1,721,096 research outputs found
Effect of variation in contact friction on the performance of the under-platform dampers
Full text linkUnder platform-dampers (UPDs) are commonly used devices in turbomachinery to mitigate the turbine blade vibrations caused by the periodically fluctuating stresses. These dampers are placed in the underside of two adjacent blades and vibration energy is partly dissipated by the friction at the blade/damper interfaces. As a result, the vibration amplitude is reduced with beneficial effects on the blade fatigue life. At LAQ AERMEC a novel test rig has been developed to accurately measure the response of a single turbine blade and the kinematics/dynamics of two adjacent UPDs. In this newly developed test rig, each damper is in contact with the under-platform of the blade on one side and with ground/fixed platform on its other side. The dampers are pressed against the blade platform by static forces applied by dead weights. A static force is also radially applied to root of the blade to clamp it to the rig, simulating the effect of the actual centrifugal force in operating conditions. Finally, a transverse periodic excitation is applied in order to excite the blade's first resonances. In this paper, the performance of different UPDs in terms of reduction of the blade vibration amplitude and shift in resonance frequency is studied at two different contact friction conditions (normal and low friction). Low friction conditions are obtained by introducing a thin layer of oil between the damper-blade contact interfaces. Experiments are performed on a real turbine blade to investigate the semi-cylindrical dampers. This profound study of UPDs provides a strong basis to understand the effect of damper with different contact conditions, to limit the blade vibratio
The effect of friction damping on the dynamic response of vibrating structures: an insight into model validation
No full textDry friction is widely used in turbomachinery in the form of under platform dampers to limit resonant vibration and avoid high-cycle fatigue failures of the blades. Most test rigs that are used to investigate the behavior of dampers aim to evaluate their performance by reduction in blade vibration amplitude. This approach is insufficient to understand local nonlinearities of the contact and influence of blade dynamics on UPDs behavior. A newly developed test rig provides the user with an unprecedented set of information: it measures contact forces and relative displacements between dampers and blade together with the overall blade response. This controlled environment, together with a state-of-the-art numerical model of the test rig, is used to provide an insight into the subject of model validation. The presented experimental and numerical study of the damper is used to highlight the relevance of an accurate representation of the constraints induced by friction contacts and to discuss the adequacy of state-of-the-art contact models
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
COVID-19: Automatic Detection of the Novel Coronavirus Disease from CT Images Using an Optimized Convolutional Neural Network
No full textIt is widely known that a quick disclosure of the COVID-19 can help to reduce its spread dramatically. Transcriptase polymerase chain reaction could be a more useful, rapid, and trustworthy technique for the evaluation and classification of the COVID-19 disease. Currently, a computerized method for classifying computed tomography (CT) images of chests can be crucial for speeding up the detection while the COVID-19 epidemic is rapidly spreading. In this article, the authors have proposed an optimized convolutional neural network model (ADECO-CNN) to divide infected and not infected patients. Furthermore, the ADECO-CNN approach is compared with pretrained convolutional neural network (CNN)-based VGG19, GoogleNet, and ResNet models. Extensive analysis proved that the ADECO-CNN-optimized CNN model can classify CT images with 99.99% accuracy, 99.96% sensitivity, 99.92% precision, and 99.97% specificity
Holocene climate phases from buried soils in Tigray (northern Ethiopia): comparison with lake level fluctuations in the Main Ethiopian Rift
No full textStratigraphic analysis of alluvial/colluvial sequences and 14C dating have been used as proxies for Holocene climate changes in the highlands of Tigray (northern Ethiopia). The studied records show alternations of buried soils and peaty' clayey sediments, pointing to wet, stabilization phases, and organic-free colluvium layers resulting from the abrupt occurrence of dry-climate episodes. The 14C dates, mostly unpublished, cluster in the 11,090-9915, 9465-9135, 8450-7330, 6720-3635, 2710-2345, and 1265-790 cal yr B.P. time spans. Evidence of subsequent pedogenesis is lacking in the area, apart from a buried humified horizon dated at 300 +- 60 14C yr B.P. (460-295 cal yr B.P.).Both the timing and the pattern of Tigray paleoclimatic events fit the corresponding framework, based on lake level changes, previously mplemented for the Main Rift Valley. These findings give further support for arguing that the forcing mechanisms of the wet/dry fluctuations during the Holocene were effective over a large scale
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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