Daegu Gyeongbuk Institute of Science and Technology
DGIST Library Institutional RepositoryNot a member yet
12664 research outputs found
Sort by
Designing and understanding disordered photocatalyst active sites for solar-light-driven CO2 conversion to hydrocarbon fuel production
No full textAmorphous photocatalyst, CO2 reduction, heterostructure, photocatalystGraphical abstract 1
Chapter 1 Introduction 2
1.1 FOSSIL FUEL DEPENDENCY 2
1.2 RECYCLING CO2 IN TERMS OF PHOTOREDUCTION 3
1.3 CURRENT STATE-OF-ART FOR CO2 PHOTOREDUCTION 4
1.4 AMORPHOUS SEMICONDUCTOR AS PHOTOCATALYST 6
1.5 ENGINEERING THE AMORPHOUS PHOTOCATALYST FOR CO2 REDUCTION 7
1.6 LIGHT ABSORPTION IN AMORPHOUS PHOTOCATALYST 7
1.7 ADSORPTION, HAPTICITY () AND PRODUCT SELECTIVITY OF CO2 MOLECULES 9
1.8 VARIABLE COORDINATION NUMBERS 13
1.9 ROADMAP OF THESIS 15
1.10 REFERENCES 17
Graphical abstract 22
Chapter 2 Characterisation and instruments analysis 23
2.1 DRS-UV-VIS SPECTROSCOPY 23
2.2 PHOTOLUMINESCENCE 24
2.3 TIME-RESOLVED PHOTOLUMINESCENCE (TRPL) ANALYSIS 25
2.4 XRD ANALYSIS 26
2.5 FE-SEM ANALYSIS 27
2.6 TRANSMISSION ELECTRON MICROSCOPY (TEM) ANALYSIS 28
2.7 ENERGY-DISPERSIVE X-RAY SPECTROSCOPY (EDS OR EDX OR EDAX) 29
2.8 X-RAY PHOTOELECTRON SPECTROSCOPY (XPS) ANALYSIS 30
2.9 BRUNAUER–EMMETT–TELLER (BET) ANALYSIS 31
2.10 TEMPERATURE PROGRAMMED DESORPTION (TPD) ANALYSIS 31
2.11 GAS CHROMATOGRAPHY (GC) ANALYSIS 32
2.12 GC-MASS SPECTROSCOPY (GC-MS) 33
2.13 X-RAY ABSORPTION FINE STRUCTURE (XAFS) 34
2.14 DIFFUSED REFLECTANCE INFRARED FOURIER TRANSFORM (DRIFTS) SPECTROSCOPY ANALYSIS 35
2.15 REFERENCES 36
Graphical abstract 39
Chapter 3 Enhancement of visible-light-driven gas-phase photocatalytic CO2 reduction by dual active sites of Ti3+ and In3+ on In2TiO5 40
3.1 INTRODUCTION 40
3.2 EXPERIMENTAL SECTION 42
3.2.1 Synthesis of In2TiO5 42
3.2.2 Synthesis of In2TiO5/MoSe2 42
3.2.3 Photocatalytic Activity 42
3.2.4 Synthesis of TiO2 nanoparticles 43
3.2.5 Synthesis of In2O3 Nanoparticle 43
3.2.6 Photoresponsive measurement 43
3.2.7 Electrochemical analysis 43
3.2.8 NMR Sample Analysis 43
3.2.9 DRIFTS Experimental Details 44
3.2.10 XAFS Experimental Details 44
3.3 MATERIALS CHARACTERISATION 44
3.4 THEORETICAL SIMULATION 45
3.5 RESULTS AND DISCUSSION 46
3.5.1 Mechanism of formation of In2TiO5 46
3.5.2 Optical and charge transfer properties 46
3.5.3 Surface composition, structural studies and morphology analysis 48
3.5.4 XAFS analysis of In2TiO5/MoSe2 54
3.5.5 Photocatalytic activity 58
3.5.6 Reaction mechanism for CO2 photoreduction 62
3.5.7 Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) 63
3.5.8 Density functional theory (DFT) simulation 65
3.6 CONCLUSION 67
3.7 REFERENCES 73
Graphical abstract 76
Chapter 4 Insights into Ti3+/Ti4+ dynamics: Exploring CO2 photoreduction pathways in gas-solid phase 77
4.1 INTRODUCTION 77
4.2 EXPERIMENTAL SECTION 79
4.2.1 Synthesis of C-TiO2/CdSe 79
4.2.2 Synthesis of A-TiO2/CdSe 79
4.2.3 Synthesis of TiO2 nanoparticles 80
4.2.4 Synthesis of CdSe Nanocrystals 80
4.2.5 Photoresponsive measurement 80
4.2.6 Electrochemical analysis 81
4.2.7 Materials Characterisation 81
4.2.8 DRIFTS Experimental Details 81
4.2.9 XAFS Experimental Details 82
4.2.10 Photocatalyst regeneration process 83
4.2.11 Computational Details 83
4.2.12 Density functional simulation 84
4.3 RESULTS AND DISCUSSION: 85
4.3.1 Method Development 85
4.3.2 Optical and charge carrier properties 85
4.3.3 Structural and morphological characterisations 87
4.3.4 Sunlight─driven photocatalytic CO2 reduction 97
4.3.5 Multi─solar photon flux─driven photocatalytic CO2 reduction 99
4.3.6 Insights into the photocatalytic CO2 reduction mechanism 100
4.4 CONCLUSION 115
4.5 REFERENCES 121
Graphical abstract 127
Chapter 5 Harnessing mixed valency of Ti3+/Ti4+ and non-stoichiometric Ag2S nanowire design in a direct Z-scheme for enhanced CH4 production 128
5.1 INTRODUCTION 128
5.2 EXPERIMENTAL SECTION 129
5.2.1 Synthesis of TiO2 nanoparticles 129
5.2.2 Synthesis of non-stoichiometric Ag2S nanowires (Ag2S NWs) 130
5.2.3 Synthesis of A-TiO2/ Ag2S NWs 130
5.3 RESULTS AND DISCUSSION 131
5.3.1 Structural and morphological analysis 131
5.3.2 Coordination environment analysis 137
5.3.3 Photocatalytic CO2 reduction 140
5.3.3.1 Solar-driven photocatalytic CO2 reduction 140
5.3.3.2 Multiphoton flux-driven CO2 photoreduction 142
5.3.4 Insights of active site determination of CO2 photoreduction 144
