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Littérature scientifique sur le sujet « Hybride uav »

Auteur : Grafiati

Publié le 1 février 2025

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Articles de revues sur le sujet "Hybride uav"

RAMESH, P. S., et J. V. MURUGA LAL JEYAN. « Comparative Analysis of Fixed-Wing, Rotary-Wing and Hybrid Mini Unmanned Aircraft Systems (UAS) from the Applications Perspective ». INCAS BULLETIN 14, n^o 1 (7 mars 2022) : 137–51. http://dx.doi.org/10.13111/2066-8201.2022.14.1.12.

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Mini Unmanned Aircraft Systems (UAS) present distinct design challenges due to their man-portable, field-deployable profile. The implications of various unmanned aerial vehicle (UAV) design configurations for Mini UAS applications are discussed in this study. Fixed-wing, rotary-wing, and hybrid Mini UAS design configurations are analysed and compared based on performance parameters specified by various manufacturers to assess appropriateness for military and civil applications. Mini UAS designed for military applications can meet most requirements in the civil domain. However, the reverse is seldom feasible because of several restrictions imposed by combat conditions. Fixed-wing Mini UAS have significant limitations for military applications, primarily because of launch and recovery considerations. For civil applications, the fixed-wing configuration provides multiple advantages. The benefit of the rotary-wing configuration's compact size to overcome various battlespace restrictions for military applications does not translate to other performance parameters, and this is a serious limitation for its applications. The hybrid profile has significant design advantages that can be leveraged for both military and civil applications. The interrelation between design, end-use requirements and terrain restrictions presented in the paper provides an insight into the implications of the design configurations of Mini UAS for various applications.

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Xu, Ronghua, Sixiao Wei, Yu Chen, Genshe Chen et Khanh Pham. « LightMAN : A Lightweight Microchained Fabric for Assurance- and Resilience-Oriented Urban Air Mobility Networks ». Drones 6, n^o 12 (16 décembre 2022) : 421. http://dx.doi.org/10.3390/drones6120421.

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Rapid advancements in the fifth generation (5G) communication technology and mobile edge computing (MEC) paradigm have led to the proliferation of unmanned aerial vehicles (UAV) in urban air mobility (UAM) networks, which provide intelligent services for diversified smart city scenarios. Meanwhile, the widely deployed Internet of drones (IoD) in smart cities has also brought up new concerns regarding performance, security, and privacy. The centralized framework adopted by conventional UAM networks is not adequate to handle high mobility and dynamicity. Moreover, it is necessary to ensure device authentication, data integrity, and privacy preservation in UAM networks. Thanks to its characteristics of decentralization, traceability, and unalterability, blockchain is recognized as a promising technology to enhance security and privacy for UAM networks. In this paper, we introduce LightMAN, a lightweight microchained fabric for data assurance and resilience-oriented UAM networks. LightMAN is tailored for small-scale permissioned UAV networks, in which a microchain acts as a lightweight distributed ledger for security guarantees. Thus, participants are enabled to authenticate drones and verify the genuineness of data that are sent to/from drones without relying on a third-party agency. In addition, a hybrid on-chain and off-chain storage strategy is adopted that not only improves performance (e.g., latency and throughput) but also ensures privacy preservation for sensitive information in UAM networks. A proof-of-concept prototype is implemented and tested on a micro-air–vehicle link (MAVLink) simulator. The experimental evaluation validates the feasibility and effectiveness of the proposed LightMAN solution.

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Wu, Yan, Dejin Kong, Qian Wang et Gang Li. « Performance Analysis of UAV-Assisted Hybrid FSO/RF Communication Systems under Various Weather Conditions ». Sensors 23, n^o 17 (3 septembre 2023) : 7638. http://dx.doi.org/10.3390/s23177638.

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Nowadays, unmanned aerial vehicle (UAV) communication systems are commonly considered as one of the key enabling technologies for 6G. The hybrid free space optical (FSO)/radio frequency (RF) system has the advantages of both FSO and RF links to improve communication system performance, and the relay-assisted system adopts multi-hop transmission and cooperative diversity methods to extend communication coverage. Thus, a joint consideration of UAV-assistedUAV assisted relay in hybrid FSO/RF transmission is meaningful. In this paper, we aim to analyze the performance of UAV-assisted multi-hop parallel hybrid FSO/RF communication systems with and without pointing errors (PE) in terms of Bit Error Rate (BER) and outage probability. In our considered system, the FSO sub-link adopts the Exponential Weibull turbulence model and the RF sub-link suffers the Nakagami fading model. With these, new mathematical formulas of both BER and outage probability are derived under the UAV-assisted hybrid FSO/RF with different modulation methods. Through numerical evaluationnumerical simulations, the performances of UAV-assisted hybrid FSO/RF systems are analyzed under different weather conditions, modulation methods, optical receiver aperture, RF fading parameters, pointing errors, and relay structures. The results demonstrate that (1) compared to hybrid FSO/RF direct links, UAV-assisted hybrid FSO/RF systems can further improve system performance; (2) the performance of UAV-assisted hybrid FSO/RF systems varies with different relay structures; (3) large receiver aperture and RF fading parameters can further improve the communication performance of hybrid FSO/RF direct links and UAV-assisted hybrid FSO/RF systems.

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Gorodetskiy, A., et M. Grabovskiy. « Technological qualities of root crops and economic efficiency of growing sugar beet hybrids by the KWS company in the conditions of "Rasavske" Ltd. of Kaharlyk district, Kiev region ». Agrobìologìâ, n^o 2(142) (22 décembre 2018) : 34–39. http://dx.doi.org/10.33245/2310-9270-2018-142-2-34-39.

