Nowadays,artificial intelligence is increasingly used to develop and support progress in many fields and industries,such as finance,medical,transportation…,especially for complex problem resolution.The paper presents...Nowadays,artificial intelligence is increasingly used to develop and support progress in many fields and industries,such as finance,medical,transportation…,especially for complex problem resolution.The paper presents how Airbus Helicopters introduces artificial intelligence in material&process activities,aiming,amongst other things,to reduce the time to market and optimize qualification then certification costs/risks.The paper integrates the results of a proof of concept,achieved on flame resistance behavior of composite materials,related to interior compartment/cargo self-extinguishing requirements(EASA regulation for Rotorcraft CS27/29§853 and 855)and demonstrates how artificial intelligence supports engineering activities.The significant novelty introduced in this work is the use of advanced data-analysis software to support engineers and experts throughout development and qualification steps.Within this study,various artificial intelligence(AI)models have been trained using available experimental datasets from Airbus Helicopters and suppliers as described in Fig.1.Following that,the trained AI model has permitted to identify the most influencing parameters and allowed to focus interest on both critical and optimal setups to help materials experts to reach targets in terms of material performance.In addition,AI model also allows predicting the fire behavior of the material,for resin/fiber reinforcement/fire agent combinations that have not been tested experimentally.This point could be particularly useful for material development purpose.This work demonstrates that,thanks to artificial intelligence support,Airbus Helicopters has improved its understanding of complex phenomenalike flame resistance behavior.Main influencing parameters have been identified for the different tests configurations.And for each parameter,strong/weak ranges have been established.Doing tests in such critical conditions during materials screening phase should help to avoid failing tests in representative helicopter configurations and permit to speed up helicopter development and certification.The presented study also paves the way for material and processes optimizations for helicopter designs.展开更多
Additive manufacturing （AM）--the process of joining materials to make parts from three-dimensional （3D） model data, usually layer upon layer-is an emerging field with a strong need for standardization. Standards s...Additive manufacturing （AM）--the process of joining materials to make parts from three-dimensional （3D） model data, usually layer upon layer-is an emerging field with a strong need for standardization. Standards serve to develop a common set of basic requirements along the value chain for a harmonized supplier-customer relationship. The benefits of standardization are experienced on both the quality and the commercial sides.展开更多
The variations of electrical conductivity and hardness across the thickness of an Al alloy 7010 plate under the temper condition T7651 were investigated. The electrical conductivity and hardness respond in a reciproca...The variations of electrical conductivity and hardness across the thickness of an Al alloy 7010 plate under the temper condition T7651 were investigated. The electrical conductivity and hardness respond in a reciprocal manner. Cross-sectional slices of the plate subjected to re-solutionising/natural ageing and re-solutionising/artificial ageing show the similar tendencies in property changes as in the as-received raw material. This clearly suggests that the property inhomogeneity across the plate thickness is inherent of the manufacturing route. The differences in properties through the plate thickness are due to the changes in the concentrations of the strengthening alloying elements in the solid solution and the associated changes in microstructure; these are believed to be mainly due to the nature of plate solidification and prolonged high temperature during the rolling operation. The combination of electrical conductivity and hardness can be used as an integral quality property indicator for assessing inhomogeneity of thick products.展开更多
Noise generated by civil transport aircraft during take-off and approach-to-land phases of operation is an environmental problem. The aircraft noise problem is firstly reviewed in this article. The review is followed ...Noise generated by civil transport aircraft during take-off and approach-to-land phases of operation is an environmental problem. The aircraft noise problem is firstly reviewed in this article. The review is followed by a description and assessment of a number of sound propagation methods suitable for applications with a background mean flow field pertinent to aircraft noise. Of the three main areas of the noise problem, i.e. generation, propagation, and ra- diation, propagation provides a vital link between near-field noise generation and far-field radiation. Its accurate assessment ensures the overall validity of a prediction model. Of the various classes of propagation equations, linearised Euler equations are often casted in either time domain or frequency domain. The equations are often solved numerically by computational aeroacoustics techniques, bur are subject to the onset of Kelvin-Helmholtz （K-H） instability modes which may ruin the solutions. Other forms of linearised equations, e.g. acoustic perturbation equations have been proposed, with differing degrees of success.展开更多
