High density array of multiferroic nanoislands in a large area

Hyun, Seung,Seo, Hosung,Yang, Il-Kyu,Kim, Youngsuk,Jeon, Gumhye,Lee, Bom-yi,Jeong, Yoon Hee,Kim, Yunseok,Kim, Jin Kon The Royal Society of Chemistry 2015 Journal of Materials Chemistry C Vol.3 No.10

<▼1><P>To extend the existing AAO mask assisted pulsed laser deposition (PLD) method, which is limited to fabricating a nanoisland array in a small area, we introduced a novel method to fabricate a high density array of multiferroic BFO nanoislands in a large area (wafer scale) by utilizing a nanoporous polymer template.</P></▼1><▼2><P>We report the innovative fabrication of a high density array of multiferroic BiFeO3 (BFO) nanoislands on a conductive substrate in a large area. The anodic aluminum oxide (AAO) template has widely been used to fabricate highly arranged nanostructures, because of easy control of pore size and perfect hexagonal pore packing. The existing AAO mask-assisted pulsed laser deposition (PLD) method is limited to fabricating a nanoisland array in a small area. To supplement the shortcoming of this method, a thick AAO membrane in a large area was electrochemically detached and floated on polystyrene (PS) film without crack. Then, a nanoporous polystyrene (PS) template was prepared by dry etching with the thick AAO membrane mask, followed by spin coating of the BFO precursor on the PS template. After removing the PS template at high temperature, we prepared a high density array of multiferroic BFO nanoislands in a large area epitaxially grown on an STO:Nb (100) substrate. A high density array of BFO nanoislands in a large area showed both ferroelectricity of individual nanoislands obtained by piezoresponse force microscopy (PFM) and macroscopic magnetism measured by a superconducting quantum interference device (SQUID) based magnetic property measurement system (MPMS). A high density array of BFO nanoislands could be employed as a next-generation memory device capable of electric writing and magnetic reading (or <I>vice versa</I>).</P></▼2>

Reduction of internal climate variability in surface temperature due to sea‐ice loss since the mid‐21st century

Hyun, Seung‐,Hwon,Yeh, Sang‐,Wook,Yoon, Jinho John Wiley Sons, Ltd 2017 International journal of climatology Vol.37 No.15

<P><B>ABSTRACT</B></P><P>Understanding the internal climate variability (ICV) is a principal challenge in projecting future climate change. In this study, we define the ICV in projection of surface temperature as the ensemble spread of surface temperature using a 30‐member ensemble simulated with the Community Earth System Model Large Ensemble (CESM‐LE) experiment, and examine how this ICV changes from the present climate to the future climate under Representative Concentration Pathway 8.5 scenario (RCP8.5). First, ICV is reduced in the future climate, particularly since the mid‐21st century. Such a decrease is primarily due to the reduction of ICV in both the Arctic (70°–90°N) and the Antarctic (65°–80°S). Our analysis further indicates that the decrease in ICV in Arctic is significant during boreal fall (September–October–November), and in particular, it is closely linked to the reduction in sea ice since the early and mid‐21st century. This implies that realistic simulation of the Arctic sea ice is a key in reducing ICV in a changing climate.</P>

Self-Positioned Nanosized Mask for Transparent and Flexible Ferroelectric Polymer Nanodiodes Array

Hyun, Seung,Kwon, Owoong,Choi, Chungryong,Vincent Joseph, Kanniyambatti L.,Kim, Yunseok,Kim, Jin Kon American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.40

<P>High density arrays of ferroelectric polymer nanodiodes have gained strong attention for next-generation transparent and flexible nonvolatile resistive memory. Here, we introduce a facile and innovative method to fabricate ferroelectric polymer nanodiode array on an ITO-coated poly (ethylene terephthalate) (PET) substrate by using block copolymer self assembly and oxygen plasma etching. First, polystyrene-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) micelles were spin-coated on poly(vinylidene fluoride-ran-trifluoroethylene) copolymer (P(VDF-TrFE)) film/ITO-coated PET substrate. After the sample was immersed in a gold precursor (HAuCl4) containing solution, which strongly coordinates with nitrogen group in P2VP, oxygen plasma etching was performed. During the plasma etching, coordinated gold precursors became gold nanoparticles (GNPs), which successfully acted as self-positioned etching mask to fabricate a high density array of P(VDF-TrFE)) nanoislands with GNP at the top. Each nanoisland shows clearly individual diode property, as confirmed by current-voltage (I-V) curve. Furthermore, due to the transparent and flexible nature of P(VDF-TrFE)) nanoisland as well as the substrate, the P(VDF-TrFE) nanodiode array was highly tranparent, and the diode property was maintained even after a large number of bendings (for instance, 1000 times). The array could be used as the next-generation tranparent and flexible nonvolatile memory device.</P>

Multi-floor cascading ferroelectric nanostructures: multiple data writing-based multi-level non-volatile memory devices

