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The modelling of astrophysical systems such as binary neutron star mergers or the formation of magnetars from the collapse of massive stars involves the numerical evolution of magnetized fluids at extremely large Reynolds numbers. This is a major challenge for (unresolved) direct numerical simulations which may struggle to resolve highly dynamical features as, e.g. turbulence, magnetic field amplification, or the transport of angular momentum. Sub-grid models offer a means to overcome those difficulties. In a recent paper we presented MInIT, an MHD-instability-induced-turbulence mean-field, sub-grid model based on the modelling of the turbulent (Maxwell, Reynolds, and Faraday) stress tensors. While in our previous work MInIT was assessed within the framework of the magnetorotational instability, in this paper we further evaluate the model in the context of the Kelvin–Helmholtz instability (KHI). The main difference with other sub-grid models (as e.g. the alpha-viscosity model or the gradient model) is that in MInIT, we track independently the turbulent energy density at sub-grid scales, which is used, via a simple closure relation, to compute the different turbulent stresses relevant for the dynamics. The free coefficients of the model are calibrated using well-resolved box simulations of magnetic turbulence generated by the KHI. We test the model against these simulations and show that it yields order-of-magnitude accurate predictions for the evolution of the turbulent Reynolds and Maxwell stresses. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae (CCSNs) are a prime source of gravitational waves. Estimations of their typical frequencies make them perfect targets for the current network of advanced, ground-based detectors. A successful detection could potentially reveal the underlying explosion mechanism through the analysis of the waveform. This has been illustrated using the Supernova Model Evidence Extractor (SMEE), an algorithm based on principal component analysis and Bayesian model selection. Here, we present a complementary approach to SMEE based on (supervised) dictionary-learning and show that it is able to reconstruct and classify CCSN signals according to their morphology. Our waveform signals are obtained from (a) two publicly available catalogues built from numerical simulations of neutrino-driven (Mur) and magneto-rotational (Dim) CCSN explosions and (b) from a third 'mock' catalogue of simulated sine-Gaussian (SG) waveforms. All of these signals are injected into coloured Gaussian noise to simulate the background noise of Advanced LIGO in its broad-band configuration and scaled to a freely specifiable signal-to-noise ratio (SNR). We show that our approach correctly classifies signals from all three dictionaries. In particular, for SNR = 15–20, we obtain perfect matches for both Dim and SG signals and about 85 per cent true classifications for Mur signals. These results are comparable to those reported by SMEE for the same CCSN signals when those are injected in only one LIGO detector. We discuss the main limitations of our approach as well as possible improvements. [ABSTRACT FROM AUTHOR]

We explore equilibrium solutions of spherically symmetric boson stars in the Palatini formulation of gravity. We account for the modifications introduced in the gravitational sector by using a recently established correspondence between modified gravity with scalar matter and general relativity with modified scalar matter. We focus on the quadratic theory and compare its solutions with those found in general relativity, exploring both positive and negative values of the coupling parameter ξ. As matter source, a complex, massive scalar field with and without self-interaction terms is considered. Our results show that the existence curves of boson stars in Palatini gravity are fairly similar to those found in general relativity. Major differences are observed for negative values of the coupling parameter which results in a repulsive gravitational component for high enough scalar field density distributions. Adding self-interactions makes the degeneracy between and general relativity even more pronounced, leaving very little room for observational discrimination between the two theories. [ABSTRACT FROM AUTHOR]

We study numerically the nonlinear stability of excited fermion–boson stars in spherical symmetry. Such compound hypothetical stars, composed by fermions and bosons, are gravitationally bound, regular, and static configurations described within the coupled Einstein–Klein–Gordon–Euler theoretical framework. The excited configurations are characterized by the presence in the radial profile of the (complex, massive) scalar field—the bosonic piece—of at least one node across the star. The dynamical emergence of one such configuration from the accretion of a cloud of scalar field onto an already-formed neutron star, was numerically revealed in our previous investigation. Prompted by that finding we construct here equilibrium configurations of excited fermion–boson stars and study their stability properties using numerical-relativity simulations. In addition, we also analyze their dynamical formation from generic, constraint-satisfying initial data. Contrary to purely boson stars in the excited state, which are known to be generically unstable, our study reveals the appearance of a cooperative stabilization mechanism between the fermionic and bosonic constituents of those excited-state mixed stars. While similar examples of stabilization mechanisms have been recently discussed in the context of ℓ-boson stars and multi-field, multi-frequency boson stars, our results seem to indicate that the stabilization mechanism is a purely gravitational effect and does not depend on the type of matter of the companion star. [ABSTRACT FROM AUTHOR]

