GIST Scholar
Not a member yet
30271 research outputs found
Sort by
Mesoporous Nitrogen-Doped Carbon Support from ZIF-8 for Pt Catalysts in Oxygen Reduction Reaction
No full textZeolitic imidazolate framework-8 (ZIF-8) has been extensively studied as a precursor for nitrogen-doped carbon (NC) materials due to its high surface area, tunable porosity, and adjustable nitrogen content. However, the intrinsic microporous structure of the ZIF-8 limits mass transport and accessibility of reactants to active sites, reducing its effectiveness in electrochemical applications. In this study, a soft templating approach using a triblock copolymer was used to prepare mesoporous ZIF-8-derived NC (Meso-ZIF-NC) samples. The hierarchical porous structure was investigated by varying the ratios of Pluronic F-127, NaClO4, and toluene. The resulting Meso-ZIF-NC exhibited widespread pore size distribution with an enhanced mesopore (2–50 nm) volume according to the composition of the reaction mixtures. Pt nanoparticles were uniformly dispersed on the Meso-ZIF-NC to form Pt/Meso-ZIF-NC catalysts, which presented a high electrochemical surface area and improved oxygen reduction reaction activity. The study highlights the important role of mesopore structure and nitrogen doping in enhancing catalytic performance, providing a pathway for advanced fuel cell catalyst design. © 2025 by the authors.TRUEsciescopu
Biocompatibility assessment of encapsulation materials for micro LED biomedical applications: in vivo and in vitro studies
No full textThe integration of Micro Light-Emitting Diodes (µLEDs) into biomedical systems holds significant promise for applications such as optogenetics, neural stimulation, and implantable biosensing. A critical challenge in realizing the clinical translation of such devices lies in ensuring the long-term biocompatibility of their encapsulation materials. In this study, we systematically evaluated the short-term (4-week) biocompatibility of three candidate encapsulation materials—Polydimethylsiloxane (PDMS), Ecoflex, and Kapton—and their respective µLEDs composites through a combination of in vitro and in vivo assays. In vitro cytotoxicity was assessed using direct contact morphology analysis, MTS mitochondrial activity assay, and Annexin-V/Propidium Iodide(PI)-based flow cytometry on L-929 fibroblasts. All materials demonstrated minimal cytotoxicity and apoptosis, with cell viability exceeding 90% and apoptotic indices remaining below 2.1%, meeting ISO 10993-5 criteria. Additionally, arsenic elution testing via inductively coupled plasma-mass spectrometry (ICP-MS) revealed concentrations far below toxicological thresholds, with Ecoflex and Kapton exhibiting undetectable levels. For in vivo evaluation, the materials were subcutaneously implanted into Sprague–Dawley rats. Histological analysis (Hematoxylin and eosin staining) conducted after 4weeks revealed no signs of necrosis or severe inflammatory response. Semiquantitative scoring indicated low fibrosis, inflammatory cell infiltration, and