Thermal expansion coefficients play an important role in the design and analysis of composite structures. A detailed analysis of thermo-mechanical distortion can be performed on microscopic level of a structure. Howev...Thermal expansion coefficients play an important role in the design and analysis of composite structures. A detailed analysis of thermo-mechanical distortion can be performed on microscopic level of a structure. However, for a design and analysis of large structures, the knowledge of effective material properties is essential. Thus, either a theoretical prediction or a numerical estimation of the effective properties is indispensable. In some simple cases, exact analytical solutions for the effective properties can be derived. Moreover, bounds on the effective values exist. However, in dealing with complex heterogeneous composites, numerical methods are becoming increasingly important and more widely used, because of the limiting applicability of the existing (semi-)analytical approaches. In this study, finite-element methods for the calculation of effective thermal expansion coefficients of composites with arbitrary geometrical inclusion configurations are discussed and applied to a heterogeneous lightning protection coating made from Dexmet® copper foil 3CU7-100FA and HexPly® epoxy resin M21. A short overview of some often used (semi-)analytical formulas for effective thermal expansion coefficients of heterogeneous composites is given in addition.展开更多
We introduce a framework for statistical inference of the closure coefficients using machine learning methods.The objective of this framework is to quantify the epistemic uncertainty associated with the closure model ...We introduce a framework for statistical inference of the closure coefficients using machine learning methods.The objective of this framework is to quantify the epistemic uncertainty associated with the closure model by using experimental data via Bayesian statistics.The framework is tailored towards cases for which a limited amount of experimental data is available.It consists of two components.First,by treating all latent variables(non-observed variables)in the model as stochastic variables,all sources of uncertainty of the probabilistic closure model are quantified by a fully Bayesian approach.The probabilistic model is defined to consist of the closure coefficients as parameters and other parameters incorporating noise.Then,the uncertainty associated with the closure coefficients is extracted from the overall uncertainty by considering the noise being zero.The overall uncertainty is rigorously evaluated by using Markov-Chain Monte Carlo sampling assisted by surrogate models.We apply the framework to the Spalart-Allmars one-equation turbulence model.Two test cases are considered,including an industrially relevant full aircraft model at transonic flow conditions,the Airbus XRF1.Eventually,we demonstrate that epistemic uncertainties in the closure coefficients result into uncertainties in flow quantities of interest which are prominent around,and downstream,of the shock occurring over the XRF1 wing.This data-driven approach could help to enhance the predictive capabilities of CFD in terms of reliable turbulence modeling at extremes of the flight envelope if measured data is available,which is important in the context of robust design and towards virtual aircraft certification.The plentiful amount of information about the uncertainties could also assist when it comes to estimating the influence of the measured data on the inferred model coefficients.Finally,the developed framework is flexible and can be applied to different test cases and to various turbulence models.展开更多
Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using fairings to shield components from high speed impingement reduces noise. Furthermore, pe...Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these fairings has been confirmed by flight tests to further enable noise reduction. Following an earlier fundamental study of the application of perforated fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of （perforated） fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1 kHz the noise is shown to increase significantly. Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency noise increase.展开更多
New carbon based coatings have been developed for cutting of light metals such as aluminum. These coatings can be used either directly on the tool or as topcoating combined with another hard base coating. Cutting test...New carbon based coatings have been developed for cutting of light metals such as aluminum. These coatings can be used either directly on the tool or as topcoating combined with another hard base coating. Cutting tests show that the coating gives good performance for materials that tend to stick to the cutting tools, such as aluminium alloys, because of the substantial reduction of appearance of the so-called built-up edge (BUE). This results in a longer life time of the tool and smoother surface finish of the cut made in the work-piece material. Especially in dry machining and deep hole drilling this coating performed very well. An overview of the properties and initial cutting results of this coating will be presented. This paper will also present results from recent industrial field tests carried out by a leading European aerospace manufacturer. Cutting forces, BUE formation and surface roughness data will be presented to explain the cutting process during dry machining.展开更多
