2,918 research outputs found
Ninth-Grade Studentsâ Perceptions Of Social Media Responsibility & Cyberbullying
At Upstate High School (pseudonym) in South Carolina, incidences of cyberbullying are on the rise. This explanatory action research study was implemented with the purpose of raising awareness of social media responsibility among ninth-grade high school students along with determining what these studentsâ perceptions of social media responsibility and cyberbullying. The study was conducted during the Fall semester of 2016 with a single group of 105 9th grade students at a high school in the upstate of South Carolina. Students who participated in the study completed an 85-item questionnaire to provide such quantitative information as their demographics, social media usage, self-esteem, methods of cyber bullying, and attitudes toward cyberbullying. Upon completion of the survey, four student participants were chosen based upon their experiences with cyberbullying to participate in a semi-structured interview to gather qualitative information about their opinions of social media, cyberbullying, and the safe usage of social media. The findings of the study showed that most students struggled to provide examples of responsible social media usage, yet most were aware of the harm that misuse of social media may cause their peers. Upon completion of the study both teachers and school administrators were presented with the findings and in turn an Action Plan was then designed to strengthen the schoolâs policy on cyberbullying, in addition to raising awareness in the school community about the dangers of irresponsible use of social media
Higgs-Stoponium Mixing Near the Stop-Antistop Threshold
Supersymmetric extensions of the standard model contain additional heavy
neutral Higgs bosons that are coupled to heavy scalar top quarks (stops). This
system exhibits interesting field theoretic phenomena when the Higgs mass is
close to the stop-antistop production threshold. Existing work in the
literature has examined the digluon-to-diphoton cross section near threshold
and has focused on enhancements in the cross section that might arise either
from the perturbative contributions to the Higgs-to-digluon and
Higgs-to-diphoton form factors or from mixing of the Higgs boson with stoponium
states. Near threshold, enhancements in the relevant amplitudes that go as
inverse powers of the stop-antistop relative velocity require resummations of
perturbation theory and/or nonperturbative treatments. We present a complete
formulation of threshold effects at leading order in the stop-antistop relative
velocity in terms of nonrelativistic effective field theory. We give detailed
numerical calculations for the case in which the stop-antistop Green's function
is modeled with a Coulomb-Schr\"odinger Green's function. We find several
general effects that do not appear in a purely perturbative treatment.
Higgs-stop-antistop mixing effects displace physical masses from the threshold
region, thereby rendering the perturbative threshold enhancements inoperative.
In the case of large Higgs-stop-antistop couplings, the displacement of a
physical state above threshold substantially increases its width, owing to its
decay width to a stop-antistop pair, and greatly reduces its contribution to
the cross section.Comment: 45 pages, 13 figures, minor corrections, references added, figures
2--5 updated, version published in Phys. Rev.
Ultrafast outflows: Galaxy-scale active galactic nucleus feedback
We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy
Relativistic jet feedback in high-redshift galaxies - I. Dynamics
We present the results of 3D relativistic hydrodynamic simulations of interaction of active galactic nucleus jets with a dense turbulent two-phase interstellar medium, which would be typical of high-redshift galaxies. We describe the effect of the jet on the evolution of the density of the turbulent interstellar medium (ISM). The jet-driven energy bubble affects the gas to distances up to several kiloparsecs from the injection region. The shocks resulting from such interactions create a multiphase ISM and radial outflows. One of the striking result of this work is that low-power jets (Pjet âČ 1043 ergs-1), although less efficient in accelerating clouds, are trapped in the ISM for a longer time and hence affect the ISM over a larger volume. Jets of higher power drill through with relative ease. Although the relativistic jets launch strong outflows, there is little net mass ejection to very large distances, supporting a galactic fountain scenario for local feedback
How frequent are close supermassive binary black holes in powerful jet sources?
