1,721,405 research outputs found
Piezoelectric units with self-tuning multi-resonant shunts for vibration absorption
Full text linkThis thesis is focused on a lightweight and modular control system formed by a piezoelectric patch connected to either a single-resonant or a multi-resonant self-tuning shunt, which can be used to mitigate the resonant response of one or multiple low-order flexural modes of a hosting structure. The aim of the study is to develop a self-contained unit, which can be bonded in batches on thin structures to decrease the low frequency flexural response generated by stationary stochastic disturbances.
To this end, the study investigates the optimal tuning of both single-resonant and multi-resonant shunts with reference to a global and a local cost function. Two configurations of the single-resonant shunt are considered, which are formed by a resistance-inductance (RL) connected respectively in series and in parallel. Instead, a single configuration of the multi-resonant shunt is investigated, which is formed by an array of parallel branches encompassing a resistance-inductance-capacitance (RLC) connected in series. The global cost function, given by the minimisation of the hosting structure time-averaged total flexural kinetic energy, is used as a reference metric to assess the optimal tuning of the shunt. Instead, the local cost function, given by the maximisation of the time-averaged electric power absorbed either by the RL single-resonant shunt or by each RLC branch of the multi-resonant shunt, is employed for the practical implementation of the self-tuning shunt.
The study shows that, with respect to the resistance and inductance shunt parameters, the two cost functions are characterised by mirror bell surfaces. Hence, the optimal shunt resistance and inductance values that would minimise the global cost function coincide with those that would maximise the local cost functions. As a result, both the single-resonant and multi-resonant shunts can be suitably tuned within the shunt itself by maximising the time-average electric power absorbed by the single-resonant shunt or by each branch of the multi-resonant shunt. The study also shows that, the tuning can be effectively implemented with a recursive two-paths tuning approach, whereby the inductance is first tuned along a constant-resistance path characterised by a bell shaped curve of the cost function and then the resistance is tuned along a constant-inductance path characterised by a bell shaped curve of the cost function too. This two-paths tuning sequence can be run recursively online such that the shunt can be adapted to variations of the electro-mechanical response of the hosting structure and piezoelectric transducer as well as to variations of the electric response of the shunt components, which can both occur in presence of temperature variations or other exogenous physical effects.
Since the optimisations along the constant resistance and constant inductance paths are characterised by non-convex cost functions, the study proposes to employ the extremum seeking algorithm to find the optimal shunt parameters that would maximise the electric power absorption. This is a model-free gradient driven search algorithm, which asymptotically leads to the maximum of the non-convex bell-shaped paths. The algorithm is based on a periodic dithering signal that perturbs the inductance and resistance tuning signals such that the resulting electric power absorbed by the shunt equally shows such a periodic signal, which is either in phase or out-of-phase with the dithering signal depending the tuning is under or over estimating the shunt parameter with respect to the optimal one that maximises the power absorption. The study shows that this algorithm suitably leads to the optimal shunt values regardless the structure is excited by a stochastic disturbance such that the power cost function undergoes significant variations over time
Shunted piezoelectric patch adaptive vibration absorber set to maximise electric power absorption: A comparison between parallel and series RL-shunts
No full textThis paper presents a comparative study on two types of shunted piezoelectric patch adaptive vibration absorbers, which
can be bonded in batches on thin-walled structures to control the broad-band resonant response of low order flexural
modes. The self-contained control units are formed by a thin piezoelectric patch connected either to a series or to a parallel
resistive-inductive (RL) network. The two components of the shunt are adapted online in such a way as to maximise the
time-averaged electric power absorbed by the shunt, which corresponds to minimising the time-averaged total flexural
response of the hosting structure. The study considers a practical demonstrator formed by a thin rectangular plate with five
piezoelectric patches connected to digital RL-shunts, which is excited in bending by a stationary white noise point force.
The aim of the paper is to contrast the tuning and vibration control properties of the series and parallel RL shunts. More
specifically, the online implementation of a recursive two-paths tuning strategy along R-constant and L-constant paths with
an extremum seeking gradient search algorithm is analysed first for the two types of shunts. Then, the vibration control
performance produced by the two types of shunts is investigated for the case where they are tuned to control the resonant
response of the first flexural mode of the plate
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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