1,721,318 research outputs found
Temperature distribution in membrane-type micro-hot-plates with circular geometry
No full textThe absence of an accurate analytical model for the temperature distribution in micro-hot-plates does not allow the systematic design of micro-heaters with high temperature uniformity in the hot region, a key issue for the fabrication of accurate gas sensors, infrared emitters with high spectral purity, and micro-reactors with uniform deposition on sufficiently large areas. Here, by considering a circular heater geometry and typical (i.e. very small) thicknesses, we reduce the three-dimensional temperature distribution to one dimension only and, by solving a form of Bessel differential equation, we express the temperature distribution in terms of modified Bessel functions. The resulting relations accurately approximate the radiation heat transfer within the heater, which is a decisive advantage as the temperature within the heater is generally very high. Finally, we demonstrate that our model has almost the same accuracy as finite element method (FEM) simulations and is therefore suitable for designing micro-hot-plates with unprecedented temperature homogeneity as well as for accurately predicting the temperature profile in generic micro-hot-plates
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
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
Classification of soft-tissue degloving in limb trauma
No full textCompressive, tortional and abrasive deforming forces are translated to the limbs during high energy trauma. The long bones may be fractured in many patterns with a varying extent of fragmentation and comminution but the soft-tissues appear to absorb the forces in a predictable way. We retrospectively reviewed a series of 79 complex limb injuries treated in a dedicated centre where the clinical notes and photo-documentation were meticulously kept and where the outcomes were known. The soft-tissue injuries were then described and revealed four patterns of injury: abrasion/avulsion, non-circumferential degloving, circumferential single plane and circumferential multi-plane degloving. These patterns occurred either in isolation or occasionally in combination. Resuturing of degloved skin was only successful in non-circumferential (pattern 2) cases. Radical excision of devitalised tissue followed by soft-tissue reconstruction in a single procedure was successful in all patterns apart from pattern 4 (circumferential multi-plane degloving). In pattern 4 we recommend serial wound excision prior to reconstruction
Describing severe limb trauma
No full textSeventy-nine severe limb injuries were retrospectively reviewed to compare the AO/ASIF and the Gustillo classifications. Specifically, the suitability of these classifications with respect to prognosis and management of these cases was compared. A healed and stable wound was the ultimate outcome measure. Surrogate outcome measures used were: the time to healing; the number of anaesthetics until the wounds were healed; and the number of operations until the wounds were healed. Any change in lifestyle following the injury was also assessed. The primary healing rates of the AO/ASIF groups showed significant (P < 0.001) inter-group differences. However, when the injuries were classified using the Gustillo system, the primary healing rates did not show any differences between the groups. Also, differences in the other outcome measures were most pronounced when using the AO/ASIF system. Importantly, changes in lifestyle correlated with the injury score when using the AO/ASIF system (P < 0.05). Unlike the AO/ASIF system, the Gustillo system was not applicable in 100% of cases. A modified AO/ASIF scoring system is proposed which provides a good predictor of outcome
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
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