angiogenesis, with all materials falling within acceptable biocompatibility ranges. Collectively, these findings confirm that PDMS, Ecoflex, and Kapton, both as standalone films and in LED-integrated forms, exhibit excellent biocompatibility in short-term implantation models. This work provides a comparative foundation for selecting safe encapsulation materials in the development of implantable µLEDs bioelectronic systems and underscores the importance of multi-dimensional evaluation frameworks in preclinical safety assessment. © 2025 Elsevier B.V., All rights reserved.FALSEsciescopuskc
Single-shot weak measurement for spin Hall effect of light using a metasurface
No full textA metasurface-enabled weak measurement is devised for a single-shot observation of the spin Hall effect of light. By using a polarization beamsplitting metasurface, we achieve a real-time tracking of the spin Hall shift, thereby enabling high-precision optical sensing in dynamic environments. © 2025 Elsevier B.V., All rights reserved
A Tripartite Synapse-Inspired Ferroelectric-Gated Phototransistors for In-Sensor Image Processing
No full text삼자 시냅스 (tripartite synapse) 시스템에서 영감을 받은 뉴로모픽 소자는 제3의 단자를 통해 시냅스 가중치를 효과적으로 조절할 수 있는 특성을 지닌다. 그러나 전기적으로 독립된 단자를 활용하여 광학적 정보를 동시에 저장하고 처리하는 방법은 아직 충분히 탐구되지 않았다. 본 연구에서는 강유전성 고분자와 유기 광활성 채널을 통합한 강유전 게이트 광트랜지스터 (Ferroelectric-Gated Phototransistor, FGPT) 를 뉴로모픽 비전 시스템을 위한 소자로 재조명하였다. 강유전 게이트 절연체 내에서의 부분 분극 전환은 광활성 채널의 선형 제어를 가능하게 하며, 강유전 절연체와 광활성 채널 계면에서의 전하 트래핑에 의해 유도되는 광게이팅 효과는 소자의 광 비휘발성 특성을 더욱 강화시킨다. 이로 인해 저장된 시각 정보는 광전도도 형태로 점진적으로 강화 (potentiation) 또는 약화 (depression) 할 수 있으며, 조절된 광전도도는 장치의 동적 범위 (153 dB) 내에서 전체 전류 수준을 완전히 포괄한다. 마지막으로, 본 연구는 FGPT를 활용하여 구조화되지 않은 환경에서 획득된 시각 정보를 센서 내에서 전처리함으로써 학습된 범위로 재보정하고, 이로 인해 비정형 환경에서도 얼굴 인식 정확도가 최대 약 40 % 향상될 수 있음을 입증하였다.|Neuromorphic devices that emulate the tripartite synapse architecture utilize a third, electrically independent terminal to modulate synaptic weight; however, a strategy that allows this terminal to simultaneously memorize and process optical information has yet to be realized. Here, we revisit the ferroelectric-gated phototransistor (FGPT)—which incorporates ferroelectric polymers and organic photoactive channels—for neuromorphic vision systems. We demonstrate that partial polarization switching within the ferroelectric gate insulator provides linear control of the photoactive channel, while a photogating effect induced by charge trapping at the ferroelectric insulator/photoactive-channel interface further strengthens the photonic non-volatile characteristics of the device. Consequently, visual information stored as photoconductance can be incrementally potentiated or depressed, and the tuned photoconductance spans the entire current level of the device, covering 153 dB of dynamic range. Finally, through in-sensor processing, we demonstrate the possibility of all-day face recognition by converting visual information obtained in unstructured environments into a pre-trained range, resulting in up to approximately 40 % higher recognition accuracy.Master1 Introduction 1
