log(M_Pl/m_3/2)

Flux compactifications of string theory seem to require the presence of a fine-tuned constant in the superpotential. We discuss a scheme where this constant is replaced by a dynamical quantity which we argue to be a `continuous Chern--Simons term'. In such a scheme, the gaugino condensate generates the hierarchically small scale of supersymmetry breakdown rather than adjusting its size to a constant. A crucial ingredient is the appearance of the hierarchically small quantity exp(-) which corresponds to the scale of gaugino condensation. Under rather general circumstances, this leads to a scenario of moduli stabilization, which is endowed with a hierarchy between the mass of the lightest modulus, the gravitino mass and the scale of the soft terms, m_modulus ~ m_3/2 ~ ^2 m_soft. The `little hierarchy' is given by the logarithm of the ratio of the Planck scale and the gravitino mass, ~ log(M_Pl/m_3/2) ~ 4pi^2. This exhibits a new mediation scheme of supersymmetry breakdown, called mirage mediation. We highlight the special properties of the scheme, and their consequences for phenomenology and cosmology.Comment: Based on talks given at PLANCK05, Trieste, Italy and PASCOS05, Gyeongju, Kore

Gas turbine blade natural frequency measurement using external casing vibrations

Currently tip timing methods are the pseudo industry standard for measuring Gas Turbine blade vibration. The physical placement of tip timing probes is however reasonably prohibitive due to the high pressure/temperature environment of a turbine. A simpler method of sensor setup would be through the use of externally mounted accelerometers to measure the casing vibration response and relate this back to the internal blade vibration.The vibration of a gas turbine casing is driven by the strong rotating pressure which develops around the rotating blade stages. The oscillating motion of the rotor blades phase modulates this pressure signal. An analytical formulation of the internal pressure signal is developed in this paper. The effects of blade motion on this internal pressure signal is then investigated as the speed of the engine is increased/decreased such that the driving frequency traverses a rotor blade natural frequency. Experimental measurements on a simplified test turbine are presented comparing the results of the analytical internal pressure signal along with results of the measured casing vibration during engine run up/down. It is shown that the spectrum of the internal pressure and casing vibration signal contains information which can be used to estimate the rotor blade natural frequencies

Surge Margin Optimization of Centrifugal Compressors Using a New Objective Function Based on Local Flow Parameters

Currently, 3D-CFD design optimization of centrifugal compressors in terms of the surge margin is one major unresolved issue. On that account, this paper introduces a new kind of objective function. The objective function is based on local flow parameters present at the design point of the centrifugal compressor. A centrifugal compressor with a vaned diffuser is considered to demonstrate the performance of this approach. By means of a variation of the beta angle distribution of the impeller and diffuser blade, 73 design variations are generated, and several local flow parameters are evaluated. Finally, the most promising flow parameter is transferred into an objective function, and an optimization is carried out. It is shown that the new approach delivers similar results as a comparable optimization with a classic objective function using two operating points for surge margin estimation, but with less computational effort since no second operating point near the surge needs to be considered

log(MPl/m3/2)

Flux compactifications of string theory seem to require the presence of a fine-tuned constant in the superpotential. We discuss a scheme where this constant is replaced by a dynamical quantity which we argue to be a 'continuous Chern-Simons term'. In such a scheme, the gaugino condensate generates the hierarchically small scale of supersymmetry breakdown rather than adjusting its size to a constant. A crucial ingredient is the appearance of the hierarchically small quantity exp(-〈X〉) which corresponds to the scale of gaugino condensation. Under rather general circumstances, this leads to a scenario of moduli stabilization, which is endowed with a hierarchy between the mass of the lightest modulus, the gravitino mass and the scale of the soft terms, m modulus ∼ 〈X〉 m3/2 ∼ 〈X〉2 msoft. The 'little hierarchy' 〈X〉 is given by the logarithm of the ratio of the Planck scale and the gravitino mass, 〈X〉 ∼ log(MPl/m3/2) ∼ 4π2. This exhibits a new mediation scheme of supersymmetry breakdown, called mirage mediation. We highlight the special properties of the scheme, and their consequences for phenomenology and cosmology. © 2005 American Institute of Physics

Surge Margin Optimization of Centrifugal Compressors Using a New Objective Function Based on Local Flow Parameters

Currently, 3D-CFD design optimization of centrifugal compressors in terms of the surge margin is one major unresolved issue. On that account, this paper introduces a new kind of objective function. The objective function is based on local flow parameters present at the design point of the centrifugal compressor. A centrifugal compressor with a vaned diffuser is considered to demonstrate the performance of this approach. By means of a variation of the beta angle distribution of the impeller and diffuser blade, 73 design variations are generated, and several local flow parameters are evaluated. Finally, the most promising flow parameter is transferred into an objective function, and an optimization is carried out. It is shown that the new approach delivers similar results as a comparable optimization with a classic objective function using two operating points for surge margin estimation, but with less computational effort since no second operating point near the surge needs to be considered

Surge Margin Optimization of Centrifugal Compressors Using a New Objective Function Based on Local Flow Parameters

Nowadays, 3D-CFD design optimization of centrifugal compressors in terms of surge margin is one major unresolved issue. On that account, this paper introduces a new kind of objective function. The objective function is based on local flow parameters present at the design point of the centrifugal compressor. A centrifugal compressor with vaned diffuser is considered to demonstrate the performance of this approach. By means of a variation of the beta angle distribution of impeller and diffuser blade, 73 design variations are generated and several local flow parameters are evaluated. Finally, the most promising flow parameter is transferred into an objective function and an optimization is carried out. It is shown that the new approach deliver similar results as a comparable optimization with a classic objective function using two operating points for surge margin estimation, but with less computational effort since no second operating point near surge needs to be considered