1,720,997 research outputs found
Plasticity of Indeterminate Field Bean in Response to Seed Density and Fertilizer Supply.
No full textField bean (
Vicia faba
minor Beck),
probably originated in the pre-historic period in the Middle East is, today,cultivated all over the world and counts among the most widely adapted grain legumes. In the Mediterraneanregion, field bean is considered a viable alternative to soybean to increase the sustainability of farming systems,because of its rusticity, and low fertilizer and pesticides requirement. Due to the indeterminate growth habit, intra-plant competition between reproductive and vegetative structures and among the developing pods may be great.Warmer winter temperatures, such those expected in the consequence of climate change, favour intra-plantcompetition, as they promote vegetative growth and flowering parallel to seed filling.
A 3-year field experiment was carried out in temperate Mediterranean conditions on loam soil with moderatelyalkaline reaction. Imposed treatments were NP fertilizer supply (0, and 120 kg N ha
and 100 kg P ha
) and seeddensity (100 and 60 seed m
, respectively indicated as Fb100 and Fb60). Heavy rainfall in autumn-winter delayedsowing date, which was performed on October 26
2017, December 11
2018, and February 12
2020.
Plants wereharvested twice each year, at the stage of full flowering with basal pods developing (65-73, BBCH) and when plantswere dead and dry (97, BBCH
A model predictive control for attitude stabilization and spin control of a spacecraft with a flexible rotating payload
No full textMany Earth Observation missions, implementing space-based microwave sensing techniques for collecting surface information, employ spinning sensors to cover large swaths of terrestrial areas, thus improving the rate at which global maps of those measured data are generated. These spacecraft (as Soil Moisture Active Passive (SMAP) developed by NASA or Copernicus Imaging Microwave Radiometer (CIMR) currently under development by Thales Alenia Space) consist of a main non-spun platform and a rotating part composed of an antenna boom, a deployable reflector and a rotation mechanism. As the reflector is designated to rotate about the nadir axis producing conically scanned antenna beams with precise surface incidence angle, the payload pointing accuracy needs to be addressed at both spin subsystem and platform level. In this work, a representative model of the dynamic behaviour of SMAP satellite is developed as a study case to design the proposed control strategies; in particular, a SMAP-like payload structural model is built using FEM commercial codes. The spacecraft is equipped with a Reaction Wheels Assembly (RWA) to accomplish both momentum compensation for the spun element and three-axis attitude control and a motor for the spin mechanism. The objective of the study is to develop the spacecraft control architecture in the frame of Model Predictive Control (MPC) theory. MPC refers to a class of algorithms in which the control action is obtained by computing an open-loop optimal sequence of control moves over a predefined time horizon; moreover, the ability to set constraints on process inputs and outputs directly in the problem formulation allows to account for actuators’ limits. In the study two operative phases of the satellite are addressed: the Spin-up, in which the 6-meter diameter antenna is spun-up to the operative condition of 14.6 RPM, and the Science Phase, in which precise nadir pointing and stability of the flexible system must be kept for acquiring high-resolution measurements. To this purpose, control–structure interaction between attitude/spin control system and flexible dynamics, as well as system's imbalances, are carefully addressed by the proposed control architecture. The nonlinear in-orbit dynamics of the flexible spacecraft is then used to evaluate the performance of the MPC controller in terms of pointing accuracy and robustness to uncertainties
A general Control/Structure Co-design framework to optimize attitude/flexible dynamics of Earth Observation (EO) satellites
No full textModern space missions for Earth Observation (EO) purposes often rely on satellites equipped with very large flexible appendages, such as antennas and solar panels, which are demanded to perform agile slew manoeuvres. In most cases, the elasticity of such systems cannot be neglected in the design of the attitude controller, as excessive elastic displacements of the structural elements may compromise their stability and pointing performance. Therefore, the integration of GNC laws in flexible space systems still represents an open challenging task, whose best solution often depends on the specific type of application. In this scenario, the most widely adopted techniques in control design are the classical but yet labour intensive tuned feedback controllers, generally integrated with low pass/notch filters to suppress the resonant peaks of the spacecraft flexible modes. Alternatively, in the early phases of spacecraft design, structure and control disciplines perform separate and time-consuming iterative sequences to avoid interactions between the flexible and rigid dynamics. In this context, as opposed to the latter approach, this paper aims at proposing an automated nested optimization framework to simultaneously optimize spacecraft structural and control dynamics, to be applicable to a wide range of flexible spacecraft. The objective of such a co-design architecture is to modify design parameters, at both structural and control levels, to minimize the mass of the spacecraft while maximizing its agility and satisfying imposed requirements. Moreover, as robust multivariable techniques have become more and more applied to ensure satisfactory robust performance margins, this paper's goal is to pose a multi-channel structured H∞ control architecture in the co-design problem. To guarantee the generality of implementation, a structural design tool (MSC Nastran) is interfaced with a coding environment (Matlab/Simulink) to set-up an autonomous exchange of information between structural and control domains. Starting from an initial definition of the spacecraft material, geometry and control requirements (in terms of loop-shaping transfer functions), relevant parameters are extracted from the structural tool and a linearized dynamic model assembled. Then, a controller is synthetized based on the provided requirements, followed by a V&V phase on the nonlinear plant of the satellite. The procedure is repeated until the stop criteria (based on tolerance and max iterations) is satisfied. Finally, the output of the proposed architecture is obtained as an optimized structural model and robust controller tailored for the satellite dynamics
An attitude/spin control architecture for a spacecraft equipped with a flexible rotating payload based on model predictive control