1.1 Limitations of conventional CMOS-based vision systems 1
1.2 Neuromorphic vision and current challenges 2
1.2.1 Neuromorphic phototransistors 2
1.2.2 Challenges in photonic memory and our approach 2
1.3 Research scope: Tripartite synapse-inspired in-sensor processing 4
2 Ferroelectric-gated phototransistors (FGPT) inspired by tripartite synapse 6
2.1 Conceptual framework: Tripartite synapse-based approach 6
2.2 Fabrication and measurement setup 10
3 Photonic response and optoelectronic non-volatile characteristics 13
3.1 Photoresponsivity and dynamic range characteristics 13
3.2 Photogating effects and photonic non-volatility (PNV) 16
3.2.1 Trap-induced photogating dynamics in FGPT devices 16
3.2.2 Ferroelectric-enhanced photonic memory retention 17
4 Electrical modulation mechanism in FGPT 22
4.1 Ferroelectric polarization and partial switching 22
4.2 Gate-induced electrical modulation of photonic memory 25
4.2.1 Ferroelectric properties optimization of P(VDF-TrFE) 25
4.2.2 Electrical modulation of stored photocurrent 27
5 Applications: Array-based processing and all-day recognition 30
5.1 Demonstration of FGPT array-based in-sensor image processing 30
5.1.1 Contrast enhancement in unstructured environments 30
5.1.2 FGPT array operation and visualization of photonic memory 31
5.2 All-day face recognition in unstructured lighting conditions 35
5.2.1 FGPT-based recognition simulation framework 35
5.2.2 Accuracy improvement and recognition performance 38
5.2.3 Neural network simulation for all-day image recognition 42
6 Conclusion 44
References 46
Acknowledgements 5
Regulation of alternative splicing patterns of the Bcl-x gene by YTHDC1
No full textYTHDC1은 mRNA 상의 N6-메틸아데노신(N6-methyladenosine, m⁶A)을 특이적으로 인식하는 핵 내 m⁶A 리더 단백질이다. 대체 스플라이싱(Alternative splicing, AS)은 고등 진핵세포에서 일어나는 전사 후 과정으로, 하나의 유전자로부터 다양한 mRNA을 생성하고 이로 하여 다양한 단백질 isoforms을 생산할 수 있게하는 mechanism이다. 기존 연구에서는 YTHDC1이 SRSF3 모집과 SRSF10 차단을 통해 대체 스플라이싱을 조절한다는 사실이 일부 밝혀졌지만, YTHDC1이 스플라이싱을 조절하는 정확한 기작에 대한 연구는 아직 부족하다. 본 연구에서는 YTHDC1을 knockdown (KD)한 세포로부터 추출한 RNA를 기반으로, RNA 스플라이싱에 대한 바이오인포매틱 분석을 수행하였다. 그 결과, 총 259개의 5' splice site (5′ SS) 선택 변화 이벤트를 확인하였으며, 이는 YTHDC1이 5′ SS 선택에 필수적인 역할을 한다는 것을 시사한다. Gene Ontology 분석 결과, YTHDC1은 전반적인 5′ SS 선택을 조절하는 기능을 가지는 것으로 나타났다. YTHDC1의 타깃 중 하나인 Bcl-x 유전자는 exon 2b을 대상으로 대체 5′ SS 선택을 통해 항세포사멸성(Bcl-xL) 및 친세포사멸성(Bcl-xS) isoforms을 생성하므로, YTHDC1의 조절 메커니즘을 연구하기 위한 모델로 선택되었다. 이후 추가적인 YTHDC1 PAR-CLIP 데이터로 YTHDC1이 Bcl-x pre-mRNA와 직접적으로 결합한다는 가능성을 확인하였다. 데이터를 검증하기 위하여 추가적인 실험을 진행하였다.
우선적으로 YTHDC1 KD 세포에서 Bcl-x의 RT-PCR 분석을 통해 RNA-seq 결과를 재확인하였으며,
YTHDC1 KD가 Bcl-xS isoform의 생성을 촉진함을 실험적으로 입증하였다.
YTHDC1이 KD 되었을 때 exon 2b가 포함되어있지 않은 Bcl-xS isofrm이 늘어났기에 YTHDC1이 exon 2b의 inclusion을 촉진되는 지를 확인하기 위해 co-overexpression 실험을 진행하였다. 2a, 2b, intron 2 일부, exon 3을 포함한 Bcl-x minigene을 활용하여 YTHDC1이 과발현되었을 때 Bcl-xS isoform 생성을 억제하고 Bcl-xL가 증가함을 확인하였다. 다만 이러한 변화량은 KD 실험때와 비교하였을 때 적은 영향력을 보여주어 Bcl-x minigene을 디자인하며 deletion된 부분이 YTHDC1 또는 다른 co-factor들과 상호작용 할 수도 있다는 가능성을 보여준다.
