1,155 research outputs found
On the Origin and Survival of UHE Cosmic-Ray Nuclei in GRBs and Hypernovae
The chemical composition of the ultra-high-energy (UHE) cosmic rays serves as
an important clue for their origin. Recent measurements of the elongation rates
by the Pierre Auger Observatory hint at the possible presence of heavy or
intermediate mass nuclei in the UHE cosmic rays. Gamma-ray bursts (GRBs) and
hypernovae have been suggested as possible sources of the UHE cosmic rays. Here
we derive the constraints on the physical conditions under which UHE heavy
nuclei, if they are accelerated in these sources, can survive in their intense
photon fields. We find that in the GRB external shock and in the hypernova
scenarios, UHE nuclei can easily survive photo-disintegration. In the GRB
internal shock scenario, UHE nuclei can also survive, provided the dissipation
radius and/or the bulk Lorentz factor of the relativistic outflow are
relatively large, or if the low-energy self-absorption break in the photon
spectrum of the prompt emission occurs above several KeV. In internal shocks
and in the other scenarios, intermediate-mass UHE nuclei have a higher
probability of survival against photo-disintegration than UHE heavy nuclei such
as Fe.Comment: accepted by ApJ, references added, 12 pages, 4 figures, emulateapj
styl
Addendum to "Coherent radio pulses from GEANT generated electromagnetic showers in ice"
We reevaluate our published calculations of electromagnetic showers generated
by GEANT 3.21 and the radio frequency pulses they produce in ice. We are
prompted by a recent report showing that GEANT 3.21-modeled showers are
sensitive to internal settings in the electron tracking subroutine. We report
the shower and pulse characteristics obtained with different settings of GEANT
3.21 and with GEANT 4. The default setting of electron tracking in GEANT 3.21
we used in previous work speeds up the shower simulation at the cost of
information near the end of the tracks. We find that settings tracking electron
and positron to lower energy yield a more accurate calculation, a more intense
shower, and proportionately stronger radio pulses at low frequencies. At high
frequencies the relation between shower tracking algorithm and pulse spectrum
is more complex. We obtain radial distributions of shower particles and phase
distributions of pulses from 100 GeV showers that are consistent with our
published results.Comment: 4 pages, 3 figure
The benefits of using a walking interface to navigate virtual environments
Navigation is the most common interactive task performed in three-dimensional virtual environments (VEs), but it is also a task that users often find difficult. We investigated how body-based information about the translational and rotational components of movement helped participants to perform a navigational search task (finding targets hidden inside boxes in a room-sized space). When participants physically walked around the VE while viewing it on a head-mounted display (HMD), they then performed 90% of trials perfectly, comparable to participants who had performed an equivalent task in the real world during a previous study. By contrast, participants performed less than 50% of trials perfectly if they used a tethered HMD (move by physically turning but pressing a button to translate) or a desktop display (no body-based information). This is the most complex navigational task in which a real-world level of performance has been achieved in a VE. Behavioral data indicates that both translational and rotational body-based information are required to accurately update one's position during navigation, and participants who walked tended to avoid obstacles, even though collision detection was not implemented and feedback not provided. A walking interface would bring immediate benefits to a number of VE applications
Signatures of photon and axion-like particle mixing in the gamma-ray burst jet
Photons couple to Axion-Like Particles (ALPs) or more generally to any pseudo
Nambu-Goldstone boson in the presence of an external electromagnetic field.
Mixing between photons and ALPs in the strong magnetic field of a Gamma-Ray
Burst (GRB) jet during the prompt emission phase can leave observable imprints
on the gamma-ray polarization and spectrum. Mixing in the intergalactic medium
is not expected to modify these signatures for ALP mass > 10^(-14) eV and/or
for < nG magnetic field. We show that the depletion of photons due to
conversion to ALPs changes the linear degree of polarization from the values
predicted by the synchrotron model of gamma ray emission. We also show that
when the magnetic field orientation in the propagation region is perpendicular
to the field orientation in the production region, the observed synchrotron
spectrum becomes steeper than the theoretical prediction and as detected in a
sizable fraction of GRB sample. Detection of the correlated polarization and
spectral signatures from these steep-spectrum GRBs by gamma-ray polarimeters
can be a very powerful probe to discover ALPs. Measurement of gamma-ray
polarization from GRBs in general, with high statistics, can also be useful to
search for ALPs.Comment: 17 pages, 3 figures. Accepted for publication in JCAP with minor
change
Open Dialogue compared to treatment as usual for adults experiencing a mental health crisis: Protocol for the ODDESSI multi-site cluster randomised controlled trial.