We explore machine learning methods to detect gravitational waves (GW) from binary black hole (BBH) mergers using deep learning (DL) algorithms. The DL networks are trained with gravitational waveforms obtained from BBH mergers with component masses randomly sampled in the range from 5 to 100 solar masses and luminosity distances from 100 Mpc to, at least, 2000 Mpc. The GW signal waveforms are injected in public data from the O2 run of the Advanced LIGO and Advanced Virgo detectors, in time windows that do not coincide with those of known detected signals. We demonstrate that DL algorithms, trained with GW signal waveforms at distances of 2000 Mpc, still show high accuracy when detecting closer signals, within the ranges considered in our analysis. Moreover, by combining the results of the three-detector network in a unique RGB image, the single detector performance is improved by as much as 70%. Furthermore, we train a regression network to perform parameter inference on BBH spectrogram data and apply this network to the events from the GWTC-1 and GWTC-2 catalogs. Without significant optimization of our algorithms we obtain results that are mostly consistent with published results by the LIGO–Virgo Collaboration. In particular, our predictions for the chirp mass are compatible (up to 3σ) with the official values for 90% of events. From these results we conclude that the combination of computer vision techniques and deep-learning methods put forward in this work is a worthy addition to the GW astronomer's toolbox. [ABSTRACT FROM AUTHOR]

We build equilibrium solutions of magnetized thick discs around a highly spinning Kerr black hole and evolve these initial data up to a final time of about 100 orbital periods. The numerical simulations reported in this paper solve the general relativistic magnetohydrodynamic equations using the bhac code and are performed in axisymmetry. Our study assumes non-self-gravitating, polytropic, constant angular momentum discs endowed with a purely toroidal magnetic field. In order to build the initial data, we consider three approaches, two of which incorporate the magnetic field in a self-consistent way and a third approach in which the magnetic field is included as a perturbation on to an otherwise purely hydrodynamical solution. To test the dependence of the evolution on the initial data, we explore four representative values of the magnetization parameter spanning from almost hydrodynamical discs to very strongly magnetized tori. The initial data are perturbed to allow for mass and angular momentum accretion on to the black hole. Notable differences are found in the long-term evolutions of the initial data. In particular, our study reveals that highly magnetized discs are unstable, and hence prone to be fully accreted and expelled, unless the magnetic field is incorporated into the initial data in a self-consistent way. [ABSTRACT FROM AUTHOR]

The thermodynamical properties of the equation of state (EoS) of high-density matter (above nuclear saturation density) and the possible existence of exotic states such as phase transitions from nuclear/hadronic matter into quark-gluon plasma, or the appearance of hyperons, may critically influence the stability and dynamics of compact relativistic stars. From a theoretical point of view, establishing the existence of those states requires the analysis of the 'convexity' of the EoS. We show indications of the existence of regions in the dense-matter EoS where the thermodynamics may be non-convex as a result of a non-monotonic dependence of the sound speed with the rest-mass density. When this happens, non-conventional dynamics may develop. In this paper we investigate the effects of a phenomenological, non-convex EoS on the equilibrium structure of stable compact stars and on the dynamics of unstable neutron stars that collapse gravitationally to black holes, both for spherically symmetric and uniformly rotating configurations. We show how the dynamics of the collapse with a non-convex EoS departs from the convex case, leaving distinctive imprints on the gravitational waveforms. The astrophysical significance of these results for microphysical EoSs is discussed. [ABSTRACT FROM AUTHOR]

Improvements in ground-based advanced gravitational wave (GW) detectors may soon allow us to observe the GW signal of a nearby core-collapse supernova. For most progenitors, likely with slowly rotating cores, the dominant GW emission mechanisms are the post-bounce oscillations of the proto-neutron star (PNS) before the explosion. We present a new procedure to compute the eigenmodes of the system formed by the PNS and the stalled accretion shock in general relativity including space–time perturbations. We apply our analysis to two core-collapse simulations and show that our improved method is able to obtain eigenfrequencies that accurately match the features observed in the GW signal and to predict the qualitative behaviour of quasi-radial oscillations. Our analysis is possible thanks to a newly developed algorithm to classify the eigenmodes in different classes (f, p, and g modes), improving our previous results. We find that most of the GW energy is stored in the lowest-order eigenmodes, in particular in the 2 g 1 mode and in the 2 f mode. Our results also suggest that a low-frequency component of the GW signal attributed in previous works to the characteristic frequency of the standing accretion shock instability should be identified as the fundamental quadrupolar f mode. We also develop a formalism to estimate the contribution of quasi-radial (l  = 0) modes to the GW quadrupolar component in a deformed background, with application to rapidly rotating cores. This work provides further support for asteroseismology of core-collapse supernovae and the inference of PNS properties based on GW observations. [ABSTRACT FROM AUTHOR]

