1,720,987 research outputs found
Increasing Autonomy of Aerospace Systems via PINN-based Solutions of HJB Equation
No full textClosed-loop optimal control is crucial for enhancing the autonomy of aerospace systems. However, its computation can be challenging, as it typically involves solving the Hamilton-Jacobi-Bellman (HJB) equation—a nonlinear partial differential equation (PDE) that poses significant numerical difficulties. This paper focuses on employing Bellman Neural Networks (BeNNs), a specialized framework within Physics-Informed Neural Networks (PINNs), to learn the solution of the HJB PDE and thereby ascertain the closed-loop optimal control. BeNNs leverage the constrained expressions from the Theory of Functional Connections and utilize shallow neural networks, trained via the Extreme Learning Machine (X-TFC) approach, to approximate the elusive solution of the HJB PDE. We achieve the solution to the nonlinear HJB by integrating the method of successive approximation with the solution of the linear Generalized HJB (GHJB) equation. The effectiveness of these frameworks is evaluated in the context of a missile pitch-plane autopilot optimal control problem. The results demonstrate that our framework can accurately compute the closed-loop optimal control within the specified domain, achieving low final errors relative to the reference states
Optimal Maneuvers Around Binary Asteroids Using Particle Swarm Optimization and Machine Learning
No full textDesigning optimal transfer trajectories and reference orbit tracking in binary asteroid systems is both challenging and computationally expensive. This paper proposes a method of bypassing the high computational overhead by leveraging a collection of known techniques. Indeed, the proposed framework is based on the combination of artificial intelligence techniques, such as the particle swarm optimization and neural networks, along with the inverse dynamics and the B-splines approximation of the trajectory. The real irregular shapes of the asteroids are considered in the free dynamics of the system, which are obtained via the mutual polyhedral model. The gravitational accelerations of the single asteroids acting on the spacecraft are approximated by using two single-layer neural networks trained via an extreme learning machine. By using a combination of these techniques, the computational time of the whole optimization is decreased from hours to minutes. The proposed approach is applied to the optimal trajectory design around the binary asteroid system, 1999 KW4, showing the feasibility of the proposed optimization approach, reducing the computational effort and time, and increasing the reliability of the obtained results. It is shown through a Monte Carlo analysis that our optimization strategy yields more accurate solutions than other optimization algorithms, such as the interior point and sequential quadratic programming methods, when a random initial guess is provided. Finally, the proposed optimization approach can be used in combination with other techniques to provide a feasible and reliable initial guess for a better solution refinement
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
3D MODELLING OF THE CENTRAL APENNINES TO DEFINE THE TECTONIC EVOLUTION AND TO SUPPORT SEISMIC HAZARD STUDIES
No full textThe central Apennines is characterized by the presence of several active faults, potentially capable of generating damaging earthquakes (as observed in the recent past). To study the still discussed tectonic evolution of the orogen and support seismic hazard studies, a 3D structural and geological modelling was carried out. As a first step, 14 2D balanced geological cross-sections were built across the central Apennines to define the main structural picture at regional scale. Cross-sections were built using MOVE (Petroleum Experts), while 3D modelling was completed using Petrel (Schlumberger). 3D results suggest a possible hybrid tectonic style for the central Apennines, indicating a transition from the dominant thin-skin tectonics (active for most of the structuring of the orogen) to a thick-skin deformation (limited to the last 3-2Ma), in which the upper portion of the crystalline basement would be involved. As key elements for the evolution of the orogen, the Permian-Triassic Pseudo-Verrucano deposits and the Upper Triassic Burano evaporites were identified as active regional detachment layers. Starting by the 3D geological model, a 3D seismic velocity model was completed implementing the appropriated interval velocity values for each geological layer. Finally, the 3D velocity model was used to make an earthquake relocation exercise. The relocated earthquakes allowed to identify a shallower westward trend of the (interpreted) brittle-ductile transition (BDT). The BDT was used to localize in depth the bottoms of the potential brittle volumes for the maximum magnitude estimation of the Sulmona (BDT at 17 km) and Caramanico (BDT at 20 km) potentially seismogenic normal faults. Results indicate a maximum magnitude of 7.09 Mw for the Sulmona and 7.22 Mw for the Caramanico cases. With the aim to simulate a more conservative scenario, a possible structural cut-off at 8 km for Sulmona, and 10 km for the Caramanico areas were tested (assuming a hypothetical a west-dipping structure at shallower depths, as observed the north of the study area). The reduced brittle volumes led to lower magnitude values (6.58 Mw for the Sulmona, and 6.78 Mw for the Caramanico faults), highlighting the importance to have a robust evaluation of the brittle volumes, especially in a potential seismogenic area like the central Apennines
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
