Publications by authors named "Hyungwoo Choi"

This paper proposes an energy-efficient multi-level sleep mode control for periodic transmission (MSC-PUT) in private fifth-generation (5G) networks. In general, private 5G networks meet IIoT requirements but face rising energy consumption due to dense base station (BS) deployment, particularly impacting operating expenses (OPEX). An approach of BS sleep mode has been studied to reduce energy consumption, but there has been insufficient consideration for the periodic uplink transmission of industrial Internet of Things (IIoT) devices.

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With the emergence of various Internet of Things (IoT) technologies, energy-saving schemes for IoT devices have been rapidly developed. To enhance the energy efficiency of IoT devices in crowded environments with multiple overlapping cells, the selection of access points (APs) for IoT devices should consider energy conservation by reducing unnecessary packet transmission activities caused by collisions. Therefore, in this paper, we present a novel energy-efficient AP selection scheme using reinforcement learning to address the problem of unbalanced load that arises from biased AP connections.

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Due to their high circulating intensities, ultra-high quality factor dielectric whispering gallery mode resonators have enabled the development of low threshold Raman microlasers. Subsequently, other Raman-related phenomena, such as cascaded stimulated Raman scattering (CSRS) and stimulated anti-Stokes Raman scattering (SARS), were observed. While low threshold frequency conversion and generation have clear applications, CSRS and SARS have been limited by the low Raman gain.

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Resonant cavity-enhanced Kerr frequency combs have been demonstrated using a range of cavity materials. Regardless of cavity type, one fundamental challenge is achieving low or flat dispersion while maintaining high-efficiency four-wave mixing (FWM). Here we demonstrate a Raman-Kerr frequency comb using a Zr-doped silica hybrid toroidal microcavity.

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A challenge in developing photovoltaic devices is to minimize the loss of electrons, which can seriously deteriorate energy conversion efficiency. In particular, minimizing this negative process in dye-sensitized solar cells (DSCs) is imperative. Herein, we use three different kinds of siloxanes, which are adsorbable to titania surfaces and polymerizable in forming a surface passivation layer, to reduce the electron loss.

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Tetrathiafulvalene (TTF), a well-known electron donor, can also behave as an electron acceptor after being adsorbed on the surface of silver nanoparticles (Ag NPs), thereby inducing a partial positive charge on the Ag NPs surface. The Ag NPs activated by TTF help propylene transport much faster than propane, i.e.

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