Strange quark stars in binaries: formation rates, mergers and explosive phenomena

The existence of strange quark stars has been proposed many years ago. More recently, the possible co-existence of a first family composed of "normal" neutron stars with a second family of strange quark stars has been proposed as a solution of problems related to the maximum mass and to the minimal radius of these compact stellar objects. In this paper we study the mass distribution of compact objects formed in binary systems and the relative fractions of quark and neutron stars in different subpopulations. We incorporate the strange quark star formation model provided by the two-families scenario and we perform a large-scale population synthesis study in order to obtain the population characteristics. In our model, below a critical gravitational mass $M_\mathrm{max}^H- \Delta M$ only normal (hadron) neutron stars exist. Then in the mass range $(M_\mathrm{max}^H- \Delta M) \leqslant M \leqslant M_\mathrm{max}^H$ strange quark stars and neutron stars coexist. Finally, above $M_\mathrm{max}^H$ all compact objects are strange quark stars. We argue that $M_\mathrm{max}^H$ is in the range $\sim 1.5-1.6 M_\odot$. According to our results, the main channel for strange quark star formation in binary systems is accretion from a secondary companion on a neutron star.This opens the possibility of having explosive GRB-like phenomena not related to supernovae and not due to the merger of two neutron stars. The enhancement in the number of compact objects in the co-existence mass range $(M_\mathrm{max}^H- \Delta M) \leqslant M \leqslant M_\mathrm{max}^H$ is not very pronounced. The number of double strange quark star's systems is rather small with only a tiny fraction which merge within a Hubble time. This drastically limits the flux of strangelets produced by the merger, which turns out to be compatible with all limits stemming from Earth and lunar experiments.Comment: 11 pages, 10 figures, minor typos corrected, ApJ, 846, 16

Time scale for the onset of Fickian diffusion in supercooled liquids

We propose a quantitative measure of a time scale on which Fickian diffusion sets in for supercooled liquids and use Brownian Dynamics computer simulations to determine the temperature dependence of this onset time in a Lennard-Jones binary mixture. The time for the onset of Fickian diffusion ranges between 6.5 and 31 times the $\alpha$ relaxation time (the $\alpha$ relaxation time is the characteristic relaxation time of the incoherent intermediate scattering function). The onset time increases faster with decreasing temperature than the $\alpha$ relaxation time. Mean squared displacement at the onset time increases with decreasing temperature

Average Case ϵ-Complexity in Computer Science: A Bayesian View

Relations between average case ϵ-complexity and Bayesian statistics are discussed. An algorithm corresponds to a decision function, and the choice of information to the choice of an experiment. Adaptive information in ϵ-complexity theory corresponds to the concept of sequential experiment. Some results are reported, giving ϵ-complexity and minimax-Bayesian interpretations for factor analysis. Results from ϵ-complexity are used to establish that the optimal sequential design is no better than optimal nonsequential design for that problem

On an extremal problem for poset dimension

Let $f(n)$ be the largest integer such that every poset on $n$ elements has a $2$-dimensional subposet on $f(n)$ elements. What is the asymptotics of $f(n)$? It is easy to see that $f(n)\geqslant n^{1/2}$. We improve the best known upper bound and show $f(n)=\mathcal{O}(n^{2/3})$. For higher dimensions, we show $f_d(n)=\mathcal{O}\left(n^\frac{d}{d+1}\right)$, where $f_d(n)$ is the largest integer such that every poset on $n$ elements has a $d$-dimensional subposet on $f_d(n)$ elements.Comment: removed proof of Theorem 3 duplicating previous work; fixed typos and reference

