If primordial black holes (PBH) with masses of constitute a non-negligible fraction of galactic dark-matter halos, their existence should have observable consequences: they necessarily collide with ...galactic neutron stars (NS), nest in their centers, and accrete the dense matter, eventually converting them to NS-mass black holes while releasing the NS magnetic field energy. Such processes may explain the fast radio bursts (FRB) phenomenology, in particular their millisecond durations, large luminosities ∼1043 erg s−1, high rate of occurrence , as well as high brightness temperatures, polarized emission, and Faraday rotation. Longer than the dynamical timescale of the Bondi-like accretion for light PBH allows for the repeating of FRB. This explanation follows naturally from the (assumed) existence of the dark-matter PBH and requires no additional unusual phenomena, in particular no unacceptably large magnetic fields of NS. In our model, the observed rate of FRB throughout the universe follows from the presently known number of NS in the Galaxy.
The parallelization, design and scalability of the PolGrawAllSky code to search for periodic gravitational waves from rotating neutron stars is discussed. The code is based on an efficient ...implementation of the F-statistic using the Fast Fourier Transform algorithm. To perform an analysis of data from the advanced LIGO and Virgo gravitational wave detectors’ network, which will start operating in 2015, hundreds of millions of CPU hours will be required—the code utilizing the potential of massively parallel supercomputers is therefore mandatory. We have parallelized the code using the Message Passing Interface standard, implemented a mechanism for combining the searches at different sky-positions and frequency bands into one extremely scalable program. The parallel I/O interface is used to escape bottlenecks, when writing the generated data into file system. This allowed to develop a highly scalable computation code, which would enable the data analysis at large scales on acceptable time scales. Benchmarking of the code on a Cray XE6 system was performed to show efficiency of our parallelization concept and to demonstrate scaling up to 50 thousand cores in parallel.
Program title: parallel PolGrawAllSky
Catalogue identifier: AEUX_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEUX_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html
No. of lines in distributed program, including test data, etc.: 163747
No. of bytes in distributed program, including test data, etc.: 28989030
Distribution format: tar.gz
Programming language: C.
Computer: Any parallel computing platform supporting MPI standard.
Operating system: Linux as well any other supporting MPI standard.
Has the code been vectorized or parallelized?: Yes, using MPI. Tested with up to 50208 processors
RAM: 1 Gigabyte per parallel task
Classification: 1.5.
External routines: MPI v.2 or newer, FFTW v.3 or newer
Nature of problem:
Search for periodic gravitational waves from rotating neutron stars.
Solution method:
The F-statistic method using the Fast Fourier Transform algorithm.
Running time:
The example provided takes approximately 30 mins with 256 processors.
Aims. To estimate the feasibility of dense-matter phase transition, we studied the evolution of the central density as well as the baryon chemical potential of accreting neutron stars. We compared ...the thin-disk accretion with and without the magnetic field torque with the spin-down scenario for a selection of recent equations of state. Methods. We compared the prevalent (in the recycled-pulsar context) Keplerian thin-disk model, in which the matter is accreted from the marginally-stable circular orbit, with the recent magnetic-torque model that takes into account the influence of stellar magnetic field on the effective inner boundary of the disk. Calculations were performed using a multi-domain spectral methods code in the framework of General Relativity. We considered three equations of state consistent with the recently measured mass of PSR J1614-2230, 1.97 ± 0.04 M⊙ (one of them softened by the appearance of hyperons). Results. If there is no magnetic torque and efficient angular momentum transfer from the disk to the star, substantial central compression is limited to the region of initial stellar masses close to the maximum mass. Outside the maximum mass vicinity, accretion-induced central compression is significant only if the angular momentum transfer is inefficient. Accounting for the magnetic field effectively decreases the efficiency of angular momentum transfer and implies a significant central compression. Conclusions. An efficient angular momentum transfer from a thin disk onto a non-magnetized neutron star does not provide a good mechanism for the central compression and possible phase transition. Substantial central compression is possible for a broad range of masses of slowly-rotating initial configurations for magnetized neutron stars. Accretion-induced central compression is particularly strong for stiff equation of state with a high-density softening.
