The disappearance of a narrow Mg II absorption system in quasar SDSS J165501.31+260517.4

In this letter, we present for the first time, the discovery of the disappearance of a narrow Mg II $\lambda\lambda2796,2803$ absorption system from the spectra of quasar SDSS J165501.31+260517.4 ($z_{\rm e}=1.8671$). This absorber is located at $z_{\rm abs} =1.7877$, and has a velocity offset of $8,423\rm ~km~s^{-1}$ with respect to the quasar. According to the velocity offset and the line variability, this narrow Mg II $\lambda\lambda2796,2803$ absorption system is likely intrinsic to the quasar. Since the corresponding UV continuum emission and the absorption lines of another narrow Mg II $\lambda\lambda2796,2803$ absorption system at $z_{\rm abs}=1.8656$ are very stable, we think that the disappearance of the absorption system is unlikely to be caused by the change in ionization of absorption gas. Instead, it likely arises from the motion of the absorption gas across the line of sight

Efficiency and power of minimally nonlinear irreversible heat engines with broken time-reversal symmetry

We study the minimally nonlinear irreversible heat engines in which the time-reversal symmetry for the systems may b e broken. The expressions for the power and the efficiency are derived, in which the effects of the nonlinear terms due to dissipations are included. We show that, as within the linear responses, the minimally nonlinear irreversible heat engines enable attainment of Carnot efficiency at positive power. We also find that the Curzon-Ahlborn limit imposed on the efficiency at maximum power can be overcomed if the time-reversal symmetry is broken

Analysis of the Teaching Strategy of English Continuation Task in Senior High School from the Perspective of Metacognitive Theory

With the emergence of new question type in the English reform of college Entrance examination, the academia has set off a research craze of "continuation task".This paper uses questionnaires and interviews with teachers to investigate and study the implementation, effect and existing problems of continuation task in senior high school English reading.Based on the teaching status and existing problems, this paper puts forward three strategies to improve the teaching effect of continuation task from the perspective of metacognitive theory, in order to help front-line English teachers in senior high schools effectively implement continuation task teaching, improve students' ability and level of continuation task, and thus improve students' English learning effect

Risk identification of PPP mode in stadiums and gymnasiums by ant colony algorithm

Aiming at the problem that the PPP model of stadiums and gymnasiums can not realize multi-dimensional risk analysis and the global risk identification ability is poor, an ant colony algorithm is proposed. Firstly, k clustering is used to cluster PPP mode data. Then, the ant colony algorithm is analyzed stochastically, and the risk set of PPP mode is obtained, which lays the foundation for later risk identification. Finally, through the random fusion function, the PPP mode risk set based on the path profile is constructed, and the optimal identification path is obtained, so as to improve the identification accuracy of PPP mode risk. MATLAB simulation shows that the ant colony algorithm proposed in this paper is superior to the risk clustering method in the overall risk identification accuracy and identification time of PPP mode. Therefore, the ant colony algorithm proposed in this paper can be used to identify the risk of PPP mode, to meet the needs of the construction of stadiums and gymnasiums