Understanding Polarization Properties of InAs Quantum Dots by Atomistic Modeling of Growth Dynamics

A model for realistic InAs quantum dot composition profile is proposed and analyzed, consisting of a double region scheme with an In-rich internal core and an In-poor external shell, in order to mimic the atomic scale phenomena such as In-Ga intermixing and In segregation during the growth and overgrowth with GaAs. The parameters of the proposed model are derived by reproducing the experimentally measured polarization data. Further understanding is developed by analyzing the strain fields which suggests that the two-composition model indeed results in lower strain energies than the commonly applied uniform composition model.Comment: in press, AIP proceedings for ICPS 2012 - 31st International Conference on the Physics of Semiconductors, July 29-August 3, 2012 Zuric

a diagnostics tool for aero engines health monitoring using machine learning technique

Abstract In this work an integrated heath monitoring platform is proposed and developed for performance analysis and degradation diagnostics of gas turbine engines. The aim is to link engine measurable data to its health status. A numerical tool has been implemented in order to calculate engine performance in design condition and to create a database of expected vales. Then different degradation levels have been introduced in the two main components, compressor and turbine of a single spool turbojet and the diagnostics instruments have been trained to detect the component fault. In order to evaluate the performance prediction two different machine learning based techniques, namely, artificial neural network (ANN) and support vector machine (SVM) have been compared. Synthetic data generation has been carried out to show how the degradation effects can affect the engine performance. The two main degradation causes considered are the compressor fouling and turbine erosion. The machine learning techniques were applied with two aims: aero-engine performance prediction and health diagnostics. The study was carried out based on three samples flights, whose data were used for the training and testing process of the prediction and diagnostics tools. The knowledge and the continuous monitoring of the engine health status can be crucial for maintenance and fleet management operations

Sourcing Hydrogen for the Production of Sustainable Aviation Fuels

Sustainable aviation fuels (SAFs) are the near-term technological solution to decarbonize the aviation industry sector. There are several pathways to obtain biojet fuels, which can be classified into four main categories, namely oil-to-jet, alcohol-to-jet, gas-to-jet, and sugar-to-jet. All of them share the need for hydrogen to obtain a drop-in fuel that can be blended with petroleum-based jet fuel. The hydrogen input requirements affect the life cycle greenhouse gas emissions, increase the biojet fuel cost and hinder the construction of distributed processing plants. This study addresses the problem of hydrogen sourcing in the production of SAFs through a systematic literature review. Techno-economic studies of biojet fuel production using different feedstocks and conversion pathways are analyzed focusing on the methods of hydrogen provision. The technological options used to generate the required hydrogen within the conversion process itself as well as externally, along with the main strategies to reduce the hydrogen demand are identified. The production yields and the hydrogen consumption of several SAF production pathways are compared. The jet fuel yields reach values as high as 0.66 for hydroprocessing of vegetable oils with external hydrogen provision, while they drop to 0.10 for production from lignocellulosic biomass with internal hydrogen sourcing. The results of the analysis highlight the real potential of four among the most promising routes for the production of biojet fuels when the burden related to hydrogen demand is properly taken into account

Mode decomposition methods for the analysis of cavitating flows in turbomachinery

Abstract The present work is aimed at the characterization of the cavitating flow regimes by applying the coupled POD/DMD technique to the vapor volume fraction field. The proposed approach provided an improved spatio-temporal-frequency description of the flow, based on the detection of the most energetic flow structures with information about their shape and size, and their decomposition into wave patterns oscillating with specific frequency and decay rate. The novel technique was applied to numerical results concerning the bubble cavitation and the supercavitation regimes of 2D water flows around a NACA hydrofoil at ambient temperature. Numerical simulations were performed by using a homogenous mixture model equipped with an extended Schnerr-Sauer cavitation model, in combination with a Volume of Fluid (VOF) interface tracking method. The proposed approached provided a better characterization of the unsteady cavitating flow, and allowed for a deeper insight about the dynamics of the vapor cavity, especially in cases involving the more chaotic regime of supercavitation. In particular, POD results figured out the most energetic coherent vapor structures associated to each cavitation regime: the first mode highlighted the main sheet cavity which grew on the hydrofoil up to detached, the second mode pointed out the cavitating/condensating doublet structures and the third mode figured out the smaller structures owning less energy but a higher frequency content. DMD modes performed a decomposition of the coherent structures detected by means of the POD analysis, into a subset of vapor pattern periodically evolving with a single frequency and a characteristic decay rate. Furthermore, results showed that the supercavitating flow structures owned characteristic frequencies which ranged from 5 to 26 Hz, while the less intensive bubble cavitation regime was characterized by frequencies ranging from 15 to 42 Hz

