296 research outputs found
Iris si iv line profiles: An indication for the plasmoid instability during small-scale magnetic reconnection on the sun
Our understanding of the process of fast reconnection has undergone a
dramatic change in the last 10 years driven, in part, by the availability of
high-resolution numerical simulations that have consistently demonstrated the
break-up of current sheets into magnetic islands, with reconnection rates that
become independent of Lundquist number, challenging the belief that fast
magnetic reconnection in flares proceeds via the Petschek mechanism that
invokes pairs of slow-mode shocks connected to a compact diffusion region. The
reconnection sites are too small to be resolved with images but these
reconnection mechanisms, Petschek and the plasmoid instability, have
reconnection sites with very different density and velocity structures and so
can be distinguished by high-resolution line-profiles observations. Using IRIS
spectroscopic observations we obtain a survey of typical line profiles produced
by small-scale events thought to be reconnection sites on the Sun. Slit-jaw
images are used to investigate the plasma heating and re-configuration at the
sites. A sample of 15 events from two active regions is presented. The line
profiles are complex with bright cores and broad wings extending to over 300
km/s. The profiles can be reproduced with the multiple magnetic islands and
acceleration sites that characterise the plasmoid instability but not by
bi-directional jets that characterise the Petschek mechanism. This result
suggests that if these small-scale events are reconnection sites, then fast
reconnection proceeds via the plasmoid instability, rather than the Petschek
mechanism during small-scale reconnection on the Sun.Comment: 10 pages, 18 Figures, to be published in Ap
Observations of supra-arcade fans: instabilities at the head of reconnection jets
Supra-arcade fans are bright, irregular regions of emission that develop
during eruptive flares, above flare arcades. The underlying flare arcades are
thought to be a consequence of magnetic reconnection along a current sheet in
the corona. At the same time, theory predicts plasma jets from the reconnection
site which would be extremely difficult to observe directly because of their
low density. It has been suggested that the dark supra-arcade downflows (SADs)
seen falling through supra-arcade fans may be low density jet plasma. The head
of a low density jet directed towards higher density plasma would be
Rayleigh-Taylor unstable, and lead to the development of rapidly growing low
and high density fingers along the interface. Using SDO/AIA 131A images, we
show details of SADs seen from three different orientations with respect to the
flare arcade and current sheet, and highlight features that have been
previously unexplained, such as the splitting of SADs at their heads, but are a
natural consequence of instabilities above the arcade. Comparison with 3-D
magnetohydrodynamic simulations suggests that supra-arcade downflows are the
result of secondary instabilities of the Rayleigh-Taylor type in the exhaust of
reconnection jets.Comment: 10 pages, 7 figures To be published in ApJ, 796, 27 (2014
Global Well-Posedness and Scattering for the Derivative Nonlinear Schrödinger Equation With Small Rough Data
Risk Assessment of Nautical Navigational Environment Based on Grey Fixed Weight Cluster
In order to set up a mathematical model suitable for nautical navigational environment risk evaluation and systematically master the navigational environment risk characteristics of the Qiongzhou Strait in a quantitative way, a risk assessment model with approach steps is set up based on the grey fixed weight cluster (GFWC). The evaluation index system is structured scientifically through both literature review and expert investigation. The relative weight of each index is designed to be obtained via fuzzy analytic hierarchy process (FAHP); Index membership degree of every grey class is proposed to be achieved by fuzzy statistics (FS) to avoid the difficulty of building whiten weight functions. By using the model, nautical navigational environment risk of the Qiongzhou Strait is determined at a “moderate” level according to the principle of maximum membership degree. The comprehensive risk evaluation of the Qiongzhou Strait nautical navigational environment can provide theoretical reference for implementing targeted risk control measures. It shows that the constructed GFWC risk assessment model as well as the presented steps are workable in case of incomplete information. The proposed strategy can excavate the collected experts’ knowledge mathematically, quantify the weight of each index and risk level, and finally lead to a comprehensive risk evaluation result. Besides, the adoptions of probability and statistic theory, fuzzy theory, aiming at solving the bottlenecks in case of uncertainty, will give the model a better adaptability and executability.</p
Immunomodulatory activity of carboxymethyl pachymaran on immunosuppressed mice induced by cyclophosphamide
The effects of immunomodulatory activity of two types of carboxymethyl pachymaran (CMP-1 and CMP-2) on cyclophosphamide (CTX)-induced mice were investigated. Both CMP-1 and CMP-2 were found to restore the splenomegaly and alleviate the spleen lesions and the mRNA ex-pressions of TLR4, MyD88, p65 and NF-κB in spleen were also increased. CMP-1 and CMP-2 could enhance the immunity by increasing the levels of TNF-α, IL-2, IL-6, IFN-γ, Ig-A and Ig-G in serum. In addition, CMP-1 could increase the relative abundance of Bacteroidetes and reduce the relative richness of Firmicutes at the phylum level. CMP-1 and CMP-2 could reduce the relative abundance Erysipelatoclostridum at the genus level. CMP-1 and CMP-2 might enhance the immune function of immunosuppression mice by regulating the gene expression in the TLR4/NF-κB signaling pathway and changing the composition and abundance of the intestinal microbiota. The results suggested that CMP-1 and CMP-2 would be as potential immunomodulatory agents in functional foods
Alleviating Behavior Data Imbalance for Multi-Behavior Graph Collaborative Filtering
Graph collaborative filtering, which learns user and item representations
through message propagation over the user-item interaction graph, has been
shown to effectively enhance recommendation performance. However, most current
graph collaborative filtering models mainly construct the interaction graph on
a single behavior domain (e.g. click), even though users exhibit various types
of behaviors on real-world platforms, including actions like click, cart, and
purchase. Furthermore, due to variations in user engagement, there exists an
imbalance in the scale of different types of behaviors. For instance, users may
click and view multiple items but only make selective purchases from a small
subset of them. How to alleviate the behavior imbalance problem and utilize
information from the multiple behavior graphs concurrently to improve the
target behavior conversion (e.g. purchase) remains underexplored. To this end,
we propose IMGCF, a simple but effective model to alleviate behavior data
imbalance for multi-behavior graph collaborative filtering. Specifically, IMGCF
utilizes a multi-task learning framework for collaborative filtering on
multi-behavior graphs. Then, to mitigate the data imbalance issue, IMGCF
improves representation learning on the sparse behavior by leveraging
representations learned from the behavior domain with abundant data volumes.
Experiments on two widely-used multi-behavior datasets demonstrate the
effectiveness of IMGCF.Comment: accepted by ICDM2023 Worksho
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