Stimuli‐responsive 3radialene radical anions dimerize reversibly in a controlled manner. An unprecedented tristate switching mechanism can be achieved by changing the solvent environment, ...temperature, or salinity of the solution. This allows the radical to be toggled between the free radical, a π‐dimer, and a σ‐dimer, which exhibit dramatically different optical, magnetic, and redox properties. The addition of salt to the radialene catholyte solution in an aqueous redox flow battery (RFB) converts the σ‐dimer to the π‐dimer and increases the electrochemical reversibility and stability of the charged species, which are advantageous for galvanostatic charge–discharge studies at neutral pH. More information can be found in the Research Article by Arthur H. Winter, C. Bejger, and co‐workers (DOI: 10.1002/chem.202302829). Illustration by Frank A. Martinez.
Aims.We analyze potentially observable phenomena during spin evolution of isolated pulsars, such as back bending and corequakes resulting from instabilities, which could result from phase transitions ...in neutron star cores. Methods.We study these aspects of spin evolution of isolated compact stars by means of analytical models of equations of state, for both constant-pressure phase transitions and the transitions through the mixed-phase region. We use high-precision 2-D multi-domain spectral code LORENE for the calculation of the evolutionary sequences of rotating neutron stars. This allows us to search the parameter space for possible instability regions, and possible changes in the stability character of rotating stars with phase transitions in their cores. Results.We determine the conditions on the density jump in constant-pressure phase transitions which leads to the back bending phenomena or to the existence of the unstable segments in the evolutionary sequences of spinning down isolated normal neutron stars. We formulate the conjectures concerning the existence of two disjoint families of non-rotating and rotating stationary configurations of neutron stars. To clarify the effect of rotation on the stability of neutron star we present the particular case of EOSs leading to marginal instability of static and rotating configurations: marginal instability point in non-rotating configurations continues to exist in all evolutionary spin-down tracks. We discuss the fate of rotating stars entering the region of instability calculating the change in radius, energy release, and spin-up associated with the corequake in rotating neutron star, triggered by the instability. The energy release is found to be very weakly dependent on the angular momentum of collapsing star.
Here, we show for the first time that main-chain organometallic polymers (MCOPs) can be prepared from Janus N-heterocyclic carbene (NHC) linkers and polynuclear cluster nodes. The crosslinked ...framework Co4S4-MCOP is synthesized via ligand displacement reactions and undergoes reversible electron transfer in the solid state. Discrete molecular cluster species can be excised from the framework by digesting the solid in solutions of excess monocarbene. Finally, we demonstrate a synthetic route to monodisperse framework particles via coordination modulation.
Abstract
If very low mass primordial black holes (PBH) within the asteroid/moon-mass range indeed reside in galactic dark matter halos, they must necessarily collide with galactic neutron stars ...(NSs). These collisions must, again necessarily, form light black holes (LBHs) with masses of typical NSs,
M
LBH
≈ 1–2
M
⊙
. LBHs may be behind events already detected by ground-based gravitational-wave detectors (GW170817, GW190425, and others such as a mixed stellar black hole–NS-mass event GW191219_163120), and most recently by microlensing (OGLE-BLG-2011-0462). Although the status of these observations as containing LBHs is not confirmed, there is no question that gravitational-wave detectors and microlensing are in principle and in practice capable of detecting LBHs. We have calculated the creation rate of LBHs resulting from these light primordial black hole (PBH) collisions with NSs. On this basis, we claim that if improved gravitational-wave detectors and microlensing statistics of the LBH events would indicate that the number of LBHs is significantly lower that what follows from the calculated creation rate, then this would be an unambiguous proof that there is no significant light PBH contribution to the galactic dark matter halos. Otherwise, if observed and calculated numbers of LBHs roughly agree, then the hypothesis of primordial black hole existence gets strong observational support, and in addition their collisions with NSs may be considered a natural creation channel for the LBHs, solving the problem of their origin, as it is known that they cannot be a product of standard stellar evolution.