Implementation and validation of an extended Schnerr-Sauer cavitation model for non-isothermal flows in OpenFOAM

Abstract In the present work cavitation in liquid hydrogen and nitrogen was investigated by using the open source toolbox OpenFOAM. Simulations were performed by means of a mass transfer model, based on the homogeneous mixture approach in combination with the Volume of Fluid (VOF) method for the reconstruction the liquid-vapor interface. Two additional transport equations were considered, i.e. the liquid volume fraction advection and the temperature equation. The implementation of an extended Schnerr- Sauer model allowed for the introduction of the thermal effects in terms of latent heat release/absorption and convective heat transfer inside the liquid-vapor interface. A set of Antoine-like equations relate the saturation conditions to the local conditions

Modeling viscous effects on boundary layer of rarefied gas flows inside micronozzles in the slip regime condition

Abstract The present work provided a numerical investigation of the supersonic flow of rarefied gas into a planar micronozzle characterized by small depth and long divergent section. 2D and 3D computational fluid dynamics (CFD) computations were performed using the continuum Navier-Stokes equations in combination with partial slip conditions at walls, based on a the establishment of the slip regime related to a Knudsen number ranging between 1 x 10-3 and 1 x 10-1. Different partial slip conditions were considered, i.e. the ideal case of pure slip conditions and the full viscous case with Maxwellian slip conditions on sidewalls and planar walls, as well as the case of Maxwellian slip just on sidewalls. The Maxwell slip model was set with a tangential accommodation coefficient equal (TMAC) to 0.8. Comparisons were based on the estimation of the global performance of the micronozzle in terms of thrust force, specific impulse, discharge coefficient and Isp-efficiency. It resulted that when the nozzle depth was neglected, 3D simulations led to the same solution obtained by means of 2D computations inside the micronozzle. The boundary layer thicknesses experienced a linear growth on the sidewalls, and the viscous losses produced a reduction of the performance of about the 95%. Significant differences were found in the prediction of the jet plume, which took the typical bell-shape form in cases involving 2D computations, yet 3D simulations estimated a plume characterized by the succession of oblique shock waves and expansion fan waves. Instead, when the nozzle depth was considered, 3D simulations underlined a completely different behavior of the flow because of the establishment of the nozzle blockage and a viscous heating. The performance suffered an intense degradation of about the 47%, and the analysis of the jet plume highlighted the formation of the Mach disk followed by the typical diamond-shaped subsonic recirculation region

Mems vaporazing liquid microthruster: A comprehensive review

none4The interest in developing efficient nano and pico-satellites has grown in the last 20 years. Secondary propulsion systems capable of serving specific maneuvers are an essential part of these small satellites. In particular, Micro-Electro-Mechanical Systems (MEMS) Vaporizing Liquid Micro-thrusters (VLM), using water as a propellant, represent today a smart choice in terms of simplicity and cost. In this paper, we first propose a review of the international literature focused on MEMS VLM development, reviewing the different geometries and heating solutions proposed in the liter-ature. Then, we focus on a critical aspect of these micro thrusters: the presence of unstable phenom-ena. In particular, the boiling instabilities and reverse channel flow substantially impact the MEMS VLMs’ performance and limit their applicability. Finally, we review the research focused on the passive and active control of the boiling instabilities, based on VLM geometry optimization and active heating strategies, respectively. Today, these ones represent the two principal research axes followed by the scientific community to mitigate the drawbacks linked to the use of MEMS VLMs.openFontanarosa D.; Francioso L.; De Giorgi M.G.; Vetrano M.R.Fontanarosa, D.; Francioso, L.; De Giorgi, M. G.; Vetrano, M. R

