1,720,968 research outputs found
Phase-field modeling of domain evolution in ferroelectric materials in the presence of defects
Full text linkThe properties of ferroelectric devices are strongly influenced, besides crystallographic features, by defects in the material. To study this effect, a fully coupled electromechanical phase-field model for 2D ferroelectric volume elements has been developed and implemented in a Finite Element code. Different kinds of defects were considered: holes, point charges and polarization pinning in single crystals, as well as grain boundaries in polycrystals, without and with additional dielectric interphase. The impact of the various types of defects on the domain configuration and the overall coercive field strength is discussed in detail. It can be seen that defects lead to nucleation of new domains. Compared to the energy barrier for switching in an ideal single crystal, the overall coercive field strength is significantly reduced towards realistic values as they are found in ferroelectric devices. Also the simulated hysteresis loops show a more realistic shape in the presence of defects
Integral equations for free-molecule flow in MEMS: recent advancements
Full text linkWe address a Boundary Integral Equation (BIE) approach for the analysis of gas dissipation in near-vacuum for Micro Electro Mechanical Systems (MEMS). Inspired by an analogy with the radiosity equation in computer graphics, we discuss an efficient way to compute the visible domain of integration. Moreover, we tackle the issue of near singular integrals by developing a set of analytical formulas for planar polyhedral domains. Finally a validation with experimental results taken from the literature is presented
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
Fluid damping modeling for MEMS sensors operating in the 10 kHz-100 kHz range in near vacuum
No full textThe work proposes and experimentally verifies a new model for the prediction of the quality (Q) factor of MEMS operating in fluid damping regime in near-vacuum, with sub-2-μm gaps, in a range of frequencies extending from ∼10 kHz (typical of state-of-the-art inertial sensors) up to 100 kHz. Such frequency range is expected to be of interest for next-generation inertial sensors; yet the quasi-static approximation, holding when the time of flight of molecules between MEMS surfaces is small with respect to the shuttle oscillation period, gradually becomes invalid with increasing frequency, claiming for new modeling tools. The proposed method is validated through eight different test structures with varying resonance frequency and air gap. The agreement between Q factor prediction and measurement is within 8% even at the highest frequency
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
Near Vacuum Gas Damping in MEMS: Numerical Modeling and Experimental Validation
No full textThis paper validates an innovative simulation tool for the prediction of gas damping occurring in MEMS working in near vacuum at frequencies in the range of 20-30 kHz. Three different families of test devices, representing standard building blocks of MEMS, have been designed, fabricated, tested, and simulated. A total of 292 structures belonging to 36 different geometries have been addressed in order to confirm the ability of the numerical model to capture the dependence on geometrical parameters and to provide a quantitative prediction. Tests have been operated both at variable pressures in a vacuum chamber and in the closed package, and demonstrate an accuracy in the order of 15%
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
On the simulation of the hysteresis loop of polycrystalline PZT thin films
No full textWe investigate experimentally and numerically the polarization hysteresis loop of a PZT thin film utilized in MEMS actuators. A fully coupled electromechanical phase-field technique is employed for the numerical prediction part, starting from a simplified model of the thin film proposed on the basis of several experimental evidences. It is shown that polycrystalline nature of the film plays a fundamental role. In particular the simulations demonstrate that grains with dielectric interfaces and stochastic orientation of the crystallographic directions have a significant impact on the overall hysteresis loop
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