303 research outputs found
Hard thermal loops in the real-time formalism
We present a systematic discussion of Braaten and Pisarski's hard thermal
loop (HTL) effective theory within the framework of the real-time
(Schwinger-Keldysh) formalism. As is well known, the standard imaginary-time
HTL amplitudes for hot gauge theory express the polarization of a medium made
out of nonabelian charged point-particles; we show that the complete real-time
HTL theory includes, in addition, a second set of amplitudes which account for
Gaussian fluctuations in the charge distributions, but nothing else. We give a
concise set of graphical rules which generate both set of functions, and
discuss its relation to classical plasma physics.Comment: 14 pages, 6 figure
A Preliminary assessment of the efficacy of a Chlorine Bleach Detection Method for use in Spiny Lobster (Panulirus argus) fisheries
Massless BTZ black holes in minisuperspace
We study aspects of the propagation of strings on BTZ black holes. After
performing a careful analysis of the global spacetime structure of generic BTZ
black holes, and its relation to the geometry of the SL(2,R) group manifold, we
focus on the simplest case of the massless BTZ black hole. We study the SL(2,R)
Wess-Zumino-Witten model in the worldsheet minisuperspace limit, taking into
account special features associated to the Lorentzian signature of spacetime.
We analyse the two- and three-point functions in the pointparticle limit. To
lay bare the underlying group structure of the correlation functions, we derive
new results on Clebsch-Gordan coefficients for SL(2,R) in a parabolic basis. We
comment on the application of our results to string theory in singular
time-dependent orbifolds, and to a Lorentzian version of the AdS/CFT
correspondence.Comment: 28 pages, v2: reference adde
Tactile Elevation Perception in Blind and Sighted Participants and Its Implications for Tactile Map Creation
Facilitating the analysis of a UK national blood service supply chain using distributed simulation
In an attempt to investigate blood unit ordering policies, researchers have created a discrete-event model of the UK National Blood Service (NBS) supply chain in the Southampton area of the UK. The model has been created using Simul8, a commercial-off-the-shelf discrete-event simulation package (CSP). However, as more hospitals were added to the model, it was discovered that the length of time needed to perform a single simulation severely increased. It has been claimed that distributed simulation, a technique that uses the resources of many computers to execute a simulation model, can reduce simulation runtime. Further, an emerging standardized approach exists that supports distributed simulation with CSPs. These CSP Interoperability (CSPI) standards are compatible with the IEEE 1516 standard The High Level Architecture, the defacto interoperability standard for distributed simulation. To investigate if distributed simulation can reduce the execution time of NBS supply chain simulation, this paper presents experiences of creating a distributed version of the CSP Simul8 according to the CSPI/HLA standards. It shows that the distributed version of the simulation does indeed run faster when the model reaches a certain size. Further, we argue that understanding the relationship of model features is key to performance. This is illustrated by experimentation with two different protocols implementations (using Time Advance Request (TAR) and Next Event Request (NER)). Our contribution is therefore the demonstration that distributed simulation is a useful technique in the timely execution of supply chains of this type and that careful analysis of model features can further increase performance
Creating a reusable cross-disciplinary multi-scale and multi-physics framework: From AMUSE to OMUSE and beyond
Here, we describe our efforts to create a multi-scale and multi-physics framework that can be retargeted across different disciplines. Currently we have implemented our approach in the astrophysical domain, for which we developed AMUSE (github.com/amusecode/amuse ), and generalized this to the oceanographic and climate sciences, which led to the development of OMUSE (bitbucket.org/omuse ). The objective of this paper is to document the design choices that led to the successful implementation of these frameworks as well as the future challenges in applying this approach to other domains
Cosmological anti-deSitter space-times and time-dependent AdS/CFT correspondence
We study classes of five-dimensional cosmological solutions with negative
curvature, which are obtained from static solutions by an exchange of a spatial
and temporal coordinate, and in some cases by an analytic continuation. Such
solutions provide a suitable laboratory to address the time-dependent AdS/CFT
correspondence. For a specific example we address in detail the calculation of
the boundary stress-energy and the Wilson line and find disagreement with the