Deep learning is driving a radical paradigm shift in wireless communications,all the way from the application layer down to the physical layer.Despite this,there is an ongoing debate as to what additional values artif...Deep learning is driving a radical paradigm shift in wireless communications,all the way from the application layer down to the physical layer.Despite this,there is an ongoing debate as to what additional values artificial intelligence(or machine learning)could bring to us,particularly on the physical layer design;and what penalties there may have?These questions motivate a fundamental rethinking of the wireless modem design in the artificial intelli gence era.Through several physicallayer case studies,we argue for a significant role that machine learning could play,for instance in parallel errorcontrol coding and decoding,channel equalization,interference cancellation,as well as multiuser and multiantenna detection.In addition,we discuss the fundamental bottlenecks of machine learning as well as their potential solutions in this paper.展开更多
The scope of this paper is to provide an E2 Eperspective of health monitoring and management(HMM)and structural health mornitoring(SHM)as an integrated system element of an integrated system health monitoring and mana...The scope of this paper is to provide an E2 Eperspective of health monitoring and management(HMM)and structural health mornitoring(SHM)as an integrated system element of an integrated system health monitoring and management(ISHM)system.The paper will address two main topics:(1)The importance of a diagnostics and prognostic requirements specification to develop an innovative health monitoring and management system;(2)The certification of a health monitoring and management system aiming at a maintenance credit as an integral part of the maintenance strategies.The development of a maintenance program which is based on combinations of different types of strategies(preventive,condition-based maintenance(CBM)and corrective maintenance…)for different subsystems or components and structures of complex systems like an aircraft to achieve the most optimized solution in terms of availability,cost and safety/certification is a real challenge.The maintenance strategy must satisfy the technical-risk and cost feasibility of the maintenance program.展开更多
The primary purpose of this study is to exploit the effect of Earth＇s non-sphericity perturbation, particularly due to the J2 term, in order to optimize the capture sequence of potential orbital debris, that is the c...The primary purpose of this study is to exploit the effect of Earth＇s non-sphericity perturbation, particularly due to the J2 term, in order to optimize the capture sequence of potential orbital debris, that is the cumulative AV associated to the transfers between one object and the others. As results of several researches and model predictions, many international agencies agree that the growing population of objects and debris in LEO （low earth orbits）, will follow a diverging trend in the future. This, in turn, would constitute a serious threat to circum-terrestrial space safety and sustainability. In LEO, the ,J disturbance is prevailing over the others, and it acts by affecting the longitude of the ascending node （Ω）, the argument of perigee （ω） and, accordingly, the true anomaly （v）. Therefore, the goal of optimizing the AV is achieved by taking advantage of the rate of variation of Ω and ω, thereby compensating for the △Ω and △ω, present between the orbital transfer vehicle （chaser） and the debris to be captured （target）. Obviously, the perturbation will lead to favourable variations of the orbital parameters only for some combinations of Ω and ω. Yet the presence of a debris population with random distribution of Ω and ω, makes this application particularly suited to the problem. The single maneuver has been modelled with a 4-impulse time fixed rendezvous and the optimization problem has been addressed by implementing a hybrid evolutionary algorithm, which adopts, in parallel, three different strategies, namely, genetic algorithm, differential evolution and particle swarm optimization.展开更多
