23,050 research outputs found
Conversores CC-CC com elevada taxa de conversão estática
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2014.Nesse trabalho é introduzida uma nova família de Conversores CC-CC com elevada taxa de conversão estática. Tais conversores tem origem a partir dos Conversores CC-CC básicos convencionais (Buck, Boost, Buck-Boost, Zeta, Cúk e Sepic), no qual inserindo a célula básica de comutação proposta no trabalho, é possível tornar esses conversores convencionais em conversores com elevada taxa de conversão estática, gerando os Conversores Propostos. A célula de comutação responsável por gerar a família de Conversores Propostos possui apenas semicondutores passivos, o que é uma vantagem para essas topologias. Além disso, a família de Conversores Propostos possui a vantagem de ser simétrica, isso possibilita a reflexão dos componentes superiores, gerando os componentes inferiores das novas estruturas. Essa reflexão é uma característica importante nas topologias propostas, pois reduz os esforços de tensão em seus interruptores. Seguindo a nomenclatura básica, os conversores propostos são chamados de: Duplo Buck Quadrático, Duplo Boost Quadrático, Duplo Buck-Boost Quadrático, Duplo Zeta Quadrático, Duplo Cúk Quadrático e Duplo Sepic Quadrático. Dos sete Conversores Propostos no trabalho, somente um não é originado pela célula básica de comutação. Este Conversor é chamado de Duplo Buck Quadrático Básico, e foi importante para consolidar os estudos dos Conversores CC-CC com elevada taxa de conversão estática. Algumas análises como etapas de operação em condução contínua, ganho estático e característica externa são apresentadas para todos os conversores propostos. Para provar as análises teóricas, os resultados experimentais em malha aberta são apresentados para o Conversor Duplo Buck Quadrático Básico, e em malha aberta, malha fechada e malha fechada com desequilíbrio de carga para o Conversor Duplo Boost Quadrático.<br
Taking Bayes Beyond Radiocarbon: Bayesian Approaches to Some Other Chronometric Methods
No full textBuilding on the models for, and practical applications of, Bayesian chronological analysis on the basis of radiocarbon and archaeomagnetism outlined by Buck (Chapter 1), Bayliss and Bronk Ramsey (Chapter 2) and Lanos (Chapter 3), this chapter looks forward to the potential of Bayesian modelling for other chronometric methods. Suitable mathematical formulations are suggested for dendrochronology, uranium-series, amino-acid racemization and trapped charge (luminescence and ESR) dating methods. Some are only initial suggestions for formulations which may lead to practical implementations. For dendrochronology, uranium-series and ESR dating the chapter offers more detailed models, initial implementations, and for the latter two, illustrative case studies which indicate the nature of inferences we can expect to make if such models are adopted more widely. By suggesting such a broad range of extensions to the Bayesian chronological framework this chapter offers great potential for substantially extending the kinds of problems that can be tackled within it, and provides encouragement to researchers who rely on a wide range of dating methods and would like to integrate them all within one coherent framework
CE Challenges: Work to Do
No full textCE has been used for more than two decades now. Despite many successes and advantages, there are still many challenges to be addressed. These challenges are both technical and organisational. In the paper we will address the current challenges of CE. Many challenges are related to the exchange of data and knowledge and to the systems that make data and knowledge exchange possible. Although much progress has been made in enabling extensive data and knowledge exchange and use, much remains to be wished. For example, there are still barriers to data exchange. Technically, these barriers may consist of different formats, differences in infrastructures and systems, and different semantics. There are also organisational and political barriers. For example, investment in information system may heavily impact upstream suppliers, while revenues of better information exchange may predominantly be gained by downstream actors. Without sharing costs and revenues, chain-wide information exchange will not be easily realised. Another barrier is the possible lack of willingness to share information, because of potential misuse of knowledge and loss of power. The paper is organised as follows. First we will describe the current manifestation of CE as described in a recent book. Second, we will list current trends in CE. Third, we will present some Critical Success Factors (CSFs) that are considered relevant for implementing and adapting CE practices. Last, we indicate some research and practical questions to be addressed, especially for areas that have a high potential and actual impact. </p
