173 research outputs found
Magnetars as Highly Magnetized Quark Stars: an analytical treatment
We present an analytical model of a magnetar as a high density magnetized
quark bag. The effect of strong magnetic fields (B > 5 x 10^{16} G) in the
equation of state is considered. An analytic expression for the Mass-Radius
relationship is found from the energy variational principle in general
relativity. Our results are compared with observational evidences of possible
quark and/or hybrid stars.Comment: 15 pages, 1 figure/Comments added and two references removed.
Accepted for publication in Astrophysical Journa
Enhancement of photoacoustic detection of inhomogeneities in polymers
We report a series of experiments on laser pulsed photoacoustic excitationin
turbid polymer samples addressed to evaluate the sound speed in the samples and
the presence of inhomogeneities in the bulk. We describe a system which allows
the direct measurement of the speed of the detected waves by engraving the
surface of the piece under study with a fiduciary pattern of black lines. We
also describe how this pattern helps to enhance the sensitivity for the
detection of an inhomogeneity in the bulk. These two facts are useful for
studies in soft matter systems including, perhaps, biological samples. We have
performed an experimental analysis on Grilon(R) samples in different situations
and we show the limitations of the method.Comment: 8 pages, 7 figure
Three approaches for the classification of protoneutron star oscillation modes
The future detection of gravitational waves (GWs) from a galactic
core-collapse supernova will provide information on the physics inside
protoneutron stars (PNS). In this work, we apply three different classification
methods for the PNS non-radial oscillation modes: Cowling classification,
Generalized Cowling Nomenclature (GCN), and a Classification Based on Modal
Properties (CBMP). Using PNS models from D simulations of core-collapse
supernovae, we find that in the early stages of the PNS evolution, typically
before seconds after the bounce, the Cowling classification is
inconsistent, but the GCN and the CBMP provide complementary information that
helps to understand the evolution of the modes. In the GCN, we note several
avoided crossings as the mode frequencies evolve at early times, while the CBMP
tracks the modes across the avoided crossings. We verify that the strongest
emission of GWs by the PNS corresponds to the -mode in the GCN, indicating
that the mode trapping region alternates between the core and the envelope at
each avoided crossing. At later times, approximately seconds after the
bounce, the three classification methods present a similar description of the
mode spectrum. We use our results to test universal relations for the PNS modes
according to their classification and find that the behaviour of the universal
relations for - and -modes is remarkably simple in the CBMP.Comment: 11 pages, 8 figures. Matches the version accepted on MNRA
Hybrid stars with sequential phase transitions: the emergence of the g mode
Neutron stars are the densest objects in the Universe, with and km, and the equation of state associated to their
internal composition is still unknown. The extreme conditions to which matter
is subjected inside neutron stars could lead to a phase transition in their
inner cores, giving rise to a hybrid compact object. The observation of
binary pulsars (PSR~J1614-2230, PSR~J03430432 and
PSR~J07406620) strongly constraints theoretical models of the equation of
state. Moreover, the detection of gravitational waves emitted during the binary
neutron star merger, GW170817, and its electromagnetic counterpart, GRB170817A,
impose additional constraints on the tidal deformability. In this work, we
investigate hybrid stars with sequential phase transitions hadron-quark-quark
in their cores. We assume that both phase transitions are sharp and analyse the
rapid and slow phase conversion scenarios. For the outer core, we use modern
hadronic equations of state. For the inner core we employ the constant speed of
sound parametrization for quark matter. We analyze more than 3000 hybrid
equations of state, taking into account the recent observational constraints
from neutron stars. The effects of hadron-quark-quark phase transitions on the
normal oscillation modes and , are studied under the Cowling
relativistic approximation. Our results show that, in the slow conversion
regime, a second quark-quark phase transition gives rise to a new ~mode.
We discuss the observational implications of our results associated to the
gravitational waves detection and the possibility of detecting hints of
sequential phase transitions and the associated ~mode.Comment: 24 pages, 9 figure
Systematic identification of phenotypically enriched loci using a patient network of genomic disorders
Background
Network medicine is a promising new discipline that combines systems biology approaches and network science to understand the complexity of pathological phenotypes. Given the growing availability of personalized genomic and phenotypic profiles, network models offer a robust integrative framework for the analysis of "omics" data, allowing the characterization of the molecular aetiology of pathological processes underpinning genetic diseases.
