6,748 research outputs found
Enabling Resonant Commutated Pole in Parallel Power FET Bridge Legs
To meet the requirements of higher current ratings and lower thermal impedances, paralleling power field-effect transistor (FET) discretes or modules is often a cost-effective or even an unavoidable solution. While paralleling FETs allows for a significant reduction in conduction loss, the switching loss is increased in hard switching applications. This paper proposes a generic soft-switching modulation scheme for parallel power FET bridge legs. Part of the paralleled FET legs is chosen as an auxiliary leg that is turned on prior to the remaining main legs. A resonant commutated pole (RCP) mode is then created, which enables the high-side FET of the auxiliary leg to achieve zero-current switching (ZCS) or quasi-ZCS, and the remaining FETs to achieve zero-voltage switching (ZVS). Thus, we can significantly reduce the switching loss that normally dominates the total power loss of high-frequency hard-switching converters particularly at partial and light loads. Experimental results from three parallel GaN high-electron-mobility transistor (HEMT) legs validate the effectiveness of this RCP-enabled solution in reducing switching losses and improving power conversion efficiencies. This paper is accompanied by supplementary JIF files demonstrating the details of RCP mode
A Conditional Variational Framework for Dialog Generation
Deep latent variable models have been shown to facilitate the response
generation for open-domain dialog systems. However, these latent variables are
highly randomized, leading to uncontrollable generated responses. In this
paper, we propose a framework allowing conditional response generation based on
specific attributes. These attributes can be either manually assigned or
automatically detected. Moreover, the dialog states for both speakers are
modeled separately in order to reflect personal features. We validate this
framework on two different scenarios, where the attribute refers to genericness
and sentiment states respectively. The experiment result testified the
potential of our model, where meaningful responses can be generated in
accordance with the specified attributes.Comment: Accepted by ACL201
Uncovering many-body correlations in nanoscale nuclear spin baths by central spin decoherence
Many-body correlations can yield key insights into the nature of interacting
systems; however, detecting them is often very challenging in many-particle
physics, especially in nanoscale systems. Here, taking a phosphorus donor
electron spin in a natural-abundance 29Si nuclear spin bath as our model
system, we discover both theoretically and experimentally that many-body
correlations in nanoscale nuclear spin baths produce identifiable signatures in
the decoherence of the central spin under multiple-pulse dynamical decoupling
control. We find that when the number of decoupling -pulses is odd, central
spin decoherence is primarily driven by second-order nuclear spin correlations
(pairwise flip-flop processes). In contrast, when the number of -pulses is
even, fourth-order nuclear spin correlations (diagonal interaction renormalized
pairwise flip-flop processes) are principally responsible for the central spin
decoherence. Many-body correlations of different orders can thus be selectively
detected by central spin decoherence under different dynamical decoupling
controls, providing a useful approach to probing many-body processes in
nanoscale nuclear spin baths
Thermal modeling and design optimization of PCB vias and pads
Miniature power semiconductor devices mounted on printed circuit boards (PCBs) are normally cooled by means of PCB vias, copper pads, and/or heatsinks. Various reference PCB thermal designs have been provided by semiconductor manufacturers and researchers. However, the recommendations are not optimal, and there are some discrepancies among them, which may confuse electrical engineers. This paper aims to develop analytical thermal resistance models for PCB vias and pads, and further to obtain the optimal design for thermal resistance minimization. Firstly, the PCB via array is thermally modeled in terms of multiple design parameters. A systematic parametric analysis leads to an optimal trajectory for the via diameter at different PCB specifications. Then an axisymmetric thermal resistance model is developed for PCB thermal pads where the heat conduction, convection and radiation all exist; due to the interdependence between the conductive/radiative heat transfer coefficients and the board temperatures, an algorithm is proposed to fast obtain the board-ambient thermal resistance and to predict the semiconductor junction temperature. Finally, the proposed thermal models and design optimization algorithms are verified by computational fluid dynamics (CFD) simulations and experimental measurements
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Desynchronizing Paralleled GaN HEMTs to Reduce Light-Load Switching Loss
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Multistaged discharge constructing heterostructure with enhanced solid-solution behavior for long-life lithium-oxygen batteries.
Inferior charge transport in insulating and bulk discharge products is one of the main factors resulting in poor cycling stability of lithium-oxygen batteries with high overpotential and large capacity decay. Here we report a two-step oxygen reduction approach by pre-depositing a potassium carbonate layer on the cathode surface in a potassium-oxygen battery to direct the growth of defective film-like discharge products in the successive cycling of lithium-oxygen batteries. The formation of defective film with improved charge transport and large contact area with a catalyst plays a critical role in the facile decomposition of discharge products and the sustained stability of the battery. Multistaged discharge constructing lithium peroxide-based heterostructure with band discontinuities and a relatively low lithium diffusion barrier may be responsible for the growth of defective film-like discharge products. This strategy offers a promising route for future development of cathode catalysts that can be used to extend the cycling life of lithium-oxygen batteries
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