The study of stolen love : Iṟaiyanār kaḷaviyal. With Commentary by Nakkīraṉār (Revised edition)
No full textOriginal edition published by Scholars Press, 1997.International audienceThe Study of Stolen Love, with Nakkīrar’s commentary, is the earliest Tamil prose work still in existence, and its influence remains clear and strong today. The work consists of three strands: A series of ancient Tamil sutras, Nakkīrar’s explication of those sutras, and the elegantly beautiful ancient court poems he has chosen to illustrate his points. In so doing he lays out the prescribed conventions that govern the composition and appreciation of akam, or “interior” poems—often called ‘love’ poems—and their literary contexts, as well as the critical apparatus that has structured commentaries by classical Tamil scholars down through the centuries, including the current era. This translation was done collaboratively by David C. Buck and the late K. Paramasivam, and originally published in 1997. The revised edition revisits notes from the first edition, and includes a new Introduction that brings the work up to date and places the Tamil original more firmly in its historical context.The Study of Stolen Love, avec le commentaire de Nakkīrar, est le plus ancien ouvrage en prose tamoule connu à ce jour et son influence demeure aujourd’hui encore évidente et forte. L’œuvre est constituée de trois éléments, les sutras en tamoul ancien, leur explication par Nakkīrar et les très beaux poèmes de cour anciens qu’il a choisis en illustration de son propos. Ce faisant, il établit les bases des conventions imposées qui règlent la composition et l’évaluation des poèmes d’akam, ou ‘intérieur’ – souvent appelés poèmes ‘d’amour’ –, et leurs contextes littéraires, aussi bien que tout l’appareil critique qui a structuré les commentaires des savants tamouls classiques à travers les siècles, y compris la période contemporaine. Cette traduction a été faite en collaboration par David C. Buck et le regretté K. Paramasivam et publiée dans sa version originale en 1997. Cette édition révisée a corrigé les notes de la première édition et comprend une introduction nouvelle qui met l’ouvrage à jour et intègre plus précisément l’original tamoul dans son contexte historique
Synthesis optimization and charge carrier transfer mechanism in LiLuSiO<sub>4</sub>:Ce, Tm storage phosphor
No full textLiLuSiO4:Ce and LiLuSiO4:Ce, Tm show very efficient charge carrier storage properties upon beta irradiation after samples have received treatment in vacuum. They outperform the commercial storage phosphor BaFBr(I):Eu2+ in many aspects. The influence of the synthesis conditions, Ce and Tm concentration, nonstoichiometry and codoping with Ca, Hf, Al and Ge are reported. Based on the results of the synthesis optimization, thermoluminescence (TL) emission and TL excitation spectra a mechanism of charge carrier transfer, storage, and recombination during irradiation and thermal or optical readout is proposed.Accepted Author ManuscriptRST/Fundamental Aspects of Materials and EnergyRST/Luminescence Material
Modeling and Analysis of High Speed Switching Buck Converter IC for Conducted Emission Estimation
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The high speed switching buck converter is widely used to reduce the cost and to improve the transient response. However, the switching voltage noise from high speed switching buck converter can be a potential problem such as conducted emission (CE) and radiated emission (RE) because of its high speed switching characteristics. The estimation of switching voltage noise from high speed switching buck converter is important to predict the impact on other device. In this paper, the modeling method of high speed switching buck converter based on the analysis of noise path is proposed so that the switching voltage from buck converter can be estimated and simulated more fast and simple without using SPICE model of buck converter IC. The proposed modeling method can replicate switching voltage in frequency domain and time domain
A spurious-free switching buck converter for portable applications
