Tiltrotor CFD part I: validation

This paper presents performance analyses of the model-scale ERICA and TILTAERO tiltrotors and of the full-scale XV-15 rotor with high-fidelity computational fluids dynamics. For the ERICA tiltrotor, the overall effect of the blades on the fuselage was well captured, as demonstrated by analysing surface pressure measurements. However, there was no available experimental data for the blade aerodynamic loads. A comparison of computed rotor loads with experiments was instead possible for the XV-15 rotor, where CFD results predicted the FoM within 1.05%. The method was also able to capture the differences in performance between hover and propeller modes. Good agreement was also found for the TILTAERO loads. The overall agreement with the experimental data and theory for the considered cases demonstrates the capability of the present CFD method to accurately predict tiltrotor flows. In a second part of this work, the validated method is used for blade shape optimisation

Covariant N=2 heterotic string in four dimensions

We construct a covariant formulation of the heterotic superstring on K3 times T^2 with manifest N=2 supersymmetry. We show how projective superspace appears naturally in the hybrid formulation giving a (partially) geometric interpretation of the harmonic parameter. The low-energy effective action for this theory is given by a non-standard form of N=2 supergravity which is intimately related to the N=1 old-minimal formulation. This formalism can be used to derive new descriptions of interacting projective superspace field theories using Berkovits' open string field theory and the the heterotic Berkovits-Okawa-Zwiebach construction.Comment: 11+3 page

On Lorentz-Violating Supersymmetric Quantum Field Theories

We study the possibility of constructing Lorentz-violating supersymmetric quantum field theories under the assumption that these theories have to be described by lagrangians which are renormalizable by weighted power counting. Our investigation starts from the observation that at high energies Lorentz-violation and the usual supersymmetry algebra are algebraically compatible. Demanding linearity of the supercharges we see that the requirement of renormalizability drastically restricts the set of possible Lorentz-violating supersymmetric theories. In particular, in the case of supersymmetric gauge theories the weighted power counting has to coincide with the usual one and the only Lorentz-violating operators are introduced by some weighted constant c that explicitly appears in the supersymmetry algebra. This parameter does not renormalize and has to be very close to the speed of light at low energies in order to satisfy the strict experimental bounds on Lorentz violation. The only possible models with non trivial Lorentz-violating operators involve neutral chiral superfields and do not have a gauge invariant extension. We conclude that, under the assumption that high-energy physics can be described by a renormalizable Lorentz-violating extensions of the Standard Model, the Lorentz fine tuning problem does not seem solvable by the requirement of supersymmetry.Comment: 22 pages, 2 figure

Ectoplasm & Superspace Integration Measure for 2D Supergravity with Four Spinorial Supercurrents

Building on a previous derivation of the local chiral projector for a two dimensional superspace with eight real supercharges, we provide the complete density projection formula required for locally supersymmetrical theories in this context. The derivation of this result is shown to be very efficient using techniques based on the Ectoplasmic construction of local measures in superspace.Comment: 18 pages, LaTeX; V2: minor changes, typos corrected, references added; V3: version to appear in J. Phys. A: Math. Theor., some comments and references added to address a referee reques

Determining carbon and nitrogen stable isotope discrimination for marine consumers

The application of stable isotope ratios to food web studies is increasing, and the use of generalised discrimination values (0.4±1.4%0 for δ13C and 3.4±1.1%0 for δ15N), which are being widely applied to many studies, may not be valid. The broad objective of this study was to evaluate the assumption that these discrimination values are applicable to a range of benthic marine consumers, and therefore appropriate to be used in trophic analyses using carbon (C) and nitrogen (N) stable isotopes in marine food webs. The first aim was to determine if there were differences in discrimination values: (1) among different groups of macroalgae when fed to specific consumers; and (2) among different types of consumers when fed on the same type of algae. The feeding treatments used representatives of brown, fleshy red, calcareous red and green macroalgal food sources, which were fed to three types of consumers: the sea urchin Heliocidaris e1ythrogramma, the hermit crabs Paguristes purpureantennatus and Calcinus dapsiles, and the gastropod Turbo torquatus. Food sources and consumers were collected from the field, and each food source was subsequently fed to each consumer in a series of controlled aquaria experiments. Replicate individuals of each consumer were sampled at regular intervals up to 56 days after initiation of the experiments. Muscle tissue was processed and analysed using mass spectrometry to determine δ13C and δ15N values. In accordance with the feeding treatments, starvation treatments were also conducted. The results showed a general trend of no change in δ13C and δ15N isotope ratios for the invertebrate consumers over time, and this was also the case for the starvation treatments. Observations during the experiments indicated that animals were active and consuming the algae in the feeding treatments compared to the starved invertebrates which remained relatively immobile. Constant feeding by invertebrates suggests that discrimination values derived from the experiment are likely to be realistic. Results indicated that δ13C and δ15N discrimination differed among groups of algae, particularly for carbon. Average δ13C discrimination values were 1.56%0 for brown algae, 2.31 %0 for fleshy red algae, 3.38%0 for calcareous red algae, 1.46%0 for green algae, while average δ15N discrimination values were 2.6­0%0, 2.03%0, 2.53%0, and 2.93%0 for the respective algal groups. δ13C and δ15N discrimination also differed among consumers when fed on the same food source. Average δ13C discrimination values were 2.67%0, 2.70%0, 2.58%0 and 1.31 %0 for the urchin Herythrogramma, the hermit crabs P. purpureantennatus and C. dapsiles and the gastropod T torquatus, respectively, while average δ15N discrimination values were 3.14%0, 3.80%0, 2.15%0 and 1.31%0 for the respective species. Thus, the results of this study indicate that different discrimination values are exhibited for different algal food sources and by different consumers under the environmental conditions within this study. Furthermore these values differed from the assumed discrimination values that are applied to many stable isotope studies. In many isotope-based food web studies, mixing models are utilised to quantify the possible contributions of different food sources to a consumer\u27s diet. This process has better outcomes than traditional gut content analysis, as it reflects actual assimilation of food sources rather than what material is found in the gut tract. The second aim was to compare results of the Isosource mixing model when using either assumed or experimentally-derived discrimination values to evaluate the contribution of the different macroalgal species to the natural diets of marine invertebrates. The assumed discrimination values of 0.4%0 for δ13C and 3.4%0 for δ15N were applied to the food source stable isotope dataset as input data for Isosource, and compared to results when the experimentally derived values were applied to the same dataset. Results from Isosource were not possible using the assumed values, due to the isotope ratios of consumers sitting outside the range of sources. However when the experimentally derived discrimination values were applied, the model ran successfully. These mixing model results indicated that brown, red and green algae all contributed to the production of consumers, but there were differences in the relative contributions of these food sources among the consumer species examined. The current study has quantified C and N discrimination for key marine invertebrate and algal types, and particularly for C these values were found to be higher (1.46-3.38%0) than those generally applied, i.e. 0.4 ± 1.4%0. The assumed discrimination values are not applicable across all food sources or consumer groups. The consequences of applying incorrect discrimination values include preventing any sources of production to be established, or leading to erroneous conclusions about an organism\u27s trophic level or food source