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The paper deals with the results of research on the study of the technological traits changes in foreign hybrids root crops of the KWS company sugar beet enterprises under the influence of long-term storage and their economic efficiency. The conducted researches are especially relevant due to insufficiently studied issues of changes in the technological traits of the root crops of the newest hybrids during their storage in the crutches on the field or at the sugar factory. Estimation of new hybrids of sugar beet by regions of the Forest-steppe allows to predict the genetically determined degree of their plasticity and stability both in the yield and the quality. Hybrids with higher resistance to extreme temperatures are especially valuable. The researches were carried out during 2014–2015 at the "Rasavske" Ltd. of Kaharlyk district, Kyiv region. The sugar content in the root crops increased from 1.6% in the Alyona hybrid to 5.9 % in the Daria hybrid and 6.1 % in the Coryda hybrid, due to the loss of moisture during their prolonged storage. The content of soluble dry matter in the root crops increased from 1.7 % in the Alyona hybrid to 7.7 % in the Coryda hybrid for the same reason. The conducted calculations of cell juice quality showed that long-term storage resulted in the highest growth of this indicator by 8.2 % in the Cesaria hybrid and by 7.5 % in the Acatsia hybrid. In the Alyona hybrid, the growth rate of cell juice quality was only 0.8 %, while the Corida hybrid had the quality of the previous level. In the Olesya hybrid, this indicator decreased by 1.8 % compared with the previous determination period (October 10). The costs of growing root crops ranged from 17,859 to 20,726 UAH/ha. The highest profit was 17435 UAH/ha and the profitability level was 86.3 % for the Alyona hybrid, while the lowest economic efficiency figures were for the profit of 10,201 UAH/ha and the profitability level of 53.7 % in the Carmelite hybrid. The highest rates of the technological traits of root crops during the long-term storage of sugar beet were determined in the Alyona hybrid. The highest yield of root crops was in the Daria hybrid – 79.8 t/ha. According to the indicators of economic efficiency the Alona hybrid was the best in terms of profit (17,435 UAH/ha) and the profitability level of 86.3 %. Key words: sugar beet, hybrids, productivity, yield, sugar content, technological traits, profit, profitability level.

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Goh, Chi Yen, Chee Yen Leow et Rosdiadee Nordin. « Energy Efficiency of Unmanned Aerial Vehicle with Reconfigurable Intelligent Surfaces : A Comparative Study ». Drones 7, n^o 2 (31 janvier 2023) : 98. http://dx.doi.org/10.3390/drones7020098.

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Unmanned aerial vehicles (UAVs) and reconfigurable intelligent surfaces (RIS) are the promising emerging technologies proposed for the 6th-Generation (6G) network to improve the capacity, reliability, and coverage of wireless communications. By integrating the UAV with RIS (RIS-UAV), the three-dimensional (3D) mobility of the UAV can be leveraged to establish strong line-of-sight links with the ground nodes, while the RIS intelligently reflect the signals toward the desired directions. However, the existing literature on RIS-UAV systems mainly assumes the use of passive elements, which suffers from the double path-loss problem. The use of active elements in RIS, which could improve the reflected link performance at the cost of increased energy consumption, has not been considered for the RIS-UAV system. Further, the energy efficiency of a RIS-UAV with active elements remains as an open direction because there is a need to investigate the feasibility of either an active or hybrid RIS-UAV implementation. This paper proposes active and hybrid RIS-UAVs and investigates the energy efficiencies of active and hybrid RIS-UAVs in comparison with existing passive RIS-UAVs and conventional UAV relays. The numerical results reveal that the proposed hybrid and active RIS-UAV relaying schemes can provide up to 14 times and 26 times improvement as compared to the passive RIS-UAV, respectively. As opposed to the active RIS-UAV that requires a larger power budget, half-duplex UAV relays that have a lower spectral efficiency, and full-duplex UAV relays that suffer from self-interference, the hybrid RIS-UAV emerges as a promising option to assist the ground communication system.

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Xia, Chuying, Xin Fu et Shijie Zhai. « Research on power configuration scheme of parallel hybrid oil-electric power system for tilt- rotor UAV ». Journal of Physics : Conference Series 2478, n^o 10 (1 juin 2023) : 102028. http://dx.doi.org/10.1088/1742-6596/2478/10/102028.

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Abstract The tilt-rotor UAV is a new type of unmanned aerial vehicle that has both the hovering capability of a rotary-wing UAV and the high-speed cruising flight capability of a fixed- wing UAV. Through the tilting system of the UAV, different working states can be switched: during the take-off and landing phases, the rotor axis is perpendicular to the ground, thus realizing aerial hovering, forward and backward flight and side flight. In the cruise flight phase, the rotor axis is perpendicular to the flight direction, thus achieving the flight attitude of a fixed-wing aircraft. The hybrid power system is a composite power system that combines fuel power with electrical power. By applying the oil-electric hybrid power system on the tilt-rotor UAV, it can combine the advantages of long range and long range of fuel power and low noise and pollution of electric power. In this paper, the tilt-rotor UAV parallel oil-electric hybrid power system power configuration scheme is studied. Firstly, the three operating modes of the oil-electric hybrid power system are introduced, including hybrid drive, drive charging and pure oil drive. The power requirements of the tilt-rotor UAV in vertical takeoff and landing, fixed-wing cruise and other flight phases are calculated, and the correspondence between the UAV flight status and the hybrid power system operation mode is established according to the working characteristics of the tilt-rotor UAV and the hybrid power system operation mode. The power configuration method for each flight phase is finally determined, and the process of the overall power configuration realization of the threshold value is described in detail.

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Radócz, László, Atala Szabó, András Tamás, Árpád Illés, Csaba Bojtor, Péter Ragán, Attila Vad, Adrienn Széles, Endre Harsányi et László Radócz. « Investigation of the Detectability of Corn Smut Fungus (Ustilago maydis DC. Corda) Infection Based on UAV Multispectral Technology ». Agronomy 13, n^o 6 (30 mai 2023) : 1499. http://dx.doi.org/10.3390/agronomy13061499.

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Corn smut fungus (Ustilago maydis [DC.] Corda) is a globally widespread pathogen affecting both forage and sweet maize hybrids, with higher significance in sweet maize. Remote sensing technologies demonstrated favorable results for disease monitoring on the field scale. The study focused on the changes in vegetation index (VI) values influenced by the pathogen. In this study, four hybrids, two forage maize and two sweet maize hybrids were examined. Artificial infection was carried out at three different doses: a low (2500 sporidium number/mL), medium (5000 sporidium number/mL) and high dose (10,000 sporidium number/mL) with a non-infected control plot for each hybrid. The experimental plots were monitored using a multispectral UAV sensor of five monochrome channels on three different dates, i.e., 7, 14 and 21 days after infection. Five different indices (NDVI, GNDVI, ENDVI, LCI, and NDRE) were determined in Quantum GIS 3.20. The obtained results demonstrated that the infection had a significant effect on the VI values in sweet maize hybrids. A high-dose infection in the Dessert R 73 hybrid resulted in significantly lower values compared to the non-infected hybrids in three indices (NDVI, LCI and GNDVI). In the case of the NOA hybrids, GNDVI and ENDVI were able to show significant differences between the values of the infection levels.

