Observation of Defect States in PT-Symmetric Optical Lattices

We provide the first experimental demonstration of defect states in parity-time (PT) symmetric mesh-periodic potentials. Our results indicate that these localized modes can undergo an abrupt phase transition in spite of the fact that they remain localized in a PT-symmetric periodic environment. Even more intriguing is the possibility of observing a linearly growing radiation emission from such defects provided their eigenvalue is associated with an exceptional point that resides within the continuum part of the spectrum. Localized complex modes existing outside the band-gap regions are also reported along with their evolution dynamics

A CFD and experimental investigation into a non-intrusive method for measuring cooling air mass flow rate through a synchronous generator

This paper presents a detailed methodology for a non-intrusive measurement of cooling air mass flow rate that enables an overall machine evaluation. This approach enables the simultaneous measurement of air mass flow with shaft torque at differing operating points, while minimising the change in air flow introduced by the measurement system. The impact of geometric parameters in the designed system are investigated using a detailed 180° CFD model. Special attention was paid to minimising their influence on pressure drop, mass flow rate through the machine and measurement uncertainty. Based on the results of this investigation, the system was designed and manufactured and the experimentally measured data was used to validate the CFD predictions. For the as optimal identified configuration, the flow rate is predicted to decrease by 2.2 % relative to unrestricted operation. The achieved measurement uncertainty is ±2.6 % at synchronous speed

CFD optimisation of the thermal design for a vented electrical machine

Optimisation algorithms hold the potential to dramatically reduce computational time whilst ensuring the optimal solution is found. Within this paper, the feasibility of using this novel approach on complex 3-D Computational Fluid Dynamics models, which are required for thermal management of electrical machines, is proven. A model of a simplified generator is parameterised with the aim of minimising the peak stator temperature by varying the axial location of a single stator vent. By generating a single parameterised case, and automating the optimisation, the simulations are run independently after initial setup, hence reducing both computational and user time. Locating a vent in the optimal position reduced the peak stator temperature by 9.4 K. A sensitivity study linking peak temperature to vent position has been carried out developing a polynomial relationship between them for the aforementioned geometry. Mass flow and pressure distribution in the vent have been analysed in detail

A CFD and experimental investigation into a non-intrusive method for measuring cooling air mass flow rate through a synchronous generator

This paper presents a detailed methodology for a non-intrusive measurement of cooling air mass flow rate that enables an overall machine evaluation. This approach enables the simultaneous measurement of air mass flow with shaft torque at differing operating points, while minimising the change in air flow introduced by the measurement system. The impact of geometric parameters in the designed system are investigated using a detailed 180° CFD model. Special attention was paid to minimising their influence on pressure drop, mass flow rate through the machine and measurement uncertainty. Based on the results of this investigation, the system was designed and manufactured and the experimentally measured data was used to validate the CFD predictions. For the as optimal identified configuration, the flow rate is predicted to decrease by 2.2 % relative to unrestricted operation. The achieved measurement uncertainty is ±2.6 % at synchronous speed

Thermal and Electromagnetic Stator Vent Design Optimisation for Synchronous Generators

© 2020 Institute of Electrical and Electronics Engineers Inc.. All rights reserved. This paper deals with the stator cooling of an air-cooled, synchronous generator with a power rating of 400 kVA, which has been improved by adding two radial vents to the stator. To ensure an optimal vent design, a novel combined thermal and electromagnetic modelling approach is developed. A parametric 3D Conjugate Heat Transfer Computational Fluid Dynamics (CFD) model is used for the thermal modelling. An electromagnetic 2D Finite Element Analysis determined the impact that venting the stator has on the loss distribution. The models are coupled by deriving analytical correlations between the combined vent width and rotor copper, rotor iron and stator iron losses. These correlations are implemented into the optimisation procedure of the parametric CFD model. Five design parameters are optimised simultaneously with the aim of minimising the peak stator winding temperature. The modelling approach was validated experimentally by thermal, torque and mass flow measurements on the benchmark machine, as well as the newly designed prototype

Post-diagnosis dietary factors and survival after invasive breast cancer.

Little is known about the effects of diet after breast cancer diagnosis on survival. We prospectively examined the relation between post-diagnosis dietary factors and breast cancer and all-cause survival in women with a history of invasive breast cancer diagnosed between 1987 and 1999 (at ages 20-79 years). Diet after breast cancer diagnosis was measured using a 126-item food frequency questionnaire. Among 4,441 women without a history of breast cancer recurrence prior to completing the questionnaire, 137 subsequently died from breast cancer within 7 years of enrollment. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated for intake of macronutrients as well as selected micronutrients and food groups from Cox proportional hazards regression models. After adjustment for factors at diagnosis (age, state of residence, menopausal status, smoking, breast cancer stage, alcohol, history of hormone replacement therapy), interval between diagnosis and diet assessment, and at follow-up (energy intake, breast cancer treatment, body mass index, and physical activity), women in the highest compared to lowest quintile of intake of saturated fat and trans fat had a significantly higher risk of dying from any cause (HR = 1.41, 95% CI = 1.06-1.87, P trend = 0.03) for saturated fat; (HR = 1.78, 95% CI = 1.35-2.32, P trend = 0.01) for trans fat intake. Associations were similar, though did not achieve statistical significance, for breast cancer survival. This study suggests that lower intake of saturated and trans fat in the post-diagnosis diet is associated with improved survival after breast cancer diagnosis

Two-pion correlations in Au+Au collisions at 10.8 GeV/c per nucleon

Two-particle correlation functions for positive and negative pions have been measured in Au+Au collisions at 10.8~GeV/c per nucleon. The data were analyzed using one- and three-dimensional correlation functions. From the results of the three-dimensional fit the phase space density of pions was calculated. It is consistent with local thermal equilibrium.Comment: 5 pages RevTeX (including 3 Figures

Proton and Pion Production in Au+Au Collisions at 10.8A GeV/c

We present proton and pion tranverse momentum spectra and rapidity distributions for Au+Au collisions at 10.8A GeV/c. The proton spectra exhibit collective transverse flow effects. Evidence of the influence of the Coulomb interaction from the fireball is found in the pion transverse momentum spectra. The data are compared with the predictions of the RQMD event generator.Comment: plain tex (revtex), 24 pages Submitted to Phys. Rev.