8,589 research outputs found
Modelling Hybrid Stars in Quark-Hadron Approaches
The density in the core of neutron stars can reach values of about 5 to 10
times nuclear matter saturation density. It is, therefore, a natural assumption
that hadrons may have dissolved into quarks under such conditions, forming a
hybrid star. This star will have an outer region of hadronic matter and a core
of quark matter or even a mixed state of hadrons and quarks. In order to
investigate such phases, we discuss different model approaches that can be used
in the study of compact stars as well as being applicable to a wider range of
temperatures and densities. One major model ingredient, the role of quark
interactions in the stability of massive hybrid stars is discussed. In this
context, possible conflicts with lattice QCD simulations are investigated.Comment: Contribution to the EPJA Topical Issue on "Exotic Matter in Neutron
Stars
Constraining strangeness in dense matter with GW170817
Particles with strangeness content are predicted to populate dense matter,
modifying the equation of state of matter inside neutron stars as well as their
structure and evolution. In this work, we show how the modeling of strangeness
content in dense matter affects the properties of isolated neutrons stars and
the tidal deformation in binary systems. For describing nucleonic and hyperonic
stars we use the many-body forces model (MBF) at zero temperature, including
the mesons for the description of repulsive hyperon-hyperon
interactions. Hybrid stars are modeled using the MIT Bag Model with vector
interaction (vMIT) in both Gibbs and Maxwell constructions, for different
values of bag constant and vector interaction couplings. A parametrization with
a Maxwell construction, which gives rise to third family of compact stars (twin
stars), is also investigated. We calculate the tidal contribution that adds to
the post-Newtonian point-particle corrections, the associated love number for
sequences of stars of different composition (nucleonic, hyperonic, hybrid and
twin stars), and determine signatures of the phase transition on the
gravitational waves in the accumulated phase correction during the inspirals
among different scenarios for binary systems. On the light of the recent
results from GW170817 and the implications for the radius of
stars, our results show that hybrid stars can
only exist if a phase transition takes place at low densities close to
saturation
Constraining the size of the narrow line region in distant quasars
We propose a proper method to measure the size of the narrow line region
(NLR) in distant quasars. The apparent angular size of the NLR is, in general,
too small to resolve technically. However, it is possible to map the NLR if
with gravitational lensing. In our method, we directly compare the observed
image of the NLR with the expected lensed images of the NLR for various source
sizes and lens models. Seeking the best fit image via the comparison
procedures, we can obtain the best-fit size and the best-fit lens model. We
apply this method to the two-dimensional spectroscopic data of a famous lensed
quasar, Q2237+0305. If the lens galaxy resembles the applied lens model, an
upper limit to the NLR size can be set 750 pc. Further, we examine how the
fitting results will be improved by future observations, taking into account
the realistic observational effects, such as seeing. Future observations will
provide us more stringent constraints on the size of the NLR and on the density
profile of the lens galaxy.Comment: 17 pages including 4 figures, accepted to Ap
Research project Mauretania: Satellites as development aids
A general discussion is presented of how satellite images and ground surveys are used to define land use. Specifically it deals with the Tagant region in Mauretania, West Africa
Task rules, working memory, and fluid intelligence
Many varieties of working memory have been linked to fluid intelligence. In Duncan et al. (Journal of Experimental Psychology:General 137:131–148, 2008), we described limited working memory for new task rules: When rules are complex, some may fail in their control of behavior, though they are often still available for explicit recall. Unlike other kinds of working memory, load is determined in this case not by real-time performance demands, but by the total complexity of the task instructions. Here, we show that the correlation with fluid intelligence is stronger for this aspect of working memory than for several other, more traditional varieties—including simple and complex spans and a test of visual short-term memory. Any task, we propose, requires construction of a mental control program that aids in segregating and assembling multiple task parts and their controlling rules. Fluid intelligence is linked closely to the efficiency of constructing such programs, especially when behavior is complex and novel
Deconfinement to Quark Matter in Neutron Stars - The Influence of Strong Magnetic Fields
We use an extended version of the hadronic SU(3) non-linear realization of
the sigma model that also includes quarks to study hybrid stars. Within this
approach, the degrees of freedom change naturally as the temperature/density
increases. Different prescriptions of charge neutrality, local and global, are
tested and the influence of strong magnetic fields and the anomalous magnetic
moment on the particle population is discussed.Comment: To appear in the proceedings of conference XII HADRON PHYSICS April,
22-27, 2012, Bento Goncalves, Wineyards Valley Region, Rio Grande do Sul,
Brazil Revised version with corrections made to the text in page
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