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Tomashuk, O. « Economic efficiency of growing corn hybrids for grain by different soil tillage technologies ». Feeds and Feed Production, n^o 87 (7 juin 2019) : 144–50. http://dx.doi.org/10.31073/kormovyrobnytstvo201987-22.

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The article presents indicators of the economic efficiency of various technologies for growing corn hybrids for grain. The results of a 3-year field trial in maize of various maturity groups grown in the right-bank Forest-Steppe under different soil tillage models are highlighted. The costs of corn grain production under conventional cultivation and deep tillage, which averages 10,330 UAH per hectare of cropping area is studied. The rate of expenditures clearly correlated with the rate of hybrid productivity. High net profit of 20,119 UAH per hectare is shown when planting mid-ripening hybrid «Adevei» using intensification of the technological process. For other hybrids, conditionally net income fluctuated at the rate of 17,000 UAH per hectare. It is established that during the cultivation of corn for grain according to conventional technology and No-till, hybrids «Adevei» and «LG 3232» were characterized by the best indicators of economic efficiency.

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Farid Danial Norazman, Ahmad Hamdan Ariffin, Mohd Rahmat Firman Sahifulddin et Irfan Abdul Rahim. « Investigation of Empennage Location Effect to the Unmanned Aerial Vehicle (UAV) Structure Characteristic ». Journal of Advanced Research in Applied Mechanics 113, n^o 1 (22 janvier 2024) : 1–12. http://dx.doi.org/10.37934/aram.113.1.112.

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Over the past few decades, unmanned aerial vehicles, commonly known as UAVs, have been widely used in a number of consumer and military applications, such as surveillance, tracking, monitoring, and aerial photography. Fixed-wing and rotary UAVs are the two primary categories in UAV. Interestingly, the hybridization of fixed-wing and rotary UAV gives better performance in terms of energy consumption and the needs of runaway. Designing new hybrid fixed wing-rotary UAV or hybrid vertical take-off and landing (VTOL) is challenging especially to identify the critical location in the UAV and material selection. Therefore, the objective of this research is to study the effect of empennage location and material selection on the structural strength of a hybrid VTOL UAV. The SolidWorks software was employed to design a 3D model of the UAV with different empennage locations, as well as perform a simulation of the structural strength of fibre glass, carbon fibre and kenaf for the hybrid VTOL UAV. The simulation analysis presents stress (Von Mises). The results show that the fibre glass (4.342 N/m2) at top empennage gives the best performance as compared to other parameters. In conclusion, this study is necessary to give a better picture of structural strength of composite materials and best design location in hybrid VTOL UAV for future research.

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Shen, Xueqiang, Jiwei Fan et Haiqing Wang. « Design and Simulation of Eight-Rotor Unmanned Aerial Vehicle Based on Hybrid Control System ». International Journal of Aerospace Engineering 2018 (5 décembre 2018) : 1–10. http://dx.doi.org/10.1155/2018/5306125.

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In order to control the position and attitude of unmanned aerial vehicle (UAV) better in different environments, this study proposed a hybrid control system with backstepping and PID method for eight-rotor UAV in different flight conditions and designed a switching method based on altitude and attitude angle of UAV. The switched process of hybrid controller while UAV taking off, landing, and disturbance under the gust is verified in MATLAB/Simulink. A set of appropriate controllers always matches to the flight of UAV in different circumstances, which can speed up the system response and reduce the steady-state error to improve stability. The simulation results show that the hybrid control system can suppress the drift efficiently under gusts, enhance the dynamic performance and stability of the system, and meet the position and attitude of flight control requirements.

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Thèses sur le sujet "Hybride uav"

Sansou, Florian. « Contrôle actif d'un micro-drone convertible face à la turbulence ». Electronic Thesis or Diss., Toulouse, École nationale de l’aviation civile, 2024. https://enac.hal.science.

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L'objectif du projet CATMAV est d'étudier le contrôle d'un micro-drone de type « tilt-wing » en environnement turbulent. La configuration générale est basée sur le principe d'un drone avion avec un fuselage classique dont l'aile est capable de basculer au cours du vol. Ce type de configuration convertible a de nombreux atouts dont une capacité de décollage et atterrissage vertical tout en gardant de bonnes performances en vol de croisière. Une importante limitation est la robustesse en présence de turbulences, notamment en milieu urbain, montagneux ou maritime. Une des innovations de ce projet est l'utilisation d'une sonde capable de mesurer le vecteur vent local ainsi que les turbulences. Ce capteur est en cours de développement au sein du programme drone de l'Enac
This PhD thesis aims at studying the control of a tilt-wing mini-UAV in turbulent environments. This type of configuration has many benefits with the capability to takeoff and land vertically while keeping good flight performances and the main body of the plane stays horizontal. However, it may be highly sensitive to wind gust and turbulences, especially in urban, mountain or maritime areas. The main objective is to contribute to the safety and flight performances of this type of flying platform. The UAV Program at Enac is currently developing a 5-hole probe to be used as a local wind and turbulence sensor. The work will concentrate on the integration of these aerological data into the control laws to achieve a faster and better dynamic response to gusts

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Hung, David, Kennon McKeever et Ricardo Ramirez. « HYBRID AUTOMATED UAV TARGET RECOGNITION SYSTEM ». International Foundation for Telemetering, 2017. http://hdl.handle.net/10150/626985.

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Accurate image classification is one of the core challenges in computer vision. At the annual AUVSI SUAS competition, this challenge is faced in the form of ground target classification from an unmanned aerial vehicle (UAV). Additionally, due to the constraints imposed by the UAV platform, the system design must consider factors such as size, weight, and power consumption. To meet performance requirements while respecting such limitations, the system was broken into two subsystems: an onboard subsystem and a ground based subsystem. This design allows the onboard subsystem, comprised of a DSLR camera and single-board computer, to capture ground target images and perform rudimentary target detection and localization. For further processing and to ultimately classify the targets in each image, data packets are sent to the ground-based subsystem via a 5 GHz wireless link. Convolutional networks are utilized on the ground to achieve state-of-the-art accuracy in classification.

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Song, H. « A hybrid martian VTOL UAV : design, dynamics and control ». Thesis, University of Surrey, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493040.

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Meyer, Danielle L. « Energy Optimization of a Hybrid Unmanned Aerial Vehicle (UAV) ». The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523493111005807.

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Thotakura, Sushant. « CO-Design of a Group-5 Power-Split Hybrid Electric UAV ». University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613750848692102.