마지막으로, YTHDC1 일부 결실된 mutant (YTH, ΔYTH)들과 m⁶A recognition 관련 트립토판을 변화시킨 mutant(W377A, W428A, W377, W428A)를 제작하여 Bcl-x minigene과 co-overexpression을 진행하여 YTHDC1의 어떠한 영역이 Bcl-x 대체 스플라이싱에 필요로 하는지를 확인했다. 그 결과 대조군으로 사용한 Wild type을 제외한 모든 mutant의 경우에서 exon 2b inclusion의 변화에 큰 영향이 없음을 관찰하였다. 이 결과는 5’ SS 선택을 조절하기 위해서 온전한 YTHDC1이 필요로 함을 시사한다. 따라서 YTHDC1은 온전한 형태로서 Bcl-x pre-mRNA의 5‘ SS 선택의 조절인자로 작용하여 Bcl-x의 exon 2b inclusion을 촉진한다는 결론을 내렸다.|YTHDC1 is a nuclear N6-methyadenosine (m⁶A) reader protein that specifically recognizes N6-methyadenosine on mRNA. Alternative splicing (AS) is an posttranscriptional process occurs in higher eukaryotic cells by which mutipled mRNA isoforms are produced from a gene. Although YTHDC1 has been shown to regulate alternative splicing through recruiting SRSF3 and blocking SRSF10 in some instances, the mechanistic insight of YTHDC1 in alternative splicing is still lacking. Using bioinformatics analysis of RNA splicing with RNAs from YTHDC1-knockdown (KD) cells. I identified 259 of altered 5’ splice site (SS) selection events indicating that YTHDC1 plays essential roles in alternative 5’ SS selection. Gene Ontology analysis showed that YTHDC1 globally regulates 5’ SS selection. Among the target 5’ SS targets of YTHDC1, I selected Bcl-x, which produces an proapototic Bcl-xS and antiapototic Bcl-xL, by alternative 5’ SS selection, to study the regulatory roles of YTHDC1 in 5’SS selection. First, I confirmed the RNA-seq results by performing RT-PCR analysis of Bcl-x in YTHDC1 KD cells to demonstrate that YTHDC1 KD promotes Bcl-xS production. Second, I applied a Bcl-x minigene including exon 2a, 2b, part of intron 2, and exon 3 to show that YTHDC1 overexpression inhibited Bcl-xS isoform. Last, I produced YTH domain deletion, m⁶A recognition amino acid mutatns to show that either YTH domain or specific amino acids (Tryptophan at postitions 377 and 428) are required for the splicing regulatory functions of YTHDC1. My results suggest that YTHDC1 is an essential regulatory protein in 5’ splice site selection.MasterI. INTRODUCTION 8
II. MATERIALS AND METHODS 4
2. 1. Cell culture, transfection, and shRNA lentivirus infection 4
2. 2. Total RNA extract and Reverse transcription (RT)-PCR 4
2. 3. Gene Ontology (GO) analysis 5
2. 4. Plasmid construction 5
2. 5. Open acess data sources 5
III. RESULTS 6
3. 1. Bioinformatics Analysis Suggests a Correlation between
YTHDC1 and Bcl-x 6
3. 2. YTHDC1 KD Regulates Bcl-x 5’ SS selection 9
3. 3. YTHDC1 Overexpression Increases Exon 2b Inclusion 12
3. 4. Full-Length YTHDC1 is Required for Regulation of
Bcl-x Alternative Splicing 14
IV. DISCUSSION 16
V. SUMMARY 18
REFERENCES 19
국문 초록 21
ACKNOWLEDGEMENT 23
CURRICULUM VITAE 2
Performance Improvement of a Suspended CVD-Grown MoTe₂ Gas Sensor via Surface Treatment
No full textThermal conductivity detector (TCD) gas sensors detect changes in surrounding gas compositions by monitoring variations in heat loss resulting from changes in the thermal conductivity of the gas. In this type of sensor, the resistance change rate caused by temperature variation is a key factor determining sensitivity, and a small thermal mass is essential for achieving fast response and high sensitivity. In this study, 2D MoTe₂, which is nanometers thick with an extremely low thermal mass while maintaining a high temperature coefficient of resistance (TCR), was selected as the sensing material. To improve resistance stability over time, reactive ion etching (RIE)-induced oxidation and atomic layer deposition (ALD) encapsulation were