24 pages, 36 figures. © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)Supermassive black hole binariesmay be detectable by an upcoming suite of gravitationalwave experiments. Their binary nature can also be revealed by radio jets via a short-period precession driven by the orbital motion as well as the geodetic precession at typically longer periods. We have investigated Karl G. Jansky Very Large Array and Multi-Element Radio Linked Interferometer Network (MERLIN) radio maps of powerful jet sources for morphological evidence of geodetic precession. For perhaps the best-studied source, Cygnus A, we find strong evidence for geodetic precession. Projection effects can enhance precession features, for which we find indications in strongly projected sources. For a complete sample of 33 3CR radio sources, we find strong evidence for jet precession in 24 cases (73 per cent). The morphology of the radio maps suggests that the precession periods are of the order of 10 6- 10 7 yr. We consider different explanations for the morphological features and conclude that geodetic precession is the best explanation. The frequently observed gradual jet angle changes in samples of powerful blazars can be explained by orbital motion. Both observations can be explained simultaneously by postulating that a high fraction of powerful radio sources have subparsec supermassive black hole binaries.We consider complementary evidence and discuss if any jetted supermassive black hole with some indication of precession could be detected as individual gravitational wave source in the near future. This appears unlikely, with the possible exception of M87.Peer reviewedFinal Published versio
Complex shock structure in the western hot-spot of Pictor A
We have carried out simulations of supersonic light jets in order to model the features observed in optical and radio images of the western hot-spot in the radio galaxy Pictor A. We have considered jets with density ratios η =10[superscript â2] â 10[superscript â4], and Mach numbers ranging between 5 and 50. From each simulation, we have generated raytraced maps of radio surface brightness at a variety of jet inclinations, in order to study the appearance of time-dependent luminous structures in the vicinity of the western hotspot. We compare these rendered images with observed features of Pictor A. A remarkable feature of Pictor A observations is a bar-shaped âïŹlamentâ inclined almost at right angles to the inferred jet direction and extending 24" (10.8h[superscript â1] kpc) along its longest axis. The constraints of reproducing the appearance of this structure in simulations indicate that the jet of Pictor A lies nearly in the plane of the sky. The results of the simulation are also consistent with other features found in the radio image of Pictor A. This ïŹlament arises from the surging behaviour of the jet near the hot-spot; the surging is provoked by alternate compression and decompression of the jet by the turbulent backïŹow in the cocoon. We also examine the arguments for the jet in Pictor A being at a more acute angle to the line of sight and ïŹnd that our preferred orientation is just consistent with the limits on the brightness ratio of the X-ray jet and counter-jet. We determine from our simulations, the structure function of hot-spot brightness and also the cumulative distribution of the ratio of intrinsic hot-spot brightnesses. The latter may be used to quantify the use of hot-spot ratios for the estimation of relativistic effects
Jet-intracluster medium interaction in hydra A - II. The effect of jet precession
We present three-dimensional relativistic hydrodynamical simulations of a precessing jet interacting with the intracluster medium and compare the simulated jet structure with the observed structure of the Hydra A northern jet. For the simulations, we use jet parameters obtained in the parameter space study of the first paper in this series and probe different values for the precession period and precession angle. We find that for a precession period P â 1âMyr and a precession angle Ï â 20°, the model reproduces (i) the curvature of the jet, (ii) the correct number of bright knots within 20 kpc at approximately correct locations and (iii) the turbulent transition of the jet to a plume. The Mach number of the advancing bow shock â1.85 is indicative of gentle cluster atmosphere heating during the early stages of the AGN's activity
Erratum: Relativistic jet feedback in high-redshift galaxies I. Dynamics
In this preamble, we describe the reason for the corrected results and
summarize the features of the published paper âRelativistic jet feedback in high-redshift galaxies I. Dynamicsâ (Mukherjee et al. 2016),
which have consequently changed. This article was originally published in MNRAS, 461, 967â983
Feedback from low-luminosity radio galaxies:B2 0258+35
Low-luminosity radio-loud active galactic nuclei (AGN) are of importance in
studies concerning feedback from radio AGN since a dominant fraction of AGN
belong to this class. We report high-resolution Very Large Array (VLA) and
European VLBI Network (EVN) observations of HI-21cm absorption from a young,
compact steep-spectrum radio source, B2 0258+35, nested in the early-type
galaxy NGC 1167, which contains a 160 kpc HI disc. Our VLA and EVN HI
absorption observations, modelling, and comparison with molecular gas data
suggest that the cold gas in the centre of NGC 1167 is very turbulent (with a
velocity dispersion of ~ 90 km/s) and that this turbulence is induced by the
interaction of the jets with the interstellar medium (ISM). Furthermore, the
ionised gas in the galaxy shows evidence of shock heating at a few kpc from the
radio source. These findings support the results from numerical simulations of
radio jets expanding into a clumpy gas disc, which predict that the radio jets
in this case percolate through the gas disc and drive shocks into the ISM at
distances much larger than their physical extent. These results expand the
number of low-luminosity radio sources found to impact the surrounding medium,
thereby highlighting the possible relevance of these AGN for feedback.Comment: 11 pages, 9 figures; Accepted for publication in Astronomy &
Astrophysic
- âŠ