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Sommer-Marquez, Alicia Estela. « Retención de clorofila en Hidrotalcitas ». Thesis, Montpellier, Ecole nationale supérieure de chimie, 2013. http://www.theses.fr/2013ENCM0002/document.

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Dans les expériences modélisant la photosynthèse, une bonne dispersion des molécules de chlorophylle est requise. Afin d'obtenir cette bonne dispersion, une solution consiste à les ancrer à un hôte. Dans cette étude, des nouveaux matériaux hybrides sont synthétisés en utilisant des hydrotalcites et un dérivé de la chlorophylle : la chlorophylline. La chlorophylline est incorporée et dispersée dans les hydrotalcites par co-précipitation ou pendant la reconstruction des hydrotalcites. Dans cette thèse est également discuté l'effet d'une irradiation par micro-onde. Dans tous les cas sont obtenus des matériaux stables, où les molécules de chlorophylline sont isolées et liées aux hydrotaltices par des liaisons avec les groupes hydroxy OH. Dans ce travail, de nouveaux matériaux sont synthétisés en utilisant les hydrotalcites et la chlorophylle a. Dans ce cas là, il est mis en valeur que la stabilisation de la chlorophylle a peut dépendre du support, à la fois par la nature et le rapport des métaux constituants les hydrotalcites. Ces matériaux hybrides obtenus (chlorophylle a/hydrotalcites) sont également stables. Ces matériaux ont été testés par lixiviation à l'acétone. Dans tous les cas, les composés lixiviés sont de la chlorophylle a, montrant ainsi que la nature et la composition des molécules sont préservées même après trente jours, bien qu'il soit à noter que dans le cas des hydrotalcites Ni/Al une faible fraction de la chlorophylle est décomposée en phéophytine. Finalement, bien que les hydrotalcites soient des composés relativement simples, ils s'avèrent tout à fait adaptés pour empêcher la dégradation des molécules de chlorophylle
In experiments modeling photosynthesis, well dispersed chlorophyll molecules are required. A solution could be to anchor them on some host. In this work, new hybrid materials are synthesized using hydrotalcite and a chlorophyll derivative : chlorophyllin. Chlorophyllin is incorporated and dispersed in hydrotalcite through simultaneous precipitation or during hydrotalcite reconstruction. The effect of microwave irradiation on the crystallization step is discussed. In all cases stable materials are obtained, chlorophyllin molecules are isolated and bonded through hydrotalcite OH groups. Also new hybrid materials are synthesized using hydrotalcites and chlorophyll a. The effect of the support composition on chlorophyll a stabilization is discussed. The stability of the adsorbed chlorophyll a is affected by the support nature and the metal ratio of the hydrotalcite. The obtained hybrid compounds (chlorophyll a on hydrotalcite) are stable. Those hybrids were tested in lixiviation with acetone. In all cases, the lixiviated compound was chlorophyll a showing that the composition and nature of the molecule was preserved even after thirty days, although Ni/Al hydrotalcites decomposed a small fraction of the chlorophyll to pheophytin. Hydrotalcites being basic compounds turn out to be an adequate material to avoid degradation of chlorophyll molecules

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Glassock, Richard R. « Design, modelling and measurement of hybrid powerplant for unmanned aerial vehicles (UAVs) ». Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/61052/1/Richard_Glassock_Thesis.pdf.

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The success or effectiveness for any aircraft design is a function of many trade-offs. Over the last 100 years of aircraft design these trade-offs have been optimized and dominant aircraft design philosophies have emerged. Pilotless aircraft (or uninhabited airborne systems, UAS) present new challenges in the optimization of their configuration. Recent developments in battery and motor technology have seen an upsurge in the utility and performance of electric powered aircraft. Thus, the opportunity to explore hybrid-electric aircraft powerplant configurations is compelling. This thesis considers the design of such a configuration from an overall propulsive, and energy efficiency perspective. A prototype system was constructed using a representative small UAS internal combustion engine (10cc methanol two-stroke) and a 600W brushless Direct current (BLDC) motor. These components were chosen to be representative of those that would be found on typical small UAS. The system was tested on a dynamometer in a wind-tunnel and the results show an improvement in overall propulsive efficiency of 17% when compared to a non-hybrid powerplant. In this case, the improvement results from the utilization of a larger propeller that the hybrid solution allows, which shows that general efficiency improvements are possible using hybrid configurations for aircraft propulsion. Additionally this approach provides new improvements in operational and mission flexibility (such as the provision of self-starting) which are outlined in the thesis. Specifically, the opportunity to use the windmilling propeller for energy regeneration was explored. It was found (in the prototype configuration) that significant power (60W) is recoverable in a steep dive, and although the efficiency of regeneration is low, the capability can allow several options for improved mission viability. The thesis concludes with the general statement that a hybrid powerplant improves the overall mission effectiveness and propulsive efficiency of small UAS.

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Arantes, Márcio da Silva. « Hybrid qualitative state plan problem and mission planning with UAVs ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-05122017-083420/.

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This paper aims to present the thesis developed in the Doctoral Programin Computer Science and Computational Mathematics of the ICMC/USP. The thesis theme seeks to advance the state of the art by solving the problems of scalability and representation present in mission planning algorithms for Unmanned Aerial Vehicle (UAV). Techniques based on mathematical programming and evolutionary computation are proposed. Articles have been published, submitted or they are in final stages of preparation.These studies report the most significant advances in the representation and scalability of this problem. Mission planners worked on the thesis deal with stochastic problems in non-convex environments,where collision risks or failures in mission planning are treated and limited to a tolerated value. The advances in the representation allowed to solve violations in the risks present in the original literature modeling, besides making the models more realistic when incorporating aspects such as effects of the air resistance. Efficient mathematical modeling techniques allowed to advance from a Mixed Integer Nonlinear Programming (MINLP) model, originally proposed in the literature, to a Mixed Integer Linear Programming (MILP) problem. Modeling as a MILP led to problem solving more efficiently through the branch-and-algorithm. The proposed new representations resulted in improvements from scalability, solving more complex problems within a shorter computational time. In addition, advances in scalability are even more effective when techniques combining mathematical programming and metaheuristics have been applied to the problem.
O presente documento tem por objetivo apresentar a tese desenvolvida no Programade Doutorado em Ciência da Computação e Matemática Computacional do ICMC/USP. O tema da tese busca avançar o estado da arte ao resolver os problemas de escalabilidade e representação presentes em algoritmos de planejamento para missões com Veículos Aéreos Não Tripulados (VANTs). Técnicas baseadas em programação matemática e computação evolutiva são propostas. Artigos foram publicados, submetidos ou se encontram em fase final de elaboração. Esses trabalhos reportamos avanços mais significativos obtidos na representação e escalabilidade deste problema.Os planejadores de missão trabalhados na tese lidam com problemas estocásticos em ambientes não convexos, onde os riscos de colisão ou falhas no planejamento da missão são tratados e limitados a um valor tolerado. Os avanços na representação permitiram solucionar violações nos riscos presentes na modelagem original, além de tornar os modelos mais realistas ao incorporar aspectos como efeitos da resistência do ar. Para isso, técnicas eficientes de modelagem matemática permitiram avançar de um modelo de Programação Não-Linear Inteira Mista(PNLIM), originalmente proposto na literatura, para um problema de Programação Linear Inteira Mista (PLIM). A modelagem como um PLIM levou à resolução do problema de forma mais eficiente através do algoritmo branch-and-cut. As novas representações propostas resultaram em melhorias na escalabilidade, solucionando problemas mais complexos em um tempo computacional menor.Além disso,os avanços em escalabilidade mostraram-se mais efetivos quando técnicas combinando programação matemática e metaheurísticas foram aplicadas ao problema.