We discuss torsional oscillations of highly magnetized neutron stars (magnetars) using two-dimensional, magneto-elastic-hydrodynamical simulations. Our model is able to explain both the low- and high-frequency quasi-periodic oscillations (QPOs) observed in magnetars. The analysis of these oscillations provides constraints on the breakout magnetic-field strength, on the fundamental QPO frequency, and on the frequency of a particularly excited overtone. By performing a new set of simulations, we are able to derive for the first time empirical relations for a self consistent model including a superfluid core which describe these constraints quantitatively. We use these relations to generically constrain properties of high-density matter in neutron stars, employing Bayesian analysis. In spite of current uncertainties and computational approximations, our model-dependent Bayesian posterior estimates for SGR 1806-20 yield a magnetic-field strength |$\bar{B}\sim 2.1^{+1.3}_{-1.0}\times 10^{15}\,$| G and a crust thickness of |$\Delta r = 1.6^{+0.7}_{-0.6}$| km, which are both in remarkable agreement with observational and theoretical expectations, respectively (1σ error bars are indicated). Our posteriors also favour the presence of a superfluid phase in the core, a relatively low stellar compactness, M / R  < 0.19, indicating a relatively stiff equation of state and/or low-mass neutron star, and high shear speeds at the base of the crust, c s > 1.4 × 108 cm s−1. Although the procedure laid out here still has large uncertainties, these constraints could become tighter when additional observations become available. [ABSTRACT FROM AUTHOR]

Gravitational waves from core-collapse supernovae are produced by the excitation of different oscillation modes in the protoneutron star (PNS) and its surroundings, including the shock. In this work we study the relationship between the post-bounce oscillation spectrum of the PNS–shock system and the characteristic frequencies observed in gravitational-wave signals from core-collapse simulations. This is a fundamental first step in order to develop a procedure to infer astrophysical parameters of the PNS formed in core-collapse supernovae. Our method combines information from the oscillation spectrum of the PNS, obtained through linear perturbation analysis in general relativity of a background physical system, with information from the gravitational-wave spectrum of the corresponding non-linear, core-collapse simulation. Using results from the simulation of the collapse of a 35 M⊙ pre-supernova progenitor we show that both types of spectra are indeed related and we are able to identify the modes of oscillation of the PNS, namely g-modes, p-modes, hybrid modes, and standing accretion shock instability (SASI) modes, obtaining a remarkably close correspondence with the time–frequency distribution of the gravitational-wave modes. The analysis presented in this paper provides a proof of concept that asteroseismology is indeed possible in the core-collapse scenario, and it may serve as a basis for future work on PNS parameter inference based on gravitational-wave observations. [ABSTRACT FROM AUTHOR]

In a recent paper, we applied a rigorous perturbed matching framework to show the amendment of the mass of rotating stars in Hartle's model. Here, we apply this framework to the tidal problem in binary systems. Our approach fully accounts for the correction to the Love numbers needed to obtain the universal I--Love--Q relations. We compute the corrected mass versus radius configurations of rotating quark stars, revisiting a classical paper on the subject. These corrections allow us to find a universal relation involving the second-order contribution to the mass δM. We thus complete the set of universal relations for the tidal problem in binary systems, involving four perturbation parameters, namely I, Love, Q and δM. These relations can be used to obtain the perturbation parameters directly from observational data. [ABSTRACT FROM AUTHOR]

We present results from three-dimensional, numerical relativity simulations of a tilted black hole-thick accretion disc system. The simulations are analysed using tracer particles in the disc which are advected with the flow. Such tracers, which we employ in these new simulations for the first time, provide a powerful means to analyse in detail the complex dynamics of tilted black hole-torus systems.We show how its use helps to gain insight into the overall dynamics of the system, discussing the origin of the observed black hole precession and the development of a global non-axisymmetric m=1 mode in the disc. Our three-dimensional simulations show the presence of quasi-periodic oscillations (QPOs) in the instantaneous accretion rate, with frequencies in a range compatible with those observed in low-mass X-ray binaries with either a black hole or a neutron star component. The frequency ratio of the dominant low-frequency peak and the first overtone is o1/f ~ 1.9, a frequency ratio not attainable when modelling the QPOs as p-mode oscillations in axisymmetric tori. [ABSTRACT FROM AUTHOR]