5.3.5 Charge carrier and reaction mechanism dynamics of CO2 photoreduction 148
5.3.5.1 Charge carrier and optical properties 148
5.3.5.2 Reaction mechanism dynamics of CO2 photoreduction. 150
5.3.6 Density functional analysis on Ag2S NWs surface 156
5.4 CONCLUSION 159
5.5 REFERENCES 165
Korean abstract 171DoctordCollectio
Identification and comparison of protein composition of biofilms in response to EGCG from Enterococcus faecalis and Staphylococcus lugdunensis, which showed opposite patterns in biofilm-forming abilities
Get PDFBacterial biofilm is resistant to conventional antibiotic treatments, leading to complications associated with many infection-related human diseases. Epigallocatechin Gallate (EGCG), a phenolic catechin enriched in green tea, is recognized for its anti-bacterial and anti-biofilm activities. In this study, we examined the protein components of the biofilms formed in the absence or presence of EGCG using Enterococcus faecalis and Staphylococcus lugdunensis, which had shown opposing patterns in biofilm formation. A clustering heatmap revealed that the two microorganisms expressed the different protein sets in response to EGCG. Proteins that were noticeably upregulated included those associated with stress responsiveness and gluconeogenesis in E. faecalis, and gene modification in S. lugdunensis. Conversely, downregulated proteins were related to tRNA-modifying enzyme activity in E. faecalis, and anabolic metabolism in S. lugdunensis. Among the proteins identified only in EGCG-responsive biofilms, enzymes involved in de novo purine biosynthesis were enriched in E. faecalis, while proteins likely to cause DNA instability and pathogenicity changes were abundantly present in S. lugdunensis. The classification based on gene ontology (GO) terms by microorganism exhibited that metabolic process or catabolic activity was at the top rank in E. faecalis with more than 33 proteins, and in S. lugdunensis, localization or transport was highly ranked with 4 proteins. These results support the hypothesis that EGCG might cause different cellular programs in each microorganism. Finally, comparison of the proteomes between two groups that form biofilms to similar extents discovered that 2 proteins were commonly found in the weak biofilm-forming groups (E. faecalis and EGCG-responding S. lugudunensis), whereas 9 proteins were common among the strong biofilm-forming groups (S. lugdunensis and EGCG-responding E. faecalis). It was suggested that these proteins could serve as potential indicators to detect the presence and predict the extent of biofilm formation by multiple microorganisms. Taken all together, proteomics data and analyses performed in this study provided useful and new information on the proteins embedded in the biofilms formed at the specific conditions, which can aid in diagnosis and the development of tailored treatment strategies. © 2024 The AuthorsTRUEscopu
ROCAS: Root Cause Analysis of Autonomous Driving Accidents via Cyber-Physical Co-mutation
No full textAs Autonomous driving systems (ADS) have transformed our daily life, safety of ADS is of growing significance. While various testing approaches have emerged to enhance the ADS reliability, a crucial gap remains in understanding the accidents causes. Such post-accident analysis is paramount and beneficial for enhancing ADS safety and reliability. Existing cyber-physical system (CPS) root cause analysis techniques are mainly designed for drones and cannot handle the unique challenges introduced by more complex physical environments and deep learning models deployed in ADS. In this paper, we address the gap by offering a formal definition of ADS root cause analysis problem and introducing Rocas, a novel ADS root cause analysis framework featuring cyber-physical co-mutation. Our technique uniquely leverages both physical and cyber mutation that can precisely identify the accident-trigger entity and pinpoint the misconfiguration of the target ADS responsible for an accident. We further design a differential analysis to identify the responsible module to reduce search space for the misconfiguration. We study 12 categories of ADS accidents and demonstrate the effectiveness and efficiency of Rocas in narrowing down search space and pinpointing the misconfiguration. We also show detailed case studies on how the identified misconfiguration helps understand rationale behind accidents. Copyright held by the owner/author(s)
