most FRBs2, in at least one case there is evidence for an extreme magneto-ionic local environment3,4 and a compact persistent radio source5. Here we report the detection and localization of the repeating FRB 20190520B, which is co-located with a compact, persistent radio source and associated with a dwarf host galaxy of high specific-star-formation rate at a redshift of 0.241 ± 0.001. The estimated host-galaxy dispersion measure of approximately 903−111+72 parsecs per cubic centimetre, which is nearly an order of magnitude higher than the average of FRB host galaxies2,6, far exceeds the dispersion-measure contribution of the intergalactic medium. Caution is thus warranted in inferring redshifts for FRBs without accurate host-galaxy identifications
Solar Ring Mission: Building a Panorama of the Sun and Inner-heliosphere
Solar Ring (SOR) is a proposed space science mission to monitor and study the
Sun and inner heliosphere from a full 360{\deg} perspective in the ecliptic
plane. It will deploy three 120{\deg}-separated spacecraft on the 1-AU orbit.
The first spacecraft, S1, locates 30{\deg} upstream of the Earth, the second,
S2, 90{\deg} downstream, and the third, S3, completes the configuration. This
design with necessary science instruments, e.g., the Doppler-velocity and
vector magnetic field imager, wide-angle coronagraph, and in-situ instruments,
will allow us to establish many unprecedented capabilities: (1) provide
simultaneous Doppler-velocity observations of the whole solar surface to
understand the deep interior, (2) provide vector magnetograms of the whole
photosphere - the inner boundary of the solar atmosphere and heliosphere, (3)
provide the information of the whole lifetime evolution of solar featured
structures, and (4) provide the whole view of solar transients and space
weather in the inner heliosphere. With these capabilities, Solar Ring mission
aims to address outstanding questions about the origin of solar cycle, the
origin of solar eruptions and the origin of extreme space weather events. The
successful accomplishment of the mission will construct a panorama of the Sun
and inner-heliosphere, and therefore advance our understanding of the star and
the space environment that holds our life.Comment: 41 pages, 6 figures, 1 table, to be published in Advances in Space
Researc
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