We study the effect of superfluidity on torsional oscillations of highly magnetised neutron stars (magnetars) with a microphysical equation of state by means of two-dimensional, magnetohydrodynamical- elastic simulations. The superfluid properties of the neutrons in the neutron star core are treated in a parametricway in which we effectively decouple part of the core matter from the oscillations. Our simulations confirm the existence of two groups of oscillations, namely continuum oscillations that are confined to the neutron star core and are of Alfv'enic character, and global oscillations with constant phase and that are of mixed magneto-elastic type. The latter might explain the quasi-periodic oscillations observed in magnetar giant flares, since they do not suffer from the additional damping mechanism due to phase mixing, contrary to what happens for continuum oscillations. However, we cannot prove rigorously that the coherent oscillations with constant phase are normal modes. Moreover, we find no crustal shear modes for the magnetic field strengths typical for magnetars. We provide fits to our numerical simulations that give the oscillation frequencies as functions of magnetic field strength and proton fraction in the core. [ABSTRACT FROM AUTHOR]

The observation of several neutron stars in the centre of supernova remnants and with significantly lower values of the dipolar magnetic field than the average radio-pulsar population has motivated a lively debate about their formation and origin, with controversial interpretations. A possible explanation requires the slow rotation of the protoneutron star at birth, which is unable to amplify its magnetic field to typical pulsar levels. An alternative possibility, the hidden magnetic field scenario, considers the accretion of the fallback of the supernova debris on to the neutron star as responsible for the submergence (or screening) of the field and its apparently low value. In this paper, we study under which conditions the magnetic field of a neutron star can be buried into the crust due to an accreting, conducting fluid. For this purpose, we consider a spherically symmetric calculation in general relativity to estimate the balance between the incoming accretion flow and the magnetosphere. Our study analyses several models with different specific entropy, composition, and neutron star masses. The main conclusion of our work is that typical magnetic fields of a few times 1012 G can be buried by accreting only 10-3-10-2M⊙, a relatively modest amount of mass. In view of this result, the central compact object scenario should not be considered unusual, and we predict that anomalously weak magnetic fields should be common in very young (< few kyr) neutron stars. [ABSTRACT FROM AUTHOR]

We couple internal torsional, magneto-elastic oscillations of highly magnetized neutron stars (magnetars) to their magnetospheres. The corresponding axisymmetric perturbations of the external magnetic field configuration evolve as a sequence of linear, force-free equilibria that are completely determined by the background magnetic field configuration and by the perturbations of the magnetic field at the surface. The perturbations are obtained from simulations of magneto-elastic oscillations in the interior of the magnetar. While such oscillations can excite travelling Alfvén waves in the exterior of the star only in a very limited region close to the poles, they still modulate the near magnetosphere by inducing a time-dependent twist between the foot-points of closed magnetic field lines that exit the star at a polar angle ≳ 0.19 rad. Moreover, we find that for a dipole-like background magnetic field configuration the magnetic field modulations in the magnetosphere, driven by internal oscillations, can only be symmetric with respect to the equator. This is in agreement with our previous findings, where we interpreted the observed quasi-periodic oscillations in the X-ray tail of magnetar bursts as driven by the family of internal magneto-elastic oscillations with symmetric magnetic field perturbations. [ABSTRACT FROM PUBLISHER]

