438 research outputs found

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

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    A system of gravity coupled to a 2-form gauge field, a dilaton and Yang-Mills fields in 2n2n 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 2n2n 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>4D>4 dimensions, the dual geometry is hermitian and determined by a D4D-4 form potential KK, generalising the K\"{a}hler potential of the four dimensional case, with the fundamental 2-form given by J~=iˉK\tilde J= i*\partial \bar \partial K. The coupling to Yang-Mills is through a term Ktr(FF)K\wedge tr (F\wedge F) and leads to a Uhlenbeck-Yau field equation J~ijFij=0\tilde J^{ij}F_{ij}=0.Comment: LaTeX, 14 pages, no figures. One reference added and interpretation revised; version to appear in Physics Letters

    Sigma models with non-commuting complex structures and extended supersymmetry

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    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

    The Wall Properties Effect on Peristaltic Transport of Micropolar Non-Newtonian Fluid with Heat and Mass Transfer

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    The problem of the unsteady peristaltic mechanism with heat and mass transfer of an incompressible micropolar non-Newtonian fluid in a two-dimensional channel. The flow includes the viscoelastic wall properties and micropolar fluid parameters using the equations of the fluid as well as of the deformable boundaries. A perturbation solution is obtained, which satisfies the momentum, angular momentum, energy, and concentration equations for case of free pumping (original stationary fluid). Numerical results for the stream function, temperature, and concentration distributions are obtained. Several graphs of physical interest are displayed and discussed

    How Does Forecasting Affect the Convergence of DRL Techniques in O-RAN Slicing?

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    The success of immersive applications such as virtual reality (VR) gaming and metaverse services depends on low latency and reliable connectivity. To provide seamless user experiences, the open radio access network (O-RAN) architecture and 6G networks are expected to play a crucial role. RAN slicing, a critical component of the O-RAN paradigm, enables network resources to be allocated based on the needs of immersive services, creating multiple virtual networks on a single physical infrastructure. In the O-RAN literature, deep reinforcement learning (DRL) algorithms are commonly used to optimize resource allocation. However, the practical adoption of DRL in live deployments has been sluggish. This is primarily due to the slow convergence and performance instabilities suffered by the DRL agents both upon initial deployment and when there are significant changes in network conditions. In this paper, we investigate the impact of time series forecasting of traffic demands on the convergence of the DRL-based slicing agents. For that, we conduct an exhaustive experiment that supports multiple services including real VR gaming traffic. We then propose a novel forecasting-aided DRL approach and its respective O-RAN practical deployment workflow to enhance DRL convergence. Our approach shows up to 22.8%, 86.3%, and 300% improvements in the average initial reward value, convergence rate, and number of converged scenarios respectively, enhancing the generalizability of the DRL agents compared with the implemented baselines. The results also indicate that our approach is robust against forecasting errors and that forecasting models do not have to be ideal.Comment: This article has been accepted for presentation in IEEE GLOBECOM 202

    Repair of low anorectal anomalies in female patients: risk factors for wound dehiscence

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    Background/purpose: Wound dehiscence after rectoperineal/vestibular fistulae repair may have adverse effects on the continence mechanism with delayed functional sequels. We report the incidence of wound complications following the sagittal anorectoplasty in a group of female patients, in addition to studying the effect of some possible risk factors.Patients and methods: This is a prospective cohort study conducted on female patients with rectoperineal or rectovestibular fistula operated during the period from January 2011 to December 2015. Patients were divided into three groups: group A (no dehiscence); group B (minor dehiscence); and group C (major dehiscence). Patients were compared regarding their age at the time of repair, the type of anorectal anomaly, the degree of dilation of the colon, and the prevalence of covering colostomy.Results: The study included 63 female patients. Group A included 34 patients (those with no dehiscence, 52.4%), group B included 17 patients (minor wound dehiscence, 26.98%), and group C included 13 patients (major wound dehiscence, 20.6%). There was no statistically significant difference between the three groups regarding the studied risk factors.Conclusion: With regard to the wound complications following the repair of rectoperineal/vestibular fistulae in the female patients, none of the studied risk factors appear to have a significant effect on the outcome.Keywords: anterior sagittal anorectoplasty, colostomy, posterior sagittal anorectoplasty, rectoperineal fistula, rectovestibular fistula, wound dehiscenc

    Geometry, Isometries and Gauging of (2,1) Heterotic Sigma-Models

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    The geometry of (2,1) supersymmetric sigma-models is reviewed and the conditions under which they have isometry symmetries are analysed. Certain potentials are constructed that play an important role in the gauging of such symmetries. The gauged action is found for a special class of models.Comment: 12 pages, LaTeX, no figures. Minor changes; version to appear in Physics Letters