1,721,002 research outputs found
A model of radiation induced leakage current (RILC) in ultra-thin gate oxides
No full textAn analytical model of Radiation Induced Leakage Current (RILC) has been developed for ultra-thin gate oxides submitted to high dose ionizing radiation. The model is based on the solution of the Schrödinger equation for a simplified oxide band structure, where RILC occurs through electron trap-assisted tunneling. The values of the model parameters have been calibrated by comparing the transmission probabilities obtained in this model with those obtained through the WKB method in the actual oxide band structure. No free fitting parameter has been introduced, and all physical constant values have been selected within the values found in literature. Different trap distributions have been considered as candidates, but the comparison between simulated and experimental curves have indicated that a double gaussian distribution in space and in energy grants the best fit of the experimental results for different ionizing particles, oxide fields during irradiation, radiation doses, and oxide thickness. Excellent matching has been found for both positive and negative RILC by using a single trap distribution. The trap density linearly increases with the radiation dose and decreases with the oxide field during irradiation. The trap distribution is spatially symmetrical in the oxide, centered in the middle of the oxide thickness, and is not modified as the cumulative dose increases
FPGA-Based Random PWM with Real-Time Deadtime Compensation
No full textThis paper presents the implementation on a field programmable gate array (FPGA) of a space vector modulator (SVM) for a voltage inverter, as an approach to the design of reusable and reconfigurable control software for electric drives. In electric drives control, a traditional “main-program-and-subroutine” architecture involves several software issues that must be re-considered at any hardware platform change. The paper describes the first step of a process whose target is the creation of a library of optimised VHDL modules that incorporates the best expertise on each part of the drive. Due to FPGA structure, the portability is intrinsic and also the flexibility will be preserved, since all new solutions can be evaluated and included in the library. Experimental results, carried on a three-phase voltage inverter, are used to highlight potentials and pitfalls of the proposed approach
Improved FPGA-based dead time compensation for SVM inverters
No full textHigh performance sensorless AC drives require the exact knowledge of the motor phase voltage in the whole speed range. The use of specific voltage sensors can be avoided if the reference voltage signals can be used instead of the actual (measured) phase voltages. Thus, an accurate compensation of inverter non-idealities is of great interest, and it represents the target of this work. The proposed algorithm overcomes the imprecision of the compensation, which arises in most of the existing methods, caused by an advanced sampling of the phase currents polarity with respect to the switching instants. The implementation of the proposed technique has been made possible solely by the use of an FPGA component, which proves, once more, to be a very attractive co-processor in modern DSP-based digital drives
Potentials and Pitfalls of FPGA Application in Inverter Drives - a Case Study
No full textWith the aid of a specific case study, this work presents the options offered by Field Programmable Gate Arrays (FPGAs) in electric drives applications. As it happened in the transition from microprocessors to digital signal processors (DSP), it is worth to analyse what are the limitations and the possible pitfalls of the FPGA-based design, compared with conventional DSP implementation. As a case study, it has been implemented a Space Vector Modulator (SVM) for a three phase voltage inverter. The proposed SVM algorithm includes a novel dead time compensation technique, whose implementation is made possible solely by the use of an FPGA component. An extended analysis of the state of the art and experimental results are included in the paper
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
Total dose dependence of radiation-induced leakage current in ultra-thin gate oxides
No full textRadiation-induced leakage current (RILC) has been studied on ultra-thin gate oxides (4 and 6 nm) irradiated with 8 MeV electrons. Both RILC and stress-induced leakage current (SILC) have been fitted with the same Fowler–Nordheim law, suggesting that RILC and SILC have similar conduction mechanisms. The RILC dependence from total dose during irradiation has been analysed and compared with the SILC dependence from the cumulative injected charge. Different growth laws of RILC and SILC have been found in the two cases. The intensity of positive and negative RILC also depends on the applied gate bias voltage during irradiation, probably reflecting different distributions of the oxide traps mediating the trap assisted tunnelling. Finally, we have presented the first evidence of a quasi-breakdown phenomenon due to ionizing radiation
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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