1,721,169 research outputs found
Chemical Looping for Combustion of Solid Biomass: A Review
Full text linkChemical looping combustion of solid biomass has the unique potential to generate energy with negative carbon emissions, while entailing an energy penalty compared to traditional combustion that is lower than that of the competing carbon capture technologies. In spite of these attractive features, research is still needed to bring the technology to a fully commercial level. The reason relies on a number of technological challenges mostly related to the oxygen carrier performance, its possible detrimental interaction with the biomass ash components, and the efficiency of the gas-solid contact with the biomass volatiles. This review is focused on these specific challenges which are particularly relevant when firing biomass rather than coal in a solid-based chemical looping combustion process. Special attention will be given to the most recent findings published on these aspects. Related performance evaluation by modeling, system integration, and techno-economic analysis will also be briefly reviewed
Precise Relative Motion and Control Strategy in the J22 Perturbed Geostationary Environment
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Polygalacturonase from Rhizoctonia fragariae: further characterization of two isoenzymes and their action towards strawberry tissue
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Investigation of in-vitro methods for measuring eggplant resistance to Verticillium dahliae.
No full textInvestigation of in-vitro methods for measuring eggplant resistance to Verticillium dahliae.
No full textDesign of Natural Collision-Free Trajectories for the Mission Extension Phase of a Remote Sensing Formation Flying Mission
Full text linkThe safety concept is of paramount importance in the trajectory design of formation flying missions. The selection of natural collision-free trajectories is based on the analysis of natural relative motion among the satellites. This is beneficial for the mission both in terms of propellant consumption and control effort, allowing a naturally safe environment. This paper focuses on a formation flying for remote sensing missions in low Earth orbit, in the direction of future Earth observation missions. We consider as a baseline the Formation Flying L-band Aperture Synthesis mission concept, proposed by the European Space Agency. This work proposes natural collision-free trajectories to extend the scientific campaign at the end of the nominal operative life of the FFLAS mission. The possibility to extend the scientific operations, before the final atmospheric re-entry phase, could provide a significant amount of data to improve meteorological and climate prediction. The scenario selected is based on a close formation flying, with a nominal inter-satellite distance in the order of tens of meters. This allows the satellites to behave as a node of a distributed payload for Earth observation, increasing the accuracy in the measurements, thanks to the increase of the radiometer's aperture size. We present two possible strategies to design the extension phase of this mission. First, a single satellite science mission is envisioned, moving the satellites on the same reference orbit, with a certain separation angle. In this new configuration, each satellite operates singularly on different orbits, as a single satellite science mission. Second, we consider the possibility to increase the relative distance among the satellites, maintaining the possibility to do Earth observation with distributed payloads. We perform some analyses to select the augmented geometry, with a bigger formation baseline in the order of tens to hundreds of meters. The analyses are driven by the need to use natural collision-free relative trajectories since at the end-of-life the low thrust control is limited. The final decay of the satellites is provided via a deorbiting low-thrust manoeuvre, to comply with the 25-year mitigation rule. The main idea is to propose disposal in less than three months. The results of the analyses are obtained including the effects of the orbital perturbations, thanks to a high-fidelity relative motion propagator. The relative orbital elements environment is introduced to assess the formation safety more straightforwardly
Attitude Control of the Disposal Phase of the eCube Mission for Atmospheric Data Acquisition
Full text linkThis paper aims at providing a new perspective on the attitude dynamics and control system of a new CubeSat mission concept for atmospheric data acquisition, in the region between 200 km and 100 km, for more accurate reentry predictions. It discusses the main challenges and the feasibility of analysing the main atmospheric parameters via onboard sensors of a 12-unit CubeSat, designed at Politecnico di Milano. The paper presents the attitude control system feasibility during the data-acquisition phase, when the disturbance given by the atmospheric density is highly affecting the CubeSat dynamics, before the atmospheric disposal. After the estimation of the maximum momentum storage and the maximum torque acting on the satellites, a control law is provided to control the attitude via reaction wheels, allowing the data acquisition from the onboard sensors. Moreover, an analysis of the desaturation strategy is presented, to satisfy the pointing accuracy for the measurements of the network of sensors. The analysis could provide a baseline for future similar mission in the same orbital region, to enhance the acquisition of atmospheric data
Synthesis of simplified endoperoxide derivatives based on the plakortin scaffold
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