A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel production. In this study, photosynthetic effciency, biochemical ...A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel production. In this study, photosynthetic effciency, biochemical pro?les and non-targeted metabolic pro?ling were studied to compare between the nitrogen-replete and deplete conditions. Slowed growth, change in photosynthetic pigments and lowered photosynthetic effciency were observed in response to nitrogen deprivation. Biochemical pro?les of the cultures showed an increased level of carbohydrate, lipids and total fatty acids, while the total soluble protein content was lowered. A trend of fatty acid saturation was observed in the nitrogen-deplete culture with an increase in the level of saturated fatty acids especially C16:0 and C18:0, accompanied by a decrease in proportions of monounsaturated and polyunsaturated fatty acids. Fifty-nine metabolites, including amino acids, lipids, phytochemical compounds, vitamins and cofactors were signi?cantly dysregulated and annotated in this study. Pathway mapping analysis revealed a rewiring of metabolic pathways in the cells, particularly purine, carotenoid, nicotinate and nicotinamide, and amino acid metabolisms. Within the treatment period of nitrogen deprivation, the key processes involved were reshu ? ing of nitrogen from proteins and photosynthetic machinery, together with carbon repartitioning in carbohydrates and lipids.展开更多
Along with the development of big data, various Natural Language Generation systems (NLGs) have recently been developed by different companies. The aim of this paper is to propose a better understanding of how these s...Along with the development of big data, various Natural Language Generation systems (NLGs) have recently been developed by different companies. The aim of this paper is to propose a better understanding of how these systems are designed and used. We propose to study in details one of them which is the NLGs developed by the company Nomao. First, we show the development of this NLGs underlies strong economic stakes since the business model of Nomao partly depends on it. Then, thanks to an eye movement analysis conducted with 28 participants, we show that the texts generated by Nomao’s NLGs contain syntactic and semantic structures that are easy to read but lack socio-semantic coherence which would improve their understanding. From a scientific perspective, our research results highlight the importance of socio-semantic coherence in text-based communication produced by NLGs.展开更多
The present study couples the acid/basis titration and the ICP analysis in order to monitor the concentrations of nitric and hydrofluoric acids, and presents into baths used to pickle alloys of titanium or stainless s...The present study couples the acid/basis titration and the ICP analysis in order to monitor the concentrations of nitric and hydrofluoric acids, and presents into baths used to pickle alloys of titanium or stainless steel, largely employed in the aeronautic industry. The pickling of the alloys releases various metallic cations able to react with HF in order to lead to metal-fluoride complexes and free H+, the last being able to react with the basis. In this study, it was determined: the most significant correlations providing the number of the protons released by the complexation of the metallic cation by the fluoride. The proposed method based on: 1) these correlations;2) the titration pH = f(VKOH) curves;and 3) the content of metallic cations determined by ICP, enables the monitoring of the content of HNO3 and HF into the pickling bath. Assuming that one bath was used for one type of alloy (alloys of Titanium for example, or alloys of stainless steel), then the proposed method appears providing reliable concentration values of both acids as well as metallic cations.展开更多
文摘Nowadays,artificial intelligence is increasingly used to develop and support progress in many fields and industries,such as finance,medical,transportation…,especially for complex problem resolution.The paper presents how Airbus Helicopters introduces artificial intelligence in material&process activities,aiming,amongst other things,to reduce the time to market and optimize qualification then certification costs/risks.The paper integrates the results of a proof of concept,achieved on flame resistance behavior of composite materials,related to interior compartment/cargo self-extinguishing requirements(EASA regulation for Rotorcraft CS27/29§853 and 855)and demonstrates how artificial intelligence supports engineering activities.The significant novelty introduced in this work is the use of advanced data-analysis software to support engineers and experts throughout development and qualification steps.Within this study,various artificial intelligence(AI)models have been trained using available experimental datasets from Airbus Helicopters and suppliers as described in Fig.1.Following that,the trained AI model has permitted to identify the most influencing parameters and allowed to focus interest on both critical and optimal setups to help materials experts to reach targets in terms of material performance.In addition,AI model also allows predicting the fire behavior of the material,for resin/fiber reinforcement/fire agent combinations that have not been tested experimentally.This point could be particularly useful for material development purpose.This work demonstrates that,thanks to artificial intelligence support,Airbus Helicopters has improved its understanding of complex phenomenalike flame resistance behavior.Main influencing parameters have been identified for the different tests configurations.And for each parameter,strong/weak ranges have been established.Doing tests in such critical conditions during materials screening phase should help to avoid failing tests in representative helicopter configurations and permit to speed up helicopter development and certification.The presented study also paves the way for material and processes optimizations for helicopter designs.
