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Ab-initio Study of Pressure Effects and Hydrogen Impurity in HgO
Minseok Choi,Chul-Hong Park 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.12
Through ab-initio pseudopotential calculations, we investigated the deformation potential of HgO semiconductors and the structural stabilities of various crystal structures under pressure. We also investigated the microscopic structure of the hydrogen (H) impurity in HgO. Especially the state of hydrogen atoms captured by an acceptor-like Hg-vacancy (VHg) is focused on. The location of H is found to be very different from the original Hg-site, forming a strong H-O bond. The capture two H atoms by VHg is found to be energetically favorable: the binding energy for one H and the second H are 1.01 eV and 0.07 eV, respectively.
Wireless Video Caching and Dynamic Streaming Under Differentiated Quality Requirements
Choi, Minseok,Kim, Joongheon,Moon, Jaekyun IEEE 2018 IEEE journal on selected areas in communications Vol.36 No.6
<P>This paper considers one-hop device-to-device-assisted wireless caching networks that cache video files of varying quality levels, with the assumption that the base station can control the video quality but cache-enabled devices cannot. Two problems arise in such a caching network: <I>file placement problem</I> and <I>node association problem</I>. This paper suggests a method to cache videos of different qualities, and thus of varying file sizes, by maximizing the sum of video quality measures that users can enjoy. There exists an interesting tradeoff between video quality and video diversity, i.e., the ability to provision diverse video files. By caching high-quality files, the cache-enabled devices can provide high-quality video, but cannot cache a variety of files. Conversely, when the device caches various files, it cannot provide a good quality for file-requesting users. In addition, when multiple devices cache the same file but their qualities are different, advanced node association is required for file delivery. This paper proposes a node association algorithm that maximizes time-averaged video quality for multiple users under a playback delay constraint. In this algorithm, we also consider <I>request collision</I>, the situation where several users request files from the same device at the same time, and we propose two ways to cope with the collision: scheduling of one user and non-orthogonal multiple access. Simulation results verify that the proposed caching method and the node association algorithm work reliably.</P>
Hydrogen passivation of oxygen vacancies in LaAlO3
Choi Minseok 한국물리학회 2022 Current Applied Physics Vol.39 No.-
Through first-principles calculation using the screened hybrid functional, we investigate the energetics and electronic structure of substitutional hydrogen (HO) in which one hydrogen replaces an oxygen atom in LaAlO3. The calculated binding energy between the hydrogen and the oxygen vacancy (VO) indicates that HO is energetically likely to form in the oxide. HO releases one electron to the conduction band, so it is a shallow donor. Most importantly, HO completely eliminates the ingap defect states associated with VO, suggesting that hydrogen can be used as passivating agent for VO acting as a carrier trap or fixed charge in the oxide and near the oxide/semiconductor interface in LaAlO3-based devices.
Choi, Woojun,Hu, Guoxiang,Kwak, Kyuju,Kim, Minseok,Jiang, De-en,Choi, Jai-Pil,Lee, Dongil American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.51
<P>This paper describes the effects of doped metals on hydrogen evolution reaction (HER) electrocatalyzed by atomically controlled MAu<SUB>24</SUB> and M<SUB>2</SUB>Au<SUB>36</SUB> nanoclusters, where M = Pt and Pd. HER performances, such as onset potential (<I>E</I><SUB>onset</SUB>), catalytic current density, and turnover frequency (TOF), are comparatively examined with respect to the doped metals. Doping Pt or Pd into gold nanoclusters not only changes the electrochemical redox potentials of nanoclusters but also considerably improves the HER activities. <I>E</I><SUB>onset</SUB> is found to be controlled by the nanocluster’s reduction potential matching the reduction potential of H<SUP>+</SUP>. The higher catalytic current and TOF are observed with the doped nanoclusters in the order of PtAu<SUB>24</SUB> > PdAu<SUB>24</SUB> > Au<SUB>25</SUB>. The same trend is observed with the Au<SUB>38</SUB> group (Pt<SUB>2</SUB>Au<SUB>36</SUB> > Pd<SUB>2</SUB>Au<SUB>36</SUB>> Au<SUB>38</SUB>). Density functional theory calculations have revealed that the hydrogen adsorption free energy (Δ<I>G</I><SUB>H</SUB>) is significantly lowered by metal-doping in the order of Au<SUB>25</SUB> > PdAu<SUB>24</SUB> > PtAu<SUB>24</SUB> and Au<SUB>38</SUB> > Pd<SUB>2</SUB>Au<SUB>36</SUB> > Pt<SUB>2</SUB>Au<SUB>36</SUB>, indicating that hydrogen adsorption on the active site of nanocluster is thermodynamically favored by Pd-doping and further by Pt-doping. The doped metals, albeit buried in the core of the nanoclusters, have profound impact on their HER activities by altering their reduction potentials and hydrogen adsorption free energies.</P> [FIG OMISSION]</BR>
Choi, Minseok,Kim, Joongheon,Moon, Jaekyun IEEE 2018 IEEE Transactions on Vehicular Technology VT Vol.67 No.4
<P>High-speed and low-latency communications are one of the major requirements for connected vehicle environments. Safety messages in vehicular networks must arrive on time for each vehicle, and the optimization of driving paths also strongly depends on low-latency traffic information. To comply with the demands, a base station take important roles to provide a short service delay for the vehicles, even at the expense of performance. The relationship between delay time and decoding performance at receiver sides in physical layers can be explained by the performance/complexity tradeoff as follows. To achieve better performance in terms of the minimization of word error rates in decoding, the receiver usually requires higher complexity, which results in larger delays. We analyze this tradeoff based on the receiver queue model. This paper proposes a novel algorithm to adaptively select one of receiver candidates under the constraint of queue stability so as not to degrade low-latency communications. Based on the configurable architecture for multi-input multioutput (MIMO) detectors, this paper shows that the proposed algorithm works well on adaptive MIMO detector selection.</P>
A video-based SlowFastMTB model for detection of small amounts of smoke from incipient forest fires
Choi Minseok,Kim Chungeon,Oh Hyunseok 한국CDE학회 2022 Journal of computational design and engineering Vol.9 No.2
This paper proposes a video-based SlowFast model that combines the SlowFast deep learning model with a new boundary box annotation algorithm. The new algorithm, namely the MTB (i.e., the ratio of the number of Moving object pixels To the number of Bounding box pixels) algorithm, is devised to automatically annotate the bounding box that includes the smoke with fuzzy boundaries. The model parameters of the MTB algorithm are examined by multifactor analysis of variance. To demonstrate the validity of the proposed approach, a case study is provided that examines real video clips of incipient forest fires with small amounts of smoke. The performance of the proposed approach is compared with those of existing deep learning models, including convolutional neural network (CNN), faster region-based CNN (faster R-CNN), and SlowFast. It is demonstrated that the proposed approach achieves enhanced detection accuracy, while reducing false negative rates.