The Egyptian Cardiothoracic Surgeon (ECTS - E-Journal)
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Comparing model and measured ice crystal concentrations in orographic clouds during the INUPIAQ campaign
No full textThis paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in-situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Forecasting model (WRF) simulations over real terrain surrounding Jungfraujoch. During the 2014 winter field campaign, between the 20 January and 28 February, the model simulations regularly underpredicted the observed ice number concentration by 103 L−1. Previous literature has proposed several processes for the high ice number concentrations in orographic clouds, including an increased ice nuclei (IN) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing IN concentrations in the model prevents the simulation of the mixed-phase clouds that were witnessed during the INUPIAQ campaign at Jungfraujoch. Additionally, the inclusion of secondary ice production upwind of Jungfraujoch into the WRF simulations cannot consistently produce enough ice splinters to match the observed concentrations. A surface flux of hoar crystals was included in the WRF model, which simulated ice concentrations comparable to the measured ice number concentrations, without depleting the liquid water content (LWC) simulated in the model. Our simulations therefore suggest that high ice concentrations observed in mixed-phase clouds at Jungfraujoch are caused by a flux of surface hoar crystals into the orographic clouds
The role of aluminium in chemical and phase segregation in a TRIP-assisted dual phase steel
No full textIn this work we have assessed the role of Al on the chemical segregation of Mn, Cr and Si during thermo-mechanical processing of a TRIP-assisted dual phase steel, based on microstructural observations backed by thermodynamic, numerical and analytical modelling. Chemical segregation in steels during casting leads to anisotropy in the microstructure (banding) and hence in mechanical properties. Although considerable attention has been paid to the effects of carbon and manganese, the segregation of other alloying elements and their influence on the resulting microstructure and properties remains largely unexplored. We demonstrate that the micro-segregation patterns of these elements established during casting remain present in the microstructure throughout the process and are not homogenised during industrial reheating cycles due to insufficient diffusion of solid solution elements. Aluminium exerts the largest individual effect of the substitutional elements on the formation of banding in these steels. Controlling micro-segregation during solidification is therefore critical for obtaining homogenous mechanical properties in the final product, as it controls the phase transformations occurring during thermo-mechanical processing and therefore the final microstructure
What Role for Small Enterprises?:Industrial clusters, industrial policy and poverty reduction
No full textA biorefinery approach to microbial oil production from glycerol by Rhodotorula glutinis
No full textThe use of biodiesel-derived glycerol as a carbon source for microbial oil production is a biorefinery engineering strategy that aims to reduce the glycerol surplus and make the microbial oil process more cost-effective. In this work, glycerol was used as the sole carbon source for the cultivation of the oleaginous yeast Rhodotorula glutinis along with only yeast extract as a nutrient supply and without pH control. Shake-flask cultivations showed that the specific growth rate and glycerol consumption of Rhodotorula glutinis were higher at lower glycerol concentrations (≤40 g L-1), while higher C/N atom ratios enhanced oil content. The present study extends the knowledge on the influence of the aeration rate and oxygen supply in cellular growth rate and microbial oil production, providing a wiser use of glycerol as an attempt to further reduce process costs. Cultivations at different air flow rates were performed in a 2 L bioreactor and showed that a low aeration rate of 0.5 L min-1 gave the best glycerol and nitrogen uptake rates, resulting in the highest growth (5.3 g L-1) and oil mass fraction (33% of the dry cell weight). A further 68% increase in cellular growth (16.8 g L-1) and a 34% oil mass fraction of the dry cell weight was achieved after applying a feeding strategy targeting combined growth and oil production. © 2016 Elsevier Ltd
Dynamic Resource Allocation for Efficient Sharing of Services from Heterogeneous Autonomous Vehicles
No full textA novel dynamic resource allocation model is introduced for efficient sharing of services provided by ad hoc assemblies of heterogeneous autonomous vehicles. The main focus is on large networks of air vehicles supported by small number of surface vehicles. A key contribution is the provision of capability to dynamically select sensors and platforms within constraints imposed by time dependencies, refueling, and transportation services. The problem is modeled as a connected network of nodes and formulated as an Integer Linear Program (ILP), with the objective of assessing solution fitness independent of computation time. The problem definition and novel formulation is developed with the intention of accommodating versatile civilian unmanned systems operations. The model is validated using a number of simple planning scenarios for which the optimal solution is known a priori. Simulation results of an illustrative scenario involving four vehicles, four sensor payloads and 7 task requests is used to demonstrate the ability of the model to plan for sensor selection, refueling, collaboration and cooperation between heterogeneous resources. Model execution times are of the order of tens of seconds on a desk top computer. Increasing mission constraints reduces the mission solution space and reduces model execution time. Prioritization of operational cost leads to missions that use less expensive resources but take longer overall to complete. Prioritization of completion time leads to shorter missions at the expense of increased overall resource cost. Missions can be successfully re-planned through dynamic reallocation of new requests during a mission. Re-planned missions are shown to be more expensive compared to the equivalent static mission planned in advance
An improved-Rhie-Chow interpolation scheme for the smoothed-interface immersed boundary method
No full textRhie-Chow interpolation is a commonly used method in CFD calculations on a co-located mesh in order to suppress non-physical pressure oscillations arising from chequer-board effects. A fully parallelised smoothed-interface immersed boundary method on a co-located grid is described in this paper. We discuss the necessity of modifications proposed by Choi [1] to the original Rhie-Chow interpolation in order to deal with a locally refined mesh. Numerical simulation with the modified scheme of Choi shows numerical dissipation due to Rhie-Chow interpolation introduces significant errors at the immersed boundary. To address this issue we develop an improved-Rhie-Chow interpolation scheme which is shown to increase the accuracy in resolving the flow near the immersed boundary. We compare our improved scheme with the modified scheme of Choi by parallel simulations of two benchmark flows i/ flow past a stationary cylinder and ii/ flow past an oscillating cylinder, both for Reynolds numbers in the range 10 - 200. Our improved scheme is significantly more accurate and compares favourably with a staggered grid algorithm. We also develop a scheme for calculating the boundary force for the direct-forcing immersed boundary method in a computationally efficient way