investigated. Meanwhile, a MEMS-based suspended trench structure was designed to minimize heat loss to the substrate, thereby enhancing thermal interaction with the surrounding gas and amplifying the temperature variation of the sensing material in response to changes in gas thermal conductivity. Finally, a TCD gas sensor employing RIE oxidized MoTe₂ demonstrated clear and repeatable responses to helium and nitrogen environments, verifying that surface-treated 2D MoTe₂ enables high sensitivity and long-term reliability in high-performance TCD gas sensors.|열전도도 검출기(TCD) 가스 센서는 주변 가스 조성의 변화를 가스의 열전도도 변화로 인한 센서의 열손실 변화를 모니터링하여 감지한다. 이때 센서의 온도 변화에 따른 저항 변화율은 민감도를 결정하는 핵심 요소이며, 빠른 응답과 높은 감도를 위해서는 센서가 작은 열용량을 가져야 한다. 본 연구에서는 나노미터 두께로 매우 얇아 작은 열용량을 가지면서도 높은 저항의 온도계수(TCR)를 유지하는 2D MoTe₂를 감지층으로 선정하고, 이 물질의 시간에 따른 저항 안정성을 개선하기 위해 반응성 이온 에칭(RIE) 산화 및 원자층 증착(ALD) 캡슐화를 실험하였다. 한편, MEMS 기반 현가형 트렌치 구조는 기판으로의 열 손실을 줄여 가스와의 열 상호작용을 강화하고, 가스 열전도도 변화에 따른 감지층의 온도 변화를 증폭시켰다. 최종적으로 RIE 산화 처리된 MoTe₂를 적용한 센서는 헬륨과 질소 환경에서 열전도도 차이에 따른 명확하고 반복 가능한 응답을 나타냈으며, 이를 통해 표면 처리된 2D MoTe₂가 고감도 및 장기 신뢰성을 갖춘 TCD 가스 센서로 활용될 수 있음을 입증하였다.MasterⅠ. Introduction
1.1 Background 1
1.2 Design strategy for improved TCD gas sensor performance 3
1.3 Challenges in using 2D-TMD materials for gas sensing 4
1.4 Thesis overview 5
1.5 Objective 6
Ⅱ. Device Fabrication and 2D Material Integration
2.1 Device concept and fabrication 7
2.2 Transfer setup 9
2.3 Synthesis, phase identification, and pattering of MoTe₂ 10
2.4 Nitrocellulose(NC) strip transfer method 12
2.4.1 Selection of transfer material 12
2.4.2 Comparison between formal and modified NC transfer method 12
2.4.3 NC strip transfer process 13
2.4.4 Results of the MoTe₂ transfer process 15
Ⅲ. Stabilization and Surface Treatment
3.1 Electrical measurement and analysis 18
3.2 Environmental instability of MoTe₂ 19
3.3 HfO₂ ALD encapsulation 20
3.4 RIE Oxidation Treatment 22
3.5 Combined RIE oxidation and ALD treatment 24
3.6 Summary 27
Ⅳ. Gas Sensing Experiments and Analysis
4.1 Gas sensing setup 29
4.2 Testing gas response 30
4.3 Limitation 31
V. Summary and Future Work
5.1 Summary 32
5.2 Future work 32
References 3
Sub-1-volt, reconfigurable Gires-Tournois resonators for full-colour monopixel array
No full textWe present an electrically reconfigurable Gires-Tournois resonator integrated with polyaniline for full-colour, energy-efficient modulation at CMOS-compatible voltages. This system achieves vibrant colour shifts across the visible spectrum within a sub-1V range, supporting ultrahigh pixel densities and wafer-scale fabrication, with bistable memory-in-pixel functionality for low-power passive matrix addressing in display applications. © 2025 Elsevier B.V., All rights reserved
Exact results on the number of gravitons radiated during binary inspiral
No full textWe derive an exact formula F(e) which provides a concrete estimate for the total number and angular momentum of gravitons emitted during the nonrelativistic inspiral of two black holes. We show that the function F(e) is a slowly growing monotonic function of the eccentricity 0 ≤ e ≤ 1 and F(1) = 1.0128 ⋯. We confirm and extend the results obtained by Page for the function F(e). We also get an exact result for the ratio ν (ei ) = 2ħN(Li , ei )/Li where the numerator 2ħN(Li , ei ) is the sum of the spin angular momentum magnitudes of the gravitons emitted and N(Li , ei ) is the total number of gravitons emitted in the gravitational waves during nonrelativistic inspiral from an initial eccentricity ei down to a final eccentricity e = 0 and the denominator Li