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Allouche, Abdel Rahman. « Growth dynamics of Hybrid halide perovskite layers and its precursors in UHV : atomic scale insight from real-time Grazing Incidence Fast Atom Diffraction ». Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP027.

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Les pérovskites hybrides halogénées se sont révélées très prometteuses pour produire à moindre coût des dispositifs optoélectroniques performants. En tant que matériau actif des cellules solaires, ces matériaux ont désormais atteint un rendement record de conversion de puissance (PCE) de 26 %, similaire à celui du silicium cristallin. Malgré des efforts de recherche importants, de nombreux défis demeurent, notamment sur les problèmes de stabilité, la compréhension du rôle des défauts et enfin sur l’accès à leur dynamique de cristallisation. Pour atteindre ces objectifs, le dépôt sous vide apparaît comme une alternative effective à la méthode conventionnelle par voie humide. En plus de répondre à la problématique majeure de la mise à l’échelle, l’approche sous vide offre un meilleur contrôle de la croissance du film et pourrait potentiellement, par une réduction de la densité des défauts, révéler les mécanismes d’instabilité et simultanément éclaircir le rôle des interfaces. En dépit d’une meilleure qualité structurale, les couches actives déposées sous vide ne donnent pas nécessairement un meilleur PCE que celles produites par la méthode en solution. Cette observation déroutante exige une nouvelle approche dans la caractérisation de la croissance. Nous proposons une méthodologie qui consiste à suivre le processus de croissance en temps réel, idéalement sous ultra-vide (UHV), par une technique sensible à la surface et qui fournit des informations sur le mode de croissance, la structure cristalline, la densité de défauts ainsi que le nombre de monocouches. Pour cela, nous utilisons la diffraction d’atomes rapides en incidence rasante (GIFAD), une technique très douce basée sur la diffusion quantique d'atomes d'hélium à une énergie autour de 1 keV. Contrairement à la diffraction électronique ou de rayons X, les atomes d'hélium sondent ici uniquement la densité électronique au niveau de la lisière de la surface, ce qui rend GIFAD exclusivement sensible à la couche supérieure. En particulier, les données de diffraction, qui contiennent des informations sensibles sur la distribution de la densité électronique au sein de la maille, affichent directement les signes d’une transition de phase sans rupture de symétrie. Des outils complémentaires fournissent des informations complémentaires sur les propriétés chimiques, électroniques et optiques de la couche. Nous avons concentré nos efforts sur la croissance de MAPbI₃ (CH₃NH₃PbI₃) et de ses constituants, MAI (CH₃NH₃I) et PbI₂, à des pressions de base de l’ordre de 10⁻¹⁰ mbar (UHV). Afin de résoudre les tout premiers stade de la croissance et la dynamique d'organisation à l'interface, nous avons sélectionné un métal cristallin, Ag(001), comme substrat. Nos résultats confirment d'abord la remarquable flexibilité de MAI et PbI₂, ils présentent tous deux une croissance quasi-épitaxiale sur Ag(001) pour MAI et sur MAI/Ag(001) pour PbI₂, malgré un fort désaccord des paramètres de maille. Pour PbI₂, la croissance adopte le mode couche par couche avec une contrainte biaxiale s'estompant graduellement jusqu’à la 8ème monocouche. Le résultat le plus remarquable de ce travail est, lors du dépôt de PbI₂ sur MAI/Ag(001), le déclenchement instantanée d’une transformation de la maille cristalline, suivi d’un changement de symétrie dans le plan (carré vers hexagonal), tout en préservant l'ordre à longue distance. Néanmoins, dans nos conditions UHV et sauf sur Ag(001), on observe un très faible coefficient de collage du MAI, même sur une couche de PbI₂ suffisamment épaisse (50 monocouches), ce qui empêche la formation d’une couche de MAPbI₃. Ce travail soulève des questions sur le rôle des impuretés provenant du gaz résiduel lorsque MAPbI₃ est déposé sous vide à des pressions de l’ordre de 10⁻⁷ mbar ou plus
Halide hybrid perovskites have shown great promise for highly efficient and cost-effective optoelectronics devices. As the active material in solar cells, these materials have now reached a record 26% Power Conversion Efficiency (PCE), similar to that of crystalline silicon. Despite significant research efforts, many challenges remain, which include solving the stability issue, understanding the role of defects and achieving a better access to their crystallization dynamics. To meet these objectives, vacuum deposition emerges as a promising alternative to the prevalent solution method. In addition to responding to the major upscaling issue, the vacuum approach offers a much greater control over the film growth and could potentially, by a reduction of the defect density, reveal the instability mechanisms and simultaneously shed some light on the role of interfaces. In spite of improved structural quality, active layers deposited in vacuum do not necessarily yield a better PCE than those produced by the solution method. This puzzling observation calls for a new approach in the growth characterization. Our work proposes a methodology that consists in monitoring the growth process in real-time, ideally in ultra-high vacuum (UHV), by a surface sensitive technique that provides information on the growth mode, the crystalline structure, the defect density as well as the number of grown layers. For that purpose, we use Grazing Incidence Fast Atom Diffraction (GIFAD), a very soft technique based on the quantum scattering of helium atoms at energy around 1 keV. As opposed to electron or X-ray diffraction, here the helium atoms probe only the electron density at the selvage of the surface, making GIFAD exclusively sensitive to the top layer. In particular, the diffraction data, which bears sensitive information on the electron density distribution within the lattice, directly displays signs of phase transitions with no symmetry breaking. Additional tools provide complementary information of the chemical, electronic, and optical properties of the layer. We focused our effort on the growth of MAPbI₃ (CH₃NH₃PbI₃) and its constituents, MAI (CH₃NH₃I) and PbI₂, at base pressures in the low 10⁻¹⁰ mbar range (UHV). To get a better access to the early stage of the growth and to the organization dynamics at the interface, we selected a crystalline metal, Ag(001), as a substrate. Our results first confirm the remarkable flexibility of MAI et PbI₂, they both exhibit a quasi-epitaxial growth on Ag(001) for MAI and on MAI/Ag(001) for PbI₂, despite a large mismatch in lattice parameters. For PbI₂, the growth proceeds layer-by-layer with a biaxial strain gradually fading out at the 8ᵗᵸ monolayer. The most remarkable result of this work is the instantaneous triggering, upon deposition of PbI₂ on MAI/Ag(001), of a continuous transformation of the crystal lattice, followed by a change of symmetry in the plane (square to hexagonal), while preserving long-distance order. However, in our UHV conditions and except on Ag(001), we observe a very low sticking coefficient of MAI, even on a sufficiently thick PbI₂ layer (50 monolayers), which prevents the formation of a MAPbI₃ layer. This work raises questions about the role of impurities from the residual gas when MAPbI₃ is grown at pressures around 10⁻⁷ mbar or higher