No full textMany Earth observation missions, implementing space-based microwave sensing techniques for collecting Earth surface information, employ spinning sensors to cover large swaths of terrestrial areas, thus improving the rate at which global maps of those measured data are generated. These spacecraft (as Soil Moisture Active Passive (SMAP) developed by NASA or Copernicus Imaging Microwave Radiometer (CIMR) currently under development by Thales Alenia Space) consist of a main non-spun platform and a rotating part composed of an antenna boom, a deployable reflector and a rotation mechanism. As the reflector is designated to rotate about the nadir axis producing conically scanned antenna beams with precise surface incidence angle, the payload pointing accuracy needs to be addressed at both spin subsystem and platform level. In this work, a representative model of the dynamic behaviour of SMAP satellite is developed as a study case to design the proposed control strategies; in particular, the SMAP-like payload structural model is built using FEM commercial codes. The spacecraft is equipped with a Reaction Wheels Assembly (RWA) to accomplish both momentum compensation for the spun element and three-axis attitude control and a motor for the spin mechanism. The objective of the study is to develop the spacecraft control architecture in the frame of Model Predictive Control (MPC) theory. MPC refers to a class of algorithms in which the control action is obtained by computing an open-loop optimal sequence of control moves over a predefined time horizon; moreover, the ability to set constraints on process inputs and outputs directly in the problem formulation allows to account for actuators' limits. In the study two operative phases of the satellite are addressed: the spin-up, in which the 6-meter diameter antenna is spun-up to the operative condition of 14.6 RPM, and the Science Phase, in which precise nadir pointing and stability of the flexible system must be kept for acquiring high-resolution measurements. To this purpose, control-structure interaction between attitude/spin control system and flexible dynamics, system's imbalances are carefully addressed by the control system. The nonlinear in-orbit dynamics of the flexible spacecraft is then used to validate the performance of the MPC controller in terms of pointing accuracy and robustness to uncertainties
Optimal design of a net of adaptive structures for micro-vibration control in large space mesh reflectors
No full textLarge deployable antennas are required for the advancement of space communications, Earth observation, radio astronomy and deep space exploration. The core requirements of a space antenna are high gain, high directivity and persistent accuracy, which are mainly dependent on the size of the reflector. Most contemporary space antennas have exceeded the size of launching vehicles, leading to the necessity of stowed concepts to overcome the limitation. Many structural models have been investigated by different organizations. Generally, mesh deployable reflectors are currently more mature compared to other foldable solutions and will be the topic of this paper. In-orbit disturbances affecting the deployed configuration can deteriorate the accuracy of the communications system. Perturbations originated by on board sources can be transmitted from the satellite platform to the supporting frame of the antenna. Furthermore, the structure accuracy is affected by thermal deformation and elastic vibration due to thrusters jetting. Undesired dynamic behaviour of structural components have to be predicted and counteracted. Therefore, vibration control is a key technology to correct the distortions altering the proper functioning of the system. An intelligent adaptive structure is introduced as a structure configured with distributed actuators and sensors and guided by a controller to modify the dynamic response of the system. In this paper, the supporting structure of a very large mesh reflector is described. The antenna reflector foldable membrane is supported by a deployable adaptive truss structure. A FEM formulation is adopted to assemble the frame and it is validated by comparing it with commercial codes. According to the presented model, the active elements can be embedded in the middle of the truss elements. Of course, active control of all the devices at the same time requires a cost from the power consumption point of view which could be not affordable in space applications. However, the effectiveness is not the same for all the actuators. In this study, an optimization procedure is performed to assess the best authority of the actuators that must be controlled for a variety of disturbances. The objective function is set as a weighted sum of power consumption of the actuators. As a study case, a feedback strategy is implemented to coordinate the simultaneous action of the devices to ensure the damping performance of the system is enhanced
Data-driven deep neural network for structural damage detection in composite solar arrays on flexible spacecraft
Full text linkA data-driven approach based on Deep Neural Network (DNN) techniques is here proposed for Structural Health Monitoring of large in-orbit flexible systems. Damage scenarios are generated via a Finite Element commercial code to train and test the machine learning model, by considering equivalent properties of the composite material of the solar panels. The fully coupled 3D equations for the flexible spacecraft are integrated to test typical profiles of attitude manoeuvres in case of different damages. The DNN model is trained using sensor-measured time series responses, with each response associated with the label of the corresponding damage scenario, and tested via k-folding approach. This methodology offers a promising approach to detect structural damage in solar arrays on spacecraft using machine learning techniques
Thermo-Mechanical Jitter in Slender Space Structures: A Simplified Modeling Approach
No full textThermally induced vibrations usually affect spacecraft equipped with light and slender appendages such as booms, antennas or solar panels. This phenomenon occurs when a thermal shock, resulting from the sudden cooling and warming phases at the entrance and exit from eclipses, triggers mechanical vibrations. The study proposed hereafter concerns the modeling and prediction of jitter of thermal origin in a long and thin plate with a sun-pointing attitude in geostationary orbit. The system's temperature and dynamics are described by a set of equations expressing the two-way coupling between the thermal bending moment and the shape of the panel. The structure is discretized and reduced to a one-degree-of-freedom simplified model able to identify a mechanism of thermal pumping that could lead to instability. Finally, the results of the analysis are compared with those obtained with a more accurate FEM modelization
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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