Hyun, Seung,Kwon, Owoong,Lee, Bom-yi,Seol, Daehee,Park, Beomjin,Lee, Jae Yong,Lee, Ju Hyun,Kim, Yunseok,Kim, Jin Kon The Royal Society of Chemistry 2016 Nanoscale Vol.8 No.3

<P>Multiple data writing-based multi-level non-volatile memory has gained strong attention for next-generation memory devices to quickly accommodate an extremely large number of data bits because it is capable of storing multiple data bits in a single memory cell at once. However, all previously reported devices have failed to store a large number of data bits due to the macroscale cell size and have not allowed fast access to the stored data due to slow single data writing. Here, we introduce a novel three-dimensional multi-floor cascading polymeric ferroelectric nanostructure, successfully operating as an individual cell. In one cell, each floor has its own piezoresponse and the piezoresponse of one floor can be modulated by the bias voltage applied to the other floor, which means simultaneously written data bits in both floors can be identified. This could achieve multi-level memory through a multiple data writing process.</P>

중국군 정치동원의 구조적 요인 연구: 마오쩌둥과 덩샤오핑 시기 사례 분석 중심

김현승 ( Kim¸ Hyun Seung ) 성균관대학교 성균중국연구소 2021 중국사회과학논총 Vol.3 No.2

본 연구의 목적은 중국 군대의 정치동원 사례 분석을 통해 중국군의 정치동원에 영향을 미친 구조적 요인을 도출하고 향후 정치동원의 가능성을 전망하는 것이다. 본 연구는 중국군이 정치문제에 동원된 것은 공산당 지도자의 정치적 목적 추구가 주된 요인이었다는 기존 연구에서 한발 더 나아가 지도자의 위상 및 영향력 뿐 아니라 지도자의 정치적 위협인식, 그리고 군대의 정치연계 수준 역시 군대의 정치동원을 결정하는 구조적 요인이 된다고 주장한다. 중국 군대가 정치에 동원된 문화대혁명과 천안문 사태를 분석한 결과 정치적 위협인식과 최고 지도자의 군대 내부 위상이라는 요인에서는 유사한 양태를 보였다. 마오쩌둥과 덩샤오핑 모두 당시의 상황을 자신의 정치적 입지를 위협하는 엄중한 상황이라고 인식하고 있었다. 국내 위상 측면에서 볼 때 마오쩌둥은 중국 공산당 초창기부터 쌓아온 군 경력으로 인해 군대 내에서 다른 누구와도 비교할 수 없는 절대적 위치를 점하고 있었다. 덩샤오핑 역시 국공내전의 승리에 결정적 역할을 한 것으로 인해 다른 군 원로들에 비해 의사결정에서 우위에 설 수 있었다. 그러나 문화대혁명 시기 군대와 천안문사태 시기 군대의 정치연계 수준은 상이했다. 문화대혁명 시기 중국군은 전문화보다는 정치공작에 치중하여 그 임무가 공산당의 통치를 지원하는데 그 초점이 맞춰져 있었다. 그러나 천안문사태 시기 중국군은 과거 혁명지원보다는 외부의 위협에 맞서 승리할 수 있는 능력을 갖추기 위해 무기장비를 현대화하고 군의 전문성을 강화하는 등 문화대혁명 시기에 비해 정치연계 수준이 상대적으로 낮은 상태였다. 중국의 정치동원 사례 분석 결과 중국의 정치지도자가 특정 사건이 정치적으로 심대한 위협이 된다고 인식하고, 군 내부의 반발을 무시할 수 있을 정도로 군에 대한통제력이 월등하다면 군대의 정치연계 수준에 관계없이 군사력을 정치문제 해결에 동원하였다는 것을 알 수 있다. 중국 군대는 중요한 시기마다 정치적 향방을 결정 하거나 결정된 사항을 관철시키는 중요한 ‘수단’으로 기능해 왔다. 이러한 이유에서 중국군의 정치동원을 결정하는 요인을 구조적으로 분석한 것은 중국 정치의 한 측면을 이해하는 중요한 과정이라 할 수 있다. In this study, structural factors that could be applied to analyse the political mobilization of the army in Chinese politics. Especially, Not only the Communist Party leader’s pursuit of political goals was a decisive factor in the Chinese army’s mobilization in political affairs, but the leader's recognition of political threats and the level of military autonomy were. According to an analysis of political mobilization of army in the Cultural Revolution and Tiananmen incident, the political threat recognition and the internal status of the top brass leader showed a similar pattern. Both Mao Zedong and Deng Xiaoping perceived the situation as a grave threat to their political position. Mao Zedong’s military career from the early days in the Chinese Communist Party gave him an unrivaled position in the army, and Deng Xiaoping was able to take the upper hand in decision-making over other military leaders because he played a decisive role in the victory of the Chinese Civil War. However, the level of autonomy of the amry during the Cultural Revolution and the Tiananmen incident was different. During the Cultural Revolution, the Chinese army focused on political affairs rather than warfighting activities, with its mission focused on supporting Communist Party. However, during the Tiananmen incident, the Chinese army was relatively autonomous than before, modernizing weapons equipment and strengthening its expertise to win against external threats rather than supporting the revolution. The two historical examples show that if a Chinese political leader recognizes a particular incident as a serious political threat and has superior control over the military to ignore internal opposition, he could mobilized the army to political affairs regardless of the level of autonomy of the military. The Chinese amry has served as an important ‘means’ to decide the political direction or to break through the obstacles. For this reason, the structural analysis of the factors that determine the political mobilization of the Chinese army is an important process of understanding one aspect of Chinese politics.

