7,906 research outputs found
On the mass distribution of neutron stars
The distribution of masses for neutron stars is analyzed using the Bayesian
statistical inference, evaluating the likelihood of proposed gaussian peaks by
using fifty-four measured points obtained in a variety of systems. The results
strongly suggest the existence of a bimodal distribution of the masses, with
the first peak around , and a much wider second peak at . The results support earlier views related to the different
evolutionary histories of the members for the first two peaks, which produces a
natural separation (even if no attempt to "label" the systems has been made
here), and argues against the single-mass scale viewpoint. The bimodal
distribution can also accommodate the recent findings of
masses quite naturally. Finally, we explore the existence of a subgroup around
, finding weak, if any, evidence for it. This recently
claimed low-mass subgroup, possibly related to core collapse events,
has a monotonically decreasing likelihood and does not stand out clearly from
the rest of the sample.Comment: 11 pp., 3 figures, submitted to MNRAS Letter
Elastic amplitudes studied with the LHC measurements at 7 and 8 TeV
Recent measurements of the differential cross sections in the forward region
of pp elastic scattering at 7 and 8 TeV show precise form of the
dependence. We propose a detailed analysis of these measurements including the
structures of the real and imaginary parts of the scattering amplitude. A good
description is achieved, confirming in all experiments the existence of a zero
in the real part in the forward region close to the origin, in agreement with
the prediction of a theorem by A. Martin, with important role in the observed
form of . Universal value for the position of this zero and
regularity in other features of the amplitudes are found, leading to
quantitative predictions for the forward elastic scattering at 13 TeV.Comment: 22 pages, 17 figures and 4 table
Effects of quantum confinement on excited state properties of SrTiO from ab initio many-body perturbation theory
The Ruddlesden-Popper (RP) homologous series SrTiO
provides a useful template for the study and control of the effects of
dimensionality and quantum confinement on the excited state properties of the
complex oxide SrTiO. We use ab initio many-body perturbation theory within
the approximation and the Bethe-Salpeter equation approach to calculate
quasiparticle energies and absorption spectrum of SrTiO
for and . Our computed direct and indirect optical gaps are in
excellent agreement with spectroscopic measurements. The calculated optical
spectra reproduce the main experimental features and reveal excitonic structure
near the gap edge. We find that electron-hole interactions are important across
the series, leading to significant exciton binding energies that increase for
small and reach a value of 330~meV for , a trend attributed to
increased quantum confinement. We find that the lowest-energy singlet exciton
of SrTiO () localizes in the 2D plane defined by the TiO
layer, and explain the origin of its localization
Photon and Pomeron -- induced production of Dijets in , and collisions
In this paper we present a detailed comparison of the dijet production by
photon -- photon, photon -- pomeron and pomeron -- pomeron interactions in
, and collisions at the LHC energy. The transverse
momentum, pseudo -- rapidity and angular dependencies of the cross sections are
calculated at LHC energy using the Forward Physics Monte Carlo (FPMC), which
allows to obtain realistic predictions for the dijet production with two
leading intact hadrons. We obtain that \gamma \pom channel is dominant at
forward rapidities in collisions and in the full kinematical range in the
nuclear collisions of heavy nuclei. Our results indicate that the analysis of
dijet production at the LHC can be useful to test the Resolved Pomeron model as
well as to constrain the magnitude of the absorption effects.Comment: 11 pages, 6 figures, 1 table. Improved and enlarged version published
in European Physical Journal
Trade-off between reproduction and mobility prolongs organisms' survival in rock-paper-scissors models
We study the spatial rock-paper-scissors model, where resource competitors'
cyclic dominance impacts organisms' energy levels. Our model assumes that
failed selection interactions can lead to energy loss, reducing the chances of
success in the spatial game and hastening decline. To prevent death by energy
insufficiency, organisms of one out of the species strategically perform a
trade-off between reproduction and mobility. When prioritising exploring more
extensive areas, organisms aim to maximise the chances of acquiring resources
to regain high energy levels. Through simulation, we examine the effect of
survival behaviour on species segregation and spatial patterns. Our outcomes
show that the trade-off between offspring generation and accelerated movement
effectively protects individuals from death due to lack of energy. Moreover,
the risk of being eliminated by an enemy in the cyclic game reduces due to the
behavioural strategy. Considering a three-state model, we quantify how the
trade-off parameter controls the organisms' energy recovery. Computing the
median organisms' survival time, we find that although individuals performing
the trade-off strategy may live longer, the organisms of other species are
negatively affected by a life expectancy reduction. Our research may elucidate
the role of adaptive survival strategies in species persistence and provide
valuable insights for ecologists.Comment: 7 pages, 5 figure
Spatial organisation plasticity reduces disease infection risk in rock-paper-scissors models
We study a three-species cyclic game system where organisms face a contagious
disease whose virulence may change by a pathogen mutation. As a responsive
defence strategy, organisms' mobility is restricted to reduce disease
dissemination in the system. The impact of the collective self-preservation
strategy on the disease infection risk is investigated by performing stochastic
simulations of the spatial version of the rock-paper-scissors game. Our
outcomes show that the mobility control strategy induces plasticity in the
spatial patterns with groups of organisms of the same species inhabiting
spatial domains whose characteristic length scales depend on the level of
dispersal restrictions. The spatial organisation plasticity allows the
ecosystems to adapt to minimise the individuals' disease contamination risk if
an eventual pathogen alters the disease virulence. We discover that if a
pathogen mutation makes the disease more transmissible or less lethal, the
organisms benefit more if the mobility is not strongly restricted, thus forming
large spatial domains. Conversely, the benefits of protecting against a
pathogen causing a less contagious or deadlier disease are maximised if the
average size of groups of individuals of the same species is significantly
limited, reducing the dimensions of groups of organisms significantly. Our
findings may help biologists understand the effects of dispersal control as a
conservation strategy in ecosystems affected by epidemic outbreaks.Comment: 8 pages, 8 figure
Adaptive movement strategy may promote biodiversity in the rock-paper-scissors model
We study the role of the adaptive movement strategy in promoting biodiversity
in cyclic models described by the rock-paper-scissors game rules. We assume
that individuals of one out of the species may adjust their movement to escape
hostile regions and stay longer in their comfort zones. Running a series of
stochastic simulations, we calculate the alterations in the spatial patterns
and population densities in scenarios where not all organisms are physically or
cognitively conditioned to perform the behavioural strategy. Although the
adaptive movement strategy is not profitable in terms of territorial dominance
for the species, it may promote biodiversity. Our findings show that if all
individuals are apt to move adaptively, coexistence probability increases for
intermediary mobility. The outcomes also show that even if not all individuals
can react to the signals received from the neighbourhood, biodiversity is still
benefited, but for a shorter mobility range. We find that the improvement in
the coexistence conditions is more accentuated if organisms adjust their
movement intensely and can receive sensory information from longer distances.
We also discover that biodiversity is slightly promoted for high mobility if
the proportion of individuals participating in the strategy is low. Our results
may be helpful for biologists and data scientists to understand adaptive
process learning in system biology.Comment: 7 pages, 7 figure
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