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Åkesson, Elsa, Maximilian Kempe, Oskar Nordlander et Rosa Sandén. « Unmanned Aerial Vehicle Powered by Hybrid Propulsion System ». Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277115.

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I samband med den globala uppvärmningen ökar efterfrågan för rena och förnybara bränslen alltmer i dagens samhälle. Eftersom flygindustrin idag är ansvarig för samma mängd växthusgaser som all motortrafik i Sverige, skulle ett byte till en avgasfri energikälla för flygfarkoster vara ett stort framsteg. Därför har projektet genom modellering framtagit ett hybridsystem av ett batteri och en bränslecell och undersökt hur kombinationen av olika storlekar på dem presterar i en driftcykel. Då batterier har hög specifik effekt men är tunga, kompletteras de med fördel av bränsleceller, som är lättviktiga och bidrar med uthållig strömförsörjning. På så sätt blir hybriden optimal för flygfarkoster. Kandidatarbetet är en del av projektet Green Raven, ett tvärvetenskapligt samarbete mellan instutitionerna Tillämpad Elektrokemi, Mekatronik och Teknisk Mekanik på Kungliga Tekniska Högskolan. Driftcykelmodelleringen gjordes i Simulink, och flera antaganden gjordes beträffande effektprofilen, samt bränslecellens mätvärden och effekt. Tre olika energihushållningsscheman skapades, vilka bestämde bränslecellseffekten beroende på vätgasnivån och batteriets laddningstillstånd. Skillnaden på systemen var vilka intervall av laddningstillstånd hos batteriet som genererade olika effekt hos bränslecellen. Det bästa alternativet visade sig vara 0/100-systemet, eftersom det var det enda som inte orsakede någon degradering av bränslecellens kapacitet.
In today’s society, with several environmental challenges such as global warming, the demand for cleanand renewable fuels is ever increasing. Since the aviation industry in Sweden is responsible for the sameamount of greenhouse gas emissions as the motor traffic, a change to a non-polluting energy source forflying vehicles would be considerable progress. Therefore, this project has designed a hybrid system of abattery and a fuel cell and investigated how different combinations of battery and fuel cell sizes perform ina drive cycle, through computer modelling. As batteries possess a high specific power but are heavy, thefuel cells with high specific energy complement them with a sustained and lightweight power supply,which makes the hybrid perfect for aviation. The bachelor thesis is a part of Project Green Raven, aninterdisciplinary collaboration with the institutions of Applied Electrochemistry, Mechatronics andEngineering Mechanics at KTH Royal Institute of Techology. The drive cycle simulations were done inSimulink, and several assumptions regarding the power profile, fuel cell measurements and power weremade. Three different energy management strategies were set up, determining the fuel cell powerdepending on hydrogen availability and state of charge of the battery. The strategies were called 35/65,20/80 and 0/100, and the difference between them was at which state of charge intervals the fuel cellchanged its power output. The best strategy proved to be 0/100, since it was the only option which causedno degradation of the fuel cell whatsoever.

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Livres sur le sujet "Hybride uav"

Wich, Serge A., et Lian Pin Koh. Typology and anatomy of drones. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198787617.003.0002.

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In this chapter we discuss the typology of drones that are currently being used for different kinds of environmental and conservation applications. Drones are also commonly known variously as Remotely Piloted Aircraft Systems (RPAS), Unmanned Aerial Vehicles (UAV), and Unmanned Aircraft Systems (UAS). We focus on the most popular aircraft types including multirotor (of various configurations), fixed wing, and hybrid ‘vertical-take-off-and-landing’ (VTOL) craft, and briefly discuss the relative pros and cons of each type. We also broadly discuss the essential components common to all remotely piloted aircraft systems, including the power source, flight controller (or autopilot), and ground control station.

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A Hybrid Jump Search and Tabu Search Metaheuristic for the Unmanned Aerial Vehicle (UAV) Routing Problem. Storming Media, 2000.

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Chapitres de livres sur le sujet "Hybride uav"

Bella, Salima, Assia Belbachir et Ghalem Belalem. « A Hybrid Architecture for Cooperative UAV and USV Swarm Vehicles ». Dans Machine Learning for Networking, 341–63. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-19945-6_25.

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Dalwadi, Nihal, Dipankar Deb et Stepan Ozana. « Nonlinear Controllers for Hybrid UAV : Biplane Quadrotor ». Dans Studies in Systems, Decision and Control, 43–59. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-9744-0_3.

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Nicolae, Maximilian, Dan Popescu, Radu Dobrescu et Cristian Mateescu. « Improving Communication Efficiency of Hybrid UAV-WSN Systems ». Dans Advances in Intelligent Systems and Computing, 407–15. Cham : Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-21290-6_41.

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Dalwadi, Nihal, Dipankar Deb et Stepan Ozana. « Multi-observer Based Adaptive Controller for Hybrid UAV ». Dans Studies in Systems, Decision and Control, 87–108. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-9744-0_5.