We study magneto-elastic oscillations of highly magnetized neutron stars (magnetars) which have been proposed as an explanation for the quasi-periodic oscillations (QPOs) appearing in the decaying tail of the giant flares of soft gamma-ray repeaters (SGRs). We extend previous studies by investigating various magnetic field configurations, computing the Alfvén spectrum in each case and performing magneto-elastic simulations for a selected number of models. By identifying the observed frequencies of 28 Hz (SGR 1900+14) and 30 Hz (SGR 1806−20) with the fundamental Alfvén QPOs, we estimate the required surface magnetic field strength. For the magnetic field configurations investigated (dipole-like poloidal, mixed toroidal–poloidal with a dipole-like poloidal component and a toroidal field confined to the region of field lines closing inside the star, and for poloidal fields with an additional quadrupole-like component) the estimated dipole spin-down magnetic fields are between 8 × 1014 and 4 × 1015 G, in broad agreement with spin-down estimates for the SGR sources producing giant flares. A number of these models exhibit a rich Alfvén continuum revealing new turning points which can produce QPOs. This allows one to explain most of the observed QPO frequencies as associated with magneto-elastic QPOs. In particular, we construct a possible configuration with two turning points in the spectrum which can explain all observed QPOs of SGR 1900+14. Finally, we find that magnetic field configurations which are entirely confined in the crust (if the core is assumed to be a type I superconductor) are not favoured, due to difficulties in explaining the lowest observed QPO frequencies (f ≲ 30 Hz). [ABSTRACT FROM AUTHOR]

Merging binary neutron stars are among the strongest known sources of gravitational waves, have features compatible with the events producing short-hard gamma-ray bursts, and might be the long--sought formation sites of high-mass number r-process elements. Numerical relativity has reached a stage where a complete description of the inspiral, merger and post-merger phases of the late evolution of close binary neutron-star systems is possible. This is allowing the systematic investigation of such a many-sided subject. This paper presents an overview of numerical relativity simulations of binary neutron star mergers and the evolution of the resulting black hole--torus systems. Such numerical work is based upon a basic theoretical framework which comprises the Einstein's equations for the gravitational field and the hydrodynamics equations for the evolution of the matter fields. The most well-established formulations for both systems of equations are briefly discussed, along with the numerical methods best suited for their numerical solution, specifically high-order finite-differencing for the case of the gravitational field equations and high-resolution shockcapturing schemes for the case of the relativistic Euler equations. A number of recent results are reviewed, namely the outcome of the merger depending on the initial total mass and equation of state of the binary, as well as the post-merger evolution phase once a black hole--torus system is produced. Such system has been shown to be subject to non-axisymmetric instabilities leading to the emission of large amplitude gravitational waves. [ABSTRACT FROM AUTHOR]

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ABSTRACT By means of two-dimensional, general relativistic magnetohydrodynamical simulations we investigate the oscillations of magnetized neutron star models (magnetars) for one particular dipolar magnetic field configuration including the description of an extended solid crust. The aim of this study is to understand the origin of the quasi-periodic oscillations (QPOs) observed in the giant flares of soft gamma-ray repeaters (SGRs). We confirm our previous findings which showed the existence of three different regimes in the evolution depending on the magnetic field strength: (a) a weak magnetic field regime B < 5 × 1013 G, where crustal shear modes dominate the evolution; (b) a regime of intermediate magnetic fields 5 × 1013 < B < 1015 G, where Alfvén QPOs are mainly confined to the core of the neutron star and the crustal shear modes are damped very efficiently and (c) a strong field regime B > 1015 G, where magnetoelastic oscillations reach the surface and approach the behaviour of purely Alfvén QPOs. When the Alfvén QPOs are confined to the core of the neutron star, we find qualitatively similar QPOs as in the absence of a crust. The lower QPOs associated with the closed field lines of the magnetic field configuration are reproduced as in our previous simulations without crust, while the upper QPOs connected to the open field lines are displaced from the polar axis. The position of these upper QPOs strongly depends on the magnetic field strength. Additionally, we observe a family of edge QPOs and one new upper QPO, which was not previously found in the absence of a crust. We extend our semi-analytic model to obtain estimates for the continuum of the Alfvén oscillations. Our results do not leave much room for a crustal-mode interpretation of observed QPOs in SGR giant flares, but can accommodate an interpretation of these observations as originating from Alfvén-like, global, turning point QPOs (which can reach the surface of the star) in models with mean surface magnetic field strengths in the narrow range of 3.8 × 1015≲ B≲ 1.1 × 1016 G (for a sample of two stiff equation of state and various masses). This range is somewhat larger than estimates for magnetic field strengths in known magnetars. The discrepancy may be resolved in models including a more complicated magnetic field structure or with models taking superfluidity of the neutrons and superconductivity of the protons in the core into account. [ABSTRACT FROM AUTHOR]

