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A novel optically activated cascode gallium nitride (GaN) high-electron-mobility transistor (HEMT) is introduced and evaluated in this paper. Furthermore, optical triggering of GaN HEMT structures by cost-effective and high-power long-wavelength light sources is proposed for the first time. In electrical domain, GaN HEMTs suffer from being normally on devices, making it more complicated to design and implement gate drivers for these devices. In optical domain, GaN devices suffer from being triggered by low-power short-wavelength light sources, making them significantly more expensive and practically unprofitable. Therefore, a new optical cascode (OC) GaN HEMT is proposed in this paper to solve the problems of both electrical and optical domains. The structure of this OC GaN HEMT includes a high-power normally on (depletion mode) GaN HEMT in combination with a low-power optical switch in cascode configuration. This OC not only realizes an overall normally off (enhancementmode) structure, but also offers activationwith cost-effective long-wavelength optical sources. It also offers a single-biased configurationwithout the need for complicated electrical gate drivers. Unlike conventional electrically activated cascode GaN HEMT structures, which may be prone to electromagnetic interference noise due to the high-frequency switching operation, the optical link in this proposed scheme is immune to external noise. The results showa high-frequency switching capability of 1MHz for theOCGaN HEMT under a bias voltage of 600 V and a current of 10 A. Less voltage and current ringing are observed in the OC compared with the electrical alternative due to the elimination of gate controlling inductance introduced in the electrical cascode configuration. [ABSTRACT FROM AUTHOR]

A soft-switched hybrid-modulation (HM) scheme is outlined for a dc-link-capacitor-less three-phase high-frequency (HF) pulsating-dc link (PDCL) isolated multistage inverter. The overall inverter comprises a front-end isolated dc/pulsating-dc converter followed by a pulsating-dc/ac converter. Because the two stages are directly connected without a dc-link capacitor, the intermediate link is a PDCL instead of a fixed-dc link as in conventional HF-link inverters. The HM modulates the pulsating-dc/ac converter such that, two of its converter legs are line-switched, while the third leg of the pulsating-dc/ac converter is switched under zero-voltage-switching condition. This is achieved by first modulating the dc/pulsating-dc converter to achieve a specific encoding of the PDCL signal, which in turn, is exploited by the modulation scheme of the pulsating-dc/ac converter to mitigate its switching loss without requiring any auxiliary circuit. Operation of the pulsating-dc/ac converter using the soft-switched HM scheme is validated using a prototype 1 kW, 72-V (dc)/208-V (ac) HF inverter. [ABSTRACT FROM AUTHOR]

The increasing prevalence of e-commerce in the consumer context raises the issue of the difference in consumer perception and behavior considering single-brand e-retailers and multi-brand e-retailers. In which situations and conditions, if any, do customers prefer one of these types of e-retailers? Little empirical research has been conducted in area. We investigate an online purchasing behavior model that includes the two types of e-retailers. The model confirms a difference in customers' perceptions between single-brand e-retailers and multi-brand e-retailers. In fact, for single-brand e-retailers, value, and implicitly quality, are indicators of repurchase intention, while in both websites, when customers believe that the brand of the product gives them prestige, they tend to repurchase. However, the impact of price on prestige differs between these two types of websites. [ABSTRACT FROM AUTHOR]