1,720,958 research outputs found
Complementing Human Perception in Remote Site Exploration using Augmented Reality - A Proof of Concept
No full textThis paper describes the proof of concept of a system for increasing situational awareness during remote site exploration using unmanned vehicles that leverages augmented reality techniques. When remote piloting an unmanned vehicle that needs to enter an unknown site, the operator may lose direct line of sight to the vehicle due to the presence of obstacles. In such a situation the operator may resort only to onboard cameras or sensors in general for situational awareness and the risk of "spatial disorientation" dramatically increases. This paper describes and demonstrates with laboratory tests the basic building blocks needed to build an augmented reality tool that would allow the operator to see an avatar of its vehicle through the obstacles, as if they were transparent, with particular attention to facilitating his/her perception of depth, a key point in making the whole concept usable. The basic idea is first presented, then, after a brief review of the mathematics behind the realization of the augmented reality tool, the rationale for the need of a calibration procedure is shown together with the details of a possible solution of the problem that is specific for this particular application. A discussion on registration errors is presented together with the results of an experimental validation using a Meta Oculus Quest and an indoor motion tracking system
MPC based optimization applied to treatment of HCV infections
Full text linkBackground and Objective: The recent introduction of antivirals for the treatment of the hepatitis C virus opens new frontiers but also poses a significant burden on public health systems. This paper presents a simulation study in which model predictive control (MPC) is proposed for optimizing the therapy aiming to obtain a reduction of the costs of therapy, while maintaining the best pharmacological control of the infection.
Methods: A dynamic model describing the evolution of hepatitis C is deployed as internal model for MPC implementation, using nominal values of parameters. Different closed-loop simulations are presented both in nominal and in mismatch conditions. In addition, a more easily implementable treatment is proposed, which is based on a discrete dosage approach, where days on/off therapy are considered instead of continuous therapy modulation.
Results: Results show that therapy modulation allows one to achieve the same infection evolution as with full therapy, with a reduction of drug consumption between 10% and 40%. The alternative discrete dosage approach shows similar results achieved with therapy modulation, both in terms of therapy effectiveness and drug consumption reduction.
Conclusions: The proposed model predictive control therapy optimization strategies appear to be effective, implementable and robust to model errors. It therefore represents a potentially useful approach to alleviate the burden of HCV therapy cost on national health systems
L1 ADAPTIVE SPEED CONTROL FOR A HELICOPTER
No full textAdaptive control theory is used to improve robustness of systems against model uncertainties and disturbances. Two of the main drawbacks of adaptive controllers is the lack of criteria to measure the robustness of the controller and the speed of the adaptation loop. In L1 adaptive control theory both problems are solved by the introduction of a low pass filter in the control input. The L1 adaptive control robustness and stability are guaranteed by numerical criteria. L1 adaptive control raised a great interest in the aerospace field due to the presence of nonlinear and uncertain dynamics that affects aircraft flight performances. Such strategy by the way has not been widely used and explored for rotorcrafts. In this article the authors propose an L1 output feedback speed controller for helicopters. The control system architecture is tested by means of a simulation test campaign through the use of a nonlinear helicopter model. Both performances and robustness of the controller are evaluated, even in presence of disturbances
Kalman Filter Based Adaptive Control Allocation
No full textIn recent years, various approaches for adaptive control allocation have been published with the goal to enable fault tolerance and improve flight performance of overactuated vehicles. Most of the presented methods are based on Model Reference Adaptive Control (MRAC) techniques and/or recursive least squares. In this study, we present a novel strategy combining concurrent learning MRAC and Kalman filtering to adapt the control effectiveness vector. The proposed strategy incorporates short term updates of the direct update as well as stationary correction through the Kalman filter. The adaptive control allocation has been evaluated using a hexacopter high fidelity simulation model. The hexacopter is controlled by an Incremental Nonlinear Dynamic Inversion (INDI) velocity controller and by a backstepping controller. In the simulation, we demonstrated the advantages of the adaptive control allocation for partial loss of effectiveness of one rotor and in nominal conditions. The adaptive control allocation avoided the crash of the hexacopter and improved tracking in forward flight compensating for effectiveness changes
L1 Adaptive Control for Small-Scale Unmanned Helicopters: Enhancing Speed Regulation
Full text linkThis paper focuses on the application of L1 adaptive control to the speed autopilot loop of small-scale unmanned helicopters. The L1 adaptive control technique is investigated for its potential to provide reliable speed control, particularly in handling external disturbances and model uncertainties. Although L1 adaptive control has been widely studied, its application to small-scale unmanned helicopters remains relatively unexplored. Through numerical simulations and a preliminary experimental test campaign conducted on a small rotary-wing platform, this paper contributes to validating L1 adaptive control as a promising solution for speed regulation in unmanned helicopter platforms
Integrated Conceptual Design and Parametric Control Assessment for a Hybrid Mobility Lunar Hopper
No full textThe lunar lava tubes are envisioned as possible hosting structures for a human base in the Moon’s equatorial regions, providing shelter from radiations, micrometeoroids, and temperature excursion. A first robotic mission is set to scout the habitability of these underground architectures in the near future. The communication inside these underground tunnels is heavily constrained; hence, the scouting system should rely on a high degree of autonomy. At the same time, the exploration system may encounter different types of terrain, requiring an adaptable mobility subsystem able to travel fast on basaltic terrain while avoiding considerable obstacles. This paper presents a cave explorer’s mission study and preliminary sizing targeting the lunar lava tubes. The study proposes using a hybrid mobility system with wheels and thrusters to navigate smoothly inside the lava tubes. The peculiar mobility system of the cave explorer requires an accurate study of the adaptability of its control capabilities with the change of mass for a given set of sensors and actuators. The combination of conceptual design techniques and control assessment gives the engineer a clear indication of the feasible design box for the studied system during the initial formulation phases of a mission. This first part of the study focuses on framing the stakeholders’ needs and identifying the required capabilities of the cave explorer. Furthermore, the study focuses on assessing a design box in terms of mass and power consumption for the cave explorer. Following different mission-level assessments, a more detailed design of the cave explorer is discussed, providing an initial design in terms of mass and power consumption. Finally, the objective shifts toward studying the performances of the guidance, navigation, and control (GNC) algorithms varying the mass of the cave explorer. The GNC significantly impacts the design box of the surface planetary system. Hence, investigating its limitations can indicate the feasibility of mass growth to accommodate, for example, more payload
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
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