1,165 research outputs found
Universality and properties of neutron star type I critical collapses
We study the neutron star axisymmetric critical solution previously found in
the numerical studies of neutron star mergers. Using neutron star-like initial
data and performing similar merger simulations, we demonstrate that the
solution is indeed a semi-attractor on the threshold plane separating the basin
of a neutron star and the basin of a black hole in the solution space of the
Einstein equations. In order to explore the extent of the attraction basin of
the neutron star semiattractor, we construct initial data phase spaces for
these neutron star-like initial data. From these phase spaces, we also observe
several interesting dynamical scenarios where the merged object is supported
from prompt collapse. The properties of the critical index of the solution, in
particular, its dependence on conserved quantities, are then studied. From the
study, it is found that a family of neutron star semi-attractors exist that can
be classified by both their rest masses and ADM masses.Comment: 13 pages, 12 figures, 1 new reference adde
Model projects as tools for cooperative urban development: The case of Haus der Statistik in Berlin
According to the New Leipzig Charter, urban development processes should be ‘a matter of all’ – the common good, climate protection and environmental justice, to name but a few aspects. Currently, new forms of innovation seeking models emerge within this context of sustainable urban planning practice - for example, real-world field laboratories and model projects. Haus der Statistik in Berlin is one such ‘model project for cooperative and common-good-oriented urban development’. It is widely recognized for its demand- and process-driven approach, as well as its project development being based on public-civic partnership. As anthropological and urbanist researchers and practitioners involved in the project, we give a situated account on the socio-political elements of the Haus der Statistik’s public-civic partnership and investigate the potentials of this model for a more sustainable urban development. The structure of the paper is threefold: Firstly, we introduce the so-called model project Haus der Statistik and its common-good orientated agenda and relate it to sustainability goals of the New Leipzig Charter. Secondly, we introduce the specific public-civic-framework in regard to its methodological framing within the context of model projects and comparable approaches that focus on collaborative, transdisciplinary and innovative methods, such as real-world field laboratories. Thirdly, we reflect on the elements of the public-civic-partnership framework that have been explored and developed at the ‘model project’ Haus der Statistik since 2015 and its implications for a more sustainable urban development.Peer Reviewe
Hole mobility in organic single crystals measured by a "flip-crystal" field-effect technique
We report on single crystal high mobility organic field-effect transistors
(OFETs) prepared on prefabricated substrates using a "flip-crystal" approach.
This method minimizes crystal handling and avoids direct processing of the
crystal that may degrade the FET electrical characteristics. A chemical
treatment process for the substrate ensures a reproducible device quality. With
limited purification of the starting materials, hole mobilities of 10.7, 1.3,
and 1.4 cm^2/Vs have been measured on rubrene, tetracene, and pentacene single
crystals, respectively. Four-terminal measurements allow for the extraction of
the "intrinsic" transistor channel resistance and the parasitic series contact
resistances. The technique employed in this study shows potential as a general
method for studying charge transport in field-accumulated carrier channels near
the surface of organic single crystals.Comment: 26 pages, 7 figure
Homothetic Wyman Spacetimes
The time-dependent, spherically symmetric, Wyman sector of the Unified Field
Theory is shown to be equivalent to a self-gravitating scalar field with a
positive-definite, repulsive self-interaction potential. A homothetic symmetry
is imposed on the fundamental tensor, and the resulting autonomous system is
numerically integrated. Near the critical point (between the collapsing and
non-collapsing spacetimes) the system displays an approximately periodic
alternation between collapsing and dispersive epochs.Comment: 15 pages with 6 figures; requires amsart, amssymb, amsmath, graphicx;
formatted for publication in Int. J. Mod. Phys.
Late-Time Behavior of Stellar Collapse and Explosions: I. Linearized Perturbations
Problem with the figures should be corrected. Apparently a broken uuencoder
was the cause.Comment: 16pp, RevTex, 6 figures (included), NSF-ITP-93-8
Observation of critical phenomena and self-similarity in the gravitational collapse of radiation fluid
We observe critical phenomena in spherical collapse of radiation fluid. A
sequence of spacetimes is numerically computed, containing
models () that adiabatically disperse and models () that
form a black hole. Near the critical point (), evolutions develop a
self-similar region within which collapse is balanced by a strong,
inward-moving rarefaction wave that holds constant as a function of a
self-similar coordinate . The self-similar solution is known and we show
near-critical evolutions asymptotically approaching it. A critical exponent
is found for supercritical () models.Comment: 10 pages (LaTeX) (to appear in Phys. Rev. Lett.), TAR-039-UN
Scalar field collapse in three-dimensional AdS spacetime
We describe results of a numerical calculation of circularly symmetric scalar
field collapse in three spacetime dimensions with negative cosmological
constant. The procedure uses a double null formulation of the Einstein-scalar
equations. We see evidence of black hole formation on first implosion of a
scalar pulse if the initial pulse amplitude is greater than a critical
value . Sufficiently near criticality the apparent horizon radius
grows with pulse amplitude according to the formula .Comment: 10 pages, 1 figure; references added, to appear in CQG(L
Self-similarity and singularity formation in a coupled system of Yang-Mills-dilaton evolution equations
We study both analytically and numerically a coupled system of spherically
symmetric SU(2) Yang-Mills-dilaton equation in 3+1 Minkowski space-time. It has
been found that the system admits a hidden scale invariance which becomes
transparent if a special ansatz for the dilaton field is used. This choice
corresponds to transition to a frame rotated in the plane at a
definite angle. We find an infinite countable family of self-similar solutions
which can be parametrized by the - the number of zeros of the relevant
Yang-Mills function. According to the performed linear perturbation analysis,
the lowest solution with N=0 only occurred to be stable. The Cauchy problem has
been solved numerically for a wide range of smooth finite energy initial data.
It has been found that if the initial data exceed some threshold, the resulting
solutions in a compact region shrinking to the origin, attain the lowest N=0
stable self-similar profile, which can pretend to be a global stable attractor
in the Cauchy problem. The solutions live a finite time in a self-similar
regime and then the unbounded growth of the second derivative of the YM
function at the origin indicates a singularity formation, which is in agreement
with the general expectations for the supercritical systems.Comment: 10 pages, 5 figure
An exact solution for 2+1 dimensional critical collapse
We find an exact solution in closed form for the critical collapse of a
scalar field with cosmological constant in 2+1 dimensions. This solution agrees
with the numerical simulation done by Pretorius and Choptuik of this system.Comment: 5 pages, 5 figures, Revtex. New comparison of analytic and numerical
solutions beyond the past light cone of the singularity added. Two new
references added. Error in equation (21) correcte
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