348 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
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 âparticipative researchâ in general and whether such research is possible within a high-security prison environment
Properties of global monopoles with an event horizon
We investigate the properties of global monopoles with an event horizon. We
find that there is an unstable circular orbit even if a particle does not have
an angular momentum when the core mass is negative. We also obtain the
asymptotic form of solutions when the event horizon is much larger than the
core radius of the monopole, and discuss if they could be a model of galactic
halos.Comment: 5 pages, 7 figure
Analysis of the feasibility of an experiment to measure carbon monoxide in the atmosphere
The feasibility of measuring atmospheric carbon monoxide from a remote platform using the correlation interferometry technique was considered. It has been determined that CO data can be obtained with an accuracy of 10 percent using this technique on the first overtone band of CO at 2.3 mu. That band has been found to be much more suitable than the stronger fundamental band at 4.6 mu. Calculations for both wavelengths are presented which illustrate the effects of atmospheric temperature profiles, inversion layers, ground temperature and emissivity, CO profile, reflectivity, and atmospheric pressure. The applicable radiative transfer theory on which these calculations are based is described together with the principles of the technique
Black Hole Critical Phenomena Without Black Holes
Studying the threshold of black hole formation via numerical evolution has
led to the discovery of fascinating nonlinear phenomena. Power-law mass
scaling, aspects of universality, and self-similarity have now been found for a
large variety of models. However, questions remain. Here I briefly review
critical phenomena, discuss some recent results, and describe a model which
demonstrates similar phenomena without gravity.Comment: 13 pages, 6 figures; Submission for the proceedings of ICGC 2000 in
the journal Preman
Stability and Observability of Magnetic Primordial Black Hole-Neutron Star Collisions
The collision of a primordial black hole with a neutron star results in the
black hole eventually consuming the entire neutron star. However, if the black
hole is magnetically charged, and therefore stable against decay by Hawking
radiation, the consequences can be quite different. Upon colliding with a
neutron star, a magnetic black hole very rapidly comes to a stop. For large
enough magnetic charge, we show that this collision can be detected as a sudden
change in the rotation period of the neutron star, a glitch or anti-glitch.We
argue that the magnetic primordial black hole, which then settles to the core
of the neutron star, does not necessarily devour the entire neutron star; the
system can instead reach a long-lived, quasi-stable equilibrium. Because the
black hole is microscopic compared to the neutron star, most stellar properties
remain unchanged compared to before the collision. However, the neutron star
will heat up and its surface magnetic field could potentially change, both
effects potentially observable.Comment: 16 pages, 5 figure
Continuous wavelet transform ridge extraction for spectral interferometry imaging
The combination of wavelength multiplexing and spectral interferometry allows for the encoding of multidimensional information and its transmission over a mono-dimensional channel; for example, measurements of a surface's topography acquired through a monomode fiber in a small endoscope. The local depth of the imaged object is encoded in the local spatial frequency of the signal measured at the output of the fiber-decoder system. We propose a procedure to retrieve the depth-map by determining the signal's instantaneous frequency. First, we compute its continuous, complex-valued, wavelet transform (CWT). The frequency signature at every position is contained in the resulting scalogram. We then extract the ridge of maximal response by use of a dynamic programming algorithm thus directly recovering the object's topography. We present results that validate this procedure based on both simulated and experimental data
Induced scalarization in boson stars and scalar gravitational radiation
The dynamical evolution of boson stars in scalar-tensor theories of gravity
is considered in the physical (Jordan) frame. We focus on the study of
spontaneous and induced scalarization, for which we take as initial data
configurations on the well-known S-branch of a single boson star in general
relativity. We show that during the scalarization process a strong emission of
scalar radiation occurs. The new stable configurations (S-branch) of a single
boson star within a particular scalar-tensor theory are also presented.Comment: 18 pages, 11 figures. Minor changes to match the published versio
Voronoi diagrams on piecewise flat surfaces and an application to biological growth
This paper introduces the notion of Voronoi diagrams and Delaunay triangulations generated by the vertices of a piecewise flat, triangulated surface. Based on properties of such structures, a generalized flip algorithm to construct the Delaunay triangulation and Voronoi diagram is presented. An application to biological membrane growth modeling is then given. A Voronoi partition of the membrane into cells is maintained during the growth process, which is driven by the creation of new cells and by restitutive forces of the elastic membrane
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