Polarization of Fast Radio Bursts: radiation mechanisms and propagation effects

Fast radio bursts (FRBs) are observed to be highly polarized. Most have high linear polarization but a small fraction show significant circular polarization. We systematically investigate a variety of polarization mechanisms of FRBs within the magnetar theoretical framework considering two emission sites inside and outside the magnetosphere. For each site, we discuss both intrinsic radiation mechanisms and propagation effects. Inside the magnetosphere, we investigate the polarization properties of both coherent curvature radiation and inverse Compton scattering by charged bunches and conclude that both mechanisms produce 100\% linear polarization at an on-axis geometry but can produce circular polarization if the viewing angle is off axis. The lack of circular polarization for the majority of bursts requires that the bunches have a large transverse dimension size. Resonant cyclotron absorption within magnetosphere may produce high circular polarization if electrons and positrons have an asymmetric Lorentz factor distribution. Outside the magnetosphere, the synchrotron maser emission mechanism in general produces highly linearly polarized emission. Circular polarization would appear at off-beam angles but the flux is greatly degraded and such bursts are not detectable at cosmological distances. Synchrotron absorption in a nebula with ordered magnetic field may reduce the circular polarization degree. Cyclotron absorption in a strongly magnetized medium may generate significant circular polarization. Faraday conversion in a medium with field reversal can convert one polarization mode to another. The two absorption processes require stringent physical conditions. Significant Faraday conversion may be realized in a magnetized dense environment involving binary systems or supernova remnants.Comment: 30 pages, 15 figures. Accepted for publication in MNRA

Path planning of mobile robot based on hybrid improved artificial fish swarm algorithm

The artificial fish swarm algorithm is easy to fall into the local optimum for robot global path planning. A hybrid improved Artificial Fish Swarm Algorithm (HIAFSA) is proposed. Firstly, the sub-optimal path is determined by A* algorithm, and then the adaptive behavior of artificial fish swarm algorithm is improved based on the inertia weight factor, and the attenuation function α is introduced to improve the visual range and moving step length of the artificial fish, balance the global path planning and local path planning, and further improve the convergence speed and quality of the solution. The experimental results show that the hybrid improved artificial fish swarm algorithm has been improved in avoiding local optimum, convergence speed and precision

The plasma suppression effect can be ignored in realistic FRB models invoking bunched coherent radio emission

One widely discussed mechanism to produce highly coherent radio emission of fast radio bursts (FRBs) is coherent emission by bunches, either via curvature radiation or inverse Compton scattering (ICS). It has been suggested that the plasma oscillation effect can significantly suppress coherent emission power by bunches. We examine this criticism in this paper. The suppression factor formalism was derived within the context of radio pulsars in which radio waves are in the low-amplitude, linear regime and cannot directly be applied to the large-amplitude, non-linear regime relevant for FRBs. Even if one applies this linear treatment, plasma suppression is not important for two physical reasons. First, for an efficient radiation mechanism such as ICS, the required plasma density is not high so that a high-density plasma may not exist. Second, both bunched coherent mechanisms demand that a large global parallel electric field ($E_\parallel$) must exist in the emission region in order to continuously inject energy to the bunches to power an FRB. In order to produce typical FRB duration via coherent curvature or ICS radiation, a parallel electric field must be present to balance the acceleration and radiation back-reaction. The plasma suppression factor should be modified with the existence of $E_\parallel$. We show that the correction factor for curvature radiation, $f_{\rm cur}$, increases with $E_\parallel$ and becomes 1 when $E_\parallel$ reaches the radiation-reaction-limited regime. We conclude that the plasma suppression effect can be ignored for realistic FRB emission models invoking bunched coherent radio emission.Comment: 9 pages, 2 figures. Accepted for publication in MNRA

