142 research outputs found
Axially symmetric gravitational fields
The present thesis consists of three parts. In the first part we give a brief historical outline of the most important results that have been obtained in the theory of axially symmetric gravitational fields. Parts II and III are devoted to two contributions by the writer to this branch of the general theory of relativity. A
bibliography of papers dealing with the subject is given at the end. This bibliography has been arranged in chronological order, and references to it are made by quoting
the authors name followed by the year of publication
Functional opponency in working memory capacity predicts cognitive flexibility in problem solving.
Cognitive flexibility is a hallmark of individuals with higher working memory capacity (WMC). Yet, research demonstrates that higher WMC individuals are sometimes more likely to adopt rigid problem-solving approaches. The present research examines a novel account for these contradictory findings—that different WMC mechanisms interact in ways that both support and constrain cognitive flexibility. Across three studies, participants completed the water jug task—a problem-solving task requiring them to first establish and then break mental set using a complex strategy. Participants then completed measures targeting three WMC mechanisms: attention control, primary memory, and secondary memory. Study 1 demonstrated that primary memory and secondary memory predict breaking mental set in opposite directions. Study 2 replicated these findings while also demonstrating that attention control moderates these effects. Study 3 replicated these results using a less restrictive sampling procedure (i.e., participants were provided the complex strategy). The present research supports the proposed theory of functional opponency in WMC
Enclothed Cognition and Controlled Attention during Insight Problem-Solving
Individual differences in working memory capacity (WMC) increase the ability, and tendency, to devote greater attentional control to a task—improving performance on a wide range of skills. In addition, recent research on enclothed cognition demonstrates that the situational influence of wearing a white lab coat increases controlled attention, due to the symbolic meaning and physical experience of wearing the coat. We examined whether these positive influences on attentional control lead to negative performance outcomes on insight problem-solving, a task thought to rely on associative processes that operate largely outside of explicit attentional control. Participants completed matchstick arithmetic problems while either wearing a white lab coat or in a no-coat control condition. Higher WMC was associated with lower insight problem-solving accuracy in the no-coat condition. In the coat condition, the insight problem-solving accuracy of lower WMC individuals dropped to the level of those higher in WMC. These results indicate that wearing a white lab coat led individuals to increase attentional control towards problem solving, hindering even lower WMC individuals from engaging in more diffuse, associative problem-solving processes, at which they otherwise excel. Trait and state factors known to increase controlled attention and improve performance on more attention-demanding tasks interact to hinder insight problem-solving
Closed timelike curves in asymmetrically warped brane universes
In asymmetrically warped spacetimes different warp factors are assigned to
space and to time. We discuss causality properties of these warped brane
universes and argue that scenarios with two extra dimensions may allow for
timelike curves which can be closed via paths in the extra-dimensional bulk. In
particular, necessary and sufficient conditions on the metric for the existence
of closed timelike curves are presented. We find a six-dimensional warped
metric which satisfies the CTC conditions, and where the null, weak and
dominant energy conditions are satisfied on the brane (although only the former
remains satisfied in the bulk). Such scenarios are interesting, since they open
the possibility of experimentally testing the chronology protection conjecture
by manipulating on our brane initial conditions of gravitons or hypothetical
gauge-singlet fermions (sterile neutrinos) which then propagate in the extra
dimensions.Comment: 24 pages, 2 figures; major corrections: CTC metric generalized from
5D to 6D, the new 6D metric satisfies the conclusions attributed
(incorrectly) to the 5D metric in v
A rotating cylinder in an asymptotically locally anti-de Sitter background
A family of exact solutions is presented which represents a rigidly rotating
cylinder of dust in a background with a negative cosmological constant. The
interior of the infinite cylinder is described by the Godel solution. An exact
solution for the exterior solution is found which depends both on the rotation
of the interior and on its radius. For values of these parameters less than a
certain limit, the exterior solution is shown to be locally isomorphic to the
Linet-Tian solution. For values larger than another limit, it is shown that the
exterior solution extends into a region which contains closed timelike curves.
At large distances from the source, the space-time is shown to be asymptotic
locally to anti-de Sitter space.Comment: To appear in Classical and Quantum Gravit
Yang-Mills Inspired Solutions for General Relativity
Several exact, cylindrically symmetric solutions to Einstein's vacuum
equations are given. These solutions were found using the connection between
Yang-Mills theory and general relativity. Taking known solutions of the
Yang-Mills equations (e.g. the topological BPS monopole solutions) it is
possible to construct exact solutions to the general relativistic field
equations. Although the general relativistic solutions were found starting from
known solutions of Yang-Mills theory they have different physical
characteristics.Comment: 13 pages LaTe
Can a circulating light beam produce a time machine?
In a recent paper, Mallett found a solution of the Einstein equations in
which closed timelike curves (CTC's) are present in the empty space outside an
infinitely long cylinder of light moving in circular paths around an axis. Here
we show that, for physically realistic energy densities, the CTC's occur at
distances from the axis greater than the radius of the visible universe by an
immense factor. We then show that Mallett's solution has a curvature
singularity on the axis, even in the case where the intensity of the light
vanishes. Thus it is not the solution one would get by starting with Minkowski
space and establishing a cylinder of light.Comment: 5 pages, RevTe
Centrifugal force induced by relativistically rotating spheroids and cylinders
Starting from the gravitational potential of a Newtonian spheroidal shell we
discuss electrically charged rotating prolate spheroidal shells in the Maxwell
theory. In particular we consider two confocal charged shells which rotate
oppositely in such a way that there is no magnetic field outside the outer
shell. In the Einstein theory we solve the Ernst equations in the region where
the long prolate spheroids are almost cylindrical; in equatorial regions the
exact Lewis "rotating cylindrical" solution is so derived by a limiting
procedure from a spatially bound system. In the second part we analyze two
cylindrical shells rotating in opposite directions in such a way that the
static Levi-Civita metric is produced outside and no angular momentum flux
escapes to infinity. The rotation of the local inertial frames in flat space
inside the inner cylinder is thus exhibited without any approximation or
interpretational difficulties within this model.
A test particle within the inner cylinder kept at rest with respect to axes
that do not rotate as seen from infinity experiences a centrifugal force.
Although the spacetime there is Minkowskian out to the inner cylinder
nevertheless that space has been induced to rotate, so relative to the local
inertial frame the particle is traversing a circular orbit.Comment: 12 pages, 2 figure
Self-gravitating clouds of generalized Chaplygin and modified anti-Chaplygin Gases
The Chaplygin gas has been proposed as a possible dark energy, dark matter
candidate. As a working fluid in a Friedmann-Robertson-Walker universe, it
exhibits early behavior reminiscent of dark matter, but at later times is more
akin to a cosmological constant. In any such universe, however, one can expect
local perturbations to form. Here we obtain the general equations for a
self-gravitating relativistic Chaplygin gas. We solve these equations and
obtain the mass-radius relationship for such structures, showing that only in
the phantom regime is the mass-radius relationship large enough to be a serious
candidate for highly compact massive objects at the galaxy core. In addition,
we study the cosmology of a modified anti-Chaplygin gas. A self-gravitating
cloud of this matter is an exact solution to Einstein's equations.Comment: 16 page
The interior solution of axially symmetric, stationary and rigidly rotating dust configurations
It is shown that the interior solution of axially symmetric, stationary and
rigidly rotating dust configurations is completely determined by the mass
density along the axis of rotation. The particularly interesting case of a mass
density, which is cylindrical symmetric in the interior of the dust
configuration, is presented. Among other things, this proves the non-existence
of homogeneous dust configurations.Comment: minor corrections to the published version, 10 page
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