21,965 research outputs found
Non Abelian Toda Theory : A Completely Integrable Model for Strings on a Black Hole Background
The present paper studies a completely integrable conformally invariant model
in 1+1 dimensions that corresponds to string propagation on the two-dimensional
black hole background (semi-ininite cigar). Besides the two space-time string
fields there is a third (internal) field with a very specific Liouville-type
interaction leading to the complete integrability. This system is known as
non-abelian Toda theory. I give the general explicit classical solution. It
realizes a rather involved transformation expressing the interacting string
fields in terms of (three) functions and of
one light-cone variable only. The latter are shown to lead to standard harmonic
oscillator (free field) Poisson brackets thus paving the way towards
quantization. There are three left-moving and three right-moving conserved
quantities. The right (left)-moving conserved quantities form a new closed
non-linear, non-local Poisson bracket algebra. This algebra is a Virasoro
algebra extended by two conformal dimension-two primaries.Comment: 41 pages, PUPT-143
An investigation of planar array system artefacts generated within an electrical impedance mammography system developed for breast cancer detection
An Electrical Impedance Mammography (EIM) planar array imaging system is being developed at the University of Sussex for the detection of breast cancers. Investigations have shown that during data collection, systematic errors and patient artefacts are frequently introduced during signal acquisition from different electrodes pairs. This is caused, in particular, by the large variations in the electrode-skin contact interface conditions occurring between separate electrode positions both with the same and different patients. As a result, the EIM image quality is seriously affected by these errors. Hence, this research aims to experimentally identify, analyse and propose effective methods to reduce the systematic errors at the electrode-skin interface. Experimental studies and subsequent analysis is presented to determine what ratio of electrode blockage seriously affects the acquired raw data which may in turn compromise the reconstruction. This leads to techniques for the fast and accurate detection of any such occurrences. These methodologies can be applied to any planar array based EIM system
From Weak to Strong Coupling in Two-Dimensional Gravity
The strong coupling physics of two dimensional gravity at C=7, 13, 19 is
deciphered, by building up on previous works along the same line (for a recent
review, of the background material, see hep-th/9408069). It is shown that
chirality becomes deconfined. The string suceptibility is derived, and found to
be real contrary to the continuation of the KPZ formula. Topological Liouville
string theories (without transverse degree of freedom) are explicitely solved.
Altough they involve strongly coupled gravity, they share many features with
the standard matrix models.Comment: LPTENS-94/25, Latex file + figure
Consistent string backgrounds and completely integrable 2D field theories
After reviewing the -function equations for consistent string
backgrounds in the -model approach, including metric and antisymmetric
tensor, dilaton and tachyon potential, we apply this formalism to WZW models.
We particularly emphasize the case where the WZW model is perturbed by an
integrable marginal tachyon potential operator leading to the non-abelian Toda
theories. Already in the simplest such theory, there is a large non-linear and
non-local chiral algebra that extends the Virasoro algebra. This theory is
shown to have two formulations, one being a classical reduction of the other.
Only the non-reduced theory is shown to satisfy the -function equations.Comment: 12 pages, uses PHYZZ
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