文摘Additive manufacturing （AM）--the process of joining materials to make parts from three-dimensional （3D） model data, usually layer upon layer-is an emerging field with a strong need for standardization. Standards serve to develop a common set of basic requirements along the value chain for a harmonized supplier-customer relationship. The benefits of standardization are experienced on both the quality and the commercial sides.
文摘The variations of electrical conductivity and hardness across the thickness of an Al alloy 7010 plate under the temper condition T7651 were investigated. The electrical conductivity and hardness respond in a reciprocal manner. Cross-sectional slices of the plate subjected to re-solutionising/natural ageing and re-solutionising/artificial ageing show the similar tendencies in property changes as in the as-received raw material. This clearly suggests that the property inhomogeneity across the plate thickness is inherent of the manufacturing route. The differences in properties through the plate thickness are due to the changes in the concentrations of the strengthening alloying elements in the solid solution and the associated changes in microstructure; these are believed to be mainly due to the nature of plate solidification and prolonged high temperature during the rolling operation. The combination of electrical conductivity and hardness can be used as an integral quality property indicator for assessing inhomogeneity of thick products.
文摘Noise generated by civil transport aircraft during take-off and approach-to-land phases of operation is an environmental problem. The aircraft noise problem is firstly reviewed in this article. The review is followed by a description and assessment of a number of sound propagation methods suitable for applications with a background mean flow field pertinent to aircraft noise. Of the three main areas of the noise problem, i.e. generation, propagation, and ra- diation, propagation provides a vital link between near-field noise generation and far-field radiation. Its accurate assessment ensures the overall validity of a prediction model. Of the various classes of propagation equations, linearised Euler equations are often casted in either time domain or frequency domain. The equations are often solved numerically by computational aeroacoustics techniques, bur are subject to the onset of Kelvin-Helmholtz （K-H） instability modes which may ruin the solutions. Other forms of linearised equations, e.g. acoustic perturbation equations have been proposed, with differing degrees of success.
文摘Thermal expansion coefficients play an important role in the design and analysis of composite structures. A detailed analysis of thermo-mechanical distortion can be performed on microscopic level of a structure. However, for a design and analysis of large structures, the knowledge of effective material properties is essential. Thus, either a theoretical prediction or a numerical estimation of the effective properties is indispensable. In some simple cases, exact analytical solutions for the effective properties can be derived. Moreover, bounds on the effective values exist. However, in dealing with complex heterogeneous composites, numerical methods are becoming increasingly important and more widely used, because of the limiting applicability of the existing (semi-)analytical approaches. In this study, finite-element methods for the calculation of effective thermal expansion coefficients of composites with arbitrary geometrical inclusion configurations are discussed and applied to a heterogeneous lightning protection coating made from Dexmet® copper foil 3CU7-100FA and HexPly® epoxy resin M21. A short overview of some often used (semi-)analytical formulas for effective thermal expansion coefficients of heterogeneous composites is given in addition.
