477 research outputs found
Threshold of Singularity Formation in the Semilinear Wave Equation
Solutions of the semilinear wave equation are found numerically in three
spatial dimensions with no assumed symmetry using distributed adaptive mesh
refinement. The threshold of singularity formation is studied for the two cases
in which the exponent of the nonlinear term is either or . Near the
threshold of singularity formation, numerical solutions suggest an approach to
self-similarity for the case and an approach to a scale evolving static
solution for .Comment: 6 pages, 7 figure
Orbital Dynamics of Binary Boson Star Systems
We extend our previous studies of head-on collisions of boson stars by
considering orbiting binary boson stars. We concentrate on equal mass binaries
and study the dynamical behavior of boson/boson and boson/antiboson pairs. We
examine the gravitational wave output of these binaries and compare with other
compact binaries. Such a comparison lets us probe the apparent simplicity
observed in gravitational waves produced by black hole binary systems. In our
system of interest however, there is an additional internal freedom which plays
a significant role in the system's dynamics, namely the phase of each star. Our
evolutions show rather simple behavior at early times, but large differences
occur at late times for the various initial configurations.Comment: 10 pages, 14 figure
Critical Phenomena Inside Global Monopoles
The gravitational collapse of a triplet scalar field is examined assuming a
hedgehog ansatz for the scalar field. Whereas the seminal work by Choptuik with
a single, strictly spherically symmetric scalar field found a discretely
self-similar (DSS) solution at criticality with echoing period ,
here a new DSS solution is found with period . This new critical
solution is also observed in the presence of a symmetry breaking potential as
well as within a global monopole. The triplet scalar field model contains
Choptuik's original model in a certain region of parameter space, and hence his
original DSS solution is also a solution. However, the choice of a hedgehog
ansatz appears to exclude the original DSS.Comment: 5 pages, 5 figure
Singularity Formation in 2+1 Wave Maps
We present numerical evidence that singularities form in finite time during
the evolution of 2+1 wave maps from spherically equivariant initial data of
sufficient energy.Comment: 5 pages, 3 figure
The Singularity Threshold of the Nonlinear Sigma Model Using 3D Adaptive Mesh Refinement
Numerical solutions to the nonlinear sigma model (NLSM), a wave map from 3+1
Minkowski space to S^3, are computed in three spatial dimensions (3D) using
adaptive mesh refinement (AMR). For initial data with compact support the model
is known to have two regimes, one in which regular initial data forms a
singularity and another in which the energy is dispersed to infinity. The
transition between these regimes has been shown in spherical symmetry to
demonstrate threshold behavior similar to that between black hole formation and
dispersal in gravitating theories. Here, I generalize the result by removing
the assumption of spherical symmetry. The evolutions suggest that the
spherically symmetric critical solution remains an intermediate attractor
separating the two end states.Comment: 5 pages, 5 figures, 1 table; To be published in Phys. Rev. D.; Added
discussion of initial data; Added figure and reference
Critical Collapse of the Massless Scalar Field in Axisymmetry
We present results from a numerical study of critical gravitational collapse
of axisymmetric distributions of massless scalar field energy. We find
threshold behavior that can be described by the spherically symmetric critical
solution with axisymmetric perturbations. However, we see indications of a
growing, non-spherical mode about the spherically symmetric critical solution.
The effect of this instability is that the small asymmetry present in what
would otherwise be a spherically symmetric self-similar solution grows. This
growth continues until a bifurcation occurs and two distinct regions form on
the axis, each resembling the spherically symmetric self-similar solution. The
existence of a non-spherical unstable mode is in conflict with previous
perturbative results, and we therefore discuss whether such a mode exists in
the continuum limit, or whether we are instead seeing a marginally stable mode
that is rendered unstable by numerical approximation.Comment: 11 pages, 8 figure
Using a prisoner advisory group to develop diversity research in a maximum-security prison
This paper addresses groupwork processes with a group of prisoners advising a research project in a maximum-security prison in England. The research project (Appreciative Inquiry into the Diversity Strategy of HMP Wakefield. RES-000-22-3441) was funded by the Economic and Social Research Council (ESRC) and lasted 9 months. The research explored the experiences of prisoners in diverse minority groupings and the strategies of the prison to accommodate the complex needs of these groups. The Prisoner Advisory Group (PAG) was made up of representatives from Black and Minority Ethnic (BME) prisoners; older prisoners (over 60s); Disabled prisoners (with physical disabilities, learning difficulties; and mental health problems); Gay, Bi-sexual and Transgender prisoners; and prisoners affiliated to Faith groups. It met regularly during the research. The paper considers the forming norming and performing aspects of establishing an effective participant voice in a prison-based project. It considers the contribution of the PAG to developing a research strategy that engaged prisoners in the research. It reflects on the nature of ‘participative research’ in general and whether such research is possible within a high-security prison environment
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Staff-prisoner relationships, staff professionalism, and the use of authority in public- and private-sector prisons
Prison privatization has generally been associated with developments in
neoliberal punishment. However, relatively little is known about the
specific impact of privatization on the daily life of prisoners, including
areas that are particularly salient not just to debates about neoliberal
penality, but the wider reconfiguration of public service provision and
frontline work. Drawing on a study of values, practices, and quality of life
in five private‐sector and two public‐sector prisons in England and Wales,
this article seeks to compare and explain three key domains of prison
culture and quality: relationships between frontline staff and prisoners,
levels of staff professionalism (or jailcraft), and prisoners' experience of
state authority. The study identifies some of the characteristic strengths
and weaknesses of the public and private prison sectors, particularly in
relation to staff professionalism and its impact on the prisoner experience.
These findings have relevance beyond the sphere of prisons and
punishment.This is the final version. It was first published by Wiley at onlinelibrary.wiley.com/doi/10.1111/lsi.12093/abstrac
Black Hole Criticality in the Brans-Dicke Model
We study the collapse of a free scalar field in the Brans-Dicke model of
gravity. At the critical point of black hole formation, the model admits two
distinctive solutions dependent on the value of the coupling parameter. We find
one solution to be discretely self-similar and the other to exhibit continuous
self-similarity.Comment: 4 pages, REVTeX 3.0, 5 figures include
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