2,333 research outputs found
Wind-Reprocessed Transients from Stellar-mass Black Hole Tidal Disruption Events
Tidal disruptions of stars by stellar-mass black holes are expected to occur
frequently in dense star clusters. Building upon previous studies that
performed hydrodynamic simulations of these encounters, we explore the
formation and long-term evolution of the thick, super-Eddington accretion disks
formed. We build a disk model that includes fallback of material from the tidal
disruption, accretion onto the black hole, and disk mass losses through winds
launched in association with the super-Eddington flow. We demonstrate that
bright transients are expected when radiation from the central engine powered
by accretion onto the black hole is reprocessed at large radii by the
optically-thick disk wind. By combining hydrodynamic simulations of these
disruption events with our disk+wind model, we compute light curves of these
wind-reprocessed transients for a wide range of stellar masses and encounter
penetration depths. We find typical peak bolometric luminosities of roughly
erg/s (depending mostly on accretion physics parameters) and
temperatures of roughly K, suggesting peak emission in the
ultraviolet/blue bands. We predict all-sky surveys such as the Vera Rubin
Observatory and ULTRASAT will detect up to thousands of these events per year
in dense star clusters out to distances of several Gpc.Comment: 16 Pages, 13 figures, 2 tables. Accepted for publication in MNRA
Torts
Covers cases on warrantless arrest (Kremer); on contributory negligence—absolute right to stop at a yellow light (Howe); on warning lights on the highway—absolute duty versus reasonable measures (Mackie); on automobiles—dangerous instrumentality doctrine—negligence (Lyness); on the tort liability of a building contractor to third persons injured after completion of work (Conger); and on silence as fraudulent concealment—vendor and purchaser—duty to disclose (Lyness
Modelling and analysis of time dependent processes in a chemically reactive mixture
In this paper, we study the propagation of sound waves and the dynamics of local wave disturbances
induced by spontaneous internal fluctuations in a reactive mixture. We consider a non-diffusive, non-heat
conducting and non-viscous mixture described by an Eulerian set of evolution equations. The model is derived from the kinetic theory in a hydrodynamic regime of a fast chemical reaction. The reactive source terms are explicitly computed from the kinetic theory and are built in themodel in a proper way. For both time-dependent problems, we first derive the appropriate dispersion relation, which retains the main effects of the chemical process, and then investigate the influence of the chemical reaction on the properties of interest in the problems studied here. We complete our study by developing a rather detailed analysis using the Hydrogen–Chlorine system as reference. Several numerical computations are included illustrating the behavior of the phase velocity and attenuation coefficient in a low-frequency regime and describing the spectrum of the eigenmodes in the small wavenumber limit.The paper is partially supported by the Research Centre of Mathematics of the University of Minho, with the Portuguese Funds from the Foundation for Science and Technology (FCT) through the Project UID/MAT/00013/2013. We wish to thank the anonymous Referees for their valuable comments and suggestions that helped us to improve the paper.info:eu-repo/semantics/publishedVersio
Probing the black hole merger history in clusters using stellar tidal disruptions
The dynamical assembly of binary black holes (BBHs) in dense star clusters
(SCs) is one of the most promising pathways for producing observable
gravitational wave (GW) sources, however several other formation scenarios
likely operate as well. One of the current outstanding questions is how these
different pathways may be distinguished apart. In this paper we suggest a new
multi-messenger observable that can be used to constrain the formation of BBH
mergers originating from SCs: the electromagnetic signal from tidal disruptions
(TDs) of stars by BBHs. Such TDs will show variability in their light curve
from the orbital motion of the disruptive BBHs, and can therefore be used to
map the BBH orbital period distribution, and thereby also the dynamical
mechanisms that eventually drive the BBHs to merger. Using an analytical
approach including General Relativistic effects, we find that the orbital
period distribution of BBHs within globular clusters peaks on timescales of
days, which we argue is unique to this assembly pathway. We propose that the
search for variable TDs in current and future EM transient surveys might be
used to constrain the merger history of BBHs in SCs.Comment: 12 pages. 4 figures. comments welcom
Synthesis, antitubercular activity and mechanism of resistance of highly effective thiacetazone analogues
Defining the pharmacological target(s) of currently used drugs and developing new analogues with greater potency are both important aspects of the search for agents that are effective against drug-sensitive and drug-resistant Mycobacterium tuberculosis. Thiacetazone (TAC) is an anti-tubercular drug that was formerly used in conjunction with isoniazid, but removed from the antitubercular chemotherapeutic arsenal due to toxic side effects. However, several recent studies have linked the mechanisms of action of TAC to mycolic acid metabolism and TAC-derived analogues have shown increased potency against M. tuberculosis. To obtain new insights into the molecular mechanisms of TAC resistance, we isolated and analyzed 10 mutants of M. tuberculosis that were highly resistant to TAC. One strain was found to be mutated in the methyltransferase MmaA4 at Gly101, consistent with its lack of oxygenated mycolic acids. All remaining strains harbored missense mutations in either HadA (at Cys61) or HadC (at Val85, Lys157 or Thr123), which are components of the bhydroxyacyl-ACP dehydratase complex that participates in the mycolic acid elongation step. Separately, a library of 31 new TAC analogues was synthesized and evaluated against M. tuberculosis. Two of these compounds, 15 and 16, exhibited minimal inhibitory concentrations 10-fold lower than the parental molecule, and inhibited mycolic acid biosynthesis in a dose-dependent manner. Moreover, overexpression of HadAB HadBC or HadABC in M. tuberculosis led to high level resistance to these compounds, demonstrating that their mode of action is similar to that of TAC. In summary, this study uncovered new mutations associated with TAC resistance and also demonstrated that simple structural optimization of the TAC scaffold was possible and may lead to a new generation of TAC-derived drug candidates for the potential treatment of tuberculosis as mycolic acid inhibitors
Corrections to scaling in 2--dimensional polymer statistics
Writing for the mean
square end--to--end length of a self--avoiding polymer chain of
links, we have calculated for the two--dimensional {\em continuum}
case from a new {\em finite} perturbation method based on the ground state of
Edwards self consistent solution which predicts the (exact) exponent.
This calculation yields . A finite size scaling analysis of data
generated for the continuum using a biased sampling Monte Carlo algorithm
supports this value, as does a re--analysis of exact data for two--dimensional
lattices.Comment: 10 pages of RevTex, 5 Postscript figures. Accepted for publication in
Phys. Rev. B. Brief Reports. Also submitted to J. Phys.
- …