Particle Acceleration in Turbulence and Weakly Stochastic Reconnection

Fast particles are accelerated in astrophysical environments by a variety of processes. Acceleration in reconnection sites has attracted the attention of researchers recently. In this letter we analyze the energy distribution evolution of test particles injected in three dimensional (3D) magnetohydrodynamic (MHD) simulations of different magnetic reconnection configurations. When considering a single Sweet-Parker topology, the particles accelerate predominantly through a first-order Fermi process, as predicted in previous work (de Gouveia Dal Pino & Lazarian, 2005) and demonstrated numerically in Kowal, de Gouveia Dal Pino & Lazarian (2011). When turbulence is included within the current sheet, the acceleration rate, which depends on the reconnection rate, is highly enhanced. This is because reconnection in the presence of turbulence becomes fast and independent of resistivity (Lazarian & Vishniac, 1999; Kowal et al., 2009) and allows the formation of a thick volume filled with multiple simultaneously reconnecting magnetic fluxes. Charged particles trapped within this volume suffer several head-on scatterings with the contracting magnetic fluctuations, which significantly increase the acceleration rate and results in a first-order Fermi process. For comparison, we also tested acceleration in MHD turbulence, where particles suffer collisions with approaching and receding magnetic irregularities, resulting in a reduced acceleration rate. We argue that the dominant acceleration mechanism approaches a second order Fermi process in this case.Comment: 6 pages, 1 figur

The dynamical mass and evolutionary status of the type-II Cepheid in the eclipsing binary system OGLE-LMC-T2CEP-211 with a double-ring disk

We present the analysis of a peculiar W~Virginis (pWVir) type-II Cepheid, OGLE-LMC-T2CEP-211 ($P_{puls}=9.393\,d$), in a double-lined binary system ($P_{orb}=242\,d$), which shed light on virtually unknown evolutionary status and structure of pWVir stars. The dynamical mass of the Cepheid (first ever for a type-II Cepheid) is $0.64\pm{}0.02\,M_\odot$ and the radius $R=25.1\pm{}0.3\,R_\odot$. The companion is a massive ($5.67\,M_\odot$) main-sequence star obscured by a disk. Such configuration suggests a mass transfer in the system history. We found that originally the system ($P_{orb}^{init}=12\,d$) was composed of $3.5$ and $2.8\,M_\odot$ stars, with the current Cepheid being more massive. The system age is now $\sim{}$200 My, and the Cepheid is almost completely stripped of hydrogen, with helium mass of $\sim{}92\%$ of the total mass. It finished transferring the mass 2.5 My ago and is evolving towards lower temperatures passing through the instability strip. Comparison with observations indicate a reasonable $2.7\cdot{}10^{-8}\,M_\odot/y$ mass loss from the Cepheid. The companion is most probably a Be main-sequence star with $T=22000\,K$ and $R=2.5\,R_\odot$. Our results yield a good agreement with a pulsation theory model for a hydrogen-deficient pulsator, confirming the described evolutionary scenario. We detected a two-ring disk ($R_{disk}\sim\,116\,R_{\odot}$) and a shell ($R_{shell}\sim\,9\,R_{\odot}$) around the companion, that is probably a combination of the matter from the past mass transfer, the mass being lost by the Cepheid due to wind and pulsations, and a decretion disk around a rapidly rotating secondary. Our study together with observational properties of pWVir stars suggests that their majority are products of a similar binary evolution interaction.Comment: 21 pages, 14 figures, 6 tables, accepted for publication in Ap

Emergence and extinction of the Givetian to Frasnian bryozoan faunas in the Kostomłoty facies zone, Holy Cross Mountains, Poland

Devonian bryozoans have been investigated from two Givetian to Frasnian localities in the Holy Cross Mts (Central Poland), representing fossiliferous ramp slope facies of the Kostomloty facies zone (north-western periphery of the Kielce carbonate platform). Thirteen genera belonging to four families and three orders have been identified. Bryozoans show close relation to previously described Givetian and Frasnian bryozoan faunas of France, but also some affinities to easterly regions (e.g., Kuzbass). The main immigration episodes are related to late Givetian and middle Frasnian deepening pulses. The replacement of locally rich and diverse Givetian carbonate bank faunas by overall impoverished Frasnian reef-complex associations largely corresponds to a major extinction event in the evolutionary history of Bryozoa. Five new species are described by 1. Morozova and O. Weis: Eridotrypella arguta, Eridotrypella exserta, Eostenopora nimia, Primorella nitida, Primorella indigena