10,293 research outputs found
Synthesis of finite displacements and displacements in continental margins
The scope of the project is the analysis of displacement-rate fields in the transitional regions between cratonal and oceanic lithospheres over Phanerozoic time (last 700 ma). Associated goals are an improved understanding of range of widths of major displacement zones; the partition of displacement gradients and rotations with position and depth in such zones; the temporal characteristics of such zones-the steadiness, episodicity, and duration of uniform versus nonunifrom fields; and the mechanisms and controls of the establishment and kinematics of displacement zones. The objective is to provide a context of time-averaged kinematics of displacement zones. The initial phase is divided topically among the methodology of measurement and reduction of displacements in the lithosphere and the preliminary analysis from geologic and other data of actual displacement histories from the Cordillera, Appalachians, and southern North America
(Anti-)Evaporation of Schwarzschild-de Sitter Black Holes
We study the quantum evolution of black holes immersed in a de Sitter
background space. For black holes whose size is comparable to that of the
cosmological horizon, this process differs significantly from the evaporation
of asymptotically flat black holes. Our model includes the one-loop effective
action in the s-wave and large N approximation. Black holes of the maximal mass
are in equilibrium. Unexpectedly, we find that nearly maximal quantum
Schwarzschild-de Sitter black holes anti-evaporate. However, there is a
different perturbative mode that leads to evaporation. We show that this mode
will always be excited when a pair of cosmological holes nucleates.Comment: 16 pages, LaTeX2e; submitted to Phys. Rev.
Quantum Coherence in Two Dimensions
The formation and evaporation of two dimensional black holes are discussed.
It is shown that if the radiation in minimal scalars has positive energy, there
must be a global event horizon or a naked singularity. The former would imply
loss of quantum coherence while the latter would lead to an even worse
breakdown of predictability. CPT invariance would suggest that there ought to
be past horizons as well. A way in which this could happen with wormholes is
described.Comment: 11 pages, DAMTP-R93/15, CALT-68-1861, Tex, 3 appended uuencoded
figure
Hawking radiation by effective two-dimensional theories
Recently proposed 2D anomaly induced effective actions for the matter-gravity
system are critically reviewed. Their failure to correctly reproduce Hawking's
black hole radiation or the stability of Minkowski space-time led us to a
modification of the relevant ``quantum'' matter stress energy tensor that
allows physically meaningful results to be extracted.Comment: 26 pages, plain late
Condensation of Tubular D2-branes in Magnetic Field Background
It is known that in the Minkowski vacuum a bunch of IIA superstrings with
D0-branes can be blown-up to a supersymmetric tubular D2-brane, which is
supported against collapse by the angular momentum generated by crossed
electric and magnetic Born-Infeld (BI) fields. In this paper we show how the
multiple, smaller tubes with relative angular momentum could condense to a
single, larger tube to stabilize the system. Such a phenomena could also be
shown in the systems under the Melvin magnetic tube or uniform magnetic field
background. However, depending on the magnitude of field strength, a tube in
the uniform magnetic field background may split into multiple, smaller tubes
with relative angular momentum to stabilize the system.Comment: Latex 10 pages, mention the dynamical joining of the tubes, modify
figure
Critical energy flux and mass in solvable theories of 2d dilaton gravity
In this paper we address the issue of determining the semiclassical threshold
for black hole formation in the context of a one-parameter family of theories
which continuously interpolates between the RST and BPP models. We find that
the results depend significantly on the initial static configuration of the
spacetime geometry before the influx of matter is turned on. In some cases
there is a critical energy density, given by the Hawking rate of evaporation,
as well as a critical mass (eventually vanishing). In others there is
neither nor a critical flux.Comment: LaTeX file, 12 pages, 4 figure
Design Criteria for Improving Safety Performance of Rural Intersections
This paper, on the one hand, aims to identify significant crash risk factors at unsignalized three-leg intersections connecting rural two-lane two-way roads and minor roads with a STOP control on the approaches (3ST) and, on the other, to make adjustments to the Highway Safety Manual (HSM) procedure, fine-tuning its Safety Performance Function (SPF) based on observation of the local context. Over an 8-year period of study, a total of 240 crashes on 35 3ST intersections were observed, with no geometric-infrastructure adjustments or changes in the Annual Average Daily Traffic (AADT) and surrounding context noted at the intersections investigated. To obtain reliable results, the study period was divided into two groups: (a) 5 years to calibrate a new SPF, and (b) the remaining 3, not included in the first dataset, were used to validate the results. A negative binomial regression model was adopted to calibrate the new SPF. It was found that the AADT on the major and minor roads, the intersection skew angle, the co-occurrence of left and right-turn lanes on the major roads, and lighting seriously affect the crash scenario
Hawking Radiation and Energy Conservation in an Evaporating Black Hole
We define the Bondi energy for two-dimensional dilatonic gravity theories by
generalizing the known expression of the ADM energy. We show that our
definition of the Bondi energy is exactly the ADM energy minus the radiation
energy at null infinity. An explicit calculation is done for the evaporating
black hole in the RST model with the Strominger's ghost decoupling term. It is
shown that the infalling matter energy is completely recovered through the
Hawking radiation and the thunderpop.Comment: 17 pages, LaTex, 3 figures available on request
Black Hole Formation and Space-Time Fluctuations in Two Dimensional Dilaton Gravity and Complementarity
We study black hole formation in a model of two dimensional dilaton gravity
and 24 massless scalar fields with a boundary. We find the most general
boundary condition consistent with perfect reflection of matter and the
constraints. We show that in the semiclassical approximation and for the
generic value of the parameter which characterizes the boundary conditions, the
boundary starts receeding to infinity at the speed of light whenever the total
energy of the incoming matter flux exceeds a certain critical value. This is
also the critical energy which marks the onset of black hole formation. We then
compute the quantum fluctuations of the boundary and of the rescaled scalar
curvature and show that as soon as the incoming energy exceeds this critical
value, an asymptotic observer using normal time resolutions will always measure
large fluctuations of space-time near the horizon, even though the freely
falling observer does not. This is an aspect of black hole complementarity
relating directly the quantum gravity effects.Comment: (Some typographical errors corrected and some equations added to
clarify the nature of the singularity in the in the semiclassical solution),
30 pagers, TIFR/TH/94-01, IC/94/1
Chiminey: Reliable Computing and Data Management Platform in the Cloud
The enabling of scientific experiments that are embarrassingly parallel, long
running and data-intensive into a cloud-based execution environment is a
desirable, though complex undertaking for many researchers. The management of
such virtual environments is cumbersome and not necessarily within the core
skill set for scientists and engineers. We present here Chiminey, a software
platform that enables researchers to (i) run applications on both traditional
high-performance computing and cloud-based computing infrastructures, (ii)
handle failure during execution, (iii) curate and visualise execution outputs,
(iv) share such data with collaborators or the public, and (v) search for
publicly available data.Comment: Preprint, ICSE 201
- …