6,188 research outputs found
Runaway massive stars as variable gamma-ray sources
Runaway stars are ejected from their formation sites well within molecular
cores in giant dark clouds. Eventually, these stars can travel through the
molecular clouds, which are highly inhomogeneous. The powerful winds of massive
runaway stars interact with the medium forming bowshocks. Recent observations
and theoretical modelling suggest that these bowshocks emit non-thermal
radiation. As the massive stars move through the inhomogeneous ambient gas the
physical properties of the bowshocks are modified, producing changes in the
non-thermal emission. We aim to compute the non-thermal radiation produced in
the bowshocks of runaway massive stars when travelling through a molecular
cloud. We calculate the non-thermal emission and absorption for two types of
massive runaway stars, an O9I and an O4I, as they move through a density
gradient. We present the spectral energy distributions for the runaway stars
modelled. Additionally, we obtain light curves at different energy ranges. We
find significant variations in the emission over timescales of 1 yr. We
conclude that bowshocks of massive runaway stars, under some assumptions, might
be variable gamma-ray sources, with variability timescales that depend on the
medium density profile. These objects might constitute a population of galactic
gamma-ray sources turning on and off within years.Comment: 10 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
A mechanism for fast radio bursts
Fast radio bursts are mysterious transient sources likely located at
cosmological distances. The derived brightness temperatures exceed by many
orders of magnitude the self-absorption limit of incoherent synchrotron
radiation, implying the operation of a coherent emission process. We propose a
radiation mechanism for fast radio bursts where the emission arises from
collisionless Bremsstrahlung in strong plasma turbulence excited by
relativistic electron beams. We discuss possible astrophysical scenarios in
which this process might operate. The emitting region is a turbulent plasma hit
by a relativistic jet, where Langmuir plasma waves produce a concentration of
intense electrostatic soliton-like regions (cavitons). The resulting radiation
is coherent and, under some physical conditions, can be polarised and have a
power-law distribution in energy. We obtain radio luminosities in agreement
with the inferred values for fast radio bursts. The timescale of the radio
flare in some cases can be extremely fast, of the order of s. The
mechanism we present here can explain the main features of fast radio bursts
and is plausible in different astrophysical sources, such as gamma-ray bursts
and some Active Galactic Nuclei.Comment: 6 pages, 1 figure. Accepted for publication in Phys. Rev.
Towards Evidence Based M-Health Application Design in Cancer Patient Healthy Lifestyle Interventions
Cancer is one of the most prevalent diseases in
Europe and the world. Significant correlations between dietary
habits and cancer incidence and mortality have been
confirmed by the literature. Physical activity habits are also
directly implicated in the incidence of cancer. Lifestyle
behaviour change may be benefited by using mobile technology
to deliver health behaviour interventions. M-Health offers a
promising cost-efficient approach to deliver en-masse
interventions. Smartphone apps with constructs such as
gamification and personalized have shown potential for
helping individuals lose weight and maintain healthy lifestyle
habits. However, evidence-based content and theory-based
strategies have not been incorporated by those apps
systematically yet. The aim of the current work is to put the
foundations for a methodologically rigorous exploration of
wellness/health intervention literature/app landscape towards
detailed design specifications for connected health m-apps. In
this context, both the overall work plan is described as well as
the details for the significant steps of application space and
literature space review. Both strategies for research and initial
outcomes of it are presented. The expected evidence based
design process for patient centered health and wellness
interventions is going to be the primary input in the
implementation process of upcoming patient centered
health/wellness m-health interventions.ENJECT COST-STSM-ECOST-STSM-TD1405-220216-07045
Modelling the gas kinematics of an atypical Lyman-alpha emitting compact dwarf galaxy
Star-forming Compact Dwarf Galaxies (CDGs) resemble the expected pristine
conditions of the first galaxies in the Universe and are the best systems to
test models on primordial galaxy formation and evolution. Here we report on one
of such CDGs, Tololo 1214-277, which presents a broad, single peaked, highly
symmetric Ly emission line that had evaded theoretical interpretation
so far. In this paper we reproduce for the first time these line features with
two different physically motivated kinematic models: an interstellar medium
composed by outflowing clumps with random motions and an homogeneous gaseous
sphere undergoing solid body rotation. The multiphase model requires a clump
velocity dispersion of km s with outflows of
km s, while the bulk rotation velocity is constrained to be
km s. We argue that the results from the multiphase
model provide a correct interpretation of the data. In that case the clump
velocity dispersion implies a dynamical mass of M,
ten times its baryonic mass. If future kinematic maps of Tololo 1214-277
confirm the velocities suggested by the multiphase model, it would provide
additional support to expect such kinematic state in primordial galaxies,
opening the opportunity to use the models and methods presented in this paper
to constrain the physics of star formation and feedback in the early generation
of Ly- emitting galaxies.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in MNRA
Runaway stars as cosmic ray injectors inside molecular clouds
Giant molecular clouds (GMCs) are a new population of gamma-ray sources,
being the target of cosmic rays (CRs) -- locally accelerated or not --. These
clouds host very young stellar clusters where massive star formation takes
place. Eventually, some of the stars are ejected from the clusters, becoming
runaway stars. These stars move supersonically through the cloud and develop
bowshocks where particles can be accelerated up to relativistic energies. As a
result, the bowshocks present non-thermal emission, and inject relativistic
protons in the cloud. These protons diffuse in the GMC interacting with the
matter. We present a model for the non-thermal radiation generated by protons
and secondary pairs accelerated in the bowshocks of massive runaways stars
within young GMCs. We solve the transport equation for primary protons and
secondary pairs as the stars move through the cloud. We present non-thermal
emissivity maps in radio and in gamma rays as a function of time. We obtain
X-ray luminosities of the order erg~s and gamma-ray
luminosities erg~s. We conclude that, under some
assumptions, relativistic protons from massive runaway stars interacting with
matter in GMCs give rise to extended non-thermal sources.Comment: 16 pages, 10 figures, accepted for publication in MNRA
The perceived role of bullying bystanders in Mexican secondary school settings
Bystanders play an important role in school bullying dynamics, having the power to provide or withhold the social rewards bullies seek. Bystander support is also beneficial for bullying victims, who experience less social and mental health problems if they have defenders.
