1,720,990 research outputs found
Piezoelectric MEMS vibrational energy harvesters: Advances and outlook
No full textPiezoelectric MEMS energy harvesters based on thin films are compact and cost-effective microgenerators for scavenging environmental vibrations. This technology is promising for the replacement of electrochemical batteries in low power autonomous sensors and microdevices capturing vibrations in the μW-mW range. Most of piezoelectric MEMS devices, reported in the last few years, exhibit low generated power/voltage and are not suitable for practical applications. This work reviews the current status of MEMS energy harvesters based on piezoelectric thin films, highlighting approaches/strategies to face the two main challenges to be addressed for high performance devices, namely generated power and frequency bandwidth. The paper introduces the theoretical principles and the main figures of merit of energy conversion in piezoelectric thin films and devices. After an overview on piezoelectric thin films for energy harvesting applications, highlighting their key properties, the manuscript reports a comprehensive survey on the state of the art for this device technology. The last section summarizes the review, highlighting key issues to be addressed and providing an insight into the future outlook to realize devices for practical applications
Nanogenerators for harvesting mechanical energy conveyed by liquids
No full textThe huge mechanical energy available in the environment, mostly in form of kinetic energy of fluids such as wind, ocean and river currents or waves, is currently harvested by cumbersome, low efficiency and high environmental impact technologies. New approaches are needed for producing more compact and distributed mechanical energy converters. Nanogenerators and related micro and nanotechnologies can help in developing new environmentally friendly and biocompatible technologies. To face this challenge, new conversion physical principle, device structures and system architectures are currently being studied and developed. This work reviews the most recent advances on nanogenerators for harvesting energy transported by liquids in the environment such as water motion in rivers and marine environments and kinetic energy in rain. It discusses the most common physical transduction mechanisms, with a focus on piezoelectric and triboelectric nanogenerators (PENG/TENG), the requirements for producing flexible devices for effective conversion and the system architectures for optimizing the fluid-device interaction for producing large and fast oscillations, such as flapping, fluttering or galloping, from quasi-static or quasi-laminar fluid motion. Additionally, the work encompasses challenges such as waterproofing and antibiofouling, important issues in sub-marine and underwater environment
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
Flexible Piezoelectric Energy-Harvesting Exploiting Biocompatible AlN Thin Films Grown onto Spin-Coated Polyimide Layers
No full textThe increasing demand of piezoelectric energy harvesters for wearable and implantable applications requires biocompatible materials and careful structural device design, paying special attention to the conformability characteristics, properly tailored to scavenge continuously electrical energy even from the tiniest body movements. This paper provides a comprehensive study on a flexible and biocompatible aluminum nitride (AlN) energy harvester based on a new alternative fabrication approach, exploiting a thin polyimide (PI) substrate, prepared by spin coating of precursors solution. This strategy allows manufacturing substrates with adjustable thickness to meet conformability requirements. The device is based on a piezoelectric AlN thin film, sputtered directly onto the soft PI substrate, without poling/annealing processes and patterned by simple and low cost microfabrication technologies. AlN active layer, grown on soft substrate, exhibits good morphological and structural properties with roughness root mean squared (Rrms) of 6.35 nm, columnar texture and (002) c-axis orientation. Additionally, piezoelectric characterization has been performed and the extracted piezoelectric coefficient value of AlN thin film resulted to be 4.93 ± 0.09 pm/V. The fabricated flexible AlN energy harvester generates an output peak-to-peak voltage of ∼1.4 V and a peak-to-peak current up to 1.6 μA, under periodical deformation, corresponding to a current density of 2.1 μA/cm2, and providing a maximum generated power of 1.57 μW under optimal resistive load. Furthermore, the AlN energy harvester exhibits high elasticity and resistance to mechanical fatigue. High quality AlN piezoelectric layers on elastic substrates with tunable thicknesses pave the way for the development of a straightforward technological platform for wearable/implantable energy harvesters and biomechanical sensors
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