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Kwon, Soon Jik,Kim, Tae Geun,Park, Youngjun,Kwon, Ohseok,Cho, Youngho The Ecological Society of Korea 2015 Journal of Ecology and Environment Vol.38 No.4
This study was performed to provide important basic data for the preservation and management of Scopura laminata, a species endemic to Korea, by elucidating the spatial characteristics of its present, potential, and future distribution areas. Currently, this species is found in the Odaesan National Park area of South Korea and has been known to be restricted in its habitat due to its poor mobility, as even fully grown insects do not have wings. Utilizing the MaxEnt model, 20 collection points around Odaesan National Park were assessed to analyze and predict spatial distribution characteristics. The precision of the MaxEnt model was excellent, with an AUC value of 0.833. Variables affecting the potential distribution area of S. laminata by more than 10% included the range of annual temperature, seasonality of precipitation, and precipitation of the driest quarter, in order of greatest to least impact. Compared to the current potential distribution area, no significant difference in the overall habitable area was predicted for the 2050s or 2070s. It was, however, demonstrated that the potential habitable area would be reduced in the 2050s by up to 270.3 km from the current area of 403.9 km; further, no potential habitable area was anticipated by the 2070s according to our predictive model. Taken together, it is anticipated that this endemic species could be significantly affected by climate changes, and hence effective countermeasures are strongly warranted for the preservation of habitats and species management.
Soon Jik Kwon,Tae Geun Kim,Youngjun Park,Ohseok Kwon,조영호 한국생태학회 2015 Journal of Ecology and Environment Vol.38 No.4
This study was performed to provide important basic data for the preservation and management of Scopura laminata, a species endemic to Korea, by elucidating the spatial characteristics of its present, potential, and future distribution areas. Currently, this species is found in the Odaesan National Park area of South Korea and has been known to be restricted in its habitat due to its poor mobility, as even fully grown insects do not have wings. Utilizing the MaxEnt model, 20 collection points around Odaesan National Park were assessed to analyze and predict spatial distribution characteristics. The precision of the MaxEnt model was excellent, with an AUC value of 0.833. Variables affecting the potential distribution area of S. laminata by more than 10% included the range of annual temperature, seasonality of precipitation, and precipitation of the driest quarter, in order of greatest to least impact. Compared to the current potential distribution area, no significant difference in the overall habitable area was predicted for the 2050s or 2070s. It was, however, demonstrated that the potential habitable area would be reduced in the 2050s by up to 270.3 km from the current area of 403.9 km; further, no potential habitable area was anticipated by the 2070s according to our predictive model. Taken together, it is anticipated that this endemic species could be significantly affected by climate changes, and hence effective countermeasures are strongly warranted for the preservation of habitats and species management.
YoungJun Park,Hongjin Kim,Joo-Young Chun,JooYoung Lee,YoungGun Pu,Kang-Yoon Lee 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4
This paper presents a wide frequency range LLC resonant controller IC for LED backlight units. In this paper a new phase-domain resonance deviation prevention circuit (RDPC), which covers a wide frequency and input voltage range, is proposed. In addition, a wide range gate clock generator and an automatic dead time generator are proposed. The chip is fabricated using 0.35 μm BCD technology. The die size is 2 x 2 mm2. The frequency of the clock generator ranges from 38 kHz to 400 kHz, and the dead time ranges from 300 ns to 2 μs. The current consumption of the LLC resonant controller IC is 4 mA for a 100 kHz operation frequency using a supply voltage of 15 V.
Carrier Transport Mechanism of Ni/Ag/Pt Contacts to p-Type GaN
Park, Youngjun,Ahn, Kwang-Soon,Kim, Hyunsoo IEEE 2012 IEEE transactions on electron devices Vol.59 No.3
<P>The carrier transport mechanisms of Ni/Ag/Pt contacts to moderately Mg-doped p-GaN (sample A) and highly Mg-doped p-GaN (sample B) were investigated. Depending on the Mg doping concentration, the dominant carrier transport mechanism could be categorized as thermionic field emission for sample A and carrier transport through the deep-level defect (DLD) band for sample B, resulting in different specific contact resistances of <TEX>$\hbox{7.1} \times \hbox{10}^{-2}$</TEX> and <TEX>$\hbox{7.0} \times \hbox{10}^{-4}\ \Omega\hbox{cm}^{2}$</TEX> for samples A and B, respectively. For sample A, the contact parameters, including a Schottky barrier height of 0.94 eV and a tunneling parameter of 0.045 eV, could be observed, yielding the substantial interfacial carriers of <TEX>$\hbox{4.5} \times \hbox{10}^{19}\ \hbox{cm}^{-3}$</TEX> and, hence, field emission through a thin barrier. For sample B, the effective barrier height associated with the DLD band was suggested to be an important parameter since the carrier transport predominantly occurred through the DLD band rather than the valence band. Accordingly, the effective barrier height was calculated to be 0.12 eV, which was low enough to explain the excellent ohmic contact.</P>
Park, Youngjun,Lee, Jang-Sik American Chemical Society 2017 ACS NANO Vol.11 No.9
<P>Emulation of biological synapses that perform memory and learning functions is an essential step toward realization of bioinspired neuromorphic systems. Artificial synaptic devices have been developed based mostly on inorganic materials and conventional semiconductor device fabrication processes. Here, we propose flexible biomemristor devices based on lignin by a simple solution process. Lignin is one of the most abundant organic polymers on Earth and is biocompatible, biodegradable, as well as environmentally benign. This memristor emulates several essential synaptic behaviors, including analog memory switching, short-term plasticity, long-term plasticity, spike-rate-dependent plasticity, and short-term to long-term transition. A flexible lignin-based artificial synapse device can be operated without noticeable degradation under mechanical bending test. These results suggest lignin can be a promising key component for artificial synapses and flexible electronic devices.</P>
Park, YoungJun,Kim, Hongjin,Chun, Joo-Young,Lee, JooYoung,Pu, YoungGun,Lee, Kang-Yoon The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4
This paper presents a wide frequency range LLC resonant controller IC for LED backlight units. In this paper a new phase-domain resonance deviation prevention circuit (RDPC), which covers a wide frequency and input voltage range, is proposed. In addition, a wide range gate clock generator and an automatic dead time generator are proposed. The chip is fabricated using 0.35 μm BCD technology. The die size is 2 x 2 mm2. The frequency of the clock generator ranges from 38 kHz to 400 kHz, and the dead time ranges from 300 ns to 2 μs. The current consumption of the LLC resonant controller IC is 4 mA for a 100 kHz operation frequency using a supply voltage of 15 V.
Flexible Multistate Data Storage Devices Fabricated Using Natural Lignin at Room Temperature
Park, Youngjun,Lee, Jang-Sik American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.7
<P>The growing interest in bioinspired and sustainable electronics has induced research on biocompatible and biodegradable materials. However, conventional electronic devices have been restricted due to their nonbiodegradable and sometimes harmful and toxic materials, which can even cause environmental issues. Here, we report a resistive switching random access memory (ReRAM) device based on lignin, which is a biodegradable waste product of the paper industry. The active layer of the device can be easily formed using a simple solution process on a plastic substrate. The memory devices show stable bipolar resistive switching behavior with good endurance and retention. Appropriate control of the maximum reset voltage and compliance current can yield multibit data storage capability with at least four resistance states, which can be exploited to realize a high-density memory device. The resistive switching mechanism may be a result of formation and rupture of carbon-rich filaments. These results suggest that lignin is a promising candidate material for an inexpensive and environmentally benign ReRAM device. We believe that this study can initiate a new route toward development of biocompatible and flexible electronics.</P>