Background 'Open Dialogue' is a social network model of crisis and continuing mental healthcare which involves elements of service delivery such as immediate response and a style of therapeutic meeting called network meetings. Although there are indications from non-randomised studies that it may help people in their recovery from severe mental health crises and improve long-term outcomes, this has yet to be tested in a randomised controlled trial. Methods This paper outlines the protocol for a multi-site cluster-randomised control trial assessing the clinical and cost-effectiveness of Open Dialogue compared to treatment as usual (TAU) for individuals presenting in crisis to six mental health services in England. The primary outcome is time to relapse, with secondary outcomes including measures of recovery and service use. Participants will be followed-up for two years, with data collected from electronic medical records and researcher-led interviews. The analysis will compare outcomes between treatment groups as well as investigating potential mediators of effect: shared decision-making and social network quality and size. Carers of a subsample of participants will be asked about their experiences of shared decision-making, carer burden, and satisfaction. Discussion This trial will provide evidence of whether Open Dialogue services implemented in the English mental health system is an effective alternative to current care and may have important implications for the organization of community mental health services. Trial registration: retrospectively registered (108 participants recruited of 570 target) on 20/12/2019, ISRCTN52653325. [Abstract copyright: Copyright © 2021. Published by Elsevier Inc.
Flavor conversion of cosmic neutrinos from hidden jets
High energy cosmic neutrino fluxes can be produced inside relativistic jets
under the envelopes of collapsing stars. In the energy range E ~ (0.3 - 1e5)
GeV, flavor conversion of these neutrinos is modified by various matter effects
inside the star and the Earth. We present a comprehensive (both analytic and
numerical) description of the flavor conversion of these neutrinos which
includes: (i) oscillations inside jets, (ii) flavor-to-mass state transitions
in an envelope, (iii) loss of coherence on the way to observer, and (iv)
oscillations of the mass states inside the Earth. We show that conversion has
several new features which are not realized in other objects, in particular
interference effects ("L- and H- wiggles") induced by the adiabaticity
violation. The neutrino-neutrino scattering inside jet and inelastic neutrino
interactions in the envelope may produce some additional features at E > 1e4
GeV. We study dependence of the probabilities and flavor ratios in the
matter-affected region on angles theta13 and theta23, on the CP-phase delta, as
well as on the initial flavor content and density profile of the star. We show
that measurements of the energy dependence of the flavor ratios will, in
principle, allow to determine independently the neutrino and astrophysical
parameters.Comment: 56 pages, 19 figures. Minor changes. Accepted by JHEP
Neutrino signatures of the supernova - gamma ray burst relationship
We calculate the TeV-PeV neutrino fluxes of gamma-ray bursts associated with
supernovae, based on the observed association between GRB 030329 and supernova
SN 2003dh. The neutrino spectral flux distributions can test for possible
delays between the supernova and the gamma-ray burst events down to much
shorter timescales than what can be resolved with photons. As an illustrative
example, we calculate the probability of neutrino induced muon and electron
cascade events in a km scale under-ice detector at the South Pole, from the GRB
030329. Our calculations demonstrate that km scale neutrino telescopes are
expected to detect signals that will allow to constrain supernova-GRB models.Comment: 7 pages, 2 figures. Accepted for publication in Phys. Rev.
Development and refinement of the open dialog adherence protocol in complex mental health care
Introduction: Open dialog (OD) is a both a therapeutic practice and a service delivery model that offers an integrated response to mental health care through mobilizing resources within the service userâs family and community networks through joint network meetings. Therapist adherence is a crucial to the effective delivery of interventions. A key way to measure this is through structured observation tools. Aims: The aim of this research project is to develop and refine the Dialogic Practice Adherence Scale, for use in OD research trials in the United Kingdom. Methods: This study was a mixed methods approach to the development of an OD practitioner adherence measure. Initial steps involved meetings and discussions with experts and a review of the literature. Content validation studies were completed using a modified Delphi technique. To assess reliability of the measure, OD network meetings were audio-recorded, and tapes were rated by two independent researchers. Inter-rater reliability and internal consistency were assessed through quantitative approaches assessing variance. Results: Results provide a description of how the OD Adherence Manual was developed in collaboration. Validation surveys showed high levels on consensus among experts in the field on the key elements of OD network meetings. Inter-rater reliability for the total score was excellent and internal consistency analyses suggest the scale is highly reliable. Discussion: The scale presented here is an initial attempt at rating practitioner adherence in OD network meetings. It provides encouraging evidence that this can be done with strong validity and reliability and can be completed by a range of raters with varying levels of clinical experience
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