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Barrett, Ron. « Hybrid Aircraft Aerodynamics and Aerodynamic Design Considerations of Hover-to-Dash Convertible UAVs ». Dans Advanced UAV Aerodynamics, Flight Stability and Control, 421–45. Chichester, UK : John Wiley & Sons, Ltd, 2017. http://dx.doi.org/10.1002/9781118928691.ch12.

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Hairi, Shahrul Malek Faizsal Bin Shahrul, Siti Juita Mastura Binti Mohd Saleh, Ahmad Hamdan Ariffin et Zamri Bin Omar. « A Review on Composite Aerostructure Development for UAV Application ». Dans Green Hybrid Composite in Engineering and Non-Engineering Applications, 137–57. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-1583-5_9.

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Ghambari, Soheila, Lhassane Idoumghar, Laetitia Jourdan et Julien Lepagnot. « A Hybrid Evolutionary Algorithm for Offline UAV Path Planning ». Dans Lecture Notes in Computer Science, 205–18. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-45715-0_16.

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Lan, Zhouqi. « The Influence of Hybrid Power System on UAV Endurance ». Dans Advances in Computer Science Research, 437–45. Dordrecht : Atlantis Press International BV, 2024. http://dx.doi.org/10.2991/978-94-6463-540-9_43.

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Phunpeng, Veena, Karunamit Saensuriwong et Thongchart Kerdphol. « Comparative Study Between Aluminum and Hybrid Composite for UAV ». Dans Research Developments in Sustainable Aviation, 175–80. Cham : Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-37943-7_23.

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Chacon-Murguia, Mario I., Luis E. Guerra-Fernandez et Hector Erives. « UAV Image Segmentation Using a Pulse-Coupled Neural Network for Land Analysis ». Dans Nature-Inspired Design of Hybrid Intelligent Systems, 175–85. Cham : Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-47054-2_11.

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Actes de conférences sur le sujet "Hybride uav"

Saikia, Prajwalita, Anand Jee, Keshav Singh, Theodoros A. Tsiftsis et Alexandros-Apostolos A. Boulogeorgos. « Hybrid-RIS Empowered UAV-Aided ISAC Systems ». Dans 2024 IEEE 100th Vehicular Technology Conference (VTC2024-Fall), 1–5. IEEE, 2024. https://doi.org/10.1109/vtc2024-fall63153.2024.10757581.

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Chinh Chu, Thi My, et Hans-Jürgen Zepernick. « Hybrid AF-DF Relaying for NOMA UAV Systems ». Dans 2024 17th International Conference on Signal Processing and Communication System (ICSPCS), 1–8. IEEE, 2024. https://doi.org/10.1109/icspcs63175.2024.10815758.

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Zhou, Lingjie, Zhihao Luo, Pengbo Jiao, Xiaojie Jin, Xin Sun et Jianmai Shi. « A Priority-Based Hybrid Algorithm for UAV Path Planning ». Dans 2024 10th International Conference on Big Data and Information Analytics (BigDIA), 518–23. IEEE, 2024. https://doi.org/10.1109/bigdia63733.2024.10808417.

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Ostermann, Tobias. « Flight Control System of a Tiltwing UAV ». Dans Vertical Flight Society 72nd Annual Forum & Technology Display, 1–9. The Vertical Flight Society, 2016. http://dx.doi.org/10.4050/f-0072-2016-11581.

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This paper describes the development and validation process of the flight control system of a tiltwing UAV with focus on the transition control. Due to the capability to tilt its main wing the special aircraft type combines the advantages of a fixed-wing aircraft concerning flight performance and energy consumption with the VTOL capabilities of a rotary-wing configuration, which implies a high flexibility for multi role operations. Thus the hybrid aircraft concept closes a gap between common configurations. A particular challenge for the flight control system is to handle the unsteady states in transition phase between horizontal and vertical flight and to ensure full control of the aircraft at any time. The presented flight control system is designed for an aircraft with a wingspan of 6.56 ft / 2 m and a maximum gross weight of 24.25 lbs / 11 kg and was tested successfully within a software simulation environment as well as partially in a free flight test campaign.

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Rabahi, Fatima Zahra, et Abdelmadjid Ait Saadi. « IoT-Enhanced Hybrid 5G-UAV Networks for Post-Catastrophe Assessment ». Dans 2024 IEEE Global Conference on Artificial Intelligence and Internet of Things (GCAIoT), 1–6. IEEE, 2024. https://doi.org/10.1109/gcaiot63427.2024.10833581.

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Lacaze, Alberto. « PEGASUS TRANSFORMING UAV/UGV HYBRID VEHICLE ». Dans 2024 NDIA Michigan Chapter Ground Vehicle Systems Engineering and Technology Symposium. 2101 Wilson Blvd, Suite 700, Arlington, VA 22201, United States : National Defense Industrial Association, 2024. http://dx.doi.org/10.4271/2024-01-3649.

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<title>ABSTRACT</title> <p>In this paper, we present Pegasus Transforming UAV/UGV Hybrid Vehicle, a unique, transformable UAS/UGV that is particularly well-suited for missions. The combination of flight and ground modalities allows Pegasus to fly to location, automatically transform into a ground vehicle, reposition, and quietly approach a target; or, Pegasus can land and “perch” for long durations, allowing for the maintenance of the custody trail and long ISR missions or emplace sensors particular for a specific mission. The sequential use of aerial and ground capabilities in this platform provides the reach usually lacking in these missions.</p> <p>The Pegasus platform was developed with DTRA/ARDEC funding in support of specialized missions where these functionalities are needed. Robotic Research, LLC has developed the system from the ground up, including: mechanical, electrical, and software designs (without using foreign-made parts). The current system is shown in <xref rid="F1" ref-type="fig">Figure 2</xref>. The system already has obstacle avoidance payloads, and has demonstrated capabilities in GPS-denied environments and SubT, while mapping and traversing line-of-sight and NLOS areas. <fig id="F1" position="float" specific-use="1col"> <label>Figure 2</label> <caption> <title>Pegasus quietly drives to a location, flies to a roof, and repositions on top of the roof to point to the OP.</title></caption> <graphic content-type="figure" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2024-01-3649_fig0001" /></fig></p>

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Almesafri, Nouf, Majed Alhammadi, Sayem Zafar et Gustavo Santos. « Power System Analysis of Solar and Hydrogen Fuel Cell Powered EVTOL UAV ». Dans ASME 2024 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2024. https://doi.org/10.1115/imece2024-145240.