文摘We introduce a framework for statistical inference of the closure coefficients using machine learning methods.The objective of this framework is to quantify the epistemic uncertainty associated with the closure model by using experimental data via Bayesian statistics.The framework is tailored towards cases for which a limited amount of experimental data is available.It consists of two components.First,by treating all latent variables(non-observed variables)in the model as stochastic variables,all sources of uncertainty of the probabilistic closure model are quantified by a fully Bayesian approach.The probabilistic model is defined to consist of the closure coefficients as parameters and other parameters incorporating noise.Then,the uncertainty associated with the closure coefficients is extracted from the overall uncertainty by considering the noise being zero.The overall uncertainty is rigorously evaluated by using Markov-Chain Monte Carlo sampling assisted by surrogate models.We apply the framework to the Spalart-Allmars one-equation turbulence model.Two test cases are considered,including an industrially relevant full aircraft model at transonic flow conditions,the Airbus XRF1.Eventually,we demonstrate that epistemic uncertainties in the closure coefficients result into uncertainties in flow quantities of interest which are prominent around,and downstream,of the shock occurring over the XRF1 wing.This data-driven approach could help to enhance the predictive capabilities of CFD in terms of reliable turbulence modeling at extremes of the flight envelope if measured data is available,which is important in the context of robust design and towards virtual aircraft certification.The plentiful amount of information about the uncertainties could also assist when it comes to estimating the influence of the measured data on the inferred model coefficients.Finally,the developed framework is flexible and can be applied to different test cases and to various turbulence models.
文摘Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these fairings has been confirmed by flight tests to further enable noise reduction. Following an earlier fundamental study of the application of perforated fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of （perforated） fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1 kHz the noise is shown to increase significantly. Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency noise increase.
基金the financial support from the European Commission.(GRD1-2001-40514/G5RD-CT2002-00672)
文摘New carbon based coatings have been developed for cutting of light metals such as aluminum. These coatings can be used either directly on the tool or as topcoating combined with another hard base coating. Cutting tests show that the coating gives good performance for materials that tend to stick to the cutting tools, such as aluminium alloys, because of the substantial reduction of appearance of the so-called built-up edge (BUE). This results in a longer life time of the tool and smoother surface finish of the cut made in the work-piece material. Especially in dry machining and deep hole drilling this coating performed very well. An overview of the properties and initial cutting results of this coating will be presented. This paper will also present results from recent industrial field tests carried out by a leading European aerospace manufacturer. Cutting forces, BUE formation and surface roughness data will be presented to explain the cutting process during dry machining.
基金supported in part by EU H2020 5G-DRIVE Programme under Grant No.814956in part by Airbus Defense and Spacein part by the UK 5G Innovation Centre(5GIC).
文摘Deep learning is driving a radical paradigm shift in wireless communications,all the way from the application layer down to the physical layer.Despite this,there is an ongoing debate as to what additional values artificial intelligence(or machine learning)could bring to us,particularly on the physical layer design;and what penalties there may have?These questions motivate a fundamental rethinking of the wireless modem design in the artificial intelli gence era.Through several physicallayer case studies,we argue for a significant role that machine learning could play,for instance in parallel errorcontrol coding and decoding,channel equalization,interference cancellation,as well as multiuser and multiantenna detection.In addition,we discuss the fundamental bottlenecks of machine learning as well as their potential solutions in this paper.
文摘The scope of this paper is to provide an E2 Eperspective of health monitoring and management(HMM)and structural health mornitoring(SHM)as an integrated system element of an integrated system health monitoring and management(ISHM)system.The paper will address two main topics:(1)The importance of a diagnostics and prognostic requirements specification to develop an innovative health monitoring and management system;(2)The certification of a health monitoring and management system aiming at a maintenance credit as an integral part of the maintenance strategies.The development of a maintenance program which is based on combinations of different types of strategies(preventive,condition-based maintenance(CBM)and corrective maintenance…)for different subsystems or components and structures of complex systems like an aircraft to achieve the most optimized solution in terms of availability,cost and safety/certification is a real challenge.The maintenance strategy must satisfy the technical-risk and cost feasibility of the maintenance program.