Low magnetic field alignment of carbon fibers in a polymer matrix for high-performance thermal interface materials
No full textCarbon-based materials like carbon nanotubes, graphene nanoplatelets, graphite, and carbon fibers (CF) are highly promising fillers for enhancing the thermal conductivity of thermal interface materials (TIMs) due to their high thermal conductivity and low thermal expansion. Aligning these fillers can further improve thermal conductivity, but current alignment methods using high magnetic fields are impractical for industrial use. In this study, we investigated the enhancement of the thermal conductivity of CF–polymer composites by aligning CF fillers with a low magnetic field. We observed up to 17 times enhancement of the thermal conductivity (from 3.1 to 52.8 W/mK) in a CF–graphene–polymer composite film by vertically aligning the CF fillers with a magnetic field of 0.75 T. The analysis of the structural properties of the films using X-ray diffraction and field-emission scanning electron microscopy imaging confirmed that the crystalline c-axis of the graphite plates in the CF was oriented perpendicular to the magnetic field direction. The large anisotropy in the diamagnetic susceptibility of the laminated graphene structure of the CF flakes is at the origin of the filler alignment. Furthermore, the thermal conductivity of the composites showed a strong correlation with the degree of filler alignment, which was dependent on the CF–graphene hybridization and the type of polymer matrix. This study provides a scalable and cost-effective method for enhancing the physical properties of carbon composites by controlling their microarchitecture using a low magnetic field. © 2024 Elsevier B.V.FALSEsciescopu
Backbone NMR chemical shift assignment for the substrate binding domain of Escherichia coli HscA
No full textHscA is a Hsp70-type chaperone protein that plays an essential role to mediate the iron-sulfur (Fe-S) cluster biogenesis mechanism in Escherichia coli. Like other Hsp70 chaperones, HscA is composed of two domains: the nucleotide binding domain (NBD), which can hydrolyze ATP and use its chemical energy to facilitate the Fe-S cluster transfer process, and the substrate binding domain (SBD), which directly interacts with the substrate, IscU, the scaffold protein of an Fe-S cluster. In the present work, we prepared the isolated SBD construct of HscA (HscA(SBD)) and conducted the solution-state nuclear magnetic resonance (NMR) experiments to have its backbone chemical shift assignment information. Due to low spectral quality of HscA(SBD), we obtained all the NMR data from the sample containing the peptide LPPVKIHC, the HscA-interaction motif of IscU, from which the chemical shift assignment could be done successfully. We expect that this information provides an important basis to execute detailed structural characterization of HscA and appreciate its interaction with IscU.FALSEkc
Buffer Parameter Optimization for Advanced Automated Material Handling Systems in Serial Production Lines
No full textAn automated material handling system (AMHS) is a production line component responsible for transporting products from one machine to another for manufacturing processes. The AMHS also acts as a buffer that enhances overall productivity by reducing the dependency on individual machine operations. This paper introduces a buffer parameter optimization algorithm designed for advanced AMHS with the capability to control the speed of individual products. The buffer parameters targeted for optimization are buffer length (distance between machines) and transfer speed. The algorithm addresses each parameter separately through two distinct optimization problems. The buffer length optimization problem is formulated with the constraint of limited space assigned to the production system. On the other hand, the transfer speed optimization problem is formulated based on the constraints of network resources and hardware limitations. The proposed algorithm employs an aggregation method to evaluate the performance of the production systems analytically. © ICROS, KIEE and Springer 2024.FALSEsciescopuskc
MIMO Imaging Method with Extrapolation-Iterative Adaptive Approach-Based Super-Resolution Technique for Automotive Radar
