4,345 research outputs found
Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare
Magnetic reconnection is a rapid energy release process that is believed to
be responsible for flares on the Sun and stars. Nevertheless, such
flare-related reconnection is mostly detected to occur in the corona, while
there have been few studies concerning the reconnection in the chromosphere or
photosphere. Here we present both spectroscopic and imaging observations of
magnetic reconnection in the chromosphere leading to a microflare. During the
flare peak time, chromospheric line profiles show significant
blueshifted/redshifted components on the two sides of the flaring site,
corresponding to upflows and downflows with velocities of (70--80) km
s, comparable with the local Alfv\'{e}n speed as expected by the
reconnection in the chromosphere. The three-dimensional nonlinear force-free
field configuration further discloses twisted field lines (a flux rope) at a
low altitude, cospatial with the dark threads in He I 10830 \r{A} images. The
instability of the flux rope may initiate the flare-related reconnection. These
observations provide clear evidence of magnetic reconnection in the
chromosphere and show the similar mechanisms of a microflare to those of major
flares.Comment: 16 pages, 5 figures, accepted for publication in ApJ
Diaqua[3,5-bis(4-pyridyl)-1H-1,2,4-triazole-κN 3](pyridine-2,6-dicarboxylato-κ3 O 2,N,O 6)nickel(II)
In the title compound, [Ni(C7H3NO4)(C12H9N5)(H2O)2], the NiII atom is coordinated in a distorted octahedral geometry by one N and two O atoms from a pyridine-2,6-dicarboxylate ligand, one N atom from a 3,5-bis(4-pyridyl)-1H-1,2,4-triazole ligand in equatorial positions and two water molecules in axial positions. The crystal packing is consolidated by intermolecular O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds
9-[4-Hydroxy-3-(hydroxymethyl)butyl]guanine monohydrate
In the molecular structure of the title compound, also named penciclovir monohydrate, C10H15N5O3·H2O, the 4-hydroxy-3-hydroxymethylbut-1-yl group is connected to guanine through an N atom of the imidazole ring. Water molecules stabilize the molecular packing by forming O—H⋯O hydrogen bonds. A three-dimensional network is generated via intermolecular N—H⋯N, N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonding
Dark Matter Annihilation via Breit-Wigner Enhancement with Heavier Mediator
We propose a new scenario that both the dark matter freeze-out in the early
Universe and its possible annihilation for indirect detection around a
supermassive black hole are enhanced by a Breit-Wigner resonance. With the
mediator mass larger than the total initial dark matter mass, this annihilation
is almost forbidden at late times. Thus, the stringent cosmic microwave
background and indirect detection constraints do not apply. However, a
supermassive black hole can accelerate the dark matter particles to reactivate
this resonant annihilation whose subsequent decay to photons leaves a unique
signal. The running Fermi-LAT and the future COSI satellites can test this
scenario.Comment: 6 pages, 3 figure
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