5,196 research outputs found
Rough matroids based on coverings
The introduction of covering-based rough sets has made a substantial
contribution to the classical rough sets. However, many vital problems in rough
sets, including attribution reduction, are NP-hard and therefore the algorithms
for solving them are usually greedy. Matroid, as a generalization of linear
independence in vector spaces, it has a variety of applications in many fields
such as algorithm design and combinatorial optimization. An excellent
introduction to the topic of rough matroids is due to Zhu and Wang. On the
basis of their work, we study the rough matroids based on coverings in this
paper. First, we investigate some properties of the definable sets with respect
to a covering. Specifically, it is interesting that the set of all definable
sets with respect to a covering, equipped with the binary relation of inclusion
, constructs a lattice. Second, we propose the rough matroids based
on coverings, which are a generalization of the rough matroids based on
relations. Finally, some properties of rough matroids based on coverings are
explored. Moreover, an equivalent formulation of rough matroids based on
coverings is presented. These interesting and important results exhibit many
potential connections between rough sets and matroids.Comment: 15page
Implications of Fermi-LAT observations on the origin of IceCube neutrinos
The IceCube (IC) collaboration recently reported the detection of TeV-PeV
extraterrestrial neutrinos whose origin is yet unknown. By the photon-neutrino
connection in and interactions, we use the \fermi-LAT
observations to constrain the origin of the IC detected neutrinos. We find that
Galactic origins, i.e., the diffuse Galactic neutrinos due to cosmic ray (CR)
propagation in the Milky Way, and the neutrinos from the Galactic point
sources, may not produce the IC neutrino flux, thus these neutrinos should be
of extragalactic origin. Moreover, the extragalactic gamma-ray bursts (GRBs)
may not account for the IC neutrino flux, the jets of active galactic nuclei
may not produce the IC neutrino spectrum, but the starburst galaxies (SBGs) may
be promising sources. As suggested by the consistency between the IC detected
neutrino flux and the Waxman-Bahcall bound, GRBs in SBGs may be the sources of
both the ultrahigh energy, eV, CRs and the ~PeV CRs that
produce the IC detected TeV-PeV neutrinos.Comment: JCAP accepted version; 8 pages, 2 figs; discussion on blazar origin
added; conclusion unchange
One Fits All: A Unified Synchrotron Model Explains GRBs with FRED-Shaped Pulses
The analysis of gamma-ray burst (GRB) spectra often relies on empirical
models like the Band function, which lacks a distinct physical explanation.
Previous attempts to couple physical models with observed data have been
confined to individual burst studies, where the model is fitted to segmented
spectra with independent physical parameters. These approaches frequently fail
to explain the spectral evolution, which should be governed by a consistent set
of physical conditions. In this study, we propose a novel approach by
incorporating the synchrotron radiation model to provide a self-consistent
explanation for a selection of single-pulse GRBs. Our sample is carefully
chosen to minimize contamination from overlapping pulses, allowing for a
comprehensive test of the synchrotron model under a unified physical condition,
such as a single injection event of electrons. By tracing the evolution of
cooling electrons in a decaying magnetic field, our model predicts a series of
time-dependent observed spectra that align well with the observed data.
Remarkably, using a single set of physical parameters, our model successfully
fits all time-resolved spectra within each burst. Additionally, our model
accurately predicts the evolution of some key features of GRBs such as the
spectral peak and light curve shapes, all of which are consistent
with observations. Our findings strongly support the notion that the spectral
and temporal evolution in GRB pulses originates from the expansion of the GRB
emission region with an initial radius of approximately cm, with
synchrotron radiation being the underlying emission mechanism.Comment: 25 pages, 18 figures, 4 table
Poly[diaqua(μ-oxalato)(μ-2-oxidopyridinium-3-carboxylato)praseodymium(III)]
In the title complex, [Pr(C6H4NO3)(C2O4)(H2O)2]n, each PrIII ion is coordinated by eight O atoms from two 2-oxynicotinate ligands, two oxalate ligands and two water molecules, displaying a distorted bicapped square-antiprismatic geometry. The carboxylate groups link adjacent praseodymium metal centres, forming layers parallel to the bc plane. The crystal packing is stabilized by intermolecular O—H⋯O and N—H⋯O hydrogen bonds
[meso-Tetrakis(4-heptyloxyphenyl)porphyrinato]nickel(II)
In the title compound, [Ni(C72H84N4O4)], the four-coordinate NiII ion in the middle of the planar 24-membered porphyrin ring is located on a crystallograpic inversion center, with Ni—N distances of 1.946 (2)–1.951 (2) Å. The 4-heptyloxyphenyl groups are twisted with respect to the porphyrin mean plane, the dihedral angles being 88.5 (3) and 79.1 (2)°
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