No full textDC–DC buck converters are essential to extending the standby time and maximizing the battery life of portable electronic devices. In a portable environment, load conditions vary drastically from heavy-load to light-load levels, depending on whether the device is in active or standby mode. These devices run in standby mode most of the time. The output spectrum of DC–DC buck converters in such an environment must also be spurious-free (i.e. of low tonal content) for them to be able to supply sensitive circuits, such as ICs in mobile communication systems. Among the various buck-converter architectures, switching converters offer the highest power conversion efficiency over a wide range of conversion ratios. Increasing the switching frequency of the buck converter enables the use of compact off-chip components and enhances the converter's integrability. However, operating at high switching frequencies increases switching losses and reduces the power conversion efficiency, especially at light loads. The ultimate goal in designing a switching buck converter is to resolve the conflict between operation at a high switching frequency and efficient power conversion, while maintaining a regulated output-voltage with low tonal content. This thesis proposes a spurious-free switching buck converter with enhanced light-load efficiency for use in noise-sensitive portable electronic devices. The proposed converter achieves low output noise by using a delta-sigma-modulator controller. Its light-load efficiency is enhanced by: 1) scaling the switching frequency of the buck converter (i.e. the sampling frequency of its delta-sigma-modulator controller) according to the load current; 2) switching its operation from continuous conduction mode (CCM) to discontinuous conduction mode (DCM) at light loads; and 3) using a new low-power current-sensing circuit. The delta-sigma modulator is designed with an input-feedforward architecture, which enables the switching frequency of its controller to be scaled without disturbing the stability of the feedback loop of the buck converter, and also reduces the controller quiescent current. The proposed switching buck converter was fabricated in a 0.13-µm digital CMOS process with a maximum switching frequency of 10 MHz, enabling the use of compact off-chip components. The results measured demonstrate that this buck converter achieves a spurious-free output with a noise floor below - 60 dBm and voltage ripples below 70 mV across its full loading range (2 mA to 800 mA). Furthermore, it achieves a power efficiency of greater than 70% over this entire range, with a peak efficiency of 95.12%.Les convertisseurs Buck DC–DC sont indispensables afin de maximi le temps de veille ainsi que la durée de vie de la batterie des appareils électroniques portatifs. Dans un environnement portatif, selon le mode actif ou de veille de l'appareil, les conditions de charge varient fortement de niveau lourd vers le niveau léger de charge. Ce type d'appareil fonctionne la plupart du temps en mode veille. Dans un tel environnement, le spectre sortant de convertisseurs Buck DC–DC doit être sans parasite (c'est-à-dire avoir un contenu tonal faible), pour permettre d'alimenter les circuits sensibles comme les circuits intégrés dans les systèmes de la communication mobile.Parmi les différentes architectures de convertisseur Buck, les convertisseurs de commutation ont la meilleure efficacité de transformation de puissance, sur une gamme plus étendue de taux de transformation. L'accroissement de la fréquence de la commutation du convertisseur Buck, permet l'utilisation de composants hors-puce compacts ainsi que l'amélioration de l'intégrabilité du convertisseur. Cependant, l'exploitation à une fréquence élevée de commutation, augmente les pertes de commutation et réduit également l'efficacité de la transformation de la puissance surtout à des charges légères. Le but final de la conception d'un convertisseur Buck de commutation est de résoudre le conflit entre le fonctionnement à une fréquence élevée de commutation et une transformation de la puissance efficace, tout en conservant une tension de sortie régulée avec un contenu tonal faible.Cette thèse propose un convertisseur Buck de commutation sans parasite avec une efficacité améliorée pour des charges légères en vue d'une utilisation dans les appareils électroniques portables sensibles au bruit. Le convertisseur proposé réalise un faible bruit sortant en utilisant un contrôleur modulateur delta-sigma. L'efficacité à charge légère est augmentée