文摘The primary purpose of this study is to exploit the effect of Earth＇s non-sphericity perturbation, particularly due to the J2 term, in order to optimize the capture sequence of potential orbital debris, that is the cumulative AV associated to the transfers between one object and the others. As results of several researches and model predictions, many international agencies agree that the growing population of objects and debris in LEO （low earth orbits）, will follow a diverging trend in the future. This, in turn, would constitute a serious threat to circum-terrestrial space safety and sustainability. In LEO, the ,J disturbance is prevailing over the others, and it acts by affecting the longitude of the ascending node （Ω）, the argument of perigee （ω） and, accordingly, the true anomaly （v）. Therefore, the goal of optimizing the AV is achieved by taking advantage of the rate of variation of Ω and ω, thereby compensating for the △Ω and △ω, present between the orbital transfer vehicle （chaser） and the debris to be captured （target）. Obviously, the perturbation will lead to favourable variations of the orbital parameters only for some combinations of Ω and ω. Yet the presence of a debris population with random distribution of Ω and ω, makes this application particularly suited to the problem. The single maneuver has been modelled with a 4-impulse time fixed rendezvous and the optimization problem has been addressed by implementing a hybrid evolutionary algorithm, which adopts, in parallel, three different strategies, namely, genetic algorithm, differential evolution and particle swarm optimization.
基金Supported by the Aerospace Malaysia Innovation Centre&Airbus Group Innovation(No.PV001-2013)the Ministry of Higher Education Malaysia HICoE grant(No.IOES-2014H)+1 种基金the Fundamental Research Grant Scheme(No.FP048-2016)the University of Malaya UMCoE RU Grant(No.RU009H-2015)
文摘A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel production. In this study, photosynthetic effciency, biochemical pro?les and non-targeted metabolic pro?ling were studied to compare between the nitrogen-replete and deplete conditions. Slowed growth, change in photosynthetic pigments and lowered photosynthetic effciency were observed in response to nitrogen deprivation. Biochemical pro?les of the cultures showed an increased level of carbohydrate, lipids and total fatty acids, while the total soluble protein content was lowered. A trend of fatty acid saturation was observed in the nitrogen-deplete culture with an increase in the level of saturated fatty acids especially C16:0 and C18:0, accompanied by a decrease in proportions of monounsaturated and polyunsaturated fatty acids. Fifty-nine metabolites, including amino acids, lipids, phytochemical compounds, vitamins and cofactors were signi?cantly dysregulated and annotated in this study. Pathway mapping analysis revealed a rewiring of metabolic pathways in the cells, particularly purine, carotenoid, nicotinate and nicotinamide, and amino acid metabolisms. Within the treatment period of nitrogen deprivation, the key processes involved were reshu ? ing of nitrogen from proteins and photosynthetic machinery, together with carbon repartitioning in carbohydrates and lipids.
文摘Along with the development of big data, various Natural Language Generation systems (NLGs) have recently been developed by different companies. The aim of this paper is to propose a better understanding of how these systems are designed and used. We propose to study in details one of them which is the NLGs developed by the company Nomao. First, we show the development of this NLGs underlies strong economic stakes since the business model of Nomao partly depends on it. Then, thanks to an eye movement analysis conducted with 28 participants, we show that the texts generated by Nomao’s NLGs contain syntactic and semantic structures that are easy to read but lack socio-semantic coherence which would improve their understanding. From a scientific perspective, our research results highlight the importance of socio-semantic coherence in text-based communication produced by NLGs.
文摘The present study couples the acid/basis titration and the ICP analysis in order to monitor the concentrations of nitric and hydrofluoric acids, and presents into baths used to pickle alloys of titanium or stainless steel, largely employed in the aeronautic industry. The pickling of the alloys releases various metallic cations able to react with HF in order to lead to metal-fluoride complexes and free H+, the last being able to react with the basis. In this study, it was determined: the most significant correlations providing the number of the protons released by the complexation of the metallic cation by the fluoride. The proposed method based on: 1) these correlations;2) the titration pH = f(VKOH) curves;and 3) the content of metallic cations determined by ICP, enables the monitoring of the content of HNO3 and HF into the pickling bath. Assuming that one bath was used for one type of alloy (alloys of Titanium for example, or alloys of stainless steel), then the proposed method appears providing reliable concentration values of both acids as well as metallic cations.
