Abstract
Millisecond magnetars produced in the center of dying massive stars are one prominent model to power gamma-ray bursts (GRBs). However, their detailed nature remains a mystery. To explore the ...effects of the initial mass, rotation rate, wind mass loss, and metallicity on the GRB progenitors and the newborn magnetar properties, we evolve 227 of 10–30
M
⊙
single star models from the pre-main sequence to core collapse by using the stellar evolution code MESA. The presupernova properties, the compactness parameter, and the magnetar characteristics of models with different initial parameters are presented. The compactness parameter remains a nonmonotonic function of the initial mass and initial rotation rate when the effects of varying metallicity and the “Dutch” wind scale factor are taken into account. We find that the initial rotation rate and mass play the dominant roles in whether a star can evolve into a GRB progenitor. The minimum rotation rate necessary to generate a magnetar gradually reduces as the initial mass increases. The greater the initial metallicity and “Dutch” wind scale factor, the larger the minimum rotation rate required to produce a magnetar. In other words, massive stars with low metallicity are more likely to harbor magnetars. Furthermore, we present the estimated period, magnetic field strength, and masses of magnetars in all cases. The typical rotational energy of these millisecond magnetars is sufficient to power long-duration GRBs.
Anthocyanins are a class of water‐soluble flavonoids, which show a range of pharmacological effects, such as prevention of cardiovascular disease, obesity control and antitumour activity. Their ...potential antitumour effects are reported to be based on a wide variety of biological activities including antioxidant; anti‐inflammation; anti‐mutagenesis; induction of differentiation; inhibiting proliferation by modulating signal transduction pathways, inducing cell cycle arrest and stimulating apoptosis or autophagy of cancer cells; anti‐invasion; anti‐metastasis; reversing drug resistance of cancer cells and increasing their sensitivity to chemotherapy. In this review, the latest progress on the anticancer activities of anthocyanins and the underlying molecular mechanisms is summarized using data from basic research in vitro and in vivo, from clinical trials and taking into account theory and practice.
Linked Articles
This article is part of a themed section on Principles of Pharmacological Research of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.11/issuetoc
Abstract Neutrino-dominated accretion flows (NDAFs) are one of the important MeV neutrino sources and significantly contribute to the cosmic diffuse neutrino background. In this paper, we investigate ...the spectrum of the diffuse NDAF neutrino background (DNNB) by fully considering the effects of the progenitor properties and initial explosion energies based on core-collapse supernova (CCSN) simulations, and estimate the detectable event rate by the Super-Kamiokande detector. We find that the predicted background neutrino flux is mainly determined by the typical CCSN initial explosion energy and progenitor metallicity. For the optimistic cases, in which the typical initial explosion energy is low, the diffuse flux of the DNNB is comparable to the diffuse supernova neutrino background, which might be detected by upcoming larger neutrino detectors, such as Hyper-Kamiokande, the Jiangmen Underground Neutrino Observatory, and the Deep Underground Neutrino Experiment. Moreover, the strong outflows from NDAFs could dramatically decrease their contribution to the neutrino background.
Long-duration gamma-ray bursts (LGRBs) and ultra-LGRBs (ULGRBs) originate from collapsars, in the center of which a newborn rotating stellar-mass black hole (BH) surrounded by a massive accretion ...disk may form. In the scenario of the BH hyperaccretion inflow-outflow model and Blandford-Znajek (BZ) mechanism to trigger gamma-ray bursts (GRBs), the real accretion rate to power a BZ jet is far lower than the mass supply rate from the progenitor star. The characteristics of the progenitor stars can be constrained by GRB luminosity observations, and the results exceed usual expectations. LGRBs lasting from several seconds to tens of seconds in the rest frame may originate from solar-metallicity ( , where Z and are the metallicities of progenitor stars and the Sun), massive ( , where M and are the masses of progenitor stars and the Sun) stars or some zero-metallicity ( ) stars. A fraction of low-metallicity ( ) stars, including Population III stars, can produce ULGRBs such as GRB 111209A. The fraction of LGRBs lasting less than tens of seconds in the rest frame is more than 40%, which cannot conform to the fraction of the demanded type of progenitor star. It possibly implies that the activity timescale of the central engine may be much longer than the observed timescale of prompt emission phase, as indicated by X-ray late-time activities. Alternatively, LGRBs and ULGRBs may be powered by a millisecond magnetar central engine.