In a realistic model of magneto-elastic oscillations in magnetars, we find that crustal shear oscillations, often invoked as an explanation of quasi-periodic oscillations (QPOs) seen after giant flares in soft gamma-ray repeaters (SGRs), are damped by resonant absorption on time-scales of at most 0.2 s, for a lower limit on the dipole magnetic field strength of G. At higher magnetic field strengths (typical in magnetars) the damping time-scale is even shorter, as anticipated by earlier toy models. We have investigated a range of equations of state and masses and if magnetars are dominated by a dipole magnetic field, our findings exclude torsional shear oscillations of the crust from explaining the observed low-frequency QPOs. In contrast, we find that the Alfvén QPO model is a viable explanation of observed QPOs, if the dipole magnetic field strength exceeds a minimum strength of about several times 10-10 G. Then, Alfvén QPOs are no longer confined to the fluid core, but completely dominate in the crust region and have a maximum amplitude at the surface of the star. [ABSTRACT FROM AUTHOR]

We perform two-dimensional simulations of Alfvén oscillations in magnetars, modelled as relativistic stars with a dipolar magnetic field. We use the anelastic approximation to general relativistic magnetohydrodynamics, which allows for an effective suppression of fluid modes and an accurate description of Alfvén waves. In addition, we compute Alfvén oscillation frequencies along individual magnetic field lines with a semi-analytic approach, employing a short-wavelength approximation. Our main findings are as follows: (a) we confirm the existence of two families of quasi-periodic oscillations (QPOs), with harmonics at integer multiples of the fundamental frequency, as was found in the linear study of Sotani, Kokkotas & Stergioulas; (b) the QPOs appearing near the magnetic axis are split into two groups, depending on their symmetry across the equatorial plane. The antisymmetric QPOs have only odd integer-multiple harmonics; (c) the continuum obtained with our semi-analytic approach agrees remarkably well with QPOs obtained via the two-dimensional simulations, allowing for a clear interpretation of the QPOs as corresponding to turning points of the continuum. This agreement will allow for a comprehensive study of Alfvén QPOs for a larger number of different models, without the need for time-consuming simulations. Finally, we construct empirical relations for the QPO frequencies and compare them to observations of known Soft Gamma Repeaters. We find that, under the assumptions of our model and if the magnetic field of magnetars is characterized by a strong dipolar component, and QPOs are produced near the magnetic pole, then one can place an upper limit to the mean surface strength of the magnetic field of about . [ABSTRACT FROM AUTHOR]

We study non-linear axisymmetric pulsations of rotating relativistic stars using a general relativistic hydrodynamics code under the assumption of a conformally flat three-metric. We compare the results of our simulations, in which the space–time dynamics is coupled to the evolution of the fluid, to previous results performed in the Cowling approximation in which the space–time dynamics was neglected. We show that the conformal flatness condition has only a small effect on the dynamics of pulsating relativistic stars and the obtained pulsation frequencies are very close to those expected in full general relativity. The pulsations are studied along various sequences of both uniformly and differentially rotating relativistic polytropes with index . For small pulsation amplitudes we identify several modes, including the lowest-order , 2 and 4 axisymmetric modes, as well as several axisymmetric inertial modes. Differential rotation significantly shifts mode frequencies to smaller values, increasing the likelihood of detection by current gravitational wave interferometric detectors. We observe an extended avoided crossing between the and first overtones (previously known to exist from perturbative studies), which is important for correctly identifying mode frequencies in the case of detection. For uniformly rotating stars near the mass-shedding limit, we confirm the existence of the mass-shedding-induced damping of pulsations and argue that it is still relevant for secularly unstable modes, even though the effect is not as strong as was previously found in the Cowling approximation. We also investigate non-linear harmonics of the linear modes and note that rotation changes the pulsation frequencies in a way that would allow for various parametric instabilities between two or three modes to take place. Although this scenario has been explored before for slowly rotating collapse, it could become very interesting in the case of rapidly rotating collapse, where the quasi-radial mode could be in resonance with inertial modes. We assess the detectability of each obtained mode by current gravitational wave detectors and outline how the empirical relations that have been constructed for gravitational wave asteroseismology could be extended to include the effects of rotation. [ABSTRACT FROM AUTHOR]

We present a comprehensive numerical study of the dynamics of relativistic axisymmetric accretion tori with a power-law distribution of specific angular momentum orbiting in the background space–time of a Kerr black hole. By combining general relativistic hydrodynamics simulations with a linear perturbative approach we investigate the main dynamical properties of these objects over a large parameter space. The astrophysical implications of our results extend and improve two interesting results that have been recently reported in the literature. First, the induced quasi-periodic variation of the mass quadrupole moment makes relativistic tori of nuclear matter densities, as those formed during the last stages of binary neutron star mergers, promising sources of gravitational radiation, potentially detectable by interferometric instruments. Secondly, p-mode oscillations in relativistic tori of low rest-mass densities could be used to explain high-frequency quasi-periodic oscillations observed in X-ray binaries containing a black hole candidate under conditions more generic than those considered so far. [ABSTRACT FROM AUTHOR]

