1,720,990 research outputs found
Autonomous underwater vehicle collision avoidance for under-ice exploration
No full textOn 22 August 2004 the Autosub-2 autonomous underwater vehicle (AUV) was on its return leg of a 144 km, 24 h under-ice mission in the Arctic sea over the Northwind Shoal off the northeast Greenland coast when it found its path blocked by a deep ice keel that had drifted across its planned mission route. After three attempts, the Autosub found a way around the keel and continued on its way to rendezvous with its mother ship. This paper reports the development, testing, and operation of collision and obstacle avoidance techniques used in the Arctic and Antarctic under-ice expeditions of the Autosub-2 AUV.<br/
Challenges of using an AUV to find and map hydrothermal vent sites in deep and rugged terrains
Full text linkIn March 2010, the Autosub6000 AUV embarked on a cruise to discover, locate and map hydrothermal vent sites in an active spreading centre, the Cayman trough in the Caribbean sea. The environment provided the challenge of steep and rugged terrain together with deep water (in places greater than 5000 m). Autosub6000 is a flight class, hydrodynamically shaped AUV, with good endurance capability, making it well suited for searching for plume signals and mapping terrain over the required moderately large areas. However, it must fly at a forward speed greater than 0.8 ms-1 to achieve control, and so it requires a capable forward look collision avoid capability. Another potential challenge is navigation. To make best use of ship time, Autosub6000 missions are commonly conducted with neither the support ship in attendance, nor an acoustic transponder long baseline network. Hence positioning is dependent upon the AUV autonomous navigation (aided by a position fix after the AUV’s descent to within ADCP bottom tracking range of the seabed). For the cruise on the UK research ship RRS James Cook, the AUV was equipped with sensors for EH (redox potential), turbidity, CTD, tri axis magnetometer, and an EM2000 multibeam sonar. The paper describes the Autosub6000 vehicle, its systems, capabilities, the missions it undertook in the deep Caribbean sea, and the discoveries it made. The missions, although ultimately very successful, were not without problems, with, for example, the steep seabed slopes, at times affecting the accuracy for the navigation system. The paper will also discuss these issues and how they might be addressed in the future. <br/
Autosub6000: its first deepwater trials and science missions
No full textIn September 2007 on RRS Discovery, theAutosub6000 autonomous underwater vehicle (AUV)completed its first deepwater engineering trials and,fitted with a multibeam bathymetric mapping sonar,carried out its first science missions less than a yearlater as part of a geology and geophysics sciencecruise onboard the RRS James Cook. This paperdescribes how the issues of energy storage, navigationand buoyancy control were tackled that specificallyaffect a deep-diving AUV, capable of operating withtrue autonomy independently of the mother ship
Low-altitude terrain following and collision avoidance in a flight-class autonomous underwater vehicle
No full textAn autonomous underwater vehicle (AUV), Autosub6000, has been shown to operate safely at altitudes as low as 3?m above rugged and complex sea floor environments. This capability is essential for future AUV missions in such environments, e.g. high-resolution surveys using colour photography or multi-beam sonar bathymetry. This was achieved through the development of an obstacle avoidance system for the AUV, incorporating relatively low-cost off-the-shelf components and simple algorithms. This paper details the specification, design, and testing at sea of Autosub6000's obstacle avoidance system. It describes how the specification of the system was influenced by the need to retrofit it into the existing control architecture, together with the pragmatic need to minimize overall complexity. The sensor used in the obstacle avoidance system is a mechanically scanned forward-looking sonar, and the control algorithm is based upon the detection of the range and elevation of the horizon relative to the AUV. The avoidance behaviour is by default to fly over obstacles but, if this is not possible, a turn-around and retry collision avoidance algorithm is invoked. Results are presented of the system's performance during recent deep-water trials of the AUV over the Casablanca Seamount region of the Atlantic Ocean
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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