1,720,958 research outputs found
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
Optimal Design of Pin-Fin Heatsinks for SiC Power Modules Based on Analytical Thermal Modeling and TLBO Algorithm
No full textThermal management has always been one of the leading technical challenges in high-power power modules. Especially in the current trend of seeking high power density of devices, optimized thermal design is crucial. This paper presents an optimal design method for pin-fin heatsinks for SiC power modules, based on analytical thermal models and Teaching Learning Based Optimization (TLBO) algorithm. First, the analytical thermal model of the pin-fin heatsink is introduced, which combines the Fourier-based conduction model and the empirical convection model. Junction temperature (Tj) can be directly estimated using this comprehensive model and has been verified to be within a 5% error by numerical simulations. Then, this paper investigates the effectiveness of TLBO in finding the optimal pin-fin heatsink with a compatible cold plate. Compared to Genetic Algorithm (GA) and Particle Swam Optimization algorithm (PSO), TLBO can converge more easily, taking only one-third of the convergence time with the same optimization target and constraint. This proposed optimal design methodology not only improves the power density of the converter system but also provides a valuable design method for researchers and engineers in the field
Phase-Shift and Duty-Ratio Control Optimization of a 6 kW Three-Port Resonant DC–DC Converter for Dual Auxiliary Voltage EV Applications
No full textIsolated three-port dc-dc converters (TPCs) facilitate integration of three voltage sources/loads in electric vehicle applications. Three-port resonant converter (TPRC) is an attractive TPC topology as it inherits the advantages of resonant converters. Phase-shift (PS) control applied to TPRCs enables independent power flow control among all ports. Phase-shift and duty-ratio (PSDR) control introduces three additional degrees of freedom providing the potential for improving the converter efficiency compared to PS control. This article presents a generalized harmonic approximation-based steady-state mathematical model for a TPRC with five-variable PSDR control. Mathematical solutions to the steady-state converter bridge voltages and the ac currents under PSDR control are provided. The proposed mathematical model is integrated with a TPRC power loss model and together are used to formulate a control optimization problem for evaluating the optimal control variables at maximum converter efficiency. The optimized five-variable PSDR control is compared against PS control using a 6 kW/100 kHz rated hardware demonstrator, with efficiency improvements as high as 12.4%
Thermal and hydraulic performance of 3D printed jet impingement configuration for SiC power modules in aerospace propulsion inverters
No full textEfficiently controlling the temperature of power electronic inverters is crucial for aerospace applications with high power density. Effective thermal management strategies could enhance the power output of power inverters to their maximum rated capacity. Jet impingement is a promising technology with outstanding heat transfer characteristics, making it a sophisticated aid for cooling innovation in power inverters. A numerical comparative study was conducted between jet impingement and traditional pin finned heat sink. In our case study, the pin fin could not effectively regulate the junction temperature to a level below 150 °C. By using a 3D printed jet impingement housing composed of polymer, the weight of the power module thermal management system could be decreased by 71 % compared to a metallic pin finned heat sink. Moreover, this approach aids in lowering the junction temperature to 129 °C, under the same boundary conditions. Additionally, a numerical study was conducted on power modules with thermal imbalance used in aerospace inverters. The study proposed various configurations of jet impingement to reduce temperature differences between power module switches, as well as minimize the pressure drop across the jet impingement housing. The primary objective is to minimize the temperature disparity between the unbalanced switches in order to improve the overall reliability and lifespan of the power module, while decreasing the pressure drop. Among all the options, the optimum design achieves a minimal temperature difference of 24 °C between the power module switches, while the pressure drop reaches 12 kPa
A Comparative Study of Single- and Multi-Cell Three- Level ANPC Inverters for Electric Aircraft Applications
No full textWith carbon emission becoming a global issue, electric aircraft holds great potential as the future of transportation. A multi-inverter configuration has been adopted in previous studies for electric propulsion systems with voltage and power levels increasing. Based on the three-level active neutral-point-clamped (ANPC) topology, this paper evaluates and compares the performance of three design cases with different numbers of parallel inverter cells, for medium-voltage high-power electric aircraft propulsion systems. With the redundant design considered, the key indicators regarding efficiency, reliability, weights, and costs of the three design cases are assessed based on the aircraft's mission profile. Moreover, a long-term economic comparison with the effect of efficiency and weight is conducted
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
- …
