1,720,961 research outputs found
Autonomous Small Body Gravimetry via A2C Path-Planning
No full textThe success of proximity operations near small bodies relies on proper characterization of the corresponding gravitational environment; the accuracy of the gravity field model is a critical element to plan safe spacecraft trajectories and constitutes a crucial aspect for the definition of the spacecraft dynamics. Currently, flight operations required for an accurate reconstruction of the gravity field are orchestrated by ground control personnel; however, automatizing such flight control processes may yield reduced operational costs and additional mission opportunities. The problem of autonomous gravity field reconstruction can be formulated as a Partially Observable Markov Decision Process; in this framework, a spacecraft moving in an unknown gravitational environment can be modeled as an agent that autonomously implements a guidance policy to obtain accurate grav-imetric measurements. Possibly compatible with limited on-board resources, advances in flight autonomy may be sought through the exploitation of novel techniques based on Reinforcement Learning (RL) and Artificial Neural Networks (ANN). The architecture proposed in this work employs a Hopfield Neural Network (HNN) for the reconstruction of the gravity field, which is represented as a spherical harmonics expansion, assuming an Exterior Gravity Field Model. The agent’s objective is to determine a trajectory around the target body that would allow the quick and precise estimation of the spherical harmonics coefficients via HNN. The algorithm adopted is the Advantage-Actor Critic (A2C), where the agent plays the roles of the Actor; such RL algorithm exploits two networks that work in parallel aiming to maximize the return, a scalar value that renders the accuracy of reconstruction of the gravity field. In particular, this works focuses on the reconstruction of the first zonal Stokes’ coefficient C2, testing the architecture on specific case studies, as well as on more generic environments. The ANN are updated using an Adam’s algorithm for the learning process, which is driven by a reward function designed to retrieve the expansion coefficient in a quick and safe manner. Results presented in this paper show that an agent with proper training performs better than one that follows random behavior, achieving the desired accuracy more often than in a random policy simulation, in a wide pool of scenarios (different initial conditions for the same asteroid and different asteroid); in addition, gravity coefficient reconstruction performance are improved if an expert-knowledge is infused into the training process. Such results allow to assess the feasibility of the method proposed, thus defining a promising starting point for further developments
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
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
STT-MRAM-based PUF architecture exploiting magnetic tunnel junction fabrication-induced variability
No full textPhysically Unclonable Functions (PUFs) are emerging cryptographic primitives used to implement lowcost device authentication and secure secret key generation. Weak PUFs (i.e., devices able to generate a single signature or to deal with a limited number of challenges) are widely discussed in literature. One of the most investigated solutions today is based on SRAMs. However, the rapid development of low-power, high-density, high-performance SoCs has pushed the embedded memories to their limits and opened the field to the development of emerging memory technologies. The Spin-Transfer-Torque Magnetic Random Access Memory (STT-MRAM) has emerged as a promising choice for embedded memories due to its reduced read/write latency and high CMOS integration capability. In this article, we propose an innovative PUF design based on STT-MRAM memory. We exploit the high variability affecting the electrical resistance of the Magnetic Tunnel Junction (MTJ) device in anti-parallel magnetization. We will demonstrate that the proposed solution is robust, unclonable, and unpredictable
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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