1,720,956 research outputs found
Design, and characterisation of impact based and non-contact piezoelectric harvesters for rotating objects
No full textThis thesis highlights two different methods of extracting electrical energy from rotational forces using impact based and non-contact based piezoelectric harvesters. In this work, the centripetal force is used as the main acting force that causes the piezoelectric harvesters to produce output power. In order to achieve this, the harvesters are mounted in a horizontal position while the rotational forces are applied. The impact based piezoelectric harvester consists of a tube with one piezoelectric pre-stressed beam mounted at each end of the tube. A ball bearing that has the freedom of movement between the two ends of the tube generates an impact force on the piezoelectric structures due to the effect of the centripetal force. The impact based piezoelectric harvester is modelled and its behaviour is analysed and verified experimentally. For the non-contact piezoelectric harvester, the applied force on the piezoelectric element is produced by a magnetic levitation system without the need for a direct physical contact. The impact of the magnet size and shape is studied and the results become a guideline that is used to design and optimize the piezoelectric harvester. The model of the non-contact piezoelectric harvester is derived and verified experimentally in order to analyse its behaviour at different boundary conditions. A comparison between the two harvesters is carried out. This includes highlighting the advantages and the limitations of each of them
Reward function design in multi-agent reinforcement learning for traffic signal control
No full textIn recent years, there has been increased interest in Reinforcement Learning (RL) for Traffic Signal Control (TSC), with implementations of RL touted as a potential successor to the current commercial solutions in place. Commercial systems, such as Microprocessor Optimised Vehicle Actuation (MOVA) and Split, Cycle, and Offset Optimisation Technique (SCOOT), can adapt to the changing traffic state, but do not learn the specific traffic characteristics of an intersection, and leave much to be desired when performance is compared to the potential benefits of using RL for TSC. Furthermore, distributed RL can provide the unique benefits of scalability and decentralisation for road infrastructure. However, using RL for TSC introduces the problem of non-stationarity where the changing policies of RL agents, tasked with optimal control of traffic signals, directly impacts the observed state of the system and therefore the policies of other agents. This non-stationarity can be mitigated through careful consideration and selection of an appropriate reward function. However, existing literature does not consider the impact of the reward function on the performance of agents in a non-stationary environment such as TSC. In this paper, we select 12 reward functions from the literature, and empirically evaluate them compared to a baseline of a commercial solution in a multi-agent setting. Furthermore, we are particularly interested in the performance of agents when used in a real-world scenario, and so we use demand calibrated data from Ingolstadt, Germany to compare the average waiting time and trip duration of vehicles. We find that reward functions which often perform well in a single intersection setting may not outperform commercial solutions in a multi-agent setting due to their impact on the demand profile of other agents. Furthermore, the reward functions which include the waiting time of agents produce the most predictable demand profile, in turn leading to increased throughput than alternatively proposed solutions
Numerical model of a non-contact piezoelectric energy harvester for rotating objects
No full textEnergy harvesting is an attractive technique for powering wireless sensors and low power devices. Harvesters delivering sufficient power from rotation for sensor applications have been developed, but difficulties are encountered when the devices to be powered are located off axis on a rotating object. In such cases, harvesters are not adapted to low frequency and high amplitude of motion, where the input force amplitude is higher than the mass available displacement. A novel approach, based on using non-contact piezoelectric energy harvester to generate power from magnetic forces due to the effect of the centripetal force is proposed in this paper. In this approach, the pre-stressed piezoelectric beams are deformed by interaction with an oscillating magnet that is supported by magnetic levitation system. Because the magnetic levitation system is nonlinear, the nonlinear spring enables operation over a wide range of large centripetal accelerations. A model of the system is presented and analyzed in order to identify the parameters that control the performance of the harvester. Theoretical investigations are followed by a series of experimental tests to validate the response predictions. With an off-axis distance of 75 mm the prototype, occupying a volume of approximately 17.74 cm3 and weighting 46 g, generated an output power ranging from 0.2 µW to 3.5 µW when the rotating speed changes from 3 rps to 5.55 rps. Further optimization of the piezoelectric harvester is carried out in order to improve the power density. An application in which the harvester can be used in is tire pressure monitoring systems. In this case, the harvester can replace the battery of the pressure sensors located inside the vehicle tire
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
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
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