Conformal Invariance and Duality in Self-Dual Gravity and (2,1) Heterotic String Theory

A system of gravity coupled to a 2-form gauge field, a dilaton and Yang-Mills fields in $2n$ dimensions arises from the (2,1) sigma model or string. The field equations imply that the curvature with torsion and Yang-Mills field strength are self-dual in four dimensions, or satisfy generalised self-duality equations in $2n$ dimensions. The Born-Infeld-type action describing this system is simplified using an auxiliary metric and shown to be classically Weyl invariant only in four dimensions. A dual form of the action is found (no isometries are required). In four dimensions, the dual geometry is self-dual gravity without torsion coupled to a scalar field. In $D>4$ dimensions, the dual geometry is hermitian and determined by a $D-4$ form potential $K$, generalising the K\"{a}hler potential of the four dimensional case, with the fundamental 2-form given by $\tilde J= i*\partial \bar \partial K$. The coupling to Yang-Mills is through a term $K\wedge tr (F\wedge F)$ and leads to a Uhlenbeck-Yau field equation $\tilde J^{ij}F_{ij}=0$.Comment: LaTeX, 14 pages, no figures. One reference added and interpretation revised; version to appear in Physics Letters

Urethral stripping for delicate excision of dorsal accessory urethra

Duplication of the urethra is a rare anomaly. The accessory urethra may be dorsal or ventral, relative to the orthotopic urethra. Dorsal urethral duplication describes a normally located meatus and another accessory epispadiac meatus. Excision of the dorsal accessory urethra is usually curative, on the condition that the ventral  orthotopic urethra is normal. However, most reports recommend surgery only when there are significant functional or cosmetic problems, for fear of possible damage to the neurovascular bundle, or the continence mechanism during surgical excision. In this  report, we describe a modification for excising the dorsal accessory channel by stripping with minimal disturbance to the glans. With continuous refinement of the  surgical technique together with more reports confirming its safety, we believe that total excision of the dorsal accessory urethra can be offered to more patients as being the standard level of care.Keywords: accessory urethra, epispadias, urethral duplicatio

Einstein Supergravity and New Twistor String Theories

A family of new twistor string theories is constructed and shown to be free from world-sheet anomalies. The spectra in space-time are calculated and shown to give Einstein supergravities with second order field equations instead of the higher derivative conformal supergravities that arose from earlier twistor strings. The theories include one with the spectrum of N=8 supergravity, another with the spectrum of N=4 supergravity coupled to N=4 super-Yang-Mills, and a family with $N\ge 0$ supersymmetries with the spectra of self-dual supergravity coupled to self-dual super-Yang-Mills. The non-supersymmetric string with N=0 gives self-dual gravity coupled to self-dual Yang-Mills and a scalar. A three-graviton amplitude is calculated for the N=8 and N=4 theories and shown to give a result consistent with the cubic interaction of Einstein supergravity.Comment: LaTeX, 69 pages, no figures; v2: minor corrections made, footnotes and references adde

Knowledge Management Systems from Description to Prescription: An Actor Network Approach

As the awareness of the importance of managing organizational knowledge grows, the issue of how to build information and communication technology (ITC)-based systems to support knowledge management activities, i.e., knowledge management support systems (KMSSs), has been raised. However, knowledge and its manipulating activities, by their very nature, are sociotechnical phenomena in which social and technical factors interweave the ways in which people work. Therefore, the success of any knowledge management support system depends not only on its technical excellence, but also on its compatibility with the social and cultural fabric of the firm in which it is embedded. In this exploratory work it is argued that actor-network theory (ANT) provides theoretical foundations for the KMSS development process. In order to apply ANT in the context of knowledge management, several concepts are introduced, namely, Business Thing, Knowledge Thing and Knowledge Actor, together with a Role ontology

Sigma models with non-commuting complex structures and extended supersymmetry

We discuss additional supersymmetries for N = (2, 2) supersymmetric non-linear sigma models described by left and right semichiral superfields.Comment: 11 pages. Talk presented by U.L. at "30th Winter School on Geometry and Physics" Srni, Czech Republic January 2010