1,366 research outputs found
Administration of planning in Lesotho: a case-study : the Ramabanta's - Semonkong Road
African Studies Seminar series. Paper presented September, 1975Since it is understood that this will be the first of a few papers to be presented to this programme of seminars, it is intended that it serve the purpose of a somewhat simple introduction to the research I am carrying out in Lesotho. The focus of that research is concerned with the processes, machinery and administration of development planning in Lesotho. âDevelopment planningâ is interpreted, not as the five-yearly preparation of a national plan, nor in orthodox terms involving
a systematic process of research - preparation - formulation - review of programmes and plans, but in a somewhat broader and less formalistic sense, to cover those tasks which the Central Planning Office, the ministerial planning units, various planning committees etc. do in fact undertake; and this includes a rather more fragmentary list of functions such as the preparation of the annual capital budget, preparation of projects for donor assistance personnel, processing of scholarships, negotiations with visiting aid missions, etc
Critical Exponents and Stability at the Black Hole Threshold for a Complex Scalar Field
This paper continues a study on Choptuik scaling in gravitational collapse of
a complex scalar field at the threshold for black hole formation. We perform a
linear perturbation analysis of the previously derived complex critical
solution, and calculate the critical exponent for black hole mass, . We also show that this critical solution is unstable via a
growing oscillatory mode.Comment: 15 pages of latex/revtex; added details of numerics, in press in Phys
Rev D; 1 figure included, or available by anonymous ftp to
ftp://ftp.itp.ucsb.edu/figures/nsf-itp-95-58.ep
Continuous Self-Similarity and -Duality
We study the spherically symmetric collapse of the axion/dilaton system
coupled to gravity. We show numerically that the critical solution at the
threshold of black hole formation is continuously self-similar. Numerical and
analytical arguments both demonstrate that the mass scaling away from
criticality has a critical exponent of .Comment: 17 pages, harvmac, six figures uuencoded in separate fil
Perturbations and Critical Behavior in the Self-Similar Gravitational Collapse of a Massless Scalar Field
This paper studies the perturbations of the continuously self-similar
critical solution of the gravitational collapse of a massless scalar field
(Roberts solution). The perturbation equations are derived and solved exactly.
The perturbation spectrum is found to be not discrete, but occupying continuous
region of the complex plane. The renormalization group calculation gives the
value of the mass-scaling exponent equal to 1.Comment: 12 pages, RevTeX 3.1, 1 figur
Criticality and Bifurcation in the Gravitational Collapse of a Self-Coupled Scalar Field
We examine the gravitational collapse of a non-linear sigma model in
spherical symmetry. There exists a family of continuously self-similar
solutions parameterized by the coupling constant of the theory. These solutions
are calculated together with the critical exponents for black hole formation of
these collapse models. We also find that the sequence of solutions exhibits a
Hopf-type bifurcation as the continuously self-similar solutions become
unstable to perturbations away from self-similarity.Comment: 18 pages; one figure, uuencoded postscript; figure is also available
at http://www.physics.ucsb.edu/people/eric_hirschman
Boosting jet power in black hole spacetimes
The extraction of rotational energy from a spinning black hole via the
Blandford-Znajek mechanism has long been understood as an important component
in models to explain energetic jets from compact astrophysical sources. Here we
show more generally that the kinetic energy of the black hole, both rotational
and translational, can be tapped, thereby producing even more luminous jets
powered by the interaction of the black hole with its surrounding plasma. We
study the resulting Poynting jet that arises from single boosted black holes
and binary black hole systems. In the latter case, we find that increasing the
orbital angular momenta of the system and/or the spins of the individual black
holes results in an enhanced Poynting flux.Comment: 7 pages, 5 figure
Self-Similar Collapse of Scalar Field in Higher Dimensions
This paper constructs continuously self-similar solution of a spherically
symmetric gravitational collapse of a scalar field in n dimensions. The
qualitative behavior of these solutions is explained, and closed-form answers
are provided where possible. Equivalence of scalar field couplings is used to
show a way to generalize minimally coupled scalar field solutions to the model
with general coupling.Comment: RevTex 3.1, 15 pages, 3 figures; references adde
On critical behaviour in gravitational collapse
We give an approach to studying the critical behaviour that has been observed
in numerical studies of gravitational collapse. These studies suggest, among
other things, that black holes initially form with infinitesimal mass. We show
generally how a black hole mass formula can be extracted from a transcendental
equation.
Using our approach, we give an explicit one parameter set of metrics that are
asymptotically flat and describe the collapse of apriori unspecified but
physical matter fields. The black hole mass formula obtained from this metric
exhibits a mass gap - that is, at the onset of black hole formation, the mass
is finite and non-zero.Comment: 11 pages, RevTex, 2 figures (available from VH
Isentropic Melting Processes in the Mantle
Batch melting of ascending mantle can be approximated as an isentropic
process, since on the time scale of melting heat flow into or out of source
regions will typically be negligible and the process is slow enough to be close to
reversible. Similarly, fractional fusion can be idealized as a series of
incremental isentropic melting steps, although the entropy of the residue
decreases in each step. Although actual melting processes (e.g., involving melt
migration, diffusion, and convective boundary layers) must deviate to some
extent from idealized isentropic conditions, modeling of mantle processes under
the assumption of constant entropy is tractable from a thermodynamic
perspective and leads to a number of insights. Here we present models of the
productivity of isentropic pressure-release melting, consider the effect of solid-solid
phase transitions on melting, and model deep crystal fractionation in
ascending melts of the mantle
Scaling of curvature in sub-critical gravitational collapse
We perform numerical simulations of the gravitational collapse of a
spherically symmetric scalar field. For those data that just barely do not form
black holes we find the maximum curvature at the position of the central
observer. We find a scaling relation between this maximum curvature and
distance from the critical solution. The scaling relation is analogous to that
found by Choptuik for black hole mass for those data that do collapse to form
black holes. We also find a periodic wiggle in the scaling exponent.Comment: Revtex, 2 figures, Discussion modified, to appear in Phys. Rev.
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