1,720,997 research outputs found
Polymeric matrix nanocomposites containing magnetic nanoparticles: from science to applications
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Triboelectric characterization of colloidal TiO2 for energy harvesting applications
Full text linkNowadays, energy-related issues are of paramount importance. Every energy transformation process results in the production of waste heat that can be harvested and reused, representing an ecological and economic opportunity. Waste heat to power (WHP) is the process of converting the waste heat into electricity. A novel approach is proposed based on the employment of liquid nano colloids. In this work, the triboelectric characterization of TiO2 nanoparticles dispersed in pure water and flowing in a fluorinated ethylene propylene (FEP) pipe was conducted. The idea is to exploit the waste heat to generate the motion of colloidal TiO2 through a FEP pipe. By placing an Al ring electrode in contact with the pipe, it was possible to accumulate electrostatic charges due to the triboelectric effect between the fluid and the inner pipe walls. A peristaltic pump was used to drive and control the flow in order to evaluate the performances in a broad fluid dynamic spectrum. The system generated as output relatively high voltages and low currents, resulting in extracted power ranging between 0.4 and 0.6 nW. By comparing the power of pressure loss due to friction with the extracted power, the electro-kinetic efficiency was estimated to be 20%
Waste Heat to Power: Technologies, Current Applications, and Future Potential
Full text linkEnergy consumption, environmental impact, and sustainability have risen fast through the ranks, achieving the first places in driving investments, policies, and concerns of all countries at any developmental stage. Energy transformation, though, must cope with nonunitary efficiency of devices and processes, which results in a distributed production of waste heat. A reduction of emissions, implying a conversion of waste heat to more noble forms of energy and a concurrent increase in efficiency of the same devices and processes, is of paramount importance. In view of the enthalpy content and distribution of the different sources of waste heat, low-grade/low-enthalpy sources below 200 °C are considered the most fertile field for research and development, with an impressive industrial growth rate. Thermodynamic cycles and thermal conversion devices based on the most relevant physical effects are herein introduced and briefly described, including both solutions that already achieved industrial maturity and less developed systems and devices whose study is still in progress. A specific focus on three application domains, selected due to their economic relevance, is done: industrial processes for the vast energy and capital availability, automotive sector for its permeation, and wearable devices for the market size. Limits and opportunities are critically discussed
Magnetic and magnetotransport properties of a Co-Sn evaporated trilayer
No full textThe aim of this work is the magnetic characterization of a Co-Sn-Co trilayer produced by thermal evaporation. Magnetization and magnetotransport measurements performed at low temperatures show that the sample has a complex behaviour related to the different morphologies of the external Co layers. A fitting procedure is introduced to disentangle the magnetization behaviour of different regions of the trilayer; three magnetic phases can be seen. Likewise, the magnetoresistance (MR) curves show the superposition of three different effects: a low-field positive MR, a slowly saturating negative MR similar to the one measured in granular systems, and an ordinary MR which becomes significant at very low temperatures. Combining magnetic and magnetotransport data, the three magnetic phases have been associated with the continuous Co underlayer, to the corrugated Co cap layer and to nanometre-sized Co islands embedded in the Sn layer ( respectively). The three-phase model coherently explains both magnetization and magnetoresistance datasets. A simple MR model based on a resistance network has been created to fit the experimental data; the fit is shown to match the main features of the experimental MR
Liquid-state pyroelectric energy harvesting
Full text linkIncreasing the sustainability of energy generation can be pursued by harvesting extremely low enthalpy sources: low temperature differences between cold and hot reservoirs are easily achieved in every industrial process, both at large and small scales, in plants as well as in small appliances, vehicles, natural environments, and human bodies. This paper presents the assessment and efficiency estimate of a liquid-state pyroelectric energy harvester, based on a colloid containing barium titanate nanoparticles and ferrofluid as a stabilizer. The liquid is set in motion by an external pump to control velocity, in a range similar to the one achieved by Rayleigh–Bénard convection, and the colloid reservoir is heated. The colloid is injected into a Fluorinated Ethylene Propylene pipe where titanium electrodes are placed to collect electrical charges generated by pyroelectricity on the surface of the nanoparticles, reaching 22.4% of the ideal Carnot efficiency of a thermal machine working on the same temperature drop. The maximum extracted electrical power per unit of volume is above 7 mW/m3 with a ΔT between electrodes of 3.9 K
On the Pyroelectric and Triboelectric Phenomena in Ferrofluids
Full text linkOwing to the waste of energy originated by any physical or chemical process, approaches for reducing the energy losses have been conceived and, nowadays, energy recovery and conversion systems represent a worldwide-recognized solution. The advent of colloidal-based cybernetic systems highlights the essential role of energy harvesting, storage, and management capabilities coped by colloidal energetic systems. In this work, an alternative to thermoelectricity generation is demonstrated by means of a magnetic colloid based on Fe3O4 nanoparticles (NPs). The ferrofluid (FF) tribo- and pyroelectric features are explored in order to increase the amount of harvested energy. The findings suggest that the FF shows both triboelectric and pyroelectric charge displacement. A capacitive electrode is more efficient for accumulating potentials up to 48 V developed by triboelectricity while a resistive one is essential to collect pyroelectric charges up to 22 nA, which helped to estimate the FF pyroelectric coefficient, reaching the remarkable value of 25.2 μCm−2 K−1. A simplified equivalent model of the inductive setup is proposed, suggesting that increasing the fluid temperature a reduction of FF inductance due to demagnetization effects occurs
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
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