par: 1) le changement de la fréquence de la commutation du convertisseur Buck (i.e. la fréquence d'échantillonnage du contrôleur modulateur delta-sigma) selon le courant de charge; 2) le passage du mode de la conduction continue (MCC) au mode de la conduction discontinue (MCD) pour les charges légères; et 3) l'utilisation d'un nouveau circuit de détection de courant à faible puissance. Le modulateur delta-sigma est conçu avec une architecture d'entrée par anticipation (input-feedforward) qui permet le changement de la fréquence de commutation de contrôleur, sans perturber la stabilité de la boucle de rétroaction du convertisseur Buck et également la reduction du courant de mise en veille du contrôleur.Le convertisseur Buck de commutation proposé a été fabriqué dans un procédé de CMOS numérique de 0.13-µm avec une fréquence maximale de commutation de 10 MHz. Ce qui permet l'utilisation des composants hors-puce compacts. Les résultats mesurés montrent que ce convertisseur Buck atteint une sortie sans parasite avec un seuil de bruit inférieur à 60 dBm et une ondulation de tension au dessous de 70 mV à travers la gamme complète du charge (2 mA à 800mA). Par ailleurs, il atteint une efficacité de puissance de plus de 70% sur cette gamme, avec une efficacité de pointe de 95,12%
The impact of P(NDI2OD-T2) crystalline domains on the open-circuit voltage of bilayer all-polymer solar cells with an inverted configuration
No full textWe fabricated P(NDI2OD-T2)/PTB7 bilayer all-polymer solar cells with an inverted configuration, where the annealing temperature was systematically varied. The current density-voltage behavior was investigated and the structural properties of the P(NDI2OD-T2) layers were characterized. Absorption spectroscopy, surface morphology, and crystallite analysis showed that increasing phase segregation of P(NDI2OD-T2) films occurred as the annealing temperature increased. We found that, as the P(NDI2OD-T2) stacking improved, with larger domains, the open-circuit voltage decreased and the saturation dark current density increased. This work provides a guide for the processing of P(NDI2OD-T2) layers to maximize the power conversion efficiency of all-polymer solar cells. (C) 2015 Author(s).open1186sciescopu
Data and code for: Variational Graph Author Topic Modeling
No full textThis is the tensorflow implementation of KDD-2022 paper "Variational Graph Author Topic Modeling" by Delvin Ce Zhang and Hady W. Lauw.
VGATM is a Graph Neural Network model that extracts interpretable topics for documents with authors and venues. Topics of documents then fulfill document classification, citation prediction, etc.
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Updated analytical solutions of continuity equation for electron beams precipitation – I. Pure collisional and pure ohmic energy losses
No full textWe present updated analytical solutions of continuity equations for power-law beam electrons precipitating in (a) purely collisional losses and (b) purely ohmic losses. The solutions of continuity equation (CE) normalized on electron density presented in Dobranskis & Zharkova are found by method of characteristics eliminating a mistake in the density characteristic pointed out by Emslie et al. The corrected electron beam differential densities (DD) for collisions are shown to have energy spectra with the index of −(γ + 1)/2, coinciding with the one derived from the inverse problem solution by Brown, while being lower by 1/2 than the index of −γ/2 obtained from CE for electron flux. This leads to a decrease of the index of mean electron spectra from −(γ − 2.5) (CE for flux) to −(γ − 2.0) (CE for electron density). The similar method is applied to CE for electrons precipitating in electric field induced by the beam itself. For the first time, the electron energy spectra are calculated for both constant and variable electric fields by using CE for electron density. We derive electron DD for precipitating electrons (moving towards the photosphere, μ = +1) and ‘returning’ electrons (moving towards the corona, μ = −1). The indices of DD energy spectra are reduced from −γ − 1 (CE for flux) to −γ (CE for electron density). While the index of mean electron spectra is increased by 0.5, from −γ + 0.5 (CE for flux) to −γ + 1(CE for electron density). Hard X-ray intensities are also calculated for relativistic cross-section for the updated differential spectra revealing closer resemblance to numerical Fokker–Planck (FP) solutions
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