Escape, capture, and levitation of matter in Eddington outbursts

Context: An impulsive increase in luminosity by one half or more of the Eddington value will lead to ejection of all optically thin plasma from Keplerian orbits around the radiating star, if gravity is Newtonian and the Poynting-Robertson drag is neglected. Radiation drag may bring some particles down to the stellar surface. On the other hand, general relativistic calculations show that gravity may be balanced by a sufficiently intense radiation field at a certain distance from the star. Aims: We investigate the motion of test particles around highly luminous stars to determine conditions under which plasma may be ejected from the system. Results: In Einstein's gravity, if the outburst is close to the Eddington luminosity, all test particles orbiting outside an "escape sphere" will be ejected from the system, while all others will be captured from their orbits onto the surface of another sphere, which is well above the stellar surface, and may even be outside the escape sphere, depending on the value of luminosity. Radiation drag will bring all the captured particles to rest on this "Eddington capture sphere," where they will remain suspended in an equilibrium state as long as the local flux of radiation does not change and remains at the effective Eddington value.Comment: 6 pages, 6 figures. To be published in Astronomy and Astrophysic

Oscillations of the Eddington Capture Sphere

We present a toy model of mildly super-Eddington, optically thin accretion onto a compact star in the Schwarzschild metric, which predicts periodic variations of luminosity when matter is supplied to the system at a constant accretion rate. These are related to the periodic appearance and disappearance of the Eddington Capture Sphere. In the model the frequency is found to vary inversely with the luminosity. If the input accretion rate varies (strictly) periodically, the luminosity variation is quasi-periodic, and the quality factor is inversely proportional to the relative amplitude of mass accretion fluctuations, with its largest value approximately Q= 1/(10 |delta Mdot/Mdot|) attained in oscillations at about 1 to 2 kHz frequencies for a 2 solar mass star

Cannabidiol in neurological and neoplastic diseases: Latest developments on the molecular mechanism of action

As the major nonpsychotropic constituent of Cannabis sativa, cannabidiol (CBD) is regarded as one of the most promising therapeutic agents due to its proven effectiveness in clinical trials for many human diseases. Due to the urgent need for more efficient pharmacological treatments for several chronic diseases, in this review, we discuss the potential beneficial effects of CBD for Alzheimers disease, epilepsy, multiple sclerosis, and neurological cancers. Due to its wide range of pharmacological activities (e.g., antioxidant, anti-inflammatory, and neuroprotective properties), CBD is considered a multimodal drug for the treatment of a range of neurodegenerative disorders, and various cancer types, including neoplasms of the neural system. The different mechanisms of action of CBD are here disclosed, together with recent progress in the use of this cannabis-derived constituent as a new therapeutic approach. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Institute of Human Genetics, Polish Academy of Sciences by the internal grant for the implementation of a single scientific activity and by the National Centre for Research and Development by the grant ONKOKAN, INNOMED/I/11/NCBR/2014info:eu-repo/semantics/publishedVersio

Stability of radiation-pressure dominated disks. I. The dispersion relation for a delayed heating alpha-viscosity prescription

We derive and investigate the dispersion relation for accretion disks with retarded or advanced heating. We follow the alpha-prescription but allow for a time offset (\tau) between heating and pressure perturbations, as well as for a diminished response of heating to pressure variations. We study in detail solutions of the dispersion relation for disks with radiation-pressure fraction 1 - \beta . For \tau <0 (delayed heating) the number and sign of real solutions for the growth rate depend on the values of the time lag and the ratio of heating response to pressure perturbations, \xi . If the delay is larger than a critical value (e.g., if \Omega \tau <-125 for \alpha =0.1, \beta =0 and \xi =1) two real solutions exist, which are both negative. These results imply that retarded heating may stabilize radiation-pressure dominated accretion disks.Comment: 11 pages, 10 figures, to be submitted to A&