81,492 research outputs found
On the non-thermal kappa-distributed electrons in planetary nebulae and HII regions: the kappa index and its correlations with other nebular properties
Recently, a suspicion arose that the free electrons in planetary nebulae
(PNe) and HII regions might have non-thermal energy distributions. In this
scenario, a kappa index is introduced to characterize the electron energy
distributions, with smaller kappa values indicating larger deviations from
Maxwell-Boltzmann distributions. Assuming that this is the case, we determine
the kappa values for a sample of PNe and HII regions by comparing the
intensities of [OIII] collisionally excited lines and the hydrogen Balmer jump.
We find the average kappa indices of PNe and HII regions to be 27 and 32,
respectively. Correlations between the resultant kappa values and various
physical properties of the nebulae are examined to explore the potential origin
of non-thermal electrons in photoionized gaseous nebulae. However, no positive
result is obtained. Thus the current analysis does not lend to support to the
idea that kappa-distributed electrons are present in PNe and HII regions.Comment: 23 pages, 6 figures, accepted for publication in Ap
H I Free-Bound Emission of Planetary Nebulae with Large Abundance Discrepancies: Two-Component Models versus Kappa-distributed electrons
The "abundance discrepancy" problem in the study of planetary nebulae (PNe),
viz., the problem concerning systematically higher heavy-element abundances
derived from optical recombination lines relative to those from collisionally
excited lines, has been under discussion for decades, but no consensus on its
solution has yet been reached. In this paper we investigate the hydrogen
free-bound emission near the Balmer jump region of four PNe that are among
those with the largest abundance discrepancies, aiming to examine two recently
proposed solutions to this problem: two-component models and Kappa electron
energy distributions. We find that the Balmer jump intensities and the spectrum
slopes cannot be simultaneously matched by the theoretical calculations based
upon single Maxwell-Boltzmann electron-energy distributions, whereas the
fitting can be equally improved by introducing Kappa electron energy
distributions or an additional Maxwell-Boltzmann component. We show that
although H I free-bound emission alone cannot distinguish the two scenarios, it
can provide important constraints on the electron energy distributions,
especially for cold and low-Kappa plasmas.Comment: 23 pages, 10 figures, accepted for publication in Ap
Subsystem Rényi Entropy of Thermal Ensembles for SYK-like models
The Sachdev-Ye-Kitaev model is an N-modes fermionic model with infinite range random interactions. In this work, we study the thermal Rényi entropy for a subsystem of the SYK model using the path-integral formalism in the large-N limit. The results are consistent with exact diagonalization [1] and can be well approximated by thermal entropy with an effective temperature [2] when subsystem size M ≤ N/2. We also consider generalizations of the SYK model with quadratic random hopping term or U(1) charge conservation
Relativistic effects on the observed AGN luminosity distribution
Recently Zhang (2005) has proposed a model to account for the well
established effect that the fraction of type-II AGNs is anti-correlated with
the observed X-ray luminosity; the model consists of an X-ray emitting
accretion disk coaligned to the dusty torus within the standard AGN unification
model. In this paper the model is refined by including relativistic effects of
the observed X-ray radiations from the vicinity of the supermassive black hole
in an AGN. The relativistic corrections improve the combined fitting results of
the observed luminosity distribution and the type-II AGN fraction, though the
improvement is not significant. The type-II AGN fraction prefers non- or mildly
spinning black hole cases and rules out the extremely spinning case.Comment: 9 pages, 4 figures, accepted for publication in PAS
Satellite Broadcasting Enabled Blockchain Protocol: A Preliminary Study
Low throughput has been the biggest obstacle of large-scale blockchain
applications. During the past few years, researchers have proposed various
schemes to improve the systems' throughput. However, due to the inherent
inefficiency and defects of the Internet, especially in data broadcasting
tasks, these efforts all rendered unsatisfactory. In this paper, we propose a
novel blockchain protocol which utilizes the satellite broadcasting network
instead of the traditional Internet for data broadcasting and consensus tasks.
An automatic resumption mechanism is also proposed to solve the unique
communication problems of satellite broadcasting. Simulation results show that
the proposed algorithm has a lower communication cost and can greatly improve
the throughput of the blockchain system. Theoretical estimation of a satellite
broadcasting enabled blockchain system's throughput is 6,000,000 TPS with a 20
gbps satellite bandwidth.Comment: Accepted by 2020 Information Communication Technologies Conference
(ICTC 2020
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