1,152 research outputs found

### Impact of inter-correlated initial binary parameters on double black hole and neutron star mergers

The distributions of the initial main-sequence binary parameters are one of
the key ingredients in obtaining evolutionary predictions for compact binary
(BH-BH / BH-NS / NS-NS) merger rates. Until now, such calculations were done
under the assumption that initial binary parameter distributions were
independent. Here, we implement empirically derived inter-correlated
distributions of initial binary parameters primary mass (M1), mass ratio (q),
orbital period (P), and eccentricity (e). Unexpectedly, the introduction of
inter-correlated initial binary parameters leads to only a small decrease in
the predicted merger rates by a factor of 2 $-$ 3 relative to the previously
used non-correlated initial distributions. The formation of compact object
mergers in the isolated classical binary evolution favors initial binaries with
stars of comparable masses (q = 0.5 $-$ 1) at intermediate orbital periods (log
P (days) = 2 $-$ 4). New distributions slightly shift the mass ratios towards
smaller values with respect to the previously used flat q distribution, which
is the dominant effect decreasing the rates. New orbital periods only
negligibly increase the number of progenitors. Additionally, we discuss the
uncertainty of merger rate predictions associated with possible variations of
the massive-star initial mass function (IMF). We argue that evolutionary
calculations should be normalized to a star formation rate (SFR) that is
obtained from the observed amount of UV light at wavelength 1500{\AA} (SFR
indicator). In this case, contrary to recent reports, the uncertainty of the
IMF does not affect the rates by more than a factor of 2. Any change to the IMF
slope for massive stars requires a change of SFR in a way that counteracts the
impact of IMF variations on the merger rates. In contrast, we suggest that the
uncertainty in cosmic SFR at low metallicity can be a significant factor at
play.Comment: accepted for publication in A&

### Explaining LIGO's observations via isolated binary evolution with natal kicks

We compare binary evolution models with different assumptions about
black-hole natal kicks to the first gravitational-wave observations performed
by the LIGO detectors. Our comparisons attempt to reconcile merger rate,
masses, spins, and spin-orbit misalignments of all current observations with
state-of-the-art formation scenarios of binary black holes formed in isolation.
We estimate that black holes (BHs) should receive natal kicks at birth of the
order of $\sigma\simeq 200$ (50) km/s if tidal processes do (not) realign
stellar spins. Our estimate is driven by two simple factors. The natal kick
dispersion $\sigma$ is bounded from above because large kicks disrupt too many
binaries (reducing the merger rate below the observed value). Conversely, the
natal kick distribution is bounded from below because modest kicks are needed
to produce a range of spin-orbit misalignments. A distribution of misalignments
increases our models' compatibility with LIGO's observations, if all BHs are
likely to have natal spins. Unlike related work which adopts a concrete BH
natal spin prescription, we explore a range of possible BH natal spin
distributions. Within the context of our models, for all of the choices of
$\sigma$ used here and within the context of one simple fiducial parameterized
spin distribution, observations favor low BH natal spin.Comment: 19 pages, 14 figures, as published in PR

### Using the D-BEST Reference Model to Compare Italian and Polish Digital Innovation Hubs

In recent years, the increasing importance of Digital Innovation Hubs (DIHs) in supporting manufacturing Small and Medium Enterprises (SMEs) has been widely studied and several works listing lessons learnt and success stories have been published. To further foster the impact of these entities on the SMEs’ environment, The European Commission has recently introduced the Smart Specialisation Platform, which contains a web service returning to its users a geo-distributed list of DIHs, allowing the user also to cluster and visualise them according to some pre-defined filters, such as the types of technologies employed. The data provided by this platform has been downloaded and a secondary data analysis, based on the websites of the DIHs has been carried on to frame the single DIHs according to the axes of the D-BEST methodology. A comparative analysis with respect to the Italian and Poland situation completes the study, to understand eventual differences and affinities among the two countries

### Temporal variability and statistics of the Strehl ratio in adaptive-optics images

We have investigated the temporal variability and statistics of the
"instantaneous" Strehl ratio. The observations were carried out with the 3.63-m
AEOS telescope equipped with a high-order adaptive optics system. In this paper
Strehl ratio is defined as the peak intensity of a single short exposure. We
have also studied the behaviour of the phase variance computed on the
reconstructed wavefronts. We tested the Marechal approximation and used it to
explain the observed negative skewness of the Strehl ratio distribution. The
estimate of the phase variance is shown to fit a three-parameter Gamma
distribution model. We show that simple scaling of the reconstructed wavefronts
has a large impact on the shape of the Strehl ratio distribution.Comment: submitted to PAS

### Incompatibility-Driven Self-Organization in Polycatenar Liquid Crystals Bearing Both Hydrocarbon and Fluorocarbon Chains

The synthesis and liquid crystal properties are reported for tri-and tetra-catenar mesogens in which both hydrocarbon and semiperfluorocarbon chains have been incorporated. In the tricatenar mesogens, the lamellar spacing in the smectic C phase of the all-hydrocarbon mesogen almost doubles when the isolated hydrocarbon chain is replaced by a semiperfluorinated chain on account of the localized segregation in different sublayers between the two chain types. In the tetracatenar materials, the replacement of at least one hydrocarbon chain by semiperfluorocarbon chains is sufficient to promote columnar phase formation, but when the molecule has two hydrocarbon chains at one end and two semiperfluorocarbon chains at the other, the requirement for localized phase segregation leads to the formation of a rectangular phase with very large lattice parameters. The juxtaposition of terminal chains of different nature within the same molecular structure thus leads to a reduction in mesophase symmetry and the emergence of more complex supramolecular organization