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Abstract The interest in electric Vertical Take-off and Landing (eVTOL) Unmanned Aerial Vehicles (UAVs) has increased with the introduction of Advanced Air Mobility (UAM) vehicles. This configuration, reliant on multiple lifting motors for vertical flight and a forward flight motor for horizontal flight, necessitates a well-designed power and propulsion system. This study explores a propulsion system combining photovoltaic (PV) panels with a hydrogen fuel cell for eVTOL UAVs. Fuel cell integration is studied to enhance the vertical flight time in which fuel cell is used to power the vertical flight motors. The PV panels are studied to be integrated with forward flight motor to analyze the improvement in forward flight time. This hybrid system aims to extend flight endurance and operational capabilities by harnessing solar and hydrogen energy. The study looks at the integration of these technologies, aiming to address typical energy limitations of batteries and enhance UAV performance regarding endurance, payload capacity, and hover time. These enhancements added to the system achieved an extended hover time of 35 minutes and 55 minutes for 3.5L and 5L hydrogen cylinders, respectively. It also allowed the eVTOL UAV to conduct 4 to 6 take-off/landing cycles, improving the UAV’s operational capability.

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Rudakevych, Pavlo, et Brian Yamauchi. « A man portable hybrid UAV/UGV system ». Dans Defense and Security Symposium, sous la direction de Grant R. Gerhart, Douglas W. Gage et Charles M. Shoemaker. SPIE, 2007. http://dx.doi.org/10.1117/12.710744.

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Almesafri, Nouf, Majed Alhammadi, Sayem Zafar et Gustavo Dos Santos. « eVTOL UAV Conversion to Hydrogen Fuel-Cell Power Source for Enhanced Endurance ». Dans ASME 2023 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/imece2023-115118.

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Abstract A study is conducted to investigate the integration of a hydrogen fuel cell power system to a small electric vertical take off and landing (eVTOL) Unmanned Aerial Vehicle (UAV) at Technology Innovation Institute (TII), Abu Dhabi. A hybrid power system is used comprising of hydrogen fuel cell for forward flight and lithium polymer batteries of vertical flight during take-off and landing phase. The hybrid power system is proposed as a substitute to the existing batteries in order to enhance the endurance of eVTOL UAVs. The eVTOL UAV used in this study is Dronepoulis ESA-90 which has four vertical flight motors and a single forward flight motor. Data simulations are conducted for the cruise power of 750 W which is consumed by the forward flight motor. The results show that the flight endurance of the UAV increased from 90 min to 272 minutes when hydrogen fuel cell power system is used. Further studies show that increasing the hydrogen pressure in the cylinder and increasing the size of the cylinder increased the flight endurance of the UAV. Increasing the size of the cylinder can potentially increase the flight endurance of the UAV as long as the overall weight remains within the maximum take-off weight limit.

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Frederick, Jr, Robert, Jennifer Pierce, Geof Morris, Dana Quick et James Winkeler. « Conceptual Design of an Unmanned Hybrid Vehicle for the Battlefield of 2012 ». Dans 1st UAV Conference. Reston, Virigina : American Institute of Aeronautics and Astronautics, 2002. http://dx.doi.org/10.2514/6.2002-3518.

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Rapports d'organisations sur le sujet "Hybride uav"

How, Jonathan P. Distributed Hybrid Information and Plan Consensus HIPC for Semi-autonomous UAV Teams. Fort Belvoir, VA : Defense Technical Information Center, septembre 2015. http://dx.doi.org/10.21236/ada627417.

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Anderson, Erin. Utilizing unmanned aircraft system (UAS) technology to collect early stand counts and to assess early plant vigor for use in early-season stress tolerance characterization of hybrid corn products. Ames (Iowa) : Iowa State University, janvier 2018. http://dx.doi.org/10.31274/cc-20240624-1576.

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Salavisa, Isabel, Mark Soares et Sofia Bizarro. A Critical Assessment of Organic Agriculture in Portugal : A reflection on the agro-food system transition. DINÂMIA'CET-Iscte, 2021. http://dx.doi.org/10.15847/dinamiacet-iul.wp.2021.05.

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Over the last few decades, the organic agriculture sector has experienced sustained growth. Globally, as well as in the European Union and Portugal, organic production accounts for just under 10% of total Utilised Agricultural Area (UAA) (FiBL, 2019; Eurostat, 2019; DGADR, 2019; INE, 2019; GPP, 2019). This growth has been seen in terms of production, number of producers, amount of retail sales, imports and exports. This article attempts to build on the multi-level perspective (MLP) of the socio-technical (ST) transitions theory by employing a whole systems analysis (Geels, 2018) of organic agriculture in Portugal, which defends an integrated vision of the systems, where multiple interactions occur within and among the niche, the regime and the landscape levels. This approach has been employed in order to develop a critical analysis of the current state of the Portuguese organic agriculture sector, stressing the multiplicity of elements that are contributing to the agro-food system´s transformation into a more sustainable one. In fact, the agro-food system is related with climate change but also has connections with other domains such as public health, water management, land use and biodiversity. Therefore, it is affected by shifts in these areas. This analysis considers developments in increasing domestic organic production, number of producers, amount of retail sales, imports, exports, market innovations, and the sector´s reconfiguration. The organic sector´s increase has been attributed to European regulation, institutionalization, standardization, farmer certification, external (government) subsidy support programs, incremental market improvements (visibility and product access), the emergence of new retailers, the rise of supporting consumers and a shift away from conventional agriculture (Truninger, 2010; DGADR, 2019; Pe´er et al, 2019). However, together with positive incentives, this sector also faces numerous barriers that are hindering a faster transformation. Difficulties for the sector to date have included: product placement; a disconnect between production, distribution and marketing systems; high transport costs; competition from imports; European subsidies focused on extensive crops (pastures, olive groves, and arable crops), entailing a substantial growth in the area of pasture to the detriment of other crops; the fact that the products that are in demand (fresh vegetables and fruit) are being neglected by Portuguese producers; expensive certification procedures; lack of adequate support and market expertise for national producers; the hybrid configuration of the sector; and price. Organic agriculture as a niche-innovation is still not greatly contributing to overall agricultural production. The low supply of organic products, despite its ever-increasing demand, suggests that a transition to increased organic production requires a deeper and faster food system reconfiguration, where an array of distinct policies are mobilized and a diversity of actions take place at different levels (Geels, 2018; Pe´er et al, 2019). This paper will attempt to contribute an overall critical assessment of the organic sector´s features and evolution and will identify some of the main obstacles to be overcome, in order to boost the sustainability transition of the agro-food system in Portugal.

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