Aims. We calculate parameters A and B of the Baym-Pines model of the hydro-elastic equilibrium of rotating neutron stars. Parameter A determines the energy increase of a non-rotating star due to a ...quadrupolar deformation of its shape. Parameter B determines residual quadrupolar deformation due to the crustal shear strain in a neutron star that spun down to a non-rotating state. Methods. The calculations of A are based on precise numerical 2D calculations for rotating neutron stars with the realistic equations of state (EOSs) of dense matter. An approximate, but quite precise, formula for B is used, which allows us to separate the contribution of the crust from the dependence on the stellar mass M and radius R. The elastic shear strain distribution within the crust is modeled following Cutler et al. (2003). Realistic EOSs of neutron star cores are used, some of them with high-density softening due to the appearance of hyperons or a phase transition to an exotic state. Results. The values A (M) and B (M) were calculated for 0.2\; M _\odot<M<0.9\; M_{max} (where M_{max} is the maximum allowable mass) for seven EOSs of neutron star core, combined with several crust models. A standard formula based on the incompressible fluid model is shown to severely underestimate the value of A. For M<0.7\; M_\odot the values of A (M) are nearly EOS-independent and are given (within a few percent) by a universal formula A=3.87\; (M/M_\odot) logical or ; \times 10 6{erg}. We derive the scaling of B with respect to R and M, also valid for a thick crust. We show that B for accreted crust strongly depends on pycnonuclear fusions at 10 6g similar to cm logical and rho>10 6g similar to cm greater than or equal to
The hexacyano3radialene radical anion (1) is an attractive catholyte material for use in redox flow battery (RFB) applications. The substitution of cyano groups with ester moieties enhances ...solubility while maintaining redox reversibility and favorable redox potentials. Here we show that these ester‐functionalized, hexasubstituted 3radialene radical anions dimerize reversibly in water. The dimerization mode is dependent on the substitution pattern and can be switched in solution. Stimuli‐responsive behavior is achieved by exploiting an unprecedented tristate switching mechanism, wherein the radical can be toggled between the free radical, a π‐dimer, and a σ‐dimer‐each with dramatically different optical, magnetic, and redox properties‐by changing the solvent environment, temperature, or salinity. The symmetric, triester‐tricyano3radialene (3) forms a solvent‐responsive, σ‐dimer in water that converts to the radical anion with the addition of organic solvents or to a π‐dimer in brine solutions. Diester‐tetracyano3radialene (2) exists primarily as a π‐dimer in aqueous solutions and a radical anion in organic solvents. The dimerization behavior of both 2 and 3 is temperature dependent in methanol solutions. Dimerization equilibrium has a direct impact on catholyte stability during galvanostatic charge–discharge cycling in static H‐cells. Specifically, conditions that favor the free radical anion or π‐dimer exhibit significantly enhanced cycling profiles.
Ester‐substituted 3radialene radical anions dimerize in solutions of water. The dimerization mode is structure specific and can be controlled by using heat, solvent, and salt. These results provide guidance for increasing the capacity of aqueous redox flow batteries containing radialene catholytes. A buildup of σ‐dimer prevents stable charge–discharge cycling. The formation of π‐dimers through the addition of salt increases the stability of the charged species.
Here, we show for the first time that main-chain organometallic polymers (MCOPs) can be prepared from Janus N-heterocyclic carbene (NHC) linkers and polynuclear cluster nodes. The crosslinked ...framework Co
S
-MCOP is synthesized
ligand displacement reactions and undergoes reversible electron transfer in the solid state. Discrete molecular cluster species can be excised from the framework by digesting the solid in solutions of excess monocarbene. Finally, we demonstrate a synthetic route to monodisperse framework particles
coordination modulation.
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