is the magnitude of the initial orbital angular momentum. If the orbit starts off with unit eccentricity ei = 1, we get the value ν(1) = 1.002 268 666 2 ± 10-10 which confirms the Page's conjecture that the true value of ν(1) will lie between 1.001⋯ and 1.003⋯. We also show that the formula F(e) for gravitons emitted, originally expressed as an infinite series, can be represented by a single function through an integral representation. © 2025 IOP Publishing Ltd and Sissa Medialab. All rights, including for text and data mining, AI training, and similar technologies, are reserved.FALSEsciescopu
Curriculum based Reinforcement Learning for 3D Control of Magnetic Microrobot Swarms
No full textMicrorobotic swarms (MS) have shown great potential in a variety of biomedical applications, including targeted drug delivery and minimally invasive surgery. However, controlling MS in 3D environments remains a significant challenge. In this study, we propose a curriculum-based reinforcement learning (RL) approach for the autonomous navigation and control of MS in a 3D space, utilizing a magnetic field gradient for actuation and a field-free point to manage swarm formation. The RL agent learns to control the swarm’s position and minimize dispersion, progressively moving from 2D to 3D environments, and finally handling up to 8 microrobots. We further integrate the A* algorithm with the Artificial Potential Field (APF) method to manage path planning in environments with static and dynamic obstacles. The results demonstrate the effectiveness of the proposed approach, showing that the MS can autonomously navigate to a target with minimal dispersion and avoid obstacles in real-time. Comparison with human control highlights the advantages of the RL-based strategy in terms of efficiency and consistency. This work lays the foundation for future advancements in autonomous microrobotic swarm systems, offering a promising solution for complex, real-world applications. © 2025 Elsevier B.V., All rights reserved
Real-Time Analysis of Solid Oxide Electrolysis Cells Manufactured by Ceramic Sintering Process via Operando TEM and Electrochemical Impedance Spectroscopy
No full textSolid oxide electrolysis cell (SOEC) degrades more rapidly than a solid oxide fuel cell. One of the primary causes of this degradation is interfacial issues between the electrode and electrolyte, such as the accumulation of oxygen ions and the lattice strain near the interface. Although extensive research has been conducted on these degradation mechanisms, most studies have relied on post-mortem microstructural analysis rather than real-time operando analysis, which limits the understanding of degradation mechanisms under real operating conditions. Additionally, while there are a few reports on operando studies using scanning transmission electron microscopy (STEM) on SOEC, comprehensive research that integrates these observations with mechanistic analysis is relatively limited. In this study, an advanced technique is applied to facilitate the identification of key degradation reactions through the correlation of electrochemical analysis with operando STEM using dense perovskite bulk electrodes. By simplifying electrode geometry and enabling quantitative impedance analysis, dense electrodes provide a clear framework for identifying interfacial and surface reactions. This methodology lays the groundwork for the real-time analysis of electrochemical properties and microstructural changes in dense bulk materials using impedance spectroscopy and STEM.FALSEsciescopu