Aluminum Mineral Processing and Metallurgy: Iron-Rich Bauxite and Bayer Red Muds

Bauxite is the main source for alumina production. With the rapid development of iron and steel industry and aluminum industry, high-quality iron ore and bauxite resources become increasingly tense. However, a lot of iron-rich bauxite and Bayer red mud resources have not been timely and effectively recycled, resulting in serious problems of environmental pollution and wastage of resources. The comprehensive utilization of iron-rich bauxite and red mud is still a worldwide problem. The industrial stockpiling is not a fundamental way to solve the problems of iron-rich bauxite and red mud. As to the recovery of valuable metals from iron-rich bauxite and red mud, there are a lot of technical and cost problems, which are serious impediments to industrial development. Applying red mud as construction materials like cement, soil ameliorant applications face the problem of Na, Cr, As leaching into the environment. However, the high-temperature reduction, smelting and alkaline leaching process is a feasible method to recover iron and alumina from iron-rich bauxite and red mud. This chapter intends to provide the reader an overview on comprehensive utilization technology of the low-grade iron-rich bauxite and Bayer red mud sources

Oscillation criteria for third-order neutral differential equations with continuously distributed delay

AbstractThe purpose of this paper is to study the oscillation of a certain class of third-order neutral differential equations with continuously distributed delay. By using a generalized Riccati transformation and integral averaging technique, we establish some new sufficient conditions which ensure that every solution of this equation oscillates or converges to zero

How Does a Review Officer and Her Incentivized Contribution Affect the Review System?

Online retail platforms have increasingly employed a new incentive strategy by recruiting review officers and offering monetary rewards for posting incentivized reviews. However, there may be unintended effects of such incentivized reviews on the review system. Using a weekly-product panel dataset, we bridge the causal links between the emergence of incentivized reviews and the reviewers’ subsequent posting behaviors. We show that the emergence of incentivized reviews exerts a positive impact on the reviewers’ overall subsequent contributions. However, we show detrimental effects of incentivized reviews on the subsequent regular (non-incentivized) reviews, reflected in reduced engagement, decreased quality, and usefulness. Our mechanism analyses by separating the title effect and the quality effect show that the positive effect of incentivized reviews can be explained by the observational learning of the high-quality content while the adverse effects may be attributed to the demotivation of regular reviewers in response to the incentivized officer-titles

Understanding Booking Intention of Consumers in Online Short Rental Platforms: Social Presence, Perceived Social Benefits, and Trust

For studying the whole process of online short rental platform consumers, which start from the attention to the booking intention, this paper based on the social presence theory, analyzed the consumers\u27 online short rental booking intention from the social perspective. Taking the consumers\u27 perceived social benefits and trust as mediators, we explored the process and mechanism of consumers\u27 booking intention on the short rental platform and constructs a research model of consumer online short rental booking intention. Then, the empirical studies have shown that social presence can influence consumers\u27 booking intention by increasing their perceived social benefits and trust. Finally, based on the results, the recommendations of online short rental platform and the host were put forward

Oscillation of second order self-conjugate differential equation with impulses

AbstractIn this paper, we investigate the oscillation of second-order self-conjugate differential equation with impulses(1)(a(t)(x(t)+p(t)x(t-τ))′)′+q(t)x(t-σ)=0,t≠tk,t⩾t0,(2)x(tk+)=(1+bk)x(tk),k=1,2,…,(3)x′(tk+)=(1+bk)x′(tk),k=1,2,…,where a,p,q are continuous functions in [t0,+∞), q(t)⩾0, a(t)>0, ∫t0∞(1/a(s))ds=∞, τ>0, σ>0, bk>-1, 0<t0<t1 <t2<⋯<tk<⋯ and limk→∞tk=∞. We get some sufficient conditions for the oscillation of solutions of Eqs. (1)–(3)

Path planning of mobile robot based on hybrid improved artificial fish swarm algorithm

The artificial fish swarm algorithm is easy to fall into the local optimum for robot global path planning. A hybrid improved Artificial Fish Swarm Algorithm (HIAFSA) is proposed. Firstly, the sub-optimal path is determined by A* algorithm, and then the adaptive behavior of artificial fish swarm algorithm is improved based on the inertia weight factor, and the attenuation function α is introduced to improve the visual range and moving step length of the artificial fish, balance the global path planning and local path planning, and further improve the convergence speed and quality of the solution. The experimental results show that the hybrid improved artificial fish swarm algorithm has been improved in avoiding local optimum, convergence speed and precision