6,178 research outputs found
On the validity of the adiabatic approximation in compact binary inspirals
Using a semi-analytical approach recently developed to model the tidal
deformations of neutron stars in inspiralling compact binaries, we study the
dynamical evolution of the tidal tensor, which we explicitly derive at second
post-Newtonian order, and of the quadrupole tensor. Since we do not assume a
priori that the quadrupole tensor is proportional to the tidal tensor, i.e. the
so called "adiabatic approximation", our approach enables us to establish to
which extent such approximation is reliable. We find that the ratio between the
quadrupole and tidal tensors (i.e., the Love number) increases as the inspiral
progresses, but this phenomenon only marginally affects the emitted
gravitational waveform. We estimate the frequency range in which the tidal
component of the gravitational signal is well described using the stationary
phase approximation at next-to-leading post-Newtonian order, comparing
different contributions to the tidal phase. We also derive a semi-analytical
expression for the Love number, which reproduces within a few percentage points
the results obtained so far by numerical integrations of the relativistic
equations of stellar perturbations.Comment: 13 pages, 1 table, 2 figures. Minor changes to match the version
appearing on Phys. Rev.
Bottom currents, submarine mass failures and halokinesis at the toe of the Sigsbee Escarpment (Gulf of Mexico) : Contrasting regimes during lowstand and highstand conditions?
We are grateful to BP for the provision of both sea-floor and subsurface data. We thank the journal editor Michele Rebesco for his continuous support, and Lorena Moscardelli, Daniele Casalbore and an anonymous reviewer for their detailed and constructive comments, which have allowed us to considerably improve the manuscript.Peer reviewedPostprin
New blazars from the cross-match of recent multi-frequency catalogs
Blazars are radio-loud active galactic nuclei well known for their non
thermal emission spanning a wide range of frequencies. The Roma-BZCAT is, to
date, the most comprehensive list of these sources. We performed the
cross-match of several catalogs obtained from recent surveys at different
frequencies to search for new blazars. We cross-matched the 1 Swift-XRT
Point Source catalog with the spectroscopic sample of the 9 Data Release
of the Sloan Digital Sky Survey. Then, we performed further cross-matches with
the catalogs corresponding to the Faint Images of the Radio Sky at Twenty cm
survey and to the AllWISE Data release, focusing on sources with infrared
colors similar to those of confirmed -ray blazars included in the
Second Fermi-LAT catalog. As a result, we obtained a preliminary list of
objects with all the elements needed for a proper blazar classification
according to the prescriptions of the Roma-BZCAT. We carefully investigated
additional properties such as their morphology and the slope of their spectral
energy distribution in the radio domain, the features shown in their optical
spectrum, and the luminosity in the soft X rays to exclude generic active
galactic nuclei and focus on authentic blazar-like sources. At the end of our
screening we obtained a list of 15 objects with firmly established blazar
properties.Comment: 8 pages, 3 figures, 1 table. Accepted for publication in Astrophysics
and Space Science on 2015 April 25. Corrected typo in Section
Fixation of genetic variation and optimization of gene expression: The speed of evolution in isolated lizard populations undergoing Reverse Island Syndrome
The ecological theory of island biogeography suggests that mainland populations should be more genetically divergent from those on large and distant islands rather than from those on small and close islets. Some island populations do not evolve in a linear way, but the process of divergence occurs more rapidly because they undergo a series of phenotypic changes, jointly known as the Island Syndrome. A special case is Reversed Island Syndrome (RIS), in which populations show drastic phenotypic changes both in body shape, skin colouration, age of sexual maturity, aggressiveness, and food intake rates. The populations showing the RIS were observed on islets nearby mainland and recently raised, and for this they are useful models to study the occurrence of rapid evolutionary change. We investigated the timing and mode of evolution of lizard populations adapted through selection on small islets. For our analyses, we used an ad hoc model system of three populations: wild-type lizards from the mainland and insular lizards from a big island (Capri, Italy), both Podarcis siculus siculus not affected by the syndrome, and a lizard population from islet (Scopolo) undergoing the RIS (called P. s. coerulea because of their melanism). The split time of the big (Capri) and small (Scopolo) islands was determined using geological events, like sea-level rises. To infer molecular evolution, we compared five complete mitochondrial genomes for each population to reconstruct the phylogeography and estimate the divergence time between island and mainland lizards. We found a lower mitochondrial mutation rate in Scopolo lizards despite the phenotypic changes achieved in approximately 8,000 years. Furthermore, transcriptome analyses showed significant differential gene expression between islet and mainland lizard populations, suggesting the key role of plasticity in these unpredictable environments
Sea floor bedforms and their influence on slope accommodation (2019)
We sincerely thank Petroleum Geo-Services (PGS) Investigação Petrolífera Limitada, and specifically David Hajovsky and Scott Opdyke, that kindly provided the dataset and allowed us to show these results. We would also like to thank Schlumberger for providing academic licenses of their software (Petrel). We are grateful to Associate Editor Kei Ogata for his support, and we sincerely thank reviewers Daniele Casalbore and Kamaldeen Omosanya for their comments and suggestions that significantly improved the quality of the manuscript.Peer reviewedPostprin
Cognitive stimulation induces differential gene expression in octopus vulgaris: The key role of protocadherins
Octopuses are unique invertebrates, with sophisticated and flexible behaviors controlled by a high degree of brain plasticity, learning, and memory. Moreover, in Octopus vulgaris, it has been demonstrated that animals housed in an enriched environment show adult neurogenesis in specific brain areas. Firstly, we evaluated the optimal acclimatization period needed for an O. vulgaris before starting a cognitive stimulation experiment. Subsequently, we analyzed differential gene expression in specific brain areas in adult animals kept in tested (enriched environment), wild (naturally enriched environment), and control conditions (unenriched environment). We selected and sequenced three protocadherin genes (PCDHs) involved in the development and maintenance of the nervous system; three Pax genes that control cell specification and tissue differentiation; the Elav gene, an earliest marker for neural cells; and the Zic1 gene, involved in early neural formation in the brain. In this paper, we evaluated gene expression levels in O. vulgaris under different cognitive stimulations. Our data shows that Oct-PCDHs genes are upregulated in the learning and lower motor centers in the brain of both tested and wild animals (higher in the latter). Combining these results with our previous studies on O. vulgaris neurogenesis, we proposed that PCDH genes may be involved in adult neurogenesis processes, and related with their cognitive abilities
Prospects for detecting the 21cm forest from the diffuse intergalactic medium with LOFAR
We discuss the feasibility of the detection of the 21cm forest in the diffuse
IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been
derived using simulations of reionization which include detailed radiative
transfer of ionizing photons. We find that the spectra from reionization models
with similar total comoving hydrogen ionizing emissivity but different
frequency distribution look remarkably similar. Thus, unless the reionization
histories are very different from each other (e.g. a predominance of UV vs.
