4,131 research outputs found
Heating of Flare Loops With Observationally Constrained Heating Functions
We analyze high cadence high resolution observations of a C3.2 flare obtained
by AIA/SDO on August 1, 2010. The flare is a long duration event with soft
X-ray and EUV radiation lasting for over four hours. Analysis suggests that
magnetic reconnection and formation of new loops continue for more than two
hours. Furthermore, the UV 1600\AA\ observations show that each of the
individual pixels at the feet of flare loops is brightened instantaneously with
a timescale of a few minutes, and decays over a much longer timescale of more
than 30 minutes. We use these spatially resolved UV light curves during the
rise phase to construct empirical heating functions for individual flare loops,
and model heating of coronal plasmas in these loops. The total coronal
radiation of these flare loops are compared with soft X-ray and EUV radiation
fluxes measured by GOES and AIA. This study presents a method to
observationally infer heating functions in numerous flare loops that are formed
and heated sequentially by reconnection throughout the flare, and provides a
very useful constraint to coronal heating models.Comment: This paper is revise
UV and EUV Emissions at the Flare Foot-points Observed by AIA
A solar flare is composed of impulsive energy release events by magnetic
reconnection, which forms and heats flare loops. Recent studies have revealed a
two-phase evolution pattern of UV 1600\AA\ emission at the feet of these loops:
a rapid pulse lasting for a few seconds to a few minutes, followed by a gradual
decay on timescales of a few tens of minutes. Multiple band EUV observations by
AIA further reveal very similar signatures. These two phases represent
different but related signatures of an impulsive energy release in the corona.
The rapid pulse is an immediate response of the lower atmosphere to an intense
thermal conduction flux resulting from the sudden heating of the corona to high
temperatures (we rule out energetic particles due to a lack of significant hard
X-ray emission). The gradual phase is associated with the cooling of hot plasma
that has been evaporated into the corona. The observed footpoint emission is
again powered by thermal conduction (and enthalpy), but now during a period
when approximate steady state conditions are established in the loop. UV and
EUV light curves of individual pixels may therefore be separated into
contributions from two distinct physical mechanisms to shed light on the nature
of energy transport in a flare. We demonstrate this technique using
coordinated, spatially resolved observations of UV and EUV emission from the
footpoints of a C3.2 thermal flare
Fundamental and second-order dark soliton solutions of 2- and 3-component Manakov equations in the defocusing regime
We present exact multi-parameter families of soliton solutions for two- and
three-component Manakov equations in the \emph{defocusing} regime. Existence
diagrams for such solutions in the space of parameters are presented.
Fundamental soliton solutions exist only in finite areas on the plane of
parameters. Within these areas, the solutions demonstrate rich spatio-temporal
dynamics. The complexity increases in the case of 3-component solutions. The
fundamental solutions are dark solitons with complex oscillating patterns in
the individual wave components. At the boundaries of existence, the solutions
are transformed into plain (non-oscillating) vector dark solitons. The
superposition of two dark solitons in the solution adds more frequencies in the
patterns of oscillating dynamics. These solutions admit degeneracy when the
eigenvalues of fundamental solitons in the superposition coincide.Comment: 29 pages, 22figure
High Temperature Corrosion Behaviors of the Superheater Materials
AbstractThe high temperature corrosion tests are performed on 20#steel, TP347H and superalloy C22. The high temperature corrosion behaviors of these superheater materials in the synthetic salt containing 80wt-%KCl+20wt-%K2SO4 have been investigated under the oxidizing atmosphere at a temperature of 650°C for 218hours. For comparison, the column diagram has been obtained by mass loss. The scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) is used to characterize the surface morphology and compositions of the corrosion products. The results have shown that the superalloy C22 exhibits the high corrosion resistance
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Dexmedetomidine post-treatment attenuates cardiac ischaemia/reperfusion injury by inhibiting apoptosis through HIF-1α signalling.
Hypoxia-inducible factor 1α (HIF-1α) plays a critical role in the apoptotic process during cardiac ischaemia/reperfusion (I/R) injury. This study aimed to investigate whether post-treatment with dexmedetomidine (DEX) could protect against I/R-induced cardiac apoptosis in vivo and in vitro via regulating HIF-1α signalling pathway. Rat myocardial I/R was induced by occluding the left anterior descending artery for 30 minutes followed by 6-hours reperfusion, and cardiomyocyte hypoxia/reoxygenation (H/R) was induced by oxygen-glucose deprivation for 6 hours followed by 3-hours reoxygenation. Dexmedetomidine administration at the beginning of reperfusion or reoxygenation attenuated I/R-induced myocardial injury or H/R-induced cell death, alleviated mitochondrial dysfunction, reduced the number of apoptotic cardiomyocytes, inhibited the activation of HIF-1α and modulated the expressions of apoptosis-related proteins including BCL-2, BAX, BNIP3, cleaved caspase-3 and cleaved PARP. Conversely, the HIF-1α prolyl hydroxylase-2 inhibitor IOX2 partly blocked DEX-mediated cardioprotection both in vivo and in vitro. Mechanistically, DEX down-regulated HIF-1α expression at the post-transcriptional level and inhibited the transcriptional activation of the target gene BNIP3. Post-treatment with DEX protects against cardiac I/R injury in vivo and H/R injury in vitro. These effects are, at least in part, mediated via the inhibition of cell apoptosis by targeting HIF-1α signalling
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