As the plausible central engine of gamma-ray bursts, a black hole (BH) hyperaccretion disk should be in a state of neutrino-dominated accretion flow (NDAF) if the accretion rate is larger than the ...ignition rate of an NDAF. A rotating stellar-mass BH surrounded by a hyperaccretion disk might be born in the center of a massive core collapsar. In the initial hundreds of seconds of the accretion process, the mass supply rate of the massive progenitor is generally higher than the ignition accretion rate, but the jets are generally choked in the envelope. Thus, neutrinos can be emitted from the center of a core collapsar. In this paper, we study the effects of the masses and metallicities of progenitor stars on the time-integrated spectra of electron neutrinos from NDAFs. The peak energies of the calculated spectra are approximately 10-20 MeV. The mass of a collapsar has little influence on the neutrino spectrum, and a low metallicity is beneficial to the production of low-energy ( 1 MeV) neutrinos. We also investigate the differences in the electron neutrino spectra between NDAFs and proto-neutron stars. Combining with the electromagnetic counterparts and multimessenger astronomy, one may verify the possible remnants of the core collapse of massive stars with future neutrino detectors.
Abstract
The detections of some long gamma-ray bursts (LGRBs) relevant to mergers of neutron star (NS)-NS or black hole (BH)-NS, as well as some short gamma-ray bursts (SGRBs) probably produced by ...collapsars, muddle the boundary of two categories of gamma-ray bursts (GRBs). In both cases, a plausible candidate of central engine is a BH surrounded by a hyperaccretion disc with strong outflows, launching relativistic jets driven by Blandford-Znajek mechanism. In the framework of compact binary mergers, we test the applicability of the BH hyperaccretion inflow–outflow model on powering observed GRBs. We find that, for a low outflow ratio, ${\sim } 50\hbox{ per cent}$, post-merger hyperaccretion processes could power not only all SGRBs but also most of LGRBs. Some LGRBs might originate from merger events in the BH hyperaccretion scenario, at least on the energy requirement. Moreover, kilonovae might be produced by neutron-rich outflows, and their luminosities and time-scales significantly depend on the outflow strengths. GRBs and their associated kilonovae are competitive with each other on the disc mass and total energy budgets. The stronger the outflow, the more similar the characteristics of kilonovae to supernovae (SNe). This kind of ‘nova’ might be called ‘quasi-SN’.
Abstract
Long-duration gamma-ray bursts (GRBs) are generally related to the core-collapse of massive stars. In the collapsar scenario, a rotating stellar-mass black hole (BH) surrounded by a ...hyperaccretion disk has been considered as one of the plausible candidates of GRB central engines. In this paper, we work on a sample including 146 long GRBs with significant jet break features in the multiband afterglows. The jet opening angles can then be obtained by the jet break time. By assuming GRB jets powered by the Blandford–Znajek (BZ) mechanism in the BH hyperaccretion system, we analyze the distributions of the long GRB luminosities and durations in the samples, and constrain the accretion rates for the different BH spins. As a result, we find that the BZ mechanism is so powerful that it is possible to interpret the long GRB prompt emissions within reasonable accretion rates.