Textile Electrode-structure Effects and Motion Artifact Minimization in Heart Activity Signal Acquisition

Hyunseung Cho,Jinhee Yang,Jeongwhan Lee,Joohyeon Lee 대한전자공학회 2021 IEIE Transactions on Smart Processing & Computing Vol.10 No.3

The purpose of this study is to compare the heart activity signal sensing performance by textile electrodes (based on size and configuration method) in order to obtain the structural requirements of motion artifact-minimizing textile electrodes suitable for heart activity signal acquisition. Computer embroidery was used to create six types of contact textile electrodes for measuring heart activity by manipulating the electrode size and method of configuration. These electrodes were attached to separate chest belts worn sequentially by eight males in good physical health. Heart activity signals were detected while the subjects stood in a static posture for 60 seconds and while they walked in place at a rate of 80 beats per minute for 60 seconds. The measurements were repeated four times. To collect the heart activity signals, a BIOPAC Systems, Inc. ECG100 electrocardiogram amplifier was used at a sampling rate of 1 ㎑, and the detected raw signals were fed through a bandpass filter. The signal power ratio of the heart activity signal detected by each type of electrode was calculated, and statistical analysis was applied to determine the heart activity signal-acquisition performance of the six electrode configurations. The results of this study indicate that, with regard to the textile electrodes’ configuration method, convex electrodes detected higher-quality signals than flat electrodes; however, no significant performance difference was found in detecting heart activity signals among the three electrode sizes. Among the structural requirements of textile electrodes for heart activity signal acquisition, the electrode configuration method was found to be an important factor that affects heart activity signal sensing in static and dynamic states. Plans for implementing a wearable platform integrating the convex textile electrodes based on this study will be investigated in future studies, along with performance improvements to develop smart clothing technology that can detect high-quality heart activity signals without time or space limitations.

Energy storage and generation through desalination using flow-electrodes capacitive deionization

Hyunseung Lim,Yuncheol Ha,Hye Bin Jung,Pil Sung Jo,Hana Yoon,Do Quyen,Namchul Cho,Chung-Yul Yoo,Younghyun Cho 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-

Flow electrodes-based capacitive deionization (FCDI) is a highly energy-efficient desalination processcompared to conventional processes, including reverse osmosis and multi-stageflash distillation. Furthermore, it provides a continuous desalinationflow with high salt-removal capacity, whereas CDIusingfixed electrodes requires additional electrode rinsing. In FCDI, salt ions are adsorbed ontoflowcarbon electrodes and stored in the electrode slurry container, which is similar to an electrochemicalflowcapacitor. Therefore, stored ions can generate energy during discharging in FCDI operation. In this study,such energy generation was systematically investigated in terms of the various discharging rates, feedconcentrations, and volume offlow-electrode slurry. We found that the results were correlated with thechanges in the salt concentration of the effluentflow. The discharging current of 50 mA showed thehighest capacity for energy generation out of all the experimental conditions; it recovered around 25% ofthe energy consumed during FCDI desalination. We believe that such energy recovery can greatly reducethe energy consumption needed for FCDI desalination. Such recycling of generated energy would makeFCDI more attractive than other conventional desalination techniques.

Monitoring of migratory insect pests on paddy fields in Jeolla province

Hyunseung Lee,Hojung Jang,Hyojin Jeong,Jung-Joon Park 한국응용곤충학회 2019 한국응용곤충학회 학술대회논문집 Vol.2019 No.10

Growth Response of Several Vegetables as Affected by Light Quality for the Production of Uniform Seedlings Applicable to Grafting Robots

Hyunseung Hwang,Hyerin Song,Changhoo Chun 한국원예학회 2018 한국원예학회 학술발표요지 Vol.2018 No.10

Comparison of foraging behavior of insect fauna in transgenic and non-transgenic rice paddy fieldsrice paddy fields

Hyunseung Lee,Kimoon Son,Suyong Lee,Sangin Shim,Jung-Joon Park 한국응용곤충학회 2021 한국응용곤충학회 학술대회논문집 Vol.2021 No.04