### The effect of pair-instability mass loss on black-hole mergers

Context. Mergers of two stellar-origin black holes are a prime source of gravitational waves and are under intensive investigation. One crucial ingredient in their modeling has been neglected: pair-instability pulsation supernovae with associated severe mass loss may suppress the formation of massive black holes, decreasing black-hole-merger rates for the highest black-hole masses.
Aims. We demonstrate the effects of pair-instability pulsation supernovae on merger rate and mass using populations of double black-hole binaries formed through the isolated binary classical evolution channel.
Methods. The mass loss from pair-instability pulsation supernova is estimated based on existing hydrodynamical calculations. This mass loss is incorporated into the StarTrack population synthesis code. StarTrack is used to generate double black-hole populations with and without pair-instability pulsation supernova mass loss.
Results. The mass loss associated with pair-instability pulsation supernovae limits the Population I/II stellar-origin black-hole mass to 50 M⊙, in tension with earlier predictions that the maximum black-hole mass could be as high as 100 M⊙. In our model, neutron stars form with mass 1−2 M⊙. We then encounter the first mass gap at 2−5 M⊙ with the compact object absence due to rapid supernova explosions, followed by the formation of black holes with mass 5−50 M⊙, with a second mass gap at 50−135 M⊙ created by pair-instability pulsation supernovae and by pair-instability supernovae. Finally, black holes with masses above 135 M⊙ may potentially form to arbitrarily high mass limited only by the extent of the initial mass function and the strength of stellar winds. Suppression of double black-hole-merger rates by pair-instability pulsation supernovae is negligible for our evolutionary channel. Our standard evolutionary model, with the inclusion of pair-instability pulsation supernovae and pair-instability supernovae, is fully consistent with the Laser Interferometric Gravitational-wave Observatory (LIGO) observations of black-hole mergers: GW150914, GW151226, and LVT151012. The LIGO results are inconsistent with high (≳ 400 km s-1) black hole (BH) natal kicks. We predict the detection of several, and up to as many as ~60, BH-BH mergers with a total mass of 10−150 M⊙ (most likely range: 20−80 M⊙) in the forthcoming ~60 effective days of the LIGO O2 observations, assuming the detectors reach the optimistic target O2 sensitivity

### Charged Particle Production in Proton-, Deuteron-, Oxygen- and Sulphur-Nucleus Collisions at 200 GeV per Nucleon

The transverse momentum and rapidity distributions of net protons and
negatively charged hadrons have been measured for minimum bias proton-nucleus
and deuteron-gold interactions, as well as central oxygen-gold and
sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net
protons at midrapidity in central nucleus-nucleus collisions increases both
with target mass for sulphur projectiles and with the projectile mass for a
gold target. The shape of the rapidity distributions of net protons forward of
midrapidity for d+Au and central S+Au collisions is similar. The average
rapidity loss is larger than 2 units of rapidity for reactions with the gold
target. The transverse momentum spectra of net protons for all reactions can be
described by a thermal distribution with `temperatures' between 145 +- 11 MeV
(p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The
multiplicity of negatively charged hadrons increases with the mass of the
colliding system. The shape of the transverse momentum spectra of negatively
charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and
central nucleus-nucleus collisions. The mean transverse momentum is almost
constant in the vicinity of midrapidity and shows little variation with the
target and projectile masses. The average number of produced negatively charged
hadrons per participant baryon increases slightly from p+p, p+A to central
S+S,Ag collisions.Comment: 47 pages, submitted to Z. Phys.

### Experimental Study of the Shortest Reset Word of Random Automata

In this paper we describe an approach to finding the shortest reset word of a
finite synchronizing automaton by using a SAT solver. We use this approach to
perform an experimental study of the length of the shortest reset word of a
finite synchronizing automaton. The largest automata we considered had 100
states. The results of the experiments allow us to formulate a hypothesis that
the length of the shortest reset word of a random finite automaton with $n$
states and 2 input letters with high probability is sublinear with respect to
$n$ and can be estimated as $1.95 n^{0.55}.

### Bose-Einstein correlations of pion pairs in central Pb+Pb collisions at CERN SPS energies

Measurements of Bose-Einstein correlations of pion pairs in central Pb+Pb
collisions were performed with the NA49 detector at the CERN SPS for beam
energies of 20A, 30A, 40A, 80A, and 158A GeV. Correlation functions were
measured in the longitudinally co-moving ``out-side-long'' reference frame as a
function of rapidity and transverse momentum in the forward hemisphere of the
reaction. Radius and correlation strength parameters were obtained from fits of
a Gaussian parametrization. The results show a decrease of the radius
parameters with increasing transverse momentum characteristic of strong radial
flow in the pion source. No striking dependence on pion-pair rapidity or beam
energy is observed. Static and dynamic properties of the pion source are
obtained from simultaneous fits with a blast-wave model to radius parameters
and midrapidity transverse momentum spectra. Predictions of hydrodynamic and
microscopic models of Pb+Pb collisions are discussed.Comment: 22 pages, 23 figure

- …