standard AdS/CFT correspondence. We trace these discrepancies to the
time-dependent effects, such as particle creation, which we further study for
specific backgrounds. We also identify specific time-dependent backgrounds that
reproduce the correct conformal anomaly. For such backgrounds the calculation
of the Wilson line in the adiabatic approximation indicates only a Coulomb
repulsion.Comment: LaTeX file, 47 pages, discussion is extended, version to appear in
PR
A Multi-Boundary AdS Orbifold and DLCQ Holography: A universal holographic description of extremal black hole horizons
We examine a stationary but non-static asymptotically AdS_3 spacetime with
two causally connected conformal boundaries, each of which is a ``null
cylinder'', namely a cylinder with a null direction identified. This spacetime
arises from three different perspectives: (i) as a non-singular, causally
regular orbifold of global AdS_3 by boosts, (ii) as a Penrose-like limit
focusing on the horizon of extremal BTZ black holes, and (iii) as an S^1
fibration over AdS_2. Each of these perspectives sheds an interesting light on
holography. Examination of the conformal boundary of the spacetime shows that
the dual to the space should involve DLCQ limits of the D1-D5 conformal field
theory. The Penrose-like limit approach leads to a similar conclusion, by
isolating a sector of the complete D1-D5 CFT that describes the physics in the
vicinity of the horizon of an extremal black hole. As such this is a
holographic description of the universal horizon dynamics of the extremal black
holes in AdS_3 and also of the four and five dimensional stringy black holes
whose states were counted in string theory. The AdS_2 perspective draws a
connection to a 0+1d quantum mechanical theory. Various dualities lead to a
Matrix model description of the spacetime. Many interesting issues that are
related to both de Sitter physics and attempts to ``see behind a horizon''
using AdS/CFT arise from (a) the presence of two disconnected components to the
boundary, and (b) the analytic structure of bulk physics in the complex
coordinate plane.Comment: 48 pages. 3 EPS figures. If you use mpage to print multiple
postscript pages on the same sheet of paper you may have difficulties with
the figures. The PDF version will print fine, as will postscript if you stick
to one page per sheet. v3: minor edits and references adde
A comment on multiple vacua, particle production and the time dependent AdS/CFT correspondence
We give an explicit formulation of the time dependent AdS/CFT correspondence
when there are multiple vacua present in Lorentzian signature. By computing
sample two point functions we show how different amplitudes are related by
cosmological particle production. We illustrate our methods in two example
spacetimes: (a) a ``bubble of nothing'' in AdS space, and (b) an asymptotically
locally AdS spacetime with a bubble of nothing on the boundary. In both cases
the alpha vacua of de Sitter space make an interesting appearance.Comment: 9 page
Making geology relevant for infrastructure and planning
The urban population is projected to rise to 66% in 2050 to 7.6 billion. This has had, and will have, a profound effect on the geological and geomorphological character of the Earth’s shallow geosphere. It is important to know the character and geometries of the geological deposits so that infrastructure is planned sensibly and sustainably, and urban areas can be reused responsibly to ensure that they help facilitate economic and social development. This brings major challenges for our cities, where there is increased pressure on resources, space and services. The geosciences have an important part to play in securing sustainable global cities - they can support urban innovation and city performance, reduce our environmental footprint and ensure greater resilience to natural hazards such as flooding and ground instability.
For more than 30 years the British Geological Survey has advanced the geoscientific understanding and 3D characterisation of urban environments, producing multi-themed spatial datasets for geohazards and ground investigation used across the environmental, planning and insurance sectors.
The BGS have collaborated with the University of Cambridge to better integrate geological data with landuse and infrastructure to look at the long-term impact on these types of activities at surface and subsurface. A 3D GeoLanduse layer was produced from the geological framework model of London. This vector-based grid means that many soil and rock properties (e.g. foundation conditions, groundwater levels, volume change potential), can be represented alongside landuse statistics and infrastructure type and correlated in the XYZ domain. Focus has been at geothermal potential of the ground surrounding residential basements and the broader correlation between geology, energy consumption and landuse at city scale using principle component analysis and cluster recognition
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