Supergravities with Minkowski x Sphere Vacua

Recently the authors have introduced a new gauged supergravity theory with a positive definite potential in D=6, obtained through a generalised Kaluza-Klein reduction from D=7. Of particular interest is the fact that this theory admits certain Minkowski x Sphere vacua. In this paper we extend the previous results by constructing gauged supergravities with positive definitive potentials in diverse dimensions, together with their vacuum solutions. In addition, we prove the supersymmetry of the generalised reduction ansatz. We obtain a supersymmetric solution with no form-field fluxes in the new gauged theory in D=9. This solution may be lifted to D=10, where it acquires an interpretation as a time-dependent supersymmetric cosmological solution supported purely by the dilaton. A further uplift to D=11 yields a solution describing a pp-wave.Comment: Latex, 26 pages, typos correcte

Thermodynamical Behaviour of Composite Stringy Black Holes

We study the thermodynamical and geometrical behaviour of the black holes that arise as solutions of the heterotic string action. We discuss the near-horizon scaling behaviour of the solutions that are described by two-dimensional Anti-de Sitter Space AdS(2). We find that finite-energy excitations of AdS(2) are suppressed only for scaling limits characterised by a dilaton which is constant near the horizon, whereas this suppression does not occur when the dilaton is non constant

Intersecting M-branes and bound states

In this paper, we construct multi-scalar, multi-center $p$-brane solutions in toroidally compactified M-theory. We use these solutions to show that all supersymmetric $p$-branes can be viewed as bound states of certain basic building blocks, namely $p$-branes that preserve $1/2$ of the supersymmetry. We also explore the M-theory interpretation of $p$-branes in lower dimensions. We show that all the supersymmetric $p$-branes can be viewed as intersections of M-branes or boosted M-branes in $D=11$.Comment: Latex, 14 pages, no figures. References adde

Integrated computer-aided working-fluid design and thermoeconomic ORC system optimisation

The successful commercialisation of organic Rankine cycle (ORC) systems across a range of power outputs and heat-source temperatures demands step-changes in both improved thermodynamic performance and reduced investment costs. The former can be achieved through high-performance components and optimised system architectures operating with novel working-fluids, whilst the latter requires careful component-technology selection, economies of scale, learning curves and a proper selection of materials and cycle configurations. In this context, thermoeconomic optimisation of the whole power-system should be completed aimed at maximising profitability. This paper couples the computer-aided molecular design (CAMD) of the working-fluid with ORC thermodynamic models, including recuperated and other alternative (e.g., partial evaporation or trilateral) cycles, and a thermoeconomic system assessment. The developed CAMD-ORC framework integrates an advanced molecular-based group-contribution equation of state, SAFT-γ Mie, with a thermodynamic description of the system, and is capable of simultaneously optimising the working-fluid structure, and the thermodynamic system. The advantage of the proposed CAMD-ORC methodology is that it removes subjective and pre-emptive screening criteria that would otherwise exist in conventional working-fluid selection studies. The framework is used to optimise hydrocarbon working-fluids for three different heat sources (150, 250 and 350 °C, each with mcp = 4.2 kW/K). In each case, the optimal combination of working-fluid and ORC system architecture is identified, and system investment costs are evaluated through component sizing models. It is observed that optimal working fluids that minimise the specific investment cost (SIC) are not the same as those that maximise power output. For the three heat sources the optimal working-fluids that minimise the SIC are isobutane, 2-pentene and 2-heptene, with SICs of 4.03, 2.22 and 1.84 £/W respectively

Massless 3-brane in M-theory

We construct supersymmetric M3-brane solutions in D=11 supergravity. They can be viewed as deformations of backgrounds taking the form of a direct product of four-dimensional Minkowski spacetime and a non-compact Ricci-flat manifold of G_2 holonomy. Although the 4-form field strength is turned on it carries no charge, and the 3-branes are correspondingly massless. We also obtain 3-branes of a different type, arising as M5-branes wrapped over S^2.Comment: This corrects a previous version in which it was mistakenly claimed that the M3-brane solutions are pseudo-supersymmetric rather than supersymmetri

Flow interactions with an aquatic macrophyte: a field study using stereoscopic particle image velocimetry

This paper reports the morphology of a natural patch of Ranunculus penicillatus and presents high-resolution measurements of flow velocities in its wake using a stereoscopic PIV field measurement system. The patch was 3.80 m long, 1.24 m wide and caused substantial changes to downstream mean velocities and turbulence. Vertical profiles of streamwise mean velocity were not logarithmic and flow was redirected under the positively buoyant canopy, enhancing vertical turbulent mixing in the wake and generating a large region where the velocity covariance u'w' was positive. Turbulent kinetic energy was enhanced downstream from the patch lateral shear layer, but not at the centre of the wake. Spectra downstream from the patch showed that turbulence was neither dominated by fine-scale nor large-scale structures, likely due to the low energy of the flow conditions and lack of a developed vortex street within the measurement domain. Sedimentation was observed at the upstream end of the patch, but not underneath the floating canopy. The methods and results of this work will be useful for planning other in situ studies. Also, the reported data on macrophyte geometry and biometrics will assist with the design of more realistic replicas for use in laboratory studies

The Black Branes of M-theory

We present a class of black $p$-brane solutions of M-theory which were hitherto known only in the extremal supersymmetric limit, and calculate their macroscopic entropy and temperature.Comment: Latex, 13 pages, minor corrections and reference adde

Classification of p-branes, NUTs, Waves and Intersections

We give a full classification of the multi-charge supersymmetric $p$-brane solutions in the massless and massive maximal supergravities in dimensions $D\ge2$ obtained from the toroidal reduction of eleven-dimensional supergravity. We derive simple universal rules for determining the fractions of supersymmetry that they preserve. By reversing the steps of dimensional reduction, the $p$-brane solutions become intersections of $p$-branes, NUTs and waves in D=10 or D=11. Having classified the lower-dimensional $p$-branes, this provides a classification of all the intersections in D=10 and D=11 where the harmonic functions depend on the space transverse to all the individual objects. We also discuss the structure of U-duality multiplets of $p$-brane solutions, and show how these translate into multiplets of harmonic and non-harmonic intersections.Comment: Latex, 67 pages, minor correction

Exact half-BPS Type IIB interface solutions I: Local solution and supersymmetric Janus

The complete Type IIB supergravity solutions with 16 supersymmetries are obtained on the manifold $AdS_4 \times S^2 \times S^2 \times \Sigma$ with $SO(2,3) \times SO(3) \times SO(3)$ symmetry in terms of two holomorphic functions on a Riemann surface $\Sigma$, which generally has a boundary. This is achieved by reducing the BPS equations using the above symmetry requirements, proving that all solutions of the BPS equations solve the full Type IIB supergravity field equations, mapping the BPS equations onto a new integrable system akin to the Liouville and Sine-Gordon theories, and mapping this integrable system to a linear equation which can be solved exactly. Amongst the infinite class of solutions, a non-singular Janus solution is identified which provides the AdS/CFT dual of the maximally supersymmetric Yang-Mills interface theory discovered recently. The construction of general classes of globally non-singular solutions, including fully back-reacted $AdS_5 \times S^5$ and supersymmetric Janus doped with D5 and/or NS5 branes, is deferred to a companion paper.Comment: LaTeX, 69 pages, 3 figures, v2: references adde