No full textThis paper proposes a MIMO imaging method that leverages an extrapolation-iterative adaptive approach to achieve super-resolution capabilities for automotive radar applications. In recent years, autonomous vehicles have incorporated 4D imaging radar systems to attain high-resolution data. The MIMO technique finds application in the design of compact vehicle radars, enabling the adoption of radar-based imaging technology. However, the conventional MIMO imaging approach, relying on the FFT algorithm, encounters challenges in realizing higher resolutions. To overcome this limitation, we propose a MIMO radar implementation founded upon a super-resolution algorithm. Specifically, we investigate the combination of extrapolation and iterative adaptive approach, an iterative algorithm that has gained popularity as a means to mitigate the complexity drawbacks associated with super-resolution techniques. Through simulations and experiments, we validate this method, showcasing its immense potential in enhancing the accuracy and precision of vehicle radar systems. © 2024 IEEE
Silver oxide integrated ionic polymer composite for wearable sensing and water purification
Get PDFIntegrating metal nanoparticles (NPs) with ionic polymer blends/composites showed immense interest for their potential in wearable sensors, soft robotic arms, flexible man-machine interfaces of biomedical devices, and water purification applications. However, conventional NPs attached ionic polymer composites exhibit limitations such as low sensitivity (ΔR/R), low total dissolved solids (TDS) reduction, and low phosphate (PO4-P) removal rate. Herein, ionic polymer composites (IPCs) using flower-shaped silver oxide (Ag2O) attached Poly (vinylidene fluoride) (PVDF)/ polyvinylpyrrolidone (PVP)/ionic liquid (IL) were designed and developed for wearable sensing and water purification. The IPCs demonstrated remarkably high ΔR/R values of 50, 10, and 3.5 corresponding to the wrist movement of 50°, finger movement of 180°, and chin movements respectively. The Ag2O-based IPC recorded a significant reduction of TDS from sewage water from 3405 ppm to 1035 ppm, elevated the dissolved oxygen (DO) levels in the sewage water from 1.2 mg/l to 6.8 mg/l, and removed approximately 87.38 % phosphate from sewage water. Due to the uniform distribution of Ag2O within pores of IPC, it demonstrated enhanced performance for wearable and wastewater treatment applications. © 2024 The Author(s)TRUEscopu
Proposal of Three-Tier Framework for AI-based Resource Management in Small Cell Networks
No full text무선 네트워크 자원 관리는 한정된 네트워크 자원(예, 주파수 및 전송 전력)을 할당함으로써 네트워크 사업자로 하여금 사용자의 서비스 요구치(요구 전송 속도 및 지연)를 만족시키는 일련의 과정을 의미한다. 그러나, 일반적인 네트워크 자원 관리 문제는 매우 높은 계산 복잡도를 갖고 있기에 이를 극복하기 위해 최근에는 많은 연구자들이 인공지능 기반의 알고리즘들을 제안했다. 따라서, 본 논문에서는 기존 인공지능 기반의 접근 방식에 대한 문제점을 제시하며 이를 해결할 수 있는 클라우드 사업자-네트워크 사업자-사용자 구조의 3 계층 프레임워크를 새롭게 제안한다. 또한, 해당 프레임워크에서 고려해야할 사항을 분석한 수학적 프레임워크를 제안한다
Frequency-Selective, Multi-Channel, Self-Powered Artificial Basilar Membrane Sensor with a Spiral Shape and 24 Critical Bands Inspired by the Human Cochlea
Get PDFA spiral-artificial basilar membrane (S-ABM) sensor is reported that mimics the basilar membrane (BM) of the human cochlea and can detect sound by separating it into 24 sensing channels based on the frequency band. For this, an analytical function is proposed to design the width of the BM so that the frequency bands are linearly located along the length of the BM. To fabricate the S-ABM sensor, a spiral-shaped polyimide film is used as a vibrating membrane, with maximum displacement at locations corresponding to specific frequency bands of sound, and attach piezoelectric sensor modules made of poly(vinylidene fluoride-trifluoroethylene) film on top of the polyimide film to measure the vibration amplitude at each channel location. As the result, the S-ABM sensor implements a characteristic frequency band of 96-12,821 Hz and 24-independent critical bands. Using real-time signals from discriminate channels, it is demonstrated that the sensor can rapidly identify the operational noises from equipment processes as well as vehicle sounds from environmental noises on the road. The sensor can be used in a variety of applications, including speech recognition, dangerous situation recognition, hearing aids, and cochlear implants, and more. © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH.TRUEsciescopu