We study small-amplitude, non-linear pulsations of uniformly and differentially rotating neutron stars employing a two-dimensional evolution code for general-relativistic hydrodynamics. Using Fourier transforms at several points inside the star, both the eigenfrequencies and two-dimensional eigenfunctions of pulsations are extracted. The centrifugal forces and the degree of differential rotation have significant effects on the mode eigenfunction. We find that near the mass-shedding limit, the pulsations are damped due to shocks forming at the surface of the star. This new damping mechanism may set a small saturation amplitude for modes that are unstable to the emission of gravitational waves. After correcting for the assumption of the Cowling approximation (used in our numerical code), we construct empirical relations that predict the range of gravitational-wave frequencies from quasi-periodic post-bounce oscillations in the core collapse of massive stars. We also find that the fundamental quasi-radial mode is split, at least in the Cowling approximation and mainly in differentially rotating stars, into two different sequences. [ABSTRACT FROM AUTHOR]

We present results from a comprehensive number of relativistic, time-dependent, axisymmetric simulations of the runaway instability of non-constant angular momentum thick discs around black holes. This second paper in the series extends earlier results where only constant angular momentum discs were considered. All relevant aspects of the theory of stationary thick discs around rotating black holes, necessary to build the equilibrium initial data used in our simulations, are presented in great detail. The angular momentum of the evolved discs is assumed to increase outwards with the radial distance according to a power law, , where corresponds to prograde discs (with respect to the black hole rotation) and to retrograde discs. The main simplifying assumptions of our approach are not to include magnetic fields or self-gravity in the discs (test-fluid approximation). Furthermore, the dynamics of the space–time is accounted for by computing the transfer of mass and angular momentum from the disc to the black hole through the event horizon. In this approximation the evolution of the central black hole, which initially is non-rotating, is assumed to follow a sequence of Kerr black holes of increasing mass and spin. All discs we build slightly overflow the potential barrier at the cusp, departing from equilibrium, so that accretion is possible. In agreement with previous results based on stationary models we find that by allowing the mass and the spin of the black hole to grow, constant angular momentum discs rapidly become unstable on a dynamical time-scale (a few orbital periods). The comparison with the results of our first paper shows that the effect of the angular momentum transfer from the tori to the black hole is to make constant angular momentum discs less unstable, increasing the time-scale for the runaway instability to grow. However, we find that non-constant angular momentum discs are dramatically stabilized for very small values of the angular momentum slope α, much smaller than the Keplerian value . Our fully relativistic and time-dependent simulations thus confirm the predictions of stationary studies concerning the stabilizing effect of non-constant angular momentum distributions. For the various disc-to-hole mass ratios considered, we systematically find that the critical values of α below which the runaway instability can exist are slightly smaller than those reported previously in the literature based on stationary studies. [ABSTRACT FROM AUTHOR]

Introduction: Defects in the regulation of apoptosis of autoreactive lymphocytes are involved in the pathogenesis of systemic lupus erythematosus (SLE). The apoptotic process relies on adequate functioning of numerous molecules, including oncogenes and diverse cytokines. p53 has been implicated in the control of the cell cycle through the stimulation of apoptosis of these autoreactive cells. Objective: To study the role of the p53 pathway on the regulation of apoptosis in SLE patients and analyze the relationship of the p53 oncoprotein with disease activity and other oncogenes (bcl-2, Fas) and cytokines (interleukin-10, IL-10, and tumor necrosis factor-α, TNF-α), implicated in the apoptotic process and the pathogenesis of SLE. Patients and Methods: p53 and bcl-2 antigen expression were determined in lyzed lymphocytes from 74 patients with SLE and 30 healthy controls. Serum levels of soluble-Fas (sFas) and cytokines IL-10 and TNF-α were studied by enzyme-linked immunonosorbent assay. Results: SLE patients had higher levels of p53 protein (0.16 ± 0.33 ng/dl) than controls (0.014 ± 0.02 ng/dl; p = 0.006). Patients with active SLE had higher levels of p53 (0.31 ± 0.48 ng/dl) than those with inactive disease (0.08 ± 0.17 ng/dl; p = 0.003) who in turn had higher levels than controls (0.01 ± 0.02 ng/dl; p = 0.035). A significant correlation was found between p53 levels and the SLE disease activity index (R = +0.24/ p = 0.04), anti-DNA antibodies (R = +0.23/p = 0.048) and IL-10 levels (R = +0.4/p = 0.004). No correlation was found between p53 levels and bcl-2, sFas or TNF-α levels. Conclusions: The p53 oncoprotein may play a role in the pathogenesis and activity of SLE. IL-10 may influence SLE activity by inhibiting the p53 and bcl-2/Fas apoptosis pathway of autoreactive cells. Copyright © 2003 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

