1,721,011 research outputs found
Electron effective masses of Scx Al1- x N and Alx Ga1- x N from first-principles calculations of unfolded band structure
Full text linkThe electron effective masses of Sc x Al 1 - xN and Al x Ga 1 - xN, two of the most promising wide bandgap materials for power and RF electronic applications, have been calculated using the predictions of the density functional theory (DFT). More specifically, the unfolding technique has been adopted to extract the effective band structure of the two alloys under investigation. It has been found that the AlGaN effective masses m - approximately follow the Vegard law. On the contrary, due to the larger amount of disorder inside the crystal, the ScAlN shows a non-monotonic change of m - as a function of the Sc concentration, which requires the DFT calculations to be consistently performed for an accurate prediction. The ScAlN effective masses as a function of Sc content have been reported in the range 0 ≤ x ≤ 0.25 for the first time
On design and analysis of a drivetrain test rig for wind turbine health monitoring
No full textThe reliability of offshore wind turbines is a key factor when estimating maintanence costs, downtime due to component failure and overall efficiency during operational life. Offshore wind turbines have limited accessibility and operate in harsh environments and, as a result, it is difficult to perform frequent checks on electrical and mechanical component. Drivetrain test rigs (DTR) are crucial to the task of: Validating the design of new components to avoid early life failure, observe the behaviour of components under load over long periods of time in a controlled environment and produce a maintanence plan that minimize costs and frequency of intervention. In this paper, after a brief introduction on the state of the art in DTR technology, is described a methodology that can be used to create an effective conceptual design for a drivetrain test rig, focusing also on the possible downscaling. The paper starts by analyzing the benefits of the drivetrain use in the wind power industry, bringing examples of real test rigs used in industrial and academical world. Once the topic is mastered it is possible to proceed with a description of the various phases needed to obtain the conceptual design, from the definition of layout to the preliminary 3D modeling. The test rig that is here designed, while inspired from full scale dynamometers used in the industry, is thought as a laboratory tool for academical use that can be used by students to investigate fault detection methods and health monitoring systems of wind turbines. It is also included a section dedicated to the possible techniques for downscaling the test rig, based on simple considerations of the drivetrain mechanical behaviour. Downscaling becomes a key factor when facing the need to test turbine components of ever increasing dimensions in laboratories with limited space and budget. The definition of a procedure to create a scaled version will allow laboratories to build test rigs of smaller dimension but with a damage model for the various components still closely linked to the one in real scale. Downscaling is also a necessity when working with limited power sources, not able to recreate the conditions that the real scale turbine encounters. The ultimate goal is to define a solid base to allow further development in the detailed design phase
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
Characterization and TCAD Simulation of the Electrostatic Potential Distortion in HV-ICs due to Losses in the Epoxy Mold Compound
No full textThe presence of space charge and leakage current within the epoxy-based mold compound (EMC) used as encapsulation material for high-voltage integrated circuits (HV-ICs) can significantly impact long-term reliability and performance of the devices when finally packaged. Moreover, the role of moisture, even if very little absorbed by the EMCs, can lead to a strong increase of the EMC conductivity, resulting in a larger electrostatic potential distortion when compared with the case of a perfectly dry insulating package. To directly measure the effects induced by space charge accumulation in dry and wet conditions, a dedicated test chip integrating a charge-sensor array has been manufactured and characterized. From the measured currents, the value of the electrostatic potential at the EMC/passivation interface has been accurately extracted. Moreover, the charge-sensor currents have been monitored during the discharging transient to investigate the concurrent coupling effects of the inner wiring and bondpads in discharge conditions
Characterization and TCAD Modeling of the Lateral Space Charge Accumulation in Epoxy Molding Compound in Packaged HV-ICs
Full text linkThe reliability of high-voltage (HV) integrated circuits (ICs) can be significantly affected by space charge accumulation at the interface between the passivation layer and the epoxy molding compound (EMC) which acts as encapsulation material. The incorporation of moisture, which significantly increases the EMC conductivity, can lead to a stronger distortion of the electric field with a consequent breakdown instability. Moreover, the distance of the integrated-circuit active regions from the peripheral bond pads and wire would require a thorough optimization. To investigate the role played by the EMC under such conditions, a dedicated test chip made by an array of charge sensors covering short distances from bon-pads has been manufactured. A novel technique has been used to estimate the amount of space charge in the EMC independent of the bias applied to the bond pads. The outcome of the experiments has been explained by performing 2-D TCAD simulations of the structure under investigation which accurately account for the charge transport mechanisms of the EMC
Leaf area transpiration (TAF) in sunflower as a physiological index of genotipic discrimination
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