Even though bystanders generally disapprove of bullying, they rarely intervene in bullying incidents. Research suggests that two factors closely related to bystander intervention in bullying are moral disengagement and self-efficacy. Cultural influences and gender may also play a part in bullying and bystander dynamics.
The main aim of this study was to explore Mexican secondary school students’ perceptions of their role in bullying situations. The study focused on gender differences in these perceptions, students' levels of self-efficacy, students’ use of moral disengagement dynamics, and student receptivity to material that encourages prosocial bystander behaviour. A questionnaire was developed to gauge students’ views on these topics, and administered to a sample of 186 secondary school students. Focus groups were also conducted to gain insight on group understandings and norms. A six-session workshop was designed and implemented to expose students to material on prosocial bystander behaviour.
Results suggested that most students feel empathy towards bullying victims and acknowledge that they have the power to make a difference. However, participants are reluctant to put ideas into action for fear of bully retaliation and the belief that they cannot rely on support from other peers and school staff. This sense of powerlessness seems to have a cultural component to it, and is more common in male students. Other gender differences were observed: females displayed higher self-efficacy to help and lower moral disengagement levels.
Research on cultural influences on bullying and bystander behaviour worldwide is needed, as well as further research on the implications, obstacles and opportunities of gender differences in this regard. Studies on what bystanders need to feel safe when helping bullying victims would also be a valuable resource for anti-bullying intervention efforts
Rare mutations and potentially damaging missense variants in genes encoding fibrillar collagens and proteins involved in their production are candidates for risk for preterm premature rupture of membranes
Preterm premature rupture of membranes (PPROM) is the leading identifiable cause of preterm birth with ~ 40% of preterm births being associated with PPROM and occurs in 1% - 2% of all pregnancies. We hypothesized that multiple rare variants in fetal genes involved in extracellular matrix synthesis would associate with PPROM, based on the assumption that impaired elaboration of matrix proteins would reduce fetal membrane tensile strength, predisposing to unscheduled rupture. We performed whole exome sequencing (WES) on neonatal DNA derived from pregnancies complicated by PPROM (49 cases) and healthy term deliveries (20 controls) to identify candidate mutations/variants. Genotyping for selected variants from the WES study was carried out on an additional 188 PPROM cases and 175 controls. All mothers were self-reported African Americans, and a panel of ancestry informative markers was used to control for genetic ancestry in all genetic association tests. In support of the primary hypothesis, a statistically significant genetic burden (all samples combined, SKAT-O p-value = 0.0225) of damaging/potentially damaging rare variants was identified in the genes of interest—fibrillar collagen genes, which contribute to fetal membrane strength and integrity. These findings suggest that the fetal contribution to PPROM is polygenic, and driven by an increased burden of rare variants that may also contribute to the disparities in rates of preterm birth among African Americans
Evolution of trees and mycorrhizal fungi intensifies silicate mineral weathering.
Forested ecosystems diversified more than 350 Ma to become major engines of continental silicate weathering, regulating the Earth's atmospheric carbon dioxide concentration by driving calcium export into ocean carbonates. Our field experiments with mature trees demonstrate intensification of this weathering engine as tree lineages diversified in concert with their symbiotic mycorrhizal fungi. Preferential hyphal colonization of the calcium silicate-bearing rock, basalt, progressively increased with advancement from arbuscular mycorrhizal (AM) to later, independently evolved ectomycorrhizal (EM) fungi, and from gymnosperm to angiosperm hosts with both fungal groups. This led to 'trenching' of silicate mineral surfaces by AM and EM fungi, with EM gymnosperms and angiosperms releasing calcium from basalt at twice the rate of AM gymnosperms. Our findings indicate mycorrhiza-driven weathering may have originated hundreds of millions of years earlier than previously recognized and subsequently intensified with the evolution of trees and mycorrhizas to affect the Earth's long-term CO(2) and climate history
Discovery of a new radio galaxy within the error box of the unidentified gamma-ray source 3EG J1735-1500
We report the discovery of a new radio galaxy within the location error box of the gamma-ray source 3EG J1735-1500. The galaxy is a double-sided jet source forming a large angle with the line of sight. Optical observations reveal a V ~ 18 magnitude galaxy at the position of the radio core. Although the association with the EGRET source is not confirmed at the present stage, because there is a competing, alternative gamma-ray candidate within the location error contours which is also studied here, the case deserves further attention. The new radio galaxy can be used to test the recently proposed possibility of gamma-ray emitting radio galaxies beyond the already known case of Centaurus A
Interviewing Peter Gow — Dundee, June 24, 2017
This interview presents an initial dialogue about Peter Gow’s trajectory as an anthropologist, trying to bring to light particularly the fieldwork experiences and events that it had not been possible to commenton and explore in the published material. Its aim is to understand more closely the particular ways in which Peter Gow had come to arrive at the insights and the analyses presented in his brilliant ethnographies with the Yine/Piro people of Amazonia
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