The former companion of hyper-velocity star S5-HVS1

ABSTRACT The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Centre at 1800 km s−1, was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6 M⊙ and was captured into a highly eccentric orbit with pericentre distance in the range of 1–10 au and semimajor axis about 103 au. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericentre distance is smaller than about $3\rm \, au$. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericentre inwards below $3\rm \, au$ and cause tidal disruption. We find an overall survival probability in the range 5 per cent to 50 per cent, depending on the local relaxation time in the close environment of the captured star, and the initial pericentre at capture. The pericentre distance of the surviving star has migrated to 10–100 au, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically $K_{\rm s}\lesssim 18.5\,$ mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*.

Dielectric Responses of Polyurethane/Zinc Oxide Blends for Dry-Type Cast Cold-Curing Resin Transformers

The influence of different concentrations (0.5, 1.0, and 2.0 wt.%) of Zinc Oxide (ZnO) filler on the dielectric properties of the cold-curing polyurethane (PU) resin is presented in this study. For this purpose, the direct DC conductivity and the broadband dielectric spectroscopy measurements were used to describe the changes in dielectric responses of PU/ZnO nanocomposites over the frequency and temperature range, respectively. It can be stated that, the 1.0 wt.% nanoparticles and lower caused a decrease in the real relative permittivity compared to the pure PU resin, while the higher concentration of nanoparticles for frequencies above 1 Hz had the opposite effect. The presence of nanoparticles in the polyurethane resin affected the segmental dynamics of the polymer chain and changed a charge distribution in the given system. These changes caused a shift of local relaxation peaks in the spectra of imaginary permittivity and dissipation factor of nanocomposites. It is suggested that the temperature-dependent transition of the electric properties in the nano-composite is closely associated with the α-relaxation and intermediate dipolar effects (IDE).

Sharp critical thresholds in a hyperbolic system with relaxation

<p style='text-indent:20px;'>We propose and study a one-dimensional <inline-formula><tex-math id="M1">\begin{document}$ 2\times 2 $\end{document}</tex-math></inline-formula> hyperbolic Eulerian system with local relaxation from critical threshold phenomena perspective. The system features dynamic transition between strictly and weakly hyperbolic. For different classes of relaxation we identify intrinsic <b>critical thresholds</b> for initial data that distinguish global regularity and finite time blowup. For relaxation independent of density, we estimate bounds on density in terms of velocity where the system is strictly hyperbolic.</p>

Relaxation model of dynamic deformation of elastic-plastic media

A variant is considered for the relaxation model of a loaded elastic-plastic medium with dislocation kinetics of plastic shearing. The model is formulated in rates and includes two independent strain rates: total strain rate, which corresponds to the rate of external action, and local rate of plastic response of the material, which represents the ability of the medium to generate strain-induced defects. This makes it possible to describe both local relaxation processes in the elastic-plastic medium and average relaxation of stresses in a loaded specimen. The model being developed amounts to microscopic ones. All model parameters are determined from independent experiments for the evolution of the dislocation continuum during loading of macroscopic specimens. The model provides an adequate description of the dynamic effects of the macroscopic response of materials depending on the strain rate: the upper and lower yield points (yield drop, yield plateau), subsequent strain hardening as well as features of cyclic and alternating loading, ideal and nonideal Bauschinger effect.

Verbalizing phylogenomic conflict: Representation of node congruence across competing reconstructions of the neoavian explosion

Phylogenomic research is accelerating the publication of landmark studies that aim to resolve deep divergences of major organismal groups. Meanwhile, systems for identifying and integrating the novel products of phylogenomic inference – such as newly supported clade concepts – have not kept pace. However, the ability toverbalizeboth node concept congruence and conflict across multiple, (in effect) simultaneously endorsed phylogenomic hypotheses, is a critical prerequisite for building synthetic data environments for biological systematics, thereby also benefitting other domains impacted by these (conflicting) inferences. Here we develop a novel solution to the conflict verbalization challenge, based on a logic representation and reasoning approach that utilizes the language of Region Connection Calculus (RCC–5) to produce consistentalignmentsof node concepts endorsed by incongruent phylogenomic studies. The approach employs clade concept labels to individuate concepts used by each source, even if these carry identical names. Indirect RCC–5 modeling ofintensional(property-based) node concept definitions, facilitated by the local relaxation of coverage constraints, allows parent concepts to attain congruence in spite of their differentially sampled children. To demonstrate the feasibility of this approach, we align two recently published phylogenomic reconstructions of higher-level avian groups that entail strong conflict in the “neoavian explosion” region. According to our representations, this conflict is constituted by 26 instances of input “whole concept” overlap. These instances are further resolvable in the output labeling schemes and visualizations as “split concepts”, thereby providing the provenance services needed to build truly synthetic phylogenomic data environments. Because the RCC–5 alignments fundamentally reflect the trained, logic-enabled judgments of systematic experts, future designs for such environments need to promote a culture where experts routinely assess the intensionalities of node concepts published by our peers – even and especially when we are not in agreement with each other.

Thermomechanical and dielectric properties of novel pyridine-based polyurethane urea elastomers

In this article, novel pyridine-based polyurethane urea elastomers were synthesized from 1,6-hexamethylene diisocyanate and poly(tetramethylene oxide) glycol of molecular weight 1400 which was chain extended with 3,4-diaminopyridine. These new heterocyclic polyurethane urea elastomers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and static mechanical measurements as a function of pyridine moieties content and the crosslinkers structure from the hard domains. This settlement of the amine groups on the pyridine rings realizes weak intermolecular hydrogen bonds compared with other pyridine derivatives studied by us. The molecular dynamics and local relaxation of these polyurethane urea elastomers were investigated using broadband dielectric spectroscopy. Results show that pyridine content slightly increases the glass transition temperature and has low dielectric strength of the segmental relaxation as a result of weaker cohesive domains.