Methods
Here we make use of patient genomic data to exploit different network-based analyses to study genetic and phenotypic relationships between individuals. For this method, we analyzed a dataset of structural variants and phenotypes for 6,564 patients from the DECIPHER database, which encompasses one of the most comprehensive collections of pathogenic Copy Number Variations (CNVs) and their associated ontology-controlled phenotypes. We developed a computational strategy that identifies clusters of patients in a synthetic patient network according to their genetic overlap and phenotype enrichments.
Results
Many of these clusters of patients represent new genotype-phenotype associations, suggesting the identification of newly discovered phenotypically enriched loci (indicative of potential novel syndromes) that are currently absent from reference genomic disorder databases such as ClinVar, OMIM or DECIPHER itself.
Conclusions
We provide a high-resolution map of pathogenic phenotypes associated with their respective significant genomic regions and a new powerful tool for diagnosis of currently uncharacterized mutations leading to deleterious phenotypes and syndromes
Color superconductivity in compact stellar hybrid configurations
The discovery of pulsars PSR J1614-2230 and PSR J0348+0432 with masses of around 2Mʘ imposes strong constraints on the equations of state of cold, ultradense matter. If a phase transition from hadronic matter to quark matter were to occur in the inner cores of such massive neutron stars, the energetically favorable state of quark matter would be a color superconductor. In this study, we analyze the stability and maximum mass of such neutron stars. The hadronic phase is described by nonlinear relativistic mean-field models, and the local Nambu-Jona Lasinio model is used to describe quark matter in the 2SC+s quark phase. The phase transition is treated as a Maxwell transition, assuming a sharp hadron-quark interface, and the "constant-sound-speed" (CSS) parametrization is employed to discuss the existence of stellar twin configurations. We find that massive neutron stars such as J1614-2230 and J0348+0432 can only exist on the connected stellar branch but not on the disconnected twin-star branch. The latter can only support stars with masses that are strictly below 2Mʘ.Facultad de Ciencias Astronómicas y Geofísica
Gravitational instabilities in Kerr space-times
In this paper we consider the possible existence of unstable axisymmetric
modes in Kerr space times, resulting from exponentially growing solutions of
the Teukolsky equation. We describe a transformation that casts the radial
equation that results upon separation of variables in the Teukolsky equation,
in the form of a Schr\"odinger equation, and combine the properties of the
solutions of this equations with some recent results on the asymptotic
behaviour of spin weighted spheroidal harmonics to prove the existence of an
infinite family of unstable modes. Thus we prove that the stationary region
beyond a Kerr black hole inner horizon is unstable under gravitational linear
perturbations. We also prove that Kerr space-time with angular momentum larger
than its square mass, which has a naked singularity, is unstable.Comment: 9 pages, 4 figures, comments, references and calculation details
added, asymptotic expansion typos fixe
Asteroseismology using quadrupolar f-modes revisited: breaking of universal relationships in the slow hadron-quark conversion scenario
In this work, we consider polar perturbations and we calculate the frequency
and damping time of the quadrupolar fundamental f -mode of compact objects,
constructed using a wide range of model-independent hybrid equations of state
that include quark matter. We give special attention to the impact of the
hadron-quark conversion speed that, in the slow case, gives rise to a branch of
slow stable hybrid stars. Moreover, we study the validity of universal
relationships proposed in the literature and find out that none of them remains
valid when slow stable hybrid stars are taken into account. This fact could
constrain the applicability of asteroseismology methods with fundamental modes
designed to estimate the properties of pulsating compact objects. We hope that
this result could be tested with the start up of the third-generation
gravitational wave observatories, which might shed some light on the f -mode
emission from compact objects.Comment: 13 pages, 13 figures. Comments are welcom
TSEMA: interactive prediction of protein pairings between interacting families
An entire family of methodologies for predicting protein interactions is based on the observed fact that families of interacting proteins tend to have similar phylogenetic trees due to co-evolution. One application of this concept is the prediction of the mapping between the members of two interacting protein families (which protein within one family interacts with which protein within the other). The idea is that the real mapping would be the one maximizing the similarity between the trees. Since the exhaustive exploration of all possible mappings is not feasible for large families, current approaches use heuristic techniques which do not ensure the best solution to be found. This is why it is important to check the results proposed by heuristic techniques and to manually explore other solutions. Here we present TSEMA, the server for efficient mapping assessment. This system calculates an initial mapping between two families of proteins based on a Monte Carlo approach and allows the user to interactively modify it based on performance figures and/or specific biological knowledge. All the explored mappings are graphically shown over a representation of the phylogenetic trees. The system is freely available at . Standalone versions of the software behind the interface are available upon request from the authors
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