We study the rates of tidal disruption of stars by intermediate-mass to supermassive black holes on bound to unbound orbits by using high-accuracy direct N-body experiments. The approaching stars from the star cluster to the black hole can take three types of orbit: eccentric, parabolic, and hyperbolic orbits. Since the mass fallback rate shows a different variability depending on these orbital types, we can classify tidal disruption events (TDEs) into three main categories: eccentric, parabolic, and hyperbolic TDEs. Respective TDEs are characterized by two critical values of the orbital eccentricity: the lower critical eccentricity is the one below which the stars on eccentric orbits cause the finite, intense accretion, and the higher critical eccentricity above which the stars on hyperbolic orbits cause no accretion. Moreover, we find that the parabolic TDEs are divided into three subclasses: precisely parabolic, marginally eccentric, and marginally hyperbolic TDEs. We analytically derive that the mass fallback rate of the marginally eccentric TDEs can be flatter and slightly higher than the standard fallback rate proportional to t −5/3 , whereas it can be flatter and lower for the marginally hyperbolic TDEs. We confirm by N-body experiments that only few eccentric, precisely parabolic, and hyperbolic TDEs can occur in a spherical stellar system with a single intermediate-mass to supermassive black hole. A substantial fraction of the stars approaching to the black hole would cause the marginally eccentric or marginally hyperbolic TDEs.

Tidal Disruption of stars by super massive central black holes from dense star clusters is modeled by high-accuracy direct N -body simulation. The time evolution of the stellar tidal disruption rate, the effect of tidal disruption on the stellar density profile and for the first time the detailed origin of tidally disrupted stars are carefully examined and compared with classic papers in the field. Up to 128k particles are used in simulation to model the star cluster around the super massive black hole, we use the particle number and the tidal radius of black hole as free parameters for a scaling analysis. The transition from full to empty loss-cone is analyzed in our data, the tidal disruption rate scales with the particle number N in the expected way for both cases. For the first time in numerical simulations (under certain conditions) we can support the concept of a critical radius of Frank & Rees (1976), which claims that most stars are tidally accreted on highly eccentric orbits originating from regions far outside the tidal radius. Due to the consumption of stars moving on radial orbits, a velocity anisotropy is founded inside the cluster. Finally we make an estimation for the real galactic center based on our simulation results and the scaling analysis.

The current situation of coronavirus disease 2019 (COVID-19) is rapidly evolving. Radiation therapy facilities are places of concentrated patient interactions. Oncology patients with immunosuppression are at a higher risk for contracting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and easily developing severe postinfection events during the SARS-CoV-2 outbreaks. This review aimed to provide some guidance and be a reference to medical professionals in radiation oncology so that they may provide oncology patients with safe and high-quality care. Methods and Materials: This paper discussed how radiation therapy departments or centers can most effectively respond to this public health emergency through summarizing the procedures and protocols implemented at hospitals in ShenZhen, China. Results: The impact of the virus in radiation therapy facilities can be mitigated and managed with appropriate and timely implementation of infection control procedures and protocols. Conclusions: In the face of acute infectious disease, it is critical to maintain strict infectious disease control procedures and to create a clear clinical workflow protocol to best protect medical staff and patients from the effect of acute infectious diseases.

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