1,721,117 research outputs found
Piezoelectric nanotransducers
No full textPiezoelectricity has already found a multitude of applications, including voltage generation, quartz oscillators, mechanical sensors and actuators, piezoelectric transformers and more. However, in the last years, intense research efforts worldwide are demonstrating that nanoscale piezoelectricity can offer outstanding advantages in comparison with conventional piezoelectrics. Nevertheless, so far, no systematic analysis of these advantages and of the associated challenges has been reported. Here, we critically review 16 unique advantages of piezoelectricity at nanoscale and also consider some of the most important open challenges, together with promising general strategies to address them. Our analysis confirms that nanotechnology can open the way to piezoelectric transducers with unprecedented performance for several applications, including mechanical energy harvesting, piezotronics, piezophototronics, implantable systems, wireless piezoelectric nanotransducers, and more
Systematic design of micro-resistors for temperature control by quasi-simultaneous heating and temperature sensing
No full textA single resistor can be used for quasi-simultaneously heating and temperature sensing. For instance, in microsystems this strategy is often employed for temperature control, flow sensors, gas sensors, material characterization, hot-wire anemometers, bio-MEMS, and more. However, the design of such integrated resistors is complex due to both many design parameters and several conflicting specifications so that until now there is no method for predicting, based on a given set of specifications, if a solution exists and, eventually, for systematic design of optimal devices. Here we determine a complete set of relations which allows to easily find if, for given specifications, a solution is possible and, if not, to identify which specifications must be relaxed. Moreover, even with very severe specifications, our relations offer insight for systematic design of optimal resistors for quasi-simultaneous heating and temperature sensing; illustrative design cases are reported
Micro-hot-plates without simply connected hot-spots and with almost-circular temperature distribution
No full textWe have recently shown that the temperature distribution in micro-hot-plates with perfectly circular geometry can be accurately expressed in terms of modified Bessel functions. However, the geometry of practical micro-hot-plates cannot be perfectly circular due to several issues, including the presence of the electrical contacts; in fact, a typical manifestation of poor circular-symmetry is the occurrence of simply-connected hot-spots. Here we systematically investigate all these issues and describe strategies for designing micro-hot-plates without simply-connected hot-spots and with an almost circular temperature distribution. FEM simulations consistently confirm that our methodology reduces the temperature deviations from ideal circular symmetry down to levels which are unimportant for most applications (e.g. less than 2.5°C for a micro-hot-plate operating at 800°C). As a result of the excellent circular symmetry, the temperature distribution in the proposed micro-hot-plates, unlike previously reported devices, can be accurately expressed in terms of the modified Bessel functions, which is a key step toward the design of micro-hot-plates with unprecedented temperature uniformity or with desired temperature profiles
Real-time monitoring of the solution growth of ZnO nanorods arrays by quartz microbalances and in-situ temperature sensors
Full text linkWet-chemistry methods have crucial advantages for the synthesis of nanostructures, including simple, low-cost, large-area, and low-temperature deposition on almost arbitrary substrates. Nevertheless, the rational design of improved wet-chemistry procedures is extremely difficult because, in practice, only post-synthesis characterization is possible. In fact, the only methods for on-line monitoring the growth of nanostructures in liquids are complex, expensive and introduce intricate artifacts. Here we demonstrate that electro-mechanically resonating substrates and in-situ temperature sensors easily enable an accurate real-time investigation of reaction kinetics and, in combination with conventional SEM imaging, greatly facilitate the rational design of optimized synthesis procedures; in particular, such a simple approach provides useful insight for the development of processes where one or more key parameters are dynamically adjusted. As a proof-of-concept, first, we accurately characterize a process for fabricating arrays of ZnO nanorods; afterwards, we design a dynamic-temperature process that, in comparison with the corresponding constant-temperature procedure, is almost-ideally energy efficient and results in ZnO nanorods with improved characteristics in terms of length, aspect ratio, and total deposited nanorods mass. This is a major step towards the rational design of dynamic procedures for the solution growth of nanostructures
An Accurate and Computationally Efficient Model for Membrane-Type Circular-Symmetric Micro-Hotplates
No full textIdeally, the design of high-performance micro-hotplates would require a large number of simulations because of the existence of many important design parameters as well as the possibly crucial effects of both spread and drift. However, the computational cost of FEM simulations, which are the only available tool for accurately predicting the temperature in micro-hotplates, is very high. As a result, micro-hotplate designers generally have no effective simulation-tools for the optimization. In order to circumvent these issues, here, we propose a model for practical circular-symmetric micro-hot-plates which takes advantage of modified Bessel functions, computationally efficient matrix-approach for considering the relevant boundary conditions, Taylor linearization for modeling the Joule heating and radiation losses, and external-region-segmentation strategy in order to accurately take into account radiation losses in the entire micro-hotplate. The proposed model is almost as accurate as FEM simulations and two to three orders of magnitude more computationally efficient (e.g., 45 s versus more than 8 h). The residual errors, which are mainly associated to the undesired heating in the electrical contacts, are small (e.g., few degrees Celsius for an 800 °C operating temperature) and, for important analyses, almost constant. Therefore, we also introduce a computationally-easy single-FEM-compensation strategy in order to reduce the residual errors to about 1 °C. As illustrative examples of the power of our approach, we report the systematic investigation of a spread in the membrane thermal conductivity and of combined variations of both ambient and bulk temperatures. Our model enables a much faster characterization of micro-hotplates and, thus, a much more effective optimization prior to fabrication
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
High light-load efficiency charge pumps
No full textHere, first, we analyze the undesired charge transfer occurring in charge pumps; afterwards we present a circuit which is less susceptible to this issue, resulting in significant improvements of the light load efficiency in charge pumps which must have a sufficiently high maximum current capability. SPICE simulations confirm the theoretical results
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