Model-Based Dynamic Performance Simulation of a Microturbine Using Flight Test Data

none3siMicroturbines can be used not only in models and education but also to propel UAVs. However, their wider adoption is limited by their relatively low efficiency and durability. Validated simulation models are required to monitor their performance, improve their lifetime, and to design engine control systems. This study aims at developing a numerical model of a micro gas turbine intended for prediction and prognostics of engine performance. To build a reliable zero-dimensional model, the available compressor and turbine maps were scaled to the available test bench data with the least squares method, to meet the performance of the engine achieved during bench and flight tests. A steady-state aeroengine model was implemented in the Gas turbine Simulation Program (GSP) and was compared with experimental operating points. The selected flight data were then used as input for the transient engine model. The exhaust gas temperature (EGT) and fuel flow were chosen as the two key parameters to validate the model, comparing the numerical predicted values with the experimental ones. The observed difference between the model and the flight data was lower than 3% for both EGT and fuel flow.openErario M.L.; De Giorgi M.G.; Przysowa R.Erario, M. L.; De Giorgi, M. G.; Przysowa, R

Pharmacokinetics and antinociceptive effects of tramadol and its metabolite O-desmethyltramadol following intravenous administration in sheep

Although sheep are widely used as an experimental model for various surgical procedures there is a paucity of data on the pharmacokinetics and efficacy of analgesic drugs in this species. The aims of this study were to investigate the pharmacokinetics of intravenously (IV) administered tramadol and its active metabolite O-desmethyltramadol (M1) and to assess the mechanical antinociceptive effects in sheep. In a prospective, randomized, blinded study, six healthy adult sheep were given 4 and 6\u2009mg/kg tramadol and saline IV in a cross-over design with a 2-week wash-out period. At predetermined time points blood samples were collected and physiological parameters and mechanical nociceptive threshold (MNT) values were recorded. The analytical determination of tramadol and M1 was performed using high performance liquid chromatography. Pharmacokinetic parameters fitted a two- and a non-compartmental model for tramadol and M1, respectively. Normally distributed data were analysed by a repeated mixed linear model. Plasma concentration vs. time profiles of tramadol and M1 were similar after the two doses. Tramadol and M1 plasma levels decreased rapidly in the systemic circulation, with both undetectable after 6\u2009h following drug administration. Physiological parameters did not differ between groups; MNT values were not statistically significant between groups at any time point. It was concluded that although tramadol and M1 concentrations in plasma were above the human minimum analgesic concentration after both treatments, no mechanical antinociceptive effects of tramadol were reported. Further studies are warranted to assess the analgesic efficacy of tramadol in sheep

Environment-Induced Reversible Modulation of Optical and Electronic Properties of Lead Halide Perovskites and Possible Applications to Sensor Development: A Review

none4siLead halide perovskites are currently widely investigated as active materials in photonic and optoelectronic devices. While the lack of long term stability actually limits their application to commercial devices, several experiments demonstrated that beyond the irreversible variation of the material properties due to degradation, several possibilities exist to reversibly modulate the perovskite characteristics by acting on the environmental conditions. These results clear the way to possible applications of lead halide perovskites to resistive and optical sensors. In this review we will describe the current state of the art of the comprehension of the environmental effects on the optical and electronic properties of lead halide perovskites, and of the exploitation of these results for the development of perovskite-based sensors.openDe Giorgi, ML; Milanese, S; Klini, A; Anni, MDe Giorgi, Ml; Milanese, S; Klini, A; Anni,