x-ray heating) we do not expect to distinguish them by means of observations of
the 21cm forest. Because the presence of a strong x-ray background would make
the detection of 21cm line absorption impossible, the lack of absorption could
be used as a probe of the presence/intensity of the x-ray background and the
thermal history of the universe. Along a random line of sight LOFAR could
detect a global suppression of the spectrum from z>12, when the IGM is still
mostly neutral and cold, in contrast with the more well-defined, albeit broad,
absorption features visible at lower redshift. Sharp, strong absorption
features associated with rare, high density pockets of gas could be detected
also at z~7 along preferential lines of sight.Comment: 12 pages, 13 figures. MNRAS, in pres
Enabling parallel computing in CRASH
We present the new parallel version (pCRASH2) of the cosmological radiative
transfer code CRASH2 for distributed memory supercomputing facilities. The code
is based on a static domain decomposition strategy inspired by geometric
dilution of photons in the optical thin case that ensures a favourable
performance speed-up with increasing number of computational cores. Linear
speed-up is ensured as long as the number of radiation sources is equal to the
number of computational cores or larger. The propagation of rays is segmented
and rays are only propagated through one sub-domain per time step to guarantee
an optimal balance between communication and computation. We have extensively
checked pCRASH2 with a standardised set of test cases to validate the
parallelisation scheme. The parallel version of CRASH2 can easily handle the
propagation of radiation from a large number of sources and is ready for the
extension of the ionisation network to species other than hydrogen and helium.Comment: Accepted by Monthly Notices of the Royal Astronomical Society. 18
pages, 20 figure
Prevalence and incidence of low back pain among runners: A systematic review
Background: Running is one of the most popular sports worldwide. Despite low back pain (LBP) represents the most common musculoskeletal disorder in population and in sports, there is currently sparse evidence about prevalence, incidence and risk factors for LBP among runners. The aims of this systematic review were to investigate among runners: prevalence and incidence of LBP and specific risk factors for the onset of LBP. Methods: A systematic review has been conducted according to the guidelines of the PRISMA statement. The research was conducted in the following databases from their inception to 31st of July 2019: PubMed; CINAHL; Google Scholar; Ovid; PsycINFO; PSYNDEX; Embase; SPORTDiscus; Scientific Electronic Library Online; Cochrane Library and Web of Science. The checklists of The Joanna Briggs Institute Critical Appraisal tools were used to investigate the risk of bias of the included studies. Results: Nineteen studies were included and the interrater agreement for full-text selection was good (K = 0.78; 0.61-0.80 IC 95%). Overall, low values of prevalence (0.7-20.2%) and incidence (0.3-22%) of LBP among runners were reported. Most reported risk factors were: running for more than 6 years; body mass index > 24; higher physical height; not performing traditional aerobics activity weekly; restricted range of motion of hip flexion; difference between leg-length; poor hamstrings and back flexibility. Conclusions: Prevalence and incidence of LBP among runners are low compared to the others running related injuries and to general, or specific population of athletes. View the low level of incidence and prevalence of LBP, running could be interpreted as a protective factor against the onset of LBP. Systematic review registration: PROSPERO CRD42018102001
A magnetar powering the ordinary monster GRB 130427A?
We present the analysis of the extraordinarily bright Gamma-Ray Burst (GRB)
130427A under the hypothesis that the GRB central engine is an
accretion-powered magnetar. In this framework, initially proposed to explain
GRBs with precursor activity, the prompt emission is produced by accretion of
matter onto a newly-born magnetar, and the observed power is related to the
accretion rate. The emission is eventually halted if the centrifugal forces are
able to pause accretion. We show that the X-ray and optical afterglow is well
explained as the forward shock emission with a jet break plus a contribution
from the spin-down of the magnetar. Our modelling does not require any
contribution from the reverse shock, that may still influence the afterglow
light curve at radio and mm frequencies, or in the optical at early times. We
derive the magnetic field ( G) and the spin period (
ms) of the magnetar and obtain an independent estimate of the minimum
luminosity for accretion. This minimum luminosity results well below the prompt
emission luminosity of GRB 130427A, providing a strong consistency check for
the scenario where the entire prompt emission is the result of continuous
accretion onto the magnetar. This is in agreement with the relatively long spin
period of the magnetar. GRB 130427A was a well monitored GRB showing a very
standard behavior and, thus, is a well-suited benchmark to show that an
accretion-powered magnetar gives a unique view of the properties of long GRBs.Comment: 5 pages, 1 figure, accepted for publication in MNRAS Letter
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