ABSTRACT We present general relativistic hydrodynamics simulations of constant specific angular momentum tori orbiting a Schwarzschild black hole. These tori are expected to form as a result of stellar gravitational collapse, binary neutron star merger or disruption, can reach very high rest-mass densities and behave effectively as neutron stars but with a toroidal topology (i.e. ‘toroidal neutron stars’). Here our attention is focused on the dynamical response of these objects to axisymmetric perturbations. We show that upon the introduction of perturbations, these systems either become unstable to the runaway instability or exhibit a regular oscillatory behaviour, resulting in a quasi-periodic variation of the accretion rate as well as of the mass quadrupole. The latter, in particular, is responsible for the emission of intense gravitational radiation for which the signal-to-noise ratio at the detector is comparable to or larger than the typical one expected in stellar-core collapse, making these new sources of gravitational waves potentially detectable. We discuss a systematic investigation of the parameter space in both the linear and non-linear regimes, providing estimates of how the gravitational radiation emitted depends on the mass of the torus and on the strength of the perturbation. [ABSTRACT FROM AUTHOR]

Pregnancy loss, often recurrent, is one of the most important clinical manifestations associated with the primary antiphospholipid syndrome. In these cases, pregnancy wastage is related to the presence of antiphospholipid antibodies, namely lupus anticoagulant and anticardiolipin antibodies, but patients do not have features of systemic lupus erythematosus or any other well-defined autoimmune disease. We report here on the outcome of 21 consecutive pregnancies in 18 patients with the syndrome who were treated with low-dose aspirin (100 mg/day) from 1 month before attempting conception and throughout the pregnancy. Low-dose prednisone (15–30 mg/day) was added for potentially non-obstetric (autoimmune-related) reasons in six pregnancies. Patients were monitored as having high-risk pregnancies. Prior to therapy, the rate of live-born babies was 6.1% (46 previous fetal losses and three live-born babies), and after therapy, it was 90.5% (21 pregnancies and 19 live-born babies). Pre-term delivery due to maternal or fetal indications was required in 15% (3/20) of the viable pregnancies. Except for prematurity (20% of viable pregnancies) and its potential associated complications, there were no significant adverse effects to either mothers or babies. Our treatment modality is advocated for prevention of pregnancy losses in patients with the ‘obstetric’ primary antiphospholipid syndrome. [ABSTRACT FROM PUBLISHER]

This study used a novel integrated technology of ceramic supported carbon membrane (CSCM) to degrade azo dyes through an anaerobic mixed culture. The CSCM worked simultaneously as biofilm support, redox mediator, and nano-filter to enhance the dye decolorization efficiency. The decolorization of Acid Orange 7 (AO7) was initially investigated with and without microorganisms in both ceramic support (CS) and CSCM reactors. The CSCM bioreactor (B-CSCM), operated with microorganisms, gave a maximum decolorization of 98% using a CSCM evolved from 10% weight (wt.) of Matrimid 5218 solution. To know the influence of permeate flow, feed concentration, and dye structure on the decolorization process, different B-CSCMs for dye removal experiments were studied over monoazo AO7, diazo Reactive Black 5 (RB5), and triazo Direct Blue 71 (DB71). The highest color removal, operated with 50 mg·L−1 feed solution and 0.05 L·m−2·h−1 of permeate flux, was 98%, 82%, and 72%, respectively, for AO7, RB5, and DB71. By increasing these parameters to 100 mg·L−1 and 0.1 L·m−2·h−1, the decolorization rate of dye solution still achieved 37% for AO7, 30% for RB5, and 26% for DB71. In addition, the system was run for weeks without apparent loss of activity. These findings make evident that the combined phenomena taking place in CSCM bioreactor result in an efficient, cost-effective, and ecofriendly azo dye decolorization method. [ABSTRACT FROM AUTHOR]