Neutrino-dominated accretion flow (NDAF) around a rotating stellar-mass black hole (BH) is one of the plausible candidates for the central engines of gamma-ray bursts (GRBs). Because the time-variant ...and anisotropic emission of neutrinos from NDAFs leads to GRB variability, NDAFs can be regarded as the sources of strong gravitational waves (GWs). We calculate the dependences of the GW strains on both the BH spin and the accretion rate. We demonstrate that, for typical GRBs with either a single pulse or multiple pulses, the GWs from NDAFs might be detected at a distance of ∼100 kpc/∼1 Mpc by the advanced LIGO/Einstein Telescope with a typical frequency of ∼ 10 - 100 Hz . Besides NDAFs, the other two competitive candidates for the GRB central engine are the Blandford-Znajek (BZ) mechanism and millisecond magnetars. We explore the GW signals from these two as well, and compare the corresponding results with NDAFs'. We find that for a certain GRB, the possible detected distance from NDAFs is about two orders of magnitude higher than that from the BZ mechanism, but at least two orders of magnitude lower than that from magnetars. The typical GW frequency for the BZ mechanism is the same as that of NDAFs, ∼ 10 - 100 Hz , while the typical frequency for magnetars is ∼2000 Hz. Therefore, the GWs released by the central engines of adjacent GRBs might be used to determine whether there is an NDAF, a BZ jet, or a magnetar in the GRB center.
Two plateaus and a following bump in the X-ray light curve of GRB 170714A have been detected by the Swift/X-ray Telescope, which could be very significant for the central engine of gamma-ray bursts ...(GRBs), implying that the origin of this burst might be different from those of other ultra-long GRBs. We propose that merging two neutron stars into a hyper-massive quark star (QS) and then collapsing into a black hole (BH), with a delay time around 104 s, could be responsible for these X-ray components. The hyper-massive QS is initially in a fluid state, being turbulent and differentially rotating, but would solidify and release its latent heat, injecting it into the GRB fireball (lasting about 103 s during the liquid-solid phase transition). A magnetic field as high as ∼1015 G can be created by dynamo action of the newborn liquid QS, and a magnetar-like central engine (after solidification) supplies significant energy for the second plateau. More energy could be released during a fall-back accretion after the post-merger QS collapses to a BH, and the X-ray bump forms. This post-merger QS model could be tested by future observations, with either advanced gravitational wave detectors (e.g., advanced LIGO and VIRGO) or X-ray/optical telescopes.
Demand‐responsive transit has gradually attracted attention in recent years for its flexibility, efficiency, and ability to meet the diverse travel demands of passengers. To improve the operational ...efficiency of demand‐responsive transit (DRT) with dynamic demand, this study innovatively investigates the DRT scheduling problem from multiple perspectives, such as multi‐vehicle, non‐fixed stop, and dynamic demand, and constructs a two‐phase DRT vehicle scheduling model. In the first phase, a static scheduling model is established with the objective of minimizing vehicle setup cost, operation cost, and CO2 emission cost according to passenger travel satisfaction. In the second phase, a dynamic scheduling model is constructed with the objective of minimizing the increased vehicle operation cost in response to dynamic demand and the penalty cost of violating the time window and rejecting passengers. In addition, in the first static phase, an improved heuristic algorithm is used to obtain optimal routes based on passengers’ subscriptions, while in the second phase, an insertion algorithm is designed to solve the dynamic scheduling model based on the previous schedule. Finally, cases are applied to a realistic network in Chaoyang District, Beijing, China, to verify the effectiveness of the proposed scheduling model. The results demonstrate that dynamic scheduling can enable more passengers to be served with a slight increase in total vehicle operating costs. Besides, the introduction of the non‐fixed stop service model can significantly reduce total travel time by up to 8.8% compared with the fixed stop service. The proposed models and solution algorithms in this study are practical for real‐world applications.
In order to improve the operational efficiency of DRT with real‐time demand, this study innovatively investigates the DRT scheduling problem from multiple perspectives such as multi‐vehicle, non‐fixed stop and real‐time demand, and a two‐phase DRT vehicle scheduling model is constructed. In addition, in the first static phase an improved heuristic algorithm is used to obtain optimum routes based on passengers's subscriptions, while in the second phase, an insertion algorithm is designed to solve the dynamic scheduling model based on the previous schedule. Finally, cases are applied into a realistic network in Chaoyang District, Beijing, China to verify the effectiveness of the proposed scheduling model.
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